Thermostatic Switch

Abstract

A trip-free manual reset thermostatic switch with a thermostatic element for actuating a switch assembly by means of an actuator. The thermostatic element is mounted for flexing movement on a base and moves from a first to a second position relative to the base in response to predetermined temperature conditions, and then remains in the second position independent of further changes in temperature. The base and thermostatic element are provided with a cover movable toward and away from the base and held captive thereto. A switch assembly is mounted within the cover. This assembly includes a first contact secured to the cover and a contact arm one end of which is also secured inside the cover and having a free end carrying a second contact normally engaged with the first contact but movable out of engagement therewith. When the thermostatic element moves into its second position, the actuator concurrently moves the contact arm to separate the contacts. The cover, when moved from a normal to a reset position relative to said base, moves the actuator to bias the thermostatic element away from its second and toward its first positon, but the contacts will remain separated and the thermostatic element will not move into its first position while said element is subject to the predetermined temperature conditions. However, the contacts will reclose and the thermostatic element will be moved into its first position in the absence of the predetermined temperature conditions.

Description

BACKGROUND OF THE INVENTION

This invention relates to thermostatic switches and more particularly to trip-free manual reset thermostatic switches.

Thermostatic switches are widely used to make or break electrical circuits in response to the occurrence of preselected thermal conditions. One type of thermostatic switch will automatically reset itself to its original switching mode in response to a change in thermal conditions. In many instances a thermostatic switch is required that will trip the switch at a predetermined temperature but will not reset automatically in normal usage. Such thermostatic switches, are therefore, designed to be reset manually.

It is desirable that such manual reset type thermostatic switches be trip-free in operation, i.e., will not permit closing of the circuit whenever the thermal conditions that cause tripping exist. While several types of trip-free manual reset thermostatic switches are known, relatively complex structure has been required to jam the contacts or lock the switch contact arm or transfer pin, and a separate movable pin or push buttom has been necessary to effect resetting. Such additional structural components tend to adversely effect the reliability and trouble-free operation of such units and substantially increase the manufacturing costs.

SUMMARY OF THE INVENTION

Among the several objects of this invention may be noted the provision of thermostatic switches that are manually resettable and trip-free; the provision of such thermostatic switches in which reset flexing of the switch contact arm and the need of separate reset buttons or pins are eliminated; the provision of such thermostatic switches in which production costs are reduced and manufacturing is simplified; and the provision of manual reset trip-free thermostatic switches which are easily and conveniently calibrated and are simple in construction and reliable in operation. Other objects and features will be in part apparent and in part pointed out hereinafter.

Briefly, a trip-free manual reset thermostatic switch of this invention comprises a base, a thermostatic element, a cover for these components, a switch assembly and an actuator for the assembly operated by the thermostatic element. This thermostatic element is mounted for flexing movement on the base and will move from a first to a second position relative to the base in response to predetermined temperature conditions, and it will remain in this second position independent of further changes in temperature. The cover provided for the base and thermostatic element is movable toward and away from the base and is held captive thereto. The switch assembly is mounted within said cover. It includes a first contact secured to the cover and a contact arm one end of which is also secured inside the cover and which has a free end carrying a second contact normally engaged with said first contact but movable out of engagement therewith. When the thermostatic element moves into its second position, the actuator concurrently moves the contact arm to separate said contacts. The cover, when moved from a normal to a reset position relative to said base, moves the actuator to bias the element away from its second and toward its first position. However, the contacts will remain separated and the thermostatic element will not move into its first position while the element remains subject to the predetermined temperature conditions. But in the absence of said predetermined temperature conditions, resetting movement of the cover will reclose the contacts and the thermostatic element will be moved back into its first position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section of a manual reset trip-free thermostatic switch of this invention illustrating this switch in a normal or untripped mode or condition with its contacts closed;

FIG. 2 is a cross-section of the switch of FIG. 1 after tripping by operation of the thermostatic element has opened the contacts thereof;

FIG. 3 is a cross-section of the switch of FIGS. 1 and 2, but illustrating the trip-free feature wherein the contacts cannot be reclosed while the thermostatic element remains subjected to the thermal conditions that actuated the switch assembly to a tripped mode;

FIG. 4 is a cross-section of the thermostatic switch of FIGS. 1-3, taken on line 4--4 of FIG. 1;

FIG. 5 is a cross-section of another embodiment of a thermostatic switch of this invention with the contacts in a tripped or open condition; and,

FIGS. 6-8 are cross-sections of still another embodiment of this invention showing the switch contacts in a normal or closed mode (FIG. 6), a tripped or open condition (FIG. 7), and illustrating the trip-free aspects thereof .

