Automatic dryer control circuit

May 5, 1964

R. Y. PEI ETAL

3,132,003

AUTOMATIC DRYER CONTROL CIRCUIT

Filed Aug. 2, 1961 3 Sheets-Sheet 1

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RUSSELL. M. SASNETT &amp; RICHARD Ϋ. PEI

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THEIR. ATTORNEY

May 5, 1964

R, Y. PEI ETAL

3,132,003

AUTOMATIC DRYER CONTROL CIRCUIT

Filed Aug. 2, 1961

Sheets-Sheet 2

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FIG.2

RUSSELL &amp; RICHARD

DI /*\ _

INVENTORS

M. SASNETT

V. PEI

THEIR. ATTORNEY

May 5, 1964

R, Y. PEI ETAL

3,132,003

AUTOMATIC DRYER CONTROL CIRCUIT

Filed Aug. 2, 1961

Sheets-Sheet 3

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THEIR ATTORNEY

3,132,963

Patented May 5, 1364

United States Patent Office ^: ' 7·

3,132,003

AUTOMATIC DRYER CONTROL CIRCUIT Richard Y. Pei, Schenectady, N.Y., and Russell M. Sasnett, Louisville, Ky., assignors to General Electric Company, a corporation of New York

Filed Aug. 2,1961, Ser. No. 128,757

Claims. (CI. 34—45)

This invention relates to domestic clothes drying machines, 'and more particularly to an electrical control system used in such machines.

'For maximum utility and saleability, a domestic clothes dryer should be capable of a number of clothes treating operations. It should, of course, be capable of fully drying a load of clothes to &gt;a condition suitable for immediate use; preferably, the drying will be fully automatic in the sense that the machine will shut itself off when the clothes are dry rather than requiring an estimate by the machine operator 'as to the length of time required for the clothes to be dried. It is further desirable that the dryer be capable of damp-drying clothes, so that they are in a condition suitable for ironing, Also, it is desirable that the dryer be capable of tumbling clothes without heat where the operator desires to fluff or freshen clothes which are already dried. . Yet a further requirement. of modern clothes dryers is that they: be able to provide -a de-wrinklingcycle: in such a cycle,, the wrinkles in certain fabrics, such as for instance synthetic fabrics of the wash-andwear type, may be removed -by elevating the dryer temperature to a point where the synthetic material assumes some degree of plasticity so that the wrinkles are eliminated, 'and then cooling .the. clothes and removing them from the machine before wrinkles can reset .themselves in the clothes.

Many control systems for achieving all or some of these various goals have been devised, and many different such arrangements are presently in machines which are commercially 'available. All of these machines do have the feature in common that the control system for the machine necessarily includes a sequence control assembly consisting o-f 'an electrically driven motor of some kind which times the opening and dosing of certain switches during a cycle of operation. A very common structure for achieving this goal is the provision of a synchronous motor which, through a -gear -train, operates a bank of cams controlling different switches so that the switches open and close at the proper time during cycles of operation to provide the desired effect. The sequence control assembly usually constitutes by far the most expensive component of -a dryer control system. It is, consequently, most desirable to eliminate this costly item without at the same time losing the ability to provide the multiplicity of functions and cycles described above.

It is consequently an object of our invention to provide a clothes dryer having an improved electrical control system wherein, without the conventionally present sequence control assembly, the machine may provide a complete automatic drying cycle, a damp-drying cycle, a fluff cyde, or a de-wrinkle cycle.

It is a further object of our invention to provide an automatic drying machine wherein an automatic drying cycle and either a fluff cycle or a de-wrinkle cycle may be provided without the necessity -for a sequence control mechanism.

A further more specific object of our invention is to achieve the above mentioned objects by a control circuit 'arrangement which includes a biasing resistance-type heater positioned physically adjacent the control thermostat of the machine, and a variable resistor in series with the biasing heater.

Yet another more -specific object of ou-r invention is to provide -the above mentioned system including a biasing heater and a variable resistor wherein these two -items are included in a circuit energized by 'the voltage induced in the start winding of the 'air-circulating and drum-turning motor of the drying machine.

In carrying out our invention -in one form thereof, we provide a clothes drying machine which has a conventional clothes container, with -a main heater positioned to heat the dothes in the container and electrically operated means for circulating air through the container. The air circulat10 ing means is operated through a first electrical circuit, and the main heater is caused to operate by the completion of : a second electrical circuit which includes- a manually operated switch so that it may be selectively opened to provide .a fluff cycle.

