EP0898649B1 - Liquid fuel injecting device for internal combustion engine - Google Patents

Description

The present invention relates to a device injection of liquid fuel for combustion engine internal.

In a conventional manner, the injection of liquid fuel in an internal combustion engine, for example a compression ignition engine, includes fuel pressure setting means in the form of an injection pump capable of put fuel under cyclic pressure in a room of variable volume arranged in a pump cylinder and delimited by a piston actuated by a camshaft kinematically linked with the main shaft or engine crankshaft.

Compressed fuel is injected through an injection nozzle which communicates by a plurality injection holes, with the working chamber or combustion of the engine, this nozzle comprising a chamber which communicates with the cylinder of the injection pump, in general through unidirectional passage means such as a non-return valve. Communication between this room and the working room or combustion is interrupted by a sliding needle supported by the action of recall means elastic, on a conical seat arranged in said nozzle upstream of said injection holes.

This needle has a cylindrical body sliding in a bore arranged in the nozzle and diameter greater than that of the conical seat of the needle on its seat, so that when the fuel pressure exceeds a certain value, called set pressure of the injector, it lifts from its seat to allow injection. When the injection pump piston will have exceeded a certain position, beyond which the pump cylinder will find put in communication with feeding means under low fuel pressure, the pressure in the nozzle drops and the injection needle is brought back to its seat, to close the nozzle, under the action of the above elastic return means.

Despite its great simplicity, this device classic has serious drawbacks. In firstly the injection pressure depends on the regime of the engine and varies with it. Then, because of the obligatorily limited force of the return spring, the end of injection is carried out at low pressure allowing more fine atomization of the fuel, which generates unburnt and soot particles.

Some of these disadvantages can be avoided by an injection device of the type proposed in FR-A-1 351 593. In such a device the fuel from the means of establishing pressure, such as a pump or accumulator, is addressed to an injection chamber delimited by a piston moving against a powerful spring, so filling the chamber with pressurized fuel during the non-injection phase. This room is directly open on the injector cavity, in which move the sealing means, such as a needle, whose lifting can be controlled, either by a circuit independent hydraulic system, either by a circuit using the combustible. When we cause the opening of the needle, and therefore the injection, the needle moves, on a long run, until it comes up against against the piston of the injection chamber, the latter as it advances which pushes back the fuel from the injection chamber to the injection nozzle, coming to close the needle.

However, such a device has disadvantages that make it unfit for use for very high injection pressures which are used in modern engines, and which would result by an increased risk of fuel leakage, and by a loss of energy due to the backflow of a part of the fuel outside the injector volume to the power circuit, not to mention the problem of oversizing of the return spring.

We have also already described in DOS 1,944 862 an injection device comprising a chamber injection, in which a differential piston moves, and who is in direct communication with the injector, control means allowing, during the non-injection phase, filling the injection chamber against the pressure of an accumulator of fuel kept in charge by a high pump pressure. However, this device has drawbacks notables. In particular, the injection pressure is not that a fraction of the pressure supplied by the pump and the end of the piston injection stroke is ensured by a pressure drop difficult to obtain with precision, especially in the case of very high pressures.

To overcome the disadvantages of these different solutions, modern evolution is concentrated on storage injection systems, also called "common rail" systems.

In such systems, an accumulator is constantly filled with fuel under high pressure by means of high pressure generators of combustible, and communicates permanently with the room of the injection nozzle upstream of the seat against which applies, thanks to control means, the range of the injection needle. A distributor allows you to make communicate said room with another room bounded by the upper side of the needle, so the needle is pressed on its seat under the effect of the pressure prevailing in the accumulator. When you want to initiate the injection, the distributor is tilted, so as to communicate said chamber delimited by the upper face of the needle with low pressure supply means to drop the pressure exerted on the upper face of the needle, so that the needle lifts.

To end the injection, you switch to again the distributor in the other position, in order to restore the accumulator pressure above the upper side of the needle, so the means return the needle to its seat without it it is necessary to drop the injection pressure. The injection is therefore carried out entirely at high accumulator pressure, preventing tearing at the end of injection.

In addition, the injection pressure is independent engine speed.

Such advantageous devices the quality of combustion and the control of unburned, however have other drawbacks. Indeed, if the needle closes badly or if the seat of the needle is damaged, the fuel present under high pressure in the accumulator will spill into the combustion chamber, with a risk of overheating and engine destruction.

In addition, the permanent pressure of the common rail, being sealed by numerous sliding pistons in bores, a significant level of leakage creates mechanical losses, heating of the fuel, and disturbs the accuracy of the dosages.

The invention proposes to remedy these disadvantages and provide an injection device allowing the fuel to be injected under high pressure, for practically the entire duration of the injection regardless of engine speed.

Another object of the invention is to realize such a device allowing, in an extremely simple, to deliver a precise and determined dose of fuel in a very short time and at very high pressure.

Another object of the invention is to realize such a device in which the injection can be secured under very strong pressure during the entire injection.

Yet another objective of the invention, is to make such a device in which we can ensure very rapid injection using means relatively slow high pressure build-up.

Yet another objective of the invention, is to make such a device with a reduced number of classic components and, in particular, to use a single pumping and metering element to supply a plurality of injectors, thus guaranteeing good balancing of the flows injected into the different cylinders.

Another object of the invention is to realize such a device in which we can do vary, in a simple way, the injection rate in progress injection, in particular to ensure the start of injection at low flow, then further injection at more high flow, according to the technique sometimes called spleen shaping.

Another objective of the invention is to obtain the advantages of common rail with a low level leak.

