EP0718859A1 - Device for the switching of an electric motor, in particular for braking an electric power tool - Google Patents

Abstract

The electric motor switching apparatus includes two alternating switches for switching the current supply to the electric motor on and off, changing the poling of a field winding of the motor and switching a braking circuit for the motor on and off. A moving contact (32') is provided for each alternating switch. The contact can move between a stationary on-contact (30') and an off-contact (28'). A device is provided for at least the moving contact by which the moving contact is guided over part of its path when switching over.

Description

The invention relates to a device for switching an electric motor, in particular for braking an electric tool.

The aim of the invention is to create a so-called brake switch for tools operated by an electric motor, the use of a suitable contact arrangement, in particular for switches with housing dimensions according to European standards, to be taken into account.

Two toggle switches are required to electrically brake an electric motor. The changeover switches are used to switch the power supply or the power supply on and off, to reverse the polarity of a field or armature winding of the electric motor and to switch an electrical brake circuit on or off. When switching off, especially when switching off quickly, there has been a disadvantage so far that an arc arises between the two stationary contacts provided for the production of the power supply, which arises from the contact break-off sparks and the switching of the inductors. This arc short-circuits the field winding of the motor, and the current, which is now only limited by the armature winding, rises so much that a backup fuse responds. Critical and therefore in need of improvement is further that an arc with the above-mentioned consequences again arises when switching on again during the braking process between the contacts for the power supply.

Up to now there have been switches for performing the electrical braking which have either two contact bridges with double interruption or two toggle contacts. With these, the contact distance is too small due to their function, so that rollovers and contact welding occur. The formation of rollovers is also promoted by switching too quickly.

The invention is intended to provide a device for switching an electrical braking of an electric motor, in particular for power tools, with stable switching positions, in which the risk of arcing, arcing and contact welding is significantly reduced by means of design measures.

According to the invention this is achieved by the features mentioned in claim 1. Preferred features which advantageously further develop the invention can be found in the subordinate claims.

Advantageously, the invention accordingly provides a device for switching an electric motor, in particular for electrically braking an electric tool, with a changeover switch for switching the power supply for the electric motor on and off, for reversing the polarity of a field or armature winding of the electric motor, and a changeover switch for Switching on and off an electrical brake circuit for the electric motor, an actuating element for the changeover switch, a movable contact provided for each changeover switch, which is movable between a stationary ON contact and an OFF contact spaced far away from it, and with an Device for at least one movable contact through which this can be guided over at least part of its movement path when switching over.

In the design according to the invention, the ON and OFF contacts are so far apart from one another with respect to an "arc-safe distance" that the occurrence of arcs and their negative effects during switching are reduced. In addition, an increased switchover time is achieved due to the enlarged contact section.

According to a preferred embodiment of the invention, the actuator is articulated on both movable contacts. According to a first alternative, the actuating member is connected to each movable contact via a spring, the arrangement preferably being such that the actuating member is articulated on a rocker arm which is connected to each movable contact via a tension spring. The springs ensure a good contact pressure on the one hand and on the other hand switch the movable contacts when the actuator becomes effective.

Alternatively, a pressure spring is provided for each movable contact, whereby it is also particularly advantageous to avoid contact welding if at least one movable contact switches over, if appropriate after a contact friction movement phase, from the corresponding stationary contact to which it was previously applied, against the action of this Pressure spring can be lifted off by means of the guide device.

According to a preferred embodiment, each guide device has a slide guide for the movable contact in a structurally simple manner, which can preferably be limited in each case by a run-on slope to generate a certain torque switching function. The slideway provided, which is preferably designed as a sliding rib, advantageously ensures on the one hand that the movable contact can fit perfectly onto the respective stationary contact and that a certain distance is still available for contact friction stands. On the other hand, a pressure point can be generated in a favorable manner by the run-up bevel when switching, which largely enables the critical phase of the contact opening or closing to be quickly exceeded.

According to a preferred embodiment of the invention, the movable contact is provided on a pivoting lever, preferably on the side thereof, which is mounted with play, this mounting preferably being designed to be rotatably displaceable and preferably being formed such that the pivoting lever is rotatably mounted in an elongated hole with lateral play is. As a result, the switching kinematics can be designed extremely easily and with few parts safely and reliably.

According to a further embodiment of the invention, the swivel lever has a plastic part with a slide rib for the slide guide, at least one guide device being preferably formed on one side of a housing for the changeover switch.

Alternatively, it is provided in the embodiment with a rocker arm that at least one slide guide for the movable contact is formed on the rocker arm.

