Electromagnetic fuel injection valve

Abstract: A valve (5) controlled by an electromagnetic metering valve (41) comprising a head (49) having a control chamber (56), a supply conduit (57), and a drain conduit (58). The head (49) also presents a cavity (67) communicating with the supply conduit (57) and in which a portion (68) of the moving element (8, 28) for closing the injection orifice (11) slides in such a manner as to choke the supply conduit (57) during injection. The supply conduit (57) communicates with a receiving chamber (59) located between a seat (51) in the body (6) of the valve (5) and the outer surface of an appendix (54) on the head (49); and the moving element (8, 28) is pushed into the closed position by the combined action of the pressure at each end, and a spring (37) located close to the injection chamber (19).

Description: The present invention relates to an electromagnetic fuel injection valve comprising a body fitted with a nozzle having at least one orifice communicating with an injection chamber supplied with pressurized fuel, and a metering valve controlled by an electromagnet. On valves of the aforementioned type, the electromagnetic metering valve normally comprises a head having a control chamber, which is normally pressurized for closing the nozzle by means of a stopper. When the metering valve is opened, the pressure in the control chamber falls so as to move the stopper and open the nozzle. Various injection valves of the aforementioned type are known, on one of which, the head of the metering valve comprises an appendix coaxial with the control chamber, and the injection valve body presents a passage for guiding the moving element of the injection valve, and which communicates with the control chamber via a conduit in the head. The injection valve body is formed in two parts connected to each other, and a rod on the moving element is pushed into the closed position by a compression spring housed in a seat adjacent to the guide passage. The head also presents an axial appendix facing an annular groove, which forms a receiving chamber communicating with the control chamber via a supply conduit. The above injection valve, which is disclosed in the document EP 304 747 A1, presents several drawbacks. Firstly, the rod guide passage in the injection valve body requires accurate machining of the body. Secondly, the rod must be arrested inside the guide passage by a calibrated ring. Thirdly, difficulty is encountered in achieving effective pressure sealing of the fuel between the inlet chamber and the guide passage. Fourthly, the supply conduit remains wide open even when the metering valve is open, thus resulting in drainage of a large amount of fuel, which must subsequently be recovered. And last but not least, the lateral thrust produced by the spring results in frequent jamming of the rod. It is also known from the document EP 450 532 A1, which represets the closest state of the art, an electromagnetic fuel injection valve comprising a hollow body fitted with a nozzle having at least one orifice, which is normally closed by a rod movable into an axial seat of the body, the orifice communicating with an injection chamber supplied with fuel under pressure. A electromagnetic metering valve comprises a head fitted inside the body and provided with an axial control chamber having an axial drain conduit and a radial fuel supply conduit. An axial cylindrical element integral with the rod is guided in a cylindrical cavity, is normally urged by the fuel under pressure to close the orifice, and is adapted to be arrested by a stop surface provided on the control chamber. It is an object of the present invention to provide a highly straightforward, reliable injection valve designed to overcome the aforementioned drawbacks typically associated with the known valves. According to the present invention, there is provided an electromagnetic fuel injection valve comprising a hollow body defining an axial seat; a nozzle fitted with said body and having at least one orifice normally closed by a pin operatively associated with a rod movable into said axial seat; an axial cavity of said nozzle coaxial with said axial seat for movably mounting said pin; said at least one orifice communicating with said axial cavity, an injection chamber supplied with fuel under pressure communicating with said axial cavity; a metering valve controlled by an electromagnet, said metering valve comprising a head fitted inside a first seat of said body and coaxial with said axial seat; an axial control chamber, an axial drain conduit coaxial with said axial control chamber; said head being provided with a cylindrical cavity coaxial with said axial control chamber and communicating therewith, an axial cylindrical element integral with said rod and guided by said cylindrical cavity, said axial control chamber being provided with a stop surface for said axial cylindrical element; a supply conduit located radially at said axial control chamber for feeding fuel under pressure into said axial control chamber; said axial cylindrical element being urged by the fuel under pressure inside said axial control chamber to cause said pin to close said at least one orifice; characterized by the fact that said supply conduit is located at said axial control chamber close to said stop surface, and said axial cylindrical element is provided with an end surface provided with grooves and adapted to be arrested by said stop surface; said end surface when so arrested ensuring in said axial