US3546894A - Frost weighing demand defrost device for refrigerators - Google Patents

Description

C. D, ESCI-IE FROST WEIGHING DEMAND DEFROST DEVICE FOR REFRIGERATORS Filed May 2, 1969 2 Sheets-Sheet l awww.

Inf/eric?? C. D. ESCI-IE Dec. l5, 1970 FROST WEIGHING DEMAND DEFROST DEVICE FOR REFRIGERATORS Filed May 2, 1969 2 Sheets-Sheet 2 United States Patent Oqce 3,546,894 Patented Dec. 15, 1970 3,546,894 FROST WEIGHING DEMAND DEFROS'I DEVICE FOR REFRIGERATORS Charles D. Esche, Newburgh, Ind., assignor to Whirlpool Corporation, a corporation of Delaware Filed May 2, 1969, Ser. No. 821,322 Int. Cl. F25d 21/02 U.S. Cl. 62-140 13 Claims ABSTRACT OF THE DISCLOSURE Apparatus for initiating a -defrost operation of a refrigeration system having an evaporator and means for defrosting the evaporator. The apparatus includes a frost collector arranged to be disposed adjacent the evaporator for collection of frost thereon concurrently with deposition of frost on the evaporator. A control mechanism is associated with the frost collector to initiate operation of the defrosting means as a result of a collection of frost on the collector having a preselected weight. The mechanism is arranged to periodically sense the weight of the collected frost. Means are provided for adjusting the mechanism to effect initiation of the defrost operation upon the Weight reaching any one of a plurality of preselected weights. The mechanism further includes means for adjusting the duration of the defrost operation.

BACKGROUND lOF THE INVENTION Field of the invention This invention relates to refrigeration systems and in particular to apparatus for controlling defrost operatlons in refrigeration systems.

Description of the prior art A large number of different devices and apparatus have been developed for sensing the need for and initiating defrosting operations in refrigeration apparatus. In one form of conventional refrigeration apparatus an evaporator provides heat exchange with the air to be cooled. Frost is deposited on the evaporator as a result of the cooling of the air, and the collection of such frost presents a serious problem in the operation of the refrigerator apparatus as it tends to block free air flow through the evaporator and decrease efficiency of operation. The amount of frost collected varies with the humidity and temperature conditions of the air being cooled. Thus it is desirable to provide a control means which is responsive to the amount of frost actually deposited on the evaporator. However, such systems are relatively complex and costly and resort is conventionally had to control mechanisms which defrost the evaporator at fixed time intervals. Such iixed interval defrosting, however, has the disadvantage of inefficiency as the defrosting is effected at times when not required such as when the air to be cooled is relatively dry cool air. On the other hand there are times when the defrosting operation of the means for defrosting the evaporator to defrost time intervals as when the air to be cooled is relatively hot humid air.

SUMMARY OF THE INVENTION The present invention comprehends an improved apparatus for controlling a defrost operation in a refrigeration system eliminating the disadvantages of the above discussed defrost controls in a novel and simple manner. More specifically, the invention comprehends an improved apparatus for initiating a defrost operation of a refrigeration system having an evaporator and means for defrosting the evaporator, the apparatus comprising a frost collection element, means for supporting the elementin juxtaposition to the evaporator to have frost collected thereon concurrently with collection of frost on the evaporator, and means responsive to an increase in the weight of the element and frost collected thereon for initiating operation of the means for defrosting the evaporator to defrost the evaporator and said element.

Still more specifically the invention comprehends the provision of such an apparatus having means for causing the sensing of the weight to be periodical.

Still more specifically, the invention comprehends the provision of such an apparatus having means for adjusting the operation thereof to initiate the defrost operation as a function of any one of a plurality of different preselected combined weights of the collection element and collected frost.

Still further more specifically the invention comprehends the provision of such apparatus having means for adjustably controlling the duration of the `defrosting operation.

The invention also comprehends the provision in such apparatus of a control mechanism including a lever, means for pivotally mounting the lever, a carrier, means for pivotally mounting the carrier adjacent the lever, means for resiliently biasing the lever and carrier to pivot the lever relative to the carrier, means on the lever for collecting frost and tending to pivot the lever in opposition to the biasing means, and switch means carried by the carrier to be actuated as a result of a preselective pivoting of the lever resulting from a preselected collection of frost on the collecting means.

Still further, the invention comprehends the provision of such a control mechanism having improved means for adjusting the operation thereof.

