US3629770A

US3629770A - Thermostat with stable switch mount

Info

Publication number: US3629770A
Application number: US83994A
Authority: US
Inventors: Jean R Fortier; Paul M Moskowitz
Original assignee: Federal Pacific Electric Co
Current assignee: CAROLINA PRODUCTION ENTERPRISES Inc A SC CORP
Priority date: 1970-10-26
Filing date: 1970-10-26
Publication date: 1971-12-21
Anticipated expiration: 1988-12-21
Also published as: CA929992A

Abstract

A line-voltage thermostat is described having a snap-switch proportioned to carry heavy line current to an electric room heater. The snap-switch is mounted on a baseplate which is to be mounted on a wall box. The screws used to mount the baseplate have long shanks so as to be accessible well forward of the baseplate. The mounting screws extend through arched straps which are sheared free of the baseplate except at their ends. This avoids upset of the calibration due to deformation of the baseplate during tightening of the mounting screws, considering mainly the area of the baseplate where the switch is mounted. The thermostat has a bimetal held at a hinge point by a single unique spring. Fixed ears project toward the bimetal to limit the extent the bimetal can be depressed, protecting the switch from damage and from calibration error due to excessive manual force on the bimetal when the thermostat is being installed or serviced.

Description

. United States Patent [72] Inventors Jean R. Fortier 3,454,919 7/ i969 Kulick 337/360 south o'mget Primary Examiner-Bernard A. Gilheany Paul M- Moskowltz, Brooklyn, N-Y. Asst-am p B Be [2]] App]. No. 83,994 Ar'tomeyPaul S. Martin [22] Filed Oct. 26,1970 V [45] Patented Dec. 21,1971 [73] As gn" Fedfl'll Plcmc Ekfll'lc l y ABSTRACT: A line-voltage thermostat is described having a NW 'h -J' snap-switch proportioned to carry heavy line current to an electric room heater. The snap-switch is mounted on a baseplate which is to be mounted on a wall box. The screws [54] THERM-OSI'EAT r g, STABLE SWITC MOUNT used to mount the baseplate have long shanks so as to be ac- 4 Claims cessible well forward of the baseplate. The mounting screws [52] U.S.Cl 337/333, extend through arched straps which are sheared free of the 337/338, 337/360, 337/372, 337/380, 337/417 'baseplate except at their ends. This avoids upset ofthe calibra- [51] Int. Cl. l-l0lh 37/52 tion due to deformation of the baseplate during tightening of [50] Field of Search 337/42, the mounting screws, considering mainly the area of the 102, 111, 333, 334, 338, 360, 363, 372, 379, 380, baseplate where the switch is mounted.

417, 337 The thermostat has a bimetal held at a hinge point by a single unique spring. Fixed ears project toward the bimetal to 1 kekl'mc's Cned limit the extent the bimetal can be depressed, protecting the UNITED STATES PATENTS switch from damage and from calibration error due to exces- 2,171,272 3/1939 m et a 337 3 sive manual force on the bimetal when the thermostat is being I installed or serviced. 74mm A 4 W 45 7% f d /0- A I Z i 26 A, *I L 4x 52 .772 if Tag-fa w if 7a 3% We 52 .wii 4% l l8 mounted on the same base-plate as the one which carries the mounting screws for securing the thermostat to the junction box. Any deformation of the thermostat base-plate caused by the mounting screws may upset the calibration. A feature of the present invention involves locating the mounting screw holes in respective arched strips that are stress-isolated from the area of the base plate that carries the switch. The strips are provided at each of the ends of the base plate, and they extend from opposite corners of the flanged base-plate. In contrast to many other configurations, this mounting-strap feature has been found extremely effective in divorcing distortions produced in the mounting structure by the tightened mounting screws from disturbing the switch-mounting area, thus making the thermostat calibration highly immune to mounting stresses.

The presently described thermostat involves a secondary plate acting as a heat shield betweenand spaced from-the bimetallic sheet and the main base-plate of the thermostat. In use, this main plate is secured by mounting screws to a wall box. The mounting screws have bearing shoulders against the mounting strips of the main base plate. These screws have upstanding stems that are slotted for screw-driver operation, and the stems project well forward of the main base plate. This feature makes the screws easily accessible to the installer, and thereby protects the bimetallic sheet in front of the subplate from damage that might be caused inadvertently by the installer in groping for deeply recessed mounting screws.

The nature of the invention will be more fully appreciated from the following detailed description of an illustrative embodiment of the invention shown in the accompanying drawings. In the drawings:

FIG. 1 is a central vertical cross section perpendicular to the front of an illustrative thermostat embodying the features of the invention;

FIG. 2 is front view of the thermostat of FIG. I with the cover and other parts in front of the bimetal removed, certain partly removed parts being shown in cross section; and a portion of the bimetal being broken away;

FIG. 3 is a rear view of the thermostat as in FIG. 2, part of the switch being broken away to expose detail of the base plate;

FIG. 4 is a horizontal cross section of the thermostat of FIGS. 1-3 looking upward from the plane 44 of FIG. 3;

FIG. 5 is an enlarged detail of FIG. 1;

FIG. 6 is a bottom view of the thermostat base plate; and

FIG. 7 is a perspective view ofa spring in FIGS. l-3.

