FR2883044A1 - FUEL INJECTOR FOR INTERNAL COMBUSTION ENGINE - Google Patents

Abstract

Fuel injector comprising a housing (5, 7, 9) having a pressure chamber (12) filled with fuel and an outer sliding needle (16) cooperating with a valve seat (20) being controlled by passing fuel from the pressure chamber (12) to at least one external injection port (26). The outer needle (16) receives an inner needle (18) also cooperating with the valve seat (20) to control at least one inner injection port (28). The pressure in the outer control chamber (40) exerts on the inner needle (16) at least indirectly a closing force directed towards the valve seat (20), and the pressure in an inner control chamber (50). exerts a closing force on the inner needle (18) .In the outer control chamber (40) a piston (19), connected to the inner needle (18), has a thrust surface (23) subjected to the pressure in the control chamber (40) for exerting an opening force on the inner needle (18) facing away from the valve seat (20).

Description

Field of the invention

  The present invention relates to a fuel injector of an internal combustion engine comprising a housing which houses a fuel-filled pressure chamber and which receives, in longitudinal sliding, an external injector needle cooperating with a valve seat delimiting the pressure chamber and thus controlling the passage of fuel from the pressure chamber to at least one external injection port, and an inner needle housed in the outer needle of the injector, the inner needle also cooperating with the seat valve and thus controlling the passage of fuel from the pressure chamber to at least one inner injection port, and an outer control chamber whose pressure exerts at least indirectly on the outer needle a closing force directed towards the seat a valve and an internal control chamber whose pressure generates at least indirectly on the inner needle, a closing force directed towards the valve seat. STATE OF THE ART One such fuel injector is known, for example described in document DE 102 22 196 A1. This injector consists of a body or casing in which is formed a pressure chamber which fills with fuel. The pressure chamber houses an external injector needle cooperating with a valve seat delimiting the pressure chamber. This controls the fuel outlet from the pressure chamber to at least one external injection port located at the valve seat or in the valve seat. The outer needle of the injector is hollow needle-shaped surrounding an inner needle which also cooperates with a corresponding sealing surface with the valve seat. The inner needle thus controls the passage of fuel to another internal injection (or ejection) port and the fuel exiting through the injection ports arrives directly into the combustion chamber of the internal combustion engine. Both the outer needle and the inner needle of the injector slide in the longitudinal direction; by bearing against the valve seat, it closes the ejection ports and lifting the seat opens them.

  The longitudinal movement of the injector needles is controlled on the one hand by the application of the pressure on the pressure surfaces provided on both the outer needle and on the inner needle of the injector so that the pressure in the pressure chamber generates an opening force applied to the needles and away from the valve seat. These opening forces oppose the hydraulic forces: on the one hand by the fuel pressure in an external control chamber and on the other hand by the fuel pressure in an internal control chamber, the pressure of the chamber of external control acting on the outer needle of the injector and as a function of the pressure in the inner control chamber, on the inner needle of the injector. The fuel pressure in the inner or outer control chamber can be adjusted by appropriate dis-positives, which allows the ratio of the opening force to the closing force to be adjusted and corresponding movement of the injector needles .

  In the case of a known injector, the pressure in the inner or outer control chamber urges the front face of the corresponding injector needle opposite side to that of the sou-pape seat while to create the force of opening, there is only a small setback above all at the inner needle. This means that the pressure in the control chamber must be lowered rather strongly to create on the inner needle a resulting opening force sufficient to move it in the opening direction. The ratio of the pressure surfaces thus complicates a rapid closure of the inner needle of the injector so that it is difficult to inject with the required accuracy a low dose of fuel such as that which corresponds, for example, to a pre-injection or postinjection in the combustion chamber. In addition, the known achievements are very complicated and therefore expensive construction which makes it difficult to commercialize them.

  DESCRIPTION AND ADVANTAGES OF THE INVENTION The present invention relates to a fuel injector of the type defined above, characterized in that in the outer control chamber a piston, connected to the inner needle, has a thrust surface on which the pressure in the control chamber exerts an opening force, the outer needle moving away from the valve seat.

  The fuel injector according to the invention offers the advantage over known injectors, a simple construction allowing good control of small doses of fuel by the injector and thus a better control work while reducing the means to implement to independently control the two needles through the use of a multi-stage injector. For this, a piston is pre-seen in the outer control chamber and the piston is connected to the inner needle of the injector; it has a pressure surface opposite the valve seat. By applying the pressure on the pressure surface, a corresponding opening force is exerted on the piston. This force depends on the pressure in the outer control chamber. Due to the pressure applied to the piston pressure surface, a portion of the closing force generated by the pressure in the inner control chamber will be compensated so that even a relatively low pressure drop in the inner control chamber results. by an opening movement of the inner needle of the injector. Since a high fuel pressure can be restored very quickly in the inner control chamber, the inner needle of the injector can be quickly closed and thus have a good dosing capacity of a small amount.

