US3037296A - Clothes dryer control apparatus - Google Patents

Description

June 5, 1962 K. D. COOLEY ETAL CLOTHES DRYER CONTROL APPARATUS 2 Sheets- Sheet 1 Filed NOV. 4, 1957 BMEEI ME Mme/Sm wm amt/mo immv E M 0 DE N T R N NA 0 mc n T W QZM HD TLL EOE RT MAS K Y B June 5, 1962 COOLEY ETAL 3,037,296

CLOTHES DRYER CONTROL APPARATUS KENNETH D. COOLEY HAROLD F. SNIDER BY ESTEL c. KANEY United States Patent 3,037,296 CLOTHES DRYER CONTROL APPARATUS Kenneth D. Cooley, Harold F. Snider, and Estel C. Raney, Fort Lauderdale, Fla., assignors to Ranco Incorporated, Columbus, Ohio, a corporation of Ohio Filed Nov. 4, 1957, Ser. No. 694,374 9 Claims. (CI. 34-45) The present invention relates to control apparatus for clothes dryers, particularly of the domestic type comprising a rotatable clothes drum, an air heater, a blower for forcing the heated air through the drum, and a motor for driving the blower and drum.

It is well known that during the clothes drying cycles of the type of dryer mentioned, with a relatively heavy or wet load of clothes, the temperature of the discharged drying air initially rises rapidly until a certain degree is reached after which the rate of rise levels off or falls to an insignificant rate, due to evaporation of moisture from the clothes, and when the clothes become nearly dried the temperature commences to rise again relatively rapidly. Accordingly, one object of the present invention is to provide an improved automatic control for a clothes dryer in which drying cycles may be terminated by means responsive to a relatively rapid rise in temperature of the discharged drying air.

As mentioned, during the initial warm-up of the drying air, the temperature rise is relatively rapid, and to prevent premature termination of the drying cycle by the means responsive to the relatively high rate of temperature rise, it is a further object of the invention to provide means to maintain the drying cycle irrespective of the operation of the means responsive to the rate of temperature rise for a period to permit the drying air to attain the temperature at which it would normally attain a low rate of rise due to evaporation of moisture from the clothes.

The length of time that the discharged air temperature remains substantially constant or rises at a relatively slow rate varies according to the amount of moisture in the clothes which may depend upon the fabric and amount of the clothes in the load. Thus, when there is an appreciable amount of water present, the rate of temperature rise of the discharged air will change from a relatively low to a relatively high rate causing the improved control to terminate the drying cycle. When the moisture content is low,

however, the rate of temperature increase may be relatively high throughout the drying cycle which would nullify the effectiveness of the rate rise responsive means. Therefore, a still further object of the invention is to provide control means to initiate, maintain and terminate a minimum drying cycle, which means becomes subjected to the control of the temperature rate responsive means during the drying cycle so that in the event substantial moisture evaporation is taking place, the operation of the cycle control means will be interrupted to permit continuation of the drying cycle until the rate of temperature increase of the discharge air becomes relatively high, indicating a dry condition of the clothes; otherwise, the cycle control means continues its minimum drying cycle control.

A still further object of the invention is the provision of a rate of temperature rise responsive means comprising two thermally responsive elements arranged to be sub jected to air exhausted from the clothes drum, one element being modified to cause it to lag in its movement relative to the other in response to relatively rapid changes in temperature and both elements actuating a control device, such as a switch, to one position when both elements are subjected to relatively even or slow changing temperatures and to move the control device to a second control position when the exhaust air temperature rises relatively rapidly so as to cause the lagging element to move less resilient contact arm 28.

3,037,296 Patented June 5, 1 962 than the other element. The rapid rise in temperature indicates a decreased moisture absorbing condition, while a relatively slow temperature rise, below a maximum, indicates a relatively heavy moisture absorption of the drying air.

Still a further object of the invention is to cycle the operation of the air heater between maximum and minimum limits so that should the temperature of the exhaust air gradually increase, as may be the case with some types of cloth, the maximum temperature will be limited to a safe degree and the temperature increasing phases of these cycles provide temperature increasing phases on which the rate of temperature increase sensing responsive may be readily eilected.

=Further objects and advantages of the invention will be apparent from the following description of a preferred embodiment, reference being had to the accompanying drawings wherein:

FIG. 1 is a schematic showing of a control apparatus embodying the invention in a clothes dryer; and

FIGS. 2, 3 and 4 are charts indicating changes in temperatures of the shielded and unshielded thermostatic power elements during drying cycles of a light load of clothes, a normal load of clothes and a relatively heavy load of clothes, respectively.

