Patent Publication Number: US-6340121-B1

Title: Fuel injector

Description:
TECHNICAL FIELD 
     This invention relates to a fuel injector for use in supplying fuel under pressure to a combustion space of an internal combustion engine. The invention relates, in particular, to an injector suitable for use in supplying fuel to an engine of the compression ignition type, the injector forming part of a common rail fuel system. It will be appreciated, however, that the injector may be used in other applications. 
     BACKGROUND OF THE INVENTION 
     In order to reduce the levels of noise and particulate emissions produced by an engine it is desirable to provide an arrangement whereby the rate at which fuel is delivered to the engine can be controlled. It is also desirable to be able to adjust other injection characteristics, for example the spray pattern formed by the delivery of fuel by an injector. 
     A known fuel injector which permits this to be achieved comprises an outwardly opening valve member which is slidable within a first bore provided in a nozzle body. The valve member is provided with a second bore within which an inwardly opening valve needle is slidable, the valve needle being engageable with a seating to control fuel flow delivery through a first set of outlet openings provided in the valve member. The valve member is also provided with a second set of outlet openings in constant communication with a part of the second bore upstream of the seating, the second set of outlet openings being located such that, when the valve member adopts an inner, closed position within the first bore, the second set of outlet openings are closed by the nozzle body. When the valve member is moved outwardly to an open position, fuel within the second bore is able to flow through the second set of outlet openings into the engine cylinder. 
     Movement of the valve needle and the valve member is controlled by means of an actuator arrangement to permit fuel delivery through a selected one or both of the first and second sets of outlet openings, thereby enabling the fuel injection characteristic to be varied, in use. A disadvantage of this arrangement is that a relatively high leakage of fuel can occur to the engine cylinder between the nozzle body and the valve member. In addition, the components of the fuel injector are subject to relatively high stresses. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a fuel injector which permits the fuel injection characteristic to be varied, in use, and which overcomes the aforementioned disadvantages of known fuel injectors having this capability. It is a further object of the present invention to provide a fuel injector in which the fuel injection characteristic can be controlled with improved accuracy. 
     According to one aspect of the present invention there is provided a fuel injector comprising a nozzle body defining a first bore and an inwardly opening valve member slidable within the first bore, the valve member being engageable with a first seating to control fuel delivery through a first outlet opening provided in the nozzle body, the valve member being provided with a second bore within which an outwardly opening valve needle is slidable, the valve needle being engageable with a second seating to control fuel delivery through a second outlet opening provided in the valve needle, the fuel injector comprising first and second control chambers for fuel, whereby fuel pressure within the first and second control chambers controls movement of the valve member and the valve needle away from their respective seatings so as to permit fuel delivery through a selected outlet opening. 
     In such an arrangement, movement of the valve needle in an outwards direction away from the second seating permits fuel delivery through the second outlet opening and movement of the valve member away from the first seating in an inwards directions permits fuel delivery through the first outlet opening. Thus, by controlling movement of the valve member and the valve needle, and injecting fuel through a selected one or more of the first or second outlet openings, the fuel injection characteristic, for example the rate of injection of fuel, can be varied, in use. 
     As movement of the valve member and the valve needle is controlled by controlling fuel pressure within the first and second control chambers, rather than being controlled directly by means of an actuator arrangement, valve needle and valve member movement, and hence the fuel injection characteristic, can be controlled with improved accuracy. 
     The valve needle may define a flow passage for fuel which communicates with a delivery chamber such that, when the valve needle is moved away from the second seating, fuel within the delivery chamber is able to flow through the flow passage for delivery through the second outlet opening. 
     The force due to fuel pressure within the flow passage serves to improve the seal between the valve member and the nozzle body, and between the valve needle and the valve member, thereby reducing fuel leakage from the injector. 
     The delivery chamber is conveniently defined by a part of the second bore provided in the valve needle and the valve member. Conveniently, the valve member may include a guide region which serves to guide sliding movement of the valve needle within the second bore. 
