GB2051229A

GB2051229A - Fuel Injection Device for an Internal Combustion Engine

Info

Publication number: GB2051229A
Application number: GB8015387A
Authority: GB
Original assignee: MAN Maschinenfabrik Augsburg Nuernberg AG
Current assignee: MAN AG
Priority date: 1979-06-01
Filing date: 1980-05-09
Publication date: 1981-01-14
Also published as: JPS55161954A; FR2457985B3; DE2922332C2; DK229280A; GB2051229B; DE2922332A1; NL7908909A; DD148080A1; FR2457985A1

Abstract

An injection valve 1 is fed with fuel at a high pressure and is opened and closed with the aid of a servo control circuit. A safety valve 47, provided in order to avoid uncontrolled injection if the needle valve 15 sticks, has a valve member 48 blocking the fuel supply duct 31 to the injection nozzle 5, in the direction of fuel flow when the needle valve 15 is supposed to be in the closed position. The valve member 48 is opened by an actuating piston 49 subject to hydraulic fluid supplied via a pressure duct 63. An electromagnet valve 37 is used for the actuation of a control piston 18 for the purpose of actuating the needle valve 15. The actuating piston 49 and the control piston 18 are both actuated by the opening of the electromagnetic valve 37; but because of the different lengths and cross-sectional areas of their pressure ducts 42 and 63, the piston 49 responds before the piston 18. <IMAGE>

Description

SPECIFICATION Fuel Injection Device This invention relates to a fuel injection device for an internal combustion engine.

A fuel injection device for internal combustion engines is known from German Offenlegungsschrift 25 29 933. A fuel presentation chamber at the needle valve of the injection valve in this known arrangement is directly connected, via a fuel feed pipe, to a high pressure reservoir which delivers fuel at a constantly high pressure. From the point of view of the use of components and the delivery of fuel to the fuel presentation chamber at the needle valve, this solution does indeed prove itself to be advantageous for normal use. However, should the needle valve stick, it becomes disadvantageous insofar as fuel is supplied continuously to the combustion chamber in too great a quantity, and the high pressure reservoir is emptied.

According to the present invention, there is provided a fuel injection device for an internal combustion engine, the device comprising: an inlet for pressurised fuel; a fuel chamber; a fuel supply duct between said inlet and fuel chamber; a needle valve in the fuel chamber for controlling the flow of fuel out of said chamber and through an injection nozzle; a control piston operatively connected to the needle valve; a first working chamber at one side of the control piston, adapted to receive a pressure fluid medium for urging the control piston in a closing direction of the needle valve; a second working chamber at another side of the control piston, adapted to receive a pressure fluid medium for urging the control piston in an opening direction of the needle valve;; a safety valve positioned in said fuel supply duct, and having a valve member which closes said duct in the direction of fuel flow; an actuating piston operatively connected to said valve member; a third working chamber at one side of the actuating piston, adapted to receive a pressure fluid medium for urging the actuating piston in an opening direction of said valve member; an electromagnetic valve adapted to operate in synchronisation with an engine to connect a control port of the valve to the pressure of, alternately, a pressure fluid medium supply line and a pressure fluid medium discharge line; and first and second pressure ducts which connect said control port with said second and third working chambers respectively, and have such configurations that, in use, said third working chamber responds more quickly than said second working chamber to pressure changes caused by actuation of said electromagnetic valve.

A fuel injection device according to the invention may have the advantage that, in use, in the event of the needle valve sticking, an associated high pressure fuel reservoir can be prevented from emptying by relatively simple constructional means, and that even in this case it is only possible to supply fuel under high pressure at the injection times regulated in synchronism with the engine. It is advantageous that the opening of the safety valve, and thus the supply of fuel from the high pressure reservoir to the fuel chamber, is regulated by the same electromagnetic valve that regulates the actuation of the control piston in the opening direction of the needle valve. This measure saves on expensive additional mechanisms.As a result of the arrangement of the valve member of the safety valve, within the fuel supply duct from the fuel inlet to the fuel chamber at the needle valve, with a closing action in the direction in which the fuel is supplied, suitability for the use of heavy oil is further advantageously ensured, since the possible fouling or sticking of the valve member cannot, by virtue of the arrangement provided, readily lead to an impairment of function. In addition to this, the arrangement of the valve member of the safety valve may ensure, in the event of failure of the pressure fluid medium control circuit, a safe shut-off of the fuel supply duct to the fuel chamber of the needle valve.

