Abstract:
A compression resistant isolator disposed between a direct fuel injector and a cylinder head of an internal combustion engine provides thermal, or thermal and vibrational isolation therebetween. A plurality of radially spaced rigid axial support members provide axial load support to maintain proper direct fuel injector positioning within the cylinder head bore. Spaces formed between the rigid axial support members may have isolation materials positioned therein. The implementation of the isolator may reduce the operating temperature of a fuel injector for direct injection, which is critical to avoid injector tip plugging.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to fuel injection systems of internal combustion engines; more particularly, to fuel injectors for direct injection; and most particularly to a device and method for thermal and acoustic isolation of a fuel injector from a cylinder head. 
       BACKGROUND OF THE INVENTION 
       [0002]    Fuel injector systems that deliver fuel to the combustion chamber of an internal combustion engine have been known for many years. The typical fuel injection system draws fuel from a fuel tank to a fuel rail mounted adjacent to the cylinder bank of the engine. The fuel injectors are electromechanical devices that deliver fuel in precise amounts and times to the respective cylinder. 
         [0003]    While the engine is running, the valve within each fuel injector is constantly being operationally cycled from an opened to a closed position. High frequency vibration is generated by the mechanical movement of the injector valves and low frequency pressure waves are generated by the movement of the fuel flowing through the injectors. Additionally, a substantial amount of heat generated in the combustion chambers of the cylinder heads may be transferred from the engine to the fuel injector. 
         [0004]    In an engine having a Direct Fuel Injector (DFI) system, atomized fuel is sprayed by the injector directly into the combustion chamber of the cylinder head. The fuel injector tip portion of the DFI typically fits through a stepped bore defined in the cylinder head that has a peripheral bottom shoulder whose top surface provides a positive stop to the bottom surface of the body of the DFI. However, direct metal-to-metal contact between the bottom surface of the DFI body and the top surface of the shoulder allows for unmitigated transfer of the vibration from the DFI to the cylinder head and allows for the transfer of heat by thermal conduction from the cylinder head to the DFI. Allowing the vibration from the DFI to propagate into the combustion chamber can adversely effect the placement of the highly precise fuel spray pattern into the combustion chamber. Moreover, allowing thermal conduction of heat from the cylinder head to the DFI can lead to injector tip plugging thereby affecting fuel metering and injector spray pattern. 
         [0005]    Prior attempts to isolate vibration and heat transfer between the DFI and the cylinder head have included, for example, the installation of a full-fitting isolation spacer between the bottom surface of the body of the DFI and the shoulder in the cylinder head bore such as a 360-degree plastic ring on top of a metal ring or a 360-degree rubber encapsulated metal ring. However, the high downward compressive pressure exerted on these existing rings and their plastic or rubber isolation materials during normal engine operation causes the materials to creep around the engaging surfaces, effectively reducing the isolation materials between the DFI and the cylinder head. Additionally, the large, cross-sectional area provided by the full-fitting isolation spacers increase the transfer of heat by conduction from the cylinder head to the DFI. The heat transferred by the spacer further promotes the creep of the existing plastic and rubber isolation materials. 
         [0006]    What is needed in the art is a method for effectively thermally and acoustically isolating the fuel injector from the cylinder head of an internal combustion engine. 
         [0007]    It is a principal object of the present invention to provide an isolator to be positioned between the fuel injector and the cylinder head that is thermally resistive and vibration absorbing and will not compress over time. 
       SUMMARY OF THE INVENTION 
       [0008]    Briefly described, a compression resistant isolator is positioned between a fuel injector and a cylinder head to minimize conductive heat transfer from the cylinder head to the fuel injector and to absorb vibration (noise) from the operating injector valve. The compression resistant isolator in accordance with the invention may be a spacer that holds the fuel injector and the cylinder head at a given axial distance from each other, thereby thermally and/or acoustically isolating the fuel injector from the cylinder head. 
