US2598556A - Electric switch - Google Patents

Description

May 27, 1952 A. l.. JuDsoN 2,598,556

ELECTRIC SWITCH Filed May 24, 1950 /N//E/v TUR 5 Jz/w/V Patented May 27, 1952 ELECTRIC SWITCH Albert L. Judson, Portland,` Oreg., assgnor to Iron Fireman Manufacturing Company, Port.-

land, Oreg.,

Application May 24, 1950, Serial No. 163,986,

2 Claims.

This invention relates generally to electric switches but more particularly to the type of electric switches which are designed to be automatically operated in response to a change ofv a condition and in which to provide greater sensitivity of operation the switch mechanism is matched with the mechanism of its condition responsive operator to cause the switch to operate with a minimum unbalance of the opposing forces of the two mechanisms.

1n the form ofV this invention to be particularly'illustrated and described herewith, the switch and operator combination is directed to the control of an electric heater for a hot water supply tan-k and the control unit of this invention is shown as a so-called strap-on type tank thermostat.

It should be understood that the business of making and selling electric hot water tanks is regularly becoming more and more competitive andthe thermostat requirements are; for regularly' increasing current handling capacity, smaller size of control, lower cost, and reliability of operation.

It is the principal obj-,ect of this invention to supply a control unit satisfying these requirements to a unique degree.

To attain the above principal object, several unique features ci this; control unit have been invented or discovered and have been made use of therein. It is well known that a bimetallic blade as commonly used with strap on thermostats is arranged in cantilever structure and will have a straight line stressV strain curve or, said in other terms, a constant spring rate. It has, therefore, been a second object of this invention to provide a switch mechanism to be operated by a bimetallic blade and which can be operated by aY member having a motion generally perpendicular to the plane of the unstressed blade and in which the restoring forcey of the switch components which oppose the movement of the member by thev blade will also have a straight line force versus movement curve.

It is aA third object of this invention to provide al switch and switchV actuatingv mechanism havinga very small frictional power loss.

It isa fourth object of this invention to provide a. switch of the stationary contacts and bridging member type in which a unique bridging member including a permanent magnet is used to prevent contact bounce in closing and tot delay the opening of the switch until the operatingl member is in motion definitely tocontinuef the: openingA operation.

It is a fifth object of this invention to pro vide a lost motion connectionV between the switch operating and restoring mechanism and the bridging member to make possible the above fourth object.

It is a sixth object of this invention to provide a switch operating mechanismin which, once the mechanism is set in motion to operate the switch, the operating force will regularlyv increase and the operating mechanism accelerate until the operation is completed.

How thesey andk other objects are attained will be understood on reference to the following description and the accompanying drawing" in which:

Fig. 1 is a perspective View of the complete switch and operator.

Fig. 2 is a bottom viewy of the. mechanism of Fig. 1.

Fig. 3 is a sectional View of the mechanism of Fig. 1.

Fig. 4' isa top view of the switch assembly only of Fig. 1 but with the top cover removed.

Fig. 5 is a fragmentary enlargementv in partial section of Fig. 4. Y

Fig. 6 is a force versus motion diagram of the switch and condition responsive operating mechanism of this invention.

Like numerals refer to like parts in the several figures of the drawing.

Referring now to the drawing there is shown a formed metal basel IlV having mounting ears l`2 and'hi'nge support I3 formed thereon.

Condition responsive bimetallic blade I4' having an operating pin receiving groove I5 at its free end is securely riveted at its other end to resilient hinge member IS- which is also riveted tohinge support I3 as shown.

Adjusting lever-I1 secured to blade I4 and hinge member I6 at its lower end is formed with a threaded hole at its upper end to receive cam following adjusting screw I3.

Adjusting stem I9 rotatably stepped intol base I l at 20 is rotatably guided at 2l in a hole formed in ther horizontal side of bracket 22 xed to base ll. Adjusting cam 23 secured to stem lil cooperates with screw !8 as stem I9 is rotated by indicating lever 24 to set the mechanism to maintain thecondition value desired.

Ears 25 laterally guide lever l1. Spring washer 26, together with cam 23, locates stem I9 between base Il and bracket 22.

Switch case 2 and cover 28 are secured. to baser Il byV two diagonally placed screws (not shown) having theirl heads located in cover recesses 29 and passing through holes (not shown) in cover 28, holes 39 in case 21, and threaded (not shown) into base Ii.

Sheet metal mechanism support 3l is formed to fit the bottom of the molded interior of case 21 and has ears 32 and 33 raised and formed to lay on raised molded ledges in diagonal corners of case 21. Ears 32 and 33 are staked to case 21 by spun rivets 34 and 35 as shown.