In a preferred arrangement, pressure in the fuel supply duct is relieved through a fuel return duct when the safety valve is closed. Thus, there may be obtained a long service life for the safety valve, since the latter is generally not subjected to pressure. An advantage to be found in a preferred fuel injection device used in multi-cylinder engines is that, should the needle valve stick, a failure of the entire engine may be avoided, since a safety valve is assigned to each injection valve.

Such an arrangement also permits one of the safety valves to remain always closed, by suitable interruption of control to the electromagnetic valve, and, as long as this condition is maintained, permits the respective cylinder to run empty, i.e.

without a supply of fuel, together with the other normally-driven pistons.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawing, the single figure of which illustrates a fuel injection device. Only those components of the fuel injection device necessary for comprehension of the invention are shown in the diagram.

An injection valve, designated as 1, consists of a multisectional valve body 2 with an upper part 3 and a lower part 4, upon which an injection nozzle 5 is mounted, on the side facing the combustion chamber, and pressed on by means of a nozzle holder 6. The latter is braced with a holder ring 7 against a support shoulder 8 of the lower part 4, and is held together with this shoulder through a fastening sleeve 9 gripping the back of its holder ring 6, by means of a screw-coupling 10 on the upper part 3.

The injection nozzle has an inlet bore 11, in the axial extension of which, in the lower part 4 of the valve body 2, a conical valve seating 1 2 is arranged for a needle valve 15, which is arranged in a bore 13 so as to be axially displaceable, and which penetrates a fuel presentation chamber.

14. The needle valve 15 5 opens on the side facing away from the combustion chamber into a working chamber 1 6 (hereinafter called the second working chamber), and in this area it is attached, by means of a coupling bearing 17, to a coaxially-aligned control piston 1 8 in the upper part 3 of the valve body 2, in such as way as to be both form- and force-locking. The control piston is so arranged to be axially movable, having a control plunger 1 9 in a bore 20, and a pressure piston 21, provided above and of a smaller diameter, in a bore 22. The axial end of the pressure piston 21 facing away from the combustion chamber plunges in to a working chamber 23 (hereinafter called the first working chamber), into which opens a pressure pipe 24.

The pressure pipe 24 consists of a bore 25, aligned axially with the control piston, in the upper part of the valve body 2; a transverse bore 27 opening into the first bore 25 at a right angle, formed radialiy inwards from the periphery of the upper part 3 and sealed by means of a plug 26; and a supply bore 28, again opening at a right angle into the second bore 27, and formed inwardly from the upper surface of the upper part 3. A connecting element 29 is set into the supply bore 28, and a part 30 of the pressure pipe 24 that lies outside the injection valve 1 is connected via this element to a high-pressure fuel reservoir, which is not shown.A high-pressure pump (also not shown) supplies fuel continuously to this high-pressure fuel reservoir, so that in the latter a constant high fuel pressure is maintained, and consequently fuel is always fed to the first working chamber 23 via the pressure pipe 24 at a constant high pressure, and a steady high pressure is always maintained in this chamber. As a result of this high pressure in the working chamber, 23, the control piston 1 8 is urged permanently in the closing direction of the needle valve 15, and endeavours to hold the latter down in the closed position.

