Patent Publication Number: US-6666388-B2

Title: Plug pin for an internal combustion engine fuel injector nozzle

Description:
The present invention relates to a plug pin for an internal combustion engine fuel injector nozzle. 
     BACKGROUND OF THE INVENTION 
     In known injectors, the nozzle is normally defined by a body having a conical wall with a number of fuel injection orifices; and the pin has a conical tip which closes the orifices by virtue of an axial force normally resulting from the force of a spring and the difference in fuel pressure on the pin and a control rod. 
     The conical tip of known pins is connected to a cylindrical portion of the pin by a truncated-cone-shaped portion, the outer surface of which forms, with the outer surface of the conical tip, an annular edge engaging a circumference of the nozzle wall to close the orifices and which is obviously subject to wear. 
     A drawback of known pins of the above type is that wear on the edge contacting the nozzle wall also shifts the contact circumference on the wall, thus also altering the closed position of the pin and consequently the travel or lift of the pin between the closed and open positions. 
     Moreover, the contact circumference gradually increases in diameter, so that, for a given opening travel of the pin, the amount of fuel injected also varies alongside wear. Consequently, the amount of fuel injected by the various injectors on the engine differs according to the different degrees of wear on the edges of the respective pins. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a plug pin for an injector nozzle, which is extremely straightforward and cheap to produce, while at the same time ensuring constant fuel injection for a given lift of the pin to eliminate the aforementioned drawbacks typically associated with known pins. 
     According to the present invention, there is provided a plug pin for an internal combustion engine fuel injector nozzle, wherein said nozzle has a conical wall with orifices for injecting fuel, and wherein said pin comprises a tip for closing said orifices; an axial force acting on said pin to cause said tip to engage said wall at a portion adjacent to said orifices; and the pin being characterized in that said tip comprises a truncated-cone-shaped portion having an outer surface resting entirely on said wall. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred, non-limiting embodiment of the invention will be described by way of example with reference to the accompanying drawings, in which: 
     FIG. 1 shows a half section of a fuel injector featuring a pin for plugging the nozzle; 
     FIG. 2 shows a larger-section portion of FIG. 1 according to the prior art; 
     FIG. 3 shows the FIG. 2 portion according to the invention; 
     FIG. 4 shows a first variation of the FIG. 3 portion; 
     FIG. 5 shows a second variation of the FIG. 3 portion. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Number  5  in FIG. 1 indicates as a whole a fuel injector for an internal combustion, e.g. diesel. engine. Injector  5  comprises a hollow body  6  connected by a ring nut  7  to a nozzle indicated as a whole by  8  and in turn comprising a body  9  having a shoulder  11  engaged by ring nut  7 . 
     Body  9  of nozzle  8  has an axial hole  12  and terminates with a seat defined by a conical wall  13  having a rounded vertex  14 . A circumferential portion  16  (FIG. 2) of conical wall  13  has a number of injection orifices  17 : advantageously, four orifices  17  equally spaced angularly and each having an axis  18  perpendicular to wall  13 . 
     Hollow body  6  (FIG. 1) has an axial hole  20  in which slides a control rod  19  controlled by the pressurized fuel inside a control chamber (not shown) having a metering valve controlled by an electromagnet. The pressurized fuel is fed along a feed conduit  21  in body  6  and along a feed conduit  22  in nozzle  8  to an annular injection chamber  23  formed about axial hole  12  in nozzle  8 . 
     One end  24  of rod  19  engages an appendix  26  of a pin  27  for closing orifices  17  and which slides inside axial hole  12 . More specifically, pin  27  has an axis A and comprises a cylindrical portion  28  guided in fluidtight manner inside a portion  29  of hole  12  in nozzle  8 ; portion  28  of pin  27  terminates at one end with a collar  31  supporting appendix  26  and which is guided inside a cylindrical seat  32  coaxial with hole  20  in body  6 ; and collar  31  is normally pushed towards nozzle  8  by a compression spring  33 . 
     Pin  27  also comprises another cylindrical portion  36  connected to portion  28  by a shoulder  37  on which the pressurized fuel in chamber  23  acts. With respect to a cylindrical surface  35  of hole  12  in nozzle  8  (FIG.  2 ), portion  36  of pin  27  has a given clearance to ensure fast fuel flow from chamber  23  to orifices  17  of nozzle  8 . 
     Pin  27  also has a substantially conical tip  38  connected to one end of portion  36  and comprising a conical portion  39  having an outer surface  40  engaging conical wall  13  of body  9  to close orifices  17 . In known injectors as shown in FIG. 2, conical portion  39  of tip  38  is normally connected to cylindrical portion  36  of pin  27  by a truncated-cone-shaped portion  41  having an outer surface  42  forming an annular edge  43  with outer surface  40  of conical portion  39 ; outer surface  42  of truncated-cone-shaped portion  41  forms an angle al with conical wall  13  of nozzle  8 ; and outer surface  40  of portion  39  forms an angle α 2  with conical wall  13 . 
     Rod  19  and spring  33  (see also FIG. 1) push edge  43  to engage a contact circumference  44 , upstream from orifices  17 , on conical wall  13  of nozzle  8 , so that tip  38  closes orifices  17 . Inevitable wear of edge  43  shifts circumference  44  on wall  13  of nozzle  8 , thus also altering the closed position of pin  27  and the travel or lift of pin  27  between the closed and open positions. 
     According to the invention, truncated-cone-shaped portion  41  has an outer surface  45  (FIG. 3) resting entirely on wall  13 , so that sealing does not depend solely on edge  43 . Surface  45  of portion  41  may rest on wall  13  as a result of elastic deformation produced by the force of spring  33  and by the difference in fuel pressure acting on rod  19  and shoulder  37 . 
     More specifically, surface  45  of portion  41  is designed to form with wall  13  a substantially zero angle with a tolerance of 0′ to ±10′. Consequently, when pin  27  is moved into the closed position, contact between surface  45  of portion  41  and wall  13  commences either at an edge  46  between truncated-cone-shaped surface  45  and the cylindrical surface of portion  36 , or at edge  43  between surface  45  and surface  40  of conical portion  39 ; and the closing force acting on pin  27  deforms surface  45  so that it rests entirely on wall  13 , as shown by the continuous lines in FIG.  3 . 
     The vertex angle α of conical wall  13 , i.e. the angle formed between a generating line of the inner surface of wall  13  and axis A, advantageously ranges between 45° and 75°; and truncated-cone-shaped portion  41  may be of a height h of 0.12 to 0.18 mm-preferably 0.15 mm-to obtain a given size of the contact surface between pin  27  and wall  13 . 
     Adjacent to orifices  17 , a recess may be provided between tip  38  of pin  27  and wall  13  of nozzle  8  to collect a certain amount of fuel and ensure uniform flow through orifices  17 , even in the event of slight misalignment of pin  27 . In the FIG. 4 variation, surface  40  of portion  39  has an annular recess  47  opposite orifices  17 ; and, in the FIG. 5 variation, the recess is defined by a basin  48  at the vertex of wall  13  of nozzle  8 . 
     The advantages, with respect to known pins, of the pin according to the invention will be clear from the foregoing description. That is, wear of edge  43  is negligible, and the working life of pin  27  is greatly increased with no need for adjustment. 
     Clearly, changes may be made to the pin as described herein without, however, departing from the scope of the accompanying claims. For example, annular recess  47  may be formed in wall  13 , or partly in wall  13  and partly in surface  40  of portion  39  of tip  38 .