Patent ID: 7481130

Claim:
A telescopic shaft for vehicle steering, assembled into a steering shaft of a vehicle and having a male shaft and a female shaft that are so fitted to each other to be able to transmit torque therebetween and move in an axial direction relative to each other, comprising: a first torque transmitting device having: a first interposing portion with a first axial groove and a second axial groove respectively provided in an outer peripheral surface of said male shaft and in an inner peripheral surface of said female shaft, first torque transmitting members including a plurality of spherical members disposed in the first and second axial grooves of said first interposing portion and rolling when said male shaft and said female shaft make relative movements in the axial direction, and an elastic member disposed adjacent in a radial direction to said first torque transmitting members in said first interposing portion, restricting said first torque transmitting members when a torque is transmitted between said male shaft and said female shaft and applying a pre-load to said male shaft and said female shaft through said first torque transmitting members when torque is not transmitted between said male shaft and said female shaft; and a second torque transmitting device having: a second interposing portion with a third axial groove and a fourth axial groove respectively provided in the outer peripheral surface of said male shaft and in the inner peripheral surface of said female shaft, and a second torque transmitting member including a cylindrical member disposed in said second interposing portion such that the cylindrical member extends parallel to both said male shaft and said female shaft, and sliding when said male shaft and said female shaft make the relative movements in the axial direction, wherein the first and second torque transmitting devices are arranged such that, in a first range of torque, torque is transmitted between said male shaft and said female shaft by the first torque transmitting members but not the second torque transmitting member, and, in a second range of torque greater than said first range, the second torque transmitting member acts to transmit torque between said male shaft and said female shaft.