US2858618A

US2858618A - Automatic control device for laundry drier

Info

Publication number: US2858618A
Application number: US493730A
Authority: US
Inventors: Ii Walter L Kauffman
Original assignee: Lovell Manufacturing Co
Current assignee: Lovell Manufacturing Co
Priority date: 1955-03-11
Filing date: 1955-03-11
Publication date: 1958-11-04
Anticipated expiration: 1975-11-04
Also published as: GB805401A

Description

w. 1... KAUFFMAN u 1 2,858,618

AUTOMATIC CONTROL DEVICE FOR LAUNDRY DRIER Nov. 4, 1958 Filed March 11, 1955 4 Sheets-Sheet l um WKWWZ; BY Q M ATTORNEY Nov. 4, 1958 v v w. L.-KAUFFMAN u 2,853,618.

' AUTOMATIC CONTROL DEVICE FOR LAUNDRY DRIER F iled March '11 1955 4 Sheets-Sheet 2 IN VENTOR i aw Nov. 4, 1958 .w. KAUFFMAN ll 2,358,618

' AUTOMATIC CONTROL DEVICE FOR LAUNDRY DRIER Filed March 11, 1955 4 Shee ts-Sheet 3 EXHAUST AIR f TEMPERATURE HEATER OFF HEATER ON 8 LBS.

IOO

MOISTURE REMOVED EXATAI MPRURE -FR ST48 TIME IN VEN TOR.

waema WILL wgizw N v 4, 1958 w. L. KAUF'FMAN I. 2,85 618 AUTOMATIC CONTROL DEVICE FOR LAUNDRY DRIER v Filed March 11, 1955 4 Sheets-Sheet 4 JNVENTOR.

United States Patent AUTOMATIC CONTROL DEVICE FOR LAUNDRY DRIER Walter L. Kaufiman II, Erie, Pa., assignor to Lovell Manufacturing Company, Erie, Pa., a corporation of Pennsylvania I Application March 11, 1955, Serial No. 493,730

4 Claims. (Cl. 3445) In-clothes dryers, the size of load,type of fabric and degree of initial wetness cause wide variations in the dry-' ing time which are more noticeable when the clothes are to be fully dried and are much less or not at all noticeable when the clothes are to be damp dried for ironing. Because of these variations, either the timer or thermal control has not heretofore produced uniform results. Withthe timer control, the user invariably tends to select toolong a drying time with the resultant overdrying and injury or excessive wear on the fabric due'to the embrittlement which accompanies 'overdrying. With the thermal control where the dryer shuts ofl at a preselected exhaust air temperature there is a tendency for the dryer toshut ,down before complete drying of articles which are hard to dry suchas shag rugs. This is particularly noticeable in small loads or in mixed loads of different fabrics. Because of these factors there is an element of i judgment in the operation of an automatic dryer.

This invention is a combined thermal and timer con trol which is intended to minimize the skill or judgment necessary to select the desired degree of dryness which will thereafter be automatically obtained without objectionable overdrying. The first step is to adjust the thermal control responding to the exhaust air temperature for the kind of fabric being dried. Synthetic's, which are never more than superficially wet, require a lower exhaust air temperature setting than shag rugs which are very hard to dry. The second step in the control involves the judgment of the operator to the size of load and involves added time required after the exhaust air temperature is up to the selected value. Depending upon these factors, the user selects additional drying time either as successive cycles controlled by exhaust air temperature or as straight timer controlled. Because the initial step of adjustment of the control has compensated for most of the variables, the selection of the added drying time re quires much less skill than as though the user were re- 7 quired to estimate total drying time for each load. The selection of the added time necessary to bring the clothes from damp to full dry condition is made before thehdryerlv starts and the entire drying cycle is thereafter automatically carried out.

In the accompanying drawing, Fig. 1 is a front elevation partly broken away of a clothes dryer; Fig.2 is a fragmentary sectional side elevation; Fig. 3 is a control diagram; and Fig. 4 is another control diagram; Fig. 5 is a'diagram illustrating the operation of the Fig. 3 control; Fig. 6 is a diagram illustrating the operation of the'Fig. 4 control; and Fig. 7 is a control diagram of another modification;

Typically, the. dryer has a cabinet 1 within which is Z,$58,5l8 Patented Nov. 4, 1958 13. In the operation of the dryer, air is drawn diagonally across the drum through an air intake slot 14 and through the perforated periphery of the drum into the fan inlet duct 10 through the openings 9 and is discharged by the fan through an outlet 15 into a lint trap 16 having a discharge 17 at the front of the dryer. Heatfor evaporating the moisture is supplied by an electric heating element 18 suitably mounted within a reflector 19 adjacent the air intake slot 14. The parts so far described are or may be of common construction and are subject to substantial variation in construction and appearance.

