GB1595888A - Electrical switches - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO ELECTRICAL SWITCHES (71) We, STANDARD TELEPHONES AND CABLES LIMITED, a British Company, of 190 Strand, London, WC2R lDU, England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to electrical switches and in particular to push-button switches provided with remotely operable release mechanism.

Items of domestic electrical equipment, for example washing machines, TV receivers, record players and the like, frequently use mains switches of the 'push to operate-push to release' type. These switches generally employ a metal pin engaging a heart shaped cam track to provide the switch action.

In many situations it is advantageous to provide remote control of such a switch and/or some means of disabling the mains supply in the event of overheating of an electrical appliance. This can be achieved by the provision of a further switch or a thermal cut-out device separate from the mains switch but such a technique is relatively expensive.

According to one aspect of the invention there is provided an electrical push-button switch of the push to make/push to break type, the switch including an actuating element coupled to the switch contacts and maintainable in its 'on' position against a return spring by -engagement of a rod mounted on the switch housing with a substantially heart-shaped cam track, and means responsive to heat and/or the-passage of an electric current for deflecting the rod around the cam track so as to provide release of the actuating element from its 'on' position to its 'off' position.

According to another aspect of the invention there is provided an electrical pushbutton switch, including a housing, a spring loaded actuating element coupled to the switch contacts and provided with a substantially heart-shaped cam portion, a rod one end of which engages -the cam portion, the other end of the rod being anchored in a toggle pivoted on the housing, in which the cam and rod are so arranged as to provide a push to operate-push to release action of the actuating element, and in which means responsiive to heat or the passage of an electric current are provided to so urge the rod around the cam by pivoted movement of the toggle as to provide trip release of the actuating element when that element is in its operated position.

Embodiments of the invention will now be described with reference to the accompanying drawings in which: Fig. 1 is a sehematic view of a push-button -switch provided with a release mechanism operable via a bimetallic strip; Fig. 2 shows a bimetallic strip element used in the switch of Fig. 1; Fig. 3 shows a switch in which the release mechanism is operated via a heat extensible wire; Fig. 4 shows a switch provided with an electromagnetic release mechanism; Fig. 5 shows a switch in which the release mechanism is operable via a thermally expandable capsule; and Fig. 6 shows the detail of a typical heart shaped cam used to provide the switch action of the switches of--Figs. 1 to 4.

Referring to Figs. 1, 2 and 6, the switch contacts (not shown) are operable via a spring loaded push-button 11 mounted on the switch housing 10 and provided with a heart shaped cam portion 12 in which a resilient bent rod or wire 13 engages to provide a 'push to make-push to release' action in the conventional manner. The rod 13 is anchored in a toggle 14 mounted on a pivot 15 and which, in the untripped condition of the switch, is held in abutment with a limit stop 16 by a relatively weak return spring 17. The toggle 14 is so arranged that, due to the tension applied to the rod 13 by the action of the spring load of the push-button, it provides an 'over centre' action to the rod. - - - A cylindrical resistive element 18 is mounted on the housing and-forms a locating support for a bent bimetallic strip 19 to one end of which an actuator strip 20 is attached e.g. spot welding. The resistive element 18 also provides for location of the return spring 17, the ends of the strip 19 and spring 18 being located in a channel 21 provided in the housing wall.

As shown in Fig. 6, the substantially heart shaped cam 12, with which the rod 13 engages to provide the switch action, has an asymmetric track 61 around which the end of the rod is caused to travel by operation of the push-button, the rod end traversing the tracks in an anti-clockwise direction. The switch is held on by engagement of the rod 13 with a shoulder 62 on the cam. In normal use, release of the switch is effected by pressure on the push-button pushing the cam portion in the direction of the arrow A causing the end of the rod 13 to abut a ramp 63 thereby deflecting the rod in the direction of the arrow B. The rod 13 is thus deflected away from the shoulder 62 permitting retraction of the push-button, in which position the rod abuts the lower portion 64 of the cam track.

With the switch in its on position, i.e. with the rod 13 engaging shoulder 62 of the cam, automatic or trip release is effected by the application of heat to the bimetallic strip 19.

This heating may be achieved by passage of an electric current through the resistor 18.

Alternatively the strip may be heated as a result of overheating of an electrical appliance to which the switch arrangement is fitted. The bimetallic strip 19 is so constructed that this heating causes the actuator strip 20 to move into abutment with the toggle 14.

Further movement of the actuator 20 pushes the toggle 'over centre' about its pivot thus permitting retraction of the push-button causing the rod 13 to abut a ramp 22 formed in the housing 10 adjacent the cam portion 12 of the push-button. Further outward movement of the push-button causes the rod 13 to be deflected by the ramp 22 out of engagement with the shoulder 62 causing release of the switch. When the bimetallic strip has cooled, with the switch in its off position, the spring 17 returns the toggle 14 to its original position against the limit stop 16. The switch has then to be manually set for its next cycle of operation.

