EP0409943B1 - Injection pump for diesel engines - Google Patents

Abstract

A fuel injection pump for diesel engines comprises at least one piston (5) which together with a piston bushing (1) forms a high-pressure chamber (6) and which is surrounded by a control sleeve. The quantity of fuel can be controlled by varying the angular position of the piston (5) with respect to the control sleeve (3). An axial bore (11) in the piston (5) connects the high-pressure chamber (6) with a control bore (12) or with a groove which forms a control edge for the beginning and end of control, in order to terminate the injection, and which co-operates with a control edge (15, 17) or with a control bore for controlling the control sleeve (3). An evacuation bore (9) is separated from a suction or feed bore (7). In addition to the control bore (12), the piston (5) or the control sleeve (3) comprises an auxiliary control bore (13) which is entirely covered by the associated edge of the beginning of control bore (15) before or at the same time as the control bore (12) and which is not released by the edge of the end of control bore (17) before the control bore (12). The control bore (12, 13) can be connected to the evacuation bore (9).

Description

The invention relates to a fuel injection pump for diesel engines, in which at least one pump piston forms a high-pressure chamber with a pump piston sleeve and is surrounded by a control sleeve, the angular position between the pump piston and control sleeve being variable for quantity adjustment, and wherein an axial bore in the pump piston provides the high pressure chamber with a control bore or connects with a groove forming a control edge and a control edge for ending the injection process, which cooperates with a control edge or control bore of the control sleeve.

DE-OS 35 90 194 describes different variants of a series pump, in one embodiment a radial bore of the piston with a control edge and a control edge of the control sleeve, and in another embodiment a groove on the piston fed by a radial bore with a control bore of the control sleeve cooperates.

DE-OS 36 30 647 describes a pump nozzle, in the injection pump of which a groove fed by a radial bore on the piston interacts with a control bore of the control sleeve. In other pump nozzles (e.g. DE-OS 31 43 073) a radial bore of the pump piston interacts with the control edges of the control sleeve. In all of them, the control sleeve can also be moved axially to adjust the start of injection.

All these injection pumps with an axial bore in the piston, which leads from the high-pressure chamber to the control openings, belong to the SIMMS design, which is characterized by a symmetrical piston that is easy and precise to manufacture. At very high injection pressures and high pump piston speeds, with modern diesel engines Speeds up to 5000 rpm and high pressure injection, this design has disadvantages.

From a certain engine speed and at a late start of injection, a quantity of fuel escapes from the injection nozzle before the start of the injection or the pre-injection in nozzles with divided injection, the so-called pre-delivery. This is undesirable because it negates the precise control of the start of injection, the shape of the injection law is distorted by an extended injection duration and a drop in pressure, and the injection adjustment range is reduced.

This disadvantageous advance is caused by the fact that from the pump piston position, in which the inlet bores are already closed, fuel flows through the axial and subsequent radial bores in the piston and / or in the control sleeve until the radial bores are completely closed. At certain pump piston speeds, this results in a pressure wave running into the axial bore, which is reflected into the high-pressure chamber if the cross-section of the radial bores is too small. These pressure peaks can exceed the injection nozzle opening pressure, causing some fuel to leak into the engine's combustion chamber.

Another cause of the advance is the throttling effect of the various holes. With successive covering of the control bore, thus with a rapid decrease in cross-section, the pressure in the high-pressure chamber rises so much according to the throttle law that the opening pressure of the valve needle is reached prematurely.

Modern vehicle diesel engines have an overrun cut-off, which switches off the fuel supply completely when ready to brake and when driving downhill. This so-called zero funding comes with the known Injection pumps suddenly turn into injections at higher speeds due to similar dynamic effects. This poses a serious security risk and also increases fuel consumption. With zero delivery, the flow path between the SIMMS bore and the control sleeve chamber must never be completely closed. The free cross-section must even remain so large that the opening pressure of the Venitl needle is not reached despite dynamic effects and throttling law.

Finally, the most precise possible adjustment of the idle injection quantity is desirable, especially in modern diesel engines with single-cylinder control, in order to ensure quiet idling. This is only imperfectly possible in the known injection pumps because the slope of the control edge establishes the relationship between the angle of rotation and the change in the injection quantity, but this slope is too steep for the idle control.

