FUEL INJECTOR

Abstract: A fuel injector having a body (12) with an axial interior cavity (36). A valve assembly (46) is axially reciprocable in the cavity (36). A fuel inlet (38) is provided at one end of the cavity (36) and an outlet (34) is provided at the other end. The outlet (34) defines a cylindrical outlet bore (52) in which is closely fitted a cylindrical end portion (50) of a valve member (48) forming part of valve assembly (46). Valve member (48) also has a shank (59) connected to end portion (50) by a somewhat tapered portion (58). Shank (59) extends from outlet (34) into cavity (36) and, in an inoperative condition of the injector, the valve member (48) is resiliently biased so that portion (58) thereof is adjacent a somewhat tapered annular valve seat (66) in outlet (34) adjacent cavity (36). Pressure of fuel admitted to cavity (36) via inlet (38) acts on the valve member (48) to move it against the resilient bias applied thereto to permit fuel flow from the cavity (36) and past valve seat (66). Fuel so passing is ejected from the outlet (34) via grooves (50a) extending along the outer surface of the cylindrical end portion (50) of the valve member (48).

Description: FUEL INJECTOR This invention relates to fuel injectors. According to the present invention there is provided a fuel injector having " structure defining a cavity and an inlet and an outlet for fuel flow respectively into and out of said cavity, a valve member mounted in the cavity for lengthwise movement therein and being resiliently biased whereby a first portion thereof is normally so biased against a valve seat formed in said outlet, whereby to close the outlet, said valve member having a surface portion positioned to be open to fuel pressure existing in said cavity when pressurised fuel is admitted thereinto via such inlet, such that the fuel pressure in use acts on the valve member to move the valve member against said resilient bias to move said valve portion away from said valve seat to open said outlet and permit fuel flow from the cavity via the outlet. Preferably said valve element has a generally cylindrical portion which moves with small clearance in a complementary generally cylindrical bore formed in said outlet when said valve member moves to effect said opening. Preferably fuel outlet passages from the injector, and forming part of said outlet, are at least partly defined by grooves on at least one of said cylindrical bore and said cylindrical portion of said valve member. The passages may be arrayed about the cylindrical bore or cylindrical valve member portion. Preferably the passages are defined between said grooves and £he opposed surface of the cylindrical bore or cylindrical valve member portion. Preferably too, the grooves are formed on the cylindrical valve member portion. The valve seat preferably comprises an inwardly convergent bore portion of the outlet. In this case, said first portion of said valve member preferably comprises a convergent surface portion thereof adjacent the cylindrical portion. The said resilient bias may be provided by a resilient compression spring interposed between an end of said cavity from which said outlet extends and sidewardly projecting portion of the valve member within said cavity. Preferably said sidewardly projecting portion is formed on a centring element operable to maintain the valve member axially aligned with the axis of said cylindrical portion and cylindrical bore during movement of the valve element. Preferably too, -the said convergent surface portion of the valve member is formed so as to be defined by a surface of revolution about the axis of said cylindrical portion which surface of revolution is concavely curved when viewed in axial section. The invention is further described with reference to the accompanying drawings in which: Figure 1 is an axial cross-section of a fuel injector constructed n accordance with the invention; Figure 2 is an axial cross-section of a valve member incorporated into the injector of figure 1; and Figure 3 is an enlarged view of the region in the circle "A" shown in figure 1. The injector 10 shown comprises a body 12 formed of two parts 14, 16. Part 14 comprises a generally cylindrical shank portion 18 which is externally threaded and a somewhat larger diameter cylindrical portion 20 at one end thereof. Portion 20 has a hollow bore 20a which is internally threaded and a threaded end portion 22 of body part 16 is threadedly received therein. Part 16 includes an outstanding flange portion 24 intermediate the ends thereof, and adjacent portion 22, and a rearwardly extending end portion 26 of cylindrical form. Part 16 is sealed to part 14 by an O-ring 40 which is received in a groove 42 formed in one face of flange 24 on part 16 and which is brought into engagement with an end face of part 14 when the parts 14 and 16 are screwed together. The dimensions of groove 42 are chosen to that when the parts 14, 16 are screwed together, the O-ring 40 is compressed, between the end face of part 14 and the 00668 ' ' base of the groove 42, to a higher compression level than the intended maximum fuel operating pressure of the injector occurring during use. Thus, the fuel pressure will not be such as to cause undesired deformation of the O-ring which deformation might result in a change of the volume of fuel delivered by the injector. The parts 14, 16 are each hollow, part 14 having in addition to bore 20a, an axial bore 28 extending from bore 20a towards an outlet end of the injector.