Kroneld P., Liedes T., Nevala K., Marjanen Y.

The aim of this study was to develop a DC – motor operated multi state (semi-active) hydraulic damping valve for selective damping for off-road vehicle cab suspension. Usually selective damping is performed with a standard on/off – valves. Strict demands with regard to the physical dimensions and economical viewpoints, led to development of an alternative construction. The valve structure is based on two contra-rotating concentrically assembled rings. Orifices are placed on the inner ring, while the outer ring has one flow channel per flow direction. Rotating the rings with respect to each other sets the state of the flow resistance. Rotating movement of the rings is achieved by the means of a DC – motor. A single motor can be used to drive two valves at the same time, thus reducing the total cost of the suspension system. The valve was designed to produce three discrete damping rates. After measuring the flow rates, the first damping state was chosen to perform equally as well-acting passive suspension system. The second damping state was chosen to be more firm and the third state softer than the passive one. The valve was then attached to a hydropneumatic agricultural tractor cab suspension system and the performance of the system was measured. As a result three discrete damping states were obtained, each suitable for different type of terrain.