Method for assembling a fuel injector and tool for use in the method

Abstract

The present invention relates to a method for assembling a fuel injector (1) comprising a retainer (2) and a nozzle body (4), wherein a clamping shoulder (8) is formed at the transition from the rod (6) to the nozzle ring (5). The retainer (2) and the nozzle body (4) are clamped by a nozzle clamping nut (7). To assemble the fuel injector, the assembly tool (16) is pushed onto the rod (6) of the nozzle body (4) up to the clamping surface (4) of the nozzle body (4). Then, a preload (Fa) is applied to the nozzle body (4) by the assembly tool (16) such that the nozzle body (4) presses against the retainer (2) at least indirectly, wherein the assembly tool (16) clamps the rod (6) of the nozzle body (4). Subsequently, the nozzle clamping nut (7) is tightened until a defined clamping force is achieved on the retainer (2) of the nozzle body (4). The clamping tool (16) used has a hollow cylindrical receiving part (17) for the rod (6) of the nozzle body (4), wherein the wall of the cylindrical receiving part (17) is constructed such that the wall deforms inward when a longitudinal force is applied to the clamping tool (16).

Description

Technical Field

[0001] This invention relates to a method for assembling a fuel injector, for example, for introducing fuel into the combustion chamber of an internal combustion engine under high pressure. Furthermore, this invention relates to an assembly tool used in the method according to the invention. Background Technology

[0002] Fuel injectors, such as those used for injecting fuel under high pressure, consist of several components, typically a retainer and a nozzle. The nozzle contains an injection opening through which fuel is introduced into the combustion chamber. Here, the nozzle is manufactured as a separate component and screwed onto the retainer by a clamping nut. Because fuel is present in both the retainer and the nozzle at pressures up to 2700 bar (270 MPa), the sealing surfaces between the nozzle and the retainer must reliably seal to prevent fuel leakage during injector operation. For this purpose, the nozzle is clamped against the retainer by a nozzle clamping nut, causing the nozzle body to press firmly against the retainer with a large force, creating the required seal. Here, the nozzle clamping nut surrounds the nozzle body and rests against a shoulder on the outer side of the nozzle body.

[0003] To ensure precise positioning of the nozzle body in the direction of rotation relative to the retainer, one or more clamping pins are provided. These pins extend partially into the retainer and partially into the nozzle, thus ensuring precise positioning during assembly. However, by tightening the nozzle clamping nut, a torque is applied to the nozzle while the retainer is fixed, subjecting the clamping pins, which are meant to hold the nozzle in its position relative to the retainer, to a strong mechanical load. This can lead to overload of the clamping pins and the nozzle body, especially during prolonged operation of the fuel injector, ultimately resulting in fuel injector failure.

[0004] To avoid this situation, a method is known from EP 1 399 668 B1, in which the nozzle body is pre-tightened against a retainer in the longitudinal direction by means of a clamping tool. Here, the nozzle body is pressed against the retainer with a large axial force, allowing the nozzle clamping nut to be tightened without applying torque to the nozzle body, or with only a small torque so that the nozzle body does not move relative to the retainer. Subsequently, the clamping tool is removed, with the nozzle body held in its position by the nozzle clamping nut and clamped against the retainer. However, in some applications it has been shown that the necessary axial force required for the nozzle body to press against the retainer is too high. Therefore, the torque introduced by the nozzle clamping nut cannot be avoided, which again leads to the aforementioned problem when assembling a fuel injector. Summary of the Invention

[0005] Advantages of this invention:

