Importance

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Abstract

A vehicle power steering system has a steering shaft with a rotational position sensor providing signal rollover so that each sensor output indicates a plurality of potential absolute steering positions separated from each other by multiples of a rollover angle. Upon each initiation of vehicle operation, the system selects, as an unadjusted steering position, one of the plurality of absolute steering positions corresponding to an initial sensor output; and the system repeatedly updates the unadjusted steering position in response to sensor output changes, including sensed rollover events. The system repeatedly tests a set of revolution offsets with the updated unadjusted steering position and excludes any which indicate an out-of-range absolute steering position. The final remaining revolution offset is latched as the correct value. Preferably, a temporary value of revolution offset used with the unadjusted position during the testing provides a return or centering torque of zero; and, once the final value is latched, the temporary value is walked incrementally toward the final value, when the return torque value is in the correct centering direction, to avoid a sudden increase in return torque or a return torque in the wrong direction. The walk ends when (1) the temporary value of revolution offset reaches the final value or (2) the true value of steering position, derived from the final value of revolution offset and the unadjusted position, reaches center, whichever occurs first. Thereafter, the final value of revolution offset is used with the updated unadjusted value to determine the absolute value, and thus return torque.

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First Claim