GB2049885A

GB2049885A - Fuel injection device for an internal combustion engine

Info

Publication number: GB2049885A
Application number: GB8014987A
Authority: GB
Original assignee: MAN Maschinenfabrik Augsburg Nuernberg AG
Current assignee: MAN AG
Priority date: 1979-05-05
Filing date: 1980-05-06
Publication date: 1980-12-31
Also published as: NL8002535A; FR2456222B1; DK162380A; DE2918147A1; FR2456222A1; DE2918147C2; GB2049885B; JPH0260864B2; JPS55151153A

Abstract

In a fuel injection device, with an injection valve supplied from a high- pressure reservoir with fuel at a constantly high pressure, and with an electrohydraulic control circuit for controlling the opening and closing of the injection valve, a safety valve is provided in the supply duct from the high-pressure reservoir to the fuel chamber of the injection valve. As shown the safety valve comprises a valve seating 115 and a valve body 2. which is supported in the open position through plate springs by a stop face 51 arranged on a support member 5, movable transversely of the closing direction of the valve body 2 to bring an inclined face 52 into effect thus reducing the spring force and allowing the valve body to seat. <IMAGE>

Description

SPECIFICATION Fuel injection device for an internal combustion engine.

This invention relates to a fuel injection device for an internal combustion engine.

In known fuel injection devices, fuel is passed by means of a fuel pump into a reservoir, where it is acted upon with constant high pressure and is fed in measured quantities to the combustion cylinders by means of injection nozzles, which are controlled by pressure from a control pump, which acts rhythmicaily upon the needle valves of the injection nozzles. A safety valve is provided in the pipe from the reservoir to an outer injection nozzle fuel chamber, to prevent emptying of the reservoir and uncontrolled escape of fuel from the injection valve should the nozzle needle stick.

The present invention is concerned particularly but not exclusively with a fuel injection device for internal combustion engines with a fuel pump delivering a constantly high fuel pressure in a reservoir, with fuel feed pipes from the reservoir to the fuel chambers at the needle valves of the injection nozzles, and with a control mechanism having a hydraulic control circuit and acted by a transmitter driven in synchronism with the engine, with which mechanism a control piston of each injection valve can be moved in order to actuate the needle valve, upon which fuel standing in the fuel chamber acts in the opening direction. This design enables the fuel pressure to be kept constant during the injection process, so that the quantity of injected fuel can be measured precisely and disturbing re-injection can be avoided.

Safety valves which are supposed to prevent excess pressure in fuel injection devices are in fact already known. With these, however, it is not possible to eliminate emptying of the reservoir in fuel injection devices for internal combustion engines where the fuel is fed through a fuel pump into a reservoir with a constantly high pressure, should the needle valve of an injection nozzle stick in the opened position.

In order to block the supply to the fuel chamber of the nozzle should the needle valve accidentally fail to shut, a suggestion has already been made in German Auslegesschrift 12 81 207, whereby a safety device is provided in the pipe from the reservoir to the injection nozzles, which device consists of a shut off device connected in the pipe and a valve with a piston section, both of which are acted upon in the opening direction by the pressure of the control pump and in the closing direction by a spring and by the reservoir pressure.

in one embodiment, the shutoff valve interacts on the side facing the pressure from the control pump with a piston. However, in this embodiment, the reservoir pressure only comes into effect near the valve and when the latter is in the closed position.

The valve is acted upon in the open position in the closing direction essentially by spring tension, and in the opposite direction, with a further piston connected, if necessary, by the pressure from the control pump which is exerted upon the control oil for the purpose of opening and closing the needle valves. When the shutoff device closes, the pressure exerted upon the fuel from the reservoir pressure is retained in the pipe from the safety device to the outer fuel chamber or chambers, so that fuel escapes from the respective nozzle if one of the nozzle needles sticks. As a result of the pulsation of the control pressure, the valve and, where appropriate, the separate piston are moved backwards and forwards with each injection process. They are thus subjected to wear which can impair their operational safety or necessitate periodic replacement of these parts.With this design it is also necessary to take precautions so that a mixing of fuel and control oil is avoided.

