US3088221A - Time comparator or drier control - Google Patents

Description

y 1963 N. J. PANSING ETAL 3,088,221

TIME COMPARATOR OR DRIER CONTROL Filed June 29, 1959 6 Sheets-Sheet 1 1/ /V 11 INVENTORS )7e/son J. P421593 Geo ye B. 10159 THf/R A TURNEY May 7, 1963 N. J. PANSING ETA]. 3,088,221

TIME COMPARATOR OR DRIER CONTROL Filed June 29, 1959 6 Sheets5heet 2 N INVENTORS )7e/so27 J. P0225112 ii: 3 Geo ye B. 105

May 7, -1983 N. J. PANSING ETAL TIME COMPARATOR OR DRIER CONTROL 6 Sheets-Sheet 3 Filed June 29, 1959 INVENTORS )7e/son J. P42751233 'eorye 5. [any *z 7' 51k ZTORNE May 7, 1963 Filed June 29, 1959 N. J. PANSING EIAL TIME COMPARATOR OR DRIER CONTROL 6 Sheets-Sheet 4 l j---m Q INVENTORS )7e/son J. an sigg 'eorqe 5. 10229 HEIR ATTORNEV May 7, 1963 N. J. PANSING ETAL TIME COMPARATOR oR DRIER CONTROL 6 Sheets-Sheet 5 Filed June 29, 1959 INVENTORS )7e/son J. Pansz'gq 6y Geogqe ,5. [039 f 111% firm/45 May 7, 1963 N. J. PANSING EI'AL TIME COMPARATOR OR DRIER CONTROL Filed June 29, 1959 6 Sheets-Sheet 6 )Ze/son J. Pansizzy G'earye 5. [any M TTORIVEY United States Patent 3,088,221 TIME COMPARATOR OR DRIER CONTROL Nelson J. Pansing and George B. Long, Dayton, Ohio, assignors to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed June 29, 1959, Ser. No. 823,7 63 16 Claims. (Cl. 34-45) This invention relates to a domestic appliance and more particularly to an improved clothes dryer.

Considerable effort has been expended in the art of domestic clothes dryers to obtain a drying system which will automatically terminate when the clothes are dried to the point at which they contain the proper amount of moistureneither under-dried nor over-dried. Close control of the end point dryness in a clothes dryer has not been solved in the prior art even though humidity sensing for such control has been tried. The difiiculty arises in the fact that a domestic clothes dryer is constantly confronted with loads of different size, different initial moisture content and difierent bulk. For instance, a clothes dryer may have placed therein a light or minimum load consisting of a few shirts or handkerchiefs. Since constant air fiow with constant heat input is utilized in current domestic dryers, an irregular load of this type is subjected to higher air flow and/or higher heat than is desirable for the moisture in the fabric. Consequently, this air flow will indicate an incorrect condition of dryness. Also, the seams and folded areas of the article of clothing dry more slowly than do the single thickness por tions. Thus, it should be seen that the dryness of a light load cannot be accurately sensed by the prior art devices.

Another irregular load for which a domestic dryer is frequently used is a bulky load wherein a densely woven fabric, such as a shag rug, is sought to be dried. Here, also, the moisture is given up very quickly from the exposed surfaces of the pile and the dryer air flow indicates a dry condition. This sensed dryness, however, is premature in that the deeper portions of the pile give up moisture much more slowly. The prior art is devoid of systems which solve this problem and provide an accurate dryness responsive system for such bulky loads. The best that the earlier teachings have offered is a dryer which will accommodate an average load, but leave the irregular light and bulky loads to happenstance. Drying is the removal of an evaporable liquid, usually water. Artificial drying is accomplished through the medium of hot air so that the evaporation may be produced at the boiling point in a saturated atmosphere, i.e. at a vapor pressure equal to the atmospheric pressure. With regard to the rate of evaporation, the moisture to be removed from materials exists either as free moisture, which evaporates in accordance with the normal liquid vapor pressure, or as hygroscopic moisture, where the normal vapor pressure is reduced by the absorptive efiect .of the material. The rate of evaporation of free moisture depends on (1) the vapor pressure of the moisture in the material corresponding to its temperature; (2) the vapor pressure of the moisture in the air corresponding .to its absolute humidity or dew-point temperature; and (3) the effective velocity of air over the material surface. For a given condition of atmosphere or air movement, the rate of evaporation is proportional to the dif- .-ference in vapor pressure between the liquid and the vapor of that liquid in the immediate vicinity. This law holds for any temperature of liquid above the dew-point of the surrounding air irrespective of the dry bulb temperature of the air.

In drying clothes it is desirable to remove only the free moisture from the clothing. If the drying cycle is terminated after this is done, the clothes are neither over- 3,088,221 Patented May 7., 1963 dried nor under-dried. If, however, the drying process is extended, the hygroscopic moisture will be removed from the fabric as well. The result of such over-drying gives rise to a fabric which is hard and rough. The fibers are brittle and the lubricity of the fabric is impaired. In some prior art dryers utilizing a conventional timer only, a rough estimate may 'be made by the operator of the drying time needed for any given load. Obviously, there is no assurance that the clothing will thus be correctly dried. "In other prior art devices, an air stream humidity sensing element is utilized and the cycle terminated when the sensing element indicates a predetermined condition of dryness. This, too, fails to compensate for loads of different size and type and cannot provide a drying system terminating at the proper point. Since the tumbling drum and other dryer components retain considerable heat when the humidity sensing element terminates the cycle, the clothing continues to dry and an over-drying condition results.

To overcome the above and other disadvantages of the prior art devices, the applicants have devised a drying system which automatically compensates for different type loads to reflect the proper rate of drying. The system further adds a periodic test period wherein the dryness of the fabric is tested in a reduced air supply for an accurate indication of its dryness condition. 'In this way, the applicants improved drying system anticipates the desired end point dryness of the fabric and terminates the drying cycle at this condition.

Accordingly, it is an object of this invention to provide in a dryer a reduced air flow preheat operation in advance of a drying cycle.

it is also an object of this invention to provide a control system for a clothes dryer which will assure maximum saturation of the dryer exhaust air.

It is another object of this invention to provide a fabric drying system wherein high heat is utilized during periods of high moisture content in the fabric and low heat during periods of low moisture content.

A further object of this invention is the provision of a humidity sensitive proper end point termination control arrangement for a drying cycle.

A still further object of this invention is the utilization of a test period in a clothes drying cycle Where air how is reduced to concentrate moisture, raise relative humidity and increase the accuracy of the humidity sensing control.

It is also an object of this invention to provide a drying control system wherein -a test or time delay period is incorporated to sense the drop in relative humidity in a given time to insure proper drying of both regular and irregular loads.

It is also an object of this invention to make the above test period automatically variable in accordance with the type of load to be dried.

Another object of this invention embodies the provision for reducing wattage input to the dryer during final stages of drying to tailor the heat input to the rate at which the clothing being dried can give up its moisture.

A more general object of this invention is to provide in a clothes dryer a termination control which will distinguish between different types of loads to insure proper dryer termination for each type load.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown.

In the drawings:

FIGURE 1 is a schematic pictorial representation of this invention;

FIGURE 2 is a sectional view of the timer of this invention;

FIGURE 3 is a sectional view taken along line 3-3 in FIGURE 2;

FIGURE 4 is a sectional view of the timer of this invention taken along line 1-4 in FIGURE 2;

FIGURE 5 is a fragmentary sectional view taken along line 55 in FIGURE 2 showing the speed changing mechanism of this timer in its normal or slow speed position; 7

FIGURE 6 is a fragmentary sectional view taken along line 55 in FIGURE 2 showing the timer speed changing mechanism in its test period or fast speed position;

FIGURE 7 is an elevational view of the timer speed changing mechanism and block-out pawl to show their operative relationship; and

FIGURE 8 is a graphic representation of a drying cycle for a regular or an irregular drying load.

With reference to FIGURE 1, the control system of this invention is suitable for use with a dryer 10 which encloses a rotatably mounted tumbler drum 12. The dryer 10 is housed in a cabinet 14 having a front loading access door 16, an air inlet 18 and an air outlet or discharge 20. Connecting the inlet 18, the tumbling drum 12 and the discharge or exhaust 20 in series flow relationship is a duct or air passage means 22. Disposed also in this series flow relationship is a heater 24 which may be energized "for either 118 volts or 236 volt operation. The air flow system of the dryer 10 is motivated by a blower or fan 26 powered by a motor or prime mover 28 which serves also to rotate the tumbling drum 12. The components of the dryer 10 described hereinabove are considered conventional and should not be construed as limitations on the application of the drying system to be described hereinafter.

