FR2497876A1 - FUEL INJECTION DEVICE AND METHOD FOR INTERNAL COMBUSTION ENGINE - Google Patents

Abstract

1. A fuel injection arrangement for an internal combustion engine comprising : an injection chamber (5) which is closed by a needle subjected to the force of a closure spring and the pressure in a discharge chamber (9) ; a control system (12) having two differential pistons which are fixed with respect to each other and comprising : - a delivery piston (13) delimiting a metering chamber (14) communicating with the injection chamber (5) and supplied with fuel at an intermediate feed pressure ; - a control piston (16) which is larger in section than the delivery piston (13), delimiting a control chamber (17) which can be subjected to a high control pressure by means of a three-way electrically operated valve system ; and - control means for discharging the discharge chamber (9) when the metered amount of fuel has been subjected to the injection pressure by the action of the high control pressure on the control piston (16) ; the dimensions of said discharge chamber (9) and the characteristics of the injector (1) being such that prior to injection the needle (2) remains in the closure position, when the injection chamber (5) is at the injection pressure obtaining in the metering chamber (14), the high control pressure being applied to the control piston (16) and the discharge chamber (9) being subjected to the control pressure ; the section (Sd ) of the discharge chamber (9) where the control pressure occurs and the closure spring (10) of the injector being such that the forces which result therefrom tending to hold the needle in the closure position are greater thant the force tending to open the needle and resulting from the action of the injection pressure in the metering chamber (14), the arrangement being characterised in that the control means for discharging the discharge chamber (9) comprise a sliding spool-type distributor (51) which is pilot-controlled by the high control pressure and by the pressure obtaining in the metering chamber (14) and that the spool of the distributor (51) is subjected on the one hand to the action of the high control pressure obtaining in a first pilot-control chamber (58) and on the other hand to the action of the pressure obtaining in a second pilot-control chamber (59), the second chamber communicating with a lower passage (66) opening into the metering chamber (14) and being capable of being closed by the delivery piston (13) and with an upper passage (67) communicating with the low pressure of the tank and being capable of being closed by the delivery piston (13), on of the said two passages being opened irrespective of the position of the delivery piston (13).

Description

Fuel injection device and method for engine

internal combustion.

  The present invention relates to a device and a fuel injection method for an internal combustion engine, in particular for a diesel engine, allowing both a pre-dose of the quantity of fuel injected per cylinder and an amplification of the injection pressure. . The control of the injection device can be done

  easy by electronic means.

  Fuel injection at constant pressure, especially

  In diesel engines, it requires the presence of high-pressure fuel around the injection needle in order to obtain a high injection pressure as soon as the needle is opened. This high pressure around the needle at the closure of the injector leads to a risk of parasitic injections due to bounce phenomena of the needle of the injector. Moreover, in the constant pressure injection systems, difficulties are encountered in developing a single control member for the servo control pressure of the injection needle, which is fast enough to ensure good regularity in the movements of the needle of the injector for the small quantities of fuel injected. It is also necessary to provide, in the constant pressure injection systems, a flow limiting device in order to avoid any fuel influx into the combustion chamber in the event of failure.

of the injector.

  When the injection system comprises means for pre-dosing with pressure amplification by means of a differential piston, it can be seen that the injection pressure is a function, for the small loads, of the quantity injected, because of the response time. control pistons and

  delivery of the fuel into the injector.

  The present invention relates to a device and a fuel injection method which eliminates these disadvantages and which combines the advantages of constant pressure injection and pre-dosed injection. Thus, in the injection device according to the invention, the fuel to be injected is subjected to the high pressure around the needle of the injector which is controlled by a piston which can be subjected to high pressure. of a control fluid. According to the invention, the pre-dosing of

  the quantity of fuel to be injected, which allows the determination

  nation with high accuracy of this amount of fuel at low pressure. Finally, the pre-dosed fuel is subject to

  pressure increase with pressure amplification allows

  so much to get a high injection pressure from a

average control pressure.

  The fuel injection device for an internal combustion engine according to the invention comprises an injection chamber closed by an injector needle. The injector is subjected to the action of a closing spring and the action of a hydraulic fluid pressure prevailing in a chamber called discharge chamber. These two actions are added in order to

  solicit the needle of the injector towards its posi-

  closure in contact with its seat. According to the invention

  the injection device comprises a system of

  with two differential pistons integral with each other.