BRIEF DESCRIPTION OF THE DRAWING Other features and advantages of the invention will be apparent from the following description taken in connecytion with the accompanying drawing wherein:

FIG. 1 is a fragmentary side elevation of an apparatus for initiating a defrost operation in a refrigeration system embodying the invention;

FIG. 2 is a fragmentary side elevation illustrating arrangement of the control mechanism as upon the initiation of a defrost operation;

FIG. 3 is a fragmentary left end view thereof;

FIG. 4 is a fragmentary top plan view thereof;

FIG. 5 is a schematic diagram of the electrical wiring of the refrigeration system;

IG. 6 is a perspective view of the control mechanism; an

FIG. 7 is a front view of a refrigerator-freezer provided with the control mechanism.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the exemplary embodiment of the invention as shown in the drawing, a refrigeration system generally designated 10 is shown to include a control mechanism 11 which is responsive to a frost condition in an evaporator 12 to initiate automatically a defrosting operation thereof. The evaporator may comprise a conventional evaporator, one form of such evaporator structure being illustrated in FIG. 7 wherein the evaporator 12 is disposed rearwardly of a false rear wall 44 at the rear of the freezer compartment 45 of a conventional refrigerator-freezer apparatus 46. As shown, the control mechanism 11 may be secured to the cabinet 47 to Ibe disposed superjacent the evaporator.

As discussed briey above, the control mechanism functions as a demand defrost device in that it effects an initiation of the defrost operation upon a frost build-up in the evaporator to a preselected point. As shown in FIG. 1,

the control mechanism 11 includes a collection element 13 which is disposed within a space 14 between the ns 15 of the evaporator 12, so as to have frost collect thereon in correspondence to the frost collection on the ns 15. 'Control mechanism 11 is arranged to sense periodically the combined weight of the element 13 and the frost collected thereon, and to initiate the defrost operation when this weight reaches a preselected weight corresponding to a defrost condition of the evaporator requiring such defrosting.

Referring briefly to FIG. 5, the refrigeration system 10 includes a compressor motor 16 connected in series with a conventional relay 17 and starting capacitor 18 to the power supply lead L-l. The compressor motor is further connected through an overload device 19, a conventional thermostat switch 20, and a defrost control switch 21 to the other power supply lead L-2. A defrost heater 22 is connected through an overload device 23 between power supply lead L-1 and the switch 21. More specically, switch 21 comprises a single pole, double-throw switch having moving contact 21a connected to power supply lead L-2, a fixed Contact 21b connected to the overload device 23, and a second fixed contact 21C connected to the thermostat switch 20. A timer motor 24 is connected between power supply leads L-1 and L-2 for continuous energization. Thus, in normal operation, the compressor motor 16 is energized when the thermostat switch 20 closes as a result of a high temperature in the space wherein the switch is disposed. The control switch 21 is normally disposed, as shown in FIG. 5, with the moving contact 21a contacting xed contact 21C to complete the circuit to power supply lead I.-2. At this time, the defrost heater 22 is not energized.

Control mechanism 11 is arranged to effect operation of defrost heater 22, as discussed above, as a result of the increase in the weight of the collected frost on element 13. More specifically, as shown in FIGS. 1 through 4 and 6, control mechanism 11 includes a lever 25 which is piv otally mounted to a frame 26 by a pivot pin 27. A double element carrier '28 is similarly pivotally mounted on the frame 26 by the pivot pin 27 to extend adjacent the lever 25. The timer motor 24 is mounted on the frame 26 and drives a generally circular cam 29. As shown in FIG. l, the lever extends past cam 29 to overlie evaporator space 14, and collection element 13 is hung from the distal end 30 of the lever 25 by a hanger 31.

The lever 25 is biased in a counterclockwise direction as seen in FIG. 1 and the carrier 28 is biased in a clockwise direction as seen therein by a spring 32 having a coil portion 32a wrapped about pin 27, a first end portion 32h engaging the lever 25, and a second end portion 32e` connected to the carrier 28 through an adjusting screw 33. The adjusting screw may be locked in an adjusted position by a suitable nut 34 so as to permit ixed adjustment of the spring biasing action tending to urge lever 2'5 and carrier 28 angularly apart on pivot pin 27. As shown in FIG. 1, switch 21 is carried `on carrier 28 to have its actuator 35 disposed closely subjaeent lever 25 to be actuated thereby as a result of a clockwise movement of the lever 25. The clockwise movement of the lever 25 is limited by an adjustable stop screw 36 carried on a bracket 37 on frame 26 to be disposed closely subjacent the lever 25.

Lever 25 is provided inwardly of end 30, with a longitudinally slot 38 adapted to receive a pointed projection 39 on the cam 29. A pin 40 is carried on cam 29 to engage periodically a turned portion 41 at the end of carrier 28.

