40 CFR § 1037.550 - Powertrain testing.

§ 1037.550 Powertrain testing.

This section describes the procedure to measure fuel consumption and create engine fuel maps by testing a powertrain that includes an engine coupled with a transmission, drive axle, and hybrid components or any assembly with one or more of those hardware elements. Engine fuel maps are part of demonstrating compliance with Phase 2 vehicle standards under this part; the powertrain test procedure in this section is one option for generating this fuel-mapping information as described in 40 CFR 1036.503. Additionally, this powertrain test procedure is one option for certifying hybrids to the engine standards in 40 CFR 1036.108.

(a) General provisions. The following provisions apply broadly for testing under this section:

(1) Measure NOX emissions as described in paragraph (k) of this section. Include these measured NOX values any time you report to us your greenhouse gas emissions or fuel consumption values from testing under this section.

(2) The procedures of 40 CFR part 1065 apply for testing in this section except as specified. This section uses engine parameters and variables that are consistent with 40 CFR part 1065.

(3) Powertrain testing depends on models to calculate certain parameters. You can use the detailed equations in this section to create your own models, or use the GEM HIL model (incorporated by reference in § 1037.810) to simulate vehicle hardware elements as follows:

(i) Create driveline and vehicle models that calculate the angular speed setpoint for the test cell dynamometer, ƒnref,dyno, based on the torque measurement location. Use the detailed equations in paragraph (f) of this section, the GEM HIL model's driveline and vehicle submodels, or a combination of the equations and the submodels. You may use the GEM HIL model's transmission submodel in paragraph (f) of this section to simulate a transmission only if testing hybrid engines.

(ii) Create a driver model or use the GEM HIL model's driver submodel to simulate a human driver modulating the throttle and brake pedals to follow the test cycle as closely as possible.

(iii) Create a cycle-interpolation model or use the GEM HIL model's cycle submodel to interpolate the duty-cycles and feed the driver model the duty-cycle reference vehicle speed for each point in the duty-cycle.

(4) The powertrain test procedure in this section is designed to simulate operation of different vehicle configurations over specific duty cycles. See paragraphs (h) and (j) of this section.

(5) For each test run, record engine speed and torque as defined in 40 CFR 1065.915(d)(5) with a minimum sampling frequency of 1 Hz. These engine speed and torque values represent a duty cycle that can be used for separate testing with an engine mounted on an engine dynamometer under § 1037.551, such as for a selective enforcement audit as described in § 1037.301.

(6) For hybrid powertrains with no plug-in capability, correct for the net energy change of the energy storage device as described in 40 CFR 1066.501. For PHEV powertrains, follow 40 CFR 1066.501 to determine End-of-Test for charge-depleting operation. You must get our approval in advance for your utility factor curve; we will approve it if you can show that you created it from sufficient in-use data of vehicles in the same application as the vehicles in which the PHEV powertrain will be installed.

(b) Test configuration. Select a powertrain for testing as described in § 1037.235 or 40 CFR 1036.235 as applicable. Set up the engine according to 40 CFR 1065.110 and 1065.405(b). Set the engine's idle speed to the minimum warm-idle speed. If warm idle speed is not adjustable, simply let the engine operate at its warm idle speed.

(1) The default test configuration consists of a powertrain with all components upstream of the axle. This involves connecting the powertrain's output shaft directly to the dynamometer or to a gear box with a fixed gear ratio and measuring torque at the axle input shaft. You may instead set up the dynamometer to connect at the wheel hubs and measure torque at that location. The preceding sentence may apply if your powertrain configuration requires it, such as for hybrid powertrains or if you want to represent the axle performance with powertrain test results.

(2) For testing hybrid engines, connect the engine's crankshaft directly to the dynamometer and measure torque at that location.

(c) Powertrain temperatures during testing. Cool the powertrain during testing so temperatures for oil, coolant, block, head, transmission, battery, and power electronics are within the manufacturer's expected ranges for normal operation. You may use electronic control module outputs to comply with this paragraph (c). You may use auxiliary coolers and fans.

(d) Engine break in. Break in the engine according to 40 CFR 1065.405, the axle assembly according to § 1037.560, and the transmission according to § 1037.565. You may instead break in the powertrain as a complete system using the engine break in procedure in 40 CFR 1065.405.

(e) Dynamometer setup. Set the dynamometer to operate in speed-control mode (or torque-control mode for hybrid engine testing at idle, including idle portions of transient duty cycles). Record data as described in 40 CFR 1065.202. Command and control the dynamometer speed at a minimum of 5 Hz, or 10 Hz for testing engine hybrids. Run the vehicle model to calculate the dynamometer setpoints at a rate of at least 100 Hz. If the dynamometer's command frequency is less than the vehicle model dynamometer setpoint frequency, subsample the calculated setpoints for commanding the dynamometer setpoints.

