【文章內(nèi)容簡介】 nd charging. Fig. 4(a) shows the open area coefficient curves with changing of rotation angle. Because the angle difference of the two different bore is 180176。 (Fig. 4(b)), so it can be modeled with a throttle valve controlled by the open area size. The distributed flow is controlled by the cylinder bore open area size, which is shown in Fig.4(b).Fig. 4. Model of valve plateTo simplify the modeling, the flow model and the valve plate model were bined to an integrated unit (Fig. 5). As one pump has nine pistons, so the whole pump model includes nine integrated piston models, which is shown in Fig. 6.Fig. 5. Encapsulation of the flow model and valve plate modelFig. 6. The whole hydraulic model of the pump Finite element method of the key partsThe stress and deformation of some key parts in pump working process should be researched by flexible body analysis[8]. The middle shaft and the piston are two typical parts needed to consider the flexibility character. It is necessary to analyze the model with FEM and to convert the rigid body to flexible one. In an FEM software environment, the flexible body of piston can be read to the dynamic model and be assembled to the whole pump model. Fig. 7 shows the finite element model of the piston with flexible characteristics. The middle shaft model was also made in the same way. Fig. 8 shows the two flexible parts in the assemble pump. Then the solver can simulate the pump and get the stress results and deformation results of the piston and the shaft. The intensity of corresponding parts is analyzed in this way. Fig. 7. Flexible body model of the pistonFig. 8. Assemble pump with flexible bodyof piston and middle shaftAccording to the above analysis, the virtual prototype of piston pump includes several different models. So interfaces are needed to connect these models into one unit. Thereby, the hydraulic interface, the dynamic interface and flexible body interface are built according to the working environment. Fig. 9 shows the relationship of these models. The virtual prototype of piston pump are built by assembling all these models together.Fig. 9. Models relationship of pump virtual prototype3 Results and DiscussionMany aspects of the piston pump can be investigated based on the pump virtual prototype, such as the output characters, the force of pistons, the stress and deformation of the pistons and the middle shaft, etc. Output characters of pumpThe output flow and pressure of pump are used directly for driving loads in the hydraulic system. So the output character is one of the most important performances of the pump. With the virtual prototype of piston pump, it is easily to get the output characters. Fig. 10 shows the output flow changing with angle of the swash plate. The flow ripple is clearly shown in the result curves. The cycle time of flow ripple is the same based on the rotation speed. The flow ripple amplitude is getting higher with the swash plate angle increasing. Besides, the flow condition in each piston chamber can also be presented with the simulation.Fig. 10. Output flow with angle of swash plateAs there are gaps between the two kidney bores in the valve plate, the output flow is discontinues. So the pressure ripple and corresponding noise are produced during fluid distribution process. One new structured valve plate with nosymmetrical kidney bores is developed [12]. This valve plate has a difference angle (index angel) between the two kidney bores. With this structure, the pressure ripple of the pump can be reduced obviously, shown in Fig. 11. Fig. 11 presents the parison of pressure condition inside piston chamber between valve plates with difference angle and without difference angel.Fig. 11. Output pressure of the pump Force on the pistonsIn the piston pump, the pistons are used for sucking and charging oil. So the fluid force on the pistons is variable and plex. With the virtual prototype of piston pump, the force on the backside of the pistons can be investigated. With different angle of swash plate (including 0176。, 176。, 5176。, 176。, 10176。, 176。, 15176。) at the same load condition, the force on each of the nine pistons is different and the force presents a periodic change with time, shown in Fig. 12. The vibration amplitude of force is getting higher with the swash plate angle increasing.In order to analyze the influence of the swash plate angle, the fluid force was simulated with the angle changing continuously. The curve in Fig. 13 shows the trend of the force. It starts with a very small value, and the value of the force rises quickly while the angle of swash