Finally, the throttling effect is also noticeable as damping when the engine is turned off. Although damped shutdown at the end of injection is generally desirable, it is undesirable at the maximum injection amount because it takes the injection process a little too long, resulting in incomplete combustion.

Attempts to prevent the advance delivery and similar dynamic phenomena by constructive measures, for example an expansion of the axial SIMMS bore, which, however, reduces the useful stroke, or larger outflow cross sections from the control sleeve chamber, have so far been unsuccessful.

It is therefore the aim of the invention to prevent or completely prevent the described dynamic effects in the case of generic injection pumps.

To solve this problem, it is proposed that a suction or feed bore separate from a discharge bore it is provided that the pump piston or the control sleeve has, in addition to the existing control bore, which serves to terminate the injection process, an auxiliary control bore which is covered earlier than or simultaneously with the control bore by the control edge assigned to it and which is not covered by the control edge in front of the control bore is released, and that the control holes can be connected to the discharge hole.

The auxiliary control bore reduces the throttling effect, which leads to the reflection of the pressure wave, and reduces the speed of the decrease in the control cross-section when turning off. As a result, pre-delivery only occurs at a much higher speed, which is usually already above the nominal speed. The speed of the cross-sectional decrease is even lower because the auxiliary control bore is completely covered even somewhat earlier than the control bore. Due to the reduced throttling effect, suddenly occurring injections are avoided at zero delivery and higher speeds. Because the auxiliary control bore is not opened before the control bore during the control, the control times remain unchanged and the useful stroke is fully preserved. The injection process is thus terminated by opening the control bore, a subsequent pressure reduction or opening of the auxiliary control bore at the earliest at the same time making it possible to achieve a faster pressure reduction and an improved closing characteristic.

From the generic CH-PS 319 362 an arrangement has become known in which the conventional control bore is replaced by several smaller control bores, the total cross section of which is equal to the cross section of the conventional control bore. There is no mention here of an auxiliary control bore, which is provided in addition to the conventional control bore and which increases the return flow cross section when the valve is turned off, beyond the cross section of the conventional control bore.

According to a preferred embodiment of the invention, the auxiliary control bore is arranged in a position relative to the control bore which corresponds to a larger injection quantity, and the auxiliary control bore and the control bore cooperate with a common control edge. This leads to low construction costs and particularly simple production, because only a precisely machined control edge is required.

In a particularly advantageous embodiment, the diameter of the auxiliary control bore is chosen to be larger than that of the control bore. This is possible without changing the control times because the control edge is at an angle and the auxiliary control bore lies at the position of the control bore corresponding to a larger injection quantity. This further reduces the throttling effect and the dynamic effects, such as pre-delivery or injection at zero delivery, are prevented even more reliably. Furthermore, it is possible to adjust the idling more finely, because the presence of two bores of different diameters at possibly substantially the same height means that only a very small quantity variation can be achieved with a relatively large angle of rotation of the control sleeve or pump piston.

In a further embodiment, the control edge can be designed such that its slope decreases at the end corresponding to the maximum injection quantity or becomes zero or negative. As a result, in this extreme state, both control bores are released from the control edge, as a result of which the injection pressure drops faster and the injection duration is somewhat shorter, which prevents incomplete combustion.

In one variant, the control bores in the pump piston and the control edges are arranged in the control sleeve, which is advantageous in terms of production technology. In another variant, the grooves forming the control edges are arranged in the pump piston and the control bores in the control sleeve, and they are both Grooves each connected to the SIMMS axial bore in the pump piston via a separate radial bore.

This variant generally has the advantage that the control sleeve has no control edges, but only control bores, and is therefore more rigid. Due to the separate radial bores at different heights of the pump piston, the throttle length of the axial bore is reduced and the possibility is gained to additionally influence the throttling effect, in particular with regard to minimal throttling when opening.

