Thermostatic switch construction

Abstract: In a snap-acting thermostat with a snap disc (30), a stationary contact support carrying a stationary con­ tact (55) and a moveable contact support arm (48) with a moveable contact (49) on it, a bumper (35) mounted for translation by the disc (30) and operatively connecting the disc (30) and the moveable contact (49) and a case (5) housing the snap disc (30), stationary contact (55), moveable contact (49) and bumper (35), interior side walls of the case (5) have guide channels (16,17) out­ board of the stationary and moveable contacts (55,49). The bumper (35) has a part substantially circular in section, extending within the compass of the guide channels (16,17) outboard of the contacts (55,49). The case (5) has a closed top (6) through which two contact terminals ex­ tend, and an open bottom (14) through which the elements enclosed by the case (5) can be mounted.

Description: This invention relates to a snap-acting thermostat having snap disc means, switch means including stationary contact support means and a stationary contact supported thereby and a movable contact support arm and a movable contact supported thereby, an actuator of substantially circular transverse cross-section mounted for translation by said disc means and operatively connecting said disc means and movable contact, guide means for said actuator, and a case housing said snap disc means, stationary contact, movable contact and actuator, said case having a top wall, an open bottom, peripheral wall means extending from said top wall and having a flat end surface disposed around said open bottom, and a closure closing the open bottom, said peripheral wall means having said guide means in the form of guide channels provided on the interior sides of said peripheral wall means, said guide channels facing one another and being on opposite sides of, spaced from and wholly outboard of said movable contact support arm and spaced from one another with respect to said movable contact support arm, said actuator extending within a compass of said guide channels outboard of said movable contact support arm, said guide channels constituting a sole guide for said actuator and said case, guide means and closure being constituted by only two separate parts. A thermostat of the above type is disclosed in DE-A-27 25 516. The case and closure of the known thermostat constitute a complete enclosure of only two separate parts. The thermal switch means can be installed from one end of the case. The actuator is guided in channels integral with the case sidewalls and located wholly outboard of the movable contact arm. The actuator or bumper consists of a thin plate guided in the channels of the case sidewalls. The thin plate is susceptible to cocking in two different planes which may cause binding or jamming of the plate. The known flat plate may be oval or round in side elevation but also in that form it is still susceptible to cocking or tilting which causes it to "grow", i. e. to increase its effective length between the disc and the switch arm thereby affecting gauging of the switch. In another embodiment a ball-shaped actuator can be used. Reference is also made to US-A-3 832 667 which discloses a thermostatic switch having an actuator or bumper which is substantially circular in transverse cross-section, but the bumper is not guided in channels of the case sidewalls wholly outboard of the movable contact arm. An additional guide part is provided having a small passage therethrough for guiding the actuator or bumper. A similar state of the art is also disclosed in US-A-3 861 032, 4 268 812 and 4 628 295. In US-A-3 496 511 the actuator or bumper is a flat disc which is free floating in the space between the contact arm and the bimetal disc. Thus it can shift and cock with respect to the contact arm and the disc which is not a satisfactory arrangement if any precision is to be obtained. The object of the invention is to provide an improved snap-acting thermostat of the recited type with an actuator that moves smoothly, with little likelihood of cocking or wedging, in its guides, with minimal effect on gauging, while retaining the advantages of simple and inexpensive design and the capability of being assembled from one end of the case. In accordance with the invention, to achieve this, the snap acting thermostat of the recited type is characterized in that said peripheral wall means have oppositely arranged projections formed integrally therewith and extending inwardly toward said actuator, that said guide channels have guide surfaces formed in the inner ends of said projections, and that the cross-sectional diameter of the actuator is smaller than the spacing between the portions of the peripheral wall means from which the projections extend. In preferred forms of the thermostat the case has a closed top through which two contact terminals extend, and an open