U.S. patent application number 13/672759 was filed with the patent office on 2013-05-16 for compressor digital control failure shutdown algorithm.
This patent application is currently assigned to Thermo King Corporation. The applicant listed for this patent is Thermo King Corporation. Invention is credited to Ryan J. Dotzenrod, Alan D. Gustafson, YoungChan Ma, Titilope Z. Sule, Herman H. Viegas.
Application Number | 20130121843 13/672759 |
Document ID | / |
Family ID | 47227530 |
Filed Date | 2013-05-16 |
United States Patent
Application |
20130121843 |
Kind Code |
A1 |
Dotzenrod; Ryan J. ; et
al. |
May 16, 2013 |
COMPRESSOR DIGITAL CONTROL FAILURE SHUTDOWN ALGORITHM
Abstract
A method of controlling the loading and unloading of a
compressor includes selectively loading and unloading a compressor
by engaging and disengaging, respectively, compressor members with
the controller in response to system load data, monitoring at least
one of the discharge pressure and the suction pressure at a
predetermined time interval for a continuous time period, storing
values based on the at least one of the discharge pressure and the
suction pressure during the continuous time period, and determining
a predetermined value indicative of compressor operation in which
the compressor members are engaged. The method further includes
comparing at least one of the stored values with the predetermined
value and providing a signal to cease operation of the compressor
when the comparison fails to indicate compressor operation in which
the compressor members are engaged.
Inventors: |
Dotzenrod; Ryan J.;
(Lakeville, MN) ; Gustafson; Alan D.; (Eden
Prairie, MN) ; Ma; YoungChan; (Bloomington, MN)
; Sule; Titilope Z.; (Columbia Heights, MN) ;
Viegas; Herman H.; (Bloomington, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Thermo King Corporation; |
Minneapolis |
MN |
US |
|
|
Assignee: |
Thermo King Corporation
Minneapolis
MN
|
Family ID: |
47227530 |
Appl. No.: |
13/672759 |
Filed: |
November 9, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61558750 |
Nov 11, 2011 |
|
|
|
Current U.S.
Class: |
417/1 |
Current CPC
Class: |
F04C 28/06 20130101;
F04C 27/005 20130101; F04C 18/0215 20130101; F04C 28/26 20130101;
F04C 2270/18 20130101; F04C 28/28 20130101 |
Class at
Publication: |
417/1 |
International
Class: |
F04C 28/06 20060101
F04C028/06 |
Claims
1. A method of controlling the loading and unloading of a
compressor, the method comprising: selectively loading and
unloading a compressor by engaging and disengaging, respectively,
compressor members with the controller in response to system load
data: loading the compressor to increase a fluid pressure from a
suction pressure to a discharge pressure when the compressor
members are engaged; unloading the compressor when the compressor
members are disengaged; monitoring at least one of the discharge
pressure and the suction pressure at a predetermined time interval
for a continuous time period; storing values based on the at least
one of the discharge pressure and the suction pressure during the
continuous time period; determining a predetermined value
indicative of compressor operation in which the compressor members
are engaged; comparing at least one of the stored values with the
predetermined value; providing a signal to cease operation of the
compressor when the comparison fails to indicate compressor
operation in which the compressor members are engaged.
2. The method of claim 1, further including the step of providing a
signal to restart the compressor after waiting for a second
predetermined time interval and if fewer than a predetermined
number of signals to cease operation of the compressor have
occurred during the second predetermined time interval.
3. The method of claim 1, wherein storing values based on the at
least one of the discharge pressure and the suction pressure during
the continuous time period means storing the maximum and minimum
values of one of the discharge pressure and the suction pressure
during the continuous time period, the method further including
calculating a difference between a stored maximum value of the one
of the discharge pressure and the suction pressure and a stored
minimum value of the one of the discharge pressure and the suction
pressure, and wherein comparing at least one of the stored values
with the predetermined value means comparing the difference with
the predetermined value.
