EP0543124B1 - Electrical switch - Google Patents

Description

The invention relates to an electrical switch according to the preamble of claim 1.

Such electrical switches are used to switch on and off electrical DC or AC circuits in which high currents of up to 20 A can flow, for example. They are used in particular in machine tools with high power consumption, for example in angle grinders or circular saws.

From DE-OS 31 26 816 an electrical switch has become known in which a slide is linearly displaceable by means of an actuating member via a push rod and a bow-shaped snap spring, a contact bridge for bridging the fixed contacts arranged in the housing of the electrical switch being attached to the slide . When the switch is turned off, an arc occurs between the contact bridge and the fixed contacts, in particular at high currents, which burns off Contacts. If copper is used as the material for the contacts, the switch becomes highly resistive after a short period of use due to the poorly conductive copper oxide resulting from the contact erosion, so that a strong, often impermissibly high heating occurs at the switch. The contact erosion can be so strong, especially in direct current operation, where, unlike in alternating current operation, that no arc-extinguishing phase crossing takes place, that the switch becomes unusable after only a few switching cycles and thus a short period of use.

To remedy these disadvantages, it is known to silver the contacts made of copper. The silver layer conducts the electrical current far better than a copper layer when contact erosion begins. However, a shortening of the theoretically possible service life of the switch cannot be completely prevented by this. Another disadvantage is the much higher price for such a silver coating.

Switches have also become known in which copper-made contact tabs with a normally closed contact are arranged in the housing, a rotatable contact rocker moved by an actuating member via a push rod and a compression spring with a switching contact bridging the normally closed contacts. The disadvantage mentioned also occurs here, namely a very strong erosion at the normally closed contact, which renders the switch unusable after only a short period of use.

The invention is therefore based on the object of developing a switch of the type mentioned at the outset in such a way that harmful contact erosion at the normally closed contacts of the contact tabs is prevented.

This object is achieved in a generic electrical switch by the characterizing features of claim 1.

The advantages achieved with the invention are, in particular, that silvering of the normally closed contacts or the entire contact tabs can be dispensed with. This saves considerable costs. No harmful erosion occurs at the normally closed contacts, so that the service life of the switch according to the invention is considerably extended. Furthermore, an improved switching function is also achieved as a result, since no incorrect switching can occur. Finally, the switch according to the invention also manages with fewer and simpler individual parts than that according to DE-OS 31 26 816.

Further advantageous embodiments of the invention are described in the subclaims. Thus, a bolt can be integrally formed on the actuating member, in particular by plastic injection molding at the same time as the actuating member is being manufactured, this bolt being suspended in a corresponding receptacle on the push rod. As a result, the rivet connection between the actuating member and the push rod previously used in the prior art is dispensable, which ultimately results in a simpler and also cheaper Assembly of the switch is achieved.

The contact rocker can be chamfered on its peripheral side facing away from the fulcrum and adjacent to the switch contact, so that the contact rocker at most partially touches the contact lugs when the switch is in the off position. This results in a reduced friction between the contact rocker and the contact lugs, so that the switch-on behavior is improved. A further improvement in the switch-on behavior is achieved by arranging a sliding plate which reduces the sliding friction on the side assigned to the housing upper part of the switch in the carrier, which in turn is attached to the push rod.

Fig. 1

einen Längsschnitt durch den erfindungsgemäßen Schalter,

Fig. 2

eine Draufsicht mit teilweisem Schnitt von der Unterseite des Schalters,

Fig. 3

schematisch die Stellung der Kontakte im eingeschalteten Zustand und

Fig. 4

schematisch die Stellung der Kontakte während des Ausschaltens.

An embodiment of the invention is shown in the drawings and will be described in more detail below. Show it

Fig. 1

a longitudinal section through the switch according to the invention,

Fig. 2

a plan view with partial section from the bottom of the switch,

Fig. 3

schematically the position of the contacts when switched on and

Fig. 4

schematically the position of the contacts during switching off.

