TPMS external code memory type tire positioning technology design
TPMS technology and tire positioning principle
The automobile tire pressure monitoring system (TPMS) is mainly used to automatically monitor the tire air pressure when the vehicle is running, and to warn the tire leakage caused by low tire pressure and high temperature and high tire pressure explosion to ensure driving safety. Tire positioning in TPMS refers to the process in which the system accepts the signal from the tire launching module and identifies and determines which tire is being used.
Proposal for tire repositioning
Because of the uneven load on the front, rear, left and right wheels, the front wheel responsible for steering, and the front and rear axle suspension angles, the tires usually have different degrees of wear and position. In order to extend the service life of the tire and achieve the simultaneous uniform wear of the four tires, it is necessary to periodically perform tire transposition. During the tire transposition process, the corresponding emission detection module will also be transposed. This results in the ID code and the tire corresponding identification relationship information originally stored in the receiving display module MCU no longer applicable to the tire position after the tire change, that is, the tire pressure and temperature information on the display screen and the corresponding relationship of the tires generate errors. If the new tire is replaced or the emission detection module of a certain tire is damaged, the user needs to replace the module. The ID code of the new module is different from the damaged emission detection module. The ID code and the corresponding identity recognition relationship information originally stored in the receiving display module MCU are no longer applicable to the ID code after replacing the module, and the receiving display module will discard the information of the replaced module, and the new module will not be displayed on the display screen. Pressure and temperature information. In this way, there is a problem of repositioning the tire when the tire is transposed or replaced.
Tire positioning technology used in existing TPMS
At present, there are four common ways to solve the problem of repositioning of TPMS tires when transposing and changing tires.
In the fixed coding type coding mode, the information of the ID code corresponding to the tire in the receiving display module MCU is solidified at the time of shipment, and cannot be changed during use. The shortcoming of this method is that the installation misplacement will lead to chaotic positioning; after the transmitter module is damaged, the user must purchase the module that is consistent with the damaged module code to the original manufacturer; when the tire is transposed, the emission detection module must be reinstalled once according to its marked position.
2 Interface input interface The input positioning technology prints the identification ID code of each transmitting module on the outer packaging or product. However, when the tire transposition or the transmitting module is damaged, the identification ID code must be input to the receiving end. re-locate. The input ID of the interface input code is 16 or 32 bits long, and the input process is complicated, which is prone to code group input errors. In addition, these buttons are very awkward in the original car with many instruments.
3 Low-frequency wake-up low-frequency wake-up positioning technology utilizes the near-field effect of low-frequency (LF) signals (125 kHz). In this scheme, there is an LF antenna near each tire; the TPMS can issue an LF signal through the LF antenna in the vicinity of the corresponding tire, separately trigger the emission detection module of the corresponding tire, and then pass the identification code through the triggered emission detection module. The RF is transmitted, and the receiving module obtains the corresponding ID through the RF signal, thereby automatically determining the tire position. The shortcoming of this positioning method is that four LF antennas need to be installed near the corresponding tires, and the installation and wiring work is large; the LF signal may falsely trigger the adjacent emission detection module; the electromagnetic environment on the vehicle is complex, and various kinds of Interference can cause interference to low frequency signals, resulting in invalid identification.
Figure 1 Schematic diagram of peripheral code memory positioning technology
4 Antenna receiving near-emissive field type The positioning technology has four receiving antennas for receiving display modules, which extend to the near field of each tire 20 to 30 cm, and the receiving antenna is controlled by a digitally controlled microwave switch. When it is necessary to receive information of a certain tire emission detecting module, only the microwave switch of the receiving antenna of the tire is turned on, and the others are all turned off, and the pressure and temperature of the tire are displayed on the receiving display. The shortcomings of this positioning technology are: the antenna wiring is complicated, the microwave switching cost is high, the RF switch isolation is not enough under the current technical level, and there is the possibility of serial code (that is, receiving information of other tires); electromagnetic interference on the vehicle may be The positioning failure is caused; the conduction timing of the RF switch is according to a certain rule, and the emission of the four tire emission detection modules is random, so that when the RF switch near a certain tire is turned on, the emission detection module of the tire is just right. No signal is emitted, resulting in a missing frame.
External code memory type tire positioning technology External code memory tire positioning technology is a new type of TPMS tire positioning technology. As shown in FIG. 1, the TPMS adopting an external code memory is also composed of a transmission detection module and a reception display module, and is characterized in that a plug-in code memory is interposed in the receiving display module, and each of the emission detection modules has a fixed The ID code is identical to the ID code of the corresponding code memory. When the tire is changed or replaced, it is only necessary to exchange or replace the plug-in code memory. The external code memory type tire positioning technology converts the problem of re-identifying the identity into the transposition setting problem of the ID code by adjusting the correspondence relationship between the ID code in the code memory of the display module and the ID code in each of the transmission detection modules, which is simple , an effective solution. The operation of plug insertion is simple and reliable. The encoding in the plug-in code memory circuit is read by I/O, which avoids the wireless reading of the ID code, and fundamentally solves the problem of interference.
