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Title:
ICE MAKER CONTROL CIRCUIT
United States Patent 3859813
Abstract:
An improved control circuit for a commercial automatic ice cube maker of the type wherein a slab of ice is formed on a freezing plate by flowing water thereover. The circuit provides a more uniform control means that is independent of atmospheric pressure effects by means of a mercury ice thickness control thermostat switch connected between the base and emitter of a transistor, such that upon sensing a predetermined temperature of the built up ice slab the thermostatic switch opens to cause the transistor to switch ON and operating relay means to stop the water pump and close the solenoid operated defrost valve while opening second relay contacts in the thermostat switch circuit such that the system is locked in its ice slab release mode. During the ice slab release mode the mercury thermostatic switch closes while a defrosting operation of the plate causes the ice slab to release and slide onto an ice cutting grid, tripping a mercury type switch, connected from the emitter to the base of the transistor, turning the transistor OFF and causing a deenergization of the relay means thereby restarting the ice making cycle of the ice maker.


Inventors:
CANTER JAMES A
Application Number:
05/416681
Publication Date:
01/14/1975
Filing Date:
11/16/1973
Assignee:
General Motors Corporation (Detroit, MI)
Primary Class:
Other Classes:
62/320
International Classes:
F25C1/12; F25D21/02; (IPC1-7): F25C1/12
Field of Search:
62/320,138,348
View Patent Images:
US Patent References:
3760600ICE-MAKING APPARATUS1973-09-25Matsui et al.
3045446Refrigerating apparatus1962-07-24Thomas
2784563Ice making apparatus1957-03-12Baker
Primary Examiner:
O'dea, William F.
Assistant Examiner:
Tapolcai Jr., W. E.
Attorney, Agent or Firm:
Barthel, Edward P.
Claims:
I claim

1. A solid state refrigeration control circuit for an automatic icemaker operative for sensing the presence of a finished slab of ice on a freezer plate and initiating an ice harvest cycle for the icemaker, means for refrigerating said plate to form an ice slab thereon, and means for defrosting the freezer plate and causing the ice slab to slide onto an ice cube cutting grid, said control comprising, in combination; a mercury ice thickness control thermostat switch; a normally open grid switch being operable upon the slab of ice sliding from the freezing plate onto the cutting grid to close; a transistor having a base, an emitter and a collector; a rectifier circuit for producing rectification of an AC power input, said rectifier circuit having one terminal connected to both said grid switch and said mercury thermostat switch, said rectifier circuit other terminal connected to the base of said transistor via biasing means; normally closed first switch means connecting said transistor base to said mercury thermostat switch; second switch means having a normally closed contact energizing the plate refrigerating means and a normally open contact for providing an electrical path when closed for energizing the freezer plate defrosting means; said mercury thermostat switch being positioned a preselected distance above the plate such that when a predetermined thickness of the ice slab is achieved the temperature of the ice slab is sensed by said mercury thermostat switch whereby said mercury thermostat switch opens causing said transistor to be triggered conductive; and transfer means operable, when energized by said conductive transistor, to open said normally closed first switch means and move said second switch means from its plate refrigerating contact to its freezer plate defrosting contact.

2. A solid state refrigeration control circuit for an automatic icemaker operative for sensing the presence of a finished slab of ice on a freezing plate and initiating an ice harvest cycle for the icemaker, means for refrigerating said plate to form an ice slab thereon, means for defrosting the freezing plate and causing the ice slab to slide onto an ice cube cutting grid, said control circuit comprising, in combination; a mercury ice thickness control thermostat switch; a grid switch being actuated upon the slab of ice sliding from the freezing plate onto the cutting grid; an NPN transistor having a base, an emitter and a collector; a bridge circuit for producing rectification of the AC power input; said bridge circuit having one terminal connected to a terminal of both said grid switch and said mercury thermostat switch, and its other terminal connected, at a junction point, to the base of said transistor through a biasing resistor; normally closed first switch contacts connecting said transistor base to the other terminal of said mercury thermostat switch, second switch means having a normally closed contact energizing the plate refrigerating means and a normally open contact for providing an electrical path when closed energizing the freezer plate defrosting means, said biasing resistor being of a value such that when a predetermined temperature of the ice slab is sensed by said thermostat mercury switch said thermostat switch opens directing the current flow through the base-emitter circuit of said transistor whereby said transistor is triggered conductive, and transfer means operable, when energized, to open said normally closed contact of said first switch means and close the normally open contact of said second switch means to energize said defrosting means and initiating the ice slab harvest cycle, said transfer means including a relay exciting coil connected, in series with the collector-emitter circuit of said transistor, between said junction point and said one terminal of said bridge circuit.

