US2390947A - Compensating thermostat - Google Patents

Description

Dec. 11, 1945. 1.. J KOCI 2,390,947

COMPENSATING THERMOSTAT Original Filed April 1 1940 C HIGH EXPANSION 5/05 Z .5 31 1..|.|.\.. Ty

24 Z 25 O 2e Z6 DU D Patented Dec. 11, 1945 COMPENSATING THERMOSTAT Ludvik J. Koci, Chicago, Ill., asslgnor to Chicago Flexible Shaft Company, Chicago, Ill., a corporation of Illinois Original application April 1, 1940, Serial No.

Divided and this application October 25, 1943, Serial No. 507,530

2 Claims.

This invention relates to compensating thermostats and is a division of my application Serial No. 327,255, filed April 1, 1940, for Thermostats, which resulted in Patent No. 2,332,518, granted October 26, 1943.

The novel principle of said patent may be described thus: that if one portion of a generally straight strip of unreversed bimetallic material (of any normal shape and variation in section modulus) is rigidly fastened or restrained against both angular and translational motion and a second portion of the strip at a point longitudinally removed from said first mentioned portion is subject to action including a reactive couple or moment acting to restrain angular motion of said second portion by permitting minimum restraint to translational motion of said second portion in a direction normal to the general length of the strip, then said second portion will exhibit a thermostatic action in the line of said direction but directed in one way or the opposite depending on whether said second portion or the portion immediately adjacent to said rigidly fastened portion, is heated. Said invention is claimed generically in said parent application and also claimed as to certain species which include the principle that the relative magnitude of the two opposite thermostatic actions above described can be varied by variation of the effective section modulus of the strip or by other means which may serve to alter the degree of restraint to angular motion of said second portion.

The present invention has for its object the embodiment of the foregoing principle in a form characterized by a strip of thermostatic material diminishing in width from its central portion toward each terminal end together with means supporting each terminal end against both angular motion and motion in a direction normal to the length of the strip, whereby to obtain a main response to the absolute temperature of a primary medium surrounding the middle portion of the strip and to compensate for temperature lags of the supporting terminal end portions of the strip.

According to the present invention the thermostatic strip inherently has considerable compensating'effect and this is of particular utility in certain applications wherein it is desired to obtain a. main thermostatic response to the absolute temperature of a gaseous or fluid medium surrounding the middle portion of the strip and to compensate for extreme temperature lags of the supported end portions.

5 normal to the general length of the strip.

Other objects and attendant advantages will be appreciated by those skilled in this art as the invention becomes better understood by reference to the following description when considered in connection with the accompanying drawing, in which:

Figure l is a plan view of a thermostat embodying the present invention;

Figure 2 is a side elevation of the structure shown in Figure 1;

Figure 3 shows an application of my invention in a thermostatic switch or means for making and breaking an electric circuit; and

Figure 4 is a side elevation showing a modified form of my invention applied in a. thermostatic switch.

Reference is made to the above mentioned patent for a further description of the novel principle first above described, whereby a main thermostatic action in one direction and a compensating thermostatic action in the opposite direction are obtained in a single strip of nonreversed, non-reentrant, thermostatic material, to obtain a net thermostatic action in a direction In said patent I have used theterms A effect and B effect in explaining the thermostatic action; and these terms will be used in a similar manner, hereinafter.

