1. Field of the Invention
The present invention relates to a rear wheel steering device for a vehicle with a suspension member having a leaf spring.
2. Description of Related Art
Recently, a four wheel steering system or a device for steering rear wheels in accordance with front wheel steering has been recommended in order to improve an operation stability while driving a vehicle at high speeds.
However, in a conventional four wheel steering device, there are several problems for a vehicle, particularly for a truck in which rear wheels are supported by both end portions of a rear axle housing and the rear axle housing is held by a chassis through a leaf spring. For this type of vehicle, the rear axle housing of which both end portions are connected to the chassis through the leaf spring has to be revolved itself around a central point positioned on a center line of the chassis along a longitudinal direction when the vehicle is steered.
An example of rotating the rear axle housing a round the center point when the rear wheels are steered is described in Japanese Patent Laid Open Publication No. 63-212109 (1988) where a structure in which a leaf spring is movable along a longitudinal direction of the chassis with respect to a laminated support bracket for supporting the leaf spring against the chassis. Under the structure, a large and heavy leaf spring has to be moved along the longitudinal direction while rear wheels are steered so that a size of a hydraulic cylinder for actuating a steering operation has to become larger and related devices such as a hydraulic control valve and a hydraulic power source have to become larger. Such a condition makes it impossible to provide an economical system.
Japanese Patent Laid Open Publication No. 62-194976 (1987) describes a steering system for steering a rear axle housing directly. Under the structure, a rear axle housing frictionally slides against a leaf spring so that a sliding surface is remarkably abraded. This abrasion is a serious problem in view of a durability of the rear wheel steering device.