Injection nozzle

An injection nozzle comprises a valve needle engageable with a seating. The needle includes a surface arranged such that when the needle occupies a fully lifted position, part of the surface is exposed to the fuel pressure within a control chamber whilst a second part of the surface is exposed to the fuel pressure within a second chamber. Independent restricted passages provide communication between the control and second chambers and a supply line. A control valve communicates with the second chamber to control operation of the injection nozzle. The control valve is actuated by an electromagnetic actuator having a core arrangement--armature air gap of tapering axial length.

This invention relates to an injection nozzle for use in the supply of fuel 
to a cylinder of an internal combustion engine. In particular, this 
invention relates to an injection nozzle including a valve needle which is 
engageable with a seating, the position of the valve needle being 
controlled by an electromagnetic actuator arrangement. 
An existing injection nozzle arrangement includes a valve needle which is 
slidable within a blind bore one end of which defines a seating with which 
the valve needle is engageable to control the delivery of fuel from one or 
more openings provided in the blind end of the bore. High pressure fuel is 
applied to the valve needle, the action of the high pressure fuel on 
angled surfaces of the valve needle tending to lift the valve needle from 
its seating. A spring located within a spring chamber acts against the end 
of the valve needle remote from the seating urging the valve needle into 
engagement with the seating. The spring chamber is arranged to be supplied 
with high pressure fuel through a restrictor, and a solenoid actuated 
valve controls the flow of fuel from the spring chamber to a suitable low 
pressure drain. 
In use, in order to commence injection the solenoid actuated valve is 
operated to permit fuel from the spring chamber to flow to the drain. The 
restrictor only permits a low rate of fuel supply to the spring chamber, 
thus the fuel pressure within the spring chamber falls. The reduction in 
pressure in the spring chamber is sufficient to enable the pressure acting 
against the angled surfaces of the valve needle to lift the valve needle 
from its seating and permit fuel flow past the seating to the or each 
opening. 
Termination of injection is achieved by closing the solenoid actuated 
valve, the fuel pressure within the spring chamber then increasing due to 
the flow of fuel into the spring chamber through the restrictor. The fuel 
pressure rises to a sufficiently high value that the combined effect of 
the fuel pressure and the spring is sufficient to return the valve needle 
into engagement with the seating against the action of the high pressure 
fuel against the angled surfaces of the valve needle. 
It is an object of the invention to provide an improved injection nozzle of 
the type described hereinbefore. 
According to a first aspect of the invention there is provided an injection 
nozzle comprising a valve needle engageable with a seating, the needle 
including a thrust surface to which fuel under pressure can be applied to 
lift the needle away from the seating, the valve needle having a surface 
associated therewith arranged such that, when the valve needle occupies a 
fully lifted position, a first part of the surface is exposed to the fuel 
pressure within a control chamber whilst a second part of the surface is 
exposed to the fuel pressure within a second chamber, wherein the control 
chamber communicates with a supply line through a first restricted passage 
and the second chamber communicates with the supply line through a second 
restricted passage independent of the first restricted passage. 
The second restricted passage is conveniently composed of a pair of 
orifices connected in series. 
According to a second aspect of the invention there is provided an 
injection nozzle comprising a valve needle engageable with a seating, the 
needle including a thrust surface to which fuel under pressure can be 
applied to lift the needle away from the seating, the valve needle having 
a surface associated therewith exposed to the fuel pressure within a 
control chamber, the fuel pressure within the control chamber being 
controlled by an electromagnetically actuated valve comprising a solenoid 
actuator having a core arrangement and an armature, an air gap being 
defined between the core arrangement and the armature, wherein the axial 
length of the air gap tapers from a maximum adjacent an edge of the 
armature to a minimum adjacent the centre thereof. 
The provision of such a tapering air gap enables the effective gap between 
the core arrangement and armature to be reduced and thus permits an 
increase in the force available. 
It will be appreciated that, in practice, the air gap may be filled with 
fuel. 
The invention also relates to a solenoid actuator suitable for use in an 
injection nozzle in accordance with the second aspect of the invention. 
The injection nozzle may further comprise a distance piece provided with a 
through bore, an insert being provided in the through bore, the distance 
piece and insert defining, in part, the control chamber. 
