GB1585437A - Index mechanism for rotary electric switch - Google Patents

Description

(54) INDEX MECHANISM FOR ROTARY ELECTRIC SWITCH (71) We, LUCAS INDUSTRIES LIMITED, a British Company, of Great King Street, Birmingham B 19 2XF, 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 index mechanism for a rotary electric switch. One known form of such an index mechanism includes an index plate which is formed around its peripheral edge with a plurality of spaced depressions, the mechanism also including at least one spring-loaded plunger which is movable towards and away from the index plate and which is arranged, when said plate is turned to a predetermined angular position, to engage one of said depressions and thereby releasably retain the index plate in the selected position. Constructions are known (see for example British Patent 1,092,972) in which the or each plunger comprises a ball which may be mounted in a recess or aperture in a housing or in a tubular guide and the spring which acts on such a plunger may comprise a leaf spring which may be located at its ends in notches or recesses formed in lugs or ears provided on a stationary plate. If, in fact, only one ball is used in such a construction (as is described for example in British Patents 747,109 and 970,025), a sideways pressure will be exerted on the index plate and on the shaft or other component on which the index plate may be mounted. Misalignment of said shaft or other component and uneven wear on associated bearings may then occur. Furthermore, if only one plunger and one spring is used, failure of the one spring will result in failure of the mechanism. In addition, the use of a leaf spring will increase the total thickness of the mechanism as measured in a direction along the rotational axis of the index plate.

The aforementioned undesirable unbalanced sideways pressure on the index plate can of course be avoided by using (as is known) a plurality of equi-angularly spaced plungers which are each loaded by a leaf spring (as is shown in British Patent 1,092,972) but this known construction still has the disadvantage of having its overall axial thickness governed by or increased by the width of the leaf springs. In addition the assembly of such a construction is likely to be time-consuming and expensive. The cost of assembly may be reduced by adopting another known construction in which a single spring band encircles all the balls or plungers (as is shown in British Patent 570,579) but this construction suffers from the aforementioned disadvantage that failure of the one and only spring will result in failure of the mechanism.

In another known construction (see for example British Patents 728,214 and 870,672) the recesses or depressions in the index plate, instead of being formed around the peripheral edge, are formed in one face of the plate and are arranged in a circular configuration therein, the plunger or plungers being spring loaded towards said face of the index plate so that it or they is or are movable in directions parallel to the rotational axis of the index plate. With such a construction, the various parts of the assembly, including the spring or springs for loading the plunger or plungers, are conveniently located axially on an index plate shaft by means of circlips or collars or similar components but such a construction makes it extremely difficult to maintain accurately a pre-determined spring pressure on the plunger or plungers because ordinary manufacturing tolerances may result in the spring or springs being disposed either somewhat nearer to or farther from the associated plunger or plungers than is intended. Alternatively, some arrangement has to be provided for adjustment of the axial position of the spring or springs and this is expensive both from the manufacturing and assembly points of view.

In other known index mechanisms (as is described for example in British Patent 745,387) there is provided a driving element and a driven element and one of such elements has a plurality of recesses which are arranged to co-operate with one or more spring-loaded plungers as before. Such a construction is however relatively expensive in that the driving and driven elements have to be separately manufactured and then assembled together.

In yet another known index mechanism (as is described for example in U.S. Patent 2,153,430) there is an index plate having a plurality of peripheral depressions but separately formed plungers are dispensed with and the or each leaf spring is shaped intermediate its ends to form an integral curved projection which in effect acts in the manner of a plunger adopted to co-act with the depressions of the index plate. The formation of such a projection necessarily increases the overall length of the spring and this in turn tends to reduce the power of the spring. It is not practicable to increase the thickness of the spring material (because of the need to form the aforementioned curved projection intermediate the ends of the spring) and accordingly the width of the spring material (especially in the middle of the spring) is usually increased. This of course leads to the previously mentioned disadvantage of increasing the overall thickness (as measured in an axial direction) of the index mechanism as a whole. Furthermore the specially-shaped spring is very difficult to make because of the varying form and stresses produced during the shaping of this form tend to cause early failure of the spring.