  A delivery piston defines a metering chamber in communication with the injection chamber of the injector and

  supplied with fuel at an intermediate pressure or

  feeding. In addition, a control piston of

  higher than that of the discharge piston, constituting the second part of the differential piston system, delimits a control chamber which can be subjected to a high

  control pressure through an electrical system.

  three-way trovanne, this high pressure being greater than the aforementioned intermediate feeding pressure. The device further comprises control means for discharging, that is to say placing at zero pressure or low pressure, the discharge chamber whose pressure acts on the needle of

  the injector, when the quantity of fuel dosed is

  in the dosing chamber was subjected to the injection pressure by the action of the high control pressure on

  the control piston delimiting the control chamber.

  The discharge chamber whose pressure acts on the

  guille of the injector is subjected before the injection phase to the action of the high pressure of the control. According to the invention, the dimensions of the discharge chamber as well as the characteristics of the injector are such that the needle remains on its seat in the closed position when the

  injection chamber is at the injection pressure

  in the dosing chamber. This situation arises when the high control pressure is exerted on the piston

  control unit delimiting the control chamber.

  The injection chamber can also be discharged, that is to say connected to the zero pressure of a hydraulic fluid reservoir, via an uncovered passage

  by the displacement of the differential piston control system

  tiel and in particular in the position corresponding to the end of

the injection phase.

  In a first embodiment of the invention, the control means making it possible to put in communication the

  discharge chamber with the tank include an elec-

  three-way trovanne. An adjustable restriction is

  interposed between the discharge chamber and the electricity

three-way trovanne mentioned above.

  In the other embodiment more particularly adapted to the case where the quantity of fuel injected is greater, the control means for connecting the discharge chamber to the reservoir comprises a slide valve controlled by the high control pressure and by the

  pressure prevailing in the dosing chamber.

  In general, the fuel injection process

  rant according to the invention consists in operating successively in the following manner. First, the needle of the injector is held in the closed position by the action of the high

  control pressure. Meanwhile, we fill up with

  a dosing chamber at a lower intermediate pressure

  above the high pressure of control, and the fuel is

  thus predisposed content in the dosing chamber has a

  pressure amplification Up to the injection pressure.

  The action of the high pressure of com-

  the needle of the injector, allowing the needle to move to the open position and injecting

  the amount of fuel pre-dosed at the injection pressure.

  Finally, the injection chamber is discharged so as to facilitate the movement of the needle to its position of

closing.

  The invention will be better understood when studying the description of

  detail of two preferred embodiments made from the attached drawings, in which:

  figs. 1 to 5 illustrate different phases of the

  tioning a first embodiment of the invention from a hydraulic diagram; and

  figs. 6-9 illustrate the same phases of

  for a variant represented in the form of a second

hydraulic diagram.

  As illustrated in FIG. 1, the injection device according to the invention comprises an injector 1 provided with an injection needle 2 capable of coming into contact with

  seat 3 in order to close the passage towards the orifices of

  jection 4. An injection chamber 5 surrounds the needle

  injection 2 and allows the supply of fuel injection

  b. The needle 2 of the injector 1 is secured to a pusher

  6 through a larger diameter part 7.

  The end of the pusher 6 opposite the needle 2 acts on a control piston 8 delimiting a discharge chamber 9. A compression spring 10 also acts via the shoulder 11 on the needle 2 in the meaning tending to close

  the passage to the injection ports 4.

  A control system 12 with two differential pistons secured to each other is mounted on the injector holder

  not shown in the figure. The control system 12 com-

  takes a discharge piston 13 of section Sr delimiting a metering chamber 14. The piston 13 is integral with a rod 15 which acts at the bottom of a control piston 16 of section Sc greater than the section Sr of the piston of discharge 13. The control piston 16 delimits a control chamber 17. A slide valve 18 comprises a slide with two portions 19 and 20 of larger diameter connected by a rod 21 which moves in a body having three chambers 22, 23 and 24 delimited by bearings of the bore of said

  body. In addition, two end chambers 25 and 26 can

  be subjected to pressure acting on one or

  The other end of the dispenser drawer 18.