         [0009]    The spacer is designed to minimize the cross-sectional area for conductive heat transfer and to maintain the injector location relative to the cylinder head. The rigid parts of the spacer are preferably made of thermally resistive materials. The remaining volume of the spacer may be filled, for example, by injection molding, with vibration absorbing and thermally resistive materials, or may be filled with ambient air if thermal isolation is of primary importance. Furthermore, the spacer may be designed to inhibit or prevent the isolation material from creeping away from the engaging surfaces under the clamping load compressive pressure. 
         [0010]    The implementation of the isolator in accordance with the invention may reduce the operating temperature of the fuel injector, especially of a direct fuel injector that is subjected to combustion chamber temperatures. 
         [0011]    In one aspect of the invention, the spacer may be designed as a rigid ring including provisions for an o-ring and/or an inner overmold. The upper o-ring glands prevent compression of the ring, while the elastomeric parts absorb vibration. 
         [0012]    In another aspect of the invention, the spacer may include two or more axial support members tied together by an annular collar to support the axial load of the injector. The surrounding volume and the radial space between the axial support members may be filled with a material that absorbs vibration and that is thermally non-conductive. In an alternative embodiment, the axial support members may be integral to the injector body eliminating the annular collar. The voids that exist between the axial support members may be filled with isolation material or ambient air. 
         [0013]    In still another aspect of the invention, the spacer is designed as a ring including outwardly extending features that support the axial load of the injector. The spacer may be a deep drawn part that is preferably comprised of a metal. The spacer may be either overmolded for thermal isolation and/or vibration absorption or left as is to utilize ambient air as the thermal isolator. 
         [0014]    In a further aspect of the invention, the spacer is formed of a powder metal. The voids in the powder metal provide a thermally non-conductive substrate. Notches formed on the interfacing surfaces of the spacer minimize thermal conduction between the injector and the cylinder head even further. The notches may also be filled with isolation material. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0016]      FIG. 1  is a side elevational view of a fuel injector-cylinder head assembly of an internal combustion engine, in accordance with the invention; 
           [0017]      FIG. 2  is a cross-sectional split view of an isolation spacer installed between the fuel injector and the cylinder head, in accordance with the invention; 
           [0018]      FIG. 3  is a top plan view of a second isolation spacer, in accordance the invention; 
           [0019]      FIG. 4  is an isometric view of the second isolation spacer integrated into the fuel injector; in accordance with the invention; 
           [0020]      FIG. 5  is a top view of a third isolation spacer, in accordance with the invention; 
           [0021]      FIG. 6  is a side elevational view of the third isolation spacer, in accordance with the invention; 
           [0022]      FIG. 7  is a side elevational view of the third isolation spacer installed between the fuel injector and the cylinder head, in accordance with the invention; 
           [0023]      FIG. 8  is a top plan view of a fourth isolation spacer, in accordance with the invention; 
           [0024]      FIG. 9  is a side elevational view of the fourth isolation spacer, in accordance with the invention; and 
           [0025]      FIG. 10  is a cross-sectional view of the fourth isolation spacer installed between the fuel injector and the cylinder head. 
       
    
    
       [0026]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates a preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    Referring to  FIG. 1 , a fuel injector-cylinder head assembly  10  of an internal combustion engine  70  includes a fuel injector  20 , a cylinder head  40 , and a compression resistant isolator  60  assembled there between. Fuel injector-cylinder head assembly  10  extends along an axis  12 . 
         [0028]    Fuel injector  20  includes a lower housing  22  and an injector tip  24  axially extending from lower housing  22 . Cylinder head  40  includes a stepped housing  42  having a center opening  44 . Fuel injector  20  is assembled in stepped housing  42  of cylinder head  40 , such that stepped housing  42  of cylinder head  40  accommodates lower housing  22  of fuel injector  20  and such that injector tip  24  extends through center opening  44  of cylinder head  40 . Fuel injector  20  may be, but is not limited to, a fuel injector for direct injection as shown in  FIG. 1 . 
