Fuel injector

Abstract

 A fuel injector including: piezoelectric actuation means, a valve arrangement comprising a nozzle including a valve seat, and a valve needle, said needle adapted to be slidable within said nozzle so as to selectively open and close the valve by respective disengagement/ engagement of the needle against the seat to allow fuel from a pressurised source to be injected into a combustion space, and hydraulic invertor means adapted such that activation/deactivation of said piezoelectric activation means provides respective retraction/extension of said needle away or to said valve seat so as to open/close the valve respectively.

Description

Technical Field

[0001] The invention relates to fuel injectors for delivering fuel into a combustion chamber such as a cylinder of an internal combustion engine. It relates in particular, but not exclusively, to fuel injectors including piezoelectric actuators used to control movement of a needle in an injector valve.

Background of the Invention

[0002] The use of piezoelectric actuators is known as an alternative to solenoids for controlling injections in a fuel injector. Typically, a stack of piezoelectric elements can be arranged to control fuel pressure within an injector fuel chamber so as to consequentially control the movement of an injector needle away from a valve seat so as to inject fuel.

[0003] Known fuel injectors of the piezoelectric actuated type can be categorised into those wherein a reduction of voltage across the piezoelectric stack initiates an injection event, so called "de-energise to inject" type injectors, and those wherein an injection event is initiated when voltage is increased across the piezoelectric element (stack), so called "energise to inject" type injectors.

[0004] The "de-energise to inject" type actuators generally have a reduced piezoelectric stack life compared to the "energise to inject" type actuators. Thus it is preferable to actuate injection when the piezoelectric stack itself is actuated, i.e. becomes elongated.

[0005] Piezoelectric actuators, typically positioned above a fuel injector nozzle, elongate when energised. Such piezoelectric actuator elongation can be utilised to provide injection in arrangements where the nozzle needle opens outwardly, such is the case with many gasoline direct injection engines. In injectors for diesel engines, injector needles are however adapted to move inwardly (retract) to release fuel. Thus, for such injectors, an inverter arrangement is required between the actuator and the needle. Mechanical inverters are known; however these have inherent disadvantages.

[0006] It is an object of the invention to overcome such disadvantages, and to provide for an improved fuel injector of the "energise to inject type" actuator.

Summary of the Invention

[0007] In one aspect of the invention is provided a fuel injector including: piezoelectric actuation means, a valve arrangement comprising a nozzle including a valve seat and a valve needle, said needle adapted to be slidable within said nozzle so as to selectively open and close the valve by respective disengagement/ engagement of the needle against the seat to allow fuel from a pressurised source to be injected into a combustion space, and hydraulic invertor means adapted such that activation/deactivation of said piezoelectric activation means provides respective retraction/extension of said needle away or to said valve seat so as to open/close the valve respectively.

[0008] The piezoelectric actuation means may include a piezoelectric element or stack of elements.

[0009] The hydraulic invertor means may be adapted such that extension or elongation of the piezoelectric element/stack causes retraction of said needle away from said valve seat, and shortening of said piezoelectric element/stack causes said needle to extend to said needle seat.

[0010] The hydraulic invertor portion may comprises: a first hydraulic chamber, and a first piston located within said first hydraulic chamber, and adapted to move within said first hydraulic chamber consequent to activation/deactivation of the piezoelectric actuation means or extension/retraction of said piezoelectric element or stack of elements, a second hydraulic chamber connected to said first hydraulic chamber via a first conduit, and also connected to a pressurised fluid/fuel source via second conduit, a second piston, adapted to be moveable within said second hydraulic chamber, said piston generally located between said first and second conduits in said second hydraulic chamber, so as to divide said second chamber into first and second volumes, said second piston being connected to said needle, and arranged such that consequent to said first piston moving in said first chamber, said second piston is adapted to move in an opposite direction in said second chamber, so as to retract/extend said needle from/to said seat on respective activation/deactivation of said actuation means.

