FUEL INJECTION SYSTEM SUITABLE FOR LOW-VISCOSITY FUELS

Description

TECHNICAL FIELD

[0001] The present invention relates to fuel injection systems for internal combustion engines, in particular, systems suitable for injection of low viscosity fuels such as DiMethyl Ether (DME) into compression-ignition engines.

BACKGROUND OF THE INVENTION

[0002] Some low-viscosity fuel injection systems have been designed following the principle of the known high-pressure common rail systems for diesel fuel, in which fuel is pressurized by a single pump into a pressure vessel or rail that is common for a plurality of injectors, and injections are controlled by electrically actuated valves placed between the common rail and the injectors. This kind of injection system is better suited for fuels with widely variable, pressure and temperature-dependent properties typical to these of DME, than injection systems based on the pump-line-nozzle or unit injector principle, partially because the processes of creating and controlling the injection energy for each injection are divided in time and therefore do not complicate each other as much as when they occur simultaneously. The subject of the present invention is a common rail fuel injection system for injecting a low viscosity fuel into internal combustion engines.

[0003] An example of a prior art injection system is disclosed in the US patent 6,189,517.

[0004] One technical difficulty that arises when a common rail injection system is designed for use with low-viscosity fuels is that, due to relatively low specific energy of low viscosity fuels such as DME, the volume to be passed through the injectors and control valves to obtain a given engine power, is relatively big. This necessitates relatively large controlled areas in the valves, which usually conflicts with the requirements of small overall dimensions, quick response times and small control and static leakages in the injection system. In the prior art injection system of US 6,189,517, the leakage problem is additionally exacerbated by the use of small area passages that connect the downstream side of the electrically actuated valves to the return line in order to eliminate possible uncontrolled injections and leakage of fuel past the closed nozzle into the engine which is possible because of the low viscosity of the DME. An improvement to this design has later been disclosed in which the electrically actuated valves are of a three-way spool type such that they can connect the injector nozzle alternately to the source of pressure and to the return line. Such a three-way spool valve partially solves the problem of parasitic leakage during the injection event that is present in the prior art system described in US6,189,517, but introduces leakages past the clearances in the spool valve. Such leakages have been found to negatively affect hydraulic efficiency and controllability even in the conventional diesel fuel injection systems. The approximately 10 times lower viscosity of DME would bring in an increase in leakage rate of about the same magnitude. Reducing clearances in the spool to limit the leakage is not technically feasible both because they are already close to a minimum and because low-viscosity fuels have poor lubricity, which greatly increases the risk of seizure in close-fit spools.

[0005] A possible solution to this is a three-way, hydraulically unbalanced valve with two tapered or flat seats, in which the pressurized volume can be isolated by relatively long precision-matched guide ensuring acceptable leakage. The basic design of such a valve is well-known in the art and is successfully utilized in the fuel injection systems to control relatively small pilot flows, as disclosed, for instance, in EP1120563A2. However, this principle can hardly be realized to control full flow of fuel to be injected, especially in the case of increased volume deliveries necessary when using DME, because the size of the valve becomes prohibitively large for the good response times and acceptable electrical power consumption to be maintained. Thus, a novel approach to the design of the hydraulic control system of the low-viscosity fuel common rail system is required.

[0006] The poor lubricity and potentially big leakage of the low-viscosity fuels, on one hand, and their low-sooting combustion properties, on the other hand, dictate the choice of relatively low injection pressures. Low fuel pressure levels not only require extra large flow areas in the control valves of the injection system, but also make it necessary to use high-flow nozzles in order to keep the injection time periods short enough for good engine fuel efficiency. The design of conventional high-pressure diesel injection nozzles which are used in the system disclosed in US6,189,517 B1, limits the size and number of injection orifices that can be used. Another unfavorable aspect of using conventional high-pressure diesel injection nozzles in a low-viscosity injection system is their relatively high cost and complexity.

