TPMS is the eternal theme of automobiles[Copy link]
New requirements for IC integration and reliability
Since most car tires are now vacuum radial tires without inner tubes, it is very convenient and easy to install the remote tire pressure monitoring module of TPMS on the wheel hub. However, the environment and temperature inside the tire are very bad when the car is running at high speed, and the pressure, temperature and humidity change greatly. Therefore, the design of this module must select components according to the requirements of military products and formulate production processes according to the requirements of industrial products. As a large-scale and wide-ranging general automotive safety product, it must also be priced according to consumer electronic products.
Smart sensors suitable for TPMS
The remote tire pressure monitoring module consists of five parts: (1) smart sensor SOC with pressure, temperature, acceleration, voltage detection and post-signal processing ASIC chip combination; (2) 4-bit to 8-bit single-chip microcomputer (MCU); (3) RF radio frequency transmission chip; (4) lithium-ion battery; (5) antenna. The shell is made of high-strength ABS plastic. All components and materials must meet the operating temperature range of -40℃ to + 125℃. Smart sensor is a pressure sensor, temperature sensor, accelerometer, battery voltage detection, internal clock and a digital signal processing ASIC unit including analog-to-digital converter (ADC), sampling/holding (S/H), SPI port, calibration (Cali -bration), data management (Data), and ID code made by integrating silicon micromachining (MEMS) technology. The module has mask programmability, that is, it can be configured using customer-specific software. It is composed of two chips, MEMS sensor and ASIC circuit, made in one package using integrated circuit technology . There is a pressure/temperature introduction hole on the top of the package to directly introduce the pressure into the stress film of the pressure sensor. The inner wall of the circular stress film fixed around the periphery is composed of a semiconductor strain gauge to form a Wheatstone measurement bridge. At the same time, this hole also directly introduces the ambient temperature into the semiconductor temperature sensor. In order to facilitate the identification of the TPMS receiver, each pressure sensor has a unique 16-bit to 32-bit ID code. The smart sensors suitable for TPMS mainly include silicon integrated capacitive pressure sensors, such as Freescale 's MPXY8020, MPXY8040 and silicon piezoresistive pressure sensors, such as GE NovaSensor 's NPX1, NPX2, Infineon SensoNor's SP12, SP12T, SP30. Silicon piezoresistive pressure sensors use high-precision semiconductor resistance strain gauges to form a Wheatstone bridge as a force-to-electricity conversion measurement circuit, with high measurement accuracy and low power consumption. The NPX and SP12 series of smart sensors both include accelerometers. The accelerometer uses the sensitivity of its mass block to motion to achieve instant startup of the car when it moves, enter the system self-check , and automatically wake up. When the car is driving at high speed, it automatically and intelligently determines the detection time cycle according to the movement speed, and uses software to set the safe period, sensitive period, and dangerous period to gradually shorten the patrol detection cycle and improve the early warning capability, saving energy. NPX2 also encapsulates an 8-bit MCU in the smart sensor. Power management is the key. With the market demand for high IC integration and high reliability of TPMS products, there are smart sensor modules such as GE NPX2 that combine the sensors and MCUs required to test various physical quantities. In the next few years, we will develop modules that include three-in-one RF transmitter chips and four-in-one modules that use mechanical energy to power themselves. By then, the remote tire pressure monitoring module will only have one module and one antenna, and the customer's secondary design will become very simple. The operating frequency of TPMS is 315MHz in North America, 433.92MHz in Europe, and 448MHz in Korea. Some people have suggested that the new standard be 868MHz. Its transmission power cannot exceed 10dBm, otherwise it will be subject to radio control. The operating modes include ASK (amplitude shift modulation) and FSK (frequency shift modulation). FSK has better anti-interference. Therefore, the requirements for the selection of RF chips are: (1) the transmission power is as large as possible; (2) the chip size is as small as possible; (3) it has a relatively good performance-price ratio. The nominal transmission power of ATMEL's T5754 and Infineon's TDK5110 is 10dBm. Lithium-ion batteries are used as batteries to ensure that the remote tire pressure monitoring module can work normally in high and low temperature environments. Traditional lithium batteries lose power at low temperatures of -40℃ and automatically discharge at high temperatures of +100℃. TADIRAN LTH2450 lithium-ion batteries can meet the requirements of TPMS in a wide temperature range. Antennas are the key to improving the transmission power of remote tire pressure monitoring modules. Antenna technology involves many factors such as the antenna's geometry, materials, and media. The overall power management of the remote tire pressure monitoring module is very important. A lithium-ion battery should provide the module with 3-5 years of working energy. Good power management and how to save power are the key. There are two ways to install the transmitter module in the car tire. One is to use the valve nozzle to install it, which is currently the most used; the other is to use a clamp buckle to install it on the wheel hub. This is the earliest method , but it will shift after vibration. No matter which method is used, the tire must be re-balanced after installing the TPMS transmitter module . The central monitor, i.e., the TPMS receiver, is mainly composed of a UHFASK/FSK RF receiving IC, a signal processing MCU, a keyboard, and an LCD display. The RF receiving IC and the signal processing MCU are installed in a box that can be installed in the car instrument box. The LCD display with a control keyboard can be installed on the dashboard. The LCD display can display the pressure, temperature, and ID code of each tire in real time, as well as sound and light alarms. Since the receiving system works in the car compartment, the ambient temperature is normal and does not change much, and the power supply can use the car's 12V or 24V power supply. Therefore, the device selection only needs to be industrial grade, and the power saving requirements are not high. When selecting an RF receiving IC, it is generally necessary to consider a higher receiving sensitivity to improve the TPMS.
