Electronic Control of Brake and Accelerator Pedals for Precise Efficiency Testing of Electrified Vehicles 2020-01-1282

Efficiency testing of hybrid-electric vehicles is challenging, because small run-to-run differences in pedal application can change when the engine fires or the when the friction brakes supplement regenerative braking, dramatically affecting fuel use or energy regeneration. Electronic accelerator control has existed for years, thanks to the popularity of throttle-by-wire (TBW). Electronic braking control is less mature, since most vehicles don’t use brake-by-wire (BBW). Computer braking control on a chassis dynamometer typically uses a mechanical actuator (which may suffer backlash or misalignment) or braking the dynamometer rather than the vehicle (which doesn’t yield regeneration). The growth of electrification and autonomy provides the means to implement electronic brake control. Electrified vehicles use BBW to control the split between friction and regenerative braking. Automated features, e.g. adaptive cruise control, require BBW to actuate the brakes without pedal input. We present a system for computer control of brake and accelerator inputs on a TBW- and BBW-equipped vehicle. The system injects analog signals into the vehicle’s wiring harness, bypassing the pedals and obviating mechanical actuation and brake-by-dyno. The system combines feedforward control based on recorded human pedal application with feedback control based on human-driven speed. This combination produces repeatable driving, enabling precise measurement of the impact (e.g. fuel or battery use) of small changes to the powertrain (e.g. engine calibration or lubricant) or test cycle (e.g. speed or grade). The system’s J2951-defined energy-efficiency rating and absolute speed-change rating were more consistent than a human’s by factors of 6.63 and 4.10, respectively. The effect of braking intensity on braking regeneration is quantified using the system.