***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 1 

## Chapter 4: **Ve hicle Simulation**  **Model 4.1**  **Purpose and Scope** In designing a regulatory GHG emission control and fuel consumption program, it is necessary to estimate the performance of technologies, verify compliance with the regulatory standards, and estimate overall benefits of the program. T he agencies developed the Greenhouse gas Emission M odel (GEM) to serve these purposes for Phase 1, which was consistent with recommendations b y the National Academies of Sciences (NAS) to use vehicle simulation to demonstrate compliance . A GEM i s currentl y being used to certify the fuel consumption and CO 2 benefits of the Phase 1 rulemaking for all heavy duty vehicles except for HD pickups and vans , which require a chassis dynamometer test for certification. While the version of GEM used in Phase 1 contain ed most of the technical and mathematical features needed to run a vehicle simulation , th e model was limited. For example :  Only manual transmissions were used in the model for all tractor and vocational vehicle simulations, which is not alway s the case for real world applications, especially for v ocation al vehicle applications  The model did not include engine torque int erruption during gear shifting  Engine control were simpl ified , with no fueling cut - off feature s  Only the agencies’ pre - specified engine fuel map s were used T he Phase 1 certification process onl y require d up to five user inputs , and all other vehicle parameters and their inputs were pre - specified by the agenc ies . 1 Phase 1 GEM onl y recognize d the benefits of aero dy namics improvement, tire rolling resistance, vehicle spee d limit er , weight reduction, and idle reduction ( onl y for high roof sleeper tractor s ) . Because the proposed Phase 2 standards are predicated on the performance of a broader range of technological improvements than Phase 1 , including changes to transmissions and better integration of engines and transmissions, a more comprehensive vehicle simulation model is required . This chapter describes a new version of this vehicle simulation model , referred to as Phase 2 GEM . It sho uld be noted that all changes to GEM described in this chapter remain potential, since the agency is proposing these changes, and will make a final determination as to what changes are appropriate only after considering the entire record after the close of the public comment period.

A National Academies of Science. “Technologies and Approaches to Reducing the Fuel Consumption of Medium and Heavy - Duty Vehicles.” 2010. Recommendation 8 - 4.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 2 

### 4.2 **M odel**  **Code Description 4.2.1**  **Engineering Foundations**  **of the**  **Model** EPA developed GEM to be a forward - looking M atlab /Simulink - based model for heavy duty ( Class 2b - 8 ) vehicle compliance in 2011 . 1 A m ore detailed description of this model and its engineering foundation can be found in Reference 1. The underl yi ng GEM code was originally developed to simulate a broad range of vehicle speeds over essentially any in - use duty

cycle. However, the official version that is used for det ermining compliance with the Phase 1 standards incorporates the regulatory dut y c yc les into the code. In other words, manufacturers cannot run other duty

cycles with the official version of GEM. We propose to continue this approach for Phase 2. In order to meet proposed Phase 2 rulemaking requirement s in recognizing most of the technologies that are measured in both engine and chassis dy namometers , GEM has be en considerabl y enhanced . S pecificall y, the agencies are proposing to implement the following key technical features into Phase 2 GEM:

• An upgraded e ngine controller , which includes e ngine fuel cut - off during braking and deceleration

• An upgraded transmission model , which includes an upgraded manual transmission , along with newly

developed a

utomatic and automated manual transmission s

• An u pgraded 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, for examp le . 

### 4.2.2 **Model Components** The GEM architecture is comprised of four sy stems: Ambient, Driver, Powertrain, and Vehicle as seen in Figure 4 - 1 . With the exception of Ambient and Driver, each s ys tem consists of one or more sub components . The function of each s ys tem and its respective component models, wherever applicable, is discussed in this chapter . M an y changes and modifications described in this chapter have resulted from numerous constructive comments from both public comments and GEM peer reviews. 2 The model has been upgraded to improve the fidelity of the model and better match the function of the simulated vehicles , which also meets our primary goal to accuratel y reflect changes in technology for compliance purposes . As part of this effort, substantial effort has been put forth to accuratel y track and audit power flows through the model to ensure conservation of energy .***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 3 **Figure 4**  **- 1**  **GEM m**  **odel structure** 

### 4.2.2.1 Am

bient Subsy stem This sy stem defines ambient conditions such as pressure, temperature, and road gradient, where vehicle operations are simulated. Just like in Phase 1 GEM , the conditions have been ma intained in accordance with standard SAE practices. The road gradient has been modified to accept a road grade that varies as a function of distance traveled. 

### 4.2.2.2 Driver Subsy stem The driver model in Phase 2 GEM has been substantially reorganized to simplify operation and to add support for distance compensated drive cycles. The result is a purely proportional - integral control driver that features a small lookahead to anticipate the drive cycle , especiall y use ful at launch where the vehicle response may be delayed due to the large effective inertia in low gears . The proposed target drive cycle consists of a road grade versus distance and a vehicle speed target as a function of the time required to achieve thos e speeds as a function of distance (i.e. desired cycle time) . The drive cycle speed can be converted to a target speed***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 4 versus distance travelled, however such a conversion involves the complication of tracking vehicle stop times separately since they

nece ssarily

occur over zero distance. Because the simulation itself is time - based , we consider the driver to be distance compensated rather than distance - based. The driver alway s operates in the time domain. To implement the distance compensated driver, the cycle time is tracked separately from simulation time, based on the ability of the target vehicle to meet the target speed trace. If the vehicle meets the target speed trace then cycle time is equivalent to simulation time as there is no difference in the distance travelled. If the vehicle under - performs the drive cycle then cycle time proceeds more slowly

than simulation time, forcing the vehicle to drive for a longer amount of time in order to cover an equivalent distance. In terms of implementation, t o apply distance compensation at each time step , the current model vehicle speed is divided by the target speed from the drive cycle. This value is integrated to produce the current cycle time and an updated speed target. The result is that if a simulated vehicle is traveling at half the drive cycle speed the simulation will progress through the drive cycle at half the rate. This behavior is disabled at speeds below 1 meter per second t o provide reasonable launch behavior (which necessarily occurs over sh ort distances), division by zero and to maintain vehicle stop times independent of small discrepancies in total distance travelled. The addition of distance compensation allow s all simulated vehicles to c omplete an equivalent trip such as traveling from po int A to point B. Without distance compensation, under powered vehicles might complete the drive cycle by time but not distance and would have done less work than higher powered vehicles as measured in ton - miles. Distance compensation also allows for the variation in road grade to be kept in sy nchronization with the drive cycle speed trace.

### 4.2.2.3 Powertrain Subsy stem The engine, transmission, electric accessories, and portions of the vehicle models from Phase 1 GEM have been upgraded and merged into a conventional vehicle powertrain s ys tem as shown in Figure 4 - 2 . The conventional powertrain sy stem contains sub - models representing the engine, transmi ssion , electric accessories , and driveline. Only conventional powertrain s are modeled in Phase 2 GEM , and no hy brid power sy stem s are modeled and certified with GEM . Rather, h ybrid powertrain s would be certified through powertrain dyn amometer tests as de scribed in Chapter 3 of the draft RIA.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 5 **Figure 4**  **- 2**  **GEM Powertrain Model**  

### 4.2.2.3.1 **Engine Subsystem** The engine model is based on a steady - state fuel map covering all engine speed and torque conditions with torque curves for wide open throttle (full load) and closed throttle (no load). The engine fuel map in Phase 2 is the input provided by users. The engine fuel map features three sets of data: engine speed, torque, and fueling rate at pre - specified engine speed and torque intervals. In - cylinder combustion process es are not modelled . The engine speed at a given point in the drive cycle is calculated from the phy sics of the downstream speeds . The quantity of torque required is calculated from the driver m odel accelerator demand, an idle speed governor, and requests from the transmission during shifts. Th e torque request is then limited by the maximum torque curve. The engine torque and speed are used to interpolate a fuel rate from the fuel map. The eng ine model also includes a constant power loss to simulate mechanical accessories. Most vehicles run a number of accessories that are driven via mechanical power from the engine. Some of these accessories are necessary for the vehicle to run, like the eng ine coolant pump or power steering, while others are only used occasionall y and at the operator’s discretion, such as the air conditioning compressor. Some heavy - dut y vehicles also use Power Take Off (PTO) to operate auxiliary equipment, such as refuse co mpact ors or lift forks . T hese w ould also be modeled as a mechanical accessory . The mechanical accessory load is proposed to be fixed for all vehicles based on regulatory subcategory , as shown below in Table 4 - 6 , Table 4 - 7 , and Table 4 - 8 . The actual power consumed for this loss would differ for actual vehicle configurations, but the agencies do not propose to allow users to change this value in GEM. If a manufacturer uses a hy

brid powertrain f

or power take - off devices, it may make use of the hy brid - PTO test procedure . See, 40 CFR 1037.52 5 .***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 6 

### 4.2.2.3.2 **Electric Subsystem** The e lectric sub system is modeled as a constant power loss. The power consumed for this loss is based on the vehicle subcategory . It represents the power loss associated with the starter, electric energy

s ystem, alternator and the electricall y driven accessories. The simplification has a negligible impact on the fuel consumption and CO 2 emissions results. The power losses for different vehicles are shown in tables from Table 4 - 5 to Table 4 - 10 . 