bottom through which the elements enclosed by the case can be mounted. The open mouth has perimetric surfaces lying in a common plane and is closed by an imperforate closure. The case is provided with a plurality of projections integral with the case, extending beyond the rest of the open mouth in a direction away from the case and defining a locating seat for the disc. The disc closure has recessed seats deeper than the projections, receiving the projections without bottoming, a substantially planar surface within the compass of the seats, engaging the disc and surfaces defining a plane outboard of the seats against which a planar surface of the disc closure abuts to close the case. A mounting stud is elongated, with a substantially straight shaft, non circular in transverse cross section, having interrupted threads along a substantial length thereof, and a shank projecting into a complementarily non-circular opening in the disc seating plate, and is staked to lock it in the plate. The stationary contact is supported by an arm having two ends, one end being mounted on the case and the other carrying the stationary contact and projecting from a wall of the case in a direction toward the bumper at an acute angle with respect to the line of translation of the bumper in a direction toward the disc. In the course of assembly, the arm bearing the stationary contact can be bent in a direction toward the perpendicular to gauge the relative positions of the stationary and moveable contacts. L shaped terminals are provided with openings in a foot to receive terminal connectors from the stationary and moveable contacts, the connectors extending through the openings in the closed or integral top of the case. The placement of the opening is such that the L shaped terminals can be mounted to provide three predetermined spacings between legs perpendicular to the feet with the openings in them. In the drawings, Figure 1 is a sectional view of one illustrative embodiment of the thermostatic switch; Figure 2 is a view in rear elevation of an unmounted moveable contact assembly, viewed in the direction from right to left in Figure 1; Figure 3 is a view in side elevation of a bumper; Figure 3A is a view in end elevation of the bumper shown in Figure 3; Figure 4 is a top plan view of an unmounted fixed contact assembly; Figure 5 is a view in side elevation of the fixed contact assembly of Figure 4; Figure 6 is a view in front elevation of the fixed contact assembly of Figure 4; Figure 7 is a bottom plan view of the empty case of the switch shown in Figure 1, without a disc closure; Figure 8 is a sectional view taken along the line 8-8 of Figure 11; Figure 9 is a sectional view taken along the line 9-9 of Figure 11; Figure 10 is a top plan view of the case shown in Figure 7, without terminals; Figure 11 is a sectional view taken along the line 11-11 of Figure 10; Figure 12 is a sectional view of another embodiment of the thermostatic switch; Figure 13 is a fragmentary sectional view of the stud shown in Figure 12, staked into a disc closure plate; Figure 14 is a view in side elevation of the stud before it is mounted in the plate; Figure 15 is a top plan view of a disc closure, reduced in size compared with the views in Figures 1-11 but of a size with the device shown in Figure 12; Figure 16 is a view in side elevation of the disc closure shown in Figure 15; Figure 17 is a fragmentary sectional view taken along the line 17-17 of Figure 15; Figure 18A is a somewhat schematic drawing showing one position of mounting of terminals on the thermostatic switch; Figure 18B is a view in side elevation showing one alternative orientation of mounting of the terminals; and Figure 18C is a view in side elevation showing still another orientation of mounting of the terminals. Referring now to Figures 1 through 11, reference numeral 1 indicates an assembled disc type thermal snap switch, which includes a case 5 with a closed top 6 integral with end walls 9 and side walls 12. The closed top 6 has terminal connector openings 7 and 8, immediately adjacent the respective end walls 9. The case 5 is thus a genenally rectangular, one-piece box with an open bottom or mouth 14. The side walls 12 have bumper guide channels 16 and 17 in them, extending from the open mouth 14 toward the top 6, as indicated in Figures 1 and 8. The open mouth 14 of the case 5 is closed with a disc closure 20, which has a recessed planar relief area 23, circular in plan, within a planar surface 124. A disc 30 extends into the area 23, but does not bottom thereon, the disc being seated on the edges along which the recessed area 23 meets the planar surface 124. As shown in Figures 15 and 16, which illustrate a disc closure that differs from the disc closure shown in Figure 1 in providing for a stud mounting, the disc closure can be provided with straps that extend along the outside of the side walls and are crimped over