[0007] Yet another negative aspect of using conventional diesel nozzles in a low-viscosity fuel system is that the leakage past the needle guide of such nozzles can also become relatively large. A disclosure of this kind is DE 102 45 736 A1, on which the preamble of the independent claim is based. It would be beneficial to design a low-viscosity fuel injection system that utilizes a nozzle which is characterized by reduced leakage and allows large opening flow areas. A reduction in the leakage can also allow cost reduction of the fuel system by making a fuel cooler redundant. The fuel cooler may otherwise be necessary because higher leakage causes conversion of more hydraulic power into heat which has to be removed from the system.

SUMMARY OF THE INVENTION

[0008] The object of the present invention is to improve fuel economy of a low viscosity fuel-powered engine with a fuel injection system of the common rail type by means of limiting the parasitic hydraulic losses due to static and control fuel leakages, improving injection controllability and reducing duration of injection. Another object of the invention is to reduce the cost of the fuel injection system, which can be achieved by reducing leakages in the system and by simplification of the nozzle design.

[0009] The fuel injection system according to the present invention incorporates a three-way electrically operated pilot valve that controls a hydraulically operated valve positioned between a common rail and a nozzle, a differential hydraulic valve positioned upstream of the nozzle with its outlet connected to the inlet of the nozzle, and an electrically operated, two-way, normally open spill valve positioned between the outlet of the hydraulically operated valve and a return line. The nozzle has a leak-free design with a poppet-type valve that is biased towards its closed position by a spring and can open outward in the direction of the engine combustion chamber when fuel pressure in the nozzle exceeds the nozzle opening pressure, which is determined by the backpressure in the combustion chamber of the engine and the force of the spring. Such nozzle design features significantly bigger, than in conventional high-pressure diesel nozzles, ratio of open effective flow area to valve lift.

[0010] All control valves in the present invention have either tapered or flat seats which provides for minimum possible leakage in the closed state of the valves. The pilot valve is very small because it only controls the little flow necessary for switching the hydraulically operated valve. Due to its small size, the pilot valve can be hydraulically unbalanced with positive sealing of both seats, and the leakage past the valve stem is also small due to its small diameter, typically 3 mm, and relatively long stem sealing length.

[0011] The hydraulically operated valve can also be made with relatively small stem diameter, typically 4 mm, because its lift can be relatively big compared to what is achievable with electrically operated valves. The sealing length of the stem can be made sufficiently long to achieve small leakage. Preferably, the hydraulically operated valve has tapered seat for positive sealing.

[0012] The spill valve can also be made very small, because its purpose is to assist the nozzle valve's and the hydraulically operated valve's closure and relieve residual pressure in the nozzle in order to limit possible leakage of the fuel into combustion chamber and/or uncontrolled injections that could otherwise be possible in case of imperfect sealing in the hydraulically operated valve and consequent pressure build-up in the nozzle.

[0013] The differential hydraulic valve performs the same function as that of the resilient check valve described in the US6,189,517 B1 referred to above. This function is to prevent the leakage of the fuel into the engine after the engine shutdown. The differential hydraulic valve stays fully open during engine operation and does not participate in the injection control.

[0014] Due to the design of the control system of the present invention, characterized by the fact that the electrically operated valves do not directly control the full flow of fuel to be injected into the engine, these valves and their actuators can be made sufficiently small to be fitted directly in the injector. This minimizes the dead hydraulic volumes and helps achieve more accurate control of fuel injection, in particular, of small fuel quantities.

[0015] Conventional high-pressure diesel injection nozzle can also be used in the present invention in cases when its injection spray pattern is more advantageous for a particular combustion system, than the spray pattern of the poppet-type nozzle. In such case the leak-off fuel from the low pressure side of the nozzle needle is connected either directly to the return line or to a backpressure regulator to achieve variable nozzle opening pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The invention will be further described in the following, in a non-limiting way with reference to the accompanying drawings in which:

Fig.1 is a schematic view of a preferred embodiment of the fuel injection system according to the present invention;

Fig.2 is a schematic view of a second embodiment of the fuel injection system according to the present invention,

and

Fig.3 is a schematic view of another embodiment of the present invention in which a conventional high-pressure diesel injection nozzle is used.

