WO2004076846A1

WO2004076846A1 - High-pressure line for a fuel injection system

Info

Publication number: WO2004076846A1
Application number: PCT/DE2003/002795
Authority: WO
Inventors: Holger Rapp
Original assignee: Robert Bosch Gmbh
Priority date: 2003-02-25
Filing date: 2003-08-21
Publication date: 2004-09-10
Also published as: EP1611342B1; EP2230397B1; CN1745243B; DE10307871A1; JP2006514201A; EP1611342A1; CN1745243A; EP2230397A1

Abstract

The invention relates to a high-pressure line between an injector (1) and a common rail (114), which fully or partially decomposes the pressure waves created when the injector (1) is actuated.

Description

High pressure line for a fuel injection system

State of the art

The invention relates to a high-pressure line for a fuel injection system for an internal combustion engine.

Based on FIG. 8, a

Fuel injection system 102 according to the prior art of an internal combustion engine. The reference numerals used here are also used in the description of the high-pressure line according to the invention.

The fuel injection system 102 shown in FIG. 8 comprises a fuel tank 104 from which fuel 106 is delivered by an electrical or mechanical fuel pump 108. The fuel 106 is conveyed to a high-pressure fuel pump 111 via a low-pressure fuel line 110. From the high-pressure fuel pump 111, the fuel 106 passes via a high-pressure fuel line 112 to a common rail 114. A plurality of injectors 1 are connected to the common rail 114, which inject the fuel 106 directly into combustion chambers 118 of an internal combustion engine (not shown). The hydraulic connection between common rail 114 and injectors 1 is made via a high-pressure line 3. At the beginning of an injection of fuel into a combustion chamber 118, the injector 1 belonging to the combustion chamber 118 is opened. As a result, the high pressure fuel 106 flows from the injector 1 into the

Combustion chamber 118. The quantity of fuel that has escaped subsequently flows from common rail 114 to injector 1.

Since modern injectors 1, in particular piezo-controlled injectors, open and close very quickly, when the injector 1 is actuated, a pressure wave arises in the high-pressure line 3, which runs from the injector 1 to the common rail 114. There the pressure wave is reflected and returns to injector 1. The faster injector 1 opens, the steeper the edges of the

Pressure wave. The steepness of the flanks of the pressure wave is also referred to below as the gradient dp / dt.

In the high-pressure line 3 and in the injector 1, the amplitude of the previously described pressure wave is superimposed on the static common rail pressure immediately after the start of an injection. As a result, the pressure in the injector 1 is not constant, but is subject to considerable time fluctuations. This is especially true not only during the injection itself, but also for the

Time period that follows an injection. Since the amount of fuel injected into the combustion chamber 118 depends, among other things, on the pressure prevailing in the injector 1 during the injection, the abovementioned pressure wave has an undesirable influence on the amount of injection. This applies on the one hand if the injection duration is longer than the running time of the pressure wave through the high-pressure line, but especially if a pressure wave triggered by a pre-injection and reflected on the common rail 114 during a subsequent main injection in the injector 1 acts. However, this also makes it clear that the quantity injected during a main injection depends to a large extent on its distance from a previous pre-injection.

Arrangements described below for reducing pressure waves in a fuel injection system 102 are known from the prior art:

A throttle (not shown) is installed in the high-pressure line 3. As a result, the pressure waves are damped; however, the throttle also reduces the injection pressure available at injector 1, which is undesirable.

In addition, a check valve (not shown) can be provided parallel to the throttle (not shown), which opens in the direction of the injector 1. This avoids throttling losses; however, the throttle is ineffective as long as fuel flows from common rail 114 to injector 1; that is during the

Injection, this arrangement is ineffective. Furthermore, such an arrangement with one check valve per injector is also very expensive.

From DE 100 60 811 AI an arrangement is known in which a damping chamber is provided in the injector 1, which is hydraulically connected to the high-pressure line 3 via a throttle.

