Information
-
Patent Grant
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6336595
-
Patent Number
6,336,595
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Date Filed
Friday, March 17, 200024 years ago
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Date Issued
Tuesday, January 8, 200222 years ago
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Inventors
-
Original Assignees
-
Examiners
- Shaver; Kevin
- Kim; Christopher S.
Agents
-
CPC
-
US Classifications
Field of Search
US
- 239 88
- 239 90
- 239 96
- 239 124
- 239 5532
- 239 5553
- 123 467
- 123 516
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International Classifications
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Abstract
A fuel injector comprising a valve needle slidable within a bore, a surface associated with the valve needle being exposed to the fuel pressure within a control chamber and an electromagnetically actuable control valve controlling communication between the control chamber and a low pressure chamber. The injector also comprises a damping arrangement arranged to damp pressure waves applied to the low pressure chamber.
Description
TECHNICAL FIELD
This invention relates to a fuel injector for use in delivering fuel under pressure to a combustion space of an internal combustion engine. In particular the invention relates to a fuel injector of the electromagnetically actuable type suitable for use in a common rail type fuel system arranged to deliver diesel fuel to a compression ignition internal combustion engine.
BACKGROUND OF THE INVENTION
A known fuel injector for use in such a fuel system is illustrated in FIG.
1
and comprises a valve needle
10
slidable within a bore
11
. The needle
10
includes a surface exposed to the fuel pressure within a control chamber
12
. The control chamber
12
is supplied with fuel from a supply passage
13
through a restriction
14
, thus fuel is only permitted to flow to the control chamber
12
at a restricted rate. An electromagnetically actuable control valve
15
controls communication between the control chamber
12
and a chamber
16
which communicates with a low pressure drain reservoir through a backleak passage which is common to several injectors. The injector of
FIG. 1
will be described in greater detail below.
Reliable, consistent operation of the control valve
15
is important to achieve as inconsistencies in the operation of the control valve may result in undesirable variations in the quantity of fuel injected and in the timing of fuel injection. Pressure waves may be transmitted to the control chamber
16
from other identical injectors via the common backleak passage. It will be appreciated that the application of pressure waves to the chamber
16
may impair the performance of the valve. It is an object of the invention to provide an injector in which this disadvantage is obviated or mitigated.
SUMMARY OF THE INVENTION
According to the present invention there is provided a fuel injector comprising a valve needle slidable within a bore, a surface associated with the needle being exposed to the fuel pressure within a control chamber, an electromagnetically actuable control valve controlling communication between the control chamber and a low pressure chamber, and a damping arrangement arranged to damp pressure waves applied to the low pressure chamber.
The damping arrangement conveniently comprises a volume which communicates with the low pressure chamber, the volume containing gas, in use. The gas, for example air, fuel vapour or a mixture thereof, is readily compressible and acts to damp pressure waves applied to the low pressure chamber.
The volume is conveniently defined by a blind drilling orientated, in use, with its blind end uppermost to retain the gas therein. The drilling conveniently extends adjacent part of the actuator for the control valve.
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 illustrating a fuel injector;
FIG. 2
is a diagrammatic view illustrating part of the injector of
FIG. 1
; and
FIG. 3
is a view similar to
FIG. 2
illustrating part of a fuel injector in accordance with an embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As described briefly hereinbefore, the fuel injector illustrated, in part, in
FIGS. 1 and 2
comprises a valve needle
10
which is slidable within a bore
11
. The bore
11
takes the form of a blind bore formed in a nozzle body
17
. Adjacent the blind end of the bore
11
, a plurality of outlet openings (not shown) is provided. The bore
11
is shaped to define a seating with which the needle
10
is engageable to control communication between the region of the bore
11
upstream of the seating and the outlet openings.
The bore
11
is supplied with fuel under high pressure, in use, through the supply passage
13
, the supply passage
13
being connected to a fuel source in the form of a common rail which, in use, is charged with fuel to a high pressure by a suitable fuel pump. As illustrated in
FIG. 1
, the supply passage
13
is shaped to define a region
18
of reduced diameter, the region
18
restricting the rate at which fuel is able to flow along the supply passage
13
towards the bore
11
.
