US3545096A - Hold circuit for a dryer - Google Patents

Description

DCC. 8, 1970 K, D, SAUSBURY ETAL 3,545,096

HOLD CIRCUIT FOR A DRYER Filed April 3, 1968 3 Sheets-Sheet 1 INVENTORS /jz/Zzzzzjy Dec. 8, 1970 K, D, SALlsBURY ETAL HOLD CIRCUIT FOR A DRYER 3 Sheets-Sheet 2 Filed April '5, 1968 DCC 3, 1970 K. D. sALlsBuRY ETAL HOLD CIRCUIT FOR A DRYER 3 Sheets-Sheet 3 INVIENTORS Filed April s, 1968 ATTORNEYS Patented Dec. 8, 1970 3,545,096 HOLD CIRCUIT FOR A DRYER Keith D. Salisbury, Arlington, Mass., and William F. Robandt, St. Joseph, Mich., assignors to Whirlpool Corporation, Benton Harbor, Mich., a corporation of Delaware Filed Apr. 3, 196s, ser. No. 718,432 Int. Cl. F26b 13/10 U.S. Cl. 34-44 7 Claims ABSTRACT F THE DISCLOSURE A hold system for a dryer which, upon preselection dries articles to a preset moisture level and allows the dryer to continue to operate without further drying until the operator restarts the heater to complete the drying cycle.

CROSS rREFERENCE TO RELATED APPLICATION The hold circuit of this invention is applicable to dryers such as described in the application entitled Tumble Pattern Sensor and Method of Drying, invented by William F. Robant and assigned to the assignee of this invention Ser. No. 714,581, `filed Mar. 20, 1968.

BACKGROUND OF THE INVENTION Field of the invention This invention relates in general to dryers, as for example clothes dryers, and in particular to a novel control circuit for turning off the heater and continuing to operate the dryer in a holding mode until the user actuates the control system to complete the drying cycle.

Description of the prior art U.S. Pat. 2,885,789 arrests operation of a dryer when V clothing reaches a damp dry condition in response to a signal from a pair of temperature sensing means. However, no provision is made to terminate heat input simultaneously with a reduction in drum speed and no hold circuitry is provided to re-initiate dryer operation.

SUMMARY In accordance with this invention a hold circuit is provided for a dryer which allows articles being dried to be held at a predetermined moisture content until the operator desires that the cycle be completed. The hold circuit can be incorporated in a control arrangement whereby speed of the driving motor is regulated as a function of variations in the tumble pattern although the present invention has utility in other forms of dryer circuitry.

BRIEF DESCRIPTION OF THEI DRAWINGS DESCRIPTION O=F THE PREFERRED EMBODIMENT FIGS. 1 and 2 are schematic views of a clothes dryer 11 which has a cabinet 12 with 'a door I13. A control panel 15 is attached to the top of the cabinet 12 and has a moisture control lknob 14. A start button 16, a hold botton -81 and a finish button 82 are also mounted on the control panel '15. As best shown in PIG. 3 the knob 14 has a pointer 17 that may be set against indicia 20 to control the shut-off point of the dryer.

FIGS. Z and 4 illustrate a stationary bulkhead 1'8 and the drum 19 of the dryer. A motor 21 is coupled to the drum '19 by belt 2.2 to drive it.

An inlet orifice 23 and an outlet oritce 24 are formed in the bulkhead `18. A heater 10 is mounted in the duct (not shown) leading to the inlet orifice 23 and a blower motor 26 with a suitable impeller is mounted in the duct (not shown) leading from the outlet orilice 24 to draw air heated by heater 10 through the dryer. Although IFIG. 4 illustrates a totally stationary bulkhead, the invention may be used where only a portion of the bulkhead is stationary.

