EP1370764B1 - Method for injecting fuel into the combustion chambers of an internal combustion engine, and fuel injection system for said engine - Google Patents

Description

The invention relates to a method for injecting fuel into the combustion chambers of an internal combustion engine according to the preamble of claim 1. Furthermore, the invention relates to a fuel injection system for an internal combustion engine according to the preamble of claim 8.

In internal combustion engines, especially in diesel engines, a type of fuel injection has increasingly been used in which a common inlet and storage line (common rail) is pressurized by a high-pressure pump under high pressure with fuel and from this the high-pressure fuel via respective high-pressure lines of a number is supplied from each injector comprehensive fuel injectors. The beginning and end of the injection of the fuel into the combustion chambers of the internal combustion engine are controlled by opening and closing the injectors provided in the fuel injectors. In addition, in each case in the leading to the fuel injectors high pressure lines a certain Kraftstoffspeichenrolumen having high-pressure accumulator may be provided. Such a type of fuel injection is known for example from DE 197 12 135 C1.

EP 0 780 569 A1 discloses an injection system as known which has a high-pressure accumulator and associated lines leading to the injection valves. To dampen pressure pulsations, the lines are connected via throttling devices on the high-pressure accumulator. Since the lines downstream of the throttling devices are small-volume compared to the pressure accumulator, in order to maintain a continuous injection, the fuel quantity flowing through the throttle devices during an injection from the pressure accumulator per unit time is the same as the injected fuel quantity per unit time. Therefore, the system pressure in the injector is the same at the beginning and at the end of an injection. As a result of the pressure pulsations generated when the injection valve closes due to the back pressure, pressure increases occur at the end of the injection.

The increasingly stringent requirements for limiting pollutant emissions from internal combustion engines tend to require ever higher injection pressures. The maximum permissible pressure in a fuel injection system of the type mentioned with regard to the material load is given by the peak pressures occurring in the system. The highest pressure peaks occur in the fuel injector at the end of the injection. The reason for this is the so-called congestion or surf pressure that occurs when the injector closes and can be up to 400 bar above the system pressure. This means that conventionally, the system pressure of the fuel injection system has to be designed to be lower by up to the said 400 bar than the maximum pressure which is acceptable in terms of material load.

The object of the invention is to provide an improved method for injecting fuel into the combustion chambers of an internal combustion engine, as well as an improved fuel injection system for an internal combustion engine.

The object is achieved by the fuel injection method specified in claim 1 or by the specified in claim 8 fuel injection system.

Advantageous embodiments of the invention are characterized in the respective subclaims.

By means of the invention, a method for injecting fuel into the combustion chambers of an internal combustion engine, in particular a diesel engine, by means of a fuel injectors comprising a number of injection valves and a fuel supplying the individual fuel injectors via respective high-pressure lines with high-pressure fuel and, in turn, via a high-pressure pump created under high pressure fueled common inlet and storage line containing fuel injection system, is controlled at the beginning and end of the injection of the fuel into the combustion chambers by opening and closing the injectors of the fuel injectors. One or more high-pressure accumulators are provided in each of the lines leading to the fuel injectors. According to the invention, it is provided that, during the injection, a defined lowering of the fuel pressure prevailing in the fuel injector from an initial pressure p1 to a pressure p2 at the time T2, when the closing of the injection valve starts, is limited by restricting the afterflow of fuel during the injection, so that the pressure rising in the fuel injector due to the back pressure when closing the injector at the end of the injection does not exceed a predetermined value. The defined reduction of the pressure prevailing in the fuel injector pressure is effected by limiting the subsequent flow in the leading from the common inlet and storage line to the Hochdruckspeichem high pressure lines.

The defined reduction of the fuel pressure in the fuel injector preferably takes place to such a value that the pressure rising in the fuel injector at the end of the injection due to the back pressure when the injector closes becomes equal to Beginning of the injection in the fuel injector prevailing fuel pressure, in particular does not exceed the system pressure P0.