The effect of these measures known from the prior art for reducing pressure vibrations in the high-pressure line is still in need of improvement, in particular because the above-mentioned problem increases as the injection pressures increase and the injectors respond faster and faster. Advantages of the invention

In a first embodiment of a high-pressure line according to the invention, it is provided that the high-pressure line consists of a first section and a second section and that the first section and the second section are connected in parallel,

A particularly advantageous embodiment of the invention is characterized in that the first section has an open end and that the second section has a closed end. According to the invention, the open end of the first section is connected to the common rail and the first section and the second

Section of the high pressure line unite in the area of the connection to the injector. With this constellation, the following can _. Effect can be exploited:

When a pressure wave is reflected at an open end, here in the first section of the high-pressure line, where the high-pressure line ends in the common rail, not only does a reflection of the pressure wave take place, but also a reversal of the sign of the amplitude. This means that after the reflection, a drop in pressure becomes an increase in pressure of the same amount.

When a pressure wave is reflected at a closed end, only the direction of the pressure wave changes, but not the sign of the amplitude. If now the first

Section with its open end and the second section with its closed end are of substantially the same length, where the first section and the second section meet, two pressure waves meet with the same amplitude, the sign of the Amplitude is positive on one pressure wave and negative on the other. As a result, the pressure waves are extinguished, so that, seen in the flow direction, there is no longer any pressure wave behind the merging point of the first section and second section. Rather, there is a constant pressure in the injector and thus also constant initial conditions, for example for a main injection following a pre-injection, regardless of their distance from one another.

In a further embodiment of the high-pressure fuel line according to the invention, the first section and the second section are hydraulically connected by a throttle. This ensures that a large part of the amplitude of the reflected pressure waves is extinguished before reaching the junction point, namely where there is a hydraulic connection between the first section and second section through the throttle, so that only very small remaining ones remain at the junction point Pressure waves arrive from the two line sections.

In a further embodiment of the high-pressure fuel line according to the invention, a throttle is introduced in section 2 of the line. As a result, part of the pressure wave is reduced and a sufficient amount of fuel can still flow from the common rail to the injector through the first section of the high-pressure line without any noteworthy pressure losses.

The effect of this high-pressure line according to the invention can be further improved by providing a check valve connected in series with the throttle in the second section. It is thereby achieved that the vacuum waves triggered by an injection, as previously, on closed end are reflected, but that in the event of any incoming excess pressure waves, the valve opens and the waves are reduced via the throttle in 's Raii, so that there is little or no reflection.

Alternatively, it can also be provided that the high-pressure line has a third section and that both the first section and the second section open into the third section, which extends between the union point and the injector. This embodiment ensures that the high-pressure line according to the invention can be connected to common rails and injectors that are already in series production without any design changes. In many embodiments and applications of the high-pressure line according to the invention, it is advantageous if the length L i of the first section and the length L _{2 of} the second section are essentially the same.

It is also advantageous in many applications if the hydraulic diameter Di of the first section and the hydraulic diameter D _{2 of} the second section are essentially the same. Finally, it is also advantageous if the sum of the squares of the hydraulic diameter Di of the first section and the hydraulic diameter D _{2 of} the second section is as large as the square of the hydraulic diameter D _{3 of} the third section.

However, these relationships are not mandatory

Prerequisite for the high pressure line according to the invention. There are also a variety of areas of application where it makes sense to deviate from these relations. For example, it may be desirable for the reflected pressure waves from sections 1 and 2 to be targeted arrive at the union point. This can then be achieved by different power lengths Li and L ₂ . In the same way, it may also be undesirable, for example, that the diameters Di, D ₂ and D _{3 of} the power sections are the same.

The disadvantages of the prior art are also improved by a one-piece high-pressure line in which one end of the high-pressure line has an enlarged diameter. As a result of this measure, the pressure on the common rail is not completely reflected at one location, but rather in the area of the increasing diameter in the high-pressure line, the pressure wave is already partially broken and reflected. As a result, the edges of the reflected pressure wave become flatter, that is, the gradient dp / dt decreases sharply. This also reduces the pressure vibrations in the area of the nozzle needle seat in the injector, which on the one hand considerably reduces the influence of the distance between two injections on the second injection and on the other hand results in significantly reduced wear on the nozzle seat.

