EP1799994B1 - Fuel injector having a stamp-molded valve seat for reducing armature stroke drift - Google Patents

Abstract

The invention relates to a method for producing a fuel injector (1) for an internal combustion engine, having a control valve that releases from a control chamber (18) or closes an outlet throttle (20), whereby a closing element (22) is placed in a valve seat (26) for closing the outlet throttle (20). The closing seat (26) is produced by stamp-molding using a stamp (30). The invention also relates to a fuel injector which is produced by the inventive method.

Description

Technical area

In internal combustion engines with fuel injection, the fuel is supplied to the individual combustion chambers of the internal combustion engine via fuel injectors with hydraulically actuated nozzle needle. For this purpose, a valve is received in the fuel injector, which is driven, for example, electromagnetically or by means of a piezoelectric actuator. Through the valve, an outlet throttle of a control chamber, which communicates with the nozzle needle, released or closed.

State of the art

From the DE 103 01 698 A1 a method for producing a fuel injector with a control valve is known, which opens or closes a drain from a control chamber through a valve seat placed in a closing element, wherein the valve seat is formed by stamping with an embossing die. From the US 2003/020039 and the US 5,694,903 A In each case, an injector for a fuel injection system is known. Through the injector, a control chamber is released or closed, which has an outlet throttle in a drain.

In fuel injectors, as are known from the prior art, a valve piece is received in the housing of the fuel injector, in which an outlet throttle is formed, which is in communication with a control chamber. The outlet throttle is released or closed by a closing element. For this purpose, a conical valve seat is formed in the valve piece, in which the outlet throttle opens. To close the outlet throttle, a spherical closing element is placed in the conical valve seat.

In order to achieve the required for the operation of an internal combustion engine high opening and closing speeds of the fuel injector, the closing element of the control valve is placed at high speed in his seat or lifted from this. This constant switching of the closing element leads to wear of the valve seat. This wear results in a Ankerhubdrift. That is, the path the closing element travels to close the drainage restrictor increases due to wear. The increased stroke of the closing element causes the stroke of the magnet armature is also increased in a solenoid-controlled valve or the Aktorhub in a piezoelectric actuator. This results in larger opening and closing times of the control valve and thus longer opening times of Einspritzöfffnung, which in turn results in higher injection quantities. These larger injection quantities of fuel into the combustion chambers of the internal combustion engine lead to higher engine emissions and higher combustion noise.

Presentation of the invention

To reduce the wear of the valve seat and thus to reduce the Ankerhubdrift is in the inventive method for producing a fuel injector for an internal combustion engine with a control valve that opens or closes an outlet throttle from a control chamber, and in which for closing the outlet throttle a closing element in a valve seat is made, the valve seat formed by stamping with an embossing die. This avoids that the valve seat wears plastic during operation of the fuel injector.

When using a spherical closing element, which is placed in a conical valve seat, the embossing die according to the invention is designed in the form of a sphere with tangentially grown truncated cone. In a particularly preferred embodiment, the truncated cone has an opening angle which is greater than or equal to the opening angle of the cone-shaped valve seat. This avoids that material, which is displaced by the embossing, forms an elevation at the side of the embossing point facing the outlet throttle. This increase leads to a stronger throttling of the fuel flow when the valve is open. As a result, the fuel volume flow flowing out of the control chamber is reduced and the opening speed of the injection openings is likewise reduced.

So that the stamping of the valve seat not the stamp, but the valve seat is deformed, the stamp is preferably provided with a surface which consists of a hard metal. In a preferred embodiment, the entire die is made of a hard metal. Carbides known to the person skilled in the art are, for example, sintered materials of tungsten carbide, titanium carbide, tantalum carbide, molybdenum carbide and cobalt. The hard metal preferably has a hardness in the range of 1300-1800 HV30.

In the case of the inventively embodied fuel injector for an internal combustion engine with a control valve which releases an outlet throttle from a control chamber or closes, wherein for closing the outlet throttle a closing element is placed in a valve seat, the valve seat is formed by stamping

In a preferred embodiment, the valve seat of the control valve is conical. The preferred closing element for closing or releasing the cone-shaped valve seat is spherical

In a further embodiment, the valve seat is formed in a valve piece, which is accommodated in the housing of the fuel injector

drawing

In the following the invention will be described in more detail with reference to a drawing.

Figur 1

Einen Kraftstoffinjektor für ein Hochdruckspeichereinspritzsystem,

Figur 1.1

Einzelheit A aus Figur 1,

Figur 2

einen kegelförmig ausgebildeten Ventilsitz, auf welchen ein Prägestempel wirkt,

Figur 3

einen Konturschrieb eines kegelförmig ausgebildeten Ventilsitzes nach dem Stand der Technik,

Figur 4

einen Konturschrieb eines kegelförmig ausgebildeten, formgeprägten Ventilsitzes in einer ersten Ausführungsform,

Figur 5

einen Konturschrieb eines kegelförmig ausgebildeten, formgeprägten Ventilsitzes in einer zweiten Ausführungsform

It shows:

FIG. 1

A fuel injector for a high-pressure accumulator injection system,

Figure 1.1

Detail A off FIG. 1 .

