GB2336627A - Fuel injector with biassing spring in blind bore in valve needle - Google Patents

Abstract

A fuel injector, for example as illustrated in the accompanying drawing, comprises a valve needle 10 slidable within a bore 12 provided in a nozzle body 14 and engageable with a seating, the needle 10 being biassed towards the seating by a spring 30, wherein the spring 30 extends within a blind bore 28 extending along part of the length of the needle 10. The valve needle 10 may define, with the bore 12, a control chamber 24 the injector further comprising a restricted passage 26 whereby fuel is supplied to the control chamber 24, a control valve 42 controlling fuel flow from the control chamber 24, the control valve 42 communicating with the control chamber 24 through a fuel flow passage 34, and a second restricted passage 58 communicating with the fuel flow passage 34 to permit fuel supply thereto at a restricted rate.

Description

2336627 1 FUEL INJECTOR This invention relates to a fuel injector for use

in delivering fuel under pressure to a cylinder of an internal combustion engine. The invention particularly suitable for use in a fuel system of the common rail type for use with a compression ignition combustion engine.

is In a conventional fuel injector, a valve needle is biased by a spring towards a seating to control fuel delivery through one or more outlet openings downstream of the seating. In some arrangement, the spring engages an end surface of the valve needle. Such arrangements have the disadvantage that the injector is of relatively large axial length. In an alternative arrangement, the valve needle includes an outwardly extending flange which the spring engages. Such an arrangement has the disadvantage that only a small part of the valve needle engages the surface of the bore within which the valve needle is slidable to guide such sliding movement. It is an object of the invention to provide an injector in which these disadvantages are reduced.

According to the present invention there is provided a fuel injector comprising a valve needle slidable within a bore provided in a nozzle body and engageable with a seating, the needle being biassed towards the seating by a spring, wherein the spring extends within a blind bore extending along part of the length of the needle.

The fuel injector is conveniently of the type intended for use in a common rail type fuel system.

2 According to another aspect of the invention there is provided an injector comprising a valve needle slidable within a bore and defining, with the bore. a control chamber, a restricted passage whereby fuel is supplied to the control chamber, a control valve controlling fuel flow from the control chamber, the control valve communicating with the control chamber through a fuel flow passage, and a second restricted passage communicating with the fuel flow passage to permit fuel supply thereto at a restricted rate.

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

The fuel injector illustrated, in part, in the accompanying drawing comprises a valve needle 10 slidable within a bore 12 formed in a nozzle body 14. The bore 12 is a blind bore and defines, adjacent its blind end, a seating with which the valve needle 10 is engageable to control the supply of fuel from the bore 12 to a plurality of small outlet openings located downstream of the seating. The bore 12 includes a region 16 of enlarged diameter defining, with the needle 10, an annular chamber which communicates with a passage 18 forming part of a supply passage whereby fuel is supplied, under high pressure, from a source of fuel under pressure, in this case a common rail charged with fuel by an appropriate fuel pump, to the bore 12. Although not illustrated in the accompanying drawing, the valve needle 10 is shaped to include a fluted region whereby fuel is able to flow from the region 16 along the length of the bore towards the seating, the needle 10 including a region adjacent the seating which is of reduced diameter which defines, with the bore 12, an annular chamber to which fuel is 3 supplied through the fluted region of the needle 10. The shape of the needle 10 is such as to define one or more thrust surfaces orientated such that the application of fuel under pressure to the bore 12 applies a force to the needle 10 urging the needle 10 away from the seating.

The upper end of the nozzle body 14 abuts a first distance piece 20 through which a passage 22 extends, the passage 22 communicating with the passage 18 of the nozzle body 14 and forming part of the supply passage. The first distance piece 20 and bore 12 of the nozzle body 14 together define a control chamber 24 to which fuel is able to flow at a restricted rate through a restricted passage 26 which communicates with the passage 22.

