Electric switch with sliding bridging contact

In an electric switch a good gliding behavior between a bridging contact and metal conductors punched out from a sheet metal blank is achieved. For this purpose the metal conductors have at least one projection extending at least over the entire range of motion of the bridging contact.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an electric switch. 
2. State of the Art 
In customary switches of this kind the metal conductors are formed as 
planar surface segments of a sheet metal blank cut out by punching from 
the originally complete sheet metal. The metal conductors are at first 
still connected with one another by connecting webs so that the sheet 
metal blank can be embedded as a whole in a base plate of insulating 
material and, in the injection molding process of the base plate, the base 
plate is partially injection molded around the metal conductors. The 
connecting webs between the metal conductors are afterwards cleared away 
by purposefully drilling through the base plate and the connecting webs. 
One or more bridging contacts are positioned in a guiding and actuating 
device by means of which they can be moved along the associated metal 
conductors. Thereby the bridging contacts rest against the metal 
conductors under the effect of pressure springs. 
In dependence on the desired switching operations two of the metal 
conductors extending in parallel to each other and over which a bridging 
contact is jointly moved are either interrupted both or only one in 
particular places, so that, with precision, two or more metal conductors 
partially having different lengths are located behind one another. In the 
transitional places between two of these metal conductors located one 
behind the other either the space between them is filled with insulating 
material of the base plate up to the level of the metal conductors or 
there is a gap between them. 
The bridging contacts are mostly punched out from sheet metal blanks. 
Sometimes they are additionally bent. If considerable production 
tolerances appear on the guiding and operating device for the bridging 
contact and/or on the base plate including the metal conductors generally 
produced as injection molded parts, for example, the surface of the base 
plate reaches the same level as the surface of one of the metal conductors 
or is even slightly higher so that the electric switching properties of 
such a switch are heavily impaired. When in a transitional plate the space 
between the metal conductors is filled with insulating material, the 
bridging contact can more easily glide over the transitional place. 
However, then it is a risk that in the process of injection molding around 
the metal conductors insulating material may be brought onto the metal 
conductor causing difficulties in making contact later on, for example, a 
delayed switch contact or a premature interruption of the contact. If, in 
the transitional places of the metal conductors, a gap is formed by an 
appropriate molding, undesired insulating material will not impede the 
making of contact. However, the risk of a deteriorated gliding behavior of 
the bridging contact may come into existence and the course of motion in 
the transitional places may be more or less impeded. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to develop a switch in such a way 
that its electric switching properties are improved at low cost. This 
problem is solved in one embodiment of the present invention in which the 
metal conductors have at least one projection extending over the entire 
area of motion of the bridging contact with the only exception of the 
transitional places between two metal conductors located one behind the 
other. The bridging contact exclusively rests against the projection of 
the metal conductors assigned to one another. This results in a clearly 
defined contact surface between the contact elements co-operating in 
pairs. This also results in constantly reliable switching properties to a 
far-reaching extent independent of possible production tolerances of the 
metal parts and the plastic parts receiving them. 
When the switch is developed with the projections formed as a bulge of the 
sheet metal blank, the projections can be made very simply at very 
favorable costs. 
When the switch is developed according to another embodiment in which the 
transitional place of the two metal conductors are positioned one behind 
the other, the transition of the bridging contact is considerably 
facilitated and the bridging contact is prevented from getting caught. 
When the switch is developed according to yet another embodiment, it is 
achieved that in a transitional place the bridging contact is moved from 
one metal conductor to that behind it without changing its height and, 
thus, also without mechanical interruption or disturbance of the course of 
motion. 
In a construction of the switch according to another embodiment, it is 
achieved that during the longitudinal movement of the bridging contact on 
its associated metal conductors the contact point between the bridging 
contact and the projection on each one of the two metal conductors on the 
bridging contact continuously changes its position. Thus, sticking of the 
projection of the metal conductor to the surfaces of the bridging contact 
against which they rest is avoided. This increases the service life of the 
bridging contact and prevents difficulties in making contact caused by 
contact wear. 
In a development of the switch in which the bridging contact is formed by a 
folded sheet metal blank, the bridging contact gets a cylindrically shaped 
bearing and a contact surface without burrs which is in both directions of 
motion effective as a skid. Thereby the gliding behavior of the bridging 
contact on the metal conductors and on the transitional places is 
considerably improved and, in addition, troubles with respect to the 
course of motion are reduced, especially in the transitional places. All 
this is achieved in a very favorable manner as far as costs are concerned. 
By another design of the switch it is also made possible to arrange 
detents in pairs extending in opposite directions in the vicinity of both 
front sides of the bridging contact. This results in a symmetrical 
mounting of the bridging contact in the guiding and operating device 
thereby avoiding the bridging contact from being brought into a slanting 
position or from being tilted. A bridging contact of this kind is also 
advantageously used independently of the features of the other embodiments 
of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The switch 20 of the embodiment to be seen from FIGS. 1 to 3 includes a 
housing 21 formed by a bottom 22, a top 23 and a cover 24. An operating 
knob 25 is arranged on the cover 24. 
