Improved electromagnetic metering valve for a fuel injector

Abstract: A metering valve (40) presenting a shutter (67) for a discharge conduit (63), and an electromagnet (42) in turn presenting a fixed core (46) and a disk-shaped armature (43) detached from and sliding on the stem (69) by means of a sleeve (71). The stem (69) is guided by a bush (83), presents a flange (88) movable inside a swirl chamber (89) with a velocity damping effect, and is fitted, prior to assembling the armature (43) and the electromagnet (42), by means of a ring nut (59), which presses a flange (84), forming one piece with the bush (83), against the body (56) of the valve (40) via the interposition of calibrated washers (87) so selected as to define the travel (h) of the stem (69).

Description: The present invention relates to an improved electromagnetic metering valve for a fuel injector, in particular for internal combustion engines. The metering valves of fuel injectors normally comprise a control chamber with a discharge conduit, which is normally kept closed by a shutter. In known metering valves, the shutter is normally kept closed by the armature of an electromagnet, with the aid of a spring, and is released to open the conduit by energizing the electromagnet to move the armature towards the core of the electromagnet. The armature of known valves is normally connected rigidly to a stem sliding in a guide, and, when closing the discharge conduit, the kinetic energy of the armature and stem is dissipated in the impact of the shutter against the valve. More specifically, in the case of a ball shutter, the kinetic energy is dissipated, via a guide plate and the ball, in the impact against the seat in the valve body. Conversely, when opening the discharge conduit, the kinetic energy due to the return movement of the armature and stem is dissipated in the impact of the stem against a stop. Such impact generates considerable force, which is proportional to the mass and velocity of the armature and stem, and is inversely proportional to impact time, which is very short. Owing to the hardness of the ball and valve body, the impact when closing the valve results in considerable rebound, which is also generated, when opening the valve, by the impact of the stem against the stop. As such, the movement of the armature, and hence the opening and closing movement of the valve, fails to provide for steady operation of the injector. Moreover, the armature moves inside a fuel discharge chamber in which the pressure and density of the fuel vary considerably. An increase in the pressure, and hence in the density, of the fuel inside the discharge chamber reduces the velocity of the armature both when opening and closing the valve. Finally, the movement of the armature itself produces, and is seriously affected by, pressure waves in the fuel inside the discharge chamber, thus further impairing steady operation of the injector. A metering valve has been proposed wherein the armature is made of magnetic material; the stem is made of nonmagnetic material to reduce cost, and is detached from the armature to simplify assembly; and the stem is guided by a sleeve forming one piece with a bell fixed to the injector body, so that the stem is arrested by a very small surface and subject to rebound. Moreover, the armature, stem and guide are assembled together with the electromagnet, so that the travel of the stem cannot be determined without also assembling the armature and the electromagnet, and cannot be measured easily for test purposes. EP-A-0 604 914 discloses a metering valve wherein the stem 92 of the armature 43 is slidably guided by the bush 83, which is fitted to a plate-shaped element 84, having an upper end wall 87 and a lower flange 90. The element 84 is secured to a shoulder 92 of the injector body 6, by means of a ring nut 82 engaging the flange 90, whereas the valve body 56 is secured to the injector body by another ring nut 58. The stem 92 is provided with a C-shaped washer 86 forming a shoulder for the armature return spring 89. The travel of the armature 43 is arrested by the lower end of the bush 83, which is engaged by the washer 86, but this washer 86 moves in a large chamber, which is comprised between the valve body 56 and the upper wall 87 and houses the entire spring 89. Therefore, no appreciable squish or dampening effect can be obtained in the this large chamber, on one hand because the washer 86 is C-shaped, thus causing the passage of the fluid from upper side to the lower side thereof, and on the other hand because the large chamber where the washer 86 moves contains a rather large volume of fluid. Document EP-A-0 404 336 discloses an electromagnetic