EP0077716B1 - Time pressure injection device with predosage - Google Patents

Abstract

An electronically controlled device for premetered pressure-time injection using high injection pressure and low feed pressure, which include one source (5-6) of medium pressure (MP) which is intermediate the high and low pressures, a two-stage rotary distributor which cyclically distributes the high and low pressure into single piping systems for each cylinder, a plurality of injection nozzles wherein, in each injector nozzle (30), a metering piston is provided (8) whose delivery chamber (21) is connected to the single piping system, and an injector control piston (11) having a control chamber (31) which is connected, via a three-channel electrovalve (9), through a medium pressure channel for the purposes of initiating injection, and through a second channel to the injection chamber (22) for purposes of initiating metering.

Description

The invention relates to the direct injection of fuel into internal combustion engines, in particular diesel engines.

It is known that, for complete combustion and good efficiency of diesel engines, it is necessary that the injection of fuel is made at a constant and high pressure. To solve this problem, injection devices of the time pressure type with electromagnetic control are already known, but which are not without their drawbacks. Indeed, given the high injection rates required by modern engines due to the high rates of supercharging for the engines of industrial vehicles or the high rotation speeds for the engines of private cars, the time allocated to inject the quantities of fuel corresponding to low load or idle speed is very low and remains of the order of magnitude of the response time of the electromagnetic actuators used to operate the injector.

To avoid this difficulty, it is known to use for each injector two electromagnetic solenoid valves or servovalves, one being reserved for controlling the start of the injection and the other having the role of ensuring the end of the injection. These two control members perfectly perform the injection function but then have other drawbacks: firstly, the injector holder has a relatively large size making it difficult to mount in the engine cylinder heads, mainly on passenger car engines; second, the inevitable dispersion of response times leads to irregularities between the injector holders; Finally, the very design of the electromagnetic solenoid valves or servo-valves which must have a very low response time inevitably leads to leaks not at the seats but by the cylinder-piston games, leaks which have a very great influence on the quantity injected for the same order time.

To avoid these latter difficulties, it is also known to make kinds of hydraulic power stations linked to a distributor, in which the piloting part of the injector (electroservovalves) is common to several injectors, the injection functions being distributed to injector holders. If this design ensures uniformity of operation between several injectors, it has the disadvantage of giving rise to harmful hydraulic phenomena in the pipes connecting the control member for controlling the injection to the injector holders. In addition, due to the fact that the high injection pressure reigns permanently on the injector needles, any failure of the control entails the very significant risk of drowning the engine, which then leads to adding limiting devices to the device. debit.

The document EP-A-032 168 describes a pressure-time injection device with electromagnetic control using a high pressure and a low booster pressure, this device comprising a medium pressure source intermediate between said high and low pressures, a rotary distributor , and on each injector holder a metering piston whose injection chamber is connected to the needle capacity of the corresponding injector.

The document EP-A-0 024 115 relates to an injection device provided with a rotary distributor with two stages for controlling the start, the end and the duration of the fuel injection.

The object of the invention is to eliminate the above drawbacks by providing a pre-metering press.on-time injection device which isolates the high pressure of the pump from the injection pressure, allowing a pre-metering of the quantity injected. , avoiding most of the harmful hydraulic phenomena on the high pressure and on the control, and finally by using only one electromagnetic element per cylinder, the hydraulic circuit being designed in such a way that the inevitable leaks of this electromagnetic element do not affect the quantity injected.

The invention consists on the one hand, to provide in a manner known per se, the usual high injection pressure and low booster pressure, a medium pressure intermediate between the two preceding ones, and on each injector holder a metering piston with an injection chamber in connection with the capacity of the injector needle, and on the other hand, to use a double rotary distributor driven in synchronism with the camshaft and alternately distributing the high pressure and the low pressure in a single pipe for each injector; in connecting the delivery chamber of this metering piston with said single pipe, with, in a known manner, discharge passages for this needle capacity and for the control chamber of the needle at the end of the piston stroke ; finally to bring this control chamber together by a non-return valve at medium supply pressure and by a three-way solenoid valve alternately with medium pressure at the start of injection and with the metering chamber at the start of metering, the instant of the end of the metering being determined by the end of the distribution of the low pressure by the distributor, and the end of the injection being determined by the end of travel of the metering piston.