[0011] The second piston may be attached to or be integral with the proximal portion of said valve needle.

[0012] The first piston may be adapted to move within said first chamber from a force provided by extension of piezoelectric stack/activation of piezoelectric actuator so as to force fluid via said first conduit to said first volume of said second chamber, consequentially increasing pressure therein so as to move said second piston against the pressure from said pressurised fuel source and consequentially retract said valve needle from said valve seat.

[0013] The fuel injector may be adapted such that deactivation of piezoelectric actuator/retraction of piezoelectric stack causes a reduction in force acting on said first piston so as to reduce pressure in the first chamber and, by means of said first conduit connecting said chambers, a consequential reduction in pressure in said first volume, so as to move said second piston in a direction towards the first conduit connection by pressure from said pressurised fuel source, and consequently force the valve needle onto said valve seat to close said valve.

[0014] The hydraulic invertor means may be located within a generally cylindrical sleeve.

[0015] The sleeve may be part of the actuator housing which encloses the piezoelectric stack or element.

[0016] The first fluid conduit may be provided by an insert, locatable or located within said sleeve.

[0017] The fuel injector may include first and/or second spring means to urge said first and/or second piston towards the piezoelectric stack/ valve tip region respectively.

[0018] The first and second chambers may be separated by a common wall.

[0019] The piston(s) include sealing rings and/or grooves.

[0020] The pressurised fuel source may be a fuel rail, fuel accumulator volume and/or a pressurised fuel source which is common to the fuel supply for injection in the injector.

Brief Description of the Drawings

[0021] The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows a schematic cross-section of a simple embodiment of the invention.

Figure 2 shows a cross-section through a fuel injector according to one example which includes a hydraulic invertor mechanism.

Figures 3, 4a and4 b show partial cross-sectional views of a tip portion of a fuel injector according to examples.

Figures 5a and b shows similar embodiments of hydraulic invertor mechanisms according to examples.

Figure 6 shows an alternative embodiment of hydraulic invertor mechanism according to an alternative example.

Description of the Preferred Embodiments

[0022] Figure 1 shows schematically a simple embodiment of the invention, showing a sectional schematic portion of a fuel injector 1. A portion of the fuel injector/actuator housing forms a generally hollow cylindrical, sleeve type arrangement 2. Within the sleeve/housing are formed two chambers; a first (upper) chamber 3 and a second (lower) chamber, designated by reference numeral 4a and 4b. These chambers are separated by a plug 5 shown in the figure as being formed integrally within the injector housing sleeve. In practical embodiments the invertor mechanism may be provided as an insert of e.g. a general sleeve construction defining the chambers and separating wall, as will be described in more detail below.

[0023] A first piston or plunger element 6 is also located within the first chamber and adapted to move within the first chamber as a result of fluid pressure within the first chamber in one direction, and the applied force (in the opposite direction) from a piezoelectric stack 7 arranged so as to contact the piston element on the other (upper) side.

[0024] The figure shows the top (proximal) portion of a fuel injector needle 8, which is slidably located within the lower chamber. At this end of the needle is a widened portion, which may alternatively be formed of an attachment rather than being integral with the needle, and which is so adapted to form a further plunger/piston 9, susceptible to movement as a result of differential fluidic pressures between the lower and upper regions/volumes (4a, 4b) of the second chamber, either side of piston 9. In the figure, only the top portion of the fuel injection needle is shown; the distal end of the needle includes a needle tip portion which is adapted to engage on a valve seat, located at the distal extremity (nozzle portion) of the valve body. Upward movement of the needle away from the valve seat allows injection of fuel into a combustion space such as a cylinder in a conventional manner. Fuel is supplied for injection via means such as one or more supply conduits and fuel chambers formed adjacent to, or located in an injector housing. Such fuel supply conduit arrangements are well known in the art and will not be described in detail hereinafter, suffice to say that any such arrangement can be utilised in conjunction with the invention.

