US3107281A

US3107281A - Automatic defrosting device

Info

Publication number: US3107281A
Application number: US82966A
Authority: US
Inventors: William S Tufts
Original assignee: Ranco Inc
Current assignee: Robertshaw US Holding Corp
Priority date: 1961-01-16
Filing date: 1961-01-16
Publication date: 1963-10-15
Anticipated expiration: 1980-10-15

Description

Oct. 15, 1963 w. s. TUFTS 3,107,281

AUTOMATIC DEFROSTING DEVICE Filed Jan. 16, 1961 s Sheets-Sheet 1 av s INVENTOR WILLIAM S. TUFTS ATTORN Oct. 15, 1963 w, s u Ts 3,107,281

AUTOMATIC DEFROSTING DEVICE Filed Jan. 16, 1961 3 Sheets-Sheet 2 I0 Fig. 2 a- INVENTOR WILLIAM S. TUFTS BY @tWd ATTORNEY Oct. 15, 1963 Filed Jan. 16, 1961 W. S. TUFTS AUTOMATIC DEFROSTING DEVICE 5 Sheets-Sheet 3 WILLIA INVENTOR M S. TUFTS ATTORNEY United States Patent 3,167,281 AUTGMATE DEFROSTENG DEVECE William S. Tufts, Columbus, Ohio, assignor to Rance Incorporated, Columbus, @hio, a corporation of Ohio Filed .lan. 16, 1961, Ser. No. 823% 6 Claims. (Cl. 2tltl-38) The present invention relates to cam operated switching devices, and more specifically to an improved switching device particularly suited for periodically initiating defrosting cycles in the cooling unit of a refrigerator, and for terminating such cycles in response to the attainment of a given defrosting temperature in the cooling unit or, after the lapse of a predetermined period of time if the termination is not effected by the attainment of the defrosting temperature.

It is one object of this invention to provide a cam operated switch means including a plurality of switch members which are operated sequentially between two control positions by the rotation of first and second cams, respectively, for initiating and terminating defrost cycles in a refrigerator, for example, the first cam being rotated by a driving means such as a timing device, and the second cam being drivingly connected with the driving means by a lost motion connecting means including resiliently yieldable means, the second cam being held against rotation by a restraining means which releases the cam for movement to operate the switch members to the sec ond control position in response to a given condition, such as the attainment of a defrosting temperature in a refrigerator.

Another object of this invention is the provisions of a cam operated switch means of the above mentioned character wherein the restraining means comprises a latch member, preferably formed of bimetal, which engages a shoulder in the surface of the second cam, and the means for causing the latch member to release the cam com prises an electrically energized element, preferably a resistance type heater, which is energized to heat the bimetal latch member to release the cam in response to an increase in temperature in the cooling unit to a predetermined defrosting temperature, and the first cam having surface thereon for engaging the latch member and cans ing it to release the second cam if the latter has not been released within a predetermined time after the defrost cycle is started.

As another object, this invention aims to provide a wholly electrically operated control device which is reliable and compact and is free of tubing for thermostatic bellows, external mechanic-a1 motion transmitting linkages, and the like, and so is adapted to be disposed in any convenient location in a refrigerator housing to which wires may be led.

Other objects and advantages of the invention will be apparent from the following description of a preferred form thereof and from the accompanying sheets of drawing forming a part of this specification and in which:

FIG. 1 is a schematic illustration of a switching device embodying the invention and shown connected in the control circuit of an electric motor driven refrigeration systern equipped with an electric solenoid operated valve for directing hot gas through the evaporator so as to effect defrosting thereof;

FIG. 2 is a plan view of the device of FIG. 1, showing certain parts thereof in different positions;

FIG. 3 is a sectional view of the device taken substantially along line 3-3 of FIG. 2; and

FIG. 4 is a view similar to FIG. 2 but showing the parts in still different positions.

Although the control device of the present invention is susceptible of other forms of construction and is adapted ice to other uses, it will be described hereinafter with reference to the controlling of periodic defrosting cycles of a refrigerator. Referring now to the drawings, there is illustrated therein a control device, generally indicated at iii, embodying the present invention and shown in FIG. 1 in association with the electrical circuit of a refrigeration system which may be controlled thereby.

The refrigeration system may be of the class having a refrigerant compressor which is operated by an electric motor M, and an evaporator or cooling unit, not shown, from which accumulations of frost periodically require removal. The energization of motor M is preferably controlled by a food compartment thermostat T of any well known construction, but which is here shown as being of the 'bimetal type.