The nozzle body
17
abuts a distance piece
19
which is shaped to include a recess which defines the control chamber
12
, an upper end surface of the needle
10
being exposed to the fuel pressure within the control chamber
12
. As described hereinbefore, the control chamber
12
communicates with the supply passage
13
through a restriction
14
. A spring
20
is located within the control chamber
12
, the spring
20
acting to apply a biasing force to the needle
10
urging the needle
10
into engagement with the seating. The recess which defines the control chamber
12
is shaped to define an internal projection which serves as a lift stop, controlling the distance through which the needle
10
can lift away from its seating. A drilling
21
is provided within the projection, the drilling
21
communicating through a further drilling
22
with a surface of the distance piece
19
remote from the nozzle body
17
. The end of the distance piece
19
remote from the nozzle body
17
abuts a valve housing
23
which is provided with a through bore
24
within which a valve member
25
is moveable. The valve member
25
forms part of the electromagnetically actuated control valve
15
. The valve member
25
is shaped to include a region of diameter smaller than the adjacent part of the bore
24
, defining an annular chamber which communicates through passages
26
with the drilling
22
, and hence with the control chamber
12
. The valve member
25
includes a region of enlarged diameter which is engageable with a seating adjacent an end of the bore
24
to control communication between the passages
26
and the low pressure chamber
16
. As illustrated in
FIG. 2
, the low pressure chamber
16
communicates with a return passage
27
provided in an actuator housing
28
which abuts the surface of the valve housing
23
remote from the distance piece
19
. The return passage
27
communicates, in use, with a backleak passage (not shown), the backleak passage being common to all of the injectors associated with the engine, the backleak passage further communicating with a low pressure fuel reservoir, for example a fuel tank.
Within the chamber
16
, an armature
29
is provided, the armature
29
being secured to the valve member
25
and moveable under the influence of an electromagnetic actuator
30
located within a bore provided in the actuator housing
28
. The actuator
30
includes a return spring arranged to bias the valve member
25
into engagement with its seating.
The lower end of the valve member
25
extends into a chamber
31
defined between the valve housing
23
and the distance piece
19
, the chamber
31
communicating through a passage (not shown) with an appropriate low pressure fuel reservoir.
A cap nut
32
is used to secure the nozzle body
17
, the distance piece
19
and the valve housing
23
to the actuator housing
28
in the usual manner.
In use, as described hereinbefore, the supply passage
13
is arranged to receive fuel under high pressure, and it will be appreciated that provided the actuator
30
is not energized, and hence the valve member
25
engages its seating, then both the bore
11
and the control chamber
12
will have high pressure fuel applied thereto. The fuel pressure within the bore
11
applies a force to appropriately angled thrust surfaces
10
a
of the needle
10
, urging the needle
10
away from its seating. The action of the fuel upon the thrust surfaces
10
a
is countered by the action of the fuel under pressure within the control chamber
12
and the action of the spring
20
. The fuel pressure within the control chamber
12
, which acts over a relatively large effective area of the needle
12
, in combination with the action of the spring
20
, is sufficient to ensure that the valve needle
10
remains in engagement with its seating.
When injection is to commence, the actuator
30
is energized, urging the armature
29
and valve member
25
to move against the action of the spring
35
of the actuator
30
, lifting the valve member
25
away from its seating. As a result, fuel is able to escape from the control chamber
12
to the chamber
16
which, as described hereinbefore, is at relatively low pressure due to its connection with the low pressure reservoir by the return passage
27
and the backleak passage. As fuel is only permitted to flow towards the chamber
12
at a low rate through the restriction
14
, it will be appreciated that the fuel pressure within the control chamber
12
falls, and as a result, the force applied to the needle
10
urging the needle
10
towards its seating also falls. A point will be reached beyond which the fuel pressure acting upon the thrust surfaces
10
a is sufficient to lift the valve needle
10
away from its seating, thus permitting fuel from the bore
11
to flow past the seating to the outlet openings, and into the combustion space with which the injector is associated.
