Hydraulic power steering apparatus

A hydraulic power steering apparatus comprising:

• an input shaft;
• an output shaft;
• a torsion bar which connects said input shaft with said output shaft coaxially so that elastic relative rotation between said shafts is generated in accordance with steering torque;
• a hydraulic actuator for generating steering assist force;
• a hydraulic control valve having a tubular outer valve element and an inner valve element which is fitted into said outer valve element so as to be capable of relative coaxial rotation;
• a rotation conversion mechanism which converts the relative rotation between said input and output shafts into relative rotation between said two valve elements;
• and
• a rotation ratio altering mechanism which varies the ratio of the relative rotation angle between said two valve elements to the relative rotation angle between said input and output shafts in accordance with an operating condition of a vehicle;
• wherein the pressure of the hydraulic fluid supplied to said hydraulic actuator is controlled in accordance with the relative rotation angle between said two valve elements,
• said outer valve element is capable of relative coaxial rotation to said input shaft and said output shaft,
• said inner valve element is formed integrally with said input shaft,
• said rotation conversion mechanism has a first supporting part which rotates together with said input shaft, a second supporting part which rotates together with said output shaft, a third supporting part which rotates together with said outer valve element, and a swinging member,
• the respective supporting parts are spaced from each other in the axial direction of said input and output shafts,
• said swinging member is supported by said first supporting part and said second supporting part so as to swing in accordance with the relative rotation between said input and output shafts, and is supported by said third supporting part so that relative rotation between said outer valve element and said inner valve element is generated by the swinging of said swinging member, and
• relative displacement of one of said first, second and third supporting parts in the axial direction to said input and output shafts by a distance corresponding to the operating condition of the vehicle is generated by means of said rotation ratio altering mechanism.