EP2078158B1 - Device for holding a fuel injector needle and associated fuel injector - Google Patents

Abstract

The device for holding a fuel injector needle comprises a support plate (40) and an axial-retention element (44) for supporting and retaining the injector needle. The axial-retention element (44) comprises a fixing portion (52) collaborating with a complementary portion of the support plate (40), and a retaining portion provided with inwardly directed radial projections (56) each having a surface for contact with the needle.

Description

The present invention relates to the general field of fuel injectors for internal combustion engines of motor vehicles.

The present invention more particularly relates to a device for maintaining a needle of a fuel injector which is controlled by emission of ultrasonic frequencies.

Conventionally, to achieve the fuel injection inside an internal combustion engine of a motor vehicle, injection systems are used that operate on the model of a valve whose open or closed state is permanently controlled. , the injected fuel dosage being then directly based on the opening time of the injector.

Such injection systems comprise an electric fuel supply pump which supplies, via a distribution manifold, all the injectors.

In order to control the amount of fuel injected, an electromagnet may be used to control the valves associated with the injectors.

In this respect, by electronically controlling the electromagnet actuating the valve of each injector, it controls the opening time thereof, having previously determined a fuel flow for each of the injectors. Thus, the amount of fuel injected depends solely on the opening time of the injectors.

Electromagnetically controlled needle type injectors, which are the most commonly used, however, have limits that hinder the improvement of engine performance, especially in terms of pollution control.

In particular, the time taken to open or close the eels are still too high, about 1 to 2 ms, which prevents the correct distribution of fuel injection over the entire opening time of the valve. The dosage is only done by the opening time of the injector which is about 0.5 ms to 1 ms.

In addition, the minimum opening time, which determines the minimum dose of fuel that can be injected, is still too important for certain operating points of the engine.

Known needle injectors also have relatively large diameter injection ports to allow the required quantities of fuel to be discharged for full load and high speed operation of the engines.

This arrangement generates fuel jets having drops of large dimensions, which slows the vaporization of the fuel and is able to promote a wetting phenomenon of the walls.

Indeed, the non-vaporized fuel tends to be deposited on the walls of the intake duct or the direct injection combustion chamber.

Such a deposit causes metering problems, particularly acute in the transient phases due to lack of knowledge of the amount of fuel that actually enters the corresponding combustion chamber. This wetting phenomenon is one of the important causes of high pollutant emissions.

Moreover, with a conventional needle injector, the opening of the needle, when the latter begins to leave his seat, it forms a liquid bubble that disappears when the needle is completely raised. Fluid flow is regularizing so. This change in the nature of the flow makes it impossible to precisely control the instantaneous flow rate of the injector.

All the aforementioned problems result in a vaporization of the fuel which can be incomplete and inhomogeneous during the preparation of the fuel mixture in the combustion chamber, imprecise dosages, with the consequence of incomplete combustion resulting in the formation of a high amount of gaseous pollutants and an energy deficit affecting engine performance.

In order to overcome these disadvantages, it was proposed by FR-A-2 801 346 of the applicant, an injection device comprising a valve provided with a shutter needle which is moved by a piezoelectric actuator.

More specifically, the device comprises a nozzle fueled at the end of which is formed an injection port closed by the shutter needle.

The device also comprises means for cyclically vibrating the nozzle and the shutter needle, such as a transducer provided with piezoelectric cells and controlled in duration and intensity by the electronic engine control system, to obtain a moving said needle and opening the injection port.

In order to allow the return of the shutter needle to its initial position, the device also comprises elastic return means housed in a cavity formed in a portion on the shutter needle.

In a similar way, the document FR-A-2,857,418 Applicant proposes to order the opening of an orifice injection of the fuel injector by a vibration generation.

The injector comprises a means for axially holding the shutter needle which is in particular provided with a nut for adjusting the value of the force exerted by a return spring mounted between the adjusting nut and the injector .

Although particularly effective, this device has the disadvantage of having a relatively large axial size and to understand a relatively complex and expensive structure.

Another example of such a device is known from the document WO 03/036077 .

The present invention therefore aims to overcome these disadvantages with the device as defined in claim 1.

The present invention also aims to provide a device for maintaining a needle of a fuel injector which is particularly simple, effective, and easy to assemble.

The invention therefore relates to a device for holding a needle of a fuel injector, which comprises a support plate and an axial retaining element of the needle of the injector.

