US3342961A

US3342961A - Thermostat having thermally responsive means for arresting the movement of one of the contacts upon cooling of the thermostat

Info

Publication number: US3342961A
Application number: US415113A
Authority: US
Inventors: Homer W Deaton; Raymond M Hutchinson
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1960-09-19
Filing date: 1964-12-01
Publication date: 1967-09-19
Anticipated expiration: 1984-09-19

Description

Sept. 19, 1967 H. w. DEATON ETAL 3,342,961

THERMOSTAT HAVING THERMALLY RESPONSIVE MEANS FOR ARRESTING THE MOVEMENT OF ONE OF THE CONTACTS UPON COOLING OF THE THERMOSTAT 1960 s sheets-sheet 1 Original Filed Sept. 19.

mmvrozzs Their Attorney m s m mm U MH 0M d .1 m e m m y 0 0 HR B Y WM' p 19, 1967 H. w. DEATON ETAL 3,342,961

THERMOSTAT HAVING THERMALLY RESPONSIVE MEANS FOR ARRESTING THE MOVEMENT OF ONE OF THE CONTACTS UPON COOLING OF THE THERMOSTAT Original Filed Sept. 19, 1960 s Sheets-Sheet 2 INVENTORS 4 Homer! Den/on,

RaymondM Hutchinson Their Afforney p 1967 H. w. DEATON ETAL 3,342,961

, THERMOSTAT HAVING THERMALLY RESPONSIVE MEANS FOR ARRESTING THE MOVEMENT OF ONE OF THE CONTACTS UPON COOLING OF THE THERMOSTAT Original Filed Sept. 19 1960 3 Sheets-Sheet 5 230 32 INVENTORS Homer W Deman 7 /i'aymona' M. Hutchinson Wygm Their Attorney United States Patent 3,342,961 THERMOSTAT HAVING THERMALLY RESPON- SIVE MEANS FOR ARRESTING THE MOVE- MENT OF ONE OF THE CONTAUTS UPON COOLING OF THE THERMOSTAT Homer W. Deaton, Cent-erville, and Raymond M. Hutchinson, Dayton, Ohio, assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Original application Sept. 19, 1960, Ser. No. 56,930, now Patent No. 3,196,553, dated July 27, 1965. Divided and this application Dec. 1, 1964, Ser. No. 415,113

4 Claims. (Cl. 200-113) This is a division of application Ser. No. 56,930, filed Sept. 19, 1960.

This invention relates to a domestic appliance and more particularly to an improved control arrangement for terminating a clothes drying cycle.

The clothes drying art has been faced with the disadvantage of venting the moisture laden exhaust products from a dryer to the outside atmosphere. For those situations where construction or other problems prevent outside venting, the condensing clothes dryer has been devised. Briefly, a condensing dryer of the type taught generally in the copending application Ser. No. 732,573, filed May 2, 1958, now Patent No. 3,032,887, issued May 8, 1962, and assigned to the same assignee as this invention may include a recirculating drying air flow system for picking up moisture from the clothes and a cooling air flow system which blows in counter flow heat transfer relationship to the recirculating air. Thus, the recirculating air picks up moisture in the tumbling drum and, while passing through a heat exchanger, is cooled by the cooling air flow system, so that the entrained moisture will be released as condensate.

Certain conditions arise however in the use of a condensing dryer. Moisture droplets are deposited within the duct work of the recirculating drying air system as the clothes are being dried. After the clothes are preferably dry, these moisture droplets start to evaporate and produce a decided cooling effect (dry bulb temperature of the recirculating air decreases). On the other hand, while the recirculating air is moisture laden, the cooling air is directed to absorbing the large latent heat load resulting from the heat of condensation. Again, as the clothes become properly dry, this latent load drops off, the heat of condensation is minimized, and the cooling air is effective to carry off the sensible heat. At this point, the dry bulb temperature of the cooling air decreases as did the temperature of the recirculating air. It is here proposed to sense either of these temperature drops with a thermostatic device which will maintain a closed circuit during rising or steady temperature conditions but which will break the circuit when a falling temperature condition occurs.

