US3229474A - Refrigerator defrosting apparatus - Google Patents

Description

Jan. 18, 1966 E. L. WILSON ETAL 3,229,474

REFRIGERATOR DEFROSTING APPARATUS Filed March 14, 1963 2 Sheets-Sheet 1 INVENTOR. EUGENE L. WILSON BENJAMIN M. SMITH J n- 1966 E. L. WILSON ETAL 3,229,474

REFRIGERATOR DEFROSTING APPARATUS Filed March 14, 1963 2 Sheets-Sheet 2 s7 ZI E- I II L] CUE LJQ Li -2 INVENTOR EUGENE L. WlLSON BENJAMIN M. SMITH 3,229,474 Patented Jan. 18, 1966 fitice 3,229,474 REFRIGERATOR DEFROSTING APPARATUS Eugene L. Wilson, 3207 Kentucky Ave., Baltimore 13, Md., and Benjamin M. Smith, 4994 Denmore Ave., Baltimore 15, Md.

Filed Mar. 14, 1963, Ser. No. 265,196 2 Claims. (Cl. 62-140) This invention relates generally to defrosting apparatus and more specifically to an electrical defroster which is independent of any timing action and assures a positive determination for the defrost cycle.

Many types of defrosting systems for both commercial and domestic refrigerator use are known today. Generally, these types of defrosters either use a separate heat source such as an electrical resistance heater or a reverse refrigeration cycle wherein the warmer refrigerant is pumped through the coils in order to defrost the evaporator. Most of the defrosters have a timer which controls the start and termination of a defrost cycle. Not only do these timers add to the expense of manufacturing the defrosting apparatus but they also provide a set defrosting cycle which oftentimes provides defrosting when it is not really necessary or, conversely, which terminates the defrost cycle before the coils become completely defrosted.

Attempts have been made to overcome this type of operation by providing a defrosting apparatus which is initiated by a build up of the frost on the coils, thus providing a defrost cycle only when it is necessary. However, once the defrosting cycle is started, a timer is still used to terminate the defrost period and thus there is no termination point related to the amount of frost on the coils. This also can result in either too short a cycle or one that extends beyond the time necessary, resulting in possible damage to the equipment and the coils.

It has been proposed that this defect could be overcome by using coils which are movable and which are supported by some resilient means whereby a defrost cycle will be started as a result of the weight of the ice building up to a predetermined amount on the coils thus causing the coils to drop and cut on a switch to an electrical heater. In this type of operation the cycle is terminated when enough of the frost has melted to reduce the weight on the coils and allow them to gradually return to their original position. To the best of our knowledge, this type of defrosting apparatus has never proved to be satisfactory, primarily due to the fact that there are too many variables which add to or subtract from the weight of the coils besides the frost alone. These include the varying weight of the refrigerant itself and the oil which is naturally in the system. Although this does not materially affect the start of the cycle under this proposed type of system, it does vary enough to hold the coils in the defrost position even when the coils are completely free from any ice.

Accordingly, it is an object of this invention to provide defrost apparatus for a refrigerating system which is entirely independent of any timing device.

Another object of this invention is to provide defrost apparatus which eliminates unnecessary defrost cycles.

Yet another object of this invention is to provide defrosting apparatus which has a positive termination point independent of the weight of the coils and the gas therein.

A further object of this invention is to provide a simplified defrosting cycle wherein the cycle is terminated by means of gas pressure which varies proportionately with the heat supplied during the defrost cycle.

These and other objects will become apparent from the following description when taken in conjunction with the drawings wherein:

FIG. 1 is a diagrammatic showing of one form of the present invention;

FIG. 2 is a schematic of the electrical circuitry used in connection with FIG. 1; and

FIG. 3 is a partial schematic of a modified version of the apparatus of FIG. 1.

Generally speaking, the invention comprises an automatic defrosting means used in conjunction with refrigerating systems including evaporator coils which comprises a means for pivotally mounting the coils at one end thereof within an enclosure, resilient means within the enclosure for supporting the other end of the coils, means within the enclosure for releasably retaining the coils in first and second positions about the pivotal mounting means, a resistant heater within the enclosure, a switch actuated by the releasable retaining means for supplying electric power to the heater when the coils are in their second position, pneumatic pressure means within the enclosure adapted to contact and move the coils from the second to the first position in response to a predetermined pressure applied thereto, and tubing coupled to the pneumatic pressure means and containing refrigerant gas which is responsive to the heat created by said resistance heater, the heat increasing the pressure of the gas within the tubing thereby actuating the pneumatic pressure means.

