WO2015091180A1

WO2015091180A1 - Fuel injection nozzle

Info

Publication number: WO2015091180A1
Application number: PCT/EP2014/077316
Authority: WO
Inventors: Guillaume LABBE; David J Lane; Eric Lecluse; Marion Balin; David Bonneau; Jean-Christophe Oge
Original assignee: Delphi International Operations Luxembourg S.À R.L.
Priority date: 2013-12-19
Filing date: 2014-12-11
Publication date: 2015-06-25
Also published as: JP2017507269A; JP6409068B2; KR20160098246A; GB201322485D0; EP3084203A1; KR102244948B1

Abstract

According to an aspect of the present invention, there is provided a fuel injection nozzle for injecting fuel into a combustion chamber of an internal combustion engine. The nozzle includes a nozzle body having a bore for receiving fuel from a supply line for pressurized fuel. At least one injection opening is provided for delivering fuel from the bore to the combustion chamber, the at least one injection opening having a total cross sectional area (A_tot). A needle is longitudinally displaceable within the bore between a closed position in which the flow of fuel through the at least one injection opening into the combustion chamber is prevented, and an injection position in which the flow of fuel through the at least one injection opening into the combustion chamber is enabled. A restriction is provided for restricting the flow of fuel through the bore. The restriction is dimensioned as a function of the total cross sectional area (A_tot) of the at least one injection opening.

Description

FUEL INJECTION NOZZLE

TECHNICAL FIELD

The present invention relates to a fuel injection nozzle, in particular a fuel injection nozzle for injecting fuel into a cylinder of an internal combustion engine.

BACKGROUND

EP 0 844 383 and EP 2 568 157 disclose a high pressure fuel injector for internal combustion engines. The fuel injector has an injection nozzle defining a bore. The bore provides a flow path for high-pressure fuel between a fuel inlet and a plurality of outlets, the fuel being received from a high-pressure fuel supply passage. The fuel injector includes a needle which is slidable within the bore. At the lower end of the bore a needle seating is defined, the needle being engageable with the seating. The outlets are provided downstream of the seating so that, when the needle is engaged with the seating, fuel is prevented from being injected. When the needle is lifted from the seating, fuel is able to flow past the seating through the outlets and into an associated combustion chamber of the engine.

The needle includes at least one downstream-facing thrust surface against which high- pressure fuel in the bore acts to provide a lifting force to the needle. A control chamber is provided in the injection nozzle at an upper end of the needle, so that the upper end of the needle is exposed to fuel pressure in the control chamber. The control chamber receives fuel at high pressure from the supply passage, and is connectable to a low-pressure drain by way of a valve. The valve therefore controls the pressure of fuel in the control chamber, and hence determines the downward closing force acting on the upper end of the needle. In this way, the direction of the net hydraulic force acting on the needle, and hence the opening and closing movement of the valve needle, can be controlled.

A restriction, in the form of a small radial clearance between the valve needle and a portion of the bore, is provided for restricting the flow of fuel through the bore between the fuel inlet and the outlets. The restriction is upstream of the downstream-facing thrust surface. The restriction therefore ensures that, when the needle is open to allow injection and communication between the control chamber and drain is then closed to initiate closing of the needle, the upward force acting on the downstream-facing thrust surface due to fuel pressure in the bore is less than the downward force acting on the upper end of the needle due to fuel pressure in the control chamber. The pressure differential that results from the restriction gives rise to a substantial net closing hydraulic force on the needle, and allows for a fast needle closure to be achieved.

At least in certain embodiments, the present invention sets out to overcome or at least ameliorate shortcomings associated with known fuel injection nozzles. In particular, at least in certain embodiments, the present invention sets out to provide a fuel injector nozzle with a fast needle closure and a controlled needle speed during the opening phase.

SUMMARY OF THE INVENTION

Aspects of the present invention relate to a fuel injection nozzle, in particular a fuel injection nozzle for injecting fuel into a cylinder of an internal combustion engine.

According to a further aspect of the present invention there is provided a fuel injection nozzle for injecting fuel into a combustion chamber of an internal combustion engine, comprising:

- a nozzle body having a bore for receiving fuel from a supply line for pressurized fuel;

at least one injection opening for delivering fuel from the bore to the combustion chamber, the at least one injection opening having a total cross sectional area A_tot; and

- a needle longitudinally displaceable within the bore between a closed position in which the flow of fuel through the at least one injection opening into the combustion chamber is prevented, and an injection position in which the flow of fuel through the at least one injection opening into the combustion chamber is enabled.

