EP2384532A1

EP2384532A1 - Direct current motor

Info

Publication number: EP2384532A1
Application number: EP09795776A
Authority: EP
Inventors: Steven Andrew Evans
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2009-01-05
Filing date: 2009-12-21
Publication date: 2011-11-09
Also published as: DE102009000028A1; CN102273050A; WO2010076256A1

Abstract

The invention relates to a direct current motor comprising a stator having a hollow space for receiving a rotor and a magnetic field creation device by means of which a rotating magnetic multi-pole field can be created. The direct current motor furthermore comprises a rotating-mounted shaft that bears said rotor and a base element connected to the shaft in a rotatably fixed manner, wherein said base element comprises a plurality of recesses. A plurality of permanent magnets are arranged in said recesses of said base element, wherein the shape of said recesses is complementary to the shape of said permanent magnets and said permanent magnets have at least one curved outside contour.

Description

description

DC MOTOR

The invention relates to a DC motor, which contains a stator with a cavity for receiving a rotor and a magnetic field generating device, with which a rotating magnetic multipole field can be generated. Furthermore, the DC motor includes a rotatably mounted shaft, which carries the rotor and a base body which is rotatably connected to the shaft, wherein the base body has a plurality of recesses. In the recesses of the base body a plurality of permanent magnets is arranged, wherein the shape of the recesses is complementary to the shape of the permanent magnet.

State of the art

From DE 19915664 A1 an electric machine with a stator and a rotor formed from a sheet stack is known. The rotor has elongate recesses, in which rectangular permanent magnets can be used to produce a magnetic multipole field. During operation of the DC motor, the magnetic field of the rotor couples to a rotating magnetic field which is generated by electromagnetic coils of the stator. As a result, the rotor is set in rotation and outputs a torque.

To provide a high usable torque, must be a large

Field strength can be provided in the air gap between the rotor and stator. For this purpose, the permanent magnets are placed as close as possible to the peripheral surface of the rotor according to the prior art. As a result, only a narrow web is available on the peripheral surface, which holds the cuboid permanent magnets against the acting centripetal force in the rotor. The transmissible over this web holding force thus limits the maximum speed of the rotor.

Based on this prior art, the present invention seeks to provide a DC motor, which has a comparable

To provide torque and has an improved speed compared to the prior art.

Disclosure of the invention

The object is achieved by a DC motor, which includes a stator having a cavity for receiving a rotor and a magnetic field generating device, with which a rotating magnetic multipole field can be generated. Furthermore, the proposed DC motor includes a rotatably mounted shaft which carries the rotor. This contains a base body which is rotatably connected to the shaft, wherein the base body has a plurality of recesses. In the recesses of the base body a plurality of permanent magnets is arranged, wherein the shape of the recesses is complementary to the shape of the permanent magnets and the permanent magnets have at least one curved outer contour.

According to the invention, it has been recognized that with radially magnetized, arc-shaped permanent magnets, an improved rotor geometry can be realized, in which the permanent magnets have a larger load-bearing contact surface to the surrounding rotor material. As a result, larger centripetal forces can be transmitted, whereby the rotational speed resistance of the rotor increases. At the same time, the inventively proposed rotor geometry is suitable for providing a virtually unchanged magnetization in the air gap between the rotor and stator, so that the available torque is only slightly reduced or even increased.

In a preferred embodiment of the invention, the arcuate permanent magnets have the shape of a circular segment, wherein the circular segment particularly preferably covers about one third of a full circle.

This can be done by mirror symmetry arrangement of two permanent magnets a circle segment of about two thirds of a full circle are covered, so that in each case two permanent magnets surround a magnetic pole piece of the rotor.

A particularly favorable manufacturability of the permanent magnets is obtained in particular when the permanent magnets have a radial termination of the length b and a tangential termination of the length a, wherein the ratio of a to b is about 1. The expert is of course familiar that this numerical value is not strictly observed. Rather, even with deviations, the advantageous effects according to the invention can still be at least partially adjusted.

