U.S. patent application number 13/713610 was filed with the patent office on 2014-06-19 for dielectric sensor arrangement and method for swashplate angular position detection.
This patent application is currently assigned to CATERPILLAR INC.. The applicant listed for this patent is Hongliu Du. Invention is credited to Hongliu Du.
Application Number | 20140169987 13/713610 |
Document ID | / |
Family ID | 50931103 |
Filed Date | 2014-06-19 |
United States Patent
Application |
20140169987 |
Kind Code |
A1 |
Du; Hongliu |
June 19, 2014 |
Dielectric Sensor Arrangement and Method for Swashplate Angular
Position Detection
Abstract
Swashplate angle sensing arrangement for a variable displacement
pump a nonrotating swashplate and a rotating pump barrel includes a
dielectric sensor in a swashplate angle sensing arrangement. The
arrangement includes a sensing probe coupled to the casing, a
sensor target coupled to the swashplate, and a controller
configured to direct an alternating current through the sensing
probe to establish an impedance between the probe and the target,
and to determine voltage across the probe. The controller is
further adapted to determine the angle of the swashplate relative
to the casing based on the determined voltage.
Inventors: |
Du; Hongliu; (Naperville,
IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Du; Hongliu |
Naperville |
IL |
US |
|
|
Assignee: |
CATERPILLAR INC.
Peoria
IL
|
Family ID: |
50931103 |
Appl. No.: |
13/713610 |
Filed: |
December 13, 2012 |
Current U.S.
Class: |
417/53 ;
417/222.1 |
Current CPC
Class: |
F04B 1/324 20130101;
F04B 1/2078 20130101; F04B 1/146 20130101; F04B 1/295 20130101;
F04B 49/12 20130101 |
Class at
Publication: |
417/53 ;
417/222.1 |
International
Class: |
F04B 49/12 20060101
F04B049/12 |
Claims
1. A swashplate angle sensing arrangement for a variable
displacement pump having a casing containing a nonrotating
swashplate adapted to pivot relative to an axis of rotation of a
pump barrel, the swashplate defining a swashplate angle relative to
a plane substantially perpendicular to the axis of rotation of the
pump barrel, the swashplate angle sensing arrangement comprising: a
sensing probe coupled to the casing; a sensor target coupled to the
swashplate; and a controller configured to direct an alternating
current through the sensing probe to establish an impedance between
the sensing probe and the sensor target, and to determine a voltage
across the sensing probe, the controller further adapted to
determine the angle of the swashplate relative to the casing based
on the determined voltage.
2. The swashplate angle sensing arrangement of claim 1, wherein the
sensing probe includes a conductive portion exposed to an interior
of the casing and a nonconductive portion disposed between the
conductive portion and the casing.
3. The swashplate angle sensing arrangement of claim 2, wherein the
conductive portion includes a wire.
4. The swashplate angle sensing arrangement of claim 1 wherein the
sensor target includes a conductive portion and a nonconductive
portion disposed between the conductive portion and the
swashplate.
5. The swashplate angle sensing arrangement of claim 1, further
including fluid media between the sensing probe and the sensor
target.
6. The swashplate angle sensing arrangement of claim 1 wherein the
controller is configured to direct the alternating current between
the sensing probe and the casing.
7. The swashplate angle sensing arrangement of claim 6 wherein the
established impedance changes as the angle of the swashplate
changes.
8. The swashplate angle sensing arrangement of claim 1 wherein the
established impedance changes as the angle of the swashplate
changes.
9. The swashplate angle sensing arrangement of claim 7 wherein the
sensing probe includes a conductive portion exposed to an interior
of the casing and a nonconductive portion disposed between the
conductive portion and the casing, the sensor target includes a
conductive portion and a nonconductive portion disposed between the
conductive portion and the swashplate, and fluid media between the
sensing probe and the sensor target.
10. A variable displacement pump, comprising: a casing; a barrel
disposed within the casing and adapted to rotate about an axis of
rotation; a nonrotating swashplate disposed in the casing and
adapted to pivot relative to the axis; a sensor target coupled to
the swashplate; a sensing probe coupled to the casing and proximate
the sensor target; and a controller configured to direct a current
across the sensing probe to establish an impedance between the
sensing probe and the sensor target, and to determine a voltage
across the sensing probe, the controller further adapted to
determine an angle of the swashplate based on the determined
voltage.
