US2901642A - Thermostatic timing control - Google Patents

Description

Aug. 25, 1959 J, s T ETAL 2,901,642

THERMOSTATIC TIMING CONTROL Filed Sept. 19, 1958 FIG.[

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I v INVENTORS i JAMES J- SMITH ROBERT 0.6RAF

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AGENT United States Patent THERMOSTATIC TIMING CONTROL James J. Smith, Logansport, and Robert D. Graf, Flora, Ind., assignors to Essex Wire Corporation Application September 19 1958, Serial No. 762,023

6 Claims. (Cl. 307*112) This invention relates to electric timer switches and more particularly to thermostatic timing controls for electric devices having mechanically operable initiating means sensitive to momentary pressure.

In certain applications it is sometimes desirable to employ a timer switch whose timing and control cycle is initiated by a mechanical impulse which may be of short duration. One example where such a switch is useful is in the control of an automatic washing machine where it is desired to temporarily reduce the speed of a rotating tub when accumulation of laundry results in an out-of-balance condition. This is accomplished by employing a timer switch mechanically actuated when an out-of-balance occurs to control electrical connections to the driving motor of the washer or its control solenoid for reducing the washer tub speed. After a time interval normally sufficient for the out-of-balance condition to be corrected, the timer switch reconnects the washer motor or its control solenoid for high speed operation. Inasmuch as one such time interval may not always be sufficiently long for the out-of-balance condition to be corrected, it is necessary that the timer switch be in condition to immediately repeat its timing cycle at the end of the timing cycle. T 0 meet this requirement, it has been accepted practice to employ motor driven timers or other expensive and sometimes complicated control devices.

Accordingly, it is an object of the present invention to provide thermostatic controls of the foregoing character which are of simple construction and few parts, which may be easily and inexpensively manufactured and which may be simply connected in circuit with the device it controls.

Other objects and advantages of the invention will be apparent from the following description and accompanying drawing in which:

Figure 1 is a plan view of a thermostatic timing switch embodying the present invention;

Figure 2 is a sectional View taken along the line 22 of Figure 1 and showing the switch connected to an electrical device which it controls;

Figure 3 is a plan view of a thermostatic timing switch embodying a modified form of the invention; and

Figure 4 is a sectional View taken along the line 44 of Figure 3 and showing the switch connected to an associated switch and an electric device which it controls.

Referring now to the drawing, Figures 1 and 2 show a thermostatic switch having a stack which includes an insulator 10, a stiff sheet metal terminal 12, two insulators 14 and 16, a bimetal strip 18, an insulator 20, a leaf spring 22, an insulator 24, and a stiff sheet metal terminal 26. This stack is mounted in the open end of an enclosure consisting of a metal channel-shaped case 28 with end wall 30 and an insulating plate 32 supported upon the stack and the edge of end wall 30. Four ears 34 formed integrally with case 28 are bent over plate 32 to clamp the switch parts inassembled relation. The case and stack 2 parts may have interfitting apertures and projections to insure their permanent alignment.

Attached to terminal 12, bimetal strip 18, leaf spring 22 and terminal 26 are respective contacts 36, 38, 40 and 42. Contact 38 is engageable with contact 36, while contact 40 is engageable with contact 42. Leaf spring 22 is biased toward terminal 26 to cause contact 48 to normally engage contact 42. An armature 44 of steel or other magnetizable material is secured to leaf spring 22 by contact 40 for cooperation with permanent magnet 46 which is secured to terminal 12 by contact 36. Contact 38 is preferably mounted upon an armature 47 of magnetizable material to effect quick separation of contacts 36 and 38. A heating coil 48 wound upon bimetal strip 18 has one end connected to contact 38 while its other end is connected to terminal 26. Bimetal strip 18 is composed of superposed layers of metals having different coefficients of expansion such that it will deflect toward spring 22 when heated by heating coil 48. A conducting strip 50, disposed on insulator 20 serves to electrically connect bimetal strip 18 to leaf spring 22. Threaded through insulating plate 32 and extending through suitable apertures in terminal 26 and leaf spring 22 is an adjusting screw 52 which engages bimetal strip 18 to normally bias contact 38 into engagement with contact 36. An actuating member or push button 54 has a shank portion 56 projecting through suitable apertures in terminal 26 and insulating plate 32 and has an enlarged lower portion 58 engaging leaf spring 22.

As shown in Figure 2, the switch is connected in circuit with an electrical device such as the control solenoid 60 for the driving motor of a washer tub. Energization of solenoid 60 causes the motor speed to increase from a low value to a higher value. One line 62 of an electric power source is connected to terminal 12 while the other terminal 26 is connected to the other line 64 by solenoid 60.

Bimetal strip 18 and leaf spring 22 are normally in the position illustrated in Figure 2 with contacts 36 and 38 engaged and with contacts 40 and 42 engaged. When lines 62 and 64 are energized, solenoid 60 is also energized through a circuit comprising line 64, solenoid 60, terminal 26, contacts 42 and 40, leaf spring 22, conducting strip 58, bimetal strip 18, contacts 38 and 36, terminal 12, and line 62. Heating coil 48 is not energized since it is shunted by a circuit including contacts 40 and 42.

