US2000398A - Thermostatic switch - Google Patents

Description

May 7, 1935. c LAUBENFELS 2,000,398

THERMOSTATIC swITcH FiledJuly 5, 1952 Patented May 7, 1935 UNITED STATES PATENT OFFICE 9 Claims.

This invention relates to improvements in thermostatically controlled switches, and particularly of the type employing a thermostatic stn'p formed of materials having diiferent thermal co- I eillcient of expansion.

The object of my invention is to provide a simple, durable and inexpensive switch for electric circuits having a simple and positive means for opening and closing the contact members of the switch controlled by a thermostatic strip of the type above described.

The idea of opening and closing electrical contacts by means of the movement of a thermostatic strip caused by temperature variations is not new. The dimculty with switches actuated by a thermostatic strip lies in the fact that the strip is slow in its movement, whereas the electrical contact should be broken suddenly to prevent arcing. It is, therefore, the object of my invention to provide means for mounting the thermostatic strip in such manner that the strip may be placed under a yieldable longitudinal compression strain to cause the strip to be bowed or curved, and in such manner that temperature change will cause the strip to have a tendency to straighten and to assume the position of a straight line, and on the line of force applied to the strip. Upon further movement of the strip, the said yieldable force will then assist in causing the strip to assume an oppositely curved position under a considerable tension in addition to that of the strip itself, and to provide in connection with the thermostatic strip means for actuating one of the contact members of the switch.

A further object is to provide in a thermostatically controlled switch of the type above described, means for applying longitudinal pressure to the strip in such manner that the reversed curvature of the strip may take place without setting up destructive strains in the strip.

A further object is to provide a thermostatic switch so constructed that it may be adjusted to operate its contact members at difierent temperatures, and in which the electrical contact members are opened and closed through a comparatively narrow temperature range, and in connection therewith means whereby the said temperature range may be easily and quickly varied at the will of the operator.

A further object is to provide a thermostatic switch utilizing a composite thermostatic strip of material in connection with a flexible element adapted to have pressure applied to it in such a manner that the rigidity of the element will be rapidly overcome to provide means for rapidly opening and closing the switch contact members, the pressure necessary to operate the flexible strip being applied through the thermostatic strip above referred to.

My invention consists in the construction, ar- 5 rangement and combination of the various parts of the device, whereby the objects contemplated are attained, as hereinafter more fully set forth, pointed out in my claims, and illustrated in the accompanying drawing, in which:

Figure 1 is a side elevation of one form of my improved switch construction.

Figure 2 is an end elevation of same.

Figure 3 is a plan view of another form of my improved switch.

Figure 4 is a detail sectional view taken on the line 4-4 of Figure 3.

Figure 5 is a side elevation of a modified form of the switch illustrated in Figures 3 and 4; and

.Figure 6 is an end elevation of same. 20

Referring to the accompanying drawing, I have used the numeral ID to indicate the base of my improved switch construction which is formed preferably of insulating material. Supported on the base I0 is a bracket II designed to pivotally support one end of a hub 12, the opposite end of the hub being pivoted in the base l0.

Said hub I2 has a flexible strip of material I3 supported therein. The downwardly extending end of the member I3 is provided with an electrical contact member l4 designed to be engaged by a coacting contact member i 5 supported by a spring it, one end of which is rigidly secured to a post IT. A set screw I8 is provided for increasing the pressure of the contact members l4 and I! when in a closed position.

A set screw 20 is provided for limiting the inward movement of the contact member IS. The upper end of the strip i3 is provided with a rounded or looped portion 2i designed to be supported between the ends of set screws 22.

The strip l3 has its edges provided with laterally extending pivot members 23 designed to be supported in bearings 24 carried by one end of a spring 25. The opposite end of the spring 25 is connected to the base ill by means of a pivot 26. A set screw 21 is mounted in a suitable support 28, and so positioned that downward pressure may be applied to the spring 25 at a point intermediate the pivot members 23 and 26 in such a manner that longitudinal pressure may be applied to that portion of the strip i3 between the pivots 23 and the hub l2, tending to buckle the central portion of the strip from a position within the pressure axis extending through the pivots 23 and I2.

