Note: Descriptions are shown in the official language in which they were submitted.
ADAPTIVE DEFROST CONTROL SYSTEM
BACKGRO~ND OF THE INVENTION
This invention relates to an adaptive defrost control
system for use in a temperature controlled device, such as a
refrigerator-freezer. The adaptive defrost control system
utilizes various types of sensed information to control the
energization of a defrost heater for de-icing the coils of an
" evaporator.
It has been recognized that energy consumption and
adverse temperature fluctuations within a refrigerated space
can be minimized by de-energizing a defrost heater as soon as
a frost load has been removed from an evaporator. It is generally
desirable to defrost as infrequent.ly as possible, but it is not
desirable to allow very large frost loads to develop because
they require more time and electrical energy to remove, thus
reducing the operating efficiency of the cooling device.
Optimum defrost operation thus requires that a
balance be struck between the competing considerations of
system operation with a frosted evaporator, the energy con-
sumed in removing a frost load from the evaporator, and the
acceptable level of temperature fluctuation caused by a
defrosting operation.
In some prior refrigerator defrosting systems, a
predetermined number of counts must be accumulated before a
defrosting operation is initiated. These counts may be defined
as either a cycling of the compressor or as an opening of the
`~ refrigerator door while the compressor is operating. However,
such a control is not responsive to the duration of door
openings, and the number of counts needed to initiate defrost
is fixed.
--1-- . ~ .,
. ~
C~
Other types of prior defrost controls have integrated
the run time of the compressor and the duration of door openings
and initiated the defrost cycle after a fixed cumulative amount
- has been reached. Alternatively, an electromechanical control
has been used to integrate the freezer temperature and the
ratio of the compressor on/off time to initiate the defrost
cycle. These types of systems rely upon expensive electrical
;~ or mechanical components, the first utiliæing a coulometer and
the second utilizing a combination of thermostatic switches
: 10 and a thermal time delay relay to perform the integrating function.
Moreover, these types of systems do not utilize the previous
defrost history, which is an important factor in providing an
efficient method of defrosting the evaporator.
Another type of defrost control system combines a
relative humidity sensor with either the number of occurrences
or the total time duration of cabinet door openings or compressor
operation. In each case the combined eEfect of the refrigerator
conditions alters ~he time interval between defrost cycles.
However, this type of defrost system does not utilize both the
number and duration o~ total door openings and the total
compressor run time which accumulates between defrost operations.
Other types of defrost systems control the interval
between defrosting operations based upon the time required for
the defrost heater to raise the evaporator to a predetermined
temperature during the previous defrosting operation. The
net result of such a system is that the defrost interval will
be inversely related to the heater "on" time during the previous
` defrost operation.
Still another type of defrost control provides a
minimum amount of time between defrost operations. This
-2-
control utilizes a conventional time based defrost timer
which is interrupted prior to defrost to allow a demand
defrost sensor to take over. The defrost operation is
prevented until the sensor indicates that a predetermined
frost load has been accumulated.
These and other types of defrost controls suffer
from the disadvantages of not taking into account both the
number and duration of door openings and the previous
defrost history. Nor do prior art defrost controls
adaptively vary the manner in which these variables are
used to initiate a defrost operation.
SU~ RY OF THE INVENTION
In accordance with one aspect of the invention there
is provided in a refrigeration system having defrosting means
and a cooled compartment accessible through a door, a defrost
control for energizing said defrosting means, comprising door
timing means for measuring and storing the duration of time
said door is open, defrost initiation means for energizing
said defrosting means at the end ol a variable defrost
interval that is determined at least partly by the measured
door open time, defrost termination means for ceasing
energization of said defrosting means after determining that
- a frost load has been removed, defrost timing means for
measuring the period of time said defrosting means has been
energized to defrost the evaporator, and adaptive means for
selectively varying the manner in which the defrost interval
is determined by the door open time in response to the time
period measured by the defrost timing means.
In accordance with another aspect of the invention
there is provided in a refrigeration apparatus having a
defrosting means and a cooled compartment accessible through
a door, a method of energizing said defrosting means at the
~ - 3 -
` end of a variable interval, comprising the steps of sensing
a variable indicating the amount of usage of said refriger-
ation apparatus, said usage being determined by the amount
of time the door of said cooled compartment has been open;
changing a stored count in response to the level of said
sensed variable; initiating a defrosting operation when said
stored count has been changed to a predetermined value;
terminating said defrosting operation in response to a
defrost sensing means; measuring the length of said
defrosting operation; and adaptively varying the rate at
which said stored count is changed by said sensed variable
during the next defrost interval as a function of said
measured defrost time.
