US2724753A - Bimetal thermostatic switch - Google Patents

Description

Nov. 22, 1955 c, MILES 2,724,753

BIMETAL THERMOSTATIC SWITCH Filed D60. 17, 1952 Inventor": Qoscoe CMHes, by MW His Attor-ne United States Patent BIMETAL rnnnr/rosrarrc SWITCH Roscoe C. Miles, Erie, Pa., assignor to General Eiectric Company, a corporation of New York Application December 17, 1952, Serial No. 326,413

2 Claims. (Cl. 200-138) My invention relates to switches and pertains more particularly to thermostatic switching means.

Some thermostatic switching arrangements include a stationary contact, a movable contact carried by a bowed resilient member and a cooperating bimetal. In response to changes in ambient temperature the bimetal deflects to one or the other side of a center line. When the bimetal deflects to one side of the center line it engages and exerts a force on the resilient member and effects bowing of the resilient member in the same direction. When the bimetal deflects in the opposite direction it bows the resilient member oppositely. When the resilient member is in one bowed position the movable contact engages the stationary contact and an electrical circuit is completed therethrongh. When the resilient member moves to the oppositely bowed position the movable and stationary contacts disengage and the circuit is broken. Movement of the resilient member from one bowed position to its oppositely bowed position is with a snapping action.

The primary object of my invention is to provide a new and improved thermostatic switch including a bowed resilient member and a bimetal adapted for actuating the resilient member and in which the resilient member is shorter than that previously required.

Another object of my invention is to provide a small low cost and wide differential thermostatic switch.

Further objects and advantages of my invention will become apparent as the following description proceeds and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

In carrying out the objects of my invention, I provide a frame, a contact carried by an arm secured to the frame and a column spring carrying a contact adapted for cooperating with the contact carried by the arm. Secured integrally to one end of the column spring is an end of a flat bimetal. The column spring is provided with an initial bow and the outer ends of the column spring and bimetal are secured to the frame.

Fig. l is an enlarged plan view showing a preferred embodiment of my invention;

Fig. 2 is a sectional view taken along the lines 2-2 in Fig. l and illustrating the column spring bowed to a position in which the contacts are closed;

Fig. 3 is a sectional view illustrating the column spring bowed to a position in which the contacts are open; and

Fig. 4 is a contact pressure-bimetal deflection curve.

In Fig. l, l have shown an embodiment of my thermostatic switching means generally designated 1. My switch 1 may be employed in any apparatus wherein operating components are to be controlled in response to temperature changes.

As seen in Figs. 1, 2, and 3, the switch 1 includes a frame 2 formed of an electrically conductive material, such as steel. The frame 2 is channel-like in construction and includes sides 3 and left and right end base portions 4 and 5, respectively. Electrically connected to a side 3 of the frame 2, as by soldering, is a conductor 6 leading to one side of a circuit (not shown) to be controlled by my switch. The switch 1 further includes a bowed resilient member or column spring 7 disposed and adapted for bowing movement between the sides 3 of the frame 2. Secured integrally to the left end of the column spring 7, as by welding, is one end of a flat bimetal 6. The other end of the bimetal 8 is secured and electrically connected to the left end base portion 4 of the frame 2. As best seen in Figs. 2 and 3, I employ a rivet 9 and a Washer 10 for securing and electrically connecting the bimetal 8 to the frame 2. However, it will be clear that other means such as welding may be alternatively employed.

The end of the bowed column spring 7 opposite the bimetal 8 is secured and electrically connected, as by welding, to the right end base portion 5 of the frame 2. Carried on the column spring 7 adjacent the end secured to the right end of the frame 2 is a contact 11. Provided for cooperating with the contact 11 is another con tact 12 carried on the underside of one end of a resilient contact arm 13. The contact arm 13 extends inwardly from the right end base portion 5 of the frame 2 between and in spaced apart relation to the sides 3 of the frame. The end of the arm 13 opposite the contact 12 is positioned in an electrically insulative sleeve 14. The sleeve 14, with the arm 13 therein, is secured to the right end of the frame 2 by portions 15 which are bent inwardly from the sides 3 of the frame and clamp the sleeve 14 to the right end base portion 5 of the frame. the contact arm 13 is both secured to the frame and electrically insulated therefrom.

