| Electronically controlled air suspension(ECAS),use air spring as its elastic element which has ideal stiffness characteristic, at the same time it can also realize the height adjustment of the vehicle body according to the driving condition, by this way it can significantly improve the riding comfort、handing stability and trafficability of vehicle. With the development of vehicle technology and people’s increasing attention to the ride experience, the assembly rate of electronically controlled air suspension system on the bus is gradually upgrading. However there is no research and development technology of electronically controlled air suspension in domestic vehicle manufacturers, which mainly rely on the introduction of electronically controlled air suspension system from abroad. Therefore the research on the key technology of the electronically controlled air suspension system is of great significance to improve the independence research and development ability, and promote the technology progress of our national bus industry.This dissertation is supported by the National Natural Science Foundation named “Research on the control mechanism and evaluation method of new steer-by-wire system based on the characteristics of the drivers”(No. 51575223) and “Research on Reconfigurable Integrated Chassis Control Strategy for Four-Wheel Independently Actuated Electric Vehicle”(No. 51505178).According to the practical needs of ECAS system in our national bus industry, the control strategy of ECAS system for bus is studied, and the application designs on related fields are done. The main research contents are as followed.(1) The types and characteristics of air springs are introduced. According to the parameters of the target bus and matching requirements, the selection of air spring is done. With the effective area and the effective volume properties of the air spring, the mathematical model of the air spring is built; The test rig of electronically controlled air suspension is set up, the established mathematical model was verified by experiment; According to the need of research, combined with the model of air spring, the full vehicle mode with 9 degrees of freedom is built and the validity of the model is verified by commercial dynamics package(Trucksim).(2) According to the working principle of ECAS system, the height control method based on layered architecture is put forward for ECAS system, which included the target height decision and the target height tracking. According to the running state of bus, the target height decision control is divided into three modules: vehicle starting control, vehicle dynamic driving control and vehicle kneeling control, and then the modular design is done for the three modules. According to the suspension frequency design and height of air spring the working heights of the air spring are designed. To solve the problems of “over-charging”, “over-discharging” and oscillation during the process of height adjustment, a PID/PWM controller is designed to realize the tracking control of the target heights. As for the height tracking of four groups of air spring, three-point measurement control strategy is used, through the static and dynamic height switching control simulation, the control strategy is verified by simulation.(3) Based on Microprogrammed Control Unit(MC9S12DG128), the hardware circuit and software program are designed to complete the development of ECAS controller prototype.(4) Combining with hardware and software systems the hardware in the loop test bench for ECAS controller is built based on Matlab/x PC Target technology. Respectively, the static body height rise and drop control、kneeling condition、bumpy road driving condition、high speed driving condition and steering condition experiments are conducted to verify the validity of the developed ECAS controller and the proposed control strategy. |
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