Positioned to be responsive to -the temperature of the clothes, we provide thermostatic means which trips when it reaches a predetermined high -temperature. The thermostatic means is 'influenced not only by the clothes temperature, but also by 'an electric resistance-type biasing 20 heater positioned in heating relation to the -thermostatic means, and which in turn is connected in series with a manually operable variable resistor. The resistor and the biasing heater are induded in -a third circuit, and when the thermostatic means -trips it causes the elements in all 25 three of the circuits to become de-energized.

The -thermostat is set so that, with the variable resistor arranged at a predetermined setting, -it will be caused to trip when the dothes reach a temperature indicating that they are 'dry, -thereby to- provide an automatic dry cyde 30 independent of time. Where a fluff cycle is desired, the biasing heater and the variable resistor -are designed to cause the thermostatic means to -trip after several minutes without any operation at -all of the main heater provided a predetermined low resistance has been selected on the 35 variable resistor. This causes a simple tumbling and air circulating operation to be provided until the thermostat trips. In this manner, either an -automatic cyde or fluff cycle may be selected. In addition, a different setting of the resistor will cause tripping of the thermostat with 40 the dothes still damp after a heat-drying operation, so as to provide a damp-dry operation when so desired.

Where a de-wrinkle cycle -is to -be furnished by -the machine, we provide a second thermostat which completes the second circuit in -its normal position but when tripped (at the de-wrinkling temperature) opens the second circuit and completes the third circuit. Completion of the third circuit energizes the biasing heater so that, after a few minutes of -air circulation without heater operation, the control -thermostat trips to shut off the machine as before. This de-wrinkle cycle causes the dothes in the ^J dryer to go to -a higher temperature than would otherwise be the case, inasmuch as 'the biasing heater circuit is not completed until the second thermostat trips -to indicate that the temperature at which de-wrinkling occurs has been reached. When this second, or de-wrinkling, -thermostat ⁵⁵ is provided, we prefer to include switch means in both the second -circuit and the third circuit for bypassing -the second thermostat so that, when fluff, damp-dry, or automatic dry is to be provided the de-wrinkle thermostat will be ineffective.

θθ The subject matter which we regard as our invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. Our invention, however, both as to organization and method of operation together with further objects and advantages thereof, may ⁶⁰ best be understood by reference to the following description taken in conjunction with the accompanying drawings.

In the drawings,

FIGURE 1 is a side elevational view of a clothes dryer incorporating our improved dryer control arrangement, ¹⁰ the view being partly broken away and partly sectionalized in order to illustrate details;

8,132,003

FIGURE 2 is a horizontal sectional view of the dryer, with certain surfaces broken away and partly sectionalized to illustrate further details;

• FIGURE 3 is a fragmentary front elevational view of the dryer illustrating the control panel thereof;

FIGURE 4 is a schematic illustration of our improved control circuit as used in. the control of the drying machine of FIGURES 1, 2, and 3; and

FIGURE 5 is a diagram showing the closure of the different manual switches in FIGURE :4 by the control buttons in FIGURE 3.

Referring now to FIGURES 1, 2, and 3 of the drawings, we have shown therein a domestic clothes dryer 1 including a clothes tumbling container or drum 2 provided with a suitable outer casing or cabinet 3 which completely encloses the drum on all sides. The drum is mounted for rotation within cabinet 3 on a substantial horizontal axis, and is generally cylindrical in shape, having a first outer wall portion 4, second and third outer wall portions 5 and 6 located respectively adjacent the ends of the drum, a back wall 7, and a front wall 8. Outer wall portions 4, 5, and 6 are imperforate over their entire length, so that the entire outer shell of the basket is imperforate; on the interior surface of central portion 4 there is provided a plurality of clothes tumbling ribs 9.

The front of drum 2 is rotatably supported within the outer casing 3 by means of a pair of idler roller wheels 10 and 11 which are rotatably secured to the top of an upwardly extending member 12 secured at its bottom to the base 12α of the machine (FIGURE 1). Rollers 10 and 11 are disposed beneath the drum in contact with portion 6 thereof. The rear end of the drum receives its support from a roller wheel 13 which is positioned beneath portion 5 of the drum in supporting and frictionally driving engagement therewith.

