Under the periodic load of automobile tires, the hysteresis loss of the rubber and the frame material and the friction between the rubber and the frame material will cause heat generation, and the mechanical properties and fatigue resistance of the materials used in the tire are closely related to the temperature. Excessively high temperature will cause serious degradation of the tire material performance and prompt rapid damage to the tire. The current main quality problems of the tire, such as "shoulder air" and "bead delamination", are due to the excessive temperature of these parts. of. Experts and scholars at home and abroad are vigorously developing smart tires to control or reduce the heat of the tires to extend the life of the tires. Among them, temperature sensors are buried in the high temperature area of ​​the tire temperature field to grasp the real-time situation of tire temperature rise, so as to guide the driver to drive safely Is an important means.
Conception of the tire temperature online detection device
Various modern smart tires capable of detecting such as temperature, pressure and speed are equipped with relevant sensors, and input detection signals related to tire temperature, pressure and vehicle speed to the electronic control unit (ECU) for technical processing [1] .
Figure 1: Schematic diagram of the overall design of a traditional temperature measurement unit.
For the on-line detection of the internal temperature of the tire, the traditional temperature measurement unit can be designed in the manner shown in FIG. 1, and the detection signal of the sensor is transmitted through the multiple switch controlled by the CPU. Although the device can complete the corresponding temperature detection, the circuit is more complicated, the structural system is more complicated, the programming is more troublesome, and the debugging work is more difficult, so it is not an ideal design plan. On the basis of referring to the new foreign smart tire technology, the author conducted a study on "intelligent detection of automobile tire safety performance and warning system for hidden dangers", and constructed the overall framework shown in Figure 2.
Figure 2: The overall block diagram of the tire intelligent detection and early warning system.
The specific functions of the system are as follows:
Through the temperature and air pressure sensor array embedded in the tire, online detection of temperature and air pressure fluctuations when the tire is running;
Information fusion and intelligent analysis of real-time detection results of tire temperature and air pressure through the sub-machine system installed on the wheel hub;
Transmit the analysis results from the slave to the host system installed on the dashboard of the cab through wireless communication;
Through the host system to determine whether the tire is overheated, overpressured or underpressured and its specific grade, give an assessment of the tire safety performance status, and determine whether to issue a tire overheated, overpressured or underpressure alarm;
By comparing with the recommended values ​​for safe use conditions of tire temperature and pressure [2], the driver is reminded of the precautions and measures to be taken when the tire has overheating, overpressure or underpressure.
Technical design of tire temperature online detection device
The author uses the tire force finite element analysis method [3] based on the composite material mechanics theory to analyze and calculate the tire temperature field, and obtain the isotherm distribution diagram of the tire carcass cross section shown in Figure 3 (in Shanghai 165SR 15 radial car tires produced by Zhengtai Rubber Factory as an example).
Figure 3: Temperature field isotherm distribution diagram (℃).
As can be seen from Figure 3, the dot areas of H1, H 2 and H3 are the locations of high temperature areas inside the tires. These positions are the hidden sources of safety accidents that cause tire "flat tires". Temperature sensors should be buried in these dot areas. And make it form a sensor array to detect and analyze the change of tire temperature online [4].
In order to overcome the shortcomings of the traditional temperature measurement scheme in Figure 1, the author designs a slave system with the PIC microcontroller as the core based on the overall block diagram (that is, the detection and analysis part in Figure 2). The temperature signal detection circuit is shown in Figure 4.
Figure 4: Schematic diagram of the circuit design of the temperature measurement unit.
In this detection circuit, the basic element for detecting the real-time temperature signal of the tire is the DS1820 digital temperature sensor, which is organically combined with the PIC microcontroller to form the core of the on-line tire temperature detection device. Because the DS1820 digital temperature sensor can directly convert the detected physical quantity into a digital quantity and send it to the PIC microcontroller for related real-time processing, it can change the traditional temperature detection method of automobile tires.
It can be seen from FIG. 4 that the system has a detection network in the form of a single bus, that is, all temperature sensors are connected to the same data communication bus of the PIC microcontroller and perform data communication with the PIC microcontroller through the bus. If the parameters such as the predetermined temperature value are set during system initialization, the entire monitoring of each high-temperature point domain of the tire can be implemented. At the same time, with the support of the corresponding software and hardware, the real-time temperature value of each high-temperature point domain of the tire can also be displayed and stored. When the temperature of the tire exceeds the limit, the temperature limit alarm signal of the corresponding point domain can be given. In addition, because the single-wire interface of the DS1820 sensor is tri-stated [5], only devices that strictly conform to the 64-bit ROM code provided by the "Automotive Tire Safety Performance Intelligent Detection and Hazard Warning System" host will respond to the host's operating commands, The remaining devices that do not match are in a high-impedance wait state. Therefore, the PIC microcontroller can not only visit all the devices on the single-wire bus, but also follow up any specified device, which creates conditions for the system to read the real-time temperature signal of the tire on demand.
In order to match the operating characteristics of the slave system, the working block diagram of the host system (that is, the control display part in FIG. 2) can be designed as shown in FIG. 
Figure 5: Working block diagram of the host system.
It can be seen from FIG. 5 that after the host system is started, the user first sets the predetermined temperature value for the safe operation of the tire according to the actual driving conditions and the recommendations of experts, then enters the host through the system ’s attached keyboard, and then sends the signal to the LED driver chip through the host To display its preset temperature. Because the predetermined safe working temperature value of the tire and the actual driving temperature detection value are displayed on the cab instrument panel through LED, the driver can clearly understand whether the tire temperature is beyond the limit, and the driver can conveniently and flexibly make follow-up according to the actual situation deal with.
Discussion on temperature sensor installation The H1, H2, and H3 point domains in Figure 3 are the high temperature areas of the tire during driving. To detect the temperature rise of the tire online, this device embeds a DS1820 digital temperature sensor in each of the above point domains to make it measure Temperature array. The sensor has excellent performance. The temperature range of its commercial application-level sensor is 0 ～ 70 ℃, the temperature range of its industrial application-level sensor is 0 ～ 100 ℃, and the temperature range of its automotive-grade sensor is -55 ～ + 125 ℃, which is fully satisfied. Requirements for temperature measurement of this device.
In addition, the DS1820 sensor is small in size and excellent in structure, and its packaging strength can meet practical needs. Its packaging size is only 5mm × 5mm, and the diameter of the connecting wire does not exceed 1mm. In the prefabricated blind holes (corresponding to the H1, H2 and H3 dot domains), when the outer tire and the inner tire are fully in contact due to air pressure, the temperature sensor can effectively detect the heat generation of the tire in the running state and pass the sub machine The microcontroller performs fusion processing on the measured temperature signal, and then transmits it to the host computer through the wireless signal transmission circuit of the slave machine, and the host computer performs the final processing.
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