EP0995031B1 - Device for injecting fuel into a diesel engine - Google Patents

Abstract

The invention concerns a device for injecting fuel into a diesel engine using a pulsating flow pump for improving the fuel performance of the engines by controlling the beginning and the end of the injection. It comprises a device (20) controlling the closing and opening of the nozzle needle (5) provided with a discharge circuit (21, 21') controlled by an electrovalve (25) in branched connection between the high pressure supply conduit (7) and the low pressure return conduit (8). The discharge circuit (21, 21') comprises a discharge valve (22) whereof the opening and the closing are slowed down by a calibrated orifice (23). The discharge valve (22) located upstream of a discharge orifice (27) provided on the return conduit (8) enables to deviate part of the non-injected fuel flow towards the nozzle needle (5) to exert thereon a closing pressure. Consequently, this results in a better control over the opening and closing of the nozzle needle (5). A calibrated valve (24) ensures that the pressure in the discharge circuit (21) is maintained between two injections. During the injection cycle, the supply of fuel towards the nozzle needle (5) is not impeded by the control device (20) components. The invention is applicable to diesel engines using pulsating injection pumps.

Description

The present invention relates to a fuel injection device for engines Diesel equipped with pulsed-flow injection pumps, this device comprising, by piston, at least one injector receiving a calibrated injector needle arranged for injecting jets of fuel calibrated in the combustion chamber of said piston, a pipe high pressure fuel supply and a low pressure return line from the combustible.

1. le début d'introduction de combustible est effectué à faible débit pour ne pas mélanger trop de combustible à l'air de la chambre de combustion pendant le délai d'allumage,

2. le débit injecté est constamment croissant pour que la combustion accompagne bien le début d'expansion associé au déplacement du piston dans le cylindre du moteur,

3. la pression de combustible est importante pour obtenir une bonne pulvérisation et par conséquent une bonne performance de mélange du combustible à l'air,

4. la fin d'injection est franche pour limiter l'introduction de combustible insuffisamment pulvérisé et réduire au mieux les queues de combustion.

The diesel engine development specifications are constantly evolving. This technical constraint is mainly linked to the fields of the environment and the economy such as pollutant emissions (nitrogen oxides, hydrocarbons, particles, etc.), the noise emitted by the engine or fuel consumption. The needs for optimizing combustion systems to take account of these changes in specifications require a particular effort on the injection process. The ideal injection that would allow for depolluted combustion would be achieved if:

1. the start of fuel introduction is carried out at low flow rate so as not to mix too much fuel with the air in the combustion chamber during the ignition delay,

2. the injected flow is constantly increasing so that combustion accompanies the start of expansion associated with the displacement of the piston in the engine cylinder,

3. the fuel pressure is important in order to obtain good spraying and therefore good performance in mixing the fuel with the air,

4. the end of injection is straightforward to limit the introduction of insufficiently pulverized fuel and to reduce combustion tails as much as possible.

• l'augmentation du rapport volumétrique de compression,
• la réduction de l'avance à l'injection,
• l'accroissement des pressions d'injection.

Ces stratégies visent à comprimer la période principale de combustion sur un intervalle de temps plus court et mieux localisé dans le début de la détente. Malgré tout, la performance de combustion reste très sensible aux détails de forme de la loi d'introduction du combustible dans la chambre de combustion.In practice, the classic strategies usually used are for example:

• increasing the compression compression ratio,
• reduction of the injection advance,
• increased injection pressures.

These strategies aim to compress the main combustion period over a shorter and better localized time interval in the beginning of the trigger. Despite everything, the combustion performance remains very sensitive to the details of the shape of the law of introduction of the fuel into the combustion chamber.

In traditional injection devices using a pulsed-flow pump, the injection pump, by discharging the fuel, gradually increases the pressure in the volumes of the pump, the pipes and the injector. This progressivity takes place before and then during the injection period. After the pump discharge stops, the injection ends with the effect of depressurization of these same volumes, the injector needle being controlled only by a simple return device comprising one or more springs.
The advantage of these injection devices relates to the start of injection which is, in this case, relatively moderate and, therefore, favorable to the points 1 and 2 mentioned above, unless a injector opening pressure too high.
On the other hand, the major drawback is that the injector does not close until the pressure has become significantly lower than the opening pressure. As a result, the end of the injection is not efficient and generates combustion tails, inducing soot emissions and penalizing the yield.

In “common-rail” constant pressure injection devices, the high pressure pump supplies all of the injectors at an almost constant and adjustable pressure to adjust the rate of introduction and atomization of the fuel. The opening and closing of each injector are controlled by a solenoid valve which makes it possible to adjust the injection advance and the quantity injected, in accordance with certain exemplary embodiments described in the publications FR-A-2 016 477, US- A-4,545,352, DE-C-42 36,882, DE-A-44 06,901 and US-A-4,249,497.
The advantage of these injection devices is the flexibility of the potential settings and above all the very good end of injection by a controlled closure, which is favorable to points 3 and 4 above.
However, the major drawback lies in the fact that at the start of the injection, the injected flow rate is very quickly at the maximum flow rate, which is detrimental to points 1 and 2 above. It is possible to neutralize the effect on the ignition deflagration (point 1) by the use of pre-injection, but there is little possibility of making the law of introduction of fuel progressive (point 2).

• un début d'injection plus modéré qu'avec les dispositifs traditionnels, favorable au point 1 ci-dessus mentionné, avec possibilité de réaliser une pré-injection,
• une pression d'injection croissante pendant toute la période d'injection, favorable au point 2 ci-dessus,
• une fin d'injection aussi nette qu'avec les dispositifs à pression constante, favorable au point 4 ci-dessus,
• une avance à l'injection réglable.

The aim of the present invention is to provide an effective solution for improving the performance of traditional injection devices using a pulsed flow pump in order to effectively satisfy the increasingly severe requirements and in particular by achieving:

• a more moderate start of injection than with traditional devices, favorable to point 1 above mentioned, with the possibility of performing a pre-injection,
• an increasing injection pressure during the entire injection period, favorable to point 2 above,
• an end of injection as clear as with constant pressure devices, favorable to point 4 above,
• an adjustable injection advance.

This object is achieved by an injection device as defined in the preamble and characterized in that it comprises a device for controlling the opening and closing of the injector needle, this device comprising a first circuit of discharge connecting the supply line and the return fuel line provided with a calibrated orifice and controlled by a solenoid valve and a second discharge circuit parallel to the first and comprising a calibrated discharge valve and a discharge orifice disposed on the return line , this second discharge circuit being in communication with the injector needle upstream of the discharge orifice, said discharge valve being arranged to ensure both the progressiveness of the start of injection and the speed of closure of this injection by deflecting the flow of uninjected fuel towards said discharge orifice which, by depressurizing the supply line, generates a pr ession of closure on the injector needle.
In one embodiment of the invention, the first discharge circuit may comprise a calibrated valve arranged upstream or downstream of the solenoid valve, this valve being arranged to maintain the injection device at a required level of pressure between two injections.

