DE102013226569A1 - Fuel injector and method of manufacturing a fuel injector - Google Patents

Abstract

The invention relates to a fuel injector (10) having an injector housing (11) which forms a high - pressure space (30) which can be connected to a high pressure source (33) and in which an injection valve member (13) is arranged in a liftable manner. According to the invention, it is provided that the high-pressure space (30) is bounded at least in regions by two elements (16; 16a; 16b, 17; 17a), an inner first sleeve-shaped element (16; 16a; 16b) having a first element (16 16a; 16b) for forming the high-pressure space (30), and a second element (17; 17a) immediately surrounding the first element (16; 16a; 16b) having a second recess (53; 53a wherein the second recess (53; 53a) surrounds the first member (16; 16a; 16b) on its outer peripheral surface (51), and wherein the second member (17; 17a) forms a radially acting compressive force on the first member (16; 16a; 16b) is connected to it.

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 the applicant is known. 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 formed deep-hole drilling 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 3000bar. 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.

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 first element immediately surrounding the second element having a second recess, wherein the second recess surrounds the first element on its outer peripheral surface, and wherein the second element is connected to form a radially acting pressure force on the first element with this.

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. Likewise, applications are conceivable in which the first recess is arranged concentrically in the first element and applications in which the first recess is arranged eccentrically in the first element.

In the latter case, provision may in particular be made for a bore arranged parallel to a longitudinal axis to be formed in the region of the first element which has the greatest wall thickness. This bore can serve in particular the leadership of fuel or the like.

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 more than 2500bar, in particular to 3000bar 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 inventive method thus enables the two elements mechanically relatively low-stress mounting, 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.

This shows in:

1 a simplified longitudinal section through a fuel injector according to the invention,

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

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

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

5 opposite the 2 Modified elements in the assembled state in longitudinal section and

6 to 8th each in cross-section further, opposite the 3 modified elements.

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

The Indian 1 illustrated fuel injector according to the invention 10 does not serve to inject fuel into the combustion chamber shown self-igniting internal combustion engine. The fuel injector 10 has a multipart trained injector 11 on, in which in a longitudinal axis 12 a nozzle needle 13 is arranged as an injection valve member liftable. The nozzle needle 13 closes in the in the 1 illustrated lowered position of the nozzle needle 13 at least one, in the injector housing 11 trained injection port 14 ,

The injector housing 11 consists in the illustrated embodiment of a combustion chamber of the engine facing nozzle body 15 , on which on the side facing away from the combustion chamber in the axial direction one of two elements 16 . 17 trained pressure body 18 , an intermediate plate 19 , a holding body 20 as well as a housing cover 21 connect.

The nozzle body 15 has a radially circumferential retaining collar 22 on that with a sleeve-shaped nozzle retaining nut 25 interacts, in turn, on the tie 22 facing away on its inner circumference a thread 26 having, with a corresponding external thread on the holding body 20 interacts to move between the nozzle body 15 and the holding body 20 the pressure body 18 as well as the intermediate plate 19 to be clamped axially.

It should be mentioned again that the structure of the injector housing described so far 11 is merely exemplary and may differ from the illustrated embodiment.

From the pressure hull 18 and the nozzle body 15 and the intermediate plate 19 is a high pressure room 30 limited in space, one in the intermediate plate 19 , the holding body 20 as well as the housing cover 21 trained deep hole 32 hydraulically with a high-pressure accumulator in the form of a rail 33 connected is. The rail 33 represents the operation of the fuel injector 10 required system pressure available, at least substantially even within the high-pressure chamber 30 prevails, the system pressure can be more than 2500bar, in particular up to 3000bar.

Inside the holding body 20 is an actuator in the form of a piezo actuator 35 arranged for at least indirect control of the lifting movement of the nozzle needle 13 serves, with the piezo actuator 35 via connecting cables 36 is electrically controlled or actuated. The of the holding body 20 and the housing cover 21 limited recording room 37 for the piezo actuator 35 forms a low pressure chamber of the injector 11 off, via a return line 38 relieved of pressure.

In the high pressure room 30 is in the area of the pressure hull 18 a leader 40 arranged on the nozzle needle 13 facing side a blind hole for receiving a coupler piston 41 having. Furthermore, in one the leader 40 as well as the intermediate plate 19 traversing longitudinal bore a piston section 42 arranged, in operative connection with the piezo actuator 35 is arranged. The coupler piston 41 acts on the nozzle needle 13 facing, from the blind hole of the guide piece 40 outstanding front side with a plate 43 together, at which there is a spring 44 supported. The feather 44 loads the coupler piston 41 with one towards the piezo actuator 35 acting axial force. On the coupler piston 41 opposite side of the plate 43 lies at this one guide sleeve 45 axially, in which the one end portion of the nozzle needle 13 dips. Between one at the nozzle needle 13 trained, radially encircling collar 46 and the guide sleeve 45 supports a compression spring 48 on the one hand, the guide sleeve 45 forming a sealing seat against the plate 43 axially presses, and the other hand, the nozzle needle 13 in the direction of its closed position force, in which the at least one injection opening 14 from the nozzle needle 13 hydraulically sealed.

With regard to the known operation of the fuel injector described so far 10 will be on the DE 10 2009 002 554 A1 referred to the applicant, which should be part of this invention.

Essential to the invention is the structural design of a limitation of the high-pressure chamber 30 forming pressure hull 18 , consisting of the two elements 16 . 17 , As in particular by the representation of the 2 and 3 recognizable are the two elements 16 . 17 each sleeve-shaped and have a common longitudinal axis 49 on. Essential to the invention is that to form a press 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 becomes characterized in the outer peripheral wall 51 of the radially inner element 16 generates a compressive stress. In addition, the radially inner element has 16 a first recess 52 on top of the high pressure room 30 Immediately limited, while the radially outer element 17 a second recess 53 for receiving the radially inner element 16 having.

