Fluid sprinkling – spraying – and diffusing – Fluid pressure responsive discharge modifier* or flow... – Fuel injector or burner
Reexamination Certificate
1999-06-14
2001-02-20
Kashnikow, Andres (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Fluid pressure responsive discharge modifier* or flow...
Fuel injector or burner
C239S572000, C239S584000
Reexamination Certificate
active
06189815
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention is based on a valve control unit for a fuel injection valve, in particular for a common rail injector.
A valve control unit of this kind for a fuel injection valve is known for instance from European Patent Disclosure EP 0 661 442 A1.
In the known valve control unit, there are two valve control chambers communicating continuously with one another in the housing body. The first valve control chamber communicates with an inflow conduit for fuel, which is connected to a high-pressure reservoir (common rail). The second valve control chamber has a passage to an outlet conduit, which can be opened and closed via a magnet valve. When the valve control unit is triggered, the outlet conduit is opened. As a result, the pressure in the second valve control chamber and thus in the first valve control chamber as well drops, so that the hydraulic imposition of pressure on one end of the valve control piston is also reduced. The other end of the valve control piston is connected to a nozzle needle for performing the injection. As soon as the hydraulic pressure imposition drops below the pressure imposition of the nozzle needle, the nozzle needle opens, so that the fuel can emerge through the injection opening into a combustion chamber. Manipulating the pressure ratios of the valve control chambers is done so as to control the valve control piston.
The terminal member of the valve control piston can be displaced in the injection event inside the first valve control chamber as far as a hydraulic stop (fuel cushion), which forms in the passage region between the first and second valve control chambers. This hydraulic stop is determined essentially by the size of the volume of the first valve control chamber. The known valve control unit has a first valve control chamber with a small volume, since only a small volume of the first valve control chamber assures that the hydraulic stop will not cause any vibration of the valve control piston and will have adequate rigidity. Because of the volumetric proportions of the first and second valve control chamber to one another, however, a considerable pressure gradient develops between the first and second valve control chambers. In the preinjection, the valve control piston can consequently move with a long valve stroke, so that a larger quantity of fuel is injected into the combustion chamber in the preinjection.
It would also be desirable to reduce the outer diameter of the terminal member of the valve control piston, so that this terminal member would have a lesser positive displacement cross section for fuel from the first valve control chamber. Reducing the outer diameter, however, necessarily increases the free volume of the valve control chamber, so that designing first valve control chamber in this way in turn leads to increased vibration on the part of the valve control piston at the hydraulic stop. Disadvantageously, the outer diameter of the terminal member of the valve control piston can therefore not be reduced, even though such a reduction, because of its reduced positive displacement cross section, would make an increased speed of motion of the terminal member possible.
OBJECT AND SUMMARY OF THE INVENTION
To minimize the preinjection quantity of fuel, the valve control unit for a fuel injection valve according to the invention has a mechanical stop for limiting the mobility of the valve control piston in a direction of a second valve control chamber.
The motion of the valve control piston is limited by a mechanical stop, which is embodied inside the housing body of the valve control unit. This mechanical stop can be embodied in various ways. In a simple variant of the invention, the valve control piston can change over in steps from a larger to a smaller outer diameter, and a counterpart step complementary to this step can be present on the housing body. To uncover the injection opening, the valve control piston can be moved with a stroke which is determined by the spacing of the two steps, when the injection opening is closed and the terminal member of the valve control piston is impinged by pressure.
Because of the embodiment of the mechanical stop, the hydraulic stop can be dispensed with, so that the first valve control chamber can be embodied with a larger volume. The first valve control chamber can advantageously have a volume of up to 60 mm
3
, while it is still assured then that no vibration with regard to the stop of the valve control piston will occur.
If the volume of the second valve control chamber is kept small in comparison with this volume of the first valve control chamber, then the pressure gradient upon opening of the outlet conduit between the first and second valve control chambers is reduced substantially. The resultant shorter stroke of the valve control piston means that initially only a small quantity of fuel is preinjected. The main injection is unaffected.
In the larger volume of the first valve control chamber, a pressure can always be embodied which is essentially equivalent to the pressure inside the high-pressure reservoir (common rail). The pressure ratios inside the first valve control chamber are thus virtually constant both when the fuel injection valve is open and when it is closed. The small volume of the second valve control chamber is pressure-relieved through the opening of the outlet conduit in the injection event. Upon reclosure of the fuel injection valve because of the closure of the outlet conduit by the magnet valve, only the small volume of the second valve control chamber has to be brought to a higher pressure level, and as a result the closing process can be accomplished faster.
The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of preferred embodiments taken in conjunction with the drawings.
REFERENCES:
patent: 1802933 (1931-04-01), Von Salis
patent: 4463901 (1984-08-01), Perr et al.
patent: 5542610 (1996-08-01), Augustin
patent: 5806766 (1998-09-01), Krueger et al.
patent: 5890653 (1999-04-01), Kelly
Boecking Friedrich
Potschin Roger
Bocanegra Jorge
Greigg Edwin E.
Greigg Ronald E.
Kashnikow Andres
Robert & Bosch GmbH
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