WO2000063553A1

WO2000063553A1 - Fuel injecting device for internal combustion engine

Info

Publication number: WO2000063553A1
Application number: PCT/FR2000/000965
Authority: WO
Inventors: André AGNERAY; Laurent Levin
Original assignee: Renault
Priority date: 1999-04-15
Filing date: 2000-04-14
Publication date: 2000-10-26
Also published as: FR2792369A1; FR2792369B1

Abstract

The invention concerns a fuel injecting device for internal combustion engine comprising an injector (1) connected to a fuel system (2) under adapted pressure, characterised in that said injector (1) comprises a nozzle (3) supplied with fuel and at the end of which is provided a fuel injection outlet (5), means (1) for cyclic vibrating of the nozzle (3), said means being controlled in duration and intensity by the electronic engine control system, and closing means (7) elastically returned against said injection outlet (5), the vibrating of the nozzle (3) and the closing means (7) ensuring the discharge of a predetermined amount of fuel.

Description

FUEL INJECTION DEVICE FOR INTERNAL COMBUSTION ENGINE

The present invention relates to a fuel injection device for an internal combustion engine intended in particular to equip a motor vehicle. The invention relates more particularly to a fuel injection device making it possible to atomize the fuel injected in the form of very fine droplets.

The fuel injection devices used today on internal combustion engines fitted to motor or road vehicles, conventionally operate on the model of a valve, the open or closed state of which is permanently controlled, the dosage of the injected fuel then done directly by the opening time.

Such injection systems include an electric fuel supply pump which supplies, via a distribution manifold, all of the injectors under a pressure having a constant difference with the pressure prevailing in the intake manifold. through a pressure regulator. By electronically controlling the electromagnet actuating the valve of each injector, one controls the beginning and the duration of opening of this one and one then determines a precise flow of fuel for each of the injectors, thus the quantity of fuel injected depends only on the opening time of the electro-injectors.

The injectors of the electromagnetically controlled needle type, which are the most commonly used, however have limits which slow down the improvement in engine performance, particularly in terms of pollution control. In particular, the times taken to open or close the needles are still too high, around 1 to 2 ms, which prevents the injection from being distributed correctly over the entire opening time of the valve. In addition, the minimum opening time, which determines the minimum dose of fuel that can be injected, is still too great for certain engine fcr.ctiûnne-r.ent points.

Known needle injectors also have injection holes of relatively large diameters to allow the delivery of the required quantities of fuel for operations at full load and high engine speeds. This arrangement generates fuel jets having drops of large dimensions, which slows down the vaporization of the fuel (and therefore the preparation of the fuel mixture) and is capable of promoting the phenomenon of wall wetting.

In fact, the non-vaporized fuel tends to settle on the walls of the intake duct or the combustion chamber (by direct injection). Such deposition leads to metering problems, particularly acute in transients due to a lack of knowledge of the quantity of fuel which actually enters the corresponding combustion chamber. This wall wetting phenomenon is one of the major causes of high pollutant emissions during cold engine starts.

In addition, with a conventional needle injector, when the needle opens when the latter begins to leave its seat, a liquid bulb forms which disappears when the needle is fully raised, the fluid flow regularizing then. This change in the nature of the flow makes any precise control of the instantaneous injector flow impossible.

Some have sought to solve these various problems, by developing injectors using piezoelectric actuators to maneuver the needle so as to reduce the duration of opening and closing of the needle, but such systems which always operate according to the principle of a valve, retain significant drawbacks related in particular to the significant dispersion affecting the size of the drops in the fuel jet leaving the nose of the injector.

All of the problems mentioned above therefore result in a vaporization of the fuel which may be incomplete and not homogeneous during the preparation of the fuel mixture in the combustion chamber, inaccurate dosages, resulting in incomplete combustion resulting in the formation of a high amount of polluting gases and an energy deficit affecting engine efficiency.

The Applicant has developed a new type of fuel injection device making it possible to solve all of these problems, the device being capable of delivering a cloud of fuel drops whose sizes are perfectly calibrated to ensure precise and sufficiently small dosing. to ensure complete and homogeneous vaporization of the injected fuel.

