US3673535A

US3673535A - Electrical switch having a snap blade means and method of calibrating the same or the like

Info

Publication number: US3673535A
Application number: US135419A
Authority: US
Inventors: David M Rosenberg; Siegfried E Manecke
Original assignee: Robertshaw Controls Co
Current assignee: Robertshaw Controls Co
Priority date: 1971-04-19
Filing date: 1971-04-19
Publication date: 1972-06-27
Anticipated expiration: 1989-06-27

Abstract

An electrical switch having a snap blade means of the overcenter variety that is confined in its movement to only the negative rate area thereof on one side of its over-center position and to a method for calibrating such an electrical switch by simple adjustments of an adjusting member engaging the snap blade means and an adjustable stop means that limits movement of the snap blade means relative to a fixed contact that cooperates with the blade means and is spaced from the stop means.

Description

United States Patent Rosenberg et a1. [4 June 27, 1972 [5 ELECTRICAL SWITCH HAVING A [561 References Cited SNAP BLADE MEANS AND METHOD OF UNITED STATES PATENTS CALIBRATING THE SANIE OR THE LIKE 3,395,375 7/1968 Risk et al. .;.....337/347 X 3,239,633 3/ 1966 Bletz ..337/347 Inventors: David g g; Siegfried R 2,879,357 3/1959 Them ..337/343 Mamke, both of lndlana County, 3,238,337 3/1966 Rosenberg et al. ...337/340 [73] Assigneez Robmshaw Controls Company, 2,814,711 11/1957 Pliut ..337 347 Richmond v 2,175,721 10/1939 Taylor ..337/345 [22] Filed Apr 19 1971 2,074,132 3/1937 Rich ..337/347 [2]] Appl. No.: 135,419 Primary Examiner-Bernard A. Gilheany Assistant Examiner-Dewitt M. Morgan Related US. Application Data [60] Continuation Of Ser. N0. 714,992, March 21, 1961, [57] ABSTRACT ti i a i 3 1, gg z 1 5 An electrical switch having a snap blade means of the overgg g i? g ggggg arc center variety that is confined in its movement to only the negative rate area thereof on one side of its over-center posi- 52] U S 337/347 29/622 337/94 tion and to a method for calibrating such an electrical switch 51 lm. c1..1111111111111113615' 176K1101h 37/12 110111 37 26 by Simple adjusmems adjusting member engaging the 58 Field of Search ..337 340 343 345 347 94- snap blade means and an adjustable means that limits movement of the snap blade means relative to a fixed contact that cooperates with the blade means and is spaced from the stop means.

12 Claims, 13 Drawing figures PATENTEDJUNZ? I972 3, 673,535 SHEET 10F 3 J D I '09 4 23 INVENTOK 23 98 DAVID MILTON ROSENBERG BY SIEGFRIED EMIL MANECKE FIG-8 g, v 15 THEIR ATTORNEYS PATENTEDJUHZ? I972 3.673535 SHEET BN3 7 .FORCE 1o LEFT FORCE T0 m :20 I A D v i DEFLECTiON |2| DEFLECTION TO RIGHT v v T0 LEFT v DEFLECTION= 1 I us To LEFT 8 n9 FIG?" y c, Q I ||7 FORCE I v TO RIGHT l v I E ll2 ME ,9', 4 7 n4 7 H\ l FIG-I2 INVENTORY DAVID MILTON ROSENBERG BYSIEGFRIED EMIL mmscxe THEIR ATTORNEYS ELECTRICAL SWITCH HAVING A SNAP BLADE MEANS AND METHOD OF CALIBRATING THE SAME OR THE LIKE This application is a continuation of application, Ser. No. 714,992, filed Mar. 21, 1961, which, in turn, is a divisional patent application of its parent patent application, Ser. No. 300,468, filed Aug. 7, I963, which, in turn, is a Continuationin-part of the copending patent application, Ser. No. 263,033, filed Mar. 5, 1963, and entitled Thennostat or the Like and Parts Therefor," now 0.8. Pat. No. 3,238,337.

This invention relates to an improved thermostat or other control device as well as to an improved method for providing such a structure or the like.

It is well known to provide a thermostat for controlling the operation of an electrical heater means for a water heater tank or the like, the thermostat including a bimetal member which senses the wall temperature of the tank and controls an electrical switch or the like to selectively energize and deenergize such heating means in accordance with the temperature sensed. By properly selecting the initial position of the bimetal member, the thermostat is adapted to maintain the temperature of the water in the tank at a selected temperature.

