Reducing Disturbances Caused by Reductions in Regenerative Brake Torque

This paper presents a method to reduce the number of occurrences of vehicle deceleration disturbances due to the reduction of regenerative braking in the presence of wheel slip. Usually, regenerative braking is disabled when wheel slip is detected in order to allow the ABS system to efficiently cycle brake pressure. When this happens, the vehicle will momentarily lose deceleration due to the reduction in both regenerative brake torque and friction brake pressure, until friction brake pressure is reapplied. Some ABS activations can be defined as nuisance events, in which full ABS control is not necessary and is exited rapidly; for example, a vehicle driving through a pothole. In these cases it is desirable to continue regenerative braking in order to keep vehicle deceleration as smooth as possible. This can be done by analyzing the magnitudes of the wheel slips in various combinations, and making intelligent decisions as to which events require the cancellation of regenerative braking, and which do not. This has the added benefit of improving real-world fuel economy.