The object of the present invention is therefore to provide an improved index mechanism which avoids all the abovementioned disadvantages.

In accordance with the invention, there is provided an index mechanism for a rotary electric switch, said mechanism comprising a rotatable index plate which is formed around its peripheral edge with a plurality of depressions, together with a housing in which is mounted a pair of opposed plungers, each of said plungers being arranged so that it is slidably mounted for movement towards and away from the rotational axis of said index plate and so that its inner end is engageable with said peripheral edge of the index plate, there being also provided in association with each plunger a length of resilient wire of substantially circular cross-section which is located at its ends in said housing and which engages intermediate its ends the outer end of the associated plunger.

Preferably, each plunger is located in a channel in the housing to guide its movement towards and away from the index plate and the outer end of each plunger is formed with a groove which locates the associated resilient wire. Furthermore the housing may be formed on one face with a pair of oppositely disposed arcuate recesses which respectively receive said resilient wires and the same face of said housing may also be formed with a centrally disposed circular recess which is adapted to receive said index plate.

Desirably, in index mechanism in accordance with the invention is also provided with adjustable stop means for adjustably limiting the angular movement of said index plate about its rotational axis. Such stop means may be arranged to be adjustable from that side of the index mechanism which in use will be presented towards the user of the mechanism and in such a case the adjustment may be made by the user. Alternatively, the stop means may be arranged to be adjustable from that side of the index mechanism which in use will be remote from the user in which case the adjustment will be pre-set by the manufacturer or assembler of the mechanism.

In each of the above-mentioned alternative arrangements, the stop means may include a fixed stop which projects outwardly from the base of the circular recess in said housing which receives the index plate, said fixed stop being adapted to co-operate with a projection formed on the adjacent face of said index plate. In the case where the stop means is adjustable from that side of the index mechanism which is presented towards the user, said stop means further comprises a stop ring having on one side an axially extending projection which can be arranged to project through any one of a series of spaced holes formed in the housing so as to form an additional stop which projects into the aforementioned recess receiving the index plate, said additional stop being also engageable with the projection formed on said index plate.

In the alternative case where the stop means is intended to be adjustable from the rear side of the index mechanism, namely that side which will be remote from the user, said stop means further comprises a stop ring which is mounted at said rearside of the index mechanism, said stop ring being adapted to be secured to said housing in any one of a plurality of relative angular positions and having a projection which projects towards said index plate so as to be engageable with a further projection formed on the index plate. In this case therefore said first mentioned projection and said further projection of the index plate will be respectively disposed on opposite faces thereof.

The invention will now be more particularly described with reference to the accompanying drawings wherein Figure 1 is an elevation of part of one example of an index mechanism for a rotary electric switch constructed in accordance with the present invention, Figure 2 is a section taken on the line 2-2 of Figure 1, Figure 3 is an "exploded" perspective view of the mechanism seen in Figures 1 and 2 but showing in particular one form of stop means that can be used to limit the angular movement of the index plate of the mechanism, and Figure 4 is a further "exploded" perspective view of the index mechanism but including now an alternative form of stop means for limiting the angular movement of the index plate.

Referring firstly to Figures land 2, tEe index mechanism shown therein is intended for use with a rotary electric switch {not shown) but which may be of anyconven- tional form, the combined assembly then being adapted to control a cycle of operations that may for example be required in a domestic appliance.

The index mechanism itself includes an index plate 10 which is conveniently moulded from a synthetic resin material and which is formed around its peripheral edge with a plurality of spaced depressions 11.

The plate 10 has a central aperture 12 which is of non-circular configuration and is adapted to be mounted on a shaft which is formed in part to a cross-sectional configuration corresponding to the shape of said aperture 12 whereby rotation of said shaft will result in angular movement of the index plate 10. Furthermore said index plate 10 has moulded therein a pair of projections 13 and 14 which project respectively from the opposite faces of the plate, each of said projections being moulded so that its radially inner end and its radially outer end are respectively integrally connected to two annuli of material so as thereby to increase the strength of the projections.