[0006] The assembly method for a fuel injector according to the present invention has the advantages of enabling high-pressure sealing assembly of the fuel injector without overloading the clamping pin or other devices during assembly, thus preventing the injector from cracking or failing during operation. The assembly method is performed on a fuel injector comprising a retainer and a nozzle body, wherein the outer side of the nozzle body is rotationally symmetrically constructed and has a larger diameter nozzle ring and a smaller diameter rod. A clamping shoulder is formed at the transition from the rod to the nozzle ring. Furthermore, the fuel injector includes a nozzle clamping nut, which is screwed internally into an external thread on the retainer, wherein the nozzle clamping nut is supported on the clamping shoulder such that the nozzle body is clamped at least indirectly against the retainer. The assembly tool used in the method has a receiving portion for the rod of the nozzle body and is pushed onto the rod of the nozzle body until the assembly tool abuts against the clamping surface of the nozzle body. Subsequently, a preload is applied to the nozzle body using the assembly tool, which presses the nozzle body at least indirectly against the retainer, wherein the assembly tool clamps the rod of the nozzle body from the side. Then, tighten the nozzle clamping nut until the specified clamping force is achieved between the nozzle body and the retainer.

[0007] Using a clamping tool, an axial force is applied to the nozzle body toward the retainer, holding the nozzle body in the assembled position, wherein the assembly tool also clamps the rod of the nozzle body from the side. Thus, the assembly tool can receive a significantly greater torque acting on the nozzle body compared to the case of axial clamping only. If the nozzle clamping nut is now tightened, the nozzle clamping nut applies torque relative to the retainer to the nozzle body through friction on the clamping shoulder; however, the assembly tool holds the nozzle body in its position by clamping it from the side in the rod region until the nozzle clamping nut is tightened with a defined torque. Subsequently, the assembly tool is removed, and the nozzle body is clamped against the retainer with the desired clamping force without mechanical overload of the fuel injector components, particularly the clamping pin between the retainer and the nozzle body. Here, the clamping is advantageously configured such that the torque received by the assembly tool is sufficient to hold the nozzle body in a defined position while tightening the clamping nut relative to the retainer with a defined torque, without the nozzle body rotating relative to the retainer. It is irrelevant whether the nozzle body is placed directly on the retainer or only indirectly, i.e., on the stationary body with other housing components (such as a throttle plate or other bodies) arranged in between.

[0008] In an advantageous extension of the method, the assembly tool is placed on a clamping surface on the nozzle body, which is formed at a surrounding flange on the shank of the nozzle body. This allows axial force to be introduced without mechanically loading the shoulder area. Consequently, the larger diameter sections of the nozzle body also deform less during assembly, which is particularly advantageous when the nozzle needle arranged in the nozzle body is guided in this section and slight deformation of the nozzle body in this area would jeopardize the guidance of the nozzle needle.

[0009] In an extension of the method according to the invention, the assembly tool is configured such that it elastically deforms inward by a preload, thereby applying a clamping force to the rod of the nozzle body by the receiving portion of the assembly tool. This can be achieved, in particular, by the hollow cylindrical receiving portion of the assembly tool being concavely arched inward on its inner side. Thus, the longitudinal force acting on the assembly tool causes radially inward deformation of the receiving portion, enabling the assembly tool to clamp the rod with a large force and thus transmit a large torque, with only a small gap between the assembly tool and the rod of the nozzle body.

[0010] In an extended version of the method, in addition to or instead of the concave arching of the inner side of the assembly tool, the outer side of the assembly tool may also be concave inward to achieve the necessary deformation of the assembly tool by longitudinal force.

[0011] In another embodiment of the method according to the invention, a hollow cylindrical intermediate member is inserted between the assembly tool and the rod of the nozzle body, wherein the clamping force between the assembly tool and the rod is transmitted through the intermediate member. Here, compared to the nozzle body or the assembly tool, the intermediate member is made of a soft material, such as a soft metal (e.g., copper) or plastic, such that the intermediate member abuts against the nozzle rod and the assembly tool with a large surface area, and can transmit a large clamping force between the assembly tool and the rod of the nozzle body. To enhance the clamping force, the intermediate member may be tapered on its inner and / or outer sides, such that the intermediate member is clamped between the assembly tool and the rod of the nozzle body by axially inserting the nozzle body into the assembly tool. Alternatively or additionally, the clamping tool may be tapered on its inner side, thereby further enhancing the clamping force acting on the rod of the nozzle body.

