Patent Application
20060071100
The present invention relates to an injection nozzle for use in a fuel injection system for an internal combustion engine. More particularly, although not exclusively, the present invention relates to an injection nozzle for use in a compression ignition internal combustion engine in which first and second valve needles are operable to control the injection of fuel into a combustion space through a plurality of nozzle outlets.
Due to increasingly stringent environmental regulations, a great deal of pressure is levied upon automotive manufacturers to reduce the level of vehicle exhaust emissions, for example, hydrocarbons, nitrogen oxides (NOx) and carbon monoxide. As is well known, an effective method of reducing exhaust emissions is to supply fuel to the combustion space at high injection pressures (around 2000 bar for example) and to adopt nozzle outlets of a small diameter in order to optimise the atomisation of fuel and so improve efficiency and reduce the levels of hydrocarbons in the exhaust gases. Although the above approach is effective at improving fuel efficiency and reducing harmful engine exhaust emissions, an associated drawback is that reducing nozzle outlet diameter conflicts against the requirement for high fuel injection flow rates at high engine loads and so can compromise vehicle performance.
So-called “variable orifice nozzles” (VON-nozzles) enable variation in the number of orifices (therefore the total orifice area) used to inject fuel into the combustion space at different engine loads. Typically, such an injection nozzle has at least two sets of nozzle outlets with first and second valve needles being operable to control whether fuel injection occurs through only one of the sets of outlets or through both sets simultaneously. In a known injection nozzle of this type, as described in the Applicant's co-pending European patent application no. EP 04250928.1, the fuel flow to a first (upper) set of nozzle outlets is controlled by an outer valve needle and the fuel flow to a second (lower) set of nozzle outlets is controlled by an inner valve needle. The inner valve needle is lifted by the outer valve needle only after the flow of fuel through the first set of nozzle outlets has reached a sufficient rate. An injection nozzle of this type enables selection of a small total nozzle outlet area in order to optimise engine emissions at relatively low engine loads. On the other hand, a large total nozzle outlet area may be selected so as to increase the total fuel flow at relatively high engine loads.
It is against this background that the present invention has been devised. The invention provides an injection nozzle for an internal combustion engine, the injection nozzle including a nozzle body provided with a bore defining a valve seating surface, and having a first nozzle outlet and a second nozzle outlet. The injection nozzle further includes a first delivery chamber upstream of said nozzle outlets, an outer valve member, moveable within the bore and itself provided with an axial bore. The outer valve member is engageable with an outer valve seat defined by the valve seating surface so as to control fuel flow from the first delivery chamber to at least the first nozzle outlet when the outer valve member lifts from its seat. The nozzle further includes an inner valve member, moveable within the axial bore and including first and second seating lines spaced apart axially from each other, both the first and second seating lines being engageable with an inner valve seat defined by the valve seating surface so as to control fuel flow from a second delivery chamber to the second nozzle outlet when the inner valve member lifts from its seat. The inner valve member defines, at least in part, a fuel flow path including an axial passage provided in the inner valve member such that fuel may flow from the first delivery chamber to the second delivery chamber.
The above arrangement optimises fuel flow efficiency to the first and second outlets without requiring a large sac volume to be disposed downstream of the inner and outer valve seats.
It is a preferred feature of the invention that the inner valve seat includes first and second seats disposed axially above and below the second outlet, respectively. It is also preferred that the first and second seating lines are defined, at least in part, by an annular groove provided on the inner valve member.
Preferably, the fuel flow path further includes at least one radial passage provided in the outer valve member and at least one radial passage provided in the inner valve member.
In a preferred embodiment, the injection nozzle includes a coupling arrangement that couples movement of the outer valve member to the inner valve member when the outer valve member moves through a distance that is greater than a predetermined distance. Still preferably, the coupling arrangement includes a sleeve member coupled to the inner valve member and a ring member coupled to the outer valve member, wherein the ring member is brought into engagement with the sleeve member when the outer valve member is moved axially through a distance that is greater than a predetermined distance so as to impart axial movement to the inner valve member.