(f) Driveline and vehicle model. Use the GEM HIL model's driveline and vehicle submodels or the equations in this paragraph (f) to calculate the dynamometer speed setpoint, ƒnref,dyno, based on the torque measurement location. Note that the GEM HIL model is configured to set the accessory load to zero and it comes configured with the tire slip model disabled.

(1) Driveline model with a transmission in hardware. For testing with torque measurement at the axle input shaft or wheel hubs, calculate, ƒnref,dyno, using the GEM HIL model's driveline submodel or the following equation:

Where:
ka[speed] = drive axle ratio as determined in paragraph (h) of this section. Set ka[speed] equal to 1.0 if torque is measured at the wheel hubs.
vrefi = simulated vehicle reference speed as calculated in paragraph (f)(3) of this section.
r[speed] = tire radius as determined in paragraph (h) of this section.

(2) Driveline model with a simulated transmission. For testing with the torque measurement at the engine's crankshaft, ƒnref,dyno is the dynamometer target speed from the GEM HIL model's transmission submodel. You may request our approval to change the transmission submodel, as long as the changes do not affect the gear selection logic. Before testing, initialize the transmission model with the engine's measured torque curve and the applicable steady-state fuel map from the GEM HIL model. You may request our approval to input your own steady-state fuel map. Configure the torque converter to simulate neutral idle when using this procedure to generate engine fuel maps in 40 CFR 1036.503 or to perform the Supplemental Emission Test (SET) testing under 40 CFR 1036.505. You may change engine commanded torque at idle to better represent CITT for transient testing under 40 CFR 1036.510. You may change the simulated engine inertia to match the inertia of the engine under test. We will evaluate your requests under paragraph (f)(3) of this section based on your demonstration that that the adjusted testing better represents in-use operation.

(i) The transmission submodel needs the following model inputs:

(A) Torque measured at the engine's crankshaft.

(B) Engine estimated torque determined from the electronic control module or by converting the instantaneous operator demand to an instantaneous torque in N·m.

(C) Dynamometer mode when idling (speed-control or torque-control).

(D) Measured engine speed when idling.

(E) Transmission output angular speed, ƒni,transmission, calculated as follows:

Where:
ka[speed] = drive axle ratio as determined in paragraph (h) of this section.
vrefi = simulated vehicle reference speed as calculated in paragraph (f)(3) of this section.

r[speed] = tire radius as determined in paragraph (h) of this section.

(ii) The transmission submodel generates the following model outputs:

(A) Dynamometer target speed.

(B) Dynamometer idle load.

(C) Transmission engine load limit.

(D) Engine speed target.

(3) Vehicle model. Calculate the simulated vehicle reference speed, νrefi, using the GEM HIL model's vehicle submodel or the equations in this paragraph (f)(3):

Where:
i = a time-based counter corresponding to each measurement during the sampling period. Let vref1 = 0; start calculations at i = 2. A 10-minute sampling period will generally involve 60,000 measurements.
T = instantaneous measured torque at the axle input, measured at the wheel hubs, or simulated by the GEM HIL model's transmission submodel.
Eƒƒaxle = axle efficiency. Use Eƒƒaxle = 0.955 for T ≥ 0, and use Eƒƒaxle = 1/0.955 for T < 0. Use Eƒƒaxle = 1.0 if torque is measured at the wheel hubs.
M = vehicle mass for a vehicle class as determined in paragraph (h) of this section.
g = gravitational constant = 9.80665 m/s 2.
Crr = coefficient of rolling resistance for a vehicle class as determined in paragraph (h) of this section.
Gi-1 = the percent grade interpolated at distance, Di-1, from the duty cycle in appendix IV to this part corresponding to measurement (i-1).
ρ = air density at reference conditions. Use ρ = 1.1845 kg/m 3.
CdA = drag area for a vehicle class as determined in paragraph (h) of this section.
Fbrake,i-1 = instantaneous braking force applied by the driver model.
Δt = the time interval between measurements. For example, at 100 Hz, Δt = 0.0100 seconds.
Mrotating = inertial mass of rotating components. Let Mrotating = 340 kg for vocational Light HDV or vocational Medium HDV. See paragraph (h) of this section for tractors and for vocational Heavy HDV.