FIG. 2

a cone-shaped valve seat, on which an embossing punch acts,

FIG. 3

a contour plot of a cone-shaped valve seat according to the prior art,

FIG. 4

a contour plot of a cone-shaped, stamped valve seat in a first embodiment,

FIG. 5

a contour plot of a conically shaped, stamped valve seat in a second embodiment

variants

FIG. 1 shows a fuel injector for a high-pressure accumulator injection system.

A fuel injector 1 comprises an injector body 2, in which a valve piston 3 is guided. The valve piston 3 acts with a front side 4 on a pressure pin 5, which is formed on a nozzle needle 6. On the side facing a combustion chamber, not shown here, at least one injection opening 7 is formed in the injector body 2. When the injection opening 7 is closed, the valve piston 3 exerts a pressure force on the pressure pin 5 of the nozzle needle 6 with its end face 4. As a result, the nozzle needle 6 is placed in a seat 8 and so closed the at least one injection opening 7. In addition to the pressure force of the valve piston 3 on the pressure pin 5 acts as a compression spring spring element 9 acts on the nozzle needle 6. The spring element 9 designed as a compression spring is preferably a spiral spring. This encloses in the FIG. 1 illustrated embodiment, the pressure pin 5 of the nozzle needle 6 and the nozzle needle 6 facing part of the valve piston 3. For this purpose, the spring element 9 is received in a valve chamber 10. The spring element 9 acts with one side on a stepped extension 11 of the nozzle needle 6 and with the other side against an end face 12 of the valve chamber 10th

The fuel supply of the fuel injector 1 via a connection piece 13 which is connected to a high-pressure accumulator, not shown here. In the connecting piece 13, a fuel filter 14 is received, in which the fuel is cleaned by particles contained therein to avoid damage due to abrasion in the fuel injector 1. The fuel filter 14 is followed by a channel 15, via which the fuel passes into a nozzle chamber 16. From the nozzle chamber 16, the fuel flows via an annular gap 17 to the injection port 7.

At the side facing away from the nozzle needle 6, the valve piston 3 ends in a control chamber 18. The control chamber 18 is supplied with fuel via an inlet throttle 19. The inlet throttle 19 also adjoins the fuel filter 14, so that there is also system pressure on the inflow side of the inlet throttle 19. From the control chamber 18, the fuel passes through an outlet throttle 20 in a low-pressure side discharge nozzle 21, which is connected, for example, with a fuel tank, not shown here.

The outlet throttle 20 can be closed or released by a ball-shaped closing element 22 here.

When the outlet throttle 20 is closed, system pressure prevails in the control chamber 18, in the valve chamber 10 and in the nozzle chamber 16. Due to the larger area of the end face which delimits the control chamber 18 than the oppositely facing surfaces of the valve piston 3, the pressure force acting in the direction of the at least one injection nozzle 7 is greater than the pressure force acting in the opposite direction and the nozzle needle 6 is placed in its seat 8 and thus closes the at least one injection opening 7. Once the closing element 22 lifts out of its seat and thus releases the outlet throttle 20, the pressure in the control chamber 18 decreases. As a result, the pressure force acting in the direction of the at least one injection opening 7 also decreases. The valve piston 3 moves in the direction of the outlet throttle 20. At the same time, the nozzle needle 6 lifts out of its seat and releases the at least one injection opening 7.

The actuation of the closing element 22 takes place in the embodiment variant shown here via an electrically controlled solenoid valve 23. Instead of the solenoid valve 23, however, a piezoelectric actuator, possibly with the interposition of a hydraulic coupler or a pressure booster could be used to actuate the closing element 22.

To facilitate the manufacture and assembly of the fuel injector 1, a valve member 24 is inserted into the injector body 2, in which the control chamber 18 including inlet throttle 19 and outlet throttle 20 is formed. Furthermore, in the valve piece 24, a bore 25 is executed, in which the valve piston 3 is guided