To provide conventional safety features in the clothes dryer 10, a high limit thermostat 30 may be included to deenergize the heater 24 in situations of undue temperature rise. The normal temperature regulations for the tumbling drum 12 is provided by a thermostat 32 which opens and closes to maintain a predetermined temperature within the tumbling drum. A door switch 34 serves to deenergize the prime mover 28 during periods in which the access door 16 is opened. When the motor 28 is connected, it should be obvious that both the air flow system and the rotation of the tumbling drum 12 will be interrupted as well. Another possible safety device is a centrifugally actuated motor switch 36 which closes whenever motor 28 is in operation as a means for limiting operation of heater 24 to those times when the blower 26 is operative.

In general, the clothes dryers in the prior art have been terminated at the end of a predetermined timed cycle or have been terminated by a sensed sudden increase in dry bulb temperatures at the exhaust 20. This invention contemplates adding a humidity sensing element 38 which acts to close a switch 40 when the relative humidity of air passing through the duct 22 is equal to or below approximately 30% RH. On the other hand, a differential is included in the operation of the switch 40 so that the switch is open when the relative humidity is greater than or equal to approximately 40% It should be obvi ous, however, that the desired differential may be varied in accordance with a particular dryer application. The sensing element 38 per se and the means by which it actuates a control switch 40 form no part of this application.

It is not always desirable to have a full air flow through the dryer 10. During Warm-up, it is desirable to utilize the concentrated heat of the heating element 24 to raise cabinet and tumbling drum temperature quickly. Further, during the drying cycle, the efficiency of the dryer 10 is lowered whenever air exhausted through the outlet 20 is not in a saturated condition. That is, if the air passes over the moistened fabric in the tumbling drum at a faster rate than the moisture can be evaporated from the fabric, the air is discharged in a nonsaturated condiapparatus is to be successful.

tion. To provide for preheat, to eliminate discharge of unsaturated air and to aid in providing accurate humidity sensing by the element 39, a damper 42 is pivotally mounted in the duct 22. The damper 42 has an opened first position, as shown in solid line, and a closed second position, asshown in dotted line. The damper includes an aperture 44 so that a limited amount of air may pass through the damper when in its closed position. In general, it may be said that the components recited hereinabove are selectively actuated by a control device or timer 220 to accomplish the various objects of this invention as follows.

The dryer 10 may be utilized to dry different type loads and may be selectively controlled to adapt the dryer for the optimum drying of these different type loads. Generally speaking, a dryer is fashioned with three types of load. A regular load wherein a standard eight or nine pound collection of cotton clothes makes up the load to be dried. This generally consists of shirts, diapers, cotton dresses and dish towels. The regular load is the one load most frequently placed within the dryer and it is to this particular load that the prior art devices have been directed. The thinking in the art apparently has been that if you satisfactorily dry the clothes load most frequently encountered, the dryer is sufiiciently successful. However, with the increase in man-made fabrics not generally conducive to fiber absorption of moisture-and the use of the dryer to dry bulky loads of articles-shag rugs or heavy bath towels-there arises a sizeable number of loads which we shall call irregular hereinafter. These so called irregular loads must be properly dried also if the One type of irregular load is a light or small load wherein several shirts and handkerchiefs are thrown into the tumbling drum 12 to be quickly dried. Where the capacity of the dryer so completely exceeds the requirements of the job, the prior art has been unable to successfully control the dryer operation to meet this reduced load. Consequently, if a dryness sensing device was used, it sensed merely a permature condition of dryness. The reason is simply that the large surface area of an article of clothing, such as a shirt or handkerchief, will quickly give up its moisture; and the air passing thereover will falsely indicate a dry condition. However, the folds of the fabric being more dense still retain a quantity of moisture which must be removed before the article is truly dry. The characteristics of this type of light load also applies to the man-made fabrics wherein a single ply of fabric evaporates its surface moisture very quickly. Here again, the folds retain substantial moisture and, thus, limit the accuracy of any device sensing the dryness condition of dryer exhaust air.

Another type of irregular load is the bulky or dense load wherein articles, such as a shag rug, are sought to be dried. Here, a fabric such as cotton may be woven into a deep pile. During the course of a drying cycle, the

tumbling drum 12 will be rotated and the heated air 'quired to repeatedly program the dryer for additional drying.

Another way of setting forth the different load situations confronting a domestic dryer is to define the loads as to their rate of moisture withdrawal. In the normal or regular load, the heat input to the tumbling drum or to the dryer is balanced to the maximum rate of moisture withdrawal and the fabric making up this load dries uniformly. In the irregular load, however, the rate of drying is non-uniform. Where light loads are involved, the

mass of the article dries more quickly than the folds. In the bulky or dense loads the surface of the fabric dries more quickly than do the deeper portions of the pile. It is to these varying load situations and varying rates of drying that the control system of this invention is directed. Further, the system provides for a minimum waste of heat by insuring that all air exhausted from the dryer 10 is saturated. To accomplish these ends, the timer system described next following is adapted.

Referring again to FIGURE 1, the timer 220 is shown in schematic fashion. Included is a synchronous timer motor 50 driving a shaft 52 at a uniform speed. Connected to the drive shaft 52 is a speed changing mechanism 54 having an adjustable gear train (explained more fully hereinafter in connection with FIGURES and 6) which may be set to rotate a timer shaft 56 at a fast or test period speed or at a normal slow speed. This speed changer or transmission 54 also includes a neutral position for the gear train wherein the timer shaft 52 is disconnected from the timer shaft 56.

The particular automatic drying cycle of this invention is controlled by three cams carried on the timer shaft 56. An energization and drying cycle control cam 58 is fixed to shaft 56 and is effective to initiate a drying cycle when a cam surface 60 forces a power supply switch blade 62 and a contact 64 into engagement with a contact 66 on a drum drive motor and timer motor switch blade 68 and, sequentially, into a contact 70 on a heater and termination control switch blade '72. The cam 58 has a primary peripheral surface 74 which engages a follower 61 on the switch blade 62 throughout the drying cycle. Another stepped down cam portion 7 6 is included during the final portion of the drying cycle so that the heaters are positively deenergized for approximately ten minutes at the conclusion of the drying cycle. This period is devoted to a no-heat tumbling operation wherein the clothes are cooled to room temperature. The drying cycle is terminated when the follower 61 drops into a deenergized cam portion 78.

The timer shaft 56 has fixed thereto a second or minimum drying time or block-out cam 80. A first raised peripheral portion 82 is effective to override a premature sensing of dryness by the element 38. This situation occurs in the beginning of the drying cycle just after the cycle is initiated. At this point, the heaters 24 have not been energized sufficiently long to raise the clothing tem perature to the point where moisture will be given up. Thus, the air flowing through the duct 22 to the discharge 20 will indicate a dry condition and the sensing element 33 will prematurely attempt to terminate the drying cycle. To prevent such a premature sensing, a lockout pawl or follower 84 rides on the cam surface 82 for an initial period (approximately ten minutes) of the drying cycle while the relative humidity is building up and the dryer is preheating. Once the terminal point 86 of the cam surface 82 passes the pawl 34, the sensing element 38 is effective to set one of several test sensing periods on a third or test sensing period cam 88, as will be described more fully hereinafter.

Another functional surface of the block-out cam 80 is the lock reset cam surface 90, which engages pawl 84 prior to the initiation of each new drying cycle to force the pawl 84 downwardly against the upward bias of a spring 92. This prepares the timer for the preheat portion of the following cycle to prevent premature dryer termination, as just explained.

Lastly, the block-out cam 80 carries a four-minute con tact plate 94 which prescribes a minimum test sensing period on the test sensing cam 88, should none of the several test sensing periods be automatically selected. The contact plate 94 operates in conjunction with contacts 96 and 98 to complete a circuit to a test sensing period solenoid shown schematically at 104).

Most significant to the sensing period concept of this invention is the functioning of the test period cam 88 which is relatively rotatably mounted on the timer shaft 56 on a sleeve bearing 102. The cam 88 is comprised of a stop portion 104 and a serrated variable test period portion 106. For purposes of explanation, the serrated portion 166 can be considered as having a four-minute test period notch 108 at one end of its arcuate length and a twelve-minute test period notch 110 at the other end. In graduated steps between notches 108 and 110 are a plurality of similar notches which predetermine the duration of selected test periods between four minutes and twelve minutes. As aforesaid, the cam 88 is mounted relatively rotatably to the timer shaft 56 and will normally rotate with the shaft 56 due to a spring 112 wrapped around the shaft and connected at one end to a stud or rivet 113 on the cam 88 and at its other end to a cam stop member 114 which is fixed to the energization cam 58.

