Characterizing Regenerative Coast-Down Deceleration in Tesla Model 3, S and X

Tesla Motors utilizes a regenerative braking system to increase mileage per charge. The system is designed to convert the vehicles’ kinetic energy during coast down into potential energy by using rotational wheel motion to charge the batteries, resulting in moderate deceleration. During this coast down, the system will activate the brake lights to notify following vehicles of deceleration. In October 2018 Tesla Motors pushed software update 2018.42v9 which increased the regenerative braking force of the Model 3. Previous studies have tabulated regenerative braking performance for Model 3’s but have not addressed recent software changes nor brake light behavior related to regenerative braking. The goal of this paper is to quantify the regenerative braking behavior of Tesla Model 3, S, and X, as well as the timing and activation criteria for the brake lights under a regen/coast-down state. Various Model 3, S, and X of different trim levels (differing by battery size and number of driven wheels) were studied by accelerating to various speeds then coasting down while measuring deceleration rates, brake pedal position, accelerator pedal position, and brake light activation timing. Preliminary results show that both Model 3 and S have very similar three-phase braking curves; an initial ramp up to a constant deceleration and gradually decreasing deceleration after a specific speed is reached. For Model S, the slope of the first phase (increasing deceleration) and the slope of the third phase (decreasing deceleration) do not vary with initial velocity. The driver may select one of two levels of regenerative braking, standard or low. Peak deceleration can be as high as 0.28g on the standard and 0.17g on low. Brake light activation delay for Model 3 ranges from 0.35 to 0.60 sec after releasing the accelerator, and the brake lights will de-activate at speeds of 7.83 mph to 8.19 mph. Likewise, the brake light activation delay on the Model S ranges from 0.43s to 0.61s, and the lights de-activate at speeds of 5.71 mph to 5.89 mph The results of this paper will help provide insight into accident reconstruction of scenarios involving Tesla vehicles undergoing regenerative braking.