Patent ID: 8561773

Claim:
A drive device comprising: a housing; an electromagnetic clutch mechanism which is accommodated in the housing, wherein the electromagnetic clutch mechanism is provided with a body to be attracted which is rotatably supported in the housing, a rotating body which is arranged to face the body to be attracted and also rotatably supported in the housing, and a coil, and wherein, in association with electricity supplied to the coil, an electromagnetic attraction force is generated between the body to be attracted and the rotating body, thereby the body to be attracted makes frictional engagement with the rotating body so that a power is transmitted between the body to be attracted and the rotating body; an annular magnet fixed on the outer circumference surface of the rotating body, wherein the annular magnet is provided with a plurality of magnetic poles arranged along the circumferential direction; and a sensor retained in the housing at a position radially outward of the annular magnet, wherein the sensor is arranged to face the annular magnet and detects a polarity change of the annular magnet in association with the rotation of the rotating body, wherein the annular magnet is provided with an annular wall portion extending toward the body to be attracted beyond a surface on which the body to be attracted is in contact with the rotating body with respect to the axial direction, wherein the annular wall portion has an inner circumference surface facing the body to be attracted in the radial direction, wherein a concave recess is formed on the inner circumference surface of the annular wall portion that is indented radially outward from the inner circumference surface of the annular magnet such that the annular wall portion is radially spaced outward from the body to be attracted, and wherein the concave recess is configured to retain abrasion powder which is produced in association with actuation of the electromagnetic clutch mechanism and is attracted by the annular magnet.