US2719894A - Two-stage thermostat - Google Patents

Description

Oct. 4, 1955 w. J. ALLAN TWO-STAGE THERMOSTAT 2 Sheets-Sheet 1 Filed Jan. 19, 1953 Bl-METAL 30 Oct. 4, 1955 w. J. ALLAN TWO-STAGE THERMOSTAT 2 Sheets-Sheet 2 Filed Jan. 19, 1953 United States Patent TWO-STAGE THERMOSTAT William J. Allan, Webster Groves, Mo., assignorto Missouri Automatic Control Corporation, St. Louis, Mo., a corporation of Missouri Application January 19, 1953, Serial No. 331,997

6 Claims. (Cl. 200-138) This invention relates to thermostats and particularly to multiple stage thermostats in which a plurality of switch contacts are closed and opened in sequence as the temperature falls and rises.

An object of the present invention is to provide a generally new and improved two-stage space thermostat which will operate reliably to sequentially close and open two pairs of switch contacts with a snap action in response to small temperature changes.

A further object is to accomplish this with a single temperature responsive element.

These and other objects and advantages which appear from the following description, when read in connection with the accompanying drawings, are the purposes of the present invention.

In the drawings:

Fig. 1 is a front view of a two-stage thermostat constructed in accordance with the present invention;

Fig. 2 is an enlarged front view of the thermostat shown in Fig. 1 with the casing removed;

Fig. 3 is an enlarged right side view of the device with the casing removed;

Fig. 4 is an enlarged bottom end view with the casing removed;

Fig. 5 is an enlarged left side view with the casing removed;

Fig. 6 is an enlarged rear view;

Fig. 7 is a cross-sectional view of the upper portion of the device and is taken on line 77 of Fig. 2;

Fig. 8 is an enlarged detail view of the right-hand adjustable contact mounting arm shown in Fig. 2, and

Fig. 9 is an enlarged detail view of the left-hand contact mounting bracket shown in Fig. 2.

Referring to the drawings, the device has a base plate 10, the rear side of which is attached to a wall mounting plate 11. The wall mounting plate 11 is provided with elongated holes 12 to receive wall mounting screws and the base plate is attached to the wall mounting plate by means of screws 13 in a manner to be described. The base plate 10 has an irregular cut out portion which is indicated by the dotted line 14, Figs. 2 and 6, and a rigid dielectric panel 15 attached to the front side of the base plate by rivets 16 covers this cut out portion. The wall mounting plate 11 likewise has a cut out portion, indicated by the full line 17 in Fig. 6, and which in general registers with the cut out portion in the base plate. This cut out in the wall mounting plate is also covered by a rigid dielectric panel 18, indicated in dotted line in Fig. 6, and it as attached to the front side of the wall plate 11 by rivets 19.

The dielectric panel 15 of the base plate 10 has attached to the back side thereof offset brackets 20, 21, and 22, see Figs. 3 and 4, which are constructed of conductive material. Brackets 20 and 21 are attached at one end of the dielectric panel 15 by rivets 23, and the bracket 22 is attached at one end to the panel 15 by a screw 24, see Fig. 3. The other ends of the brackets are provided with clearance holes to receive attaching's'crews 13. The

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dielectric panel 18 on the wall mounting plate has at tached to the front side thereof three elongated terminal plates, indicated at 25, 25a, and 25b, constructed of conductive material, each of which is provided at one end with a tapped hole to receive one of the attaching screws 13 and at its other end with a tapped hole to receive one of the terminal attaching screws 26, 27, or 28. The ter minal plates are attached to the panel 18, as by passing lug portions 29 thereof through the panel and clamping them over. The base plate and wall mounting plate are therefore detachably connected by screws 13 and the offset brackets 20, 21, and 22, it will be seen, provide a space between the base plate and the wall mounting plate for the connection of circuit leads to the terminal plates.

Pivotally supported on the front and upper central portion of the base plate 10 is a generally U-shaped bimetallic temperature responsive element generally indicated at 30. Attached centrally to the loop portion of element 30, as by rivets 31, is a U-shaped mounting bracket 32 having perforated legs which freely receive a pivot 33. The pivot 33 is rigidly mounted on the base plate 10 and is provided with an insulating sleeve 34 and insulated washers 35 and 36, see Fig. 7, so that the element 30 is electrically insulated from the pivot 33 and the base plate 10. The downwardly extending legs 37 of element 30 are provided with extensions 38 attached thereto by means of screws 39. The extensions 38 are formed, as indicated at 40, so as to have small lateral offsets and thin, resilient contact-carrying strips 41 which carry movable contacts 42 and 43 are provided and overlay the oifset portions of leg extensions 38 so as to absorb impact and minimize contact bounce. The leg extensions 38 and resilient strips 41 are of conductive material and the extensions 38 are of magnetic material.

