Electrical rotary switch

An electrical rotary switch has a casing, a rotor supported within the casing for rotation, a moving contact mounted on the rotor for rotation with the rotor, and four fixed contacts located laterally of the rotor for short-circuiting by the moving contact. Each fixed contact has a contact body in the casing for contact by the moving contact and a leg extending from the contact body and projecting out of the casing for insertion through a circuit board and soldering to the circuit board for mechanical and electrical connection.

The present invention relates to an electrical rotary switch for controlling an electrical appliance.

BACKGROUND OF THE INVENTION

An electrical switch of the type concerned has a casing, a rotor therein, a moving contact mounted on the rotor for turning therewith, and a plurality of fixed contacts in the casing for short-circuiting by the moving contact to switch on an electrical appliance. The casing typically has a pair of side extensions with holes to enable use of screws or bolts to fix the switch at a desired location. Electric cables are usually used to connect the switch, by its fixed contacts, to the relevant electrical circuit. This has been the traditional way of fixing and connecting an electrical switch of the type concerned for many years.

The invention seeks to provide a new or otherwise improved electrical rotary switch that can relatively more easily be located and connected for use.

SUMMARY OF THE INVENTION

According to the invention, there is provided an electrical rotary switch comprising a casing, a rotor supported within the casing for rotation about an axis of rotation, a moving contact mounted on the rotor for rotation therewith, and a plurality of fixed contacts located laterally of the rotor for short-circuiting by the moving contact. At least one of the fixed contacts has a contact body in the casing for contact by the moving contact and a leg extending from the contact body and projecting out of the casing for insertion through a circuit board and soldering therewith for mechanical and electrical connection.

Preferably, the leg extends substantially perpendicular to the contact body.

More preferably, the contact body has a first end for contact with or by the moving contact and a second end connected with the leg.

It is preferred that the contact body is bent about a plurality of axes substantially parallel to the leg.

It is preferred that the casing comprises an upper part and a lower part connected together and holding the contact body captive between them.

It is further preferred that the leg extends through the lower part of the casing.

In a preferred embodiment, the contact body and the leg are two distinct members in contact with each other.

More preferably, the contact body and the leg comprise respective conductive strips that are relatively thicker and thinner respectively.

More preferably, the contact body is bent about a plurality of axes substantially parallel to the leg.

Further more preferably, the contact body has a first end for contact with or by the moving contact and a second end resiliently bearing against the leg.

Yet further more preferably, the leg has an upper end against which the second end of the contact body resiliently bears and a lower end projecting out of the casing, wherein the casing comprises an upper part and a lower part connected together and holding the contact body and the upper end of the leg captive between them.

Yet further more preferably, the upper end of the leg is folded and engaged by the upper part of the casing.

It is preferred that the casing is of a substantially flat square shape, having four corners each housing one respective said fixed contact.

In a preferred embodiment, the rotor has a side radially extending about the axis of rotation and a rotor periphery having a undulating profile surrounding the axis of rotation, resiliently against which rotor periphery the fixed contacts bear for sliding contact with the moving contact so as to be short-circuited thereby, and wherein the moving contact comprises a base at the rotor side and a plurality of parts adjacent the rotor periphery for contact by the fixed contacts, the parts being integrally connected to the base and folded therefrom to extend substantially parallel to the axis of rotation, at least one of the parts having an undulating profile matching with that of an adjacent part of the rotor periphery.

More preferably, the undulating profile of the rotor periphery comprises alternating crests and valleys, and the undulating profile of said at least one part of the moving contact extends continuously over at least two adjacent said valleys.

More preferably, the undulating profile of the rotor periphery comprises alternating crests and valleys, and the undulating profile of said at least one part of the moving contact comprises at least two adjacent valleys matching with that of the rotor periphery.

More preferably, the moving contact fits over the rotor, with its base lying on the rotor side and its periphery meeting the rotor periphery.

More preferably, the moving contact is produced by way of a deep-draw manufacturing process from a blank of material.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring to the drawings, there is shown an electrical rotary switch100embodying the invention, which has a generally flat square casing110, a rotor120, a moving contact130mounted on the rotor120and four fixed contacts140located generally within respective corners of the casing110surrounding the rotor120. The casing110(shown in a horizontal position) is formed by a flat square base111and a matching lid112closing upon an open upper side of the base111.

