Patent ID: 9097284
Filing Date: 2015-08-04
Classification: B60B,C21D,F16C

Abstract:
1. A vehicle wheel bearing apparatus comprising: an outer member formed, on its inner circumference, with double row outer raceway surfaces and shoulder portions are formed between the double row outer raceway surfaces, the shoulder portions are formed as cylindrical portions, a step portion, with a tapered or circular arc cross section, is formed between the cylindrical portions, the outer member having a thin wall with a minimum wall thickness at the double row outer raceway surfaces is set at about 4 mm to reduce the size and weight of the wheel bearing apparatus while increasing rigidity; an inner member includes a wheel hub that is integrally formed with a wheel mounting flange at its one end, said wheel hub outer circumference surface includes double row inner raceway surfaces arranged opposite to the double row outer raceway surfaces; double row balls are freely rollably contained between the outer raceway surfaces and inner raceway surfaces, respectively, of the outer member and the inner member; a pitch circle diameter of the double row ball group of the outer-side is larger than a pitch circle diameter of the double row ball group of the inner-side and the shoulder portions are axially parallel on the outer member and the shoulder portions are at different radial distances from an axis of the bearing; at least the outer member and the wheel hub are formed of medium/high carbon steel including carbon of 0.40-0.80% by weight; the inner and outer raceway surfaces are formed, respectively, with predetermined hardened layers having a surface hardness of 58˜64 HRC; a grain size number of austenite crystal grains of a metallographic structure in the hardened layers is selected larger than #7; and a distance (L) exists between the double row outer raceway surfaces, the distance (L) is equal to or greater than 14 mm, a hardened layer is provided only in the double row outer raceway surfaces and the shoulder portions and step portion remain as non-hardened portions and the hardened layer on the double row outer raceway surfaces between ends of the outer raceway surfaces is substantially constant and the hardened layer is prohibited from spreading down the shoulder to make it possible to provide impact resistance, strength, durability and accuracy and provide a reduction of manufacturing costs of the bearing apparatus.