US2588688A - Thermostatically actuated switch - Google Patents

Description

March 11, 1952 W. J. ALLAN THERMOSTATICALLY ACTUATED SWITCH Filed Nov. 30, 1949 Patented Mar. 11, 1952 UNITED STATES PATENT FFICE THERMOSTATCALLY ACTUATED SV/ITCII Application November 39, 1949, Serial No. 130,130

(Cl. 20G-138) Claims.

This invention relates generally to thermostatically operated Switches, and more particularly to devices of this character having a friction clutch connecting the thermostatic actuator and the switch mechanism which connection is arranged to slip after actuation of the switch mechanism and therefore permit overtravel of the thermostatic actuator.

Thermostatic switches having 'this type of connection, which is commonly referred to as a slip-friction connection, are capable of actuating thev switch mechanism in response to a relatively small directional change in temperature occurring in either direction at any point over a wide temperature range. This feature is particularly desirable when the device is used as a furnace stack-switch to detect operation of an oil burner or the like. In such use it is essential that the thermostatic switching device respond quickly to the initial rise or fall in stack temperature which follows as the burner is ignited or extinguished.

However, in this type of switch it will be seen that after actuation of the switch in response to a temperature change in either direction, some additional change in temperature will be required in that same direction in order to cause the thermostatic actuator to respond and overcome the friction of the clutch before it can slip,

and that subsequently a directional change in '1 temperature opposite and equal to this additional temperature change will have to occur before the actuating mechanism can start to operate the switch in the opposite direction. It follows therefore that the greater the clutch friction, the wider will be the temperature differential required to operate the switch. While it is desirable on one hand to limit the clutch friction in order to minimize the operating differential, it is also desirable on the other hand to provide ample clutch friction, so as to insure that the switch mechanism will be actuated and that slipping of the clutch will not occur under any conditions during actuation of the switch mechanism from one position to the other.

The present invention has for its primary object the provision of a device of the above character inV which both of these desirable characteristics are achieved.

A furthery object is to provide a thermostatically actuated switching device having a friction clutch connection between the thermostatic. element and the switching mechanism in which. a predetermined degree of clutch friction is provided for actuation of the switch and in which this degree of friction is reduced upon further response of the thermostatic element to temperature change after actuation of the switch is accomplished in either direction.

A further object is to provide a generally new and improved band type friction clutch for use in a device of the above character which is simple and reliable in operation and economical in construction.

A further object is to provide a generally new and improved double throw furnace stackswitch capable of responding to relatively slight changes in temperature in either direction throughout a wide temperature range.

Other objects and advantages of the invention will become apparent upon reading the following detailed description in connection with the accompanying drawing.

In the drawing;

Fig. 1 is a plan view of a thermostatically actuated switching device constructed in accordance with the present invention;

Fig. 2 is a side elevation in part of the device shown in Fig. 1;

Fig. 3 is a front view looking into the interior of the casing and taken on line 3-3 of Fig. 2;

Fig. 4 is a sectional view taken on line 4 4 of Fig. l;

Fig. 5 is a sectional view taken on line 5 5 of Fig. ti; and

Fig. 6 is an enlarged view of one of the friction clutch bands shown apart from its cooperating elements.

Referring to the drawing, the device comprises a casing IU having a front cover II attached thereto by screws I2. Extending from the rear wall of the casing I0 is a bushing I3 which serves as a support member for a helical bimetallic coil I4 with its mounting sleeve I5, and additionally journals a torque rod IS. The support bushing I3 is rmly attached at its inner end to the rear wall of the casing I0 by the provision of a reduced portion at its inner end which is entered into an aperture in the rear wall of casing and then riveted or spun over as indicated at Il in Fig. 4.

