A wheel support bearing assembly includes inner and outer members (1 and
2) and at least one row of rolling elements (3) operatively interposed
between the inner and outer members (1 and 2) and an annular sealing
device (5) sealing an open end of an annular space defined between the inner
and outer members (1 and 2). The sealing device (5) includes
first and second annular sealing plates (11 and 12) fitted to different
members out of the inner and outer members (1 and 2). Each of the
first and second sealing plates (11 and 12) includes a generally
cylindrical wall (11a or 12a) and a radial wall (11b
or 12b) assembled together to represent a generally L-shaped
section. The first sealing plate (11) is fitted to one of the inner and
outer members (1 and 2) that serves as a rotating member. An elastic
member (14) mixed with a powdered magnetic material is bonded by vulcanization
to the radial wall (11b) of the first sealing plate (11).
A protective cover (18) made of a non-magnetic material is positioned on
one side adjacent an exterior of the multi-pole magnet (14) with a predetermined
air gap left therebetween that the number of revolution can be detected through
the protective cover (18).