According to a further aspect of the invention there is provided a control 
valve comprising a valve member slidable within a bore, the valve member 
including a region of enlarged diameter which is engageable with a seating 
defined around an end part of the bore, and a region of reduced diameter 
upstream of the seating, the region of reduced diameter defining, with the 
bore, an annular chamber which communicates with a valve inlet port. 
It will be appreciated that when the valve member engages its seating, fuel 
is unable to flow from the inlet port through the annular chamber and 
escape from the bore, such flow being permitted when the valve member is 
lifted from its seating. Further, as the seating is defined around the 
bore, the seating diameter is substantially equal to the bore diameter 
thus the valve member is substantially pressure balanced when in 
engagement with its seating.

The injection nozzle illustrated in the accompanying drawings comprises a 
nozzle body 10 within which a blind bore 12 is provided. Part way along 
the blind bore 12, an annular gallery 14 is formed, and adjacent the blind 
end of the bore 12, a substantially conical seating area is formed. The 
blind end of the bore 12 communicates with small openings (not shown) in a 
conventional manner. 
A valve needle 16 is slidable within the blind bore 12, the valve needle 16 
including a first region 16a of diameter substantially equal to the 
diameter of the bore 12 so as to form a substantially fluid tight seal 
therewith and a reduced diameter second region 16b permitting fuel to flow 
between the valve needle 16 and nozzle body 10, the interconnection 
between the first and second regions 16a, 16b taking the form of an angled 
thrust surface 16c located within the annular gallery 14. The end of the 
valve needle 16 adjacent the blind end of the bore 12 is shaped so as to 
take conical form and is engageable with the seating so as to form a 
substantially fluid tight seal therewith. The exposed part of the end of 
the valve needle also acts as a thrust surface. 
The end of the valve body 10 remote from the blind end of the bore 12 abuts 
a first distance piece 18 which is provided with a through bore 20 
arranged to align with the blind bore 12. An insert 22 is located within 
the through bore 20, the first distance piece 18, insert 22 and end of the 
valve body 10 together defining a control chamber 24 within which a spring 
26 is located, the spring 26 being engaged between the insert 22 and an 
end of the valve needle 16, and biasing the valve needle 16 into 
engagement with its seating. 
The insert 22 includes a projection 22a which extends into the control 
chamber 24 and defines a lift stop arranged to limit movement of the valve 
needle 16. An axially extending drilling is provided in the projection 22a 
extending from an end thereof which faces the valve needle 16, the 
drilling defining a chamber 28 which communicates through a passage 30 
with an annular chamber 32 defined between the insert 22 and the first 
distance piece 18. Flow of fuel through the passage 30 is restricted by a 
restriction or orifice 30a. 
The end of the first distance piece 18 remote from the valve body 10 abuts 
a second distance piece 34, the first and second distance pieces 18, 34 
together with the insert 22 defining a second annular chamber 36 which 
communicates with the first annular chamber 32 through a restricted 
annular edge filter 38 which is arranged to filter the flow of fuel 
between the first and second annular chambers 32, 36. 
A recess 40 is provided in the end of the insert 22 remote from the valve 
needle 16 such that the insert 22 together with the second distance piece 
34 define a chamber. The second distance piece 34 is provided with a pair 
of bores 35a, 35b which communicate with the chamber defined between the 
insert 22 and the second distance piece 34, a valve member 42 being 
slidable within the bore 35a. The valve 42 carries, at its end remote from 
the first distance piece 18, an armature 44 which is moveable under the 
influence of the magnetic field of a solenoid actuator assembly 46. The 
valve member 42 includes an enlarged diameter region 42a which is 
engageable with a conical seating formed around an end part of the bore 
35a within which the valve member 42 is located, an adjacent part 48 of 
the valve member 42 being of reduced diameter so as to define an annular 
chamber. The annular chamber communicates through a passage 50 with the 
annular chamber 36 defined between the first and second distance pieces 
18, 34 and the insert 22. 
