GB2295881A

GB2295881A - Control valve

Info

Publication number: GB2295881A
Application number: GB9424022A
Authority: GB
Inventors: Richard Michael Turner
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1994-11-29
Filing date: 1994-11-29
Publication date: 1996-06-12
Also published as: GB9424022D0

Abstract

A fluid control valve includes a plug (30) which is slidably received in a bore (28) in a part (25B) of a valve member. The wall of the part defines ports through which in use fuel can flow to impinge on the surface of the plug, the ports opening into a circumferential groove (31) formed in the wall of the bore. In order to minimise cavitation erosion of the surface of the plug inclined grooves (37) are formed on said surface to induce fuel swirl. <IMAGE>

Description

CONTROL VALVE This invention relates to a control valve for incorporation in a fuel system of an internai combustion engine, the system comprising a fuel injection nozzle having a fuel inlet and an outlet, the outlet being positioned to direct fuel into a combustion chamber of the engine, the nozzle incorporating a fuel pressure actuated valve member which is biased to the closed position and which is moved to allow fuel to flow through the outlet when the fuel pressure at the inlet attains a predetermined value, a source of fuel under pressure and a control valve interposed between the source of fuel and said inlet, said control valve having a first position in which the inlet of the nozzle is connected to said source of fuel and a second position in which said inlet is connected to a drain, the control valve comprising a valve body, a stepped bore having a wider and narrower portion, formed in the valve body, a stepped valve member having wider and narrower portions slidable in the bore, a first seating surface defined in the bore, the valve member having an intermediate portion which connects the wider and narrower portions, said intermediate portion being shaped for sealing engagement with said first seating surface when the control valve is in said first position, an actuator having an output member which is coupled to the valve member, a drilling formed in the wider portion of the valve member, the inner end of the drilling defining a second seating surface, a plug slidable within the drilling, the plug being shaped for sealing engagement with said second seating surface when the control valve is in said second position, a reaction surface for said plug, first passage means defined in the valve body and the valve member and which is blocked by the engagement of the plug with said second seating surface when the control valve is in said second position, said first passage means connecting said source of fuel with the nozzle inlet, and second passage means defined by the valve body and valve member, said second passage means being blocked by the engagement of the valve member with the first seating surface when the control valve is in said first position, said second passage means connecting the nozzle inlet to said drain.

In a practical arrangement of the valve the first passage means includes a circumferential groove which is formed in the drilling adjacent the second seating surface and ports are formed in the wall of the valve member through which fuel flows into the groove. The fuel which flows through these ports impinges on the adjacent cylindrical surface of the plug and can cause cavitation erosion of the surface of the plug.

The object of the invention is to provide a control valve of the kind specified in a simple and convenient form.

According to the invention the surface of the plug is provided with inclined grooves.

In the accompanying drawings: Figure 1 is a diagrammatic block diagram of a fuel system incorporating the valve, and Figure 2 of sectional side elevation of the valve.

With reference to Figure 1 of the drawings the system comprises a fuel injection nozzle 10 of the type which has a resiliently biased fuel pressure actuated valve member movable by fuel under pressure at an inlet 11 of the nozzle away from a seating to allow fuel flow from the inlet to an outlet orifice or orifices. The nozzle in use is mounted on an engine so that the fuel spray which issues from the outlet orifice is directed into a combustion chamber of the engine for ignition therein.

Fuel is supplied to the nozzle inlet 11 of the nozzle from a source 12 of fuel at high pressure under the control of a control valve 13. The valve 13 in the example incorporates an electromagnetic actuator and the supply of electric current to the actuator is determined by an electronic control system 14 which is responsive to a number of engine operating parameters and desired operating parameters.

The control valve 13 has an inlet 15 which is connected to the source 12, a outlet 16 which is connected to the nozzle inlet 11 and a drain outlet 1 7 which is connected to a low pressure source the pressure of which is substantially lower than that of the source 12. It will be appreciated that the pressure of fuel provided by the source 12 is higher than the pressure required to lift the valve member of the nozzle from the seating.

The construction of the control valve is seen in Figure 2 and it comprises a valve body 18 in which is formed a stepped bore having a narrower portion 19A and a wider portion 19B. At the junction of the two portions of the bore there is formed a circumferential groove 20 which is connected by a first passage 21 to the control valve outlet 16. The end wall of the groove adjacent the portion 19A of the bore is inclined inwardly to form a fixed truncated conical seating surface 22.

In the wider portion 19B of the bore intermediate the groove 20 and the end of the valve body there is formed a further circumferential groove 23 and this groove is connected by a second passage 24 to the valve inlet 15.

Slidable in the bore is a stepped valve member having a narrower portion 25A and a wider portion 25B. These two portions of the valve member form with the respective portions of the bore a good sliding fit so as to minimise fuel leakage along the small working clearance.

Disposed between the wider and narrower portions of the valve member is an intermediate portion the first part 26A of which adjacent the wider portion 25B of the valve member, has a diameter which is less than that of the wider portion 25B but which is slightly greater than that of the narrower portion 25A.

The second part 26B of the intermediate portion is of smaller diameter than the narrower portion 25A of the valve member and is radiused at its ends. The second part of the intermediate portion forms with the narrower portion 1 9A of the bore an annular chamber which is connected by a third passage 27 to the drain outlet 1 7. Furthermore, the step which is defined between the two parts 26A and 26B of the intermediate portion is engageable with the seating surface 22 to form a seal and preferably is of truncated conical form having a cone angle slightly smaller than that of the seating surface.

