WO2004005699A1

WO2004005699A1 - Injector for an injection system

Info

Publication number: WO2004005699A1
Application number: PCT/DE2003/001702
Authority: WO
Inventors: Jürgen Dick; Heinz Lixl; Johann Massinger; Martin Simmet
Original assignee: Siemens Aktiengesellschaft
Priority date: 2002-07-02
Filing date: 2003-05-26
Publication date: 2004-01-15
Also published as: EP1530680B1; EP1518050B1; WO2004005704A1; EP1530680A1; EP1518050A1

Abstract

The invention relates to an injector (11) for an injection system which can be used for injecting fuel in the cylinder of an internal combustion engine. A similar injection system is known as an injection common rail system. A pressure drop which is produced at the level of injection holes (5) of the injector (11) during injection by reason of relatively long pipelines (32) between a high pressure accumulator (31) and the injector (11), generates undesirable pressure waves, in particular during a multiple injection. Said phenomenon adversely effects the homogeneity of an injection process. The aim of the invention is to design a high pressure hole (2) which is arranged in the injector casing in the form of a buffer accumulator (VI, V2, Vn). The aim is achieved, for example by embodying said high pressure hole (2) in the form of a multilevel hole.

Description

description

Injector for an injection system

According to the preamble of the main claim, the invention is based on an injector for an injection system, which is designed for injecting fuel into an internal combustion engine. In such a system, the injector is connected by means of a high-pressure line to a high-pressure accumulator (rail) of the injection system, which provides the fuel required for injection into a cylinder of the internal combustion engine. The fuel is provided by a high-pressure pump with a certain operating pressure in the high-pressure accumulator. During an injection process, which is initiated by lifting the nozzle needle from its seat in a nozzle unit of the injector, there are pressure drops and pressure waves or vibrations in the injection system, since the connecting lines between the high-pressure accumulator and the generally several connected to the high-pressure accumulator Injectors are relatively long. These effects are particularly disadvantageous, particularly in the case of multiple injections with short time intervals, since they can impair the intended course of the injection.

So far, this problem has been attempted by constructing the connecting lines between the high-pressure accumulator and the injectors as short as possible. This was achieved, for example, by arranging the high-pressure accumulator as close as possible to the cylinder head of the internal combustion engine. The fuel is then led to the nozzle unit of the injector via the shortened connecting lines and a high-pressure bore arranged in the injectors with a constant bore diameter. Although this arrangement represents a certain improvement, it does not provide satisfactory results, in particular for rapid multiple injections. The invention is based on the object of developing an injector for fuel injection in such a way that, in particular, the pressure drops and oscillations and their interactions occurring in the multiple injection of fuel are reduced and a more uniform injection is made possible. This object is achieved with the features of claim 1.

In the injector according to the invention, in accordance with the characterizing feature of the main claim, the high-pressure bore, which is made inside the injector, is designed such that it forms the largest possible buffer store for the fuel. The high pressure hole is in close proximity to the injection holes of the nozzle unit. As a result, the length of the connecting lines between the high-pressure accumulator and the connected injectors can advantageously be regarded as less critical, since the pressure drop occurring during the injection can in particular be compensated for by the buffer volume that is made available within the injector by the high-pressure bore according to the invention. Furthermore, it is considered to be particularly advantageous that the solution according to the invention also largely suppresses the undesirable effects on the rail and the other injectors.

The measures listed in the dependent claims provide advantageous developments and improvements to the injector specified in claim 1. A particularly favorable solution is seen in the fact that the high-pressure bore in the injector is designed as a stepped bore. The stepped bore can have two or more drilling stages, each of which is drilled with a different drilling diameter. As a result, the pressure waves propagating in the individual bore stages are reflected irregularly on the bore walls, so that they partially compensate for or weaken one another. The damping of the pressure waves is the more pronounced the more drilling stages can be attached to the high-pressure drilling.

