GB2345741A - Pressure balanced control valve - Google Patents

Abstract

A control valve comprising a valve member 22 slidable within a bore 21 and engageable with a first seating 21a to control communication between first (supply) 23 and second 14 passages and engageable with a second seating 25a to control communication between the second and third passages. The valve member is fluid pressure balanced both when it engages its first seating and when it engages its second seating. The valve is intended for use with a fuel injector. The third passage is preferably partially defined by drilling, 28,29 in the valve member. The first and second seatings are preferably formed in respective housing parts 20,24 which are relatively located by projections on one housing part which cooperate with recesses on the other. The first and second seatings preferably have diameters substantially equal to the bore 21.

Description

CONTROL VALVE This invention relates to a control valve suitable for use in controlling the operation of a fuel injector, for example, of the type intended for use in a fuel system of the common rail type. The invention also relates to a fuel injector, for example for use in a common rail type fuel system, including such a control valve.

In a known fuel injector for use in a fuel system of the common rail type, a valve needle is resiliently biased towards a seating to control communication between a delivery chamber located upstream of the seating and a plurality of outlet openings located downstream of the seating. The needle is provided with one or more thrust surfaces exposed to the fuel pressure within the delivery chamber and orientated such that the application of fuel under pressure to the delivery chamber applies a force to the needle urging the needle away from its seating. A three-way control valve is provided to determine whether the delivery chamber is supplied with fuel from the common rail, or whether the delivery chamber is vented to a relatively low pressure fuel reservoir.

It is an object of the invention to provide a control valve suitable for use in such a fuel injector which is of relatively simple form and which does not require the application of large operating forces to move the valve member thereof.

Another object is to provide a fuel injector including such a control valve.

According to the present invention there is provided a control valve comprising a valve member slidable within a bore and engageable with a first seating to control communication between first and second passages and engageable with a second seating to control communication between the second and third passages, wherein the valve member is fluid pressure balanced both when it engages its first seating and when it engages its second seating.

The third passage may be defined, in part, by an axially extending drilling provided in the valve member whereby a chamber defined between an end of the valve member and the bore is vented.

Conveniently, the first and second seatings are formed in respective housing parts, one of the housing parts being provided with projections arranged to cooperate with recesses formed in the other of the housing parts to correctly locate the housing parts relative to one another.

The invention also relates to a fuel injector comprising a valve needle slidable within a bore and defining, with the bore, a delivery chamber, the injector including a first passage which communicates, in use, with a source of fuel under high pressure, a second passage which communicates with the delivery chamber, and a third passage which communicates with a low pressure fuel reservoir, and a control valve of the type defined hereinbefore arranged to control communication between the first, second and third passages.

The invention will further be described, by way of example, with reference to the accompanying drawing which is a sectional view of part of a fuel injector including a control valve in accordance with an embodiment of the invention.

The fuel injector illustrated in Figure 1 is intended for use in a fuel system of the common rail type for use in supplying fuel under high pressure to a cylinder of a compression ignition internal combustion engine. The injector comprises a nozzle body 10 having a bore 11 formed therein within which a valve needle 12 is reciprocable. The bore 11 is of stepped form and includes an upper end region of diameter substantially equal to the diameter of the adjacent part of the needle 12 serving to guide the needle 12 for sliding movement within the bore 11. The bore 11 also includes a region of diameter greater than the diameter of the adjacent part of the needle 12, the needle 12 and this part of the bore 11 together defining a delivery chamber 13 to which fuel is supplied through a passage 14 defined, in part, by a drilling 15 provided in the nozzle body 10 which communicates with an annular gallery 16. The needle 12 is shaped for engagement with a conical seating, the cooperation between the needle 12 and the seating being such as to prevent communication between the delivery chamber 13 and one or more outlet openings located downstream of the seating when the needle 12 engages the seating, such communication being permitted when the needle 12 is lifted from the seating. The part of the needle 12 exposed to the fuel pressure within the delivery chamber 13 is shaped to define thrust surfaces orientated such that the application of fuel under pressure to the delivery chamber 13 results in the application of a force to the needle 12 urging the needle 12 away from the seating.

The nozzle body abuts a spring housing 17 which is provided with a blind bore containing a spring 18. The spring 18 is engaged between the blind end of the bore and a spring abutment member 19 which is carried by the needle 12. The spring 18 serves to bias the needle 12 into engagement with the seating. The bore which contains the spring 18 is vented to a low pressure fuel reservoir through a suitable passage (not shown).

