Trw Limited

Philip Browne

Adrian Szabo

Stephen Harvey

Andrew Williams

A current measurement circuit suitable for measuring the flow of current along a path in an electrical circuit such as a part of an electric power assisted steering system comprises a current measurement resistor that is located in series in the electrical path through which a current to be measured may flow, a first measurement sub-circuit that measures the voltage dropped across at least a part of the resistor and produces a first output signal, and a second measurement sub-circuit that measures the voltage dropped across at least a part of the resistor and produces a second output signal, and in which the electrical connections of the two sub-circuits to the resistor are independent of each other.

Current measurement circuit

A method and apparatus diagnoses a correct operation of a phase or star point isolation relay in an electric power steering system of the kind including a motor drive circuit and at least one phase isolation relay which connects a part of the drive circuit to a phase of the motor. The relay is opened during shutdown to isolate the motor phase from the part of the drive circuit and is normally closed during operation of the motor to connect the phase to the part of the drive circuit. The method includes the steps of: closing the relay; demanding a current through the motor phase associated with the relay that is equal to a predetermined value; measuring at least one characteristic of the phase current in that phase after a predetermined period of time has elapsed, the elapsed time being less than a time needed for the phase current to reach the demanded current value; comparing the measured characteristic of the phase current with a reference characteristic of the phase current; and, in the event that the measured characteristic does not correspond with the reference characteristic, opening the relay and subsequently repeating the steps.

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Bromsgrove, United Kingdom

Philip Browne