[0017] Like reference numbers are used to designate corresponding parts of the systems depicted in the drawings.

DETAILED DESCRIPTION OF THE INVENTION

[0018] Referring to Fig.1, there is provided a low-viscosity fuel feed system including a fuel tank 1, a feed pump 2 and associated components (not shown), a high-pressure pump 3, a common rail 4, to which a plurality of injectors 5 are connected, and an engine management system 6. A hydraulically operated valve 7 is connected between the common rail 4 and the inlet of a nozzle 8, the inlet of the hydraulically operated valve 7 being connected to the common rail 4. The hydraulically operated valve preferably has a precision-matched stem and forms an outlet chamber 9 and a control chamber 10, and is preferably biased towards its closed position by a resilient means 11. The control chamber 10 of the valve 7 can be connected by a three-way pilot valve 12 to either the common rail 4 or a return line 13, depending on commands from the Engine Management System (EMS) 6. The outlet of the hydraulically operated valve 7 is connected to the inlet of the nozzle 8 via a differential hydraulic valve 14. The nozzle 8 has a valve stem 15 with a guide 16 and a poppet 17. A resilient means 18 biases the nozzle towards closed position, and the nozzle can open when the pressure in the nozzle is built up sufficiently high to overcome the force of the resilient means 18 and the force of backpressure acting on the poppet 17 which, in use, is the pressure in the combustion chamber of the engine (not shown). A spill valve 19 that is controlled by the EMS 6, is connected between the outlet of the hydraulically operated valve 7 and the return line 13.

[0019] The differential hydraulic valve 14 is designed such that, once it is open, the area of the valve that is exposed to the pressure of the fuel is sufficiently big to hold the valve open against the force of the valve's return spring when the pressure in the valve is anywhere from slightly below the feed pressure in the system or above that level. In case of engine being stopped and the feed pressure falling below a predetermined level, the valve 14 closes and the area of the valve exposed to the pressure upstream of the valve becomes relatively small, such that a pressure above the feed pressure level is required to re-open the valve 14. The design of such a valve is known in the art and is disclosed, for example, in the US Patent No.6,189,517 B1.

[0020] The system according to the embodiment of Fig.1 works as follows: in a no-injection state but with the engine running, there is feed pressure downstream of the feed pump 2 and in the return line 13; the high-pressure pump pressurizes the fuel to a certain level and maintains that level in the common rail 4. The valves 12 and 19 are not activated by the EMS 6. The three-way pilot valve 12, in its de-activated position, connects the common rail 4 to the control chamber 10 of the hydraulically operated valve 7. The pressure from the common rail, combined with the force of the resilient means 11, holds the valve 7 in its closed position. The spill valve 19 is open, connecting the outlet of the hydraulically operated valve 7 to the return line 13. The differential hydraulic valve 14 is open, and pressure in the nozzle 8 equals pressure in the return line 13. The nozzle is closed by the combined force of the resilient means 18 and the backpressure acting on the poppet 17.

[0021] To begin an injection, the EMS applies a control current to the pilot valve 12, which disconnects the control chamber 10 of the hydraulically operated valve 7 from the common rail 4 and connects it to the return line 13. The pressure in the control chamber 10 falls and allows the common rail pressure acting on the valve 7 from the outlet chamber 9 to open the valve 7 against the force of the resilient means 11. At about the same time, the EMS closes the spill valve 19, so that the fuel cannot escape to the return line 13 while the hydraulically operated valve 7 is open. Fuel pressure in the line connecting the outlet chamber 9 of the valve 7 and the nozzle 8 rises and, upon reaching the nozzle opening pressure, the nozzle opens with the poppet 17 moving towards the combustion chamber of the engine, and fuel injection begins.