Referring to FIG; 1 of the drawings, the invention is shown in a control apparatus for a conventional electrical heater type clothes dryer, and for sake of clarity only the portions thereof essential to the understanding of the invention are illustrated. It will be understood by those familiar with the art thatthe control apparatus could also control a solenoid valve of a gas burner type clothes dryer instead of the electric heater type disclosed. The control apparatus comprises a timer device 10 including a synchronous motor arrangedto drive a shaft 11 through suitable gearing, not shown, at the rate of about one revolution each twelve minutes, and the shaft has switch actuating cams 13-, 14, attached thereon. Shaft 11 is preferably driven through a slip clutch (not shown) to permit manual rotation thereof by a knob 16 attached to the outer end thereof to initiate operation of the dryer and to supersede automatic control, if desired.

Cam 13 opertates electric switches 18 and 19, switch 18 comprising a spring arm 20 having a finger 21 which rides the cam periphery, and a contact 22 which engages a double contact 23 when arm 20 is flexed upwardly by the cam. Contact 23 is attached to the free end of a flexible contact arm 24 which may be flexed upwardly by arm 29 to engage contact 23 with a contact 27 carried on a As is explained hereinafter switch 18 controls the circuit of the clothes drum and blower motor and switch 19 controls the air heater circuit and carn 13 may close both switches at once or only switch 18. 9

Cam 13 has a dwell 30 which causes contact arm 20 to drop the position shown in FIG. 1 to open switches 18, 19 to de-energize the dryer. Adjacent the dwell 30 is a rise 31 which, when the cam 13 is rotated clockwise as viewed in the drawing, causes contact arm 20 to be tlexed upwardly and engage contacts 22, 23, 27 to close both the motor and heater circuits. Preferably, a notch 32 is formed in the periphery of cam 13 to providea detent to indicate to the operator that the cam has been set in the starting position. Cam 13 has a drop 33 arranged to cause contact arm 20 to drop and separate contact 23 from contact 27 to open the heater circuit switch 19 while maintainin contact 22 in engagement with contact 23. A second drop 34 on cam 13 is arranged to cause contact arm 20 to drop into dwell 30 and separate contacts 22, 23 to open the motor switch'18.

Step 33 is positioned from notch 32 such that switch 19 will be opened approximately nine minutes after timer is energized, and step 34 is positioned relative to step 33 so that the motor switch 18 will be opened approximately three minutes after opening of the heater switch 19.

Cam 14 operates a switch 36 comprising a spring contact arm 37 carrying a contact 38 which is arranged to engage a fixed contact 39 supported on a terminal 40. Contact arm 37 has a finger 41 which rides on cam 14, and the cam is shaped to maintain contacts 38, 39, in engagement except momentarily when finger 41 drops into a notch 42 which is positioned to register with finger 41 approximately eight minutes after initiation of operation of timer 10.

The construction of the timer device 10 including the switches operated by the cams is like that well known in the art and the details thereof are therefore not more fully shown.

In the form of the invention shown, the means responsive to the rate of moisture removal comprises two similar thermally responsive power elements 43, 44. Element 43 comprises a rigid cylindrical body 45 having a plunger 46 which moves axially in and out of the end thereof in accordance with changes in volume of a liquid contained in a tube 47 and bulb 48 connected with the interior of the body. The construction of thermal element 43 is like that shown in the patent application of Frederick A. Greenawalt, Serial Number 345,065, filed March 27, 1953, although it is to be understood that any other suitable thermally responsive element may be utilized in the practice of the invention.

The thermally responsive element 44 is like the element 43 except the bulb 49 thereof has a coating of insulating material 50 thereon to reduce the rate of heat exchange between the liquid within the bulb and the air surrounding the bulb. Bulbs 48, 49 are both placed in the exhaust air duct 51 of the dryer, only a portion of which appears in the drawings, so that the two bulbs are subjected to the temperature of the air as it is discharged from the clothes drying drum of the dryer.

An L-shaped lever 53 is pivoted at 54 to the plunger 46 of thermally responsive element 43 and the left hand end thereof is engaged by the plunger 55 of element 44. Lever 53 is urged downwardly by a tension spring 56 connected thereto as shown.

Vertical movement of plunger 46 of thermal element 43 is arranged to open and close a toggle switch comprising a contact arm 57 pivoted at its right hand end and which has a contact 58 arranged to engage a fixed contact 59 during the time the temperature of the bulb 48 is below a certain maximum which may be 180 F, for example. Contact arm 58 is connected to lever 53 through a toggle spring 60 which is insulated from lever 53 and which snaps contact arm 57 upwardly to a stop 61 when the temperature of bulb 48 reaches approximately 180 F. and snaps the arm back to contact 59 when the temperature of bulb 48 falls to 140 F. Any suitable switch could be used which will open and close by movement of plunger 46 corresponding to exhaust air temperatures of approximately 180 F. and 140 F., respectively, and the construction shown is more or less schematic.