- * Bore 28 terminates, at the end closest the outlet end of the injector, in a transverse annular end surface 28a. Part 16 has an axial bore 30. In the assembled condition of the two parts, as shown, the bores 28, 30 are arranged end to end so as to together define an elongate cylindrical cavity 36 within the interior of body 12. This cavity is sealed, save for an axially positioned outlet 34, formed at an outlet end of portion 18 of part 14, and an opposed axially positioned inlet 38 formed in portion 26 of part 16. A valve assembly 46 is mounted within cavity 36. This comprises an elongate valve member 48 having a generally cylindrical end portion 50 which is arranged at the outlet end of the injector and which is received within a complementary cylindrical bore 52, forming a portion of outlet 34. Portion 50 terminates in a transverse outer end face 50b. Valve member 48 also includes an elongate shank 59 which is interconnected with cylindrical portion 50 via a generally convergent portion 58 of the valve member. The outlet 34 includes a bore 60 of slightly greater diameter than shank 59 and which extends over that part of the outlet 34 adjacent the surface 2"8a. Surface 28a forms one end of cavity 36. Intermediate this bore 60 and the bore 52 of the outlet 34, "there is provided a stepped outwardly divergent valve seat 66 which is of a form best shown in figure 3. More particularly valve seat 66 is formed as a surface of revolution about the axis of the injector and that surface or revolution is generally convex when viewed in axial section. The valve seat is made up of three frustoconical surfaces 66a, 66b, 66c arranged in that order from the bore 60 to the bore 52. Surface 66a is of relatively small slope relative to the axis of the injector, as viewed in axial section, whereas surface 66c is of relatively greater slope. Surface 66b is of intermediate slope. It has been found satisfactory to make surface 66a of slope of the order of 10°, surface 66b of slope of the order of 30°, and surface 66c of slope of the order of 40°, relative to the axis of the injector. The portion 58 of valve member 48 intermediate cylindrical end portion 50 and shank 59 is of generally concave cross-section when viewed in axial section. The surface of portion 58 defines a first section 58a of generally frustoconical configuration of slope approximately 30° relative to the axis of the shank and which extends from the cylindrical portion 50 in the direction towards the shank 59. The surface of portion 58 also defines a section 58b which joins section 58a and shank 59 and which is defined as a surface of revolution which is arcuate in transverse section. The member 48 extends from the portion 50, inwardly through the outlet 34 with the portion 58 adjacent valve seat 66 and with the shank 59 extending through bore 60 and into the cavity 36. The end of shank 59 remote from portion 50 is threaded. A guide element 70 forming part of valve assembly 46 is of hollow cylindrical form and is fitted over shank 59 adjacent the threaded end thereof. Guide member 70 has a first portion 72 adjacent the aforementioned threaded end of the shank and which is of relatively small cross-sectional size compared with the side to side diameter of the chamber 36. Guide member 70 also has an enlarged flange 74 at the end thereof closest to the outlet 34, this being made of diameter only slightly less than the diameter of the bore 28 within which the flange 74 is positioned. The flange 74 has a series of cutout portions 74a in the periphery thereof so as to permit fluid flow communication between the portions of chamber 36 which are to either axial side of the flange. Guide member 70 is constrained against movement along the valve member 48 in the direction away from portion 50 of member 48 by means of two nuts 78, 80 threadedly received on the aforementioned threaded end portion of the shank 59 of member 48. A helical compression spring 84 is interposed between member 70 and transverse end surface 28a of the portion 18 of part 14. Spring 84 acts on member 48 through member 74 to resiliently bias the valve member 48 to a closed position (shown) at which the portion =58 of valve member 48 engages the