Abstract:
An outwardly opening fuel injector comprises a valve needle movable within a bore and engageable with a seating to control the supply of fuel from the bore, the needle being moveable outwardly of the bore to move the needle away from its seating, the needle being biased towards its seating by a spring, the spring engaging a spring abutment arrangement associated with a part of the needle remote from the part thereof engageable with the seating, the spring abutment arrangement further acting to guide movement of the needle.

Description:
FIELD OF THE INVENTION 
     This invention relates to a fuel injector for use in supplying fuel to a combustion space of a compression ignition internal combustion engine. In particular, the invention relates to an injector of the outwardly opening type which can be controlled using an electronic control arrangement. Such an injector is suitable for use in, for example, a common rail type fuel system. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided an outwardly opening fuel injector comprising a valve needle movable within a bore and engageable with a seating to control the supply of fuel from the bore, the needle being moveable outwardly of the bore to move the needle away from its seating, the needle being biased towards its seating by a spring, the spring engaging a spring abutment arrangement associated with a part of the needle remote from the part thereof engageable with the seating, the spring abutment arrangement further acting to guide movement of the needle. 
     The spring abutment arrangement may comprise a spring abutment member carried by the part of the needle remote from the part thereof engageable with the seating. 
     The spring abutment member conveniently takes the form of a sleeve which surrounds part of the needle. The sleeve may be in screw threaded engagement with the needle, or alternatively may be secured thereto by welding, using a spring clip, or using any other suitable technique. 
     The spring abutment member may be arranged to guide movement of the needle by engaging part of the wall of the bore within which the needle is located. Alternatively, the spring abutment member may be arranged to engage the wall of a second bore formed in a separate member, the second bore extending coaxially with the bore within which the needle is located. 
     The injector conveniently further comprises a piezo-electric actuator arrangement. The piezo-electric actuator arrangement may comprise an actuator arranged to move a piston to control the fluid pressure within a control chamber, part of the needle being exposed to the fluid pressure within the control chamber. 
     The spring abutment arrangement may, alternatively, comprise a guide region arranged to guide the needle for sliding movement, a fixing region for securing the guide region to the needle and an abutment region arranged to engage the spring, the guide region transmitting the spring load from the abutment region to the fixing region. Two of the regions may, if desired, be integral with one another. 
     The guide region may be slidable within a bore formed in a sleeve located with a nozzle body. 
     The invention will further be described, by way of example, with reference to the accompanying drawings, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view illustrating an injector in accordance with an embodiment of the invention; 
     FIG. 2 is an enlargement of part of FIG. 1; 
     FIGS. 3 and 4 illustrate modifications to the embodiment illustrated in FIGS. 1 and 2; 
     FIGS. 5 and 6 are views similar to FIGS. 1 and 2 illustrating an alternative embodiment; 
     FIG. 7 illustrates a modification to the arrangements of FIGS. 1 to  6 ; and 
     FIG. 8 is a sectional view illustrating a further alternative embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The injector illustrated in FIGS. 1 and 2 comprises a nozzle body  10  having a through bore  12  formed therein. The bore  12  is shaped, adjacent its lower end, to define a seating  14 . A valve needle  16  is located within the bore  12 , the needle  16  including, at its lower end, a region  18  of enlarged diameter which is engageable with the seating  14  to control communication between a part of the bore  12  upstream of the seating  14  and a chamber  20  defined between part of the bore  12  downstream of the seating  14  and a part of the enlarged diameter region  18  of the needle  16 . A plurality of outlet openings  22  are provided in the nozzle body  10  and arranged such that, as the needle  16  moves downwardly away from the seating  14 , the openings  22  come into communication with the chamber  20  to permit delivery of fuel through the openings  22 . 
     The upper end of the needle  16  is provided with a screw thread formation  24  which engages a corresponding formation provided upon the interior of a spring abutment arrangement in the form of a spring abutment member  26 . The spring abutment member  26  takes the form of a cylindrical sleeve of outer diameter slightly smaller than the diameter of the adjacent part of the bore  12 . It will be appreciated that the engagement of the spring abutment member  26  with the wall of the bore  12 , and the engagement of the region  18  of the needle  16  with the lower end of the bore  12  guides the needle  16  for movement along the axis of the bore  12 . 