(4) Example. The following example illustrates a calculation of ƒnref,dyno using paragraph (f)(1) of this section where torque is measured at the axle input shaft. This example is for a vocational Light HDV or vocational Medium HDV with 6 speed automatic transmission at B speed (Test 4 in Table 2 of 40 CFR 1036.540).

kαB = 4.0
rB = 0.399 m
T999 = 500.0 N·m
Crr = 7.7 kg/tonne = 7.7·10-3 kg/kg
M = 11408 kg
Cd = 5.4 m 2
G999 = 0.39% = 0.0039
Fbrake,999 = 0 N
vref,999 = 20.0 m/s
Fgrade,999 = 11408·9.81·sin (atan(0.0039)) = 436.5 N
Δt = 0.0100 s
Mrotating = 340 kg

(g) Driver model. Use the GEM HIL model's driver submodel or design a driver model to simulate a human driver modulating the throttle and brake pedals. In either case, tune the model to follow the test cycle as closely as possible meeting the following specifications:

(1) The driver model must meet the speed requirements for operation over the highway cruise cycles as described in § 1037.510 and for operation over the transient cycle as described in 40 CFR 1066.425(b). The exceptions in 40 CFR 1066.425(b)(4) apply to the transient cycle and the highway cruise cycles.

(2) Send a brake signal when operator demand is zero and vehicle speed is greater than the reference vehicle speed from the test cycle. Include a delay before changing the brake signal to prevent dithering, consistent with good engineering judgment.

(3) Allow braking only if operator demand is zero.

(4) Compensate for the distance driven over the duty cycle over the course of the test. Use the following equation to perform the compensation in real time to determine your time in the cycle:

Where:
vvehicle = measured vehicle speed.
vcycle = reference speed from the test cycle. If vcycle,i-1 < 1.0 m/s, set vcycle,i-1 = vvehicle,i-1.

(h) Vehicle configurations to evaluate for generating fuel maps as defined in 40 CFR 1036.503. Configure the driveline and vehicle models from paragraph (f) of this section in the test cell to test the powertrain. Simulate multiple vehicle configurations that represent the range of intended vehicle applications. Use at least three equally spaced axle ratios or tire sizes and three different road loads (nine configurations), or at least four equally spaced axle ratios or tire sizes and two different road loads (eight configurations). Select axle ratios to represent the full range of expected vehicle installations.

(1) Determine the vehicle model inputs for M, Mrotating, Cd, and Crr for a set of vehicle configurations as described in 40 CFR 1036.540(c)(3). Instead of selecting axle ratios and tire sizes based on the range of intended vehicle applications as described in this paragraph (h), you may select axle ratios and tire sizes such that the ratio of engine speed to vehicle speed covers the range of ratios of minimum and maximum engine speed to vehicle speed when the transmission is in top gear for the vehicles in which the powertrain will be installed. Note that you do not have to use the same axle ratios and tire sizes for each GEM regulatory subcategory.

(2) For hybrid powertrain systems where the transmission will be simulated, use the transmission parameters defined in Table 1 of 40 CFR 1036.540 to determine transmission type and gear ratio. Use a fixed transmission efficiency of 0.95. The GEM HIL transmission model uses a transmission parameter file for each test that includes the transmission type, gear ratios, lockup gear, torque limit per gear from Table 1 of 40 CFR 1036.540, and the values from 40 CFR 1036.503(b)(4) and (c).

(i) [Reserved]

(j) Duty cycles to evaluate. Operate the powertrain over each of the duty cycles specified in § 1037.510(a)(2), and for each applicable vehicle configuration from paragraph (h) of this section. Determine cycle-average powertrain fuel maps by testing the powertrain using the procedures in 40 CFR 1036.540(d) with the following exceptions:

(1) Understand “engine” to mean “powertrain”.

(2) If the preceding duty cycle does not end at 0 mi/hr, transition between duty cycles by decelerating at a rate of 2 mi/hr/s at 0% grade until the vehicle reaches zero speed. Shut off the powertrain. Prepare the powertrain and test cell for the next duty-cycle. Start the next duty-cycle within 60 to 180 seconds after shutting off the powertrain. Do not run the powertrain or change its physical state before starting the next duty cycle. If the next duty cycle begins at 0 mi/hr vehicle speed, key on the vehicle and start the duty-cycle after 10 seconds, otherwise key on the vehicle and transition to the next duty cycle by accelerating at a rate of 1 mi/hr/s at 0% grade for vehicle configurations given in Table 2 of 40 CFR 1036.540 or 2 mi/hr/s at 0% grade for vehicle configurations given in Tables 3 and 4 of 40 CFR 1036.540, then stabilize for 10 seconds at the initial duty cycle conditions.

(3) Calculate cycle work using GEM or the speed and torque from the driveline and vehicle models from paragraph (f) of this section to determine the sequence of duty cycles.

(4) Calculate the mass of fuel consumed for idle duty cycles as described in paragraph (n) of this section.

(5) Warm up the powertrain as described in 40 CFR 1036.527(c)(1).

(k) Measuring NOX emissions. Measure NOX emissions for each sampling period in grams. You may perform these measurements using a NOX emission-measurement system that meets the requirements of 40 CFR part 1065, subpart J. If a system malfunction prevents you from measuring NOX emissions during a test under this section but the test otherwise gives valid results, you may consider this a valid test and omit the NOX emission measurements; however, we may require you to repeat the test if we determine that you inappropriately voided the test with respect to NOX emission measurement.

