Patent ID: 7324887

Claim:
A wheel speed detection system comprising: a rotator configured to rotate on an axle center of a wheel together with the wheel, and plural concave and convex portions formed on a periphery of the rotator along a rotational direction with predetermined intervals therebetween; a sensor head disposed so as to face a surface of the convex portion with certain distance therebetween, and constituted with a coil to generate alternate current magnetic field therearound under supply of alternate current; a detector configured to excite the coil by supplying alternate current to generate eddy current on the concave and convex portions, and outputs alternate current detection signals corresponding to a change in an amount of the eddy current generated with rotation of the rotator; a pulse converter configured to convert the alternate current detection signals into pulse signals according to preset threshold levels; and a speed calculator configured to calculate rotational speed of the wheel based on the pulse signals, the wheel speed detection system further comprising a threshold shifter configured to shift the threshold levels corresponding to actual facing distance between the surface of the convex portion and the sensor head, wherein the pulse converter is configured to conduct conversion into the pulse signals according to the shifted threshold levels when the threshold levels are shifted by the threshold shifter, and wherein the threshold shifter is configured to obtain a difference between a default average, which is an average of the alternate current detection signals when a preset facing distance between the surface of the convex portion and the sensor head is the certain distance, and an average of the alternate current detection signals actually outputted from the detector, and shifts the threshold levels corresponding to the difference.