Information
-
Patent Grant
-
6729554
-
Patent Number
6,729,554
-
Date Filed
Thursday, October 4, 200122 years ago
-
Date Issued
Tuesday, May 4, 200420 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Mar; Michael
- Bui; Thach H
Agents
-
CPC
-
US Classifications
Field of Search
US
- 239 90
- 239 96
- 239 88
- 239 5338
- 239 5339
- 251 3001
- 251 1291
-
International Classifications
-
Abstract
A fuel injector is provided which is designed to suppress unwanted vibrations of a nozzle needle-actuating piston, thereby avoiding the injection of an excess quantity of fuel. The fuel injector comprises an actuator and a displacement amplifying chamber filled with fluid to which a large-diameter piston and a small-diameter piston working as the nozzle needle-actuating piston are exposed. The displacement amplifying chamber works to amplify and transmit displacement of the large-diameter piston by the actuator to the small-diameter piston. The fuel injector also includes a stopper which restricts movement of the small-diameter piston toward the displacement amplifying chamber to a given range, thereby suppressing the unwanted vibrations of the small-diameter piston.
Description
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to a fuel injector for internal combustion engines, and more particularly to an improved structure of a fuel injector designed to suppress unwanted vibrations of a nozzle needle-actuating piston for avoiding injection of an excess quantity of fuel.
2. Background Art
Hydraulic fuel injectors equipped with a piezoelectric valve actuator are used in internal combustion diesel engines of automotive vehicles. Such a fuel injector includes a large-diameter piston moved by the expansion and contraction of the piezoelectric valve actuator, a pressure chamber filled with hydraulic fluid, and a small-diameter piston which are arranged in alignment with each other. The movement of the large-diameter piston causes the hydraulic fluid in the pressure chamber to change in pressure which moves the small-diameter piston. The small-diameter piston then actuates a control valve.
When it is required to emit a fuel spray, the piezoelectric valve actuator is energized and expands to increase the hydraulic pressure in the pressure chamber through the large-diameter piston. This causes the expansion of the piezoelectric valve actuator to be amplified hydraulically and transmitted to the small-diameter piston. The small-diameter piston then moves downward and opens the control valve. When the control valve is opened, it will cause the pressure in a back pressure chamber to drop, thereby lifting up a nozzle needle to initiate fuel injection. Contracting the piezoelectric valve actuator will cause the small-diameter piston to move upward, thereby closing the control valve to terminate the fuel injection.
The above type of fuel injector, however, has the drawback in that during the contraction of the piezoelectric valve actuator, the control valve may be re-opened to inject an excess fuel into the engine undesirably. This is because the small-diameter piston overshoots due to its inertia when lifted upward and then moves downward as a reaction to open the control valve again. The small-diameter piston is exposed at its end to the pressure chamber and thus continues to oscillate for a relative long period of time. The amplitude of the oscillation increases and decreases cyclically as a function of width of an actuator-energizing pulse signal inputted to the piezoelectric valve actuator, thereby resulting in a change in quantity of fuel injected into the engine. Specifically, the quantity of fuel injected which is changed in proportion to the width of the actuator-energizing pulse signal changes undesirably due to the oscillation of the small-diameter piston.
SUMMARY OF THE INVENTION
It is therefore a principal object of the invention to avoid the disadvantages of the prior art.
It is another object of the invention to provide an improved structure of a fuel injector which is designed to minimize unwanted vibrations of a nozzle needle-actuating piston for avoiding injection of an excess quantity of fuel.
According to one aspect of the invention, there is provided a fuel injector which comprises: (a) a housing; (b) a control valve disposed movably within the housing to displace a needle for emitting a fuel spray; (c) a large-diameter piston disposed slidabley within the housing; (d) a small-diameter piston disposed slidably within the housing to move the control valve; (e) a displacement amplifying chamber filled with fluid to which the large-diameter piston and the small-diameter piston are exposed, the displacement amplifying chamber working to amplify and transmit displacement of the large-diameter piston to the small-diameter piston; (f) an actuator working to displace the large-diameter piston; and (g) a stopper restricting movement of the small-diameter piston toward the displacement amplifying chamber.