The depending leg 53' of lever 53 is arranged to move a contact member 62 to the right and engage a contact 63 carried thereby with a fixed contact 64 and this will occur when the movement of plunger 46 exceeds movement of plunger 55 by a predetermined amount as is more fully explained hereinafter.

The electrical heating element of the dryer is shown at 66 and it is arranged to heat air which is then directed through the clothes drum (not shown) in a conventional manner, and the circuit for element 66 includes power line L1 of a conventional 230 v. three-wire system, switch 19, wire 67, contacts 59, 58, contact arm 57, wire 68 to one side of heater 66 and the opposite side of the heater is connected to L2 of the power circuit. In conventional constructions it is desirable to place a switch in the L2 side of the circuit for heater 66 so that both sides of the heater may be broken when the dryer is de-energized, but for the sake of clarity this switch has been omitted.

The fan and clothes drum of the dryer are driven by an electric motor 70 and the circuit for this motor includes line L1, switch 18, wires 71, 72 to one side of the motor, and wire 73 to N of the power circuit.

The circuit for the synchronous motor of the timer device 10 comprises N of the power lines, which is attached to one terminal thereof, and the other terminal is connected by wire 75 to switch 36, wires 74, 71, switch 18 to L1. An alternate circuit to L1 around switch 36 may be established for the timer motor through wire 75 to contacts 64, 63, contact arm 62, wires 72, 71 and switch 18.

The operation of the control apparatus is as follows:

Assuming that a relatively light load of clothing is placed in the drum of the dryer, such as one-quarter of a pound, the operator turns the knob 16 clockwise, as viewed in the drawings, to the on position which rotates cams 13, 14 to close switches 18, 19, 36 which energize the blower motor 70, heater element 66 and the motor of the timer device 10, through the circuits described previously. It has been found that with a light load of clothing, or clothing having a relatively low water content, the discharge air temperature will maintain a more or less steady and relatively rapid rise until a dry condition is reached, which temperature rise is illustrated by the full line in the graph shown in-FIG. 2, and the clothes will become dried within a relatively short period, such as from 6 to 8 minutes as a minimum, depending on the the degree of heat applied to the air. The insulation 50 on bulb 49 prevents the thermal element 44 from responding at the same rate as does thermal element 43 and therefore plunger 55 lags in movement relative to the movement of plunger 46 and under these conditions contacts 63 and 64 will be closed by lever 53 shortly after commencement of operation of the dryer and will be maintained closed until after switch 36 has been opened and reclosed by cam 13. The broken line in the graph of FIG. 2 illustrates the temperature rise of the liquid in bulb 49 as compared to the exhaust air temperature. It will be noted that in the event the load is so light that the exhaust air temperature reaches 180 F., power element 43 will open contacts 59, 60 to de-energize the heater and will reclose the contacts when the air temperature falls to F. The lag in response of element 44 causes contacts 63, 64 to be closed on each heating cycle. At the end of approximately 8 minutes the notch 42 of cam 13 moves into registration with finger 41 and arm 37 drops to open switch 36. The opening of switch 36 would break the timer circuit except for the fact that the alternate circuit for the timer is now closed through contacts 63, 64, at least during the rise in discharge air temperature, and the timer therefore continues to operate and recloses switch 36 to re-establish the timer circuit through the latter. After another minute of operation, the timer opens the heater circuit at switch 19 and after three more minutes of operation cam 13 opens switch 18 to de-energize the blower motor and the timer motor. It will be seen that since the rate of moisture removal was not sutficient to cause a leveling of the rate of rise of discharge air temperature, the dryer was operated for a minimum drying time as determined by the timer device.

