EP3580445B1

EP3580445B1 - Fuel injector nozzle assembly

Info

Publication number: EP3580445B1
Application number: EP18705587.6A
Authority: EP
Inventors: Thomas CAWKWELL
Original assignee: Delphi Technologies IP Ltd
Current assignee: Delphi Technologies IP Ltd
Priority date: 2017-02-10
Filing date: 2018-02-09
Publication date: 2022-09-14
Anticipated expiration: 2038-02-09
Also published as: WO2018146249A1; GB2559598B; EP3580445A1; GB201702265D0; GB2559598A

Description

TECHNICAL FIELD

The present invention relates to a fuel injector and more particularly to means for varying the injection rate during the needle lift.

BACKGROUND OF THE INVENTION

Known fuel injectors, specifically diesel injectors, are provided with a nozzle assembly wherein a needle valve member reciprocally moves under the influence of pressure difference to alternatively enable or prevent injection events. The needle is further provided with a needle motion controller (NMC) that is a collar member provided with a throttle orifice defining a controlled fluid communication generating, when the needle moves, a pressure difference between an upstream chamber and a downstream chamber of the nozzle.
The flow rate through the throttle orifice is continually increasing as the needle lifts so, in order for the needle to reach its final stop, or fully open position, the throttle orifice must be sized such that the pressure difference across the NMC, generating forces acting on the NMC does not exceed the force lifting the needle at maximum flow rate. This bias towards maximum flow rate means that the NMC has little effect on the initial rate of injection.
For low initial rates of injection, a method known as Inlet Needle Orifice (INO) is employed which continually flows fuel at rail pressure into a control chamber wherein protrudes the needle head extremity. This continual leak decreases the rate of pressure decay in the control chamber which decreases the rate of needle lift. The leak rate is set by a single orifice which sets the damping rate for all needle lifts. INO does not offer the flexibility to apply different levels of damping force at different needle lifts.
NOx formation can be decreased by reducing the quantity of fuel burnt during the premixed combustion phase preceded by a high injection rate in order to maintain combustion efficiency for small injections. Neither NMC nor INO offer this functionality to achieve this performance.
Document WO2013/034543 A1 describes a fuel injector having a valve assembly comprising an NMC in the form of a restrictive element which is movable with the needle of the fuel injector and which restricts flow through a bore of the fuel injector via a variable communication comprising a fixed damping fluid communication and an unrestricted fluid communication. The variable communication evolves from a restricted flow state, when the valve assembly is in a closed position preventing fuel injection, to an unrestricted state when the valve assembly is lifted away from the closed position.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to resolve the above mentioned problems in providing a nozzle assembly of a fuel injector comprising a body having a peripheral wall defining an inner space wherein is guided a valve assembly comprising a needle member and a needle motion controller, hereafter NMC. Said NMC cooperates with the inner face of said body to divide said inner space in an upstream chamber and a downstream chamber, the NMC being provided with a variable fluid communication comprising the fixed damping fluid communication and the unrestricted fluid communication between said chambers. the variable fluid communication evolving from a restricted flow state when the valve assembly is in a closed position preventing fuel injection, to an unrestricted flow state when the valve assembly is lifted away from said closed position.
Also, the fixed fluid communication is active when the valve assembly is in closed position and, the unrestricted fluid communication is inactive in closed position and, becoming active and predominant over the fixed fluid communication when the valve assembly lifts away from said closed position.
Also, said variable fluid communication comprises a shutter member, that activates the unrestricted fluid communication after the needle has lifted away from the closed position and, wherein said shutter member, deactivates said unrestricted fluid communication when the valve assembly approaches said closed position. Also, said NMC is a collar member defining an outer cylindrical face joining an upstream face partly defining the upstream chamber and, a downstream face partly defining the downstream chamber, said unrestricted fluid communication comprising inner channels opening in said outer face.
Also, said inner channel extends from said aperture in the outer face to an opening arranged in the downstream face.
Also, the NMC is provided with a plurality of said inner channels, each having an opening in the outer face.
Also, the shutter member is integral to the wall of the body.
Also, the inner section of the downstream chamber is narrower than the inner section of the upstream chamber, the inner face of the wall being provided with an annular shoulder joining said different sections, the shutter member being defined by the portion of the narrower wall next to said shoulder.
Also, in a closed position of the valve assembly, the shutter closes the opening of the inner channel arranged in the NMC outer face, the variable fluid communication being in a closed state and wherein, a needle motion toward an opposed open position moves said channel aperture in the larger upstream portion where it uncovers and opens beyond said shoulder face, opening said unrestricted fluid communication.
Also, said NMC is a collar member having an upstream face partly defining the upstream chamber and a downstream face partly defining the downstream chamber, the NMC being further provided with a drilling extending between an upstream opening arranged in said upstream face and a downstream opening arranged in said downstream face.
In another example not forming a part of the invention, the shutter member is a ring fixed to the nozzle body and provided with an annular transverse upper face parallel to the NMC downstream face that, when the needle is in closed position, defines a clearance with the NMC downstream face defining therebetween the fixed damping fluid communication.
Also, in this case, the radial width of the ring upper face is larger than the downstream opening of the drilling, said upper face covering said downstream opening and also an area surrounding said downstream opening so that, when the needle initiates a lift away from its closed position, the clearance from said shutter upper face to said NMC downstream face enlarges, opening said unrestricted fluid communication.
The invention further extends to a fuel injector of a fuel injection equipment of an internal combustion engine comprising a nozzle assembly as previously described.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described by way of example with reference to the accompanying drawings in which:

Figure 1 is a section along a main axis of a fuel injector as per a first embodiment of the invention.
Figure 2 is a magnified portion of figure 1.
Figure 3 is a needle motion controller of the injector, partly defining said second fluid communication.
Figures 4, 5, 6 and 7 are four sketches illustrating consecutive operation phases of the injector as per the invention.
Figure 8 is a plot of pressure signal indicative of the invention and of the prior art.
Figures 9, 10 and 11 show an example of an alternative variable section fluid communication, which is not part of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the invention is now described in reference to the figures 1 to 3 where, figure 1 is a section along a main axis X of a nozzle assembly 14 of a fuel injector 12, only the nozzle being shown, several of said injectors 12 being comprised in a fuel injector equipment 10 of an internal combustion engine. Said nozzle assembly 14 comprises a body assembly 16 defining an inner space S, in which is axially X guided a valve assembly 18 comprising a needle member 20 and a needle motion controller 22, hereafter NMC 22. Said valve assembly 18 is downwardly urged toward a closed position CP by a valve spring 24 compressed between an upper guide member 26 of the body assembly 16 and a spring seat 25 of the needle member 20.
For clarity and simplification purposes throughout the description reference is made to the arbitrary top-down orientation of the figure. Words and expression such as "upper, downward, top, over, below..." may be used without any limitation intent.
More particularly for this embodiment, the body assembly 16 comprises said upper guide member 26 arranged atop a barrel member 28 itself over a nozzle body member 30 that forms the thinner and lower part of the body. The nozzle body 30 is received in a lower recess provided in the barrel 28 and, said three assembly members 26, 28, 30 are firmly kept together by a lower capnut, not shown, maintaining the nozzle body 30 and the barrel member 28 and, by an upper capnut, not shown either, maintaining the barrel member 28 to an upper injector member not shown, compressing therebetween the upper guide member 26. In known alternatives, the nozzle body member upwardly extends integrating the barrel member in a monobloc component.
The inner space S has a large section upper portion LP and a narrow section lower portion NP, the larger upper portion LP being mainly in the barrel member 28 and, the narrow lower portion NP being entirely defined in the nozzle body 30. Said two portions LP, NP join in the upper part of the nozzle body member 30 firstly via an intermediate sloped portion IP upwardly extending from the inner wall 32 of the narrow portion NP to a first cylindrical face 34 then, secondly via a small annular shoulder face 36 outwardly radially extending from said first face 34 to a slightly larger second cylindrical face 38 that upwardly opens in the upper face 40 of the nozzle body member which sealingly cooperates with the barrel lower recess in which is engaged the nozzle body.
The radial width of said shoulder face 36 defining a radial offset RO between said first 34 and second 38 cylindrical faces, as visible on the magnified figure 2. Also, as visible on said figure, the inner face 42 of the barrel member and said first cylindrical face 34 have substantially identical cross-sections, the second cylindrical face 38 forming an intermediate enlargement.
The valve assembly 18 main component is the elongated needle member 20 extending axially X from a head end, guided in a bore of the upper guide member 26 and partly defining a control chamber 44, to a tip end that cooperates with a seating face defined on the inner face of the nozzle body 30 at the bottom end of the narrow portion NP, for opening or closing spray holes therein drilled in the wall of the nozzle body member 30. The needle member 20 further comprises, arranged in its lower part, a lower guiding portion in slide-fit adjustment with the inner wall 32 of the narrow portion NP so that, said needle member 20 is guided between said head and said lower guiding portion.