The fuel injection nozzle comprises a restriction for restricting the flow of fuel through the bore. The restriction is dimensioned as a function of the total cross sectional area A_tot of the at least one injection opening. The term total cross sectional area A_tot refers to the cumulative cross sectional area of said at least one injection opening. It will be appreciated that, at least in certain embodiments, the cross sectional area of the or each injection opening can vary along its length. The cross sectional area of said at least one injection opening as described herein refers to the cross sectional area measured at the exit of said at least one injection opening, that is at an end of the at least one injection opening which is open to the combustion chamber.

The restriction can have a hydraulic diameter which is a function of -^— , where A_tot is the

³ Atot

total cross sectional area of the at least one injection opening. The function can be a linear function. The reciprocal of the hydraulic diameter of the restriction can be a linear function of the total cross sectional area. The gradient of the linear function can be— ^ where a is a constant and L is the longitudinal length of the restriction.

The relationship between the hydraulic diameter and the total cross sectional area can be defined by an affine transformation. The affine transformation can comprise a translation. The translation can be a function of the reciprocal of the longitudinal length L of the restriction. The translation can be a function of where b is a constant and L is the longitudinal length of the restriction. The hydraulic diameter of the restriction can follow the equation: l a b

where D_hyd is the hydraulic diameter, L is the longitudinal length of the restriction, A_tot is the total cross sectional area of the at least one injection opening, and a and b are constants. The constant a could range from 1 1 .5 to 22, for example. The constant b could range from 2 to 4.5, for example.

The fuel injection nozzle can comprise an upstream region having an upstream cross section and a downstream region having a downstream cross section, the upstream cross section being larger than the downstream cross section. The restriction could be disposed in the upstream region. In a variant, the restriction could be disposed in the downstream region.

The restriction can be defined between the nozzle body and the flange. The restriction can be formed by a flange. The flange could be disposed on the needle. In a variant, the flange could be disposed on the nozzle body.

An upper surface of the flange can have a cross sectional area, perpendicular to a longitudinal central axis of the needle, between 200 and 800 times the total cross sectional area A_tot of the at least one injection opening. The cross sectional area of the flange can be between 400 and 600 times the total cross sectional area A_tat of the at least one injection opening. The cross sectional area of the flange can be approximately 500 times the total cross-sectional area A_tot of the at least one injection opening.

The fuel injection nozzle can comprise a spring for biasing the needle towards said closed position. The needle can comprise an annular collar forming a spring seat for said spring. The annular collar can also define said restriction. The restriction can be formed between said annular collar and the bore. In use, the flow of fuel between the annular collar and the nozzle body can be restricted. The annular collar can comprise a flange. The restriction can be defined between the nozzle body and the flange.

Alternatively, or in addition, the annular collar can comprise one or more apertures to form said restriction for restricting the flow of fuel. For example, the one or more apertures can extend through the flange. The apertures can each be in the form of a through bore extending through the flange. The flange can slidingly cooperate with the bore in the nozzle body at least substantially to form a seal. In this arrangement, the annular collar forms a piston within the bore. The fuel flow from the supply line to the injection openings is through the one or more apertures formed in said flange.

The annular collar can be formed integrally with the needle. Alternatively, the annular collar can be formed separately and mounted to the needle. For example, the annular collar can be press-fitted onto the needle. According to a still further aspect of the present invention there is provided a fuel injection nozzle for injecting fuel into a combustion chamber of an internal combustion engine, comprising:

a nozzle body having a bore for receiving fuel from a supply line for pressurized fuel;

- at least one injection opening for delivering fuel from the bore to the combustion chamber; and

a needle longitudinally displaceable within the bore between a closed position in which the flow of fuel through the at least one injection opening into the combustion chamber is prevented, and an injection position in which the flow of fuel through the at least one injection opening into the combustion chamber is enabled; and a spring for biasing the needle towards said closed position;

wherein the needle comprises an annular collar forming a spring seat and a restriction for restricting the flow of fuel through the bore. The restriction can optionally be dimensioned as a function of the total cross sectional area A_tot of the at least one injection opening. The restriction can be formed between said annular collar and the bore. The annular collar can comprise a flange. The restriction can be defined between the nozzle body and the flange. The annular collar can be formed integrally with the needle. Alternatively, the annular collar can be formed separately and mounted to the needle. The annular collar can, for example, be press-fitted onto the needle.

