US2736970A - Laundry dryers - Google Patents

Description

March 6, 1956 J, A. ENGEL LAUNDRY DRYERS Filed Dec. 1'7, 195] HEAT Imoron r HEAT I MOTOR ON ON OFF OFF I NVEN TUE J. ANTHONY ENGEL.

BY H

ATT URNEY United States PatentO LAUNDRY DRYERS J. Anthony Engel, Syracuse, N. Y., assignor, by mesne assignments, to The Murray Corporation of America, Detroit, Mich., a corporation of Deiaware Application December 17, 1951, Serial No. 262,066

8 Claims. (Cl. 34--45} This invention relates to laundry dryers, and more particularly to a control system and operating cycle therefor.

In dryers of the type described, there is generally employed a tumbling drum for laundry operating in conjunction with air heating elements, and means for circulating or translating heated air through the drum, together with various independent thermostatic controls.

The present invention is directed to a system wherein a single manual control is utilized for commencing a cycle of operations, and in which a single thermostatic control is utilized for effecting over-all subsequent control over the heating element, tumbling drum and air circulation, whereby the various functions are commenced and terminated in an eflicient, shortened cycle dependent on the minimum length of time required to reach various controlling temperatures.

The invention is further directed to a dryer control system particularly adapted to effect drying to a large extent by evaporation induced by radiant heat, and in which air utilized for carrying off evaporated moisture is exhausted at a temperature not greatly exceeding room temperature, so as to minimize wastage of heat and avoid undue heating of the surrounding air in which the dryer is located.

The above and other novel features of the invention will appear more fully hereinafter from the following detailed description when taken in conjunction with the accompanying drawings. It is expressly understood that ,the drawings are employed for purposes of illustration only and are not designed as a definition of the limits of theinvention, reference being had for this purpose to the appended claims.

In the drawings, wherein like parts are indicated by like reference characters:

Figure 1 is a front elevation of a laundry dryer with parts broken away, to which the control system is applied;

Figure 2 is a View of the control switch, partly in section, together with the control circuit; and

Figure 3 is a temperature time chart efiected by the control switch. I

Referring to the drawings, there is shown in Figure 1 a cabinet structure having mounted therein a substantially cylindrical casing 12 within which is a perforate revolving laundry-containing drum 14. The drum 14 may be of the type commonly in use having an access door in the front wall thereof in alignment with a front wall cabinet access door, such parts not being shown since they form no part of the invention.

The drum is adapted to be rotated at a tumbling speed by a motor 16 through a belt drive 18. The casing 12 in an upper portion thereof is provided with an electrical heating element 20 of the infra-red radiant type, and adjacent such element are a number of inlet louvres 22 to permit entrance of air from within the cabinet 10 into the casing 12. Air is withdrawn from the casing 12 through a duct 24 having a centrifugal blower 26, belt driven as at 28 by the motor 16. Air exhausted from the casing 12 is delivered to the surrounding atmosphere through an exhaust port 30.

Control over the operation of the machine is made dependent upon the temperature within the casing 12, through the employment of a thermostatic device of the type, for example, comprising a sealed bulb connected to a switch actuating expansion bellows. For this purpose, the sealed bulb 32 is located within the casing 12, such bulb being connected by a conduit 34 to a thermostatic control switch assembly 36 located conveniently on an inclined rear cabinet panel 37. The control switch (see Figure 2) comprises a casing 38 having a front panel 49 through which projects a push knob control 42, the knob being mounted upon a pin 44 slidable in a boss 46 on the inside surface of the panel 40. Such pin is provided with a flange 48 adapted to engage a spring contact leaf 50, the contact leaf being adapted by movement of the knob 42 inwardly to engage the contact leaf 52 to close an electrical circuit through contacts 51 and 53 for the purpose of energizing the heating unit 20.