     The valve member may have a first surface associated therewith, the first surface being exposed to fuel pressure within the first control chamber. The first surface may be carried by a first piston member which is movable with the valve member. The valve needle may have a second surface associated therewith, the second surface being exposed to fuel pressure within the second control chamber. The second surface may be carried by a second piston member which is movable with the valve needle. 
     The valve needle may be provided with a plurality of appropriately positioned second outlet openings. Alternatively, or in addition, the nozzle body may be provided with a plurality of appropriately positioned first outlet openings. 
     The fuel injector may include a third control chamber for fuel, the third control chamber communicating with the second control chamber by means of a restricted flow passage, fuel pressure within the third control chamber acting on a third surface associated with the valve needle to urge the valve needle outwardly from the second bore. In use, when fuel pressure within the second control chamber is reduced, fuel pressure within the third control chamber acting on the third surface serves to bias the valve needle away from its seating to permit fuel delivery through the second outlet opening. 
     According to a second aspect of the invention, there is provided a fuel injector comprising a nozzle body defining a first bore and an inwardly opening valve member slidable within the first bore, the valve member being engageable with a first seating to control fuel delivery through a first outlet opening provided in the nozzle body, the inwardly opening valve member being provided with a second bore within which an outwardly opening valve needle is slidable, the valve needle being engageable with a second seating to control fuel delivery through a second outlet opening provided in the valve needle, the valve needle defining a flow passage for fuel which communicates with a delivery chamber such that, when the valve needle is moved away from the second seating, fuel within the delivery chamber is able to flow through the flow passage for delivery through the second outlet opening. 
     This provides the advantage that fuel pressure within the flow passage acts in a radially outwards direction and serves to improve the fluid-tight seal between the valve member and the nozzle body and between the valve needle and the valve member, thereby reducing leakage from the fuel injector. 
    
    
     BRIEF DESCRIPTION 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 of a fuel injector in accordance with an embodiment of the present invention; 
     FIGS. 2 and 3 are enlarged views of a part of the fuel injector in FIG. 1; and 
     FIGS. 4 and 5 are views of the fuel injector in FIGS. 1 to  3  when in first and second fuel injecting positions respectively. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 to  3 , the fuel injector comprises a nozzle body  10  provided with a blind bore  11  within which a valve member  12  is slidable. As indicated in FIG. 2, the bore  11  includes a region  11   a  of reduced diameter and a region  11   b  of larger diameter at its end remote from the region  11   a . The diameter of the valve member  12  adjacent the region  11   a  is substantially the same as the diameter of the region  11   a  such that the region  11   a  serves to guide sliding movement of the valve member  12  within the bore  11 . Additionally, the region  11   b  has substantially the same diameter as the adjacent part of the valve member  12  such that movement of the valve member  12  is also guided by the bore region  11   b . The bore  11  is also shaped to define a seating surface  11   c  with which a surface of the valve needle  12  is engageable to control fuel delivery through a first set of outlet openings  14  provided in the nozzle body  10 . 
     The bore  11  defines an annular chamber  16 , the annular chamber  16  being supplied with fuel under high pressure through a supply passage  18  formed in the nozzle body  10  and other parts of the fuel injector housing, from a source of high pressure fuel (not shown), for example the common rail of a common rail fuel system. The valve member  12  includes a region  12   a  which defines, together with a part of the bore  11 , a first delivery chamber  20  for fuel, the delivery chamber  20  communicating with the annular chamber  16  by means of a narrow clearance defined between the valve member  12  and the nozzle body  10  such that, in use, fuel delivered to the annular chamber  16  is able to flow into the chamber  20 . Conveniently, the narrow clearance may be defined, in part, by grooves, flats or slots provided on the surface of the valve member  12 . 