The rotor120has a generally circular disc-like body129located centrally inside the casing110for rotation about a central axis of rotation X (vertical as shown) over 360° in opposite directions. The rotor120includes a central shaft125which projects upwardly from the rotor body129out of the casing110through the lid112along the axis X to enable manual turning of the rotor120. A turning knob (not shown) is usually fitted to the shaft125to facilitate turning.

The rotor body129has a peripheral flange121surrounding the axis X and a flat open lower end122having an end side or surface radially extending with respect to the axis X. The flange121has an undulating or wavy profile formed by a ring of twelve evenly-spaced arcuate crests127, with a flat V-shaped valley128between adjacent crests127. The twelve valleys128are situated at, say, 1stto 12thangular position about the axis X. The fixed contacts140bear resiliently against the valleys128to define twelve stable angular positions for the rotor120and to slidingly make/break contact with/from the moving contact130.

The moving contact130has a generally flat horizontal main body or base139and three integral rim parts or tabs131,132and133upstanding therefrom at the 1stto 4th, the 8thand 9thand the 11thvalley positions respectively. The moving contact130fits from below over the lower end122of the rotor body129, with its base139underlying the lower end surface and its tabs131to133lying around the side and meeting the rotor's peripheral flange121. An axial projection at the rotor's lower end122fitting through a central aperture134of the base139is expanded by heat to secure the moving contact130to the rotor120.

The first contact tab131is the widest and extends continuously over the 1stto 4thvalley positions, having a wavy profile matching with that of the adjacent portion of the rotor's flange121but slightly radially expanded therefrom for contact with or by the fixed contacts140. The second contact tab132spans continuously over the 8thand 9thvalley positions, also having a wavy profile matching with that of the adjacent portion of the rotor's flange121but slightly radially expanded therefrom for contact with or by the fixed contacts140. The third contact tab133is the narrowest and is generally flat (slightly curved) as shown, or it may be slightly V-shaped, to guard the corresponding valley128at the 11thposition likewise for contact with or by the fixed contacts140.

In general, the moving contact130is mounted fast on the rotor120for rotation therewith, with its base139and contact tabs131to133enclosing the rotor's lower end122and the contact tabs131to133slightly radially protruding beyond the rotor's flange121for contact with or by the fixed contacts140.

The moving contact130is produced by way of a deep-draw manufacturing process which involves the use of a plug201and a die202, as illustrated inFIGS. 7A to 7D. The plug201has a uniform cross-section which corresponds to the inner cross-section of the moving contact130as defined in part by the inner surfaces of the wavy-profiled contact tabs131and132and the flat contact tab133. The die202has a central through bore or cavity203which has a cross-section corresponding to the outer cross-section of the moving contact130as defined in part by the outer surfaces of the wavy-profiled contact tabs131and132and the flat contact tab133. The cross-section remain constant at the top end of the cavity203over a relatively short distance greater than the thickness of the moving contact130, and then widens gradually downwards.

Production of the moving contact130starts with a blank130D of metal material such as copper alloy, which is initially stamped out from a much larger base sheet to a shape corresponding to the flat development of the moving contact130. The blank130D includes three peripheral protrusions corresponding to the contact tabs131to133laid flat.

To commence the deep-draw process, the blank130D is initially placed on the upper end of the die202, or upon the lower end of the plug201, at the right position aligned with the plug201or as determined by reference to its central aperture134(FIG. 7A). Upon pressing down of the plug201into the cavity203of the die202, the blank130D is folded with its peripheral protrusions about the edge of the lower end of the plug201through 90° until the protrusions turn vertically upright to form the contact tabs131to133(FIGS. 7B to 7C), whereupon the moving contact130is created.

As the protrusions corresponding to the first and second contact tabs131and132are being folded, they are simultaneously stretched to acquire their wavy profiles as mentioned above. Pressing of the plug201deeper to reach the wider part of the cavity203allows release of the contact130from the plug201(FIG. 7D).

A similar plug (201) and die (202) are shown inFIGS. 8A and 8Bfor illustration purposes only, which are used to make a similar moving contact (130) whose contact tabs are different in terms of position and width.

The four fixed contacts140are located generally within respective corners of the casing110, laterally around the rotor120and moving contact130for short-circuiting by the moving contact130, whereby the switch100is closed. The fixed contacts140have identical construction and are interchangeable for ease of production and assembly.