The inner face of that portion of the strip between the members I2 and 23 is formed of a material 29 having a lower co-efiicient of expansion than that of the material of the strip I3.

The operation of this form of my switch is as follows:

Assuming that the parts are set in the position illustrated by solid lines in Figure 1, and that an increase in temperature takes place, then the strip I3 will expand faster than the adjoining member 29, causing the thermostatic element formed by said strip to straighten and to move into the axis of pressure between the members 23 and I2. The lower end of the strip I3 will then move in the opposite direction from the thermostatic strip or in a direction as viewed in Figure 1.

The movement of the thermostatic element and the lower end of the member I3 is gradual until the thermostatic strip approaches the axis of pressure. Upon further rise in temperature the said strip will have a tendency to bend in the opposite direction, after which rapid movement will take place and the strip moved to the dotted line position shown in Figure 1, due to the buckling action caused by the compression strain imparted by the member 25.

As the lower end of the member I3 is operated through its initial portion of movement, the member I5 will follow the contact I4 due to the resiliency of the spring I6 until the spring I6 engages the inner end of the set screw 20, which takes place at the time the rapid movement of the thermostatic element, so that a rapid separation of the contacts I4 and I5 is accomplished, and a substantially constant pressure maintained between said contact members during the initial part of the movement of the thermostatic strip. As the temperature is lowered, a reverse operation of the thermostatic strip and the contact members will be accomplished.

The yieldable member provides means whereby an amplified movement of the contact member I4 is accomplished over what might be accomplished if the member 23 were carried by a fixed support, thereby providing means whereby a large separation may be provided between the contacts I4 and I5.

The set screws 22 provide means whereby the tendency of the thermostatic strip to assume either one of its oppositely bowed conditions may be increased or decreased as the adjustment of the set screws will impart to the thermostatic strip a bending strain. 7

The set screw I8 providesmeans whereby the working pressure between the contacts I4 and I5 may be varied at the will of the operator to meet the working conditions of the switch. A conductor may be connected to the spring I6 to form one part of an electrical circuit, while a conductor 3| may be connected to the member 25 to form the other conductor of said electrical circuit. The set screw 20 provides means for adjusting the critical point of the movement of the member I3, at which the separation of the members I4 and I5 takes place.

In Figures 3 and 4 I have illustrated another form of electrical switch in which the numeral 33 indicates the base having brackets 34 and 35 supporting thermostatic strips 36. The ends of said strips are designed to rest on the bulged portion 31 formed in a flexible element 38, preferably in the form of a narrow strip of thin sheet metal.

One end of the element 38 is also secured to the bracket member 35.

One end of the element 38 is provided with an electrical contact member 39 designed to engage a coacting contact member 40 carried by a spring 4|, supported by a bracket 42. A conductor 43 is connected to said spring while the conductor 44 is connected to the element 38. A set screw 45 is designed to engage the spring M for varying the pressure between the contact members 39 and 40. Set screws 46 are provided for placing tension on the thermostatic elements 36, whereby the switch may be adjusted to operate at different temperatures.

The base 33 is also provided with a support 41 having a set screw 48, the central portion of which is provided with a head 49 fixed thereto. The inner end of the set screw supports a compression spring 50, one end of which is designed to engage the outer surface of the bulged portion 31. The tension of said spring is varied by the set screw 48.

The operation of this form of my invention is as follows:

Assuming that the parts are arranged in the manner illustrated by solid lines in Figure 1, and that the temperature is increased, then the free ends of the members 36 will be bowed downwardly as indicated by dotted lines, causing pressure to be applied to the bulged portion 31. Continuing the increase in temperature, stresses will be set up in the member 31 to overcome the rigidity of the member 31, at which time the central portion of the member 31 will be rapidly bulged downwardly as indicated by dotted lines, causing the free end of the member 38 to be elevated and with it the contact member 39.

The contact member 4|] follows the contact member 39 through the initial part of its movement, said movement being limited by a stop 5i, so that a rapid separation of the contacts 39 and 40 will take place as the free end of the member 38 is snapped upwardly.