  Compression fate 27 is mounted in the end chamber 25. The fuel, for example gas oil in the case of a diesel engine, is at atmospheric pressure in the tank 28. It is sucked by a low pump pressure 29 providing a pressure kept constant by the regulator

  mounted between the outlet of the pump 29 and the return to the

  see 28. A high pressure pump 31 is force-fed by the low pressure pump 29 and puts the fuel at high pressure

  constant Pc which can reach 200 bars and which is the

  order. The control pressure is maintained

  aunt by two regulating devices placed in series 32 and 33 between the output of the high pressure pump 31 and the return to the tank 28. The constant pressure occurring between the two regulators 32 and 33 is an intermediate pressure Pg called gavage pressure lower than the high pressure control Pc. The fuel at the booster pressure can therefore

  enter through a damping nozzle 34 and a check valve

  return 35 mounted in line 36 to the part

bottom of the dosing chamber 14.

  The fuel at the high-pressure control Pc feeds via line 37 a hydraulic accumulator 38, the chamber 22 of the slide valve 18 and the end chamber 26 of the same distributor via a three-way solenoid valve. 39 mounted in the bypass line 40. The high-pressure fuel can pass from the chamber 22 in the chamber 23 according to the position of the slide and feed through the pipe 41, the control chamber 17 of the

  control system 12 with a differential piston.

  The fuel at the high pressure control P is

  line 42 to a second electro-

  three-way valve 43 connected by an adjustable nozzle 44 to the

  discharge chamber 9 of the injector 1.

  The lower part of the metering chamber 14 is connected by

  the pipe 45, 46 to the injection chamber 5.

  The end chamber 27 of the distributor 18 is connected by the line 47 to the line 48 back to the

  28. The same is true of Chamber 24 of the

  scorer 18 via a damping nozzle 49.

  The rod side of the control piston 16 is also connected by the pipe 48a, 48 to the reservoir 28. It is the same on the rod side of the pilot piston 8 of the injector 1 by the

  channel 8a as well as the third channel of the two elec-

  three-way trovannes 39 and 43 through the lines 48 and 43a. The bore inside which the discharge piston 13 can move has in its lower part an opening communicating with the pipe 45 and in its upper part

  an opening communicating with a pipe 50. The

  these two openings is such that in the rest position,

  the discharge piston 13 discovers the opening of the

  50 and 50 closes the opening of the pipe 45. The two pipes 45 and 50 are connected to the injection chamber 5. In the rest position, the pipe 50 and thus the injection chamber 5 are in communication with the rod side of the control piston 16 that is to say with

  the low pressure of the fluid reservoir 28 through

  of the return line 48a, 48.

  Fig. 1 just described illustrates the position

  different elements of the injection device according to the in-

  vention during the rest phase. The different phases of operation will now be described with reference to the

Fig. 2-5.

  In all these figures where the identical elements bear the same references, the passage of the fuel through the two solenoid valves 39 and 43 is shown schematically by the black triangles which correspond to the opening position making two channels communicate respective solenoid valves. In the rest position as shown in FIG. 1, the three-way solenoid valve 39 allows the fuel to enter the high control pressure Pc in the lower chamber 26 of the distributor 18 whose upper face bears on the compression spring 27. The latter is chosen so that that the force developed by the high control pressure Pc in the lower chamber 26 is greater than that of the spring. The dispenser slide 18 is thus moved in a position such that it allows communication between the chambers 22 and 23 as shown in FIG. 1. The control chamber 17 is filled with fuel at the

  high pressure control P through the can

  41. The delivery chamber 14 has a minimum volume, the discharge piston 13 filling it almost completely in view of the low position of the delivery system.

differential piston 12.

  Still in this rest position, the three-way solenoid valve 43 is controlled so as to subject the discharge chamber 9 to the high control pressure Pc through the nozzle 44 so that the needle 2 of the injector 1 is

kept in closed position.

  Fig. 2 illustrates the pre-dosing phase of the fuel to be injected. The solenoid valve 39 is controlled so as to

  communicating the chamber 26 of the distributor 18 with the canali-

  48 under the action of the spring 27, the dispenser spool 18 thus moves so as to

  connect rooms 23 and 24, which also

  in communication through the nozzle 49 the

  control chamber 17 with the tank 28 through

41 and 48.

