WO1998049443A1

WO1998049443A1 - Internal combustion engine fuel injecting device

Info

Publication number: WO1998049443A1
Application number: PCT/FR1998/000778
Authority: WO
Inventors: André AGNERAY; Laurent Levin
Original assignee: Renault
Priority date: 1997-04-25
Filing date: 1998-04-17
Publication date: 1998-11-05
Also published as: FR2762648B1; EP0977946A1; FR2762648A1

Abstract

The invention concerns an internal combustion engine fuel injecting device (1) connected to a circuit (2) supplying fuel under adapted pressure, said injector (1) comprising an injection nozzle (8) at the end (14) of which is arranged at least an aperture for injecting fuel (10). The invention is characterised in that said injector (1) co-operates with cyclic vibration means (6) controlled by the engine electronic control system to cause the injection nozzle (8) to vibrate, said injection nozzle (8) being adapted to eject a predetermined amount of fuel at each one of its oscillations.

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 using a piezoelectric actuator 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 continuously 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, the start and the opening time of the latter are controlled and a precise flow of fuel is determined for each of the injectors, thus the quantity of fuel injected depends only 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 hinder the improvement of engine performance, in particular 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 long for certain engine operating 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 a deposit causes metering problems, particularly acute in the transients due to a lack of knowledge of the amount of fuel which actually enters the corresponding combustion chamber. This phenomenon of wall wetting 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 the problems mentioned above therefore result in a vaporization of the fuel which may be incomplete and non-homogeneous during the preparation of the fuel mixture in the combustion chamber, imprecise dosages, with the result of incomplete combustion resulting in the formation of '' a high quantity of polluting gases and an energy deficit affecting engine performance. The object of the present invention is therefore to solve all of these problems by proposing an injection device capable of delivering a cloud of fuel drops whose sizes are perfectly calibrated to ensure precise metering and sufficiently small to ensure the complete and homogeneous spraying of the injected fuel.

The fuel injection device for an internal combustion engine according to the invention 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 at least one fuel injection orifice is provided.

According to the invention, the injection device is characterized in that the injector cooperates 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 injection nozzle being adapted to eject a predetermined quantity of fuel at each of its oscillations.

According to another characteristic of the fuel injection device which is the subject of the invention, the injection nozzle is formed by a plurality of channels of suitable dimensions, joined together in a bundle.

According to another characteristic of the fuel injection device object of the invention, the channels forming the injection nozzle are adapted to be supplied with fuel by capillarity.

According to another characteristic of the fuel injection device which is the subject of the invention, these channels have injection orifices adapted to eject the fuel in the form of droplets of given sizes.

According to another characteristic of the fuel injection device which is the subject of the invention, the injector has an elastically deformable part which cooperates with the means for cyclic vibration controlled by the electronic engine control system, the injection nozzle being secured to this deformable part.

According to another characteristic of the fuel injection device which is the subject of the invention, this elastically deformable part is formed by a chamber extending in the extension of a fuel tank to which the fuel supply circuit is connected by the 'through a pilot valve whose opening is controlled according to the filling level of said tank.

According to another characteristic of the fuel injection device which is the subject of the invention, the fuel tank incorporated in the injector cooperates with regulation means making it possible to adjust the pressure to the pressure prevailing in the engine air intake circuit.

According to another characteristic of the fuel injection device which is the subject of the invention, the vibration setting means are formed by a piezoelectric actuator.

Such an electronically controlled injection device allows very precise control of the size of the drops injected and, moreover, is completely independent of the flow rate and the duration of injection.

The characteristics and advantages of the present invention are presented in more detail below by describing an embodiment of the invention, by way of nonlimiting example, the description referring to the appended drawings in which:

FIG. 1 represents an overall view of the injection device according to the invention;

Figures 2A and 2B are views in longitudinal section of the injection device of Figure 1 detailing its operation;

Figure 3 is a partial sectional view of an intake duct of an internal combustion engine equipped with a fuel injection device according to the invention.