As shown in FIG. 4, the outlet orifice 24 is generally above center and to one side of the dryer and arrows X, Y, and Z illustrate various paths which articles in the dryer can ta'ke. Arrow X shows a path near the top of the outlet orice 24 and results when the drum speed is relatively high. Arrow Y passes generally over the center of the outlet orifice 24 and results from a slightly lower drum speed. Arrow Z illustrates a path belo'w the orifice 24 and corresponds to a drum speed which is too slow. From the standpoint of heat transfer to the wet clothing, which of course directly determines the drying rate, a band between arrows X and Y ygives the optimum tumbling pattern within the drum. Thus, to maintain an optimum tumbling speed, the drum speed is continuously varied throughout the drying cycle so clothing always follows the path between arrows X and Y in tumbling through the heated air drawn through the drum. An additional benefit of the control system is that as the drum speed is continuously varied to force clothing to follow the above defined trajectory, the changing speed breaks up any regular tumbling pattern the clothing might establish thereby causing it to ball This balling effect is highly detrimental to proper drying since the clothing on the inside of the ball is not exposed to heated air and comes out damp 'while the clothing on the fringes of the load is over-dried.

In order to sense when the clothing is following the trajectory between arrows X and Y, a pair of thermistors 28 and 29 are located immediately behind the air outlet 24 through which air exits from the drum. If clothing follows the arrow Y, heated air must pass through damp clothing before going out the portion of the grill in which thermistor 28 is located. However, heated air does not go through the clothing load before passing by thermistor 29. If clothing follows the arrow Y thermistor 28 runs about 10 F. cooler than thermistor 29. Thus, to control the drum speed so that the clothing follows a path between arrows X and Y, a speed control circuit for the motor receives inputs from thermistors 28 and 29 and continuously varies the drum speed so that the temperature differential between thermistors 2 `Sand 29 is maintained at a maximum.

As the clothing within the drum begins to dry, hot air passing through the partially dried clothing no longer is cooled as much as it was at the beginning of the cycle when the clothing was completely soaked. Thus, near the end of the drying cycle thermistor 28 begins to approach thermistor 29 in temperature. It has been experimentally determined that the temperature differential between thermistors 28 and 29 is linearly related to the percent moisture retention of the load, when it follows the path between arrows X and Y. Thus, by using the temperature differential between the two thermistors, a source of signal for an extremely accurate dry control is obtained.

The housewife sets knob 14 to the desired moisture retention and presses start button 16 to start the dryer. If the housewife wishes to hold the articles being dried at a predetermined moisture level, she presses button 81. When the articles reach the predetermined moisture level the heaters cut ot andthe drum speed drops to approximately 39 r.p.m. The` clothing continues to tumble at the predetermined moisture level until the housewife returns anddepresses the nish button 82. The dryer will then complete the drying cycle and turn oi. This prevents the clothing from becoming completely dry prior to the arrival of the housewife at the dryer. Thus, lshe can remove the clothing from the dryer precisely when it terminates which prevents wrinkles from setting in new permanent press fabrics. v

As best shown in FIGS. a and 5b commonly available A.C. power, as for example 110 volts, is connected between terminals B and N of the dryer. A 220v volt supply is connected between terminals B and C. A door switch 31 is connected to terminal B and is open when the door 13 is open. When door 13 is closed, the switch 31 closes to connect terminal B with contact 32 of switch 16. Contact 32 is connected to a thermostat switch 33 which is in series with a centrifugal switch-34 actuated by motor 21 when it comes up to speed, a heater switch 36 and the heater 10. The other side of the heater is connected to terminal C.

A second terminal 37 of Switch 16 is connected to hold relay 38 which has its other side connected to terminal N. The relay 38 has an armature which moves linkages 35 to control switches 36 and 39.

Switch 39 has one contact connected to contact 32 of switch 16. A second contact 41 is connected to a lead 42. A cool-down thermostat 43 is connected between contact32 and lead 42.

A normally closed switch 44 has one contact connected to contact 41 and a second contact 46 connected to one side of relay 38.

A hold switch 86 comprises the hold button 81 and a pair of contacts 87 and 88. Contact 87 is connected to a contact 89 of switch 16. Lead 91 connects contact 88 to one side of relay 92 which has its other side connected to point N. The relay 92, when energized, closes switches 93 and 94 by linkages 96 and 97. Switch 93 is connected between contact 87 and relay 92 and provides holding current for relay 92 when button 81 is released.