According to one embodiment of the method according to the invention, it is provided that the supply of the fuel from the common inlet and storage line to the Fuel injectors via two provided in the leading to the fuel injectors high pressure lines, a certain fuel storage volume having high-pressure accumulator takes place.

When two high-pressure accumulators are used, the high-pressure accumulator closer to the injector is preferably designed with a smaller volume than the one located further upstream. At least one high-pressure accumulator, preferably the larger one, is associated with a quantity-limiting valve, which preferably lies downstream of the respective high-pressure accumulator.

According to one embodiment of the method according to the invention, the limitation of the afterflow of the fuel is effected by throttle points provided in the high-pressure lines leading from the common supply and storage line to the high-pressure accumulators.

According to another embodiment, the limitation of the afterflow of the fuel by the dimensioning of the diameter D2 of the leading from the common inlet and storage line to the high-pressure accumulators high pressure lines.

One advantage of the injection method according to the invention is that it is possible to work with a high injection pressure at the start of injection without there being any inadmissible overloading of the material in the fuel injector.

Furthermore, the invention provides a fuel injection system for an internal combustion engine, in particular a diesel engine, which supplies a number of each injector comprehensive fuel injectors and the individual fuel injectors with fuel under high pressure fuel and in turn acted upon by a high-pressure pump at high pressure with fuel common inlet - And storage line, and in each case one or more, in particular two, provided in the leading to the fuel injectors high pressure lines, a contains certain fuel storage volume having high-pressure accumulator, wherein the beginning and end of the injection of the fuel is controlled in the combustion chambers by opening and closing the injection valves of the fuel injectors. According to the invention, it is provided that the fuel storage volume of the high-pressure accumulator and the flow resistance of the high-pressure lines leading from the common inlet and storage line to the individual high-pressure accumulators are dimensioned taking into account the maximum injection quantity and duration so that during injection, less fuel in the High pressure accumulator nachströmt is injected as a lowering of the prevailing in the fuel injector fuel pressure is from an initial, to the system pressure slightly lower pressure p1 to a fuel pressure p2 at time T2, when the closing of the injector starts, so that due to the back pressure when closing the injector At the end of the injection in the fuel injector increasing pressure does not exceed a predetermined value.

The fuel storage volume of the high-pressure accumulators and the flow resistance of the high-pressure accumulators leading to the high-pressure accumulators are preferably dimensioned such that the pressure rising in the fuel injector at the end of the injection due to the stagnation pressure does not exceed the fuel pressure prevailing at the beginning of the injection in the fuel injector, in particular the system pressure P0

According to one embodiment of the fuel injection system according to the invention, it is provided that the flow resistance of the high-pressure lines leading from the common supply and storage line to the high-pressure accumulators is determined by throttle points

According to another embodiment of the invention, it is provided that the flow resistance of the leading from the common inlet and storage line to the high-pressure accumulators high pressure lines is determined by the diameter D2.

As in the case of the fuel injection method according to the invention, it is also an essential advantage in the fuel injection system according to the invention that high pressures can be used at the start of injection without resulting in unacceptable material overloads in the fuel injectors.

In a fuel injection without the inventive reduction of the pressure prevailing in the fuel injector fuel pressure to the end of the injection, if the same high initial pressures to be achieved, the fuel injectors would be designed for the much higher pressures that occur due to the occurring when closing the injector congestion or surf pressures.

• Figur 1 ein schematisiertes Blockschaltbild eines Teils eines Kraftstoffeinspritzsystems gemäß einem Ausführungsbeispiel der Erfindung;
• Figur 2 eine schematisierte Querschnittsansicht, die den das Einspritzventil umfassenden Teil eines Kraftstoffinjektors zeigt;
• Figur 3 ein Diagramm, welches die im Kraftstoffinjektor während eines Einspritzvorgangs herrschenden Druckverhältnisse für eine herkömmliche Kraftstoffeinspritzung darstellt; und
• Figur 4 ein Diagramm, welches die im Kraftstoffinjektor während des Einspritzvorgangs herrschenden Druckverhältnisse gemäß einem Ausführungsbeispiel der Erfindung darstellt.

