**UNITED STA TES ENVIRONMENTA**  **L PROTECTION A GENCY**  NATIONAL VEHICLE AND FUEL EMISSIONS LABORATORY

2565 PLYMOUTH ROAD ANN ARBOR, MI 48105
- 2498

OFFICE OF AIR AND RADIATION June 2015 MEMORANDUM SUBJECT: Possible Tractor , Trailer, and Vocational Vehicle Standards Derived from Alternative

Road Grade Profiles FROM: Lauren Steele, Houshun Zhang, OTAQ/ASD TO: Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium
- and Heav y - Duty

Engines and Vehicles
- Phase 2
- Docket EPA
- HQ
- OAR
- 201 4
- 0827 **Introduction** The purpose of this memorandum is to illustrate some possible effects on the calcula ted fuel consumption and CO 2 emissions of vehicles caused by variations in the test procedure for simulating road grade in the Greenhouse gas Emissions Model (GEM). This memorandum presents possible road grade profiles other than the one presented in the proposal , as well as an analy sis of exploratory work using the Phase 2 GEM with alternate road grades
. 1 The road grade profiles described below include two that were developed by the Department of Energy ’s National Renewable Energy L aboratory ( NREL ) and one that was developed b y the agencies. For completeness the proposed profile that is in Phase 2 GEM is described as well. It is a goal of the agencies to select the most appropriate road grade profile(s) on the basis of being nationally representa tive as well as reasonabl y similar to real
- world driving conditions. It is not the agencies’ intent to cause the standards to become more or less stringent as a result of selection of road grade profile. An y effect on stringency is minimized by the fact that both the b aseline case and the stringency case will be simulated in GEM with the same road grade profile. However, it is expected that various engine and driveline technologies will perform differently over different road grade profiles, thus changin g the resulting numerical results in all cases. The agencies acknowledge that if a road grade profile is very aggressive, some vehicles may not be able to follow the full trace at speed. In the preamble to this rulemaking we request comment on the merits of develop ing variable speed highway cy cles
. O ur goal is to adopt a cy cle that is challenging enough to ensure that vehicles continue to be built for real world performance, while mainta ining the simulated vehicle operation within a range for which GEM has been validated
.

1 In the preamble this memo is referred to as being dated in April (note 194 Section III) and May (note 240 Section IV and note 264 Section V). The exploratory w ork described below w as conducted in April and May 2015.2

**Proposed Road Grade Profile** T he agencies are proposing an interim road grade profile for development of the proposed standards, as shown below in Figure 1, in both the 55 mph and 65 mph cy cles . The grade profile was developed by Southwest Research Institu t e (SwRI ) on a 12.5 mile stretch of restricted
- access highway during on
- road tests conducted for EPA’s validation of the Phase 2 version of GEM. Th e minimum grade in the interim profile is
- 2.1 percent and the maximum grade is 2.4 percent. The profile includes 30 percent of the distance at grades of +/
- 0.5 percent. Overall, the profile includes approximately 50 percent of the time in relatively flat terrain with road gradients of less than 1 percent
.

**Figure 1**  **: Proposed Road Grade Profile for 55 m**  **ph and 65 m ph Drive Cycles**  The following charts illustrate the degree to which the SwRI road grade profile in GEM matches the national ly representative profile , as characterized by NREL
. In Figure 2, the GEM profile has generally lower magnitude grades than the national data, with a lack of grades between 2 and 4%. In Figure 3 the majority of half hills in the GEM profile a re of length 0.5 to 1.5 miles, with a lack of half hills less than 0.5 mi and longer than 1.5 miles. - 4 - 2 0 2 4

0 2 4 6 8 10 12 14**G r** **a d** **e (** **% )** 

**Distance (mi)**  **Ro ad**  **Gra de on**  **the 55 m**  **ph and 65 mph**  **Cy cles** 3

**Figure 2**  **: Comparison of National**  **Cumulative Absolute Road Grade with SwRI Route**  **(Source: NREL)**

**Figure 3**  **: Comparison of National C**  **umulative Half Hill Distance**  **with SwRI Route (Source: NREL)** 4

**NREL Road Grade Profiles** A complete description of the methodology for generating the NREL road grade profiles, as well as several other possi ble alternate profiles, is found in a May 2015 report titled, “ Development of Road Grade Profiles Representative of US Controlled Access Highway s ,” available in the docket. Numerical representations of these distance
- based profiles are also available in t he docket, in a format that is ready for modeling. Th e minimum grade in the example 55 mph NREL profile shown in Figure 4 is
- 3.1 p ercent and the maximum grade is 3.8 percent. The majority of the profile is within a range of g rades of +/
- 2 percent. Of the five nationally

representative 55 mph profiles generated by NREL in the final report, this one was selected as the example because the shorter length of the synthetic profile (compared to the relatively long local routes) has many advantages . Also, th e road grade i s steeper than in the other sy nthetic profile. Th e minimum grade in the example 65 mph NREL profile shown in Figure 5 is
- 2.2 p ercent and the maximum grade is 3.3 percent. The majority of the profile is within a range of g rades of +/
- 2 percent. Of the four nationally

representative 65 mph profiles generated by NREL in the final report, this one was selected as the example because the shorter length of the s ynthetic profile (compared to the relativel y long local routes) has man y ad vantages. Also, the length of distance spent in a steep down
slope is less than in the other sy nthetic profile.

