1. Field of the Invention
This invention relates to a four-wheel steering apparatus of a vehicle, that is, an apparatus for steering also the rear wheels in conformity with the steering of the front wheels by the steering wheel.
2. Description of the Prior Art
Heretofore, it has usually been the case with the steering of a four-wheel vehicle that only the front wheels are steered by the steering wheel. However, steering only the front wheels has given rise to problems in respect of manoeuvrability and dirigibility, including the problem that lateral slippage occurs to the rear wheels depending on the running condition and the turning radius is limited so that small turns cannot be made. In view of this, four-wheel steering apparatuses for steering also the rear wheels with the front wheels have recently be studied and proposed.
That is, in a four-wheel steering apparatus, if the rear wheels are steered in the same direction as the direction of steering of the front wheels during running at a relatively high speed, a lateral force is applied to the front and rear wheels at a time and therefore, the posture of the vehicle can be substantially kept on the tangential line of the turning circle without any phase delay from the steering of the steering wheel and, for example, the lane change during high speed running can be accomplished smoothly. Also, if the rear wheels are steered in the direction reverse to the direction of steering of the front wheels during very low speed running, the direction of the vehicle can be changed greatly and thus, no trouble will occur even in a case where it is necessary to turn the vehicle greatly in a narrow space for the purpose of tandem parking or bringing the vehicle into a garage.
Such a four-wheel steering apparatus can theoretically be realized by various systems, but the use of many electrical means or hydraulic means will lead to a relatively high cost and a complicated mechanism and further to problems in respect of maintenance and reliability such as safety when trouble occurs.