A fuel supply duct 31, which branches off from the pressure pipe 24 within the valve body 2, is provided for the supply of fuel to the fuel chamber 14 at the needle valve 1 5. The fuel supply duct 31 consists in particular of a bore 32, formed offcentre in the lower part 4 of the valve body 2, and opening into the fuel chamber 14, to which bore a further bore 33 is connected in the upper part 3 of the valve body 2. This bore 33 opens into a transverse bore 35, which is formed in from the outer side of the upper part 3, and sealed by means of a plug 34, and which is once more connected, va a connecting duct 36 aligned with the supply bore 28, to the transverse bore 27 of the pressure pipe 24.It is evident from the above that this construction has the advantage of requiring only one common external fuel supply pipe for the feeding of two internal injection-valve pipes.

In addition to this, an electromagnetic valve 37 is arranged on the upper side of the valve body, and is part of an hydraulic control circuit described below. The valve 37 comprises a mechanical control part 38, the internal structure of which is well-known, and which is therefore not shown here in detail, and an electrical control part 39, which is not shown here for the same reason. A pressure supply line 40, which is connected to a high-pressure reservoir supplying hydraulic fluid at constant pressure (not shown), opens into the mechanical control part 38 of the valve 37, as does a discharge line 41, which is connected to a reservoir (also not shown) for the purpose of feedback and pressure relief of the supplied hydraulic oil.The pressure supply line 40 is connected by a control port of the electromagnetic valve 37, within the valve body 2, to a first pressure duct 42 leading to the second working chamber 1 6. The electric part 39 of the valve 37 is connected, via an electric lead 43, to a transmitter G, which is driven in synchronism with the engine.Through this transmitter G, the valve 37 can be controlled open and shut by strokes, in such a way that the second working chamber 1 6 at the control piston 1 8 can be connected alternately to the pressure supply line pipe 40, containing hydraulic fluid at a constant pressure, for the purpose of actuating the control piston 1 8 in the direction in which the needle valve 15 opens, orto the discharge line 41 for the purpose of returning the needle valve 1 5 to its closed position.The working surface 44, effective in the opening direction, on the needle valve 1 5 in the area of the fuel chamber 14, and the working surface 45 on the control piston 1 8 in the second working chamber 16, are measured so as to be individually smaller, but together greater than the working surface 46 of the control piston 18 that plunges into the first working chamber 23. This ensures that when the pressure in the second working chamber 1 6 is relieved, the needle valve 1 5 is lifted by the hydraulic control circuit, and, as a result of the fuel being under constant pressure in the fuel presentation chamber 14, the injection process can now take place. When the hydraulic control circuit is released by timed (rhythmic) switching of the valve 37, the needle valve 15, in consequence of the force now prevailing on the control piston in its closing direction, is pushed back and pressed onto its valve seating 12.

The arrangement described above is assigned a safety valve 47, the components of which are advantageously built-in to the valve body 2, in the upper part 3 of the injection valve 1, as shown in the diagram. The safety valve 47 consists of a valve ember 48, shown in this embodiment to be in the form of a metal ball, and an actuating piston 49. The valve member 48 is arranged within the fuel supply duct 31 to the fuel chamber 14; in the embodiment shown, it is within the connecting duct 36. On the inner wall of the connecting duct 36, longitudinal guide ribs 50 are formed inwards in a radial direction, which serve to guide the valve member 48, while allowing the fuel to flow past. At the lower end of these longitudinal guide ribs 50, the connecting duct 36 is narrowed in cross-section, to form a conical valve seating 51 for the valve member 48.The valve member 48 can be closed off at the valve seating 51 in the direction of the flow of fuel present there, for the purpose of blocking the fuel supply duct 31 to the fuel chamber 14.

The actuating piston 49 of the safety valve 47 is formed as an actuation element for the valve member 48, and also as a valve in itself, whereby, with a conical valve surface 52 serving as a valve closing element, it interacts with a valve seating 53, correspondingly adapted, in a fuel return duct 54, in such a way that the fuel situated between the valve member 48 of the safety valve 47 and the fuel chamber 14, in the area of the fuel supply duct 31, is relieved of pressure via the fuel return duct 54 when the safety valve 47 is closed.

Behind the actuating piston 49 a third working chamber 55 is arranged, which is formed by a bore 57, formed inwards in the valve body and running parallel to the bore 25, and sealed to the outside by means of a plug 56.

