US2776352A - Electric snap-action switch devices - Google Patents

Description

Jan. 1, 1957 N. R. DAVIS ELECTRIC SNAP-ACTION SWITCH osvxczs .2 Sheets-Shee 1 Filed Feb. 2, 1954 INVENTOR ATTORNEYS ELECTRIC SNAP-ACTIGN SWITCH DEVICES Neville Ryland Davis, Eis'hops'Stortford, England, as-

signor to Sunvic "Controls Limited, London, England, a British company Application February 2, 1954, Serial No. 407,723

Claims priority, application Great lirita'in February 19,1955

.6 (Ilaims. (Cl. 200-422) This invention relates to electricsnap-action switch devi'ces of the :kind comprising .a flexible contact-carrying element :and .a compression element, the two elements, which may be formed integrally with one another or maybe'separate elements, forming an overcentre assembly in which the contact-carryingelement maintains the other element in compression. In-a common arrangement of such switch device the contact-carrying element is a spring blade fixed at one end so asto form-a-centilever, the free end .of which carries the moving contact, :and *the contact is moved by the application of pressure to the blade at a point adjacent the fixing thereof. Switches of the character above indicated are, for example, described and claimed in the specifications of British Letters Patent Nos. 419,917 and 585,972.

Snap-action switch devices ofthe kind referred to have the advantage for certain applications of requiring only very small movement of an actuating member for-causing flexure of the spring blade. Such switch devices are also frequently employed in thermally operated'devices, for example thermostats and energy regulators such as described in applicants British Letters Patent No. 517,538, "U. S. Patent No. 2,646,479, granted July '21, 1953, and U. S. Patent No. 2,726,300, granted December 6, 1955, in' which applications it is convenient to employ a'thermal device of the bimetal type for operation of the switch. Bimeta'l devices are, however, more adapted to the provision of a comparatively large operating movement'and small operating force rather than the small operating movement and relatively large force normally employed for the actuation of snap-action switches of the kind indicated.

The present invention has for its objects 'to provide a snap-action switch device of'the kind referred to, adapted for operation by comparatively small forces, whereby arrangements according to the invention are well adapted for use in thermostats and energy regulators incorporating thermal elements of bimetal type. his to be understood, however, that the invention is not limited to arrangements employing bimetal operation of the switch but has equal application in snap-action switches.

According to the present invention, in a switch of the kind referred to, the end of the contact-carrying element remote from the contact carried thereby is mounted and connected with an operating member for rotational movement of said member and said element in unison with one another about an axis perpendicular or substantially perpendicular to the plane of contact movement. Conveniently, the operating member may be of strip orvother elongated form extendingbetween the pivo-ted'end thereof .into engagement with an abutment so that small forces applied between said abutment and the free end ofsaid operating member will be magnified at said end of the contact-carrying element to cause flexure of the contactcarrying member and operation of the switch. The switch may, according to its application, be-operated by displacement of said abutment, that is to say, said abutment is movable for causing operation of the switch in'response 'to external movements. Altern'atively,the operating member may be arranged for deflection or deformation thereof in response to predetermined operating conditions whereby to cause operation of the switch, for example'said member may be a bimetal strip, the operating forcefor the switch being thus developed between the ends of the operating member. Themovement'of the free end of the operating member or change in shape ofsaid member, such as where the latter comprises a bimetal strip, will be comparatively'large as compared with the displacement of the moving contact so that the switch device may be made sensitive to displacementratherthan to operating pressure.

Reference will now'be made by way of example to "the accompanying drawings, in which:

Fig. 1 is'a perspective view showing a room thermostat accordingto one embodiment of the invention;

Fig. -2 is a fragmentary cross-sectional elevation on the line IIII of Fig. 1;

Fig. :3 is aperspective view showing an .energy regulator according to another embodiment of the invention; and

Figs. 4 and 5 are elevations in section of a thermostat 'according'to a further embodiment of the invention; Figs. 4 and 5 being taken on longitudinal planes perpendicular to one another.

