Information
-
Patent Grant
-
6209805
-
Patent Number
6,209,805
-
Date Filed
Friday, May 14, 199925 years ago
-
Date Issued
Tuesday, April 3, 200123 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Andrus, Sceales, Starke & Sawall
-
CPC
-
US Classifications
Field of Search
US
- 237 96
- 237 5331
- 237 5332
- 237 5333
- 237 5334
- 237 5335
- 237 5338
- 237 5339
- 237 5851
- 237 5853
- 237 5855
- 251 3001
-
International Classifications
-
Abstract
A fuel injector comprises a valve needle biased by a spring towards a seating. An electromagnetic actuator arrangement is operable to vary the magnitude of the biasing force applied to the needle by the spring.
Description
BACKGROUND OF THE INVENTION
This invention relates to a fuel injector for use in supplying fuel under pressure to a combustion space of a compression ignition internal combustion engine. In particular, the invention relates to a fuel injector of the type in which the commencement of injection is controlled using an electromagnetic actuator. The invention is particularly suitable for use in a pump/injector arrangement, but it will be appreciated that the invention may be used in other applications.
In a known pump/injector arrangement, the commencement of injection is controlled by controlling the fuel pressure within a control chamber, the fuel pressure within the control chamber applying a force to a valve needle urging the needle towards its seating. The fuel pressure within the control chamber is controlled using an appropriate electromagnetically actuated valve. Such an arrangement is relatively complex and difficult to control accurately.
SUMMARY OF THE INVENTION
According to the present invention there is provided a fuel injector comprising a valve needle biased by a spring towards a seating, and an electromagnetic actuator arrangement arranged to vary the magnitude of the biasing force applied to the needle by the spring.
In such an arrangement, the spring is conveniently arranged to apply a sufficiently large biasing force to the needle to ensure that injection does not occur when the actuator is energised to a first energization level. Upon energizing the actuator to a second energization level, the actuator acts against the spring to reduce the magnitude of the biasing force applied to the needle by the spring to a level sufficient to allow movement of the injector needle thus allowing injection to commence.
Preferably, the actuator includes an armature carried by a control member, the spring load being transmitted to the needle through the control member.
As the fuel injector does not rely upon the operation of a valve to control injection, the number of drillings, bores and other features which must be provided in the injector can be reduced thereby simplifying construction. The fuel injector is further relatively easy to control, thus permitting accurate control of the timing of injection.
The invention is particularly suitable for use in a pump/injector arrangement in which the timing of fuel injection relative to the timing of closing a drain valve controls the injection pressure. Clearly, in such an arrangement, the invention permits improved control of the injection pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will further be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1
is a sectional view of a fuel injector in accordance with an embodiment; and
FIG. 2
is a view of part of the injector of
FIG. 1
to an enlarged scale.
DETAILED DESCRIPTION OF THE INVENTION
The fuel injector illustrated in the accompanying drawings comprises a nozzle body
10
which is provided with a blind bore
12
. A valve needle
14
is slidable within the bore and is engageable with a seating defined adjacent the blind end of the bore to control communication between the bore
12
and one or more outlet openings which communicate with the bore
12
downstream of the seating. The bore
12
is shaped to define an upper region of diameter substantially equal to the diameter of the adjacent part of the needle
14
which guides the needle
14
for sliding movement in the bore
12
. This part of the bore
12
is shaped to define an annular gallery
16
which communicates with a supply passage
18
. The bore
12
further defines a lower region of enlarged diameter which houses a reduced diameter portion of the needle
14
and defines with the adjacent part of the needle
14
, a chamber from which fuel is supplied, in use, past the seating to the outlet openings. The valve needle
14
is shaped to include a plurality of flutes which define flow paths between the annular gallery
16
and the chamber defined between the lower part of the bore
12
and the adjacent part of the needle
14
. At the intersection between the upper, relatively large diameter part of the needle
14
and the reduced diameter part thereof, a thrust surface is defined which is exposed to the fuel pressure within the chamber.
The upper surface of the nozzle body
10
abuts a distance piece
20
which is provided with a through bore into which an end part of the needle
14
extends. A load transmitting member
22
engages the upper part of the needle
14
and is located in a part of the bore of the distance piece
20
of enlarged diameter. Drillings
24
are provided in the distance piece
20
, the drillings
24
communicating with the supply passage
18
.
The upper surface of the distance piece
20
abuts the lower end surface of a second distance piece
26
which is provided with drillings
28
communicating with the drillings
24
of the first distance piece
20
. The second distance piece
26
is further provided with a through bore which includes a region of relatively large diameter defining a spring chamber
30
. A control member
32
extends into the spring chamber, the lower end of the control member
32
including an outwardly extending flange
34
, the upper surface of which carries a shim
36
, a helical compression spring being engaged between a step defined at an end of the spring chamber
30
and the upper surface of the shim
36
. The spring
38
biases the member
32
in a downward direction in the orientation illustrated, biasing the lower end surface of the member
32
into engagement with the load transmitting member
22
, hence biasing the valve needle
14
into engagement with the seating.