In general, the control device is independent of the injection circuit high fuel pressure during the injection cycle, the discharge valve and the solenoid valve being closed.

Depending on the case, the closing pressure can be applied directly to the needle injector or via a piston.

In an alternative embodiment, the control device may include a delay arranged downstream of the calibrated orifice and arranged to delay the opening of the valve of discharge so as to cause the momentary opening of the injector needle for pre-inject fuel.

According to the embodiments selected, the calibrated orifice can be integrated into the valve. dump. Likewise, the orifices, valve, flap and solenoid valve of the control device can be partially or totally integrated into the assembly carrying the injector.

In a fuel injection device comprising several injectors for one same diesel engine, the return fuel lines of each injector can advantageously be linked together to a common return gallery. This gallery common return valve may be subject to a calibrated return valve arranged to maintain a pressure level required in said return pipes of each injector.

Similarly, the first discharge circuits can be linked together by a gallery common control valve, which may also be subject to a calibrated control valve arranged to maintain a required level of pressure in said discharge circuits each injector.

In some embodiments, the common return gallery and the gallery of common control can be connected to each other by a calibrated control valve.

• la figure 1 est un schéma fonctionnel de la configuration de base du dispositif d'injection selon l'invention,
• les figures 2 à 7 représentent un exemple de réalisation du dispositif selon l'invention, dans lesquelles :
  • la figure 2 est une vue en coupe axiale selon l'axe II-II de la figure 4,
  • la figure 3 est une vue en coupe axiale selon l'axe III-III de la figure 4,
  • la figure 4 est une vue en coupe radiale selon l'axe IV-IV de la figure 3,
  • la figure 5 est une vue de détail en coupe selon l'axe V-V de la figure 4,
  • la figure 6 est une vue de détail en coupe de la vanne de décharge, et
  • la figure 7 est une vue de détail en coupe du clapet taré,
• la figure 8 est un schéma fonctionnel d'une première variante de configuration du dispositif d'injection de la figure 1,
• la figure 9 est un schéma fonctionnel d'une seconde variante de configuration du dispositif d'injection de la figure 1,
• la figure 10 est un schéma fonctionnel d'un perfectionnement apporté à la configuration du dispositif d'injection de la figure 1, permettant d'effectuer une pré-injection,
• la figure 11 est un schéma fonctionnel d'un autre perfectionnement apporté à la configuration du dispositif d'injection de la figure 1, permettant de régler simultanément plusieurs dispositifs d'injection d'un même moteur,
• les figures 12 à 15 sont des schémas fonctionnels de différentes variantes de configuration du dispositif de la figure 11,
• les figures 16 à 19 représentent un exemple de réalisation du dispositif d'injection illustré schématiquement dans la figure 14 et simplifié par l'absence du piston qui agit sur l'aiguille d'injecteur, dans lesquelles :
  • la figure 16 est une vue en coupe axiale selon l'axe XVI-XVI de la figure 18,
  • la figure 17 est une vue en coupe axiale selon l'axe XVII-XVII de la figure 18,
  • la figure 18 est une vue en coupe radiale selon l'axe XVIII-XVIII de la figure 17,
  • la figure 19 est une vue de détail en coupe de la vanne de décharge et de l'orifice de retard,
• les figures 20 et 21 représentent partiellement un second exemple de réalisation du dispositif d'injection illustré schématiquement dans la figure 14, dans lesquelles :
  • la figure 20 est une vue en coupe axiale similaire à la figure 16,
  • la figure 21 est une vue en coupe axiale similaire à la figure 17,
• et les figures 22 à 25 représentent des diagrammes d'injection correspondant à différentes configurations du dispositif d'injection, dans lesquelles :
  • la figure 22 correspond à un dispositif d'injection traditionnel,
  • la figure 23 correspond au dispositif d'injection de la figure 1,
  • la figure 24 correspond au dispositif d'injection de la figure 8,
  • la figure 25 correspond au dispositif d'injection de la figure 10.

The present invention and its advantages will appear better in the following description of different embodiments, illustrated by way of nonlimiting example, with reference to the appended drawings, in which:

• FIG. 1 is a functional diagram of the basic configuration of the injection device according to the invention,
• FIGS. 2 to 7 represent an exemplary embodiment of the device according to the invention, in which:
  • FIG. 2 is a view in axial section along the axis II-II of FIG. 4,
  • FIG. 3 is a view in axial section along the axis III-III of FIG. 4,
  • FIG. 4 is a view in radial section along the axis IV-IV of FIG. 3,
  • FIG. 5 is a detail view in section along the axis VV of FIG. 4,
  • FIG. 6 is a detailed view in section of the relief valve, and
  • FIG. 7 is a detailed view in section of the calibrated valve,
• FIG. 8 is a functional diagram of a first variant configuration of the injection device of FIG. 1,
• FIG. 9 is a functional diagram of a second variant configuration of the injection device of FIG. 1,
• FIG. 10 is a functional diagram of an improvement made to the configuration of the injection device of FIG. 1, making it possible to perform a pre-injection,
• FIG. 11 is a functional diagram of another improvement made to the configuration of the injection device of FIG. 1, making it possible to simultaneously adjust several injection devices of the same engine,
• FIGS. 12 to 15 are functional diagrams of different variant configurations of the device of FIG. 11,
• FIGS. 16 to 19 represent an exemplary embodiment of the injection device illustrated diagrammatically in FIG. 14 and simplified by the absence of the piston which acts on the injector needle, in which:
  • FIG. 16 is a view in axial section along the axis XVI-XVI of FIG. 18,
  • FIG. 17 is a view in axial section along the axis XVII-XVII of FIG. 18,
  • FIG. 18 is a view in radial section along the axis XVIII-XVIII of FIG. 17,
  • FIG. 19 is a detailed view in section of the discharge valve and the delay orifice,
• FIGS. 20 and 21 partially represent a second embodiment of the injection device illustrated diagrammatically in FIG. 14, in which:
  • FIG. 20 is a view in axial section similar to FIG. 16,
  • FIG. 21 is a view in axial section similar to FIG. 17,
• and FIGS. 22 to 25 represent injection diagrams corresponding to different configurations of the injection device, in which:
  • FIG. 22 corresponds to a traditional injection device,
  • FIG. 23 corresponds to the injection device of FIG. 1,
  • FIG. 24 corresponds to the injection device of FIG. 8,
  • FIG. 25 corresponds to the injection device of FIG. 10.

