Switch Assembly

The present invention relates to switch assemblies and more particularly to snap-action switch assemblies. Electric switches may suffer from a number of problems. For example, when an electric switch in an electrical circuit is operated away from a switched state, arcing between the electrical contacts, and/or erosion of the contact material, may occur, especially when the contacts break apart relatively slowly. Another problem is that undesirable contact bounce may occur when a contact is formed (as the switch is operated to a switched state) . This may also cause arcing between the electrical contacts, and/or erosion of the contact material. Electric switches arranged to provide a mechanical snap- action, in order to mitigate at least some of the above- mentioned problems, are known. Electric switches comprising an arrangement of magnets for creating a magnetic snap-action are also known. However, both of these types of electrical switch have been found to be prone to at least some, if not all, of the problems described above.

The present invention seeks to provide an improved switch, and seeks to mitigate or remove at least some of the above-mentioned disadvantages.

According to a first aspect of the invention, there is provided an electric switch assembly comprising a pair of terminals for connection to an electric circuit, an operator mechanism for actuating the switch assembly to and from a switched state in which a pathway for electric current is defined between the pair of terminals, and a magnet exerting a magnetic force, wherein the switch assembly is operable away from the switched state by way of a mechanical snap-action, and the switch assembly is arranged such that the magnetic force enhances the mechanical snap-action. The enhanced snap-

action produces a particularly rapid contact break when the switch assembly is operated away from a switched state. This has been found to reduce arcing, and erosion of the contact material. The switch assembly may be operable to the switched state by way of a mechanical snap-action, the switch assembly being arranged such that the magnetic force enhances that mechanical snap-action. Enhancing the mechanical snap-action with the magnetic force tends to result in faster build up of the electrical contact pressure in the switched state. This has been found to reduce contact bounce, arcing, and/or erosion of the contact material.

It will be appreciated that the mechanical snap-action may ^¬ be achieved in a number of different ways. The mechanical snap-action is typically effected by the operator mechanism. The operator mechanism may comprise a biasing member (for example a spring) for storing energy released in the mechanical snap-action.

Aspects of the present invention may be applicable to a number of different types of switch. However, the switch assembly is preferably a rocker switch assembly.

The switch assembly may comprise a single magnet exerting the magnetic force. In such an embodiment, the single magnet may be arranged to act on material that is influenced by a magnetic field (for example ferromagnetic material, or paramagnetic material) . The switch assembly may comprise a plurality of magnets exerting the magnetic force. The plurality of magnets may be arranged to act on each other. Alternatively or additionally, one or more of the plurality of magnets may be arranged to act on material that is influenced by a magnetic field.

In the switched state, the switch assembly preferably forms a contact through which the electrical current may pass. The

switch assembly is preferably arranged such that the magnetic force acts in proximity to the contact. At least one magnet may be located in proximity to the contact. The presence of the magnetic force in proximity to the contact is thought to influence the severity and/or character of arcing. In embodiments of the invention comprising a plurality of magnets, a pair of magnets may be located either side of the contact when the switch is in the switched state. The contact is preferably formed on the terminal. The switch assembly may be arranged such that the magnetic force acts in proximity to a terminal. At least one magnet may be located in proximity to a terminal. In some embodiments of the invention, the contact may be formed in a location remote from the terminal. The magnetic force tends to rapidly decrease with separation from the magnet. In the switched state, the magnet and the object on which it acts (for example a second magnet, or a piece of material that is influenced by the magnetic force) may be in contact with one another, or in close proximity to one another. The switch assembly may be operable between only two states. For example the switch assembly may be operable between a neutral state (in which no electrical connection is made between the terminals) and a switched state (in which an electrical connection is established between the terminals) . Alternatively the switch assembly may be operable directly between two different switched states (in each switched state a pathway being defined between different terminals for different electrical circuits) . More preferably, the switch assembly is operable between a multiplicity of states. For example, the switch assembly may be operable between a neutral state and two different switched states. The switch assembly may comprise a plurality of pairs of terminals for connection to an electric circuit, the switch assembly being operable

between a plurality of switched states, in each switched state a pathway for electric current being defined between one of the pairs of terminals. The switch assembly may be away from, to, or more preferably between, the plurality of switched states by way of a mechanical snap-action, and the switch assembly is preferably arranged such that the magnetic force enhances the mechanical snap-action. It will be appreciated that the pairs of terminals may include a common terminal. For example, in the embodiment described below with reference to Figures 1 to 3, the switch assembly comprises two pairs of terminals but only three terminals in total.

The switch assembly may include a magnet associated with each contact (for example a magnet associated with each contact on the operator mechanism, and a magnet associated with each contact on the terminals) .

