Fuel injector electromagnetic metering valve

Abstract: The valve comprises a shutter (67) for the drain conduit (63) of the control chamber (61) of the injector; and an electromagnet (42) having a fixed core (46) with a seat (48) for a coil (47) which is energized to operate the armature (43) controlling the shutter (67). The core (46) presents two coaxial annular pole pieces (72, 73), the outer one (72) of which is shorter than the inner one (73) and fitted with a ring (76) of magnetic material partially closing the seat (48) and enabling a substantial reduction in the diameter of the armature (43). The smaller diameter of the armature (43) enables it to be fitted to the body (6) of the injector by means of a larger-diameter threaded ring nut (82). The armature (43), together with a return spring (89), is fitted to a plate (84) having a sleeve (83) for guiding the stem (69); and the assembly is then fitted to the body (6) independently of the electromagnet (42) by screwing the ring nut (82) inside a seat (93) in the body (6).

Description: The present invention relates to a fuel injector electromagnetic metering valve. The metering valves of fuel injectors generally comprise a control chamber with a drain conduit normally closed by a shutter which, in known metering valves, is normally closed by the armature of an electromagnet, and is released to open the conduit by energizing the electromagnet so as to move the armature towards the core of the electromagnet. The electromagnets of known metering valves generally present two coaxial pole pieces defining a seat for a cylindrical coil, while the armature is -in the form of a disk designed to close the magnetic circuit of the core and the diameter of which is normally substantially larger than the outside diameter of the core coil seat. The armature is normally guided by a sleeve fitted to the injector body by means of a threaded ring nut and into which the armature is subsequently inserted. It is known from the document EP-A-483 769 a fuel injector having an electromagnetic metering valve including a disk armature secured to a stem. The stem is axially guided by a sleeve fitted into the injector's body by a first ring nut, whereas the electromagnet is fitted on the injector's body by another ring nut. Since the first ring nut has an inside diameter less than the outside diameter of the armature, and the return spring is housed in a hole of the core, the armature cannot be preassembled independently of the electromagnet. A major drawback of the metering valves of the aforementioned type is that they fail to enable the metering valve assembly to be checked and/or tested separately prior to final assembly. It is an object of the present invention to provide a straightforward, highly reliable metering valve of the aforementioned type, designed to overcome the aforementioned drawback typically associated with known valves. According to the present invention, there is provided an electromagnetic metering valve of a fuel injector comprising an electromagnet with a fixed magnetic circuit including a magnetic core; and a coil energizable to displace an armature against the action of a compression spring for controlling the metering function; said core comprising an annular seat for said coil; said electromagnet being fitted to a body of the injector by a threaded ring nut external to said body; said armature being in form of a disk and being integral with a stem guided by an axial sleeve; a further ring nut being screwed inside a threaded seat of said body for fitting said sleeve inside said body; characterized by the fact that said spring is located between a washer secured to said stem and a wall integral with said sleeve; said further ring nut having an inside diameter greater than the outside diameter of said armature; said armature, said spring and said axial sleeve being preassembled to form an assembly, said assembly being fitted by said further ring nut inside said body independently of said electromagnet. A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a half section of a fuel injector featuring a metering valve adjusting device in accordance with the present invention; Figure 2 shows a larger-scale of a detail in Figure 1. Number 5 in Figure 1 indicates a fuel injector, e.g. for a Diesel internal combustion engine. Injector 5 comprises a hollow body 6 having an axial cavity 7 in which slides a control rod 8. At the bottom, body 6 is connected to a nozzle 9 terminating with one or more injection orifices 11 communicating with an axial cavity 12. Body 6 presents an appendix 13 having a hole 14 in which is inserted an inlet fitting 16 connected in known manner to a normal high-pressure, e.g. 1200 bar, fuel supply pump. Hole 14 communicates with a first inclined conduit 17 in turn communicating with a second conduit 18 substantially extending along body 6. Nozzle 9 presents an injection chamber 19 communicating with cavity 12, and a conduit 21 connecting conduit 18 to chamber 19, and is fitted on to body 6 by means of a ring nut 26. Orifice 11 is normally closed by the tip of a pin 28 connected to rod 8 and having a shoulder 29 on which the pressurized fuel in chamber 19 acts. A compression spring 37 is fitted between a shoulder 33 of cavity 7 in body 6 and a plate 36, and which contributes towards pushing rod 8 