Four-wheel steering system for vehicle

Motor vehicles – Steering gear – Each wheel steerable

Patent

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Details

180414, 180433, 91448, B62D 512, B62D 714

Patent

active

057183040

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

(1) Field of the Invention
The present invention relates to a four-wheel steering system and, more particularly, to a four-wheel steering system which can enhance cornering safety by optimally adjusting a rear wheel steering angle in response to the vehicle speed, the front wheel steering angle and the lateral acceleration.
Particularly, the present invention relates to an independent steering system which can independently steer each rear wheel.
(2) Description of Related Art
Generally, a conventional steering system for a vehicle comprises a handling mechanism consisting of a steering wheel, a steering shaft and a column, a gear mechanism consisting of a steering gear mounted on a frame and a link, and a link mechanism consisting of a pitman arm, a drag link and a tie rod.
Such steering systems are designed to adjust the directional orientation of front wheels by gearing the tie rod to the left or right in response to the rotating direction of the gear installed at the end of the steering shaft. In recent years, a power steering system which can improve the handling safety has become popular.
However, since the steering systems are designed such that only the front wheels are steered, a problem that a car body is inclined suddenly and unstable during turns while at high speed occurs. Accordingly, in recent years, a four-wheel steering system which can steer the front wheels and the rear wheels simultaneously has been developed.
Examples of the four-wheel steering system are disclosed in U.S. Pat. Nos. 4,778,023, 4,781,262, 4,821,830, 4,888,613 and 5,220,974.
However, most of the prior four-wheel steering systems are designed to adjust the rear wheels by only one rear wheel actuator.
This can provide stability during simple cornering but cannot obtain a speedy response of the wheel on the inner side of the turn because of the inertia of the system during a quick lane change or a slalom running. As a result, over steering such that the rear end of the vehicle body is thrown to the outer side of the turn and the marginal performance and stability of the vehicle are deteriorated.


SUMMARY OF THE INVENTION

The present invention is made in an effort to solve above described problems.
It is an object of the present invention to provide a four-wheel steering system which can enhance a cornering safety by optimally adjusting a rear wheel steering angle in response to the vehicle speed, the front wheel steering angle and the lateral acceleration.
It is another object oft he invention to provide an independent steering system which can independently steer each rear wheel.
To achieve the objects, the present invention provides a four-wheel steering system comprising: a steering wheel, front and rear pumps driven by an engine for generating hydraulic pressure, a front direction control valve having ports which close and open in accordance with a rotating direction of the steering wheel, a front actuator having left and right chambers to which the hydraulic pressure is supplied through a fluid passage selected by the front direction control valve, an electronic control unit for controlling a steering of the rear wheels in response to signals transmitted from a vehicle speed sensor, a steering angle sensor and a steering amount feedback sensor, a first solenoid valve for returning the hydraulic pressure generated from the rear pump to a reservoir tank or supplying the hydraulic pressure in response to a signal transmitted from the electronic control unit as an, actuating pressure, a second solenoid valve for returning the hydraulic pressure generated from the rear pump to the reservoir tank or supplying the hydraulic pressure in response to the signal transmitted from the electronic control unit, a first rear direction control valve for changing a flowing direction of the hydraulic pressure supplied from the first solenoid valve in response to the signals from the electronic control unit, a second rear direction control valve for changing a flowing direction of the hydraulic pressure supp

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