In the preferred mode of the invention, a damper is disposed within the displacement amplifying chamber to suppress vibrations of the small-diameter piston.
The damper is implemented by a hole formed in a ring plate secured or fitted slidably within the displacement amplifying chamber.
The stopper is implemented by a ring plate which is secured in the displacement amplifying chamber with a surface opposed to an end of the small-diameter piston through a given gap.
The housing has formed therein a first cylindrical chamber within which the large-diameter piston is disposed and a second cylindrical chamber within which the small-diameter piston is disposed. The first cylindrical chamber communicates with the second cylindrical chamber through the displacement amplifying chamber. The second cylindrical chamber extends eccentrically to a longitudinal center line of the first cylindrical chamber to define a surface at a junction of the first and second cylindrical chambers which is exposed to the second cylindrical chamber and works as the stopper.
According to the second aspect of the invention, there is provided a fuel injector which comprises: (a) a housing; (b) a control valve disposed movably within the housing to displace a needle for emitting a fuel spray; (c) a large-diameter piston disposed slidabley within the housing; (d) a small-diameter piston disposed slidably within the housing to move the control valve; (e) a displacement amplifying chamber filled with fluid to which the large-diameter piston and the small-diameter piston are exposed, the displacement amplifying chamber working to amplify and transmit displacement of the large-diameter piston to the small-diameter piston; (f) an actuator working to displace the large-diameter piston; (g) a first cylindrical chamber formed in the housing within which the large-diameter piston is disposed; (h) a second cylindrical chamber formed in the housing within which the small-diameter piston is disposed, the second cylindrical chamber communicating with the first cylindrical chamber through the displacement amplifying chamber, a longitudinal center line of the second cylindrical chamber extending eccentrically to a longitudinal center line of the first cylindrical chamber. The small-diameter piston is arranged coaxially with the control valve on one side of the displacement amplifying chamber.
In the preferred mode of the invention, the actuator is implemented by one of a piezoelectric device and a magnetostrictor, the control valve being moved to control fluid pressure within a back pressure chamber to which an end of the needle is exposed for opening a spray hole. The large-diameter piston is arranged coaxially with the actuator on one side of the displacement amplifying chamber. The small-diameter piston is arranged coaxially with the control valve on the other side of the displacement amplifying chamber.
The longitudinal center line of the second cylindrical chamber is shifted a distance e from the longitudinal center line of the first cylindrical chamber. The distance e satisfies a relation of 2
e>D−d
where D is diameter of the large-diameter piston and d is diameter of the small-diameter piston.
The longitudinal center line of the second cylindrical chamber extends eccentrically to the longitudinal center line of the first cylindrical chamber to define a surface at a junction of the first and second cylindrical chambers which is exposed to the second cylindrical chamber and works as a stopper restricting movement of the small-diameter piston toward the displacement amplifying chamber.
According to the third aspect of the invention, there is provided a fuel injector which comprises: (a) a nozzle needle displaced to open a spray hole; (b) an actuator displacing the nozzle needle, the actuator having a longitudinal center line extending eccentrically to a longitudinal center line of the nozzle needle; and (c) a housing within which the actuator is disposed, the housing being clamped on an internal combustion engine at two points provided symmetrically with respect to a line extending perpendicular to the longitudinal center lines of the nozzle needle and the actuator.
In the preferred mode of the invention, the housing has formed therein a high-pressure passage through which fuel is supplied to the spray hole. The high-pressure passage has a longitudinal center line extending perpendicular to a common line to which the longitudinal center lines of the actuator and the nozzle needle extend perpendicular.
BRIEF DESPCRIPTION OF THE DRAWINGS
The present invention will be understood more fully from the detailed description given hereinbelow and from the accompanying drawings of the preferred embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments but are for the purpose of explanation and understanding only.
In the drawings:
FIG. 1
is a vertical sectional view which shows a fuel injector according to the first embodiment of the invention;
FIG. 2
is a partially enlarged sectional view which shows an internal structure of the fuel injector of
FIG. 1
;
FIG.
3
(
a
) is a partially sectional view which shows a check valve disposed in a chamber within which a large-diameter piston is disposed;
FIG.
