Patent Publication Number: US-6216964-B1

Title: Fuel injector

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an injector for use in supplying fuel to a combustion space of an internal combustion engine. The invention relates, in particular, to an injector of the outwardly opening type suitable for use in supplying fuel to an engine of the compression ignition type. 
     Part of a typical injector of the outwardly opening type is illustrated in FIG.  1 . As shown in FIG. 1, the injector comprises a needle  1  slidable within a bore  2  formed in a nozzle body  3 . The bore  2  defines a seating with which the needle  1  is engageable to control the supply of fuel to a chamber  4 . The position of the needle  1  also determines how many of a plurality of outlet openings  5  communicate with the chamber  4 . 
     Part of the needle  1  downstream of the seating is of diameter substantially equal to the adjacent part of the bore  2  and engagement therebetween guides movement of the needle  1 . It has been found, however, that fuel may leak between this part of the needle  1  and the bore resulting in inefficient combustion of fuel and high levels of emissions. Where the injector is used with a fuel system of the direct injection type, the level of leakage may be increased due to dilation of the bore  2 . 
     SUMMARY OF THE INVENTION 
     The disadvantage described hereinbefore can be reduced by increasing the axial length of the region of the needle which engages the bore to guide the movement of the needle, and this can be achieved by providing the needle with a fuel supply passage which communicates with one or more outlet openings provided in the needle rather than in the nozzle body. However, by providing the outlet openings in the needle rather than the nozzle body, angular movement of the needle, in use, may result in the delivery of fuel being incorrectly orientated where the fuel injector is not mounted vertically. 
     According to a first aspect of the invention there is provided an injector comprising a valve needle slidable within a bore formed in a nozzle body, the valve needle including an axially extending fuel supply passage which communicates with at least one outlet opening provided in the needle, wherein the end of the supply passage adjacent the outlet opening is closed by a plug, the plug having an inner end region which is arranged to be located, in use, adjacent the, or at least one of the, outlet openings and shaped to modify the flow characteristics of the fuel flow upstream of at least one of the said outlet openings. 
     The plug may, for example, be shaped to define a recess, for example of conical or part spherical form, or may include a projection of, for example, cylindrical or conical form. The inner end region of the plug may be shaped to generate cavitation upstream the outlet openings, or may increase or decrease other hydraulic disturbances upstream of the outlet openings. 
     The fuel injector may further comprise lock means arranged to restrict angular movement of the needle about the axis of the needle relative to the nozzle body. 
     The lock means conveniently comprises a lock member extending within formations provided in the valve needle and the nozzle body. The lock member may take the form of a pin, and the formations may define a groove or slot in the upper end surface of the valve needle and a groove or recess formed in the upper surface of the nozzle body. 
     The injector in accordance with this embodiment of the invention is advantageous in that as angular movement of the needle is restricted, if the needle includes one or more outlet openings, the orientation of fuel sprays formed at the outlet openings, in use, remain fixed. 
     The valve needle may carry an annular abutment member which is engageable with the seating to control the flow of fuel past the seating. 
     The abutment member may be an interference fit or may be secured to the valve needle by, for example, welding or brazing. 
     The use of an abutment member carried by the valve needle simplifies manufacture of the valve needle. 
     According to a second aspect of the invention there is provided a fuel injector comprising a valve needle slidable within a bore formed in a nozzle body, and lock means arranged to restrict angular movement of the needle about the axis of the needle relative to the nozzle body. 
     According to a third aspect of the invention there is provided a fuel injector of the outwardly opening type comprising a valve needle slidable within a bore provided in a nozzle body, the bore defining a valve seating, the valve needle carrying an annular abutment member which is engageable with the seating to control the flow of fuel past the seating. 
     According to another aspect of the invention there is provided a fuel injector comprising a valve needle slidable within a bore formed in a nozzle body, wherein the diameters of the needle, the bore and the outer periphery of the nozzle body are chosen to optimize stress levels within the nozzle body and the needle, thereby restricting the leakage of fuel between the needle and the nozzle body to an acceptable level. 