In accordance with the present invention, an
adaptive defrost control system for a refrigerator-freezer
or the like utilizes various types of information to control
the energization of the defrost heater. The control takes
into account the number and duration of freezer and fresh
food compartment door openings, the duration of the previous
defrosting operation, and the total accumulated compressor
run time since the previous defrost operation.
Defrosting is provided at variable intervals as
determined by a weighted accumulation of the number and
duration of freezer and fresh food door openings, with the
weighting functions being adaptably controlled as a function
of the time required to perform the previous defrost
operation.
The defrosting operation is prevented, regardless
of the number and duration of door openings, until a
predetermined minimum cumulative amount of compressor run
time has elapsed.
The control stores a count which is decremented by
the weighting functions during a door-open interval. The
- 3a -
control checks for minimum compressor run time when the stored
count reaches zero to determine whether the defrost indication
is due to an excessive number of door openings. Under such a
condition, that portion of the control process which varies
the weighting functions is disabled. This prevents the con-
trol from adapting the next defrost interval due to an abnormal
condition, such as excessive door openings.
The count is decremented by different amounts
depending upon whether the fresh food door or the freezer door
is open. Moreover, the count is decremented by a particular
amount during a first period of the door-open interval and by
a lesser amount thereafter. This feature compensates for the
first few seconds of the door-open interval which accounts
for a large amount of the frost formed on the evaporator
coils.
The control, in the event of a power outage, is
reset to a point just short of a defrost operation. This
prevents the occurrence of a missed defrost operation which
may impair the efficiency or even damage the components of the
refrigerator.
The adaptive defrost control system includes a
microcomputer which allows the use of a minimum number of
hardwired components, thereby reducing space requirements
and providing for a relatively inexpensive system. The
microcomputer may also perform other functions within the
refrigerator, such as controlling the compressor run time
and the temperature within the refrigerated compartments.
The control tends to force the length of a defrosting
operation to a predetermined desired value. The control com-
pares the length of the previous defrost operation to the
desired value and varies the weighting functions in accordance
with the comparison. The control does not operate to define
a fixed time interval which must elapse before the next
defrost operation.
The control defrosts the evaporator coils only when
necessary; therefore, energy consumption is reduced and
temperature performance is improved. The control also adapts
to varying conditions of refrigerator use and operating con-
ditions and hence, system efficiency is greatly improved.
Other features of the invention will be apparent from
the following description and from the drawings. While an
illustrat.ive embodiment of the invention is shown in the drawings
and will be described in detail herein, the invention is
susceptible of embodiment in many forms and it should be under-
stood that the present disclosure is t:o be considered as an
exemplification of the principles of t,he invention and it is
not intended to limit the invenkion to the embodiment illustrated.
BRIEF DESCRIPTION OF T~IE DRAWINGS
Fig. 1 is a front elevational view of a refrigerator-
freezer with portions of the freezer door, the fresh food door
and the cabinet wall broken away to reveal the components therein;
Fig. 2 is a sectional view taken along line 2-2 of
Fig. l;
Fig. 3 is an enlarged elevational view of a portion
of the evaporator, the defrost heater and the bi-metal sensor
utilized by the present invention;
Fig. 4 is a block diagram of the adaptive defrost
control system of the present invention;
Fig. 5 is a partial schematic diagram of the control
logic shown in block form in Fig. ~; -
V
7, .
Fig. 6 is a schematic diagram of the temperature
sensing circuit of the control logic shown in block form in
Fig. 4;
Fig. 7 is a schematic diagram of the evaporator fan,
condenser fan, and compressor circuits of the adaptive defrost
control system of the present invention; and
Fig. 8a, 8b and 8c, comprise a single flow chart of
the control program contained in the control logic.
DESCRIPTION OF THE PR~FERRED EMBODIMENT
- Turning to Figs. 1, 2 and 3, a conventional refrigera-
tor-freezer 20 is illustrated in conjunction with the unique
adaptive defrost control system. The refrigerator-freezer 20
includes a cabinet 22 which may enclose a plura:Lity of re-
frigerated compartments, cooled by a forced air refrigeration
system A fresh food compartment door 24 in conjunction with
the cabinet 22 and a divider wall 26 enclose a fresh food
compartment 28. A freezer compartment 30 is enclosed by the
cabinet 22, the divider wall 26, and a freezer door 32. The
fresh food and freezer compartments are cooled by passing
refrigerated air into the compartments through a discharge air
duct 34 and appropriate outlet means such as outlet grill 36,
illustrated in the freezer compartment. A similar outlet
grill tnot shown) is provided in the fresh food compartment
28.