3
(
b
) is a perspective view which shows a ring plate working as a stopper restricting movement of a small-diameter piston;
FIG. 4
is a graph which shows relations between the quantity of fuel injected and the width of a pulse signal applied to a piezoelectric actuator in cases where the ring plate of FIG.
3
(
b
) is used and not used;
FIG.
5
(
a
) is a partially enlarged sectional view which shows an internal structure of a fuel injector according to the second embodiment of the invention;
FIG.
5
(
b
) is a view which shows an overlap of eccentric cylindrical chambers within which a large-diameter piston and a small-diameter piston are disposed;
FIG.
6
(
a
) is a partially sectional view which shows a check valve when a sufficient amount of fuel is stored in a displacement amplifying chamber;
FIG.
6
(
b
) is a partially sectional view which shows a check valve when an insufficient amount of fuel is stored in a displacement amplifying chamber;
FIG.
7
(
a
) is a partially enlarged sectional view which shows an internal structure of a fuel injector according to the third embodiment of the invention;
FIG.
7
(
b
) is a view which shows an overlap of eccentric cylindrical chambers within which a large-diameter piston and a small-diameter piston are disposed;
FIG. 8
is a sectional view which shows a fuel injector mounted in an engine block; and
FIG. 9
is a plan view, as taken along the line A—A in
FIG. 8
, which shows a clamper retaining a fuel injector in an engine block.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings, wherein like reference numbers refer to like parts in several views, particularly to
FIG. 1
, there is shown a fuel injector
100
according to the invention. The following discussion will refer to, as an example, a common rail fuel injection system in which the fuel injector
100
is provided for each cylinder of a diesel engine. The common rail fuel injection system includes a common rail which accumulates therein fuel supplied from a fuel tank elevated in pressure by a fuel pump installed in the engine. When it is required to inject the fuel into the engine, the fuel stored in the common rail under high pressure is supplied to the fuel injectors
100
.
The fuel injector
100
includes, as shown in
FIG. 1
, a hollow cylindrical injector housing
110
in which a piezoelectric actuator
1
is disposed detachably, annular plates
120
and
130
in which fluid passages are formed, a nozzle body
140
, and a retainer
150
having the annular plates
120
and
130
and the nozzle body
140
disposed therein in a liquid-tight form. The injector housing
110
has formed therein a high-pressure fuel passage
62
which extends longitudinally of the injector housing
110
and communicates with the common rail through a fuel inlet pipe
63
. A fuel outlet pipe
65
is installed in an upper portion of the injector housing
110
opposite the fuel inlet pipe
63
. The fuel flowing into a drain passage
64
is discharged from the fuel outlet pipe
65
to the fuel tank.
The injector housing
110
is made of a hollow cylinder which has a longitudinal hole or chamber
12
formed eccentrically to the longitudinal center line of the injector housing
110
. The longitudinal chamber
12
extends parallel to the high-pressure fuel passage
62
. The drain passage
64
extends downward through a gap between an inner wall of the longitudinal chamber
12
and the piezoelectric actuator
1
. The piezoelectric actuator
1
consists essentially of a thin-walled metallic hollow cylindrical housing
11
, a laminated piezoelectric device (also called a piezo stack)
12
, a rod
13
, a disc head
14
, and a bellows
15
. The disc head
14
is coupled with the rod
13
to be slidable. The bellows
15
extends from a lower end of the housing
11
to cover the rod
13
and connects with the periphery of the disk head
14
. The vertical movement of the rod
13
causes the bellows
15
to expand or contract, thereby allowing the disk head
14
to move vertically. The bellows
15
provides a pre-load to the piezoelectric device
12
.
The piezoelectric device
12
are coupled electrically to leads
16
a
and
16
b
of a connector
16
installed on an upper end of the housing
11
. The piezoelectric device
12
is insulated electrically from the housing
11
through an insulator (not shown) and held by a retaining nut
17
fitted in the upper end of the housing
11
. A ring shim
19
is disposed between a flange of a body
18
of the connector
16
and a shoulder formed on an upper inner wall of the longitudinal chamber
61
to seal a gap between the connector
16
and the longitudinal chamber
61
. The shim
19
also serves as a spacer for adjusting the vertical position of the piezoelectric actuator
1
within the longitudinal chamber
61
to regulate the injection characteristics of the fuel injector
100
(e.g., the amount of fuel to be sprayed) finely.