The motor 21 has a run winding 47 and a start winding 48. First sides of these windings are connected to lead 42. The other side of winding 48 is connected to a centrifugal Switch 49 which opens when the motor comes up to speed and has its other -side connected to a capicitor C1. The other side of capacitor C1 is connected to terminal N. A condensor C2 is connected from terminal N to winding 48. A triac 51 has its anode connected to winding 47 and its cathode connected to terminal N. A gate electrode 52 is connected to a resistor R1 and the anode of a diode D1. The cathode of diode D( is connected to the secondary 53 of transformer T1. The other sides of secondary 53 and resistor R1 are connected to terminal N.

Al full wave rectier bridge 154 comprising diodes D2, D3, D4 and D5 is connected between terminal N and a resistor R3. The other side of resistor R3 is connected to lead 42. A resistor R2 is connected from the junction point of diodes D2 and D3 to a lead 54. A lead 56 is connected to the junction of diodes D4 and D5. A Zener diode D0 is connected between leads 54 and 56. A capacitor C3 is connected across Zener diode D5.

The primary 57 of transformer T1 is connected to line 54 and to the collector of a transistor T10. The emitter of transistor T10 is connected to a resistor which has its other side connected to lead 56. A resistor R5, a unijunction transistor T0 and a resistor R3 are connected in series between lead 54 and 56.

A variable resistor R2 and a capicitor C11 are connected between lines 54 and 56. The emitter of transistor T0 is connected to the point between resistor R1 and capacitor C11. A. diode D7 has its cathode also connected to this point and it-s anode connected to resistors R0, R0 and the collector of transistor T2. The other side of resistor R8 is connected to lead 54. A resistor R11 is connected between the emitter of transistor T2 and lead 56. The other side of resistor R0 is connected to the base of transistor T2.

A resistor R10 is also connected to the base of transistor T2 and to point H. A capacitor C4 is connected between point H and lead 56.

Refer to FIG. 5b wherein points D, K,.E, H, F and G correspond to the same points in FIG. 5a.

The motor 21 has an output shaft 58 which drives a tachometer 61. The ytachometer 61 provides an A.C. input voltage to a bridge circuit 62. The tachometer 61 has an output coil 63 connected across points M 'and O of bridge 62. Resistor R13 is connected between points Q and O and resi-Stor R14 is connected between points O and P. Thermistor 28 is connected between points M and P and thermistor 29 is connected between points M and Q. A resistor R12 is connected between point Q and lead 56. A wiper contact 65 engages resistor R12 and is connected to the anode of diode D14. The cathode of diode D14 is connected to resistor R10.

A resi-Stor R15 and capacitor C12 are connected in series between point Q and the base of a transistor T3.

A transformer T20 has its primary 64 connected between leads 42 and 56. The secondary 66 of transformer T20 is connected across a full wave rectifier bridge 67 having diodes D3, D3, D10 and D11. A resistor R10 is connected from the junction of diodes D3 and D10 to lead 68. A capacitor C5 and Zener diode D12 are connected in parallel between leads 68 and 69.

Resistors R11 and R13 are connected in series across leads 68 and 69. A capacitor C3 is connected across resistor R10. The junction point between resistors R11 and R13 is connected to the base of transistor T3, and a resistor R20 is connected between the emitter of transistor T3 and lead 69.

Resistor R21 and capacitor C0 are connected in series between leads 68 and 69. Resistor R22 is connected between the emitter of transistor T3 and the junction point between resistor R21 and capacitor C3. Capacitor C1 is connected across R21.

A resistor R23, transistor T5 and a capacitor C10 are connected in series between leads 68 and 69. A resistor R25 is connected across capacitor C10.

A Zener diode D13 and resistor R24 are connected in series between the collector of transistor T5 and the point between resistor R21 and capacitor C0. A resistor R20 is connected between lead 68 and the base of transistor T5.

A capacitor C0, transistor T4 and relay coil 71 are connected in series between leads 68 and 69. The base of transistor T4 is connected to capacitor C10.

