Study Of Displacement Digital Regulation For Variable Displacement Compressor Of Automobile Air Conditioning

Automobile industry is a brace of national economy industry. It is important that researching on improving air conditioning system's control level and working performance to satisfy continuously rising use need of consumer, which also can bring great competitive dominance. The pneumatic control valve is extensively adopted in the variable displacement compressor in automobile air conditioning system currently. The pneumatic control valve rod opening is changed by the digital driving mechanism while the temperature of the inside carriage and thermal parameter of system working substance is changed. The result is that output displacement adjustment is realized and the comfort demand of inside carriage is satisfied. This kind of valve which has control lag, is inconvenient to interface with the computer because of pure gas dynamics adjustment, can't adopt the advanced control strategy and algorithm and can't adapt the trend of development of modern electronic and auto-control technology development. Not only is the control quality of automobile air conditioning system reduced, but also the compatible control between air conditioning and other systems in automobile also can't be carried out. According to the above-mentioned circumstance, a kind of new capacity auto control component stepping digital control valve is developed in this paper. The ideal control of kinematical velocity and position accuracy is carried out by the stepping digital control technology which it has wide controllable scope, the good input-output linearity and higher technology potential in the application in the variable displacement compressor.Base on the structural composition of the swash plate variable displacement compressor and its control valve is expounded, the basic principle and the realized target of implementing compressor displacement adjustment by control valve is described in the way of qualitative analysis. The adjusting methods of other variable displacement compressors are introduced in detail with comparison and the advantage of various method and currently physically applied circumstance is pointed out. The mathematics model is built up respectively to each element of digital control system of stepping digital control valve and the each element transfer function is deduced in this paper. The simulation of digital control system model is carried out by MATLAB which has strong analysis function, and the dynamic unit-step response curve is obtained and response characteristic and system stability also is analyzed. And the PID control technology is introduced into the common control system, the conclusion is acquired which control system with PI has better dynamic response characteristic. Last, the dynamic model of digital control valve is built up. The variation relation curves between input pulse and rod opening and crankcase pressure in control valve are obtained. The theory laws are provided for further research on displacement adjusting of variable displacement compressor.In the end, the formation project of digital control valve is put forward in this paper. Stepping motor which work as electromechanical interface element is introduced into the project, digital signal can be received directly and the accurate control of rotational speed and rotary angular displacement is realized by software programming according to the control need in order to reach the fine and accurate control of the opening of control valve. The PID digital control system of control valve is designed by ourselves in this paper, and specific experimental test system project is put forward and the foundation is built for further research on certificating digital control valve model and its control system.