Abstract:
A fuel injection system for an internal combustion engine includes a fuel injector pocket, formed within a cylinder head, for housing an injector which sprays fuel into a combustion chamber defined by the cylinder head and a piston crown. The injector is mounted with an isolator which is loaded at a lower, elastic rate during lower power operation, with the elastic load element being stacked solid and subject to higher rate column loading during high power operation of the engine and injection system. The isolator controls unwanted injector ticking noise, while protecting the integrity of the injector&#39;s tip seal.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. Provisional patent application 61/144,513, Filed on Jan. 14, 2009, which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an internal combustion engine having fuel injectors mounted within a cylinder head and spraying fuel into the engine&#39;s combustion chambers. 
         [0004]    2. Related Art 
         [0005]    Most spark ignited internal combustion engines used in automotive vehicles have employed fuel systems with either a carburetor, or more recently, multiple fuel injectors mounted in an intake manifold or within individual intake ports. Each of these systems provides fuel to the engine via the intake manifold. Although manifold/port mounted fuel injectors have generally been satisfactory, and indeed, a great improvement as compared with carburetor systems, automotive designers are increasingly moving to the use of direct fuel injection with spark ignited engines. With a direct injection system, fuel injectors are typically mounted through the fire deck of the engine&#39;s cylinder head and provide fuel directly into each of the engine&#39;s combustion chambers. 
         [0006]    As used with spark ignition engines, direct injection has been found to be beneficial in terms of improved fuel economy, coupled with reduced exhaust emissions. Although direct injection has been used in many types of diesel engines for years, this new application of direct injection in gasoline engines intended for use in automotive vehicles has created a problem because the higher pressures utilized with direct injection have caused unwanted noise or “tick” while the engine is idling; under certain cases the tick may become more pronounced at high speeds and loads. This tick noise, resulting from injector needle impact, has not generally been a problem with most diesel engines, but has definitely proved to be an issue with direct-injected spark ignited engines, as well as with some diesel engines. 
         [0007]    It would be desirable to provide a system allowing a low noise signature for gasoline and diesel direct injection fuel systems, while at the same time preserving the durability of fuel injectors. This presents a challenge, because if the injector&#39;s mounting is softened to the point where ticking noise is attenuated at idle, the corresponding movement of the injector within the cylinder head&#39;s injector pocket at high loads may cause adverse durability affects upon injector tip seals. 
       SUMMARY OF THE INVENTION 
       [0008]    According to an aspect of the present invention, a fuel injection system for an internal combustion engine includes a cylinder head and an injector pocket formed in the cylinder head, with the pocket having a lower wall and an outer wall. A fuel injector is mounted within the injector pocket. An isolator is mounted between the injector and the lower wall of the injector pocket. The isolator includes an isolation ring having a generally annular base in contact with the lower wall and the outer wall. The isolation ring further includes an annular, cantilevered, inwardly extending load member having an upper contact surface extending above the annular base, with the annular load member being loaded elastically in bending during operation of the injector at idle, and with the annular base being column loaded compressively during higher-load operation of the injector. 
         [0009]    According to another aspect of the present invention, an isolator may further include a pusher ring, interposed between the upper contact surface of the isolation ring load member and a lower portion of the fuel injector, with the pusher ring bearing upon only the load member during operation of the injector at idle, but with the pusher ring bearing upon the load member and upon the annular base during higher-load operation of the injector. The upper contact surface of the load member and the upper contact surface of the annular base define a static clearance gap which must be closed by force imposed by the injector and pusher ring upon the load member in order for both the load member and the upper portion of the annular base of the isolator to react to loads from the pusher ring and injector. 
         [0010]    According to another aspect of the present invention, a method for mounting a fuel injector to a cylinder head of an internal combustion engine includes forming a pocket in a cylinder head with the pocket having a lower wall and an outer wall, and mounting a fuel injector within the pocket, with an isolator interposed between the injector and the lower wall of the injector pocket. The method further includes reacting to lower amplitude, axially directed injector forces with an elastic load member incorporated within the isolator, and reacting to higher amplitude, axially directed injector forces with a column loaded portion of the isolator. 
         [0011]    According to an aspect of the invention, the elastic load member comprises an annular, cantilevered, inwardly extending load member, as described above, and having an upper contact surface extending above an annular base seated against the lower wall of the injector pocket. 
         [0012]    It is an advantage of a fuel injection system according to the present invention that objectionable ticking noise which is particularly prevalent in engines having direct cylinder injectors, will be avoided, while at the same time protecting injector tip seals from harm which could otherwise occur as a result of a compliant and quiet mounting system. 
         [0013]    It is an advantage of a system according to the present invention that a dual rate load deflection curve is established for the response of the injector mount to the pressures imposed upon the injector while the injector is operating at any regime from idle to full output. 
         [0014]    It is yet another advantage of a fuel injection system according to the present invention that the isolator used in the present system is readily tunable to accommodate changes in engine operating parameters. 
         [0015]    Other advantages, as well as features of the present invention, will become apparent to the reader of this specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a schematic representation of a portion of an engine having a fuel injection system according to the present invention. 
           [0017]      FIG. 2  is a partially schematic representation of an injector mounted in a cylinder head according to an aspect of the present invention. 
           [0018]      FIG. 3  shows a portion of the injector of  FIG. 2  with specificity related to the isolator portion of the injector mounting system. 
           [0019]      FIGS. 3A and 3B  illustrate individual components of a two-piece isolation system according to the present invention. 
           [0020]      FIG. 4  is an enlargement of a portion of  FIG. 3 , showing an isolation system in greater detail. 
           [0021]      FIG. 5  shows the isolation system of  FIG. 4  in a compressed state corresponding to high load operation. 
           [0022]      FIG. 6  illustrates an alternative embodiment in which the isolation device includes a single isolation ring. 
           [0023]      FIG. 7  shows a force/displacement curve for both a prior art isolator and a device according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]      FIG. 1  illustrates an engine,  2 , having a crankshaft,  8 , with a piston,  4 , and a connecting rod,  6 , attached thereto, for reciprocating motion within a cylinder,  5 , formed in a cylinder block,  16 . A cylinder head,  26 , is mounted at the top of engine  2 . A fuel injector,  10 , is mounted through cylinder head  26  so as to supply fuel directly to the combustion chamber defined by cylinder head  26  and piston  4 . 
         [0025]      FIG. 2  is a partially schematic representation of a fuel injection system having an injector isolator according to an aspect of the present invention. Fuel injector  10  receives fuel through a supply system including a fuel rail cap,  12 , which is mounted to the top of injector  10 . Injector  10  has a generally cylindrical outer body,  14 , which is mounted within an injector pocket,  30 , formed in cylinder head,  26 . Injector  10  has a tip,  18 , with a tip seal,  22 , which is preferably formed from a plastics material such as polytetrafluoroethylene. Injector tip  18  extends through fire deck  34  of cylinder head  26 . Because fire deck  34  and the upper surface of piston  4  configure a combustion chamber, injector  10  is deemed to be a direct injector. Tip seal integrity is important because the tip seal prevents high pressure gases from leaking from the combustion chamber past the injector. 
         [0026]    Injector pocket  30  has an outer wall,  30   a , which is generally cylindrical, and a lower wall,  30   b , which is generally annular. Injector  10  is mounted within injector pocket  30  including surfaces  30   a  and  30   b , with an isolator,  43 , being mounted between injector  10  and lower wall  30   b  of injector pocket  30 . 