Roller 13 is secured on a shaft 14 supported in bearings 15. Shaft 14 is secured to pulley 16 which is driven from a belt 17 in turn powered by a pulley 18 mounted on the end of the shaft 19 of an induction-type electric motor 20. The motor, pulleys, and. roller 13 are so proportioned to drum 2 and to each other that drum 2 is rotated by roller 13 at the appropriate speed to provide tumbling action for articles of clothing placed therein.

In order that a stream of drying air be introduced into and passed through the clothes drum, the drum is provided with a central aperture 21 in its front wall 8 and with a plurality of perforations 22 extending in an annulus around back wall 7. Rigidly secured to the rear wall 23 of casing 3 by any desired means such as, for instance, welding at suitable points 24, is a baffle member 25 which has secured thereto heating means such as an electric heater 26, appropriately insulated from the baffle member. Heating elements 26 may be annular in shape so as to be generally co-extensive with perforations 22 in drum 2. A baffle member 27 is rigidly secured to the back wall 7 of the drum outside the ring of perforations 22 and within the stationary baffle 25 so that an annular air inlet 28 is, in effect, formed by the baffles 25 and 27. Baffle 27 is further provided with an annular series of openings 29. In this manner, a passage is formed for air to enter annular opening 28 between the baffles, pass over the heating elements 26, and through openings 29 and perforations 22 into the interior of drum 2.

In addition to the air guiding function, the baffles 25 and 27 help rollers 10, 11, and 13 support the drum 2. Secured to the central portion 30 of baffle 27 is a bracket 31 to which in turn is secured a stub shaft member 32 substantially coaxially positioned relative to drum 2. The central portion of baffle 25 has a slot-like opening 34 formed therein. The slot is suitably formed (as is more fully described in application Serial No. 789,869, filed January 29, 1959, by William F. Simpson and assigned to the same assignee as this invention, now U.S. Patent No. 3,009,259), so as to permit stub shaft 32 a limited amount of movement in the vertical direction but virtually no move ·

ment in the horizontal direction. Thus, the slight vertical motions of the drum which result from the tumbling of the clothes can be accommodated while at the same time undesirable horizontal motion is affirmatively prevented by engagement of stub shaft 32 in slot 34.

The front opening 21 of the drum is substantially closed by means of a stationary bulkhead generally indicated by the numeral 35. Bulkhead 35 is made up of a number of adjacent members including the inner surface 36 of an access door 37 mounted on the dryer cabinet, a stationary frame 38 for the door, the inner surface 39 of an exhaust duct 40, and an annular flange 41 mounted on the frame 38 and on the duct wall. It will be noted that a suitable clearance is provided between the inner edge of the drum opening 21 and the edge of bulkhead 35 so that there is no rubbing between the drum and bulkhead during rotation of the drum. In order to prevent any substantial air leakage through opening 21 between the interior and the exterior of the drum a suitable ring seal 42, preferably formed of felt-like material, is secured to flange 41 in sealing relationship with the exterior surface of drum wall 8.

Front opening 21, in addition to serving as part of the air flow through the drum, also serves as a means whereby clothes may be loaded and unloaded from the drum. The door 37, whose inner surface forms part of the bulkhead closing the opening, is mounted on cabinet 3; when the door is opened, clothes may be inserted into, or removed from the drum through the door frame 38. It will be noted that the door includes an outer flat imperforate section 43 and an inwardly extending hollow section 44 mounted on the flat outer section. Hollow section 44 extends into the door frame 38 when the door is closed and the door surface 36 which comprises part of the combination bulkhead 35 is actually the inner wall of the hollow section.

The air outlet from the basket is provided by a perforated opening 45 formed in the inner wall 36 of hollow door section 44. The bottom wall section of door 34 and the adjacent wall of door frame 38 are provided with aligned openings 46 and 47, opening 47 providing the entrance to duct 40. As shown, a lint trap 48, which may comprise a fine mesh bag, is preferably positioned in exhaust duct 40 at opening 47, the bag being supported by the door. Duct 40 leads to suitable air moving means which may, as shown, comprise a centrifugal blower 49 mounted on the motor shaft and thus driven directly by motor 20. The outlet of blower 49 communicates with an outlet duct 50 (FIGURE 2) which extends to an opening 51 in the back 23 of cabinet 3.