The control device 10 comprises a box-like housing '11 which is preferably molded from a suitable insulating material, such as Bakelite or other plastic, and which serves to house a cam operated switch means for controlling the defrost cycles of the refrigerator. The switch means comprises a group of flexible electrical switch members in the form of spring leaves or

blades

12, 13 and 14- mounted within the housing 11. Blade 12 has a contact 12a at one end thereof and has its other end secured to the rear wall 11b of housing 11 by means of a terminal lug 12b which extends through an opening in the rear wall and is fixed therein by staking. Blade 13 has, near one end thereof, a double contact 13a in registration with contact 12a, and is secured at its other end to housing 11 by a terminal lug 13b extending through an opening in housing wall 11b. Blade 14 is likewise provided at one end thereof with a contact 14:: in registration with contact 13a and is secured at its other end to housing 11 by a terminal lug 14b extendirn through an opening in housing wall 11b.

Switch members of

blades

12 and 14 are held in spaced relation by a spacer member 16 which is retained therebetween by reduced end portions 16b and 160 projecting through openings in blades 12 and 14- respectively. Spacer member 16 extends freely through an opening in blade 13, which blade may be referred to as an intermediate switch member, so that relative movement is permitted between the latter and the

spaced blades

12 and 14 to open and close the contacts thereof.

Rotary, coaxial cam means, comprising a first cam 18 and a second cam 19, are provided for effecting the movement of the switch members, or

blades

12, 13 and 14 to cause contact 13a to alternatively be in engagement with contacts 12a and 14a so as to make and break certain later described electric circuits therethrough for controlling the defrosting cycles of the refrigerator. *Cam 1-8, the periphery of which is adapted to be engaged by blade 12, is secured to a shaft 21 for rotation therewith. Shaft 21 has a reduced end portion 21a journaled in an opening lie in housing wall 11b, and is connected through suitable reduction gearing, not shown, for rotation by an electric timer motor 22 at a rate which may be in the order of one revolution per day, although any other suitable rate may be utilized. Timer motor 22 is energized through

conductors

23, 24 connecting the motor between lines L1 and L2 which supply suitable electric power, such as volts, A.-C., to the refrigerator.

Cam 19, the periphery of which is adapted to be engaged by intermediate switch member 13 for controlling movement thereof, is mounted on an enlarged portion 21b or shaft 21 for rotation relative to cam 18 and relative to a flange 210 on the shaft. An arcuate slot 19a is defined in cam 19 and flange 210 is provided with a tab 21d which is in engagement with slot 1% and serves as a lost motion connection to limit the relative rotation between cams i9 and 18. An extension spring 25 is to engage shoulder 19 a. gaged, spring 25 yields to permit rotation of cam 18.

connected at one end to a lug 21a of flange 21c and has its other end connected to a lug 191) formed in cam 19. Spring 25 is led around a drum portion 21 of shaft 21 and serves to yieldab'ly connect cam 19 to the drive means for rotation with cam 18.

its other end with a hook portion 2611 which is adapted When shoulder 19a is so en- An electrically energized resistance type heater 27 is disposed adjacent latch member 26 and is secured to housing 11 by

terminal lugs

27b, 27c fixed in openings in housing wall 11b, and serves to heat bimetal latch member 26 for actuation thereof to release cam 19 for rotation by spring 2 5 in a manner which will become ap parent as the description proceeds.

The surface of cam 19, which is adapted to be engaged by blade 13, extends from portion 19d thereof around in a counter-clockwise direction as viewed in the drawings, and terminates in a surface 19 adjacent a steep shoulder forming a step between that surface and surface 190 of the cam. Cam 18, the surface of which is adapted to be engaged by blade 12. for controlling its movement, has a cam surface 18a of the same radial magnitude as surface 1%, and has a sloping surface 1812 which rises from surface 18a to a generally circular surface 130 of substantially greater radial magnitude than surface 19d of cam 19. Surface 180 extends in a counterclockwise direction, as viewed in the drawings, and terminates in a surface portion 18d adjacent an abrupt step or shoulder between that portion and surface 18a.

The rotation of shaft 21 by timer motor 22 during normal operation of the refrigerator and prior to initiation of a defrost cycle will cause

cams

18 and 19 to be 7 rotated in unison, cam 19 being held by spring 25 in the position relative to cam 18 which is illustrated in FIG. 1,

until shoulder 19:: of cam 19 engages hook portion 26a of latch member 26. During such rotation, it will be ob served that blade 12 is engaged with surface 18d and contact 12a is held in engagement with contact 13a, while spacer member 16 holds blade 14 with contact 14a thereof spaced from contact 13a.

