ELECTROMAGNETICALLY-CONTROLLED FUEL INJECTION VALVE FOR DIESEL ENGINES

Abstract: An electromagnetically-controlled fuel injection valve (1) for diesel engines includes a body (2) having an upper electromagnetic metering valve (11) which con­ trols communication between a control chamber (14) sup­ plied with the pressurised fuel and a discharge port (A). The metering solenoid valve, which itself con­ stitutes a unit independent of the rest of the in­ jection valve, is supported by a head element (10) con­ nected to the body (2) of the injection valve (1) by axial clamping means (l8) and has an appendage (9) which carries the control chamber (14) and the discharge port (A) and is inserted in an axial seat (8) in the body with the interposition of double sealing means (16,17).

Description: The present invention relates in general to electromagnetically-controlled fuel injection valves for diesel engines. More particularly, the invention relates to an injection valve for diesel engines, including a body having an axially extending cavity communicating at one end with an injection nozzle, a needle slidably mounted into the cavity and operatively associated with the nozzle for controlling communication between the nozzle and an injection chamber, which communicates with a passage for the supply of fuel under pressure, a control chamber supplied with the fuel under pressure through an inlet port to maintain the needle in a closed position, an upper electromagnet metering valve controlling the communication between the control chamber and a discharge port, the opening of which causes a pressure drop in the control chamber and the consequent displacement of the needle to an open position, the metering valve including a head element secured to the body by axial clamping means and provided with an axial passage for an electromagnetically operable obturator for the discharge port, an appendage integral with the head element carrying said discharge port and at least part of said control chamber, the appendage being inserted in an axial seat of the body supplied with fuel under pressure and communicating with the opposite end of the cavity. An injection valve of the above type is known from the DE-A-3 227 742, wherein the head element carries an appendage provided with a threaded inner bush securing into the appendage an outlet bore carrying member. The head element carries the metering valve and is detachable from the valve body. Since the bush is provided with only a part of the control chamber, and the inlet port of the pressure fuel is provided on a body element, the removal of the metering valve leaves several delicate components of the metering exposed and not connected to the associated control chamber. Therefore an effective test of the metering valve when so removed or before being assembled cannot be carried out. It is also known from the EP-A-0 196 265 an injection valve including an appendage housed in a threaded bore of a body, whereby the metering valve is removable form the injection valve. A holed insert is provided between the obturator and the threaded bore and is sealed at the opposite ends on the appendage and on the threaded bore. However, such an insert is not removable from the valve as a whole with the metering valve. The object of the invention is to provide an injection valve where the metering valve is structurally and functionally independet from the rest of the valve. This object is achieved by the injection valve of the invention, which is characterised in that said appendage is also provided with said inlet port communicating with the seat, a double sealing means being provided between the seat and the appendage for sealing a space therebetween, whereby the metering valve including the appendage of the head element, carrying the inlet port, the control chamber and the discharge port, are structurally and functionally independent of the rest of the injection valve and can be separately tested. By virtue of this characteristic, the metering solenoid valve with the control chamber and the discharge port constitue an autonomous unit which can be subjected in a convenient and easy manner to the operations necessary for the calibration of the discharge port and calibration and setting up of the metering solenoid valve, before the assembly of the injection valve. In other words, the metering solenoid valve discharge port - control chamber unit may to advantage be tested independently, with obvious practical advantages. Preferably, the double sealing means include complementary frontal conical sealing surfaces between the body and the head element, and an annular resilient member coaxial with the appendage. According to another aspect of the invention, the appendage has an associated variable-thickness block for limiting the opening travel of the needle. According to another characteristic of the invention, the needle may have two different diameters in correspondence with its portion on which the pressure in the control chamber acts and its portion on which the pressure in the injection chamber acts. According to another aspect, the second passage for the supply of fuel to the injection chamber includes a ring of apertures formed in the body around the needle. The needle may be a single piece or, alternatively, two pieces. Further characteristics of the invention will become apparent during the detailed description which follows with reference to the appended drawings, provided purely by way of non-limiting example, in which: Figure 1 is a schematic longitudinal sectional view of an injection valve according to the invention, and Figure 2 is a cross-sectional view taken on the line II-II of Figure 1. With reference to the drawings, a fuel injection valve for diesel engines is schematically and generally indicated 1. The valve 1 comprises essentially a body 2 forming a lower injection nozzle 3 the opening and closing of which is controlled by a needle 4 movable axially within a central cavity 5 in the body 2. The lower zone of this cavity 5 forms an injection chamber 6 into which the fuel is directed under pressure by a pump, not illustrated, through supply passages 7 formed in the body 2. As is seen in Figure 2, two supply panels 7 and two smaller-diameter apertures 23 for the engagement of centering stops 24 are provided. The upper end of the cavity 5 defines a seat 8 to which the fuel is also supplied under pressure through an inlet port Z. An axial appendage 9 is engaged in this seat 8, an annular groove of the appendage 9 forming a space therebetween and is integral with an element 10 applied in the form of a head to the top of the body 2 and carrying a metering solenoid valve 11. The obturator of the solenoid valve 11, indicated 12, is slidable in an axial passage of the element 10 and cooperates with a fuel discharge port A formed in the upper part of the appendage 9 and communicating with a control chamber 14 also formed in this appendage 9. The control chamber 14 communicates with a cavity 5 through a variable-thickness block 15 for limiting the opening travel of the needle 4. In the embodiment illustrated, this needle 4 is formed by two axial portions 4a, 4b: it should be noted, however, that it could alternatively be formed in a single piece. In both cases, the region of the needle 4 which faces the control chamber 14, indicated 4c, conveniently has a diameter which is different from, normally larger than, that of its portion 4d on which the fuel pressure in the thrust chamber 6 acts. The control chamber 14 is in communication with the seat 8, which through the groove of the appendage communicates with the inlet duct of the body and with the inlet port Z. In order to isolate this control chamber 14 hermetically from the fuel discharge downstream of the discharge port A, a double seal is provided between the appendage 9 and the ends of the seat 8, formed in the lower part by a resilient annular washer 16 and in the upper part by complementary frontal conical sealing surfaces 17. Alternatively, these frontal sealing surfaces 17 could be replaced by an annular washer similar to the washer 16. In the embodiment illustrated, the head element 10 is fixed to the body by means of a ring nut 18. In addition or alternatively to this ring nut 18, the head element 10 may be clamped to the body 2 by means of a threaded coupling between the appendage 9 and the seat 8. In the embodiment illustrated, the head element 10 is not in effect fixed directly to the body 2 but is connected thereto by an intermediate member 19 which is fixed to the body 2 in its turn by means of a ring nut 20 and by means of a centering system including a bush 21 surrounding the needle 4 and an eccentric reference pin 22. The operation of the injection valve 1 is generally known: in the condition in which the discharge port A is closed by the obturator 12 of the solenoid valve 11, the needle 4 is kept in the lowered position to close the injection nozzle 3 and prevent the escape of pressurised fuel in the injection chamber 6. As soon as the discharge port A is opened, the consequent drop in pressure in the control chamber 14 enables the needle 4 to rise against the action of the pressure in the chamber 6, enabling the injection of fuel through the nozzle 3. The configuration of the needle 4, with its regions 4c, 4d of different diameters, enables the force applied to the needle 4 to be varied in this phase, while the presence of the supply apertures 7 enables the accumulated volume of pressurised fuel to be increased, larger passage sections being provided. The integration of the solenoid valve 11 with the discharge port A and the control chamber 14 in the head element 10 enables the pressure modulation and the rate of flow through the discharge port A to be checked separately and independently, before the assembly of the valve 1. This enables the necessary calibration and setting up of the entire pressure control system upstream of the needle 4 to be carried out more easily.