The end of the valve needle 10 which is exposed to the fuel pressure within the control chamber 24 is provided with a blind bore 28. A spring 30 is located within the bore 28, the spring 30 engaging the lower end surface of the first distance piece 20 and being arranged to bias the valve needle 10 into engagement with its seating. The upper end surface of the valve needle 10 is shaped to include an annular projection 32 through which grooves extend, the projection 32 being arranged to engage the lower end surface of the first distance piece 20 upon movement of the needle 10 away from its seating to limit the stroke of the valve needle 10, the grooves ensuring that fuel from the control chamber 24 is able to flow to or from the bore 28 throughout the range of movement of the valve needle 10.

The first distance piece 20 is further provided with a second restricted flow passage 34 providing a restricted flow path between the control chamber 24 and a passage 36 provided in a valve housing 38 which 4 abuts the upper surface of the first distance piece 20. The valve housing 38 is provided with a through bore 40 within which a valve member 42 is slidable. The valve member 42 includes a region of reduced diameter which defines, with the bore 40, an annular chamber 46 which communicates with the passage 36. The valve member 42 further includes a region 48 of enlarged diameter which is engageable with a seating defined around an upper end of the bore 40 to control the flow of fuel from the chamber 46 to a chamber 50 which communicates through passages (not shown) with a suitable low pressure drain, for example the fuel tank.

The upper end of the valve member 42 carries an armature 52 which is located so as to be moveable under the influence of an electromagnetic actuator (not shown), a spring (not shown) being arranged to bias the valve member 42 towards the position shown in which the enlarged region 48 engages the seating. The actuator and spring are located within a nozzle holder 54 which abuts the upper end surface of the valve housing 38, a cap nut 56 being in screw-threaded engagement with the nozzle holder 54 and securing the nozzle body 14, first distance piece 20 and valve housing 38 to the nozzle holder 54. The valve housing 38 is provided with a passage 60 and a recess defining, with the first distance piece 20, a chamber 62, the passage 60 connecting the chamber 62 to the chamber 50. The lower end of the valve member 42 is exposed to the fuel pressure within the chamber 62 and, as the fuel pressure therein is low, the valve member 42 is substantially pressure balanced and the generation of a hydraulic lock preventing movement of the valve member 42 is avoided.

A further restricted flow passage 58 is provided in the first distance piece 20 and provides a restricted flow path between the drilling 22 and the drilling 36.

In use, with fuel under high pressure supplied to the supply passage 18, and with the control valve defined by the valve member 42, bore 40 and actuator in the closed position illustrated, fuel under high pressure is supplied to the bore 12, acting upon the angled thrust surfaces associated with the valve needle 10 to apply a force to the valve needle 10 urging the valve needle 10 away from its seating. The control chamber 24 is also supplied with fuel under high pressure to apply a force to the needle 10 urging the needle 10 towards its seating. Further, the spring 30 acts to urge the valve needle 10 towards its seating. The magnitudes of these forces are such that the effective force applied to the valve needle 10 holds the needle 10 in engagement with its seating.

In order to commence injection, the actuator is energized to cause movement of the valve member 42 away from its seating thus permitting fuel to escape from the control chamber 24 to the chamber 50 and low pressure drain. The rate at which fuel is able to escape from the control chamber 24 is higher than the rate at which it can flow to the control chamber 24 through the restricted drilling 26. As a result, the fuel pressure within the control chamber 24 fails. The reduced fuel pressure acting on the upper end of the valve needle 10 reduces the force urging the valve needle towards its seating, and a point will be reached beyond which the forces acting on the valve needle 10 urging the valve needle 10 away from its seating are able to overcome those urging the needle towards its seating. The valve needle 10 will then lift away from its seating permitting fuel to flow from the bore 12 to the outlet openings.

6 Movement of the fuel needle 10 away from its seating is limited by the engagement of the projection 32 with the lower surface of the first distance piece 20.

