US 3521377 A
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Description (OCR text may contain errors)
Jill 21, 1970 v A, NIEWYK ETAL 3,521,371
I DRYER CONTROL SYSTEM Q 2 Sheets-Sheet 1 Filed May 31, 1968 R 1 INVENTOR B9%% I ATTORNEYS July 21, 1970 NlEwYK ET AL DRYER CONTROL SYSTEM 2 Sheets-Sheet 2 Filed May 31. 1968 Y M M //o (00L D0 WA! IN VENTOR Gav/m0 JAM (E lax m! Q4 g ATTORNEYS I I "United States Patent O 3,521,377 DRYER CONTROL SYSTEM Anthony Niewyk, St. Joseph, and Donald E. Janke, Benton Harbor, Mich., assignors to Whirlpool Corporation, Benton Harbor, Mich., a corporation of Delaware Filed May 31, 1968, Ser. No. 733,647
Int. Cl. F26b 19/00 US. Cl. 34-53 24 Claims ABSTRACT OF THE DISCLOSURE A dryer control system which utilizes moisture sensing electrodes and which has a dryness selector switch located in a low impedance portion of the electrical circuit, is disclosed. The dryer may be operated with either a time cycle or an automatic cycle so that the dryer may be operated with a plurality of settings to obtain varying degrees of dryness as determined by a dryness selector switch.
BACKGROUND OF THE INVENTION Field of the invention This invention relates in general to control circuits for dryers and in particular to electronic dryer controls which utilize moisture sensing electrodes and timer motors.
Description of the prior art A number of dryness controls in the prior art utilize capacitors with shunt moisture sensing probes which contact fabric being dried in a dryer. The resistance of the fabric varies as a function of its moisture content and the capacitor is charged through a resistor which is in series with it and is discharged through moisture sensing electrodes and the fabric which engages the electrodes. When the voltage developed across the capacitor reaches a predetermined value, the termination of the operating cycle of the dryer is initiated and thus, it the tumble pattern of the fabric prevents the fabric from touching the moisture sensing probes for a long enough period, pre mature termination of the drying cycle may result. The prior art illustrates a number of electronic dryness controls in which the dryness setting is selected by varying the resistor in series with the capacitor-moisture electrode combination. Since the value of this resistor must be very high, the switch used for varying the resistance must be of a very high quality so that current leakage through the switch is maintained below a minimum level. Such selector switches are very expensive.
SUMMARY OF THE INVENTION The present invention comprises a dryness control for a fabric dryer which has a timer motor controlled by moisture sensing electrodes connected in a parallel arrangement with a capacitor. An electronic gate as, for example, a silicon controlled rectifier is connected to the timer motor and is gated by a neon connected across the capacitor. A plurality of switches controlled by the timer motor progressively vary the resistance in series with a capacitor to adjust its time constant and thereby cycle the timer motor on and off. The electronic dryness control of this invention allows switching to be made at a low impedance point of the circuit so as to reduce current leakage. The dryer may have either a time cycle or an automatic cycle and premature termination of the dryer cycle is prevented by the circuit of this invention.
Otheh objects, features and advantages of the present invention will be readily apparent from the following detailed description of certain preferred embodiments ice thereof taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram for a dryer incorporating the invention;
FIG. 2 is a switching diagram for the control switch of the invention;
1316. 3 illustrates the control switch of the invention; an
FIG. 4 is a program chart for the dryer control.
DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates the wiring diagram for an electric dryer and shows input power leads L and L and neutral lead N. The main motor 51 has one terminal connected to the neutral lead N and has a run winding 52 and a start winding 53. A centrifugal switch 54 is connected between the run winding and start winding, as shown. The run winding is connected to a push-to-start switch 56 which is connected to a door switch 57 that is in turn connected to the power lead L A switch 3 is connected between switch 57 and switch 54 and is actuated by a cam 58 that is driven by the timer motor. The timer motor is designated by the numeral 59 and is in parallel with a diode 62. A diode 63 is connected between lead 64 of the timer motor and lead 61, which is connected to the run winding of motor 51. A diode 66 is connected to the diode 63 and to a resistor R A resistor R is connected between the resistor R and the second lead 67 of timer motor 59. A resistor R is connected from lead 67 through a diode 69 which has its opposite side connected to a capacitor C The other side of the capacitor C is connected to lead 68 which is connected to the neutral power lead N. An electronic gate 71 which might be, for example, a silicon controlled rectifier is connected between leads 67 and 68 and has its control electrode 72 connected to resistors R and R The other side of resistor R is connected to lead 68 and the other side of resistor R is connected to a neon 73 which is connected to lead 74 and a junction between diode 69 and capacitor C A capacitor C is connected between resistor R and lead 68 and is in parallel with a resistor R and a Zener diode 76. A lead 77 is connected to the junction point between the resistor R and the Zener diode 76. Lead L is connected to a heater 78 which is connected to a switch 2 that is controlled by cam 79. The other side of switch 2 is con nected to lead 61 It is to be realized that the heater element 78 may be replaced by a gas valve and associated apparatus in a gas operated dryer. Switch 4 has one side connected to lead 68 and the other side connected to lead 67. A rotating contact 81 of a manual selector switch, designated generally as numeral 82 in FIG. 3, is connected to lead 67 by wiper contact 83. Rotary contact 81 of switch 82 is engageable with switches 5, 6, 7, 8, 9, 10 and 11, which have their opposite contacts connected to the lead 68. Cams 84-91 respectively engage the contacts of switches 4-11 to actuate them. These cams are on the output shaft of the timer motor 59. Switches 12, 13 and 14 are connected to lead 74 and are operable by cams 92, 93 and 94 which are also driven by the timer motor 59. The switch 12 is connected to resistor R which has its opposite side connected to lead 77. The switch 13 is connected to resistor R which has its opposite side connected to lead 77. The switch 14 is connected to lead 77. A plurality of resistors R R R R R and R are connected in series between lead 77 and a switch 20 which has its opposite side connected to a contact bus 96. A switch 19 is connected between the junction point between resistors R and R and bus 96. A switch 18 is connected between resistors R and R and bus 96. A
switch 17 is connected between resistors R and R and bus 96, and a switch 16 is connected between resistors R and R and bus 96. A switch 15 is connected between resistors R and R and bus 96. Cams 97-102 respectively engage switch contacts of switches 15-20 and are mounted on the output shaft of the timer motor 59. A pair of moisture sensing electrodes 103 and 104 are connected between the ground of the chassis and a resistor R The other side of resistor R is connected to a switch 21 which has its other terminal connected to the bus 96 A cam 106 controls switch 21 and is mounted on the output shaft of the timer motor 59.
FIG. 3 illustrates the switch 82. The rotary contact 81 of switch 82 has a position indicia 107 which may be read against position indicating numerals 108 mounted about the switch 82. The contacts for switch 82 are represented by indicia 109. It is to be noted that the wiper contact 83 always engages the contact 83 and that the rotary contact 81 may be rotated to various selected positions to connect various ones of switches -11 to wiper contact 83.
FIG. 2 illutrates the switching sequence for the switch 82. Contact 1, for example, is connected to switch 5, contact 2 is connected to switch 6, contact 3 is connected to switch 7, contact 4 is connected to switch 8, contact 5 is connected to switch 9, contact -:6 is connected to switch and contact 12 is connected to switch 11, as shown in FIG. 3. As shown in FIG. 2, in position 1, contact 7 is connected to contact 12. In position 2, contacts 1 and 7 are connected to contact 12. In position 3, contacts 1 and 2 and 7 are connected to contact 12, etc. Thus, for each of the 12 positions of the rotary switch 82 different contacts of the switch will be connected together, as shown in FIG. 2.
FIG. 4 illustrates a program chart for the dryer control system of this invention, and it is to be noted that it is divided into five portions. The. first portion exists when the dryer is off and is designated by numeral 117. The next portion of the program chart is designated by the numeral 118 and is labeled automatic dry. The third portion of the program chart is labeled timed dry and is designated by the numeral 119. The next portion is labeled cooldown and is designated by the. numeral 110, and the fifth portion is labeled runout and is designated by the numeral 111. The switches 2-21 are illustrated on the left portion of the program chaIt.
When the rotor 81 of switch '82 is set to a selected position, as shown in FIG. 2, various contacts of the switch will be connected together. As shown in FIG. 2, for the particular embodiment illustrated, there are positions of the rotor 81 which produce twelve different combinations of electrical contacts. The cycle of the machine is broken down into automatic or timed with six of the cycles being automatic corresponding to positions 1-6 and six of the cycles being timed corresponding with positions 7-12. For example, position 9 results in a forty minute timed drying cycle whereas position 4 corresponds to an automatic control cycle corresponding to a particular dryness of the fabric within the dryer.