  According to an advantageous development, the piston is surrounded by an inner sleeve delimiting radially outwardly the inner control chamber. There is thus a limitation of the inner control chamber vis-à-vis the outer control chamber made possible by a simple construction. Equally advantageously, there is a development in which the piston and the inner needle of the injector are in one piece which allows an optimal meeting between the piston and the inner needle of the injector.

  In order to control the fuel pressure in the inner control chamber or in the outer control chamber, there is provided an inner supply throttling element opening into the inner control chamber and correspondingly there is a control member. external supply throat opening into the outer control chamber. In order to lower the fuel pressure, an internal outlet throttling member opens the link to the leakage fuel line itself connected to the leakage chamber in which there is no pressure. Likewise, an external output throttling member connected to the leakage line communicates with the outer control chamber. Between the inner outlet throttle and the leaking fuel line, there is provided a first control valve; correspondingly between the outer outlet throttle and the leakage line, a second control valve is provided. The two control valves are 2/2-way distributor so that the inner outlet throttle or the outer outlet throttle can be connected to or cut off from the leakage line. This embodiment makes it possible to separately control the pressure in both the inner control chamber and the outer control chamber, since the first control valve and the second control valve are controlled independently of one another.

  Advantageously, the pressure chamber, the internal feed throttle and the external feed throttle are connected to a high pressure accumulator which stores fuel at the injection pressure.

  According to another advantageous development, the inner outlet throttling member and the outer outlet throttling member are connected to a multi-stage valve, preferably a 3/3 way distributor having a valve element of control that can take at least three switching positions. This makes it possible to regulate the pressure by a single control valve in both the internal control volume and the external control volume independently, which results in a lower cost than the production of the two 2/2 dispensers. tract. The arrangement of the control chambers and the pressure surfaces connected thereto advantageously makes it possible, by means of a simple 3/3-way distributor, to control the two needles independently of one another. All that is needed is a 3/3-way distributor that connects one of the two throttle bodies to the leakage line. Such a valve is of a particularly-simple construction to achieve.

  It is particularly advantageous to have a 3/3 way distributor whose control element is moved by a piezoelectric actuator. There is thus a possibility of very fast control of the control valve and can be controlled without difficulty any number of intermediate positions for the control valve elements.

  Drawings The present invention will be described below using two embodiments of a fuel injector according to the invention shown in the accompanying drawings in which: - Figure 1 is a longitudinal section of a first example of A fuel injector, a large part of the control installations of this injector is shown only schematically, - Figure 2 shows a second embodiment of a fuel injector shown as in Figure 1.

  Description of the embodiments

  Figure 1 shows schematically in longitudinal section a fuel injector according to the invention and certain components supplying the fuel injector. The fuel injector 3 consists of a housing formed of a valve body 5, a control body 7 and a throttle plate 9; these three elements are clamped against each other in this order by a clamping device not shown in the drawing. The body 5 comprises a pressure chamber 12 connected by a high pressure line 14 passing through the valve body 5, in the control body 7 and through the throttle plate 9 to be connected to a high pressure accumulator 1 The high pressure accumulator 1 contains fuel under a predetermined high pressure corresponding to the injection pressure that is to say the pressure with which the fuel is injected into the combustion chamber. The pressure chamber 12 has an outer needle 16 of piston-shaped injector and having an outer sealing surface 25 cooperating with a valve seat 20 delimiting the pressure chamber 12.

  The outer sealing surface 25 is made so that when the outer needle 16 of the injector comes against the valve seat 20, the external injection orifices (or ejection orifices) 26 are closed while the when the outer needle 16 is raised from the valve seat 20, these ports communicate with the pressure chamber 12. The outer needle 16 of the injector is guided by its median segment in the pressure chamber 12; the two sections of the pressure chamber 12 thus formed are hydraulically connected by ground portions 17 to the outer needle 16 of the injector. Starting from the guided segment, the outer needle 16 widens from the seat of the poppet 20 forming a thrust shoulder 35 and joining a segment 116 of enlarged diameter. The enlarged segment 116 is surrounded by an outer sleeve 29; an outer closing spring 30 is placed with pressure prestressing between the outer sleeve 29 and a spring-loaded spring shovel 31 connected to the outer needle of the injector 16. A spring-loaded cup 31 and an outer needle can be provided. injector 16 made in one piece. The outer closing spring 30 presses on the one hand the outer sleeve 29 against the control body 7 and on the other hand the outer needle 16 of the injector against the seat of the poppet 20.