### 4.2.2.3.3 **Transm ission Sub**  **system** The transmission subsy stem features three different variants representing the three major ty pes of transmissions that are currently in use in the heavy - dut y s ector , which are the transmission ty

pes on whose performance the various proposed standards are predicated . The variants are manual transmission (MT ), automated manual transmission (AMT) , and automatic transmission (AT) (planetary gear set with torque converter) . The different transmission models are built from similar components, but each features a unique control algorithm matching behaviors observed during vehicle testing 3 . 4.2.2.3.3.1 Transmission Gear Selection All of the transmission models use a dy namic shift algorithm to determine the operating gear over the cycle 3 . This employ s a rule based approach utilizing the engine torque curve and fuel map to select gears that optimize efficient engine operation and provide a torque reserve as a traditional transmission calibration would. 4.2.2.3.3.2 Clutch The clutch model in Phase 2 GEM replaces the simplified model found in Phase 1 GEM . The original clutch model had no transition between the fully engaged and fully

disengaged states and provided no commensurate torque impulse to the driveline. In the new clutch model, engagement and disengagement occur over time, torque is conserved across the clutch and the inertial effects of accelerating and decelerating the upstream inertias are captured . 4.2.2.3.3.3 Gearbox The gearbox model has also been substantially revised in Phase 2 GEM to provide more realistic operation. The gearbox contains gear ratios and efficiencies for each gear . Each gear also has spin (churning) loss torques that can vary by current gear number and input speed. GEM assumes higher efficiency for direct drive than an y other gear for manual and automated manual transmissions. Shifting behavior is more realistic than in Phase 1 GEM with appropriate delays provided by

a s yn chronizer clutch model. This layout is mo st similar to a manual transmission, but the application for a planetary gearbox is a reasonable approximation as this ty pe of gearbox can utilize a variety of topologies . A detailed description on the shifting strategy can be seen in reference 3

. The gearbox rotational inertias are split between a common input inertia, common output inertia and a gear s pecific inertia. The common inertias represent rotational inertia alway s coupled to the input or output shafts . T he gear specific inertias are added or removed as gears are engaged or disengaged and incur additional losses .***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 7 4.2.2.3.3.4 Hydrodynamic Torque Converter The torque converter model in Phase 2 GEM simulates a lockup - ty pe torque converter. The torque multiplication and resulting engine load are calculated via torque ratio and K - factor cur v es that vary

as a function of speed ratio. A base torque ratio curve is used for all simulations and the K - factor curve is scaled based on the engine torque curve to provide a good match between the torque converter stall speed and the engine ’ s speed at maximum torque. This approximation could result in some simulation differences for highl y specialized vehicles equipped with torque converters matched to their specialized duty cycle, but for the vast majority of vehicles , the effect of this approximation on simulated CO 2 emissions is negligible. The lockup behavior of the torque converter is accomplished by integrating a clutch model similar to the one discussed in Chapter 4.2.2.3.3.2 . The torque converter model also contains a pump loss torque that varies with input speed to simulate the power required to operate the pump on an automatic transmission. 4.2.2.3.3.5 Manual Transmission &Control The manual transmission ( MT ) is composed of the clutch and gearbox sy stems discusse d above. The gearbox spin losses for a particular simulation are scaled with the vehicle class. The manual transmission features minimal gear specific inertia. Control of the MT is accomplished via a low speed clutch engagement model that gets the vehic le moving b y feathering the clutch during launch. Shifts are accomplished b y reducing the requested engine load, disengaging the clutch, shifting the gearbox to the new gear and reengaging the clutch. In heavier vehicles shifting is accomplished by doubl e - clutching to match transmission input speeds rather than relying purel y on the gearbox sy nchronizers. 4.2.2.3.3.6 Automatic Transmission &Control The automatic transmission ( AT ) is composed of the torque converter and gearbox sy stems discussed above. The gearbox g ear specific inertias and spin loss torques are higher as would be expected from a conventional planetary automatic transmission gearbox. The AT is allowed to shift under load. During up shifts and torque converter lockup the engine output torque is slightly

reduced to minimize the resultant torque pulse encountered by decelerating the engine inertia. Torque converter lockup will be controlled by a predetermined lookup table or lockup strategy algorithm and at this time is not expected to be among the avai lable user inputs with the possible exception of indicating the lowest gear in which lockup may occur. 4.2.2.3.3.7 Automated Manual Transmission &Control The automated manual transmission (AMT ) features the same clutch and gearbox models as the manual transmission wi th the addition of an inertia brake to slow the gearbox input inertia during upshifts. Control of the AMT during launch features a clutch feathering routine similar to the MT. Upshifts are handled by limiting the engine load, disengaging the clutch and s hifting the gearbox to neutral. The inertia brake is then applied to slow the transmission input inertia before the gearbox engages the new gear. With the new gear engaged the clutch is reengaged and the engine is again allowed to operate at full load. Downshifts are handled by shifting the gearbox to***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 8 neutral and accelerating the gearbox input up to a speed matching the desired gear using the engine. 

### 4.2.2.3.4 **Driveline** The driveline s ys tem contains all of the components that convert the torque at the transmission output to force at the wheels. This includes drive shafts as well as driven axles, consisting of a differential, brakes and tires. Except as specified below, we are not proposing to change the Phase 1 GEM approach to driveline modeling . For example, both Phase 1 and Phase 2 GEM can model all axles individually , or a single composite axle can be substituted to reduce simulation time. 4.2.2.3.4.1 Driveshaft The driveshaft is a simple component for transferring torque while adding additional rotational inertia. 4.2.2.3.4.2 Fina l Drive The final drive is modeled as a gear ratio change and an associated fixed efficiency . Various combinations of spin loss and efficiency , including a look - up table as a function of wheel speed and axle output torque, were considered . Table 4 - 1 below shows the comparisons between single value and look - up table efficiency approaches for a Class 6 box truck simulation. **Table 4**  **- 1**  **Axle Efficiency Modeling and Comparisons**  **Axle Study Results (Box Truck) Fixed Efficiency v. Look** **- up Table**  **Fuel Econom** **y ( MPG** **)**

**Drive Cycle**  **Look -**  **up T**  **able MPG**  **Fixed 95.5%** 

**Efficiency MPG**  **Difference 55**  **mph 11.19**  **11.15 0.36%**  **65 mph**  **9.13 9.06**  **0.77% C**  **ARB HHDDT**  **8.43 8.29**  **1.67%** In this table, 95.5 percent is a fixed efficiency , which is intended to be used as the GEM predefined value. As can be seen, the difference between these two approaches is fairl y small, and the fuel econ o my with the fixed efficiency is more conservative ( lower) than the look - up table approach as far as certifications are concerned. We are open to the approach of using a look - up table and request comment on its use . At this time, however, a single efficiency value***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 9 was selected to simplify

simulation and model inputs. The final drive model also adds some rotational inertia to the sy stem. 4.2.2.3.4.3 Brakes The brake sy stem on each axle applies a torque to the axle proportional to the brake pedal position from the driver model. T he scaling factor to determine this force is based on engine maximum torque , transmission multiplication and final drive ratio . 4.2.2.3.4.4 Tires The tire component model transfers the torques and rotational inertias from upstream components to a force and equivalent mass that is passed to the vehicle model. This conversion uses the loaded tire radius and adds the tire ’ s rotational inertia. The force associated with the tire rolling resistance is also applied when the vehicle is moving. The magnitude of this force i s determined b y the coefficient of rolling resistance, vehicle static mass and current grade. The proposed new version of GEM would make tire size a manufacturer - specified input rather than use a predefined value as was done for Phase 1. Manufacturers wou ld specify tire size in terms of loaded radius or perhaps tire revolutions per mile . Other than this, tires are being modeled the same as in Phase 1. 

### 4.2.2.4 Vehicle The v ehicle sy stem consists of the chassis, its mass and forces associated with aerodynamic drag , rolling resistance, and changes in road grade. The aerody namic force is calculated from the air density , vehicle speed, frontal area and drag coefficient. The vehicle sy stem also contains the vehicle speed integrator that computes acceleration from the input force and equivalent mass which is integrated to generate vehicle speed and distance traveled. 

### 4.2.3 **Capability, Features, and Computer Resources** GEM is a flexible simulation platform that can model a wide variety of vehicles with conventional powertrains from Class 2b to Class 8. The key to this flexibility

is the component description files that can be modified or adjusted to accommodate vehicle - specific information. Parameters such as vehicle weight, engine fuel map, transmission gear ratios, tire radius, or axle ratio can all be changed as inputs by the user in this fashion. The proposed P hase 2 GEM predefines all drive cycles (the Transient m ode, as defined by the California Air Resources Board (C ARB ) in the ir Highway Heavy - Dut y Diesel Transient ( HHDDT ) cycle, and EPA GEM constant speed cycles at 65 mph and 55 mph, each with varying road grade). The agencies also pre - defined many

key paramete rs, since those parameters are either hard to quantif y due to lack of certified testing procedures or difficult to obtain due to proprietary barriers. Examples of these parameters include transmission shifting strategies, transmission gear mechanical efficiency , and transmission spin and pumping loss. The values selected for these parameters are a result of substantial testing found in the Southwest Research Institute Report4 , as well as confidential discussions with engine, chassis and component manufacturers.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 10 During simulation the GEM tracks the status of many components and the status of all of the modeled losses. This information provides an energy audit to ensure the model conserves energy . The fuel consumed and vehicle speed trace s are immediatel y available in the generated report, while the larger data set is available in a M atlab .mat file or a comma - separated values (CSV) file. 

### 4.2.3.1 GEM Executable The agencies propose to require that vehicle manufacturers use the Phase 2 GEM executable version , which does not require the use of Matlab or Simulink software , for demonstrating compliance with the proposed CO 2 and fuel consumption standards . In this form, a precompiled executable format is used for certification. Its computational requirements are minimal . When using th e minimum recommended 2 GHz processor and 4 GB of RAM , a single simulation should complete in 10 seconds and generate 100 MB output files. Inputs from the manufacturers are provided in a text file, and the results are available in a generated report. 