  The metering chamber 14 is subjected to the booster pressure P. When the pressure in the control chamber 17 reaches a value below P x Sr / Sc, the differential piston system 12 is returned under the effect of the pressure. Pg feeding in the chamber 14. Fuel therefore enters the metering chamber 14 from the pipe 36. During this phase, the nozzles 49 and 34 allow to damp the movement of the differential piston system 12

to avoid any oscillation.

  In this phase, the three-way solenoid valve 43 remains in the initial position, the high control pressure P thus prevailing in the discharge chamber 9 which maintains

  the needle 2 of the injector 1 in the closed position.

  Fig. 3 illustrates the accumulation phase. When the amount of fuel corresponding to that which it is desired to inject has entered the metering chamber 14, the supply voltage of the solenoid valve 39 is cut off as illustrated in FIG. 3. The high pressure control PC

  penetrates again into the end chamber 26 of the

  18, which moves to communicate the chambers 22 and 23 again subjecting the control chamber 17 to the high control pressure Pc via the pipe 41. The amount of pre-measured fuel in the chamber assay 14 is therefore put at an amplified injection pressure equal to the pressure Pr = Pc x Sc / Sr. Fuel can not flow to Injector 1 since the high control pressure

  PC still reigns in the discharge chamber 9, the electro-

  valve 43 remaining in the initial position. The fuel is

  located in the accumulator 38 facilitates the replacement

  pleating of the control chamber 17 despite an instantiated

tantané important.

  The dimensions of the discharge chamber 9 are chosen so that its section Sd and the structure of the injector

  and in particular the strength of the spring 10 are such that the

  2 remains in the closed position even when the

  injection chamber 5 is subject to the pressure of in-

  Then, it is sufficient that the following inequality be obtained: P x Sd + Fr> Pr (Sa-Ss) where F is the force developed by the spring 10, Sa is the section of the portion 7 and Ss is the section of the portion of

  the needle 2 in contact with its seat 3.

  Fig. 4 illustrates the injection phase. The solenoid valve 39 remains in the position shown in FIG. 3. According to the setting required by the operation of the heat engine, it is turned on at a precise instant the solenoid valve 43 so as to control it to communicate the discharge chamber 9 via the adjustable nozzle 44 with the tank 28 via the pipe

  43a. When the pressure Pd prevailing in the chamber of de-

  load 9 drop from its initial value equal to the high pressure

  Pc to a value such that we have the rela-

  following: Pr (Sa Ss Fr> Pd x Sd,

  the needle 2 of the injector 1 is lifted and the injection

  mence at an injection pressure Pi which is equal to the pressure

  Prion Pr reigning in the metering chamber 14. Under the effect of the high control pressure Pc acting on the control piston 16, the delivery piston 13 delivers the amount of fuel pre-dosed in the metering chamber 14

  to the injection chamber 5 through the pipes 45 and 46.

  The variable nozzle 44 makes it possible to regulate the speed of the pressure drop in the discharge chamber 9 and thus to adjust the speed of the lifting movement of the needle 2

  the injector. An action on the restriction formed by the

  Stage 44 thus makes it possible to easily modify the injection law.

  Fig. 5 illustrates the phase corresponding to the end of

  injection. The two solenoid valves 39 and 43 remain

  in the positions shown in fig. 4. When the amount of pre-dosed fuel in the metering chamber 14 has been completely discharged, the underside of the delivery piston 13 closes the opening of the

  pipe 45 connecting the metering chamber 14 through

  The dimensions of the discharge piston 13 as well as the spacing of the openings communicating with the pipes 45 and 50 are such that at the same time the upper face of the piston of the piston

  discharge 13 discovers the orifice of the pipe 50

  putting pressure on the injection chamber

  5 to discharge through the lines 46, 50, 48a and 48 back to the reservoir 28. The needle 2 of the injector

  then closes under the effect of the setting spring 10.

  The power supply of the electro-

  three-way valve 43 which returns to the position shown in FIG. 1 allowing the high pressure Pc to recharge

  the discharge chamber 9. The various elements of the

  tif go back to the position shown in fig. 1.

  The variant which has just been described is more particularly

  adapted to an application that requires the injection of a minimum amount of fuel of about 6 mm3 per stroke which is the case for example for engines for light vehicles. In the case where it is necessary to inject at idle a larger amount of fuel (for example about 15 to 20 mm3 per stroke) that is to say for industrial vehicle engines, it is preferred to replace as illustrated on the fig. 6 the three-way solenoid valve 43 of the previous embodiment by a slide valve 51 controlled by the high pressure control Pc and by the pressure

  delivery valve Pr prevailing in the metering chamber 14.

