US3036173A

US3036173A - Condition responsive electrical switch mechanism

Info

Publication number: US3036173A
Application number: US776087A
Authority: US
Inventors: Laurence M Perkins
Original assignee: Allen Bradley Co LLC
Current assignee: Allen Bradley Co LLC
Priority date: 1958-11-24
Filing date: 1958-11-24
Publication date: 1962-05-22
Anticipated expiration: 1979-05-22

Description

y 1962 L. M. PERKINS 3,036,173

SIVE ELECTRICAL SWITCH MECHANISM CONDITION RESPON Filed Nov. 24. 1958 2 Sheets-Sheet 1 INVENTOR LAURENCE M. PERKINS BY M, for, [M

ATTORNEYS y 1962 L. M. PERKINS 3,036,173

CONDITION RESPONSIVE ELECTRICAL SWITCH MECHANISM Fil'ed Nov. 24, 1958 2 Sheets-Sheet 2 L o v I I v 27 A -D INVENTOR D a- C LAURENCE M. PERKINS BY awe n64, f x, Ja'az, A E

DEFLECTION (MOVEMENT OF SWITCH PARTS) ATTORNEYS Uite States 3,036,173 CONDITION RESPONSIVE ELECTRICAL SWITCH MECHANISM Laurence M. Perkins, Elm Grove, Wis., assignor to Allen- Bradley Company, Milwaukee, Wis., a corporation of Wisconsin Filed Nov. 24, 1958, Ser. No. 776,087 4 Claims. (Cl. 200-83) The present invention relates to electrical switches and particularly relates to switches having operating snap action contacts arranged for alternative movement to circuit open and closed positions responsive to relatively slowly advancing actuation initiated by condition responsive means, such as a spring balanced bellows responsive to fluid pressure variations.

It is an object of the present invention to provide a compensating means for minimizing the differential in force exerted over and above that necessary to actuate a switch toggle mechanism by means of an actuator in operating association with condition responsive means, whereby optimum operation of said switch will be responsive primarily to the minima and maxina range of the condition variation afiecting said condition responsive means.

It is another object of the present invention to provide a compensating means for an electrical switch having a switch actuator mechanism including a positive spring rate biasing means, wherein said compensating means acts to minimize the switch operating differential by means of utilizing a resilient biasing means having an inherent negative spring rate and being operatively combined with the actuator mechanism to cancel out at least a portion of said positive spring rate over a selected spring deflection ran e.

It is another object of the present invention to balance the positive spring rate of a spring balanced, bellows operated, condition responsive electrical switch by means of utilizing the negative spring rate portion of a coned disk spring operating in conjunction therewith to thereby minimize the operating differential of the switch. These and other objects of this invention will appear in the description to follow with reference to the accompanying drawings which form a part hereof, in which there is set forth by way of illustration, but not of limitation, a specific form in which this invention may be embodied.

In the drawings:

FIG. 1 is an elevational side view, in vertical section, of a pressure responsive actuator upon which a snap action switch is mounted, and including differential compensating means in accordance with the present invention;

FIG. 2 is a cross sectional view taken along lines 22 of FIG. land with a portion broken away to more clearly illustrate the compensating means in the form of a coned disk spring washer;

FIG. 3 is a cross sectional view of the preferred coned disk spring washer;

FIG. 4 is a front elevational view of the actuator of FIG. 1;

FIG. 5 is an enlarged fragmentary view of a portion of FIG. 1 illustrating, in particular, the relationship of the coned disk member and its cooperating associated members;

FIG. 6 is a fragmentary sectional view taken along lines 6-6 of FIG. 5;

FIG. 7 is a graph of a typical load-deflection characteristic curve of a coned disk spring washer; and

FIG. 8 is a graph of the load-deflection curve representative of the operation of a pressure actuated switch assembly, such as that illustrated in the embodiment of FIGS. 1-3.

iiice Referring more particularly to the accompanying drawings, a preferred embodiment of the invention is shown in a form suitable for use as a pressure control apparatus for refrigerators, pumps, compressors, or other devices requiring condition responsive controls. The illustrated pressure control device is incorporated in a U-shaped metal frame I supporting from its base portion a threaded inlet fitting '2. leading to and entering an expansible metal bellows 3. The bellows 3 is housed within an inverted, bell-shaped, spring cup or cage 4, which, in turn, is attached at its base to a tapered cylindrical fitting 5. The bell-shaped cup 4 and the fitting 5 are arranged to move in unison with the expansion and contraction of the bellows 3. An actuating rod 6 threadingly engages the fitting 5 and extends upwardly therefrom, as viewed in FIG. 1. Thus, the rod 6 may be adjusted for relative spacing from the bellows 3 to limit downward motion thereof. Circumjacently seated relative to the bellows 3 and the spring cup 4 is a counterbalancing compression, main spring 7 which acts to urge the spring cup 4 in a direction in opposition to pressure within the bellows 3.

