US2867704A - Thermostatic snap acting switch - Google Patents

Description

Jan. 6, 1959 N; MILLER THERMOSTATIC SNAP ACTING SWITCH Filed May 21. 1957 Ma ma Mil/e2" THERMOSTATIC SNAP ACTENG SWITCH Nicholas Miller, Chicago, Ill., assignor to The Dole Vaive Company, Morton Grove, Ill., a corporation of Illinois Application May 21, 1957, Serial No. 669,633

11 Claims. (Cl. 200-444 This invention relates to improvements in thermostatic control devices and more particularly relates to a thermostatically operated snap acting switch adapted for controlling the operation of air conditioners and the like. I

A principal object of the invention is to provide a simple form of thermostatically operated switch in which the temperature of operation of the switch may be adjusted at the selection of the operator.

A further object of the invention is to provide a simple and improved thermostatic snap acting switch arranged with a view toward utmost eificiency and compactness.

Still another object of the invention is to provide a thermostatically operated snap acting switch for air conditioners and the like in which the temperature range of operation of the switch may be adjusted at the selection of the operator, and having a snap lever operating the snap blade for the switch and acted on by the thermal element of the switch, in which the points of application of the forces acting on the snap lever lie substantially in the same plane and in the mid-position of the temperature adjustment of the switch the direction of the forces is substantially perpendicular to said plane, thereby reducing friction and increasing the efiiciency of operation of the switch.

Still another object of the invention is to provide a thermostatically controlled snap acting switch particularly adapted for air conditioners and the like in which a thermal element having an extensible power member acting against a lever is provided to operate the snap blade for the switch, and in which the fulcrum for the lever is yieldable to accommodate over-travel of the power member of the thermal element without injury to the switch.

A still further object of the invention is to provide a simple and improved form of thermostatically controlled snap acting switch in which a power type of thermal element having an extensible power member serves to operate and acts against one end of a snap lever for operating the switch, in which the fulcrum for the snap lever is adjustable to vary the temperature range of operation of the switch, and in which an over-travel safety spring biases the fulcrum for the snap lever in its extended position, and is incorporated within the adjusting means for the snap lever and yields upon overtravel conditions, to accommodate over-travel of the power member of the thermal element without injury to the snap acting switch.

These and other objects of the invention will appear from time to time as the following specification proceeds and with reference to the accompanying drawing wherein:

Fig. 1 is a transverse sectional view taken through a thermostatic snap acting switch constructed in accordance with the invention;

Fig. 2 is a view in side elevation of the switch shown in Fig. l, with an end cover for the switch casing removed and certain other parts removed and shown in section; and

Fig. 3 is a fragmentary detail sectional view illustrating Meiji Patented Jan. 6, 1959 the relative positions of the reaction points of the switch actuating mechanism with respect to each other.

In the embodiment of the invention illustrated in the drawing, a frame 10 generally U-shaped in cross-section and having parallel legs 11 and 12 extending from the base of the U forms the frame for the casing for the switch. The leg 11 has a casing 13 of a thermal element 15 extending therethrough, with a clamping ring 16, clamping the casing 13 of the thermal element to a cylinder 17 thereof, maintained in abutting engagement with the inner side of the leg 11 by a return spring 19 of the thermal elementlS.

The leg 12 is shown as having an anchor 20 for a dial knob (not shown) abutting the outer side thereof and rotatably mounted on an internally threaded boss 21 extending through the leg 12. and spun or otherwise secured thereto. A friction spring washer 22 is shown as being interposed between a shoulder 23 of the boss 21 and the inner face of the portion of the anchor 20 engaging the outside of the leg 12, to prevent unintentional rotation of said anchor.