In a further, modified embodiment, the auxiliary control bore is arranged in the direction of the pump axis above or below the control bore in the piston or in the control sleeve and the control sleeve or the pump piston have two control edges at the same distance as the control bore and auxiliary control bore. This version has the further advantage over the first version that the radial bores (control bores or feed lines to the grooves) leading away from the axial SIMMS bore of the piston lie at different heights and the cross-section of the piston is less weakened and the pressure waves in the SIMMS well arrive at the tax openings at different times. The throttle length also decreases. In a variant which is favorable in terms of production technology, the control bores are arranged in the pump piston and the control edges in the control sleeve. If in one variant the control bore and auxiliary control bore are arranged in the control sleeve and the control edges in the piston, the control sleeve is structurally less weakened.

A second control edge is preferably arranged in such a way that it is only reached by the auxiliary bore with a maximum injection quantity, as a result of which a shortened injection duration at full load can also be achieved in this embodiment.

Finally, in all embodiments and their variants, it is advantageous to arrange all control bores and control edges offset twice by 180 °.

Figur 1

einen Längsschnitt durch eine erfindungsgemäße Einspritzdüse in einer ersten Ausführungsform,

Figur 2

einen Schnitt nach der Linie AA in Fig. 1 in vergrößerter Darstellung,

Figur 3

das Detail B der Fig. 1, abgewickelt und vergrößert,

Figur 4

eine Variante der ersten Ausführungsform im Längsschnitt,

Figur 5

einen Schnitt nach der Linie DD in Fig. 4 in vergrößerter Darstellung,

Figur 6

das Detail C der Fig. 4, abgewickelt und vergrößert,

Figur 7

eine zweite Ausführungsform der erfindungsgemäßen Einspritzpumpe im Längssschnitt,

Figur 8

das Detail E der Fig. 8, abgewickelt und vergrößert,

Figur 9

eine Variante der zweiten Ausführungsform, und

Figur 10

einen Schnitt nach der Linie FF in Fig. 9.

Various embodiments of the invention and their variants are described below with the aid of illustrations. Show:

Figure 1

2 shows a longitudinal section through an injection nozzle according to the invention in a first embodiment,

Figure 2

2 shows a section along the line AA in FIG. 1 in an enlarged view,

Figure 3

detail B of FIG. 1, developed and enlarged,

Figure 4

a variant of the first embodiment in longitudinal section,

Figure 5

3 shows a section along the line DD in FIG. 4 in an enlarged view,

Figure 6

the detail C of FIG. 4, developed and enlarged,

Figure 7

a second embodiment of the injection pump according to the invention in longitudinal section,

Figure 8

the detail E of FIG. 8, developed and enlarged,

Figure 9

a variant of the second embodiment, and

Figure 10

a section along the line FF in Fig. 9th

The essential parts of an injection pump of the types to which the invention relates have the same reference numerals in all figures. 1 denotes a pump piston liner with a recess 2, 3 a control sleeve inserted into this recess, which is rotated, for example, to set the quantity and raised and lowered for spray adjustment, 4 a separating sleeve surrounding the pump piston liner 1, 5 a pump piston driven by a camshaft (not shown), 6 one High-pressure chamber, 7 a schematically indicated inlet bore or feed bore, 8 a high-pressure bore, which is connected to a nozzle needle chamber, not shown, and 9, a discharge bore for the fuel that occurs during the shutdown. Open-up means the closing of the control openings, with which the pressure build-up in the high-pressure chamber 6 and consequently the injection begins; under control, the opening of the control openings, whereby the injection is stopped.

In a first embodiment of the invention, the pump piston 5 has an axial bore 11 extending from its end face 10, which is connected to a radial control bore 12 and a likewise radial auxiliary control bore 13. The control sleeve 3 has an upper control edge 15 which extends horizontally all round and forms the control edge, and an inclined control edge 17 which forms a window 16. The control sleeve 3 is shown in a position 14, which corresponds to an early start of injection. The position 14 ', 17' indicated by dashed lines corresponds to a late start of injection. By rotating the control sleeve 3 or the pump piston 5, different parts of the control edge 17 are assigned to the control bores 12, 13, as will be explained in more detail below.