11. The variable displacement pump of claim 10 further including
fluid media disposed between the sensor target and the sensing
probe.
12. The variable displacement pump of claim 10, wherein the sensing
probe is sealed within the casing.
13. The variable displacement pump of claim 10, wherein the sensing
probe includes a conductive portion exposed to an interior of the
casing and a nonconductive portion disposed between the conductive
portion and the casing.
14. The variable displacement pump of claim 10, wherein the angle
of the swashplate is determined relative to a plane substantially
perpendicular to the axis of rotation.
15. The variable displacement pump of claim 10 wherein the sensor
target includes a conductive portion and a nonconductive portion
disposed between the conductive portion and the swashplate.
16. The variable displacement pump of claim 10 wherein the
established impedance changes as the angle of the swashplate
changes.
17. A method for monitoring an angle of a nonrotating swashplate
disposed to pivot relative to an axis in a variable displacement
pump comprising: directing an alternating current across a sensing
probe coupled to a casing of the pump to establish an impedance
between the sensing probe and a sensor target coupled to the
swashplate; determining a voltage across the sensing probe; and
determining the angle of the swashplate based upon the determined
voltage.
18. The method of claim 17 wherein directing an alternating current
includes directing an alternating current across the sensing probe
to establish an impedance between the sensing probe through fluid
media disposed between the sensing probe and the sensor target.
19. The method of claim 18 wherein the sensing probe includes a
conductive portion exposed to an interior of the casing and a
nonconductive portion disposed between the conductive portion and
the casing, the sensor target includes a conductive portion and a
nonconductive portion disposed between the conductive portion and
the swashplate, and the fluid media is hydraulic fluid.
20. The method of claim 17 further including changing the angle of
the swashplate based upon the determined angle.
Description
TECHNICAL FIELD
[0001] This patent disclosure relates generally to a method and
apparatus for monitoring variable displacement hydraulic pumps and,
more particularly, to a method and arrangement for monitoring an
angle of a swashplate.
BACKGROUND
[0002] Variable displacement pumps are commonly used in many
different types of hydraulic systems. Some vehicles commonly
include hydraulic pumps that are driven by an engine or motor in
the vehicle to generate a flow of pressurized fluid. The
pressurized fluid may be used for any of a number of purposes
during the operation of the vehicle. A machine, for example, may
use the pressurized fluid to propel the machine around a work site
or to move a work implement on the machine.
[0003] A variable displacement pump typically draws operating
fluid, such as, for example, oil, from a reservoir and applies work
to the fluid to increase the pressure of the fluid. The pump may
include a pumping element, such as, for example, a series of
pistons, that increase the pressure of the fluid. The pump may also
include a variable angle swashplate that drives the pistons through
a reciprocal motion to increase the pressure of the fluid.
[0004] A pump that includes a variable angle swashplate may also
include a mechanism that varies the angle of the swashplate to
change the stroke length of the pistons and thereby vary the
displacement of the pump. The displacement of the pump may be
decreased by changing the angle of the swashplate to shorten the
stroke length of the pistons. Alternatively, the displacement of
the pump may be increased by changing the angle of the swashplate
to increase the stroke length of the pistons.
[0005] The amount of pressurized fluid required from a variable
displacement pump may vary depending upon the particular operating
conditions of the system or vehicle that relies upon the pump. In a
vehicle application, for example, the overall efficiency of the
vehicle may be improved by varying the displacement of the pump to
match the requirements of the vehicle. If the vehicle requires less
pressurized fluid, the angle of the swashplate may be changed to
decrease the stroke length of the pistons. Conversely, if the
vehicle requires more pressurized fluid, the angle of the
swashplate may be changed to increase the stroke length of the
piston.
[0006] A vehicle or system may include a control system that
monitors the operating requirements and controls the operation of
the pump to match the requirements. To effectively match the output
of the pump with the requirements of the vehicle or system, the
control system monitors the current output of the pump by, for
example, sensing the angle of the swashplate. If the control system
can accurately determine the angle of the swashplate, the control
system can accurately estimate the current output of the pump. The
control system can then adjust the angle of the swashplate to match
the requirements of the vehicle.