The disk head
14
of the piezoelectric actuator
1
is, as clearly shown in
FIG. 2
, connected to a large-diameter piston
2
through a rod
21
. The injector housing
110
has also disposed therein a small-diameter piston
4
which is coupled to the rod
21
through a displacement amplifying chamber
3
in alignment. The small-diameter piston
4
works to move a valve member
51
of a three-way valve
51
. The large-diameter piston
2
and the small-diameter piston
4
are disposed slidably within large-diameter and small-diameter longitudinal chambers formed in a cylinder
66
fitted within the injector housing
110
and oriented in alignment with each other through the displacement amplifying chamber
3
filled with the fuel. The displacement amplifying chamber
3
works to transmit the longitudinal displacement of the large-diameter piston
2
to the small-diameter piston
4
. Specifically, the stroke of the large-diameter piston
4
(i.e., the vertical movement of the piezoelectric device
12
) is amplified through the fuel within the displacement amplifying chamber
3
as a function of a difference in diameter between the large-diameter piston
4
and the small-diameter piston
2
and transmitted to the small-diameter piston
2
. Note that the three-way valve
51
has a known structure, and explanation thereof in detail will be omitted here.
A check valve
22
is disposed beneath the large-diameter piston
2
. The check valve
22
, as clearly shown in FIG.
3
(
a
), consists of a valve plate
24
, a conical spring
25
, and an annular holder
26
. The valve plate
24
works to open or close a low-pressure passage
23
formed in the large-diameter piston
2
leading to a drain passage
64
and is urged by the conical spring
25
against the end of the large-diameter piston
2
at all times. The holder
26
is of a cup-shape and secured at the periphery thereof on the periphery of the end of the large-diameter piston
2
. The holder
26
has formed in the center thereof a hole
27
which establishes communication between a chamber in the holder
26
and the displacement amplifying chamber
3
. A drop in pressure in the displacement amplifying chamber
3
due to, for example, fuel leakage will cause the valve plate
24
to move downward, as viewed in FIG.
3
(
a
), against the spring pressure produced by the conical spring
25
, so that the fuel flows from the low-pressure passage
23
into the displacement amplifying chamber
3
, thereby avoiding the production of bubbles in the displacement amplifying chamber
3
. The large-diameter piston
2
is, as viewed in
FIG. 2
, urged by a coil spring
28
disposed around the rod
21
toward the piezoelectric actuator
1
, while the small-diameter piston
4
is urged by a coil spring
29
disposed therearound into constant engagement with the valve member
51
.
The three-way valve
5
works as a control valve which establishes or blocks communication between a fluid passage
52
leading to a back pressure chamber
71
formed behind an end of a nozzle needle
7
and a high-pressure passage
53
or a low-pressure passage
54
to thereby control the pressure in the back pressure chamber
71
. The high-pressure passage
53
communicates with the high-pressure fuel passage
62
. The low-pressure passage
54
communicates with the drain passage
64
. When the piezoelectric actuator
1
is energized by a pulse signal so that it expands, it will cause the large-diameter piston
2
to push the small-diameter piston
4
through the fuel in the displacement amplifying chamber
3
, so that the valve plate
51
is moved downward to open the low-pressure passage
54
. When the low-pressure passage
54
is opened, the fuel in the back pressure chamber
71
flows into the drain passage
64
through the three-way valve
64
, thereby lifting up the nozzle needle
7
to initiate the fuel injection. When deenergized, the piezoelectric actuator
1
contracts to move the small-diameter piston
4
upward through the large-diameter piston
2
. This causes the valve plate
51
to be lifted up by the pressure of the fuel in the high-pressure passage
53
to open the high-pressure passage
53
, so that the fuel flows from the high-pressure fuel passage
62
into the back pressure chamber
71
, thereby moving the nozzle needle
7
downward.