During injection of fuel, as fuel is permitted to flow towards the bore
11
at a restricted rate through the restriction
18
, and as fuel is able to escape from the bore
11
by being injected through the outlet openings, it will be appreciated that the fuel pressure within the bore
11
falls, and thus the magnitude of the force urging the valve needle
10
away from its seating is reduced.
In order to terminate injection, the actuator
30
is de-energized, the valve member
25
returning into engagement with its seating under the action of the spring of the actuator
30
. As a result, fuel is unable to escape from the control chamber
12
to the low pressure chamber
16
, and as fuel is permitted to flow to the chamber
12
through the restriction
14
, the fuel pressure within the control chamber
12
will rise and thus the force urging the needle
10
into engagement with its seating will rise. A point will be reached beyond which the needle
10
moves into engagement with its seating as a result of the fuel pressure within the control chamber
12
and the action of the spring
20
overcoming the action of the fuel under pressure upon the thrust surfaces
10
a
. Once the needle
10
has moved into engagement with its seating, fuel injection terminates. As, during injection, the fuel pressure within the bore
11
falls, it will be appreciated that termination of injection occurs more rapidly than would otherwise be the case. Additionally, it will be appreciated that as the internal projection which serves as a lift stop reduces the volume of the control chamber
12
, repressurisation of the control chamber
12
can be achieved relatively quickly, thereby aiding rapid closure of the valve needle
10
.
As discussed hereinbefore, the low pressure chamber
16
is connected to a common backleak passage. As a result, there is risk that the operation of other injectors associated with the engine may result in pressure waves being transmitted along the backleak passage and along the return passage
27
to the low pressure chamber
16
, and the action of the pressure waves upon the valve member
25
and armature
29
may impair the operation of the control valve
15
such that the control valve
15
does not open immediately upon energization of the actuator
30
or in the control valve
15
opening prematurely. Similarly, movement of the valve member
25
into engagement with its seating may be impaired.
In accordance with the invention, a damping arrangement is provided in association with the low pressure chamber
16
to damp pressure waves, and hence reduce the risk of the operation of the control valve
15
being impaired. In the embodiment illustrated in
FIG. 3
, the damping arrangement comprises a volume
33
defined by a blind drilling
34
which extends adjacent the actuator
30
and which communicates with the low pressure chamber
16
. The orientation of the blind drilling
34
is such that, in use, air or fuel vapour, or a mixture thereof, will become trapped within the drilling
34
. The valve is operated in a vertical plane and the drilling is filled continuously by trapping fire bubbles which are separated during the violent fuel depressurisation which occurs within chamber
16
. As such gases are readily compressible, pressure waves transmitted to the chamber
16
along the return passage
27
will be damped to a large extent by the presence of the compressible gases within the volume
33
. The damping of the pressure waves applied to the low pressure chamber
16
reduces the risk of the performance of the control valve
15
being impaired, and as a result, consistent, reliable operation of the injector is more readily achievable.
Although in the description hereinbefore, the damping arrangement comprises a blind drilling which extends adjacent the actuator
30
, it will be appreciated that other techniques may be used to damp the application of pressure waves to the low pressure chamber
16
.
Claims
- 1. A fuel injector comprising a valve needle slidable within a bore, a surface associated with the valve needle being exposed to a fuel pressure within a control chamber, an electromagnetically actuable control valve controlling communication between the control chamber and a low pressure chamber, and a means for damping pressure waves applied to the low pressure chamber, said means for damping comprises a volume for containing gas, in use, the volume communicating with the low pressure chamber, the volume defined by a blind drilling in an actuator housing, said actuator housing defining a return passage and an actuator compartment having an actuator disposed therein, said blind drilling being oriented, in use, with its blind end uppermost to retain the gas therein, said blind drilling being separate and distinct from each of said return passage and said actuator compartment, said blind drilling further being spaced apart from said actuator and said actuator compartment by said actuator housing.
- 2. The fuel injector as claimed in claim/wherein the drilling extends generally parallel with part of an actuator for the control valve.
Priority Claims (1)
Number |
Date |
Country |
Kind |
9906092 |
Mar 1999 |
GB |
|
US Referenced Citations (5)