Accordingly, it is an object of this invention to provide means for sensing a falling temperature condition in a condensing dryer.

It is another object of this invention to provide a condensing dryer having a recirculating air flow system and a cooling air flow system with means in the outlet of said cooling air system for sensing a falling temperature to terminate a clothes drying cycle.

A more specific object of this invention is the provision of a thermostat for sensing the point at which temperature starts to decrease.

Another object of this invention is the provision of a thermostat for sensing a falling temperature, wherein said thermostat includes a pair of bimetal levers, one of said bimetal levers operating in response to a rising temperature to maintain a circuit closed and the other of said 3,342,961 Patented Sept. 19, 1967 bimetal levers operating upon a falling temperature to prevent the maintenance of said circuit closed.

Generally speaking, the object of this invention is the provision of a thermostat having a pair of bimetals, one

of which bimetals permits the effective operation of the other of said bimetals in one direction only.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown.

In the drawings:

FIGURE 1 is a fragmentary perspective view of a condensing dryer with parts broken away to show the recirculating air flow system and the cooling air flow system;

FIGURE 2 is a top elevational view of a thermostat suitable for use with the condensing dryer of FIGURE 1;

FIGURE 3 is a side elevational view of the thermostat shown in FIGURE 2;

FIGURE 4 is an end elevational view taken along line 4 in FIGURE 2;

FIGURE 5 is a sectional view taken along line 55 in FIGURE 3;

FIGURE 6 is an elevational view of another thermostat suitable for use with this invention; and

FIGURE 7 is a schematic wiring diagram of the falling temperature sensing dryer termination arrangement of this invention.

In accordance with this invention and with reference to FIGURE 1, a condensing type clothes dryer 10 is illustrated. The clothes dryer 10 is comprised of a casing having a top panel 12, a back panel 14 and side panels, such as 16. A control housing 18 is disposed on the top panel 12 and supports a knob 19 for initiating and controlling the drying cycle in accordance with the teachings of this invention. A tumbling drum 20 is disposed within the casing and interposed between a front bulkhead 22 and a rear bulkhead 24. The tumbling drum 20 is comprised of a rear wall 26 perforated at 27 which is rotatably supported on a stub shaft 28 journaled on the rear bulkhead 24. Further, the tumbling drum 20 includes an annular front wall 30 terminating in a cylindrical access collar 32 which is relatively rotatably supported by a front port plate 34 carried on the front bulkhead 22. The access opening formed by the collar 32 is closed by a door shown at 36. A lint collecting housing 38 is carried by the door 36 and projects into the access opening collar 32 of the 1 lecting housing.

The recirculating air flow system is defined by perforations 40 in the front port plate 34 which open into a front duct 42. The front duct 42 has an opening 44 into an inlet header 46 for a heat exchanger or condenser shown generally at 48. The condenser 48 is comprised of a flexible conduit 53 to a rear duct 64) behind the rear bulkhead 24. A rear duct has an opening 62 through the rear bulkhead 24 into an annular chamber formed by a generally channel shaped annular pan 64 fastened to the front side of the bulkhead 24. The annular channel or heater housing provides the means for enclosing and supporting the annular heating elements 66 in juxtaposition of the perforated rear wall 26 of the tumbling drum.

Thus, recirculating drying air is impelled by the blower 54 through the flexible conduit 58 to the rear duct 60.

' From the outlet opening 62 in the rear duct 60 air enters the heater chamber formed by the channel pan 64. The air is heated by the heating element 66 and enters the tumbling drum 20 through the perforations 27 in the drum wall 26. Moisture is entrained from the clothes in the tumbling drum and this moisture-laden air flows out of the drum by way of the access opening collar 32 and the lint collecting housing 38 into the front duct 42 by way of the port plate openings 40. This air is channeled through the inlet header 46 for the condenser 48 and through the tubes 50 into the outlet header 52. While traveling through the condenser tubes 50, moisture is deposited therein by the cooling air flow system which will be described next following and this moisture flows by gravity into the outlet header 52 where an opening 70 channels the moisture to a mating opening 72 in a removable substantially enclosed envelope-like condensate container 74. The inlet opening 72 in the condensate container 74 is the only opening in this completely enclosed container and thus the condensate container 74 may be slidably removed from the dryer and carried in vertical fashion to any suitable drain.