### 4.2.3.2 GEM M atlab /Simulink Model The Matlab/Simulink version of the GEM source code will be released for users that desire a more detailed look at the inner workings of the model. The s ys tem requirements for the M atlab /Simulink version of GEM include M atlab , Simul ink and StateFlow software from Mathworks (version 201 4a or later) and a compatible compiler . 5 The recommended hardware for the M atlab release of GEM is 2+ GHz processor and 4 GB of RAM. The output data from a GEM simulation into M atlab is approximately 500 MB, depending on the simulation configuration and outputs selected. Simulations inside M atlab /Simulink using the source code take approximately 2 to 3 minutes. Although the source code is available to users, all of the component in itialization files, control strategies and the underl yi ng M atlab /Simulink/Stateflow based models may not be used for determining compliance. Onl y the executable version can be used when producing official truck certification results. Also, it should be pointed out that EPA will not provide any

technical support for the use of the GEM source code because it is beyond the scope of the agency ’s responsibilities and resources. 

### 4.2.4 **Peer Review o f Phase 2**  **GEM** The agencies conducted a peer review of Phase 2 GEM which has been submitted for public review in this NPRM. The peer review was conducted b y an independent contractor and includes four reviewers. Additional details regarding the peer review and EPA’s responses to the peer review comments can be found in the docket2 . The agencies also met with and received comments from the Engine Manufacturers Association, along with other industry stakeholders, during the development of Phase 2 GEM, which identified some areas of concern with GEM. In response, the agencies made changes as necessary .***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 11 

### 4.3 **Validation of Phase 2**  **GEM Simulations** This chapter presents the results of an engineering evaluation of the ability of the computer model in GEM to accuratel y simulate actual engine and vehicle performance. Note that this version differs from the compliance version in that it was possible to use actual values for vehicle parameters that are locked in the compliance version of GEM. For example, validations used actual vehicle curb weights. They also incorporated actual shift strategies where available. This is appropriate because the purpose of the validations was to evaluat e the engineering basis of the model, rather than to evaluate whether the policy of locking certain parameters is appropriate. 

### 4.3.1 **Experimental Tests for GEM**  **Validation** Working with Southwest Research Institute (SwRI) , EPA has invested significant ly in variou s truck tests in order to collect data to validate Phase 2 GEM. The technical research workshop held at SwRI, San Antonio, TX, December 10 - 11 details all of these tests 6

. Th e following truck test s were carried out b y SwRI for the purpose of model validation :

• Class 6 Kenworth T270 vocational box truck with AT

• Class 6 Ford F - 650 vocational t ow truck with AT

• Class 8 Kenworth T700 line haul truck with AMT

• Class 8 New Fl ye r refuse truck with AT The key specifications for thos e trucks are listed in Table 4 - 2 . **Table 4**  **- 2**  **Vehicle Specifications of Heavy -**  **Duty Trucks Tested at Southwest Research Institute Truck**  2013 Kenworth

T700 2012 Kenworth

T270 2011 Ford

F - 650 Tow

truck 2012 New

Flyer Refuse **Engine /Rated P**  **ower ( hp**  **)** Cummins ISX

455 Cummins ISB

240 Cummins

ISB 270 Cummins

ISL 345 **Transmission** Eaton

F016E310C - LAS Allison 2100 Allison

2200 RDS Eaton

FO16E310C - LA In order to full y validate the model, e ach truck was tested over six different driving cycles including regulatory cycles and non - regulatory cycles . They

are the EPA GEM 55mph (with and without grade) , EPA GEM 65mph (with and without grade) , the transient portion of the C ARB Heavy - Dut y Diesel Truck ( HDDT ) cy cle, the World Harmonized Vehicle C ycl e (WHVC) , the High - efficiency Truck Users Forum (HTUF) Class 6 Parcel Delivery Cycle, and the National Renewable Energy L aboratory

(NREL) Combined International L ocal and Commuter Cycle (CILCC) cycle (wh ich is a utility vehicle cycle) . The inclusion of driving cycles in addition to those used for Phase 1 certification was done to expand the range of operation . Some of the cycles are very aggressive (especially

for Class 8 trucks) , such as the CI LCC and Parcel Delivery cycles , with many

stops and rapid accelerations. EPA evaluated the***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 12 results from these additional cycles to improve the modeling capability and its response to highl y transient conditions, thus providing additional confidence in model fidel ity . All trucks were tested on a chassis dynamometer. In addition, the engine and transmission from the F - 650 tow truck were tested in a powertrain dyn amometer cell. More information on the vehicle chassis and powertrain dy

namometer setups and tests can found in the Southwest Research Institute Report 7

. Considering that procurement of trucks for model validations would be time consuming and expensive , EPA developed a compreh ensive approach to quantify variants of vehicles in order to maximize te sting efficiency . This was done by varying aero dy

namic drag and tire rolling resistance , as well as using weights to simulate different trucks, affording coverage of a wide range of vehicles. For tractors, varying these parameters also reflects the effec ts of pulling different types of trailers , which would impact the combined drag, rolling resistance, and weight of the vehicle. In this sense, this simultaneously provides validation data for both tractors and trailers. Three vehicles were selected for this portion of the test program and they are: the Kenworth T270 box truck, the Kenworth T700 truck with a 53 foot box trailer , and the F - 650 tow truck. The first two tru cks were tested on a chassis dy namometer , whil e the third one was tested on a powertrain s ystem dy namometer . A total of six drive cycles were tested : EPA GEM 55 mph, EPA GEM 65 mph, C ARB HHDDT , WHVC, NRELCILCC , and HTUF Parcel Delivery cycle . An additional set of six tests were run for each driving cycle listed above to evaluate the impact of various vehicle characteristics on CO 2 emissions and fuel efficiency . The characteristics of the six test modifications are listed below : 1. Add ing 800 to 1 , 000 pounds to the vehicle’s tare weight depending on the vehicle class 2. Add ing 15 percent to the vehicle - specific constant value representing the vehicle’s frictional load to simulate higher rolling resistance tires 3. Reduc ing the vehicle - specific constant value representing the vehicle’s frictional load by 15 percent to simu late lower rolling resistance tires 4. In creas ing the vehicle - specific coefficient representing aerody namic effects by

15 percent to simulate a higher aerody namic drag vehicle 5. Decreas ing the vehicle - specific coefficient representing aerody namic effects by

15 percent to simulate a lower aerodynamic drag vehicle 6. Running a new set of road load coefficients, to represent a vehicle configuration optimized for fuel efficiency for each vehicle that was tested , which consists of the lowest rolling resistance as well as the lowest aerody namic drag coefficient Three valid replicate tests were conducted for each vehicle and characteristic over each driving cycle. A valid replicate was defined as a successful test run in which all data was collected without regeneration of the diesel particulate filter. The following parameters were measured or recorded during all tests :***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 13  Vehicle speed as a function of time

 Engine fuel rate as a function of time

 Engine speed as a f

unction of time

 Gear number as a function of time

 Engine load (Nm ) as a function of time

 Emissions (NO X , HC, CO, CO 2 , N 2 O, CH 4 ) as a function of time in g/s

 Measured cycle fuel economy ( MPG ) and emissions (NO X , HC, CO, CO 2 , PM, N 2 O, CH 4 )

 Grade as function of time for the cycle with road grade if tested 

### 4.3.2 **Results of the GEM Validations**  Taking into account all of the vehicles and test configurations mentioned above, more than 130 vehicle variants were tested, allowing GEM to be comprehensivel y validated against a very well - defined and robust set of test data. The results displayed in through Figure 4 - 3 through Figure 4 - 6 show the of comparison between the GEM simulations and testing data of the Class 8 Kenworth T700 truck , Class 6 Ford F - 650 tow truck, Class 6 Kenworth T270 box truck , and New Fl yer refuse truck respectivel y . In all figures shown here for 55 and 65mph cycles, road grade is not included.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 14 **Figure 4**  **- 3**  **GEM Validation against Class 8**  **Kenworth T700 Truck**  **c hassis**  **t ests** 

**Figure 4**  **- 4**  **GEM validation against**  **Class 6**  **Ford F**  **- 650**  **tow truck powertrain tests**

**2 3**  **4 5**  **6 7**  **8 9**  **10 11** 

**2 4**  **6 8**  **10 G** **E M** **[ M** **P G** **]**

**Chassis Dynamometer**  **[MPG] 55 MPH**  **65 MPH CARB**  **Parcel Ut**  **ility WHVC**  **1:1 1:1**  **- 5%**  **1:1+5%**

**6 7**  **8 9**  **10 11**  **12 13**  **14 15**  **16**

**6 8**  **10 12**  **14 16** **G E** **M [** **M P** **G ]** 

**Powe rtra**  **in T**  **est [MPG]**  **55 MPH**  **65 MPH**  **CARB Parcel**  **Ut ility**  **WHVC 1:**  **1 -**  **5% 1:**  **1+5% 1:**  **1******* E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 15 **Figure 4**  **- 5**  **GEM validation against**  **Class 6**  **Kenworth T270 box truck**  **chassis tests** 

**Figure 4**  **- 6**  **GEM validation against**  **New Flyer refuse truck chassis tests**  **5 6**  **7 8**  **9 10**  **11 12**  **13 14** 

**5 7**  **9 11**  **13 G** **E M** **[ M** **P G** **]**

**Chassis Dynamometer**  **[ MPG]**  **55 MPH**  **65 MPH**  **CARB Par**  **cel Ut**  **ility WHVC**  **1:1 1:1**  **- 5%**  **1:1+5%**

**2 3**  **4 5**  **6 7** 

**2 3**  **4 5**  **6 7** **G E** **M [** **M P** **G ]** 

**Chassis Dynamome**  **ter [M**  **PG] 55**  **MPH 65**  **MPH CARB**  **Utility WHVC**  **1:1 1:1**  **- 5%**  **1:1+5%******* E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 16 A review of the data indicates that there is g ood agreement between the GEM simulations and testing data obtained over the wide range of vehicles and conditions . In general, the accuracy of the model simulations against the testing data is very well controlled with an error of less than ±5 percent , although there are a few outliers of the transient simulation cases for Class 8 truck s due to the nature of the high variability of chassis dy

namometer tests . The range of vehicles tested and simulated included vehicles that varied in terms of all of the proposed regulatory

inputs. Thus, the agencies believe that the accuracy of G EM is sufficient to simulate the benefits of the range technologies that form the basis of the proposed standards. Figure 4 - 7 shows the overall comparison between the simulation and test results when combining all of the testing and simulation into one figure. O verall , the simulation and test result correlate well .

