Wheel position detector and tire inflation pressure detector having the same

Claim 1

A wheel position detector used for a vehicle having a plurality of wheels, each of which includes a tire mounted on a vehicle body, the wheel position detector comprising: a transmitter that is arranged at each wheel, and includes a first control portion for generating and transmitting a frame including specific identification information; and a receiver that is arranged at the vehicle body, receives the frame transmitted from the transmitter of one of the wheels via a reception antenna at a reception time, and includes a second control portion for performing wheel position detection for specifying the one of the wheels and storing a relationship between the one of the wheels and the specific identification information, wherein each transmitter further includes an acceleration sensor that outputs a detection signal corresponding to acceleration, which has a gravity acceleration component varying with a rotation of a respective wheel mounting the transmitter, wherein the first control portion of the transmitter at each wheel detects an angle of the transmitter based on the gravity acceleration component in the detection signal from the acceleration sensor, wherein each wheel has a central axis as a center of the wheel, a predetermined position of a circumference of the wheel is referred as a zero degree position, and the angle of the transmitter is defined by the transmitter, the center and the zero angle position, wherein the transmitter at each wheel repeatedly transmits the frame every time the angle of the transmitter reaches a specified value, the wheel position detector further comprising: a wheel speed sensor for each wheel that detects a tooth of a gear, which rotates in association with the wheel, wherein the gear of each wheel has an outer periphery, which provides teeth as conductive portions and a plurality of intermediate portions between the teeth so that the conductive portions and the intermediate portions are alternately arranged along the outer periphery, and a magnetic resistance of a tooth is different from a magnetic resistance of an intermediate portion, wherein the second control portion acquires gear information indicating a tooth position of the gear based on a detection signal from the wheel speed sensor, wherein the second control portion sets a variation allowance based on the tooth position when the receiver receives the frame, wherein the second control portion excludes a certain wheel from a candidate of the one of wheels mounting the transmitter that transmits the frame when the receiver receives the frame, and the tooth position of the certain wheel is not disposed within the variation allowance after the variation allowance is set, wherein the second control portion registers a remaining wheel as the one of wheels mounting the transmitter that transmits the frame, wherein the second control portion changes the variation allowance every time the receiver receives the frame, wherein the second control portion sets another variation allowance based on another tooth position when the receiver receives a new frame, and wherein the second control portion changes the variation allowance to a new variation allowance, which is provided by an overlap portion between the variation allowance and another variation allowance.