Fig. 3 shows a similar switch construction in which automatic or trip operation is achieved by heat extension of a thin stretched wire. As before the switch arrangement is provided with a rod 13 engaging a substantially heart shaped cam 62 and anchored in a pivoted toggle 14. A relatively thin resilient, electrically resistive, e.g. NICHROME, wire 25 is stretched between anchors 26 and 27 and around a peg 28. One anchor 27 is secured to one arm 29 of a relatively strong spring 30 mounted on a peg 31 extending from the housing 10. The resilience of the spring urges the arm 29 towards the toggle 14, the arm 29 being restrained by the wire 25.

In some applications terminals 32 are provided to permit the passage of an electric current through the wire 25.

With the switch in its on position automatic or trip release is effected by heating the wire 25 e.g. by passage of an electric current. Heat extension of the wire allows the spring cam 29 to push the toggle 14 'over centre' about its pivot 15 thus releasing the rod 13 from the cam shoulder 62 as before. With the switch released, as the wire cools the spring arm 29 is drawn back to its original position and the return spring replaces the toggle to reset the switch.

In the arrangement shown in Fig. 4 an electromagnetic arrangement provides for trip release of the switch. The switch has the previously described rod and cam mechanism providing the switch action. A solenoid 41 is mounted on the switch housing adjacent the toggle 14 and is provided with a freely slidable plastics rod core 42 to one end of which a soft iron core portion 43 is secured. The other end of the core 42 is profiled to form a cone 44. A return spring 45 holds the core assembly in abutment with a limit stop 46.

Tripping of the switch is effected by passing a current through the solenoid, the resultant magnetic field causing the soft iron core position to move into the solenoid, the cone 44 deflecting the toggle 14 so as to release the rod 13 from the cam shoulder 62. When the solenoid current is switched off the core assembly is urged back against the limit stop 46 by the spring 45 and the toggle 14 is reset by the spring 17.

Fig. 5 shows a switch in which tripping is effected via a thermally expandable capsule 51 which may be advantageously of the type filled with a gas or vapour and having a flexible Belleville spring diaphragm. Such a capsule is described in our co-pending application No. 06165/78, Serial No. 1571754.

Such a capsule has a flexible corrugated diaphragm movable, by gas pressure, from a first stable position to a second astable or metastable position.

In the switch shown in Fig. 5 the rod and cam mechanism is employed to provide the switch action, but the toggle is dispensed with and the rod 53 is elongated and is anchored beneath a mount 55 secured to the switch housing. A thermal capsule 51 is mounted on the housing 10 beneath the rod 53.

Tripping of the switch of Fig. 5 is effected when the temperature of the capsule exceeds a predetermined maximum, e.g. as a result of overheating of an appliance to which the switch is fitted. Heat expansion of the capsule 51 forces the rod 53 away from the switch housing 10 thus disengaging the rod from the cam 12, permitting release of the switch.

When the capsule cools a return spring 54 urges the rod 53 back into engagement with the cam 12.

In some applications a thick film heater 57 may be disposed on the housing 10 in thermal contact with the capsule so as to provide for remote control of the switch.

WHAT WE CLAIM IS:- 1. An electrical push-button switch of the push to make/push to break type, the switch including an actuating element coupled to the switch contacts and maintainable in its 'on' position against a return spring by engagement of a rod mounted on the switch housing with a substantially heart-shaped cam track, and means responsive to heat and/or the passage of an electric current for deflecting the rod around the cam track so as to provide release of the actuating element from its 'on' position to its 'off' position.

2. A switch as claimed in claim 1, and in which said means includes a thermally ex pandable capsule arranged in abutment with the rod.

3. A switch as claimed in claim 2, and in which said capsule is of the type filled with a gas or vapour and provided with a Belleville spring diaphragm operable via the pressure of the vapour or gas.

4. An electrical push-button switch, in cluding a housing, a spring loaded actuating element coupled to the switch contacts and provided with a substantially heart-shaped cam portion, a rod one end of which engages the cam portion, the other end of the rod being anchored in a toggle pivoted on the housing, in which the cam and rod are so arranged as to provide a push to operated push to release action of the actuating ele ment, and in which means responsive to heat or the passage of an electric current are pro vided to so urge the rod around the cam by pivoted movement of the toggle as to provide trip release of the actuating element when that element is in its operated position.

5. A switch as claimed in claim 4, and wherein the trip release means includes a bimetallic strip arranged adjacent the toggle and so constructed as to urge the toggle around the pivot when heat is applied to the strip.

6. A switch as claimed in claim 4, and wherein the trip release means includes a further spring arranged adjacent the toggle, and a relatively thin resistive heat extensible wire coupled to the spring, the arrangement being such that, when the wire is extended by the application of heat thereto, the spring urges the toggle around the pivot so as to trip the switch.

7. A switch as claimed in claim 6, and wherein said wire is coupled to first and second terminals whereby an electrical current may be passed through the wire.

8. A switch as claimed in claim 4, and wherein said trip release means includes an electromagnetic device.

9. A switch as claimed in claim 8, and wherein said electromagnetic device includes a solenoid arranged adjacent the toggle and provided with a freely slidable core whereby rotation of the toggle is effected.