This form of my invention differs somewhat from the form before described in that the member 31 assumes the dotted line position under constant strain to return to its original position, so that as soon as the temperature is reduced a small amount, said member 31 rapidly returns to its normal position, allowing the contact member 39 to rapidly move toward the contact member 40. As soon as the contact is made between said members then said contact is maintained under uniform pressure due to the resiliency of the spring 40 until its return movement is completed.

One difiiculty heretofore experienced in thermostatic switches lies in the fact that a considerable amount of temperature variation takes place to cause opening and closing of the switch contacts, due to the slow action of the flexible elements. I have overcome this difficulty to a large extent by providing the spring 50 which may have pressure applied thereto by the set screw 48 and pressure applied to the member 31 by said spring to the critical point where the change in shape of said member 31 takes place, so that'only a slight movement of the members 36 is necessary to overcome the rigidity of the member 31,

thereby providing a narrow temperature variation to accomplish the opening and closing of the switch contact. The temperature at which the switch contacts may be operated may be varied by the set screws 46.

It will readily be seen that the set screws 46 may be released to such an extent that the inner ends of the members 36 may be supported above the member 31 so that a considerable increase in temperature would have to take place before the free ends of said members actually engage the member 31, after which a very slight additional rise in temperature would cause the switch contacts to open.

In Figures and 6 I have illustrated a slight modification of the structure shown in Figures 3 and 4, in which the numeral 52 illustrates the base to which a. bracket 53 is secured, said bracket supporting upright members 54 formed of material having a low co-efllcient of expansion.

Supported between the upper ends of the members 54 is a flexible member 56 constructed similar to the member 38 and having a bulged portion 56 and a contact member 51 carried by its outer end and designed to engage a contact member 58 carried by a spring 59. A set screw 60 is provided for increasing or decreasing the tension of the spring 59.

Supported in the bracket 53 is a set screw 6| having its upper end provided with a recess 62 in which is mounted the lower end of a bar 63 formed of material having a high co-efllcient of expansion. The upper end of the bar 63 is designed to engage the convex surface of the bulged portion 56 as shown in Figure 5.

The operation of this form of my device is very similar to that of the mechanism illustrated in Figures 3 and 4.

It will be seen that any increase in the temperature will cause the member 63 to expand and lengthen, and cause the member 56 to be bulged inwardly and the free end of the member 55 to be bent downwardly. The set screw 6| provides means for applying initial longitudinal pressure to the member 63, whereby a critical pressure may be imparted to the member 56 at any predetermined temperature, thereby providing means whereby the temperature variation necessary to accomplish the opening and closing of the contacts 58 may be reduced to a minimum.

Thus it will be seen that I have provided an improved thermostatic switch in which a flexible element is employed for imparting quick movement to contact members of an electric circuit. Said flexible element is either in the form of a thermostatic strip or supported separately and actuated by temperature controlled means such as an expanding column or a warping thermostatic strip, and in which the constant pressure may be maintained between the contact members during the initial part of the movement of said flexible element; and in the form illustrated in Figures 1 and 2 means is provided whereby yieldable longitudinal pressure may be applied to the flexible element to increase the movement of said element as it assumes either of its curved conditions; and in Figures 3 and 4 means is provided whereby very delicate adjustment may be made to decrease the temperature variation at which the switch points are opened and closed.

The switch mechanism is so constructed as to eliminate excessive wear and bending movement of the flexible elements whereby the life of the switch may be greatly increased.

The switch is formed of few parts whereby the initial cost of material is reduced.

I claim as my invention:

1. In a device of the class described, a base, a thermostatic strip supported thereon, yieldable means for applying longitudinal pressure to said strip to normally retain the strip in either of two oppositely arched conditions and to permit the ends of the strip to separate as it moves from one of its arched conditions to the other due to temperature changes, and adjustable means for imparting a transverse bending strain to a portion of said strip to change the tendency of said strip to assume one of said curved conditions.