[0007] A variable displacement pump may include a sensor to monitor
the angle of the swashplate. A swashplate sensor may be based on
any of several different principles. For example, a sensor may be
based on mechanical, light, electrical, magnetic or Hall-effect
principles. Typically, however, the known sensors that are based on
these principles are either unsuitable for use in a variable
displacement pump, may result in a significant increase in the
overall cost in the pump, may not be adequately robust to withstand
the demands of operation, or may be affected by interference in the
system, such as ferrous material in pump fluid.
[0008] For example, one type of swashplate angle sensor,
manufactured by Rexroth, is based on a combination of electrical
and magnetic principles known as the Hall Effect. This sensor
utilizes permanent magnets that are attached to the swashplate and
which extend outside the pump casing. A Hall-effect semiconductor
chip is disposed between the permanent magnets. By directing a
current through the semiconductor chip and measuring the resulting
voltage across the chip, the angle of the swashplate may be
determined. However, obtaining an effective seal between the pump
casing and the magnet projecting outside the pump casing is
difficult and expensive. In addition, any magnetic materials near
the sensor may interfere with the operation of the sensor. U.S.
Pat. No. 6,848,888 to Du et al. attempts to overcome some of the
shortcomings of prior art Hall Effect sensors.
[0009] It is desirable that a pump flow measuring arrangement would
provide reliable information in a rugged working environment,
regardless of temperature variations, significant system vibration,
frequent pressure fluctuations, metal debris in the operating fluid
of the pump, cavitations, and various noises. It is further
desirable that such an arrangement be economical to manufacture and
operate.
SUMMARY
[0010] According to an aspect of the disclosure, a swashplate angle
sensing arrangement for a variable displacement pump having a
casing containing a nonrotating swashplate adapted to pivot
relative to an axis of rotation of a pump barrel is provided. The
swashplate defines a swashplate angle relative to a plane
substantially perpendicular to the axis of rotation of the pump
barrel. The swashplate angle sensing arrangement includes a sensing
probe coupled to the casing, a sensor target coupled to the
swashplate, and a controller. The controller is configured to
direct an alternating current through the sensing probe to
establish an impedance between the sensing probe and the sensor
target, and to determine the voltage across the sensing probe. The
controller is further adapted to determine the angle of the
swashplate relative to the casing based on the determined
voltage.
[0011] According to another aspect, the disclosure provides a
variable displacement pump having a casing, a barrel disposed
within the casing and adapted to rotate about an axis of rotation,
and a nonrotating swashplate disposed in the casing and adapted to
pivot relative to the axis. The pump further includes a sensor
target coupled to the swashplate, a sensing probe coupled to the
casing and proximate the sensor target, and a controller. The
controller is configured to direct a current across the sensing
probe to establish an impedance between the sensing probe and the
sensor target, and to determine the voltage across the sensing
probe, the controller further adapted to determine the angle of the
swashplate relative to the casing based on the determined
voltage.
[0012] According to yet another aspect, the disclosure provides a
method for monitoring the position of a nonrotating swashplate
disposed to pivot relative to an axis in a variable displacement
pump, the pump including a barrel rotatable about said axis within
a casing. The method includes providing a sensor target coupled to
the swashplate, and providing a sensing probe coupled to the casing
and proximate the sensor target. The method further includes the
steps of directing an alternating current across the sensing probe
to establish an impedance between the sensing probe and the sensor
target, determining the voltage across the sensing probe, and
determining the angle of the swashplate relative to the casing
based upon the determined voltage.
BRIEF DESCRIPTION OF THE DRAWING(S)
[0013] FIG. 1 is a schematic illustration of a swashplate angle
sensing arrangement in conjunction for monitoring the angular
position of a swashplate in a variable displacement pump shown in
as a diagrammatic side profile cutaway view;
[0014] FIG. 2 is a diagrammatic end view of the valve plate of the
pump of FIG. 1, taken along line II-II;
[0015] FIG. 3 is a diagrammatic illustration of the swashplate
angle sensing arrangement of FIG. 1;
[0016] FIG. 4 is a view of the sensing probe taken along line IV-IV
in FIG. 3;
[0017] FIG. 5 is a representation of the dielectric characteristics
of components of the swashplate angle sensing arrangement of FIG.