During the early part of the drying cycle, the moisture in thecloth'es is evaporated at a rapid rate and the latent heat of vaporization limits the rise in temperature of the air exhausted by the blower 12 to a value of the order of 140 to 150 F. When the air reaches'this temperature, the bulk of the moisture has been evaporated but there remains enough moisture in the clothes so that the clothes are merely damp dried suitable for ironing. The time required for the clothes to reach the damp dry condition naturally depends upon the size of the load and the degree of initial wetness. Except for light loads,-the exhaust air temperature has been found to be a very reliable indication of when the clothes are damp dry. As the clothes are progressively dried beyond the damp dry condition, less of the heat'goes into vaporizing the moistureand more of the heat goes into raising the temperature of -the clothes and air. In this further drying operation, the size of the load and the type of fabric become increas ngly important and introduce substantial varia tions in" the relationship between the exhaust'air temperature and the degree of dryness. For example, an an exhaust air temperatureof 180 which might correspond to full dry for broadcloth shirts will not corre spond to full dry for shag rugs. In other words, the exhaust air temperature is a less reliable indicator of the full dry condition. The'exhaust air temperature, however, does automatically indicate when normal sized loads of clothes are damp dry and does automatically take care of indicating when the great bulk of the moisture in the clotheshas been evaporated. For light loads, the heat by-"asses the clothes so the rise in exhaust air temperature is hi her than could be expected from the moisture remainingin the clothes.

In order to take care of variations which are not accurately reflected in the exhaust air temperature, it is proposed to utilize a control in which the initial part of the drying cycle corresponding to that required to bring theclothes to a damp dry condition is controlled by the exhaust air temperature and the final part of the drying cycle 'necessaryto bring the clothes to a full dry con dition is preselected'by the judgment of the operator in accordance with the size of load and type of fabric. .Because of the-damp dry condition the clothes have an essentially constant amount of moisture, it is not necessary that the operator also estimate the initial wetness. This results in a control which can be adjusted with a minimum of skill so as to fully dry without overdrying' any load;

In the control diagram shown in Fig. 3, the heating element 18 is connected across a grounded neutral 230 volt power supply 20 through contacts 21 and a safety thermostat 22 which cuts off theheatingelement under "abnormal conditions such as when the belt driving the ascents terfered with. The contacts 21 are mounted ona rod- 23 which is depressed to the contact closing position by any one of the cam projections 24a-e on a cam 25 acting through a lever 26 pivoted at 27 and associated with an; over-center spring 28. The depression of the lever 26' by the projections24a-a moves the lever. past the-center line of the spring 28'. after which the contacts 21 are,,closed under the pressure developed. by the spring 28; The contacts 21 are opened underthe control ofa thermostatic bulb 29 connected to a bellows 3% having an adjustable abutment 31. which engages the lower end of the rod 23. The thermostatic bulb 29 is arranged in heat transfer relation to the exhaust air discharged by" the blower 12 so that the bulb. 29 has essentially the same temperature asv the exhaust air. As the temperature of the bulb 29 rises, the bellows 30 expands and moves the rod 23.upward, until it moves above the center line of thespring 28 after which the contacts 21 are opened with:

The illustration of the snap action opena. ing and closing of the contacts 21 is diagrammatic and asnap action.

commercially available snap action switches have substantially different; appearances. The contacts 21 merely control the heating-elementlo. The contacts 21 haveno control over the; motor 32 for driving'the drum 2 and blower 12. The motor'32, is connected acrossone side of the power; supply Zilthrough a switch 33 controlled by a cam 34. arranged so that the motor 32 is energized whenever the contacts 21 are closed'to energize the heat; ing element18 and the motor 32 continues to be. energized after the" contacts 21 cut off the. power to the:

heating element.