A particularly advantageous solution is also seen in making the individual drilling stages of the high-pressure drilling narrower in the flow direction of the fuel, for example. You start at the top of the injector with the widest hole and then drill the next hole with a smaller diameter so that the narrowest hole is formed in the area of the nozzle tip. Such an arrangement of the individual drilling stages can be carried out particularly easily in terms of production technology. From a fluidic point of view, there is also the advantage that the pressure waves are damped the more they have moved from their actual point of origin at the tip of the nozzle needle.

In an alternative embodiment of the invention, the bore diameter can be increased from step to step.

Due to the length of the individual drilling stages in the high-pressure bore, the volume for the fuel to be stored can also be specified in a simple manner. It seems advantageous to make the volume for the individual drilling stages smaller in the flow direction of the fuel. In this way, a relatively large storage volume for the fuel is obtained in the upper part of the injector, since there is usually enough space available for the expansion of the high-pressure bore. In the case of the lower drilling stages, on the other hand, the volume can be designed in such a way that the damping effect of the pressure waves is particularly pronounced.

A further improvement in the damping effect for the pressure waves can also be achieved if the transition between two drilling stages is provided with a beveled, in particular with a conical, ring surface. At the The pressure waves are also broken and partially absorbed in the ring surface.

In order to avoid that new vibrations can form at the transition between two adjacent drilling stages due to different flow velocities in the individual drilling stages, it is proposed in an alternative embodiment of the invention to design the transitions continuously. Such stepless transitions, which are, for example, arc-shaped, can be easily manufactured using a correspondingly shaped profile cutter.

It also seems favorable to influence the pressure waves or vibrations by drilling stages of different lengths.

Another advantageous solution also results from the fact that in the case of a further step-shaped bore arranged parallel to the high-pressure bore, the individual bore stages of which expand from top to bottom, the adjacent cross-sectional areas of the two bores are designed to be inversely proportional to one another. This ensures that the partition between the two holes always maintains the same thickness. With this solution, the injector can be made slim overall without jeopardizing the necessary strength in the high pressure area.

It is also advantageous that the two bores are drilled parallel to the longitudinal axis of the injector housing and have an access opening at the upper end of the injector housing. These access openings provide good access for connecting electrical lines for the piezoelectric actuator and an external fuel line.

The injector according to the invention is particularly well suited for use in a common rail injection system. Particularly when injecting diesel fuel, a very high fuel pressure is used, so that here the intensity of the pressure waves and the vibrations is particularly high.

An embodiment of the invention is shown in the drawing and will be explained in the description below.

FIG. 1 shows a schematic illustration of a cross section through an injector according to the invention,

Figure 2 shows schematically two transition between two drilling stages and

FIG. 3 shows a common rail injection system with an arrangement of four injectors according to the invention.

In Figure 1, an embodiment of an injector 10 according to the invention is shown in a schematic representation. In the cross-sectional drawing, an injector housing 1 can first be seen, into which an axially parallel, step-shaped longitudinal bore is made. The longitudinal bore can be seen in the right part of Figure 1 and is designed as a high pressure bore 2. It has an access opening 13 at its upper end, to which an external fuel line can be connected, for example with a screw thread.

A further step-shaped bore 10 is made in the left part of FIG. Your drilling stages are preferably designed so that the drilling diameters widen from top to bottom towards the nozzle tip. At the upper end of the injector housing 1 there is also an access opening 13, at which an electrical connection and control lines for the piezoelectric actuator 9 can be provided.

The two stepped bores 2, 10 lying next to one another are preferably designed with their bore diameters in such a way that in a bore cross-section the two neighboring cross-sectional areas 14a, 14b behave inversely proportional to each other. In addition to a narrower hole, there is a larger hole, so that the sum of the drill cross-sections is preferably constant in different stages. This advantageously ensures that the wall thickness between the two bores is always homogeneous and sufficiently strong to withstand the high fuel pressure.