The actuating piston 49 consists in particular of a pressure disc 58 contiguous to and bordering the third working chamber 55, and a main body portion 60, situated in a bore 59, which joins up with the disc in the direction of the valve member 48. This main body portion 60 in turn carries an extension plunger 61 of a smaller diameter, which plunges into the fuel return duct 54. At the front end of the extension plunger 61 the conical surface 52 is formed as a valve closing element. A connecting rod 62, which is of smaller crosssection, and the front end of which fits against the valve member 48, is connected to the conical surface 52.

A second pressure duct 63 opens into the working chamber 55 behind the actuating piston 49. This pressure duct 63 is formed in the upper part 3 of the valve body 2 as a bore, and branches off from the first pressure duct 42 of the servo control circuit (which leads to the second working chamber 1 6 at the control piston 18 of the injection valve 1), after it leaves the control port of the electro-magnetic valve 37 and, like the working chamber 55, it is filled with hydraulic fluid. However, the second pressure duct 63 could alternatively be connected to a second control port of the electromagnetic valve 37, should one be available. The second pressure duct 63 is approximately a third shorter than the first pressure duct 42 leading to the second working chamber 1 6 at the control piston, and its crosssectional area is approximately four times as large.The point of this will be seen from the following explanation of the function of the safety valve 47 in its interaction with the other parts of the injection valve 1.

For a consideration of function, one would start from a condition of the needle valve 1 5, which is in the closed position. The valve 1 5 is held down in this position by the control piston 18, by the fuel pressure present in the first working chamber 23. The safety valve 47 is closed, i.e. its valve member 48 is pressed against the valve seating 51 in the fuel supply duct 31 by the fuel pressure present therein. In addition to this, the fuel return duct 54 is opened by the valve surfaces 52, 53, so that the fuel present in the area between the closed valve member 48 of the safety valve 47 and the closed needle valve 1 5 in the fuel chamber 14, is depressurised.

If a signal for an injection phase is now fed from the engine-synchronised transmitter G via the lead 43 into the electromagnetic valve 37, a control element in the mechanical control part 38 of the valve 37 will be moved electromagnetically, so that the pressure of hydraulic fluid present in the pressure supply line 40 will now be passed on to the hydraulic fluid situated in the pressure ducts 42 and 63 to the second and third working chambers 1 6 and 55 of the control piston 1 8 and safety valve 47 respectively.Because of the difference in the lengths of the pressure transfer paths and crosssectional surfaces of the two ducts 42 and 63, and also because of the working surface 64 effective in the opening direction, at the pressure disc 58 of the actuating piston 49, which is smaller than the working surface 45 of the control piston 1 8 (in the second working chamber 16), also effective in the opening direction, the actuating piston 49 is activated with a minimal length of forward stroke.The consequence of this is that the fuel return duct 54 is shut off by the raised actuating piston 49 by means of the valve surfaces 52, 53, and, since the valve member 48 of the safety valve 47 is now lifted from its valve seating 51, the fuel supply duct 31 to the fuel chamber 14 is open again, and thus fuel is again present under pressure in the fuel chamber 14.

This pressure now bears upon the working surface 44 of the needle valve 1 5 that is operative in the opening direction, and is added to the pressure present in the second working chamber 1 6 at the working surface 45 of the control piston 1 8 that is operative in the opening direction.

Since the sum of the forces exerted by these two pressures is greater than that due to the pressure exerted in the first working chamber 23 on the working surface 46 of control piston 1 8 that operates in the closing direction, the needle valve 1 5 is raised from the valve seating 12 as pressure is exerted on its working surface 44, and the injection process is initiated.

The duration of injection is controlled by the engine synchronised transmitter G, whereby the electro-magnetic valve 37 is caused to switch at the end of the injection phase, with the consequence that the pressure ducts 42 and 63 connect with the discharge line 41, thus relieving pressure, the second pressure duct 63 again responding before the first pressure duct 42. The consequence of this is that, in turn, as the pressure in the pressure duct 63 falls, so does the pressure operating in the opening direction on the actuating piston 49 of the safety valve 47. The latter is closed again by the pressure of the fuel operating on its valve member 48, and the fuel return duct 54 is simultaneously opened again, so that the fuel situated in the area of the fuel supply duct 31 between the valve member 48 and the fuel chamber 14 is again relieved of pressure.