As illustrated in FIG. 1, the solenoid actuator arrangement 46 is housed 
within a nozzle holder 52, the nozzle body 10 and the first and second 
distance pieces 18, 34 being secured to the nozzle holder 52 by means of a 
cap nut 54. The nozzle holder 52, the first and second distance pieces 18, 
34 and nozzle body 10 are all provided with bores which together define a 
high pressure fuel supply line 56 arranged to supply high pressure fuel to 
the annular gallery 14. A restrictor 58 is provided in the high pressure 
fuel line 56 within the first distance piece 18 to restrict the rate of 
fuel delivery to the annular gallery 14, and upstream of the restrictor 
58, a restricted passage 60 is arranged to permit the supply of fuel from 
the high pressure fuel supply line 56 to the control chamber 24. Upstream 
of the restricted passage 60, a second restricted passage 62 is arranged 
to permit the supply of fuel from the high pressure fuel supply line 56 to 
the first annular chamber 32. The combination of the second restricted 
passage 62, passage 30 and orifice 30a provides a restricted flow path 
between the chamber 28 and the supply line 56. 
The solenoid actuator assembly 46 comprises a generally cylindrical core 
member 64, and a cylindrical yoke 70, windings 66 being located between 
the core member 64 and yoke 70. The ends of the core member 64 and yoke 70 
are substantially coplanar as illustrated most clearly in FIG. 2. The core 
member 64 includes a central passage within which a spring 68 is located, 
the spring 68 engaging an end of the valve member 42 biasing the valve 
member 42 into engagement with its seating. 
As illustrated most clearly in FIG. 2, the surface of the armature 44 which 
faces the solenoid actuator assembly 46 is of annular, frusto-conical form 
such that the air gap between the inner edge of that surface of the 
armature 44 and the solenoid actuator assembly 46 is smaller than the air 
gap at the peripheral edge of the armature 44. The part of the valve 
member 42 which extends through the armature 44 is of conical form, the 
cone angle thereof matching that of the armature 44. It will be 
recognised, therefore, that when the solenoid actuator assembly 46 is 
energised to lift the valve member 42 from its seating, movement of the 
valve member 42 towards the solenoid actuator assembly 46 is limited by 
engagement between the valve member 42 and the core member 64, the 
armature 44 not coming into contact with the solenoid actuator assembly 
46. The presence of a relatively small air gap between the armature 44 and 
solenoid actuator assembly 46 results in the force generated by the 
solenoid actuator assembly 46 being relatively large. 
The material used for the valve member 42 is harder than the relatively 
soft core member 64, thus in the absence of an additional stop or movement 
limiter, movement of the valve member 42 is limited by engagement of the 
end thereof with the core member 64. In use, such engagement will 
initially result in deformation of the core member 64 until it is shaped 
to match the end of the valve member 42, whereon the engagement will be 
spread over a relatively large area. 
In use, in the position illustrated in the accompanying drawings, high 
pressure fuel is supplied to the supply line 56 thus the annular gallery 
14 and the control chamber 24 are filled with fuel at high pressure. The 
action of the high pressure of the fuel on the end of the valve needle 16 
located within the control chamber 24 together with the action of the 
spring 26 thereon is sufficient to maintain the valve needle 16 in 
engagement with its seating against the action of the fuel pressure 
against the thrust surface 16c and any other angled surfaces of the valve 
needle 16 tending to lift the valve needle 16 from its seating. Further, 
the valve member 42 is held in engagement with its seating by the spring 
68, the valve member 42 being substantially pressure balanced in this 
position as the diameter of the seating line is substantially equal to 
that of the bore 35a. 
In order to commence injection, the solenoid actuator assembly 46 is 
energised to lift the valve member 42 from its seating. Such movement of 
the valve member 42 results in fuel flowing to a suitable low pressure 
drain from the control chamber 24 and chamber 28 at a rate greater than 
the rate of fuel flow into the control chamber 24 and chamber 28 through 
the restricted passages 60, 62, and hence in the fuel pressure within the 
control chamber 24 and chamber 28 falling. 
The reduction in the fuel pressure within the control chamber 24 results in 
a reduction in the force applied to the end of the valve needle 16 
resulting, subsequently, in the valve needle 16 being lifted from its 
seating, and hence in the commencement of injection. 