Alternatively, or in addition, the flange can comprise one or more apertures to form the restriction. The one or more apertures can extend through the flange. The apertures can each be in the form of a through bore extending through the flange. The flange can slidingly cooperate with the bore in the nozzle body. In this arrangement, the annular collar forms a piston within the bore. According to a further aspect of the present invention there is provided a fuel injector comprising a fuel injection nozzle of the type described herein.

Within the scope of this application it is expressly envisaged that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible. BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying Figures, in which:

Figure 1 shows a longitudinal cross section of a fuel injection nozzle in accordance with a first embodiment of the present invention;

Figure 2 shows a detailed view of the lower tip of the injection nozzle shown in

Figure 1 ;

Figure 3 shows a transverse cross section of the fuel injection nozzle in accordance with an embodiment of the present invention;

Figure 4 shows a graphical representation of the relationship between the hydraulic diameter D_hyd and the total cross sectional area A_tot for different injection nozzles; and

Figure 5 shows a longitudinal cross section of a fuel injection nozzle in accordance with a second embodiment of the present invention. DETAILED DESCRIPTION

A fuel injection nozzle in accordance with a first embodiment of the present invention will now be described with reference to the accompanying Figures.

A fuel injection nozzle 1 according to an aspect of the present invention is shown in Figure 1. The represented injection nozzle 1 is configured for delivering fuel into a combustion chamber (not shown) of an associated internal combustion engine. The injection nozzle 1 has particular application in a compression-ignition engine (i.e. a diesel engine), but the present invention could be implemented in an injection nozzle 1 for a spark-ignition engine (i.e. a gasoline engine).

The terms "upper" and "lower" are used herein to describe the relative position of features of the injection nozzle 1 and are not limiting on the scope of protection conferred. References to the "lower" end of the injection nozzle 1 are to the end disposed proximal to the combustion chamber (shown on the lower side of Figure 1 ). Conversely, references to the "upper" end of the injection nozzle 1 are to the end disposed distal from the combustion chamber (shown on the upper side of Figure 1 ). Furthermore, the terms "upstream" and "downstream" are used herein in relation to the direction of fuel flow through the injection nozzle 1 and into the combustion chamber in normal use.

The injection nozzle 1 extends along a longitudinal axis XX'. The injection nozzle 1 comprises a nozzle body 3 and a bore 5 formed therein for receiving fuel from a supply line for pressurized fuel. The injection nozzle 1 is provided with a needle 7 that is displaceable along the longitudinal axis XX', within the bore 5. The bore 5 includes an enlarged upper region 9 which communicates with a high pressure supply passage 1 1 through which fuel at high pressure is supplied. The needle 7 is provided with a thrust surface 10 of frusto-conicai form that is exposed to fuel pressure within the bore 5. A needle seating 13 is defined at a lower end of the bore 5. The needle seating 13 has a frusto-conicai form with which a tip 14 of the needle 7 is engageabie. Downstream of the seating 13, the nozzle body 3 is provided with a plurality of injection openings 15 (only one of which is shown in Figures 1 and 2) in communication with a sac volume 17 defined in the lowermost tip 19 of the bore 5. The injection openings 15 permit high-pressure fuel within the bore 5 to be injected into the combustion chamber (not shown) of the associated internal combustion engine. When the needle 7 is engaged with the seating 13, fuel is prevented from being injected from the injection nozzle 1 into the combustion chamber. In this case, the needle 7 can be said to be in a closed position. When the needle 7 lifts away from the seating 13, the tip 14 of the needle 7 disengages from the seating 13 and fuel is injected into the combustion chamber through the injection openings 15. In this condition, the needle 7 can be said to be in an injection position.

As shown in Figure 1 , the injection nozzle 1 comprises a restriction 21 for restricting the flow of fuel through the bore 5. The restriction 21 is formed with a restrictive pressure reduction element in the form of a flange 23 provided on the needle 7. The flange 23 is carried on a cylindrical shaft portion 25 of the needle 7. The flange 23 is annular and extends radially outwardly from the needle 7 and has a larger cross-sectional area than the average cross sectional area of the rest of the needle. As will be explained in more detail below, when the needle 7 operatively lifts from the seating 13, the flange 23 gives rise to a pressure drop in the fuel flow path through the bore 5 between the high pressure supply passage 1 1 and the injection openings 15.

