GB1579561A

GB1579561A - Ganged switch protected against explosion

Info

Publication number: GB1579561A
Application number: GB16892/77A
Authority: GB
Original assignee: BBC Brown Boveri AG Switzerland; BBC Brown Boveri France SA
Current assignee: BBC Brown Boveri AG Switzerland; BBC Brown Boveri France SA
Priority date: 1976-04-22
Filing date: 1977-04-22
Publication date: 1980-11-19
Also published as: DE2617606C3; DE7612574U1; FR2349204B1; DE2617606A1; DE2617606B2; FR2349204A1; YU39676B; YU104577A

Description

(54) A GANGED SWITCH PROTECTED AGAINST EXPLOSION (71) We, BROWN, BOVERI & CIE AK TIENGESELLSCHAFT, Postfach 351, 6800 Mannheim 1, Federal Republic of Germany, a German Company, 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 state ment This invention relates to an explosionproof ganged switch comprising a plurality of superimposed switch units, in each of which there is provided at least one switching device.

Such explosion-proof ganged switches are frequently required to be used where one or more switching functions are to be performed in situations exposed to an explosion hazard but without having to take additional safety precautions.

For this purpose it is the practice to arrange the necessary switching devices in the form of a single pair of contacts or a double pair of contacts in an explosion-proof compartment.

In the majority of cases each explosion-proof compartment is so designed that a double contact pair and a cam disc for the switching of one phase are arranged therein. In such a case the external dimensions of the compartment demand practically the whole of the available space in its own plane.

Furthermore it is necessary for the switch shaft to pass through the respective superimposed explosion-proof compartments, whilst the cam discs for operating the contacts are, as already mentioned, situated inside the explosion-proof compartments. If, for example, in such a switch the surfaces of a switch compartment unit do not extend exactly plane-parallel with respect to each other in the gang direction, there exists the danger that, contrary to the requirements of the Federal Republic of Germany Safety Regulations VDE Specification 0171, the gap width at several places will be too large, consequently, in order to achieve a minimum gap width, high quality surfaces having a low degree roughness must be provided, in which case the cost of production of such a switch compartment, and consequently of an explosion-proof switch, with such compartments, becomes very expensive.

An object of this invention is to provide an explosion-proof ganged switch having a small structural volume and a small explosion-proof switch compartment volume as well as having variable switching functions, wherein a disc which operates the associated switching devices is located externally of the explosion-proof compartment.

According to the present invention an explosion-proof ganged switch comprises a plurality of switch units arranged in a stack, each such switch unit having at least two explosion-proof chambers disposed around the plane of a disc located externally of the two chambers and mounted on a switch shaft extending through the stack, each such chamber accommodating a switching device operable in response to rotation of the disc by the switch shaft.

Preferably, the stacked switch units comprise a plurality of juxtaposed structures and the two chambers of a switch unit are formed between two adjacent structures.

Conveniently, a switch unit at one end of the stack comprises a structure nearest said one end of the stack and a juxtaposed closure plate which together form the two chambers of the switch unit at said one end of the stack therebetween. The switch unit at the other end of the stack may comprise a structure nearest said other end of the stack and a juxtaposed wall of a housing of an indexing mechanism of the switch, which together form the two chambers of the switch unit at the said other end of the stack therebetween.

Advantageously, each of the juxtaposed structures may comprise a symmetrical moulded part which is open on one side, and has at least two recesses which are closed in an explosion-proof manner by a plate of a material which prevents or hinders arc formation. It is particularly advantageous if the outer surface of the plate is covered with cast resin so that the chambers are thereby constructed so as to be gap-free to prevent arcing.

The switching device accommodated in a chamber may comprise a contactless switching device, such as an amplifier, which is actuable remotely through an electric or magnetic field by means of an element which is actuable by the associated disc, or may comprise two co-operating switch contacts operable by a plunger which extends out of the chamber and is engagable by the associated disc.

