ELECTRIC MOTOR HAVING A COMMUTATOR AND BRUSH FOR THE ELECTRIC MOTOR

Abstract

An electric motor has a commutator and at least one brush with a concavely curved brush surface as a running surface for the commutator. The brush has two parallel running in ribs, which protrude perpendicularly above the brush surface. The running in ribs each have a radius of curvature which is greater than a radius of curvature of a convex commutator surface. The running in ribs are arranged eccentrically and at a spacing from one another such that they are offset with respect to two opposing surface outer edges of the brush surface. The running in ribs are arranged such that they are inclined at an angle of inclination with respect to the surface outer edges.

Claims

1. An electric motor, comprising: a commutator having a convex commutator surface; and at least one brush with a concavely curved brush surface as a running surface for said commutator, wherein said at least one brush having two parallel running in ribs, protruding perpendicularly above said concavely curved brush surface, wherein said running in ribs each having a radius of curvature being greater than a radius of curvature of said convex commutator surface, wherein said running in ribs disposed eccentrically and at a spacing from one another such that they are offset with respect to two opposing surface outer edges of said concavely curved brush surface, and wherein said running in ribs disposed such that they are inclined at an angle of inclination with respect to said two opposing surface outer edges.

2. The electric motor according to claim 1, wherein said running in ribs extend substantially over an entire width of said concavely curved brush surface.

3. The electric motor according to claim 1, wherein the angle of inclination is an acute angle.

4. The electric motor according to claim 3, wherein the angle of inclination is dimensioned such that it is in an angular range between 2° and 10°.

5. The electric motor according to claim 1, wherein said running in ribs have a triangular cross-sectional form.

6. The electric motor according to claim 3, wherein the angle of inclination is dimensioned such that it is in an angular range between 4° and 6°.

7. A brush for an electric motor, comprising: a concavely curved brush surface having two protruding running in ribs and two opposing surface outer edges, said running in ribs being parallel to one another, wherein said running in ribs disposed eccentrically and at a spacing from one another such that said two running in ribs are offset with respect to said two opposing surface outer edges of said concavely curved brush surface, and wherein said running in ribs being disposed such that said running in ribs being inclined at an angle of inclination with respect to said two opposing surface outer edges.

8. The brush according to claim 7, wherein the brush is a carbon brush.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0031] FIG. 1 is a schematic illustration of a brush system of an electric motor with two brushes, which are each supported against a commutator in a tubular holder via a brush pressure spring, according to the invention;

[0032] FIG. 2 is a perspective view of the brush, looking onto a brush surface of the brush which is directed towards the commutator, with two mutually spaced, radially raised running in ribs in the non-bedded-in new state of the brush;

[0033] FIG. 3 is a front view of the brush, looking onto the brush surface;

[0034] FIG. 4 is a sectional view of the brush taken along the section line IV-IV shown in FIG. 3;

[0035] FIG. 5 is a plan view of the brush;

[0036] FIG. 6 is an illustration of a detail of the brush in a corner region VI shown in FIG. 3 in a front view; and

[0037] FIG. 7 is a sectional view of the brush taken along the section line VII-VII shown in FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

[0038] Mutually corresponding parts are always denoted by the same reference signs in all figures.

[0039] A detail of an electric motor 2, or the commutator and brush system thereof, is illustrated in FIG. 1. In this case, the brush system, which is not shown in more detail, is configured in the form of an annular disk and is arranged eccentrically around a commutator 4 of the electric motor 2. The brush system contains two (carbon) brushes 6, which are in contact with the commutator 4. The commutator and brush system furthermore contains two tubular (brush) holders 8 as a brush shaft or brush holder in which the brushes 6 are guided radially with respect to the commutator 4 and perpendicularly to one another.

[0040] Here and below, “axially” or an “axial direction A” is, in particular, understood to be a direction which is parallel (coaxial) to the motor axis of the electric motor 2, i.e. perpendicular to the end faces of the commutator 4. Accordingly, here and below, “radially” or a “radial direction R” is, in particular, understood to be a direction along a radius RK of the commutator 4 which is orientated perpendicularly (transversely) to the motor axis of the electric motor 2. Here and below, “tangentially” or a “tangential direction T” is, in particular, understood to be a direction along the circumference of the commutator 4 or the electric motor 2 (circumferential direction, azimuthal direction), i.e. a direction which is perpendicular to the axial direction A and to the radial direction R.

[0041] To generate a drive force between the brushes 6 and the commutator 4, the commutator and brush system moreover contains two brush pressure springs 10, which each lie in one of the tubular holders 8, between the brushes 6 and a radially outer tubular-holder base 12. For clarification, one of the tubular holders 8 is illustrated broken away in FIG. 2.

[0042] In the electric motor 2, the brushes 6 serve for the transmission of current to the commutator 4 rotating during operation of the electric motor 2 and therefore to the windings (not illustrated in more detail) of the rotor of the electric motor 2. For the transmission of current, the brushes 6 have a respective connection cable 14 on their upper lateral surfaces. For simple contacting of the brushes 6, the connection cable 14 leads out of a longitudinal slot 16 extending in the tubular holder 8 in each case.

