Patent Application
20090072656
The invention relates to a four-pole electric motor drive with a hammer brush holder system.
Electric motor drives which have a stator and a rotor are already known, it being possible for the rotor to contain a rotor shaft, a laminated rotor core and a commutator fitted with segments. Such types of electric motor drives are used for example in motor vehicles as drive motors in connection with a power steering system, an automatic braking system and a cooling fan.
Furthermore, brush systems are already known in which the carbon brushes are guided in cartridge-type brush holders. A disadvantage of these brush systems is that in operation they are susceptible to sand and other dirt. The result of this can be that the carbon brushes are no longer able to move in the desired manner in the respective holder but become jammed. This results in failure of the brush system and consequently of the entire electric motor drive.
Moreover, brush systems are already known in which so-called hammer holders are employed as brush holders. The disadvantage of these systems is the high space requirement, which is a hindrance in small motors.
A plastic hammer brush holder arrangement is known from EP 0 651 472 B1, which has a brush support arm, one end of which is fitted with a brush receiver and the other end is fitted with a rotatable bearing arrangement. Furthermore, the free outer faces of the brush support arm are fitted with a noise-deadening and/or noise-damping sheath.
A plastic hammer-type brush holder in the form of a pivoted arm for an electric machine is known from EP 0 791 988 B1. Here a box-shaped brush receptacle is provided at one end of the pivoted arm and at least one pivoted bearing arrangement at the other end. Furthermore, the pivoted arm contains a thin-walled web connecting the pivoted bearing arrangement to the box-shaped brush receptacle. Said thin-walled web spreads open, at least at one of its ends, into the lateral longitudinal walls of the box-shaped brush receptacle, which essentially run parallel to the connecting web.
The object of the invention consists in specifying a four-pole electric motor drive whose brush system can be constructed with simple and economical means and is nevertheless insensitive to sand and other dirt.
This object is achieved by a four-pole electric motor drive having the features stated in claim 1. Advantageous embodiments and developments of the invention are revealed in the dependent claims.
The advantages of the invention are, in particular, that the operation of the electric motor drive, both in service and also in the event of ingress of sand or other dirt, is longer than with known electric motor drives. This can be attributed to the fact that the carbon brushes are not guided inside a cartridge-type brush holder but in each case in a box-shaped brush receiver of a brush support arm, whose outer end has a rotatable bearing arrangement. In such a bearing arrangement the sliding surfaces are reduced to a minimum. Due to a clever arrangement of these sliding surfaces and of the spring elements of the brush system, which advantageously are leg springs, it can be ensured to a large extent that these surfaces are protected against contaminants. In addition, a brush system according to the invention has a reduced number of components and can be realized in a space-saving and economical manner.
It is particularly advantageous that the brush system realized as a hammer brush holder is equipped with only two brush support arms in whose brush receiver one carbon brush is used in each case, and that each of the commutator segments which are offset from each other by 1800 are interconnected via an electrical conductor. The existence of a total of four carbon brushes is simulated by these connections, although only two carbon brushes are present. Compared to the prior art, this represents a considerable saving in the number of components employed, and therefore also a considerable space saving. The architecture described above particularly favors the use of hammer brush holder systems which potentially require inherently a lot of space, even in conjunction with four-pole applications.
In this case the two brush support arms are offset by 90° from each other on the frame of the brush system.
This has the advantage that a comparatively large amount of space remains on the frame for mounting the interference suppression components required for a brush system and—if desired—a thermal protection device. In addition, there is still plenty of space which can be used for cooling air openings.
The necessary electrical connections between the carbon brushes and the interference suppression components are advantageously realized by means of one of more solid wire links. This saves further space. Furthermore, solid wire is a low-cost component which is readily available in the trade and which can be easily installed in the brush system. Moreover, use of solid wire has the advantage that additional components can be easily incorporated in the system at a later date since the necessary electrical contact between the solid wire and the additional component can be made without prior removal of insulation, etc.
Further advantageous features of the invention are revealed in their exemplary explanation with the aid of the figures, in which:
The electric motor drive as shown has a stator 1, with a total of four associated stator poles la. Furthermore, said drive has a rotor 2, with associated rotor shaft 3, a laminated rotor core 5 containing rotor teeth 4, and a commutator 7 fitted with segments 6. The segments 6 are distributed equidistantly around the periphery of the commutator. Each of the segments is arranged at a specified distance from the respective adjacent segment around the periphery of the commutator.
In addition, the illustrated electric motor drive has a brush system 8, which is realized in the form of a hammer brush holder system whose carbon brushes make contact with the segments 6 of the commutator 7 during operation.
These additional components include two brush support arms 10 embodied in the form of a hammer holder. Each of these brush support arms 10 has a first end at which a brush receiver 11 is located. A carbon brush 13 is inserted in this brush receiver 11. During the operation of the electric motor drive no relative movement occurs between the respective carbon brush 13 and the associated brush support arm 10. Furthermore, each of these brush support arms has a second end at which it is connected to the frame 9 by means of a rotatable bearing arrangement 12. A leg spring 18, which extends in the axial direction, is inserted in each case in the region of the rotatable bearing arrangement 12. If the carbon brush 13 moves outwards in the radial direction, that is to say is lifted off from the commutator, then the leg spring 18 is pretensioned. If the carbon brush 13 moves inwards in the radial direction, that is to say in the direction of the commutator, then the leg spring 18 is unloaded.
In a brush system constructed in such a way the sliding surfaces are minimized during operation. They occur only in the region of the rotatable bearing arrangements 12 of the brush support arms 10 and can be arranged in such a way that they are largely protected from contaminants. Advantageously, the carbon brushes 13 themselves are firmly inserted in the brush receivers 11 of the brush support arms 10 and in operation make no relative movements in relation to the respective brush support arm.
In addition, the hammer brush holder system shown in
The necessary electrical connections between the carbon brushes 13, the interference suppression components 15, 20 and an electrical connecting cable 16 are made using one or more solid wire links 17. Solid wire is a low-cost component which is readily available in the trade and can be easily cut each time to the necessary length, then bent into the desired shape and finally attached to the frame 9, which is preferably fitted with wire guideways, inside which clamping means for retaining the solid wire are provided.
Furthermore, a recess is provided in the profiled frame 9, in which—if this is required—a thermal protection element 19 can be inserted, as denoted by the broken line in
As already explained above, the electric motor drive according to the invention is a four-pole drive. According to the embodiment shown in
This is illustrated in
As
According to a further embodiment, not illustrated in the figures, a total of four brush support arms in each of whose brush receivers one carbon brush is inserted, are provided on the frame. However, this additional embodiment is not preferred since, compared to the embodiment shown by
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 004 399.6 | Sep 2007 | DE | national |
