DAMPED OPENING POPPET COVERED ORIFICE FUEL INJECTION NOZZLE

Abstract: A poppet covered orifice fuel injection nozzle (5) for use in a direct injection type diesel engine has a spray tip (12) with a spring biased poppet valve (30) journaled for reciprocable movement therein, the lower reduced diameter free end of the spray tip and the head (31) of the poppet valve having opposed frusto-conical valve seat surfaces (22,33) with a differential angle of about 2° so that seating engagement occurs at the outer peripheral edges thereof. The poppet valve has a fuel supply passage (35) extending through the stem (31) thereof for flow communication with a plurality of circumferentially spaced apart radial discharge orifices (36) that are inclined and located so as to discharge fuel parallel to and directly across the valve seat surface (33) of the poppet valve. A retainer (42) is sealingly fixed to the free stem end of the poppet valve and a damping piston (50) encircles the stem of the poppet valve in position to cooperate with the retainer for one-way damping of valve movement in a valve opening direction.

Description: This invention relates to liquid fuel injection nozzles for internal combustion engines and, in particular, to such an injection nozzle of the outward damped opening poppet valve type for use in a direct injection type diesel engine. Fuel injection nozzles of the outward opening, poppet valve type for use in diesel engines are well known. In this type of injection nozzle, there is provided a closure member, in the form of a poppet valve, that is movable to an open position relative to an associate valve seat by a high pressure pump, and that is movable to its closed position in seating engagement with the valve seat by a spring acting on a collar positioned so as to loosely encircle the valve stem of the poppet valve whereby it can abut against an enlarged head at the inner end of the valve stem of the poppet valve. Exemplary embodiments of such fuel injection nozzles that have spray discharge orifices associated with the poppet valve that are uncovered upon opening movement of the poppet valve are disclosed, for example, in US patent nos. 2,521,224; and 4,082,224. However, because of current and future emission standards, all such prior known injection nozzles appear to be unsuitable for use in direct injection type diesel engines because of poor injected fuel penetration at light engine loads, which can also result in high smoke levels. Accordingly, an improved injection nozzle of the outward opening, poppet valve type has been disclosed in US patent no. 4693424, wherein the arrangement is such that the valve stem of the poppet valve has a fuel passage therein to supply fuel to circumferentially spaced apart relatively fluid dynamically thick radial discharge orifices that are located and inclined so as to discharge fuel parallel to and directly across the frusto-conical seating surface of the head of the poppet valve which in turn is adapted to seat against the outer edge of a frusto-conical valve seat encircling the lower discharge end of the spray tip body of the injection nozzle. DE-A-3137972 discloses a damping piston controlling the movement of an annular head of a valve to an open position. It is therefore, a primary object of the present invention to provide an improved damped opening, only, fuel injection nozzle for use in direct injection type diesel engines that is operable in a manner whereby to substantially eliminate carbon build-up on the cooperating spray discharge elements thereof without affecting the spray pattern of the fuel being discharged therefrom by the use of a poppet valve and an arrangement of spray orifices whereby the spray orifices are covered upon closure of the poppet valve, a damping piston being used to reduce the initial rate of injection so as to reduce engine noise and emissions. To this end, a poppet covered orifice fuel injection nozzle in accordance with the present invention is characterised over US-A-4693424 by the features specified in the characterising portion of claim 1. Accordingly, the present invention provides an improved damped opening fuel injection nozzle of the outward opening, poppet valve type wherein the valve stem of the poppet valve has a fuel passage therein to supply fuel to circumferentially spaced apart, relatively fluid dynamically thick, radial discharge orifices that are located and inclined so as to discharge fuel parallel to and directly across the frusto-conical seating surface of the head of the poppet valve which in turn is adapted to seat against the outer edge of a frusto-conical valve seat encircling the lower discharge end of the spray tip body of the injection nozzle, a damping piston being associated with the poppet valve to slow the opening movement of the poppet valve. The present invention is now described, by way of example, with reference to the following detailed description of the invention to be read in connection with the accompanying drawings; in which Figure 1 is an enlarged