"Referring first to Fig. l, the thermostat therein illustrated is of the bimetal-operated kind in which the temperature responsive element comprises a bimetal strip shown at 1,'whilst the moving contact carrying element comprises a thin tlexiuie blade or contact arm 2 of spring metal having a tongue 3 formed therein as described in the complete specification of British Letters Patent No.

585,972, aforesaid, to which attention is hereby directed. The contact arm carries a moving contact 4 co-operating with a fixed contact 5, which latter is carriedvon a double cranked metal support 6 secured, such as by means of a screw 7, to a base plate 8 of insulating material. The tongue 3.is received at its free end in a notch at 9 in an upstanding abutment 16 mounted on the baseplateb. In the example illustrated the abutment 19 comprises an upturned portion of a metal member 11 fixed to the base 8, such as by a screw not visible in the drawing. The end of the contact arm 2 remote from the contact 4 is secured, such as by rivets 12, to a crankedendportion 13 of the bimetal strip 1. It will be observed that due to the crankedformation of the bimetal strip,namely the vertical portion 14, the strip 1 is of such shape as to extend over the contact arm and switchparts and in position substantially parallel with the contact arm. Alternatively tothe rivets 12 the contact arm 2 may be otherwise secured to the portion 13 of the bimetal strip by otherrneans, forexample by spot-welding.

The member 11 is provided with .a threaded bore in which is received a screw -15 which provides a fixed but adjustable abutment. This screw is provided with a circumferential groove at 16 and the end of the eontactarm 2 is perforated whereby on assembly to be positioned on said screw with saidarm in thegrooveasismore clearly shown in the sectional cross elevation of Fig. 2. The portion 13 of the bimetal strip is'provided with a perforation 17 having appreciable clearance with respect -to the screw 15. The contact -arm 2 and bimetal strip 1 are by this means locked against lateral and longitudinal movement by engagement of the perforation in the arm 2 in said groove, whilst at the same time freedom of rotational movement of the arm and strip are permitted about a transverse axis of said strip. It may be noted that 'due to the bowed formation of the tongue 3, .the latter exerts a pull on the arm Zmoving the latter to the 3 left hand in Fig. l and thereby holding the perforated end of contact arm 2 in engagement with the right hand part of the groove 16 so as to provide a pivotal point adjacent said part.

It will be understood that the thinness of the arm 2 provides for location of the arm in the groove 16 in a manner approaching that of a knife-edge pivot.

The base 8 carries a further cranked support 18 having a threaded bore in which is threaded an adjusting screw 19 which provides an adjusting abutment, the lower end of this screw abutting against the free end of the bimetal strip 1.

In the operation of the device shown in Fig. 1, upward movement of the contact arm 2 from the base member will bring the moving contact 4 into engagement with the fixed contact 5 whilst downward movement of the contact arm 2 toward the base member will open the contacts. Change of room temperature will cause curvature of the bimetal strip 1, in the example illustrated, so that increase of temperature will cause said strip to assume a curvature which is convex downwardly, that is to say, convex on the underside of the strip. The position of the screw 15 is such that at all times the right hand part of the contact arm tends to move toward a stable position in the clockwise direction in Fig. 1 so that said contact arm continually biases the contact strip 1 in said clockwise direction to hold the free end of said strip against the lower end of the adjusting screw 19 On change of temperature, the curvature of the bimetal strip as above described will impart a rotational movement to the connected ends of the bimetal strip and the contact arm about a major transverse axis of the arm adjacent the screw 15 as above indicated, whereby to cause the contact arm to move with respect to the notch 9 so as to actuate the moving contact 4 to the open position with snap action. Conversely, fall of temperature will allow the contacts to reclose with snap action. The temperature setting of the thermostat is determined by the adjusting screw or abutment 19.