The function of the test sensing period cam 88 depends on the operation of a second pawl member 116 which is interconnected by a connecting piece or pawl carrier segment 122 with the first lock-out pawl member 84 and movable therewith. Restraining both pawls 84 and 116 is a dog lock portion 118 which actuates to release the pawl connector 122 in response to the energization of the solenoid 10th. The dog lock 118 may have a spring biased normal position overlying the pawl connector 122. This dog lock 118 may include schematically a cam surface 129 for resetting the pawls 116 and 84 beneath the dog lock 118 at the beginning of each drying cycle. It should be obvious that the pawls 84- and 116 move upwardly in response to the upward biasing effect of spring 92 if the dog lock 118 is removed from on top of the pawl connecting portion 122 and the blockout cam portion 82 is not engaged with pawl 84. Conversely, the timer is reset merely by rotating a users knob 132 clockwise. With this movement shaft 56 and cam 80 will be rotated until the lock reset cam surface forces the pawl 84 downwardly.

Pawl 116 and pawl connector 122 will follow, camming the dog lock 118 leftwardly until it again returns to overlying locking engagement with the pawl connector 122.

In accordance with conventional practice, a three-wire residential power supply 126 may be utilized wherein a power supply line L2 is connected to a contact 128 which is movable axially with the timer shaft 56. Cooperat ng with the contact 128 is a contact 130 which is engaged when the users knob 132 is pressed inwardly by an operator to initiate the drying cycle. This push-pull on-off switch is of conventional design.

After the knob 132 is pressed inwardly and rotated to the start position, the timing cycle is energized as follows. Power flows from L2 through the on-ofi contacts 128 and 130, the line 134, switch blade 62, contact 64, contact '66, timer motor switch blade 68, lines 135, 136, and the timer motor 50 to ground. With the energization of the timer motor 50, the motor shaft 52 will be rotated to drive a speed changing mechanism in the transmission 54. The structural details of this transmission will be described more fully hereinafter. Suffice it for the purposes of schematic representation to say that the transmission 54 has a speed changing lever or gear shift 138 which in a raised position 139, predetermines a slow or normal speed rotation for the timer shaft 56. At this point, it is also important to emphasize that the gear shift lever 138 is interconnected with the pawls 84 and 116 and is also actuated by the movement of solenoid 100. That is, with the dog lock 118 in blocking engagement with the pawl carrier segment or connector 122, the clutch 138 is retained in the slow speed position 139, as shown structurally in FIGURE 5, to be described hereinafter. The gear shift 138 also has a fast position, shown structurally in FIGURE 6 and schematically at 140. Intermediate the slow speed gear situation 139 (detailed in FIGURE 5) and the fast speed situation of 140 (detailed in FIGURE 6), there is an intermediate or neutral position 142 wherein the motor drive shaft 52 is disengaged from the timer shaft 56.

General Timer Operation At the beginning of a drying cycle (during dryer preheat and primary moisture evaporation) the timer shaft 56 is rotated at a slow speed with the speed changing mechanism or gear shift lever 138 in the gear situation of 139 (detailed in FIGURE This situation will continue for the first phase of the drying operation and prior to the time that the sensing element first senses a dry condition. After this first sensation of dryness, the speed changing lever 138 of transmission 54 is conditioned for the fast speed position 140 and/or the neutral position 7 142. Only during the cooling ofi period of the drying cycle will the speed changing mechanism 54 return to its slow speed operation, i.e. during the test sensing periods prescribed by the said first sensation of dryness and utilized thereafter by this invention, the timer motor 50 will be driving the timer shaft 56 at fast speed in a clockwise direction, or it will be disengaged therefrom to permit the shaft 56 a spring-biased counterclockwise return when the speed changing mechanism 54 has its gear shift lever 138 in the neutral position 142.

Preheat Operation-Regular Load With the manual rotation of the knob 132 to initiate a drying cycle, the follower 61 of the switch blade 62 will beraised by the cam surface 60 to a position on the cam a This energization will start the rotation of tumbling drum 12 and will drive the fan 26 recreate a circulation of air through the tumbling drum and the exhaust duct 22. Simultaneously, and from the switch blade contacts 64, 66 and '70, the heater 24 will be energized from line 148, the high limit safety thermostat 30, the temperature regulating thermostat 32, the heater 24, line 150, relay switch blade 152 of relay 151, the centrifugal motor switch 36 to the other side of the line L1. This places the heater 24 across 236 volts. The above energized circuit presents an instantaneous situation since the sensing element 38 and, more particularly, the sensing element switch 40, is placed in the circuit with the control solenoid 100 from the main switch blade contacts 64, 66 and 70, through line 148, line 154, the sensing element switch blade 40, line 156, line 158, and the solenoid 100 to ground. The first rush of air through the duct 22 is below approximately 30% relative humidity and the sensing element 38 momentarily senses a dry condition to close the switch 40. This closing of switch 40 serves to energize the solenoid 100 which simultaneously closes the damper 42, opens the relay switch 152 and closes the relay switch 153 and removes the dog lock 118 from blocking engagement with the pawl and speed changing carrier 122; However, during this initial phase of the drying cycle, the pawl 84 bears against the block-out portion 82 of the cam 80 and, thus, the removal of the dog lock 118 is ineffective. That is, the timer motor 50 continues to drive the shaft 56 at its normal slow speed and the pawls 84 and 116 are unable to move upwardly in response to the spring 92. As aforesaid, the interconnection between the gear shift lever 138 and the pawl carrier 122 prevents the movement of the lever 138 to its fast speed or neutral position. The reversal of switches 152 and 153 serves to connect the heater 24 across 118 volts instead of the 236 volts and, thus, the heater is energized from the switch blade contacts 64, 66, 70, through line 148, high limit switch 30, thermostat 32, one half of heater 24, line 160, relay switch blade 153 to ground. This energizes the heater 24 for low heat at the beginning of the drying cycle; It should again be emphasized that this is a situation of rather short duration which conditions the dryer for low heat and reduces air flow immediately after 'energization of the dryer to start a drying cycle. The rapid preheat occurring during vtive humidity curve has not seated in one of the the plate 94 wipes the contacts .118 prevents the lifting of the pawl reduced air flow stimulates the dryerto commence drying faster and more efliciently.

Normal Drying Operation-"Regular" Load Referring to both FIGURES l and 8, we will assume a regular load of laundry has been placed in the tumbling drum 12 to be dried. The graph in FIGURE 8 charts relative humidityas the ordinate against time as the abscissa. The drying curve followed by the regular load is shown as a dashed line. Thus, we see the drying cycle initiated in the neighborhood of 30% R.H. As aforesaid, instantaneously the solenoid 100 is energized, the damper 42 closed, and the heater 24 energized for low heat on 118 volts at approximately 1600 watts. The small aperture 44 in the damper 42 permits a reduced flow of air through the tumbling drum 12 and, thus, allows for a rapid preheat of the dryer structure and the wet clothing within the tumbling drum 12. This reduced air flow also prevents wasting heat by exhausting heated air from the exhaust opening 20 which has not been saturated by evaporated moisture from the still unheated wet regular load. Again, referring to the graph of FIG. -8, the relative humidity of the air flow passing the sensing element 38 is shown to increase rapidly from 30% to approximately R.H. in the first few minutes of dryer operation. (Between approximately 30% and 70% RH. the dashed line curve follows the same path as the solid line curve.) Although the damper was closed and the heat reduced instantaneously at the beginning of the cycle, the sensing element 38 soon senses the increased relative humidity and at the point 164 on the graph has indicated an exhaust air relative humidity of approximately 40% which is sufi'icient to deenergize the solenoid and, thus close the relay switch blade 152 to establish a 236- volt connection for the full heater 24 and high heat of 4400 watts, as well as opening the damper 42 for full air flow through the tumbling drum 12. This then establishes bling drum. During this normal period, the relative humidity curve of the exhaust air will rise until it reaches approximately 90%, at which point, a steady state drying condition occurs. This state will remain for a period of time until the bulk of the free moisture is removed from the clothing and the curve starts a descending relaportion 166. During this normal high air flow, high heat drying portion of the curve, the humidity sensing element 38 has maintained the switch 40 in an open condition and the solenoid 100 has been deenergized.

However, as the relative humidity of the drying regular clothes load reaches approximately 30% at control point 168 on the curve, the humidity sensing element 38 will close the switch 40 and the solenoid 100 will be energized 'to close the damper 42, switch the heater 24 for low heat and select the test sensing period adaptable to the type load being dried.

