WHEEL BEARING APPARATUS

One object of the present invention is to provide a wheel bearing apparatus which can solve problems of prior art and thus achieve improved detection accuracy and sealability by increasing the rigidity of the second cap. According to the present invention, there is provided a wheel bearing apparatus comprising an outer member; an inner member including a hub wheel and at least one inner ring; double row rolling elements contained between the inner raceway surfaces and outer raceway surfaces of the inner member and outer member; a pulser ring adapted to be fitted onto the outer circumference of the inner ring and having characteristics alternately and equidistantly varying along its circumferential direction; a cup-shaped second cap press-formed of steel sheet and fitted on the inboard-side end of the outer member; and a rotational speed sensor mounted on the second cap at a radially outer position thereof, the rotational speed sensor being arranged oppositely to the pulser ring via a predetermined axial air gap characterized in that a cup-shaped first cap is press-fitted into the inner circumference of an inboard-side end of the outer member via a predetermined interference, the first cap being press-formed of non-magnetic austenitic stainless steel sheet and comprising a cylindrical fitting portion press-fitted into the inner circumference of the inboard-side end of the outer member, a disc portion extending radially inward from the fitting portion and opposing to the pulser ring via a small axial gap; that said rotational speed sensor is arranged oppositely to the pulser ring via the first cap with being abutted against or closed to the disc portion of the first cap; and that said second cap is press-fitted into the inner circumference of an inboard-side end of the outer member via a predetermined interference.