US2440025A - Electric switch - Google Patents

Description

April 20, 1948' s. A. SINGLETON l 2,440,025

ELECTRIC SWITCH Filed Aug. 6, 194:5r

2O E20 F/Q/ EJ Altorney Patented Apr. 20, 1948 ELECTRIC SWITCH Sidney Arthur Singleton, Eiiingham, England, as-

signor to Thermega Limited, London, England,

a British company Application August 6, 1945, Serial No. 609,082 In Great Britain May 3, 1944 18 Claims.

This invention relates to thermostats and switches for controlling electrical circuits and has for its object to provide a thermostat or switch having a snap action in both directions of operation so that a quick make and break of the circuit is achieved. l

If a strip of springy material of curved transverse section is subjected to a force tending to bend it into a longitudinal curve it will, up to a point, resist the force, until, when said force reaches a given value, the strip will suddenly collapse. Conversely, when the strip is relieved of the bending force, it will regain its original shape, but in the initial stages of its return movement the vspring will exert little force until on reaching a certain point the force increases suddenly and the spring snaps back to its original shape.

The present invention has for its object to provide a thermostat or switch having a snap action in both directions of operationiby making use of the above mentioned properties of a transversely curved spring strip.

To this end an electric switch according to the i invention includes in combination ablade spring xed at one end and acted upon between its ends by an abutment, whereby the spring is flexed, said spring carrying at its free end a movable contact held against a xed contact by a member acting laterally against a transversely'curved spring strip which is held at one end and bears between its ends against a fulcrum abutment I carried by the blade spring between the first mentioned abutment and the movable contact, whereby on exerting pressure on the blade spring or on the curved strip said curved strip collapses about the fulcrum thereby relieving the blade spring, thus permitting it to straighten out and bring the movable contact away from the relatively iixed contact, the curved strip suddenly snapping back to its straight condition when the pressure is relieved, whereby the blade spring is forced back to its curved condition thereby bringing the contacts together again.

In a thermostatic switch according to the invention the pressure may be exerted on the transversely curved strip by the action of a bimetallic strip acting laterally against said curved strip, the bimetallic strip having its low expansion side directed towards the blade spring so that on a 2 rise in temperature the force exerted by the bimetallic strip increases until the transversely curved strip collapses about the fulcrum, thereby relieving the blade spring and thus permitting it to straighten out and bring the moving contact away from the fixed contact.

The transversely curved strip may be fixed to the blade spring at a point between the fixed end of the blade spring and the abutment against which said blade spring bears, and the bimetallic strip may bear on the transversely curved strip at a point between the free end of the latter and the fulcrum abutment.

In a non-thermostatic switch according to the invention there may be provided an actuating member for exerting pressure on the blade spring at a point between the fulcrum abutment and the held end of the transversely curved spring. Alternatively the actuating member may exert pressure on the blade spring at a point between the fulcrum abutment and the free end of the transversely curved strip.

In order that the invention may be more completely understood two embodiments thereof will now be described by way of example with reference to the accompanying drawings in which:

Fig. 1 shows to an enlarged scale a thermostatic switch according to the invention, in longitudinal section;

Fig. 2 is a section on the line II-II in Fig. 1;

Fig. 3 is a section on the line III-III in Fig. 1;

Fig. 4 shows the transversely curved strip in plan;

Fig. 5 is an end view of the strip looking from the right of Fig. 4;

Fig. 6 shows to an enlarged scale a non-thermostatic switch in longitudinal section; and

Fig. '7 shows a modied thermostatic switch according to the invention in longitudinal section.

In the embodiment shown in Figs. l to 5 the thermostat comprises a rigid metal strip I carrying the fixed contact 2, and a bimetallic strip 3 disposed substantially parallel with the rigid strip, the two strips being spaced apart in an insulating holder 4 and the bimetallic strip 3 having its high expansion side facing away from the rigid strip i so that a rise in temperature will cause curvature of the bimetallic strip towards the rigid strip.