The boss 21 is shown as having a hollow adjusting screw 24 threaded therein and extending within the inside of the leg 12 into the interior of the switch casing. The hollow adjusting screw 24 forms an adjustable mounting for a plunger 25 slidably extending therethro-ugh and forming a fulcrum for a snap or actuating lever 27 at its inner end. The term snap lever is not intended to designate the lever 27 as a lever that moves with a snap action, but is used to refer to the lever as the actuating means for the snap acting switch, as will more clearly appear as the specification proceeds. A relatively heavy over-travel safety spring 29 is mounted within the hollow adjusting screw 24 and abuts a head 30 of the plunger 25 at its inner end and a disc 31 at its outer end, shown as being retained within the hollow adjusting screw 24 by staking an inner wall portion of the adjusting screw into engagement therewith.

The over-travel safety spring 29 is sutliciently strong to normally act as a solid member and hold the plunger 25 in position to provide a fixed fulcrum for the snap lever 27, but to accomodate the plunger 25 to yield upon over-travel of a power member of piston 33 of the thermal element, to prevent damage to a snap blade 35 of a snap acting switch 36, upon over-temperature conditions and upon conditions where the plunger 25 is adjusted to eliect operation of the switch at a substantially lower temperature than the ambient temperature to which the thermal element is subjected.

A calibration plate 37 is fixed to the adjusting screw 24 and has an arm 39 engageable with the anchor 20, to effect turning movement of the calibration plate 37 and the adjusting screw 24 upon turning movement of the anchor 20, as by a dial knob (not shown), to vary the spacing between the inner end of the plunger 25 and a reduced diameter engaging end 40 of the power member 33 of the thermal element 15. The farther away the inner end of the plunger 25 is from the end of the reduced diameter end 40 of the power member 33, the greater will be the travel of said power member required to pivot the snap lever 27 and effect closing of the switch 36. Adjustable movement of the end of the plunger 25 away from the reduced diameter end of the power member 33 will, therefore, increase the temperature at which the switch 36 closes. In a contrary manner, adjustable movement of the end of the plunger 25 toward the reduced diameter end 40 of the power member 33 will reduce the travel of the power member 33 required to effect closing of the switch 36,,and will therefore reduce the temperature at which said switch operates.

At temperature conditions where the ambient temperature is and the switch is set to close at 90, and it is .7 a desired that the switch close at 70, turning of the adjusting screw 24 to position the plunger 25 to effect closing of the switch at 70 will effect compression of the spring 29, the spring returning as the piston 40 is retracted by lowering of the ambient temperature to 70.

The thermal element 15 is shown as being a well known form of power or high motion type of thermal element in which a fusible thermally expansible material con tained within the casing 13 acts against a diaphragm (not shown) clamped within said casing by the clamping ring 16, to extend the power member 33 with respect to the cylinder 17 on increases in temperature sufficient to effect fusion of the fusible thermally expansible material contained within the casing 13, as shown and described in Patent No. 2,368,181 which issued to Sergius Vernet on Jan. 30, 1945, and no part of the present invention, so not herein shown or described further.

The power member 33 is returned within the cylinder 17 upon reductions in temperature by the spring 19 seated at one end in a spring seat 41 having a right angled portion 43 riveted or otherwise secured to the base of the U-shaped frame 10, with the spring seat 41 extending inwardly from said base within the switch casing. The opposite end of the return spring 19 is seated on a flange 44 of a generally cylindrical spring saddle or retainer 45, encircling the cylinder 17 and mounted as its outer end on the reduced diameter end 40 of the power member 33 and abutting the shoulder formed at the junction of said reduced diameter end with the enlarged diameter portion of the power member 33.

The snap acting switch 36 is shown as comprising a spring metal switch arm 47 riveted or otherwise secured to an inturned leg 49 of a terminal 50, extending through an end cover 51 for the switch casing, and insulated therefrom. The switch arm 47 is preferably made from a spring material having good electrical conductivity, such as commercial bronze or beryllium copper and has a contact 53 on its free end, engageable with a stationary contact 54 on an inturned leg 55 of a terminal 56, extending through and suitably insulated from the end cover plate 51. The resilient switch arm 47 is biased to normally maintain the movable contact 53 in engagement with the stationary contact 54.

The contact 53 is moved to an open position with respect to the contact 54 by operation of the snap blade 35 through an operator 57, which may be in the form of an insulator rod having a reduced diameter end 59 extending through the switch arm 47 and having a second reduced diameter end 60 extending through the snap blade 35, so that snapping of the blade 35 into the position shown in Fig. 1 into engagement with a stop 63, will effect opening of the contact 53 with respect to the contact 54.

