A FUEL INJECTOR FOR INTERNAL COMBUSTION ENGINES

Abstract: A fuel injector valve for internal combustion engines includes a slide valve (10) journalled in a valve guide (8). The slide valve is composed of a rearmost, comparatively thick section (11) and a foremost, comparatively thin section (12) extending downwards into a bore (13) in the atomizer (9). The foremost section (12) is as an exchangeable unit secured to the section (11) and provided with a shank (28) carrying at its foremost end a cylindrical end portion (29) which may open or close the nozzle holes. Due to the thin and long shank (28) the foremost section is so flexible that the end section (29) will conform itself to the bore (13) of the atomizer, i.e. independently of how the rearmost section is journalled in the valve guide (8). This entails that the foremost section of the slide valve may be manufactured independently of the manufacturing of the rearmost slide section (11).

Description: A fuel injector for internal combustion engines. The invention relates to a fuel injector valve for internal combustion engines, including a hollow slide valve guide fixedly disposed in the external housing of the injector and the foremost end of which is designed as an atomizer closed in front and provided with a central bore, said atomizer having in its side wall a number of transversely extending nozzle holes for the injection of atomized fuel, a slide valve axially displaceable in the guide for opening and closing the nozzle holes and having a foremost section with a cylindrical end section carried by a shank and which is journalled with tight fit in the bore of the atomizer in order to close the nozzle holes when the valve is in the closed position; said injector valve having a flow passage through which pressurized fuel may flow past the slide valve and on to the nozzle holes when the slide occupies its opening position in which its end section exposes the holes, and a closure spring acting against the fuel pressure for holding the slide in its closing position. The disclosure of DK patent No. 149 141 deals with a fuel injector valve of this type, wherein the slide valve and its foremost section which project down into the atomizer are comparatively rigid in the trans- verse direction, thereby requiring the slide be mounted completely coaxially with the bore in the atomizer. Even a very slight failing alignment between the slide and the atomizer bore may entail failure in the fuel injector valve. The rearmost slide valve section journalled in the valve guide has a comparatively large diameter and is ground to size to fit into the valve guide whereas the foremost slide section projecting down into the bore of the atomizer has a smaller diameter and is ground to size so that the cylindrical end section is journalled with tight fit within the atomizer bore. In order to ensure tight barring of the nozzle holes, even when the fuel pressure in the flow passage immediately before and after the actual fuel injection attains very high values, such as 800 to 1000 bar, the end section must fit extremely precisely in the atomizer bore and, consequently, the clearance between the end section and the bore typically amounts to 10 to 15 μm. The demand for full coaxiality between the end section of the slide valve and the rearmost section journalled in the valve guide necessitates that the two sections are ground in the same setting-up and, consequently, the connection between the end section and the remainder of the slide valve must have such a high stiffness against transverse bending that the shearing force provided by the cutting force of the grinder does not result in any noticeable bending of the slide valve. Prior to grinding, the slide valve consisting of steel has been hardened to a glass-hard state, meaning that the handling as well as the grinding of the slide valve must be effected very cautiously in order to pre¬ vent the slide valve from breaking as a consequence of its brittleness. This circumstance in unison with the high demands for coaxiality and tolerances of the ground surfaces result in that the slide valve is expensive to manufacture. It is a further inconvenience that the entire slide valve has to be exchanged when the end section is worn down. The dispatch and exchange of the slide valve is also difficult due to the brittleness of the slide because even a rather slight transverse impingement may cause breaking of the slide valve. It is the object of the invention to provide a slide valve with a longer lifetime than the prior art slide valve and which is easier to manufacture, handle and exchange. For this purpose the fuel injector valve accord¬ ing to the invention is characterized in that the axial length of the end section of the slide valve at most is of the same order of magnitude as the diameter of the bore in the atomizer, and that the length of the shank is at least several times longer than the axial length of the end section. Due to the short length of the end section of the slide valve and the long length of the shank the foremost section of the slide valve is so flexible that the bore in the atomizer automatically aligns the end section