The present invention aims, particularly but not exclusively, to provide a fuel injection device which avoids the above difficulties and disadvantages, and a safety valve of which is suitable for a high hydraulic pressure (ca. 1000 bar) and for operation with a heavy oil, and which permits a short closing time ( < 300 ms).

Movement cf the safety valve without a pressure medium should also be possible, and precautions should be taken to ensure a rapid drop in pressure in the supply duct between the safety valve and the fuel chamber of an injection nozzle.

According to the present invention, there is provided a fuel injection device for an internal combustion engine, the device being provided with a safety valve between an inlet for pressured fuel and an injection nozzle/needle valve assembiy, the safety valve comprising an inlet duct, an outlet duct, a valve seating between said inlet and outlet ducts, a valve body which engages said seating, and a support member having a support face which is movable transversely of the closing direction of the valve body, into and out of a support position in which it supports said valve body directly or indirectly in an open position.

In preferred embodiments, the safety valve may be closed suddenly when the support member is moved quickly under hydraulic pressure. Such a design may also be suitable as an emergency valve, where the operating position can only be reestablished by manual intervention or by dismantling.

In one further embodiment of the invention, the said support face is substantially plane and adjoins an inclined face of said support member, which member is movable transversely of said closing direction such that support of said valve body Is transferred between said support face and said inclined face, thereby to effect opening and closing of the safety valve. Also, the gradient of the inclined face should be greater than is necessary to be self-limiting.These measures may ensure that the safety valve may be brought back into the open position by actuation of the support member, that the valve body engages the valve seating under full hydraulic pressure, and that movement of the support member by the direct or indirect influence of the valve body upon the inclined surface, assists, effects and/or completes the removal of the horizontal member directly as a result of the pressure af fuel in the inlet duct. A roller is expediently arranged to bear on the said support and inclined surfaces.

In another development of the invention, a support rod extends in a guide bore between said valve body and said support face and comprises telescopic rod portion which are resiliently urged apart, an annular space is provided adjacent said valve seating, from which space said outlet duct extends, at an angle to said inlet duct, said support rod and guide bore are formed with respective valve surfaces which close as the safety valve opens, an annular groove is formed in said guide bore, and a leakage duct extends from said groove, at an angle to said guide bore. The said valve body may comprise a valve cone carried on a shaft which engages in said guide bore, or a ball, which is guided by ribs in said inlet duct.In both cases, the valve body may advantageously be substantially enveloped in fuel, such that it is "floating" therein, when open. Both said valve seating and said valve surfaces are advantageously frusto-conical. The said annular groove is advantageously disposed between said annular space and said valve surfaces.

Such a design may be distinguished by an economic construction and simple assembly.

These measures permit a practically frictionless positioning of the valve body, so that temporary delays as a result of friction in the closing movement cannot occur. On the other hand, the valve body may be brought suddenly onto the valve seating by means of the hydraulic fuel pressure which, advantageously in this fuel injection device, is effected by very high reservoir pressure. A further great advantage is that the outlet duct (to the fuel chamber of the injection nozzle) possesses, after closing, a connection to the leakage outlet duct along the shaft of the valve cone or along the support rod, so that hydraulic pressure existing in the supply duct to the injection nozzle fuel chamber is reduced by the draining of fuel into the leakage outlet.The sealing lock of the said valve surfaces is tightly shut by the resilient tension which telescopically expands the support rod. During movement of the support face of the support member, the resilient tension may assist the movement of the support member until it operates continuously by itself, and may increase the acceleration of the valve body in the direction of the valve seating. Finally, this design affords a rinsing of the annular clearance between the shaft or the support rod and the guide bore, which rinsing is at a constantly low rate but nevertheless prevents resinification. Naturally, in the preferred "floating"' position of the valve body, and thus of the shaft of the valve cone, and of the support rod, friction or corrosion welding with the guide bore cannot occur. Such welding has previously led to considerable diffculty and damage in known designs.