The ring member and the sleeve member may have respective first and second end faces, the first end face of the ring member being opposed to and spaced apart from the first end face of the sleeve member by the predetermined distance when the outer valve member and the inner valve member are seated.
The invention also extends to a fuel injector incorporating an injection nozzle as described above, the fuel injector including an actuator, preferably a piezoelectric actuator, for controlling axial movement of the outer valve member.
By way of example, the invention will now be described with reference to the accompanying drawings, in which:
a and 7b are sectional views of an injection nozzle in accordance with a second embodiment of the invention; and
a and 8b are sectional views of an injection nozzle in accordance with a third embodiment of the invention.
In the following description, the terms “upper” and “lower” are used having regard to the orientation of the injection nozzle as shown in the drawings. Likewise, the terms “upstream” and “downstream” are used with respect to the direction of fuel flow through the nozzle from a fuel inlet line to fuel outlets.
Referring to
Fuel is supplied to the injector via an inlet 39 from, for example, a common rail or other appropriate source of pressurised fuel, which is also arranged to supply fuel to one or more other injectors. Pressurised fuel is communicated from the inlet 39, through an inlet passage 38 and an accumulator volume 34, to an annular chamber 7 defined within the bore 8 between the nozzle body 6 and an upper end region 10a of the outer valve needle 10. The upper end region 10a has a diameter substantially equal to that of the nozzle body bore 8 such that co-operation between these parts serves to guide movement of the outer valve needle 10 as it reciprocates within the bore 8, in use. Spiral flutes machined into the upper end region 10a provide a flow path for fuel to be communicated from the annular chamber 7, through the bore 8 and into a first delivery chamber 50. The delivery chamber 50 is defined between the outer surface of the outer valve needle 10 and a region of the nozzle body bore 8 upstream of the outlets 12, 18.
Toward its blind end, the bore 8 defines a seating surface 22 of conical form, terminating in a sac volume 20 constituting a second delivery chamber. The seating surface 22 defines an outer valve seating 24 with which a lower end region 10b of the outer valve needle 10 is engageable to control fuel injection through the first set of outlets 12. The outer valve needle 10 is biased towards the outer valve seating 24 by means of a first closing spring 26 in conjunction with fuel pressure in a spring chamber 26a in which the spring 26 is housed. The outer valve needle 10 is operable to move away from the outer valve seating 24, against the force provided by the biasing spring 26 and fuel pressure, by means of a piezoelectric actuator 30.
The piezoelectric actuator 30 comprises a stack 32 of piezoelectric elements arranged within the accumulator volume 34, and an electrical connector 40 to enable a voltage to be applied across the stack 32. In use, the accumulator volume 34 is filled with high pressure fuel so as to apply a hydrostatic loading to the stack 32. The piezoelectric actuator 30 is coupled to the outer valve needle 10 by way of a hydraulic amplifier arrangement 42. Varying the voltage applied to the stack 32 causes the stack 32 to extend and contract and this movement is transmitted via the hydraulic amplifier arrangement 42 to the outer valve needle 10.
The inlet ends of the first and second set of outlets 12, 18 extend radially away from the seating surface 22 so that their outlet ends open at the outer surface of the nozzle body 6. It will be appreciated that in the figures, only a single outlet of each of the first and second sets of outlets 12, 18 is shown with the outlet of each set being disposed at a different axial position along the main axis of the nozzle body 6. However, in practice, each set of outlets 12, 18 may include a plurality of outlets.
The blind end of the axial bore 16 provided in the outer valve needle 10 defines a chamber 62 which serves to accommodate the upper end of the inner valve needle 14. The chamber 62 is in communication with the nozzle body bore 8 via radial passages 53, in the form of cross drillings provided in the outer valve needle 10, which provide a venting function for the chamber 62. In addition, pressurised fuel within the chamber 62 acts on the inner valve needle 14 to provide a force to bias the inner valve needle 14 against its valve seating 25.
The lower end region 10b of the outer valve needle 10 is provided with radial passages 52, which define part of a flow passage means. One end of each passage 52 communicates with the delivery chamber 50 and the other end of each passage 52 communicates with the axial bore 16.