Air is refrigerated as a result of being passed in
heat exchange relationship with an evaporator 38 and is forced
by an evaporator fan 40 into the refrigerated compartments 28
and 30. Return air is circulated through an air inlet 42
and a duct (not shown) in divider 26 to the-evaporator 38.
The refrigeration apparatus includes a conventional compressor
44, condenser 46, and accumulator or header 48, interconnected
through tubing to the evaporator 38 to effect the flow of
refrigerant thereto. A condenser fan 50 circulates air through
-the condenser 46, and may be energized concurrently with the
compressor 44 and the evaporator fan 40.
The evaporator 38 and the evaporator fan 40 are dis-
posed within an evaporator compartment 52 which is enclosed by
the cabinet 22 and a rear wall 54 of the reezer compartment
30. A conventional bi-metal sensor 56 is located adjacent the
coils of the evaporator 38 near the header 48. The bi-metal
sensor 56 operates to terminate the defrosting operation in a
manner to be described.
Disposed between the coils of the evaporator 38 in
the form of a loop is a defrost heater 58, Fig. 3, which is
periodically energized by the adaptive defrost control of the
present invention to de-ice the evaporator 38. The defrost
heater 58 may be a conventional resistive heater that is
energized directly from the a.c. line under the control of a
relay or triac.
A freezer door switch 60 having an actuating rocker
arm 60a and a contact 60b is mo~nted on the cabinet 22 so that
the rocker arm 60a contacts the closed freezer door 32. A
similar fresh food door switch 62 having an actuating rocker arm
62a and a contact 62b is mounted on the cabinet 22 with the
rocker arm 62a in contact with the closed fresh food compartment
door 24. The rocker arms 60a and 62a are spring loaded so that
when one of the doors 24 or 32 is opened, the corresponding
rocker arm 6Oa or 62a moves outwardly, out of contact with the
corresponding door 24 or 32, thereby causing the contact 60b or
62b of the switch 60 or 62 to close.
Referring to Fig. 4, a block diagram of the adaptive
defrost control system is illustrated, which may be implemented
using digital logic or through the use of a microcomputer.
In the preferred embodiment illustrated, a single chip micro-
computer 64 is used to implement the defrost control. The
micro-computer integrated circuit may be a conventional,
single-chip device and may include on the chip, a 1,024 x 8-bit
program read only memory, or ROM 66, and a 64 x 4-bit scratch
pad random access memory, or RAM 68. The microcomputer 64 also
contains a central processing unit, or CPU 70 which performs
the various computations used in the adaptive control process.
The ROM 66 contains the control program, the control logic,
and the constants used during control execution. The R~M 68
contains registers which store the several variables used in
the control program. Also included in the RAM 68 are a fresh
food seconds timer register 71, a freezer seconds timer
register 73, and a minute timer register 72. While for pur-
poses of clarity the RAM 68 has been illustrated as containing
separate storage registers for each variable, it is to be
understood that each storage register may contain the value
of several variables over the course of a program execution.
In the illustrated embodiment, microcomputer 64 is
implemented by using an American Microsystems, Inc. 52000
Microcomputer which has, in addition to the ROM 66, the RAM 68
and the CPU 70, a switch interface and a seconds timer (not
shown) for the 60 Hz. power line which powers the defrost control
and the associated components.
The inputs to the microcomputer 64 include the fresh
food door switch 62, the freezer door switch 60, a defrost
sensor 74, and clock pulse circuitry 76 which controls the
internal timing of the microcomputer 64. Another input to
the microcomputer 64 is from a temperature sensing circuit 78
which controls the energization of the compressor 44 in accord-
ance with the temperature of the fresh food and freezer com-
partments 28 and 30.
Outputs from the microcomputer 64 are coupled to
energize the defrost heater 58, the evaporator fan 40, the
condenser fan 50 and the compressor 44.
The adaptive defrost control system utilizes various
data to determine when a defrost operation should be initiated.
These data include the number and duration of freezer and
fresh food compartment door openings, the duration of the
previous defrosting operation, and the total accumulated com-
pressor run time since the previous defrosting operation. The
number and duration of compartment door openings are indicated
by the door switches 60 and 62 associated with the two compart-
ment doors 2~ and 32. The durat.ion o~ the defrosting operation
is determined by monitoring the bi-metal sensor 56 and measuring
the amount of time it takes from the start of the defrosting
operation until the evaporator 38 reaches a predetermined
temperature, such as 55F, indicating that the frost has been
removed.
