Common rail fuel pump

A common rail fuel supply system, for use in an internal combustion engine, the system comprising a common rail fuel volume for supplying fuel to a plurality of fuel injectors of the engine and at least one common rail fuel pump,

• wherein said at least one common rail fuel pump comprises:
• a pumping plunger that is reciprocable within a plunger bore provided in a pump housing under the influence of a cam drive arrangement to cause fuel pressurization within a pump chamber, wherein the drive arrangement includes a cam driven drive member coupled to the plunger to impart drive thereto, in use, so that the plunger performs a pumping cycle including a pumping stroke and a return stroke;
• an inlet metering valve operable to permit control of the quantity of fuel supplied to the pump chamber during the return stroke of the plunger;
• and
• an outlet valve for controlling the supply of pressurized fuel from the pump chamber, through an outlet passage to the common rail fuel volume during the pumping stroke in circumstances in which the inlet metering valve is closed;
• wherein the outlet passage communicates with a pump outlet that is substantiauy co-axially aligned with the inlet metering valve and the plunger;
• wherein the inlet metering valve is operable:
• i) to open during the return stroke to permit fuel to be supplied to the pump chamber from a low pressure source, and ii) to close part way through the return stroke in order to meter the quantity of fuel that is supplied to the pump chamber during the return stroke;
• and
• wherein the or each common rail fuel pump is arranged to supply fuel through a respective pump outlet to the common rail fuel volume.