The timer of this invention includes another feature which effects a minimum four-minute test period should the notches 106 rotate completely past the pawl 116 before the first control point such as 168 is reached. Such an occurrence is more likely to occur with the ,regular" load in which case the control point for energizing the solenoid 100 is reached after a period in excess of the approximate IO-minute block-out arrangement by the portion 82 of cam 80. For this purpose, the block-out cam 80 includes a four-minute contact plate 94 which Will engage and connect the contacts 96, 98 if the pawl 116 notches 106 by the time that 96, 98. Note that the plate 94 is aligned with the contacts 96, 98 in the situation depicted in FIGURE 1 only, i.e. when the dog lock carrier 122. Once the solenoid 100 is energized at a control point after the minimum time block-out period controlled by cam portion 82, the entire pawl carrier 122 will raise and the contacts 96,

98, which are integral therewith, will be moved radially inwardly from the rotating path of the plate 94. This, of course, will negate the function of contacts 96, 98 and the test period will be predetermined in a natural manner with the pawl 116 in one of the best period notches 106 most indicative of the load being dried, and best suited to sense the dryness of the load.

Determination of Test Sensing Period-Regular Load As the solenoid 100 is energized, the dog lock 118 will be withdrawn from overlying the pawl carrier 112 and the pawls 84 and 116 will be free to move upwardly in response to the spring 92. Assuming a minimum time of about ten minutes has elapsed during the normal course of drying, the block-out portion 82 of cam 80 has moved out of blocking engagement with the pawl 84 and the pawl 116 moves upwardly to engage one of the notches 106. The speed with which the drying operation reaches the first solenoid energization (graph point 168) after the minimum time prescribed by the block-out portion 82 determines which of the notches 106 into which the pawl 116 will fall. The notch selected is indicative of the type load being dried and prescribed the duration of each successive test period. In the case of a regular load with approximately a normal amount of water retention (say eight-pound load with eight pounds of water), the cam 88 will have rotated with shaft 56 so that the pawl 116 overlies approximately the four-minute test period notch 108. At the instant solenoid 101] is energized, pawl 116 moves into the notch 108 and the cam 88 is locked in position. The timer shaft 56, together with the cams 58 and 80, will rotate relatively to the cam 88 during the balance of the drying cycle until the lock reset cam surface 9t? of cam 8t! releases pawl 116 from the selected notch or cam '88. Such release will occur only if the sensing element 38 does not register an exhaust air relative humidity greater than 40% during test period selected four minutes in case of the hypothetical regular load just mentioned. As referred to hereinbefore, the initial upward or locking movement of the pawl 116 also shifts the lever 138 of the speed changing mechanism to its fast position 140 and sets up a locking arrangement whereby the gear shift lever 138 may not again return to its slow speed position 139. On the graph in FIGURE 8, this situation is reached at the point 168 when the successive test period portion of the cycle is initiated.

Test Period Operation-Regular Load During the test period which is shown substantially etween the 30% and 40% relative humidity lines on the graph, the air flow and the heat are reduced. In view of the heat buildup in the tumbling drum 12, the relative humidity of the reduced c.f.m. exhaust air will start to increase along that portion 170 of the curve (FIGURE 8). If the regular load is not quite dry, the relative humidity will again increase to the actuating point of approximately 40% wherein the humidity sensing element 38 will cause the switch 40 to open, which will, in turn, deenergize the solenoid 100 and return the dryer 10 to full air flow with high heat. It should be recognized at this point that the drying load is approaching the proper dryness end point and the relative humidity will again start to fall along that portion of the curve 172. As the 30% RH. point is reached, the switch 40 will again close to indicate the lower limits of the test period and low heat low air flow will be reestablished. Again, the relative humidity will or may start to increase along the curve portion 174. But in this instance, there is not suflicient moisture left in the clothes under a low heat low air flow condition to attain the actuating point for the solenoid and relative humidity will reverse Within the test period and start falling along a curve 176 and the drying cycle will be terminated after the no-heat segment 76 of the cam 58 passes the follower 61. During the test period, the functioning of the timer motor 50, the speed changing mechanism 54, the cams 5S and 88, are as follows.

As aforesaid, the cam 88 is locked against further rotation at the beginning of the first test sensing period (point 168 in FIGURE 8). This is accomplished when the pawl 116 moves into a notch 106 in accordance with the time that it takes for the exhaust air relative humidity to reach approximately 30% RH. after the minimum initial time period controlled by block-out cam surface 82. This has been found to give an indication of the type load being driedregular or irregular. Where the moisture is given up uniformly throughout the entire load, the load is termed regular and, generally, a short or four-minute test period will suffice. To put it another way, a regular load approaches the proper end point dryness with a uniform rate of drying or moisture evaporation. Thus, a short test period is sufficient to indicate whether the load is truly dry. On the other hand, an irregular load does not have an even rate of drying and, thus, a longer test period with the pawl 116 in one of the notches 106 closer to the twelve-minute test period 110 is found desirable to insure a complete and proper drying end point for the irregular load. This irregular load will be described next following, but for the purposes of either a regular or irregular load, the drive mechanism will work as follows (see FIGURE 1). When the pawl 116 locks into a notch such as 168 in cam 88, a gear shift lever 138 will assume a position 144} and in accordance with an altered gear train in the speed changer 54, the shaft 56 will be rotated at a fast speed. This moves cam 58 and the cam stop 114 affixed thereto in a rotating movement, as shown by the arrow on cam 58. If the cam 58 reaches a point on the periphery of the drying cycle portion 74, the successive test periods will terminate and a no-heat cycle along cam surface 76 will be initiated just prior to the end of the drying cycle. Note that the stop portion 194 of test period cam 88 is located relative to drying cycle cam 58 and cam stop 114 in accordance with the particular notch 106 in which the pawl 116 is locked. This prescribes the test period duration since the amount of the peripheral edge 74 of the cycle cam 58 on which the follower 61 can operate is thus limited.

In a normal or regular load, cam 58 and, thus, cam stop 114 may rotate or oscillate back and forth several times limited in one direction by the point 180 of cam 58 and by the stop 104 of cam 88. Thus, the limits of the test period are defined. If the solenoid 100 is again deenergized to indicate the clothing is not quite dry before the point 180 of cam 58 is reached, the gear shift 138 will assume the neutral position 142, the drive shaft 52 will be disengaged from the timer shaft 56 and the spring 112 will force the cam 58 to rotate counterclockwise until the stop 114 strikes the cam protuberance 104. This may be repeated several times until the relative humidity of the exhaust air fails to rise to the approximately 40% RH. level prior to the time that the cam 58 reaches point 180, i.e. the end of the last test sensing period. In the last test sensing period also (curve portion 174 in FIG- URE 8) the solenoid 109 remains energized to close the damper 42 and condition the heater 24 for 118 volt low heat operation. As the follower 61 of the power supply switch blade 62 reaches the no-heat start point 180 on cam 58, power to the heater 24 and to the humidity sensing control system will be interrupted. Substantially, simultaneously the lock reset portion 96* of cam 80 will force the pawl carrier 1-22 downwardly and reconnect the timer motor driving shaft 52 to the timer shaft 56 for normal slow speed timing operation. Thus conditioned the timer cam 58 will program a no-heat portion of the drying cycle for approximately 10 minutes during which time the clothes are cooled to handling temperature. The drying cycle terminates when the follower 61 drops into cam portion 7 8, thereby deenergizing the entire dryer. In this way, the regular clothes load is properly dried 'user knob 132.

Preheat Operatinlrregular Load I With reference now to FIGURE '8 and, more particularly, the solid line graph thereon, the explanation of the drying cycle for such items as a shag rug will be clearly set forth. Atthe beginning of the drying cycle, the relative humidity of air circulating through the tumbling drum will be at room conditions. Similarly, the temperature of the dryer components will be approximately room temperature and the fabric placed within the tumbling drum will be approximately at that temperature at which the washing operation was terminated, assuming, of course, that the drying operation immediately follows the washing cycle. It is one of the objects of this invention to prevent wasting heat during the initial portion of the drying cycle. Since neither the shag rug nor the dryer components are up to drying temperatures, it is desirable to retain as much heat within the dryer 18 until such drying temperatures are reached. The humidity sensing element 38 maintains the switch 40 closed when the relative humidity of the exhaust air is somewhere below 30%. .It is believed that exhaust air with a relative humidity below thisfigure is substantially dry and not serving any drying purpose. As the cycle is initiated, the control solenoids 180 will be immediately energized from L2, contacts 128, 130, line 134, the power supply switch blade 62, contacts 64, 66 and 70, heater and control system switch blade 72, line 148, line 154, humidity sensing switch 40, line 156, line 158, solenoid 100 to ground. The energization of the solenoid 100 will reverse the switches of relay 151 closing the low heat relay switch 153 and opening the high heat relay switch 152. Simultaneously, the damper 142 will be moved to its dashed line closed position and the air flow through the tumbling drum reduced in accordance with the size of an aperture 44 in the damper 42. This aperture may be approximately one inch in diameter to allow a minimum air flow to pass the'sensing element 38. With the heater 24 thus energized, the temperatures within the dryer cabinet 14 will immediately rise. Prime mover or motor 28 is energized at this time from L2, contacts 128, 138, line 134, power supply switch blade 62, contacts '64, 66, drive motor switch blade 68, line 135, line 144, the door switch 34 and the motor 28 to ground. With the energization of motor 28, the blower 26 will be energized to induce a flow of air through the tumbling drum 12, which is now being rotated by the motor 28. This preheat operation or period is of rather 'short duration and terminates at point 164 on the irregular load graph of FIGURE 8. At this point, which occurs at approximately 40% relative humidity for the exhaust air in duct 22, the sensing element switch 40 will be opened to deenergize the solenoid 100 and the damper 42 will return to its open position and the relay 151 will be repositioned to energize the heater 24 for a high heat or 4400 watt input drying operation. This concludes the preheat operation and the irregular load advances into the normal drying operation.