There is also provided a housing 14a which may also be formed in a synthetic resin material and which on one face is formed with a centrally arranged circular recess, indicated by reference numeral 15, in which said index plate 10 is located. Said housing 14a is also formed with a central circular aperture 16 through which in use will extend a part of said shaft which is of circular cross-section.

Associated with the aforementioned index plate 10 is a pair of plungers 17 and 18 which are mounted in said housing 14 so as to be slidable therein in directions towards and away from the rotational axis of said index plate 10. The housing 14 is also formed with a pair of oppositely disposed arcuate recesses 19 and 20 which are so formed that ribs 21 and 22 will be formed between said central recess 15 and said arcuate recesses 20 and 19 respectively. In said ribs 21 and 22 are formed passages 23 and 24 which, together with channels 23a and 24a, form guides for said plungers 17 and 18. The inner ends of said plungers 17 and 18 are shaped to a rounded or chamfered configuration and said inner ends are adapted to engage the peripheral edge of the index plate 10 whereby said index plate can be releasably retained in a predetermined angular position when said inner ends of the plunger 17 and 18 respectively engage a pair of oppositely disposed depressions 11 ofthe index plate 10.

The outer ends of said plungers 17 and 18 are each formed with a slot 25 or 26 (which preferably extends to a distance approximately half-way down the plunger) having side walls which may be of parallel or inwardly converging configuration and through this slot extends a length of resilient wire 27 or 28. Each resilient wire 27 or 28 is of substantially circular configuration in cross-section and is curved or bowed along its length, the two ends of each spring engaging the outer walls of the opposite ends of an arcuate recess 19 or 20. Said opposite ends of each arcuate recess 19 or 20 are each shaped to provide a spring-engaging edge which is formed by the intersection of a pair of planar wall portions 19a and l9b or 20a and 20b having an included angle lying within the range 90"--170". Thus a portion of each spring 27 or 28 intermediate its ends extends through the slot 25 or 26 formed in the associated plunger and the arrangement is such that each plunger will be spring loaded by its spring in a radially inward direction so that when said index plate 10 is turned to a position in which a pair of opposite depressions 11 are aligned with the inner ends of said plungers 17 and 18 then said plungers will move inwardly into said depressions under the influence of their springs and thereby releasably retain said index plate. Nevertheless said plate can be moved to a new angular position if desired and the initial movement of the index plate towards its new position will result in said plungers 17 and 18 being pushed radially outwardly against the pressures exerted by said springs 27 and 28. Furthermore, with the plungers 17 and 18 assembled to the housing and engaging the bottoms of said guide channels 23a and 24a, there is a clearance of approximately .008" between each resilient wire 27 or 28 and the bottom of the associated recess 19 or 20. This helps to stabilise the wires 27 and 28 and precludes the necessity of having to hold their ends by additional retention means.

The housing is also formed with a pair of oppositely disposed threaded apertures 29 and 30 which are adapted to receive screws (not shown) whereby a cover plate 31 (see Figure 2) can be attached to the mechanism, Figure 1 being shown with said cover plate removed. The inner face of said cover plate 31, together with said passages 23 and 24 formed in the ribs 21 and 22, and the sides and bottoms of the channels 23a and 24a, all locate and constrain the plungers 17 and 18.

The above described construction forms an extremely neat and compact assembly in which the index plate 10, the plungers 17 and 18, and their associated springs 27 and 28 are all located in recesses formed in one face of said housing 14a. The springs themselves are, as previously mentioned, formed from lengths of spring wire of circular crosssection and thus the thickness of said springs, plungers, and index plate (as measured in a direction along the rotational axis of the index plate) is very much less than has hitherto been attainable. This presents an attractive advantage in that the index assembly will have a very neat appearance and of course would require less space in the domestic appliance of other apparatus in which it is intended to be used.