The operator mechanism may comprise a moving contact assembly, the switch assembly being arranged such that when the operator is in the switched state, the moving contact assembly defines the pathway for electric current between the pair of terminals. The moving contact assembly may comprise a pivotably mounted armature for defining at least part of the pathway for electric current between the pair of terminals. The moving contact assembly may comprise one or more contacts at the ends of the armature. According to a further aspect of the invention there is provided an electric switch assembly comprising a pair of terminals for connection to an electric circuit, an operator mechanism for actuating the switch assembly to and from a switched state in which a pathway for electric current is defined between the pair of terminals, and a magnet exerting a magnetic force, wherein the switch assembly is operable to the switched state by way of a mechanical snap-action, and the switch assembly is arranged such that the magnetic force

enhances the mechanical snap-action. Enhancing the mechanical snap-action with the magnetic force results in a faster formation of the electrical contact, and faster build up of contact pressure in the switched state. This has been found to reduce contact bounce, arcing, and/or erosion of the contact material.

The switch assembly is preferably arranged such that the magnetic force resists movement of the switch away from the switched state. The switch assembly may be arranged such that, in the switched state, the contacts are held together by the magnetic force. The switch assembly may thereby reduce contact bounce when the switch is operated to the switched state. Such an arrangement may also enhance the snap-action away from, and/or to, the switch state. The switch assembly may be arranged such that the magnetic force biases the switch assembly into the switched state. It will be appreciated that the switch assembly may be biased into the switched state by purely the magnetic force, but is more preferably biased by a combination of a mechanical force and the magnetic force. Biasing the switch into the switched state with the magnetic force has been found to enhance the quality of the contact closing in switched state, resulting in higher contact pressure, lower power-loss across contacts and/or lower contact temperature-rise. Such an arrangement may also enhance the snap-action away from, and/or to, the switch state.

It will be appreciated that features described with reference to the one aspect of the invention are equally applicable to any other aspect of the invention.

Various embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings of which:

Figure 1 is a sectional view of a switch assembly- according to a first embodiment of the invention, the switch assembly being in a switched state; Figure 2 is a sectional view of the switch assembly of the Figure 1 in which the switch assembly is being moved away from the switched state; and

Figure 3 is a sectional view of the switch assembly of the Figure 1 in which the switch assembly has been moved from the switched state in Figure 1, to a second switched state.

Figure 1 shows an electric rocker switch assembly 1 according to a first embodiment of the invention. The switch assembly 1 is mounted in a housing 10 (only the edge of which is shown in Figures 1 to 3) and is incorporated into an electrical circuit (not shown) .

Referring to the switch assembly 1 in detail, the underside of the assembly 1 comprises a first pair of electrical terminals 3a, 3b and a second pair of electrical terminals 3b, 3c (the central terminal 3b is common to both pairs of terminals) . All the terminals are electrically conductive and the outer two terminals 3a, 3c include plate- like contacts 4 on their upper surface. Wires (not shown) are attached to the base of each terminal 3a, 3b, 3c at a retaining screw, and the switch assembly is therefore incorporated into the electric circuit (not shown) .

The switch assembly 1 includes an operator mechanism 5. The operator mechanism comprises a generally T-shaped rocker 7 and a moving contact assembly 9. The rocker 7 is mounted in the housing 10 with the upper, generally horizontal, portion of the T shape facing outwards. This upper portion of the rocker is exposed through an opening in the housing 10,

enabling a user to access the rocker 7 and operate the switch assembly.

The rocker 7 is pivotably mounted about a central axis positioned across the width of the switch (i.e. in a direction into the page in Figures 1 to 3) . The pivoting movement of the rocker 7 is constrained by the presence of the housing 10. The rocker 7 is therefore pivotable between a position in which the left-hand side L of the upper portion of the rocker 7 is slightly depressed (i.e. the position shown in Figure 1) and a position in which the right-hand side R of the upper portion of the rocker 7 is slightly depressed (i.e. the position shown in Figure 3) .

The rocker 7 includes a spring-loaded plunger assembly comprising a spring 13 and a plunger 15 mounted in the upright portion of the T-shape. The spring 13 is arranged to bias the plunger 15 against the central portion of a moving contact assembly 9. The plunger forms a knife-edge along its lower end, and therefore presses against the moving contact assembly 9 across a relatively thin area. The moving contact assembly 9 comprises a conductive arcuate armature 17, the centre of which is pivotably mounted on, and in electrical contact with, the top of the central terminal 3b. The armature 17 extends either side of the central pivot, to positions above the two outer terminals 3a and 3c. The moving contact may therefore be pivoted onto any one of the pairs of terminals 3a, 3b and 3b, 3c. On the underside of either end of the armature 17, there are provided two contacts 18 (in the form of a segment of a sphere) for contacting the plate-like contacts 4 on the outer terminals 3a and 3c when the moving contact is pivoted. Thus the moving contact assembly 9 is able to define a pathway for electric current between each pair of terminals 3a, 3b and 3b, 3c.

According to the first embodiment of the invention, the switch assembly further comprises two pairs of magnets 19 and 21. The first pair of magnets 19 is associated with the first pair of contacts 3a, 3b. The first pair of magnets 19 comprises a magnetic steel inlay 19a at the end of the moving contact assembly armature 17, and in proximity to the contact 18, together with a ring magnet 19b at the upper end of the terminal 3a in proximity to the plate-like contact 4. The second pair of magnets 21 is associated with the second pair of terminals 3b, 3c and comprises a magnetic inlay 21a and ring magnet 21b in corresponding locations on the other end of the armature 21a and the terminal 3c.