The diameter expansion of the high pressure line can either be frustoconical or stepped. According to the invention, this embodiment also includes high-pressure lines in which a separate connecting piece with an enlarged diameter, in particular with a frustoconical or conical enlarged diameter, is attached to the common rail.

Instead of the conical shape, the diameter can also increase in length in a non-linear manner, which leads to a curved, conical inner shape.

As previously mentioned, those described above can be used constructive features of the high-pressure line according to the invention can be combined with one another in order to optimize the operating behavior of a special fuel injection system by suitable selection and dimensioning of the high-pressure line according to the invention.

Further advantages and advantageous refinements of the invention can be found in the following drawing, its description and the patent claims.

drawing

Show it:

FIG. 1 shows a high-pressure line according to the prior art,

characters

2 - 7 embodiments of the invention

High pressure lines, and

Figure 8 is a schematic representation of a

Fuel injection system.

Description of the embodiments

1, which represents a high-pressure line 3 known from the prior art, which hydraulically connects a common rail 114 to an injector 1, the pressure wave already mentioned several times and its temporal and local course in the high-pressure line 3 are to be explained in more detail.

For this purpose, an xp diagram is shown on the left of the high pressure line 3. Here x represents a length coordinate of the high pressure line 3, the zero point of which The connection between the injector 1 and the high-pressure line 3 lies, the Y-axis of the diagram labeled "p" represents a pressure p (x) in the high-pressure line 3. The high-pressure line 3 has a length L, that is to say a pressure wave emanating from the injector 1 reaches the common rail 114 when the location coordinate is x = L and is reflected there.

On the left of the high-pressure line 3, an x-p diagram is shown, which shows the pressure curve in the

High-pressure line 3 represents when the pressure wave moves from the injector 1 in the direction of the common rail 114. The diagram on the left of the high-pressure line 3 shows a snapshot at a time when there is a maximum 5 of the pressure wave between the injector 1 and the common rail 114. The direction of the pressure wave is represented by an arrow 7. When looking at the p-x diagram shown on the left of the high-pressure line 3, it is noticeable that the pressure wave has the form of a pressure drop compared to the static pressure in the high-pressure line 3. This is also immediately obvious if one realizes that the opening, in particular the sudden opening, of the injector 1 injects fuel from the injector 1 into the combustion chamber 118 (see FIG. 8), so that a pressure decrease in the injector 1 takes place.

As a result, a pressure wave with a negative amplitude (pressure reduction) arises, which runs from the injector 1 in the direction of the common rail 114 through the high-pressure line 3. The amplitude of the pressure wave is m z igur i with n DCA.CAV -.-- HC.I_.

When the pressure wave now reaches the common rail 114, the common rail 114 acts like an open end with a static pressure with respect to the pressure wave. At this open end, the pressure wave is reflected, that is, it changes their running direction and now runs from the common rail 114 in the direction of the injector 1. At the same time, however, the sign of the amplitude changes, so that a pressure drop becomes a pressure increase. This is indicated by the px diagram on the right of the high pressure line 3. The direction of arrow 7 has been reversed from the illustration on the left side of high-pressure line 3. The pressure drop has also resulted in a pressure increase, as the comparison of the pressure waves in the px diagrams on the left and right of the high-pressure line 3 shows.

When the reflected pressure wave reaches injector 1, the pressure in injector 1 is subject to considerable fluctuations. Starting from a static pressure p _scat , which is shown in the px diagrams, the pressure in the injector increases by the amplitude A.

If an injection is taking place at the time when the pressure wave arrives at injector 1 and thus the pressure in the injector is subject to very large fluctuations in time, this has a direct influence on the amount of fuel injected. As a result, the metering accuracy of the injector 1 and thus the emission behavior of the internal combustion engine deteriorate. The running culture of the internal combustion engine can also suffer.