In Fig. 2 it can be seen that the control bore 12 and the auxiliary control bore 13 enclose an angle with each other and that the bores are designed as through bores. This corresponds to a doubling of the control elements, even if the control sleeve 3 contains two windows 16 rotated by 180 ° with respect to one another.

Fig. 3 shows schematically the associated arrangement of the control members in a settlement. The control sleeve 3 is only symbolized by the control edge 15 and the control edge 17 forming the window 16. One rotation of the control sleeve corresponds to a shift to the left or right in the illustration. The pump piston 5 is only indicated by the control bore 12 and the auxiliary control bore 13 in different positions.

The position 20 of the control bore 12 corresponds to the top dead center of the pump piston 5 with zero delivery, the position 23 the bottom dead center. In position 21, the control bore just overlaps the control edge 15 and the control edge 17. However, because of their small distance, it is never completely covered, so that there is no funding (zero funding). The auxiliary control bore 13 occupies the position 22 at this time. Since this is also never completely covered, its free cross-section contributes to the fact that no promotion by dynamic effects takes place even at high speed.

When idling, that is to say with a very small delivery quantity, the control bore 12 is in position 24 and the auxiliary control bore 13 is in the assigned position 25. It can be seen that the idle speed is set very finely at this point by the slight slope of the control curve part 26 leaves. Above all, however, with the help of the dotted positions 31, 32 of the control bore 12 and the auxiliary control bore 13, the main effect of the invention can be recognized shortly beforehand, by means of which the advance is prevented. It is essential for this effect that the open cross-section is still very large shortly before the shutdown due to the presence of two bores, in other words that the control bore 12 and the auxiliary control bore 13 lie in such a way that they are completely or simultaneously covered, that is, at this moment, the control edge 15 touches both control holes or the auxiliary control hole slightly earlier. The diameter of the auxiliary control bore 13 is selected so that it is not released from the control edge 17 before the control bore 12. The auxiliary control bore 13 is thus “in the shadow” of the control bore 12 with respect to the control edge 17. As a result, it does not come into effect during the control and the entire working area is thus retained.

The problem with certain engines is that the injection takes too long at the maximum injection quantity. This can be remedied by extending the control edge 17 by the piece 30 shown in broken lines, which is horizontal here, but a lesser or even a negative one Can have slope. As a result, at the maximum injection quantity, shutdown takes place via the control bore and the auxiliary control bore, as a result of which it runs faster and the injection duration is somewhat shorter.

In a variant of the first embodiment, the movement relationships are reversed according to FIG. 4. The control sleeve 3 now has a control bore 40 and an auxiliary control bore 41, but instead the pump piston 5 has a control groove 42 and a control groove 44 on its jacket, which form a control edge 43 and a control edge 45. The grooves 42, 44 are connected to the axial bore 11 in the interior of the piston 5 via a radial bore 46 and possibly also a further radial bore 47. FIG. 5 shows the control bores 40, 41 in cross section, the piston 5 being in the position in which the control groove 42 is at the same height as the control bores 40, 41.

6 again shows schematically a development of the piston skirt in a somewhat modified form, in which the grooves 42, 44 are not connected to one another, but are each connected to the axial bore 11 by the radial bores 46, 47. The control bore 40 and the auxiliary control bore 41 are shown in dash-dot lines. The control edge 45 merges into a horizontal part 48 for zero delivery on the left and into a horizontal part 49 for maximum injection quantity on the right. Everything else is analogous to FIG. 3.

In the other embodiment of the invention according to FIG. 7, the auxiliary control bore 51 is located under the control bore 50. Both are in this embodiment, for example, in the piston and open into the axial bore 11. The control sleeve 3 has a control edge 52, an auxiliary control edge 53, which with the Auxiliary control bore 51 cooperates, and a control edge 54. The edges 53, 54 form a window 55, which is also offset by 180 ° can be duplicated if it is also the control bores 50, 51. With the same effect as in the first embodiment, the auxiliary control bore 51 can also be larger than the control bore 50, although the overall height increases somewhat.