The four stationary contact members 36, 31, 38, and 39 are each electrically independent and are independently supported on surfaces formed in case 21 for the purpose. These contact members are made of steel with a surface plating of a higher conductivity metal and each member carries a respective silver contact point 4I, 42, 43, 44 as shown. Also threaded into the top surface of each contact member is a wire attachment screw numbered 45, 46, 41, and 48 respectively. From Fig. l, it will be noticed that switch cover 2B has recesses molded therein which will clear screws 45 and 48 but are not large enough to uncover the entire top surfaces of contact members 35 to 39. Cover 28, therefore, locks members 33 to 39 securely in their respective positions.

The electric switch mechanism illustrated is a two circuit switch structure, one circuit to be attached to screws 45 and 46 and the other to 41 and 48. Therefore, to close one circuit, members 36 and 31 must be electrically connected and, to close the other circuit, members 33 and 39 must be connected. rlhe purpose of the switch is to alternately close and open the above noted circuits with an operation of the mechanism in one direction first opening one circuit then closing the other while an operation of the mechanism in the other direction first opens the other circuit, then closes the one.

The actual closing and opening of the circuits is done by the bridge member 49 loosely carried in a bridge carrier 50 arranged for a bell crank type of operation.

Spring 5I is strained between ear 52 formed upwardly on support 3i and tail 53 formed downwardly on carrier 59. n this arrangement two horizontally spaced knife edges 54 formed on carrier 5B are pressed into grooves formed in two horizontally spaced fulcrum elements 55 formed upwardly on support 3l. downwardly depending side elements of carrier 50 are formed to cooperate at 59 with the roofed ends of the T-shaped head of insulating operating pin 51 of which the stem end is rounded to rockably engage the grooved free end bimetallic blade I4.

It should be particularly noted that bridge 49 loosely carried between the forked ends of carrier 59 is a at bar of conducting metal plated with silver over its contact surfaces and centrally perforated with an elongated rectangular hole into which is pressed permanent bar magnet 58. Each of the contact members 36, 31, 38, and 39 has an ear 59 extending tov/ard the center of the switch structure and these being of magnetic material have a greater or lesser influence on magnet 59, depending on their nearness thereto.

The strap on thermostat comprising the illustrated form of the invention of this application is operated as follows: Utilizing the holes 69 in ears I2 of base Ii for attachment purposes, the thermostat is strapped to a surface of a. hot water pipe or tank, thus bringing the underside of bimetallic blade in position. to be influenced by As shown, the l the changing temperature of the pipe or tank. Electric circuits to control the heating of the pipe or tank are hooked to terminal screw pairs 45, 46 and 41, 48. On a dial (not shown) adjacent to pointer 24, the pointer is set to a desired temperature. In setting this pointer to the desired dial reading, cam 23 is rotated and moves lever I1 through screw I3 to set bimetallic blade I4 to a position where, when the pre-set temperature has been reached, blade I4 will press upward on pin 51 with sufficient force to rock carrier 50 in a clockwise direction about its points of pivot on fulcrum elements 55 and to move bridge 49 away from contacts 4I and 42 and into engagement with contacts 43 and 44. When the pipe or tank then cools somewhat, the temperature stress of blade I 4 is reduced and the greater force of spring 5I on carrier 59 overcomes the pressure of blade I4 on carrier 50 through pin 51 and carrier 59 rocks in a counterclockwise direction causing bridge 49 to leave contacts 43 and 44 and return to contacts 4I and 42.

Within the operating range of the switch it should be remembered that the centerline of spring 5I remains close to but always below the horizontal line through the pivot contact of carrier 59 and fulcrums 55. It is therefore apparent that within this operating range the force of spring 5I on carrier 50 remains substantially constant and the torque acting to rock the carrier in the counterclockwise direction (refer to Fig. 3) is this substantially constant spring factor combined with a variable lever arm factor which is the perpendicular distance of the spring axis from the pivot line. Due to this arrangement of parts this torque is greatest when operating pin 51 is in its lowest position, least when pin 51 is in its highest position and varies directly with the vertical position of pin 51.

Likewise blade I4 is a mechanically and thermally stressed cantilever structure, the strain of the free end of which from its neutral position will be substantially proportional to the stress on the free end as applied in a direction perpendicular to its unstressed plane. Since this is the direction on which blade I4 and pin 51 act, one on the other, it is seen that the force of blade I4 acting on carrier 59 through pin 51 results in a clockwise torque on carrier 50 and this clockwise torque varies directly with the vertical position of pin 51 being greatest when pin 51 is in its lowest position and least when pin 51 is in its highest position. Thus both the clockwise and counterclockwise torques acting on carrier 50 increase as the carrier is rocked in a counterclockwise direction and decrease as the carrier is rocked in a clockwise direction.