  An inner needle 18 slides longitudinally in the outer needle 16 of the injector; this inner needle is guided in the outer needle 16 at the enlarged segment 116. The inner needle 18 tapers towards the valve seat 20 by forming a pressure shoulder 22 and at its end on the side of the valve seat, the end forms an inner sealing surface 27 cooperating with the valve seat 20. When pressing against the valve seat 20, the inner injection ports 28 are closed; these orifices are released as soon as the inner needle 18 moves away from the valve seat 20. An inner volume 24 is formed between the inner needle 18 and the outer needle 16 of the injector; this intermediate volume is connected by one or more transverse bores 21 to the pressure chamber 12. Thus, there is always the same fuel pressure in the inner volume 24 and in the pressure chamber 12. This fuel pressure is that of the high pressure accumulator 1.

  An outer pressure chamber 40 is formed in the control body 7. This chamber is on the one hand delimited by the front face of the outer needle 16 on the opposite side to that of the sou-pope seat and by the outer sleeve 29 and on the other hand by the throttle plate 9. The outer control chamber 40 receives a piston 19 connected to the inner needle 18 and whose end face not facing the inner needle 18 defines inside a chamber The inner control chamber 50 is delimited radially outward by an inner sleeve 34 guided on the piston 19 and supported by a closing spring 32, inside against a cup or spring plate 33; this cup is connected to the inner needle 18. The piston 19 and the inner needle 18 are integrally connected; they can also be in one piece. The inner closing spring 32 provides in the same manner as the outer closing spring 30 that the inner sleeve 34 is pressed against the throttle plate 9 and at the same time the inner needle 18 is pushed against the seat valve 20 by the spring plate 33.

  For supplying the control chambers 40, 50 with fuel, the throttle plate 9 has different supply and outlet ports. An external supply throttle member 41 connects the high pressure line 14 to the outer control chamber 40. To discharge the pressure, there is provided an outer outlet throttling member 44 for connecting the outer control chamber 40. to the leakage fuel line 65; this leakage line 65 opens into a leaky fuel chamber not shown in the drawings and in this chamber there is still a low fuel pressure. Between the external outlet throttling member 44 and the leakage line 65, there is a first controlled valve 55 which can be made in the form of a 2/2-way distributor and which either cuts or frees the fuel passage from In the same way, the throttle plate 9 has an internal supply throttling orifice 42 connecting the high pressure line 14 to the inner control chamber 50. The liquid outlet is provided by the inner outlet throttling member 43 which can be connected by a second control valve 60 to the leakage oil line 65. The second control valve 60 is also provided as a 2/2-way distributor and can either release or cut the communication.

  The operation of the fuel injector is as follows: It is possible to inject either with all the injection orifices (or ejection orifices) 26, 28 or selectively only through the internal ejection orifices 28 or through the orifices. External ejection 26. If it is desired to inject fuel only through the internal injection ports 28, the second control valve 60 is actuated so that the internal throttle member 43 remains connected to the oil line. The pressure in the inner control chamber 50 decreases so that the closing force on the piston 19 or the inner needle 18 decreases. As in the intermediate volume 24, the same high fuel pressure prevails as in the pressure chamber 12, the pressure shoulder 22 is subjected to the pressure of the fuel which gives an opening force applied to the inner needle 18; it moves away from the valve seat 20 and releases the internal ejection ports 28. The opening movement is favored by the application of pressure to the pressure surface 23 of the piston 19 which, due to the still high fuel pressure prevailing in the outer control chamber 40 results in a considerable opening force applied to the piston 19. In these circumstances, it suffices to have a relatively low pressure drop in the inner control chamber 50 to obtain a sufficient resultant opening force applied to the inner needle 18. To complete the injection, the second control valve 60 is again actuated and the connection between the inner outlet throttling member 43 is cut off. and the leakage line 65. The pressure then starts to increase in the inner control chamber 50 so that a hydraulic force is applied again to the piston 19 and pushes the piston 19 and thus the piston interior 18 towards the valve seat 20.