As can be seen from FIG. 2, where the switch is shown in the off position, the electrical switch 1 of the present exemplary embodiment is designed as a two-pole closer or on-off switch and has an upper housing part 2 shown in longitudinal section in FIG. 1 and a lower housing part 3. The upper housing part 2 encompasses the upper edge of the lower housing part 3 and is connected to the lower housing part 3 in a snap-in or snap-in manner. Of course, the upper and lower parts of the housing can also consist of a single piece. On the upper housing part 2 there is a cantilever 11 with an attachment 4 attached to it, on which in turn an actuating member designed as a push cap 5 is rotatably mounted on a pin 6. The pusher cap 5 is under the pressure of a helical compression spring 12 attached to the arm 11.

A bolt 7 is formed on the end of the pusher cap 5 assigned to the upper housing part 2. If the pusher cap 5 is made of plastic, as is customary, the bolt 7 can be injection molded at the same time as the pusher cap 5 is being produced. The bolt 7 of the pusher cap is suspended in a receptacle 8 of a push rod 9, which projects into the interior of the electrical switch 1, so that the rotatable pusher cap 5 is articulated on the push rod 9 eccentrically. At the point where the push rod 9 penetrates the upper housing part 2, there is a seal 10 which prevents dirt from penetrating into the electrical switch.

If the pusher cap 5 is actuated against the pressure of the helical compression spring 12, it rotates about the pin 6 (dashed position in FIG. 1) and takes the push rod 9 with the bolt 7 via the receptacle 8. As a result, the push rod 9 arranged in a corresponding guide in the upper housing part 2 is moved to the right in FIG. 1. After releasing the pusher cap 5, it is returned to the starting position by the pressure of the helical compression spring 12 and the push rod 9 is moved in the opposite direction (to the left in FIG. 1). Thus, the push rod 9 is moved linearly in the arrow direction 14 by the pusher cap 5.

In the interior of the electrical switch 1 there is arranged a movable contact member which thereby bridges the contacts and which consists of a contact rocker 15 which is rotatably mounted in the upper housing part 2. In the central area of this contact rocker 15 there is a conical extension 16 on which one end of a compression spring 17 is held. The other end of the compression spring 17 is held by a further extension 18, which comes from a carrier 19, which in turn is attached to the end of the push rod 9 located inside the electrical switch 1. On the carrier 19 there is a sliding plate 13 facing the upper housing part 2 and in contact therewith. Due to the lower sliding friction coefficient, this sliding plate reduces the frictional force when the carrier 19 moves. In addition, a lubricant can be located between the sliding plate 13 and the upper housing part 2 .

The contact rocker 15 made of insulating material, for example plastic, is divided in two on its peripheral side facing away from the fulcrum. The part 21 of the peripheral side facing the push rod 9 carries a planar switching contact 22, which is U-shaped in plan view, as can be seen in particular in FIG. 2. This switch contact 22 can consist of surface silver-plated copper. As can further be seen from FIG. 2, the part 20 of the contact rocker 15 facing away from the push rod 9, which is adjacent to the switching contact 22, is beveled on the peripheral side, so that the part 20 of the contact rocker 15 is in the off position of the switch does not abut or only partially abuts the contact lugs 23 ', 23' 'located in the lower housing part 3. This results in a reduced friction between the contact rocker 15 and the contact tabs 23 ', 23 ", which improves the switch-on behavior.

The contact lugs 23 ', 23''made of copper have a molded-on rectangular connector 25 with a through hole 26. On both sides of the lower housing part 3 there is a contact lug 23' and 23 '' per pole of the two-pole electrical switch 1 in one of the connectors 25 corresponding receptacle 24 is inserted so that the two contact tabs 23 ', 23''with their normally closed circular contacts 29', 29 '' in plan view are essentially opposite each other. In the receptacle 24, a U-shaped, on the connecting piece 25 adjacent connecting element 27 made of brass is used, at the U-middle piece to Through hole 26 corresponding thread 28 is attached so that the electrical conductors can be attached to the connector 25 with a corresponding screw.