The mounting sleeve I5 is tted over the projecting support bushing I3 and removably attached thereto by a screw I3. The bimetallic coil I4 is rigidly secured at its inner end to the outer end of the sleeve I5 by a screw I9, and is rigidly secured at its outer end to the outer end of the torque rod I5 by a screw iSa. The torque rod I6 projects inwardly through its journal I3 and into the casing IQ. Fitted on the inner end of the torque rod i6 is a hub member 2i) having a bore 2| which receives the torque rod i6 in press t relationship. The hub 26 is further rigidly attached to the rod I6 for rotation therewith by a set screw 22. The hub member 2i) has a cylindrical portion 23 of reduced diameter at one end on which is tted in press t relationship a centrally perforated dise like clutch element 24. The clutch element 24 is further rigidly connected to the hub member 29 by spinning or riveting over of the reduced end of the hub member. The hub and clutch element 24 are therefore mounted for rotation with the torque rod i6.

The clutch element 24 is preferably constructed of hard pressed or resin bonded iiber and is provided with side anges 25, and a polished peripheral surface 25, which lies between the anges 25. Referring to Fig. 3, there is a clutch band assembly comprising left and right hand members generally indicated at 27 and 28, each of which have arcuately formed portions 29 and 34 respectively which overlay opposite portions of the periphery 26 of the clutch element 24. The arcuate portions 29 and 39 are each provided with two inwardly formed projections 3l which extend transversely the width of the member. The inwardly formed projections 3l engage the periphery 23 and space the arcuate portions 29 and 38 therefrom. Projections 3l are rounded as indicated and therefore provide substantially a line contact with the periphery 25. rIhe flanges 25 of the element 24 retain the clutch band assembly in vertical alignment.

The members 27 and 28 have downwardly extending straight portions 32 and 33 respectively each of which is provided with a pair of flanges 34 and 35 respectively. The iianges 34 are spaced so as to overlap the flanges 35 and a pivot pin 3B is provided which passes through perforations in the flanges 34 and 35 and thereby pivots the members 27 and 28 at this point. The members 27 and 2B are further provided with straight portions 37 and 38 respectively at their upper ends, which straight portions are perforated and receive the opposite coiled ends of a tension spring 39. The clutch band assembly is thus resiliently held in position on the clutch element 24.

Mounted within the casing and on the rear wall thereof as by rivets 49 is a panel 4l of dielectric material. Mounted on the panel 4l as by screws 42 are left hand and right hand bracket like members 43 and 44. Members 43 and 44 vare provided with angularly formed portions 45 and 45 which extend outwardly from the rear wall of the casing on both sides of the clutch band assembly and are provided with threaded apertures at their outer ends which vreceive threaded stop screws 47 and 48. The stop screws 47 and 48 are in alignment with the clutch band assembly and are arranged to be engaged by the lower straight ends of members 27 and 2S and thereby limit the rotation of the clutch band assembly in both directions.

Pivotally mounted on the panel 4l between the members 43 and 44 is a swinging contact arm` 49. Contact arm 49 is mounted on a pivot 59 which is supported by a bracket I mounted on the panel 4I as by screws 52. The outer end of arm 49 extends between a pair of angularly formed tangs 53 and 54 which are formed as an integral part of the lower straight portions 32 and 33 of the clutch band members and as the clutch band assembly rotates the arm is engaged by one or the other of the tangs. The bracket members 43 and 44 are further provided-with angularly formed and 6l on opposite sides thereof which are arranged to be engaged by cooperating contacts 62 and 63 carried by the resilient switch blades 58 and 59 respectively. The resilient blades 58 and 59 are so formed as to normally rest against the portions 55 and 56. Connections are made with the members 43 and 44 at the points 64 and 65 and with the pivoted contact arm 49 at 66 for the circuit leads 67, 63 and 69 respectively.