The relay coil 71 controls a linkage 59. A wiper arm 72 is connected to the emitter of transistor T4 and forms a part of potentiometer 73. This is the moisture control element and knob 14 is connected by shaft 74 to control the position of wiper arm 72. A switch 101 has its movable contact connected to lead 68 and moves between contacts 102 and 103. Contact 102 is connected to resistor R21 which has its other side connected to potentiometer 73. Contact 10'3 is connected to resistor R20 which has its other side connected to wiper arm 72. Switch 101 is controlled by relay 92 through linkage 96.

In operation, the speed of motor 21 is maintained so that optimum speed of tumbling occurs. The user places clothing or other articles vto be dried in the dryer and sets pointer 17 by knob 14 to the desired final moisture content of the articles. This sets Wiper arm 72 of potentiometer 73 to a particular resistance.

The door 13 is closed which closes door switch 31 and the start button 16 is momentarily depressed to engage contacts 32 and 37. Assume that the hold button is not depressed in this example. This supplied power to relay 38 which closes switches 36 and 39. Switch 39 supplies holding current to relay 38 through normally closed switch 44.

The heater will be energized through normally closed safety thermostat 33 and centrifugal switch 34 when the motor 21 comes up to speed.

Switch 39 also provides power on line 42 to a motor speed control circuit and a dry control circuit. Normally open thermostat switch 43 is open unless the temperature in the exhaust stack of the dryer reaches a high temperature as, for example, 110 F.

Both the motor speed control and the dryer control receive signals from the bridge circuit 62.

The motor 21 starts with normally closed centrifugal switch 49 allowing current to pass through the start winding 48 and start capacitor C. As the motor comes up to speed, switch 49 opens and the run winding 47 continues to energize the motor.

The tachometer 61 is driven by motor 21 through shaft 58. The tachometer induces a voltage in winding 63 which varies in frequency and magnitude with the speed of motor 21.

Bridge 62 includes thermistors 28 and 29 (see FIG. 4 for their mounting positions) and resistors R13 and R14. Resistor R13 has a lower resistance than resistor R14. When the dryer starts, the resistance of thermistors 28 and 29 are the same due to their resistance versus temperature curves being identical. Thus, at the initiation of the cycle, a signal voltage appears at point Q. Also, any time that the resistance of thermistor 28 approaches the resistance of thermistor 29, a signal voltage will appear at point Q because of the initial unbalance of the bridge. It should be remembered that the voltage magnitude at point Q of the bridge 62 depends on two factors, (l) the speed of motor 21 and (2) the temperature difference between thermistor 28 and 29.

The signal voltage at point Q is utilized to regulate the speed of motor 21 so that the tumbling pattern is maintained at an optimum. This signal controls the firing point of triac 51 which regulates power supplied to run winding 47 in the following manner:

Voltage for the motor speed control is supplied by line 42 through resistor R3. This is full wave rectified by bridge circuit 154. The full wave rectified A.C. then passes through a current limiting resistor R2 and is applied to iilter capacitor C3 whose output voltage is clipped by Zener diode D6.

Capacitor C3 has a small capacitance so that it does not maintain a set level of ripplefree D.C. voltage on line 54. Instead, this voltage rises and falls, giving a generally clipped full wave signal, as shown by curve 78 above line 54. This is important because triac 51 must be red at a controlled point in each half cycle of A.C. power and the firing point must be synchronized to power on the A.C. line.

Wiper arm 65 is set on resistor R12 to preset a desired voltage. This voltage is half wave rectified by diode D14 and furnished to lter capacitor C4. The voltage across capacitor C4 is thus proportional to the signal voltage at point Q.

The voltage on capacitor C4 supplies base drive to transistor T2.

If the signal voltage at point Q is high, transistor T2 will be driven into saturation and the voltage appearing at its collector will be low. Thus, current passing through resistor R8 each time the voltage rises at point Q is shunted to ground through transistor T2 and does not pass through diode D7 to capacitor C11. All charge current to capacitor C11 must pass through resistor R7. Resistor R7 is set such that the voltage level on capacitor C11 builds at a slow rate. At a predetermined level, the voltage on capacitor C11 res unijunction transistor T6 and the charge dumps from capacitor C11 through transistor T6 and resistor R6. This creates a voltage drop across resistor RG which biases switching transistor T10 on. A current pulse is then drawn through the primary 57 of pulse transformer T1. This generates a pulse across the secondary 53 of the pulse transformer T1 and triac 51 is tired through diode D1. Once triac 51 fires, power is delivered to the motors run winding 47. Note that a high magnitude of signal voltage at point Q results in delayed tiring of triac 51 and motor 21 is caused to run at a low speed.