     The bore  12  defines a step  28  with which a second spring abutment member  30  engages. A compression spring  32  is located between the spring abutment member  26  and the second spring abutment member  32  to bias the valve needle  16  in an upward direction, in the orientation illustrated, the bias the region  18  of the needle  16  into engagement with the seating  14 . In order to allow the use of a spring of relatively small diameter but constructed of relatively large diameter wire, the screw thread formation  24  is conveniently of generous root radius and of a suitable pitch to allow the spring  32  to pass the screw thread formation  24  by rotating the spring  32  relative to the needle  16 , the spring abutment member  26  being secured to the needle  16  after the spring  32  has been located upon the needle  16 . Such a screw thread formation further has the advantage that stress concentrations are reduced. It has been found that the use of a small, close fitting thread can form a reasonably good seal due to the long flow path for escaping fluid. 
     The spring abutment member  26  is conveniently secured to the needle  16  to avoid undesirable relative rotation therebetween, in use, by inserting a pin  34  though openings provided in the spring abutment member  26 , the pin  34  extending within a groove or other formation formed in the upper end surface of the needle  16 . Alternatively, the pin may engage within castellation like formations provided in the spring abutment member. As further alternatives, a conventional lock nut, lock screw or other thread locking technique may be used. 
     As illustrated in FIGS. 1 and 2, the bore  12  communicates with a supply passage  36  through which fuel is supplied to the bore  12  from a suitable source of fuel under pressure, in use, for example the common rail of a common rail fuel supply system which is charged with fuel at a high pressure by an appropriate fuel pump. In order to ensure that the second spring abutment  30  does not restrict the flow of fuel towards the seating  14 , in use, openings  38  are provided in the second spring abutment member  30 . 
     The face of the nozzle body  10  remote from the end thereof including the seating  14  abuts a piston housing  40  which includes a drilling forming part of the supply passage  36 , and a through bore within which a piston member  42  is slidable. The through bore, piston member  42 , the adjacent face of the nozzle body  10  and part of the bore  12  together define a control chamber  44 . Clearly, the upper end faces of the valve needle  16  and the spring abutment member  26  are exposed to the fluid pressure within the control chamber  44 , thus the fluid pressure within the control chamber  44  applies a force to the needle  16  which acts against the action of the spring  32  and the action of the fluid pressure within the nozzle body  10 . 
     The piston housing  40  engages a nozzle holder  46  within which a piezo-electric actuator  48  in the form of a stack of piezo ceramic material is located. The lower end of the actuator  48  engages an anvil  50  which, in turn, engages a slip plate  52 . The slip plate  52  engages the upper end of the piston member  42 . The slip plate  52  and the adjacent end of the piston member  42  are shaped to compensate for slight misalignment between the axis of the actuator  48  and that of the piston member  42 . A spring  54  is engaged between the piston member  42  and the upper surface of the piston housing  40  to bias the piston member  42  towards the actuator  48 . The spring  54  takes the form of a wave spring, but it will be appreciated that other types of spring, for example a disc spring or a helical compression spring, could be used. 
     The nozzle body  10  and piston housing  40  are secured to the nozzle holder  46  by a cap nut  64 . 
     In use, fuel under pressure is supplied through the supply passage  36  to the bore  12 . The diameter of the seating  14  and that of the spring abutment member  26 , and the force applied to the needle  16 , are chosen to ensure that the application of fuel under pressure to the bore  12  does not cause movement of the needle  16  away from the seating  14  at this time. It will be appreciated that the force applied by the spring may be reduced compared with a conventional arrangement as the diameter of the spring abutment member can be relatively large. 
     A small amount of leakage of fuel between the bore  12  and the spring abutment member  26  occurs, thus fuel is supplied at a low rate to the control chamber  44 . Leakage also occurs at a controlled rate between the piston member  42  and the through bore provided in the piston housing  40 , permitting fuel to escape from the control chamber  44  to a low pressure drain reservoir, for example the fuel tank. The fuel pressure within the control chamber  44  is therefore relatively low. An optional radial seal, such as an ‘O’ ring, may be provided between the slip plate  52  and the bore of the nozzle holder  46 . This would substantially eliminate the flow of fuel from the control chamber  44  to the low pressure drain reservoir. 
