U.S. patent application number 16/952706 was filed with the patent office on 2022-05-19 for linear compressor and internal collision mitigation.
The applicant listed for this patent is Haier US Appliance Solutions, Inc.. Invention is credited to Gregory William Hahn, Joseph Wilson Latham.
Application Number | 20220154714 16/952706 |
Document ID | / |
Family ID | |
Filed Date | 2022-05-19 |
United States Patent
Application |
20220154714 |
Kind Code |
A1 |
Latham; Joseph Wilson ; et
al. |
May 19, 2022 |
LINEAR COMPRESSOR AND INTERNAL COLLISION MITIGATION
Abstract
A linear compressor or method of operation may provide for
driving a motor of the linear compressor to a reference current and
detecting a sampled current during driving the motor. The linear
compressor or method may also provide for calculating a variance in
current using the sampled current, determining the calculated
variance exceeds a variance threshold, and restricting the
reference current based on determining the calculated variance
exceeds the variance threshold.
Inventors: |
Latham; Joseph Wilson;
(Louisville, KY) ; Hahn; Gregory William; (Mt.
Washington, KY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Haier US Appliance Solutions, Inc. |
Wilmington |
DE |
US |
|
|
Appl. No.: |
16/952706 |
Filed: |
November 19, 2020 |
International
Class: |
F04B 49/10 20060101
F04B049/10; F04B 53/16 20060101 F04B053/16 |
Claims
1. A method of operating a linear compressor to correct an internal
collision between a linear compressor and a shell enclosing the
linear compressor, the method comprising: driving a motor of the
linear compressor to a reference current; detecting a sampled
current during driving the motor; calculating a variance in current
using the sampled current; determining the calculated variance
exceeds a variance threshold; and restricting the reference current
based on determining the calculated variance exceeds the variance
threshold.
2. The method of claim 1, wherein the sampled current comprises a
peak supply current value, and wherein the reference current
comprises a reference peak current value.
3. The method of claim 1, wherein the sampled current comprises a
root mean square (RMS) current value, and wherein the reference
current comprises a reference RMS current value.
4. The method of claim 1, wherein the calculated variance is a
recursive variance.
5. The method of claim 1, wherein calculating variance comprises
calculating a difference in a previously sampled current and the
sampled current, and calculating variance based on the difference
in a previously sampled current and the sampled current.
6. The method of claim 1, wherein driving the motor comprises
driving the motor over a plurality of electrical cycles, and
wherein detecting the sampled current comprises detecting a
discrete sampled current value for each electrical cycle of the
plurality of electrical cycles.
7. The method of claim 6, wherein the sampled current value is a
maximum absolute value of current for a corresponding electrical
cycle.
8. The method of claim 1, wherein detecting the sampled current
comprises detecting a predetermined-number set of sampled current
values, and wherein calculating variance comprises calculating
variance of the predetermined-number set of sampled current
values.
9. The method of claim 8, wherein calculating variance comprises
calculating a mean value of the predetermined-number of set of
sampled current values.
10. The method of claim 1, wherein determining the calculated
variance exceeds the variance threshold comprises determining
multiple calculated variance values exceed the predetermined
variance, and wherein restricting the reference current is
contingent on determining multiple calculated variance values
exceed the predetermined variance.
11. A method of operating a linear compressor to correct an
internal collision between a linear compressor and a shell
enclosing the linear compressor, the method comprising: driving a
motor of the linear compressor to a reference current over a
plurality of electrical cycles; detecting a sampled current,
detecting the sampled current comprising detecting a discrete
sampled current value for each electrical cycle of the plurality of
electrical cycles; calculating a variance in current using the
sampled current; determining the calculated variance exceeds a
variance threshold; and restricting the reference current based on
determining the calculated variance exceeds the variance threshold
independent of a piston position of the motor.
12. The method of claim 11, wherein the sampled current comprises a
peak supply current value, and wherein the reference current
comprises a reference peak current value.
13. The method of claim 11, wherein the sampled current comprises a
root mean square (RMS) current value, and wherein the reference
current comprises a reference RMS current value.
14. The method of claim 11, wherein the calculated variance is a
recursive variance.
15. The method of claim 11, wherein calculating variance comprises
calculating a difference in a previously sampled current and the
sampled current, and calculating variance based on the difference
in a previously sampled current and the sampled current.
16. The method of claim 11, wherein the sampled current value is a
maximum absolute value of current for a corresponding electrical
cycle.
17. The method of claim 11, wherein detecting the sampled current
comprises detecting a predetermined-number set of sampled current
values, and wherein calculating variance comprises calculating
variance of the predetermined-number set of sampled current
values.
18. The method of claim 17, wherein calculating variance comprises
calculating a mean value of the predetermined-number of set of
sampled current values.
19. The method of claim 11, wherein determining the calculated
variance exceeds the variance threshold comprises determining
multiple calculated variance values exceed the predetermined
variance, and wherein restricting the reference current is
contingent on determining multiple calculated variance values
exceed the predetermined variance.
Description
FIELD OF THE INVENTION
[0001] The present subject matter relates generally to a compressor
for an appliance, such as a refrigerator appliance.
BACKGROUND OF THE INVENTION
[0002] Certain refrigerator appliances include sealed systems for
cooling chilled chambers of the refrigerator appliance. The sealed
systems generally include a compressor that generates compressed
refrigerant during operation of the sealed system. The compressed
refrigerant flows to an evaporator where heat exchange between the
chilled chambers and the refrigerant cools the chilled chambers and
food items located therein.
[0003] Recently, certain refrigerator appliances have included
linear compressors for compressing refrigerant. Linear compressors
generally include a piston and a driving coil housed, and may be
housed within a sealed shell. The driving coil generates a force
for sliding the piston forward and backward within a chamber.
During motion of the piston within the chamber, the piston
compresses refrigerant. Motion of the piston within the chamber is
generally controlled such that the compressor does not crash into
the inner shell (i.e., as an internal collision). Such internal
collisions can damage various components of the linear compressor
and can be extremely loud or bothersome to nearby users.
[0004] Even when a linear compressor is operating appropriately
(e.g., to avoid inducing a crash from the piston motion), it is
possible for a series of internal collisions to be caused by a
sizeable impact, such as a refrigerator door being slammed or the
linear compressor being tipped. Unfortunately, a single collision
can be followed by a series of internal collisions as the linear
compressor moves within the shell, creating sudden changes in the
back-EMF of a motor, which makes controlling the linear compressor
difficult. Nonetheless, it can be difficult to predict or quickly
determine when such a series of internal collisions is occurring.