The closed

contacts

12a, 13a complete a circuit for the energization of an electric fan F which serves to circustantially simultaneous deenergization of fan P, will result in a rise in temperature in the cooling unit for removal of frost therefrom. During this time the cam 18 will continue to rotate as shown in FIG. 2.

A thermally actuated switch 40, which may be of any conventional construction but is illustrated herein as of the snap acting bimetal type, islocated in the refrigerator so as to be responsive to the rise in temperature in the cooling unit during the defrosting operation.

When a predetermined temperature for effecting the defrosting is attained in the cooling unit, thermally actuated switch 40 completes a circuit which may be traced from line L1 through switch 46*, conductor 41, heater Z7, and conductor 42, to line L2, thereby energizing heater 27 to heat bimetal latch member 26. -As latch member 26 is heated, it will bend to the position illustrated in dot-and-dash lines in FIG. 2. to release cam 19 for rotation with respect to cam 18 under the influence of spring 25. Such rotation of cam '19 will permit blade 13 to drop from surface 19f bringing contact 13a once again into engagement with contact 1201 for reestablishing the energization of the circuit for. fan F, and simultaneously moving contact 13a awayjfrom contact 14:: for termination :of the energization of solenoid S. Thereupon, the refrigeration system resumes its cooling function and, as the temperature of the cooling unit decreases toward its normal value, the thermally responsive switch 40 opens and terminates the energization of heater 27. Bimetal latch member 26, therefore, cools and resiliently engages the surface of cam 18, which it follows until it is re-engaged by the shoulder 19a of cam 19*.

The device of this invention includes a fail-safe feature for the prevention of inordinately high temperatures occurring in the cooling unit and food compartment in the event that, for some reason such as malfunction of switch rotation into its FIG. 4 position with respect to cam 18 late air in the refrigerator over the evaporator thereof.

This circuit may be traced from line L1 through conductor 51 connected. to terminal 131),

contacts

12a and 13a, conductor 32 leading from terminal 12b, fan F,

and conductor 33 to line L2.

As shaft 21 continues to rotate, latch member 26 will restrain cam 19 from further rotation with cam '13, and the continued rotation of the latter will wind spring 25 about drum portion 2:1 Such continued rotation of cam 18 will permit blade 12 to drop from surface 18d ,to surface 18a, whereupon blade 13 will engage cam survalve which is provided for directing hot refrigerant" through the evaporator of the refrigerator for defrosting thereof. This circuit may be traced from line L1 through conductor 31', contacts 13a and 14a, conductor and with respect to the switch members 1 2, '13 and 14. The latter are thereby returned to their normal positions with contacts 13a, 14a open and contacts 121;, 13a closed to energize fan F.

From the foregoing detailed description of one embodiment of the present invention, it will be appreciated that there has been provided thereby a particularly reliable and effective cam operated switch device which is well adapted to the controlling of refrigerator defrosting operations and which includes a fail-safe feature of operation. It will also be appreciated that the invention achieves the eifectivecontrol of a plurality of circuits through the use of cams having limited rotation relative to one another, whichrelative rotation is controlled by a latch mechanism which is operable in one manner under normal conditions and in another manner under abnormal conditions.

Although this invention has been described with reference to specific forms of switch devices and specific uses thereof, it is understood that the invention isnot limited thereto, but rather the invention includes all those modifications, adaptations, and uses as are reasonably embraced by the scope of the claims hereof. 7

Having described my invention, I claim:

1. Control apparatus comprising a pair of spaced contact'members, an intermediate contact memberl disposed 7 between said pair of contact members, said pair of contact members and said intermediate contact member being movable relative to one another to alternatively make In the event of such a failure,

contact members to control movement thereof, a second rotatable cam engageable by said intermediate contact member to control movement thereof, means for rotating said first cam in one direction of rotation with respect to said contact members, resilient means between said cams for yieldably urging said second cam to rotate in said one direction with said first cam, restraining means for releasably holding said second cam against rotation by said resilient means, rotation of said first cam when said second cam is so restrained being effective to move said one of said pair of contact members out of engagement with said intermediate contact member and to move the other of said pair of contact members into engagement with said intermediate contact member, and electrically energized means for operating said restraining means to release said second cam for rotation with respect to said first carn, said second cam thereby being effective to move said intermediate contact member out of engagement with said other pair of contact members and into engagement with said one of said pair of contact members.

2. Control apparatus as defined in claim 1, wherein said restraining means comprises a birnetal latch member, and said electrically energized means comprises a resistance type heater adjacent said latch member.

