US3009256A - Control system for clothes dryers - Google Patents

Description

Nov. 21, 1961 Filed July 9, 1959 D. W. LYNCH CONTROL SYSTEM FOR CLOTHES DRYERS 3 Sheets-Sheet 1 FIGJ INVENTOR. DONALD w. LYNCH BY 1L2 f imm,

HIS ATTORNEY Nov. 21, 1961 D. w. LYNCH CONTROL SYSTEM FOR CLOTHES DRYERS Filed July 9, 1959 3 Sheets-Sheet 2 lZn.

INVENTOR.

D NALD W. LYNCH BY w ,0 4 I v HIS ATTORNEY Nov. 21, 1961 D. w. LYNCH CONTROL SYSTEM FOR CLOTHES DRYERS 5 Sheets-Sheet 3 Filed July 9, 1959 79 AMBIENT TEMPERATURE COMPENSATING CONTROL PIC-1.3

INVENTOR LYN c H H l 5 ATTORNEY United States Patent 3,009,256 CONTROL SYSTEM FOR CLOTHES DRYERS Donald W. Lynch, Louisville, Ky., assignor to General Electric Company, a corporation of New York Filed Juiy 9, 1959, Ser. No. 825,976 8 Claims. (Cl. 34--45) My invention relates to clothes drying machines, and more particularly to automatic control systems for use in such machines for controlling the drying operation.

There are at the present time several domestic clothes drying machines commercially available where the length of the drying cycle is controlled indirectly by the dryness of the clothes. This is generally effected by using a thermostatic control, on the basis that a predetermined rise in the clothes temperature indicates that the heat supplied to the clothes is no longer being used to vaporize moisture from them but instead is free to raise their temperature. In other words, such control systems utilize a predetermined high temperature as a trip point for shutting off the means provided for heating the clothes. Depending upon other structural features of the different drying machines, a single such occurrence may be provided or several such occurrences may be provided in a single drying sequence. In either event, it is important for optimum operation that suitable changes be made to the trip temperature at which the heaters are shut off to compensate for variations in the ambient temperature. This results from the fact that when the temperature of the air taken in for circulation over the heaters and through the clothes container is quite low, it atfects substantially the temperature to which the heaters can raise the air before it enters the basket. Since the air flow has a substantial efiect on the drying of the clothes as well as the heat, variations in the temperature of the air passing through the basket will not, provided they are fairly small, have too substantial an effect on the length of time it takes to dry the clothes. However, where a thermostat is so calibrated that it trips when clothes are dry and the air being taken in is at an ambient temperature of 70 degrees Fahrenheit, for instance, it will readily be understood that should the ambient temperature drop to 50 degrees a much greater temperature rise will be necessary for the thermostat to be tripped. This has the result, if not com pensated for, of excessively lengthening the drying cycle to the extent that the clothes are dry long before the end of the cycle. In fact, if the temperature drop is sufliciently great-as may be the case where a dryer is kept in an unheated basement or garage-the dryer may continue to operate without shutting off until manually turned to its off position. Because of this it is of high importance to provide suitable compensating means responsive to the temperature of the ambient air being drawn into the dryer.

It is therefore an object of this invention to provide improved economical means of compensating for the ambient temperature changes in a dryer having a thermostatic control of the general type described.

It is further an object of the invention to achieve this compensation by suitable variation of [the heating effect of a biasing heater positioned in heating relation to the main thermostat.

Yet a further object of the invention is to achieve this variation of the heating effect of the biasing heater by providing diiferent resistances in parallel with each other and in series with the biasing heater, with means sensitive to ambient temperature for opening the circuits to diiferent resistances at different ambient temperatures.

A further general object of the invention is to vary the heating elfect of the biasing heater by providing at least two parallel paths with a switch in one of them so that when the switch is open a first resistance is provided and Patented Nov. 21, 1961 when the switch is closed a second resistance is provided, and to operate the switch in response to the occurrence of a predetermined condition such as, for instance, the above specifically described ambient temperature condition.