Normal Drying Operation-Irregular Load During the short preheat period the fabric, in this case the shag rug, and the dryer components are brought up high heat high air flow drying is in line with the concept of this invention to insure maximum moisture content for any air exhausted from the dryer '10. Up to the point 164, no conclusion has been made by the timer of this invention to determine the type of load in the tumbling drum .12. During the preheat operation the solenoid 100 was energized to close the damper 42 and adjust the heaters .for low heat l600-watt operation. It will be noted on the schematic showing of FIGURE 1 that the energization of solenoid .100 will also remove a dog lock 118 from blocking engagement with a pawl carrier 122. But during this initial stage of the drying operation, we have not reached a stable drying condition and the type load cannot yet be accurately sensed. For this reason, an enlarged or block-out portion 82 is formed on the minimum test period or block-out cam to prevent the pawl 84 from moving upwardly. The pawl 116, being integrally formed with the pawl 84, also cannot move and the removal of the dog lock 118 during this initial drying phase is ineffectual to release the pawl carrier. Normally, also, the energization of solenoid serves to shift the clutch lever 138 in the speed changingmechanism 54. Even though it is not so shown in FIGURE 1, the gear shift lever 138 is interconnected with the pawl carrier 122 and is, thus, prevented from being shifted by the energization of the solenoid 100 during the preheat operation.

As cited immediately above, the normal portion of midity of the air exhausted will increase rapidly during this early portion 200 of the drying cycle. Due to the .bulk or dense construction of a heaving rug, the surface 'area thereof is comparatively small to the mass of the rug; Therefore, the air passing over the tumbling rug will quickly dry this surface and the relative humidity of the exhaust air will soon start decreasing along the irregular curve falling rate portion 202, thereby giving erroneously a sensation of dryness for the shag rug.

Determination of Test Sensing Periodlrregular Load It will be noted that this fallacions sensing of dryness in the dense shag rug comes earlier than the falling rate portion 166 of the regular load curve. Obviously, the humidity condition of the circulating air is not truly appraising the dryness of the bulky or shag rug load. Deep within the pile of the rug, most of the moisture still remains. However, this early falling rate curve is an indication of the type load being dried. Where such load happens to be a light load of man-made fabrics, the largest surface of such fabrics, will dry quickly, whereas the fold and seams retain moisture. This may be equated to the bulky or shag rug load wherein the surface area quickly dried leaving moisture still entrained deep within the pile of the article. The recognition of characteristics of irregular vs. regular loads in a drying cycle has led to one of the major concepts of this invention a timer'which can sense the type load being dried and then automatically make compensating adjustments to adapt a test sensing period to the particular drying load.

Mechanically and with reference to FIGURES 1 and 8, this is accomplished as follows for the hypothetical shag rug load. As the condition of exhaust air bypassing the sensing element 38 reaches a control point condition 204,

.the sensing element 38 reacts to close the switch 40. This spring 92. Depending on the length of time that has elapsed prior to reaching the control point condition 204, the pawl 116 will snap into one of the notches 106 of the rotating cam 88. As best seen in the graph of FIG- URE 8, it takes less time for the irregular load to reach its control point 204 than it does for the regular load to reach control point 168. Thus, it is proper to assume that the pawl 116 will fall into one of the notches 106 nearer to the twelve-minute test period notch 110. -With the upward movement of the pawl carrier 122 and the continued energization of the solenoid 100, the clutch lever 138 will be held in a fast speed position 140 and the dryer will be conditioned for a test period operation suitable for use with the particular fabric load being dried.

Test Period Operationlrregular Load Immediately after the control point 204 has been reached and the solenoid 100 energized, the test period operation of the instant drying cycle commences. These test periods will continue consecutively until the sensing element 38 fails to register an increase in exhaust air relative humidity during one of the test periods. At this point, the drying cycle will move into a no-heat operation prior to cycle termination.

In operation, the test period works as follows. As the condition of the exhaust air in duct 22 reaches the approximate 30% R. H. level (control point 204 of the graph), the sensing element switch 40 will close to energize the solenoid 100. The damper 42 will be closed and the heater 24 switched for low heat operation with switch 153 being closed and 152 opened. A reduced c.f.m. low heat air flow will, thus, be established with a minimum sensing quantity of air allowed to pass through the aperture 44 in the damper 42. This restricted air flow overcomes the fallacious indication of dryness evidenced by the rapidly falling rate curve portion 202. Since the shag rug is not truly dry and the moisture within the dense pile continues to be given off, the reduced air flow will increase in relative humidity and the drying curve will again increase along a curve portion 206. Simultaneously with the closing of the damper and the low heat adjustment for heater 24, the solenoid 100 serves to pull a gear shift lever 138 to establish a fast speed driving relationship between the timer motor 50 and the timer shaft 56. The mechanical structure of this gear shift mechanism will be set forth hereinafter in connection with FIGURES 6 and 7. Sufiice it to say that after the first test period is established at control point 204, the shaft 56 will be ro tated at fast speed along the curve portion 260 and will be disconnected from timer motor 50 along the curve portion 208 so that the next following test period may be reestablished. schematically, this is accomplished when the upward movement of pawl 116 locks the cam 88 against rotation. Since earns 53 and 80 are afiixed or keyed to the shaft 56, they will continue to rotate with shaft 56 at the fast speed programmed into the speed changing mechanism 54. As cam 58 rotates with the power supply follower 61 on cam portion 74, the integral cam stop 114 will be rotated as well. The spring 112, being connected both to the pawl-stopped cam 88 and to the cam stop 114, will wind itself around the cam shaft 56. Should the relative humidity sensed by the element 38 rise to the upper actuating point for switch 40 (equal to or above approximately 40% the switch 40 will open to deenergize the solenoid 100. The deenergization of the solenoid will again open the damper 42 and adjust the heater 24 for high heat operation. *It will also release the clutch lever 138 for return to a neutral position wherein the shaft 52 will be disengaged rom shaft 56 and the spring 112 will bias the cam 58 in a counterclockwise direction until the cam stop 114 engages the raised portion 104 on the fixed cam 88. At the completion of this spring biased return (along curve portion 208), another test sensing period is ready to begin.

During the spring biased return of cam 58 the dryer is again operating with high heat and high air flow and tends to entrain moisture from the shag rug faster than the rug can give up such moisture. Thus, again the rela tive humidity will fall quickly to the next following control point level, say 209 along the 30% RH. line and the solenoid will be again energized to initiate the second test sensing period which will be identical in duration with the first. The test sensing period continues with the fast driving relationship of cam 58 followed by a neutral driving relationship in which the cam returns to a test period start position. Throughout the consecutive test periods, the shag rug continues to give up its mois ture from its dense pile. Intermittently, along curve portions 206, the air flow is reduced as is the heat to minimize exhausting unsaturated hot air to the atmosphere. As the test periods continue, the effect of this invention is to increase the efficiency of the dryer by eliminating the waste of exhausting dry hot air. The system also maintains a close observation on the condition of the dense load being dried. This is to assure against overdrying wherein the fabric can become rough and the fibers brittle. After a period of time determined by the quantity of materials or rugs in the dryer, the last control point 210 will be arrived at. Hereto, the solenoid 100 will again be energized as the humidity sensing switch 40 is closed. The air flow will be again reduced and the heater input decreased from 4400 watts to 1600 watts. With the reduced air flow over the rug, there may be a period along the curve portion 212 wherein the moisture again starts to cause an increase in exhaust air relative humidity. However, the condition of the rug is so close to its true correct dry point that the relative humidity fails to rise to the switch 40 actuating point of approximately 40%. Consequently, the relative humidity of the reduced flow exhaust air tops out and starts to fall. It must be remembered that during the last test period, the solenoid 100 is continuously energized and the cam 53 is being rotated at a fast speed. If the follower 61 of the power supply switch blade 62 reaches the drop off point on the periphery of cam 58, the power supply will be broken between contacts 66 and 70 to deenergize the heater 24 and the humidity control system, thereby restoring full air flow. A no-heat portion of the cycle is, thus, initiated along the cam portion 76.