A stop `bracket 42 is mounted on frame 26 subjacent the carrier 21S to limit the downward, or clockwise, pivoting thereof.

The operation on control mechanism 11 is extremely simple while yet providing the above described highly desirable control of the frosting operation. As indicated above, timer motor 24 operates continuously to drive came 29 in a counterclockwise direction as seen in FIG. l. Periodically, i.e., once during each revolution of cam 29, the projection 39 bears against the underside of lever 25 and pivotally raises the lever about pivot 27 to raise the collection element 13 and frost collected thereon relative to space 14. Pin 40 engages the end -41 of the carrier 28 to lift the carrier substantially concurrently with the lifting of lever 25.

As the counterclockwise rotation of the cam 29 continues, projection 39 enters slot 38 of the lever 25 permitting the lever to pivot downwardly against the biasing force of spring 32 as the result of the total weight of the element 13 and the frost collected thereon. As thecarrier 28 is now supported by the pin y40, the lever moves downwardly toward the carrier. If the total weight of the collected frost and the element 13 are suicient to swing the lever 25 against the biasing action of spring l32 to cause the lever to engage actuator 35 of switch 21, the moving contact 21a is thrown from fixed contact 210 to xed contact 21b thereby disconnecting the compressor motor 16 and connecting the defrost heater 22 between power supply leads L-1 and L-Z, to initiate the defrosting operation. If, however, the total weight of element 13 and the frost collected thereon is insuflicient to pivot the lever 25 against the biasing action of spring 32 sufficiently to engage actuator 35, switch 21 remains as shown in FIG. 5 and no defrosting operation is initiated during this cycle of the cam 29. As the cam 29 continues its counterclockwise rotation, pin 40 moves sufiiciently downwardly to permit the carrier 28 to pivot downwardly and engage the limit stop 42. At the same time, the lever 25 is permitted to pivot downwardly until it engages the adjustable limit stop screw 36 thereby increasing the angular displacement between the carrier and lever. The carrier and lever will remain in the downward position against stops 42 and 36 respectively, until the cam once again brings pin y40 and projection 39 upwardly to engage the carrier 28 and levers 25 as discussed above relative to the previous cycle. The sensing of the weight of element 13 and collected frost is again conducted as discussed above and a defrost operation initiated or the control allowed to further cycle in a manner as discussed above depending on the total weight of the element and collected frost.

The weight of frost necessary to effect an initiation of v defrosting operation is controlled by the adjustable screw 33 which provides a variable biasing between the lever 25 and carrier 28. More specifically, spring end 32C may be xed to a washer 43 through which the screw 33 passes. Thus, as the screw is threaded into the carrier, the washer 43 is urged to the right, as seen in FIG. 1, thereby increasing the force biasing the lever 25 upwardly and thereby increasing the weight of frost on element 13 necessary to initiate the defrost operation. A reverse threading of screw 33 effects an opposite control of the preselected weight, i.e., it permits a decrease in the weight necessary to effect the defrost initiation.

Adjustable stop 36 provides a further highly desirable feature in control 11 in permitting an adjustment of the period of the defrost operation. By adjusting screw 36 to its maximum upward disposition, as shown in FIG. 1, a minimum defrost operation time is obtained as the pin 40 permits the carrier 28 to move downwardly from the lever 25 at an earlier point of time. By adjusting the screw 36 downwardly, the lever 25 is permitted to move further in a clockwise direction assuming that suicient weight of frost on element 13 is present to overcome the biasing force of spring 32. Thus, carrier 28 must move downwardly a greater distance to terminate the defrost operation as the switch 21 must move further downwardly to disengage actuator 35 vfrom the now more downwardly disposed lever 25.

During a defrost operation, the frost on element 13 will melt and the weight tending to bias the lever 25 downwardly may decrease to below that necessary to maintain the lever 25 in actuating relationship to switch actuator 35. When this occurs the defrost operation is terminated by opening of switch 21, i.e., the throwing of moving contact 21a from fixed contact 2lb to fixed contact 21e. If the weight of the frost on element 13 is not decreased to the point where the lever 25 is spaced from actuator to terminate the defrost operation as a result of the defrosting of element 13, the defrost operation is terminated automatically by the movement of the pin suficiently to permit both the lever 25 and carrier 28 to pivot downwardly, i.e., in a clockwise direction, to engage the lever 25 with the stop screw 36 while permitting the carrier to continue to move downwardly to stop 42 and thereby carry the switch away from the lever. Thus, control 11 provides selective termination of the defrost operation either by a sulicient removal of frost from collection element 13, or lby a maximum time of defrost as controlled by cam 29. It should be noted that the sensing of the weight of frost on element 13 is periodically effected in contradistinction to those devices wherein the slow build-up of frost on a sensing element gradually causes the movement of a sensing means to effect a control operation at the instant a preselected weight is reached. In such gradual control devices, the refrigeration system may be over-sensitive in that any vibration as in closing of the refrigerator door or any slight shock forces may initiate the defrost operation at times when the total weight is not yet the preselected Weight. In the control 11, on the other hand, sensing of the weight of the collected -frost on the element 13 is effected periodically so that during a major portion of time, vibrations and shocks imparted to the refrigeration system ha-ve no effect on the operation of the control. While the Weight of element 13 is a part of the total weight sensed lby the control mechanism 11, the element weight remains constant at all times and, thus, may be cancelled out by suitable selection of the spring parameters. Thus, control mechanism 11 provides substantial improvement in operation over conventional frost sensing devices Iwhich sense the total weight of the evaporator, as such a system provides a -variable weight in the evaporator corresponding to the amount of refrigerant present therein at any given time.

