Information
-
Patent Grant
-
6302333
-
Patent Number
6,302,333
-
Date Filed
Monday, April 19, 199925 years ago
-
Date Issued
Tuesday, October 16, 200122 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Scherbel; David A.
- Kim; Christopher S.
Agents
-
CPC
-
US Classifications
Field of Search
US
- 239 1021
- 239 1022
- 239 5339
- 239 5337
- 239 88
- 239 90
- 239 93
- 239 95
-
International Classifications
-
Abstract
An injector for a fuel injection system is provided with an injector housing in which a piezoelectric stack is located and with a valve housing connected with the injector housing in which a valve closing device with a jet needle is displaceably located. The valve closing device can be actuated by the piezoelectric stack. The valve closing device can be reset by a return device. A hydraulic following amplifier is located between the piezoelectric stack and the jet needle of the valve closing device. The amplifier has a displacement piston actuated by the piezoelectric stack. A control piston located downstream from the displacement piston and increases the displacement travel. A working piston that actuates the jet needle and increases the actuating force.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
This application claims the priority of German application 198 17 320.2, filed in Germany on Apr. 18, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an injector for fuel injection systems of the type comprising
an injector housing in which a piezoelectric stack is located,
a valve housing connected with the injector housing in which a valve closing device, which can be operated by the piezoelectric stack, and provided with a jet needle, is displaceably mounted,
a return device being provided by means of which the valve closing device can be returned,
a displacement piston actuated by the piezoelectric stack being located between the piezoelectric stack and the jet needle of the valve closing device, and
a control piston located downstream from the displacement piston that increases the adjustment travel.
An injector of the above noted general type is known from German Patent Document DE 195 19 191 C2. A hydraulic distance transformation unit is located between a piezoelectric stack and the jet needle of the injector. This unit has a displacement piston and a control piston located downstream from the displacement piston. However, the fact that the actuating force for the jet needle decreases during the travel transformation is disadvantageous.
A fuel injector for internal combustion engines is known from German Patent Document DE 195 00 706 A1, said valve having a hydraulic travel amplifier for converting a travel of the piezoelectric actuator. In this valve, passages that supply a fluid and carry fluid away are separate from one another, with the fluid being guided into an annular space by a passage located in the valve housing. However, the disadvantage of this injector is that, although the travel is amplified, the actuating force is reduced at the same time by the law of the lever. It is also disadvantageous that the passage of the fuel injector is subjected to a bending stress while fuel is being supplied to the annular chamber.
Reference is made regarding additional prior art to European Patent Document EP 0 218 895 B1, from which a metering valve for metering fluids or gases with a piezoelectric actuator is known. The pressure with which the valve is actuated acts on the piezoelectric actuator directly. At the pressures of approximately 1000 bars that develop in fuel injection systems, exact function of the valve is no longer guaranteed because of losses in the actuating travel of the jet needle. It is also disadvantageous that, after the jet needle lifts out of the valve seat, the fuel sprays uncontrollably into the combustion chamber through the resulting gap.
A goal of the present invention is to provide an injector of the type referred to above with which fuel injection can be performed with high accuracy and precision and without loss of fuel by transformation of the travel.
According to the invention, this goal is achieved by providing an arrangement wherein a working piston is provided for hydraulic following amplification that actuates the jet needle and increases the actuating force.
By using a hydraulic follower amplifier in the form of a working piston it is possible to decouple the system in terms of force. The travel of the piezoelectric stack is transmitted to a displacement piston. A control piston connected downstream from the displacement piston which increases the adjustment travel produced by the piezoelectric stack moves at a specified transformation ratio toward the jet needle. The jet needle is then actuated by a working piston that increases the actuating force.
The travel amplification according to the invention is decoupled from the force because the application of force to open the jet needle comes only from the system pressure, for example a rail pressure. Since there is no loss of power in the transformation, the actuation of the piezoelectric stack also does not have a negative influence on the opening of the jet needle.
In a highly advantageous improvement of certain preferred embodiments of the invention, provision is made such that a pressure compensating chamber is located for a hydraulic length compensation of the piezoelectric stack between the displacement piston and the control piston, said chamber being connected on one side with an overflow line of the control piston and on the other side with an overflow line of the displacement piston.
The pressure compensating chamber according to the invention together with its hydraulic compensating volume serves to compensate temperature and elongation effects of the piezoelectric stack.
