Speed sensor utilizing a stator which includes two circumferentially spaced elements which are interconnected by a low magnetic permeability member. The elements have alternating regions which provide a variation in magnetic permeability. A rotor which is arranged for rotation about a rotational axes includes alternating regions of magnetic permeability which interact with the stator. A magnet is located between the elements of the stator and the structural interconnection therebetween. A coil of wire is placed around the structural interconnecting member to sense variations in magnetic field which are caused by the change in reluctance as the respective regions of magnetic permeability of the elements and rotor pass one another.

An electromagnetic clutch for a motor vehicle drive assembly to produce a rotational connection between a rotational drive element and the shaft of the assembly wherein the electromagnetic clutch is also configured to function as a pulse generator for recording the rotational speed of the assembly.

The tachometer of the present invention has a stator member with a pair of opposed stator elements. The stator member is mounted on the apparatus. Windings are provided on the stator elements in which the electric signal is generated. A magnetic means is provided for establishing a magnetic flux between the stator segments. For this purpose, magnets may be mounted on the exterior of the stator segments and the portions of the apparatus adjacent the segments used as the flux return path. Or, magnets may bridge the two stator segments. A magnetically permeable rotor is mounted on the apparatus shaft. The rotor may be formed of steel laminations with no rotating winding and has a plurality of peripheral projections that alter the reluctance of the magnetic path in the teeth as they rotate, inducing a speed responsive signal in the windings. The maximum speed of the rotor is limited only by the strength of the steel.

Several embodiments of tachometers generators for use in controlling the speed of electrical motor driven tools. In each embodiment a toothed rotor (28, 52, 72, 92, 122) is fixed for rotation with the motor armature shaft (23, 53, 73, 93, 124) and a sensor (31, 55, 75, 96, 126) is juxtaposed to the rotor. The sensor is comprised of a core (32, 56, 76, 98, 127) having a first end portion (33, 57, 77, 99, 128) juxtaposed at a first location relative to the rotor and a second end portion (36, 58, 78, 101, 129) that is juxtaposed to the rotor at a second, spaced location. A permanent magnet (37, 59, 79, 102, 131) is interposed between the second end portion and the rotor with one of its poles aligned with a second end portion and the other of its poles aligned with the rotor. A coil (38, 61, 81, 103, 132) is wound around an intermediate portion (34, 62, 82, adjacent 99, adjacent 128) of the core so that a voltage will be generated in the coil by the alternating magnetic flux passing through the core during rotation of the rotor, which voltage is indicative of the speed of the armature shaft. The compact construction facilitates installation in close places and the device provides a strong signal and exhibits a high signal to noise ratio.

A variable reluctance pickup for producing electrical pulses in response to the rotation of an adjacent toothed wheel comprises a probe assembly situated tangentially to the path of the wheel teeth. The sensor comprises an elongated core surrounded by a coil and having permanent magnets of opposed polarity at each end of the core. A pole piece extending laterally from one end of the core extends to a point adjacent the path of the teeth of the rotating part. The electrical pulses produced upon part rotation are double the size of pulses produced in the case where only one magnet of equivalent strength to the two magnets is used.