FUEL-INJECTION ASSEMBLY

Abstract: A fluid rail assembly (1) supports a fuel-metering injector (2) and a charge-delivery injector (3) on an engine. The charge-delivery injector (3) includes flutes spaced about the interior of a nozzle (15) thereof to promote formation and delivery of a charge of fuel and air having desired spray characteristics. The fluid rail body includes passages (6,7,9) that provide air to assist in delivering fuel from the fuel-metering injector (2) through the charge-delivery injector (3) to the engine, the passages (6,7,9) being constructed to inhibit back-flow of fuel therethrough.

Description: Technical field This invention relates to a fluid rail assembly adapted to deliver a fuel-air charge directly into an engine combustion chamber as specified in the preamble of claim 1, for example as disclosed in WO-A-88/07628. A fuel injector arrangement is disclosed in WO-A-86/00960 in which a solenoid coil assembly of the fuel injector is cooled by supplying air thereto by a circuitous channel surrounding a housing of the solenoid coil assembly. A fluid rail assembly according to the present invention is characterised by the features specified in the characterising portion of claim 1. Summary of the drawings Figure 1 is a transverse sectional view of a fluid rail mounted on an engine cylinder head, showing an injector for delivering a charge of fuel and air directly into one of the engine combustion chambers, and showing an injector for metering fuel to the charge-delivery injector. Figure 2 is an enlarged sectional view of a portion of the charge delivery injector shown in Figure 1, showing internal flutes provided to generate an advantageous injector spray pattern. Figure 3 is an end view of the injector shown in Figure 2. Figure 4 is an enlarged sectional view similar to Figure 2 of another charge-delivery injector, showing alternative internal flutes provided to generate an advantageous injector spray pattern. Figure 5 is an end view of the injector shown in Figure 4. Figure 6 is a sectional view similar to Figure 1 of another fluid rail, showing an alternative air supply construction. Figure 7 is a sectional view, taken along line A-A of Figure 6, showing further details of the alternative air supply construction. Figure 8 is a sectional view similar to Figure 1 of yet another fluid rail, showing another alternative air supply construction. Detailed description Referring firstly to Figure 1, a fluid rail assembly has a fluid rail body 1 that supports fuel-metering injectors 2 and charge-delivery injectors 3 and associated electrical wiring and connectors 4 on an engine so each injector 3 may deliver a charge of fuel and air to its associated combustion chamber 5. Rail body 1 has a longitudinal air supply passage 6 aligned with the charge-delivery injectors 3. Passage 6 supplies air to a peripheral air supply passage channel 7 surrounding a housing 8 of solenoid coil assembly in each charge-delivery injector 3. Each channel 7 supplies air to a drilled air supply passage 9 containing a cup restrictor 10 that provides a calibrated orifice in passage 9. Each passage 9 supplies air to an air space 11 between an end of the associated fuel-metering injector 2 and body 1; each air space 11 is a wedge-shaped volume that is not occupied by a generally C-shaped elastomeric gasket 12 sandwiched between the end of the associated fuel-metering injector 2 and body 1. A drilled passage 13 connects each air space 11 to an aperture 14 in a nozzle 15 of the associated charge-delivery injector 3. Within each injector 3, aperture 14 opens into a region 16 surrounding a stem of its valve 17. Each injector 2 delivers metered fuel through its air space 11 and passage 13 to the aperture 14 of the associated charge-delivery injector 3, and through aperture 14 into the region 16 of injector 3. When the solenoid coil of that charge-delivery injector 3 is energized, its armature 18 is attracted against the bias of a return spring 19 to open valve 17. Air flow from passage 6 through channel 7, passage 9, air space 11, passage 13, aperture 14 and region 16 then delivers the fuel into the associated combustion chamber 5. The arrangement of supplying air flow into air space 11 using a circuitous route from the air supply passage 6 around the housing 8 of the solenoid coil assembly in each charge-delivery injector 3 provides two useful advantages in that the air flow supplied to air space 11 serves to cool the solenoid coil assembly before that air flow reaches air space 11, and in that the circuitous route of the air flow inhibits any tendency for back-flow of fuel from the fuel-metering injector 2 entering the air supply passage 6. By arranging for the solenoid coil assembly of each charge-delivery injector 3 to be positioned away from the direct flow path of the air-fuel charge supplied to the nozzle 15 through the air space 11, passage 13 and aperture 14, it is possible to keep the direct flow path of the air-fuel charge relatively short, thus avoiding any tendency of stratification occurring in the air-fuel charge before it reaches the nozzle 15. A secondary air flow path allows air flow upwardly through the clearance space between the outer