a ledge 15 in the outside of the case. This is a conventional way of securing the disc closure to the case 5. The disc closure 20 also has wings or tabs, not here shown, by which the switch is surface mounted, which is a conventional arrangement. Within the case 5, a bumper 35, which in the embodiment shown in Figures 1,3 and 3A has a cylindrical mid section 37 and spherically curved end sections 38 and 39, is closely but freely slidably mounted between and extending within the guide channels 16 and 17. The bumper 35 bridges between and connects operatively the disc 30 and a moveable contact arm 48 of a moveable contact assembly 43. The moveable contact assembly 43 includes a terminal connector plate 44 with stabilizing wings 46, a terminal connector finger 45 projecting through the terminal connector opening 8 in the closed top 6, and a contact 49. The contact arm 48 is bent up at its end opposite the contact 49 to provide a lip 50 which is spot welded to the connector plate 44. The moveable contact assembly is mounted in the case, with the wings 46 in channels in the body, and the finger 45 extending through the opening 8 and projecting far enough above the outer surface of the top 6 to permit its securement to a terminal, as shown in Figure 1. A fixed contact assembly 54 is mounted on the inside surface of the opposite end wall 9 from the terminal connector plate 44. The fixed contact assembly 54 includes a fixed contact 55 mounted on a fixed contact arm 56. The fixed contact arm 56 is a part of a fixed contact terminal plate 58, which includes, besides the arm 56, wings 59 and a contact terminal connector finger 60. The fixed contact assembly 54 is mounted in the case, with the finger 60 projecting through the opening 7 in the top of the case and the wings 59 engaging channel-defining surfaces in the side walls 12, corresponding to the channels in which the moveable contact assembly is mounted. The general construction and contact of both the moveable contact assembly 43 and the fixed mounting assembly 54 are conventional. The exception is in the construction of the fixed contact arm 56, which, in this embodiment, makes an acute angle with the long axis or axis of translation of the bumper 35, in a direction toward the disc 30. As shown particularly in Figures 8,9 and 11, the outer margins of the open bottom 14 lie in the same plane. Inboard of the margins, and flanking a recessed seat 18 are 4 projections 110, each with a centering face 111. The moveable contact arm 48 is narrower in the transverse dimension than the diameter of the cylindrical portion 37 of the bumper 35, as indicated in Figure 7. That cylindrical portion 37 is slideably caged within the guide channels 16 and 17, formed in inwardly extending projections 16' and 17' of the case side walls 12, as also indicated in that figure. In assembling this embodiment of switch, the empty case is oriented with the open bottom facing upward. The moveable contact assembly is fit in place in the conventional way, followed by the fixed contact assembly. The bumper 35 is then slid into place in the guide channels 16 and 17. If there is any variation in the effective length of the bumper, or in the position of the moveable contact 49 with respect to the fixed contact 55, a gauging tool can be arranged automatically to bend the arm 56 toward the horizontal to the desired position. The disc 30 is then placed in the locating seat defined by the faces 111 of the projections 110, where it will be retained while the disc closure 20 is mounted. The disc closure 20 is, in all respects save the provision of a mounting stud, the same as the disc closure 120 of the embodiment next to be described. Referring now to Figures 12 through 17, reference numeral 101 indicates a second embodiment of switch of this invention identical with the embodiment shown in Figures 1 through 11 except for the provision of a spherical bumper 135 and a mounting stud 127, the latter requiring means for mounting the stud in the disc closure. In this embodiment, a disc closure 120 is identical with the disc closure 20 of the first embodiment, except for the provision of a square opening 125 in the center of the planar recessed area 23. The disc closure 120 has a planar area 124 surrounding the disc relief area 23 and adapted to close completely the open bottom of the case 5. Straps 122, are crimped over ledges 15 shown in figures 9 and 10. Recessed seats or pockets 121 are positioned and shaped complementarily to the projections 110 on the case, but are deeper than the projections, so that the projections do not bottom out in the seats 121. This ensures that the planar area 124 butts a flat surface 19 of the side and end walls which defines a plane around the open bottom, outboard of the projections 110, so that the disc closure totally closes the open bottom. At the same time, the extension of the projections 110 into the recesses 