The cooling air system for the condenser 48 is comprised of a cooling air blower 76 connected by way of a fan-shaped duct 78 to the rear side of the condenser tubes 50. The blower 76 is effective to draw air through a screened opening 80 at the front of the condenser tubes 50, over the outside of the condenser tubes 50 and into the duct 78, from which point the air is impelled to the atmosphere. This relatively cool air will cool the condenser tubes 50 and cause condensation of moisture from the recirculating air therein.

A single prime mover or motor 82 is effective through a belt and pulley system (not shown) behind the rear bulkhead 24 to rotate the tumbling drum 20 and to drive the cooling air blower 76 and the recirculating air blower 54.

Note also that the condenser 48 is removable for pcriodic cleaning. A latch arm 84 (shown in the unlatched position) may be released to permit the entire condenser assembly of screen, tubes and end plates to be slidably removed from between the inlet header 46 and the outlet header 42. Water is simply run over and through the tachment within a dryer duct. A generally U-shaped bimetal thermostat sensing arm 98 having a free end 99 and a fixed end 101 is fastened to the underside of the base 94 by

rivets

100 and 102. The thermostat sensing arm 98 may be made of a .025 bimetal such as sold under the trade name More-flex and extends around the left end of the base 94 into overlying relationship with a contact button 104 forming a part of the rivet 102. An electrical connector spade 106 is fastened to the rivet 100 and the connected end of the bimetal 98 such that the spade 106, the contact button 104, and the bimetal 98 are all electrically connected. Note that the bimetal 98 carries a contact button 108 which extends through the free end 99 of the bimetal arm to engage the fixed contact 104 on the thermostat base 94. With an increase in temperature the free end 99 of the sensing arm will move upwardly away from the base 94.

At the left end of the thermostat base 94 a pair of

notches

110, 112 are formed to receive a U-shaped bimetal thermostat holding clutch 114. This clutch includes an upstanding leg or arm 116 and an upstanding leg or arm 118 interconnected by an integral base 120 fastened as by a rivet 122 to the underside of the base 94. The thermostat holding clutch 114 may be formed of any suitable bimetal material such as a .020 More-flex bimetal. The object of the operation for the thermostat holding clutch 114 is for the

upstanding arms

116 and 118 to move toward each other upon an increase in temperature. This object may be accomplished in bimetals in a variety of ways by utilizing different lengths, different materials and combinations of different materials and lengths-the desideratum being merely to get the contact 108 to back off or return as quickly as possible at the point where temperature starts to fall.

condenser tubes 50 to remove any sediment which might accrue therein over extended usage.

The two air flow systems have been shown by arrows in FIGURE 1-the solid arrows indicating the recirculating air fiow and the dashed arrows indicating the cooling air flow for the condenser 48.

As aforesaid, the condensing dryer 10 is known to possess certain temperature drop characteristics which are indicative of clothes dryness Within the tumbling drum 20. It has been determined that these sudden temperature drops may be sensed to terminate the drying cycle when the clothes are at the proper end point dryness. In the recirculating air flow system slight moisture droplets are deposited during the time when the moisture is intense. As the clothes near their proper end point dryness, this moisture starts to evaporate and a sudden decrease in temperature is noted within the

ducts

58 and 60. Similarly a decided drop in temperature is noted within the cooling air flow system in the duct 78. This latter is due to the fact that the cooling air is no longer carrying away the relatively large heat of condensation brought about by the action of the condenser on the recirculating air. It is, thus, the object of this invention to provide a thermostatic device, such as the

thermostats

90 or 92 in either the cooling air flow duct 78 (solid line in FIGURE 1) or the rear duct 60 (phantom line in FIGURE 1) to sense this sudden drop in sensible temperature as the means for terminating the drying cycle.

