US3109717A

US3109717A - Clothes dryer controls

Info

Publication number: US3109717A
Application number: US846151A
Authority: US
Inventors: Daniel E Clapp
Original assignee: KING SCELEY THERMOS CO
Current assignee: KING SCELEY THERMOS CO; KING-SCELEY THERMOS Co
Priority date: 1959-10-13
Filing date: 1959-10-13
Publication date: 1963-11-05
Anticipated expiration: 1980-11-05

Description

. Nov. 5, 1963 D. E. CLAPP CLOTHES DRYER CONTROLS 2 Sheets-Sheet 1 Filed Oct. 15, 1959 FIEZ.

INVENTORI E. CLAPP DANIEL ATTYS United States Patent 3,109,717 CLOTHES DRYER CONTROLS Daniel E. Clapp, Somerton, Philadelphia, Pa., assignor, by mesne assignments, to King-Seeley Thermos Co., Ann Arbor, Mich., a corporation of Michigan Filed Oct. 13, 1959, Ser. No. 846,151 34 Claims. (Cl. 34-45) This invention concerns a system for an automatic electric clothes dryer whereby the drying may be discontinued when the clothes reach a predetermined dryness. The system preferably enables selection of various conditions of dampness or dryness of clothes being dried in the dryer. The present invention also relates more broadly to a novel type of thermal switch control.

Heretofore the drying of clothes in an electric clothes dryer has been terminated in response to temperature sensed by a thermostat mounted either somewhere around the drum or in the exhaust duct. In some cases two such thermostats have been employed, and these have been often set at difierent temperatures, frequently about 30 F. apart. Where two thermostats are employed, one thermostat serves for full or heavy loads and the other thermostat serves for light loads.

In all dryers the shutoif temperature is very critical. If it is too high, severe overheating and possible scorching of the clothes may result. If it is too low, the clothes will not be completely dry. There is also a tendency for thermal overshoot to occur which will cause scorching or burning of clothes even though the dryer has been shut off. Therefore, rather precise control is required it completely dry clothes are to be obtained. Many dryers are designed to shut cit prior to complete drying, just to avoid the difficulties which arise in the absence of precision control and shutofl".

In the course of drying, the temperature of the dryer is relatively constant. In dryers that recirculate air, the temperature may reach a level of 160 whereas in non-recirculating or open circuit types the temperature runs about 130. As the clothes begin to dry, however, the temperature within the dryer rises rapidly. This rapid rate of rise tends to produce overshoot. If the temperature is set too low, the dryer will shut olf prematurely with relatively damp clothes.

In some instances it is desirable to provide clothes sufliciently damp for ironing purposes. Present dryers ordinarily are not capable of automatically providing the ideal damp dry condition. Most dryers have employed clock timers and these timers make it necessary for the operator to guess how long the clothes must be in the dryer to come out damp. Alternatively, the number of cycles of a thermal timer may be counted in order to guess the proper condition for damp clothes suitable for ironing.

Moist dryers also provide for continued rotation of the drum and blower without any application of heat for a period of from 5 to minutes after the thermostat attains dry temperature. This serves to make certain of the drying of heavier sections in clothes and prevents the operator from receiving burns upon removal of the clothes.

The present invention is directed to a dryer control system in which the danger of thermal overshoot is essentially eliminated, and only a single thermostat need be employed for loads of all sizes. The present invention also permits alternative settings (for obtaining clothes completely dry or damp dry and suitable for ironing.

More specifically, the present invention is directed to a control circuit for a heating unit of an electric clothes dryer. The circuit includes a line switch and a thermally operable cycling switch having a pair of contacts arranged to open and close intermittently to regulate the average 3,1 69,7 1 7 Patented Nov. 5, 1 963 power input to the heating unit. One of the contacts is controlled by a thenmomotive member tending to move it away from the other contact when heated. A resistance heater is mounted in heat-transfer relationship with the thermomotive member and is arranged to be intermittently energized. A thermally responsive means is in heat-transfer relationship with the temperature derived from the heating unit and operates in conjunction with the cycling switch to decrease the ratio of time during which the heating unit is energized to the time during which it is deenergized as the sensed temperature increases. The line switch is arranged for manual closure to initiate a drying operation, and means are provided to open the line switch when a predetermined ratio of time of energization to time of deenergization of the heating unit is reached. The heating unit remains deenergized thereafter until a new drying operation is initiated by another manual closure of the line switch.