10. A switch as claimed in claim 9, wherein said core comprises a first nonmagnetic portion disposed within the solenoid and coupled to a second magnetic portion, disposed adjacent the solenoid, movement of the core being effected by electromagnetic attraction of the magnetic portion towards the solenoid.

11. An electrical push-button switch substantially as described herein with reference to Fig. 6 together with Figs. 1 and 2, or Fig. 3, or Fig. 4 of the accompanying drawings.

12. An electrical push-button switch, including a housing, a spring loaded actuating element coupled to the switch contacts and provided with a substantially heart shaped cam track, a ramp provided on the housing adjacent the cam track, a rod one bent end of which engages the cam track, the rod engaging a shoulder formed in the track to hold the switch on, the other end of the rod being anchored in a toggle pivoted on the housing, a bimetallic strip element arranged adjacent the toggle, and means for heating the bimetallic strip element so as to bend that element towards the toggle, in which the cam and rod are so arranged as to provide a push to operate-push to release action of the actuating element, and in which the switch is so constructed that heating of the bimetallic strip element when the switch is in its 'on' condition causes the strip element to rotate the toggle about the pivot allowing the bent end of the rod to be drawn against the ramp by the spring action of the actuating element thereby disengaging the rod end from the shoulder so as to release the swtich.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. When the capsule cools a return spring 54 urges the rod 53 back into engagement with the cam 12. In some applications a thick film heater 57 may be disposed on the housing 10 in thermal contact with the capsule so as to provide for remote control of the switch. WHAT WE CLAIM IS:-

1. An electrical push-button switch of the push to make/push to break type, the switch including an actuating element coupled to the switch contacts and maintainable in its 'on' position against a return spring by engagement of a rod mounted on the switch housing with a substantially heart-shaped cam track, and means responsive to heat and/or the passage of an electric current for deflecting the rod around the cam track so as to provide release of the actuating element from its 'on' position to its 'off' position.

2. A switch as claimed in claim 1, and in which said means includes a thermally ex pandable capsule arranged in abutment with the rod.

3. A switch as claimed in claim 2, and in which said capsule is of the type filled with a gas or vapour and provided with a Belleville spring diaphragm operable via the pressure of the vapour or gas.

4. An electrical push-button switch, in cluding a housing, a spring loaded actuating element coupled to the switch contacts and provided with a substantially heart-shaped cam portion, a rod one end of which engages the cam portion, the other end of the rod being anchored in a toggle pivoted on the housing, in which the cam and rod are so arranged as to provide a push to operated push to release action of the actuating ele ment, and in which means responsive to heat or the passage of an electric current are pro vided to so urge the rod around the cam by pivoted movement of the toggle as to provide trip release of the actuating element when that element is in its operated position.

5. A switch as claimed in claim 4, and wherein the trip release means includes a bimetallic strip arranged adjacent the toggle and so constructed as to urge the toggle around the pivot when heat is applied to the strip.

6. A switch as claimed in claim 4, and wherein the trip release means includes a further spring arranged adjacent the toggle, and a relatively thin resistive heat extensible wire coupled to the spring, the arrangement being such that, when the wire is extended by the application of heat thereto, the spring urges the toggle around the pivot so as to trip the switch.

7. A switch as claimed in claim 6, and wherein said wire is coupled to first and second terminals whereby an electrical current may be passed through the wire.

8. A switch as claimed in claim 4, and wherein said trip release means includes an electromagnetic device.

9. A switch as claimed in claim 8, and wherein said electromagnetic device includes a solenoid arranged adjacent the toggle and provided with a freely slidable core whereby rotation of the toggle is effected.

10. A switch as claimed in claim 9, wherein said core comprises a first nonmagnetic portion disposed within the solenoid and coupled to a second magnetic portion, disposed adjacent the solenoid, movement of the core being effected by electromagnetic attraction of the magnetic portion towards the solenoid.

11. An electrical push-button switch substantially as described herein with reference to Fig. 6 together with Figs. 1 and 2, or Fig. 3, or Fig. 4 of the accompanying drawings.

12. An electrical push-button switch, including a housing, a spring loaded actuating element coupled to the switch contacts and provided with a substantially heart shaped cam track, a ramp provided on the housing adjacent the cam track, a rod one bent end of which engages the cam track, the rod engaging a shoulder formed in the track to hold the switch on, the other end of the rod being anchored in a toggle pivoted on the housing, a bimetallic strip element arranged adjacent the toggle, and means for heating the bimetallic strip element so as to bend that element towards the toggle, in which the cam and rod are so arranged as to provide a push to operate-push to release action of the actuating element, and in which the switch is so constructed that heating of the bimetallic strip element when the switch is in its 'on' condition causes the strip element to rotate the toggle about the pivot allowing the bent end of the rod to be drawn against the ramp by the spring action of the actuating element thereby disengaging the rod end from the shoulder so as to release the swtich.