DC motor for an actuator
Patent Information
- Application Number
- EP2023710845
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2023-03-08
- Publication Date
- 2026-01-14
AI Technical Summary
Existing DC motors for actuators have complex and cost-intensive assembly processes due to the attachment of permanent magnets and end shields, which complicates the manufacturing and increases production costs.
A DC motor design featuring a rotor with a laminated core and a magnetic ring that is either one-piece or composed of separately attached magnets, with a pole tube and end shields that utilize a locking hook connection and inwardly projecting lugs for secure attachment without additional fasteners, simplifying the assembly and reducing costs.
The design achieves a simple and secure attachment of the magnetic ring and end shields, reducing assembly complexity and costs while ensuring axial and rotational stability, thus enhancing the motor's production efficiency and service life.
Smart Images
Figure EP2023055883_12092024_PF_FP_ABST
Abstract
Description
[0001] DESCRIPTION
[0002] DC motor for an actuator
[0003] The invention relates to a DC motor, in particular for an actuator.
[0004] Such a DC motor is known, for example, from DE 198 33 802 A1. The DC motor disclosed therein comprises a rotor with an armature winding, which is arranged in a rotationally fixed manner on a rotatable rotor shaft, and a magnetic ring with several separate permanent magnets distributed over the circumference, which circumferentially enclose the armature winding of the rotor. Furthermore, the disclosed DC motor comprises a first bearing plate with a first bearing arrangement, by means of which the rotor shaft is rotatably mounted, wherein the first bearing plate is arranged on a first axial side of the magnetic ring and bears axially against the magnetic ring. In addition, the DC motor has a commutator, which is arranged axially adjacent to the rotor and in a rotationally fixed manner on the rotor shaft.Furthermore, the disclosed DC motor has a pole tube which circumferentially surrounds the magnetic ring and is arranged in a pot-shaped housing in which the pole tube on the one hand axially rests against the housing itself, wherein the pole tube on the other hand axially rests against the bearing shield and is thus fixed in the axial direction.
[0005] The bearing plate and the housing of the DC motor disclosed in DE 198 33 802 A1 are, for example, screwed, riveted, glued, or welded together, making assembly relatively complex and thus costly. DE 195 27 984 A1 and EP 0 305 915 A1 each further disclose a DC motor circumferentially surrounded by a tubular housing. A bearing plate is arranged at each of the two axial ends of the housing and is connected to the housing via locking hooks. The permanent magnets of the DC motor disclosed in DE 195 27 984 A1 are laboriously secured in the housing, for example, by gluing.
[0006] The invention is therefore based on the object of creating a DC motor, in particular for an actuator, which is characterized by a particularly simple structure with regard to the fastening of the permanent magnets and the bearing shields.
[0007] This object is achieved by a DC motor having the features of main claim 1.
[0008] A DC motor, particularly for an actuator, comprises a rotor with an armature winding that is arranged in a rotationally fixed manner on a rotatable rotor shaft. The rotor typically has a laminated core formed from stacked electrical sheets and comprising a plurality of pole teeth, each wound with enameled copper wire, whereby a coil is formed on each pole tooth, forming a pole of the rotor. The entirety of the wound and electrically connected coils is referred to as the armature winding. The DC motor further comprises a stationary permanent-magnetic magnet ring that circumferentially encloses the armature winding of the rotor. This magnet ring can either be formed in one piece or, alternatively, comprise a magnet retaining ring with a plurality of separately attached permanent magnets, which are arranged and fastened at a distance from one another, for example, along the circumference of the magnet ring.To ensure the rotor's rotation, an air gap is formed between the rotor and the magnetic ring, completely encircling the rotor, so that there is no direct contact between the rotor and the magnetic ring or between the rotor and the permanent magnets. The magnetic ring preferably extends axially over the entire axial length of the rotor or over the entire axial length of the rotor's laminated core.
