Research on tire monitoring system based on wireless transmission mechanism

0 Introduction
Tires are the only parts of a car that come into contact with the road surface. During driving, driving and braking forces are generated between the tire pattern and the ground. The inflated tire has a certain stiffness and hardness, which can be used to carry the weight of the entire vehicle. The inflated tire also has a certain elasticity, which can mitigate the impact from the weight of the vehicle and the uneven road surface, and improve the smoothness and ride comfort of the vehicle. The stiffness, hardness and other properties of the tire are not only related to the material and production process of the tire itself, but are also largely affected by the air pressure and temperature during its working state. Practice has proved that appropriate air pressure and temperature can effectively reduce tire wear, improve tire adhesion, and improve the driving safety of the car.

1 The influence of tire pressure and temperature on car use
When the tire pressure is too low, the elastic hysteresis loss of the tire becomes significantly larger when the car is driving, which will not only increase the driving resistance of the car, but also cause the tread to crack and age prematurely. When the car is driving at high speed, the tire temperature will rise due to the friction between the inside and outside of the tire, and then the tire pressure will rise. In severe cases, a tire blowout may occur, leading to traffic accidents and endangering the safety of life and property. According to statistics, about 30% of traffic accidents are caused by abnormal tire pressure and temperature, and this proportion is even higher on highways.
Practice shows that when the tire inflation pressure is inconsistent with the rated value and the tire temperature exceeds 90°C, the tire wear will be aggravated and the life will be greatly shortened. For example, if the pressure is 0.03 MPa lower than the rated value, the life will be shortened by 25%; if the pressure is 0.06 MPa higher than the rated value, the life will be shortened by more than 15%; when the tire temperature is higher than 95°C and the vehicle is driving at high speed, it may cause a tire blowout. Therefore, it is necessary to monitor the tire pressure and temperature in real time.

2 The significance of tire pressure and temperature monitoring
During driving, it is difficult for drivers to judge the tire pressure and temperature based on their feelings and experience, and it is impossible to stop frequently to use special instruments for testing. Therefore, tire pressure and temperature monitoring has the following significance:
(1) It can monitor tire pressure and temperature in real time, and can detect tire pressure and temperature conditions in time, so that the driver can adjust the driving state of the car as soon as possible, so that the tire pressure and temperature can return to normal as soon as possible, which can effectively prevent tire blowouts and traffic accidents. It belongs to "active" safety protection;
(2) Through monitoring, the car tires can work at standard pressure as much as possible, thereby extending the tire service life and reducing fuel consumption to a certain extent;
(3) It can ensure that the tire pressure is uniform, reduce the occurrence of brake deviation and side slip, and avoid wear of related components such as steering system and suspension system.

3 Types and advantages and disadvantages of foreign tire monitoring systems
The development of foreign tire monitoring systems started earlier and is equipped with more models. Because there is a certain numerical relationship between tire temperature and air pressure, the indicators directly monitored by foreign tire monitoring systems are all air pressure. In summary, they can be divided into three types: direct, indirect and hybrid.
3.1 Direct system The
direct system is to install the pressure sensor directly on each tire. Each pressure sensor transmits the monitored pressure value to the central processing module in the form of an electrical signal through a wireless transmitter. After signal conversion, the position of the tire with abnormal pressure is displayed on the monitoring device in the cab. The advantage of the direct system is that it can monitor the instantaneous air pressure of each tire, and the positioning is accurate and the display is eye-catching, but the structure is more complicated and the sensor is not convenient to install.
3.2 Indirect system
Compared with the direct system, the indirect system has a simple structure and lower cost. It does not directly monitor the tire pressure, but indirectly calculates the tire pressure by analyzing other tire parameters (such as tire vibration or tire rolling radius). If the calculated difference in pressure of each tire exceeds the alarm threshold, the monitor will alarm and show that there is abnormal tire pressure, but it cannot display which tire has abnormal pressure. In addition, if the pressure of more than two tires drops at the same time, the system cannot alarm. In addition, it is greatly affected by the speed of the vehicle. As the speed increases, the monitoring accuracy of the indirect system will also decrease.
3.3 Hybrid system
The hybrid system is a combination of the direct system and the indirect system, taking into account the advantages of both systems. Only two pressure sensors are installed on the four-wheel vehicle, so that the pressure of multiple tires can be monitored at the same time, overcoming the shortcomings of the indirect system; due to the simplified structure, its cost is also low; but it cannot measure the real-time pressure of each tire.

