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Product classification and technology of tire pressure monitoring system (TPMS)

Product Classification and technology of tire pressure monitoring system TPMS

1. Tire pressure monitoring system is divided into indirect TPMS and direct TPMS. Indirect TPMS is implemented by modifying the software on the ABS of the vehicle by comparing the rotational speed of the tire (the rotational speed of the deflated tire is faster than that of the normal tire). Indirect TPMS product defects: A, coaxial or more than 2 tires are out of air and cannot be displayed. B. It fails when the speed is above 100km/h

2. The direct type (tire intelligent monitoring system) has four core (bottleneck) technologies:

a, the stability and reliability of wireless signal transmission (especially the signal transmission at high speed)

b, the service life of the sensor (maintenance free use)

c, the accuracy of alarm presentation (no error alarm, false alarm)

d, the pressure resistance of the sensor

3. From the 100 year history of automobile development, Tire blowout has always been a worldwide problem. Intelligent tire monitoring system, as a safety product that can effectively prevent automobile tire burst, is also widely used as a standard safety configuration by automobiles, like airbags and ABS

with the development of highways, the acceleration of automobile speed and the promotion of federal legislation, tire intelligent monitoring system has been paid more and more attention. At present, the intelligent tire monitoring system is not widely used in medium and low-grade vehicles due to price factors. With the application of new technologies, the improvement of mass production and the intensification of competition, the tire intelligent monitoring system will move from aristocracy to ordinary people like computers and

it is necessary to inflate the tire correctly. This problem has aroused great attention. Everyone still remembers that in 2000, American manufacturers took back tires and cars because of a large number of flat tires and rollovers. A large number of data show that correct inflation of tires will greatly reduce the possibility of tire blowout. It is precisely because of this fact that former U.S. President Bill Clinton signed the act on strengthening the recovery, identification and documentation (tread) of transportation equipment that year. On the basis of this act, the National Highway Traffic Safety Administration (NHTSA) regulations of the U.S. Department of transportation (DOT) were soon issued

according to the final regulations published on the NHTSA official station, newly manufactured light vehicles in the United States will be gradually introduced into TPMS from November 2003 to October 31, 2006. In the transition phase of introducing the system, NHTSA approved two standard standby systems. These two backup systems are called direct system and indirect system respectively

direct TPMS: it is required to use pressure sensors in each tire and install wireless transmitters to send pressure information from the inside of the tire to the system on the central receiver module

indirect TPMS: a system that requires the use of the vehicle's anti lock braking system (ABS) to determine changes in tire pressure. ABS determines whether the wheels are locked through the vehicle speed sensor, so as to decide whether to start the anti lock system. For systems equipped with wheel speed sensors on all four wheels, the upgrading of such software can be used to monitor the change of vehicle speed. Low tire pressure will also lead to the change of vehicle speed. When the tire pressure decreases, the weight of the vehicle will make the tire diameter smaller, which in turn will lead to changes in vehicle speed. After correct calculation, this speed change can be used to trigger the alarm system to warn the driver. Each system has its own advantages. The direct system can provide more advanced functions. With the direct system, the actual instantaneous pressure inside each tire can be measured at any time, and it is easy to determine the faulty tire. The indirect system is relatively cheap. Using the indirect system, cars that have been equipped with four-wheel ABS (each tire is equipped with a wheel speed sensor, and the travel is 500-600mm) only need to upgrade the software. However, at present, this kind of system has no direct system with high accuracy. It can not determine the faulty tire at all, and the system calibration is extremely complex. In addition, in some cases, such systems will not work properly: for example, the pressure of two tires on the same axle is low

there is also a composite TPMS, which combines the advantages of each system. The composite system is equipped with direct sensors in two tires that are diagonal to each other and a 4-wheel indirect system. Compared with all direct systems, this composite system can reduce the cost and overcome the disadvantage that the indirect system can not detect multiple tires at the same time with low air pressure. However, it still cannot make a slight difference. It only provides real-time data of the actual pressure in all four tires on the subdivision specification of the products produced. Only the direct system has this function

obviously, the direct sensing system is more effective. Based on such a view, some people may predict that when NHTSA modifies the TPMS regulation in 2005, it will use the direct sensing system to replace all the indirect systems during the transition period. If the situation is true, there will be a huge TPMS hardware market. Another possibility is that NHTSA requires either all direct systems or composite systems to eliminate all indirect systems. Either way, there will be a large direct TPMS market