Referring now to the drawings, a wall box B is suitably supported in an opening in wall W. The thermostat has a main mounting plate 10 having side flanges l2 and top and bottom flanges 14 which provide stiffening and which space the central area 16 away from wall W. Arched mounting straps l8 and 20 extend integrally from top and bottom flanges l4 and initially are in the plane of flat central area 16. The edges of these straps are cut clean and do not bind or interlock with the adjoining metal. I-Iorizontal'and

vertical slots

22 and 24 are provided in straps l8 and 20 for screws 26. Each of these screws has a laterally projecting shoulder or flange 28 overlying strap 18 (20), a fiber washer 30 behind the strap that holds the screw captive, and an elongated stem 32 that has a screwdriver slot at its upper end.

A switch 34 is screwed to area 16 at the rear of the main mounting plate so as to be received in box B. Short posts 34a extend integrally from switch 34 at each of the mounting points, providing an air space between area 16 of main mounting plate 10 and switch 34.

Holes or slots 38 in flanges l4 are provided for admitting and discharging convection air currents, for carrying away heat generated in switch 34. These slots do not extend to the extremities of straps I8 and 20 so that those straps are integral with relatively strong portions of flanges 14.

A secondary plate 40 is secured to main mounting plate I0 by four screws 42 in area 16. These screws extend from the rear of plate 10 through spacing sleeves 44 that are of plastic, ceramic or other solid thermal insulation. The space between

plates

10 and 40 is a second convection air space for carrying away any heat that was developed originally in the switch and that reached plate 10 in some small degree. Secondary plate 40 has sidewalls 40a along its vertical margins. At the bottom, each sidewall 40a is bent at right angles to form arms 40b; and bimetal-locating lugs 40c extend from these arms 40b. Arms 40b form a hinge or fulcrum across ambient temperature sensing bimetal 46 near its bottom edge. Lugs 40c extend through a pair of holes 460 in the bimetal. A biasing spring 48 (FIG. 7) has a very wide V-shaped central portion 48a that is received at its apex in a slot 40d. Spring 48 has reverse-bent portions or hooks 48b extending about the upper and lower sides of lugs 40c. bearing against the side of bimetal 46 that faces plate 40. Slot 40d is transverse to plate 40 and is aligned with ears 40c. Spring 48 is of wire that is nearly as thick as slot 40d is wide. Because of the fit of spring part 48a in slot 40d, part of spring 48 near its extremity at the left as viewed in FIG. 2 bears against the bottom face of one lug 40c and part of the spring near its right-hand extremity bears against the top face of the other lug 400. The overall effect of this configuration is to provide dependable pressure of the spring against bimetal 46, a pressure that remains consistent among many thermostats and mechanically stable in each thermostat. The small movement that may be exerted on the bimetal by one end of the spring acting about the pivot represented by the related arm 40b is canceled by a like opposite movement at the other arm 40b.

Remote from the lower hinged end of the bimetal, near the top of the bimetal, there is a cam-follower in the form of a button 50 secured rigidly to the bimetal. A cam 52-is supported on a rotatable shaft 54 for cooperation with cam-follower 50. A reduced end portion 54a of shaft 54 extends through a hole in secondary plate 40. The shoulder formed by the largediameter portion of shaft 54 at the front of plate 40 forms a stable bearing surface against plate 40. Small diameter portion 54a extends through plate 40. Shaft 54a is held in assembly to plate 40 by a special washer 56 that is force-fitted over shaft extension 54a to bear against a further washer 58 at the back of secondary plate 40.

Switch 34 in the form illustrated, is a double pole switch, having two separate switching parts of the so-called microswitch or overcentering snap-switch variety. The switch is in a normal" stable configuration when its rod 34b is released, and the switch is operated" or moved out of its normal" position when rod 34b is pushed deeper into the switch body. For each pole of the switch, a set screw 60 is provided in bimetal 46 and cooperates with the end of rod 34b remote from switch 34. This rod extends through oversize holes in

plates

10 and 40, and is guided by a bushing 34c of the switch. The switch biases rod 34b outward, so that rod 34b normally biases its set screw 60 toward the left (FIG. I) and away from the switch. This effect causes button 50 to bear against cam 52. When the bimetal is subjected to a rising ambient temperature, its center portion becomes arched toward the right as viewed in FIG. I causing rod 34b to reverse the condition of switch 34 from normal" to its operated condition. Screw 60 is used to provide for calibration, and cam 52 enables the user to adjust the set point of the thermostat. Cam 52 has an extreme position or portion (not shown) which coacts with cam-follower 62 for deflecting bimetal 46 to the right in such a way as to insure operation of both poles of switch 34 out of their normal condition for even the lowest temperature to be experienced by the thermostat. Cam 52 represents a conventional off operator for both poles of the switch. Various combinations of switches are used in various thermostats, sometimes including a snap switch at one pole and a slow-acting switch operated by cam-follower 62 as the other pole. At other times, both poles of the switch are snap switches and are arranged to operate at or nearly at the same set-point.