3.
[0018] FIG. 6 is a representation of the equivalent dielectric
analysis circuit of the arrangement of FIG. 3.
[0019] FIG. 7 shows a diagram of a correlation of measured voltage
to swashplate angle in an exemplary embodiment of a swashplate
angle sensing arrangement according to the disclosure.
DETAILED DESCRIPTION
[0020] This disclosure relates to a method, system, and arrangement
for controlling a variable displacement hydraulic pump 10. More
specifically, the disclosure relates to a method, system and
arrangement for monitoring the angular position of a swashplate 12
in a variable displacement pump 10. The method and arrangement are
suited for a variety of physical configurations of variable
displacement hydraulic pumps, and the controls may be implemented
by software and a controller for virtually any system that
incorporates a variable displacement pump.
[0021] An exemplary embodiment of a variable displacement pump 10
is illustrated in FIG. 1. As shown, pump 10 includes a barrel 14
that is disposed in a casing 16 to rotate about a barrel axis 18.
Barrel 14 defines a series of chambers 20, two of which are
illustrated in FIG. 1. The chambers 20 are typically spaced in a
circular array at equal intervals about the barrel axis 18. Each
chamber 20 includes an outlet port 22. The barrel 14 is held
tightly against a valve plate 24 by means of a compressed
cylinder-barrel spring 26 and pressure force within the barrel 14
itself. As may best be seen in FIG. 2, the valve plate 24 includes
an intake port 28 and a discharge port 30, the significance of
which will be explained below.
[0022] Returning to FIG. 1, the pump 10 also includes a series of
pistons 32, and the swashplate 12, which has a driving surface 36.
One piston 32 is slidably disposed in each chamber 20. One end of
each of the pistons 32 is disposed toward the outlet port 22 and
the other end is disposed toward and biased into engagement with
the driving surface 36 of the swashplate 12. The pistons 32 are
typically held against the swashplate 12 by either a fixed
clearance device or a positive force hold-down mechanism, such as,
for example, a spring (not shown). For purposes of this disclosure,
the fixed clearance device or positive force hold-down mechanism
will be referred to as a spring.
[0023] In the illustrated embodiment, each piston 32 is connected
to a slipper 38. Connection of each piston 32 with a respective
slipper 38 includes a joint, such as, for example, the illustrated
ball and socket joint 40, each slipper 38 being disposed between a
respective piston 32 and swashplate 12. Each joint 40 allows for
relative movement between swashplate 12 and a respective piston
32.
[0024] The swashplate 12 may be disposed at an angle relative to
casing 16. For the purposes of the present disclosure, the angle
.alpha. will be measured from a line z that is drawn
perpendicularly from barrel axis 18. One skilled in the art will
recognize, however, that the swashplate angle may be measured using
a different reference point.
[0025] A shaft 42 may be connected to barrel 14 by any appropriate
mechanism. Rotation of the shaft 42 causes a corresponding rotation
of barrel 14 about barrel axis 18. The shaft 42 may be driven by an
appropriate power source 44 (illustrated schematically), such as an
engine, for example, an internal combustion engine. One skilled in
the art will recognize, however, that the shaft 42 may be driven by
another type of power source 44, such as, for example, an
electrical motor.
[0026] The barrel 14 rotates at a constant angular velocity
.omega.. When barrel 14 is rotated, the combination of the angled
driving surface 36 of swashplate 12 and the force of the spring
(not shown) in each chamber 20 will drive each piston 32 through a
reciprocating motion within each chamber 20. As a result, each
piston 32 periodically passes over each of the intake and discharge
ports 28, 30 of the valve plate 24. The angle of inclination a of
the swashplate 12 causes the pistons 32 to undergo an oscillatory
displacement in and out of the barrel 14, thus drawing hydraulic
fluid into the intake port 28, which is a low pressure port, and
out of the discharge port 30, which is a high pressure port.
