Investigations of the Temperature Behaviour of the Piston Cylinder Assembly in Axial Piston Pumps

In this paper the temperature behaviour of the piston cylinder assembly in swash plate type axial piston pumps is investigated. For the theoretical investigations a mathematical model is used that allows the calculation of the nonisothermal gap flow between piston and cylinder. For this purpose the Reynolds Equation, the energy equation and the equations of motion have to be solved. The gap flow and the pressure distribution in the gap is calculated by solving the Reynolds Equation numerically with a finite volume method. The temperature distribution is obtained by solving the energy equation over the piston cylinder assembly also numerically with a finite volume method. It is known that the piston undergoes an eccentric motion in the cylinder that has a significant influence on the gap flow. To calculate this motion a simplified equation of motion, based on the external forces, the hydrodynamic forces and the forces caused by elastic deformation, is used. A method is described that combines the calculation of these three equations and that allows calculation of the gap flow and the temperature distribution in the assembly depending on the design and the operating parameters of the machine. The experimental investigations were made on a standard pump that was modified for the measurements. The temperature distributions in the whole cylinder block of the machine and the dynamic pressure in the displacement chamber were measured under real operating conditions using a telemetry unit. The results were used to verify the simulation model.