Adding sensors configured to detect significant movement or noise
from the linear compressor may permit extensive collisions to occur
before the system is able to detect and stop such the collisions.
Additionally or alternatively, adding such sensors may undesirably
increase the complexity or expense of an appliance. This may, in
turn, lead to a poor user experience, reduce reliability, or
unacceptably increase the cost of the linear compressor.
[0005] As a result, it would be useful to provide a linear
compressor design or method of operation for quickly detecting or
mitigating internal collisions of the linear compressor against an
inner surface of a surrounding shell. In particular, it would be
advantageous to provide a system or method for detecting or
mitigating internal collisions without requiring a separate
sensor.
BRIEF DESCRIPTION OF THE INVENTION
[0006] Aspects and advantages of the invention will be set forth in
part in the following description, or may be obvious from the
description, or may be learned through practice of the
invention.
[0007] In one exemplary aspect of the present disclosure, a method
of operating a linear compressor to correct an internal collision
between a linear compressor and a shell enclosing the linear
compressor is provided. The method may include driving a motor of
the linear compressor to a reference current and detecting a
sampled current during driving the motor. The method may also
include calculating a variance in current using the sampled
current, determining the calculated variance exceeds a variance
threshold, and restricting the reference current based on
determining the calculated variance exceeds the variance
threshold.
[0008] In another exemplary aspect of the present disclosure, a
method of operating a linear compressor to correct an internal
collision between a linear compressor and a shell enclosing the
linear compressor is provided. The method may include driving a
motor of the linear compressor to a reference current over a
plurality of electrical cycles and detecting a sampled current.
Detecting the sampled current may include detecting a discrete
sampled current value for each electrical cycle of the plurality of
electrical cycles. The method may further include calculating a
variance in current using the sampled current, determining the
calculated variance exceeds a variance threshold, and restricting
the reference current based on determining the calculated variance
exceeds the variance threshold independent of a piston position of
the motor.
[0009] These and other features, aspects and advantages of the
present invention will become better understood with reference to
the following description and appended claims. The accompanying
drawings, which are incorporated in and constitute a part of this
specification, illustrate embodiments of the invention and,
together with the description, serve to explain the principles of
the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] A full and enabling disclosure of the present invention,
including the best mode thereof, directed to one of ordinary skill
in the art, is set forth in the specification, which makes
reference to the appended figures.
[0011] FIG. 1 is a front elevation view of a refrigerator appliance
according to exemplary embodiments of the present disclosure.
[0012] FIG. 2 is a schematic view of certain components of the
exemplary refrigerator appliance of FIG. 1 with respective
exemplary oil cooling circuits according exemplary embodiments of
the present disclosure.
[0013] FIG. 3 provides a section view of an exemplary linear
compressor according to exemplary embodiments of the present
disclosure.
[0014] FIG. 4 provides a section view of the exemplary linear
compressor of FIG. 3, illustrating a flow path according to
exemplary embodiments of the present disclosure.
[0015] FIG. 5 provides an exemplary chart of experimental
electrical motor parameter estimates.
[0016] FIG. 6 provides an exemplary chart of experimental
electrical motor parameter estimates.
[0017] FIG. 7 provides a flow chart illustrating a method of
operating a linear compressor according to exemplary embodiments of
the present disclosure.
DETAILED DESCRIPTION
[0018] Reference now will be made in detail to embodiments of the
invention, one or more examples of which are illustrated in the
drawings. Each example is provided by way of explanation of the
invention, not limitation of the invention. In fact, it will be
apparent to those skilled in the art that various modifications and
variations can be made in the present invention without departing
from the scope of the invention. For instance, features illustrated
or described as part of one embodiment can be used with another
embodiment to yield a still further embodiment. Thus, it is
intended that the present invention covers such modifications and
variations as come within the scope of the appended claims and
their equivalents.
[0019] As used herein, the terms "first," "second," and "third" may
be used interchangeably to distinguish one component from another
and are not intended to signify location or importance of the
individual components. The terms "upstream" and "downstream" refer
to the relative flow direction with respect to fluid flow in a
fluid pathway. For example, "upstream" refers to the flow direction
from which the fluid flows, and "downstream" refers to the flow
direction to which the fluid flows. The term "or" is generally
intended to be inclusive (i.e., "A or B" is intended to mean "A or
B or both").
[0020] Turning now to the figures, FIG. 1 depicts a refrigerator
appliance 10 that incorporates a sealed refrigeration system 60
(FIG. 2). It should be appreciated that the term "refrigerator
appliance" is used in a generic sense herein to encompass any
manner of refrigeration appliance, such as a freezer,
refrigerator/freezer combination, and any style or model of
conventional refrigerator. In addition, it should be understood
that the present disclosure is not limited to use in refrigerator
appliances. Thus, the present subject matter may be used for any
other suitable purpose, such as vapor compression within air
conditioning units or air compression within air compressors.
[0021] In the illustrated exemplary embodiment shown in FIG. 1, the
refrigerator appliance 10 is depicted as an upright refrigerator
having a cabinet or casing 12 that defines a number of internal
chilled storage compartments. In particular, refrigerator appliance
10 includes upper fresh-food compartments 14 having doors 16 and
lower freezer compartment 18 having an upper drawer 20 and a lower
drawer 22. The drawers 20 and 22 are "pull-out" drawers in that
they can be manually moved into and out of the freezer compartment
18 on suitable slide mechanisms.
[0022] FIG. 2 provides schematic views of certain components of
refrigerator appliance 10, including a sealed refrigeration system
60 of refrigerator appliance 10. In particular, FIG. 2 provides
exemplary oil cooling circuit with sealed refrigeration system 60
according exemplary embodiments of the present disclosure. It
should be understood that, except as otherwise indicated, the
exemplary oil cooling circuit of FIG. 2 may be modified or used in
or with any suitable appliance in alternative exemplary
embodiments. For example, the exemplary oil cooling circuit of FIG.
2 may be used in or with heat pump dryer appliances, heat pump
water heater appliance, air conditioner appliances, etc.
[0023] A machinery compartment of refrigerator appliance 10 may
contain components for executing a known vapor compression cycle
for cooling air. The components include a compressor 64, a
condenser 66, an expansion device 68, and an evaporator 70
connected in series and charged with a refrigerant. As will be
understood by those skilled in the art, refrigeration system 60 may
include additional components (e.g., at least one additional
evaporator, compressor, expansion device, or condenser). As an
example, refrigeration system 60 may include two evaporators.