If the output voltage at point Q is low (which is the case when bridge 62 is balanced due to thermistor 29 being hotter than thermistor 28 thereby insuring that its resistance is lower than thermistor 28, or when the motor is rotating slowly causing tachometer 61 to generate a low voltage) capacitor C4 will have a low voltage appearing across it. This biases transistor T2 to a nonconductive state and current passes to capacitor C11 via resistor R8 and diode D7, as well as through resistor R7. This insures that unijunction transistor T6 is tired early in each half cycle and thus triac 51 fires early in each half cycle. The motor 21 now runs at a higher rate of speed due to the increased power supplied to run winding 47. In summary, with signal voltage low at point Q, the motor runs at a relatively high rate of speed.

As shown in FIG. 4, it is to be noted that the tumble pattern of the clothing should follow a trajectory lying somewhere between the rows X and Y. The control circuit of this invention assures this in the following manner. When the drying cycle is initiated, thermistors 28 and 29, are, of course, at equal temperatures. This causes the bridge 62 to be unbalanced and the output at point Q tends to be high due to the effect of the thermistors. This effect alone would tend to slow the motor down and the clothing would be expected to follow the arrow Z. However, with the clothing following the arrow Z, the motor is rotating at such a low speed that tachometer 61 applies a very small voltage to bridge 62. Although the thermistor bias tends to slow the motor down, the input to the bridge is so low that no appreciable signal appears at point Q. Thus, the motor control circuit applies firing pulses to triac 51 early in each half cycle of the A.C. line and motor 21 speeds up. The clothing is thus not allowed to follow the path of arrow Z simply because bridge 62 will be supplied with insufficient voltage to produce an output of any magnitude at point Q with the motor rotating at such a slow speed.

Assuming the motor is rotating at a higher speed, which causes the clothing to follow the trajectory of arrow X, both thermistors 28 and 29 are covered by the clothing. Thus, their temperature and resistance become equal. Due to the different resistance of resistors R13 and R14, a high signal voltage appears at point Q. Also, since motor speed is high, the magnitude of tachometer output is high causing the input to the bridge to be high. Thus, both bridge unbalance and high motor speed cause the output at point Q to be high. Capacitor C4 now charges to a high value and saturates transistor T2. This insures that the firing pulse delivered to triac 51 via pulse transformer T1 is delayed in each half cycle of A.C. line voltage, causing motor 21 to slow down. Thus, clothing no longer follows the path of the arrow X.

When the clothing follows the path of arrow Y, thermistor 28 is shielded from hot air passing through air outlet 24 while thermistor 29 receives hot air. This causes thermistor 29 to heat above thermistor 28 and its resistance value drops. Bridge 62 now tends toward balance and the output voltage at point Q decreases. The charge level on capacitor C4 decreases correspondingly and transistor T2 begins to go out of saturation. This allows earlier charging of capacitor C11 in each half cycle of A.C. line voltage and the triac 51 is fired earlier. Thus, the motor speed up. By this action, the clothing is caused to continuously oscillate in a band lying between arrows X and Y.

It should be noted that when clothing is lirst placed in the dryer, the drum speed for an optimum tumble pattern is different than the drum speed for an optimum tumble pattern near the end of the drying cycle after the clothing has nearly dried. It has been found that the average drum speed must increase as the cycle progresses to keep the clothin-g in the band defined by arrows X and Y. The speed control of this invention regulates the average drum speed such that it does increase throughout the cycle of operation thereby maintaining an optimum tumble pattern throughout the cycle. It is also noted that since the clothing is forced to oscillate in a band between arrows X and Y, any established tumbling patterns are broken up and the clothing is always placed directly in the path of the heated air. This not only assures minimum drying time but also assures that the clothing will not ball which would lead to overdrying of the outside of the load while the inside remained damp.