Since the pressure at which the switch will change from its normal position is governed by the force exerted by the main spring 7, a range adjustment is also provided for increasing or decreasing the compression of the main spring. The range adjustment is a means of altering the setting of the upper operating pressure or temperature to which the control apparatus is responsive, and comprises a slotted adjustment head 8 rotatably mounted on the exposed face of an L-shaped panel 9. The extending L-portion of the panel 9 is adapted for attachment to the frame 1 and to provide a support for the snap action switch I0. The slotted adjustment head 8 engages a stamped pinion 11 riveted to a shaft extending therefrom directly beneath the extended portion of the panel 9. Pinion I1 meshes with a compression regulating gear 12 to rotate a threaded shaft 13 encircling the actuator rod 6 and the fitting 5. Rotation of the shaft '13 moves a threadingly engageable, plate-like, spring retainer 14 which is held from rotation by a pair of indicator ears 15 in slidable engagement with oppositely disposed edges of the panel 9. The axial displacement of the spring retainer 14 may be measured by a scale etched or otherwise marked on the margin of the face of the panel 9'adjacent one of the indicator ears 15, as shown in FIG. 4. Thus, variations in pressure exerted upon the bellows from fluid entering the inlet 2 will cause an upward travel of the actuator rod 6, pressure at which movement occurs being dependent upon the loading of the main spring 7 which may be adjusted by the setting of the spring retainer 14.

Many installations require both a lower and an upper pressure operational range setting, as in the case of household well Water pumps, which are very often set for an upper water pressure of, for instance, 50 p.s.i. and a lower pressure of, for instance 25 p.s.i. Such maxirna-minima setting determines the frequency of operation of the pump. In the present actuator mechanism this adjustment is made by means of the slotted head 20 rotatably mounted on the face of the panel 9 directly below the range adjustment head 8, as viewed in FIGS. 1 and 4. In the present construction, the slotted head 20 is shaft connected directly to a pinion 21 by riveting or other operation. The stamped pinion 21 meshes with a gear 22 conveniently mounted coaxially relative to the slotted head 8 and its pinion '11. The gear 22 is fastened to a cam member 23 traveling in unison therewith. A cantilever spring 24, as shown in FIGS. 5 and 6, is riveted at its stationary end by means of rivets 24' to the top frame portion extending from the panel 9 and is also riveted at 25' to a plate 25 having an upwardly extending car 26. Thus, rotation of the slotted head 20 will cause the cam 23 to rotate on its axis by means of the pinion 21 meshing with the gear 22 which, in turn, will cause the cantilever spring 24 to be stressed upwardly or to be released in a downward direction as viewed in FIGS. 1

and 4.

A supporting frame 30 (see FIG. 2) is riveted at each corner thereof directly to the top plate portion of the panel 9 and provides a means of supporting a Belleville or coned disk spring washer 31 in the relieved portion 32 centrally located thereof. The actuating rod 6 is received by a radially flanged conical collar 33 extending through the central opening of the spring washer 31 and retained therein by means of the radially extending flange portion. The lower surface of the collar 33 is arranged for seating engagement with opposed, raised nibs 27 of plate 25. The actuator rod 6 terminates at its upper end in a conical tipped insulated actuator 34. The actuator 34 may protrude, as shown, through an opening 35 in the insulating housing 36 of the snap switch mechanism to mechanically engage an inner spring arm 37 for alternative opening and closing of the respective parts of the switch mechanism 10 as will hereinafter be described. It will be understood, however, that switch mechanisms other than the specific construction shown and described herein may be substituted without departing from the scope of the present invention.

The inner spring arm 37 of the disclosed mechanism 10 may be formed integrally of a stamped or punched member formed of fiat spring material having a punched out area forming a contact carrier arm 38, said arms emanating from a common base 39. For aid in adjustment the elements 37-39 may also be formed separately and joined with one another, as desired (not shown). Thus, the contactor element may be fastened directly to the housing 36, sandwiched between the housing and a relatively stiff L-shaped terminal member it). The terminal member 40 will thereby be in electrical contact with the contactor element and include a tapped opening for receiving a conducting terminal screw 28'. The member 40 is further provided with an arm 41 overlying the spring arm 37 so as to serve as a stop for the outward movement of said spring arm.