Another object of the invention is to reduce the energy consumption of the injection device.

Another objective of the invention is to obtain these advantages without the use of electronic means, poorly adapted to certain environments.

• une buse d'injection comprenant, pour chaque chambre de travail:
  • une cavité de buse qui communique avec une chambre de combustion par au moins un orifice d'injection,
  • des moyens d'obturation permettant d'interrompre et de rétablir cycliquement la communication entre ladite cavité de buse et ladite chambre de combustion,
• et des moyens de délivrance de combustible liquide sous haute pression, susceptibles de délivrer cycliquement une quantité dosée de combustible liquide sous haute pression,
• lesdits moyens de délivrance communiquant, à travers des moyens de communication cyclique, avec une chambre d'injection de volume variable délimitée par une paroi d'un élément mobile rappelé, à chaque cycle, par des moyens de rappel élastiques jusqu'à une butée fixe établissant la valeur minimale dudit volume variable de ladite chambre d'injection, et qui communique, en permanence, avec ladite cavité de buse, ladite chambre d'injection étant destinée à recevoir momentanément ladite quantité dosée de combustible liquide, une chambre d'injection (26, 34) étant prévue pour chaque chambre de travail,
• ladite quantité dosée de combustible liquide étant délivrée cycliquement par lesdits moyens de délivrance dans ladite chambre d'injection, pendant la phase de fermeture cyclique desdits moyens d'obturation de la buse d'injection,

   caractérisé en ce que lesdits moyens de rappel élastique comportent un volume de fluide sous pression, agissant sur ledit élément mobile.The subject of the invention is a device for discontinuous and cyclic injection of liquid fuel sprayed under high pressure into a combustion chamber of an internal combustion engine with a working chamber of variable volume which comprises,

• an injection nozzle comprising, for each working chamber:
  • a nozzle cavity which communicates with a combustion chamber through at least one injection orifice,
  • shutter means making it possible to interrupt and restore cyclically the communication between said nozzle cavity and said combustion chamber,
• and means for delivering liquid fuel under high pressure, capable of cyclically delivering a metered quantity of liquid fuel under high pressure,
• said delivery means communicating, through cyclic communication means, with an injection chamber of variable volume delimited by a wall of a movable element recalled, at each cycle, by elastic return means up to a fixed stop establishing the minimum value of said variable volume of said injection chamber, and which permanently communicates with said nozzle cavity, said injection chamber being intended to temporarily receive said metered quantity of liquid fuel, an injection chamber ( 26, 34) being provided for each working chamber,
• said metered quantity of liquid fuel being delivered cyclically by said delivery means into said injection chamber, during the phase of cyclic closure of said means for closing the injection nozzle,

characterized in that said elastic return means comprise a volume of fluid under pressure, acting on said movable element.

Preferably said movable element, the wall delimits the aforesaid injection chamber, is formed by a piston sliding in a cylinder to delimit said room. Because the pressures of share and others of the piston can be practically balanced, the risk of leakage from the piston can be practically deleted.

In a particularly preferred manner, the fluid under pressure contained in the volume and exerting its booster can be fuel kept under pressure in an accumulator.

Preferably the movable element or piston can be designed to seal any leaks between the room injection and said volume of liquid fuel under pressure, when applied to its stop.

The pressurized fluid can act on said mobile element by means of a multiplication means, in particular a differential piston.

The injection nozzle can advantageously be a conventional type nozzle, containing three cavities, know a first room or bag communicating by injection ports with the combustion chamber, a second bedroom communicating with the first bedroom and having a seat, said chamber being delimited by the lower part of a sliding needle, the end has a scope which may apply on said seat to interrupt this communication, and a third cylindrical chamber in which slides a part, forming a piston, of the needle, of so as to form a third above the needle room associated with control means.

The sealing means, formed, for example, by such a needle, can be ordered, for their opening, by electromagnetic means like this is in itself known.

These sealing means can be sensitive at the pressure of the liquid fuel in the cavity nozzle, for example the aforesaid second chamber, of so that when a high pressure is established in this cavity, the needle lifts up against its return means to a stop position. This solution is preferred in the present invention and can be simply obtained by direct communication and permanent between said nozzle cavity and said chamber injection.

Said sealing means can be sensitive, for their closure, to a return spring.

They can also be sensitive, for their closing, by the action of a pressurized fluid, especially liquid fuel.

However, preferably, said means shutter can be sensitive, for their closure, to the direct action of the aforesaid movable element of the room injection, so that the movable element, when returns to its stop position, moves the sealing means to a sealing position.

This solution is particularly advantageous, because it ensures that the injection of liquid fuel sprayed into the combustion chamber is ensured at high pressure, including in the very last moments of the injection.

The stop of the movable element can then be constituted by said sealing means, such as the needle, when they arrive in their closed position. However, it is also possible to provide a positive stop. fixed, for example formed by a shoulder or a seat of the injection chamber, against which the element mobile comes to apply after closing the above shutter means, such as a needle, and then continued still a very short stroke thanks to an elastic contact between the movable element and said shutter means, for example by simple elastic compression of the shutter needle when it has a shape elongate.

Fuel delivery means liquid under high pressure can be quite conventional and in particular include a simple pump usual alternative injection whose piston is in constant contact with the cam of a camshaft. advantageously this pump can be metered, for example by comprising, as is known for injection pumps, a helical discharge ramp and an adjustment of angular position of the pump piston.

We can use centralized means pressure build up for multiple devices injection associated with each piston and the pump can then be a conventional distributor pump.