[0022] To end the injection, the EMS de-activates the pilot valve 12, which then disconnects the control chamber 10 from the return line 13 and connects it back to the common rail. The pressure in the control chamber 10 rises and, together with the resilient means 11, forces the valve 7 down towards the closed position. Any throttling effect in the seat of the valve 7 assists the valve closure. During the closing period of valve 7 and corresponding reduction of its flow area, the fuel continues to be injected from the open nozzle and the pressure in the nozzle falls. Typically, the hydraulically operated valve 7 closes first and then, when the pressure in the nozzle falls down sufficiently, the nozzle also closes. Following this, the EMS opens the spill valve 19 so that a relatively high residual pressure that may have been left in the nozzle at the nozzle closing is relieved back into the return line 13. This minimizes the risk of the fuel leaking through the closed nozzle into the combustion chamber, which leads to increased exhaust emissions.

[0023] If it becomes necessary, the closure of the valve 7 and the nozzle 8 can be made quicker by relatively early re-opening of the spill valve 19. Such an early re-opening will increase the rate of pressure decay in the nozzle and downstream of the hydraulically operated valve 7 and therefore assist in earlier closing of the valve and the nozzle. This mode of operation may be beneficial in the conditions where very small injections, such as pilot injections, have to be performed.

[0024] Other possibilities also exist in controlling the injection pattern with the present invention. For instance, the pilot valve can be cycled ON/OFF in the first part of fuel injection to modulate the injection pressure through controlling the lift of the hydraulically operated valve 7.

[0025] Another embodiment of the present invention, illustrated in Fig.2, differs from the preferred embodiment of Fig.1 in that, instead of a three-way pilot valve, a two-way pilot valve 20 is used to control the hydraulically operated valve 7. In this embodiment, the control chamber 10 is connected to the common rail with a channel having a restriction 21, and the flow area of this restriction and the maximum flow area of the pilot valve 20 are set in such a way that, with the valve 20 fully open, the pressure in the control chamber 10 of the hydraulically operated valve 7 falls and allows the valve 7 to open. The system may also be designed in the way known in the high-pressure diesel fuel injectors, such that the valve 7, upon approaching the fully open position, closes off the entrance to a channel 22 connecting the control chamber 10 with the pilot control valve 20, thus minimizing the leakage from the common rail, past the restriction 21, control chamber 10 and the open poppet valve 20 back to the return line 13.

[0026] In the embodiment shown in Fig.3, the design of the system according to the present invention is in principle the same as described above, but a conventional nozzle 8 is used. The nozzle has a needle 23 with a precision-matched guide 24 that isolates the nozzle pressure chamber 25 from the spring chamber 26. The spring chamber 26 is connected either directly to the return line 13 or, as shown in the Fig.3, to a pressure regulator 27 which may be made electronically controlled to set optimum nozzle opening pressure at each engine operating condition.

[0027] The invention is not limited to the above-described embodiments, but several modifications are possible within the scope of the following claims.

Claims

1. A fuel injection system for an internal combustion system, comprising an Engine Management System (EMS) (6), a fuel feed pump (2), a high-pressure pump (3) supplying fuel under pressure to a common rail (4) and a plurality of injectors (5), each injector (5) comprising a hydraulically operated valve (7) comprising an outlet chamber 9 connected to the common rail (4) and a control chamber (10), the valve (7) being designed such that, in its closed position, the valve prevents the flow out of the outlet chamber (9), each injector (5) further comprising an electrically operated pilot valve (12) adapted to control the pressure in the control chamber (10) thereby controlling the position of the hydraulically operated valve (7), and a return line (13), wherein a nozzle (8) with a resilient means 18 that biases
the nozzle towards closing, is connected to the outlet of the hydraulically operated valve (7) in such a way that pressure at the outlet of the hydraulically operated valve (7) tends to overcome the force of the resilient means (18) and open the nozzle (8), characterized in that an electrically operated spill valve (19) is connected between the outlet of the hydraulically operated valve (7) and the return line (13).

2. A fuel injection system according to claim 1, characterized in, that the electrically operated pilot valve (12) is a three-way valve that can alternately connect the control chamber (10) to either the common rail (4) or the return line (13).

3. A fuel injection system according to claim 1, characterized in, that the control chamber (10) is connected via a restriction (21) to the common rail (4)
and the electrically operated pilot valve (12) is a two-way valve that can connect the control chamber (10) to the return line (13), wherein the flow areas of the restriction (21) and the open pilot valve (12) are chosen such that, in an open position of the pilot valve (12), the pressure in the control chamber (10) falls and allows the pressure in the outlet chamber (9) to open the valve.

