1. Field of the Invention
The present invention relates to a fuel injection system for an internal combustion engine, and more particularly, to a fuel injection system including a fuel pump which periodically transmits pressurized pulses of fuel from the fuel pump through a conduit to a fuel injection valve.
2. Description of the Prior Art
A wide variety of fuel injection systems include a cam driven fuel pump which periodically transmits pressurized pulses of fuel from the fuel pump through a conduit to one or more fuel injector valves. Typically these fuel injector valves are spring biased to a closed position and open when the pressure at the fuel injector valve exceeds a predetermined pressure level. As the amplitude of the pressure pulse present at the fuel injector valve decreases below a predetermined threshold level, the force provided by the spring bias closes the needle valve of the fuel injection valve and terminates the injection of fuel into an engine cylinder.
A 1936 United Kingdom patent specification Ser. No. 443,124 discloses an invention by Amery which relates to an improvement for fuel injection systems of the type described above. In the system disclosed by Amery the fuel injector valve is opened when the fuel pressure at the valve reaches a predetermined level. An auxiliary cam-operated control valve is provided to generate a fluid pressure which is applied to the back side of the fuel injector valve to forcefully close the injector valve at predetermined times independent of the fuel pressure at the discharge end of the fuel injector valve. In accordance with the Amery system, commencement of fuel injection depends on the timing of the mechanically driven fuel pump while the termination of the fuel injection depends on pressure applied to the closing piston within the fuel injector valve under the control of the cam operated control valve.
An inherent characteristic of engine speed driven fuel injection systems is that the pressure available for injection decays rapidly at low engine speeds due to the slower pumping action of the fuel pump.
U.S. Pat. No. 4,069,800 (Kanda et al) discloses a fuel injection system which utilizes accumulators to maintain a uniform fuel supply pressure at the fuel injector valve. A spring biased servo valve within the fuel injector valve controls the opening and closing of the fuel injector valve. U.S. Pat. No. 4,036,192 (Nakayama) discloses a related fuel injection system which is intended to eliminate dribbling of fuel from fuel injection nozzles following the termination of each fuel injection pulse.
U.S. Pat. No. 3,952,711 (Kimberley et al) discloses a fuel injection nozzle with independent opening and closing control. In this common rail system which utilizes an accumulator to provide a uniform source of fuel pressure at the fuel injection valve, the opening of the nozzle valve is controlled by a compression spring in a conventional manner, but an independent means is provided to control the nozzle valve biasing forces during opening and closing of the nozzle. U.S. Pat. No. 3,416,506 (Steiger) discloses another type of common rail fuel injector system which utilizes a pressure accumulator to maintain a uniform pressure level at the fuel injector valve.