Electromagnetic clutch and manufacturing method of magnetic path forming member therefor

A method of manufacturing a magnetic path forming member for an electromagnetic clutch comprising a first magnetic member with a large-diameter cylindrical portion made of a magnetic metal, a second magnetic member with a small-diameter cylindrical portion made of a magnetic metal and contained in said large-diameter cylindrical portion, an annular member of a non-magnetic material interposed between and joined to said large and small-diameter cylindrical portions to constitute said magnetic path forming member having a clutch contact surface at a front end thereof, a friction clutch arranged between the clutch contact surface formed at the front end surface of said magnetic path forming member and an armature, and an electromagnet arranged behind said magnetic path forming member for generating magnetic flux between said large and small-diameter cylindrical portions, said method comprising:

• making the inner diameter of said clutch contact surface at the front end portion of said large-diameter cylindrical portion and the outer diameter of said clutch contact surface at the front end portion of said small-diameter cylindrical portion substantially the same respectively as the outer and inner diameters of said annular member;
• positioning said annular member relative to said first and second magnetic members with the front end surface of said annular member receding more than a predetermined distance (L1) from the front end surfaces of said large and small-diameter cylindrical portions;
• joining the outer and inner surfaces of said annular member respectively to the inner surface of said large-diameter cylindrical portion and the outer surface of said small-diameter cylindrical portion;
• and
• forming said clutch contact surface by cutting the front end surfaces of said large and small-diameter cylindrical portions so that the front end surface of said annular member recedes by said predetermined distance (L1) from the front end surfaces of said large and small-diameter cylindrical portions.