Greenhouse Gas Emissions Model (GEM)
User Guide, v3.5.l
Vehicle Simulation Tool for Compliance with
the Greenhouse Gas Emissions Standards
and Fuel Efficiency Standards for Medium
and Heavy-Duty Engines and Vehicles -
Phase 2 Technical Amendments
United States
Environmental Protection
^1 Agency
-------
Greenhouse Gas Emissions Model (GEM)
User Guide, v3.5.l
Vehicle Simulation Tool for Compliance with
the Greenhouse Gas Emissions Standards
and Fuel Efficiency Standards for Medium
and Heavy-Duty Engines and Vehicles -
Phase 2 Technical Amendments
Assessment and Standards Division
Office of Transportation and Air Quality
U.S. Environmental Protection Agency
Ł% United States
Environmental Protection
^1 Agency
EPA-420-B-20-055
December 2020
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Table of Contents
I. Introduction 1
II. Installation 1
II.A. Installation Instructions 1
II.B. Contents of Installation Package 4
ILB.l. Sample Input Files 4
H.B.2. GEM Executable 4
III. Model Description 4
III.A. GEM Architecture 5
III.A.l. Drive Cycles and Cycle Average Engine Fuel Map 6
III.B. Vehicle Parameters for Each Regulatory Subcategory 6
III.B.l. Tractor Vehicle Parameters 7
in.B.2. Vocational Vehicle Parameters 9
III.B.3. Trailer Vehicle Parameters 12
IV. GEM Input Files 14
IV.A. Tractor Input Files 15
IV.B. Vocational Input Files 21
IV.C. Trailer Input Files 26
IV.D. Supplemental Input Files 28
IV.D.1. Engine Input File for Tractor and Vocational Vehicles 28
IV.E. Transmission Input File for Tractor and Vocational Vehicles 31
IV.E.l. Optional Powertrain Input File for Tractor and Vocational Vehicles 33
IV.E.2. Optional Axle Input File for Tractor and Vocational Vehicles 35
V. GEM Output File Structure 35
V.A. Standard GEM Outputs for Compliance 36
VI. Running GEM 36
VI.A. Preparing for GEM Simulation 36
VI.B. Running GEM from the Start Menu Icons 37
VI.C. Testing Input Files for Errors 38
VI.D. Cycle Average Engine Fuel Map for Tractor and Vocational Vehicles 39
VI.E. Running GEM from the Command Prompt and Advanced Options 41
VII. Final Notes 43
Appendix A: Changelog 44
Summary of Changes for 3.4 from 3.0 44
Changes for 3.5 44
Changes for 3.5.1 45
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I. Introduction
The Greenhouse Gas Emissions Model (GEM) was first created by EPA as part of the "Heavy-
Duty Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium- and
Heavy-Duty Engines and Vehicles: Phase 1" rulemaking finalized in 2011. The model was
developed to serve as a means for determining compliance with EPA's GHG emissions and
NHTSA's fuel consumption Phase 1 vehicle standards for Class 7 and 8 combination tractors and
Class 2b-8 vocational vehicles.
For the Phase 2 rulemaking, significant enhancements were made to the model. In addition to the
model released with the Notice of Proposed Rulemaking (NPRM), additional refinements were
made to the model based on public comments received from our NPRM and subsequent Notice of
Data Availability (NODA) releases.
This User Guide describes the Phase 2 GEM release, GEM P2v3.5, published with the Phase 2
technical amendment (TA). The following sections include installation instructions, a general
model description, and instructions for running the model, including a description of the necessary
input and resulting output files. A more detailed description of the model architecture and updates,
including changes made in each release are available in the docket associated with each release,
particularly in Chapter 4 of the Phase 2 RIA.
II. Installation
EPA developed Phase 2 GEM to be a forward-looking Matlab/Simulink-based model for heavy-
duty (Class 2b-8) vehicle compliance for the Phase 2 rulemaking. The model is a free, desktop
computer application provided as an executable to be operated on a single computer. Since it is
provided as an executable, the user is not required to have access to the Matlab/Simulink software
packages.1 The following minimum computer specifications are required for the model to run:
- Operating System: 64-bit Windows 7 or newer
- CPU: 2 GHz processor
- Memory: 4 GB of RAM
II.A. Installation Instructions
The downloadable installation file is available on EPA's website (see Figure 1) at:
https://www.epa.gov/regulations-emissions-vehicles-and-engines/greenhouse-gas-emissions-
model-gem-medium-and-heavy-duty.
A link to the most recent GEM installer is located on this page. The installer includes the model
executable, supporting software (MATLAB Runtime) and several sample input file templates. A
copy of the GEM User Guide is also available separately on the website for convenient reference.
The GEM executable, sample files and documentation require about 10 MB of free space. Users
1 The Matlab and Simulink models that make up the GEM source code are available in the docket to the Phase 2
rulemaking. Please see Docket: EPA-HQ-OAR-2014-0827 available at: www.regulations.gov.
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that do not have the Matlab Compiler Runtime application installed will need about 700 MB of
free space.
Currently, GEM is only available to computers using 64-bit Windows operating systems
(Windows 7 and newer). To request a CD of this software instead of downloading, or to request
assistance if having trouble with accessibility of this software, please send an email request to
OTAQ@epa.gov.
United States
B-'/X EnvironmentaJ Protection
Agency
Environmental Topics Laws & Regulations About EPA
| Search EPA.gov
1
Regulations for Emissions from Vehicles and
Engines
CONTACT US
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Greenhouse Gas
Greenhouse Gas Emissions Model
(GEM) for Medium- and Heavy-
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On this page:
Overview of GEM
Phase 2 GEM simulation model
Phase 1 GEM simulation model v2.0.1
Overview of GEM
GEM is a free, desktop computer application that estimates the
greenhouse gas (GHG) emissions and fuel efficiency performance of
specific aspects of heavy-duty (HD) vehicles. GEM is designed to
operate on a single computer-
Phase 2 GEM Simulation
Model
(Supporting the Final HD Vehicle GHG Emissions and Fuel Efficiency
Rules)
Related Topic
Regulations for
Greenhouse Gas
Emissions from
Commercial Trucks &
Buses
Advanced Light-Outv
Powertrain and Hybrid
Analysis (ALPHA! Tool
You will need Free
Viewers and Adobe
Reader to view some
of the files on this
page. See EPA's
About PDF page to
learn more.
The model documentation provides details on how to install and
use the model. The PDF file also contains the input files that were
used to determine the stringency of the final GHG Emissions Standards and Fuel Efficiency Standards
for Medium-duty and HD Vehicles. The downloadable installation file below contains the application
executable files for the active version of Phase 2 GEM for simulating vehicle compliance.
GEM User Guide for Phase 2: Vehicle Simulation Tool for Compliance with GHG Emissions
Standards and Fuel Efficiency Standards for MP and HD Engines and Vehicles fPDF)
(52 pp, 1.0MB, EPA-420-B-16-067, July 2016)
Download the executable version of GEM P2V3.0 setup x64 f EXE) (i pa, &04 mb, July 2016)
^ Top of Page
Figure 1: EPA Website to Obtain GEM Installation Package
To install GEM, run the "GEM_P2v3.5_Setup_x64" executable to start the setup wizard that will
walk through the installation process. Users have the option of choosing a separate location for
their Phase 2 GEM installation but using the default folder as seen in Figure 2 is recommended.
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The instructions throughout this User Guide assume the user has installed Phase 2 GEM in the
default locations with the default folder names.
Users have the option of choosing a separate location for their Phase 2 GEM installation but
using the default folder as seen in Figure 2 is recommended. The instructions throughout this
User Guide assume the user has installed Phase 2 GEM in the default locations with the default
folder names.
0
Select Destination Location
Where should Phase 2 GEM be installed?
Setup will install Phase 2 GEM into the following folder.
To continue, dick Next. If you would like to select a different folder, dick Browse.
1 a I Ž Ip^sI
At least 6.4 MB of free disk space is required.
Select Start Menu Folder
Where should Setup place the program's shortcuts?
Setup will create the program's shortcuts in the following Start Menu folder.
To continue, dick Next. If you would like to select a different folder, dick Browse.
Browse...
[ ] | Cancel
Figure 2: Destination and Start Menu Folder for Phase 2 GEM Download
Phase 2 GEM requires the use of Matlab Compiler Runtime r2014a and the Microsoft Visual
C++ 2005 or 2008 Redi stributable (x64). The installer will warn users if their computers do not
have the necessary software installed. The setup wizard will install Matlab Runtime Compiler
R2014a (version 8.3) if the box shown on the left side of Figure 3 is checked. A pop-up window
will initiate installation of this software and will remain displayed until installation is complete.
For computers that already have the Matlab Runtime installed, users can uncheck this box to skip
this step. The final screen message as shown below on the right side of Figure 3 appears when
Phase 2 GEM installation has completed.
jj§) Setup - Phase 2 GEM
l*aJ
Select Additional Tasks
Which additional tasks should be performed?
Select the additional tasks you would like Setup to perform while installing Phase 2
GEM, then dick Next.
Additional icons:
W\ Create a desktop icon
Dependencies
f7\ Install Matiab Compiler Runtime
| CBack [| Next > | | Cancel |
Setup - Phase
Completing the Phase 2 GEM
Setup Wizard
Setup has finished installing Phase 2 GEM on your computer
The application may be launched by selecting the installed
icons.
Click Finish to exit Setup.
Figure 3: Installation Windows; Matlab Runtime Compiler R2014a is Required
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II.B. Contents of Installation Package
Once installed, files are stored in the installation location selected (i.e., C:\Program FilesMJS
EPA\Phase 2 GEM\ by default) and are also available from the Start Menu, under the folder
named "EPA Phase 2 GEM". The start menu folder contains shortcuts to the different operating
modes of GEM as well as documentation, the sample input files and an uninstaller.
II.B.l. Sample Input Files
Sample input files are stored with the Phase 2 GEM executable. The "Sample Input Files -
RELOCATE BEFORE USE" folder includes: sample vehicle input files for each of the three
vehicle regulatory subcategories; four folders with example engine, transmission, axle and
powertrain input files; and files to generate cycle averaged fuel maps. A description of each of
these input files and instructions for running the model are provided in later sections of this guide.
Due to file permissions on most installations, GEM is not permitted to use the sample input files
in the location they are installed by default. The recommendation is for users to copy the
contents of the sample input files folder to a location where the user has read and write
permissions to minimize these issues. Users can then easily run GEM and the output results will
be saved in the same folder as the input data.
II.B.2. GEM Executable
EPA and NHTSA require tractor and vocational vehicle manufacturers to use the Phase 2 GEM
executable for demonstrating compliance with the CO2 and fuel consumption standards.2
However, Phase 2 GEM does not offer a graphical user interface (GUI) for users to provide their
vehicle parameters. Instead, inputs are provided in a comma delimited (.csv) file. Results are
available in a generated report that can be viewed using either a text editor or spreadsheet. The
following sections will describe the model, the input files, and the output files in more detail.
III. Model Description
Phase 1 GEM was updated in order to meet Phase 2 rulemaking requirements. Phase 2 GEM
improves the fidelity of the Phase 1 model to better match the function of the simulated vehicles
and accurately reflect changes in technology for compliance purposes. Many of the
modifications were the result of numerous constructive comments from both the public and
GEM peer reviews3. The following sections describe the model with an emphasis on the
additional vehicle parameters available in the Phase 2 upgrade of the model. Users are directed to
Chapter 4 of the RIA for more detailed information regarding the model architecture and
validation.
2 Trailer manufacturers will use a GEM-based equation but are not required to use GEM. For convenience, this User
Guide provides instructions for using GEM for trailers, but manufacturers cannot use GEM for demonstrating
compliance.
3"Peer Review of the Greenhouse gas Emissions Model (GEM) and EPA's Response to Comments," Docket # EPA-
420-R-15-009, June 2015.
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III.A. GEM Architecture
The GEM architecture is comprised of four systems: Ambient, Driver, Powertrain, and Vehicle
as seen in Figure 4. The Powertrain and Vehicle systems consist of one or more subcomponent
models and a description of the subcomponent models is available in Chapter 4 of the Phase 2
GHG RIA.
GEM Vehicle Mode t
[vehicl
GEM_CVM powertrain
vehicle
Scope
driver
[powertrain] ^>-
[driver]
[ambient]
[vehicle]
[system _busj
[ambient]
Memory
~
sy stem_bus
buscxjl
sy stem_bus
bus_out
sy stem_bus
massoutkg
force_out_N
bus_out
force_in_N
veh_spd_mps
busoiit
ambient
Figure 4: Simulink Structure of GEM Vehicle Model
EPA and NHTSA are adopting additional regulatory subcategories to better represent the heavy-
duty vehicles. These subcategories are reflected in GEM with additional vehicle models. Phase 2
GEM also incorporates improvements to the duty cycles, including the addition of idle cycles for
vocational vehicles, and modified cruise cycles that account for changes in road grade.