The inner valve needle 14 is shaped to include three regions: an upper stem region 14a, a lower region 14c, and a step region 14b which is intermediate, and so separates, the stem region 14a and the lower region 14c. The step region 14b is of cylindrical form having a diameter which is substantially the same as the bore 16 provided in the outer valve needle 10. As a result, the step region 14b serves to guide movement of the inner valve needle 14 as it is moved into and out of engagement with the inner valve seating 25 to control fuel injection through the second outlets 18.
The lower region 14c of the inner valve needle 14 has a diameter substantially equal to that of the bore 16 and is provided with an axially extending blind bore 72. The blind end of the bore 72 communicates with the delivery chamber 50 by way of radial drillings 70 disposed substantially in line with the radial drilling 52 provided in the outer valve needle 10 when both needles 10, 14 are seated. The bore 72 and the radial drillings 70 provided in the inner valve needle 14, together with the radial drillings 52 provided in the outer valve needle 10, together define flow passage means which constitutes a secondary or supplementary flow path for fuel. When the outer valve needle 10 lifts away from the outer valve seating 24, fuel is able to flow from the upper delivery chamber 50 into the first outlets 12 directly past the outer valve seating 24. When the inner valve needle 14 lifts away from the inner valve seating 25 also, fuel is either able to flow from the upper delivery chamber 50 into the second outlets 18 directly past the outer valve seating 24 (a ‘primary flow path’) or indirectly through the secondary flow path past the inner valve seat 25.
The fuel passageways provided by the outer and inner valve needles 10, 14 serve to limit the restriction to fuel flow through the secondary fuel flow path 52, 70, 72 to an acceptable level whilst the lower region 14c guides axial movement of the inner valve needle 14 through co-operation with the adjacent region of the bore 16. Lateral movement of the lower region 14c due to the high pressure fuel flowing through the supplementary flow path, in use, is thus substantially eliminated. As a result, concentricity of the valve tip is improved and so a more effective and reliable seal against unwanted ingress of fuel into the combustion chamber is achieved. Moreover, since the entire length of the lower region 14c of the inner valve needle 14 is in contact with the bore 16 in the outer valve needle 10, the wear resistance of the inner valve needle 14 is improved.
The mechanism through which movement of the inner valve needle 14 is controlled will now be described with reference to
The ring member 80 includes a first, upper end face 80a and a second, lower end face 80b, the lower end face 80b abutting a step or shoulder 15 defined by the step region 14b of the inner valve needle 14. The internal diameter of the ring member 80 is greater than the diameter of the stem region 14a, such that the stem region 14a passes through the ring member 80 and defines a clearance fit therewith. It will be appreciated that, in the position shown in
The upper end face 80a of the ring member 80 opposes a first, lower end face 82a of a second annular member 82 in the form of a sleeve. The sleeve member 82 is a separate and distinct part from the inner valve needle 14 and has an external diameter that is less than that of the bore 16 and an internal diameter that is substantially equal to the diameter of the stem region 14a. Put another way, the sleeve member 82 is an interference fit with the stem region 14a and so is coupled to the inner valve needle 14 through frictional contact.
The lower end face 82a of the sleeve member 82 and the upper end face 80a of the ring member 80 are separated by a distance ‘L’ that is predetermined at manufacture. When the outer valve needle 10 is caused to lift, in use, the upper end face 80a of the ring member 80 will be brought into contact with the lower face 82a of the sleeve 82, thus causing the inner valve needle 14 to move also. The distance ‘L’ therefore determines by what amount it is necessary for the outer valve needle 10 to lift away from the outer valve seating 24 before interacting with the inner valve needle 14 and conveying movement thereto. It should be appreciated that the lower end face 82a of the sleeve member 82 and the upper end face 80a of the ring member 80 are at maximum separation (i.e. predetermined distance ‘L’) when both the inner valve needle 14 and the outer valve needle 10 are seated.