According to a general characteristic, the axial retaining element comprises a fixing portion cooperating with a complementary portion of the support plate, and a retaining portion provided with inwardly directed radial projections each comprising a contact surface with the needle.

With such a device, axial retention of the needle is thus obtained in a particularly simple and effective manner, and this in a reduced space requirement.

The device may comprise an elastic return member intended to be mounted between the injector and the support plate.

The retaining portion comprises axial lugs axially extending the fastening portion, each axial lug being provided at its lower end with one of the radial projections.

The device may advantageously comprise a clamping ring radially surrounding the axial tabs of the retaining portion and mounted to bear against them. The clamping ring can be opened at a point of its circumference.

In one embodiment, the backing plate further comprises a stud having a planar contacting surface with an upper end of the needle.

In one embodiment, the retainer is separate from the backing plate.

Thus, each of these two elements can be particularly simple and economical to manufacture. Indeed, with such a device, it is not necessary to provide at the support plate forms or bores specific to the maintenance of the needle.

The invention also relates to a fuel injector for an internal combustion engine of a motor vehicle provided with a needle mounted axially displaceable in a body of the injector, and a device for holding the needle comprising a plate of support and an axial retaining element of the needle of the injector as defined above

Advantageously, the injector comprises a sealed chamber inside which is mounted the device for holding the needle, and separated from a circulation circuit of the fuel to be injected.

Advantageously, the sealed chamber is filled with a fluid, especially a low pressure fluid.

In one embodiment, in a closed position of the needle, an axial space is provided between an end surface of the needle holding device and the injector body.

In one embodiment, the support plate is shaped to have an acoustic impedance greater than that of the needle. In other words, the support plate comprises a mass and a density such that it achieves an acoustic blocking for the waves propagating in the needle. The acoustic compression waves are then reflected in compression waves.

Alternatively, it is also conceivable to provide a support plate which has an acoustic impedance substantially equal to or less than that of the needle. The acoustic compression waves are then reflected in relaxation waves.

Advantageously, the injector also comprises vibrating means capable of causing mechanical oscillations of the needle.

• la figure 1 est une vue en coupe axiale d'un injecteur de carburant comprenant un dispositif de maintien d'une aiguille de l'injecteur selon un premier mode de réalisation de l'invention ;
• la figure 2 est une vue en perspective d'un élément de retenue du dispositif de la figure 1 ;
• la figure 3 est une vue en perspective d'une bague de serrage du dispositif de la figure 1 ;
• la figure 4 est une variante de réalisation de l'injecteur de carburant de la figure 1 ; et
• les fleurets 5 et 6 sont des vues en coupe axiale d'un injecteur de carburant comprenant des dispositifs de maintien de l'aiguille de l'injecteur selon des second et troisième modes de réalisation de l'invention.

The present invention will be better understood on reading the detailed description of embodiments taken as non-limiting examples and illustrated by the appended drawings, in which:

• the figure 1 is an axial sectional view of a fuel injector comprising a device for holding a needle of the injector according to a first embodiment of the invention;
• the figure 2 is a perspective view of a retaining element of the device of the figure 1 ;
• the figure 3 is a perspective view of a clamping ring of the device of the figure 1 ;
• the figure 4 is an alternative embodiment of the fuel injector of the figure 1 ; and
• the foils 5 and 6 are views in axial section of a fuel injector comprising holding devices of the needle of the injector according to second and third embodiments of the invention.

On the figure 1 , there is shown the general structure of a fuel injector for an internal combustion engine of a motor vehicle, designated by the general reference numeral 10.

As seen in this figure, the injector 10, which has a general shape of revolution about a central axis XX 'supposed vertical, comprises a body 12 inside which is mounted axially displaceable a needle 14 shutter .

As will be described in more detail below, the injector 10 also comprises a device 16 for holding the needle 14 in position inside the body 12.

The body 12, of generally cylindrical outer shape, comprises a stepped bore 18 formed along the entire length thereof. The bore 18 is coaxial with the X-X 'axis.

It comprises a first stage 18a of small diameter inside which the needle 14 is slidably mounted, and a second stage 18b of large diameter extending axially upwardly the first stage 1 8a.

The body 12 also comprises a closure cap 19 mounted at the upper free end of the second stage 18b, and which has an orifice 19a coaxial with the axis X-X '. The second stage 18a of the bore 18 thus delimits with the shoulder 14b and with the closure cap 19, a chamber 21.

