US2687620A

US2687620A - Defroster control

Info

Publication number: US2687620A
Application number: US267245A
Authority: US
Inventors: Robert G Raney
Original assignee: Ranco Inc
Current assignee: Robertshaw US Holding Corp
Priority date: 1952-01-19
Filing date: 1952-01-19
Publication date: 1954-08-31
Anticipated expiration: 1971-08-31

Description

Patented ug. 31;, 1954 IED STATES ATENT OFFICE DEFROSTER CIONTROL Robert G. Raney, Columbus, Ohio, assignor to Rance, Incorporated, Columbus, Ohio, a corporation of Ohio 4 Claims.

'I'he present invention relates to control mechanisms, and more particularly to a control for automatically effecting defrosting cycles in the evaporators of mechanical refrigerators.

The principal object of the present invention is the provision of a defrosting control for a mechanical refrigerator which is capable of initiating defrosting cycles in the evaporator of the refrigerator at desired intervals, which may be determined without reference to the amount of frost accumulated on the evaporator, and which terminates or prevents initiation of such cycles by means including a thermal responsive device responsive to the temperature of the evaporator and having an expansible element which expands beyond its normal volume when the evaporator is below freezing and which contracts when the temperature of the evaporator is above the freezing point of water so that in the event of failure of the element to operate for any reason defrosting cycles cannot be initiated, or if initiated, will be discontinued.

A more specific object of the invention is the provision of a defrosting control for mechanical refrigerators which includes an expansible element which is expanded beyond its normal volume by the freezing of water therein maintained in close heat transfer relation with the evaporator and which is effective while expanded to permit the initiation of a defrosting cycle in the evaporator by means including a power source independent of the expansible element, and which causes defrosting cycles to terminate when the volume thereof is normal, or less than when expanded as described, whereby in the event of failure of the element to expand for any reason, such as leakage of fluid therefrom, defrosting cannot occur or continue.

Other objects and advantages of the invention will be apparent from the following description or' a preferred form of the invention, reference being made to the accompanying drawing in which:

Fig. 1 is a diagrammatic illustration of a refrigerating system having a defroster control associated therewith and embodying the invention;

Figs. 2, 3, 4 are schematic views of certain parts of the control as seen substantially along line 3 3 of Fig. 1, the several views showing the parts in their respective positions during different phases of operation of the control; and

Fig. 5 is a fragmentary sectional view of a part of the defroster control and evaporator of the 2 refrigerator shown in Fig. 1, but taken on a larger scale,

It has been found desirable to establish defrosting cycles in the evaporators of mechanical refrigerators at relatively frequent intervals to prevent an appreciable body of frost from accumulating thereon which would impair the efficiency of the evaporator and otherwise interfere with the use thereof. It has also been found advantageous to apply heat to the evaporators during the defrosting cycles to melt the frost quickly therefrom to prevent the refrigerated articles in the evaporator and refrigerator cabinet from attaining undesirable elevated temperatures. Common methods of applying heat to the evaporators include attaching electric heating elements to the evaporators and connecting the heaters in circuit during the defrosting cycle, and directing warm refrigerant gas through the evaporators during the defrosting cycles. In any event and particularly where heat is applied to the evaporators it is important that the defrosting cycle does not exceed the minimum time required to bring the evaporator slightly above the melting point of frost, otherwise spoilage of food and the like is apt to occur as well as possible injury to the refrigerator.

The present invention contemplates a defrosting control mechanism of the character referred to which is dependable, accurate and which terminates cr prevents initiation of the defrosting cycles in the event of a defect inthe defrost cycle terminating mechanism. Although the invention can be embodied in control mechanisms for refrigerators in which the defrosting of the evaporators thereof is effected by different methods, such as merely interrupting the refrigerating lcycles until the frost on the evaporator melts or directing hot refrigerant gas through the evaporator, for the purposes of illustration, the invention is shown embodied in a control mechanism I0 connected with a conventional compressor-condenser-expander refrigerating system comprising an evaporator E, and a compressor C which is driven by an electric motor lVI and which withdraws refrigerant from the evaporator E through a tube ll, compresses the refrigerant and discharges the compressed refrigerant to a condenser B, from whence the condensed refrigerant is returned to the evaporator through a conduit VI2, as is well known in the art. The motor M is connected with a suitable source of electric power supplied through lines Ll, L2. One terminal of the motor M is connected with line LI through a thermostatically operated switch I3 and the other terminal of the motor is connected with line L2 through a normally closed switch in the control l, and which is explained more fully hereinafter. The thermostatically operated switch I3 is of conventional construction and is adapted to close and open the motor circuit in response to predetermined temperatures in the refrigerator to establish normal refrigerating temperatures in the evaporator which temperatures are generally below 32 F. As is well known, the operation of the evaporator at temperatures below 32 F. results in moisture condensing from the air surrounding the evaporator on the evaporator surfaces where it freezes and forms an insulating coating which interferes with efficient heat transfer between the air and the evaporator.