An embodiment of the invention and advantageous developments thereof will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a side elevation of an explosionproof ganged switch according to the invention shown partly in section Figure 2 is a plan view of the explosionproof switch shown in Figure 1; Figure 3 is an end elevation of the explosion-proof switch shown in Figures 1 and 2, partly in longitudinal section in the region of an axial coupling element; Figure 4 is a sectional view of a switch unit having a switching position and cam disc, the section being taken above the position where the lead-through conductors of a switch compartment element are situated; Figure 5 is a sectional view similar to that in Figure 4, wherein the switch compartment is provided with a contactless switching device; Figure 6 shows the external wiring of a plurality of contactless switching devices shown in Figure 5.

In Figure 1 there is shown an explosionproof ganged switch 21, which includes an indexing mechanism housing 23 provided with fixing slots 22 and having a switch shaft extension 24, which can be coupled to a profiled switch shaft 25, which is extendable according to the axial length of the ganged cam switch 21. The profiled switch shaft 25 carried several cam discs 27 arranged in such a manner that these are each situated at the level of the individual gang units 26 of the switch.

The cam discs 27 have working segments 27a and idling segments 27b; they are also provided with holes 27c shaped so that a plurality of triangular surfaces 27d are formed therein for accommodating the profiled switch shaft, which is made of square cross section material. A plurality of identical switch compartment structures or elements (which are further referred to below) are arranged in a stack about the cam discs 27 so as to form a cam switch gang unit. The profiled switch shaft 25 is arranged so that it can be extended to cater for the numbers of switch compartment structures in the stack.

At the top, that is to say at the side remote from the indexing mechanism housing 23 containing the indexing mechanism 23a, there is arranged a closure plate 28, the dimensions and shape of which are matched to the cam switch gang units 26. The profiled switch shaft 25 extends beyond the closure plate 28 by a length X, so that an operating device, not shown in the drawing, can be coupled to the profiled switch shaft 25. The closure plate 28 and the cam switch gang units 26, as well as the indexing mechanism housing 23, are provided with diametrally arranged bores 29, which penetrate these parts in the axial direction of the ganged assembly. In the closure plate 28 these bores take the form of countersunk bores 29a. In addition the closure plate 28 is provided with tapped bores 30 in order that the ganged cam switch 21 may be mounted on a suitable mounting surface, for example, a wall panel 34 or a casing cover 35 as shown in Figure 1. At the lower end there is provided a support surface 33, which rests upon a frame 36 so as to support the switch. The surface of the closure plate 28, which is directed towards the individual cam switch gang units 26 (26a, 26b in Figure 3) is provided with bosses, of which only one, 28a, is visible in Figure 3. These bosses are directed coaxially and concentrically with respect to the axes of the respective bores 29 and each surround the bore 29 in the region of the closure plate 28. These bosses 28a are of hollow cylindrical form.

The individual cam switch gang units 26 are constructed as shown in Figure 4. As seen therein two switch compartment elements 32 are juxtaposed, of which the lefthand switch compartment element is shown open, and the right-hand one is only represented in outline with hatching. The lefthand switch compartment element 32 includes an explosion-proof switch compartment 42 into which are introduced the lead-through conductors 41 for fixed contact members 50. The lead-through conductors 41 are introduced into the explosion-proof switch compartment 42 in an explosion-proof manner. There are two fixed contact members 50, which can be bridged over by a bridge 44, which is actuated by means of a plunger 43. Upon the contact bridge 44 there are mounted movable contact members 44b, which co-operate with the fixed contact members 50. These movable contact members 44b co-operate by contacting the supports 51 of the fixed contact members 50. The movable contact bridge 44 is urged in the closing direction by means of two compression springs 45. The plunger 43 is brought out of the switch compartment 42 through the bore 55 in an explosion-proof manner. In the closed condition of the switch compartment it is sealed by a plate 52 shown in Figure 1, which is secured by a mass of cast resin 54. In this way a perfect seal is produced.