control chamber a residual gap in communication with said supply conduit, and causing a lateral surface of said axial cylindrical element to partially close said supply conduit, thus choking fuel flow towards said axial drain conduit. A preferred non-limiting embodiment of the present invention will be described with reference to the accompanying drawings, in which: Fig. 1 shows a section of an injection valve in accordance with the present invention; Fig. 2 shows a partial larger-scale section of a detail in Fig. 1; Fig. 3 shows a section of a variation of the Fig. 2 detail; Fig. 4 shows a section of a further detail on the injection valve, according to a further variation of the present invention. Number 5 in Fig. 1 indicates a fuel injection valve for an internal combustion engine, e.g. a diesel engine. Injection valve 5 comprises a hollow, externally tapered body 6 preferably formed in one piece and having an axial cavity 7 in which slides a control rod 8 forming part of the usual moving element of the injection valve 5. At the bottom, body 6 is fitted with a nozzle 9 terminating with one or more injection orifices 11 communicating with an axial cavity 12. Body 6 also presents an appendix 13 having one or more holes 14 housing one or more supply fittings 16 connected in known manner to a normal high-pressure, e.g. 1200 bar, fuel supply pump. At least one of holes 14 communicates with a first inclined conduit 17 in turn communicating with a second conduit 18 substantially extending along body 6. Nozzle 9 in turn presents a small injection chamber 19 communicating with cavity 12. According to a variation of the present invention, upstream from injection chamber 19, supply conduit 18 presents a calibrated diaphragm 90 for reducing the pressure in chamber 19 to slightly below line pressure and so accelerating closure of the nozzle at the end of the injection phase. Nozzle 9 also presents a conduit 21 located at conduit 18 and communicating with chamber 19. Nozzle 9 is positioned on body 6, with cavity 12 and conduit 21 respectively aligned with cavity 7 and conduit 18, by means of locating pins 22 engaged inside respective locating holes 23, 24 formed respectively in body 6 and nozzle 9, and is secured to body 6 by a ring nut 26 screwed on to the same. Orifice 11 is normally maintained closed by a stopper consisting of the substantially conical tip 27 of a pin 28 forming part of the moving element of injection valve 5 and sliding inside cavity 12. Pin 28 presents a shoulder 29 on which the pressurized fuel inside chamber 19 acts for opening orifice 11 as explained in more detail later on. Pin 28 is connected to control rod 8 by a pin 31 and a plate 36, or may be formed in one piece with rod 8, in which case, plate 36 is dispensed with. Cavity 7 of body 6 presents a portion 32 substantially adjacent to nozzle 9 and terminating at the top with a shoulder 33; and rod 8 presents a smaller-diameter portion 34 contacting plate 36. Between shoulder 33 and plate 36, there is provided a compression spring 37, the pressure exerted by which is less than that exerted by the fuel on shoulder 29, but which contributes towards pushing pin 28 downwards. Body 6 also presents a further conduit 38 connecting portion 32 of cavity 7 to a drain chamber 39, for assisting the sliding action of rod 8 inside cavity 7. Injection valve 5 also comprises a metering valve indicated as a whole by 41 and in turn comprising an electromagnet 42 controlling an anchor 43. Electromagnet 42 is fitted to body 6 by means of a further ring nut 44, and presents a drain fitting 46 connected in known manner to the fuel tank. Anchor 43 is pushed down by a spring, presents a radial groove 47 connecting fitting 46 to chamber 39, and is connected rigidly to an actuator controlling metering valve 41 and consisting of a cylindrical stem 48. Metering valve 41 also comprises a head 49 housed inside a seat 51 formed in body 6 and coaxial with cavity 7. More specifically, head 49 comprises a flange 52 normally resting on shoulder 53 of body 6; and a cylindrical appendix 54 housed inside seat 51. Head 49 presents an axial control chamber 56 communicating with a calibrated radial supply conduit 57 and with a calibrated axial drain conduit 58, and may be formed to advantage from compacted, sintered metal powder. Supply conduit 57 communicates with a receiving chamber 59 formed between seat 51 and the lateral surface of appendix 54, and defined axially by two annular seals 61, 62 fitted between appendix 54 and seat 51. Seals 61, 62 are separated axially, and rest respectively on shoulder 63 of appendix 54 and shoulder 64 of seat 51. Receiving chamber 59 communicates with at least one of holes 14 via a radial conduit 66 in body 6. By virtue of the ample mating surface, with no relative movement, between the outer surface of appendix 54 and the smaller-diameter bottom portion of seat 51, and by virtue of seal 62 resting on shoulder 64 perpendicular to the axis of body 6, any possibility of fuel leakage from conduit 66 into seat 51 is prevented. According to one characteristic of the present invention, appendix 54 extends downwards, and presents a cylindrical cavity or seat 67 communicating with control chamber 56 and in which slides a top cylindrical portion 68 of rod 8. Supply conduit 57 is located close to the blend surface 69 between seat 67 and control chamber 56, so that the gap between surface 69 and the top surface 71 of portion 68 forms an extension of control chamber 56. Portion 68 is preferably larger in diameter