Carbon brush for a DC excited brushed motor with a single narrow starting surface

Abstract

Carbon brush (9) for a DC excited brushed motor (1) comprising two longitudinal sides (11) arranged parallel to each other and two transverse sides (12) also arranged parallel to each other, which are substantially perpendicular to the longitudinal sides (11), wherein the four sides (11, 12) are bounded by two opposite end faces (13), characterized in that the carbon brush (9) has a single contact surface (19) arranged on an end face (13) and which has a width (z) that is between 40% and 90% of the total width of the carbon brush (z G ) lies, and has a height (h) which is a maximum of 0.5 mm, wherein the approach surface (19) extends parallel to the transverse side and perpendicular to the longitudinal side.

Description

[0001] The present invention relates to a carbon brush for a DC excited brushed motor having the features of the preamble of claim 1, a brush holder and a DC excited brushed motor with asymmetric pitch.

[0002] In commutator motors, current is supplied from the power supply or control unit via carbon brushes that contact the commutator, which is divided into several segments and serves to reverse the current. The segments are insulated from each other around the circumference of the commutator and, as the rotor—consisting of the armature windings, motor shaft, and commutator—rotates, they are energized sequentially via the carbon brushes. Each carbon brush moves from one segment to the insulated space or groove between two segments, simultaneously contacting and short-circuiting or bridging the two adjacent segments, which results in a change in the current signal. The transition of the carbon brushes between adjacent segments leads to the formation of current ripples. It is known to mount or guide the carbon brushes in carbon holders. The carbon holders are arranged on a carrier plate of a brush holder and are radially aligned.Each carbon brush, held in its holder, has a connecting wire leading to one of the electrical components mounted on the carrier plate. During operation, a pressure spring presses the carbon brush against the commutator segments of the DC motor.

[0003] When commissioning a new DC motor, a specific break-in period is required for the carbon brush. During this break-in period, the contact surface of the carbon brush is ideally precisely aligned with the commutator's circumferential surface through a specific grinding process. It is desirable that the carbon brush exhibits good running characteristics and that any changes in its circumferential position relative to the backing plate are prevented to avoid incorrect commutation and the associated noise.

[0004] The object of the present invention is to provide a carbon brush for a DC excited brushed motor which enables stable running, has good running-in properties and occupies a stable position on the carrier plate of a brush holder.

[0005] This problem is solved by a carbon brush for a DC-excited brushed motor with the features of claim 1. Advantageous embodiments of the invention are described in the dependent claims.

[0006] Accordingly, a carbon brush for a DC-excited brushed motor is provided, comprising two parallel longitudinal sides and two parallel transverse sides, which are essentially perpendicular to the longitudinal sides, with the four sides bounded by two opposing end faces. The carbon brush has a single running surface located on one end face, the running surface having a width between 40% and 90% of the total width of the carbon brush and a maximum height of 0.5 mm, extending parallel to the transverse side and perpendicular to the longitudinal side. Such a narrow running surface prevents negative tilting effects in the new condition, which could create a running mark outside the center of the brush.

[0007] Preferably, the longitudinal sides have at least one step through which the longitudinal sides converge towards the end face, resulting in two converging side surfaces that enclose an angle of at least 60°, preferably approximately 90°. It is advantageous if the converging side surfaces are triangular or rounded and form an edge at the end face that constitutes the only contact surface.

[0008] Preferably, the contact surface is formed by two surfaces enclosing an obtuse angle, which is particularly greater than 120° and less than 160°, and preferably about 150°. The obtuse angle ensures stability and prevents the contact surface from being damaged during assembly.

[0009] It is advantageous if the approach surface is linear.

[0010] In an advantageous embodiment, the approach surface is arranged axially symmetrically in the middle of the longitudinal sides.

[0011] It is advantageous for the running characteristics if the approach surface between the transverse sides is located at approximately ¼ of the total height.

[0012] Furthermore, a brush holder comprising a carrier plate and radially aligned carbon holders on this carrier plate is provided, wherein a previously described carbon brush is arranged in each carbon holder.