The injector 10 also comprises at its lower end a nozzle 20 of generally tubular shape and extending along the axis X-X '. The inside diameter of the nozzle 20 is substantially equal to that of the first stage 18a of the bore 18.

The proximal end 22 of the nozzle 20, in contact with a lower face of the body 12, is intended to be supplied with fuel, and the free or distal end 24 thereof is adapted to allow a fuel injection to the fuel. inside a combustion chamber of the engine (not shown).

In this regard, the body 12 of the injector further comprises a substantially radial projection 26 provided with a bore 28 passing through said body 12 and opening at the level of the first stage 18a of the stepped bore 18, so as to allow the inlet fuel at the nozzle 20. The projection 26 is here located axially near the lower face of the body 12.

To allow a fuel injection, the shutter needle 14 comprises a cylindrical portion 14a, of smaller diameter on the order of a few tenths of a millimeter to the diameter of the first stage 18a of the bore 18, so as to create a passage axial ring 30 for the fuel between the first stage 18a of the bore 18 and the needle 14 and between the nozzle 20 and said needle.

The cylindrical portion 14a is extended at an upper end by a shoulder 14b shaped to fit precisely with the first stage 18a of the bore 18 and thus limit any fuel leakage to the second stage 18b. The upper end of the shoulder 14b is projecting inside the second stage 18b. '

In order to be able to obstruct the distal end 24 of the nozzle 20, the needle 14 comprises at its lower free end an axially projecting head 32 adapted to come into contact with this distal end 24. The distal end 24 therefore forms a seat for the needle 14. Thus, in this so-called "closing" position, the fuel can not be injected into the combustion chamber.

In order to maintain this closing position, the device 16 is mounted inside the second stage 18b of large diameter of the bore 18.

The device 16 comprises in particular a support plate 40, an elastic return member 42 mounted between the body 12 of the injector 10 and the support plate 40, and an axial retaining element 44 of the needle 14 mounted on said plate 40.

The support plate 40, of generally cylindrical shape, is mounted in the vicinity of the upper end of the second stage 18b of the bore 18. It has a relatively small axial dimension, and comprises a cylindrical protuberance 46 of reduced diameter relative to to that of the plate 40. It extends axially downward along the axis XX 'from a lower surface 48 of the plate 40.

The surface 48 forms an abutment surface for an upper end of the elastic return member 42, here made in the form of a spring. The lower end of the elastic member 42 bears against a radial connecting surface 50 of the body 12 formed between the second stage 18b and the first stage 18a of the bore 18.

The resilient return member 42 exerts an axial force on the support plate 40 so as to keep it away from the connecting surface 50. The axial force is directed axially upwards.

As regards the axial retention element 44 made in one piece, the latter comprises an annular fixing portion 52 mounted to bear against the abutment surface 48. The fixing portion 52 extends axially from a lower end by axial tabs 54.

In order to fix the retaining element 44 on the support plate 40, the fixing portion 52 comprises a threaded bore 52a cooperating with a corresponding thread 46a formed on the outer surface of the protuberance 46.

The axial dimension of the fixing portion 52 is here equal to that of the protrusion 46. Its radial dimension is smaller than the radial dimension of the support plate 40 so as to leave free, at the abutment surface 48, a annular surface for the support of the upper end of the elastic member 42 of return.

The tabs 54, here four in number, are circumferentially evenly distributed over the fixing portion 52. Each tab 54 comprises a first inclined portion 54a extending outwardly which is extended at its lower free end by a second portion 54b axial. The circumferential dimension of the tabs 54 is greater here at their implant level than at their free end.

To allow axial retention of the needle 14 inside the body 12 of the injector, each of the tabs 54 is extended at its lower end; by a protrusion 56.

The projections 56 extend radially inward and have a generally rounded or spherical shape. They each bear against a contact zone formed at an upper end of the shoulder 14b of the needle 14. Thus, each projection 56 comprises a contact surface with the needle 14.

Said contact zones are made here in the form of an annular groove 60. Of course, it is also conceivable to provide contact zones of different design.

The relative radii of curvature of the projections 56 and the groove 60 define the type of locking performed. If the projections 56 have a greater radius of curvature than the groove 60, the support plate 40 is integral with the end of the needle 14. Otherwise, the support plate 40 is secured to the support and the needle 14 is made only in an axial direction.