A spring-pressed ball detent 54 mounted in the boss 46 is adapted to engage an annular groove 56 in the pin 44, so as to hold the knob 42 in its inward position against the urge of the leaf spring 50. The structure thus described is adapted to close a circuit through a relay coil 58 which in turn closes contacts 60 adapted to energize the heater coil 25) by completing a connection to a standard source of supply of 220 v. The thermostatic bulb 32 and the conduit 34 lead to a closed expansion chamber 62 mounted inside the rear wall 64 of the casing 38, such chamber being of generally hat-shaped section. The rim flange 66 is adapted to bear against a casing partition member 68. Within the chamber 62 is a sealed bellows 70 having an external flange 72 held against a shoulder 74 on the internal wall of the chamber 62, an annular sealing disk 76 acting to rigidly hold the bellows in place with its flange 72 in sealed engagement with the shoulder 74. 7 7 Slidably mounted through an aperture 78 in the partition wall 68 is a sleeve member 8%) having a rear shoulder 82 adapted to be engaged by the end wall 34 of the bellows 7 (i, such sleeve being adapted to be resiliently held against the bellows by a coil compression spring 86 bearing against the shoulder 82 and the partition 68. Threaded within the sleeve for adjustment purpose is a pin 88 having an insulating tip 90 adapted to bear against a resilient contact leaf 92. Such contact leaf carries a contact 93 adapted to engage with a contact 94 mounted upon a bimetallic heat sensitive contact arm 96. The leaves 50, 52 and 92 are mounted upon an insulating multiple bracket member 9.8 and the bimetallic member is supported upon an insulating bracket member 100. The bracket member is provided with stops 192 and M4 to limit the permissible bending of the bimetallic arm and supports a low current resistance heating element 106 positioned immediately adjacent the bimetallic arm. The bimetallic arm, when heated by the resistance unit 106, is adapted to be bent upwardly so as to engage the stop 164.

The contacts 93 and 94 on the contact leaf 2 and bimetallic arm 96 are connected to a solenoid Tilt; which in turn actuates switch contacts in circuit with the motor 16, such motor for convenience being connected between one side of the 220 v. line and the neutral connection. The resistance heater 106 is connected in parallel with the motor 16, so that whenever the motor is energized, the

heating unit will heat the bimetallic arm 96, causing the same to move the bimetallic arm 94 rearwardly into engagement with the stop 104. v

' it will be seen that the thermostatic bulb 32 is so arranged within the casing 12 as to be responsive to an increase in temperature within the casing. When the manual button 42 is moved inwardly to close the circuit between the contact leaves 50 and 52, the infra-red heater is energized and upon the temperature within the easing 12 reaching a predetermined temperature such as 170 F., the expansion of the fluid within the bulb 32 is sufficient to cause the bellows 70 to move the pin 83 enough 'so as to in turn bend contact leaf 92 to close a circuit between contacts 93 and 94. Thus, the motor 16 within the casing which would tend to cause the motor starting contact 93 to separate from the contact 94, cuting off the motor. In order to prevent such an occurrence, the heater resistance 106 creates sufficient heat to cause the bimetallic arm 96 to move against the stop 104. By such means, the motor starting contacts 93 and 94 are biased and will remain closed, even though the bellows-actuated pin recedes slightly in response to a drop of temperature within the casing 12. In practice, a drop in temperature of 35-50 may be expected, and the bimetallic strip and its stops are so correlated with to the thermostatically actuated bellows as to permit the motor to run until the temperature drops below 120 F.

V The tumbling of the clothes is effected by rotation of the drum 14- which is heated in its passage past the infrared heating coils 20. By such an arrangement, the infra red heating coil 20 effects evaporative drying action of the tumbling laundry by radiation primarily, and by contact of the heated drum with the clothes. The blower 26 circulates or translates air through the drum at a low rate whereby to exhaust air from the drum as it accumulates moisture evaporated from the laundry. The laundry within the drum is preferably retained at a low temperature, for example, in the range of 135, to efiect an etficie'nt drying operation, it being appreciated that the higher the temperature of the air exhausted from the blower 30, the lower is the efficiency of the apparatus.