By way of illustration, the operation of an automatic dry cycle. will be described. For example, if rotor 81 of switch 82 is moved to the position 3, the No. 3 setting in the automatic dry cycle will result. As shown in FIG. 2, contacts 1, 2, 7 and 12 of switch 82 will be electrically connected together by the rotor 81. As shown in FIG. 4, note that in the off position, only switch 14 is closed. The switch 57 is closed when the door of the dryer is closed and the machine may be started by pushing switch 56. This will energize start and run windings 52 and 53 of motor 51 and will also energize the program control circuitry through the diode 63. The diode 66, resistor R capacitor C resistor R and the Zener diode 76 comprise a regulated DC power supply. The capacitor C will be charged from this DC power supply through switch 14 which, as shown in FIG. 4, is closed at this time. Since there is no resistance in the charging circuit, the capacitor C will charge very quickly. At a predetermined voltage across the capacitor C the neon 73 will fire and turn on the SCR 71. The motor 59 will therefore be energized and will begin to rotate thereby advancing the cams which control switches 2-21. The switch 3 will therefore be closed by cam 58 and as the motor 51 begins to run, the centrifugal switch 54 will disconnect the start winding 53 and connect the nun winding through the switch 3 to the power supply. Thus, as long as motor 51 continues to run, the control circuit will be. energized. The heater 78 is energized by the closing of switch 2, as shown in FIG. 4. Notice also that switch 4 has been closed. Switch 4 shunts the SCR 71 and turns it off. However, motor 59 continues to be energized through switch 4 until switch 4 opens. Thus, the motor 59 drives the cam 84 until the switch 4 opens. Simultaneously, as shown in FIG. 4, cam 97 closes switch 15 and cam 106 closes switch 21. The capacitor C will then begin to charge through the resistor R Sensor probes 103 and 104 shunt the capacitor C so that the capacitor is prevented from charging until the clothes bridging the sensors are dry. When the fabric bridging the sensors 103 and 104 are dry enough to allow the voltage on the capacitor C to reach the breakdown voltage of the. neon 73, the SCR 71 will be turned on again and motor 59 will again be energized. The motor will drive cam to close switch 5, as shown in FIG. 4, which will again turn off the SCR 71. The motor 59 will continue to rotate until switch 5 opens. At this time switch 16 will have closed so that now the capacitor C can charge through the series combination of resistors R and R After the SCR 71 has fired again, the motor 59 will commence to run and switch 6 will close.
Thus, the motor 59 will continue to run until the switch 6 opens again. At this time switch 17 will have been closed by cam 99 and capacitor C will be charged through the series combination of resistors R R and R Thus, each time the motor 59 advances, one more resistor is added to the charging circuit. This means that the resistance shunting the capacitor C will need to be higher in order to allow the capacitor C to charge up. Thus, the fabric will have to dry a little more each time before the capacitor C is charged up. After the capacitor C has charged through switch 17, SCR 71 will be turned on thereby allowing motor 59 to rotate. This will cause switch 7 to close. However, it is to be observed from FIGS. 2 and 3 that in the position 3 of rotor 81 the switch 7 is not connected to the rotating contact 81 and thus the SCR 71 will not be shunted out at this time. Therefore, the SCR 71 will remain on until switch 11 closes in the timed dry interval. Notice from FIGS. 2 and 3 that contact 12 which is connected to switch 11 is contacted by the rotating contact 81 in all of the automatic dry settings. Also notice, in FIG. 4, that switch 11 will remain closed throughout the timed dry cycle. Therefore, the motor 59 will continue to run until the cooldown portion hasbeen reached.
