Abstract: A dynamoelectric machine for generating an electric current having the frequency thereof proportional to the shaft speed of the machine. The generator is preferably of the permanent magnet type particularly suitable for use as a wheel speed indicator or tachometer-generator. The stator has an inner and outer tubular portion, with the inner portion disposed for limited radial movement with respect to the outer housing and having one end of the rotor journalled thereon for holding a substantially constant air gap at the rotary pole thereof. The limited movement of the inner stator portion is resisted by frictional forces created by the permanent magnet and by the axial bias of a thrust bearing. The remaining end of the rotor is journalled in a bearing registered in the outer stator housing. The machine gives magnetic saturation at the stator poles at 30% of rated speed and produces a strong signal output at low speeds.

Abstract: A cumulative running time indicator for use with an engine has a ceramic resonator-controlled oscillator that drives an electronic divider, a multiplexer, and a stepping motor which is connected through a gear train to a mechanical display showing elapsed time. The running time indicator operates only when an electrical generator, which is mechanically coupled with the engine, produces sufficient voltage to operate the indicator circuits. Sufficient voltage is produced at all engine speeds above a threshold speed which is less than engine idling speed. The generator supplies ac voltage to doubler circuit that has two separate outputs -- one for supplying large pulses of current for the stepping motor, and a partially isolated second output for other electronic loads. A tachometer output signal is provided at an auxiliary output terminal and is buffered to prevent disablement of the running time indicator by short circuits and externally applied voltages at the auxiliary output terminal.