The movement of the valve needle 16 away from its seating is sufficient to 
bring the end thereof into engagement with the projection 22a thus closing 
the end of the drilling defining the chamber 28. The flow of fuel from the 
control chamber 24 is thus terminated, the communication between the 
supply line 56 and the control chamber 24 through the restricted passage 
60 resulting in the pressure within the control chamber 24 increasing to 
substantially the same pressure as the supply line 56. As the valve member 
42 is lifted from its seating, the fuel pressure within the chamber 28, 
and hence the pressure applied to a central part of the end of the valve 
needle 16 remains at a relatively low level, and is insufficient to move 
the valve needle 16 towards the seating, even though part of the end of 
the valve needle 16 is exposed to the increased pressure within the 
control chamber 24. 
In order to terminate injection, the solenoid actuator assembly 46 is 
de-energised, the valve member 42 moving under the action of the spring 68 
into engagement with its seating. Such engagement terminates the flow of 
fuel from the passage 50, the communication between the supply line 56 and 
chamber 28 through the restricted passage 62, passage 30 and orifice 30a 
resulting in an increase in the fuel pressure within the chamber 28. Such 
an increase in fuel pressure together with the action of the spring 26 is 
sufficient to move the valve needle 16 against the action of the fuel 
pressure applied to the thrust surface 16c and other angled surfaces of 
the valve needle 16, such movement continuing until the valve needle 16 
engages its seating whereon injection is terminated. 
As illustrated in FIG. 2, the end of the drilling defining the chamber 28 
is of relatively large diameter, hence when the valve needle 16 engages 
the projection 22a, a relatively large area of the end of the valve needle 
experiences the pressure within the chamber 28. A relatively small 
increase in fuel pressure within the chamber 28 is therefore necessary to 
cause movement of the valve needle 16, the relatively small pressure 
increase being experienced over a relatively large part of the end surface 
of the valve needle 16. 
As the control chamber 24 is at high pressure before the valve member 42 is 
moved into engagement with its seating in order to terminate injection, 
the amount of fuel which must flow through the restricted passage 62 in 
order to result in movement of the valve needle 16 is relatively low thus 
termination of injection occurs rapidly after de-energisation of the 
solenoid actuator assembly 46. 
It will be recognised that the operating characteristics of the injection 
nozzle are dependent upon a number of factors including the diameter of 
the end surface of the valve needle 16, the areas of the thrust surface 
16c and other angled surfaces of the valve needle 16 against which fuel 
acts in order to lift the valve needle from its seating, and also the 
relative effective diameters of the restrictor 58 and restricted passages 
60, 62. For example, if the effective flow restriction of the restrictor 
62, passage 30 and orifice 30a is low then on de-energisation of the 
solenoid actuator assembly 46, the fuel pressure within the chamber 28 
rises at a high rate. Thus movement of the valve needle 16 into engagement 
with its seating can be achieved rapidly, the reduction in effective 
restriction to flow having the disadvantage that when the valve member 42 
is lifted from its seating, a greater amount of fuel will flow past the 
valve member 42 to the low pressure drain, fuel being able to flow to the 
valve member 42 from the supply line 56 through the restricted passage 62. 
The provision of the edge filter 38 traps relatively large particles 
carried by the fuel, preventing such particles from reaching the valve 
member 42 thus such particles are prevented from jamming the valve member 
42 in its open position. It will be recognised that if such jamming did 
occur, a situation may be achieved in which the valve needle 16 remains 
lifted from the seating, insufficient pressure being achieved in the 
chamber 28 to cause the valve needle 16 to move towards its seating. 
Clearly, therefore, it is important to ensure that particles which could 
cause such jamming of the valve member 42 are prevented from reaching the 
valve member 42 thus the provision of additional filter means in the form 
of the edge filter 38 is desirable. 
The use of the insert 22 and first distance piece 18 to define the control 
chamber 24 enables the provision of a control chamber of small volume. 
Where the control chamber is of relatively large volume, the relatively 
large quantity of fuel therein can be compressed by a significant amount, 
thus accurate control of the valve needle may not be possible, the use of 
a small volume control chamber reducing this disadvantage.