of the slide valve to its own longitudinal axis so that the end section does not necessarily have to be completely coaxial with the rearmost slide valve sec- tion journalled in the valve guide. Owing to the fact that the end section of the slide valve by itself con¬ forms to the bore, the wearing of the end section and the atomizer will be diminished in relation to the wearing of the prior art injector in which even a very slight misalignment between the end section and the atomizer may result in seizing and rapid wearing of the atomizer. In view of the fact that it is no longer necessary that the foremost and rearmost end sections of the slide valve have to be completely coaxial, the foremost section of the slide valve may be manuafctured independently of the rearmost section. In accordance with the invention this is utilized in facilitating the manufacturing of the slide valve in that the cylindric- al external side of the foremost end section of the slide valve is finally ground to size independently of the grinding of the slide section to be journalled in the valve guide. By grinding the foremost, comparative¬ ly thin section and the rearmost, comparatively thick slide valve section, each in a respective setting-up, it is obtained, on one hand, that the risk of breaking the foremost, glass-hard slide valve section during grinding has been considerably reduced because this section does not have to carry the weight of the whole slide valve and, on the other hand, the grinding of the thick, rearmost section may be effected at a high cutting force and consequently rapidly, because the poor strength of the foremost slide valve section does not any longer restrain the cutting force. When the foremost slide valve section is worn down and must be exchanged, it is according to the invention possible merely to exchange the foremost slide valve section comprising the shank and the end section and thus allow the rearmost slide valve section to remain in operation, thereby reducing to a consider- able degree the expenses incurred by the exchange and facilitating the dispatching and handling of the necessary spare parts. The lifetime of the slide valve has further been enhanced by a preferred embodiment in which at least the foremost part of the cylindrical external surface of the end section consists of an erosion-resistant material, such as Stellite 6. The erosion-resistant material reduces the wearing of the front end of the end section that may occur when the end section by the opening of the injector valve exposes the nozzle holes, and the fuel starts flowing at very high velocities through the nozzle holes. The high flow velocities occurring at the opening of the valve immediately next to the extreme end of the end section apply heavy pressure loads thereon. The erosion-resistant material is capable of receiving said loads, thereby prolonging the lifetime of the slide valve. Examples of embodiments of the invention will now be described in detail with reference to the schematical drawings, in which Pig. 1 is an axial section through an embodiment of the injector valve, the slide valve being shown in the opening position. Fig. 2 is an axial section on a larger scale through the foremost part of the injector valve illus¬ trated in Fig. 1, the slide valve being shown in the closing position, Fig. 3 is a sectional view of a side elevation of the foremost section of the slide valve, Fig. 4 is a cross-section through the slide valve along the line IV-IV in Fig. 3, Fig. 5 is an axial view through the foremost part of a second embodiment of the injector valve, and Fig. 6 is a cross-section along the line Vl-vi in Fig. 5 through the foremost section of the slide valve. The fuel injector valve illustrated in Figs l, 2 and 5 has an elongated external housing 1 which at its rearmost end has a head 2 by which the injector valve in a known manner may be mounted in the cylinder cover of an internal combustion engine and be connected with a fuel pump, not shown. The head 2 includes a fuel oil inlet 3 which is in flow connection with a duct 4 extending through a central thrust piece 5 and a valve member 6 journalled in a valve housing 7, the rearmost end of which abuts on a forwards facing shoulder on the thrust piece 5 and whose fore- most end has a conical surface kept in tight abutment on a corresponding conical surface on a valve guide 8 which at its rearmost end fits tightly into housing 1 and carries at its foremost end an atomizer 9 pro¬ jecting through housing 1 and into the combustion chamber of the engine cylinder, not shown, when the injector valve is mounted on the cylinder cover. A slide valve generally designated 10 is axially displaceable internally of the valve guide 8 and includes a rearmost section 11 whose cylindrical external surface is ground to size and journalled with tight fit in a central guide bore in valve guide 8. The slide section 11 carries a foremost slide section 12 that is substantially thinner than the rearmost section 11 and projects into a central bore 13 in the atomizer. A central tube 14 extending into the rearmost section of the slide valve is integral with the valve guide 8 and has a forwards