[0025] The upper region of the second chamber includes a fluidic connection 10 to, for example, a fuel source such as a fuel pressure rail; this may be manifested as a bore or other suitable conduit. The first and second chambers are connected fluidly by means of further conduit, such as a bore 11. This may be formed integral with the injector/actuator sleeve. Alternatively, the conduit/bore may be provided as an insert to overcome practical difficulties encountered when manufacturing a bore within the injector housing.

[0026] In operation, electrical actuation of the piezoelectric stack will cause elongation thereof, such that it contacts and forces the piston/plunger element 6 downwards against fluid pressure in the first chamber. This results in high pressure in the first chamber, this pressure being higher than the fuel rail pressure, such that fluid (fuel) is forced, via conduit 11, from the first chamber into the lower portion of the second chamber, increasing the pressure therein, and consequentially urging the valve needle to move upwards against the lower pressure in the upper region (volume) of the lower chamber, the fluid therein can exit via bore 10. As a result the valve needle tip is lifted upwardly away (i.e. retracted) from the valve seat, allowing fuel to be injected into a combustion chamber.

[0027] Deactivation of the piezoelectric element allows a reduction in the pressure in the first chamber, and via the conduit 11, a consequent reduction in pressure in the lower region (volume) of the second chamber. The higher pressure in the upper region (volume) of the lower chamber provided from e.g. pressurised fuel volume such as a fuel rail, acts against the piston formed at the one end of the valve needle, so as to move the needle downwards until the tip engages with the seat to close the valve and stop fuel flow.

[0028] Figure 2 shows a sectional view of a practical fuel injector 12 according to one aspect. Within an actuator housing 13 is located a piezoelectric actuator 14 including a stack of piezoelectric elements. The stack is supplied by an electrical connection means 15 towards the top of the housing.

[0029] The lower portion of the injector includes a nozzle body 16, within which core is located a valve needle 17, shaped to form a sliding fit within the nozzle body, and moveable along a vertical axis so as to open and close the valve by selective engagement/disengagement with a valve seat 21. The nozzle body is located onto the actuator housing by means of nut 19. The valve needle is slidable within a bore provided within an injector nozzle body. The valve needle includes a needle tip region 20, which is engageable with a valve (needle) seat 21 at one end of nozzle body so as to control fuel injection to a combustion space by selective closing and opening of an orifice formed between the needle tip and the valve seat. Fuel is supplied to the needle tip region by annular bores 22 or other type of conduits, from a widened recess volume 23 within the nozzle body, and fuel supplied to this volume by further conduit means (not shown).

[0030] Between one end of the piezoelectric stack and proximal end of the needle is located a hydraulic inverter unit 24 which will be explained in more detail below. An intermediate element 27 may be located between the distal end of the piezoelectric element (stack) and the inverter unit

[0031] The piezoelectric actuator is selectively operable, via the hydraulic inverter unit, to control movement of the valve needle between a non-injecting position, in which it is seated against the valve needle seat and an injecting position in which the valve needle is lifted away from the valve needle seat, and furthermore such that actuation of the piezoelectric stack causes the needle to lift away (upwardly) so as to retract it from the valve seat.

[0032] Figure 3 shows cross-sectional view showing the tip portion of the fuel injector according to an embodiment in more detail, in order to show the location of the hydraulic invertor unit; similar components have like reference numerals. Likewise figures 4a and b show cross-sectional views of the tip portion elements of the fuel injector according to examples, specifically showing the nozzle portion and adjacent hydraulic invertor unit; in these figures the components would be attached/fitted to a main actuator body.