Accordingly, it is an object of this invention to provide an improved thermostat or the like of the above described type and which has one or more of the novel features of this invention hereinafter described or illustrated.

Another object of this invention is to provide improved methods for providing such a thermostat or the like.

Other objects, uses and advantages of this invention are apparent from a reading of this description, which proceeds with reference to the accompanying drawings forming a part thereof and wherein:

FIG. 1 is a perspective view of the improved thermostat of this invention.

FIG. 2 is a bottom view of the thermostat illustrated in FIG. 1 and has the rear cover thereof removed.

FIG. 3 is an axial cross-sectional view taken on line 3-3 of FIG. 2.

FIG. 4 is an enlarged fragmentary view of the temperature selecting means of the thermostat illustrated in FIG. 3.

FIG. 5 is a view similar to FIG. 3 and illustrates the thermostat in another operating position thereof.

FIG. 6 is a cross-sectional view taken on line 6--6 of FIG. 3.

FIG. 7 is an enlarged cross-sectional view taken on line 7-7 of FIG. 3 with the background structure removed.

FIG. 8 is a cross-sectional view taken on line 8-8 of FIG. 3.

FIG. 9 is a cross-sectional view taken on line 9-9 of FIG. 3.

FIG. 10 is a view similar to FIG. 3 and illustrates another embodiment of this invention.

FIG. 11 is a schematic graph illustrating the deflection and force of a snap spring as utilized according to the teachings of this invention.

FIG. 12 is a schematic graph illustrating the deflection and force of a bimetal member as utilized according to the teachings of this invention.

FIG. I3 is a schematic graph illustrating the deflection and force of the snap spring and bimetal member when utilized together according to the teachings of this invention.

While the various features of this invention are hereinafter described and illustrated as being particularly adaptable to provide a water heater tank thermostat or the like, it is to be understood that the various features of this invention can be utilized singly or in any combination thereof to provide other control devices or the like.

Therefore, this invention is not to be limited to only the embodiments illustrated in the drawings, because the drawings are merely utilized to illustrate one of the wide variety of uses of this invention.

Referring now to FIG. I, the improved thermostat or the like of this invention is generally indicated by the reference numeral and comprises a substantially cup-shaped housing 21 formed of suitable insulating material or the like and having the rear or open end thereof closed by a rear cover plate 22 formed of metal or the like.

The housing 21 is provided with a plurality of input and output terminal posts 23 for respectively interconnecting the thermostat 20 to a power source and to the heater means or other electrical devices of a water heater tank or. the like, the terminal posts 23 comprising conventional threaded screwlike members.

The thermostat 20 is so constructed and arranged in a manner hereinafier described that the same is adapted to automatically maintain the temperature of the water in a water heater tank at a temperature selected by the manual setting of a rotatable indicating knob 24 carried by the housing 21 in a manner hereinafter described, whereby the pointer 25 of the knob 24 will indicate proper temperature setting as provided by the scale 26 carried on a plate 27 secured to the housing 21 in any suitable manner.

The particular details of the thermostat 20 will now be described and reference is made to FIGS. 2 and 3 wherein a substantially flat bimetal member 28 is disposed in the cavity 29 of the housing 21 and has opposed

ends

30 and 31.

The end 30 of the bimetal member 28 is secured by rivets 32 or the like to the middle leg 33 of a plural leg member 34 having its

outer legs

35 and 36 respectively secured to the housing 21 by

rivets

37 and 38 or the like. The middle leg 33 of the plural leg member 34 forms a leaf spring-like member that normally tends to move downwardly toward the housing 21 in FIG. 3 and carry the end 30 of the bimetal member 28 therewith.

A calibration screw plate 39 is disposed in the housing 21 below the plural leg member 34 and is secured to the housing 21 by the previously described

rivets

37 and 38, the calibration screw plate 39 having a threaded aperture 40 passing substantially centrally therethrough and having an end flange 41 projecting outwardly beyond the wall 42 of the housing 21.

A calibration screw or externally threaded adjusting member 43 passes through aligned

apertures

44 and 45 in the plate 27 and housing 21 to be threadedly received in the threaded aperture 40 of the calibration screw plate 39 as illustrated in FIG. 3, whereby the free end 46 of the calibration screw 43 engages the middle leg 33 to limit movement thereof toward the housing 21.

