Fuel injector and method of adjusting the travel of a fuel injector shutter

Abstract: A shutter in the form of a needle (19) is controlled by a rod (8) in turn controlled by an electromagnetic metering valve (24) and which acts on the needle (19) via a cylindrical plate (47) formed in classes differing in terms of height (h). The plate (47) for fitment between the rod (8) and the needle (19) is selected from the class corresponding to the travel of the needle (19) required to open one or more orifices (11) in the nozzle (10); and, to absorb any transverse components of the forces exchanged between the rod (8) and needle (19) and so prevent wear of the contacting surfaces of the needle (19) and nozzle (10), the plate (47) is guided inside the injector body (6) with a very small clearance, e.g. in the region of 0.02 mm.

Description: The present invention relates to a fuel injector and a method of adjusting the travel of a fuel injector shutter. The travel setting of the shutter on a fuel injector nozzle is extremely important in that it determines the maximum delivery and consequently also the opening and the closing time of the injector; and, on known injectors, it is adjusted by means of washers on the end of the shutter or needle control rod on which the pressurized fuel acts. The washers are therefore subject to wear, due to the severe dynamic stress to which they are subjected, and, what is more, in no way contribute towards reducing or eliminating any transverse forces transmitted by the rod to the needle, thus resulting in wear of the mating surfaces between the needle and nozzle. Document EP 548916A discloses a fuel injector comprising a shutter in form of a needle for closing the nozzle. The needle is controlled by a coaxial rod in turn controlled by an electromagnetic metering valve. The rod acts on the needle via a substantially cylindrical plate guided by a seat coaxial with the rod. The mutually mating surfaces of the plate and the needle, as well as those of the plate and the rod, are however flat. It is an object of the present invention to provide an extremely straightforward, reliable fuel injector comprising a shutter, and designed to overcome the aforementioned drawbacks typically associated with known devices. According to the present invention, there is provided a fuel injector comprising a shutter, wherein the shutter is in form of a needle travelling axially for opening and closing a nozzle; comprising a control rod coaxial with said needle and axially slidable to control the travel of said needle via a substantially cylindrical plate; said plate and said control rod being mutually engaged by a first pair of mating surfaces, said plate and said needle being mutually engaged by a second pair of mating surfaces; a hollow body having an axial cavity in which slide said control rod and said plate, said axial cavity including a sleeve for precision-fit guiding an end portion of said control rod, and a coaxial seat for guiding said plate, said sleeve forming a control chamber defined by a terminal surface of said end portion; and an electromagnetic metering valve including an electromagnet controlling an armature, so that when said electromagnet is energized the fuel is drained from said control chamber and the fuel pressure in an injection chamber causes said needle to open said nozzle, and when said electromagnet is de-energized the control chamber is closed to cause the fuel pressure inside said control chamber to act on said terminal surface thus holding said needle as to close said nozzle; characterized by the combination of the following features: said coaxial seat is machined accurately as to present a very small clearance with respect to the cylindrical surface of said plate; and one mating surface of each of said pairs is flat and the other mating surface of each of said pairs is convex; whereby said plate absorbs any transverse components of the forces exchanged between said control rod and said needle and due to misalignment of said control rod and said needle. According to a further characteristic of the present invention, said plate is formed in different classes in terms of height, a plate in one of said classes being selected for fitment between said rod and said needle so as to adjust the travel of the needle to conform with the required opening of the nozzle. 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 shutter travel adjusting device in accordance with the present invention; Figure 2 shows a larger-scale section of a detail in Figure 1; Figure 3 show a section along line III-III in Figure 2. Number 5 in Figure 1 indicates a fuel injector, e.g. for a diesel internal combustion engine, comprising a hollow body 6 with an axial cavity 7 in which slides a control rod 8. At the bottom, body 6 is fitted by means of a ring nut 9 with a nozzle 10 terminating with one or more injection orifices 11 communicating with an axial cavity 12 of nozzle 10. Body 6 presents an appendix 13 connected to a high-pressure, e.g. 120 MPa, fuel supply fitting 14 communicating, via a conduit 16 in body 6 and a conduit 17 in nozzle 10, with an injection chamber 18 in turn communicating with cavity 12. Orifice 11 is normally closed by a needle type shutter 19 housed coaxially with rod 8 inside cavity 12 and presenting a larger-diameter portion 21 which is guided in sliding manner inside a seat 22 formed in nozzle 10 and coaxial with cavity 12, and forms a shoulder 23 on which the pressurized fuel in chamber 18 acts. Injector 5 also comprises a metering valve 24 controlled by an electromagnet 26 controlling an armature 27; metering valve 24 comprises a head 28 housed inside a seat 29 formed in body 6 and coaxial with cavity 7; and head 28 presents a sleeve 30 for precision-fit guiding the top portion 31 of rod 8. Sleeve 30 forms a control chamber 32 defined by the upper surface 33 of portion 31 of rod 8, which presents a larger surface than shoulder 23 of needle 19; and control chamber 32 communicates, via