In carrying out my invention in one form thereof, 1 provide a clothes drying machine which has a conventional clothes container with a main heater positioned to heat the clothes in the container. Thermostatic means are positioned to be responsive to the temperature of the clothes in the container and are also acted on by an electric resistance-type biasing heater which is positioned in suitable heating relation to the thermostatic means. When the thermostatic means senses a predetermined high temperature, due to the combination of the clothes temperature and the biasing heater, it causes a first switch to open to stop operation of the main heater. As thus far described, it is clear that the more effective the biasing heater, the lower the clothes temperature which will trip the thermostatic means.

In series with the biasing heater we provide at least two conductors connected in parallel with each other. One of the two conductors includes a switch, and the resistances of the conductors are so proportioned that a first resistance in series with the biasing heater is pro vided with the second switch open and a second difierent resistance when the second switch is closed. Means are provided responsive to the occurrence of a predetermined condition (such as a rise in the ambient temperature to a predetermined level) to automatically open the second switch; when this occurs, the relatively low resistance path of energization for the biasing heater is changed to a relatively high resistance path, and the biasing heater must consequently be energized through a circuit which allows less power than before to be used in the heater and therefore decreases its effectiveness.

With the heat output of the biasing heater thus decreased, the clothes temperature required to trip the main thermostatic means must then be higher. This rise in the clothes temperature may be made to substantially oifset the rise in the ambient temperature.

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

In the drawings,

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

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

FIGURE 3 is a schematic illustration of my improved control circuit.

Referring now to FIGURES 1 and 2 of the drawings, I have shown therein a domestic clothes dryer 1 including a clothes tumbling container or drum 2 provided within a suitable outer casing or cabinet 3 which completely encloses it on all sides. The drum is mounted for rotation within a cabinet 3 on a substantially 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 accompanying 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 and 11 which are rotatably secured to the top of an upwardly extending member 12 secured at its bottom to the base 12a of the machine (FIGURE 1). It will be observed that 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 mounted on a shaft 14 supported in bearings 15. Shaft 14 is secured to a pulley 16 which is driven from a belt 17 in turn powered by a pulley 18 mounted on the end of a shaft 19 of an 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 an appropriate speed to provide tumbling action for articles of clothing placed therein.

In order that a stream of drying air may 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 26 appropriately insulated from the baffle member. Heating elements 26 may be annular in shape so as to be generally coextensive with the perforations 22 in drum 2. A bafile member 27 is rigidly secured to the back wall 7 of the drum outside the ring of perforations 22 and within the stationary baffie 25 so that an annular air inlet 28 is, in effect, formed by the two bafiles 25 and 27. Battle 27 is further provided with an annular series of openings 29; in this manner a passage is provided for air to enter annular opening 28 between the bafiles, pass over the heating elements 26, through openings 29 and then through perforations 22 into the interior of drum member 2.

In addition to the air guiding function, the battles 25 and 29 help the rollers 10, 11 and 13 support the drum 2. Secured to the central portion 30 of bathe 27 is a bracket 31 to which in turn is secured a stub shaft member 32 arranged substantially coaxial with drum 2. The central portion 30 of baffle 27 has an opening 34 formed therein in the form of a slot. The slot is suitably formed (as more fully described in application S.N. 789,869 filed January 29, 1959, by Willam F. Simpson and assigned to the same assignee as this invention) so as to permit stub shaft 32 a limited amount of movement in the vertical direction but 'virtually no movement in a 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 afiirmatively prevented by the 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 the 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 path through the drum, also serves as a means whereby clothes may be loaded into and unloaded from the drum. The door 37, whose inner surface forms part of the bulkhead closing the opening, is mounted on cabinet 3 and when the door is opened clothes may be inserted into or removed from the drum through the door frame 33. It will be noted that the door includes an outer fiat imperforate section 43 and an inwardly extending hollow section 44 mounted on the fiat 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 this 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 frame 38.

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 by motor 20. The outlet of blower 49 communicates with an outlet duct 50 (FIG- URE 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 51a, 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, the outlet duct 50, and opening 51 to atmosphere.