A spatially and functionally favorable concept arises in particular when the two changeover switches are arranged symmetrically in a single housing in separate chambers, when the fastening element consists of a slide switch which pivots the movable contacts when the pressure spring or the tension spring of each movable one Contact is supported on the shift lever or the rocker arm, and when the slide switch is mounted in the housing in the region of a wall that separates the two housing chambers with the two-way switches.

Fig. 1

eine teilschematisierte Darstellung eines ersten Ausführungsbeispiels einer erfindungsgemäßen Vorrichtung in einer Stellung, in der die elektrische Stromversorgung für einen Elektromotor ausgeschaltet ist;

Fig. 2

eine Darstellung der Vorrichtung gemäß Fig. 1 in einer Mittelstellung des beweglichen Kontaktes;

Fig. 3

einen Schnitt entlang der Schnittlinie III-III in Fig. 2;

Fig. 4

eine teilschematisierte Darstellung eines zweiten Ausführungsbeispiels einer erfindungsgemäßen Vorrichtung in einer Stellung, in der die elektrische Stromversorgung für einen Elektromotor ausgeschaltet ist;

Fig. 5

eine Darstellung der Vorrichtung von Fig. 4 in einer mittleren Stellung des Kipphebels;

Fig. 6

eine Darstellung der Vorrichtung gemäß Fig. 4 in einer Stellung, in der die elektrische Stromversorgung für einen Elektromotor eingeschaltet ist; und

Fig. 7

einen Schnitt entlang der Schnittlinie VII-VII in Fig. 6, wobei der bewegliche Kontakt und der Kipphebel in ihrer Mittelstellung dargestellt sind.

Further details, features and advantages of the invention can be found in the subsequent description part, in which an embodiment of the invention is explained in more detail with reference to the accompanying drawings. Show it:

Fig. 1

a partially schematic representation of a first embodiment of a device according to the invention in a position in which the electrical power supply for an electric motor is switched off;

Fig. 2

a representation of the device of Figure 1 in a central position of the movable contact.

Fig. 3

a section along the section line III-III in Fig. 2;

Fig. 4

a partially schematic representation of a second embodiment of a device according to the invention in a position in which the electrical power supply for an electric motor is switched off;

Fig. 5

an illustration of the device of Figure 4 in a middle position of the rocker arm.

Fig. 6

an illustration of the device of Figure 4 in a position in which the electrical power supply for an electric motor is turned on. and

Fig. 7

a section along the section line VII-VII in Fig. 6, wherein the movable contact and the rocker arm are shown in their central position.

1 shows a basic illustration of a first exemplary embodiment of the invention with a housing 10, in which, as can be seen from FIG. 3, the front cover-like housing wall 11 is omitted in order to see into a front housing chamber 12. As can also be seen in this connection with FIG. 3, the housing 10 consists of two closed housing chambers 12 and 13.

1, the housing chambers 12 and 13 have a right common side wall 14, a left common side wall 15, a common lower wall 16 and a common upper wall 17. The walls 14 to 17 are formed in one piece with a partition 18 and consist of a insulating plastic.

A changeover switch 19 is accommodated in the front housing chamber 12, and a changeover switch 20 for switching off the power supply for the electric motor is located in the rear housing chamber 13. The changeover switches 19 and 20 are used to switch the power supply on and off, to reverse the polarity of a field or armature winding of the electric motor and to switch an electrical brake circuit on or off and are constructed symmetrically with respect to the partition 18. They are operated together by a slide valve 21 which passes through the upper wall 17 and is guided in the partition wall 18. The shift lever 21 has in the region of its lower end a right-angled protruding arrangement of pins 22 and 23, which are each surrounded by a pressure spring 24 and 25, which is supported by the slide switch 21, the pressure spring 24 a pivot lever 26 of the Changeover switch 20 and the pressure spring 25 acted upon a pivot lever 27 of the changeover switch 19.

The changeover switch 19 includes, as can best be seen in connection with FIG. 2, a stationary OFF contact 28 which is guided via a conductor 29 through the side wall 14 to the outside of the housing 10. In the area of the bottom wall 16 there is a stationary ON contact 30, which is connected to an electrical conductor 31, which is also led out of the housing 10 through the side wall 14. At the free end of the pivot lever 27 there is a lateral contact 32 which can be brought into contact with either the OFF contact 28 or the ON contact 30 by moving the pivot lever 27. The pivot lever 27 is mounted via a pivot joint 42 with play in an elongated hole 33 of a connecting plate 34 such that the movable contact 32 can also be moved perpendicular to the pivot plane of the pivot lever 27 for a contact lifting and a contact upward movement. Accordingly, the bearing pin 23 is arranged with play in a larger bore 35 of the pivot lever 27. The connection 34 is guided via an electrical line through the wall 15 to the outside of the housing 10.