The upper end of the piezoelectric actuator 9 is fixed to the injector housing 1. Its lower end is designed to be movable and acts on a nozzle needle 6, which is arranged in a nozzle unit 11, when the length changes axially. The nozzle needle 6 can open or close the 11 fuel-tight in response to control signals on the actuator with its lower conical part of the injection holes 5 of the ^'nozzle assembly.

To control the nozzle needle 6, a high-pressure chamber 7 as well as an inlet throttle 3 and an outlet throttle 8 are further provided in the nozzle unit 11. The inlet throttle 3 is connected to an inlet line 4, which is fed by the high-pressure bore 2 and essentially conveys the fuel under high pressure to the nozzle needle 6, so that the fuel emerges via the injection holes 5 when the nozzle needle 6 is lifted and into the combustion chamber Internal combustion engine can be injected.

With its entire volume VI, V2, Vn, the high-pressure bore 2 forms a buffer store for the fuel to be injected. In the upper part of the high-pressure bore VI, a connection for an external connecting line is provided at the access opening 13, which can be firmly connected to the high-pressure bore 2, for example by means of a union nut. The fuel to be injected, for example gasoline or diesel, becomes the injector 11 via the connecting line promoted. The black arrow above the high-pressure bore 2 should indicate the direction of flow of the fuel.

In contrast to a conventional cylindrical bore, the high-pressure bore 2 is designed as a multiple stepped bore. In Figure 1, three drilling stages with the drilling diameters dl, d2 and dn are shown as an example. The uppermost drilling step has the largest diameter d1, while the drilling steps below it are each designed with a smaller diameter d2, dn. The number of drilling stages is freely selectable and depends on the injector type or the intended use. Alternatively, subsequent bores can also be further developed.

Furthermore, it is provided that the length of the bores is preferably chosen so that the largest possible buffer volume is created, but sufficient wall thicknesses remain for the high-pressure bore. The uppermost drilling step has a length L1 and the subsequent drilling steps have the lengths L2 and Ln. In this way, a certain volume VI, V2, Vn for the fuel to be stored can thus be specified for each drilling stage with very simple means, since the individual volumes V are based on the trigonometric formula

V = π * d / 4 * L can be calculated (d = drilling diameter, L = length of the drilling).

The aim is to make the storage volume of the entire buffer storage as large as possible, so that, depending on the type of engine for which the injector 1 is to be used, the high-pressure storage (rail) known per se of a commercially available common rail injection system can possibly be saved. Of ^'further the injection with the injector of the invention can be made easier and cheaper. In addition, the necessary installation space in the vehicle is advantageously reduced, so that the injection system, particularly in the case of combustion engines, gates with many cylinders and in tight spaces in the engine compartment.

In an alternative embodiment of the invention, the individual volumes VI, V2, Vn are designed as a function of operating conditions of the internal combustion engine. For example, the uppermost volume VI could be made somewhat smaller, the volume V2 larger and the volume Vn smaller or the same size again. In this way, requirements of the internal combustion engine can be optimized, for example with regard to emissions, engine performance and fuel consumption.

A further important advantage of the invention is also seen in that the different drilling diameters d1, d2, dn dampen the pressure waves or vibrations occurring during the injection process. Since the pressure waves on the side walls of the individual drilling stages are broken, reflected and absorbed irregularly, the damping results in a more uniform injection process. Precise control is particularly important in the case of multiple injection, in which the fuel is injected in several individual injection pulses at the shortest time intervals. The buffer store of the high pressure bore 2 also supports this injection process.

FIG. 2 shows an enlarged view of a section of the high-pressure bore 2 of the injector 11 explained in FIG. 1. In particular, the transitions 20 that form between two adjacent drilling stages are explained in FIG. According to the invention, the transitions 20 are designed, for example, with a beveled, in particular a conical, ring surface. This soft transition, for example from diameter d1 to diameter d2, reflects the pressure waves even more diffusely and absorbs them, so that the damping properties are further improved. Between the two drilling stages d2 and dn, for example, the edges of the annular surface 20, which each arise between a drilling stage and the annular surface, were further rounded off with a corresponding tool, so that a stepless transition from the drilling stage d2 to the drilling stage dn is produced. This prevents new pressure waves or vibrations from occurring at the edges, which could impair the even course of the injection.