The operation of the dryer 1 is controlled by a new and improved control system, one embodiment of which is shown in the circuit diagram of FIGURE 3. As shown there, the entire control system of the machine is energized across a three wire power supply system including supply conductors 52 and 53 and a neutral conductor 54. For domestic use, the conductors 52 and 53 will normally be connected across a 220 volt power supply with volts appearing between the neutral line 54 and each of these conductors.

The drive motor 20 includes a main winding 55 and a start winding 56 which are connected in parallel with each other between supply conductor 52 and neutral conductor 54. Specifically, the circuit, starting a supply conductor 52, passes through a switch 57, then through the windings 55 and 56 in parallel with each other, a standard motor protector device 58, a switch 59 positioned (FIGURE 1) to be opened when the door 37 is opened and closed when the door is closed, and neutral conductor 54. Included in the parallel branch circuit of auxiliary winding 56 is a switch 60 controlled by a centrifugal mechanism 61 rotatable with the motor; when the motor comes up to a certain speed upon energization of the windings 55 and 56, the device 61 will cause switch 60 to open thereby de-energizing winding 56 and permitting the motor to continue running on winding 55 alone.

Returning to switch 57 which is in series with both windings of the motor, this switch is under the control of a cam member 62 which in turn is driven by a timer motor 63 when energized. The timer motor also controls a cam member 64 which operates a switch 65. As well as being driven by the timer motor 63 when energized, the cams 62 and 64 are manually presettable to a desired position by means of a control member 66 which is generally provided in a readily accessible position such as, for instance, as shown in FIGURE 1, on the backsplasher 67 secured to the top of cabinet 3. As also shown in FIGURE 1, the timer motor 63 and the cam and switches controlled thereby form together a control assembly 68 which is generally positioned within backsplasher 67 as shown. The energizing circuit for timer motor 63, starting with supply conductor 52, passes through switch 65, a switch 69 controlled by centrifugal mechanism 61 and closed thereby at the same time that switch 60 is opened, a main thermostatic device 70, preferably in the form of a bimetal element as shown, and timer motor 63 to conductor 54. The bimetal thermostatic means has a high temperature trip position in which it moves into engagement with a contact 7i]. and a low temperature reset position in which it moves into engagement with a contact 72. The circuit through the timer motor 63 is completed when element 70 engages contact 71. Alternatively, when element 70 engages contact 72, a circuit is completed, starting at supply conductor 52, through switches 65 and 69, bimeta l element 70, contact 72, protective device 73, and the heaters 26 to conductor 53.

It will be observed in FIGURE 1 that the thermostatic device 70 is positioned at the front of the dryer onthe bulkhead 35 directly below the air outlet 45 from the drum. The thermostatic element 70 is thus 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 thermostatic means 70, a biasing heater 74 is provided in close physical relation ship with element 70 so as to be in heating relation thereto. The heater 74 is of relatively high resistance compared to heater 26 (for instance approximately 1100 ohms for heater 74 and 10 ohms for heater 26 may be pro vided), so that its power consumption compared to the main heater is exceedingly small. In fact, the small size of heater 74 and the desirability of having it close to the thermostatic element 70 generally causes the preferred construction, in practice, to provide for a unitary assembly within a single casing, which assembly includes both the biasing heater 74 and the thermostatic element 70.

The biasing heater 74 is energized through a circuit which, starting at conductor 52, extends through a group 79 of parallel connected conductors, the biasing heater 74, and neutral conductor 54, the group constituting an ambient temperature compensating control and being positioned in any suitable location (such as backsplasher 67) Where it may sense the ambient temperature.

Group 79 includes three conductors 80, 81 and 82. While any combination of suitable resistances may be provided for the purpose to be explained directly herebelow, I provide as one means of carrying out my invention a relatively high resistance 83 in conductor 80, a smaller resistance 84 in conductor 81, and a very small resistance, which may be that inherent in the wire itself, in the third conductor 82. In series with the resistances in conductors 81 and 82 are a pair of thermostatically responsive devices 85 and 86 respectively which may, as shown, be simply small bimetallic cantilever switch members. Thermostats 85 and 86 are positioned, as shown in FIGURE 2, to be responsive to the ambient temperature, that is, to the temperature of the air surrounding the dryer which will be drawn into the dryer by the blower for heating and circulation through drum 2. Thermostats 85 and 86 are calibrated so that they each close at a different ambient temperature; the thermostat 85 closes at the higher temperature (on decreasing ambient temperatures), preferably on the order of 90 F. White theother thermostat 86 closes at a substantially lower ambient temperature, which may be on the order of 70.

