Fluid sprinkling – spraying – and diffusing – Fluid pressure responsive discharge modifier* or flow... – Fuel injector or burner
Reexamination Certificate
2000-08-29
2001-07-10
Douglas, Lisa Ann (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Fluid pressure responsive discharge modifier* or flow...
Fuel injector or burner
C239S533500, C239S584000
Reexamination Certificate
active
06257507
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a unit fuel injector of the type with an open injector, comprising an injector body with an axial space, which ends in an injector cap with injection bores, comprising an injection plunger guided in the axial space and serving as a closing-off element, which injection plunger bounds in the axial space a pressure space from which the injection bores extend.
A unit fuel injector of the type with an open injector is known, for example, from EP 460 693 A1. It has the special feature that the injection plunger is a pumping element and closing element at the same time. These unit fuel injectors also have the problem when they are used in high-power diesel engines—which are usually supercharged—with respect to the minimizing of consumption and emissions that the injection requirements differ considerably between idling and full load.
During idling and at low compression pressure, the rate of injection is low and the ignition delay is long. During the ignition delay, as little fuel as possible is to be injected as slowly as possible, and nevertheless atomized well. At full load and a high engine speed, on the other hand, the rate of injection is great—in the case of supercharged high-power engines even particularly great—and the duration of injection is to be as short as possible, since only a limited crank angle is of course available for the injection. All in all, optimizing combustion with regard to consumption and emissions requires a uniform distribution of the fuel in the combustion chamber and defined atomization.
The greater the differences in rates and speeds, the more difficult it is to optimize combustion with constant injector cross sections. Although it is known from EP 470 348 A1 and DE 44 32 686 C2 to provide a number of rows of injection bores and two concentric plunger needles in unit fuel injectors, in which the pumping element and closing element are separate, in order in this way to be able to adapt the cross section of the injector to the operating state, these solutions concern only the valve function and consequently cannot be transferred to the open unit fuel injectors of the generic type. Due to their special structural design, there is a different relationship between the cross section of the injector and the injection pressure.
SUMMARY OF THE INVENTION
The invention is therefore based on the object of being able to adapt the cross section of the injector and the delivery rate to the respective operating state even in the case of unit fuel injectors of the generic type. Adaptation is to be understood here as meaning both the control during operation and the design.
This is achieved according to the invention by the features that
a) the injector cap (
3
) has a first group (
60
) and a second group (
61
) of injection bores (
60
,
61
), of which the first group (
60
) is assigned to the injection plunger (
15
) and the second group (
61
) can be closed off separately from the first,
b) the injection plunger (
15
) has an axial bore (
30
), in which a plunger needle (
31
) is guided, the needle part of which interacts with a seat (
21
;
62
;
72
) formed in the interior of the injector cap (
3
), the second group of injection bores (
61
) being assigned to the plunger needle (
31
),
c) the plunger needle (
31
) has a plunger part (
32
) on which a compression spring (
35
) acts in a downward direction and which bounds a control chamber (
50
) in the axial bore (
30
),
d) the control chamber (
50
) can be fed a control medium, which raises the plunger needle (
31
) against the force of the compression spring (
35
) with respect to the injection plunger (
15
), so that said needle follows the movement of said plunger.
The two groups of injection bores can be closed off separately, the first by the injection plunger, the second by the plunger needle, which in certain load states also acts as the injection plunger. In these states, not only the injector cross section but also the pump characteristics are changed. This is possible only because both closing elements are pumping elements.
During idling and at low load, the plunger needle remains closed. As a result, in this operating state the volume of the delivery space is initially small. Furthermore, the effective area of the injection plunger is only that of a circular ring and is therefore smaller, which means a relatively higher injection pressure, in particular during hydrostatic pressure transmission from the pump drive to the injection plunger. Finally, the injector cross section is only the sum of the cross sections of the one row of injection bores. The injection bores may be relatively small, in order to achieve a long duration of injection. This makes the injection pressure high, which improves the atomization of the fuel.
At higher part load or full load and a high engine speed, the plunger needle is drawn into the injection plunger. As a result, the injection bores of the further row are also open, thereby increasing the available cross section of the injection bores. Furthermore, the volume of the delivery space and the plunger area—now comprising the area of the injection plunger and the needle—is greater. This means a considerably greater delivery rate per unit of time at the same engine speed. There is consequently a threefold effect.
All this is achieved with relatively low additional technical outlay. What is more, the control is also not sophisticated, since it only needs two positions of the plunger needle. Consequently, exact positioning of a final control element is not required. The engine controller only has to be provided with a threshold value or a curve in the characteristic map, at which value or curve a switch is made from one mode to the other. All in all, it is possible in this way to adjust both the delivery rate and the effective injector cross sections, even independently of each other.
In an advantageous design, the feeding of the control medium to the control chamber takes place through a feeding bore in the injector body and a branch bore in the injection plunger, with a longitudinal groove being provided in the injector body or in the injection plunger. Consequently, the problem of continuously varying the pressure in the control chamber moving with the injection plunger is elegantly solved.
A further simplification is obtained if the injection plunger has a stop fixing the uppermost position of the plunger needle. As a result, vibrations of the plunger needle are avoided and the control pressure does not need to be maintained exactly. As a result, the unit fuel injector is insensitive to pressure losses in the event of wear.
In an advantageous development, the injection plunger has at its outer wall an annular space, which connects the fuel feed to a return flow when the injection plunger is closed. As a result, once injection has been completed the excess pressure in the fuel feed line can be relieved and flushing and cooling can be carried out at the same time, without colliding with the feed of control medium.
To allow the entire engine characteristic map to be covered optimally and the limits between the two ranges to be chosen optimally, it has proven to be advantageous to choose the ratio of the diameters of the injection plunger and needle part of the plunger needle to be in the range between 1:2 and 1:3, the diameter of the first group of injection bores to be less than that of the second group of injection bores, and the ratio of the cross section of all the injection bores of the first group to that of all the injection bores of the second group to be greater than the ratio of the effective cross sections of the injection plunger and injection needle.
The shape and design of the closing elements, as well as the grouping and arrangement of the injection bores, may vary considerably within the scope of the invention and be adapted to the requirements of the pumping function. A particularly advantageous solution is that the injector cap has on the inside a conical seat and the second group of injection bores is ar
Dolenc Anton
Morell Josef
Schmidt Harald
Bachman & LaPointe P.C.
Douglas Lisa Ann
Steyr-Daimler-Puch Aktiengesellschaft
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