Specifically, the agencies implemented the following key technical features into Phase 2 GEM
along with many others:
Upgraded engine controller which includes engine fuel cut-off during braking and
deceleration and a cycle average method to supplement the steady state fuel map for
transient simulation which can optionally be applied to the cruise cycles.
Upgraded transmission model which includes automatic and automated manual
transmissions. Optional transmission power loss input and torque converter properties are
also available.
Upgraded driver model with a distance-compensated driver that will drive the
certification drive trace over a prescribed distance regardless of increased drive time due
to vehicle under-performance.
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Increased options for number of driven axles including the ability to include axle power
losses measurement data.
With these upgrades, the model can recognize most technologies that could be evaluated in both
engine and chassis dynamometers and is better able to reflect changes in technologies for
compliance purposes. See Chapter 4 of the RIA for more information about these upgrades.
III.A.l. Drive Cycles and Cycle Average Engine Fuel Map
Phase 2 GEM utilizes three drive cycles including a transient cycle and two cruise speed cycles.
The transient mode is defined by California Air Resources Board (CARB) in their Highway
Heavy-Duty Diesel Transient (HHDDT) cycle. The cruise speed cycles are represented by two
nominally constant speed 65 mph and 55 mph cycles, each with varying road grade. For
vocational vehicles two additional idle measurements are utilized, one simulating parked idling
operation and the other idling in traffic. Each regulatory subcategory is assigned a specific set of
drive cycle weightings.
The agencies recognize the limitation of the steady state engine fuel map for transient simulation
and are requiring that a cycle average fuel map be generated to supplement the steady state fuel
map for the transient cycle. Additionally, users have the option to apply the cycle average
method to the 55 and 65 mph cruise cycles as well. A summary of the procedure to generate the
cycle average map(s) is provided in section VI.D of this Guide. A detailed description and
justification for the cycle average method can be found in Chapter 4 of the Phase 2 GHG RIA.
III.B. Vehicle Parameters for Each Regulatory Subcategory
GEM can simulate a wide variety of Class 2b to Class 8 vehicles. The key to this flexibility is the
component description files that can be modified or adjusted to accommodate a variety of
vehicle-specific information. Phase 2 GEM includes several variations to match potential
powertrain options and the regulatory subcategories in the Phase 2 rulemaking. Each regulatory
subcategory is associated with specific vehicle parameters and technology options.
Many key parameters in GEM are predefined, since those parameters are either hard to quantify
due to lack of certified testing procedures or difficult to obtain due to proprietary barriers.
Examples of these parameters include transmission shifting strategies and engine inertia. The
values selected for these parameters are a result of substantial testing by EPA, as well as
confidential discussions with engine, chassis and component manufacturers. Some default
parameters have optional overrides, which require additional testing.
Each vehicle category has a set of user-defined parameters. These parameters include vehicle
technologies or component attributes that impact CO2 emissions and fuel consumption but have
the potential to vary across manufacturers. Depending on the regulatory category, parameters
such as aerodynamic performance, tire rolling resistance, vehicle weight, engine fuel map,
transmission gear ratios, tire radius, or axle ratio can be changed as inputs by the user.
The sections to follow outline the regulatory vehicle categories that manufacturers may select in
GEM for compliance and summarize the predefined and user-defined and parameters applicable
to each subcategory as well as regulatory citations for associated testing procedures. Details on
the file formats for entering the user defined parameters are discussed in GEM Input Files.
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III.B.l. Tractor Vehicle Parameters
GEM recognizes sixteen variations (regulatory subcategories) of combination tractors. Class 8
tractors can have day or sleeper cab configurations with low, mid, or high roof heights. Class 7
tractors are only available in a day cab configuration but also have low, mid, or high roof
options. GEM also recognizes Class 8 heavy-haul tractors with a single vehicle for all cabs and
roof heights, and six optional heavy Class 8 tractor subcategories to represent tractors with
higher gross combined weight rating (GCWR) that are designed for heavy-haul operation in
Canada.
Within GEM, high roof tractors are simulated as pulling a standard box van. Mid roof tractors
and low roof tractors are simulated as pulling tank and flatbed trailers, respectively. The standard
box van for high roof tractor simulations also includes a skirt, which impacts the modeled
aerodynamic drag area input, CdA. Note that in MY 2027 and later, GEM will subtract 0.3 m2
from the user's CdA input value for high roof tractors to account for improved box trailer
aerodynamics.
Table 1 through Table 3 summarize some of the predefined modeling parameters for default
tractor subcategories. The standard Class 8 payload is 19 tons. All Class 8 heavy-haul tractors,
including the optional heavy Class 8, have a payload of 43 tons. The Class 7 payload is 12.5
tons. Sleeper cab tractors are assigned drive cycle weightings that are more representative of
long-haul driving. Drive cycle weightings for day cab tractors are more representative of short-
haul driving with more transient cycle operation.
Table 1: Class 8 Combination Tractor Predefined Modeling Parameters
Sleeper Cab
Day Cab
Heavy Haul
Roof Height
High
Mid
Low
High
Mid
Low
All
Total Weight (kg)
31978
30277
30390
31297
29529
29710
53750
Number of Axles
5
5
5
Payload (tons)
19
19
43
Drive Cycle
Weighting
CARB HHDDT
0.05
0.19
0.19
GEM 55 mph
0.09
0.17
0.17
GEM 65 mph
0.86
0.64
0.64
Table 2: Class 7 Combination Tractor Predefined Modeling Parameters
Day Cab
Roof Height
High
Mid
Low
Total Weight (kg)
22679
20910
21091
Number of Axles
4
Payload (tons)
12.5
Drive Cycle
Weighting
CARB HHDDT
0.19
GEM 55 mph
0.17
GEM 65 mph
0.64
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Table 3: Heavy Class 8 Combination Tractor Predefined Modeling Parameters
Sleeper Cab
Day Cab
Roof Height
High
Mid
Low
High
Mid
Low
Total Weight (kg)
53750
52049
52162
53069
51301
51482
Number of Axles
5
5
Payload (tons)
43
43
Drive Cycle
Weighting
CARB HHDDT
0.05
0.19
GEM 55 mph
0.09
0.17
GEM 65 mph
0.86
0.64
Table 4 shows the predefined modeling parameters that are consistent across all tractor types.
These common parameters include ambient temperature, efficiencies and accessory powers. The
calculations for overall rolling resistance and the distribution of weight savings are also
consistent for all simulated tractors.
Table 4: Common Predefined Modeling Parameters for All Simulated Combination Tractors
Electrical Accessory Power (W)
1200
Mechanical Accessory Power (W)
2300
Environmental air temperature (°C)
25
Weight Reduction (lbs)
Add l/3*weight reduction to payload mass,
Subtract 2/3*weight reduction from the vehicle simulated mass
Trailer Tire Crr (kg/t)
6.0
Overall Tire Crr Calculation (kg/t)
= 0.425*Trailer Crr + 0.425*Drive Crr + 0.15*Steer Crr
GEM allows the user to modify or adjust performance information for certain components in
order to quantify the reduction in tractor fuel consumption and CO2 emissions. More information
on the specific inputs and the procedures to determine them for combination tractors are listed in
section IV. A.
In Phase 1, a default engine and transmission were applied to all GEM-simulated combination
tractors. Phase 2 GEM requires tractor manufacturers to supply an engine fuel map and specific
transmission information as separate input files to the model. Manufacturers also have the option
to use engine and transmission performance data obtained from a powertrain test in their GEM
runs and replace the engine and transmission files with a single powertrain file. Additionally,
manufacturers can optionally include data for transmission and/or axle power loss the
appropriate supplemental input file. These input files have specific requirements, available in the
Supplemental Input Files section of this Guide.
Table 5: Default Transmission Losses for Simulated Combination Tractors
MT or
AMT
Gearbox
Mechanical
Efficiency
9 or more gears
96% for low gears, 98% high gears,
except 100% for 1:1 gear ratio
fewer than 9 gears
100% for 1:1 gear ratio, 98% for rest of gears
Spin Loss
12.3-30.1 Nm, varies with speed
AT
Gearbox
Mechanical Efficiency
99.5% for 1:1 gear ratio, 98% for rest of gears
Spin Loss
40.5 - 65.2 Nm, varies with speed
8
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The default transmission losses in Table 5 are used if transmission power loss information is not
provided within the transmission input file. The default losses are different whether the
transmission is a manual (MT), automated manual (AMT) or a planetary type automatic
transmission (AT). The "low gears" mentioned in the MT or gearbox efficiency of Table 5 only
applies when the total gear number of a transmission is greater than 9. In this type of
transmission, the low gear efficiency of 96% will be used for gear number less than or equal to
the greater of total number of gears divided by two or the total number of gears minus 6. Taking
a transmission with 10 gears for example, the greater of 10/2 or 10-6, would be 5. Thus, gears 1 -
5 would have 96% efficiency.
Phase 2 GEM also accounts for additional technology improvements that reduce CO2 and fuel
consumption but are not easily captured in the vehicle simulation. These reduction values vary
for each technology. The effect of vehicle speed limiter, weight reduction and neutral idle
technology improvement inputs will impact the vehicle simulation. The remaining technologies
improvements are applied as post-process percent reductions to the results from the vehicle
simulation. More detail on the available technology improvement options for tractors and how to
determine the inputs is provided in section IV. A.
III.B.2. Vocational Vehicle Parameters
GEM recognizes nine variations of vocational vehicles based on both vehicle weight class and
duty cycle. Class 8 vocational vehicles are considered heavy heavy-duty (HHD). Classes 6 and 7
are medium heavy-duty (MHD), and Classes 2b-5 are considered light heavy-duty (LHD). As
demonstrated in Table 6, Table 7 and Table 8 weight, number of axles, aerodynamic drag area
and payload are the same for all of the vehicles within a weight class. Vehicles within each
weight class are further categorized using three duty cycles (Regional, Multi-purpose and Urban)
by varying the drive cycle weightings associated with each composite duty cycle.
The regulations describe the drive cycle weighting factors for each subcategory in 40 CFR
1037.510. Manufacturers should consult the regulations at 40 CFR 1037.510(c) as well as 40
CFR 1037.140(g-h) and 40 CFR 1037.150(z) for instructions on how to select the appropriate
subcategory in which to certify a vocational vehicle configuration. The reasoning behind the
regulations can be found in the preamble of the Phase 2 GHG Rule Section V.D. 1 .e.
Table 6: Vocational Heavy Heavy-Duty (Class 8) Vehicle Predefined Modeling Parameters
Regulatory Subcategory
HHD
Duty Cycle
Regional
Multi-Purpose
Urban
Total weight (kg)
19051
Aerodynamic Drag Area - CdA (m2)
6.86
Payload (tons)
7.50
Electrical Accessory Power (W)
1200
Mechanical Accessory Power (W)
2300
ARB Transient Drive Cycle Weighting
0.20
0.54
0.90
GEM 55 mph Drive Cycle Weighting
0.24
0.23
0.10
GEM 65 mph Drive Cycle Weighting
0.56
0.23
0.00
Parked Idle Cycle Weighting
0.25
0.25
0.25
Drive Idle Cycle Weighting
0.00
0.17
0.15
Non-Idle Cycle Weighting
0.75
0.58
0.60
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Table 7: Vocational Medium Heavy-Duty (Class 6-7) Vehicle Predefined Modeling Parameters
Regulatory Subcategory
MHD
Duty Cycle
Regional
Multi-Purpose
Urban
Total weight (kg)
11408
Aerodynamic Drag Area - CdA (m2)
5.40
Payload (tons)
5.60
Electrical Accessory Power (W)
900
Mechanical Accessory Power (W)
1600
ARB Transient Drive Cycle Weighting
0.20
0.54
0.92
GEM 55 mph Drive Cycle Weighting
0.24
0.29
0.08
GEM 65 mph Drive Cycle Weighting
0.56
0.17
0.00
Parked Idle Cycle Weighting
0.25
0.25
0.25
Drive Idle Cycle Weighting
0.00
0.17
0.15
Non-Idle Cycle Weighting
0.75
0.58
0.60
Table 8: Vocational Light Heavy-Duty (Class 2b-5) Vehicle Predefined Modeling Parameters
Regulatory Subcategory
LHD
Duty Cycle
Regional
Multi-Purpose
Urban
Total weight (kg)
7257
Aerodynamic Drag Area - CdA (m2)
3.40
Payload (tons)
2.85
Electrical Accessory Power (W)
500
Mechanical Accessory Power (W)
1000
ARB Transient Drive Cycle Weighting
0.20
0.54
0.92
GEM 55 mph Drive Cycle Weighting
0.24
0.29
0.08
GEM 65 mph Drive Cycle Weighting
0.56
0.17
0.00
Parked Idle Cycle Weighting
0.25
0.25
0.25
Drive Idle Cycle Weighting
0.00
0.17
0.15
Non-Idle Cycle Weighting
0.75
0.58
0.60
GEM also provides seven custom chassis subcategories for manufacturers that know the specific
end-use of their vehicles. These custom chassis subcategories are listed in Table 9, and are based
on the standard vocational subcategories. In contrast to the standard vocational subcategories,
custom chassis utilize default inputs for several of the parameters, particularly the engine and
transmission. Use of the custom chassis subcategories reduces the number of required inputs but
also limits the ability to apply some technology improvements. Further details on how to input
data for these subcategories is described in the Vocational Input Files section of this Guide.