[0009] The DC motor further comprises a first bearing plate with a first bearing arrangement, by means of which the rotor shaft is rotatably mounted. For this purpose, the bearing plate can have a bearing means that accommodates the rotor shaft and supports the rotor shaft at least radially. The first bearing plate is arranged on a first axial side of the magnetic ring. The DC motor further comprises a commutator, which is arranged axially adjacent to the rotor on a second axial side of the magnetic ring in a rotationally fixed manner on the rotor shaft and is electrically connected to the armature winding. Accordingly, the commutator is arranged on the opposite side of the magnetic ring with respect to the first bearing plate.
[0010] Furthermore, the DC motor comprises a second bearing plate arranged axially adjacent to the commutator, having a second bearing arrangement by means of which the rotor shaft is rotatably mounted. For this purpose, the bearing plate has, for example, a bearing means that receives the rotor shaft and supports the rotor shaft at least radially. The second bearing plate is preferably arranged adjacent to the axial end of the commutator facing away from the magnetic ring. The second bearing plate has a sliding contact arrangement that contacts the commutator radially, wherein the sliding contact arrangement preferably has a sliding contact body that bears radially directly against the commutator and rubs against the commutator during the rotation of the rotor.The sliding contact bodies can, for example, be electrically connected to a voltage source, whereby the armature winding is supplied with electrical current via the sliding contact bodies and the commutator, which causes the magnetization of the coils.
[0011] In addition, the DC motor includes a pole tube that circumferentially encloses the rotor, the two bearing plates, and the magnet ring. The pole tube forms a housing for the DC motor, into which the aforementioned components of the DC motor are preferably inserted axially. Furthermore, the pole tube serves as a return ring. Of course, another housing can be arranged radially surrounding the pole tube.
[0012] The magnetic ring rests against one of the bearing shields on one of the two axial sides and against an end stop on the pole tube on another of the two axial sides. For example, the magnetic ring can rest against the first bearing shield on the first axial side, with the magnetic ring then resting against the end stop of the pole tube on the second axial side. Alternatively, the magnetic ring can rest against the end stop on the first axial side and against the second bearing shield on the second axial side. Thus, the end stop can be arranged either on the first axial side of the magnetic ring or on the second axial side of the magnetic ring, with the magnetic ring always resting against the bearing shield that is arranged on the axial side of the magnetic ring opposite the end stop. Consequently, the magnetic ring is essentially axially fixed and secured against displacement by the end stop on the one hand and by one of the bearing shields on the other.For this purpose, the pole tube preferably has a structure that projects radially inward from the inner wall of the pole tube, against which the magnetic ring rests and against which the magnetic ring is pressed by the opposite bearing plate. The inwardly projecting structure can be formed, for example, by a circumferential shoulder or, alternatively, by several inwardly projecting stop elements.
[0013] In a particularly advantageous embodiment of the invention, the pole tube has the end stop, against which the magnetic ring rests, on the commutator side. In addition, the first bearing plate rests against the magnetic ring on the other axial side. The magnetic ring therefore rests against the end stop with its axial end facing away from the first bearing plate and against the first bearing plate on the first axial side, whereby the magnetic ring is fixed in both axial displacement directions. The first bearing plate is axially positioned such that the magnetic ring is pressed against the commutator-side end stop with a defined contact force and is thus secured against displacement by a form-fitting fit between the first bearing plate and the end stop.
[0014] In a particularly advantageous embodiment of the invention, the two bearing plates are each fastened to the pole tube by means of a locking hook connection formed by locking hooks. For this purpose, the pole tube has an engagement structure at both axial ends into which the locking hooks of the respective bearing plate can engage, wherein the locking hooks are oriented such that, once the locking hooks have engaged, the bearing plates can no longer be moved against the assembly-related insertion direction. In particular, the locking hooks of the first bearing plate are axially positioned such that the pressing of the magnetic ring against the end stop is ensured, i.e., the locking hooks only engage in the engagement structure when the bearing plate has been pushed far enough into the pole tube for the bearing plate to rest against the magnetic ring.During assembly of the DC motor, after inserting the rotor and the magnetic ring, the end shields are pushed into the pole tube at both axial ends of the pole tube until the respective locking hooks engage with the corresponding engagement structure of the pole tube, thereby securing the end shields against outward axial displacement. The press fit of the first end shield on the magnetic ring additionally ensures that an axially outward-acting preload force is exerted on the end shield, pressing the locking hooks against the engagement structure so that the locking hooks firmly engage in the engagement structure. The locking hooks also provide anti-twist protection for the end shields. Furthermore, the asymmetrical distribution of the locking hooks over the circumference allows the rotational orientation of the end shields to be determined, so that the end shields can only be inserted into the pole tube in a specific rotational position.
