DESIGN AND TEST OF AN INTELLIGENT ENERGY EFFICIENT VALUE TO DECREASE PRESSURE PULSATION IN POWER STEERING SYSTEMS

Abstract

In a joint research project BMW and IFAS analyzed two well known hydraulic phenomena occurring in power steering systems, in order to reduce noises, that are caused by these phenomena.
The research project was subdivided into three tasks. The first task incorporated the analysis of the power steering system of a BMW 5 series passenger car. During this analysis an impulsive pressure pulsation phenomenon known as rattling as well as a periodic pressure oscillation called shuddering were measured. Both phenomena result in distracting noises within the passenger cabin and occur during certain different driving manoeuvres.
The second task included the construction of two test benches to reproduce rattling and shuddering independent from the car. A comparison of the measured data obtained by driving tests with the collected data from the test benches verified their functionality and accuracy. Another advantage of the test rig is that it provides easy access to the power steering system's components. Modifications can therefore be carried out in a short amount of time.
Finally an intelligent valve was designed and tested at the two test benches. The valve can detect the two different hydraulic phenomena without the need of sensor signals and without causing high pressure drops. In case of rattling the valve softens the return line of the power steering system and in case of shuddering the return line is hardened. A softer return line reduces pressure pulsations while a harder return line is insensitive to periodic pressure oscillations.
This paper describes a solution for two different hydraulic phenomena (rattling and shuddering) occurring in power steering systems. The solution is the integration of an intelligent energy efficient valve into the power steering system's return line, which changes the stiffness of the return line depending on the occurring phenomenon without affecting the sensation of the steering. The functionality of the presented valve is proven by means of the test results obtained from two test rigs designed to reproduce the described phenomena.