In the following an embodiment of the invention will be explained with reference to the drawing. Show it:

• Figure 1 is a schematic block diagram of a portion of a fuel injection system according to an embodiment of the invention;
• Figure 2 is a schematic cross-sectional view showing the part of a fuel injector comprising the injection valve;
• FIG. 3 is a diagram illustrating the pressure ratios for a conventional fuel injection prevailing in the fuel injector during an injection event; and
• FIG. 4 shows a diagram which represents the pressure conditions prevailing in the fuel injector during the injection process according to an exemplary embodiment of the invention.

In the part of a fuel injection system shown in Figure 1, reference numeral 5 denotes one of typically several fuel injectors for injecting fuel into the combustion chambers of an internal combustion engine, in particular a diesel engine. The fuel injectors 5 are controlled by means of a control unit not shown in Figure 1 so that an optimally matched to speed and load condition of the engine fuel quantity is injected. From a fuel supply, also not shown in FIG. 1, the fuel is initially supplied to a common supply and storage line 1 by means of one or more high-pressure pumps 6, from which high-pressure lines 2, 4a, 4b serving to supply the individual fuel injectors 5 branch off.

One or more high-pressure accumulators 3a, 3b are provided in the high-pressure lines 2, 4a, 4b leading to the fuel injectors 5. The part of the high-pressure line leading from the common supply and storage line 1 to the high-pressure accumulator 3a is designated by the reference numeral 2, whereas the sections of the high-pressure line leading from the high-pressure accumulators 3a, 3b to the fuel injector 5 bear the reference symbols 4a and 4b. The high-pressure accumulators 3a and 3b are associated with quantity-limiting valves 14a and 14b, which are preferably downstream of the high-pressure accumulators 3a, 3b, but may also be upstream.

The high-pressure accumulators 3 a, 3 b act as oil-elastic accumulators, in whose fuel storage volume the fuel supplied to the fuel injectors 5 is supplied under the high-pressure supplied by the common supply and storage line 6.

Also, the common inlet and storage line 1 typically has the function of an oil-elastic storage in which the supplied under the high pressure pump 6 supplied high pressure fuel for further distribution to the high pressure accumulator 3a, 3b via the high pressure lines 2, 4a, 4b is maintained.

The cross-sectional view shown in Figure 2 shows a part of the injector 7 of the fuel injector 5, which projects into the combustion chamber of the internal combustion engine and an injection nozzle 13, via which the fuel is injected into the combustion chamber. In this part of the injector 7, an injection valve is formed, which is formed by the tip 9 of a longitudinally displaceably mounted in the fuel injector 5 in a known manner nozzle needle 8 and a cooperating with the nozzle needle tip 9 nozzle needle seat 10. When opening the injection valve 9, 10 located in an antechamber 11, supplied under high pressure via the high-pressure line 4a, 4b in the fuel injector 5 fuel for injection via the injection nozzle 13 is released. Upstream of the nozzle needle tip 9 is a blind hole 12, from which the injection nozzle 13 branches off.

The opening and closing of the injection valve 9, 10 and thus the beginning and the end of the injection of the fuel into the combustion chamber of the internal combustion engine is controlled by the above-mentioned control unit.