4. The method of claim 3, wherein the comparison fails to indicate
compressor operation in which the compressor members are engaged
when the difference is not equal to or greater than the
predetermined value at any time during the continuous time
period.
5. The method of claim 3, wherein the difference represents an
increase in discharge pressure.
6. The method of claim 3, wherein the difference represents a
decrease in suction pressure.
7. The method of claim 1, further including calculating a direction
of the slope of the at least one of the discharge pressure and the
suction pressure for the continuous time period, and wherein
comparing at least one of the stored values with the predetermined
value means comparing the direction with the predetermined
value.
8. The method of claim 7, wherein the comparison fails to indicate
compressor operation in which the compressor members are engaged
when the direction of the slope does not change during the
continuous time period.
9. The method of claim 7, wherein the comparison fails to indicate
compressor operation in which the compressor members are engaged if
the direction of the slope of the discharge pressure does not
change from negative to positive during the continuous period.
10. The method of claim 7, wherein the comparison fails to indicate
compressor operation in which the compressor members are engaged if
the direction of the slope of the suction pressure does not change
from positive to negative during the continuous period.
11. The method of claim 1, further including determining a maximum
pressure differential between the discharge pressure and the
suction pressure at each time interval and determining a minimum
pressure differential between the discharge pressure and the
suction pressure at each time interval, and further including
calculating a difference between the determined maximum pressure
differential and the determined minimum pressure differential, and
wherein comparing at least one of the stored values with the
predetermined value means comparing the difference with the
predetermined value.
12. The method of claim 11, wherein the comparison fails to
indicate compressor operation in which the compressor members are
engaged when the difference did not rise by the predetermined value
during the continuous time period.
13. The method of claim 1, further including calculating the ratio
of the discharge pressure to the suction pressure over the
continuous time period, and wherein comparing at least one of the
stored values with the predetermined value means comparing the
calculated ratio with the predetermined value.
14. The method of claim 13, wherein the comparison fails to
indicate compressor operation in which the compressor members are
engaged when the calculated ratio drops below the predetermined
value.
15. The method of claim 14, wherein the predetermined value is
approximately 1.4
16. The method of claim 1, wherein the compressor is a scroll
compressor.
Description
RELATED APPLICATION DATA
[0001] The present application claims priority under 35 U.S.C.
.sctn.119 to Provisional Patent Application No. 61/558,750, filed
Nov. 11, 2011, the disclosure of which is hereby incorporated by
reference.
BACKGROUND
[0002] The present invention relates to an algorithm for a
compressor controller that initiates a shutdown of the compressor
in the event of a digital control valve or other failure.
[0003] In a conventional digital scroll compressor, a solenoid
valve in communication with both the compressor discharge line and
the compressor suction line is energized to modulate the compressor
capacity for load control. The solenoid directs compressed
discharge gas to separate the orbiting scroll from the fixed scroll
while the compressor prime mover remains energized. In some
applications, the bearings and other components are lubricated by
virtue of the pressure differential between the low and high sides
of the compressor in lieu of an oil pump. During separation of the
scroll set this pressure differential will typically be
insufficient to provide adequate oil to the bearings and other
components, thus limiting the duration that the compressor can
safely operate with the scrolls separated.
SUMMARY
[0004] A compressor controller, among other things, monitors and
records suction and discharge pressure data of a digital scroll
compressor over time, and specifically over a series of duty
cycles. Based on this data, an algorithm determines if the digital
solenoid valve is stuck or if the scroll set otherwise remains
disengaged. If so, the controller initiates a shutdown of the prime
mover of the compressor.
[0005] In one embodiment of a method of controlling the loading and
unloading of a compressor, the method includes selectively loading
and unloading a compressor by engaging and disengaging,
respectively, compressor members with the controller in response to
system load data, loading the compressor to increase a fluid
pressure from a suction pressure to a discharge pressure when the
compressor members are engaged, and unloading the compressor when
the compressor members are disengaged. The method also includes
monitoring at least one of the discharge pressure and the suction
pressure at a predetermined time interval for a continuous time
period, storing values based on the at least one of the discharge
pressure and the suction pressure during the continuous time
period, and determining a predetermined value indicative of
compressor operation in which the compressor members are engaged.