In accordance with the accompanying drawings, only the elements necessary for the understanding of 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 Figure 3, there is seen in cross section an intake duct 12 formed through the cylinder head 16 of an internal combustion engine of the multicylinder type with spark ignition. This duct 12 opens out through an inlet orifice on the underside of the cylinder head 16 defining the roof of a combustion chamber 15. This inlet orifice conventionally serves as a seat for a stem valve 13 slidably mounted in a housed guide in the cylinder head 16. The opening of the valve 13 is controlled by suitable means, not shown, such as a camshaft.

The fuel supply to the engine is of the electronically controlled multipoint type by which each combustion chamber 15 is supplied with fuel by at least one fuel injector 1. The injector 1 extends, according to the particular embodiment shown, directly into one of the intake ducts serving the combustion chamber 15, in this case the duct 12.

The injector 1 is arranged so that its ejection nozzle 8 is directed towards the head of the valve 13 in order to direct the jet of fuel 11 directly into the combustion chamber 15 through the intake orifice, when the opening of the valve 13. The body of the injector 1 is fixed in the cylinder head 16 by its end upper, which is also connected to a fuel supply line 2.

Referring to FIG. 1, the body of the injector 1 which is the subject of the present invention has been detailed. The injector body comprises, in its upstream part in the direction of flow of the fuel, a buffer tank 4 having a membrane 5 for pressurizing. This tank 4 is supplied by a line 2 for supplying the fuel under a suitable pressure. Between the pipe 2 and the tank 4 is interposed an electrically controlled valve 3 whose function is to control the filling level of the tank 4.

The reservoir 4 communicates with a chamber 7, the elastically deformable walls of which cooperate with cyclic pressurization means such as a plate made of piezoelectric material 6. The chamber 7 is extended by a nozzle 8 formed by a plurality of inlet channels 9 of the fuel of progressive sections, arranged in a bundle. This nozzle 8 is integral with the chamber 7 so that the cyclic deformations of the latter under the action of the pressurizing means, causes the vibration of the nozzle 8 and the ejection of the fuel.

The channels 9 open at the downstream end 14 of the nozzle 8 through suitable orifices forming injection noses 10 through which the fuel is ejected in the form of a jet 11 of droplets of suitable sizes. These channels have shapes and are made of materials adapted to allow the creation of sufficient capillary forces necessary for filling them with fuel from chamber 7.

According to Figures 2a and 2b, the operation of the injector 1 which has just been described is as follows. The valve 3 being normally kept closed, the pressure of the fuel filling the tank 4 follows the pressure prevailing in the intake duct 12 by virtue of the pressurizing membrane 5. The pressure balance prevailing between the interior of the body of the injector 1 and the outside of the latter combined with the suitable shape of the conduits 9, make it possible to ensure by capillary filling of the conduits 9 with fuel from the chamber 7 and the reservoir 4 as and when ejection of the fuel, while retaining the fuel inside the channels 9 in the absence of vibration of the latter by the surface tension acting at the level of the orifices 10.

The tank is kept filled by controlling the valve 3. When the quantity of fuel in the tank 4 falls below a given threshold, detected by a sensor not shown here, the valve 3 is then opened until the filling of the tank 4 at the required threshold, then valve 3 is closed again. The variations in volume in the tank 4 due to the quantities of fuel ejected through the orifices 10 and to the quantities of fuel passing through the valve 3 are sufficiently small compared to the total volume of the tank 4 so that the variations in pressure can be compensated by the pressurizing membrane 5.

Thus, in accordance with the invention, the pressure of the supply circuit can be relatively low and the valve of simplified design, in particular have a response time much longer than that of a conventional injector.

The shape of the chamber 7, between points A and D, and the nature of the materials used for the production of its walls, are therefore adapted so as to generate, under the action of the cyclic pressurization means 6, an oscillation of the nozzle 8 whose amplitude is maximum at the orifices 10 of the channels 9. To do this, the piezoelectric plate 6 is secured to the wall of the chamber 7 by gluing and its electrodes are formed by two parallel faces, l 'one (AD) being in contact with one injector at the wall of the chamber 7 and the other (CB) having its free surface.