It will be appreciated that during injection, fuel continues to flow to the control chamber 24 at a restricted rate, and fuel continues to flow from the control chamber 24 to the chamber 50. Further, a small amount of fuel escapes through the restricted drilling 58 to the chamber 50 and drain. The dimensions of the restricted passages 26, 34, 58 are chosen to ensure that the quantity of fuel escaping to the low pressure chamber 50 during injection is at an acceptable level.

In order to terminate injection, the actuator is de-energized resulting in movement of the valve member 42 into engagement with its seating under the action of the spring, such movement terminating the flow of fuel from the control chamber 24 to the low pressure drain, and as fuel continues to flow to the control chamber 24 through the restricted passage 26, and through the restricted passage 58 to the passages 34, 36 and chamber 24, the fuel pressure within the passages 34, 36 and the control chamber 24 rises thus the force acting on the valve needle urging the valve needle towards its seating increases, and a point will be reached beyond which the valve needle 10 commences movement towards the seating, the engagement of the valve needle 10 with its seating terminating injection. As mentioned hereinbefore, the dimensions of the restricted passages 26, 34, 58 are chosen to maintain the rate at which fuel escapes at an acceptable level. Additionally, the dimensions are selected to ensure that the fuel pressure within the control chamber 24 rises at an acceptably high rate to permit termination of injection at the desired instant.

7 It will be appreciated that as the spring 30 is located within a blind bore 28 extending along the axis of the upper part of the valve needle 10 rather than by a spring engaging the end surface of the needle, the spring biasing of the valve needle 10 is achieved without requiring the injector to be of great length, and without reducing the area of the valve needle 10 which is in sliding engagement with the bore 12 acting to guide movement of the valve needle 10. Additional advantages of locating the spring 30 within a bore formed in the valve needle 10 are that the volume of the control chamber 24 can be reduced and the mass of the needle can be reduced, thus improving the dynamic response of the injector and improving the quality of injection. Further, as the spring 30 engages the lower end surface of the first distance piece 20 manufacture of the first distance piece 20 is relatively simple, there being no requirement to provide any locating features on the first distance piece.

The arrangement described hereinbefore may be modified in a number of respects. For example, the electromagnetic actuator could be replaced by another type of actuator, for example an actuator which includes a piezo electric stack. In use, the stack is controlled to take its extended form when injection is not to occur, the stack holding the valve member in engagement with its seating, injection being permitted when the length of the stack is reduced to allow the valve member to move away from its seating.

It will appreciated that the restricted passage 58 could be omitted, but that in such an arrangement, in order to pressurize the control chamber to an extent sufficient to cause movement of the valve needle, the passages 34, 36 and the chamber 46 would be pressurized. In the absence of the restricted passage 58, such pressurization would result 8 from the flow of fuel through the restricted passage 26 alone. Clearly, in such an arrangement, termination of injection would occur a relatively long time after closure of the control valve. By using an additional restricted passage, pressurization of the various passages and chambers can occur more rapidly thus permitting greater control of injection.

9

Claims (4)

1. A fuel injector comprising a valve needle slidable within a bore provided in a nozzle body and engageable with a seating, the needle being biassed towards the seating by a spring, wherein the spring extends within a blind bore extending along part of the length of the needle.

2. A fuel injector comprising a valve needle slidable within a bore and defining, with the bore, a control chamber, a restricted passage whereby fuel is supplied to the control chamber, a control valve controlling fuel flow from the control chamber, the control valve communicating with the control chamber through a fuel flow passage, and a second restricted passage communicating with the fuel flow passage to permit fuel supply thereto at a restricted rate.

3. A common rail fuel system comprising a common rail, a fuel pump arranged to charge the rail with fuel to a high pressure, and a plurality of fuel injectors of the type claimed in Claim 1 or Claim 2.

4. A fuel injector substantially as hereinbefore described with reference to the accompanying drawing.