Development of Water Hydraulic Proportional Valves Driven by Positive Cam Mechanism

This paper describes development of water hydraulic proportional valves. The valves are spool-type and the spool is driven by a stepping motor and positive cam mechanism. The cam is always placed between two cam followers and the return spring is omitted. The rotational angle of the cam and the displacement of the spool is linear. The experimental results of static characteristics are also shown: internal leakage and pressure gain against spool displacement, flow rate characteristics with no load and flow rate against load pressure. Although the spool is overlap, the dead band was not observed in the flow rate characteristics with no load because of the leakage passing through the clearance around the spool. In addition, non-linearity of the spool displacement against the rotational angle of the cam was below 0.2% and the hysteresis was hardly observed even though the spool displacement was not feed backed.