The switch assembly is operable between switched states (shown in Figures 1 and 3) by pivoting the rocker 7, which in turns causes pivoting of the moving contact assembly 9.

Referring first to Figure 1, when the left-hand side L of the rocker is depressed, the spring-loaded plunger 15 presses just to the right-hand side of the centre of the armature 17 of the moving contact assembly 9. Thus the moving contact assembly 9 is pivoted onto, and held against, the right-hand terminal 3c by the mechanical pressure exerted by the spring-loaded plunger on the moving contact assembly. The contact 18 is also held against the contact plate 4 of the terminal 3c by the magnetic attraction between the second pair of magnets 21a and 21b. The contact assembly 9 therefore defines an electrical connection between the second pair of contact terminals 3b, 3c.

To move the switch assembly 1 away from this switched state, and towards another switched state (in which the contact assembly 9 defines an electrical connection between the other pair of terminals 3a, 3b) , the user depresses the right-hand side R of the rocker. Since the rocker 7 is generally T-shaped, the lower end of the spring-loaded plunger

15 is drawn across the central region of the armature 17. As the plunger 15 approaches the pivot point on the central terminal 3b, it is pushed upwards, thereby compressing the spring 13. In the absence of any magnetic forces, when the rocker 7 is level and the spring loaded plunger 15 is directly above the pivot point on the central terminal 3b, the switch assembly 1 would momentarily be in an inherently unstable equilibrium. A slight additional downward movement of the right-hand side R of the rocker 7 would draw the plunger 15 across the pivot, allowing the spring 13 to rapidly extend and thereby quickly moving the contact assembly 9 onto the first pair of terminals 3a, 3b, in a mechanical snap-action. A purely mechanical snap-action arrangement has been found to still allow the contact to break relatively slowly, resulting in intense arcing, and possible erosion of the material on the contacts. Furthermore, when the switch adopts the second switched state, the armature may be susceptible to contact bounce. In the first embodiment of the invention, the pairs of magnets 19, 21 enhance the mechanical snap-action, and substantially reduce the above-mentioned drawbacks. As the switch 1 is being moved from the switched state in Figure 1 to the switched state in Figure 3, the plunger 15 is drawn across the centre (and thus the pivot point) of the moving contact assembly 9. In the position shown in Figure 2, the plunger 15 has moved past the pivot point, and in the absence of the magnets 19, 21 would have already caused the moving contact assembly 9 to pivot onto the first pair of terminals 3a, 3b. However, in the first embodiment of the invention, the attraction between the second pair of magnets 21a, 21b holds the contacts on the second terminal 3c together. The attraction between the pair of magnets 21 is relatively strong

because they are in close proximity to each other. Only when the rocker 7 has been further depressed on the right-hand side R, is the force of the plunger 15 on the moving contact assembly 9 sufficient to pivot the armature 17 of the moving contact assembly 9 onto the first pair of contacts 3a, 3b.

At the point the contact on the second pair of terminals 3b, 3c breaks (i.e. the point the moving contact assembly 9 begins to pivot) , the plunger 15 is already exerting a considerable moment on the armature 17. The moving contact assembly 9 is therefore subjected to a violent snap-action away from the second pair of terminals 3b, 3c and onto the first pair of terminals 3a, 3b. This results in an especially quick-break between the contacts 18, 4 and reduces arcing and material erosion at those contacts. The magnets have also been found to be important in successfully establishing electrical contact when the moving contact assembly initially contacts the terminals after the switch assembly has been operated to a switched state (for example from the state in Figure 1 to the state in Figure 3) . In the first embodiment of the invention, the first pair of magnets 19a, 19b assist the closing of the contact by holding the contacts 18, 4 together and reducing the risk of contact bounce. In addition, the contacts are held together at higher contact pressure than they would be with purely a mechanical pressure. Higher contact pressure has been found to result in lower electrical contact resistance, lower power-loss across the contacts and reduced contact heating. The risk of arcing and contact erosion may be reduced.

It is also thought that the presence of the magnet in the vicinity of the contacts, may have some beneficial effect on the severity or character of any arcing that might occur. Whilst the present invention has been described and illustrated with reference to a particular embodiment, it will

be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. For example, the switch assembly need not necessarily be in the form of a rocker switch assembly. The switch assembly need not necessarily be operable between switched states; for example the switch assembly may be operable from a neutral state to a switched state, or between a multiplicity of switched states. The switch need not necessarily contain permanent magnets acting upon each other; for example in the above described embodiment of the invention, the magnetic steel inlays 19a, 21a may be replaced by soft-iron that is influenced by the magnetic force from the ring magnets 19b, 21b. It will be appreciated that the magnetic snap action and the mechanical snap action may be achieved in a number of different ways. Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims.