Patent Publication Number: US-6905083-B2

Title: Internal combustion engine fuel injector and relative fabrication method

Description:
The present invention relates to an internal combustion engine fuel injector comprising an injector body having a seat for a metering valve in turn having an injector control rod control chamber; and to a method of fabricating the injector. 
     BACKGROUND OF THE INVENTION 
     As is known, the injector metering valve control chamber is supplied with pressurized fuel by an inlet conduit communicating with the delivery side of a high-pressure pump via a high-pressure fuel vessel common to all the injectors, and also has a drain conduit normally closed by a shutter controlled by the armature of an electromagnet. 
     The metering valve of the injector is normally defined by a valve body in the form of a sleeve closed at one end by an end wall comprising the drain conduit of the control chamber; the lateral wall of the sleeve guides the control rod controlling opening of the injector nozzle, and comprises the control chamber inlet conduit; and the valve body is housed in a seat in the injector body, and has a flange which is locked hermetically against a shoulder of the injector body by a threaded ring nut. 
     Known injectors of this sort have various drawbacks. In particular, machining inside the valve body is difficult, especially in the region of the end wall which must define the precise volume of the control chamber; the outer surface of the sleeve must form a chamber for distributing fuel from the delivery side of the high-pressure pump to the control chamber inlet conduit, so that one or more high-pressure fuel seals must be provided between the outer surface of the sleeve and the relative seat in the injector body; the presence of the seals complicates assembly of the injector components; and the locking action of the ring nut on the valve body flange is distributed over a relatively extensive area of the flange. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an internal combustion engine fuel injector which is extremely reliable, is cheap and easy to produce, and provides for eliminating the drawbacks of known injectors. 
     According to the present invention, there is provided an internal combustion engine fuel injector comprising an injector body having a seat for a metering valve in turn having a control chamber for controlling a control rod; said control chamber having a pressurized-fuel inlet conduit, and a drain conduit controlled by a corresponding shutter; characterized in that said control chamber is defined by two coaxial parts fixed in said seat; one of said parts guiding said control rod and having one of said conduits; and the other of said parts closing said control chamber and having the other of said conduits. 
     According to the present invention, there is also provided a fabrication method, characterized by comprising the steps of:
         forming said injector body with a seat for said metering valve;   forming said control chamber in two parts, one for guiding said control rod and having one of said conduits, and the other for closing said control chamber and having the other of said conduits;   subsequently inserting said parts inside said seat; and   locking said parts to each other in said seat by means of a fastening member.       

     Given the importance of the response time of injector metering valves to control by the electromagnet, and since response time can be adjusted by adjusting the diameter of the control chamber inlet and/or drain conduit, the metering valve must have a given pair of conduit diameters for each type of engine. In known technology, for a given injector, a wide range of metering valves must therefore be fabricated, each with the given pair of conduit diameters designed for the type of engine to which the injector is fitted. The injectors according to the invention therefore have the advantage of enabling the two component parts of the metering valve control chamber to be selected, at assembly, with the required two conduit diameters, thus simplifying part storage during fabrication. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A number of preferred, non-limiting embodiments of the invention will be described by way of example with reference to the accompanying drawings, in which: 
         FIG. 1  shows a partial mid-section of a fuel injector in accordance with a first embodiment of the invention; 
         FIG. 2  shows a larger-scale section of a detail in  FIG. 1 ; 
         FIG. 3  shows the same section of a variation of the  FIG. 2  embodiment; 
         FIG. 4  shows a partial mid-section of a further embodiment of the invention; 
         FIG. 5  shows the same section of a variation of the  FIG. 4  embodiment; 
         FIG. 6  shows a partial mid-section of a further embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Number  5  in  FIG. 1  indicates as a whole an internal combustion engine fuel injector comprising a hollow, tapering injector body  6  having an axis  7  and shown only partly in FIG.  1 . One end of injector body  6 , at the bottom in  FIG. 1 , has a nozzle (not shown) with one or more injection orifices normally closed by a pin. Injector body  6  also comprises an appendix  8  having a pressurized-fuel supply conduit  9  communicating with a fitting  10  connected to a high-pressure fuel pump via a high-pressure fuel vessel or so-called common rail common to all the injectors on the engine. 
     Conduit  9  communicates with the injector nozzle via a conduit  11 . The pin closing the nozzle is normally kept in the closed position by a cylindrical control rod  12  movable axially along a seat  13  formed in injector body  6  and coaxial with axis  7 . Control rod  12  is controlled by a metering valve indicated as a whole by  14  and controlled by a normally de-energized electromagnet  15  housed in another seat  16  formed in injector body  6 , at the opposite end to the nozzle, and also coaxial with axis  7 . More specifically, electromagnet  15  controls an armature  17  which is movable, and secured in any known manner, inside seat  16 , and which is pushed by a spring  18  to act on a shutter of valve  14  defined, for example, by a ball  19  associated with a plate  21  having a locating cavity. 
     Metering valve  14  is housed in another seat  23  coaxial with axis  7  and between seat  13  of rod  12  and seat  16  of electromagnet  15 , and comprises a control chamber  24  having a fuel inlet conduit with a calibrated hole  26 , and a fuel drain conduit with another calibrated hole  27 . Calibrated hole  27  is normally closed by ball  19  of shutter  19 ,  21 , while pressurized fuel is fed continually into control chamber  24  through calibrated hole  26 , and pushes rod  12  downwards into the  FIG. 1  position to keep the nozzle of injector  5  closed. 
     When electromagnet  15  is energized, armature  17  is raised to release plate  21  and ball  19 , so that the fuel in control chamber  24  is drained through calibrated hole  27  and a drain chamber  28 , and rod  12  is raised by the pressure of the fuel acting on the opposite end, and possibly also by an auxiliary spring (now shown), so that the pin opens the nozzle. 
     According to the invention, control chamber  24  is formed in two coaxial parts  29 ,  31  fixed inside intermediate seat  23  in injector body  6 . One of the two parts is defined by a hollow member defined by a cylindrical bush  29 , which is fixed inside intermediate seat  23  as shown in detail later on, comprises calibrated hole  26  of the inlet conduit, and has a cylindrical through opening  32  in which is guided a portion  33  of control rod  12 . The other of the two parts defining control chamber  24  is defined by a plug member  31  having calibrated hole  27  of the drain conduit, and which is also fixed inside intermediate seat  23  of body  6 . 
     Cylindrical opening  32  of bush  29  must be precision machined to guide portion  33  of rod  12  accurately in its movement, while at the same time sealing in the pressurized fuel; portion  33  comprises two annular grooves  34  for lubricating opening  32  with the same fuel; plug member  31  comprises a bottom surface  35  for arresting an end surface  36  of rod  12  defining the bottom of control chamber  24 ; and end surface  36  is truncated-cone-shaped so as to leave the outlet of inlet conduit  26  clear even when rod  12  is in the top limit position. 
     Bush  29  has a precision machined cylindrical outer surface  37  comprising an annular groove  38  forming a distribution chamber for distributing pressurized fuel from conduit  9  to calibrated hole  26  of the inlet conduit of control chamber  24 , and terminates with two annular end edges  39  and  41 , which are also precision machined, also as regards squareness with respect to axis  7 . 
     The diameter of portion  33  of rod  12  may advantageously be at least half the diameter of outer surface  37  of bush  29 . Preferably, the diameter of portion  33  of rod  12  may be roughly 4.3 mm, and the diameter of outer surface  37  may be 8 mm or less. 
     Intermediate seat  23  of metering valve  14  comprises a top portion  42 , a perfectly cylindrical intermediate portion  43 , and a bottom portion  44 . Top portion  42  is threaded for the purpose explained later on; cylindrical intermediate portion  43  is precision machined to receive surface  37  of bush  29 ; and bottom portion  44  of seat  23  is slightly larger in diameter than intermediate portion  43 , and forms an annular shoulder  46  with seat  13 . 
     To fix bush  29  inside intermediate seat  23 , cylindrical portion  43  of seat  23  and outer surface  37  of bush  29  are machined to interfere slightly, so that bush  29  can be driven easily inside seat  23  with no danger of deforming bush  29  or injector body  6 , while at the same time ensuring perfect sealing of the pressurized fuel in annular groove  38 , both upwards in FIG.  1  and downwards. Bush  29  is driven inside seat  23  so that edge  39  contacts annular shoulder  46  of portion  44 , thus accurately defining the axial position of bush  29  inside its seat. Said interference may preferably range between 5 and 10 microns, and the surface of portion  43  and/or surface  37  of bush  29  may be lapped, as opposed to ground, to reduce fabrication cost. 
     Plug member  31  comprises a top surface  47  ( FIG. 2 ) having a truncated-cone-shaped depression  48  coaxial with calibrated hole  27  and for centering the action of ball  19  on hole  27 . In addition to calibrated hole  27 , the drain conduit also comprises a larger-diameter prehole  49  forming an additional volume to that of control chamber  24 ; plug member  31  comprises an annular surface  50  contacting the top edge  41  of bush  29 , and which is precision machined to engage edge  41  in pressurized-fuel tight manner; and plug member  31  comprises a lateral surface  51  of substantially the same diameter as outer surface  37  of bush  29 , and which engages with a minimum amount of clearance the cylindrical surface of a connecting portion  52  between intermediate portion  43  and threaded portion  42  of intermediate seat  23 . 
     Top surface  47  of plug member  31  comprises an annular portion  53 , which is also precision machined and is engaged by a ring nut  54  having an externally threaded lateral wall  56  by which it screws inside threaded portion  42  of intermediate seat  23 . Ring nut  54  has substantially the same outside diameter as the lateral surface of plug member  31  and outer surface  37  of bush  29 , so that its action in fastening plug member  31  is exerted on the thickness of bush  29 , with no lever arm being formed with the pressure of the fuel in control chamber  24  or with the reaction of shoulder  46  of portion  44  of intermediate seat  23 . 
     The thickness of wall  56  of ring nut  54  is preferably about 40% that of bush  29 , and, to concentrate the fastening action of ring nut  54  on a small surface area of plug member  31 , ring nut  54  has a bottom annular projection  57  of a width equal to about a third of the thickness of wall  56 . Moreover, projection  57  is located adjacent to the inner surface of wall  56 , so as to act substantially along the centerline of the thickness of bush  29 . 
     In the  FIG. 1 and 2  embodiment, plug member  31  comprises a flange  58  integral with a coaxial cylindrical appendix  59  having flat bottom surface  35  of plug member  31 . Appendix  59  is housed with a limited amount of clearance inside opening  32  of bush  29 , and is of such a length as to leave the outlet of calibrated hole  26  of the inlet conduit clear. Flat surface  35 , the length of prehole  49 , and truncated-cone-shaped end surface  36  of rod  12  therefore define the volume of control chamber  24 . Obviously, on account of the length of prehole  49 , calibrated hole  27  is preferably formed through the truncated-cone-shaped top surface  48  of plug member  31 . 
     In the  FIG. 2  embodiment, appendix  59  of plug member  31  comprises an annular groove  60  adjacent to flange  58  to permit precision machining of the lateral surface of appendix  59  and surface  50  of flange  58 . Sealing between flange  58  and the surface of top edge  41  is achieved easily over the whole surface of edge  41  by the squareness of edge  41  and surface  50  of flange  58  with respect to axis  7 . 
     To assemble metering valve  14  inside injector  6 , bush  29  is first driven inside cylindrical portion  43  of intermediate seat  23 —e.g. by first heating body  6  and cooling bush  29  with liquid nitrogen—so that edge  39  of bush  29  rests on shoulder  46  of portion  44  of seat  23 . Appendix  59  of plug member  31  is then inserted inside opening  32  of bush  29 . And finally, ring nut  54  is screwed inside threaded portion  42  of seat  23  to so fasten surface  50  of plug member  31  against top edge  41  of bush  29  as to ensure sealing of the pressurized fuel in chamber  24 . 
     In the  FIG. 3  variation, the inner portion of top edge  41  of bush  29  has an annular recess  61  housing a seal  62  of elastomeric material. Seal  62  provides for sealing between flange  58  and edge  41  of bush  29  over a smaller diameter than in  FIGS. 1 and 2 , so that less fastening pressure is required of ring nut  54 , and groove  60  in  FIG. 2  may also be dispensed with, since such sealing may even be achieved in the presence of minor roughness of the portion of metal surface  50  adjacent to appendix  59 . Obviously, in addition to the steps described relative to the  FIGS. 1 and 2  injector, assembly of metering valve  14  in  FIG. 3  also comprises inserting seal  62  inside annular recess  61 . 
     In the  FIGS. 4 and 5  embodiment, plug member  31  is defined by a straightforward disk  63  engaged by projection  57  of ring nut  54  for fluidtight assembly to edge  41  of bush  29 . To allow pressurized fuel flow through calibrated hole  26  of the inlet conduit into control chamber  24 , an end portion  64  of portion  33  of rod  12  is smaller in diameter to form a gap  66  with through opening  32  of bush  29 . The volume of gap  66  is added to that of control chamber  24  to compensate for the reduction in volume caused by the reduction in the length of prehole  49 . Since disk  63  has a shorter prehole  49  than in the  FIGS. 1-3  embodiments, calibrated hole  27  in disk  63  may be formed working through prehole  49 , so that the two are more easily made coaxial. 
     In the  FIG. 5  variation, as in  FIG. 3 , bush  29  comprises annular recess  61  housing seal  62  of elastomeric material to reduce the diameter of the sealing area and ensure sealing even in the presence of minor roughness of the two contacting metal surfaces. 
     The  FIGS. 4 and 5  variations are assembled in the same way as the  FIGS. 1-3  embodiments already described. 
     According to the invention, the method of fabricating injector  5  comprises the steps of:
         forming injector body  6  with seat  23  for metering valve  14 ;   forming control chamber  24  in two parts  29 ,  31 , part  29  guiding control rod  12  and having one of conduits  26 ,  27 , and part  31  closing control chamber  24  and having the other of conduits  26 ,  27 ;   subsequently inserting parts  29  and  31  inside seat  23 ; and   locking parts  29  and  31  to each other inside seat  23  by means of a fastening member  54 .       

     More specifically, the method comprises the steps of:
         forming said seat  23  in said injector body  6  with at least one cylindrical portion  43  of a given diameter, with a shoulder  46  at one end, and with a threaded portion  42  at the other end;   forming one of said parts in the form of a bush  29  having a substantially cylindrical axial through opening  32 , and an outer surface  37  having an annular groove  38  at said inlet conduit  26 ;   machining the outer surface  37  of bush  29  to such a diameter as to obtain a small amount of interference with said cylindrical portion  43  of seat  23 ;   forming the other of said parts in the form of a plug member  31  for engaging a first end  41  of said bush  29  in fluidtight manner;   forming said fastening member in the form of a ring nut  54  for engaging said plug member  31 ;   driving said bush  29  firmly inside said cylindrical portion  43  of seat  23  so that a second end  39  of bush  29  rests on said shoulder  46 ;   inserting said plug member  31  inside said seat  23 ; and   screwing said ring nut  54  inside said threaded portion  42  to ensure pressurized-fuel sealing between said plug member  31  and said first end  41  of bush  29 .       

     The advantages, as compared with known injectors, of the injectors according to the invention will be clear from the foregoing description. In particular, forming control chamber  24  in two parts  29 ,  31  simplifies machining of the inside of chamber  24 ; driving bush  29  into cylindrical portion  43  of seat  23  provides for direct sealing of the pressurized fuel in distribution chamber  38 ; whereas the slight interference between bush  29  and cylindrical portion  43  prevents any deformation of the two parts during assembly, and makes subsequent grinding superfluous. 
     Being substantially of the same diameter as bush  29  and plug member  31 , the fastening force of ring nut  54  is exerted over the thickness of bush  29 ; projection  57  of ring nut  54  provides for concentrating the fastening force over a smaller diameter, thus ensuring optimum fastening; and forming the two calibrated holes  26 ,  27  in two separate parts  29 ,  31  enables parts  29 ,  31  to be selected when assembling injector  5 , thus simplifying part storage. 
     Clearly, changes may be made to the injectors and fabrication method as described herein without, however, departing from the scope of the accompanying Claims. 
     For example, bush  29  may be other than circular in section; top surface  47  of plug member  31  may be flat as opposed to truncated-cone-shaped; and the inlet conduit of control chamber  24  and the drain conduit may be parallel and perpendicular to rod  12  respectively. 
       FIG. 6  shows a further embodiment of the present invention, in which any parts similar or corresponding to those of the other embodiments are indicated using the same reference numbers. 
     More specifically, the  FIG. 6  injector differs from those in  FIGS. 1-5  by bush  29  being fixed conventionally to injector body  6  as opposed to interferentially. 
     More specifically, as shown in  FIG. 6 , bush  29  is inserted radially loosely inside injector body  6 , and two sealing rings  72 ,  73  of elastomeric material are provided on opposite axial sides of annular groove  38 , between injector body  6  and bush  29 , to prevent the high-pressure fuel fed into annular groove  38  along feed conduit  9  from leaking into the gap between injector body  6  and bush  29 . 
     Also, seat  23  housing bush  29  comprises a wider top chamber  74  defined axially by an annular shoulder  75  of injector body  6 , and which houses plug member  31  and ring nut  54 ; and bush  29  has a substantially T-shaped section, and comprises a wide top end portion  76  resting on annular shoulder  75 .