Referring to Figure 1, the injection device 1 for diesel engines comprises, in known manner, a low pressure line 2 which supplies fuel to a pump 3 with pulsed flow. This pump 3 feeds an injector 4 provided with a needle injector 5 by a non-return valve 6 and a high pressure pipe 7. The injector 4 is also connected to a low pressure return line 8. A control valve 9 of the discharge from pump 2 can be mounted as a bypass on the non-return valve 6. The injector needle 5 is subjected to the action of one or more calibration springs 10 and controls the high pressure fuel jets 11 that enter the combustion chamber (not shown) of a piston of a diesel engine (not represented). The cavity containing the calibration spring or springs 10, not connected to the upper pressure, is in communication with said low pressure return pipe 8.

The injection device 1, in accordance with the present invention, comprises, on the side of the injector 4, a control device 20 acting directly on the injector needle 5 to improve steering both at opening and closing. This device control 20 includes a first discharge circuit 21 bypass between the fuel supply 7 and return 8 pipes. It has an opening calibrated 23, a calibrated valve 24 and a solenoid valve 25 controlled by a solenoid 26. The control device 20 also includes a second parallel discharge circuit 21 ′ on the first and comprising a calibrated discharge valve 22 and a discharge orifice calibrated 27 provided on the return pipe 8. This second discharge circuit 21 'is in communication with the injector needle 5 upstream of the discharge orifice 27. Each Diesel engine injector 4 will receive the same control device 20.

• une pièce A, qui constitue l'injecteur 4 proprement dit, dans laquelle sont ménagés le logement de guidage 14 pour l'aiguille d'injecteur 5, l'arrivée de la canalisation d'alimentation 7 haute pression de combustible dans une chambre annulaire 15, suivie d'une chambre tubulaire 15a, les deux chambres étant disposées autour de l'aiguille, un siège conique 12a recevant la pointe 5a de l'aiguille, et les buses d'injection 12,
• une pièce B, qui sert de butée à l'aiguille d'injecteur 5, dans laquelle sont ménagées la base de la cavité 13 recevant la tête 5b de l'aiguille et la suite de la canalisation d'alimentation 7 haute pression,
• une pièce C, qui constitue le corps du porte-injecteur, dans laquelle sont ménagés le reste de la cavité 13 recevant le ressort de tarage 10, le reste de la canalisation d'alimentation 7 haute pression, le début du circuit de décharge 21 et une partie du second circuit de décharge 21' en communication avec ladite cavité 13,
• une pièce D, qui constitue le bloc principal du dispositif de contrôle 20, dans laquelle sont ménagés la suite du circuit 21', la canalisation retour 8 du combustible, la vanne de décharge 22 et son orifice calibré 23, le clapet taré 24 et l'orifice de décharge 27,
• une pièce E, qui constitue l'ensemble électrovanne, dans laquelle est ménagée l'électrovanne 25 avec son solénoïde de commande 26.

Referring to Figures 2 to 7, the injection device 1 is illustrated according to a preferred embodiment of the invention in which the control device 20 is fully integrated in an injector assembly 40 containing the injector 4. This injector 4 of standard shape carries the injector needle 5 whose tip 5a closes fuel injection nozzles 12 when the needle is in the low position. This injector needle 5 is conventionally controlled by a calibration spring 10 which exerts pressure on its head 5b, the spring and the head being housed in a cavity 13 coaxial with a guide housing 14 receiving said needle. The injector assembly is composed of several parts assembled one on the other to facilitate the integration of the control device 20. More particularly, from bottom to top, this injector assembly 40 comprises:

• a part A, which constitutes the injector 4 proper, in which are formed the guide housing 14 for the injector needle 5, the arrival of the high pressure fuel supply line 7 in an annular chamber 15 , followed by a tubular chamber 15a, the two chambers being arranged around the needle, a conical seat 12a receiving the point 5a of the needle, and the injection nozzles 12,
• a part B, which serves as a stop for the injector needle 5, in which the base of the cavity 13 receiving the head 5b of the needle and the continuation of the high pressure supply pipe 7 are formed,
• a part C, which constitutes the body of the injector holder, in which are formed the rest of the cavity 13 receiving the calibration spring 10, the rest of the high pressure supply line 7, the start of the discharge circuit 21 and part of the second discharge circuit 21 ′ in communication with said cavity 13,
• a part D, which constitutes the main block of the control device 20, in which the continuation of the circuit 21 ′ is provided, the return line 8 of the fuel, the discharge valve 22 and its calibrated orifice 23, the calibrated valve 24 and l discharge port 27,
• a part E, which constitutes the solenoid valve assembly, in which the solenoid valve 25 is provided with its control solenoid 26.

In this embodiment, the calibrated orifice 23, also called nozzle, is integrated in the valve discharge 22 (Figure 6), this valve comprising a calibrated return spring 22 '. The valve calibrated 24 comprises a calibrated return spring 24 'and radial orifices 28 (FIG. 7). The solenoid valve 25 includes a return spring 25 '. The discharge port 27, called also nozzle, connects the second discharge circuit 21 'to the low return line 8 pressure between parts C and D. The first discharge circuit 21 is bypassed with the high pressure supply line 7, passes through the calibrated orifice 23, the calibrated valve 24 and the solenoid valve 25 to the low pressure return line 8. This first circuit discharge 21 is divided into a second parallel discharge circuit 21 'crossing the discharge valve 22 and discharge port 27 to the return line 8. The cavity 13 of the calibration spring 10 is in communication with this second discharge circuit parallel 21 'upstream of the discharge orifice 27.