The selector knob 24 is press fitted on a knurled portion 47 of the calibration screw 43 at a point outside the housing 21, whereby the indicating pointer 25 thereof is adapted to be moved across the dial face 26 in unison with rotation of the calibration screw 43, the calibration screw 43 being adapted to be rotated relative to the housing 21 by inserting a screw driver or the like in the bifurcated end 48 thereof.

In this manner, the end 30 of the bimetal member 28 is adapted to be raised and lowered in FIG. 3 by movement of the calibration screw 43 in and out of the housing 21, whereby as the end 30 of the bimetal member 28 is moved upwardly a higher temperature setting is provided for the thermostat 20. Conversely, downward movement of the end 30 of the bimetal member 28 in FIG. 3 provides a lower temperature setting for the thermostat 20.

A movable motion transmitting member or tie bar 49 is disposed in the housing 21 and is formed of suitable insulating material or the like, the member 49 having a plurality of slot means 50, 51, and 52 passing therethrough in the manner illustrated in FIG. 7. The slot means 50 of the member 49 is defined in part by opposed surface means 53 and 54, which are substantially straight and parallel to each other while the slot means 51 is defined between

opposed surfaces

55 and 56 respectively defining substantially triangular portions having the

apexes

57 and 58 thereof facing each other and disposed apart a desired distance for a purpose hereinafter described. The slot means 52 of the member 49 is defined between opposed surface means 59 and 60, the opposed surface 59 defining a substantially triangular portion having an apex 61 disposed substantially intermediate the spaced straight portions of the opposed surface means 60. The portions 62 of the member 49 are separated from each other by a recess 63 which intersects the slot means 52 for a purpose hereinafter described.

The movable end 31 of the bimetal member 28 is operatively interconnected to the member 49 to cause vertical movement of the member 49 in FIG. 3 and, thus, to control the operation of a pair of

electrical switches

64 and 65 disposed in the housing 21.

In particular, the movable end 31 of the bimetal member 28 is divided into three

legs

66, 67, and 68, with the middle leg 67 being bent out of the plane of the

outer legs

66 and 68. In this manner, the legs 66-68 of the free end 31 of the bimetal member 28 can be press fitted through the slot means 50 of the member 49, whereby the legs 66-68 are placed under compression between the

opposed surfaces

53 and 54 of the slot means 50in the manner illustrated in FIG. 7.

This press fit interconnection of the free end 31 of the bimetal member 28 to the member 49 prevents any lost motion between the free end 31 of the bimetal member 28 and the lever 49.

The free end 69 of the middle leg 67 of the bimetal member 29 can be bent transversely in the manner illustrated in FIG. 3 to prevent the member 49 from moving to the right relative to the bimetal member 28 while movement of the member 49 to the left relative to the bimetal member 28 is prevented by shoulders 70 of the bimetal member 28.

The electrical switch 64 comprises a fixed contact 71 and a cooperable and movable contact 72, the fixed contact 71 being carried on a conductive plate 73 secured to a post 74 of the housing 21 by a conductive rivet 75 interconnected to one of the terminal posts 23.

The movable contact 72 is carried by a resilient switch blade 76 having one end 77 thereof secured to a post 78 of the housing 21 by a conductive rivet 79 interconnected to one of the terminal posts 23. The other end 80 of the resilient switch blade 76 passes through the slot means 51 of the member 49 and is normally biased against the apex 57 of the surface means 55 of the member 49, regardless of the position of the member 49 relative to the housing 21.

As illustrated in FIG. 7, the end 80 of the switch blade 76, when disposed against the apex 57 of the surface means 55 of the member 49, is normally spaced from the apex 58 of the surface means 56 thereof a distance of approximately 0.012 of an inch for a purpose hereinafter described.

Thus, it can be seen that when the movable end 31 of the bimetal member 28 moves downwardly from the position illustrated in FIG. 3 to the position illustrated in FIG. upon the bimetal member 28 sensing an increase in temperature value, the member 49 causes the movable contact 72 to move into electrical contact with the fixed contact 71.

The electrical switch 65 comprises a fixed contact 81 and a movable contact 82 cooperable with the fixed contact 81, the fixed contact 81 being carried on a conductive plate 113 secured to a post 83 of the housing 21 by a conductive rivet 84 interconnected to one of the tenninal posts 23.

