Patent ID: 7264080

Claim:
A method for controlling valve stiffness in a power steering system for a vehicle comprising the steps of: engaging a pinion and a spool shaft with respect to one another for turning at least two wheels of a vehicle in response to rotation of a steering wheel from an on-center orientation; variably assisting movement of the pinion with a hydraulic power steering device having a valve movable between a closed configuration and an open configuration; moving the valve from the open configuration to the closed configuration in response to rotation of the spool shaft relative to the pinion from an on-center orientation to assist the pinion in rotation for turning the at least two wheels; first disposing a torsion rod having a first stiffness between the pinion and spool shaft to resist rotation of the spool shaft relative to the pinion from the on-center orientation and resist movement of the valve from the open configuration to the closed configuration; second disposing a magnetic coupling having a variable second stiffness in parallel with the torsion rod to resist rotation of the spool shaft relative to the pinion from the on-center orientation and resist movement of the valve from the open configuration to the closed configuration wherein the first stiffness and the variable second stiffness cooperate to define an overall valve stiffness; varying the variable second stiffness generated by the magnetic coupling with an electric coil to vary the overall valve stiffness; and maximizing the variable second stiffness generated by the magnetic coupling when the spool shaft and the pinion are on-center with respect to one another.