If new push button 54 be depressed upon occurrence of an out-of-balance condition in the washer tub, armature 44 is biased into engagement with magnet 46 to separate contacts 40 and 42. Since contacts 40 and 42 no longer shunt heating coil 48, it is connected in series with solenoid 60 to reduce the voltage supplied thereto below its operating or on value. As bimetal strip 18 becomes heated by heating coil 48, it tends to deflect away from terminal 12 and after a predetermined time interval becomes sufliciently heated to pull armature 44 away from magnet 46 thereby separating contacts 36 and 38 while permitting contacts 40 and 42 to engage.

Opening of contacts 36 and 38 interrupts the circuit to heating coil 48 and solenoid 60 and both will remain deenergized until bimetal strip 18 cools to effect engagement of contacts 36 and 38. Engagement of contacts 36 and 38 reenergizes solenoid 60 to increase the motor speed to its high value. In the event the out-of-balance condition has not been corrected, the switch is in position to repeat the foregoing cycle.

In Figures 3 and 4 there is shown a modified form of the above described control comprising a thermostatic switch 70 adapted for use with an associated single-pole, double-throw switch 72. Switch 70 has a flexible leaf spring 74, a terminal 76, and a bimetal strip 78 interleaved and supported between insulators 80. The stackof switch parts may be mounted in the open end of an enclosure consisting of a metal channel-shaped case 82 with end wall 84 and an insulating plate 86 supported upon the stack and the edge of end wall 84. Ears 88 and 20 formed integrally with case 02 are bent over plate 86 to clamp the switch parts in assembled relation.

Attached to leaf spring 74 is a contact 92 which is mounted upon the face of a permanent magnet 94'. A cooperating contact 96 is attached to bimetal strip 78 and is mounted upon an armature 9'3 of steel or other magnetizable material. A thin disc of non-magnetizable material may be positioned upon the face of armature 98 to prevent sticking of the armature 98 on magnet 94. A heating element or coil 102 wound upon bimetal strip 78 has one end connected to contact 96 and has the other end connected to terminal 76. Bimetal strip 78 is composed of superposed layers of metals having different coefiicients of expansion with the high expanding layer on the lower side of strip 78 as viewed in Figure 4 such that bimetal strip 78 will deflect away from leaf spring 74 when heated by heating coil 102. Threaded through insulating plate 86 is an adjusting screw 104 which engages bimetal strip 78 to normally bias contact 96 into engagement with contact 92. An actuating member or push button 106 of insulating material has a shank portion 108 slidably mounted in a suitable aperture in insulating plate 86 and has an abutment portion 110 engaging the free end of bimetal strip 78.

Mounted adjacent switch 70 is an associated singlepole, double-throw, two-position, push button switch 72 which may be of any suitable type and may be, if desired, formed as an integral part of switch 70. Switch 72 is illustrated as comprising a pair of contact arms 112 and 114 which carry at their free ends a pair of relatively fixed contacts 116 and 118, respectively. A flexible contact arm 120 is disposed intermediate contact arms 112 and 114 and carries at its free end a movable contact 122 which is alternatively engageable with contacts 116 and 118. A movable actuator or push button 124 of insulating material is slidably mounted in switch '72 and carries an arm 126. A U-shaped spring 128 is rockably mounted upon the free end of arm 120 and the free end of arm 126 to provide snap-acting, overcenter movement of arm 120 between two alternative positions upon movement of push button 124. Push button 124 is in engagement with push button 1'06 at all times and the two will move conjointly.

As shown in Figure 4, switches 70 and 72 are connected in circuit with an electrical device such as the control solenoid 60 described above. One line 62 of an electric power source is connected to bimetal strip 78 while the other power line 64 is connected by solenoid 6t; to contact arm 120 carrying movable contact 122. Terminal 76 is connected by lead 130 to contact arm 112 which carries normally open contact 116 while leaf spring 74 is connected by lead 132 to contact arm 114 carrying normally closed contact 118.

The various switch parts are normally in the positions illustrated in Figure 4, with contacts $2 and 94 engaged, with contacts 116 and 122 separated, with contacts 1'18 and 122 engaged. While lines 62 and 64 are energized, solenoid 60 is energized through a circuit comprising line 64, solenoid 6% contact arm 120, contacts 122 and 1113, contact arm 11%, lead 132, leaf spring 74, contacts 92 and 96, bimetal strip 73, and line 62. Heating coil 102 is not energized since its circuit is interrupted by separated contacts 11-6 and 122.

