EP0721092A2

EP0721092A2 - Controlling defrost in a refrigerated compartment

Info

Publication number: EP0721092A2
Application number: EP95120450A
Authority: EP
Inventors: John P. Duve
Original assignee: Eaton Corp
Current assignee: Eaton Corp
Priority date: 1995-01-06
Filing date: 1995-12-22
Publication date: 1996-07-10
Also published as: CN1151507A; CA2166571A1; EP0721092A3; BR9600423A; JPH08254375A

Abstract

An electromechanical defrost control system (10) for a refrigerator which uses the compressor cycling thermostat (14) to incrementally advance a ratchet (30) each compressor cycle. The ratchet (20) drives a cam (18) which closes a defrost heater selector switch (16) when a predetermined accumulated number of compressor cycles have occurred. Upon the compartment being heated, the thermostat (14) incrementally advances the cam (18) which returns the selector switch (16) to the compressor operating position and de-energizes the defrost heater (25).

Description

BACKGROUND OF THE INVENTION

The present invention relates to controlling operation of an electrically operated defroster for refrigerated compartments such, as for example, the freezer compartment in a refrigerator and particularly refrigerators of the type produced in high volume for household usage. Refrigerators manufactured for household usage are sold in a highly competitive market place and it is necessary to reduce the manufacturing cost to a minimum in order to compete in this market.
Heretofore, it has been common place in household refrigerators to employ a small subfractional horsepower motor for driving an electromechanical timer to actuate and diactuate a switch for energizing and de-energizing an electrical heater provided for defrosting/deicing the freezer compartment. This timer motor driven switch arrangement for controlling a defrost heater has proven to be relatively cost effective. However, the small synchronous timing motors are notorious for field problems of low torque and thus frequent burn-out due to current overloading of the fine wire coils employed therein which results in annoying and costly field service replacement of the defrost timer. Where all-electronic controllers have been employed for such defrost heater control, it has been found that the electronics required have resulted in a controllers that have not been cost competitive with electro-mechanical controllers. Thus, it has long been desired to find a way or means of simply and reliably defrosting a refrigerated compartment, particularly in household refrigerators without using a timing motor driven programmer or complex and costly electronic controls.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an electromechanical programmer for energizing and de-energizing a defrost heater for a refrigerated compartment without the need for a motor driven timing mechanism.
It is another object of the present invention to energize the defrost heater for a refrigerated compartment by electro-mechanical means upon completion of a certain accumulated number of on/off cycles of the refrigerant compressor.
The present invention provides a cam operated selector switch for selecting between operation of the refrigerator compressor and a defrost heater. The cam is operated by an advanced mechanism incrementally advanced during each on/off cycle of the compressor; and, the cam is operative upon a predetermined number of accumulated advances to move the selector switch from a position energizing the compressor to a position completing a circuit for the defrost heater. Upon the next incremental advancement of the advancement mechanism, the selector switch is returned to a position de-energizing the defrost heater and a position selecting compressor operation. The advance mechanism preferably comprises an advance pawl and ratchet where the advance pawl is pivoted by a connecting means in the form of a linkage actuated by a temperature sensing element in the refrigerated compartment. The temperature sensing element also actuates and de-actuates a line power switch to the cam operated selector switch. The refrigerated compartment temperature sensor advances and retracts the advanced pawl each occurrence of the opening and closing of the line switch by the refrigerated compartment temperature sensor. A separate temperature sensor de-actuates the defrost heater upon warming of the compartment by the defrost heater in the event of a failure of the compressor controlling temperature sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawing comprises a schematic of a control system for a refrigerator compressor and defrost heater embodying the principals of the present invention.

DETAILED DESCRIPTION

Referring to the drawing, the control system of the present invention is indicated generally at 10 and includes a refrigerated compartment indicated by dashed outline and reference numeral 12 which has disposed therein a temperature transducer means such as a thermostatic control or thermostat indicated generally at 14. Control 14 operates an advance mechanism which effects operation of a selector switch indicated at generally at 16 which is operated by a cam 18. The cam is advanced by an advance mechanism indicated generally at 20 which is operatively connected to the thermostat 14 as indicated by the dashed line in the drawing.
Selector switch 16 selects between a position operating a refrigerant compressor 22 generally located remotely from the compartment 12 and a defrost heater 25 generally associated with the compartment 12.
The thermostat 14 includes a line switch indicated generally at 24 which has a movable contact arm 26 connected to one side L1 of a power line and a stationary contact 28 which is connected to the common terminal of switch 16 which comprises preferably a single-pole double-switch 16. Switch 16 has one side contact 30 thereof connected to junction 32 which is connected to one side of the compressor 22 and one side of a freezer fan motor 34. The opposite side of the compressor 22 is connected to power line junction 36 on side L2 of the power line; and, the opposite side of fan 34 is connected to power line junction 38 on power line L2.
Switch 16 has another opposite side contact 40 which is connected to one side of defrost heater 25 which has its opposite side connected to one terminal of a thermostatic switch indicated generally at 42 which has the other side thereof connected to power line junction 44 on line L2. Switch 42 is operated by a defrost temperature sensor 46 associated with the refrigerated compartment 12.
Switch 16 is biased to the position closing against contact 30 for compressor energization by a suitable bias means such as spring 48 and has a cam follower 50 provided on the movable arm of the switch.
The advance mechanism 20 preferably comprises a pivoted advance pawl 52 which engages upon upward movement, teeth 54 of ratchet wheel 56 which is connected as indicated by dashed line in the drawing for, upon rotational movement, rotating cam 18. Pawl 52 is connected to a link member 58 which is pivoted for movement by the thermostat temperature sensing element 60. Link member 58 is also connected with a lost-motion slotted connection and pin 62 to the arm 26 of switch 24 as indicated in dashed line in the drawing.
If desired, a door switch 64 may be connected in series with an interior light 66.
In operation, it will be understood that after a predetermined number of accumulated incremental advances of the ratchet wheel 56 by pawl 52, on the order of 8 to 12 compressor cycles typically, cam 18 acts against cam follower 50 to move switch 16 from the position shown in dashed outline of the drawing to the position shown in solid outline for contacting side contact 40 which effects and energization of the defrost heater and de-energization of the compressor. Upon the defrost heater raising the compartment 12 to a predetermined temperature, temperature sensor 60 is operative to close line switch 24 and move linkage member 58 for retracting pawl 52 an amount sufficient to incrementally advance ratchet wheel 56 and cam 18 to return the switch 16 to the position shown in dashed outline closing against contact 30 and to re-energize the compressor.
The present invention thus provides a unique and novel electromechanical system for energizing a refrigerator defrost heater after an accumulated number of refrigerant compressors cycles without the need for a motor driven timing mechanism.
Although the invention has hereinabove been described with respect to the illustrated embodiment, it will be understood that the invention is capable of modification and variation and is limited only by the following claims.