The plate
130
has formed therein a passage
72
that is a high-pressure passage which communicates the high-pressure fuel passage
62
and the back pressure chamber
71
directly without passing through the three-way valve
5
and leads to the high-pressure passage
53
through an orifice. Specifically, the high-pressure fuel passage
62
communicates with the back pressure chamber
71
through the passage
72
at all times, thereby avoiding a quick drop in pressure in the back pressure chamber
71
for lifting up the nozzle needle
7
slowly when the fuel injection is initiated and facilitating a quick elevation in pressure in the back pressure chamber
71
for moving the nozzle needle
7
quickly when the fuel injection is terminated.
A ring plate
8
, as clearly shown in FIG.
3
(
b
), is fitted within the cylinder
66
and rests on a shoulder on an inner wall of the cylinder
66
. The ring plate
8
has a given thickness and faces the end of the small-diameter piston
4
through a given gap (i.e., the displacement amplifying chamber
3
). Specifically, the ring plate
81
has, as shown in FIG.
3
(
b
), the stopper surface
81
on which the small-diameter piston
4
hits when lifted upward, thereby defining a range of displacement of the small-diameter piston
4
which does not induce unwanted vibrations of the small-diameter piston
4
. The ring plate
81
has formed in the center thereof a hole
82
which is smaller in diameter than the small-diameter piston
4
and works as a damper to suppress vibrations of the small-diameter piston
4
through the flow of fuel therethrough. The ring plate
81
is located at a given interval away from the end of the large-diameter piston
2
without interfering the motion of the large-diameter piston
2
.
In a case where the ring plate
81
is not used, after the large-diameter piston
2
and the small-diameter piston
4
are lifted up fully, the small-diameter piston
2
is free to move within the cylinder
66
and thus oscillates, so that it may move downward to open the three-way valve
5
again. The use of the ring plate
81
minimizes an undesirable upward movement of the small-diameter piston
4
and avoids oscillations thereof at unwanted greater amplitudes. This prevents the three-way valve
5
from re-opening by the oscillations of the small-diameter piston
4
, thus avoiding a reduction in pressure within the back pressure chamber
71
which causes the nozzle needle
7
to move upward immediately after moving downward and a temporal stop of movement of the small-diameter piston
4
, thereby avoiding the injection of excess fuel.
FIG. 4
illustrates the quantity of fuel sprayed from the fuel injector
100
for cases where the ring plate
8
is used and not used. It is advisable that the quantity of fuel injected, as expressed by the ordinate axis, increase in proportion to the width of a pulse signal, as expressed by the abscissa axis, applied to the piezoelectric actuator
1
. However, when the ring plate
8
is not used, the oscillations of the small-diameter piston
4
may cause the three-way valve
5
to open undesirably to emit a fuel spray. The amplitude of oscillation of the small-diameter piston
4
increases and decreases cyclically with an increase in width of a pulse applied to the piezoelectric actuator
1
in relation to the mass and spring coefficients of peripheral parts. Alternatively, when the ring plate
8
is used, the ring plate
8
works to suppress the vibrations of the small-diameter piston
4
, thereby causing the quantity of fuel injected to increase in proportion to an increase in width of a pulse signal applied to the piezoelectric actuator
1
, which minimizes a variation in quantity of fuel injected, especially when it is required for the fuel injector
100
to emit a fuel spray finely.
FIGS.
5
(
a
) and
5
(
b
) show the fuel injector
100
according to the second embodiment of the invention. The same reference numbers as employed in the first embodiment refer to the same parts, and explanation thereof in detail will be omitted here.
The housing
110
has a first cylindrical chamber
67
formed therein coaxially with the longitudinal chamber
61
within which the large-diameter piston
2
is disposed slidably. A cylindrical block
160
is disposed in alignment with the housing
110
and has formed therein a second cylindrical chamber
68
within which the small-diameter piston
4
is disposed slidably. The first cylindrical chamber
67
extends in alignment of the longitudinal center line thereof with that of the housing
110
and eccentrically to the second cylindrical chamber
68
in communication therewith. The displacement amplifying chamber
3
is defined in a junction of the first and second cylindrical chambers
67
and
68
.
The longitudinal center line of the first cylindrical chamber
67
is shifted, as clearly shown in FIG.
