EP1172552B1 - Fuel injection device for internal combustion engine - Google Patents

Description

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 for atomizing the injected fuel in the form of very fine droplets as required.

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

Such injection systems comprise an electric fuel supply pump which supplies, through the channel of a distribution manifold, all the injectors under a given pressure. By electronically controlling the actuator of the valve of each injector, it controls the start and the duration of opening thereof and then determines a precise amount of fuel injected.

Electromagnetically controlled needle-type injectors have limitations that inhibit engine performance. In particular the time taken to open or close the needles are still too high, about 1 to 2 ms, which prevents to phase the injection ideally on all motor ranges. In addition, the minimum opening time, which determines the minimum dose of fuel that can be injected, is still too important for certain engine operating points.

Known needle injectors also have injection orifices of relatively large diameters to allow the required quantities of fuel to be discharged for operations at full load and high engine speeds. This arrangement generates fuel jets having drops of large dimensions, which slows the vaporization of the fuel (and therefore the preparation of the fuel mixture) and is able to promote the wetting phenomenon of the walls.

Indeed the non-vaporized fuel tends to be deposited on the walls of the combustion chamber. Such deposition causes metering problems, particularly acute transients for lack of knowledge of the amount of fuel actually mixed with the air in the combustion chamber. This wetting phenomenon is one of the important causes of high pollutant emissions during cold engine starts.

Moreover, with a conventional needle injector, when the needle opens when the needle begins to leave its seat, a bulb of liquid is formed which disappears when the needle is completely raised, the fluid flow is regulating then. This change in the nature of the flow makes it impossible to precisely control the instantaneous flow rate of the injector.

Some have tried to solve these problems by developing injectors using piezoelectric actuators to maneuver the needle to lower the opening and closing time of the needle, but such systems that still operate according to the principle of a valve, retain significant disadvantages related in particular to the significant dispersion affecting the size of the drops in the fuel jet at the end of the nose of the injector. Thus, in document FR 2 758 369, a piezoelectric transducer in the form of a rod transmits its elongation to a sliding pusher which transmits it (in thrust only) itself to a valve flap whose return to the closed position is provided by elastic means. Such a solution has the disadvantage of a too long response time related to the importance of the kinematic chain.

DE 3010985 and US 5330100 disclose injection devices comprising a system for opening the needle by translation associated with a secondary jet spray system at the outlet of the ejection nose, in these devices the liquid web flows continuously during the entire opening time and is refragmented by the vibrations generated in the vicinity of the ejection nose as soon as the contact between the liquid and the end of the nose takes place.

A first disadvantage of this type of solution lies in the low atomization capacity of the liquid when the ejected liquid layer is important, see an atomization capacity limited to only one short moment at the beginning of the contact of the liquid layer as well as at the end of the ejection. Between these two moments the contact is made for a period of time too short for the vibrations and displacements generated at the end of the ejection nose can: either be transmitted in the form of a surface wave in the liquid which the nebulize is generated local pulses on the fluid sheet which has the effect of fragmenting the fluid sheet.

A second disadvantage of this type of solution is a too long response time due to the opening mode which requires translating the entire mass of the needle.

According to the document U.S. 5025766 an injection device is known whose nose vibrates around a frequency of 35 kHz and comprising a ball of a given mass held in abutment against the seat of the injection nose by a prestressing spring. At each oscillation an opening appears between the seat of the injection nose and the ball, thus allowing the ejection of a quantity of fluid for a very short period of time corresponding to the oscillation period, which makes it possible to nebulise the liquid with a high rate. However, one drawback is that on the one hand the twists of the ball on the seat, and on the other hand the oscillating behavior of the system consisting of the mass of the ball and the prestressing spring, do not allow rigorous control of the ball. vibratory behavior of the nose-ball assembly and therefore the opening moment for dosing the fluid which results in the fuel being injected in an uncontrolled manner.

All of the problems mentioned above thus 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 altering the efficiency of the engine.