There are many possible variations in the system thus broadly described. In one system, for example, the resistance heater is connected in circuit with the contacts of the cycling switch, tending to open that switch when the contacts are closed, and permitting reclosure of the switch through the cooling of the thermomotive member after the contacts have opened. In order to vary the ratio of on to off time, provision is made to resiliently displace one contact by means of its opposing contact. The greater this displacement, the greater is the time the contacts remain closed since the resistance heater needs to be energized for a longer time to overcome the displacement and separate the contacts. Such displacement is called contact overclosure. The thermally responsive means may be arranged to cause such overclosure, and to progressively reduce the overclosure, and thereby reduce the ratio of on to ofi? time, as the sensed temperature increases.

Another system in accordance with the present invention modifies the .efiect of the heater element which is thermally associated with the bimetal supporting one of the contacts of the thermal switch. The heating effect can be modified in such a system by the ratio of open to closed contact time of another thermal switch or by other suitable means.

In some instances, the thermally responsive switch may be used to actuate a differentially moving element which will, when a certain degree of differential movement has been achieved, open the switch. Alternatively, the switch may be used directly as a means for terminating a dryer heating cycle by being set so that, when it opens initially, it interrupts a relay circuit which opens a switch in the main heating unit circuit.

For a better understanding of the present invention, reference is made to the following drawings:

FIGURE 1 shows schematically a circuit for an electric clothes dryer heating unit together with a sectional view of a preferred form of thermostatic unit located in the dryer vent or exhaust duct;

FIGURE 2 is a view taken along line 22 of FIG- URE 1;

FIGURE 3 shows a preferred arrangement of the selection and control unit for the dryer system of FIGURE '1 in rear elevational view partially in section;

FIGURE 4 is a view from the bottom of the structure of FIGURE 3;

FIGURE 5 is a sectional view taken along line 5-5 of FIGURE 7 shows a schematic circuit for a further modified dryer system in accordance with the present invention; and

FIGURE 8 shows a schematic circuit for still another 3 modified dryer system in accordance with the present invention.

Referring to FIGURE 1, the main dryer heating unit is connected across power lines L1 and L2 through

switch elements

13 and 14, one or both of which are asso ciated with a U-shaped thermomotive member generally designated 15. A pair of switch contacts 16 in the main dryer heating unit circuit are so designed that at some time in the operation of the dryer when a predetermined condition of dryness exists, they will begin to cycle open and closed under the effect of a bimetallic thermostatic member 17. Bimetalllic member 17 is thermally associated with the dryer duct 18 in such a way that it will assume different positions corresponding to different air temperatures in said duct. Contact 20 of switch contacts 16 is connected directly to the dryer heating unit 10, whereas contact 21 is connected to line L1. Across the power lines L1 and L2, parallel with the series circuit of heating unit and switch 16 is connected a heater element 23 which is wound about one leg 24 of U-shaped bimetallic member 15. This heater is thus connected in parallel with the dryer heating unit 10* when the contacts 16 are closed. A heater element 25 similar to heater 23 is connected in parallel with the dryer heating unit 10 and in series with switch 16 and is thermally associated with the other leg 26 of the U-shaped bimetallic member 15. Thus, the heater element 23 is constantly connected across lines L1 and L2 when switches '13 and 14 are closed whereas heater element 25, like the dryer heating unit 10, is connected across the power lines only when the contacts of switch 16 are closed. As will be further explained later, initially in the drying cycle switch 16 remains closed so that

heaters

23 and 25 and dryer heatingunit 10 are continuously energized. While the

heaters

23 and 25 have been shown in parallel with main dryer heating unit 10, it will be appreciated that their common connection shown adjacent switch 14 might equally well be connected to a neutral or lower voltage line rather than apply full line voltage to these heaters.

Bimetallic member '17 is preferably located within and fixed in good thermal contact with a highly conductive dish of sheet metal insert 27 in duct 18 which protrudes into the main air stream being exhausted from the dryer through the duct 11. The insert 27 may be fixed to the duct by welding or other appropriate means with the bimetal 17 and its associated assembly already fixed in place. The assembly includes a spring-like member 28 essentially coextensive with the bimetal, and these two members are conductively fixed at one end to the insert 27 by a conductive rivet 30 and at the other end by suitable fastening means to a dead extension 31. The extension 31, as may be seen in FIGURE 2, is adapted to overlie and bear against projection 32 on resilient member 33. Member 33 serves as a restoring element and with conductive support blade 34 supports contact 21. Support blade 34 may be anchored to a reference frame portion 35 of the dryer, which is preferably part of a suitable switch housing. Contact 20 is supported by a bimetallic member 36 which is surrounded by a heater element 37, preferably connected in series with the contact 20, so that its energization depends upon

contacts

20, 21 being closed. The bimetallic member 36 is supported on another portion 38 of the switch housing which provides support portion 35.