The upper end of the control member
32
defines a step with which a shim
40
engages, the shim acting to locate an armature
42
, a screw-threaded member
44
securing the armature
42
and shim
40
to the member
32
. The armature
42
is moveable under the influence of a magnetic field generated, in use, by a first winding
46
forming part of an actuator arrangement
48
located within an actuator housing
50
. A passage
52
extends through the actuator housing
50
, the passage
52
communicating with the drillings
28
.
The upper surface of the actuator housing
50
abuts a valve housing
54
which includes a drilling
56
communicating with the passage
52
. The valve housing includes a through bore
58
within which a valve member
60
is slidable, the valve member
60
including a region which is dimensioned to engage a seating defined by part of the through bore
58
. The through bore
58
and valve member
60
together define an annular chamber
62
located upstream of the seating which communicates through a drilling
64
and a recess
66
formed in the upper surface of the valve housing
54
with the drilling
56
. The lower end of the valve member
60
is secured to an armature
68
by means of a screw-threaded member
70
which engages a screw-threaded part of the valve member
60
. The armature
68
is moveable under the influence of a magnetic field generated, in use, by a second winding
72
forming part of the actuator
48
.
A shim
74
is located beneath the screw-threaded member
70
, a helical compression spring
76
being engaged between the shim
74
and the upper surface of the screw-threaded member
44
.
The upper surface of the valve housing
54
abuts the lower end of a pump housing
78
which includes a bore
80
within which a pumping plunger
82
reciprocal under the influence of a cam and tappet arrangement, against the action of a return spring
84
.
It will be appreciated that the shims
36
,
40
,
74
are selected depending upon the intended application of the injector, the shims setting the prestressing of the springs
38
,
76
and the travel of the control member
32
.
In use, whilst the plunger
82
is being withdrawn from the plunger bore
80
under the action of the spring
84
, and with the first and second windings
46
,
72
of the actuator
48
de-energized, the valve member
60
is biased by the spring
76
away from the seating, thus permitting communication between a source of fuel under low pressure which communicates with a chamber
86
located downstream of the seating and the plunger bore
80
. As a result, fuel flows to the plunger bore
80
, the flow of fuel continuing until the plunger
82
reaches its outermost position. It will be appreciated that during this stage of the operation of the injector, the fuel pressure applied to the valve needle
14
, and in particular to the angled thrust surfaces thereof exposed to the fuel pressure within the bore
12
, is relatively low. The force applied to the valve needle
14
by the application of fuel under pressure is therefore insufficient to lift the valve needle
14
away from its seating, the spring
38
acting to ensure that the valve needle
14
remains in engagement with the seating.
Once inward movement of the plunger
82
commences, whilst the actuator
48
remains de-energized, fuel is displaced from the plunger bore
80
past the valve member
60
and seating to the low pressure reservoir. When it is determined that pressurization of fuel should commence, the second winding
72
is energized resulting in movement of the armature
68
towards the winding
72
and bringing the valve member
60
into engagement with the seating. This movement breaks the communication between the plunger bore
80
and the low pressure fuel reservoir, and as fuel is no longer permitted to escape from the plunger bore
80
, continued inward movement of the plunger
82
pressurises the fuel in the plunger bore
80
and passages in communication therewith. During this stage of the operation of the injector, although the fuel pressure applied to the needle
14
increases, the fuel pressure is still insufficient to cause movement of the valve needle away from its seating against the action of the spring
38
.
When injection is to commence, the first winding
46
is energized attracting the armature
42
towards the winding
46
. This attractive force is transmitted through the control member
32
to the spring
38
, and it will be appreciated that as a result, the biasing force applied to the needle
14
by the spring
38
is reduced. The reduction in the biasing force applied to the needle
14
is sufficient to permit the valve needle
14
to lift from its seating under the action of the fuel pressure within the bore
12
. Such movement of the needle
14
allows fuel to flow past the seating to the outlet openings, thus commencing injection.
In order to terminate injection, the second winding
72
is de-energized, and as a result the valve member
60
lifts away from its seating under the action of the spring
76
. The movement of the valve member
60
permits fuel to escape to the low pressure fuel reservoir, thus permitting a rapid reduction in the fuel pressure within the plunger bore
80
and other passages within the injector. The fuel pressure applied to the needle
14
therefore falls, and as a result of the reduced pressure applied to the needle
14
, the needle
14
returns into engagement with its seating under the action of the spring
38
to terminate injection. If desired, the first winding
46
may also be de-energized when the second winding
72
is de-energized, thus increasing the magnitude of the biasing force applied to the valve needle
14
by the spring
38
at the termination of injection.
