Thermostat assembly

Abstract: A thermostat assembly includes a spring washer (G) in­ terposed between a switch case (A) and a bimetal disc (F) for biasing such disc (F) into firm engagement with the disc hou­ sing (E) to enhance heat transfer and dampen bouncing of the disc (F).

Description: Background of the Invention This application relates to the art of thermostats and, more particularly, to thermostats of the type that use a bimetal disc operative in response to temperature changes for opening and closing a switch. Although the invention is particularly applicable to thermostat assemblies, it will be appreciated that the improved spring washer of the present application can also be used in other environments. Thermostat assemblies of a known type include a bimetal disc positioned between a switch case and a metal disc housing. Heat is transferred to and from the bimetal disc through the metal disc housing. Poor heat transfer takes place if the bimetal disc is not in firm engagement with its metal housing under all operating conditions. In DE-A-27 18 690, on which the two-part form of independent claim 1 is based, there is provided an elastomer ring between the switch case and the bimetal disc to urge the disc against a metal support element which is in thermal contact with the metal disc housing for maintaining the bimetal disc in firm engagement with its metal housing to provide enhanced heat transfer. The elastomer ring engages the bimetal disc radially inwardly of its periphery. Summary of the Invention The object of the present invention is to provide an improved thermostat assembly having a bimetal disc biased into firm engagement with its metal housing. According to the invention there is provided a thermostat assembly of the type as defined in independent claim 1 having a spring washer interposed between a switch case and a bimetal disc and acting on the disc only adjacent its outer periphery for biasing such disc into firm engagement with its metal housing. In one embodiment, the biasing means is in the form of a spring washer having a flat ring-like base portion. Resilient attaching means is provided on the spring washer for attaching same to a switch case. In a preferred embodiment, the resilient attaching means comprise a pair of opposite spring fingers extending generally perpendicular from the base portion of the spring washer adjacent the inner periphery thereof. Locating means may be provided on the spring washer for locating and maintaining a predetermined relationship between the spring washer and the bimetal disc during assembly. The locating means may be in the form of a plurality of circumferentially-spaced locating tabs having first tab portions extending outwardly from the outer periphery of the base portion, and second tab portions extending generally perpendicular to the first tab portions. The disc biasing means for biasing against the bimetal disc includes a plurality of circumferentially-spaced disc biasing tabs extending outwardly from the outer periphery of the base portion and being bent downwardly from the base portion at angles of less than 30°. The opposite biasing means is provided on the spring washer for biasing against an end surface on the switch case in opposition to the disc biasing means. The opposite biasing means may comprise a set of biasing tabs complementary to the disc biasing means. The thermostat and a spring washer disclosed herein is economical to manufacture and assemble. Brief Description of the Drawing Figure 1 is an exploded perspective illustration of a thermostat assembly; Figure 2 is a top plan view of a spring washer constructed in accordance with the present application; Figure 3 is an end elevational view taken generally on line 3-3 of Figure 2; Figure 4 is a partial cross-sectional elevational view taken generally on line 4-4 of Figure 2; Figure 5 is a partial cross-sectional elevational view taken generally on line 5-5 of Figure 2; Figure 6 is a bottom plan view looking into a switch case in the general direction of arrows 6-6 of Figure 1; Figure 7 is an inverted partial cross-sectional elevational view taken generally on line 7-7 of Figure 6; and Figure 8 is a partial cross-sectional elevational view taken generally on line 8-8 of Figure 1, and with portions removed for clarity of illustration. Description of a Preferred Embodiment Referring now to the drawing, wherein the showings are for purposes of illustrating a preferred embodiment of the invention only and not for purposes of limiting same, Figure 1 shows a ceramic switch case A having a closed end 12 and an open end 14 providing access to a hollow interior. A peripheral wall 16 extends between closed end 12 and open end 14. A stationary contact support B has an electrical contact 18 mounted thereon. Stationary contact