METHOD FOR ASSEMBLING A FUEL INJECTOR AND TOOL FOR USE IN THIS METHOD

Description

[0001] The invention relates to a method for assembling a fuel injector, such as is used, for example, to introduce fuel under high pressure into the combustion chamber of an internal combustion engine. Furthermore, the invention relates to an assembly tool such as is used in the method according to the invention. State of the art

[0002] Fuel injectors, such as those used to inject fuel under high pressure, consist of several components, usually a holder and a nozzle. The nozzle contains the injection openings through which the fuel is introduced into the combustion chamber. The nozzle is manufactured as a separate component and screwed to the holder with a clamping nut. Since fuel is present within the holder and nozzle at a pressure of up to 2700 bar (270 MPa), the sealing surface between the nozzle and the holder must be securely sealed to prevent fuel from escaping during operation of the fuel injector. For this purpose, the nozzle is clamped against the holder using a nozzle clamping nut, so that the nozzle body is pressed against the holder with great force, creating the necessary tightness. The nozzle clamping nut surrounds the nozzle body and rests on a shoulder on the outside of the nozzle body.

[0003] To ensure precise positioning of the nozzle body in the direction of rotation relative to the retaining body, one or more dowel pins are provided, some of which extend into the retaining body and some into the nozzle, thus ensuring precise positioning during assembly. However, when the retaining body is fixed, screwing on the nozzle retaining nut exerts a torque on the nozzle, placing significant mechanical stress on the dowel pins intended to hold the nozzle in position relative to the retaining body. This can lead to excessive stress on the dowel pins or the nozzle body and, particularly during extended operation of the fuel injector, ultimately to fuel injector failure.

[0004] To avoid this, a method is known from EP 1 399 668 B1 and DE10224241 A1 in which the nozzle body is pre-tensioned longitudinally against the holding body by means of a clamping tool. The nozzle body is pressed against the holding body with such a high axial force that the nozzle clamping nut can be tightened without exerting any torque on the nozzle body or only with such a small torque that the nozzle body does not move relative to the holding body. The clamping tool is then removed, with the nozzle body being held in position by the nozzle clamping nut and clamped against the holding body. In some applications, however, it has been shown that the necessary axial force with which the nozzle body would have to be pressed against the holding body is too high.This means that the torque introduced by the nozzle retaining nut cannot be avoided, which can lead to the problems already described above when assembling the fuel injector. Disclosure of the invention Advantages of the invention

[0005] The assembly method according to the invention for a fuel injector has the advantage of enabling high-pressure-tight assembly of the fuel injector without overloading the dowel pins or other devices during assembly, which prevents breakage or failure of the injector during operation. The assembly method is carried out on a fuel injector comprising a holding body and a nozzle body, wherein the outer side of the nozzle body is rotationally symmetrical and has a nozzle collar with a larger diameter and a shaft with a smaller diameter. A clamping shoulder is formed at the transition between the shaft and the nozzle collar. In addition, the fuel injector comprises a nozzle clamping nut which is screwed with an internal thread into an external thread on the holding body, wherein the nozzle clamping nut is supported on the clamping shoulder, such that the nozzle body is clamped at least indirectly against the holding body.The assembly tool used in the method has a receptacle for the shaft of the nozzle body and is pushed over the shaft of the nozzle body until the assembly tool rests against a clamping surface of the nozzle body. A preload force is then exerted on the nozzle body using the assembly tool, which presses the nozzle body at least indirectly against the holding body. The assembly tool clamps the shaft of the nozzle body laterally by elastically deforming the assembly tool inward due to the preload force, whereby the receptacle of the assembly tool exerts a clamping force on the shaft of the nozzle body. The nozzle clamping nut is then screwed on until a defined contact force is achieved between the nozzle body and the holding body.

[0006] The clamping tool exerts an axial force on the nozzle body in the direction of the holding body, holding the nozzle body in an assembly position. The assembly tool also clamps the shaft of the nozzle body laterally. This allows the assembly tool to absorb a significantly greater torque on the nozzle body than would be the case with only axial pressure. When the nozzle clamping nut is screwed on, it exerts a torque on the nozzle body relative to the holding body due to the friction on the clamping shoulder. However, the assembly tool holds the nozzle body in position by laterally clamping the nozzle body in the area of ​​the shaft until the nozzle clamping nut has been screwed in with a defined torque.The assembly tool is then removed and the nozzle body is clamped against the holding body with the desired contact force without mechanically overloading parts of the fuel injector, in particular the dowel pins between the holder body and the nozzle body. The clamping is advantageously designed so that the torque that the assembly tool can absorb is sufficient to hold the nozzle body in the defined position, while the clamping nut is tightened with the defined torque against the holding body without the nozzle body rotating relative to the holding body. It is irrelevant whether the nozzle body rests directly on the holding body or only indirectly, i.e. with additional housing parts such as a throttle plate or other bodies in between.

