Motor vehicles – Steering gear – No mechanical connection between steering shaft and steering...
Reexamination Certificate
1999-02-01
2001-01-23
Mai, Lanna (Department: 3611)
Motor vehicles
Steering gear
No mechanical connection between steering shaft and steering...
Reexamination Certificate
active
06176341
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to a vehicle steering system and, more particularly, to a vehicle steer-by-wire steering system providing road wheel force feedback to the hand-operated steering wheel.
Land vehicles are commonly equipped with a set of road wheels that rotate to allow easy movement of the vehicle. Automotive vehicles are conventionally equipped with a pair of front wheels that are controllably steerable to enable the vehicle to turn left and right as it maneuvers on land. In the past, vehicle steering systems commonly employed a direct mechanical connection between the hand-operated steering wheel and the steerable wheels, which typically included the front two wheels, of an automotive vehicle. As an operator rotated the hand-operated steering wheel, a mechanical linkage through the vehicle's tie-rods actuated the steerable road wheels in either the left or right direction, generally with the assistance of a power-assisted steering motor.
Recently, steer-by-wire steering systems have been introduced into automotive vehicles to provide easy-to-steer road wheel control. Included in a typical steer-by-wire steering system is a steering wheel subassembly for monitoring the angular position of the steering wheel, wheel actuation controllers, and corresponding electric motor actuators for controlling actuation of the individual wheels. The steer-by-wire steering system turns the road wheels left and right with the motor actuators which in turn are controlled by controllers in response to tracking the sensed position of the steering wheel. In contrast to prior steering systems, the steer-by-wire steering system does not employ a mechanical linkage between the steering wheel and the individual steerable wheels. For safety and reliability, the steer-by-wire steering system generally employs redundant steering wheel sensors, redundant controllers, and redundant motor actuators.
In the conventional steer-by-wire vehicle steering system, torque sensors are generally employed to sense forces which deflect the steerable road wheels, such as when a vehicle road wheel forcibly contacts a roadside curb or other opposing object. The torque sensor signals are read by a local controller and sent to a hand wheel controller via a bus. The hand wheel controller uses the torque signals to actuate the hand wheel motor to provide rotational resistance such that the operator of the vehicle may feel resistance to turning the road wheel. However, the use of torque sensors adds additional components to the steering system, which increases the cost, as well as requires low noise signal conditioning circuitry and hardware/software compensation to correct for non-linearity of the torque sensors. Further, torque sensors are generally susceptible to error due to drift over temperature and often require calibration.
Accordingly, it is therefore one object of the present invention to provide for an efficient steering system for a vehicle which provides steering resistance to the hand-operated steering wheel in response to resistance of the road wheels. It is a further object of the present invention to provide for a vehicle steering system and method for steering the road wheels of a vehicle equipped with a steer-by-wire steering system. It is yet another object of the present invention to provide for a vehicle steer-by-wire steering system and method that does not require additional torque sensors and other components associated therewith to provide feedback to the hand-operated steering wheel.
SUMMARY OF THE INVENTION
The present invention provides for a steer-by-wire steering system and method for steering a vehicle by controlling steering of one or more vehicle road wheels and providing force feedback to the hand-operated steering wheel so that the vehicle operator may feel steering force resistance. The vehicle steering system includes a position sensor for sensing angular position of a road wheel, a hand-operated steering wheel for controlling directivity of the road wheel, a steering wheel sensor for sensing position of the steering wheel, a steering wheel actuator for actuating the hand-operated steering wheel, and a controller for receiving the sensed steering wheel position and the sensed road wheel position and calculating control signals, preferably including a road wheel control signal and a steering wheel control signal, as a function of the difference between the sensed road wheel position and the steering wheel position. The controller commands the road wheel actuator to provide controlled steering of the road wheel in response to the road wheel control signal. The controller further commands the steering wheel actuator to provide feedback force actuation to the hand-operated steering wheel in response to the steering wheel control signal. The road wheel control signal and steering wheel control signals are preferably scaled to compensate for difference in gear ratio between the steering wheel and the road wheel. In addition, the road wheel control signal and steering wheel control signal may each have a gain set so that the road wheel control signal commands greater force actuation to the road wheel than the feedback force applied to the steering wheel.
The method of steering a vehicle having a steer-by-wire steering system according to the present invention includes the steps of sensing position of a hand-operated steering wheel and sensing position of a road wheel. The method further includes calculating a control signal as a function of the difference between the sensed road wheel position and the sensed steering wheel position. The control signal preferably includes a road wheel control signal and a steering wheel control signal which may be scaled to compensated for gear ratio differences. The method further includes the steps of commanding actuation of the road wheel in response to the road wheel control signal to provide controlled steering of the road wheel, and commanding actuation of the hand-operated steering wheel in response to the steering wheel control signal to provide force feedback to the hand-operated steering wheel.
The present invention preferably implements two position control loops, one for the road wheel and one for the hand wheel. The position feedback from the steering wheel becomes a position command input for the road wheel control loop and the position feedback from the road wheel becomes a position command input for the steering wheel control loop. A road wheel error signal is calculated as the difference between the road wheel command input (steering wheel position feedback) and the road wheel position. Actuation of the road wheel is commanded in response to the road wheel error signal to provide controlled steering of the road wheel. A steering wheel error signal is calculated as the difference between the steering wheel position command (road wheel position feedback) and the steering wheel position. The hand-operated steering wheel is actuated in response to the steering wheel error signal to provide force feedback to the hand-operated steering wheel.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.
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patent: 5908457 (1999-06-01), Higashira
patent: 6012540 (2000-01-01), Bohner et al.
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patent: 6059068 (2000-05-01), Kato et al.
patent: 6069505 (2000-05-01), Babanezhad
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Delphi Technologies Inc.
Funke Jimmy L.
Mai Lanna
McKinley Kevin
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