In Figures 1, 2, and 3 are; shown a diagrammatic embodiment of the present invention. Here, the letter C designates a frame structure having upstanding ends provided with coplanar slots D within which the end portions of a bimetallic strip K are positioned so as to be free to have longitudinal movement but restrained against both angular and translational movement under temperature changes. The strip K preferably but not necessarily of uniform thickness, is shaped so as to be diminishing in width from its central portion ll toward each terminal end l2, thereby providing tapered end portions H of decreasing graduated rigidity. Assuming that the under side of the strip is the high temperature side, if the strip is heated at its end portions as by conduction from the frame structure C, the central portion of the strip will tend to move upwardly in the direction indicated by the end arrows in Figure 2, this being the A eflect above mentioned; and conversely, if the central portion of the strip is heated to a temperature above that of the end portions the strip will tend to move downwardly at the central portion in the direction indicated by the center arrow in Figure 2, this being the B eliect" above mentioned. If-the thermostatic strip were of uniform section modulus throughout its length a uniform change in temperature of the strip throughout its length would produce no lateral movement of the strip, that is, movement normal to the face of the strip, for the reason that the A and B effects would be equal and the tendency of the middle portion of the strip to move down ward would be exactly balanced by the tendency of the end portions to move the middle portion upward. It will be seen that if one of these efiects can be caused to predominate, the balance will be disturbed and the net movement in one direction or the other with uniform change in temperature of the strip, can be produced. This net movement is the resultant thermostatic action in a direction normal to the general length of the strip and may be described as the vector um of the A and B effects.

Referring to Figure 2, I have illustrated graphically and diagrammatically the thermostatic action when heat is applied to different portions of the strip along its length. For example, if the middle portion of the strip at the section line is heated, say degrees, the middle portion of the strip will move downward in proportion to the width of the section diagram x at said section line 0. This is the B efiect. This effect diminishes as the point of heat application moves toward the left or the right; for example, if new a point at the section line I is heated 10, motion at the middle portion of the strip at section line 0 will move downward an amount proportional to the width of the section diagram X at said section line I, and similarly if the portion at the section line 2 is heated 10 the resultant motion of the middle portion of the stri will be less and of a magnitude corresponding to the reduced width of the diagram X at the section line 2. If now the strip is similarly heated 10 at the section line 3, there will result no motion of the middle portion of the strip, for the reason that this section 3 is located at the nodal point of the diagram, that is, the point at which the thermostatic action reverses. If the strip is heated 10 at the section line 4 the thermostatic action will be in the opposite direction, that is, upward and of relative magnitude indicated by the width of the section diagram'Y at said section line 4. This description as well as the diagram is theoretical for the purpose of illustrating the principle; and it will be apparent that the width of the section diagrams X and Y represents relative magnitude of deflection of the strip at the middle point 0 in response to a unit rise in temperature at any given point along its length, also that the example of a unit rise of 10 at any given section line is theoretical because actually there is gradual heat conduction to ad: joining portions of the strip.

The diagram Figure 2 shows a very desirable characteristic of my invention, namely, that of v a gradually reducing thermostatic response in one direction, passing through a nodal point (i. e., the point of no response), and then into a gradually increasing response in the opposite direction, considering the effect of the application of heat to successive points along the length of the strip. This is of particular utility when compared with prior compensating thermostats; for example, prior instances of applying compensation usually have involved the use of a second thermostat distinct from the main thermostat and acting in a direction opposite from the main thermostat, or a second thermostat fastened to the otherwise free end of the main thermostat but reversed in the location of its high temperature side. If we consider the effect of the application of heat to successive points along the length of the latter mentioned structure it would be apparent that as we proceed from the fixed end of the main thermostat strip we would obtain gradually decreasing thermostatic action in one direction as far as motion of the free end of the strip is concerned until we encounter the junction of the two strips at which there would be a very sudden transition to maximum thermostatic action in the opposite direction followed by gradually decreasing thermostatic action in this same opposite direction as we approach the free end of this combination strip. As distinguished from such prior structures, my invention locates that ortion of the thermostat having maximum primary thermostatic response closest to the region of the temperature which it is desired to control and locates that portion of the thermostat possessing maxi- 'mum opposition or compensating response in a region closest to that region whose temperature variations it is desired to compensate. In practical cases these two regions are seldom separated by an accurate dividing line or plane but gradually merge one into the other; and for this reason it is highly desirable that the response of the remaining portions (i. e., those possessing less than maximum response) of any compensating thermostat shall show the same characteristic, that is, the gradual merging of the main response into that of the secondary.

