A New Control Strategy to Reduce Steering Torque Without Perceptible Vibration for Vehicles Equipped With Electric Power Steering

This paper proposes a new electric power steering control strategy, which significantly reduces the effort needed to change the steering direction of stationary vehicles. Previous attempts to reduce undesirable steering vibration have failed to reduce the steering torque because high-assist gains tend to produce oscillation or increase noise sensitivity. Herein, to eliminate this vibration, a new control strategy was developed based on pinion angular velocity control using a newly developed observer based on a simplified steering model. Tests yielded excellent estimations of the pinion angular velocity, and this made it possible to eliminate vibration at all steering wheel rotation speeds. Experiments with a test vehicle confirmed significant steering torque reduction, over a wide range of steering wheel speeds, without vibration transmission to the driver. The proposed control strategy allowed use of an assist gain more than three times higher than is conventional. Additionally, the proposed control strategy does not require supplemental sensors.