The unique design and operating cycle of the switch mechanism is illustrated in the force versus motion diagram shown in Fig. 6 in which the horizontal axis M-M is the motion axis with the vertical lines ML and MH setting the lower and higher limits respectively of the motion in the operating range of pin 51. The vertical axis F-F is the axis of torques acting to rock carrier 59. Clockwise torques being represented above the line M-M while counterclockwise torques are represented below the line M-M and both are increasing in magnitude` in a direction away from the line MHM.

On the chart then line B-B shows the design torque characteristic of the bi-metallic blade while the line S-S is the design torque charaotefist 0f the Spring. For ease of comparison, the reection of the line S--S is drawn above the M^M axis and is shown as the dash line SI-S. From this it will be seen that at the mid-position of motion of pin 51 the opposing design torques on carrier 59 are equal and opposite while at the lower positions of pin 51 the spring torques are greater than the blade torques and at the upper positions of pin 51 the blade torques are greater than the spring torques at any position of comparison. In the neutral position (a) the opposing torques would be balanced but unstable because of the divergence of lines SI-S and B-B and once the balance is disturbed the System could not of itself return to this (a) position. For instance, should the temperature to which the blade is subjected be lowered slightly, the characteristic line B-B would be lowered slightly and counterclockwise motion of carrier l5l) would be started slowly and increase in velocity because the counterclockwise torque (Sl-S) would be increasing at a greater rate than the clockwise torque (B-B) and motion would stop abruptly at the counterclockwise limit of travel, as when bridge 49 is stopped by contacts 4l and 42.

Now to cause the switch to throw in the clockwise direction of carrier 50, it will be necessary (unless cam 23 is shifted) to increase the temperature to which the blade is subjected until the torque characteristic B-B is raised to the position Bl--BI which intercepts the line SI-S at the lower limit of motion indicated by the line MI in Fig. 6. Carrier 50 will then start to rock in the clockwise direction and since during this movement the clockwise torque decreases at a lesser rate than the decrease of counterclockwise torque, this motion is at a regularly increasing rate until suddenly stopped at the upper limit of travel indicated in Fig. 6 by line MH and, of course, caused by bridge 49 coming to rest against contacts 43 and 44. counterclockwise torque is then indicated by the point d and clockwise torque bythe point c in Fig. 6.

In like manner it is seen that now for the switch to throw to the opposite or counterclockf wise position the temperature to which blade I4 is subjected will have to be reduced to movelthe force vs. motion curve of the blade to the position B2-B2 of the iigure. Then, as motion starts in the counterclockwise direction, the. counterclockwise torque (line Sl-S) increases at a greater rate than does the clockwise torque (line B2-B2) and the motion continues at a regularly increasing rate until bridge 49 suddenly comes to rest against contacts 4| and 42.

It is seen, therefore, that operation of the switch is completely under control of the bimetallic blade I 4 whose force Versus motion curve is shifted by a changing condition which is temperature in this case and the switch operation diiierential force is the vertical distance between the lines BI-Bl and B2-B2 of the curve.

An important feature of this invention is the looseness with which bridge 49 is held by carrier 59 and the attraction which magnet 58 has for the pair of ears 59 to which it is nearest at the particular throw of the switch. The effect of these conditions is that at the beginning of motion of the switch in either direction the magnet holds bridge 49 in place until an appreciable velocity of motion is attained by carrier 50 at which time it bumps bridge 49 away from the contacts and opens the circuit with a continuing and increasing motion but that up to the time of breaking the circuit the switch contact pressure is maintained by the magnet. No gradual fading of contact pressure and consequent heating of the contacts is experienced which is a unique advantage of the structure over the prior art devices.

Having thus set out the objects of my invention, shown one form of structure practicing my invention and explained the unique effectiveness thereof, I claim:

1. An electric switch comprising a iirst pair of spaced contacts, a second pari of spaced contacts, a bridging element rockable between said first pair of contacts and said second pair of contacts to alternately bridge each of said pairs of contacts, a permanent magnet fixed to said bridging element, individual stationary magnetizable elements adjacent each of said contacts, one pair of said individual elements adjacent said rst pair of contacts being adapted to cooperate with -said magnet to bias said bridging element toward said first pair of contacts, another pair of said individual elements adjacent said second pair of contacts being adapted to cooperate with said magnet to bias said bridging element toward said second pair of contacts and operating means loosely cooperating with said bridging element to rock said bridging element alternately into bridging arrangement with said rst and said second pairs of contacts.

2. An electric switch comprising a pair of spaced contacts, .a stop means, a bridging element rockable between said pair of spaced contacts and said stop means to alternately electrically connect and isolate said contacts, a permanent magnet fixed to said bridging element, individual stationary magnetizable elements adjacent each of said contacts, said pair of individual elements adjacent said pair of contacts being adapted to cooperate with said magnet to bias said bridging element toward said pair of contacts, and operating means loosely cooperating with said bridging element to rock said bridging element alternately into bridging arrangement with said pair of contacts and against said stop means.

ALBERT L, JUDSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number

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