     When injection is to commence, the actuator is energised to extend in length resulting in movement of the piston member  42  against the action of the spring  54 . Such movement pressurizes the fuel within the control chamber  44  thus increasing the downward force applied to the needle  16 , and a point will be reached beyond which the needle  16  is able to move in a downward direction, outward of the bore  12 , to permit fuel to flow to the chamber  20  and through one or more of the openings  22 . The rate at which fuel can escape from the control chamber  44  to the low pressure drain reservoir is chosen to be at a sufficiently low level that the pressure within the control chamber  44  remains high throughout the desired injection period. 
     The rate at which fuel is delivered is dependent upon the number of openings  22  which are brought into communication with the chamber  20  by the movement of the needle  16 . The distance through which the needle  16  moves depends upon the magnitude of the extension of the actuator  48 . Clearly, therefore, the rate of injection can be controlled by appropriate control of the extension of the actuator  48 . 
     In order to terminate injection, the actuator  48  is deenergised and returns to substantially its original length. As a result, the piston member  42  moves under the action of the spring  54 , reducing the fluid pressure within the control chamber  44  thus reducing the magnitude of the downward force applied to the needle  16 , and as a result the needle  16  is able to return into engagement with the seating  14  under the action of the spring  32 . 
     In the event that the actuator fails during injection, the leakage of fuel from the control chamber  44  to the low pressure drain will eventually cause the fuel pressure within the control chamber  44  to fall to a sufficiently low level to terminate injection, thus the injector is fail-safe. The leakage of fuel from the bore  12  to the control chamber  44 , in use, compensates for gradual changes in the length of the actuator  48 , for example resulting from temperature changes. 
     FIG. 3 illustrates a modification in which the spring abutment member  26  is secured to the upper end of the needle  16  by welding after appropriate location of the spring  32  rather than using a screw thread formation, and FIG. 4 illustrates an arrangement in which the spring abutment member  26  is secured in position using a spring clip  56 . In both of these arrangements, the presence of fuel under pressure between the needle  16  and the spring abutment member  26  may expand the spring abutment member  26  to compensate for dilation of the bore  12 , thus reducing leakage of fuel from the bore  12 . 
     The embodiment illustrated in FIGS. 5 and 6 differs from that described hereinbefore in that a distance piece  58  is located between the nozzle body  10  and the piston housing  40 , thus allowing a spring of relatively large diameter to be used. The spring abutment member  26  engages the wall of a second bore  60  extending through the distance piece  58  in order guide movement of the needle  16 . Clearly, in order to ensure that the needle  16  is properly guided, the second bore  60  must be coaxial with the bore  12  of the nozzle body  10 , and this is achieved by a plurality of fingers  62  which are integral with the distance piece  58 , the fingers  62  defining the lower end of the bore  60 . The fingers  62  locate, in use, within the upper end of the bore  12  to ensure that the bore  12  is coaxial with the second bore  60 . The fingers  62  further define a plurality of flow paths along which fuel flows, in use, from the supply passage  36  to the bore  12 . 
     Operation of the embodiment of FIGS. 5 and 6 is as described hereinbefore with reference to FIGS. 1 and 2, and so will not be described in detail. 
     It will be appreciated that the embodiment of FIGS. 5 and 6 may be modified using the modifications illustrated in FIGS. 3 and 4. 
     FIG. 7 illustrates a modification which can be incorporated into any of the embodiments described hereinbefore. In the modification of FIG. 7, the lower end of the needle  16  protrudes from the bore  12 , the lower end of the needle  16  being of increased diameter and being engageable with a seating defined around a lower end of the bore  12 . The needle  16  is provided with a plurality of outlet openings  22   a  which are positioned in axially spaced locations such that the number of openings  22   a  through which fuel can be delivered at any instant is controlled by controlling the position of the needle  16 . The openings  22   a  communicate with the interior of the bore  12  through drillings  22   b  provided in the needle  16 . 
     FIG. 8 illustrates a fuel injector which, in many respects, is similar to or identical to the arrangements described hereinbefore, and only the important distinctions between the arrangement of FIG.  8  and those described hereinbefore will be described. 
     In the arrangements described hereinbefore, the spring abutment arrangement comprises a sleeve which is screw-threaded upon an end region of the needle. In the arrangement of FIG. 8, the spring abutment arrangement comprises a guide region in the form of a sleeve  70  which surrounds part of a needle  71 . The diameter of the sleeve  70  and the adjacent part of the needle  71  is such as to ensure that fuel is only able to escape therebetween at a restricted rate. The sleeve  70  is slidable within a bore formed in a hollow cylindrical member  72  which is received within an upper part of the bore  73  within which the needle  71  is received and moveable. The sleeve  70  and member  72  are a sufficiently good fit that the sleeve  70  is able to slide within the bore of the member  72 , but leakage therebetween is restricted to a very low rate. 