After termination of injection, continued inward movement of the plunger displaces further fuel to the low pressure reservoir.
By ensuring that the attractive force between the first winding
46
and armature
42
rises as rapidly as possible, the timing at which commencement of injection occurs can be controlled relatively accurately, even allowing for slight inaccuracies in the effective area of the valve needle
14
exposed to the fuel pressure within the bore
12
urging the needle
14
away from its seating. As the timing of commencement of injection can be controlled relatively accurately, the injection pressure can also be controlled accurately using the apparatus described hereinbefore.
In an alternative mode of operation, rather than energizing the first winding
46
separately for each injection, the first winding
46
may be continuously energized to ensure that injection commences as soon as a predetermined pressure is reached, the predetermined pressure being dependent upon the rate of the spring
38
, the magnitude of the attractive force between the actuator
48
and armature
42
, and the effective area of the valve needle
14
exposed to the fuel pressure within the bore
12
. In this mode of operation, the magnitude of the attractive force between the actuator
48
and the armature
42
can be varied, in use, to vary the pressure at which coramencement of injection occurs.
Although in the embodiments described hereinbefore, the invention is incorporated into a pump injector arrangement, it will be appreciated that the invention is also applicable to other types of fuel injector in which the commencement of injection is controlled electronically, the invention being applicable to arrangements both where the timing of commencement of injection is controlled and arrangements in which commencement of injection is to occur when a predetermined pressure is reached.
Claims
- 1. A fuel injector comprising a valve needle biased by a biasing force applied by a spring towards a seating an electromagnetic actuator arrangement arranged to vary the magnitude of the biasing force applied to the needle by the spring and a valve operable to control a timing of commencement of fuel pressurization, wherein the valve includes a valve member slidable within a bore provided in a valve housing, the valve being engageable with a seating defined by the bore, andwherein the valve member and the bore together define a chamber for fuel which communicates with a source of fuel under low pressure, the valve member being engageable with the seating to control communication between a drilling provided in the valve housing and the chamber.
- 2. A fuel injector as claimed in claim 1, wherein the spring comprises a helical compression spring.
- 3. A fuel injector as claimed in claim 2, wherein the spring is arranged to apply a sufficiently large biasing force to the needle to ensure that injection does not occur when the actuator arrangement is energized to a first energization level, the actuator arrangement acting against the spring to reduce the magnitude of the biasing force applied to the needle by the spring to a level sufficient to allow movement of the valve needle thus allowing injection to commence when the actuator arrangement is energized to a second energization level.
- 4. A fuel injector as claimed in claim 3, wherein the actuator arrangement includes an armature carried by a control member which cooperates with the needle, the spring applying a load to the needle which is transmitted to the needle through the control member.
- 5. A fuel injector as claimed in claim 1, wherein the valve is controllable independently of the electromagnetic actuator arrangement.
- 6. A fuel injector comprising a valve needle biased by a biasing force applied by a spring towards a seating, an electromagnetic actuator arrangement arranged to vary the magnitude of the biasing force applied to the needle by the spring and a valve operable to control a timing of commencement of fuel pressurization, wherein the valve includes a valve member slidable within a bore provided in a valve housing, the valve being engageable with a seating defined by the bore, wherein the valve member and the bore together define a chamber for fuel which communicates with a source of fuel under low pressure, the valve member being engageable with the seating to control communication between a drilling provided in the valve housing and the chamber, andwherein the drilling provided in the valve housing communicates with a plunger bore within which a plunger is reciprocal, reciprocal movement of the plunger causing fuel pressurization within the plunger bore when the valve member is moved against the seating.
- 7. A fuel injector as claim in claim 6, wherein the spring comprises a helical compression spring.
- 8. A fuel injector as claimed in claim 7, wherein the spring is arranged to apply a sufficiently large biasing force to the needle to ensure that injection does not occur when the actuator arrangement is energized to a first energization level, the actuator arrangement acting against the spring to reduce the magnitude of the biasing force applied to the needle by the spring to a level sufficient to allow movement of the valve needle thus allowing injection to commence when the actuator arrangement is energized to a second energization level.
- 9. A fuel injector as claimed in claim 8, wherein the actuator arrangement includes an armature carried by a control member which cooperates with the needle, the spring applying load to the needle which is transmitted to the needle through the control member.
- 10. A fuel injector as claimed in claim 6, wherein the valve is controllable independently of the electromagnetic actuator arrangement.
Priority Claims (1)
Number |
Date |
Country |
Kind |
9812901 |
Jun 1998 |
GB |
|
US Referenced Citations (4)
Foreign Referenced Citations (3)
Number |
Date |
Country |
0 823 549 A2 |
Feb 1998 |
EP |
0 823 549 A3 |
Jun 1998 |
EP |
2 307 513 |
May 1997 |
GB |