Model of a Four-Position Unbalanced Hydraulic Valve

The present paper proposes and models a four-position unbalanced valve that was introduced by the author in 2006 [1] in a hydraulic system used to save and recover braking power. The valve modulates the oil flow from a free-wheeling mode to braking-and-storing energy, to full braking, to recovering energy and accelerating a load. The valve design achieves this by combining the operating characteristics of the sliding and the rotary operation. The key goals of the present analysis are to demonstrate that the four-position operation is attainable, and to evaluate the valve stability during the transient and the steady state modes of operation and compare it with the stability of the conventional stepped-spool valves. The normal, freewheeling position of the valve is determined by locating its spool in between the two springs of unequal stiffness, thus making it “unbalanced”. The solid model of the proposed design is presented and analysed here.