Extending within the wider portion 25B of the valve member is a drilling 28 at the inner end of which is formed a frusto conical seating surface 29 and slidable in the drilling with a working clearance similar to the working clearance between the valve member and the wall of the bore, is a free pin or plug 30. The inner end portion of the plug is of truncated conical form having a cone angle which is greater than that of the seating surface 29 and the plug is engageable with the seating surface to form a seal. Adjacent the seating surface there is formed in the wall of the drilling 28 an annular groove 31 which by way of ports in the wider portion of the valve member is in constant communication with the groove 23 . Moreover, the inner end of the drilling 28 is in communication by way of a passage 32 and a cross passage in the valve member, with the groove 20.

The plug 30 is in engagement with a fixed surface 33 which conveniently forms part of the housing of the valve. Moreover, the narrower portion 25A of the valve member is coupled to the output member of an actuator. In the example the output member is an armature 34 which is associated with a solenoid 35. A coiled compression spring 36 is located between the core of the solenoid and the armature 34 and the spring acts as a return spring which biases the seating surface 29 into engagement with the plug 30. When the seating surface 29 is in engagement with the plug the step defined by the parts 26A and 26B of the valve member is clear of the seating surface 22.

When the solenoid is energised as shown in Figure 2, the aforesaid step is in sealing engagement with the seating surface 22, and the seating surface 29 is lifted away from the plug.

When the solenoid is energised fuel can flow from the source 12 by way of the second passage 24, the gap between the plug and the seating surface 29, the first passage 32 and the passage 21 to the fuel injection nozzle. The pressure of fuel acts on the valve member of the nozzle to lift the valve member of the nozzle from its seating to allow fuel flow to the engine. When the solenoid is de-energised the spring 36 urges the seating surface 29 into engagement with the plug to halt the supply of fuel to the nozzle. In addition, the aforesaid step is lifted from the seating surface 22 and the fuel pressure in the passage 21 and the various passages in the nozzle is relieved to drain through the third passage 27 and this allows rapid closure of the valve member in the nozzle.

The pressure of fuel which is supplied to the injection nozzle is of the order of 1000 BAR and therefore it is necessary to control the various areas of the valve member which are exposed to the high pressure fuel so that reliable and rapid movement of the valve member of the nozzle is obtained. In the situation where the solenoid is energised the high pressure of fuel acts upon the end area of the valve member defined at the inner end of the bore 28 to urge the valve member towards the solenoid. However, an opposing force is generated by the fact that the high pressure of fuel acts upon the annular end area of the valve member defined between the intermediate part 26A and the wider portion 25B of the valve member.These areas are made to be substantially equal so that when the solenoid is deenergised the spring 36 will move the valve member so that the seating surface 29 engages the plug. When the valve member is in engagement with the plug the valve member is substantially pressure balanced at least so far as the high pressure fuel is concerned.

The plug 30 is not secured to the end surface 33 of the housing but is held in engagement therewith mainly by the action of the spring 36 when the solenoid is de-energised, and by the high pressure of fuel which acts on its inner end surface when the solenoid is energised. A small step may be provided on the plug outside the seating line of the plug and seating surface 29 to ensure that the plug remains in contact with the end surface particularly when the solenoid is energised. In practice however it is thought that imperfections in the seating surface 29 and the frusto conical surface of the plug will probably ensure that the plug is maintained in engagement with the end surface by fuel under pressure. The extent of movement of the valve member between its two extreme positions can be adjusted by altering the axial length of the plug.

When the solenoid 35 is energised and the valve member is lifted away from the plug 30 fuel at high pressure flows into the annular groove 31 from the groove 23 by way of the ports in the wider portion of the valve member. In effect jets of fuel at high pressure are directed at the surface of the plug and cavitation erosion of the plug can take place. In order to minimise erosion the cylindrical surface of the plug over that portion which is exposed to the groove 31 is provided with helical or like, inclined grooves 37 which extend between a pair of axially spaced circumferential grooves. The action of the fuel flowing in the inclined grooves is to induce swirl in the fuel and in addition, angular movement may be imparted to the plug 30 so as to prevent continuous impingement of the fuel jets on the same portions of the surface of the plug.

The valve member when the solenoid is energised, is actuated by a pull action and this tends to make operation of the control valve more consistent than is the case when a push action is used. Although as described the valve member is rigidly coupled to the armature so that the engagement of the valve member with the seating surface 22 determines the minimum gap between the armature and the solenoid, the connection between the armature and the valve member may incorporate resilient means to permit overtravel of the armature when the valve member engages the seating surface. In this case it is necessary to provide some arrangement which ensures that there is a minimum air gap between the armature and the core member of the actuator after movement of the valve member and armature.

Although as described the valve member is coupled to an electromagnetic actuator it may be operated by other means such for example, as an hydraulic servo or a piezo electric actuator.

Claims

1. A control valve of the kind specified in which said first passage means includes a circumferential groove which is formed in the drilling adjacent the second seating surface and ports formed in the wall of the valve member through which fuel flows into the groove, the surface of the plug at which the fuel flowing through the ports into the circumferential groove is directed, being provided with a plurality of inclined grooves, said grooves acting to induce fuel swirl.

2. A control valve according to Claim 1, in which said inclined grooves terminate at their opposite ends in a pair of circumferential grooves respectively.