US3100826A - Snap switch having presetting means responsive to current flow - Google Patents

Description

1 1963 I KJELLMAN 3,100,826

SNAP SWITCH HAVING PRESETTING MEANS RESPONSIVE TO CURRENT FLOW Filed April 11, 1960 4 Sheets-Sheet 1 FIG. 1..

INVENTOR THOMAS K KJELLMAN ATTORNEY SNAP SWITCH HAVING PRESETTING MEANS RESPONSIVE TO CURRENT FLOW Filed April 11, 1960 Aug. 13, 1963 T. K. KJELLMAN I 4 Sheets-Sheet 2 FIG. 2,.

1o INVENTOR THOMAS K. KJELLMAN-.

ATTORNEY 1963. 'r. K. KJELLMAN I 3,100,826 .SNAP SWITCH HAVING PRESETTING MEANS RESPONSIVE Tb CURRENT FLOW Filed April 11, 1960 Q 4 Sheets-Sheet s FIG. 8. I

l/l/l/l/l/l/l/l/l/l/l/l/l/l/l/l/l/l/l/ INVENTOR THOMAS K. KJELLMAN ATTRNEY Aug. 13, 1963 T. K. KJELLMAN 0,

' SNAP SWITCH HAVING PRESETTING MEANS RESPONSIVE T0 CURRENT FLOW Filed April 11, 1960 4 Sheets-Sheet 4 13'. FIG 9.

ATTORNEY -to the return side of the line. .not affect the contour of the switch blade since its prefer- United States Patent 3,100,826 SNAI SWITCH HAVING PRESETTING MEANS RESPONSIVE T0 CUNT FLOW Thomas K. Kjellman, Timoninm, Md, assignor to The Bendix Corporation, a corporation of Delaware Filed Apr. 11, I960, er. No. 21,334 9 Claims. (ill. Mil-113) This invention relatesto electrical switches of that type which utilize a temperature or current-responsive device such as :a bimetal strip to assist or control the switching operation; it is particularly adapted for, but not limited to, sensitive instruments such as humidistats, thermostats and the like wherein the sensing element controls a quickacting toggle or snap switch to avoid sparking at the contacts, with resultant contact erosion.

An object of the invention is to provide a switch of the type specified wherein almost one hundred percent of the work required to throw the switch is performed by the line current, leaving practically zero work for the sensing element to effect the final switching operation, while .at'the same time all the advantages of a snap or toggle action are retained with practically unlimited contact forces available to meet design specifications.

Another object is to provide a highly sensitive snap 3,100,826 Patented Aug. 13, I963 ice ' the travel of the power element with respect to the switch switch capable of handling heavy-duty switching, and a this with a minimumI R drop across the switch.

Another object is to provide a relatively simple snap switch which effects a self-cleaning or wiping action between contacts during each switching cycle.

Another object is to provide a switch assembly particularly adapted for instruments such as humidistats, thermostats and the like utilizing sensing elements wherein a relatively small amount of work is available to obtain sensitivity.

A further object is to provide an improved humidity and/ or temperature sensing and control instrument.

In attaining the foregoing objects, a conductive thermal arm or bar (in practice a strip of bimetal) is interposed in the control circuit and has located on the movable end or other movable portion thereof a pair of contact members spaced to meet switch-throwing requirements. These contacts remain in fixed spaced relation but move bodily with said arm when it responds to current flow and when it cools following current cut-off. This arm may be aptly termed a switdh-presetting power element since it presets the actual switching member for the final switchthrowing act and it does practically all the switching work. The switching member is in the form of a snapvaction switch blade having coacting contacts movable between the said power element contacts. This switch blade may be of the conventional toggle or snap type which as it approaches its dead-center position requires a progressively-increasing actuating force but needs only a relatively small force to throw it past such position; it is preferably located in the control circuit posterior of and .in series with the motor or other device to be controlled,

so that when on contact is made, the current flows through the switch blade and the power arm or bar back This flow of current does either on or off contact is made, and this movement continues until the thermal power arm or element is broughtup against adjustable stop means which limits blade throw line. At this point the switch blade is almost to its dead-center position, requiring a minimum of force to throw it past dead center against the opposite contact.

. of the various parts of the switch are readily adaptable for both heavy and light duty installations; it (the switch) can take a high initial flow of current without danger of destruction simply by substituting the proper type. of

thermal power arm or element. As the respective parts of the switch go through the switching cycle, the contacts rub againstone another with a resultant wiping or cleaning action which breaks, in shear, welds due to an initial inrush of current and deters contact erosion.