The structure shown in FIGURE 2 provides a thermally responsive switch which is capable of producing an infinite number of heating effects by permitting an infinite number of time contacts are open to the time they are closed ratios. Ordinarily, in such a switch, instead of the dead extension 31 hearing against the projection 32, a cam member would be provided. The usual cam, or the present extension functions to cause over-closure of contact 21 against contact 20. Bimetal 36 is so oriented that upon heating it tends to move contact 20 away 4. from contact 21, and the amount of over-closure determines the amount of heating by heater 37 required to produce sufficient movement by bimetal 36 to cause the

contacts

20, 21 to break. It will be obvious that the high expansion side of bimetal 36 is on the side next to contact 20 in order to make the contact 20 move away from contact 21 upon heating of the bimetal. In this case, in place of the cam, the dead extension 31 provides the effective over-closure of the contacts by bearing against projection 32. The amount of pressure which extension 31 exerts is dependent upon the temperature of air in the duct .18 and its efiect upon the bimetal 17. Bimetal 17 has its high expansion side away from the duct, so that the hotter the air in the duct, the less the overclosure of

contacts

20, 21. Thus, the higher the temperature in the duct, the more easily the

contacts

20, 21 can open and the smaller the ratio of closed to open time of the switch 16. The longer the switch 16 is open the greater the difference in effects of

heaters

23 and 25 since the heating effect of heater 23 is constant, while the heating effect of heater 2-5 as well as dryer heating unit 10 is reduced. This means that the heating efiiect on bimetal leg 24 produced by heater 23 is constant, but the heating effect on bimetal leg 26 is lessened.

The switch unit illustrated in FIGURE 2 is believed to be novel in combination with the thermomotive memher which produces over-closure in place of a cam memher or the like. The use of this novel combination of elements will find no limitation to'the field of dryer control systems but should be widely useful whereever a change in thermal switch cycling rate is to be varied as a function of temperature or thermal effect which may readily be sensed.

Bimetallic member 17 is set with such initial pressure on blade 33 as to represent an overclosure of

contacts

20,21 so extensive that continuous energization of heater 37 will not cause the contacts to open under the conditions of constant duct temperature representing normal drying. During this period,

heaters

23 and 25 will be continuously energized and will therefore cause maximum deflection of

legs

24 and 26. Since their high expansion side is at the top, as viewed in FIGURE 3, the deflection of leg 26 will cause the free end of leg 24 to move upward. After the duct temperature rises to effect a lessening of the overclosure of

contacts

20, 21, switch 16 begins to cycle on and off and the resultant reduced energization of heater 25 permits leg 26 to cool, and the free end of leg 24 is thereby moved downward.

The U-shaped bimetallic member 15 is the element which is used to release the switches 14'and 13, and thereby terminate the dryer cycle. This may be accomplished by a variety of mechanisms of which the mechanism shown in FIGURES 3, 4 and 5 might constitute a preferred embodiment. As can be seen, the

U-shaped bimetal member 15, which for clarity is shown without the heater elements in place, has the free end of its leg 26 aflixed to the housing structure 40 at a suitable angle provided by an inclined surface on boss 41 to which it is affixed. A re-inforcing ridge 42 is provided at the common base of the U-shaped element by folding a portion of the base at right angles, and,

because it extends completely across the base, it lends lateral rigidity to the whole structure. At the free end of leg 24, a detent member 43 is provided folded from the leg at right angles thereto. The structure is preferably arranged so that the detent member will engage a saw-toothed shaped groove in a wheel 45 mounted on a shaft 46 within the housing 40. There may be a number of such grooves provided, the difference being their radial distance from shaft 46. In the arrangement shown in FIGURE 3, the groove 49, which is shown as engaged by detent 43, is farther from the center than groove 48. It will thus be apparent that less cooling of leg 26 is required to disengage detent 43 from groove 48 than required to disengage detent 43 from groove 49. Ordinarily clothes are damp dry, suitable for ironing, as soon as the temperature in the duct begins to rise. Thus, groove 48 may be used to stop the dryer when the clothes are damp dry, whereas groove 49 allows the clothes to become completely dry, a condition which involves a significant duct temperature change. The radial position of groove 48 is selected such that the slightest cooling of leg 24 will release wheel 45. Upon release, wheel 45 will be rotated to a position in which associated switches 13 and 14 are open. Spring 51 is affixed to the wheel 45 by a pin 50 and to housing 40 by another pin 52. Pin 50' passes through a slot 53 in housing 40 which permits its rotation from off position to the furthest groove. The slot may also serve to limit the total excursion or travel of the wheel 45. Also supported on the shaft 46, which is journaled in the housing 40, is a cam member 55 which actuates switches 13 and 14 which are preferably mounted within the housing 40 and so positioned that whenever one of the