**Figure 4**  **: Example NREL road grade profile for 55 m ph cycle** 5 **Figure 5**  **: Example NREL road**  **grade profile for 65 m ph cycle** 
**EPA Road Grade Profile**  The profile depicted in Figure 6 is 11.48 miles (18.44 km) long, its longest half hill spans 2.87 miles (4.47 km) and its highest grade equals 2.5%
. It was developed to align with the national road grade data using a methodology

differing from NREL’s and may offer some advantages
. Of several profiles developed by EPA, this one was selected for analy sis in part due to its aggressive uphill. A complete description of t he methodology for generating the EPA road grade profile is found in a May 2015 memorandum titled, “ Development of an Alternative, Nationally Representative, Activit y Weighted Road Grade Profile for Use in EPA GHG Certification of Medium
- and Heav y - Dut y Ve hicles, ” available in the docket
.6 **Figure 6**  **: Example EPA road grade profile for both cruise cycles**  **Exploratory Work Analyzing the Effect**  **i n GEM of**  **Alternative Road Grade Profiles** The agency

has conducted exploratory work to e valuate the effects on vehicle performance as simulated in GEM of appl yi ng different road grade profiles. The objective of this analysis is to understand how the default transmission auto
- shift responds to demands to move heav y vehicles over different road grades. This auto
- shift is being used for the stringency development as well as the future compliance tool under the Phase 2 rulemaking. 2 , 3 The results are inconclusive, but do offer insights as to how GEM could be further improved to represent more realistic real
- world driving conditions. For this anal ys is, three profiles were examined: (1) the EPA profile described above and presented i n Figure 6 (Profile 1); an amplified version of Profile 1 referred to as Profile 2, and (3) the proposed profile described above and presented in Figure 1 (“Baseline”) . Figures 7 and 8 show the road grade s and elevation s, respectively , of these three prof iles explored in this study
.

2 Newman, K., Dekraker, P., Zhang, H. S anchez, J., et al, “ Development of Greenhouse Gas Emissions Model (GEM) for Heavy
- and Medium
- Duty Vehicle Compliance, ” S AE Technical Paper, October 6
- 9, 2015
. 3 Newman, K., Kargul, J., and Barba, D., “ 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
- 11427 **Figure 7**  **Alternate Road Grade Profiles Explored**

**Figure 8**  **Alternate Elevation Profiles Explored** It can be seen that Profiles 1 and 2 are similar in term of shape, except that Profile 2 has a higher road grade up to 4%. In fact, Profile 2 was derived from Profile 1 by multiply ing a constant to Profile 1 in order to achieve a maximum road grade of 4%. This hy pothetic al road grade is mainly used to check how the auto - shifting algorithm respond s with a road grade up to 4%, and was not designed to align with the national data. The Baseline and Profile 1 have similar road grade in term s of maximum road g rade, although elevation is quite different. Compared to the Baseline, both Profiles 1 and 2 have a long hill, which can test how the default transmission auto
- shift responds to this condition. In order to evaluate the impact of the road grade on the ve hicle performance as well as check the fidelity of the default transmission auto
- shi f t, a vehicle with the key

parameters defined in Table 1 is selected for **-4 -3**  **-2 -1**  **0 1**  **2 3**  **4 5** 

**0 5**  **10 15**  **20 25** **R o** **a d** **G r** **a d** **e (** **% )** 

**Distance (km)**  **Profile 1 Profile 2**  **Baseline**

**-60 -40**  **-20 0**  **20 40**  **60 80** 

**0 5**  **10 15**  **20 25** **E l** **e v** **a t** **i o** **n (** **m )** 

**Distance (km)**  **Profile 1 Profile 2**  **Baseline**8

this study , which represents a class 8 tractor with specifications aligning with some technologies that could be adopted in the 2027 timeframe.

**Table 1**  **Class 8 Combination Tractor Sleeper Cab Modeling Param eters**  Regulatory Class Class 8 Combination Sleeper Cab
- High Roof Engine 455hp rating map for 2027 Transmission gear ratio [0 14.8 10.95 8.09 5.97 4.46 3.32 2.45 1.81 1.35 1] Gearbox Efficiency 98% for the gear with a 1:1 gear ratio, and 96% for all other gears CdA 4 Steer CRR (kg/t) 4.3 Drive CRR (kg/t) 4.5 Trailer CRR (kg/t) 4.7 Axle Mechanical Efficiency 96% Total w eight (kg) 31978 Axle ratio 2.26 Number of Axles 5 Default Axle Configuration 6x4 Electrical Accessory Pow er (W) 300 Mechanical Accessory Pow er (W) 1000 Environmental Air Temperature (°C) 25

Payload (tons) 19 Figures 9 and 10 below present the simulated results of the vehicle described in Table 1 over Profile 1 and a 65 mph drive cy cle
.