The bottom 22 is made by injection molding from a thermoplastic material 
having good electric insulating properties. The bottom 22 comprises a base 
plate 26, in the upper side 27 of which are embedded two sheet metal 
blanks 28 and 29 with various metal conductors (FIG. 3) and the associated 
connecting lugs 31 and 32 (FIG. 1). The connecting lugs 31 and 32 project 
vertically downwards from the underside 33 of the base plate 26 and are 
aligned in two rows. 
Five longitudinal walls 34 to 38 and two transverse walls 39 and 40 are 
arranged on the upper side 27 of the base plate 26. The five longitudinal 
walls 34 to 38 are arranged with a particular spacing in parallel to one 
another and with their two ends adjoining the transverse walls 39 and 40. 
Thus, the two outer longitudinal walls 34 and 38 form together with the 
transverse walls 39 and 40 a closed enveloping wall of the bottom 22. 
The two longitudinal walls 35 and 36 as well as the two longitudinal walls 
37 and 38 are spaced from one another with the same clear spacing. 
Together with the associated portion of the transverse walls 39 and 40 
they each border a chamber 41 or 42. Therein a slide 43 or 44 is 
accommodated, which slide 43 or 44 is shorter than the associated chamber 
41 or 42. The internal width of the chamber 41 and 42 and the width of the 
slides 43 and 44 are adapted to one another in such a way that the slides 
43 and 44 are linearly guided in the chambers 41 and 42, respectively. 
The slides 43 and 44 are developed in the same way. Each of the slides 43 
and 44 has three recesses which are transversely aligned to its direction 
of displacement. The recesses are open in a downward direction, that is, 
towards the base plate 26, and at least partially closed in the upward 
direction. In accordance with the requirements of the circuit diagram, a 
bridging contact is inserted into one or each of several of the recesses. 
With regard to the slide 43, there are the two bridging contacts 45 and 
46. With regard to the slide 44, there are the two bridging contacts 47 
and 48. The bridging contacts are each pressed downwards by a helical 
compression spring 49, which is supported at the cover 24 of the slide. 
The longitudinal walls 35 and 36 as well as walls 37 and 38 assigned to 
each other in pairs and the base plate 26 together form part of a guiding 
and operating device 50 for the slides 43 and 44 and the bridging contacts 
arranged thereon. The chambers of the bottom part, in particular, the 
chambers 41 and 42 for the slides 43 or 44, respectively, are covered by 
the top part having a bottom 51, the underside of which is at least smooth 
and planar in the area of the chambers 41 and 42. Thus, the bottom 51 of 
the top part 23 forms another component part of the guiding and operating 
device 50. It prevents the slides 43 and 44 from giving way in an upward 
direction due to the reaction force of the helical compression springs 49. 
In the area of the base of the two chambers 41 and 42, the bottom 51 is 
provided with a longitudinal slot of a particular width. Through this slot 
extends an operating rib 52 or 53 each firmly connected with the slide 43 
or 44 and, in general, integrally formed onto it. The operating ribs 52 
and 53 are provided with a rack profile 54 or 55, respectively, on the 
sides facing each other. This rack profile engages a pinion 56 which is 
rotatably mounted by means of a vertically aligned bearing pin 57. The 
bearing pin 57 is integrally formed onto the upper part 23. The hub 58 of 
the pinion 56 extends through an opening 59 in the cover 24. The operating 
knob 25 is connected with the hub 58 in a manner protected against 
twisting. 
The two sheet metal blanks 28 and 29 connected with the base plate 26 (FIG. 
3) include two portions 61 and 62 or 63 and 64, respectively, which 
relative to the center plane of the slides 43 or 44 are arranged beside 
each other. Alongside the center line of each blank portion the sheet 
metal blank is provided with a projection each having the shape of a bulge 
as is illustrated in FIG. 4 for the blank portion 61 by the projection 65. 
In the same manner the blank portion 62 is provided with the projection 
66, the blank portion 63 with the projection 67 and the blank portion 64 
with the projection 68. Against these projections rest the bridging 
contacts in the slides 43 and 44, so that an exactly defined contact point 
is reached. In addition, each projection may be formed as a metal coating 
on the sheet metal blank. 
In accordance with the requirements of the circuit diagram for the switch 
20, the two blank portions 61 and 62 as well as the blank portions 63 and 
64 assigned to each other are either partially connected or separated from 
each other by means of longitudinally extending punchings 69, 71 or 72. 
The blank portions 61 to 64 are divided into individual portions of 
different lengths by means of transversely extending punchings each 
adjoining one of the longitudinally extending punchings 69, 71 or 72. 
These longitudinal portions form the metal conductors 81 to 86 in the area 
of the sheet metal blank 28 and the metal conductors 87 to 90 in the area 
of the sheet metal blank 29. 
