Patent ID: 8635960

Claim:
A free ball bearing comprising: a main body that has a ball retainer where a ball-retaining recess having an inner surface of a semi-circular recessed surface is formed; a plurality of retainer balls that is disposed on the semi-circular recessed surface of the main body and a main ball that has a diameter larger than the retainer balls and is rotatably supported through the retainer balls; a cover portion that surrounds the ball retainer of the main body while ensuring a predetermined internal space; a retained ball-pressing ring that has a ring-shaped pressing member that is inserted in between the semi-circular recessed surface of the main body and the main ball and presses the retainer balls, and is disposed to be movable in the internal space in the depth direction of the ball-retaining recess, between a pressing position where the retainer balls are pressed and a releasing position where the retainer balls are released; and a releasing mechanism that moves the retained ball-pressing ring from the pressing position to the releasing position by applying a displacement force to the retained ball-pressing ring, wherein a main ball protrusion opening having a diameter smaller than the diameter of the main ball is formed through the cover portion, a portion of the main ball protrudes from the main ball protrusion opening toward a tip end side, an air suction hole that communicates with the internal space and is open to a base end side opposite the tip end side is formed through at least one of the main body and the cover portion, the retained ball-pressing ring includes a driving ring portion disposed between an outer circumferential surface of the ball retainer and an inner circumferential surface of the cover portion, the driving ring portion has an inner circumferential surface disposed close to the outer circumferential surface of the ball retainer through a first gap allowing air to flow and an outer circumferential surface disposed close to the inner circumferential surface of the cover portion through a second gap allowing air to flow, a groove circumferentially extending or a wear ring is disposed on at least one of the inner circumferential surface and the outer circumferential surface of the driving ring portion, and the first gap and the second gap are sized such that a displacement force is applied to the retained ball-pressing ring toward the base end side of the internal space when the air in the internal space is sucked through the air suction hole.