N0 Heat Operation-Irregular Load With the switch blade follower 61 on the no-heat cam portion 76, power is still directed to the drive motor 28 and the timer motor 50 through the contacts 64, 66. During the test sensing period, as related herein above, the shaft 56 has been driven at either a fast speed in a clockwise direction or is coasting in a counterclockwise position in response to the biasing effect of spring 112. During the final test period, as indicated along curve portion 212, for a bulky load, the reset portion 90 of the cam 30 will engage the block-out pawl 34. Thus, the pawl 84 is cammed downwardly against the upward bias of spring 92 to reset the pawl carrier 122 in its lower position. Since the gear shift lever 138' is integrally associated with the pawl carrier 122, the speed changing mechanism 54 will be reset to a slow driving relationship, as seen structurally in FIGURE 5. Once the lock reset point 90 engages the pawl 84 to reestablish the slow driving relationship of shaft 56, the test period is complete. Following this, the timer will move through a prescribed noheat course along the cam portion 76 until the follower 61 drops into the cam portion 78, shown in FIGURE With this action, power to the dryer motors 28 and 50 and to the timer control system is deenergized and the drying cycle completed.

The control system of this invention is designed to end the drying cycle while the material being dried retains a little moisture. It is known that relative humidity is a function of temperature as well as moisture. Thus, the clothes drying cycle is terminated with the fabric at a 15 slightly elevated temperature. This temperature will drop as the fabric reaches room temperature and the retained moisture will aid in giving the fabric the same relative humidity as its surrounding atmosphere. Another factor which must be consideretd is that the sensing element 38 is sensing a relative humidity of the circulating air and not the fabric itself. The slight retention of moisture in the fabric at the conclusion of this drying cycle will not be noticed when the fabric reaches an equilibrium condition with the surrounding atmosphere, i.e., the relative humidity or hygroscopic moisture retention of the fabric assumes a correct figure when the fabric is cooled. The fibers are neither brittle nor is the fabric rough when the proper drying termination occurs. Only the free moisture .is removed from the fabric and the hygroscopic moisture is retained. This is accomplished through the use of a test period technique, the duration of which is adapted to a particular clothes load and the repetitive nature of which serves to bracket in on the proper end point dryer termination.

The explanation set forth in connection with the regular load and the irregular load is believed to adequately define the concept of this invention to allow any one skilled in the art to design a timer in accordance with these inventive precepts. For purposes of clarity, and with reference to FIGURE 2, the applicants have embodied this design into a timer 220, wherein equivalent par-ts carry identical reference numerals to those used in 7 connection with FIGURE 1. The timer is comprised of a body portion 222 having a top wall portion 224, a bottom wall portion 226 and side walls 228 and 230. A

removable front plate 232 is fastened as at 234- to an open ,end 236 of the timer body 222. Similarly, a timer motor support plate 238 closes a rearward open end 240.

. Centrally located in the timer body 222 is a central partition 242 which separates the timer body into a speed changing or transmission chamber 54 and a cam actuated timing portion 244. A timer shaft 56 extends axially through the cam actuated timer chamber or compartment 244 and is journaled at 246 in an enlarged bearing portion of the central partition 242 and in an opening 248 in the front cover 232. The timer shaft 56 is adapted for limited axial movement to open and close the main line contacts 128 and 130, more clearly seen in FIGURES 3 and 4. To mechanically actuate the contact 128 into engagement with the contact 130, a contact carrier or support (FIGURES 3 and 4) 250 is formed with an actuating arm 252 which is engaged by the rearward surface 254 of the cam 80 when the shaft 56 is pushed inwardly. To provide for limited axial movement of the timer shaft 56, the shaft is bifurcated at 256 to receive a driving element 258 inserted therein. In accordance with conventional practice, the timer shaft 56 may include a rod 260 aflixed to the shaft for rotation therewith. A cam portion "262 formed on the front cover 232 will serve to cam theshaft 56 in an axially outward direction during final rotation of the shaft 56. This axially outward movement removes the biasing surface 254 of the cam 80 from the contact support plate 250 and the main line contacts 128 and 130 are disengaged.

The actuating cams for the timing mechanism of this invention are carried on the timer shaft 56 and adapted for axial movement therewith. The block-out cam 80 is aflixed to a support sleeve 264 which, in turn, is keyed or fastened in any suitable manner to the timer shaft 56.

The drying cycle cam 58 is loosely fitted over the shaft' 56 but is restrained against axial movement and extensive rotational movement by a cam retention bracket or disc 266. This bracket has several finger portions 268 WhlCh extend through an oversized opening 270 in the cam 258.

On the opposite' side of the cam 58 is another disc-like portion 272 having openings into which the finger portions 268 insert. Both the disc-like portion 272 and the bracket 266are secured to the timer shaft 56 and, thus,

limit the axial movement of the cam 58. Further, the

finger portions 268 in extending through the cam apertures 270 limit the relative rotational motion of the cam and provide for snap action of the contact switch blades 62, 68 and 72. As seen in FIGURE 2, it is possible to form one of the bracket fingers as at 274 with an extended terminal portion 114 to serve as the cam stop 114 which rests against the enlarged portion 104 of the cam 88.

Interposed between the generally shaft-fixed cams 58 and 80 is the test period determining cam 88' which is supported on and fixed to a bearing sleeve 102 relatively rotatably carried on the timer shaft 56. In FIGURE 2, it can be seen that raising the pawl 116 into engagement with one of the teeth 106 in cam 88 will aflix the cam 88 so that the shaft 56 and the cams 58 and 80 may continue to rotate relatively to the cam 88.

Reference may now be had to FIGURES 2, 5, 6 and 7 for a more particular description of the pawl carrier assembly of FIGURE 7 which provides for the interaction of pawls 84, 116, four minute minimum test period contacts 96, 98 and timer speed charging lever 138. Within the speed changing compartment 54 a pawl manipulating link 280 is pivotally mounted on a pin 282,

through partition 242, a washer 281 being interposed for ease of movement. The link 280 is biased by a spring For interconnecting the pawls 84 and 116 with the pawl manipulating link or lever 280 an aperture 288 is formed in the partition 242. A pin 290 extends through the.

aperture 288 and connects to the pawl manipulating link 280 as at 292. Thus, as the link 280 pivots about the point 282, the pin 290 will be moved up or down in an arcuate path. Rotatably mounted to the pin 290, as at 294, is a pawl lift link 296. This link 296 is fastened to the pawl support or carrier 122 which integrally connects the pawls 84, 116 :and the contacts 96, 98 for movement as one unit. With this relationship of parts, when the pawl actuating link 280 moves from the spring depressed position of FIGURE 5 to the raised or counterclockwise pivoted position of FIGURE 6, the rod 290, the lift link 296, and, thus, the pawls 84 and i116 raise as well. Of course, the final determining factor as to whether the pawls 84 and 116 will raise depends on the freedom of pawl 84 to move upwardly. This upward movement is made possible by the removal of the block-out portion 82 of cam 80 from biasing engagement with the pawl 84. It should now be seen (FIGURE 7) that the carrier 122 will be acted upon by the direct biasing effect of the spring 92 and the indirect biasing elfect of spring 284. These springs 92, 284 are effective to lift the pawls 84, 116 if the cam 80 is in the correct relationship to pawl 84. Another factor limiting the movement of the pawl actuating link 280 is a gear carrier support 300 which has an exmotor 50 through a motor shaft 52. Permanently interconnected with the gear 302 is a larger driving gear 304 carried on a shaft 306 which is journaled in the removable rear wall 238 and in the central partition 2 42. Also carried by the shaft 306 is an elongated driving gear 308 which rotates at the same speed as does gear 304. For the purpose of the two-speed driving arrangement of this invention, the pinion 302 and the driving gears 304 and 308 retain the same driving relationship for either slow speed or fast speed.

The two-speed arrangement of this timer is effected by the particular relationship of a gear carrier support plate 300 which is relatively pivotally mounted at 310 to the driving gear shaft 306. On the carrier support plate 300 V 17 is arranged a slow speed gear assembly 311 having an integrally formed large gear portion 312 and a small gear portion 313.

The assembly 311 is journalled in an opening 320 in the carrier plate 309. At the other side of .the gear carrier plate 30%) is an opening 318 which journals a fast speed gear 314.