Fig. 3 illustrates an energy regulator embodying the invention, the switch assembly and bimetal strips employed in the energy regulator being similar to that described with reference to Figs. 1 and 2. The energy regulator thus comprises an illustrated base plate 8 on which a support 6 is secured by a screw 7, this support carrying a fixed contact 5. The co-operating contact 4 is mounted on a spring contact arm 2 having a tongue 3, as described with reference to Fig. 1, located in a groove 9 in an upstanding part 10 of a metal member 11 secured to the base plate. The arm 2 is secured to a bimetal strip 1 and supported therewith by means of a screw 15 from the metal member 11 all in the manner described with reference to Figs. 1 and 2. In the energy regulator of Fig. 3 the adjusting screw or abutment 19 is carried in a tapped perforation in a second bimetal strip which is located vertically above the strip 1 and extends parallel or substantially parallel with the latter. The end of the strip 30 remote from the screw 19 is secured such as by rivets 31 and 32 to the base 33 of a U-shaped supporting member 34 one limb of which is shown only fragmentarily. The ends of the limbs of the U-shaped member 34 are turned outwardly as can be seen at 35 in the case of one of said limbs and this out-turned end is received in a perforation at 36 in a trunnion 37 upstanding from the base member 8. Similarly, the out-turned end of the other limb of the U-shaped member, said end being in alignment with the end 35, is received in a perforation in a second upstanding trunnion 38, only fragmentarily shown in the drawing. Conveniently, the trunnions 37 and 33 are formed integrally by a stamping and pressing operation with the member 11. It will be seen that the supporting member 33, 34 is arranged substantially in the same general plane as the bimetal strip 30 with the latter disposed between the two limbs of said member. The arrangement provides for rotation of the bimetal strip 30 about a transverse axis thereof which may be located substantially at the centre of length of said strip or at any desired intermediate point of the latter.

The U-shaped member is provided with a tail portion 39 extending in line with the bimetal strip 30 to engage with the peripheral surface of a cam 40 which is carried on an adjusting shaft 41 journalled in a block 42 secured to the base 8 for movement of said shaft on an axis substantially in line with the major axis of the bimetal strip 1.

The bimetal strip 1 carries a heating element or winding 43 which is connected in circuit with the contacts 4 and 5 so as to be energised either in series or in parallel with the load device. Alternatively, the bimetal strip 1 may itself be arranged to carry the load current. In all these arrangements the device provides energy regulation in the manner of the device fully described in the complete specification of British Letters Patent No. 517,538 and U. S. No. 2,646,479. The bimetal strip 30 is arranged to deflect in the same direction as the strip 1 for given changes of temperature whereby to provide compensation for variations of ambient temperature. It will be understood that the device may be modified by providing the heating element or winding on the strip 30 or arranging for the latter to carry the load current, whilst the strip 1 will then provide the compensation for variations of ambient temperature.

The output of the device is adjustable by the shaft 41 and cam or adjusting member 40, the latter determining the position of the tail portion 39 of the U-shaped member and thereby determining the vertical position of the free end of the strip 30. It will be seen that the length of the strip 30 and the extension or tail portion 39 of the U-shaped member can be selected to provide any desired relation between the displacement of the tail portion 39, that is to say the change of radius of the cam 40 for a given angular movement of the cam 41, on the one hand, and the free end of the bimetal strip on the other hand. For example, a ratio of 3:1 or 4:1 may be employed. In such cases, the maximum lift of the cam, namely from the off position (minimum radius), to the illustrated full on position (maximum radius) may be for example A to cause a movement of the order of of the screw 19, whereby to provide corresponding accuracy of control and consistency of production and operation with commercial production methods.

Referring now to Figs. 4 and 5, the thermostat therein shown comprises a main frame member in which is riveted a pillar 51 providing a fixed abutment corresponding with the screw 15 of Figs. 1, 2, and 3, this pillar having a peripheral groove at 52 serving to locate the pivoted end of a spring metal contact arm 53 corresponding exactly with the contact arm 2 of the previous figures. Thus, this contact arm is provided with a curved tongue 54, one end of which is received in a groove at 55 in an upstanding part 56 pressed out of the frame member 50 and forming an abutment, the latter being formed with an opening at 57 to accommodate the tongue 54 as can be most clearly seen in Fig. 5. The contact arm 53 carries a moving contact 58 riveted in a perforation in the free end of said arm and co-operating with a fixed con- H tact 59 which is riveted in a perforation in the end of a supporting member 60 of metal strip. The strip 60 is secured to the frame member 50 by means of rivets 61 and insulating bushes 62 and 63.