The end of the spring housing 17 remote from the nozzle body 10 abuts a first valve housing 20 which is provided with a blind bore 21 within which a valve member 22 is slidable. The valve member 22 includes a region 22a of enlarged diameter which includes a surface which is engageable with a first seating 21 a defined around an open end of the bore 21 and of diameter substantially equal to that of the majority of the bore 21. A region 22b of the valve member 22 is of reduced diameter and defines, with the bore 21, an annular chamber which communicates through a first, supply passage 23 with the common rail of the fuel system. The valve member 22 further includes a region 22d of piston like, sealing fit within the bore 21.

The surface of the first valve housing 20 remote from the spring housing 17 abuts a second valve housing 24. The second valve housing 24 is provided with a through bore 25 of diameter substantially equal to the diameter of the bore 21, the bore 25 also receiving part of the valve member 22. The bore 25 defines a second seating 25a with which a surface of the enlarged diameter region 22a of the valve member 22 is engageable. The second seating 25a is of diameter substantially equal to that of the majority of the bore 25. The first and second valve housings 20,24 together define a chamber 26 of enlarged diameter which communicates with the drillings forming the passage 14. It will be appreciated that the passage 14 forms the second passage referred to hereinbefore, and that the engagement of the valve member 22 with the first seating 21a controls communication between the first and second passages.

In order to ensure that the bore 25 of the second valve housing 24 is correctly located relative to the bore 21 of the first valve housing 20, the second valve housing 24 is provided with a series of projections 24a which are received within an end, enlarged diameter region of the bore 21, ensuring that the bore 25 and bore 21 are coaxial.

Adjacent the enlarged diameter region 22a of the valve member 22, the valve member 22 includes a further reduced diameter region 22c which defines, with the bore 25, an annular chamber. The annular chamber communicates through cross-drillings 27 provided within the valve member 22 with a blind drilling 28.

The blind drilling 28 extends along the axis of the valve member 22, and opens into a chamber defined between the valve member 22 and the blind end of the bore 21. It will be appreciated that the cross-drillings 27 and drilling 28 provide a communication path between the annular chamber defined, in part, by the reduced diameter region 22c and the chamber formed between the valve member 22 and the bore 21. The valve member 22 is further provided with cross-drillings 29 located adjacent the blind end of the drilling 28 and arranged to open into an enlarged diameter region of the bore 25 which forms a chamber 30 within which an armature 31 is located. The armature 31 is secured to the valve member 22. The armature 31 is moveable under the influence of an actuator (not shown) located within an actuator housing 32 to which the first and second valve housings 20,24, the spring housing 17 and the nozzle body 10 are secured by means of a cap nut 33. The actuator includes a spring arranged to bias the valve member 22 towards the position illustrated in the drawing in which the enlarged region 22a thereof engages the first seating 2 la.

The chamber 30 is vented to an appropriate low pressure fuel reservoir, for example the fuel tank, through a passage (not shown). It will be appreciated that as the chamber 30 is vented to a low pressure reservoir, the presence of the cross-drillings 27,29 and the drilling 28 results in the annular chamber defined, in part, by the reduced diameter region 22c of the valve member 22 is also held at a relatively low pressure. It will further be appreciated that the crossdrillings 27,29 and drilling 28 form part of the third passage referred to hereinbefore.

In use, with the supply passage 23 connected to a common rail charged to a suitably high pressure, and with the actuator de-energized, it will be appreciated that, as the valve member 22 engages the first seating 2 la and is spaced from the second seating 25a, the delivery chamber 13 communicates through the second passage and the chamber 26 with the third passage. As a result, the delivery chamber 13 is at a relatively low pressure, the fuel pressure within the delivery chamber being insufficient to lift the valve needle 12 away from its seating, and as a result the valve needle 12 remains in engagement with its seating due to the action of the spring 18. It will be appreciated, therefore, that injection of fuel is not taking place. The seating diameter of the first valve seating 21 a is substantially equal to the diameter of the bore 21. As a result, it will be appreciated that the valve member 22 is substantially fuel pressure balanced, thus only a relatively low magnitude biasing force need be applied to the valve member 22 to ensure that the valve member 22 remains in the position illustrated.

