Rotor for electromagnetic coupling

A rotor for a six-pole electromagnetic coupling, said rotor comprising first and second annular members made of material having low magnetic reluctance, said first annular member having an annular pocket defined by an axially facing wall having an outer margin and by a radially inwardly facing wall, said radially inwardly facing wall being defined by the inner surface of an annular flange projecting axially from the outer margin of said axially facing wall and having an axially facing end, said second annular member comprising a hub located within said first annular member in radially spaced relation therewith and further comprising a disc formed integrally with and projecting radially outwardly from said hub, said disc having an outer periphery, having an axially facing working face and having an oppositely facing non-working face, two radially spaced and circumferentially extending rows of circumferentially spaced slots formed through said disc to define magnetic poles on the working face of the disc, there being intervening bridges between the slots in each row, said disc being located in said pocket with the non-working face of the disc spaced axially from the axially facing wall of the pocket and with the outer periphery of the disc spaced inwardly from the radially inwardly facing wall of said pocket by a narrow air gap, said air gap causing an additional magnetic pole to be defined on the end of said flange, a ring made of material having high magnetic reluctance and sandwiched between the non-working face of said disc and the axially facing wall of said pocket, means securing said ring rigidly to the non-working face of said disc and to at least one of said walls of said pocket, said ring extending radially and circumferentially along substantially all of the non-working face of said disc and serving to structurally reinforce the disc and particularly the bridges between said slots.