Pump with electrically actuated flow control

Claim 1

A pump unit comprising a housing defining a pumping chamber, a fluid inlet and a fluid outlet in said housing communicating with said pumping chamber, a pair of cooperating gear members in said pumping chamber for pumping fluid from said inlet to said outlet, means supported in said housing defining a variable orifice in said outlet, said means defining said variable orifice including a part of a pintle member and a valve seat, means supporting said pintle member for movement relative to said valve seat to control the size of the variable orifice, an electric motor supported on said housing for moving said pintle member relative to said valve seat to control the size of said orifice, a flow control valve in said housing for bypassing fluid from said outlet to said inlet, said flow control valve including a spool valve member located in a bore in said housing and which is movable therein, said spool valve member being positionable between a first position blocking communication between said inlet and outlet and a full relief second position providing maximum communication between said inlet and outlet to control bypassing of fluid from said outlet to said inlet, a spring biasing said spool valve member into said first position blocking communication between said inlet and outlet, said spring being located in chamber means at one end of said spool valve member, said spool valve member having one face surface acted upon by the pressure on one side of said orifice, said spool being movable by the pressure on one side of the orifice to said full pressure relief second position or a flow control position intermediate said first and second positions, flow passages in said housing communicating the pressure on the other side of said orifice to said chamber means, a pilot valve carried by said spool valve and which opens in response to pressure in said chamber means exceeding a predetermined value, passage means to said inlet communicating the pressure in said chamber means to inlet upon opening of said pilot valve, and means for restricting the rate of pressure build-up in said chamber means during relief of the pressure in said chamber means by opening of said pilot valve to cause said spool valve to move from a flow control position to said full pressure relief second position, said means for restricting pressure build up comprising a restricted portion of said flow passages and said passage means to said inlet having a substantially greater cross-sectional area throughout its extent than said restricted portion of said flow passage.