4 Application and characteristics of domestic tire monitoring system
At present, there are no corresponding mandatory regulations requiring the installation of tire monitoring system in the country. Many car owners are not aware of the importance of tire condition monitoring. Installation will incur an additional cost. Therefore, neither private car owners nor transportation business owners will take the initiative to install such systems. Moreover, the system needs to be wired and fixed in the car during installation, which affects the appearance, etc., which also affects the application of tire monitoring system in China to a certain extent.
At present, the models equipped with tire monitoring system include: Audi series, BMW series, Mercedes-Benz series, Citroen CS, Shanghai GM Buick, Lavida 1.6 L Pinxuan version, Lavida 2.0 L Pinxuan version, Roewe 550G1.8 T Pinshi version, etc. These models are equipped with tire pressure monitoring system. Its characteristic is that when a tire on the car has abnormal air pressure,
the display device in the cab will light up a yellow warning light and display "LOWTIRE" or other warning words to remind the driver to take corresponding measures to ensure driving safety. In terms of the composition and working principle of the tire monitoring system installed in these domestic models, the main shortcomings are as follows:
(1) It is not bound to the model, and the standard tire pressure needs to be set manually. In addition, many sensors are required, the system structure is complex, and the installation is cumbersome;
(2) The system operation is greatly affected by the vehicle speed. When the vehicle speed exceeds 30 m/s, the error of the monitored air pressure value is large, and it cannot serve as a safety alarm when the car is driving at high speed;
(3) Original tires must be used. If other tires are used, the system cannot eliminate the impact caused by tire inconsistency;
(4) The voice anti-interference ability is poor, the radio frequency efficiency is not high, and the coding error correction is poor;
(5) When the vehicle is driving in a harsh environment, it is easy to miss reports;
(6) In addition, there are also problems such as short sensor life and poor durability. [page]

5 Design of tire monitoring system based on wireless transmission mechanism Aiming
at the situation of domestic tire monitoring system, based on summarizing the research experience of predecessors, absorbing its advantages, optimizing the design for its shortcomings, and fully considering the influence of automobile tire pressure and temperature on automobile power, fuel economy, handling stability and driving smoothness, the design of the whole system is realized by establishing mathematical models, designing electronic circuits and hardware, and compiling corresponding control software. The design process is shown in Figure 1.

Through the design of the system, the following technical indicators can be achieved:
(1) Wireless data transmission and reception is realized. A 433 MHz RF chip is planned to be used in conjunction with peripheral circuits to form a wireless transceiver module. By modulating and sending the sampled data using FSK, the anti-interference ability of the communication is improved;
(2) Redundant error detection code is written to realize the communication protocol and data error correction, so that it is placed in the data packet together with the synchronization header and data, and the data is redundantly error-checked by continuously sending data packets from the lower computer to the upper computer;
(3) It can automatically identify wheels and tires of different specifications;
(4) The speed range of reliability work is expanded. When the vehicle speed is in the range of 0 to 120 km/h, the tire pressure and temperature can be accurately and reliably monitored, and an alarm can be issued for abnormal conditions.

6 Conclusions
Through a comprehensive analysis of the effects of tire pressure and temperature on the power, fuel economy, handling stability, and driving smoothness of the vehicle, the tire monitoring system is designed using the wireless transmission mechanism. It can provide a reasonable tire inflation pressure and vehicle loading weight according to the actual situation of the specific vehicle, and alarm when a dangerous situation occurs. It has
the characteristics of low power consumption, reliable signal transmission, and low cost.