Clothes dryer temperature control system

A clothes dryer temperature control system or circuit is provided with a thermally biased thermostat adjacent to the air outlet of the drying drum. Further, a thermally biased control thermostat is provided adjacent the air inlet of the dryer drum. The two thermostats are controlled through a multiple contact switch controller which allows the dryer to operate in a high heat, medium heat, low heat, and damp dry heating cycles. Additionally, in a gas dryer embodiment a trimmer thermostat is located in circuit with the thermally biased resistor of the thermally biased air inlet thermostat so as to decrease the response time of this thermostat on its first cycle to prevent damage to clothing during initial operation of a gas dryer.

BACKGROUND OF THE INVENTION 
The present invention relates to an automatic clothes dryer and in 
particular to an electric control circuit for use during a clothes drying 
cycle which provides thermal bias to the operating thermostats used in the 
dryer circuitry. 
Clothes dryers are known to employ an operating thermostat which senses the 
exhaust air temperature from the dryer during the drying cycle. Small 
heating elements are placed adjacent the thermostat to provide a thermal 
bias. The provision of a thermal bias causes the thermostat to operate at 
a lower exhaust air temperature and is commonly used to lower the maximum 
exhaust air temperature at which the operating thermostat reacts thereby 
cycling a main heater. 
The use of operating thermostats located at the air inlet for a gas dryer 
is taught by U.S. Pat. No. 3,322,415 issued May 30, 1967 to Joseph P. Lux. 
The use of a bias thermostat to effect the operation of the operating 
thermostat relative to changes in ambient temperature is disclosed in U.S. 
Pat. No. 3,318,016 issued May 9, 1967 to Glen R. Chafee, Jr. A similar 
circuit is also disclosed in U.S. Pat. No. 3,116,983 issued to G. R. 
Chafee, Jr. on Jan. 7, 1964. 
U.S. Pat. No. 3,409,994 issued Nov. 12, 1968 to Melvin A. Menk teaches a 
thermally biased thermostat located in the output exhaust path of the 
dryer drum outlet side. Such a circuit is also shown and disclosed in U.S. 
Pat. No. 4,842,192 issued Jun. 27, 1989 to Range et al where a bias 
thermostat is provided on the dryer drum outlet side. 
U.S. Pat. No. 5,443,541 issued to me on Aug. 22, 1995 teaches electric 
clothes dryer having two coils selectively operable by various thermostats 
to control partial heating of the air entering the dryer drum. 
While the use of thermally biased thermostats is known in the art, there 
has been no use of a thermally biased thermostat to sense the temperature 
of the air stream, upstream from the dryer drum (clothes container). These 
thermostats have been associated with the air stream, down stream from the 
drum. 
SUMMARY OF THE INVENTION 
The present invention is directed towards a novel use of a thermally biased 
control thermostat adjacent the air inlet of a dryer drum. By utilizing a 
thermally biased thermostat at the inlet, it is possible to provide dryer 
heating cycles which operate at below maximum heating conditions. 
There is also provided a thermally biased thermostat at the air inlet of 
the dryer drum which has a decreased cycle response time on the first 
cycle of dryer operation by using a trimmer thermostat to effectively 
energize the bias resistor to bias (reduce) the temperature at which the 
inlet thermostat will open circuit the heating device. This is 
particularly useful for use in operation with dryers where the dryer heats 
up quickly during the first cycle and when there may be an air blockage or 
heavy load in the clothes dryer. In particular, the use of the trimmer 
thermostat has advantage in gas appliances. 
In accordance with one aspect of the present invention there is provided a 
control circuit for operating a clothes dryer having a dryer drum, a drum 
air inlet and a drum air outlet permitting an air stream to pass through 
the dryer drum and a heating device for heating the air stream before the 
air stream passes through the dryer drum. The control circuit comprises a 
first thermally biased thermostat mounted to the dryer adjacent the drum 
air inlet and electrically connected in series with the heating device. 
The first thermally biased thermostat is responsive to temperature of the 
air stream, prior to the air stream passing through the dryer drum to move 
between open and closed positions for controlling corresponding heating 
and non-heating operation of the heating device. The thermally biased 
thermostat includes a first heat biasing resistor which when energized 
alters thermal response of the first thermally biased thermostat. A switch 
temperature controller is mounted to the dryer for controlling operation 
of the dryer. The switch temperature controller has at least one dryer 
operation position corresponding to a heat setting below maximum heating 
that initiates and maintains the heating operation of the heating device. 