The inventively proposed rotor can be made for example by means of an injection molding of a filled plastic. Particularly preferably, the proposed rotor is made of a plurality of stampings, which are punched by means of a complementary shaped tool from a sheet, such as a transformer sheet. A plurality of stamped sheets is then fixed in a torsionally rigid manner on the DC motor shaft, for example by means of an exact fitting, so that along the longitudinal extension of the shaft there results an approximately cylindrical laminated core as the rotor main body.

In one embodiment of the invention, identical sheet metal cuts can be used for the laminated core. In this case, a constant cross-section results along the long extension of the rotor. In a development of the invention, at least two different sheet metal sections can be used, so that the cross section of the rotor is not constant along the longitudinal extent.

In this case, at least one stamped sheet according to one particularly preferably has

Sheet metal section tangential connecting webs and / or radially extending ribs. As a result, the field shaping of the multipole field of the rotor can be optimized at the expense of the holding forces of the permanent magnets and thus the rotational speed resistance, and vice versa. In this way either a slow running DC motor with comparatively high torque or a fast running DC motor with lower torque can be made. The invention will be explained in more detail below with reference to embodiments and figures without limiting the general concept of the invention. It shows

1 shows a cross section through a DC motor proposed according to the invention, FIG.

FIG. 2 shows a section from the cross section of a rotor according to the invention,

FIG. 3e in a sheet-metal section of a punching plate which can be used for producing the rotor basic body according to a first exemplary embodiment,

FIG. 4 shows a sheet-metal section of a stamping sheet usable for producing the rotor base body according to a second exemplary embodiment,

FIG. 6 shows a sheet-metal section of a stamping sheet usable for producing the rotor basic body according to a third exemplary embodiment,

FIG. 6 shows a sheet-metal section of a stamping sheet usable for producing the rotor base body according to a fourth exemplary embodiment,

FIG. 7 shows a cross section through a permanent magnet used according to the invention.

Figure 1 shows a DC motor according to an embodiment of the invention. The motor includes a stator 100 and a rotor 200. The stator 100 includes a plurality of pole shoes 1 15, which are separated by slots 1 10 from each other. In the illustrated embodiment, the stator 12 slots 1 10 and 12 pole pieces 1 15 on. The pole shoes 1 15 are over a

Yoke 140 connected to each other to guide the magnetic flux. In a preferred embodiment, the pole pieces 1 15 and the yoke 140 can be made in one piece.

Furthermore, the stator 12 comprises coils each having N turns of an electrical conductor, for example enamel-insulated copper wire. The turns Run partially through the slots 1 10. The coils as such are known in the art and therefore not shown in the figure. The coils of the stator 100 are cyclically acted upon by means of a switching device, not shown, with an electric current. In this way, a magnetic multipole field is created whose orientation relative to the stator 100 changes cyclically. Such a magnetic field is referred to in the context of the present invention as a rotating magnetic field.

The expert is familiar with the fact that the geometry shown with 12 Polschuhπ 1 15 is selected only by way of example. In other embodiments of the invention, the stator may also have a greater or lesser number of pole pieces.

In the cylindrical interior of the stator 100, the rotor 200 is located. The rotor 200 has an axis of rotation 120. The axis of rotation surrounds a

Essentially cylindrical body. The outer surface of the main body of the rotor 200 is separated from the inner surface of the stator 100 by an air gap 130.

Permanent magnets 270 are embedded in the rotor 200. The permanent magnets

270 have an arcuate, in particular a sector-shaped, cross-section. The permanent magnets 270 also generate a magnetic multipole field which, when the DC motor is in operation, couples to the rotating multipole field of the stator. In this way, the rotor 200 rotates with the rotating magnetic field of the stator, whereby a Nutzdrehmoment from the rotor 200 is discharged.

In the illustrated embodiment, the permanent magnets 270 have a circular sector shape with about 120 ° opening angle. In each case two permanent magnets 270 are spaced apart on their inner side facing the shaft 120 by means of a rib 250.

Two permanent magnets 270 each hold a pole piece 210. The pole piece 210 serves to guide the multipole field generated by the permanent magnet. Between two each pair of pole piece 210 enclosing pairs of permanent magnets 270 is a pole piece 220th arranged. In order to be able to manufacture the pole shoes 220 and 210 in one piece, these are connected to one another via webs 260 and ribs 250.

