Information
-
Patent Grant
-
6400066
-
Patent Number
6,400,066
-
Date Filed
Friday, June 30, 200024 years ago
-
Date Issued
Tuesday, June 4, 200222 years ago
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Inventors
-
Original Assignees
-
Examiners
- Sircus; Brian
- Zarroli; Michael C.
-
CPC
-
US Classifications
Field of Search
US
- 310 346
- 123 472
- 239 1021
- 239 1022
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International Classifications
-
Abstract
A fuel injector comprises a tube assembly, a stem assembly, and a plurality of sets of piezoelectric elements. The tube assembly includes a seat defining an opening through which fuel enters an internal combustion engine. The stem assembly includes a cap and a stem that are relatively movable with respect to one another. A gap is located between the stem and cap when the stem contiguously engages the seat such that fuel flow through the opening is prevented. A first set of piezoelectric elements moves the cap in response to a first electric field, and a second set of piezoelectric elements moves the first set of piezoelectric elements in response to a second electric field. A sensor measuring the gap compensates the second electric field for physical changes in at least one of the tube and stem assemblies.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an electronic compensator for a piezoelectric actuator, and more particularly to a fuel injector actuator having a plurality of sets of piezoelectric elements, at least one of which is connected to an electronic compensator circuit.
A conventional piezoelectric element is a ceramic structure whose axial length changes in the presence of an electric field created by applying a voltage across the element. In typical applications, the axial length of the element can change by, for example, approximately 0.12%. In a stacked configuration of elements, the change in the total axial length of the stack is equal to the sum of the changes in axial length of each element in the stack. As is known, applying a voltage to a piezoelectric element, or to a stack of piezoelectric elements, results in a nearly instantaneous expansion of the actuator and an instantaneous movement of any structure connected to the actuator.
It is known to use a single set of piezoelectric elements, i.e., a stack of piezoelectric elements across which a common voltage is applied, to actuate a fuel injector for an internal combustion engine. Such piezoelectric actuators precisely open and close an injector valve element for precisely metering fuel flow into a combustion chamber.
The thermal and pressure effects present in the piezoelectrically actuated injector's operating environment can cause dimensional changes within the injector. These dimensional changes result in a change to the injector's stroke, causing an unstable shift in its flow characteristics. To compensate for the dimensional changes, it is known to fabricate injectors from exotic materials, which exhibit low thermal expansion. In addition, it is also known to calibrate injector strokes to anticipate elongation of the valve body. However, these methods are costly and inefficient.
SUMMARY OF THE INVENTION
Advantages of the claimed invention include increasing the stroke of the piezoelectric actuator, compensating for thermal expansion in different operating condition, and compensating for mechanical deformation under different fuel pressures and assembly stresses.
The present invention provides a fuel injector that comprises a tube assembly having a longitudinal axis extending between a first end and a second end; a seat secured at the second end of the tube assembly, the seat defining an opening; a stem assembly including a cap movable with respect to the tube assembly and a stem movable with respect to the seat, the stem moving between a first position wherein the stem contiguously engages the seat such that fuel flow through the opening is prevented and a second position wherein the stem is spaced from the seat such that fuel flow through the opening is permitted; a gap between the cap and the stem in the first position, the gap promoting sealing between the seat and the stem in the first position and being eliminated in the second position of the stem; a first set of piezoelectric elements contiguously engaging the cap, the first set of piezoelectric elements moving the cap in response to a first electric field; and a second set of piezoelectric elements moving the first set of piezoelectric elements in response to a second electric field.