valve seat ' 66 of outlet 34. The member 48 is, however, movable against such bias in a direction from right to left as' iewed in figure 1. In the closed position of the valve member 48, the section 58a of the surface of portion 58 of the valve member sealingly engages the surface portion 66b of the valve seat 66. The surface section 58b, at least, is opposed to and spaced from the surface 66a of the valve seat. Because of this spacing, and clearance between bore 66 and shank 59, at least the surface section 58b is in fluid flow communication with the cavity 36, even when the valve member 48 is in its closed position. The location of the portion 58 of valve member 48 when closed is shown in figure 3 by broken line 58' . The portion 50 of valve member 48 is provided with an array of lengthwise extending grooves 50a on its side surface and these define, between the grooves 50a and the bore 52 passages which communicate between the surface section 58a on the valve member portion 58, at locations adjacent portion 50, and with the outermost transverse end face 50b of the portion 50 * . Because of the presence of the surface 66c on the valve seat 66, % which surface is at a relatively greater slope to the axis of the injector than the adjacent part of the surface section 58a on valve member portion 58, there is defined between these, in the closed condition of the valve member 48, a small annular gap into which the grooves 50a provide communication. In the closed condition, flow from the gap between the surface/66a and the surface section 58b, to the annular space between surface section 58a on valve member 48 and the adjacent surface 66c is precluded by virtue of the engagement of the valve member portion 58 with the valve seat surface 66b. When, however, the member 48 is moved against the resilient bias provided by spring 84 so as to move the portion 58 away from engagement with surface 66b, such flow can occur thereby permitting flow into the passageways defined by the grooves 50a and thence outwardly from the outlet end of the injector. The portion 26 of part 16 of the injector has a necked outlet end 26a which is externally threaded and which is arranged to be connected to a fuel supply line which is in turn, in use of the injector, connected to a fuel pump. In operation, with valve member 48 in the closed position, pressurised fuel is applied to the inlet 38 from the aforementioned supply line to the injector, and thence passes into the cavity 36 so as to fill the cavity 36, it being borne in mind that, as mentioned, the periphery of flange 74 of member 70 is cut out in such a fashion as to permit free communication of liquid between the portions of the cavity 36 to either side thereof. Fuel so admitted is forced to enter the outlet 34, passing down between the clearance gap between bore 60 and that part of the shank 59 of member 48 which is adjacent thereto. Such liquid passes into the outlet 34 to the location where the portion 58 of member 48 sealingly engages the surface 66b of the valve seat 66. The pressure of fuel so entering the chamber 36 and outlet 34 acts against the surface section 58b on portion 58 of member 48 and, if sufficient fuel pressure is available, so acts against the portion 58 as to move the valve member 48 from right to left as shown in figure 1 against the resilient bias of spring 84. When this occurs, liquid may pass from the cavity 36 through the outlet 34 via the grooves 50a as described. When the valve member 48 moves to the open condition fluid pressure within the chamber 36 is able to.act upon each of the sections 58a, 58b of the surface of portion 58. Accordingly, that pressure acts on a greater area than was the case prior to opening of the valve member. Thus, once opening is initiated, the additional force then acting on the member 48 causes a very quick and sudden completion of the opening movement. Opening, however, terminates when the pressure force so generated by fuel acting against the valve member reaches an equilibrium state with the resilient force applied in the reverse direction by the spring 84. Of course, the latter force increases on opening movement of the valve member. When a degree of opening movement has been reached at which the spring force can overcome the pressure force acting on the member 48, the spring 84 acts to revert the valve member 48 to its closed position. On such reversion, the spring force becomes reduced whereupon the valve member is again moved to the open condition under action of fluid pressure in chamber 36. 