grooves

48, 49 is engaged by detent 43, the

switches

13, 14 are closed but whenever the wheel 45 is released to return to its rest position under the urging of spring 51, the

switches

13, 14 are released and returned to open position. Shaft 46 preferably extends through the front of housing 40 so that knob 59 may be fixed to it. Knob 59 is provided with a skirt 60 which may be calibrated against some sort of reference marking on the housing 40.

Thus, as shown in FIGURE 3, when the knob 59 is positioned so as to cause detent 43 to engage groove 48, the movement of leg 24 of bimetllic member 15 required to release the detent is extremely small and will occur after slightest temperature change sufficient to cause contacts 16 to begin to cycle open. On the other hand, when detent 43 is made to engage groove 49, the amount of movement of leg 24 of U-shaped bimetal required for detent 43 to escape groove 49 is much greater. It will, therefore, only occur when the air temperature in the duct has risen to such a point which represents totally dry clothes and which by design reduces the over-closure of contacts 16 to such a point that the ratio of time they are open to the time they are closed will cause

heaters

23 and 25 to produce the required differential motion to release the wheel 45.

In operation knob 59 is turned from zero position in which switches 13 and 14 are open to one of a plurality of positions representing different degrees of clothes dryness. Selection is based on calibrations on skirt 60 of knob 59 and a reference mark on housing 40. These calibrations enable the knob to be turned to the exact position at which the detent 43 will enter a groove whose radial position will determine the point at which the wheel 45 will be released and the dryer shut off. The dryer will operate the dryer heating unit and the motor drive for a rotating drum (not shown)v functioning to effect drying in the usual way. Air will be exhausted from the dryer during the drying process and its temperature in the duct may be on the order of 130 F. and relatively constant, until the drying stops. If the knob is set for damp dry, as soon as the slightest change in air temperature occurs, the resultant slight differential motion in U-shaped bimetal will cause detent to release the wheel 45 and the dryer heating unit will be shut oif. If a greater degree of dryness is required a higher air duct temperature will be required to produce sufiicient dilferential motion to release the wheel, and the clothes will be correspondingly drier than damp dry. Depending on the circuitry, the motor may continue to drive the dryer for a predetermined period after the dryer heating unit is deenergized. It will also be observed that in addition to the differential motion the cycling of contacts :16 reduces the energy input to heating unit 10, thereby tending to lessen any tendency for thermal inertia to cause burning or scorching of v to line L1 through switch 66.

clothes after the dryer heating unit is dc-energized completely.

FIGURE 6 shows a modified circuit for the same purpose in which a conventional dryer temperature sensing member may be employed rather than the sensing device directly mechanically controlling the over-closure of the contacts of a thermal switch suggestedby the first embodiment of the present invention. In this case, the dryer heating unit, load 65, is connected across lines L1 and L2 through suitable switches 66 and 67. Switch 66 is associated with a U-shaped bimetallic member 68, essentially like element 15 in the embodiment of FIG- URES 1-5. In this case, however, the heater elements 69 and 70 associated with legs 71 and 72 are connected to a low voltage circuit by connection to neutral line N rather than in parallel with the main dryer heating unit. The sensing device 75 in this case can be any type of arrangement which tends to open and close its circuit cyclically in proportion to the heating effect upon it. It may be located in the exhaust duct, or elsewhere in the dryer where air temperature measured by it is proportional to the drying effect upon the laundry. The sensing device is preferably so arranged that as temperature increases the amount of on-to-off time (time ratio of closed to open circuit condition) decreases. The sensing element is preferably arranged across a neutral line and the heater element 76 of a thermally controlled switch '77, the heater element, in turn, being connected In this case, the main heating unit or load is normally connected across the line L1, L2 through switches 66 and 67. Switch 77 is connected in series with the coil 30 of a holding relay through one or both of parallel switches 78 and 79. Switch '78 is manually operated through a cam system common with that of switch 66 and tends to be closed just for a moment in moving to a damp-dry condition or until the switch operating mechanism is released in a dry position. That moment of closure for damp-dry is sufficient to energize relay coil 80 and, upon its energization, switch 79 will be closed thereby keeping the circuit energ led until some interruption occurs. In parallel with the holding coil 80 is heater element so that if switch 67 is held closed the cycling of switch 77 will cause alternate heating and cooling. Heater element 69, by contrast, is connected directly across the power line without passing through the contacts of thermally actuated switch '77. Also across the line L1 and neutral line N is a drive motor 82 which is intended to move the blower and any rotating mechanism of the dryer such as a clothes tumbler. The connection to the motor and to each of the heating elements is made across switch 66 so that as long as this switch is closed this motor will be actuated.