In another likewise highly advantageous feature of certain preferred embodiments of the invention, provision can also be made for a pressure pad to be located between the jet needle and the working piston for hydraulic length compensation for the jet needle, with a length compensating chamber with a compensating spring being located between the pressure pad and the working piston.
As a result of this design according to the invention, hydraulic length compensation is achieved for the jet needle, due to thermal and hydraulic changes in length.
The injector according to the invention is suitable for jet needles that open outward as well as those that open inward using the same operating principle.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is an overall side sectional view of an injector constructed according to a preferred embodiment of the invention;
FIG. 2
is an enlargement of a portion of circle “X” in
FIG. 1
;
FIG. 3
is a sectional view through an injector with a jet needle that opens inward, constructed in accordance with another preferred embodiment of the invention; and
FIG. 4
is an enlargement of a portion of circle “Y” in FIG.
3
.
DETAILED DESCRIPTION OF THE DRAWINGS
The injector
1
shown in
FIG. 1
has an injector housing
2
, a piezoelectric guide
3
in which a piezoelectric stack
4
is located and a valve housing connected with injector housing
2
by means of a union nut
5
. A valve closing device
7
is displaceably mounted in valve housing
6
.
Valve closing device
7
has tappet
8
as a jet needle with a valve stem
9
into which tappet
8
fits.
At the end of the valve stem
9
facing the combustion chamber, a sealing member is provided in the form of a shoulder
10
. Valve housing
6
, shoulder
10
, and a separating device connected with valve stem
9
, which is designed as a pressure compensating cylinder
11
, form an annular gap
12
that is filled with fuel during operation. When valve
1
is open, a precisely metered quantity of fuel is sprayed from annular gap
12
into a combustion chamber, not shown in the drawing. For this purpose, a flow restricter
13
is used that is pressed by a spring device
14
against a cross-sectional area of shoulder
10
of valve stem
9
. Spring device
14
abuts a cylindrical stop
15
.
An annular chamber
16
is formed between piezoelectric guide
3
and injector housing
2
, in which chamber a line
17
that supplies fuel to valve
1
terminates. From here the fuel flows through bores
18
into annular gap
12
.
Piezoelectric stack
4
is located completely in the low-pressure area of passages that carry fuel away and therefore is not adversely affected by the fuel supplied at very high pressure. The reverse flow of fuel in this pressure area takes place in an annular chamber
19
where it escapes from the end of piezoelectric stack
4
that faces away from the combustion chamber.
If a control voltage is applied to piezoelectric stack
4
, it produces in known fashion an elongation of piezoelectric stack
4
, causing valve closing device
7
to open, since a corresponding gap results between shoulder
10
of valve stem
9
and a valve seat
6
and/or the flow restricter
13
. To end the injection process, the control voltage is switched off, whereupon piezoelectric stack
4
again shrinks to its original length. Jet needle
8
is returned by a jet needle spring
51
that abuts an annular bead
55
of jet needle
8
.
FIG. 2
shows the transmission of force from piezoelectric stack
4
to jet needle
8
to open it. Piezoelectric stack
4
is surrounded by a protective tube
20
provided with a seal
20
A on the end. The sealing cap
20
A of protective tube
20
is located axially between piezoelectric stack
4
and a displacement piston
21
, and thus actuates the piston when piezoelectric stack
4
lengthens. A control piston
22
is located axially in front of displacement piston
21
relative to the combustion chamber. Control piston
22
has a smaller effective pressure area than displacement piston
21
. The hydraulic transformation ratios result from the different geometries and/or diameter ratios of the displacement piston
21
and control piston
22
. A piezoelectric stack pretensioning is produced by a plurality of cup springs
23
arranged one behind the other, said springs being located in a pressure compensating chamber
24
. Pressure compensating chamber
24
is filled with test oil or with fuel. Filling and/or pressure compensation are performed by deliberate leaks between control piston
22
, displacement piston
21
, and the surrounding cylindrical housing
25
. A feed
26
terminates in cylindrical housing
25
, said feed being connected with the annular supply chamber
16
. In this fashion, cylindrical housing
25
is mounted axially and nonrotatably. As a result of the specified transformation ratio between displacement piston
21
and control piston
22
, control piston
22
is moved more than displacement piston
21
.
