The Theory And Experiment Studies On Three Assignment Windows Axial Piston Pump Assignment

As the crucial power components in hydraulic system, axial piston pump has the characters of high pressure, wide speed adjustable range and easy-changed assignment structure and can meet the requirement of hydraulic system for simplifying loop, saving energy and protecting environment. The adoption of hydraulic pump to control directly the movement of hydraulic cylinder is the most direct way to improve the efficiency and energy of electro-hydraulic technology, which is also the international research hotspot in this field and a large amount of research upon this field has made. The present hydraulic system is value-controlling mostly which has disadvantage that leads to great throttling loss and decrease the using efficiency of system energy. It is clearly known that the most effective way to change this situation is to adopt the direct-controlling technology of pump without value-controlling. That is, by controlling the flow or rotate speed of hydraulic pump to change the flow to system and controlling the displacement, speed and output force of cylinder. According to the differential object, pump-control technology include pump-control motor and pump-control cylinder, pump control cylinder again include pump-control symmetric cylinder and pump-control differential cylinder. Passing more than20years'efforts the direct pump-control technology has made a lot of progress, developing the high dynamic response ratio and servo pump, introducing variable speed control technology, solving the tight prepressing problem of two cavity in hydraulic cylinder, especially for the symmetric cylinder, the control technology has perfected very well and applying it into aviation. But to the differential hydraulic cylinder which is widely used in hydraulic technology can still not meet the present need, though a lot of progress has been made. And to make up for the asymmetric flow of differential cylinder, many auxiliary methods has to be adopted such as using hydraulic transformer which is consist of hydraulic cylinder and motor to compensate the asymmetrical flow; adopting hydraulic controlled check valve compensate oil to balance differential cylinder flow difference. However, owing to the special structure of differential cylinder, the present technology can still not be made as pump-control symmetric cylinder which can use only one hydraulic pump controlling the movement of differential cylinder in the closed loop and without auxiliary components. To obtain the goal, the article will come up with the theory that applies asymmetric assignment method in axial piston pump to control differential cylinder according to the idea that asymmetric valve controlling asymmetric cylinder and on the basis of theory analysis, through the procedure of modeling construction, simulation, three-dimensional entity modeling to developing a new type hydraulic pump. The article will also include experimental contrast under different operating mode to work out a reasonable structural parameters of the new type pump key elements to accomplish the goal that the pressure pulsation effect of new type pump has the same level with the present pump, eventually realizing the single pump can compensate the asymmetric area of differential cylinder, control the movement of differential cylinder in closed loop and optimize circuit structure. The detailed procedures are in the following:redesign and remodel the present axial piston pump, keep the discharged window of the axial piston pump and redesigning the suction window into two windows in which one window links to rod cavity of the cylinder and the other one connects to low pressure oil tank to structure the three assignment windows axial piston pump, by changing the displacement or rotate speed of the pump to control the movement of the differential cylinder directly. To obtain goals of simplifying the oil-way and improving the energy efficiency of system which is better than the present technology that uses hydraulic valve to compensate the circuit of differential cylinder area difference. Meantime three assignment windows axial piston pump still can output two flows belonging to different pressure to control the movement of two hydraulic actuators. In the process of redesigning and remodeling, first, general simulation software of mechanical and electrical system SimulationX must be used to construct the hydraulic pump simulation model under the consideration of the movement character of single piston, compressibility oil and assignment area change with rotary angle. Then, digital simulation must be used to determine the key parameters of the primary elements in the pump, especially the size of cylinder and suspension groove of port plate, digital simulation is also used to analyze the flow features and pressure features of the pump; second, after the model pump is made out, the pressure flow, volumetric efficiency and noise of the pump under various rotate speed, must be tested on the experimental platform, in the end the validity of the principle and simulation design can be verified. The assignment windows structure of the redesigning and remodeling pump has two ways with series connection and parallel connection; third, the Matlab/Simulink software will be used to construct simulation model of closed system which pump control differential cylinder at variable speed. By simulated study on different operating mode during the movement of differential cylinder, according to operation requirement of closed loop, the output flow, pressure of the pump and the displacement, output force and speed of the differential cylinder are tested on the experimental platform, eventually the result of simulation is proofed by the result of test. The result of research shows that three assignment windows axial piston pump which is made according to the new assignment theory can completely balance the asymmetrical flow of the two cavity in differential cylinder and will play a more important role in the future application of concrete equipment.