Abstract:
The present invention provides a jet for providing orifice damping in the fuel delivery system of a compression-ignition combustion engine, wherein the jet ( 100 ) is formed by means of a deep draw process and comprises a hollow cylindrical body ( 102 ) having first and second ends ( 104, 106 ), the first end ( 104 ) being open to enable unrestricted flow of fuel therethrough, in use, the second end ( 106 ) comprising an orifice ( 110 ) therein having a smaller cross-sectional area than the opening in the first end ( 104 ), to restrict the flow of fuel therethrough and dampen pressure waves in the fuel, in use, the second end ( 106 ) being shaped so as to provide resistance to pressure changes occurring in the fuel delivery system, in use.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a jet for providing orifice damping in the fuel delivery system of a compression-ignition combustion engine, a fuel delivery system for a compression-ignition combustion engine comprising such a jet, and to a method of manufacturing a jet for providing orifice damping in the fuel delivery system of a compression-ignition combustion engine. 
       BACKGROUND OF THE INVENTION 
       [0002]    In a known compression-ignition internal combustion engine, such as a diesel engine or gas engine, combustion takes place in one or more combustion chambers or cylinders. Air is compressed in the cylinder by a piston and fuel is injected into the compressed air. The heat of the compressed air spontaneously ignites the fuel in the cylinder. 
         [0003]    Fuel is injected into the cylinders at high pressure, which is typically achieved using a high pressure pump to pressurise fuel in a rail cavity which, in turn, is connected to a plurality of injectors, each of which is associated with one cylinder of the engine. 
         [0004]      FIG. 1  shows a conventional common rail delivery system  1  for a compression-ignition combustion engine. The rail  2  comprises an inlet pipe  4  into which fuel is pumped under high pressure by a high pressure pump  3 . The rail  2  also includes a plurality of outlet pipes  5 , one for each of the engine&#39;s cylinders, through which fuel is delivered to the injectors  6 . 
         [0005]      FIG. 2  is a sectional view of a conventional rail for a compression-ignition combustion engine. Referring to  FIG. 2 , the outlet  7  of each pipe  5  is connected to a fuel injector (not shown), which controls the flow of fuel into a corresponding engine cylinder. 
         [0006]    Each injector typically comprises a nozzle through which fuel is injected into the corresponding cylinder. The flow of fuel through the injector nozzle is controlled by a valve needle which is movable along a primary axis of the injector body and may be lifted from a valve seat adjacent to the nozzle in order to allow fuel to flow through the nozzle and be injected into the cylinder. 
         [0007]    In order to achieve efficient combustion in a cylinder it is important to be able to control the quantity and the timing of the fuel delivered to a cylinder. There is a problem with such high pressure fuel delivery systems that large pressure differences are caused by the opening and closing of the valve. For example, when the valve needle of the injector  6  is lifted into an injecting state, there is a large pressure difference between the rail  2  and the pressure at the injector  6 . This pressure difference can cause pressure waves to travel along the pipes  5  connecting each injector  6  to the rail cavity  8 . Such pressure waves are undesirable since they can affect the amount of fuel which is injected into a cylinder when the valve needle is lifted. For example, a pressure wave may result in unexpectedly high pressure at the nozzle, causing an increased amount of fuel to be injected into the cylinder when the valve is opened. This could lead to increased hydrocarbon emissions due to incomplete combustion of the fuel in the cylinder. Alternatively, a pressure wave may result in unexpectedly low pressure at the nozzle, causing less fuel than expected to be injected into the cylinder when the valve is opened. This may result in reduced engine power output. 
         [0008]    A known technique for reducing the effect of pressure waves in the fuel delivery system is the inclusion of a jet, in the pipe  5  between the injector  6  and the rail cavity  8 , in order to provide orifice damping. 
         [0009]      FIG. 3  shows a conventional jet which is used to provide orifice damping in the fuel supplied by a rail to an injector in a diesel engine or gas engine. The known jet  10  is formed by machining a metal blank  12  having a substantially cylindrical form. An aperture or orifice  14  is formed in one end of the blank  12  such that the flow of fuel into the jet is restricted. An axial bore  16  is formed in the opposite end of the blank to create a conduit through which fuel flows from the rail  2  under pressure after it has passed through the orifice  14 . 
