Device for estimating tire air pressure state, and device for detecting wheel speed signal frequency

摘要

A wheel speed is detected by a wheel speed detecting means (12), and a wheel speed signal is outputted to a reference value setting means (14). At the reference value setting means, the wheel speed signal is corrected such that a center of an amplitude of the wheel speed signal becomes a zero reference, and the wheel speed signal is amplified by carrying out a predetermined processing. Further, a selecting means (16) selects, of the wheel speed signals during a predetermined period of time, wheel speed signals whose S/N ratios are poor, which are not to be used. A frequency detecting means (18) judges a tire air pressure state by an air pressure state judging means (20) from a number of times an amplified wheel speed signal crosses the zero reference (a number of times a sign changes). <IMAGE>