         [0029]    Isolator  60  is positioned within stepped bore  42  such that isolator  60  is positioned adjacent to lower housing  22  encircling injector tip  24 . Accordingly, isolator  60  has an outer circumferential contour  62  that fits into stepped housing  42  and that is wider than center opening  44 . Isolator  60  further includes a center aperture  64  adapted to receive injector tip  24 . Isolator  60  is designed to withstand a compressive load from fuel injector  20 . Isolator  60  is further designed with a reduced cross-sectional area to reduce conductive heat transfer from cylinder head  40  to fuel injector  20 , and especially injector tip  24 , while maintaining the location of fuel injector  20  relative to cylinder head  40 . Isolator  60  is still further designed to absorb vibration (noise) from the injector&#39;s operating valve. Isolator  60  is formed of materials that will limit the isolator&#39;s compression and that provide thermal and/or acoustic isolation of fuel injector  20  from cylinder head  40 . Isolator  60 .may be formed from multiple materials. For example, the main body of isolator  60  may be formed of a compressively rigid and thermally resistive material and the remaining volume may be filled with a vibration absorbing and/or thermally resistive material, or may be left as is to use ambient air as a thermal isolator. Isolator  60  may be designed as an isolation spacer having a variety of configurations as shown in  FIGS. 2-10 . 
         [0030]    Referring to  FIG. 2 , a first isolation spacer  100  is shown assembled within stepped housing  42  of cylinder head  40  and adjacent to lower housing  22  of fuel injector  20 . As can be seen in the figure, isolation spacer  100  has an annular rigid body  110  that includes a radial flange  111  and a collar  113  forming recess  112  for radially receiving an o-ring  114 . Radial flange  111  extends outwards from collar  113  and faces lower housing  22  of fuel injector  20 . Collar  113  serves as a load bridge between the fuel injector and cylinder head thereby, while making minimal contact with the cylinder head, assisting in supporting an axial load of fuel injector  20 , and preventing compression of o-ring  114 . O-ring  114  disposed in recess  112  absorbs vibration from the cycling valve in fuel injector  20 . O-ring  114  may be replaced with another elastomeric material, such as an inner elastomeric overmold. 
         [0031]    To minimize conductive heat transfer from cylinder head  40  to fuel injector  20 , body  110  may be formed of a thermally non-conductive or thermally resistive material. Furthermore, body  110  of spacer  100  includes a larger width section  115  and a reduced width section  116 , that define a volume, such as chamber  45 . As a result, contact areas  118  between spacer  100  and injector tip  24  of fuel injector  20  as well as between spacer  100  and stepped housing  42  of cylinder head  40  are minimized, thereby reducing the areas of the path available for heat transfer from the engine. Chamber  45  may be filled with an isolation material, such as a material that absorbs vibrations from the injector&#39;s operating valve and/or with a material that may also be thermally non-conductive or thermally resistive. For example, ambient air may be used as thermal isolation. 
         [0032]    To further improve vibration-absorbing properties of spacer  100 , recess  112  may be filled completely or partially with an isolation material that is thermally non-conductive and absorbs vibration. It may further be possible to form spacer  100  from a metal that is overmolded, for example, with a thermally non-conductive material or thermally resistive material. 
         [0033]    Referring to  FIG. 3 , a second isolation spacer  200  includes rigid axial support members  212  tied together by an annular rigid collar  210 . Axial support members  212  support the axial load of fuel injector  20  When assembled, for example, in fuel injector-cylinder head assembly  10  shown in  FIG. 1 . Isolation spacer  200  including axial support members  212  may be a separate part as illustrated in  FIG. 3  or may be integral with lower housing  22  of fuel injector  10  as illustrated in  FIG. 4 . 