• Au repos, l'électrovanne 25 est ouverte. Toutes les autres vannes ou clapets 22, 24 sont fermés sous l'effet des ressorts 22', 24'. Aucun débit ne traverse le dispositif d'injection 1. La pression résiduelle dans ce circuit est maintenue à un niveau requis par le clapet taré 24.
• Au début du refoulement et après la fermeture des orifices de remplissage de la pompe 3, celle-ci délivre son débit au travers du clapet anti-retour 6. La pression croit dans la canalisation d'alimentation 7 ainsi que devant la vanne de décharge 22, dans son orifice calibré 23 et devant le clapet taré 24. Lorsque le débit qui traverse l'orifice calibré 23 et le clapet taré 24 est suffisant, la vanne de décharge 22 s'ouvre et laisse passer le débit dans le second circuit de décharge parallèle 21' vers la canalisation retour 8. Une partie de ce débit est déviée vers la cavité 13 du ressort de tarage 10 qui est en amont de l'orifice de décharge 27. Ce débit crée dans la cavité 13 une pression, appelée pression de fermeture, qui assure, par sa poussée sur l'aiguille d'injecteur 5, le maintien en position fermée de l'injecteur 4.
• Le début de l'injection est piloté par le signal électrique sur le solénoïde 26 qui ferme l'électrovanne 25. Le débit au travers du clapet taré 24 s'interrompt. Le débit au travers de l'orifice calibré 23 de la vanne de décharge 22 combiné à l'effort fourni par le ressort 22' ferme progressivement la vanne de décharge 22. La pression de combustible appliquée à l'aiguille d'injecteur 5 dans la chambre 15 et appelée pression d'ouverture croit, tandis que la pression de fermeture appliquée du coté du ressort de tarage 10 décroít, jusqu'à ce que l'aiguille d'injecteur 5 s'ouvre. L'injection débute dès cette ouverture. La modulation du début de l'injection dépend principalement de la vitesse de fermeture de la vanne de décharge 22.
• Lorsque l'injection est établie, les vannes ou clapets 22, 24, 25 sont fermés. La totalité du débit fourni par la pompe d'injection 3 est acheminée vers l'aiguille d'injecteur 5 sans aucune restriction et génère des jets d'injection 11 avec toute la pression dont est capable le dispositif d'injection 1.
• La fin de l'injection est déclenchée quand le signal électrique sur le solénoïde 26 est interrompu. L'électrovanne 25 s'ouvre sous l'effet de son ressort 25'. La pression de fermeture sur la vanne de décharge 22 est brusquement réduite. Cette vanne s'ouvre alors rapidement. La pression dans le circuit d'injection décroít légèrement du fait du faible débit de décharge acheminé vers l'orifice de décharge 27. En parallèle, la montée en pression du côté du ressort de tarage 10 sur l'aiguille d'injecteur 5 assure sa fermeture. L'aiguille d'injecteur 5 se fermant, l'injection s'interrompt brusquement, avant que la chute de pression dans la canalisation d'alimentation 7 haute pression ne soit significative. Le débit, encore fourni par la pompe d'injection 3 traverse la vanne de décharge 22 et les orifices 23 et 27 pour s'évacuer dans la canalisation retour 8. Les pressions de fermeture et d'ouverture, de part et d'autre de l'aiguille d'injecteur 5 étant voisines, l'aiguille reste fermée sous l'action de son ressort 10. La pression décroít progressivement par l'effet de la décharge au travers de l'orifice de décharge 27 et de la canalisation retour 8.
• Lors de l'arrêt du refoulement de la pompe d'injection 3, provoqué par l'ouverture de ses orifices de décharge, la pression décroít fortement dans l'ensemble du dispositif d'injection 1. Dès que le débit traversant l'orifice calibré 23 est suffisamment faible, la vanne de décharge 22 se ferme sous l'effet de son ressort 22'. La pression de fermeture assurant le maintien en position fermée de l'aiguille d'injecteur 5 s'élimine progressivement. La pression résiduelle dans l'ensemble du circuit haute pression est alors contrôlée par le clapet taré 24 combiné éventuellement à l'action du clapet de contrôle 9 de la pompe d'injection 3.

The operation of the injection device 1 according to the invention is described as follows.

• At rest, the solenoid valve 25 is open. All the other valves 22, 24 are closed under the effect of the springs 22 ', 24'. No flow passes through the injection device 1. The residual pressure in this circuit is maintained at a level required by the calibrated valve 24.
• At the start of the discharge and after the filling ports of the pump 3 have been closed, the latter delivers its flow through the non-return valve 6. The pressure increases in the supply line 7 as well as in front of the discharge valve 22 , in its calibrated orifice 23 and in front of the calibrated valve 24. When the flow which passes through the calibrated orifice 23 and the calibrated valve 24 is sufficient, the discharge valve 22 opens and allows the flow to pass in the second discharge circuit parallel 21 'to the return pipe 8. Part of this flow is deflected towards the cavity 13 of the calibration spring 10 which is upstream of the discharge orifice 27. This flow creates in the cavity 13 a pressure, called pressure of closure, which ensures, by pushing on the injector needle 5, the maintenance of the injector 4 in the closed position.
• The start of the injection is controlled by the electrical signal on the solenoid 26 which closes the solenoid valve 25. The flow through the calibrated valve 24 is interrupted. The flow through the calibrated orifice 23 of the discharge valve 22 combined with the force provided by the spring 22 'gradually closes the discharge valve 22. The fuel pressure applied to the injector needle 5 in the chamber 15 and called opening pressure increases, while the closing pressure applied on the side of the calibration spring 10 decreases, until the injector needle 5 opens. The injection begins as soon as it opens. The modulation of the start of the injection depends mainly on the closing speed of the discharge valve 22.
• When the injection is established, the valves or flaps 22, 24, 25 are closed. The entire flow supplied by the injection pump 3 is routed to the injector needle 5 without any restriction and generates injection jets 11 with all the pressure which the injection device 1 is capable of.
• The end of the injection is triggered when the electrical signal on the solenoid 26 is interrupted. The solenoid valve 25 opens under the effect of its spring 25 '. The closing pressure on the discharge valve 22 is suddenly reduced. This valve then opens quickly. The pressure in the injection circuit decreases slightly due to the low discharge flow routed to the discharge port 27. In parallel, the increase in pressure on the side of the calibration spring 10 on the injector needle 5 ensures its closing. The injector needle 5 closing, the injection abruptly stops, before the pressure drop in the supply line 7 high pressure is significant. The flow rate, still supplied by the injection pump 3, passes through the discharge valve 22 and the orifices 23 and 27 to evacuate in the return pipe 8. The closing and opening pressures, on either side of the injector needle 5 being neighboring, the needle remains closed under the action of its spring 10. The pressure gradually decreases by the effect of the discharge through the discharge orifice 27 and the return line 8 .
• When stopping the delivery of the injection pump 3, caused by the opening of its discharge orifices, the pressure decreases sharply in the entire injection device 1. As soon as the flow through the calibrated orifice 23 is sufficiently weak, the discharge valve 22 closes under the effect of its spring 22 '. The closing pressure ensuring that the injector needle 5 is kept in the closed position is gradually eliminated. The residual pressure in the entire high pressure circuit is then controlled by the calibrated valve 24 possibly combined with the action of the control valve 9 of the injection pump 3.

Depending on the integration possibilities, the construction choices and the modes of operation of the injection device 1 according to the invention, it is possible to envisage different variants.

With reference to FIG. 8, it is possible to add a piston 30 which acts directly on injector needle 5. In this configuration, the hydraulic pressure generated by the flow released by the discharge valve 22 passing through the calibrated discharge orifice 27 acts indirectly on the injector needle 5 via a piston 30. The volume death is therefore more restricted. Therefore, the discharge closing the injector 4 requires a lower pressure drop at the supply line 7. The end of the injection is improved. The cross section of the piston 30 can be equal or greater than that of the housing 14 of the needle 5 in order to increase the thrust of closing.