Circuit Design of External Code Memory Figure 2 is a block diagram of the circuit implementation of the TPMS system. This article mainly describes the external plug-in code memory circuit, and does not involve the circuit of the transmitter and the display itself. The design of the external code memory circuit includes two parts, one is the connection part with the host, that is, the design of the connection circuit, and the other is the design of the memory.
Figure 2 TPMS system circuit block diagram
1 Design of the connection circuit The connection circuit is the interface that connects the code memory circuit to the main controller circuit. Since it is applied in automobiles, it is necessary to consider the reliability of the interface, and there are several designs as follows.
(1) plug and socket 
Figure 3 shift memory circuit
Figure 4 diode storage matrix
Through the connection interface circuit of the plug and the socket, the advantage of this design is that the sockets commonly used in the market can be used; the disadvantage is that the size is relatively large.
(2) The card holder makes a gold-plated joint on the PCB, that is, a gold finger. Insert the PCB directly into the socket through the gold finger and connect it with the gold finger and the socket. This design is simple and low in cost, but has poor resistance to vibration and low reliability.
(3) The SIM card or IC form the storage circuit in the SIM card, and the code in the memory is read through the SIM card or the IC card interface; the interface is also implemented in the SIM card, and the interface design for the SIM cartoon is adopted. The advantages are high reliability, small size, and the disadvantage is high cost. During the implementation of the solution, a plug with a snap lock was selected on the connector circuit to ensure reliability.
2 Code Memory The design memory has many forms and can be divided into two types: shift memory and matrix memory. It can be done with separate components or with mature circuits on the market. Circuits for automotive electronics applications have high requirements for electromagnetic compatibility. Several specific circuits are listed below.
(1) Shift memory As shown in Fig. 3, when data is written, each time the clock signal arrives, the D1 data is shifted into the register, and all the data is shifted to the right by one bit. When reading data, every time the clock signal arrives, all data is shifted to the left by one bit, and the value on the D1 port is read out. The advantage is that the I/O port is occupied less. The disadvantage is that the reading speed is slow, and the clock synchronization is required. Actually, On the top is the serial port.
(2) The matrix memory can be realized by a switch, a diode, a mos tube, a triode or a PLA. The advantage is that the reading speed is fast, and the disadvantage is that it occupies more I/O ports, which is actually a parallel port.
â— Diode memory matrix As shown in Figure 4, the diode memory matrix is ​​actually a diode encoder. When one of the lines on PTB0~PTB3 is low level and the other lines are high level, PTB0~ can be read. The value on PTB3; there is a pull-up resistor on PTB0~PTB3, the logic connected to the diode is “0â€; the unconnected is logic “1â€. When the four lines on PTB0 to PTB3 are sequentially low, PTB0 to PTB3 can read four 4-bit codes together to form a 16-bit code.
â— MOS tube and triode storage matrix
Figure 5 tube storage matrix
As shown in Figure 5, the MOS transistor and triode memory matrix are in principle identical to the diode memory matrix, except that the diode is replaced by a MOS transistor and a triode. In the selection of the memory circuit, in order to avoid the influence on the clock in the electromagnetic environment of the automobile, the shift memory is abandoned, and the matrix memory is selected, although the number of occupied I/O ports is large, but the reliability is high and read. Take it fast. There are two options to choose from. One is the high-low temperature parallel port data storage chip, and the other is the diode matrix memory circuit. The advantage is that the circuit is simple and reliable and the cost is low.
Implementation of external code memory tire positioning technology Each of the emission detection modules corresponds to a plug-in external code memory (ID coded plug), and the ID code stored in the code circuit of the code plug and the corresponding emission detection module are solidified in the memory. The ID code is the same. An ID code code socket is arranged next to each tire data display area on the display module. When a plug-in code memory is inserted into the ID code code socket, the receiver reads the ID code in the plug-in code memory through the positioning ID code socket, and The ID code and the corresponding tire data display area are associated with each other. Each time the power is turned on, the receiving display module reads the ID code inserted in the plug-in external code memory (ID code plug) on ​​each socket, and then resets the ID code stored in the receiving display module MCU to correspond to the tire. Relationship information and save it. After the corresponding information transmitted by the transmitting module, the receiving module reads the ID code therein, and determines which tire sends a signal according to the ID code in the receiving display module MCU and the corresponding positioning relationship information of the tire, and the pressure and temperature. The information is displayed in the corresponding area. When the user is in use, if the tire needs to be transposed, the corresponding plug-in code memory can be transposed. After the next power-on, the receiving display module resets the ID code stored in its MCU and the corresponding positioning relationship information of the tire to ensure that the information is displayed in the correct position. If the user finds that a transmitter is damaged, simply purchase a launch detection module kit (plug-in external code memory as an accessory) on the market. Since a plug-in external code memory is included in the transmitter, simply disconnect the plug-in external code memory of the damaged transmitter module and reinsert the random new plug-in code memory. After the next power-on, the receiving display module resets the ID code stored in its MCU and the corresponding positioning relationship information of the tire to ensure that the signal sent by the new emission detecting module is displayed in the correct position.
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