of. the contacts 21. The timer motor 35'is also in series with a switch 37' controlled by a cam 38 and closed so long as the contacts 33- controlling the motor 32. are

closed. This. meansthat the timer motorv 35 is always in conditionfor operation whenever the dryer is operating even though thetimer; motor 35 never runs except when the heating element 18 isde-energized. The slip-clutch- 34a permits the cams 25, 34'and 38 to be manually set by meansof a control knob 39'fixed to the timer shaft 40. The cams 34 and-38-are rigidly fixed to the timer shaft 40. The cam 25 is loose on the timer shaft 40 and is connected thereto by a lostmotion connection diagrammatically illustrated as a h1g4]. projecting through. a slot. 42. in the cam25 and spring 43. The lost motion connection between the; timer shaft 40 and the cam- 25 permits projections 24ae on the cam 25, which close the contacts 21, to move-out of the. way after'the contacts have vbeen closed so as not to block the opening of the contacts under the action of the thermostatic bellows 30. The lost motionconnection iswell understood and is only diagrammatically illustrated.

In the use of the Fig. 3' dryer control, the operator starts the operation by turning the control knob 39 in a clockwisedirection to the desired position and by setting: the adjustment 31 of. thethermostat 29. loads, the temperature adjustment should be lower forsynthetic fibers and higher for fibers. difiicult to dry such as shag rugs. ment should be higher. The first position of the control knob will be damp dryin which the firstof the projections Moon the cam 25' closes the heater contacts 21. There are four additional projections 24b, 24c, 24d, and

24a on the cam 25 which are successivelybrought intoplay as the control knob 39 is turned in a clockwise direc.--

tion, These additional projections,as will be. hereinafter explained, add successive cycles of heat input to the dryer and are selected in accordance with the judgment of the operator as to the weight and type of='cloth'es tube-fully For, normal For light loads, the temperature: adjustdried. Before the first projection 24a has closed the contacts 21- on the heater 18, the cams-34 and 38 have the liilt trap 15'. Let us assume that the operator has a normal sized load of clothes of a fabric which is easy to dry. If this load is to be fully dried, the operator will turn the control knob 39 to a position in which the projection 24b on the cam 25 is slightly to the right of the upperend of the rod 23. As the projection 24a moves past the upper end of the rod 23, the contacts 21 are closed so that the cam projection 2411' does not close the contacts 21. The initial drying operation with this setting of the control knob 39v will be to damp dry the clothes. This willlbe'determinedby the-rise in temperature of'the thermostatic: bulb; 29' to. a temperature in the range of' rom.2.l:4.01E;.to: 150 F; Th s temperature range will vary; somewhatwiththe-dryer heat input and dryer construction butwill. be a. definite figure for any particular dryerdesign;

to any selectedyaluei When the exhaust air temperature' reaches the selected value,.the expansion of the bel'-- lows 30. moves; the rod 21. upward and opens the heater contacts 21 andsimultaneously' closes the timer contacts- 3.6, astshown in Fig.3. This. starts the rotation of the timer. shaft. 40: moving the cams 25,34, and 38 in a counterclockwisedirection; The rotation ofv the timer shaft 405-QOI1I1I1U6S until the projection 24a.engagesthelever. 26. andv closes the heater contacts. 21 and. at the" same, timezopens the. timer. motorcontacts 36. The length of time required=toreclose-thecontacts. 21 by theprojec tion.24a.is, determined-by the speed. of the timer motor shaft. 40. and. by the spacing between the projections 24a.

and 2412. This time will ordinarily be of theorder of 5 minutes-andiduring this time-the circulation of air through thev drum inthc absenceof the heat from the' heating element.. 1.8.willzresult in a cooling down of the clothes and dryer. Accordingly, when the heater. contacts 21. are: reclosed by theecam' projection. 24a, the temperature has dropped sothat a substantial period of time W1il.b6:1'6+- quiredto raisethe exhaust air. temperature back to the;

selected-1407150." P. value. The amount of heatim partedv during. this additional drying cycle will besufe ficient to. fully. dry a normal loadof easy to dry. clothes. When the exhaust air temperaiure reaches the selected.

value .attheend. of this seconddrying cycle the. contacts 21areagain openedand the contacts 36 in series with the timer, motor-35 are again closed starting the rotationof.

the .timer. shaft. 40, Which.continues until the circuit to thetimer. motor is interrupted by the opening of the con-.-

tacts-37. This .addsa further cool. downperiod during which the exhaust air temperature-drops because the air. continues. to. circulatethrough the drum without: any" heat input. At the endofthe finalcool down period the would have turned .the knob to the full limit 'in a clock wise-.directi;on. bringingtheprojection 24c slightly to the right of the rod 23. This would have resulted in'five' successive cycles during each of which the exhaust air temperature was-.broughtpup to the selected -l50 F. val-uecfo'llowed .by a cool down periodduring which thevblower continues to operate 7 to circulate air through ti'l'fidlllIIL-Wlththe heating element 18 cut olf. These five successive cycles will result in the full drying of the most.

difficult load.-.