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Table 9: Vocational Custom Chassis Subcategories and Associated Vehicle in GEM
Custom Chassis Subcategory
GEM Simulated Vehicle
Emergency Vehicles
HHD Urban
Cement Mixers and Other Mixed-Use Applications
HHD Urban
Refuse Vehicles
HHD Urban
Coach Buses
HHD Regional
Transit Bus, Other Bus and Drayage Tractors
HHD Urban
Motor Homes
MHD Regional
School Bus
MHD Urban
Table 10 provides the predefined modeling parameters that are consistent across all vocational
vehicle types. These common parameters include ambient temperature, the calculations for
overall rolling resistance and how weight reduction is applied. Note that some factors which
were common across tractors vary with vocational weight class.
Table 10: Common Predefined Modeling Parameters for All Vocational Vehicles
Environmental Air Temperature (°C)
25
Weight Reduction (lbs)
Add l/2*weight reduction to payload mass,
Subtract l/2*weight reduction from the simulation vehicle mass
Overall Tire Crr (kg/t)
0.7*Drive Crr + 0.3*Steer Crr
GEM allows a user to enter performance information for certain components in order to model
and quantify improvements the manufacturer is making to its vehicles. Table 10 lists the user-
defined modeling parameters for vocational vehicles in addition to a reference to the applicable
test methods in the regulation. Phase 2 GEM continues to allow vocational vehicle manufacturers
to model their vehicle's tire rolling resistances, but also requires axle configuration, axle ratio,
and loaded size of the tires for standard vocational chassis subcategories. The model also
provides the option to account for aerodynamic drag as a wind-averaged change in aerodynamic
drag area (delta CdA).
For the non-custom chassis vocational categories Phase 2 GEM requires manufacturers to supply
an engine fuel map and specific transmission information for each distinct engine and
transmission in the vehicles being modeled. Manufacturers also have the option to use engine
and transmission performance data obtained from a powertrain test in their GEM runs and
replace the engine and transmission files with a single powertrain file. Additionally,
manufacturers can optionally include data for transmission and/or axle power loss the
appropriate supplemental input file. These input files have specific requirements, as will be
discussed in the Supplemental Input Files section of this Guide.
The default transmission losses in Table 11 are used if transmission power loss information is
not provided within the transmission input file. The default losses are different whether the
transmission is a manual (MT), automated manual (AMT) or a planetary type automatic
transmission (AT). The "low gears" mentioned in the MT or gearbox efficiency only applies
when the total gear number of a transmission is greater than 9. In this type of transmission, the
low gear efficiency of 96% will be used for gear number less than or equal to the greater of total
number of gears divided by two or the total number of gears minus 6. Taking a transmission with
11
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10 gears for example, the greater of 10/2 or 10-6, would be 5. Thus, gears 1-5 would have 96%
efficiency.
Table 11: Default Transmission Losses for Vocational Vehicles
MT or
AMT
Gearbox
Mechanical
Efficiency
9 or more gears
96% for low gears, 98% high gears,
except 100% for 1:1 gear ratio
fewer than 9 gears
100% for 1:1 gear ratio, 98% for rest of gears
Spin Loss
HHD
12.3 - 30.1 Nm, varies with speed
MHD
9.1 - 22.3 Nm, varies with speed
LHD
5.9 - 14.5 Nm, varies with speed
AT
Gearbox
Mechanical Efficiency
99.5% for 1:1 gear ratio, 98% for rest of gears
Spin Loss
HHD
40.5 - 65.2 Nm, varies with speed
MHD
26.2 - 42.1 Nm, varies with speed
LHD
23.5 - 37.9 Nm, varies with speed
Similar to the tractor model, Phase 2 GEM accounts for additional vocational vehicle
technologies that reduce CO2 and fuel consumption but are not easily captured in the vehicle
simulation. These reduction values vary for each technology. The vehicle speed limiter, weight
reduction, neutral idle, and start-stop options will impact the vehicle simulation. The remaining
technologies improvements are applied as post-process g/ton-mile or percent reductions to the
results from the vehicle simulation. Table 12 directs users to the corresponding regulation
reference to determine appropriate values to apply for each technology. These technology
improvements are available to all vocational subcategories.
Table 12: Technology Improvement Options for Vocational Vehicle Manufacturers
Technology Improvement
Regulation Reference
Vehicle Speed Limiter (MPH or NA)
40 CFR 1037.520(d)
Delta Power Take Off Fuel (g/ton-mile)
40 CFR 1037.520(k) and 1037.540
Weight Reduction (lb)
40 CFR 1037.520(e)
Neutral Idle (Y/N)
40 CFR 1037.520(h)
Start-Stop (Y/N)
40 CFR 1037.520(h)
Automatic Engine Shutdown
40 CFR 1037.520(h)
Accessory Load (%)
40 CFR 1037.520Š
Tire Pressure System (%)
40 CFR 1037.520Š
Other (%)
40 CFR 1037.520Š
IILB.3. Trailer Vehicle Parameters
The agencies are adopting an equation-based compliance approach for box trailer manufacturers
and they are not required to certify their trailers using GEM (see 40 CFR 1037.515). However,
the equations for each box trailer subcategory are based on the simulated trailers described in this
section. Note that non-box trailers do not use GEM or the GEM-based equation for compliance
and a discussion of non-box trailers is not included in this User Guide. The following description
of the trailer model as it applies to box trailers is included for informational purposes only.
12
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The agencies are adopting a set of predefined modeling parameters to establish consistent
tractor-trailer models from which box van trailer manufacturers can compare their vehicle
improvements. GEM recognizes four variations of box van based on length. Long box vans
(trailers that are longer than 50-feet) are represented by either a 53-foot dry van or a 53-foot
refrigerated van pulled by a Class 8 high roof sleeper cab tractor in GEM and are given the same
long-haul drive cycle weightings as the Class 8 high roof sleeper cab tractors mentioned
previously. GEM models all short box vans (box trailers 50-feet in length and shorter) as a
single-axle, solo 28-foot dry van or refrigerated van pulled by a Class 7 high roof day cab tractor
with a 4x2 drive axle configuration.
Table 13 summarizes the predefined modeling parameters for long and short box vans,
respectively. All long box vans are modeled with tandem axles and a payload of 19 tons and
drive cycle weightings that are more representative of long-haul driving (i.e., 86 percent at 65-
MPH, 9 percent at 55-MPH and 5 percent transient). All short box vans are modeled with a
single axle, a payload of 10 tons, and drive cycle weightings more representative of short-haul
driving with 64 percent at 65-MPH, 17 percent at 55-MPH, 19 percent transient. The vehicle
weight varies between dry vans and refrigerated vans to account for the weight of the
refrigeration unit, and weight also varies proportional to the length of the trailer. The baseline
CdA values were obtained from EPA's aerodynamic testing.
Table 13: Predefined Modeling Parameters for Box Trailers
Regulatory Subcategory
Long Box
Dry Van
Long Box
Refrigerated
Van
Short Box
Dry Van
Short Box
Refrigerated
Van
Tractor Type
C8 Sleeper Cab - High Roof
C7 Day Cab - High Roof
Total weight (kg)
31978
33778
18306
20106
Baseline CdA Values (m2)
6.0
6.0
5.6
5.6
Tractor Engine
15L 455 HP
11L 350 HP
Tractor Drive Axle Configuration
6x4
4x2
Number of Axles
5
3
Payload (tons)
19
10
CARB HHDDT Drive Cycle Weighting
0.05
0.19
GEM 55 mph Drive Cycle Weighting
0.09
0.17
GEM 65 mph Drive Cycle Weighting
0.86
0.64
Table 14 shows the predefined modeling parameters that are consistent across all trailer types.
Many of these common parameters are associated with the simulated tractor in the tractor-trailer
model. The calculations for overall rolling resistance and the distribution of weight savings are
consistent with the calculations for GEM-simulated tractors.
13
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Table 14: Common Predefined Modeling Parameters for All Box Trailers
Gearbox Efficiency
100% for 1:1 gear ratio, 96% for lower gears or 98% for
rest of gears
Axle Drive Ratio
3.7
Electrical Accessory Power (W)
300
Mechanical Accessory Power (W)
1000
Loaded Tire Size (rev/mi)
512
Steer Tire Crr (kg/t)
6.54
Drive Tire Crr (kg/t)
6.92
Overall Tire Crr (kg/t)
= 0.425*Trailer Crr + 0.425*Drive Crr + 0.15*Steer Crr
Weight Reduction (lbs)
Add l/3*weight reduction to pay load mass
GEM allows a user to modify or adjust performance information for certain components in order
to model and quantify improvements the manufacturer is making to its vehicles. The trailer
program has three user-defined parameters and one pre-defined technology improvement option
that has a specified reduction value associated with its use (see Table 15). Trailer manufacturers
can change their tire rolling resistance, aerodynamic drag and cumulative weight reduction.
GEM applies an additional percent improvement value to trailers that have tire pressure systems
installed on their simulated trailer. Separate percentage values apply for tire pressure monitoring
systems (TPMS) and automatic tire inflation systems (ATIS).
Table 15: User-Defined Modeling Parameters and Technology Improvement Options for Trailers
Modeling Parameter
Method of Determining Parameter
Trailer Tire Crr (kg/t)
40 CFR 1037.515(b)
Change in Aerodynamic Drag Area, ACdA (m2)
40 CFR 1037.515(c) and 40 CFR 1037.526
Weight Reduction (lb)
40 CFR 1037.515(d)
Tire Pressure Systema
1.2% for ATIS, 1.0% for TPMS, 0 if no system
a Note 40 CFR 1037.515(a) specifies the tire pressure system values in decimal format, because trailers use a GEM-based
equation for compliance. The GEM input file described in this Guide uses percent-based input values for tire pressure systems.
IV. GEM Input Files
As mentioned previously, Phase 2 GEM does not offer a graphical user interface (GUI) for users
to provide their vehicle parameters. Instead, inputs are exclusively provided to the model in a
.csv file. Phase 2 GEM executable can be initiated using the Start Menu, or a command prompt.
The following subsections describe the input file structures, which are consistent for each
method of running the model.
Some manufacturers may create a script to automatically generate their input files in CSV
(comma separated value) format. Others may wish to manually populate their files using a
spreadsheet tool, such as Microsoft Excel, to easily view the input fields in a column format. For
illustration purposes, the sample input data in this document are shown in tabular spreadsheet
like format. Users may use Microsoft Excel or any other text editor, to create or edit their input
files. If using a spreadsheet program be sure to save the files in CSV format.
14
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The top of the input file for each of the regulatory categories has three lines that list the
regulatory category, manufacturer name and model year (see Sample 1). User entries in the
second column determine the processing that will be applied to the file. The first line contains
the regulatory category and must contain "Tractor", "Vocational" or "Trailer" as appropriate for
the vehicles being simulated. Manufacturer name can be in any format, but it should be
consistent with other regulatory documents from the manufacturer. Model year must be
expressed as a four-digit number.
Sample 1: Input File Header Information
Regulatory Category
Tractor
Manufacturer Name
EPA
Model Year
2018
The subsequent lines of the input file list the model inputs with one simulation listed per line.
The first two columns contain a Run ID and the Regulatory Subcategory for each run. The Run
ID is a unique value that will be used to identify the run (e.g., vehicle VIN) and can be any
combination of letters, numbers and separators such as dash ("-"), periods ("."), or underscores
("_"). The Regulatory Subcategory determines the vehicle and associated predefined parameters
that are to be simulated along with the standard that is applied for compliance. Additional detail
is provided in the following sections regarding the columns and requirements specific to each
regulatory category. Each is accompanied with snippets containing selected columns from the
sample input files.
IV.A. Tractor Input Files
Tractor Sample 1 shows a sample of the first two columns for a tractor input file. Table 16 shows
corresponding subcategory identifiers for use in column two. The first 10 are the standard
regulatory subcategories. The final six (starting with HC8) are the optional heavy Class 8 tractor
subcategories that represent tractors designed for heavy-haul operation in Canada. Manufacturers
may optionally certify their tractors as heavy Class 8, using the subcategories shown starting in
MYs 2021. See Section III.B.4.a of the preamble to this rulemaking for a discussion of these
optional tractor subcategories. Note these tractors are separate from the C8 HH subcategory that
is used for U.S.-based heavy-haul tractors.