It will thus be seen that if the temperature is above 90 both thermostats 85 and 86 will be opened so that the circuit for the biasing heater has to pass through the relatively high resistance 83. The provision of a relatively to be supplied to the heater with the result that a greater amount of heat from the clothes in the drum 2 is required before thermostat 70 trips. Thus, a relatively high ambient temperature causes a relatively high dlothes temperature to be required before the thermostat 70 trips. When the temperature is between 90 and 70, the thermostat closes, and a smaller resistance 84 is in the circuit in series with biasing heater 74 so that the heater is more effective and a lower temperature from the clothes in the drum is required to trip thermostat 70. Thus, a lowering of the ambient temperature causes a lowering of the clothes temperature required to trip the thermostat 70. In similar fashion, when the ambient temperature is below 70, thermostat "86 closes to provide a very low resistance path in series with biasing heater '74, the biasing heater is fully effective, and a relatively low temperature of the clothes causes tripping of the thermostat 70.

' For a full understanding of the invention, let it now be assumed that a load of ordinary cottons is to be dried, and that the machine is located in a room where the temperature of the air to be drawn into the machine is 75. The dial 66 is appropriately marked so that when the timer is set to run for a relatively long period it indicates that a heavy load of moisture-absorbent clothes is to be dried, for an intermediate period it indicates that ordinary cottons are to be dried, and for short periods it indicates that synthetics are to be dried. With an average type load such as ordinary cottons, the dial 66 is set so that approximately /3 of the time available is provided. This closes switches 57 and 65; also, with the temperature 75, thermostat 86 is opened and thermostat 85 is closed. In addition, since the cycle is just starting, the main thermostat 70' is in its cool or re-set position where it engages contact 72 to provide an energizing circuit for the heaters 26 and to prevent the timer motor 63 from operating.

Provided the door is closed so that switch 59 is closed, drive motor 20 will then start in operation. When it has come up to speed, the start winding 56 is de-energized and switch 69 is closed by centrifugal mechanism 61. The closing of switch 69 completes an energizing circuit for heaters 26 which thereupon start to heat the air as it is drawn into the drum 2 by the blower 49.

At the same time, the biasing heater 74 is energized in series with the parallel resistance 83 and 84. The combination of resistances 83 and 84 is that which is selected for connection in the circuit when the ambient temperature is between 70 and that is, when thermostat 85 is closed and when thermostat 86 is opened. The inclusion of resistance 84 in the circuit by the closing of thermostat 85 has the desired compensating effect onbiasing heater 74. The condition of the thermostats 8-5 and 86 is not, of course, affected by the progression of the drying cycle, and if as is normally true the ambient temperature remains constant within a few degrees during the drying cycle, the combination of resistances 8'3 and 84 will continue to determine the ambient temperature compensation effect on biasing heater 74.

As stated, the heaters 26 are energized; after a period of such energization, and in accordance with the effect of biasing heater 74 as modified by group 79, the thermostat 70 will trip in response to a rise in the clothes tem perature and will engage contact 71. This de-energizes heaters 26 and energizes timer motor 63 which then continues to operate until such time as the thermostatic element 70 resets and engages contact 72. At this point, of course, the heaters 26 are re-energized and the timer motor 63 is de-energized. This causes the temperature to rise again, and when the predetermined point is again reached the thermostat again causes de-energization of the heater and re-energization of the timer. It will be seen that this sequence will continue until such time as the timer has caused the cams to rotate to the off position high resistance in series with heater 74 causes less powerat which point all circuits within the dryer will be opened 7 and the sequence will be terminated, with the clothes within the drum being completely dry.