The upper groove region 10d and the lower groove region 10e together form the recessed region or groove of the outer valve needle 10 and define, together with the adjacent region of the seating surface 22, an annular volume 64 for fuel at the inlet end of each of the first outlets 12. The upper and lower seating lines 11, 13 engage the outer valve seating 24 at respective first and second seats 24a, 24b thereof.
In a manner similar to that of the outer valve needle 10, the lower region 14c of the inner valve needle 14 is provided with a grooved or recessed region which defines, at respective upper and lower edges thereof, the upper and lower seating lines 73, 75 that are arranged axially above and below the second outlets 18, respectively, when the inner valve needle 14 is seated. Put another way, the second outlets 18 are arranged intermediate the positions at which the seating lines 73, 75 engage first and second seats 25a, 25b. More specifically,
Operation of the injector 2 will now be described. Fuel under high pressure is delivered from a high pressure fuel source (e.g. a common rail) to the annular chamber 7 via the inlet 39, the inlet passage 38 and the accumulator volume 34. Hence, fuel is delivered to the bore 8 and thus the upper and lower delivery chambers 50, 20. Initially, the piezoelectric actuator 30 is energised so that the stack 32 is in an extended state and the injection nozzle 4 is in the position shown in
During this initial de-energisation of the actuator 30, the outer valve needle 10 is caused to move through a distance less than the distance ‘L’. The ring member 80 is carried with the outer valve needle 10 during this initial movement because of the frictional engagement between the parts and so the upper end face 80a of the ring member 80 approaches, or moves towards, the opposing end face 82a of the sleeve member 82. At the same time, the lower end face 80b of the ring member 80 will disengage from the shoulder 15 of the step region 14b. Providing that the distance through which the outer valve needle 10 moves is less than the pre-determined distance ‘L’, the upper end face 80a of the ring member 80 does not engage the lower end face 82a of the sleeve member 82. Therefore, the inner valve needle 14 remains seated against the inner valve seating 25, under the influence of pressurised fuel within the chamber 62 acting on the upper end of the inner valve needle 14.
When the outer valve needle 10 is moved through this initial amount, pressurised fuel is able to flow along the primary flow path from the upper delivery chamber 50, past the upper seating line 11 into the annular volume 64 and thus through the first outlets 12 into the combustion chamber (not shown). Fuel will also be able to flow along the secondary flow path from the upper delivery chamber 50, through the radial passages 52 and the axial bore 16 into the lower delivery chamber 20.
During this phase of injector operation, it will be appreciated that movement of outer valve needle 10 is decoupled from the inner valve needle 14. Whilst the inner valve needle 14 is seated against the inner valve seating 25, fuel is neither able to flow from the upper delivery chamber 50 past the first seat 25a, nor from the lower delivery chamber 20 past the second seat 25b, to the second outlets 18. The above described condition represents fuel injection optimised for relatively low power applications since only a relatively small volume of fuel is injected through the first set of relatively small outlets 12 only.
If, at this point, it is necessary to terminate injection through the first outlets 12, the piezoelectric actuator 30 is re-energised to its initial energisation level causing the stack 32 to extend. As a result, the outer valve needle 10 is caused to re-engage with the outer valve seating 24, at both the first and second seats 24a, 24b, under the influence of the biasing force of the closure spring 26 in conjunction with fuel pressure within the spring chamber 26a. Under these circumstances, the injection nozzle 4 again takes up the position shown in
As the inner valve needle 14 lifts away from the inner valve seating 25, fuel within the lower delivery chamber 20 is able to flow past the lower seating line 75 and through the second outlets 18 into the combustion chamber, supplementing the fuel flowing past the outer valve seating 24 and through the first outlets 12. In addition, fuel is also able to flow to the second outlets 18 from the upper delivery chamber 50 and past the upper seating line 73 (see
a and 7b show an alternative embodiment of the invention that further improves the flow efficiency of the injection nozzle 4. Where appropriate, like parts to those previously described are denoted with like reference numerals. The embodiment in
It is a further optional feature (illustrated in
A method by which the inner and outer valve needles 14, 10 of the above described embodiments may be assembled within the nozzle body 6 will now be described. Initially the ring member 80 is caused to receive the stem region 14a of the inner valve needle 14 so that the lower face 80b of the ring member 80 abuts the step region 14b. With the ring member 80 in position, the sleeve member 82 is then caused to receive the stem region 14a such that the ring member 80 is retained on the inner valve needle 14. In order to set the predetermined distance ‘L’, a spacer tool, such as a shim of thickness ‘L’ (not shown), is positioned against the upper end face 80a of the ring member 80, whereby the sleeve member 82 is pushed so as to engage the shim. When the shim is removed, the necessary separation of distance ‘L’ is established between the upper end face 80a of the ring member 80 and the lower end face 82a of the sleeve member 82.
