Transient Regenerative Braking in BEVs: Telemetry Analysis for Driver Controllability Evaluation.

Human perception of discomfort and controllability during transient longitudinal motion in vehicles is still not well understood. This thesis develops a methodology to evaluate these mechanisms from the driver’s perspective, following a Human Centric Approach with a focus on Regenerative Brake System (RBS). Regenerative braking in Battery Electric Vehicles (BEVs) is a key technology that improves energy efficiency: recovers kinetic energy during deceleration and converts it into electrical energy, which is then stored in the vehicle’s battery. Proper calibration can improve driver comfort and improve accelerator pedal control, thus optimizing energy recovery; this is demonstrated by reducing the reliance on the brake. From a driver point of view, the regenerative brake can be characterized by two main variables: • Delay [s], time it takes for the regenerative braking system to activate after the driver lifts off the accelerator; • Jerk [m/s3], slope of transient deceleration generated. Nine different transient regenerative braking configurations (3×3 combinations of delay and jerk) were selected based on typical values observed in commercial BEVs. A series of tip-out tests was conducted using an instrumented dummy vehicle to validate the implementation of these configurations through the calibration process. A driving experiment using the Chase Car Method (CCM) was conducted with 21 participants. Each driver followed a lead vehicle’s velocity profile while minimizing use of the brake pedal. Every participant tested three different configurations. A controllability study was conducted by analyzing telemetry data using a Generalized Linear Mixed Model (GLMM), which relates the number of brake presses (response) to main setup parameters and kinematic variables (explanatory variables), while accounting for differences in individual driving styles as a random effect. The analysis showed that a one-unit increase in jerk reduces the expected number of brake presses by approx 17%, whereas a one-unit increase in delay increases it by approx 15%. Finally, the inverse link function of the GLMM, together with additional analyses on pedal usage, was employed to define a region of acceptable vehicle configurations.