A transparent cover 64 encloses that portion of the thermostat containing bimetal 46. Slots 640 at the top and bottom provides for convection air currents entering the cover and moving along the front and back of bimetal 46. Knob 66 fixed to shaft 54 operates cam 52. An edge portion of knob 66 extends laterally through a slot (not shown) in cover 64 for changing the set-point of the thermostat, A cover plate 68 has lateral lugs that are received in retaining slots 69, one such slot being provided in each sidewall 40a near the bottom thereof and another such slot being provided in each sidewall 40a near the top thereof for receiving lateral lugs of plate 68. All slots 69 open upward, so that plate 68 slides down into the slots, when the plate is being mounted. Cam 52 is received in an oversized hole in plate 68.

A so-called anticipator resistor 70 is held against bimetal 46 by a retaining clip 72 that is riveted to the bimetal. Flexible insulated connecting wires 700 from resistor 70 extend through drawn

holes

74 and 76 in

plates

40 and 10, respectively. The anticipator wires extend to the rear of plate where suitable electrical connections are made, customarily to the load-side terminals of the two poles of switch 34.

In mounting the thermostat, cover 64 is snapped off the ends of plate 40, knob 66 is removed and plate 68 is slid upward and removed. At the top of the thermostat, slotted stem 32 of one screw 26 is easily engaged for operation because it extends well forward of plate 40, through an oversized hole in that plate. Near the bottom of the thermostat, there is an opening 46b, and stem 32 of the lower screw 26 extends to a convenient level close to the plane of the bimetal for easy access and operation. Screws 26 are therefore easily operable from the front of the thermostat, and they drive their respective straps l8 and 20 .firmly backward (and against) the mounting ears of box B. Despite the considerable deformation of straps l8 and 20 that is possible, area 16 is not warped or distorted in this operation. Consequently the relationship of screw(s) 60 and switch rods 34b which is critically adjusted at the factory in a calibration operation, is not disturbed.

A pair of stops 78 extend forward as integral parts of secondary plate 40. Stops 78 resist positively any deflection of bimetal 46 beyond a certain point. In the absence of such stops 78, careless pressure applied to bimetal 46 could drive rods 34b too far into the body of switch 34, possibly causing permanent deformation or other damage to the switch. This might not disable the switch, but the thermostat calibration could be upset.

We claim:

1. A thermostat including a base plate having a switchmounting area, a bimetallic sheet disposed generally parallel to said switch-mounting area, a switch mounted on said base plate in said area, means forming a calibrated coupling between said switch and said bimetallic sheet, and mounting straps at opposite ends of the base plate, the extremities of each mounting strap extending integrally from margins of the base plate at the opposite ends thereof, each of said straps having an aperture spaced from said extremities for receiving a mounting screw to secure the thermostat to a wall box without deforming said switch mounting area,

2. A thermostat in accordance with claim 1, including a secondary plate between the bimetallic sheet and the base plate and separated by respective air spaces therefrom, and respective screws in said apertures, each of said screws having a shoulder bearing against the related strap and having a screwdriver-slotted stern projecting well forward of said base plate.

3. A thermostat in accordance with claim 1, wherein said straps are curved toward each other so as to dispose said screw-receiving apertures substantially inward from the opposite-end margins of said base plate 4 A thermostat in accordance with clam; 1, wherein said base plate is a rectangular metal sheet having marginal flanges, and wherein said straps extend substantially form the comers thereof.

Claims

1. A thermostat including a base plate having a switch-mounting area, a bimetallic sheet disposed generally parallel to said switch-mounting area, a switch mounted on said base plate in said area, means forming a calibrated coupling between said switch and said bimetallic sheet, and mounting straps at opposite ends of the base plate, the extremities of each mounting strap extending integrally from margins of the base plate at the opposite ends thereof, each of said straps having an aperture spaced from said extremities for receiving a mounting screw to secure the thermostat to a wall box without deforming said switch mounting area.

2. A thermostat in accordance with claim 1, including a secondary plate between the bimetallic sheet and the base plate and separated by respective air spaces therefrom, and respective screws in said apertures, each of said screws having a shoulder bearing against the related strap and having a screwdriver-slotted stem projecting well forward of said base plate.

3. A thermostat in accordance with claim 1, wherein said straps are curved toward each other so as to dispose said screw-receiving apertures substantially inward from the opposite-end margins of said base plate.

4. A thermostat in accordance with claim 1, wherein said base plate is a rectangular metal sheet having marginal flanges, and wherein said straps extend substantially form the corners thereof.