One falling temperature sensing thermostat 92 is shown in FIGURES 2, 3, 4 and 5. The thermostat 92, which may be installed in the same fashion as thermostat 90, is comprised of a thermostat base 94 of insulating material, such as a 4 inch phenolic. The base 94 is ported at 96 for at- Between the

upstanding arms

116 and 118 of the clutch 114 is a thermostat operating arm 126 of brass or other suitable material. The operating arm 126 includes a contact button 128 at one end thereof and at the other end thereof a pair of depending tabs or

ears

130 and 132. Carried by the

ears

130 and 132 is an operating arm pin 134 for pivotally supporting the operating arm 126. The

upstanding legs

116 and 118 of the thermostat holding clutch 114 include

oversized holes

136 and 138 to permit the pin 134 to pivot freely in the upstanding legs of the bimetal clutch as well as permitting the

legs

116 and 118 of the clutch to move laterally in relationship to the pin 134.

The base 94 also carries another electrical connecting spade 140 which is connected by means of a wire or electrical conductor 142 to the operating arm 126the terminal end 144 of the wire being welded or otherwise suitably connected to the top of the operating arm 126.

With the foregoing construction it should now be seen that a switch has been'provided between the electrical connecting

spades

106 and 140, namely, the switch as defined by the

contacts

108 and 128. The thermostat 92 will operate as follows. When the thermostat is disposed in an air stream such as in the position indicated bythermostat in FIGURE 1, the air temperature will rise as the clothes drying cycle is initiated. As the temperature rises, the bimetal thermostat sensing arm 98 will open up with the contact 108 pushing the contact 128 ahead of it. At the same time, the rising air temperature will cause the upstanding legs or

arms

116, 118 of the clutch 114 to move inwardly, thereby biasingly gripping the legs. and 132 of the thermostat operating arm 126. As aforesaid, the temperature in the duct will continue to rise so long as the clothes are drying with the sensing arm 98 and operating arm 126 assuming the phantom line positions of FIGURE 3. However, when the fabric has ceased to give up moisture, the heat of condensation within the condenser 48 will cease and the dry bulb temperature within the duct 78 will drop suddenly. The bimetal sensing arm 98 will sense this sudden drop in temperature and will tend to retract to the position shown in solid line in FIGURE 3. However, the 'rate of relaxation for the bimetal holding clutch 114 is slower than the bimetal sensing arm 98, therefore the holding clutch 114 will retain the operating arm 126 in the phantom line position of FIGURE 3. Thus, with the contact 108 backing toward its normal position and the contact 128 in its phantom line position, the switch will be broken and the drying cycle terminated.

Turning now to the thermostat embodiment 90 shown in FIGURE 6, the thermostat is shown comprised of an open boxlike support base or receptacle 160 having a back wall 165 from which extends

upstanding walls

162, 164, and 166. Externally fastened to the wall 162 is an electrical spade connector 168 and to the receptacle wall 164 is an electrical spade connector 170. A bimetal thermostat sensing arm 172 is electrically connected to the spade 168 and to the support base wall 162 by a rivet 174. The sensing arm 172 carries a contact 176 on the free end thereof which is movable in accordance with the thermal fiexation of the bimetal 172. The back wall 165 of the support base 160 has pivotally supported thereon a ratchet wheel 178 which has a ratchet or serrated portion 180 along one section of the wheels periphery. The wheel 178 may be of nylon or other uitable electrically non-conducting material. Attached as at 181 to the wheel 178 is a metal thermostat operating arm 182 having a contact 184 in normal engagement with the contact 176. Such normal engagement ofthe

contacts

176 and 184 may be accomplished by mounting the casing back wall 165 vertically as shown or by spring loading the wheel 178 in the counterclockwise direction. One end of the arm 182 is connected electrically through a pigtail 186 to the spade 170. Disposed upon the wall 166 of the support base 160 is a second bimetal holding clutch arm 190 which has a pawl portion 192 in juxtaposition to the teeth or serrations 180 of the ratchet wheel 17 8.

