EPA Provides Testing Guidance for Electric Vehicles

EPA conducts an integrated motor vehicle and engine emission compliance program. Vehicles are evaluated as prototypes prior to production, and if their design meets applicable criteria, they are licensed into commerce. Similarly, California Air Resources Board approval is required for introducing vehicles into commerce in the state of California. Following that introduction, EPA may still conduct assembly line testing of new vehicles as well as in-use testing of vehicles. The light-duty in-use testing program includes a surveillance program with the possibility of confirmatory testing designed to check the vehicle’s performance against that set forth in the manufacturer’s application for certification. Significant discrepancies revealed in testing, including the failure to use good engineering judgment in establishing the range for BEVs, risk an enforcement action by EPA. 

For its confirmatory testing, EPA requests that light-duty BEV manufacturers submit vehicle-related instructions at least two weeks before testing to ensure sufficient time to prepare for testing. These instructions should include clear directions on how to prepare the vehicle for the confirmatory testing as well as any special directions unique to the vehicle. The manufacturers should include in the instructions how to place the vehicle in “dyno mode,” items that may interfere with the testing and cannot be turned off by dyno mode, information regarding current and voltage measurement, and important details for multicycle testing (MCT) (which uses a single full depletion test to determine range and AC energy consumption for multiple drive cycle types), such as expected time and distances achieved on the two constant speed portions of the test. EPA also provides details relating to the desired state of the vehicle’s battery and its safety-related settings when providing the vehicle for testing. Finally, EPA makes it clear, if there was any doubt, that its regulations take precedence over relevant industry standards. Some of these key areas are discussed in more detail below. 

Requirements for Current and Voltage Measurement

For current and voltage measurement, manufacturers must include the direction of the flow of current, the number of current clamps required, and the preferred method to install them. If the vehicle requires more than four clamps, manufacturers should inform the certification engineer in advance of testing and provide detailed clamping instructions. Manufacturers should also inform the certification engineer if a hoist or special tools are required to install current clamps and clearly mark and provide such tools for testing. EPA prefers Pomona #6383-02, or sheathed banana plug, connections on voltage taps, so it asks manufacturers to inform the certification engineer if these taps cannot be installed for technical reasons. EPA advises that vehicles that do not provide voltage taps and require controller-area network data acquisition to measure voltage may experience testing delays of up to a week. 

Battery State and Safety-Related Settings

Vehicles should be delivered to the agency with a battery state of charge set for completing a road-load dynamometer derivation to determine set coefficients. There may be delays or rescheduling if the battery needs charging or being “driven down.” Vehicles should be able to be tested safely on a chassis dynamometer, which usually means having a dyno mode. Dyno mode should lock out automatic ride-height adjusting as well as allow for running repeatable coastdowns during the road-load derivation. Dyno mode should also shut off any systems that are applicable to the real-world driving but can interfere with a chassis dynamometer test, disable the headlights or daytime running lights, and allow the use of cruise control on constant speed portions of the MCT. If necessary, the manufacturer should disable the headlights or the daytime running lights before providing the vehicle to EPA for confirmatory testing.

Charging of Vehicles at NVFEL

EPA does not charge the vehicles in the chassis dynamometer cell. The agency takes breaks during the testing as provided in the Society of Automotive Engineers’ standard SAE-J1634. During the constant-speed cycle of the MCT, these breaks nominally occur every 60 minutes, and EPA does not consider energy drawn from the battery while the vehicle is turned off to be usable battery energy included in the MPGe and range calculations. EPA also clarifies that it uses human drivers to perform the tests. Therefore, manufacturers should provide best practices to avoid unnecessary battery draw.

EPA will drive the vehicle until it cannot keep up with the trace, so the agency must be able to place the vehicle in neutral once the battery is drained after the MCT for charging outside of its chassis dynamometer cell. EPA uses a Level 2 240V electric vehicle supply equipment (EVSE) to charge the vehicle after the testing is complete, and it provides NEMA 6-50 and NEMA 14-50 outlets in case a manufacturer wishes to supply its own vehicle EVSE. Finally, EPA expects the 12V batteries on the vehicle to be kept at proper charge by its onboard charging and battery management system — it will not put trickle charging systems on the vehicle unless that is how the vehicle is designed to operate for the end user.

Regulations Take Precedence

EPA states that although the controlling regulations reference the SAE-J1634 standard, the regulations take precedence in case the standard conflicts with them. EPA lists four examples of potential conflicts, including a reminder that EPA will not adjust MPGe and range for BEVs testing with over 6,200 miles, per 40 CFR § 600.006(g)(5). EPA shows a degree of flexibility by allowing processes from various versions of SAE-J1634 as long as they do not conflict with the regulations and a prior approval is sought from the agency under 40 CFR § 600.116-12(a)(5).

EPA’s guidance may suggest to BEV manufacturers proposed practices to ensure timely and smooth confirmatory testing and important reminders regarding the agency’s testing requirements. This is especially important for new vehicles with extended range (i.e., more than 200 miles per charge). Failure to follow EPA’s guidance may not only result in delays but may also lead to BEVs underperforming in areas of MPGe and range.