         [0010]    The reduction in the flow area of the fuel through the orifice  14  before it reaches the injector  6  has the effect of smoothing out any pressure waves which are propagating along the pipe  5  between the injector  6  and the rail  2 . Accordingly, fluctuations in the amount of fuel injected when the injector valve is opened are reduced. 
         [0011]    However, there is a problem with the conventional jet  10  in that it is expensive to manufacture. As mentioned above, the conventional jet  10  is formed by drilling a blank  12 . Additional processing of the blank  12 , such as grinding and heat treatment, may also be required. Each of these processing steps incurs a cost which contributes to the total cost of the finished jet. 
         [0012]    It is therefore an object of the present invention to provide a jet for orifice damping in the fuel delivery system of a compression-ignition combustion engine which substantially overcomes or mitigates the problems associated with the conventional jet described above. 
       SUMMARY OF INVENTION 
       [0013]    According to a first aspect of the present invention, there is provided a jet for providing orifice damping in the fuel delivery system of a compression-ignition combustion engine, wherein the jet is formed by means of a deep draw process and comprises;
       a hollow cylindrical body having first and second ends,   the first end being open to enable unrestricted flow of fuel therethrough, in use,   the second end comprising an orifice therein having a smaller cross-sectional area than the opening in the first end, to restrict the flow of fuel therethrough and dampen pressure waves in the fuel, in use, the second end being shaped so as to provide resistance to pressure changes occurring in the fuel delivery system, in use.       
 
         [0017]    Thus, the present invention provides a jet which is simple and more economical to manufacture, yet is able to resist the changes of pressure which occur within the fuel delivery system of a compression-ignition combustion engine. 
         [0018]    Preferably, the second end comprises a part-spherical region extending inwardly from a wall of the cylindrical body. Advantageously, said part-spherical region may project outwardly from the cylindrical body. Alternatively, said part-spherical region may project into the cylindrical body. 
         [0019]    Preferably, said part-spherical region terminates in a flat region. More preferably, said orifice is formed within the flat region and is co-axial with the primary axis of the cylindrical body. 
         [0020]    Advantageously, the jet comprises a pair of orifices in the part-spherical region, said pair of orifices being disposed at spaced apart locations equidistant from, and on opposite sides of the primary axis of the cylindrical-body. 
         [0021]    Advantageously, the second end may alternatively comprise a flat region extending inwardly from and substantially perpendicularly to the wall of the cylindrical body. Said orifice may be formed in the flat region co-axial with the primary axis of the cylindrical body. 
         [0022]    Advantageously, said flat region comprises a concentric rib or a cruciform rib. 
         [0023]    The jet may advantageously comprise a pair of orifices in the flat region, said pair of orifices being disposed at spaced apart locations equidistant from, and on opposite sides of the primary axis of the cylindrical body. 
         [0024]    Advantageously, the second end comprises a part-spherical region which projects from the flat region and terminates in a second flat region, said orifice being formed in the second flat region. 
         [0025]    Advantageously, the part-spherical region projects outward from the cylindrical body. Alternatively, the part-spherical region may project into the cylindrical body. 
         [0026]    According to a second aspect of the present invention, there is provided a fuel delivery system for a compression-ignition combustion engine, the system comprising a jet as described above;
       a high pressure pump for pressurising fuel in the delivery system; and   a rail cavity for receiving pressurised fuel from the high pressure pump via an inlet pipe, the rail cavity having at least one outlet pipe for conveying fuel to at least one respective fuel injector.       
 
         [0029]    Preferably, said jet is disposed in said outlet pipe or said inlet pipe. Alternatively, said jet may be disposed between said pump and said rail cavity. Advantageously, said jet may be formed integrally with any one of said high pressure pump, said rail cavity, said inlet pipe or said outlet pipe. 