downwards. Injector 5 also comprises a metering valve 40 in turn comprising a sleeve 41 for supporting an electromagnet 42 controlling an armature 43. Sleeve 41 is fitted to body 6 by means of a further ring nut 44, and presents a shoulder 45 on which rests a core 46 of ferromagnetic, e.g. sintered powder, material. Core 46 presents a seat 48 in which is housed an electric coil 47 embedded in a resin 49. Sleeve 41 also presents a bent edge 50 which provides for securing a disk 52 against a further flat surface 51 of core 46. Disk 52 forms one piece with a drain fitting 53 aligned with an axial hole 57 in core 46 and connected in known manner to the fuel tank; and sleeve 41 is fitted in known manner with a base 54 made of insulating material and fitted as usual with the pin 55 of coil 47. Metering valve 40 also comprises a head 56 housed inside a seat in body 6, coaxial with cavity 7, and fitted to body 6 by a threaded ring nut 58 screwed on to the internal thread 59 of a drain chamber 60 inside body 6 and extending axially between the upper surface of head 56 and the lower surface of electromagnet 42. Head 56 also presents an axial control chamber 61 communicating with a calibrated radial inlet conduit 62, and with a calibrated axial drain conduit 63. Inlet conduit 62 communicates with a receiving chamber 64 in turn communicating with hole 14 via a radial conduit 66 in body 6. Control chamber 61 is defined at the bottom by the upper surface of rod 8. By virtue of the larger area of the upper surface of rod 8 as compared with that of shoulder 29, the pressure of the fuel, together with spring 37, normally keeps rod 8 in such a position as to close orifice 11 of nozzle 9. Drain conduit 63 of control chamber 61 is normally closed by a shutter in the form of a ball 67 on which a stem 69 integral with armature 43 acts; and armature 43 presents radial openings 71 for connecting drain chamber 60 to hole 57 in core 46 and consequently to drain fitting 53. Core 46 is externally cylindrical, and presents two coaxial annular pole pieces 72, 73 (Figure 2) forming seat 48 of coil 47; and armature 43 is disk-shaped for closing the magnetic circuit, including core 46, between pole pieces 72 and 73. According to the present invention, the magnetic circuit comprises an element 76 of magnetic material, for partially closing seat 48. More specifically, element 76 is in the form of a ring having two flat parallel surfaces 77, 78, an outside diameter substantially equal to that of core 46, and an inside diameter slightly larger than the outside diameter of inner pole piece 73. Pole pieces 72, 73 present two parallel pole surfaces 79, 80 so that the length of the outer pole piece 72 is less than that of inner pole piece 73, and the difference between the two lengths is substantially equal to the thickness of ring 76 between surfaces 77 and 78. Ring 76 is fitted to outer pole piece 72 with surface 78 contacting pole surface 79. Pole surfaces 79 and 80 may present a layer 81 of nonmagnetic material for preventing the upper surface of armature 43 from directly contacting pole surfaces 79, 80. Surface 77 of ring 76 thus lies in the same plane as surface 80 of pole piece 73, but the distance between pole piece 73 and ring 76 is much smaller than the width of seat 48 of coil 47, so that the diameter of armature 43 may be reduced enormously as compared with that required for closing the magnetic circuit on pole piece 72. For example, the diameter of armature 43 may be so selected that the portion facing surface 77 of ring 76 presents substantially the same area as the portion facing pole piece 73. As a result, the mass of armature 43 is greatly reduced, thus reducing the force required for operating it in either direction; and seat 48 may be enlarged as compared with known techniques, for housing a larger number of turns of coil 47 and so reducing the operating current required. Moreover, seat 48 enables the turns of coil 47 to be coated or embedded in a larger quantity or thickness of resin 49, thus enhancing the protection and extending the working life of coil 47. The small diameter of armature 43 also permits the passage of a ring nut 82 with a larger inside diameter than armature 43. More specifically stem 69 is guided by a sleeve 83 fitted to a plate-shaped element 84, and presents a groove 85 in which is inserted a C-shaped washer 86. Plate 84 presents an end wall 87 with holes 88 enabling communication between the portions of chamber 60 above 60b and below 60a plate 84; and, between end wall 87 and washer 86, there is provided a preloaded compression spring 89 which acts as a return spring for drawing armature 43 downwards when electromagnet 42 is de-energized. Plate 84 presents a flange 90 which, by means of a calibrated washer 91, rests on a shoulder 92 of body 6. The assembly consisting of armature 43, spring 89 and plate 84 is fitted inside body 6 by means of threaded ring nut 82, which is screwed inside a threaded seat 93 in body 6 and acts on flange 90 of plate 84. As such, the armature 43 assembly is preassembled and then fitted to body 6 independently of both the head 56 and electromagnet 42 assemblies, thus enabling the three assemblies of injector 5 to be checked and/or tested prior to final assembly. Injector 5 as described above operates as follows. Electromagnet 42 is normally