Abstract:
A fuel injector for the direct injection of fuel into the combustion chamber of a mixture-compressing internal combustion engine having external ignition includes a valve housing formed by a nozzle body, and a seal which seals the fuel injector from a cylinder head of the internal combustion engine. The seal has a sleeve-type design with a structured cross section and extends across the axial length of the nozzle body.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a fuel injector for direct injection of fuel, which fuel injector is provided with a seal. 
   BACKGROUND INFORMATION 
   Published European patent document EP 0 828 075 describes a fuel injector for the direct injection of fuel into the combustion chamber of an internal combustion engine, which has a device for adjusting the temperature in the region of the valve tip so as to reduce deposits in this area. The device is embodied in the form of a coating made of a thermally conductive material on the valve tip. 
   Disadvantages of the fuel injector described in the European patent document EP 0 828 075 are the high demands regarding the accuracy of fit of the components and the complicated installation, which is involved and thus cost-intensive. 
   Furthermore, a fuel injector for the direct injection of fuel into the combustion chamber of a mixture-compressing internal combustion engine having external ignition is described in published German patent document DE 101 09 407. It includes a valve housing formed by a nozzle body, and a sealing ring which seals the fuel injector from a cylinder head of the internal combustion engine. The sealing ring has a convexly arched profile, the two ends of the sealing ring axially overlapping in the form of a step. 
   Particularly disadvantageous in the fuel injector described in published German patent document DE 101 09 407 is the air gap between the fuel injector and the cylinder head, which allows only limited heat transfer. This is disadvantageous in reducing deposits on the valve tip since the temperature in the region of the spray-discharge orifices must be as low as possible so as to avoid deposits. 
   SUMMARY 
   In contrast, the fuel injector according to the present invention has the advantage that a seal is situated between the cylinder head and the nozzle body, the seal extending over the entire axial length and having a suitable structure, thereby providing not only a reliable sealing effect but effective heat dissipation away from the nozzle body as well. 
   It is particularly advantageous that any desired cross sections are possible, e.g., corrugated tubes, convoluted bellows, and smooth tubular bodies having protuberances formed in a variety of shapes. 
   In an advantageous manner the seal may also be made up of a plurality of layers, which gives it higher stability and makes it less likely to be damaged during the installation. 
   In addition, it is advantageous that a cover plate, which functions as heat shield, may be situated on a discharge-side end of the seal. The cover plate may have an opening for the spray-discharged fuel jets or it may have a plurality of spray-discharge openings. 
   The seal may be produced from a metallic material having an amorphous structure, so that a smooth surface is able to be achieved. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a schematic cross-sectional view through a conventional fuel injector. 
       FIG. 2  shows a schematic cross-sectional view of a first example embodiment of a fuel injector according to the present invention. 
       FIG. 3  shows a schematic cross-sectional view of a second example embodiment of a fuel injector according to the present invention. 
       FIG. 4  shows a schematic cross-sectional view of a third example embodiment of a fuel injector according to the present invention. 
       FIG. 5  shows a schematic cross-sectional view of a fourth example embodiment of a fuel injector according to the present invention. 
       FIG. 6  shows a schematic cross-sectional view of a fifth example embodiment of a fuel injector according to the present invention. 
       FIG. 7  shows a schematic cross-sectional view of a sixth example embodiment of a fuel injector according to the present invention. 
   

   DETAILED DESCRIPTION 
   Before example embodiments of a fuel injector  1  according to the present invention are described in greater detail in connection with  FIGS. 2 through 7 , for a better understanding of the present invention, a conventional fuel injector  1  will be briefly explained in terms of its essential components on the basis of  FIG. 1 . 
   Fuel injector  1  is configured for fuel-injection systems of mixture-compressing internal combustion engines with externally supplied ignition. Fuel injector  1  is suited, e.g., for the direct injection of fuel into a combustion chamber  2  of an internal combustion engine. 
   Fuel injector  1  includes a nozzle body  3 , which is sealed from a cylinder head  5  of the internal combustion engine by a sealing ring  4 . Sealing ring  4  is made of, for instance, an elastomeric material such as a Teflon-coated material and provides the sealing effect in cylinder head  5  as a result of a slightly larger diameter compared to nozzle body  3 . 
   Furthermore, fuel injector  1  includes a housing  6 , an electric plug-in contact  7  for actuating fuel injector  1 , and a fuel feed  8 , via which the fuel is conveyed. Fuel may be supplied via a fuel-distributor line, for example, which is not shown further. 
