Diesel engine electromagnetic fuel injector

Abstract: An injector comprising a plunger (1) for controlling fuel passage between an injection chamber (3) and at least an injection orifice (4) formed in an injection nozzle (5); and an electromagnetic fuel metering valve (6) for controlling fuel passage through a drain orifice (7) between a control chamber (8), supplied with fuel under pressure, and a low-pressure chamber (11), so as to reduce the fuel pressure in the control chamber (8) to a given value and so displace the plunger; characterised by the fact that pressurized fuel is supplied to the injection chamber (3) and control chamber (8) by means of a single fitting (13) connected to a supply pipe (14) and coming out inside a supply orifice (15) formed in the injector body (2) and communicating with the control chamber (8) and a duct for supplying fuel to the injection chamber (3).

Description: The present invention relates to a Diesel engine electromagnetic fuel injector of straightforward, compact design and a high degree of reliability. Injectors of this type usually comprise a plunger sliding inside the injector body, for controlling fuel passage between an injection chamber, supplied with fuel under pressure, and at least one injection orifice formed in an injection nozzle secured to the body; and an electromagnetic fuel metering valve for controlling fuel passage through a drain orifice between a control chamber, supplied with fuel under pressure, and a low-pressure chamber, and reducing the pressure of the fuel in said chamber by draining the same through said orifice. Appropriate surface portions of the plunger are exposed to the fuel inside the injection and control chambers, so that the pressures inside the same and exerted on said surface portions raise the plunger when the pressure inside the control chamber falls to a given value, thus enabling fuel supply through the injection orifices on the nozzle. Injectors of the type briefly described above present a number of drawbacks. Firstly, they are extremely complex in design and of large size, particularly radially. In fact, for feeding pressurized fuel into the control and injection chambers, two separate fittings are provided, each connected to a respective delivery line. Moreover, two ducts are required inside the injector for respectively connecting said fittings to the injection and control chambers. As a result of the injection chamber being located at the bottom of the injector, the first of said ducts is extremely long and comprises a number of portions formed in various parts of the injector. For forming both said ducts, therefore, numerous holes and cavities must be formed inside the injector body and connected members. Moreover, additional holes must be provided for housing the plunger, some of which must be appropriately ground for ensuring correct guiding of the plunger during its movement. A further drawback of injectors of the aforementioned type is that they fail to provide for accurate metering of the fuel, especially when operated frequently. This is often caused by malfunctioning of the fuel metering valve as a result of incorrect operation of the armature forming part of the valve and controlling displacement of the plugging member on the same. Said armature, in fact, is not always guided accurately during its movement, and often contacts the core of the electromagnet facing it. It is also known from the document DE-A-32 27 742 an electromagnetic fuel injector having a hollow body housing a nozzle and a pair of sleeves, one of which acting as a guide of the plunger and the other acting as a portion of the control chamber, the remaining portion of which is provided in another body secured to the hollow body. The fuel under pressure is supplied by an orifice coming out inside an annular chamber formed between the two sleeves and communicating with the control chamber and the injection chamber through a pair of necks provided within the two sleeves. It is also known from the document EP-A-0 228 578 another electromagnetic fuel injector having a hollow body housing a single sleeve slidably guiding the plunger. The fuel under pressure is supplied to the injection chamber and the control chamber by a single orifice inclined with respect to the axis of the sleeve and coming out inside an annular chamber formed between the outer surface of the sleeve and an axial hole in the body. The plunger is provided with another annular chamber communicating with the former annular chamber via at least one radial hole formed in the sleeve. The aim of the present invention is to provide an electromagnetic fuel injector of the type briefly described above, designed to overcome the