The snap blade 35 may be made from stainless steel and is mounted at its end opposite the stop 63 on a leg 66 of a snap blade support 67. The snap blade support 67 has lateral projections 69 projecting laterally from opposite sides thereof and engaging within generally V-shaped fulcrum notches 70, formed in opposite parallel spaced legs 71 of a bracket 72, mounted on the inner side of the leg 12 of the switch casing.

The snap blade support 67 also has an arm 73 extending outwardly therefrom at generally right angles with respect to the snap blade 35, and having nibs 74 extending laterally from opposite sides thereof and engaging within bearing slots 75 formed within parallel spaced leg portions 76 of the snap lever 27, adjacent the end of said snap lever opposite from the power member 33 of the thermal element 15.

The inner end of the plunger 25 engages the snap lever 27 intermediate the ends thereof within a recess 77,

formed in a base 79 of said snap lever and recessed adistance sufficient to position the point of engagement of the plunger 25 with the snap lever in a plane extending through the point of engagement of the reduced diam eter end 40 of the power member 33 with the base 79 of the snap lever and the point of engagement of the bearing slots with the nibs 74 of the snap blade support 67 and the center of rotation of projections 69 in notches 7! Thus, the points of application of the forces acting on the snap lever 27 lie substantially in the same plane, and in the mid-position of the temperature adjustment of the switch, the direction of the forces is substantially perpendicular to said plane.

The free end of the snap blade 35 engages within a recessed portion 80 of an overcenter spring 81. The overcenter spring 81 is shown as being generally U-shaped in cross-section, and as having a tongue 83 projecting from its opposite leg from the recess 80, and having rocking engagement within a recessed portion 84 of the leg 11 of the switch casing.

The overcenter spring 81 besides serving as an overcenter spring to hold the snap blade 35 into engagement with the stop 63 to hold the contacts of the switch 36 in an open position, and also to hold the snap blade 35 into engagement with a stop 85 to accommodate closing of the contacts 53 and 54- by the bias of the spring arm 47, exerts a substantially constant force on the end of the snap blade 35, to cause said snap blade to snap the contact 53 into an open position, and to accommodate the contact 53 to engage the contact 54 with a snap action.

A return spring blade 87 is provided to return the snap blade support 67 and snap lever 27 upon cooling of the thermal element and retractible movement of the power member 33 with respect to the cylinder 17 of the thermal element. The return spring blade 87 is shown as extending along the snap blade support 67 and snap blade 35 and as being riveted to said snap blade support by the rivets securing the snap blade 35 to said blade support. The return spring 57 is biased outwardly from the snap blade support 67 and snap blade 35 toward the thermal element 15 and has engagement at its inner end with an abutment 38 extending within the switch casing, from the base of the U-shaped frame 10 of said swltch casing, and biases the snap blade 35 and snap blade support 67, as well as the snap lever 27, in a direction to effect opening of the contacts 53 and 54, as the power member 33 retractibly moves within the cylinder 17 of the thermal element 15.

A stop 89 extending inwardly from the base of the U-shaped casing portion 10, is provided to l1m1t pivotal movement of a snap lever 27 in a counterclockwise direction upon over-temperature conditions and over-extension of the power member 33 of the thermal element, as the plunger 25 retractibly moves against the over-travel safety spring 29.