The movable contact 82 is carried by a switch blade 85 having one end 86 thereof secured to a conductive plate 87 by rivets 88 or the like, the conductive plate 87 being secured to a post 89 of the housing 21 by a conductive rivet 90 interconnected to one of the tenninal posts 23 in the manner illustrated in FIG. 8.

The other end 91 of the switch blade 85 passes through the slot means 52 of the member 49 in such a manner that the end 91 of the switch blade 85 is compressed between the opposed surface means 59 and 60 of the member 49 to prevent any lost motion between the member 49 and the switch blade 85.

For example, reference is made to FIG. 7 wherein it can be seen that the

portions

61 and 62 of the slot means 52 are so constructed and arranged that the same slightly bow the switch blade 85 as the switch blade 85 passes through the slot means 52 to place the same under compression in the slot means 52 and, thereby, prevent any lost motion between the switch blade 85 and the member 49.

A leg 92 extends outwardly from the end 91 of the switch blade 85 and is bent transversely relative thereto to prevent outward movement of the lever 49 relative to the switch blade 85.

As illustrated in FIG. 9, the switch blade is divided into three

legs

93, 94 and 95 intermediate its ends 86 and 91. The

outer legs

93 and 95 are suitably crimped at 96 in the manner illustrated in FIGS. 3 and 9 to place the middle leg 94 under compression whereby the switch blade 85 is rendered snapacting for a purpose hereinafter described.

A leaf spring 97 is disposed in the housing 21 and has one end 98 thereof secured to the conductive plate 87 by the same rivets 88 that secure the switch blade 85 to the conductive plate 87.

The leaf spring 97 is interconnected to the middle leg 94 of the switch blade 85 by a rivet 99 and normally tends to move downwardly toward the housing 21 in the manner illustrated in FIG. 3 to aid the snap-acting function of the switch blade 85.

The free end 100 of the leaf spring 97 is engaged by a threaded adjusting member 101 threadedly disposed in an internally threaded bore 102 formed in the housing 21, the adjusting member 101 being adapted to limit downward movement of the leaf spring 97 in FIG. 3 to provide a means for establishing the desired snap point of the switch blade 85.

Therefore, it can be seen that as the movable end 31 of the bimetal member 28 tends to move downwardly in FIG. 3 upon an increase in sensed temperature value, the member 49 also tends to move downwardly therewith and imposes a downward force on the switch blade 85. When a sufficient downward force is imposed on the switch blade 85 by the member 49, the switch blade 85 snaps downwardly in the manner illustrated in FIG. 5 whereby the electrical contact between the

contacts

81 and 82 is abruptly terminated while the

contacts

72 and 71 are brought into electrical contact with each other.

Conversely, when the movable end 31 of the bimetal member 28 tends to move upwardly upon a decrease in sensed temperature value, the switch blade 85 subsequently snaps upwardly when a sufficient force has been applied thereto by the member 49 tending to pull the same upwardly whereby the contact 82 is snapped into electrical engagement with the contact 81 while the

contacts

72 and 71 are snapped open in the manner illustrated in FIG. 3.

The rear cover 22 of the thermostat 20 is substantially cupshaped to telescopically receive the rear of the housing 21 in the manner illustrated in FIG. 3, the housing 21 having a pair of opposed recesses 103 formed therein and terminating in shoulders 104 as illustrated in FIG. 1.

The rear cover 22 has a pair of inwardly biased tangs 105 which are adapted to snap into the recesses 103 when the cover 22 and housing 21 are telescoped together whereby the ends of the tangs 105 of the cover 22 catch against the shoulders 104 to secure the cover 22 to the housing 21.

In addition, the cover 22 has a slot 106 passing therethrough to snap fittingly receive the flange 41 of the calibration screw plate 39 in the manner illustrated in FIGS. 1 and 3 whereby not only does the calibration screw plate 39 provide an anchor for the back cover 22, but also the calibration screw plate 39 acts as a conductor to pick up and transfer surface temperature to the bimetal member 28.

If desired, the cover 22 can have a pair of outwardly directed ears or lugs 107 in the manner illustrated in FIG. 1 whereby the thermostat 20 can be secured to the desired surface by suitable fastening members passing through apertures 108 in the lugs 107.

Altemately, or additionally, the back cover 22 can be provided with ears 109, FIG. 1, which provide means for mounting the thermostat 20 to a suitable appliance by the use of spring brackets which snap down on the ears 109 at the points 1 10.