    
    
     BRIEF DESCRIPTION OF THE VIEWS OF THE DRAWINGS 
     The invention will further be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a sectional view illustrating part of a typical injector; 
     FIG. 2 is a sectional view illustrating part of an injector in accordance with an embodiment of the invention; 
     FIG. 3 is a sectional view along the line  3 — 3  in FIG. 2; 
     FIGS. 4 a ,  4   b ,  4   c  and  4   d  illustrate modifications to the embodiment of FIG. 2; 
     FIG. 5 a  is an enlarged view of part of the injector of FIG. 2; and 
     FIGS. 5 b  and  5   c  are views similar to FIG. 5 a  illustrating modifications thereto. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The fuel injector illustrated, in part, in FIGS. 2 and 3 comprises a valve needle  10  which is slidable within a bore  12  formed in a nozzle body  14 . The bore  12  is a through bore, and defines, at its lower end, a seating  16  with which an enlarged diameter region  10   a  of the valve needle  10  is engageable. A significant portion of the bore  12  upstream of the seating  16  is of diameter substantially equal to the diameter of the adjacent part of the needle  10 , engagement between the needle  10  and the wall of the nozzle body  14  defining this part of the bore  12  acting to guide sliding movement of the needle  10  within the bore  12 . The diameters of the needle  10 , the bore  12  and the outer periphery of the nozzle body  14  are chosen to optimize stress levels and minimize leakage of fuel between the needle  10  and the nozzle body  14  whilst providing a sufficient clearance to permit lubrication and free movement of the needle  10 . 
     The needle  10  is provided with an axially extending, blind drilling  18 , the lower end of which is closed by means of a plug  20  which may be brazed in position or may, for example, comprise a grub screw. The drilling  18  communicates with a plurality of outlet openings  22  which are located such that when the needle  10  engages the seating  16 , the outlet openings  22  are obscured by the adjacent parts of the nozzle body  14 . Movement of the valve needle  10  in the opening direction moves the enlarged region  10   a  of the valve needle  10  away from the seating  16 , further movement resulting in one or more of the outlet openings  22  occupying a position in which it is no longer obscured by the nozzle body  14 . The outlet openings  22  may, as illustrated, be located at different axial positions and may point in different directions, particularly where the injector is to be mounted in a non-vertical orientation. The openings  22  may be of non-circular cross-sectional shape, if desired. 
     Adjacent its blind end, the drilling  18  communicates with a plurality of cross drillings  24  to permit communication between the bore  12  and the drilling  18 . The cross drillings  24  may be spaced apart in the axial direction, if desired. In use, the bore  12  is supplied with fuel under high pressure from an appropriate source of fuel under pressure, for example a common rail charged with fuel to a high pressure by an appropriate fuel pump through a supply drilling  26  provided in the nozzle body  14 . 
     The end of the needle  10  remote from the enlarged diameter region  10   a  thereof is provided with an external screw-thread formation  10   b  of large root radius and external diameter which engages an annular guide member  28  of external diameter substantially equal to the diameter of the adjacent part of the bore  12 , the guide member  28  further assisting in guiding sliding movement of the needle  10  within the bore  12 . The use of the illustrated screw thread formation is advantageous in that the leakage of fuel between the needle and guide member can be reduced. It will be appreciated that, if desired, a conventional screw thread formation may be provided. A spring  30  engages the guide member  28 , the spring  30  being in engagement with a spring abutment member  32  located within the bore  12 , the spring  30  acting to bias the valve needle  10  in a closing direction towards a position in which the enlarged diameter region  10   a  thereof engages the seating  16 . As illustrated, the spring abutment member  32  is provided with a plurality of openings to ensure that the flow of fuel along the bore  12  is not impeded to a significant extent by the presence of the spring abutment member  32 . 