It will be highly desirable to have the air exhausted as little above room temperature as possible, so as to minimize the heat lost merely through excess heating of the air circulated through the dryer. Thus the heat added to air entering through the louvres 22 by the heater 20 is preferably equivalent to that consumed by evaporation within the tumbling drum. By utilizing a low rate of air flow, the entering air may be heated to a higher temperahire, more effective for evaporative purposes, and yet discharge at a low temperature.

So long as evaporation of moisture from laundry contained within the drum continues, such evaporation acts to reduce the temperature of the air as it circulates therethrough. However, as the laundry approaches a dry state, the rate of evaporation reduces, and the cooling effect of such evaporation is substantially reduced, so that the temperature within the casing tends to increase. When the laundry becomes substantially dry, evaporation substantially discontinues, and when this occurs, the temperature Within the casing 12 rises at a relatively rapid rate, the rapid rate being in part due to the low rate of air circulation. This factor is utilized to open the circuit to the heating element 20 to discontinue the drying operation. In order to effect thisresult, the pin 88 actuated by the thermostatic bellows 70 is adaptedto resiliently bow the contact leaf 92 into engagement with the manually operated push pin 44 moving the same sufficiently outward to release the detent 54 so that the spring contact leaf will return the manual control 42 to the off position as shown.

At this point, the infra-red heating coil 20 is deenergized. The motor 16, however, continues to run, tumbling the laundry within the drum and drawing air through the casing, discharging the same through the outlet 30. The temperature gradually decreases within the casing 12, and when the temperature drops to the thermostatic bellows has retracted sufficiently to cause the leaf contact 93 and 94 to separate, opening the circuit to the motor 16 and the resistor 106.

In Figure 3, the temperature at the thermostatic bulb 32 is indicated by curves illustrating a typical cycle. At the point 112, the temperature has risen to approximately 170", at which time the motor 16 is energized. After this, there is a drop in temperature for the reasons previously set forth; the motor continuing to run, and the curve continues relatively flat at a temperature of or thereabouts for a period until substantially all the moisture is evaporated from the laundry contained within the drum. Such point is roughly indicated as at 114. The temperature thereafter rises to the value indicated at 116 when the infra-red heating coil 20 is de-energized, and thereafter, the motor continues to rotate the drum and draw air therethrough until the temperature drops to a value indicated approximately at 118, or 120 F., when the motor circuit is broken. The temperature at 118 is less than the temperature at the point 112 where the motor commences to operate by reason of the bias placed upon the contact 94 by the bimetallic arm 96.

It will be appreciated that any particular temperature limits for effecting the operations described may be selected, it being the primary object of the invention to quickly build the infra-red radiation within the drum prior to commencing rotation and ventilation. Since the a heating coil 20 is located near the top of the drum, laundry in the bottom of the drum, when not rotating, is in a safe place, and will be protected from undue heating effect during this period, even though the temperature created within the drum is allowed to build up to a value in excess of the operating temperature during drum rotation. Since it is desirable to dry to a large extent by efiicient radiation and physical contact, rather than by excess heating of large amounts of air, it is desirable to have the radiation effective before any forced circulation of air through the drum takes place. However, thereafter, the circulation of air through the drum is suflieient to assist the evaporation of moisture by radiation by carrying off moisture at approximately the rate of evaporation. It is not, however, desired to heat the air entering the drum to any substantial degree, other than for the purpose of aidingevaporation and compensating for the cooling efiect of evaporation within the drum, and it is not desired to flow substantial quantities of air through the drum. Consequently, evaporation is balanced against the quantity of heat imparted to the air entering the drum so as'to maintain a relatively low temperature of the air being discharged. The air entering at a low volumetric rate is heated to provide the necessary heat value to be expended in evaporation.