support B is receivable within the hollow interior of switch case A, and a projection 20 thereon is extendable through a slot 22 in closed end 12. Projection 20 is receivable in a hole 24 in a terminal 26 that is receivable in a recess 28 in closed end 12 aligned with slot 22. Projection 20 is then spun over to fasten stationary contact support B with terminal 26. Movable contact support C is receivable within the hollow interior of switch case A, and has an elongated movable switch arm 32 welded and crimped thereto. A movable contact 34 is carried by the free end portion of movable switch arm 32. Movable contact support C has a projection 36 thereon extendable through a slot 38 in closed end 12. A terminal 40 is receivable in a recess 42 in closed end 12 aligned with slot 38. A hole 44 in terminal 40 receives projection 36 on movable contact support C. Projection 36 is then spun over for fastening terminal 40 with support C. A transfer pin D is positioned and guided within the hollow interior of switch case A for longitudinal movement, and cooperates with switch arm 32 for moving movable contact 34 into and out of engagement with stationary contact 18. An aluminum housing E has a central circular recess 50 therein surrounded by a shoulder 52. A plurality of bendable securing tabs 54 on housing E are formable into firm engagement with shoulders 56 provided by corner recesses 58 on switch case A. Aluminum housing E thereby closes open end 14 of switch case A. Bimetal disc F spans recess 50 in housing E, and a peripheral surface portion of disc F engages shoulder 52. Mounting tabs 60 are provided on housing E for mounting the assembled thermostat. A spring washer G constructed in accordance with the present application biases against an end surface on switch casing A and against bimetal disc F for maintaining same in firm engagement with shoulder 52 on housing E. The biasing action takes place in both of the oppositely bowed positions of bimetal disc F, as well as positions therebetween, and enhances heat transfer between the disc and housing. Spring washer G also provides damping action to reduce bouncing of bimetal disc F when it snaps between its opposite positions. Bimetal disc F is normally bowed downwardly into recess 50 in housing E, and electrical contacts 18, 34 are closed. When bimetal disc F reaches a predetermined temperature, it snaps to a reversed curvature and moves transfer pin D longitudinally to bend switch arm 32 and separate movable contact 34 from stationary contact 18. Figures 2-5 show spring washer G as including a flat ring-like base portion 70 having inner and outer peripheries 72, 74. Inner periphery 72 defines a central hole in spring washer G through which transfer pin D freely moves. Resilient attaching means is provided for attaching spring washer G to switch case A. In the arrangement shown, the resilient attaching means is in the form of a pair of opposite resilient spring fingers 76, 78 located adjacent inner periphery 72. Disc biasing means is provided on spring washer G for biasing bimetal disc F into firm engagement with shoulder 52 on housing E. In the arrangement shown, the disc biasing means is in the form of four disc biasing tabs 80, 82, 84 and 86 circumferentially-spaced around base portion 70. As shown in Figure 5, each disc biasing tab is bent downwardly relative to flat base portion 70 at an angle loss than 30°, and preferably around 15°. The outer curved ends of disc biasing tabs 80-86 lie on the periphery of a circle having a diameter that is approximately same as the diameter of bimetal disc F. Figure 5 also shows a finger 76 as having a first short portion 90 inclined upwardly from flat base portion 70 at an angle of about 60°, a second elongated portion 92 extending at an angle of about 60° to first portion 90, and a third or terminal portion 94 extending at an angle of about 60° to second portion 92. The intersection 96 of the second and third portions 92, 94 defines an engaging portion that grippingly engages the bottom surface of a recess in switch case A. Opposite biasing means is provided on spring washer G for biasing against an end surface on switch case A in opposition to disc biasing tabs 80-86. The opposite biasing means is in the form of four opposite biasing tabs 102, 104, 106 and 108 circumferentially-spaced around flat base portion 70. Opposite biasing tabs 102-108 are bent upwardly from flat base portion 70 at angles less than 30° and preferably about 15°. Locating means is provided for locating and maintaining a predetermined relationship between spring washer G and bimetal disc F during assembly of same into the thermostat housing. The locating means is in the form of four resilient locating tabs 110, 112, 114 and 116 circumferentially-spaced around flat base portion 70. As shown