[0024] Within refrigeration system 60, refrigerant generally flows
into compressor 64, which operates to increase the pressure of the
refrigerant. This compression of the refrigerant raises its
temperature, which is lowered by passing the refrigerant through
condenser 66. Within condenser 66, heat exchange with ambient air
takes place so as to cool the refrigerant. A condenser fan 72 is
used to pull air across condenser 66 so as to provide forced
convection for a more rapid and efficient heat exchange between the
refrigerant within condenser 66 and the ambient air. Thus, as will
be understood by those skilled in the art, increasing air flow
across condenser 66 can, for example, increase the efficiency of
condenser 66 by improving cooling of the refrigerant contained
therein.
[0025] An expansion device (e.g., a valve, capillary tube, or other
restriction device) 68 receives refrigerant from condenser 66. From
expansion device 68, the refrigerant enters evaporator 70. Upon
exiting expansion device 68 and entering evaporator 70, the
refrigerant drops in pressure. Due to the pressure drop or phase
change of the refrigerant, evaporator 70 is cool relative to
compartments 14 and 18 of refrigerator appliance 10. As such,
cooled air is produced and refrigerates compartments 14 and 18 of
refrigerator appliance 10. Thus, evaporator 70 is a type of heat
exchanger which transfers heat from air passing over evaporator 70
to refrigerant flowing through evaporator 70.
[0026] Collectively, the vapor compression cycle components in a
refrigeration circuit, associated fans, and associated compartments
are sometimes referred to as a sealed refrigeration system operable
to force cold air through compartments 14, 18 (FIG. 1). The
refrigeration system 60 depicted in FIG. 2 is provided by way of
example only. Thus, it is within the scope of the present
disclosure for other configurations of the refrigeration system to
be used as well.
[0027] In some embodiments, an oil cooling circuit 200 according
exemplary embodiments of the present disclosure is shown with
refrigeration system 60. Compressor 64 of refrigeration system 60
may include or be provided within a shell 302 (FIG. 3) that also
holds a lubrication oil therein. The lubrication oil may assist
with reducing friction between sliding or moving components of
compressor 64 during operation of compressor 64. For example, the
lubrication oil may reduce friction between a piston and a cylinder
of compressor 64 when the piston slides within the cylinder to
compress refrigerant, as discussed in greater detail below.
[0028] During operation of compressor 64, the lubrication oil may
increase in temperature. Thus, oil cooling circuit 200 is provided
to assist with rejecting heat from the lubrication oil. By cooling
the lubrication oil, an efficiency of compressor 64 may be
improved. Thus, oil cooling circuit 200 may assist with increasing
the efficiency of compressor 64 (e.g., relative to a compressor
without oil cooling circuit 200) by reducing the temperature of the
lubrication oil within compressor 64.
[0029] In optional embodiments, oil cooling circuit 200 includes a
heat exchanger 210 is spaced apart from at least a portion of
compressor 64. A lubrication oil conduit 220 extends between
compressor 64 and heat exchanger 210. Lubrication oil from
compressor 64 may flow to heat exchanger 210 via lubrication oil
conduit 220. As shown in FIG. 2, lubrication oil conduit 220 may
include a supply conduit 222 and a return conduit 224. Supply
conduit 222 extends between compressor 64 and heat exchanger 210
and is configured for directing lubrication oil from compressor 64
to heat exchanger 210. Conversely, return conduit 224 extends
between heat exchanger 210 and compressor 64 and is configured for
directing lubrication oil from heat exchanger 210 to compressor
64.
[0030] Within heat exchanger 210, the lubrication oil may reject
heat to ambient air about heat exchanger 210. From heat exchanger
210, the lubrication oil flows back to compressor 64 via
lubrication oil conduit 220. In such a manner, lubrication oil
conduit 220 may circulate lubrication oil between compressor 64 and
heat exchanger 210, and heat exchanger 210 may reduce the
temperature of lubrication oil from compressor 64 before returning
the lubrication oil to compressor 64. Thus, oil cooling circuit 200
may remove lubrication oil from compressor 64 via lubrication oil
conduit 220 and return the lubrication oil to compressor 64 via
lubrication oil conduit 220 after cooling the lubrication oil in
heat exchanger 210.
[0031] In some embodiments, heat exchanger 210 is positioned at or
adjacent fan 72. For example, heat exchanger 210 may be positioned
and oriented such that fan 72 pulls or urges air across heat
exchanger 210 so as to provide forced convection for a more rapid
and efficient heat exchange between lubrication oil within heat
exchanger 210 and ambient air about refrigeration system 60. In
certain exemplary embodiments, heat exchanger 210 may be disposed
between fan 72 and condenser 66. Thus, heat exchanger 210 may be
disposed downstream of fan 72 and upstream of condenser 66 relative
to a flow of air from fan 72. In such a manner, air from fan 72 may
heat exchange with lubrication oil in heat exchanger 210 prior to
heat exchange with refrigerant in condenser 66.
[0032] In additional or alternative embodiments, heat exchanger 210
is positioned at or on condenser 66. For example, heat exchanger
210 may be mounted to condenser 66 such that heat exchanger 210 and
condenser 66 are in conductive thermal communication with each
other. Thus, condenser 66 and heat exchanger 210 may conductively
exchange heat. In such a manner, heat exchanger 210 and condenser
66 may provide for heat exchange between lubrication oil within
heat exchanger 210 and refrigerant within condenser 66.
[0033] In certain exemplary embodiments, heat exchanger 210 may be
a tube-to-tube heat exchanger 210 integrated within or onto
condenser 66 (e.g., a portion of condenser 66). For example, heat
exchanger 210 may be welded or soldered onto condenser 66. In
optional embodiments, heat exchanger 210 is disposed on a portion
of condenser 66 between an inlet and an outlet of condenser 66. For
example, refrigerant may enter condenser 66 at the inlet of
condenser 66 at a first temperature (e.g., one hundred and fifty
degrees Fahrenheit (150.degree. F.)), and heat exchanger 210 may be
positioned on condenser 66 downstream of the inlet of condenser 66
such that refrigerant immediately upstream of the portion of
condenser 66 where heat exchanger 210 is mounted may have a second
temperature (e.g., ninety degrees Fahrenheit (90.degree. F.)).