When the cooldown portion has been reached, switch 11 and switch 2 will open and switch 12 will close heater element 78 will therefore be deenergized. Capacitor C will then be allowed to charge through resistor R Notice at this time that the fabric is not shunting capacitor C because the switch 21 has been opened. After the neon 73 has been fired and the SCR 71 has been turned on, the motor 59 will begin to rotate thereby closing switch 4. Switch 4 will remain closed during the runout period and will keep motor 59 energized. When the off period is reached, switch 4 will be opened and so will switch 3. When switch 3 opens the, entire dryer circuit will be deenergized including the drive motor '51. I
If a timed dry cycle is selected by switch 82, the following operation will occur. Suppose, for example, that position 9 is selected by the rotary contact 81 of switch 82, contacts 3 to 7 will be connected together. Notice that in all of the timed dry settings that contact 6 which is connected to switch is always connected to the rotating contact 81. The. dryer is again started by depressing switch 56 and the circuit will be energized as described in the automatic cycle operation above. Switch 10 will be closed during the entire automatic dry cycle and motor 59 will continue to rotate until the timed dry portion has been reached. At this time switch 13 will have closed, as shown by FIG. 4. Notice also that throughout the timed dry portion the switch 21 will be opened so that the fabric in the dryer does not shunt capacitor C Capacitor C will charge through resistor R the SCR 71 will be turned on and the motor 59 will begin to rotate. Switch 9 will then close, thereby shorting out the SCR 71 and turning it ofif. The motor 59 will continue to rotate until the switch 9 opens. The capacitor C will again be charged through the resistor R The SCR 71 will be turned on again and the motor 59 will continue to rotate. The switch 8 will then close turning off SCR 71. Motor 59 will continue to rotate, until switch 8 opens.
The capacitor C will then charge through the resistor R again, the SCR 71 will be turned on again and the motor 59 will begin to rotate. The switch 7 will be closed at this time thereby turning off the SCR 71. The motor 59 will continue to rotate until switch 7 opens. At this time capacitor C will charge through the resistor R again. The SCR will be turned on and the motor 59 will again begin to rotate, and switch 6 will be closed. It is to be observed from FIGS. 2 and 3 that switch 6 is connected to contact 2. When the rotor 81 of switch 82 is in position 9, contact 2 will not be connected to the rotor 81. Therefore, no shunt will be provided for the SCR 71 and it will remain on and the motor '59 will continue to rotate throughout the remaining portion of the timed dry cycle. When switch 4 closes, the SCR 71 will be turned off but motor 59 will continue to rotate until the switch 4 opens at the beginning of the cooldown cycle 110. The operation of the cooldown anl runout portions of the timed dry cycle will be the same as described above with respect to the automatic cycle operation.
The diode 69 and resistor R insure complete discharge of capacitor C every time the'SCR 71 is turned on. Diode 62 is a commutating diode which prevents the SCR 71 from turning on due to the inductive voltage spikes which occur when power to the cam drive timer motor 59 is interrupted. Resistor R insures that the SCR 71 will remain on during the negative portion of the AC voltage.
In the particular circuit configuration illustrated in FIG. 1, the motor 59 operates from a half wave voltage supply. However, if a triac or other bilateral device were used in place of the SCR 71, the motor 59 could be operated from a full wave supply.
It is also to be noted that the dryness selector switch shown in FIG. 3 is not connected in the charging circuit of the capacitor C so that the electrical curren leakage is considerably reduced.
Although the preferred embodiment illustrated in the figures utilizes cam control switches, it is to be realized that the motor 59 may be connected to a switch of the rotary type. Such switch might be constructed from circuit boards, for example. Thus, various equivalents of the cam actuated switches are known to those skilled in the art and will not be described in detail.
Although minor modifications might be suggested by those versed in the art, it should be understood that we wish to embody within the scope of'the patent warranted hereon all such modifications as 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 defined as follows:
1. A control circuit for laundry appliance having a timer motor comprising,
an electronic switch with a gate electrode in circuit with the motor,
shorting means connected in parallel with said electronic switch, and
a gate control circuit connected to the gate electrode of said electronic gate.
2. A control circuit according to claim 1 wherein said electronic switch is connected in series with said timer motor.
3. A control circuit according to claim 2 wherein said electronic switch is a silicon controlled rectifier.
4. A control circuit according to claim 3 wherein said shorting means connected in parallel with said electronic switch comprises a switch controllable by the timer motor.
5. A control circuit for a laundry appliance having a timer motor comprising,
a silicon controlled rectifier having a gate electrode and connected in series with the motor,
a first plurality of switches controllable by said motor connected in parallel with said silicon controlled rectifier, and a gate control circuit connected to the gate electrode of said silicon controlled rectifier.