This causes electricity to flow through a circuit path that energizes the 
first heat biasing resistor of the thermostat. The first heat biasing 
resistor continually heats the first thermally biased thermostat to reduce 
the temperature below a maximum temperature setting at which the first 
thermally biased thermostat cycles on and off to reduce the temperature of 
the air stream entering the dryer drum through the dryer air inlet. 
In accordance with another aspect of the present invention, there is 
provided a control circuit for operating a clothes dryer having a dryer 
drum, a drum air inlet and a drum air outlet permitting an air stream to 
pass through the dryer drum, and a heating device for heating the air 
stream before the air stream passes through the dryer drum. The control 
circuit comprises a first thermally biased thermostat mounted to the dryer 
between the heating device and the dryer drum air inlet and electrically 
connected in series with a heating device. The first thermally biased 
thermostat is responsive to temperature of the air stream prior to the air 
stream passing through the dryer drum to move between open and closed 
positions for controlling the corresponding heating and non-heating 
operation of the heating device. The thermally biased thermostat includes 
a first heat biasing resistor which when energized alters the thermal 
response of the first thermally biased thermostat. The control circuit 
further includes a trimmer thermostat mounted in the air stream downstream 
of and adjacent the heating device. The trimmer thermostat is electrically 
connected in series with the first heat biasing resistor. The trimmer 
thermostat is responsive to the temperature of the air stream flowing 
through the heating device to move between an initially closed position 
enabling electrical energization of the first heat biasing resistor and an 
open position inhibiting electrical energization of the first heat biasing 
resistor. The control circuit further includes a switch temperature 
controller mounted to the dryer for controlling operation of the dryer. 
The switch temperature controller has at least one dryer start up position 
that initiates the heating operation of the heating device and causes 
electricity to flow through the circuit path including the trimmer 
thermostat. This electrically energizes the first heat biasing resistor 
and causes the first heat biasing resistor to pre-heat the first 
thermostat prior to the air stream being overly heated to thereby reduce 
first cycle response time of the first thermally biased thermostat. 
BRIEF DESCRIPTION OF THE DRAWINGS 
For a better understanding of the nature and objects of the present 
invention reference may be had to the accompanying diagrammatic drawings 
in which: 
FIG. 1 is a partial perspective of a clothes dryer of this invention; 
FIG. 2 is a view of the diffuser for a gas dryer used in the dryer of FIG. 
1; 
FIG. 3 is a view of the diffuser for an electric dryer showing the heating 
devices for the dryer of FIG. 1; 
FIGS. 4, 5, 6 and 7 are circuit diagrams utilized by gas dryer of FIGS. 1 
and 2 showing the various contact positions respectively for high heat, 
medium heat, low heat and damped heat operation; and, 
FIGS. 8, 9, 10 and 11 are circuit diagrams utilized by the electric dryer 
of FIGS. 1 and 3 showing the various contact positions respectively for 
high heat, medium heat, low heat and damped heat operation.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIGS. 1 to 3 a domestic clothes dryer 10 is shown. FIG. 2 
shows a gas dryer diffuser whereas FIG. 3 shows an electric dryer 
diffuser, both numbered 20. 
Dryer 10 has a cabinet or housing 12 on which is mounted a control panel 14 
having a selector switch 15 which allows the user to select various drying 
modes and degrees of dryness of the clothes undergoing drying. The control 
panel 14 is also provided with a start switch 66. Cabinet 12 has a door 16 
mounted on the front panel to allow access to clothes in the drum or 
clothes container 18. Drum 18 is mounted in cabinet 12 so as to allow for 
rotation therein. 
Drum 18 is mounted within the cabinet 12 so that the rear of the drum 18 is 
substantially surrounded by a diffuser 20, shown in more detail in FIGS. 2 
and 3. The drum 18 is provided with a flat disc shaped member 22 at the 
rear thereof which contains a plurality of apertures such as 24, providing 
an air inlet for the drum for the passage of drying air therethrough. 
Referring to FIG. 2, the diffuser 20 is shown for a gas dryer. Air entering 
the diffuser 20 of FIG. 2 is heated by a gas flame in a burner 21 located 
in the air stream prior to entering the diffuser 20. The diffuser 
circulates the heated air stream about the rear surface of the dryer drum 
so that the air enters the drum air inlet relatively evenly. An additional 
thermostat 32, referred to as a trimmer thermostat is located downstream 
of the air flow (indicated by arrows 19) from burner 21. The purpose of 
this trimmer thermostat is described in more detail with the description 
of the circuit of FIGS. 4 to 7. 