Movement of the needle 7 is performed by controlling the fuel pressure within a control chamber 27. The needle 7 has an upstream end 29, (only a lower part of which is shown in Figure 1 ). A spring (not shown) is provided to urge the needle 7 towards the closed position. The upstream end 29 of the needle 7 is received in the control chamber 27, such that an end surface of the needle 7 is exposed to fuel pressure in the control chamber 27.

Fuel pressure within the control chamber 27 is controlled by means of an actuation system (not shown) which will be familiar to those skilled in the art. For example, the actuation system may include a three-way valve which controls whether fuel flows from the high- pressure fuel supply passage 1 1 to the control chamber 27 whilst the flow of fuel between the control chamber 27 and a low pressure drain is prevented, or whether fuel can flow from the control chamber 27 to the low pressure drain and the flow of fuel from the high-pressure fuel supply passage 1 1 to the control chamber 27 is prevented. The operation of the three- way valve is controlled, for example, by means of a solenoid or piezoelectric actuator. In a variant, the three-way valve of the actuation system can be replaced by a two-way valve.

The nozzle body 3 has two distinct parts, namely an upstream large-diameter portion 31 and a downstream small-diameter portion 35. The injection openings 15 are disposed at the end of the small-diameter portion 35. More precisely, the injection openings 15 are arranged at the tip 39 of the small-diameter portion 35, which is located, in use, within the combustion chamber of the associated engine (not shown). The bore 5 of the nozzle body 3 is formed of an upstream region 41 , and a downstream region 43. The downstream region 43 has an internal diameter De. The needle 7 runs co- axially through both the upstream and downstream regions 41 , 43 of the bore 5.

Fuel enters the bore 5 from the high-pressure fuel supply passage 1 1 through a fuel inlet 45 provided at an upper end of the upstream region 41 of the bore 5. The bore 5 defines a flow path for fuel from the fuel inlet 45, through upstream region 41 and into the downstream region 43, and towards the injection openings 15. In use, fuel fills both the upstream region 41 and the downstream region 43, which together define an accumulator volume for fuel.

The flange 23 is provided on the needle 7 in the downstream region 43 of the bore 5. The flange 23 is annular in form and has a diameter D, which is smaller than the internal diameter D_e of the downstream region 43 of the bore 5, as shown in Figure 3. The flange 23 is therefore arranged to define, together with an adjacent portion 53 of the inside surface 51 of the bore 5, the restriction 21 for restricting the flow of fuel along the fuel flow path between the fuel inlet 45 and the injection openings 15. The restriction 21 is defined around the outer peripheral surface of the flange 23, between the flange 21 and the adjacent portion 53. Hence, the restriction 21 takes the form of an annular passage or clearance. As will be explained below, the dimension of the restriction 21 is defined to result in a pressure drop across the flange when the needle 7 is in the injection position and fuel is flowing through the bore 5. In this way, when the needle 7 is in the injection position, a reduced fuel pressure is present downstream of the flange compared to that upstream of the flange 21. The dimension of the restriction 21 is defined as follows. The restriction 21 has a hydraulic diameter D_hyd which can be defined by the following equation:

A

D_hyd = 4 * - where A is the cross sectional area of the restriction 21 ; and P is the wetted perimeter of the cross-section of the restriction 21 . In other words, the wetted perimeter P is the perimeter of the cross section of the restriction 21 which, in use, is in contact with fuel.

As shown in Figure 3, the restriction 21 is an annular gap, with an outside diameter which is equal to the internal diameter D_e of the downstream region 43 of the bore 5, and an inside diameter which is equal to the diameter of the flange Dj. Therefore, the hydraulic diameter is defined by the following equation:

Dhyd = D_e— Di The injection openings 15 have a total cross sectional area A_tot. The total cross sectional area A_tot of the injection openings 15 is defined herein as being the total area available for the flow of fuel through the injection openings 15. That is, for an injection nozzle 1 having a plurality of injection openings, the total cross-sectional area A_tot is the sum of the cross- sectional area of each injection opening. The cross sectional area of an injection opening as described herein refers to the cross sectional area measured at the exit of the injection opening, that is at a lower end of the injection opening which opens into the combustion chamber. In the present embodiment, the restriction 21 is dimensioned as a function of the total cross sectional area A_tot of the injection openings 15. The total cross sectional area A_tot is fixed for a given injection nozzle 1 . However, it will be appreciated that the total cross sectional area A_tot can be different for different injection nozzles 1 .. For example, the total cross sectional area A_tot can range from 0.05 to 0.15 mm² for different injection nozzles 1 .

