Fuel pump

A self-regulated fuel pump assembly of a fuel injection system of an internal combustion engine, the fuel pump assembly being adapted to be arranged between a low pressure tank and a high pressure reservoir, the fuel pump assembly comprising:

• a pump body defining an inlet fluid communication controlled by an inlet valve for enabling an inlet fuel quantity to enter a compression chamber;
• a piston which varies the volume of said compression chamber and pressurizes the fuel, wherein pressurized fuel is expelled and delivered into a high pressure space, comprising the high pressure reservoir, via an outlet fluid communication controlled by an outlet valve;
• and
• a mechanical regulating valve arranged in the pump body which modulates the pressure in the high pressure space so that the pressure matches engine demand, modulation of the pressure in the high pressure space by the mechanical regulating valve requiring adjustment of the inlet fuel quantity, adjustment of the volume of the high pressure space wherein is stored the pressurized fuel and, control of a return fluid communication enabling fuel to exit the high pressure reservoir;
• wherein the mechanical regulating valve comprises a spool valve member slidably arranged in a valve bore provided in the pump body, said spool valve member controlling the inlet fluid communication, the volume of the high pressure space and, the return fluid communication;
• and
• wherein the mechanical regulating valve further comprises a valve spring biasing the spool valve member toward a first extreme position where the inlet fluid communication is fully open and the return fluid communication is closed, and wherein the pressure in the high pressure space biases the spool valve member toward a second extreme position where the inlet fluid communication is closed and the return fluid communication is open, the biasing force of the spring being opposed to the biasing force of the outlet pressure.