1. Field of the Invention
The present invention relates to a coupling structure of a shaft body and a shaft joint.
2. Description of Related Art
A steering apparatus for a vehicle comprises: a steering shaft with one end connected to a steering wheel; a transmission shaft having, on one end thereof, a shaft joint connected to the other end of the steering shaft; and a pinion shaft coupled to the other end of the transmission shaft through the shaft joint and having a pinion meshing with the mid portion of a rack shaft which extends in the left and right direction of the vehicle.
The coupling structure of a shaft joint and a shaft body composed of a steering shaft or a pinion shaft is disclosed, for example, in Japanese Patent Application Laid-Open No. 2000-310232.
According to the coupling structure of Japanese Patent Application Laid-Open No. 2000-310232, an end of the shaft body has a non-circular engagement portion having a pair of parallel flat faces on a part of circular circumferential surface, and a slip-off preventing groove with both ends facing the flat faces. The shaft joint has an engagement groove with which the engagement portion is engaged so that relative rotation is impossible, and two concentric bores facing the engagement groove. A nut member having an edge portion is press-fitted into one of the bores. Moreover, a plate body is held on the outer circumference of the shaft joint. The plate body comprises a curved portion having through bores corresponding to the above-mentioned bores, respectively, and a regulating tongue extending from one end of the curved portion and inserted into the engagement groove. In this plate body, the periphery of the bore on the side opposite to the regulating tongue is referred to as a supported portion, which is supported between the edge portion and the shaft joint by press-fitting the nut member into one of the through bores.
The shaft body and the shaft joint are coupled up by: inserting the engagement portion of the shaft body into the engagement groove of the shaft joint from the edge side in the depth direction of the engagement groove to engage the engagement portion with the engagement groove; inserting a bolt into the through bores of the plate body, the bores of the shaft joint and the slip-off preventing groove; and tightening the bolt into the nut member so that relative movement in the axial direction and relative rotation are impossible. In this case, with the insertion of the engagement portion into the engagement groove, the regulating tongue of the plate body is deflected, and, after the engagement portion is engaged with the engagement groove, the regulating tongue is elastically restored, comes into contact with one side of the engagement portion, and regulates the movement of the engagement portion in a direction opposite to the insertion direction.
In the coupling structure constructed as described above, however, since the plate body is fastened to the shaft joint by supporting the flat supported portion, the fastening strength of the plate body is not sufficient and the plate body trembles. Thus there has been a demand for improvement. In order to increase the fastening strength of the plate body, the plate body may be fastened by welding or caulking. However, since both of these techniques are special fastening techniques, there arise problems of poor workability and high costs.