Upon the near completion of the drying of the laundry, the temperature rises substantially above the low temperature value referred to. This temperature rise serves as an indication that the drying operation is completed or substantially completed, and is utilized to discontinue the operation of the infra-red heating coil, following which the drum rotation and air circulation is continued until the laundry is reduced to a temperature safe to handle without discomfort. It will be understood that the air flowing through the discharge outlet will bemore near room temperature than the air at the bulb 32, and that the position of the bulb may bevaried somewhat to provide an optimum control situation dependent on air temperature within the drum, as distinguished from the temperature of freshly heated air in the immediate region of the heater element 20.

From the foregoing, it will be seen that provision is made for quickly bringing the apparatus to a temperature for effective drying before air circulation commences, and that the drying time thereafter is automatically controlled by the temperatures existing within the casing, resulting from the balance of evaporation and heat introduced by the moderate flow of air therethrough. With varying loads, the length of drying time is automatically varied in proportion. Although solenoids 58 and 108 have been shown for closing the various power circuits, it will of course be understood that the contacts 51 and 53 and 93 and 94 may be interposed in place of the solenoid contacts 60 and 110, if it be desired to directly control the power circuits, and thereby eliminate such solenoids. Any safety thermostatic switch such as 120 may be inserted in the heater coil circuit. Such switch would only operate should the temperature within the casing rise to a danger point due to failure of the mechanism to function properly.

Although a single embodiment of the invention has been illustrated and described, it is to be understood that the invention is not limited thereo. As various changes in the construction and arrangement may be made without departing from the spirit of the invention, as will be apparent to those skilled in the art, reference will be had to the appended claims for a definition of the limits of the invention.

What is claimed is:

1. In a laundry dryer, a housing, a rotatable tumbling drum contained therein, means for rotating said drum, means for heating air within said housing, means for translating air heated by said heating means through said drum and exhausting such air outside said housing, means for activating said heating means, and means including a single thermostat for activating said translating means only upon establishment of and during the maintenance of a predetermined drying temperature in said cabinet by said heating means, and deactivating said heating means upon establishment of a predetermined temperature elevated above said drying temperature.

2. In a laundry dryer, a housing, a rotatable tumbling drum contained therein, means for rotating said drum, electrical means for heating air within said housing, means for translating air heated by said electrical means through said drum and exhausting such air outside said housing, a switch for closing a circuit to said heating means, and means including a single thermostat for activating said translating means only upon establishment of and during the maintenance of a predetermined drying temperature in said cabinet by said heating means, and deactvating said heating means upon establishment of a predetermined temperature elevated above said drying temperature.

3. In a laundry dryer, a cabinet, a perforate rotatable drum contained therein, including motor means for rotating said drum, electrical heating means within said cabinet, means for translating air through said heating means and drum and in contact with fabrics contained therein, and exhausting said air outside said cabinet, a switch for closing a circuit to said motor means, a switch for closing a circuit to said heating means, said last-named switch having means for yieldingly holding said switch closed upon actuation thereof, thermostatic means responsive to a temperature in said cabinet for closing said firstnamed switch upon establishment of an effective drying temperature in said cabinet, means for retaining said firstnamed switch closed through a limited range of temperature below the switch closing temperature and above room temperature, and means establishing a connection from said thermostatic means with said heating means switch for opening said heating means switch upon establishment of a temperature elevated above said drying temperature.

4. In a laundry dryer, a casing, a tumbling drum therein, a motor for driving said drum, an air heater, and means driven from said motor for translating heated air through said drum and discharging such air into the surrounding atmosphere, a switch manually movable for energizing said heater, a switch for energizing said motor, thermostatic means acting in response to a predetermined temperature within said casing for closing said motor switch whenever and only when the temperature within the casing reaches a predetermined drying temperature, said last-named means acting to actuate said manually movable switch to de-energize said heater upon a predetermined further increase in the temperature within said casing, and means responsive to the closing of said motor switch for establishing a temperature range below said predetermined temperature, and above room temperature during which said motor switch will remain closed.

