In these kinds of pulleys, when the pulley body is caused to rotate upon receiving a rotation driving force from a belt, the outer ring of said ball bearing fitted thereto rotates together with the pulley body.

In the case of the bearing whose pitch circle diameter is within 7.5 mm to 21 mm, if the profile deformation quantity of the raceway groove of the inner ring is selected to be 2 μm or smaller, the adverse effects owing to the waviness, such as the early wear, are prevented. Therefore, in the deep groove ball bearing of the present invention, the profile deformation quantity of the raceway groove of the inner ring is selected to be 2 μm or smaller (see FIG. 14).

Further, to achieve the object of the present invention, there is provided a deep groove ball bearing according to a second aspect of the present invention, having a plurality of balls located between an inner ring and an outer ring, wherein a pitch circle diameter of the bearing is 21 mm or smaller, and a profile deformation quantity of a raceway groove of the inner ring is 2 μm or smaller.

It is therefore an object of the invention to provide a means which is able to suppress abnormal noise under cold ambient or prevent the same from occurring with the functions of a pulley secured, taking the durability and production cost into consideration.

A deep groove ball bearing has an inner ring, an outer ring and a plurality of balls located between the inner ring and the outer ring. A profile deformation quantity of a raceway groove of the inner ring and a profile deformation quantity of the outer ring are limited to values at which the maximum surface pressure values of them are each 1.6 GPa or smaller.

In the case of the bearing whose pitch circle diameter is within 7.5 mm to 21 mm, if the profile deformation quantity of the raceway groove of the inner ring is selected to be 2 μm or smaller, the adverse effects owing to the waviness, such as the early wear, are prevented. Therefore, in the deep groove ball bearing of the present invention, the profile deformation quantity of the raceway groove of the inner ring is selected to be 2 μm or smaller (see FIG. 14).

Further, to achieve the object of the present invention, there is provided a bearing device using any of the deep groove ball bearings mentioned above. In the bearing device, the bearing has an internal clearance when the bearing stands alone, and the bearing is assembled into the bearing device while being pre-loaded.Any of the deep groove ball bearings is pre-loaded and then is used with a predetermined surface pressure being applied thereof.