an inlet conduit 34, with the high-pressure fuel from fitting 14, and, via a drainage conduit 36, with a drainage chamber 37 in turn communicating with the fuel tank. Portion 31 of rod 8 presents an annular groove 38 for more evenly distributing the fuel pressure from high-pressure control chamber 32 to a low-pressure chamber 39 which communicates with drainage chamber 37 via a conduit 41 formed in body 6, so that said low pressure is atmospheric. Groove 38 provides for eliminating or reducing the transverse components of the forces generated by said pressure reduction via precision fit 30-31, thus eliminating the wear caused by the surface of portion 31 sliding along a generating line of the inner surface of sleeve 30. At the bottom, chamber 39 presents a smaller-diameter portion 42 engaged by a smaller-diameter portion 43 of rod 8; and, at the bottom, portion 42 forms a shoulder 45 defining a chamber 44 in which is housed a compression spring 46 resting, at the top, on shoulder 45 and, at the bottom, on a plate 47 located between portion 31 of rod 8 and top portion 21 of needle 19. Electromagnet 26 is normally de-energized so that, by means of a further spring 48, armature 27 acts on a ball shutter 49 to close drainage conduit 36 of control chamber 32. The fuel pressure inside control chamber 32 therefore acts on surface 33 of top portion 31 of rod 8, and, together with the action of spring 48, is greater than the fuel pressure on shoulder 23 of needle 19, so that rod 8 is held down together with plate 47 and needle 19 which thus closes orifice 11 of nozzle 10. When electromagnet 26 is energized, armature 27 is raised so that the fuel pressure in chamber 32 opens metering valve 24; the fuel is drained from chamber 32 along conduit 36 into chamber 37 and back to the tank; and the fuel pressure in injection chamber 18, which is now greater than the remaining pressure on surface 33 of rod 8 and the force exerted by spring 37, raises needle 19 to open orifice 11 and so inject the fuel contained inside chamber 18 and conduits 16, 17. When electromagnet 26 is again de-energized, armature 27 is lowered rapidly by spring 48 to close control chamber 32, so that, by means of rod 8 and spring 46, the pressurized fuel again lowers needle 19 to close orifice 11. According to the present invention, to adjust the travel of needle 19, plate 47 is formed in different modular classes in terms of height h. Provision may conveniently be made for plates 47 of five classes differing in height h by 0.02 mm; and the class of plate 47 to be fitted in each case between rod 8 and needle 19 is so selected that height h corresponds to the required travel of needle 19, e.g. in terms of maximum delivery of the injector. Plate 47 also provides for absorbing any transverse components of the forces exchanged between and inevitably due to slight misalignment of rod 8 and needle 19, for which purpose, plate 47 slides inside a guide formed by a seat 51 (Figure 2) defined by the bottom portion of chamber 44, and the surface of which is machined so as to mate accurately, i.e. with a very small clearance of, say, 0.02 mm, with the cylindrical surface of plate 47. As plate 47 is housed inside the low-pressure portion of chamber 44, and on account of the pressures in chambers 32 and 18, rod 8, plate 47 and needle 19 are never detached and move integrally with one another as though in one piece, thus eliminating any dynamic stress on adjusting element 47 and hence wear on the contacting parts. As is known, injector 5 operates at a pressure of over 120 MPa in chambers 18 and 32 (Figure 1); and, as surfaces 23 and 33 subjected to this pressure are in the region of 12-16 mm 2 , the forces involved are roughly 2000 N, any transverse components of which may therefore impair smooth sliding of rod 8 inside cavity 7, of top portion 31 of rod 8 inside sleeve 30, and of portion 21 of needle 19 inside seat 22, which present a very close tolerance fit, e.g. with a radial clearance of about 0.001 mm. According to a further characteristic of the present invention, the cylindrical surface of plate 47 presents a flat portion 52 (Figures 2 and 3) defining a passage into low-pressure chamber 44 for the fuel seeping from high-pressure chamber 18 and between the mating surfaces of seat 22 and portion 21 of needle 19. Moreover, plate 47 contacts rod 8 and/or needle 19 by means of at least one pair of mating surfaces comprising a convex surface and a flat surface. More specifically, at the top, plate 47 presents a small truncated-cone-shaped portion 53 terminating at the top with a flat surface 54 engaging a convex surface 56 at the bottom end of portion 43 of rod 8; which portion 53 also provides for effectively centering and guiding and so preventing slippage of spring 46 inside chamber 44. At the bottom, plate 47 presents a slightly convex surface 57 engaging a flat surface 58 of portion 21 of needle 19; and the forces between mating surfaces 54,56 and 57,58 are so transmitted that the transverse components of the forces exchanged between and due to any misalignment of rod 8 and needle 19 are absorbed by plate 47. The advantages of the adjusting device according to the present invention will be clear from the foregoing description. In particular, it provides for adjusting the travel of needle 19 in a region not subjected to dynamic stress, and for absorbing any transverse components of the forces exchanged between rod 8 and needle 19. Clearly, changes may be made to the adjusting device as described and illustrated herein without, however, departing from the scope of the claims. In particular, plate 47 may present two flat surfaces engaging convex mating surfaces of rod 8 and needle 19, and vice versa; mating surfaces 54,56 and 57,58 in one or both pairs may be both convex, or one convex and the other concave; plate 47 may present a different number of, e.g. two diametrically-opposed, flat portions 52; and flat portions 52 may be replaced by axial or helical grooves.

