Abstract
Because of the substantial improvements in vehicle ride comfort over the last few years, it is not just the handling properties of the shock absorber, but its acoustic behavior as well which is increasingly becoming the focal point of interest. A detailed examination of the shock absorber's piston valve system is necessary in order to optimize the acoustic behavior. One way of achieving this is to adopt a procedure that utilizes a combination of test rig tests and simulations. Simulation enables the different parameters to be varied and saves time in the process. It also produces results for internal parameters that would otherwise be difficult to measure. Extensive test rig tests have been carried out to provide the data for parameterizing special damper configurations and to validate the simulation models. For this purpose, a special test rig has been constructed at the Institute of Hydraulics and Pneumatics at TU Dresden, which, in addition to enabling the resistance behavior of the piston valve to be determined as a function of the pressure difference, the volume flow rate and the oil temperature, also makes it possible to measure the deflection of the piston valve's disks by means of a displacement sensor.
For the computer-aided analysis of the dynamics of the shock absorber's piston valve system, a model of a monotube shock absorber has been created using the "ITI-SIM" simulation software. The shock absorber model contains a description of the following:
· The dynamics of the piston with respect to mass
· The pressure build-up in the shock absorber's chambers
· The elasticity of the oil and the cylinder wall as a function of pressure and temperature
· A gas accumulator model in the compensation chamber
· Friction between the piston and the cylinder
· The behavior of the valve
Special, separate FE calculations of the valve disks are used to parameterize the spring elements of the simulation model. The simulation can output as results all the kinematic and hydraulic characteristics of the shock absorber, such as piston travel, piston speed, resultant force on the piston, pressures in the piston chambers and volume flow rates in the shock absorber.