When injection of fuel is to commence, the actuator is energized, attracting the armature 31 in such a manner as to move the valve member 22 to lift the enlarged diameter region 22a thereof away from the first seating 2 1 a and to bring the region 22a into engagement with the second seating 25a. As a result of the movement of the valve member 22, the communication between the second and third passages is broken, and communication is permitted between the first, supply passage 23 and the second passage. The communication between the first and second passages results in the delivery chamber 13 being pressurized, and a point will be reached beyond which the application of fuel under pressure to the thrust surfaces of the needle 12 exposed to the pressure within the delivery chamber 13 will be sufficient to lift the needle 12 against the action of the spring 18 away from its seating. As a result, fuel is able to flow from the delivery chamber 13 to the outlet openings and is injected into the associated combustion space of the engine.

It will be appreciated that the movement of the valve member 22 can be achieved relatively easily as only a relatively low magnitude resilient force was applied thereto to hold it in its rest position, and hence the magnitude of the force which must be overcome in order to move the valve member 22 is relatively low. As a result, a relatively low power actuator may be used, if desired. Further, as the chamber defined between the valve member 22 and the blind end of the bore 21 is vented to the chamber 30 and fuel reservoir through the drilling 28 and cross-drillings 29, it will be appreciated that the formation of a hydraulic lock in the control valve is avoided. Further, after movement of the control valve member 22 has taken place, as the diameter of the seating line of the second seating 25a is substantially equal to the diameter of the bore 25, and the bore 25 is of diameter substantially equal to that of the blind bore 21, it will be appreciated that the valve member 22 is substantially fluid pressure balanced, and so the magnitude of the attractive force which must be applied to the armature 31 by the actuator in order to hold the control valve member 22 in this position is relatively low.

When injection is to be terminated, the actuator is de-energized and the valve member 22 returns to its original position under the action of the resilient biasing of the valve member 22. As the valve member 22 is fuel pressure balanced, it will be appreciated that the magnitude of the force necessary to move the valve member 22 is relatively low. The movement of the valve member 22 breaks the communication between the first and second passages, and restores communication between the second and third passages. As a result, the fuel pressure within the delivery chamber 13 is rapidly reduced, and a point will be reached beyond which the fuel pressure within the delivery chamber 13 is insufficient to hold the needle 12 in its lifted position, and the needle 12 will return into engagement with its seating under the action of the spring 18, thus terminating the supply of fuel to the outlet openings, and terminating injection.

It will be appreciated that the injector described hereinbefore is advantageous in that the quantity of fuel escaping to the fuel reservoir can be reduced compared to other known types of common rail fuel injector. Further, as the termination of injection is achieved by rapidly reducing the fuel pressure within the delivery chamber, termination of injection occurs quickly, relatively little fuel is delivered at low pressure and as a result, the emission of particulates can be reduced.

Although in the embodiment described hereinbefore, the fuel injector is intended for use in a common rail type fuel system, it will be appreciated that the injector is also suitable for use in other types of fuel system in which fuel is supplied to the injector from a source of fuel under pressure, a control valve being used to control the timing of fuel injection. The control valve may also be suitable for use in other applications. The invention is also suitable for use with injectors of the two stage lift type for controlling the initial rate of injection.

Claims (8)

1. CLAIMS 1. A control valve comprising a valve member slidable within a bore and engageable with a first seating to control communication between first and second passages and engageable with a second seating to control communication between the second and third passages, wherein the valve member is fluid pressure balanced both when it engages its first seating and when it engages its second seating.
2. 2. The control valve as claimed in Claim 1, wherein the third passage is defined, in part, by an axially extending drilling provided in the valve member such that a chamber defined between an end of the valve member and the bore is vented.
3. 3. The control valve as claimed in Claim 1 or Claim 2, wherein the first and second seatings are formed in respective housing parts, one of the housing parts being provided with projections arranged to cooperate with recesses formed in the other of the housing parts to correctly locate the housing parts relative to one another.
4. 4. The control valve as claimed in any of Claims 1 to 3, wherein the first seating has a diameter substantially equal to the diameter of the bore within which the valve member is slidable.
5. 5. The control valve as claimed in any of Claims 1 to 4, wherein the second seating has a diameter substantially equal to the diameter of the bore within which the valve member is slidable.
6. 6. A fuel injector comprising a valve needle slidable within a bore and defining, with the bore, a delivery chamber, the injector including a first passage which communicates, in use, with a source of fuel under high pressure, a second passage which communicates with the delivery chamber, and a third passage which communicates with a low pressure fuel reservoir, and a control valve as claimed in any of Claims 1 to 5, the control valve being arranged to control communication between the first, second and third passages.
7. 7. A control valve as hereindescribed with reference to the accompanying drawing.
8. 8. A fuel injector as hereindescribed with reference to the accompanying drawing.