The foregoing and other objects and advantages will become apparent in view of the following description taken in conjunction with the drawings, wherein:

FIG. 1 is a view in perspective of a combined temperature and relative humidity controller embodying the features of the invention;

FIG. 2 is a top plan view thereof;

FIG. 3 is a view in section and side elevation with the facing side wall removed;

FIG. 4 is a view in end elevation partly broken away;

FIG. 5 is a view taken substantially on the line 5--5, FIG. 3;

FIG. 6 is a view of the base assembly taken substantially on the line 6-6, FIG. 3;

FIG. 7 is a view of the said base assembly as in FIG. 6 but with the switch blade and coacting parts removed to expose the temperature-responsive power member;

FIG. 8 is a view similar to FIG. 7 but showing the power member removed to expose the excess current shunt bar;

51G. 9 is a plan view of the leaf spring switch member; an

FIGS. 10 to 10d are diagrammatic representations of theswitch as it undergoes the switching cycle. The improved switch is shown installed in a humidity and relative temperature controldevice which can either function as a thermostat, a humidistat, or a combined thermostat and humidistat, i.e., it can regulate temperature as a function of relative humidity. The working parts are encased as best shown in FIGS. '1 and 3; the switch assembly proper being located in a bottom case, here shown as being made up of a molded plastic topsection 10 and a base 10' fitted into the open bottom of the section 10. Removably fitted over the section 10' is a metallic case or shell 11, secured in place by small screw bolts 12.

The switch proper comprises a leaf spring switch blade of the toggle or snap type, note FIG. 9, made of conductive material such as sheet copper; and since the instrument is here shown adapted to sense both temperature and relative humidity, two of these blades 13 and 13' are utilized, :each blade being identical in construction and hence like parts in each blade bear like reference numerals. The rear (leftlland end as viewed in FIG. 9)

ends of the blades terminate in a common integral anchoring section. 'llhe manner in which these blades perform is well known although the specific structure tfior carrying 17. Each one of the switch blades is formed with a slot '18, to accommodate connecting or banger brackets for the humidity and temperature elements in a manner to be described. A plate '19 overlies both switch blades and at its front end is formed with downturned abutment members 19', one rfior each blade, while its opposite end is secured to the said base by the screws. 17. Each downturned abutment 19 is notched as at 20, and the free end edge of each bowed spring tongue 14' engages in these notches. The notch 20 is so ocated with respect to the axial line of thrust of the tongue 14' and the point of connection of the blade to its actuator (here the humidityresponsive element 31 or temperature-responsive element 46, to be described) that whenthe latter point passes through the blades over-center thrust line in either a contact make or break direction, the contact-carryingsec- .tion. or extremity 14 will snap to contact make or .break position. The contacts 16 and 21 or 15 and 22, however, remain in engagement until the said point of connection flexes past dead center in either direction. The term snap switc as used herein, refers to switches incorporating a switch blade or resilient switch [assembly which function in a generally similar manner, i.e., maintain contact until flexed or otherwise actuated past a deadcenter position. At its rear end, the plate 19 has a tongue projecting therefrom, which is bent downwardly and passes through a slot and terminates in an exteriorly accessible terminal 19".

The contacts 21 and 22 are carried on the free end of a contact preset and power bimetal arm 23, which at its one end is also fixed to the base member by the screw bolts 17. In the present instance, the upper contact 22 is fixed on the free end of the power arm 23 by means of an offset piece 24, secured to the arm 23 as at 24'. ln practice, the piece 24 is bendable for the purpose of adjusting the spaced relation of the contacts. Obviously, other means may be adopted for adjustably and shiftably mounting these contacts; they could be mounted on a shiftable support independently of the arm 23 and moved or driven by the arm to their respective preset positions. Adjacent the center throw line of the switch blade 13 against stop means, which may be provided in any suitable manner. As best shown in FIGS. 4 and 7, the stop means is provided by laterally-projecting contact portions 25 and 25 dormed on the bar 23, which come against abutment screws 26, 26' and 27, 27', adjustable to determine withexactitude the point where the movement of the arm 23 terminates in the switching operation.