than rod 8, and such that the force generated by the fuel pressure on surface 71 is greater than that generated on shoulder 29 of pin 28, thus providing for effective closure of orifice 11. Surface 71 is arrested against surface 69 of seat 67, as shown by the dotted line in Fig.1, so that surface 69 acts as a stop surface for rod 8. To prevent total elimination of the gap between portion 68 and surface 69, surface 71 presents a number of grooves 72, e.g. radial grooves, so that, when portion 68 of rod 8 is arrested against surface 69, the lateral surface of portion 68 partially closes supply conduit 57, thus choking fuel flow towards drain conduit 58, and metering valve 41 thus acts substantially as a three-way valve. Head 49 is secured to body 6 by a ring nut 73 screwed into a threaded seat in body 6 and acting on a bell-shaped member 74 having a depression 76 (Fig.2) communicating with the drain chamber via holes 77. Bell-shaped member 74 forms one piece with a sleeve 78 for guiding stem 48, and drain conduit 58 in head 49 terminates at the top with a conical portion 79 engaged by a ball type stopper 81 controlled by stem 48. In the Fig.3 variation, drain conduit 58 is engaged by a stopper consisting of a plate 82, so that conical portion 79 of conduit 58 is eliminated; and the upper surface of flange 52 presents an annular groove 80 for increasing the volume of the chamber formed by depression 76. The injection valve described operates as follows. Electromagnet 42 is normally de-energized, so that anchor 43 is maintained by its spring in the Fig.1 position; ball 81 or plate 82 (Fig.s 2 and 3) are positioned by stem 48 so as to close drain conduit 58; control chamber 56 is therefore pressurized and, together with the pressure exerted by spring 37, overcomes that exerted on shoulder 29; and rod 8 is held down, together with pin 28, so that tip 27 closes orifice 11. When electromagnet 42 is energized, anchor 43 is raised, so that stem 48 releases stopper 81 or 82; and the fuel pressure inside chamber 56 opens metering valve 41, thus draining the fuel through holes 77 into drain chamber 39 and back to the tank. At this point, the fuel pressure in injection chamber 19, being greater than the pressure remaining in control chamber 56 plus that exerted by spring 37, raises pin 28 together with rod 8. This is ensured, even with a small capacity chamber 19 upstream from the injection orifices, i.e. with no need for accumulating additional fuel and so reducing the pressure beneath shoulder 29, by virtue of the conical portion of drain conduit 58 and ball stopper 81 providing for considerable outflow and so practically eliminating the pressure in chamber 56. When rod 8 is arrested against surface 69 of seat 67, tip 27 of pin 28 opens orifice 11, so that the fuel in chamber 19 is injected into the engine; and portion 68 of rod 8 partially closes supply conduit 57, thus minimising the amount of fuel fed into drain chamber 39 via control chamber 56. When electromagnet 42 is de-energized, anchor 43 is moved back down by its spring, so as to close drain conduit 58; the pressurized fuel supplied by conduit 57 via grooves 72 restores the pressure inside chamber 56; and, when the pressure in chamber 56, together with that of spring 37, exceeds the pressure exerted on shoulder 29, moving element 8, 28 again moves down to close orifice 11. The combined action of a small-sized chamber 19 upstream from the injection holes and of a calibrated diaphragm 90 along the supply conduit provides for troublefree downward movement of the moving element, with no substantial difference required in the diameter of portion 68 of rod 8 and shoulder 29 of pin 28, as well as for reducing the specific load on rod 8. In the Fig.4 variation, the guide of stem 48 of anchor 43 consists of a cylindrical recess 83 formed in head 49 and coaxial with cavity 67, thus eliminating bell-shaped member 74 (Fig. 1); head 49 presents a diaphragm 84 housing drain conduit 58; and the control chamber consists exclusively of the gap between upper surface 71 of portion 68 and stop surface 69 of cylindrical seat 67. Cylindrical recess 83 presents axial grooves 85 for enabling communication between the control chamber and drain chamber 39; and stem 48 may of course act on drain conduit 58 by means of a ball 81 or plate 82 type stopper, in the same way as described previously. Operation of the Fig.4 variation is the same as described with reference to Fig.s 1-3. The advantages of the injection valve according to the present invention will be clear from the foregoing description. In particular, it provides for simplifying machining of body 6 by eliminating the need for precision machining of seat 51; and, by virtue of choking supply conduit 57, it provides for reducing the amount of fuel drained along conduit 58 at each injection cycle. Moreover, the fact that spring 37, via plate 36, acts directly on pin 28 as opposed to rod 8, prevents any possibility of cylindrical portion 68 of rod 8 jamming inside sliding seat 51. Finally, any fuel leakage from receiving chamber 59 through seat 67 in no way impairs the efficiency of the injection valve. To those skilled in the art it will be clear that changes may be made to the injection valve as described and illustrated herein. For example, spring 37 may be fitted directly to a portion of pin 28 as opposed to plate 36; moving element 8, 28 may be formed in one piece; and, to prevent flexing, in the case of an extremely long rod 8, this may present the same diameter as portion 68.