     The end of the nozzle body  10  remote from the seating  16  engages a distance piece  34  which is provided with a drilling which communicates with the supply drilling  26 . The distance piece  34  includes a through bore  36  which is offset from the axis of the distance piece  34 , and within which a piston member  38  is slidable. The piston member  38 , the bore  36 , the upper part of the bore  12  and the upper surfaces of the needle  10  and guide member  28  together define a control chamber  40 , the fuel pressure within which applies a force to the needle  10  urging the needle  10  in an opening direction against the action of the spring  30 . 
     The piston member  38  is biased by an appropriate spring  42  in a direction urging the piston member  38  away from the nozzle body  10 . A piezoelectric actuator  44  is arranged such that energization thereof can apply a force to the piston member  38  through an appropriate anvil member  46 , if desired, to move the piston member  38  and hence vary the fuel pressure present within the control chamber  40 . 
     The end surface of the valve needle  10  remote from the enlarged diameter region  10   a  thereof is provided with a diametrically extending groove or slot  48 , and the adjacent parts of the guide member  28  are provided with recesses which, in use, effectively act as extensions of the slot  48 . A recess  50  is formed in the surface of the nozzle body  14  adjacent the distance piece  34 , for example using a Woodruff cutter. A pin  52  is located within the slot  48 , the ends of the pin  52  extending into the recess  50 . It will be appreciated that the engagement between the pin  52  and the walls defining the slot  48  and the recess  50  acts to restrict angular motion of the needle  10  relative to the nozzle body  14 , thus ensuring that the orientation of the outlet openings  22  relative to the nozzle body  14  does not change, in use. The engagement of the pin  52  within the slot  48  and the recesses formed in the guide member  28  further ensure that undesirable release of the guide member  28  from the needle  10  does not occur. The dimensions of the slot  48 , the recesses provided in the guide member  28  and the recess  50  are chosen to ensure that axial sliding movement of the needle  10 , in use, is not impeded. 
     Rather than using the pin  52  to avoid release of the guide member  28  from the needle  10 , a lock nut or weld may be used to avoid such release, or the guide member may simply be welded to the needle, the screw thread formations being omitted. In such arrangements, the pin  52  functions only to restrict angular movement of the needle  10  relative to the nozzle body  14 . 
     In use, with fuel supplied under pressure to the bore  12  through the supply drilling  26 , and with the actuator  44  occupying an energization state in which the piston member  38  is permitted to occupy a position in which the fuel pressure within the control chamber  40  is relatively low, the valve needle  10  is urged by the spring  30  and by the fuel pressure within the bore  12  to occupy a position in which the enlarged diameter region  10   a  thereof engages the seating  16 . The guide member  28  is conveniently of diameter such that the fuel pressure within the bore  12  applies a force to the needle  10  assisting the spring  30 . Clearly, in this position, injection of fuel does not take place. 
     In order to commence injection, the actuator  44  is energized to move the piston  38  against the action of the spring  42 , thereby increasing the fuel pressure present within the control chamber  40 . The piston member  38  is conveniently of relatively large diameter, a relatively small movement thereof being sufficient to vary the pressure within the control chamber  40  by an extent sufficient to control operation of the injector. As only a small degree of movement of the piston member  38  is required, it will be appreciated that the actuator  44  may be relatively small. Such an increase in fuel pressure increases the force applied to the valve needle  10  acting in the opening direction, and a point will be reached beyond which the fuel pressure present within the control chamber  40  is sufficient to move the valve needle  10  against the action of the spring  30  to move the enlarged diameter region  10   a  of the valve needle  10  away from the seating  16 . The extent of movement of the valve needle  10  is dependent upon the energization of the actuator  44 , and depending upon the magnitude of movement of the needle  10 , one or more of the outlet openings  22  may become uncovered thereby permitting fuel to flow from the bore  12  through the drillings  24  and axially extending blind drilling  18  to be delivered to a combustion space of an associated engine through a desired number of the outlet openings  22 . 