In an advantageous embodiment, said cyclic communication means arranged between said means for delivering liquid fuel under high pressure and said volume injection chamber variable, include a one-way means of communication.

In addition, they may, in particular include a valve arranged upstream of said unidirectional means and arranged so as to put said means high pressure establishment in communication with a low pressure discharge, causing the closing of said unidirectional means, so that said metered amount of fuel can be determined by the duration of closure of said valve.

Said valve may simply be a valve two-way.

In the event that the above sealing means of the nozzle are sensitive to their closing, to the pressure in a cavity, containing fuel liquid, a valve, preferably the above-mentioned valve disposed upstream of said unidirectional means, can be provided, to put said cavity in communication with a discharge to authorize the opening of said means shutter.

In this case the same valve controls the setting to the discharge of said high establishment means pressure and said fuel-containing cavity liquid acting, for the closing operation, on said shutter means, so that when said valve is closed, said delivery means deliver the high pressure liquid fuel at said injection chamber through said communication means unidirectional, while the opening of said valve causes the end of said delivery and, simultaneously, authorizes the opening of said sealing means and injecting the fuel into the combustion chamber.

We can also establish a gap between when dosing ends and when injection, letting the pump piston push back fuel under pressure to its top dead center, the pressure remaining then maintained thanks to a profile cam dish. In this case the closing time of the valve determines the dosage of the volume injected, since the fuel dose received by the injection chamber is determined by the effective stroke of the pump between the closing time and reaching top dead center. At otherwise the subsequent opening of the valve determines the time of start of injection.

In another embodiment one can use, to open the sealing means, the drop pressure due to the descent of the pump piston after its top dead center. We can then advantageously recover, on the drive means of the piston pump, the expansion energy of the fuel volume compressed between the pump piston and the sealing means, such as the needle.

In this case the function of valve two tracks can be ensured by a rotating distributor classic pump and electrically controlled valve becomes useless.

The invention is remarkably suitable for when injecting liquid fuel into a several cylinders including injection nozzles specific to each cylinder. The pump or means of delivery of high pressure liquid fuel is then connected separately to each nozzle by conduits identical specifics, and means are arranged for address the fuel successively to the different nozzles. These means can be simply constituted of a single conventional dispenser pump and it's remarkable that we can advantageously connect this pump to a low pressure discharge by a single valve two-way whose simple command allows to determine all the operations of the injection cycles, less adopting the purely hydromechanical solution defined above.

In this case, the aforementioned means of recall elastic elements of the movable elements are preferably constituted by a single centralized means, for example, a single accumulator containing liquid fuel under high pressure and acting on said elements mobile, the mobile elements being preferably arranged in the respective nozzles in coaxial alignment with the means for closing said nozzles.

The aforesaid one-way means of communication are then advantageously arranged, individually, at each nozzle to reduce the quantity of fuel compressed and not injected.

In order to vary the fuel flow injected during the injection phase, for example establishing a low injection rate at the start of injection and a significant flow during the rest of the injection, the device can advantageously include means for bringing fuel from from the injection chamber to the nozzle cavity with a flow rate limited in such a way that at the start of the injection, the injection rate is equal to a determined rate from the injection chamber, reduced by a flow corresponding to the increase in volume in the cavity of nozzle caused, for example, by the lifting of the means sealing the injector.

To this end, for example, provision may be made for have, in direct communication between the room injector and injector cavity, throttle or nozzle with calibrated orifice, limiting the flow addressed to the injector cavity, the sealing means, such that the needle is then associated with means to control the needle lift during a fixed term. This means can itself be a throttle slowing the evacuation of fluid from shutter control.

This means can possibly be arranged as a variable section choke so as to ensure lifting the needle according to a determined time profile.

• les figures 1 à 4 représentent un dispositif d'injection selon une première forme de réalisation de l'invention pendant quatre situations successives, à savoir, successivement, une phase de balayage et réalimentation de la pompe, une phase de dosage, la position de début d'injection et la position de fin d'injection,
• les figures 5 à 8 représentent quatre phases de fonctionnement d'une autre forme de l'invention,
• les figures 9 à 12 représentent d'autres formes de réalisation de l'injecteur de l'invention,
• la figure 13 représente une vue d'une forme de réalisation de l'invention dans une disposition coaxiale des éléments du dispositif.
• la figure 14 représente une vue d'un dispositif d'injection centralisé pour un moteur polycylindre.

Other advantages and characteristics of the invention will appear on reading the following description, given by way of nonlimiting example, and referring to the appended drawings, in which:

• FIGS. 1 to 4 represent an injection device according to a first embodiment of the invention during four successive situations, namely, successively, a phase of sweeping and recharging of the pump, a dosing phase, the start position injection and the injection end position,
• FIGS. 5 to 8 represent four operating phases of another form of the invention,
• FIGS. 9 to 12 show other embodiments of the injector of the invention,
• FIG. 13 represents a view of an embodiment of the invention in a coaxial arrangement of the elements of the device.
• FIG. 14 represents a view of a centralized injection device for a polycylinder engine.

We first refer to Figures 1 to 4.

The injection device described is associated to a cylinder 1 of a diesel engine, in which slides a piston 2 and delimiting, above it, a chamber combustion and working 3 closed by a cylinder head 4. Preferably placed centrally and coaxially to the chamber in which the driving piston 2 slides, is finds an injector 6 which can be produced in any way quite conventional. This injector has a nozzle 7, the lower end of which opens into the chamber working 3 and which has an internal cavity forming a succession of three rooms, namely a first chamber or bag 8 of low volume, in communication permanent with working chamber 3 through holes injection 9, a second chamber 10 located above a conical seat 11 and a third cylindrical chamber 12 on the bottom, forming a stop, from which rests a spring 13 which pushes back towards the bearing surface 11 a conventional shutter needle 14 sliding in the cylindrical chamber 12, the front end of which, narrowed, has a bearing range 15 which is applied from tight against the seat 11.