4. A fuel injection system according to claim 3, characterized in, that the hydraulically operated valve (7) is adapted to close the connection between the control chamber (10) and the pilot valve (12) when valve (7) is in an open position.

5. A fuel injection system according to any one of the preceding claims, characterized in, that there is a resilient means (11) that biases the hydraulically operated valve (7) towards its closed position.

6. A fuel injection system according to any one of the preceding claims, characterized in, that the nozzle (8) incorporates a valve stem (15) with a poppet (17) designed such that pressure in the nozzle, acting on a part of the poppet, can overcome the force of the resilient means (18) and backpressure outside the nozzle and open the nozzle by moving the stem (15) with the poppet (17) outward in the direction of the engine combustion chamber.

7. A fuel injection system according to any one of claims 1-5, characterized in, that the nozzle (8) incorporates a needle (23) with a guide (24) forming a pressure chamber (25) communicating with inlet of the
nozzle and a spring chamber (26), designed such that pressure in the pressure chamber (25) acting on a part of the needle (23) can overcome the force of the resilient means (18) and open the nozzle by moving the needle (23) in the direction away from the combustion chamber of the engine, further wherein the spring chamber (26) is connected to the return line (13).

8. A fuel injection system according to claim 7, characterized in, that the spring chamber (26) is connected to a pressure regulator (27).

9. A fuel injection system according to claim 8, characterized in, that the pressure regulator (27) is electronically controlled by the EMS (6).

10. A fuel injection system according to any one of the preceding claims, characterized in, that a differential hydraulic valve (14) is installed upstream of the nozzle (8), the valve (14) being designed such that it is closed when the pressure upstream of the valve (14) is below a feed pressure which is characteristic to a running engine and that it is open when pressure upstream of the valve (14) is at or above a feed pressure which is characteristic to a running engine.

Ansprüche

1. Kraftstoffeinspritzsystem für ein Verbrennungskraftsystem, das ein Motor-Management-System (Engine Management System - EMS) (6), eine Kraftstoffzuführpumpe (2), eine Hochdruckpumpe (3), die einem Common Rail (4) mit Druck beaufschlagten Kraftstoff zuführt, und eine Vielzahl von Injektoren (5) aufweist, wobei jeder Injektor (5) ein hydraulisch betriebenes Ventil (7) aufweist, das eine mit dem Common Rail (4) verbundene Auslasskammer (9) und eine Steuerkammer (10) umfasst, wobei das Ventil (7) derart ausgelegt ist, dass das Ventil in seiner geschlossenen Position das Ausströmen aus der Auslasskammer (9) verhindert, wobei jeder Injektor (5) weiterhin ein elektrisch betriebenes Steuerventil (12), das dazu ausgelegt ist, den Druck in der Steuerkammer (10) zu regeln und dadurch die Position des hydraulisch betriebenen Ventils (7) zu steuern, und eine Rücklaufleitung (13) aufweist, wobei eine Düse (8) mit einer elastischen Einrichtung (18), die die Düse in Richtung des Schließens vorspannt, mit dem Auslass des hydraulisch betriebenen Ventils (7) derart verbunden ist, dass der Druck am Auslass des hydraulisch betriebenen Ventils (7) dazu neigt, die Kraft der elastischen Einrichtung (18) zu überwinden und die Düse (8) zu öffnen,
dadurch gekennzeichnet, dass ein elektrisch betriebenes Überströmventil (19) zwischen den Auslass des hydraulisch betriebenen Ventils (7) und die Rücklaufleitung (13) geschaltet ist.

2. Kraftstoffeinspritzsystem nach Anspruch 1, dadurch gekennzeichnet, dass das elektrisch betriebene Steuerventil (12) ein Drei-Wege-Ventil ist, das die Steuerkammer (10) wechselweise entweder mit dem Common Rail (4) oder mit der Rücklaufleitung (13) verbinden kann.