The projections 56 cooperate with the groove 60 so as to allow axial retention of the needle 14 in its closed position. In other words, the axial lugs 54 and the projections 56 of the element 44 constitute a retaining portion for the needle 14.

In order to ensure the contact of the projections 56 with the groove 60, the device 16 also comprises an annular clamping ring 62 radially surrounding the tabs 54 and coming into contact with the outer surface thereof. It has here an axial dimension slightly lower than that of the legs 54.

The clamping ring 62 is open at a point of its circumference ( figure 3 ), to facilitate its mounting on the tabs 54. Once mounted on the axial retaining element 44, it exerts a radial force directed inwardly so as to bring the lugs 54 relative to each other and thus to limit substantially the risk of rupture of the contact between the projections 56 and the groove 60. The needle 14 is thus maintained in its closed position, safely.

In order to avoid an axial separation of the clamping ring 62 relative to the retaining element 44, that may comprise, at the outer surfaces of the second portions 54b of the lugs 54, protrusions directed radially outwardly engageable with grooves of corresponding shape formed the bore of the ring 62. This limits any axial displacement downwards of the ring 62.

In order to inject fuel, to allow the passage from the closed position to an open position in which the head 32 releases the distal end 24 of the nozzle 20, the injector also comprises, at the level of the here, a stack 70 of piezoelectric active components, which under the application of an electric field, deform in thickness.

To fix the stack 70 on the nozzle 20, it comprises in the vicinity of its distal end 24, a radial collar 72, here made of material with said nozzle, and against which bears the stack 70.

For this purpose, the injector 10 further comprises a nut 74 provided with an elastic prestressing system which is mounted on the nozzle 20 so as to sandwich the stack 70 between the abutment element 72 and said nut 74. These elements 72 and 74 are conventionally used for fuel injectors controlled by emission of ultrasonic frequencies.

The stack 70 consisting of a plurality of piezoelectric active components makes it possible to add the thickness deformations generated by each of them, the resulting deformation of the total displacement of the stack 70 remaining below the limit of elastic deformation of the nut 74.

In order to allow the stack 70 to vibrate, the electronic engine control system is used. In this regard, it sends two pulses corresponding to the beginning and the end of the fuel injection. Between these two impulses, he generates a train of waves at a predetermined frequency so as to supply alternating voltage to the stack 70, and thus cause its deformation.

This generates an elastic stress that is transmitted to the nozzle 20 as well as the needle 14. Indeed, the nozzle 20 and the needle 14 are sized to resonate at the excitation frequency of the stack 70.

Thus, the needle 14 which initially closes the distal end 24 of the nozzle 20, deforms under the impulse provided to it when it starts to oscillate. This deformation is distributed elastically over the entire length of the needle 14 to the support plate 40 of the axial retaining element 44.

The proper response of the needle 14 on the one hand, and the nozzle 20 on the other hand, makes it possible to oscillate the head 32 of the needle 14 with a variation of phase and amplitude. This variation is reflected by the opening of the nozzle, the height of the opening depending on the relative difference between the amplitude of oscillation of the distal end 24 of the nozzle and that of the head 32.

In the variant embodiment illustrated in figure 4 on which the identical elements bear the same references, the shoulder 14b of the needle 14 here comprises a plurality of ovoid grooves 82, here four in number, associated with the projections 56 of the axial tabs 54 of the retaining element 44. Thus, at each protrusion 56 is associated a groove 82.

In the embodiments illustrated above, the injector 10 comprises an outgoing needle. It is easy to see that it is also possible, without departing from the scope of the invention, to provide, as illustrated in FIG. figure 5 an injector 10 which comprises a so-called incoming head 84 situated entirely inside of the nozzle 20, the distal end 24 of the nozzle 20 being shaped accordingly.

Under these conditions, to keep the injector 10 closed, the elastic return member 42 is disposed between the closure cap 76 of the injector 10 and the support plate 40. The elastic return member 42 here exerts an axial force on the support plate 40 so as to bring it closer to the connecting surface 50. The axial force is here directed downwards.

The embodiment illustrated in figure 6 differs from that of the figure 1 in that the support plate 40 comprises a relatively large axial dimension.

Indeed, the support plate 40 is shaped so as to have a sufficient mass to present acoustic conditions of quasi-locking the end of the needle 14. Thus, the support plate 40 is able to create a acoustic impedance breaking so as to symmetrically return the compression waves.