[0013] Furthermore, a DC-excited brushed motor with asymmetrical pitch is provided, comprising armature windings for forming coils, a commutator with circumferentially uniformly distributed segments, at least one pair of carbon brushes for supplying power to the coils, comprising two carbon brushes bearing against the segments by means of contact surfaces, a motor shaft, and a number n of permanent magnets in the stator for generating a magnetic field, where n is even, greater than or equal to 2, and a multiple of 2, wherein the coils and the commutator are mounted on the motor shaft as a rotatable rotor, and the motor is designed to assume exclusively two coil states, wherein a first coil state exists when one of the two carbon brushes of the at least one brush pair short-circuits two adjacent segments and the other carbon brush of the at least one brush pair bears against a single segment, and a second coil state exists.if both carbon brushes of at least one pair of brushes are in contact with a single lamella, and the pitch ratio of these two coil states is at least 9:1, and the carbon brushes are designed as described above.

[0014] The pitch ratio indicates the proportions of the coil states during one armature rotation, where the first value defines the proportion of the first coil state and the second value defines the proportion of the second coil state. For example, with a pitch ratio of 9:1, the motor is in the medium state for 90% of the armature rotation and in the weak state for 10%. The motor can be, for example, a four-pole motor consisting of two connected two-pole motors. This can include four brushes arranged symmetrically every 90°. With multiple brush pairs, these are preferably mirrored axially; that is, with four brushes, opposite brushes have the same polarity and the same segment overlap. However, only two brushes can also be used if the armature coils are short-circuited to each other. For a six-pole motor, three brush pairs can be used, and so on.

[0015] The two coil states that can be assumed exhibit reduced ripple, resulting in significantly quieter operation of the motor. Preferably, the pitch ratio is at least 8:2. Generally, the more secondary coil states there are relative to the primary coil states, the less noise is produced.

[0016] It is advantageous if the number of commutator segments is not a multiple of four. Preferably, the magnetic field is four-pole.

[0017] In a preferred embodiment, a single brush pair is provided, with two brushes arranged on the commutator at a 90° angle to each other. It is preferred that the first coil state exists when one of the two brushes short-circuits two adjacent segments and the second brush is in contact with a single segment, and the second coil state exists when both brushes are each in contact with a single segment. A coil state in which a total of four segments are short-circuited is never assumed.

[0018] The division ratio (T) is preferably determined by T=T31−T3, where T3 is the overlap ratio for the second coil state and by T3=360°−20*(a−b)360° is given, whereby a=β2+γ−δ2, b=δ2−γ2 is, and b

[0019] ​The motor is preferably dimensioned such that it has a lamella width in a range between 2.5mm and 10mm, a slot width between two lamellae in a range between 0.2mm and 0.8mm and / or a brush width in a range between 1.5mm and 4mm.

[0020] In an advantageous embodiment, the motor is an internal rotor motor whose rotor, formed from the coils, the commutator, and the motor shaft, is arranged inside the magnetic poles. Preferably, the number of laminations is ten and the number of brush pairs is one.

[0021] Furthermore, an adjustment system for a sunroof of a motor vehicle is provided, wherein the adjustment system has a previously described DC excited brushed motor with asymmetric pitch.

[0022] A preferred embodiment of the invention is explained in more detail below with reference to the drawings. Similar or functionally equivalent components are designated by the same reference numerals in the figures. The figures show: Fig. 1: A schematic representation of a DC excited brushed motor with asymmetrical pitch, Fig. 2: a second schematic representation of a DC excited brushed motor, Fig. 2a: a schematic representation of the motor geometry to describe a commutation ratio, Fig. 3: A spatial view of a carbon brush, Fig. 4: A top view of the carbon brush of the Fig. 3, Fig. 5: a longitudinal section through the carbon brush of the Fig. 4 along line AA, Fig. 6: A top view of a coal scuttle with the carbon brush of the Fig. 3, Fig. 7: A spatial view of a connecting wire of the carbon brush of the Fig. 3, as well as Fig. 8: A top view of a DC excited brushed motor with carbon brushes Fig. 3.

