EP2891789B1 - Fuel injector and method for producing a fuel injector - Google Patents

Description

State of the art

The invention relates to a fuel injector according to the preamble of claim 1, as he, for example, from DE 10 2009 002 554 A1 Furthermore, the invention relates to a method for producing a fuel injector according to the invention.

The known fuel injector is used for injecting fuel into the combustion chamber of a self-igniting internal combustion engine. The fuel injector has a multipart injector housing, which forms a high-pressure space in a partial area. Within the high-pressure chamber, a guide piece for a coupler piston is arranged, which serves for the at least indirect control of the lifting movement of a nozzle needle arranged in a liftable manner in the injector housing. The high pressure chamber is connected on the one hand via a bore formed within the injector with a high pressure source (rail), and on the other hand is hydraulically in communication with injection openings formed in the injector. Such a high-pressure space forming a relatively large storage volume also serves, in particular, as a storage medium close to the nozzle and causes the amplitudes of pressure oscillations, which arise as a result of the injections when releasing the injection openings, to be considerably reduced. Furthermore, the need for relatively costly trained deep hole bores is at least partially reduced by such a high-pressure space. If, as in the cited prior art, additional components are arranged within the high-pressure chamber, it is necessary to form the injector housing in the region of the components or the high-pressure chamber with a relatively small wall thickness, since the outer diameter of the injector due to the installation space determined by the internal combustion engine usually limited.

The trend in modern diesel injection systems is more and more to higher system or injection pressures. While current injection systems have a rail or system pressure of approximately 2.500 bar maximum, future systems are considered, in which the rail or system pressure is up to 3000 bar. The pressure prevailing inside the high-pressure chamber causes a tensile stress acting on the material of the component or the injector housing on the component (injector housing) delimiting the high-pressure chamber. Since, as explained above, for receiving components within the high-pressure chamber in the usually existing installation spaces of fuel injectors, the wall thickness of the component (injector) is relatively low, increased pressures cause increasing material stress and thus the risk of cracks or damage. Although it is theoretically conceivable to make the increased tensile stresses controllable by a particularly high-quality material for the injector housing or to compensate at least partially, which has correspondingly higher strength values, however, for cost and other reasons such materials are often undesirable or usable.

From the US Pat. No. 4,894,900 . EP 1 757 800 A1 . DE 10 2007 008 863 A1 . EP 2 626 546 A1 and EP 2 626 545 A1 In addition, fuel injection valves are known in which high pressure leading cavities are formed, which are at least partially surrounded by two housing parts.

Disclosure of the invention

Based on the illustrated prior art, the present invention seeks to further develop a fuel injector according to the preamble of claim 1 such that the possible system pressure can be increased within a high-pressure chamber with constant inner and outer dimensions of the injector only by constructive measures without For example, materials with higher strength must be used.

This object is achieved in a fuel injector with the features of claim 1, characterized in that the high-pressure chamber is limited at least partially by two elements, an inner first, preferably sleeve-shaped element having a first element arranged in the first recess for forming the high-pressure chamber, and a second element immediately surrounding the first element with a second recess, wherein the second recess, the first element surrounds its outer peripheral surface, and wherein the second element is connected to form a radially acting pressure force on the first element with this. The first recess is arranged eccentrically in the first element and in the region of the first element having the greatest wall thickness, a bore arranged parallel to a longitudinal axis is formed. This bore can serve in particular the leadership of fuel or the like.

In other words, this means that two immediately surrounding and interconnected elements form the boundary of the high-pressure space, wherein the outer element exerts a radially acting pressure force on the inner element. This compressive force causes compressive stresses to arise within the wall of the inner element in the side facing the high-pressure chamber which counteract the tensile stresses caused as a result of the system pressure and thus at least partially compensate for them. As a result, the tensile stresses occurring on the inner wall of the inner element are less than tensile stresses that would occur without the outer element in the wall of the inner element.

Advantageous developments of the fuel injector according to the invention are listed in the subclaims.

To form the radial compressive force, it is provided in particular that a press fit is formed between the outer diameter of the first element and the inner diameter of the second element.

An over the entire circumference of the two elements of equal mechanical stress is achieved when the second element is sleeve-shaped, wherein the second recess is arranged concentrically in the second element.

However, there are also applications conceivable in which the second element is sleeve-shaped, wherein the second recess is arranged eccentrically in the second element.