5
(
b
), from that of the second cylindrical chamber
68
so that a sectional area, as indicated by A, of an overlap of the first and second cylindrical chambers
67
and
68
may be smaller than a sectional area of the second cylindrical chamber
68
, thereby defining a crescent-shaped surface
83
on an end of the housing
110
around the periphery of the first cylindrical chamber
67
which works, like the ring plate
8
of the first embodiment, as a stopper on which the small-diameter piston
4
hits when lifted upward.
The holder
26
of the check valve
22
is not secured on the end of the large-diameter piston
2
and placed in a lower end portion of the first cylindrical chamber
67
(i.e., the displacement amplifying chamber
3
) so that the holder
26
may not be lifted up following the upward movement of the large-diameter piston
2
. Thus, when the small-diameter piston
4
displaces, it will cause the fuel to flow into the hole
27
formed in the holder
26
, thereby suppressing the vibrations of the small-diameter piston
4
. The sectional area of the overlap of the first and second cylindrical chambers
67
and
68
is, as described above, smaller than that of the second cylindrical chamber
68
, which works as a damper suppressing the vibrations of the fuel (i.e., the vibrations of the small-diameter piston
4
) when flowing therethrough.
The check valve
22
works like the one in the first embodiment. Specifically, when a sufficient amount of fuel is, as shown in FIG.
6
(
a
), stored in the displacement amplifying chamber
3
, the pressure urging the valve plate
24
into constant contact with the end of the large-diameter piston
2
(i.e., the sum of the spring pressure of the conical spring
25
and the fuel pressure in the displacement amplifying chamber
3
) is greater than the pressure in the low-pressure passage
23
. Thus, even when the large-diameter piston
2
is lifted up, the valve plate
24
is kept closing the low-pressure passage
23
. Alternatively, when the amount of fuel stored in the displacement amplifying chamber
3
is too small to keep the valve plate
24
closing the low-pressure passage
23
, the upward movement of the large-diameter piston
3
, as shown in FIG.
6
(
b
), causes the valve plate
24
to move out of engagement with the end of the large-diameter piston
2
, thereby opening the low-pressure passage
23
, so that the fuel flows from the low-pressure passage
23
into the displacement amplifying chamber
3
, thereby keeping the pressure in the displacement amplifying chamber
3
at a desired level. The first cylindrical chamber
67
communicates with the second cylindrical chamber
68
through a gap between the outer wall of the holder
26
and the inner wall of the first cylindrical chamber
67
and the central hole
27
in the holder
26
.
As apparent from the above discussion, the second cylindrical chamber
68
is shifted laterally from the first cylindrical chamber
67
so as to define the stopper surface
83
which works to suppress undesirable motion of the small-diameter piston
4
. This eliminates the need for installing a separate stopper in the housing
110
, thus avoiding an increase in manufacturing costs of the fuel injector
100
. The small-diameter piston
4
is not installed in the longitudinal chamber
61
and in the cylindrical block
160
, thereby decreasing the length of the first cylindrical chamber
67
which is difficult to machine because of the eccentricity thereof.
Instead of the annular plates
120
and
130
in the first embodiment, only an annular plate
170
is disposed between the cylindrical block
160
and the nozzle body
140
. The high-pressure fuel passage
62
is, thus, different in geometry from the one in the first embodiment.
FIGS.
7
(
a
) and
7
(
b
) show the fuel injector
100
according to the third embodiment of the invention.
The three-way valve
5
is located coaxially with the small-diameter piston
4
. Specifically, a longitudinal center line of the small-diameter piston
4
is in alignment with the center of the valve member
51
of the three-way valve
5
(i.e., a line along which the valve member
51
moves). The three-way valve
5
works as a control valve which establishes or blocks communication between the fluid passage
52
leading to the back pressure chamber
71
formed behind the back end of the nozzle needle
7
and the high-pressure passage
53
leading to the high-pressure passage
62
or the low-pressure passage
54
leading to the drain passage
64
to thereby control the pressure in the back pressure chamber
71
. The nozzle needle
7
is disposed slidabley within a chamber formed in the nozzle body
140
which extends along a longitudinal center line of the nozzle body
140
and works to open and close spray holes
73
selectively.
