Apparatus and method for producing a desired return torque in a vehicle power steering system having a rotational steering position sensor
First Claim
1. Method for producing a desired return torque in a vehicle power steering system having a steering position varying through a total range about a center position, the vehicle power steering system having a steering shaft with an actuator coupled thereto for the provision of return torque and a rotational position sensor providing an output signal varying between a minimum value and a maximum value with consecutive rotations of the steering shaft through a rollover angle, whereby rollover transitions are generated between such consecutive rotations, the total range of the steering position being greater than a single rollover angle so that each output of the rotational position sensor indicates a plurality of potential steering positions separated from each other by integer multiples of the rollover angle, the method comprising:
- upon initiation of vehicle operation, initially choosing an unadjusted steering position from the plurality of potential steering positions corresponding to a sensed initial output of the rotational position sensor;
repeatedly updating the unadjusted steering position in response to output changes of the rotational position sensor, including sensed rollover transitions, so that the unadjusted steering position varies continuously over the total range of the steering position;
starting with a predetermined set of revolution offsets differing by integer multiples of the rollover angle, repeatedly testing the unadjusted steering position as it is updated to determine which of the revolution offsets in combination with the unadjusted steering position provide potential steering positions which are outside the total range of steering position and excluding those revolution offsets so determined;
while at least two revolution offsets remain unexcluded, deriving a first return torque command and providing the first return torque command to the actuator to produce a first return torque;
after only one final revolution offset remains unexcluded, deriving an absolute steering position from the one final revolution offset in combination with the unadjusted steering position, deriving a second return torque command from the derived absolute steering position and providing the second return torque command to the actuator to produce a second return torque.
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Accused Products
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.
134 Citations
19 Claims
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1. Method for producing a desired return torque in a vehicle power steering system having a steering position varying through a total range about a center position, the vehicle power steering system having a steering shaft with an actuator coupled thereto for the provision of return torque and a rotational position sensor providing an output signal varying between a minimum value and a maximum value with consecutive rotations of the steering shaft through a rollover angle, whereby rollover transitions are generated between such consecutive rotations, the total range of the steering position being greater than a single rollover angle so that each output of the rotational position sensor indicates a plurality of potential steering positions separated from each other by integer multiples of the rollover angle, the method comprising:
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upon initiation of vehicle operation, initially choosing an unadjusted steering position from the plurality of potential steering positions corresponding to a sensed initial output of the rotational position sensor; repeatedly updating the unadjusted steering position in response to output changes of the rotational position sensor, including sensed rollover transitions, so that the unadjusted steering position varies continuously over the total range of the steering position; starting with a predetermined set of revolution offsets differing by integer multiples of the rollover angle, repeatedly testing the unadjusted steering position as it is updated to determine which of the revolution offsets in combination with the unadjusted steering position provide potential steering positions which are outside the total range of steering position and excluding those revolution offsets so determined; while at least two revolution offsets remain unexcluded, deriving a first return torque command and providing the first return torque command to the actuator to produce a first return torque; after only one final revolution offset remains unexcluded, deriving an absolute steering position from the one final revolution offset in combination with the unadjusted steering position, deriving a second return torque command from the derived absolute steering position and providing the second return torque command to the actuator to produce a second return torque. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A vehicle power steering system comprising, in combination:
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a rotational steering member controlling the attitudinal direction of a vehicle steering wheel through steering apparatus having a steering position varying through a total range about a center position; an actuator coupled to the rotational steering member for the provision of return torque; a rotational position sensor providing an output signal varying between a minimum value and a maximum value with consecutive rotations of the steering shaft through a rollover angle, whereby rollover transitions are generated between such consecutive rotations, the total range of the steering position being greater than a single rollover angle so that each output of the rotational position sensor indicates a plurality of potential steering positions separated from each other by integer multiples of the rollover angle; first means effective upon initiation of vehicle operation for initially choosing an unadjusted steering position from the plurality of absolute steering positions corresponding to a sensed initial output of the rotational position sensor; second means for repeatedly updating the unadjusted steering position in response to output changes of the rotational position sensor, including sensed rollover transitions; third means for repeatedly testing the unadjusted steering position as it is updated, starting with a predetermined set of revolution offsets, to determine which of the revolution offsets in combination with the updated unadjusted steering position provide potential steering positions which are outside the total range of steering position and excluding those revolution offsets so determined; fourth means effective while at least two revolution offsets remain unexcluded for deriving a first return torque command and providing the first return torque command to the actuator to produce a predetermined first return torque; and fifth means effective after only one final revolution offset remains unexcluded for deriving an absolute steering position from the one final revolution offset in combination with the updated unadjusted steering position, deriving a second return torque command from the derived absolute steering position and providing the second return torque command to the actuator to produce a second return torque. - View Dependent Claims (15, 16, 17, 18, 19)
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Specification