The piezoelectric plate 6 is polarized in a direction perpendicular to the electrodes, so that when a voltage is applied between these electrodes, by necking effect the piezoelectric plate 6 stretches in its two planar directions, the state of stress on the two faces being different this has the effect of creating a bending of the plate which results locally in a change of curvature of the wall of the chamber 7. The bending of the wall of the chamber 7 causes in bending the part 8 of the body 1, namely the injection nozzle, with maximum displacement at its end 14 at the orifices 10.

The displacement generated at the end of the nozzle 14 makes it possible to expel through each orifice 10 a micro-quantity of liquid which gives rise to a drop 11 ejected with a certain speed. For each cycle of electric voltage applied to the piezoelectric plate 6, it passes through two symmetrical bending deformation states which causes the end of the nozzle 14 to oscillate between two symmetrical positions E and F linked to an amplitude given oscillation. At each passage through one of these points E or F of maximum amplitude, the fuel drops are ejected. For a tension cycle, two drops of fuel are ejected per orifice.

By varying the value of the electric voltage applied between the electrodes of the wafer 6, it is possible to obtain a more or less significant effect of bending of the body 7 and thus to adjust the value of the amplitude of the oscillation at the end 14 of the nozzle. This makes it possible to vary the quantity of liquid ejected by each orifice during the oscillation cycle and thus to vary the diameter of the ejected drops. Each vibration cycle producing the ejection of a determined number of drops of fuel, it is therefore possible to precisely dose the quantity of fuel injected by electronically controlling the source of electric power by the engine control system to obtain the desired number of cycles. . Between the two bending states of the chamber 7 which causes the fuel to be ejected from the channels 9, the action of the capillary forces inside the channels 9 makes it possible to ensure that they are constantly filled with fuel from the tank 4 to ports 10.

Thus, in accordance with the invention, the ejection of the drops through the orifices 10 at the end 14 of the nozzle 8 is effected by the sole action of the oscillatory movement in bending of the latter. Oscillating movement in bending, which causes on the one hand a local overpressure in the liquid at the level of the nozzle and on the other hand a setting in motion of the same liquid confined in the nozzle, the two effects contributing simultaneously to the formation and to the ejection of the drops. Thus, it is the vibration of the end 14 of the nozzle 8 which provides the kinetic energy necessary for the ejection of the drop.

The shape of the injector 1 and more particularly of the nozzle 8, is therefore suitable for obtaining a natural amplification of the movement. The beam structure of the channels 9 perfectly meets this objective. Likewise, it is important that the structure chosen can reach high resonant frequencies allowing the injection of a high number of drops of fuel per second.

The injector according to the invention therefore operates without a valve since the channels 9 open freely to the atmosphere, the retention of the liquid in the nozzle 8 operating simply by virtue of the surface tension of the liquid and the action of the capillary forces. A liquid meniscus is thus naturally formed on each orifice 10 of the nozzle 8, a meniscus which prevents the flow of fluid as long as the pressure difference between the liquid contained in the nozzle and the surrounding atmosphere does not exceed a given value.

This sufficiently low pressure difference in the fuel between the orifices 10 of the nozzle 8 and the buffer tank 4 located upstream in the body of the injector 1 is simply obtained by virtue of the diaphragm 5 for pressurizing.

To generate deformations in the body of the injector 1 or in the vicinity of the nozzle 8, it is possible to use piezoelectric materials or else magnetostrictive materials. It suffices that these materials deform under the influence of an electric or magnetic field and therefore allow the application of stresses generating the desired deformations.