         [0030]    According to a third aspect of the present invention, there is provided a method of manufacturing a jet for providing orifice damping in the fuel delivery system of a compression-ignition combustion engine, the method comprising;
       forming hollow a cylindrical body by means of a deep draw process,   the cylindrical body comprising first and second ends,   the first end being open to enable unrestricted flow of fuel therethrough, in use,   the second end comprising an orifice therein having a smaller cross-sectional area than the opening in the first end, to restrict the flow of fuel therethrough and dampen pressure waves in the fuel, in use, the second end being shaped so as to provide resistance to pressure changes occurring in the fuel delivery system, in use.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0035]    Embodiments of the present invention will now be described, by way of example, with reference to  FIGS. 4 to 14  of the accompanying drawings, in which: 
           [0036]      FIG. 1  shows a common rail fuel delivery system for a compression-ignition combustion engine; 
           [0037]      FIG. 2  is a sectional view of a conventional rail for a compression-ignition combustion engine; 
           [0038]      FIG. 3  is a sectional view of a conventional jet for providing orifice damping in the rail of  FIG. 2 ; 
           [0039]      FIG. 4  is a perspective sectional view of a first embodiment of a jet according to the present invention; 
           [0040]      FIG. 5  is a sectional view of the jet of  FIG. 4 ; 
           [0041]      FIG. 6  is a perspective sectional view of a second embodiment of a jet according to the present invention; 
           [0042]      FIG. 7  is a perspective sectional view of a third embodiment of a jet according to the present invention; 
           [0043]      FIG. 8  is a sectional view of the jet of  FIG. 7 ; 
           [0044]      FIG. 9  is a perspective sectional view of a fourth embodiment of a jet according to the present invention; 
           [0045]      FIG. 10  is a sectional view of the jet of  FIG. 9 ; 
           [0046]      FIG. 11  is a perspective sectional view of a fifth embodiment of a jet according to the present invention; 
           [0047]      FIG. 12  is a perspective sectional view of a sixth embodiment of a jet according to the present invention; 
           [0048]      FIG. 13  is a perspective sectional view of a seventh embodiment of a jet according to the present invention; and 
           [0049]      FIG. 14  is a perspective sectional view of a eighth embodiment of a jet according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0050]    A deep draw metal forming process is generally performed by stretching sheet metal stock around a punch. The sheet metal is clamped around its edges and is pressed into a die cavity by the punch in order to create a product having the desired shape. In this way, different shapes of product can be produced by varying the respective geometries of the die cavity and the punch. 
         [0051]    By means of the above-described deep draw process, it is possible to produce jets which can withstand the large variations in pressure which occur within a common rail fuel delivery system. More specifically, it is known that during running of a compression-ignition combustion engine with a common rail fuel delivery system the fluid pressure on the upstream side of the orifice of a jet (i.e. on the same side as the rail cavity) may be as much as 300 bar higher than the pressure on the downstream side of the orifice (i.e. on the injector side), when the injector valve opens. As will be described in more detail below, embodiments of the present invention provide jets formed using a deep draw process which are shaped so as to be sufficiently resistant to such pressure differences. 
         [0052]    Referring to  FIG. 4 , a first embodiment of a deep drawn jet  100  according to the present invention comprises a generally cylindrical body  102 . The cylindrical body  102  has an open end  104  at one end and is formed with a pressure resistant structure  106  at the opposite end. The pressure resistant structure  106  comprises a part-spherical portion  108  and a flat portion  109 . The part-spherical portion  108  extends from the cylindrical body  102  with a constant radius, having its centre at a point on the primary axis (A-A) of the cylindrical body  102 . The part-spherical portion  108  terminates at the flat portion  109 . An orifice  110  is formed in the flat portion  109 , the orifice  110  being co-axial with the primary axis of the cylindrical body  102 . 
         [0053]    Referring to  FIG. 5 , the cylindrical body  102  has a wall thickness, s, which is equivalent to the thickness of the metal sheet stock from which the jet  100  is formed. The cylindrical body  102  has a height H, and diameter D and, typically, H=1 to 1.5D. The orifice  110  has a diameter d 1 , the flat portion  109  has a diameter d 2 , and the part-spherical portion  108  has radius R. Typically, d 2 =1 to 1.5d 1  and R=D/2. 