[0027] The angle .alpha. of swashplate 12 relative to casing 16
controls the stroke length of each piston 32 and the displacement
rate of pump 10. Increasing the swashplate angle .alpha. will
result in a greater stroke length of each piston 32. Conversely,
reducing the swashplate angle .alpha. will result in a reduced
stroke length of each piston 32. An increase in the stroke length
of each piston 32 will increase the amount of fluid that is
pressurized to the predetermined level during each rotation of
barrel 14. A decrease in the stroke length of each piston 32 will
decrease the amount of fluid that is pressurized to the
predetermined level during each rotation of barrel 14. In an
embodiment, the rotational range of swashplate 12 may be limited to
a minimum displacement position of approximately negative
20.degree. and a maximum displacement position of approximately
positive 20.degree..
[0028] The swashplate 12 angle .alpha. of inclination may be
controlled by any appropriate angle control mechanism 46, and is
typically based upon the requirements of a discharge pressure
and/or discharge flow rate. The swashplate 12 angle .alpha. of
inclination, for example, may be controlled by a hydraulically
controlled mechanism, which may include, by way of further example,
one or more actuating pistons (not shown). Such mechanisms are
disclosed, for example, in U.S. Pat. Nos. 6,375,433 and 6,623,247,
and will not be described further in this disclosure, as they will
be familiar to those of skill in the art. One skilled in the art
will recognize, however, that another type of mechanism, such as,
for example, a solenoid driven actuator or a servomechanism, may be
used to vary the angle .alpha. of swashplate 12. In order to
provide instruction to the angle control mechanism 46, a controller
48 may be provided.
[0029] Controller 48 may include an electronic control module that
has a microprocessor and a memory. As is known to those skilled in
the art, the memory is operatively connected to the microprocessor
and stores an instruction set and variables. Associated with the
microprocessor and part of electronic control module may be various
other known circuits such as, for example, power supply circuitry,
signal conditioning circuitry, and solenoid driver circuitry, among
others.
[0030] The controller 48 may be programmed to control the operation
of pump 10 based on different input parameters. For example, in a
machine, controller 48 may monitor the motions of a work implement
or the requested movement of the machine itself to determine the
demand for pressurized fluid. For example, when controller 48
determines that the pressurized fluid requirements exceed the
current output of pump 10, controller 34 may adjust angle control
mechanism 46 to increase the angle .alpha. of swashplate 12 and
thereby increase the displacement of pump 10.
[0031] The controller 48 of this disclosure may be of any
conventional design having hardware and software configured to
perform the calculations, and send and receive appropriate signals
to perform the disclosed logic. The controller 48 may include one
or more controller units, and may be configured solely to perform
the disclosed strategy, or to perform the disclosed strategy and
other processes of the machine (not shown). The controller 48 be of
any suitable construction, and may include a processor (not shown)
and a memory component (not shown). The processor may be
microprocessors or other processors as known in the art. In some
embodiments, the processor may be made up of multiple processors.
In one example, the controller 48 comprises a digital processor
system including a microprocessor circuit having data inputs and
control outputs, operating in accordance with computer-readable
instructions stored on a computer-readable medium. Typically, the
processor will have associated therewith long-term (non-volatile)
memory for storing the program instructions, as well as short-term
(volatile) memory for storing operands and results during (or
resulting from) processing.
[0032] The processor may execute instructions for generating
swashplate angle signal and controlling the angle .alpha. of the
swashplate 12, such as the methods described herein. Such
instructions may be read into or incorporated into a computer
readable medium, such as the memory component, or provided external
to processor. In alternative embodiments, hard-wired circuitry may
be used in place of or in combination with software instructions to
implement a swashplate angle method. Thus, embodiments are not
limited to any specific combination of hardware circuitry and
software.
[0033] The term "computer-readable medium" as used herein refers to
any medium or combination of media that participates in providing
instructions to processor for execution. Such a medium may take
many forms, including but not limited to, non-volatile media,
volatile media, and transmission media. Non-volatile media
includes, for example, optical or magnetic disks. Volatile media
includes dynamic memory. Transmission media includes coaxial
cables, copper wire and fiber optics.
[0034] Common forms of computer-readable media include, for
example, a floppy disk, a flexible disk, hard disk, magnetic tape,
or any other magnetic medium, a CD-ROM, any other optical medium,
punch cards, paper tape, any other physical medium with patterns of
holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory
chip or cartridge, or any other medium from which a computer or
processor can read.
[0035] The memory component may include any form of
computer-readable media as described above. The memory component
may include multiple memory components.