In Figure 3 I have shown the thermostatic strip K applied in a thermostatic switch for controlling an electric circuit. This mounting of the strip K is the same as in Figures 1 and 2. A screw 23 threaded in the frameportion C is arranged for adjustment to act as a stop to limit the downward movement of the strip intermediate itsends, in this instance at the middle point. A lever 24 pivoted at 25 to an upright portion l4 of the frame, carries a leaf spring 26 which extends forwardly along the strip K and carries on its under side an insulation button 21 adapted to contact the strip and on its top side a contact 28 positioned to engage a stationary contact 29 to control a circuit (not shown) for exercising a control function. A thumb screw 3| in the end portion l4 permits of adjustment of the position of the lever 24 and the spring 26 whereby to apply more or less lateral pressure on the strip and thus change the temperature at which the strip will act to flex the spring 26 and move the contact 28 into or out of engagement with the contact 29. The stationary contact 29 alsoacts as a stop to limit the upward movement of the strip. Here, the thermostatic strip is mounted in the same manner as in Figures 1 and 2 so that its end portions are subject to angular restraint and to the reactive couple explained in my parent application, by permitting a limited amount of movement in a direction along the length of the strip in the slots D-D provided for reception of these ends. Theoretically, the thermostatic action is as described above in reference to Figures 1 and 2. However, thisform is limited in its applications because of the resistance to sliding motion of the portions of the strip in the slots D-D. In actual practice I prefer to rigidly clamp the end portions of the strip against both angular and lon itudinal movement and to provide some degree of elastic softness in the longitudinal direction by corrugating the strip or by buckling it as shown in Figure 4. In this form the strip K is supported in a frame structure similar to that of Figures 1, 2, and 3, having a central portion 43 provided with supporting abutments 44 and 45, against the upper surface of which are secured the end portions 01' the strip K by suitable means such as large headed screws 46 and 41, the screws passing through openin s 48 and 49, respectively. These screws serve to secure the ends of the strip against the supporting abutments 44 and 45 and to prevent relative angular movement of the ends of the strip. Here the screws 46 and 41 fixedly clamp the terminal end portions and hold the.

strip under lengthwise compression so that the intermediate portion of the strip is buckled, substantially as shown. With this construction it-is possible to obtain friction-free snap acting operation of the switch of a degree determined by the amount of longitudinal compressive stress to which the strip is subjected. In other respects the thermostatic switch of Figure 4 is the same as in Figure 3 and like reference numerals with prime marks are applied to like parts.

It is believed that this invention provides a compensating thermostat which is desirable from the viewpoint oi efliciency, dependability, accuracy, economy in cost of manufacture, and maximum freedom from the eti'ect of transient conditions. I

While I have described and illustrated specific embodiments of the invention, this has been by way of illustration and not limitation, and I do not wish to be limited except as required by the prior art and the appended claims, in which I claim:

1. A thermostatic device for indicating or controlling the temperature or a primary medium and tor compensating for the eii'ect of variati in temperature of an uncontrolled second medium, comprising a non-reversed, non-reentrant strip 01' thermostatic material, the strip diminishing in width from its central portion toward each terminal end whereby each end portion of the strip is of decreasing graduated rigidity, means supporting each terminal end of the strip against both angular motion and motion in a direction normal to its length, the entire length of the strip intermediate the supported terminal ends being responsive to temperature changes throughout said length. said central portion being primarily responsive to the surrounding medium and thereby responding in a thermostatic action in one direction normal to the length of the strip, said end portions of diminishing width being primarily responsive to the temperature of said supporting means and thereby responding in a thermostatic action opposite in direction from that of the first described thermostatic action, the thermostatic strip responding at its central portion in a net efiective thermostatic action which is the vector sum of the first and second described thermostatic actions and thus in the direction of that described thermostatic action which predominates, the described angular restraint being imposed directly by said terminal ends and directly through said end portions oi decreasing width, whereby to obtain a main response to the absolute temperature 01' said primary medium surrounding the middle portion of the strip and to compensate for variations in temperature of the supporting means due to variations in temperature of said uncontrolled second medium. I

2. A thermostatic device as set forth in claim 1, in which the end portions of the thermostatic strip are fixedly held in such manner as to compressively stress the strip in a longitudinal direction so as to obtain snap-acting operation.

LUDVIK J. KOCI.

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