Also secured in the sleeve 14 for being insulated from the frame 2 is a contact stop member 16. The stop member 16 extends from both ends of the sleeve 14 and includes one end 17 which extends inwardly between and in spaced apart relationship to the sides 3 of the frame 2. The end 17 extends over the resilient contact arm 13. When the contacts 11 and 12 are closed in the manner shown in Fig. 2 the end 17 of the stop member 16 limits movement of the contact arm 13 and the contact 12; and, when the contacts are open in the manner shown in Fig. 3 the resilient arm 13 and the contact 12 are spaced apart from the end 17 of the stop member The opposite end of the stop member 16, indicated by 18, extends outwardly from the frame 2 and is adapted for having a conductor 19 leading to the opposite side of the circuit to be controlled suitably electrically connected thereto as by soldering. It will be seen that in this arrangement closing of the contacts 11 and 12 will complete a circuit from the conductor 6 through the frame 2, the bimetal 8, column spring 7, across the con- Facts 11 and 12 and through the stop member 16 to the conductor 19.

To facilitate description of my invention, 1 shall hereinafter refer to downward deflections of the bimetal 8 as being caused by increases in ambient temperature and upward deflections as being caused by decreases in ambient temperature. It will be seen, of course, that these temperature responsive deflections of the bimetal would be reversed if the bimetal itself was reversed or turned over.

In the solid lines in Fig. 2 the bimetal ii is shown as being deflected to a position above a center line indicated by 20, in which position the column spring 7 is bowed upwardly and the contacts 11 and 12 are closed. Upon an increase in ambient temperature the bimetal 8 deflects downwardly past the center line 26 and toward the solid line position thereof in Fig. 3 whereby the column spring 7 is flexed with an undulatory or wavy movement starting at the bimetal 8. In dash lines in Fig. 2 the column spring 7 is shown as flexed to a position in which it is just about to be rendered unstable and to snap to the downwardly bowed position thereof shown in solid lines In this manner 1 in Fig. 3. Snapping of the column spring 7 to the downwardly bowed position and resultant rapid opening of the contacts 11 and 12 are effected when the ambient temperature reaches a predetermined high.

The location of the contacts adjacent the end of the column spring 7 and the undulatory movement with which the column spring is flexed by the deflecting bimetal 8 from the upwardly bowed position of Fig. 2 to the downwardly bowed position of Fig. 3 insure both a wide temperature differential between the oppositely bowed positions of the column spring 7 and positive pressure between the contacts until the contacts are snapped fully open. This is illustrated by the contact pressure-bimetal deflection curve of Fig. 4 from which it will be seen that a predetermined initial pressure indicated at 21 exists between the contacts 11 and 12 when the contacts are closed. This initial pressure is determined by the bow initially provided in the column spring 7. Thereafter as the bimetal deflects downwardly across the center line 20 the contact pressure is increased and is greater than the initial pressure when it reaches point 22 on the curve. From point 22 the pressure suddenly drops to Zero due to rapid snapping of the column spring 7 to its downwardly bowed position. It will be seen that the bimetal 8 does not exert a zero force on the column spring as it passes through the center line 20 and therefore there is never a zero pressure between the contacts at any time prior to the actual snapping of the column spring to its downwardly bowed position. As a result, the contact 11 is never momentarily positioned a short distance from the contact 12 and the contacts are positively opened. Thus, contact damaging arcing and lag in the operation of apparatus controlled by the switch are minimized. When the contacts 11 and 12 are engaged in the manner shown in Fig. 2, the resilient arm 13 is flexed upwardly and is engaged and limited by the end 17 of the stop member 16. During the above-described opening of the contacts 11 and 12 through undulatory movement of the column spring 7 from the upwardly bowed to the downwardly bowed positions thereof, the contact 12 is caused by the resilient arm 13 to follow the contact 11 momentarily before the contacts are fuily opened. This following movement of the contact 11 and the undulatory movement of the column spring 7 causes the contacts 11 and 12 to be separated with a wiping action whereby arcing is further minimized and the contacts are maintained substantially clean for insuring positive engagement thereafter.