aforementioned drawbacks, i.e. which is of straightforward, compact design, and provides for a high degree of reliability under all operating conditions. With this aim in view, according to the present invention, there is provided a Diesel engine electromagnetic fuel injector comprising: a plunger sliding inside the injector body, for controlling fuel passage between an injection chamber, supplied with fuel under pressure, and at least one injection orifice formed in an injection nozzle secured to said body; an electromagnetic fuel metering valve for controlling fuel passage, through a drain orifice, between a control chamber, supplied with fuel under pressure, and a low-pressure chamber, so as to reduce the pressure of the fuel in said control chamber by draining the same through said orifice; surface portions of said plunger being exposed to the fuel inside said injection chamber and said control chamber, so that the pressures inside said chambers and acting on said surface portions displace said plunger when the pressure in said control chamber falls to a given value; said fuel under pressure being supplied to said injection chamber and said control chamber by means of a single fitting connected to a supply pipe and coming out inside a fuel supply orifice formed in said body and communicating with said control chamber and with a supply duct for feeding fuel into said injection chamber, a first portion of said supply duct being formed inside a first sleeve housed inside an axial hole in said body and inside which said plunger slides axially; and comprising a second axial hole defining said control chamber and being coaxial with said first hole, said second hole communicating with and being smaller than said first hole; characterised in that said second hole is formed in said body at a second end thereof opposite to said first end, said fuel supply orifice communicating with said second hole via an orifice of appropriate diameter having its axis substantially perpendicular to the axis of said second hole; said first axial hole also housing an intermediate sleeve adjacent to said first sleeve, and another sleeve adjacent to said intermediate sleeve, said supply duct including other portions formed substantially inside said intermediate sleeve and said other sleeve. The present invention will be described in detail, by way of a non-limiting example,with reference to the accompanying drawings, in which: Fig.1 shows an axial section of the injector according to the present invention; Fig.2 shows a section along line II-II in Fig.1. The injector according to the present invention substantially comprises a plunger 1 sliding inside the injector body 2, for controlling fuel passage between an injection chamber 3, located at the bottom of the injector, and the combustion chamber of a cylinder on the engine through at least one injection orifice 4 formed in an injection nozzle 5 secured to body 2. Said injector also comprises an electromagnetic fuel metering valve 6 for controlling fuel passage through a drain orifice 7 between a control chamber 8, located at the top of the injector and supplied with fuel under pressure, and a low-pressure chamber 11. Plunger 1 presents surface portions 9 exposed to the fuel inside injection chamber 3, and surface portions 10 exposed to the fuel inside control chamber 8. The respective pressures inside chambers 3 and 8 thus act respectively on surface portions 9 and 10 for raising plunger 1, as described later on, when the pressure inside control chamber 8 falls to a given value. According to the present invention, pressurized fuel is fed into injection chamber 3 and control chamber 8 by means of a single fitting 13 connected to a pressurized fuel supply pipe 14. Said fitting 13 comes out inside a supply orifice 15 formed in body 2 and communicating with control chamber 8 via an orifice 12 of appropriate diameter, as shown clearly in Fig.1. Orifice 15 also communicates with injection chamber 3 via a duct formed substantially inside two sleeves 16 and 17 housed in an axial hole 19 in body 2, which also houses a third sleeve 18. Said duct comprises an annular cavity 20 formed in the end wall of, and coaxial with, hole 19, and inside which fuel supply orifice 15 also terminates. Said duct also comprises an axial groove 23 formed in top sleeve 16; an annular chamber 24 formed between sleeves 16 and 17 and hole 19; and at least a radial hole 25 formed in sleeve 17. Plunger 1 presents a projection 28 on which rests one end of a helical spring 31 located between projection 28 and top sleeve 16 so as to normally secure the bottom end of plunger 1 against a seat on nozzle 5, thus closing injection orifices 4. A top portion 29 of plunger 1 