[0034] Heat exchanger 210 may also be positioned on condenser 66
upstream of the outlet of condenser 66 such that refrigerant
immediately downstream of the portion of condenser 66 where heat
exchanger 210 is mounted may have a third temperature (e.g., one
hundred and five degrees Fahrenheit (105.degree. F.)), and
refrigerant may exit condenser 66 at the outlet of condenser 66 at
a fourth temperature (e.g., ninety degrees Fahrenheit (90.degree.
F.)). Thus, refrigerant within condenser 66 may increase in
temperature at the portion of condenser 66 where heat exchanger 210
is mounted during operation of compressor 64 in order to cool
lubrication oil within heat exchanger 210. However, the portion of
condenser 66 downstream of heat exchanger 210 may assist with
rejecting heat to ambient air about condenser 66.
[0035] Turning now to FIGS. 3 and 4, various sectional views are
provided of a linear compressor 300 according to an exemplary
embodiments of the present disclosure. As discussed in greater
detail below, linear compressor 300 is operable to increase a
pressure of fluid within a chamber 312 of linear compressor 300.
Linear compressor 300 may be used to compress any suitable fluid,
such as refrigerant. In particular, linear compressor 300 may be
used in a refrigerator appliance, such as refrigerator appliance 10
(FIG. 1) in which linear compressor 300 may be used as compressor
64 (FIG. 2). As may be seen in FIG. 3, linear compressor 300
defines an axial direction A and a radial direction R. Linear
compressor 300 may be enclosed within a hermetic or air-tight shell
302. In other words, linear compressor 300 may be enclosed within
an internal volume 303 defined by shell 302. For instance, linear
compressor may be supported within internal volume 303 by one or
more mounting springs 305, which may generally dampen oscillations
or movement of linear compressor 300 relative to shell 302. When
assembled, hermetic shell 302 hinders or prevents refrigerant or
lubrication oil from leaking or escaping refrigeration system 60
(FIG. 2).
[0036] Linear compressor 300 includes a casing 308 that extends
between a first end portion 304 and a second end portion 306 (e.g.,
along the axial direction A). Casing 308 includes various
relatively static or non-moving structural components of linear
compressor 300. In particular, casing 308 includes a cylinder
assembly 310 that defines a chamber 312. Cylinder assembly 310 may
be positioned at or adjacent second end portion 306 of casing 308.
Chamber 312 may extend longitudinally along the axial direction
A.
[0037] In some embodiments, a motor mount mid-section 314 (e.g., at
the second end portion 306) of casing 308 supports a stator of the
motor. As shown, the stator may include an outer back iron 364 and
a driving coil 366 sandwiched between the first end portion 304 and
the second end portion 306. Linear compressor 300 may also include
one or more valves (e.g., a discharge valve assembly 320 at an end
of chamber 312) that permit refrigerant to enter and exit chamber
312 during operation of linear compressor 300.
[0038] In some embodiments, a discharge valve assembly 320 is
mounted to the casing 308 (e.g., at the second end portion 306).
Discharge valve assembly 320 may include a muffler housing 322, a
valve head 324, and a valve spring 338.
[0039] Muffler housing 322 may include an end wall 326 and a
cylindrical side wall 328. Cylindrical side wall 328 is mounted to
end wall 326, and cylindrical side wall 328 extends from end wall
326 (e.g., along the axial direction A) to cylinder assembly 310 of
casing 308. A refrigerant outlet conduit 330 may extend from or
through muffler housing 322 and through shell 302 (e.g., to or in
fluid communication with condenser 66--FIG. 2) to selectively
permit refrigerant from discharge valve assembly 320 during
operation of linear compressor 300.
[0040] Muffler housing 322 may be mounted or fixed to casing 308,
and other components of discharge valve assembly 320 may be
disposed within muffler housing 322. For example, a plate 332 of
muffler housing 322 at a distal end of cylindrical side wall 328
may be positioned at or on cylinder assembly 310, and a seal (e.g.,
O-ring or gasket) may extend between cylinder assembly 310 and
plate 332 of muffler housing 322 (e.g., along the axial direction
A) in order to limit fluid leakage at an axial gap between casing
308 and muffler housing 322. Fasteners may extend through plate 332
into casing 308 to mount muffler housing 322 to casing 308.
[0041] In some embodiments, valve head 324 is positioned at or
adjacent chamber 312 of cylinder assembly 310. Valve head 324 may
selectively a passage that extends through the cylinder assembly
310 (e.g., along the axial direction A). Such a passage may be
contiguous with chamber 312. When assembled, valve spring 338 may
be coupled to muffler housing 322 and valve head 324. Valve spring
338 may be configured to urge valve head 324 towards or against
cylinder assembly 310 (e.g., along the axial direction A).
[0042] A piston assembly 316 with a piston head 318 may be slidably
received within chamber 312 of cylinder assembly 310. In
particular, piston assembly 316 may be slidable along the axial
direction A within chamber 312. During sliding of piston head 318
within chamber 312, piston head 318 compresses refrigerant within
chamber 312. As an example, from a top dead center position, piston
head 318 can slide within chamber 312 towards a bottom dead center
position along the axial direction A (i.e., an expansion stroke of
piston head 318). When piston head 318 reaches the bottom dead
center position, piston head 318 changes directions and slides in
chamber 312 back towards the top dead center position (i.e., a
compression stroke of piston head 318). As, or immediately prior
to, piston head 318 reaching the top dead center position,
expansion valve assembly 320 may open. For instance, valve head 324
may be urged away from cylinder assembly 310, permitting
refrigerant from chamber 312 and through discharge valve assembly
320 to refrigerant outlet conduit 330.
[0043] It should be understood that linear compressor 300 may
include an additional piston head or additional chamber at an
opposite end of linear compressor 300 (e.g., proximal to first end
portion 304). Thus, linear compressor 300 may have multiple piston
heads in alternative exemplary embodiments.
