Under the cyclic load, the hysteresis loss of the rubber and the skeleton material and the friction between the rubber and the skeleton material cause the heat generation, and the mechanical properties and fatigue resistance of the material used for the tire are closely related to the temperature. Excessive temperature can lead to serious degradation of tire material performance, prompting rapid tire damage. The main quality problems of the current tires, such as "shoulder space" and "bead delamination", are caused by excessive temperature in these parts. of. Experts and scholars at home and abroad are vigorously developing smart tires to control or reduce the heat generation of tires to extend the service life of tires. In the high temperature region of tire temperature field, temperature sensors are embedded to grasp the real-time situation of tire temperature rise, so as to guide drivers to drive safely. It is an important means.
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Conception of tire temperature on-line detection device
In various modern smart tires capable of detecting such as temperature, pressure and speed, relevant sensors are installed to input detection signals concerning tire temperature, pressure and vehicle speed to an electronic control unit (ECU) for technical processing [1]. .
Figure 1: Schematic diagram of the overall design of a traditional temperature measurement unit.
For on-line detection of the internal temperature of the tire, the conventional temperature measuring unit can be designed in the manner shown in Figure 1, and the detection signal of the sensor is transmitted through the multi-way switch controlled by the CPU. Although the device can complete the corresponding temperature detection, the circuit has more complicated links, 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. Based on the reference of foreign new smart tire technology, the author carried out the research on "automobile tire safety performance intelligent detection and hidden danger early warning system" and constructed the overall framework shown in Figure 2.
Figure 2: Overall block diagram of the tire intelligent detection and stability warning system.
The specific functions of the system are as follows:
Online detection of temperature and pressure fluctuations during tire travel by an array of temperature and pressure sensors embedded inside the tire;
Information fusion and intelligent analysis of the real-time detection results of tire temperature and air pressure by the sub-machine system of the device on the hub;
The analysis result is transmitted from the slave to the host system of the device on the cab dashboard by wireless communication;
Through the host system to determine whether the tire is overheated, overpressure or underpressure and its specific grade, give a tire safety performance evaluation, and determine whether to issue tire overheat, overvoltage or undervoltage alarm;
By comparing with the recommended value of the tire temperature and pressure safe use conditions [2], the driver should be reminded of the precautions and measures to be taken when the tire is overheated, overpressured or under pressured.
Technical design of tire temperature on-line detection device
The author uses the finite element analysis method of tire force based on the theory of composite mechanics [3] to analyze and calculate the temperature field of the tire, and obtain the isotherm profile of the tire carcass shown in Figure 3. Take the 165SR 15 radial car tire produced by Zhengtai Rubber Factory as an example).
Figure 3: Temperature field isotherm distribution (°C).
It can be seen from Fig. 3 that the H1, H2 and H3 dot fields are the locations of the high temperature zones inside the tires. These locations are the hidden dangers of safety accidents such as tire puncture. The temperature sensors should be buried in these dot fields. And make it a sensor array to detect and analyze the temperature changes of the tire in real time [4].
In order to overcome the shortcomings of the traditional temperature measurement scheme of Figure 1, the author designed a sub-machine system with PIC microcontroller as the core (ie, the detection and analysis part in Figure 2) according to the overall block diagram. The temperature signal detection circuit is shown in Figure 4.
Figure 4: Schematic diagram of the circuit design of the temperature measurement unit.
In the detection circuit, the basic component for detecting the real-time temperature signal of the tire is the DS1820 digital temperature sensor, which is combined with the PIC microcontroller to form the core of the tire temperature on-line detection device. Because the DS1820 digital temperature sensor converts the detected physical quantities directly into digital quantities and sends them to the PIC microcontroller for real-time processing, it can change the traditional temperature sensing method of automotive tires.
As can be seen from FIG. 4, 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 data communication is performed with the PIC microcontroller through the bus. If the parameters such as the predetermined temperature value are set at the time of system initialization, the whole process monitoring of each high temperature point 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 field of the tire can also be displayed and stored. When the tire temperature exceeds the limit, the temperature limit alarm signal of the corresponding point domain can be given.
In addition, since the single-wire interface of the DS1820 sensor is tri-stated [5], only devices that strictly comply with the 64-bit ROM code provided by the "Car Tire Safety Performance Intelligent Detection and Hazard Warning System" host will respond to the host's operating commands. The remaining inconsistent devices are in a high-impedance wait state. Thus, the PIC microcontroller can either access all of the devices on the single-wire bus or follow up on any given device, which creates the 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 (ie, the control display portion 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 of the tire safe work according to the actual driving conditions and the expert suggestion, and then inputs the host through the system accessory keyboard, and then sends a signal to the LED driving chip via the host. To display its preset temperature. Since the predetermined safe working temperature value of the tire and the actual temperature detection value of the driving are displayed on the dashboard of the cab through the LED, the driver can have a clear understanding of whether the tire temperature exceeds the limit, and the driver can conveniently and flexibly follow the actual situation. deal with.
Temperature sensor installation discussion The H1, H2 and H3 dot fields in Figure 3 are the high temperature areas of the tire during driving. In order to detect the temperature rise of the tire on-line, the device embeds a DS1820 digital temperature sensor in the above-mentioned dot fields to make it a test. Temperature array. The sensor has excellent performance, its commercial application level sensor temperature range is 0 ~ 70 ° C, industrial application level sensor temperature range is 0 ~ 100 ° C, and automotive-specific sensor temperature range is -55 ~ + 125 ° C, fully satisfied The temperature measurement work requirements of this device.
In addition, the DS1820 sensor is small in size and well-structured. The package strength can meet the practical needs. The package size is only 5mm × 5mm, and the diameter of the connecting wire is not more than 1mm. It is enough to be embedded in the surface of the tire body without affecting the performance of the tire itself. In the prefabricated blind holes (corresponding to the H1, H2 and H3 dot fields), when the tire casing and the inner tube are sufficiently close to each other due to the air pressure, the temperature sensor can effectively detect the heat generation condition of the tire under running conditions, and pass the sub-machine The microcontroller fuses the measured temperature signal and transmits it to the host through the wireless signal transmitting circuit of the slave, and the host performs final processing.
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