Wheel position detector and tire inflation pressure detector having the same

A wheel position detector 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 of specifying the one of the wheels and storing a relationship between the one of the wheels and the specific identification information about the transmitter,
• wherein each transmitter 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 at 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 conductive portions and the intermediate portions are alternately arranged along the outer periphery, and a magnetic resistance of 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 at a specified cycle based on a detection signal from the wheel speed sensor,
• wherein the second control portion corrects the tooth position indicated in the gear information based on a time difference between time to acquire the gear information and time to receive the frame so that the second control portion calculates the tooth position when the receiver receives the frame, and
• wherein the second control portion specifies the one of wheels mounting the transmitter that transmits the frame, based on the tooth position at the reception time.