, Preferably, but not necessarily, the switch is provided with means (tor shunting excess current from flowing through the power arm or bar 23 in the case of a short along the longitudinal center line of'the shunt bar and at 'its far end has fixed thereto a coacting shunt contact 30,

compare FIGS. 3 and 7. When current flows through the power arm or bar 23 and it is deformed upwardly to preset the section 14 of the switch blade 13, contact 30 engages contact 29. That part of the power arm 23- lying between the contacts 21 and 30 plus the shunt bar 28 will (or 13') the power bimetal arm or bar 23 is brought up then make up a return circuit in parallel with the remaining part of the arm 23 to the left'of contact 21, and the resistance or" this shunt circuit is such as to provide the desired safety factor. c a a As heretofore noted, the instrument in which the switch is used in the present instance is'a combined thermostat and humidistat. Accordingly, a humidity-sensing element in the form of a hair rope 31 is looped over a stationary hook 32 at one end of the case or cap 11 and has its free ends secured in terminals which are hooked to the one end of an adjustable bracket 33. The bracket 33 is knife edged at one extremity for engagement in a notch 34, formed in the adjacent top wall of the case 11 and about which the bracket pivots when adjusted. A short control shaft 35, adapted to receive a control knob, not shown, is threaded through a bushing 36 to the fixed adjacent wall of the casing 11 and carries a member 37 at its lower or inner end which projects through a key slot formed in the bracket 33 and engages beneath the latter.

. through an eye 41 fixed in the upper end of a hanger bracket 42, note FIG. 5, and the latter extends through registering slots 43 and 44 formed, respectively, in the top wall of the case 10 and the abutment \plate 19 and then through the slot 18 in the leaf spring blade 13, and at its lower or inner end is extended laterally beneath the said blade. Should. the moisture content or relative humidity of the air increase, the hair element will relax and permit the switch blade to flex downwardly, and if the moisture content or the relative humidity decreased, the

opposite effect will occur.

A temperature-responsive element is indicated at 46,

and this element, as is the case with the humidity element, is anchored at one end to a hook 47 and at its opposite end to a bracket 47", the latter being provided with a piv otal knife edge engaging in a notch 34' and is adjustably,

supported by means of a control or setting assembly similar in all respects to that used for the humidity element,

and hence like parts have been given like reference numerals with the exception that a prime has been added. The center bracket indicated at 48 is provided to hold the knife edge pivots of the brackets 33 and 33' e in place; it has oppositely projecting spring legs which engage in slots formed in said brackets.

A hanger'bracket 49 has its upper end connected to the bimetal temperature element 46 by' means ofa pin and slot connection, as indicated at 50, and at its lower end projects through registering slots 5-1 and 52 formed, respectively, in the top wall of the case 10' and the abutment member 19 and also through the slot 18 formed in the leaf spring blade 13' and at its lower end is projected laterally for engagement beneath the said blade. Should the temperature of the surrounding ambient air increase, I

the bimetal temperature element 46 will relax in a downward direction, and should the temperature decrease, the opposite effect will occur.

The hanger brackets 42 and 49 may be made up of a single piece of plastic or other insulating material and assembled by inserting each through the registering slots provided therefor from beneath the switch blade 13 and I Operation The switch, as exemplified herein, is of the simple onoff type. In FIG. 10, the switch assembly is shown diagrammatically; it could be either the humidity or temperature control switch of FIGS. 1 to 9, inclusive, which constitute actual assembly drawings. Here the switch blade :13, 14 and 14' of the assembly drawings is made up of a blade proper 13A, which corresponds to the tongue 14' of the leaf spring type of blade of the actual switch, and a spring 14A, which corresponds to the resilient extremity 14 of the blade. The contact presetting and power arm or bar is indicated at 23A and the abutment member at 19A. The switch contacts and stops for the power arm have been given numbers corresponding to like parts in the assembly drawings. in FIG. 10, the bottom of the casing functions as'the stop 26. The switch is shown controlling a motor 532 i In the position of the parts in FIGS. 10 and 10a, the contact 16 is against the on contact 21, and at this time the motor will be energized, current flowing from the line to the motor and then throughthe abutment member 19A, switch blade 13A, and to the return side of the line by way of power arm 23A. FIG. =10a shows the relative positions of the parts upon closing of the motor circuit, and FIG. 10b shortly after the motor has ben energized and current flows through the power arm 23A. Note that at this time the power arm has been deformed due to current flow, so that its free contact-carrying extremity has moved upwardly against its stop 27 (stops 26 and 27 not shown'in FIGS. la-l0d) to the point where the contact end of the switch blade lies slightly short of its throw line when moving in the off direction, and which line passes through the pivot point 20A of the blade and the point of connection 54 of its spring to the hanger bracket 42 or 49. These points correspond, respectively, to the notch 20 of FIG. 3 and the point where the hanger bracket 42 engages beneath the blade 13. As the free extremity 'of the power arm 23 moves upwardly or counterclockwise, the contact 21 remains in engagement with the contact 16 while at the same time the spacing between the contacts 2!]. and 22 remains constant. quired to preset the switch blade 13A to this position is furnished entirely by the power arm 23A.