Referring to FIG. 3 a heater assembly for an electrical clothes dryer 10 is 
shown. A pair of electrical heating elements 26 and 28 are mounted on 
insulators in the diffuser 20. These elements are standard heating 
elements and are capable of separate electrical energization. The elements 
26 and 28 pass through insulators such as those shown at 30 in the 
diffuser 20. The diffuser is made to mate with the revolving drum so that 
there is good communication between the drum and the diffuser for the hot 
air steam. 
A thermally biased temperature sensor or thermostat 34 is shown mounted on 
the side of the diffuser 20 for the gas dryer shown in FIG. 3 and on the 
top of the electric dryer as shown in FIG. 2. This thermostat 34 is 
designed to open before the temperature of the air entering the clothes 
drum reaches a temperature that might damage the clothes being dried. A 
second temperature sensor or thermostat 36, located in both FIGS. 2 and 3 
adjacent thermostat 34, has a higher temperature rating and is generally 
regarded as an ultimate safety thermostat rather than a controlling 
thermostat. 
Referring to FIG. 1, an additional thermally biased temperature sensor or 
thermostat 40 is located at or near the front of the cabinet so as to 
monitor the temperature of the air stream as it leaves the rotating drum. 
Temperature sensor 40 controls the drying process. 
A housing 44 is mounted so as to be in airflow communication with drum 20 
via the air flow outlet of the drum. A lint filter 45 is shown for 
trapping lint just as the air enters housing 44. Air is drawn from housing 
44 into blower housing 46 by a blower in housing 46 driven by motor 47. 
The air leaving blower housing 46 exits the dryer via pipe or duct 48. 
Referring to FIGS. 4 to 7 the basic control circuit of the present 
invention in relation to a gas clothes dryer is shown. Power is fed to 
terminal 50 designated as L.sub.1. The neutral terminal is shown at 59. 
Terminal 50 is connected to one pole 56 of timer motor control switches 58 
and 53. The terminal 54 of switch 53 is connected to terminal 57 of 
selector switch 15. The other pole 61 for terminal 57 in switch 62 of 
selector switch 15 is connected to pole 74 of thermally biased thermostat 
40 located on the outlet air stream side of the dryer drum. 
The biased thermostat 40 is provided with a resistor heating element 41 
connected across terminal 102 of centrifugal switch 104 and terminal 78 of 
switch 80 of selector switch controller 15. Switch 80 has a pole 82 
connected to pole 84 of switch 86. The other pole 88 of switch 86 is 
connected to biasing resistor 90 of thermally biased thermostat 34. 
Thermostat 34 has a terminal 91 connected to the resistor 90. Thermostat 
34 has a terminal 94 connected to gas burner 21 to the flame detector 242, 
in series with ignitor 244. Also terminal 94 is connected to one side of 
main coil 246 and safety coil 248 of burner 21. 
Thermostat 40 is connected at pole 74 via trimmer thermostat 32 to bias 
resistor 90 of thermostat 34. Trimmer thermostat 32 is located adjacent 
the gas burner 21 in FIG. 2. Pole 76 of thermostat 40 is connected via 
safety thermostat 36 to one side of burner 21 at ignitor 244, booster coil 
240 and safety coil 248. The main coil 246 and booster coil 240 are 
connected at terminal 250 to terminal 252 of switch 254. The other pole 
256 of switch 254 is also a pole of switch 260. The other pole of switch 
260 is connected to pole 102 of motor centrifugal switch 104. Pole 256 is 
connected to timer motor 108. 
Dryer air exhaust system indicator lamp 200 is connected across poles 70 
and 72 of the safety thermostat 36. Thermostat 36 is calibrated so that it 
trips to "open position" only when abnormal blockage of air flow exists. 
When it trips, indicator lamp 200 lights up to indicate to a user that the 
dryer air flow is abnormally restricted and that filter or exhaust system 
of dryer should be verified and cleaned. 
Terminal 60 of timer control switch 58 is connected to timer motor 108 and 
to terminal 64 of motor start switch 66. 