An annular chamber
29
is supplied with system pressure (rail pressure) from annular chamber
16
from supply line
26
by an annular groove
27
and a diagonal bore
28
located in control piston
22
. Annular chamber
29
is formed between control piston
22
and a sliding sleeve
30
.
If piezoelectric stack
4
receives a control voltage, the protective tube
20
, displacement piston
21
, and control piston
22
are displaced in the direction of arrow B. A leading control edge
31
opens between control piston
22
and sliding sleeve
30
, producing a high-pressure connection through annular chamber
29
with a bore
32
in sliding sleeve
30
and therefore to a working cylinder and/or working pressure chamber
33
connected therewith, which is located radially between sliding sleeve
30
with trailing control edge
36
and cylindrical housing
25
and axially between one end of cylindrical housing
25
and a working piston
34
. As a result of working pressure chamber
33
being charged with high pressure, working piston
34
is displaced in the same direction as control piston
22
in the direction of arrow B. As a result of the pretensioning spring
35
, sliding sleeve
30
follows working piston
34
and seals off pressure chamber
33
with trailing control edge
36
. Sliding sleeve
30
follows the working piston
34
until it again strikes the leading control edge
31
between control piston
22
and sliding sleeve
30
and/or blocks this control edge. As a result, the working pressure chamber
33
is hydraulically tight and a working piston remains in this position. As may be seen, displacement piston
21
specifies the path for the following amplifier consisting of displacement piston
21
, control piston
22
, sliding sleeve
30
, and working piston
34
, which is then switched to jet needle
8
.
Because of the differences in diameter of the effective piston areas between displacement piston
21
and control piston
22
, control piston
22
travels a greater distance.
If the control voltage is removed from piezoelectric stack
4
, displacement piston
21
will be pushed back by the cup springs
23
. The increase in volume in pressure compensating chamber
24
enables return spring
52
, pretensioned between jet needle
8
and an axial depression in the end of control piston
22
, to push control piston
22
backward together with sliding sleeve
30
against the direction of arrow B. As a result, an annular gap
38
is produced between trailing control edge
36
and working piston
34
that makes it possible for oil to flow out from working cylinder
33
in the direction of pressure pad
42
and further into annular chamber
19
. The escaped amount allows working piston
34
to return to its starting position.
A hydraulic length compensating chamber
39
for jet needle
8
, produced by thermal and hydraulic changes in length, is thus formed by cylindrical housing
25
, working piston
34
, compensating spring
40
, compensating bore
41
, and pressure pad
42
. Changes in length and therefore changes in volume are compensated by bore
41
. In this manner, even if jet needle
8
is compressed, working piston
34
always abuts the return control edge.
Protective tube
20
has the purpose of ensuring that the piezoelectric stack
4
does not come in contact with fuel.
A hydraulic length compensation of piezoelectric stack
4
is achieved by the deliberate leakage
73
of control piston
22
and a capillary
74
machined in the outside diameter of displacement piston
21
through which leakage reaches the return line and/or annular chamber
19
.
For practical purposes, there are two systems, one on the piezoelectric stack side and the other on the jet needle side, with the parts always being under pretension and therefore always ensuring a contact, regardless of lengthwise expansion effects or temperature differences. It is also important in this respect that the overflow feed into pressure compensating chamber
24
roughly corresponds to the amount that escapes from it through the overflow line in displacement piston
21
(capillary).
This also means that the pressure in pressure compensating chamber
24
must be lower than the spring force of return spring
52
. Cup springs
23
ensure that the displacement piston
21
always abuts the piezoelectric stack
4
and the piezoelectric stack
4
is simultaneously pretensioned.
The mechanical performance of piezoelectric stack
4
is used exclusively for valve positioning. In other words, this means that the increase in force has nothing directly to do with piezoelectric stack
4
. Therefore, it is not the piezoelectric force that is used to actuate jet needle
8
, but only the pressure developed in the pressure chamber of working cylinder
33
, and this pressure is proportional to the actuating force.
The embodiment described above relates to a jet needle
8
that opens outward, while the direction of travel of piezoelectric stack
4
corresponds to the direction of travel of the opening of the jet. It is advantageous to keep the loss of oil through lengthwise groove
19
to 3 to 5 bars counterpressure (cavity formation, cavitation).
