A pair of toothed elements of magnetically permeable material are coaxially mounted for relative rotation with their teeth spaced opposed in rotational registration. The toothed elements are further mounted in magnetic circuit with magnets and a coil whereby magnetic flux provided by the magnets follows two separate magnetically parallel flux paths including the pair of toothed elements and the coil. As the toothed elements are relatively rotated, the net reluctance of the flux path through the tooth elements varies and causes a voltage to be induced in the coil which alternates at a frequency representative of the relative speed of rotation of the toothed elements. The other of the magnetically parallel flux paths is of a fixed reluctance and does not extend through the pair of toothed elements.
A tachometer assembly comprises two toothed rings (68, 70) in approximate axial register. The rings have similar peripheries of which the teeth (69, 71) are closely spaced in the axial direction of the rings. Magnetic flux in a path extending axially of the teeth varies as the rings rotate and is sensed by a coil (74) disposed coaxially of the rings.
An in-axle annular rotational speed sensor assembly (52) for drive axles (10) is provided which mounts directly to the drive axle differential bearing adjusters (36) in a relatively available and protected space (50) within the axle housing. The assembly utilizes the ferromagnetic adjuster to define a portion of the magnetic flux path (108) and maintains a large axial separation between the adjuster and the air gap (102) between the arrays of rotor and stator teeth (82, 100).
A tachometric device is provided with a D.C. electric motor a shaft of which drives a pair of permanent magnets to rotate. A first permanent magnet controls a speed indicator unit; a second permanent magnet is rotatably mounted within a winding the terminals of which are connected to a negative feed back circuit for controlling the speed of the motor.
A tachogenerator, for use for example, in motor speed control circuits, comprising a rotatable permanent magnet, a stationary coil spaced from the magnet, and an annular member of magnetic material disposed eccentrically with respect to the axis of rotation of the magnet and formed with at least one projection which extends into the space between the magnet and the coil for forming a path for magnetic flux coupling with the coil, the position of the projection being adjustable, for example by incremental angular movement of the annular member, so as to vary the output voltage from the coil for a given speed of rotation of the magnet.
A digital tachometer for generating electrical pulses at a rate indicative of the speed of rotation of a shaft-like member. A first toothed disk having N teeth is affixed to the shaft and a housing having a second set of M teeth is fixed with respect to the shaft and positioned around the toothed disk. As the shaft rotates, individual ones of the teeth on the outer periphery of the disk which is affixed to the rotating shaft alternatively pass into and out of close proximity to individual ones of the teeth of the outer housing resulting in periodic increases and decreases in the reluctance of the system. A sensing coil is positioned with respect to the housing so as to generate an electrical current which varies as the reluctance changes from one polarity to another as the shaft rotates. At each point of maximum reluctance and at each point of minimum reluctance, the polarity of the reluctance and correspondingly the slope of the current waveform changes and these changes are detected by a slope-change detector circuit which generates a digital signal in response thereto. The rate of generation of these digital signals is therefore indicative of the speed of rotation of the shaft and the speed of rotation can be sensed over a very wide range from very slow rotational speeds to very high speeds.
