| Compared with the traditional mechanical transmission, there are much more advantages for hydraulic transition, such as higher transferred power, easier method of control and adjustment, smoother transmission, wider range of velocity. In modern mechanical industries, especially the mechanical engineering industry, hydraulic transmission is employed more and more widely. As the core component of hydraulic system, the performance of the pumps determines the function and performance of the whole system to great extent.For piston pumps can reach high working pressure and rotate speed, vary the displacement easily, have compact structure and high power density, they are one of the widely used power components in hydraulic system. They are employed in a lot of fields, from large hydraulic machines weighing more than one million ton to small hydraulic clamps, from ordinary machines fastened to the floor to mobile vehicles, from civil machinery to military weapons. Hydraulic components are mostly mature. However, many engineers and researchers are trying their best to improve the working life and performance of piston pumps all the time, especially the axial piston pump.The excavator is important equipment in modern industry, which is dispensable for mine firms and construction firms. The power components of excavator are also axial piston pumps. For an excavator, it maybe has to rotate, shake the arm, move the arm, shovel, and walk. What's more, the working environment is complex and usually bad. The excavator consumes great amount of power when being working. In order to performance excellently and use the power of the engine effectively, the excavator has to performance several movement simultaneously, furthermore, it has to control these movement separately. Therefore, the hydraulic circuit of the excavator develops from the initial single pump system to today's double-pump system or multi-pump system. Japan's hydraulic excavator has technical advantages over others in this regard with hydraulic transmission and control system. The hydraulic pump of the foreign company mostly employs the integration technology. Firstly, they integrate several pumps to one pump, simplifying the transmission device of the main pump and facilitating the installation and maintenance of other components. Secondly, in regard with the control system, they don't use a single power control method any more, which is used originally, but integrate pressure-cut-off control, cross-power control, and negative-flow control into one pump, forming compound control that have several control function at the same time to meet the requirement of fuel-efficient, improvement of efficiency and smoothness. With the development of electronic control, the hydraulic pump with electro-hydraulic proportional control came out on the basis of development of compound control, what's more, hydraulic pumps with digital control for excavators also appeared in recent years.In recent years, though we have yet done a lot of work in the field of upgrading the technical performance, there is a wide gap in integration, reliability and stability compared with the foreign products. Our studies are also conducted on the basis of foreign technology (especially the Japanese technology). Our target is to produce axial piston pump comparable with foreign products, and form the capability to continue the follow-up research.Because this kind of axial piston pump is developed from separate axial piston pump, the design method of the common axial piston pump is also suitable for this double-pump. The design method of axial piston is very mature already. First, we conduct motion analyses, stress analyses, and oil film of the key friction pairs. We get the size and structure by the calculation of all components, mainly including the transmission shaft, transmission gears, the cylinder block and the control plate. In order to improve the life of axial piston pump, we optimize the key friction pairs in the field of material and structure, improving the quality of oil film and the ability of anti-wear and anti-friction. Fox example, we introduce static pressure support by modify the structure of the control plate. After the design of the components, we conduct the design of integration. We have to solve the problem of layout of these components and the optimization of the structure on the whole with the help of SolidWorks 3D graphics software and CosmosWork analyse software. We must ensure that all components have sufficient strength, life and good processing technology, and the structure of the pump is compact, and is easy to install and maintainThen we analyses and design the control system. Here we employ compound control system by integrating cross-power control system, negative-flow system, and variable-power system into one pump, playing to their respective advantages and achieving the best control. We use the AMEsim software to simulate the static and dynamic conditions, solving the problem of the design of adjusting and control device in the compound system, integrating these three control methods in a simple manner. At the same time, we must ensure that these control methods would not interfere with each other, and the whole control system has good stability. At last, we measure the performance of the designed pump, and compare the result with the simulation. They both show that the compound control manner has excellent control ability. Before the negative-flow control method works, the two pumps work vary it's displacement according to their loads, therefore, the pressure of the two pumps may be not equal, but their displacement is both varied by adjusting the current of proportional solenoid. If we have to limit the displacement of the pumps, we can input certain controlpressure at the negative-flow control access. In this way, the pump will jump out of the constant-power control, and vary the oil supply according the control pressure.After the design, we give strict standard to the processing and assembly of the components, which is always overlooked by the designers in the design of axial piston pump. The practical experience shows that a excellent design only will play its part by the support of good processing and assembling skills. Through the tests and measurements, it showed that the actual pump reach the design target and indict a direction to improve the pump. In the following steps, we will try to integrate the hydraulic technologies with electronic technologies, and introduce computers into the double-pump to achieve digital control system, which will help to improve the integration and stability of the hydraulic system. |
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