The operation of the thermostat 20 of this invention will now be described.

After the thermostat 20 has been mounted to the water heater tank or the like and the power source lines and heater means or other electrical devices have been appropriately interconnected to the terminal posts 23 thereof, the operator sets the pointer 25 to the desired temperature, such as F.

as illustrated in FIG. 1 whereby the end 46 of the calibration screw 43 properly positions the end 30 of the bimetal member 28 relative to the housing 21.

Assuming that the temperature being sensed by the bimetal member 28 is below the temperature that would cause the thermostat 20 to turn off the heater means of the water heater tank, the

switches

64 and 65 are disposed in the position illustrated in FIG. 3 whereby suitable electrical current is directed to the heater means of the water heater tank.

However, as the temperature of the water in the water heater tank increases to the selected temperature, the movable end 31 of the bimetal member 28 tends to move downwardly .from the position illustrated in FIG. 3 until the same exerts sufficient downward force on the member 49 to cause the switch blade 85 to snap downwardly to the position illustrated in FIG. 5 whereby the

contacts

81 and 82 are snapped open while the

contacts

72 and 71 are snapped closed so that the heating means for the water heater tank is de-energized as the temperature of the water in the tank is at the selected temperature value.

With the thermostat 20 disposed in the position illustrated in FIG. 5 and the temperature of the water in the water tank decreasing below the selected temperature, the end 31 of the bimetal member 28 tends to move upwardly from the position illustrated in FIG. 5 until the same exerts sufficient force to cause the switch blade 85 to snap in an upward direction to snap close the

contacts

81 and 82 and to snap open the

contacts

71 and 72 to again energize the heating means of the water heater tank.

During this last operation, it may be that the

contacts

71 and 72 had become stuck in their closed position while the member 49 is being snapped upwardly. However, it can be seen from FIG. 7 that the member 49 can move relative to the switch blade 76 before the apex 58 of the lower surface means 56 thereof comes into contact with the switch blade 76 whereby the member 49 can apply a hammer blow to the switch blade 76 to unstick the

contacts

71 and 72 should the same become stuck during operation of the thermostat 20.

Thus, it can be seen that the thermostat 20 can cycle in such a manner to maintain thetemperature value of the water in the water heater tank at the selected temperature value.

Therefore, it can be seen that an improved thermostat or the like is provided by this invention as well as improved parts for such a thermostat or the like.

While the thennostat 20 previously described has been illustrated as a single pole double throw unit, it is to be understood that the same can be constructed in a like manner to form a single pole single throw unit by simply eliminating the fixed contact 71 and switch blade 78 in the manner illustrated in FIG. 10 whereby another thermostat of this invention is generally indicated by the reference numeral 111 and parts thereof similar to the thermostat previously described or indicated by like reference numerals followed by the reference letter a.

As illustrated in FIG. 10, the fixed contact 71 and switch blade 76 have been eliminated whereby the member 490 merely controls the operation of the electrical switch 65a in the manner previously described.

However, when the member 49 of the thermostat 20 was snapped downwardly from the position illustrated in FIG. 3 to the position illustrated in FIG. 5, the engagement between the

contacts

71 and 72 thereof limited the downward movement of the member 49 upon the snap action of the switch blade 85.

Therefore, in order to limit the downward movement of the member 49a of the thermostat 111 illustrated in FIG. 10, an adjusting screw 112 is adjustably carried by the housing 21a to limit downward movement of the member 49a after the contacts 81a and 82a have been snapped open in the manner previously described, the adjusting screw 112 being engageable by the end of the member 49a.

Therefore, it can be seen that the thermostat of this invention can be modified in any desired manner while still performing the desired functions of this invention.

The particular details of the operation of the snap switch blades or springs and 85a in combination with the

bimetal members

28 and 28a will now be described and reference is made to FIGS. 1 1-13.

As illustrated in FIG. 11, the snap spring blade 85a or 85 is illustrated in full lines in its most leftward position and in dotted lines in its most rightward position after it has snapped over center, the over center position being illustrated by the vertical line 114. Such movement of the snap spring blade 85:: is represented by the horizontal line whereby point 0 on line 115 is the dead center position of snap spring blade 85 and points A and D on line 115 are the extreme positions of deflection of the snap spring blade 85:: from its center position 0.