FIGS. 3 and 4
show an injector in which jet needle
8
′ opens inward to inject fuel. This means that the actuating direction of piezoelectric stack
4
′ is opposite to the direction of actuation of jet needle
8
′. In this embodiment, we have used the same reference numbers with a corresponding superscript for those parts that have the same functions as in the embodiment according to
FIGS. 1 and 2
. That is, the injector
1
′, injector housing
2
′, guide
3
′, valve housing
6
′, valve closing device
7
′ and protective tube
20
′ correspond in function to
FIGS. 1 and 2
.
In contrast to the embodiment according to
FIG. 1
, an annular line
16
is not provided for supplying rail pressure, but a stub
43
. An overflow line
44
is provided to return fuel. The piezoelectric pretensioning can be set in pressure compensating chamber
24
′ by cup springs or coil springs
23
′. In this injector system, the direction of travel must be reversed when piezoelectric stack
4
′ is actuated. In this case, the space in which a spring
56
is located is only a vent space. The pressure compensating chamber
24
′ on the other hand is compressed with a control voltage on piezoelectric stack
4
.
In addition, a difference in diameter is operational in pressure compensating chamber
24
′. The difference in the diameters of the effective piston areas of compensating piston
21
′ and control piston
22
′ in order to achieve the desired transformation ratios and hence a greater travel for control piston
22
′, result from a smaller effective end area
46
that acts in the direction of piezoelectric stack
4
′, by comparison with an effective end area of
21
′, which is directed toward jet needle
8
′. If the pressure compensating chamber
24
′ is made smaller by a control voltage on piezoelectric stack
4
′, a pressure buildup occurs in this chamber that actuates control piston
22
′ opposite to the direction of action of piezoelectric stack
4
′ in the direction of arrow C. With control piston
22
′ in this displacement direction, it carries sliding sleeve
30
′ in direction C as well. As a result of this displacement, pressure release occurs in a working cylinder
33
′ which corresponds to the working cylinder in the embodiment shown in
FIGS. 1 and 2
. The pressure relief occurs in working cylinder
33
′ into overflow line
44
through bores
48
in working piston
34
′. Since the direction is reversed in this embodiment, it means that the leading control edge
31
′ closes jet needle
8
′ and trailing control edge
36
′ between sliding sleeve
30
′ and working piston
34
′ opens jet needle
8
′ and hence creates a connection between supply line
43
and injection holes
49
for injecting fuel.
To close injection holes
49
following elimination of the control voltage from piezoelectric stack
4
′, a pressure buildup again occurs via leading control edge
31
′ in working cylinder
33
′, since sliding sleeve
30
′ encounters working cylinder
34
′ by return control edge
36
′, interrupting the connection to overflow line
44
. This means that when jet needle
8
′ is in its closed position, the full system pressure is available in the pressure chamber of working cylinder
33
′, since the pressure chamber of working cylinder
33
′ is supplied with the full system pressure through diagonal bores
53
in sliding sleeve
30
′ by means of leading control edge
31
′ in conjunction with supply line
26
′ and an annular chamber
50
between sliding sleeve
30
′ and control piston
22
′. If working piston
34
′ shifts slightly, leading control edge
31
′ opens immediately and forms the connection to the high-pressure side at this edge. It is only when control piston
22
′ is displaced in direction C as a result of a control voltage being applied to piezoelectric stack
4
′ that the pressure in working cylinder
33
′ drops accordingly and jet needle
8
′ can open to inject fuel.
The fuel supply for the pressure compensating chamber
24
′ comes through a connecting passage
54
in control piston
22
′ to the feed
26
.
Just as in the case of the coil spring
35
in the embodiment shown in
FIGS. 1 and 2
, sliding sleeve
30
is pressed by a cup spring
35
′ against working piston
34
′. The control piston
22
′ is returned by a cup spring
52
′ that abuts working piston
34
′.
It is also advantageous in this regard to keep the flow of overflow oil through lengthwise groove
19
to 3 to 5 bars counterpressure.
The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.
Claims
- 1. Injector for fuel injection systems, comprising:an injector housing in which a piezoelectric stack is located, a valve housing connected with the injector housing in which a valve closing device, which is operated by the piezoelectric stack, and provided with a jet needle, is displaceably mounted, a return device being provided by means of which the valve closing device is returned, a displacement piston actuated by the piezoelectric stack being located between the piezoelectric stack and the jet needle of the valve closing device, and a control piston located downstream from the displacement piston that increases adjustment travel, wherein a working piston downstream from the control piston is provided for hydraulic following amplification that actuates the jet needle and increases an actuating force.