By way of example, the injection device comprises a body 1 which in its part supporting the piezoelectric plate 6 measures 1 millimeter in total and about 1 centimeter in its width and its length, the nozzle has a length close to 20 millimeters and a thickness of the order of 0.2 millimeters at its end where is located a row of circular orifices 10 30 microns in diameter. We then obtain the ejection of a double beam of drops with excitation frequencies ranging from 40 kH to 400 kH, and this for an applied alternating voltage of the order of 10 volts peak. The diameter of the drops is a function of the amplitude of the applied voltage and the operating frequency. The speed of the drops depending on the operating point chosen varies from 5 to 15 meters per second. The response time of the device for an oscillation of the nozzle and the simultaneous ejection of drops of fuel is approximately 10 microseconds. To ensure a fuel flow compatible with the operation of an engine, a device operating at 250 kH has 170 orifices 10 of 30 microns in diameter at the end of the nozzle.

The injector 1 according to the invention independently of the advantages which it presents in terms of metering and vaporization of the fuel, thanks in particular to the precise calibration which it allows for the size of the droplets, is moreover particularly suitable for operating the fuel injection when the intake valve 13 is lifted and thus inject the fuel directly into the combustion chamber 15.

Effect, during the opening of the intake valve 13, the flow of intake air filling the combustion chamber 15 at a speed of about 70 meters per second in the vicinity of the neck of the valve. This flow assists the ejection of fuel and drives the drops which are ejected in a bundle of the orifices 10 to propel them directly into the chamber 15 through the opening of the valve. The difference between the ejection speed of the drops, between 5 and 10 meters per second and that of the air flow, causes abrasion of the fuel drops and contributes to their evaporation.

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 the means described as well as their combinations if these are carried out according to the spirit.

Thus the body 1 of the injector can thus be placed closer to the neck of the valve 13 or more upstream in the intake duct 12, see outside of the intake duct in an arrangement provided in the cylinder head , the end of the nozzle 8 opening into the intake duct 12 at a point located either near the neck of the valve or further upstream.

Thus, according to different embodiments, the injection orifices can be circular, square or any other geometric shape, the transverse dimensions of the orifices being able to be reduced to a few microns, for example of the order of ten to thirty microns . The section of the orifices makes it possible to calibrate the size of the drops formed, the calibration of the size of the drops can then be modified by varying the amplitude of oscillation of the nozzle.

Claims

[1] Fuel injection device for an internal combustion engine comprising an injector (1) connected to a fuel supply circuit (2) under a suitable pressure, said injector (1) comprising an injection nozzle (8 ) at the end (14) of which is provided at least one fuel injection orifice (10), characterized in that said injector (1) cooperates with cyclic vibration means (6) controlled by the system electronic engine control so as to cause mechanical oscillations in flexion of the injection nozzle (8), said injection nozzle (8) being adapted to eject a predetermined quantity of fuel at each of its oscillations.

[2] Fuel injection device according to claim 1, characterized in that said injection nozzle (8) is formed by a plurality of channels (9) of suitable dimensions, joined in a bundle.

[3] Fuel injection device according to claim 2, characterized in that said channels are adapted to be supplied with fuel by capillary action.

[4] Fuel injection device according to claim 3, characterized in that said channels (9) have injection orifices (10) adapted to eject the fuel in the form of droplets of given sizes.

[5] Fuel injection device according to any one of claims 1 to 4, characterized in that said injector (1) has an elastically deformable part (7) which cooperates with said cyclic vibration means (6) controlled by the electronic engine control system, said injection nozzle (8) being integral with this deformable part (7).

[6] Fuel injection device according to claim 5, characterized in that said elastically deformable part is formed by a chamber (7) extending in the extension of a fuel tank (4) to which the circuit is connected (2) fuel supply via a pilot-operated valve (3) whose opening is controlled according to the filling level of said tank (4).

[7] Fuel injection device according to claim 6, characterized in that said fuel tank (4) cooperates with regulating means making it possible to adjust the pressure prevailing in said tank (4) to the pressure prevailing in the air intake circuit (12) of the engine.

[8] Fuel injection device according to any one of claims 1 to 5, characterized in that said vibration means are formed by a piezoelectric actuator.