GB2059160A

GB2059160A - Electrical switch

Info

Publication number: GB2059160A
Application number: GB7932727A
Authority: GB
Original assignee: United Gas Industries Ltd
Current assignee: United Gas Industries Ltd
Priority date: 1979-09-20
Filing date: 1979-09-20
Publication date: 1981-04-15
Also published as: GB2059160B

Abstract

A thermostatically-controlled switch has bi-metallic means 11a, 11b which moves a plastics moulding 23 so as to change over two-position switch contacts 12-14. The centre movable contact 13 is located at one end of a flexible contact strip 25, the other end of which is secured to the moulding 23. A guide member 29 also secured to the moulding 23 provides a gap through which the contact strip 25 passes, the gap being shorter than the distance moved by the moulding 23 in changing over the switch contacts. The position of the gap relative to the contact strip 25 may be adjusted by loosening screw 30 and pivoting the guide member 29 before tightening the screw again. <IMAGE>

Description

SPECIFICATION Electrical switch This invention relates to two-position electrical switches.

The invention provides a two-position electrical switch comprising a pair of stationary contacts and a movable contact therebetween, the movable contact being mounted on one end of an elongated flexible contract strip which itself is mounted towards its other end on structure which is movable through a distance to change over the contacts being made, and a guide member also mounted on said structure to move therewith and providing a gap adjacent said one end of said contact strip through which the contact strip passes, said gap being narrower than said distance, said guide member being adjustable so as to centralize the gap with respect to the contact strip by means of a single pivot point about which the guide member may be rotated and then locked.

Preferably said guide member is of metal and said structure is of a low friction plastics material. The single pivot point may be a screw mounting.

The electrical switch may be thermostatically controlled by bimetallic means connected to move said structure.

A specific embodiment of the invention is shown in the accompanying drawings, in which: Figure lisa plan view with-some parts broken away of the interior parts of a thermostatic switch, Figure la is a scrap view to an increased scale in the direction of arrow A of Figure 1, Figure2 is a view in the direction of arrow B of Figure 1 some parts broken away, Figure 3 is a plan view of a thermostatic switch of Figure 1 when mounted in a casing, and Figure 4 is an underneath view of an adjacent dial of Figure 3.

Referring first to Figures 1, la and 2, the thermostatic switch shown uses the flexing of two bimetallic strips 1 la, 1 lb to sense ambient temperature to open and close two-position electrical switch contacts 12,13,14 (Figure 2). The bimetallic strips are rigidly secured together at end 16, the upper strip 1 lea being cranked to allow clearance between the strips. A rotatable cam 18 bears on a follower (not shown) carried by the upper strip to adjust the location of the upper strip up and down, against the resistance of a spring 19. A shaft 20 carrying the cam extends through the upper strip and when the switch is assembled in its housing 21 (Figure 3) carries a knob 22 whereby the shaft 20 and cam 18 can be rotated. This adjustment alters the temperature at which the switch contacts change over.

The lower bimetallic strip 1 b carries at its free end a moulding 23 of plastics material. The moulding has at one end a post 24 on which is secured one end of a flexible contact strip 25. At its free end contact strip 25 carries centre contact 13 of the two-position switch.

A pair of parallel normally stationary bars 27,28 extend one on either side of contact 13 and carry the stationary contacts 12, 14 respectively. In order to make the switch in either position the contact strip 25 is moved up or down, as is shown most clearly in Figure 2. In the figures the bars 27, 28 are not shown in full in order that the other switch structure can be seen better. The positions of the bars can be adjusted indpendently of one another by means not shown, in order to alter the points of operation of the switch.

On the side of the moulding 23 an adjustable guide member 29 of brass is secured by a single screw 30.

The guide member is L-shaped, the end limb of the L having a central opening through which the contact strip 25 extends, as seen best in Figure la. The central opening has abutments either side of the contact strip leaving a narrow gap for the strip 25. A magnet 31 mounted in the moulding 23 is located between a pair of soft iron armature plates 32, so that the moulding is pulled positively toward either of its extreme positions.

As the temperature reaches the temperature set by knob 22 the bimetallic strips reach a state of tension at which the magnetic attraction of magnet 31 is overcome and the switch contacts are changed over.

As the guide member moves with the moulding one or other of the abutments contacts the flexible contact strip 25 and flexes it so as to engage the respective stationary contact with greater pressure.

This ensures a positive contact. When changing over, this greater pressure is first released, the system therefore starting to accelerate before the contacts separate. This avoids flickering on and off of the contacts as the switch changes over. The gap must be centralized relative to the contact strip so as to obtain substantially equal pressure in both directions of movement. This is effected by loosening the screw 30 and tilting the guide member about the screw so raising or lowering the gap.

As described above, the knob 22 (Figures 3 and 4) turns shaft 20 so as to determine the average temperature at which the switch contacts change over. A housing 33 for the thermostatic switch carries an index plate 34 carrying temperature indices against which a pointer 35 on the upper side of the knob may be set. The underside of knob 22 shown in Figure 4 has an opening for fitting over the shaft 20. The knob is of transparent plastics material to those of the index plate 34. An adjustable stop member 37 carrying a pair of stops may be positioned on the knob so as to limit the range of temperatures through which the knob can be turned and this stop member is located by reference to the indices on disc 36.

