EP1642021B1 - Fuel injection system for internal combustion engines - Google Patents

Abstract

Each fuel injector comprises high and low pressure terminal (2), with low pressure terminals opening into collector line (3). Fuel injectors are energisable via a piezoelectric actuator. Between collector line and pressureless fuel return flow (5) are fitted members (6) for maintaining fuel pressure. Throttle (7) is incorporated between opening of low pressure terminals into collector line and injector side inlet of pressure maintaining members in collector line. Preferably members are formed by pressure maintaining valve, or electric fuel pump. Independent claims are included for fuel injector.

Description

Technical area

In accumulator injection or "common rail injection", pressure generation and injection are decoupled. The injection pressure is generated independently of the engine speed and the injection quantity and is in the "rail" - the fuel storage - ready for injection. Injection timing and injection quantity are calculated in the electronic control unit and implemented by an injector on each engine cylinder. The injector has the task to set the start of injection and injection quantity.

In addition to the control of the injector via a piezo element, the control of the injector via a solenoid valve is known. While in solenoid valves sufficiently large valve lifts for use of the solenoid valve can be generated as a control valve, additional measures must be taken in a control of an injector with a piezoelectric element. This has the reason that with a piezoelectric element only a very small stroke can be generated, which lies in the per thousand range with respect to the length of the piezoelectric element. This small stroke must be transformed to operate the control valve during continuous operation of the injector. For this purpose, for example, a hydraulic translator is used.

State of the art

In the prior art, control and leakage quantities of the injector or injectors are discharged via a non-pressurized fuel return and fed into the fuel tank. For some injectors for diesel engines, however, the leakage oil in the injector must have a defined pressure. These injectors include piezo-controlled common rail injectors. In these injectors, a hydraulic coupler is arranged between the piezoelectric actuator and the control valve, which increases the travel of the piezoelectric actuator. For this purpose, a coupler space is present, the filling of which requires a defined, lying above the ambient pressure leak oil pressure.

Out DE-A 199 52 513 is a fuel injection system for internal combustion engines with at least one injector, or connected to a non-pressurized fuel return are known. Between the injector (s) and the fuel return means are provided for maintaining a leakage oil pressure in the injector (s). In particular, the means for maintaining a leak oil pressure in or in the injectors of one or more pressure holding valves.

DE-A 101 04 634 relates to a fuel injection system for internal combustion engines with a plurality of injectors, wherein the injectors each have a high-pressure port and a low-pressure port, the low-pressure ports open into a manifold, with an arranged between manifold and a non-pressurized fuel return pressure holding valve, wherein the manifold is designed as a pressure accumulator.

In these prior art fuel injection systems, the pressure load of the pressure holding valve to maintain the pressure on the low pressure side of the injectors up to 20 bar is very high. Likewise, the manifold (return rail) and the actuator and an optional bellows are exposed to high loads by this pressure.

Presentation of the invention

The fuel injection system according to the invention avoids the disadvantages occurring in the prior art and allows a pressure relief of several system components, in particular of the actuator and / or the manifold and / or the pressure holding valve and / or the bellows. A further advantage is that the fuel injection system according to the invention can be used for common rail systems, in which either at least one pressure-holding valve or at least one electric fuel pump sets the injector-coupler space for filling under a pressure necessary for this purpose. In this case, if necessary, the pressure-maintaining valve can be omitted and this results in a cost savings, wherein the functional scope is maintained even without pressure holding valves. Further advantages of the fuel injection system according to the invention are that no additional moving internal parts are needed and thus wear and high production costs are avoided. Further, no additional adjustment operations are required over the prior art fuel injection system.

These advantages are achieved by a fuel injection system for internal combustion engines with multiple injectors, wherein the injectors each have a high pressure port and a low pressure port, the low pressure ports open into at least one manifold, with a between the manifold and means for maintaining the fuel pressure, wherein between the low-pressure port of each injector and the means for maintaining the fuel pressure at least one throttle is arranged.

The at least one throttle ensures that the pressure required on the low-pressure side of the injector is set at high load points. At low load points this ensures the means to maintain fuel pressure. Since the high pressures are represented by the throttle, only the low pressures of the means for maintaining the fuel pressure are required after the throttle, which then causes the substantial relief of the entire low-pressure system.

In addition to the advantages listed above, the fuel injection system according to the invention has the further advantage that the production claim for the at least one throttle is very low.