A curve 116 is plotted on the

lines

114 and 115 and represents the force provided by the snap spring blade 85a in any of its deflected positions, the curve 1 16 being very similar to a sine wave curve.

Thus, it can be seen the snap spring blade 85a or 85 has no force tending to move the same in a particular direction when the blade 85a or 85 is disposed at positions A, O and D.

However, as the snap spring blade 85a or 85 is deflected from point A to point B, the snap spring blade has an increasing force tending to move itself back to the left to point A. Similarly, as the snap spring blade 85a or 85 is deflected from point 0 to point C, the blade has an increasing force tending to move itself back to the right to point D.

This force of the snap spring blade 850 or 85 between points, A, B and D, C is known as the positive rate range of the snap spring blade.

However, as the snap spring blade 85a or 85 is deflected from point B toward point 0 or from point C toward point 0, the opposing force of the snap spring blade decreases whereby movement of the blade between the points B, 0 and C, O is known as the negative rate range of the snap spring blade.

The thermostats of this invention utilize the negative rate range of the snap spring blade 85a or 85 in a manner now to be described.

As illustrated in FIG. 1, the fixed contact 81a or 81 is so constructed and arranged that the same limits the movement of the snap spring blade 850 or 85 to the left at point E on the curve 116.

Similarly, the adjustable stop means 112 of FIG. 10 or the contact 71 of FIG. 5 is so constructed and arranged that the same limits movement of the snap spring blade 85a or 85 to the right at point F on the curve 1 16.

Thus, it can be seen that the movement of the snap spring blade 8511 or 85 is limited between the points E and F on the curve 116 by the fixed contact and stop means so that the entire range of movement of the snap spring blade 850 or 85 is the negative rate range thereof and never snaps over center.

The use of the change in force of the snap spring blade 85a or 85 between points E and F will later be described.

Reference is now made to FIG. 12 wherein the vertical line 117 represents the bimetal member 280 or 28 at rest and the horizontal line 118 represents deflection of the

bimetal member

28a or 28 to the left.

Thus, as the

bimetal member

28a or 28 is deflected to the left from its at rest point 119 to point 120, the bimetal member exerts an increasing force tending to move the bimetal member back to position 119, the force being represented by the substantially straight line 121.

By combining the deflection force curve of the snap spring blade 85a or 85 with the deflection force curve of the bimetal member 280 or 28, it can be seen that the contact carried by the snap spring blade 85a or 85 can be substantially snapped between its closed and opened positions without requiring the snap spring blade 85a or 85 to be snapped over center.

For example, reference is now made to FIG. 13 wherein the action of the thermostats of this invention is graphically illustrated.

As illustrated in FIG. 13, point E represents the contact closed position of the movable snap spring blade contact 82a or 82 and point P represents the contact open position thereof whereby it can be seen that the snap spring blade 85a or 85 never reaches its dead center position 0.

Without any bimetal efiect, the

contacts

820, 81a or 82, 81 will be closed with the amount of pressure indicated at point E.

As the temperature increases, the

bimetal member

28a or 28 will start building up force in opposition to the snap spring blade force. When the temperature sufficiently increases so that the bimetal force equals or just exceeds the snap spring force, the

contacts

824, 81a or 82, 81 will open a slight amount and the snap spring force will be reduced. The bimetal force will also be reduced but not as much as the snap spring force and, consequently, the

bimetal member

28a or 28 will continue to open the

contacts

82a, 81a or 82, 81 until the contact 82a or 82 hits, in effect, the stop means 1 12 or 71.

At this point the snap spring force will have been reduced along line EF to point F. The bimetal force will have reduced along line EG to point G. Since, at this time, the bimetal force is greater than the snap spring force, the bimetal will push the snap spring, in effect, against the stop means.

Since the

contacts

82, 81a or 82, 81 are now in the opened position at point F, the temperature will begin to drop. As the temperature drops, the bimetal force will be reduced along line GF.

When the bimetal force reduces to point F or slightly less, the snap spring force will start to move the contact 82a or 82 away from its stop means. As it moves away, the snap spring force increases at a greater rate than the bimetal force, and it thus closes the

contacts

820, 81a or 82, 81 with a snap action.

The snap force changes from point F to point E while the bimetal force changes from point F to point H.

The

contacts

82a, 810 or 82, 81 are now closed and the temperature will again start to rise. As the temperature rises, the bimetal force will increase along line HE.