6. A control circuit according to claim 5 comprising a first plurality of cams connected to the timer motor and respectively engageable with the first plurality of switches.
7. A control circuit according to claim 6 comprising a selector switch in circuit with said first plurality of switches to connect various combinations of said switches in the control circuit.
8. A control circuit according to claim 1 wherein said gate control circuit comprises a charging circuit.
9. A control circuit according to claim 8 comprising moisture sensing electrodes connected in parallel with at least a portion of said charging circuit to provide a discharge path.
10. A control circuit according to claim 8 wherein said charging circuit includes a capacitor.
11. A control circuit according to claim 9 including a resistor in series with said moisture sensing electrodes.
12. A control circuit for a laundry appliance having a timer motor comprising,
an electronic switch with a gate electrode in circuit with the motor,
from said charging circuit comprises a moisture sensingelectrode switch.
14. A control circuit according to claim 10 comprising a first charging resistor forming a portion of said charging circuit.
15. A control circuit for a laundry appliance having a timer motor comprising,
an electronic switch with a gate electrode in circuit with the motor, shorting means connected in parallel with said electronic switch, a gate control circuit comprising a charging circuit including a capacitor connected to the gate electrode of said electronic gate, and a plurality of parallel charging paths of varying resistance forming a portion of said charging circuit and a second plurality of switching means for selectively varying the resistance in said charging circuit by selectively connecting various ones of said parallel charging paths. 16. A control circuit according to claim 15 wherein said second plurality of switching means are controlled by said timer motor.
17. A control circuit according to claim 16 wherein one of said parallel charging paths comprises a plurality of resistors connected in series, a third plurality of switching means connected in circuit with said plurality of resistors to selectively place difierent resistors in circuit in the charging path, and said third plurality of switching means controlled by said timer motor.
18. The method of controlling a fabric dryer having a timer motor and an electronic switch in series therewith comprising the steps of gating on said electronic switch to energize the timer motor,
periodically shorting out said electronic switch to energize said timer motor while the electronic switch is olf, and
controlling the electronic gate with a charging circuit.
19. The method of claim 18 including discharging the charging circuit through moisture sensing electrodes.
20. A fabric dryer comprising,
a chamber for receiving fabrics to be dried, drying means arranged to cause evaporation of moisture from the fabrics,
means for tumbling fabrics in said chamber,
electrically operated sequence control means effective after a predetermined length of operation to terminate operation of said drying means,
a circuit providing control of said sequence control means by said conductors and including an electronic gate in circuit with said motor,
a shorting means connected in parallel with said electronic gate, and
a gate control circuit connected to the gate control electrode of said electronic gate.
21. A fabric dryer according to claim 20 comprising spaced conductors positioned to bridge fabrics tumbling in said chamber whereby said conductors are provided with a relatively low resistance electrical bridge when there is substantial moisture in fabrics bridging said conductors, a charging circuit connected in circuit with said spaced conductors and forming a portion of said gate control circuit, and impedance means in circuit with said charging circuit.
22. A fabric dryer according to claim 21 including means for varying the impedance of said impedance means 23. A fabric dryer comprising,
a chamber for receiving fabrics to be dried, drying means arranged to cause evaporation of moisture from the fabrics,
means for tumbling fabrics in said chamber,
spaced conductors positioned so as to bridge fabrics tumbling in said chamber,
a timer motor,
a silicon controlled rectifier connected in series with said timer motor,
a neon gate connected to the control electrode of said silicon controlled rectifier,
a capacitor connected to said neon gate,
means for shorting said silicon controlled rectifier comprising a plurality of switches in parallel with said silicon controlled rectifier,
a plurality of cams connected to said timer motor and engageable with said plurality of switches,
a manual selector switch for connecting selected combinations of said plurality of switches in circuit, means for charging said capacitor, and
means for selectively connecting said spaced conductors to said condenser.
24. A fabric dryer according to claim 23 wherein said means for charging said capacitor includes a second plurality of switches connected to said capacitor, a second plurality of cams engageable with said second plurality of switches and driven by said timer motor, and a plurality of impedances connected in circuit with said second plurality of switches to control the charging time of said capacitor.
References Cited UNITED STATES PATENTS 3,402,478 9/1968 Hetrick 3453 3,404,466 10/1968 Reid 34-53 JOHN J. CAMBY, Primary Examiner U.S. Cl. X.R. 34-45