In a variant of the invention, it is provided that all injectors are connected via their low-pressure connections to a common manifold. It can be present between the manifold and the respective injector a connecting line to make the manifold short and simple geometry can. In the variant of the fuel injection system according to the invention with a single manifold for all injectors, it is sufficient to provide a throttle between the low-pressure port of the injector and the means for maintaining the fuel pressure, in particular in the common manifold.

In another embodiment of the invention a plurality of manifolds are provided. For example, each cylinder bank of a V-engine can be assigned its own manifold. This embodiment of the fuel injection system according to the invention may have advantages in terms of the required installation space and the cost of connecting the low-pressure connections of the injectors with the respective manifold. The use of a plurality of mutually independent manifolds requires the arrangement of at least one throttle per manifold between the low pressure port of the respective injector and the respective means for maintaining the fuel pressure, in particular the arrangement of a respective throttle in each manifold.

In a preferred embodiment of the present invention, the means for maintaining the fuel pressure is a pressure holding valve. Back pressure valves are proven and mature components that can be used. Preferably, in the fuel injection system according to the invention with pressure-holding valve, a throttle arranged in front of the injector-side inlet of the pressure holding valve. Even with the throttle positioned in front of the pressure-maintaining valve, the functional range of the pressure-maintaining valve is retained, although a pressure relief of the pressure-retaining valve is established in comparison to the prior art. The throttle also results in a pressure relief of other system components, in particular the manifold, the actuator and the bellows.

The bellows is designed such that it can receive the axial stroke of the actuator for controlling the injector, in particular a piezoelectric actuator. Here, the bellows is firmly connected to the actuator and the actuator bore, so that a fluid-tight seal of the actuator module with respect to the other areas of the injector is achieved.

In another preferred embodiment of the present invention, the means for maintaining the fuel pressure is an electric fuel pump. Electric fuel pumps are known in the art and proven pumps that are designed in the tank of a motor vehicle in modular design, and are used in particular in internal combustion engines in order to supply sufficient fuel in all operating conditions. Preferably, in the fuel injection system according to the invention with an electric fuel pump, a throttle is arranged in the collecting line in front of the electric fuel pump. In this variant of the present invention, the scope of functions is also available without pressure-holding valve, so that no pressure-holding valve is required and thus costs can be saved.

In one variant of the invention, the high-pressure connections of the injectors are supplied with fuel by at least one common rail, so that the advantages of the fuel injection system according to the invention also come into play in so-called common-rail injection systems.

In addition to the invention, it is provided that the injectors each contain a piezoelectric element for controlling the injector and a hydraulic translator for the translation of the piezoelectric element stroke. About this embodiment of the invention, the piezoelectric element hub preferably via a hydraulic medium, in particular fuel, in a coupler space of the hydraulic translator to an injector needle transferable, wherein the coupler space is filled via the at least one throttle with the hydraulic medium. By present in the fuel injection system according to the invention at least one throttle between the low pressure port of the injector and the means for maintaining the fuel pressure (in particular the pressure holding valve or the electric fuel pump), the necessary for filling the coupler space pressure in high load points. For small load points, this ensures the pressure maintenance valve or the electric fuel pump. Since the high Kopplerbefüllungsdrücke be represented by the throttle, only the low pressures of the pressure holding valve or the electric fuel pump are required after the throttle, which then causes the significant relief of the entire low-pressure system. With the choice of the throttle diameter, the pressure holding valve opening pressure or the pressure of the electric fuel pump, if necessary, the pressure for the coupler filling can be applied.

drawing

Reference to the drawings, the invention will be explained in more detail below.

• Fig. 1 eine schematische Darstellung eines Kraftstoffeinspritzsystems gemäß dem Stand der Technik,
• Fig. 2 ein erfindungsgemäßes Kraftstoffeinspritzsystem mit Elektrokraftstoffpumpe,
• Fig. 3 ein erfindungsgemäßes Kraftstoffeinspritzsystem mit Druckhalteventil und
• Fig. 4 einen Schnitt durch einen Kraftstoffinjektor, der über einen Hochdrucksammelraum (Common Rail) mit unter hohem Druck stehenden Kraftstoff beaufschlagt ist und durch einen als Piezoaktor ausgebildeten Aktor angesteuert wird.