When the bimetal force reaches point E, the

contacts

82a, 810 or 82, 81 will snap open and the cycle will be repeated in the above manner.

Thus, it can be seen that the thermostats of this invention only utilize the negative rate range of a snap spring to provide a snap action movement of a movable contact between its opened and closed positions.

The calibration procedure utilized to obtain the abovedescribed snap action for the thermostat 111 of FIG. 10 is as follows:

1. Only the parts 21a, 85a, 49a, 112, 65a, and 101a are assembled together as illustrated in FIG. 10.

2. The screw 101a is turned inward until the snap spring blade 85a snaps downward.

3. The screw 112 is then turned inward until contacts 820 and 81a just make contact. This position can be detected with a continuity tester connected to the rivet 90 and the rivet 84.

4. The screw 112 is then turned out about one-half turn to provide a very slight gap such as ten thousandths of an inch.

5. The screw 10111 is then turned out until the snap spring blade 85a snaps to close contacts 820 and 81a.

The calibration procedure utilized to obtain the abovedescribed snap action for the thermostat of FIG. 3 is as follows:

1. Only the

parts

21, 101, 85, 81, 49, 71, 72, 76, and 79 are assembled together in the manner illustrated in FIG. 3.

2. The screw 101 is then turned inward until the switch blade 85 snaps downward.

3. The support for contact 71 is then adjusted to provide a slight gap between

contacts

81 and 82.

4. The screw 101 is then turned out until the snap spring 85 snaps to close

contacts

81 and 82.

Therefore, it can be seen that it is a relatively simple procedure to provide the above calibration for the thermostats 20 and 1 11 in order to have the snap action previously described.

What is claimed is:

1. In a method for making an electrical switch having a movable snap spring blade means of the over-center variety provided with an end that cooperates with a pair of spaced stop means to limit movement of said end of said snap blade means, the improvement comprising the steps of adjusting an adjusting member of said switch to cause said snap spring blade means to move said end away from one of said stop.

means, adjusting the other stop means for said snap spring blade means to hold said end of said snap spring blade means slightly spaced from said one stop means, thereafter adjusting said adjusting member to cause said snap spring blade means to move said end toward said one stop means and place said end thereof against said one stop means whereby subsequent movement of said end of said snap spring blade means as limited by said stop means will only be on one side of the overcenter position of said snap spring blade means, and, thereafter, operatively associating a bimetal member with said snap spring blade means to cause movement of said snap spring blade means between said stop means in relation to temperature sensing condition of said bimetal member.

2. In a method as set forth in claim 1, the further improvement wherein said adjusting steps cause said subsequent movement of said end of said snap spring blade means to be in only the negative rate area of said snap spring blade means on said one side of the over-center position thereof.

3. In a method as set forth in claim 1, the further improvement of including the step of forming said one stop means from an electrical contact and providing an electrical contact on said end of said blade means to cooperate therewith.

4. In a method as set forth in claim 3, the further improvement of including the step of adjusting said other stop means to move said contact carrying end of said blade means into electrical contact with said stop means contact after said first adjusting step and before said second adjusting step.

5. In a method as set forth in claim 4, the further improvement of including the step of testing the electrical contact between said contacts after the step of adjusting said other stop means to place said blade means contact into contact with said stop means contact.

6. In a method as set forth in claim 1, the further improvement of including the step of interconnecting a movable blade to said snap blade means, said movable blade engaging said other stop means when said end of snap blade means is subsequently moved away from said one stop means.

7. In a method as set forth in claim 6, the further improvement of including the step of forming said one stop means from an electrical contact and providing an electrical contact on said end of said blade means to cooperate therewith.

8. In a method as set forth in claim 7, the further improve ment of including the step of forming said other stop means from an electrical contact and providing an electrical contact on said blade to cooperate therewith.

9. In a method for making an electrical switch having a movable snap spring blade means of the over-center variety provided with a contact carrying en'd movable between a fixed contact and an adjustable stop means spaced from said fixed contact and having an adjusting member engaging an intermediate portion of said blade means, the improvement comprising the steps of adjusting said adjusting member in a direction toward said snap blade means until it causes said snap blade means to snap away from said fixed contact and against said stop means, adjusting said stop means toward said fixed contact to cause said blade means contact to just make contact with said fixed contact, thereafter, adjusting said stop means away from said fixed contact to provide a slight gap between said fixed contact and said blade means contact, then adjusting said adjusting member in a direction away from said blade means until said blade means snaps its contact against said fixed contact, and, thereafter, operatively associating a bimetal member with said snap blade means to cause movement of said snap blade means between said positions thereof in relation to temperature sensing conditions of said bimetal member.