121 below the level of the planar surface 124 of the disc closure 20 ensures the continued proper location of the disc with respect to the bumper after the device is assembled. Conventionally, the disc is either located in a shallow well in the case or in a separate piece between the case and the disc closure, in which case it is easy for the disc to slip out of position, or else detents are formed in the disc closure to keep the disc centered. In the latter arrangement, the disc is supported on a set of pads, which has a detrimental effect on the heat transfer to the disc. In the present construction, because the closure always mates with the case on the flat surfaces outboard of the recesses, and the edge of the disc relief being the support surface for the disc, the construction of the device of this invention provides reliable gauging and consistent thermal response. At the same time, because the seats 121 are merely recessed and do not involve openings, it provides a totally enclosed package as well. In the particular embodiment of stud mounted switch shown in Figures 12 through 17, the square hole 125 receives a square shank 126 of a stud 127. The stud has a shaft 128 with interrupted threads 129 through most of its length. The shank 126 is initally square and the shaft 128 is initially rectangular. The shank 126 is reduced with respect to the shaft to provide a shoulder 130. Accordingly, in the embodiment illustrated, the threads 129 are interrupted on all four flat sides of the shaft. As shown in Figure 13, the shank 126 is inserted in the opening 125 and staked to secure it to the disc closure. The advantages of the use of the spherical bumper include the availability of accurately formed spheres, the fact that they require no orientation for their insertion, the fact that they move with a minimum of friction, and that their rotation has no effect on their gauging. The advantage of the square shanked stud is that the disc closure and stud can be made and assembled automatically on a single machine. Referring now to Figures 18A through 18C, a terminal assembly 165 is provided that is particularly adapted to use with "multi-fit" connectors which have receptacle spacings on increments of 5 millimeters. To accomplish this, the terminal assembly 165 is made up of two L-shaped blades 167, each with a foot 168 and an outwardly projecting leg 171. The foot 168 has in it a finger receiving opening formed to receive either the fixed contact terminal connector finger 60 or the moveable contact terminal finger 45, the two fingers being identically dimensioned at their outer ends. The finger receiving opening is centered in the direction lengthwise of the foot 168 exactly 2 1/2 millimeters from the center line in the direction of its width of the outwardly projecting leg 171. Thus, when the terminals are oriented as shown in Figure 18A, the distance between the center line of outwardly projecting legs 171 is 20 millimeters; when oriented as in Figure 18B, 15 millimeters, and when oriented as in Figure 18C, 10 millimeters. In this way, the same terminal blades can be used to provide a terminal assembly that will fit three different standard connectors. The case in each embodiment is made with a seat dimensioned to receive the terminal foot in either orientation, as indicated in Figure 12 as well as in Figures 18A-18C. Numerous variations in the construction of the thermostatic switch, within the scope of the appended claims, will be apparent to those skilled in the art in the light of the foregoing disclosure. Merely by way of example, the transverse cross sectional shape of the stud can be varied, provided that the shank is non-circular. The case can be of different shapes and dimensions. It can even be cylindrical, with guide channels on diametrically opposed surfaces. The number of projections and corresponding seats can vary from three to more than four, and their particular configurations can vary, as long as they do not bottom in the disc closure recesses. It can be appreciated that the disc closure can be provided with wings for surface mounting or for a clip mount, or have a welded clip for a pipe mount or welded strap for surface mounting. The bumper can assume various shapes in transverse section, as, for example, an oval shape, but for ease of manufacture and ready availability, preferrably, either a cylindrical bumper with spherical contact faces or, a spherical bumper, has many advantages. The stud mounting arrangement is particularly useful with the thermostat switch of this invention, but has other applications. The L-shaped terminals adaptable to three different standard connectors can also be incorporated into other controls and the like, and instead of the fingers, the locating means can take the form of rivets, or sockets into which a toe, depending from the end of the foot, projects, for example. These variations are merely illustrative.

