Patent ID: 6698197
Filing Date: 2004-03-02
Classification: F15B,F16H,F16K

Abstract:
In a closed loop hydrostatic transmission including a pump adapted to supply pressurized fluid, a motor adapted to receive said pressurized fluid, and high pressure and low pressure conduits for communicating fluid between said pump and said motor; a source of relatively low pressure make-up fluid adapted for fluid communication with said low pressure conduit; a relief and check valve assembly disposed between said source of make-up fluid and said high pressure conduit; said assembly including a relief valve member operable, in the presence of fluid pressure in said high pressure conduit in excess of a predetermined maximum pressure to be biased open, in opposition to the biasing force of a relief spring, to permit fluid communication from said high pressure conduit to said low pressure conduit; and said assembly including a check valve member operable, in the presence of fluid pressure in said high pressure conduit which is less than the pressure of said relatively low pressure make-up fluid, to be biased open, in opposition to the biasing force of a check spring, to permit fluid communication from said source of make-up fluid to said high pressure conduit; characterized by:(a) said check spring being disposed in a spring chamber bounded on one side by a member which is substantially fixed relative to said check valve member in the absence of relatively high pressure in said high pressure conduit; (b) a normally-closed drain valve having an inlet in fluid communication with said spring chamber, and an outlet in fluid communication with a system reservoir; and (c) wherein, in response to a predetermined input, said drain valve will move from its normally-closed condition to an open condition, draining said spring chamber to said system reservoir, and causing said check valve member to open under the influence of said relatively low pressure make-up fluid.