Development of Cam-Drive Type Proportional Valve for Water Hydraulics

This paper describes the development of water hydraulic proportional valves. These valves are spooltype and the spool is driven by a positive cam mechanism with an appropriate motor, such as a stepping motor or servo motor, depending on the application. The cam is placed precisely between two cam followers so that no gap is left between the cam and followers. Accordingly, no return spring is required. The rotational angle of the cam and the displacement of the spool are linear. Mathematical models of static characteristics of the valves are derived. Experimental results for the 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 overlaps with sleeve, no dead band was observed in flow rate characteristics with no load because of leakage passing through the clearance around the spool. In addition, the nonlinearity of spool displacement against the rotational angle of the cam was below 0.2% and hysteresis was hardly observed. Feedback control of the displacement of water hydrostatic bearings is conducted as an application of the developed valve.