If the pusher cap 5 is depressed, the push rod 9 with the carrier 19 moves in the right direction according to FIG. 1, as already described. In this case, the abutting end of the compression spring 17 is also moved via the extension 18 and the compression spring 17 moves from the first inclined position shown in FIG. 1 to an unstable intermediate position in which it stands approximately radially to the peripheral side of the contact rocker 15. In this unstable intermediate position, a slight further movement in the actuating direction of the push-button cap 5 is sufficient to cause the compression spring 17 to jump over into the second inclined position. The contact rocker 15 is carried along by the other end of the compression spring 17 via the extension 16 and snaps from the off to the on position, which can be seen in more detail in FIG. 3. When the contact rocker 15 snaps, the bevel of the part 20 moves past the normally closed contacts 29 ′, 29 ″, after which the normally closed contacts 29 ′, 29 ″ slide against the non-beveled point of the part 20 of the contact rocker 15. When the contact rocker 15 moves further into the on position, the switch contact 22 located on part 21 finally comes into contact with the normally closed contacts 29 ', 29'', as can be seen in FIG. 3, so that a conductive electrical connection between the two contact tabs 23 ', 23''.

If the pusher cap 5 is released again, the push rod 9 with the carrier 19 according to FIG. 1 moves in the left direction, as already described. The reverse direction of movement for the switch-on process is carried out, the switch contact 22 located on part 21 of the contact rocker 15 being withdrawn from the normally closed contacts 29 ', 29' ', so that finally the beveling of the part 20 of the contact rocker 15 between the normally closed contacts 29' , 29 ''. The electrical connection is thus interrupted again and the switch is in the off position shown in FIG. 2.

Occasionally, it can happen that the switch contact 22 welds to the normally closed contacts 29 ', 29' 'during the passage of current in the on position. In these cases, loosening of the switching contact 22 when the trigger cap 5 is released may not be guaranteed, so that the switch remains in the on position. For such cases, a wedge-shaped nose 30 is attached to the carrier 19, which then comes into contact with an extension 31 on the contact rocker 15 when the carrier 19 is moved in accordance with FIG. 1, so that the contact rocker 15 with the spring force of the helical compression spring 12 is pushed away from the normally closed contacts 29 ', 29' 'and thus the off position is reached.

When the switch contact 22 is released from the normally closed contacts 29 ', 29''after the trigger cap 5 has been released, an arc arises between the switch contact 22 and the contact tabs 23', 23 ''. In order to avoid contact erosion, the contact lug 23 'has the on the Contact rocker 15 is arranged in the side of the lower housing part 3 facing away from the off position (left contact lug in FIG. 2), an extension arranged on the normally closed contact 29 'in the direction of the contact contact rocker 15, the so-called extinguishing lug 32.

The mode of operation of the extinguishing flag 32 can be seen in more detail in FIG. 4. When the switching contact 22 is withdrawn from the normally closed contacts 29 ', 29'', the switching contact 22 runs through the distance along the part 33 of the contact lug 23''which lies between the normally closed contact 29''and the connecting piece 25, and along the extinguishing lug 32 When the switching contact 22 is opened by the normally closed contacts 29 ', 29''and when the switching contact 22 and the normally closed contacts 29', 29 '' are switched off, arcs 34 ', 34''which arise are moved by the moving switching contact 22 to the part 33 as well as carried on the firefighting flag 32. Since the switching contact snaps due to the action of the compression spring 17 (see FIG. 1), the arc 34, 34 '' is moved away from the normally closed contacts 29 ', 29''within a very short period of time, so that the arc 34', 34 '' is almost immediately present between the switching contact 22 and the part 33 and the extinguishing flag 32. Because of the short period in which the arc 34 ', 34''is located at the normally closed contacts 29', 29 '', there is no significant contact erosion. Both arcs 34 ', 34''extinguish when the switch for direct current is used as soon as the distance between the switching contact 22 and the extinguishing flag 32 has exceeded a certain size required for maintaining the arc. When using the switch with alternating current, the arc can go out before the phase crosses zero. This creates by the at Switching-off process occurring arcs 34 ', 34''only on the extinguishing lug 32 and the part 33 of the contact lug 23''a contact erosion, but not on the normally closed contacts 29', 29 '' used for the current passage in the on position, which consequently does not further is disruptive to the function of the switch. Destruction of the normally closed contacts 29 ', 29''by contact erosion advantageously does not occur, so that the use of expensive silver for the normally closed contacts 29', 29 '' can be dispensed with and nevertheless has a much longer service life than conventional ones provided with copper contacts Switches is reached.