     The valve member  12  is provided with a blind bore  22  within which a second valve member  24 , or valve needle, is slidable, the bore  22  including a region  22   a  of reduced diameter, having substantially the same diameter as the adjacent part of the valve needle  24 , such that movement of the valve needle  24  within the bore  22  is guided by the bore region  22   a . The valve needle  24  includes, at its lowermost end, a region  24   a  of enlarged diameter which is engageable with a seating  26  defined by a lower surface of the valve member  12  to control fuel delivery through a second set of outlet openings  28  provided in the valve needle  24 . The bore  22  defines a step  22   b  which abuts one end of a compression spring  38 , the other end of the compression spring  38  being in abutment with a sleeve member  40  located within the bore  22  and through which the valve needle  24  extends. The spring  38  is arranged such that the valve needle region  24   a  is biased against the seating  26 . 
     The valve needle  24  is also provided with a blind bore  30  which defines a flow passage  32  for fuel, the flow passage  32  communicating, via cross drillings  34  provided in the valve needle  24 , with a second delivery chamber  36  defined by the bore  22  and the outer surface of the valve needle  24 . The delivery chamber  36  communicates with the annular chamber  16  via cross drillings  35  provided in the valve member  12  such that, in use, when fuel under high pressure is supplied to the annular chamber  16 , fuel is able to flow from the chamber  16  into the delivery chamber  36  through the drillings  35 , and from the delivery chamber  36  into the flow passage  32  through the drillings  34 . When the valve needle  24  is moved outwardly away from the seating  26 , fuel in the flow passage  32  is able to flow out through the second set of outlet openings  28 . 
     At its uppermost end, the nozzle body  10  abuts a distance piece  42  which is provided with a bore  44 , a piston member  46  being slidable within the blind bore  44 . At its uppermost end, the piston member  46  includes a stop member  46   a  which serves to limit the extent of upward movement of the piston member  46  within the bore  44 , in use. The piston member  46  defines a spring chamber  47  which houses a second compression spring  48 . A nut  50  is also housed within the spring chamber  47 , the nut  50  being in screw-threaded engagement with a projection  24   b  at the uppermost end of the valve needle  24 , the nut  50  being in abutment with the uppermost end surface of the sleeve member  40  and being retained in position by means of a locking pin member  52 . One end of the compression spring  48  abuts a shim  54  connected with the upper end of the valve member  12  and the lower end surface of the piston member  46 , the spring  48  acting on the shim  54  and, hence, the valve member  12  and serving to bias the valve member  12  in a downwards direction against the seating surface  11   c.    
     The piston member  46  is farther provided with a bore  56 , which communicates with the spring chamber  47 , a load transmitting member  58  being slidable within the bore  56 . The lowermost end of the member  58  is in connection with the projection  24   a  forming part of the valve needle  24  such that the member  58  is movable with the valve needle  24 . The blind end of the bore  44  and the upper end face of the piston member  46  together define a first control chamber  60  for fuel, fuel under high pressure being supplied to the control chamber  60 , in use, through a restricted drilling  62  provided in the distance piece  42  which communicates with a further drilling provided in the distance piece  42  forming part of the supply passage  18  for fuel. 
     The distance piece  42  abuts, at its end remote from the nozzle body  10 , a housing  64  which is provided with a blind bore  66  within which a second piston member  68  is slidable. The piston member  68  is provided with a blind bore which defines, in part, a spring chamber  71  for a compression spring  70 , the load transmitting member  58  extending into the chamber  71 . The lower end  78  of the piston member  68  is provided with a slot, the slotted lower end  78  of the piston member  68  and the upper end face of the distance piece  42  together defining a clearance gap  79  which serves to limit the extent of movement of the piston member  68  within the bore  66 , in use. 
