Low effort, proportional control valve

Claim 1

A fluid control circuit for regulating operation of a doubleacting hydraulic motor and including a source of fluid under pressure and a control valve body defining a bore, an inlet chamber being in communication with the bore and the source, service chambers being respectively in communication with the control valve bore in axially spaced apart relation on opposite sides of the inlet chamber, drain means also being in communication with the control valve bore in axially spaced apart relation from each service chamber and a spool reciprocably arranged in the control valve bore and having a neutral position wherein the spool blocks the inlet chamber from communication with both service chambers, the spool being movable in opposite directions from its neutral position for respectively communicating the service chambers with the inlet chamber and drain means, metering means being movable with the control valve spool to Provide a variable opening between the inlet chamber and the respective service chambers as the spool is moved from its neutral position toward its respective positions providing substantially free communication with the respective service chambers, and comprising a dump valve forming a bore having one end in free communication with the inlet chamber, a dump spool being movable arranged in the dump valve bore for separating its one end from its other end, the dump valve bore having an opening in communication with drain, the dump spool being movable toward the one end of the dump valve bore to block the inlet chamber from the drain opening and toward the other end of the dump valve bore to communicate the inlet chamber with the drain opening, spring means urging the dump spool toward the one end of the dump valve bore, the spring means being selected to establish a differential pressure between the inlet chamber and each of the respective service chambers when they are communicated by the metering means and to establish the only substantial force tending to urge the dump spool toward the one end of the dump valve bore and limit communication between the inlet chamber and drain opening when the control valve spool is in its neutral position, means forming passages in said control valve body comprising a branched passage communicating the other end of the dump valve bore with the control valve bore at a location intermediate each service chamber and the adjacent, axially spaced apart drain means, and regulating means being movable with the control valve spool and in regulating communication with the passages to communicate the other end of the dump valve bore with the respective service chambers when they are placed in communication with the inlet chamber by the control valve spool and to communicate the other end of the dump valve bore with drain when the control valve spool is in its neutral position, the regulating means comprising axially elongated peripheral slots formed in the control valve spool for selectively communicating the branched passages with the respective service chambers and drain chambers.