Ruotsalainen P., Nevala K., Marjanen Y.

The aim of this study was to design and test adjustable hydro-pneumatic damper for cab suspension. The goal was to made simple and cheap solution. Damping behaviour of different terrain types had to be noticed. Terrain type varies from field to road driving. In this study the semi-active damper has been carried out with hydraulic direct acting cartridge type 2/2-way proportional flow control valve. Applicability of the valve to semi-active damper was tested in cab suspension test environment. Valve was tested with two natural and one artificial vibration stimulation track. With these results it was possible to discover proportional valves capability to work as a multi state damper. Flow-pressure curves and dynamic testing were carried out in laboratory. Dynamic test with forced vibration was focused to stability in damping frequencies and step response between different states. As a result, this research gave a lot of new information about proportional valves applicability to work as a semi-active damper and information about damping behaviour. Also, proportional valves precise step responses and stability was investigated in closed hydraulic system. Research showed that proportional valve can work in cab suspension damper as good as multi fixed orifice damper. Two direction flow in proportional valve was found to stay stable in cab suspension working conditions. Proportional valve has also capability to work as continuous state damper which could lead better damping results with appropriate control system.