Power-assisted steering system and method with compensation...

Motor vehicles – Steering gear – With electric power assist

Reexamination Certificate

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Details

C701S042000

Reexamination Certificate

active

06250421

ABSTRACT:

TECHNICAL FIELD
The present invention is directed to power-assisted steering systems, and is specifically directed to systems that attenuate an undesirable torque or pulling force at a manually operated steering member.
BACKGROUND OF THE INVENTION
Power-assisted steering systems are known in the art. One example type of a powered-assisted steering system is a system that includes an electrical power assist motor and that is commonly referred to as an electric assist steering system. Typically, an electrical assist steering system that utilizes a rack and pinion gear set provides assistance force by using the electric motor to either (i) apply rotary force to a steering input shaft connected to the pinion gear, or (ii) apply linear force to a steering member that has the rack teeth thereon. The electric motor in such a system is controlled in response to sensed force (e.g., torque) applied to a manually operated steering member (e.g., a vehicle steering wheel) by an operator, and possibly other sensed parameters (e.g., vehicle speed).
The torque applied by the vehicle operator to the steering wheel is sensed via a torque sensor. Torque sensors for power-assisted steering systems are known in the art. A typical torque sensor for a power-assisted steering system is operatively connected between a steering input shaft and an output shaft. The input shaft is connected to the steering wheel and the output shaft is connected to the pinion of the rack and pinion steering gear set. The torque sensor includes a torsion bar connecting the input shaft to the output shaft. The torque sensor further includes a rotary position sensor adapted to monitor the amount of relative rotation between the input shaft and the output shaft that occurs as torque is applied to the steering wheel. The amount of relative rotation is functionally related to the strength of the torsion and the amount of steering torque applied to the steering wheel.
Due to the connection between the steering wheel and the rack and pinion steering gear set that is provided by the input shaft, the torsion bar, and the output shaft, torque from the rack and pinion steering gear set may also be transmitted to the steering wheel. Typically, a certain amount of torque (e.g., a resisting force) is desirable to provide the vehicle operator a certain amount of steering feel. However, torque applied to the steering wheel as a result of some types of vehicle events may be undesirable.
SUMMARY OF THE INVENTION
In accordance with one aspect, the present invention provides a power-assisted steering system for a vehicle that has steerable front wheels that are inflated. The system includes a manually operated steering member for steering input from a vehicle operator. Means relays forces between the steering member and the steerable front wheels. Means provides an assist steer force to steer the steerable wheels in response to a force applied to the steering member. Means monitors an inflation pressure of one of the front wheels. Means provides a compensating steer force to the steerable wheels, responsive to the monitored inflation pressure, which attenuates force transmitted to the steering member due to front wheel inflation condition.
In accordance with another aspect, the present invention provides a method of controlling a power-assisted steering system for a vehicle that has steerable front wheels that are inflated. Forces are relayed between a manually operated steering member and steerable front wheels. An assist steer force to steer the steerable wheels is provided in response to a force applied to the steering member. An inflation pressure of one of the front wheels is monitored. A compensating steer force is provided to the steerable wheels, responsive to the monitored inflation pressure that attenuates force transmitted to the steering member due to front wheel inflation condition.


REFERENCES:
patent: 3806869 (1974-04-01), Davis, Jr.
patent: 5116254 (1992-05-01), Sano et al.
patent: 5238079 (1993-08-01), Gorim
patent: 5481459 (1996-01-01), Bungeler
patent: 5752208 (1998-05-01), Lerner
patent: 5925083 (1999-07-01), Ackermann

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