The device also includes a pump 16 of a classic type allowing the establishment of a high fuel pressure. This pump is made up a pump cylinder 17 in which can slide a delivery piston 18 returned to its neutral position bottom by a spring 19 against the cam 20 of a camshaft 21 kinematically attached to the crankshaft (not shown) of the motor. The compression chamber 17 communicates via a conduit 22 in which is arranged a simple two-position valve 23 with the low pressure fuel supply 24. On the other hand, the compression chamber 17 communicates directly with the aforesaid third bedroom 12 by through a conduit 25, opening into a conduit 30.

The device according to the invention comprises another cavity or injection chamber 26 in which slides a movable member 27, consisting of a piston, to encounter a powerful reminder 28, which could be a spring, but which is according to the invention a volume of pressurized fluid, for example a filled accumulator pressurized liquid fuel, preferably arranged to urge the piston 27 with force substantially constant throughout the useful stroke of the piston. The injection chamber 26 communicates constantly with the aforesaid second chamber 10 via a conduit 29 Finally, the communication between room 26 and room compression 17 is provided by the conduit 31 in which is interposed a one-way valve 32.

In the rest position, the piston or movable element 27 abuts against a front stop 33 of chamber 26, so that the volume of chamber 26 is minimal.

Advantageously, the stop 33 achieves a sealing seat, so that in this position the piston 27, no leakage from accumulator 28 to the room 10 is not possible.

The operation is as follows.

In the scanning position shown on Figure 1, the injection needle 14 is applied to its seat 11 by the return spring 13. The element or movable piston 27 is applied against its stop 33 by the powerful spring 28. The piston 18 of the pump starts its descent under the action of cam 20. The two-way valve positions 23 is in the open position, so the pump chamber 17 and the third cavity 12 are are found at low fuel pressure.

In the second room 10 the value of the pressure is low enough that the needle is applied against its seat by the spring 13. The displacement of the pump piston 18, changes the pressures little.

The rest of the process is represented in Figure 2: at a time t determined in the cycle of engine, the two-way valve 23 is closed quickly. injection piston 18, continuing its stroke, raising immediately the fuel pressure in the chamber 17 and, therefore, in room 12. Simultaneously the liquid is expelled to the injection chamber 26 and the piston 27 is pushed back against its powerful spring, while the same pressure builds up in the second chamber 10. High fuel pressure liquid in chamber 17, chamber 26, the second room 10 and the third room 12, is determined by the force of the spring 28, the restoring force of which is almost constant preference. So liquid fuel is subjected to high pressure, which will be the injection pressure, for example 1600 bars.

As long as the two-position valve 23 is closed and the injection pump piston 18 continues its delivery stroke, the injection piston 27 moves back by compressing its elastic means 28 by force constant and storing in room 26 of the fuel from chamber 17.

At time t + Δt, i.e. when the desired fuel dose has been entered, under the high injection pressure, in chamber 26 and where the injection itself must begin, the valve at two positions 23 is quickly reopened as shown in figure 3.

Room 17 and third room 12 are immediately put on low pressure, notwithstanding a possible continuation of the descent of the pump piston 18. Immediately, the one-way valve 32 closes and room 26 is isolated from the room pumping 17.

The third bedroom 12 is low pressure, the high pressure prevailing in chamber 10 will raise the injection needle 14 which will compress its return spring 13, until it comes to rest on its upper stop, establishing communication, through the first chamber 8 and the injection orifices 9, with the engine working chamber. Consequently, the liquid fuel under high injection pressure is injected and sprayed into the working chamber.

This high pressure injection continues during the entire displacement time of the piston 26 under the action of its return means 28 until the stop of the piston against its stop 33, so that a volume of fuel corresponding to all and only the entire dose previously delivered to the chamber 26, is ejected through the orifices 9.

At the end of injection, shown in the figure 4, the movable element 27 abuts against the seat 33 and the pressure in the second chamber 10 suddenly drops to the point of becoming insufficient vis-à-vis the force elastic return spring 13 of needle 14, which is then abruptly brought into abutment against his seat.

Dosage and start of injection may be regulated independently of each other by the only control of a simple two-position valve 23.

We can also shift the end time dosing and the start of the injection, for example using a cam having a high profile part flat to stop sending fuel into the metering chamber 26, while maintaining the pressure in the third chamber 12, the instant of injection being able to be freely chosen on the cam plate by opening of valve 23. In this case the fuel is pumped out of pump 16 from the moment of valve 23 closes and for the remainder of the displacement of the pump piston 18 towards neutral high.

Finally, we can also, without opening the valve 23, wait for a pressure drop in chamber 12 caused by the return of the piston 18 to its neutral position low.

The injection phases are, moreover, completely independent of the position of the cam 20.

Pump 16 can therefore be rustic and low flow since it has a large part of the engine cycle to deliver fuel to the chamber injection.

In the examples which have just been described the pump 16 is not directly arranged to deliver an adjustable dose of fuel, this dose being quantified by the stroke of the piston 18 traveled during the valve closing time Δt.

We can see, however, that we can also use engine fuel injection pumps classic type with an inverted helical ramp and a rotation device around the piston pin pump so that a port can be closed and opened discharge in the wall of the pump cylinder. The pump piston then performs the function of the two-position valve 23.

