GB2043347A - Electrical switch - Google Patents

Abstract

An electrical switch having a body 12 rotatably mounting a shaft 40 provided with a contact member, which is electrically insulated from the shaft, several contacts 34 to 38 spaced around the shaft and selectively engageable by the contact member, which also contacts an arcuate terminal 33 to connect the latter electrically with any selected one of the contacts, the contact member includes clip-type contacts 68, 70 and 69, 71 carried by an insulating block fitted on the shaft, which has flats to prevent relative rotation of the block, and to provide shoulders locating the block axially. A resilient plate 50, similarly mounted on the shaft, and spaced by shoulders thereon from the insulating block, urges balls 54, 55 into contact with depressions 15a in the body to define click-in positions corresponding to engagement of the contact member with selected contacts. <IMAGE>

Description

SPECIFICATION Electrical switch This invention relates to electrical switches of the type which can selectively connect a terminal to any one of a plurality of electrical contacts.

One known switch of this type comprises a moulded, plastics body in which is rotatably mounted an actuating shaft. The terminals and the contacts are mounted on the body with the shaft electrically connected to the terminal. The contacts are spaced around the shaft and the latter carries a radial arm electrically connected to the shaft. Rotation of the shaft moves the arm from contact to contact to provide selection. The body has indentations and the shaft carries a resilient detent member urged into engagement with one of the indentations. Each contact is associated with a corresponding indentation which provides a "click in" position to locate the arm in engagement with the associated contact.

In this known switch, electrical current passes through the actuating shaft, in use, and, accordingly, it is essential that the switch is mounted in a position in which the shaft is electrically insulated from accidental contact with metal objects. This arrangement can be dangerous if there is a high voltage across the shaft.

The present invention provides a switch of this type which avoids this problem and which can be of very simple construction.

In accordance with this invention an electrical switch comprises a body rotatably mounting a shaft, an arcuate terminal on the body and concentric with the shaft, a plurality of contacts spaced concentrically around the shaft, a contact member on the shaft and engaged with said terminal, the contact member being selectively engageable with the contacts by rotation of the shaft to connect the selected contact electrically with the terminal, the contact member including an electrical insulating part serving to mount the member on the shaft.

Reference is now made to the accompanying drawings, wherein: Figure 1 is a plan view of a switch according to the invention; Figure 2 is a sectional elevation of the switch on the line 2-2 of Figure 1; Figure 3 is a sectional plan view on the line 3-3 of Figure 2; Figure 4 is an exploded perspective view of parts of the switch, and Figure 5 is a part-sectional view of the parts of Figure 4 in assembled state, but excluding bearing balls shown in Figure 4.

The switch shown comprises a moulded plastics body 11 comprising a dish-shaped portion 12 and an integral outwardly extending flange 13 at the mouth of the portion 12. The dish-shaped portion has a central aperture 14 encircled by a plurality of partfrustoconical projections 15 extending radially of the aperture. These projections define depressions 1 5a therebetween. The flange 13 is provided with radially extending channels 20 to 26 and with fixing holes 27, 28 for receiving fixing screws or bolts.

A terminal 30 is mounted in the two channels numbered 20 and 21 and has end portions 31,32 engaged in respective channels with an arcuate portion 33 extending therebetween. The arcuate portion is located in the mouth of the dish-shaped portion 12 and follows the contours thereof. Respective contacts 34 to 38 are mounted in the other channels 22 to 26. The terminal and the contacts are rivetted in position.

A metal shaft 40 is rotatably engaged in the aperture 14 in the base of the dish-shaped portion 12. The shaft 40 is made from a cylindrical length of rod by removing portions to define flats. An upper part of the shaft is provided with opposite parallel flats 41, 42 and a lower part of the shaft is provided with opposite parallel flats 43,44, co-planar with the other two flats respectively, a cylindrical portion 45 being left between the upper and lower flats. A groove 46 is provided around the shaft adjacent the lower end.

A resilient plate 50 has a central aperture 51 complementary to the lower part of the shaft 40 having the flats 43,44, and is fitted on the shaft in abutment with a shoulder defined by the cylindrical portion 45.