As seen in the example illustrated with reference to Figures 2 to 7, it is possible to incorporate into the injector assembly 40 containing the injector 4, all or part of the components of the control device 20, namely the discharge valve 22, the calibrated valve 24, the solenoid valve 25 and the calibrated orifices 23, 27. It is still possible to combine the calibrated orifice 23 with the discharge valve 22 as illustrated or make them separately.

In addition, the calibrated valve 24 can be placed upstream, as in FIGS. 1 to 8, or in downstream of the solenoid valve 25 with reference to FIG. 9. This configuration has the effect of limit the volume closed between the calibrated orifice 23 and the seat of the solenoid valve 25. The the operating precision of the discharge valve 22 is improved and the possibility to better slow its closing by using a smaller calibrated orifice 23 becomes possible without risk of inadvertent opening due to pressure pulsations.

It should be noted that the variant embodiments illustrated in FIGS. 8 and 9 are cumulative.

Furthermore, it is possible to use an injection pump 3 having a control of the quantity injected by ramps on the pump piston, which allows either to limit the pumped quantity to optimize the energy required for pumping, i.e. to control injection in emergency mode. This backup mode is then obtained by leaving the solenoids, or by forcing mechanically, with a view to permanent closing the solenoids.

It is still possible to apply the control device 20 to an injection line shortened, possibly until the supply line 7 high is removed pressure, including an injector pump.

• de contrôler l'avance à l'injection, le début de l'injection dépendant quasi exclusivement du positionnement, dans le cycle, du début du signal électrique sur le solénoïde 26 de l'électrovanne 25,
• de doser la quantité injectée, qui est principalement dépendante de la durée du signal électrique sur le solénoide 26 de l'électrovanne 25, en tenant compte de la loi de refoulement de la pompe d'injection 3,
• d'assurer la sécurité de fonctionnement. Sans signal électrique, l'électrovanne 25 de commande reste ouverte et la vanne de décharge 22 laisse passer tout le débit de combustible vers le circuit de décharge 21 dans la canalisation retour 8. Dans le cas où les vannes 22, 25 resteraient bloquées en position fermée, la quantité maximale injectée est limitée à la quantité refoulée par la pompe d'injection. Cette quantité peut être ajustée par le mode secours de la pompe dans le cas où la pompe d'injection est traditionnelle.

The above description demonstrates that the invention achieves the objects mentioned. In particular, this injection device allows:

• controlling the injection advance, the start of the injection depending almost exclusively on the positioning, in the cycle, of the start of the electrical signal on the solenoid 26 of the solenoid valve 25,
• to dose the quantity injected, which is mainly dependent on the duration of the electrical signal on the solenoid 26 of the solenoid valve 25, taking into account the discharge law of the injection pump 3,
• ensure operational safety. Without an electrical signal, the control solenoid valve 25 remains open and the discharge valve 22 lets all of the fuel flow pass to the discharge circuit 21 in the return line 8. In the case where the valves 22, 25 remain blocked in position closed, the maximum quantity injected is limited to the quantity delivered by the injection pump. This quantity can be adjusted by the pump emergency mode in the case where the injection pump is traditional.

• l'ajustement de la pression résiduelle obtenu par le clapet taré 24, ce qui évite la cavitation dans le dispositif d'injection 1,
• la maítrise du gradient de débit en début d'injection, calibrée par le diamètre de l'orifice calibré 23 et la force du ressort 22' de la vanne de décharge 22,
• la pression d'ouverture de l'aiguille d'injecteur 5, maítrisée par le tarage du ressort 10 de ladite aiguille. La pression de fermeture ne dépend pas de la pression d'ouverture, ce qui évite de surdimensionner le ressort de tarage 10 de l'aiguille d'injecteur 5. La fermeture est provoquée par la pression générée par le débit acheminé dans les circuits de décharge 21, 21' vers la canalisation retour basse pression 8 au travers de l'orifice de décharge 27. A cet effet la somme des sections des orifices calibré 23 et de décharge 27 doit être supérieure à la somme des sections des buses d'injection 12 alimentant les jets de combustible 11.

This injection device 1 can be further optimized by:

• the adjustment of the residual pressure obtained by the calibrated valve 24, which avoids cavitation in the injection device 1,
• control of the flow gradient at the start of injection, calibrated by the diameter of the calibrated orifice 23 and the force of the spring 22 'of the discharge valve 22,
• the opening pressure of the injector needle 5, controlled by the setting of the spring 10 of said needle. The closing pressure does not depend on the opening pressure, which avoids oversizing the calibration spring 10 of the injector needle 5. The closing is caused by the pressure generated by the flow conveyed in the discharge circuits 21, 21 'to the low pressure return line 8 through the discharge orifice 27. For this purpose the sum of the sections of the calibrated orifices 23 and of discharge 27 must be greater than the sum of the sections of the injection nozzles 12 feeding the fuel jets 11.

It is still possible to improve this injection device 1, in particular by providing a control member for pre-injection. In that case, the opening of the discharge valve 22 is delayed to leave the injector needle 5 the possibility to start opening under the effect of a supply pressure of fuel higher than its calibration pressure. It is then quickly closed before the main injection. Referring to Figure 10, a delay port 31 is interposed between the calibrated orifice 23 and the return pipe 8, whether upstream, downstream or incorporated into the calibrated valve 24 or the controlled solenoid valve 25. This orifice delay 31 can therefore be added to any configuration of the injection device 1 previously described.

• la pression de la canalisation d'alimentation haute pression 7 monte sous l'effet de la pompe d'injection 3,
• une partie du débit refoulé s'échappe au travers des orifices calibré 23 et de retard 31, du clapet taré 24 et de l'électrovanne commandée 25,
• la pression nécessaire à l'ouverture de l'aiguille d'injecteur 5 est atteinte ce qui génère la pré-injection,
• lorsque la pression continue de croítre, le débit traversant l'orifice calibré 23 devient tel que la différence de pression provoque l'ouverture de la vanne de décharge 22,
• sous l'effet de la décharge dans le circuit 21' dont le débit est freiné par l'orifice de décharge 27, la poussée assurant la fermeture de l'aiguille d'injecteur 5 interrompt alors la pré-injection.

