Design of TPMS system based on intelligent sensor MPXY8320A

1 Development History and Trends of TPMS System

1.1 Development History of TPMS System

In the international market, in 1997, General Motors began to use the indirect tire pressure monitoring system TPMS (Tire Pressure Monitoring System); in May 2000, direct TPMS was launched in the United States; the world's new car data released in 2002 showed that Ford's Lincoln Continental, Daimler-Chrysler's Dodge minivan and Chrysler 300M series models launched this summer will all be equipped with direct TPMS. Many European car manufacturers have also equipped their mid-to-high-end models with direct TPMS, including BMW's Z8, Opel's 2002 Vita, Citroen's C5, Aston Martin's super sports car Vanquish, Pontiac's flagship Bonneville SE, etc. Domestic automobile manufacturing giants have also begun to consider TPMS as a standard configuration of original equipment. In May 2003, Japan's ALPS Electric Company obtained the TPMS technology that does not use batteries from Germany's IQMobil GmbH and signed an exclusive patent licensing contract. The TPMS developed with this technology has passed the European and American radio wave certification tests, and industrial samples were provided in June 2004, and mass production began in 2005. my country also started the production of TPMS by introducing technology around 2000.

1.2 Development Trend

Direct TPMS and indirect TPMS each have their own advantages and disadvantages. Direct TPMS can measure the current pressure inside each tire at any time, and it is easy to identify the faulty tire. Indirect TPMS is relatively cheap. Using the indirect system, cars that are already equipped with 4-wheel ABS (each tire is equipped with 1 wheel speed sensor) only need to upgrade the software; however, at present, such systems are not as accurate as direct systems and cannot detect the situation where multiple tires are under-pressure or over-pressure at the same time. Obviously, direct TPMS is more effective. Therefore, direct TPMS is gradually replacing indirect TPMS and becoming the mainstream of tire pressure monitoring systems. However, active MEMS TPMS sensors/transmitters require batteries to provide power, which inevitably brings some disadvantages, such as limited battery life and the presence of batteries makes it difficult to reduce the weight of the transmitter. In the long run, passive MEMS TPMS will become the trend of future TPMS development with its incomparable advantages.

2 Passivation

If the in-tire module can be made passive (i.e. without battery), the above problems can be solved. To achieve the above goals, the following mainly describes several implementation solutions for the development of wireless passive TPMS:

① The module inside the tire has a power generation device that converts the mechanical energy of the tire into electrical energy. This is a piezoelectric power generation solution.

② Energy is transmitted from the outside of the tire through the electromagnetic field to drive the module inside the tire to work and transmit pressure information. This is a magnetic field electromagnetic coupling solution.

③ Electromagnetic waves are emitted from the outside of the tire, and then reflected after hitting the built-in components of the tire module, while carrying back pressure information. This is a surface acoustic wave passive wireless sensor solution.

3 External coding memory tire positioning

The external coding memory tire positioning technology is a new type of TPMS tire positioning technology. The TPMS using the external coding memory is also composed of a transmitting detection module and a receiving display module. The receiving display module is connected to a plug-in coding memory, and each transmitting detection module has a fixed ID code that is consistent with the ID code of the corresponding coding memory. When the tire is replaced or replaced, it is only necessary to replace or replace the plug-in coding memory. The external coding memory tire positioning technology converts the problem of re-identification into the problem of ID code transposition setting by adjusting the corresponding relationship between the ID code in the display module coding memory and the ID code in each transmitting detection module. It is a simple and effective solution. The plug-in operation mode is simple and reliable. The code in the plug-in coding memory circuit is read through I/O, which avoids the use of wireless reading of ID code, and fundamentally solves the problem of interference. The implementation principle is shown in Figure 1.

When the system is working, the central receiving and processing module first reads the ID code in the external coding memory in turn, and then resets the ID code stored in the memory of the receiving display module and the corresponding positioning relationship information of the tire, and saves it. Once the central module receives the information transmitted by the tire detection module, it will immediately decode the received information. After obtaining the ID code, it can be determined from which tire the transmitting detection module is based on the previously set ID corresponding positioning relationship information, and perform corresponding display and other actions. The design of the external coding memory can be divided into two parts: the interface circuit and the ID memory: the interface circuit is the connection interface between the external memory and the main controller. According to the application environment of the car, the reliability and shock resistance of the interface should be considered; the memory can be in the form of a shift memory (simple, requiring fewer I/O ports of the main controller, and a slightly slower reading speed), a matrix memory (fast reading speed, occupying more I/O ports of the main controller) or a SIM card and IC card (high reliability, small size, and high cost). Considering all factors, this system uses a shift memory. The workflow is: whenever a new tire is installed or the tire is replaced, immediately switch to the ID reading operation interface, plug the corresponding external coding memory into the reading interface, read the ID and assign it to the tire position. After reading, the external memory (card) can be removed.

4 TPMS system

4.1 Basic principles

The detection module installed inside the tire measures the pressure and temperature inside the tire in real time, and sends the pressure and temperature signals wirelessly. The main control module installed in the cab receives the wireless signal, processes the data, and then displays the measurement results on the display device, realizing real-time monitoring of the tire condition during driving. The basic structure of TPMS is shown in Figure 2.

4.2 Hardware Design

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The main controller circuit principle is shown in Figure 3. The main controller module uses a stable and reliable microcontroller C8051F531A, which has a built-in oscillation circuit and an enhanced SPI interface, an external SPI wireless receiving chip MC33594 and a parallel LCD module that is simple and convenient to operate.

The detection module consists of a highly integrated chip MPXY8320A microcontroller and a power supply for tire pressure measurement. The circuit principle of the detection module is shown in Figure 4. MPXY8320A works at DC 2.1~3.6 V and has low power consumption to extend battery life. The biggest feature of MPXY8320A is that it integrates an 8-bit MCU, a pressure sensor for heavy-duty tires, a temperature sensor, a power supply voltage monitoring, an acceleration sensor on the XZ axis, and an RF transmission module. Therefore, MPXY8320A is a highly integrated chip designed for tire pressure measurement of vehicles. Due to the high integration of the device, it has excellent performance in terms of size, power consumption, and electromagnetic compatibility.

5 Software Design

The program flow of the main software modules is shown in Figure 5.