If, on the other hand, the injector 1 is closed at the point in time at which the reflected pressure wave reaches it, it represents a closed end for the pressure wave and the wave is reflected in the direction of the rail again, this time while maintaining its amplitude. Finally, a very weakly damped, standing wave then forms in the line, the pressure in injector 1 oscillates for a long time after an injection, and there is a considerable influence on the distance between two Injections on the second injection.

A gradient dp / dt is shown qualitatively in the p-x diagram on the left of the high-pressure line 3. This representation is not entirely correct, since a time course of the pressure "p" cannot be represented in a p-x diagram; However, because of the constant speed of propagation of the pressure wave in the high pressure line 3, there is a direct relationship between the slope of the flank of the pressure wave, as shown in the px diagram according to FIG. 1, and as defined in connection with the invention, namely as a change over time Fuel pressure in the high pressure line 3, also referred to here as the gradient dp / dt.

FIG. 2 shows a first exemplary embodiment of a high-pressure line 3 according to the invention. The high-pressure line 3 is designed in two parts. It has a first section 3.1 and a second section 3.2. The first section 3.1 connects the common rail 114 to the injector 1 and has a length Li and a hydraulic diameter Di.

The second section 3.2 has a length L? and a hydraulic diameter D ₂ . The first section 3.1 and the second section 3.2 meet and open into one another where they are connected to the injector 1.

In contrast to the first section 3.1, the second section 3.2 has a closed end 9. The hydraulic diameters Di and D can be essentially the same. Likewise, it can be advantageous in many applications if the lengths Li and L ₂ are essentially the same. However, the invention is not based on this Dimensioning limited.

If the injector 1 is now opened, as already explained in detail with reference to FIG. 1, a pressure wave arises in the form of a pressure drop which runs through both the first section 3.1 and the second section 3.2 of the high-pressure line 3. As already explained with reference to FIG. 1, the pressure wave is reflected at the open end of the first section 3.1, namely where it ends in the common rail 114, and changes its sign in the process. This means that a drop in pressure becomes an increase in pressure.

The situation is different with the reflection of the pressure wave at the closed end 9 of the second section 3.2. There the pressure wave only changes its direction, but not the sign of its amplitude. The pressure wave reflected by the closed end 9 of the second section 3.2 is still a pressure drop. If the reflected pressure wave of the first section, which is now a pressure increase, and the reflected pressure wave of the second section 3.2, which is still a pressure drop, meet where they open into the injector 1, the reflected ones are deleted Pressure waves of the first section 3.1 and the second section 3.2, so that the pressure "p" in the injector 1 remains constant over time.

This means that the pressure wave generated by the opening of the injector 1 by natural law no longer has any negative influence on the amount of fuel injected.

FIG. 3 shows a further exemplary embodiment of a high-pressure line 1 according to the invention. A significant difference to the embodiment according to Figure 2 is that between injector 1 and the first section 3.1 and the second section 3.2 there is a third section 3.3 of the high pressure line. The third section 3.3 has a hydraulic diameter D ₃ and a length L ₃ . It can be advantageous if the sum of the squares Di ² + D ₂ ^{2 of} the hydraulic diameters Di and D _{2 is} equal to the square D ₃ "of the hydraulic diameter D _{3 of} the third section 3.3. The processes in the first section 3.1 and in the second section 3.2 in this exemplary embodiment correspond to the processes which were previously described with reference to the exemplary embodiment according to FIG. 2.

The mode of operation of the second section 3.2 with a closed end 9 is to be clarified once again on the basis of this second exemplary embodiment. The p-x diagrams to the right and left of the high-pressure line, which are designated by I, show the pressure wave on the way from injector 1 to common rail 114 or to the closed end 9. In the p-x diagram to the left of

High-pressure line 3, which is designated II, the reflected pressure wave is shown on its way from the common rail 114 through the first section 3.1 to the injector 1

As already explained with reference to the description of FIG. 1, the pressure wave undergoes a sign reversal upon reflection on the common rail 114, so that a pressure drop becomes an increase in pressure.