[0023] In Fig. Figure 1 shows an electric motor 1 with a stator 2 and a rotor 3, wherein the rotor 3 has a motor shaft 4, armature windings forming coils 5, and a commutator 6, and rotates about an axis of rotation 100. The stator 2 comprises two pole pairs and a pole cap (not shown), which form four permanently excited stator poles 7. This is an internal rotor motor. Ten commutator segments 8 are arranged evenly spaced circumferentially on the commutator 6 of the four-pole motor 1. Two carbon brushes 9 are positioned against the commutator segments 8 at an angle α of 90° to the axis of rotation. A DC voltage, e.g., as a PWM signal, is applied to the two carbon brushes 9 by a control device (not shown), so that a current I is established. The segment-brush system thus serves as a known mechanical commutation system for the commutator motor 1.The commutator segments 8 are evenly distributed around the circumference of the commutator 6, with the carbon brushes 9 sliding on them during the rotation of the rotor. Thus, each carbon brush 9 periodically comes into contact with a slot 8a or an insulated space between two commutator segments 8. The carbon brushes 9 have a contact surface 10 that is larger than a slot 8a, so that the carbon brushes 9 can briefly short-circuit adjacent commutator segments 8. The transition of the carbon brushes 9 between adjacent commutator segments 8 leads to the formation of current ripples exhibiting a slot frequency. The motor 1 has an asymmetrical pitch. In the section . Fig. In the commutation state shown in Figure 1, the first carbon brush 9 covers a single segment 8 while simultaneously the second carbon brush 9 short-circuits two segments 8. This represents a so-called intermediate coil state; two coils 5 are short-circuited and the remaining coils 5 are energized equally, with the current level for each of these coils 5 being 1.

[0024] Such DC-excited brushed motors with asymmetrical pitch have three different coil states, regardless of the number of slots: weak, medium, and strong. This can be determined by the total resistance at the armature and the resulting current ripple. Depending on the current state of the motor, the available coils are energized to varying degrees. This results in different magnetic forces, which in turn create different repulsions between the armature and the permanent magnet / stator. These repulsions generate vibrational noise that affects the slot frequency and its multiples.

[0025] In the high-current coil state, four laminations 8 are commutated, and correspondingly four coils 5 are short-circuited. Four further coils 5 are uniformly energized with a current level of 1, and the remaining two coils 5 are energized more strongly with a current level of 2. The more heavily energized coils 5 generate a high current ripple.

[0026] The weak coil state occurs as a transition state during rotation when the carbon brush has a narrow contact area compared to the lamella width. In this state, only two lamellae 8 are commutated, and thus four coils 5 are uniformly energized at a current level of 1. Six further coils 5 are energized less strongly, each at a current level of 2 / 3.

[0027] Generally, coils 5 with lower current flow produce lower current ripple. Since the current ripple of the high-current coil state is twice that of the medium-current coil state, this state should be avoided to reduce noise. The current ripple of the low-current state is one-third lower than that of the medium-current state.

[0028] A brushed DC motor must pass through at least two coil states during rotation, with the standard medium state always being generated. The weak and strong coil states can be selected by geometrically adjusting the lamination width, slot width, and carbon brush width. To optimize the slot frequency for noise reduction, the motor should remain in the weak coil state for as long as possible and should never enter the strong coil state.

[0029] Regardless of the current coil state, the total energy in the armature remains constant. Therefore, a DC motor can generate the desired torque while still reducing the vibration noise associated with the slot frequency.

[0030] In the Fig. 2 and Fig. Figure 2a shows schematic representations of a DC-excited brushed motor to define a division ratio of the coil states or the commutation, also called the commutation ratio. The commutator 6 has a diameter in the area of ​​the running surfaces (commutator outer diameter) D. a The motor 1 has a lamella width x in the circumferential direction to the axis of rotation of the rotor at the running surface, which corresponds to a lamella angle β. (β=bπ*360°Da) This corresponds to a slot width y provided between each pair of slats, which corresponds to a slot angle. γ(γ=360°π*sin−1yDa) This corresponds to the following: The carbon brushes have a width z in the circumferential direction to the rotational axis of the rotor at the running surface, which corresponds to a brush angle. δ(γ=360°π*sin−1zDa) This corresponds to two carbon brushes enclosing a position angle α along the circumference to the axis of rotation.