injector, wherein the shutter bouncing is reduced by having the armature 32 detached from the element 30 secured to the shutter 24. It is an object of the present invention to provide a highly straightforward, reliable metering valve of the above type, designed to overcome the aforementioned drawbacks typically associated with known devices, and which provides for perfectly steady operation of the injector. This object is solved by a valve according to claim 1 which is delimited against EP-A-0 604 914. Two preferred non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a partly sectioned view of a fuel injector incorporating a metering valve in accordance with the present invention; Figure 2 shows a larger-scale section of the metering valve of the Figure 1 injector. With reference to Figure 1, number 5 indicates a fuel injector, e.g. for a diesel engine, comprising a hollow body 6 in which slides a control rod 8, and which is connected at the bottom to a nozzle 9 terminating with one or more injection orifices 11. Body 6 also presents an appendix 13 in which is inserted an inlet fitting 16 connected to a standard high-pressure fuel supply pump. By means of conduits 17, 18 and 21 (Figure 1), a hole 14 (Figure 2) in appendix 13 communicates with an injection chamber 19 of nozzle 9; orifice 11 is normally kept closed by a pin 28 connected to rod 8 by a plate 100; pin 28 presents a shoulder 29 on which the pressurized fuel in chamber 19 acts; and a compression spring 37 assists in pushing plate 100 and hence pin 28 downwards. Injector 5 also comprises a metering valve 40 comprising a sleeve 41 (Figure 2) supporting an electromagnet 42 for controlling a disk-shaped armature 43. Sleeve 41 is fitted to body 6 by means of a thread 44 which screws on to an external thread of body 6, and sleeve 41 presents a shoulder 45 on which rests a magnetic core 46 of electromagnet 42. Between the bottom edge of sleeve 41 and a shoulder 38 of body 6, there are fitted a number of calibrated washers 39 so selected as to define the axial position of core 46 at a predetermined distance from the top surface of disk 43. Core 46 is annular and presents a central hole 49; an annular seat 48 of core 46 houses a standard electric coil 47 for activating electromagnet 42; sleeve 41 presents a bent edge 50 connecting core 46 to a disk 52 forming one piece with a discharge fitting 53 coaxial with hole 49 and connected to the fuel tank; and a cover 54 made of insulating material and fitted with a standard pin 55 of coil 47 is co-molded in known manner on to sleeve 41. Metering valve 40 also comprises a body 56 presenting a flange 57, which is normally kept contacting a shoulder 58 of body 6 of the injector by a ring nut 59; ring nut 59 is threaded externally and screwed on to a thread of a discharge chamber 60 formed in body 6 as explained in more detail later on; and chamber 60 extends axially from the top surface of ring nut 59 to the bottom surface of core 46. Body 56 of valve 40 also presents an axial control chamber 61 communicating with a calibrated radial inlet conduit 62, and with a calibrated axial discharge conduit 63; inlet conduit 62 communicates with hole 14; control chamber 61 is defined at the bottom by the top surface of rod 8; and, by virtue of the greater area of the top surface of rod 8 as compared with that of shoulder 29 (Figure 1), the pressure of the fuel, with the aid of spring 37, normally keeps rod 8 in such a position as to close orifice 11 of nozzle 9. Discharge conduit 63 of control chamber 61 is normally kept closed by a shutter in the form of a ball 67, which rests in a conical seat formed by the plane of contact "X" with conduit 63. Ball 67 is guided by a guide plate 68 on which acts a stem 69 associated with disk 43; and disk 43 forms one piece with a sleeve 71 sliding axially on stem 69, presents a shoulder 72 engaged by an open ring 73 fitted inside a groove 74 on stem 69, and presents slots 76 to improve the armature magnetically and hydrodynamically and to assist fuel flow from chamber 60 to central hole 49 of core 46. Stem 69 extends a given length inside hole 49, and terminates with a small-diameter portion 77, which provides for supporting and anchoring a first compression spring 78 housed inside hole 49, between stem 69 and disk 52. A second compression spring 79, of much greater flexibility than spring 78, is fitted between disk 43 and ring nut 59, and normally keeps disk 43 resting on open ring 73 of stem 69. It should be pointed out that disk 43 moves inside an ample portion "A" of discharge chamber 60 - which is normally full of air-fuel mixture - and therefore generates pressure waves. Stem 69 slides inside