**Figure 4**  **- 7**  **Com parison**  **of model simulations and**  **chassis test**  **results for the**  **130 vehicle test**  **configurations** While it is encouraging that GEM accuratel y simulates overall vehicle performance in an absolute sense, i t is actually more important that GEM is accurate in relative comparison s. This is because the agencies used the same version of GEM to calculate the stringency of the proposed standards as was used to evaluate baseline performance for th is rulemaking. The ultimate purpose of this new version of GEM will be to evaluate changes or additions in technology , and compliance is demonstrated on a relative basis to the numerica l standards that were also derived from GEM. The importance of relati ve comparisons can be further explained with the following simplified example.

**2 4**  **6 8**  **10 12**  **14 16** 

**2 4**  **6 8**  **10 12**  **14 16** **G E** **M (** **M P** **G )** 

**Expe ri**  **menta l T**  **es ts**  **( MPG)**  **1:1**

**1:1+ 5%**  **1:1 -**  **5% Res**  **ults******* E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 17 Assume you have two simulation models: one that say s a baseline vehicle with Bin 3 aero dy namics and a conventional automatic transmission would be 90 g/ton - mile, and another th at said the same vehicle would be 95 g/ton - mile. Assume also that there was a similar vehicle that was the basis of the new standards that had Bin 4 aero dy namics and a dual - clutch transmission. If both models simulated the second vehicle as being 10 g/ton - mile better than the baseline vehicle, then the models would work equally well for compliance as long as they were also used to set the standards. With the first model, we would set the standard at 80 g/ton mile. And with the second, we would set th e standard at 85 g/ton - mile. In both cases, manufacturers adding Bin 4 aero dy namics and dual - clutch transmission s would meet the standard. In other words, the two models would be equivalent in terms of measuring the effect of the change in technology on emissions , even though the absolute values were significantly different . As is shown below, GEM indeed performs better in this relative sense . T he results from the T700 and T270 trucks, and powertrain tests for the F - 650 tow truck shown in Figure 4 - 3 through Figure 4 - 5 , can also be presented in a format to evaluate GEM’s ability to mea sure the relative impact of a technology . Table 4 - 3 shows an example of relative comparisons to illustrate how the re lative comparison is done with the T700 truck. For simplicity , only the results from the Class 8 T700 tractor on the 65mph cycle are shown in this table . The column labeled as Chassis Test Fuel Economy Result (MPG) shows the testing results, while the column with GEM Fuel Economy Result (MPG) shows the GEM simulation resu lts. Each row represents a single change to the vehicle configuration , relative to the baseline case. The “Delta” in the last column is the difference between the impact of the vehicle configuration change as measured o n the chassis dy namometer and simul ated in GEM (which sometimes differs from the apparent delta due to rounding) . For example, the row with the “+15 percent Crr” variable compares GEM results to chassis test results for a vehicle that is the same as the baseline vehicle except that it has tires with a coefficient of rolling resistance 15 percent higher than the baseline vehicle. For this example, chassis testing indicates the change in rolling resistance increases fuel consumption for this cycle by 3.9 percent , while GEM predicts it would increase b y 4.9 percent , but the delta difference is only 1. 0 percent as shown in the last column . **Table 4**  **- 3**  **Sam ple of Relative Com** **parisons for T700 Truck**

Drive Cycle Vehicle Attribute Variables Chassis

Test Fuel Economy Result (MPG) GEM Fuel

Economy Result (MPG) Impact of

Variable on Chassis Test Result Impact of

Variable on GEM Simulation Result Delta 65 mph Baseline 6.84 6.61 0.0% 0.0% 0.0% 65 mph +907 kg 6.86 6.55 - 0.3% 0.9% - 1.2% 65 mph +15% Crr 6.57 6.28 3.9% 4.9% - 1.0 % 65 mph - 15% Crr 7.27 6.96 - 6.3% - 5.3% - 1.0% 65 mph +15% Cd 6.31 6.05 7.7% 8.4% - 0.7% 65 mph - 15% Cd 7.63 7.25 - 11.5% - 9.8% - 1.8% 65 mph Optim ized

Package 8.08 7.65 - 18.1% - 15.8% - 2.3%***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 18 The same methodology

was applied to all other cases including three different trucks, and six driving cycles and six vehicle variables. The differences between the chassis test and GEM results from all of these comparisons are plotted in Figure 4 - 8 .

**Figure 4**  **- 8**  **Relative com parisons between tests and GEM results**  In Figure 4 - 8 , the horizontal axis represents the test number of each truck. It can be seen that the majority

of cases have less than ± 2 - 3 percent difference. E xcellent correlation was obtained between the F - 650 tow truck powertrain test data and GEM results, where all of the comparisons had an error less than ± 2 percent . However, a few outliers with an error greater than 3 percent can be found in the Class 8 T700 and Cl ass 6 T270 data. This is no t unexpected since a ll the tests for both T700 and T270 trucks were conducted on the chassis dy namometer , while the tests for F - 650 tow truck were conducted in the powertrain dy namometer cell 8 . The recent finding s from the SwRI program sponsored by EPA show that chassis dy namometer tests have higher variability

than powertrain tests , as discussed below 9

. The driver behavior in the chassis dy namometer is one of the biggest contributors to the variability . This becomes even more an issue when a driver drive s a very heavy vehicle like a Class 8 truck to follow a targeted vehicle speed trace in the chassis dy namometer cell, specificall y for those highly transient cycles, such as C ARB HHDDT, NREL CILCC, and HTUF Class 6 Parcel Delive ry

c yc les. In contrast, a robot driver is used in the powertrain test for F - 650 truck test s , thus removing this major source of variability . In addition, many other testing conditions, such as air temperature and coolant temperature, can be more stably controlled during powertrain than in chassis dy namometer tests . The findings also include man y other sources of variability

in the chassis dy

namometer tests , such as tire temperature, thermal management during idle, and transmission oil temperature . 9 , 10 Because of the man y

**- 5%**  **- 4%**  **- 3%**  **- 2%**  **- 1%**  **0% 1%**  **2% 3%**  **4% 5%** 

**0 10**  **20 30**  **40 50** **R e** **l a** **t i** **v e** **E r** **r o** **r b** **e t** **w e** **e n** **G E** **M a** **n d** **T e** **s t**  **T7 00** 

**T2 70**  **F650******* E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 19 uncertainties due to the variability of chassis dy namometer test ing , it has been very challenging to match GEM resul ts with chassis dy namometer test results in the same range of accuracy as the comparisons against the powertrain tests , specifically for those highl y transient cycles . In some cases, it is hard to quantify which method, vehicle simulation or chassis dy namometer test, is more accurate. Therefore, considering the favorable comparison between the powertrain tests and GEM simulation results, it is fair to say that the overall accuracy of the GEM to represent the relative changes in fuel economy of a real world vehicle should be in the range of ±2 - 3 percent . Figure 4 - 7 and Figure 4 - 8 , respectivel y, show the GEM accuracy against over 130 vehicle variants o n an absolute and a relative bas is . All are done in a total vehicle configuration, which includes all vehicle components, such as engine, transmissi on, and driveline. Since certification would be done in a total vehicle form for CO 2 emissions and fuel efficiency , these ty pes of comparisons are the most important because they demonstrate that GEM is capable of capturing the impact on the total vehicle CO 2 emissions and fuel consumption due to technology improvement of individual components . In order to show the fidelity of GEM in modeling individual components in a more detailed level , the comparisons for the key components must be demons trated as well. Displayed in Figure 4 - 9 through Figure 4 - 11 are the comparisons of engine speed, fuel rate , and transmission gear numbers as function of time over the CARB HHDDT cycle for Class 8 T700 truck.

**Figure 4**  **- 9**  **Engine speed comparisons over the**  **WHVC for a Class 8 T700 truck** 0 100 200 300 400 500 600 700 400 600 800 1000 1200 1400 1600 1800 2000 2200

Ti me( s)EngineSpeed(RPM) GEM Te st D at a***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 20 **Figure 4**  **- 10**  **Engine fuel rate**  **com parisons over**  **the WHVC for a Class 8 T700 truck** 

**Figure 4**  **- 11**  **Transmission gear com** **parisons over the**  **WHVC for a Class 8 T700 truck** 0 100 200 300 400 500 600 700 0 5 10 15 20 25

Ti me ( s)FuelRate(g/s) GE M

Te st D at a

0 100 200 300 400 500 600 700 0 1 2 3 4 5 6 7 8 9 10

Ti me ( s)TransmissionGear GE M

Te st D at a***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 21 As shown in Figure 4 - 9 through Figure 4 - 11 , reasonably good comparisons between GEM simulations and tests ar e obtained. GEM basically can capture detailed behaviors of the engine and transmission. To further provide more complete picture o n the GEM validations, Figure 4 - 12 and Figure 4 - 13 show another set of examples for an F - 650 tow truck. Shown in these two figures are the comparisons of engine speed and transmission output shaft torque over the W orld H armonized V ehicle C yc le (WHVC) between powertrain dy namometer test s and GEM results. As can be seen from these two figures, reasonable comparisons are again obtained between GEM and actual test results .