The temperature responsive element comprises a bimetal strip 64, which, similarly to the bimetal strips 1 and 30 of Figs. 1, 2, and 3, is secured, such as by rivets 65, to the contact arm 53 and is provided with a clearance perforation 66 accommodating the head of the pillar 51. The relative positions of the arm 53 and strip 64 about the pivoting axis thereof is determined by means of an grasses adjusting member or screw 67 received in a tapped perforation in the end of the strip 64 extending to theright tofithepillar 51 in the drawings, and abuttiugagainst the upper surface of thearm 53. During the riveting-operation Orother operation securing.the farm 53 to the strip 7 164,3'8PEGQ1' is inserted between tthe arm and strip :so that after zthe fixing operation, said spacer may be .removed and the bimetal strip is thenionly loosely held :to thetcontactgarm, for example with-raielearance of 2025 vthousanclths of an inch. The t'operatingpositions :of the arm and strip with respect to one another are tthen determined by the ,position .of the adjusting member or screw 67 in the end of the strip, and due to the assembly gap just above -described, .it tis ipossible to vary the position of the arm .overian .appreciable angle with respect to the strip for providing a current zero setting of the switch.

The position of the free end (left hand in Figs. 4 and 5) of the bimetal strip 64 is determined by an adjusting screw 68 received in a tapped perforation in the frame member 50 and abutting against the under surface of the strip 64. Said free end is biased into engagement with the screw 68 by means of a leaf spring member 69 which is secured to the frame member 60. Conveniently, for this purpose, the leaf spring 69 is provided with an enlarged end 70 having a rectangular slot through which a portion of reduced width at 71 of the frame member 50 extends, whilst a disc 72 also having a rectangular slot is placed on the portion 71 after the blade spring 69, and said portion 71 is bifurcated and riveted over the disc 72 as can clearly be seen at 73 in Fig. 4, whereby to hold the end 70 of spring 69 rigidly between the disc 72 and the shoulders formed on the end of the frame member 50 by the reduced portion 71. The screw 68 may be locked in position by a locking washer 74.

It will be understood that the screw 67 is employed to provide the zero setting of the thermostat during assembly, whilst the operating setting of the thermostat is determined by the adjusting screw 68.

The frame member 50 and strip 60 extend beyond the right hand rivet 61 so as to provide terminal portions which are 50a and 60a whereby the thermostat may be connected in circuit. Conveniently, the thermotat may be enclosed within a metal container comprising a tube 75 one end of which is substantially closed by the disc 72 and the other end of which receives an insulating closure and spacer member 76 comprising a tubular part accommodating the frame member 50 and strip 60 adjacent the rivets 61 and an end wall having slot openings 77 and 78 through which the terminal parts of the frame member 50 and strip 60 extend. The free space within the closure member is substantially filled by an insulating cement as shown at 79.

It will be seen that the switch device according to the invention provides for comparatively large movement of the operating or adjusting member, to effect a smaller movement of the switch contacts without involving complicated pivoted lever mechanism, and an acceptable accuracy of control is therefore readily obtainable without high standards of accuracy in manufacture and assembly.

What I claim is:

1. An electric snap-action switch having cooperating contacts comprising in combination a spring blade carrying one of the cooperating switch contacts, an operating member mechanically connected with said spring blade at a part of the latter remote from said contact, a fixed abutment supporting said operating member and said spring blade adjacent said part for rotational movement of said operating member and spring blade together with one another in the plane of contact movement, said abutment having a groove and said spring blade having a perforation engaging in the groove of said abutment, a second abutment, and a compression element mechanically connected with said spring blade and with said second abutment so as to be maintained in compression by said spring (blade to hold the latter in place inthe,groovein said fixed abutment :by .the compression force :in said -.cornpression element and to cause snap actionoftsaid icontacttinirespouse to rotational movement of said part of saidspring blade about saidtfixedabutment whensaidoperating mem her is rotationally displaced about said fixed abutment.