To improve work efficiency and reduce the production cost of the entire system, the nominal sensitivity of ATMEL's T5743 and Infineon's TDK5210 are both above -100dBm.
Developing towards high integration
The automobile tire pressure monitoring system is a life safety warning system for drivers and passengers . In the field of automotive electronics, TPMS is an eternal theme. The TPMS transmitter module will develop towards high integration, singularization, and wireless passivity. Michelin Group and Goodyear Tire & Rubber Company bury pressure, temperature monitoring and signal transmission devices in the tire sidewalls. These devices play a role during the entire life of the tire (generally 1 to 7 years). Goodyear Tire & Rubber Company of the United States is one of them, using RFID technology as the basis for the development of smart tires . The company cooperated with Siemens VDO Auto Parts Company and successfully developed a sensor with an RFID card the size of a button battery. In addition to being able to sense changes in tire pressure and tire body temperature and transmit signals reflecting such changes, the sensor also has the function of identifying the tire, that is, it can be used for tire history traceability recording. Shanghai Jiaotong University is also developing and researching TPMS. The SAW sensor they launched can simultaneously measure tire pressure, temperature and transmit data, which not only realizes passive measurement and wireless transmission of intelligent tire information, but also has Chinese independent intellectual property rights. Manufacturing is turning to China China is becoming the world's largest automobile market. China's automobile demand and ownership have shown an accelerating growth trend. The number of cars owned has exceeded 26 million. In the next five years, China will become the world's second largest automobile sales country after the United States. Automobile safety products will become a market hotspot, and the annual growth rate in the future can reach 50%. Among them, the market capacity of TPMS technology products alone will reach 200,000 sets by the end of 2005, nearly 700 million yuan; in 2006, it will reach 500,000 sets, nearly 1.7 billion yuan. The United States and Europe have successively enacted laws to require that all cars be equipped with TPMS in the next few years. Therefore, the demand for TPMS is increasing day by day. In the face of large-volume products, the production cost needs to be reduced , and the production of TPMS is turning to China. In the next few years, China will surely become a major producer of TPMS. At present, hundreds of design companies and manufacturers in China have begun to develop, design and produce TPMS. The United States accelerates the development of TPMS . According to a recent survey by the American Society of Automotive Engineers, 260,000 traffic accidents in the United States are caused by low tire pressure or leakage each year. In addition, 75% of tire failures each year are caused by tire leakage or insufficient inflation. Due to the huge economic losses caused each year, the US government requires automakers to accelerate the development of TPMS systems in order to reduce the occurrence of tire accidents. Therefore , in 2000, the US Congress passed the TREAD Act. One of the requirements of the TREAD Act is that by 2007, all cars sold in the United States must be equipped with tire pressure monitoring systems. The National Highway Traffic Safety Administration (NTHTSA) requires that by 2007, all cars sold in the United States must be equipped with tire pressure monitoring systems, and has proposed a timetable for car manufacturers to implement: 10% of cars sold in the U.S. market in 2004, 35% in 2005, 65% in 2006, and 100% in 2007. Related links The meaning of TPMS TPMS is the abbreviation of "Tire Pressure Monitoring System" , which is mainly used to automatically monitor the tire pressure in real time when the car is driving , and to alarm for tire leakage and low pressure to ensure driving safety. The TPMS system is a life safety early warning system for drivers and passengers.
Main types of TPMS
At present, TPMS is mainly divided into two types: one is indirect TPMS, which compares the speed difference between tires through the wheel speed sensor of the car ABS to achieve the purpose of monitoring tire pressure . Its disadvantage is that it cannot judge the situation of two or more tires being deflated at the same time and the speed exceeding 100 kilometers per hour. The other is direct TPMS, which uses a pressure sensor with lithium-ion battery as power source installed in each tire to directly measure the tire pressure and transmit it to the monitor installed on the driving platform through radio frequency modulation. The monitor displays the tire pressure and temperature at any time, and the driver can intuitively understand the pressure status of each tire. When the tire pressure is too low, leaking, too high, or the temperature is too high, the system will automatically alarm. Direct TPMS is superior to indirect TPMS in terms of function and performance. Many European car manufacturers have installed direct TPMS in their own models. Most domestic car manufacturers have begun to conduct research in this area.
Composition of TPMS system
The TPMS system mainly consists of two parts: the remote tire pressure monitoring module (Remote Tire Pressure Monitoring) installed in the car tire and the central monitor (LCD display) installed on the car's dashboard. The tire pressure and temperature measurement module is directly installed in each tire, and the measured signal is modulated and transmitted through high-frequency radio waves (RF). A TPMS system has 4 or 5 (including spare tire) RTPM modules. The central monitor receives the signal transmitted by the RTPM module and displays the pressure and temperature data of each tire on the screen for the driver's reference. If the tire pressure or temperature is abnormal , the central monitor will send different alarm signals according to the abnormal situation to remind the driver to take necessary measures.
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