a guide 82 comprising a cylindrical bush 83, and a bottom flange 84 presenting axial holes 86; flange 84 is forced by ring nut 59 against flange 57 of body 56 of valve 40 with the interposition of calibrated washers 87 so selected as to define the travel "h" of stem 69; and stem 69 presents an integral bottom flange 88 with a considerable surface "S" by which stem 69 is arrested against the bottom surface "Y" of flange 84. Flange 88 of stem 69 is housed inside a swirl or "squish" chamber 89 in which the fluid between surface "S" of flange 88 and the corresponding surface "Y" of flange 84 is compressed between said surfaces (S and Y) to dampen the movement of stem 69 and disk 43 ("squish" effect). Bush 83 and ring nut 59 form a gap 91 enabling the fluid to flow from chamber 89 through holes 86 into discharge chamber 60. Ring nut 59 locks washers 87, guide 82 of stem 69 and body 56 of metering valve 40 to injector body 6, which is deformed elastically by the axial force generated by the tightening torque of ring nut 59. When body 56 is subjected to high pressure in chamber 61, the axial force opposes that generated by the tightening torque to restore the elastic deformation of body 6. Since ring nut 59 locks both guide 82 and body 56 of valve 40, however, said elastic deformation in no way affects the mutual position of plane "X" and surface "Y", so that there is no variation in travel "h" of stem 69. Metering valve 40 of injector 5 operates as follows. When coil 47 is energized, core 46 attracts disk 43 which, by means of shoulder 72 and ring 73, positively raises stem 69 in opposition to spring 78; and flange 88 of stem 69 generates inside swirl chamber 89 a swirling or squish effect by which the fluid in chamber 89 is compressed and expelled to dampen the stoppage of stem 69 and so prevent rebound and provide for steadier operation of metering valve 40 and injector 5. Though stem 69 is arrested with flange 88 against the surface of flange 84 of guide 82, and disk 43 is arrested with shoulder 72 against ring 73, the respective kinetic energies are absorbed separately by virtue of disk 43 being detached from stem 69. Since disk 43 moves in portion "A" of chamber 60, its movement is also slowed, thus further reducing the kinetic energy to be absorbed, while the variation in pressure in portion "A" in no way affects the movement of stem 69. The pressure of the fuel in chamber 61 therefore opens shutter 67 to discharge the fuel in chamber 60, which is fed back to the tank; and the pressure of the fuel in chamber 19 (Figure 1) acts on shoulder 29 of pin 28 to raise pin 28 and inject the fuel in chamber 19 through orifice 11. When coil 47 (Figure 2) is de-energized, spring 78 pushes down stem 69, which, via ring 73, lowers disk 43; the kinetic energy of disk 43 is dissipated by spring 79 independently of that of stem 69; and the kinetic energy of stem 69 is partly dissipated by the swirling or "squish" effect generated by flange 88 in the fluid inside chamber 89. As a result, the impact of stem 69 on plate 68, of plate 68 on ball 67, and of ball 67 on the seat in discharge conduit 63, is greatly reduced with substantially no rebound; ball 67 closes discharge conduit 63; the pressurized fuel restores the pressure inside control chamber 61; and pin 28 (Figure 1) closes orifice 11. The structure of metering valve 40 also provides for defining and/or measuring the travel "h" of stem 69 without assembling core 46 or disk 43 to body 6. Travel "h" in fact is defined by appropriately selecting and fitting calibrated washers 87 between body 56 of valve 40 and guide 82 of stem 69 by means of ring nut 59. At which point, spring 79 and sleeve 71 are fitted on to stem 69, and disk 43 is locked in place by inserting open ring 73 inside groove 74. Since stem 69 at this point is maintained contacting guide 82 by spring 79 and disk 43, the travel "h" of stem 69 is measured by simply placing the end of a normal travel gauge on the top end of portion 77 of stem 69, and moving stem 69 until ball 67 contacts its seat. Finally, body 6 is closed by assembling sleeve 41 fitted beforehand with disk 52, electromagnet 42 and spring 78. The advantages of metering valve 40 will be clear from the foregoing description. In particular, stop surface "S" of flange 88 and the "squish" effect provide for eliminating rebound of stem 69 both when opening and closing shutter 67; the fact that disk 43 is detached from stem 69 reduces the kinetic energy to be dissipated by stem 69 on striking flange 84 and on ball 67 striking its seat; and the arrangement of guide 82 and stem 69 enables the travel of stem 69 to be defined and/or measured without assembling electromagnet 42.