facing shoulder restrain¬ ing the rearwards movement of slide valve 10. A closure spring 16 rearwardly abutting on the valve guide 8 and forwardly on a rearwards facing shoulder 17 at the rear end of the slide valve sec¬ tion 11 is received in a hollow space 15 in the valve guide so that the closure spring loads the slide valve in the forwards direction towards the closing position shown in Fig. 2. The inlet duct 4 is through transverse bores and a following valve seat 18 in communication with a flow passage 19 extending through pipe 14 and dis¬ charging in front into a distributor chamber 20 pro- vided in the slide valve and which chamber through transverse bores 21 is in flow connection with an annular chamber 22 defined between the external side of the slide valve and the surrounding parts of the valve guide. A conical seating 23 is formed in valve guide 8 at the foremost end of the chamber 22, and the slide valve is at the front end of section 11 provided with a corresponding conical seating 24 which in the closing position of the injector valve is urged sealingly in abutment on seating 23 by closure spring 16. The foremost section 12 of the slide valve is at its backwards end provided with a threaded portion 25 screwed into a central bore at the foremost end of the slide valve section 11 so that a rearwards directed shoulder 26 on section 12 abuts on the front end of section 11. A safety pin 27 inserted through unitary bores in slide valve sections 11 and 12 prevents the foremost section from unintentionally rotating clear of the rearmost section 11. This safety against releasing may also be effected in other ways, e.g. by glue, such as Loctite (reg. Trademark). The shoulder 26 merges forwardly into a comparatively thin and elongated shank 28 the foremost end of which carries an end section 29 with a cylindrical external surface 30 journalled tightly fitting into the bore 13 of the atomizer. In the wall of the atomizer there is provided a number of transversely extending nozzle holes 31 so positioned that the end section 29 bars the nozzle holes when the injector valve is in the closing posi- tion illustrated in Fig. 2, whereas the end section 29 in the opening position of the injector valve (Fig. 1) has been moved so much backwards that the nozzle holes are completely exposed. When the valve member 6 abuts on the valve seat 18, preheated oil may over a transverse bore in thrust piece 5 flow through the injector valve and keep it heated. When the pressure of the fuel oil in inlet 3 rises sharply immediately prior to initi¬ ating the injection, the valve member 6 is displaced to the rear into the position shown in Fig. 1 and bars the passage for circulating oil, following which the fuel oil flows past the valve seat 18 down through the passage 19 and out into chamber 22 in which the pressure in the oil builds up until it overcomes the force exerted by the closure spring 17 and the slide valve is moved rearwards from the closing position shown in Fig. 2. Immediately after the seatings 23 and 24 have been moved apart, the fuel oil flows for¬ wards into the space surrounding the shank 28 and passes through recesses 32 therein on to the part of the bore 13 positioned in front of the end section 29. Due to the fact that the end section 29 in the closed position of the injector extends a distance for¬ wards past the nozzle holes 31, a pressure build-up is effected in the fuel oil in front of the end section 29 prior to exposing the nozzle holes, meaning that the fuel oil substantially from the beginning of the injec¬ tion is injected at full pressure, thereby ensuring a good combustion. The foremost section 12 and the rearmost sec- tion 11 of the slide valve are ready-made as two separate units which are assembled only immediately before mounting the slide valve 10 in the injector valve. The comparatively thick slide valve section 11 may due to its large rigidity against transverse bending be processed at a high cutting force. The foremost section 12 is in the embodiment illustrated in Figs 2, 3 and 4 composed of two ele¬ ments, viz. the shank 28 and a ring 33 consisting of an erosion-resistant material, such as Stellite 6. At its foremost end the shank 32 has a larger diame¬ ter and is there provided with three longitudinal recesses 32 distributed along the circumference and allowing, as mentioned, the fuel oil to pass internally past the ring 33. The recesses 32 leave in the fore- most end of the shank three radially protruding lobes 34 to which the ring 33 is secured, for instance by means of hard soldering. Alloy 50 may be used as the solder. This two-parted implementation of the foremost section 12 of the slide valve is extremely appropri- ate for mass production, the ring 33 and the shank 28 being both easy to manufacture in a NC-automaton. If appropriate, the shank may of course be designed with more than three radially protruding lobes. If the foremost section 12 of the slide valve shall only be produced on a smaller scale, it may appropriately be implemented as shown in Figs 5 and 6. The foremost section is there manufactured from a single steel blank on the foremost end section and a distance up