[0007] In an advantageous development of the method, the assembly tool rests on a clamping surface on the nozzle body, which is formed on a circumferential shoulder on the shaft of the nozzle body. This allows the axial force to be applied without mechanically stressing the area of ​​the clamping shoulder. The larger diameter section of the nozzle body is also subjected to less deformation during assembly, which is particularly advantageous when the nozzle needle arranged in the nozzle body is guided in this section of the nozzle body and even slight deformation of the nozzle body in this area can impair the nozzle needle guidance.

[0008] In a further development of the method according to the invention, the assembly tool is concavely curved inward on the inside. As a result, a longitudinal force acting on the assembly tool causes a radially inward deformation of the receptacle, so that the assembly tool, which is designed with only slight play relative to the shaft of the nozzle body, clamps the shaft with high force, thus enabling the transmission of high torque.

[0009] In a further development of the method, the outer side of the assembly tool can also be concavely curved inwards, in addition to or instead of a concave curvature of the inner side of the assembly tool, in order to achieve the necessary deformation of the assembly tool by the longitudinal force.

[0010] In a further embodiment of the method according to the invention, a hollow cylindrical intermediate piece is inserted between the assembly tool and the shaft of the nozzle body, wherein the clamping force between the assembly tool and the shaft is transmitted through the intermediate piece. The intermediate piece is made of a material that is softer than the nozzle body or the assembly tool, for example of a soft metal (e.g. copper) or even of a plastic, so that it rests against the nozzle shaft and the assembly tool over a large area and can transmit a high clamping force between the assembly tool and the shaft of the nozzle body. In order to increase the clamping force, the intermediate piece can be conical on its inner side and / or on its outer side so that it is clamped between the assembly tool and the shaft of the nozzle body simply by inserting the nozzle body axially into the assembly tool.It is also possible that instead or additionally the clamping tool is conically shaped on its inside, so that the contact pressure on the shaft of the nozzle body is additionally increased.

[0011] The clamping tool according to the invention for use in the method according to the invention has a hollow cylindrical receptacle for the shaft of a nozzle body, wherein the wall of the cylindrical receptacle is designed such that the inner wall of the receptacle deforms inwardly when a longitudinal force is applied to the clamping tool. This exerts a clamping force on the shaft of the nozzle body, which serves to absorb or exert a torque on the nozzle body. The deformability of the clamping tool can advantageously be achieved by forming notches, grooves, or channels on the outer side, which preferably run in the longitudinal direction of the cylindrical receptacle.Advantageously, it is also possible to manufacture the hollow cylindrical holder of the clamping tool from an inner cylinder and an outer cylinder that are firmly connected to each other, with the inner cylinder being made of a material with a lower modulus of elasticity than the outer cylinder. A longitudinal force deforms the cylindrical holder inward, creating the desired clamping force on the nozzle body shaft. drawing

[0012] The drawing shows illustrations of the method according to the invention. Figure 1 shows a longitudinal section through a known fuel injector with an assembly tool according to the invention, Figures 2, 3 and 4 in the same representation as Figure 1 Variants of the assembly tool, and Figure 5 shows a longitudinal section through another assembly tool according to the invention. Description of the embodiments

[0013] In Figure 1A fuel injector known from the prior art is shown in longitudinal section, with only the essential parts being shown. In addition, the Figure 1 an assembly tool for carrying out the method according to the invention. The fuel injector 1 comprises a holding body 2 and a nozzle body 4, which are clamped against each other by means of a clamping nut 7. This creates a liquid-tight connection between the two bodies, which seals the fuel-carrying channels leading from the holding body 2 into the nozzle body 4, even at high fuel pressure. The nozzle body 4 has on its combustion chamber side - in the Figure 1 right - end has several injection openings 9 through which the fuel is sprayed out under high pressure during operation of the fuel injector. To control the injection, a longitudinally displaceable nozzle needle is arranged within the nozzle body 4, which Figure 1is not shown for the sake of clarity and is sufficiently known from the prior art. The nozzle body 5 is essentially rotationally symmetrical and is fixed in its position relative to the holding body 2 by dowel pins 12. The dowel pins 12, of which there are usually at least two, protrude into corresponding bores or recesses in both the holding body 2 and the nozzle body 4, whereby they are usually not arranged rotationally symmetrically in order to determine a clear position of the nozzle body 4 relative to the holding body 2 and thus rule out incorrect assembly. The nozzle body 4 has a nozzle collar 5 with a larger diameter, to which a shaft 6 with a smaller diameter is connected, which extends to the end of the nozzle body 4 on the combustion chamber side. At the transition between the shaft 6 and the nozzle collar 5, a clamping shoulder 8 is formed on the nozzle body 4, on which clamping shoulder the clamping nut 7 engages.In addition, a circumferential shoulder 14 is formed on the shaft 6, on which a clamping surface 13 is formed, which is oriented in the same way as the clamping shoulder 8, but is significantly smaller in diameter.