[0036] The controller 48 may be enclosed in a single housing. In
alternative embodiments, the controller 48 may include a plurality
of components operably connected and enclosed in a plurality of
housings. The controller 48 may be an integral part of a control
panel and may be fixedly connected to a terminal box (not shown).
In another embodiment, the controller 48 may be fixedly attached to
a prime mover, a generator, and/or a frame of a machine (not
shown). In still other embodiments, the controller 48 may be
located in a plurality of operably connected locations including
being fixedly attached to a frame, a prime mover, a generator, a
terminal box, and/or remotely to the machine (not shown).
[0037] The controller 48 may be configured to generate a pump angle
signal as a function of, for example, desired pump output flow or
desired pump output pressure. In one embodiment, the pump angle
signal may be a signal that commands the swashplate angle control
mechanism 46 to modify the angle .alpha. of the swashplate 12.
[0038] In order to determine and control flow rate from the pump
10, it is necessary to accurately identify and control the angle
.alpha. of the pump swashplate 12. In accordance with the
disclosure, a swashplate angle sensing arrangement 50 in the form
of a dielectric sensor may be engaged with pump 10 to sense the
angle .alpha. of swashplate 12, as shown, for example, in FIGS. 1
and 3. In the illustrated embodiment, the swashplate angle sensing
arrangement 50 includes a sensing probe 52 and a sensor target 54
along with fluid media 56 disposed within the pump casing 16. Those
of skill in the art will understand that the sensing probe 52 and
sensor target 54 should be appropriately sized for the pump 10 and
utilize materials operative under the applicable working conditions
for the design of the pump 10.
[0039] In the illustrated arrangement 50, the sensing probe 52 is
coupled to and exposed to an interior of the pump casing 16. The
sensing probe 52 acts as a conductor, and may be of any appropriate
design. By way of example only, referring to FIGS. 3 and 4, the
sensing probe 52 may be an conductive portion or electrode 58
mounted on a steel pump casing 16, with a nonconductive portion, or
insulator 60 separating the electrode 58 from the pump casing 16.
The electrode 58 maybe of any appropriate design, and may be, for
example, a conductive metal wire. The insulator 60 likewise may be
of any appropriate design formed of a non-magnetic material, such
as, by way of example only, plastic, Teflon, or Plexiglas. For
example, the insulator 60 may have a circular shape and may include
a central opening 62 through which a metal wire electrode 58
extends. Insulator 60 may be disposed and sealed directly in an
opening 64 in the pump casing 16, or surrounded by a further
conductive layer 66, as illustrated in FIGS. 3 and 4. The sensing
probe 52 may secured to the casing 16 by any appropriate
arrangement, such as, for example fasteners, such as screws or the
like (not shown). Those of skill will recognize that alternate
sensing probe designs may be utilized.
[0040] The sensor target 54 is disposed opposite the sensing probe
52, that is, on the swashplate 12. The sensor target 54 may be
secured to the swashplate 12 by any appropriate arrangement, such
as, for example, one or more fasteners, such as screws or the like
(not shown). The sensor target 54 is disposed on the swashplate 12
at a position such that the position of the sensor target 54
relative to the sensing probe 52 varies with the position of the
swashplate 12. For example, the sensor target 54 may be disposed
along an edge of the swashplate 12.
[0041] As with the sensing probe 52, the sensor target 54 may be of
any appropriate design. In an embodiment, the sensor target 54
similarly includes a conductive portion 68 surrounded by a
nonconductive portion or insulator 70.
[0042] The swashplate angle sensing arrangement 50 further includes
a controller 48. While the controller 48 of the swashplate angle
sensing arrangement is illustrated as the controller 48 configured
to control the angle of the swashplate 12, it will be appreciated
that one or more controllers may be provided.
[0043] The controller 48 is configured to cause an alternating
current from a power source 72 to be supplied to the sensing probe
52. By establishing an alternating current between the electrode 58
of the sensing probe 52 and the pump casing 16, which likewise acts
as an electrode in contact with conductive layer 66, impedance is
established between the electrode 58 and the pump casing 16, when
metallic. The established impedance will depend upon both the fluid
media 56 contained between the pump casing 16 and the sensor target
54 near the surface of the electrode 58. Together, the fluid media
56 and the sensor target 54 may be referenced as media. As the
angle .alpha. of the swashplate 12 changes, the media between the
electrode 58 and the pump casing 16 changes. This change will
consequently result in a change in the boundary conditions for the
current path, and, as a result, the impedance.
