GB2350662A

GB2350662A - Valve for a fuel injector

Info

Publication number: GB2350662A
Application number: GB9912917A
Authority: GB
Inventors: Paul Francis Garland
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1999-06-03
Filing date: 1999-06-03
Publication date: 2000-12-06
Also published as: GB9912917D0

Abstract

A valve comprises member 18 slidable within a bore and including abutment 30 which is frusto-conical arranged to cooperate with a seating surface 20 of frusto-conical form. The seating surface is of smaller cone angle than the abutment surface. Preferably the difference in the cone angles is between 1{ and 2{. Member 18 preferably has a sleeve 31 secured to it by a split ring 32 or by a circlip, welding or a screw thread. The outer diameter of sleeve 31 is substantially equal to that of the sealing line between the valve member and seat. In this way the valve may be pressure balanced. Preferably the valve is used to control communication between a control chamber and a drain in a fuel injector and is electromagnetically actuated. Particulate contaminants caught between surfaces 20, 30 tend to become crushed upon closure of the valve so that they are small enough to flow between the surfaces when the valve is opened.

Description

2350662 VALVE AND FUEL INJECTOR INCORPORATING SAME This invention relates

to a valve for controlling communication between a region of a passage upstream of a seating and a region downstream of the seating. The invention is particularly suitable for use in controlling the operation of a fuel irijec;Qwp The invention also relates to a fuel injector incorporating such a valve.

In a typical common rail fuel injector, an electromagnetically actuable valve is used to control the fuel pressure within a control chamber to control the magnitude of a force applied to a valve needle of the injector, thereby controlling the position occupied by the needle and controlling fuel injection. The valve typically comprises a valve member slidable within a bore, an enlarged end region of the member being engageable with a seating defined around an end part of the bore. The seating is defined by a frusto-conical seating surface, the corresponding surface of the valve member also being of frusto-conical form. The cone angle of the surface of the valve member is smaller than that of the surface defining the seating, thus the seating line, the line of engagement between the seating surface and the valve member, is at the radially innermost part of the seating surface.

It has been found that particulate contaminants carried with the fuel when the valve is open tend to cause wear at the seating line which may result in leakage of the valve. It is an object of the invention to provide a valve and a fuel injector incorporating such a valve which is of improved wear resistance.

According to the present invention there is provided a valve comprising a valve member slidable within a bore the valve member including an abutment 2 surface which is of frusto-conical form and which is arranged to cooperate, in use, with a seating surface of frusto-conical form, the seating surface being of smaller cone angle than the abutment surface.

In such an arrangement, the seating line is spaced from the radially inner edge of the seating surface, and as fuel flows towards the seating line, the flow area gradually reduces. The reduced flow area acts to collect large contaminant particles, and repeated movement of the valve member towards and away from the seating surface serves to crush or otherwise break down contaminant particles such that, by the time they are able to flow past the seating line they are sufficiently small that wear at the seating line is unlikely to occur or will occur at a reduced rate. Further, the fuel flow rate at the seating line when the valve is open is sufficiently high that it serves to wash small contaminant particles away from the seating line.

The valve member may carry a sleeve of outer diameter substantially equal to the diameter of the seating line such that when the valve member engages the seating, the valve member is substantially pressure balanced.

The invention further relates to a fuel injector incorporating such a valve. The valve conveniently controls the fuel pressure within a control chamber. This may be achieved by providing a restricted flow path between the control chamber and a source of fuel under pressure, the valve controlling communication between the control chamber and a low pressure drain.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which:- 3 Figure 1 is a sectional view of a fuel injector incorporating a valve in accordance with an embodiment of the invention; and Figure 2 is a view, to an enlarged scale, illustrating part of the injector of Figure 1.

Figure 1 illustrates a fuel injector intended for use with a common rail fuel system. The fuel injector comprises a nozzle body 10 having a blind bore formed therein within which a valve needle 11 is slidable. The valve needle 11 is engageable with a seating defined adjacent the blind end of the bore to control communication between the bore and a plurality of outlet openings (not shown) located downstream of the seating. The bore communicates through a supply passage 12 with a fuel inlet 12a which communicates in use, with a source of fuel under high pressure in the form of a common rail charged to a suitably high pressure by an appropriate fuel pump.

The nozzle body 10 abuts a distance piece 13 which is provided with a bore which is coaxial with the bore of the nozzle body 10, the bore of the distance piece 13 defining, with the nozzle body 10 and needle 11, a control chamber 14 within which a spring is located, the spring applying a biasing force to the needle 11 urging the needle 11 towards it seating. The control chamber 14 communicates through drillings 15 provided in the distance piece 13 with the supply passage 12. The drillings 15 are provided with regions of relatively small diameter forming restrictions to the rate at which fuel can flow towards the control chamber 14.