[0044] In certain embodiments, linear compressor 300 includes an
inner back iron assembly 352. Inner back iron assembly 352 is
positioned in the stator of the motor. In particular, outer back
iron 364 or driving coil 366 may extend about inner back iron
assembly 352 (e.g., along a circumferential direction). Inner back
iron assembly 352 also has the outer surface. At least one driving
magnet 362 is mounted to inner back iron assembly 352 (e.g., at the
outer surface of inner back iron assembly 352). Driving magnet 362
may face or be exposed to driving coil 366. In particular, driving
magnet 362 may be spaced apart from driving coil 366 (e.g., along
the radial direction R by an air gap). Thus, the air gap may be
defined between opposing surfaces of driving magnet 362 and driving
coil 366. Driving magnet 362 may also be mounted or fixed to inner
back iron assembly 352 such that the outer surface of driving
magnet 362 is substantially flush with the outer surface of inner
back iron assembly 352. Thus, driving magnet 362 may be inset
within inner back iron assembly 352. In such a manner, the magnetic
field from driving coil 366 may have to pass through only a single
air gap between outer back iron 364 and inner back iron assembly
352 during operation of linear compressor 300.
[0045] As may be seen in FIG. 3, driving coil 366 extends about
inner back iron assembly 352 (e.g., along the circumferential
direction). Generally, driving coil 366 is operable to move the
inner back iron assembly 352 along the axial direction A during
operation of driving coil 366. As an example, a current may be
induced in driving coil 366 by a current source (e.g., included
with or in connection with a controller 367) to generate a magnetic
field that engages driving magnet 362 and urges piston assembly 316
to move along the axial direction A in order to compress
refrigerant within chamber 312, as described above. In particular,
the magnetic field of driving coil 366 may engage driving magnet
362 in order to move inner back iron assembly 352 and piston head
318 the axial direction A during operation of driving coil 366.
Thus, driving coil 366 may slide piston assembly 316 between the
top dead center position and the bottom dead center position during
operation of driving coil 366.
[0046] In optional embodiments, linear compressor 300 includes
various components for permitting or regulating operation of linear
compressor 300. In particular, linear compressor 300 includes a
controller 367 that is configured for regulating operation of
linear compressor 300. The controller 367 is in, for example,
operative, communication with the motor (e.g., driving coil 366 of
the motor). Thus, the controller 367 may selectively activate
driving coil 366, for example, by supplying current to driving coil
366, in order to compress refrigerant with piston assembly 316 as
described above. In some embodiments, controller 367 directs or
regulates current according to a predetermined control loop. For
instance, as would be understood, such a control loop may regulate
the supply voltage [e.g., peak voltage or root mean square (RMS)
voltage] of a supplied current to a desired reference voltage. To
that end, controller 367 may include a suitable component for
measuring or estimating a supply current, such as an ammeter.
Additionally or alternatively, controller 367 may be configured to
detect or mitigate an internal collision (e.g., according to one or
more programmed methods, such as method 700).
[0047] The controller 367 includes memory and one or more
processing devices such as microprocessors, CPUs or the like, such
as general or special purpose microprocessors operable to execute
programming instructions or micro-control code associated with
operation of linear compressor 300. The memory can represent random
access memory such as DRAM, or read only memory such as ROM or
FLASH. The processor executes programming instructions stored in
the memory. The memory can be a separate component from the
processor or can be included onboard within the processor.
Alternatively, the controller 367 may be constructed without using
a microprocessor (e.g., using a combination of discrete analog or
digital logic circuitry; such as switches, amplifiers, integrators,
comparators, flip-flops, AND gates, and the like) to perform
control functionality instead of relying upon software.
[0048] Linear compressor 300 also includes one or more spring
assemblies 340, 342 mounted to casing 308. In certain embodiments,
a pair of spring assemblies (i.e., a first spring assembly 340 and
a second spring assembly 342) bounds driving coil 366 along the
axial direction A. In other words, a first spring assembly 340 is
positioned proximal to the first end portion 304 and a second
spring assembly 342 is positioned proximal to the second end
portion 306.
[0049] In some embodiments, each spring assembly 340 and 342
includes one or more planar springs that are mounted or secured to
one another. In particular, planar springs may be mounted or
secured to one another such that each planar spring of a
corresponding assembly 340 or 342 are spaced apart from one another
(e.g., along the axial direction A).
[0050] Generally, the pair of spring assemblies 340, 342 assists
with coupling inner back iron assembly 352 to casing 308. In some
such embodiments, a first outer set of fasteners 344 (e.g., bolts,
nuts, clamps, tabs, welds, solders, etc.) secure first and second
spring assemblies 340, 342 to casing 308 (e.g., a bracket of the
stator) while a first inner set of fasteners 346 that are radially
inward (e.g., closer to the axial direction A along a perpendicular
radial direction R) from the first outer set of fasteners 344
secure first spring assembly 340 to inner back iron assembly 352 at
first end portion 304. In additional or alternative embodiments, a
second inner set of fasteners 350 that are radially inward (e.g.,
closer to the axial direction A along the radial direction R) from
the first outer set of fasteners 344 secure second spring assembly
342 to inner back iron assembly 352 at second end portion 306.
[0051] During operation of driving coil 366, the spring assemblies
340, 342 support inner back iron assembly 352. In particular, inner
back iron assembly 352 is suspended by the spring assemblies 340,
342 within the stator or the motor of linear compressor 300 such
that motion of inner back iron assembly 352 along the radial
direction R is hindered or limited while motion along the axial
direction A is relatively unimpeded. Thus, the spring assemblies
340, 342 may be substantially stiffer along the radial direction R
than along the axial direction A. In such a manner, the spring
assemblies 340, 342 can assist with maintaining a uniformity of the
air gap between driving magnet 362 and driving coil 366 (e.g.,
along the radial direction R) during operation of the motor and
movement of inner back iron assembly 352 on the axial direction A.
The spring assemblies 340, 342 can also assist with hindering side
pull forces of the motor from transmitting to piston assembly 316
and being reacted in cylinder assembly 310 as a friction loss.
[0052] In optional embodiments, inner back iron assembly 352
includes an outer cylinder 354 and a sleeve 360. Sleeve 360 is
positioned on or at the inner surface of outer cylinder 354. A
first interference fit between outer cylinder 354 and sleeve 360
may couple or secure outer cylinder 354 and sleeve 360 together. In
alternative exemplary embodiments, sleeve 360 may be welded, glued,
fastened, or connected via any other suitable mechanism or method
to outer cylinder 354.
[0053] When assembled, sleeve 360 may extend about the axial
direction A (e.g., along the circumferential direction). In
exemplary embodiments, a first interference fit between outer
cylinder 354 and sleeve 360 may couple or secure outer cylinder 354
and sleeve 360 together. In alternative exemplary embodiments,
sleeve 360 is welded, glued, fastened, or connected via any other
suitable mechanism or method to outer cylinder 354. As shown,
sleeve 360 extends within outer cylinder 354 (e.g., along the axial
direction A) between first and second end portions 304 and 306 of
inner back iron assembly 352 130. First and second spring
assemblies 340, 342 and are mounted to sleeve 360 (e.g., with inner
set of fasteners 346 and 350).