Claims: A fuel injector comprising a shutter, wherein the shutter is in form of a needle (19) travelling axially for opening and closing a nozzle (10, 11); comprising a control rod (8) coaxial with said needle (19) and axially slidable to control the travel of said needle (19) via a substantially cylindrical plate (47); said plate (47) and said control rod (8) being mutually engaged by a first pair of mating surfaces (54, 56), said plate (47) and said needle (19) being mutually engaged by a second pair of mating surfaces (57, 58); a hollow body (6) having an axial cavity (7) in which slide said control rod (8) and said plate (47), said axial cavity (7) including a sleeve (30) for precision-fit guiding an end portion (31) of said control rod (8), and a coaxial seat (51) for guiding said plate (47), said sleeve (30) forming a control chamber (32) defined by a terminal surface (33) of said end portion (31); and an electromagnetic metering valve (24) including an electromagnet (26) controlling an armature (27), so that when said electromagnet (26) is energized the fuel is drained from said control chamber (32) and the fuel pressure in an injection chamber (18) causes said needle (19) to open said nozzle (10, 11), and when said electromagnet (26) is de-energized the control chamber (32) is closed to cause the fuel pressure inside said control chamber (32) to act on said terminal surface (33) thus holding said needle (19) as to close said nozzle (10, 11); characterized by the combination of the following features: said coaxial seat (51) is machined accurately as to present a very small clearance with respect to the cylindrical surface of said plate (47); and one mating surface (54, 58) of each of said pairs is flat and the other mating surface (56, 57) of each of said pairs is convex; whereby said plate (47) absorbs any transverse components of the forces exchanged between said control rod (8) and said needle (19) and due to misalignment of said control rod (8) and said needle (19). A fuel injector as claimed in Claim 1, characterized in that said clearance is in the region of 0.02 mm. A fuel injector as claimed in Claim 1 or 2, characterized in that said control rod (8) comprises an annular groove (38) to reduce the transverse components of the fuel pressure in said sleeve (30). A fuel injector as claimed in any previous Claim, characterized in that said plate (47) presents a convex surface (57) engaging a flat surface (58) of said needle(19). A fuel injector as claimed in Claim 4, characterized in that said plate (47) also presents a truncated-cone-shaped portion (53) terminating with a flat surface (54) engaging a convex surface (56) of said control rod (8). A fuel injector as claimed in Claim 5, wherein a compressing spring (46) is provided between said plate (47) and a shoulder (45) of a low-pressure chamber (44) formed by said axial cavity (7) for assisting the fuel pressure in closing said nozzle (10, 11), characterized in that said truncated-cone-shaped portion (53) provides for guiding and centering said compression spring (46) inside said low-pressure chamber (44), to prevent said compressing spring (46) from slipping against the walls of said low-pressure chamber (44). A fuel injector as claimed in any previous Claim, characterized in that said plate (47) is formed in different classes in terms of height (h); a plate (47) in one of said classes being selected for fitment between said control rod (8) and said needle (19), so as to adjust the travel of said needle (19) to conform with the required opening of said nozzle (10, 11). A method for adjusting the travel of a fuel injector shutter, wherein the shutter is in form of a needle (19) travelling axially for opening and closing a nozzle (10, 11), and is controlled by an axially slidable control rod (8) coaxial with said needle (19) via a substantially cylindrical plate (47); said control rod (8) and said plate (47) being housed in an axial cavity (7) of a hollow body (6) including a sleeve (30) for precision-fit guiding an end portion (31) of said control rod (8), and a coaxial seat (51) for guiding said plate (47), said sleeve (30) forming a control chamber (32) defined by a terminal surface (33) of said end portion (31); an electromagnetic metering valve (24) including an electromagnet (26) controlling an armature (27) so that when said electromagnet (26) is energized the fuel is drained from said control chamber (32) and the fuel pressure in an injection chamber (18) causes said needle (19) to open said nozzle (10, 11), and when said electromagnet (26) is de-energized the control chamber (32) is closed to cause the fuel pressure inside said control chamber (32) to act on said terminal surface (33) thus holding said needle (19) as to close said nozzle (10, 11); characterized by providing said plate (47) in different modular classes in terms of height (h), and by selecting the class of said plate (47) to be fitted in each case between said control rod (8) and said needle (9), so that said height (h) of the plate (47) selected corresponds to the required travel of said needle (19) to conform with the required opening of said nozzle (10, 11).

Inventors: RICCO MARIO, RICCO, MARIO
Applicants: ELASIS SIST RICERCA FIAT NEL M, ELASIS SISTEMA RICERCA FIAT NEL MEZZOGIORNO SOCIETA CONSORTILE PER AZIONI
Application year: 1995
Main classification: F02M61
IPC codes: F02M61, F02M47, F02M51