1. A two-position electrical switch comprising a pair of stationary contacts and a movable contact therebetween, the movable contact being mounted on one end of an elongated flexible contact strip, which itself is mounted towards its other end on structure which is movable through a distance to change over the contacts being made, and a guide member also mounted on said structure to move therewith and providing a gap through which said contact strip passes adjacent said movable contact, said gap being shorter than said distance but parallel

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Electrical switch This invention relates to two-position electrical switches. The invention provides a two-position electrical switch comprising a pair of stationary contacts and a movable contact therebetween, the movable contact being mounted on one end of an elongated flexible contract strip which itself is mounted towards its other end on structure which is movable through a distance to change over the contacts being made, and a guide member also mounted on said structure to move therewith and providing a gap adjacent said one end of said contact strip through which the contact strip passes, said gap being narrower than said distance, said guide member being adjustable so as to centralize the gap with respect to the contact strip by means of a single pivot point about which the guide member may be rotated and then locked. Preferably said guide member is of metal and said structure is of a low friction plastics material. The single pivot point may be a screw mounting. The electrical switch may be thermostatically controlled by bimetallic means connected to move said structure. A specific embodiment of the invention is shown in the accompanying drawings, in which: Figure lisa plan view with-some parts broken away of the interior parts of a thermostatic switch, Figure la is a scrap view to an increased scale in the direction of arrow A of Figure 1, Figure2 is a view in the direction of arrow B of Figure 1 some parts broken away, Figure 3 is a plan view of a thermostatic switch of Figure 1 when mounted in a casing, and Figure 4 is an underneath view of an adjacent dial of Figure 3. Referring first to Figures 1, la and 2, the thermostatic switch shown uses the flexing of two bimetallic strips 1 la, 1 lb to sense ambient temperature to open and close two-position electrical switch contacts 12,13,14 (Figure 2). The bimetallic strips are rigidly secured together at end 16, the upper strip 1 lea being cranked to allow clearance between the strips. A rotatable cam 18 bears on a follower (not shown) carried by the upper strip to adjust the location of the upper strip up and down, against the resistance of a spring 19. A shaft 20 carrying the cam extends through the upper strip and when the switch is assembled in its housing 21 (Figure 3) carries a knob 22 whereby the shaft 20 and cam 18 can be rotated. This adjustment alters the temperature at which the switch contacts change over. The lower bimetallic strip 1 b carries at its free end a moulding 23 of plastics material. The moulding has at one end a post 24 on which is secured one end of a flexible contact strip 25. At its free end contact strip 25 carries centre contact 13 of the two-position switch. A pair of parallel normally stationary bars 27,28 extend one on either side of contact 13 and carry the stationary contacts 12, 14 respectively. In order to make the switch in either position the contact strip 25 is moved up or down, as is shown most clearly in Figure 2. In the figures the bars 27, 28 are not shown in full in order that the other switch structure can be seen better. The positions of the bars can be adjusted indpendently of one another by means not shown, in order to alter the points of operation of the switch. On the side of the moulding 23 an adjustable guide member 29 of brass is secured by a single screw 30. The guide member is L-shaped, the end limb of the L having a central opening through which the contact strip 25 extends, as seen best in Figure la. The central opening has abutments either side of the contact strip leaving a narrow gap for the strip 25. A magnet 31 mounted in the moulding 23 is located between a pair of soft iron armature plates 32, so that the moulding is pulled positively toward either of its extreme positions. As the temperature reaches the temperature set by knob 22 the bimetallic strips reach a state of tension at which the magnetic attraction of magnet 31 is overcome and the switch contacts are changed over. As the guide member moves with the moulding one or other of the abutments contacts the flexible contact strip 25 and flexes it so as to engage the respective stationary contact with greater pressure. This ensures a positive contact. When changing over, this greater pressure is first released, the system therefore starting to accelerate before the contacts separate. This avoids flickering on and off of the contacts as the switch changes over. The gap must be centralized relative to the contact strip so as to obtain substantially equal pressure in both directions of movement. This is effected by loosening the screw 30 and tilting the guide member about the screw so raising or lowering the gap. As described above, the knob 22 (Figures 3 and 4) turns shaft 20 so as to determine the average temperature at which the switch contacts change over. A housing 33 for the thermostatic switch carries an index plate 34 carrying temperature indices against which a pointer 35 on the upper side of the knob may be set. The underside of knob 22 shown in Figure 4 has an opening for fitting over the shaft 20. The knob is of transparent plastics material to those of the index plate 34. An adjustable stop member 37 carrying a pair of stops may be positioned on the knob so as to limit the range of temperatures through which the knob can be turned and this stop member is located by reference to the indices on disc 36. CLAIMS

1. A two-position electrical switch comprising a pair of stationary contacts and a movable contact therebetween, the movable contact being mounted on one end of an elongated flexible contact strip, which itself is mounted towards its other end on structure which is movable through a distance to change over the contacts being made, and a guide member also mounted on said structure to move therewith and providing a gap through which said contact strip passes adjacent said movable contact, said gap being shorter than said distance but parallel thereto, said guide member being adjustable to locate the gap with respect to the contact strip by means of a single pivot point about which the guide member may be rotated to adjust the gap parallel to said distance.

2. A switch as claimed in claim 1 wherein said guide member is of metal and said structure is of a low-friction plastics material.

3. A switch as claimed in claim 1 or claim 2, wherein said single pivot point is a screw mounting the guide member on said structure.

4. A switch as claimed in any of claims 1 to 3 which is thermostatically controlled by bimetallic means connected to move said structure.

5. A thermostatically-controlled switch as claimed in claim 4 wherein the temperature at which the bimetallic means operates the switch is adjustable by a cam rotatabie by a manual knob.

6. Athermostatically-controlled switch substantially as described hereinbefore with reference to the accompanying drawings.