is housed in sliding manner inside top sleeve 16 so as to guide plunger 1 as it slides longitudinally. Control chamber 8 is conveniently defined by a hole formed in body 2, coaxial with hole 19 and communicating with the same as shown in Fig.1. The diameter of the hole defining control chamber 8 is considerably smaller than that of hole 19, and the axis of orifice 15 is conveniently perpendicular to that of holes 8 and 19. Bottom sleeve 18 is also housed inside a cavity 34 formed in nozzle 5, which is positioned angularly in relation to body 2 by means of a radial pin 32 inserted between sleeve 18, body 2 and nozzle 5, as shown clearly in the Fig.2 section. An elastic annular element 35 is provided between sleeves 18 and 17 for ensuring slackfree assembly. Body 2 presents a projection 36 for angularly positioning the injector on the cylinder head. Between top sleeve 16 and the end surface of hole 19, a ring 37 is provided for sealing between annular cavity 20 and control chamber 8. Metering valve 6 substantially comprises a plugging member, consisting for example of a ball 38, for controlling fuel passage through drain orifice 7 from control chamber 8 to a low-pressure chamber 11 communicating with the same. Plugging member 38 is activated by a disc-shaped armature 40 attracted by the core 41 of an electromagnet and loaded by a spring 42 located between core 41 and armature 40, and exerting on anchor 40 a force in the opposite direction to that produced by the electromagnet. A further helical spring 45 is provided between armature 40 and a surface 46 of body 2, for exerting uniform pressure on armature 40 and so guiding the same during its movement. Between armature 40 and core 41, an annular spacer 47 is provided for preventing the surface of armature 40 facing core 41 from contacting the same. The injector according to the present invention operates as follows. Pressurized fuel is fed along pipe 14 and through fitting 13 into supply orifice 15. A first stream of pressurized fuel is thus fed into control chamber 8 through hole 12, and a second stream into injection chamber 3 along the duct formed by annular cavity 20, axial groove 23, annular chamber 24 and radial holes 25. Surface portions 9 and 10 exposed respectively to the fuel inside injection chamber 3 and control chamber 8 are thus subjected to the respective pressures inside said chambers. When metering valve 6 is de-activated, in which case the pressure is substantially the same in both chambers 3 and 8, the resultant of the pressures acting on surface portions 9 and 10 holds the end of plunger 1 against the seats on nozzle 5, thus closing injection orifices 4. When, on the other hand, metering valve 6 is activated, armature 40 is attacted by core 41, thus detaching plugging member 38 from its seat; a predetermined amount of fuel is allowed to flow from control chamber 8 into low-pressure chamber 11 through orifice 7; and the pressure inside control chamber 8 drops to a given value. The resultant of the pressures acting on plunger 1 is thus reversed, thus raising plunger 1 against the elastic reaction of spring 31, and enabling a predetermined amount of fuel to be supplied through injection orifices 4 of nozzle 5. During its movement, armature 40 is guided by spring 45 exerting substantially uniform pressure on the periphery of armature 40. Moreover, in the top limit position, the top surface of armature 40 is prevented from contacting core 41 by spacer ring 47. The injector according to the present invention is extremely straightforward in design and requires no complicated, intricate mechanical machining for its manufacture. Body 2, in fact, need simply be provided with orifice 15 and holes 8 and 19, while the duct connecting supply orifice 15 with injection chamber 3 is formed substantially inside sleeves 16 and 17. Moreover, a single fitting 13 is sufficient for feeding pressurized fuel into both control chamber 8 and injection chamber 3. Plunger 1 is guided extremely accurately by top portion 29 connected in sliding manner inside sleeve 16, the sliding surfaces of which may be ground with no difficulty whatsoever. Correct angular positioning of nozzle 5 in relation to body 2 is achieved solely by means of pin 32 housed inside easily-formable cavities. Valve 6 provides for accurately metering the amount of fuel injected at each cycle, by virtue of spring 45 guiding armature 40 during its movement, and by virtue of spacer 47 preventing armature 40 from directly contacting and adhering to core 41. The injector according to the present invention is extremely compact, especially radially, and may be connected quickly and easily to the injection pump by virtue of featuring only one fitting.

