Tire air pressure monitoring device

A tire pneumatic pressure monitoring device, comprising:

• a tire pneumatic pressure sensor installed on a tire of each wheel to detect a pneumatic pressure acting on the tire;
• an acceleration sensor installed on the tire of each wheel to detect an acceleration in a prescribed direction acting on the tire;
• a transmitter arranged on each wheel to detect a rotational position of the wheel based on a detected value of the acceleration sensor for transmitting the pneumatic pressure along with identification information unique to each transmitter via a wireless signal;
• a receiver installed on a vehicle body to receive the wireless signal;
• a rotational position detection unit installed on the vehicle body to detect the rotational position of each wheel when a specific identification information has been transmitted;
• a wheel position determination unit that acquires the rotational position of each wheel a plurality of times to accumulate rotational position data for each wheel and determines a wheel position corresponding to the rotational position data with a least dispersion degree among the rotational position data as the wheel position of the transmitter corresponding to the specific identification information;
• and
• a detection inhibition unit that inhibits detection of the rotational position of each wheel by the rotational position detection unit when a braking control to control a wheel cylinder pressure of the wheel is being executed, wherein
• the wheel position determination unit is configured to convert the rotational position of the wheel to a vector on a two dimensional plane with its origin as a starting point and the circumferential point of a unit circle as an ending point, calculate a scalar quantity of an average vector of each rotational position data as a dispersion characteristic value and determine a maximum value of each dispersion characteristic value as that with a least dispersion degree.