We now refer to Figures 5 to 8, in which the components having the same functions that in the previous description have the same reference figures.

This embodiment is intended for injections in several stages, for example with a pre-injection, limiting leaks and losses mechanical, and minimizes the influence of compressibility of liquid fuel on operation of the device.

In this embodiment, the conduit 30 is removed and the pipe 25 coming from the pump 16 opens through a one-way valve 32, directly in a room 34 which constitutes, at the times the second chamber of injector 12 and the chamber injector replacing chamber 26. The needle has an extension 48 whose diameter is greater than that of the seat of the needle 14 and which is likely to slide through a hollow movable piston 50 forming the movable element of the injection chamber 34 and which can itself slide in a cylinder forming a chamber 35 into which a fuel accumulator opens liquid under high pressure 28. Extension 48 has, in chamber 35, a flange 49, the diameter is significantly smaller than that of the chamber 35 and which allows the thrust of a spring to be received reminder 13 for the needle. The upper end of the extension 48, beyond the flange, slides in a cylinder for determining the third chamber 12 of the needle to form a piston whose diameter is intermediate between that of the needle seat and that of the extension 48.

The volume of the chamber 35, and therefore accumulator 28, communicate with the third chamber 12 via a initially radial duct then axial 51 practiced in the extension 48 and which opens out, through a terminal throttle, in bedroom 12. In addition, this is connected to the low-pressure fuel source 24 through a valve 52 located near chamber 12 and a conduit 53.

In the loading position shown in FIG. 5, the first and second valves 23, 52 are closed and the pump 16 delivers fuel under strong pressure through the conduit 25 in the chamber 34 of so that the piston 50 moves in the direction of the arrow and pushes back the fuel located in the room 35 towards accumulator 28. All the forces formed by fuel and spring 13 on the needle 14 keeps it pressed against its seat 11. After the top dead center of the pump the valve 32 closes and the cam recovers compression energy from the volume of fuel contained in the chamber 17 and the conduit 25. The pressure in the different injector cavities 6 is then determined by the pressure in the accumulator 28. Opening the first valve 23 causes the valve to drop the pressure in the pump. We can then open the valve 52 as seen in Figure 6. This results in a immediate drop in pressure in third chamber 12 so that the needle 14 is pushed back into position opened. Room 34 is then in communication with the first chamber 8 and the fuel of chamber 34 is ejected and sprayed under the pressure of the piston 50 subjected to the pressure prevailing in the accumulator 28. Throttling in conduit 51 prevents accumulator to empty.

You can then quickly close the valve 52, as shown in Figure 7, so that this first injection phase, which constitutes a pre-injection, ends, the needle 14 being pushed towards its seat, due to the increased pressure in chamber 12 and the action of spring 13. We can thus, by several successive openings and closings of valve 52, cause a multiple injection steps. The end of the injection is obtained, as the shows figure 8, when the entire injectable dose contained in room 34 was ejected and the piston 50 came into sealing abutment on its seat 33, so that the pressure in chamber 34, reduced at its minimum volume, drop and the needle closes quickly under the effect of spring 13 and pressure which is exerted on the differential surface between the extension 48 and the chamber 12. The valve 52 is then closed.

We understand that the control of the needle is extremely fast and precise, especially since the valve 52 can be placed in the immediate vicinity of the third room 12. In addition, no transfer is necessary between an injection chamber and the second injector chamber so the injected dose is insensitive to fuel compressibility. Finally the leak is limited to scanning chamber 12 through choking for the short duration of the injection.

We now refer to Figures 9 to 12 which represent embodiments in which the needle is closed positively by the movable element of the injection chamber.

In Figure 9 we see an injector 6 similar to that of Figure 1 and of which the third chamber 12 does not have a return spring. The needle 14 continues upwards with a long extension 37 sliding in the injector body and opening into an injection chamber 26 connected to the conduit 25 via valve 32 and conduit 30. The piston 27, which delimits the injection chamber 26, is called up by its reminder means, namely the accumulator 28 as well as a spring 54, only useful stopped.

When the pump 16 delivers the fuel towards the injection chamber 26, the chamber 12 is under pressure and the needle 14 is pressed against its seat 11. Meanwhile the piston 27 lifts and the volume of the chamber 35 increases, the piston 27 moving away from the end of the rod 37 of the needle.

The operation is analogous to that of the device of FIG. 1. When the valve 23 opens the pressure in the third chamber 12 drops and the needle lifts immediately until it comes abutment against the bottom of the chamber 12. The piston 27 is starts to descend from its high position and the fuel is ejected through line 29 and chamber 10. Towards the end of the descent of the piston 27 urged by the pressure prevailing in accumulator 28, piston 27 meets the end of the rod 37 and brings back the needle down in the closed position. Once the needle 14 applied against its seat 11, the rod 37 forms a stop for piston 27. Spring 54 is simply intended to ensure the closure of the needle 14 and the maintaining the piston in the minimum volume position of chamber 26 when, for example when the engine is stopped, the pressure in accumulator 28 has not yet been established.

We refer to Figure 10, which shows a device similar to that of FIG. 9, but in which the needle 14 has a second bearing sealing 62 which cooperates with a seat provided in the room 12 and prevents leaks likely to come from of accumulator 28 by the clearance between needle 14 and the nozzle body 7.