This device, described in patent application No. FR97 / 05129, is of the type comprising an injector connected to a fuel supply circuit under a suitable pressure, this injector comprising an injection nozzle at the end of which is formed at least one fuel injection orifice and this injector cooperating with means of cyclic vibration controlled by the electronic engine control system so as to cause mechanical oscillations in bending of the injection nozzle, this nozzle injection being adapted to eject a predetermined quantity of fuel at each of its oscillations.

The object of the present invention is to improve this new type of injection device by proposing a new body architecture. injector simpler to produce, in particular in that it is no longer necessary to have an injection nozzle formed by a plurality of channels of suitable dimensions, joined in a bundle.

The fuel injection device for an internal combustion engine according to the invention comprises an injector connected to a fuel circuit under a suitable pressure.

According to the invention, the fuel injection device for an internal combustion engine is characterized in that the injector comprises a nozzle supplied with fuel and at the end of which is an orifice for fuel, means for cyclically vibrating the nozzle, these means being controlled in duration and intensity by the electronic engine control system, and shutter means resiliently biased against the injection orifice. The vibration of the nozzle and the shutter means which are integral with it by the vibratory means ensuring the ejection of a predetermined quantity of fuel.

According to another characteristic of the injection device which is the subject of the invention, the end of the nozzle where the injection orifice is formed is extended by a flange shaped to vibrate with high amplitudes. According to another characteristic of the injection device which is the subject of the invention, the obturating means are formed by a rod of which a flared end forms a valve, this rod being mounted axially movable inside the nozzle and being elastically secured to this same nozzle.

According to another characteristic of the injection device which is the subject of the invention, the rod is provided at its end opposite to the orifice with a predetermined mass.

According to another characteristic of the injection device which is the subject of the invention, the rod is secured to the body of the nozzle by means of an elastic cup.

According to another characteristic of the injection device which is the subject of the invention, the means for cyclically vibrating the nozzle are formed by a transducer.

According to another characteristic of the injection device which is the subject of the invention, the transducer comprises piezoelectric ceramics.

According to another characteristic of the injection device which is the subject of the invention, the transducer comprises a magnetostrictive material. The objects, aspects and advantages of the present invention will be better understood from the description given below of various embodiments of the invention, presented by way of non-limiting examples, with reference to the accompanying drawings, in which :

FIG. 1 represents an overall view, in axial section, of the injection device according to the invention;

Figures 2 to 5 schematically explain the operating principle of the injection device according to the invention;

Figure 6 is an axial sectional view detailing the end of the injector shown in Figure 1;

Figure 7 is a partial sectional view of an internal combustion engine cylinder head equipped with a fuel injection device according to the invention.

FIG. 8 is a schematic view of the control circuit of the transducer shown in FIG. 1.

In accordance with the appended drawings, only the elements necessary for understanding the invention have been shown. In addition, to facilitate reading of these drawings, the same parts have the same references from one figure to another.

Referring to FIG. 1, the body of the injector object of the present invention has been detailed.

The body of the injector essentially comprises three separate members cooperating with each other.

The first member, placed in the upper part of the injector, is made up of means capable of generating vibrations in a longitudinal mode at ultrasonic frequencies such as a transducer 1.

The second member, arranged in the lower part of the injector in the extension of the first element, consists of oscillator means 2 mechanically coupled to the vibration generating means. These oscillator means are, in the illustrated embodiment, essentially constituted by a frustoconical nozzle 3 in which the vibrations from the transducer 1 are amplified.

The nozzle 3 has an internal cavity 15 intended to be filled with pressurized fuel by means of a radial bore 14 for supplying the fuel coming to connect to a pressurized fluid supply circuit 16. The cavity 15 opens out at the lower end of the nozzle 3 by an injection orifice 5 The lower opening 5 of said nozzle 3 is extended by a fine collar 10 of divergent frustoconical shape. When the nozzle 3 is set into vibration, this flange 10 is excited at a frequency close to resonance generating large amplitudes of vibrations at its periphery 11.