The method further includes comparing at least one of the stored
values with the predetermined value and providing a signal to cease
operation of the compressor when the comparison fails to indicate
compressor operation in which the compressor members are
engaged.
[0006] Other aspects of the invention will become apparent by
consideration of the detailed description and accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a sectional view of a scroll compressor with the
scrolls engaged and having a controller for use with an embodiment
of the invention.
[0008] FIG. 2 is another sectional view of the scroll compressor of
FIG. 1, with the scrolls disengaged.
[0009] FIG. 3 is a plot of the discharge and suction pressures of
the scroll compressor of FIGS. 1 and 2, and of the control valve
applied voltage, vs. time.
[0010] FIG. 4 is a flow chart of a control algorithm embodying the
invention.
[0011] FIG. 5 is a flow chart of another control algorithm
embodying the invention.
[0012] FIG. 6 is a flow chart of another control algorithm
embodying the invention.
[0013] FIG. 7 is a flow chart of another control algorithm
embodying the invention.
DETAILED DESCRIPTION
[0014] Before any embodiments of the invention are explained in
detail, it is to be understood that the invention is not limited in
its application to the details of construction and the arrangement
of components set forth in the following description or illustrated
in the following drawings. The invention is capable of other
embodiments and of being practiced or of being carried out in
various ways. As used herein and in the appended claims, the terms
"upper", "lower", "top", "bottom", "front", "back", and other
directional terms are not intended to require any particular
orientation, but are instead used for purposes of description
only.
[0015] Referring to FIG. 1, a portion of a compressor 10 is shown
and comprises a generally cylindrical shell 100 having secured at
one end thereof a cap 104. A transverse partition 108 extends to
the periphery of the shell 100 and separates the compressor into a
high pressure side 112 and a low pressure side 114.
[0016] A drive shaft or crankshaft 120 having an eccentric crank
pin 124 is rotatably journaled in a bearing 128 in a main bearing
housing 132. The crankshaft 120 is driven by a prime mover (not
shown) external to the shell 100. The prime mover may be, for
example, a diesel engine, an electric motor, or any other machine
capable of driving the crankshaft 120. The main bearing housing 132
includes a generally cylindrical portion 150 that defines a flat
thrust bearing surface 152 on which is supported an orbiting scroll
member 156. The orbiting scroll member 156 includes an end plate
160 and a spiral vane or wrap 164 extending therefrom. Projecting
from the opposing face of the end plate 160 is a cylindrical hub
170 having a journal bearing 174 therein and in which is rotatively
disposed a drive bushing 180 having an inner bore 184 in which the
crank pin 124 is drivingly disposed. The crank pin 124 has a flat
on one surface which drivingly engages a flat surface (not shown)
formed in a portion of the bore 184 to provide a radially compliant
driving arrangement therebetween such that the crank pin 124 and
the drive bushing 180 do not substantially rotate relative to one
another. The orbiting scroll member 156 further includes an inlet
190 in fluid communication with a suction port 194 adjoining the
shell 100 at the low pressure side 114.
[0017] A non-orbiting scroll member 200 includes an end plate 204
and a wrap 208 projecting therefrom which is positioned in meshing
engagement with the wrap 164 of the orbiting scroll member 156. The
non-orbiting scroll member 200 has a centrally disposed discharge
passage 212 that communicates with a recess 216, which in turn is
in fluid communication with an oil separator 220 positioned in the
high pressure side 112. The oil separator 220 is in fluid
communication with a discharge port 224 adjoining the shell 100.
Due to the orientation of the compressor 10, an oil sump 228 is
located at a lower portion of the high pressure side 112 and
receives oil separated by the oil separator 220. An oil tube 230
extends through the partition 108 and provides oil to the bearings
and other components (not shown) via the pressure difference
between the high pressure side 112 and the low pressure side 114.