Claims

A defrost control system for a refrigerator having a cooled compartment comprising:
(a) compressor means operable upon electrical energization for circulating refrigerant for cooling the compartment;

(b) heater means operable upon electrical energization to effect defrosting of said compartment;

(c) temperature transducer means operable to provide movement of an actuator means in response to the temperature in said compartment reaching certain levels;

(d) pawl means connected for pivotal movement by said actuator member;

(e) ratchet means operable to be sequentially advanced by said pawl means and including a cam for advanced therewith;

(f) first switch means including cam follower means movable between a first position and a second position by said cam upon a desired number of accumulated incremental advances thereof, said switch means operable to energize only said compressor in said first position and operable to energize only said heater means in said second position;

(g) second switch means connected with said first switch means and said second switch means connected to said actuator means, wherein said sensing means is operable when said first switch means is in said first position to open and close said second switch means for cycling said compressor means in response to temperature changes in said compartment.
The control system defined in claim 1, wherein said first switch means comprises a single-pole double-throw switch.
The control system defined in claim 1, further comprising means biasing said first switch means to the first position.
The control system defined in claim 1, wherein said cam is a rotary cam.
A defrost control system for a refrigerator having an electrically operated compressor circulating refrigerant for cooling a compartment comprising;
(a) temperature transducer means operable to provide movement of an actuator means in response to the temperature in said compartment reaching certain level;

(b) heater means operable upon electrical energization to effect defrosting of said compartment;

(c) selector switch means operable, upon connection to a source of electrical power, and actuation between a first and second condition to selectively energize one of said compressor means and said heater means in the first condition and the other in said second condition;

(d) summing means connected to be incrementally advanced by each movement of said actuator means, and upon a predetermined accumulated number of said advances operative to effect change of said selector switch means between said first and second condition an upon the next subsequent incremental advance operative to cause said selector switch means to return to said first condition;

(e) line switch means series connected with said selector switch means and operatively connected to said actuator means for energizing and de-energizing said compressor in response to changes in the sensed temperature of said compartment.
The control system defined in claim 5, wherein said summing means includes a rotary cam advanced by a ratchet and pawl, said pawl being connected to said actuator means.
The defrost control system defined in claim 5, wherein said selector switch means comprises a single-pole double-throw switch.
The defrost control system defined in claim 5, further comprising means biasing said selector switch to said first position.
The defrost control system defined in claim 5, wherein said accumulator means includes a rotary cam rotated by a ratchet wheel indexed by a pawl pivoted by said actuator means.
The control system defined in claim 5, wherein said line switch means comprises a thermostat.
A method of controlling defrosting in a compartment cooled by an electrically operated compressor circulating refrigerant there through comprising:
(a) providing a thermally responsive actuator and actuating a power line switch and energizing the compressor when the sensed temperature rises above a first level and de-actuating said switch and de-energizing the compressor when the sensed temperature falls below a second level;

(b) incrementally advancing a cam with each cycle of energization and de-energization of said compressor;

(c) switching power from the compressor to a defrost heater in response to said cam being advanced a certain accumulated number of incremental advances; and,

(d) switch power from the defrost heater to the compressor upon the next sequential incremental advance of said cam;
The method defined in claim 11, wherein said incrementally advancing includes pivotally moving a pawl with said actuator and advancing a ratchet wheel connected to the cam.
A defrost control system for a compartment cooled by circulation of refrigerant comprising:
(a) compressor means operable upon electrical energization for effecting said refrigerant circulation;

(b) heater means operable upon energization to effect defrosting said compartment;

(c) temperature transducer means operable to provide movement of an actuator means in response to the temperature in said compartment reaching certain level;

(d) advance means operable to be incrementally advanced by said actuator means for each on/off cycle of said compressor means;

(e) cam means responsive to said incremental advancement of said actuator means;

(f) selector switch means operated by said cam means selecting operation of said heater means upon an accumulated number of said incremental advancements of said advance means;

(g) line switch means operable to connect and disconnect said selector switch to a source of power in response to movement of said actuator means.