The stamping comprising the contact element is substantially U-shaped with spaced parallel legs terminating in the common base 39, thus defining the spring arm 37 in the form of a blade disposed within the contact arm 38, having a outwardfree end spacedin appreciable distance from the inner edge of the base of the U-shaped contact arm 38. The opposed, spaced end and edge are provided with centrally aligned, oppositely disposed tips or other means (not shown) for engaging respective

cupshaped end caps

42 and 43. interposed between the

end caps

42 and 43 is an expansion spring 4 4 which causes the arms 37 and 38 to spread out of longitudinal alignment to the extent of producing a substantial flexure in the spring arm 37 in a direction away from the main longitudinal axis of the contactor element. It is significant to note that the arms 37 and 38 are so constructed as to be capable of crossing the longitudinal planes of one another in passing through alternate operating positions. To limit the normal deflection of the arm37 and at the same time insure against derangement of the expansion spring 44, there is provided a stop 45 against which'the arm 37 comes to rest. The arm 38 carries at its free, end oppositely disposed contacts 46 and 47 which are adapted to engage and disengage stationary contacts 48 and 49, the latter constituting control positions between which the contact arm 38 is alternatively. actuated in the functioning of the switch mechanism. An electrical circuit .(not shown) is completed through the terminal screw 5th 4 prises two components which are the differential caused by the differential force of the switch unit and the differential travel of the switch.

The differential due to the differential force of the switch has been found to equal the quotient of the differential force divided by the bellows area, whereas the differential due to differential travel of the switch is equal to the quotient of the differential travel multiplied by the effective spring rate, divided by the bellows area. The sum ofthe numerical values of these two factors (without taking account of Whether they are plus or minus) gives the total differential. Thus, if the net spring rate is negative, the differential is increased by this factor just as much as thought the net spring rate were of the same magnitude, but positive.

As an example, a selected switch assembly of the nature illustrated and described included spring rates approximately as follows:

Wan? p.s.i.

The net difierential will equal the summation of the firstcomponent and the second component, without reor 2.35+1.07-.=3.42 p.s.i.

calculation of the net'differential of gard to the sign,

In a comparison,

a switch which does not include a negative spring rate means, such as the coned disk washer 31, will establish that the first component caused by the differential force of the switch will equal whereas the second component created by the differential travel of the switch equal amount to approximately the, differential of the snap action switch, itself;

Referring now to the coned diskewasher illustrated in FIG. 3, and taken in connection with the curve of FIG,

6, it will be apparent that the spring washer 3 1 is of a thickness t, and has its central opening 5 1' elevated'above the horizontal by the dimension h. It will be apparent from the curve of FIG. 7 that springs of the. nature of Referring more particularly to the improved actuating mechanism, it will be apparent that it is desirable to minimize theoperating differential .of the apparatus in its various assembled components. This differential com that disclosed in FIG. 3 provide aload-deflection curve which defines, in part, a positive spring rate, and after reaching a maximum load, takes on the characteristics ofa negative spring rate. For instance, a Belleville coned a disk washer, as illustrated in'FIG. 3 and having a ratio of h/tequal to 2.8 will provide the curve of FIG. 6. It

is preferred to use only the deflection portion set forth between the limits A and D, which represent the negative spring rate, and further reflect a deflection range substantially equivalent to the switch travel. Obviously, it will be apparent that a certain portion of the usable curve preferably extends at eitherend beyond the portion AD to represent overtr-avel of the switch contacts. A family of such curves may be established for coned disk washers of varying ratios of h/t as set forth in Wahl, Mechanical Springs, published by Penton, Cleveland, 1944, first edition, at page 239. It is desired, however, in the preferred embodiment, to utilize a spring having a ratio of approximately 2.8 in order to utilize the curve having the greatest negative spring rate portion and which does not pass through a zero load ordinate.

With reference to FIG. 7, it will be apparent that a simple load-deflection curve of the operation of the snap action switch with, and without, the coned disk spring washer may be illustrated in the form of a parallelogram in which the area thereof represents the amount of Wonk performed by the movement of switch parts. The ideal, which is approached by the construction of the present application, is found in the rectangle described by the points ABCD in bold lines on the graph, whereas, the work diagram ABC'D represents the movement of the various switch parts without the benefit of the coned disk spring washer, such as utilized in the present invention. Thus, although the movement of the switch parts remains substantially identical in either case and the force for moving the parts of the snap action switch 10 remains the same, the operating differential is minimized by the amount represented by the negative spring rate of the washer 31 thereby permitting subtraction of the amount of force needed for switch operation by the amount represented by the line ED.

It will be apparent that the in its preferred embodiment, a condition responsive switch mechanism having minimum diflerential of operation provided by balancing the negative spring rate of a coned disk spring against the positive spring rate of other operating spring biased components of said switch mechanism.