Claims: An electromagnetic metering valve for a fuel injector, comprising a valve body (56), a shutter (67) for a discharge conduit (63) of a control chamber (61) provided in said body (56), and an electromagnet (42) presenting a fixed magnetic core (46) and a movable armature formed by a disk (43), said disk (43) acting on said shutter (67) by means of a stem (69) normally pushed elastically to keep said shutter (67) in a position wherein said conduit (63) is closed; said stem (69) being engaged in an axially sliding manner by a fixed bush (83) adapted to arrest the travel of said stem (69) for opening said conduit (63); characterized in that said fixed bush (83) is integral with a first flange (84) secured to said body (56), a swirl chamber (89) communicating with a discharge chamber (60) being located between said body (56) and a surface (Y) of said first flange (84); said stem (69) being provided with a second flange (88) housed in said swirl chamber (89), said second flange (88) presenting a surface (S) adapted to be arrested by said surface (Y) of said first flange (84), the opening movement of said stem (69) being dampened by rapid compression of the fuel between said surface (Y, S) of said flanges (84, 88) and expulsion from said swirl chamber (89). A valve as claimed in Claim 1, characterized in that said second flange (88) is integral with said stem (69) and is adjacent to said shutter (63); said shutter being formed of a ball (63) guided by a guide plate (68) adapted to be engaged by said second flange (88). A valve as claimed in Claim 1 or 2, characterized in that said disk (43) is detached from said stem (69); a first spring (78) normally pushing said stem (69) into a closed position; and said disk (43) being maintained resting on said stem (69) by a second spring (79) of a much greater flexibility than said first spring (78). A valve as claimed in Claim 3, characterized in that said core (46) is annular; said disk (43) being formed in one piece with a sleeve (71), said stem (69) sliding inside said sleeve (71); a ring (73) being fitted to said stem (69) for being engaged by a shoulder (73) of said disk (43) under the urge of said second spring (79). A valve as claimed in Claim 4, characterized in that said disk (43) is movable within an ample portion (A) of said discharge chamber (60); any rebound and any variation in the conditions of said fuel in said ample portion (A) having a negligible effect on the movement of said stem (69). A valve as claimed in any previous Claim, characterized in that said first flange (84) is forced against said body (56) by a threaded ring nut (59) cooperating with a thread of a body (6) of the injector, so that the distance between said surface (Y) of said first flange (84) and a plane (X) of contact of said shutter (67) with said discharge conduit (63) is unaffected by the forcing of said ring nut (59). A valve as claimed in Claims 2 and 6, characterized in that said swirl chamber (6) communicates with said discharge chamber (60) through at least one hole (86) provided in said first flange (84) and a gap (91) provided between said bush (83) and said ring nut (59). A valve as claimed in Claim 6 or 7, characterized in that said first spring (78) is located inside said core (46), between said stem (69) and a fixed member (52); said second spring (79) being located between said disk (43) and said ring nut (59). A valve as claimed in one of the foregoing Claims from 4 to 8 dependent on Claim 3, characterized in that said stem (69) arrests said disk (43) by means of an open ring (73) inserted inside a groove (74) on said stem (69). A valve as claimed in one of the foregoing Claims from 6 to 9, characterized in that said bush (83) is fixed by said threaded ring nut (59) via the interposition of calibrated washers (87) prior to assembling said disk (43) and said electromagnet (42); said washers (87) being so selected as to achieve a predetermined travel (h) of said stem (69). A valve as claimed in Claim 9 or 10 dependent on Claim 8, characterized in that said electromagnet (42) and said fixed member (52) are fitted to a sleeve (41) presenting a thread (44) which is screwed to an external thread of said body (6) of the injector via the interposition of further calibrated washers (39) so selected as to define the position of said core (46) in relation to said stem (69).

Inventors: RICCO MARIO, RICCO, MARIO
Applicants: ELASIS SIST RICERCA FIAT NEL M, ELASIS SISTEMA RICERCA FIAT NEL MEZZOGIORNO SOCIETA CONSORTILE PER AZIONI
Application year: 1996
Main classification: F02M47
IPC codes: F02M63, F02M51, F02M59, F02M47