The distance piece 13 abuts a valve housing 16 illustrated in greater detail in Figure 2. The valve housing 16 is provided with a drilling forming part of 4 the supply passage 12. The valve housing 16 is further provided with a stepped through bore 17 within which a valve member 18 is located. The valve member 18 includes, at its upper end, a region 19 of relatively large diameter which is engageable with a frusto-conical seating surface 20 provided at an end of the bore 17. The enlarged diameter region 19 is engageable with the seating surface 20 to control communication between a drilling 21 which communicates with the drillings 15 provided in the distance piece 13 and a chamber 22 which communicates, in use, with a port 22a of the injector which is connected to a back leak line which, in turn, conununicates with a source of fuel under relatively low pressure. The chamber 22 is therefore held at a relatively low pressure, in use. The chamber 22 communicates through a drilling 23 with a recess 24 defined, in part, by the distance piece 13 and into which a lower end of the valve member 18 extends. The drilling 23 ensures that fuel is able to flow to or from the recess 24, thus ensuring that movement of the valve member 18 is not impeded, in use.

The upper end of the valve member 18 carries an armature 25 which is moveable under the influence of an electromagnetic actuator 26 located within a recess formed in a nozzle holder 27. The valve member 18 and armature 25 are spring biased towards the position illustrated in Figure 2 by means of a spring 28.

The nozzle body 10, distance piece 13 and valve housing 16 are secured to the nozzle holder 27 by means of a cap nut 29.

As illustrated most clearly in Figure 2, the enlarged diameter region 19 of the valve member 18 defines a frusto-conical abutment surface 30 which is of larger cone angle than that of the seating surface 20. As a result, when the valve member 18 abuts the seating surface 20, a seal is formed around a seating line of diameter equal to the diameter of the outermost part of the abutment surface 30. As a result, where fuel under high pressure is applied to the drilling 21, a relatively large effective area of the valve member 18 is presented to the fuel under pressure applying a force to the valve member 18 urging the valve member 18 away from the seating surface 20. In order to counter this force, a sleeve 31 is provided around the lower end of the valve member 18. The sleeve 31 is carried by the valve member 18, and is a substantially fluid tight seal therewith. Further, a substantially fluid tight seal is formed between the sleeve 31 and the bore 17. The sleeve 31 is of outer diameter substantially equal to that of the seating line. As a result, when the valve member engages the seating surface 20 and fuel under high pressure is applied to the drilling 21, the valve member 18 is substantially fuel pressure balanced.

As illustrated in Figure 2, the sleeve 31 is conveniently secured to the valve member 18 by means of a split ring 32, circlip or other member located within an annular groove formed in the valve member 18. It will be appreciated, however, that the sleeve 31 may be secured to the valve member 18 using any suitable technique, for example by means of welding or by means of a screw-thread connection.

Although as illustrated in Figures 1 and 2, the valve member 18 protrudes from the lower end of the bore 17, it will be appreciated that this need not be the case. However, it is thought that assembly will be easier where the valve member 18 protrudes from the lower end of the bore 17.

6 In use, with the supply passage 12 connected to a source of fuel under high pressure and with the actuator 26 de-energized, the valve member 18 will occupy the position illustrated in Figure 2 due to the action of the spring 28. As a result, fuel will be unable to escape from the control chamber 14, thus the control chamber 14 will be pressurized to substantially the same pressure as that within the supply passage 12 and bore of the nozzle body 10. The effective area of the valve needle 11 exposed to the fuel pressure within the control chamber 14 is large compared to the effective area of the needle 11 exposed to the fuel pressure within the bore of the nozzle body 10. As a result, a relatively large magnitude force is applied to the needle 11 assisting the spring in urging the needle 11 into engagement with its seating. As a result, fuel injection does not take place. The fuel pressure applied to the valve member 18 is high, but as the valve member 18 is substantially pressure balanced, movement of the valve member 18 as a result of the application of fuel under high pressure thereto does not occur.