Reference may now be had to FIGURE 7 for a more particular description of the motion of the gear carrier support plate 330. The carrier plate is formed with an aperture 318 in which the fast speed gear 314 is rotatably mounted and a slow speed aperture 326 in which the slow speed gear assembly 311 is carried. As explained hereinbefore, the plate 300 is ported at 310 to pivot about the shaft 366 and is controlled in its pivotal motion by the solenoid operated gear shift lever 138 which is hooked around a turned up portion 322 on the carrier plate 300. It should thus be seen that when the solenoid 1% is energized, the gear shift arm 138 will be drawn leftwardly to pivot the gear plate 360 in a clockwise direction. This pivotal movement is against the bias of a spring 321 which is afiixed at 324 to the side wall 228 of the timer casing. Each time that the solenoid 100 is energized, the fast speed gear 314 is pivoted upwardly into driving engagement with a timer shaft-aflixed driven gear 332. The timer shaft gear 332 is carried on an axially fixed shaft portion 334 which is journaled in the partition 336. Although the shaft 334 is not fixed to the timer shaft 56, it will transmit rotational movement thereto through the integral tongue 258 and bifurcated end 256 of the timer shaft 56. Any suitable locking disc arrangement 337 may be utilized to secure the timer shaft gear 332 to the shaft 334.

To summarize the two speed operation of the timer shaft 56, the timer motor 50 operates to drive a shaft 52 to which the pinion 392 is connected. The gear 304 is driven from the pinion 302 and transmits this rotational motion to the gear 3%. Both the slow speed gear 314 and the high speed gear 312 are drivingly connected to the gear 393 and both will be constantly rotated by gear 308. However, when the solenoid 100 is energized, the lever 138 causes the plate 300 to pivot to the position shown in FIGURE 6 wherein the fast speed gear 314 is engaged directly with the timer shaft gear 332 and the timer shaft will be rotated at fast speed, as during the test sensing periods.

The operation of the solenoid actuated dog lock 118 will now be explained as it relates to the alternating fast speed gear shift position 14% and neutral position 142 (FIGURE 1). Referring to FIGURE for the timer gear driving situation prior to the energization of solenoid 100, the dog 286 of the pawl actuating link 280 is shown bearing against the dog lock portion 118 of the carrier plate 300. This prevents the pawls 84 and 116 from lifting, since they are interconnected with the dog 286 through the links 280, 2&6 and 2%. However, once the solenoid 19!} is energized (relative humidity below 30% at sensing element 38), the plate 389 pivots in a clockwise direction to the arrangement of FIGURE 6 and the dog 286 is biased by the spring 284 to a position against an edge 340 of the plate 3%. In this situation, fast speed is established for the timer shaft 55 and the cams 58 and 80. On the other hand when the solenoid 160 is deenergized (relative humidity above 40% at sensing element 38), the shift lever 138 will attempt to move to the slow speed position of FIGURE 5. This, however, is prevented by the engagement of the dog 285 with the stop portion 322 on the carrier plate 300. In this intermediate position, neither gear 314 nor the gear 313 is engaged with the timer shaft gear 332. Thus, the timer motor 50 is completely disengaged from the timer shaft 56 and the timer shaft is free to move in response to the return bias of the shaft spring 112. This situation occurs during all but the last test sensing period, as described hereinabove.

It should now be seen that an improved timer has been provided whereby automatic termination of a drying cycle can be accurately accomplished. This timer concept embodies means for eliminating waste of heated air without its proper saturation with moisture. It provides further for sensing the type of load being dried and in response thereto prescribing a test period adapted particularly for that load sensed. Still further, it embodies means for utilizing the sensing period programmed to minimize over-drying the load and to insure an accurately dried fabric which can then be cooled to room temperature.

While the embodiments of the present invention as herein disclosed, constitute preferred forms, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. In combination with a clothes dryer having means for inducing air flow through said clothes, controllable means for heating said air flow with high and low heat input, means for restricting said air fiow and means for sensing the humidity of said air flow on the exhaust side of said clothes, a timer comprising, means for controlling said restricting means to reduce said air flow and for controlling said heating means for low heat input in response to a predetermined low humidity condition sensed by said sensing means to concentric humidity, means releasably associated with said control means and simultaneously actuatable therewith for setting a repeatable variable clothes dryness test period operable between said predetermined low humidity condition and a predetermined high humidity condition when said control means reduces said air flow and controls said heating means for low heat input, and means for terminating said drying when said sensing means senses a dry condition throughout one of said repeatable test periods.

2. In combination with a dryer having means for inducing air flow through said dryer, controllable means for heating said air flow with high and low heat input, means for restricting said air flow and means for sensing a moisture condition of said air flow on the exhaust side of said dryer, a timer comprising, means for controlling said restricting means to reduce said air flow and for controlling said heating means for low heat input in response to a predetermined decreased moisture condition sensed by said sensing means, means actuated by said control means for initiating a variable moisture condition test period operable between said predetermined decreased moisture condition and a predetermined increased moisture condition when said control means re duces said air flow and controls said heating means for low heat input, and means for terminating said drying when said sensing means senses a condition of no free moisture throughout said test period.

3. In combination with a dryer having means for inducing a drying air flow through said dryer, means for restricting said air fiow and means for sensing a moisture condition of said air flow on the exhaust side of said dryer, a cycle governing device comprising, means for controlling said restricting means to reduce said air flow in response to a predetermined first moisture condition sensed by said sensing means, means actuated by said control means for setting the duration of at least one variable moisture condition test period operable between said predetermined first moisture condition and a predetermined second moisture condition above said first moisture condition when said control means reduces said air flow, and means for terminating said drying when said sensing means fails to sense said predetermined second moisture condition throughout one of said at least one moisture condition test period.

4. In combination with a fabric dryer having means for inducing a drying air flow through said fabric, means for reducing said air flow and means for sensing a moisture condition of said fabric on the exhaust side of said fabric,

19 a timer comprising, means for controlling said reducing means in response to predetermined first and second moisture conditions sensed by said sensing means respectively to reduce and increase said air flow periodically before the termination of said drying, means activated by said control means for setting a repeatable variable moisture condition test period operable between said first and second moisture conditions when said control means reduces said air flow, and means for terminating said drying when said sensing means senses a dry condition throughout one of said repeatable test periods.

5. A clothes drying system comprising, a rotatably mounted container, means for rotating said container, air passage means connected to said container, means for creating a stream of air in series flow relationship through said container and said passage means, means for heating said air, means in said passage means having a first position for restricting said air and a second position for passing said air, said restricting means having means for passing a limited amount of said air when said restricting means is in said second position, a humidity sensing element in said air passage means, and a control device for governing said drying system, said control device havmg a timer shaft, means for driving said shaft, speed changing means between said shaft and said driving means for rotating said shaft at a fast and slow speed including means for disengaging said driving means from said shaft, a drying cycle cam on said shaft for selectively actuating a plurality of switches to energize and deenergize circuits associated with said driving means, said heating means, said air stream creating means and said rotating means, said drying cycle cam having a stop member, a variable clothes dryness sensing period cam relatively rotatably mounted on said shaft and having a stop portion selectively engageable with said stop member and a serrated test period portion, said serrated portion having a plurality of notches, a minimum drying time cam on said shaft having a block-out portion and a minimum sensing period electrically conducting contact plate, a follower for said minimum drying time cam having a first pawl for engaging said block-out portion, a second pawl integral therewith for engaging one of said plurality of notches and a pair of switch contacts in series electrical fiow relationship with one of said plurality of switches for engaging said contact plate if said second pawl does not engage said one of said notches, a solenoid responsive to said humidity sensing element or the engagement of said switch contacts with said contact plate for controlling said pawls, said speed changing means, said heating means and said air restricting means, whereby when said first pawl is out of engagement with said block-out portion, said second pawl engages said one of said notches, said speed changing rneans is shifted to fast speed and said air restricting means IS moved to said first position for a clothes dryness sensing period in accordance with the said one of said notches engaged by said second pawl.