         [0054]    The jet  100  as shown in  FIG. 4  is oriented with the open end  104  uppermost. In general, this is the orientation in which the jet  100  is formed by the deep draw process. More specifically, a suitably shaped metal blank is clamped around its edge and a punch presses the blank down into a suitably shaped die cavity. Accordingly, the open end  104  of the resulting jet  100  corresponds to the clamped part of the original metal blank, and the part-spherical portion  108  and flat portion  109  are formed between the punch and the bottom of the die cavity. However, it should be noted that, when installed in a fuel delivery system in place of the. conventional jet  10  shown in  FIG. 2 , the deep drawn jet  100  will be oriented in the pipe  5  such that the open end  104  is proximal to the injector and the part-spherical portion  108  is proximal to the rail cavity  8 . Accordingly, in use, fuel will be pumped from the rail cavity  8 , along the pipe  5  through the orifice  110  along the cylindrical body  102  of the jet  100  and out through the open end  104  to the injector  6 . 
         [0055]    A finite element analysis (FEA) of the deep drawn jet of  FIG. 4  determined that it could withstand a pressure difference in excess of 1500 bar in the inlet direction of the jet, i.e. where there is a higher pressure on the rail side of the jet, and similarly a pressure difference in excess of 1500 bar in the outlet direction, i.e. where there is a higher pressure on the injector side of the jet. 
         [0056]    Referring to  FIG. 6 , a second embodiment of a jet according to the present invention is similar to that of  FIGS. 4 and 5 , with the exception that there is no flat portion  109  and instead of a single, co-axial orifice  110 , there are a pair of orifices  110   a ,  110   b . The pair of orifices  110   a ,  110   b  are formed in the part-spherical portion  108  at spaced apart locations, equidistant from, and on opposite sides of the primary axis of the cylindrical body  102 . The distance between the orifices  110   a ,  110   b  is labelled d 3  in  FIG. 6 . 
         [0057]    A finite element analysis (FEA) of the deep drawn jet of  FIG. 6  determined that it could withstand a pressure difference in excess of 1500 bar in the inlet direction of the jet and similarly a pressure difference in excess of 1500 bar in the outlet direction. 
         [0058]    Referring to  FIG. 7 , the third embodiment of a jet according to the invention includes a pressure resistant structure  106  which has a bell-shape, comprising a first flat portion  130 , a curved portion  132 , and a second flat portion  134 . The first flat portion  130  extends inwardly and radially from the edge of the cylindrical body  102 . The curved portion  132  projects from the first flat portion  130  and terminates at the second flat portion  134 . The curved portion  132  may have a radiussed or part-spheroidal form. An orifice  110  is formed in the second flat portion  134 , the orifice  110  being co-axial with the primary axis of the cylindrical body  102 . 
         [0059]    Referring to  FIG. 8 , the height of the cylindrical body  102  is H and the height of the pressure resistant structure  106 , i.e. the combined height of the first and second flat portions  130 , 134  and the curved portion  132 , is h. The wall thickness of the cylindrical body  102  is s. The diameter of the orifice  110  is d 1  and the diameter of the second flat portion  134  is d 2 . Typically, H=1 to 1.5D, d 2 =1 to 1.5d 1  and h=2 to 2.5s. 
         [0060]    A finite element analysis (FEA) of the deep drawn jet of  FIG. 7  determined that it could withstand a pressure difference of around 1200 bar in. the inlet direction of the jet and a pressure difference of around 1100 bar in the outlet direction. 
         [0061]    In an alternative arrangement of the embodiment shown in  FIG. 7 , the bell-shaped portion may be inverted such that the curved portion  132  projects into the cylindrical body  102  of the jet  100 . 
         [0062]    Referring to  FIG. 9 , the fourth embodiment of a jet according to the invention includes a pressure resistant structure  106  which comprises a concentric rib  140 . The concentric rib  140  is co-axial with the primary axis of the cylindrical body  102 , and is formed in a flat region  142  which extends inwardly and radially from the edge of the cylindrical body  102 . The orifice  110  is disposed at the centre of the flat region  142  and is formed co-axially with the primary axis of the cylindrical body  102 . The concentric rib  140  projects from the flat region  142  on the outer surface of the jet  100 , and on the opposite side of the flat region  142  there is a correspondingly shaped trough  144 . 
         [0063]    Referring to  FIG. 10 , the height of the cylindrical body  102  is H and the height of the pressure resistant structure  106 , i.e. the height that the concentric rib  140  projects from the surface of the flat region  142 , is h. The wall thickness of the cylindrical body  102  is s. The diameter of the orifice  110  is d 1  and the inner diameter of the concentric rib  140  is d 2 . Typically, H=1 to 1.5D, d 2 =1 to 1.5d 1  and h=0.5 to 0.75s. 