In order to facilitate the insertion of the sheet metal blanks 28 and 29 in 
the mold in the production process of the bottom part 22 and in the 
process of injection molding therearound, the connecting lugs 31 or 32 are 
arranged in the inside rim of the sheet metal blanks 28 and 29, which 
connecting lugs in the longitudinal direction of the adjacent metal 
conductors are at first connected to one another by means of a web 91 to 
retain a proper arrangement and alignment of the various metal conductors. 
These webs 91 are later on removed by a bore 92 each indicated by 
dash-dotted lines in FIG. 3. In a similar way webs also exist in other 
plates of the sheet metal blanks which are later also removed by a bore. 
In the transitional place between two metal conductors positioned one 
behind the other in the direction of displacement of the slides 42 and 44, 
the material of the base plate 26 can be positioned at the same level as 
the sheet metal blank outside of the projections of the metal conductors 
as is shown in FIG. 5. However it is more suitable if the baseplate 26 has 
a slot 93 between two metal conductors positioned one behind the other as 
is shown in FIG. 6. 
In order to provide that the bridging contact will not get caught on such a 
transitional place or its displacement is only disturbed, it is suitable 
to arrange a guide rib 94 at least on one side of the metal conductor 
(FIG. 7). The height of the guide rib 94 is at least substantially the 
same as the height of the projections adjacent to the gap 93, for example 
the projection 65, of the metal conductors positioned one behind the other 
in the transitional place, for example the metal conductors 81 and 82. 
Alternately, the height of the guide rib 94 is at most slightly higher 
than the projections. In both directions the slope portions 95 adjoin the 
guide rib 94, which slope portions 95 facilitate a gliding upwards of the 
bridging contact on the guide rib 94. 
The gliding of a bridging contact from a projection of one metal conductor 
to a projection of the other metal conductor or from one guide rib to the 
projection of an adjacent metal conductor can also be facilitated in that 
in the transitional place the projection of the metal conductor does not 
end with sharp edges, as is shown at the left-hand side of FIG. 5 by way 
of the metal conductor 96 and its projection 97, but that the end portion 
of the metal conductor is constructed in a sloped manner as can be seen on 
the right-hand side of FIG. 5 by way of the metal conductor 98 and the end 
portion 99 of its projection 100. 
The improvement of the gliding properties of the bridging contacts on the 
metal conductors and also the electric switching capabilities of these 
parts is additionally improved in that the bridging contacts 45 to 48 are 
formed by a folded sheet metal portion as can be seen from FIGS. 8 to 10. 
The folded back of a bridging contact of this kind, just as the folded 
back 101 of the bridging contact 45 (FIG. 9), faces the metal conductors. 
These bridging contacts are at first punched out in the shape of an H. 
They are folded alongside the center line of the web of the H-profile, so 
that thereafter they have a U-shaped side view (FIG. 8). In the center of 
the web, the bridging contacts have a small projection which serves to 
guide the helical compression springs 49. 
Due to its being developed from a symmetrically formed sheet metal blank a 
detent 107 or 108 is formed in the area of each of the two front sides 105 
and 106 of the bridging contact on both shanks 102 and 103 of the sheet 
metal portion 104 which is made by a release and simultaneous slight 
bending, as long as the sheet metal blank 104 has not been folded. Each of 
the bridging contacts can be engaged on a locking surface of the slide 
both in the longitudinal direction and in the transverse direction. 
In order to reduce the mechanical wear of the projections it is suitable to 
give the projection at least partially a course which within the width of 
a bridging contact deviates from the line of motion of a particular point 
of the bridging contact, so that in a relative movement of the bridging 
contact with regard to the metal conductors the contact point does not 
only move on the metal conductors but also on the bridging contact. This 
is illustrated by the embodiment of a switch 110 according to FIG. 11. In 
this embodiment, the bridging contacts 111 and 112 are arranged on a 
single swivelling member, not shown in detail in the drawing, which is 
swivellably mounted on the bottom part 113 by means of a circular recess 
118. Each of the bridging contacts 111 and 112 move during a swivelling 
motion of the swivelling member on a circular path of motion. All of the 
metal conductors with their projections 114 to 117 extend linearly. This 
is why in a movement of the swivelling member a relative motion of the 
projection of the metal conductor relative to the folded back portion is 
always started. A relative motion of the contact point on the bridging 
contacts reducing wear can also be reached by another combination of the 
course of the path of motion of a bridging contact and the base of the 
projection of the metal conductors co-operating with it. In a linear 
movement of the bridging contact the basis of the projection of the metal 
conductors co-operating with it can also be a straight line, which however 
includes a pointed angle with the line of motion of a point of the 
bridging contact as shown in FIG. 12, or a curved path as shown in FIG. 
13. In a curved, in particular, a circular path of motion of the bridging 
contact, the base of the projection of the metal conductors can as well be 
curved or circular as long as the line of motion of a point of the 
bridging contact is not congruent with the course of the projection.