in Figure 4, each locating tab includes a first elongated portion 120 extending outwardly from base portion 70 in the same plane therewith and a second portion 122 extending substantially perpendicular to first portion 120. The included angle between first and second portions 120, 122 is preferably slightly greater than 90° to allow for springback. Axially of spring washer G, the terminal ends of second portions 122 are spaced substantially further from flat base portion 70 than the terminal ends of disc biasing tabs 80-86. The terminal ends of second portions 122 on the locating means preferably lie on the periphery of a circle having a diameter slightly greater than the diameter of the circle on which the ends of tabs 80-86 and 102-108 lie. The circumferential width of locating tabs 110-116 is substantially less than the circumferential width of biasing tabs 80-86 and 102-108 so that the locating tabs are readily bendable out of the way when housing E is assembled to case A. Figure 6 shows the interior of switch case A as having opposite spaced-apart bosses 140-142 with opposed generally U-shaped transfer pin guideways 144, 146 in which transfer pin D is guided for longitudinal reciprocal movement. Elongated rectangular recesses 148, 150 at the base of the guideways extend longitudinally of transfer pin D for receiving resilient spring fingers 76, 78 on spring washer G as shown in Figure 7. Recessed cavities 160, 162 in bosses 140, 142 are provided for receiving at least portions of biasing tabs 102-108 on spring washer G. The flat bottom surfaces of cavities 160, 162 are engaged by opposite biasing tabs 102-108 as shown in Figure 7. When spring washer G, bimetal disc F and housing E are assembled, switch case A is inverted from the position shown in Figure 8. With the case so inverted, spring washer G can be attached to the bosses within the hollow interior of switch case A. Bimetal disc F is then placed within the locating tabs which are on a slightly greater diameter circle than the diameter of the bimetal disc. Thus, bimetal disc F is freely received within the locating tabs but is located and maintained in a predetermined relationship relative to spring washer G while housing E is attached to switch case A. When housing E is attached, flat surface 53 adjacent shoulder 52 engages the terminal ends of the locating tabs to push same upwardly out of the way. The axial clearance between disc housing E and the bottom of switch case A is sufficient to allow such displacement. The outer terminal ends of the disc biasing tabs engage bimetal disc F closely adjacent the outer periphery thereof for firmly biasing same into engagement with shoulder 52. Regardless of whether the thermostat assembly is mounted in the position shown in Figure 8, in an inverted position, or in positions therebetween, spring washer G will always firmly bias the bimetal disc into engagement with its aluminum housing E to provide enhanced heat transfer. When bimetal disc F snaps to a reversed curvature from that shown in Figure 8, transfer pin D moves upwardly into engagement with switch arm 32 for moving movable contact 34 out of engagement with stationary contact 18. In the reversed curvature position of bimetal disc F, the disc biasing means is still operative to maintain firm engagement of the disc with aluminum housing E. When the bimetal disc cools, it snaps back to the position shown in Figure 8 for allowing transfer pin D to move longitudinally toward housing E and allow the switch contacts to close. In the reversed curvature position of bimetal disc F, the biasing force of switch arm 32 acting through transfer pin D also biases bimetal disc F into firm engagement with its housing E. The attaching means defined by resilient spring fingers 76, 78 also defines a locating means for locating spring washer G centrally of the switch case during assembly of housing E thereto. With bimetal disc F held within locating tabs 110-116, both spring washer G and bimetal disc F are located on switch case A in substantially centered axial alignment with the center of recess 50 in housing E and with the longitudinal axis of transfer pin D. As previously mentioned, the outer ends of disc biasing tabs 80-86 and the outer periphery of bimetal disc F lie approximately on the circumference of a common circle. When tabs 80-86 are flexed during assembly of the thermostat, the ends of such tabs will lie on the circumference of a circle having a diameter slightly greater than the diameter of the circle on which the periphery of disc F lies. Tabs 80-86 will then engage the edge intersection between the periphery of disc F and the surface of disc F that faces toward transfer pin D. In any event, tabs 80-86 preferably engage disc F at or closely adjacent the aforementioned edge intersection.