In operation As shown in the drawing the device is in an intermediate position. The contacts -62 and 5I--63 being engaged the circuits controlled thereby are both closed. The bimetallic element I4 is so constructed that its action in response to an increase in temperature causes clockwise ro.- tation of the torque rod I6, as viewed in Fig. 3, and therefore causes clockwise rotation of the clutch element 24 and the clutch band assembly which is held in frictional engagement therewith by the spring 39. When the temperature to which the device is sensitive increases suiiiciently, the tang 54 of the right hand clutch band member 28 will engage the contact arm 49 causing the outer end of it to swing leftward, thus causing the contacts 6I and 63 to part. During this move.. ment the resilient contact arm 58 will ileX, the resilient contact arm 59 will be deiinitely stopped by the bracket portion 56, and the circuit including the leads 88 and 69 will therefore be broken.

As the temperature continues to increase the clutch element 24 and the clutch band assembly will continue to rotate clockwise until the lower end of the clutch band element 27 engages the stop screw 47. rWhen this occurs, further rota-,- tion of the clutch band assembly will be prevented. It will now be noted that any further increase in torque beyond this point due to a further increase in temperature will cause the member 2 7 to tend to pivot counterclockwise about its pivot 36 thereby tending to spread the upper ends of the clutch band assembly against the tension of spring 39. This tendency, it will be clearly seen, results in a substantial reduction in fric-A tion between the band assembly andthe clutch element 24. When this reduced friction is overcome by a still further increase in torque due to further increase in temperature, the clutch element 24 will slip with relation to the members 27 and 28 and continue to slip until the tempera; ture ceases to increase.

Upon a decrease in temperature the normal friction between the clutch element 24 and the clutch band assembly will be restored immedi ately as the pressure between the lower end of member 27 and stop screw 47 is relieved by the action of the bimetallic element as it begins to respond in an opposite direction. As the temperature continues to decrease further, the clutch band assembly will rotate counterclockwise causing the outer end of the switch arm 49 to be swung toward the right rst moving contacts 6| and 63 into engagement to re-establish the connection between leads 68 and 69, then partr ing contacts 6U and 62 to break the circuit whichvmcludes the leads 67 and 69 and thereafter;

causing the lower end of member 28 to engage stop screw 46, whereupon the normal friction between the element 2a and the clutch band assembly will again be reduced.

It will be understood that by increasing. the arm length between the pivot 36 and the stop screws A'i and 48 with relation to the arm length between the pivot 36 and the points of attachment of the spring 39, a mechanical advantage will result which will cause further reduction in friction as torque is applied after one or the other of the stop screws is engaged. It has been found however that a satisfactory reduction in lfriction is achieved when the device is proportioned generally as shown in the drawing.

It will also be noted that the switch arm 49 is engaged by the inner side of members 21 and 28 and that the resistance to movement ofthe arm 49 imposed by the resilient switch blades 58 and 59 acts through the pivot 36 to augment the tension of spring 39 to increase the friction between the band members and element 2'4. While this added advantage may be obtained only in a construction as illustrated in which a pair of oppositely acting clutch bands is employed, it is to be understood that in its broader aspects the invention contemplates any arrangement in which the resilient means, which holds the clutch members in frictional engagement, is

hinged so as to be movable toward and away A from the periphery of said disc member, each of said band members having a portion extending laterally of the axis of said disc member, which portions are spaced and lie substantially parallel and alongside each other, resilient means normally urging said hinged band members into frictional engagement with said disc member, resilient switch structure arranged to be engaged by at least one of said lateral portions as said disc member is rotated in at least one direction, and stop means arranged to be alternately engaged by said lateral portions as said disc member is rotated oppositely, the engagement between said lateral porti-on and said switch structure being on such side of said lateral portion as to cause the pressure between the clutch bands and disc member to be increased as said switch structure is being actuated, and the engagement between said clutch lateral portions and said stop means being on the opposite sides of said lateral porti-0n whereby pressure between said clutch bands and disc member will be decreased as said disc member tends to rotate after said stop means is engaged by either of said lateral portions.

