DIRECT-CURRENT ELECTRIC MOTOR AND USE THEREOF AS A DRIVE OF A LIFTGATE

Abstract

A DC electric motor for driving a tailgate of a vehicle is provided, the DC electric motor including a rotor and a stator, the rotor being rotatably supported about an axis of rotation, at least one of the rotor and the stator having a magnetic asymmetry for generating an asymmetric magnetic interaction between the rotor and the stator, wherein the rotor and the stator are configured to assume first positions and second positions relative to each other, wherein a higher holding torque acts between the rotor and the stator in one of the first positions than in one of the second positions due to the asymmetry.

Claims

1. A DC electric motor for driving a tailgate of a vehicle, the DC electric motor comprising a rotor and a stator, the rotor being mounted for rotation relative to the stator about an axis of rotation, wherein, the rotor and/or the stator comprises a magnetic asymmetry means for generating an asymmetric magnetic interaction between the rotor and the stator, wherein the rotor and the stator are configured to assume first positions and second positions relative to each other, wherein a higher holding torque acts between the rotor and the stator in one of the first positions than in one of the second positions due to the asymmetry means.

2. The DC electric motor according to claim 1, wherein the magnetic asymmetry means comprises a physical manipulation of the rotor or a part thereof.

3. The DC electric motor according to claim 1, wherein the magnetic asymmetry means comprises a physical manipulation of the stator or a part thereof.

4. The DC electric motor according to claim 1, wherein the magnetic asymmetry means comprises an inhomogeneity of the material and/or magnetic properties of the rotor or a part thereof.

5. The DC electric motor according to claim 1, wherein the magnetic asymmetry means comprises an inhomogeneity of the material and/or magnetic properties of the stator or a part thereof.

6. The DC electric motor according to claim 1, wherein the rotor and/or the stator comprises at least two pole pieces, wherein the asymmetry means is positioned in one or in a part of the pole pieces.

7. The DC electric motor according to claim 1, wherein the DC electric motor comprises at least two magnets and the magnetic asymmetry means is implemented by an asymmetric switching of at least one of the magnets.

8. Use of the DC electric motor according to claim 1 as a drive for a tailgate of a motor vehicle, the DC electric motor and the asymmetry means being configured in such a way that the holding torque of the DC electric motor is greater than or equal to the torque which the tailgate generates by its own weight on the drive and in particular on the rotor.

Description

BRIEF DESCRIPTION

[0046] Some of the embodiments will be described in detail, with references to the following Figures, wherein like designations denote like members, wherein:

[0047] FIG. 1A shows a schematic representation of an exemplary embodiment of a DC electric motor;

[0048] FIG. 1B shows the DC electric motor from FIG. 1, which has assumed one of the first positions.

[0049] FIG. 2 shows the variation of the holding torque depending on the angle of rotation for a DC electric motor without asymmetry means; and

[0050] FIG. 3 shows the variation of the holding torque depending on the angle of rotation for a DC electric motor according to FIG. 1A and FIG. 1B;

DETAILED DESCRIPTION

[0051] FIG. 1A shows a schematic representation of a DC electric motor 100, which is a four-magnet motor with six rotor poles 110. The DC electric motor comprises a rotor 102 and a stator, which in this representation comprises the magnets 104. The rotor 102 is mounted for rotation relative to the stator about the axis of rotation 106.

[0052] Furthermore, the illustrated DC electric motor 100 is equipped with additional auxiliary magnets 108 which improve the running characteristics of the motor.

[0053] The rotor 102 is rotationally symmetrical about the axis of rotation 106. A pole piece 112 is positioned at each radial end of the rotor poles 110 and extends circumferentially out of the respective rotor pole 110 in both directions.

[0054] Four of the six rotor poles 110 are equipped with a pole piece 112 which has an asymmetry means 114. Two of the pole pieces 112 each have the same design, so that three types of pole pieces 112 are installed in the illustrated DC electric motor 100. The first type comprises pole pieces 112a which have no asymmetry means 114. The first type of pole pieces 112a is symmetrical about a mirror axis extending radially from the axis of rotation 106 through the respective rotor pole. The second type comprises pole pieces 112b having an asymmetry means 114 formed on one side in the circumferential direction. The third type comprises pole pieces 112c having an asymmetry means 114 formed on one side in the circumferential direction but located on the circumferentially opposite side of the rotor pole 110 than the asymmetry means 114 of the pole pieces 112b.

[0055] In the embodiment shown, the asymmetry means 114 are configured as a one-sided shortening of the pole pieces 112b, 112c. Furthermore, the side of the pole pieces 112b, 112c facing the stator is bevelled by the asymmetry means 114. In principle, other asymmetry means are also conceivable, which are not shown in this illustration. For example, the pole pieces 112b, 112c could be made of different materials or alloys than the pole pieces 112a. Further, the pole pieces 112b, 112c could have holes or cavities that affect the magnetic properties of the pole pieces 112b, 112c. In another embodiment, the rotor poles could be of different lengths such that the air gap between the pole pieces 112b, 112c and the magnets 104 is smaller or larger than the air gap between the pole pieces 112a and the magnets 104.

