Ball bearing

A ball bearing comprising:

• an outer ring including on the inner peripheral surface thereof an outer ring raceway having an arc-shaped cross section, wherein said arc-shaped section has a constant radius over its length;
• an inner ring including on the outer peripheral surface thereof an inner ring raceway having an arc-shaped cross section;
• and
• a plurality of balls respectively interposed rollably between said outer and inner ring raceways,
• wherein, where the outside diameter of said outer ring is expressed as D, the inside diameter of said inner ring is expressed as d, the pitch circle diameter of said respective balls is expressed as Dp, the following equations (1), (2), (3) and (4) can be satisfied:
• x=Db/{D−d)/2}, (1)
• y=Dp/{(D+d)/2}, (2)
• x≧0.3, (3)
• and
• y<1.0, (4)
• and
• further wherein, where the diameter of said respective balls is expressed as Db, the radius of curvature of the section shape of said outer ring raceway is expressed as Ro, and the radius of curvature of the section shape of said inner ring raceway is expressed as Ri, the following equations (5) and (6) can be satisfied:
• 0.53<Ro/Db<0.65, (5)
• and
• 0.52<Ri/Db<0.65, (6)
• to thereby make the rotation torque of the ball bearing lower and also prevent the Brinell impression from generating.