Mounted on opposite sides of the pivotally mounted element 30, and adjacent the lower ends of leg extensions 38 are stationary contacts 42a and 43a which cooperate respectively with movable contacts 42 and 43 to control separate electrical circuits. Contact 42a is mounted in a fixed bracket 44 of conductive material, which is jointly attached with offset bracket 20 to the dielectric panel 15 by means of rivets 23. The contact 42a is, therefore, electrically connected to terminal plate 25 which receives the terminal attaching screw 28. The bracket 44, see Figs. 4 and 9, is provided with three perpendicularly formed portions 45, 46, and 47. The bracket portion 45 is provided with a screw threaded perforation which receives the screw threaded stationary contact 42a. The bracket portion 46 is also provided with a screw threaded perforation which receives an attaching screw 48 which clamps a permanent magnet 49 to the bracket, as indicated, and the bracket portion 47 is also provided with a screw threaded perforation which receives a threaded stop member 50. The threadedly adjustable stop member 50 is constructed of non-conducting material, or at least it has a non-conducting tip.

The right-hand stationary contact 43a is mounted on the lower end of a lever 51 which is pivoted intermediately of its length on the screw 24. The screw 24 serves the dual purpose of providing a pivot for lever 51 and for attaching one end of the offset bracket 22 to the dielectric panel 15. The other end of the offset bracket 22 being connected to the terminal plate 25b by a screw 13, and the lever 51 being pressed against the head of its pivot 24 by a spring washer 52, the stationary contact 43a is, therefore, electrically connected to the terminal plate 25b, which receives the terminal attaching screw 26. The stationary contact 43a is mounted for threaded adjustment in a perpendicularly formed leg 53 on the lower end of lever 51. Lever 51 is further provided at the same end with a perpendicularly formed lug 54 on 3 which is clamped a second permanent magnet 56 by means of an attaching screw 57.

The upper end of lever 51 is provided with a perpendicularly formed lug 58 in which is mounted a screw 59 which bears against a cam surface 60. The cam surface 60 is formed on the exterior of a sleeve member 61, which sleeve is in turn mounted for rotation on a stud 62. The stud 62 is attached to the base plate 10, see Figs. 5 and 6, as by riveting. The sleeve member 61 is further provided at its outer end with a thumb knob 63, having a pointer 64 to indicate its angular position with relation to a dial 65 on the cover, see Fig. 1. The screw 59 in lever 51 is held firmly against the cam surface 60 by a relatively strong spring 66 which is connected at one end to the upper end of lever 51 and anchored at its other end on the pivot 33. The relationship of movable contact 43 and stationary contact 43a may therefore be adjusted by turning the thumb knob 63.

The U-shaped bracket 33, which pivotally mounts the temperature responsive element 30, is provided with a leg extension 67 to which is attached one end of a flexible lead 68. The other end of the flexible lead 68 is connected to a conducting plate 69. The plate 69 is jointly connected with one leg of the offset bracket 21 to the panel by rivets 23. The other leg of offset bracket 21 is connected to the terminal plate 25a by a screw 13, whereby the central loop portion of the temperature responsive element is electrically connected to terminal plate 251:, which receives the terminal attaching screw 27. It will be seen, therefore, from the foregoing, that stationary contacts 42a and 43a are electrically connected to terminal attaching screws 28 and 26 respectively and that the movable contacts carried on the legs of the element 30 are jointly connected to the terminal attaching screw 27. The lead 68 connecting pivot bracket 32 with conducting plate 69 is extremely flexible so as not to offer any significant resistance to the free rotation of element 30 on its pivot 33.