[0033] The nozzle body may be provided with a bore 25 which may define a first upper delivery chamber for receiving fuel under high pressure and a second lowed delivery chamber 22 for fuel. Towards the distal end 26 of the internal surface of the bore is of frusto-conical form so as to define a valve seating surface. The arrangement of the fuel supply conduits, bores and fuel chamber is such that vertical movement of the injector needle acts to open and close the injector valve by successively lifting the needle tip away from the seat to allow fuel to be injected into a combustion chamber under pressure before closing the valve and cutting fuel flow by the needle tip closing (re-engaging on the seat). As mentioned, various arrangements are known in the art of mechanisms and designs which control the flow and pressure of fuel for injection and will not be detailed here, suffice to say that the invention can be used in conjunction with any such designs. Fuel is supplied to the injector from a high pressure fuel source such as from a common rail or accumulator volume, and flows through conduit(s) formed, for example, between the actuator housing and hydraulic invertor housing/nozzle body to a nozzle supply chamber formed by a widened portion of the bore in the upper region of the nozzle body.

[0034] Located within the actuator housing is a piezoelectric stack 14. The inverter unit 24 is located generally between an actuator (piezoelectric stack) and the nozzle body 19. Again an injection needle 17 is slidably located within a bore formed in a nozzle body. The nozzle body may be attached to actuator housing via a nut which also forms a sleeve. Alternatively as shown in figure 3b and c, the nozzle body may be attachable/attached directly to the actuator housing without the use of a nut. In alternative arrangements the nozzle body may be attached to one end of the inverter unit, particularly if the inverter unit not located within the actuator housing.

[0035] The inverter unit can be provided as an insert having a housing of sleeve construction incorporating the elements of the invertor; this is may be insertable or located within the actuator housing. Alternatively elements of the invertor unit are located within the fuel injector (e.g. within the actuator housing without a separate inverter sleeve). Thus the hydraulic invertor housing and in some examples also the injector nozzle body, are located within an overall actuator housing. The hydraulic invertor unit may be contained in a sleeve which may be provided separate to, or integral with, the actuator housing Specifically the hydraulic invertor unit is adapted and configured such that extension (elongation of the stack) causes upward movement of the injector needle, and conversely retraction of the stack causes downward movement of the needle. Examples of the hydraulic actuator unit for actuating the needle in conjunction with the piezoelectric stack is shown and described in more detail in figures 5 and 6.

[0036] Figure 5a and 5b show similar embodiments of the hydraulic invertor unit in more detail, also showing a portion of the actuator housing 13 in which it is located. The hydraulic invertor unit includes a first cup-formed hollow cylindrical member 28 which is closed at one end by a wall 29 of the member 28; the opposite (piezoelectric stack) end is open-ended. Within this is located a piston 30, which is urged by spring means 36 away from the wall end, so as to form a first hydraulic chamber 38. The exterior face of the piston abuts (i.e. is in contact with) the end of the piezoelectric stack 14 or an intermediate member (intermediate between the exterior piston face and the distal end of the piezoelectric stack). A first sleeve member 31 which includes an internal annular ridge 32 may be provided for location within the actuator inner sleeve and to locate the cup member. In addition, the annular ridge locates a further second sleeve member 33 which is of hollow cylindrical form. In alternative embodiment of figure 5b, the first and second sleeve members may be integrally formed.

[0037] Within the second sleeve member is located a second piston 34 so as to define as second hydraulic chamber 39 bounded by the second sleeve member, piston and exterior face of the cup member. Second spring means 37 are located within this chamber so as to urge the second piston away from the exterior face of the cup member. The second piston is attachable/attached to the proximal end of the nozzle needle 17or alternatively is integral with it.

[0038] The first hydraulic chamber is fluidly connected to the lower region (volume) 41 of the second chamber by a fluid path/conduit (not shown). The second hydraulic chamber 39 can be regarded as comprising a first (upper) volume 40 bounded by the wall, second sleeve and top face of the piston and a second lower volume 41, bounded by the bottom face of the piston, second sleeve and the and bottom face of the piston. Differential pressures in the first and second volumes will cause a corresponding force on the piston and so as to consequently slidably move the needle 17 upwards or downwards, that is to say from and to an open/closed (retracted/extended) position. The upper portion of the second hydraulic chamber is connected to a pressurised supply of fuel.