• la fig. 1 est un schéma général du dispositif;
• la fig. 2 est un schéma détaillé d'un injecteur et du porte-injecteur; et
• les fig. 3 à 8 sont des schémas partiels illustrant les diverses phases du fonctionnement.

Other features of the invention will appear in the following description of an embodiment taken as an example and shown in the attached drawing, in which:

• fig. 1 is a general diagram of the device;
• fig. 2 is a detailed diagram of an injector and the injector holder; and
• fig. 3 to 8 are illus partial diagrams trating the various phases of operation.

The device taken as an example corresponds to a four-cylinder engine, and it comprises a single distributor pump assembly corresponding to the box on the left in FIG. 1 designated by the reference EPD, this assembly being joined by four pipes Ci, C ₂ , C ₃ , C ₄ to four EPI injector holder assemblies, only one of which is shown in FIG. 1, and each corresponding to one of the cylinders.

The EPD distributor pump assembly comprises two pumps 2 and 4 rotating synchronously while being driven by the engine, either at engine speed, or at half speed like the camshaft. The fuel is sucked into the tank via a filter 1 by the booster pump 2. The discharge pressure of this booster pump, or BP pressure (5 to 10 bars) is regulated by the regulator 3. The fuel is then brought to high pressure HP (for example up to 1000 bars) by pump 4, this high pressure HP being regulated by regulator 5. Finally, between the outlet of regulator 5 and the return to the tank is interposed a third regulator 6 giving rise to an average pressure MP of the order of 30 to 40 bars.

The stator 40 of the distributor pump has a bore in which a rotor 41 can rotate at half the engine speed for a four-stroke engine or at the engine speed for a two-stroke engine. This rotor has two stages, namely a high pressure stage A and a low pressure stage B. The high pressure fuel HP penetrates axially into stage A and it is led by a radial bore 32 in a hole 33 of 15 to 20 ° of arc. The stator 40 is pierced with conduits 36, 37, 38 and 39 connected to the pipe Ci, the conduits 38 and 37 corresponding respectively to stages A and B. There are naturally three other series of similar bores corresponding to the three other connecting pipes C ₂ , C _s and C ₄ and distributed cyclically in the stator 40 in the usual feeding order _N 1-3-4-2cc.

The central bore of stage B is connected to the low pressure BP and radial conduits 34 distribute this pressure in a large light obscured over approximately 20 ° by the circular boss 35. The light 33 and the boss 35 are determined and wedged on the rotor 41 in such a way that, when the conduits 38, 39 and 36 are in communication with the HP, the latter cannot pass to the BP through the conduit 37, and only when the conduits 36 and 37 are in communication with the BP, conduit 38 cannot receive the HP.