     The lower end of the sleeve  70 , in the orientation illustrated, abuts an annular spring abutment member  74  which engages the upper end of a spring  75 , the other end of which engages a spring abutment member  76  located against a step formed in the bore  73 . The upper end of the sleeve  70  abuts a fixing member in the form of a nut  77  which is in screw-threaded engagement with the upper end region of the needle  71 . The nut  77  is conveniently provided with a formation  78  permitting the introduction of a fixing pin which cooperates with both the nut  77  and the needle  71  to secure the nut  77  against rotation relative to the needle  71 . If desired, the pin and the formation  78  may be omitted, and instead the nut  77  secured against rotation relative to the needle  71  by means of welding, using a spring clip or any other suitable technique. 
     As illustrated in FIG. 8, the nut  77  is received within a bore  79  formed in a distance piece  80 , the bore  79  defining a chamber which forms part of a control chamber, the fuel pressure within which is controlled by means of an actuator arrangement, for example of the type illustrated in FIGS. 2 and 6. The bore  79  is of reduced diameter compared to the part of the bore  73  within which the member  72  is located. It will be appreciated, therefore, that the lower surface of the distance piece  80  adjacent the bore  79  defines a step against which the member  72  is engageable. 
     In use, fuel under high pressure is supplied to the bore  73  through appropriate passages (not shown). It will be appreciated that the fuel pressure within the bore  73  is high, applying a relatively high magnitude upwardly directed force, in the orientation illustrated, to the member  72 , urging the member  72  into engagement with the step. The engagement between the member  72  and the step defined by the distance piece  80  is sufficient to form a seal between the member  72  and the distance piece  80 . As the member  72  and the sleeve  70  together form a substantially fluid tight seal, and the sleeve  70  and needle  71  together form a substantially fluid tight seal, it will be appreciated, therefore, that fuel is only able to flow from the bore  73  to the bore  79  at a very restricted rate. 
     The dimensions of the needle  71  are such that the application of fuel under pressure to the bore  73  applies an upwardly directed force to the needle  71 . This force results from the diameter of the sleeve  70  being greater than the diameter of the lower end of the needle  71  where it is guided for sliding movement in the bore  73 . The action of the spring  75  serves to assist the action of the fuel under pressure in urging the needle in an upward direction, the action of the spring  75 , the spring load being applied to the needle  71  through the abutment member  74 , sleeve  70  and nut  77 . The action of the fuel under pressure and the spring  75  is sufficient to ensure that the needle  71  is held in the position illustrated in which outlet openings similar to the openings  22   a  illustrated in FIG. 7 are obscured by the lower end of the bore  73 . Injection of fuel is therefore not taking place. 
     When fuel injection is to occur, the actuator is energized to increase the fuel pressure within the chamber defined, in part, by the bore  79 , thus applying a downwardly directed force to the needle  71 . A point will be reached beyond which the magnitude of the downwardly directed force will be sufficient to cause the needle  71  to move against the action of the spring  75  and the fuel under pressure within the bore  73  to a position in which fuel injection can occur. Fuel injection is terminated by relieving the fuel pressure within the control chamber defined, in part, by the bore  79 , the needle  71  returning to the position illustrated under the action of the spring  75  and the fuel pressure within the bore  73 . 
     It will be appreciated that, if desired, the sleeve  70  may be formed integrally with either the spring abutment member  74  or the nut  77 . It will further be appreciated that as the member  72  forms a substantially fluid tight seal with the distance piece  80 , the fit of the member  72  within the bore  73  need not be a sealing fit, and the member  72  can adopt a position in which the needle  71  is held substantially co-axially with the bore  73 , compensating for any slight manufacturing inaccuracies. 
     As the diameter of the member  72  is immaterial for the purposes of controlling the operation of the injector, unlike the arrangements illustrated in FIGS. 1 to  4 , it will be appreciated that the diameter of the member  72  can be chosen to ensure that the bore  73  is of diameter sufficient to enable the spring  75  to be of a desired diameter and rate. The operation of the injector can therefore be optimised.