diameter of each solenoid coil housing 8 and the rail body 1, radially inwardly through slots 23 in the base of the cover 21 into a cavity surrounding armature 18, downwardly through apertures 22 in the armature 18 into a cavity surrounding return spring 19, and downwardly through an annular orifice 20 between the valve stem and a top of nozzle 15 into region 16. The secondary air flow through orifice 20 is a small percentage of the air flow through the orifice in restrictor 10, but is sufficient to purge any fuel that may migrate into the secondary air flow path. For ease of assembly and service, each charge-delivery injector 3 can be installed and removed as a unit from the fluid delivery rail body 1. The solenoid coil assembly is secured to the nozzle 15 by press-fitting the nozzle 15 within a core 24 of the solenoid coil assembly. O-rings above and below passage 13 and aperture 14 seal against migration of fuel between nozzle 15 and fluid rail body 1 whilst permitting a sliding clearance between nozzle 15 and fluid rail body 1 that allows easy installation and removal of charge-delivery injector 3. Within each injector 3, a C-shaped washer 25 fits about the stem of valve 17 and rests on the top of nozzle 15 to provide a seat for return spring 19. Washer 25 has an inner diameter smaller than an upper end of the stem of valve 17 in order to capture valve 17 if an upper spring retainer 26 or an associated lock-ring 27 should break. Return spring 19 is calibrated by selecting a washer 25 of appropriate thickness, or by selecting an armature spring 28 of appropriate force. Travel of valve 17 is calibrated by adjusting set-screw 29 to position armature 18 at a desired distance above the top of the solenoid coil assembly, and employing nut 30 to lock set-screw 29 in place. Certain details of the structure at the top of charge-delivery injectors 3 are set forth in US patent application 369 508 filed concurrently in the name of L. W. Weinand; the disclosure of that application is incorporated by reference. The position of the fuel-metering injectors 2 relative to the charge-delivery injectors 3 was selected to minimize the overall height of the fluid rail assembly. Fuel is supplied to the fuel-metering injectors 2 by a longitudinal passage 31 that intersects the sockets for injectors 2. Fuel supply passage 31 is located above fuel-metering injectors 2 to permit easy exit of any vapor generated within the injectors or the injector sockets. Because the fluid rail body 1 is solid and the charge-delivery injectors 3 are rigidly secured in the body 1, the spacing between injectors 3 is not adjustable. This requires accurate control of the spacing between the holes in the cylinder heads that receive nozzles 15. To accommodate mounting of the fluid rail assembly on the engine without excessively tight machining tolerances, the openings around nozzles 15 are larger than when the spacing between injectors 3 is adjustable, and a copper washer 32 and an O-ring 33 seal the opening about each nozzle 15. Washer 32 protects O-ring 33 against direct exposure to combustion chamber gases, and conducts heat away from the O-ring. Washer 32 has an interference fit on nozzle 15 and a clearance fit within the O-ring groove in the top of the head. When injector 3 is installed, nozzle 15 deforms the inner portion of washer 32 into a conical shape, thereby effecting a tight seal. The orifice in each restrictor 10 inhibits back-flow of fuel into passage 9. In addition, the offset of passages 9 (about 90 degrees) from passage 6 inhibits back-flow of fuel into the air supply passage 6. In the absence of provisions to inhibit such back-flow, fuel might be transferred from the fuel-metering injector 2 associated with one combustion chamber 5 to the charge-delivery injector 3 associated with another combustion chamber 5; in that event, fuel would be unevenly distributed amongst the combustion chambers 5. An auxiliary air reservoir 34 extends longitudinally through fluid rail body 1. Drilled passages 35 connect reservoir 34 to the air supply channels 7 that surround the solenoid coil assemblies of the charge-delivery injectors 3. In some applications, reservoir 34 may provide the sole air supply to channels 7, replacing air supply passage 6. Because reservoir 34 is connected to channels 7 through passages 35, and because passages 35 are offset about 180 degrees from passages 9, use of reservoir 34 as the sole air supply to channels 7 would further inhibit the possibility that fuel might be transferred from the fuel-metering injector 2 associated with one combustion chamber 5 to the charge-delivery injector 3 associated with another combustion chamber 5. The solenoid coil assembly of each charge-delivery injector 3 has terminals 36 that exit at the bottom of the solenoid coil housing 8 and are connected by insulated wires to electrical connector 4. If desired, a terminal block 37 may be employed to connect the wires to terminals 36. A pin 38 carried by nozzle 15 is received in a slot in body 1 to assure that nozzle aperture 14 is aligned with body passage 13. As shown in Figures 2-3, nozzle 15 has internal flutes 51 spaced about the inside of the nozzle at the bottom of region 