Claims: A snap-acting thermostat having snap disc means (30), switch means including stationary contact support means and a stationary contact (55) supported thereby and a movable contact support arm (48) and a movable contact (49) supported thereby, an actuator (35;135) of substantially circular transverse cross-section mounted for translation by said disc means (30) and operatively connecting said disc means (30) and movable contact (49), guide means for said actuator (35;135), and a case (5) housing said snap disc means (30), stationary contact (55), movable contact (49) and actuator (35;135), said case (5) having a top wall (6), an open bottom (14), peripheral wall means (9, 12) extending from said top wall (6) and having a flat end surface (19) disposed around said open bottom (14), and a closure (20;120) closing the open bottom (14), said peripheral wall means (9, 12) having said guide means in the form of guide channels provided on the interior sides of said peripheral wall means (12), said guide channels (16, 17) facing one another and being on opposite sides of, spaced from and wholly outboard of said movable contact support arm (48) and spaced from one another with respect to said movable contact support arm (48), said actuator (35;135) extending within a compass of said guide channels (16, 17) outboard of said movable contact support arm (48), said guide channels (16, 17) constituting a sole guide for said actuator (35;135) and said case (5), guide means and closure (20;120) being constituted by only two separate parts, characterized in that said peripheral wall means (12) have oppositely arranged projections (16',17') formed integrally therewith and extending inwardly toward said actuator (35; 135), that said guide channels (16, 17) have guide surfaces formed in the inner ends of said projections, and that the cross-sectional diameter of the actuator (35; 135) is smaller than the spacing between the portions of the peripheral wall means from which the projections extend. Thermostat according to claim 1, characterized in that the actuator (35) is cylindrical through a center section (37), with spherical end parts (38, 39). Thermostat according to claim 1, characterized in that the actuator (135) is spherical. Thermostat according to claim 1, characterized in that said closure (120) has a mounting stud (127) projecting in a direction away from said case, said stud (127) being elongated and axially, substantially straight, non-circular in transverse cross-section, having interrupted threads (129) along a substantial length thereof, said stud (127) having a non-circular shank (126) projecting into an opening (25) in said closure (120) and staked to lock it in said closure (120). Thermostat according to claim 4, characterized in that the stud (127) is rectangular in transverse cross-section and the opening (125) is complementarily rectangular. Thermostat according to claim 1, characterized in that said case (5) has a plurality of projections (110) integral therewith and extending beyond said open bottom (14) in a direction away from said case (5) and each defining a centering face (111) for said disc means (30), said closure (20;120) having recessed seats (121) deeper than said projections (110), receiving said projections (110) without bottoming. Thermostat according to claim 6, characterized in that said closure (20; 120) has a planar surface (124) outboard of said seats (121) and engaging said flat end surface (19) of said peripheral wall means (9; 12), said planar surface (124) surrounding a disc relief area (23) disposed within the compass of said seats (121), said planar surface (124) intersecting the relief area (23) along an edge defining a support for said disc means (30). Thermostat according to claim 1, characterized in that said stationary contact support means is accessible to a gauging tool from the open bottom (14) of the case (5) before the closure (20) is put into place, said stationary contact means including an arm (56) having two ends, one end being mounted on said case (5) and the other end carrying said stationary contact (55) and projecting from a wall (9) of said case (5) in a direction toward said actuator (35) at an acute angle with respect to the line of translation of said actuator (35) in a direction toward said disc means (30), whereby said stationary contact (55) can be bent upwardly to gauge the operating clearances of the disc-actuator-movable contact mechanism. Thermostat according to claim 1, characterized in that the stationary contact support means has an arm (56) with a part with a terminal connector connected thereto and the movable contact support arm is electrically connected to a terminal connector, that said case top wall (6), has terminal connector apertures (7, 8) in it, spaced from one another, a finger (45) of one of said stationary and movable contact terminal connectors extending through one of said apertures (7, 8) and a finger (60) of the other of said terminal connectors extending through the other of said apertures (7, 8), said apertures (7, 8) being 15 millimeters apart, center to center, and two terminals (167), L-shaped in side elevation, each with an outwardly projecting leg (171) and a foot (168) with a terminal connector opening in it receiving one of said terminal connector fingers (45, 60), said openings being 2.5 millimeters from the center of the outwardly projecting leg (171), thicknesswise, whereby, depending upon the orientation of said terminals (167) with respect to one another, they can be spaced 10, 15 or 20 millimeters apart.

Inventors: WELLS GORDON KEITH, WELLS, GORDON KEITH
Applicants: EMERSON ELECTRIC CO, EMERSON ELECTRIC CO.
Application year: 1988
Main classification: H01H37
IPC codes: H01H37