Defrosting is provided at variable intervals as
determined by a weighted accumulation of the number and duration
of freezer and fresh food door openings. The microcomputer 64
stores a number or count that must be decremented to zero before
a defrost operation is initiated. This count, referred to as
TBD (time before a defrost operation is required), is decremented
by a first predetermined amount for each second of the first 10
seconds that the freezer door 32 is open and thereafter
decremented by a second amount. The TBD count is decremented
by a third predetermined amount for each second of the first
10 seconds that the fresh food compartment door 24 is open, and
- thereafter decremented by a fourth amount.
The Gontrol weights the first 10 seconds of door
opening more heavily than the rest of the "door-open" interval,
i.e., the variable TBD is decremented by a certain amount
during the first lO seconds that a door is open, and by a lesser
amount thereafter. The amount of frost accumulated during the
initial interchange of the dry refrigerated air with the moist
ambient air is greater than for following intervals of the same
duration. That is, the large temperature differential during
the initial lO seconds causes a rapid interchange of air which
results in the forming of a larye amount of frost.
The variable TBD is decremented by different amounts
depending upon whether the fresh food compartment door 24 is
open or the freezer compartment door 32 is open. These
decrementing values, also referred to as weighting functions
and denoted as CDEC and FDEC, respectively, are varied by an
adaptive portion of the control process to force the length
of the defrosting operation toward a predetermined desired
value, such as 16 minutes. The decrementing variables are
adaptively varied as a function of the previous defrost history
and the duration of the most recent defrost operation. How-
ever, the control does not operate to define a defrost interval
that must elapse before the next defrost operation. Rather,
it is a comparison of the length of a defrost operation to a
desired value, not the mere length o the defrost operation
itself, that determines the magnitude and direction of change
in the weighting functions that are used to determine when the
-10 ~
~L~4~30
next defrost operation is necessary.
The decrementing values CDEC and FDEC are updated,
when necessary, by adding to them an integer multiple of a
correction factor CFCR, which is derived by comparing the actual
defrost time, denoted ACTDEF, with a desired defrost time DESDEF.
The particular integer multiple used depends upon the decrementing
yariable being updated. In general, CECR is multiplied by 3
when updating CDEC, and by 4 when updating FDEC.
Normally, once the number TBD has been decremented
to zero, the defrost heater 58 is energized. However, inhibiting
means (and a compressor timer) are provided for preventing the
initiation of a defrost operation if TBD reaches zero before a
predetermined minimum amount of compressor operating time has
been accumulated. The control chec]cs for minimum compressor
run time when TBD reaches zero to determine whether the
defrost indication is due to an excessive number of door openings.
Under this condition, the adaptive portion of the control
process is disabled. As the adaptive defrost con~rol takes
into account the previous history of the defrosting operations,
it is desirable to prevent the control from adaptively varying
the decrementing variables CDEC and FDEC due to an abnormal
condition, such as excessive door openings.
The defrost control is reset by the control logic
to initiate defrost shortly after a power interruption. The
control utilizes a volatile storage system which loses all
storage data if a power intçrruption occurs. Therefore, if a
power interruption occurs immediately before defrost is to be
initiated, the loss of data could cause a missed defrost
operation. Depending upon ambient conditions, several missed
defrosts could cause failure of the system. Consequently,
81)
this feature ensures that a defrost operation will take place
within a relatively short time after a power interruption.
In Figs. 5, 6 and 7, the circuit of the adaptive
defrost control system shown in block form in Fig. 4, is
illustrated in detail. Two power supply inputs VGG and VDD
for the microcomputer 64, Fig. 5, are both connected to a
source of supply potential V+ which, illustratively, may
supply 8.5 volts to the microcomputer 64. Another power
supply input Vss is connected to ground potential GND.
A clock input CLK is connected to the source of
ground potential GND through a capacitor Cl and a line 79.
The line 79 .is also connected to the supply voltage V+
through a resistor Rl. The resistor Rl and the capacitor
Cl form the clock pulse circuitry 76 for the internal clock
of the microcomputer 64.
The door-open information is inputted to the micro-
computer 64 over two input lines Kl. and K2. The contact 60b
of the freezer door switch 60 is connected to the input K2
through a resistor R2 and to supply potential V+ through a
resistor R3. Similarly, the contact 62b of the fresh food
door switch 62 is connected to the input Kl through a resistor
R4 and to voltage supply V+ through a resistor ~5. The
opposite terminals of both switches are connected together and
to the source of ground potential GND. The input K2 is also
connected to ground potential GND through a capacitor C2 and
to voltage supply V+ through a capacitor C3. Input Kl is
connected to GND through a capacitor C4 and to V+ through a
- capacitor C5.