• - dans un alésage 18 un piston 8 dont la face supérieure forme avec l'alésage 18 une chambre de refoulement 21 qui est reliée à l'arrivée haute pression par un conduit 29, correspondant à Ci, C₂, C₃ ou C₄ selon le cas, tandis que sa face inférieure forme une chambre de dosage et d'injection 22. Par ailleurs, le piston 8 est percé par des conduits 20a et 20b qui permettent, lorsque le piston est en position basse, c'est-à-dire pour le volume minimum de la chambre d'injection 22, de mettre respectivement la chambre 22 en communication avec un conduit 19 et le conduit 23 avec la moyenne pression 26 par les conduits 43 et 42.
• - Dans un alésage 17, un piston de commande 11 dont la face supérieure forme avec cet alésage une chambre de commande 31, la face inférieure du piston de commande 11 étant en appui sur un poussoir 13 dont l'autre extrémité s'appuie sur l'aiguille 14 de l'injecteur; la buse 15 et la cale de course 16 de cet injecteur sont fixées par des moyens connus au corps 30. L'injecteur 15 ainsi que son ressort 12 sont de type classique.
• - Une vanne 9 à trois voies à commande électromagnétique dont la voie commune est reliée par 24 à la chambre de commande 31, la première voie étant reliée par 28:
• - d'une part à la chambre d'injection 22, un clapet anti-retour 50 étant interposé sur la ligne de telle façon que le combustible ne puisse se diriger de la chambre d'injection 22 vers la première voie 28,
• - d'autre part à la chambre de refoulement 21, un clapet anti-retour 51 étant interposé sur la ligne de telle façon que le combustible ne puisse se diriger que de la chambre de refoulement 21 vers la première voie 28, un ajutage 52 étant par ailleurs placé en aval du clapet anti-retour 51, tandis que la deuxième voie, qui correspond à la position excitée de l'électrovanne, est reliée à l'arrivée 26 de la moyenne pression.
• - Un clapet anti-retour 10 permettant par les conduits 26, 25 puis 27 de remplir la chambre de commande 31 par le combustible à moyenne pression MP.
• - Enfin, le conduit 23 relie la chambre d'injection 22 à la capacité d'aiguille 7 tandis que le conduit 19 précité est relié à la chambre de commande 31 de telle manière que la fin de course d'injection du piston d'injection 8 produise la décharge de la capacité d'aiguille 7 vers la moyenne pression et de la décharge de la capacité d'injection 22 vers la chambre de commande 31 afin d'assurer une refermeture rapide de l'aiguille.

The EPI injector holder assembly comprises the injector 15 and the injector holder 30, shown in more detail in FIG. 2. It is arranged to receive:

• - In a bore 18 a piston 8 whose upper face forms with the bore 18 a discharge chamber 21 which is connected to the high pressure inlet by a conduit 29, corresponding to Ci, C ₂ , C ₃ or C ₄ according to the case, while its underside forms a metering and injection chamber 22. Furthermore, the piston 8 is pierced by conduits 20a and 20b which allow, when the piston is in the low position, that is to say say for the minimum volume of the injection chamber 22, to put the chamber 22 respectively in communication with a conduit 19 and the conduit 23 with the medium pressure 26 via the conduits 43 and 42.
• - In a bore 17, a control piston 11, the upper face of which forms with this bore a control chamber 31, the lower face of the control piston 11 being supported on a pusher 13, the other end of which rests on the needle 14 of the injector; the nozzle 15 and the stroke block 16 of this injector are fixed by known means to the body 30. The injector 15 and its spring 12 are of conventional type.
• - A three-way electromagnetic control valve 9, the common channel of which is connected by 24 to the control chamber 31, the first channel being connected by 28:
• on the one hand to the injection chamber 22, a non-return valve 50 being interposed on the line in such a way that the fuel cannot direct itself from the injection chamber 22 towards the first channel 28,
• - on the other hand to the discharge chamber 21, a non-return valve 51 being interposed on the line so that the fuel can only go from the discharge chamber 21 to the first channel 28, a nozzle 52 being also placed downstream of the non-return valve 51, while the second channel, which corresponds to the excited position of the solenoid valve, is connected to the inlet 26 of the medium pressure.
• - A non-return valve 10 allowing the conduits 26, 25 and then 27 to fill the control chamber 31 with the medium pressure fuel MP.
• - Finally, the conduit 23 connects the injection chamber 22 to the needle capacity 7 while the aforementioned conduit 19 is connected to the control chamber 31 so that the end of injection stroke of the injection piston 8 produces the discharge of the needle capacity 7 towards the medium pressure and the discharge of the injection capacity 22 towards the control chamber 31 in order to ensure rapid reclosing of the needle.

If we designate by Sc the section of the control chamber 31 and Pc the control pressure, and on the other hand Sa the needle section, Ss the section of its seat, Pi the injection pressure, and R the thrust of the spring 12, the movements of the assembly of the needle 14, of its plunger 13 and of the control piston 11 involve on the one hand a hydraulic lifting force of the needle, of value Pi. (Sa -Ss) directed upwards, and a control push Pc - Sc + R which is directed downwards.