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

In the 4 is the course of the tensile stress δ of the two elements 16 . 17 shown how he is due to one in the high pressure room 30 prevailing (hydraulic) pressure at a distance r from the longitudinal axis 49 established. In particular, it can be seen that in the lateral surface 51 of the radially inner element 16 acting pressure or the corresponding tensile stress as a result of the radially outer element 17 in the radially inner element 16 induced compressive stress is reduced with increasing distance r and only in the area of the second recess 53 of the radially outer element 17 take their maximum.

To increase the tightness during axial clamping of the pressure hull 18 or the radially inner element 16 between the nozzle body 15 and the intermediate plate 19 can it according to the 5 be provided that the radially inner element 16 has a slightly greater length l than the radially outer element 17 , so that in the joined state of the two elements 16 . 17 the radially inner element 16 with his face 55 , at least on one, preferably on both faces 55 something over the face 56 the radially outer element 17 protrudes. During axial distortion of the pressure hull 18 with the nozzle retaining nut 25 becomes thereby on the inner element 16 generates a compressive stress, which is a particularly good seal of the high-pressure chamber 30 allows radially outward, wherein in the installed state, the two end faces 55 . 56 preferably on the nozzle body 15 or the intermediate plate 19 issue.

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

In the 7 is additionally shown the case in which also the radially inner element 16a has a different wall thickness a, that is, that the first recess 52a eccentric to the longitudinal axis 57 of the radially inner element 16a is arranged.

Last is in the 8th the case illustrated in which at the radially inner element 16b that basically according to the radially inner element 16a of the 7 is formed, in the region of the largest wall thickness a an additional longitudinal bore 60 is designed to guide pressure medium, wherein the longitudinal axis of the longitudinal bore 60 parallel to the longitudinal axis 57 the first recess 52a runs.

The fuel injector described so far 10 or the inventive design of the pressure hull 18 can be modified or modified in many ways without departing from the spirit of the invention.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102009002554 A1 [0001, 0033]

Claims (13)

Fuel injector ( 10 ) with an injector housing ( 11 ), one with a high pressure source ( 33 ) connectable high pressure space ( 30 ), in which an injection valve member ( 13 ) is arranged in a liftable manner, characterized in that the high-pressure space ( 30 ) at least in regions of two elements ( 16 ; 16a ; 16b . 17 ; 17a ) is limited, an inner first, preferably sleeve-shaped element ( 16 ; 16a ; 16b ) with one in the first element ( 16 ; 16a ; 16b ) arranged first recess ( 52 ; 52a ) for the formation of the high-pressure space ( 30 ), and one the first element ( 16 ; 16a ; 16b ) immediately surrounding second element ( 17 ; 17a ) with a second recess ( 53 ; 53a ), wherein the second recess ( 53 ; 53a ) the first element ( 16 ; 16a ; 16b ) on its outer peripheral surface ( 51 ), and wherein the second element ( 17 ; 17a ) forming a radially acting compressive force on the first element ( 16 ; 16a ; 16b ) is connected to this. Fuel injector according to claim 1, characterized in that for the formation of the compressive force between the outer diameter (D) of the first element ( 16 ; 16a ; 16b ) to form a press fit is greater than the inner diameter (d) of the second recess ( 53 ; 53a ) of the second element ( 17 ; 17a ). Fuel injector according to claim 1 or 2, characterized in that the second element ( 17 ) is sleeve-shaped, and that the second recess ( 53 ) concentrically in the second element ( 17 ) is arranged. Fuel injector according to claim 1 or 2, characterized in that the second element ( 17a ) is sleeve-shaped, and that the second recess ( 53a ) eccentric in the second element ( 17a ) is arranged. Fuel injector according to one of claims 1 to 4, characterized in that the first recess ( 52 ) concentric in the first element ( 16 ) is arranged. Fuel injector according to one of claims 1 to 4, characterized in that the first recess ( 52a ) eccentric in the first element ( 16a ; 16b ) is arranged. Fuel injector according to claim 6, characterized in that in the region of the first element having the greatest wall thickness (a) ( 16b ) one parallel to a longitudinal axis ( 57 ) arranged bore ( 60 ) is trained. Fuel injector according to one of claims 1 to 7, characterized in that the first element ( 16 ; 16a ; 16b ) the second element ( 17 ; 17a ) at least on one end face, preferably on both end faces, not in the injector housing ( 11 ) mounted state axially surmounted. Fuel injector according to claim 8, characterized in that between the first element ( 16 ; 16a ; 16b ) and at least one, the first element ( 16 ; 16a ; 16b ) axially limiting component ( 15 . 19 ) An axial compressive stress can be formed. Fuel injector according to one of claims 1 to 9, characterized in that the two elements ( 16 ; 16a ; 16b . 17 ; 17a ) Part of the injector housing ( 11 ) are. Fuel injector according to one of claims 1 to 10, characterized in that in the high-pressure chamber ( 30 ) a pressure of more than 2500bar prevails. Fuel injector according to one of claims 1 to 11, characterized in that the thermal expansion coefficient of the radially inner element ( 16 ; 16a ; 16b ) is equal to or greater than the thermal expansion coefficient of the radially outer element ( 17 ; 17a ). Method for producing a fuel injector ( 10 ) according to one of claims 1 to 12, in which two elements (11) surrounding each other radially ( 16 ; 16a ; 16b . 17 ; 17a ) are joined together, characterized in that prior to joining the radially inner element ( 16 ; 16a ; 16b ) and / or the radially outer element ( 17 ; 17a ) is / are heated.

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