3. A solid state refrigeration control circuit for an automatic icemaker operative for sensing the presence of a finished slab of ice on a freezing plate and initiating an ice harvest cycle for the icemaker, means for refrigerating said plate to form an ice slab thereon, a hot gas solenoid controlled valve operative for defrosting the freezing plate and causing the ice slab to slide onto an ice cube cutting grid, and pump means for distributing water on the freezing plate, said control circuit comprising, in combination; a mercury ice thickness control thermostat switch; a grid switch being actuated upon the slab of ice sliding from the freezing plate onto the cutting grid; an NPN transistor having a base, an emitter and a collector; a diode bridge rectifier for producing full wave rectification of the AC power input; said bridge rectifier having one terminal connected to a terminal of both said grid switch and said mercury thermostat switch, and its other terminal connected, at a junction point, to the base of said transistor through a biasing resistor; said other terminal also connected to one side of an exciting coil of a double pole-double throw relay, the other side of said exciting coil connected to said transistor collector, said relay including a first single pole section and a second double pole section, the normally closed contact of said single pole section connecting said transistor base to the other terminal of said mercury thermostat switch, the normally closed contact of said second double pole section operative for energizing the plate refrigerating means and the normally open contact thereof operative for providing an electrical path when closed energizing the freezer plate hot gas solenoid for defrosting the plate, the ohmic value of said biasing resistor being such that when a predetermined temperature of the ice slab is sensed by said thermostat mercury switch said thermostat switch opens directing the current flow through the base-emitter circuit of said transistor, whereby said transistor is triggered conductive to energize said exciting coil and open said normally closed contact of said first single pole section and close the normally open contact of said second double pole section of said relay to energize the hot gas solenoid and initiating the ice slab h harvest cycle.

Description:
This invention relates to automatic refrigerating apparatus and more particularly to an improved control circuit for an automatic ice maker.

It is an object of this invention to provide an improved control circuit for an automatic ice cube making apparatus to sense the thickness of a finished slab or layer of ice and initiate an ice harvest cycle that does not require adjusting for variations in altitude between the place of manufacture and the altitude of the place of installation. The prior art, as exemplified in U.S. Pat. No. 2,784,563 issued Mar. 12, 1957, to Baker and assigned to the same assignee as the instant invention, uses an interlocking electro-mechanical system for sensing the thickness of a slab of ice incorporating a thermostatic switch, an ice harvesting relay, a heating element to heat the thermostatic switch expansible and contractable gas filled bulb and its sealed tube between the bulb and the thermostat together with miscellaneous other switches. This system has proved satisfactory once adjusted for variations introduced because of differing atmospheric pressures. That is, the ice maker requires readjusting between its point of manufacture and the final location where it is installed depending upon whether it is at a higher or lower altitude. The bulb heating element, which also requires a time consuming operation for servicing, is necessary to provide the bulb within the ice slab feeler receptacle with a small amount of heat to quickly raise the temperature of the gas expanding the bulb and closing the thermostatic switch as explained in U.S. Pat. No. 2,995,905 issued Aug. 15, 1916 to Ayres et al., the disclosure of which is incorporated by reference herein.

It is therefore another object of this invention to provide a transistorized control circuit for an automatic ice maker wherein a slab or layer of ice is formed on an inclined freezing plate by flowing water thereover, the slab being released from the plate when an ice thickness control mercury sensor switch is cooled by the built up ice slab. The cooled sensor switch opens causing the transistor to switch ON and trip open a relay stopping the water pump and closing the defrost solenoid controlled valve; while at the same instant by means of opening the relay in the sensor switch circuit the control system is locked in the slab release mode. During the ice slab release operation the sensor switch recloses. When the ice slab moves onto the cutting grid its presence causes a closing of a switch resulting in the transistor being turned OFF dropping out the relay and restarting the ice making cycle.

In the accompanying drawing, FIG. 1 is a circuit diagram illustrating the electrical components of a preferred embodiment of the present invention.

Referring now to FIG. 1, a preferred embodiment of the invention is illustrated as indicating a step-down transformer 10 with the 115 volt power mains indicated at L1 and L2 connected via wires 11 and 12 to the primary of the transformer 10. The transformer 10 steps down the line voltage to a low voltage, as for example about 14 volts, suitable for use in heating the cutting wires of an ice dissector, cutter or grid 14 such that the slab of ice slides automatically onto the cutting grid where the grid cuts the ice slab into a plurality of ice cubes which fall through the grid into a storage bin. An example of one such automatic ice making apparatus is shown and described in the above-mentioned U.S. Pat. No. 2,784,563 to Baker and assigned to the assignee of the present invention, the disclosure of which is incorporated by reference herein.

The wires 16 and 17 are connected from the secondary of the transformer to the grid 14 with the line 17 shown fused at 18. A small amount of current is drawn from the transformer secondary to provide the necessary low voltage suitable for use is heating the cutting wires of the grid with no danger of injury or shock to those operating the ice maker. The secondary of the transformer is shown connected to a full wave bridge rectifier 20, comprising diodes 21, 22, 23 and 24 and a filter capacitor 26 to provide the necessary D.C. voltage for the circuit. While a full wave D.C. power supply rectifier is shown it will be appreciated that a D.C. power supply using a half wave rectifier could be used without departing from the scope of the invention.