During operation of motor 20, the rotation of blower 49 causes air to be drawn into cabinet 3 through a suitable opening 52 (FIGURE 1) provided at the front of the machine, through annular opening 28, over heaters 26, through openings 29 and perforations 22 into drum 2, across the drum, through perforated opening 45 and aligned openings 46 and 47 into duct 40, and then through the blower 49, outlet duct 50, and opening 51 into atmosphere.

The operation of dryer 1 is controlled by a new and improved control system shown in the circuit diagram of FIGURE 4. As shown there, the entire control system of the machine may be energized across a three wire power supply system which includes supply conductors 53 and 54 and a neutral conductor 55. For domestic use, the conductors 53 and 54 will normally be connected across a 220 volt power supply, with 110 volts appearing between the neutral line 55 and each of the conductors.

As previously stated, the drive motor 20 is preferably of the induction type, including a main winding 56 and a start winding 57 which are connected in parallel with each other across the supply conductor 53 and neutral conductor 55. Specifically, the motor energizing circuit, starting at supply conductor 53, passes through a conductor 58, the bimetallic element 59 of a thermostat 69, and a conductor 61 which leads to a pushbutton switch

3,132,003 by Everett D. Morey and assigned to General Electric Company, assignee of the present invention.

From the heater 71 and thermistor 75 in parallel with each other, a switch 76 when closed is connected to the end of conductor 55. Thus, during the operation of the machine, a closed loop circuit which includes the start winding 57 is provided as follows: starting with the winding 57, the loop passes through conductor 72, resistance 73 and contact 74, the heating element 71 and thermistor 75, switch 76, conductor 55, switch 64, and protector 63 back to the other end of the start winding 57. .

In this manner, because of the well known induction of voltage across the start winding 57 during operation of motor 20 even though the start winding is disconnected from the source of power, the induced voltage may be utilized for the energization of the heater 71. It will be understood that the heater 71 may be made smaller and more economically where it is used in connection with a lesser voltage than line voltage, such as is true where the voltage induced in winding 57 is the source of power. For instance, a typical induced voltage in the start winding of an induction motor operated on 110 volts 60 cycle current would be on the order of 50 to 60 volts. This, then, constitutes one aspect of our invention, although it will be understood that, in connection with the various other aspects of our inventon which are to be brought out, a biasing heater energized in the regular manner across a conventional source of power rather than from the start winding may be provided.

It will be noted that even when switch 76 is open, the closed loop circuit described in connection with the energization of element 71 may be provided across the switch through the bimetallic element 77 of a thermostat generally indicated at 78. When a certain high temperature is reached, as will be more fully explained herebelow, the element 77 connects contacts 79 and 80 together thereby to complete a path across switch 76 through a suitable resistor 81. In this manner, the induced power loop for resistor 71 may be provided with the adjustment of resistor 81 automatically included whenever switch 76 is opened, the completion of the loop being dependent upon the position of element 77 when switch 76 is open.

In an untripped position, as shown, the element 77 helps to complete an energizing circuit for the main heaters 26 as follows: starting at conductor 53, the main heater circuit passes through a manually operable switch 82, 'the element 77 in its untripped position, heaters 26, a safety thermostat 83, a conductor 84, a switch 85 which is closed by centrifugal mechanism 68 at the same time that switch 67 is moved to its running position, and then back to conductor 54. This then places the heating element across the 220 volt potential, thereby causing substantial heating to be provided by the elements 26. So that, at appropriate times, the completion of the heating element circuit will not be dependent upon element 77 of thermostat 78, a switch 86 is included in a bypass around the element 77, it being understood that closure of switch 86 prevents the element 77 from being effective . to control the circuit for energizing the heaters 26.

The circuit includes one additional element which has not been described thus far, a high impedance solenoid device 87 which, when energized, causes its plunger to strike a bell type device 88. The solenoid 87 is connected directly in parallel with the bimetal element 59 of thermostat 60 so that when the element 59 opens the motor circuit described, the main winding 56 is in series •with the solenoid 87. Since this solenoid is a relatively high impedance device, and the main winding of an induction motor is a relatively low impedance device, the 70 main part of the voltage drop is across the solenoid. This causes the solenoid to become energized so that its plunger strikes bell 88. At the same time, so little voltage is impressed across the winding 56 that it is effectively de-energized, thus causing the motor to stop. As the biased to an open position but which may be closed so as to connect conductor 61 to the main winding 56. The circuit then proceeds from the main winding 56 to a conventional bimetallic thermostatic protective device 63, a door operated switch 64 which is closed when the door 37 is closed and open when the door is open, and then to conductor 55. It will be understood that the pushbutton switch 62 is positioned so as to be readily available to an operator. This is preferably effected by providing it on the control: panel 65 of the machine, the control panel being positioned on the top surface 66 of cabinet 3 at the back thereof as shown in FIGURES 1 and 3.

