Patent Publication Number: US-6340017-B1

Title: Fuel injector

Description:
TECHNICAL FIELD 
     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. Such an injector is suitable for use in, for example, a common rail type fuel system. 
     BACKGROUND OF THE INVENTION 
     A typical, known fuel injector of the outwardly opening type is shown in FIG. 1, and includes a valve needle  10  which is slidable within a bore  12 , the valve needle  10  including a valve needle guide region  12   a . The valve needle  10  is engageable with a seating  14 , defined by a fuel injector nozzle body  16 , to control the supply of fuel from the bore  12  to the cylinder of an associated engine, fuel being delivered through first and second outlet openings occupying different axial positions on the valve needle  10 . The valve needle  10  is biased against the seating  14  by means of a spring  18 , and by means of fuel pressure, and is movable away from its seating  14  by means of a piezoelectric actuator arrangement, only part of which is shown, which includes a piezoelectric stack which is arranged to control fuel pressure within a control chamber, defined, in part by a bore  22  provided in an upper housing part. A surface associated with the valve needle  10  is exposed to fuel pressure within the control chamber, an increase in fuel pressure within the control chamber causing the valve needle  10  to move outwardly within the bore  12  away from the seating  14 , against the force of the spring  18  and the fuel pressure, and thereby permitting fuel within the bore  12  to flow into the engine cylinder through the one or more of the outlet openings depending on the extent of movement of the valve needle  10  away from the seating  14 . 
     A problem with fuel injectors of this type is that, as the valve needle  10  moves away from its seating  14 , fuel within the bore  12  is able to leak past the valve needle guide region  12   a  into the engine cylinder. This leads to a poor fuel spray characteristic which can result in an inefficient combustion of fuel and high levels of emissions. In addition, as the bore  12  is prone to dilate due to the high pressure of fuel within the bore, the level of fuel leakage from the bore can increase during the service life of the injector. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a fuel injector of the outwardly opening type which alleviates the aforementioned problems. 
     According to the present invention there is provided an outwardly opening fuel injector comprising a valve needle movable within a bore provided in a nozzle body and engageable with a seating to control the supply of fuel from the bore, the valve needle being biased towards its seating and being moveable outwardly of the bore to move the valve needle away from its seating, the fuel injector further comprising a sleeve member which is moveable with the valve needle, the valve needle and the sleeve member together defining a chamber for fuel such that, in use, fuel pressure within the chamber serves to dilate the sleeve member to reduce fuel leakage from the injector. 
     As the sleeve member dilates due to fuel pressure within the chamber, the seal between the nozzle body and the sleeve member is improved and fuel leakage from the bore is reduced or prevented. 
     The chamber may be supplied with fuel by a clearance passage which may be defined, at least in part, by formations, for example flats, slots, grooves or flutes, provided on the surface of the valve needle. 
     Conveniently, the sleeve member may be provided with first and second outlet openings occupying different axial positions on the sleeve member. In use, movement of the valve needle away from the seating into a first fuel injecting position may cause the first outlet opening to be exposed to permit fuel delivery through the first outlet opening, and movement of the valve needle away from the seating into a second fuel injecting position may cause the second outlet opening to be exposed to permit fuel delivery from both outlet openings. 
     First and second sets of outlet openings may be provided, each set including one or more outlet opening. The first and second outlet openings may be of different size or may provide a different fuel spray cone angle to permit the fuel injection characteristic to be varied, in use. 
     The sleeve member may be engageable with a further seating defined by the nozzle body, movement of the valve needle into the second fuel injecting position causing the sleeve member to engage the further seating. Thus, when the valve needle is moved away from its seating into the second fuel injecting position, fuel is unable to flow past the further seating. In this way, the seal between the nozzle body and the sleeve member is further improved and fuel leakage from the injector is further reduced. 
     Preferably, a surface associated with the valve needle is engageable with an additional seating defined by the bore to limit outward movement of the valve needle within the bore. 
     The surface associated with the valve needle may preferably be defined by a step in the surface of the sleeve member. The additional seating may preferably be defined by a step in the surface of the bore. 
     According to a second aspect of the present invention, there is provided an outwardly opening fuel injector comprising a valve needle movable within a bore provided in a nozzle body and engageable with a seating to control the supply of fuel from the bore, the valve needle being biased towards its seating and being moveable outwardly of the bore to move the valve needle away from its seating, a surface associated with the valve needle being engageable with an additional seating defined by the bore to limit outward movement of the valve needle within the bore. 
     Conveniently, the fuel injector may include a sleeve member which is movable with the valve needle, the sleeve member defining the surface which is engageable with the further seating. 