In operation of the switch, as the temperature to which the casing 13 of the thermal'element 15 is sub ected rises to an extent suflicient to effect fusion of the fusible thermally expansible material contained within the easing 13, the power member 33 will extensibly move wlth respect to the cylinder 17 and fulcrum the snap lever 27 about the inner end of the plunger 25. Thls in turn will pivot the snap blade support about the bearing recesses 70 in the bearing brackets 71 against the return spring 87. As the snap blade support 67 pivots a distance sufficient to bring the free end of the snap blade 35 past dead center with respect to theovercenter snap spring 81, the overcenter spring 81 will exert a force on the end of the snap blade 35 and cause said snap lever to snap into engagement with the stop 85 and accommodate the contact 53 to snap into engagement with the contact 54, by the bias of the resilient blade 47. As the temperature to which the casing 13 of the thermal element 15 is subjected is reduced to an extent sufficient to accommodate the spring 19 to retractibly move the power member 33 with respect to the cylinder 17, the return spring 87 will pivot the snap blade support 67 and snap lever 27 in a clockwise direction until the end of the snap blade 35 has passed a dead center position with respect to the overcenter spring 81, at which time said overcenter spring will snap the snap blade intoen-' gagement with the stop 63 and open the circuit between the contacts 53 and 54 with a snap action.

It will be understood that various modifications and variations of the present invention may be effected without departing from the spirit and scope of the novel concepts thereof.

I claim as my invention:

1. A thermostatic snap acting switch comprising a switch casing, a rockable snap blade and lever within said casing and respectively pivotable about parallel axes, an overcenter spring rockingly mounted at one end in said casing in advance of said snap blade and having rocking engagement with said snap blade at its opposite end, means operating said snap lever to move said snap blade in a direction to effect closing of an energizing circuit comprising a thermal element having a power member extensibly movable upon increases in temperature and having operative engagement with said snap lever, and a fulcrum for said snap lever disposed within said casing on the opposite side of said lever from said power member and selectively adjustable from the outside of said casing to vary'the temperature range of operation of said switch.

2. A thermostatic snap acting switch comprising a switch casing, a rockable snap blade and lever within said casing and respectively pivotable about parallel axes, an overcenter snap spring rockingly mounted at one end in said casing in advance of the end of said snap blade and having rocking engagement with said blade at its opposite end, a switch operated by said snap blade, means operating said snap lever comprising a thermal element having an extensible power member engageable with an end of said snap lever, a fulcrum for said snap lever engageable with said snap lever intermediate the ends thereof on the opposite side of said lever from said power member, and yieldable means biasing said fulcrum into an extended fulcrum position within said casing and yieldable to accommodate over-travel of said power member upon over-temperature conditions.

3. A thermostatic snap acting switch comprising a switch casing, a rockable snap blade and snap lever within said casing, an overcenter snap spring rockingly mounted in said casing in advance of said snap blade and having rocking engagement with said snap blade, a switch operated by said snap blade, means operating said snap lever in one direction to effect snap operation of said switch into one position, comprising a thermal element mounted in said casing having an extensible power member engageable with said snap lever, a fulcrum for said snap lever extending within said casing and adjustable from the outside of said casing to vary the position of said fulcrum with respect to said power member and thereby vary the temperature range of operation of said switch, and yieldable means contained within the adjusting means for said fulcrum, biasing said fulcrum into an extended fulcruming position and yielding upon over-travel of said power member to prevent damage to said snap blade upon over-temperature conditions.

4. In a thermostatic snap acting switch, a switch casing, a snap blade within said casing, a support for one end of said snap blade rockingly mounted within said casing and respectively pivotable about parallel axes, a snap lever having operative connection with said support in spaced relation with respect to said snap blade for rockably moving said support and snap blade, an overcenter snap spring rockingly mounted in said casing in advance of said snap blade and having rocking engagement with the free end of said snap blade, a thermal element having an extensible power member engageable with said snap lever, a fulcrum for said snap lever extending parallel with said power member and having engagement with said snap lever intermediate the ends thereof on the opposite side of said lever from said power member, and means operable from the outside of said switch casing for moving said fulcrum toward or from said power member and thereby varying the temperature range of operation of said snap blade.