Ensuite, les séquences opératoires sont les mêmes que celles déjà décrites en référence aux figures 1 à 7.The operation of the pre-injection sequence is described as follows:

• the pressure of the high-pressure supply line 7 rises under the effect of the injection pump 3,
• part of the pumped flow escapes through calibrated orifices 23 and delay 31, the calibrated valve 24 and the controlled solenoid valve 25,
• the pressure required to open the injector needle 5 is reached, which generates the pre-injection,
• when the pressure continues to increase, the flow rate passing through the calibrated orifice 23 becomes such that the pressure difference causes the opening of the discharge valve 22,
• under the effect of the discharge in the circuit 21 ′, the flow of which is braked by the discharge orifice 27, the thrust ensuring the closure of the injector needle 5 then interrupts the pre-injection.

Then, the operating sequences are the same as those already described with reference to FIGS. 1 to 7.

• suppression éventuelle des clapets tarés 24 individuels,
• collecte dans une galerie de retour commune des débits de décharge de l'ensemble des injecteurs du moteur,
• collecte dans une galerie de contrôle commune des débits de contrôle et de commande de l'ensemble des injecteurs du moteur, cette galerie pouvant être confondue à la précédente,
• réglage de la pression dans la galerie de retour commune par un clapet de retour à tarage réglable ou à tarage fixe, ce réglage permettant de modifier la pression d'ouverture des injecteurs,
• réglage de la pression dans la galerie de contrôle commune par un clapet de contrôle à tarage réglable ou à tarage fixe, ce réglage permettant de modifier la dynamique d'ouverture des vannes de décharge 22. Dans le cas de la pré-injection, ce réglage agit particulièrement sur le dosage de la quantité pré-injectée. Le mode de réglage peut être soit indépendant, soit couplé suivant la méthode de raccordement.

Considering now all of the injectors fitted to the same diesel engine and taking into account that the calibration of the springs remains difficult to repeat identically in each control device 20, it can be expected that operation strictly at identical to said injectors is difficult to obtain. In order to better control the balancing of the operation of these injectors and possibly be able to perform joint adjustment of said injectors, the following arrangements can be considered:

• possible deletion of the 24 individual calibrated valves,
• collection in a common return gallery of discharge rates from all of the engine injectors,
• collection in a common control gallery of control and command flow rates for all of the engine injectors, this gallery can be confused with the previous one,
• adjustment of the pressure in the common return gallery by a return valve with adjustable setting or fixed setting, this setting making it possible to modify the opening pressure of the injectors,
• adjustment of the pressure in the common control gallery by a control valve with adjustable calibration or fixed calibration, this adjustment making it possible to modify the opening dynamics of the relief valves 22. In the case of pre-injection, this adjustment acts particularly on the dosage of the pre-injected quantity. The adjustment mode can be either independent or coupled according to the connection method.

Figures 11 to 15 illustrate five alternative embodiments making it possible to jointly control all the injectors of the same engine.
In FIG. 11, the low pressure return pipes 8 are connected together to a common return gallery 32 comprising a return valve 33 allowing the pressurization of the pipes 8 and therefore the adjustment of the opening pressure of the needles injector 5. In this case, the common and external adjustment of the back pressure applied to the control devices 20 is not provided.
The configuration of FIG. 12 is similar to that of FIG. 11 with the only difference that the calibrated valve 24 has been removed to avoid any difference in behavior of the individual calibrated valves 24.
In FIG. 13, the control devices 20 do not comprise a calibrated valve 24 and are connected together at the outlet of the controlled solenoid valves 25, to a common control gallery 34. This common control gallery 34 is connected to the gallery of common return 32 by a control valve 35 allowing the pressurization of the control devices 20 as well as the adjustment of the pre-injection dosage. In this case, the common and external adjustment of the opening pressure of the injector needles is not provided.
In FIG. 14, the common control galleries 34 and return 32 are separated and each connected to its valve 35 and 33. It is therefore possible to adjust the pressure of the control devices 20, the pressure of opening of the injector needles 5 as well as the dosage of the pre-injection.
The configuration of Figure 15 is similar to that of Figure 13 with the only difference that the common return gallery 32 is supplemented by its return valve 33. It is therefore possible to adjust the pressure of the pressure devices in common and externally control 20 by modulating the pressure difference between the control galleries 34 and return 32, the opening pressure of the injector needles 5 as well as the pre-injection dosage.

Of course, these different configurations of return galleries 32 and control 34 common to all injectors, pressurized together or separately, can be combined with the variant embodiments described with reference to FIGS. 1 to 10.

Figures 16 to 19 are similar to Figures 2, 3, 4 and 6 and illustrate a form of preferred embodiment of an injection device corresponding substantially to FIG. 14 and simplified by the absence of the piston acting on the injector needle. The device control 20 is fully integrated into an injector assembly 40 containing the injector 4 and composed of parts A to E. The differences lie in the fact that the circuits of return and control are separated. Room C receives return line 8 which communicates directly with the cavity 13 of the calibration spring 10 of the injector needle 5 by the discharge orifice 27. This return pipe 8 is intended to be connected to the common and exterior return gallery 32. In room D, line 36 is intended to be connected to the common and external control gallery 34. Room E is supplemented by the delay orifice 31 and a conduit 37 connecting this delay port 31 with the solenoid valve controlled 25.

In this embodiment, the calibrated orifice 23 is also integrated into the discharge valve 22 (Figure 19) and the delay orifice 31 is arranged coaxially with this relief valve 22 and at its calibrated orifice 23. The calibrated valve 24 has been eliminated.

