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A new magnetic circuit design for the Wiegand Effect has resulted in a rugged, stable transmission-mounted speed signal generator to provide a digital speedometer/odometer readout, and to provide an input for microprocessor vehicle management systems. The device requires no electrical input, and delivers a uniform signal at TTL level from zero speed. It can directly replace existing flexible cable drives.

The Wiegand Effect has been applied as an ignition trigger in several configurations of automotive distributors. Recent advances in the design of magnetic excitation systems for the Wiegand Effect have made possible considerable improvement in such distributors. The improved magnetic circuit has made possible the development of a crankshaft position sensor for deriving the top-dead-center and speed signals. The design lends itself to actuation by suitable notched discs, or directly from the teeth of the flywheel ring gear.

The Wiegand Effect is a new magnetic phenomenon occurring in a specially work-hardened small diameter ferro-magnetic wire. When subjected to an appropriate magnetic field, a sudden, very rapid flux change occurs. A substantial voltage pulse may be induced in a sensing coil wound around the Wiegand wire, or in its proximity. No electrical input is required, and with the appropriate excitation the pulse is essentially independent of the rate of flux change of the externally applied field. The characteristics of the Wiegand Effect are of interest in a number of automotive applications.