When fuel injection is to commence, the actuator 26 is energized, attracting the armature 25 to move against the action of the spring 28 and lifting the valve member 18 away from the seating surface 20. As the valve member 18 is substantially fuel pressure balanced, the force which must be applied by the actuator is relatively small. Fuel is thus able to escape from the control chamber 14 past the seating line to the chamber 22 from where it is able to flow to the low pressure fuel reservoir. Such a flow of fuel results in the fuel pressure within the control chamber 14 falling, the dimensions of the passages 15 being chosen to ensure that the fuel pressure within the control chamber 14 falls in such circumstances, and to minimize leakage during this phase of the operation of the injector. The fuel pressure within the control chamber 14 will fall to a point beyond which the magnitude of the downward 7 force applied to the needle 11 falls to a level sufficient to permit the needle I I to lift away from its seating. The movement of the needle I I allows fuel to flow to the outlet openings and through the outlet openings to the cylinder of combustion space with which the injector is associated.

When injection is to be terminated, the actuator 26 is de-energized, the valve member 18 returning into engagement with its seating due to the action of the spring 28. As a result, fuel is no longer able to escape from the control chamber 14, and the communication between the control chamber 14 and the supply passage 12 results in the control chamber 14 becoming pressurized to a level sufficient to cause the needle I I to return into engagement with its seating, thus terminating injection.

In Figure 2, the angles of the abutment surface 30 and the seating surface 20 have been exaggerated for clarity. In practice, it is thought that the differential angle between these surfaces will be between approximately 11 and approximately 20. The distance through which the needle 11 is lifted, in use, is expected to fall within the range approximately 20/-jrn to approximately 40pm.

Whilst the valve member 18 is lifted from the seating surface 20, it will be appreciated that the area through which fuel is able to flow decreases as the ftiel flows towards the seating line. As a result, particulate contaminants carried by the flow of fuel will tend to become caught between the abutment surface 30 of the valve member 18 and the seating surface 20. Subsequent movement of the valve member 18 towards the seating surface 20 will tend to crush or otherwise breakdown any particulate contaminants trapped between the abutment surface and the seating surface 20 until they are sufficiently 8 small to flow between the valve member 18 and the seating surface 20 when the valve member 18 is lifted from the seating surface 20. Further, when the valve member 18 is lifted from the seating surface 20, the fuel flow rate between the valve member 18 and seating surface 20 is high, and so particulate contaminants which are able to pass therebetween flow past the seating line at a relatively high rate, the fuel flow washing such contaminants away from the seating surface. As a result, the risk of damage to the seating surface by particulate contaminants is reduced.

A further advantage of the arrangement is that, in the event that wear of the seating surface does occur, then any seat migration which occurs as a result of the wear will reduce the diameter of the seating line. The reduced diameter of the seating line will result in the valve being pressure biased towards a closed position, assisting the spring. In prior arrangements, such wear and seat migration would result in the diameter of the seating line increasing, the valve member would then be pressure biased open, against the action of the spring, and the application of fuel under pressure to the valve may cause the valve to open at undesirable points in the operation of, for example, a fuel injector.

Although the valve is described, hereinbefore, in relation to a common rafl fuel injector of the type in which the valve is used to control communication between a control chamber and a low pressure fuel reservoir, it will be appreciated that the valve is suitable for use in other applications. For example, the valve could be used to control communication between a supply passage and a control chamber of a common rail fuel injector. It may also be used in other types of fuel injector and in non-fuel injector applications.

9

Claims

1. A valve comprising a valve member slidable within a bore, the valve member including an abutment surface which is of frusto-conical form and which is arranged to cooperate, in use, with a seating surface of frustoconical form, the seating surface being of smaller cone angle than the abutment surface.

2. The valve as clahned in Claim 1, wherein the difference in cone angle between the abutment surface of the valve member and the seating surface is between 1' and 2'.

3. The valve as claimed in Claim 1 or Claim 2, wherein the abutment surface abuts the seating surface at a seating line, the valve member carrying a sleeve having an outer diameter substantially equal to the diameter of the seating line such that when the valve member engages the seating, the valve member is substantially pressure balanced.

4. The valve as claimed in Claim 3, wherein the sleeve is secured to the valve member by means of a member located within an annular groove formed in the valve member.

5. The valve as claimed in Claim 3, wherein the sleeve is secured to the valve member by means of welding or by means of a screw thread connection.

6. A fuel injector including a valve as claimed in any of Claims 1 to 5.

7. The fuel injector as claimed in Claim 6, wherein the valve is arranged to control fuel pressure within a control chamber.

8. The fuel injector as claimed in Claim 7, comprising a restricted flow path between the control chamber and a source of fuel under pressure, the valve being arranged to control communication between the control chamber and a low pressure drain.

9. A valve as herein described with reference to the accompanying drawings.

10. A fuel injector as herein described with reference to the accompany' g drawings.