The use of lever 25 and carrier 28 permits the application of suitable mechanical advantages in control mechanism 11 for improved sensitivity. Further, by virtue of the adjustable screw 33, variations in the parameters of spring 32 may be cancelled out by the refrigerator manufacturer so as to permit the accurate preselection of the frost Weight necessary to initiate operation of the defrosting cycle.

Having described my invention as related to the ernbodiment shown in the accompanying drawings, it is my intention that the invention be not limited by any of the details of description, unless otherwise specified, but rather, be construed broadly within its spirit and scope as set out in the accompanying claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Apparatus for initiating a defrost operation of a refrigeration system having an evaporator and means for defrosting the evaporator, said apparatus comprising:

a frost collection element;

means for supporting said element in juxtaposition to said evaporator to have frost collected thereon concurrently with collection of frost on the evaporator; and

means responsive to an increase in the Weight of said element and frost collected thereon to a preselected weight for initiating operation of the means for defrosting the evaporation to defrost the evaporator and said element.

2. The refrigeration system apparatus of claim 1 wherein said last named means includes means for sensing said weight periodically and precluding initiation of 6 operation of the means for defrosting the evaporator at all other times.

3. The refrigerationl system apparatus of claim 1 wherein said supporting means comprises a lever mechanism and last named means comprises a switch means actuated by a preselected movement of said lever mechanism.

4. The refrigeration system apparatus of claim 1 wherein said supporting means includes a cam means for cyclically deactivating said last named means for permitting initiation of operation of the means for defrosting the evaporator only periodically.

5. The refrigeration system apparatus of claim 1 further including means for adjusting said apparatus to effect initiation of operation of the means for defrosting the evaporator at any one of a plurality of different preselected weights.

6. The refrigeration system apparatus of claim 1 further including means for adjustably controlling the duration of operation of the means for defrosting the evaporator.

7. The refrigeration system apparatus of claim 1 further including means for terminating the operation of the means for defrosting the evaporator after a preselected time subsequent to the initiation of operation thereof.

8. The refrigeration system apparatus of claim 1 further including means for terminating operation of the means for defrosting the evaporator when the weight of said element and frost thereon decreases to a preselected weight as a result of removal of frost from said element in the defrosting operation.

9. The refrigeration system apparatus of claim 1 further including means for periodically sensing the weight of said element and frost thereon after initiation of the operation of the means for defrosting the evaporator to terminate operation `when the weight of said element and frost thereon decreases to a preselected Weight as a result of removal of frost from said element in the defrosting operation.

10. Control mechanism comprising:

a lever; means for pivotally mounting said lever;

a carrier; means for pivotally mounting said carrier subjacent said lever;

means for resiliently biasing said lever and carrier to pivot said lever relative to said carrier; means on said lever for collecting frost and tending to pivot said lever in opposition to said biasing means;

and switch means carried by said carrier to be actuated as a result of a preselection pivoting of said lever resulting from a preselected collection of frost on said collecting means.

11. The control mechanism of claim 10 further including means supporting the lever against the Weight of said collecting means and frost, and means periodically vitiating said supporting means to pivot the weight to urge the lever to actuate said switch means.

12. The control mechanism of claim 11 wherein said vitiating means comprises an adjustable screw.

13. The control mechanism of claim 11 including means for adjusting the biasing force of said means for resiliently biasing said lever and carrier.

References Cited UNITED STATES PATENTS 1,815,383 7/1931 Scullen 62--139 2,511,419 6/1950 Smith 62--140 3,229,474 l/ 1966 Wilson 62-140 MEYER PERLIN, Primary Examiner U.S. Cl. XR. 62-l5l, 157

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