The shaft is slightly deformed adjacent the plate, as shown in figure 5 at 40a, to hold the latter in position.

The plate is elongate and has a hole 52, 53 adjacent each end, each of which locates a respective bearing ball 54, 55. As apparent from figures 2 and 3, the shaft is mounted so that the balls 54, 55 are resiliently urged by the plate 50 into engagement in respective depressions 15a in the body, a reaction surface being provided by a clip 57 engaged in the groove 46 and bearing against the bottom of the body.

Also mounted on the shaft 40 is a contact member 60. The contact member is fitted on the upper part of the shaft by means of an aperture 61 complementary thereto. The member abuts against a shoulder defined by the cylindrical portion 45 of the shaft and is held in position by deformation 40b of the shaft.

The member comprises a block 63 of insulating material and it is the block 63 that abuts against the cylindrical portion 45 of the shaft. Two metal contact elements 64,65 are rivetted to the block 63, at opposite faces thereof, each element having a central aperture, such as 66, to prevent contact of the element with the shaft. Each element has a pair of contact arms 68, 69 and 70,71 respectively, which extend diametrically of the shaft and the body. The elements are resilient with the free end of each arm urged towards contact with the free end of the adjacent arm of the other element. The contact member 60 is located by the shaft 40 relative to the body such that one pair of arms 68,70 grips one of the contacts 34 to 38 therebetween to make an electrical contact and the other pair of arms 69,70 similarly grips the terminal 30.

It can be seen that the contact member 60 electrically connects the terminal 30 to one of the contacts and rotation of the shaft 40 causes the member to engage different contacts whilst maintaining engagement with the terminal 30. Such connection is made without the shaft forming a part of the circuit. The depressions 15a define "click-in" positions for the balls 54, 55 corresponding to the positions in which the member engages with a contact. The upper flats 41,42 on the shaft facilitate fitting of a knob on the shaft to rotate the latter.

Claims (9)

1. An electrical switch comprises a body rotatably mounting a shaft, an arcuate terminal on the body and concentric with the shaft, a plurality of contacts spaced concentrically around the shaft, a contact member on the shaft and engaged with said terminal, the contact member being selectively engageable with the contacts by rotation of the shaft to connectthe selected contact electrically with the terminal, the contact member including an electrical insulating part serving to mount the member on the shaft.

2. An electrical switch according to Claim 1, wherein the shaft is generally cylindrical but has one end part provided with at least one axially extending flat, the insulating part of the contact member having an aperture complementaryto said one end part for fitting of the part on the shaft.

3. An electrical switch according to Claim 2, wherein a portion of the shaft adjacent said end part is cylindrical and defines a shoulder against which said insulating part abuts.

4. An electrical switch according to Claim 3, wherein the shaft is deformed adjacent the contact memberto hold said insulating part against said shoulder.

5. An electrical switch according to any preceding Claim, wherein the contact member comprises a pair of elongate contact elements secured to the insulating part and which co-operate to engage opposite sides of the terminal and a selected one of the contacts.

6. An electrical switch according to Claim 3, or Claim 4 or 5 as appendant to Claim 3, wherein the opposite end part of the shaft is also provided with at least one flat, and a resilient plate is fitted on said opposite end for non-rotation relative to the shaft, said cylindrical portion of the shaft also defining a shoulder against which the plate abuts, detent means, and a plurality of depressions in the body and spaced concentrically around the shaft, said plate serving to urge the detent means into engagemenu with a selected one of said depressions, each selected depression corresponding to a respective selected contact.

7. An electrical switch according to Claim 6, including a groove in said opposite end part, and a clip engaged in the groove and abutting against the body to provide a reaction surface against the resilient urging action of the resilient plate.

8. An electrical switch according to claim 6 or 7, wherein two diametrically opposite detents are provided and urged by the resilient plate into engagemenu with respective depressions in the body, the detents being in the form of bearing balls.

9. An electrical switch constructed substantially as herein described with reference to the accompanying drawings.