Preload device of ball bearing and motor having the preload device

1. A constant preload device of a ball bearing, the preload device comprising:

an elastic member having a hollow shape with openings at both sides in an elastic direction; and

two holders which are inserted into the openings at the both sides of the elastic member, respectively,

wherein each of the holders includes:

a flange part configured to contact an end portion of the opening, into which the holder is inserted, to regulate an extension of the elastic member in the elastic direction thereof; and

a claw part configured to engage with the other holder such that the holders are slidable with respect to each other between a first position and a second position along the elastic direction,

wherein in the first position the claw parts of the respective holders contact each other to regulate separation therebetween in the elastic direction such that the elastic member is held between the holders to have a first length which is shorter than a free length of the elastic member, and in the second position the claw parts of the respective holders are separated by a distance in the elastic direction such that the elastic member is held between the holders to have a second length which is shorter than the first length, and

wherein when the preload device applies preload to the ball bearing, the ball bearing is contacted to the preload device only at an outer ring of the ball bearing.

2. The constant preload device according to claim 1 ,

wherein the ball bearing and the preload device are provided on an inner peripheral surface of a cylindrical bearing liner and an outer peripheral surface of one of the holders is fittingly fixed on the inner peripheral surface of the bearing liner.

3. A motor having the preload device according to claim 1 .

4. The constant preload device according to claim 1 , wherein the elastic member is outwardly exposed from the holders so as to be visible from an outer peripheral direction thereof.

5. The constant preload device according to claim 1 , wherein the preload device applies preload to the ball bearing when the holders are in the second position.

6. The constant preload device according to claim 1 ,

wherein the ball bearing and the preload device are provided on an inner peripheral surface of a substantially cylindrical bearing liner, the bearing liner has a convex part provided on an inner peripheral surface thereof, the convex part has a smaller inner diameter than that of the inner peripheral surface, one of the holders contacts the convex portion and the other holder contacts the outer ring of the ball bearing when the holders are in the second position.

7. The constant preload device according to claim 1 , wherein the claw part of one of the holders projects a larger distance away from the flange of the one holder than the claw part of the other holder projects away from the flange of the other holder, and in the first position and the second position a portion of the claw part of the one holder is disposed between the flange and the claw part of the other holder.

8. The constant preload device according to claim 1 , wherein each of the holders includes more than one said claw part disposed in spaced relation to each other, and the holders are rotatable relative to each other for selectively contacting their respective claw parts together.