Internal-combustion engines – Charge forming device – Fuel flow regulation between the pump and the charge-forming...
Reexamination Certificate
2000-01-19
2001-07-03
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel flow regulation between the pump and the charge-forming...
C123S1980DB
Reexamination Certificate
active
06253741
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to diesel engines and, more particularly, to a system for preventing fuel pump air ingestion in a diesel engine.
BACKGROUND ART
Modern electronically controlled diesel distributor-type injection pumps control the delivery of fuel to the injectors by pumping the full stroke of the high pressure pumping plungers, and controlling the start and end of injection with a high pressure spill solenoid valve. These pumps also have “snubber” valves in the high-pressure delivery outlets. The snubber valves perform many functions, but mainly act as check valves in the delivery direction, allowing fuel to flow freely towards the injector, but controlling the return flow pressure drop in the fuel line with an orifice. This orifice allows the reflected pressure wave from the injector to dissipate back into the fuel distributor, so that the fuel delivery line pressure is dropped, preventing secondary injections.
If air is introduced into this high-pressure fuel pump section, it will collect in the high-pressure fuel line to the injector. The air will then be compressed by the action of the high-pressure pumping element and expanded back through the return flow orifice. The same compression and expansion action is repeated continuously, without the air being dispersed. As long as air is being continually compressed and expanded, insufficient injection pressure will be generated and fuel delivery through the fuel injector to the engine will be adversely affected. The result is an engine that cannot be started without mechanical (service) intervention, to bleed out the air in the high-pressure fuel line system.
If the vehicle operator allows the vehicle to run out of fuel, air will be delivered to the fuel injection system, eventually getting into the high pressure pumping chamber and injector fuel lines, causing the engine to cease operation due to fuel starvation. When the operator attempts to rectify this problem by adding fuel to the fuel tank and supply system, the air that is trapped in the high pressure pumping system will not be purged without mechanical (service) intervention.
Typically, other methods of preventing air ingress usually use the fuel tank level indicator system to warn that the vehicle is about to run out of fuel. Because of the large width to depth aspect ratio of typical vehicle fuel tanks, it is difficult to make this system accurate. Thus, there is the potential to shut down the vehicle even with measurable fuel quantity left in the tank.
The disadvantages associated with these conventional prevention methods have made it apparent that a new technique for preventing air ingestion in a diesel fuel pump is needed. Preferably, the new technique should be more accurate then a system using a fuel tank level indicator. The new system should also shut down the vehicle with as little measurable fuel left in the fuel tank as possible.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved and reliable means for preventing fuel pump air ingestion. Another object of the invention is to provide a system which only shuts down the fuel system when a minimal amount of fuel remains in the fuel tank. An additional object of the invention is to allow easy priming of a fuel pump after running out of fuel.
In one preferred embodiment of the present invention, a device for preventing fuel pump air ingestion in a diesel fuel system includes a diesel engine having a plurality of injectors. The injectors receive a supply of diesel fuel from a fuel injection pump at a high pressure. The fuel injection pump receives the supply of diesel fuel from a transfer pump at a transfer pressure through a transfer pressure gallery. The supply of diesel fuel is stored in a fuel tank coupled to the transfer pump through a fuel line. To prevent air from entering the diesel fuel system, a low pressure sensing switch is coupled to the transfer pressure gallery and senses the transfer pressure. When the transfer pressure drops below a predetermined pressure a controller disables the fuel injection pump. Once the transfer pressure rises above the predetermined pressure level, the controller again initiates operation of the fuel injection pump.
The present invention achieves an improved and reliable means for preventing fuel pump air ingestion. Also, the present invention is advantageous in that it allows the vehicle to operate as long as practically possible before disabling the fuel system.
Additional advantages and features of the present invention will become apparent from the description that follows, and may be realized by means of the instrumentalities and combinations particularly pointed out in the appended claims, taken in conjunction with the accompanying drawings.
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Drouillard Jay
Ford Global Technologies Inc.
Gimie Mahmoud
Yuen Henry C.
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