In a modification of the design discussed in the previous paragraph, the sealing lock between said valve surfaces is arranged in the guide bore between said annular space (to the outlet duct) and said annular groove (to the leakage duct). In this design the leakage duct is blocked when the safety valve is in the open position, and is only connected to the outlet duct when the safety valve is in the closed position. This measure makes it possible for the annular clearance between the support rod and the wall of the guide bore to be designed with a large diameter, so that pressure is reduced particularly quickly in the outlet duct and in the supply duct to the injection nozzle fuel chamber through the leakage outlet duct, and thus the escape of fuel from the nozzle, if the nozzle needle should stick, is further reduced.

When the valve body consists of a ball valve which is acted upon by the support rod, spring tension acting in the inlet direction or the closing direction upon the ball valve is advantageously provided, whereby straying of the ball valve as a result of its comparatively favourable flow configuration is eliminated without diminishing the character of a floating positioning.

In another embodiment, a clearance -- for the purpose of rinsing -- is provided between the shaft (of the valve cone) and the support rod on the one hand, and their guide bore on the other, the size or diameter of which clearance is designed, in the manner known for passing a flow in a capillary tube, in such a way that a pressure head exists in relation to the surrounding pressure at rheleakage outlet. In this way the precise design of the clearance can be facilitated, as well as the rinsing at the shaft of the valve cone being increased, since, in a valve cone with a shaft, clearance between the shaft and the guide bore is kept smaller than the clearance between the section of the support rod lying above the sealing lock and the guide bore.

If the support member is actuated by means of an energy source such as electric current or compressed air, the open position ofthe safety valve, at which the valve body is supported by the support face on the support member, is the operative position, and the design is such, or such means are provided, that the support member returns automatically to a resting position, with the safety valve closed, if the energy supply is switched off or interrupted. This can be advantageously achieved by providing an electromagnet for the rotational or translational movement of the support member, and by ensuring that, when the magnet is in its operative position, the valve body in its open position is supported directly or indirectly, such as by a support rod and/or roller arranged upon it, against the support face of the support member.

In such preferred embodiments of the invention, a fuel injection device may be particularly suitable for operation with heavy oil and a high reservoir pressure, while its use or the use of its components where lighter fuel or lower reservoir pressure is used is equally possible and equally advantageous.

For a better understanding and to show how the same may be carried into effect, reference will now be made, by way of exampie only, to the accompanying diagrammatic drawings, in which: Figure 1 shows a fuel injection device for an internal combustion engine, with a safety valve; Figure 2 shows a portion of the safety valve of Figure 1, on an enlarged scale and in crosssection; Figure 3 shows the safety valve of Figure 2, in a closed position; Figure 4 shows another safety valve on a further enlarged scale; and Figure 5 shows this safety valve in crosssection along the line V-V of Figure 4.

In Figure 1, in a fuel injection device (only partially illustrated), with a reservoir H and an injection valve E in a supply duct H1 1 from the reservoir H to an outer nozzle fuel chamber El, in which a needle valve E2 engages, a safety valve S with a shutoff device is provided for the prevention of uncontrolled escape of fuel from the injection nozzle E3 if the needle valve E2 sticks. The fuel is fed by means of a fuel pump (not illustrated) into the reservoir H. Here it is acted upon by constantly high pressure, and is passed from here in measured quantities by means of injection valves E, controlled by pressure acting rhythmically on their needle valves E2 from a control pump (not illustrated) or by the effect of an electromagnetic valve E4, to the combustion cylinders of the internal combustion engine.