    
    
     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 illustrating a typical, known fuel injector of the outwardly opening type; 
     FIG. 2 is a sectional view of an embodiment of a fuel injector in accordance with the present invention; 
     FIG. 3 is an enlarged view of a part of the fuel injector shown in FIG. 2; and 
     FIGS. 4 and 5 shown the fuel injector in FIGS. 2 and 3 in first and second fuel injecting positions respectively. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 2 and 3, the fuel injector of the present invention includes a nozzle body  26  which is provided with a through bore  28  within which a valve needle  30  is slidable. The bore  28  includes an enlarged diameter region  28   a , an intermediate region  28   b  of reduced diameter and a lower region  28   c  of further reduced diameter, the bore defining a step  28   d  between the intermediate region  28   b  and the lower region  28   c . A sleeve member  32  is received within the bore  28 , the outer surface of the sleeve member  32  being of stepped form and defining a step  32   a  which is engageable with the step  28   d  defined by the bore  28 . The valve needle  30  extends through the sleeve member  32 , the valve needle  30  including an end region  30   a  of enlarged diameter which projects through the lower open end of the through bore  28  and the sleeve member  32  and which is engageable with a seating  34  defined by the nozzle body  26 . The valve needle  30  also includes a region of reduced diameter  30   b  which defines, together with the inner surface of the sleeve member  32 , a delivery chamber  48  for fuel. 
     The sleeve member  32  is biased by means of a compression spring  36  and fuel pressure towards a position in which part of the lower surface  35  of the sleeve member  32  engages the enlarged end region  30   a  of the valve needle  30  forming a seal at a seating  35   a , the compression spring  36  being housed within a spring chamber  38  defined by the intermediate region  28   b  of the bore  28 . The sleeve member  32  is provided with first and second sets of outlet openings  33 ,  37  respectively, one end of each outlet opening  33 ,  37  communicating with the delivery chamber  48  such that movement of the valve needle  30  away from the seating  34  permits fuel to flow from the delivery chamber  48  out through the first set of outlet openings  33 , or through both sets of outlet openings  33 ,  37 , depending on the extent of movement of the valve needle  30  away from the seating  34 . 
     The end of the spring  36  remote from the sleeve member  32  abuts a first abutment member  40 , the abutment member  40  engaging, at its end remote from the spring  36 , a second compression spring  42  which is housed within a spring chamber  44  defined by the enlarged diameter region  28   a  of the bore  28 . The end of the compression spring  42  remote from the first abutment member  40  is in abutment with a second abutment member  46  which abuts or is connected to a guide member  47  associated with the valve needle  30 , the guide member  47  serving to guide sliding movement of the valve needle  30  within the bore  28 . The abutment member  40  is secured to the valve needle  30 , the spring force due to the spring  42  acting on the abutment member  40  and thereby serving to bias the valve needle  30  into a position in which the enlarged end region  30   a  of the valve needle  30  engages the seating  34  defined by the nozzle body  26 . The compression spring  36  is pre-loaded with a lower load than the pre-load of the compression spring  42 . 
     In use, fuel is supplied to the chamber  44  through a supply passage  46  provided in the end of the nozzle body  26  remote from the seating  34 , the supply passage  46  communicating with a source of fuel at high pressure such as, for example, a common rail of a common rail fuel system, to permit fuel to be delivered to the chamber  44 . Fuel within the chamber  44  is able to flow to the spring chamber  38  via flats, slots or grooves machined on the surface of the valve needle  30 . Fuel delivered to the spring chamber  38  is able to flow to the delivery chamber  48  by means of a narrow clearance passage  50  which is defined between the inner surface of the sleeve member  32  and flats, slots or grooves provided on the surface of the valve needle  30 . The effective areas of the valve needle  30  exposed to fuel pressure within the bore  28  are chosen to ensure that, in use, with fuel under high pressure delivered to the bore  28 , the valve needle  30  is urged against the seating  34  by the fuel pressure and the spring  42  to prevent fuel delivery into the engine cylinder or other combustion space. 
     In use, movement of the valve needle  30  away from the seating  34  is controlled in a conventional way, for example by means of a piezoelectric actuator arrangement (not shown). A surface associated with the valve needle  30  may be exposed to fuel pressure within a control chamber, fuel pressure within the control chamber being controlled by varying the energisation level, and hence the axial length, of a piezoelectric stack. Alternatively, valve needle movement may be controlled directly by varying the axial length of the piezoelectric stack. In a further alternative embodiment, movement of the valve needle  30  may be controlled in a conventional way by means of an electromagnetic actuator arrangement. 
     In use, fuel under high pressure is supplied to the annular chamber  44  through the supply passage  46 , fuel flowing into the spring chamber  38  and into the delivery chamber  48  via the clearance passage  50 . The surface  35  of the sleeve member  32  is biased into sealing engagement with the enlarged end region  30   a  by means of the spring  36  and by fuel pressure and a seal is maintained at the seating  35   a . The first and second sets of outlet openings  33 ,  37  remain covered by the nozzle body  26  and fuel is unable to flow out through the outlet openings into the engine cylinder. 