By adjustment: of the abutment 31, the: setting of the. exhaust. air temperature can be adjusted Because the clothes temperature as reflected by the exhaust air temperature is limited, the danger of overdrying the fibers with the resultant excessive wear due to brittleness is minimized even if the operator should turn the control knob 39 to the maximum drying position there would still not be dangerous overdrying of the clothes. From one aspect, the operator selects the number of drying cycles which correspond to the degree of dryness desired and will vary with the size of the load and the type of fabric being dried; The initial drying cycle merely brings the clothes to a damp dry condition and the added four cycles possible take care of the difliculty of drying different sized loads of difierent fabrics.

In the Fig. 4 control, the exhaust air temperature is used to determine when the clothes are damp dry and a timer is adjusted by the operator to add the additional drying time to bring the clothes to full dry. Because the damp dry clothes have an essentially uniform concentration of moisture less skill is required to estimate the added time required to fully dry the clothes. Surprisingly, the Fig. 4 control obtains almost perfect compensation for the weight of the clothes being dried.

The damp dry control is shown utilizing a nonrecycling thermostat which closes contacts 44, 45 in the circuit of timer motor 46. The contacts 45 are mounted on a rod 59 and, are held in either open or closed position by an

over-center device

59c, 59d. When the exhaust air temperature rises to the value corresponding to damp dry (140-l50 F. for a normal sized load), a bellows 48 associated wtih a thermostatic bulb 49 expands and moves the contacts 45 against the contacts 44 thereby closing the circuit to the timer motor. The timer motor 46 drives a shaft 50 through a slip clutch 51. Fixed to the timer shaft 50 is a cam 52 controlling the motor 32 which drives the drum 2 and the blower 12, a cam 53 which controls contacts 54 in circuit with the dryer heating element 18, and a cam 55 which controls contacts 56 in the circuit of the timer motor 46. The timer shaft 50 can be manually set by a control knob 57 which is turned in a clockwise direction to select the desired added drying time before the drying operation is started. The added drying time selected will depend upon the type of fabric, a factor which the operator is most familiar with. Ordinarily, the timer can be set to add anywhere as from 1 to 30 minutes additional drying time after the clothes have reached a damp dry condition as reflected by the temperature of the air exhausted through the lint trap 15.

'To set the dryer in operation, the operator first sets the control knob by turning it in a clockwise direction thereby determining the additional drying time .after the clothes are damp dried. The setting of the additional drying time closes contacts 57 in the circuit of the dryer motor 32 and starts the rotation of the drum and the operation of the blower 12. The setting of the timer shaft 50 also closes the contacts 56 in the circuit of the timer motor 46 and moves the projection 58 on the cam 53 clear of the upper end of a rod 59a carrying the heater contacts 54. The second step necessary to start the drying operation is to push a start button 60 at the lower end of a rod 59 carrying the timer contacts 45. The rods 59 and 59a are in axial alignment so that when the rod 59 is pushed upward, the rod 59a moves upward and moves the contacts 54 to the closed position energizing the heating element 18. The upward movement of the rod 59 opens the contacts 44, 45 in the circuit of the timer motor. There is an over-center spring 61 associated with a lever 61a connected to the rod 59a carrying the heater contacts 54 which acts to hold the contacts 54 in either the opened or closed position. The push button 60 is not mechanically connected to the rod 59 or to the contacts 44 but is biased away from these parts by spring 62 so that after the push button 60 is de- '6 pressed to close the

contacts

54 and 44, 45, it is re tracted by the spring 62 out'of the way so as not to interfere with the subsequent opening of these contacts. -A

similar over-center spring 590 is associated with a lever 59d connected to the rod 59.. Because the pushing of the start button 60 opens the contacts 44, 45 in the circuit' of the timer motor 46, the initial stage of the operation of the dryer is solely under the control of the