**Figure 4**  **- 12**  **Engine speed comparisons over the**  **WHVC for a n**  **F -**  **650 tow**  **truck** 0 500 1000 1500 2000 2500

0 500 1000 1500 2000EngineSpeed(RPM)

Tim e (s) Te st GEM***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 22 **Figure 4**  **- 13**  **Transmission output torque**  **comparisons over the**  **WHVC for a n**  **F -**  **650 tow**  **truck** 

### 4.4 **EPA and NHTSA**  **HD Vehicle Compliance Model**  As described earlier, GEM is a computer model that simulates vehicle operation to predict CO 2 emissions and fuel consumption for a wide variety of heav y - duty vehicles. This section describes how that computer model is used as a compliance tool to evaluate vehicle performance relative to the applicable standards. The engineering evaluation of GEM discussed in Chapter 4.3 was not limited by computing time and presumes all inputs to be accurate. However, using GEM as a compliance tool requires some simplification of the model. It also requires the elimination of user inputs that cannot be verified b y the agencies. As disc ussed below, such simplifications are being proposed for Phase 2, but to a lesser degree than was done for Phase 1. The Phase 2 GEM of EPA and NH T SA ’s vehicle compliance simulation model is similar t o Phase 1 GEM in many respects. However, it differs from the Phase 1 version in two major aspects. T he first involves the significant improvements described in Chapter of 4.2.1. Second, Phase 2 GEM provide s user s the opportunity to enter additional vehicle and engine parameters for the actual vehicle being simulated . As noted above, Phase 1 GEM onl y allow s a maximum of five user defined inputs for tractors. These are: the aerodyn amic drag co efficient , tire rol ling resistance, vehicle speed limiter, weight reduction, and idle reduction. For vocational vehicles there is only

one user defined input: tire rolling resistance. In contrast, the proposed Phase 2 GEM allows the use r to input many more engine and vehicle parameters , including most of those that have the biggest impact o n emissions . Inparticular, it allows vehicle manufacturers to input their own engine fuel maps. Key driveline parameters , such as transmission gear number versus gear ratio, axle ratio, and tire rolling radius, are also part of the manufacturer inputs.

- 1000 - 500 0 500 1000 1500 2000

0 500 1000 1500 2000TransmissionOuputTorque(NM)

Ti me (s) Te st GEM***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 23 There are still some GEM input parameters that are proposed to be pre - defined by the agencies . For some, such as shifting strategy , this is due to the fact that the parameters are hard to measure and quantif

y due to the lack of well - defined test procedures . For others , the manufacturer s consider the parameter value s to be proprietary and are reluctant to share the information with other parties. E xamples of those items include the transmissi on gear shifting strategy table and gear mechanical eff iciency . T he modeling parameters associated with torque converte r s for automatic transmission would be a lso pre - defined by the agencies. The inertias of all rotational parts, vehicle weights and accessory power losses are also default parameters defined by

the agencies . Finally , in order to have a consistent basis for the standards, the vehicle weights and payloads are pre defined by vehicle class and duty

cycle . Table 4 - 6 and Table 4 - 7 list all of the proposed GEM input parameters for tractors and Table 4 - 8 through Table 4 - 10 list the predefined parameters for vocational vehicles . T hese tabl es also include weighting factors for each driving cycle for the determination of composite CO 2 in g/ton - mile. It is important to note that, for man y of these parameters, publicly available information on the values for current and future vehicles is l imited. Manufacturers have provided values to the agencies, but have generall y identified them as confidential business information. Nevertheless, we have used this information to inform our estimation of appropriate default values. 

### 4.4.1 **Predefined GEM**  **Values** 4.4.1.1 Transmissions O ne of the major changes in Phase 2 GEM is to allow manufacturer s to enter their transmission gear ratio versus gear number . Whe n entering this information, manufacturer s also have an option to select the ty pe of transmission, which is either manual , automated manual or automatic with a torque converter . Mechanical efficiency for each gear is pre - defined by the agencies as shown in Table 4 - 5 through Table 4 - 10 . Pre - specification was required due to the lack of a reliable, repeatable, and cost - effective test procedure. One of the areas that required significant development work was the transmission shift strategy for use in the compliance tool . This was required because transmission suppliers have been reluctant to provide their shifting strategies to vehicle manufacturers for vehi cle certification due to their concern over protecting intellectual property. The shifting strategy in the proposed Phase 2 GEM includes the agencies’ internally developed auto matic shift algorithm 3 . The impact of the use of the agencies’ default transmission shifting as opposed to using manufacturers’ shifting strategies has been evaluated and the results are presented in Table 4 - 4 .***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 24 **Table 4**  **- 4**  **Impact of the Agencies’ Default Shifting Strategy Compared to Transmission Manufacturers’**  **Strategies Truck**  **Cycle M**  **anufacturer Shift Strategy**  **Fuel Economy (MPG)**  **EPA Defined**

**Shift Strategy**  **Fuel Economy (MPG)**  **Difference (%)** T270 Box Truck GEM 55 mph 11.36 11.36 0 T270 Box Truck GEM 6 5 mph 9.24 9.24 0 T270 Box Truck C ARB HHDDT 8.39 8.44 0.60 F - 650 Tow Truck GEM 55 mph 14.49 14.57 0.55 F - 650 Tow Truck GEM 65 mph 12.03 12.14 0.91 F - 650 Tow Truck C ARB HHDDT 10.32 10.72 3.88 T700 Class 8 Truck GEM 55 mph 7.96 7.96 0 T700 Class 8 Truck GEM 65 mph 6.59 6.59 0 T700 Class 8 Truck C ARB HHDDT 3.9 3.94 1.02 The M anufacturer column in Table 4 - 4 represents the simulation results using the shifting tables and strategies provided by the transmission manufacturer, while the EPA column represents the results using EPA’s default shif t algorithm . The transmission manufacturer and EPA fuel econom y results are essentially the same despite the different shifting strategies. There is a noticeable difference in fuel econom y results for the C ARB H HDDT cycle, but it is still relativel y small. Itshou ld be pointed out that in the case of 55 and 65 mph cruise speed cycles, there are few, if an y, shifts . Phase 2 GEM includes three type s of transmissions as discussed in Chapter 4.2.2.3.3 . They are manual transmission s (MT) , automated manual transmission s (AMT) and automatic transmissions (AT) . Due to l ack of test data fo r other ty pes of transmission s , GEM was not able to be validate d in time against th e se three case s: 1. Dual clutch transmission (DCT) 2. Dual clutch transmission with a torque converter 3. Allison TC - 10 automatic transmission The agencies are proposing use of AMT to model case 1; use of AT to model case 2, and use of AT to model case 3. The manufacturers would still have the option to use powertrain dy namometer tests to quantify the benefits of these or an y other special transmissions , rather than use the pre - defined values. The detailed test procedure of the powertr ain dy namometer tes ts are described in Chapter 3 of the draft RIA 

### 4.4.1.2 Axle s Axle ratios for all model sub - categories would be user defined. Default axle mechanical efficiency is pre - defined by

the agencies. Based on comments that the agencies receive related to this NPRM, we may

adopt provisions in the final rule that would allow m anufacturer s to override the default mechanical efficiency and input their own values; however, the inputs would be determined b y using the prescribed test procedure described b y Chapter 3 .8 of the draft RIA .***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 25 Ty pical base Class 8 tractors have one steer and two drive axles, while ty pical base Class 7 tractors have one steer and one drive axle. The trailer used for both Class 7 and Class 8 tractor s in simulation modeling has two axles. All HH D vocational vehicle categories have 3 axles, while all others only have two. 

### 4.4.1.3 Weights It is assumed that the vehicle unloaded weight will vary by vehicle subcategory . Taking tractors as an example, the total weight ranges from 65,500 to 70,500 lbs, while for Class 7 tractors weight ranges from 46,500 to 50,000 lbs. The payload capacity varies as shown in Table 4 - 5 through Table 4 - 10 . The development of these weights is discussed in Chapter 3 of the draft RIA. 

### 4.4.1.4 Inertia All of the inertias for rotational parts, including engine, transmission and axle, are pre defined based on a combination of the agencies’ engineering judgment and confidential business information from OEMs. The default inertia values were used during GEM validation against respective trucks and they will be used as the default values for all of the vehicles certified using GEM. Thus, the vehicle OEM will not have flexibility to enter their own inertias. 

### 4.4.1.5 Accessory L oad The agencies are assuming that all trucks, including tractors and vocational vehicles, carry a constant electrical load as well as mechanical load when operated over the agencies’ certification drive cycles. Those agency derived values were used when GEM validations were carried out against experimentally derived data from SwRI . All of the default, pre - specified valu es are shown in Table 4 - 5 through Table 4 - 10 , and would be used as the default values for all vehicle certification. 