[0031] According to the invention, the components of the motor are now dimensioned in such a way that the strong coil state is never reached.

[0032] The division ratio T of the coil states medium to weak results from the following relationships for asymmetric commutation and two brushes with α = 90°: T=T31−T3, where T3 is the overlap ratio for the overlap with three lamellae and by T3=360°−20*(a−b)360° is given, whereby a=β2+γ−δ2, b=δ2−γ2 is. The following applies: b <a, so dass ausschließlich zwei oder drei Lamellen von den Kohlebürsten überdeckt sind. Eine Überdeckung von vier Lamellen ist dabei ausgeschlossen.

[0033] Preferably, the ratio T of the coil states from medium to weak is at least 9:1, meaning that for 90% of the armature rotation, the motor is in the medium state, and for 10% of the armature rotation, it is in the weak state. The ratio of 9:1 thus indirectly relates to the time spent transitioning between different states. It is particularly preferred if several coil states are weak and the proportion of weak coil states increases.

[0034] The motor is preferably dimensioned such that x is in a range between 2.5mm and 10mm, y is in a range between 0.2mm and 0.8mm and z is in a range between 1.5mm and 4mm.

[0035] By adjusting the commutator overlap as described above, a reduction in the noise of the slot frequency can be achieved, while maintaining the stability of the brush system.

[0036] The Fig. Figures 3 to 5 show a carbon brush 9 that is suitable for a DC excited brushed motor with asymmetric pitch and the previously defined pitch ratio and exhibits particularly good running-in and running characteristics.

[0037] The carbon brush 9 has two parallel longitudinal sides 11, which, in the installed state, extend substantially perpendicular to the axis of rotation 100, and two transverse sides 12, also parallel to each other, which are substantially perpendicular to the first longitudinal sides 11 and also extend perpendicular to the axis of rotation 100. The four sides 11, 12 are covered by two opposing end faces 13 and define a rectangular longitudinal cross-sectional area.

[0038] The longitudinal sides 11 have two steps 14, 15 through which the longitudinal sides 11 converge towards the end face 13. The first step 14 forms a pair of parallel side surfaces 16, the distance between which is smaller than the distance between the longitudinal sides 11 before the first step 14. The second step 15 extends to the end face 13. In the area of ​​the second step 15, the longitudinal sides 11 converge continuously, resulting in two converging side surfaces 17 that enclose an angle □ of at least 60°, preferably approximately 90°. The two steps 14, 15 are provided to achieve a desired width dimension of a leading surface. The first step 14 is optional. It can be provided for inserting the carbon brush into existing carbon holders that are too wide, or if, for manufacturing reasons, it is not possible to reduce the carbon to the required width at the strand area.During the running-in of the carbon brush, the width z is chamfered or rounded to break the edges of the second step 15.

[0039] The converging side surfaces 17 in the area of ​​the second step are triangular in shape. They form an edge 18 with a width z and a height h at the end face 13. The edge 18 represents the starting surface 19 of the carbon brush. The starting surface 19 extends over a width z that is between 40% and 90% of the total width of the carbon brush z. G This corresponds to the overall width being the length of the transverse sides. The starting surface is positioned centrally between the longitudinal sides 11. As the carbon brush runs in, the width z is chamfered or rounded to break the edges of the second step 15. The width of the starting surface z is, for example, greater than 2 mm.

[0040] As in the average of the Fig. As shown in Figure 5, the contact surface 19 is formed by the edge 18. The edge 18 is preferably linear. However, it can also be flattened or rounded with a maximum height h of 0.5 mm. The overall height of the carbon brush h G corresponds to the length of the longitudinal sides. The edge 18 is formed by two surfaces 20, 21 that enclose an obtuse angle λ. The angle λ is preferably greater than 120° and less than 160°, particularly about 150°. The approach surface 19 is located between the transverse sides 12 at approximately ¼ of the total height h. G It is arranged. It extends parallel to the transverse sides 12 and perpendicular to the axis of rotation 100. Only this single approach surface 19 is provided.