Pole 68 of start switch 66 is connected to pole 116 of centrifugal switch 
110 which in turn is connected to "run" winding 118 of the blower and drum 
drive motor 47 shown in FIG. 1. The other end of run winding 118 is 
connected to terminal 114 which is connected to terminal 120 of switch 
122. The other terminal 124 of switch 122 is connected to neutral terminal 
59. 
Pole 64 of start switch 66 is connected to pole 126 via poles 107 and 111 
of switch 109. The blade 126 of centrifugal switch 110 is shown in its 
"start" position, i.e. bridging poles 116 and 128. Pole 128 is connected 
to "start" winding 130 of motor 47. The other end of start winding 130 is 
connected to terminal 114 which is connected to terminal 120 of door 
switch 122 and also connected to terminal 106 of motor centrifugal switch 
104. 
Basically the circuit functions as follows: Control timer is set by the 
operator to a setting calculated to give a predetermined desired degree of 
"dryness" to the clothes in dryer drum 18 at the end of the drying cycle. 
The other variable set by the operator is the dry air temperature at 
selector switch 15. With the control timer switch set to dry, the switches 
53 and 58 are closed. Therefore contacts 56 and 60 plus contacts 56 and 54 
are closed, and, with air temperature selected (switch 15), the operator 
depresses the "start" button on switch 66 and the windings 118 and 130 are 
energized and motor 47 begins to run. As the motor gains speed centrifugal 
switches 104 and 110 snap to the alternate state closing contacts 116, 
126, 102 and 106. The operator may now allow the start switch 66 to return 
to its unabridged position opening contacts 64 and 68. Run winding 118 is 
now energized through idler spring switch 109 and switch blade 126 of 
switch 110. Idler spring switch is closed when the belt, driving the drum 
from motor drive pulley, is in place. If this belt breaks, switch 109 
opens and motor stops turning. 
Similarly, current for the burner 21 is supplied via temperature switch 15, 
safety thermostat 36 (located on diffuser), and drum outlet thermostat 40. 
It will be noted that thermostat 34 carries current from switch 102 to 
main coil 246, flame detector 242 and safety coil 248. 
For regular timed dry cycle, switch 260 is closed, contacts 256 and 258 are 
closed and timer motor run until contact 54 and 56 of switch 53 open and 
de-energize the burner circuit. A few minutes later, contacts 56 and 60 of 
switch 58 opens and stop main motor 47 and timer motor 118. For automatic 
dry cycle, the timer motor will not advance as long as the gas heater or 
burner 21 is energized because switch 260 is open, contacts 256 and 252 of 
switch 254 are closed, flame detector switch 242 is open and thereby, 
timer motor 108 is in series with the gas valve main coil 246 which has a 
high impedance. Also, in that position, through burner circuit L.sub.1 
voltage is maintained at ignitor 244, at terminal 250 and at other side of 
timer motor 108. 
As the clothes begin to dry, the temperature of the air exiting the drum 
begins to increase and thermostat 40 controls the energization of the 
valve main coil 246 (through low resistance ignitor 244) and safety coil 
248. 
The gas dryer has five basic temperature control settings which are 
referred to as high heat, medium heat, low heat, damp dry and fluff. The 
selector switch 15 is set to meet these five temperature settings and the 
contact settings for these temperature settings are shown respectively in 
FIGS. 4, 5, 6 and 7. For the fluff temperature setting the terminals 57 
and 61 of contact 62 of temperature switch 15 are open. 
Referring to FIG. 4 there is shown the high heat temperature condition 
wherein the contact or switch 62 is closed so that there is a contact 
across terminals 57 and 61. Switches 86 and 80 remain open. In this high 
heat condition, a circuit path is provided through thermostat 40 and 36 
and also through trimmer thermostat 32 to bias resistor 90 of thermostat 
34. 
The purpose of trimmer thermostat 32 which is located on the diffuser plate 
just downstream of the combustion chamber or burner 21 is such that this 
trimmer thermostat 32 is calibrated so that it will stay closed for the 
first 2 to 4 minutes during the heating cycle. During this time the 
internal heater 90 of the inlet control bias thermostat 94 will heat up to 
offset the thermal inertia of thermostat 34. This will prevent thermostat 
34 from overshooting its temperature of air entering the drum. The air 
entering the drum typically will result in an overshoot of temperature 
when larger loads are placed in the drum or there are restrictions in the 
drum or in the airflow through the dryer. Temperature overshooting will 
have a less effect when there is good air flow through the dryer drum. 