[0044] Thus, in the illustrated embodiment, the nonconductive
portion or insulator 60 of the sensing probe 52 and the fluid media
56 act as dielectrics placed between the neighboring electrodes and
may be considered as equivalent to a combination of a capacitor and
a resistor that will duplicate the current-voltage behavior for a
given application. The change of the media between the casing 16,
the sensing probe 52 and the sensor target 54, and/or the change of
the geometry of the spacing between the same will result in the
change of the impedance of the equivalent circuit.
[0045] The change in impedance changes the voltage V.sub.out
measured at output 74 across the resistor R.sub.L. Accordingly, the
swashplate angle sensing arrangement 50 is sensitive to the angle
.alpha. of the swashplate 12 such that the resulting voltage
V.sub.out measured at the output 74 associated with the sensing
probe 52 provides an indication of the angular position of the
swashplate 12 in the form of a sensor signal to the controller 48.
The controller 48 may then correlate the measured voltage V.sub.out
at output 74 across the resistor R.sub.L with a position of the
swashplate 12, and, accordingly, a swashplate angle .alpha. to
determine the corresponding flow rate or pressure of the pump
output based upon the measured voltage V.sub.out, which information
may be utilized in further control or alteration of the pump
output.
[0046] The basic principle of the dielectric sensing arrangement
may be seen in FIGS. 3, and 5-6. With composite media of the fluid
media 56 and the sensor target 54, the sensing probe 52 and the
pump casing 16 form an electric circuit that can be considered as
the combination of several individual capacitors made of three
different materials (collectively identified by the reference
numeral 50 in FIG. 5). Thus, the three materials are those of the
insulator 60, the fluid media 56, and the sensor target 54.
[0047] In an embodiment, since the dielectrics of the insulator 60,
the fluid media 56, and the sensor target 54 considered are
non-perfect, the constants are replaced with complex numbers to
account for the losses. Thus, the dielectric characteristics of the
materials are represented by the following equations where
.di-elect cons..sub.T is the dielectric constant of the sensor
target 54; .di-elect cons..sub.I is the dielectric constant of the
insulator 60; and .di-elect cons..sub.O is the dielectric constant
of the fluid media 56:
.di-elect cons..sub.T=.di-elect cons..sub.T'-j.di-elect
cons..sub.T''
.di-elect cons..sub.I=.di-elect cons..sub.I'-j.di-elect
cons..sub.I''
.di-elect cons..sub.O=.di-elect cons..sub.O'-j.di-elect
cons..sub.O''
[0048] The primed and double-primed quantities are frequency
dependent. Accordingly, with fixed components, an accurate
equivalent circuit for the sensing probe 52 is possible only for a
single frequency in the region near the relaxation frequency.
[0049] Neglecting the resistance of the sensing probe 52, the
resistance of the pump casing 16, and other parasitic capacitance
and inductance, the swashplate angle sensing arrangement 50 can be
represented by the equivalent circuit identified as reference
numeral 50 in FIG. 6. Thus, an equivalent circuit of an embodiment
of a swashplate angle sensing arrangement 50 may be obtained as
illustrated in FIG. 6, where both R.sub.1 and R.sub.2 are internal
resistances of the sensor. Under the excitation of a sinusoidal
input voltage E.sub.i(j.omega.), the current through the load
resistor I(j.omega.), the output voltage across the load resistor
V.sub.o(j.omega.), and the voltage across the electrodes (i.e., the
voltage across the electrode 58 of the sensing probe 52, and the
steel casing 16) V.sub.p(j.omega.) can all be calculated from this
equivalent circuit shown in FIG. 6.