Claims: Thermostat including a housing (E) having an internal disc receiving recess (50) surrounded by a shoulder (52), a bimetal disc (F) spanning said recess (50) and having an outer peripheral surface portion engaging said housing (E) adjacent said shoulder (52), a switch case (A), resilient means positioned between said bimetal disc (F) and said switch case (A) for biasing said peripheral surface portion of said disc (F) into firm engagement with said housing shoulder (52), characterized in that said resilient means comprises a spring washer (G) having disc biasing means (80, 82, 84, 86) acting on the disc only adjacent the disc outer periphery and the spring washer (G) having opposite biasing means (102, 104, 106, 108) acting against the switch case (A) in opposition to the disc biasing means (80, 82, 84, 86). Thermostat according to claim 1, characterized by including locating means (110, 112, 114, 116) on the spring washer (G) for locating and maintaining the position of the bimetal disc (F) relative to the spring washer (G) during assembly of same into the housing (E). Thermostat according to claim 2, characterized in that the spring washer (G) has resilient attaching means (76, 78) engaging interior surface portions to the switch case (A) for attaching the spring washer (G) to the switch case (A). Thermostat according to claim 3, characterized in that the spring washer (G) includes a flat ring-like base portion (70) having inner (72) and outer (74) peripheries, the attaching means (76, 78) extending from the base portion (70) adjacent the inner periphery (72) and the locating means (110, 112, 114, 116), the disc biasing means (80, 82, 84, 86) and the opposite biasing means (102, 104, 106, 108) extending from the base portion (70) adjacent the outer periphery (74). Thermostat according to claim 4, characterized in that said locating means (110, 112, 114, 116) comprises a plurality of circumferentially spaced locating tabs (110, 112, 114, 116) and said disc biasing means (80, 82, 84, 86) comprises a plurality of circumferentially spaced disc biasing tabs (80, 82, 84, 86). Thermostat according to claim 5, characterized in that said disc biasing tabs (80, 82, 84, 86) have a circumferential width that is greater than the circumferential width of said locating tabs (110, 112, 114, 116). Thermostat according to claim 5 or 6, characterized in that the disc biasing tabs (80, 82, 84, 86) have outer ends lying in an unflexed condition on the periphery of a circle having a diameter that is approximately the same as the diameter of the bimetal disc (F), and in a flexed assembled condition said outer ends of said disc biasing tabs (80, 82, 84, 86) lying on the periphery of a circle having a diameter slightly greater than the diameter of the bimetal disc (F) to engage the edge intersection between the periphery of the bimetal disc (F) and the surface of the disc (F) facing the spring washer (G). Thermostat according to claim 7, characterized in that the locating tabs (110, 112, 114, 116) have outer terminal ends lying on the periphery of a circle having a diameter greater than the diameter of the bimetal disc (F) and greater than the diameter of the circle on which the outer ends of the disc biasing tabs (80, 82, 84, 86) lie. Thermostat according to any one of claims 5 to 8, characterized in that each of the locating tabs (110, 112, 114, 116) includes a first portion (120) extending outwardly from the base portion (70) and a second portion (122) extending substantially perpendicularly to the first portion (120). Thermostat according to claim 5, characterized in that the locating tabs (110, 112, 114, 116) have terminal ends spaced a greater axial distance from the base portion (70) than the terminal ends of the disc biasing tabs (80, 82, 84, 86). Thermostat according to any one of claims 5 to 10, characterized in that the disc biasing tabs (80, 82, 84, 86) are inclined out of the plane of said base portion (70) at angles less than 30°. Thermostat according to claim 11, characterized in that the opposite biasing means (102, 104, 106, 108) comprise a plurality of opposite biasing tabs (102, 104, 106, 108) inclined out of the plane of said base portion (70) at angles less than 30° on the opposite side of the plane of said base portion (70) than said disc biasing tabs (80, 82, 84, 86). Thermostat according to any one of claims 5 to 12, characterized in that the locating tabs (110, 112, 114, 116) extend from the plane of the base portion (70) on the same side as the disc biasing tabs (80, 82, 84, 86). Thermostat according to any one of claims 3 to 13, characterized in that the attaching means (76, 78) comprises a pair of opposite resilient spring fingers (76, 78) received in elongated recesses (148, 150) of the switch case (A).

Inventors: FUNK BRADLEY DEAN, WELLS GORDON KEITH, FUNK, BRADLEY DEAN, WELLS, GORDON KEITH
Applicants: EMERSON ELECTRIC CO, EMERSON ELECTRIC CO.
Application year: 1990
Main classification: H01H37
IPC codes: H01H3, H01H37