Apparatus, method, and program for detecting decrease in tire air pressure

A method for detecting a decrease in an air pressure of a tire attached to a vehicle, comprising:

• a rotation speed detection step of periodically detecting rotation speeds of tires of the respective wheels of the vehicle;
• an acceleration calculation step of calculating, based on rotation speed information obtained in the rotation speed detection step, accelerations of the respective tires;
• an acceleration variation calculation step of calculating, based on accelerations of the respective tires calculated in the acceleration calculation step, acceleration variations of the respective tires;
• a comparison step of comparing acceleration variations of the respective tires calculated in the acceleration variation calculation step;
• a presumption step of presuming, when a comparison result by the comparison step shows that an acceleration variation of a tire is larger than acceleration variations of the other tires, a pressure decrease of the tire;
• an examination step of identifying, based on the tire rotation speed information of the respective wheels, a tire having a rotation speed that is higher than the rotation speeds of the other tires or that is lower than a predetermined criterion;
• and
• a determination step of determining, when a tire identified in the estimation step is identical with a tire identified in the examination step, a pressure decrease of the tire,
• wherein the predetermined criterion defines a degree at which, when four tires have a normal internal pressure and when one of the four tires is fitted with a snow chain, the tire has a lower rotation speed than the rotation speeds of the other tires,
• the examination step further identifies, based on the tire rotation speed information of the respective wheels, a tire having a rotation speed lower than the rotation speeds of the other tires, and
• the determination step determines that a tire has a decreased air pressure when the tire identified in the presumption step is identical with the slowest tire identified in the examination step and when the slowest tire is positioned at a driven wheel.

A program which causes, in order to detect a decrease in an air pressure of a tire attached to a vehicle, a computer to function as:

• an acceleration calculation means for calculating, based on rotation speed information obtained from a rotation speed detection means for periodically detecting rotation speeds of tires of the respective wheels of the vehicle, 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;
• a presumption means for presuming, when a comparison result by the comparison means shows that an acceleration variation of a tire is larger than acceleration variations of the other tires, a pressure decrease of the tire;
• an examination means for identifying, based on the tire rotation speed information of the respective wheels, a tire having a rotation speed that is higher than the rotation speeds of the other tires or that is lower than a predetermined criterion;
• and
• a determination means for determining, when a tire identified by the presumption means is identical with a tire identified by the examination means, a pressure decrease of the tire,
• wherein the predetermined criterion defines a degree at which, when four tires have a normal internal pressure and one of the four tires is fitted with a snow chain, the tire has a lower rotation speed than the rotation speeds of the other tires,
• the examination means is further configured to identify, based on the tire rotation speed information of the respective wheels, a tire having a rotation speed lower than the rotation speeds of the other tires, and
• the determination means is configured to determine that a tire has a decreased air pressure when the tire identified by the presumption means is identical with the slowest tire identified by the examination means and when the slowest tire is positioned at a driven wheel.