The object of the invention is to propose a new type of fuel injection device to solve all of these problems, the device being able to deliver with a high accuracy and a very short response time a cloud of drops of fuel whose sizes are very close and small enough to ensure the complete and homogeneous vaporization of the injected fuel.

US 4,389,999 A discloses a fuel injector according to the preamble of appended claim 1.

The Applicant has already proposed devices at least partially meeting this purpose in the French patent applications No. 99-43732 filed on April 15, 1999 and in the patent application No. 99-14548 filed on 19/11 / 1999. The present invention is an alternative solution.

The invention achieves its purpose through a fuel injection device as claimed in the appended claim 1.

Thus, according to the present invention, an injection device is provided whose opening at the level of the ejection nose is solely a function of the expanded or compressed state of the valve needle bearing at the level of the nose, the variation of state being generated by an electrically controlled ultrasound excitation source. In this type of operation where the opening is done by deformation of the needle and no longer by translation, the oscillations phenomena of mass-spring type are removed. At each oscillation a given amount of elastic deformation energy is transmitted into the stem and is expended in expansion-compression with a loss due to internal relaxations of the material constituting the rod, the rest of the energy being absorbed by the attenuation due to the crushing of the fluid blade wedged between the ejection nose and the valve forming the end of the needle. The oscillations occur at a frequency close to 50 KHz, which makes it possible to generate short opening times and thus to finely atomize the ejected liquid.

Furthermore, the injection device according to the invention has one or more of the following characteristics.

The shutter means are formed by a rod whose flared extremity forms a valve, this rod being mounted axially movable inside the transducer and being elastically fastened with the same transducer, in an area situated in an upper part of the transducer made in the form of cylinder narrower than the rest of the transducer.

The shutter means forming a valve are constantly biased against the end of the nozzle serving as a seat for the valve by an elastic return device that can be formed of a damping material, this elastic and damping device supporting the assembly composed by the three elements that are the transducer, the rod and the valve, these three elements being themselves resiliently secured.

The shutter means forming a valve are brought against the end of the nozzle after each opening by the contraction of the rod which follows the expansion of the rod during each vibration cycle.

The shutter means forming a valve remain pressed against the end of the nozzle outside the phases of deformation of the rod by means of elastic and damping return means bringing the entire transducer, the rod and the shutter means against the end of the nozzle forming a seat for the valve.

The elastic and damping return means for applying the shutter means against the end of the nozzle and supporting the entire transducer and the rod is made of a material for damping the transmission of vibrations between the transducer and the body of the injection box.

The elastic and damping return means for applying the shutter means against the end of the nozzle makes it possible to make up for the possible clearance due to thermal expansion between the transducer, the rod and the injection nozzle, without any effective modification of the prestressing ensuring the seal.

The injection housing contains the transducer, the rod and the damping material.

A flow restrictor is placed inside the nozzle in the annular space between the rod and the inner cylindrical surface of the nozzle so that during the ejection of the fluid, the flow of liquid passing through the nozzle is defined precisely by the space between the rod and the flow limiter.

The cyclic vibrating means of the rod are formed by a transducer comprising a mechanical amplification system and elastically connected to the rod to transmit the amplified deformations.

For the centering of the rod and shutter means in the vicinity of the end of the nozzle is provided an annular guide having channels for the passage of the liquid against which rests the rod so that the shutter means can be moved coaxially with the end of the nozzle.

The channels formed in the neck to let the liquid pass can serve as a flow limiter.

The transducer has a stack of more than two active components.

The active components of the transducer are formed in a piezoelectric material.

The active components of the transducer are formed in a magnetostrictive material.

The mass of the transducer associated with the damping piece constitutes a dissipative system having a very large response time with respect to the excitation times of the transducer, so that the deformations of the rod and the shocks occurring at the seat induce no setting in motion of the body of the transducer; only the end of the cylinder terminating the transducer at its upper part oscillates on either side of the initial equilibrium position, these oscillations being transmitted in the rod.

