Electric power steering control with torque ripple and road disturbance damper

Abstract

An electric power steering control for a motor vehicle reduces motor torque ripple and road generated disturbances communicated to the vehicle handwheel while promoting system stability. In deriving an output command torque signal to the EPS motor, the control (1) derives an electric motor speed signal, (2) differentiates the electric motor speed signal, (3) stores a schedule of gain as an increasing function of electric motor torque, (4) modifies the differentiated estimated electric motor speed signal in response to the gain to provide a damping correction value and (5) derives the output command signal responsive to the damping correction. In a preferred embodiment, the control (1) stores power assist torque data as a function of handwheel torque and vehicle velocity, (2) provides a vehicle velocity signal, (3) provides a handwheel torque signal, (4) modifies the handwheel torque signal in response to the damping correction value, (5) derives a power assist torque value from the stored power assist torque data in response to the vehicle velocity signal and the modified handwheel torque signal and (6) derives the output command signal from the power assist torque value. The control may use an electric motor voltage signal as an estimate of electric motor speed and, for high torque loads, may use the pulse on-time parameter in a pulse width modulated, current switching control to represent the voltage of the controlled electric motor, and therefore the estimate of electric motor speed, so that no additional sensor is needed. The control may use separate stored relationships between the pulse width on-time and electric motor voltage for different commutation modes of the pulse width modulated, current switching control.

Dependencies are inferred from the claim text.