(l) [Reserved]

(m) Measured output speed validation. For each test point, validate the measured output speed with the corresponding reference values. If the range of reference speed is less than 10 percent of the mean reference speed, you need to meet only the standard error of the estimate in Table 1 of this section. You may delete points when the vehicle is stopped. If your speed measurement is not at the location of fnref, correct your measured speed using the constant speed ratio between the two locations. Apply cycle-validation criteria for each separate transient or highway cruise cycle based on the following parameters:

Table 1 of § 1037.550 - Statistical Criteria for Validating Duty Cycles

Parameter a Speed control
Slope, a; 1 0.990 ≤a 1 ≤1.010.
Absolute value of intercept, |a 0| ≤2.0% of maximum ƒnref speed.
Standard error of the estimate, SEE ≤2.0% of maximum ƒnref speed.
Coefficient of determination, r 2 ≥0.990.

a Determine values for specified parameters as described in 40 CFR 1065.514(e) by comparing measured and reference values for ƒnref,dyno.

(n) Fuel consumption at idle. Determine the mass of fuel consumed at idle for the applicable duty cycles described in § 1037.510(a)(2) as follows:

(1) Measure fuel consumption with a fuel flow meter and report the mean idle fuel mass flow rate for each duty cycle as applicable, m

fuelidle.

(2) If you do not measure fuel mass flow rate, calculate the idle fuel mass flow rate for each duty cycle, m

fuelidle, for each set of vehicle settings, as follows:

Where:
MC = molar mass of carbon.
wCmeas = carbon mass fraction of fuel (or mixture of test fuels) as determined in 40 CFR 1065.655(d), except that you may not use the default properties in Table 1 of 40 CFR 1065.655 to determine α, β, and wC for liquid fuels.
n
exh = the mean raw exhaust molar flow rate from which you measured emissions according to 40 CFR 1065.655.
xCcombdry = the mean concentration of carbon from fuel and any injected fluids in the exhaust per mole of dry exhaust.
xH2Oexhdry = the mean concentration of H2O in exhaust per mole of dry exhaust.
m
CO2DEF = the mean CO2 mass emission rate resulting from diesel exhaust fluid decomposition over the duty cycle as determined in 40 CFR 1036.535(b)(7). If your engine does not use diesel exhaust fluid, or if you choose not to perform this correction, set m
CO2DEF equal to 0.
MCO2 = molar mass of carbon dioxide.
Example:
MC = 12.0107 g/mol
wCmeas = 0.867
n
exh = 25.534 mol/s
xCcombdry = 2.805·10−3 mol/mol
xH2Oexhdry = 3.53·10−2 mol/mol
m
CO2DEF = 0.0726 g/s
MCO2 = 44.0095
m
fuelidle = 0.405 g/s = 1458.6 g/hr

(o) Create GEM inputs. Use the results of powertrain testing to determine GEM inputs for the different simulated vehicle configurations as follows:

(1) Correct the measured or calculated fuel masses, mfuel[cycle], and mean idle fuel mass flow rates, m

fuelidle, if applicable, for each test result to a mass-specific net energy content of a reference fuel as described in 40 CFR 1036.535(f), replacing m
fuel with mfuel[cycle] where applicable in Eq. 1036.535-4.

(2) Declare fuel masses, mfuel[cycle], in g/cycle. In addition, declare mean fuel mass flow rate for each applicable idle duty cycle, m

fuelidle. These declared values may not be lower than any corresponding measured values determined in this section. If you use multiple measurement methods as allowed in 40 CFR 1036.540(d), follow 40 CFR 1036.535(g) regarding the use of direct and indirect fuel measurements and the carbon balance error verification. These declared values, which serve as emission standards, collectively represent the powertrain fuel map for certification.

(ii) For testing with torque measurement at the wheel hubs, use Eq. 1037.550-8 setting ka equal to 1.

(iii) For testing with torque measurement at the engine's crankshaft:

Where:
f
nengine = average engine speed when vehicle speed is at or above 0.100 m/s.
v
ref = average simulated vehicle speed at or above 0.100 m/s.
Example:
f
nengine = 1870 r/min = 31.17 r/s
v
ref = 19.06 m/s

(4) Calculate positive work, W[cycle], as the work over the duty cycle at the axle input shaft, wheel hubs, or the engine's crankshaft, as applicable, when vehicle speed is at or above 0.100 m/s.

(5) Calculate engine idle speed, by taking the average engine speed measured during the transient cycle test while the vehicle speed is below 0.100 m/s.

(6) The following table illustrates the GEM data inputs corresponding to the different vehicle configurations for a given duty cycle:

[86 FR 34477, June 29, 2021]

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