Mounted in the holder 4 between the two above mentioned strips and adjacent to the rigid strip is a blade spring 5 carrying the movable contact 6, and mounted on the rigid strip I about half way along it is anlabutment 1 in the form of a tension screw which bears against the blade spring 5 through an insulating plate 8, and riveted or otherwise secured to the blade spring at 9 between the tension screw 'l and the holder 4 is a strip of spring metal I which is curved in transverse section. (See Fig. 3.)

Carried in the free end of the bimetallic strip 3 is an adjusting screw II which bears against an insulating button I2, for example of porcelain, iixed to the free end of the transversely curved strip I0, and forces this strip against a fulcrum abutment I3 constituted by a dimple formed, by pressing, in the blade spring between the tension screw I and the movable contact 6 which is carried on the free end of said blade spring.

The free end of the transversely curved strip IU is attened to receive the button I2, as shown at I4 in Figs. 4 and 5, the edges of the strip being turned up at an angle alongside the ilattened area as shown at I5 (Fig. 5). If desired 'both ends of the strip I0 may be thus shaped.

This sha-ping of the free end or both ends of the strip IIl helps to retain the transversely curved shape of the spring and makes it more reliable with less chance of variation in strength or loss of shape at its centre due to fatigue.

Preferably the tension screw abutment I bears on the blade spring 5 at a point midway between the fulcrum abutment I3 and the point 9 at which the transversely curved strip I0 is attached to the blade spring 5.

The tension screw 'l and adjusting-screw II are adjusted so that when the thermostat is at the lowest temperature to which it is normally to be subjected, the transversely curved strip I0 is straight longitudinally, whileA the blade spring 5, of which the normal shape is straight, is flexed to a curvature which maintains the movable contact 6 in engagement with the ilxed contact 2, this flexing of the blade spring being produced by the force exerted by the adjusting screw II, which is transmitted to the blade spring 5 through the transversely curved strip I0 and the fulcrum abutment I3.

As the temperature rises, the bimetallic stri-p 3 bends towards the rigid strip I, and the adjusting screw I I exerts a still greater force on the transversely curved strip I0, which, however, still remains straight so that the pressure on the contacts 2, 6, actually increases, the blade spring 5 distorting to permit the movement of the bimetallic strip 3.

When the temperature reaches a predetermined value the transversely curved strip I0 suddenly collapses about the fulcrum abutment I3 thereby relieving the blade spring 5 of the pressure exerted thereon through the fulcrum abutment I3, about which the transversely curved strip I0 is now kinked. Accordingly the blade spring 5 suddenly assumes its normal straight shape, and in so doing, withdraws the movable contact 6 from the xed contact 2, thereby suddenly breaking the circuit.l

As the temperature falls again, the transversely curved strip I0 tends to straighten, but, since at rst it cannot exert much force, the resilience of the blade spring 5 resists this tendency and consequently, as the bi-metallic strip 3 cools and moves away from the rigid strip I, the transversely curved strip I0, still in its kinked condition, follows this movement bodily and the blade spring 5 moves with it, the fulcrum abutment I3 remaining in engagement with the transversely curved strip I0.

Accordingly at first the contacts 2 and B separate still further, until, when a predetermined temperature is reached during cooling, the transversely curved strip Ill suddenly snaps back to its straight condition and forces the blade spring 5 back to its curved condition thereby bringing the contacts 2 and 6 together again.

In a modied form of thermostat according to the invention shown in Fig. 7 the rigid strip I of Fig. 1 may be replaced by a bimetallic strip disposed with its high expansion side facing away from the other bimetaliic strip 3 so that on a rise in temperature the two bimetallic strips move towards one another. With such an arrangement greater sensitivity of the thermostat is obtained because, as the temperature rises, the movement of the bimetallic strip I carrying the contact 2 will add to the force on the transversely curved strip IIJ thereby causing the latter to collapse after a smaller rise in temperature than is the case when the contact 2 is stationary as in the construction shown in Figs. 1 and 2.

In both the foregoing constructions, instead of the tension screw l, the adjustment screw II may be arranged to bear on the blade spring 5 at a point between the fulcrum abutment I3 and the point 9 at which the transversely curved strip I0 is attached to the blade spring 5, in which case the point at which the adjusting screw II bears is ,preferably midway between the fulcrum abutment I3 and the connection 9 between the transversely curved strip I0 and the blade spring 5. In such constructions the tension screw l occupies the position shown for the adjustment screw II in Fig. 1.