2. In a thermostatic switching device, a disc- `like friction clutch member, a bi-metallic coil for rotating said member, a pair of arcuate clutch band members adapted to frictionally engage opposite portions of the periphery of said disc member, said band members being pivotally` connected so as to open and close with relation to the periphery of said disc member and each of said band members having a portion extending laterally of the axis of said clutch member, which portions are spaced and lie substantially parallel and alongside each other, resilient means normally urging said band members in frictional engagement with said disc member, yieldable switch structure arranged to be alternately engaged by said lateral portions thereby to be actuated in opposite directions as said disc member is rotated oppositely, and stop means arranged to be alternately engaged by said lateral portions as said disc member is rotated in either direction beyond that amount required to actuate the switch, said switch structure being arranged to be engaged by such sides of said lateral portions as will result in causing the reaction between said switch structure and said disc member to tend to close said band members and thereby increase the pressure between said band members and said disc member,

p and said stop means being arranged to be engaged by the opposite sides of said lateral portions whereby the reaction between said disc member and said stop means will tend to spread said band members thereby to reduce friction as said disc member tends to rotate after engagement with said stop means.

3. In a thermostatc switching device, a circular friction clutch member, a thermostatic element for rotating said member oppositely in response to `directional temperature change, a clutch band assembly comprising a pair of clutch band members having arcuate portions adapted to frictionally engage opposite portions of the periphery of said circular member, said band members being pivotally connected so as to open and close with relation to said circular member, each of said band members having a portion extending laterally of the axis of said circular member and on the other side of their pivoted connection, said laterally extending portions lying alongside each other, resilient means normally urging said band members into frictional engagement with said disc member, switch structure including a contact arm disposed between said laterally extending portions and arranged to be alternately engaged by the inside surfaces thereof for the actuation of the switch as said circular member is rotated oppositely, and stop means arranged so as to be engaged by the outside surfaces of said laterally extending portions when said disc member is rotated in either direction beyond that amount necessary to actuate the switch.

4. In a therm-ostatic switching device, a circular vfriction clutch member mounted for rotation, a temperature responsive device connected to said member for rotating it cppositely in response to directional temperature changes, a pair of clutch engaging elements lying perpendicular to the axis of said clutch member and being arranged to frictionally engage opposite portions of the periphery of said clutch member, said elements being pivotally connected so as to open and cl-ose scissors-like with respect to the periphery of said clutch member, each of said elements having portions extending laterally of said clutch member which portions lie alongside each other in spaced relationship, resilient means normally urging said elements closed and into fricti-onal engagement with said clutch member, stop means arranged to be alternately engaged by said laterally extending portions, and by such sides `thereof as will cause said clutch engaging elements to tend to spread or open as said clutch member is urged rotationally in either direction after said stop means hasV been engaged, Vand control means to be actuated by movement of at least one of said laterally extending portions.

5. Ina device of the class described, a disclike friction clutch member having a continuous centrally recessed periphery, a bi-metallic coil for rotating'said disc member, a clutch band assembly comprising a pair of arcuate band members having portions arranged to engage opposite portions of the peripheryvof said disc and arranged to enter said peripheral recess whereby they are constrained against longitudinal movement, said band members being pivotally connected so as to open and close with relation to said disc member, each of said band members having a portion extending laterally of the axis of said disc member, which portions lie alongside each other in spaced relationship, resilient means normally urging said band members into frictional engagement with the bottom of said peripheral recess, yieldable switch structure arranged to be alternately engaged by said lateral portions for its actuation as said disc member is rotated oppositely, and stop means arranged to be alternately engaged by said lateral portions as said disc member is rotatedoppositely beyond thatamount necessary to actuate the switch, said switch structure being arranged to beengaged by such sides of said lateral portions as to cause" the pressure between the clutch bands andthe disc member to ybe increased ,as said switch'is being actuated, and the engagement between'the said lateral portions and said stop means being on thefopposite sides of said lateral portions whereby pressureV betweenV said clutch bands andsaid disc member will be decreased as said disc member is urged to rotate after said stop means has been engaged.

l WILLIAM J. ALLAN.

v REFERENCES CITED l The following references are of record in the file of this patent:v y y' UNITED STATES PATENTS Rosche June 14, 1949

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