Finally, the third member is constituted by a cylindrical rod 4 housed movable axially inside the nozzle 3 and whose lower end of frustoconical shape 7 extends outside of the nozzle 3. This end 7 forming a valve is adapted to come into contact with the inner surface of the nozzle 3 delimiting the lower opening 5 of the nozzle 3, surface defining a seat for said valve, and thus for closing the fuel injection orifice.

The other end of the rod 4 is provided with a mass 8 connected elastically by a cup 9 to the nozzle

3. This cup 9 exerts an elastic restoring force tending to apply the end 7 of the rod 4 against the surface surrounding the injection orifice 5 of the nozzle 3.

The value of the mass 8 and the rigidity of the cup 9 are chosen to form a system having a very long response time in relation to the durations of excitation of the transducer 1. The connection between the nozzle 3 and the transducer 1 takes place through a coupling by flange 36 and counter flange 34 tightened one against the other by means of screws 13 and nuts. The transmission of vibrations between the transducers 1 and the nozzle 3 thus takes place with a strong elastic coupling provided by the prestressing means constituted by the screw-nut connections 13.

The transducer 1 is dimensioned to transmit a maximum of stress at the junction 12 with the nozzle 3, this maximum of stress corresponding to a minimum of amplitude of vibration for the material.

It is, moreover, at the level of the flange 36 integral with the nozzle 3 that the supply channel 14 is formed radially, making it possible to supply the cavity 15 with a fuel (liquid or gas) under pressure.

The transducer 1 comprises a zone 17 made up of active piezoelectric or magnetostrictive components, which, respectively under the application of an electric or magnetic field, deform in thickness. This part 17 is sandwiched between two other elements 18 and 19 made of an elastic material. The connection between the elements 17, 18, and 19 is ensured by prestressing means such as a screw 20.

As shown in Figure 8, the engine control computer sends two pulses corresponding to the beginning and at the end of the injection, during this duration an ultrasonic frequency generator 38 sends a wave train (level 5V) at an excitation frequency given at the input of an amplifier 39, which makes it possible to attack the alternative voltage piezoelectric ceramics (of the order of + 40V to -40V) at the same ultrasonic frequency during the injection period.

Under the application of an electrical voltage on the common electrode of the two piezoelectric ceramics, these deform and generate an elastic stress which is transmitted to the lower end of nozzle 3 where the flange 10 is located. .

The nozzle 3 is dimensioned to resonate at the excitation frequency of the active components 17 and to amplify the longitudinal displacements up to the level of the collar 10. This collar 10 is also dimensioned to resonate at the excitation frequency -so that the displacements produced at the level of the support zone of the valve 7 surrounding the opening 5, are amplified to reach a maximum at the ends of this same flange at the points.

The rod 4, initially closing the opening 5 by its end 7 forming a valve, deforms under the impulse which is provided to it when the nozzle 5 starts to oscillate. This deformation is distributed elastically over the entire length of the rod 4 and is reflected at the interface between the rod 4 and the mass 8. The proper response of the rod 4 on the one hand and of the nozzle 3 on the other hand allow the end 7 and the opening 5 to oscillate with a phase and amplitude variation. This variation results in the opening of an annular slot 21 between, the rod 4 and the cylindrical end of the nozzle 3, the width of the slot depending on the relative difference between the amplitude of oscillation of the opening. 5 and the amplitude of oscillation of the valve 7.

FIG. 2 describes the relative variation in position between the end 7 of the rod 4 (points Ai) and the opening 5 of the nozzle 3 (points Bi) for 3 cycles of oscillation of the resonator assembly. Figure 3 illustrates the positions of points Ai and Bi as a function of time.

The opening of the annular slot 21 is therefore oscillating with a maximum amplitude equal to the maximum difference in amplitude of vibration between the valve 7 and the opening 5 as indicated in FIG. 4. The opening frequency of the slit then depends on the excitation frequency chosen for the transducer 1 and on the natural frequencies of the rod 4.

