Title of Invention

ELECTRIC MACHINE WITH PERMANENT MAGNET

Abstract

Electrical machine, comprising a rotor, stator and a permanent magnetic element, which is fastened on rotor or on stator whereby the permanent magnetic element borders an air gap between the rotor (2) and stator (4), whereby the shell surface of the perment magnetic element (3) has a cylinder shape, so that the air gap (7) has a constant width and whereby the permanent magnetic element (3) has on the side opposite to the air gap (7) a non-cylindrical shell surface, so that the permanent magnetic element (3) has in the circumferential direction a different thickness, is characterized through a spring (6) in order to elastically bed the permanent magnetic element (3).

Full Text

Electric Machine with Permanent Magnet Prior Art The present invention is with regard to an electric machine such as, for example, an electro motor or a generator with a rotor, a stator and a permanent magnet. These types of electric machines have been well established in prior art. For example, electro motors that have the permanent magnet mounted either at the stator or at the rotor are established thereby. The permanent magnet is usually linked to the rotor and/or the stator by means of bonding. In the case of these kinds of electric machines, the influence on the moment waviness is affected by an air gap that is present between the rotor and the stator. The larger the air gap is in this connection, the greater the magnetic loss that impacts negatively on the torque transmission. In order to achieve low detent torque and low moment waviness respectively, the air gap of the permanent magnet will consequently have to increase in size in the peripheral direction towards the exterior of the pole. Depending on the type of employment, applications are now available that require a high detent torque as e.g., for a butterfly valve and so forth in the area of servo motors, while there are those that require a low moment waviness as e.g., in the steering area. The thickness of the air gap between the stator and the rotor in the pole area is however modified preferably in a symmetrical manner, on the basis of the technical measures thus required, which results in the above mentioned loss in the case of torque transmission. Advantages of the Invention The advantage of the electric machine in accordance with the invention with characteristics of Claim 1 is that the air gap between the rotor and the stator remains constant along the entire axial length, in spite of which, in accordance with the invention, the detent torque and the moment waviness respectively of the electric machine can be modified. Another advantage of the constant air gap between the stator and rotor is that a magnet chip guard can be dispensed with. The permanent magnetic element is designed in such a manner for this purpose that its shell that faces the air gap has a cylindrical shape. This, in a simple manner, enables keeping the breadth of the air gap constant if the component that is located at the other side of the air gap also has a cylindrical shaped shell. Furthermore, the permanent magnetic element has a non-cylindrical shell at that side which faces away from the air gap. Depending on the geometric design, a small and high detent torque respectively and/or low and high moment waviness respectively can be achieved with the help of this non-cylindrical shell. Depending on the application, the permanent magnetic element can thereby be located at the rotor or at the stator. If it is located at the rotor, the inner peripheral surface of the permanent magnetic element is designed with a shape that deviates from a cylindrical one. If it is located at the stator, the outer peripheral surface of the permanent magnetic element is designed with a non-cylindrical shape. The sub claims present other advantageous details of the invention. In accordance with a preferred design of the present invention, the thickness of the permanent magnetic element modifies itself uninterruptedly. In accordance with another preferred design of the invention, the thickness of the permanent magnetic modifies itself erratically. This can be implemented, for example, by providing in-section U-shaped, tube-shaped recesses. The permanent magnetic element is to be built preferably in such a manner that it displays, in the direction of the axis, a middle section with a constant thickness and a respective end section that has a non-cylindrical shape at that side that is turned away from the air gap. The magnetic flux behaviour of the permanent magnetic element is thus varied along the axial direction so that the electrical machine can be designed for different applications. The reduced thickness at the permanent magnetic element is particularly preferred, located approximately in the middle of the homopolar area. An electrical machine with a high detent torque and high moment waviness respectively can be prepared using this type of design. This tapering in the middle of the homopolar