Figure 1.1 shows the detail A from FIG. 1 ,

Figure 1.1 shows the valve piston 3 in its upper position, that is, with an open injection port 7. For closing the injection port 7, the outlet throttle 20 is closed. For this purpose, the closing element 22 is placed in a valve seat 26. Thus, the closing element 22, the outlet throttle 20 closes pressure-tight, the valve seat 26 is formed in a conically shaped end face 32 of the valve member 24. In the embodiment shown here, the outlet throttle 20 opens to the closing element 22 in the form of a cone. By closing the outlet throttle 20, the connection to the low-pressure part of the fuel system is interrupted. Via the inlet throttle 19, which is connected via an annular space 27 and an inlet channel 28 to the high-pressure accumulator, the control chamber 18 is supplied with fuel under system pressure. As a result, the pressure in the control chamber 18 also rises again to system pressure. Due to the increasing pressure in the control chamber 18, the pressure force acting on the valve piston 3 increases and the valve piston 3 is moved in the direction of the at least one injection opening 7. Since the valve piston 3 is in communication with the pressure pin 5 of the nozzle needle 6 via the end face 4, the nozzle needle 6 is likewise moved in the direction of the at least one injection opening 7 and closes it.

The closing element 22 is connected via a piston 29 to an armature of the solenoid valve 23. When using a piezoelectric actuator instead of the solenoid valve 23 of the piezoelectric actuator acts directly on the piston 29th

In order to avoid that the valve seat due to the high speeds with which the closing element 22 is placed in this wears, resulting in a larger armature stroke and thus a greater closing time results, the valve seat 26 is formed in the fuel injector according to the invention. By embossing the Hertzian surface pressure is reduced by an increase in the bearing ratio. This means that the contact surface of the closing element 22 on the valve seat 26 is increased by the stamping. Due to the reduced surface pressure, a lower force acts on the valve seat 26, whereby its wear is reduced. Another advantage of the form-stamping of the valve seat 26 is that the material is solidified in the embossing area. The material hardening results in a further reduction of wear. Also roughness peaks that arise due to production, smoothed

By stamping the valve seat 26, the seat wear is anticipated, thus minimizing wear between the valve seat 26 and the closure member 22 during operation. As a result, the increase in the pilot injection quantity due to the increased during operation of the fuel injector armature stroke can be largely prevented. Increasing injection quantities during operation of the internal combustion engine lead to increased emission of the internal combustion engine, to an increase in the combustion noise and to a greater load on the entire internal combustion engine.

For embossing of the valve seat 26, for example, an embossing die made of a hard metal is used, which is designed in the form of the closing element 22.

FIG. 2 shows a valve seat, in which an embossing stamp is placed.

In order to avoid that forms on the flow restrictor 20 side facing the valve seat 26 during compression molding an elevation is formed in a valve with spherical closure member 22 and conical valve seat 26 of the die 30 in the form of a ball with tangentially grown therefrom truncated cone 31. By the truncated cone 31 is prevented from forming a survey along the spherical shape by the material is embossed by the shape of the truncated cone 31 along the direction of the likewise conically shaped valve seat 26.

If such a survey forms during the stamping of the valve seat 26, the flow cross-section is reduced when the valve is open. The valve thus acts as a throttle, whereby the fuel flow rate flowing from the outlet throttle 20 is reduced. Such a reduced fuel volume flow leads to a slower pressure reduction in the control chamber 18 and thus also to a reduced opening speed of the nozzle needle 6. This also results in a changed injection behavior, which can adversely affect the combustion process in the combustion chamber of the internal combustion engine.

The truncated cone 31 preferably has an opening angle α ₁ , which is greater than the opening angle α _{2 of} the valve seat 26. At the same opening angle α _{1 of} the truncated cone 31 and opening angle α _{2 of} the valve seat 26, it is possible that a part of the material in the stamping in Direction of the outlet throttle 20 is pressed. In this case, a burr forms at the transition from the valve seat 26 into the outlet throttle 20, at which the opening angle changes. This burr leads to a negative influence on the fuel flow.

In a preferred embodiment, the opening angle α ₁ is greater by 0 to 10 degrees than the opening angle α _{2 of} the valve seat 26. A larger opening angle α _{1 of} the truncated cone 31 causes the embossing point in the region of the valve seat 26 on the side of the truncated cone 31 forms a survey, which acts as an additional throttle for the fuel flow.

Even with non-spherical closing element 22, wear on the valve seat 26 can be reduced by shaping the shape of the valve seat 26. In order to avoid a conical valve seat 26 that forms a survey in the region of the valve seat 26, even with non-spherical closing element 22 of the die 30, which is in the form of the closing element 22, preferably provided with a truncated cone 31 whose opening angle α ₁ greater than the opening angle α _{2 of} the valve seat 26. Thus, in the case of a conical valve seat 26, the closing element 22 may be formed next to the spherical shape, for example also in the form of a paraboloid or a cylinder.

In addition to the truncated cone 31, it is also possible for the embossing stamp 30 to end in the form of a cone whose point angle is greater than or equal to the opening angle α _{2 of} the valve seat 26.