Said housing 1 4a is provided on one side with a projecting externally threaded boss 32 which is used in mounting the index mechanism in its required position and the base of said recess 15 is also provided with an outwardly directed projection 33 forming part of stop means which will now be described.

Thus referring to Figure 3 there is shown therein adjustable stop means for limiting the angular movement of the index plate 10 to prevent it from being rotated through one or more complete turns, and in the construction shown in Figure 3 said stop means is adjustable from that side of the mechanism which in use will be remote from the user so that the setting of the stop means will be effected by the manufacturer or assembler of the mechanism. Thus the aforesaid projection 33 (which is conveniently of generally rectangular form) formed in the base of the recess 15 of the housing 14a forms a fixed stop which can engage in use in one angular position of the index plate 10 with the projection 13 formed on one face thereof.

The further projection 14 formed on the opposite face of said index plate 10 is adapted to engage with an adjustable stop 34 formed on one side of a stop ring 35. Said ring is formed around its periphery with a plurality of notches 36 and said stop ring 35 can be set in any one of a plurality of angular positions by arranging that screws extending through said threaded apertures 29 and 30 project into any selected opposed pair of notches 36. Said stop ring 35 has a central aperture of circular configuration forming a clearance with respect to the shaft 37 as seen in Figure 3 so that said stop ring will remain stationary after it has been set in position.

Thus in one direction of angular movement of the index plate 10 the projection 13 of the index plate will engage the fixed projection 33 whereas in the other angular direction of rotation the projection 14 of the index plate 10 will engage the adjustable stop formed by the projection 34 of the stop ring 35.

In the alternative form of stop means shown in Figure 4, adjustment can be effected from that side of the mechanism which is presented to the user and in this case although said index plate 10 can be formed as above described so that it has two projections 13 and 14 disposed on opposite faces of the plate only one of said projections namely projection 13 will actually be utilized. Thus movement of the index plate 10 in one angular direction will be limited by engagement of said index plate projection 13 and said housing projection 33 as above described. Angular movement in the opposite direction will be limited on the other hand by engagement of said index plate projection 13 with a further projection 38 which extends axially from a stop ring 39. The housing 14a is formed with a plurality of angularly spaced apertures 40 which each extend through the housing into the aforesaid recess 15 and the arrangement is such that said stop ring 39 can be passed over said threaded boss 32 and into an annular recess 41 formed in the housing so that the projection or stop 38 projects through one of said apertures 40 into the recess 15 and is there engageable by said index plate projection 13 as previously mentioned. After said stop ring 39 has been set in the desired position the aforesaid annular recess 41 is closed by a rubber seal 42 which will prevent ingress of dirt into the index mechanism and which will also serve to hold said stop ring 39 in position whenever the coacting nut is not assembled to the threaded boss 32. Said housing 14a is also formed with a projecting lug 43 which in use will be engaged with a co-acting recess or aperture in a mounting plate (not shown) to prevent rotation of the housing.

Thus in either of the constructions shown in Figures 3 and 4 the shaft 37 will rotate within the interior of the threaded boss 32, the housing 14a of course remaining stationary, whilst the index plate 10 which is carried by the non-circular part of the shaft will be turned as the shaft itself is turned and similarly said shaft will be attached to a rotatable part of the rotary switch itself so that said part of the switch will turn with the index plate.

As above described the index plate 10, the housing 14a and the shaft are all formed in a synthetic resin material (such as a glass-filled nylon-say 20Y e 30% glassr a glassfilled thermoplastic) but in an alternative construction they can be each made as diecastings. Moreover, if diecasting or if synthetic resin materials are used, the shaft and index plate may be integral with each other.