The non-orbiting scroll member 200 is secured to the main bearing
housing 132 through a plurality of circumferentially spaced bolts
(not shown) extending through associated sleeve members and
configured to allow limited axial movement of the non-orbiting
scroll member 200 with respect to the orbiting scroll member
156.
[0018] In order to allow orbiting motion of the orbiting scroll
member 156 and prevent relative rotation between the orbiting
scroll member 156 and the non-orbiting scroll member 200, an Oldham
coupling 232 is disposed between the cylindrical portion 150 of the
main bearing housing 132 and the end plate 160 of the orbiting
scroll member 156.
[0019] A solenoid valve 240 is connected by a control line 252 to a
fitting 256 extending through the shell 100. The solenoid valve 240
is configured to receive a pulse width modulation signal from a
control module or controller 244 based in part on data supplied
from a load sensor 248, such as a temperature or pressure sensor.
An internal fluid line 260 connects the fitting 256 to a passage
264 in communication with a chamber 268. The solenoid valve 240
includes a discharge connecting tube 270 and a suction connecting
tube 274 affixed to the discharge tee 278 and suction tee 282,
respectively.
[0020] A recess 234 is formed in the non-orbiting scroll member 200
in communication with a compression pocket at an intermediate
pressure through a bleed hole 236. The intermediate pressure within
recess 234, along with the discharge pressure within recess 216,
will exert an axial biasing force on the non-orbiting scroll member
200 to thereby urge the tips of the respective wraps 164, 208 into
sealing engagement with the opposed end plates 160, 204. The
solenoid valve 240 is closed such that the chamber 268 is in fluid
communication with the suction tee 282.
[0021] Although the compressor illustrated and described with
regard to FIGS. 1 and 2 is a scroll compressor, the compressor can
be any type of compressor (using refrigerant or another fluid, such
as air) with a digital or other unloading device. In particular,
the compressor can be of the type in which the bearings and other
components are lubricated by a high/low pressure differential
rather than by an oil pump.
[0022] In operation, the orbiting scroll 156 orbits relative to the
non-orbiting scroll 200, drawing system refrigerant through the
suction tee 282 and the suction port 194 and into the inlet 190.
The intermeshing wraps 164, 208, as known by those of ordinary
skill in the art, progressively decrease the size of a refrigerant
containing pocket formed therein as the refrigerant is moved
radially inward. This action compresses the refrigerant, which is
discharged sequentially through the centrally disposed passage 212,
the recess 216, the oil separator 220, the discharge port 224, and
the discharge tee 278 for use in the refrigerant system.
[0023] To unload the compressor, the solenoid valve 240 energizes
in response to a signal from the controller 244. Referring to FIG.
2, this signal opens the solenoid valve 240, allowing high pressure
refrigerant discharge to flow through the control line 252, the
internal fluid line 260, the passage 264, and into the chamber 268.
The pressure within the chamber 268 is increased such that the
resultant applied force from the gas will overcome the previously
described axial biasing force on the non-orbiting scroll member
200. The non-orbiting scroll member 200 will therefore move
axially, disengaging the non-orbiting scroll 200 from the orbiting
scroll 156. The leakage path formed between the two scrolls 156,
200 effectively eliminates compression of the refrigerant.
[0024] To load the compressor, the controller 244 deenergizes the
solenoid valve 240. Referring to FIG. 1, this closes the solenoid
valve 240, which discharges the gas within the chamber 268 back
through the passage 264, the internal fluid line 260, the control
line 252, and to the suction tee 282, which moves the orbiting and
non-orbiting scrolls 156, 200 back into engagement.
[0025] The control module 244 switches the solenoid valve 240, and
thus the compressor 10, between engaged and disengaged states while
the prime mover remains energized. One or more load sensors 248,
such as temperature or pressure sensors, alone or in combination,
provide system load data to the control module 244. The control
module 244 adjusts the pulse width of the control signal to
modulate the compressor 10 between its full load and no-load states
to meet the system demand for refrigerant. Rather than being
directly responsive to the difference between set point and real
time parameters (e.g., of temperature or pressure), the modulation
frequency is a function of the duty cycle calculated by the
controller to meet the system demand.