A retaining piece I6 secured to the free end of the strip I carrying the fixed contact 2 may be bent round as at Il to extend past the outside of the free end of the transversely curved strip Il) to act as a stop to prevent the strip from moving sufiiciently far in the cooling direction to cause separation of the contacts should the thermostat cool down much below the lower limit of its operative temperature range.

The holder 4 for the strips and blade spring may conveniently be in the form of an insulating body, e. g. of porcelain, steatite, or an insulating plastic, having a substantially rectangular cross-section and formed with a channel I8 (Fig.

2) in one of its longitudinal faces to receive the blade spring 5 and the rigid strip I, and with a similar channel in its other longitudinal face to receive the bimetallic strip 3. The strips and the blade spring are secured in position by nuts i9 and bolts 20, the bolts passing through holes in the strips and insulating body, and being provided with insulating sleeves ZI. Mica or other insulation 22 is provided under the bolt heads and nuts, and between the blade spring 5 and the strip I to complete the insulation.

A thermostat of the form particularly described above is particularly useful for sealing into a glass tube which is evacuated or contains an inert gas, and for the purpose of holding the thermostat firmly in such a tube, spring lugs 23 may be provided at the ends of the insulating body, the free ends of these lugs bearing against the side of the tube. Such lugs may be formed by the bent up ends of strips of spring metal 24 secured in the channels of the insulating body by means of the bolts 2U.

The invention may also be applied to non-thermostatic switches by providing, instead of the bimetallic strip, a push button by means of which pressure can be exerted on the transversely curved strip, the button being spring urged away from the transversely curved strip so that pressure on the latter is relieved when the push button is released.

Such a construction of switch is shown in Fig. 6 and comprises a rigid metal strip I carrying the ilxed contact 2 and a blade spring 5 carrying the movable contact 6, both these elements being mounted substantially parallel to one another in an insulating holder 4, lead wires 25 being connected to the spring 5 and strip I, which are separated by insulation 26.

Mounted on the rigid strip I, about half wayA along it, is an abutment in the form of a tension screw 1 which bears against the blade spring 5 through an insulating plate 8, and, riveted or otherwise secured to the blade spring at 9, between the tension screw 1 and the holder 4, is the transversely curved spring strip I0, which bears between its ends against a fulcrum abutment I3 constituted by a dimple formed in the blade spring 5 between the rst mentioned abutment 1 and the moving contact 2.

Also mounted in the insulating holder 4 on the opposite side thereof from the rigid strip I is a leaf spring 26 which, at its free end, carries an insulating button y21, for example of porcelain, which passes freely through a hole in the spring 26 and has a collar 21a resting against the face of the spring, the free end of the transversely curved 'strip I0 bearing against the other end of the button 21.

On pressing the button 21 the free end of the transversely curved strip I!) is ipushed towards the rigid strip I until the curved strip I suddenly collapses about the iulcrum abutment I3, thereby relieving the blade spring 5 of the pressure exerted thereon through the fulcrum abutment i3 about which the transversely curved strip I is now kinked. Accordingly the blade spring suddenly assumes its normal shape and in so doing withdraws the moving contact 6 from the fixed contact 2.

On releasing the press button the transversely curved strip III returns to its normal position thereby permitting the blade spring 5 to close the contacts again.

Instead of mounting the push button 21 on a leaf spring 26 the button, if not too heavy and if mounted without much friction, may be guided in a xed holder since, in such conditions the transversely curved strip will'always return to its normal position on release of the push button.`

The functions of the tension screw I and of the actuating member or ipush button 21 may be interchanged. In such a construction the push button 21 is carried by and will operate through the rigid strip I at the point of application of tension screw 1, shown in Fig. 6, while the tension screw 1 will take the place of member 21 and will be carried by a rigid member 26.

In this case the push lbutton 21 will bear on the spring strip 5 and less movement but more pressure will be required to operate it than when the button bears upon the transversely curved spring IIJ, as shown in Fig.`6.

