| Along with the development of high way construction in china, road transportation will play a more important role in Chinese national economy. Chinese Automobile industry is faced with the serious problem for its development: the first is to increase the vehicle's handling stability and comfortable with high speed driving; the second is to decrease the damage to the high way surface. The buses and heave trucks fitted with air suspension for increasing comfort and decreasing the damage to the high way surface have been widely used in USA,Japan and Euro. Their governments encourage the automobile company to produce the vehicles with air spring suspension and consumers to use them through making the law and policy. The using result is to gain very good benefit in economy and society. At present China is in the stage to import and to digest the technology of air spring. The vehicles with air spring suspension will have very good sell market in China. Some automobile companies,universities and institutes have launched to research the function of air spring suspension to mate with vehicle and to design control strategy one after another.The writer of this paper had been participate in a project of JiLin Science and technology's development in 2001 "The research of Automobile electronic control system for air spring suspension". The thesis is a part of the research for the project. The main work is to research into control strategy and control system for air spring suspension. At the same time a test bed for air spring suspension has been designed. It can provide test method to verify the control strategy.1,Characteristic analysis of air spring system The system is consisted of air spring,electro-magnetic valve and air compressor. The paper firstly analyze for nonlinear stiffness characteristic of the air spring and provide four type of hypothesis to nonlinear stiffness of the air spring, that is: rubber material nonlinear,composite of rubber and lining cloth nonlinear,contact nonlinear and geometry nonlinear. Using test method relation curve between stiffness of air spring and on/off time of electro-magnetic valve had been established and the formula has been drawn up. Therefore the preparation has been made for designing of a PID controller. Also deduct the state-space of the system.2,The strategyThe conventional air suspension with the mechanopneumatic valve has some disadvantages. Such as: higher costs due to linkages required for axle guidance, space requirements for installation, more vulnerable to mechanical damage and high air consumption during driving.The above mentioned disadvantages had to be eliminated by the development of a new system. This was possible in a cost efficient way by creating an electronically-controlled air suspension system, abbreviated ECAS. The core components of the system for a fully air suspended vehicle are: modular solenoid valve block, height sensors, electronic control unit (ECU), and remote control unit.The basic function of the ECAS – The distance between axle and body is transformed by the inductive height sensors into an electrical signal and is subject in the micro-computer of the ECU to a continuous comparison of a 'desired' and 'actual' values. If a deviation is detected, the ECU activate the solenoid valves for either pressuring or exhausting the air bellows until the desired level is reached again.Strategy of automatic control – Remaining within the requirements of the basic function, which is 'static level control', the control strategy is to aim towards minimizing the duty cycles of the system components. Thus air and energy consumption will be considerably reduced, and life time and reliability of the components are increased. When the vehicle is running, static changes of level can occur for instance by minor leakage or aerodynamic effects. These changes will be corrected with a certain delay of significantly increased response time,typically 60 seconds. That means the air suspension works as a passive suspension, only depends...
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