Claims: An electromeccanically-controlled fuel injection valve for diesel engines, including a body (2, 19) having an axially extending cavity (5) communicating at one end with an injection nozzle (3), a needle (4) slidably mounted into the cavity (5) and operatively associated with the nozzle (3) for controlling communication between the nozzle (3) and an injection chamber (6), which communicates with a passage (7) for the supply of fuel under pressure, a control chamber (14) supplied with the fuel under pressure through an inlet port (Z) to maintain the needle (4) in a closed position, an upper electromagnet metering valve (11) controlling the communication between the control chamber (14) and a discharge port (A), the opening of which causes a pressure drop in the control chamber (14) and the consequent dispaclement of the needle (4) to an open position, the metering valve (11) including a head element (10) secured to the body (2, 19) by axial clamping means (18) and provided with an axial passage for an electromagnetically operable obturator (12) for the discharge port (A), an appendage (9) integral with the head element (10) carrying said discharge port (A) and at least part of said control chamber (14), the appendage (9) being inserted in an axial seat (8) of the body (2, 19) supplied with fuel under pressure and communicating with the opposite end of the cavity (5), characterised in that, a double sealing means (16, 17) being provided between the seat (8) and the appendage (9) for sealing a space therebetween, said appendage (9) is also provided with said inlet port (Z), said inlet port (Z) communicating with said space which is in communication with an inlet duct of said body (2, 19), whereby the metering valve including the appendage (9) of the head element (10), carrying the inlet port (Z), the control chamber (14) and the discharge port (A), are structurally and functionally independent of the rest of the injection valve and can be separately checked. An injection valve according to Claim 1, characterised in that the double sealing means (16, 17) include an annular resilient member (16) coaxial with the appendage (9) for sealing one end of the seat (8), and complementary frontal conical surfaces (17) between the body (2, 19) and the appendage (9) of the head element (10) for sealing the other end of the seat (8). An injection valve according to Claim 1 or 2, characterised in that the appendage (9) is provided with an annular groove providing said space. An injection valve according to anyone of the previous Claims, characterised in that said body (2, 19) include a first body element (2) housing a portion (4a) of the needle (4) having a relatively small diameter, and a second body element (19) housing the head element (10) and a portion (4c) of the needle (4) having a relatively large diameter, the body elements (2 and 19) being mutually secured by a ring nut (20), centering means (21, 22) including a bush (21) surrounding the passage (5) and an eccentric reference pin (22) being provided for mutually centering the two body elements (2 and 19) when so mutually secured. An injection valve according to Claim 4, characterised in that a variable thickness block (15) is housed it the second body element (19) at the other end of the cavity (5) for separating the end of the appendage (9) from the end of the large diameter portion (4c) of the needle (4), thus adjustably limiting the opening travel of the needle (4).

Inventors: TURCHI, SERGIO, VALETTO, ALESSANDRO
Applicants: WEBER S.R.L.
Application year: 1988
Main classification: F02M47
IPC codes: F02M65, F02M51, F02M47, F02B3