Also a combination of materials may be used, such as, for example, a die-cast housing, a steel shaft and a synthetic resin index plate but ideally the use of a similar material for at least the housing and the index plate will enhance the durability of the mechanism because the co-acting stops of the housing and the index plate will then be of similar material and will therefore not abrade each other. Thus, the housing and the index plate may both be formed of a synthetic resin such as Acetal (R.T.M.); or they may both be formed of a die-cast material; or they may both be formed of a glass-filled nylon. In all cases however the plungers are desirably formed of a homogeneous synthetic resin such as Acetal (R.T.M.).

As an alternative to the use of plungers 17 and 18 as above-described, synthetic resin carriers may be provided which are similarly guided in channels formed in the housing 14a. Each carrier is formed at its inner end with a hemi-spherical depression for locating a ball bearing which is engageable with the index plate, and is formed at its outer end with a slot for locating the associated wire spring.

WHAT WE CLAIM IS: 1. An index mechanism for a rotary electric switch, said mechanism comprising a rotatable index plate which is formed around its peripheral edge with a plurality of depressions, together with a housing in which is mounted a pair of opposed plungers, each of said plungers being arranged so that it is slidably mounted for movement towards and away from the rotational axis of said index plate and so that its inner end is engageable with said peripheral edge of the index plate, there being also provided in association with each plunger a length of resilient wire of substantially circular cross-section which is located at its ends in said housing and which engages intermediate its ends the outer end of the associated plunger.

2. An index mechanism as claimed in Claim 1 wherein each of said plungers is located and guided by a channel formed in said housing.

3. An index mechanism as claimed in either of the preceding claims wherein each plunger is formed in its outer end with a slot through which the associated length of resilient wire extends.

4. An index mechanism as claimed in any one of the preceding claims wherein the inner end of each plunger is shaped to receive and locate a separately formed ball which is arranged to engage the periphery of said index plate.

5. An index mechanism as claimed in any one of the preceding claims wherein the mechanism is provided with adjustable stop means for adjustably limiting the angular movement of said index plate about its rotational axis.

6. An index mechanism as claimed in Claim 5 wherein said stop means is arranged to be adjustable from that side of the mechanism which in use will be presented towards the user of the mechanism.

7. An index mechanism as claimed in Claim 5 wherein said stop means is arranged to be adjustable from that side of the mechanism which in use will be remote from the user of the mechanism.

8. An index mechanism as claimed in any one of Claims 5-7 wherein said adjustable stop means embodies radially extending stops which are formed on said index wheel, each of said stops being integrally connected at its radially inner and outer ends respectively to two annuli of material.

9. An index mechanism as claimed in Claim 6 wherein the adjustable stop means embodies a stop ring having a projection extending axially from one face thereof, said housing being formed on that side which in use will be presented to the user of the mechanism with a plurality of angularly spaced apertures so that said stop ring can be angularly adjusted by the user to a position in which said stop ring projection projects through a selected one of said angularly spaced apertures and forms a stop inside the housing.

10. An index mechanism as claimed in Claim 9 wherein there is provided an annular seal which is formed of resilient material and which is assembled to the in situ exterior face of the stop ring after the latter has been set in the desired position.

11. An index mechanism as claimed in any one of the preceding claims wherein said housing is formed on one face with a pair of arcuate recesses which respectively receive said resilient wires and also with a centrally disposed circular recess which receives said index plate.

12. An index mechanism as claimed in any one of the preceding claims wherein said index plate and said housing are each formed from a synthetic resin material.

13. An index mechanism as claimed in any one of Claims 1--12 wherein said index plate and said housing are each formed as a diecasting.

14. An index mechanism as claimed in any one of the preceding claims wherein the index plate and the shaft are made integral with each other.

15. An index mechanism as claimed in Claim 11 wherein each of said arcuate recesses is shaped at each end to provide a resilient wire-engaging edge formed by the intersection of two planar wall portions having an included angle lying within the range of 90"--170".

16. An index mechanism for a rotary electric switch, said mechanism being substantially as hereinbefore described with reference to and as shown in Figures 1 and 2, or Figure 3, or Figure 4 of the accompanying drawings.