3. Kraftstoffeinspritzsystem nach Anspruch 1, dadurch gekennzeichnet, dass die Steuerkammer (10) über eine Drosselung (21) mit dem Common Rail (4) verbunden ist und dass das elektrisch betriebene Steuerventil (12) ein Zwei-Wege-Ventil ist, das die Steuerkammer (10) mit der Rücklaufleitung (13) verbinden kann, wobei die Strömungsbereiche der Drosselung (21) und des offenen Steuerventils (12) so gewählt sind, dass bei geöffneter Position des Steuerventils (12) der Druck in der Steuerkammer (10) fällt und es dem Druck in der Auslasskammer (9) erlaubt, das Ventil zu öffnen.

4. Kraftstoffeinspritzsystem nach Anspruch 3, dadurch gekennzeichnet, dass das hydraulisch betriebene Steuerventil (7) so ausgelegt ist, dass es die Verbindung zwischen der Steuerkammer (10) und dem Steuerventil (12) schließt, wenn das Ventil (7) sich in einer geöffneten Position befindet.

5. Kraftstoffeinspritzsystem nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass eine elastische Einrichtung (11) vorhanden ist, die das hydraulisch betriebene Ventil (7) in seine geschlossene Position vorspannt.

6. Kraftstoffeinspritzsystem nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Düse (8) einen Ventilschaft (15) mit einem Teller (17) umfasst, die derart ausgelegt sind, dass Druck in der Düse, der auf einen Teil des Tellers wirkt, die Kraft der elastischen Einrichtung (18) und den Gegendruck außerhalb der Düse überwinden und durch Bewegen des Schafts (15) mit dem Teller (17) nach außen in Richtung der Motorverbrennungskammer die Düse öffnen kann.

7. Kraftstoffeinspritzsystem nach einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, dass die Düse (8) eine Nadel (23) mit einer Führung (24) umfasst, die eine Druckkammer (25) bildet, die mit dem Einlass der Düse und einer Federkammer (26) in Verbindung steht, die derart ausgelegt ist, dass Druck in der Druckkammer (25), der auf einen Teil der Nadel (23) wirkt, die Kraft der elastischen Einrichtung (18) überwinden und durch Bewegen der Nadel (23) in die Richtung weg von der Verbrennungskammer des Motors die Düse öffnen kann, wobei ferner die Federkammer (26) mit der Rücklaufleitung (13) verbunden ist.

8. Kraftstoffeinspritzsystem nach Anspruch 7, dadurch gekennzeichnet, dass die Federkammer (26) mit einem Druckregler (27) verbunden ist.

9. Kraftstoffeinspritzsystem nach Anspruch 8, dadurch gekennzeichnet, dass der Druckregler (27) durch das EMS (6) elektronisch gesteuert ist.

10. Kraftstoffeinspritzsystem nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass ein hydraulisches Differentialventil (14) stromaufwärts von der Düse (8) installiert ist, wobei das Ventil (14) so ausgelegt ist, dass es geschlossen ist, wenn der Druck stromaufwärts von dem Ventil (14) unter einem Zufuhrdruck liegt, der für einen laufenden Motor charakteristisch ist, und dass es offen ist, wenn der Druck stromaufwärts von dem Ventil (14) auf oder über einem Zufuhrdruck liegt, der für einen laufenden Motor charakteristisch ist.

Revendications

1. Système d'injection de carburant pour un système à combustion interne, comprenant un système de gestion de moteur (EMS) (6), une pompe d'alimentation de carburant (2), une pompe haute pression (3) alimentant du carburant sous pression vers une rampe commune (4) et plusieurs injecteurs (5), chaque injecteur (5) comprenant une vanne actionnée hydrauliquement (7) comprenant une chambre de sortie (9) reliée à la rampe commune (4) et une chambre de commande (10), la vanne (7) étant conçue de telle sorte que, dans sa position fermée, la vanne empêche l'écoulement vers l'extérieur de la chambre de sortie (9), chaque injecteur (5) comprenant de plus une vanne pilote actionnée électriquement (12) adaptée pour commander la pression dans la chambre de commande (10) en commandant ainsi la position de la vanne actionnée hydrauliquement (7), et une ligne de retour (13), une buse (8) ayant des moyens élastiques (18) qui rappellent la buse en direction de la fermeture, et reliée à la sortie de la vanne actionnée hydrauliquement (7) de telle manière qu'une pression à la sortie de la vanne actionnée hydrauliquement (7) a tendance à surmonter la force des moyens élastiques (13) et à ouvrir la buse (8), caractérisé en ce qu'une vanne de remplissage actionnée électriquement (19) est connectée entre la sortie de la vanne actionnée hydrauliquement (7) et la ligne de retour (13).