In operation, the heating unit 65 will receive its energization from power lines L1 and L2 through closed switches 66 and 67. As the laundry reaches damp-dry condition, the switch 77 will begin to cycle open and closed, and the temperature as sensed by sensing device tends to increase. This will effectively interrupt current holding coil and if switch 78 is not held closed by its cam to permit dry laundry, i.e., if it is set for damp'dry, the opening of switch 79 upon de-energization of coil 80 will de-energize heater 70. As a consequence, birnetal leg '72 will cool, and, as previously described,

will release the holding mechanism almost immediately so that the clothes If switch '78 is held closed, however, cycling can proceed,

V and release will be delayed because of the greater radial position of the groove.

The circuit of FIGURE 7 is an embodiment of the present invention which eliminates the need for the U- shaped bimetallic element. However, it employs a heatsensitive device, preferably adjacent to the duct, to produce over-closure of the contacts of a thermally actuated switch. In the arrangement shown, bimetal 85 is conductively afiixed' to a portion 86 of the exhaust contacts 90, 91. Bimetal 92 is so arranged with its high expansion side toward its supported contact that, upon heating, contact 91 will tend to move away from contact 90. Contact 90 is connected through switch 93 to line L1. Thus, when contacts 90 and 91 are closed, one of the dryer heating units 94, preferably supplying half of the dryers heating load requirements, is energized. When the contacts are separated, the heating unit 94 is deenergized. Heating unit 95 is connected directly to line L1 without passing through the switch contacts 90 and 91. Both heating units are connected through switch 96 to line L2. In parallel with switches 90, 91 is a resistance heater 97. When current flows through resistance 97 before flowing through heating unit 94, the current flowing through heating unit 94 is materially reduced. This is to be contrasted with complete elimination of current flow in other embodiments. When contacts 90 and 91 close, however, heater 97 is short-circuited so that heater element cannot reduce the current flow and hence its heating effect upon unit 94.

The heater 97 is associated with a bimetal 98 which supports contact 99 opposed to a contact 109 positioned on a resilient arm 101 whose position may be selected by a conventional cam means (not shown) to over-close contact 100 against'contact 99. The direction of flexing of arm 98 under heating from heater 97 is selected to tend to open the

contacts

99 and 100. Motor 103 is connected by parallel parts through switch 96 and thermal switch 107 to line L2 on one side and to the neutral line N on the other. When switches 93 and 106 open, the motor 103 continues to operate.

Switches

99, 100 are so designed that, by the amount of over-closure of contact 100, the temperature at which the switch will first open is predetermined. Since it is in series with the solenoid105, once it opens, the solenoid will be de-energized releasing to their biased open position the

switches

93 and 96 as well as the self-holding relay switch 106. Opening of switch 106prevents reactivation of the holding coil. As a consequence of the release of

switches

93 and 96, all current to the heating unit will stop and heating will terminate. V

The time delay built into switch 107 of the thermal relay will cause switch 197 to remain closed for some time even'though its heater 104 which is in series with

contacts

99, 100 has been de-energized. This is accomplished by making the thermal mass of the switch sufficiently great to retain sufficient heat to maintain the switch closed for the desired period of time after the heating unit is de-energized. Therefore, motor 103 will remain across the lines L2 and N and continue to operate for a 7 time determined by the time constants of the thermal relay even after the dryer heating units are de-energized. Such continued operation is desirable in many cases to prevent over-heating of laundry as a result of thermal build-up or some other thermal effects. Motor 103 is connected by parallel paths through switch 96 and through thermal relay 107 to line L2 on one side andto neutral line N on the other.

