Patent ID: 8471695

Claim:
A tire air pressure monitoring device for monitoring the air pressure of a tire mounted to a vehicle having two or more tires to be monitored, comprising: an air pressure sensing device that senses air pressure information of the tire and is adapted to be mounted at a prescribed position on the tire so as to rotate with the tire; a transmitting device that transmits the sensed air pressure information of the tire; a rotary position sensing device that senses the rotary position of the air pressure sensing device as the tire rotates; a period of rotation calculating device that calculates the period of rotation of the tire based on the rotary position sensed by the rotary position sensing device; a period of rotation disruption sensing device that senses disruption in the period of rotation based on a change in the period of rotation calculated by the period of rotation calculating device; and a transmission control device that outputs commands to transmit the air pressure information of the tire to the transmitting device based on a disruption in the period of rotation sensed by the period of rotation disruption sensing device.