Research On Key Technology For Wireless Tire Pressure Monitoring Of Commercial Buses

Currently more research efforts are focused on the tire pressure monitoring system(TPMS) of passenger cars, however, research on TPMS of commercial buses has been rare.The TPMS of commercial buses have problems of poor reliability and unstable signaltransmission. In order to improve the reliability and wireless transmission performance ofTPMS of commercial buses, simulation and design of the configuration antenna,electromagnetic wave propagation model of rotating component, system control softwareand algorithms are studied in this dissertation. Main research tasks include the following.Comprehensively considering the impacts of rotating antenna, wheel, vehicle bodyand non-ideal ground, the concept of configuration antenna is proposed. Through buildingthe electromagnetic field simulation model, the antenna parameters in simulation are usedto optimize the design of antenna matched circuit and to improve the performance ofwireless transmission. The simulation results indicate that radiation variations in differentdirections of configuration antenna are bigger than that of single antenna, and antennaradiation pattern has several zero points. The power of configuration antenna in maximalradiation direction on non-ideal ground is smaller than that of on ideal ground, and antennapower pattern is mainly influenced by the conductivity changes of different grounds. Whenground roughness is more than8cm, the influence on configuration antenna performanceemerges. During rotating, for configuration antenna, the fluctuation of gain is apparent, theresistance part of input impedance changes significantly while change of reactance part isminor, impedance matching design is therefore necessary. The experiment shows that thereceiving probabilities are more than90percent after using configuration antennaimpedance matching design.An electromagnetic wave diffraction propagation model of rotating component isdeduced and established, and simulation analysis is conducted. Simulation results showthat the path loss varies with the rotation angles, the path loss is related with parameters ofrotating component radius, working frequency, rotating velocity, the distance betweentransmitter and receiver, transparent aperture size and antenna height. Considering the distance difference between the direct propagation path and reflection propagation path aswell as Doppler frequency shift caused by changes of rotation velocity and incident wavedirection, a dual-path propagation model of rotating component is deduced and set up.Simulation results show that the path loss varies with the rotation angles, and thefluctuation range and magnitude of path loss of the parallel polarized wave is smaller thanthe vertical polarized wave. The path loss has relationships with rotating component radius,working frequency, rotation velocity, the distance between transmitter and receiver,dielectric constant as well as antenna height. The diffraction path loss of antenna placed inthe cab or on chassis of commercial bus, and the path loss of dual-path propagation aresimulated. Results indicate that the path loss of antenna on chassis is smaller than that of inthe cab. It is suggested that it is better to place antenna on chassis and near the tire as muchas possible to ensure the receiving performance. In order to verify the propagation model,path loss test of rotating component is carried out, and the results show that the presentedmethod and established propagation model are close to actual situation and reasonable.Control software and algorithms of TPMS system are studied. High frequency and lowfrequency communication protocols, software process, signal conditioning algorithm, thealgorithm of the temperature compensation and software filter in low temperature conditionare proposed. Key points of software anti-interference design are elaborated, and theprevention strategy for false alarm is designed.