The dry control portion of the invention is shown in FIG. b. The voltage at point Q is also used to control the termination point of the drying cycle. Power on line 42 passes through the primary 64 of stepdown transformer T20 and appears on the secondary 66 at a reduced voltage. Bridge circuit 67 full wave rectifies the output of transformer T20 and applies it to a filter capacitor C5 via current limiting resistor R15. Zener diode D12 regulates the voltage across capacitor C5 to a DJC. level consistent with the ratings of components within the dry control circuitry.

Potentiometer 73 forms part of a voltage divider consisting of a fixed resistor R27, potentiometer 73, and relay coil 71. Thus, the initial setting of potentiometer wiper 72 determines the emitter voltage of transistor T4. Transistor T4 is connected in a regenerative fashion with transistor T5. lf a voltage of magnitude greater than the emitter voltage of transistor T1 appears at the base of transistor T4, it begins to conduct. This draws current from the base of transistor T5 which also begins conduction. As transistor T5 goes into conduction, the base drive to transistor T4 is reinforced and the pair of transistors cascade into conduction. When these two transistors become conductive, the drying cycle is terminated as described below.

The time when transistors T5 and T1 cascade into conduction is controlled by the signal voltage at point Q which is A.C. coupled to the base of transistor T2 via a resistor R and capacitor C12. As long as the clothing within the drum is damp, the motor speed control insures that it oscillates within the band defined by arrows X and Y. When clothing follows arrow Y, output at point Q is low and the voltage coupled to transistor T5 is correspondingly low. Thus, transistor T5 does not conduct and charge does not pass to capacitor C5 through resistor R22. When clothing follows the path of arrow X, output at point Q causes transistor T2 to conduct and charge begins to accumulate on capacitor C8. However, as long as clothing within the drum is damp, it cools thermistor 28 when clothing follows arrow Y. This assures that the charge applied to capacitor C8 while the clothing follows arrow X -is bled away from the capacitor while the clothing follows arrow Y.

This alternate charging and discharging of capacitor C8 does not allow the voltage at point U to rise to a level exceeding the 'Zener voltage of Zener diode D12 and thus current does not pass through Zener diode D12 and resistor Rm to circuit point V. This assures that with damp clothing in the dryers drum, transistors T4 and T5 are not cascaded into conduction. However, as the clothing begins to dry, thermistor 28 is not cooled by clothing following arrow Y and the resistance of the two thermistors begins to equalize. Now the signal voltage at point Q remains at a high level for an extended period of time. This signal voltage is continuously coupled to transistor T3 and it remains conductive on a continuous basis. Thus,

the charge level on capacitor C3 builds until it rises above the Zener voltage of Zener diode D12. Current now passes to circuit point V and transistors T4 and T5 cascade into conduction. The amount of current which must be supplied at point V to cascade the two transistors is determined by the emitter bias on transistor T4 which is, of course, preset by potentiometer 73. This permits the termination point of the drying cycle to be varied by potentiometer 73 and thus the nal moisture retention of the clothing may be varied.

When transistor T4 and T5 cascade into conduction, relay coil 71 is energized, thereby opening switch 44 and breaking power to relay coil 38. When relay coil 38 drops out, contacts 36 and 39 open. This breaks power to the machines heater 10. However, note that normally open cool-down thermostat 43 has closed during the drying cycle since the exhaust stack temperature has risen. Power continues to be supplied through thermostat 43 to line 42. This keeps motor 21 running until the exhaust stack temperature drops far enough for thermostat 4,3 to open, whereupon the cycle of operation is terminated and the clothes may be removed from the machine.

If at initiation of the cycle of operation the housewife depresses hold button 81 after depressing start button 16, the dryer operates until a predetermined moisture retention is reached (for example, 25%). The dryer will disconnect power to the heater and drop the drum speed to a slower speed (for example, 39 rpm.) and continue to operate under these conditions until the housewife returns and presses the finish button 82. The dryer will then reapply power to the heater 10 and will increase the drum speed until the moisture content set by knob 14 is reached. The dryer then turns off and the clothes may be removed.