According to the operating cycle shown in Figure 2, the end of the end 7 of the rod 4 on the edges of one end 5 of the nozzle 3 can occur with a very low relative speed, not inducing elastic shock high intensity. According to another operating mode illustrated in FIG. 5, the docking speed between the two ends is maximum and generates an elastic shock at each oscillation. The elastic shock occurs by contact in the area of the opening 5 and is partly transmitted into the collar 10.

The excitation corresponding to the shock being very short in time, it makes it possible to generate several modes of vibration of the flange 10, in particular at frequencies higher than the excitation frequency of the transducer 1. These modes of vibration at higher frequencies are superimposed on the fundamental resonance mode excited by the displacements of the end of the nozzle 3.

As shown in Figure 6, the flange 10 can then deform with a series of nodes and oscillating bellies between the area of the opening 5 and the end 11 of the flange. When the slot 21 opens, the pressurized liquid is ejected through this slot in the form of a liquid cone which follows the internal surface of the flange 10. The liquid film 22 during its contact with the flange 10 is repulverized by the vibrations of this same collar into fine droplets 23.

The opening angle of the collar 10 also makes it possible to adjust the opening angle of the droplet spray. 23 thus formed or gas, regardless of the ejection time.

The minimum opening time of the injection device is of the same order as the excitation period applied to the transducer 1, which excitation can take place at a few tens of kilohertz, typically 50 kHz, which allows minimum opening times. of the order of 20 μs. This makes it possible to deliver micro-quantities of liquid during a reduced period of time compared with more conventional injection devices where the minimum time to operate the opening and closing of the injection nose is rather 300 μs.

Referring to Figure 7, there is shown a mode of implantation of an injector according to the invention in an internal combustion engine of a motor vehicle.

The fuel supply to the engine is of the electronically controlled multipoint type by which each combustion chamber 25 is supplied directly with fuel by at least one fuel injector 1 opening into the chamber.

The injector body is fixed to the cylinder head 24 of the engine at its upper end by means that are not shown, this upper end being also connected to a fuel supply line that is also not shown. The tightness to the right of the well 28 of the injector is ensured by a ring 26 machined in the mass of the nozzle 3 and located at a vibration node. This ring 26 is held in sealed application on the edge 27 of the injection well 28.

A shell 29 which can be split into two symmetrical parts is fitted around the nozzle 3 between the ring 26 and the flange 10, the shell being fixed to the ring 26 by means of positioning pins 30. The shell 29 is dimensioned to touch on the one hand the nozzle 3 and on the other hand the wall of the well 28 with a spacing 31 corresponding to the thickness of thermal layer so as to avoid the accumulation of heat towards the end αe ιa ouse 3.

According to a particular embodiment of the injector which is the subject of the present invention, the transducer 1 comprises an annular half-cylinder 18 made of titanium with a diameter of 30 mm and a length of 24 mm, another half-cylinder 19 with a diameter of 30 mm and of length 45 mm including a thread 32 and a conical excavation 33.

A screw 20 makes it possible to prestress two rings of piezoelectric ceramics (external diameter 30 mm, internal diameter 10 mm, thickness 6 mm) between 18 and 19, the ceramics being arranged with antiparallel polarizations. A nickel electrode 35 is interposed between the ceramics. The end of the cylinder 19 includes a shoulder

34 forming a counter-flange on the side of the excavation 33. This shoulder 34 includes holes in which screws 13 are inserted, making it possible to prestress the nozzle 3 on the cylinder 19.

The titanium nozzle 3 consists of a frustoconical piece section converging in the direction of the opening 5. This piece has in its upper part a shoulder 36 forming a flange intended to come into contact with the counter-flange 34 carried by the cylinder 19 .

The nozzle 3 has an external diameter varying from 30 mm to 5 mm at its end 5 and an internal diameter varying from 10 mm to 3 mm. A cone with an external diameter of 15 mm is machined or attached (for example by welding) to the end of the nozzle 3 to form the flange 10. The thickness of this flange 10 varies from 0.5 mm in the zone 5 to 0 , 1 mm at the end 11.