• a) au-delà d'une valeur seuil, auquel cas la section débitante par l'ouverture est supérieure à celle du limiteur de débit et le débit de l'injecteur est alors fonction de la pression et de la section de passage du limiteur de débit de sorte que les quantités injectées sont contrôlées précisément par le nombre de cycles d'ouverture du clapet,
• b) en dessous de la valeur seuil citée plus haut, la section débitante par l'ouverture est inférieure à celle du limiteur de débit et le débit instantané de l'injecteur est alors fonction à chaque oscillation de la pression et de la section de passage générée par l'ouverture de sorte que les quantités injectées sont contrôlées dans ce cas par l'amplitude de déplacement et par le nombre d'oscillations commandées permettant ainsi de réduire encore la quantité minimale injectée et d'augmenter le taux de nébulisation du liquide.

The quantities of fuel delivered by the injector can be controlled in two ways consisting of controlling a displacement of the valve:

• a) above a threshold value, in which case the flow section through the opening is greater than that of the flow restrictor and the flow of the injector is then a function of the pressure and the flow section of the flow limiter. flow rate so that the quantities injected are precisely controlled by the number of opening cycles of the valve,
• b) below the threshold value mentioned above, the flow section through the opening is smaller than that of the flow restrictor and the instantaneous flow rate of the injector is then function at each oscillation of the pressure and the flow section generated by the opening so that the injected quantities are controlled in this case by the displacement amplitude and the number of controlled oscillations thus further reducing the minimum amount injected and increase the nebulization rate of the liquid.

• la figure 1 représente une vue d'ensemble, en coupe axiale, du dispositif d'injection selon l'invention;
• les figures 2 et 3 représentent, en vue de dessus, la partie limiteur de débit et la partie guide de la tige situées dans la buse du dispositif d'injection ;
• la figure 4 représente les déplacements de l'extrémité de la tige par rapport à la buse au cours du temps ;
• la figure 5 est une vue en coupe axiale représentant l'implantation sur une culasse de l'injecteur représenté à la figure 1 ainsi que les éléments de commandes électriques des céramiques piézo-électriques ;

The aims, aspects and advantages of the present invention will be better understood from the following description of an embodiment of the invention, presented by way of non-limiting example, with reference to the appended drawings. wherein:

• FIG. 1 represents an overall view, in axial section, of the injection device according to the invention;
• Figures 2 and 3 show, in top view, the flow limiting portion and the guide portion of the rod located in the nozzle of the injection device;
• Figure 4 shows the movements of the end of the rod relative to the nozzle over time;
• Figure 5 is an axial sectional view showing the implantation on a cylinder head of the injector shown in Figure 1 and the electrical control elements of piezoelectric ceramics;

In accordance with the accompanying 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 Figure 1, the body of the injector object of the present invention was detailed. The body of the injector essentially comprises three distinct members cooperating with each other.

The first member is composed of the injection box 15, which has an internal cavity 10 intended to be filled with pressurized fuel via an axial drilling 16 of fuel supply coming to connect to a supply circuit of fluid under pressure. The cavity 10 opens at the lower end 6 of the nozzle 3 via an injection orifice 5.The housing 15 has inside a stepped portion 11 on which is disposed a support element 9 made of a damping material, which support member receives the rear portion 18 of a transducer 1.

The second member consists of means capable of generating vibrations in a longitudinal mode at ultrasonic frequencies such as a transducer 1, which transducer has a stepped portion 12 serving as a mechanical amplifier and ends in the upper part by a tube of cylindrical shape 2 in which are transmitted the vibrations from the transducer 1, the end of the tube 2 has an elastic securing zone 8 with a rod 4 described below so that the longitudinal vibrations are transmitted in the rod 4 from its end located in zone 8.

The third member is constituted by a rod 4 housed axially movable inside the nozzle 3 and whose frustoconical lower end 7 extends outside the nozzle 3. This end 7 forming a valve is adapted for contacting 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 to close the fuel injection port.

