Wheel-support rolling bearing unit and method of manufacturing the same

A wheel-support rolling bearing unit comprising:

• an outer ring having first and second outer raceways formed in its inner peripheral surface;
• a hub having a flange formed on the outer peripheral surface of one end thereof, said hub having a first inner raceway which is disposed on its middle portion in an axial direction thereof and is confronted with said first outer raceway of said outer ring, said hub having a stepped part and a cylindrical portion disposed at the other end of hub, a step surface being defined on said hub by said stepped part, said cylindrical portion further comprising a second stepped part having an outer diameter smaller than that of said stepped part;
• an inner ring fit to said stepped part of said hub with interference while the end surface of said inner ring is brought in contact with said step surface of said hub, said inner ring having a second inner raceway which is formed on its outer peripheral surface and is confronted with said second outer raceway of said outer ring;
• a plurality of first rolling elements located between said first inner raceway and said first outer raceway;
• and
• a plurality of second rolling elements located between said second inner raceway and said second outer raceway;
• wherein a caulking portion, which is formed by plastically deforming said cylindrical portion, is protruded beyond at least said inner ring thus fit to said hub,
• wherein an outer diameter of said stepped part is smaller than that of a portion of said hub where said first inner raceway is formed, and
• wherein a pre-load is applied to said first and second rolling elements by bringing said end surface of said inner ring in contact with said step surface of said stepped part prior to the caulking, and
• wherein a static friction force which acts on said inner ring by the interference fitting is larger than an axial load acting on said inner ring by the pre-load applied to said rolling elements.