RELATED APPLICATION DATA
[0001] The present application claims priority under 35 U.S.C. § 119 to Provisional Patent
Application No.
61/558,750, filed November 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.
According to an aspect of the invention there is provided 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.
[0006] The method may further include 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.
[0007] Storing values based on the at least one of the discharge pressure and the suction
pressure during the continuous time period may mean 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.
[0008] Optionally, 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.
[0009] The difference may represent an increase in discharge pressure.
[0010] The difference may represent a decrease in suction pressure.
[0011] The method may further include 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 comparing at least one of the stored values with the predetermined value means
comparing the direction with the predetermined value.
[0012] Optionally, 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.
[0013] Optionally, 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.
[0014] Optionally, 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.
[0015] The method may further include 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 include calculating a difference between the determined
maximum pressure differential and the determined minimum pressure differential, and
comparing at least one of the stored values with the predetermined value means comparing
the difference with the predetermined value.
[0016] Optionally, 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.
[0017] The method may further include calculating the ratio of the discharge pressure to
the suction pressure over the continuous time period, and comparing at least one of
the stored values with the predetermined value means comparing the calculated ratio
with the predetermined value.
[0018] Optionally, the comparison fails to indicate compressor operation in which the compressor
members are engaged when the calculated ratio drops below the predetermined value.
[0019] The predetermined value may be approximately 1.4.
[0020] The compressor may be a scroll compressor.
[0021] Other aspects of the invention will become apparent by consideration of the detailed
description and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] 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.
[0023] Fig. 2 is another sectional view of the scroll compressor of Fig. 1, with the scrolls
disengaged.
[0024] 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.
[0025] Fig. 4 is a flow chart of a control algorithm embodying the invention.
[0026] Fig. 5 is a flow chart of another control algorithm embodying the invention.
[0027] Fig. 6 is a flow chart of another control algorithm embodying the invention.
[0028] Fig. 7 is a flow chart of another control algorithm embodying the invention.
DETAILED DESCRIPTION
[0029] 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.
[0030] 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.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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.
[0037] 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.
[0038] 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.
[0039] 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.
[0040] 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.
[0041] 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.
[0042] 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° F ambient and 15° F box conditions, with a 50% duty
cycle (e.g., 5 seconds on, 5 seconds off).
[0043] Referring to plot 304, during the loading phase of a cycle 308, the valve 240 is
deenergized (V
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
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.
[0044] 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.
[0045] 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.
[0046] 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).
[0047] 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.
[0048] 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).
[0049] 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.
[0050] 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.
[0051] 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.
[0052] Various features and advantages of the invention are set forth in the following 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; or
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.
10. 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.
11. The method of claim 10, 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.
12. 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.
13. The method of claim 12, wherein the comparison fails to indicate compressor operation
in which the compressor members are engaged when the calculated ratio drops below
the predetermined value.
14. The method of claim 13, wherein the predetermined value is approximately 1.4.
15. The method of claim 1, wherein the compressor is a scroll compressor.