Each fixed contact140is formed by two separate/distinct members in contact with each other, namely a contact body140″ which is located horizontally in the casing110for contact by the moving contact130and a vertical leg149which extends downwardly from the contact body140″, at right angles thereto, and projects out of the casing110through its base111for external connection.

The contact body140″ has a generally U-shaped configuration, being formed by a copper (or copper alloy) strip that is bent through an angle of about 90° twice, about two vertical axes, into a series of first, second and third integrally connected sections141,142and143, taken in a direction outwardly from the axis X. From the second section142, the first section141is curved smoothly outwardly and then inwardly into a spoon-like end141A which bears resiliently against the rotor's peripheral flange121for sliding contact with or by any one of the moving contact tabs131to133. The first section141is sufficiently long and is shaped as described to achieve an optimum resilience and contact pressure upon the moving contact130.

The second section142is short and flat and interconnects the first and third sections141and143via respective curved bends each of an angle substantially 90°, together forming a generally rectangular U-shaped bend142U. The third section143is folded at about mid-length outwardly through an angle of about 35° to yield an inclined flat end143A for connecting or contacting the leg149.

The leg149is made from another copper strip, having a lower flat pin149A and an upper butt149B that is wider than the pin149A. The butt149B has a top end149C that is folded through an angle of 90° to stick out horizontally on one side and includes a flat lump149D on the vertical surface on the opposite side for contacting the contact body140″.

Turning to the casing110or the base111thereof, its side wall113extends along the complete periphery without any openings and defines four corners each having a rectangular bay114. The bay114is oriented at an angle of about 45° as shown and is shaped to match the outer shape of the bend142U of the associated fixed contact body140″ for locating the same in position. A rectangular knob115on a bottom wall116of the base111in the bay114fixes the contact body140″ by holding its second section142against the side wall113.

Put differently, the knob115defines a narrow gap with the side wall113into which the second section142is press fitted, whereby the bend142U is held in the bay114, bearing with its outer surface against the side wall113. The first and third sections141and143on opposite sides of the bend142U are slightly deflectable inwardly. The first section141is exposed to resiliently bear against the rotor body129and moving contact130for contact making/breaking.

Referring specifically toFIG. 6, after the contact body140″ has been fitted in the right place in the casing base111, the leg149is inserted downwardly into the base111at a position adjacent the end143A of the contact body140″, with its pin149A passing through a small slot117in the bottom wall116. The leg149descends until its folded top end149C engages upon a plateau118on the base111. During insertion of the leg149, the end143A of the contact body140″ is displaced sideways by the leg149to thereby eventually bear resiliently against the butt149B by its lump149D, whereupon the contact body140″ and the leg149are properly located and connected together to form the complete fixed contact140.

The rotor120with the moving contact130mounted thereunder is installed into the casing base111after all the four fixed contacts140have been fitted in place. The lid112is finally closed upon the base111and secured therewith by snap connections119, thereby holding the contact body140″ and the leg's butt149B captive between them. The lid112is shaped on the underside of its four corners to engage upon the contact body140″ and the leg149by its folded top end149C, thereby holding them in position.

Considering all the four fixed contacts140, their pins149A are arranged to project out from the bottom of the switch casing110as switch terminals at the four corners of an imaginary square which fits the arrangement of the holes of a standard circuit board for mounting electronic components. The pins149A have a cross-section that is slightly smaller than that of the circuit board holes such that they can be inserted through the appropriate holes and then soldered with the relevant conducting tracks/pads on the other side of the circuit board for both mechanical and electrical connection.

The design of the fixed contacts140or in particular the switch terminals149A makes it possible for the subject rotary switch100to be simultaneously mounted and connected on a circuit board in the same manner as most electronic components. This way of fixing and connecting the switch100is easy and convenient as it eliminates the traditional use of screws for fixing and cables/wires for connection, taking advantage of a circuit board that often exists in most if not all electrical appliance and is usually located behind a control panel where the switch100is most likely needed.

The contact bodies140″ are made from conductive strips that are relatively thinner for flexibility compared with the conductive strips producing the legs149, which are relatively thicker for rigidity. The strips may be of different materials or compositions to achieve the desired properties e.g. resilience and solderability.

The invention has been given by way of example only, and various modifications of and/or alterations to the described embodiment may be made by persons skilled in the art without departing from the scope of the invention as specified in the appended claims.