Show it:

• 1 is a schematic representation of a fuel injection system according to the prior art,
• 2 shows an inventive fuel injection system with electric fuel pump,
• Fig. 3 shows an inventive fuel injection system with pressure-holding valve and
• Fig. 4 shows a section through a fuel injector, which is acted upon by a high-pressure accumulator (common rail) with fuel under high pressure and is driven by an actuator designed as a piezoelectric actuator.

variants

Fig. 1 shows a schematic representation of a fuel injection system according to the prior art.

It is a fuel injection system with six cylinders 1, which are shown schematically as circles. Each cylinder 1 is associated with an injector (not shown), which has a low-pressure connection 2. The low pressure ports 2 open into a manifold 3. Here, the manifold 3 is designed as an accumulator in which the pressure required on the low pressure side of the injector is maintained. The manifold 3 is connected via a schematically illustrated pressure-holding valve 4 with the non-pressurized fuel return 5 in connection, so that in all injectors a same, is present above the ambient pressure fuel pressure. For example, the pressure holding valve opens only from a pressure of 10 bar, so that the fuel pressure in the manifold 3 is at least 10 bar.

Fig. 2 shows an inventive fuel injection system with electric fuel pump.

An only schematically indicated in Fig. 2 internal combustion engine 36 comprises six cylinders 1, which are each acted upon by a fuel injector 38 shown in more detail in Fig. 4 with high pressure fuel. The fuel injectors shown in greater detail in FIG. 1 are arranged in the cylinder head region 37 of the internal combustion engine 36. Between the manifold 3 and the non-pressurized fuel return 5, which is in communication with a fuel tank 35 of a vehicle, an electric fuel pump 6 is arranged in this embodiment of the invention as a means for maintaining the fuel pressure. Further, located in the manifold 3 before the electric fuel pump 6, a throttle 7. In this combination of throttle 7 and electric fuel pump 6, no pressure-holding valve is required to maintain the force pressure on the low pressure side of the injectors. Further, the electronic fuel pump 6 only needs to deliver fuel at a low pressure. For example, in the case of a cross section of the throttle 7 of 0.5 mm, a 5 bar electric fuel pump 6 is sufficient.

Fig. 3 shows a fuel injection system according to the invention with pressure-holding valve.

The internal combustion engine 36 may be configured, for example, as a 6-cylinder internal combustion engine, wherein the embodiment variant is shown as a 6-cylinder engine only by way of example. According to the design, internal combustion engines with four, five, eight or 10 or 12 cylinders can also be supplied with the fuel injection system proposed according to the invention. Between the manifold 3 and the non-pressurized fuel return 5, which opens into the fuel tank 35 of a motor vehicle, a pressure-maintaining valve 8 is provided in this embodiment of the present invention as a means for maintaining the fuel pressure. Further, located in the manifold 3 before the pressure-holding valve 8, a throttle 7. In this combination of throttle 7 and pressure-holding valve 8, the pressure-maintaining valve 8 is depressurized, so that it may have a lower opening pressure. For example, in the case of a throttle 7 with a cross section of 0.5 mm, a 5 bar pressure-maintaining valve is sufficient to maintain the required fuel pressure on the low-pressure side of the injectors.

The illustration according to FIG. 4 can be taken from a fuel injector which is connected to a high-pressure reservoir (common rail) and which can be actuated via an actuator designed as a piezoactuator.

The fuel injector 38 shown in Fig. 4 comprises a high pressure system 9 and a low pressure system 10. The actuation of the fuel injector 38 via an actuator 11, which is provided in the illustration of FIG. 4 with a schematically indicated piezoelectric crystal stack 12, which is in Energizing lengthens. The piezo-crystal stack 12 acts on an actuating piston 18. The actuating piston 18 acts on a hydraulic booster 13. The hydraulic booster 13 amplifies the only small stroke of the piezoelectric crystal stack 12 when current is supplied to the actuator 11. The hydraulic booster 13 comprises an actuating piston 15 whose End face 16 protrudes into the hydraulic coupling chamber 14 of the hydraulic booster 13. The piezoelectric crystal stack 12 of the actuator 11 and the coupling space 14 of the hydraulic booster 13 can be enclosed by a thin wall 43 as well as by a bellows 42, with which the relative movement of the piezoelectric crystal stack 12 during its energization and associated with this actuating piston 18 relative to the hydraulic coupling space 14 is made possible.

