Electric motor with brake

Claim 1

In an electric motor having a built-in brake, and including a wound stator having an inner cylindrical surface, a motor shaft journaled coaxially of the stator, a rotor mounted on the motor shaft and having an outer cylindrical surface, there being a narrow annular gap between the confronting surfaces of the stator and rotor, the rotor being divided along at least a substantial portion of its axial length into two coaxial parts, a first one of said parts being a central core having an outer conical surface, the second one of said parts being an outer crown uniformly slotted on its outer surface in that portion thereof that covers the first part, the crown having an inner conical surface of the same conicity as the outer surface of the central core, between the conical surfaces of the two rotor parts there being an inner airgap; one of the two rotor parts being rigidly fixed on the motor shaft against turning with respect thereto but being axially shiftable with respect thereto, the brake having one friction part fixed with respect to the stator, and another friction part cooperating with the one friction part and connected to the said other part of the rotor, the improvement which comprises: the outer crown of the rotor being uniformly slotted outside and inside, the iron thickness between the bottoms of the two slots being as small as possible, the outside slots of the crown having approximately square form in order to minimize the leakage flux, the width of the inner slots being sufficient to prevent the magnetic fluX from returning by crossing the inner slots, the crown being fixed on the motor shaft by two supports which are separated from the rotor core by an airgap wide enough so that a loss of the motor flux is reduced practically to zero and so that the most part of the active magnetic flux is obliged to close through the central core to produce the maximum braking force when the motor is supplied with electric current and the brake is free, and means to shift said other part of the rotor and said other friction part axially of the motor shaft to brake the motor when the motor is not supplied with electric current.