Suitable material for the die is any material which is harder than the material from which the valve seat 26 is made. Particularly suitable as material for the Embossing dies 30 are, for example, hard metals selected from the group of hard metals K 01 - K 40. Depending on the composition, the hardness of these hard metals is 1300-1800 HV 30. The hard metals are sintered materials of tungsten carbide, titanium carbide, tantalum carbide, molybdenum carbide and cobalt. In addition to the hard metals, pressure-resistant ceramics, for example, which are harder than the material from which the valve seat 26 is made, are also suitable.

FIG. 3 shows a contour plot of a cone-shaped valve seat according to the prior art.

On the abscissa 33 of the in FIG. 3 The diagram shown, the length of the conically shaped end face 32 of the valve member 24 is shown in mm, in which the valve seat 26 is formed. The ordinate 34 shows the surface roughness in μm. The line designated by reference numeral 35 shows the surface of the conically shaped end face of the valve piece 24 before the closing element 22 is placed in the valve seat 26 for a first time. It can already be clearly seen here that the surface of the end face 32 of the valve piece 24 has a production-related roughness. The million-time switching of the closing element 22 leads to wear in the valve seat 26. By the closing element 22 creates a recess 36 in the region of the valve seat 26. The recess 36 has a depth of wear 37, which is significantly greater than the average surface roughness of the end face 32 of Valve piece 24. Due to the very small opening or closing paths of the closing element 22, the wear depth 37 leads to a significantly longer closing path for closing the control valve. This also leads to a slower closing of the injection opening 7 and thus to a larger amount of fuel which is injected into the combustion chamber. This leads to higher engine emissions and higher combustion noise

FIG. 4 shows a Konturschrieb a conically shaped valve seat, in which the valve seat is molded with a spherical die

FIG. 4 can be seen that the surface 35 is significantly smoother before the first closing of the control valve when the valve seat 26 is embossed. The embossing depth in which the valve seat 26 is embossed is designated by reference numeral 39. Due to the spherical embossing punch the form-stamped valve seat 26 has the cross section of a circle segment. As a result, an elevation 40 forms toward the outlet throttle 20. The survey 40 leads when the outlet throttle 20 is open, that the flow area is reduced. For this reason, the valve seat 26 acts when the outlet throttle 20 is open as an additional throttle.

By embossing the valve seat 26, the material is solidified in the region of the valve seat 26. This material consolidation as well as the larger contact surface of the closing element 22 in the valve seat 26 cause a recess 36 to form a recess 36 with a comparison to the non-embossed valve seat 26 only a small closing depth 37 even after a large number of opening and closing movements of the closing element 22.

FIG. 5 shows the end face 32 of the valve member 24 with molded therein valve seat 26 when a spherical die is used, in which tangentially from the ball a truncated cone grows. Even with the use of such embossing stamp shows that the roughness of the surface 35 before the first closing of the control valve is less than in a non-embossed valve seat 26. The conical approach to the stamper 30 is only a slight elevation 40 on the outlet throttle 20 facing Side of the valve seat 26. Even when using a stamping die 30 in the form of a ball tangentially resulting truncated cone 31 is formed after a large number of opening and closing movements of the closing element 22 a recess 36 with a comparison with the non-form-stamped valve seat 26 only low wear depth 37th The embossing depth of the form-stamped valve seat 26 is also in FIG. 5 designated by reference numeral 39.

LIST OF REFERENCE NUMBERS

1

fuel injector

2

injector

3

plunger

4

front

5

pushpin

6

nozzle needle

7

Injection port

8th

Seat

9

spring element

10

valve chamber

11

stepped extension

12

Front side of the valve chamber 10

13

spigot

14

Fuel filter

15

channel

16

nozzle chamber

17

annular gap

18

control room

19

inlet throttle

20

outlet throttle

21

drain connection

22

closing element

23

magnetic valve

24

valve piece

25

drilling

26

valve seat

27

annulus

28

inlet channel

29

piston

30

dies

31

truncated cone

32

front

33

abscissa

34

ordinate

35

Surface before first closing

36

deepening

37

wear depth

38

seat width

39

embossing depth

40

survey

α ₁

Opening angle of the truncated cone 31

α ₂

Opening angle of the valve seat 26

Claims (3)

1. Method for producing a fuel injector (1) for an internal combustion engine, with a control valve which releases or closes an outflow from a control space (18) by means of a closing element (22) placed into a valve seat (26), and the valve seat (26) being formed by stamp-moulding by means of a stamping die (30), characterized in that the outflow from the control space (18) has an outflow throttle (20), and the stamping die (30) is designed in the form of a ball with a cone frustum (31) arising tangentially from it.
2. Method according to Claim 1, characterized in that the cone frustum (31) has an opening angle (α₁) which is larger than or equal to the opening angle (α₂) of the conically designed valve seat (26).
3. Method according to one of the preceding claims, characterized in that the surface of the stamping die (30) consists of a hard metal.

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