[0015] The second bearing plate, on the other hand, has an additional stop structure that, for example, abuts the end face of the pole tube. This stop structure also allows an outward preload force to be exerted on the second bearing plate, ensuring a firm engagement of the locking hooks in the engagement structure. Using the locking hook connection, not only the bearing plates themselves but also the magnetic ring are fastened to the pole tube in a single step and without additional fasteners, thus ensuring simple and secure attachment of the bearing plates and the magnetic ring.
[0016] In a particularly preferred embodiment of the invention, the first bearing plate has a plurality of, in particular two, essentially axially extending arms against which the magnetic ring bears axially. The arms thus extend from a bearing plate base body at least in the axial direction, but can also extend in sections in the radial direction, for example in an arcuate manner. In addition, the arms are preferably elastically deformable at least to a small extent. The elastic deformability basically depends on the geometry of the arms and their material selection. Due to the elastic deformability of the arms, they can be elastically deformed and thus preloaded during installation of the first bearing plate, ensuring firm engagement of the locking hooks in the engagement structure.In addition, the bearing shield base body can be equipped with a relatively rigid geometry in the area of the bearing arrangement, which enables secure mounting of the rotor shaft.
[0017] In a further preferred embodiment of the invention, the first bearing plate has a plurality of radially outwardly extending webs, from each of which a locking hook extends axially towards the magnetic ring. The bearing plate thus preferably has a type of skeletonized geometry, with a solid bearing plate base body in the region of the bearing arrangement, from which the webs extend radially outwards in a star shape as far as the inner wall of the pole tube. From each radial end of a web, a locking hook extends axially towards the magnetic ring, whereby the locking hooks do not extend as far as the magnetic ring. The locking hooks can be formed in the immediate vicinity of the base body or have axially extending arms to whose ends the actual hooks are attached. These arms are slightly radially elastically deformable so that the hooks engage in the corresponding recesses upon reaching an engagement structure after being inserted.
[0018] In a further advantageous embodiment of the invention, the locking hooks are each formed integrally with the first and second bearing plates. The locking hooks are thus integrated into the respective bearing plate, for example, into a plastic bearing plate manufactured by injection molding, so that the locking hooks do not need to be additionally mounted to the bearing plate. This results in advantages in terms of production time and costs, as well as in terms of the tolerance chain, particularly with regard to the contact force of the first bearing plate against the magnetic ring.
[0019] The end stop is preferably formed by a plurality of lugs extending radially inward from an inner wall of the pole tube. Particularly preferably, the pole tube has three lugs evenly distributed over the circumference, which do not extend radially beyond the inner circumference of the magnet ring, thus forming the stop in a simple manner.
[0020] The magnetic ring preferably has recesses corresponding to the lugs, into which the lugs engage in a form-fitting manner. The recesses are preferably semi-cylindrical depressions extending axially from the end face of the magnetic ring, into which the lugs engage. During assembly, the magnetic ring is pushed onto the lugs with the recesses so that the lugs are at least partially enclosed by the recess in the circumferential direction, thereby preventing rotation of the magnetic ring. Consequently, the magnetic ring is secured by the stop against both axial displacement and rotation, which would be very complex to achieve with an additional stop component.