[0041] In the Fig.Figures 6 to 8 show the arrangement of a carbon brush 9 in a carbon brush holder 22. The carbon brush holder 22 is arranged on a carrier plate 23 of a brush holder 24 and is radially oriented. The brush holder 24 surrounds the rotor, which is rotatable about the axis of rotation. A connecting wire 25 leads from each carbon brush 9 held in the holder 22 to one of the electrical components held on the carrier plate 23. The carbon brush 9 is arranged in the carbon brush holder 22 with certain tolerances, resulting in some play. This play is compensated by the contact surface. Due to its low height and central position, this surface allows the carbon brush to run in quickly and centrally, so that it contacts the carrier plate as close as possible to the center of its axis at the 90° position. A torsion spring 26 engages in a recess on the rear longitudinal side 11 and provides preload. The torsion spring 26 rests against the brush holder 24.The second edges 15 prevent negative tilting effects in the new carbon brush, which can create a running track outside the center of the brush. This is crucial because a misalignment of the running track can cause asymmetries in the running directions as well as an incorrect commutation ratio.

[0042] During the break-in process, the carbon brush has its only contact surface on the tangentially extending surface that rests on the commutator segments. This contact surface runs tangentially to the circumferential direction. Thus, only the edge of the carbon brush rests on the commutator segment's circumferential surface. Due to the small height and width of this contact surface, the carbon brush has a small contact area, which leads to both a higher contact pressure on the commutator segments and a higher current density at the interfaces between the carbon brush and the commutator segments. During the break-in process, the edge is worn away by mechanical wear as the commutator's outer diameter wears into the carbon.During the running-in process, the straight leading edge 19 initially rests on the commutator at a single point in the center and is then gradually formed into a radius corresponding to the commutator lamella circumferential surface, penetrating ever deeper into the carbon brush. The leading edge becomes concave and thus widens in both height and width. This creates additional carbon guidance along the commutator lamella circumferential surface. The angle between the converging side surfaces is chosen to be so shallow as to prevent the edge from breaking off at its ends.

[0043] The second chamfered edge (15) prevents the carbon brush from tilting (due to brush holder play, which is greatest when new) and causing the sharp outer edges of the contact surface (19) to interact with the commutator. This prevents the edges from penetrating the commutator slots, which would lead to severe sparking and have a very negative impact on EMC (as well as negative noise effects at slot frequencies). Furthermore, it prevents the transmission of micro-vibrations to the commutator segments (which would be most noticeable at the outer edge of the contact surface), thus preventing unwanted high-frequency noise.