The other end of the rod 4 is elastically connected to the transducer 1 in the zone 8 located at the end of the tube 2, the elastic connection being ensured in the mass of the material by a weld or a mechanical connection with a higher prestressing than the stresses generated in this area during the operation of the transducer.

The transducer 1 is placed coaxially with the nozzle 3 via guides 25 in the cavity 10 of the injection box on the support piece 9 formed of a material both damping and elastic. The part 9 terminates in the zone of contact with the stepped portion 11 of the injection box 15 by a washer 14 having very low friction characteristics so that the transducer 1 can be almost free to rotate with respect to the nozzle. injection 3.

The rod 4, passing through the transducer 1 to its end in the zone 8, is inserted through the guide 27 ensuring the coaxiality of the shutter means 7 forming a valve with the seat 6 of said valve 7. When the valve 7 comes into contact with the seat 6, a preload of a fixed value is exerted between the transducer 1 and the injection housing 15, which prestressing results in a contraction of the material 9 and an additional translation of the rod 4 relative to the transducer 1. The rod 4 is then mechanically held in this position and secured to the end of the tube 2 over a length corresponding to the zone 8. In this zone 8, the tube 2 then consists of a solid part made of the material of the rod 4 surrounded by of the material of the emitter part 19 of the transducer, this emitting part preferably being chosen in the same material as the rod 4. The part 9 exerts an elastic restoring force t in order to remove the transducer 1 from the nozzle 3, which causes the end 7 of the rod 4, integral with the transducer 1, to be applied against the seat 6.

The mass of the transducer 1 associated with the damping piece 9 constitutes a dissipative system having a very large response time with respect to the excitation times of the transducer 1, so that the deformations of the rod and the shocks occurring at the of the seat 6 do not induce movement of the body of the transducer 1, only the end of the cylinder 2 oscillates on either side of the initial equilibrium position, which oscillations are transmitted in the rod 4.

The transducer 1 is sized to transmit a maximum of stresses at the level of the stepped junction 12 with the tube or cylinder 2, this maximum of stresses corresponding to a minimum amplitude of vibration for the material.

The transducer 1 comprises a zone 17 consisting of piezoelectric or magnetostrictive active 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 provided by prestressing means such as a threaded shaft 20 or a screw. The stack of several active components 17 makes it possible to add the thickness deformations generated by each of the rings, the resulting deformation of the total displacement of the stack of rings remaining below the limit of elastic deformation of the prestressing means 20. The reduction of the diameter of the part 19 to the part 2 amplifies the longitudinal deformations generated in the part 19 into the zone 8 where the transmission takes place in the rod 4.

As indicated in FIG. 5, the motor control computer 33 sends two pulses corresponding to the beginning and at the end of the injection, during this time an ultrasonic frequency generator 32 sends a wave train (level 5V) at a given frequency in accordance with FIG. input of an amplifier 34, which makes it possible to attack the piezoelectric ceramics 17 in alternating voltage (of the order of + -60V) at the same ultrasonic frequency during the injection duration.

Under the application of an electrical voltage on the electrodes of piezoelectric ceramics, they deform and generate an elastic stress which is transmitted to the end of the tube 2 and this deformation propagates in the rod 4 until at the end 7 where the shutter means are located.

The assembly composed of the transducer 1 and the rod 4 is sized to resonate with the excitation frequency of the active components 17 and to amplify the longitudinal displacements up to the level of the lower end of the rod 4.

The rod 4, initially closing the opening 21 at its end 7 forming a valve, deforms under the impulse supplied to it when the end of the tube 2 starts to oscillate. This deformation is distributed elastically over the entire length of the rod 4 and is reflected at the end of the rod 4 where the ejection takes place. The proper response of the rod 4 makes it possible to oscillate the end 7 and thus to make the opening 21 appear cyclically.

Figure 4 describes the position variation of the end 7 of the rod 4 (points Ai) with respect to the end 6 of the nozzle 3 (points Bi) for an oscillation cycle of the resonator assembly.