6. A clothes drying system comprising, a rotatably mounted container, means for rotating said container, air passage means connected to said container, means for creating a stream of air in series flow relationship through said container and said passage means, means for heating said air, means in said passage means having a first portion for restricting said air and a second position for passing said air, said restricting means having means for passing a limited amount of said air when said restricting means is in said second position, a humidity sensing element in said air passage means, and a control device for governing said drying system, said control device having a timer shaft, means for driving said shaft, speed changing means between said shaft and said driving means for rotating said shaft at a fast and slow speed including means for disengaging said driving means from said shaft, a drying cycle cam on said shaft for selectively actuating a plurality of switches to energize and deenergize circuits associated with said driving means, said heating means; said air stream creating means and said rotating means, said drying cycle cam having a stop member, a variable clothes dryness sensing period cam relatively rotatably mounted on said shaft and having a stop portion selectively engageable with said stop member and a serrated test period portion, said serrated portion having a plurality of notches, a minimum drying time cam on said shaft having a block-out portion, a follower for said minimum drying time cam having a first pawl for engaging said block-out portion and a second pawl integral therewith for engaging one of said plurality of notches, a solenoid responsive to said humidity sensing element and in series electrical flow relationship with one of said plurality of switches for controlling said pawls, said speed changing means, said heating means and said air restricting means, whereby when said first pawl is out of engagement with said blockout portion, said second pawl engages said one of said plurality of notches, said speed changing means is shifted to fast speed and said air restricting means is moved to said first position for a clothes dryness sensing period in accordance with the said one of said notches engaged by said second pawl.

7. A method of controlling a fabric drying cycle by a dryer having means for creating an air flow, means for reducing said air flow, means for sensing the dryness of said air and a variable heating means comprising the steps of, applying a reduced air flow and reduced heating during a first portion of said drying cycle, applying an increased air flow and an increased heating during a second portion of said drying cycle, applying a reduced air flow and reduced heating during a third portion of said drying cycle, repeating said third portion of said cycle, and sensing the dryness of said fabric during said third portions of said drying cycle wherein said air flow and said heating are reduced until said fabric is dry, said steps of applying and sensing being under the control of said sensing means.

8. A method of controlling a clothes drying cycle by a dryer having an air circulating means, a damper connected to said air circulating means and a variable heating means comprising the steps of, closing said damper and adjusting said heating means to a low heat during a first portion of said drying cycle, opening said damper and adjusting said heating means fora high heat during a second portion of said drying cycle, intermittently closing said damper and intermittently simultaneously adjusting said heating means for low heat to initiate each of a series of third portions of said drying cycle, and sensing the dryness of said clothes during said third portions of said drying cycle until said clothes are dry.

9. A method of controlling a fabric drying cycle by a dryer having an air circulating means, means for restricting said air circulating means and a variable heating means comprising the steps of, energizing said restricting means and adjusting said heating means to a low heat during a first portion of said drying cycle, deenergizing said restricting means and adjusting said heating means for a high heat during a second portion of said drying cycle, intermittently energizing said restricting means and intermittently simultaneously adjusting said heating means for low heat to initiate each of a series of third portions of said drying cycle, and sensing the dryness of said fabric during said third portions of said drying cycle for controlling said restricting means and said heating means whereby said restricting means is dryness responsively energized and said heating means is dryness responsively adjusted for low heat until said fabric is dry.

10. In combination with a dryer having means for producing air flow through said dryer, controllable means for heating said air flow, means for restricting said air flow and means for sensing a moisture condition of said air flow on the exhaust side of said dryer, a timer comprising, means for controlling said restricting means to reduce said air flow in response to a predetermined descreased moisture condition sensed by said sensing means, means actuated by said control means for initiating a variable moisture condition test period operable between said predetermined decreased moisture condition and a predetermined increased moisture condition when said control means reduces said air flow, and means for terminating said drying when said sensing means senses a condition of no free moisture throughout said test period.

11. In combination with a dryer having means for producing air flow through said dryer, controllable means for heating said air flow with first or second heat input, means for restricting said air flow and means for sensing a moisture condition of said air flow on the exhaust side of said dryer, a timer comprising, means for controlling said restricting means to reduce said air flow and for controlling said heating means for said first heat input in response to a predetermined decreased moisture condition sensed by said sensing means, means actuated by said control means for initiating a variable moisture condition test period operable between said predetermined decreased moisture condition and a predetermined increased moisture condition when said control means reduces said air flow and controls said heating means for said first heat input, and means for terminating said drying when said sensing means senses a condition of 110 free moisture throughout said test period.

12. An arrangement for controlling a dryer in a drying cycle for moist fabric comprising, means for initiating the drying of said moist fabric, means for sensing predetermined first and second moisture conditions leaving said fabric before said fabric is dry, means actuatable after a delayed interval in response to the sensing of said predetermined first moisture condition by said sensing means for selecting a fabric moisture test period variable in duration in accordance with the time elapsed between the initiation of said drying and the sensing of said first moisture condition, and means for repeatedly comparing the time period necessary to raise the moisture condition leaving said fabric from said first moisture condition to said second moisture condition with said fabric moisture test period until said fabric is dry.

13. An arrangement for controlling a dryer having means for producing an air flow and means for changing said air flow in a drying cycle for moist fabric comprising, means for initiating the drying of said moist fabric in said air flow, means for sensing predetermined first and second moisture conditions in said air flow downstream from said fabric before said fabric is dry, means actuatable after a delayed interval in response to the sensing of said predetermined first moisture condition by said sensing means for selecting a fabric moisture test period variable in duration in accordance with the Hme elapsed between the initiation of said drying and the sensing of said first moisture condition, and means for repeatedly comparing the time period necessary to raise the moisture condition of said air flow downstream from said fabric from said first moisture condition to said second moisture condition with said fabric moisture test period while said air flow is being changed until said fabric is dry.

14. A method of controlling a fabric drying cycle by a dryer having means for creating an air flow, means for reducing said air flow, means for sensing the dryness of said air flow and means for variably heating comprising the steps of, applying a reduced air flow and reduced heating during the first portion of said drying cycle, applying an increased air flow and an increased heating during a second portion of said drying cycle, intermittently applying a reduced air flow and a reduced heating to initiate each of a series of third portions of said drying cycle, and sensing a dryness of said fabric during said third portions of said drying cycle until said fabric is dry.

15. A method of controlling a fabric drying cycle by a dryer having means for creating an air flow, means for reducing said air flow, means for sensing the dryness of said air flow and means for variably heating comprising the steps of, applying an unrcduced air flow and an unreduced heating during a first portion of said drying cycle, intermittently applying a reduced air flow and a reduced heating to initiate each of a series of second portions of said drying cycle, and sensing a dryness of said fabric during said second portions of said drying cycle until said fabric is dry.

16. In combination with a dryer having means for producing air flow through said dryer, controllable means for heating said air flow, means for restricting said air flow and means for sensing a moisture condition of said air flow on the exhaust side of said dryer, means for controlling said restricting means to reduce said air flow in response to a predetermined decreased moisture condition sensed by said sensing means, means actuated concurrently with said control means for initiating a variable moisture condition test period operable between said predetermined decreased moisture condition and a predetermined increased moisture condition when said control means reduces said air flow, and means for terminating said drying when said sensing means senses a condition of no free moisture throughout said test period.

References Cited in the file of this patent UNITED STATES PATENTS 2,170,763 OhlsOn Aug. 22, 1939 2,741,856 Hall Apr. 17, 1956 2,775,047 Morrison Dec. 25, 1956 2,819,540 Toma et a1 Jan. 14, 1958 2,820,304 Horecky I an. 21, 1958 2,851,789 Dunkelman Sept. 16, 1958 2,863,224 Zehrbach Dec. 9, 1958 2,895,230 Reiley July 21, 1959 2,970,383 Hughes Feb. 7, 1961 3,028,680 Conlee Apr. 10, 1962 FOREIGN PATENTS 225,397 Australia Apr. 30, 1959

Claims (1)

12. AN ARRANGEMENT FOR CONTROLLING A DRYER IN A DRYING CYCLE FOR MOIST FABRIC COMPRISING, MEANS FOR INITIATING THE DRYING OF SAID MOIST FABRIC, MEANS FOR SENSING PREDETERMINED FIRST AND SECOND MOISTURE CONDITIONS LEAVING SAID FABRIC BEFORE SAID FABRIC IS DRY, MEANS ACTUATABLE AFTER A DELAYED INTERVAL IN RESPONSE TO THE SENSING OF SAID PREDETERMINED FIRST MOISTURE CONDITION BY SAID SENSING MEANS FOR SELECTING A FABRIC MOISTURE TEST PERIOD VARIABLE IN DURATION IN ACCORDANCE WITH THE TIME ELAPSED BETWEEN THE INITIATION OF SAID DRYING AND THE SENSING OF SAID FIRST MOISTURE CONDITION, AND MEANS FOR REPEATEDLY COMPARING THE TIME PERIOD NECESSARY TO RAISE THE MOISTURE CONDITION LEAVING SAID FABRIC FROM SAID FIRST MOISTURE CONDITION LEAVING MOISTURE CONDITION WITH SAID FABRIC MOISTURE TEST PERIOD UNTIL SAID FABRIC IS DRY.

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