15
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Tractor Sample 1: Input File Run ID and Regulatory Subcategory Inputs
Run ID
Regulatory Subcategory
Unique Identifier
(e.g. C8_SC_HR)
Sample_l
C8 SC HR
Sample_2
C7 DC MR
Sample_3
C8 HH
Sample_4
HC8 SC LR
Sample_5
HC8 DC MR
Sample_6
C8 DC MR
Sample_6a
C8 DC MR
Sample_7
C8 SC LR
Sample_8
C8 SC HR
PT_Samplel
C8_SC_HR
Table 16: Tractor Input File Naming Convention for Tractor Regulatory Subcategories
GEM Input Name
Regulatory Subcategory Description
C8SCHR
Class 8 Combination, Sleeper Cab - High Roof
C8SCMR
Class 8 Combination, Sleeper Cab - Mid Roof
C8SCLR
Class 8 Combination, Sleeper Cab - Low Roof
C8DCHR
Class 8 Combination, Day Cab - High Roof
C8DCMR
Class 8 Combination, Day Cab - Mid Roof
C8DCLR
Class 8 Combination, Day Cab - Low Roof
C8HH
Class 8 Combination, Sleeper Cab - Heavy Haul
C7DCHR
Class 7 Combination, Day Cab - High Roof
C7DCMR
Class 7 Combination, Day Cab - Mid Roof
C7DCLR
Class 7 Combination, Day Cab - Low Roof
HC8SCHR
Heavy Class 8 Combination, Sleeper Cab - High Roof
HC8SCMR
Heavy Class 8 Combination, Sleeper Cab - Mid Roof
HC8SCLR
Heavy Class 8 Combination, Sleeper Cab - Low Roof
HC8DCHR
Heavy Class 8 Combination, Day Cab - High Roof
HC8DCMR
Heavy Class 8 Combination, Day Cab - Mid Roof
HC8DCLR
Heavy Class 8 Combination, Day Cab - Low Roof
The next columns in the input file are for information regarding the tractor powertrain. The
primary items are the engine and transmission file names or the powertrain file name. A
description of the content of these supplemental input files is located at the end of this section.
The text in the fields of the input file must exactly match the file name, including the .csv
extension for GEM to run properly. In the Sample Input Files folder provided with GEM, the
supplemental files are in separate Axle, Engine, Powertrain and Transmission subfolders. GEM
searches for the supplemental files from the same location as the vehicle input file. As a result,
the subfolder name must be included in the File Name fields to direct the model to the files. If
users have their engine, transmission, powertrain and axle files in the same folder as the vehicle
input file, only the filename is needed.
16
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Tractor Sample 2: Input File Reference to Engine, Transmission, and Powertrain Input Files
Engine
Engine
Transmission
Data
Idle Speed
at CUT
Data
File Name
RPM
File Name
Engines\EPA_2018_D_GENERIC_455_trans_c...
600
Transmissions\EPA_AMT_10_C78_4490.csv
Engines\EPA_2018_D_GENERIC_350_trans_ c...
650
Transmissions\EPA_AMT_10_C78_4490.csv
Engines\EPA_2018_D_GENERIC_600_trans_ c...
600
Transmissions\EPA_AMT_10_C78_4490.csv
Engines\EPA_2018_D_GENERIC_600_trans_ c...
600
Transmissions\EPA_MT_13_C78_4543.csv
Engines\EPA_2018_D_GENERIC_455_trans_ c...
600
Transmissions\EPA_AMT_10_C78_4490.csv
Engines\EPA_2018_D_GENERIC_455_trans_ c...
600
Transmissions\EPA_AT_10_C78_8001.csv
Engines\EPA_2018_D_GENERIC_455_trans_ c...
650
Transmissions\EPA_AT_10_C78_8001.csv
Engines\EPA_2018_D_GENERIC_455_trans_ c...
600
Transmissions\EPA_AMT_10_C78_4490_power_l...
Engines\EPA_2018_D_GENERIC_455_all_cyc_...
600
Transmissions\EPA_AMT_10_C78_4490.csv
Powertrains\EPA_Sample_Powertrainl.csv
600
Powertrains\EPA_Sample_Powertrainl.csv
Manufacturers may choose to perform powertrain testing to obtain the engine and transmission
performance for their GEM simulations. In order to indicate to GEM that powertrain data is
provided, users would provide the same powertrain input file name in both the Engine and
Transmission file name fields of the tractor input file as seen in the last row of Tractor Sample 2.
Another powertrain parameter in this section is the engine idle speed. This allows calibrated idle
speeds to be set at the vehicle level without the need for multiple engine input files. The idle
speed in this column will be used to interpolate the idle fuel maps within the engine input file to
adjust the estimated fuel consumption and emissions. For more information on the appropriate
value to enter see 40 CFR 1036.510.
Tractor Sample 3 shows the next columns containing the tractor performance parameters and
several vehicle characteristics that are user-defined in GEM. Procedures or guidance to
determine the appropriate value for each of these parameters is available in Table 17, with
further information available in the preamble to the Phase 2 rulemaking.
17
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Tractor Sample 3: Input File Performance Parameters and User-Defined Vehicle Characteristics
Drive Axle
Drive
Axle
Drive Axle
Aerodynamic
Steer Axle
Tire
Drive Axle
1 Tire
Drive Axle
2 Tire
Drive
Axle Tire
Configuration
Ratio
Data
Aerodynamic
Drag Area
(CdA)
Rolling
Resistance
Level
Rolling
Resistance
Level
Rolling
Resistance
Level
Loaded
Tire Size
(e.g. 6x4)
#
File Name
mA2
kg/t
kg/t
kg/t
rev/mi
6x4
3.08
NA
5.4
6.9
6.9
6.9
500
4x2
3.42
NA
5.1
6.9
6.9
NA
500
6x4
3.23
NA
NA
6.9
6.9
6.9
500
6x4
3.12
NA
5.07
7
6.8
6.8
512
6x4
3.45
NA
5.35
6.9
6.9
6.9
500
6x4
3.45
NA
5.18
6.9
6.9
6.9
512
6x4
3.45
NA
5.18
6.9
6.9
6.9
512
6x4 D
3.12
Axles\EPA_Axle.csv
4.88
6.9
6.9
6.9
500
6x4
3.08
NA
5.4
6.9
6.9
6.9
500
6x4
3.08
NA
5.4
6.9
6.9
6.9
500
Table 17: User-Defined Modeling Parameters for Class 7 and Class 8 Combination Tractors
Modeling Parameter
Method of Determining Parameter
Drive Axle Configuration
40 CFR 1037.520(g)(2)
Drive Axle Ratio
40 CFR 1037.520(g)(3)
Drive Axle data file (Optional)
40 CFR 1037.560
Aerodynamic Drag Area, CdA (m2)
See 40 CFR 1037.520(b)
Steer Axle Tire Rolling Resistance (kg/t)
40 CFR 1037.520(c)
Drive Axle 1 Tire Rolling Resistance (kg/t)
Drive Axle 2 Tire Rolling Resistance (kg/t)
Drive Axle Loaded Tire Size (rev/mi)
See 40 CFR 1037.520(c)
The Drive Axle Data File Name field points to the location and name of the optional axle file.
Note, if users do not use an optional axle file, then "NA" should be entered. The format of this
field is similar to the engine and transmission file fields. For tractors that have a single rear axle
(i.e., 4x2 axle configuration), the users input an "NA" into the Drive Axle 2 Tire Rolling
Resistance Level field for those vehicles. Also, heavy-haul tractors (third row) have a default
Aerodynamic Drag Area (CdA) of 5.0 m2 within GEM, so users also input an "NA" into that
field for heavy-haul tractors.
There are limits associated with each user-defined input value. Drive Axle Configuration is a text
input and the allowable options are "6x4", "4x2", "6x4D", or "6x2". Vehicles with more than
two drive axles are instructed to use the "6x4" configuration in the model. All tractors with
"6x2" axle configurations are modeled with five axles with two steer tires, 4 non-drive tires and
4 drive tires. All tractors with "6x4" axle configurations are modeled with five axles with two
steer tires and eight drive tires. The only difference in GEM between "6x2" and "6x4" axles is an
additional 1 percent loss for "6x4" axles to account for the inter-axle losses. All tractors with
"6x4D" axle configurations are modeled as "6x2" axles on the cruise cycles and "6x4" axles on
18
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the transient cycle. All tractors with a "4x2" axle are represented by a four-axle tractor with two
steer tires and four drive tires Table 18 shows the limits for the remaining six tractor inputs in the
model. GEM will produce an error if any of these values are out of the acceptable range and will
round any values beyond their specified decimal limits.
Table 18: Minimum and Maximum Limits for User-Defined Values in Tractor Input Files
User-Defined Parameter
Units
Number of
Decimals
Minimum
Value
Maximum
Value
Drive Axle Ratio
#
2
1.00
20.00
Aerodynamic Drag Area (CdA)
mA2
2
3.00
8.00
Steer Axle Tire, Rolling Resistance Level
kg/t
1
3.0
20.0
Drive Axle 1 Tire, Rolling Resistance Level
kg/t
1
3.0
20.0
Drive Axle 2 Tire, Rolling Resistance Level
kg/t
1
3.0
20.0 or NA
Drive Axle Loaded Tire Size
rev/mi
0
100
1000
The remaining columns in the tractor input file are for the optional technology improvements.
These technology improvement fields cannot be blank in the input file. The first three tractor
technology improvements, shown in Tractor Sample 4, will directly impact the vehicle
simulation. Vehicle speed limiters reduce the maximum allowable speed of the vehicle during
the simulation to the user-specified value. Weight reduction reduces the overall vehicle weight
(and increases payload). If no weight reduction is used, then input "0". Neutral-idle reduces the
fuel consumption of the engine when a simulated automatic transmission vehicle is idling. If the
vehicle includes neutral-idle technology, then input "Y", otherwise enter "N".
Tractor Sample 4: Technology Improvements
Technology Improvement
Technology Improvement
Technology Improvement
Vehicle Speed Limiter
Weight Reduction
Neutral-Idle
MPH or NA
lbs
Y/N
NA
0
N
NA
100
N
NA
0
N
NA
0
N
NA
0
N
NA
0
Y
NA
0
Y
NA
0
N
NA
0
N
NA
0
N
The remaining technology improvements, shown in Tractor Sample 5, have specific percent
reductions that manufacturers will apply for the given technology fields. If the technology
improvement(s) is not applicable to the vehicle being simulated, then input "0". The Other field
may be used for several technologies, including results from any off-cycle testing that
manufacturers may perform. Reference 40 CFR 1037.520 for general information or regarding
19
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how to determine percent values. All values of "Y", "N", or "NA" must be in UPPERCASE
LETTERS. Lowercase letters will produce an error.
Tractor Sample 5: Technology Improvements with Pre-Defined Percent Improvements
Technology
Improvement
Technology
Improvement
Technology
Improvement
Technology
Improvement
Technology
Improvement
Intelligent
Controls
Accessory Load
Extended Idle
Reduction
Tire Pressure
System
Other
%
%
%
%
%
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Table 19: Technology Improvement Options for Tractor Manufacturers
Technology Improvement
Regulation Reference
Vehicle Speed Limiter (MPH or NA)
40 CFR 1037.520(d)
Weight Reduction (lb)
40 CFR 1037.520(e)
Neutral Idle, AT only (Y/N)
40 CFR 1037.660
Intelligent Controls (%)
40 CFR 1037.520(j)
Accessory Load (%)
40 CFR 1037.520(j)
Extended Idle Reduction, Sleeper Cabs Only (%)
40 CFR 1037.520(j)
Tire Pressure System (%)
40 CFR 1037.520(j)
Other (%)
40 CFR 1037.520(j)
Table 19 directs users to the corresponding regulation reference to determine appropriate values
to apply for each technology. Similar to the user-defined parameters, these technology
improvements also have limits. The format and limits for the technology improvements are
shown in Table 20. Input values with additional decimal places will be rounded to the
appropriate precision. Input values outside the minimum and maximum range specified will
produce an error.
20
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Table 20: Minimum and Maximum Limits for Technology Improvement Values in Tractor Input File
Modeling Parameter
Units
Number of
Decimals
Minimum
Maximum
Vehicle Speed Limiter
MPHorNA
1
54.0
65.0
Weight Reduction
lb
0
0
40,000
Neutral Idle, Automatic Transmissions Only
Y/N
-
-
-
Intelligent Controls
%
1
1.0
10.0
Accessory Load
%
1
1.0
10.0
Extended Idle Reduction, Sleeper Cabs Only
%
1
1.0
10.0
Tire Pressure System
%
1
1.0
10.0
Other
%
1
1.0
50.0
IV.B. Vocational Input Files
Consistent with the other regulatory categories, the first two columns, as shown in the sample in
Vocational Sample 1, contain a Run ID and the Regulatory Subcategory for each run. For
vocational vehicles, there are nine standard and seven custom chassis regulatory subcategories in
GEM and Table 21 shows codes to use in the Regulatory Subcategory column. See Section
V.B.2.b of the preamble to this rulemaking for a discussion of these optional custom chassis
subcategories. For the standard regulatory subcategories, the R, M and U suffixes only alter the
duty cycle weighting. GEM will calculate results for each of the possible weighting to report in
the output.