2. Système d'injection de carburant selon la revendication 1, caractérisé en ce que la vanne pilote actionnée électriquement (12) est une vanne trois voies qui peut alternativement connecter la chambre de commande (10) à la rampe commune (4) ou à la ligne de retour (13).

3. Système d'injection de carburant selon la revendication 1, caractérisé en ce que la chambre de commande (10) est connectée par l'intermédiaire d'un étranglement (21) à la rampe commune (4) et la vanne pilote actionnée électriquement (12) est une vanne à deux fois qui peut connecter la chambre de commande (10) à la ligne de retour (13), dans lequel les surfaces d'écoulement de l'étranglement (21) et de la vanne pilote ouverte (12) sont choisies de sorte que, dans une position ouverte de la vanne pilote (12), la pression dans la chambre de commande tombe et permet à la pression dans la chambre de sortie (9) d'ouvrir la vanne.

4. Système d'injection de carburant selon la revendication 3, caractérisé en ce que la vanne actionnée hydrauliquement (7) est adaptée pour fermer la liaison entre la chambre de commande (10) et la vanne pilote (12) lorsque la vanne (7) est dans une position ouverte.

5. Système d'injection de carburant selon l'une quelconque des revendications précédentes, caractérisé en ce qu'il y a des moyens élastiques (11) qui rappellent la vanne actionnée hydrauliquement (7) en direction de sa position fermée.

6. Système d'injection de carburant selon l'une quelconque des revendications précédentes, caractérisé en ce que la buse (8) incorpore une tige de soupape (15) ayant un champignon (17), conçue de telle sorte qu'une pression dans la buse, agissant sur une partie du champignon, peut surmonter la force des moyens élastiques (18) et une contre pression à l'extérieur de la buse et ouvrir la buse en déplaçant la tige (15) avec le champignon (17) vers l'extérieur dans la direction de la chambre de combustion du moteur.

7. Système d'injection de carburant selon l'une quelconque des revendications 1 à 5, caractérisé en ce que la buse (8) incorpore une aiguille (23) ayant un guide (24) formant une chambre de pression (25) communiquant avec une entrée de la buse et une chambre de ressort (26), conçue de telle sorte qu'une pression dans la chambre de pression (25) agissant sur une partie de l'aiguille (23) peut surmonter la force des moyens élastiques (18) et ouvrir la buse en déplaçant l'aiguille (23) dans la direction s'éloignant de la chambre de combustion du moteur, dans lequel de plus la chambre de ressort (26) est reliée à la ligne de retour (13).

8. Système d'injection de carburant selon la revendication 7, caractérisé en ce que la chambre de ressort (26) est reliée à un régulateur de pression (27).

9. Système d'injection de carburant selon la revendication 8, caractérisé en ce que le régulateur de pression (27) est commandé électroniquement par le EMS (6).

10. Système d'injection de carburant selon l'une quelconque des revendications précédentes, caractérisé en ce qu'une vanne hydraulique différentielle (14) est installée en amont de la buse (8), la vanne (14) étant conçue de telle sorte qu'elle est fermée lorsque la pression en amont de la vanne (14) est en dessous d'une pression d'alimentation qui est une caractéristique d'un moteur fonctionnant et qu'elle est ouverte lorsque la pression en amont de la vanne (17) est au niveau ou au-dessus d'une pression d'alimentation qui est caractéristique d'un moteur fonctionnant.

Drawing