Hybrid control method for fuel pump using intermittent recirculation at low and high engine speeds

In a fuel supply system for an internal combustion engine, having a fuel tank, a low pressure fuel feed line for delivering low pressure fuel to an inlet passage of a reciprocating piston, engine-driven fuel pump, the pistons receiving fuel in a charging phase from a charging chamber fluidly connected to the inlet passage and discharging high pressure fuel in a discharge phase into a discharge line for delivering high pressure fuel to a common rail having a plurality of fuel injection nozzles for injecting fuel into the cylinders of the engine, a one-way check valve situated in the discharge line between the pistons and the common rail, and a control valve operatively connected between the piston and the check valve for diverting excess fuel discharged from the piston, to the pump inlet passage, a method for controlling fuel quantity delivery to the common rail, comprising:

• establishing at least two control regimes corresponding to a respective low engine speed pump operation and high engine speed pump operation;
• during low speed operation, feeding unregulated low pressure fuel to the charging chamber of the pistons and at a location between the pistons and the common rail, operating said control valve between nozzle injection events to divert excess fuel discharged from the pistons, to said pump inlet passage, thereby establishing an intermittent low pressure recirculation circuit through the pump;
• and
• during high speed operation, operating said control valve between piston discharges to regulate the quantity of low pressure feed fuel to the charging chamber and delivering all of the fuel discharged from the pistons, to the common rail.