Turning now more specifically to the drawings, there is shown in FIG. 1 an evaporator coil 11 having a closed circuit configuration through the condenser and compressor 21 which is driven by a motor 23 through mechanical coupling 25. Also shown are the normal dissipating plates 13 directly connected to the evaporator coil 11. The coil 11 is supported in a movable manner by means such as a U-shaped supporting structure 15 which is mounted pivotally at 19 to the base 17 of the enclosure. For purposes of clarity the remaining part of the enclosure is not shown.

In the specific illustration of FIG. 1, an arm 27 extends from the support structure 15 and moves substantially vertically as the support member rotates about pivot 19. In order to provide a support for the outer end of the structure 15, a compression spring 29 is located below the arm 27. Spring 29 rests on base cup 33 which is mounted on the base portion 35 of the enclosure. Secured to the top of the spring is a cup 31 which bears against the adjustable screw 37. By providing the adjustable screw, the position of the coils in their dry or defrosted condition may be set with relation to spring 29. Since the positioning of the coils higher above plate 31, by means of screw 37, would require a greater compression of spring 29 before actuation of switch 51, a larger total coil and frost weight would be needed for such actuation. Accordingly, such adjustment provides a means whereby the start of the defrost cycle can be adjusted in accordance with varying amounts of frost accumulation on the coils 11 and plates 13. Thus, the same result is achieved as would be if the tension of spring 29 were adjustable and the plate 31 were to bear directly against arm 27.

A bellows 39 is also mounted below arm 27 on the base 35. This bellows may be made of a material such as copper which will not be attacked by normal refrigerant gases in use today. A capillary tube 41 connects the inner chamber of the bellows to the low side of the evaporator coil at 43 for purposes which will be more thoroughly discussed as the description proceeds. It will be evident that, as the bellows expands, the plate 45 secured to the top thereof will abut against the adjustable screw 47, thus providing an upward force against the arm 27 resulting in a return of the coils to the refrigerating position.

A lever 49 is secured to the outer end of arm 27 by means such as welding and, as indicated schematically in FIG. 2, is connected to a two position snap action switch 51 employing springs 63 and 65. Therefore, the lever can only be in one of two positions, the first of which is as shown in FIG. 1 when the refrigerating process is normally underway and the second position being that of a lowered position which initiates the defrost cycle.

A switch 51 is actuated by the lever 49 and controls the basic refrigerating and defrost power supply. Switch 51 is connected by means of leads 53 and 54 to the motor 23 and resistance heater 59.

The operation of the device will be explained in connection with the electrical schematic of FIG. 2 and the apparatus of FIG. 1. With the device in the position shown in FIG. 1, the normal refrigerating condition exists with the compressor-condenser 21 delivering the refrigerant to the evaporator coils in the usual manner. When the frost is accumulated on the coils to a sufificient extent, the additional weight overcomes the tension of the compression spring 29 and the coils commence to drop in a counter clockwise direction about pivot 19. When the coils have dropped far enough to force the lever 49 past its midpoint position the snap action of the springs will force the lever down into its second position, thereby holding the coils against the force of the compression spring 29. 4

Under the refrigerating cycle the bellows are designed so that they are in their nonexpanded condition since the gas in the lower side of the evaporator coils and in the capillary tubing 41 is at a low temperature and pressure.

When the coils are in their lowered position, the snap action lever 49 moves the double pole switch 51 to the position illustrated in FIG. 2. In this position, the circuit from the power source 67 to the motor 23 has been broken by removing the switch blade from the contact 56. This stops the operation of the motor 23 and terminates the operation of the compressor-condenser 21. At the same time the switch blade makes contact with terminal 58, completing the circuit to the heater 11 by means of lead 53 through the fail safe thermostat 57. The thermostat 57 may be of any of the well known types, and has no effect on the operation of the device with the exception that if the coils should get bound in their down or defrost position, the excess amount of heat generated by the electrical heater 59 would cause the bimetallic arm 60 of the thermostat to contact terminal 62, removing the power supply from heater 59 and closing the circuit to the motor through alternate lead 55, thus resuming the refrigeration operation.

As the heater 59 begins operation the frost on the coils starts to melt, and when the point is reached wherein all the frost has been eliminated from the coils the temperature of the gas within the evaporator coil 11 will begin to rise. As the temperature of the gas rises the pressure within the coil will also rise due to the fact that the increased temperature causes the refrigerant gas to expand. This also causes the pressure in the capillary tubing 41 to increase, which raises the pressure in the interior chamber of the bellows 39 causing it to expand. Depending upon the position of screw 47, the bellows will contact the screw at a predetermined pressure forcing the coil arm 27 upwardly which rotates the coils clockwise about pivot 19. When the arm 27 has been raised to a point just beyond the center point of the snap action lever 49 the springs will cause the arm 27 to snap back into its first position. This operation provides a positive termination of the defrost cycle since the arm 27 moves the switch 51 from contact with terminal 58 which opens 4 the circuit to the heater, and contacts terminal 56 which closes the circuit to the motor.