The device of FIG. 11 is analogous to that of FIG. 9 except for the fact that the piston 27 abuts on a seat 33 in the injection chamber 26 after putting needle 14 in compression. In this case a short stroke spring 13 is shown in the chamber 12 so as to press the needle 14 onto its seat 11, even in the case where, the accumulator 28 is not under pressure, the piston 27 is not stressed. In this embodiment, length and diameter of the rod 37 are chosen so that the needle 14 is applied against its seat 11 by the piston 27 shortly before that it has reached its stop position 33, the rest of the needle descent being authorized by deformation under compressive stress of the rod 37.

The embodiment of Figure 12 is similar to that of Figure 5 except that the needle 14 is closed, as on the Figure 9, by the impact of the injection piston 50 on the stop 56 presented by the needle.

We now refer to Figure 13.

In this embodiment, well suited at high fuel introduction rates, the nozzle, injection chamber and its movable element, and the pump generating the high pressure are coaxially aligned on the axis of the nozzle 7.

The piston 18 of the pump slides in a cylindrical chamber 17 defined inside the element mobile 65 with differential piston recalled in direction injection by the elastic return means constituted by the pressurized fluid 35, for example air, in communication with an accumulator 36. Communication between the arrival of low pressure fluid by the valve at two channels 23 and the pump chamber 17 takes place at through a radial passage in the movable element 34 and communicating with the valve 23 via of a longitudinal light formed in the surface of the movable element 65.

The injection chamber 26 is arranged under the movable piston 65 and we see its end stop race 33. The conduit 31 making it possible to communicate the pump 16 and the chamber 26 is an axial duct which runs in an extension 43 which exceeds, towards nozzle, beyond the active piston surface of the Exhibit 65 which delimits room 26 and which presents, at its free end, a radial notch 44. A valve unidirectional 32 sealingly sliding on said extension 43 and normally applied against the face nozzle 7 by a spring such as, for example, a belleville washer. When this valve lifts the channel 31 puts the pump 16 in communication with the chamber 26. We finally see that the needle 14, which is represented in the figure in its raised position, presents its upper end with respect to a volume 12 located under the end of the extension 43 containing the channel 31, volume also delimited by the valve 32 when it is in its closed position.

During the scanning phase the cam 20 is in a position which allows the pump piston 18 to lift and suck fuel from the source low pressure 24 through valve 23 in position of communication so that the pump chamber 17 fill.

After a certain time, the cam 20 having turned, the piston 18 will move down. Has a instant t during this downward movement we close the two-way valve 23. The fuel present in the pump will then be pressurized so that the valve 32 lifts against its return means and that the fuel pressurized in the pump is transferred to room 26, so the room mobile 65 lifts and the volume of chamber 26 increases, while high pressure is established in chamber 10, as well as in volume 12 located above of needle 14 through which the fuel gaining chamber 26. Needle 14 remains therefore strongly applied to its seat.

At time t + Δt the valve 23 is opened. consequently the pressure drops immediately in the pump 16 and in the volume into which the channel 31 opens and which communicates with the third bedroom 12. At this time needle 14 lifts due to pressure existing in the second bedroom 10 until coming in stop as in the injection position shown on Figure 6 in which the volume of the chamber 12 is become minimum. The elastic return means 35, 36 push the movable element 65 down and push back the fuel from the injection chamber 26 to the second chamber 10 from which it is expelled through the orifices 9 and sprayed.

Towards the end of its descent the piston 65 comes from the lower end of its end piece 43, make contact with needle 14 in its position raised shown in the figure. The pursuit of lowering of the moving part 65 then drives the needle 14 down until it is applied to its seat, which allows a sudden closure of the needle while the pressure in chamber 10 remains still at its high value, so that we get a end of injection of excellent quality. Once the needle 14 arrived at the stop, the moving part 65 goes down again slightly down, thanks to elastic compression of its extension 43 containing the channel 31 then stops definitively by contacting the stop 33.

We understand that in this embodiment, very advantageous when you have compressed air, no return spring for needle 14 is necessary since the needle is applied to its seat by the elastic tension existing in the extension 43 of the piece 65 itself firmly applied against its seat 33 by the pressure of the means 35, 36.

Furthermore, the device shown is particularly compact and fuel paths at the outlet of the pump 16 are particularly reduced, which minimizes the influence of the compressibility of the fuel on the accuracy of the injected dose and also allows, in the case of an engine with several cylinders, to provide injection devices practically identical and therefore delivering doses practically identical in each cylinder, including during diets where only very small doses are injected.

We now refer to Figure 14.

In this figure, two of the four injectors 6, of a device according to the invention designed for a four-cylinder engine. These injectors 6 are, for example, identical to that of FIG. 1. The piston 27 of each injector delimits, by its other wall, a recall chamber 38. All of the booster 38 are connected directly to a single accumulator high pressure liquid fuel 39.

Furthermore, the device includes a pump common distributor 40 actuated by a motor shaft.

The pump 40 is of a conventional type for multi-cylinder engine injection devices and therefore does not need to be described. It includes a rotor 41 with four radial pistons 42 sliding in the pump cylinders 57 in which they move during the rotation of the rotor, under the effect of a cam fixed 58 whose known profile is determined by the number cylinders and therefore injectors 6. The lower part of the rotor forms a distributor 59 capable of sending pressurized liquid fuel successively to the different injectors 6 by conduits 60 which replace the conduits 25 in FIG. 1 and terminate to the conduit 30 of the different injectors. Otherwise, the pump chamber 57 communicates permanently with a central duct 61 connected to a fuel source low pressure 24 through a two-way valve positions 23, and in parallel, of a conduit 63 with a one-way valve 64.

This pump 40 can also be used to maintain the high pressure in the accumulator 39, through a set communicating with the conduit 61 and comprising a unidirectional means 46 and a conventional pressure control valve 47 for such accumulators, and connected to the accumulator by a conduit 45.