10. In a method as set forth in claim 9, the further improvement wherein said steps cause said snap blade means to move between said fixed contact and said stop means in only the negative rate area of said snap blade means on one side of the over-center position thereof.

11-. In a method for making an electrical switch having a movable snap spring blade means of the over-center variety provided with a contact carrying end movable relative to a first fixed contact and having an adjusting member engaging an intermediate portion of said blade means, said blade means being interconnected to a blade provided with a contact carrying end movable relative to an adjustable fixed contact, the improvement comprising the steps of adjusting said adjusting member in a direction toward said blade means until it causes said blade means to snap away from said first fixed contact and move said contact of said blade against said second fixed contact, adjusting said second fixed contact to provide a slight gap between said first fixed contact and said contact of said blade means, thereafier, adjusting said adjusting member in a direction away from said blade means until said blade means snaps said contact thereof against said first fixed contact, and, thereafter, operatively associating a bimetal member with said snap blade means to cause movement of said snap blade means between said positions thereof in relation to temperature sensing conditions of said bimetal member.

12. In a method as set forth in claim 11, the further improvement wherein said steps cause said snap blade means to move relative to said first fixed contact in only the negative rate area of said snap blade means on one side of the overcenter position thereof.

I! i R i

Claims

1. In a method for making an electrical switch having a movable snap spring blade means of the over-center variety provided with an end that cooperates with a pair of spaced stop means to limit movement of said end of said snap blade means, the improvement comprising the steps of adjusting an adjusting member of said switch to cause said snap spring blade means to move said end away from one of said stop means, adjusting the other stop means for said snap spring blade means to hold said end of said snap spring blade means slightly spaced from said one stop means, thereafter adjusting said adjusting member to cause said snap spring blade means to move said end toward said one stop means and place said end thereof against said one stop means whereby subsequent movement of said end of said snap spring blade means as limited by said stop means will only be on one side of the over-center position of said snap spring blade means, and, thereafter, operatively associating a bimetal member with said snap spring blade means to cause movement of said snap spring blade means between said stop means in relation to temperature sensing condition of said bimetal member.

8. In a method as set forth in claim 7, the further improvement of including the step of forming said other stop means from an electrical contact and providing an electrical contact on said blade to cooperate therewith.

9. In a method for making an electrical switch having a movable snap spring blade means of the over-center variety provided with a contact carrying end movable between a fixed contact and an adjustable stop means spaced from said fixed contact and having an adjusting member engaging an intermediate portion of said blade means, the improvement comprising the steps of adjusting said adjusting member in a direction toward said snap blade means until it causes said snap blade means to snap away from said fixed contact and against said stop means, adjusting said stop means toward said fixed contact to cause said blade means contact to just make contact with said fixed contact, thereafter, adjusting said stop means away from said fixed contact to provide a slight gap between said fixed contact and said blade means contact, then adjusting said adjusting member in a direction away from said blade means until said blade means snaps its contact against said fixed contact, and, thereafter, operatively associating a bimetal member with said snap blade means to cause movement of said snap blade means between said positions thereof in relation to temperature sensing conditions of said bimetal member.

11. In a method for making an electrical switch having a movable snap spring blade means of the over-center variety provided with a contact carrying end movable relative to a first fixed contact and having an adjusting member engaging an intermediate portion of said blade means, said blade means being interconnected to a blade provided with a contact carrying end movable relative to an adjustable fixed contact, the improvement comprising the steps of adjusting said adjusting member in a direction toward said blade means until it causes said blade means to snap away from said first fixed contact and move said contact of said blade against said second fixed contact, adjusting said second fixed contact to provide a slight gap between said first fixed contact and said contact of said blade means, thereafter, adjusting said adjusting member in a direction away from said blade means until said blade means snaps said contact thereof against said first fixed contact, and, thereafter, operatively associating a bimetal member with said snap blade means to cause movement of said snap blade means between said positions thereof in relation to temperature sensing conditions of said bimetal member.

12. In a method as set forth in claim 11, the further improvement wherein said steps cause said snap blade means to move Relative to said first fixed contact in only the negative rate area of said snap blade means on one side of the over-center position thereof.