Detailed explanation of the Construction Principle and Maintenance of TPMS (Two)

At present, there are two main solutions for tire pressure monitoring system (TPMS), direct system and indirect system.

 

The direct tire pressure monitoring system uses the tire pressure sensor installed in each tire to directly measure the tire air pressure, and displays and monitors the tire air pressure. When the tire air pressure is too low or there is leakage, the system will automatically alarm.

 

The indirect tire pressure monitoring system uses the wheel speed sensor of the automobile ABS to compare the speed difference between the tires to monitor the tire pressure.

 

The structure and principle of Volkswagen's indirect tire pressure monitoring system

 

The tire pressure monitoring system installed on the domestic Volkswagen car system uses the wheel speed signal provided by the wheel speed sensor to estimate the change in the dynamic radius of the tire, and then converts it into the change in tire pressure to achieve the function of tire pressure monitoring.

 

This type of pressure monitoring system is an economical device for indirect measurement of tire pressure. There are no hardware changes except for the addition of buttons and wiring harnesses. The system uses the wheel speed signal to estimate the dynamic radius of the tire, which depends on changes in many parameters, such as vehicle speed, load, tire inflation pressure, and tire slip due to acceleration, braking, and lateral forces. In addition, the key impact is the tire characteristics, such as tire size, corner stiffness, tire structure and other parameters caused by changes in tire dynamic radius, the system regards it as interference. The system must estimate the change of tire pressure through self-learning by referring to the above parameters, and at the same time, it must also filter the interference signal to achieve accurate and timely tire pressure monitoring and alarm.

 

In order to make the system work properly, the following operations must be completed:

 

1. Set the theoretical tire pressure. The user needs to adjust the four tire pressures to the rated value in advance, and then activate the system self-learning to obtain the theoretical tire pressure by pressing the reset button in the car or the function menu in the instrument.

 

2. System self-learning. The self-learning process is best carried out on a straight road, through the self-learning system to obtain the necessary reference value, and then automatically enter the tire pressure monitoring state.

 

3. Tire pressure alarm. After the self-learning is completed, if a tire pressure is low (low tire pressure sensor), the system will remind the driver to run flat by the warning light and warning sound on the instrument.

 

The tire pressure monitoring system will only recognize the tire pressure loss when the tire dynamic radius change value reaches 0.22%. That is, when the tire pressure drops to 70% to 75% of the initial tire pressure, an alarm is issued (at this time, the tire pressure loss is 0.4 to 0.5×105 Pa), and the system will remind the driver to check the tire pressure through the warning light on the meter. Sometimes due to some interference, the system may not alarm at a given threshold value of tire pressure loss. At this time, as long as the tire pressure continues to decrease by about 0.2×105 Pa, the wireless tire pressure monitoring system will soon alarm.

 

Under normal circumstances, when the vehicle travels 2~3km, the system can recognize the loss of tire pressure and alarm. The recognition process of tire pressure loss has a great relationship with the road surface condition, driving style and driving conditions. The driving style of the car, frequent braking, steering, bumps, and soft roads will greatly increase the time and mileage of tire pressure loss recognition. In addition, the recognition process of tire pressure loss is closely related to the state of self-learning. The shorter the self-learning time is, the longer the time to identify the tire pressure loss is, and even the tire pressure loss cannot be identified in the limit state.

 

The tire pressure monitor sensor is installed on the four wheels of the car, which can directly sense the tire pressure and also monitor the tire temperature. This method is much more advanced and sensitive. In general, the tire sensor cost is relatively low, and it is more convenient to replace the tire sensor when a problem occurs.