The opening of the annular slot 21 is oscillating and equal to the vibration amplitude of the valve 7 relative to the end 6 as shown in Figure 4. The frequency of opening of the slot depends on the frequency of excitation chosen for the transducer 1.

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 be 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 to more conventional injection devices where the minimum time to operate the opening and closing of the injection nose is rather 300 μs. [0054]

Referring to Figure 5, 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 of the engine is electronically controlled multipoint type by which each combustion chamber 35 is supplied directly with fuel by at least one fuel injector opening into the chamber.

The body of the injector is fixed to the cylinder head 24 of the engine at its upper end by means not shown, this upper end being also connected to a fuel supply line 16 also not shown.

The seal at the well 31 of the injector is provided by an O-ring 29 maintained in application between the junction 11 and the edge 30 of the injection well 31.

According to a particular embodiment of the injector which is the subject of the present invention, the transducer 1 comprises a cylinder 18 of steel 20 mm in diameter and 25 mm in height having in its upper part a threaded shaft 20.

The threaded shaft 20 of the cylinder 18 makes it possible to preload piezoelectric ceramic rings 17 (external diameter 20 mm, internal diameter 6 mm, thickness 2 mm) between the cylinders 18 and the emitting part 19. The ceramics are arranged with parallel polarizations, electrodes 13 being interposed between each pair of ceramic.

A titanium rod 4 having 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 transducer 1. An elastic and damping washer 9 has an orifice allowing the rod 4 to pass and bears on the surface lower 11 of the cavity 10.

The rod 4 is secured to the transducer 1 in the zone 8 after having constrained the washer 9 to a certain prestressing value, the transducer 1 remaining resting on the washer 9. This residual preload makes it possible to apply the conical end 7 of the rod 4 on the zone 6 of the nozzle 3, the contact force then being maintained by the elasticity of the assembly of rod 4 and washer 9. The preload applied allows on the one hand the sealing of the opening 21 of the nozzle 3 when the fluid 16 is supplied with a given pressure and secondly the catch of possible wear in the contact zone of the valve 7 with the nozzle 3.

The elasticity of the material of which the washer 9 is formed is chosen so that it makes it possible to compensate for variations in length between the rod 4 and the nozzle 3 due to thermal expansion without any effective modification of the value of the prestressing ensuring the seal.

The mass of the transducer and the rigidity of the washer 9 are chosen to form a system having a very large response time with respect to the excitation times of the transducer of the order of 1 to 20 milliseconds maximum. The material of which the cup is made may be based on polymers having a very high rate of attenuation of dynamic elastic deformations.

When a variable voltage of the order of 60 volts is applied to the terminals of the ceramics via the common electrodes 13, the ceramics deform in thickness and the deformations are transmitted throughout the structure.

The amplitude of oscillation for a voltage of 60 volts applied to each electrode is close to 20 microns, leaving an opening 5 generating a fluid film whose thickness is of the same order (20 microns). This fluid film is fragmented by the closure of the opening 21 which occurs after a very short time (every 20μs).

The device thus makes it possible to generate, as needed, very fine droplets. The modulation of the amplitude of the opening 21 makes it possible to modulate the size of the drops and thus the flow rate with response times of the order of 20 microseconds.

When controlling the displacement of the valve 7 beyond a threshold value, the flow section through the opening 21 is greater than that of the flow restrictor 26 and the flow rate of the injector is then a function of the pressure and The injected quantities are precisely controlled by the number of opening cycles and the size of the drops by the value of the displacement.

When the displacement of the valve 7 is controlled below the threshold value mentioned above, the flow section through the opening 21 is smaller than that of the flow restrictor 26 and the instantaneous flow rate of the injector is then a function at each oscillation of the pressure and the passage section generated by the opening 21. In this case, the injected quantities are controlled by the displacement amplitude and by the number of oscillation controlled, the minimum quantity injected can be further reduced and the increased nebulization rate of the liquid.