In the form of the invention shown, an electric heating coil I5 is disposed adjacent to the evaporator E in close heat exchange relation therewith so that the evaporator may be quickly heated to melt the frost therefrom. One terminal of the heater coil is connected to line LI as shown, and the other terminal thereof is connected to line L2 through a normally open switching mechanism in the control I0, described hereinafter.

The control mechanism I0 includes a suitable housing or casing having an insulating block I8 to which one end of three parallel spring contact strips 2c, A2|, 22 are anchored. The lower endsof the

spring strips

20, 2|, 22 carry

contact members

24, 25, 2S, respectively, and the

strips

20, 22 are tied together by an insulating plug 28 which extends through an opening 29 through the strip 2| and has its ends riveted to the two outer strips. The

strips

20, 2|, 22 are biased to the left, as viewed in Fig. l, and the contact 25, which is a double contact, i. e., it projects from opposite sides of the strip 2 I, is adapted to engage alternately with contact 24 or contact 26. Contact strip 2| is connected with line L2, contact strip 20 is connected with one terminal of the motor M, contact strip 22 is connected with one terminal of the heater element 25, as shown. lfhus, when contact 25 engages contact 24, the compressor motor M will operate under the control of thermostatic switch I3 and when contact 25 engages contact 26, the heater I5 will be energiZed and the motor circuit broken,

Contact strip 20 is urged against'the periphery of a cam 32 which is attached to a shaft 33 rotatably mounted in a wall of the casing I1 by a bushing 34. The cam 32 is driven clockwise, as viewed in Figs. 2 to 4, at the rate of one revolution per clay by a synchronous motor 35 which is drivingly connected with the shaft through a gear train including pinion 3'I and a drive gear `38 attached to the shaft. Preferably, a knob 39r is attached to the outer end of the shaft 33 to permit manual setting of the cam 32, and suitable slip clutch means, not shown, may be provided to prevent movement of the synchronous motor Vthrough rotation of the shaft by the knob. The

cam 32 has a step formation 4I on the periphery thereof which causes the spring 20 to drop therefrom once each revolution of the cam and snap to the lower portion of the cam. This action is illustrated in Figs. 3 and 4 which show the spring 20 not long prior to dropping from the step 4I and immediately after dropping therefrom, respectively. The cam 32 hasa gradual rise from the step and the spring strip 20 is gradually moved to the right, as is illustrated in Figs. 2, 3. a

\ The contact .stripy 2| is adapted to be moved by the strip 2u te theright where it is locked i'n that position by a latch 43 which is carried on the end of a spring arm 44. The spring arm 44 is in turn connected to the underside of a lever 45 which is pivoted to the casing |'l by a pin 41. The lever 45 is normally urged downwardly by a tension spring 48, the ends of which are connected to the lever and casing, respectively. The latch 43 has a camming surface 50 which is engaged by the lower end of contact strip 2| as the latter moves from its left hand position to its right hand position and delects the spring arm 44 to permit the strip to move to the right of the latch proper whereupon the latch springs upwardly to retain the strip in its right hand position. This action is illustra-ted by reference to Figs. 2 and 3. The contact strip 2| is latched in position as described during the approach of the cam step 4I to the contact strip 20 and where the latter strip drops from the step of the cam, the strip 22 snap moves tothe left therewith and engages contact 26 with contact 25. Thus,

contacts

24, 25 are snapped open and

contacts

25, 26 are snapped closed thereby interrupting normal refrigerating cycles in the evaporator and energizing the heating element I5.