[0021] In a further advantageous embodiment of the invention, the lugs are arranged asymmetrically along the inner circumference of the pole tube, with the recesses being arranged correspondingly asymmetrically along the circumference of the magnetic ring. The angle between two adjacent lugs of the pole tube or two adjacent recesses of the magnetic ring thus varies over the circumference of the DC motor, so that the magnetic ring can only be pushed onto the lugs with the recesses in a specific rotational position. This ensures that the magnetic poles of the magnetic ring are correctly aligned. This is particularly advantageous when using an anisotropic magnet.
[0022] In a further particularly advantageous embodiment of the invention, the first bearing arrangement is formed by a first plain bearing formed integrally with the first bearing plate, wherein the rotor shaft is mounted directly in the first plain bearing. The first bearing plate and thus the integrated plain bearing are preferably made of a plastic with particularly good sliding properties, so that the rotor shaft can rotate directly in the plain bearing without an additional, separate bearing element. This simplifies the assembly of the DC motor and reduces production costs compared to a prior art DC motor, while still achieving a relatively long service life of the plain bearing.
[0023] In a further advantageous embodiment of the invention, the sliding contact arrangement has a plurality of sliding contact holders formed integrally with the second bearing plate. For this purpose, the second bearing plate is preferably manufactured as an injection-molded part from a plastic with electrical insulating properties, allowing complex geometries to be realized relatively quickly and cost-effectively. The sliding contact holders accommodate the sliding contact bodies rubbing against the commutator and press them against the commutator, for example, using a corresponding spring. The integration of the sliding contact holders into the second bearing plate eliminates the need for a separate, cost-intensive sliding contact holder.
[0024] In another particularly advantageous embodiment of the invention, the pole tube has a plurality of pockets distributed along the inner circumference, into which the locking hooks engage. The pockets can be rectangular, for example, but have at least one straight edge into which the locking hook can engage. The pockets can be formed, for example, as a recess extending from the inner surface, but can alternatively also be designed like a window, as a radially continuous opening in the pole tube wall.
[0025] A particularly preferred embodiment is explained in more detail with reference to the accompanying drawings. They show:
[0026] Figure 1 is a perspective partial sectional view along the rotational axis of the DC motor according to the invention,
[0027] Figure 2 is a longitudinal sectional view of the DC motor of Figure 1 through the arms of the first bearing plate axially adjacent to the magnetic ring,
[0028] Figure 3 is a longitudinal sectional view of the DC motor of Figure 1 through the end stop of the pole tube adjacent to the magnetic ring, the course of which is indicated schematically in Figure 4,
[0029] Figure 4 is a cross-sectional view of the pole tube of the DC motor of Figure 1, and
[0030] Figure 5 is a perspective view of the magnetic ring of the DC motor of Figure 1.
[0031] Fig. 1, Fig. 2, and Fig. 3 show a DC motor 10 for an actuator. The DC motor 10 comprises a rotor 14 that is rotationally fixedly mounted on a rotatable rotor shaft 12 and has a laminated core 141 formed from a plurality of stacked electrical sheets. The star-shaped laminated core 141 has a plurality of pole teeth 142, each equipped with a coil 143 wound from enameled copper wire. The coils 143 are all electrically interconnected and form the armature winding 16.
[0032] The DC motor 10 further comprises a hollow cylindrical and anisotropic magnetic ring 20 with a plurality of magnetic poles integrated into the magnetic ring 20, which circumferentially enclose the armature winding 16. Each coil 143 through which electric current flows during operation, together with the pole tooth 142 forming the magnetic core, forms an electromagnetic pole of the rotor 14. The electromagnetic poles interact with the poles of the permanent magnets to generate the rotational movement of the rotor 14.
[0033] The DC motor 10 comprises a first spider-shaped bearing plate 30, which is arranged on a first axial side A of the magnetic ring 20. The bearing plate 30 is made of a particularly lubricious plastic material and has a first bearing arrangement 38, which is formed by a first, hollow-cylindrical plain bearing 39 integrated into the first bearing plate 30, wherein the rotor shaft 12 is rotatably mounted directly in the plain bearing 39.