[0012] The clamping tool according to the invention has a hollow cylindrical receiving portion for the rod of the nozzle body, wherein the wall of the cylindrical receiving portion is configured such that the inner wall of the receiving portion deforms inward when a longitudinal force is applied to the clamping tool. This applies a clamping force to the rod of the nozzle body, which is used to receive or apply torque to the nozzle body. The deformability of the clamping tool can advantageously be achieved by a notch, groove, or slot constructed on the outer side, preferably extending in the longitudinal direction of the cylindrical receiving portion. Advantageously, the hollow cylindrical receiving portion of the clamping tool can also be made of an inner and outer cylinder that are fixedly fitted together, wherein the inner cylinder is made of a material having a lower elastic modulus than the outer cylinder. Due to the longitudinal force, the cylindrical receiving portion deforms inward, thereby forming the desired clamping force acting on the rod of the nozzle body. Attached Figure Description

[0013] The accompanying drawings show an illustration of the method according to the invention. The drawings illustrate:

[0014] Figure 1 : Longitudinal section of a known fuel injector with an assembly tool according to the invention;

[0015] Figure 2 , 3 And 4: such as Figure 1 The illustration shows variations of the assembly tools, and

[0016] Figure 5 : Another longitudinal section of the assembly tool according to the invention. Detailed Implementation

[0017] exist Figure 1 The image shows a longitudinal section of a fuel injector known from the prior art, where only key components are shown. Furthermore, Figure 1 An assembly tool for performing the method of the present invention is shown. The fuel injector 1 includes a retainer 2 and a nozzle body 4 clamped together by means of a clamping nut 7. This establishes a liquid-tight connection between the two bodies, sealing the fuel guide passage from the retainer 2 to the nozzle body 4 even under high fuel pressure. The nozzle body 4 is located on its combustion chamber side (in... Figure 1 The nozzle (right side) has multiple injection openings 9, through which fuel is injected under high pressure during operation. To control injection, a longitudinally movable nozzle needle is arranged within the nozzle body 4. For clarity, this nozzle needle... Figure 1Not shown and well known from the prior art. The nozzle body 5 is constructed substantially rotationally symmetrically and is fixed in position relative to the retainer 2 by clamping pins 12. Clamping pins 12 (of which there are usually at least two) extend into corresponding holes or notches in the retainer 2 and the nozzle body 4, wherein they are generally not rotationally symmetrically arranged to determine the precise position of the nozzle body 4 relative to the retainer 2 and thus prevent incorrect assembly. The nozzle body 4 has a larger diameter nozzle ring 5, which engages with a smaller diameter rod 6, which extends to the combustion chamber side end of the nozzle body 4. At the transition from the rod 6 to the nozzle ring 5, a clamping shoulder 8 is formed on the nozzle body 4, onto which a clamping nut 7 acts. Furthermore, a circumferential flange 14 is constructed on the rod 6, on which a clamping surface 13 is formed, which is oriented in the same manner as the clamping shoulder 8 but constructed to be significantly smaller in diameter.

[0018] An internal thread 10 is constructed in the clamping nut 7, which engages with an external thread 11 constructed on the retainer 2. The nozzle body 4 is clamped against the retainer 2 by tightening the clamping nut 7, which acts on the clamping shoulder 8. Because force is introduced onto the clamping shoulder 8, a torque is applied to the nozzle body 4 when tightening the clamping nut 7, resulting in a mechanical load on the clamping pin 12. To prevent damage to the clamping pin 12 and / or the nozzle body 4, and to ensure precise positioning of the nozzle body 4 relative to the retainer 2, an assembly tool 16 is used when assembling the nozzle body 4 onto the retainer 2. Figure 1 As shown, the assembly tool 16 has a cylindrical receiving portion 17 that receives the rod 6 of the nozzle body 4, wherein a small gap is maintained only relative to the inner wall of the receiving portion 17. The assembly tool 16 is pushed onto the rod 6 until the assembly tool 16 abuts against the clamping surface 13 of the surrounding flange 14. By means of the assembly tool 16, an axial preload is now applied to the nozzle body 4, which presses the nozzle body 4 against the retainer 2 in the axial direction. Because the cylindrical receiving portion 17 of the assembly tool 16 is concave inwardly arched, and the cylindrical receiving portion 17 is elastically compressed by the applied axial preload, the cylindrical receiving portion 17 deforms slightly inward and thereby clamps the rod 6 of the nozzle body 4. Therefore, the assembly tool 16 can receive and compensate for the torque acting on the nozzle body 4 not only by clamping the rod 16 but also by friction on the clamping surface 13. After the nozzle body 4 is secured in this manner with the aid of the assembly tool 16 and subjected to axial preload, the nozzle clamping nut 7 is now tightened onto the external thread 11 until the desired preload is achieved relative to the retainer 2. Subsequently, the assembly tool 16 is removed.

[0019] By clamping with rod 6, assembly tool 16 can compensate for the very high torque acting on nozzle body 4. Therefore, nozzle clamping nut 7 can be tightened onto retainer 2 with high torque, enabling a large axial clamping force on nozzle body 4 on retainer 2 without displacement of nozzle body 4 relative to retainer 2 during assembly and without the risk of mechanical overload on clamping pin 12 or nozzle body 4, which could otherwise bend under high mechanical and hydraulic loads during further operation of the fuel injector and potentially cause fuel injector failure.

[0020] exist Figure 2 In the middle, in with Figure 1 In the same figures, another embodiment of the assembly tool 16 according to the invention is shown, as this assembly tool can be used in the method according to the invention. Figure 1 In a different implementation, the cylindrical receiving portion 17 of the assembly tool 16 is concave and arched inwards on both the inner and outer sides. This is advantageous when applying the axial preload F. a The deformation of the assembly tool 16 was enhanced during this period, resulting in an inward clamping force F. i The force is applied to the side of the assembly tool 16 and causes that side to deform inward. The thinner the wall of the cylindrical receiving part 17, the easier it is for the wall to arch inward and clamp the rod 6 of the nozzle body 4 when an axial preload is applied. However, it is important to note that plastic deformation of the assembly tool must be avoided during fuel injector assembly.

[0021] exist Figure 3 Another embodiment of the assembly tool 16 according to the invention is shown, which can be used in the method according to the invention. Figure 1 and Figure 2 Unlike other embodiments, here a cylindrical intermediate member 19 is arranged between the cylindrical receiving portion 17 of the assembly tool 16 and the rod 6. The intermediate member 19 is implemented as a hollow cylinder and transmits the clamping force between the assembly tool 6 and the nozzle body 4 through its position between the assembly tool 16 and the rod 6. The intermediate member 19 is made of a relatively soft material, such as a soft metal like copper or a polymer. Due to its flexibility, the intermediate member 19 transmits the clamping force over a large area of ​​the rod 6.

[0022] To improve clamping force, the intermediate part 19 can also be tapered on its outer side, such as in... Figure 4 As shown in the diagram. Due to its tapered shape, the intermediate member 19 is held between the assembly tool 16 and the nozzle body 4 by pushing the assembly tool 16 onto the rod 6. Alternatively, the inner side of the assembly tool 16, i.e., the receiving part 17, can also be tapered to enhance the holding of the intermediate member 19 when pushed onto the rod 6.

[0023] exist Figure 5Another assembly tool is shown in longitudinal section, which can be used in the method according to the invention. The cylindrical receiving portion 17 of the assembly tool 16 is here composed of two concentrically arranged hollow cylinders, namely an inner cylinder 21 and an outer cylinder 22, which are fixedly connected to each other. Here, the two cylinders 21, 22 are made of materials with different elastic moduli, wherein the inner cylinder 21 has a lower elastic modulus than the outer cylinder 22. Due to the different deformation characteristics, the inward movement of the cylindrical section 17 is easier, thereby increasing the clamping force F. i This ensures that the rod 6 of the nozzle body 4 is reliably clamped.

[0024] To provide the necessary flexibility on its outer side, the assembly tool 16 may also be provided with structures such as grooves or slots, which preferably extend along the longitudinal direction of the assembly tool 16. These structures reduce the strength on the outer side and increase deformability, which enhances the clamping force F. i .

[0025] In the illustrated embodiment, the assembly tool 16 acts on the clamping surface 13 of the surrounding flange 14. Alternatively, the clamping tool 16 may also be positioned at the dome of the nozzle body 4, i.e., at the end of the nozzle body 4 on the combustion chamber side in the area where the injection opening 9 is constructed. If the surrounding flange 14 is absent from the nozzle body 4, the assembly tool 16 may also act directly on the clamping shoulder 8 and apply the necessary axial preload there.

Claims

1. A method for assembling a fuel injector (1), the fuel injector comprising a retainer (2) and a nozzle body (4), wherein, The nozzle body (4) is rotationally symmetrically constructed on its outer side and has a larger diameter nozzle ring (5) and a smaller diameter rod (6), wherein a clamping shoulder (8) is formed at the transition from the rod (6) to the nozzle ring (5), and the fuel injector has a nozzle clamping nut (7) that can be screwed into the external thread (11) on the retainer (2) with an internal thread (10), wherein the nozzle clamping nut (7) is supported on the clamping shoulder (8) such that the nozzle body (4) is clamped at least indirectly against the retainer (2). Its features are, - Provide an assembly tool (16) with a receiving part (17) for the rod (6) of the nozzle body (4). Insert the assembly tool (16) above the rod (6) of the nozzle body (4) until the assembly tool (16) is against the clamping surface (13) of the nozzle body (4). - A preload (F) is applied to the nozzle body (4) by the assembly tool (16). a ), such that the nozzle body (4) presses against the retainer (2) at least indirectly, wherein the assembly tool (16) is configured such that the assembly tool is subjected to a preload (F) a The rod (6) deforms inward and thus clamps the nozzle body (4). - Tighten the nozzle clamping nut (7) until a defined clamping force is achieved between the nozzle body (4) and the retainer (2).

2. The method according to claim 1, characterized in that, The nozzle body (4) is clamped by the assembly tool (16), such that the assembly tool (16) receives the torque transmitted to the nozzle body (4) by the nozzle clamping nut (7), such that the nozzle body (4) does not rotate relative to the retainer (2) when the nozzle clamping nut (7) is tightened until a limited clamping force is reached.

3. The method according to claim 1 or 2, characterized in that, The assembly tool (16) is placed on the clamping surface (13) on the nozzle body (4), which is formed at the surrounding flange (14) on the rod (6) of the nozzle body (4).

4. The method according to claim 3, characterized in that, The receiving part (17) of the assembly tool (16) is constructed in a hollow cylindrical shape and arches inward in a concave shape on the inner side.

5. The method according to claim 1 or 4, characterized in that, The assembly tool (16) is concave and arched inward on its outer side.

6. The method according to claim 3, characterized in that, Before clamping the assembly tool (16), a hollow cylindrical intermediate piece (19) is introduced between the rod (6) of the nozzle body (4) and the assembly tool (16), wherein the clamping force is transmitted between the assembly tool (16) and the rod (6) through the intermediate piece (19).

7. The method according to claim 6, characterized in that, The intermediate component (19) is tapered on its inner and / or outer sides.

8. The method according to claim 6 or 7, characterized in that, The assembly tool (16) is tapered on its inner side.

9. An assembly tool for use in the method according to any one of claims 1 to 8, characterized in that, The assembly tool (16) has a hollow cylindrical receiving portion for the rod (6) of the nozzle body (4), and the wall of the hollow cylindrical receiving portion is constructed such that the inner wall of the hollow cylindrical receiving portion deforms inward when a longitudinal force is applied to the assembly tool (16).

10. The assembly tool according to claim 9, characterized in that, The wall of the assembly tool (16) has a notch or groove on the outer side.

11. The assembly tool according to claim 9, characterized in that, The wall of the assembly tool (16) has grooves on the outer side.

12. The assembly tool according to claim 9, characterized in that, The hollow cylindrical receiving part of the assembly tool (16) is composed of an inner column (21) and an outer column (22), which are fixedly joined to each other. The inner column (21) is made of a material with a lower elastic modulus than the outer column (22).

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