It will thus be observed that a drying cycle wherein the cycle is dependent to a substantial extent on the tripping of a thermostat sensitive to the clothes temperature has been provided which in an economical manner provides for compensation for the ambient temperature. It will readily be seen that if, with the ordinary cotton load, the temperature should have been, for instance, 60, thermostat 86 would have closed and a substantially lower clothes temperature would have caused tripping; by the same token, a high temperature above 90 would have caused opening of both thermostats 85 and 86 and the clothes temperature required to trip thermostat 7 would also have been raised.

It will thus be seen that an economical and effective systemis provided for tailoring the operation of the clothes drying machine 1 to the occurrence or variation of a particular condition such as, for instance, the ambient temperature. It will be recognized that while a particular automatic sequence has been described, in which the operation of the heater and the timer are completely alternative to each other, my invention is of value in other types of drying cycles, including those where operation of the heaters and timer is concurrent part of the time, and even those where the operation of the timer is continuous; in fact, the ambient compensation feature has its usefulness unimpaired even if all timing means be eliminated and the thermostatic means provide the sole control.

It will further be recognized that the biasing heater may be made to operate continually as shown, or that its operation may be contingent on some other factor such as the operation of the main heaters 26. In the present embodiment it is deemed preferable that the operation of the biasing heater be continuous, but it is readily conceivable that in some cases, particularly where the operation of the heaters and the time motor is not completely alternative in nature, it might be desirable to have the biasing heater operate at the same time as the main heaters.

Another point to be noted is that while each group of conductors has been shown to include three conductors, it is readily apparent that as few as two and as many as desired may be provided without departure from our invention. Also, while conductors of varying resistance have been shown, it will readily occur that this arrangement is not necessarily the only one which may be effective. For instance, if equal resistances are placed in two parallel conductors, it is well known that if the circuit through one of the conductors is opened the resistance in the circuit is then twice as large as when the connections are completed through the two parallel conductors. Thus, far from being limited from different resistors in each conductor it will readily be apparent that the differing resistance effect may be obtained even with like resistors. Also, a compensating resistance change is obtainable with the switch means in series with the higher resistance, particularly where the lower resistance is still fairly substantial (as opposed to a short circuit).

While in accordance with the patent statutes I have described what at present is considered to be the preferred embodiment of my 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 the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a clothes drying machine, a clothes container, a main heater positioned to heat clothes in said container, first thermostatic means positioned to be responsive to the temperature of clothes in said container, an electric resistance type biasing heater positioned in heating relation to said first thermostatic means, first switch means controlling operation of said main heater, said first thermostatic means causing said first switch means to open in response to a predetermined high temperature, at least two parallel connected conductors in series with said biasing heater, each of said conductors having a different resistance included therein, the one of said conductors including the lesser of said resistances further including a second switch means in series with said lesser resistance, and second thermostatic means positioned to be responsive to the ambient temperature, said second thermostatic means causing opening and closing of said second switch means when the ambient temperature rises above and falls below a predetermined level, whereby the effect of said biasing heater on said first thermostatic means is modified and the clothes temperature required to cause said first thermostatic means to open said first switch means is increased and decreased with increases and decreases in the ambient temperature.

2. In a clothes drying machine, a clothes container, a main heater positioned to heat clothes in said container, first thermostatic means positioned to be responsive to the temperature of clothes in said container, an electric resistance type biasing heater positioned in heating relation to said thermostatic means, first switch means controlling operation of said main heater, said first thermostatic means causing said first switch means to open in response to a predetermined high temperature, at least two parallel connected conductors in series with said biasing heater, at least one resistor and at least one second switch means connected in said conductors, said conductors providing a greater resistance when said second switch means is open and a lesser resistance when said second switch means is closed, second thermostatic means positioned to be responsive to the ambient temperature, said second thermostatic means causing opening and closing of said second switch means when the ambient temperature rises above and falls below a predetermined level, whereby the effect of said biasing heater on said first thermostatic means is modified and the clothes temperature required to cause said first thermostatic means to open said first switch means is increased and decreased with increases and decreases in the ambient temperature.