longitudinal, cross-sectional view of a preferred embodiment of a fuel injection nozzle constructed in accordance with the invention, showing the upper tube like fitting thereof partly in elevation; Figure 2 is an enlarged longitudinal, cross-sectional view, similar to Figure 1, but showing an alternate embodiment of a fuel injection nozzle constructed in accordance with the invention; and Figure 3 is a further enlarged cross-sectional view of a portion of the poppet valve, per se, of an injection nozzle taken at the circle 3 of Figure 1. Referring now first to Figure 1, there is illustrated a preferred embodiment of an outward opening, poppet covered orifice fuel injection nozzle (hereinafter referred to as an injection nozzle), generally designated 5, constructed in accordance with the invention. The injection nozzle 5 is of a type that is adapted to be mounted, for example, in a suitable nozzle receiving socket formed for this purpose in the cylinder head, not shown, of a direct injection type diesel engine with the spray tip end thereof suitably located so as to discharge fuel into an associated combustion chamber of the diesel engine, the injection nozzle 5 being adapted to be axially retained, for example, by a suitable yoke type clamp, not shown, in a manner well known in the art. The injection nozzle 5, in the construction illustrated is provided with a multi-piece nozzle housing that includes a (tube-like) inlet nut fitting 10 and a spray tip 12 suitably secured together in a conventional manner. Thus in the construction illustrated, the inlet nut fitting 10 is secured to the spray tip 12 by threaded engagement of internal threads 14 thereof with the external threads 15 at the upper end of the spray tip 12, with reference to Figure 1, whereby the upper end flange surface 12a of the spray tip 12 abuts against one side of a ring seal 11, the opposite side of ring seal 11 abutting against a lower face 16 of the inlet nut fitting 10. As shown, the inlet nut fitting 10 is provided with an axial stepped bore therethrough to define a circular stepped upper wall 17 forming an inlet passage that extends downward from the upper or free end, not shown, of the inlet nut fitting 10 so as to open at its other end into a cylindrical fuel chamber 20 defined in part by a circular internal wall 18 in the lower tubular portion of this inlet nut fitting 10. Circular walls 18 and 17 are interconnected by a flat shoulder 19. In addition, the inlet nut fitting 10 at its upper end is provided with suitable external threads, not shown, whereby a fuel supply tube and associate tube coupling, both not shown, can be secured thereto so that the injection nozzle 5 can be intermittently supplied with fuel, for example, as by a high pressure distribution pump, not shown, in a conventional manner. Spray tip 12, of stepped external cylindrical configuration, is provided with an axial bore therethrough so as to define a valve stem guide wall 21 of a predetermined internal diameter, which at its lower free end is encircled by a (frusto-conical) valve seat 22 of a predetermined included angle. As shown in Figure 1, the lower outer peripheral end of the spray tip 12 is relieved as by a chamfer 23 so as to intersect the valve seat 22 and to define therewith a so-called knife edge whereby the valve seat 22 is of a predetermined maximum external diameter. Preferably, the chamfer 23 is formed at an angle of about 15° to 20° relative to the longitudinal axis of the spray tip 12. Fuel discharge from the lower end of the spray tip 12 is controlled by means of an injection valve in the form of a poppet valve 30 that includes a head 31 with an (elongated) valve stem 32 extending therefrom, the lower portion of the valve stem being of a predetermined external diameter whereby it is reciprocably and sealingly guided by the valve stem guide wall 21 and which is of an axial extent so as to extend loosely into the cylindrical fuel chamber 20 but axially spaced apart from flat shoulder 19, when the poppet valve 30 is in a valve closed position as shown in Figure 1. The head 31 of the poppet valve 30 is preferably of a predetermined maximum external diameter corresponding to the external diameter of the valve seat 22 and is provided with an (annular frusto-conical) valve seat surface 33 formed complementary to valve seat 22 but with a predetermined included angle such that preferably the valve seat 22 and valve seat surface 33 effect seating engagement at least at one and preferably at both their outer peripheral edges. Preferably, as shown, the head 31 below the valve seat surface 33 is also provided with a chamfer 34 formed complementary to the chamfer 23 of the spray tip 12. However, because of the usual manufacturing tolerance encountered in mass production of injection nozzles, some overlap of the valve seat surface 33 of the poppet valve 30 relative to the valve seat 22 can be tolerated. Accordingly, in a particular injection nozzle application, the poppet valve 30 is selectively mated to a spray tip 