According to Figures 2 to 4, the safety valve with a shut off device consists of a housing 11, 12, if necessary in a divided form, with an inlet duct 111, 121, an outlet duct 112, 122-atan angle to the latter - and a leakage duct 1 13, 123, together with a guide bore 1 14, 124 extending in the inlet duct direction. A conical seating surface 1 5, 125 for a valve body either a valve cone 2 with a shaft 21 (Figures 2 and 3) or a ball valve 3 (Figure 4) - is provided in the upper section of the guide bore 1 14, 124.The shaft 21 of the valve cone 2 is guided in the upper section of the guide bore 114 with clearance, while the ball valve 3 is guided by means of ribs 128, arranged in the upper section of the guide bore 124, which ribs extend roughly in the flow direction and thereby afford ducts 127 for flow around the ball valve 3.

When the valve cone 2 and the ball valve 3 are in the open position, they are supported by means of a support rod 41 or 42 against a support face 51, lying perpendicular to the inlet direction, of a horizontal support member 5, which (and this is not illustrated) can be moved by means of a rotary or iifting magnet of a stepping motor, or by hand or otherwise, in such a way that the support face 51 disengages itself from the support rod 41, 42.

A surface 52, which is inclined towards the stop face 51, is joined to the latter. The inclination of this inclined surface is self-limiting, i.e. it is of such dimensions that self-locking between the support rod 41, 42 and the support member 5 narrower than its inclined surface 52 does not and cannot arise. Instead of an actually horizontal member, some kind of cam plate 5' can, for example, also be provided.

The section of the support rod 41 facing away from the valve body is telescopically divided. The support rod portions 411 and 412 are acted upon in an outwardly direction by spring tension - in this case by a set of plate springs 413. A roller 414 is arranged on the support rod portion 412 opposite the support member 5.

The design of the support rod 42 and the support member 5 according to Figure 4 corresponds roughly to that according to Figure 2, the spring tension according to Figure 4 being provided by a coil spring 423.

The value of the spring tension of the plate springs 413 or the coil springs 423 is greater in the tensed state and smalier in the relaxed state than the force exerted upon the valve body by the hydraulic pressure.

In the guide bore 114 below the leakage outlet duct 1 13, and in the guide bore 124 above the leakage outlet duct 123, a conical valve seating surface 11 6, 126 and, on the upper support rod 411,421, a conical valve surface 416, 426 are provided, which each fcrm a sealing lock with each other, which, when the safety valve is in the open position, is closed as a result of the bracing of the support rod 41, 42 against the support face 51 and as a result of the spring tension, of the plate springs 413 or the coil springs 423.

In Figure 2, the safety valve is in the open position and the fuel (such as heavy oil) flows out of the inlet duct 111 round the valve cone 2, and through the annular clearance situated between the shaft 21 or the support rod section 411 1 and the wall of the guide bore 114. The diameter of this annular clearance is, as discussed above, predetermined, and permits rinsing with a small amount of fuel in order to avoid resinification or seizing.

If the support face 51 is now disengaged very quickly from the support rod 41 with its roller 414, the support rod is expanded, the support rod section 412 is promptly moved downwards by the spring tension into a position as shown in Figure 3, and at the same time the entire support rod 41 is moved downwards by the hydraulic pressure onto the valve cone 2. By this time, the safety valve is closed. Pressure occurring in the outlet duct 112 and in the duct to the outer injection nozzle fuel chamber can be reduced through the annular clearance, and through the draining of fuel through the leakage duct 1 13. Fuel cannot escape from the nozzle of the injection valve. As a result of the steep gradient of the inclined surface 52 the movement of the support member 5 is assisted both the hydraulic pressure and by the spring tension.

The support member 5 can be operated in response to known monitoring methods, for instance by scanning of the sounds emitted from the needle valve E2 during correct functioning, of an inductively monitored gate for the needle valve E2, by an inductive motion pickup, or by an electronic gate. As a rule, it is essential that the support member 5 is engaged during all operational functions, and if one or all of these functions fails, that it automatically returns.