In this cycle, the ignitor 244 is energized and gets red hot. When this is 
detected by the flame detector, (the flame detector will open when it is 
hot enough), the detector, de-energizes the ignitor and energizes the main 
valve coil 246. The booster and safety coils are energized at the same 
time as the ignitor coil. As the main valve opens, gas will flow. The gas 
hits the hot ignitor and ignites into flame. This flame will keep the 
flame detector open. The burner 21 then heats the air in the air stream 
which enters the air inlets of the dryer drum. With good air flow the 
inlet control thermostat will not open and neither will the safety 
thermostat. As the clothes dry, air coming out of the drum gets hotter and 
reaches the point where the outlet thermostat 40 opens and cuts off the 
gas valve and flame. As thermostat 40 cools down it resets and restarts 
the heating process until the timer runs out. 
A problem can occur when the air flow is restricted or larger loads are 
placed in the dryer drum. This will result in less air flow through the 
drum and the air entering the drum air inlet will get hotter quicker. The 
purpose of the air inlet thermostat 34 is to cycle on and off to prevent 
excessive air temperature at drum inlet. Because the trimmer thermostat 
remains on for the first 2 to 4 minutes of the cycle, it allows heater 90 
of thermostat 92 to heat up initially during the initial heating phase. 
This will prevent over heating of the clothes in the dryer drum in the 
event there is a blockage. The trimmer thermostat 32 prevents over heating 
by a slow heating of thermostat 34 (because of its mass and the time 
required to heat it), in the first thermostat opening cycle when dryer is 
started from a cold condition. It should be understood that burning of the 
gas in a gas dryer can result in a quick rise in the temperature of the 
air flow stream. After the first cycle, the inlet thermostat has warmed up 
and it will keep cycling to prevent over heating and hence at this time 
the trimmer thermostat 32 opens. Consequently, there is no longer a 
biasing of resistor 90 in thermostat 34 by the trimmer thermostat 32. As 
the clothes dry, the outlet control thermostat 40 will start to cycle on 
and off. When this thermostat opens and in the automatic cycle the timer 
will advance and this will go on until the timer runs down and cools off 
the clothes. The lower the air flow, the faster the inlet control 
thermostat 34 will cycle open and closed reducing the energization of the 
burner 21 so that the heating rate of the burner 21 is reduced during 
dryer operation. 
Referring to FIG. 5 there is shown the medium heat selection of selector 
switch 15. In this condition contact switch 62 is closed and contact 
switch 86 is closed. In this condition, the trimmer thermostat 32 is of no 
use as resistor 90 is energized directly from switch 86. The operation of 
the medium heat condition will operate much the same as the high heat 
condition shown in FIG. 4. However because the selector switch 15 has 
contact switch 86 closed, there will be a continuous energization of the 
bias resistor heating element 90 of thermostat 34. Consequently the biased 
inlet control thermostat 34 will start cycling sooner and quicker through 
its cycles. This will keep the air entering the drum at a lower 
temperature. 
Referring now to FIG. 6, there is shown the selector switch combination for 
a low heat condition. In this situation the contacts switches 62, 86 and 
80 are all shown in a closed position. This circuit will work similar to 
that described for the medium heat circuit shown in FIG. 5 except that the 
resistor 41 of the outlet biased thermostat 40 is energized. This will 
make the drum outlet thermostat start to cycle sooner during the drying 
cycle. The advantage of this is that both the temperatures at the dryer 
drum inlet and the dryer drum outlet are monitored at a lower level to 
satisfy the low heat setting selected and accordingly the heat entering 
the dryer and the heat leaving the dryer drum will be at a lower rate 
during the entire drying cycle. 
Referring now to FIG. 7 there is shown the damp dry selection for the 
selector switch 15 wherein contacts which 62 is closed, contact switch 86 
is open and contact switch 80 is closed. The circuit shown in this 
selection for selector switch 15 will operate in much the same fashion as 
the high heat circuit shown in FIG. 4. Except that the selector switch 80 
is closed and as a result the drum outlet thermostat 40 will trip sooner 
and its cycling will advance the timer to the off position before the 
clothes are fully dry allowing them to be damp dried. 