de-energized, so that armature 43 is held by return spring 89 in the down position in the accompanying drawings; stem 69 keeps ball 67 in the position closing drain conduit 63; and the pressure generated in control chamber 61 acts on the upper surface of rod 8 having a greater surface area than shoulder 29, and, together with the action of spring 37 (Figure 1), overcomes the pressure on shoulder 29 so that rod 8 is held down together with pin 28 which closes orifice 11. When electromagnet 42 is energized, armature 43 is raised and arrested with its upper surface on layer 81 (Figure 2) of the magnetic circuit. Alternatively, calibrated washer 91 may be so selected that armature 43 is arrested with washer 86 against the edge of sleeve 83, thus preventing armature 43 from contacting pole surfaces 79, 80, and enabling layer 81 on core 46 to be dispensed with. The residual pressure of the fuel in chamber 61 therefore opens metering valve 40 so as to discharge the fuel through calibrated hole 63 into drain chamber 60a, and through holes 88 into drain chamber 60b, from where it is fed through openings 71, hole 57 and conduit 53 back into the tank. The pressure of the fuel in injection chamber 19 now overcomes the force exerted by spring 37 and raises pin 28 which opens orifice 11 so as to inject the fuel in chamber 19. When electromagnet 42 is de-energized, armature 43 is restored rapidly to the down position by spring 89, so as to close drain conduit 63 by means of ball 67; and the pressurized incoming fuel from conduit 62 restores the pressure inside control chamber 61 so as to lower pin 28 and close orifice 11. The advantages of the metering valve according to the present invention will be clear from the foregoing description. In particular, ring 76 provides for reducing the diameter of armature 43 and so enabling the armature 43 assembly to be assembled independently of head 56 of valve 40 and electromagnet 42. Moreover, the smaller diameter of armature 43 provides for reducing the mass of the armature, hydrodynamic resistance, and the parasitic currents induced by coil 47, which in turn provides for reducing the size of return spring 89, core 46 and, hence, electromagnet 42 as a whole, so that the entire control assembly of injector 5 may be miniaturized. Finally, for a given size of core 46, the width of seat 48 may be increased for embedding coil 47 in a greater quantity of resin 49. Ring 76 may present a depression for receiving pole piece 72; and armature 43 may present an upper surface divided by a step into two separate parts respectively facing ring 76 and pole piece 73.

Claims: An electromagnetic metering valve (40) of a fuel injector (5) comprising an electromagnet (42) with a fixed magnetic circuit (46, 76) including a magnetic core (46); and a coil (47) energizable to displace an armature (43) against the action of a compression spring (89) for controlling the metering function; said core (46) comprising an annular seat (48) for said coil (47); said electromagnet (42) being fitted to a body (6) of the injector (5) by a threaded ring nut (44) external to said body (6); said armature (43) being in form of a disk and being integral with a stem (69) guided by an axial sleeve (83); a further ring nut (82) being screwed inside a threaded seat (93) of said body (6) for fitting said sleeve (83) inside said body (6); characterized by the fact that said spring (89) is located between a washer (86) secured to said stem (69) and a wall (87) integral with said sleeve (83); said further ring nut (82) having an inside diameter greater than the outside diameter of said armature (43); said armature (43), said spring (89) and said axial sleeve (83) being preassembled to form an assembly, said assembly being fitted by said further ring nut (82) inside said body (6) independently of said electromagnet (42). An electromagnetic metering valve (40) as claimed in Claim 1, wherein said core (46) comprises a pair of coaxial annular pole pieces (72, 73); characterized by the fact that the outer pole piece (72) of said pair has a length less than the length of the inner pole piece (73) of said pair, said outer pole piece (72) being fitted with a ring (76) having a thickness equal to the difference of said two lengths; the outside diameter of said armature (43) being smaller than the outside diameter of said coil (47). An electromagnetic metering valve (40) as claimed in Claim 1 or 2, characterized by the fact that said sleeve (83) and said wall (87) are comprised in a member substantially in form of a plate (84); said further ring nut (82) acting on a flange (90) of said plate (84). An electromagnetic metering valve (40) as claimed in Claim 3, characterized by the fact that a calibrated washer (91) is provided between said flange (90) and a shoulder (92) of said body (6). An electromagnetic metering valve (40) as claimed in Claim 3 or 4, characterized by the fact that said wall (87) is provided with holes (88) enabling a chamber (60a) inwards of said plate (84) to communicate with a chamber (60b) outwards of said plate (84).

Inventors: BRUNI GIOVANNI, RICCO MARIO, BRUNI, GIOVANNI, RICCO, MARIO
Applicants: ELASIS SISTEMA RICERCA FIAT, ELASIS SISTEMA RICERCA FIAT NEL MEZZOGIORNO SOCIETA CONSORTILE PER AZIONI
Application year: 1993
Main classification: F02M47
IPC codes: F02M59, F02M47