The present invention also provides a fuel injection system that comprises a fuel injector and a control circuit. The fuel injector includes a tube assembly having a longitudinal axis extending between a first end and a second end; a seat secured at the second end of the tube assembly, the seat defining an opening; a stem assembly including a cap movable with respect to the tube assembly and a stem movable with respect to the seat, the stem moving between a first position wherein the stem contiguously engages the seat such that fuel flow through the opening is prevented and a second position wherein the stem is spaced from the seat such that fuel flow through the opening is permitted; a gap between the cap and the stem in the first position, the gap promoting sealing between the seat and the stem in the first position and being eliminated in the second position of the stem; a first set of piezoelectric elements moving the stem assembly in response to a first electric field; and a second set of piezoelectric elements moving the first set of piezoelectric elements in response to a second electric field. The control circuit includes a first driver supplying a first electrical signal generating the first electric field; a second driver supplying a second electrical signal generating the second electric field; a sensor measuring the gap and providing an output signal proportional to gap size; and a controller comparing the output signal to a reference signal and adjusting the second electrical signal in response to changes in the gap size.
The present invention also provides a method of compensating a fuel injector for thermal expansion and mechanical deformation. The fuel injector includes a tube assembly having a longitudinal axis extending between a first end and a second end, a seat secured at the second end of the tube assembly and defining an opening, a stem assembly including a cap movable with respect to the tube assembly and a stem movable with respect to the seat, the stem moving between a first position wherein the stem contiguously engages the seat such that fuel flow through the opening is prevented and a second position wherein the stem is spaced from the seat such that fuel flow through the opening is permitted, a gap between the cap and the stem in the first position, a first set of piezoelectric elements moving the stem assembly in response to a first electric field, and a second set of piezoelectric elements moving the first set of piezoelectric elements in response to a second electric field. The method comprises generating an output signal that is proportional to at least one of thermal expansion and mechanical deformation in at least one of the tube and stem assemblies; comparing the output signal with a reference signal; and adjusting the second electric field in response to variations between the output signal and the reference signal.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawing, which is incorporated herein and constitutes a part of this specification, illustrates an embodiment of the invention, and, together with the general description given above and the detailed description given below, serve to explain features of the invention.
FIG. 1
is a cross-sectional view of a fuel injector including a piezoelectric actuator according to the claimed invention.
FIG. 2
is a schematic illustration of a control circuit for a piezoelectric actuator according to the claimed invention.
FIG. 3
is a diagram illustrating four examples of lift summation for a two set piezoelectric actuator according to the claimed invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A fuel injector can include a piezoelectric multi-element actuator that changes in length in response to an electric field, which is created by a control voltage applied across the piezoelectric elements. The actuator can be coupled to a valve member for opening and closing the fuel injector.
Referring to
FIG. 1
, a fuel injector includes a tube assembly
10
having a first end portion
20
, a central portion
22
, and a valve body
24
at a second end portion. The first portion
20
, central portion
22
, and valve body
24
can be aligned along an axis
15
and can be fixed together. A seat
26
having an opening
28
is fixed to the valve body
24
at an opposite end from the central portion
22
. Fuel can be supplied to a chamber
34
connected to the opening
28
.
A stem assembly
40
extends along the axis
15
and is reciprocally mounted with respect to the seat
26
. The stem assembly
40
moves between a first position wherein the stem assembly
40
contiguously engages the seat
26
such that fuel flow through the opening
28
is prevented and a second position wherein the stem assembly
40
is spaced from the seat
26
such that fuel flow through the opening
28
is permitted. A resilient element (not shown), which can be located in the chamber
34
, biases the stem assembly
40
toward the first position.
The stem assembly
40
is displaced toward the first position by a piezoelectric actuator assembly
50
. According to the claimed invention, the piezoelectric actuator includes at least a first set of piezoelectric elements
52
and a second set of piezoelectric elements
54
that are assembled together in series, and can be commonly aligned along,:the axis
15
. These two sets
52
,
54
can operate individually or simultaneously; the control voltages, and hence the electric fields, for each set
52
,
54
can be static or dynamic; and the stack lengths can be equal or different, as needed and available.
According to the claimed invention, the stem assembly
40
includes a stem
46
, which cooperatively engages the seat
26
, and a cap
48
that is moved by the piezoelectric actuator
50
with respect to the tube assembly
10
.