Referring to FIGS. 8 to 11 the basic control circuit of the present 
invention in relation to an electric clothes dryer is shown. Circuit 
components shown in these Figures having the same function as circuit 
components in FIGS. 4 to 7 bear the same numerical designations. Power is 
fed to the two terminals 50 and 52 designated as L.sub.1 and L.sub.2 
respectively. The neutral terminal is shown at 59. Terminal 50 is 
connected to one pole 56 of timer control switch 53 and 58. The terminal 
54 of switch 53 is connected to terminal 57 of temperature selector switch 
15. The other pole 61 for terminal 57 in switch 62 of selector switch 15 
is connected to a first pole 70 of safety thermostat 36. The function of 
thermostat 36 is to cut power to the dryer heating coils 26, 28 in the 
event the dryer overheats above safe temperatures. The other pole 72 of 
safety thermostat is connected to pole 74 of thermally biased thermostat 
40 located on the outlet air stream side of the dryer drum. 
The biased thermostat 40 is provided with a resistor heating element 41 
connected across terminal 76 of the thermostat 40 and terminal 78 of 
switch 80 of selector switch 15. Switch 80 has a pole 82 connected to pole 
84 of switch 86. The other pole 88 of switch 86 is connected to biasing 
resistor 90 of thermally biased thermostat 34. Thermostat 34 has a 
terminal 92 connected to the biasing resistor 90 and outer heating coil 26 
of the electrical heating device for the electric clothes dryer. The other 
terminal 94 of thermostat 34 is connected to pole 76 of thermostat 40, to 
resistor 98 and to one side of inner heating coil 28 of the electrical 
heating device. Inner electric heating coil 28 and outer electric heating 
coil 26 of the electrical heater are connected at 100 to pole 102 of 
centrifugal switch 104. The other pole 106 of centrifugal switch 104 is 
connected to line terminal 52. 
Terminal 60 of motor controlled switch 58 is connected to timer motor 108. 
The other pole of timer motor 108 is connected to terminal 103, and to 
pole 256 of switch 260. The other pole 256 of switch 260 is connected to 
neutral terminal 59. Also connected to neutral terminal 59 are poles 82 
and 84 respectively of switches 80 and 86 of switch controller 15. 
Pole 68 of start switch 66 is connected to pole 116 of motor centrifugal 
switch 110 which in turn is connected to "run" winding 118 of the drum and 
blower drive motor 47 shown in FIG. 1. The other end of run winding 118 is 
connected to terminal 114 which is connected to terminal 120 of switch 
122. The other terminal 124 of switch 122 is connected to neutral terminal 
59. 
The blade of centrifugal switch 110 is shown in its "start" position, i.e. 
bridging poles 116 and 128. Pole 128 is connected to "start" winding 130 
of motor 47. The other end of start winding 130 is connected to terminal 
114 which is connected to terminal 120 of door switch 122. The other 
terminal 124 of door switch 120 is connected to neutral terminal 59. 
Basically the circuit functions as follows: Control timer is set by the 
operator to a setting calculated to give a predetermined desired degree of 
"dryness" to the clothes in dryer drum 18 at the end of the drying cycle. 
The other variable set by the operator is the temperature of drying cycle 
at selector switch 15. With the control timer set, switches 53 and 58 are 
closed, and control temperature selected, the operator depresses the 
"start" button on switch 66 and the windings 118 and 130 are energized and 
motor 47 begins to run. As the motor gains speed centrifugal switches 104 
and 110 snap to the alternate state closing contacts 116, 126 and 102 and 
106. The operator may now allow the start switch 66 to return to its 
unabridged position opening contacts 64 and 68. Run winding 118 is now 
energized through high limit thermostat 132 and switch blade 126 of switch 
110. 
Similarly, current for the two heating elements 26 and 28 is supplied via 
control timer, switch 53, selector switch 15, safety thermostat 36 
(located on diffuser), drum outlet temperature thermostat 40 to inner coil 
26 and inlet drum temperature thermostat 34 to outer coil 26. 
For regular timed dry cycle, switch 260 is closed, contacts 256 and 258 are 
closed and timer motor run until contact 54 and 56 of switch 53 open and 
de-energize the heater circuit. A few minutes later, contacts 56 and 60 of 
switch 58 opens and stop main motor 47 and timer motor 108. 
For automatic dry cycle, the timer motor will not advance as long as the 
inner heater coil 28 is energized from L.sub.1 because resistor 98 
maintains a potential of L.sub.1 on terminal 103. 
As the clothes begin to dry, the temperature of the air exiting the drum 
begins to increase and dryer outlet thermostat 40 controls the 
energization of coils 26 and 28. When either the safety thermostat 36 or 
the drum outlet thermostat 40 opens, resistor 98 is then fed to the 
L.sub.2 potential through low resistance inner heater coil 28 and timer 
motor runs. 