During a rise in temperature, the bimetal sensing arm 172 moves in a clockwise direction, as does the bimetal pawl arm 190. The action of the sensing arm biases the operating arm 182 and thereby rotates the ratchet wheel 178 clockwise. At the same time the pawl portion 192 of the clutch 190 is engaged with the ratchet Wheel to permit clockwise rotation only. Upon a decrease in temperature, the bimetal 172 will return to its normal relaxed position more quickly than the bimetal 190. But the relatively slow relaxation of the clutch arm 190 keeps the pawl in the ratchet wheel for retaining the contact 154 at the highest level reached during temperature rise due to the bias of the bimetal 172. When the contact 17 6 falls away from the contact 184, the switch will open to interrupt a circuit.

The novel dryer termination cycle of this invention will now be described with reference to FIGURE 7 where in the thermostat 90 has been used by way of example only. It should be recognized that the thermostat '92 will work equally well in the circuit and that either

thermostat

90 or 92 may he placed in either the cooling air duct 78 of the rear duct 60. To control the dryer in accordance with the concepts of this invention a timer 2% is provided having'an intermittently rotatable timer shaft 202,'a heater cam 204, a timer motor cam 206, a prime mover and interior lamp cam 208 and a timer motor 210 for rotating the timer shaft 202. A power, source L' ,L and a neutral (N) provide a 230-volt source of power for the dryer. The timer heater cam 204 operates a timer switch 212 on a timer contact to selectively condition the drying heater 66 for operation. In the heater circuit a motor speed switch 214 is included and adapted to be closed when the motor 82 is running. This is a safety means to insure that the motor is operating and thus the tumbling drum rotating before the heater 66 can be energized.

The timer motor 210 is controlled by the timer motor switch 216 operating on a contact 218. In parallel with the timer motor 210 is the thermostat 90 which has its

movable switch contacts

176 and 184 in series electrical flow relationship with a coil 220 for operating a relay switch 222 in series with the timer motor 210 and the timer switch 216.

The primary motor 82 is energized through a timer switch 224 actuated by the cam 208 and a timer contact 226. A door switch 228 is positioned between the timer switch 224 and the motor 82 and movable between a door opened contact 230 when dryer door 36 is open and a door closed contact 232 when the dryer door is closed.

As a safety feature, the circuit includes a means for by-passing the control system and running out the time cycle in those cases where the load to be dried has retained such a small amount of moisture that no significant drop in temperature occurs for the thermostat '90 to sense. This safety action is accomplished by a limiter thermostat 236 in the front duct of the dryer 10. This safety device includes a switch blade 238 which operates between a heater contact 240 and a heater by-pass contact 242 in series with the timer motor 210. Thus, a small load of say one pound or less might be placed in the dryer 10 and the cycle initiated. If the amount of moisture given up is insignificant, the temperature in the

ducts

76 and 60 will continue to rise without a noticeable decrease. When the temperature passes a predetermined level above the highest temperature normally sensed by the thermostat 90, the switch blade 238 will move to the contact 242 and the timer motor 210 will be continuously energized until the entire cycle is run out.

In operation one will place a quantity of damp fabric within the tumbling drum 20 and close the door 36, thereby positioning the door switch blade 229 on the door closed contact 232. The timer starting knob or actuator 19 will be turned manually, thereby rotating the cam shaft 202 to close the timer switches 212, 216 and 224. The tumbling drum 20 and the

blowers

54 and 76 will be operated when the motor 82 is energized from L through line 246, timer switch blade 224, timer contact 226, line 248, the door switch blade 229, the door closed contact 232 and motor 82 to the neutral (N) side of the line. Thus, both the recirculating drying air flow system and the cooling air flow system are initiated.

Substantially simultaneous with the operation of the air flow systems and the motor 82, the heater 66 will be energized on 230 volts from L through timer switch blade 212, timer heater contact 213, the limiter thermostat switch blade 238, thermostat contact 240, the heater 66 and the motor speed switch 214 to L Also substantially simultaneous with the operation of the heater '66 and the motor 82 is the operation of the timer motor 210 when the timer switch 216 is closed on the timer contact 218. However, instantaneously, the timer motor 210 is deenergized as the coil 220 of the relay switch 222 is energized as follows: from L line 246, timer switch blade 21 6, timer contact 218, line 250, the bimetal sensing arm 172,

contacts

176 and 184, the operating arm 182, the terminal connector 170, the coil 220 to the neutral (N) side of the line. The energization of the coil 220 will lift the switch blade 222 and open the circuit to the timer motor 210, thereby deenergizing the timer motor throughout the clothes drying portion of the cycle.

