Patent ID: 8568036

Claim:
A vehicle wheel bearing apparatus comprising: an outer member formed with double row outer raceway surfaces on an inner circumference; an inner member formed with double row inner raceway surfaces on an outer circumference, the double row inner raceway surfaces are arranged opposite to the double row outer raceway surfaces; double row rolling elements are freely rollably contained between the outer raceway surfaces and the inner raceway surfaces, respectively, of the outer member and the inner member; either one of the outer member or inner member is integrally formed, on an outer side end, with a wheel mounting flange to mount a wheel, a plurality of bolt apertures is equidistantly formed in the wheel mounting flange along a circumference, and the wheel is adapted to be secured on the wheel mounting flange by a plurality of bolts secured in the bolt apertures, the wheel mounting flange includes a plurality of reinforcement ribs, each reinforcement rib includes a pair of opposing sides and a web connecting the opposing sides; and cut-out portions are formed between the bolt apertures, the cut-out portions avoid the vicinity of each bolt aperture, and that each cut-out portion is formed as a circular arc configuration so that a deepest portion is positioned closely to a pitch circle diameter of the bolt apertures, the deepest portion of each cut-out portion is positioned radially outward of the pitch circle diameter of the bolt apertures, each cut-out portion is continuous with the outer circumference of the wheel mounting flange, a center of a radius of curvature of each cut-out portion is positioned on an extension of a line passing through a center of the wheel mounting flange and a center of mutually adjacent bolt apertures, a relationship of R 1 =0.7-1.5 PCDb exists between the radius of curvature R 1 of each cut-out portion and the pitch circle diameter PCDb, the circular arc configuration extends to the wheel mounting flange outer circumference such that the cut-out portions intersect the wheel mounting flange outer circumference at a position, the position is adjacent the web between the opposing sides connected by the web of the same reinforcement ribs on the wheel mounting flange.