3. Control apparatus as defined in claim 1, wherein said first cam includes means for engaging and operating said restraining means to release said second cam for said rotation with respect to said first cam.

4. Control apparatus comprising a plurality of contact members movable relative to one another to provide first and second operative positions for controlling current flow, a first rotatable cam engageable by one of said contact members to control movement thereof, a second rotatable cam engageable by another of said contact members to control movement thereof, drive means for rotating said first cam in one direction of rotation with respect to said contact members, resilient means between said cams for yieldably urging said second cam to rotate in said one direction with said first cam, restraining means for releasably holding said second cam against rotation by said resilient means, rotation of said first cam when said second cam is so restrained being effective to move said one contact member to provide said first operative position of said members, and actuating means for operating said restraining means to release said second cam for rotation with respect to said first cam by said resilient means, said second cam thereby being eifective to move said other contact member to provide said second operative position.

5. Control apparatus as defined in claim 4, wherein said first cam includes means for engaging and operating said restraining means to release said second cam for said rotation with respect to said first cam.

6. Control apparatus comprising a plurality of contact members movable relative to one another to provide first and second operative positions for controlling current flow, first and second rotatable cams coaxially arranged in side by side relation and adapted to have relative rotation, said first cam being engageable by one of said contact members to control movement thereof, said second cam being engageable by another of said contact members to control movement thereof, drive means for rotating said first cam in one direction of rotation with respect to said contact members, resilient means between said cams for yieldably urging said second cam to rotate in said one direction with said first cam, said second cam having a shoulder thereon, a movable latch member for engaging said shoulder to hold said second cam against rotation by said resilient means, said first cam moving said one contact member to said first operative position of said members after a predetermined angular movement relative to said second cam, actuating means for moving said latch member from engagement with said shoulder to release said second cam for rotation with respect to said first cam by said resilient means, said second cam thereby being effective to move said other contact member to provide said second operative position, and said first cam comprising a rise thereon for engaging and moving said latch member from said shoulder upon angular rotation of said first cam relative to said second cam beyond said predetermined angular movement in the event said actuating means fails to operate said latch to release said second cam.

References Cited in the file of this patent UNITED STATES PATENTS 1,935,371 Osborne et a1 Nov. 14, 1933 2,562,481 Swayze July 31, 1951 2,690,526 Morrison Sept. 28, 1954 2,815,411 Schwarzenbach et a1 Dec. 3, 1957 2,970,454 Everhard et a1. Feb. 7, 1961 2,975,612 Everhard Mar. 21, 1961 2,979,580 Timm et al. Apr. 11, 1961

Claims

4. CONTROL APPARATUS COMPRISING A PLURALITY OF CONTACT MEMBERS MOVABLE RELATIVE TO ONE ANOTHER TO PROVIDE FIRST AND SECOND OPERATIVE POSITIONS FOR CONTROLLING CURRENT FLOW, A FIRST ROTATABLE CAM ENGAGEABLE BY ONE OF SAID CONTACT MEMBERS TO CONTROL MOVEMENT THEREOF, A SECOND ROTATABLE CAM ENGAGEABLE BY ANOTHER OF SAID CONTACT MEMBERS TO CONTROL MOVEMENT THEREOF, DRIVE MEANS FOR ROTATING SAID FIRST CAM IN ONE DIRECTION OF ROTATION WITH RESPECT TO SAID CONTACT MEMBERS, RESILIENT MEANS BETWEEN SAID CAMS FOR UIELDABLY URGING SAID SECOND CAM TO ROTATE IN SAID ONE DIRECTION WITH SAID FIRST CAM, RESTRAINING MEANS FOR RELEASABLE HOLDING SAID SECOND CAM AGAINST ROTATION BY SAID RESILIENT MEANS, ROTATION OF SAID FIRST CAM WHEN SAID SECOND CAM IS SO RESTRAINED BEING EFFECTIVE TO MOVE SAID ONE CONTACT MEMBER TO PROVIDE SAID FIRST OPERATIVE POSITION OF SAID MEMBERS, AND ACTUATING MEANS FOR OPERATING SAID RESTRAINING MEANS TO RELEASE SAID SECOND CAM FOR ROTATION WITH RESPECT TO SAID FIRST CAM BY SAID RESILIENT MEANS, SAID SECOND CAM THEREBY BEING EFFECTIVE TO MOVE SAID OTHER CONTACT MEMBER TO PROVIDED SAID SECOND OPERATIVE POSITION.