The first cylindrical chamber
67
and the second cylindrical chamber
68
are, like the second embodiment, not co-axial. If the distance between the centers of sectional areas of the first and second cylindrical chambers
67
and
68
is, as shown in FIG.
7
(
b
), defined as e, and diameters of the large-diameter piston
2
and the small-diameter piston
4
are defined as D and d, respectively, a relation of 2
e>D−d
is preferably satisfied. This defines the crescent-shaped surface
83
on the end of the housing
110
around the periphery of the first cylindrical chamber
67
which works as a stopper on which the small-diameter piston
4
hits when lifted upward, thereby avoiding undesirable movement of the small-diameter piston
4
causing unwanted fuel injection. The sectional area A of the overlap of the first and second cylindrical chambers
67
and
68
is smaller than that of the second cylindrical chamber
68
and thus works as a damper suppressing the vibrations of the fuel (i.e., the vibrations of the small-diameter piston
4
) when the fuel flows therethrough.
The piezoelectric actuator
1
is disposed within the housing
110
eccentrically to the nozzle needle
7
, thereby providing an area sufficient to form the high-pressure passage
62
adjacent the piezoelectric actuator
1
. It is advisable that the high pressure passage
62
, as shown in
FIG. 9
, be opposed to the longitudinal center line of the piezoelectric actuator
1
across the longitudinal center line of the nozzle needle
7
and that the longitudinal center lines of the high-pressure passage
62
, the piezoelectric actuator
1
(i.e., the large-diameter piston
2
), and the nozzle needle
7
(i.e., the small-diameter piston
4
) intersect a common center line a, thereby allowing a peripheral wall of the high-pressure passage
62
to be thick enough to ensure a desired strength of the periphery wall of the high-pressure passage
62
.
The piezoelectric actuator
1
, the rod
21
, and the large-diameter piston
2
are co-axial. The small-diameter piston
4
, the valve member
51
of the three-way valve
5
, and the nozzle needle
7
are co-axial. This avoids the twist of the small-diameter piston
4
caused by the moment acting on the small-diameter piston
4
resulting from the reaction of the valve member
51
when moved, thus ensuring a steady fuel injection operation. The small-diameter piston
4
is co-axial with the nozzle needle
7
and disposed within the cylindrical block
160
which is separate from the housing
110
, thereby facilitating ease of machining the eccentric chambers
61
and
67
.
The fuel injector
100
is installed, as shown in
FIG. 8
, in an engine head
9
using a clamp
80
. The clamp
80
, as clearly shown in
FIG. 9
, has a pair of tines. The tines are fitted in parallel grooves
170
and
180
formed in an outer wall of the housing
110
to hold the housing
110
. The clamp
80
is attached to the engine head
9
through a bolt
81
in contact of the bottom of a vertical wall
82
with the surface of the engine head
9
. The vertical wall
82
extends downward from the end of the clamp
80
. The bolt
81
is so located that the longitudinal center line thereof intersects the common center line a in FIG.
9
. The retainer
150
of the fuel injector
100
is disposed in contact with the bottom of a hole formed in the engine head
9
through a gasket
92
. The head of the nozzle body
140
is exposed to a combustion chamber
91
.
The clamp
80
works as a lever which multiplies the force clamping the fuel injector
100
. Specifically, the clamp
80
is pivoted about a fixed point (i.e., fulcrum) at which the bottom of the vertical wall
82
rests on the surface of the engine block
9
. The force produced by fastening the bolt
81
is multiplied and exerted on the grooves
170
and
180
of the housing
110
. The grooves
170
and
180
are so formed in the peripheral wall of the housing
110
as to extend parallel to each other symmetrically with respect to the common center line a and perpendicular to the longitudinal center lines of the large-diameter piston
2
, the small-diameter piston
4
, and the high-pressure passage
62
. This causes two points of action to be defined in the grooves
170
and
180
at which the clamping force acts uniformly, thereby decreasing the deformation of the piezoelectric actuator
1
even if it has a relatively small flexural strength.