Moisture laden air will be carried through the condenser 48 where it will deposit the moisture in the form of condensate. As the cooling air picks up this heat of condensation, the temperature within the cooling air duct 78 will continue to rise. Since the thermostat is disposed in the duct 78, the bimetals 172 and will flex in accordance with the increase in temperature. More particularly, the clutch pawl 190 will move into engagement with the teeth of the ratchet wheel 178. Simultaneously, the bimetal 172 will bias the operating arm 182 upwardly throughout the temperature increase within the duct 78. After the highest temperature is reached (indicated by the operating arm 182 in phantom line in FIG- URE 6), the bimetal 172 will quickly start to respond to the dropping temperature within the duct 78. The bimetal 172 will return to its normal position more quickly than will the slower acting bimetal 190, which remains engaged with the teeth 180 of the ratchet wheel 178. Thus, bimetal 190 retains or immobilizes the operating arm 182 in its highest phantom line position. As the contact 176 quickly backs away from the contact 184, the circuit to the relay coil 220 is broken and the relay switch 222 will close thereby energizing the timer motor 210 to run out the cycle.

As the timer motor 210 returns to operation, it will next open the timer switch blade 212 to deenergize the heater 66. This will initiate a cool-off period during which the fabric temperature is lowered to a condition more suitable for handling. After an interval of approximately ten minutes, the

timer switch blades

216 and 224 will be opened to terminate the drying cycle.

In brief, the timer operates in three steps. First, the timer switches 212, 216 and 224 are closed. Second, timer switch 212 opens while the

switches

216 and 224 remain closed. Lastly, the

switches

216 and 224 are opened to terminate the cycle.

It should now be seen that an improved drying cycle has been provided including a thermostat which senses a. drop in temperature in a dryer and uses such drop to break a circuit and terminate the drying cycle. The specific thermostats of this invention are simple in construction and dependable in operation. More generally, the thermostats of this invention provide a means for using a pair of bimetals to sense a temperature drop, one being effective during a rising temperature and the other being effective during a falling temperature.

While the embodiments of the present invention as herein disclosed, constitute preferred forms, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. In a thermostat for sensing a falling temperature comprising a thermostat base, first and second electrical connectors on said base, a thermostat sensing arm having a first portion connected to said first electrical connector on one side of said thermostat base and having a second contact portion extending around said base for movement in response to temperature, a U-shaped thermally responsive holding clutch fastened to the thermostat base and having a pair of arms extending away from said base and movable toward each other upon a rise in temperature, a pin extending between said arms, a thermostatic operating arm pivotally supported by said pin between said arms and having a contact portion in juxtaposition to said second contact portion on said thermostat sensing arm for movement therewith, and flexible electrical conducting means extending between said thermostat operating arm and said second electrical connector, said operating arm being moved by said sensing arm upon increase in temperature and restrained by said holding clutch upon decrease in temperature.

2. A thermostat for sensing a falling temperature comprising, a support having first and second electrical connectors, a ratchet pivotally connected to said support and having an arm fastened thereto for rotation therewith, means electrically connecting said arm to said first electrical connector, 2. first thermally responsive device connected to said second electrical connector, biasingly engaged with said operating arm and adapted to drivingly rotate said ratchet wheel in one direction, a second thermally responsive pawl on said support juxtaposition to said ratchet wheel and movable upon an increase in temperature into engagement with said ratchet wheel to permit rotation in one direction only, said second thermally responsive pawl remaining engaged with said ratchet wheel for a period during which said first thermally responsive device moves out of engagement with said operating arm in response to a decrease in temperature.

3. A thermostat for sensing a falling temperature comprising, a support having first and second electrical connectors, a ratchet movably connected to said support and having an arm fastened thereto for movement therewith, means electrically connecting said arm to said first electrical connector, a first thermally responsive device connected to said electrical connector, biasingly engaged with said operating arm and adapted to motivate said ratchet in one direction, a second thermally responsive pawl on said support in juxtaposition to said ratchet and movable upon an increase in temperature into engagement with said ratchet to permit motivation in one direction only, said second thermally responsive pawl remaining engaged with said ratchet for a period during which said first thermally responsive device moves out of engagement with said operating arm in response to a decrease in temperature.

4. A thermostat for sensing a falling temperature comprising, a support having first and second electrical connectors, brake means having first and second brake portions, said first brake portion movably connected relative to said support and including an arm fastened thereto for movement therewith, means electrically connecting said arm to said first electrical connector, a first thermally responsive device connected to said second electrical connector, biasingly engaged with said arm and adapted by movement in one direction upon a rise in temperature to motivate said first brake portion, said second brake portion including a second thermally responsive means on said support in juxtaposition to said first brake portion and movable upon a rise in temperature into engagement with said first brake portion in a manner to permit motivation of said first brake portion by said first thermally responsive device when said first thermally responsive device is moving in said one direction only, the second thermally responsive means of said second brake portion remaining engaged with said first brake portion for retaining said arm for a period during which said first thermally responsive device moves out of engagement with said arm in response to a decrease in temperature thereby to break acircuit between said first and second electrical connectors.

References Cited UNITED STATES PATENTS 1,743,053 l/1930 Traver 200-113 1,952,129 3/1934 Hardman.

2,487,154 11/1949 Lloyd.

2,678,379 5/1954 Fry 200138 X BERNARD A. GILHEANY, Primary Examiner.

T. MACBLAIN, H. A. LEWITTER, Assistant Examiners.

Claims

4. A THERMOSTAT FOR SENSING A FALLING TEMPERATURE COMPRISING, A SUPPORT HAVING FIRST AND SECOND ELECTRICAL CONNECTORS, BRAKE MEANS HAVING FIRST AND SECOND BRAKE PORTIONS, SAID FIRST BRAKE PORTION MOVABLY CONNECTED RELATIVE TO SAID SUPPORT AND INCLUDING AN ARM FASTENED THERETO FOR MOVEMENT THEREWITH, MEANS ELECTRICALLY CONNECTING SAID ARM TO SAID FIRST ELECTRICAL CONNECTOR, A FIRST THERMALLY RESPONSIVE DEVICE CONNECTED TO SAID SECOND ELECTRICAL CONNECTOR, BIASINGLY ENGAGED WITH SAID ARM AND ADAPTED BY MOVEMENT IN ONE DIRECTION UPON A RISE IN TEMPERATURE TO MOTIVATE SAID FIRST BRAKE PORTION, SAID SECOND BRAKE PORTION INCLUDING A SECOND THERMALLY RESPONSIVE MEANS ON SAID SUPPORT IN JUXTAPOSITION TO SAID FIRST BRAKE PORTION AND MOVABLE UPON A RISE IN TEMPERATURE INOT ENGAGEMENT WITH SAID FIRST BRAKE PORTION IN A MANNER TO PERMIT MOTIVATION OF SAID FIRST BRAKE PORTION BY SAID FIRST THERMALLY RESPONSIVE DEVICE WHEN SAID FIRST THERMALLY RESPONSIVE DEVICE IS MOVING IN SAID ONE DIRECTION ONLY, THE SECOND THERMALLY RESPONSIVE MEANS OF SAID SECOND BRAKE PORTION REMAINING ENGAGED WITH SAID FIRST BRAKE PORTION FOR RETAINING SAID ARM FOR A PERIOD DURING WHICH SAID FIRST THERMALLY RESPONSIVE DEVICE MOVES OUT OF ENGAGEMENT WITH SAID ARM IN RESPONSE TO A DECREASE IN TEMPERATURE THEREBY TO BREAK A CIRCUIT BETWEEN SAID FIRST AND SECOND ELECTRICAL CONNECTORS.