The electric clothes dryer is capable of five heat settings using the 
selector switch 15. The five heat settings are high heat, medium heat, low 
heat, damp dry and fluff. The contact switches are shown for each of these 
five heat settings respectively in FIGS. 8 through 11. For the fluff 
temperature, switch 62 is open and heater is not energized. 
In the high heat setting of FIG. 8, the switch 62 is closed completing a 
circuit path through contact poles 57 and 61. Switches 80 and 86 are open. 
Consequently, a circuit path through switch 62, safety thermostat 36, 
thermostat 40 is provided to the inner and outer coils. Further, the 
circuit to the outer coil is provided through thermostat 34. The high heat 
setting is useful for when general mixed fabrics are in the dryer drum. 
Both the inner and outer heater coils 26 and 28 are energized and the 
dryer heats up and dries the clothes. With good air flow, the inlet 
control thermostat 34 will not open, neither will the safety thermostat 
36. As the clothes dry, air coming out of the drum gets warmer and warmer 
and reaches a predetermined temperature where the outlet thermostat 40 
opens and cuts off power to the heater coils. It then cools down and 
resets the heating process till the timer runs to cool down the load and 
reaches the off position. 
When larger loads are in the dryer or there is a restriction in the exhaust 
stream then both heater coils 26 and 28 will be energized and the air flow 
passing over these coils in the diffuser will be reduced. The air entering 
the drum will get hotter at the drum inlet causing thermostat 34 to open 
and cut the outer coil 26 out of the heating loop. This will prevent the 
clothes in the dryer from over heating. As the clothes get dryer the 
outlet control thermostat will also start to cycle on and off as the 
temperature sensed by the outlet control thermostat 40 will reach its 
temperature setting. When this outlet thermostat 40 opens in automatic 
cycles the timer advances and the main motor will continue to run and 
rotate the drum as the clothes cool down and the timer motor 108 will turn 
off the dryer. 
Referring to FIG. 9, the same circuit as FIG. 8 is shown except the switch 
contacts for the selector switch 15 are different. In the medium heat 
position shown in FIG. 9, contacts 57 and 61 of switch 62 are closed, 
contacts 82 and 78 of switch 80 are open, and contacts 84 and 88 of switch 
86 are closed. The cycling of the clothes dryer to heat the clothes within 
the drum will be the same for the most part as described herein before for 
FIG. 8. The only difference will be that due to the fact that contacts 84 
and 88 of switch 86 are closed, this results in bias heater 90 of bias 
thermostat 34 being heated. Consequently, this reduces the temperature 
setting at which bias thermostat 34 will cycle open and closed. 
Consequently the cycling of the inlet dryer air flow biasing thermostat 
will cycle faster and as a result the outer heating coil 26 will be 
removed from the dryer circuit more often keeping the temperature entering 
the dryer drum at a lower temperature. 
Referring to FIG. 10, the low heat cycle is shown for the selector switch 
15 which shows each of the contact switches 62, 80 and 86 being closed 
across their respective terminals. With respect to switches 62 and 86 
being closed as in FIG. 9, the circuit works as it would in the medium 
heat position except that the thermally bias outlet thermostat is now 
biased with its internal heating resistor 41 being energized. This makes 
the outlet drum thermostat start to cycle at a reduced temperature and as 
a result the drying cycle starts to cycle sooner. The advantage of this 
system is that both temperatures at the drum inlet and the drum outlet are 
moderate and lowered to satisfy the low heat setting selected. 
Referring to FIG. 11, the damp dry temperature selection for selector 
switch 15 is shown. In this setting the switches 62 and 80 are closed and 
switch 86 remains open. This selection works the same as the high heat 
selection of FIG. 8 except that the switch 86 is closed. As a result drum 
outlet thermostat is biased across resistor 41 and trips sooner in the 
cycle. This will allow the timer motor 108 to advance quicker to the off 
position before the clothes are fully dried and a damp dried cycle is 
obtained. 
Accordingly, the use of the thermally biased thermostats 40 and 34 of the 
present invention located respectively at the air outlet of the dryer drum 
and air inlet of the dryer drum allows for the use of a five position 
selector switch 15 to provide five dryer settings. 
Various alternatives will be obvious to those skilled in the art, but 
applicant wishes to be limited only the scope of the following claims.