While the present invention has been disclosed in terms of the preferred embodiments in order to facilitate better understanding thereof, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments and modifications to the shown embodiments witch can be embodied without departing from the principle of the invention as set forth in the appended claims. For example, the three-way valve
5
is used to open and close the spray hole formed in the head of the nozzle body
140
, however, the invention is not limited to the same. Another known mechanism may be used to open and close the spray hole. Further, the actuator
1
is implemented by a piezoelectric device, however, another element such as a magnetostrictor may be used as long as it is so constructed as to expand and contract in response to input of an electric signal.
Claims
- 1. A fuel injector comprising:a housing; a control valve disposed movably within said housing to displace a needle for emitting a fuel spray; a large-diameter piston disposed slidably within said housing; a small-diameter piston disposed slidably within said housing to move said control valve; a displacement amplifying chamber filled with fluid to which said large-diameter piston and said small-diameter piston are exposed, said displacement amplifying chamber working to amplify and transmit displacement of said large-diameter piston to said small-diameter piston; an actuator working to displace said large-diameter piston; a stopper restricting movement of said small-diameter piston toward said displacement amplifying chamber; and a damper disposed within said displacement amplifying chamber to suppress vibrations of said small-diameter piston, wherein said damper is implemented by a hole formed in a ring plate secured or fitted slidably within said displacement amplifying chamber.
- 2. A fuel injector comprising:a housing; a control valve disposed movably within said housing to displace a needle for emitting a fuel spray; a large-diameter piston disposed slidably within said housing; a small-diameter piston disposed slidably within said housing to move said control valve; a displacement amplifying chamber filled with fluid to which said large-diameter piston and said small-diameter piston are exposed, said displacement amplifying chamber working to amplify and transmit displacement of said large-diameter piston to said small-diameter piston; an actuator working to displace said large-diameter piston; and a stopper restricting movement of said small-diameter piston toward said displacement amplifying chamber, wherein said stopper is implemented by a ring plate which is secured in said displacement amplifying chamber with a surface opposed to an end of said small-diameter piston through a given gap, said ring plate having formed therein a hole working as a damper suppressing vibrations of said small-diameter piston.
- 3. A fuel injector comprising:a housing; a control valve disposed movably within said housing to displace a needle for emitting a fuel spray; a large-diameter piston disposed slidably within said housing; a small-diameter piston disposed slidably within said housing to move said control valve; a displacement amplifying chamber filled with fluid to which said large-diameter piston and said small-diameter piston are exposed, said displacement amplifying chamber working to amplify and transmit displacement of said large-diameter piston to said small-diameter piston, the small-diameter piston being arranged coaxially with said control valve on one side of said displacement amplifying chamber; an actuator working to displace said large-diameter piston; a first cylindrical chamber formed in said housing within which said large-diameter piston is disposed; a second cylindrical chamber formed in said housing within which said small-diameter piston is disposed, said second cylindrical chamber communicating with said first cylindrical chamber through said displacement amplifying chamber, a longitudinal center line of said second cylindrical chamber extending eccentrically to a longitudinal center line of said first cylindrical chamber, wherein the longitudinal center line of said second cylindrical chamber is shifted a distance e from the longitudinal center line of said first cylindrical chamber, the distance e satisfying a relation of 2e> D−d where D is diameter of said large-diameter piston and d is diameter of said small-diameter piston.
- 4. A fuel injector as set forth in claim 3, wherein said actuator is implemented by one of a piezoelectric device and a magnetostrictor, said control valve being moved to control fluid pressure within a back pressure chamber to which an end of the needle is exposed for opening a spray hole, said large-diameter piston being arranged coaxially with said actuator on one side of said displacement amplifying chamber, the small-diameter piston being arranged coaxially with said control valve on the other side of said displacement amplifying chamber.
Priority Claims (2)
Number |
Date |
Country |
Kind |
2000-306150 |
Oct 2000 |
JP |
|
2000-399972 |
Dec 2000 |
JP |
|
US Referenced Citations (13)
Foreign Referenced Citations (5)
Number |
Date |
Country |
19844996 |
Apr 2000 |
DE |
0816670 |
Jan 1998 |
EP |
0909891 |
Apr 1999 |
EP |
11-166653 |
Jun 1999 |
JP |
11-351098 |
Dec 1999 |
JP |