When the stem assembly
40
is in the first position, a gap
47
separates contiguous engagement between the stem
46
and the cap
48
. It is desirable to have a minimal gap
47
to promote sealing between the seat
26
and the stem
46
. However, if the gap
47
is too large, the stroke of the stem
46
due to the displacement of the piezoelectric actuator
50
is diminished, and if the gap
47
is absent, i.e., there is contiguous engagement of the stem
46
and cap
48
in the first position of the stem assembly
40
, the sealing force between the stem
46
and the seat
26
may be relieved.
In practice, the fuel injector exhibits dimensional changes due to thermal and pressure effects present in the injector's operating environment. These dimensional changes have a direct effect upon the injector's operating characteristics and performance. The claimed invention determines and, if necessary, corrects for these dimensional changes. Specifically, the size of the gap
47
between the stem
46
and the cap
48
is determined and compared to a target range for the gap
47
.
Referring also to
FIG. 2
, a sense-coil
60
can be used to determine the size of the gap
47
between the stem
46
and the cap
48
. The sense-coil
60
is located so as to surround the junction between the stem
46
and the cap
48
. As shown in
FIG. 1
, for example, a bobbin for the sense-coil
60
and a guide bushing for the stem
46
can be combined into a single multi-function unit.
During the injector's operation, changes in internal fuel pressure and external temperature will cause the injector to experience dimensional changes. These dimensional changes. will result in an increase/decrease of the gap
47
between the stem
46
and the cap
48
. The sense-coil
60
outputs a signal, which corresponds to the size of the gap
47
, to a controller
62
. The controller
62
interprets and compares the output signal to one or more reference signals that correspond to a target gap range. If correction is required, i.e., if the size of the gap
47
is outside the target gap range, a closed loop circuit compensates the voltage applied to the second set of piezoelectric elements
54
to maintain the target gap range. The closed loop circuit can include the sense-coil
60
, the controller
62
, a driver
64
supplying the compensated voltage signal, and the second set of piezoelectric elements
54
. Controlled actuation of the second set of piezoelectric elements
54
permits control of the gap size, and allows for optimizing injector performance.
Another driver
66
supplies a voltage signal generating the electric field for the first set of piezoelectric elements
52
. As shown in
FIG. 3
, the voltage signal applied across the first set of piezoelectric elements
52
can be different from the voltage signal applied across the second set of piezoelectric elements
54
. Accordingly, the claimed invention can improve performance and control flexibility of a piezoelectrically actuated fuel injector . For example. the first and second sets of piezoelectric elements
52
,
54
can increase the valve lift, compensate for component length changes due to thermal load and mechanical load, or shape a particular lift trace.
The claimed invention is not limited to two sets of piezoelectric elements, and can included three or more sets of piezoelectric elements.
While the present invention has been disclosed with reference to certain embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the present invention, as defined in the appended claims. Accordingly, it is intended that the present invention not be limited to the described embodiments, but that it have the full scope defined by the language of the following claims, and equivalents thereof.
Claims
- 1. A fuel injection system comprising:a fuel injector including: a tube assembly having a longitudinal axis extending between a first end and a second end; a seat secured at the second end of the tube assembly, the seat defining an opening; a stem assembly including a cap movable with respect to the tube assembly and a stem movable with respect to the seat, the stem moving between a first position wherein the stem contiguously engages the seat such that fuel flow through the opening is prevented and a second position wherein the stem is spaced from the seat such that fuel flow through the opening is permitted; a gap between the cap and the stem in the first position, the gap being eliminated in the second position of the stem; a first set of piezoelectric elements moving the stem assembly in response to a first electric field; and a second set of piezoelectric elements moving the first set of piezoelectric elements in response to a second electric field; and; a control circuit including: a first driver supplying a first electrical signal generating the first electric field; a second driver supplying a second electrical signal generating the second electric field; a sensor measuring the gap and providing an output signal proportional to gap size; and a controller comparing the output signal to a reference signal and adjusting the second electrical signal in response to changes in the gap size.
- 2. The fuel injection system according to claim 1, wherein the sensor includes a coil surrounding the gap.
