For example, in a gear support shaft of a transmission of a vehicle including an engine, various types of ball bearings, such as a deep groove ball bearing and an angular contact ball bearing, are widely used.
A ball bearing of this type includes the following main components: an inner race having a radially outer surface in which an inner raceway surface is formed; an outer race arranged on an outer side of the inner race, and having a radially inner surface in which an outer raceway surface is formed; a plurality of balls interposed between the inner raceway surface of the inner race and the outer raceway surface of the outer race in a freely reliable manner; and a retainer arranged between the inner race and the outer race, for retaining the balls equiangularly. Any one of the inner race and the outer race is mounted to a stationary part such as a housing, and another one of the inner race and the outer race is mounted to a rotary part such as a rotation shaft.
In particular, drive motors for electric vehicles and hybrid vehicles tend to be downsized and rotated at high speed for higher efficiency, and hence the rotary part such as the rotation shaft is rotated at high speed in accordance therewith. As a result, there arise problems of deformations of a retainer due to a lack of lubrication, torque (heat generation), a centrifugal force, and the like. The deformations of the retainer due to the lack of lubrication and the torque (heat generation) can be solved by appropriately designing a shape of the retainer. Further, the deformation of the retainer due to the centrifugal force can be suppressed by using a lightweight retainer made of a synthetic resin.
There have been proposed various lightweight retainers made of the synthetic resin for the purpose of suppressing the deformation of the retainer due to the centrifugal force. Examples of the retainer of this type include a retainer having a crown shape including a circular main part, pairs of elastic pieces equiangularly and integrally provided at intervals to project from a surface on one side in an axial direction of the main part, and pockets that are provided in a recessed form between the pairs of the elastic pieces and retain balls in a freely reliable manner. In this crown-shaped retainer, the balls are held from only one side. Thus, when a great centrifugal force is applied, due to irregular deformation, the balls may drop off from the pockets, or interfere with other components such as the inner race and the outer race.
In order to eliminate such risks, there have been proposed various retainers of an axial coupling type, for retaining the balls from both sides (for example, refer to Patent Literature 1). The retainer disclosed in Patent Literature 1 has a structure in which a pair of annular members are coupled to each other in an axial direction. The pair of annular members each include an annular proximal portion and post portions integrally provided at equal intervals to project upright from each of the annular proximal portions. The pair of annular members are opposed to each other in a manner that the post portions of one of the annular members are snatched with midpoints between the post portions of another of the annular members. Then, the pair of annular members are coupled to each other so as to form pockets for retaining the balls between the post portions adjacent to each other.