[0026] When the scroll set is disengaged, the pressure differential
required to lubricate the bearings and other components (in the
absence of an oil pump) is insufficient for continuous operation.
As a result, the duration of time that the compressor 10 can be
safely operated in the disengaged mode is limited. If the solenoid
valve 240 remains in the open position for an extended period of
time, damage may occur to the compressor 10 requiring replacement
of multiple components, or, for non-serviceable compressors, total
compressor replacement.
[0027] The controller is configured to chart the compressor
discharge pressure and suction pressure over time. Referring to
FIG. 3, plots 300, 304 show pressure vs. time and solenoid valve
voltage vs. time for corresponding time periods and for a given
ambient and conditioned space temperature. As an example, the plots
300, 304 are based on an operating condition of 15.degree. F.
ambient and 15.degree. F. box conditions, with a 50% duty cycle
(e.g., 5 seconds on, 5 seconds off).
[0028] Referring to plot 304, during the loading phase of a cycle
308, the valve 240 is deenergized (V.sub.closed) and the scroll set
(scroll members 156, 200) is biased together or engaged (see, e.g.,
FIG. 1). During an unloading phase of the cycle 308, a voltage
(V.sub.open) is applied to the solenoid valve 240 and the scroll
set disengaged (see, e.g., FIG. 2). In normal operation, the
discharge pressure trace 310 and the suction pressure trace 314 are
out of phase, as shown in plot 300 of FIG. 3. For example, as the
discharge pressure 310 decreases over the cycle 308, the suction
pressure 314 increases. Specifically, when the solenoid valve 240
closes and the scroll set moves to the engaged position, the
refrigerant discharge pressure 310 increases while the suction
pressure 314 decreases over the same time period. When the solenoid
valve 240 opens and the scroll set moves to the disengaged
position, the discharge pressure 310 decreases while the suction
pressure 314 increases. Similar plots can be derived for additional
operating conditions.
[0029] Referring to FIGS. 3 and 4, in one embodiment of a control
algorithm, the routine begins at step 400, in which the discharge
pressure is monitored at a predetermined time interval, for
example, every 0.5 seconds, over the course of a continuous time
period, for example, one minute (or any time period sufficient to
include a number of duty cycles). During this continuous time
period the maximum and minimum values of discharge pressure
monitored are stored in the controller 244. At the end of the
continuous time period (step 404), the controller 244 calculates
the difference between the stored maximum value and the stored
minimum value (step 408) and determines whether the discharge
pressure increased a certain amount, for example, 5 psi, at any
time during the continuous time period (step 412). If the discharge
pressure did not increase by at least 5 psi within the continuous
time period, then a shutdown signal is sent from the controller 244
(step 416) to shut down the compressor 10 (i.e., deenergize the
prime mover). The shutdown signal indicates that the solenoid valve
240 may be stuck in the open position or that the scroll set
remains otherwise disengaged.
[0030] To avoid nuisance shutdown cycles, the controller 244, after
waiting a certain time interval, for example, 15 minutes (step
420), and if fewer than three shutdowns have occurred (step 424)
sends a signal to restart the compressor 10 and the control
algorithm is reinitiated (step 428). If the controller 244, after
once more completing steps 400-412, determines that the discharge
pressure has not increased by 5 psi within the continuous time
period, the controller again shuts down the compressor 10 in
accordance with step 416. As previously noted, the controller 244
is programmed to allow a certain number, for example, three, such
shutdowns and restarts during a continuous one hour period, at
which point an error code will be displayed on the controller 244
(step 432) and the compressor 10 will not restart without
service.