Should a heavier and more moisture laden load of clothes be placed in the dryer and the drying cycle started as described relative to the lighter load, the temperature at bulb 48 will rise as indicated by the full line in FIG. 3 until a leveling oif occurs which indicates that the heated air is absorbing considerable moisture from the clothes, and the temperature of the liquid in insulated bulb 49, which is represented by the broken line, will shortly thereafter rise to the same temperature as that of the liquid in bulb 48. This is indicated at point a on the graph and at this time contact 63 will be separted from contact 64 as shown in FIG. 1. Assuming that the amount of moisture present in the clothes is sufficient to bring about the temperature plateau eflect, which opens contacts 63, 64 as described, within eight minutes after initiation of the dryer cycle, finger 41 drops into notch 42 of cam 14 and causes switch 36 to open and break the timer circuit, which tie-energizes the timer to interrupt its timer cycle. Switches 18, 19 will then be maintained closed to continue the drying cycle until such time as the moisture content of the clothes materially decreases'which results in the discharge air temperature rising relatively rapidly, as indicated at the point b in FIG. 3, and bulb 48 will correspondingly increase in temperature and cause plunger 46 to move upwardly more rapidly than plunger 55 to thereby tilt lever 53 counterclockwise and close contacts 63, 64 to re-energize the timer circuit. The reoperation of the timer closes switch 66 to maintain the timer circuit independently of the position of contacts 63, 64 and opens switches '19, and 18 in the sequence described to terminate the heating cycle and then the blower motor operation, as described previously. It will be noted that during the first eight minutes of operation under the load conditions mentioned, contacts 63, 64 may or may not be closed depending upon the heater capacity or the temperature of the dryer mechanism at the start of the drying cycle, etc., but this action has no effect on the timer which is maintained energized through switch 36 for the first eight minutes.

It has been found that with exceedingly heavy wet load the temperature of the exhaust air is apt to gradually increase until it reaches a relatively high degree, such as 180 F. This condition is illustrated by the heavy line in FIG. 4. When the temperature of the exhaust air reaches 180 F. the plunger 46 of the thermally responsive element 43 is extended to the point where it elevates the lever 53 to a position in which spring 60 snaps contact arm 57 upwardly to separate contacts 58, 59 to there by break the circuit of heater 66. As explained previ ously, the contact arm 57 is held upwardly until the plunger 46 has receded or descended to a position corresponding to 140 F. in the discharged air temperature at which time contacts 58 close on 59 and re-establish the heater circuit. This is illustrated at point d on the drawing and upon re-energization of the heater element the temperature of the air commences to increase once more and if a substantial or an appreciable amount of moisture is still being removed from the load the rate of rise of temperature of bulb 48 is approximately the same as that of the shielded bulb 49 so that contacts 63, 64 will not be closed and the timer will remain de-energized. This cycling of the heater element may continue until such time as the heating cycle rises at a rate which is so much faster than the rate of rise of the insulated or shielded bulb 49 that the lever 53 is tilted to close contacts 63, 64 which again re-energizes the timer motor causing cam 14 to reclose switch 36 and maintain the circuit of the timer motor in the alternate circuit around contacts 63, 64. The drying cycle is then terminated in the manner described previously, that is to say, cam 13 first opens switch 19 to de-energize the heater and after approximately three minutes switch 18 is opened to de-energize the blower motor and timer motor.

It will be seen that by limiting the temperature of the discharge air as described, repeated samplings of the rate of temperature increase can be taken according to the relative rates of temperature changes in the bulbs 48, 49.

An important advantage of the improved control system is that the operator of the clothes dryer need not be concerned with adjustments of the control apparatus to compensate for the weight of the clothes, the degree of moisture therein or ambient temperature or humidity to secure the proper degree of drying, and once set, the control apparatus maintains automatically the most eflicient and economical control of the drying cycle.

While but one form of the invention has been disclosed it is to be understood that other forms, modifications and adaptations could be made all falling within the scope of the claims which are attached hereto. It is to be understood that the dryer apparatus referred to in the claims is not necessarily limited to clothes dryers but includes drying apparatus for other materials.

We claim:

1. A control system for drying apparatus utilizing heated air as a drying medium and comprising: control means operative to initiate, maintain and terminate a drying cycle; means including a control device movable between first and second control positions in response, respectively, to relatively rapid and relatively slow rates of temperature increases of air discharged from the clothes to be dried; and means operative during said drying cycle to establish cooperative relation between said control means and said control device so that in the event said control device is in said first control position the operation of said control means is continued and operative when said control device is in said second control position to interrupt operation of said control means to prolong said drying cycle until said control device shifts to said first control position to effect continuation of operation of said control means to complete the drying cycle.

2. A control system for drying apparatus utilizing heated air as a drying medium and comprising: control means operative to initiate, maintain and terminate a drying cycle; two thermally responsive elements responsive to the temperature of the discharged drying air and having different rates of response, a control device movable between first and second control positions by relative responses of said thermal elements in response, respectively, to a relatively rapid and a relatively slow rate of temperature increase of air discharged from the clothes to be dried; and means operative during said drying cycle to subject the operation of said control means to said control device so that should said control device he in said first control position the operation of said control means is continued and in the event said control device is in said second control position, the operation of said control means is interrupted to prolong said drying cycle until after said control device shifts to said first control position to efiect continuation of operation of said control means to complete the drying cycle.

