Coupling device

The invention relates to a coupling device for mechanically coupling a fuel rail to a cylinder head of a combustion engine .

Coupling devices for mechanically coupling a fuel rail to a cylinder head of a combustion engine are in widespread use, in particular for internal combustion engines. Fuel can be supplied to an internal combustion engine by the fuel rail through a fuel injector. The fuel rail can be coupled to the cylinder head in different manners.

In order to keep pressure fluctuations during the operation of the internal combustion engine at a very low level, internal combustion engines are supplied with a fuel accumulator to which the fuel injectors are connected and which has a relatively large volume. Such a fuel accumulator is often re ^¬ ferred to as a common rail. Known fuel rails comprise a hollow body with recesses in form of fuel injector cups, wherein the fuel injectors are arranged.

The object of the invention is to create a coupling device for mechanically coupling a fuel rail to a cylinder head of a combustion engine which is simply to be manufactured and which facilitates a reliable and precise coupling between the fuel rail and the cylinder head.

The objects are achieved by the features of the independent claim. Advantageous embodiments of the invention are given in the sub-claims. The invention is distinguished by a coupling device for mechanically coupling a fuel rail to a cylinder head of a combustion engine. The coupling device comprises a fuel injector cup being designed to be hydraulically and mechanically coupled to the fuel rail and being arranged and designed to face the cylinder head, a first fastening element facing the fuel injector cup and being designed to be fixedly coupled to the cylinder head, at least one first spring element being arranged between the first fastening element and the fuel injector cup and/or being arrangeable between the fuel injector cup and the cylinder head, a support element being ar ^¬ ranged between the fuel rail and the cylinder head and being designed to be fixedly coupled to the fuel rail, a second fastening element being in engagement with the support element and being designed to be fixedly coupled to the cylinder head, and at least one second spring element being arranged between the second fastening element and the support element and/or being arrangeable between the support element and the cylinder head. The at least one first spring element consists of a metal or comprises a metal, and the at least one second spring element consists of a plastic or comprises a plastic.

This has the advantage that the at least one first spring element consisting of a metal or comprising a metal can keep the displacement of the fuel injector cup small. Furthermore, the at least one second spring element consisting of a plas ^¬ tic or comprising a plastic can compensate the tolerances of the components of the fuel rail and the cylinder head to achieve a minimum mechanical stress for these components.

In an advantageous embodiment one first spring element is arranged between the first fastening element and the fuel in- jector cup and a further first spring element is arrangeable between the fuel injector cup and the cylinder head. The first spring elements consist of a metal or comprise a metal. This has the advantage that the coupling of the fuel injector cup with the cylinder head allows an assembly of the cylinder head and the fuel rail without a direct contact between the cylinder head and the fuel injector cup. Consequently, a noise transmission between the cylinder head and the fuel rail can be kept small.

In a further advantageous embodiment one second spring element is arranged between the second fastening element and the support element and a further second spring element is arrangeable between the support element and the cylinder head. The second spring elements consist of a plastic or comprise a plastic. This has the advantage that the coupling of the sup ^¬ port element with the cylinder head allows an assembly of the cylinder head and the fuel rail without a direct contact between the cylinder head and the support element. Consequently, a noise transmission between the cylinder head and the fuel rail can be kept small.

In a further advantageous embodiment at least one of the fas ^¬ tening elements is a screw.

Exemplary embodiments of the invention are explained in the following with the aid of schematic drawings. These are as follows :

Figure 1 an internal combustion engine in a schematic view,

Figure 2 a fuel feed device with a coupling device in a perspective view, and Figure 3 the coupling device in a longitudinal sectional view along line III-III' of Figure 2.

Elements of the same design and function that occur in dif ^¬ ferent illustrations are identified by the same reference character .

A fuel feed device 10 is assigned to an internal combustion engine 22 (Figure 1) which can be a diesel engine or a gasoline engine. It includes a fuel tank 12 that is hydraulically connected with a fuel pump 14. The output of the fuel pump 14 is connected to a fuel inlet 16 of a fuel rail 18. In the fuel rail 18, the fuel is stored for example under a pressure of about 200 bar in the case of a gasoline engine or of about 2,000 bar in the case of a diesel engine. Fuel injectors 20 are connected to the fuel rail 18 and the fuel is fed to the fuel injectors 20 via the fuel rail 18. The fuel injectors 20 are arranged in a cylinder head 70 of the internal combustion engine 22 (Figure 3) . Preferably, the fuel injectors 20 are not in direct contact with the cylinder head 70.