region is particularly preferred. Identical moment behaviour can thereby be achieved for electric machines that have an anti-clockwise and clockwise rotation. In order to achieve low detent torque and low moment waviness respectively, the thickness reduction is effected at the transition between two pole areas at the side of the permanent magnet that is turned away from the air gap. Particularly preferred are the thickness reductions that are symmetrically executed for identical moment behaviour in the case of an anti-clockwise and clockwise rotation respectively. It is of advantage when the permanent magnetic element is supported with the help of a spring element at the stator and rotor respectively. Disadvantages occurring thereby due to varying temperature expansions of individual components and of the adhesive intermediary layer as in the case of the previous, usual sticking together of the magnet and the stator and rotor respectively can be eliminated since the spring element takes over the equalising function without cracks or something similar developing in the components. Particularly preferred is that the spring element is thereby located in recesses in the permanent magnetic element, which influences the moment waviness and the detent torque respectively. Drawing The invention is explained with the help of illustrations of the preferred exemplary embodiment, described subsequently in greater detail. Figure 1 is a longitudinal section of an electric machine according to the first exemplary embodiment of the present invention Figure 2 is a schematic cross-sectional view of the electric machine shown in Figure 1 Figure 3 is an enlarged, detailed view of Figure 2 Figure 4 is a schematic cross-sectional view of an electric machine according to a second exemplary embodiment of the present invention Figure 5 is an enlarged partial view of Figure 4 and Figure 6 is a schematic cross-sectional view of an electric machine according to a third exemplary embodiment of the present invention Description of the Exemplary Embodiment Figures 1 to 3 present an electric machine 1 in accordance with the first exemplary embodiment of the present invention. The electric machine 1 comprises of a stator 4 and a rotor 2 at which a laminated rotor disc pack 5 as well as a permanent magnetic element 3 are located. The permanent magnetic element 3 is made up of a six-pole ring magnet with a phase angle a of 60°. The ring magnet is manufactured cost-effectively through sintering. An air gap 7 that is located between the permanent magnetic element 3 and the stator 4 is constant in the axial direction X-X of the electric machine 1 as well as in the peripheral direction. This is enabled by the fact that the outer shell of the permanent magnetic element 3 is designed as a cylinder. The inner shell of the stator 4 is also designed as a cylinder so that the air gap 7 circulating the entire rotor exhibits a constant breadth. As can be particularly seen in Figures 2 and 3, the permanent magnetic element 3 is connected to the rotor disc pack 5 and thus to the rotor 2 through a spring 6. The spring 6 is a ring-shaped spring and displays elastic properties in a radial direction as well as in the peripheral and axial direction of the rotor. For this purpose, the spring 6 has projecting regions 10 that are fixed in recesses 8 at the inner periphery of the ring magnet. As can be seen in Figures 2 and 3, the recesses 8 are respectively allocated at the transition regions 9 between the contiguous poles of the ring magnets. The recesses 8 are thereby essentially U-shaped and can possess an undercut to provide the spring 6 with a better hold. Furthermore, the recesses 8 are designed symmetrically at the pole transition region 9. As a result of providing the recesses 8, the ring magnet 3 displays a non-cylindrical shape at that side that faces away from the air gap 7. The permanent magnetic element 3 thus displays a reduced thickness d at pre-determined positions. Thereby, subject to the size and the geometric design of the recess 8, an impact can be achieved on the detent torque and the moment waviness respectively, despite which the air gap 7 can be prepared with a constant breadth. Designing an air gap with the least breadth is thereby simple. Furthermore, a radial centring of the permanent magnetic element 3 is achieved with the help of the spring 6. In the exemplary embodiment displayed in Figures 1 to 3, the recess 8 is not designed along the entire axial length of the permanent magnetic element 3 but only at the respective ends (compare with Figure 1). The magnetic flow is thereby influenced only in a smaller periphery due to the recesses 8. It is, however, also conceivable that the recesses at the permanent magnetic element at that side that is turned away from the air gap 7 runs along the entire axial length of the permanent magnetic element. It should, furthermore, be observed that the spring 6 does not have to be designed as a completely closed ring and that is also possible to use