12, such that the valve seat surface 33 of its head 31 can overhang the valve seat 22 of the spray tip 12 by a maximum of 0.01 mm or the valve seat of the spray tip 12 can overhang the valve seat surface 33 of the poppet valve head 31 by a maximum of 0.01 mm. However, in another preferred injection nozzle application, the assembly of the poppet valve 30 and spray tip 12 is ground on its outside peripheral surface, as necessary to ensure zero overhang of the poppet valve 30 and spray tip 12. The reason for limiting such overhang is due to the fact that any exposed surface radially outward of the actual sealed interface of the valve seat 22 and valve seat surface 33 can and will be wetted by fuel during the injection cycle and fuel thus collected on such exposed wetted surfaces can result in high hydrocarbon emissions during the combustion process then occurring in the associated combustion chamber, not shown. Thus it is desirable to reduce such surface area which can be wetted by fuel to a minimum. In addition, with the chamfered spray tip 12 and head 31 arrangement shown, it appears that any carbon deposit which may engage any exposed valve seating surface either will fall off and/or burn off more readily due to the preferred range of the chamfer angle described hereinabove. Preferably the differential angle between the included angles of the valve seat 22 and that of the valve seat surface 33, should be about or preferably less than 2°, whereby sealing will always occur at least at the outer edge of the valve seat 22 or at the outer edge of the valve seat surface 33 and, preferably at both their outer annular edges. Thus, by way of an example, in a particular application, the included angle of the valve seat 22 was 149°15′ relative to the longitudinal axis of the injection nozzle, while that of the valve seat surface 33 was 151°. With this arrangement, the volume of fuel trapped outside of fuel discharge orifices 36, described next hereinafter, yet inside of the valve seat engagement surfaces will be held to a minimum. Extending axially through the valve stem 32 of the poppet valve 30 is an internal fuel passage 35 that is open at the upper free end of the valve stem for flow communication with the fuel in the cylindrical fuel chamber 20 and which at its lower end is in flow communication with the plurality of circumferentially equally spaced apart, radially outward extending, and downwardly directed fuel discharge orifices 36 which are of predetermined diameters, as desired. As best seen in Figure 3, the axis of each such fuel discharge orifice 36 is inclined at an angle parallel to the surface of the valve seat surface 33 on the head 31 of the poppet valve 30 and each such fuel discharge orifice 36 is axially located so that the valve seat surface 33 is substantially tangent as close as possible to the lower outlet end of each such fuel discharge orifice 36, as shown in this Figure, so as to provide for maximum fuel spray penetration upon opening movement of the poppet valve 30 during a fuel injection cycle. For this reason and as described in the above-identified US patent no. 4693424, each of the fuel discharge orifices 36 is relatively fluid dynamically thick, with preferably an L/D ratio in the order of 4 to 8, wherein L is the effective axial length of a fuel discharge orifice and D is the diameter of the fuel discharge orifice. Thus in a particular embodiment, each fuel discharge orifice 36 had a nominal length L of 1.25 mm and an average diameter D of 0.194 mm, with each fuel discharge orifice 36 having an L/D ratio of approximately 6.4. Also as shown, the total cross-sectional flow area of the internal fuel passage 35 is made substantially greater than the combined cross-section flow area of the fuel discharge orifices 36. In addition, although the fuel discharge orifices 36 are illustrated as all of them having a small gap uniform between the lowest edge of the fuel discharge orifice 36 and the corner of the valve seat surface 33 which may be on the order of about 0.05 mm or less, it should be realized, however, that for the purposes of controlling the discharge orifice area versus lift for a particular engine application, the height of the fuel discharge orifices 36 may be staggered. In such a situation the highest fuel discharge orifice 36 may be, for example, 0.15 mm above the corner of the valve seat surface 33 but, however, at least one or more of the fuel discharge orifices 36 are still located approximately 0.05 mm above the corner of the valve seat surface 33 to insure penetrating fuel sprays as soon as the poppet valve 30 lifts from the valve seat 22. In addition, the valve stem 32 of poppet valve 30 can be provided with at least one radial equalizing orifice 37 located so as to effect flow communication between internal fuel passage 35 and the fuel chamber 20 whereby to prevent hydraulic locking of the nozzle assembly. The poppet valve 30 is normally biased to a valve closed position relative to the valve seat 22, the position shown, by means of a valve