Characterizing Regenerative Coast-Down Deceleration in Tesla Model 3, S, and X 2020-01-0883

Tesla Motors vehicles utilize a regenerative braking system to increase mileage per charge. The system is designed to convert the vehicles’ kinetic energy during coast-down into electrical 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. The goals of this study were to analyze and quantify the regenerative braking behavior of the Tesla Model 3, S, and X, as well as the timing and activation criteria for the brake lights during the coast-down state. A total of seven Tesla vehicles (two Model 3, three Model S and two Model X) were tested in both Standard and Low regenerative braking modes. All three Tesla models exhibited similar three-phase behavior: an initial ramp-up phase, a steady-state phase, and a non-linear ramp-down phase at low road speeds. Phase 1 was less than one second in length. Phase 2 average steady-state decelerations observed were -0.19 g in Standard mode and -0.10 g in Low mode. At high speeds, test vehicles usually exhibited a low-jerk gradual ramp-up phase between the initial ramp-up and steady-state. The end of Phase 2 occurred when the speed of the vehicle dropped to 10-14 mph. All vehicles tested exhibited a delay in brake light activation relative to accelerator pedal lift-off and the resultant onset of longitudinal deceleration in Standard mode; this delay averaged 0.55 seconds for the Model S, 0.59 seconds for the Model X, and 0.35 seconds for the Model 3. The results of this study will provide insight for accident reconstructionists investigating crashes involving Tesla vehicles engaged in regenerative coast-down braking.