The NMC 22 represented in section in figures 1 and 2 and in 3D in figure 3 is a thick collar member, or thick washer, provided with an axial central opening 46 through which extends the needle member 20, the NMC 22 being fixed to the needle member 20 by press-fit. Said NMC 22 defines an upwardly oriented upstream face 48, visible on figure 3, opposed to a downwardly oriented downstream face 50, hidden on figure 3. Said two faces 48, 50 are joined by a peripheral cylindrical outer face 52 that is slide-fit adjusted against the first cylindrical face 34 of the upper end of the nozzle body. A position shoulder 54 integral to the needle member may be provided for the NMC downstream face 50 to abut against.
Other means such as welding may be used to fix the NMC on the needle and, alternatively the valve assembly 18 may be made monobloc integrating the needle and the NMC in a single component. In another alternative, the NMC is not fixed to the needle, the central opening 46 being slide-fit adjusted to the needle member 20.
Furthermore, the NMC 22 is provided with a throttle aperture 56 extending between the upstream face 48 and the downstream face 50 and also with a plurality of inner channels 58 opening in the downstream face 50 and in the outer face 52 where they define an outer aperture 60. The throttle 56 is a small and calibrated channel defining a fixed fluid communication F1 of fixed section permanently open between an upstream chamber UC that is above the NMC 22 and, a downstream chamber DC below said NMC 22. The inner channels 58 have a large section which, in closed position CP of the valve assembly 18, have their outer aperture 60 sealed by the slide-fit of the first cylindrical face 34 of the nozzle body, said first cylindrical face 34 being a shutter member to said inner channels 58.
The upstream chamber UC has the large section of the large portion LP of the body assembly 16 and, it extends from the upper guide member 26, throughout the barrel member 28 down to the NMC upstream face 48, said upstream chamber UC also integrating the very upper end of the nozzle body member defined by the slightly larger second cylindrical face 38.
On the other side of the NMC 22, the downstream chamber DC integrates the narrow portion NP, the intermediate sloped portion IP and finally the minor adjacent large portion defined by the first cylinder face 34 that is still below the NMC downstream face 50.
In use, briefly explained in reference to the figures 4 to 7, fuel at high pressure enters and fills the upstream chamber UC, then flows through the throttle 56 into the downstream chamber DC wherein it is ready to be sprayed.
In a first stage, figure 4, there is high pressure in the control chamber 44 generating a closing force which, along with the force of the valve spring 24, maintains the valve assembly 18 is in closed position CP. Fuel spray is prevented, the outer aperture 60 of the inner channels of the NMC 22 are closed by the shutter formed by the first cylindrical face 34, the upstream chamber pressure PU is substantially equal to the downstream chamber pressure PD.
In a second stage, figure 5, the control chamber pressure drops and the opening force generated by the downstream chamber pressure PD on the tip end initiates a needle lift motion enabling beginning of fuel spray through the injection holes. During this phase, the outer aperture 60 of the inner channels remains closed and, as the valve assembly 18 upwardly moves, a limited fuel quantity flows through the throttle 56 damping and slowing said initiation of the opening motion of the valve assembly. The volume of the upstream chamber UC reducing and the volume of the downstream chamber DC increasing, said throttle fixed damping fluid communication F1 generates a pressure difference across the NMC 22 that maintains a low net force and low opening velocity of the valve assembly.
In a third stage, figure 6, as the valve assembly 18 continues to lift up, the outer aperture 60 of the inner channels open above the shoulder 54 in the upstream chamber portion and, the area of said aperture 60 that becomes uncovered by the second cylindrical face 38 continuously increases opening an unrestricted fluid communication F2 between the downstream chamber DC and the upstream chamber UC. The opening area of said outer aperture 60 increases as the needle moves up toward the opening position OP. Since said inner channels 58 have a large section, said unrestricted fluid communication F2 does not restrict the flow between the chambers annealing the damping effect of the fixed fluid communication F1. In other words, in the course of this third stage, the unrestricted fluid communication F2 is closed at start and fully opens at end and between said extreme states, the unrestricted fluid communication F2 continuously opens.