• Au repos, l'électrovanne 25 est ouverte et la vanne de décharge 22 est fermée sous l'effet de son ressort 22'. Aucun débit ne traverse l'ensemble injecteur 40. La pression résiduelle dans ce circuit est maintenue à un niveau requis par la galerie de contrôle commune 34 et son clapet de contrôle 35 non représenté.
• Au début du refoulement et après la fermeture des orifices de remplissage de la pompe 3, celle-ci délivre son débit au travers du clapet anti-retour 6. La pression croít dans la canalisation d'alimentation 7 ainsi que devant la vanne de décharge 22 et dans son orifice calibré 23. Mais le débit est freiné par l'orifice de retard 31 qui engendre une augmentation de la pression dans la chambre 15 située autour de l'aiguille d'injecteur 5 de manière suffisante pour provoquer son ouverture et réaliser ainsi une pré-injection.
• Lorsque le débit qui traverse l'orifice calibré 23 et l'orifice de retard 31 est suffisant, la vanne de décharge 22 s'ouvre et laisse passer le débit dans le circuit de décharge parallèle 21' vers la cavité 13 du ressort de tarage 10. Ce délestage entraíne une chute de pression dans la chambre 15 de l'aiguille d'injecteur 5 et une augmentation de la pression dans la cavité 13 qui pousse sur l'aiguille d'injecteur 5 pour la fermer et interrompre la pré-injection. La pressurisation de la cavité 13 est assurée par l'orifice de décharge 27 et par la galerie de retour commune et extérieure 32 combinée à son clapet de retour 33 non représenté.
• Le début de l'injection est piloté par le signal électrique sur le solénoïde 26 qui ferme l'électrovanne 25. La diminution du débit au travers de l'orifice calibré 23 et de la vanne de décharge 22 combinée à l'effort fourni par le ressort 22' ferme progressivement la vanne de décharge 22. La pression de combustible appliquée à l'aiguille d'injecteur 5 dans la chambre 15 croit, tandis que la pression de fermeture appliquée du coté du ressort de tarage 10 décroit, jusqu'à ce que l'aiguille d'injecteur 5 s'ouvre. L'injection débute dès cette ouverture.
• Lorsque l'injection est établie, la vanne de décharge 22 et l'électrovanne commandée 25 sont fermées. La totalité du débit fourni par la pompe d'injection 3 est acheminée vers l'aiguille d'injecteur 5 sans aucune restriction et génère des jets d'injection 11 avec toute la pression dont est capable le dispositif d'injection 1.
• La fin de l'injection est déclenchée quand le signal électrique sur le solénoide 26 est interrompu. L'électrovanne 25 s'ouvre sous l'effet de son ressort 25'. La pression de fermeture sur la vanne de décharge 22 est brusquement réduite. Cette vanne s'ouvre alors rapidement. La pression dans le circuit d'injection décroit légèrement du fait du faible débit de décharge acheminé vers la galerie de contrôle commune 34. En parallèle, la montée en pression du côté du ressort de tarage 10 sur l'aiguille d'injecteur 5 assure sa fermeture. L'aiguille d'injecteur 5 se fermant, l'injection s'interrompt brusquement, avant que la chute de pression dans la canalisation d'alimentation 7 haute pression ne soit significative. Le débit, encore fourni par la pompe d'injection 3 traverse la vanne de décharge 22 pour s'évacuer dans les galeries de retour 32 et de contrôle 34. Les pressions de fermeture et d'ouverture, de part et d'autre de l'aiguille d'injecteur 5 étant voisines, l'aiguille reste fermée sous l'action de son ressort 10. La pression décroit progressivement par l'effet de la décharge au travers desdites galeries 32, 34.
• Lors de l'arrêt du refoulement de la pompe d'injection 3, provoqué par l'ouverture de ses orifices de décharge, la pression décroít fortement dans l'ensemble du dispositif d'injection 1. Dès que le débit traversant l'orifice calibré 23 est suffisamment faible, la vanne de décharge 22 se ferme sous l'effet de son ressort 22'. La pression de fermeture assurant le maintien en position fermée de l'aiguille d'injecteur 5 s'élimine progressivement. La pression résiduelle dans l'ensemble du circuit haute pression est alors contrôlée par le clapet de contrôle 35 (non représenté) prévu sur la galerie de contrôle commune 34 combiné éventuellement à l'action du clapet de contrôle 9 de la pompe d'injection 3.

The operation of the injection device, with reference to Figures 16 to 19, is described as follows.

• At rest, the solenoid valve 25 is open and the discharge valve 22 is closed under the effect of its spring 22 '. No flow passes through the injector assembly 40. The residual pressure in this circuit is maintained at a level required by the common control gallery 34 and its control valve 35 not shown.
• At the start of the discharge and after the filling ports of the pump 3 have been closed, the latter delivers its flow through the non-return valve 6. The pressure increases in the supply line 7 as well as in front of the discharge valve 22 and in its calibrated orifice 23. However, the flow rate is slowed down by the delay orifice 31 which generates an increase in the pressure in the chamber 15 located around the injector needle 5 sufficiently to cause it to open and thus achieve pre-injection.
• When the flow through the calibrated orifice 23 and the delay orifice 31 is sufficient, the discharge valve 22 opens and lets flow through the parallel discharge circuit 21 'to the cavity 13 of the calibration spring 10 This load shedding causes a pressure drop in the chamber 15 of the injector needle 5 and an increase in the pressure in the cavity 13 which pushes on the injector needle 5 to close it and interrupt the pre-injection. The pressurization of the cavity 13 is provided by the discharge orifice 27 and by the common and external return gallery 32 combined with its return valve 33 not shown.
• The start of the injection is controlled by the electrical signal on the solenoid 26 which closes the solenoid valve 25. The reduction in the flow rate through the calibrated orifice 23 and the relief valve 22 combined with the force supplied by the spring 22 'gradually closes the discharge valve 22. The fuel pressure applied to the injector needle 5 in the chamber 15 increases, while the closing pressure applied on the side of the calibration spring 10 decreases, until that the injector needle 5 opens. The injection begins as soon as it opens.
• When the injection is established, the discharge valve 22 and the controlled solenoid valve 25 are closed. The entire flow supplied by the injection pump 3 is routed to the injector needle 5 without any restriction and generates injection jets 11 with all the pressure which the injection device 1 is capable of.
• The end of the injection is triggered when the electrical signal on the solenoid 26 is interrupted. The solenoid valve 25 opens under the effect of its spring 25 '. The closing pressure on the discharge valve 22 is suddenly reduced. This valve then opens quickly. The pressure in the injection circuit decreases slightly due to the low discharge flow routed to the common control gallery 34. In parallel, the increase in pressure on the side of the calibration spring 10 on the injector needle 5 ensures its closing. The injector needle 5 closing, the injection abruptly stops, before the pressure drop in the supply line 7 high pressure is significant. The flow rate, still supplied by the injection pump 3 passes through the discharge valve 22 to evacuate in the return 32 and control galleries 34. The closing and opening pressures, on either side of the the injector needle 5 being adjacent, the needle remains closed under the action of its spring 10. The pressure gradually decreases by the effect of the discharge through said galleries 32, 34.
• When stopping the delivery of the injection pump 3, caused by the opening of its discharge orifices, the pressure decreases sharply in the entire injection device 1. As soon as the flow through the calibrated orifice 23 is sufficiently weak, the discharge valve 22 closes under the effect of its spring 22 '. The closing pressure ensuring that the injector needle 5 is kept in the closed position is gradually eliminated. The residual pressure in the entire high pressure circuit is then controlled by the control valve 35 (not shown) provided on the common control gallery 34 possibly combined with the action of the control valve 9 of the injection pump 3 .

