US 4,947,116 AGranted

Inductive speed sensor employing phase shift

AssigneeHamilton Standard Controls, Inc.

InventorsWarren W. Welcome, Daniel R. Sparks

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Abstract

A speed detector, for use with a tone wheel having metal teeth, employs two coils positioned in offset relation near the tone wheel for interacting with the tone wheel teeth and thus changing their respective inductances. The coils preferably include iron cores to enhance magnetic coupling. One coil is in a phase sense oscillator circuit and the other is an a tuned sensor network. The oscillator is coupled to, and drives, the tuned network. The change in coil inductances effects a phase shift of the resulting signals in the oscillator and the tuned network, the magnitude of that phase shift typically being double that for a comparable single coil system. The output signals of the oscillator and tuned network provide inputs to a phase condition detector which looks for a reversal in their phase sequence and uses such event to provide timing reference pulses for a final determination of speed in a known manner.

Claims13

Dependent claims

A speed detector apparatus for use in combination with a tone wheel having multiple metal teeth, the detector apparatus and tone wheel being adapted for relative displacement, comprising:

an oscillator including a first inductive sensing coil adapted to be positioned adjacent to passing teeth on said tone wheel to thereby change inductance, the oscillator having a first output signal having a frequency determined at least partly by the inductance of said first coil;
a tuned circuit interconnected with said oscillator and including a second inductive sensing coil, said tuned circuit being driven by said oscillator to provide a second output signal and said second inductive sensing coil being adapted to be positioned adjacent to passing teeth on said tone wheel to thereby change inductance;
said first and said second inductive sensing coils being offset from one another relative to the passing teeth on the tone wheel such that their respective said changes of inductance are relatively out of phase;
the phase of said second output signal relative to said first output signal shifting cyclically as a function of the relative positioning of said teeth to the respective said first and second sensing coils during said relative displacement of said tone wheel;
and
means coupled to said oscillator and said tuned circuit for detecting a predetermined condition of the phase shift between said first and said second output signals and thereby providing timing reference signals recurring at intervals representative of the relative speed of the tone wheel.

3 more elements

Dependencies are inferred from the claim text.