Hold button 81 closes switch 86 which applies power to hold relay 92 which closes switches 93, 94 and moves switch 101 so that it engages contact 1013. Relay switch 93 energizes relay 92 through contact 89, switch 16 and contact 32. Switch 94 bridges thermostat 43 and power is supplied to line 42. Switch 101 puts resistor R28 into the dry control circuitry. Resistor R22 assures that relay 71 will be energized when the moisture content reaches the desired hold level (for example 25%). The motor control and dry control operate as previously described except the cut-olf point for the dry control is determined by resistor R28.

When the articles in the dryer reach the moisture content of 25 for example, relay 71 is energized. This opens switch 44 and relay 38 drops out. This opens switches 36 and 39. Power is thus terminated to the heater 10. However, since relay switch 94 is closed due to energization of relay 92, power continues to be supplied to line 42 indefinitely. Since the heaters have been cut off, the operating characteristics of thermistors 28 and 29 Slow the motor 21 to a speed of about 39 r.p.m.

When the housewife returns and wishes to complete the drying cycle she pushes finish button 82. This button is connected to switch 16 and disconnects contacts 32 and 89 and connects contacts 32 and 37. This energizes relay 38 and de-energizes relay 92.

Relay 38 initiates the drying cycle as described under the condition where the hold button had not been depressed and the dryer operates until the moisture content set by knob 14 is reached at which time the relay 71 is energized and the dryer is turned off as previouslyv described.

The hold cycle could also be modied by adding a timer which would move switch 16 a preset time after the hold condition had been reached. This would insure that the dryer could not operate indenitely in the hold mode should the housewife forget to initiate termination of the cycle.

Thus, it is seen that this invention provides a hold circuit for a dryer which allows a user to selectively hold 9 the articles being dried at a preset moisture level until it is desired to finish the drying cycle.

The principles of the invention explained in connection with the specific exemplications thereon will suggest many other applications and modications of the same.

It should be understood that we wish to embody within the scope of the patent warranted hereon all such modilications as may reasonably and properly come within the scope of our contribution to the art.

The embodiments of the invention in which an exclusive property or privilege is claimed are delined as follows:

1. A hold circuit for a dryer having a heater and a motor for operating the dryer, a motor control circuit, a moisture detecting means responsive to a tirst predetermined moisture level and to a second variable moisture level, selectively operable control means connected in circuit with the heater and receiving an input from the moisture detecting means to interrupt the drying cycle by reenergizing the heater at said first moisture level while the motor continues to be energized and means operable to reenergize the heater to complete the drying cycle at said second moisture level.

2. A circuit according to claim 1 wherein said motor is a variable speed motor and the control means is connected in circuit with the motor control circuit to control the speed of the motor to a standard hold speed.

3. A circuit according to claim 1 wherein the control means comprises a hold switch, a hold relay connected in circuit with the hold switch, a motor energize hold switch connected in circuit with the motor control circuit and controlled by the hold relay, a heater control circuit 10 including a heater control switch, and the hold relay connected to control the heater control switch.

4. A circuit according to claim 3 having a moisture control circuit forming a portion of the moisture detecting means, normal and hold moisture setting means in the moisture control circuit, a moisture switch connected to the normal and hold lmoisture setting means and controlled by the hold relay to connect the hold moisture setting means in circuit when the hold switch has been closed.

5. A circuit according to claim 4 having a nish control, the finish control connected in circuit with the hold relay to de-energize it and connect the normal moisture setting means in circuit to reenergize the heater.

6. A circuit according to claim 5 wherein the nish switch de-energizes the hold relay, energizes the heater, opens the motor energize hold switch, and connects the normal moisture setting means in circuit with the motor control circuit.

7. A circuit according to claim 6 wherein the control means is connected in circuit with the heater and the motor control circuit to turn them olf when a predetermined moisture level has been reached after the iinish control has been energized.

References Cited UNITED STATES PATENTS 3,253,347 5/ 1966 Kripke 34-46 3,286,359 11/1966 Orr et al. 34-53 3,460,267 8/ 1969 Lorenz 34-45 EDWARD I. MICHAEL, Primary Examiner

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