The skilled person is of course familiar that the proposed rotor does not have to have eight permanent magnets 270 in each embodiment of the invention. Depending on the geometry of the stator, the person skilled in the art can also provide a different geometry of the rotor with a larger or a smaller number of permanent magnets 270 and accordingly a number of pole shoes 210 and 220 adapted thereto. The invention does not teach adherence to the geometry shown in FIG

Solution principle.

Figure 2 shows a section of about 90 ° from the rotor shown in Figure 1. The essential advantage of the invention will be clarified with reference to FIG. Figure 2 shows in cross-section two arcuate permanent magnets 270, which each enclose a pole piece 210 partially. The pole pieces 210 are connected via webs 260 to the pole piece 220 visible in the central part of the picture.

Upon rotation of the rotor 200 about the axis of rotation 120, the permanent magnets 270 are accelerated radially outwards by the acting centripetal force. As a result, the permanent magnets 270 with their outer surface 275 at least partially, i. in the area of the partial surfaces 240 and 245, make positive contact with the surface of the pole shoe 220. The pole piece 220 carries the forces acting on the surfaces 240 and 245 via a tensile stress in the shaft 230. The shaft 230 has a relation to the prior art increased material thickness, which allows the transmission of larger forces and thus higher speeds of the rotor. Since the magnetic flux is concentrated in the region of the pole shoes 210 and 220, the increased material thickness 230 remains unaffected by that in the air gap

130 achievable magnetic field strength and thus ultimately also without influence on the usable torque generated by the rotor 200.

In a preferred embodiment of the invention, the main body of the rotor 200 is formed by a laminated core, which has a plurality of

Includes punching plates, which are arranged on the shaft 120. Of the Sheet metal section of the punching plates thus indicates the cross section of the rotor 200. If only identical punching plates are used to construct the basic body of the rotor 200, then the rotor 200 has a constant cross section along its longitudinal extent. If different punching plates are used, the cross section of the rotor changes along its longitudinal extent. In this way, the magnetic and mechanical properties of the rotor can be optimized. Exemplary embodiments for different stamped sheets are given below.

FIG. 3 shows a first exemplary embodiment of a stamped sheet metal for a rotor 200 proposed according to the invention. An opening is arranged centrally in the stamped sheet metal and serves to receive the shaft 120. The sheet-metal section according to FIG. 3 also has four pole shoes 210. These are limited by two recesses 300 and 305, which are provided for receiving the permanent magnets 270. Two recesses 300 and

305 are separated by a rib 250.

Between two adjacent recesses 300 and 305 further pole pieces 220 are respectively arranged on the side facing away from the pole piece 210. Each pole piece 210 is connected to its adjacent pole pieces 220 by a web 260. In this way, the sheet metal section can be made in one piece and with maximum stability. The recesses 300 and 305 are complementary to the outer shape of a permanent magnet 270, i. the permanent magnet can be introduced with predetermined tolerances in the recess. To fix the permanent magnet, a potting compound or an adhesive may be provided. In a further embodiment of the invention, the tolerances of the dimensions of the openings 300 and 305 and the permanent magnets 270 may be selected such that a clamping of the permanent magnet 270 in the opening 300 or 305 results.

FIG. 4 shows a further embodiment of a sheet metal section according to the present invention. The sheet-metal section according to FIG. 4 again has four pole shoes 210, which are connected by means of webs 260 to the respective adjacent pole shoe 220. Each pole piece 210 is surrounded by an opening 300. The opening 300 has the shape of a circular sector with an opening angle of about 240 °. This means that in the opening 300 two permanent magnets can be accommodated with an approximately third circular sector-shaped cross-section. Due to the absence of the ribs 250, the magnetic flux between two adjacent

Permanent magnet 270 in the opening 300 not disturbed. By the webs 260, the sheet metal section according to Figure 4 can still be made in one piece.