Following opening of the contacts in the above-described manner and upon a decrease in ambient temperature the bimetal 8 deflects from the solid line position of Fig. 3 past the center line 20 and toward the solid line position thereof in Fig. 2. This causes the column spring 7 to flex from the downwardly bowed position to its upwardly bowed position with an undulatory or wavy movement. In dash lines in Fig. 3 the column spring 7 is shown as flexed to a position in which it is just about to become unstable and to snap to its upwardly bowed position. Snapping of the column spring 7 to the upwardly bowed position and closing of the contacts 11 and 12 are effected when the ambient temperature decreases to a predetermined low. In a manner substantially the inverse of that in which the contacts are opened the undulatory flexing movement of the column spring 7 causes the contacts 11 and 12 to be maintained positively opened until the column spring is snapped to its upwardly bowed position. This insures rapid positive closing of the contacts whereby contact damaging arcing and lag in starting of the apparatus controlled by the switch are minimized.

When the contact 11 is snapped into engagement with the contact 12 in the manner just described the resilience of the arm 13 causes the contact 12 momentarily to yield before being stopped by the end 17 of the stop member 16 in the manner and position shown in Fig. 2. This yielding of the contact 12 and the undulatory movement with which the column spring 7 is bowed upwardly causes the contacts 11 and 12 to engage with a wiping action whereby arcing is further minimized and the contacts are maintained substantially clean for insuring positive engagement therebetween.

it will be seen that in my switch the resilient member or column spring 7 is shorter than that which would be required to obtain the same result if a non-integral bimetal was employed for engaging and actuating the column spring. That is, of the bimetal 8 was not secured integrally to one end of the column spring 7 in the manner shown in the drawing the colurrm spring would have to be as long as the total length of the column spring 7 and the bimetal 8. Thus, my construction results in a saving in material which can be substantial when thermostatic switches are to be manufactured in large quantities. Also my construction eliminates the necessity for mounting both a column spring and a bimetal element. With an integral arm including both a bimetal element and a column spring element, a single mounting suffices.

While I have shown and described a specific embodiment of my invention, I do not desire my invention to be limited to the particular form shown and described and I intend by the appended claims to cover all modifications within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a thermostatic switch, a contact, a bowed resilient member, another contact carried on said resilient member adjacent one end thereof for cooperating with said firstmentioned contact, said resilient member being fixedly supported at said one end, said resilient member being effective when in one bowed position for closing said contacts, said resilient member being efiective when in an oppositely bowed position for opening said contacts, and a flat bimetal fixedly supported at one end and having its other end secured integrally to the end of said resilient member opposite said contacts, said bimetal extending in a direction opposite to said resilient member, said resilient member being flexed and unstabilized with an undulatory movement by temperature responsive deflections of said bimetal, said undulatory movement of said resilient member commencing at said bimetal, said undulatory movement of said resilient member during opening of said contacts being effective for maintaining positive pressure between said contacts until said contacts snap fully open and for insuring positive engagement when said contacts close, said resilient member being unstabilized only after said bimetal deflects across and beyond a center line extending between the bowed positions of said resilient member whereby a wide temperature differential is required to unstabilize said resilient member.

2. In a thermostatic switch, a frame, a contact carried by and insulated from said frame, a resilient member, another contact carried on said resilient member adjacent one end thereof for cooperating with said firstrnentioned contact, and a flat bimetal secured integrally to the end of said resilient member opposite said contacts, the outer ends of said resilient member and bimetal being secured to said frame, said resilient member being flexed and unstabilized with an undulatory movement by temperature responsive deflections of said bimetal, said undulatory movement of said resilient member commencing at said bimetal, said undulatory movement of said resilient member during opening of said contacts being effective for maintaining positive pressure between said contacts until said contacts snap fully open and for insuring positive engagement when said contacts close, said resilient member being unstabilized only after said bimetal deflects across and beyond a center line extending between the points at which the outer ends of said resilient member and said bimetal are secured to said frame whereby a wide temperature differential is required to unstabilize said resilient member.

References Cited in the file of this patent UNITED STATES PATENTS 1,622,721 Hook Mar. 29, 1927 1,680,429 Mottlau Aug. 14, 1928 1,695,103 Hook Dec. 11, 1928

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