A plastic part 37 is fastened to the swivel lever 27 in a region between the bore 35 and the end-side contact 32, on which a sliding rib 38 pointing perpendicularly to the front wall 11 is formed, which in the position shown in FIG. 2 is on an arc-shaped sliding rib 40 below Effect of the pressure spring 25 rests. The sliding rib 40 is arcuate. 1 and 2 only dashed lines 39 and 41 belonging to the sliding rib 40 are shown, on which the sliding rib 38 from the level of the sliding rib 40 when pivoting the pivot lever 27 to abut the movable contact 32 with the stationary contact 28 or 30 is performed. The bevels 39 and 41 can be designed like a ramp at 45 ° or as a transition curve profile.

The operation of the device for switching an electrical braking of an electric motor takes place in a simple manner from the position shown in FIG. 1 by pushing the slide switch 21 into the housing 10 in the direction of the arrow shown in FIG. 1. Initially, there is still a laterally shifting contact friction between the contacts 32 and 28 over a certain pivoting range until the sliding rib 38 reaches the run-up slope 39. During a switching movement, the movable contact 32 is quickly raised onto the sliding rib 40 and a reliable contact separation is thus achieved. Upon further pivoting of the pivot lever 27, the sliding rib 38 reaches the run-up slope 41, and the movable contact 32 comes into sliding contact with the stationary contact 30 until the end position is reached, which is dashed in FIG. 1.

The changeover switch 20 is constructed symmetrically to the changeover switch 19, but, for functional reasons, has an opposite contact assignment insofar as the stationary contacts are swapped there in terms of function.

The device according to the invention can thus advantageously be used to realize large contact openings, rubbing contacts, a simple construction with simple parts and easy assembly.

4 to 7 is a second embodiment of a device according to the invention with a housing 10 'and a modified slide switch 21' with an integrated button and compression spring. Insofar as this second exemplary embodiment has identical or similar parts, the same reference numerals as in the first exemplary embodiment, but with an apostrophe, have been used for simplification. To avoid repetitions, only the differences between the second exemplary embodiment and the first exemplary embodiment are described below explained, with corresponding modifications of components have a reference symbol with an apostrophe.

The second embodiment differs from the first embodiment essentially in that the changeover switches 19 'and 20' always assume a stable ON or OFF position, while in the case of the changeover switches 19 and 20 of the first embodiment also intermediate positions of the movable contact 32 in addition to the associated pivot lever 27 are possible.

The switch slide 21 ', which has an actuating button 50 at its upper end to achieve a reset function and which is supported on the housing 10' via a compression spring 51, is, as can be seen in connection with FIG. 7, in the region of the partition wall 18 'of the housing 10' out. It has a groove-shaped recess 52 for the pivotable mounting of a pin 53, which is integrally formed or attached to a rocker arm 54 on the side. The rocker arm 54 is pivotally mounted at 55 (see also FIG. 7) on the partition 18 'via a lateral pin 56 and can be pivoted between the position shown in FIG. 4 and FIG. 6, its position according to FIG. 4 being the OFF Position and its position according to FIG. 6 is assigned to the ON position of the changeover switches 19 'and 20'.

The rocker arm 54 has a front end 57 which is guided laterally against a portion of the partition 18 '. The partition 18 'is open in the pivoting range of the rocker arm 54. In the area of the front end 57 of the rocker arm 54, hook-in pins 58 and 59 are formed on both sides for a tension spring 60 and 61, which extend from there obliquely at an angle of approximately 15 ° in the direction of the movable contacts 32 '. The tension springs 60 and 61 are hooked at their other end to a plastic part 62 or 63, each on the pivot lever 27 'for the movable contact 32 'are attached. The springs 60 and 61 on the one hand achieve a desired safe contact pressure in the switching positions due to their line of action and their preload. On the other hand, they serve to switch the movable contacts 32 '. This takes place in such a way that when the slide switch 21 'is pressed in, the movable contact 32' initially remains in its respective switch position until the tension springs 60, 61 are further stretched due to the pivoting of the rocker arm 54 and their direction of action is greater than that of the swivel joint 42 '. directional switching position (dead position) are pivoted out. As a result, a sufficiently large torque is generated which overcomes the contact friction and leads to the movable contact 32 'immediately jumping into the second stable position. In the event that the intended spring force is not sufficient by welding or gluing the contacts, two opposing contact tearing ribs 66 are provided on the slide switch 21 ', each at the OFF or ON switching position of the pivoting lever 27' of the movable contact 22 'are spaced apart and only, as shown in FIG. 5, engage the pivoting levers 27' in the region of the center position of the rocker arm 54 in order to tear open the contacts.