3. The apparatus defined in claim 2 wherein said first thermostatic means comprises a bimetallic element.

4. In a clothes drying machine, a clothes container, a main heater, air circulating means arranged to circulate ambient air over said heater and then into said container, first thermostatic means positioned to be responsive to the temperature of clothes in said container, an electric resistance type biasing heater positioned in heating relation to said first thermostatic means, first switch means controlling operation of said main heater, said first thermostatic means causing said first switch means to open in response to a predetermined high temperature, at least two paralle connected conductors in series with said biasing heater, at least one resistor and at least one second switch means connected in said conductors, said conductors providing a. greater resistance when said second switch means is open and a lesser resistance when said second means is closed, and second thermostatic means positioned to be responsive to the temperature of the ambient air, said second thermostatic means controlling said second switch means and opening said second switch means when the ambient air temperature rises to a predetermined level whereby variations in the temperature of the air circulated over said main heater and into said container are compensated for by variations in the effect of said biasing heater on said first thermostatic means.

5. In a clothes drying machine, a clothes container, a main heater, control means for limiting the length of operation of said machine, manually operable means for presetting the duration of control means operation, air circulating means arranged to circulate ambient air over said main heater and then into said clothes container, first thermostatic means positioned to be responsive to the temperature of clothes in said container, an electric resistance type biasing heater positioned in heating relation to said first thermostatic means, first switch means controlling operation of said main heater and of said control means, said first thermostatic means causing said first switch means to de-energize said main heater and energize said control means upon sensing a predetermined high temperature, and causing said first switch means to energize said main heater and de-energize said timer upon sensing a predetermined low temperature, at least two parallel connected conductors in series with said biasing heater, at least one resistor and at least one second switch means connected in said conductors, said conductors providing a greater resistance when said second switch means is open and a lesser resistance when said second switch means is closed, and second thermostatic means responsive to the temperature of the ambient air, said second thermostatic means controlling said second switch means and opening said second switch means when the ambient air temperature rises to a predetermined level.

6. The apparatus defined in claim 2 wherein said biasing resistance is connected to operate continuously during a drying operation.

7. In a clothes drying machine, a clothes container, a main heater positioned to heat ciothes in said container, first thermostatic means positioned to be responsive to the temperature of clothes in said container, an electric resistance type biasing heater positioned in heating relation to said first thermostatic means, means controlling operation of said main heater, said first thermostatic means causing said controlling means to shut off said main heater in response to a predetermined high temperature, at least two parallel connected conductors in series with said biasing heater, at least one resistor and at least one switch means connected in said conductors, said conductors providing a greater resistance when said switch means is open and a lesser resistance when said switch means is closed, and second thermostatic means positioned to be responsive to the ambient temperature, said second thermostatic means causing opening and closing of said one switch means when the ambient temperature rises above and falls below a predetermined level, whereby the effect of said biasing heater on said first thermostatic means is modified and the clothes temperature required to cause said first thermostatic means to shut ofi said main heater is increased and decreased with increases and decreases in the ambient temperature.

8. In a clothes drying machine, a clothes container, a main heater positioned to heat clothes in said container, first thermostatic means positioned to be responsive to the temperature of clothes in said container, an electric resistance type biasing heater positioned in heating relation to said thermostatic means, means controlling operation of said main heater, said first thermostatic means causing said controlling means to shut ofi said main heater in response to a predetermined high temperature, at least two parallel connected conductors in series with said biasing heater, at least one resistor and at least one switch means connected in said conductors, said conductors providing a greater resistance when said switch means is open and a lesser resistance when said switch means is closed, second thermostatic means positioned to be responsive to the ambient temperature, said second thermostatic means causing opening and closing of said switch means when the ambient temperature rises above and falls below a predetermined level, whereby the etfect of said biasing heater on said first thermostatic means is modified and the clothes temperature required to cause said controlling means to shut oif said main heater is increased and decreased with increases and decreases in the ambient temperature.

References Cited in the file of this patent UNITED STATES PATENTS 2,775,047 Morrison Dec. 25, 1956 2,851,790 Worst Sept. 16, 1958 2,878,579 Fuchs Mar. 24, 1959

Images