` The determination of whether a door is open is made
by comparing the voltage on input lines Kl and K2 to a reference
-12-
voltage which is inputted to a KREF input of the microcomputer
64. In the preferred embodiment, the voltage on the KREF input
is zero volts. If the switch contact controlled by the rocker
arm 60a or 62a corresponding to the input K2 or Kl is open,
a signal is detected on one of these K lines by comparing the
voltage on the line to a voltage on the KREF input. If the
contact 60b or 62b associated with the particular "K" line is
closed, a low state signal is detected by comparison with the
voltage on the KREF input.
A RUN/WAIT control input is connected to supply
potential V+. Another "K" line input K8 is connected to
supply potential V+ through a resistor R6.
Two additional data inputs Il and I4, described
hereinafter, monitor the run time of compressor 44 and the
defrost heater 58 operating time, respectively.
Referring specifically to Fig. 6, there is illustrated
the temperature sensing circuit 78 which periodically sends
a trigger signal to the microcomputer 6~ to energize the com-
pressor 44 in response to the difference between the ~emp-
erature within the refrigerator and a desired temperature,or "set point". For a detailed description of the operation
of the temperature sensing circuitry 78, reference should be
made to United States Patent No. 4,2~7,851 which issued to
Stephen Paddock and Andrew Tershak on November 3, 1981.
Briefly, when the temperature sensed by a thermistor 80 rises
above the set point as determined by a potentiometer 82
and a voltage divider network consisting of resistors R7 and
R8, the output of a comparator Ul will change to a low state,
indicating that
- 13 -
cooling is required. This low state signal is sent to the
input of a comparator U2 through an RC circuit consisting of a
resistor R9 and a capacitor C6 which causes the output of U2
to assume a high state.
Conversely, when the temperature sensed by the
thermistor 80 is below the set point, the output of the com
parator Ul assumes a high state which is coupled to the input,
of U2 through the RC network consisting of the resistor R9 and
the capacitor C6. The high state input causes the output of
the comparator U2 to assume a low state.
The output of comparator U2 is sent over a line 84 to
the input Il, Fig. 5, through a resistor R10. The line 84 is
also connected to the voltage supply V-~ through a resistor Rll
and the input Il is connected to GND t:hrough a capacitor C7.
Referring to Fig. 7, the fan, compressor and heater
circuits are illustrated in detail. A transformer and rectifying
circuit 85 provides suitable voltages for the various components
of the control. ~n a.c. line voltage of approximately 120
volts is provided between a line 86 and a ground line 88 to the
evaporator fan 40, the condenser fan 50 and the compressor 44
through a relay contact 90a of a conventional compressor relay
90. The contact 90a is a normally open contact which is closed
by an associated actuating coil 9Ob. A diode Dl, connected
across the actuating coil'9Ob, dissipates the back emf generated
by the coil 90b when it is switched from an energized to a de-
energized state.
Also connected between the line 86 and the ground
linè 88 are the defrost heater 58, the bi-metal sensor 56, a
sensing coil 92, and a movable contact 94a of a relay 9~. The
0
movable contact 94a is a normally open contact which is closed
by an actuating coil 94b having a diode D2 connected thereacross
to dissipate the back emf of the coil.
; The actuating coils 90b and 94b each have a terminal
,, ~ . .
90c and 94c, respectively, connected to a line 96 which has a
fully rectified d.c. voltage of 15 volts impressed thereon.
The other terminals of actuating coils 90b and 94b are connected
via lines 98 and 100, respectively, to other components of the
control.
Running through the sensing coil 92 is a sensing line
102 which is connected at one end to the defrost sensor 74,
which may be a reed switch, and at its other end to ground
potential GND. The reed switch defrost sensor 74 has a normally
open movable contact 74a which closes in response to current
flowing through the sensing coil 92. The other end of the
- defrost sensor 74 is connected by a line 108 to an input I4,
Figure 5, of the microcomputer 64 t:hrough a resistor R12. The
line 108 is connected to supply voltage V-~ through a resistor
R13. The input I4 is connected to ground potential GND through
a capacitor C8.
The transformer and rectifying circuit 85, Fig. 7, also-
provides a half-wave rectified output of 60 Hz. over line 110
to an input 112a of a driver circuit 112 through a resistor R14,
Fig. 5. The input 112a is connected to ground potential GND
through a capacitor C9. The driver circuit 112 amplifies the
voltage appearing at the input 112a and sends the output over
a line 114 to an input I8 of the microcomputer 64. The line
114 is connected to supply potential V~ through a resistor R15.