[0014] An internal thread 10 is formed in the clamping nut 7, which engages with an external thread 11 formed on the holding body 2. By screwing the clamping nut 7, which engages the clamping shoulder 8, the nozzle body 4 is clamped against the holding body 2. Since the force is introduced at the clamping shoulder 8, a torque is exerted on the nozzle body 4 when screwing the clamping nut 7, which leads to a mechanical load on the clamping pins 12. In order to prevent damage to the clamping pins 12 and / or the nozzle body 4 and at the same time to position the nozzle body 4 clearly with respect to the holding body 2, the following procedure is used: When mounting the nozzle body 4 on the holding body 2, an assembly tool 16 is used, as shown in the Figure 1is shown. The assembly tool 16 has a cylindrical receptacle 17 that accommodates the shaft 6 of the nozzle body 4, but with only slight play relative to the inner wall of the receptacle 17. The assembly tool 16 is pushed over the shaft 6 until the assembly tool 16 comes into contact with the clamping surface 13 of the circumferential shoulder 14. An axial preload force is then exerted on the nozzle body 4 via the assembly tool 16, which presses the nozzle body 4 against the holding body 2 in the axial direction. Since the cylindrical receptacle 17 of the assembly tool 16 is concavely curved inwards and the cylindrical receptacle 17 is elastically compressed by the application of the axial preload force, the cylindrical receptacle 17 is deformed slightly inwards and thereby clamps the shaft 6 of the nozzle body 4.This allows the assembly tool 16 to absorb and compensate for a torque acting on the nozzle body 4 both through the clamping of the shaft 16 and through the friction on the clamping surface 13. After the nozzle body 4 has been fixed in this way by the assembly tool 16 and subjected to an axial preload force, the nozzle clamping nut 7 is screwed onto the external thread 11 until the desired preload force of the nozzle body 4 relative to the holding body 2 is achieved. The assembly tool 16 is then removed.

[0015] By clamping the shaft 6, the assembly tool 16 can compensate for very high torques on the nozzle body 4. The nozzle clamping nut 7 can therefore be screwed onto the holding body 2 with a high torque, so that a high axial contact force of the nozzle body 4 on the holding body 2 can be achieved without the position of the nozzle body 4 being shifted relative to the holding body 2 during assembly and without risking mechanical overloading of the clamping pins 12 or the nozzle body 4, which could otherwise yield during further operation of the fuel injector due to the high mechanical and hydraulic loads and lead to failure of the fuel injector.

[0016] In Figure 2 is in the same representation as Figure 1 a further embodiment of the assembly tool 16 according to the invention is shown, as it can be used in the method according to the invention. In contrast to the embodiment of the Figure 1the cylindrical receptacle 17 of the assembly tool 16 is concavely curved inwards on both the inside and outside. This increases the deformation of the assembly tool 16 during the application of the axial preload force Fa, so that an inwardly directed clamping force Fi acts on the sides of the assembly tool 16 and deforms it inwards. The thinner the walls of the cylindrical receptacle 17, the more easily they will bulge inwards when the axial preload force is applied and clamp the shaft 6 of the nozzle body 4. However, care must be taken to ensure that plastic deformation of the assembly tool is excluded during assembly of the fuel injector.

[0017] In Figure 3 A further embodiment of an assembly tool 16 according to the invention is shown, as it can be used in the method according to the invention. In contrast to the embodiments of Figures 1 and 2Here, a cylindrical intermediate piece 19 is arranged between the cylindrical receptacle 17 of the assembly tool 16 and the shaft 6. The intermediate piece 19 is designed as a hollow cylinder and, through its position between the assembly tool 16 and the shaft 6, transmits the clamping force between the assembly tool 6 and the nozzle body 4. The intermediate piece 19 is made of a relatively soft material, for example, a soft metal such as copper or a polymer. Due to its flexibility, the intermediate piece 19 transmits the clamping force over a large area of ​​the shaft 6.

[0018] In order to increase the clamping force, the intermediate piece 19 can also be conically shaped on its outside, as shown in Figure 4is shown. Due to its conical shape, the intermediate piece 19 is clamped between the assembly tool 16 and the nozzle body 4 simply by sliding the assembly tool 16 over the shaft 6. Alternatively to this design, the inside of the assembly tool 16, i.e. the receptacle 17, can also be conical in design in order to reinforce the clamping of the intermediate piece 19 when sliding it over the shaft 6.