[0050] For an embodiment, for example, the transfer functions are
as follows:
G I ( j.omega. ) .apprxeq. j.omega. ( R 1 + R 2 ) + 1 j.omega. ( R
L ( R 1 + R 2 ) + R 1 R 2 ) C + R L + R 1 ( 1 ) G Vo .apprxeq.
j.omega. R L ( R 1 + R 2 ) C + R L j.omega. ( R L ( R 1 + R 2 ) + R
1 R 2 ) C + R L + R 1 ( 2 ) ##EQU00001##
[0051] The parameters in the transfer functions can be identified
by input and output data at different frequencies around the
operating point. To obtain the best sensitivity to the impedance
change, parameter selections may be made such that the sensitivity
of the transfer function with respect to its parameters is
optimized. As an example, consider |G|.sup.2=GG*, where G* is the
complex conjugate of G. The necessary conditions for obtaining
optimal sensitivity for each parameter for this case is:
.differential. .differential. p j ( .differential. .differential. q
i ( G vo ( j.omega. ) ) G vo * ( j.omega. ) ) ) = 0 ( 3 )
##EQU00002##
[0052] where q.sub.i is the sensitive parameter, and p.sub.j
represents the design variable.
[0053] Those of skill in the art will appreciate that the resultant
correlation between the measured voltage and the swashplate angle
will be dependent of various factors including, but not limited to,
the presence or absence of hydraulic fluid media 56 between the
sensing probe 52 and the sensor target 54, the respective
materials, sizes and shapes of each of sensing probe 52, the sensor
target 54, and the insulator 60, and their respective impedances. A
resultant correlation of voltage to angular position of the
swashplate 12 for a model of an embodiment including a triangularly
shaped sensor target 54 is illustrated in FIG. 7. In this way, the
relative shapes, sizes, and materials may be optimized in order to
provide a desirable curve, for example, such a embodiment that
provides a straight line correlation of voltage to swashplate
angle.
INDUSTRIAL APPLICABILITY
[0054] The disclosed swashplate angle sensing arrangement 50
utilizes the principles of a dielectric sensing arrangement to
determine the angular position of a swashplate 12, and,
accordingly, the fluid flow in a variable displacement pump 10 to
be utilized in a hydraulic system. Embodiments of the disclosed
arrangement may provide for better system performance.
[0055] Embodiments of the swashplate angle sensing arrangement 50
and a variable displacement pump 10 utilizing the same may provide
reliable determination of the swashplate angle .alpha.. Embodiments
may be very robust. Embodiments may be implemented with simplified
packaging, and may be very robust and rugged in use.
[0056] Embodiments of the swashplate angle sensing arrangement 50
may provide reliable and accurate measurements, regardless of
ferrite debris in the fluid media 56 contained within the pump 10.
Similarly, embodiments may provide such reliable and accurate
measurements, regardless of one or more adverse operating
conditions, including, for example, but not limited to, dramatic
temperature variations, significant system vibration, frequent
pressure fluctuations, cavitations, and various noises.
[0057] It will be appreciated that the foregoing description
provides examples of the disclosed system and technique. However,
it is contemplated that other implementations of the disclosure may
differ in detail from the foregoing examples. All references to the
disclosure or examples thereof are intended to reference the
particular example being discussed at that point and are not
intended to imply any limitation as to the scope of the disclosure
more generally. All language of distinction and disparagement with
respect to certain features is intended to indicate a lack of
preference for those features, but not to exclude such from the
scope of the disclosure entirely unless otherwise indicated.
[0058] The use of the terms "a" and "an" and "the" and "at least
one" and similar referents in the context of describing the
invention (especially in the context of the following claims) are
to be construed to cover both the singular and the plural, unless
otherwise indicated herein or clearly contradicted by context. The
use of the term "at least one" followed by a list of one or more
items (for example, "at least one of A and B") is to be construed
to mean one item selected from the listed items (A or B) or any
combination of two or more of the listed items (A and B), unless
otherwise indicated herein or clearly contradicted by context.
[0059] Recitation of ranges of values herein are merely intended to
serve as a shorthand method of referring individually to each
separate value falling within the range, unless otherwise indicated
herein, and each separate value is incorporated into the
specification as if it were individually recited herein. All
methods described herein can be performed in any suitable order
unless otherwise indicated herein or otherwise clearly contradicted
by context.
[0060] Accordingly, this disclosure includes all modifications and
equivalents of the subject matter recited in the claims appended
hereto as permitted by applicable law. Moreover, any combination of
the above-described elements in all possible variations thereof is
encompassed by the disclosure unless otherwise indicated herein or
otherwise clearly contradicted by context.
* * * * *