  In this variant where the identical elements bear the same references, the slide of the distributor 51 comprises two portions of larger diameter 52 and 53 interconnected by a rod 54 and moves in a bore having three chambers 55, 56 and 57 delimited by ranges and two control chambers 58 and 59 for moving the drawer. The first control chamber 58 is connected to the high control pressure by the pipe 61 which is itself connected to the pipe 42. The pipe 60 also allows the fuel to be conveyed at high pressure.

  control unit Pc into the chamber 57.

  The chamber 55 is connected to the reservoir 28 via

  channel 62 which encloses a damping nozzle.

  Variable Restriction 63. Line 64 connects the

  chamber 56 to the discharge chamber 9 of the injector 1.

  The second control chamber 59 communicates via the pipe 65 with a low passage 66 opening into the metering chamber 14 and can be closed by the piston of

  repression 13 during its downward movement. The canal

  65 also communicates with a high passage 67 which communicates with the rod side of the control piston 16 and through the pipeline 48a and 48 with the reservoir 28. The passage 67 can be closed by the discharge piston 13 in its upward movement. . The spacing of the up and down passages 66 and 67 and the height of the piston 13 are chosen so that one of the two passages is always cleared.

  regardless of the position of the delivery piston.

  their, the orifices of the ducts 45 and 50 which connect the injection chamber 5 respectively to the metering chamber 14 and to the reservoir via the pipe 48a, are each offset downwards relative to the orifices of the low passages and 66 and 67. In this way, the orifices

  ducts 45 and 50 are closed by the pressure piston

  13 in its movement either upwards or downwards after the respective low and high passages 66 and 67. It is

  as well as in its downward movement, the piston of

  firstly closes the orifice communicating with the channel 66 of the low passage, then when it continues its

  movement downwards, the orifice communicating with the canali-

  45. In the same way, when the piston

  13 moves upward, first closing the door.

  Line 50 and the hole in the high passage 67.

  In the rest position shown in FIG. 6, the second control chamber 59 of the slide valve 51 is in communication with the low pressure of the reservoir of

  fluid 28 by the pipes 65 and 67 which make it

  48 in this position, the discharge piston 13 discovers the orifice of the upstream passage 67. The high control pressure Pc prevailing in the first control chamber 58 causes a

  moving the dispenser drawer 51 putting in communica-

  The high control pressure Pc from line 60 thus reigns through line 64 into discharge chamber 9. As a result, needle 2 of injector 1 is in the closed position. Fig. 7 illustrates the pre-dosing phase which is done as in the previous variant by a control action on the three-way solenoid valve 39. As previously, the opening of the solenoid valve 39 allows the movement of the dispenser drawer 18 and the filling from the metering chamber 14 to the feeding pressure Pg, the differential piston 12 moving upwards. During this phase, it will be noted that the second control chamber 59 is subjected to the feeding pressure Pg that prevails in the metering chamber 14 via the low passage 66 and the pipe 65. As previously, the quantity dosed at the end

  of this step in the metering chamber 14 is proportionally

  at the opening time of the solenoid valve 39.

  Fig. 8 illustrates the injection phase. As soon as

  trovanne 39 returns to its original position resulting in

  also the return to the rest position of the distribution drawer

  18, the high control pressure Pc is established in the control chamber 17. The pressure P which prevails in the metering chamber 14 increases gradually. As soon as this pressure becomes higher than the high control pressure Pc, the valve spool 51 is caused to move under the action of the upper pressure prevailing in the second pilot chamber 59. This movement illustrated in FIG. 8 communicates the chambers 55 and 56 of the slide valve 51. The pressure in the discharge chamber 9 can therefore fall via the pipes 64 and

62 and Variable Adjustment 63.

  Given the delay times of the different movable drawers of the distributor 51 and the distributor 18, the pressure

  Injection Pi = Pc x Sc / Sr is established before opening.

  needle 2 of the injector which moves as before under the action of this pressure prevailing in the

injection chamber 5.