[0043] The commutator 4 has a number of commutator segments (not shown in more detail) on its outer circumferential side, which commutator segments extend in the axial direction A, and therefore parallel to the motor axis (not shown in more detail) extending perpendicularly into the plane of the drawing, and are arranged such that they are distributed with respect to one another on the circumferential side to form axial gaps filled, for example, with an insulating material. On the commutator side, the commutator segments form a contact surface (referred to below as commutated surface 18) with the respective brush 6, wherein the commutator surface 18 is convexly curved owing to the cylindrical form of the commutator 4. In this case, the radius of curvature of the commutator surface 18 on the commutator side corresponds to the commutator radius RK.

[0044] The end face of the brush 6, which faces the commutator 4, is also referred to below as the brush head, wherein the brush head is provided with a concave head recess which has a brush surface 20 as a contact surface or running surface.

[0045] The construction of the brush is explained in more detail below with reference to FIGS. 2 to 7.

[0046] In this case, FIGS. 2 to 7 show a new state of the brush 6. It can be seen that the brush 6 has two running in ribs 22, which are raised in the radial direction R, i.e. they project from the remaining contact regions of the brush contact surface 20 in the direction of the commutator 4. These running in ribs are spaced from one another in the axial direction A in such a way that as large a spacing as possible is formed between the two running in ribs 22. In this case, the running in ribs 22 are each arranged on an azimuthal or tangential surface outer edge 24 of the brush 6 so that a contact region of the brush 6 is formed between the running in ribs 22 which corresponds substantially to the brush surface.

[0047] The running in ribs 22 extend completely between the two axially extending surface outer edges 26 of the concave brush surface 26. In the new state, when the electric motor 2 is fully assembled, the running in ribs bear against the commutator 4, or against its commutator segments, and therefore against the convex commutator surface 18, merely with contact points 28 (FIG. 5) in the middle or center.

[0048] The radially protruding running in ribs 22 each have a radius of curvature RE (FIG. 5), also referred to as a running in or bedding in radius, which is greater than the radius of curvature RK of the commutator surface 18.

[0049] As can be seen in particular in FIG. 3, the approximately linear running in ribs 22 extend substantially over the entire tangential width of the brush surface 20. In this case, the running in ribs 22 extend at an angle of inclination α with respect to the tangential direction T of the brush surface 20. The angle of inclination α is, for example, 5°.

[0050] The connection cable 14 and the brush 6 are connected to one another via a stamped contact, for example. In this case, a cable end 30 of the connection cable 14 on the brush side is inserted into the conductive powder of the brush 6 and the powder is subsequently hardened to form the brush 6. The connection cable 14 is configured as a braided power cable (mesh braid), for example, and has a stranded end as a connection region at the cable end 32 opposite the cable end 30.

[0051] The end-face corner regions of the brush head are each provided with an edge chamfer 34 (shown in more detail in FIG. 6). The edge chamfer 34 has a chamfer angle β of 45°±5°, for example.

[0052] A can be seen by way of example in FIG. 4 and FIG. 7, the running in ribs 22 have a substantially triangular cross-sectional form. In particular, the running in ribs 22 have a cross-sectional form in the form of a right-angled triangle, wherein the edge chamfer 34 forms a cathetus. The running in ribs 22 have a radial rib height H with which they protrude above the bush surface 20.

[0053] In a suitable dimensioning, the brush 6 has, for example, a radial length of approximately 8.8 cm and an axial height of approximately 4.2 cm and a tangential width of approximately 3.25 cm, wherein the radius of curvature RE is dimensioned to be 5.6 cm±0.5 cm, for example. In this case, the running in ribs 22 have, for example, a rib height H of approximately 0.16 cm.

[0054] In the course of the bedding in procedure of the brush 6, the running in geometry of the brush contact surface 20, which is formed by the running in ribs 22, ensures that the brush 6 has an increasing contact or load-bearing region as the running in process continues, until the axial surface outer edges 24 of the brush 6 are also load-bearing and a running in gap between the brush surface 20 and the commutator surface 18 is consequently reduced to zero (0).

[0055] The invention is not restricted to the exemplary embodiments described above. Instead, other variants of the invention can also be derived therefrom by a person skilled in the art without deviating from the subject matter of the invention. In particular, all individual features described in connection with the exemplary embodiments can also be combined with one another in another manner without deviating from the subject matter of the invention.

[0056] The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: [0057] 2 Electric motor [0058] 4 Commutator [0059] 6 Brush [0060] 8 Tubular holder [0061] 10 Brush pressure spring [0062] 12 Tubular-holder base [0063] 14 Connection cable [0064] 16 Longitudinal slot [0065] 18 Commutator surface [0066] 20 Brush surface [0067] 22 Running in ribs [0068] 24 Surface outer edge [0069] 26 Surface outer edge [0070] 28 Contact point [0071] 30 Cable end [0072] 32 Cable end [0073] 34 Edge chamfer [0074] A Axial direction [0075] R Radial direction [0076] T Tangential direction [0077] RK Radius of curvature/commutator radius [0078] RE Radius of curvature/running in radius [0079] α Angle of inclination [0080] β Chamfer angle [0081] H Rib height