Accordingly a switch according to the invention may be constructed for low pressure high movement operation (Fig. 6 construction) or vice versa.

From the foregoing it will be observed that the invention also includes an electric switch comprising in combination a blade spring, fixed at one end and acted upon between its ends by an abutment, whereby the spring is iiexed, said spring carrying at its free end a movable contact held against a xed contact by a transversely curved spring strip which is held at one end and bears between its ends against a fulcrum abutment carried by the blade spring between the iirst mentioned abutment and the moving contact, whereby on exerting pressure on the transversely curved strip by pushing an actuating member acting laterally on said curved strip either directly or through the blade spring, the transversely curved strip collapses about the fulcrum, thereby relieving the blade spring and thus permitting it to straighten out and bring the movable contact away from the xed contact, the strip sud denly snapping back to its straight condition when pressure on the actuating member is relieved, whereby the blade spring is forced back to its curved condition thereby bringing the contacts together again.

What I claim is:

1. An electric switch including in combination a support, a blade `spring fixed at one end to said support, an abutment bearing on said spring between the ends of the latter, to iiex said spring, a movable contact carried at the free end of said blade spring, a iulcrum abutment carried by said blade spring between the first mentioned abutment and the movable contact, a second contact adapted to be contacted by said movable Contact, a transversely curved spring strip bearing between its ends on said fulcrum abutment, means holding said transversely curved spring strip at one end, and actuating means to increase the pressure between said transversely curved strip and said fulcrum abutment whereby after a predetermined pressure said curved strip collapses about said fulcrum to relieve the `pressure exerted on said blade spring and to allow said blade spring to straighten out and to carry said movable contact suddenly away from said second contact.

2. A thermostatic switch including in combination a support, a blade spring iixed at one end to said support, an abutment bearing on said spring between the ends of the latter, to flex said spring, a movable contact carried at the free end of said blade spring, a fulcrum abutment carried by said blade spring between the first mentioned abutment and the movable contact, a fixed contact, a transversely curved spring strip bearing between its ends on said fulcrum abutment, means holding said transversely curved spring strip at one end, and a bimetallic strip bearing laterally against said transversely curved spring strip, the bimetallic strip having its low expansion side directed towards the blade spring so that on a rise in temperature the force exerted by the bimetallic strip increases until the transversely curved strip collapses about the fulcrum, thereby relieving the blade spring and thus permitting it to straighten out and bring the moving contact away from the iixed contact.

3. A switch according to claim 1 wherein the transversely curved strip is xed to the blade spring at a point between the xed end of the blade spring and the abutment against which said blade spring bears.

4. A thermostatic switch according to claim 2 wherein the transversely curved strip is iixed to the blade spring at a point between the iixed end of the blade spring and the abutment against which said blade spring bears.

6. A thermostatic switch including in combi` nation a support, a blade spring fixed at one end to said support; an abutment bearing on said spring between the .ends oi the latter, to flex said spring, a movable contact carried at the free end of said blade spring, a fulcrum abutment carried by said blade spring between the first mentioned abutment and the movable contact, a ilxed contact, a transversely curved spring strip bearing between its ends on said fulcrum abutment, means holding said transversely curved spring strip at one end, and a bimetallic strip bearing laterally on the transversely curved strip at a point between the free end of the latter and the fulcrum abutment, the bimetallic strip having its low expansion side directed towards the blade spring.

'7. A thermostatio switch including in combination a support, a blade spring fixed at one end to said support, a bimetallic strip having its low expansion side facing the blade spring, an