5. In a thermostatic snap acting switch, a casing, a snap blade within said casing, a support therefor rockingly mounted within said casing, a snap lever connected at one of its ends with said support in parallel spaced relation with respect to the axis of rocking movement thereof, for rockably moving said support and snap blade,

an overcenter snap spring rockingly mounted in said casing in advanceof said snap blade and having rocking engagement with said snap blade, a thermal element mounted in said casing and having an extensible power member extending generally parallel to said snap blade and extensible upon predetermined increases in temperature, an engaging connection between said power mem her and said snap lever at the end thereof opposite said support, a fulcrum for said snap lever extending generally parallel to said power member and having engagement with said snap lever intermediate the ends thereof on the opposite side of said lever from said power member, means selectively operable from the outside of said casing for moving said fulcrum toward or from said power member to vary the temperature range of operation of said snap blade, and a spring biasing said fulcrum in extended relation with respect to said casing and normally acting as a solid member and yielding upon over-travel of said power member upon over-temperature conditions.

6. In a thermostatic snap acting switch particularly adapted for air conditioners and the like, a casing, a snap blade within said casing, a support therefor rockingly mounted within said casing, a snap lever connected at one end with said support in spaced relation with respect to the axis of rocking movement thereof for rockably moving said support and snap blade, a yieldable switch arm spaced from said snap blade and having a contact thereon biased by said switch arm into one position, an operator connecting said snap blade with said switch arm for operating said switch arm to move said contact into another position, an overcenter snap spring rockingly mounted in said casing in advance of said snap blade and having rocking engagement with the end of said snap blade, a thermal element having an extensible power member extending generally parallel to said snap blade, an engaging connection between said power member and the opposite end of said snap lever from said support, a fulcrum extending within said casing generally parallel to said power member and having engagement with said snap lever intermediate its ends, and means operable from the outside of said casing for adjusting the position of said fulcrum with respect to said power member and the temperature range of operation of said switch arm, said means including an over-travel spring biasing said fulcrum into a fulcruming position and normally acting as a solid member and accommodating retractible movement of said fulcrum upon over-travel of said power member effected by over-temperature conditions.

7. In a thermostatic snap acting switch, a switch casing, a snap blade within said casing, a support for said snap blade, means mounting said support for rocking movement comprising a fixed fulcrum, an arm extending from said support generally perpendicular to said snap blade, a snap lever having rocking engagement with said arm at one end in outwardly spaced relation with respect to said fixed fulcrum, a fulcrum for said snap lever disposed within said casing and having engagement with said snap lever intermediate the ends thereof, a thermal element mounted in said casing and having a power member extending generally parallel to said fulcrum for said snap lever and extensible upon predetermined increases in temperature and engaging the opposite side of said lever from said fulcrum for said lever, an overcenter snap spring rockingly mounted in said casing in advance of said snap blade and having rocking engagement with the free end of said snap blade, and a return spring secured to said snap blade and support and biasing said snap blade and support to cause said snap lever to follow said power member upon retractible movement thereof, upon reductions in temperature, the center of rotation of said snap blade support relative to said fixed fulcrum and the points of engagement of said snap lever with said arm on said snap blade support and of said fulcrum with said snap lever and of said power member with said snap lever all being substantially in a single plane and the direction of all forces acting on said snap lever being substantially perpendicular to said plane, thereby reducing sliding friction upon operation of said lever.

8. In a thermostatic snap acting switch, a switch casing, a snap blade within said casing, a support for said snap blade, means mounting said support for rocking movement comprising a fixed fulcrum, an arm extending from said support generally perpendicular to said snap blade, a snap lever having rocking engagement with said arm at one end in outwardly spaced relation with respect to said fixed fulcrum, a fulcrum for said snap lever disposed within said casing and having engagement with said snap lever intermediate the ends thereof, a thermal element mounted in said casing and having a power member extending generally parallel to said fulcrum for said snap lever and extensible upon predetermined increases in temperature and engaging the opposite side of said lever from said fulcrum for said lever, an overcenter snap spring rockingly mounted in said casing in advance of said snap blade and having rocking engagement with the free end of said snap blade, and a return spring secured to said snap blade and support and biasing said snap blade and support to cause said snap lever to follow said power member upon retractible movement thereof, upon reductions in temperature, the center of rotation of said snap blade support relative to said fixed fulcrum and the points of engagement of said snap lever with said arm on said snap blade support and of said fulcrum with said snap lever and of said power member with said snap lever all being substantially in a single plane and the direction of all forces acting on said snap lever being substantially perpendicular to said plane when the temperature adjustment for said switch is in mid-position, thereby reducing sliding friction upon operation of said lever, said fulcrum for said snap lever comprising a plunger and a hollow screw threaded within said casing and carrying said plunger and adjustably movable to vary the position of the end of said plunger with respect to said power member and the temperature range of operation of said switch.

