High pressure fuel pump with mechanical pressure regulation

A high pressure fuel pump in which a pumping plunger is driven by a cam follower in contact with a profile of a rotating cam, the pumping plunger reciprocating axially in a pumping chamber between a retracting motion during which fuel is delivered to the pumping chamber and a pumping motion during which the plunger pressurizes fuel in the pumping chamber, said pressurized fuel flowing through a pump outlet passage to a pressurized common rail, said fuel pump comprising:

• an inlet metering valve arranged to control a quantity of fuel delivered to the pumping chamber during retracting motion of the pumping plunger, said inlet metering valve including:
• a metering valve member arranged to control fuel flow between a pump inlet and a metering passage leading into said pumping chamber, said metering valve member movable between a closed position preventing fuel flow into the pumping chamber and an open position allowing fuel to fill the pumping chamber, movement of said metering valve member from said closed position to said open position defining a variable flow area that increases as said metering valve member moves from said closed position toward said open position, said metering valve member biased toward said closed position by an inlet metering check valve spring compressed between said metering valve member and said actuator piston;
• an actuator piston in an actuator bore exposed to pressure in said common rail, said actuator piston biased toward a first position corresponding to low pressure in said common rail and movable toward a second position corresponding to maximum pressure in said common rail, said actuator piston including a valve stop that determines a metering position of said metering valve member, said actuator piston biased toward said first position by an actuator spring compressed between an interior shoulder of said actuator bore and said actuator piston;
• wherein said metering valve member opens during retracting motion of said pumping plunger against the bias of said inlet metering check valve spring to a metering position in contact with said valve stop, said metering position defining a variable flow area which is a function of the pressure in the common rail communicated to the actuator bore, said metering valve member moving away from said closed position only when fuel pressure in said pump inlet is greater than fuel pressure in said metering passage, thereby acting as a pump inlet check valve.