In the safety device according to Figures 4 and 5, which is otherwise as described above and operates in the same fashion, the sealing lock in the open position is closed between the outlet duct 122 and leakage outlet 123. Thus a clearance of relatively large dimensions can be provided in the annular clearance. In the closed position, as represented by the dotted line, the outlet duct 122 as well as the duct to the outer injection nozzle fuel chamber El can thus be relieved even more quickly of the pressure inside them.

Naturally, the designs illustrated and discussed above can also be advantageously employed under less difficult conditions, for instance, using low pressures or less viscous mediums.

Claims

1. A fuel injection device for an internal combustion engine, the device being provided with a safety valve between an inlet for pressurised fuel and an injection nozzle/needle valve assembly, the safety valve comprising an inlet duct, an outlet duct, a valve seating between said inlet and outlet ducts, a valve body which engages said seating, and a support member having a support face which is movable transversely of the closing direction of the valve body, into and out of a support position in which it supports said valve body directly or indirectly in an open position.

2. A device according to claim 1, wherein said support face is substantially plane and adjoins an inclined face of said support member, which member is movable transversely of said closing direction such that support of said valve body is transferred between said support face and said inclined face, thereby to effect opening and closing of the safety valve.

3. A device according to claim 2, wherein the gradient of the inclined face is sufficinetly great to preventing self-limiting.

4. A device according to claim 1, 2 or 3, wherein said valve body is supported via a roller which engages said support face.

5. A device according to any preceding claim, wherein a support rod extends in a guide bore between said valve body and said support face and comprises telescopic rod portions which are resiliently urged apart, an annular space is provided adjacent said valve seating, from which space said outlet duct extends, at an angle to said inlet duct, said support rod and guide bore are formed with respective valve surfaces which close as the safety valve opens, an annular groove is formed in said guide bore, and a leakage duct extends from said groove at an angle to said guide bore.

6. A device according to claim 5, wherein said valve body comprises a valve cone carried on a shaft which engages in said guide bore.

7. A device according to any one of claims 1 to 5, wherein said valve body comprises a ball, which is guided by ribs in said inlet duct.

8. A device according to any preceding claim, wherein said valve body, when open, is substantially enveloped by fuel in said inlet duct, in use.

9. A device according to any preceding claim, wherein said valve seating is frusto-conical.

10. A device according to claim 5 or any of claims 6 to 9 as appendant thereto, wherein said valve surfaces are frusto-conical.

11. A device according to claim 5 or any of claims 6 to 10 as appendant thereto, wehrein said annular groove is disposed between said annular space and said valve surfaces.

12. A device according to claim 5 or any of claims 6 to 10 as appendant thereto, wherein said valve surfaces are disposed between said annular space and said annular groove.

13. A device according to claim 7 or any of claims 8 to 12 as appendant thereto, comprising resilient means for biassing said ball into a closed position.

14. A device according to claim 5 or any of claims 6 to 13 as appendant thereto, wherein clearance is provided between said support rod and said guide bore to allow leakage flow of fuel to said leakage duct.

1 5. A device according to claim 14 as appendant to claim 6, wherein clearance between said shaft and said guide bore is less than said clearance between said support rod and said guide bore.

16. A device according to any preceding claim, including means for moving said support member, which means is arranged to move said support face out of said support position in the event of a failure or interruption in energy supply.

17. A device according to any preceding claim, comprising electromagnetic means for rotational or translational movement of said support member to move said support face into and out of said support position.

1 8. A device according to any preceding claim, including means for monitoring operation of said needle valve, and initiating closure of the safety device in the event of a malfunction of the needle valve.

1 9. A device according to any preceding claim, wherein said valve body is arranged to be acted on in its closing direction by pressure of fuel in said duct.

20. A fuel injection device substantially as hereinbefore described with reference to Figures 1 to 3 or Figures 1, 4 and 5 of the accompanying drawings.

21. An internal combustion engine provided with a fuel injection device according to any preceding claim.