When a bellows 42 is used, on the one hand, a relative movement of the piezoelectric crystal stack 12 to the hydraulic coupling chamber 14, which is integrated in the housing of the fuel injector 31 and on the other hand reaches a seal between the relatively movable components 12 and 14. The hydraulic coupling chamber 14 is enclosed by a housing 44, and acted upon by the coupling chamber pressure p _K. From a system space 20, which encloses both the piezoelectric crystal stack 12 and the hydraulic booster 13, 44, the low pressure port 2 extends to the manifold 3. In the manifold 3 open according to the illustration in Figures 2 and 3, the respective low pressure ports 2 of further cylinder 1 of the internal combustion engine 36. The manifold 3 extends to the means for maintaining the fuel pressure, which may be formed either as a pressure holding valve 8 or by the electric fuel pump 6 to the fuel supply of the internal combustion engine 36 according to the schematically indicated in Figures 2 and 3 embodiments or can be formed to act on a high pressure pump 34. In the manifold 3, in which the respective low pressure ports 2 of the cylinder 1, starting from the fuel injectors 38 and the means 6, 8 for maintaining the fuel pressure in the system space 20, the throttle element 7 is added. The low-pressure connection 2 may be formed, for example, as a screw 17, so that at the prevailing within the system pressure chamber 20 pressures a leak-free Seal between the system space 20 and in the low pressure port 2 is ensured.

As shown in FIG. 4, the hydraulic booster 13 includes a housing 44 which limits the hydraulic coupling space 14. The housing 44 is supported on the one hand via a coil spring on a support disc received on the actuator piston 18 of the actuator 11 and on the other hand biased by a further helical spring on a support disc which is received on the actuating piston 15. The diameter of the actuating piston 18 is dimensioned larger than the diameter of the actuating piston 15, so that a hydraulic pressure transmission is achieved by interposition of the hydraulic coupling chamber 14. The actuating piston 15 acts on a guide piston 23. The guide piston 23 in turn is guided in a discharge channel 22 which is provided in the housing 39 of the fuel injector 38. About the drain passage 22 of the system space 20 and the control chamber 24 are connected to each other. The outlet channel 22, which connects the system chamber 20 and the control chamber 24 with each other, is closed or released via a closing element 19. The closing element 19 is in the illustration of FIG. 4 in its closed position, i. its closing element seat 21 provided, which is formed at the discharge point of the drain passage 22 into the control chamber 24. On an end face, for example, the hemispherical formable closure member 19 is biased by a spring element 26. The spring element 26, which may be a plate spring, is supported on an end face 29 of a needle-shaped injection valve member 27. The control chamber 24 is always acted upon by a high-pressure line, which is connected to one of the high-pressure ports 40 of a high-pressure accumulator 31 (common rail), with high-pressure fuel. The high-pressure accumulator 31 in turn is acted upon via a supply line 32 via a high pressure pump 34 with fuel under high pressure and stores it. Depending on the configuration of the injection system of the internal combustion engine 36, the high-pressure pump 34 can be preceded by an electric fuel pump 6 acting as a prefeed pump.

The system space 20 of the fuel injector 38 on its low-pressure side 10 may be limited on the one hand by a thin-walled wall 43, on the other hand, the system space 20 may also be sealed by a bellows 42. In particular, the formation of a limitation of the system space 20 via a deformable bellows 42 advantageously offers the possibility of compensating elongations during energization of the actuator 11 due to a longitudinal expansion of the piezoelectric crystal stack 12 while at the same time maintaining the sealing effect. Via the pressure prevailing in the system space 20, the hydraulic coupling space 14 is filled. Between the housing 44, which encloses the hydraulic coupling chamber 14, and the actuating piston 15 and the actuating piston 18 are formed gaps, via which the fuel volume on the low pressure side 10 of the fuel injector 38 and the first filling of the hydraulic coupling chamber 14 enters this.

First, consider the case where the direct injection internal combustion engine fuel injection system shown in FIG. 1 includes a pressure holding valve 8 on the low pressure side 10 of the fuel injector 38.