Another, structurally particularly preferred embodiment provides that the first element projects axially beyond the second element at least on one end face, preferably on both end faces, in the non-assembled state. Such a configuration causes in the installed state of the two elements in which they are axially braced within the injector, the high-pressure chamber is sealed radially and securely over the radially inner first element safely and reliably, so that leakage of fuel in the direction of the second element is avoided ,

For this purpose, it is necessary that an axial compressive stress can be formed between the first element and at least one component axially delimiting the first element. Such axial compressive stress can be achieved in practice by means of axial clamping elements, for example a union nut or the like.

The use of the invention is particularly useful in applications in which the pressure in the high-pressure chamber is more than 2500 bar, in particular up to 3000 bar or above.

Such a fuel injector is usually exposed to different operating conditions or operating temperatures, which may range in the case of cold start, for example, from -30 ° C to more than 150 ° C during operation. In order to always be able to exert sufficient compressive stresses on the radially inner first element over the entire temperature range and thus to ensure the functional reliability or mechanical strength of the fuel injector, it is additionally provided in a further embodiment of the invention that the coefficient of thermal expansion of the radially inner element be equal or is greater than the thermal expansion coefficient of the radially outer element. In the simplest case, this condition is fulfilled if the radially inner element and the radially outer element consist of the same material.

The invention also includes a method for producing a fuel injector according to the invention, in which two elements radially surrounding one another are joined together. According to the invention, it is provided that the radially inner element is cooled down before the joining and / or the radially outer element is heated. The erfindüngsgemäße method thus allows the two elements mechanically relatively low-stress mounting in which in particular an exciting removal of surfaces of the two elements is safely and reliably avoided.

Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and from the drawing.

Fig. 1

einen vereinfachten Längsschnitt durch einen Kraftstoffinjektor,

Fig. 2

zwei hülsenförmige Elemente zur Begrenzung eines Hochdruckraums im Längsschnitt,

Fig. 3

die beiden Elemente gemäß Fig. 2 im montierten Zustand im Längsschnitt sowie im Querschnitt,

Fig. 4

eine Darstellung des Verlaufs der Zugspannung der beiden Elemente bei unter Hochdruck stehendem Hochdruckraum,

Fig. 5

gegenüber der Fig. 2 modifizierte Elemente in montiertem Zustand im Längsschnitt und

Fig. 6 bis Fig. 8

jeweils im Querschnitt weitere, gegenüber der Fig. 3 modifizierte Elemente.

This shows in:

Fig. 1

a simplified longitudinal section through a fuel injector,

Fig. 2

two sleeve-shaped elements for delimiting a high-pressure chamber in longitudinal section,

Fig. 3

the two elements according to Fig. 2 in the assembled state in longitudinal section and in cross section,

Fig. 4

a representation of the course of the tensile stress of the two elements in high-pressure high-pressure space,

Fig. 5

opposite the Fig. 2 Modified elements in the assembled state in longitudinal section and

Fig. 6 to Fig. 8

each in cross-section further, opposite the Fig. 3 modified elements.

The serve Fig. 1 to 7 only the illustration of the technical doctrine while the Fig. 8 an embodiment of the invention shows.

The same elements or elements with the same function are provided in the figures with the same reference numerals.

The Indian Fig. 1 shown fuel injector 10 is used for injecting fuel into the combustion chamber of a self-igniting internal combustion engine, not shown. The fuel injector 10 has a multi-part injector housing 11, in which in a longitudinal axis 12, a nozzle needle 13 is arranged as a liftable injection valve member. The nozzle needle 13 closes in the in the Fig. 1 shown lowered position of the nozzle needle 13 at least one, formed in the injector 11 injection port 14th

In the exemplary embodiment shown, the injector housing 11 consists of a nozzle body 15 facing the combustion chamber of the internal combustion engine, on the side remote from the combustion chamber in the axial direction a pressure body 18 formed of two elements 16, 17, an intermediate plate 19, a holding body 20 and a housing cover 21 connect.

The nozzle body 15 has a radially circumferential retaining collar 22 which cooperates with a sleeve-shaped nozzle retaining nut 25, which in turn on the side facing away from the retaining collar 22 on its inner circumference has a thread 26 which cooperates with a corresponding external thread on the holding body 20 to between the nozzle body 15 and the holding body 20 to compress the pressure body 18 and the intermediate plate 19 axially.