exhaust air thermostat

48, 49 having a temperature adjustment diagrammatically indicated at 48a. When the exhaust air temperature reaches the value corresponding to dampdry as selected bythe adjustment 48a, the expansion of the bellows 48 depresses the rod 59 and closes the contacts 44, 45 and thereby starts the rotation of the timer motor 46 to add the additional drying time selected by the operator. If 'the minimum added time is selected, the timer motor 46 almostimmediately turns the cam 53 to a position in which the raised portion 58 depresses the rod 59a and opens the contacts 54 in the circuit of the heating element 18, as shown in Fig. 4. At this point, a raised portion 63 on the timer motor cam 55 is still holding the contacts 56 in the timer motor circuit closed and a raised portion 64 on the dryer motor cam 52 is still holding .the contacts 57 closed. Accordingly, the drum continues to rotate and the blower continues to circulate air through the dryer for a cool down period duringwhich the temperature of the clothes and dryer is brought down to a lower value at which the clothes are more comfortably handled. This cool down period will ordinarily be from 4 to 5 minutes duration. At the end of this cool down period, the clothes will be damp dried.

If a substantial amount of added drying time is selected so as to bring the clothes to the fully dried position the operation above described will be preceded by a timer controlled cycle during which the heating element 18 is' energized. This added time control drying cycle may last as long as 30 minutes in the case of fabrics which are difficult to dry such as shag rugs. At the end of the added drying time, the raised portion 58 on the cam" 53 opens the contacts 54 in the circuit of the heating element 18 and the cool down period described above follows the opening of the circuit to the heating element.

In both types of control the exhaust air temperature is used to select the damp dry condition of the clothes and a timer i adjusted by the operator to determine the addi tional drying necessary to bring the clothes up to the full air is circulated through the dryer with the heating element off. In the Fig. 4 control, the timer merely deter-- mines the additional drying time during which heat shall be supplied to the dryer so as to bring the clothes to thefully dried position. Both controls have a cool down; period which is more necessary in the case of the Fig. 3- control but is desirable in both controls. In the Fig. 3

control if there were no cool down period the additional drying cycles would be of such short duration as to be: of no practical value. In the Fig. 4 control where the cool down period appears solely at the end of the cycle it has only the function of reducing the clothes temperature so that-the clothes can be more comfortably handled.

In Fig. 5 is a diagram of the exhaust air temperature for the Fig. 3 control, the full lines indicating the periods when: the heat is on and the dotted lines indicating the periods when the heat is off.

In Fig. 6 is a diagram of the percentage of moisture removal for the Fig. 4 control having a fixed setting of the exhaust :airtemperature thermostat 48, .49Iand a fixed setting for the, addedtime. forzthetimer 46. .T he dryer is designedzfor iamormal load of 8 pounds-of clothes and inathe rangeotfialOapounds.of;clothes axfixed-exhaust air temperaturesettin'g turnson the timera fixed:tirne-before tl1=fllbths are fully dried. Surprisingly, for light loads, e.,. g .t2.'.4 lbs.,;the control p'roducesjfully dried clothes by thegsame setting usedfor: the 610'1b.loads. This'is surprisingxbecauseathe; percentage of l'moisture :rernoved at the'cfixedtexhaust tair temperature :at :which the timer 46 isrturned.on=varics from l2; /2% fortheZ lb. load to 90% for thextnormaltor .8 vlb. load.and"92. /2% for the 10 lb. loath Xetades'pite thezwidezvariation, all of the loads wereifully dried-without overdrying and without touching the. dryer contro-l setting. Thesettingfor normal loads (8, lb.) workedsequallyiwelltonilight loads (2-4 lbs.) and onfhQfiVie-nthan normallloadsr(ltlbst). This produced substantiallyperfectcompensationlfor thesizeof the load and provided complete protection :from 'fiber embrittlemen t;,accompanying overdrying. The .calibration of the Eigt 4tcontrol is very simple. The exhaust air temperature :isgsetgfor 90%,.;moisture removal at normal load and the added-timeis ,setgto bring the normal load to full dry. 'Ehesetwosettings willythen produce fully dry clothes for any sizeofloadwithoutioverdrying.