Note that these centralized means of maintaining the pressure in the accumulator 39 will draw a minimal equivalent amount of fuel and balanced on the injection of each cylinder.

During operation, the pump 40 rotates with the engine. The control of valve 23 makes it possible to address successively to each of the injectors 6 a quantity metered fuel which reaches via line 60 and the one-way valve 32 to the injection chamber 26 of the injector. Each injector works as in the case of the device shown in Figures 1 to 4.

We therefore understand that we can, using a single simple two-way valve, ensuring one way extremely precise injection control in each of the cylinders, using only one dispensing dosing pump 40 and a single return means elastic 39. In addition, the injection is carried out with constant characteristics from one cylinder to another since the injection chambers 26 are nearby immediate of the second cavities 10 and that the conduits 60 can be easily designed to have volume identical internals.

Of course, the means of metering and ordering the needles described above can also be applied to this case from a centralized device for several cylinders.

In particular we can provide for replacement of valve 23 by the rotary distributor and using the return of the pump pistons to open injectors. The injection advance will then be set by the angular position of the cams 58 of the pump 40 in a manner known per se.

We refer to Figure 3. To ensure a temporal flow profile during injection with a low-flow initial injection portion followed by high-flow injection, there is provision in line 29 a nozzle or throttling member 65 which limits the flow through this communication to the value maximum flow rate desired for injection.

A second nozzle 66 is arranged in the shutter needle lever control line 30 14.

At the start of injection the rapid increase in fuel pressure from the chamber injection is communicated to the nozzle cavity 10 and raises the needle 14. This lifting is however not instantaneous because the nozzle 66 slows the evacuation of the fuel from chamber 12 located above the needle, so it takes a while to reach the fully open stop position. In due to nozzle 65, the flow ultimately injected during the entire rise of the needle, which causes an increase volume of cavity 10 is equal to the regulated flow via communication 29 minus the required speed increase in volume of the cavity 10. A times the needle in the stop position this last flow is canceled and all nominal flow through communication 29 is discharged through the injection nozzle 9.

You can also make the nozzle needle lift braking in the form of a variable section 67, the section being modified during the progression of the lifting of the needle 14, which allows to obtain, at the start of injection, any desired flow.

Of course the nozzles 65 and / or 66, 67 could be functionally replaced by a adequate dimensioning (diameter and length, and by pressure loss consequence), lines 29 and 30.

Claims (34)

1. Device for the discontinuous and cyclic injection of atomized liquid fuel at high pressure into a combustion chamber (3) of an internal combustion engine with variable-volume working chamber, which includes,

   an injection nozzle (7) comprising, for each working chamber :

   · a nozzle cavity (10, 34) which communicates with the combustion chamber via at least one injection orifice (9),

   · shut-off means (14) allowing the communication between the said nozzle cavity (10, 34) and the said combustion chamber (3) to be interrupted and re-established cyclically,

   and means (16, 40) of delivering liquid fuel under high pressure, these means being capable cyclically of delivering a metered amount of liquid fuel under high pressure,

   the said delivery means (16, 40) communicating, via cyclic-communication means, with a variable-volume injection chamber (26, 34) delimited by one wall of a moving element (27,50,65) returned , at each cycle, by elastic return means (28, 36, 39) towards a fixed stop (33, 37, 56) establishing the minimum value of the said variable volume of the said injection chamber, and which permanently communicates with the said nozzle cavity (10, 34), the said injection chamber being intended temporarily to receive the said metered amount of liquid fuel, an injection chamber (26, 34) being provided for each working chamber,

   the said metered amount of liquid fuel being delivered cyclically by the said delivery means (16, 40) into the said injection chamber during the phase of cyclic closure of the said means (14) of shutting off the injection nozzle,