'As a result of this, on an application of fuel pressure into the chamber 36, the valve member is moved to effect repeated cycles of instantaneous opening and closing movements. Thes'e ensure that fuel is ejected from the injector as fine droplets, as is desired for proper operation. Such ejection continues until fuel is no longer supplied to the injector so- as to cause the fuel in the cavity 36 to be pressurized. The injector 10 is installed in an internal combustion engine in the same fashion as conventional injectors, the threaded part 14 being screwed into.the usual threaded opening in the engine leading to the engine combustion chamber. The described injector has been found to be particularly satisfactory in use. The arrangement of the generally cylindrical bore 52 and the grooved cylindrical portion 50 of the member 48 has been found to provide particularly effective operation. The configuration of the valve seat 66 in the outlet 34, as described, has been found to be simple to produce and, in cooperation with the described configuration II of the surface of portion 58 on the valve member 48, provides particularly effective sealing between the outlet 34 and valve member 48. The cooperating cylindrical portion 50 and bore 52 provide for accurate guidance of the member '48 so as to effect linear opening and closing movements. .This guidance is facilitated by the provision of the guide member 70 and its flange 74. The periphery of the flange 74, aside from locations where the cut out portion 74a are provided may be of cylindrical form of diameter only slightly less than that of bore 28, whereby the flange 74 is slidingly guided in the bore 28, thus ensuring good guidance of the valve member. The provision for egress of fuel from the injector via the grooves 50a also has the advantage that passageways through which such egress of fuel from the injector occurs (being the passageways between the grooves 50a and bore 52) are constituted by surfaces which move relative to each other during opening and closing movement of the valve member 48. That is to say, those parts of the passageway defined on the grooves 50a move relative to the parts thereof which are formed as parts of the bore 52. The consequence of this is that any tendency to blockage of these passageways is minimised, since small particles which might otherwise cause blockage tend to be ground between the portion 50 and bore 52 to reduce their size. In ' practice, it has been found that a minimal amount of fine machining is necessary to form the injector, the only fine machining operations being 11 to machine the outlet 34, the cylindrical portion 50 and portion 58. on the valve member 48, and to lap the valve member into the valve seat 66. Generally, it is sufficient to arrange that the difference in diameters of the cylindrical bore 52 and the cylindrical portion 50 on valve member 48 be of the order of 0.0 * 1mm whereby to give a gap width between these of one half that value. The arrangement of the injector 10 whereby the valve member 48 presents, at the cylindrical portion 50, an end face 50b of substantial area open to the interior of the combustion chamber of the engine with which the injector is used, permits the injector to be used*, in conjunction with a suitable pump for supply of fuel, so that the injector is operative to control the fuel injection process whereby to prevent undesirably high peak cylinder pressures occurring. Once the injector is open and fuel injection is taking place the area of the member 48 which is subjected to combustion chamber pressure is substantially equal to the area which is subjected to pressure of fuel being injected. More particularly, the cylinder pressure acts against the face 50b while the fuel pressure in cavity 36 and outlet 34 acts against an equal cross sectional area presented by the member 48. The latter areas are if , , where r. is the radius of the cylindrical portion 50. On the other hand, before opening of the valve, the effective area against which fuel pressure 2 acts is represented by1ϊr 2 where r 2 is the radius of the member 48 where the surface of portion 58 first meets the surface 66b, counted in the direction away from cavity 36. By suitable selection of the areas represented bytfr, and1fr 2 , then, the force generated by the combustion pressure in the combustion chamber acting against the member 48 can be made effective to a desired extent to tend to clo ' se the injector once it is opened. That is to say, if there is a substantial difference between these areas, a relatively high fuel delivery pressure will be necessary before opening of the valve can occur. That delivery pressure may then be very high relative to the combustion chamber pressure even after ignition is effected, so that the delivery pressure is sufficient to cause continued operation of the injector until all of a preset fuel delivery volume from the fuel pump has been delivered. On the other hand, if the areas * 2- 2 ffI^ andlfr_ are more nearly equal, the fuel delivery pressure needed to cause opening of the injector may be less relative to the combustion chamber pressure so that, on rise in cylinder pressure on initiation of