[0034] The DC motor 10 further comprises a commutator 18 with a plurality of contact elements 19 distributed along its circumference. The commutator 18 is arranged on a second axial side B of the magnetic ring 20 adjacent to the magnetic ring 20.
[0035] Furthermore, the DC motor 10 has a second bearing plate 40, which is arranged axially adjacent to the commutator 18 on the second axial side B of the magnetic ring 20, wherein the second bearing plate 40 is arranged on the side of the commutator 18 opposite the magnetic ring 20. The second bearing plate 40, like the first bearing plate 30, is made of a particularly lubricious plastic material and comprises a second bearing arrangement 44, which is formed by a second, hollow-cylindrical, second plain bearing 45 integrated into the second bearing plate 40, wherein the rotor shaft 12 is mounted directly in the second plain bearing 45.
[0036] Furthermore, the second bearing plate 40 has a sliding contact arrangement 46 with sliding contact holders 48 integrated into the second bearing plate 40, which extend axially in the direction of the commutator 18, as can be clearly seen in Fig. 1 and Fig. 2. In each sliding contact holder 48, a radially displaceable sliding contact body 49 is arranged, which is pressed towards the commutator 18 by a sliding contact spring (not shown), whereby each sliding contact body 49 is in permanent sliding contact with the contact plates 19 of the commutator 18 rotating during operation. The sliding contact bodies 49 are electrically conductive and electrically connected to a voltage source (not shown), whereas the contact plates 19 are electrically connected to the armature winding 16.The sliding contact between the sliding contact bodies 49 and the contact elements 19 closes the circuit between the armature winding 16 and the voltage source, so that current flows through the individual coils 143 of the armature winding 16. This magnetizes the coils 143, and the electromagnetic field generated in the coils 143 is intermittently reversed by the various interconnected contact elements 19 of the commutator 18 by reversing the current direction in the coils 143, thereby generating or maintaining the rotational movement of the rotor 14.
[0037] In addition, the DC motor 10 comprises a hollow cylindrical pole tube 50 which circumferentially encloses the rotor 14, the two bearing plates 30, 40 and the magnet ring 20. The pole tube 50 has an end stop 52 which is formed by three lugs 54 extending radially inward from an inner wall 56 of the pole tube 50, as shown in Fig. 3 and Fig. 4, wherein the lugs 54 are distributed asymmetrically, i.e. unevenly, over the circumference and have a circular cross-section with respect to the radial extension direction. Axially, the lugs 54 are arranged on a common transverse plane, wherein the lugs 54 are arranged axially adjacent to, but spaced from, the commutator 18 on the side of the commutator 18 facing the first axial side A.
[0038] The magnetic ring 20 has three recesses 22 corresponding to the lugs 54 of the pole tube 50, which are distributed asymmetrically over the circumference of the magnetic ring 20 in the same way as the lugs 54, as shown in Fig. 5. The recesses 22 extend radially from a radial inner wall 201 of the magnetic ring 20 to a radial outer wall 202 of the magnetic ring 20 and have a substantially semi-cylindrical cross-section, with each recess 22 being open to an end face 203 of the magnetic ring 20. The outer diameter of the magnetic ring 20 substantially corresponds to the inner diameter of the pole tube 50, so that the magnetic ring 20 bears radially on the inside against the pole tube 50. Axially, the magnetic ring 20 bears against the end stop 52, with the recesses 22 being pushed axially onto the lugs 54 and circumferentially encompassing the lugs 54.As a result, the magnetic ring 20 is secured against displacement in a first axial direction and against rotation in the circumferential direction, wherein the magnetic ring 20 can only be pushed onto the noses 54 in a specific rotational position due to its magnetic anisotropy due to the asymmetrical arrangement of the noses 54.
[0039] The first bearing plate 30 has two arms 34 extending radially from the first plain bearing 39 in a first section 301 and axially in a second section 302, wherein the magnetic ring 20 bears axially against the arms 34, as shown in Fig. 1 and Fig. 2. The arms 34 extend axially so far that a relatively large free space is formed between the plain bearing 39 and the rotor 14. The two arms 34 are preferably arranged radially opposite one another and press the magnetic ring 20 axially against the end stop 52, so that the magnetic ring 20 is axially secured against displacement in a second axial direction and is thus completely fixed within the pole tube 50.