The diagram shown in FIG. 3 shows the pressure ratios plotted against time in a conventional injection of fuel into the combustion chamber of an internal combustion engine. The curve marked A shows the pressure prevailing in the antechamber 11 in front of the injection valve 9, 10 fuel pressure, which is equal to the system pressure P0 when the injection valve is closed; the curve labeled B shows the pressure in the blind hole 12 during the injection process. The beginning of the injection process, in which the injection valve 9, 10 begins to open, is denoted by T1 ', the end of the injection process, in which the injection valve 9, 10 begins to close, is denoted by T2. As the curve B shows, at the beginning of the injection, the pressure in the blind hole 12 increases relatively quickly from the pressure 0 at time T1 'to the pressure P1 at the time T1, which is almost equal to the system pressure prevailing in the antechamber 11. The ruling in the vestibule 11 fuel pressure has dropped slightly at time T1 due to the fuel extraction against the system pressure P0. During the period from T1 to T2, ie while the injection valve 9, 10 is open, the pressure in the blind hole 12 substantially corresponds to the pressure in the antechamber 11. During the closing of the injection valve 9, 10, the pressure in the blind hole 12 drops from the time T2 at; where the pressure substantially still corresponds to the pressure in the antechamber 11, to the pressure 0 at time T2 'from, at which time the injection valve 9, 10 is completely closed, so the nozzle needle tip 9 in the nozzle needle seat 10 is applied.

Due to the congestion or surf pressure occurring when closing the injection valve 9, 10 takes place in the antechamber 11, a rapid pressure increase, which may be up to 400 bar above the system pressure. As curve A in FIG. 3 shows, this pressure peak decays again under a plurality of oscillations until time T3. As already explained at the beginning, these pressure peaks occurring when closing the injection valve 9, 10 represent a substantial load on the fuel injector 5.

FIG. 4 shows a corresponding diagram in which the pressure conditions prevailing in the fuel injector 5 are shown as a function of time, as in FIG occur the fuel injection method according to the invention or in the fuel injection system according to the invention. In FIG. 4, the pressure prevailing in the blind hole 12 of the fuel injector 5 is shown again by the curve B, the curve A shows the pressure prevailing in the antechamber 11. The closed at the injection valve 9, 10 in the antechamber 11 completely fully applied system pressure is designated P0. When opening the injector 9, 10 so when releasing the nozzle needle tip 9 from the nozzle needle seat 10 at time T1 'begins a rapid increase in the pressure in the blind hole 12 of the fuel injector 5 fuel pressure until it practically reaches the time prevailing in the vestibule 11 fuel pressure at time T1. The latter has fallen slightly at the time T1 due to the fuel extraction against the system pressure P0.

According to the invention takes place during the injection, a defined reduction of prevailing in the vestibule 11 of the fuel injector 5 fuel pressure from the initial pressure P1 at time T1 to the fuel pressure P2 at time T2, when the closing of the injector 9, 10 begins. The fuel pressure P2 at time T2 has such a lowered value that the pressure rising due to the back pressure when closing the injection valve 9, 10 at the end of the injection does not exceed a predetermined value. In the embodiment shown in Figure 4, the said defined reduction of the fuel pressure to a value such that the increasing due to the back pressure when closing the injector 9, 10 pressure does not exceed the prevailing at the beginning of the injection in the fuel injector 5 fuel pressure, in particular the system pressure P0 ,

Returning again to the exemplary embodiment of the fuel injection system according to the invention shown in FIG. 1, the fuel storage volumes of the high-pressure reservoirs 3a, 3b and the flow resistance of the high-pressure line 2 leading to this from the common supply and storage line 1 are dimensioned taking into account the maximum injection quantity and duration the pressure drop shown in FIG. 4 results. In detail, the pressure drop is caused by the fact that the fuel via the high-pressure line 2 can flow less quickly to the high-pressure accumulators 3a, 3b and the fuel injector 5, as he via the injection nozzle, see Figure 2, in the combustion chamber of the internal combustion engine is injected. This limitation of the afterflow of the fuel can be carried out by a throttle point, which is provided in the leading from the common inlet and storage line 1 to the high-pressure accumulator 3a high-pressure line 2, or, which is preferable, by a dimensioning of the diameter D2 (inner diameter) of the common inlet and storage line 1 to the high-pressure accumulator 3a leading high-pressure line 2 and the length thereof. Throttle point or line cross-section and the high-pressure storage volumes are of course tuned to the highest load case, namely when the internal combustion engine is running at full load. So that the required injection quantity can be injected in the available time, then the rail pressure (system pressure) is to be selected highest. At partial load, the fuel pressure in the inlet and storage line 1 is lowered. Due to the limited fuel overrun, however, a drop in the pressure in the antechamber 11 according to curve A according to FIG. 4 can also be observed at partial load.