In this embodiment, the support plate 40 also comprises a cylindrical stud 86 which extends axially downwards the protrusion 46. The stud 86 is centered on the axis X-X '. It comprises, at its lower end, a flat contact surface mounted in abutment against a planar upper surface of the shoulder 14b of the needle 14. The stud 86 and the needle 14 are thus shaped so as to obtain a surface contact between these two elements.

To ensure good transmission of the waves emitted by the stack 70 to the support plate 40 of the axial retaining element 44, the chamber 21 contains a fluid at low pressure. Indeed, a fluid promotes the propagation of waves. This propagation is also ensured by the existence of the plane contact surfaces of the plot 86 and the needle 14, which can also be rectified in this respect.

Thanks to the shoulder 14b of the needle 14, the chamber 21 is separate or separate from the high pressure fuel circulation circuit, which allows two fluids of different natures to be used. In other words, the chamber 21 is sealed. In order to allow evacuation of the low pressure fluid contained in the chamber 21, the orifice 19a may be used.

In one embodiment, the support plate 40, the protrusion 46 and the stud 86 are made in one piece.

Advantageously, in a closed position of the needle 14, an axial space (not referenced) is provided between an upper end surface 49 of the support plate 40 of the needle holding device and the closure cap 19 of the body of the injector.

In other words, a first axial length L between a lower surface of the closure cap 19 and the distal end 24 of the nozzle 20 is greater than a second axial length L1 defined by the axial distance between the upper surface 49 of the plate. 40 and the contact surface of the pad 86 and the needle 14, which is added to a third axial length L2 itself defined by the axial distance between said contact surface of the pad 86, and the needle 14 and the distal end 24 of the nozzle 20. The axial space has an axial dimension ε which corresponds to the geometric tolerances of the elements of the injector 10 and to any thermal variations.

The axial space is filled with the fluid present inside the sealed chamber 21. A fluid film is thus interposed between the end surface 49 and the cover 19 for closing the body 12 of the injector, which makes it possible to achieve acoustic coupling between the support plate 40 of the device for holding the needle. and the body 12 of the injector. Thus, it becomes possible to reduce the size of the support plate 40, and reduce the axial size of the needle holding device. Advantageously, the axial dimension ε of the axial space is as small as possible so as to obtain a strong acoustic coupling.

Of course, it is readily conceivable that it is also possible to provide such support plate 40 and protuberance for an injector 10 to incoming head.

Claims (11)

1. Device for holding a needle of a fuel injector, the device comprising a bearing plate (40) and an injector needle axial-retention element (44) provided with inwardly directed radial projections (56) each comprising an area for contact with the needle, characterized in that the axial-retention element (44) comprises a securing portion (52) collaborating with a complimentary portion of the bearing plate (40) to secure the retention element against the said plate, and a retention portion axially extending the said securing portion and provided with axial tabs (54), each axial tab (54) comprising, at its lower end, one of the radial projections (56).
2. Device according to Claim 1, further comprising a binding ring (62) radially surrounding the axial tabs (54) and mounted bearing against them.
3. Device according to Claim 2, in which the binding ring (62) is open at one point on its circumference.
4. Device according to any one of the preceding claims, in which the bearing plate (40) further comprises a peg (86) provided with a flat contact surface for contact with an upper end of the needle.
5. Device according to any one of the preceding claims, in which the axial-retention element (44) is separate from the bearing plate (40).
6. Motor vehicle internal combustion engine fuel injector comprising a needle (14) mounted such that it can be moved axially in a body of the injector, and a device for holding the needle according to any one of the preceding claims.
7. Injector according to Claim 6, comprising a sealed chamber (21) in which the holding device (16) is mounted and which is separate from a circuit through which the fuel that is to be injected flows.
8. Injector according to Claim 7, in which the sealed chamber (21) is filled with a fluid, notably a low-pressure fluid.
9. Injector according to any one of Claims 6 to 8, in which, when the needle (14) is in the closed position, an axial space is created between the end surface (49) of the needle holding device and the body of the injector.
10. Injector according to any one of Claims 6 to 9, in which the bearing plate (40) is shaped in such a way as to have an acoustic impedance that exceeds that of the needle.
11. Injector according to any one of Claims 6 to 10, comprising vibration-instigating means (70) capable of causing mechanical oscillations of the needle.

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