direct tire pressure monitoring system components

in view of such a large market potential, many companies have stepped up the introduction of direct TPMS solutions. Because NHTSA's requirements are currently only applicable to light vehicles, excluding double rear axle vehicles, there is the most room for the development of passenger cars and light trucks. Such a system consists of four or five tire modules (depending on whether the spare tire is equipped with sensors) and a central receiver module. The tire module is composed of pressure sensor, temperature sensor (PV = NRT), control module (such as ASIC or MCU), transmitter and antenna, and battery. It can also include more external systems, such as low-frequency (LF) detectors that start transmission (so that the module can be used not only as a transmitter, but also as a transceiver), inertia switches, or power supplies without built-in batteries. NHTSA does not require these functions, but they can make the system more perfect. A simple receiver module consists of a central antenna, a receiver IC and an interface connected to the rest of the vehicle. The general interface includes controller area network (can) interface, which is usually equipped in the vehicle body controller. The data is processed by the body controller. When the tire pressure is low, it can be used to warn the driver. Many companies are seeking to provide more functions in the receiver module, as well as functions such as providing automatic tire positioning to each tire in the LF signal startup format (it can detect whether the tire rotates on the premise that the system will recalibrate the upper and lower collets or the upper and lower bearing plates with different axes or different centers), distributed antennas, etc., so as to distinguish themselves from the market. If the correct transmission carrier frequency and communication protocol are used, the receiver system can be integrated with the keyless entry system. The driver can understand various data through a simple indicator integrated into the instrument panel display, a rearview mirror integrated with the display, or a screen separately installed on the instrument panel. As long as the warning that the tire pressure is 25% lower than the normal pressure can be sent to the driver, these systems can meet the requirements of NHTSA for direct TPMS

tpms is imperative to be put into production, but considering the short time before it is put into production, many companies have begun to produce a simple system that can meet the requirements of NHTSA. This market is currently very narrow, but it will develop into a large-scale market in the near future. In order to promote rapid product development, we propose the following direct TPMS system. Although the system is simple and the component cost is low, it meets all the requirements of NHTSA regulations. The simplest system consists of a sensor/transmitter module equipped in four tires and a central receiver

tire module: Hardware

sensor is a capacitive MEMS pressure sensor, which is designed to meet the requirements of TPMS in terms of temperature and media compatibility. This is a single pressure and temperature sensor with power management and digital output functions. The media protection filter in the kit can protect its silicon chip from environmental impact. The system has four operation modes: standby mode (power consumption of 600 Na), measuring air pressure mode, measuring temperature mode and output data reading mode. The device requires the controller to provide at least five pins: two pins are used to control its operation mode, two pins are used for data serial exchange, and the other one is used to receive data. The 8020 also has a reset pin, which acts as an output terminal and sends a reset signal to the controller about every hour. The controller is a device that combines 8-bit flash MCU and UHF Transmitter in a 32-pin QFP package. The single chip microcomputer is connected to the sensor to retrieve the air pressure and temperature data regularly. It is also connected to the transmitter with it, and sends data with 315 or 434MHz according to the different crystal oscillators used

tire module: software

the industry standard adopted by many TPMS suppliers is that the service life of the tire module is years. Because the tire module is powered by a lithium battery (lithium battery capacitance is usually 200 - 300 ma-h), an efficient algorithm is required. The software of TPMS is very simple, with only three main functions: measurement, data processing and transmission. The efficiency of the algorithm is related to time. The system designer must make clear the following questions: does the receiver display the pressure of each tire, or only the low pressure of the alarm? The tire module can check the low pressure threshold, which uses less energy than is required to obtain a complete 8-bit value. What is the measurement frequency of air pressure and temperature? Is it necessary to measure both air pressure and temperature, or is one parameter measured more frequently than the other

is the temperature compensation function required (i.e. changing the low-voltage alarm threshold as a function of temperature)? If necessary, is it deployed at the tire end or at the receiver end? The more times the tire module performs calculations, the shorter the battery life

what is the frequency of data transmission? How many bits are there in each data frame? The transmitter consumes battery power faster than any other part, so often transmitting shorter data frames usually helps to prolong battery life. What happens when the air pressure drops? In order to ensure that the data can reach the receiver in any harsh environment, the tire module should be able to send warning signals for many times. On the basis of answering these standard questions, an intelligent algorithm can avoid data conflicts when multiple tire modules send data at the same time as much as possible. In order to avoid data loss caused by conflict, the module should send multiple data frames in a random time interval between each data frame, rather than one data frame. This will greatly reduce the possibility of data loss, but it will also shorten the service life of the battery and increase the complexity of the receiver software. The ideal compromise is to send data frames every 10 - 100 ms between the two sides. In addition to these standard issues, suppliers also want to provide more functions to distinguish themselves from the market, including automatic detection, lf start, automatic tire positioning including spare parts, battery cancellation and other functions

receiver module: the contribution of hardware

products is immeasurable

the simplest receiver module contains a UHF receiver, a central antenna, and an interface with other parts of the car.

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