A numerical calculations of fluid flow of a shock absorber valve

Noise concerns in shock absorbers can be divided into two categories. The first is fluid flow noise, or “swish noise”, caused by the oil being forced through openings in the valves. The type and temperature of the oil, its velocity and the orifice geometry all have an effect on this. In addition, the structural design of the shock absorber shell may either reduce or amplify the noise. The second type of shock absorber noise is often described as regular operational noise or “chuckle noise”. It can be observed in vehicles during low-displacement, higher-frequency events, such as driving over a slightly rough road. This effect measurable as a force discontinuity into the vehicle and can come from a number of sources in the shock absorber, e.g. hydraulic transitions. It is often traceable to the valve discs closing and opening, but can also be caused by cavitation/aeration in the oil and air being pulled through the valves. The work on noise improvement reported in this paper has been started using conventional shock absorbers to be extended and will cover in the future variable damping shock systems as well. The paper gives an overview about the configurations of a typical valve system including three basic regimes of operation which correspond to the amount of oil flowing through a valve cavity. The aim of this work was to propose a finite element fluid flow model which can be used in order to reduce the velocity of fluid flow through a cavity of a shock absorber valve. High flow velocity can cause high-content frequency vibrations and, in turn, audible noise. The model will be used for initial screening of new valve concepts and on the other hand to improve the currently use ones.