In a fourth stage, figure 7, the control chamber pressure rises again forcing the valve assembly to revert toward the closed position CP. Since the force from the pressure difference across the NMC 22 is now acting in the same direction as the valve motion, the start of closing motion is slower because there is little or no restriction and therefore, little of no pressure difference across the NMC 22. As the restriction section decreases, the pressure difference increases which increases the valve closing force and the valve motion.
Following the graphs of figure 8, where are compared the injection rates of injectors against time, said injectors having a damping throttle, equivalent to F1, plot 1, a permanently open non-damping aperture, equivalent to F2, plot 2 and, an injector as per the invention with a variable fluid communication comprising the fixed damping fluid communication F1 and the unrestricted fluid communication F2, plot 3.
Plot 1 (F1 only, damping throttle), shows that the needle lift is constantly slow and so is the injection rate.
Plot 2 (F2 only, no damping), shows that the needle lift is fast throughout the needle motion and, when reaching the closed position CP the needle tip hits the seating face potentially damaging the surfaces.
Plot 3 (current invention), shows that the needle initial opening, left to right, and final closing, right to left, stages are damped and slow since it is only during valve initial opening, and final closing, that the pressure difference around the NMC works against needle motion direction, the area indicated A1 following the same curve in plot 3 as in plot 1 and, in the later lift stage, in an opening motion or early closing stage in a closing motion, plot area indicated A2, the valve assembly 18 accelerates and moves even faster than plot 2, joining said plot 2 by the fully open position OP. Said change in injection rate between the A1 and the A2 areas is indicative of a variable fluid communication comprising the damped F1 followed by the unrestricted F2 fluid communications. As shown on plot 3 the damping effect of the throttle 56 ends quite suddenly when the outer aperture 60 lifts over the shoulder 54.
In reference to the figures 9, 10 and 11 is now described an example wherein, the intermediate sloped portion IP of the nozzle body upwardly joins a larger portion defining said first cylindrical face 34. The previous second cylindrical face is removed. The NMC 22 has its outer face 52 in slide-fit adjustment against said first cylindrical face 34 and, it is provided with several drillings 62, four being represented, joining the upstream face 48 where each defines an upstream aperture 64, to the downstream face 50 where each defines a downstream aperture 66. This example, which is not part of the invention further comprises a shutter member 68 that is a ring arranged below the NMC 22, in the intermediate sloped portion IP. Said shutter member 68 is positioned in said sloped portion IP thanks to a sloped under face complementary arranged against the sloped face of the body. The shutter member 68 also has an annular transverse upper face 70 parallel to the NMC downstream face 50 and arranged right below the downstream openings 66 of the drillings 62, said upper face 70 having a radial width W much larger than said downstream opening.
In closed position CP of the valve assembly 18, said shutter upper face 70 does not contact said NMC downstream face 50 but lies within a very small clearance C defining the damping fluid communication F1, the throttle restriction being created by said clearance C through which the fuel has to flow.
When the valve assembly 18 lifts up toward the open position OP, the clearance C increases to a distance where the damping effect is reduced and does not dominate the needle motion and wherein, unrestricted fuel flow through the drillings 62 is enabled.
This example presents the shutter member 68 being positioned into the nozzle body thanks to a sloped under face. The important means is to accurately position the upper face 70 so defining the clearance C. Should the nozzle body have another shape then, other known means of positioning would be chosen, such as welding, screwing.