:2. An *TCIECHiC ;-snap-aetion switch having Jeooperating contacts {comprising .in. combination a spring blade tcarry .ingaone of zthecoqperatingswitch contacts, .an operating .member mechanically connected with said spring blade at a partof the latter :remote irom -said eontact, a rfixefd abutment for supporting said operating member and said spring blade zadjacentesaid ;part for rotational movement of said operatingmember-andspring blade together with one another in the plane of contact movement, said fixed abutment having a groove, and said spring blade "having a perforation providing an edge engaging in the groove in said fixed abutment, and said operating member being provided with an aperture in alignment with the perforation in said spring blade and having an operating clearance with said fixed abutment, a second abutment, and a compression element mechanically connected with said spring blade and with said second abutment so as to be maintained in compression by said spring blade to hold the latter in place in the groove in said fixed abutment by the compression force in said compression element and to cause snap action of said contact in response to rotational movement of said part of said spring blade about said fixed abutment when said operating member is rotationally displaced about said fixed abutment.

3. An electric snap-action switch having cooperating contacts comprising in combination a spring blade carrying one of the cooperating switch contacts, an operating member connected mechanically with said spring blade at a part of the latter remote from said contact, a fixed abutment for supporting said operating member and said spring blade adjacent said part for rotational movement of said operating member and spring blade together with one another in the plane of contact movement, said fixed abutment having a groove and said spring blade being provided with a perforation having an edge engaging in the groove in said fixed abutment and said operating member being provided with an aperture in alignment with the perforation in said spring blade and having an operating clearance with said fixed abutment, and said fixed abutment being adjustable for variably positioning said spring blade with respect to said operating member, a second abutment, and a compression element mechanically connected with said spring blade and with said second abutment so as to be maintained in compression by said spring blade to hold the latter in place in the groove in said fixed abutment by the compression force in said compression element and to cause snap action of said contact in response to rotational movement of said part of said spring blade about said fixed abut ment when said operating member is rotationally displaced about said fixed abutment.

4. An electric snap-action switch as defined in claim 1, wherein said operating member comprises a first bimetal strip having a free end, and including a second bimetal strip mounted for rotation on an axis parallel with the axis of rotation of said first bimetal strip and located intermediately of the ends of said second bimetal strip, said second bimetal strip having free ends, an adjusting abutment carried by a free end of one of said bimetal strips and engaging a free end of the other bimetal strip, and an adjusting member operable upon the end of said second bimetal strip remote from the free end of said first bimetal strip whereby a given movement derived from said adjusting member to displace said second bimetal strip about its axis of rotation will produce a smaller movement of the other free end of said second bimetal strip, and means for heating one of said bimetal strips under control of the opening and closing of the switch contacts.

5. An electric snap-action switch as defined in claim 4, wherein said adjusting member comprises a rotatable cam having a controlling surface which cooperates with said second bimetal strip for determining the position of said adjusting abutment carried by said second bimetal strip.

6. An electric snap-action switch as defined in claim 1, wherein said operating member and spring blade are loosely connected for relative movement toward or from one another, and including an adjusting member for varying the distance between said member and blade.

References Cited in the file of this patent UNITED STATES PATENTS.

2,135,864 Weber Nov. 8, 1938 8 Parks Jan. 17, Eaton Aug. 22, Riche Feb. 13, Riche Apr. 1, Youhouse Oct. 25, Thomson Nov. 29, Koci May 2, Kaminky May 30, Miller June 3, Spina et a1 Jan. 6, Zuckerman Nov. 10,

FOREIGN PATENTS Great Britain Aug. 22, Italy Dec. 21,

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