In fig; ,7 is shown another :control diagram in which the -,operator-selccts the 'addedtime for drying as in Fig. 4. IH'EthlS"C.QI1lIRQ1, the. timer motor -65 is connected across one..-sit e. of the .230 volt line and drives a cam 66 controllingthe currentto the. dryer heater 18, a cam 67 controlling ithe current :to the drum and fan 'motor 32 and a mfi-nUfill's:dia-1 '6 8.by which the timer can be reset. The heater 1.8:.is connected across the 230 volt line through aswitch, 69,:contr0lled by the cam66. The drum motor 1 is co nected across one side of "the 230 volt line to a switch 70tcontrolled byithe cam 67.

flhe dryer is-started by turning'the dial 68 counterclockwise-to the 'on. position or as much past the .on" position -;as the operator-desires added drying time controlled-bythe position. of the cam 67. This closes the switch 69 in series with the heater 18 and the switch 70 in series with the motor 32. Thetimer 65 does not start at this time but remains stationary.

Assoon as the exhaust air temperature comes up to the value determined by the adjustable normally open thermostat 71, a circuit is closed to the timer motor 65 which also extendsthrough a normally closed thermostat 72 and the,

switch 70 in series with the drum motor 32.

After the timer motor 65 starts because the thermostat 71 has closed, the timer runs until it has used up the elapsed timeset in by the .cam 67.. If only a small amount of added time was set in by the cam 67, the timer motor 65 may run continually until all of this time is used up. If a larger amount of added time is set in by the cam 67, the exhaust air-temperature may rise sufficiently to open the normally closed thermostat 72 thereby interrupting the circuit to the timer motor 65 and to the heater 18 and permitting the drum motor 32 to keep running with the heater shut ofi. When the normally closed thermostat 72 recloses due to a drop in the exhaust air temperature, the timer motor starts again.

When the added time set .in by the cam 67 is used up, the heater switch 69 opens and an auxiliary contact 73 is closed which keeps the timer 65 running. The timer runs for the cool-down period controlled by thecam 67 at the end of which the switch 70 in series with the drum motor opens shutting off the dryer 7t and likewise the timer. 65.

In the Fig. 7 control, the thermostat 72 should not be open except when the thermostat 71 is closed. This would normally take place because the thermostat 72 is in essence an over-temperature thermostat which would always have a higher operating point than the thermostat 71.

As .in the Fig. 4 control, the thermostat 71 can-determine the damp dry condition for normal clothes and the 8 timer '65 scan determine/the full dry condition; This eliminates thezneed ifOI' estimating load sizes and leaves only thesneedtfor.;a;setting which depends on the type of fabric. The..-adjustability-0f'the exhaust air'thermostat '71 and :ofuthe .tinter;65.;permits automatic drying without overdrying.

In clothes dryers ithere'are two factors which afr'ect the rate of drying, the state at which heat is transmitted-to the cloitlres-and' the =ra'te -at which the clothes absorb the heat. The rate at which the heat is transmitted to the clothes is a function of dryer design and'except for the initial 'warm-up period-when heat is dissipated in warming u'p the metal parts is essentially constant for any dryer.

The rate at whichclothes absorb the heat is a functionof the kind of fabric. Thick fabrics such as shag rugs give up moisture relatively slowly whilesynthetic fabric which are only superficially-wet give-up moisture quite readily.

As the moisture isevaporated the heat of evaporation For any particular kind of fabric the exhaust air temperature is primarily'an lowers the exhaust air' temperature.

would not be'irnp'ortan't because only when the residual water reached'oneand three-fourths pounds would the exhaust air temperatnrerise to 150 F.

Accordingly, by selecting an exhaust air temperature corresponding to 'a fixedamount of residual moisture (which might, "for example, range from F. for synthetics tel-60 F. for shag rugs) a control which adds a fixed amount of drying time after reaching this temperature will-fully dry .any size lead with any degree of initial wetness. The only variable would be in the type of fabric which would determine whether the fabric was easy or hard to dry; The controlwhich uses exhaust air temperature corresponding to damp dry followed by a fixed time of drying accord ngly eliminates all of the variibles' except the type of fabric and offers the possibility of an automatic dryer control which eliminates most of the variables atfezting the drying time.