[0054] Outer cylinder 354 may be constructed of or with any
suitable material. For example, outer cylinder 354 may be
constructed of or with a plurality of (e.g., ferromagnetic)
laminations. The laminations are distributed along the
circumferential direction in order to form outer cylinder 354 and
are mounted to one another or secured together (e.g., with rings
pressed onto ends of the laminations). Outer cylinder 354 defines a
recess that extends inwardly from the outer surface of outer
cylinder 354 (e.g., along the radial direction R). Driving magnet
362 may be positioned in the recess on outer cylinder 354 (e.g.,
such that driving magnet 362 is inset within outer cylinder
354).
[0055] In some embodiments, a piston flex mount 368 is mounted to
and extends through inner back iron assembly 352. In particular,
piston flex mount 368 is mounted to inner back iron assembly 352
via sleeve 360 and spring assemblies 340, 342. Thus, piston flex
mount 368 may be coupled (e.g., threaded) to sleeve 360 in order to
mount or fix piston flex mount 368 to inner back iron assembly 352.
A coupling 370 extends between piston flex mount 368 and piston
assembly 316 (e.g., along the axial direction A). Thus, coupling
370 connects inner back iron assembly 352 and piston assembly 316
such that motion of inner back iron assembly 352 (e.g., along the
axial direction A) is transferred to piston assembly 316. Coupling
370 may extend through driving coil 366 (e.g., along the axial
direction A).
[0056] Piston flex mount 368 may define at least one passage 369.
Passage 369 of piston flex mount 368 extends (e.g., along the axial
direction A) through piston flex mount 368. Thus, a flow of fluid,
such as air or refrigerant, may pass through piston flex mount 368
via passage 369 of piston flex mount 368 during operation of linear
compressor 300. As shown, one or more refrigerant inlet conduits
331 may extend through shell 302 to return refrigerant from
evaporator 70 (or another portion of sealed system 60) (FIG. 2) to
compressor 300.
[0057] Piston head 318 also defines at least one opening (e.g.,
selectively covered by a head valve). The opening of piston head
318 extends (e.g., along the axial direction A) through piston head
318. Thus, the flow of refrigerant may pass through piston head 318
via the opening of piston head 318 into chamber 312 during
operation of linear compressor 300. In such a manner, the flow of
fluid (that is compressed by piston head 318 within chamber 312)
may flow through piston flex mount 368 and inner back iron assembly
352 to piston assembly 316 during operation of linear compressor
300.
[0058] As shown, linear compressor 300 may include features for
directing oil through linear compressor 300 and oil cooling circuit
200 (FIG. 2). One or more oil inlet conduits 380 or oil outlet
conduits 382 may extend through shell 302 to direct oil to/from oil
cooling circuit 200.
[0059] Optionally, oil inlet conduit 380 may be coupled to return
conduit 224 of oil cooling circuit 200 (FIG. 2). Thus, from heat
exchanger 210, lubrication oil may flow to linear compressor 300
via oil inlet conduit 380. Optionally, oil inlet conduit 380 may be
positioned at or adjacent sump 376. Thus, lubrication oil to linear
compressor 300 at oil inlet conduit 380 may flow into sump 376. As
discussed above, oil cooling circuit 200 may cool lubrication oil
from linear compressor 300. After such cooling, the lubrication oil
is returned to linear compressor 300 via oil inlet conduit 380.
Thus, the lubrication oil in oil inlet conduit 380 may be
relatively cool and assist with cooling lubrication oil in sump
376.
[0060] In some embodiments, linear compressor 300 includes a pump
372. Pump 372 may be positioned at or adjacent a sump 376 of shell
302 (e.g., within a pump housing 374). Sump 376 corresponds to a
portion of shell 302 at or adjacent a bottom of shell 302. Thus, a
volume of lubrication oil 377 within shell 302 may pool within sump
376 (e.g., because the lubrication oil is denser than the
refrigerant within shell 302). During use, pump 372 may draw the
lubrication oil from the volume 377 within sump 376 to pump 372 via
a supply line 378 extending from pump 372 to sump 376. For
instance, a pair of check valves within a pump housing 374 at
opposite ends of pump 372 may selectively permit/release oil
to/from pump housing 374 as pump 372 oscillates within pump housing
374 (e.g., as motivated by oscillations of casing 308).
Additionally or alternatively, the volume of lubrication oil 377
may be maintained at a predetermined level (e.g., even with a
vertical midpoint of pump 372) while pump 372 is actively
oscillating.
[0061] An internal conduit 384 may extend from pump 372 (e.g., pump
housing 374) to an oil reservoir 386 defined within casing 308. In
some embodiments, oil reservoir 386 is positioned radially outward
from the chamber 312 of cylinder assembly 310. For instance, oil
reservoir 386 may be defined to extend along the circumferential
direction (e.g., about the axial direction A) as an annular chamber
around chamber 312 of cylinder assembly 310.
[0062] Generally, lubrication oil may be selectively directed to
cylinder assembly 310 from oil reservoir 386. In particular, one or
more passages (e.g., radial passages) may extend from oil reservoir
386 to the chamber 312. Such radial passages may terminate at a
portion of the sliding path of piston head 318 (e.g., between top
dead center and bottom dead center relative to the axial direction
A). As piston head 318 slides within chamber 312, a sidewall of
piston head 318 may receive lubrication oil. In optional
embodiments, the radial passages terminate at a groove 388 defined
by the cylinder assembly 310 within the chamber 312. Thus, the
groove 388 may be open to the chamber 312. Lubrication oil from oil
reservoir 386 may flow into chamber 312 of cylinder assembly 310
(e.g., via radial passages to the groove 388) in order to lubricate
motion of piston assembly 316 within chamber 312 of cylinder
assembly 310.
