Control means for variable displacement pump

Control means for a variable displacement pump driven by an engine, said control means comprising:

• a movable control ram operably connected to said pump for regulating the output flow from said variable displacement pump between a maximum and a minimum;
• biasing means urging said ram in a direction to provide maximum flow from said variable displacement pump;
• a charge pump driven by the engine for supplying fluid under pressure to said variable displacement pump;
• a first conduit extending from said charge pump to said variable displacement pump for carrying said fluid;
• an orifice in said first conduit whereby said fluid flowing therethrough causes a pressure difference thereacross;
• a second conduit extending between said variable displacement pump and said control ram;
• a speed valve located in said second conduit and including a spring-biased spool movable therein in response to said pressure difference across said orifice, and independently of the output pressure of said variable pump between a first position permitting fluid flow to said control ram from said variable displacement pump and a second position preventing such flow;
• a first pilot conduit connected between said first conduit on the downstream side of said orifice and one end of said speed valve and a second pilot conduit connected between said first conduit on the upstream side of said orifice and the other end of said speed valve, whereby, when said pressure difference is low, said spring-bias moves said spool to a position wherein said control ram is positioned to provide for maximum fluid flow from said variable speed pump, and, when said pressure difference is high, said spool is moved by higher pressure in said second pilot conduit to a position wherein said control ram provides for minimum fluid flow from said variable displacement pump.