  Correspondingly, the outer needle 18 is opened. In this case, only the first control valve 55 is actuated to lower the pressure in the outer control chamber 40. The hydraulic force applied against the front face the outer needle 16 on the opposite side to that of the poppet seat thus decreases which allows the hydraulic pressure acting on the pressure shoulder 35 to lift the outer needle of the valve seat 20 and to release the outer discharge ports 26. The outer valve sealing surface 25 is made to seal the outer injection ports 26 with respect to the pressure chamber 12 as well as with respect to the intermediate chamber 24. To terminate the injection, the first control valve 55 is actuated again and the outer needle 16 of the injector returns to its closed position.

  In order to inject fuel with all the injection ports 26, 28, the second control valve 60 is first actuated and the inner needle 18 is opened as described above. In general, the diameter of the inner injection orifices 28 and that of the external injection orifices 26 are not identical, and the internal injection orifices 28 have, for example, a smaller diameter than the external injection orifices 26. is particularly advantageous if only a very small amount of fuel must arrive in the combustion chamber for pre-injection. Depending on the moment at which the outer needle 16 of the injector opens, the first control valve 55 is controlled substantially simultaneously or with a certain delay with respect to the second control valve 60 and the connecting member is connected. external outlet throttling 44 to the leaking fuel line 65. The pressure in the control chamber 40 thereby drops and the outer needle 16 opens as described above following the inner needle. 18. The injection is completed by again actuating the two control valves 55, 60 which then cut the connection with the leakage oil line 65. As the fuel pressure decreases again in the outer control chamber 40 and in the inner control chamber 50, both the inner needle 18 and the outer needle 16 of the injector are pushed into their closed position.

  FIG. 2 shows a second embodiment of a fuel injector 3 according to the invention. The actual construction of this fuel injector 3 is identical to that of the example shown in FIG. 1 so that the description given below is limited to the design differences of the control valves. For this reason, the operation of a control valve will be limited. Indeed, instead of two control valves 55, 60 as in the embodiment of Figure 1, the second embodiment has only one control valve 70 in the form of a 3/3 way distributor. The control valve 70 includes a control valve chamber 72 into which the inner outlet restrictor 43 and the outer outlet restrictor 44 open. A control valve member 74 is placed in the chamber This element is movable in the control valve chamber 72 against the force of a return spring 79. The control valve member 74 is connected to a control piston 75 which reaches a chamber. hydraulic coupling 76. A pressure piston 78 also enters the hydraulic coupling chamber 76. This piston is connected to a piezoelectric actuator 80 whose width is variable so that according to the voltage applied to the piezoelectric actuator 80, the pressure piston 78 penetrates more or less into the hydraulic neck chamber 76. The chamber 72 of the control valve is further connected to a leakage line 77 opening into a e leakage fuel chamber not shown in Figure 2.

  The operation of this exemplary embodiment is as follows: To open the inner needle 18, the piezoelectric actuator 80 is supplied so that the control piston 75 moves the control valve member 74 of the maximum stroke h2. Thus, the control valve member 74 exits its first switch position shown in Fig. 2 to move to a third switch position; it means that it comes into abutment against the opposite stop. The inner throttle member 43 is thus connected to the leakage line 77 while the outer throttle member 44 remains closed. The pressure then drops in the inner control chamber 50 so that the inner needle 18 opens as has already been described with regard to the first embodiment; by opening the needle releases the inner injection ports 28. To complete the injection, the piezoelectric actuator recalls the pressure piston 78 in its output position so that the control piston 75 moves away also of the control valve chamber 72 and the control valve member 74 switches back to the first switching position in which it closes the leakage line 77.

  If, on the other hand, it is desired to inject fuel only with the external injection ports 26, the piezoelectric actuator 80 is actuated to drive the control valve element 74 to its median position; in this position, he only runs the race hl. Therefore, the pressure decreases both in the inner control chamber 50 and also in the outer control chamber 40 and corresponding pressure surfaces are designed with passage resistances within the valve chamber of the valve. control 72 so that the pressure in the inner control chamber 50 is always sufficient to hold the inner needle 18 against the valve seat 20. Ain-si, only the outer needle 16 opens and releases the orifices. External injection 26. Thereafter, the control valve element 74 is returned from this second switching position to the first switching position so that the control chambers 40, 50 refill with fuel and the needle 16 is returned to its closed position.