- 2. Injector according to claim 1, wherein an effective pressure area of the control piston is smaller than that of the displacement piston.
- 3. Injector according to claim 1, wherein a sliding sleeve is located between the control piston and the working piston, at which sliding sleeve a leading control edge and a trailing control edge are provided to increase the pressure and reduce the pressure in a working chamber of a working cylinder located between the control piston and working piston.
- 4. Injector according to claim 2, wherein a sliding sleeve is located between the control piston and the working piston, at which sliding sleeve a leading control edge and a trailing control edge are provided to increase the pressure and reduce the pressure in a working chamber of a working cylinder located between the control piston and working piston.
- 5. Injector according to claim 1, wherein at least one pretensioning device is located between the piezoelectric stack and the jet needle.
- 6. Injector according to claim 2, wherein at least one pretensioning device is located between the piezoelectric stack and the jet needle.
- 7. Injector according to claim 3, wherein at least one pretensioning device is located between the piezoelectric stack and the jet needle.
- 8. Injector according to claim 1, wherein a pressure compensating chamber is provided for a hydraulic length compensation of the piezoelectric stack between the displacement piston and the control piston, said compensation chamber being connected on the one hand with an overflow line of the control piston and on the other hand with an overflow line of the displacement piston.
- 9. Injector according to claim 2, wherein a pressure compensating chamber is provided for a hydraulic length compensation of the piezoelectric stack between the displacement piston and the control piston, said compensation chamber being connected on the one hand with an overflow line of the control piston and on the other hand with an overflow line of the displacement piston.
- 10. Injector according to claim 3, wherein a pressure compensating chamber is provided for a hydraulic length compensation of the piezoelectric stack between the displacement piston and the control piston, said compensation chamber being connected on the one hand with an overflow line of the control piston and on the other hand with an overflow line of the displacement piston.
- 11. Injector according to claim 5, wherein a pressure compensating chamber is provided for a hydraulic length compensation of the piezoelectric stack between the displacement piston and the control piston, said compensation chamber being connected on the one hand with an overflow line of the control piston and on the other hand with an overflow line of the displacement piston.
- 12. Injector according to claim 1, wherein a pressure pad is provided for hydraulic length compensation for the jet needle between the jet needle and the working piston, with a length compensating chamber with a compensating spring being located between the pressure pad and the working piston.
- 13. Injector according to claim 2, wherein a pressure pad is provided for hydraulic length compensation for the jet needle between the jet needle and the working piston, with a length compensating chamber with a compensating spring being located between the pressure pad and the working piston.
- 14. Injector according to claim 3, wherein a pressure pad is provided for hydraulic length compensation for the jet needle between the jet needle and the working piston, with a length compensating chamber with a compensating spring being located between the pressure pad and the working piston.
- 15. Injector according to claim 5, wherein a pressure pad is provided for hydraulic length compensation for the jet needle between the jet needle and the working piston, with a length compensating chamber with a compensating spring being located between the pressure pad and the working piston.
- 16. Injector according to claim 8, wherein a pressure pad is provided for hydraulic length compensation for the jet needle between the jet needle and the working piston, with a length compensating chamber with a compensating spring being located between the pressure pad and the working piston.
- 17. Injector according to claim 1, wherein a reversal of direction between the displacement piston and the control piston takes place, which jet needle opens inward against the direction of piezoelectric actuation of the piezoelectric stack.
- 18. Injector according to claim 1, wherein the piezoelectric stack is surrounded by a piezoelectric guide.
- 19. Injector according claim 18, wherein an annular chamber is formed between the piezoelectric guide and the injector housing, in which annular chamber a fuel supply line terminates.
Priority Claims (1)
Number |
Date |
Country |
Kind |
198 17 320 |
Apr 1998 |
DE |
|
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Number |
Name |
Date |
Kind |
5413076 |
Koenigswieser et al. |
May 1995 |
|
5697554 |
Autwaerter et al. |
Dec 1997 |
|
5931390 |
Hoffmann et al. |
Aug 1999 |
|
Foreign Referenced Citations (3)
Number |
Date |
Country |
19500706A1 |
Jul 1996 |
DE |
19519191C2 |
Dec 1996 |
DE |
0218895B1 |
Apr 1987 |
EP |