In the present embodiment, the hydraulic diameter D_hyd of the restriction 21 is a function of the reciprocal of the total cross sectional area A_tot. In particular, the hydraulic diameter D_hyd is defined by the following equation:

1 a b

Dhyd L L where D_hyd is the hydraulic diameter, L is the longitudinal length of the restriction 21 , A _tot is the total cross sectional area of the injection openings 15, and a and b are constants. In the present embodiment, a ranges from 1 1 .5 to 22 and b ranges from 2 to 4.5. The corresponding area covered by the above equation with the above ranges of values for a, b, and A tot, is shown in Figure 4. More precisely, Figure 4 shows values of— as a function of

^Dhyd

the total cross sectional area A_tot, for several types of injectors, each having a different total

? L cross sectional area A_tot, ranging from 0.05 to 0.15 mm . The different values of for each

^Dhyd

value of the total cross sectional area A_tot and for each value of the constants a and b are represented by the shaded area represented in Figure 4.

The flange 23 therefore divides the accumulator volume into two separate pressure control volumes, referred to hereafter as bore volumes. An upper bore volume 55 is formed between a top end of the bore 5 and the flange 23, and a lower bore volume 57 is formed between the flange 23 and the seating 13. When the needle 7 is in the injection position, the fuel pressure in the upper bore volume 55 is greater than the fuel pressure in the lower bore volume 57, by virtue of the restriction 21.

According to the present embodiment of the present invention, the flange 23 is a component of the injection nozzle 1 separate to the needle 7. The flange is arranged to be press-fitted to the shaft portion of the needle 7, so that the flange 23 is not moveable with respect to the needle 7. The flange therefore moves with the needle 7 as the needle 7 slides within the bore 5. One advantage of making the flange separately from the needle 7 is that the bar size required for manufacturing the needle 7 can be reduced, thereby reducing manufacturing cost and waste material during manufacture. However, it will be appreciated that in alternative embodiments of the invention the flange could be an integral feature of the needle.

The upper surface of the flange is arranged to have a cross-sectional area, perpendicular to the longitudinal axis XX', between 200 and 800 times larger than the total cross-sectional area A_tot of the openings 15 and preferably approximately 500 times larger. Providing this area ratio means that the needle 7 will move during closure at approximately the same speed as the fuel in the vicinity of the flange 23.

The operation of the injection nozzle 1 in accordance with an embodiment of the present invention will now be described with reference to Figures 1 to 3.

With the needle 7 in the closed position, the tip 14 of the needle 7 is engaged with the seating 13 in order to prevent flow of fuel out of the injection openings 15 in the combustion chamber. In this position, high-pressure fuel fills the upstream and downstream regions 41 , 43 of the bore 5. Since the flow of fuel is inhibited, the pressure within the upper and lower bore volumes 55, 57 either side of the flange 23, is the same. At this stage, communication between the control chamber 27 and the drain is closed, so that the fuel pressure in the control chamber 27 is high.

Accordingly, the combined downward or closing force acting on the needle 7 due to fuel pressure in the control chamber 27 acting on the control piston 29 and the downward force provided by the spring is greater than the upward or opening force acting on the needle 7 due to the pressure of fuel acting on the thrust surface 10 of the needle 7. This results in a net downward or closing force on the needle 7, and the needle 7 remains in the closed position. As the fuel pressure within the upper and lower bore volumes 55, 57 is the same, the upward and downward forces acting on the flange 23 due to the fuel pressure in the respective volumes balance each other.

In order to open the needle 7, the three-way valve is operated to open the connection between the control chamber 27 and the low-pressure drain, thereby reducing the pressure within the control chamber 27. As the pressure in the control chamber 27 reduces, the resulting downward force acting on the upstream end 29 of the needle 7 decreases, and eventually a point is reached at which the upward force exerted on the thrust surface 10 of the needle 7 due to fuel pressure within the lower bore volume 57 is larger than the downward force acting on the needle 7 due to fuel pressure within the control chamber 27 combined with the downward force due to the spring. At this point, a net upward or opening force acts on the needle 7, and the needle 7 is displaced upwardly away from the seating 13 towards the injection position.