If, in such a configured fuel injection system for direct injection internal combustion engines 36 of the control chamber 24 via the energization of the actuator 11 relieved of pressure flows from the control chamber 24 via the fuel passage 22 in the system space 20 over. From the system space 20, the fuel volume diverted from the control chamber 24 flows via the connection 17 into the low-pressure connection 2. All low pressure ports 2 of the fuel injectors 38 open into the manifold 3. The other fuel injectors 38 of the internal combustion engine 36 are indicated in Fig. 4 only schematically. In the manifold 3, the throttle 7 is received in front of the injector-side inlet 41 of the pressure holding valve 8. Through the throttle point 7 in the manifold 3 can be ensured in an advantageous manner that adjusts the necessary for filling the hydraulic coupling chamber 14 pressure in high load points. At low load points, however, the pressure level necessary for filling the hydraulic coupling chamber 14 can be applied via the pressure-maintaining valve 8. At low load points, the pressure level on the low-pressure side 10 of the fuel injector 38 in the system space 20 is such that a filling of the hydraulic coupling chamber 14 via the gaps between the housing 44 and the actuating piston 18 on the one hand and on the gap between the actuating piston 15 and the housing 44th the pressure translator 13 on the other hand can be done. In low load points prevail after the throttle 7 only the low pressures that can be generated by the pressure holding valve, whereby the substantial relief of the low pressure side 10 of the fuel injector 38 is achieved. With the dimensioning of the throttle diameter of the throttle point 7, or the opening pressure of the pressure holding valve 8 - in this configuration of a fuel injection system - can be adjusted if necessary, the required for the filling of the hydraulic coupling chamber 14 via the system space 20 pressure.

In the embodiment of a fuel injection system for internal combustion engines described above, the delivery of fuel from the fuel tank 35 to high-pressure pump 34, in which the fuel is compressed to a very high pressure of about 1500 bar and more, takes place via a first fuel supply line 8.1.

If, according to a variant of a fuel injection system, an electric fuel pump 6, which in this case represents the means for holding the pressure, is provided at a pressure relief of the control chamber 24 by energizing the actuator 11, an outflow of fuel volume from the control chamber 24 in the system space 20 analog From the system space 20, the fuel flows via the port 17 into the low-pressure port 2, which applies to all fuel injectors 38, which are provided according to the number of cylinders to be supplied with fuel internal combustion engine 36 at this. In this case, a throttle point 7 is also formed in the manifold 3, in which all low-pressure ports 2 of the fuel injectors 38 open. The throttle body 7 is located at the confluence of all low-pressure connections 2 in the manifold 3 in front of the input end 41 serving as a feed pump electric fuel pump 6. The electric fuel pump 6 delivers fuel from the fuel tank 35 and the second fuel supply line 6.1 to the high-pressure pump 34. The high-pressure pump 34 in turn acted upon the high-pressure accumulator 31 (common rail) via the supply line 32 with fuel under very high pressure. The fuel level is in the range between about 1500 and 1600 bar.

In this case, it is achieved by the throttle point 7 at high load points that due to the pressure prevailing in the system space 10, a filling of the hydraulic coupling chamber 14 via the leakage gaps between the displacer 18 and the housing 44 and the actuating piston 15 and the housing 44 sets. In the case of small load points, the pressure necessary to fill the coupler can be maintained by the electric fuel pump 6 serving as the feed unit. As a result, only the low pressures of the electric fuel pump, which can be between about 3 and 8 bar, prevail after the throttle point 7. As a result, a substantial relief of the low-pressure side 10 of the fuel injector 10 can be achieved. By choosing the diameter of the throttle point 7 in the manifold 3 and the delivery pressure of the electric fuel pump 6, the pressure in the system space 20 for filling the hydraulic coupling chamber 14 can be changed by the guide gaps, if necessary. If an electric fuel pump 6 is used together with a high-pressure pump 34, the electric fuel pump 6 assigned to the fuel tank serves as an advance delivery unit for the high-pressure pump 34, which is not designed to be self-priming. The supply line 6.1 branches off in this case from the fuel line, which is assigned to the fuel tank 35, and leads to the high-pressure pump 34th

By the design of the throttle diameter of the throttle 7 in the manifold 3, the setting of the opening pressure of the pressure holding valve 8 and the delivery pressure of the electric fuel pump 6 different filling pressures for filling the hydraulic coupling chamber 14 of the hydraulic booster 13 as required, can be preset.