2. In a device of the class described, a base, a thermostatic strip supported thereon, yieldable means for applying longitudinal pressure to said strip to normally retain the strip in either of two oppositely arched conditions and to permit the ends of the strip to separate as it moves from one or its arched conditions to the other due to temperature changes, adjustable means for imparting a transverse bending strain to a portion of said strip to change the tendency of said strip to assume one of saidcurved conditions, two contact members, means for fixing one of said contact members, and means for operatively connecting the other contact member to the movable strip whereby the contact member will be moved to closed or open positions as the arched condition of the strip is reversed.

3. A thermostatic switch comprising a base, a strip of flexible material having a laterally bulged portion near one end, and means for securing the last end of said strip to said base, contact means carried by the free end of said strip, a coacting contact member, yieldable means for supporting the last contact member in contact with the first member, means for adjusting the tension of said yieldable means, and temperature operated means for applying pressure laterally to said bulged portion.

4. A thermostatic switch comprising a base, a flexible thermostatic strip, means pivotally supporting one end of said strip to said base, means pivotally supporting the opposite end of said strip and for applying yieldable longitudinal pressure thereto to cause the central portion of said strip to tend to buckle laterally, each end of said strip having portions extending beyond said pivot members, a contact member carried by the free end of one of said extending portions, a coacting contact member, yieldable means supporting the last contact member, means for adjusting the tension of said yieldable means, means for limiting the movement of the last contact member, and means for adjusting the free end of the other extension portion of said thermostatic strip to increase or decrease the tendency of the thermostatic strip to buckle in either direction.

5. A thermostatic switch comprising a base, a flexible thermostatic strip, means pivotally supporting one end of said strip to said base, means pivotally supporting the opposite end of said strip and for applying yieldable longitudinal pressure thereto to cause the central portion of said strip to tend to buckle laterally, one end of said strip having a portion extending beyond its corresponding pivot member, a contact member carried by the free end of said extending portion,

a coacting contact member, yieldable means supporting the last contact member, means for adjusting the tension of said yieldable means, and means for limiting the movement of the las contact member.

6. A thermostatic switch comprising a base, a flexible thermostatic strip, means pivotally supporting one end of said strip, a yieldable and transversely arranged pressure applying strip supported with one end adjacent to the opposite end of said thermostatic strip, means pivotally connecting the adjacent ends of said strips, means for supporting the other end of said yieldable strip to said base, and an adjustable means for increasing or decreasing the lateral stress of said yieldable strip as applied longitudinally to said thermostatic strip.

7. A thermostatic switch comprising a base, a flexible thermostatic strip, means pivotally supporting one end of said strip to said base, means pivotally supporting the opposite end of said strip and for applying yieldable longitudinal pressure thereto to cause the central portion of said strip to tend to buckle laterally, said means comprising a strip of transversely arranged yieldable material having one end pivoted to the yieldably supported end of said thermostatic strip, and its opposite end pivoted to said base, and a set screw supported by said base having one end engaging the strip of yieldable material, whereby the longitudinal pressure as applied to the thermostatic strip may be increased or decreased.

8. A thermostatic switch comprising a base, a flexible element adapted to suddenly change its shape when a predetermined pressure is applied thereto, contact members, means operated by the sudden movement of said flexible element for moving one of said contact members toward or from the other, adjustable means controlled by the temperature variation for applying or releasing the predetermined pressure as applied to said flexible element, and means separate and independent of said temperature controlled means for applying yieldable initial pressure to said flexible element to act in unison with the pressure applied by said temperature controlled means to decrease the temperature variation necessary to open and close said contacts, and means for adjusting the pressure as applied by the initial controlling means.

9. A thermostatic switch comprising a base, a

flexible element adapted to suddenly change its shape when a pre-determined pressure is applied thereto, means for mechanically applying an initial pressure to said element, tending to deform the same, contact members, means actuated by the element as it changes its shape for moving one of said contact members toward or from the other, temperature controlled means for applying pressure to said element to assist the initial pressure applying means whereby the element will suddenly change its shape when the combined pressure of the first and second pressure applying means is equal to the pre-determined pressure, and means for adjusting the first and second pressure applying means independently whereby the temperature variation necessary to open and close said contacts may be decreased.

CLARENCE R. LAUBENFELS.

Images