In operation, main heating units will remain fully energized until such time as the air temperature in the exhaust duct rises sufiiciently to cause bimetal 85 to reduce its pressure on support 89 sufficiently that contacts 90 and 91. will begin cycling open and shut. At that time the heating efiect of heating element 94 will be diminished as the result of its series connection with heater element 97 when contacts 90, 91 are open. The greater the percentage of time the contacts 90, 91 are open, the greater will be the effect of heater 97 on bimetal 98. Thus depending upon the over-closure of contact against cor1- tact 99 as a result of manually selected pressure on spring support 1411. In this way, any effective duct temperature corresponding to a particular condition of laundry dryness, can be selected as the condition at which the

contacts

99, 100 will first open. opened,

contacts

99, 100 will interrupt the current flow to holding coil 195 and as a result of spring loading or the like opposing the efiect of holding coil 105, switches 93, 96 and 106 will open thereby terminating the flow of current to the heating units 94' and 95. Because of the delay in thermal switch 107, the motor 103 will continue to drive the blower and/ or tumbler while the dryer is cooling down somewhat, the time delay built into the thermal switch 107 being sufficient to permit suificient cooling for safety and to assure the preselected condition of laundry.

Referring finally to FIGURE 8, a further modified dryer control system is illustrated. In this case, instead of just one sensing element 110 affixed to the housing 111, there is a second similar sensing element 112 which may be in the same or other location. Sensing element 110 is preferably a bimetal and is provided with a dead extension 113 which applies pressure to resilient sup port blade 114 for contact 115. Opposing contact 116 is supported on a bimetallic support blade 117 which is preferably thermally associated with a heater connected in series with the contacts so that the bimetal is heated only when the switch contacts are closed. The conditions a for and time of the first opening of the contacts is determined by the amount of over-closure of contact against contact 116. The

contacts

115 and 116 are in series with one of the two main

dryer heating units

118 and 119. The heating unit 118 is preferably of the same size as heating unit 119' and shares half the heating load of the dryer. The heating units are connected in parallel through a pair of relay-associated

switches

120 and 121 to lines L1 and L2, respectively. Connected to the neutral line through relay switch 123 is the holding coil 122 which acts upon common actuating means to hold all three

switches

120, 121, and 123 closed. Also connected in parallel with holding coil 122 is blower and/ or tumbler drive motor 124. Both the realy holding coil 122 and the motor are connected through selector switch 126. If: the selector switch is positioned so that its completes a circuit through contact 127, the circuit will then be energized when contact 128 is closed against contact 129, which is normally the case during operation. On the other hand, if selector switch 126 is closed against contact 130, the neutral line circuit will be energized when contact 131 is closed against contact 132, which also is the normal condition during operation.

Contacts

128 and 131 are insulated from one another by insulator 136 and connected to a common support 134 which is a dead extension of thermostat member 112 by a forked member including the insulator 136. Forkedmemher 135 is designed to produce greater over-closure of contact 131 against contact 132 than the over-closure achieved in any given position of arm 134 by contact 128 against contact 129.

Contacts

129 and 132 may be spring loaded, or otherwise suitably arranged, to produce the over-closure effect. Thus, it will be understood that these pairs of

contacts

128 and 129 and 131 and 132 are designed to open at diiferent temperatures, and when open, the holding coil 122 will be deenergized' and release the

switches

120, 121 and 123, which, under spring pressure or the like, will open and thus terminate the heating effect upon

heating units

118 and 119. The se-' In this system once' arranged to terminate drying when clothes are dry.

Various embodiments of the present invention have been described in orderto better illustrate the scope of the present invention. As will be clear to those skilled in the art, many other embodiments are possible within the scope of the invention. All modifications within the scope of the'claims are intended to be within the scope and spirit of the present invention. t

I claim:

1. In an electric clothes dryer, a heating unit and an electric control circuit, said control circuit including a line switch and a thermally operable cycling switch having a pair of contacts arranged to open and close intermittently to regulate the average power input to the heating unit, a thermomotive member controlling one contact tending to move it away from the other contact when heated, a resistance heater in heat-transfer relationship with said thermomotive member arranged to be intermittently energized, thermally responsive means in heattransfer relationship with the temperature derived from said heating unit operating in conjunction with said cycling switch to decrease the ratio of time during which the heating unit is energized to the time during which the heating unit is deenergized as the sensed temperature increases, means for closing said line switch to initiate a drying operation, means arranged to open said line switch completely to end a drying operation when a predetermined ratioof time of energization to time of deenergization of said heating unit is reached, and means to hold said switch open thereafter.

2. The system of claim 1 in which the thermally responsive means includes a thermomotive member acting upon a resilient support for one of the switch contacts to determine the amount of contact overclosure.

3. The system of claim 2 in which the thermomotive member is a bimetal positioned to sense dryer exhaust temperature and so oriented that upon heating its effect is to lessen the overclosure of the contacts.

4. The system of claim 3 in which a heater element is thermally associated with the bimetal support for one of the thermally responsive cycling switch contacts and said heater element is connected in series with said switch contacts so that the heater element is energized only when the contacts are closed.