5. In a laundry dryer, a housing, a rotatable tumbling drum contained therein, motor means for rotating said drum, electrical means for heating air within said housing, means actuated by said motor means for translating air heated by said electrical means through said drum and exhausting such air outside said housing, a switch for closing a circuit to said motor means, a switch for closing a circuit to said heating means, said last-named switch having means for yieldingly holding said switch closed upon actuation thereof, thermostatic means for closing said first-named switch upon establishment of a predetermined drying temperature in said cabinet, for opening said heating means switch upon establishment of a temperature elevated above said drying temperature, said air translating means being operative after the closing of said first-named switch for establishing a lower temperature for opening said first-named switch.

6. In a laundry dryer, a shell, a perforate tumbling drum within the shell, an electric motor for driving said drum, an air inlet for said shell, an electric heater for the air inlet, an air outlet for said shell, means driven by said motor for moving air through said inlet, through said shell, and out said outlet, a temperature-sensitive device within said shell, an expansible chamber device associated with said temperature-sensitive device, a switch for energizing said electric heater, manually settable means for closing said switch and forming the sole means for closing said switch, means actuated by the expansible chamber device for resetting said settable device to open said switch upon the existence of a predetermined maximum temperature within said shell, a switch for said motor, and means actuated by said expansible chamber device to close said switch and retain the switch closed whenever the temperature-sensitive device exceeds a predetermined minimum temperature, less than the predetermined maximum, and to open said switch when the temperaturesensitive device is below said minimum.

7. In a laundry dryer, a shell, a perforate tumbling drum within the shell, an electric motor for driving said drum, an air inlet for said shell, an electric heater for the air inlet, an air outlet for said shell, means driven by said motor for moving air through said inlet, through said shell, and out said outlet, a temperature-sensitive device within said shell, an expansible chamber device associated with said temperature-sensitive device, a switch for energizing said electric heater, manually settable means for closing said switch and forming the sole means for closing said switch, means actuated by the expansible chamber device for resetting said settable device to open said switch upon the existence of a predetermined maximum temperature within said shell, a switch for said motor, means actuated by said expansible chamber device to close said switch and retain the switch closed whenever the temperature-sensitive device exceeds a predetermined minimum temperature, less than the predetermined maximum, and to open said switch when the temperature-sensitive device is below said minimum, and means to lower the predetermined minimum temperature by a fixed increment above which said motor switch remains closed subsequent to closure thereof.

8. A laundry dryer comprising a tumbling drum, means for translating air through said drum, and means for driving said tumbling drum and said translating means, means for heating the air drier to translation through said drum, a control device sensitive to the temperature of the air passing through said drum comprising a thermostatic bela 7 lows, including a plunger actuated thereby through a range of movement in proportion to the temperature'of said air, a motor switch actuated by said plunger and closed thereby during all movement of the plunger beyond an initial portion of the range of movement thereof, a manual plunger aligned with said thermostatic plunger and having an end adapted to abut against the end of said thermostatic plunger, means for establishing a range of movement from said plunger from an off position to an on position and a switch associated therewith and actuated thereby for energizing said heating means, and adapted to be open or closed in accordance with the corresponding position of said plunger, the on position of said plunger placing the end thereof within the range of movement of the end of said thermostatic plunger, means for biasing said plunger to the oil position, detent means for holding said plunger in the on position with its end in the range of movement of the end of said thermostatic plunger, whereby said thermostatic plunger upon reaching a predetermined maximum temperature will move said manual plunger from the on position, and release said detent for movement of the manual plunger to the otf position.

References Cited in the file of this patent UNITED STATES PATENTS 2,296,063 Shaw Sept. 15, 1942 2,398,880 Broglie Apr. 23, 1946 2,467,525 Cobb Apr. 19, 1949 2,524,438 Graves Oct. 3, 1950 2,564,867 Weber et a1 Aug. 21, 1951 2,564,868 Weber et a1 Aug. 21, 1951 2,583,850 Kautfman Jan. 29, 1952

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