Internal-combustion engines – Charge forming device – Fuel injection system
Patent
1999-07-23
2000-05-30
Miller, Carl S.
Internal-combustion engines
Charge forming device
Fuel injection system
123585, F02M 3204
Patent
active
060679646
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
The invention is based on a fuel injection system for an internal combustion engine.
Fuel injection systems of this type are known, for example, from DE 43 37 048 C2. On the one hand, a dual-fuel injector is provided, which is used for the layered injection of fuel and an additive fluid, for example diesel fuel and water, in order to reduce the pollutant emissions of the engine and if need be, to improve the efficiency. On the other hand, in the known injection system, the so-called common rail technique is also used, in which all of the fuel injectors serving the engine are supplied with high-pressure fuel from a common rail pressure reservoir.
In the known fuel injection system, it is disadvantageous that for each individual injector, a complicated and relatively expensive 3/2-way valve is required for quantity metering of the additive fluid and another 3/2-way valve is required for controlling the diesel injection quantity. In order to store up the additive fluid, the fuel supply from the common rail pressure reservoir to the injection valve is interrupted by the first 3/2-way valve and at the same time, a pressure chamber that encompasses the fuel injector and in which high-pressure fuel is stored, is relieved toward the low-pressure fuel side through a corresponding position of the first 3/2-way valve. Due to the pressure difference produced in the pressure chamber, additive fluid is fed into the pressure chamber by way of a corresponding line, which displaces the corresponding volume of fuel. Then, the first 3/2-way valve is brought back into a position that produces a connection between the common rail pressure reservoir and the pressure chamber in the injection valve. The other 3/2-way solenoid valve is provided for the precise quantity metering of the fuel quantity to be injected, which should follow the stored up additive fluid in the injection blast brought about by the next valve opening, and this other 3/2-way solenoid valve connects the rear of the injector needle, which is held in the closed position by a spring, alternatively either to the common rail pressure reservoir or to the low-pressure fuel side and as a result, chronologically controls the stroke of the valve needle, the opening and closing of the valve, and therefore the desired injection quantity.
In principle, the known fuel injection system requires both of the precisely operating and therefore complicated 3/2-way control solenoid valves for each individual injector in order to be able to precisely meter both the desired fuel quantity and the required quantity of additive fluid.
ADVANTAGES OF THE INVENTION
In order to simplify the design and thereby reduce the cost of its manufacture, the fuel injection system will be set forth hereinafter. As a result, the two complex and expensive 3/2-way solenoid control valves can be replaced with simpler and less expensive 2/2-way valves, which simultaneously raises the possibility of shifting the quantity metering for the additive fluid to a single, precisely operating metering valve that can serve an entire group of injectors. Whereas the second 2/2-way valve only controls the opening and closing time for the storing up of additive fluid, the quantity metering for the fuel quantity to be injected is produced by means of a corresponding time control of the first 2/2-way valve in the injection line between the common rail pressure reservoir and the pressure chamber.
In order to assure uniform pressure conditions in the line system and in particular, in order to prevent a degassing of the additive fluid--as a rule water--when the boiling point is exceeded, even at high temperatures, the use of a check valve is suggested between the second 2/2-way valve and the low-pressure fuel side.
It is also advantageous if, on the blunt end of its injector tappet, the injector needle supports a small piston in the radial extension, which piston protrudes into a chamber that is acted on with high pressure from the common rail pressure reservoir and is in turn sealed off in a pressure-tight m
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Harndorf Horst
Ruoff Manfred
Greigg Edwin E.
Greigg Ronald E.
Miller Carl S.
Robert & Bosch GmbH
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