16. Flutes 51 promote filling in of the initially hollow spray pattern created by nozzle 15 and valve 17. That effect is believed to be due to the fact that tapered surfaces 52 of different lengths are exposed at the bottom of nozzle 15 when valve 17 is opened; the longer tapered surfaces between flutes 51 create a greater pressure drop than the shorter tapered surfaces at the ends of flutes 51; the different length surfaces 52 accordingly generate adjacent fuel streams of differing velocities that promote turbulence and mixing which, in turn, fills the hollow cone to produce a more uniform spray density. Flutes 51 are not exposed to the combustion products in combustion chamber 5 and accordingly are not readily susceptible to plugging. Moreover, the diverging surfaces on nozzle 15 and the head of valve 17, in combination with the lack of crevices on the outside of nozzle 15, discourages formation of deposits that could migrate. As shown in Figure 1, the stem of valve 17 is guided in nozzle 15 by the upper portion of nozzle 15 and a triangular portion of the valve stem near the head of valve 17. This construction assures good alignment of the head of valve 17 and the mating, sealing portions of surfaces 52 at the end of nozzle 15 to effect a tight seal therebetween. As shown in Figures 4-5, the stem of another valve 117 has a cylindrical boss 153 instead of the triangular portion of valve 17. Boss 153 is guided in the associated nozzle 115, and flutes 151 extend past boss 153 to deliver the fuel from the region 116 surrounding the stem of valve 117 within nozzle 115. Flutes 151 also promote filling in of spray pattern created by nozzle 115 and valve 117. Figures 6-7 illustrate another fluid rail body 201 in which an axially-extending groove 254 connects an air space 211 (at the end of fuel-metering injector 202) with a drilled air supply passage 209 that extends from an air supply channel 207 surrounding housing 208 of the solenoid coil assembly in a charge-delivery injector 203. As in the Figure 1 embodiment, air space 211 is the wedge-shaped volume that is not occupied by a generally C-shaped elastomeric gasket 212 sandwiched between the end of fuel-metering injector 202 and body 201. Other details of the Figure 2 fluid rail assembly are similar to the Figure 1 embodiment. Figure 8 illustrates yet another fluid rail body 301 in which an axially-extending groove 354 and a peripherally-extending groove 355 connect air space 311 (at the end of fuel-metering injector 302) with a drilled air supply passage 309 that extends from an air supply channel 307 surrounding housing 308 of the solenoid coil assembly in a charge-delivery injector 303. As in the other embodiments, air space 311 is the wedge-shaped volume that is not occupied by a generally C-shaped elastomeric gasket 312 sandwiched between the end of fuel-metering injector 302 and body 301. Other details of the Figure 3 fluid rail assembly are similar to the other embodiments. The constructions of Figures 6-8 further inhibit the back-flow of fuel to minimize the possibility that fuel might be transferred from the fuel-metering injector associated with one combustion chamber to the charge-delivery injector associated with another combustion chamber.

Claims: A fluid rail assembly having a body (1;201;301) supporting a fuel-metering injector (2;202;302) and a charge-delivery injector (3;203;303), said body having a space (11;211;311) between the end of said fuel-metering injector (2;202;302) and the body, said charge-delivery injector (3;203;303) including a charge-delivery valve (17;117), a solenoid having an armature (18) for operating said valve (17;117), a valve stem connecting said valve (17;117) to said armature (18), and a nozzle (15;115) having an aperture (14), said nozzle (15;115) surrounding said valve stem; and said body including a first passage (13) extending directly from said space (11;211;311) to said aperture (14), and a second passage (9;209;309) for supplying air to said space (11;211;311) to assist delivery of fuel from said fuel-metering injector (2;202;302) to said nozzle (15;115), characterised in that said nozzle (15;115) is received in said body (1;201;301); said aperture (14) is a lateral aperture opening into a region (16;116) within said nozzle (15;115) about said valve stem below said solenoid; said fuel-metering injector (2;202;302) is adapted to deliver fuel through said space (11;211;311), said first passage (13) and said lateral aperture (14) to said region (16;116) within said nozzle (15;115); and air is supplied to said second passage (9;209;309) by a circuitous route which includes a channel (7;207;307) surrounding a housing (8;208;308) of the solenoid coil assembly. A fluid rail assembly according to claim 1, characterised in that said second passage (9) includes a cup restrictor (10) and the circuitous route of the air flow surrounding the housing (8;208;308) of the solenoid coil assembly is constructed to inhibit back-flow of fuel therethrough.

Inventors: ALBERTSON, WILLIAM CONRAD, POSPIECH, GERALD EDWARD, WEINAND, LOUIS HARRY
Applicants: GENERAL MOTORS CORPORATION
Application year: 1990
Main classification: F02M67
IPC codes: F02M67, F02M51, F02M61