Commutation Device for Electrical Machine

Abstract

A commutation apparatus for an electric machine, having brushes with a front face which lies against the peripheral surface of a collector which has a plurality of collector segments separated by gaps, is designed in such a manner that a contact edge which runs obliquely to the gaps is formed on the front face of at least one brush.

Claims

1. A commutation apparatus for an electric machine (4), having a brush arrangement (19) with a plurality of brushes (20), the front face (23) of which lies against the peripheral surface of a collector (22) which has a plurality of collector segments (25) separated by gaps (26), characterized in that a protruding contact edge (24) which runs obliquely to the gaps (26) between the collector segments (25) is formed on the front face (23) of at least one brush (20).

2. The commutation apparatus according to claim 1, characterized in that the contact edge (24) is rectilinear.

3. The commutation apparatus according to claim 1, characterized in that the brush (20) has a rectangular cross-sectional area and the contact edge (24) runs diagonally on the front face (23) of the brush (20).

4. The commutation apparatus according to claim 1, characterized in that the brush (20) has a rectangular cross-sectional area and the contact edge (24) runs parallel to the longitudinal sides of the brush (20).

5. The commutation apparatus according to claim 1, characterized in that the longitudinal sides of the brush (20) with a rectangular cross-sectional area run parallel to the gaps (26).

6. The commutation apparatus according to claim 1, characterized in that the longitudinal sides of the brush (20) with a rectangular cross-sectional area run obliquely to the gaps (26).

7. The commutation apparatus according to claim 1, characterized in that the collector segments (25) and the gaps (26) run parallel to the rotor longitudinal axis (27) of the electric machine (4).

8. The commutation apparatus according to claim 1, characterized in that the contact edge (24) is formed integrally with the brush (20).

9. The commutation apparatus according to claim 1, characterized in that the contact edge (24) forms an angle with the gaps (26) of at most 30.

10. The commutation apparatus according to claim 1, characterized in that the width of the contact edge (24) corresponds to at most the gap width of the gaps (26).

11. The commutation apparatus according to claim 1, characterized in that the angle of the contact edge (24) relative to the gaps (26) is dimensioned so that the contact edge (24) bridges the gaps (26).

12. An electric machine, in particular a starter motor, having a commutation apparatus (17) according to claim 1.

Description

[0018] Further advantages and expedient embodiments can be found in the further claims, the description of the figures, and the drawings, wherein:

[0019] FIG. 1 shows a starting device for an internal combustion engine, in longitudinal section, having an electric starter motor with armature coils which are fed current via a commutation apparatus,

[0020] FIG. 2 shows a view of the front face of a brush of the commutation apparatus, with a contact edge which runs obliquely,

[0021] FIG. 3 shows a view of the brush according to section line III-III of FIG. 2,

[0022] FIG. 4 shows a commutation apparatus, having a brush with an obliquely oriented contact edge for bridging the gaps between adjacent collector segments,

[0023] FIG. 5 shows an illustration, corresponding to FIG. 4, of a commutation apparatus, having an obliquely oriented brush with a rectilinear contact edge.

[0024] In the figures, the same components are indicated by the same reference numerals.

[0025] FIG. 1 shows a starting device 1 for an internal combustion engine, accommodating an electric starter motor 4 as the electric machine in a housing 2 which has a forward end plate 3. The rotor shaft 5 of the starter motor 4 drives, via a planetary gear 6, a drive shaft 11 on which a driver 8 of a freewheel device 7 is arranged in a manner allowing axial displacement, and is coupled to the drive shaft 11 in the direction of rotation. The driver 8 is supported via support rollers 9 on a roller collar 10, which is formed integrally with a starter pinion 12. Upon an axial advancement, the starter pinion 12 moves from a retracted, inoperative position into an advanced engagement position with the ring gear of an internal combustion engine.

[0026] The axial advancement of the starter pinion 12 is performed using an electromagnetic starter relay 13, which has an axially adjustable lifting armature 14 which is coupled to a forked lever 15. Upon an axial adjusting movement of the lifting armature 14, the fork lever 15 mounted on the housing is pivoted, thereby moving the driver 8, including the starter pinion 12, in the axial direction.

[0027] The electric starter motor 4 is designed as an internal rotor motor, and has an armature 16 which is connected to the rotor shaft 5 in a torque-proof manner and which contains electrically excitable armature coils. The coils in the armature 16 are energized via a commutation apparatus 17. The electromagnetic field generated by the electrical armature coils interacts with the magnetic field of permanent magnets 18 disposed on the inside of the stator which surrounds the armature.

[0028] The commutation apparatus 17 has a plurality of brush assemblies 19 configured as spring-brush units, each of which comprises, on the housing, a brush 20 formed as a carbon brush and a brush spring 21. The commutation apparatus 17 also comprises a collector 22 on the armature. The carbon brushes 20 are forced against the peripheral surface of the collector 22 by the brush springs 21. Carbon brushes 20 and brush springs 21 are suitably accommodated in brush holders which are fixed to the housing of the starter motor. A total of six spring-brush units 19 are evenly distributed over the circumference.

[0029] The collector 22 which rotates with the rotor shaft 5 comprises a plurality of brush segments electrically separated from each other via gaps. The brush segments, including the gaps between them, run parallel to each other and parallel to the rotor longitudinal axis of the electric machine 4.

[0030] FIG. 2 shows the front face of a brush 20 which is pressed radially against the peripheral surface of the collector by the force of a spring element. A contact edge 24 which protrudes beyond the front face 23, at least relative to the lateral edge region of the front face, is situated on the front face 23. The contact edge 24 thus forms the furthest-projecting extension on the front face 23. The contact edge 24 runs approximately diagonally on the front face 23 of the brush 20, which has a rectangular cross-sectional area. The contact edge 24 is formed integrally with the brush 20.

[0031] The contact edge 24 is constructed in a straight line on the front face 23, and forms an angle with respect to the longitudinal sides of the rectangular brush which is between a minimum angle and a maximum anglefor example, between at least 10 relative to the longitudinal side and a maximum of, for example, 30.

[0032] FIG. 4 shows a section of an electric machine 4, having a commutation apparatus 17 which comprises the collector 22 rotating with the rotor shaft and a plurality of brushes 20, each of which is forced by a spring element radially towards the peripheral surface of the collector 22. The brushes 20 are designed as in the embodiment of FIGS. 2 and 3, and have a contact edge 24 which runs diagonally, which is designed as an extension, and is in contact with the collector segments 25. The collector segments 25 are separated from each other via gaps 26. The collector segments 25 and the gaps 26 run parallel to the rotor longitudinal axis 27.

[0033] The contact edge 24 on the front face bridges the gaps 26 due to the oblique orientation, such that in each position of the rotating collector 22 relative to a brush 20, the gap 26 is bridged and a portion of the contact edge 24 contacts a collector segment 25 which is adjacent to the bridged gap 26. This ensures that the brushes 20 do not plunge into the gaps 26 when the collector 22 rotates.

[0034] FIG. 5 shows an embodiment of a commutation apparatus 17 of an electric machine 4. In FIG. 5 as well, the brushes 20 have a projecting contact edge 24 which runs obliquely relative to the collector segments 25 and the gaps 26, and thereby bridges the gaps 26 in any rotational angle position of the collector 22. However, the contact edge 24 is aligned parallel to the longitudinal sides of the brush 20 with a rectangular cross-section, and runs centrally on the front face of the brush 20. The brush 20 is set obliquely overall, such that the longitudinal sides of the brushes 20 are at an angle to the gaps 26.