Operation Referring to Fig. l of the drawings, the element 30 is shown in a cold or contracted position in which both sets of contacts are open and in which the inside of the left leg extension 38 is held in an attracted position against the stop 50 by the permanent magnet 49. Under these conditions, if the temperature ambient to the device increases, the element legs 37 will tend to spread laterally outward an equal amount but, due to the fact that the device is pivoted at 33 and its left leg is held against stop 56 by the magnet 49, the entire expansion of the element will be resolved into an outward movement of the right leg, thereby causing contact 43 to be moved toward stationary contact 43a. As the right leg extension 38, which is of magnetic material, approaches the permanent magnet 56, it enters a magnetic field strong enough to cause the contact 43 to be moved rapidly into engagement with contact 430, resulting in a snap-action closing of the contacts. The closing of contacts 43 and 43a completes an electrical circuit between terminal lead attaching screws 26 and 27 which is traced as follows; terminal plate 251), attaching screw 13, offset bracket 22, pivot screw 24, lever 51 to contact 43a, contact 43a and contact 43, leg 38 and element 30 to pivoting bracket 33, lead 67, conducting plate 68, rivets 23, otfset bracket 21, attaching screw 13, and terminal plate 25a to terminal screw 27.

With the closing of contacts 43 and 43a, both legs of element 30 are now restrained from further spreading so that any further increase in temperature will result in a stress being built up in element 30. When this stress reaches a predetermined value, the left leg extension 38 breaks away sharply from the restraining magnet 49 and moves the contact 42 into engagement with stationary contact 42a with a snap action. The closing of contacts 42 and 42a completes an electrical circuit between terminal lead attaching screws 28 and 27 in a manner which is traced as follows; terminal plate 25, attaching screw 13, ofiset bracket 20, fixed bracket 44, contacts 42a and 42, left leg extension 38 and element 30 to pivoting bracket 33, lead 67, conducting plate 68, rivets 23, offset bracket 21, attaching screw 13, and terminal plate 25a to attaching screw 27. It will be seen therefore that any two circuits having a common lead which is connected at 27 will be sequentially closed with a snap action in response to continued rising temperature.

it is to be pointed out at this time that the stationary contact 42a is so positioned with relation to magnet 49 that the armature, left leg extension 38, is not moved beyond the field of influence of the magnet 49 when contacts 42 and 42a are closed. This arrangement insures that the left leg extension of the element will always be in an attracted position against stop 50 when in an unstressed condition. However, the stress build up in element 30, which is required to break away from the magnet 49, is great enough so that suflicient residual stress still remains in the element after breaking away and closing the contacts to retain this closed contact position against reattraction by the magnet at that temperature. This residual stress is also sufiicient to provide the necessary contact pressure. Upon a subsequent drop in temeprature, this stress in element 30 is gradually relaxed, and at some decreased value of this stress, the influence of magnet 49 will move the leg extension 38 rapidly to the right, thus breaking contacts 42 and 42a with a snap action. It is to be understood that the value of the decreased stress in element 30, at which the magnet 49 attracts the leg extension 38 to break the contacts, is yet snfiicient to maintain satisfactory contact pressure.

As the temperature continues to decrease after contacts 42 and 42a are broken and left leg extension 38 is again held against stop 50, an opposite stress will be built up in element 30 due to the restraint of stop 56 on the left leg and the restraint of magnet 56 on the right leg. At some point, as the temperature continues to decrease, this stress will reach a value suflicient to cause right leg extension 38 to sharply break away from magnet 56, resulting in the breaking of contacts 43 and 43a with a snap action. The internal circuits hereinbefore traced are thus sequentially broken with a snap action in response to a continued decrease in temperature.

The temperature at which contacts 43 and 43a close and open may be varied by the rotation of thumb knob 65. This action rotates the lever 51, thereby jointly moving the stationary contact 43a and the magnet 56 with respect to the movable contact 43 and the armature, right leg extension 38. The temperature change required to effect the closing of contacts 42 and 42a after contacts 43 and 43a are closed may be varied by adjusting stop screw 50. As stop screw 50 is screwed outward, that is toward the right, the armature, left leg extension 33, is permitted to approach the magnet 49 more closely, thereby entering a stronger magnetic field. The stress build up in element 30, and consequently the temperature change, will now have to be greater to cause left leg extension 38 to break away from this new position. The fixed bracket 44, which mounts the stationary contact 42a, the magnet 49, and stop screw 50, may be made adjustable with relation to the left leg extension 38 by such means as the lever 51 or the like and the stationary contact 43a and magnet 56 may be mounted on a fixed bracket, instead of in the way shown and described. In either case the effect will be the same; that is, the relationship between the movable contact 43 and fixed contact 43a will be varied when the knob 63 is turned.

It will be seen from the foregoing that the legs of the single temperature responsive element act in opposite directions in effecting the sequential closing or opening of the contacts. By this arrangement, any tendency of carry over from one stage to the other due to the momentum imparted to a single contact arm in effecting a snap action is precluded, so that the device may be constructed and adjusted to operate on a very small temperature change between the stages.