         [0064]    A finite element analysis (FEA) of the deep drawn jet of  FIG. 9  determined that it could withstand a pressure difference of around  800  bar in the inlet direction of the jet and a pressure difference of around  700  bar in the outlet direction. 
         [0065]    Referring to  FIG. 11 , the fifth embodiment of a jet according to the invention includes a pressure resistant structure  106  which comprises an inverted spherical shape  150 . The fifth embodiment is similar to the first embodiment, with the exception that the spherical portion  150  projects into the cylindrical body  102  of the jet  100 . In  FIG. 11 , the radius of curvature of the inverted spherical shape  150  is labelled r. The diameter of the orifice is labelled d 1  and the diameter of the central portion of the spherical shape is labelled d 4  and, typically, d 4 =1 to 1.5d 1 . 
         [0066]    A finite element analysis (FEA) of the deep drawn jet of  FIG. 11  determined that it could withstand a pressure difference of around 750 bar in the inlet direction of the jet and a pressure difference of around 850 bar in the outlet direction. 
         [0067]    Referring to  FIG. 12 , the sixth embodiment of a jet according to the invention includes a pressure resistant structure  106  which comprises a flat region  160 . The flat region  160  extends inwardly and radially from the edge of the cylindrical body  102 . The orifice  110  is disposed at the centre of the flat region  160  and is formed co-axially with the primary axis of the cylindrical body  102 . 
         [0068]    A finite element analysis (FEA) of the deep drawn jet of  FIG. 12  determined that it could withstand a pressure difference of around 650 bar in the inlet direction of the jet and a pressure difference of around 550 bar in the outlet direction. 
         [0069]    Referring to  FIG. 13 , the seventh embodiment of a jet according to the invention is similar to the above-described sixth embodiment with the exception that there are two orifices  110   a ,  110   b  in the flat region  160  rather than a single, centrally located orifice. The pair of orifices  110   a ,  110   b  are formed in the flat region  160  at spaced apart locations, equidistant from, and on opposite sides of the primary axis of the cylindrical body  102 . The distance between the orifices  110   a ,  110   b  is labelled d 3  in  FIG. 13 . 
         [0070]    A finite element analysis (FEA) of the deep drawn jet of  FIG. 13  determined that it could withstand a pressure difference of around 600 bar in the inlet direction of the jet and a pressure difference of around 550 bar in the outlet direction. 
         [0071]    Referring to  FIG. 14 , the eighth embodiment of a jet according to the invention includes a pressure resistant structure  106  which comprises a cross-shaped rib  180 . The cross-shaped rib  180  is centred on the primary axis of the cylindrical body  102 , and is formed in a flat region  182  which extends inwardly and radially from the edge of the cylindrical body  102 . A pair of orifices  110   a ,  110   b  are formed in the flat region  182  at spaced apart locations, equidistant from, and on opposite sides of the primary axis of the cylindrical body  102 . The cross-shaped rib  180  projects from the flat region  182  on the outer surface of the jet  100 , and on the opposite side of the flat region  182  there is a correspondingly shaped trough  184 . In  FIG. 14 , the depth of the trough  184  is labelled h, and is equivalent to the distance which the rib  180  projects from the surface of the flat region  182 . Each arm of the rib  180  has a length L 1  and a width L 2 . 
         [0072]    A finite element analysis (FEA) of the deep drawn jet of  FIG. 14  determined that it could withstand a pressure difference of around 550 bar in the inlet direction of the jet and a pressure difference of around 550 bar in the outlet direction. 
         [0073]    Although the jets according to the present invention have been described as for use between the rail cavity and the fuel injector of the fuel delivery system of a compression ignition combustion engine, it will be appreciated by those skilled in the art that such jets may advantageously be disposed at other locations within the fuel delivery system. For example, a jet may be disposed at the outlet of a high pressure pump used to pressurise fuel in the delivery system, at the inlet or outlets of the common rail volume, or at any other location where it is necessary to reduce the effects of pressure waves within the fuel flow. 
         [0074]    It will be understood that the embodiments described above are given by way of example only and are not intended to limit the invention, the scope of which is defined in the appended claims.