FIG. c shows the relative positions of the switch blade 13A and its associated parts immediately following responseof the hair element to a decrease in the relative humidity of the ambient air beyond a predetermined or selected value, causing a slight upward pull on the hanger bracket 42. Since the switch blade had already been moved counterclockwise to almost its dead-center position, the force and distance required to trip the blade is very small. Hence the switch can be made highly sensitive and its plus or minus tolerances reduced to meet exacting specifications. This also provides for utilization of a wider range of humidity element types than would otherwise be possible.

FIG. 10d shows the relative positions of the switch blade and its associated parts shortly after off contact It will be observed that the force reis made. Since current is no longer flowing through the power arm or bar 23A, the latter has cooled and its free extremity has undeformed downwardly against its stop 26, presetting the blade 13A slightly short of its throw or over-center line when the blade is moving toward its on position. Now should the relative humidity increase above its selected value, the humidity element will relax and the suspension point :54 will be pulled down wardly below the over-center line by spring 14A, returningrthe parts to the on position shown in FIG. 10a, completing the cycle.

In the event it is desired to use the switch to energize a control circuit in both switch blade positions, then the upper contact 22 need only be wired into the other control circuit and the latter provided with a return which by-passes the bimetal power arm or bar 23A.

What I claim is:

1. in a thermal switch for an electrical control circuit, an actuator responsive to a switching force, a switch-presetting arm having a free extremity deformable as a function of current flow, a pair of spaced contacts mounted on the free extremity of said arm, a resilient said contacts and arm being wired in circuit in a manner such that when one of the switching contacts engages its coacting arm contact in a first switching position current flows through the arm and deforms the latter causing its free extremity to advance said blade towards the opposite switching position a distance determined by said stop means to thereby preset said member adjacent one side of said throw line'ready for throw past dead center in response to movement of said actuator, and when the other of the switching contacts engages its coacting arm contact current flow is cut off from said arm and its free extremity moves back towards its first switching position and repositions said switching member adjacent the opposite side of said throw line ready for throw past dead center by said actuator.

2. A switch as claimed in claim '1 wherein said switch blade is anchored at one extremity and at its opposite contact extremity is formed with an integral prestressed bowed spring tongue having a free end edge thrusting against an abutment member approximately on the deadcenter throw line of the blade and the switching force of said actuator is applied to the blade back of this point of thrust in a plane substantially parallel to blade fiexure.

3. A switch as claimed in claim 1 wherein the switch blade and contact-presetting arm are mounted in a manner such that when the switching and arm contacts are engaged and the armmoves to preset the switch blade, the engaged contacts rub against one another and reduce the tendency toward contact erosion.

4. In a thermal switch for an electrical control circuit, an actuator responsive to a switching force, a switch-presetting arm anchored at one extremity and having a free extremity deformable in clockwise and counterclockwise directions as a :function of current flow, a pair of contacts fixed in predetermined spaced relation on the free extremity of said arm, one of said contacts being electrically insulated from the arm and the other contact being in conductive relation to the arm, a resilient switch blade anchored at one extremity and having a pair of contacts on its opposite extremity interposed between and coacting with said arm contacts, said blade being designed to have a snap action past a dead-center throw line in response to movement of said actuator, stop means located on opposite sides of and adjacent to said throw line for limiting the travel of said arm and the contacts carried thereby, said contacts and arm being Wired in circuit in a manner such that when one of the switch blade contacts engages its coacting arm contact in a first switching position current flows through the arm and deforms the latter whereupon its free extremity advances said blade toward the opmoves back towards its undeformed position and resets said blade adjacent the opposite side of said center line for return throw past dead center by said actuator.

5. An instrument for switching an electrical circuit as a function of ambient air conditions, comprising: a flexible switch blade provided with a pair of contacts and having a snap action past a dead-center throw line to alternate switching positions in response to a switching force, a blade-presetting arm at least in part deformable as a function of current flow, said arm being anchored at on extremity and carrying on its opposite free extremity a pair of spaced contact-s, one of which is electrically insulated from the arm and the other of which. is in electrical con- 7 ducting relation .to the arm, said contacts and arm being wired in circuit in a manner such that when one of the blade contacts engages the conducting arm contact current flows through said and deforms the latter in a direc- "tion to move the switch blade back towards the insulated contact position and when the other blade contact engages the insulated arm cont-act current flow is cut off from said arm and it undeform-s and moves the said blade back towards the insulated or conductive contact position, stop means effective to limit the travel of said arm in either direction with respect to said center line, and means responsive to changes in ambient air conditions for snapping the blade from its preset position past said throw line.