[0063] Along with the chamber 312 and oil reservoir 386, casing 308
may define an oil exhaust 390. In some embodiments, oil exhaust 390
extends from oil reservoir 386. For example, oil exhaust 390 may
extend through casing 308 outward from oil reservoir 386. Oil
exhaust 390 may thus be in fluid communication with oil reservoir
386. During use, at least a portion of the lubrication oil urged to
oil reservoir 386 may flow to the oil exhaust 390 (e.g., as
motivated by pump 372). From oil exhaust 390, lubrication oil may
exit the casing 308 (and linear compressor 300 generally). In
certain embodiments, oil exhaust 390 is connected in fluid
communication to the oil outlet conduit 382. Thus, pump 372 may
generally urge lubrication oil from the internal volume 303,
through casing 308, and to the oil outlet conduit 382. Oil outlet
conduit 382 may be coupled to supply conduit 222 of oil cooling
circuit 200 (FIG. 2). Thus, pump 372 may urge lubrication oil from
sump 376 into supply conduit 222. In such a manner, pump 372 may
supply lubrication oil to oil cooling circuit 200 in order to cool
the lubrication oil from linear compressor 300, as discussed
above.
[0064] Separate from or in addition to oil exhaust 390, casing 308
may define a gas vent 392. In particular, gas vent 392 extends
through from oil reservoir 386 to the internal volume 303. As
shown, gas vent 392 is defined in fluid parallel with oil exhaust
390. Thus, fluid is separately directed through gas vent 392 and
oil exhaust 390. Generally, gas vent 392 may be sized to restrict
fluid more than oil exhaust 390. For example, the minimum diameter
of gas vent 392 may still be smaller than the minimum diameter of
the oil exhaust 390. Optionally, the minimum diameter of gas vent
392 may be less than two millimeters while the minimum diameter of
oil exhaust is greater than four millimeters. Along with being
smaller in diameter, the gas vent 392 may further be shorter in
length than oil exhaust 390. Under typical pumping operations, a
greater volume of lubrication oil may be motivated through oil
exhaust 390 than gas vent 392. Nonetheless, gas (e.g., produced
during an outgassing within oil reservoir 386) may be permitted to
internal volume 303 through gas vent 392 while permitting the
continued flow of lubrication oil from oil reservoir 386 to oil
exhaust 390 or chamber 312.
[0065] Gas vent 392 may be defined at an upper portion of casing
308 (e.g., at an upper end of oil reservoir 386). Additionally or
alternatively, gas vent 392 may extend above the discharge valve
assembly 320 (e.g., parallel to the axial direction A). Gas vent
392 may further be located below (e.g., lower along a vertical
direction V than) oil exhaust 390. In some embodiments, gas vent
392 is located at the second end portion 306 of casing 308. Fluid
from gas vent 392 may be directed forward into internal volume
303.
[0066] In some embodiments, an oil shield 394 is provided in front
of gas vent 392. As shown, oil shield 394 may be disposed on casing
308 (e.g., at second end portion 306). Between oil shield 394 and,
for example, muffler housing 322, a drip passage may be defined.
Between oil shield 394 and, for example, muffler housing 322, a
drip passage may be defined. For instance, oil shield 394 may
extend outward from casing 308 to a curved or inward-extending wall
portion 396. Additionally or alternatively, oil shield 394 may
extend about a portion of muffler housing 322. For instance, oil
shield 394 may extend 180.degree. along a top side of muffler
housing 322. During use, lubrication oil discharged through gas
vent 392 may be directed downward to the sump 376. During use, oil
shield 394 may prevent lubrication oil from striking shell 302
(e.g., at a high velocity, which might otherwise cause atomizing of
lubrication oil within internal volume 303).
[0067] Turning now to FIGS. 5 and 6, during use of a linear
compressor (e.g., linear compressor 300--FIG. 3), it is possible
for the linear compressor to be suddenly shifted or inadvertently
struck, such as when the door to the corresponding appliance (e.g.,
refrigerator appliance 10--FIG. 1) is slammed shut. Such a shift or
strike may cause the linear compressor to collide repeatedly with
an enclosing shell. For instance, with respect to the exemplary
embodiments of FIG. 3, muffler housing 328 may collide with an
internal surface of shell 302. Such internal collisions may be
repeated as linear compressor 300 rocks or oscillates on support
springs 305.
[0068] FIGS. 5 and 6 provide a pair of exemplary charts that
illustrate experimental electrical motor parameter estimates
obtained during an internal collision event and resulting changes
in one or more control parameters (e.g., reference current
according to a disclosed method of operation). In particular, FIG.
5 illustrates a detected line L-S and a reference line L-R over a
span of time (e.g., measured in seconds or according to discrete
electrical cycles of the motor). FIG. 6 illustrates a calculated
variance line L-V and a variance threshold line L-T over the same
span of time.
[0069] Generally, detected line L-S charts changes, over time, in a
detected supply current (e.g., at or to the motor of linear
compressor 300). Reference line L-R charts changes, over time, in a
reference current, which may be used as a control parameter of a
control loop for the motor of linear compressor 300 (e.g., adjusted
in response to changes in the detected supply current). Calculated
variance line L-V charts changes, over time, in variance values
calculated from the values of the detected line. Generally, a
variance threshold value may remain constant (e.g., as a
predetermined value) and, thus, variance threshold line L-T is flat
over time. As will be described in detail below, values of the
reference current may be changed based on (e.g., in response to)
one or more determinations that one or more calculated variance
values exceed the variance threshold value. Notably, changes in the
reference current may be independent of the position of the piston
within the linear compressor (e.g., such that an internal collision
can be detected without prohibiting a separate monitoring sequence
for determine a hard or soft crash of the piston within the motor).
It is noted that although detected supply current values, reference
current values, and calculated variance values are illustrated as a
peak current values, another suitable value (e.g., RMS) of current
may be similarly used.
[0070] Turning now to FIG. 7, exemplary methods (e.g., method 700)
of operating a linear compressor are illustrated. Such methods may
be applied to any suitable linear compressor (e.g., linear
compressor 300) to detect or correct an internal collision of the
linear compressor against an enclosing shell (e.g., shell 302), as
would be understood in light of the present disclosure. In some
embodiments, the below-described methods may be initiated or
directed by controller 367 (e.g., as or as part of a software
program that the controller 367 is configured to initiate).
[0071] Advantageously, methods described herein may permit the
corresponding linear compressor to quickly detect or mitigate
internal collisions of the linear compressor against an inner
surface of a surrounding shell. Additionally or alternatively, such
methods may advantageously be performed without requiring an
additional or detected sensor assembly.