The switch compartment element 32 is provided with a hole 49 positioned laterally with respect to the switch compartment 42, said hole including an arcuate portion and a right angled portion. The centre of the arcuate portion, the apex of the right-angled portion and the central axis of the cam disc lie upon a common line. A hole of similar shape is also provided in the closure plate 28, the indexing mechanism housing 23, and, in the case where several switch compartment elements 32 are superimposed in the stack, a hole is likewise provided in the moulded plates 46, which are arranged between said elements, and which are also provided with moulded projections which mate with cavities in the switch compartment elements. Consequently, by introducing into the holes a similarly uniformly shaped moulded member, it is possible to locate the various individual members in congruent relationship, namely the particular switch compartment element 32, the appertaining moulded plate 46, the closure plate 28 and the indexing mechanism housing 23, whereby these members are correctly aligned with respect to the axis of symmetry of the cam discs 27 and of the profiled switch shaft 25, so that the functioning cycle of the cam discs 27 in each cam disc gang unit 26 is not adversely influenced. For holding the plate 52, having the function of covering the explosion-proof switch compartment 42, there is provided an annuiar rebate 53 surrounding the switch compartment, and having its side walls slightly undercut, so that the plate 52, which is provided with a peripheral lip (not shown in the drawing) can snap into this undercut portion and be retained therein.

As may further be seen in Figure 4, there are provided, symmetrically with respect to the axis of symmetry of the cam shaft, further cavities 57, through which pass the lead-through conductors 41, of which a terminal 41a shown at the top of the drawing takes the form of a spade lug, to which electrical leads can be clamped if desired.

The conductor lead-through terminal shown at the foot of the drawing is, by comparison, slightly modified. The conductors extend outwardly to form external terminals 39, 39a, 40, 40a and 61 (Figure 5). The cavities 57 extend parallel to the cam disc axis and to the profiled switch shaft and, in the finished and assembled ganged cam switch, form channels 59 serving to receive coupling members, not shown in the drawing, for coupling together the adjacent individual switch compartment elements 32. For the purpose of further reducing the weight of the assembly it is also possible to provide further holes in these elements, these holes being positioned at that side of the switch compartment 42, which is remote from the holes 49. The cavities 57 are formed with slots 58, which are open in the direction towards the other one of the two switch compartment elements 32.

The space occupied by the cam disc 27, indicated by the reference number 32a, is of semicircular shape in both the right hand and the left hand switch compartment elements, and the plunger 43 projects partly into this space. Also the external diameter of the space 32a is dimensioned to allow the cam disc 27 to have free clearance therein.

In Figure 1 there is shown an extension 32b in the form of a radial flange projecting into the space 32a, and having an aperture therein for the passage of the profiled switch shaft 25, and serving to define the axial height position of the cam disc of the particular switch compartment element 32.

The switch compartment element 32d shown in Figure 5 consists of an open member formed by die casting, injection moulding or casting, preferably of a duroplast.

Instead of using a mechanically operated switching mechanism according to the embodiment represented in Figure 4, it is possible to provide an electronic contactless switching device (see Figure 5). In this embodiment the external dimensions of the switch compartment element 32d are the same as those of the already described element 32, and again the hole 49 is similarly provided. On the other hand the two cavities 57 are not used in this instance. The switch compartment element 32d, which is completely integral is provided with an additional lead-through conductor, at the end of which is a connecting terminal 61. The switch compartment element 32d includes an explosion-proof space 62, which occupies almost the total area of said element 32d except for that region wherein the hole 49 is situated. The element 32d is furthermore bisected, in the region of its central axis, by the guide bore 63, in which a plunger 67 is urged outwardly by the pressure of a spring 68. The switch compartment element furthermore possesses blind bores 64 and grooves 65, which, when the switch gang units are superimposed, produce, together with the slots 58, the channels inside the ganged cam switch.

The contactless circuit arrangement within the switch compartment ele ment may, for example, be an arrangement which is mounted upon a printed circuit plate 66.

Thus in the component according to Figure 5, there may be a field plate or a Hall generator (not shown), and an operational amplifier 70c, the component being operated by means of a magnet 69 mounted upon the plunger 67.

Alternatively, the contactless circuit arrangement may be composed of semi-conductors and may be actuated by the magnet 69.

