Fuel injection pump with positive displacement delivery valve having two port areas opened according to fuel flow rate

Claim 1

A liquid fuel injection pump for a multicylinder internal combustion engine having a fuel injection nozzle for each cylinder for injecting a fuel charge into the cylinder when supplied with fuel under pressure above a predetermined level, a charge pump operable to generate periodic pulsed charges of pressurized fuel, a fuel distributor between the charge pump and the injection nozzles providing a delivery passage for sequentially delivering the pulsed charges of fuel to the several nozzles, a reciprocable delivery valve disposed in said delivery passage and providing a passageway for conducting fuel past the delivery valve, said delivery passage providing a stop for fixing the closed position of the delivery valve, and a spring biasing the delivery valve toward the stop against the pressure generated by the charge pump, characterized in that the delivery valve is a positive displacement delivery valve which closes said passage to prevent the flow of fuel in either direction when the delivery valve is engaged with the stop, said passageway having port means providing a restricted passage to accommodate only a low fuel flow rate when the delivery valve is displaced from the stop by a first distance, said port means providing a larger fuel flow area when the delivery valve is displaced from the stop its maximum distance to accommodate the unrestricted flow of fuel at high fuel flow rates whereby the delivery valve retracts after the delivery of each pulsed charge of fuel to a nozzle to reduce the residual pressure downstream of the delivery valve below the predetermined level at all fuel flow rates and to a lower level at high fuel flow rates than at low fuel flow rates.