along the side, corresponding to the intended face for journalling in the bore 13 of the 5 atomizer, of which a layer of erosion resistant materi¬ al has been welded, such as Stellite 6. The shoulder 26 and the shank 28 are manufactured by turning and a central bore 35 that is longer than the cylindrical end section 29 is drilled from the front end of the 10 blank. The portion 36 of the shank positioned behind the end section 29 and having a smaller diameter than .the end section 29 but a larger diameter than the part of the shank 28 positioned behind, is sub¬ sequently provided with an appropriate number, e.g. 15. four, longitudinal grooves 37 distributed along the circumference and having a radial depth that is a little larger than the wall thickness of the annular end section 29 so that the grooves discharge into bore 35 and establish flow connection between the 20 parts of the bore 13 of the atomizer positioned at the rear and in front of the end section 29. As final treatment the foremost slide valve section 12 the external surface of the end section 29 is ground to size. 25 The flow passage allowing the combustible to flow past the slide valve includes the recesses 32 of the embodiment illustrated in Fig. 2 whereas they include the grooves 37 and the bore 35 in the embo¬ diment illustrated in Fig. 5. 30 Instead of the illustrated threaded assembling between the two extreme sections, the sections may of course be assembled in another way, for instance by means of press fit or by a similar joining method. The shank may further be designed in another way, e.g. as a 35 number of parallel and thin rods connecting the rear¬ most section of the shank with the end section 29. The essential feature of the shank according to the inven¬ tion is its flexibility allowing the end section 29 to conform to the bore 13 independently of the journalling bearing of the rearmost slide valve section in the valve guide 8.

Claims: P A T E N T C L A I M S 1. A fuel injector valve for internal combustion engines, including a hollow slide valve guide (8) fixedly disposed in the external housing (1) of the injector valve and the foremost end of which is designed as an atomizer (9) closed in front and pro¬ vided with a central bore (13), said atomizer having in its side wall a number of transversely extending nozzle holes (31) for the injection of atomized fuel, a slide valve (10) axially displaceable in the guide for opening and closing the nozzle holes and having a fore¬ most section (12) with a cylindrical end section (29) carried by a shank (28) and which is journalled with tight fit in the bore (13) of the atomizer in order to close the nozzle holes when the valve is in the closed position; said injector valve having a flow passage (3,4,19,21,13; 32) through which pressurized fuel may flow past the slide valve (10) and on to the nozzle holes (31) when the slide occupies its opening position in which its end section (29) exposes the holes, and a closure spring (16) acting against the fuel pressure for holding the slide in its closing position, charac¬ terized in that the axial length of the end section (29) of the slide valve is at most of the same order of magnitude as the diameter of the bore (13) in the ato- mizer, and that the length of the shank (28) is at least several times longer than the axial length of the end section (29) . 2. A fuel injector valve according to claim 1, characterized in that the end section (29) is a cylindrical ring (33) secured on the shank (28). 3. A fuel injector valve according to claim 2, characterized in that the shank (28) at its end facing towards the ring has radially extending lobes (34), preferably at least three, to which the ring (33) is secured, preferably by means of soldering. 4. A fuel injector valve according to claim 1, characterized in that the shank (28) and the end sec¬ tion (29) are manufactured from one blank, of which the end forming the end section includes a central bore (35) which in the area above the end section is in flow connection with the part of the central bore (13) of the atomizer positioned above the end section. 5. A fuel injector valve according to any of the preceding claims, characterized in that at least the foremost part of the cylindrical external surface (30) of the end section consists of an erosion-resistant material, such as Stellite 6. 6. A fuel injector valve according to any of the preceding claims, characterized in that the foremost section (12) of the slide valve comprising the shank (28) and the end section (29) are exchangeable as a unit independently of the remainder of the slide valve (10). 7. A method of use in the manufacturing of a slide valve for a fuel injector valve according to any of claims 1 to 6, characterized in that the cylindrical external surface (30) of the foremost section (12) of the slide valve is finally ground to size independently of the grinding of the slide section (11) to be journalled in the valve guide (8).

Inventors: LARSEN POUL ERIK, PEDERSEN PETER SUNN, LARSEN, POUL, ERIK, PEDERSEN, PETER, SUNN
Applicants: MAN B & W DIESEL GMBH, MAN B&W DIESEL A/S
Application year: 1992
Main classification: F02M61
IPC codes: F02M61