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings and more particularly to FIGS. 1-4, a manual reset trip-free thermostatic switch of this invention is indicated generally at reference character 1. Switch 1 includes a cup-shaped base 3, within which is mounted for flexing movement a thermostatic element 5, an inverted cup-shaped cap or cover 7, a switch assembly 9 secured to the inner top portion of the cover, and an actuator 11. Preferably the base 3 is formed of metal and has an opening 13 permitting unobstructed heat exchange between the ambient atmosphere and the exposed undersurface of thermostatic element 5 which is edge-supported on the periphery of a depressed central portion 15 of base 3. The thermostatic element 5 is a snap-acting composite thermostatic bimetallic disk such as disclosed in U.S. Pat. No. 1,448,240. Because of the nondevelopable or dished shape of disk element 5, it will snap from one curvature position (FIG. 1) to an opposite curvature position (FIG. 2) upon the temperature increasing, for example, to a preselected level. As is known to those skilled in the art, these snap-acting bimetallic thermostatic elements may be so fabricated that under normal usage conditions the element can be cooled to ambient and lower temperatures after reversing curvature without resetting or returning to its original curvature. Thus it is a manual reset thermostat and will not automatically return or reset but must be physically urged to snap to its normal curvature.

The operation or flexing of disk 5 from its first position (FIG. 1) to its other or second position (FIG. 2) in response to predetermined temperature conditions elevates or moves upwardly actuator or transfer pin 11. This pin is axially slideable with a central bore 17 of a generally cylindrical pin guide 19 having a recessed undersurface 21 to accommodate the flexing movement of disk 5. Transfer pin 11 is fluted to minimize friction during axial movement of the pin within bore 17.

The upper end of pin 11 is spaced slightly away (FIG. 1) from a concave intermediate portion 23 of a switch or contact arm 25 carrying one contact 27 of switch assembly 9 on its free end. The other end of contact arm 25 is secured by cold welding or the like to the inner end of a terminal assembly 31 which extends through the cover 7 to provide a terminal lug 33 and is secured thereto thus firmly mounting contact arm 25 on cover 7. Switch arm 25, as shown in plan in FIG. 4, is fan shaped with a generally W-shaped relief slot 34. Another terminal assembly 35 similar to assembly 31 is also secured to cover 7 and has an inner angled end portion 37 extending through its cover to which is welded, or otherwise secured, another or fixed contact 39 positioned for making engagement by contact 27. Thus contact 39 is also firmly secured to cover 7 and is mechanically and electrically connected to a terminal lug 41 of assembly 35. Switch arm 25 is so formed and mounted that its contact is normally firmly biased against fixed contact 39 in a circuit closed mode. A post 43 is integrally formed as a central boss on cap or cover 7 and projects inwardly and axially relative to transfer pin 11 so as to be engageable with the concave upper surface of the intermediate portion 23 of switch arm 25.

Cover 7 and switch assembly 9 are a unitary assembly movable toward and away from the base. The lower end of the cover 7 is outwardly flanged as indicated at 45 and is reciprocally movable axially toward and away from the base within an annular gage ring or sleeve 47. Ring 47 is secured within cup-shaped base 3 by the formation of an inwardly directed flange 49. Annular sleeve 47 has a lip or overhanging flange 51 projecting inwardly from its upper margin and overlying cover flange 45 thus establishing a stop or upper limit of travel for cover 7 which is biased upwardly into a normal position (FIG. 1) by a spring or wave washer 53 which is pocketed in an annular compartment 55 formed between the flanged lower surface of cover 7 and the upper surface of the outer margin of pin guide 19.

Cover 7, formed of insulating material, such as any molded thermosetting synthetic material conventionally used for fabricating electrical switch housings, has an upwardly projecting central lobe or button 57 which is pressed downwardly toward base 3 and against the bias of spring 53 to effect resetting. Conventional electrical connectors may be connected to terminal lugs 33 and 41 to interconnect switch 1 into a circuit to effect circuit-making or breaking functions in response to preselected thermal conditions.