6. An instrument for switching anelectrical circuit as a function of ambient air conditions, comprising: a flexible switch blade anchored at one extremity and having opother of which is in electrical conductive relation to the arm, said blade contacts being located for alternate switching engagement with said arm contacts, said contacts being wired in circuit in a manner such that when one of the blade contacts engages the conductive arm contact current flows through said arm and deforms the latter in a direction to move the switch blade back towards the insulated contact position, and when the other blade contact engages the insulated arm contact, current flow is cut off from said aim and it moves the said blade back towards the insulated or conductive contact position, stop means effective to limit the travel of said blade in either direction with respect to said center line, an actuating member engaging said blade, means responsive to changes inarnbient air conditions for applying a switching force to said actua-ting member, and a shunt circuit for limiting the flow of current through said blade-presetting arm to a safe value.

7. In a switch for controling an electrical circuit, a pair of spaced contacts, a resilient switch blade anchored at one extremity only and having a pair of contacts on its oppositeextremity interposed between and coacting with said spaced contacts, said blade being formed with an integral prestressed bowed spring tongue having one end projecting free, an abutment member coaeting with said tongue in a manner such that the free end of the latter thrusts against said abutment member at a point approximately on the dead-center throw line of the blade, and biases the contact extremity of the blade toward one or the other of its alternate contact positions, an actuator connected directly at its one extremity to an intermediate portion of said blade between said thrust point and the anchored extremity of the blade, means responsive to changes in a condition of the ambient air directly connected to the opposite extremity of said actuator, the switching force of said actuator being applied to the blade in a plane substantially parallel to the direction of blade flexure.

8. In a switch for controlling an electrical circuit as a function of changes in the condition of the ambient air, a housing, a pair of spaced contacts supported by said housing, a resilient switch blade anchored at its one extremity,

to said housing and having a pair of contacts on its oppo'site extremity interposed between and coacting with said spaced contacts, said blade being formed with an integral prestressed bowed spring tongue having one end projecting tree, an abutment member coacting with said tongue and providing a fixed thrust point for the free end of the latter 1 actuator, and means accessible exteriorlyof said housing for adjusting the tension of said humidity element.

9. A switch as claimed in claim 8 wherein a temperatureresponsive element is also connected directly to said actuator and there are me ans accessible exteriorly of said housing for adjusting the temperature response of said temperature element.

References (Zited in the file of this patent UNITED STATES PATENTS 2,052,564 Grady Sept. 1, 1936 2,170,748 Eaton Aug. 22, 1939 2,189,996 Riche Feb. 13, 1940 2,351,408 Marcy Oct. 12, 1943 2,454,320 Hornbostel Nov. 23, 1948 2,813,173 Risacher et a1 Nov. 12, 1957

Claims (1)

1. 8. IN A SWITCH FOR CONTROLLING AN ELECTRICAL CIRCUIT AS A FUNCTION OF CHANGES IN THE CONDITION OF THE AMBIENT AIR, A HOUSING, A PAIR OF SPACED CONTACTS SUPPORTED BY SAID HOUSING, A RESILIENT SWITCH BLADE ANCHORED AT ITS ONE EXTREMITY TO SAID HOUSING AND HAVING A PAIR OF CONTACTS ON ITS OPPOSITE EXTREMITY INTERPOSED BETWEEN AND COACTING WITH SAID SPACED CONTACTS, SAID BLADE BEING FORMED WITH AN INTEGRAL PRESTRESSED BOWED SPRING TONGUE HAVING ONE END PROJECTING FREE, AN ABUTMENT MEMBER COACTING WITH SAID TONGUE AND PROVIDING A FIXED THRUST POINT FOR THE FREE END OF THE LATTER APPROXIMATELY ON THE DEAD-CENTER THROW LINE OF THE BLADE TO BIAS THE CONTACT EXTREMITY OF THE BLADE TOWARD ONE OR THE OTHER OF ITS ALTERNATE CONTACT POSITIONS, AN ACTUATOR HAVING ITS ONE EXTREMITY CONNECTED DIRECTED TO AN INTERMEDIATE PORTION OF SAID BLADE BETWEEN SAID THRUST POINT AND THE ANCHORED EXTREMITY OF THE BLADE, AN ELONGATED FLEXIBLE HUMIDITY-RESPONSIVE ELEMENT SUPPORTED AT ITS OPPOSITE EXTREMITIES FROM SAID HOUSING AND AT AN INTERMEDIATE POINT HAVING A CONNECTION WITH THE OPPOSITE EXTREMITY OF SAID ACTUATOR, AND MEANS ACCESSIBLE EXTERIORLY OF SAID HOUSING FOR ADJUSTING THE TENSION OF SAID HUMIDITY ELEMENT.

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