FIG. 3 shows a schematic arrangement for a common rail injection system, as is used for example in diesel injection. It shows the high-pressure accumulator (rail) 31 described above and known per se, to which a total of four injectors 11 are hydraulically connected via four connecting lines 32. The size of the high-pressure accumulator 31 and the number of connected injectors 11 essentially depends on the number and the volume of the combustion chambers (cylinders) of the type of engine used. In this case, the four injectors 11 are provided for a four-cylinder engine.

The fuel is pumped into the high-pressure accumulator 31 at high pressure by a high-pressure pump 33, which is connected to the high-pressure accumulator 31, and is then available for injection in the individual buffer accumulators of the connected injectors 11. The high-pressure pump 33 is in turn supplied by a fuel pump 35. For this purpose, the fuel pump 35 pumps the fuel from a storage container (symbolized by the arrow in FIG. 3) with a lower overpressure via lines 36 and one or more filter units 34 to the high-pressure pump 33. The injection holes 5 (FIG 1) opened or closed again and thus the injection process can be controlled.

Claims

claims

Injector for an injection system, which is designed to inject fuel into an internal combustion engine, the injector (11) being connectable to a high-pressure accumulator (31) of the injection system via a pressurized fuel line (32), and to a high-pressure bore (2), through which the fuel can be guided to the injection holes (5) of the injector (11) by means of a controllable nozzle needle (6), characterized in that the high-pressure bore (2) of the injector (11) acts as a buffer store (Vl, V2, Vn) for the lower Pressurized fuel is formed.

Injector according to claim 1, characterized in that the high-pressure bore (2) is designed as a stepped bore.

Injector according to claim 1 or 2, characterized in that the high pressure bore (2) is formed with at least two bore diameters (dl, d2, dn).

Injector according to claim 3, characterized in that subsequent bore diameters (dl, d2, dn) of the high-pressure bore (2) towards the nozzle tip are made narrower or alternatively further.

Injector according to claim 4, characterized in that the first drilling diameter (dl) of the stepped bore (2) is larger than the second drilling diameter (d2) and this is larger than a third drilling diameter (dn) if necessary.

Injector according to one of the preceding claims, characterized in that the volume (Vl, V2, Vn) of the individual drilling stages which takes up the fuel under consideration adjustment of the space in the injector (11) and / or operating conditions of an engine is formed.

7. Injector according to one of the preceding claims, characterized in that the individual drilling stages have a beveled, in particular a conical, annular surface at their transitions (20).

8. Injector according to one of the preceding claims, characterized in that the transition (20) between two adjacent drilling stages is stepless.

9. Injector according to one of the preceding claims, characterized in that the individual drilling stages have different lengths (Ll, L2, Ln), the lengths (Ll, L2, Ln) towards the nozzle tip according to a predetermined

Decrease ratio.

10. Injector according to one of the preceding claims, characterized in that in the injector housing (1) in at least one drilling stage of the high-pressure bore (2), a further step-shaped bore (10) is arranged in parallel, that its bore diameter widen from top to bottom, and that in at least one bore of the high-pressure bore (2) a cross-sectional area (14a) is formed inversely proportional to a cross-sectional area (14b) of the further step-shaped bore (10).

11. Injector according to one of the preceding claims, characterized in that the high-pressure bore (2) and / or the further bore (10) are drilled parallel to the longitudinal axis of the injector housing (1) and an access opening (13) at the upper end of the injector housing (1) ) exhibit.

12. Injector according to one of the preceding claims, characterized in that the injector (11) for a common Rail injection system, in particular for the injection of diesel fuel.