     The upper end of the load transmitting member  58  and the blind end of the bore provided in the piston member  68  together define a clearance gap  85 , the clearance gap  85  being smaller than the clearance gap  79  defined between the slotted end  78  of the piston member  68  and the distance piece  42  such that, in use, when the piston member  68  is moved in a downwards direction against the action of the spring  70  beyond an amount which exceeds the clearance gap  85 , the blind end of the bore in the piston member  68  moves into engagement with the upper end surface of the load transmitting member  58 , downward movement of the piston member  68  thereby being transmitted to the load transmitting member  58  and, thus, to the valve needle  24 . 
     The bore  66  provided in the housing  64  defines, together with the upper end face of the distance piece  42 , a second control chamber  72  for fuel and the blind end of the bore  66  defines, together with the upper surface of the piston member  68 , a third control chamber  80  for fuel, the third control chamber communicating with the spring chamber  71  by means of a restricted drilling  82  provided in the piston member  68 . The control chamber  80  communicates with the supply passage  18  by means of a further drilling  84  provided in the housing  64  such that, in use, fuel under high pressure is supplied to the third control chamber  80  through the supply passage  18 . Fuel supplied to the control chamber  80  is able to flow into the control chamber  72  at a relatively low rate by means of the restricted drilling  82 . The control chamber  60  and the control chamber  72  communicate with a low pressure fuel reservoir under the control of respective control valve arrangements, as will be described hereinafter, by means of drillings  61 ,  77  and drillings  74 ,  76  respectively provided in the distance piece  42  and the housing  64 . 
     As shown in FIG. 1, the housing  64  abuts a further housing  88  within which a first control valve arrangement, referred to generally as  90 , is arranged, the control valve arrangement  90  including a first valve member  92  which is moveable within a bore provided in the housing  88  under the action of an actuator arrangement  94  arranged within a housing  96 . The actuator arrangement  94  shown in FIG. 1 is an electromagnetic actuator arrangement which includes an armature  92   a  in connection with the valve member  92 . Similarly, the injector includes a second control valve arrangement, referred to generally as  98 , which is arranged within a further housing  103 . The second control valve arrangement  98  comprises a second valve member  100  in connection with an armature  100   a  of an associated electromagnetic actuator arrangement  102 , the actuator arrangement  102  being arranged within a further housing  104 . It will be appreciated, however, that the actuator arrangements  94 ,  102  need not be of the electromagnetic type and may, for example, be piezoelectric actuator arrangements. 
     In use, actuation and de-actuation of the actuator arrangements  94 ,  102  causes the armatures  100   a ,  92   a  respectively, and hence the valve members  100 ,  92  to move within their respective bores between open and closed positions. When the actuator arrangement  102  is actuated, the valve member  100  is moved to an open position in which fuel within the second control chamber  72  is able to flow, via the drillings  74 ,  76 , to the low pressure fuel reservoir or drain. When the actuator arrangement  102  is de-actuated, the valve member  100  is moved to a closed position in which communication between the control chamber  72  and the low pressure fuel reservoir is broken. Similarly, when the actuator arrangement  94  is actuated, the valve member  92  is moved to an open position in which fuel within the first control chamber  60  is able to flow, via the drillings  61 ,  77 , to the low pressure fuel reservoir. When the actuator arrangement  94  is de-actuated, the valve member  92  is moved to a closed position in which communication between the control chamber  60  and the low pressure fuel reservoir is broken. 
     In use, with the actuator arrangements  94 ,  102  de-actuated, fuel under high pressure is supplied to the annular chamber  16  from the source of fuel at high pressure through the supply passage  18  defined by drillings provided in the housings  64 ,  88 ,  96 ,  104 , the distance piece  42  and the nozzle body  10 . Fuel in the annular chamber  16  is able to flow, via the drillings  35 , into the second delivery chamber  36  and into the first delivery chamber  20  via the narrow clearance defined between the valve member  12  and the nozzle body  10 . Fuel under high pressure is also supplied to the control chamber  60  via the drilling  62 . As the valve member  92  is in its closed position, fuel supplied to the control chamber  60  is unable to flow to the low pressure reservoir. The surface of the piston member  46  is therefore exposed to fuel under high pressure within the control chamber  60 , the force due to fuel pressure within the control chamber  60  thereby urging the piston member  46  in a downwards direction. The force applied to the piston member  46 , is transmitted, via the spring  48  and the shim  54 , to the valve member  12 , the valve member  12  being urged against the seating surface  11   c  due to the force applied to the piston member  46  and due to the spring force of the spring  48 . With the valve member  12  seated against the seating  11   c , fuel within the chamber  20  is unable to flow out through the first set of outlet openings  14  into the engine cylinder or other combustion space. 