When, for example, the temperature of thermostatic element 5 rises above some predetermined level, it will snap from its normal position (FIG. 1), in which the contacts 27 and 39 are closed, and move transfer pin 11 upwardly to separate contacts 27 and 39 (FIG. 2). The transfer pin has a length slightly less than the distance between the undersurface of concave portion 23 of switch arm 25 and the upper surface of disk 5 when in its cool or normal position (FIG. 1). This provides a small degree of lost motion to permit the disk to creep slightly as its temperature approximates the preselected actuation temperature thus allowing some upward movement of the transfer pin without having it contact the undersurface of arm 25. As soon as the thermostatic element snaps to an opposite curvature, as shown in FIG. 2, the contacts of switch assembly 9 are instantaneously opened.

If cover 7 is moved toward its reset position and toward base 3 by downward manual pressure against lobe 57, post 43 will contact the upper surface of portion 23 of switch arm 25 and apply force through pin 11 to the central portion of disk 5, while depressing spring 53. If, however, the temperature of thermostatic element 5 is still above a preselected resetting temperature, it cannot be caused to snap into its normal (FIG. 1) curvature before cover 7 bottoms relative to base 3. As long as transfer pin 11 continues to be urged upwardly by the still hot disk 5, contacts 27 and 39 remain open, as shown in FIG. 3. Thus, while thermostatic element 5 is subject to the temperature conditions that caused it to move to its FIG. 2 curvature, the switch assembly 9 remains in its open mode and is trip-free. Also, contacts 27 and 39 will be separated, even if cover 7 is held in its reset position, upon the temperature of disk 5 rising above its predetermined level and reversing curvature.

The embodiment of FIG. 5 functions in the same manner as does the trip-free manual reset thermostatic switch of FIGS. 1-4, but differs structually in two respects. Instead of a fixed reset post 43, as in FIGS. 1-4, the FIG. 5 switch is provided with an optional movable or adjustable post 43a which is threaded and has a slotted top or outer end 59 for adjustment in a threaded bore 61 of modified lobe 57a of cover 7a. Post 43a constitutes a calibration screw which may be used to calibrate the temperature at which the thermostatic switch and its thermostatic element may be reset. This is particularly useful in miniaturized switches built in accordance with the invention. By adjusting the distance, post 43a projects from the inner surface of cover 7a, the thermostatic element will reset at different temperatures thereof. Thus while the typical manual reset thermostatic element will not under ambient temperature conditions of normal usage reset automatically, it can be caused to reverse curvature or reset from its FIG. 5 position at varying temperatures.

The other structural difference involves the omission of gage ring 47 which is accomplished without losing the function thereof, viz., the establishing of the amount and limits of travel of cover 7 relative to base 3. In FIG. 5 the side walls of cup-shaped base 3a are provided with slots, one of which is illustrated at 63. During assembly, a spacer finger or shim 65 is inserted to prevent compression of wave washer 53 and establish the upper limit of travel or maximum displacement position of cover 7 relative to the base. The upper edge of cup 3a is then crimped to form inwardly directed flange 49a which directly overlies outturned flange 45 of cover 7.

Referring now to a further embodiment, the trip-free manual reset thermostatic switch of FIGS. 6-8 functions in accordance with the principles of the present invention as described in regard to previous embodiments, but differs in that manual resetting is accomplished by moving or pulling the cover away from the base. In this switch embodiment, a base 3b has a pair of integrally formed mounting ears and thermostatic element 5a provided with a central aperture 69 through which projects a modified actuator or transfer pin or shaft 11a, preferably fabricated of an insulating material such as a synthetic resin material. The lower end of shaft 11a is flattened as indicated at 71 and is spaced slightly below disk 5a in its normal position (FIG. 6) to permit a small degree of lost motion so as to accommodate some disk creep before it snaps at predetermined temperature conditions to its reverse curvature (FIG. 7). An enlarged upper end portion 73 of shaft 11a which extends upwardly beyond the upper surface of a switch arm 25a (modified to have an aperture 75) has a head 77 spaced away (FIG. 6) from a central counterbore 79 of a modified button 57b which has a central bore 81 within which upper shaft extension 73 axially slides.

This thermostatic switch embodiment has a modified switch assembly 9a secured to and concertedly movable with cover 7a. In this instance a fixed contact 39a is secured to the undersurface of a modified terminal assembly 35a with a laterally projecting terminal lug 41a, and a mating contact 27a is mounted on the upper surface of a switch arm 25a, the other end of which is fixed to the inner end of a modified terminal assembly 31a. Switch arm 25a biases contact 27a to a normally closed or engaged position in firm contact with contact 39a in the normal operating position (FIG. 6).