[0072] At 710, the method 700 includes driving a motor of a linear
compressor to a reference current. For instance, a variable
reference current may be used to induce a current in the driving
coil of the motor and motivate movement of the piston within the
linear compressor, as described above. Moreover, the motor may be
driven in a generally continuous or uninterrupted manner such that
710 extends over a plurality of electrical cycles (e.g.,
represented on a sine wave of current, as would be understood).
[0073] Generally, the motor may be driven according to any suitable
reference current control loop. As an example, a supply voltage may
be directed to the motor to activate the motor. Subsequently, the
supply voltage may be adjusted to reduce a difference or error
between a sample current (e.g., peak current or RMS current)
supplied to linear compressor and the reference current (e.g.,
reference peak current or reference RMS current). The sample
current may be measured or estimated using any suitable method or
mechanism. For example, an ammeter may be used to measure the
sample current as a peak current. A voltage selector of the
controller may operate as a proportional-integral (PI) controller
in order to reduce the error between the sample current and the
reference current. At a start of 710, the reference current may be
a default value (e.g., a default peak current value or peak RMS
value) that may subsequently be adjusted (e.g., increased or
decreased) during subsequent steps of the method 700, as discussed
in greater detail below, such that method 700 reverts to (or
otherwise continues with) driving the motor in order to adjust the
amplitude of the supply voltage and reduce the error between the
current supplied to linear compressor and the adjusted reference
current.
[0074] At 720, the method 700 includes detecting a sampled current
during 710. In other words, as the motor is being driven, the
current being supplied to the motor may be sampled (e.g., as a peak
supply current value or an RMS current value). In some embodiments,
720 includes detecting discrete sampled values over time. Thus, as
the motor continues to be driven, sampled values of supply current
to the motor may continue to be detected. In optional embodiments,
a discrete sampled current value is detected for each electrical
cycle. Thus, as least one sampled value may be obtained for a
corresponding electrical cycle. The sampled value may be detected,
for instance by detecting a maximum value of current during each
electrical cycle. Additionally or alternatively, the sampled
current value may include a maximum absolute value of current for
each corresponding electrical cycle such that the sampled current
value is detected in terms of magnitude of the supplied
current.
[0075] In certain embodiments, 720 may include detecting a
predetermined-number set of sampled current values. For instance,
the set may include a window of sequential current values to be
stored in the controller. Thus, as a new sampled current value is
detected, it may be stored within the set or window. This may
continue until the set or window is full (i.e., the predetermined
number of sampled current values are obtained). Optionally, the set
or window may be a rolling set such that a new sampled current
value may displace the oldest previously sampled current value
within the set.
[0076] At 730, the method 700 includes calculating a variance in
current using the sampled current. The calculated variance may be a
recursive variance and, thus, be representative of sampled current
values detected over time (e.g., over a plurality of electrical
cycles even when no previous sampled current values are maintained
or stored in memory). Generally, the sampled current may be used
within a programmed variance formula. Such variance formulas are
known, and the programmed variance formula may be provided as or
include the same. As an example, the programmed variance formula
(Var(X)) may be or include
Var .function. ( X ) = 1 n .times. i = 1 n .times. .times. ( x i -
.mu. ) 2 ##EQU00001##
wherein x.sub.i are the detected sampled current values, n is the
number of samples for which the variance is calculated, and .mu. is
the mean of the values for x.sub.i (e.g., calculated as rolling
average, moving average, weighted average, etc.). Optionally, the
variance may be calculated from the predetermined number set. In
some such embodiments, n is the predetermined number and the values
of the predetermined-number set are used for the samples x.sub.i.
Thus, 730 may include calculating a mean value of the
predetermined-number of set of sampled current values.
[0077] Optionally, 730 may include calculating the variance from a
change in sampled values (.DELTA.X). Thus, 730 may include
calculating a difference in a previously sampled current and the
sampled current (i.e., contemporary sampled current), and
calculating variance based on the difference in a previously
sampled current and the sampled current. As an example, the
programmed variance formula may be or include
Var .function. ( .DELTA. .times. .times. X ) = 1 n .times. i = 1 n
.times. .times. ( .DELTA. .times. .times. x i - .mu. ) 2
##EQU00002##
wherein .DELTA.x.sub.i are the samples of the calculated difference
in sampled current values, n is the number of samples for which the
variance is calculated, and .mu. is the mean of the values for
.DELTA.x.sub.i (e.g., calculated as rolling average, moving
average, weighted average, etc.). Advantageously, anomalous changes
in variance between individual sampled current values may be
prevented from affecting large changes in any control parameters
based on the calculated variance.
[0078] At 740, the method 700 includes determining the calculated
variance exceeds a variance threshold. For instance, the calculated
variance value of 730 may be compared to a predetermined variance
threshold value (e.g., current peak threshold value or current RMS
value) and it may be determined that the calculated variance value
of 730 is greater than the variance threshold value. Optionally,
this may be repeated such that multiple (e.g., sequential)
calculated variance values may be determined to exceed the variance
threshold value.
[0079] At 750, the method 700 includes restricting the reference
current based on 740. Specifically, in response to one or more
determinations that the calculated variance exceeds the variance
threshold, the reference current used to drive the motor may be
decreased. This may be done independent of the piston position of
the motor (e.g., as noted above).
[0080] Optionally, the decrease may be a reduction of the reference
current (e.g., the reference current value at the moment of the
determination at 740) by a predetermined reduction value.
Additionally or alternatively, a reduction formula may be provided
to make variable reductions to the reference current (e.g., based
on the magnitude of the reference current value at the moment of
the determination at 740).
[0081] In certain embodiments, 750 requires the calculated variance
to repeatedly exceed the variance threshold. Thus, 750 may be
contingent on (e.g., prompted by) determining multiple calculated
variance values exceed the predetermined variance. In some such
embodiments, the multiple calculated variance values may require a
set number (e.g., count or instances) of the calculated variance
exceeding the variance threshold. Additionally or alternatively,
the determinations may all be required to occur within a set time
period or number of cycles.
[0082] After the reference current is restricted, the restricted or
decreased reference current may be used to drive the motor. If
subsequent electrical cycles (e.g., a set number of cycles or
predetermined period of time) elapse without further determinations
that the calculated variance exceeds the reference threshold, the
reference current may be increased (e.g., incrementally) until the
adjusted reference current is equal to the default reference
current value (or another predetermined reference current
value).
[0083] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the
claims, and may include other examples that occur to those skilled
in the art. Such other examples are intended to be within the scope
of the claims if they include structural elements that do not
differ from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal languages of the claims.
* * * * *