Vocational Sample 1: Input File Run ID and Regulatory Subcategory Inputs
Run ID
Regulatory Subcategory
Unique Identifier
(e.g. HHD_R)
Sample_l
HHD R
Sample_2
HHD M
Sample_3
LHD U
Sample_4
LHD M
Sample_5
LHD U
Sample_6
LHD U
Sample_7
MHD
Sample_8
LHD
CC_Sample_l
HHD CC RF
CC_Sample_2
HHD CC EM
CC_Sample_3
HHD CC CM
CC_Sample_4
HHD CC OB
CC_Sample_5
HHD CC CB
CC_Sample_6
MHD CC MH
CC_Sample_7
MHD CC SB
PT_Samplel
HHD M
PT_Samplel
HHD
21
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Table 21: Vocational Input File Naming Convention for Vocational Regulatory Subcategories
GEM Input Name
Regulatory Subcategory Description
HHDR
Heavy-Heavy Duty, Regional
HHDM
Heavy-Heavy Duty, Multipurpose
HHDU
Heavy-Heavy Duty, Urban
MHDR
Medium-Heavy Duty, Regional
MHDM
Medium-Heavy Duty, Multipurpose
MHDU
Medium-Heavy Duty, Urban
LHDR
Light-Heavy Duty, Regional
LHDM
Light-Heavy Duty, Multipurpose
LHDU
Light-Heavy Duty, Urban
HHDCCEM
Emergency Vehicles
HHDCCCM
Cement Mixers and Other Mixed Use Applications
HHDCCRF
Refuse Vehicles
HHDCCCB
Coach Buses
HHDCCOB
Transit Bus, Other Bus and Drayage Tractors
MHDCCMH
Motor Homes
MHDCCSB
School Bus
The next columns (3-5) in the input file are for the engine and transmission or the powertrain
input filenames as shown in Vocational Sample 2. A description of the content of these
supplemental input files is located in section IV.D. The text in the fields of the input file must
exactly match the file name, including the .csv extension for the code to run properly.
Vocational Sample 2: Input File Reference to Engine, Transmission, and Powertrain Input Files
Engine
Engine
Transmission
Data
Idle Speed at CUT
Data
File Name
RPM
File Name
Engines\EPA_2018_D_GENERIC_350_trans_c...
650
Transmissions\EPA_MT_10_HHD.csv
Engines\EPA_2018_D_GENERIC_350_trans_c...
650
Transmissions\EPA_AT_5_HHD_LU3.csv
Engines\EPA_2018_D_GENERIC_200_trans_ c...
750
Transmissions\EPA_AT_6_LHD_LU3.csv
Engines\EPA_2018_D_GENERIC_200_trans_ c...
750
Transmissions\EPA_AT_6_LHD_LU3.csv
Engines\EPA_2018_D_GENERIC_200_trans_ c...
750
Transmissions\EPA_AT_6_LHD_LU2.csv
Engines\EPA_2018_G_GENERIC_300hp_trans...
600
Transmissions\EPA_AT_6_LHD_LU2.csv
Engines\EPA_2018_D_GENERIC_270_trans_ c...
750
Transmissions\EPA_AT_6_MHD_LU3.csv
Engines\EPA_2018_D_GENERIC_200_trans_c...
750
Transmissions\EPA_AT_6_LHD_LU3.csv
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
Powertrains\EPA_Sample_Powertrainl.csv
600
Powertrains\EPA_Sample_Powertrainl.csv
Powertrains\EPA_Sample_Powertrain2.csv
600
Powertrains\EPA_Sample_Powertrain2.csv
22
-------
In the Sample Input Files folder provided with GEM, the supplemental files are stored in
separate Axle, Engine, Powertrain and Transmission subfolders. GEM searches for the
supplemental files from the same location as the vehicle input file. As a result, the subfolder
name must be included in the File Name fields, as shown in Vocational Sample 2, to direct the
model to the files. If users have their engine, transmission, powertrain and axle files in the same
folder as the vehicle input file, only the filename is needed. Manufacturers may choose to
perform powertrain testing to obtain the engine and transmission performance for their GEM
simulations. In order to indicate to GEM that powertrain data is provided, users would provide
the same powertrain input file name in both the Engine and Transmission File Name fields of the
tractor input file, as seen in the last row of Vocational Sample 2. Note that the custom chassis
subcategories (rows 9-15 of the sample input file) use default engines and transmissions within
GEM and manufacturers input "NA" in those fields.
The next columns of the sample input file are shown in Vocational Sample 3 and contain the
vocational performance parameters and vehicle characteristics that are user-defined in GEM. A
description of these parameters is given in Table 22 and additional information is available in
Section V.D of the preamble to the Phase 2 rulemaking. For vehicles that have a single rear axle
(i.e., 4x2 axle configuration), the users input an "NA" into the Drive Axle 2 Tire Rolling
Resistance Level field. As shown in Vocational Sample 3, custom chassis manufacturers only
specify the drive axle configuration and tire rolling resistance values; all other user-defined fields
are marked "NA".
Vocational Sample 3: Input File Performance Parameters and User-Defined Vehicle Characteristics
Drive Axle
Drive
Axle
Drive Axle
Aerodynamic
Improvement
(Delta)
Steer Axle
Tire
Drive Axle 1
Tire
Drive Axle
2 Tire
Drive
Axle
Tire
Aerodynamic
Rolling
Rolling
Rolling
Loaded
Configuration
Ratio
Data
Drag Area
Resistance
Resistance
Resistance
Tire
(CdA)
Level
Level
Level
Size
(e.g. 6x4)
#
File Name
mA2
kg/t
kg/t
kg/t
rev/mi
6X4
3.73
NA
0
7.7
7.7
7.7
530
6X4 D
4.33
Axles\EPA_Axle.csv
0
7.7
7.7
7.7
530
4x2
4.09
NA
0
6.2
6.2
NA
500
4x2
4.09
NA
0
6.2
6.2
NA
500
4x2
4.09
NA
0
6.2
6.2
NA
500
4x2
4.09
NA
0
6.2
6.2
NA
500
4x2
3.8
NA
0.2
6.2
6.2
NA
500
4x2
4.09
NA
0
6.2
6.2
NA
500
6X4
NA
NA
NA
7.7
7.4
7.4
NA
6X4
NA
NA
NA
7.3
7.1
7.1
NA
6X4
NA
NA
NA
7.7
7.7
7.7
NA
4x2
NA
NA
NA
7.7
6.9
NA
NA
6x2
NA
NA
NA
7.7
6.8
6.8
NA
4x2
NA
NA
NA
7.6
7.5
NA
NA
4x2
NA
NA
NA
7.7
7.7
NA
NA
6x4
3.54
NA
0
6.9
6.9
6.9
512
6x4
3.54
NA
0
6.9
6.9
6.9
512
23
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Table 22: User-Defined Modeling Parameters for Vocational Vehicles (All Weight Classes)
Modeling Parameter
Method of Determining Parameter
Engine data file
40 CFR 1036.535 and 1036.540
Engine Idle Speed
40 CFR 1036.510
Transmission data file
40 CFR 1037.520(g)(1) and optionally 1037.565
Powertrain data file (Optional)
40 CFR 1037.550
Drive Axle Configuration
40 CFR 1037.520(g)(2)
Drive Axle Ratio
40 CFR 1037.520(g)(3)
Drive Axle data file (Optional)
40 CFR 1037.560
Aerodynamic Drag Area, Delta CdA (m2)
40 CFR 1037.520(m) and 40 CFR 1037.527
Steer Axle Tire Rolling Resistance (kg/t)
40 CFR 1037.520(c)
Drive Axle 1 Tire Rolling Resistance (kg/t)
Drive Axle 2 Tire Rolling Resistance (kg/t)
Drive Axle Loaded Tire Size (rev/mi)
See 40 CFR 1037.520(c)
There are limits associated with each user-defined input value. Drive Axle Configuration is a text
input and the allowable text is "6x4", "4x2", "6x4D", or "6x2". Vehicles with more than two
drive axles are instructed to use the "6x4" configuration in the model. All vehicles with "6x2"
axle configurations are modeled with five axles with two steer tires, 4 non-drive tires and 4 drive
tires. All vehicles with "6x4" axle configurations are modeled with five axles with two steer tires
and eight drive tires. The only difference in GEM between "6x2" and "6x4" axles is the
additional 1 percent loss for "6x4" axles to account for the inter-axle losses. All vehicles with
"6x4D" axle configurations are modeled as "6x2" axles on the cruise cycles and "6x4" axles on
the transient cycle. All vehicles with a "4x2" axle are represented by four axles with two steer
tires and four drive tires.
The Drive Axle Data File Name field points to the location and name of the optional axle file.
The format of this field is similar to the engine and transmission file fields shown in Vocational
Sample 2. Table 23 shows the limits for the next six vocational inputs in the model. GEM will
produce an error if any of these values are out of the acceptable range and will round any values
beyond their specified decimal limits. The aerodynamic improvement for vocational vehicles is
measured as a delta CdA and not the absolute CdA value used in the tractor program.
Table 23: Minimum and Maximum Limits for User-Defined Values in Vocational Input File
User-Defined Parameter
Units
Number of
Decimals
Minimum
Value
Maximum
Value
Drive Axle Ratio
#
2
1.00
20.00
Aerodynamic Drag Area (Delta CdA)
mA2
2
0.00
4.00
Steer Axle Tire, Rolling Resistance Level
kg/t
1
3.0
20.0
Drive Axle 1 Tire, Rolling Resistance Level
kg/t
1
3.0
20.0
Drive Axle 2 Tire, Rolling Resistance Level
kg/t
1
3.0
20.0 or NA
Drive Axle Loaded Tire Size
rev/mi
0
100
1000
The next columns in the vocational input file are for the optional technology improvements.
These technology improvement fields cannot be blank in the input file. Five of the next six
vocational technology improvements, shown in Vocational Sample 4, will directly impact the
vehicle simulation. Vehicle speed limiters reduce the maximum allowable speed of the vehicle
24
-------
during the simulation to the user-specified value. Weight reduction reduces the overall vehicle
weight (and increases payload) as noted previously in Table 10. Neutral-idle reduces fueling
when a simulated automatic transmission vehicle is idling, Start-Stop reduces fueling when the
simulation comes to a stop in the transient drive cycle and drive idle cycle, and Automatic
Engine Shutdown reduces fueling during the parked idle cycle.
Reference the preamble Section V.C.I.a.iv for a description of the three workday idle reduction
options. If the vocational vehicle will be built with a hybrid power take-off (PTO) and testing
was conducted according to 40 CFR 1037.540, the Delta PTO value obtained from that test
procedure may be entered. Please note these inputs are case-sensitive. All values of "Y", "N", or
"NA" must be in UPPERCASE LETTERS. Lowercase letters will produce an error.
Vocational Sample 4: Technology Improvements
Technology
Improvement
Technology
Improvement
Technology
Improvement
Technology
Improvement
Technology
Improvement
Technology
Improvement
Vehicle
Speed
Limiter
Delta PTO
Fuel
Weight
Reduction
Neutral-Idle
Start-Stop
Automatic
Engine
Shutdown
MPHorNA
g/ton-mile
lbs
Y/N
Y/N
Y/N
NA
0
0
N
N
Y
NA
0
0
N
N
Y
NA
0
0
N
N
N
NA
0
0
Y
N
N
NA
0
0
N
Y
Y
NA
0
0
Y
N
Y
NA
0
0
Y
N
N
NA
0
0
Y
N
N
NA
0
0
N
N
N
NA
0
0
N
N
N
NA
0
0
N
N
N
NA
0
0
N
N
N
NA
0
0
N
N
N
NA
0
0
N
N
N
NA
0
0
N
N
N
NA
0
0
N
N
Y
NA
0
0
N
N
Y
The remaining three technology improvements, shown in Vocational Sample 5, have specific
percent reductions that manufacturers will apply for the given technology fields. The "Other"
field may be used for several technologies, including results from any off-cycle testing that
manufacturers perform. See Table 12 and, generally, 40 CFR 1037.520 for the appropriate
percent values.