The various parameters above are determined in such a way that the control thrust is much greater than the hydraulic lifting force when Pc = Pi = HP, and that this control thrust is much less than the hydraulic lifting force when Pc = MP and that Pi = HP.

Thanks to the large difference between HP and MP, this condition can be satisfied very easily with large safety coefficients and with the usual dimensions, with the pressure values indicated above.

The operation of the assembly, which is obviously cyclical, periodically includes injection phases, and pre-dosing phases interspersed with the previous ones.

At the end of the dosing, the edge X of the boss 35 of the low pressure stage B of the distributor closes the conduit 37, then the edge Z of the high pressure side A uncovers the conduit 38, allowing the high pressure HP by the conduits 39 and 36 to enter the discharge chamber 21, which, on the one hand, by means of the injection piston 8, puts the injection chamber 22 under identical pressure since the fuel cannot go from the chamber 22 to the control chamber 31 due to the non-return valve 50, and on the other hand puts under the same pressure the control chamber 31 by the conduit 53 and the solenoid valve 9 which is in the rest position and authorizes the communication between 28 and 24 (fig. 2). According to this schematic diagram, it can be seen that the internal leaks from the solenoid valve 9 do not modify the quantity supplied in the injection chamber 22 under high pressure since the non-return valve 50 is sealed and the fuel source which establishes the high pressure in the control chamber 31 is directly the HP pump 4 via the conduits 38, 39, 36, 29 and 53. A throttle 52 is judiciously placed on the line 53 downstream of the non-return valve 51 of such that the pressure prevailing upstream of the inlet 28 of the three-way solenoid valve 9 is always less than the pressure prevailing in the injection chamber 22 which leads the non-return valve 50 to always be closed as soon as pressurization of 21. The non-return valve 10 prevents this high pressure from discharging in the medium pressure, and the pipe 23 also transmits this high pressure to the needle capacity 7. This is therefore in the exposed case higher where the pressi ons at 22, 31 and 7 are equal to the high pressure and, as we have seen, the control thrust, much greater than the hydraulic lifting force of the needle, keeps it in contact with its seat. This is illustrated by the diagram in fig. 3.

At the desired time for injection, and according to an electronic synchronism determined with precision in accordance with the position of the engine, the solenoid valve 9 is energized which puts the conduits 24 and 26 into communication, allowing the high pressure prevailing in the control chamber 31 to drop to the level of the medium pressure. This new state is illustrated in fig. 4. We are therefore in the case described above where the medium pressure prevails at 31, and the high pressure at 7, and where, as we have seen, the control thrust becomes much less than the hydraulic lifting force , the latter then lifting the needle to allow fuel to be injected.

The quantity of fuel previously predosed in the injection chamber 22 is then discharged under the high pressure HP by the piston 8. Simultaneously, or with appropriate offsets, on the one hand the lower edge of the piston 8 closes the conduit 23 while the hole 20b puts the conduit 43 in communication with the medium pressure, and on the other hand the fuel remaining in the chamber 22 can be discharged into the control chamber 31 through the conduit 19 thanks to the hole 20a, which has for effect of ensuring a good rapid closure of the injector under the combined effect of its spring 12, of the pressure drop in 7 and of the pressure increase in 31, and at the same time of avoiding any rebound of the needle thanks to this recharging of the control chamber 31. This phase is illustrated in FIG. 5.

When the injection is complete, the solenoid valve 9 remaining energized, the edge W of the high pressure stage A of the distributor closes the conduit 38, then the edge Y of the low pressure stage B comes to clear the conduit 37, allowing the low pressure to prevail on the upper face of the corresponding piston 8. This being is illustrated by FIG. 6.

Under the conditions defined above, if the supply to the solenoid valve 9 is cut off, the latter returns to the rest position as illustrated in FIG. 7 by connecting the conduits 24 and 28; the medium pressure then enters the control chamber 31 by the non-return valve 10, then from there by the solenoid valve 9 into the injection chamber 22 by the non-return valve 50 with a throttle 44 and delivers the piston 8 upwards since the upper face of this piston is at low pressure BP; medium pressure cannot flow to low pressure due to the non-return valve51.