     During fuel injection, relatively little leakage of fuel between the needle  10  and the nozzle body  14  occurs. Remote from the seating  16 , the fuel present between the needle  10  and the nozzle body is at high pressure and applies relatively large magnitude forces to the needle  19  and nozzle body  14  tending to expand the nozzle body  14  and compress the needle  10 . However, the pressure of fuel between the needle  10  and the nozzle body  14  adjacent the seating  16  is relatively low and the fuel pressure within the drilling  18  is sufficiently high to expand the needle  10  to an extent sufficient to limit leakage between the needle  10  and the nozzle body  14  to an acceptable level. 
     In order to terminate injection, the actuator  44  is returned to its initial energization state thereby permitting movement of the piston member  38  to reduce the fuel pressure within the control chamber  40  to an extent sufficient to allow the valve needle  10  to return to its closed position under the action of the spring  30 . 
     As described hereinbefore, the arrangement illustrated in FIGS. 2 and 3 is advantageous in that the angular orientation of the valve needle  10  relative to the nozzle body  14  remains substantially fixed, in use, thus the orientation of the fuel sprays formed at the outlet openings  22 , in use, is fixed. Such an arrangement is particularly advantageous where the fuel injector is mounted in a non-vertical position. 
     A further advantage is that as, at the commencement of injection, the effective area of the needle  10  exposed to fuel under pressure does not change significantly, the actuator does not need to be able to cope with a sudden change in the load applied thereto by the needle, thus the actuator can be smaller and less costly than in other arrangements. 
     In the arrangement illustrated in FIGS. 2 and 3, the plug  20  is of simple form, for example taking the form of a simple grub screw. FIGS. 4 a ,  4   b ,  4   c  and  4   d  illustrate arrangements in which the plug  20  is shaped to modify the fuel flow characteristics upstream of the outlet openings  22 . In the arrangement illustrated in FIG. 4 a , the plug  20  includes an integral, axially extending projection  20   a  of cylindrical form which extends to a position upstream of the outlet openings  22 . In the arrangement of FIG. 4 b , the inner end of the plug  20  is shaped to define a recess of part spherical form. The arrangement of FIG. 4 c  is similar to that of FIG. 4 b  but in which the recess is of frusto-conical shape. FIG. 4 d  illustrates an arrangement in which the inner end of the plug  20  is shaped to define a projection of frusto-conical shape. In each case, the shape of the formation or recess provided at the inner end of the plug  20  is shaped to benefit the formation of spray by generating cavitation upstream of the outlet openings  22  or by increasing or decreasing other hydraulic disturbances upstream of the outlet openings  22 . 
     FIG. 5 a  illustrates the lower end of the needle  10 , in particular illustrating the enlarged diameter region  10   a  thereof and the plug  20 . The manufacturing process involved in machining a needle of this form is relatively complex, and FIGS. 5 b  and  5   c  illustrate modifications to the arrangement of FIG. 5 a  which may be used to simplify the manufacturing process. In the arrangement illustrated in FIG. 5 b , the enlarged diameter region  10   a  of the needle  10  is of relatively small axial extent, and acts to locate a separate annular abutment member  54 , the exposed end surface of which is shaped to sealingly engage the seating  16 , in use. The abutment member  54  may be secured to the needle  10  using, for example, a brazing or welding technique, or alternatively the abutment member  54  may be an interference fit with the needle  10 . As denoted by the arrows in FIG. 5 b , the abutment member  54  would be introduced, during assembly, from the end of the needle  10  remote from the enlarged diameter region  10   a  thereof. 
     FIG. 5 c  illustrates a modification to the arrangement of FIG. 5 b  in which the enlarged diameter region of the needle  10  is omitted, the abutment member  54  being inserted onto the needle  10  from beneath, as denoted by the arrows in FIG. 5 c.    
     Although the injector described hereinbefore is intended to be controlled using a piezo electric actuator, it will be appreciated that the invention is also applicable to injectors controlled using other types of control arrangement.