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

Claims (16)

**WARNING** start of CLMS field may overlap end of DESC **. other. Thus, the housing and the index plate may both be formed of a synthetic resin such as Acetal (R.T.M.); or they may both be formed of a die-cast material; or they may both be formed of a glass-filled nylon. In all cases however the plungers are desirably formed of a homogeneous synthetic resin such as Acetal (R.T.M.). As an alternative to the use of plungers 17 and 18 as above-described, synthetic resin carriers may be provided which are similarly guided in channels formed in the housing 14a. Each carrier is formed at its inner end with a hemi-spherical depression for locating a ball bearing which is engageable with the index plate, and is formed at its outer end with a slot for locating the associated wire spring. WHAT WE CLAIM IS:

1. An index mechanism for a rotary electric switch, said mechanism comprising a rotatable index plate which is formed around its peripheral edge with a plurality of depressions, together with a housing in which is mounted a pair of opposed plungers, each of said plungers being arranged so that it is slidably mounted for movement towards and away from the rotational axis of said index plate and so that its inner end is engageable with said peripheral edge of the index plate, there being also provided in association with each plunger a length of resilient wire of substantially circular cross-section which is located at its ends in said housing and which engages intermediate its ends the outer end of the associated plunger.

2. An index mechanism as claimed in Claim 1 wherein each of said plungers is located and guided by a channel formed in said housing.

3. An index mechanism as claimed in either of the preceding claims wherein each plunger is formed in its outer end with a slot through which the associated length of resilient wire extends.

4. An index mechanism as claimed in any one of the preceding claims wherein the inner end of each plunger is shaped to receive and locate a separately formed ball which is arranged to engage the periphery of said index plate.

5. An index mechanism as claimed in any one of the preceding claims wherein the mechanism is provided with adjustable stop means for adjustably limiting the angular movement of said index plate about its rotational axis.

6. An index mechanism as claimed in Claim 5 wherein said stop means is arranged to be adjustable from that side of the mechanism which in use will be presented towards the user of the mechanism.

7. An index mechanism as claimed in Claim 5 wherein said stop means is arranged to be adjustable from that side of the mechanism which in use will be remote from the user of the mechanism.

8. An index mechanism as claimed in any one of Claims 5-7 wherein said adjustable stop means embodies radially extending stops which are formed on said index wheel, each of said stops being integrally connected at its radially inner and outer ends respectively to two annuli of material.

9. An index mechanism as claimed in Claim 6 wherein the adjustable stop means embodies a stop ring having a projection extending axially from one face thereof, said housing being formed on that side which in use will be presented to the user of the mechanism with a plurality of angularly spaced apertures so that said stop ring can be angularly adjusted by the user to a position in which said stop ring projection projects through a selected one of said angularly spaced apertures and forms a stop inside the housing.

10. An index mechanism as claimed in Claim 9 wherein there is provided an annular seal which is formed of resilient material and which is assembled to the in situ exterior face of the stop ring after the latter has been set in the desired position.

11. An index mechanism as claimed in any one of the preceding claims wherein said housing is formed on one face with a pair of arcuate recesses which respectively receive said resilient wires and also with a centrally disposed circular recess which receives said index plate.

12. An index mechanism as claimed in any one of the preceding claims wherein said index plate and said housing are each formed from a synthetic resin material.

13. An index mechanism as claimed in any one of Claims 1--12 wherein said index plate and said housing are each formed as a diecasting.

14. An index mechanism as claimed in any one of the preceding claims wherein the index plate and the shaft are made integral with each other.

15. An index mechanism as claimed in Claim 11 wherein each of said arcuate recesses is shaped at each end to provide a resilient wire-engaging edge formed by the intersection of two planar wall portions having an included angle lying within the range of 90"--170".

16. An index mechanism for a rotary electric switch, said mechanism being substantially as hereinbefore described with reference to and as shown in Figures 1 and 2, or Figure 3, or Figure 4 of the accompanying drawings.