The half-wave rectified voltage appearing at input I8 is
utilized by the seconds timer (not shown)of thè microcomputer 64.
--15--
.
g~c~
The unfil-tered rectified 15 volt output on line 96
is filtered by an LC circuit composed of an inductor Ll and a
capacitor C10 and is sent over a line 116 to a regulating cir-
cuit 118. The output of the regulating clrcuit 118 is sent
over line 120 to the various parts of the control as supply
potential V+, illustratively equal to +8.5 volts.
A control output Al of the microcomputer 64 is
connected to an input 112b of the driver circuit 112 through a
resistor R16. The driver 112 acts to isolate the microcomputer
64 from the balance of the circuit. The voltage appearing at
the input 112b is amplified and is sent over the line 100 to
the actuating coil 94b of the relay 94, Fig. 7.
Another control output A2 is connected through a
resistor R17 to an input 112c of the driver circuit 112. The
driver circuit 112 amplifies the voltage appearing at input
112c and sends the amplified voltage over the line 98 to the
terminal of the actuating coil 90b of the relay 90.
The control circuitry illustrated in Figs. 5 and 6,
except the door switches 60 and 62, may be mounted on a circuit
board 122 which in turn may be mounted behind a control panel
124 located in one of the refrigerated compartments, Fig. 1.
Referring now to Figs. 8a-8c, the control program
of the adaptive defrost control system will be described. The
program cycle is executed once each second to continuously update
the system condition.
A block 150, Fig. 8a, initializes the variables used
in the control program. The time before defrost count stored
- in the TsD register is assigned a value of zero minut~s. The
value stored in the CDEC register, which represents the number
of minutes TBD is decremented each second during the first 10
seconds of fresh food door opening, is assigned a value of 24
minutes per second. The value s-tored in the FD~C register,
which represents the number of minutes TBD is decremented each
second during the first 10 seconds of freezer door opening, is
assigned a value of 32 minutes per second. A MINRUN register,
the value of which represents the minimum amount of compressor
run time before a defrost can be initiated, is assigned a value
of 360 minutes or 6 hours. An adaptive defrost enable flag ADF
is enabled by assigning to it a value of 1. An ACTDEF register,
the value of which represents the actual length of defrost time
is assigned a value of zero minutes. The seconds timer registers
71 and 73 are assigned a value of 10 seconds and the minute
timer register 72 is set equal to 60 seconds.
A decision block 152 then determines whether the Eresh
food door is open. The block 152 senses the input Kl of the
microcomputer 64 and determines whether a low state signal is
present thereon, indicating that the fresh food compartment
door 24 is open. If affirmativej then the seconds timer 71 is
decremented by 1 second b~ a block 153 and control passes to a
decision block 154.
The decision block 154 determines whether the fresh
food compartment door 24 has been opened for less than or e~ual
to 10 seconds. This is accomplished by the block 154 reading
the contents of the seconds timer register 71. If the block
154 determines that the contents of the seconds timer register
71 is greater than zero, then a block 156 decrements the value
of TBD (i.e. the count) by the current value stored in the CDEC
register.
If the block 154 had determined that the fresh food
compartment doox was open for greater than 10 seconds, i.e. the
8~
contents of the seconds register was less than or equal to zero,
then block 158 would have decremented the value of TBD by 1.
Control ~rom the blocks 156 and 158 passes directly to a
decision block 160.
If block 152 determined that the fresh food door 24
was closed, control would pass to a block 155 which would reset
the seconds timer register 71 to 10 seconds. Control from the
block 155 advances to the decision block 160.
The decision block 160 determines whether the freezer
door is o~en by monitoring the input K2 of the microcomputer
64 with the same st~ps as were performed by the block 152.
If the block 160 determines that the freezer door is open, then
a block 161 decrements the value stored in the freezer seconds
timer by one. A decision block 162 then determines whether
the door has been open less than or equal to 10 seconds. If
this is the case, a block 164 decrem~nts TBD by FDEC. If such
is not the case, a block 166 decrements TB~ by 2. Control from
block 164 and 166 shifts to a decision block 168.
If block 160 determines that the freezer door is not
open, then a block 163 resets the freezer seconds timer register
73 to 10 seconds. Control then shifts to the decision block 168.
The decision block 168, Fig. 8b, determines whether
the compressor is on. This is performed by monitoring the
input Il of the microcomputer, Fig. 5, to determine whether it
carries a high state signal. This high state signal is sent by
the temperature sensing circuit 78 to indicate that cooling is
required and to instruct the microcomputer 64 to energize the
compressor 44. If cooling is required, then a high state signal
is sent from the output ~2 to the line 98 to energize the
actuating coil 90b, Fig. 7, of relay 90 which closes the movable
-18-
38~
contact 90a. The compressor 44 is then energized along with the
condenser fan 50 and the evaporator fan 40.