'abutment carried by said bimetallic strip and bearing on the blade spring between the ends of the latter to ilex said spring, a movable contact carried at the free end of said blade spring, a fulcrum abutment carried by said blade spring to be disposed between the first mentioned abutment and the movable contact, a contact mounted on said bimetallic strip, a transversely curved spring strip bearing between its ends on said fulcrum abutment, means holding said transversely curved spring strip at one end, and a tact, a transversely curved spring strip bearing between its ends on said 'fulcrum abutment, means holding said transversely curved spring strip at one end, a member acting laterally against the transversely curved spring strip at or nearthe free end thereof to exert pressure on said blade spring and thereby to hold the movable contact against the fixed contact, and\ an actuating memberacting on the blade spring at a point between the fulcrum abutment and v ing one of its ends secured to one face of' said holder, a fixed contact carried at the other end of said rigid strip, a bimetallic strip having one of its ends secured tothe opposite face of said holder, said bimetallic strip extending parallel to said rigid strip and having its low expansiony side directed towards Vsaid rigid strip, a blade spring disposed between' said rigid and bimetallic strips, and having one of its ends secured to said first mentioned face of the holder, a movable contact carried by said blade spring and cooperating with said fixed contact, an abutment bearing on said blade spring between the ends of the latter,l to ilex said spring, a fulcrum abutment carried by said blade spring between said first mentioned abutment and the movable second bimetallic strip bearing laterally against bimetallic strip increases until the transversely curved strip collapses about the fulcrum, thereby relieving the blade spring and thus permitting it to straighten out and bring the movable contact away from the fixed contact, the rate of increase of said force being itself increased by the employment of the two oppositely directed bimetallic strips, and the sensitivity of the switch correspondingly increased.

8. An electric switch including in combination a support, a blade spring fixed at one end to said support, an abutment bearing on said spring between the ends of the latter to ilex said spring. a movable contact carried at thc free end of said blade spring, a fulcrum abutment carried by said blade spring between the lrst mentioned abutment and the movable contact,

.a fixed contact, a transversely curved spring strip bearing between its ends on said fulcrum abutment, means holding said transversely curved spring strip at one end, and an actuating versely curved spring strip, said actuating member acting laterally against said curved strip at or near the free end thereof.

9. An electric 'switch including in combination a support, a blade spring fixed at one end to said support, a movable contact carried at the member for exerting pressure on the transfree end of said blade spring, a fuicrum abut- 15 fixed and movable contacts, the provision of a ment carried by said blade spring, a fixed ooncontact, a transversely curved spring strip secured at one'end to said blade spring between said first mentioned abutment and the insulating holder, said transversely curved spring strip bearing between its ends on said fulcrum abutment, and said bimetallic strip bearing laterally against said transversely curved spring strip. l1. A switch according to claim` 10 wherein the insulating holder is provided with oppositely inclined spring lugs on each of two opposite faces thereof to hold the switch firmly and centrally in a glass tube into which it is to be sealed.

12. A switch according to claim 1 wherein an end of the transversely curved spring strip vis formed with a flattened area.

13. A thermostatic switch according to claim 2 wherein an end of the transversely curved spring strip is formed with a flattened area.

14. A thcrmostatic switch according to claim l0 wherein an end of the transversely curved spring strip is formed with a flattened area.

15. A switch according to claim 1 wherein an end of the transversely curved spring strip is formed. with a flattened area and the edges of said strip alongside said flattened area are turned over at an angle to said flattened area.

16. A switch according to claim 2 whereinv an end of the transversely curved spring strip is formed with a flattened area and the edges of said strip alongside said flattened area are turned over at an angle to said flattened area.

1'1. A switch according to claim 10 wherein an end of the transversely curved spring strip is formed with a flattened area and the edges of said stripl alongside said flattened area are turned over at an angle to said flattened area.

A18. In an electric switch having a ilxed contact, resilient member xed at one end, a movable contact secured to the free end of said resilient member and adapted to contact with said fixed contact, an adjustable abutment bearing against and forming a fuicrum for said resilient member and an actuating member adapted to exert pressure on said resilient member for controlling the relative positions of said fulcrum abutment provided on said resilient Emails CITED member intermediate its free end and said adjustable abutment and'of a spring strip curved The following references are of record in the in transverse section having one end mounted me 0f this IIB-tent:

on said resilient member at a point located be- UNH-ED ENTS tween said adjustable abutment and the iixed`4 STATES PAT end of said resilient member, said curved strip Number Name Date being interposed between the fuicrum abutment 23601333 McDowell et al- Oct- 21. 1941 on said resilient. member and said actuating member and having its free end contacted by l0 said actuating member. v

SIDNEY ARTHUR SINGLEION.

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