[0039] When a voltage is applied across the stack from an external voltage source, the stack length will increase, and as a result one end of the stack pushes against a first piston member portion of the hydraulic inverter unit, causing pressurisation in the upper chamber of the unit, and causing fluid (such as fuel) therein to be forced via first conduit into the lower region of lower chamber, increasing the pressure therein, and causing a piston member located at the top end of the needle located in the second chamber to move upwards, causing upward vertical movement of the needle. The piezoelectric stack may be surrounded by a sleeve and include an end piece. In any case, the end piece or a surface of the sleeve abuts (i.e. is in contact with) the first piston member.

[0040] Figure 6 shows an alternative embodiment similar to the figure 5 embodiment, showing alternative design of hydraulic inverter unit. The hydraulic inverter unit 24 is shown on its own and can be provided as a unit locatable by e.g. insertion within a fuel injector, e.g. within the inner sleeve of the actuator housing. However in alternative embodiments the unit may be attached to the end of the actuator housing rather than located within it; in any case the invertor unit is generally located between the distal end of the piezoelectric actuator element (stack) and the proximal portion of the needle/nozzle body.

[0041] The unit includes a generally hollow cylindrical (outer) sleeve housing 42. The housing is separated into two (first and second) hydraulic chambers 38, 39, by a wall 29 of a cup shaped portion including inner sleeve 33, generally forms the second hydraulic chamber. Located within the (upper) first hydraulic chamber 38 is a first piston 30, urged away from the proximal face of the wall by spring means 36 to provide the volume of the chamber. The exterior face of the piston abuts (i.e. is in contact with) the end of the piezoelectric stack or alternatively an intermediate member (which is intermediate between the face and the distal end of the piezoelectric stack).

[0042] The sleeve 33 also defines a second hydraulic chamber 39, A second piston 34, connectable to (or integral with) the proximal end of the nozzle needle (not shown) divides the second hydraulic chamber into a first and second volumes 40,41. The lower volume of the first hydraulic chamber is fluidly connected to the lower volume 41 of the second chamber (the lower volume being bounded by the distal face of the wall, sleeve and the top face of the needle) by a conduit 45. This conduit may be formed by a bore in the sleeve member, or alternatively by an insert. On the outer perimeter of the sleeve is located a collar member for appropriate location/retention within the actuator housing. The upper (first) volume 40 of the second chamber is fluidly connected to a pressurised fuel source via orifice 46.

[0043] The following will now describe the operation of the above described examples. To provide injection, the piezoelectric stack is energized and this may be initiated via a command signal from the Electronic Control Unit of a vehicle. Extension of the piezoelectric element/stack pushes (or causes the intermediate member to push) against piston 30 so as to force the piston downwards, decreasing the volume in the first hydraulic chamber 38, and consequentially increasing the pressure therein. This causes fluid (fuel) to move through the conduit 45 (joining the two hydraulic chambers) causing an increase in pressure in the lower volume 41 of the second chamber. The needle shaft 17 is urged upwards due to a higher pressure in the lower volume 41 of the second hydraulic chamber than in the upper volume 40 thereof, wherein fuel can exits the upper volume of the second hydraulic chamber to a pressurised fuel source. Lifting of the needle away from the nozzle seat allows fuel to be injected. Conversely to close the valve, the piezoelectric stack is de-energized. This reduces the downward force on the first piston and with the assistance of the first spring means, allows the first piston to move upwards, thus reducing the pressure in the first hydraulic chamber. As a consequence of fluid flowing though the connecting conduit between the two hydraulic chamber, the pressure in the lower volume of the second hydraulic chamber is consequentially reduced. The pressure in the upper volume of the second chamber provided by the pressurized fuel source becomes higher than the reduced pressure on the lower volume, causes a downward force on the second piston (with the assistance of downward force from the second spring means), and hence pushes the needle downwards so as to close the valve by engaging the needle tip to the valve (nozzle) seat.