     During this stage of operation, fuel under high pressure is also supplied, via the drilling  84 , to the control chamber  80 , a force being applied to the surface of the piston member exposed to fuel within a control chamber  80  to urge the piston member  68  in a downwards direction. Fuel within the control chamber  80  is able to flow, at a restricted rate, through the drilling  82 , into the spring chamber  71  and, thus, into the control chamber  72 . With the valve member  100  in its closed position, high pressure fuel within the control chamber  72  is unable to flow to the low pressure fuel reservoir. The effective areas of the piston member  68  exposed to fuel pressure within the control chambers  80 ,  72  and the effective area of the sleeve  40  exposed to fuel pressure within the chamber  16 , are chosen to ensure that, during this stage of operation, the valve needle  24  is urged is an upwards direction such that the enlarged valve needle region  24   a  remains seated against the seating  26  and fuel delivery does not take place through the second set of outlet openings  28 . Thus, during this stage of operation, fuel injection does not take place through either the first or second sets of outlet openings  14 ,  28 . 
     When it is desired to commence fuel injection through the first set of outlet openings  14 , the actuator arrangement  94  is actuated to move the valve member  92  to its open position, high pressure fuel within the control chamber  60  thereby being able to flow, via the drillings  61 ,  77 , to the low pressure reservoir. As fuel pressure within the first control chamber  60  is reduced, the force applied to the surface of the piston member  46  is also reduced. Under these circumstances, the force acting on the lower end face of the sleeve member  40  due to fuel pressure within the annular chamber  16  is sufficient to overcome the spring force due to the spring  48  combined with the reduced force applied to the piston member  46  such that the piston member  46  and the valve member  12  are urged in an upwards direction, the valve member  12  thereby moving away from the seating surface  11   c  to the position shown in FIG.  4 . Fuel within the chamber  20  is therefore able to flow out through the first set of outlet openings  14  into the engine cylinder. As shown in FIG. 4, the extent of upward movement of the piston member  46 , and hence the valve member  12 , is limited by the clearance gap defined by the blind end of the bore  44  and the upper surface of the stop member  46   a.    
     During this stage of operation, as the actuator arrangement  102  remains de-actuated, fuel pressure within the second and third control chambers  72 ,  80  remains high and thus, the valve needle  24  remains in a position in which the enlarged region  24   a  is seated against the seating  26 . The second set of outlet openings  28  therefore remain covered by the valve member  12  and fuel is unable to flow out through the second set of outlet openings  28 . It will be appreciated that, as shown in FIG. 2, as the clearance gap  85  is greater than the clearance gap defined between the stop member  46   a  and the blind end of the bore  44 , upward movement of the valve member  12  away from the seating surface  11   c  is not transmitted, via the load transmitting member  58 , to the piston member  68 . This ensures the net force on the valve needle  24  is in an upwards direction, the enlarged end region  24   a  of the valve needle  24  therefore remaining seated against the seating  26  to prevent fuel delivery through the second set of outlet openings  28 . 
     In order to cease fuel injection, the actuator arrangement  94  is de-actuated, thereby moving the valve member  92  to its closed position such that fuel pressure within the first control chamber  60  is increased. The force due to increased fuel pressure within the first control chamber  60 , combined with the spring force  48 , is sufficient to urge the piston member  46  and, hence, the valve member  12 , in a downwards direction, thereby urging the valve member  12  against the seating surface  11   c  to close communication between the first delivery chamber  20  and the first set of outlet openings  14 . 