As the needle 7 lifts off the seating 13, fuel begins to flow out from the openings 15 and into the combustion chamber. While the high-pressure fuel passage 1 1 continues to supply fuel to the bore 5, the pressure at the lower end of the bore 5, in the lower bore volume 57, reduces due to fuel being injected into the combustion chamber. This helps to slow the initial speed at which the needle 7 lifts because the upward pressure exerted by the fuel on the thrust surface 10 reduces.

Furthermore, because fuel flows into the lower bore volume 57 past the flange 23 and therefore through the restriction 21 , the fuel pressure in the lower bore volume 57 is reduced compared to the fuel pressure in the upper bore volume 55. As a result, the fuel pressure acting on each side of the flange 23 is no longer balanced, and instead the flange 23 applies a downward force on the needle 7. The upper surface area of the flange 23 thereby forms an upstream-facing thrust surface which is exposed to fuel pressure in the upper bore volume 55 to produce a downward component of force on the needle 7.

Accordingly, as fuel flows through the bore 5, it applies a pressure against the upstream- facing thrust surface of the flange 23 and as such also helps to reduce the speed at which the needle 7 moves upwards away from the seating 13. In addition, the movement of the flange 23 through the fuel gives rise to a drag effect that also attenuates the speed of the needle 7. Hence, the flange 23 has the effect of damping the opening movement of the needle 7 against the flow of fuel in the opposite direction to the movement of the needle 7. It is noted that the downward component of force acting on the needle 7 through the flange 23 is not sufficient to overcome the upward components of force acting through the thrust surface so a net upward force continues to act to open the needle 7. The needle 7 eventually reaches a maximum lift position, and fuel continues to flow from the high-pressure fuel passage through the bore 5 and through the openings 15 into the combustion chamber.

When the desired amount of fuel has been delivered to the combustion chamber, the valve is operated to close the connection to drain and to allow high-pressure fuel to flow into the control chamber 27. The pressure in the control chamber 27 increases, so that the downward or closing force acting on the needle 7 through the upstream end 29 of the needle 7 rises. Eventually, the combined downward forces acting on the needle 7 exceed the upward forces acting on the needle 7, resulting in a net downward force on the needle 7 that causes the needle 7 to move in a closing direction.

As previously noted, since the restriction provides a pressure drop across the flange 23, a higher pressure is present in the upper bore volume 55 than is present in the lower bore volume 57 downstream of the flange 23. The resulting downward force applied to the needle 7 through the flange 23 by the pressure of fuel acting on the upstream-facing thrust surface provides an additional component of closing force that increases the speed of needle 7 closure.

The closing operation finishes when the needle 7 engages with the seating 13 and prevents further fuel flow out of the openings 15 until a further opening operation is carried out.

It will be appreciated that the effect of the restriction 21 on the movement of the needle 7 exhibits hysteresis. During the opening of the injection nozzle 1 , the flange 23 damps the movement of the needle 7, allowing good control of small injection volumes. During needle 7 closing, the flange boosts the closing speed of the needle 7, which allows rapid termination of injection.

The longitudinal length L, or thickness, of the flange 23, taken in a direction parallel to a central axis of the needle 7, is relatively small compared to the diameter D, of the flange 23. A thin flange 23 is preferable for reducing the mass of the flange 23, and therefore the moving mass of the needle 7. In another embodiment, a point or localised restriction can be defined between the inside surface of the nozzle body and the edge of the flange. For example, the flange can be profiled to define a sharp or pointed outer edge. Figure 5 shows a longitudinal cross section of a fuel injection nozzle 101 in accordance with a second embodiment of the present invention. Like reference numerals are used for like components, albeit increased by 100 for clarity.

The injection nozzle 101 comprises a nozzle body 103 and a bore 105 formed therein for receiving fuel from a supply line for pressurized fuel. The injection nozzle 101 is provided with a needle 107 that is movable along the longitudinal axis XX'. A high pressure supply passage 1 1 1 supplies high pressure fuel to the bore 105 for injection through a plurality of injection openings 1 15. A needle seating 1 13 is defined at a lower end of the bore 105 for cooperating with a tip 139 of the needle 107 to close the injection openings 1 15. When the needle 107 is engaged with the seating 1 13, fuel is prevented from being injected from the injection nozzle 101. When the needle 107 lifts from the seating 1 13, the injection openings 1 15 are opened and fuel is injected.