Obviously the magnet 69, instead of being mounted on the plunger 67, could be inte grated with the cam disc 27, in which case the plunger 67, the spring 68 and the corresponding bore 63, could be omitted. The entire contactless circuit arrangement is completely encased in cast resin in the explosion-proof space 62.

Figure 6 shows several interconnected contactless switch compartment elements 32d, which are interconnected in a suitable manner to a motor control device.

The individual switch compartment elements, of which as shown in Figure 5, two form a cam switch gang unit, are assembled to form a ganged cam switch, in the manner already shown in more detail in Figures 1 and 3. When the individual cam switch gang units are being assembled together, the relative alignment of the individual units is ensured by those surfaces of the switch compartment elements, which are directed transversely to the switch axis. Thus, the lowest one of the cam switch gang units is first of all mounted upon the indexing housing 23; thereafter the cam disc is inserted upon the profiled switch shaft and a moulded plate 46 is fitted, thereafter follows a further cam switch gang unit, and a further moulded plate, and so on, and finally the closure plate 28 is fitted. The stacking of the units can be more satisfactorily carried out by inserting suitably shaped moulded compartments into the holes 49. Then after stacking the switch compartment elements, the ganged cam switch is axially compressed by means of threaded bolts 31 (Figure 3), carrying washers 31b, and having at the other end a correspondingly threaded clamping component 31c in the form of a slotted, forked or triangular nut with a locking collar.

Furthermore there may be provided a further locking disc, which is not shown in the drawing, for example, a dished spring washer, in order to prevent accidental loosening of the bolts. For the purpose of preventing distortion of the switch compartment elements or of the cam switch gang units, and to extend the length of any creep paths, there is also inserted, into the bores 29 which are axially aligned with the boss 28a carried by the closure plate 28, a suitably extended spacing tube 47 (see Figure 3), this insertion being done before the mounting of the indexing mechanism 23 and the closure plate 28, one free end of the tube 47 abutting against the annular surface of the boss 28a and the other free end of the tube 47 projecting into the conical countersink 48 of the indexing mechanism housing 23. This conical countersink 48 serves to ensure the positive alignment of the indexing mechanism housing 23 with respect to the cam switch gang units, and also serves for the compensation of tolerances.

WHAT WE CLAIM IS: 1. An explosion-proof ganged switch comprising a plurality of switch units arranged in a stack, each such switch unit having at least two explosion-proof chambers disposed around the plane of a disc located externally of the two chambers and mounted on a switch shaft extending through the stack, each such chamber accommodating a switching device operable in response to rotation of the disc by the switch shaft.

2. A switch as claimed in Claim 1, wherein the stacked switch units comprise a plurality of juxtaposed structures and the two chambers of a switch unit are formed between two adjacent structures.

3. A switch as claimed in Claim 2, wherein a switch unit at one end of the stack comprises a structure nearest said one end of the stack and a juxtaposed closure plate structure which together form the two chambers of the switch unit at said one end therebetween.

4. A switch as claimed in Claim 3, wherein a switch unit at the other end of the stack comprises a structure nearest said other end of the stack and a juxtaposed wall of a housing of an indexing mechanism of the switch, which together form the two chambers of the switch unit at said other end therebetween.

5. A switch as claimed in any one of Claims 2 to 4, wherein the juxtaposed structures comprises symmetrical moulded parts, open on one side, with at least two recesses which are closed in an explosion-proof manner by a plate of a material which prevents or hinders arc formation, one outer surface of the plate being covered with mouldable material so as to be gap-free to prevent arcing.

6. A switch as claimed in Claim 5, wherein the plate of the arc-quenching material is provided with a peripheral sealing lip.

7. A switch as claimed in any preceding claim, wherein a switching device accommodated in a chamber is a contactless switching device, which is actuatable remotely through an electric or magnetic field by means of an element which is actuatable by the associated disc.

8. A switch as claimed in Claim 7, wherein the contactless switching device is composed of semi-conductors and can be actuated magnetically.

9. A switch as claimed in Claim 7, wherein the contactless switching device comprises an amplifier with a field plate or Hall generator.

