Patent Publication Number: US-2011067675-A1

Title: Fuel injection assembly with optimized heat coupling between fuel injection device and cylinder head

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on German Patent Application 10 2009 029 088.5 filed Sep. 2, 2009. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is based on a fuel injection assembly. 
     2. Description of the Prior Art 
     Diesel engine injection devices, such as injectors, unit fuel injectors, etc., are built into the cylinder head of the diesel engines, and during engine operation they inject the fuel into the combustion chamber. In the process, they more or less rapidly take on the temperatures that occur in the engine compartment. Depending on the way in which they are built in, a more or less wide air gap is located between the injector and the cylinder head, or the cylinder head hood. This air gap prevents the heat transfer between the cylinder head and its attached parts, on the one hand, and the injection device, on the other. In operation, for instance because of pressure reduction at the attached part guides and hydraulic valves, or as a result of the intrinsic heating of the electrical components, the injection device can warm up faster than the air- or water-cooled cylinder head or its attached parts. Particularly in injection devices for high pressures (&gt;1300 bar), damage to the components of the injection device can be caused by the high temperatures that occur. 
     In DE 102 34 324 A1, the fuel injector is built into an injector bore in the cylinder head. Before the injector is installed, a coolant jacket sleeve is built or inserted into the injector bore in order thereby to form a cooling jacket that surrounds the injector. The coolant jacket sleeve is made from a copper alloy or a corrosion-resistant steel and provides for a better heat transfer, but only if the injector rests with a precise fit with its jacket face on the wall of the injector bore. An annular gap that is otherwise present impairs the heat transfer, and the injector can heat up more strongly than the cooled cylinder head. 
     OBJECT AND SUMMARY OF THE INVENTION 
     By comparison, it is the object of the present invention to improve the temperature transition from the injection device to the forced-cooled cylinder head in such a way that at practically all times, the injection device assumes the temperature of the cooled cylinder head. 
     According to the invention, an air gap that is otherwise present between the injection device and the cylinder head or its attached parts is filled with a highly heat-conducting liquid (such as heat-conducting paste or oil) whose thermal conductivity is higher than that of air, or with an elastically deformable, heat-conducting component whose thermal conductivity is higher than that of air. As a result, the heat transfer between the injection device and the cylinder head is improved so much that harmful temperatures for the components of the injection device are avoided. In other words, at practically all times, the injection device assumes the temperature of the cooled cylinder head, so that on average, a lower temperature level than would occur without the invention occurs at the injection device. The thermal conductivity of the heat-conducting liquid or of the elastically deformable, heat-conducting component is at least 10 times, and preferably at least 100 times, higher than that of air. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of preferred embodiments taken in conjunction with the drawings, in which: 
         FIG. 1  shows a first exemplary embodiment of the fuel injection assembly of the invention; and 
         FIG. 2  shows a second exemplary embodiment of the fuel injection assembly of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The fuel injection assembly  1 , shown schematicey in  FIG. 1 , of an internal combustion engine includes a fuel injector  2  for injecting fuel into a combustion chamber  3  of the engine. The fuel injector  2  is inserted, forming an annular gap  4 , into an injector bore  5  of a cylinder head  6  of the engine and fixed there. 
     The annular gap  4  is filled over its entire axial length, that is, between its ends toward and away from the combustion chamber, with a heat-conducting liquid (such as oil) or a heat-conducting medium  7  whose thermal conductivity is higher than that of air. The heat transfer from the fuel injector  2  to the cooled cylinder head  6  is improved markedly by this liquid or pastelike heat-conducting medium  7 , in comparison to the air gap that is otherwise present, by even the factor of 150 to 400 if heat-conducting paste is used. As a result of the improved cooling of the fuel injector  2 , harmful temperatures for the components of the fuel injector  2  are avoided, and the fuel injector  2  assumes the temperature of the cooled cylinder head  6  practically at all times, so that on average, a lesser temperature level occurs at the fuel injector  2  than would occur without the heat-conducting medium  7  filling it. 
     The annular gap  4 , on its end toward the combustion chamber  3 , is sealed off from the combustion chamber  3  by a sealing element  8 , which is disposed between the fuel injector  2  and the cylinder head  6 , so that upon filling of the annular gap, no heat-conducting medium  7  gets into the combustion chamber  3 . After the filling with the heat-conducting medium  7 , the annular gap  4  is sealed off from the outside, or closed, on its end remote from the combustion chamber  3  by a further sealing element  9  (such as a radial shaft sealing ring, O-ring, etc.). 
     As indicated in dashed lines in  FIG. 1  with a cylinder head hood  10  as an example, the gap  4  may also be embodied between the fuel injector  2  and attached parts of the cylinder head  6 . 
     The fuel injection assembly  1  shown in  FIG. 2  differs from the exemplary embodiment of  FIG. 1  only in that in it, instead of a liquid or pastelike heat-conducting medium  7 , a separate component  20  of elastically deformable, heat-conducting material, such as elastomer or silicone, is used. The elastic component  20  is embodied as a sleeve, hose or cuff and is drawn, conforming closely, over part of the injector  2  and then mounted together with the fuel injector  2  in the cylinder head  6 . Next, by means of a suitable clamping device, the elastic component  20  is pressed inside the annular gap  4  axially such that in the radial direction, it rests on both the cylinder head  6  and the fuel injector  2  without an air gap. The clamping device may for instance be formed by a collar on the fuel injector  2 , by other machine elements, or as shown in  FIG. 2 , by a screw element  21 . By means of the clamping device, the elastic component  20  is pressed axially against a shoulder abutment  22 , toward the combustion chamber, of the cylinder head  6 , as a result of which, because of its elasticity, it deflects radially and rests on the cylinder head  6  and on the fuel injector  2  without an air gap. The elastic component  20  has a far better thermal conductivity than air. This is the case for instance with elastic materials, such as elastomer or silicone, that have a very high proportion of metal components, such as copper, magnesium, etc. 
     The foregoing relates to the preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.