Wheel position detection apparatus and tire air pressure detection apparatus having the same

A wheel position detection apparatus applied to a vehicle in which a plurality of wheels provided with tires are attached to a vehicle body, the wheel position detection apparatus comprising:

• transmitters, each of which is provided in a corresponding one of the plurality of the wheels, and has a first controlling section that produces and transmits a frame including specific identification information;
• a receiver that is provided in the vehicle body and has a second controlling section, the second controlling section receiving the frame transmitted from each of the transmitters through a reception antenna and carrying out a wheel position detection to specify which wheel the transmitter that has transmitted the frame is provided in, and to store the plurality of the wheels in association with the identification information of the transmitters provided in the plurality of the wheels, respectively,
• wherein each of the transmitters includes an acceleration sensor that outputs a detection signal depending on an acceleration including a gravitational acceleration component that varies in connection with rotation of the wheels in which the corresponding transmitters are provided,
• wherein each of the first controlling sections detects an angle of the corresponding one of the transmitters in accordance with the gravitational acceleration component included in the detection signal of the corresponding one of the acceleration sensors, with a central axis of the corresponding one of the wheels set as a center and with an arbitrary position along a circumferential direction set as zero degree, and transmits the frame repeatedly at a timing when the angle becomes a predetermined angle,
• wherein the second controlling section acquires gear information indicating tooth positions of gears in accordance with detection signals of wheel speed sensors that output the detection signals depending on transits of teeth of the gears that are rotated in connection with the plurality of the wheels, and sets an allowable range of variability in accordance with the tooth position at the reception timing of the frame, when the tooth position at the reception timing of the frame after the allowable range of variability is set is beyond the allowable range of variability, the corresponding one of the wheels is eliminated from candidates of the wheel to which the transmitter that has transmitted the frame is attached, and the remaining of the wheels is registered as a wheel to which the transmitter that has transmitted the frame is attached,
• wherein the second controlling section changes the allowable range of variability depending on a road surface condition indicated by roughness of a road surface every time the frame is received, so that the allowable range of variability is set wider for a road surface that is rough than for a road surface that is not rough, and
• wherein the second controlling section changes the allowable range of variability every time the frame is received, and sets an overlapping part of the allowable range of variability set in accordance with the tooth position at the reception timing of the frame and the allowable range of variability set at the reception timing of the last frame as a new allowable range of variability.