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The basis for the high accuracy of STPMS
The critical challenge encountered by the STPMS algorithm in the development process is the problem of thermal expansion of tires when running. If the thermal expansion value of the tire cannot be accurately calculated, STPMS will not be able to accurately calculate the under-pressure value of the tire, and thus the tire cannot be made correctly. Pressure alarms may even cause false alarms.
After our research on this issue, we developed an original method using GNSS data,Thermal Tire Model Algorithm, can accurately calculate the expansion value of the tire due to the heat generated by running, and solve the problem of being unable to accurately issue an under-pressure alarm due to the thermal expansion of the tire due to running.
To know the importance of the hot tire model, just look at the following actual data: when the car reaches the hot tire equilibrium while walking at a speed of about 60 kilometers per hour, the expansion value produced is about 2% of the wheel diameter, and Tire deflation and underpressure 20% only reduces the wheel diameter by about two thousandths, a difference of ten times. To accurately calculate the tire underpressure value, an accurate hot tire model is required.
Key Factors in Hot Tire Models
- As the car tires travel, they expand due to heat generated by friction with the road surface.
- Braking while the vehicle is moving will also increase friction with the road surface and generate heat, causing thermal expansion. This is the conversion of kinetic energy into thermal energy.
- If the vehicle fails to accelerate according to the acceleration of gravity when driving downhill, the friction with the road surface will increase and generate heat, causing thermal expansion. This is the conversion of potential energy into thermal energy.
- When the tire temperature rises due to hot tires and is higher than the ambient temperature, heat will be dissipated through the wheel frame and the air.
- Based on the above factors of hot tire operation, a mathematical operation model is established to describe the above hot tire situation, which is the hot tire model.
Thermal tire model operation flow chart
The left side is the operation process, and the right side is the description of each step. where time is represented by T0Start, the time till now is Tc, each time period is Ti, each time interval is DT, and the current time is t. In each period of time, the net heat HAN of the tire at that time is obtained, and then the travel distance shortening correction amount DCT of the tire is calculated from the net heat, where αxxSpecify the expansion coefficient for the tire, βxxSpecify the inverse specific heat for the tire, AS is the accumulated system net thermal heat, and DTF is the constant coefficient that converts the increase in the tire outer diameter into the shortening of the travel distance.