Claims: A Diesel engine electromagnetic fuel injector comprising: a plunger (1) sliding inside the injector body (2), for controlling fuel passage between an injection chamber (3), supplied with fuel under pressure, and at least one injection orifice (4) formed in an injection nozzle (5) secured to a first end of said body (2); an electromagnetic fuel metering valve (6) for controlling fuel passage, through a drain orifice (7), between a control chamber (8), supplied with fuel under pressure, and a low-pressure chamber (11), so as to reduce the pressure of the fuel in said control chamber (8) by draining the same through said orifice (7); surface portions (9, 10) of said plunger (1) being exposed to the fuel inside said injection chamber (3) and said control chamber (8), so that the pressures inside said chambers and acting on said surface portions displace said plunger (1) when the pressure in said control chamber (8) falls to a given value; said fuel under pressure being supplied to said injection chamber (3) and said control chamber (8) by means of a single fitting (13) connected to a supply pipe (14) and coming out inside a fuel supply orifice (15) formed in said body (2) and communicating with said control chamber (8) and with a supply duct for feeding fuel into said injection chamber (3), a first portion (23) of said supply duct being formed inside a first sleeve (16) housed inside an axial hole (19) in said body (2) and inside which said plunger (1) slides axially; and comprising a second axial hole (8) defining said control chamber and being coaxial with said first hole (19), said second hole (8) communicating with and being smaller than said first hole (19); characterised in that said second hole (8) is formed in said body (2) at a second end thereof opposite to said first end, said fuel supply orifice (15) communicating with said second hole (8) via an orifice (12) of appropriate diameter having its axis substantially perpendicular to the axis of said second hole (8); said first axial hole (19) also housing an intermediate sleeve (17) adjacent to said first sleeve (16), and another sleeve (18) adjacent to said intermediate sleeve (17), said supply duct including other portions formed substantially inside said intermediate sleeve (17) and said other sleeve (18). An injector as claimed in Claim 1, characterised in that said intermediate sleeve (17) houses a spring (31) coaxial with said plunger (1) and designed to secure the same in a position wherein it closes said injection orifices (4), said supply duct comprising an annular cavity (20) formed in said body (2), coaxial with said first hole (1), and inside which terminates said fuel supply orifice (15) and said first portion (23). An injector as claimed in Claim 1 or 2, characterised in that said first portion is formed of an axial groove (23) of said first sleeve (16), said supply duct also comprising an annular chamber (24) formed between said body (2) and said first sleeve (16) and said intermediate sleeve (17); and at least a radial hole (25) formed in said intermediate sleeve (17). An injector as claimed in one of the foregoing Claims, characterised in that said other sleeve (18) is also housed inside a cavity (34) on said injection nozzle (5); said nozzle (5) being positioned angularly in relation to said body (2) by means of a radial pin (32) inserted between said other sleeve (18), said body (2) and said nozzle (5); an annular elastic element (35) being provided between said other sleeve (18) and said intermediate sleeve (17). An injector as claimed in one of the foregoing Claims, wherein said electromagnetic metering valve (6) comprises a mobile plugging member (38) for controlling fuel passage through said drain orifice (7) from said control chamber (8) to said low-pressure chamber (11), and which is activated by a disc-shaped armature (40) attracted by an electromagnet core (41) and loaded by a spring (42) located between said core (41) and said armature (40) and exerting force on said armature (40) in the opposite direction to that exerted by said core (41); characterised in that a second helical spring (45) is located between said armature (40) and said body (2), coaxial with said armature (40), and designed to exert pressure on and guide said armature (40) during its movement. An injector as claimed in Claim 5, characterised in that an annular spacer (47) is provided between said armature (40) and said core (41) for preventing the surface of said armature (40) facing said core (41) from contacting the corresponding surface of said core (41).

Inventors: DE MATTHAEIS SISTO LUIGI, SFARZETTA MARIO, DE MATTHAEIS, SISTO LUIGI, SFARZETTA, MARIO
Applicants: ELASIS SISTEMA RICERCA FIAT, ELASIS SISTEMA RICERCA FIAT NEL MEZZOGIORNO SOCIETA CONSORTILE PER AZIONI
Application year: 1990
Main classification: F02M51
IPC codes: F02M47, F02B3, F02M61, F02M51, F02M55