[0031] Referring to FIGS. 3 and 5, in another embodiment of a
control algorithm, the routine begins at step 500, in which the
suction pressure is monitored at a predetermined time interval, for
example, every 0.5 seconds, over the course of a continuous time
period, for example, one minute. During this continuous time period
the maximum and minimum values of suction pressure are stored in
the controller 244. At the end of the continuous time period (step
504), the controller calculates the difference between the stored
maximum value and the stored minimum value (step 508) and
determines whether the suction pressure decreased a certain amount,
for example, 2 psi, at any time during the continuous time period
(step 512). If the suction pressure did not decrease by at least 2
psi, the shutdown signal is sent from the controller 244 (step 516)
to deenergize the prime mover. The absence of a pressure decrease
of at least 2 psi signals that the scroll set remains in a
disengaged state. The controller will energize the prime mover as
previously described, steps 520-528 and, after three such
shutdowns, generate the error code (step 532).
[0032] Referring to FIGS. 3 and 6, in another embodiment of the
control algorithm, the slope of the discharge pressure trace 310
and the slope of the suction pressure trace 314 are monitored and
stored by the controller over the course of a continuous time
period (step 600). At the end of the continuous time period (step
604), the controller 244 analyzes the discharge pressure slope
and/or the suction pressure slope profiles and determines the
change in slope(s) over the time period (step 608). As previously
described, the discharge pressure of the refrigerant increases when
the solenoid valve 240 is deenergized, i.e., the slope of the
discharge pressure changes from negative to positive upon closing
the solenoid valve. The suction pressure of the refrigerant
decreases when the solenoid valve 240 is deenergized, i.e., the
slope of the suction pressure changes from positive to negative
upon closing the solenoid valve. If the discharge pressure slope
does not change from negative to positive, or if the suction
pressure slope does not change from positive to negative during the
time period (step 612) the controller 244 initiates the shutdown
sequence previously described (steps 616-632), indicating that the
system remains disengaged. In this algorithm, the discharge and
suction pressures can be analyzed alone or in combination, and the
controller-initiated signal can be triggered by either condition or
by a combination of conditions.
[0033] Referring to FIGS. 3 and 7, in another embodiment of the
control algorithm, the difference between the discharge pressure
and the suction pressure is monitored at a predetermined time
interval for a continuous time period (step 700), during which the
maximum and minimum difference values are stored in the controller.
At the end of the time period (step 704) the controller 244
calculates the difference between the stored maximum value of
pressure differential and the stored minimum value of pressure
differential (step 708) and determines whether the differential
rose by at least a certain amount, for example, 10 psi, during the
continuous time period (step 712). If not, the controller sends a
shutdown signal (step 716) to deenergize the prime mover and
continues with the shutdown sequence as necessary (steps
720-732).
[0034] In another embodiment of the control algorithm, the pressure
ratio, which is the ratio of the discharge pressure to the suction
pressure, can be monitored continuously by the controller 244. If
this ratio drops below a predetermined ratio, for example, 1.4, at
any time during compressor operation, the shutdown signal and
sequence are initiated.
[0035] Any of the algorithms can be activated during digital
operation of the compressor 10. In some compressor systems, the
compressor is operable in both a digital and non-digital mode
(e.g., to facilitate a change in a parameter setpoint or a change
in system environment) and the controller 244 may direct the
compressor 10 to switch from digital to non-digital mode during a
period in which the scroll set is stuck in the disengaged position.
The controller 244 is configured to continue to monitor the
algorithm embodied in steps 700-732 and the pressure ratio of the
compressor for an additional time period, for example, one minute,
immediately after the compressor 10 is transitioned out of the
digital mode, to ensure normal operation and, if necessary,
initiate the shutdown signal and sequence as previously
described.
[0036] The above-described embodiments can be used together to
monitor the compressor system. Alternatively, one or more of the
embodiments can be used as a backup to another of the embodiments.
In some applications, one or more of the embodiments may be
preferable. The numerical values provided for pressure,
temperature, length of time, or any other parameter above are
exemplary only and not limiting within the scope of the
invention.
[0037] Various features and advantages of the invention are set
forth in the following claims.
* * * * *