Composite magnet of electromagnet and permanent magnet, and eddy current retarder

An eddy current retarder, comprising a rotary shaft, a brake drum coupled to the rotary shaft, and stationary magnet unit disposed on the inside of the brake drum in the radial direction, wherein the stationary magnet unit comprises:

• an annular base portion;
• a plurality of iron core portions extending outward in the radial direction from the outer peripheral edge of the base portion and spaced at intervals in the circumferential direction;
• a plurality of coils wound on the outer peripheral surfaces of respective pairs of the plurality of iron core portions;
• magnetic pole pieces arranged at the ends of the iron core portions so as to be opposed to the inner peripheral surface of the brake drum;
• the iron core portions and the coils forming a plurality of electromagnets;
• and
• at least one permanent magnet buried in the iron core portion of each of said electromagnets, with the magnetic pole surfaces being directed in the radial direction;
• wherein said eddy current retarder produces a braking force in the brake drum only when an electric current is supplied to the coils to cause an eddy current to be generated by a magnetic field due to the electromagnets and the corresponding permanent magnets.