Interior permanent magnet motor and rotor structure therefore

A method of assembling a rotor structure for an interior permanent magnet electric motor comprising:

• providing a plurality of thin plates, each having a main body with two opposing major faces, a central opening and at least one window;
• fixing a set of the plates together to form a laminated rotor core having a first end and a second end, the at least one window in each plate being aligned with a corresponding window of an adjacent plate so that the windows together form an elongate pocket that extends along at least a part of the length of the core starting at a first end of the core,
• locating a permanent magnet in the pocket that has a first end that protrudes slightly from the first end of the stack;
• and
• securing a further plate to the first end of the stack that includes an integral retention feature which projects away from the main body of the plate to project above a window in the plate that receives the protruding first end of the magnet so that the retention means engages the first end of the magnet thereby to retain the magnet in the pocket.