3. A control sysem for a clothes dryer having an air heater, a clothes container and means for passing air over the heater and through the container, said control system comprising an electric powered timer device for controlling the heater, said device being manually settable to render said heater effective and operative to subsequently render said heater ineffective after a predetermined timing movement, a circuit for said timer device including parallel branches, one branch including a first control switch and the other branch a second control switch, two thermally responsive elements responsive at difierent rates to increases in temperature of air discharged from over the clothes and operating to close said first switch by differential in response to a relatively rapid rate of temperature rise of the discharged air and to open said switch in response to a relatively low rate of increase in the discharged air temperature, and means to momentarily open said second switch after a predetermined period of operation of said timer device whereby the circuit to said timer is broken after a predetermined period of operation of said timer when the rate of temperature rise is relatively low and the timer circuit is closed to continue operation of the timer when the rate of temperature rise of the discharged air is relatively high.

4. A control system as defined in claim 1 and having means, subject to the operation of said control means, to reduce the temperature of said air in response to a predetermined maximum temperature of the discharge air and to then increase the temperature of said air in response to the reduction in discharge air temperature to a lower temperature, whereby the temperature of the discharged air is alternately lowered and raised from and toward a relatively high temperature limit after attaining a predetermined high temperature.

5. In a drying apparatus having electrically energized means to pass heated air into contact with material to be dried to provide a drying cycle and including an air heater and a blower, control mechanism for initiating and automatically terminating operation of said heater and blower and comprising: a circuit including a first switch to control said heater; electrically operated timer means to open said switch after a predetermined period of operation thereof; circuit means to energize said electric timer means, including a main circuit and two parallel circuits connected in series with said main circuit, said main and two parallel circuits including second, third and fourth switches, respectively; manually settable means to close said second switch; sensing means responsive to the temperature of the drying air discharged from the material to be dried and operable in response to an increase in rate of temperature rise above a given rate of temperature rise to move said fourth switch from an open to a closed position; and means to maintain said third switch normally closed and to open and reclose the last mentioned switch during said predetermined period of operation of said timer means.

6. Control mechanism in a drying apparatus as defined in claim including means to cause the temperature of the air discharged from the material to be dried to fluctuate between a predetermined high limit and a materially lower temperature.

7. In a drying apparatus having means to pass heated air into contact with material to be dried to provide a drying cycle, control mechanism for initiating and automatically terminating the supply of heated air by said means and comprising: settable means to operate the first mentioned means for initiating a drying cycle; timer means to terminate said supply of air after a predetermined period of operation thereof; means to initiate operation of said timer means; and alternative means to control operation of said timer means, one of said alternative means being responsive to the temperature of the drying air discharged from the material to be dried and operable in response to an increase in rate of temperature rise above a given rate of temperature rise to render said timer operative, and said other alternative means being operable to maintain operation of said timer means during an initial portion of said predetermined period of operation of said timer means.

8. In a drying apparatus and control mechanism there for as set forth in claim 7 characterized by said other alternative means being operable after said initial portion of said predetermined period to condition said timer means to discontinue operation and subject to the control of said one alternative means.

9. In a drying apparatus having means comprising a blower and a heater to pass heated air into contact with material to be dried to provide a drying cycle, control mechanism for initiating and automatically terminating operation of said heater and comprising: means to initiate operation of the first mentioned means to establish a drying cycle; means to terminate operation of said heater of air including sensing means responsive to the temperature of the drying air discharged from the material to be dried and operable in response to an increase in rate of temperature rise above a given rate of temperature rise to effect termination of operation of said heater; and means to maintain operation of said heater and blower during a substantial period following initiation of the drying cycle by said second mentioned means, irrespective of the operation of said sensing means whereby the response of said sensing means to the rapid rise in dis charge air temperature normally occurring during the period immediately following initiation of a drying cycle is ineffective to terminate the drying cycle.

References Cited in the file of this patent UNITED STATES PATENTS 1,567,710 Carroll Dec. 29, 1925 1,846,752 Picard et a1 Feb. 23, 1932 2,654,961 Manecke Oct. 13, 1953 2,717,455 Harris et al. Sept. 13, 1955 2,743,531 Steward May 1, 1956 2,744,337 Raney May 8, 1956 2,769,246 Shapter Nov. 6, 1956 2,775,047 Morrison Dec. 25, 1956 2,820,304 Horecky Jan. 21, 1958 2,825,146 Kostelich Mar. 4, 1958 2,851,789 Dunkelman Sept. 16, 1958 2,878,579 Fuchs Mar. 24, 1959 2,895,230 Reiley Apr. 20, 1959

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