   characterized in that the said elastic return means comprise a volume of fluid under pressure, acting on the said moving element.
2. Device according to Claim 1, characterized in that the said elastic return means (28, 36, 39) comprise an accumulator of fluid under pressure.
3. Device according, to either of Claims 1 and 2, characterized in that the said moving wall is formed by a plunger (27, 50, 65) sliding in a cylinder.
4. Device according to one of Claims 1 to 3, characterized in that the said nozzle cavity and the said injection chamber constitute a single chamber (34).
5. Device according to Claims 2 to 4, characterized in that the said plunger (50) is a hollow plunger capable of sliding around part (48) of the said shut-off means (14).
6. Device according to one of Claims 1 to 5, characterized in that the said elastic means (28, 36, 39) of returning the said moving element (27, 50, 65) push the moving element back with a force which is substantially constant throughout the ejection of the dose of fuel contained in the said injection chamber (26, 34).
7. Device according to one of Claims 1 to 6, characterized in that, in order to vary the flow rate of fuel injected, it comprises restriction means (65) so that the volume displaced by the shut-off means (14) as it opens reduces the rate of delivery into the chamber at the start of injection, normal delivery rate being reached when the shut-off means (14) reach the fixed stop position.
8. Device according to Claim 7, characterized in that it comprises constant- or variable-restriction means (66, 67) on a passage (30) connected to a chamber (12) for controlling the shut-off means (14), so as to control the rate at which the said shut-off means lift.
9. Device according to either of Claims 7 and 8, characterized in that the said moving element (27, 65) interacts with a stop (33) which acts as a sealing seat limiting leaks between the said injection chamber and the said pressurized return fluid.
10. Device according to one of Claims 2 to 9, characterized in that the said fluid under high pressure contained in an accumulator (28, 36, 39) at substantially constant pressure is liquid fuel.
11. Device according to one of Claims 1 to 8, characterized in that the means (14) of shutting off the nozzle are sensitive to a difference in pressure between the said nozzle cavity (10, 34) and a control cavity (12).
12. Device according to one of Claims 1 to 10, characterized in that the said shut-off means (14) are controlled by electromagnetic means.
13. Device according to one of Claims 1 to 12, characterized in that the said shut-off means (14) are sensitive, for closing them, to a return spring (13).
14. Device according to one of Claims 1 to 13, characterized in that the said shut-off means (14) are sensitive, for closing them, to the action of a fluid under pressure, especially liquid fuel.
15. Device according to one of Claims 1 to 13, characterized in that the said shut-off means (14) are sensitive, for closing them, to the action of the said moving element (27, 50) in such a way that when the moving element (43) regains its against-the-stop position, it displaces the shut-off means (14) towards a sealing position.
16. Device according to Claim 15, characterized in that the said fixed stop (37, 56) for the moving element (27, 50) consists of the said shut-off means (14) in their closed position.
17. Device according to Claim 15, characterized in that the moving element (27, 50) compresses the said shut-off means (14) onto their seat (11) before it reaches its stop (33).
18. Device according to one of Claims 1 to 17, characterized in that the said means for delivering liquid fuel under high pressure include a plunger-type pump (16, 40) actuated by a shaft driven by the engine.
19. Device according to Claim 18, characterized in that the said pump is a metering pump, especially of the type having a helical discharge ramp and plunger angular-position adjustment.
20. Device according to one of Claims 1 to 19, characterized in that the said means of cyclic communication which are arranged between the said means (16, 40) for delivering liquid fuel under high pressure and the said variable-volume injection chamber (26, 34) include a one-way communication means (32).
21. Device according to Claim 20, characterized in that the said cyclic communication means include a valve (23) arranged upstream of the said one-way means (32) and arranged in such a way as to place the said means of establishing high pressure in communication with a low-pressure discharge (24) therefore causing the said one-way means to close so that the said metered amount of fuel is determined by the stroke travelled by the pump plunger during the time taken for the said valve (23) to close.
22. Device according to Claim 21, characterized in that the said valve (23) is a two-way valve.
23. Device according to Claim 14, taken in isolation or in combination with one of Claims 17 to 21, characterized in that a cavity (12) containing liquid fuel, to which fuel the said shut-off means (14) are sensitive for closing them, can be placed in communication with a discharge (24) by means of a valve (23, 52) so as to allow the said shut-off means to open.
24. Device according to Claims 21 to 23, characterized in that the same valve (23) controls the connection-to-discharge (24) of the said means (16) of establishing high pressure and of the said cavity (12) containing the liquid fuel acting, for the closed position, on the said shut-off means (14), so that when the said valve is closed, the said delivery means deliver the liquid fuel under high pressure to the said injection chamber (26) through the said one-way communication means (32), whereas opening the said valve brings about the end of the said delivery and, at the same time, allows the said shut-off means to open until they reach their stop and allows the fuel to be injected into the combustion chamber.
25. Device according to Claim 23, characterized in that the said cavity (12) containing the liquid fuel acting, for the closed position, on the said shut-off means (14) is in communication with a volume (28, 35) containing fuel under pressure acting as a means for elastically returning the said moving element (50).
26. Device according to Claim 25, characterized in that the said chamber (12) containing liquid fuel, to which fuel the said shut-off means (14) are sensitive for controlling them, can be connected to a discharge (24) via a second valve (52), and in that the communication of the said chamber (12) with the said volume (35, 28) of liquid fuel under pressure is by means of a restriction.
27. Device according to Claim 24, characterized in that the profile of the cam acting on the plunger has a flat part allowing the pressure in the said cavity (12), to which pressure the said shut-off means are sensitive, to be sustained so that the instant at which the said valve opens, and therefore the moment of injection, can be chosen to lie on the flat part of the cam while at the same time being offset from the end of filling of the said injection chamber.
28. Device according to Claim 10, alone or in combination with any one of Claims 11 to 27, in which the means of establishing high pressure comprise a plunger-type pump, characterized in that the shut-off means are sensitive, for opening them, to the pressure drop brought about by the downstroke of the plunger of the pump for establishing high pressure.
29. Device according to one of Claims 1 to 28, characterized in that the said injector and the said injection chamber (26, 34) are aligned coaxially.
30. Device according to Claim 29, characterized in that the said means (16) of establishing high pressure is aligned coaxially with the injector.
31. Device according to one of Claims 1 to 30, characterized in that it includes, for an engine having a number of working chambers, a number of injection nozzles (6) and unique and centralized means (40) for delivering and metering liquid fuel under high pressure, these means being connected separately to each nozzle by a substantially identical specific pipe (60), the said means of establishing high pressure being arranged to send liquid fuel under high pressure to the said nozzles in succession.
32. Device according to Claim 31, characterized in that the said elastic means of returning the said moving elements (27) comprise a common accumulator (39) containing liquid fuel placed under high pressure and acting on the said moving elements (27).
33. Device according to Claim 32, characterized in that the said unique and centralized means (40) of delivering liquid fuel under high pressure are connected to the said accumulator (39) so as to sustain the high pressure in the abovementioned accumulator by means of a pressure regulator and a one-way means.
34. Device according to one of Claims 32 and 33, characterized in that the said means (40) of establishing high pressure consist of a unique pump (40) associated with distributor means (59) and in that the said pump is connected to a low-pressure feed means by a valve (23) which ensures that all of the injectors of the device operate in succession.

Images