The extinguishing flag 32 is preferably aligned with the part of the contact flag 23 'located between the normally closed contact 29' and the connecting piece 25 and with the same width as the contact flag 23 '. Production is particularly simple if the extinguishing flag 32 and the contact flag 23 'consist of a common part. Furthermore, it has been shown that an effective prevention of contact erosion is achieved even with a length of between 2 and 5 mm of the extinguishing tab 32.

The invention is explained on a switch provided with a contact rocker. It can also be used on other switches, for example on those in which the contact member is moved linearly or the push rod is articulated or fastened directly to the actuating member. Essential to the invention, however, is the arrangement of an extinguishing tab on the normally closed contact of the contact tab, which is arranged on the side of the housing facing away from the contact member in the off position.

Reference symbol list:

1:

Electrical switch

2:

Upper part of the housing

3:

Lower part of the housing

4:

approach

5:

Pusher cap

6:

Cones

7:

bolt

8th:

admission

9:

Push rod

10:

poetry

11:

boom

12:

Helical compression spring

13:

Sliding plate

14:

Arrow direction

15:

Contact rocker

16:

Approach (on contact rocker 15)

17:

Compression spring

18:

Approach (to beam 19)

19:

carrier

20:

Part of the contact rocker (facing away from the push rod 9)

21

Part of the contact rocker (facing the push rod 9)

22:

Switch contact

23 ', 23' ':

Contact flag

24:

admission

25:

Connector

26:

Through hole

27:

Connector

28:

thread

29 ', 29' ':

Break contact

30:

nose

31:

approach

32:

Firefighting flag

33:

Part (between normally closed contact and connector on the contact lug)

34 ', 34' ':

Electric arc

Claims (12)

1. Electric switch with a lower housing part (3) and an upper housing part (2) which can be locked together, whereby contact lugs (23', 23") with a home contact (29', 29") are arranged in recesses of the lower housing part (3), a contact element with a switching contact (22) is arranged in the upper housing part (2), the contact element, by means of a compression spring (17) and a push rod (9), which protrudes out of the upper housing part (2) and onto which an operating element is hinged, can be moved to catch between an off-position, in which the switch contact (22) does not touch the home contact (29', 29"), and an on-position in which the switch contact touches the home contact (29',29"), characterised in that on the contact lug (23') arranged on the side of the lower housing part (3) averted from the contact element in the off-position a reset lug (32) comprising an extension is attached to the home contact (29').
2. Electric switch according to Claim 1, characterised in that the reset lug (32) is aligned with the longitudinal part of the contact lug (23').
3. Electric switch according to Claim 1 or 2, characterised in that the reset lug (32) has the same width as the contact lug (32).
4. Electric switch according to one of Claims 1 to 3, characterised in that the reset lug (32) and the contact lug (23') are a common element.
5. Electric switch according to one of Claims 1 to 4 characterised in that the reset lug (32) is between 2 and 5 mm long.
6. Electric switch according to one of Claims 1 to 5, characterised in that the operating element (5) is rotatably fixed to a step (4) on the upper housing part and the push rod (9) is hinged eccentrically on the operating organ (5).
7. Electric switch according to Claim 6, characterised in that the eccentric hinging of the push rod (9) on the operating element (5) is made of a bolt (7) formed on the operating element (5) which is inserted into a recess (8) on the push rod (9).
8. Electric switch according to Claim 7, characterised in that the operating element (5) is made of plastic and the bolt (7) on the operating element (5) is injection moulded.
9. Electric switch according to one of Claims 1 to 8, characterised in that the contact element comprises a contact rocker (15) pivot mounted in the lower housing part (2) which on its peripheral side averted from the point of rotation comprises a first part (20) and a second part (21) bearing the switch contact (22).
10. Electric switch according to Claim 9, characterised in that part (20) of the contact rocker (15) is tapered on its peripheral side averted from the point of rotation and adjacent to the switch contact.
11. Electric switch according to Claim 9 or 10, characterised in that inside the electric switch (1) on the end of the push rod (9) a carrier (19) for supporting one side of the compression spring (17) is arranged whereby on the carrier (19) there is a slide sheet (13) facing the upper housing part (2).
12. Electric switch according to Claim 11, characterised in that there is lubricant between the slide sheet (13) and the upper housing part (2).

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