return spring 40 loosely encircling a portion of the valve stem 32 within the cylindrical fuel chamber 20. As shown, one end or lower end of the valve return spring 40, which is of predetermined force, abuts against the upper end of the spray tip 12, while the opposite or upper end, with reference to Figure 1, of the valve return spring 40 abuts against the lower end of a collar 41 which in turn abuts against the lower end of a retainer 42 suitably fixed, as by a press fit or weld to the upper free end portion of the valve stem 32. The retainer 42 and collar 41 are each of cylindrical tubular configuration with each having an outside diameter suitably less than the internal diameter of the circular internal wall 18 in the inlet nut fitting 10 whereby they are loosely slidable therein. With this arrangement, the retainer 42 is fixed to the valve stem 32 against axial movement relative thereto and in fluid tight engagement therewith. The collar 41 however is provided with, for example, circumferentially spaced apart flats 41a on its outer peripheral surface so as to define with the circular internal wall 18, a plurality of axial extending passages for the free flow of fuel therethrough. Also as shown, the collar 41 is thus positioned so as to abut at its lower end against an upper end surface 44a of a tubular lift stop 44 positioned in cylindrical fuel chamber 20 so as to be supported on the upper free end surface of the spray tip 12 whereby to limit opening movement of the poppet valve 30. As shown, the collar 41 is of stepped external configuration so as to define an upper reduced diameter portion 41b and a lower portion 41c having the flats 41a, these portion being interconnected by a flat shoulder 41d. Now in accordance with the invention a tubular damping or damper piston 50 is positioned so as to loosely encircle the collar 41. The external diameter of the damping piston 50 is preselected relative to the internal diameter of circular internal wall 18 whereby there is provided a predetermined diametral clearance between these elements so as to prevent significant fuel flow through this clearance to thus dampen the motion of the poppet valve 30 during opening movement of this poppet valve 30. As shown, the bore through the damping piston 50 preferably defines at least an upper inclined wall 51 of a predetermined angle relative to an inclined lower surface 42a of retainer 42 and a straight wall 52 of an internal diameter substantially greater than the external diameter of the upper reduced diameter portion 41b of collar 41. As shown in Figure 1, the effective axial extent of the damping piston 50 is preselected relative to the effective axial extent of collar 41 so that when the damping piston 50 sealingly abuts against the inclined lower surface 42a of retainer 42, the position shown, a "piston gap" will exist between the lower end surface of the damping piston 50 and flat shoulder 41d of collar 41. As illustrated, the axial extent of this "piston gap" is a predetermined amount less than the preselected, axial extent of the poppet valve 30 "lift". As should now be apparent, poppet valve "lift" is controlled by engagement of the collar 41 against the tubular lift stop 44 during opening movement of poppet valve 30. During operation, as pressurized fuel is supplied to the injection nozzle 5 at a pressure sufficient to cause opening movement of the poppet valve 30, then as this poppet valve 30 begins to open, the fuel which is, in effect, substantially trapped in the cylindrical fuel chamber 20 below the damping piston 50 will force the damping piston 50 to a position at which it is pressed upward into so-called sealing engagement against the retainer 42, the position shown in Figure 1, so as to shut off any fuel flow between these elements. However, limited fuel flow can still occur in the flow path defined by the previously described diametral clearance so as to allow continued opening movement of the poppet valve 30 at a controlled damped rate, as desired. Thereafter, upon valve closing movement of poppet valve 30, a gap opens between the damping piston 50 and the retainer 42, allowing fuel to flow from the portion of the cylindrical fuel chamber 20 above the damping piston 50 through this gap into the portion of the cylindrical fuel chamber 20 below the damping piston 50. Thus the closing movement of poppet valve 30 is not damped. Accordingly, the subject arrangement provides for a "one-way" damping feature means, that is, the motion of poppet valve 30 is damped only during opening movement of the poppet valve 30. The size of this gap is controlled by the axial extent of the previously described "piston gap", which should be large enough to insure good flow between the damping piston 50 and retainer 42 during valve closing movement, but it must be small enough so that when the poppet valve 30 re-opens, this gap is overcome before significant poppet valve 30 lift takes place. In a particular injection nozzle application this "piston gap" was about 0.05 mm. An alternate