The foregoing description is intended to be illustrative of the principles of the invention and not limiting. Exclusive use of all modifications within the scope of the appended claims is contemplated.

I claim:

1. In a two-stage, snap-action thermostat, a pair of spaced control devices arranged to be moved oppositely to outward and inward control positions, stop means for limiting the inward and outward movement of said control devices, magnetic means acting upon one of said devices to move it from its outward to its inward control position with a snap action and to releasably hold it there, magnetic means acting upon the other of said devices as it approaches its outward position to move it to its outward position with a snap action and releasably hold it there, and a flexible expanding and contracting temperture responsive actuator between said devices, operatively connected at its opposite ends to said devices and being free to shift relative to said devices so as to continuously react uniformly between said devices as it responds to temperature changes.

2. A dual control thermostat comprising two spaced control devices having limited movement oppositely between first and second control positions, a temperature responsive actuator between said devices having oppositely acting ends which are operatively connected to said control devices and which move in a direction toward and away from said devices in response to directional temperature changes, said actuator being movable between said devices so as to react equally between them at all times, means for releasably holding one of said devices in its first operative position once it is moved there, so as to cause the actuation of the other control device first when said actuator responds to a change in temperature in one direction to move said devices to their second control positions, and so as to effect the snap action actuation of said first mentioned releasably held device from its first to second control position when subsequently moved there by said actuator upon a further change in temperature in the same direction, and means for releasably holding said other device in its second control position once it is moved there, so as to cause the actuation of said first mentioned device first when said actuator acts in response to a directional change in temperature to return said devices to their first control positions, and so as to effect the snap action actuation of said other device from its second to first position when subsequently moved there by said actuator in response to a further change in temperature in this last mentioned direction.

3. A two-stage thermostat comprising an intermediately pivoted bimetal strip, a control device adjacent each end of said strip, said devices having first and second control positions and being operatively associated with the ends of said strip in such manner as to be actuated to like control positions when said strip warps in one direction or the other in response to temperature change, permanent magnet means for releasably holding one of said de vices in its first control position and permanent magnet means for releasably holding the other of said control devices in its second control position.

4. In a dual control thermostat, a temperature responsive element comprising a bimetal strip formed in a general U-shape and pivotally supported intermediately of its ends, a stationary contact adjacent the end of each of its legs and on the outsides thereof, a cooperating movable contact carried by each leg of said element, a permanent magnet for releasably holding one leg of said element in an open contact position once it is moved there, and a permanent magnet for releasably holding the other of said legs in a closed contact position once it is moved there.

5. In a two-stage, snap-action thermostat, a bimetal strip pivotally supported intermediately of its ends, a movable contact carried at each end of said strip and on the same side thereof, a cooperating stationary contact adjacent each end of said strip, a permanent magnet adjacent one end of said strip and on the side opposite said contacts for attracting said element end to an open contact position and for releasably holding it there, said magnet having sufiicient attractive force to move said element end from a closed to open contact position with a snap action when the bending stress in said element falls below a predetermined value, and permanent magnet means acting at the other end of said element to attract said other end to a closed contact position and to releasably hold it there.

6. In a device of the class described, a bimetal strip pivotally supported intermediately of its ends, a movable contact carried at each end of said strip and on the same side thereof, a stationary contact adjacent each end of said strip and on the same side thereof as said movable contacts and being adapted to be engaged by said movable contacts and to stop movement of the ends of said strip in a closing direction upon engagement of said movable contacts, an armature carried at each end of said strip, stop means adjacent one end of said strip and on the side thereof opposite said stationary contact for limiting movement of that end of said strip in a contact opening direction, a permanent magnet adjacent said stop member and on the same side of said strip for attracting said end from a closed contact to open contact position and against said stop member, said stop member being adjustable so as to vary the approach of said strip end to said magnet thereby to vary the force by which said end is retained in a contact opening direction, and a permanent magnet adjacent the other end of said strip and on the same side as said stationary contact for attracting said other end to a closed contact position.

References Cited in the file of this patent UNITED STATES PATENTS 2,249,259 Shaw July 15, 1941 2,309,193 Holmes Jan. 26, 1943 2,374,097 Holmes Apr. 17, 1945 2,403,798 Holmes July 9, 1946 2,622,170 Van Toorn Dec. 16, 1952

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