5. The system of claim 4 in which the contacts of the thermally responsive cycling switch are placed in series with the main heating unit.

6. The system of claim 1 in which a pair of heater elements are connected to the respective contacts of the thermally responsive cycling switch such that one heater element will be energized only if the switch contacts are closed and the other heater element will be energizable even when its contacts are open, and means are provided whereby the resulting differential temperature between the two heater elements is employed to open the line switch.

7. The system of claim 1 in which the contacts of the thermally responsive cycling switch are arranged in a circuit with a heater and said heater is thermally associated with a thermal relay adapted to open a switch in series with the heating unit.

8. The system of claim 7 in which the thermal relay is set to open after a predetermined amount of heating and a relay adapted to be held closed magnetically, including switch contacts in series with the holding coil and switch contacts in series with the main heating unit, is de-energized by the opening of contacts of the thermal relay.

9. The system of claim 8 in which the heater of the thermal relay is in parallel with the contacts of the thermally responsive switch and short out the heater when they are closed.

10. The clothes dryer of claim 7 in which means is provided to selectively adjust the thermal relay to selectively obtain difierent degrees of dryness corresponding to predetermined temperature conditions.

11. The clothes dryer of claim 1 in which means is provided to open the line switch upon a predetermined condition of the cycling switch in order to obtain dampdry laundry and selection means for alternative selection of damp-dry or dry laundry.

12. A regulating means for a thermal system including a source of heat, comprising a thermally operable cycling switch having a pair of contacts arranged to open and close intermittently, a thermomotive support for one of the contacts and a resilient support for the other contact, a member acting upon the resilient support for one of the contacts to produce overclosure of said contacts, including a thermomotive member adapted to be positioned to respondto the heating effect of said source of heat and thereby produce an overclosure of the contacts responsive to that effect, and means operating to disconnect said source of heat at a predetermined ratio of the time during which said contacts are in closed position to the time during which said contacts are in open position.

13. The switch construction of claim 12 in which each of the thermomotive members is a bimetal and in which a heater element is associated with the bimetal supporting one of the contacts of the thermally responsive switch.

14. The system of claim 13 in which the bimetal is thermally associated With the exhaust duct of a clothes dryer.

15. In an electric clothes dryer, a main heating unit and an electric control circuit for said heating unit, said circuit including a current operable thermally responsive cycling switch having a pair of contacts for determining when the main heating unit is to be de-energized, a thermomotive member supporting one of said contacts and tending upon heating to move its supported contact away from the other contact, a support for the other of said contacts adapted to impose varying amounts of pressure upon the said one contact to secure varying degrees of overclosure, a temperature sensing means adapted to act upon the thermally responsive switch to supply an effect representative of the thermal condition of the laundry in the dryer as imposed thereon by the main heating unit, a thermomotively adjusted dilferential movement release device adapted to release a switch upon predetermined signal, a pairof heater elements thermally associated with separate thermomotive parts of the difierential movement release device to produce the diflerential movement, said heater elements being connected to the respective contacts of the thermally responsive switch so that when the contacts open one of the heater elements is deenergized but the other continues to function.

16. The system of claim 15 in which the contacts of the thermally responsive cycling switch are in series with the heating unit and so arranged that as the heating progresses the contacts are opened more and the total of heating effect of the main heating unit is reduced.

17. The structure of claim 16 in which the thermomotively adjusted differential movement release device consists of a U-shaped bimetallic member and the heater elements are associated with the respective legs of the bimetallic member, the unconnected end of one leg of which bimetallic member is fixed so that the unconnected end of the other leg reflects any differential movement therebetween.

18. The system of claim 17 in which the heater elements are connected in parallel with the main heating unit.

19. The system of claim 17 in which the heater elements are connected to a common neutral line.

20. The system of claim 17 in which the temperature sensing means is a bimetal in temperature sensing position adapted to act upon the contacts support of the thermally responsive switch to thereby change the pressure on its contacts.

21. The system of claim 20 in which the bimetal temperature sensing means is connected to the exhaust duct of the dryer 'in position to thermally sense the temperature of the exhaust stream.

22. The systemof claim 21 in which the bimetal sensingmea-ns is fixed within a recessed member which is fixed relative to the exhaust duct so that it protrudes into the air stream'within said duct.

23. The system of claim 17 in which the differential movement release device is adapted to engage a member biased upon release to return to position in which it will open a switch in series with the heater element.