     When injection is to be commenced, the piezoelectric actuator is energised such that fuel pressure within the control chamber acting on a surface associated with the valve needle  30  provides a downwards force on the valve needle  30  which is sufficient to overcome the force due to fuel pressure within the bore  28 . Thus, the valve needle  30  is moved outwardly, the enlarged end region  30   a  moving away from the seating  34  to expose the first set of outlet openings  33 , as shown in FIG. 4, the force due to the spring  36  and fuel pressure maintaining the seal at the seating  35   a . Thus, during this stage of operation, fuel within the delivery chamber  48  is able to flow out through the first set of outlet openings  33  into the engine cylinder. Additionally, fuel pressure within the delivery chamber  48  acts on the sleeve member  32  in a radially outward direction, thereby serving to dilate the sleeve member  32  and improve the seal between the sleeve member  32  and the bore region  28   a , fuel within the spring chamber  38  therefore being unable to escape from the fuel injector between the nozzle body  26  and the sleeve member  32 . 
     In order to terminate injection, the piezoelectric actuator arrangement is de-energised from the first energisation level, causing fuel pressure within the control chamber acting on the surface associated with the valve needle  30  to be reduced. The valve needle  30  therefore moves inwardly due to fuel pressure within the bore  28  until the enlarged end region  30   a  of the valve needle  30  engages the seating  34  defined by the nozzle body  26 . Fuel is therefore unable to flow out through the first set of outlet openings  33  and fuel injection ceases. 
     Alternatively, in order to increase the fuel injection rate, the piezoelectric actuator may be energised to a second, higher energisation level causing fuel pressure within the control chamber acting on the surface associated with the valve needle  30  to be further increased, the valve needle  30  thereby moving outwardly away from the seating  34  into a second fuel injecting position, as shown in FIG. 5, with both the first and second outlet openings  33 ,  37  exposed such that fuel within the delivery chamber  48  is delivered through both the first and second sets of outlet openings  33 ,  37 . The extent of outward movement of the valve needle  30  away from the seating  34  is limited by engagement between the stepped surface  32   a  provided on the sleeve member  32  and the seating  28   d  defined by the bore  28 , the stepped surface  32   a  provided on the sleeve member  32  engaging the seating  28   d  so as to form a substantially fluid-tight seal such that fuel within the spring chamber  38  is unable to flow past the seating  28   d . The effect of the seal formed at the seating  28   d , in addition to the effect of the dilation of the sleeve member  32 , causes the seal between the nozzle body  26  and the sleeve member  32  to be further improved. Thus, during this stage of operation, fuel leakage between the nozzle body  26  and the sleeve member  32  is substantially eliminated. 
     In order to cease fuel injection the piezoelectric actuator is de-energised, causing fuel pressure within the control chamber acting on the surface associated with the valve needle  30  to be reduced, thereby causing the valve needle  30  to move inwardly until the enlarged end region  30   a  engages the seating  34 , as shown in FIG. 3, causing fuel injection through the first and second sets of outlet openings  33 ,  37  to be terminated. Alternatively, if it is desired to inject fuel at a decreased rate, the piezoelectric actuator may be de-energised to the first energisation level, thereby causing the valve needle  30  to move inwardly to the position shown in FIG. 4 in which only the first set of outlet openings  33  are exposed. 
     The invention provides the advantage that, as the enlarged end region  30   a  of the valve needle is sealingly engageable with a seating defined by both the sleeve member  32  and the nozzle body  26 , the seating can be manufactured more easily. Additionally, as the sleeve member  32  is a separate component, the first and second sets of outlet openings  33 ,  37  can also be manufactured relatively easily, prior to assembly of the fuel injector. The first and second sets of outlet openings  33 ,  37  provided in the sleeve member  32  can also be positioned in close proximity to the end face of the sleeve member  32  and, thus, the valve needle  30  need only be moved by a relatively small amount away from the seating  34  in order to commence injection. 
     In an alternative embodiment, the lower outlet opening  33 , or set of outlet openings, may be provided by forming a recess or groove in the lower surface  35  of the sleeve member  32 . By providing first and second sets of outlet openings  33 ,  37  having a different number of openings in each set, or having openings of different size, or having openings with a different fuel spray cone angle, it will be appreciated that by selectively injecting fuel from either the first set of outlet openings  33  alone, or from both the first and second sets of outlet openings  33 ,  37  together, by controlling the extent of movement of the valve needle  30  away from the seating  34 , the fuel injection characteristics can be varied, in use. It will also be appreciated that a different number of outlet openings to those shown in the accompanying Figures may be provided in the sleeve member. A third or further set of outlet openings may be provided in the sleeve member, the actuator arrangement being arranged to control movement of the valve needle between first, second, third or further fuel injecting positions.