Abstract:
A fuel injector assembly comprising an injector body having a leading end, a fuel inlet passage, a backleak passage and a trailing end that terminates in an end surface; a cap that fits over the trailing end of the injector body to define therebetween a chamber for receiving fuel from said backleak passage; and a seal for sealing said chamber to prevent the flow of fuel therefrom, wherein said seal is disposed between said end surface of the trailing end and an inlet end of said fuel inlet passage.

Description:
FIELD OF THE INVENTION 
     The invention relates to fuel injector assemblies and to engines comprising such fuel injector assemblies. 
     BACKGROUND TO THE INVENTION 
     Conventional fuel injectors have an axially extending threaded connection at their trailing end for attachment to a high pressure fuel delivery pipe. The minimum bend radius permitted in this pipe can cause installation problems and limits the height of the assembly. 
     It is known to provide fuel injectors that have an injector body provided with an entry projecting from the side of the injector body for connection to the high pressure fuel delivery pipe. This arrangement avoids, or at least reduces, the height problem. However, such side entry fuel injectors give rise to problems where an engine top cover is to be installed over the installed injector. Specifically, such covers include an aperture to allow the cover to be installed over the fuel injector and the aperture is fitted with an aperture seal. If such a cover is fitted over an installed side entry injector, the aperture seal may be damaged or destroyed. If the side entry is not perpendicular to the injector body, it may be possible to avoid this problem by removing the seal prior to installing the engine cover and subsequently fitting and adjusting the seal. However, this increases the installation work required and if the angle of the side inlet is made steeper relative to the injector body to make it easier to install the engine cover, the height reduction benefit obtained by having a side entry is reduced. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention, there is provided a fuel injector assembly comprising: 
     an injector body having a leading end, a fuel inlet passage, a backleak passage and a trailing end that terminates in an end surface; 
     a cap that fits over the trailing end of the injector body to define therebetween a chamber for receiving fuel from said backleak passage; and 
     a seal for sealing said chamber to prevent the flow of fuel therefrom, wherein said seal is disposed between said end surface of the trailing end and an inlet end of said fuel inlet passage. 
     Thus, the present invention provides a fuel injector assembly having a backleak chamber that is of simple construction. 
     Advantageously, said seal comprises an O-ring. Conveniently, said cap comprises a substantially cylindrical body having a groove formed on an inner surface thereof for seating said O-ring. Alternatively, or in addition, said injector body may comprise a groove for seating said O-ring. 
     Conveniently, the inlet end of the fuel inlet passage is defined in a sidewall of the injector body, and said cap comprises an opening, through which, in use, fuel is supplied to said fuel inlet passage. 
     Advantageously, the fuel injector assembly comprises an inlet connector having a fuel delivery passage and being securable to said cap such that it extends through said opening and fuel can pass from said fuel delivery passage into said fuel inlet passage. 
     Conveniently, said cap comprises an outlet that is connectable to a backleak return pipe and in flow communication with said chamber. 
     In a second aspect of the present invention, an internal combustion engine fitted with a fuel injector assembly according to the first aspect of the present invention is provided. Conveniently, said engine is fitted with a cover and said trailing end of the injector body and said cap are disposed externally of said cover. 
     According to a third aspect of the present invention, there is provided a fuel injector assembly comprising: 
     an injector body having a leading end, a fuel inlet passage, a backleak passage and a trailing end that terminates in an end surface; 
     a cap that fits over the trailing end of the injector body to define therebetween a chamber for receiving fuel from said backleak passage; and 
     a seal for sealing said chamber to prevent the flow of fuel therefrom, wherein said seal is disposed between said end surface of the trailing end and an inlet end of said fuel inlet passage; wherein said seal comprises an O-ring; 
     wherein the inlet end of the fuel inlet passage is defined in a sidewall of the injector body, and said cap comprises an opening, through which, in use, fuel is supplied to said fuel inlet passage. 
     According to a fourth aspect of the present invention, there is provided a fuel injector assembly comprising: 
     an injector body having a leading end, a fuel inlet passage, a backleak passage and a trailing end that terminates in an end surface; 
     a cap that fits over the trailing end of the injector body to define therebetween a chamber for receiving fuel from said backleak passage; and 
     a seal for sealing said chamber to prevent the flow of fuel therefrom, wherein said seal is disposed between said end surface of the trailing end and an inlet end of said fuel inlet passage, wherein said seal comprises an O-ring; and 
     wherein said cap comprises an outlet that is connectable to a backleak return pipe and in flow communication with said chamber. 
     Preferred and/or optional features of the first, third and fourth aspects of the invention may be incorporated within the internal combustion engine of the second aspect, alone or in appropriate combination. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a partial cross-sectional view of a fuel injector installed in an engine top cover looking in the direction of the arrows I in  FIG. 2 ; 
         FIG. 2  is a plan view of the fuel injector looking from above as viewed in  FIG. 1 ; 
         FIG. 3  is a partial cross-sectional view of a fuel injector installed in an engine top cover looking in the direction of the arrows I in  FIG. 4 ; and 
         FIG. 4  is a plan view of the fuel injector looking from above as viewed in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring to  FIGS. 1 and 2 , a fuel injector  10  comprises an injector body  12  and a fitting in the form of a cap  14  that fits onto the injector body. The injector body  12  is essentially a plain cylinder and has a leading end  16  fitted with a nozzle  18  (indicated schematically) and a trailing end  20 , on which the cap  14  is fitted. The leading end  16  of the injector body and nozzle components may be of any suitable known type and may include features to assist with fitting and sealing in a port  68  of an engine  66 . 
     The injector body  12  is provided with a backleak passage  22  that extends from an inlet end (not shown) to an outlet end  24  that is located in a transverse end surface  26  of the injector body. The injector body  12  is additionally provided with a fuel inlet passage  30  that extends in the lengthways direction of the injector body parallel to the axis  34  of the injector body. The fuel inlet passage  30  serves to deliver high pressure fuel to the leading end  16  of the injector body for supply to an engine  66  via the nozzle  18 . The fuel inlet passage  30  has an inlet end  32  defined by a cross drilling that extends perpendicular to the axis  34  of the injector body  12  through the side of the injector body. The inlet end  32  of the fuel inlet passage includes a conical sealing surface for mating with an inlet connector  36 . 
     The cap  14  is a metal part comprising a generally cylindrical body  38  that is closed at one end by a transverse wall  40  and is sized to be a clearance fit over the trailing end  20  of the injector body  12 . The inside of the cylindrical body  38  is provided with a groove, in which an O-ring  42  is seated for sealing against the injector body  12 . However, it will be appreciated that the injector body  12  may instead be provided with the groove, in which the O-ring  42  is seated for sealing against the inside of the cylindrical body  38 . Alternatively, corresponding grooves could be formed in both the cylindrical body  38  and the injector body  12 . 
     The cap  14  is provided with a generally tubular extension  44  that is formed integrally with the cylindrical body  38  and projects from the body substantially perpendicular to the axis of the body  38 . The tubular extension  44  defines an opening in the cap  14 , through which fuel is supplied to the inlet end  32  of the fuel inlet passage  30 . 
     The inlet connector  36  is a generally cylindrical body provided with an axially extending fuel delivery passage  46  that is made up of a series of drillings. Those drillings may include one that is sized to receive an edge filter  48 . The drilling at the upstream end of the fuel delivery passage  46  provides a conical surface  50  for sealingly engaging a suitably shaped end of a high pressure fuel delivery pipe (not shown). At the same end, the inlet connector  36  is provided with external threading  49 , by means of which a union nut can be used to couple the high pressure fuel delivery pipe to the inlet connector  36 . 
     The leading end of the inlet connector  36  has a conical surface  52  that leads into an externally threaded portion  54  that engages an internal threading  55  provided at the inner end of the tubular extension  44  of the cap  14 . A hexagonal formation  56  is provided on the inlet connector  36  so that it can be firmly secured to the cap  14  by screwing the threading  54  into the internal threading  55  of the tubular extension  44 . The conical surface  52  is shaped to complement the conical sealing surface of the inlet end  32  of the fuel inlet passage  30  so that when the inlet connector  36  is screwed into position in the tubular extension  44 , the two surfaces mate to form a seal between the inlet connector  36  and the injector body  12 . The engagement between the two conical surfaces additionally fixes the cap  14  to the injector body  12  so that relative movement between the two parts  12 ,  14  is substantially prevented. 
     When the cap  14  is secured in place on the free end  20  of the injector body  12 , the transverse wall  40  is disposed opposite and spaced apart from the transverse end surface  26  of the injector body  12  to define a backleak vent chamber  60  therebetween, in which fuel from the backleak passage  22  is received. The cap  14  is provided with an outlet connection  62  for connection to a backleak return pipe (not shown). In the embodiment, the outlet connection  62  is a push-fit connector, on which a backleak return pipe can sealingly engage by push-fitting, although alternative connections (such as, for example, a screwed fitting) can be used. The outlet connection  62  is in fluid communication with the backleak vent chamber  60  so that backleak fuel from the chamber  60  can flow into the backleak return pipe for return to a low pressure fuel reservoir. 
     In use, the injector assembly  10  is fitted to an engine  66  by first fitting the leading end  16  of the injector body  12  (without the cap  14  and inlet connector  36 ) into an inlet port  68  in the engine cylinder head. An engine top cover  70  is then fitted over the injector body  12  onto a cover seat provided on the engine such that the trailing end  20  of the injector body projects through an aperture provided in the engine top cover (in practice a multi-cylinder engine will have a plurality of injector bodies fitted in respective inlet ports  68  and the engine top cover will have respective apertures for the injectors). The engine top cover  70  is provided with a sealing element  72  around the aperture, which sealingly engages the injector body  12 . 
     Once the engine top cover  70  is secured in place, the cap  14  is fitted onto the trailing end  20  of the injector body  12  bringing the O-ring  42  provided on the cylindrical portion  38  of the cap  14  into engagement with injector body  12 . It is preferred that, prior to fitting the cap  14 , the tubular extension  44  is at least roughly aligned with the inlet end  32  of the fuel inlet passage  30 . The inlet connector  36  is then inserted into the tubular extension  44  of the cap  14  and rotated to bring the threading  54  into engagement with the internal threading  55  of the tubular extension. When the conical surface  52  of the inlet connector  36  starts to engage the conical sealing surface of the inlet end  32  of the fuel inlet passage  30 , any misalignment will be corrected automatically and the inlet connector  36  can be screwed firmly into position by means of a spanner applied to the hexagonal formation  56 . If the tubular extension  44  is not well aligned with the inlet end  32  of the fuel inlet passage  30  when the leading end of the inlet connector  36  is screwed in, the cap  14  can be rotated relative to the injector body  12  until the conical surface  52  is felt to engage in the conical sealing surface of the inlet end  32 . Once the inlet connector  36  is firmly screwed into position, relative movement between the cap  14  and injector body  12  is substantially prevented and the backleak vent chamber  60  is sealed against leakage between the cap  14  and injector body  12  by the O-ring  42 . 
     To complete the fitting process, a high pressure fuel delivery pipe (not shown) is secured to the inlet connector  36  by pressing the end of the pipe into the conical surface  50  and threading a union nut onto the threading  49 . Additionally, a backleak pipe (not shown) is push-fitted onto the outlet connection  62 . 