As will now be evident, this invention provides a device wherein the defrost cycle is started only when necessary and terminated, not by any timer nor by a decrease of weight about the coils, but by a positive determination that the coils themselves are free of any frost throughout.

FIG. 3 shows a modification of the above discussed invention wherein refrigerant gas is contained within a thermal bulb 71 which is located adjacent the plates surrounding the evaporator coil. Again, the heat will react on the gas within the thermal bulb, raising its temperature and pressure which increases the pressure within the capillary tube 69 causing the bellows to expand. While the embodiment of FIG. 3 has been found to operate satisfactorily, it does not absolutely assure a complete defrost of the entire coil since the bulb 71 must be located somewhere along the length of the coil. However, the basic principle of the invention is still provided since termination of the defrost cycle is controlled by a gas expansion governed by the heat generated in the evaporator coils and plates. In both embodiments the capillary tubing has enough flexibility to allow for the relatively small movement of the coils.

It is to be understood that the present invention has been described and shown in one particular illustrative manner but is not to be considered limited thereto. The location of the various support members, heaters and pneumatic device could be varied without departing from the invention. Additionally, other means for placing the coils in either of two positions could be used in place of the snap action lever. One example would be the use of dual magnets to which the lever would be attracted, therefore preventing the lever from attaining a position between the refrigerating and defrost cycles.

Accordingly, the invention is limited only by the scope of the following claims.

We claim:

1. In refrigerating apparatus,

an evaporator cooling coil pivotally mounted at one end thereof,

resilient means for supporting the other end of said coil,

means for releasably retaining the other end of said coil in first and second positions about said pivotal mount,

means for heating said coil,

switch means actuated by said coil when in said second position for initiating operation of said heating means,

a bellows means responsive to the pressure in said cooling coil for contacting and moving said coil from said second to said first position at a predetermined pressure thereby disconnecting said heating means, and

means for varying the point at which the bellows moves said coil in order to adjust the return of said coil to said first position.

2. In a refrigerating system including evaporator cooling coils mounted within an enclosure, automatic defrosting means comprising,

means for pivotally mounting said coils at one end thereof within said enclosure,

resilient means within said enclosure for supporting the other end of said coils,

means within said enclosure for releasably retaining said coils in first and second positions about said pivotal mounting means,

a resistance heater within said enclosure,

a switch actuated by said releasably retaining means for supplying electric power to said heater when said coils are in said second position,

pneumatic p essure means within said enclosure adapted to move said coils from said second to said first position in response to a predetermined pres sure applied thereto,

tubing means coupled to said penumatic pressure means and containing a refrigerant gas responsive to the heat created by said resistance heater, said heat increasing the pressure of said gas Within said tubing means thereby actuating said pneumatic pressure means, and

means for adjusting the point at which said pneumatic pressure means moves said coils.

References Cited by the Examiner UNITED STATES PATENTS Dick 62-156 X Kagi 62-140 Hull 62209 X Heitman 62-140 Smith 62140 Johnson 62140 10 ROBERT A. OLEARY, Primary Examiner.

Claims (1)

1. IN REGRIGERATING APPRATUS, AN EVAPORATOR COOLING COIL PIVOTALLY MOUNTED AT ONE END THEREOF, RESILIENT MEANS FOR SUPPORTING THE OTHER END OF SAID COIL, MEANS FOR RELEASABLY RETAINING THE OTHER END OF SAID COIL IN FIRST AND SECOND POSITIONS ABOUT SAID PIVOTAL MOUNT, MEANS FOR HEATING SAID COIL, SWITCHING MEANS ACTUATED BY SAID COIL WHEN IN SAID SECOND POSITION FOR INITATING OPERATION OF SAID HEATING MEANS, A BELLOWS MEANS RESPONSIVE TO THE PRESSURE IN SAID COOLING COIL FOR CONTACTING AND MOVING AND MOVING SAID COIL FROM SAID SECOND TO SAID FIRST POSITION AT A PREDETERMINED PRESSURE THEREBY DISCONNECTING SAID HEATING MEANS, AND MEANS FOR VARYING THE POINT AT WHICH THE BELLOWS MOVES SAID COIL IN ORDER TO ADJUST THE RETURN OF SAID COIL TO SAID FIRST POSITION.

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