Claims: An electromagnetic fuel injection valve comprising a hollow body (6) defining an axial seat (7); a nozzle (9) fitted with said body (6) and having at least one orifice (11) normally closed by a pin (28) operatively associated with a rod (8) movable into said axial seat (7); an axial cavity (12) of said nozzle (9) coaxial with said axial seat (7) for movably mounting said pin (28); said at least one orifice (11) communicating with said axial cavity (12), an injection chamber (19) supplied with fuel under pressure communicating with said axial cavity (12); a metering valve (41) controlled by an electromagnet (42), said metering valve (41) comprising a head (49) fitted inside a first seat (51) of said body (6) and coaxial with said axial seat (7); an axial control chamber (56, 67), an axial drain conduit (58) coaxial with said axial control chamber (56, 67); said head (49) being provided with a cylindrical cavity (67) coaxial with said axial control chamber (56, 67) and communicating therewith, an axial cylindrical element (68) integral with said rod (8) and guided by said cylindrical cavity (67), said axial control chamber (56, 67) being provided with a stop surface (69) for said axial cylindrical element (68); a supply conduit (57) located radially at said axial control chamber (56, 67) for feeding fuel under pressure into said axial control chamber (56, 67); said axial cylindrical element (68) being urged by the fuel under pressure inside said axial control chamber (56, 67) to cause said pin (28) to close said at least one orifice (11); characterized by the fact that said supply conduit (57) is located at said axial control chamber (56, 67) close to said stop surface (69), and said axial cylindrical element (68) is provided with an end surface (71) provided with grooves (72) and adapted to be arrested by said stop surface (69); said end surface (71) when so arrested ensuring in said axial control chamber (56, 67) a residual gap in communication with said supply conduit (57), and causing a lateral surface of said axial cylindrical element (68) to partially close said supply conduit (57), thus choking fuel flow towards said axial drain conduit (58). An electromagnetic fuel injection valve as claimed in Claim 1, wherein said axial drain conduit (58) is connected to a drain chamber (39) by activating a control element (48) integral with an anchor (43) of said electromagnet (42); characterized by the fact that said control element (48) is guided by means (78, 83) axially integral with said head (49) and coaxial with said cylindrical cavity (67). An electromagnetic fuel injection valve as claimed in Claim 2, characterized by the fact that said guide means (78, 83) comprise a cylindrical guide member (83) in one piece with said head (49); said drain chamber (39) comprising at least one groove (85) in said cylindrical guide member (83). An electromagnetic fuel injection valve as claimed in Claim 3, characterized by the fact that said cylindrical guide member (83) consists of a cylindrical recess (83) separated from said cylindrical cavity (67) by a diaphragm (84) supporting said axial drain conduit (58); said axial control chamber (67) being formed exclusively by the gap between said end surface (71) and said stop surface (69). An electromagnetic fuel injection valve as claimed in one of the foregoing Claims, characterized by the fact that said first seat (51) houses a pair of annular seals (61, 62) for defining an annular fuel receiving chamber (59) communicating with said supply conduit (57); one (62) of said seals (61, 62) resting on a flat shoulder (64) of said first seat (51), and the other (61) of said seals (61, 62) resting on a flat shoulder (63) of said head (49). An electromagnetic fuel injection valve as claimed in Claim 5, wherein said injection chamber (19) is adjacent to said pin (28), and said rod (8) is held in the closed position with the aid of a compression spring (37); characterized by the fact that said spring (37) is housed in a second seat (32) close to said injection chamber (19). An electromagnetic fuel injection valve as claimed in one of the foregoing Claims 2 to 4, characterized by the fact that said control element (48) acts on said axial drain conduit (58) via a stopper in form of a ball (81) or disk (82).

Inventors: BRUNI GIOVANNI, DE MATTHAEIS SISTO LUIGI, RICCO MARIO, BRUNI, GIOVANNI, DE MATTHAEIS, SISTO LUIGI, RICCO, MARIO
Applicants: ELASIS SISTEMA RICERCA FIAT, ELASIS SISTEMA RICERCA FIAT NEL MEZZOGIORNO SOCIETA CONSORTILE PER AZIONI
Application year: 1992
Main classification: F02M47
IPC codes: F02M47, F02M51