If the decision block 16B determines that the compressor
is on, then the minute timer 72 is decremented by one second by a
block 169. Then a decision block 170 determines whether the
minute timer 72 has expired, i.e. is equal to zero. If this is
the case, then a block 171 resets the value stored in the minute
timer 72 to 60 seconds. A block 172 then decrements the contents
of the register TBD by one and a block 174 decrements the value
stored in the MINRUN register by one.
If desired, the control program can be modified so that
the register TBD will be decremented at a greater rate by block
172 whenever excessive compressor run times are being experienced.
For example, the register TBD could be decremented by six each
time the system goes through the control program and the com-
pressor has been operating continuously for thirty minutes or
more. This would tend to shorten th~3 time until the next defrost
operation takes place, but the actual time required is still a
function of the number and duration of door openings.
Control then passes from block 174, or from block
170 in the event that the minute timer has not expired, to a
decision block 176. However, if the decision block 168 had
determined that the compressor was not on, control would shift
back to the block 152 to begin another program execution.
The decision block 176 determines whether the contents
of the MINRUN and TBD registers are less than or equal to zero.
If the values stored in either the MINRUN or TBD registers are
greater than zero, then control passes to another decision block
178 which tests to determine whether the ~INRUN value is not
equal to zero and TBD is equal to zero. If the determination
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is affirmative, then TBD has been decremented to zero before
the minimum amount of compressor 44 run time has accumulated
because of an excessive number of door openings. Therefore,
control shifts to a block 180 which assigns a value of zero
to the adaptive defrost enable flag ADF, thereby disabling an
adaptive portion of the defrost control process, which is
described below. It will be appreciated that during the first
run through the control program the value of TBD will always
be less than or equal to zero, since TBD was initialized to
zero by block 150.
If the determination made in block 178 is negative, a
block 182 assigns a value of 1 ~o the adaptive defrost enable
flag, thereby enabling the adaptive portion of the control pro-
gram. Contro:l from the blocks 180 and 182 passes directly back
to the decision block 152 to continue the control program.
If the decision block 176 decides that MINRUN is
less than or equal to zero and that TBD is less than or equal
to zero, a block 184 initiates defrosting o the evaporator
coils by enabling output A2 in Fig. 5. The output A2 de-
energizes the line 98, Fig. 7, causing the actuating coil 90b
of relay 90 to open the movable contacts 90a. When the movable
contact 90a is open, the evaporator fan 40, the condenser fan
50 and the compressor 44 are de-energized.
Next, the output Al of the microcomputer 64, Fig. 5,
is energiæed by-the block 184, thereby energizing the line 100
and hence the actuating coil 94b of relay 94, Fig. 7. The
energization of the actuating coil 94b causes the movable
contact 94a to close. Because the evaporator 38 is at a low
temperature, the bi-metal sensor 56 is bent into contact with
the defrost heater 58, thereby completing a circuit through
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9~
the movable co~tact 94a, the sensing coil 92, the defrost
heater 58 and the bi-metal sensor 56. The defrost heater 58
is consequently energized by the lines 86 and 88 and begins
to raise the temperature of the evaporator coils 38. Once
the block 184 has initiated defrost, control shifts to a
block 186.
The block 186, Fig. 8b, monitors the minute timer 72
and assigns the actual length of time the defrost heater 58
has been energized to the ACTDEF register. A decision block
188 then determines whether the value stored in the ACTDEF
register is less than a constant value, denoted`MAXDEF,
which represents the maximum allowable defrost time. The
value of MAXDEF is stored in the ROM 66 and in the preferred
embodiment is set equal to 21 minutes.
If the decision block 188 determines that the value
stored in the ACTDEF register is less than the MAXDEF value,
then a decision block 190 determines whether the bi-metal
sensor 56 has moved out of contact with the defrost heater 58,
indicating that the evaporator 38 has been warmed sufficiently
to remove the frost load. If current is flowing through the
sensing coil 92, indicating that the movable contact 94a is
closed and that the bi-metal sensor 56 is in contact with the
defrost heater 58, the contact 74a of the reed switch defrost
sensor 74 will oscillate at 120 Hz. This condition of the
contact 74a of the defrost reed switch sensor 74 causes a low
state signal to appear at the input I4 of the microcomputer
64. Consequently, if a low state signal is detected at the
input I4 by the block 190, the bi-metal sensor 56 is not open
and hence control passes back to the block 186 which updates
the value of ACTDEF.