Claims

[1] Carbon brush (9) for a DC excited brushed motor (1) comprising two longitudinal sides (11) arranged parallel to each other and two transverse sides (12) also arranged parallel to each other, which are substantially perpendicular to the longitudinal sides (11), wherein the four sides (11,12) are bounded by two opposite end faces (13), characterized by , that the carbon brush (9) has a single leading-edge surface (19) arranged on an end face (13) and having a width (z) between 40% and 90% of the total width of the carbon brush (z G ) lies, and has a height (h) which is a maximum of 0.5 mm, wherein the approach surface (19) extends parallel to the transverse side and perpendicular to the longitudinal side. [2] Carbon brush according to claim 1, characterized by, that the longitudinal sides (11) have at least one step (15) through which the longitudinal sides (11) converge towards the end face (13), resulting in two converging side surfaces (17) that enclose an angle (φ) of at least 60°, preferably about 90°. [3] Carbon brush according to claim 2, characterized by , that the converging side surfaces (17) are triangular or rounded and form an edge (18) on the front face (13) which forms the only running surface (19). [4] Carbon brush according to any one of the preceding claims, characterized by , that the approach surface (19) is formed by two surfaces (20, 21) which enclose an obtuse angle (λ). [5] Carbon brush according to any one of the preceding claims, characterized by , that the angle (λ) is greater than 120° and less than 160°. [6] Carbon brush according to any one of the preceding claims, characterized by , that the angle (λ) is approximately 150°. [7] Carbon brush according to any one of the preceding claims, characterized by , that the approach surface (19) is linear. [8] Carbon brush according to any one of the preceding claims, characterized by , that the approach surface (19) is arranged axially symmetrically in the middle of the longitudinal sides (11). [9] Carbon brush according to any one of the preceding claims, characterized by , that the approach surface (19) between the transverse sides (12) extends to approximately ¼ of the total height (h G ) is arranged. [10] Brush holder (24) comprising a support plate (23) and carbon holders (22) arranged radially on this support plate (23), wherein a carbon brush (9) according to one of the preceding claims is arranged in each carbon holder (22). [11] DC excited brushed motor (1) with asymmetrical pitch comprising armature windings for forming coils (5), a commutator (6) with circumferentially uniformly distributed segments (8), at least one pair of brushes for supplying power to the coils (5), comprising two carbon brushes (9) bearing against the segments (8) by means of contact surfaces (19), a motor shaft (4), a number n of permanent magnets in the stator for forming a magnetic field, wherein n is even, greater than or equal to 2 and a multiple of 2, wherein the coils (5) and the commutator (6) are mounted on the motor shaft (4) as a rotatable rotor, characterized bythat the motor is designed to assume exclusively two coil states, wherein a first coil state exists when one of the two carbon brushes (9) of the at least one brush pair short-circuits two adjacent laminations (8) and the other carbon brush (9) of the at least one brush pair is in contact with a single lamination (8), and a second coil state exists when both carbon brushes (9) of the at least one brush pair are in contact with a single lamination (8), wherein the pitch ratio (T) of these two coil states is at least 9:1, and wherein the carbon brushes (9) are designed according to any one of claims 1 to 9. [12] DC excited brushed motor according to claim 11, characterized by that the division ratio (T) is at least 8:

2. [13] DC excited brushed motor according to claim 11 or 12, characterized by , that the number of lamellae of the lamellae (8) of the commutator (6) is not a multiple of four. [14] DC excited brushed motor according to any one of the preceding claims 11 to 13, characterized by , that the motor has a single pair of brushes with two carbon brushes (9) arranged on the commutator (6) at an angle (α) of 90° to each other. [15] DC excited brushed motor according to any one of the preceding claims 11 to 14, characterized by that the magnetic field is quadripolar. [16] DC excited brushed motor according to claim 14 or 15, characterized by , that the first coil state is present when one of the two carbon brushes (9) short-circuits two adjacent lamellae (8) and the second carbon brush (9) is in contact with a single lamella (8) and the second coil state is present when both carbon brushes (9) are each in contact with a single lamella (8). [17] DC excited brushed motor according to any one of the preceding claims 11 to 16, characterized by, that the division ratio (T) by T=T31−T3, is given, where T3 is the coverage ratio for the second coil state and by T3=360°−20*(a−b)360° is given, whereby a=β2+γ−δ2, b=δ2−γ2 is, and b [18] DC excited brushed motor according to any one of the preceding claims 14 to 17, characterized by , that the width of the lamella (8) (x) is in a range between 2.5mm and 10mm, the slot width between two lamellae (y) is in a range between 0.2mm and 0.8mm and / or the width of the brush (z) is in a range between 1.5mm and 4mm. [19] DC excited brushed motor according to any one of the preceding claims 11 to 18, characterized by ​, that the motor is an internal rotor motor, the rotor of which is formed from the coils (5), the commutator (6) and the motor shaft (4) is arranged inside the magnetic poles (7). [20] DC excited brushed motor according to any one of the preceding claims 14 to 19, characterized by that the number of lamellae is ten. [21] Adjustment system for a sunroof of a motor vehicle, wherein the adjustment system comprises a DC excited brushed motor with asymmetric pitch according to any one of the preceding claims 11 to 20.

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