Vehicle steering system

A steering system in a motor vehicle having steerable front and rear road wheels, comprising:

• a steering wheel for turning the front road wheels;
• means including an actuator for actuating the rear road wheels to turn in the direction opposite to the direction of turning of the front road wheels only when said steering wheel is turned with a torque larger than a predetermined value;
• and
• a power steering device having a hydraulic servo including a pair of servo chambers separated by a servo piston and having one of said chambers pressurized while the other is drained when turning the front road wheels;
• said actuator comprising a reciprocative actuator rod connected at opposed ends thereof to the rear road wheels in such a manner as to turn the same when displaced from a neutral position thereof, a holding means for holding said actuator rod at the neutral position so long as the difference in pressure between said servo chambers is smaller than a predetermined value, an actuator housing through which said actuator rod passes to project from the opposed ends thereof, said actuator housing having a pair of smaller-diameter cylindrical actuator chambers and a larger-diameter cylindrical actuator chamber interposed between said smaller-diameter actuator chambers in a manner to define a pair of annular shoulders at the opposed ends thereof;
• said holding means comprising a pair of annular spring seats slidably disposed in said larger-diameter actuator chamber and also slidably mounted on said actuator rod and a coil spring interposed between said spring seats and placed around said actuator rod in a manner to urge said spring seats against said shoulders;
• said actuator further comprising a pair of annular actuator pistons slidably disposed in said respective smaller-diameter actuator chambers to fluidly separate same from said larger-diameter actuator chamber and fixedly mounted on said actuator rod in a manner to contact said respective spring seats when said actuator rod is in the neutral position thereof, said smaller-diameter actuator chambers being fluidly connected to said servo chambers in such a manner that said actuator rod is actuated to move in the direction opposite to the direction of movement of said servo piston.