The plastic part 62, which is designed as a spring-holding and movement-guiding part, has a molded-on pin 67 which is guided during the switching process via a sliding rib 40 ′ which is formed on the rocker arm 54. Like the sliding rib 40 of the first exemplary embodiment, the sliding rib 40 'has chamfers 41' and 39 '. For their mode of operation, reference is made to the above explanations.

The plastic part 63, which is designed as a spring holding and movement guide part, has an inwardly pointing pin 68, which in the second exemplary embodiment according to FIG a wall section 69 is slidably guided. The wall section 69 also serves to guide the slide switch 21 '. Alternatively, a sliding rib 40 ′ for the pin 68 can also be provided on the wall 69 here, in order to provide a movement sequence mirror-symmetrical to the partition 18 for the two pivoting levers 27 ′ in addition to the movable contacts 32 ′.

Claims (17)

Device for switching an electric motor, in particular for electrically braking an electric tool, with
two change-over switches (19, 19 ', 20, 20') for switching the power supply for the electric motor on and off, for reversing the polarity of a field or armature winding of the electric motor and for switching on and off an electrical brake circuit for the electric motor;
an actuator (21, 21 ') for the changeover switches (19, 19', 20, 20 ');
a movable contact (32, 32 ') provided for each changeover switch (19, 19', 20, 20 '), which is between a stationary ON contact (30, 30') and an OFF contact spaced far away from them with respect to arcs (28, 28 ') is movable; and with
a device (40, 40 ') for at least one movable contact (32, 32'), by means of which this can be guided over at least part of its movement path when switching over. Device according to claim 1, characterized in that the actuating member (21, 21 ') is articulated on both movable contacts (22, 32'). Device according to claim 1 or 2, characterized in that the actuating member (21, 21 ') is connected to each movable contact (32, 32') via a spring (24, 25, 60, 61). Device according to one of the preceding claims, characterized in that the actuating member (21 ') is articulated on a rocker arm (54) which is connected to each movable contact (32') via a tension spring (60, 61). Device according to one of the preceding claims, characterized in that at least one movable contact (32) when switching over after a contact friction movement phase from the corresponding stationary contact (28, 30) on which it previously touched, against the action of a pressure spring (24, 25) can be lifted off by means of the guide device (40). Device according to one of the preceding claims, characterized in that each guide device has a sliding guide (40, 40 ') for the movable contact (32, 32'), which is delimited by bevels (39, 39 ', 41, 41'). Device according to one of the preceding claims, characterized in that each movable contact (32, 32 ') is provided laterally on a pivot lever (27, 27'). Apparatus according to claim 7, characterized in that the pivot lever (27) has a plastic part (37) with a slide rib (38) for the slide guide (40). Apparatus according to claim 7 or 8, characterized in that the pivot lever (27) is rotatably mounted in an elongated hole (33) with lateral play. Device according to claim 4, characterized in that at least one slide guide (40 ') for the movable contact (32') is formed on the rocker arm (54). Device according to one of claims 6 to 10, characterized in that at least one swivel lever slide guide is provided on a wall (11, 69) of a housing for the changeover switches (19, 19 ', 20, 20'). Device according to one of the preceding claims, characterized in that the two changeover switches (19, 19 ', 20, 20') in a single housing (10, 10 ') in separate chambers (12, 12', 13, 13 ') are symmetrical are arranged to each other. Device according to one of the preceding claims, characterized in that the actuating member consists of a slide switch (21, 21 '). Apparatus according to claims 4 and 13, characterized in that two opposing contact ripping ribs (65, 66) are provided on the switching slide (21 '), each of the movable contact (32' in the OFF or in the ON switching position. ) are spaced. Device according to one of claims 7 to 14, characterized in that a spring holding and movement guide part (62, 63) is provided on each pivot lever (27, 27 '). Apparatus according to claim 5, characterized in that the pressure springs (24, 25, 60, 61) are arranged between the respective movable contacts (32, 32 ') and the slide switch (21) or the rocker arm (54). Apparatus according to claim 13, characterized in that the slide switch (21, 21 ') is mounted in the housing (10, 10') in the region of a wall (18, 18 ', 69) which the two housing chambers (12, 12' , 13, 13 ') with the changeover switches (19, 19', 20, 20 ') located therein.

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