Thanks to the throttle 44, but above all to the low relative value of the pressure difference between MP and BP, the time during which this dosage must take place retains a relatively large value, even for low load regimes, which makes it possible to fine-tune by the electronic calculator which controls the injection.

On the other hand if it is the solenoid valve 9 which triggers the start of injection, it is stage B of the distributor which determines the end of the injection at the precise instant when the edge X comes to close off the conduit 37, as illustrated in FIG. 8, which interrupts the upward movement of the piston 8, therefore ends the metering in the injection chamber 22. The electronic computer, which is synchronized with the engine cycle, knows exactly when the conduit 37 is closed and can so accurately calculate the time of dosage.

The invention thus allows injection under very high pressure, perfectly constant and regulated, and precise pre-dosing while using for each cylinder only one solenoid valve, which opens and closes only once per cycle, serving both to trigger the start of injection and the start of dosing.

Claims (5)

1. An electromagnetically actuated premeter- ing-type pressure-time injection apparatus using a high injection pressure and a low feed pressure, of the type comprising a source (5-6) of medium pressure (MP) intermediate between said high and low pressures, a rotary distributor and, on each injector carrier (30), a metering piston (8) whose injection chamber (22) is connected to the needle chamber (7) of the corresponding injector (15), characterised in that:

- the rotary distributor is a two-stage distributor distributing the high and low pressure cyclically in dependence on the number of cylinders in single ducts (C_l to C₄) for each cylinder, without overlap of the high and low pressure communication times;

- the high pressure is the injection pressure;

- the discharge chamber (21) of the metering piston (8), which is opposite to the injection chamber (22), is in communication with said single duct (29) (C_i) of the corresponding cylinder;

- the control chamber (31) of a control piston (11) of the injector is connected on the one hand to the medium pressure by a nonreturn valve (10) disposed in the direction which permits the feed to said chamber and, on the other hand, by way of a three-way electromagnetically operated valve (9), by one way to the medium pressure, for the commencement of injection, and by the other way to the injection chamber (22) for the commencement of the metering operation; and

- an electronic device synchronised with the rotary movement of the distributor and the enginetriggers off the commencement of injection and the commencement of the metering operation, by way of the electromagnetically operated valve (9).

2. An injection apparatus according to claim 1 characterised in that the various parameters, section and calibration of the injector and said medium pressure (MP) are so determined that the control thrust tending to close the needle (14) of each injector is much greater than the hydraulic lift force of said needle when the high injection pressure obtains both in the injection chamber (7) and in the control chamber (31), and much less than said hydraulic lift force when the medium pressure obtains in the control chamber (31) and the high pressure in the needle chamber (7).

3. Apparatus according to one of the preceding claims characterised in that the hydraulic connection between said other way (28) of the electromagnetically operated valve (9) and said injection chamber (22) is made by way of a non- return valve (50) permitting a discharge flow from the valve (9) towards the injection chamber (22), and that there is also provide a hydraulic connection (53) between said discharge chamber (21) and said other way (28), comprising another non-returnvalve (51) which permits the discharge flow from the chamber (21) towards the valve (9), and a constriction means (53) which, upon said flow taking place, generates a pressure drop sufficient to hold the first non-return valve (50) closed and to make the premetered amount (22) intensitive to the internal leakage of the electromagnetically operated valve (9).

4. Apparatus according to one of the preceding claims characterised in that said metering piston (8) comprises passages (20a, 20b) cooperating with fixed conduits (42, 43. 29, 23) opening into its cylinder in order to ensure, at the end of the injection movement, discharge of the needle chamber (7) towards the medium pressure and discharge of the injection chamber (22) towards the control chamber (31).

5. An injection apparatus according to one of the preceding claims characterised in that the high pressure and the medium pressure are produced from a single pump (4) by means of a regulator (5-6) having two discharge stages.

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