[0040] In addition, the first bearing plate 30 has three axially extending locking hooks 32, each extending axially from a radial end of a radially outwardly extending web 36 in the direction of the magnetic ring 20, as shown in Fig. 1 and Fig. 3. Furthermore, the second bearing plate 40 also has three axially extending locking hooks 42, which extend axially from the bearing plate 40 in the direction of the magnetic ring 20. The pole tube 50 also has a total of six window-like pockets 58, 59 distributed along the circumference, with three pockets 59 on the first axial side A of the magnetic ring 20 being assigned to the locking hooks 32 of the first bearing plate 30 and three further pockets 58 on the second axial side B of the magnetic ring 20 being assigned to the locking hooks 42 of the second bearing plate 40 and being arranged correspondingly thereto.The locking hooks 32, 42 each have an axially outwardly extending projection 33, 43, wherein each locking hook 32, 42 tapers from the projection 33, 43 on its respective radial outer side toward the locking hook tip. Due to the taper, the locking hooks 32, 42 are pressed radially inward during assembly, i.e., during insertion of the bearing shields 30, 40 into the pole tube 50, whereby the locking hook arms 37 are elastically deformed. As soon as the locking hooks 32, 42 reach the pockets 58, 59, the locking hooks move radially outward. Each pocket 58, 59 receives the locking hook 32, 42 assigned to it in the end position of the bearing plates 30, 40, wherein each pocket 58, 59 has an engagement surface 581, 591 which is engaged behind by the respective projection 33, 43 of the locking hook 32, 42.This secures each bearing plate 30, 40 against axial displacement contrary to the assembly-related insertion direction, whereby the respective locking hook connection additionally secures the bearing plates 30, 40 against twisting.
[0041] The locking hooks 32 of the first bearing plate 30 on the first axial side A of the magnetic ring 20, or their projection 33, are positioned with respect to the axial end of the arms 34 on the magnetic ring side such that, in order for the locking hooks 32 to engage in the corresponding pockets 59, the arms 34 axially adjacent to the magnetic ring 20 must undergo a slight elastic deformation in both the axial section 302 and the radial section 301. Thus, when inserting the first bearing plate 30, a certain assembly force must be applied in order to cause the locking hooks 32 to engage in the pockets 59. The elastic deformation of the arms 34 causes an axial contact force on the magnetic ring 20, which presses the magnetic ring 20 against the end stop 52 and securely fastens the magnetic ring 20.Furthermore, due to the elastic deformation of the arms 34, an axial outward-acting counterforce is exerted on the first bearing plate 30, which presses the projections 33 of the respective locking hooks 32 against the corresponding engagement surface 591 of the pockets 59, thus ensuring a firm fit of the first bearing plate 30. In addition, the locking hooks 32 engaging in the pockets 59 act as anti-twist protection for the first bearing plate 30.
[0042] The second bearing plate 40, on the other hand, has a plurality of stop means 41 distributed around the circumference, which, in the end position of the second bearing plate 40, bear axially against the end face 55 of the pole tube 50 on the second axial side B of the magnetic ring 20. The locking hooks 42 of the second bearing plate 40 on the second axial side B of the magnetic ring 20, or their respective projection 43, are positioned with respect to the stop means 41 bearing against the end face 55 such that in order for the locking hooks 42 to engage in the corresponding pockets 58, the stop means 41 must undergo a slight elastic deformation. Thus, when inserting the second bearing plate 40, a certain assembly force must be applied to cause the locking hooks 42 to engage in the pockets 58.The elastic deformation of the stop means 41 causes an outwardly directed axial force which is exerted on the second bearing plate 40 and thus presses the projections 43 of the respective locking hooks 42 against the corresponding engagement surfaces 581 of the pockets 58 and thus ensures a firm fit of the second bearing plate 40.
