Spring regulated variable flow electric water pump

A variable flow electric water pump for use in an engine coolant system of a motor vehicle, the electric water pump comprising:

• a pump housing defining a fluid chamber, a motor chamber, a fluid inlet and a discharge port providing a flowpath for coolant flowing through said fluid chamber, and an interface established between said fluid inlet and said fluid chamber defining a flange surface;
• an electric motor disposed in said motor chamber of said pump housing and including a stationary stator assembly and a rotor unit having a rotor shaft supported for rotation about a longitudinal axis and extending into said fluid chamber;
• an impeller fixed to said rotor shaft for rotation in said fluid chamber and operable to pump coolant from said fluid inlet to said discharge port, said impeller having an outer rim surface aligned with said flange surface of said pump housing;
• and
• a biasing arrangement for normally locating said rotor unit in a first position that is axially offset relative to said stator assembly for locating said impeller in a retracted position within said fluid chamber to provide a low flow characteristic between said fluid inlet and said discharge outlet when said impeller is driven by said rotor shaft at a low rotor-speed, said biasing arrangement being configured to exert a preload on said rotor unit,
• wherein a first clearance gap is established between said outer rim surface of said impeller and said flange surface of said pump housing when said impeller is located in its retracted position, said first clearance gap being configured to decrease the coolant flow rate between said fluid inlet and said discharge outlet,
• wherein rotation of said impeller at a high rotor speed causes said rotor unit to overcome said preload and move to a second position axially aligned with said stator assembly for causing said impeller to move from its retracted position into an extended position within said flow chamber to provide a high flow characteristic between said fluid inlet and said discharge outlet,
• wherein a second clearance gap is established between said flange surface of said pump housing and said outer rim surface of said impeller when said impeller is located in its extended position, said second clearance gap configured to increase the coolant flow rate between said fluid inlet and said discharge outlet, and
• wherein said first clearance gap is larger than said second clearance gap.