How to compare the right of the second

Section 3.2 arranged px diagrams I and II reveals, when the pressure wave is reflected at the closed end 9 there is no sign reversal of the amplitude, that is to say the pressure drop is only reflected at the closed end 9, that is to say it changes its direction of travel, but not its sign, if the pressure waves according to the px diagrams, which are labeled II in FIG. 3, meet each other where the first section 3.1 and the second section 3.2 open into the third section 3.3 the pressure waves, because of their different signs, completely out, so that there is no more pressure wave in the third section 3.3 and in the injector 1.

The embodiment according to FIG. 4 largely corresponds to the embodiment shown in FIG. 3, a throttle 11 being provided only in the second section 3.2. The injector 1, which is connected to the third section 3.2, is not shown in FIGS. 4, 5, 6 and 7 for reasons of space.

The pressure wave in the second section 3.2 is damped by the throttle 11, so that a complete extinction of the pressure bores at the junction of the first section 3.1 and the second section 3.2 no longer takes place. This apparent disadvantage compared to the exemplary embodiment according to FIG. 3 can, however, be advantageous in certain applications, especially when one considers that modern fuel injection systems work with multiple injection and such multiple injections are carried out over a very large speed range of the internal combustion engine. Due to the wide speed range of the internal combustion engine, the time interval between multiple injections is also very different, depending on the speed of the

Internal combustion engine. The arrangement according to the invention of the throttle 11 in the second section 3.2 can in some cases improve the overall operating behavior of the internal combustion engine over the entire speed range and under all load conditions, even if in certain cases Load points and speeds may not completely eliminate the pressure waves.

In the exemplary embodiment according to FIG. 5, the throttle 11 is not introduced into the section 2 of the line 8, but rather connects the first section 3.1 and the second section 3.2 with one another. Since the pressure waves running away from the injector in sections 1 and 2 of line 3 have the same sign, the throttle has no influence on these waves - there are none

Pressure difference at the throttle. However, the waves reflected at the rail or at the closed end of section 2 have different signs. If they reach the throttle 11, there is a damped pressure equalization between sections 1 and 2 and as a result the reflected waves run in a strongly weakened form, but with opposite signs to the union point, where they completely cancel each other out. In the exemplary embodiment according to FIG. 6, the second section 3.2 also represents a hydraulic connection between the third section 3.3 and the common rail 114, although a throttle 11 and a check valve 13 are present in the second section 3.2. The check valve 13 allows fuel to flow back from the second section 3.2 into the common rail. The check valve closes in the other direction. The check valve remains closed with incoming pressure waves with a negative sign and thus continues to represent a closed end with unchanged function.

If, on the other hand, a pressure wave with a positive sign arrives at the check valve, this opens and the pressure wave experiences the throttle 11 as a line termination, at which it is either not reflected at all or only weakly. In the exemplary embodiment according to FIG. 7, the high-pressure line 3 is again made in one piece and has a diameter-widened region 3.4. In the exemplary embodiment shown in FIG. 7, the area 3.4 with a larger diameter is conical, the end with the larger diameter opening into the common rail 114. However, the invention is not limited to conical diameter expansions, but can also include, for example, step-shaped or stepless, but not linear diameter expansions. An important effect of this diameter-enlarged area 3.4 is that the incoming pressure wave is not suddenly reflected at the end of the line, but that it is partially reflected over the entire diameter-enlarged area 3.4. The rest of the pressure wave, which reaches the common rail 114, is reflected there in the manner described above and changes its sign. Due to the partial reflection of the pressure wave in the area 3.4 with an enlarged diameter, the pressure wave contour is "smoothed" immediately, which results in a reduction in the amplitude of the reflected wave (see the px diagram on the far left in FIG. 7) and in particular in a much flatter flank dp / dt of the reflected pressure wave. As a result, the pressure fluctuations within the injector 7 are smaller due to the reflected pressure wave and extend over a longer period of time. As a result, the influence of the distance between two injections on the second one is considerably reduced and the accuracy of the metering of the injection quantities is thus increased.