The latch 43 is adapted to suddenly release the contact strip 2| when the lever 45 is lowered about its pivot to a predetermined position' and the Contact strip snaps to the left moving contact 25 from engagement with contact 25 into engagement with contact 24, thereby breaking the circuit of the heating element I5 and reestablishing the circuit for the refrigerator motor M.

The lever 45 is normally maintained in its raised position, to render the latch 43 operative to latch the Contact strip 2| as described, by an expansible element expanded beyond its normal volume by means utilizing the force of the expansion of more or less confined water subjected to the temperature of the evaporator and frozen thereby. When the ice melts due to warming of the evaporator, the expansible element returns to its normal volume which permits the spring 48 to lower the lever 45 and release the strip 2| from the latch 43.

The expansible element referred to includes' a cup shape base member 52 having a centraLbored neck portion 53, the base of which joins a cross bore in the base member to form a conduit 54 from the side to the interior of the base member. A rubber or rubber-like hollow cylindrical member 55 is tted over the neck 53 and has a flange 53 at the lower end thereof which abuts the inside of the bottom wall of the base member 52. The upper end of the member 55 is closed by a relatively thick Wall. A sleeve 5|] surrounds the member 56 and connes it to longitudinal movement in the sleeve when pressures inside the member are sucient to stretch the elastic walls thereof. The lower end of the sleeve BB has a flange 5| whichengages the upper side of the flange 58, and the top edges of the base member 52 are overturned against the upper side of the sleeve flange and force the latter flange again-st the flange 58 andv tightly seal the latter ange with the bottom wall of the member 52. Thus, the interior of the member 55 is fluid tight except for the conduit 54.

A plunger 52 is slidingly received in the upper end of the sleeve and rests against the top end of the expansible member 56. The upper end of plunger 52 is connected with the lever 45 through a screw 53 which is threaded through an opening in lthe lever 45 and which is locked in place by a nut 64 when the proper spacing of the plunger and lever has been established by adjusting the screw in the lever.

A capillary tube 65 is connected in the conduit 54, and the interior of the expansible member 56, the conduit 54 and tube are filled with a suitable non-freezing liquid, such as a mixture of water and glycerin, and when the volume .of the liquid increases, the member 56 is extended upwardly in the sleeve 60 to force the plunger 62 upwardly and raise the lever 45 to position the latch.43 to lock strip 2l, as described. When the volume of the liquid in the member 56 decreases, the member recedes or contracts and the plunger62 descends to permit spring 38 to lower the lever 45 and cause the latch 43 to release the strip 2 l In the form shown, the tube '65 is connected with a water containing device comprising a cup shape member having the closed wall thereof clamped to the side of the evaporator E by a nut 1 I and threaded stud 12 formed on the member 10 and extending through an opening in the evaporator. The member 10 has a chamber 14 therein in which pure water is sealed by a resilient diaphragm which has a peripheral rim 16 which is received in an annular groove 11 in the member 10. The rim 16 is tightly clamped in the groove by a cap 18 having a rim 19 which backs the rim 16 and forces it into the groove, as shown. The cap 18 is held in place by the edges of the member 10 turned thereagainst.

The cap 18 has a chamber 8| therein, and a pair of

bores

82, 83 leading from the exterior of the cap to the chamber. One end of the tube 65 is attached in the bore 82, and the chamber and tube are filled with the mixture of water and glycerin described previously, by introducing the liquid therein through a filling tube 86 connected in the bore 83. After filling of the cap chamber 8| and the tube 65 is effected, the tube 86 is sealed as shown at 81. It will be seen that the water freezing in the chamber 14 will expand and force the diaphragm 15 to the right, thereby forcing liquid into the expansible member 56 from the tube 65, causing the member to be stretched and elongated to move the plunger 62 upwardly and raise the latch 43 to its operative position whereby defrosting cycles can be initiated. The water freezes in the chamber when the temperature of the evaporator at the part to which member 10 is clamped is reduced below the freezing point of water, which is theoretically 32 F., but which may actually require a lower temperature due to supercooling of the water.