Instead of two high-pressure accumulators 3a, 3b shown in FIG. 1, only one high-pressure accumulator can be used. When two high-pressure accumulators are used, the high-pressure accumulator 3b, which is located closer to the injector and is preferably integrated in the injector, is preferably designed with a smaller volume than the further upstream high-pressure accumulator 3a.

The smaller second high-pressure accumulator 3b is mainly due to the short distance to the Düsenlöchern'a damper function. Due to the short connection can be effected by fast flow of fuel from the high-pressure accumulator 3b in front of the nozzle holes 13, a rapid pressure equalization, which reduces the amplitude of the surf pressure. The lines 4a and 4b are formed with a large cross-section to ensure an unimpeded fuel Nachfluss.

The quantity-limiting valves 14a, 14b serve primarily to prevent the flow of fuel and continuous injection in the case of needle clamps. In addition, they also have a damping function, which is caused by the displaceable piston and the flow channels formed in the valve. The quantity limiting valves have a favorable effect on the decay behavior of the pressure oscillation at the end of injection. For one optimal function, the flow control valves are preferably downstream of the output of at least the larger high-pressure accumulator 3a to install.

LIST OF REFERENCE NUMBERS

1

common inlet and storage line

2

High-pressure line

3a, 3b

High-pressure accumulator

4a, 4b

High-pressure line

5

fuel injector

6

high pressure pump

7

injector

8th

nozzle needle

9

Nozzle needle tip

10

Nozzle needle seat

11

anteroom

12

blind

13

injection

14a, 14b

Flow regulator

Claims (13)