Claims

1. A fuel injector including:

piezoelectric actuation means,

a valve arrangement comprising a nozzle including a valve seat and a valve needle, said needle adapted to be slidable within said nozzle so as to selectively open and close the valve by respective disengagement/ engagement of the needle against the seat to allow fuel from a pressurised source to be injected into a combustion space, and

hydraulic invertor means adapted such that activation/deactivation of said piezoelectric activation means provides respective retraction/extension of said needle away or to said valve seat so as to open/close the valve respectively.

2. A fuel injector as claimed in claim 1 wherein said piezoelectric actuation means includes a piezoelectric element or stack of elements.

3. A fuel injector as claimed in claim 2 wherein said hydraulic invertor means is adapted such that extension or elongation of the piezoelectric element/stack causes retraction of said needle away from said valve seat, and shortening of said piezoelectric element/stack causes said needle to extend to said needle seat.

4. A fuel injector as claimed in claims 1 to 3 wherein said hydraulic invertor portion comprises:

a first hydraulic chamber, and

a first piston located within said first hydraulic chamber, and adapted to move within said first hydraulic chamber consequent to activation/deactivation of the piezoelectric actuation means or
extension/retraction of said piezoelectric element or stack of elements.

a second hydraulic chamber connected to said first hydraulic chamber via a first conduit, and
also connected to a pressurised fluid/fuel source via second conduit,

a second piston, adapted to be moveable within said second hydraulic chamber, said piston generally located between said first and second conduits in said second hydraulic chamber, so as to divide said second chamber into first and second volumes, said second piston being connected to said needle, and arranged such that consequent to said first piston moving in said first chamber, said second piston is adapted to move in an opposite direction in said second chamber, so as to retract/extend said needle from/to said seat on respective activation/deactivation of said actuation means.

5. A fuel injector as claimed in wherein said second piston is attached to or integral with the proximal portion of said valve needle.

6. A fuel injector as claimed in claims 4 or 5 wherein said first piston is adapted to move within said first chamber from a force provided by extension of piezoelectric stack/activation of piezoelectric actuator so as to force fluid via said first conduit to said first volume of said second chamber, consequentially increasing pressure therein so as to move said second piston against the pressure from said pressurised fuel source and consequentially retract said valve needle from said valve seat.

7. A fuel injector as claimed in claims 4 to 6 adapted such that deactivation of piezoelectric actuator/retraction of piezoelectric stack causes a reduction in force acting on said first piston so as to reduce pressure in the first chamber and, by means of said first conduit connecting said chambers, a consequential reduction in pressure in said first volume, so as to move said second piston in a direction towards the first conduit connection by pressure from said pressurised fuel source, and consequently force the valve needle onto said valve seat to close said valve.

8. A fuel injector as claimed in claims 1 to 7 wherein said hydraulic invertor means is located within a generally cylindrical sleeve.

9. A fuel injector as claimed in claims 1 to 8 wherein said sleeve is part of the actuator housing which encloses the piezoelectric stack or element.

10. A fuel injector as claimed in claims 1 to 9 wherein said first fluid conduit is provided by an insert, locatable or located within said sleeve.

11. A fuel injector as claimed in claims 1 to 10 including first and/or second spring means to urge said first and/or second piston towards the piezoelectric stack/ valve tip region respectively.

12. A fuel injector as claimed in claims 1 to 11 wherein said first and second chambers are separated by a common wall.

13. A fuel injector as claimed in any previous claim wherein said piston(s) include sealing rings and/or grooves.

14. A fuel injector as claimed in any previous claim wherein said pressurised fuel source is a fuel rail, fuel accumulator volume and/or a pressurised fuel source which is common to the fuel supply for injection in the injector.

Drawing