Patent ID: 8130090

Claim:
An apparatus for detecting a decreased air pressure of a tire attached to a vehicle, comprising: a rotation velocity detection means for periodically detecting rotation velocities of tires of the respective wheels of the vehicle; an acceleration calculation means for calculating, based on rotation velocity information obtained from this rotation velocity detection means, accelerations of the respective tires; an acceleration variation calculation means for calculating, based on the accelerations of the respective tires calculated by the acceleration calculation means, acceleration variations of the respective tires; a comparison means for comparing the acceleration variations of the respective tires calculated by the acceleration variation calculation means; an estimation means for estimating, when a comparison result of the comparison means shows that an acceleration variation of a certain tire is greater than acceleration variations of the other tires, a decrease in air pressure of the certain tire; a test means for determining, based on the tire rotation velocity information of the respective wheels, a tire having a rotation velocity that is faster than the rotation velocities of the other tires or that is further slower than a predetermined reference; and a judgment means for judging, when a certain tire identified by the estimation means is identical with the tire identified by the test means, a decrease in air pressure of the certain tire.