Experimental Validation of a New Design Concept for the Increase of Efficiency of the Hydraulic Drive System in Mobile Working Machines

In mobile working machines like excavators, hydraulic actuators and drives are indispensable due to their advantages of a high power to weight ratio, robustness and the good power transmission over medium distances by the hydraulic fluid. Axial piston machines can deliver a large volume flow at a high operation pressure with high efficiency and are therefore widely used as system pump or drive motor. The three essential tribological contacts piston / bushing, sliding shoe / swash plate and valve plate / cylinder block strongly influence the machine's efficiency and so the complete drive system. The paper on hand focuses on the experimental validation of a new design concept to increase the efficiency of the tribological contact between valve plate and cylinder block in an axial piston pump. Due to the different pressure forces at the high- and low-pressure side, the cylinder block tilts and holds this preferred position almost constant. Therefore, the gap height is not constant. In the area of minimum gap height, the danger of solid body contact increases. In addition, the heat dissipation is decreased, which can lead to local constant high temperature hot-spots. Both can destroy the surface structure or the coating. A new design concept has been developed to reduce these risks, thus increasing the efficiency, the lifetime and making it possible to dispense of leaded coating materials. In this design concept, pressure pockets are added in the area of minimum gap height. The simulation study shows a high potential of this concept. The experimental results of the prototype parts, which are measured on a special test rig and presented in this paper, confirm the simulations and validate the potential of the new design concept in this way.