LIST OF REFERENCES

X: main axis
S: inner space
LP: large portion
NP: narrow portion
IP: intermediate sloped portion
RO: radial offset
UC: upstream chamber
DC: downstream chamber
CP: closed position
OP: open position
F1: fixed damping fluid communication
F2: variable fluid communication
C: clearance

10: fuel injection equipment
12: fuel injector
14: nozzle assembly
16: body assembly
18: valve assembly
20: needle member
22: needle motion controller - NMC
24: valve spring
25: spring seat
26: upper guide member
28: barrel member
30: nozzle body member
32: inner face of the narrow portion
34: first cylindrical face
36: shoulder face
38: second cylindrical face
40: upper face of the nozzle body
42: inner face of the barrel
44: control chamber
46: central opening of the NMC
48: upstream face of the NMC
50: downstream face of the NMC
52: outer face of the NMC
54: shoulder
56: throttle
58: inner channel
60: outer aperture of the inner channel
62: drillings - 2nd embodiment
64: upstream opening
66: downstream opening
68: shutter member
70: upper face of the shutter member

Claims

Nozzle assembly (14) of a fuel injector (12) comprising a body (16) having a peripheral wall defining an inner space (S) wherein is guided a valve assembly (18) comprising a needle member (20) and a needle motion controller, hereafter NMC, (22) cooperating with the inner face of said body (16) to divide said inner space (S) in an upstream chamber (UC) and a downstream chamber (DC), the NMC (22) being provided with a variable fluid communication comprising the fixed damping fluid communication (F1) and the unrestricted fluid communication (F2) between said chambers (UC, DC), said variable fluid communication (F1, F2) evolving from a restricted flow state (F1), when the valve assembly (18) is in a closed position (CP) preventing fuel injection, to an unrestricted flow state (F2) when the valve assembly (18) is lifted away from said closed position (CP),
wherein the fixed fluid communication (F1) is active when the valve assembly (18) is in closed position (CP) and, the unrestricted fluid communication (F2) is inactive in closed position (CP) and, becoming active and predominant over the fixed fluid communication (F1) when the valve assembly lifts away from said closed position (CP),

wherein said variable fluid communication (F2) comprises a shutter member (34) that activates the unrestricted fluid communication (F2) after the needle (20) has lifted away from the closed position (CP) and, wherein said shutter member (34) deactivates said unrestricted fluid communication (F2) when the valve assembly (18) approaches said closed position (CP),

wherein said NMC (22) is a collar member defining an outer cylindrical face (52) joining an upstream face (48) partly defining the upstream chamber (UC) and, a downstream face (50) partly defining the downstream chamber (DC), said unrestricted fluid communication (F2) comprising inner channels (58) opening in said outer face (52),

wherein the shutter member (34) is integral to the wall of the body,

wherein the inner section of the downstream chamber (DC) is narrower than the inner section of the upstream chamber (UC), the inner face of the wall being provided with an annular shoulder (36) joining said different sections, the shutter member (34) being defined by the portion of the narrower wall next to said shoulder (36) and,

wherein, in a closed position (CP) of the valve assembly, the shutter (34) closes the opening of the inner channel (58) arranged in the NMC outer face (60), the variable fluid communication (F1, F2) being in a closed state and wherein, a needle motion toward the open position (OP) moves said channel aperture (60) in the larger upstream portion (38) where it uncovers and opens beyond said shoulder face (36), opening said unrestricted fluid communication (F2).
Nozzle assembly (14) as claimed in claim 1 wherein said inner channel (58) extends from said aperture (60) in the outer face to an opening arranged in the downstream face (DC).
Nozzle assembly (14) as claimed in any of the claims 1 or 2 wherein the NMC (22) is provided with a plurality of said inner channels (58), each having an opening in the outer face.
Nozzle assembly (14) as claimed in claim 1 wherein said NMC (22) is a collar member having an upstream face (48) partly defining the upstream chamber (UC) and a downstream face (50) partly defining the downstream chamber (DC), the NMC (22) being further provided with a drilling (56) extending between an upstream opening arranged in said upstream face and a downstream opening arranged in said downstream face.
Fuel injector (12) of a fuel injection equipment (10) of an internal combustion engine comprising a nozzle assembly (14) as claimed in any of the preceding claims.