Figures 20 and 21 are views similar to Figures 16 and 17. They illustrate only parts C and D of the injector assembly 40 to show a variant of embodiment in which the injector needle 5 is closed by the action of a piston 30. This piston 30 is housed and guided in a cavity 38 arranged coaxially and just above of the cavity 13. This cavity 38 is surmounted by a compression chamber 39 receiving the upper part of the piston 30 and being in communication with the discharge circuit parallel 21 '. This piston 30 is held in abutment against the injector needle 5 by a spring 41. It also has an internal conduit replacing the discharge orifice 27 which puts the compression chamber 39 into communication with the return pipe 8. In this embodiment, the operation is similar to that of the embodiment previous. The only difference is that the addition of piston 30 allows considerably reduce the volume to be compressed to close the injector needle 5.

• quatre configurations possibles dans le cas d'un dispositif de contrôle comportant les orifices 23 et 27,
• huit configurations possibles dans le cas d'un dispositif de contrôle permettant la pré-injection et comportant les orifices 23, 37 et 31.

A remark should be made about the orifices 23, 27, 31 provided in the different variant embodiments described above. These orifices can be of the "capillary" type for which the pressure drop is proportional to the flow rate or of the "nozzle" type for which the pressure drop increases in proportion to the square of the flow rate. It is then possible to combine these different types to obtain:

• four possible configurations in the case of a control device comprising the orifices 23 and 27,
• eight possible configurations in the case of a control device allowing pre-injection and comprising orifices 23, 37 and 31.

• en modulant la rapidité d'ouverture de l'aiguille d'injecteur en combinaison avec le choix du volume à comprimer pour la pousser.
• en faisant évoluer, en fonction du régime de rotation du moteur ou éventuellement de la quantité injectée, certaines caractéristiques comme par exemple le dosage de la pré-injection.

Depending on the combination used, it is then possible to act on various behaviors of the injection device.

• by modulating the speed of opening of the injector needle in combination with the choice of the volume to be compressed to push it.
• by changing, depending on the engine rotation speed or possibly the quantity injected, certain characteristics such as for example the dosage of the pre-injection.

In the case of using capillaries, these can be produced for example by machining of a groove is helical on the cylindrical part of the valve guide, the valve, piston or force-fitted pin, either spirally on a flat surface in contact with another surface

Now, the injection diagrams corresponding to different embodiments of the injector device 1 are described with reference to FIGS. 22 to 25.
In each diagram are represented four curves a to d corresponding from top to bottom to the lifting of the injector needle 5 (curve a), to the flow of fuel injected by the nozzles 12 into the combustion chamber of a piston d a diesel engine (curve b), at the pressure supplied by the injection pump 3 (curve C) and at the pressure in the pipe 7 at the inlet of the injector 4 (curve d). These curves are represented as a function of time for a fraction of the cycle.

FIG. 22 represents the injection diagram of a conventional and known injection device corresponding to the prior art of the invention. It is clearly observed that the end of the injection is very inefficient which is detrimental to the performance of the engine and to the emissions of smoke.
FIG. 23 represents the injection diagram of the injection device of FIG. 1, in which the control of the closing of the injector needle 5 is carried out by the control device 20. It is observed that the end of the injection is very much improved. On the other hand, the start of the injection remains abrupt, which can generate combustion noises.
FIG. 24 represents the injection diagram of the injection device of FIG. 8, in which the injector needle 5 is controlled by the piston 30. It is observed that the end of injection is further improved. This solution is therefore very satisfactory for the performance of the engine. However, combustion noises are still present.
FIG. 25 represents the injection diagram of the injection device of FIG. 10, in which is provided the delay orifice 31 which makes it possible to carry out a pre-injection before the main injection. This solution provides the correction necessary for the attenuation of the combustion noise at the start of the injection. It therefore combines all the advantages. It is understood that the pre-injection cycle can be added to that of the main injection according to the synchronization of the commands.

Claims (13)

1. Fuel injection device (1) for Diesel engines equipped with a pulsating injection pump (3), this device comprising, per piston, at least one injector (4) receiving a calibrated injector needle (5) designed to inject calibrated pressurized fuel jets (11) into the combustion chamber of said piston, a high pressure fuel supply conduit (7) and a low pressure fuel return conduit (8), characterized in that it comprises a control device (20) for opening and closing said needle (5), this device comprising a first discharge circuit (21) connecting the supply conduit (7) and the return conduit (8) for the fuel, provided with a calibrated orifice (23) and controlled by an electrovalve (25) and a second discharge circuit (21') parallel to the first one and comprising a calibrated relief valve (22) and a discharge orifice (27) arranged on the return conduit (8), this second discharge circuit (21') communicating with the injector needle (5) upstream from the discharge orifice (27), said relief valve (22) being designed to make sure that both the start of the injection is progressive and that this injection closes quickly by diverting the flow of fuel which is not injected towards said discharge orifice (27) which, when depressurizing the supply conduit (7), generates a closing pressure on the injector needle (5).
2. Device according to claim 1, characterized in that the first discharge circuit (21) comprises a calibrated flap (24) arranged upstream or downstream from the electrovalve (25), this flap being designed to keep the injection device (1) at a required pressure level between two injections.
3. Device according to claim 1 or 2, characterized in that the control device (20) is separated from the high pressure fuel injection circuit (7) during the injection cycle, the relief valve (22) and the electrovalve (25) being closed.
4. Device according to the one of the claims 1 to 3, characterized in that the closing pressure is applied directly on the injector needle (5).
5. Device according to one of the claims 1 to 3, characterized in that the closing pressure is applied on the injector needle (5) by means of a piston (30).
6. Device according to one of the claims 1 to 5, characterized in that the control device (20) comprises a delay orifice (31) arranged downstream from the calibrated orifice (23) and designed to delay the opening of the relief valve (22) so as to cause the momentary opening of the injector needle (5) to perform a pre-injection of fuel.
7. Device according to any of the claims 1 to 6, characterized in that the calibrated orifice (23) is incorporated in the relief valve (22).
8. Device according to any of the claims 1 to 7, characterized in that the orifices, valve, flap and electrovalve (22 - 25, 27, 31) of the control device (20) are partially or totally incorporated into the unit bearing the injector (4).
9. Fuel injection device (1) comprising several injectors for the same Diesel engine, according to any of the previous claims, characterized in that the return fuel conduits (8) of each injector (4) are connected to one another to a joint return tunnel (32).
10. Device according to claim 9, characterized in that the joint return tunnel (32) is fixed to a calibrated return valve (33) designed to maintain a required level of pressure in said return conduits (8) of each injector.
11. Device according to claim 9 or 10, characterized in that the first discharge circuits (21) are connected to one another by a joint control tunnel (34).
12. Device according to claim 11, characterized in that the joint control tunnel (34) is fixed to a calibrated control valve (35) designed to maintain a required level of pressure in said discharge circuits (21) of each injector.
13. Device according to claim 11, characterized in that the joint return tunnel (32) and the joint control tunnel (34) are connected to one another by a calibrated control valve (35).

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