The associated sequence of movements is shown schematically in FIG. The positions 50, 51 of the control bores correspond to the top dead center of the piston at medium load, the opening in positions 50 ', 51' is just completed, the dotted positions 57, 58 proving immediately beforehand that here too the pre-delivery prevents Effect occurs. The positions 50 ″, 51 ″ correspond to the bottom dead center of the piston movement. The positions 70, 71 occur at zero delivery, the throttling effect also being reduced here by the addition of the second bore 71. The positions 80, 81 correspond to the shutdown at full load, with accelerated shutdown also taking place here due to the interaction of the auxiliary control bore 81 with the auxiliary control edge 56, which shortens the injection duration.

FIGS. 9 and 10 show a variant of the second embodiment in which the movement conditions are reversed again. Here, the control sleeve 3 has a control bore 60 and an auxiliary control bore 61 and the pump piston 5 on its outer surface has a control groove 62, an auxiliary control groove 63, an expanded control groove 64 and radial bores 65 which connect the control grooves 62, 63, 64 to the axial bore .

Claims (9)

1. Fuel injection pump for diesel engines, on which at least one pump piston (5) with a pump piston bush (1) forms a high-pressure chamber (6) and is surrounded by a control sleeve (3) so that the angular position between pump piston (5) and control sleeve (3) can be varied for the quantity setting and so that an axial bore (11) in the pump piston (5) connects the high-pressure chamber (6) to a control bore (12,50) or to a groove (42,44,62,64) forming a downwards control edge and an upwards control edge for the completion of the injection process whereby this groove cooperates with a control edge (15,17,52,54) or control bores (40,60) of the control sleeve (3), characterized in that a suction or supply bore (7) which is separated from an outlet bore (9) is provided, that the pump piston (5) or the control sleeve (3), in addition to the provided control bore (12,40,50,60) used for the completion of the injection process, has an auxiliary control bore (13,41,51,61) which is completely covered earlier than or at the same time as the control bore (12,40,50,60) so that the throttle effect is reduced during downwards control by the additional auxiliary control bore and in that the auxiliary control bore is not uncovered by the downwards control edge (17,45,54,64) before the control bore (12,40,50,60) and in that the control bores (12,13,40,41,50,51,60,61) can be connected to the outlet bore (9).
2. Fuel injection pump according to claim 1, characterized in that the auxiliary control bore (13,41,51,61) is located in a position relative to the control bore (12,40) which corresponds to a greater injection quantity and in that the auxiliary control bore (13,41,51,61) and the control bore (12,40,50,60) cooperate with a common upwards control edge (15,43,53,63).
3. Fuel injection pump according to claim 1 or 2, characterized in that the auxiliary control bore (13,41) is larger than the control bore (12,40).
4. Fuel injection pump according to claim 1, 2 or 3, characterized in that the inclination of the downwards control edge (17,45) is reduced, zero or negative at the end (30,49) corresponding to the maximum injection quantity.
5. Fuel injection pump according to one of claims 1 to 4, characterized in that the grooves (42,44) forming the downwards control edges and upwards control edges are disposed in the pump piston (5) and in that both grooves (42,44) are in each case connected to the axial bore (11) in the pump piston (5) via their own radial bore (46,47).
6. Fuel injection pump according to one of claims 1 to 5, characterized in that the auxiliary control bore (51,61) is disposed in the direction of the pump axis over or under the control bore (50,60) in the pump piston (5) or in the control sleeve (3) and in that the control sleeve (3) or the pump piston (5) has two upwards control edges (52,53,62,63), the distance of which is equal to the distance between the auxiliary control bore (51,61) and the control bore (50,60).
7. Fuel injection pump according to one of claims 1 to 6, characterized in that the control bore (12,50) and the auxiliary control bore (13,51) are formed in the pump piston (5) and the control edges (15,17,52,53) are formed in the control sleeve (3).
8. Fuel injection pump according to one of, claims 1 to 7, characterized in that a second downwards control edge (56) is provided which is reached by the auxiliary bore only if the maximum quantity is injected.
9. Fuel injection pump according to one of claims 1 to 8, characterized in that all control bores (12,13,40,41,50, 51,60,61) and control edges (15,17,43,45,53,54,63,64) are disposed so that they are double displaced through 180°.

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