### 4.4.1.6 Tires Tire radius is a user defined input; however, the agencies do provide default values for all vehicle sub - categories. Static loaded tire radius is used in GEM for all simulations for every combination tractor and the default value can be overridden b y the vehicle OEM. The trailer tire coefficient of rolling resistance ( Crr , trailer tires) assumes a constant value f or all trailer tires. This value was developed through tire testing performed by the SmartWay Transport Partnership. 11 

### 4.4.1.7 Idle C yc le and Its Modeling As described in Chapter 3.4 .2 of this draft RIA, w e are proposing the addition of an idle only cycle to de termine both fuel consumption and CO 2 emissions when a vocational vehicle is idling, and to recognize technologies that either reduce the fuel consumption rate or shut the engine off (and restart) during short - term idle events during the workday . B ased on user inputs, GEM would calculate CO 2 emissions and fuel consumption at both zero torque (neutral idle) and***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 26 with torque set to Curb - Idle Transmission Torque (as defined in 40 CFR 1065.510(f)(4) for variable speed engines) for use in the CO 2 emission calcul ation in 40 CFR 1037.510(b). We are also proposing that GEM would calculate reduced CO 2 and fueling for stop - start sy stems, based on an assumption that the effectiveness would represent a 90 percent reduction of the emissions that would occur if the vehicle had operated at Curb - Idle Transmission Torque over this cycle. This cycle is propose d to be applicable for all subcategories of vocational vehicles (HHD, MHD and LHD) using an y of the proposed composite duty cycles ( Regional, Multi - Purpose, or Urban composite duty

cycles ) . More can be seen in Chapter 3.4.2.3 about the idle cycle. Chapte r 4.5 discusses how these idle technologies are modeled as part of technology improvements that are recognized in GEM. 

### 4.4.1.8 Transient Adjustment Factor As described in Chapter 2, fuel consumption during transient engine operation ty picall y is higher than during steady - state operation. The difference can vary significantly , but the trend is generall y consistent. Because the GEM simulation relies on steady - state fuel maps to predict emissions for all the cycles, including the transient cycle, the agencies are proposing to appl y a transient adjustment to GEM results for the transient cycle. 

### 4.4.1.8.1 **Transient Engine Testing** To evaluate the need for a transient adjus tment factor, we compared the results from 28 individual engine dyn amometer tests. Three different engines were used to generate this data, and these engines were produced b y two different engine manufacturers. One engine was tested at three different po wer ratings (13 liters at 410, 450 & 475 hp) and the other engines ranged from medium heav y - dut y (6.7 liters, 300 hp) to heavy heavy - dut y (15 liters , 455 hp) service classes. For each engine and rating our proposed steady - state engine dy namometer test pro cedure was conducted to generate the data table to represent that particular engine in GEM. Next, GEM simulated various vehicles in which the engine could be installed. For each of the GEM duty

cycles we are proposing, namely the urban local ( C ARB HHDDT ) , urban highway with road grade ( GEM 55 mph), and rural highway with road grade ( GEM 65 mph) duty cycles, we determined the GEM result for each vehicle configuration, and we saved the engine output shaft speed and torque information that GEM utilized to interpolate the steady- state engine data table for each vehicle configuration We then had this same engine output shaft speed and torque information programmed into the engine dyn amometer controller, and we had each engine perform the same duty c ycles that GEM demanded of the simulated version of the engine. We then compared the GEM interpolated results to the measured engine dy namometer results. We concluded that for the 55 mph and 65 mph duty cycles, GEM’s interpolation of the steady - state data tables wa s sufficiently accurate versus the measured results. This is reasonable because even with changes in road grade, the 55 mph and 65 mph duty cycles do not demand rapid changes in engine speed or load. They are nearl y steady - state, just like the data table s themselves. However, for the CARB HHDDT cycle, we observed a consistent bias, where GEM consistently

under - predicted fuel consumption and CO 2 emissions. This low bias over the 28 engine tests ranged from 4.2 percent low to 7.8 percent low. When we aggregated these results by engine, the results were between 5 and 6 percent . We understand that use of an engine dy namometer test with GEM inputs o f torque and speed to quantify the impact of using a steady state engine fuel map would not be perfect, since this approach would not consider the***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 27 interaction of the driver model of GEM in response to individual vehicle component dy namics. Also, the input torque and speed values calculated in GEM and input into the engine dy namometer are onl y targeted values and they are not the real measured engine torque and speed . S ince the engine may not be able to follow the target ed speed trace, there may be some discrepancy compared to the vehicle performance obtained from GEM . Accessory loads between th e engine test and GEM simulation are also different. In spite of these differences , it is a common fact that steady state operation is different from transient operation , specificall y in a diesel engine. The most significant difference between steady stat e and transient behavior is the smoke control during acceleration. Diesel engine s must limit the fueling in order to prevent smoke during rapid acceleration. In contrast, there is no such issue during steady state mapping. Furthermore , all modern diesel engines use a fueling cut - off technique to shut off the fueling during deceleration based on a manufacturer - defined set of conditions. In addition, thermal management is another major factor to that may create a difference between steady st ate and transient fueling. The a ftertreatment sy stem is very sensitive to exhaust temperature in order to maintain optimal performance of selective catal ytic reduction device s . P ost fueling must be injected into the exhaust stream once the exhaust temperature is below certain criteria, typically in the range of 200 degrees Celsius . Insteady state fueling mapping, the engine alway s follows the defined testing procedure ; thus , the engine run s hotter even at light loads than in a transient condition at the same speed and torque, thus thermal management may not even kick in. Because of these differences, engine manufacturer s ty picall y include at least two distinguished engine calibration s into the engine control unit

– one for t ypicall y on - highway operation , and the other for transient operation, such as urban and mountain ous area s . We are confident that this low bias in GEM results using a steady state fuel map would continue to exist well into the future if we were to test additional engines. However, with the range of the results that we have generated so far we are somewhat less confident in proposing a single numerical value to correct for this bias over the C ARB HHDDT drive cycle. T he procedure used to derive this proposed correction adjustment factor, although reasonable, may still need more refinement. 

### 4.4.1.8.2 **Proposed Value for the Transient Adjustment Factor** Based on the limited testing that was performed for this analy sis, the agencies are proposing a transient adjustment factor of 1.05. This means that the simulated transient cycle GEM results (that are generated based on steady - state fuel maps) would be multiplied by 1.05 before being output from the GEM co mpliance tool. The higher output value would be the official GEM result. This 1.05 factor reflect s the engine at the lower end of the range for the three engines, with the other two engines indicating values of 1.06 or 1.07 might be appropriate. The agen cies are proposing the lower value because we do not want to allow manufacturers to gain an advantage from powertrain testing without making some improvement to the powertrain. The test results indicate that an adjustment of 1.07 would allow the I SX engin e (which showed a lower transient difference) to show a 2 percent improvement without making an y improvements. The agencies recognize that there is significant uncertainty in the proposed value and will***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 28 continue to evaluate the adjustment. The agencies wo uld likely consider values in the range of 1.00 to 1.07. 

### 4.4.1.9 Tractor Tables Table 4 - 5 through Table 4 - 7 display the predefined GEM parameters proposed for the Phase 2 tractor co mpliance model. The predefined parameters were developed using the same methodology

used in Phase 1. Man y of the parameters are based on the vehicles EPA selected to test at SwRIand are considered to reasonabl y represent the fleet in the ir respective categories. For example, the transmission gear ratio, axle ratio, tire diameters, and all accessory losses used for all tractors shown in these three tables are from the Kenworth T700 truck tested at SwRI. All of the other predefined parameters, such as th e engine power rating, vehicle weight, payload, follow the Phase 1 structure. The gear mechanical efficiency as well as axle mechanical efficiency was developed based on several verbal communications from stakeholders. For further detail regarding how th ese parameters are chosen and used in GEM see Chapter s 4.4.3 to 4.4.9. **Table 4**  **- 5**  **Class 8 Com** **bination Tractor Sleeper Cab Predefined Modeling Param eters** 

Regulatory Class Class 8 Combination Class 8 Combination Class 8 Combination Sleeper Cab - High Roof Sleeper Cab - Mid Roof Sleeper Cab - Low Roof Gearbox Efficiency 98% for the gear with a 1:1 gear ratio, and 96 % for all other gears 98% for the gear with

a 1:1 gear ratio, and 96% for all other gears 98% for the gear with a 1:1 gear ratio, and 96% for all other gears Axle Mechanical Efficiency 95.5% 95.5% 95.5% Total weight ( kg ) 31978 30277 30390 Number of Axle s 5 5 5 Default Axle Configuration 6x4 6x4 6x4 Electrical Accessory Power ( W) 300 300 300 Mechanical Accessory Power ( W ) 1000 1000 1000 Environmental Air T em

perature ( ° C) 25 25 25 Payload (tons) 19 19 19 Weight Reduction (lbs) Add 1/3*weight reduction to Payload tons Add 1/3*weight

reduction to Payload tons Add 1/3*weight

reduction to Payload tons Tire Crr =0.425* Trailer Crr+0.425* Drive Crr+0.15* Steer Crr =0.425* Trailer Crr+0.425* Drive Crr+0.15* Steer Crr =0.425* Trailer Crr+0.425* Drive Crr+0.15* Steer Crr Drive Cycles & Weightings: CARB HHDDT 0.05 0.05 0.05 GEM 55 mph 0.09 0.09 0.09 GEM 65 mph 0.86 0.86 0.86***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 29 **Table 4**  **- 6**  **Class 8 Com** **bination Tractor Day Cab Predefined**  **Modeling Param eters**  Regulatory Subcategory Class 8 Combination Class 8 Combination Class 8 Combination Day Cab - High Roof Day Cab - Mid Roof Day Cab - Lo w Roof Gearbox Efficiency 98% for the gear with a 1:1 gear ratio, and 96% for all other gears 98% for the gear with a 1:1 gear ratio, and 96% for all other gears 98% for the gear with a 1:1 gear ratio, and 96% for all other gears Axle Mechanical Efficiency 95.5% 95.5% 95.5% Total weight ( kg ) 31297 29529 29710 Number of Axle s 5 5 5 Default Axle Configuration 6x4 6x4 6x4 Electrical Accessory Power ( W) 300 300 300 Mechanical Accessory Power ( W ) 1000 1000 1000 Environme ntal air temperature ( ° C) 25 25 25

