Fluid sprinkling – spraying – and diffusing – Fluid pressure responsive discharge modifier* or flow... – Fuel injector or burner
Reexamination Certificate
1999-09-13
2001-07-10
Scherbel, David A. (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Fluid pressure responsive discharge modifier* or flow...
Fuel injector or burner
C239S533900, C239S533120, C239S585500
Reexamination Certificate
active
06257506
ABSTRACT:
PRIOR ART
The invention relates to a fuel injection nozzle for self-igniting internal combustion engines, having a nozzle body, in which a conical seat face from which injection ports originate is formed at the bottom of a blind bore. A valve needle which is guided displaceably with a guide portion in the inlet region of the blind bore counter to a closing force and counter to the fuel flow direction and on the end of a valve shaft adjoining the guide portion has a closing cone cooperating with the seat face. The valve shaft circumferentially defines an annular chamber for fuel delivery. Such fuel injection nozzles are disclosed for instance in German published, non-examined Patent Application DE-OS 37 34 587 and German Utility Model 93 0 992.0.
In the fuel injection nozzle disclosed by DE-OS 37 34 587, in order to prevent the so-called blowback of the combustion gases, a control passage for the injection fuel is provided that is varied by the valve needle as a function of the stroke and whose flow cross section decreases in the closing stroke of the valve needle, down to a throttle cross section that decouples the relief wave on the pump side from the fuel pressure in the blind bore.
In the fuel injection nozzle disclosed in German Utility Model 93 01 992.0, a guide sleeve that surrounds the valve shaft and has a conically embodied face end and, in its portion near the conical face end, a plurality of recesses extending as far as the conical face end prevents the closing cone from covering some or all of the injection ports as a consequence of play or eccentricity of the valve needle, or if lateral forces in a short opening stroke act on the valve needle, which coverage would impair the combustion process.
One problem of such fuel injection nozzles is that even a short stroke of the valve needle results in large flow quantities. Especially in the pre-stroke range, the stroke-dependent characteristic curve of the flow is very steep.
Aside from deleterious combustion events, this is also problematic because different fuel injection nozzles with different tolerances thus produce very different flow quantities, with the same stroke.
It has furthermore been demonstrated that a graduated injection, or at least one that increases slowly at the injection onset, in general leads to an improvement in the emissions figures of the engines.
It is therefore the object of the invention to refine a fuel injection nozzle of this generic type in such a way that an aforementioned production tolerances, particularly in the range of the prestroke, do not deleteriously affect the injection event, and that at least at the injection onset, a slowly increasing injection is attained.
ADVANTAGES OF THE INVENTION
This object is attained, in a fuel injection nozzle of the type described at the outset, in that in the transitional region between the valve shaft and the closing cone, a throttle device of variable throttle cross section is disposed, by which the injection cross section can be varied as a function of the axial displacement of the valve needle.
The disposition of this kind of throttle device has the particularly great advantage that not only can the injection cross section be varied thereby in such a way that it increases continuously at the onset of the injection event, but also that the injection cross section can be varied in such a way that particularly in the prestroke range, only slight flow changes occur during a stroke motion of the valve needle, and as a consequence, production tolerances are much less disruptive than in known fuel injection nozzles.
As to the embodiment of the throttle device, the most various versions are conceivable.
One advantageous version provides that the throttle device includes a shoulder, formed in the annular chamber, and a control edge disposed adjacent to it and spaced apart from it on the valve shaft, which control edge is adjoined downstream by at least one conical face. By means of the shoulder, the control edge spaced apart from it, and the at least one conical face adjoining the control edge downstream thereof, a throttle with a throttle cross section that decreases as a result of axial displacement of the valve needle is made possible in a way that is highly advantageous, because it is technologically easy to accomplish.
One advantageous version provides that the control edge substantially faces the shoulder. As a result, a defined initial throttle cross section is advantageously realized.
In another advantageous version, the control edge is disposed slightly downstream of the shoulder. As a result, upon a slight axial displacement, the initial throttle cross section is kept unchanged at first, until the control edge overtakes the shoulder.
With regard to the conical face adjoining the control edge, once again the most various versions are conceivable.
The conical face is advantageously defined as a function of the disposition of the control edge opposite the shoulder.
Thus one advantageous version provides that the conical face adjoining the control edge has a smaller cone angle than the conical seat face. As a result, in cooperation with the initial throttle cross section determined by the spacing of the control edge from the shoulder, an initial throttling of the injected fuel quantity is attained in which the conical seat face of the valve needle is also, in a highly advantageous way, included in the throttling process.
It is moreover also possible for the conical face adjoining the control edge to have a larger cone angle than the conical seat face.
In a further exemplary embodiment of a throttle device, which is advantageous in terms of its manufacture, it is provided that a sleeve axially displaceable counter to the restoring force of a spring is disposed in the annular chamber and rests with a conically embodied face end on the outer annular face of the conical seat face, and in it, at least two openings of different opening cross sections are provided that can be uncovered in succession by axial displacement of the valve needle. Such a sleeve has the very great advantage in particular that it is not only easy to make but is also easy to assemble, especially even outside the nozzle body.
As to the disposition and embodiment of the openings of different opening cross section that can be uncovered in succession by axial displacement of the valve needle, they can purely in principle have the most various shapes. One advantageous version provides that a first opening is disposed above a control edge, formed on the valve shaft, in the jacket of the sleeve, and a second opening whose opening cross section is smaller than that of the first opening is disposed below the control edge embodied on the valve shaft. The opening provided in the conical face then thus takes on the task of initial throttling, while conversely the opening provided in the jacket enables a valve needle stroke- dependent decrease in the throttle cross section as a result of axial displacement of the valve needle. The opening provided in the jacket may be elliptical, oval, round, triangular, quadrilateral, or polygonal in shape.
In another advantageous version it is provided that two rows of perforations one above the other are disposed in the jacket of the sleeve, and the downstream row of perforations has a smaller total opening cross section than the upstream row of perforations. This version of the throttle device advantageously enables filtering of the injected fuel cross section.
Another advantageous version provides that a sleeve axially displaceable counter to the restoring force of a spring is disposed in the annular chamber and rests with a conically embodied face end on the outer annular face of the conical seat face and that facing the sleeve in the valve shaft is at least one recess, cooperating with the sleeve, whose opening cross section, on the end of the sleeve toward the guide portion, increases steadily toward the conical seat face.
Yet another advantageous version provides that a sleeve which can be slaved by an axial displacement of the valve needle and is
Boecking Friedrich
Hofmann Karl
Greigg Edwin E.
Greigg Ronald E.
Nguyen Dinh Q.
Robert & Bosch GmbH
Scherbel David A.
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