Figure 2 shows a perspective view of the fuel feed device 10. Figure 3 shows the fuel feed device 10 with the fuel injector 20. The fuel injector 20 has a fuel injector body 24. The fuel injector 20 is suitable for injecting fuel into a combustion chamber 25 of the internal combustion engine 22 (Figure 1) . The fuel injector 20 comprises a fuel inlet portion 26. Furthermore, a cavity 28 is arranged in the fuel injector body 24. In an injection mode fuel can flow from the fuel inlet portion 26 to the cavity 28 and further to an injection nozzle 29. Subsequently, the fuel may be injected into the combustion chamber 25. In a non-injecting mode a fuel flow through the cavity 28 and an injection of fuel into the com ^¬ bustion chamber 25 is prevented.

The fuel feed device 10 comprises a fuel injector cup 30 which is part of a coupling device 40. The fuel injector cup 30 is in engagement with the fuel inlet portion 26 of the fuel injector 20. The fuel injector cup 30 has a through hole 42.

The fuel injector cup 30 is mechanically and hydraulically coupled to the fuel rail 18 by a first pipe 44. The first pipe 44 enables a fluid flow from the fuel rail 18 to the fuel injector 20. The fuel feed device 10 comprises a second pipe 46. The second pipe 46 enables a fluid flow from the fuel injector 20 back to the fuel tank 12.

The coupling device 40 further comprises a first fastening element 48. In the shown preferred embodiment, the first fastening element 48 is a screw. The first fastening element 48 is extending through the through hole 42. The first fastening element 48 is in engagement with the cylinder head 70. If the fastening element 48 is a screw, the fastening element 48 can be fixedly coupled to the cylinder head 70.

The coupling device 40 further comprises first spring elements 50, 52. One first spring element 50 is arranged axially between the fastening element 48 and the fuel injector cup 30. Another first spring element 52 is arranged axially be ^¬ tween the fuel injector cup 30 and the cylinder head 70. The first spring elements 50, 52 consist of a metal or comprise a metal . The coupling device 40 further comprises a support element 56 which is arranged between the fuel rail 18 and the cylinder head 70. The support element 56 is shaped as a bracket and is fixedly coupled to the fuel rail 18, for example by brazing or welding.

The coupling device 40 further comprises a second fastening element 58 which is in engagement with the support element 56. In the shown preferred embodiment, the second fastening element 58 is a screw. The second fastening element 58 is extending into a blind hole 59 which is arranged in the cylinder head 70. If the second fastening element 58 is a screw, it can be in engagement with the cylinder head 70. By this the second fastening element 58 can be fixedly coupled to the cylinder head 70.

The coupling device 40 further comprises second spring elements 60. One second spring element 60 is arranged between the second fastening element 58 and the support element 56. A further second spring element 62 is arranged between the sup ^¬ port element 56 and the cylinder head 70. The second spring elements 60, 62 consist of a plastic or comprise a plastic.

Due to the first spring elements 50, 52 a direct contact be ^¬ tween the cylinder head 70 and the fuel injector cup 30 can be prevented. Conseguently, a noise transmission between the cylinder head 70 and the fuel rail 18 can be kept small. The advantage that the first spring elements 50, 52 consist of a metal or comprise a metal is that the displacement of the fuel injector cup 30 and the fuel injector 20 can be kept small. Conseguently, the variation of the position of the in ^¬ jection nozzle 29 can be kept small. Consequently, a favora- ble spray distribution in the combustion chamber 25 can be obtained .

Due to the second spring elements 60, 62 a direct contact be ^¬ tween the cylinder head 70 and the support element 56 can be prevented. Consequently, a noise transmission between the cylinder head 70 and the fuel rail 18 can be kept small. The advantage that the second spring elements 60, 62 consist of a plastic or comprise a plastic is that a high elasticity between the fuel rail 18 and the cylinder head 70 can be obtained. Consequently, the tolerances of the components of the fuel feed device 10 which may result in mechanical stress in particular during the mounting of the fuel feed device 10 can be compensated in a very good manner.

The use of a metal for the first spring elements 50, 52 and the use of a plastic for the second spring elements 60, 62 result in a very good combination of a low stress for the components of the fuel feed device 10 in particular during the mounting of the fuel feed device 10 and an exact posi ^¬ tioning of the fuel injector 20 in the cylinder head 70.