**Figure 9**  **V ehicle speed traces, gear number, engine speed and torque over 65**  **mp h cycle for Profile 1**  1200 1300 1400 1500 1600 1700 1800 1900 50 60 70 80 90 100 110 120 130

Ti me (S)VehSpd/Engspd*10/Gear#*10

Ve h Ta rget ed sp eed (mph) Ve h Sp eed (mph) Gear # En gi ne s peed (rpm )9 **Figure 10**  **Engine operating points over 65 mph cycle for Profile 1** From Figure 9 , it can be seen that the engine is under
- power ed during the long hill operation because the vehicle is unable to follow the targeted vehicle speed trace. The transmission stay s i n the top gear. The engine operating points as shown in Figure 10 seem to make sense, suggesting that the auto
- shifting is able to handle this road grade profile up to 2.5%. Th e situation changes when higher road grade with a maximum of 4% is evaluated. Figure 11 and 12 below present the simulated results of the vehicle described in Table 1 over Profile 2 and a 65 mph drive cy cle.

**Figure 11**  **Vehicle speed traces, gear number , engine speed and torque over 65 m**  **ph cycle for Profile 2** 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 -500 0 500 1000 1500 2000 2500

RPMTorque(Nm) Full T orque Engine Operat in g Po in ts

1200 1300 1400 1500 1600 1700 1800 1900 40 60 80 100 120 140 160 180

Ti me (S )VehSpd/Engspd*10/Gear#*10 Ve h Ta rget ed sp eed (m ph)

Ve h Sp eed (m ph) Gear # En gine sp eed (rpm )10 **Figure 12**  **Engine operating points over 65 mph cycle for Profile 2** Figure 11 shows that the vehicle cannot meet the targeted speed trace due to the under
- powered engine. When the vehicle climbs the hill, there is a long delay for 50 seconds before shifting to lower gear. This results in the engine operating points mov ing to the lower speed end along the full torque curve as indicated in Figure 12 . In reality , the truck ru nning on the road should also have a minimum engine speed limit. I n contrast, the default auto
- shifting algorithm currently allow s the engine speed to drop below 900 rpm without shifting. These behaviors indicate an opportunit y to improve GEM for the fin al rulemaking . Another key observation and area for improvement is how the engine behaves during climbing once the transmission shifts to a lower gear. As can be seen in Figure 11 , the engine first drops the speed a little bit after 1520 seconds , and then keeps rising for more than 80 seconds without shifting. This causes the engine to run along the peak torque curve while the speed rises, which is not a very efficient zone. Table 2 shows the tractor performance in grams of CO 2 per ton - mile over the individual GEM drive cy cles as well as the composite cy cle with weightings for a sleeper cab tractor, using the three different highway cruise road grade profiles explored in this study
. No road grade was applied to the ARB Transient cy cle. As expected, the vehicle emits more CO 2 when driving the more aggressive road grade using Profile 2. **Table 2**  **GEM perform ance**  **(g CO 2**  **/ton -**  **mi )**  **of a hypothetical 2027 c**  **lass 8 sleeper cab tractor over 3**  **road grade profiles**  Baseline Profile 1 Profil e 2 55m ph 62.24 58.63 68.5 65m ph 71.73 67.13 74.28 ARB 128.17 128.17 128.17 Weighted 73.69 69.42 76.45 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 -500 0 500 1000 1500 2000 2500

RPMTorque(Nm) Full To rque En gine Operat ing Po int s11

This exploratory

work illustrates areas for improvement in the calibration of the agency ’s transmission auto - shift as indicated b y Figure s 11 and 12 , when high road grade is used for highway cruise drive cy cles. To attain the agencies’ goal of represent ing r eal world driving, we believe we would need to make correction s on the GEM auto
- shifting
. In the preamble , the agenc ies ha ve asked stakeholders for comments, hopefully supported b y testing data , to help us to calibrate our auto
- shift model. More importantly , EPA has developed a comprehensive testing plan to obta in first
- hand testing data. This plan includes the powertrain test s for both medium heavy
- duty and heav y heavy
- dut y powertrain s conducted at SwRI , and heav y heavy
- duty powertrain s with three transmission setups at Oak Ridge National Laboratory . Up to eight different road grade profiles will be tested, and a large data set will be collected to see how the transmissions are shifted, thus recalibrating some model constants used in the auto
- shifting table. I t is expected that a well
- calibrated GEM would be able to address a wider range of operations including high road gra de routes.