Also, the pressure then falls off in the second working chamber 16, the pressure exerted in the first working chamber 23 on the surface 46 effective in the closing direction exceeds that exerted on the working surface 44 of the needle valve 15, and thus the needle valve 1 5 is returned to its closed position.

This cycle is repeated every time suitable control of the electromagnetic valve is effected by the engine-synchronised transmitter G.

In a modification, hydraulic control fluid can be supplied to the first working chamber, rather than fuel. Also, fuel in the fuel chamber 14 need not act on the needle valve 1 5 in an opening direction, control thereof then being effected only via the first and second working chambers 23 and 16.

Claims

1. A fuel injection device for an internal combustion engine, the device comprising: an inlet for pressurised fuel; a fuel chamber; a fuel supply duct between said inlet and fuel chamber; a needle valve in the fuel chamber for controlling the flow of fuel out of said chamber and through an injection nozzle; a control piston operatively connected to the needle valve; a first working chamber at one side of the control piston, adapted to receive a pressure fluid medium for urging the control piston in a closing direction of the needle valve; a second working chamber at another side of the control piston, adapted to receive a pressure fluid medium for urging the control piston in an opening direction of the needle valve; a safety valve positioned in said fuel supply duct, and having a valve member which closes said duct in the direction of fuel flow;; an actuating piston operatively connected to said valve member; a third working chamber at one side of the actuating piston, adapted to receive a pressure fluid medium for urging the actuating piston in an opening direction said said valve member; an electromagnetic valve adapted to operate in synchronisation with an engine to connect a control port of the valve to the pressure of, alternately, a pressure fluid medium supply line and a pressure fluid medium discharge line; and first and second pressure ducts which connect said control port with said second and third working chambers respectively, and have such configurations that, in use, said third working chamber responds more quickly than said second working chamber to pressure changes caused by actuation of said electromagnetic valve.

2. A device according to claim 1, wherein said first working chamber is connected to receive pressurised fuel from said inlet.

3. A device according to claim 1 or 2, wherein said fuel chamber serves also as a working chamber in which pressurised fuel acts to urge the needle valve in an opening direction.

4. A device according to claim 1,2 or 3, including a transmitter for transmitting control signals to said electromagnetic valve in synchronisation with an engine.

5. A device according to any preceding claim, wherein said actuating piston is provided with a valve surface which co-operates with a valve seating to connect a fuel return duct with the portion of said fuel supply duct downstream of said safety valve, only when said safety valve is closed, thereby to relieve pressure in said portion.

6. A device according to any preceding claim, wherein said first pressure duct is connected directly to said control port and said second pressure duct branches from said first pressure duct.

7. A device according to any preceding claim, wherein said second pressure duct is approximately two-thirds the length of, and has a cross-sectional area approximately four times as great as, the first pressure duct.

8. A device according to any preceding claim, wherein said valve member is a metal ball.

9. A device according to claim 8, wherein said ball is guided for longitudinal movement along the fuel supply duct between said inlet and the safety valve, by means of ribs formed in the walls of the duct, and engages a frusto-conical valve seating formed in the fuel supply duct.

10. A device according to claim 2 or any one of claims 3 to 9 as appendant thereto, wherein said actuating piston comprises a main body portion, a pressure disc secured to the main body portion and positioned in the third working chamber, an extension plunger secured to the main body portion and plunging into said fuel return duct, and a connecting rod between the extension plunger and said valve member, the extension plunger being formed with said valve surface for controlling flow of fuel through said fuel return duct.

11. A device according to any preceding claim, wherein said safety valve and said control piston are housed in a common body.

12. A fuel injection device substantially as hereinbefore described with reference to the accompanying drawing.