Fuel injection system

A fuel injection system for an internal combustion engine, the system comprising:

• a plurality of pumps arranged to supply respective flows of pressurized fuel to a common accumulator volume that supplies the pressurized fuel in turn to a plurality of fuel injectors;
• an engine control unit for controlling the flow rate of pressurized fuel into the accumulator volume in response to engine load;
• and
• an engine load data input for inputting engine load data to the engine control unit;
• wherein at least one pump of the plurality has an uncontrolled fuel output;
• and
• at least one other pump of the plurality comprises a fuel output control responsive to the engine control unit to control the aggregate flow rate of pressurized fuel from the pumps into the accumulator volume, wherein the amount of fuel pressurized by the at least one other pump is capable of being varied at a given engine speed, thereby varying the flow rate of pressurized fuel from the at least one other pump at the given engine speed.

A method of operating a fuel injection system of an internal combustion engine, the method comprising:

• driving a plurality of pumps to supply respective flows of pressurized fuel to a common accumulator volume;
• and
• controlling the amount of fuel pressurized by at least one, but less than all, of the plurality of pumps in response to engine load, thereby controlling the flow rate of pressurized fuel therefrom to control the aggregate flow rate of pressurized fuel from the pumps into the accumulator volume
• wherein the amount of fuel pressurized by at least one of the plurality of pumps is varied over a range of settings at a given engine speed.