combustion, there may be developed against face 50b a force sufficient to move member 48 to close * the injector against the fuel delivery pressure force acting thereon. Thus, in the latter instance the valve member is sensitive to the combustion chamber pressure rise in a way tending to curtail that rise to not surpass a predeter inable pressure. When the combustion chamber pressure reaches the predetermined level, the valve member 48 is moved to its closed position, interrupting fuel supply, so curtailing combustion and consequent further combustion chamber pressure rise. The extent to which this effect occurs is dependent not only on the area differences mentioned, but also on various other factors including the selected fuel delivery pressure, but it has been found practicable to so select the variables including 2 the areasTTr. and "^Tr- as to provide the useful characteristic that the peak combustion pressure % '" reached in the cylinder is controlled so as to"not reach undesired proportions. In my copending international patent application entitled "LIQUID PUMP" filed the same day as the present application, there is described a pump suitable for use in conjunction with the present fuel injector whereby to permit fuel cutoff by the injector under the circumstances immediately above described. The disclosures of that specification are hereby incorporated into the present specification to form part thereof. It will be appreciated, however, that the effect described may be achieved by use of any supply pump which has the characteristic that fuel delivery can be interrupted by the described backward movement of the valve member 48. The described construction has been advanced merely by way of explanation and many modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.

Claims: CLAIMS : 1. A fuel injector having structure defining a cavity and an inlet and an outlet for fuel flow respectively into and out of said cavity, a valve member mounted in the cavity for lengthwise movement therein and being resiliently biased whereby a first portion thereof is normally so biased against _. valve ^ seat formed in said outlet, whereby to close 'the outlet, said valve member having a surface portion positioned to' be open to fuel pressure existing in said cavity when pressurised fuel is admitted thereinto via such inlet, such that the fuel pressure in use acts on the valve member to move the valve member against said resilient bias to move said valve portion away from said valve seat to open said outlet and permit fuel flow from the cavity via the outlet. 2. A fuel injector according to claim 1, wherein said valve element has a generally cylindrical portion which moves with small clearance in a complementary generally cylindrical bore formed in said outlet when said valve member moves to effect said opening. 3. A fuel injector according to claim 2, wherein fuel outlet passages from the injector, and forming part of said outlet, are at least partly defined by grooves on at least one of said cylindrical bore and said cylindrical portion of said valve member. 4. A fuel injector according to claim 3, wherein said passages are arrayed about the cylindrical bore or 'cylindrical valve member portion. 5. A fuel injector according to claim 4, wherein the passages are defined between said grooves and the opposed surface of the cylindrical bore or cylindrical valve member portion. 6. A fuel injector according to claim 5, wherein the grooves are formed on the cylindrical valve member portion. 7. A fuel injector according to any preceding one of claims 2 to 6, wherein said valve seat comprises an inwardly convergent bore portion of the outlet. 8. A fuel injector according to claim 7, wherein said first portion of said valve member comprises a convergent surface portion thereof adjacent the cylindrical portion. 9. A fuel injector according to any preceding claim, wherein said resilient bias is provided by a resilient compression spring interposed between an end of said cavity from which said outlet extends and a sidewardly projecting portion of the valve member within said cavity. 10. A fuel injector according to claim 9, wherein said sidewardly projecting portion is formed on a 8 17 centring element operable to maintain the valve member axially aligned with the axis of said cylindrical portion and cylindrical bore during movement of the valve element. 11. A fuel injector according to claim 8, 9 or 10, wherein said convergent surface portion of the * valve member is formed so as to be defined by a surface of revolution about the axis of said cylindrical portion which surface of revolution is concavely curved when viewed in axial section.

Inventors: LAMPARD ROBERT DOUGLAS, LAMPARD, ROBERT, DOUGLAS
Applicants: LAMPARD ROBERT DOUGLAS, LAMPARD, ROBERT, DOUGLAS
Application year: 1985
Main classification: F02M61
IPC codes: F02M61