Claims (8)

1. Fuel injection device for an internal combustion engine, of the type which comprises a fuel-fed injection housing (15) terminated by a cylindrical nozzle (3) at the end of which is formed an injection orifice (5), a cyclic vibration-inducing transducer (1) arranged inside the housing and controlled in duration and intensity by the electronic control system of the engine, and shut-off means (7) arranged at the end (6) of the nozzle (3) which are returned by elastic return means against the said end (6), the elastic return means being composed, on the one hand, of a rod (4) to which are fixed the said shut-off means (7) and which passes through the body of the injection device as far as a region (8) where the said rod is fixed to the transducer (1) and secures the shut-off means to the transducer, and, on the other hand, of damping means (9) for damping the fixed assembly formed by the transducer (1), the rod (4) and the shut-off means (7), so that the shut-off means are returned against the end (6) of the nozzle, characterized in that the vibration inducted in the transducer generates an alternate contraction and expansion deformation in the rod (4) such that for each vibration cycle the expansion experienced by the rod is manifested by an elongation of the said rod, generating a displacement of the shut-off means (7), which are fixed elastically to the said rod, with respect to the end of the nozzle (6), which displacement makes it possible, throughout the duration of the cycle, to expose an opening (21) through which a defined quantity of fuel is ejected.
2. Fuel injection device according to Claim 1, characterized in that the valve-forming shut-off means (7) are returned against the end of the nozzle (6) after each opening by the contraction of the rod (4) which follows the expansion of the said rod during each vibration cycle.
3. Fuel injection device according to Claims 1 and 2, characterized in that the valve-forming shut-off means (7) remain pressed against the end of the nozzle (6) outside the deformation phases of the rod (4) by virtue of the damping elastic return means (9) returning the assembly consisting of the transducer (1), the rod (4) and the shut-off means (7) against the end of the nozzle (6) forming a seat for the valve.
4. Fuel injection device according to Claim 1, characterized in that the shut-off means (7) formed by the valve-forming flared end of the rod (4) are fixed elastically to the said rod (4), which rod (4) is mounted so that it can move axially inside the transducer (1) and is itself fixed elastically to this same transducer (1) in a region (8) situated in the upper part (2) of the transducer (1).
5. Fuel injection device according to Claim 1, characterized in that the damping elastic return means (9) serving to apply the shut-off means (7) against the end of the nozzle (6) and supporting the assembly consisting of the transducer (1) and the rod (4) are composed of a material which enables the transmission of vibrations between the transducer (1) and the body of the injection housing (15) to be damped.
6. Fuel injection device according to Claim 1, characterized in that the mass of the transducer (1) associated with the damping element (9) constitutes a dissipative system having a very high response time with respect to the excitation durations of the transducer (1), with the result that the deformations of the rod and the impacts occurring at the seat (6) do not cause the body of the transducer (1) to start moving, with only the end of the upper part (2) of the transducer oscillating on either side of the initial position of equilibrium, these oscillations being transmitted into the rod (4).
7. Fuel injection device according to Claim 1, characterized in that the damping elastic return means (9) serving to apply the shut-off means (7) against the end of the nozzle (6) make it possible to compensate for any play due to the thermal expansions between the transducer (1), the rod (4) and the nozzle (3) without effectively modifying the prestress ensuring the sealing function.
8. Fuel injection device according to Claim 1, characterized in that the fuel quantities delivered by the injector can be controlled in two ways which consist in controlling a displacement of the valve (7)

   a) above a threshold value, in which case the discharging cross section through the opening (21) is greater than that of a flow limiter (26) and the injector delivery rate is then dependent on the pressure and on the passage cross section of the flow limiter (26), so that the injected quantities are precisely controlled by the number of opening cycles of the valve (7),

   b) below the aforementioned threshold value, the discharging cross section through the opening (21) being smaller than that of the flow limiter (26) and the instantaneous injector delivery rate this being dependent for each oscillation on the pressure and on the passage cross section generated by the opening (21), so that the injected quantities are controlled in this case by the displacement amplitude and by the number of controlled oscillations, thereby making it possible to further reduce the minimum injected quantity and to increase the degree of liquid atomization.

Images