When the Water in the chamber 14 is in the liquid state its volume is reduced as compared with its volume when frozen and the contractive tendency of the member 56 causes the liquid to move the diaphragm 15 to the left and permit the elastic member to shorten and cause the arm 45 to be lowered by the spring 38 and release the strip 2l from the latch 43, or prevent latching of the strip, as the case may be. Hence, the defrosting cycles are terminated when the ice in chamber 14 melts, which will occur whenever the member 10, which is responsive to the temperature of the evaporator, reaches a temperature at which the frost is melted from the evaporator. In practice, the member 10 should be located on the part of the evaporator which has the lowest temperature during the defrosting cycle, although its location may be otherwise determined, if desired.

In the event there is accidental loss of liquid or water, for any cause, the expansible member 56 will be contracted so that the latch 43 cannot engage the strip 2| and consequently defrosting cycles'cannot take place. Thus, the device fails safe, which is highly desirable, particularly where heat is applied to the evaporator during the defrosting cycles.

Another advantage of the defroster control described is that the expansion of the frozen water provides an abundance of power at the critical temperature in the evaporator for terminating the defrosting cycles so that the device can be made to.operate.positively and accurately in terminat- -ing the defrost cycles. Furthermore, the accuracy of the Idevice is not affected by changes in atmospheric pressure or by the passage of the tube 65 through an area having a temperature below that of the evaporator, as is the case of vapor lled pressure responsive devices.

While I have described but one form of the invention, it is to be understood that other forms, modifications and adaptations could be employed without departing from the scope of the appended claims. Y Y

Having described my invention, I now claim:

l. A control mechanism for a refrigerating system comprising, an electric switch, including a switch member mon/able between two switching positions, a latch member movable to a position to block movement of said switch member from one of said switching positions to the other switching position, an expansible element connected with said latch member and operative to move said latch member to said position to block said movement of said switch member when said element is expanded and to cause movement of said latch member to release said switch member when said element is contracted, said element having water in a portion thereof and said portion adapted to be disposed in heat exchange relation with the evaporator of the refrigerating system to cause expansion of said element when said water is frozen and contraction of said element when the frozen water melts, and power means to move said switch member periodically from said other switching position to said one switching position.

2. A control mechanism for a refrigerating system comprising, an electric switch including a switch member movable between two switching positions, means normally urging said switch member to one of said positions, a latch movable into position to block movement of said switch member from the other of said positions to said one position, an expansible element connected with said latch member and operative when expanded to move said latch to said position to block said movement of said switch member, and

to cause said latch to move to a position to release said switch member when said element contracts, said element having water in a portion thereof and said portion adapted to be disposed in heat exchange relation with the evaporator of the refrigerating system to cause expansion of said element when said water is frozen and contraction of said element when the frozen water melts, and an actuating device to move said switch member periodically from said one position to said other position.

3. In a refrigerating system including an evaporator, means to circulate refrigerant through the evaporator to normally maintain the temperature thereof below the freezing point of water, and means to melt frost from the evaporator, the combination of means to control operation of the frost melting means comprising a member movable to a predetermined position periodically, an expansible thermally responsive element having a part thereof in close heat exchange rela'- tion with the evaporator and containing a medium which causes expansion of said element when the temperature of said part is reduced to the freezing temperature of water, and means actuated by expansion of said element and'movement of said member to said position to initiate and maintain operation of said frost melting means.

4. In a refrigerating system including anY evaporator, means to circulate refrigerant through the evaporator to normally maintain the temperature thereof below the freezing point of water, and electrically operated means to melt frost from the evaporator, the combination of means to control operation of the frost melting means comprising a switch member movable between first and second control positions to initiate and terminate operation of the frost melting means respectively, power means to periodically move said member from said second to said rst control position, an expansible thermally responsive element having a part thereof in close heat exchange relation with the evaporator and containing a medium which causes expansion of said `element when the temperature of said part is reduced to the freezing temperature of water, and means actuated by expansion of said element toretain said member in said second position and actuated by contraction of said element to release said member for movement to said rst position.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,990,663 Muly Feb. 12, 1935 2,066,235 Smilack Dec. 29, 1936 2,459,083 lVlEcCloy Jan. 11, 1949 2,500,298 Smith' Mar. 14, 1950 2,583,661 Morrison Jan. 29, 1952