Active Damping Wheel-Torque Control System to Reduce Driveline Oscillations in a Power-Split Hybrid Electric Vehicle

Power-split hybrid electric vehicles (HEVs) provide a great opportunity to improve fuel economy and emissions. This power-split hybrid system has inherent low damping in driveline since it uses planetary gear sets to directly connect the engine, the generator, and the motor to the driveline for improved vehicle efficiency, thus lacking a clutch or a torque converter that provides the conventional vehicles with driveline damping. When they are subjected to acceleration or disturbances, the low damping in the driveline may cause torsional vibrations. Since the power-split control system is closed loop in nature, these torsional vibrations can result in sustained driveline oscillations. These oscillations can be very objectionable to the driver as they affect the vehicle´s drivability. In this paper, we present the design of an active damping wheel-torque control system to suppress such oscillations to improve the drivability of a power-split HEV. To the best of our knowledge, this is the first reported use of an active damping wheel-torque control system to suppress the driveline oscillations in a power-split HEV. Simulations in a power-split HEV environment and experimental tests in the field using a Ford Escape Hybrid demonstrate the effectiveness of the proposed system in suppressing the oscillations. The driveline disturbances are suppressed to below the perceptible level of wheel torque (<100 Nmiddotm). Additional simulations are performed to validate the system to other key factors that can affect its performance. Even with increased motor/generator disturbances by a factor of 2 and change in driveline stiffness of plusmn50%, the proposed control system can still effectively suppress driveline oscillations and thereby improve drivability.