         [0034]    Axial support members  212  extend from an inner diameter  214  to an outer diameter  216  of spacer  200 . In the example shown, axial support members  212  do not extend radially beyond an outer circumferential contour of lower housing  22  of fuel injector  20 . Collar  210  may be positioned between inner diameter  214  and outer diameter  216 , for example, in the center of axial support members  212 . In the example shown having three support members, support members  212  may be preferably spaced apart from each other at  120  degrees. Arrangements of axial support members  212  at other angles may be possible. While three axial support members  212  are shown in  FIGS. 3 and 4 , it may be possible to design spacer  200  with two or more axial support members  212 . 
         [0035]    A radial space  217  formed between axial support members  212 , collar  210 , and an outer diameter  216  and a radial space  218  formed between axial support members  212 , collar  210 , and an inner diameter  214  may be filled with a material that absorbs vibrations form the oscillating fuel injector  20  and that may also be thermally non-conductive or thermally resistive. If not filled with a vibration absorbing material, ambient air is used as thermal isolation in spaces  217  and/or  218 . Collar  210  may be formed from a thermally resistive material. 
         [0036]    When integrated into lower housing  22  of fuel injector as shown in  FIG. 4 , collar  210  may be eliminated by extending axial support members  212  radially from a reduced diameter section  220  of lower housing  22 . The radial space  222  between axial support members  212  and between reduced diameter section  220  may be filled with a material that absorbs vibrations from the oscillating fuel injector  20  and that may also be thermally non-conductive or thermally resistive. If not filled with a vibration absorbing material, ambient air is used as thermal isolation in space  222 . 
         [0037]    Referring to  FIGS. 5 through 7 , a third isolation spacer  300  includes an annular body  310  and a plurality of rigid tabs  312  radially spaced along and outwardly protruding from an outer circumferential contour of body  310 . Body  310  and tabs  312  have preferably the same height  314  as shown in  FIG. 6 . Tabs  312  help support the axial load of fuel injector  20  when assembled between fuel injector  20  and cylinder head  40  as shown in  FIG. 7 . 
         [0038]    Body  310  and tabs  312  may be formed from a rigid thermally resistive material or may be, for example, a stamped or deep drawn part comprised, for example, of a metal. The deep drawn part may be overmolded with an elastomeric material for vibration absorption or may be left as is to utilize ambient air as the thermal isolator. It may further be possible to fill the radial space between tabs  320  with a material that is vibration-absorbent and that may also be thermally non-conductive. 
         [0039]    Referring to  FIGS. 8 through 10 , a fourth isolation spacer  400  includes an annular body  410  having a plurality of notches  412  integrated in the interfacing surfaces  414 . Spacer  400  may be formed from a powder metal. The voids in the powder metal provide a thermally non-conductive substrate for body  410 . 
         [0040]    Notches  412  minimize contact areas  418  between spacer  400  and lower housing  22  of fuel injector  20  as well as between spacer  400  and stepped housing  42  of cylinder head  40 , thereby minimizing thermal conduction between fuel injector  20  and cylinder head  40  when spacer  400  is installed between fuel injector  20  and cylinder head  40 . The size and number of notches  412  is chosen such that a desired support of the axial load of fuel injector  20  by spacer  400  is achieved. While notches are shown in  FIG. 9  as having a rectangular cross-section, other cross-sections may be used. It may be possible to fill notches with an acoustical and/or thermal isolation material. 
         [0041]    The implementation of a compression resistant isolator  60  (as shown in  FIG. 1 ), such as isolation spacers  100 ,  200 ,  300 , and  400  (as shown in  FIGS. 2-10 ) thermally isolates fuel injector  20  from cylinder head  40  reducing the operating temperature of the tip of the fuel injector. By keeping the temperature of injector tip  24  relatively low, plugging of the injector tip  24  is reduced. 
         [0042]    Furthermore, implementation of a compression resistant isolator  60  (as shown in  FIG. 1 ), such as isolation spacers  100 ,  200 ,  300 , and  400  (as shown in  FIGS. 2-10 ) acoustically isolates fuel injector  20  from cylinder head  40  by absorbing vibration (noise) from the oscillating fuel injector  20 . 
         [0043]    While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described aspects, but will have full scope defined by the language of the following claims.