25
-------
Vocational Sample 5: Technology Improvements with Pre-Defined Percent Improvements
Technology Improvement
Technology Improvement
Technology Improvement
Accessory Load
Tire Pressure System
Other
%
%
%
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Similar to the user-defined parameters, these technology improvements also have limits. The
format and limits for the technology improvements are shown in Table 24. Input values with
additional decimal places will be rounded to the appropriate precision. Input values outside the
minimum and maximum range specified will produce an error.
Table 24: Minimum and Maximum Limits for Technology Improvement Values in Vocational Input File
Modeling Parameter
Units
# of Decimals
Minimum
Maximum
Vehicle Speed Limiter
MPHorNA
1
54.0
65.0
Weight Reduction
lb
0
0
10,000
Delta PTO
g/ton-mi
3
0.000
3.000
Neutral Idle, Automatic Transmissions Only
Y/N
-
-
-
Start-Stop
Y/N
-
-
-
Automatic Engine Shutdown
Y/N
-
-
-
Accessory Load
%
1
1.0
10.0
Tire Pressure System
%
1
1.0
10.0
Other
%
1
1.0
50.0
IV.C. Trailer Input Files
The next lines of the trailer input file contain the model inputs. In the first two columns, shown
in Trailer Sample 1, the user provides a Run ID and the Regulatory Subcategory for each run.
26
-------
For trailers, there are four regulatory subcategories modeled in GEM and Table 25 shows the
naming convention. While the trailer program does include reduced standards for some trailer
types, trailer manufacturers do not use GEM for compliance, and we did not configure GEM
with additional subcategories for those trailers. These four vehicles are sufficient to create the
GEM-based equation used in trailer compliance.
Trailer Sample 1: Input File Run ID and Regulatory Subcategory Inputs
Run ID
Regulatory Subcategory
Unique Identifier
(e.g. LDV)
LDV 1
LDV
LRV 1
LRV
SDV 1
SDV
SRV_1
SRV
Table 25: Trailer Input File Naming Convention for Trailer Regulatory Subcategory Inputs
GEM Input Name
Regulatory Subcategory Description
LDV
Long Dry Van
LRV
Long Refrigerated Van
SDV
Short Dry Van
SRV
Short Refrigerated Van
The next few columns contain the trailer performance parameters and technology improvement
options that are user-defined in GEM shown in Trailer Sample 2. A description of these
parameters has been provided in prior sections and additional information is available in the
preamble to the Phase 2 rulemaking. Note the aerodynamic improvement for trailers is measured
as a delta CdA and not the absolute CdA value used in the tractor program.
Trailer Sample 2: Input File Performance Parameters and User-Defined Vehicle Characteristics
Aerodynamic
Improvement (Delta)
Trailer Tire
Aerodynamic Drag
Area (CdA)
Rolling
Resistance Level
mA2
kg/t
0
6
0
6
0
6
0
6
Technology
Improvement
Weight Reduction
lbs
0
0
0
Technology
Improvement
Tire Pressure System
%
0
0
0
There are limits associated with the user-defined and technology improvement input values as
shown in Table 26. GEM will produce an error if the fields are blank or if any of these values are
out of the acceptable range. Users that wish to model their vehicle with weight reduction can
enter the cumulative weight reduction value (0 to 5,000 lbs or "NA"). The tire pressure system is
a set percent value for use of an automatic tire inflation system or a tire pressure monitoring
27
-------
system. See 40 CFR 1037.515, noting the ATIS and TPMS values listed in the regulation are in
decimal format because trailers will use a GEM-based equation for compliance.
Table 26: Minimum and Maximum Limits of Technology Improvements in Trailer Input File
User-Defined Parameter
Units
Minimum Value
Maximum Value
Aerodynamic Drag Area (CdA)
m2
0
4
Tire Rolling Resistance Level (TRRL)
kg/t
3
20
Weight Reduction
lbs
0
5000
Tire Pressure System
%
0
10
IV.D. Supplemental Input Files
Supplemental input files are required to provide the necessary component data to GEM. The
GEM installation package contains sample input files including four folders of supplemental
input files as follows:
Axles: 1 example axle definition file
Engines: 30 example steady-state and cycle average engine definition files
Powertrains: 2 example powertrain definition files
Transmissions: 11 example transmission definition files
Tractor and vocational vehicle manufacturers are required to generate separate engine and
transmission input files or a single powertrain input file for GEM. A vehicle manufacturer would
generate a separate engine and transmission file for each engine and transmission used in its
vehicles, or separate powertrain files for each engine and transmission combination tested. The
axle input file is optional for manufacturers that would like to include more axle loss
information. As discussed in the following section, each of the different types of supplemental
input files consist of various sections (tables) within each file. Examples from the sample input
files are included as well. Some of these tables and columns are required while others are
optional. These files must be in .csv format to be properly read by GEM. Each of the
supplemental files consist of tables which must be separated by an empty row to be processed
correctly. Manufacturers are recommended to choose a consistent naming convention that
provides unique file names for each of these supplemental input files. The GEM trailer model
does not use these supplemental input files and instead relies on default values built into the
trailer model.
IV.D.l. Engine Input File for Tractor and Vocational Vehicles
There are two basic formats for the Engine component input file for GEM. The standard format
uses a complete fuel map of the engine which is interpolated during simulation. Due to the
potential inaccuracy of interpolating a steady state fuel map to simulate more transient operation,
as occurs during the ARB transient cycle, an additional cycle average map is required which
contains results from a set of transient tests. More details on the formatting of these tables and on
the cycle average method are presented below and described generally in section VLB. The
second file format uses three different cycle average fuel maps, one for each test cycle. The main
fuel map is reduced to only include the low speed points which allows adjustments to be made
for differences in the idle speed of the engine tested and the vehicle being simulated.
28
-------
The first line of the GEM engine input file reports the GEM version for which the input is
intended. The first section consists of various engine parameters such as Manufacturer Name,
Combustion Type, Fuel Type, Family Name, Calibration ID, and Displacement, as shown in
Engine Sample 1. Combustion Type and Fuel Type have specific options for a manufacturer to
choose. The user can choose any name for the other header fields, but the names should be
consistent with other regulatory documents from the manufacturer.
Engine Sample 1: Input File Header Information
GEM P2v3.5 Engine Definition
Manufacturer
Name
Combustion Type
Fuel Type
Family Name
Calibration
ID
Displacement
(e.g. Cummins)
(Compression Ignition /
Spark Ignition)
(Diesel / Gasoline
/LNG/CNG)
(e.g. abcl2345)
(e.g. 123abc)
liters
EPA
Compression Ignition
Diesel
GENERIC
1
7
The next three sections in the engine input file specify the operating range of the engine. An
example with specific numbers removed, is provided in Engine Sample 2. The first section, titled
"Engine Full Load Torque Curve", specifies the maximum torque curve for the engine, and is
used to define the upper bound on engine torque in the simulation. Similarly, the third section,
titles "Engine Motoring Torque Curve" defines the lower bound from the motoring torque curve.
The second section provides the maximum torque curve of a parent engine, which is used to
estimate the transient torque response of the engine during simulation. The test procedures for
each of these inputs including the number of speed and torque points to measure can be found in
40 CFR 1065.510.
Engine Sample 2: Operating Range of the Engine
Engine Full Load Torque Curve
Speed
Torque
RPM
Nm
###
###
###
###
Parent Engine Full Load Torque Curve
Speed
Torque
RPM
Nm
###
###
###
###
Engine Motoring Torque Curve
Speed
Torque
RPM
Nm
###
###
###
###
29
-------
The next two sections in the engine input file contain information on the fuel consumption as
shown in Engine Sample 3 and Engine Sample 4. The data is detailed in three columns including
engine speed in RPM, torque in Nm and fuel consumption in grams per second.
The "Engine Idle Fuel Map" is only required for vocational vehicles and provides data on fuel
consumption during extended idling, corresponding with the parked idle cycle weighting for
vocational vehicles in Table 6, Table 7 and Table 8. The fuel map data should consist of the four
test points specified in 40 CFR 1036.535. The table will be interpolated based on the idle speed
entered for the tractor or vocational vehicle and torque estimated from the simulation.
Engine Sample 3: Engine Idle Fuel Map
Engine Idle Fuel Map
Speed
Torque
Fuel Rate
RPM
Nm
grams/ sec
###
###
###
###
###
###
The "Engine Fuel Map" can exist in two forms, either as a full engine map or a limited low speed
map if cycle average data is provided for each test cycle. The procedures to select the test points
and run the test can be found in 40 CFR 1036.535.
Engine Sample 4: Engine Fuel Map
Engine Fuel Map
Speed
Torque
Fuel Rate
RPM
Nm
grams / sec
###
###
###
###
###
###
The remaining sections in the engine input file include the cycle average fuel maps titled
"Transient Cycle Average Fuel Map", "55 MPH Cruise Cycle Average Fuel Map" and "65 MPH
Cruise Cycle Average Fuel Map" shown in Engine Sample 5. The section for the ARB Transient
cycle is required while the others are optional if a complete engine fuel map is provided. Each
section consists of columns for engine cycle work in kWh, the ratio of engine speed to vehicle
speed (more detail on this in Section VLB), and fuel consumed over the cycle in grams. The
section for the ARB Transient cycle contains additional columns for engine speed and load at
idle. This information, along with the idle speed from the tractor of vocational input file is used
to adjust the fuel consumption calculation for differing idle conditions.
30
-------
Engine Sample 5: Cycle Average Fuel Maps
Transient Cycle Average Fuel Map
Engine Cycle Work
Simulation N/V
Fuel Mass
Idle Speed
Idle Torque
kWh
rev / m
grams
RPM
Nm
###
###
###
###
###
###
###
###
###
###
55 MPH Cruise Cycle Average Fuel Map
Engine Cycle Work
Simulation N/V
Fuel Mass
kWh
rev / m
grams
###
###
###
###
###
###
65 MPH Cruise Cycle Average Fuel Map
Engine Cycle Work
Simulation N/V
Fuel Mass
kWh
rev / m
grams
###
###
###
###
###
###
IV.E. Transmission Input File for Tractor and Vocational Vehicles
The first line of the GEM transmission input file reports the GEM version number for which the
file is intended. The first section, as shown in Transmission Sample 1 contains basic information
on the transmission such as Manufacturer Name, Type, and Model Name. The vehicle
manufacturer can choose any Manufacturer Name and Model Name for the transmission, but it
should remain consistent with other regulatory documents. The transmission field Type has
specific options for the manufacturer to choose.
Transmission Sample 1: Input File Header Information
GEM P2v3.4 Transmission Definition
Manufacturer Name
Type
Model Name
(e.g. Eaton)
(AMT / MT/AT/ DCT)
(e.g. 7100)
EPA
AMT
HHD
If the transmission is an automatic transmission where the torque converter clutch lockup can
occur in a gear lower than the GEM default of 3rd gear, an additional column may be added to
specify the minimum lockup gear. The Minimum Lockup Gear input does not apply for AMT
and manual transmissions. The optional additional transmission header information for automatic
transmissions is shown in Transmission Sample 2.
31
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Transmission Sample 2: Optional Input File Header Information for Automatic Transmissions
GEM P2v3.5 Transmission Definition
Manufacturer Name
Type
Model Name
Minimum Lockup Gear
(e.g. Eaton)
(AMT/MT/AT/DCT)
(e.g. 7100)
Number / NA
EPA
AT
HHD
3
The next section in the GEM transmission input file contains information on the transmission
gear ratios as shown in the sample shown in Transmission Sample 3. If engine torque is limited
when operating in a specific gear, the limit amount should be entered in the appropriate column.
This will constrain simulated engine torque when operating in the specified gear and alter the
shift strategy accordingly.
Transmission Sample 3: Transmission Gear Ratio Information
Transmission Gears
Gear Number
Gear Ratio
Input Torque Limit
#
#
Nm
1
#
#
2
#
#
The next section, titled "Transmission Power Loss" is optional and can be used to include data
on transmission losses. Instructions for obtaining this information are found in 40 CFR 1037.565.
The format of the power loss table is shown in Transmission Sample 4. When providing power
loss information not all gears need to be included. Neutral, signified by gear number zero, is
optional. If loss information is provided for a given gear, all higher gears must also be included.
For example, supplying data for only 8th gear on a 10-speed transmission would not be valid,
data would need to be provided for 8th, 9th and 10th gears. The data points for this section are
transmission input speed and torque as well as total power loss across the transmission, in kW, at
each point. If power loss data is not provided, GEM uses default loss maps which are scaled
based on the regulatory subcategory of the vehicle and type of transmission.
Transmission Sample 4: Optional Transmission Power Loss Information
Transmission Power Loss
Gear Number
Input Speed
Input Torque
Power Loss
#
RPM
Nm
kW
#
#
#
#
#
#
#
#
The final section in the transmission input file, which is also optional and only available for
automatic transmissions contains data on the torque converter characteristics as shown in
Transmission Sample 5. The test procedure to generate the information can be found in 40 CFR
1037.570. This section contains columns for speed ratio, torque ratio and the calculated k-factor
in RPM per square root Nm. If this data is not provided, GEM generates torque converter
properties based on the engine torque curve.