Depression of push button 124 upon occurrence of an out-of-balance condition in the washer tub causes spring 128 to snap over to its alternate position separating contacts 116 and 122 and engaging contacts 114 and 122. Push button 106 also will be depressed to downwardly deflect bimetal strip 78 and leaf spring 74 whose contacts 96 and 92 remain in engagement. Heating coil 102 is now connected in series with solenoid 60 to the power source in a circuit comprising line 64, solenoid 6-0, contact arm 120, contacts 122 and 116, contact arm 122, lead 130, terminal 76, heating coil 102, bimetal strip 73 and line 62. The relative resistance values of solenoid 60 and heating coil 102 are such that the voltage applied to solenoid 60 is below its operating or on value. As bimetal strip 78 becomes heated by heating coil 102, it tends to deflect away from leaf spring 74 and after a predetermined time interval, becomes sufficiently stressed to snap spring 128 over center to separate contact 122 from contact 114 and to cause contact 122 to engage contact 118. The resistance of leaf spring 74 to deflection is greater than the holding force between permanent magnet 94 and armature 98, and the internal strain developed in bimetal strip 78 to operate switch 72 also pulls armature 98 away from permanent magnet 94 thereby separating contacts 92 and 96 with a snap action.

Opening of contacts 92 and 96 interrupts the circuit to solenoid 60 while opening of contacts 116 and 122 interrupts the circuit to heating coil 102 and both are accordingly deenergized. Bimetal strip 78 cools to effect engagement of contacts 92 and 96 which occurs with a snap action due to attraction of armature 98 by permanent magnet 94. Engagement of contacts 92 and 96 reenergizes solenoid 6t) to increase the motor speed to its high value. As in the case of the control illustrated in Figures 1 and 2, the modified control illustrated in Figures 3 and 4 is in position to immediately repeat its operating cycle if the out-of-balance condition has not been corrected during the preceding cycle.

While the invention has been illustrated and described in its preferred embodiments and has included certain details, it should be understood that the invention is not to be limited to the precise details herein illustrated and described since the same may be carried out in other ways falling within the scope of the invention as claimed.

What is claimed is:

1. A thermostatic timing control for an electrical device connected to a source of eelctric power comprising a thermally responsive element, means for heating said thermally responsive element, switch means operative to open and close a circuit to said electrical device in response to heating and cooling of said thermally responsive element, second switch means operative in one position to close a circuit including said first switch means and said electrical device and operative in an alternate position to connect said electrical device and said heating means in series connection, an actuator for actuating said second switch from said one position to said alternate position, restraining means for retaining said second switch in said alternate position, said thermally responsive element being effective when heated to a predetermined temperature to overcome said restraining means for returning said second switch to said one position, and said thermally responive element being effective to open said first switch means upon returning said second switch to said one position.

2. The thermostatic timing control as defined in claim 1 wherein said second switch means comprise a pair of contacts closed in said one position and opened in said alternate position, said pair of contacts being connected in series with said first switch means and being connected in shunt with said heating means.

3. The thermostatic timing control as defined in claim 1 wherein said second switch means comprise a movable contact alternatively engageable with first and second fixed contacts, said first fixed contact being connected in circuit with said first switch means, said second fixed contact being connected in circuit with said heating means, said movable contact being connected in circuit with said electrical device, said movable contact and said first fixed contact being engaged in said one position of said second switch and said movable contact and said second fixed contact being engaged in said alternate position of said second switch.

4. A thermostatic timing control for an electrical device connected to a source of electric power comprising a normally closed switch; a bimetal member for opening said first switch when heated; a heating element for heating said bimetal member; a second switch operative in one position to close a circuit including in series connection said first switch, and said electrical device and operative in an alternate position to connect in series connection said heating element and said electrical device; an actuator for actuating said second switch from said one position to said alternate position; restraining means for retaining said second switch in said alternate position, and said bimetal member being efiective when heated to a predetermined temperature to open said first switch and overcome said restraining means for returning said second switch to said one position.

5. The thermostatic timing control as defined in claim 4 wherein said first switch comprises a relatively fixed first contact and a cooperating second contact carried by said bimetal member; wherein said second switch comprises a third contact carried by a flexible member and a relatively fixed fourth contact, said third contact normaly being biased into engagement with said fourth contact in said one position of said second switch, said actuator being disposed to deflect said flexible element toward said bimetal member to separate said third and fourth contacts in said alternate position of said second switch; wherein said restraining means comprise magnetic means cooperating with said flexible element adopted to be attracted for retaining said flexible element in said alternate position of said second switch; wherein said bimetal member is disposed for engagement with said flexible element in its said alternate position for returning said flexible element to its said one position when said bimetal member is heated to a predetermined temperature by said heating element; and wherein said first, second, third and fourth contact and said electrical device are connected in series connection to said power source, said heating element being connected in shunt with said third and fourth contacts.

6. The thermostatic timing control as defined in claim 4 wherein said first switch means comprise a first contact carried by said bimetal member and a cooperating second contact normally engaging said first contact carried by a flexible element; wherein said second switch comprises a third movable contact alternatively engageable with fourth and fifth fixed contacts, said third contact engaging said fourth contact in said one position of said second switch and engaging said fifth contact in said alternate position of said second switch; and wherein said first, second, third and fourth contacts and said electrical device are connected in series connection to said power source, said heating element being connected between said first contact and said fifth contact.

No references cited.

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