a plurality of individual spring elements or an open ring as a spring. The spring element also enables equalisation in the case of temperature-dependent, varying elongation of individual rotor components. An electric machine in accordance with a second exemplary embodiment of the present invention is subsequently described with reference to Figures 4 and 5. In contrast to the first exemplary embodiment, there are no U-shaped recesses at the permanent magnetic element 3 of the second exemplary embodiment at that side that is turned away from the air gap 7 but there are tapering regions 11. As can be seen more precisely in Figure 5, the tapering region 11 in the middle of every homopolar region of the poles is designed as the pole of the ring magnet 3. The permanent magnetic element thus displays a reduced thickness d in the middle of the homopolar region N, S. The regions 11 thereby taper symmetrically towards the middle of the respective homopolar regions starting from an inner diameter Di that is present at the transition region 9 between congruent poles (compare Figure 5 whereby the constant inner diameter Di is marked with dashes). The permanent magnetic element 3 thus has a non-cylindrical shape at that side that is turned away from the air gap 7 so that the detent torque and the moment waviness respectively are influenced on the one hand and a lower magnetic loss can be achieved on the other through the constant and smaller air gap 7. Figure 6 illustrates an electric machine in accordance with a third exemplary embodiment of the present invention. The third exemplary embodiment essentially corresponds to the second exemplary embodiment whereby, however, unlike the second exemplary embodiment, the tapered region 11 is not in the middle of the homopolar region of the magnet but at the transition region 9 between congruent magnet poles N, S. This exemplary embodiment otherwise corresponds to the second exemplary embodiment in all respects so that descriptions provided there can be referred to. Claims 1. Electric machine comprising of a rotor (2), a stator (4) and a permanent magnetic element (3) that is fixed at the rotor (2) or at the stator (4), whereby the permanent magnetic element (3) borders an air gap (7) between the rotor (2) and the stator (4), whereby the shell of the permanent magnetic element (3) that faces the air gap (7) exhibits a cylindrical shape so that the air gap (7) displays a constant breadth and whereby the permanent magnetic element (3) exhibits a non-cylindrical shell at that side that is turned away from the air gap (7) so that the permanent magnetic element (3) displays varying thickness in the peripheral direction. 2. Electric machine according to Claim 1 characterised in that a variation in the thickness of the permanent magnetic element (3) takes place uninterruptedly at that side that is turned away from the air gap (7) 3. Electric machine according to Claim 1 characterised in that a variation in the thickness of the permanent magnetic element (3) takes place erratically at that side that is turned away from the air gap (7). 4. Electric machine according to one of the previous claims characterised in that the permanent magnetic element (3) exhibits a reduced thickness (d) in each case at the middle of the homopolar regions. 5. Electric machine according to one of Claims 1 to 3 characterised in that the permanent magnetic element (3) displays a reduced thickness (d) at the transition regions (9) between the congruent poles. 6. Electric machine according to Claim 4 or 5 characterised in that the reduced thickness (d) of the permanent magnetic element (3) is designed symmetrically at the middle of the homopolar regions and at the transition region (9) between the congruent poles respectively. 7. Electric machine according to one of Claims 3 to 6 characterised in that the reduced thickness (d) is formed by a recess, in particular an essentially in-section U-shaped recess. 8. Electric machine according to one of the previous claims characterised in that a spring element (6) is to be mounted elastically at the permanent magnetic element (3). 9. Electric machine according to Claim 8 characterised in that the spring element (6) is fixed in a recess that is present in the permanent magnetic element (3). 10. Electric machine according to one of the preceding claims characterised in that the permanent magnetic element (3) exhibits a constant thickness in the peripheral direction at the middle region lying in the axial direction (X-X) and a non-constant thickness in the peripheral direction respectively at its ends that lie in the axial direction (X-X).

Documents:

1668-chenp-2005-abstract.pdf

1668-chenp-2005-claims.pdf

1668-chenp-2005-correspondnece-others.pdf

1668-chenp-2005-correspondnece-po.pdf

1668-chenp-2005-description(complete).pdf

1668-chenp-2005-drawings.pdf

1668-chenp-2005-form 1.pdf

1668-chenp-2005-form 18.pdf

1668-chenp-2005-form 3.pdf

1668-chenp-2005-form 5.pdf

1668-chenp-2005-pct.pdf

abs-1668-chenp-2005.jpg