The start winding 57 is connected through a centrifugally operated switch 67: in parallel with the main winding and in series with all the other elements described in connection with the main winding circuit. Switch 67 is controlled by a centrifugal mechanism, schematically indicated by the numeral 68, which rotates with the rotor 69 of the motor 20. As the motor comes up to speed, the switch 67 is moved from the position shown wherein it completes the circuit for winding 57 in parallel with winding 56 to a down position wherein the switch 67 is connected to a conductor 70. When the switch 67 engages the conductor 70, the circuit for energizing the main winding 56 of the motor bypasses start switch 62 so that a release of the.start switch and a consequent opening thereof have no effect upon the running of the machine. It will thus be understood, in connection with motor 20, that the motor is started by depression of button 62 which thus completes an energizing circuit-through the windings 56 and 57 in parallel with - each other so that the motor starts. Then, when the motor comes up to speed the start winding is disconnected by the movement of switch 67 under the influence of centrifugal device 68, and a circuit for winding 56 is completed independently of start button 62 which may then be released.

Returning now to the thermostat 60, it is positioned so as to be able to sense the temperature of clothes which are located within the drum 4. One desirable position for the thermostatic device in order to effect this purpose is in the front of the dryer as shown, on the bulkhead 35 directly below the air outlet 45 from the drum. By :so positioning thermostat 60, it is effective to.sense the temperature of the exhaust air leaving the drum, which temperature is very close to the actual .clothes temperature. In addition to the clothes temperature as a factor affecting the operation of thermostat 60, a biasing heater 71 is included in the thermostat in close physical relationship with the bimetallic element 59 so as to be in heating relation thereto. The heater 71 is a relatively high resistance device compared to the main heater 26 (for example, approximately 500 ohms may be provided for heater .71 and 10 ohms for heater 26), so that its 55 power consumption .compared to the mam heater is exceedingly small. In fact, as will be explained further herebelow,-by one feature of our invention we cause the biasing heater .71 to be operated through the power generated in start winding 57 of motor 20 during the operation of the machine.

Specifically, a conductor 72 may be provided which joins start winding 57 to the resistance element 73 of a variable resistor including a movable contact 74 in turn connected to the biasing element 71. While it is not an essential feature of our invention, we prefer to include, in the circuit with biasing heater 71, for ambient temperature compensation,: a thermistor-type device 75 in parallel therewith, it being- understood that a thermistor is a metallic resistance element having a very substantial negative thermal , coefficient, the element generally being derived from a mixture .of iron, nickel, and cobalt. The use and operation of such a structure does not constitute ^appUraffcm^^Na’sls^sIffled on July 9, 1959, 75 motor stops, the switch 85 insures opening of the heater

3,133, . 7 circuit and the switch 67 opens the bypass around start switch 62 so that all components of the machine are then effectively de-energized..

Referring to FIGURE 3, the control panel 65 includes, in addition to start switch 62, manually operable control 5 members which are typical of those which may be provided in order to effect suitable opening and closing of the manually operable devices discussed in connection with FIGURE 4. These may be provided in the form of buttons 89, 91, and 92, together with a dial member 93 having a pointer 94 arranged to register with any one of four different selectable points 95, 96, 97, and 98 around the dial 93. It will be understood that the dial is directly connected to the movable contact 74. When pointer 94 registers with point 95, contact 74 provides the maximum resistance in circuit, with progressively decreasing resistances being in the' circuit at points 96, 97, and 98. These values may, for instance be, respectively, approximately 1400, 450, 275, and 170 ohms.

Switch 89 provides an automatic complete drying cycle when it is depressed and the pointer 94 is set to station 95.