  To inject fuel through all the injection ports 26, 28, the control valve element 74 is first driven into the third switching position; this means that this element first runs through the full race h2. The pressure in the inner control chamber 50 then drops as described above and the inner needle 18 begins its opening movement. Thereafter, the control valve member 74 is moved to an average position, i.e., in the second switching position, so that now also the outer output throttling member 44 is connected to the control line. 77. As after lifting the inner needle 18 relative to the valve seat 20, the entire internal sealing surface 27 of the valve is biased by the fuel pressure in the intermediate volume 24; the inner needle 18 retains its open position also if, despite the decrease in pressure in the outer control chamber 40, a portion of the opening force disappears as the corresponding hydraulic force is applied to the pressure surface 23 decreases. Due to the drop in pressure in the outer control chamber 40, the outer needle 16 begins to move and the fuel is thus injected through all the injection ports 26, 28. To complete the injection, it leads back the control valve member 74 in the first switch position in which the leak line 77 is closed and the control chambers 40, 50 are again filled with high pressure fuel.

  Instead of the piezoelectric actuator 80 acting via a hydraulic coupling chamber 76 on the control valve member 74, it is also possible to move the element of the control valve 74, for example, by causing a piezoelectric actuator 80 to act directly on the control valve element 74. It is also possible to envisage a coupling between the piezoelectric actuator 80 and the control valve element 74. a mechanical coupler for example a rocking lever and the adaptation can be done according to the existing efforts and the desired switching times. For the control it is also possible to use a solenoid valve switching in three positions.

Claims (10)

  1) A fuel injector of an internal combustion engine comprising a housing (5, 7, 9) which houses a pressure chamber (12) which can be filled with fuel, and which slidably receives an external injector needle ( 16) cooperating with a valve seat (20) delimiting the pressure chamber (12) and thereby controlling the passage of fuel from the pressure chamber (12) to at least one external injection port (26), as well as an inner needle (18) housed in the outer needle (16) of the injector, the inner needle also cooperating with the valve seat (20) and thereby controlling the passage of fuel from the pressure chamber (12) to the minus one inner injection port (28), and an outer control chamber (40) whose pressure exerts at least indirectly on the inner needle (16) a closing force directed towards the valve seat (20), and that an interior control room (50) whose pressure generates at least indirectly on the inner needle (18) a closing force directed towards the valve seat (20), characterized in that in the outer control chamber (40) a piston ( 19), connected to the inner needle (18), has a thrust surface (23) subjected to the pressure in the control chamber (40) for exerting an opening force on the inner needle (18), directed away from the valve seat (20).   2) fuel injector according to claim 1, characterized in that the piston (19) is surrounded by an inner sleeve (34) which delimits radially outwardly the inner control chamber (50).   3) fuel injector according to claim 1, characterized in that the piston (19) and the injector needle (18) are made in one piece.   4) A fuel injector according to claim 1, characterized in that the outer control chamber (40) fills with high pressure fuel through an external supply throttle (41) and this chamber can be connected to a leakage fuel line (65) via an external outlet throttling member (44), the connection of the outer throttle member (44) and the leakage line (45) being opened or closed by a first control valve (55).   A fuel injector according to one of claims 1 or 4, characterized in that the inner control chamber (50) is filled by means of an internal supply throttle (42) with high pressure fuel and can be connected to a leakage line (65) by an inner outlet throttle (43), the connection of the inner outlet throttle (43) and the leakage line (65) being opened or closed by a second control valve (60).   6) Fuel injector according to any one of claims 4 or 5, characterized in that the first control valve (55) and the second control valve (60) are controlled independently of one another.   7) Fuel injector according to any one of claims 4 or 5, characterized in that the pressure chamber (12), the internal feed throttle member (42) and the throttle member external power supply (41) are connected to a high-pressure accumulator which stores fuel at the injection pressure.   8) A fuel injector according to claim 1, characterized in that the outer control chamber (40) is connected to an external supply throttle (41) and the inner control chamber (50) is connected to a internal feed throttling member (42), the inner control chamber (50) being connected by an inner outlet throttling member (43) and the outer control chamber (50) by a throttling member of external outlet (43) to a 3/3 way distributor constituting the control valve (70) connected to the leakage line (77).   Fuel injector according to claim 8, characterized in that the control valve (70) comprises a movable control valve element (74) which can take at least three switching positions and which in the first position of switchover, closes the connection to the leakage line (77) and which, in the second switching position, connects both the inner outlet throttle (43) and also the outer output throttle ( 44) to the leakage line (77), which in a third switch position connects only the inner outlet throttle (43) to the leakage line (77).   Fuel injector according to one of claims 8 or 9, characterized in that the control valve (70) comprises a movable control valve element (74) displaced at least indirectly by a piezoelectric actuator (80). ).