   Disadvantages of the sealing rings  4  in the conventional configuration is, in particular, the poor heat transfer between nozzle body  3  and cylinder head  5  because of an air gap  9  on the discharge side between fuel injector  1  and cylinder head  5 . In order to counter the threat of coking of the spray-discharge orifices of directly-injecting fuel injectors  1  as a result of the high temperatures in combustion chamber  2 , the lowest possible temperature is to be desired in the region of the valve tip. This prevents a complete evaporation of the fuel remaining in the region of the valve tip after the injection process. If the fuel remains liquid, the combustion residue and impurities are unable to deposit in the region of the valve tip and are carried away during the next injection cycle. 
   The poor heat transfer between fuel injector  1  and cylinder head  5  in the conventional configuration is counteracted by a seal  10  configured according to the present invention, as illustrated by example embodiments shown in  FIGS. 2 through 7 . 
   Seals  10  described below all have in common the fact that they are designed as corrugated tubes and thus not only provide excellent sealing action but also offer a sufficiently large contact surface for an effective heat transfer between fuel injector  1  and cylinder head  5 . Seals  10  are designed in such a way that they are short and broad in the non-installed state, but are pressed together slightly by the installation and become longer as a result. This makes it possible to achieve an excellent fit. 
   Seals  10  are made of a material that exhibits great thermal conductivity, e.g., a metal foil having an amorphous structure, so that it is possible to achieve a very smooth surface with the advantage of a simple and damage-free installation. 
   Cavities  16  formed between fuel injector  1  and seal  10  by the different cross-sectional forms may be used for passing through a coolant. 
   In the following, example embodiments for fuel injectors  1  provided with corresponding seals  10  will be described. With the exception of the inventive measures provided according to the present invention, fuel injectors  1  according to the present invention may be designed similar to the conventional fuel injector illustrated in  FIG. 1 . 
     FIG. 2  shows a first example embodiment of a fuel injector  1  configured according to the present invention. Here, in the simplest manner, seal  10  has the form of a corrugated tube. Seal  10  is open at both sides and is thus able to be mounted in an especially uncomplicated manner. Seal  10  may be premounted on nozzle body  3  of fuel injector  1  and then inserted into cylinder head  5  together with it. 
     FIG. 3  shows a second example embodiment of a fuel injector  1  configured according to the present invention. In this example embodiment, seal  10  has the form of a tubular seal  10  having protrusions  11 . Protrusions  11  are approximately semicircular in section. The advantage of this embodiment is a slightly larger contact surface on nozzle body  3  resulting in improved thermal conductivity. 
     FIG. 4  shows a third example embodiment of a fuel injector  1  configured according to the present invention. In this case seal  10  has a pleated design and has been formed into expansion bellows  10 . The thermal conductivity and sealing ability correspond approximately to that of the first example embodiment described in  FIG. 2 . 
     FIG. 5  shows a fourth example embodiment of a fuel injector  1  configured according to the present invention. Here, seal  10  is made up of a plurality of layers  12  in a sandwich-like manner. This increases the durability of seal  10 , in particular, which is unable to deform as easily during installation and thus is less likely to be damaged. The individual layers  12  may in turn be designed in the form of a corrugated-tube and be bonded to each other, or they may be joined to each other only at their ends. 
     FIG. 6  shows a fifth example embodiment of a fuel injector  1  configured according to the present invention. Here, seal  10  may have the same cross-sectional design as seals  10  according to the example embodiments illustrated in  FIGS. 2 through 5 , the corrugated tube design having been chosen in  FIG. 6 . In addition, on a discharge-side end  13 , it is provided with a cover plate  14  which has an opening  15  for the fuel jets injected into combustion chamber  2  from at least one spray-discharge orifice of fuel injector  1 . Cover plate  14  additionally has the function of a heat shield and protects the spray-discharge orifices from the high temperature prevailing in the combustion chamber, the high temperatures increasing the coking tendency of the spray-discharge orifices. 
     FIG. 7  shows a sixth example embodiment of a fuel injector  1  configured according to the present invention. Here, as in the example embodiment shown in  FIG. 6 , seal  10  may have the same sectional design as seals  10  illustrated in  FIGS. 2 through 5 , the corrugated tube design having been chosen in  FIG. 7  as well. Seal  10  has a cover plate  14  on a discharge-side end  13 , into which the spray-discharge orifices  17  may be worked directly. Cover plate  14  also assumes the function of a heat shield and protects the discharge-side end of fuel injector  1  from the temperature prevailing in the combustion chamber. 
   The present invention is not restricted to the example embodiments shown, but is also applicable to other cross-sectional forms of seals  10 , as well as to a wide variety of construction types of fuel injectors  1 , such as fuel injectors  1  having an interface to an intake manifold or a common-rail system. 
   In addition, the individual features of the various example embodiments may be combined with each other as desired.