Payload (tons) 19 19 19 Weight Reduction (lbs) Add 1/3*weight reduction to Payload tons Add 1/3*weight

reduction to Payload tons Add 1/3*weight

reduction to Payload tons Tire Crr =0.425* Trailer Crr+0.425* Drive Crr+0.15* Steer Crr =0.425* Trailer Crr+0.425* Drive Crr+0.15* Steer Crr =0.425* Trailer Crr+0.425* Drive Crr+0.15* Steer Crr Drive Cycles & Weightings: CARB HHDDT 0.19 0.19 0.19 GEM 55 mph 0.17 0.17 0.17 GEM 65 mph 0.64 0.64 0.64***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 30 **Table 4**  **- 7**  **Class 7 Com** **bination Tractor Predefined**  **Modeling Param eters**  Regulatory Subcategory Class 7 Combination Class 7 Combination Class 7 Combination Day Cab - High Roof Day Cab - Mid Roof Day Cab - Lo w Roof Gearbox Efficiency 98% for the gear with a 1:1 gear ratio, and 96% for all other gears 98% for the gear with a 1:1 gear ratio, and 96% for all other gears 98% for the gear with a 1:1 gear ratio, and 96% for all other gears Axle Mechanical Efficiency 95.5% 95.5% 95.5% Total weight ( kg ) 22679 20910 21091 Axle Base 4 4 4 Default Axle Configuration 4x2 4x2 4x2 Electrical Accessory Power ( W) 300 300 300 Mechanical Accessory Power ( W ) 1000 1000 1000 Environme ntal air temperature ( ° C) 25 25 25

Payload (tons) 12.5 12.5 12.5 Weight Reduction (lbs) Add 1/3*weight reduction to Payload tons Add 1/3*weight

reduction to Payload tons Add 1/3*weight

reduction to Payload tons Tire Crr =0.425* Trailer Crr+0.425* Drive Crr+0.15* Steer Crr =0.425* Trailer Crr+0.425* Drive Crr+0.15* Steer Crr =0.425* Trailer Crr+0.425* Drive Crr+0.15* Steer Crr Drive Cycles & Weightings: CARB HHDDT 0.19 0.19 0.19 GEM 55 mph 0.17 0.17 0.17 GEM 65 mph 0.64 0.64 0.64 

### 4.4.1.10 Vocational Tables Table 4 - 8 through Table 4 - 10 display the predefined GEM parameters proposed for use for the vocational vehicle compliance model . Many of the parameters are based on the vehicles EPA selected to test at SwRIand are considered to reasonabl y represent the fleet in the ir respective categories. For example, the Kenworth T270 truck and Ford F - 65 0 tow truck are used as vehicles to represent the MHD and LHD vocational vehicle fleet , while the Kenworth T700 and New Fl yer refuse truck s are used to represent the fleet of HHD vocational vehicles. With those vehicles as reference , it helps to determine the ty pe of transmission and its gear ratio , tire diameters, and all accessory losses used for all vocational vehicles shown in these three tables. Tire radius and axle ratios were selected , using good engineering judgment and stake holder input, to reflect reasonable final drive ratios to match with our modeled transmissions. With the exception of the Multi - purpose and Urban HHD vehicles, the engine power rating is the same as in Phase 1. For these two subcategories, the agencies s elected 11L - 345 hp engines because this is a more ty

pical power rating for vehicles that are not long haul. O ther parameters , such as the engine power rating, vehicle weight, payload, weight reduction, tire rolling resistance, front al area, and axle base, etc . follow the Phase 1 structure. The gear mechanical efficiency as well as axle mechanical efficiency is selected based on the inputs from stakeholders. The weighting of steer tire Crr and drive tire Crr is different than in Phase 1 to better reflect the weight distribution over the steer and drive axles. The assignment of 50 percent of reduced weight back to payload***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 31 is different than in P hase 1 and not the same as for tractors. See the draft RIA Chapter 2 for details. Chapter 4.4.3 to 4.4.9 explain s how these parameters are used in GEM. The agencies propose to expand the number of vocational sub categories from three ( in Phase 1) to nine ( in P hase 2) . It can be seen from Table 4 - 8 through Table 4 - 10 , the agencies are also proposing to add an idle cycle for vocational vehicles to the duty cycles used in Phase 1 certification . **Table 4**  **- 8**  **Vocational HHD V**  **ehicle Predefined**  **Modeling Param eters** 

Regulatory Subcategory HHD HHD HHD Regional Duty Cycle Multi - Purpose Duty Cycle Urban Duty Cycle Gearbox Efficiency 98% for the gear with a 1:1 gear ratio, and 96% for all other gears 98% for all gears 98% for all gears Axle Mechanical Efficiency 95.5% 95.5% 95.5% Total weight (kg) 19051 19051 19051 Number of Axles 3 3 3 Electrical Accessory Power (W) 300 300 300 Mechanical Accessory Power (W) 1000 1000 1000 Environmental Air Temperature (°C) 25 25 25

C dA (m2 ) 6.86 6.86 6.86 Tire Crr =0.7* Drive Crr + 0.3* Steer Crr 0.7* Drive Crr + 0.3* Steer Crr =0.7* Drive Crr + 0.3* Steer Crr Payload (tons) 7.50 7.50 7.50 Weight Reduction (lbs) Add 0.5*weight reduction to Payload tons Add 0.5*weight

reduction to Payload tons Add 0.5*weight

reduction to Payload tons Drive Cycles & Weightings: CARB HHDDT 0.50 0.82 0.94 GEM 55 mp h 0.28 0.15 0.06 GEM 65 mph 0.22 0.03 0.00 Idle cycle 0.10 0.15 0.20***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 32 **Table 4**  **- 9**  **Vocational MHD V**  **ehicle Predefined**  **Modeling Param eters**  Regulatory Subcategory MHD MHD MHD Regional Duty Cycle Multi - Purpose Duty Cycle Urban Duty Cycle Gearbox Efficiency 98% for all gears 98% for all gears 98% for all gears Axle Mechanical Efficiency 95.5% 95.5% 95.5% Total weight (kg) 11408 11408 11408 Number of Axles 2 2 2 Electrical Accessory Power (W) 300 300 300 Mechanical Accessory Power (W) 1000 1000 1000 Environmental Air Temperature (°C) 25 25 25

C dA (m2 ) 5.40 5.40 5.40 Tire Crr =0.7* Drive Crr + 0.3* Steer Crr 0.7* Drive Crr + 0.3* Steer Crr =0.7* Drive Crr + 0.3* Steer Crr Payload (tons) 5.60 5.60 5.60 Weight Reduction (lbs) Add 0.5*weight reduction to Payload tons Add 0.5*weight

reduction to Payload tons Add 0.5*weight

reduction to Payload tons Drive Cycles & Weightings: CARB HHDDT 0.50 0.82 0.94 GEM 55 mph 0.28 0.15 0.06 GEM 65 mph 0.22 0.03 0.00 Idle cycle 0.10 0.15 0.20***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 33 **Table 4**  **- 10**  **Vocational LHD V**  **ehicle Predefined**  **Modeling Param eters**  Regulatory Subcategory LHD LHD LHD Regional Duty Cycle Multi - Purpose Duty Cycle Urban Duty Cycle Gearbox Efficiency 98% for all gears 98% for all gears 98% for all gears Axle Mechanical Efficiency 95.5% 95.5% 95.5% Total weight (kg) 7257 7257 7257 Number of Axles 2 2 2 Electrical Accessory Power (W) 300 300 300 Mechanical Accessory Power (W) 1000 1000 1000 Environmental Air Temperature (° C ) 25 25 25

C dA (m2 ) 5.40 5.40 5.40 Tire Crr =0.7* Drive Crr + 0.3* Steer Crr 0.7* Drive Crr + 0.3* Steer Crr =0.7* Drive Crr + 0.3* Steer Crr Payload (tons) 2.85 2.85 2.85 Weight Reduction (lbs) Add 0.5*weight reduction to Payload tons Add 0.5*weight

reduction to Payload tons Add 0.5*weight

reduction to Payload tons Drive Cycles & Weightings: CARB HHDDT 0.50 0.82 0.94 GEM 55 mph 0.28 0.15 0.06 GEM 65 mph 0.22 0.03 0.00 Idle cycle 0.10 0.15 0.20 