32
-------
Transmission Sample 5: Torque Converter Characteristics
Torq
ue Converter Properties
Speed Ratio
Torque Ratio
K Factor
RPM/sqrt(Nm)
#
#
#
#
#
#
IV.E.l. Optional Powertrain Input File for Tractor and Vocational Vehicles
In lieu of providing separate engine and transmission performance data, a single powertrain test
input can be used for GEM simulation. Procedures for generating the data to populate a
powertrain input file can be found in 40 CFR 1037.550. This section summarizes the input file
format.
The first line of the GEM input file for powertrain contains the GEM version for which it is
intended. Next are three header sections, shown in Powertrain Sample 1, each contain a single
row of data summarizing the engine, transmission and combined powertrain tested. The engine
parameters include engine rated power which is used to scale the default powertrain during
simulation to match the engine. The powertrain test configuration contains information on
whether the measurements provided in the following sections were conducted at the transmission
output or at the wheel hubs.
Powertrain Sample 1: Input File Header Information
GEM P2v3.5 Powertrain Definition
Engine Manufacturer
Name
Combustion Type
Fuel Type
Family Name
Calibration
ID
Rated
Power
(e.g. Cummins)
(Compression Ignition /
Spark Ignition)
(Diesel / Gasoline
/ LNG / CNG)
(e.g. abcl2345)
(e.g. 123abc)
kW
EPA
Compression Ignition
Diesel
abc
CAL1
340
Transmission
Manufacturer Name
Type
Gears
Model Name
(e.g. Eaton)
(AMT / MT / AT / DCT)
Number
(e.g. 7100)
EPA
AMT
10
abcl
Powertrain Family
Name
Calibration ID
Powertrain Test
Configuration
(e.g. abcdl2345efg)
(e.g. 123abc)
(1: Trans. Output,
2: Wheel Hubs
EPA
CAL1
1
The next section in the powertrain input file contains data on engine fuel consumption at idle as
shown in Powertrain Sample 2. For powertrains with a singular fixed idle speed this section
would contain a single row while those with a calibratable idle speed must feature multiple
33
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entries spanning the range of options. Each entry must contain the idle speed setpoint and fuel
consumption rates for idling in gear and when parked, the latter of which is only required for
vocational vehicles. This data is used by GEM for vocational idle fuel consumption and to adjust
for differences between tested and simulated idle speeds. The procedures for collecting the
necessary data can be found in 40 CFR 1037.550(o).
Powertrain Sample 2: Engine Idle Fuel Consumption
Idle Fuel Rate
Idle Speed
Drive
Parked
RPM
grams / sec
grams / sec
#
#
#
#
#
#
The final three sections contain the powertrain cycle fuel maps and are somewhat analogous to
the cycle average fuel maps of the engine input file. Each contain columns for work, N/V and the
measurement of fuel consumed. The data for work and N/V are relative to the point of
measurement, which was noted as Powertrain Test Configuration in the file header. The map for
the ARB transient features an additional column to report the calibrated engine idle speed used in
the test. This data is used to adjust for differences in idle speed between the tested powertrain
and the vehicle simulation.
Powertrain Sample 3: Additional Performance Information
Transient
Powertrain Cycle Work
N/V
Fuel Mass
Idle Speed
kWh
rev / meter
grams
RPM
#
#
#
#
#
#
#
#
55 MPH Cruise
Powertrain Cycle Work
N/V
Fuel Mass
kWh
rev / meter
grams
#
#
#
#
#
#
65 MPH Cruise
Powertrain Cycle Work
N/V
Fuel Mass
kWh
rev / meter
grams
#
#
#
#
#
#
34
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IV.E.2. Optional Axle Input File for Tractor and Vocational Vehicles
The first row of the GEM input file for axles provides the GEM version and the subsequent rows
contain user-specified details including Manufacturer Name, Family Name, and Type, as shown
in Axle Sample 1. The user can type any text in the first two fields, but the names should be
consistent with other regulatory documents from the manufacturer. The valid options for axle
type are "SINGLE", "TANDEM" and "TANDEM WITH DISCONNECT".
Axle Sample 1: Input File Header Information
GEM P2v3.5 Axle Definition
Manufacturer Name
Family Name
Type
(e.g. Dana)
(e.g. abcdl2345efg)
EPA
EPA
TANDEM WITH DISCONNECT
The next rows contain two comma separated tables for Axle Loss and Disconnect Axle Loss, as
shown in Axle Sample 2. Each section includes output speed in RPM, output torque in Nm, and
power loss in kW. See 40 CFR 1037.560 for the test procedure to map axle efficiency and
determine appropriate values for this input file's tables. The disconnect axle losses are only
included by axles of type "TANDEM WITH DISCONNECT".
Axle Sample 2: Axle Loss Table in Axle Input File
Axle Loss
Output Speed
Output Torque
Power Loss
RPM
Nm
kW
#
#
#
#
#
#
Disconnect Axle Loss
Output Speed
Output Torque
Power Loss
RPM
Nm
kW
#
#
#
#
#
#
V. GEM Output File Structure
An output file will be generated when the vehicle simulation is complete and will automatically
save to the same location as the input file. When users run GEM from the Start Menu or
command prompt, the output file name will be given the same name as the input file with a
" result.csv" appended. During the simulation an error log file will be generated, even if there
are no errors, with the same base name as the input file with an "_errors.txt" extension. Identical
output files are generated for each of the methods.
35
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V.A. Standard GEM Outputs for Compliance
Each output file is aligned to the input file for the simulated vehicle, with additional columns if
the .csv file populated with the model's results. Sample 2 shows the standard results of an
example simulation. These results fields are the same for each vehicle type, but their exact
column location in the file varies. The first result column indicates the date and time when the
simulation was performed. The next two columns are the raw GEM CO2 emissions and fuel
consumption values. The next two columns are the Family Emissions Limit (FEL) values EPA
and NHTSA use for compliance. For trailers and vocational vehicles, EPA's FEL CO2 results are
reported as integer values and for tractors, the results are reported with a single decimal place
precision. NHTSA's FEL fuel consumption results are calculated from those CO2 values and are
reported with four decimal place precision for vocational vehicles and trailers, and five decimal
place precision for tractors to ensure consistency between the agencies' results. The vocational
vehicles have additional GEM and FEL C02 Emissions and Consumption result columns,
highlighted below in yellow, for each of the duty cycles, Regional, Multipurpose and Urban.
Sample 2: Example Results Columns in GEM Output File
Date/Time of
Run
GEM C02
Emissions
GEM
Consumption
FEL C02
Emissions
FEL
Consumption
Subfamily
Subfamily
FEL
Subfamily
Volume
YYYY-MM-DD
HH:MM:SS
g C02 /
ton-mile
gal / 1000
ton-mile
g C02 /
ton-mile
gal / 1000
ton-mile
Name
g C02 /
ton-mile
#
YYYY-MM-DD
HH:MM:SS
###
###
##(.#)
##(.####)
YYYY-MM-DD
HH:MM:SS
###
###
##(.#)
##(.####)
The final three columns of the output file are left blank by the model. Manufacturers would
manually add the appropriate subfamily name, target FEL for the given subfamily, and the
volume of vehicles that will use the resulting FEL value prior to submitting their output file for
compliance. The final three columns of the output file are left blank by the model. Manufacturers
would manually add the appropriate subfamily name, target FEL for the given subfamily, and the
volume of vehicles that will use the resulting FEL value prior to submitting their output file for
compliance.
VI. Running GEM
There are two options for running GEM. The first option directly accesses the program's
executable file via one of the Start Menu entries or a GEM icon on the desktop. This initiates a
GEM pop-up window to select an input file and run the model. The second option uses the
command prompt, which will similarly initiate GEM, but also has several options to generate
additional output information. Each of these options is described in the following sections.
VI.A. Preparing for GEM Simulation
Prior to running GEM, an important consideration is to locate the necessary input files. Many
computers will produce errors if users try to alter files in a folder where they do not have write
permissions such as the default installation folder (C:\Program FilesYUS EPAVPhase 2 GEM).
See the previous sections for a description of the input files and their formats.
36
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VLB. Running GEM from the Start Menu Icons
Users can access Phase 2 GEM from a collection of Start Menu icons found within the EPA
Phase 2 GEM folder. The "Phase 2 GEM" shortcut runs the certification version of GEM while
"Phase 2 GEM Check Inputs" and "Phase 2 GEM Cycle Creation" provide other functionality
discussed in the following sections.
A pop-up window will ask the user to select an input file. By default, the program will first look
in the installation folder. As mentioned previously, all the input files should be moved to a
separate location to avoid permission warnings. In this example, the files were moved to the
desktop and the folder was renamed GEM P2 Sample Input Files. Navigate to the input files
folder and select the appropriate input file to begin the simulation.
Once the input file is selected, the program will begin to run. A status window will step through
each configuration as it runs, as shown in Figure 5. At any point in the simulation, users can stop
the model by clicking the red "X" at the top right corner of the status window. A new window
will appear that asks, "Cancel current simulation?" If the user chooses "Yes", the execution will
stop once the current simulation has completed (which may take a few seconds) and produce an
output file with only the configurations that completed.
Processing "C:\Users\User111\Desktop\GEP.1 P2 Sample Input Files\GEM_tractor_sample_inputs.csv
Processing Run ID Sample_1
Processing Run ID Sample_2
US Environmental Protection Agency
GEM P2v3.0
Completed
15%
Figure 5: Sample Status Window Showing Progress of GEM Simulations
The status window will indicate when the simulations are complete with a message similar to
Figure 6. The resulting output file will be saved in the same location as the input file and will be
given the same name as the input file with a " result.csv" extension added to the end. When the
simulation is complete, users can close the status window by clicking the red "X" in the top right
corner of the window. If an error occurs in any simulation, the window will indicate which
configurations failed and the model will continue to the next simulation. See Section VI.C of this
Guide for examples of errors and a description of the _errors.txt file produced.
H
11=11 s
n ui/ca^iiiy r\un iu wainpic
Processing Run ID Sample 5
Processing Run ID Sample 6
Processing Run ID Sample 7
Processing Run ID Sample 8
.UUlll[JICLb.
.Complete!
.Complete!
.Complete!
.Complete!
1 sb|
Processing Run ID PT Samplel
Batch Simulation Complete!
Complete!
Ł
< E
rrr
1 ~
COMPLETE!
Figure 6: Sample Status Window Showing Complete GEM Simulations
37
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VI.C. Testing Input Files for Errors
Prior to running a GEM simulation with a large number of runs, users are recommended to test
their input files for errors. GEM will ensure the appropriate data is included in the required input
file fields, file headers and data are in the proper format, and supplemental input files exist with
the representative information. Note that some GEM inputs are case-sensitive and will produce
an error if inputs do not exactly match.
To test an input file, initiate the "Phase 2 GEM Check Inputs" shortcut and select an input file as
before. GEM will run through each line of the input file and search for errors. Figure 7 shows the
status window that appears when checking for errors. The status bar will progress as GEM
checks each Run ID and indicate "FAIL!" or "Input Valid!" Users can close this window and
check the output files for more detailed information.
Processing Run ID Sample_1
Processing Run ID Sample_2
Processing Run ID Sample_3
Processing Run ID Sample_4
Processing Run ID Sample_5
Processing Run ID Sample_6
Processing Run ID Sample 7
FAIL!
FAIL!
.FAIL!
FAIL!
.FAIL!
...Input Valid!
65% WITH 5 ERRORS!
Figure 7: Status Window Checking a GEM Input File for Errors
Once an input test ends (by completing the check or after being terminated by the user), the two
standard result.csv and _errors.txt files are created. The results file will simply display if the
inputs were valid or produced an error, as shown in Sample 3. Users are instructed to see the
error file for details.
Sample 3: Example Results.csv Output File Generated when Testing GEM Inputs
Regulatory Category
Manufacturer Name
Model Year
GEM Version
Run ID
Unique Identifier
Sample_l - ERROR: see error file for details!
Sample_2 -- ERROR: see error file for details!
Sample_3 - ERROR: see error file for details!
Sample_4 -- ERROR: see error file for details!
Sample_5 -- Input Validated
Sample_6 -- ERROR: see error file for details!
Sample_7 - ERROR: see error file for details!
Sample_8 -- ERROR: see error file for details!
PT_Samplel - ERROR: see error file for details!
38
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Figure 8 shows the error output file from this example which provides details about each error.
Error messages describe the powertrain area with the error, file location, line item and text
description.
US EPA Phase 2 GEM P2v3.5 Error Log
Sample_l -- Invalid Engine Definition File EPA_2018_D_GENERIC_350_trans_cyc_avg.csv Line 2131 Incorrect Transient....