The lower edge of inverted cup-shaped cover 7a has an out-turned flange 45a and spring washer 53 is pocketed within an annular compartment 55a formed between the lower surface of lip 51 of sleeve 47 and the upper surface of flange 45a thus urging or biasing the cover 7a toward base 3b.

When thermostatic element 5a is subject to predetermined temperature conditions, it will snap from its FIG. 6 curvature to that of FIG. 7 and move pin or shaft 11a downwardly thereby tripping switch assembly 9a to open contacts 27a and 39a. If cover 7a is moved away from base 3b and toward its reset position as shown in FIG. 8, switch arm 25a and its movable contact 27a will remain spaced apart from contact 39a when the disk 5a is subjected to the predetermined temperature conditions. In the absence of such thermal conditions, however, thermostatic element 5a will manually reset and permit the switch assembly to return to the normal contacts-closed condition illustrated in FIG. 6.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

What is claimed is:

1. A trip-free manual reset thermostatic switch comprising:

a base;

a thermostatic element mounted for flexing movement on said base and adapted to move from a first to a second position relative to said base in response to predetermined temperature conditions and to remain in said second position independent of further changes in temperature;

a cover for said base and thermostatic element movable toward and away from said base and held captive thereto;

a switch assembly including a first contact mounted within said cover and a contact arm one end of which is secured inside the cover and having a free end carrying a second contact normally engaged with said first contact but movable out of engagement therewith;

an actuator adapted, when said thermostatic element moves into its second position, concurrently to move said contact arm to separate said contacts;

said cover adapted, when moved from a normal to a reset position relative to said base, to move said actuator to bias said element away from its second and toward its first position whereby the contacts will remain separated and said thermostatic element will not move into its first position while said element is subject to said predetermined temperature conditions and whereby the contacts will reclose and the thermostatic element will be moved into its first position in the absence of said predetermined temperature conditions.

2. A thermostatic switch as set forth in claim 1 which further includes means biasing the cover and switch assembly away from the base into the normal position thereof and in which the cover is moved against said bias to said reset position whereby resetting of the thermostatically tripped switch assembly is effected by pressing said cover toward the base in the absence of said predetermined temperature conditions.

3. A thermostatic switch as set forth in claim 1 which further includes means biasing the cover and switch assembly toward said base and into the normal position thereof and in which the cover is moved against said bias to said reset position whereby resetting of the thermostatically tripped assembly is effected by pulling said cover away from the base in the absence of said predetermined temperature conditions.

4. A thermostatic switch as set forth in claim 2 wherein the actuator is a transfer pin slidably interposed between the thermostatic element and one side of an intermediate portion of said contact arm and in which the cover includes a post adapted to engage the other side of the intermediate portion of said movable arm.

5. A thermostatic switch as set forth in claim 3 in which the actuator is a transfer pin coupling the thermostatic element and said movable arm for substantially conjoint movement, and said transfer pin includes an extension in sliding engagement with and having a lost-motion connection with said cover.

6. A thermostatic switch as set forth in claim 1 wherein the base is generally cup shaped and has an inwardly directed flange spaced from the bottom thereof and constituting means retaining said cover on the base for limited movement relative thereto.

7. A thermostatic switch as set forth in claim 6 wherein the cover is of generally inverted cup shape and has an outwardly directed flange reciprocally movable within said base.

8. A thermostatic switch as set forth in claim 7 which includes means biasing the cover away from the base.

9. A thermostatic switch as set forth in claim 7 which includes means biasing the cover toward the base.

10. A thermostatic switch as set forth in claim 7 which includes spring means interposed between the cover and the base, said spring means being constituted by a spring washer.

11. A thermostatic switch as set forth in claim 7 which further includes an annular mamber interposed between the inner surface of the base and the outer surface of the cover, said annular member having an inwardly directed flange overlying the outwardly directed flange of said cover to limit the movement of the cover relative to the base.

12. A thermostatic switch as set forth in claim 7 in which the cup-shaped base is provided with a plurality of slots adapted to transitorily receive spacer shims to serve as spacer gages during assembly of said cover and base thereby to establish the maximum displacement position of the cover relative to the base when forming the inwardly directed flange of the base.

13. A thermostatic switch as set forth in claim 4 wherein the post is integrally formed with the cover.

14. A thermostatic switch as set forth in claim 4 wherein the post is movable relative to the cover whereby the temperature at which the thermostatic element may be reset to its first from its second position is adjustable.