Claims

Expectations .

1. High-pressure line (3) for a fuel injection system for an internal combustion engine, characterized in that the high-pressure line (3) consists of a first section (3.1) and a second section (3.2), and that the first section (3.1) and the second section (3.2) are connected in parallel.

2. High-pressure line according to claim 1, characterized in that a throttle (11) is provided in the second section ^' (3.2).

3. High-pressure line according to the preceding claim 2, characterized in that a check valve (13) connected in series with the throttle (11) is provided in the second section (3.2).

4. High-pressure line according to claim 3, characterized in that the check valve (13) with the throttle (11) ^' is attached to the end of the second section (3.2) and that the check valve allows a fuel flow out of the second section (3.2).

5. High-pressure line according to one of the preceding claims, characterized in that the first section (3.1) has an open end and that the second section (3.2) has a closed end (9).

6. High pressure line according to one of the preceding. Claims, characterized in that the first section (3.1) and the second section (3.2) are hydraulically connected by a throttle (11).

7. High-pressure line according to one of the preceding claims, characterized in that the high-pressure line (3) has a third section (3.3) ^' and that' both the first section (3.1) and the second section (3.2) in the third section (3.3) open.

8. High-pressure line according to one of the preceding claims, characterized in that a length (L _x ) of the first section

(3.1) and a length (L ₂ ) of the second section (3.2) are substantially the same.

9. High-pressure line according to one of the preceding claims, characterized in that a hydraulic diameter (D _x ) of the first section (3.1) and a hydraulic diameter (D ₂ ) of the second section (3.2) are substantially equal to s _. ind.

10. High-pressure line according to one of the preceding claims, characterized in that the sum of the hydraulic diameter (Di) of the first section (3.1) and the hydraulic diameter (D ₂ ) of the second section (3.2) is substantially equal to the hydraulic diameter (D ₃ ) of the third section (3.3).

11. High-pressure line (3) according to one of the preceding claims, characterized in that one end of the first section (3.1) of the high-pressure line (3) has a diameter widening (3.4).

12. High-pressure line (3) according to one of the preceding claims, characterized in that the diameter extension (3.4) is designed according _to one of claims 13 to 15.

13. High pressure line (3) for a fuel injection system for an internal combustion engine, characterized in that one end of the high pressure line (3) has an enlarged diameter (3.4).

14. High-pressure line according to claim 13, characterized in that the diameter of the high-pressure line (3) in the area of the diameter widening (3.4) increases continuously ^' .

15. High-pressure pipe according to claim 14, characterized in that the _p diameter enlargement (3.4) is frustoconical.

16. High-pressure line according to claim 14, characterized in that the diameter of the high-pressure line (3) increases in steps in the region of the diameter widening (3.4).

17. High-pressure line according to one of the preceding claims, characterized in that the high-pressure line. (3, 3.1, 3.3) connects a common rail (114) and an injector (1).

18. High-pressure line according to claim 17 and 3 or 4, characterized in that the section (3.2) with the check valve (13) and the throttle (11) is also connected to the common rail (114).

19. Fuel injection system (102) for an internal combustion engine with a common rail (114) and an injector (1) per cylinder of the internal combustion engine and with a common rail (114) and injector (1) hydraulically connecting high-pressure line (3), thereby characterized in that the high pressure line (3) is a high pressure line (3) according to one of the preceding claims.

20. Fuel injection system (102) for an internal combustion engine with a common rail (114) and an injector (1) per cylinder of the internal combustion engine and with a common rail (114) and injector (1) hydraulically connecting high-pressure line (3), characterized that the high pressure line (3) is a high pressure line (3) according to one of the preceding claims.