Electric power steering system

An electric power steering system comprising:

• an input shaft connected to a steering wheel, said input shaft provided with a multi-angle portion;
• an output shaft connected to a steering gear, said output shaft provided with a multi-angle portion, said input and output shafts arranged such that said multi-angle portion encircles said multi-angle portion of said output shaft by a predetermined distance;
• an elastic member connecting said input shaft with said output shaft,
• a steering torque detecting means for detecting a steering torque between said input shaft and said output shaft and for generating a signal in response to a torsional deformation of said elastic member,
• an electric motor controlling rotation of the output shaft by a control signal from a control device in response to the detecting signal from the steering torque detecting means;
• and
• a mechanical clutch device interposed between said electric motor and said output shaft, said mechanical clutch device controlling an intermittent transmission of the rotation of the electric motor to said output shaft in response to a relative rotation between said input shaft and said output shaft detected by the steering torque detecting means, such that the relative rotation between said input and output shafts detected by the steering torque detecting means by which said mechanical clutch device is controlling an intermittent transmission of the rotation of the electric motor to said output shaft is predetermined to value which is smaller than a value of relative rotation between said input and output shafts detected by the steering torque detecting means at which said electric motor begins to rotate, said mechanical clutch device including an outer sleeve coaxially disposed with and having a gap in regard to said multi-angle portion of said output shaft and decreasing the rotational force of said electric motor transmitted to said output shaft, engaging members interposed in said gap and being engaged at an inner surface of said outer sleeve and an outer surface of said output shaft, and spring members interposed in said gap and disposed between said engaging members, said spring members providing spring force directed toward each of said engaging members and in the direction of relative rotation between said input shaft and said output shaft so to urge said engaging members toward the engagement between the engagement members and the inner surface of said outer sleeve and the outer surface of said output shaft and increasing the engaging force of said engaging members by being compressed in response to the relative rotation between said input shaft and said output shaft.