9. In a thermostatic snap acting switch, a switch casing, a snap blade within said casing, a support for said snap blade, means mounting said support for rocking movernent comprising a fixed fulcrum, an arm extending from said support generally perpendicular to said snap blade, a snap lever having rocking engagement with said arm at one end in outwardly spaced relation with respect to said fixed fulcrum, a fulcrum for said snap lever disposed within said casing and having engagement with said snap lever intermediate the ends thereof, a thermal element mounted in said casing and having a power member extending generally parallel to said fulcrum for said snap lever and extensible upon predetermined increases in temperature and engaging the opposite side of said lever from said fulcrum for said lever, an overcenter snap spring rockingly mounted in said casing in advance of said snap blade and having rocking engagement with the free end of said snap blade, a return spring secured to said snap blade and support and biasing said snap blade and support to cause said snap lever to follow said power member upon retractible movement thereof, upon reductions in temperature, said fulcrum for said snap lever comprising a plunger and a hollow screw threaded within said casing and carrying said plunger and adjustably movable to vary the position of the end of said plunger with respect to said power member and the temperature range of operation of said switch, and an over-travel spring contained within said hollow screw and biasing said plunger in extended relation with respect to said screw and accommodating retractible movement of said plunger upon over-travel of said power member, the center of rotation of said snap blade support relative to said fixed fulcrum and the points of engagement of said snap lever with said arm on said snap blade support and of said plunger with said snap lever and of said power member with said snap lever all being substantially in a single plane and the direction of all forces acting on said snap lever being substantially perpendicular to said plane when the temperature adjustment for said switch is in mid-position, thereby reducing sliding friction upon operation of said lever.

10. In a thermostatic snap acting switch particularly adapted for air conditioners and the like, a casing, a snap blade within said casing, a support therefor rockingly mounted withinsaid casing, a snap lever connected at one end with said support in spaced relation with respect to the axis of rocking movement thereof for rockingly moving said support and snap blade, a fulcrum within said casing having engagement with said snap lever intermediate its ends, thermostatic means engaging the opposite end of said snap lever from said support for actuating said lever, an overcenter snap spring rockingly mounted in said casing in advance of said snap blade and having rocking engagement with the end of said snap blade, a yieldable switch arm spaced from said snap blade and having a contact thereon biased by said switch arm into one position, said snap blade and switch arm extending in general parallel relation with respect to each other, and an operator connecting said snap blade with said switch arm for operating said switch arm to move said contact into another position.

11. In a thermostatic snap acting switch particularly adapted for air conditioners and the like, a casing, a snap blade within said casing, a support therefor rockingly mounted within said casing, a snap lever connected at one end with said support in spaced relation with respect to the axis of rocking movement thereof for rockably moving said support and snap blade, a yieldable switch arm spaced from said snap blade and having a contact thereon biased by said switch arm into one position, an operator connecting said snap blade with said switch arm for operating said switch arm to move said contact into another position, an overcenter snap spring rockingly mounted in said casing in advance of said snap blade and having rocking engagement with the end of said snap blade, a

thermal element having an extensible power member extending generally parallel to said snap blade, an engaging connection between said power member and the opposite end of said snap lever from said support, a fulcrum extending within said casing generally parallel to said power member and having engagement with said snap lever intermediate its ends, and means operable from the outside of said casing for adjusting the position of said-fulcrum with respect to said power member and the temperature range of operation of said switch arm.

References Cited in the file of this patent UNITED STATES PATENTS 2,611,845 Miller Sept. 23, 1952 2,658,121 Gray et al Nov. 3, 1953 2,691,084 Miller Oct. 5, 1954 2,738,397 Slonneger Mar. 13, 1956

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