[0043] Consequently, the end shields 30, 40 are only fastened in the pole tube 50 by the respective latching hook connection, wherein the magnetic ring 20 is additionally secured both axially and against rotation by means of the end stop 52 with the lugs 54, whereby the DC motor 10 according to the invention is characterized by a particularly simple and cost-effective manufacture.
Claims
PATENT CLAIMS 1. DC motor (10) in particular for an actuator comprising: - a rotor (14) with an armature winding (16) which is arranged in a rotationally fixed manner on a rotatable rotor shaft (12), - a magnetic ring (20) with several permanent magnets distributed over the circumference, which circumferentially enclose the armature winding (16) of the rotor (14), - a first bearing plate (30) with a first bearing arrangement (24) by means of which the rotor shaft (12) is rotatably mounted, wherein the first bearing plate (30) is arranged on a first axial side (A) of the magnetic ring (20) and - a commutator (18) which is arranged axially adjacent to the rotor (14) on a second axial side (B) of the magnetic ring (20) in a rotationally fixed manner on the rotor shaft (14), - a second bearing plate (40) arranged axially adjacent to the commutator (18) with a second bearing arrangement (44) by means of which the rotor shaft (12) is rotatably mounted, wherein the second bearing plate (40) has a sliding contact arrangement (46) radially contacting the commutator (18), - a pole tube (50) which circumferentially encloses the rotor (14), the two bearing plates (30, 40) and the magnetic ring (20), wherein the magnetic ring (20) bears against one of the bearing plates (30, 40) on one of the two axial sides (A, B) and bears against an end stop (52) on the pole tube (50) on another of the two axial sides (B, A).
2. DC motor (10) according to claim 1, characterized in that the pole tube (50) has the end stop (52) against which the magnetic ring (20) rests on the commutator side and the first bearing shield (30) rests against the magnetic ring (20) on the other axial side (A).
3. DC motor (10) according to claim 1 or 2, characterized in that the two bearing plates (30, 40) are each fastened to the pole tube (50) by means of a locking hook connection formed by locking hooks (32, 42).
4. DC motor (10) according to one of the preceding claims, characterized in that the first bearing plate (30) has substantially axially extending arms (34) against which the magnetic ring (20) bears axially.
5. DC motor (10) according to one of the preceding claims, characterized in that the first bearing plate (30) has a plurality of radially outwardly extending webs (36), from the respective end of which a locking hook (32) extends axially in the direction of the magnetic ring (20).
6. DC motor (10) according to one of claims 3-5, characterized in that the locking hooks (32, 42) are each formed integrally with the first and the second bearing plate (30, 40).
7. DC motor (10) according to one of claims 2-6, characterized in that the end stop (52) is formed by a plurality of lugs (54) which extend radially inwards from an inner wall (56) of the pole tube (50).
8. DC motor (10) according to claim 7, characterized in that the magnetic ring (20) has recesses (22) corresponding to the lugs (54) into which the lugs (54) engage in a form-fitting manner, whereby an anti-twist device for the magnetic ring (20) is formed.
9. DC motor (10) according to claim 8, characterized in that the lugs (54) are arranged asymmetrically along the inner circumference of the pole tube (50), wherein the recesses (22) are arranged in a corresponding manner asymmetrically along the circumference of the magnetic ring (20).
10. DC motor (10) according to one of the preceding claims, characterized in that the first bearing arrangement (38) is formed by a first plain bearing (39) which is formed integrally with the first bearing plate (30), wherein the rotor shaft (12) is mounted directly in the first plain bearing (39).
11. DC motor (10) according to one of the preceding claims, characterized in that the sliding contact arrangement (46) has a plurality of sliding contact holders (48) which are formed integrally with the second bearing plate (40).
12. DC motor (10) according to one of claims 3-9, characterized in that the pole tube (50) has a plurality of pockets (58, 59) distributed along the inner circumference, into which the locking hooks (32, 42) engage from the inside.
13. DC motor (10) according to one of the preceding claims, characterized in that the first bearing plate (30) is made of a plastic material.