10. A switch according to Claim 7, wherein the contactless switching device is actuatable by a magnet carried on the disc or on a plunger operable by the disc.

11. A switch as claimed in any one of the Claims 1 to 6, wherein the switching device comprises two co-operating switch contacts

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. grated with the cam disc 27, in which case the plunger 67, the spring 68 and the corresponding bore 63, could be omitted. The entire contactless circuit arrangement is completely encased in cast resin in the explosion-proof space 62. Figure 6 shows several interconnected contactless switch compartment elements 32d, which are interconnected in a suitable manner to a motor control device. The individual switch compartment elements, of which as shown in Figure 5, two form a cam switch gang unit, are assembled to form a ganged cam switch, in the manner already shown in more detail in Figures 1 and 3. When the individual cam switch gang units are being assembled together, the relative alignment of the individual units is ensured by those surfaces of the switch compartment elements, which are directed transversely to the switch axis. Thus, the lowest one of the cam switch gang units is first of all mounted upon the indexing housing 23; thereafter the cam disc is inserted upon the profiled switch shaft and a moulded plate 46 is fitted, thereafter follows a further cam switch gang unit, and a further moulded plate, and so on, and finally the closure plate 28 is fitted. The stacking of the units can be more satisfactorily carried out by inserting suitably shaped moulded compartments into the holes 49. Then after stacking the switch compartment elements, the ganged cam switch is axially compressed by means of threaded bolts 31 (Figure 3), carrying washers 31b, and having at the other end a correspondingly threaded clamping component 31c in the form of a slotted, forked or triangular nut with a locking collar. Furthermore there may be provided a further locking disc, which is not shown in the drawing, for example, a dished spring washer, in order to prevent accidental loosening of the bolts. For the purpose of preventing distortion of the switch compartment elements or of the cam switch gang units, and to extend the length of any creep paths, there is also inserted, into the bores 29 which are axially aligned with the boss 28a carried by the closure plate 28, a suitably extended spacing tube 47 (see Figure 3), this insertion being done before the mounting of the indexing mechanism 23 and the closure plate 28, one free end of the tube 47 abutting against the annular surface of the boss 28a and the other free end of the tube 47 projecting into the conical countersink 48 of the indexing mechanism housing 23. This conical countersink 48 serves to ensure the positive alignment of the indexing mechanism housing 23 with respect to the cam switch gang units, and also serves for the compensation of tolerances. WHAT WE CLAIM IS:

1. An explosion-proof ganged switch comprising a plurality of switch units arranged in a stack, each such switch unit having at least two explosion-proof chambers disposed around the plane of a disc located externally of the two chambers and mounted on a switch shaft extending through the stack, each such chamber accommodating a switching device operable in response to rotation of the disc by the switch shaft.

operable by a plunger which extends out of the chamber and is engageable by the associated disc.

12. A switch as claimed in any preceding claim, wherein a switching device is provided with at least two electrical conductors which are led out of the chamber in an explosion-proof manner.

13. A switch as claimed in Claim 12, wherein the conductors are provided with extensions which project into recesses in the switch units in such a manner that when the switch units are stacked the conductor extensions can be interconnected in by means of suitably designed contact bridges.

14. A switch as claimed in Claim 12 or Claim 13, wherein conductors are arranged in mutually staggered formation.

15. A switch as claimed in any preceding claim, wherein the switch units are held together in a stack by at least two securing elements penetrating said units and diametrally placed with respect thereto.

16. A switch as claimed in any preceding claim, wherein the switch units are located in the stack by means of at least one hollow cylindrical fitting element which extends through the switch units in a direction normal thereto.

17. A switch as claimed in any preceding claim, wherein the switch units are provided with means for preventing inadvertent misalignment of the switch units, said means being moulded to correspond in adjacently situated switch units.

18. A switch as claimed in any preceding claim, wherein the switch shaft can be extended to cater for the number of switch units in the stack.

19. A switch as claimed in any preceding claim, in that each switch unit is provided with means serving to secure the stacked switch units to a support.

20. An explosion-proof ganged switch constructed and arranged to operate substantially as hereinbefore described with reference to the accompanying drawings.