24. The system of claim in which the thermally responsive member is controlled through its heater element in thermal association with the bimetal supporting one of the contacts and the sensing means is a cycling switch which changes its ratio of open to closed contact time in response to sensed heating effects, said sensing switch being connected in series with the heater element in response to temperature changes. 7

25. The system of claim 24 in which the sensing means and the heater element are in a circuit separate from the thermally responsive switch.

26. The system of claim 23 in which said member is Y a spring biased wheel having grooves therein engageable by the release device and an associated cam adapted to actuate the switch in series with the main heating unit.

27. The system of claim 26 in which stop means is provided to insure stoppage of the device at open-contact positiorrof the switch means.

28. The system of claim 27 in which calibrated means is provided to position the rotatable device against the urging of the biasing spring means to any one of a plurality of positions at which the differential movement release device engages a groove in said member, the grooves being provided at different radial distance in order to require different amounts of differential movement to release the device to open a switch position.

29. In an electrical clothes dryer a main heating unit and control circuit for said heating unit, said circuit including a current operable cycling thermally responsive switch having a pair of contactsior determining when the main heating unit is to be deenergized, a thermomotive member supporting one of said contacts and tending upon heating to move its supported contact away from the other contact, a support for the other of said contacts adapted to impose varying amounts of pressure upon the contacts to secure varying degrees of overclosure, a temperature sensing means adapted to act upon the thermally responsive switch to supply an effect representative of the thermal condition of the laundry in the dryer as imposed thereon by the main heating unit, a

second thermal switch having a heater element and a thermomotive support for one contact and a resilient support for the other contact, said resilient support permitting selective overclosure of the contacts of said sec- 12 ond thermal switch and said heater element being energized in a pattern representative of the thermal effect on the first thermal switch, a relay operated series switch in series with the main heating unit, said relay acting to i keep said switch closed until the second thermal switch opens.

30. The system of claim 29 in which the heater element for the second thermal switch is in parallel to contacts of the first switch whereby when the contacts of the first thermal switch are closed the heater element is shorted out but when the contacts are open the heater element is energized thereby affecting-the bimetal support for one of the contacts of the second thermal switch.

31. The system of claim 30 in which the parallel circuit of first thermal switch contacts and the heater of the second thermal switch is in series with the main heating unit.

, 32. In an electric clothes dryer, a heating unit, an electrical control circuit therefor, said control circuit including a line switch and a thermally responsive cycling switch, said cycling switch comprising a pair of contacts, a thermomotive member controlling the position of one of said 1 contacts and a resistance heater in heat-transfer relationship with said thermomotive member connected in circuit with said contacts, thermally responsive means inheattransfer relationship with the temperature derived from said heating unit arranged to decrease the ratio of closed contact to open contact time in relation to increase in temperature beyond a predetermined temperature, means operating to open said line switch when apredetermined ratio of closed contact to open contact time is reached, a separate circuit including a motor, and thermal means to open said separate circuit after the elapse of a predetermined time following the opening of said line switch.

33. The system of claim 32 wherein said thermal means comprises a pair of contacts in said separate circuit, a

thermomotive member controlling the position of one of said contacts, and a resistance heater in heat-transfer relationship with said thermomotive member, said heater being in series circuit with said heating unit.

34. The system of claim 33 wherein said thermomotive member is adapted to keep said contacts in closed position when heated and to open said contacts when cooled.

References Cited in the tile of this, patent UNITED STATES PATENTS

Claims

12. A REGULATING MEANS FOR A THERMAL SYSTEM INCLUDING A SOURCE OF HEAT, COMPRISING THERMALLY OPERABLE CYCLING SWITCH HAVING A PAIR OF CONTACTS ARRANGED TO OPEN AND CLOSE INTERMITTENTLY, A THERMOMOTIVE SUPPORT FOR ONE OF THE CONTACTS AND A RESILIENT SUPPORT FOR THE OTHER CONTACT, A MEMBER ACTING UPON THE RESILIENT SUPPORT FOR ONE OF THE CONTACTS TO PRODUCE OVERCLOSURE OF SAID CONTACTS, INCLUDING A THERMOMOTIVE MEMBER ADAPTED TO BE POSITIONED TO RESPOND TO THE HEATING EFFECT OF SAID SOURCE OF HEAT AND THEREBY PRODUCE AN OVERCLOSURE OF THE CONTACTS RESPONSIVE TO THAT EFFECT, AND MEANS OPERATING TO DISCONNECT SAID SOURCE OF HEAT AT A PREDETERMINED RATIO OF THE TIME DURING WHICH SAID CONTACTS ARE IN CLOSED POSITION ON THE TIME DURING WHICH SAID CONTACTS ARE IN OPEN POSITION.