It should be mentioned again that the construction of the injector housing 11 described so far is merely an example and may deviate from the illustrated embodiment.

Of the pressure body 18 and the nozzle body 15 and the intermediate plate 19, a high-pressure chamber 30 is spatially limited, via a formed in the intermediate plate 19, the holding body 20 and the housing cover 21 depth bore 32 hydraulically with a high-pressure accumulator in the form of a rail 33 is connected. The rail 33 provides the system pressure required during operation of the fuel injector 10, which at least substantially also prevails within the high-pressure chamber 30, wherein the system pressure may be more than 2500 bar, in particular up to 3000 bar.

Within the holding body 20, an actuating element in the form of a piezo-actuator 35 is arranged, which serves for the at least indirect control of the lifting movement of the nozzle needle 13, wherein the piezo-actuator 35 is electrically actuated via connecting lines 36 and actuated. The limited by the holding body 20 and the housing cover 21 receiving space 37 for the piezo-actuator 35 forms a low-pressure chamber of the injector 11, which is depressurized via a return line 38.

In the high pressure chamber 30, a guide piece 40 is arranged in the region of the pressure body 18, which has a blind hole for receiving a coupler piston 41 on the side facing the nozzle needle 13. Further, in a guide piece 40 and the intermediate plate 19 traversing longitudinal bore a piston portion 42 is arranged, which is arranged in operative connection with the piezoelectric actuator 35. The coupler piston 41 acts on the nozzle needle 13 facing, protruding from the blind hole of the guide piece 40 end face with a plate 43 together, on which a spring 44 is supported. The spring 44 loads the coupler piston 41 with an axial force acting in the direction of the piezoactuator 35. On the side facing away from the coupler piston 41 side of the plate 43 is located on a guide sleeve 45 axially, into which the one end portion of the nozzle needle 13 is immersed. Between a trained on the nozzle needle 13, radially extending collar 46 and the guide sleeve 45, a compression spring 48 is supported, on the one hand axially presses the guide sleeve 45 to form a sealing seat against the plate 43, and on the other hand, the nozzle needle 13 in the direction of its closed position kraftbeaufschlagt in which the at least one injection opening 14 is hydraulically sealed by the nozzle needle 13.

With regard to the known operation of the fuel injector 10 so far described is on the DE 10 2009 002 554 A1 referred to the applicant.

Essential to the invention is the structural design of a pressure medium 18 forming a boundary of the high-pressure chamber 30, consisting of the two elements 16, 17. As in particular with reference to the illustration of FIGS. 2 and 3 can be seen, the two elements 16, 17 are each sleeve-shaped and have a common longitudinal axis 49. It is essential to the invention that to form an interference fit in the joined state of the two elements 16, 17, the outer diameter D of the radially inner first element 16 is slightly larger than the inner diameter d of the radially outer second element 17. After the axial joining of the two elements 16, 17 is thereby generated in the outer peripheral wall 51 of the radially inner member 16, a compressive stress. In addition, the radially inner element 16 has a first recess 52 which directly delimits the high-pressure chamber 30, while the radially outer element 17 has a second recess 53 for receiving the radially inner element 16.

In the in the FIGS. 2 and 3 illustrated embodiment, the two elements 16, 17 each have the same axial extent or length I. The joining of the two elements 16, 17 is preferably carried out by heating the radially outer element 17 and / or cooling the radially inner element 16, so that after the joining of the two elements 16, 17, the two end faces of the elements 16, 17 flush complete each other.

In the Fig. 4 the course of the tensile stress δ of the two elements 16, 17 is shown, as it adjusts itself from the longitudinal axis 49 at a distance r due to a (hydraulic) pressure prevailing in the high-pressure chamber 30. In particular, it can be seen that the pressure or the corresponding tensile stress acting in the lateral surface 51 of the radially inner element 16 is reduced with increasing distance r as a result of the compressive stress induced in the radially inner element 16 by the radially outer element 17 and only in the region of second recess 53 of the radially outer member 17 occupies its maximum.

To increase the tightness during axial clamping of the pressure body 18 and the radially inner element 16 between the nozzle body 15 and the intermediate plate 19, it may according to the Fig. 5 be provided that the radially inner member 16 has a slightly greater length I than the radial outer element 17, so that in the joined state of the two elements 16, 17, the radially inner element 16 protrudes with its end face 55, at least on one, preferably at both end faces 55 slightly above the end face 56 of the radially outer member 17. During axial clamping of the pressure body 18 with the nozzle retaining nut 25, a compressive stress is thereby generated on the inner member 16, which allows a particularly good sealing of the high-pressure chamber 30 radially outward, wherein in the installed state, the two end faces 55, 56 preferably on the nozzle body 15 and abut the intermediate plate 19.