A coil 28 of a double pole-double throw relay 30 has one side connected by wires 31 and 32 to one output terminal 33 of the bridge rectifier 20 while wire 34 connects the other side of the coil 28 to the collector 35 of an NPN transistor 36. The bridge rectifier 20 is also connected from its other terminal 38 by lines 39 and 41 to switch means 40 which in the preferred form is a pivotal or tilt type mercury switch having tubular-like glass member with liquid mercury and electrical contacts sealed therein as shown in U.S. Pat. No. 2,887,852, issued May 25, 1959 to Thomas for an Ice Maker. As disclosed by the Thomas patent, the ice slab slides onto the ice cutting grid, actuating the switch means 40 and causing the switch means 40 to trip closed. The grid switch 40 is connected by lines 42 and 43 to the base 44 of the transistor 36, while the lines 43, 42 and 46 connect the transistor base 44 to first switch means in the form of movable contact 47 of the single pole section of double pole-double throw (DP-DT) transfer means or relay 30 whose fixed contact 48 is in turn connected by wire 49 to one lead of a mercury slab thickness temperature sensor switch 50. The thickness sensor mercury switch 50 is connected by lines 51 and 52 to the emitter 54 of the transistor 36.

Terminal 62 of the transformer primary is connected by lines 63 and 64 to fixed contact 65 of a double pole-double throw service switch 66 whose movable contact 67 is connected by line 68 to power line L1. Fixed contact 65 is connected via lines 64 and 69 to an ice collecting bin thermostat electric switch having a movable contact 70, which may be of any desired conventional construction. The lines 71 and 72 connect the fixed contact 73 of the bin thermostat through an overload thermostat 74. The line 75 connects the overload thermostat 74 to electric motor windings 76 and 77 of a motor-compressor unit (not shown) while lines 78 and 79 respectively, lead to a conventional start relay 80 including a coil 81 and movable contact 82. The relay fixed contact 83 is connected via line 84 through motor start capacitor 85 and thence connected by line 86 to terminal 87 energized by the other line side L2 of the power source.

The power line L2 is also connected by wires 88 and 89 to water pump motor windings 90 which is in turn connected by wire 91 to fixed terminals 92, 93 and second movable contact 94 of the service switch 66. The movable contact 94 is shown connected via wires 95 and 96 to the ice maker's condenser fan motor windings 97 which is in turn connected by wire 98 to the L2 side of the power source. The wire 99 is connected from terminal 100 to the fixed contact 102 of the relay 30 and thence through relay second switch movable contact 103 and wire 104 to terminal 105 and thence to the line L1 of the power source. The other fixed contact 106 for movable contact 103 is connected by line 107 to the coil 108 of a solenoid controlling a defrost hot gas valve such as shown, for example, in U.S. Pat. No. 3,049,894 issued Aug. 21, 1962 to J. R. Pichler et al., the disclosure of which is incorporated by reference herein. As described in the Pichler patent, when the hot gas solenoid valve is actuated, hot refrigerant gas flows to an evaporator plate causing the plate to be warmed resulting in the ice slab being released to slide down the inclined plate surface onto a cutter wire grid. The transistor 36 has a biasing resistor 110 which is shown connected by line 43 to the transistor base 44 and by lines 31 and 111 to the cathode of a diode rectifier 112 while line 114 connects the anode of the diode 112 via line 115 to the transistor collector 35. It will be noted that the diode 112 is not required provided the transistor has a high enough breakdown voltage.

In operation assume the ice maker unit is making ice with the pump motor 90 energized, the mercury ice thickness control thermostat or sensor switch 50 closed and with the mercury grid switch 40 open. When the ice thickness control thermostat switch 50 is cooled to the desired temperature, which in the disclosed form is about 35.5° F. by the build up of the ice slab on the evaporator plate, the switch 50 opens causing the emitter 54 base 44 junction to be forward-biased by the current flow in resistor 110. The transistor 36 switches On to conduct allowing current to flow in the collector 35 to emitter 54 circuit energizing the relay coil 28, tripping the DP-DT relay 30 and causing movable contact 103 to move to fixed contact 106 stopping the water pump motor 90 and condenser fan 97 and completing the current path through line 107 energizing the hot gas solenoid coil 108 for the defrost and ice slab release cycle.

At the same time by moving the movable contact 47 of relay 30 away from fixed contact 48 to open line 49 connected with the ice slab sensor thermostatic switch 50 the control circuit is locked in the slab release mode of operation. While the ice slab release cycle is in operation, wherein warming the evaporator plate is occurring, the mercury sensor thermostatic switch 50 warms and recloses. Upon the ice slab being released from the evaporator plate, its presence on the cutting grid 14 causes a pivoting and closing of the mercury grid switch 40 with the result that the transistor 36 is now reverse-biased and will not conduct, i.e., is turned OFF, dropping out the relay coil 30 and returning the first and second switch means 47 and 103 to their ice slab making position shown initiating a new ice making cycle. It will be noted that the closing of the grid switch 40 will normally be only momentarily but the grid switch 40 will remain closed if for any reason the ice slab remains on the top of the cutting grid 14.

While the embodiment of the present invention constitutes a preferred form, it is to be understood that other forms might be adopted.