It will also be apparent, though not specifically illustrated in the drawings, that the coned disk spring 31 may be inverted from the position shown in FIGS. 1 and 5 and removed in the said inverted position to the opposite side of the collar 33 between the upper surface of the collar and the lower flanged portion on the actuator 34, and be equally eflfective in its operation without departing from the scope of the present invention.

I claim:

1. In a switch actuating mechanism having a contact operating reaction spring with a positive spring rate throughout its operating range, an actuator bearing against said reaction spring to deflect the same, a force exerting means characterized in its movement by a positive loaddeflection ratio and being disposed to work against said actuator to move the actuator against the reaction spring; the combination therewith of a difierential balancing spring having a negative spring rate throughout at least a portion of its operating range, support means for said balancing spring, said balancing spring arranged for coaction with said actuator, and means restricting the deflection of said balancing spring relative to said support means and said actuator to a deflection range incorporating only the inherent negative spring rate range of said balancing spring, the negative spring rate characteristics of said balancing spring being selected to substantially balance the summation of respective positive spring rate of the said reaction spring and the positive load-deflection ratio of said force exerting means, whereby the work required to move the reaction spring through a given length of travel will be confined to a minimum value.

2. In a switch actuating mechanism having a contact operating reaction spring with a positive spring rate throughout its operating range, an actuator bearing present invention provides,

against said reaction spring to deflect the same, a 'force exerting means characterized in its movement by a positive load-deflection ratio and being disposed to work against said actuator to move the actuator against the range of the disc reaction spring;

the combination therewith of a differential balancing spring comprising a coned disc spring having a negative spring rate throughout at least a portion of its operating range, support means for said balancing spring, said coned disc spring being disposed for coaction with said actuator, and means restricting the deflection of said balancing spring relative to said support means and the said actuator to a deflection range incorporating only the inherent negative spring rate range of said balancing spring, the negative spring rate characteristics of said balancing spring being selected to substantially balance the summation of respective positive spring rate of the said reaction spring and the positive load-deflection ratio of said force exerting means, whereby the work required to move the reaction spring through a given length of travel will be confined to a minimum value.

3. In a switch actuating mechanism having a contact operating reaction spring with a positive spring rate throughout its operating range, an actuator bearing against said reaction spring to deflect the same, a force exerting means comprising a fluid pressure actuated means having a positive spring rate and working against said actuator to move the actuator against the reaction spring, a main spring having a positive spring rate throughout its operating range and disposed to work against the action of said pressure actuated means; the combination therewith of a differential balancing spring comprising a coned disc spring having a negative spring rate throughout at least a portion of its operating range, a support for said balancing spring, a stop member on said actuator bearing against the balancing spring at the side opposite said support, and means restricting the travel of said actuator relative the support to a range limiting the deflection of said balancing spring to its inherent negative spring rate range, the negative spring rate characteristics of said balancing spring being selected to substantially balance the summation of respective positive spring rates of the said reaction spring, the bellows and the main spring, whereby the work required to move the reaction spring through a given length of travel will be con-fined to a minimum value.

4. In a pressure responsive switch actuating mechanism including a contact operating reaction spring having a positive spring rate throughout its operating range, a pressure actuated bellows responsive to fluid pressure and having a positive spring rate throughout its operating range, a threaded actuator rod having a radially extending stop portion intermediate its ends and being threadingly secured at one end to the free end of said bellows and movable therewith responsive to pressure exerted thereon, said actuator rod being adjustable in axially opposed directions relative to said bellows and adapted to work against said reaction spring; a main spring having a positive spring rate and disposed to work against the action of said bellows when pressure is exerted thereon; the combination therewith of a cone-shaped disc spring having a negative spring rate throughout at least a portion of its operating range, a seating member defining a concave recessed spring seating portion, said disc spring being seated in the recess of said seating member, the radially extending stop portion of said actuator member being arranged for abutting engagement with said disc spring at the side thereof opposite said recessed seating member, the recessed seating member and the adjustable actuator rod defining a working deflection spring to limit the spring to its negative spring rate operating range, said disc spring being thereby disposed to permit the negative spring rate component thereof to counteract the positive spring rate components of the bellows, the reaction spring and the main spring, thereby reducing the work component required a given length of travel'to a minimum value.

References Cited in the. file of this patent UNITED STATES PATENTS Spencer May 12, 1936 Fawkes Jan. 12, 1943 M r in; et'a'l- -,+-;---e---- p Nutt eta-1. July 27, 1943 LeWPQl'd Nov. 26, 1946 Stadler- Aug. 14, 1951 McCloy May 6, 1952 Ralston j Mar. 22, 1955 Bexner et a1 Jan. 3, 1956 Davis Feb. 25, 195.8