[0019] In Figure 51 shows a longitudinal section of another assembly tool, such as can be used in the method according to the invention. The cylindrical receptacle 17 of the assembly tool 16 is formed here by two concentrically arranged hollow cylinders, an inner cylinder 21 and an outer cylinder 22, which are firmly connected to one another. The two cylinders 21, 22 are made of materials with different moduli of elasticity, with the inner cylinder 21 having a lower modulus of elasticity than the outer cylinder 22. The different deformation behavior facilitates the inward movement of the cylindrical section 17 and thus increases the clamping force F i, so that the shaft 6 of the nozzle body 4 is securely clamped.

[0020] To create the necessary flexibility, the assembly tool 16 can also be provided with structures on its exterior, such as grooves or flutes, which preferably run in the longitudinal direction of the assembly tool 16. The structures reduce the strength on the exterior and increase the deformability, which increases the clamping force F i .

[0021] In the exemplary embodiments shown here, the assembly tool 16 engages the clamping surface 13 of the circumferential shoulder 14. Alternatively, the clamping tool 16 can also be positioned on the tip of the nozzle body 4, i.e., on the combustion chamber-side end of the nozzle body 4 in the area where the injection openings 9 are also formed. If the circumferential shoulder 14 is missing from the nozzle body 4, it is also possible for the assembly tool 16 to engage directly on the clamping shoulder 8 and apply the necessary axial preload there.

Claims

1. Method for assembling a fuel injector (1) which comprises a holding body (2) and a nozzle body (4), wherein the outside of the nozzle body (4) is designed to be rotationally symmetrical and has a nozzle collar (5) larger in diameter and a shaft (6) smaller in diameter, wherein a clamping shoulder (8) is formed at the transition of the shaft (6) to the nozzle collar (5), and having a nozzle clamping nut (7) which by way of an internal thread (10) can be screwed into an external thread (11) on the holding body (2), wherein the nozzle clamping nut (7) is supported on the clamping shoulder (8) in such a way that the nozzle body (4) is braced at least indirectly in relation the holding body (2), characterized by - providing an assembling tool (16) having a receptacle (17) for the shaft (6) of the nozzle body (4), - attaching the assembling tool (16) over the shaft (6) of the nozzle body (4) until the assembling tool (16) comes to bear on a clamping surface (13) of the nozzle body (4), - applying a preload force (Fa) to the nozzle body (4) by means of the assembling tool (16) in such a way that the nozzle body (4) is pressed at least indirectly against the holding body (2), wherein the assembling tool (16) is formed in such a way that it is inwardly deformed by the preload force (Fa), thereby clamping the shaft (6) of the nozzle body (4), - screwing on the nozzle clamping nut (7) until a defined contact pressure force is achieved between the nozzle body (4) and the holder body (2).

2. Method according to Claim 1, characterized in that the nozzle body (4) is clamped by the assembling tool (16) in such a way that the assembling tool (16) absorbs the torque transmitted to the nozzle body (4) by the nozzle clamping nut (7) in such a way that the nozzle body (4) does not rotate when screwing the nozzle clamping nut (7) until the defined contact pressure force relative to the holding body (2) is reached.

3. Method according to Claim 1 or 2, characterized in that the assembling tool (16) rests on a clamping surface (13) on the nozzle body (4), which is formed on an encircling step (14) on the shaft (6) of the nozzle body (4).

4. Method according to Claim 3, characterized in that the receptacle (17) of the assembling tool (16) is designed to be hollow cylindrical and on the inside is curved concavely inwards.

5. Method according to Claim 1 or 4, characterized in that the assembling tool (16) is on its outside curved concavely inwards.

6. Method according to Claim 3, characterized in that, before pressing the assembling tool (16), a hollow cylindrical intermediate piece (19) is inserted between the shaft (6) of the nozzle body (4) and the assembling tool (16), whereby the clamping force is transmitted between the assembling tool (16) and the shaft (6) by way of the intermediate piece (19).

7. Method according to Claim 6, characterized in that the intermediate piece (19) is conically shaped on its inside and / or on its outside.

8. Method according to Claim 6 or 7, characterized in that the clamping tool (16) is conically shaped on its inside.

9. Clamping tool for use in a method according to one of Claims 1 to 8, characterized in that the clamping tool (16) has a hollow cylindrical receptacle (17) for the shaft (6) of a nozzle body (4), and the wall of the cylindrical receptacle (17) is designed in such a way that the inner wall of the receptacle (17) deforms inwardly when applying a longitudinal force to the clamping tool (16).

10. Clamping tool according to Claim 9, characterized in that the wall of the clamping tool (16) has notches, grooves or flutes on the outside.

11. Clamping tool according to Claim 9, characterized in that the hollow cylindrical receptacle (17) of the clamping tool (16) consists of an inner cylinder (21) and an outer cylinder (22) which are fixedly joined to one another, wherein the inner cylinder (21) consists of a material with a lower modulus of elasticity than the outer cylinder (22).