     Starting from the position shown in FIGS. 1 to  3 , with the actuator arrangement  94  de-actuated and the valve member  92  in its closed position, in order to inject fuel through the second set of outlet openings  28  the actuator arrangement  98  is actuated such that the valve member  100  moves to its open position. Fuel within the second control chamber  72  is therefore able to flow, via the drillings  74 ,  76 , to the low pressure fuel reservoir. As fuel flow between the third control chamber  80  and the second control chamber  72  occurs at a relatively low rate, via a restricted drilling  82 , it will be appreciated that the fuel pressure within the third control chamber  80  remains high. As fuel pressure within the second control chamber  72  is reduced, the force due to fuel under high pressure within the third control chamber  80  moves the piston member  68  downwardly into the position shown in FIG. 5, the blind end of the bore provided in the piston member  68  abutting the load transmitting member  58  to move the member  58 , and hence the valve needle  24 , in a downwards direction against the force applied to the surface of the sleeve member  40  due to fuel pressure within the annular chamber  16 . The enlarged region  24   a  of the valve needle  24  is therefore moved away from the seating  26 , fuel thereby being able to flow out through the second set of outlet openings  28 . 
     As the actuator arrangement  94  is de-actuated, fuel pressure within the control chamber  60  remains high and the valve member  12  is therefore maintained in its seated position against the seating surface  11   c . Thus, during this stage of operation fuel injection only takes place through the second set of outlet openings  28 . As shown in FIG. 5, the extent of movement of the enlarged region  24   a  of the valve needle  24  away from the seating  26  is limited by the clearance gap  79  defined between the lower end  78  of the piston member  68  and the distance piece  42 , movement of the enlarged region  24   a  away from the seating  26  terminating when the lower end  78  of the piston member  68  abuts the distance piece  42 . 
     In order to cease fuel injection, the actuator arrangement  102  is de-actuated, thereby moving the valve member  100  into its closed position such that high fuel pressure is re-established in the second control chamber  72 , the piston member  68  and the valve needle  24  thereby being urged upwardly. Thus, the enlarged region  24   a  of the valve needle  24  is urged against the seating  26  to close the second set of outlet openings  28 , thereby terminating fuel injection. 
     In order to permit fuel delivery at an increased rate, both the valve members  92 ,  100  are moved to their open positions, by actuating both actuator arrangements  90 ,  102  respectively, to reduce fuel pressure in both the first and second control chambers  60 ,  72 . Under these circumstances, the valve member  12  is biased in an upwards direction, as the force applied to the surface of the piston member  46  exposed to fuel pressure in the first control chamber  60  is reduced, the valve member  12  thereby moving away from the seating surface  11   c  to expose the first set of outlet openings  14 . Additionally, as fuel pressure within the second control chamber  72  is also reduced, the piston member  68  is urged in a downwards direction. Thus, the valve needle  24  is also moved away from its seating  26  to expose the second set of outlet openings  28 . Fuel injection therefore takes place through both the first and second sets of outlet openings  14 ,  28 . 
     By providing first and second sets of outlet openings  14 ,  28  of different size, or having a different number of openings in each set, or having openings with a different spray cone angle, selectively opening the first or second set of outlet openings  14 ,  28 , or both sets of outlet openings, by controlling fuel pressure within the second and third control chambers  72 ,  80  permits the fuel injection characteristic to be varied, in use. Furthermore, fuel pressure within the flow passage  32  acts in a radially outwards direction, thereby serving to improve the seal between the valve member  12  and the nozzle body  10  and, in addition, the seal between the valve needle  24  and the valve member  12 . Thus, leakage from the fuel injection is reduced. The arrangement is also advantageous as movement of the fuel member  12  and the valve needle  24  can be controlled with greater accuracy by controlling fuel pressure within the first and second control chambers  60  and  72 .