Abstract: An apparatus and method is provided for energizing a multiple-turn winding of an electromagnetic coupling having an armature and a rotor separated by an air gap; in response to the closure of the air gap, the energization of the winding is reduced so as to reduce the torque coupling between the armature and rotor. By reducing the initial torque coupling between the armature and rotor the frictional vibrations of the coupling--which occur during engagement of the armature and rotor and which generate audible noise--are reduced and the coupling engages more smoothly and quietly. Preferably, the energization of the winding is reduced in response to the increased magnetic inductance of the winding resulting from the closure of the air gap between the armature and rotor. Also, the torque coupling between the armature and rotor is preferably minimized in response to the increased magnetic inductance so as to provide 100% slippage upon initial contact of the rotor with the armature.

Abstract: The electrical brake coils of a trailer are energized when the stoplight switch of the towing vehicle is closed and the trailer surges forwardly with respect to the towing vehicle to cause the wiper of a rheostat to move relatively along the resistor of the rheostat. A hazard switch for causing the stoplights of the towing vehicle to flash is connected in parallel with the stoplight switch in the stoplight circuit of the towing vehicle. The resistor of the rheostat is formed with a normally non-conductive portion which prevents the brake coils from being repetitively pulsed with current when the hazard switch is actuated. Once surge braking has been initiated, however, the non-conductive portion of the resistor is rendered conductive so that current will be supplied continuously to the brake coils over the full range of movement which the trailer undertakes during surge braking.

Abstract: An electric step motor has a rotor member and a stator member aligned on a common axis with one of the two members having two pairs of interdigital pole teeth extending perpendicularly to the axis. The two pairs of pole teeth are axially spaced from each other with the inner pole teeth in each pair spaced both radially and circumferentially from the outer pole teeth in that pair. A pair of coils are associated with the two pairs of interdigital pole teeth for magnetizing the inner and outer pole teeth in each pair with opposite polarities when the corresponding coil is energized. The other member has multiple permanent magnets spaced circumferentially from each other and located axially between the two pairs of interdigital pole teeth so that energization of either coil draws the permanent magnets into register with a selected pair of interdigital pole teeth.