[0056] Due to the reduced extension of the pole pieces 112b, 112c and the widened air gap located at the position of the asymmetry means 114 between the pole pieces 112b, 112c and the magnets 104, the magnetic flux between the rotor and the respective magnets 104 is reduced at the pole pieces 112b, 112c with the asymmetry means 114. The rotor 102 will therefore prefer a position at rest in which the magnetic flux of the magnets 104 through the rotor 102 is at a maximum. The strong magnetic flux through the pole pieces 112a creates a holding torque that holds the rotor 102 in one of these positions. These positions are the positions previously referred to as the first positions.

[0057] FIG. 1B shows the DC electric motor 100 of FIG. 1A which has moved to one of the first positions. In the illustration, the poles of the lateral magnets 104 are shown as north poles and the poles of the top and bottom magnets 104 are shown as south poles. The configuration of the magnets 104 is exemplary and could be the other way around. It is merely for the purpose of understanding embodiments of the invention.

[0058] In the position shown in FIG. 1B, the rotor 102 is oriented so that the magnetic flux 120 through the rotor 102 is at a maximum. The first type of pole pieces 112a are located centrally in front of the lateral magnets 104. The second type pole pieces 112b and the third type pole pieces 112c are located in front of the upper and lower magnets 104, with the asymmetry means 114 facing the north pole magnets 104. In this configuration, the asymmetry means 114 act as a focus for the magnetic field lines 120 that pass through the rotor poles towards the south poles. The asymmetry means 114 increase the distance between the pole pieces 112a, 112b and the north pole magnets 104 so that the magnetic flux from the north poles via the asymmetry means 114 is less than the magnetic flux from the rotor poles 110 to the south pole magnets 104.

[0059] Without the asymmetry means 114, the magnetic flux, represented by the field lines 120, would be able to change from one rotor pole to the other much more easily, i.e., without much force, which would make the motor run more smoothly. The curve of the holding torque of such a motor without asymmetry means is shown in FIG. 2.

[0060] Due to the four magnet 104 configuration, a DC electric motor 100 of FIGS. 1A and 1B has four equivalent first positions in which the pole pieces 112a face one of the magnets 104. In embodiments with two magnets 104 there would be two first positions, in embodiments with six magnets 104 there would be six first positions, and so on. The number of first positions in this and similar configurations is therefore equal to the number of magnets 104.

[0061] FIG. 2 shows the variation of the holding torque M of a DC electric motor 100 with four magnets 104 without asymmetry means 114 dependent on the phase . The curve describes a uniform sine or cosine curve. Shown here is a sine curve shifted by 90 over the entire phase , i.e., one full revolution or 360 of the rotor 102. The four magnets 104 result in four maxima and minima each. The flanks of the points at which the holding torque is particularly high are even and steady, which would result in the smooth operation of a corresponding motor. The rotor 102 of such a motor would be able to easily change from one position to the next, which is normally desired as this realizes low power losses and low noise during operation of the motor.

[0062] FIG. 3 shows the variation of the holding torque M dependent on the phase of the DC electric motor 100 from FIGS. 1A and 1B. The asymmetry means 114 distorts the curve of the holding torque from a sine or cosine curve to another periodic function. The four first positions A, which can be assigned to the four magnets 104, are the points with the highest holding torque M.

[0063] The slopes of the holding torque curve around the first positions A are steeper compared to the curve shown in FIG. 2, and the amplitude of the holding torque M is higher. The curve between two first positions A results from the particular design of the asymmetry means 114 from FIGS. 1A and 1B. With other or differently configured asymmetry means 114, the curve of the holding torque M would be configured accordingly.

[0064] For a use according to embodiments of the invention of the DC electric motor 100, the holding torque M in one of the first positions A should be at least as great, or greater, than the torque, in particular the maximum torque, which the tailgate of a motor vehicle exerts on the drive by its own weight.

[0065] Although the invention has been illustrated and described in greater detail with reference to the exemplary embodiments, the invention is not limited to the examples disclosed, and further variations can be inferred by a person skilled in the art, without departing from the scope of protection of the invention.

[0066] For the sake of clarity, it is to be understood that the use of a or an throughout this application does not exclude a plurality, and comprising does not exclude other steps or elements.

LIST OF REFERENCE SIGNS

[0067] 100 DC electric motor [0068] 102 Rotor [0069] 104 Magnet [0070] 106 Axis of rotation [0071] 108 Auxiliary magnet [0072] 110 Rotor pole [0073] 112 Pole piece [0074] 112a Pole piece (first type) [0075] 112b Pole piece (second type) [0076] 112c Pole piece (third type) [0077] 114 Asymmetry means [0078] 120 Magnetic field line [0079] Phase [0080] M Holding torque [0081] A first position