By inventively proposed inclusion of a throttle point 7 in the manifold 3, both an electric fuel pump 6 and a pressure holding valve 8 with respect to its pressure load in high load points of the internal combustion engine 36 are mechanically relieved, which has a significant relief of the low pressure system 10 of the fuel injector 38 result. The pressure-maintaining valve 8 and the electric fuel pump 6 can therefore be made smaller in terms of their strength. In particular, the proposed solution according to the invention avoids the use of additional mechanical components which are to be manufactured or moved, as a result of which adjusting operations can also be dispensed with on these additional inner parts to be provided.

LIST OF REFERENCE NUMBERS

1

cylinder

2

Low pressure port

3

manifold

4

Pressure holding valve

5

Fuel return

6

Electric fuel pump

6.1

first supply line

7

throttle

8th

Pressure holding valve

8.1

second supply line

9

High pressure system fuel injector

10

Low pressure fuel injector

11

actuator

12

Piezo crystal stack

13

hydraulic translator

14

hydraulic coupling room

p _K

Coupling chamber pressure

15

actuating piston

16

Face actuating piston

17

connection

18

actuating piston

19

closing element

20

system space

21

Closing element seat

22

drain channel

23

guide piston

24

control room

25

Control Room feed

26

spring element

27

Injection valve member

29

Front side injection valve member

31

High-pressure collecting space (Common Rail)

32

supply line

34

High pressure pump

35

Fuel tank

36

Internal combustion engine

37

Cylinder head region

38

fuel injector

39

casing

40

High pressure

41

injector side entrance of 6, 8

42

bellow

43

wall

44

Housing coupling space

Claims (10)

1. Fuel injection system for internal combustion engines having a plurality of fuel injectors (38), with the fuel injectors (38) having in each case one high-pressure port (40) and in each case one low-pressure port. (2), and with the low-pressure ports (2) opening out into at least one collecting line (3), and with it being possible for the fuel injectors (38) to be actuated by means of a piezoelectric actuator (11), having a means (6, 8) for maintaining the fuel pressure arranged between the collecting line (3) and an unpressurized fuel return line (5), (35), and with the fuel injector (38) having a system space (20) in which a pressure level prevails which is suitable for filling a hydraulic coupling space (14), characterized in that a throttle (7) is arranged in the collecting line (3) between the opening-out point of the low-pressure ports (2) of the fuel injectors into the collecting line (3) and the injector-side inlet (41) of the means (6, 8) for maintaining the fuel pressure.
2. Fuel injection system according to Claim 1, characterized in that the means for maintaining the fuel pressure on the low-pressure side is designed as a pressure-maintaining valve (8).
3. Fuel injection system according to Claim 1, characterized in that the means for maintaining the fuel pressure on the low-pressure side is formed by an electric fuel pump (6).
4. Fuel injection system according to Claim 1, characterized in that the high-pressure ports (40) of the fuel injectors (38) are acted on with highly pressurized fuel from at least one high-pressure collecting space (31).
5. Fuel injection system according to Claim 1, characterized in that the stroke of the piezoelectric actuator (11, 12) can be transmitted via a hydraulic medium, in particular fuel, by means of a hydraulic coupler space (14) of the hydraulic transmitter (13) to an injection valve member (27), with it being possible for the hydraulic coupler space (14) to be filled with the hydraulic medium via the at least one throttle (7).
6. Fuel injection system according to Claim 1, characterized in that in relatively high load ranges of an internal combustion engine (36), it is possible by means of the throttle (7) for a coupling space pressure p_K to be maintained in the collecting line (3).
7. Fuel injection system according to Claims 2 or 3, characterized in that, at low load points of the internal combustion engine (36), the pressure required for filling the hydraulic coupling space (14) is maintained by means of the pressure-maintaining valve (8) or the electric fuel pump (6).
8. Fuel injection system according to Claim 1, characterized in that the initial filling of the hydraulic coupling space (14) takes place via leakage gaps between an actuating piston (15) and a housing (44) and/or via leakage gaps between an actuating piston (18) and the housing (44), with the housing (44) being enclosed by the system space (20).
9. Fuel injection system according to Claim 3, characterized in that the electric fuel pump (6) is connected upstream of a high-pressure pump (34) on the low-pressure side (10) of the fuel injector (38).
10. Fuel injection system according to Claim 2, characterized in that the pressure-maintaining valve (8) is connected in the collecting line (3) upstream of a fuel tank (35).

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