     It will be appreciated that the embodiment provides a side entry fuel injector  10  that can easily be installed to an engine fitted with an engine top cover  70 . Since the injector body  12  can be installed separately from the cap  14  and inlet connector  36  and is simply a generally cylindrical body, it is relatively easy to fit the engine top cover  70  over the installed injector body  12  without the risk of damaging or destroying the engine top cover aperture seal  72 . The cap  14  and inlet connector  36  can easily be fitted to the injector body  12  once the engine top cover  70  is installed. Thus, the advantages of height reduction available when side entry fuel injectors are used can be readily obtained even when an engine top cover has to be installed over the fuel injectors. 
     It will further be appreciated that the above-described embodiment provides an injector assembly having a backleak chamber that can be sealed by means of a single O-ring. Accordingly, the manufacturing cost, assembly time, and associated assembly cost, are minimized. 
     As mentioned previously, the O-ring  42  is preferably retained in a groove formed on the inside surface of the cylindrical body  38  of the cap  14 . Accordingly, during assembly, the O-ring  42  is placed in the groove and the cap  14  is pushed onto the trailing end  20  of the injector body  12 . In the case that the groove is formed on the outside surface of the injector body  12 , the O-ring  42  is first pressed over the trailing end  20  of the injector body  12  in order to locate it in the groove and, subsequently, the cap  14  is push-fitted in place on the trailing end  20  of the injector body  12 . With both of the aforementioned configurations, the fact that the O-ring  42  is disposed between the end surface  26  of the injector body  12  and the inlet end  32  of the fuel inlet passage  30  means that there is no risk of the O-ring  42  being damaged by the edges of the cross drilling at the inlet end  32  of the fuel inlet passage  30  during assembly. Such damage could occur if the O-ring  42  were disposed at a point further along the injector body  12 , closer to the nozzle  18 , and on the opposite side of the inlet end  32  of the fuel inlet passage  30 . 
     A further advantage of the above-described embodiment is that, by virtue of the fact that the O-ring  42  is disposed between the end surface  26  of the injector body  12  and the inlet end  32  of the fuel inlet passage  30 , the high pressure fuel connection between the inlet connector  36  and the injector body  12  is disposed outside of the backleak chamber  60 . Accordingly, in the event that the inlet connector  36  is not properly mated with the conical surface at the inlet end  32  of the fuel inlet passage  30 , either during assembly or subsequent servicing, any fuel leakage will be visible on the outside of the injector body  12 . For example, fuel may leak out from the open end of the cylindrical body  38  of the cap  14 . This is convenient since it provides a clear indication that there is a fault with the injector assembly  10 . By contrast, if the inlet connector  36  were disposed within the backleak chamber  60 , any fuel leakage would flow into the backleak chamber  60  and through the backleak return pipe to the low pressure fuel reservoir. This would mean that any fault may go unrecognized. Thus, in the event of a fault, the injector assembly of the described embodiment increases the chances of the fault being diagnosed. 
     It will be appreciated that the backleak vent chamber  60  does not have to be provided between the transverse end surface  26  of the injector body  12  and the transverse wall  40  of the cap  14 . Instead, a fitting could be provided with a suitably positioned recess such that the backleak vent chamber is defined between the fitting and a sidewall of the injector body  12 . 
     It will be appreciated that the position of the outlet connection of the cap  14  or fitting can be selected to accord with a particular engine, to which it is to be installed so as to provide optimum routing of the backleak return. One alternative position for the outlet connection is indicated by dashed lines in  FIG. 2 . Alternatively, the cap  14  may be provided with two outlet connections  62  in order to facilitate the connection of the backleak chambers of each of a plurality of injectors of the engine in series. 
       FIG. 3  shows an alternative configuration of the engine top cover aperture seal  72 .  FIG. 4  shows alternative positions of the outlet connections  62 . 
     It is envisaged that the cap  14  or fitting will be made of a suitable metal, for example steel. However, it might also be made of a non-metallic material that has the required properties such as ceramics or suitable engineering plastics.