A titanium rod 4 with a diameter of 2 mm and comprising a conical end 7 with an external diameter of 5 mm is inserted in the axis of the nozzle 3. A cup 9 having a rigidity markedly greater than that of the rod 4 along its length, comprises an orifice allowing the rod 4 to pass and bears on the upper surface of the shoulder 36 of the nozzle 3. A cylindrical mass 8 comprising a thread is screwed onto the other end of the rod 4 comprising a thread. The mass 8 is screwed until the desired preload is obtained, making it possible to apply the conical end 7 of the rod 4 to the zone 5 of the nozzle.

3, the contact force then being maintained by the elasticity of the rod 4 and cup 9 assembly. The applied prestress allows on the one hand the sealing of the opening 5 of the nozzle 3 when the fluid 16 is supplied with a given pressure and on the other hand the possible wear compensation in the zone of contact of the valve 7 with the nozzle 3.

The value of the mass 8 and the rigidity of the cup 9 are chosen to form a system having a very long response time relative to the durations of excitation of the transducer of the order of 40 miliseconds at most. The material of which the cup is made can be based on polymers having a very high rate of attenuation of elastic deformations in dynamics.

When a variable voltage of the order of 40 volts is applied to the terminals of the ceramics by means of the common electrode 35, the two ceramics deform in thickness and the deformations are transmitted throughout the structure.

For an excitation frequency of 50 kHz the structure is resonant with an oscillation amplitude profile depending on the position on the axis shown Figure 10. The supply of fluid 16 and the maintenance of the injector can be done respectively at the shoulders 34 and 36 which are. vibration nodes. The nozzle 3 then transmits the vibrations up to the level of the end of the nozzle 3 where the opening 5 is formed which in turn elastically deforms the rod 4.

The amplitude of oscillation for a voltage of 40 Volts applied is close to 20 microns, thus leaving an opening 21 generating a fluid film whose thickness is of the same order (20 microns). This fluid film is then shattered by the vibrations of the collar 10, which vibrations can reach 100 microns at the end 11 with the amplification factor linked to the reduction in thickness.

The device thus makes it possible to generate very fine droplets. For example, for a supply pressure of 50 Bars, the ejection speed of a liquid such as petrol is around 100 m / s, with an opening time of 20 μs the fluid will have traveled 2 mm along the collar whose active surface in vibration extends over 5 mm which leaves a sufficient contact area so that the vibrations of the collar can couple with the fluid film and nebulize it.

Of course, the invention is in no way limited to the embodiments described and illustrated which have been given only by way of example. On the contrary, the invention includes all the technical equivalents of means described as well as their combinations if these are carried out according to his spirit.

Claims

[1] Fuel injection device for an internal combustion engine comprising an injector (1) connected to a fuel circuit (2) under a suitable pressure, characterized in that said injector (1) comprises a nozzle (3) powered in fuel and at the end of which is provided a fuel injection orifice (5), means (1) for cyclical vibration of the nozzle (3) said means being controlled in duration and intensity by the system electronic engine control, and shutter means (7) elastically recalled against said injection orifice (5), the activation of the nozzle (3) and the shutter means (1) ensuring the ejection of a quantity of predetermined fuel.

[2] Fuel injection device according to claim 1, characterized in that the end of the nozzle (3) where the injection orifice (5) is provided is extended by a collar (10) shaped to vibrate with high amplitudes.

[3] Fuel injection device according to any one of claims 1 to 2, characterized in that said shutter means are formed by a rod (4) whose flared end (7) forms a valve, said rod (4) ) being mounted movable axially inside said nozzle (3) and being elastically secured to said nozzle (3).

[4] Fuel injection device according to claim 3, characterized in that said rod (4) is provided at its end opposite the orifice (5) with a predetermined mass.

[5] Fuel injection device according to any one of claims 3 to 4, characterized in that said rod (4) is secured to the body of the nozzle (3) via an elastic cup (9 ).

[6] Fuel injection device according to any one of claims 1 to ό, characterized in that said means for cyclical vibration of the nozzle (3) are formed by a transducer (1).

[7] Fuel injection device according to claim 6, characterized in that said transducer comprises piezoelectric ceramics.

[8] Fuel injection device according to claim 6, characterized in that said transducer comprises a magnetostrictive material.