The depression of button 89 causes switches 76, 82 and 86 all to be closed as shown in FIGURE 5. Consequently, when start switch 62 is closed, the motor 20 starts operation with resulting rotation of the drum 2 and forced 25 air flow through the drum. In addition, the. closure of switch 85 together with the position of switches 76, 82, and 86 causes a completion of the heater circuit so that the air is heated before being blown over the clothes. In addition the position of movable contact 74 causes resistance heater 71 to have only a small effect on the thermostat, the calibration being such that most of the heating of the element 59, except under unusual temperature conditions externally, will be caused by the air which has contacted with the clothes. 35

As a result, the temperature of element 59 will gradually rise as the clothes become drier and drier and more and more of the energy provided by elements 26 is carried off with the air in the form of heat rather than being absorbed by the clothes for the purpose of moisture 40 evaporation. When the temperature of the air contacting the thermostat element 59 has risen to a level indicating dryness of 'the clothes, the element 59 will trip to its open position. This causes the motor circuit to be completed only through the solenoid 87 which is then 45 energized to give an audible signal indicating that the end of the cycle has been reached. Also, the high impedance device §7 in series with the main winding 56 causes virtual de-energization of the main winding 56 so that the motor ceases to rotate; as a result, switches 50 67 and 85 return to the up position in which switch 67 prevents motor energization except through start switch 62 and switch 85 prevents energization of the heaters 26 In this manner a complete automatic cycle is provided, the machine being fully shut off at the end of the cycle. 55

The damp dry cycle of the machine is substantially the same, with the single difference that ’the dial pointer 94 is set to station 96. As a result, biasing heater 71 provides a degree of heating greater than that appropriate for automatic drying. This causes the trip temperature 60 of element 59 to be reached at a somewhat lower temperature of the clothes, the calibration being selected so that the temperature is one at which the clothes are still in the condition generally known as “damp dry.”

For a de-wrinkling operation, which is highly suitable 65 for the drying of synthetic fabrics where the avoidance of wrinkles in the fabrics is important, the third button 91 is pushed with the dial pointer 94 set at position 97. With button 91 depressed, switch 82 is closed but switches 76 and 86 are open as shown in FIGURE 5, so that energization of the heater element 26 is dependent upon the position of element 77 of thermostat 78. It will further be seen that completion of the energizing loop for heating element 71 is also dependent upon element 77 due to the fact that the switch 76 has been opened. As a result, the thermostatic element 59 is subject to the air temperature increase provided by element 26 without any -biasing effect .thereon at all. Because of this, a relatively high temperature of the clothes is reached (in the vicinity of 165° F.) which, as previously explained, is suitable to make wash and wear type clothes somewhat plastic so 'that whatever wrinkles are in them are eliminated. At this temperature, the lack of any bias on element 59 has prevented it -from yet tripping, and the thermostat 78 is so regulated that it will trip from the position shown into engagement with contacts 79 and 80. This tripping action of element 77 causes a de-energization of the heaters 26 and energization of the biasing element 71. Because very little of resistor 73 is in series with the 15 element 71, a high degree of heating effect by element 71 is provided on bimetal 59. Consequently, even without the continued heating of heater 26, the strong biasing effect of element 71 will cause the thermostat 60' to trip after several minutes during which -the temperature with20 in -the dryer is actually gradually lowered rather than increased by virtue of the continued blowing of unheated air through 'the dryer. When the thermostat 60 trips, the machine shuts itself off as previously described.

For the fourth one of the four possible cycles, the fluff operation, button 92 is pushed and the dial is set so that pointer 93 registers with station 98. The pushing of button 92 causes switch 82 to be opened, with switches 76 and 86 being closed, as shown in FIGURE 5. The position of the dial causes a substantial amount of heating to 30 be provided by element 71 with respect to' bimetal 59, with no heating whatsoever being provided by the heaters 26 because of the opening of switch 82. Operation thus will be provided without any heating but with the ordinary air blowing and clothes tumbling being provided. Because of the strong biasing effect of the element 71, after a period of several minutes, generally on the order of i0 to 15, the trip temperature of element 59 will have been reached by the sole action of element 71, and element 59 will trip to shut off the machine as previously described.

It will thus be seen that our improved control system effects the four conventionally desired cycles for a dryer so that all four may be selectively provided in the usual manner without, however, any requirement for inclusion in the control system of a sequence control assembly.

While in accordance with the patent statutes we have described what at present is considered to be the preferred embodiment of our invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is therefore aimed in the appended claims to cover all such equivalent variations as fall within the true spirit and scope of our invention.