The injection nozzle 101 comprises a control chamber (not shown) for controlling the needle 107. A spring 159 is provided to bias the needle 107 towards the closed position. The spring 159 is a coil spring disposed around the needle 107. An annular collar 161 is fixedly mounted to the needle 107. The collar 161 defines a spring seat 162 for supporting a lower end of the spring 159. An annular flange 123 is defined by the annular collar 161 for restricting the flow of fuel through the bore 105. The diameter D, of the flange 123 is substantially equal to the internal diameter D_e of the bore 105. The flange 123 slidlingly engages the sidewall of the bore 105 at least substantially to form a seal. A plurality of apertures 163 is formed in the flange 123. The apertures 163 in the present embodiment are in the form of a plurality of bores extending through the flange 123 substantially parallel to the longitudinal axis XX' of the injection nozzle 101 . The apertures 163 are operative to establish fluid communication past the annular collar 131.

In use, when the needle 107 operatively lifts from the seating 1 13, a pressure drop is established below the flange 123. The apertures 163 collectively form a hydraulic cross- sectional area which is equivalent to that formed by the restriction 121 in the first embodiment described herein. The apertures 163 in the flange 123 can be configured such that the effective hydraulic cross-sectional area is a function of the total cross sectional area Atot of the injection openings 1 15. The relationship of the hydraulic cross-sectional area to the total cross sectional area A_tot can be equivalent to the relationship defined herein relating the hydraulic diameter D_hyd to the total cross sectional area A_tot in accordance with the first embodiment of the present invention. It will be understood that the annular collar 161 forms a damping piston within the injection nozzle 101 . By restricting the flow of fuel past the annular collar 161 , the apertures 163 can reduce the rate of lift (rise) of the needle 107. The rate of opening of the needle 107 can be reduced due to hydraulic damping as the annular collar 161 moves through the fuel within the bore 105, and also a pressure drop across the annular collar 161. The pressure drop occurs due to depressurization below the annular collar 161 resulting in a net force in a direction towards the needle tip 139. It will be appreciated that the annular collar 161 provides the dual function of defining the spring seat 163 for the spring 159 and also forming the apertures 163 for controlling the flow of fuel within the bore 105. In a variant of the second embodiment of the injection nozzle 101 , the restriction 121 is an annular gap formed between the bore 105 and the flange 123. The restriction 121 has an outside diameter which is equal to the internal diameter D_e of the bore 105 and an inside diameter which is equal to a diameter D, of the flange 123. The injection openings 1 15 have a total cross sectional area A_tot. The restriction 121 is dimensioned as a function of the total cross sectional area A_tot of the injection openings 1 15. The hydraulic diameter D_hyd of the restriction 121 is a function of the reciprocal of the total cross sectional area A_tot. The relationship between the hydraulic diameter D_hyd and the total cross sectional area A_tot. is unchanged from that defined herein for the first embodiment. In this arrangement the annular collar 161 provides the dual function of defining the spring seat 163 for the spring 159 and also forming the restriction 121 for controlling the flow of fuel within the bore 105.

It will be appreciated that various changes and modifications can be made to the first and second embodiments of the injection nozzle 1 ; 101 described herein. For example, any other suitable restriction may be provided, and defined, at least in part, by the flange or any other suitable restrictive element.

In a variant, the injection nozzle can include a flange 23 comprising a recessed portion comprising a flat on its outer surface which defines, together with the bore, the restriction. A plurality of flats could be provided to avoid unbalanced loads on the flange and the needle. In this variant, the annular edge of the flange is in sliding contact with the inside surface of the bore so as to allow for free movement of the needle within the bore. In this case, fuel is only able to flow between the flat and the bore, and not around the whole circumference of the flange. Multiple flats could be provided on the flange, at angularly spaced locations, in order to provide multiple restrictions. The flats can be arranged so that the total cross- sectional area provided by the multiple restrictions provides the desired total pressure drop across the flange. Any other shaped recesses or formations, such as one or more channels or grooves, could be used instead of or in addition to flats.

In another variant, the restriction could be provided by an orifice in the flange in the form of one or more holes extending from the upper surface of the flange to the lower surface of the flange. In this arrangement, the outer circumference of the flange may be arranged to provide a sliding fit with the inner surface of the bore so as to allow sliding movement of the needle within the bore. In this case, fuel is only able to flow through the restriction, and not around the outer surface of the flange. Multiple orifices can be provided to define a plurality of restrictions through the flange. Orifices can be provided in any shape or form suitable to achieve the required functionality.