In the Fig. 6 the case is shown in which the radially inner member 16 has a constant wall thickness a, while the radially outer member 17a viewed in the circumferential direction has a variable wall thickness A, which is caused by the second recess 53a eccentric to the longitudinal axis 54 of the second element 17a is arranged.

In the Fig. 7 In addition, the case is shown in which the radially inner element 16a has a different wall thickness a, ie, that the first recess 52a is arranged eccentrically to the longitudinal axis 57 of the radially inner member 16a.

Last is in the Fig. 8 the case of the invention shown in which in the radially inner member 16 b, which basically according to the radially inner member 16 a of Fig. 7 is formed, in the region of the largest wall thickness a an additional longitudinal bore 60 is formed for guiding pressure medium, wherein the longitudinal axis of the longitudinal bore 60 is parallel to the longitudinal axis 57 of the first recess 52a.

Claims (10)

1. Fuel injector (10) having an injector housing (11) which forms a high-pressure chamber (30), which high-pressure chamber is connectable to a high-pressure source (33) and in which high-pressure chamber an injection valve element (13) is arranged such that it can perform stroke movements, wherein the high-pressure chamber (30) is delimited at least in regions by two elements (16; 16a; 16b, 17; 17a), an inner, first, preferably sleeve-shaped element (16; 16a; 16b) with a first recess (52; 52a) arranged in the first element (16; 16a; 16b) for forming the high-pressure chamber (30), and a second element (17; 17a) which directly surrounds the first element (16; 16a; 16b) and which has a second recess (53; 53a), wherein the second recess (53; 53a) surrounds the first element (16; 16a; 16b) at the outer circumferential surface (51) thereof, and wherein the second element (17; 17a) is connected to the first element (16; 16a; 16b) such that a pressure force acting radially on said first element is generated, characterized in that the first recess (52a) is arranged eccentrically in the first element (16a; 16b), and in that, in that region of the first element (16b) which has the greatest wall thickness (a), there is formed a bore (60) which is arranged parallel to a longitudinal axis (57).
2. Fuel injector according to Claim 1,
   characterized
   in that, for the generation of the pressure force, between the outer diameter (D) of the first element (16; 16a; 16b) is, for the purposes of forming an interference fit, greater than the internal diameter (d) of the second recess (53; 53a) of the second element (17; 17a).
3. Fuel injector according to Claim 1 or 2,
   characterized
   in that the second element (17) is of sleeve-shaped form, and in that the second recess (53) is arranged concentrically in the second element (17).
4. Fuel injector according to Claim 1 or 2,
   characterized
   in that the second element (17a) is of sleeve-shaped form, and in that the second recess (53a) is arranged eccentrically in the second element (17a).
5. Fuel injector according to one of Claims 1 to 4,
   characterized
   in that the first element (16; 16a; 16b) projects axially beyond the second element (17; 17a) at least at one face side, preferably at both face sides, when not in a mounted state in the injector housing (11).
6. Fuel injector according to Claim 5,
   characterized
   in that an axial compressive stress can be generated between the first element (16; 16a; 16b) and at least one component (15, 19) which axially delimits the first element (16; 16a; 16b).
7. Fuel injector according to one of Claims 1 to 6,
   characterized
   in that the two elements (16; 16a; 16b, 17; 17a) are part of the injector housing (11).
8. Fuel injector according to one of Claims 1 to 7,
   characterized
   in that a pressure of over 2500 bar prevails in the high-pressure chamber (30).
9. Fuel injector according to one of Claims 1 to 8,
   characterized
   in that the coefficient of thermal expansion of the radially inner element (16; 16a; 16b) is equal to or greater than the coefficient of thermal expansion of the radially outer element (17; 17a).
10. Method for producing a fuel injector (10) according to one of Claims 1 to 9, in which two elements (16; 16a; 16b, 17; 17a) which radially surround one another are joined together,
    characterized
    in that, before the joining process, the radially inner element (16; 16a; 16b) is cooled and/or the radially outer element (17; 17a) is heated.

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