1. Field of the Invention
The present invention relates to a vane pump, and more particularly to an improvement in assembling a vane pump, in particular, in adjustably fixing a vane pump cam ring to a vane pump housing in such a way that an eccentricity between the cam ring and a rotor can be eliminated.
2. Description of the Prior Art
Vane pumps are incorporated in a power-operated steering system of an automotive vehicle for instance.
A vane pump is roughly made up of a housing, a drive shaft rotatably supported within the housing, a cam ring fixed to an annular recessed portion of the housing, a rotor fixed to the drive shaft and rotatably housed within the cam ring, and a plurality of vanes fitted to slots formed in the rotor so as to be slidably movable in the radial direction of the rotor in contact with the elliptical inner circumferential surface of the cam ring.
In the vane pump as described above, it is necessary to fix the cam ring to the housing under consideration of mutual positional relationship between the two in such a way that the center of the elliptical inner circumferential surface of the cam ring coincides with the center of the rotor; that is, there exists no eccentricity between the two.
In the prior-art method of fixing the cam ring to the housing, a housing pin hole is formed in the radial direction of the housing passed through the cylindrical wall of the housing; a cam ring pin hole is bored in the radial direction of the cam ring at such a position that the housing pin hole matches the cam ring pin hole, and a single locating pin is pressure-fitted into these two pin holes to fix the cam ring to the housing. In the prior-art method as described above, however, although the cam ring can be fixed to the annular recessed portion of the housing, since only a single locating pin is fitted to a single pair of pin holes, it is impossible to fix the cam ring to the housing with a center of the cam ring accurately located at a center of the rotor where there exist dimensional errors in these elements, and further it is impossible to adjust the mutual relationship between the cam ring and the rotor or to correct an eccentricity between the two elements. In case there exists an eccentricity between these two elements, the outer circumferential surface of the rotor may be brought into contact with the elliptical inner circumferential surface of the cam ring, thus resulting in abnormal wear or short service time and abnormal vibrations or loud mechanical noise.
To overcome the above drawbacks, a method of selective assembly has been adopted, in which the dimensions of the two elements are measured and a set of two elements having counterbalanced dimensional errors are selected for assembling each vane pump. However, this method requires much time, thus lowering the work efficiency.
Further, since a tension is always applied to the rotor by a drive belt engaged with a vane pump pulley, when the vane pump is in operation, there inevitably exists an eccentricity between the rotor and the cam ring in spite of the fact that the vane pump is assembled in accordance with the method of selective assembly.
The arrangement of the prior-art vane pump will be described in more detail hereinafter with reference to the attached drawings under DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS.