Fuel injector

Abstract

A fuel injector (1) with a housing (2) which comprises a first housing part (3) and a second housing part (4), wherein the housing parts bear against one another at a sealing surface and are braced against one another by a clamping device (5). A clamping pin (18) protrudes into a first recess (20) in the first housing part and into a second recess (21) in the second housing part (4), and thus defines the position of the first housing part (3) and the second housing part (4) with respect to one another. The material of the clamping pin (18) is a light metal or a light metal alloy.

Description

[0001] The invention relates to a fuel injector, such as can be used, for example, to introduce fuel under high pressure into a combustion chamber of an internal combustion engine. State of the art

[0002] In internal combustion engines, a fuel-air mixture is ignited in the combustion chambers. This mixture is created, for example, by directly injecting fuel into the combustion chamber. The fuel is forced under high pressure through one or more very small injection ports of a fuel injector and finely atomized upon exiting, creating an ignitable mixture with the air in the combustion chamber. Particularly in compression-ignition engines, the fuel must be injected at very high pressures of up to 2700 bar (270 MPa) to achieve the necessary mixing of fuel and air for effective combustion. The corresponding fuel injectors have a longitudinally movable nozzle needle within their housing, which opens and closes the injection ports through its longitudinal movement. The multi-part housing consists of at least two housing sections that abut each other at a sealing surface.

[0003] Since high-pressure bores and recesses pass through this sealing surface, a reliable seal is necessary for the entire service life of the fuel injector. For this purpose, the housing parts are clamped together with considerable force using a clamping device, usually a clamping nut. If the sealing surfaces are carefully machined, a reliable seal is achieved without the need for additional sealing materials. However, during the assembly of the fuel injector, the alignment of the housing parts relative to each other must be precise so that the high-pressure channels can conduct the fuel without restriction. For this purpose, a clamping pin or several clamping pins are provided, which engage in corresponding recesses in the adjacent housing parts and ensure precise alignment of the housing parts relative to each other. Such clamping pins for a fuel injector are known, for example, from DE 103 09 058 A1 or DE 10 2008 056519 A1.

[0004] When the clamping nut is tightened, a torque is applied to the housing parts against each other, while the clamping pins prevent movement of the housing parts. This, however, leads to a mechanical shear stress on the clamping pins. The clamping pins are usually made of hardened steel and transfer this shear stress to the nozzle body or the retaining body, resulting in corresponding mechanical stresses that act continuously there. If further stresses are added during operation, such as during the installation of the fuel injector in the internal combustion engine or due to hydraulic or thermal stresses, this can potentially lead to fuel injector failure. Advantages of the invention

[0005] In contrast, the fuel injector according to the invention has the advantage that permanent mechanical stress on the fuel injector caused by the clamping pins is avoided, thus preventing a malfunction of the fuel injector. For this purpose, the fuel injector has a housing comprising a first housing part and a second housing part, which abut each other at a sealing surface and are clamped against each other by a clamping device. The position of the first housing part and the second housing part relative to each other is determined by a clamping pin that projects into a first recess in the first housing part and into a second recess in the second housing part. The clamping pin is made of a light metal or a light metal alloy.

[0006] Unlike hardened steel, light metals exhibit plastic deformation even at relatively low temperatures. If the spring pins are mechanically pre-tensioned as a result of fuel injector assembly, the spring pins undergo plastic deformation and relaxation during operation, when the fuel injector is heated by the internal combustion engine. This reduces the mechanical stresses in the housing. This lowers the risk of damage to the spring pins or the nozzle body during fuel injector operation when additional loads act on the housing due to thermal stresses or mechanical forces. In a first advantageous embodiment of the invention, the spring pin material creeps plastically at temperatures below 150 °C.This results in material relaxation at temperatures typically reached during injector operation in an internal combustion engine, without the need for separate heating of the fuel injector to relieve stress. Particularly advantageous is the occurrence of mechanical relaxation within a temperature range of 50 °C to 100 °C.

[0007] In a further advantageous embodiment of the invention, the spring pin is made of aluminum or an aluminum-containing alloy. Magnesium can also be used according to the invention. These metals possess the desired properties, particularly when suitable alloys are used, and the properties can be specifically tailored by the addition of these metals.

[0008] In a further advantageous embodiment of the invention, the spring pin is formed from a metal foam. This further reduces the weight and facilitates the creep or relaxation of the material. The use of spring pins in the form of hollow cylinders also serves this purpose. The spring pin can also be designed as a spiral spring pin, that is, from a coiled sheet of metal. This gives the spring pin additional flexibility and reduces its weight compared to a solid design. Since the spiral spring pin behaves similarly to a spring, it can be provided with a radial preload if the recesses into which the spring pin is inserted are appropriately designed, which simplifies assembly.

[0009] According to the invention, the spring pin is designed such that it breaks into two or more pieces when a predetermined maximum load is exceeded. This reduces the stress acting on the housing and prevents damage to the nozzle body or the retaining body. The broken spring pin is still able to provide rotational fixation. If necessary, the relatively inexpensive spring pin can be replaced if the breakage is detected during the assembly of the fuel injector. For this purpose, the spring pin has one or more longitudinal grooves on its outer surface, which represent the predetermined breaking points and whose depth and shape allow the maximum force to be adjusted.

[0010] In a further advantageous embodiment, the spring pin is coated with a plastic or ceramic material. This coating facilitates the assembly of the spring pin. Furthermore, this coating can also exhibit relaxation behavior and thus reduce some of the stresses. drawing

[0011] The drawing shows various embodiments of the fuel injector according to the invention. Fig. 1 shows a longitudinal section through a fuel injector according to the invention, and Figs. 2, 3, 4 and 5 show various embodiments of tension pins according to the invention, as preferably used in a fuel injector according to Fig. 1 can be used. Description of the exemplary implementations

[0012] In Fig. 1 Figure 1 shows a longitudinal section through a fuel injector 1 according to the invention, showing only the essential parts of the fuel injector 1. The fuel injector 1 serves to inject fuel under high pressure, for example, into a combustion chamber of an internal combustion engine, and has a housing 2 comprising a first housing part in the form of a retaining body 3 and a second housing part in the form of a nozzle body 4. The retaining body 3 and the nozzle body 4 abut each other at a sealing surface 6 and are clamped against each other by a clamping nut 5. The clamping nut 5 encompasses the nozzle body 4 and is screwed into an external thread 9 on the retaining body 3, with the clamping nut 5 bearing against a shoulder 13 on the nozzle body 4. A longitudinal bore 10 is formed inside the retaining body 3, which transitions into a pressure chamber 7 formed in the nozzle body 4.Fuel can be introduced under high pressure into the fuel injector and thus also into the pressure chamber 7 via the longitudinal bore 10. This chamber can be emptied through several injection openings in the nozzle body 4 (not shown in the drawing). The clamping force of the clamping nut 5 is therefore selected such that the two housing parts 3 and 4 are clamped against each other in a high-pressure-tight manner, so that even under high pressure in the longitudinal bore 10 or in the pressure chamber 7 no fuel escapes to the outside.

[0013] To control the injection, a valve piston 11 is arranged in the longitudinal bore 10, which bears against a nozzle needle 8 arranged in the pressure chamber 7 via a pressure piece 12, so that the valve piston 11, the pressure piece 12 and the nozzle needle 8 always move synchronously in the longitudinal direction. In the exemplary embodiment of the Fig. 1 The valve piston 11, the pressure piece 12, and the nozzle needle 8 are manufactured as a single piece; however, these components can also be manufactured separately. The nozzle needle 8 interacts with a valve seat formed in the nozzle body 4 (not shown in the drawing) to open and close the injection ports, so that these are either connected to or hydraulically separated from the pressure chamber 7. To preload the nozzle needle 8 against the valve seat, a closing spring 15 is arranged in the pressure chamber 7. One end of the spring is supported by the retaining body 3, and the other end by a spring plate 14, which rests against the pressure piece 12.

[0014] Since the retaining body 3 and the nozzle body 4 must be precisely aligned with each other to ensure proper function, the position of these two housing parts relative to each other is determined by at least two clamping pins 18. For this purpose, two recesses 20 in the form of bores are formed in the retaining body 3 and two recesses 21 in the form of grooves are formed in the nozzle body 4, into which the clamping pins 18 project. Fig. 1 The two tension pins are arranged exactly in a central section plane of the fuel injector, however, they are often positioned slightly off-center to prevent incorrect assembly during the production of the fuel injector.

[0015] During the assembly of the fuel injector, the two clamping pins 18 are inserted into the recesses 20 of the retaining body 3, and the nozzle body 4 is then positioned so that the clamping pins 18 also protrude into the recesses 21. The clamping nut 5 is then screwed onto the external thread 9. Since the clamping nut 5 rests against the shoulder 13, it transmits a torque to the nozzle body 4 when screwed in. The clamping pins 18 prevent the nozzle body 4 from rotating relative to the retaining body 3. However, this generates corresponding shear forces on the clamping pins 18, which are also transmitted to the nozzle body 4 and the retaining body 3, resulting in corresponding mechanical stresses in these housing parts 3 and 4. Since further forces act on the housing during operation of the fuel injector 1, particularly due to the high fuel pressure inside (up to 2700 bar), these forces must not become excessive.

[0016] To limit the stress on the housing 2 caused by the tension pins 18, the tension pins 18 are made of a light metal or a light metal alloy. Light metals have the property of plastic creep under stress, particularly at temperatures between 50 and 150 °C. This relaxation process leads to a reduction in the mechanical stresses in the housing 2, i.e., in the retaining body 3 and the nozzle body 4, and on the tension pins 18, thus preventing mechanical failure of the housing parts 3 and 4 during operation of the fuel injector. Light metals or light metal alloys that exhibit corresponding creep behavior at temperatures below 150 °C are preferably used, since such temperatures regularly occur during operation of the fuel injector in an internal combustion engine. Aluminum and magnesium, or alloys containing at least one of these metals, are particularly suitable as light metals.

[0017] The tension pins 18 can, as in Fig. 1 shown to be designed as solid metal pins. However, other designs are also possible, as shown in the Fig. 2 bis 5 depicted. The Fig. 2 Figure 18 shows a spring pin 18 having a metallic core with a coating 22, the coating being of which can be made of various materials. Possible materials include plastics, ceramics, or material mixtures that are softer than the metallic core. The thickness of the coating is shown in the figure. Fig. 2 For clarity, the thickness is shown very large, but in reality it is no more than 0.1 mm. The coating 22 leads to a better distribution of forces and thus supports the relaxation of the spring pin.

[0018] In Fig. 3 Another tension pin according to the invention is shown, which is designed as a hollow cylinder. The slightly reduced strength facilitates the relaxation of the material and also saves material and weight. A further embodiment is shown in Fig. 4 The figure shows where the spring pin is designed as a spiral spring pin. By winding a metal foil, a rigid yet flexible spring pin can be manufactured. The winding also gives the spring pin a slight radial elasticity, allowing it to be manufactured with a slight oversize compared to the diameter of the recesses 20 and 21. This allows it to be easily clamped in these recesses, thus facilitating assembly.

[0019] Fig. 5 shows an embodiment of the present invention in which the tension pin 18 is also manufactured as a hollow cylinder, but in contrast to the embodiment according to Fig. 3The injector has several longitudinal grooves 24 on its outer surface. These longitudinal grooves 24 serve as predetermined breaking points, allowing the tension pin 18 to break in a controlled manner into two pieces along these grooves 24 during assembly if it is subjected to excessive stress. If this is detected during the assembly of the fuel injector, the tensioning screw can be easily loosened and the tension pin 18 replaced. Breaking along the longitudinal grooves 24 during operation of the fuel injector also prevents excessive forces from being exerted on the housing components.

Claims

1. Fuel injector (1) having a housing (2) comprising a first housing part (3) and a second housing part (4), wherein the housing parts bear against one another at a sealing surface and are braced against one another by a clamping device (5), and having a spring pin (18), which protrudes into a first recess (20) in the first housing part and into a second recess (21) in the second housing part (4), thus defining the position of the first housing part (3) and of the second housing part (4) relative to one another, wherein the material of the spring pin (18) is a light metal or a light metal alloy, characterized in that the outside of the spring pin (18) has predetermined breaking points in the form of one or more longitudinal grooves (24), so that if a predetermined mechanical load is exceeded, the spring pin (18) breaks into at least two parts.

2. Fuel injector according to Claim 1, characterized in that the material of the spring pin (18) creeps plastically at temperatures below 150°C.

3. Fuel injector according to Claim 2, characterized in that the material of the spring pin (18) creeps plastically in a temperature range of from 50°C to 150°C, preferably 50°C to 100°C.

4. Fuel injector according to Claim 2 or 3, characterized in that the light metal is aluminium.

5. Fuel injector according to Claim 2 or 3, characterized in that the light metal alloy contains aluminium and / or magnesium.

6. Fuel injector according to one of Claims 1 to 5, characterized in that the spring pin (18) is manufactured from a metal foam.

7. Fuel injector according to one of Claims 1 to 5, characterized in that the spring pin (18) is in the form of a hollow cylinder.

8. Fuel injector according to one of Claims 1 to 5, characterized in that the spring pin (18) is in the form of a spiral spring pin.

9. Fuel injector according to Claim 8, characterized in that the spring pin (18) is inserted into the recesses (20; 21) with a radial preload.

10. Fuel injector according to one of Claims 1 to 9, characterized in that more than one spring pin (18) is arranged in the housing (2).

11. Fuel injector according to one of Claims 1 to 10, characterized in that the spring pin (18) is guided in the recesses (20; 21) with very little radial play.

12. Fuel injector according to one of Claims 1 to 11, characterized in that the spring pin (18) has a coating (22) made of a plastic or a ceramic.

13. Fuel injector according to one of Claims 1 to 12, characterized in that the first housing part is a holding body (3) and the second housing part is a nozzle body (4).

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