By having the thermostat 72 set for a few degrees higher-temperature than the thermostat 71, the drying can be carried out at temperatures low enough to prevent injury or overdrying of any fabrics, even the synthetics. For example, the normally open thermostat 71 might be set to close at "F. and to open at 130 F., while the normally closed thermostat 72 might be set to open at F. and to close at' 135 F., all temperatures being exhaust air temperatures. With these values, the thermostat 71 star-ts the timer then adds the selected amount of drying time but because of the thermostat 72, the timer stops when the exhaust air temperature reaches 165 F. and starts again when the exhaust air temperature drops to 135 Ft, thereby preventing drying at such high temperatures as to injure delicate fabrics. With this control, the timer does not measure elapsed time but measures additional drying time at temperatures below 165 F.

What is claimed as new is:

1. In a clothes dryer of the type having a rotatable clothes receiving drum, a heater associated with the drum, a circuit for the heater including contacts, a blower for exhausting air from the drum, and a motor drive for the bfower and drum, the combination of a control movable to an the dryer by energizing the heater through the said contacts and starting the motor drive for the drum and blower, a timer initially de-energized in the on posi+ on position for starting the operation of tion of the control, said timer having a control for stopping the operation of the dryer by de-energizing the heater by opening said contacts and stopping the motor drive, a circuit for the timer branching from the heater circuit, an operator actuated selecting means for selecting the time interval after which the timer operated control stops the operation of the dryer, and normally open thermostat means in said timer circuit but not in said heater circuit closed in response to the exhaust air temperature for starting the operation of the timer without interrupting the heater when the exhaust air temperature reaches the value corresponding to the damp dry clothes for normal sized loads.

2, In a clothes dryer of the type having a rotatable clothes receiving drum, a heater associated with the drum, a blower for exhausting air from the drum, and a motor drive for the blower and drum, the combination of a control movable to an on position for starting the operation of the dryer by energizing the heater and starting the motor drive for the drum and blower, a timer initially de-energized in the on position of the control, said timer having a control for stopping the operation of the dryer by de-energizing the heater and stopping the motor drive, an operator actuated selecting means for selecting the time interval after which the timer operated control stops the operation of the dryer, a normally open thermostat means responsive to the exhaust air temperature for closing a circuit to the timer when the exhaust air temperature reaches the value corresponding to the damp dry clothes for normal sized loads, a normally closed thermostat in the timer circuit and in the circuit to the heater for interrupting both the timer and heater, but not the motor, upon excessive exhaust air temperature.

3. In a clothes dryer of the type having a rotatable clothes receiving drum, a heater associated with the drum, aheater circuit including a switch controlling the heater, a blower for exhausting air from the drum, and a motor drive for the blower and drum, a motor circuit including another switch controlling the motor, the combination of a control movable to an on position for starting the operation of the dryer by closing the heater switch and closing the motor switch, a timer initially de-energized in the on position of the control, said timer having a control for stopping the operation of the dryer by opening the heater and motor switches, an operator actuated selecting means for selecting the time interval after which the timer operated control stops the operation of the dryer, and a circuit to the time extending through the motor switch, and thermostat means in said timer circuit but not in said heater circuit having normally open contacts closed in response to the exhaust air temperature for starting the operation of the timer without interrupting the heater when the exhaust air temperature reaches the value corresponding to damp dry clothes for normal sized loads.

4. In a clothes dryer of the type having a rotatable clothes receiving drum, a heater associated with the drum, a switch controlling the heater, a blower for exhausting air from the drum, and a motor drive for the blower and drum, another switch controlling the motor, the combi nation of a control movable to an on position for starting the operation of the dryer by closing the heater switch and closing the motor switch, a timer initially deenergized in the on position of the control, said timer having a control for stopping the operation of the dryer by opening the heater and motor switches, an operatoractuated selecting means for selecting the time interval after which the timer operated control stops the operation of the dryer, a circuit to the timer extending in series through the motor switch, a normally closed thermostat connected in series with the heater and a normally open thermostat, said normally open thermostat closing at an exhaust air temperature corresponding to damp dry clothes for normal sized loads and said normally closed thermostat being closed at an exhaust air temperature corresponding to damp dry clothes for normal sized loads and opening at a higher exhaust air temperature whereby the timer measures drying time at temperatures between the temperature corresponding to damp dry clothes for normal sized loads and said higher exhaust air temperature.

References Cited in the file of this patent UNITED STATES PATENTS 2,505,041 Gorsuch Apr. 25, 1950 2,548,313 Kauffman Apr. 10, 1951 2,590,808 Wagner Mar. 25, 1952 2,621,423 Clark Dec. 16, 1952 2,743,532 Steward May 1, 1956