### 4.4.1.11 Trailer T ables Trailers are simulated using the same GEM models as the tractor program . T here are only minor di fferences between the trailer and tractor modeling parameters and inputs . Table 4 - 11 lists all of the predefined vehicle parameters of trailer baseline models. T he predefined modeling parameters for the long box dry van trailer subcategory are identical to the Class 8 high - roof sleeper cab tractor subcategory . T he other trailer subcategories differ in tractor cab ty pe, total weight, aerodynamic characteristics, number of axles, payload, and drive cycle. For example, the refrigerated trailers include a refrigeration unit whi ch adds weight and slightl y improves aerodyn amic performance (reduces CdA). Sho rt box vans are half the length, have a single axle , and are pulled by a day cab tractor which reduces total weight and the total payload carryi ng capacity . The drive cycle weightings are consistent with the tractor program. Long box trailers are simulated as being pulled b y sleeper cabs, and therefore have the long - haul drive cycle weightings. The short box trailers are pulled by day cabs and have the short - haul weightings. Similar to the tractor program, trailer manufacturers can provide aerody namic drag, tire rolling resistance and weight reduction inputs to the model. T he key differences between the trailer and tractor options are that aerody namic drag is submitted as a change in drag (delta CdA) for trailers , which is compared to the baseline CdA values shown in Table 4 - 11 within GEM, and***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 34 only adju stments to trailer tire rolling resistance are allowed . A list of weight reduction options is available in 40 CFR 1037.520 and manufacturers have the option to indicate that their trailers use Automatic T ire Inflation S ys tems (ATIS) f or a predefined addit ional performance improvement . Additional information about each trailer subcategory is found in Chapter 2.10 of this draft RIA. **Table 4**  **- 11**  **Predefined Mod**  **eling Param eters**  **for Box**  **Trailer s**  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 C 8 Day Cab - High Roof Engine Fuel Map 15L - 455 HP Gear ratio 12.8, 9.25, 6.76, 4.9, 3.58, 2.61, 1.89, 1.38, 1, 0.73 Gearbox Efficiency 98% for 1:1 gear ratio, and 96 for all other gears Axle Mechanical Efficiency 95.5% Total weight (kg) 31978 33778 15191 16991 Baseline CdA Values (m2 ) 6.2 6.1 6.1 6.0 Number of Axles 5 4 Payload (tons) 19 10 Default Axle Configuration 6x4 Electrical Accessory Power (W) 300 Mechanical Accessory Power (W) 1000

Steer Tire RR 6.54 Drive Tire RR 6.92 Tire Radius (m) 0.5 Axle Drive Ratio 3.7 Tire Crr =0.425* Trailer Crr+0.425* Drive Crr+0.15* Steer Crr Weight Reduction (lbs) Add 1/3*weight reduction to Payload tons Drive Cycles & Weightings: CARB HHDDT 0.05 0.19 GEM 55 mph 0.09 0.17 GEM 65 mph 0.86 0.64 Payload (tons) 19 7 

### 4.5 **Technolog y**  **I mprovements**  **that Are Recognized**  **in GEM w**  **ithout Simulation**  The development of GEM as a compliance tool has required the agencies to balance the need for simplicity against the rigor of the model. As part of that process, the agencies have identified several technologies and technological improvements that would b e difficult to accuratel y simulate, but that should be recognized during certification. These would be recognized in the proposed Phase 2 GEM through post - simulation adjustments to the results. This is similar to what was done in Phase 1, where the GEM i nterface included pull - down menus for manufacturers to select these adjustments. For this reason, these adjustments have come to be known as pull - down technolog ies .***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 35 Phase 2 GEM would continue to recognize those technologies that would be difficult to mode l accuratel y . In addition to those recognized in Phase 1 , the technology list is expanded to a much wider range as discussed in the next few paragraphs of this Chapter . In contrast to the Phase 1 approach, Phase 2 GEM uses a different approach in recognizing these technologies. First of all, all technology improvements are built into GEM . Default improvement values for each of these technologies, developed by the agencies after consulting various stakeholders and searching f

or literature values , are implemented into GEM. The user can only select either “Y” or “N” in the GEM input file, where Y means that the technology is included, while N means the vehicle does not have this technology . This means that users have no flexib ility to enter their own values. For some of these technologies, such as predictive cruise control and Automatic T ire Inflation S ys tems ( AT IS ) , the actual benefit is dependent on how operators behave in the real world . For example, ATIS would be of very l ittle benefit where a driver made sure on a dail y basis that the tires were properl y inflated, but would have large benefits where a driver never checked the tires. For other technologies, the benefits of the technology are small relative to the difficulty of rigorousl y simulating it. The agencies believe the technology improvement approach is an appropriate compromise that will achieve the regulatory goal of incentivizing the use of the technology . In this proposed approach, the GEM software would adjust the simulation results to decrease the g/ton - mile results that are output by the model. For example, with a technology that is assigned a 1 percent benefit, the official result for a vehicle that was simulated as having 500 g/ton - mile CO 2 emissions would be reported as having an emission rate of 495 g/ton - mile. The technology

improvement values used for tractors are shown in Table 4 - 12 . These va lues represent the agencies’ best judgment about the appropriate value for each of these technologies. We are generall y assigning minimum values to be conservative and not overestimate the actual in - use benefits. These values were developed based on all available information, including information from stakeholders .***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 36 **Table 4**  **- 12**  **Tractor Technolog y Im** **provement V**  **alues** Technology Improvement Class 8 Sleeper Cabs Class 8 Day

Cabs Class 7 Day

Cabs Class 8 Heavy Haul

Tractors Single Drive Axle ( 6x2 or 4x2 ) C onfiguration 2.5% 2.5% N/A 2.5% Part - time Single Drive Axle 6x2 C onfiguration a 2.5% 2.5% N/A 2.5% Lo w F riction Axle L ubricant 0.5% 0.5% 0.5% 0.5% Automated Manual, Automatic, and Dual C lutch T ransmissions 2% 2% 2% 2% Predictive Cruise control 2% 2% 2% 2% High Efficiency Air Conditioning Compressor 0.5% 0.5% 0.5% 0.5% Electric Accessories 1% 1% 1% 1% Extended Idle Reduction 5% N/A N/A N/A Automat ic Tire Inflation System (ATIS) 1% 1% 1% 1% Note : a A 2.5% reduction over the 55 mph and 65 mph cycles and no reduction over the CARB HHDDT cycle For vocational vehicle s , the technologies in Table 4 - 13 would be considered .

**Table 4**  **- 13**  **Vocational Vehicle Technology Improvement**  **Values** Technology Improvement Regional Duty Cycle Multi - Purpose Duty Cycle Urban Duty Cycle HHD Single Drive Axle ( 6x2 or 4x2) C onfiguration 2.5% 2.5% 2.5% HHD Part - time Single Drive Axle 6x2 C onfiguration a 1.0% 0.3% 0.1% Lo w F riction Axl e L ubricant 0.5% 0.5% 0.5% HHD Automated Manual or Dual C lutch T ransmissions 2 .3 % N/A N/A PTO Delta Fuel (g/ton - mile) 0 to 30 0 to 30 0 to 30 Neutral I dle Emissions during idle cycle calculated using torque and speed values from idle fuel map with the transmission in drive and neutral , 10% and

90% of the cycle time , res pe c tively b Stop - S tart I dle Reduction 90 percent reduction of idle - cycle emissions calculated using torque and speed values from idle fuel map with the transmission in drive b Notes: a Based on 2.5% reduction over the 55 mph and 65 mph cycles and no reduction over the CARB HHDDT cycle b See idle fuel consumption test procedure at 40 CFR 1036.535 (d) . For trailer s , the following technologies in Table 4 - 14 would be considered .

**Table 4**  **- 14**  **Trailer Technology Im** **provement Values**  Technology Im

provement Effectiveness Automatic Tire Inflation Systems 1.5%***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 37 I f a manufacturer believe s that the CO 2 reduction benefits assigned b y the agencies are an underestimate, they

have the option to perform powertrain testing or request (and demonstrate) credit in the off

- cycle technology

process.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

4 - 38 

## References 1 http://www.epa.gov/otaq/climate/gem.htm 2 “Peer Review of the Greenhouse gas Emissions Model (GEM) and EPA's Response to Comments,” fo und in the docket of this rulemaking, EPA

–420 - R - 15 - 009 3 K. Newman, J. Kargul, and D. Barba, “Development and Testing of an Automatic Transmission Shift Schedule Algorithm for Vehicle Simulation, “SAE Int. J. Engines 8(3):2015, doi: 10.4271/2015 - 01 - 1142 4 Reinhart, T.E. (2015, June). Commercial Medium - and Heavy - Duty Truck Fuel Efficiency Technology Study

– Report #1. (Report No. DOT HS 812 146). Washington, DC: National Highway Traffic Safety Administration. 5 MatLab information (© 1994 - 2010 The MathWorks, Inc.) can be found at http://www.mathworks.com/products/matlab. Simulink information (© 1994 - 2010 The MathWorks, Inc.) can be found at http://www.mathworks.com/products/simulink . StateFlow info rmation (© 1994 - 2010 The MathWorks, Inc.) can be found at http://www.mathworks.com/products/stateflow 6 US EPA, “Technical Research Workshop supporting EPA and NHTSA Phase 2 Standards for MD/HD G reenhouse Gas and Fuel Efficiency

— Decem ber 10 and 11, 2014,” http://www .epa.gov/otaq/climate/regs - heavy - duty .htm 7 J. W. Anthony, J.V. Sarlashkar, A. Phan, C. E. Roberts, Jr., H. Zhang, J. Sanchez, M. Spears, A. Cullen, Powertrain test cell and its test procedure development for greenhouse gas emission measurements, ASME Int. J. , [in press] 8 SwRI, “GEM Validation ”, Technical Research Workshop supporting EPA and NHTSA Phase 2 Standards for MD/HD Greenhouse Gas and Fuel Efficiency

— December 10 and 11, 2014, http://www.epa.gov/otaq/climate/regs heavy - duty.htm 9 J. Anthony, J. Sarlashkar, H. Zhang, J. Sanchez, M. Spears, A. Cullen, Chassis testing versus powertrain testing for heavy - duty vehicle greenhouse gas emission measurements, SAE 2014 Commercial Vehicle Engineering Congress, Oct. 7 - 9, 2014 10 H. Zhang, M . Spears, and A. Cullen, Technology recognition for the next phase heavy - duty greenhouse gas emission and fuel efficiency standards, SAE 2014 Commercial Vehicle Engineering Congress, Oct. 7 - 9, 2014 . 11 United States Environmental Protection Agency. SmartW ay Transport Partnership July 2010 e - update accessed July 16, 2010, from http://www.epa.gov/smartwaylogistics/newsroom/documents/e - update - july - 10.pdf