If, however, a high state signal is detected at the
input I4, the bi-metal sensor 56 is in an open state and
control passes to a decision block 192, Fig. 8c, which
determines if the adaptive defrost enable flag ADF is enabled.
If the value of ADF is equal to 1, then a block 194 subtracts
the value of a constant DESDEF, stored in the ROM 66 and which
represents the desired length of time to perform a defrost
operation, from the value of ACTDEF and assigns the integer
portion of the result to the correction factor register CFCR.
The constant DESDEF, in the preferred embodiment, is set
equal to 16 minutes.
A block 196, in conjunction with the block 194, Fig.
8c, comprise the adaptive portion of the control program. The
block 196 updates the decrementing values stored in the
registers CDEC and FDEC by adding to them an integer multiple
of the value stored in the register CFCR. As previously men-
tioned, the value stored in the CDE,C register is updated by
adding to it the current correction factor value stored in the
CFCR register multipled by 3. The decrementing value stored
in the EDEC register is updated by adding to it the current
correction factor value stored in the CFCR register multiplied
by 4.
The adaptive portion of the control process varies
the values stored in the CDEC and FDEC registers so as to take
into account the previous defrost history. When an integer
multiple of the correction factor CFCR is added to the values
-` of CDEC and FDEC, the count will be decremented during
the next defrost interval by a greater or lesser amount when
a compartment door is open. Whether the count is decremented
by a greater or lesser amount depends upon the length of the
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.
0
immediately preceding defrost operation, as compared to the
desired defrost operation duration DESDEF. Generally, if the
value stored in the ACTDEF register is less than the value of
DESDEF, then the values stored in the CDEC and FDEC registers
will be made smaller resulting in a larger accumulated frost
load than before on the evaporator 38, which in turn requires
a longer defrost operation to remove.
Alternatively, if the value of ACTDEF is greater
than the value of DESDEF, the values stored in the CDEC and
FDEC registers will be made larger, resulting in a smaller
frost load accumulation than before. This condition results
in a shorter defrost operation duration for the next defrost
operation.
Consequently, the adaptive portion of the control
process tends to force the duration of the defrost operation
towards the predetermined optimum duration DESDEF by taking
into account the previous defrost history.
A block 198, Fig. 8c, then assigns the value of
~,640 minutes to the variable TBD. Control passes directly
to the block 198 if the decision block 192 determines that
the variable ADF is equal to zero. Control after block 198
then shifts to a block 200.
If the decision block 188 determines that the actual
defrost time ACTDEF is equal to or has exceeded the maximum
defrost time MAXDEF, then control shifts to a block 202 which
resets the decrementing variables CDEC and FDEC to their
inLtialized values and assigns a value of zero minutes to the
~variable TBD. It should be noted that this assignment of
values will cause the next defrost operation to take place as
soon as the minimum compressor 44 run time ~INRUN has elapsed.
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Control from the block 202 shifts directly to the
block 200 which resets the value of MINRUN to the initialized
value of 360 minutes. A block 204 then terminates the defrost
operation by de-energizing the output Al, causing the line 100
and the actuating coil 94b to become de-energized. This
causes the movable contact 94a to open, thereby removing the
source of electrical power supplied through lines 86 and 88
from the defrost heater 58. The evaporator fan 40, the
condenser fan 50 and the compressor 44 may then be energized
by the output A2 if the temperature sensing circuit 78 so
indicates.
Control from the block 204 then shifts back to the
block 152, Fig. 8a, to begin another program execution.
It should be noted that should a power outage occur,
the control program upon power resumption will initiate a
defrost operation after 360 minutes of compressor 44 operation.
This is due to the particular assignment of values made by the
block lS0, Fig. 8a, which assigns a. value of zero minutes to
the TBD register and 360 minutes to the MINRUN register
immediately following power restoration.
Some or all of the concepts embodied in the present
invention may be implemented through the use of discrete
components, such as counters, digital logic components, or
the like.
Those skilled in the art will appreciate that
numerous variations on the control scheme disclosed herein
are comprehended by the present invention. For example it
would be possible to determine the interval between defrost
~ operations by adaptively varying the starting magnitude of
the stored count, rather than the manner in which the count is
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0
changed, as a function of the compartment door openings. It
would also be possible to adaptively vary the stored count as
a function of only the number of door openings or only the
duration of door openings, rather than combine both of these
variables as in the illustrated em~odiment. Further, it
would be possible to adaptively vary the stored count as a
function of other variables that indicate either the usage or
operating environment of the refrigeration apparatus.
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