In another arrangement, recessed portions can be provided in the nozzle body. The recessed portions, along with the outer surface of the flange defining restrictions in the fuel flow path past the flange. Again, the outer surface of the flange is arranged to provide a sliding fit with the inner surface of the nozzle body, so as to allow sliding movement of the needle within the bore region. As such, fuel is only able to flow through the restrictions, and not past the remainder of the outer surface of the flange. In another embodiment, an annular flow path around the periphery of the flange may also be provided. It will be appreciated that any suitable number of recessed portions may be provided. The recessed portions could be made by machining the nozzle body to create the recesses, or by incorporating the recess shape into a moulding process for forming the nozzle body.

Any other suitable means for providing a pressure drop across the restrictive element could also be utilised, as could a combination of different types of restriction. Again, the restrictions are arranged so that the total cross-sectional area provided by the restrictions provides the desired total pressure drop. Multiple restrictions can be arranged in series within the fuel flow path through the injection nozzle. The flange can have two or more grooves formed circumferentially around its outer peripheral surface. The two grooves can define a plurality of protruding annular portions, which also extend circumferentially around the flange. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Claims

CLAI MS:

1 . A fuel injection nozzle for injecting fuel into a combustion chamber of an internal combustion engine, comprising:

at least one injection opening for delivering fuel from the bore to the combustion chamber, the at least one injection opening having a total cross sectional area (A_tot); and

- a needle longitudinally displaceable within the bore between a closed position in which the flow of fuel through the at least one injection opening into the combustion chamber is prevented, and an injection position in which the flow of fuel through the at least one injection opening into the combustion chamber is enabled;

the fuel injection nozzle comprising a restriction for restricting the flow of fuel through the bore;

wherein the restriction is dimensioned as a function of the total cross sectional area (Atot) of the at least one injection opening.

2. A fuel injection nozzle as claimed in claim 1 , wherein the restriction has a hydraulic diameter(D_hyd) which is a function of , where A_tot is the total cross sectional area of the at least one injection opening.

3. A fuel injection nozzle as claimed in claim 1 or claim 2, wherein the hydraulic diameter (D_hyd) follows the equation:

1 _ a b

Dhyd L L where D_hyd is the hydraulic diameter, L is the longitudinal length of the restriction, Atot is the total cross sectional area of the at least one injection opening, and a and b are constants.

4. A fuel injection nozzle as claimed in claim 3, wherein the constant a ranges from 1 1.5 to 22; and the constant b ranges from 2 to 4.5.

5. A fuel injection nozzle as claimed in any one of the preceding claims, comprising an upstream region having an upstream cross section and a downstream region having a downstream cross section, the upstream cross section being larger than the downstream cross section, and wherein the restriction is disposed in the upstream region.

6. A fuel injection nozzle as claimed in any one of claims 1 to 4, comprising an upstream region having an upstream cross section and a downstream region having a downstream cross section, the upstream cross section being larger than the downstream cross section, and wherein the restriction is disposed in the downstream region.

7. A fuel injection nozzle as claimed in anyone of the preceding claims, wherein the restriction is formed with a flange disposed within the bore so that the restriction is defined between the nozzle body and the flange.

8. A fuel injection nozzle as claimed in claim 7, wherein the flange is disposed on the needle.

9. A fuel injection nozzle as claimed in claim 7, wherein the flange is disposed on the nozzle body.

10. A fuel injection nozzle as claimed in any one of claims 1 to 6, wherein the fuel injection nozzle comprises a spring for biasing the needle towards said closed position; wherein the needle comprises an annular collar forming a spring seat and defining said restriction.

1 1 . A fuel injection nozzle as claimed in claim 10, wherein the annular collar comprises a flange and said restriction is defined between the nozzle body and the flange.

12. A fuel injection nozzle as claimed in claim 10, wherein the annular collar comprises one or more apertures to form said restriction.

13. A fuel injection nozzle as claimed in claim 12, wherein the annular collar comprises a flange and said one or more apertures extend through the flange.

14. A fuel injection nozzle as claimed in any one of claims 10 to 13, wherein the annular collar is formed integrally with the needle; or the annular collar is mounted to the needle.

15. A fuel injector comprising a fuel injection nozzle as claimed in any one of the preceding claims.