FIG. 5 shows a further embodiment of a sheet-metal section for a rotor 200 according to the invention. The sheet-metal section according to FIG. 5 in turn has a plurality of recesses 300 and 305 which are separated from each other by a rib 250. The rib 250 connects a pole piece 210 at its base to the base of two adjacent pole pieces 220. In this way, the sheet metal section of Figure 5 can be made in one piece. Despite the absence of the webs 260, the sheet-metal section according to FIG. 5 has

Contact surfaces 240 and 245, which allow a force transmission between permanent magnets 270 in the openings 300 and 305 and the pole piece 220. Thus, the sheet metal section according to FIG. 5, despite missing webs 260, can exert a holding force opposing the centripetal force on the permanent magnets 270.

A fourth embodiment of a sheet metal section is shown in FIG. The sheet metal section according to FIG. 6 is characterized in that neither ribs 250 nor webs 260 are arranged between the pole shoe regions 210 and the pole shoe regions 220. This results in the least possible disturbance of the magnetic flux of the permanent magnets 270, which can be arranged in the openings 300.

Nevertheless, the sheet metal section according to FIG. 6 is also suitable for exerting a holding force on the permanent magnets 270 via the contact surfaces 240 and 245 and for holding them in their position in the rotor 200 even at high rotational speeds.

Finally, FIG. 7 shows the cross section of a permanent magnet 270. The permanent magnet 270 has a circular sector-shaped base area. Thus, the permanent magnet 270 has a circular outer boundary surface 275, which adjoins the pole piece 220 and the contact surface 240 when the permanent magnet is used in a rotor. Furthermore, the permanent magnet 270 has a circular inner boundary surface 274 which, when the permanent magnet 270 is used in a rotor 200, adjoins the pole shoe 210.

The magnetization 271 of the permanent magnet 270 shown points radially outward. When using the permanent magnet 270 in a rotor according to the invention, the magnetic flux thus proceeds from the surface 275 through the pole piece 220 of the rotor to a pole piece 15 of the stator.

From there, the magnetic circuit connects via the yoke 140 to an adjacent pole piece 1 15, from there via the air gap 130 to the pole piece 210 of the rotor and from there to the inner surface 274 of the permanent magnet 270.

Preferably, the circular sector-shaped permanent magnet 270 has a

Opening angle of 120 °. In the embodiment shown in FIG. 7, the permanent magnet has a radial termination of length b and a tangential termination of length a, which have a ratio of approximately 1: 1. This means that the length a corresponds approximately to the length b. Both measures support the radial magnetization 271 shown in FIG.

The skilled person is of course familiar that the present invention is not limited to the illustrated embodiments. The present description is therefore not to be regarded as limiting, but as illustrative.

Claims

claims

1 . DC motor, containing

a stator (100) having a cavity for receiving a rotor (200) and a magnetic field generating device with which a rotating magnetic multipole field can be generated, - a rotatably mounted shaft (120) carrying the rotor (200),

a base body, which is non-rotatably connected to the shaft (120), the base body having a plurality of recesses (300, 305),

- A plurality of permanent magnets (270) which are arranged in the recesses (300, 305) of the base body, wherein the

Shape of the recesses (300, 305) to the shape of the permanent magnet (270) is complementary, characterized in that

- The permanent magnets (270) have at least one curved outer contour.

2. DC motor according to claim 1, characterized in that the permanent magnets (270) have the shape of a circle segment.

3. DC motor according to claim 2, characterized in that the

Circular segment has an opening of about 110 ° to about 130 °.

4. DC motor according to one of claims 2 or 3, characterized in that the permanent magnets (270) have a radial magnetization (271).

5. DC motor according to one of claims 2 or 4, characterized in that the permanent magnets (270) have a radial termination of the length b and a tangential termination of the length a, wherein the ratio of a to b about 0.9 to about 1.1.

6. DC motor according to one of claims 1 to 5, characterized in that the base body is composed of a plurality of layered punching plates, wherein the punching plates have at least two different laminations.

7. DC motor according to claim 6, characterized in that at least one stamped sheet according to a sheet-metal section tangential connecting webs (260) and / or radially extending ribs (250). 8 DC motor according to one of claims 1 to 7, characterized in that in each case two permanent magnets (270) surround a pole piece (210).