- 3. The fuel injection system according to claim 1, wherein changes in the gap size are proportional to physical changes in at least one of the tube and stem assemblies.
- 4. The fuel injection system according to claim 3, wherein the physical changes include at least one of thermal expansion and mechanical deformation.
- 5. The fuel injection system according to claim 1, wherein electromechanical extension and contraction of the first set of piezoelectric elements is along a first axis, and electromechanical extension and contraction of the second set of piezoelectric elements is along a second axis substantially parallel to the first axis.
- 6. The fuel injection system according to claim 1, wherein electromechanical extension and contraction of the first set of piezoelectric elements is along a first axis, and electromechanical extension and contraction of the second set of piezoelectric elements is along a second axis substantially collinear to the first axis.
- 7. The fuel injection system according to claim 1, wherein the first electric field moves the stem assembly from the first position to the second position.
- 8. The fuel injection system according to claim 7, wherein the second electric field also moves the stem assembly from the first position to the second position.
- 9. A method of compensating a fuel injector for thermal expansion and mechanical deformation, the fuel injector including a tube assembly having a longitudinal axis extending between a first end and a second end, a seat secured at the second end of the tube assembly and defining an opening, a stem assembly including a cap movable with respect to the tube assembly and a stem movable with respect to the seat, the stem moving between a first position wherein the stem contiguously engages the seat such that fuel flow through the opening is prevented and a second position wherein the stem is spaced from the seat such that fuel flow through the opening is permitted, a gap between the cap and the stem in the first position, a first set of piezoelectric elements moving the stem assembly in response to a first electric field, and a second set of piezoelectric elements moving the first set of piezoelectric elements in response to a second electric field, the method comprising:generating an output signal that is proportional to at least one of thermal expansion and mechanical deformation in at least one of the tube and stem assemblies; comparing the output signal with a reference signal; and adjusting the second electric field in response to variations between the output signal and the reference signal.
- 10. The method according to claim 9, the generating an output signal includes measuring the gap.
- 11. A fuel injector comprising:a tube assembly having a longitudinal axis extending between a first end and a second end; a seat secured at the second end of the tube assembly, the seat defining an opening; a stem assembly including a cap movable with respect to the tube assembly and a stem movable with respect to the seat, the stem moving between a first position wherein the stem contiguously engages the seat such that fuel flow through the opening is prevented and a second position wherein the stem is spaced from the seat such that fuel flow through the opening is permitted; a gap between the cap and the stem in the first position, the gap being eliminated in the second position of the stem; a first set of piezoelectric elements contiguously engaging the cap, the first set of piezoelectric elements moving the cap in response to a first electric field; and a second set of piezoelectric elements moving the first set of piezoelectric elements in response to a second electric field, wherein the second electric field also moves the stem assembly from the first position to the second position.
- 12. The fuel injector according to claim 11, comprising:a sensor measuring the gap and being electrically interconnected with the second electrical field.
- 13. The fuel injector according to claim 12, wherein the sensor includes a coil surrounding the gap.
- 14. The fuel injector according to claim 12, wherein the gap has a size that is proportional to physical changes in at least one of the tube and stem assemblies.
- 15. The fuel injector according to claim 14, wherein the physical changes include at least one of thermal expansion and mechanical deformation.
- 16. The fuel injector according to claim 11, wherein electromechanical extension and contraction of the first set of piezoelectric elements is along, a first axis, and electromechanical extension and contraction of the second set of piezoelectric elements is along a second axis substantially parallel to the first axis.
- 17. The fuel injector according to claims 16, wherein the first and second axes are substantially collinear.
- 18. The fuel injector according to claim 11, wherein the first electric field moves the stem assembly from the first position to the second position.
- 19. The fuel injector according to claim 11, wherein electromechanical extension and contraction of the first set of piezoelectric elements is along a firstlaxis, and electromechanical extension and contraction of the second set of piezoelectric elements is along a second axis substantially collinear to the first axis.
- 20. The fuel injector according to claim 11, wherein the second electric field also moves the stem assembly from the first position to the second position.
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