Trw Limited

Zf Automotive UK Limited

Nikhil Koppattil Prahlad

Xiao-Dong Sun

Philip March

Sankar Cherangara

A method of operating an electric power assisted steering system of the kind in which an electric motor applies an assistance torque to a part of the steering system as a function of an assistance torque signal, the assistance torque reducing the force required by the driver to turn a steering wheel, comprises during normal operation generating an assistance torque signal that is dependent on the torque applied by the driver, and during a fault operation in which the torque applied by the driver is not reliably known to the system generating an assistance torque signal that is derived from a first term that has a value that varies as a function of the angular position of the steering relative to a changeable datum, the angular position of the changeable datum being updated in the event that the direction of rotation of the steering changes.

Electrical power assisted steering system

An electric power assisted steering system comprises a first part that in use determines the sign of a first signal indicative of the position of a part of the steering, and a second part that in use determines the sign of a second signal indicative of the velocity of a part of the steering. A processing unit that in use determines whether the steering wheel is moving away from a centre position or returning to the centre position from the determined signs of the two signals, and sets a value of a torque damping component using different tunes for when the steering wheel is moving away from the centre and when term and when the steering wheel is returning to the centre. The processing unit may blend the two tunes when it detects a change in the direction of steering corresponding to a return to centre following movement away from centre or movement away from centre following a return to centre.

Power steering systems

A motor drive circuit comprises a motor having a plurality of phases, a switching circuit comprising a plurality of electrical switches, a motor current controller that generates voltage demand signals to be passed to a drive circuit for the switches that in turn generate pulse width modulated switching signals for the switching circuit that cause the switches to selectively connect the phases to a power supply so as to cause current to flow through the phases of the motor, and a motor torque controller that produces a demand signal that is fed to an input of the current controller, the motor current controller responding to an error signal that is at least partially dependent on the value of the demand signal. The torque controller in use updates the demand signal at a first sample rate. The motor drive circuit further comprises a downsampling circuit that in use modifies the demand signal under certain operating conditions so that the demand signal is only updated at a second sample rate that is lower than the first rate.

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Solihull, United Kingdom

Nikhil Koppattil Prahlad