         [0027]      FIGS. 3 ,  3 A,  3 B,  4  and  5  illustrate various details of isolator  43  and show interaction with injector  10  and with injector pocket  30 , including surfaces  30   a  and  30   b . According to an aspect of the present invention, isolator  43  includes an isolation ring,  42 , and a pusher ring,  49 . Isolation ring  42  has a generally annular base,  44 , which is in contact with lower wall  30   b  of injector pocket  30 . Annular load member  46  is cantilevered from base  44  and extends inwardly from base  44 . Load member  46  has an upper contact surface,  48 , which extends above annular base  44 .  FIG. 3A  is a perspective view of a pusher ring  49 , and  FIG. 3B  is a perspective view of isolation ring  42 . Pusher ring  49  is interposed between upper contact surface  48  of primary ring  42  and a wedge-shaped lower portion,  40 , of injector  10 . Pusher ring  49  has an injector contact surface,  56 , which interacts with lower portion  40  of injector  10 . Pusher ring  49  also has a lower contact surface,  50 , which contacts upper contact surface  48  of load member  46 , causing load member  46  to deflect downward, so as to close axial clearance gap  58  ( FIG. 4 ) in response to axially directed force from injector  10 . This force is applied in the Z direction noted in the various Figures. 
         [0028]    As best seen in  FIG. 4 , upper contact surface  48  of isolation ring  42  and lower contact surface  50  of pusher ring  49  define a static, axial clearance gap,  58  extending between surfaces  54  and  50 . Gap  58 , which exists during idle and lower power operation of engine  2 , allows pusher ring  49  to bear upon only annular load member  46  of isolation ring  42 . In this manner, vibration of injector  10  is results in elastic bending or loading of load member  46 . This compliance prevents unwanted injector tick noise at idle and lower power operation. On the other hand, during higher power operation, shown in  FIG. 5 , load member  46  is deformed elastically by an amount sufficient to close axial clearance gap  58  to a point at which annular base  44  of isolation ring  42  is subjected to column loading by surface  50  of pusher ring  49 . In effect, pusher ring  49  and isolation ring  42  are stacked solid, and further increases in axially directed force will cause little change in the deflection of ring  42  and pusher  49 . In this manner, unwanted movement of injector  10 , and particularly, unwanted motion of injector tip  18 , will be prevented. 
         [0029]    One of the effects of the present invention is depicted graphically in  FIG. 7 , which includes two plots of force and resultant axial displacement for an injector. The axial, or Z, direction is shown in  FIGS. 2 ,  3 ,  4 ,  5 , and  6 . Curve A in  FIG. 7  shows a very aggressive force displacement curve typical of a conventional steel isolator ring. This ring will exhibit undesired tick noise because the applied force builds too rapidly with displacement. 
         [0030]    Curve B in  FIG. 7  shows the dual rate force/displacement trend of the present inventive isolator. For lower force levels imposed by injector  10  upon the isolator, increasing, but controlled displacement is permitted with a relatively soft force/displacement characteristic. However, when a tunable force threshold is reached, load member  46  will deform elastically to the degree that surfaces  50  and  54  will abut, or stack solid, which will have the effect of greatly increasing the force/displacement characteristic, or stiffness, of isolator  43 , thereby protecting the integrity of injector tip seal  22 . As noted above, this condition is depicted in  FIG. 5 . 
         [0031]      FIG. 6  illustrates an embodiment of the present invention in which injector  10  has a blunt end,  38 , formed thereupon, with end  38  interacting directly with isolation ring  42 . The embodiment of  FIG. 6  operates in much the same manner as the embodiment shown in the previous figures, it being understood that upper annular surface  54  of annular base  44  and the lowermost portion of squared-off injector base  38  define an annular gap,  62  which when closed, will mean that not only load member  46 , but also annular portion  44 , will react against the axial forces imposed upon isolation member  42  in the illustrated Z direction.  FIG. 6  shows an injector operating either at idle or another low power regime. 
         [0032]    In a preferred embodiment, pusher ring  49  is configured from steel, for strength reasons. Isolation ring  42  is preferably configured from a dissimilar material, such as aluminum or a plastics material, such as polytetrafluoroethylene. Contructing rings  42  and  49  from dissimilar materials provides beneficial friction damping between the two rings. 
         [0033]    The foregoing invention has been described in accordance with the relevant legal standards, thus the description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiment may become apparent to those skilled in the art and fall within the scope of the invention.