embodiment of an injection nozzle, generally designated 5′, in accordance with the invention is shown in Figure 2, wherein similar parts are designated by similar numerals but with the addition of a prime (′) where appropriate. In this injection nozzle 5′, the collar 41 is not used and, instead, the valve return spring 40 is positioned so as to act directly on the flat, tubular damping piston 50′ whereby to normally bias its flat upper surface 50a′ into substantial sealing engagement with the inclined lower surface 42a′ of retainer 42′. Thus in this alternate embodiment injection nozzle 5′ structure, the "one-way" only damping feature is dependent upon some gap separation between the damping piston 50′ and retainer 42′ during closing movement of the poppet valve 30. During poppet valve 30 opening movement, damping will occur in the same manner as previously described with reference to the injection nozzle 5. By the use of a one-way damping piston 50, 50′ to slow opening movement of the associate poppet valve 30, the initial rate of fuel injection from an injection nozzle 5, 5′ can be reduced while still permitting a fast closing movement of the associate poppet valve 30. It will be appreciated by those skilled in the art, that this can be further enhanced, if desired for a given application, by staggering the fuel discharge orifice 36 heights above the valve seat surface 33. Thus if two low "pilot" spray fuel discharge orifices 36 are used, for example, the flow area at the beginning of injection can be limited to these fuel discharge orifices 36 by damping the opening movement of the poppet valve 30. Obviously, with no damping, the poppet valve 30 can overshoot such "pilot" orifice holes and go to the full valve open position too rapidly.

Claims: 1. A poppet covered orifice fuel injection nozzle (5) for use in a direct injection type diesel engine, the injector nozzle including an injector body (10,12) having an inlet (17) for pressurized fuel at one end thereof and having a spray tip (12) at the opposite end thereof; the spray tip (12) having a discharge free end and having a stepped through bore (21) of predetermined internal diameter therein at its discharge free end with an annular frusto-conical valve seat (22) encircling the axial through bore (21) at the discharge free end of the spray tip (12); an enlarged diameter fuel chamber (20) in the injector body; an outward opening poppet valve (30) operatively positioned in the injector body (10,12), the poppet valve (30) including an annular head (31) with a frusto-conical valve seat surface (33) positioned for movement between a closed position and an outward open position relative to the frusto-conical valve seat (22) and a valve stem (32) extending from the annular head (31) that is slidably received in the axial through bore (21) and has its free end loosely received in the fuel chamber (20), the poppet valve (30) having an internal passage (35) in fluid communication at one end with the inlet (17) and terminating at its other end in circumferentially spaced apart radial discharge orifices (36) that are inclined and located so as to discharge fuel parallel to and substantially directly across the frusto-conical valve seat surface (33) of the annular head (31); a retainer (42) sealingly fixed to the valve stem (32) at the free end thereof opposite the annular head (31); a valve lift stop means (44) operatively located in the fuel chamber (20); and a spring (40) operatively positioned in the fuel chamber (20) and operatively associated with the poppet valve (30) to normally bias the annular head (31) of the poppet valve (30) to the closed position; the frusto-conical valve seat (22) and the frusto-conical valve seat surface (33) together with the discharge free end of the spray tip (12) being configured so that the frusto-conical valve seat surface (33) will effect sealing engagement with the frusto-conical valve seat at substantially the outer peripheral edge thereof with substantially no overhang of these elements with respect to each other whereby to prevent fuel wetting during injection when the annular head (31) is moved to the open position and to prevent fuel flow from the discharge orifices (36) when the annular head is in the closed position; characterised by a radial equalizing orifice (37) interconnecting the internal passage (35) to the fuel chamber (20); and a tubular damping piston (50) loosely encircling the valve stem (22) next adjacent to the retainer (42) within the fuel chamber (20), the damping piston (50) controlling the movement of the annular head (31) to the open position; and a collar (41) of stepped external configuration loosely encircling the valve stem (32) between the spring (40) and a portion of the damping piston (50), the collar being adapted to engage the valve lift stop means (44) whereby to control lift of the poppet valve (30).

Inventors: SCZOMAK, DAVID P.
Applicants: GENERAL MOTORS CORPORATION
Application year: 1988
Main classification: F02M61
IPC codes: F02M61, B05B1, F02B3