1. Method for injecting fuel into the combustion chambers of an internal combustion engine, in particular a diesel engine, by means of a fuel injection system which contains a number of fuel injectors (5), each comprising an injection valve (9, 10), and a common rail (1), which supplies the individual fuel injectors (5) with highly pressurized fuel by way of respective high-pressure lines (2, 4a, 4b) and to which in turn highly pressurized fuel is admitted by way of a high-pressure pump (6), the fuel being fed from the common rail (1) by way of one or more high-pressure reservoirs (3a, 3b) provided in each of the high-pressure lines (2, 4a, 4b) leading to the fuel injectors (5), and the beginning and end of the fuel injection into the combustion chambers being controlled by opening and closing of the injection valves (9, 10) of the fuel injectors (5), characterized in that during injection the continued flow of fuel is limited in such a way that less fuel continues to flow to the high-pressure reservoirs (3a, 3b) than is injected, so as to bring about a defined reduction of the fuel pressure prevailing in the fuel injector (5) from an initial pressure p1, which is slightly lower than the system pressure, to a pressure p2 at the instant T2 when closing of the injection valve (9, 10) commences, so that the pressure in the fuel injector (5), increasing due to the back pressure generated as the injection valve (9, 10) closes at the end of injection, does not exceed a predefined value, the defined reduction of the fuel pressure prevailing in the fuel injector (5) being brought about by limiting the continued flow of fuel in the high-pressure lines (2) leading from the common rail (1) to the high-pressure reservoirs (3a, 3b).
2. Method according to Claim 1, characterized in that the defined reduction of the fuel pressure in the fuel injector (5) is brought about in such a way that the pressure in the fuel injector (5), increasing due to the back pressure generated as the injection valve (9, 10) closes at the end of injection, does not exceed the fuel pressure prevailing in the fuel injector (5) on the commencement of injection, in particular the system pressure P0.
3. Method according to Claim 1 or 2, characterized in that fuel is fed from the common rail (1) to the fuel injectors (5) by way of two high-pressure reservoirs (3a, 3b) provided in each of the high-pressure lines (2, 4a, 4b) leading to the fuel injectors (5) and having a specific fuel storage volume.
4. Method according to Claim 3, characterized in that where two high-pressure reservoirs (3a, 3b) are used, the high-pressure reservoir (3b) situated closer to the injector has a smaller volume than the high-pressure reservoir (3a) situated further upstream.
5. Method according to Claim 3 or 4, characterized in that a quantity-limiting valve (14a, 14b), which is in each case preferably situated downstream of the high-pressure reservoir (3a, 3b), is associated with at least one high-pressure reservoir (3a, 3b).
6. Method according to Claim 3, 4 or 5, characterized in that the continued flow of fuel is limited by restrictors provided in the high-pressure lines (2) leading from the common rail (1) to the high-pressure reservoirs (3a, 3b).
7. Method according to Claim 3, 4 or 5, characterized in that the continued flow of fuel is limited by the design diameter D2 of the high-pressure lines (2) leading from the common rail (1) to the high-pressure reservoirs (3a, 3b).
8. Fuel injection system for an internal combustion engine, in particular a diesel engine, which contains a number of fuel injectors (5), each comprising an injection valve (9, 10), and a common rail (1), which supplies the individual fuel injectors (5) with highly pressurized fuel and to which in turn highly pressurized fuel is admitted by way of a high-pressure pump (6), together with one or more, especially two, high-pressure reservoirs (3a, 3b) provided in each of the high-pressure lines (2, 4a, 4b) leading to the fuel injectors (5) and having a specific fuel storage volume, the beginning and end of the fuel injection into the combustion chambers being controlled by opening and closing of the injection valves (9, 10) of the fuel injectors (5), characterized in that the fuel storage volume of the high-pressure reservoirs (3a, 3b) and the flow resistance of the high-pressure lines (2) leading from the common rail (1) to the high-pressure reservoirs (3a, 3b) are designed to take account of the maximum injection quantity and injection period, so that during injection less fuel continues to flow to the high-pressure reservoirs (3a, 3b) than is injected, so as to bring about a reduction of the fuel pressure prevailing in the fuel injector from an initial pressure p1, which is slightly lower than the system pressure, to a fuel pressure p2 at the instant T2 when closing of the injection valve (9, 10) commences, so that the pressure in the fuel injector (5), increasing due to the back pressure generated as the injection valve (9, 10) closes at the end of injection, does not exceed a predefined value.
9. Fuel injection system according to Claim 8, characterized in that the fuel storage volume of the high-pressure reservoirs (3a, 3b) and the flow resistance of the high-pressure line (2) leading from the common rail (1) to the high-pressure reservoirs (3a, 3b) are designed so that the pressure in the fuel injector (5), increasing due to the back pressure generated as the injection valve (9, 10) closes at the end of injection, does not exceed the fuel pressure prevailing in the fuel injector (5) on the commencement of injection, in particular the system pressure P0.
10. Fuel injection system according to Claim 8 or 9, characterized in that in an arrangement with two high-pressure reservoirs (3a, 3b), the high-pressure reservoir (3b) situated closer to the injector in each case has a smaller volume than the high-pressure reservoir (3a) situated further upstream.
11. Fuel injection system according to Claim 8, 9 or 10, characterized in that a quantity-limiting valve (14a, 14b), which is in each case preferably situated downstream of the high-pressure reservoir (3a, 3b), is associated with at least one high-pressure reservoir (3a, 3b).
12. Fuel injection system according to any one of Claims 8 to 11, characterized in that the flow resistance of the high-pressure lines (2) leading from the common rail (1) to the high-pressure reservoirs (3a, 3b) is determined by restrictors.
13. Fuel injection system according to any one of Claims 8 to 11, characterized in that the flow resistance of the high-pressure lines (2) leading from the common rail (1) to the high-pressure reservoirs (3a, 3b) is determined by their diameter D2.

Images