  Fig. 9 illustrates the phase corresponding to the beginning of the end of the injection. In its downward movement, the piston 13 first discovers the high passage 67. At the same time it

  closes the low passage 66. At this moment the opening of the canali-

  50 is still closed while the opening of the pipe 45 is discovered allowing the continuation of the injection. The high control pressure Pc prevailing in the

  first pilot chamber 58 thus becomes again

  the pressure in the second pilot chamber 59 which is connected by the lines 48a and 48 to the reservoir 28. The distributor valve 51 moves

  so again towards his resting position putting in communica-

  chambers 56 and 57 and allowing the high pressure

  order to enter the test room again.

  9. This results in a complementary effort to

  ture of the needle 2 of the injector, an effort that is favorable to a very clear injection. When pursuing his

  downward movement the piston 13 then discovers the opening

  ture of the pipe 50 allowing the discharge of the injection chamber 5 and the displacement of the needle 2 towards

its closing position.

Claims (8)

  A fuel injection device for an internal combustion engine comprising: an injection chamber (5) closed by a needle subjected to the action of a closing spring and the pressure prevailing in a reaction chamber;   charge (9); a different two-piston control system   integral springs (12) comprising: - a delivery piston <13) delimiting a metering chamber (14) in communication with the injection chamber (5) and fed with fuel at an intermediate boosting pressure; a control piston (16) with a section greater than that of the discharge piston (13) delimiting a control chamber (17) which can be subjected to a high control pressure via a three-way solenoid valve system; channels; and control means for discharging the discharge chamber (9) when the metered fuel quantity has been subjected to the injection pressure by the action of the high control pressure on the control piston (16); characterized in that the dimensions of said discharge chamber (9) as well as the characteristics   of the injector (1) are such that before injection, the needle   (2) remains in the closed position, when the injection chamber (5) is at the injection pressure prevailing in the   metering chamber (14), the high control pressure is exerted   on the control piston (16) and the discharge chamber   (9) being subject to the control pressure.   2. Injection device according to claim 1, characterized in that the section (Sd) of the discharge chamber (9) exerts the control pressure and the closing spring (10) of the injector are such that the resulting faces tending to keep the needle in the closed position are greater than the force tending to open the needle and resulting from the action of the injection pressure in the dosing chamber (4).   Injection device according to claim 1 or   2, characterized in that the control means for   discharging the discharge chamber (9) comprise a distribution   slide scorer (51) controlled by the high control pressure and the pressure in the dosing chamber (14). 4. Injection device according to claim 3, characterized in that the valve spool (51) is subjected firstly to the action of the high control pressure in a first control chamber (58) and secondly to the action of the pressure in a second control chamber (59), the second chamber communicating with a low passage (66) opening into the metering chamber (14) and can be closed by the piston of discharge (13) and with a high passage (67) communicating with the reservoir and can be closed by the discharge piston (13), one of the two aforementioned passages being clear regardless of the   position of the discharge piston (13).   5. Injection device according to claim 4, characterized in that the orifices of the conduits (45, 50) connecting the injection chamber respectively to the metering chamber (14) and the discharge (28) are closed by the delivery piston (13) respectively after the high and aforementioned low (67, 66).   6. Injection device according to any one of   preceding claims, characterized in that the   injection chamber (5) can be unloaded via   of a passage (50) discovered by the control system   (12) with two differential pistons in the corresponding position laying at the end of the injection.   7. Device according to any one of the claims   preceding, characterized by the fact that the means of   to discharge the discharge chamber (9) comprise   a three-way solenoid valve (43) and a re-   movable (44) interposed between the discharge chamber (9) and   the three-way solenoid valve (43).   8. Fuel injection method for combustion engine   internal composition with pre-dosing, accumulation and amplification of pressure, characterized in that it comprises the following steps: the needle (2) of an injector (1) in an injection chamber (5) is kept closed; ) by the action of a high control pressure, while filling with   fuel a metering chamber (14) at a pressure   intermediate and then gradually subjecting the fuel thus predosed contained in the metering chamber (14) to an amplification of pressure up to the injection pressure; - the action of the high control pressure is suppressed   on the needle (2) of the injector, which allows the   of the needle (2) in the open position and the injection   the amount of fuel prddose to the injection pressure   tion; and the injection chamber (5) is discharged so as to facilitate the movement of the needle (2) in a closing manner.