Sample_2 -- Invalid Engine Definition File EPA_2018_D_GENERIC_350_trans_cyc_avg.csv Line 2131 Incorrect Transient....
Sample_3 -- Invalid Technology Improvement Automatic Engine Shutdown Value "F" not recognized must be "Y" or "N"
Sample_3 -- Invalid Axle Definition File EPA_AxleB.csv- Unable to open file
Sample_4 -- Unknown Regulatory Sub Category "LHQ" see Documentation for Valid Options
Sample_6 - Invalid Engine Definition File EPA_2018_G_GENERIC_300hp_trans_cyc_avg.csv Line 2 Incorrect Data Field ....
Sample_6 -- Invalid Engine Definition File EPA_2018_G_GENERIC_300hp_trans_cyc_avg.csv Line 2403 Incorrect Data....
Sample_6 -- Invalid Engine Definition File EPA_2018_G_GENERIC_300hp_trans_cyc_avg.csv Line 2403 Incorrect Data....
Sample_6 -- Invalid Engine Definition File \EPA_2018_G_GENERIC_300hp_trans_cyc_avg.csv Incorrect number of Engine....
Sample_7 -- Invalid Technology Improvement Start-Stop Value "T" not recognized must be "Y" or "N"
Sample_8 -- Invalid Drive Axle 2 Tire Rolling Resistance Level should be NA for Axle configuration 4x2
PT_Samplel -- Invalid Powertrain Definition File EPA_Sample_Powertrainl.csv Line 22 Incorrect Transient Data Field....
Figure 8: Example _Errors.txt Output File Generated when Testing GEM Inputs
Users should correct any errors in their files and rerun the test until they receive a confirmation
that all of the inputs are valid. Once completed, the input files are now ready to be used in a
GEM simulation.
VI.D. Cycle Average Engine Fuel Map for Tractor and Vocational Vehicles
Tractor and vocational vehicle manufacturers must include a cycle average fuel map for the
transient cycle within the engine input file and can optionally apply cycle average fuel maps to
the 55 and 65 mph cruise cycles. The cycle average method involves using GEM to generate a
collection of engine dynamometer test cycles based upon a collection the vehicle simulations.
These simulated vehicles are intended to span the range of potential vehicle applications for the
engine. The engine is run over each of the cycles on the dynamometer and summarized in the
cycle average map by work, the average speed (represented via N/V) and fuel consumed. Testing
over the ARB transient also requires average speed and load at idle to be recorded. As discussed
in Section IV.D. 1 the cycle average map is interpolated to determine fuel consumer over the test
cycle.
Included in this GEM installation package are two sample vehicle input files that serve as an
example of the inputs needed to generate the dynamometer cycles the cycle average map:
1. "GEMtractorEnginePrepinputs.csv" for tractor vehicles, and
2. "GEMvocationalEnginePrepinputs.csv" for vocational vehicles
These input files rely on different engine input files located in the sample subfolder "Engines"
and transmission input files located in the subfolder "Transmissions". Note the sample axle file
is not used when creating the cycle average map.
To generate cycles for the cycle average map six, eight, or nine vehicle configurations are
simulated in GEM, depending on the vehicle class(s) that may use the engine as defined in40
CFR 1036.540. Engines used in heavy-haul tractors are evaluated over six specific heavy-haul
39
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and sleeper cab configurations. Engines installed in vocational vehicles qualifying as Light HDV
or Medium HDV are evaluated over eight light- and medium-heavy duty configurations. Engines
installed in vocational vehicles qualifying as Heavy HDV and for tractors that are not heavy-haul
tractors are evaluated over nine-day cab and sleeper cab configurations. The example
EnginePrep files show some of the default values that may be applied. The method of selecting
appropriate axle ratios, tire sizes and other parameters to construct the cycle generation
configurations intended to cover the expected range of potential vehicles where the engine will
be used is defined in 40 CFR 1036.540. Note the configurations may vary by test cycle therefore
separate simulations may be required.
As mentioned in Section IV.D.l the engine input file exists in two formats, a full steady-state
engine map and cycle average map for the ARB transient or a cycle average map for all three test
cycles. The engine input file for cycle generation similarly varies depending on the expected
format. If creating a final engine input using the steady-state map, the same steady-state map
should also be included for cycle generation. If the final engine input uses the three-cycle
average map, the steady-state map should be omitted.
The EnginePrep input files are used with the GEM executable (i.e., the "Phase 2 GEM Cycle
Creation" executable from the Start Menu). Each simulation line in the input file will generate
three engine cycle files in .csv format corresponding to the transient, 55-mph, and 65-mph drive
cycles. These output files are named with the text of the unique identifier of the simulation
followed by the drive cycle (e.g., "EngineXYZ_cyclel_transient_cycle.csv"). The .csv files
include the average vehicle speed over the drive cycle and three columns defining the engine
cycle: Time (sec), Engine Speed (RPM) and Engine Torque (Nm). A sample of a generated cycle
file is shown in Sample 4.
Sample 4: Generated Test Cycle File
GEM P2v3.5 Engine Test Cycle
Configuration ID:2018_Engine350_all_cyc_prep_cyclel
Simulation Average Vehicle Speed: #.### m/sec
Simulation Crankshaft Work: ##.### kWh
Time
Engine Speed
Engine Torque
Vehicle Moving
sec
RPM
Nm
BOOL
#
#
#
#
#
#
#
#
The engine cycle files are then used to test the actual engine according to 40 CFR 1065 to
generate the following results that will be added to the end of the engine input file with the
appropriate headers as described previously in Section IV.D.l:
1) N/V Ratio (rev/meter) calculated from time average engine speed during engine test divided
by average vehicle speed from the generated cycle. Note the average vehicle speed is
determined by GEM and is stored in the GEM output file containing the engine cycle.
2) Positive cycle work (kWh) calculated from the engine test.
3) Total fuel mass for the test corrected for mass-specific net energy content of the fuel,
according to 40CFR 1036.540.
40
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Two additional parameters are included for the ARB transient to enable correction of fuel
consumption at idle, which could vary based upon different transmissions or idle speed
calibrations.
4) Average speed at idle where the idle portions are identified via the idle flag in the generated
cycle output file.
5) Average torque at idle where the idle portions are identified via the idle flag in the generated
cycle output file.
VI.E. Running GEM from the Command Prompt and Advanced Options
Users can also initiate GEM using the command prompt where additional functionality is
available beyond what is provided in the start menu shortcuts. The default installation directory
for the GEM executable is "C:\Program FilesMJSEPA\Phase 2 GEM. Users can then initiate the
same "Select an Input File" pop-up window as when using the start menu links by executing
GEM.exe with no additional arguments.
In this example, the executable is stored in the default Program Files location and the input files
are located in a folder on the desktop. The program will directly initiate a status window similar
to Figure 9.
lcrosoft Windows LUersion b.1.7601 J
Copyright (c) 2009 Microsoft Corporation. fill rights reserved.
:\Users\UserName>cd C:\Program FilesMJS EPfi\Phase 2 GEM
:\Program FilesNUS EPfi\Phase 2 GEM>GEM.exe "C:\Users\UserNarie\Desktop\GEM P2 Sa
mple Input Files\GEM_tractor_sample_inputs.csu"
C:\Program FilesSUS EPA\Phase 2 GEM>
Figure 9: Command Prompt to Initiate GEM and Directly Apply Input Files (no File Selection Window)
As mentioned previously, the command prompt method of running GEM has several options that
can alter the output format or generate additional data. These options are included after the main
command as single-letter flags with a dash (e.g., GEM.exe "Path\Filename" -t) and users may
include more than one flag in a single command. The available flags are shown in Table 27.
Users desiring greater detail regarding how the GEM results were calculated have various
options to do so. The -d option enables many additional columns in the results.csv file showing
some intermediate calculations including various statistics for each test cycle, helpful for
understanding the cycle average fuel map calculations, along with items like the final payload
(which may have been adjusted if weight reduction was included), and additional information
from the idle calculations.
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Table 27: Command Line Options for GEM
Command
Flag
Option Name
Description
-vN
Model output
verbosity
N = 0 (default) logs only the data required for certification,
N = 1 turns on the model's energy auditing
N = 2 or 3 add additional signals of interest for debugging.
-d
Detailed output
Generates additional cycle-specific data columns in the results.csv file
-P
Preserve files
Preserve the simulation raw output as a .mat file for later examination
-t
Test inputs
Disables simulation but allows the user to test the input file for errors such
as out of range parameters (see Section VI.C)
-n
No tech improvements
Turns off all technology improvements and result modifiers
-i
Save model inputs
Exports the model parameters before simulation; useful for later running
Simulink version.
-c
Console Only
Disables the status display window and runs in a console mode
-e
Engine cycle
generation
Exports the engine speed and load data from each simulation of each phase
to a separate file for use in cycle average testing (see Section VLB)
-s
Stringency mode
Bypasses requirement of cycle average map for ARB transient cycle and
rounding of input parameters is disabled.
The -e flag is used to generate the cycle average maps (Section VLB) and the -t flag is used to
test the input files prior to running GEM (Section VI.C). The console option may be of interest to
users who wish to automate their GEM runs. When users apply the -c flag, the output generally
shown in the GEM status window is displayed in the command window instead as shown in
Figure 10.
lcrosoft Windows [Uersion 6.1.7601]
opyright 2009 Microsoft Corporation. All rights reserved.
C:\Users\UserName>cd C:\Program FilesNUS EPASPIiase 2 GEM
C:\Progran Files\US EPA\Pliase 2 GEM>GEM.exe "C:\Users\UserName\Desktop\GEM P2 Sa
mple Input Files\GEM_tractor_sample_inputs .csu" -c
C:\Program Files\US EPA\Pliase 2 GEM>US Environmental Protection Agencv
GEM P2v3.0
Processing "C:\Users\UserName\Desktop\GEM P2 Sample Input Files\GEM_tractor_sanp
le_inputs.csu"
rocessing Run ID Sample_l Completef
rocessing Run ID Sample_2 Complete?
rocessing Run ID Sample_3 Complete?
rocessing Run ID Sample_4
Figure 10: Command Prompt Display When Using the Console Only Option
The -p option preserves the model output .mat file, which could be opened with MATLAB to
examine the raw simulation data. This in conjunction with the -v verbosity control enables
additional model outputs to be saved. Finally the -i option saves the model input data should the
user wish to rerun the simulation in Simulink where additional data may be extracted.
42
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VII. Final Notes
Users are encouraged to look through the additional information provided in the Documentation
folder included with the GEM installation. For more information on the Phase 2 rule or the
Technical Amendments, please see Docket EPA-HQ-OAR-2014-0827 available at
www.regulations.gov.
43
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Appendix A: Changelog
Summary of Changes for 3.4 from 3.0
Fixed typo in Class 7 default tractor transmission torque limits
Revised engine idle control
o Reduced gains for improved stability
o Added feed forward for a smoother transition to idle
Improved handling of larger input tables
o Engine torque curves previously could exceed size allowed by model executable
o Tables are now pre-interpolated to fit within allowable dimensions
Revised engine cycle generation outputs
o Corrected engine cycle generation torque output from model based on simulated
inertia and rate limited speed target
o Added output of simulated crankshaft work to cycle header
Added scaling of powertrain simulation default engine & transmission maps based on
new rated power input
Recalibrated driver over-speed allowance on cruise cycles from 3 mph to 2.5 mph
Increased weight reduction input range for tractors up to 25k lbs
Changed fuel map interpolation to be consistent between simulation and post processing
Moved idle speed parameter from engine file to the main (vehicle) file
Added adjustment to cycle average fuel for differences between tested and simulated idle
o Added inputs in transient cycle average map for speed and load when stopped
o Regression lookup of cycle average map uses only portions with vehicle moving
o Post process adjustment to fuel consumption based on simulated idle speed
Fixed bug where parked fuel map was used for ARB transient idle correction
o Parked fuel map is now only required for vocational vehicles
Adjusted accessory work correction for powertrain inputs to exclude work that is
provided by the inertia of the vehicle
Added ability to print detailed output (-d) when using engine cycle generation (-e)
Detailed output columns rearranged
ARB Transient detailed output columns for engine work, average speed and load only use
portions with vehicle moving only
Added vocational output columns with result of each cycle weighting (where applicable)
Added detailed output columns for idle speed and load for transient simulation
Added torque converter input table featuring speed ratio, torque ratio and k-factor to
transmission input file
Added check that engine fuel map contains a sufficient number of points
Changes for 3.5
Increased tractor weight reduction limit to 45000 lbs
Modified stringency mode (-s) to disable input range checking
Improved component input file parsing for better error handling
44
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Changes for 3.5.1
Fixed issue with parsing torque converter table when transmission power loss not present
Fixed issue with default engine map for vocational vehicles using 3 cycle average maps
Fixed incorrect cycle weighting factor for HHD vocational vehicles
45
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