Following assembly of the inner valve needle 14, the ring member 80, and the sleeve member 82, the combined inner valve needle 14 and ring/sleeve assembly 80, 82 is pushed into the bore 16 of the outer valve needle 10. The inner and outer valve needles 14, 10 together are then inserted into the nozzle body bore 8 such that the seating lines 11, 13 of the outer valve needle 10 engage with their respective seats 24a, 24b of the outer valve seating 24 and the seating lines 73, 75 of the inner valve needle 14 engage with their respective seats 25a, 25b of the inner valve seating 25. Following assembly of the nozzle a bedding operation is performed in order to establish effective seals at the inner and outer seatings 24, 25. The seat bedding operation comprises applying a constant predetermined axial force to the outer valve needle 10, causing the upper and lower seating lines 11, 13 to “bed in” over the upper and lower seats 24a, 24b respectively. As an alternative to applying a predetermined constant axial force to the outer valve needle 10, the bedding in operation could also be dynamic.
It will be understood by those who practice the invention and those skilled in the art, that various modifications and improvements may be made to the invention without departing from the scope of the invention, as defined by the claims. Accordingly, reference should be made to the claims and other conceptual statements in determining the scope of the invention.
For example, although the inner valve needle 14 is forced into engagement with its seating 25 by the ring member 80 abutting the shoulder of the step region 14b, it is possible that, in use, the lower end face 80b of the ring member 80 may wear such that a clearance is established between the lower end face 80b and the shoulder 15 when the inner and outer valve needles 14, 10 are seated. This may compromise the seal established by the inner valve needle 14. A resilient member such as a helical spring (not shown) may be arranged within the chamber 62 to provide a further biasing force to the inner valve needle 14. Such a spring may abut against the upper end face 82b of the sleeve member 82 such that the biasing force is transmitted to the inner valve needle 14 via the frictional coupling between these parts. Alternatively the spring may abut a separate abutment member located within the chamber 62.
Furthermore, although the ring member 80 and the sleeve member 82 are coupled to the outer valve needle 10 and inner valve needle 14, respectively, through frictional contact, it will be appreciated that coupling may be achieved through alternative means, for example by gluing or soldering. Further, the ring member 80 may be in the form of a “C” shaped pin member having lateral resilience, by which means the ring member 80 maintains frictional contact with the bore 16.
In addition, although in the above described embodiments, the flow passage means of the inner valve needle 14 is defined by the axial bore 72 and the radial drillings 52, it will be appreciated that this need not be the case. For example, the inner valve needle 14 may be supplied with a passage extending along substantially its entire length for performing the function of supplying pressurised fuel to the lower delivery chamber 20.
It should be understood that although the injection nozzle 4 of the present invention has been described as suitable for use within an injector having a piezoelectric actuator, it is entirely possible that the injector may include an alternative form of actuator for moving the needles 10, 14. For example, instead of a piezoelectric actuator, the outer valve needle 10 may be moved by means of an electromagnetic actuator. Moreover, although the piezoelectric actuator 30 is described here as being coupled to the outer valve needle 10 via a hydraulic amplifier arrangement 42, as an alternative the actuator may be mechanically coupled to the outer valve needle 10.
| Number | Date | Country | Kind |
|---|---|---|---|
| 04256105.0 | Oct 2004 | EP | regional |
