GB2033977A

GB2033977A - Flywheel

Info

Publication number: GB2033977A
Application number: GB7933806A
Authority: GB
Original assignee: Teldix GmbH
Current assignee: Rockwell Collins Deutschland GmbH
Priority date: 1978-09-28
Filing date: 1979-09-28
Publication date: 1980-05-29
Also published as: GB2033977B

Abstract

A flywheel comprises a rotor (7) with a annular flywheel mass (1), a magnetic bearing device with controllable coils for mounting the rotor (7) free of contact, the magnetic bearing having two radial pole plates (14, 15) on the stator pole with a permanent magnet (24) between them and two electrical coils, a rotor ring (6) being connected to the flywheel mass (1) to provide annular air gaps between the pole surfaces (10, 11) of the rotor ring 6 and the pole surfaces (22, 23) of the pole plates (14, 15) and a mechanical auxiliary bearing, Figure 3, having an annular limb 59 which extends between extensions 56, 57 of the pole shoes 20, 21. If tilting or axial misalignment of the rotor occurs, the auxiliary bearing acts to limit such misalignment and reset the flywheel. The auxiliary bearing acts as an emergency bearing in the event of failure by the magnetic bearing. The auxiliary bearing may alternatively be a rolling contact bearing having one race fixed to the stator and the other race engageable with the rotor if misalignment occurs. <IMAGE>

Description

SPECIFICATION Flywheel This invention relates to a flywheel arrangement comprising a rotor having the flywheel mass and a magnetic bearing device with controllable coils.

Such a flywheel is known from German Offenlegungsschrift No. 25 00211. These flywheels are used in space technology particularly for the purpose of stabilizing satellites and in fact are used to produce reaction moments based on changes in rotational speed or to produce a defined reference direction based on a largely constant angular momentum.

Furthermore, these flywheels are used to store energy from which store it can be regained. In all applications, the construction of the rotor bearing with regard to its life span, power consumption and loadability is decisive. In the flywheel known from German Offenlegungsshrift No. 25 00211, the rotor which has the flywheel mass is therefore mounted free of contact using a magnetic bearing device. Here, an actively controlled stabilization of the rotor takes place in the direction of the axis of rotation, whereby the axial position of the rotor is detected with the aid of suitable position sensors and appropriate forces act axially on the rotor via control devices and electrical coils. The remaining degrees of freedom are stabilized passively. A magnetic bearing device is known from U.S.

Patent Specification No. 4043614, containing an annular and axially magnetized permanent magnet and a rotor ring with a U-shaped crosssection between two disc shaped pole plates. The pole plates and the rotor ring have radially opposite pole surfaces, a narrow air gap being provided between them. The magnetic circuit of the permanent magnet is completed by the air gaps, in which radially directed tension forces are applied to the rotor ring. Coils which are energised in dependence on the radial position of the rotor ring by means of suitable control devices are arranged in the peripheral regions of the pole plates, whereby active stabilization of the rotor in a radial direction is brought about in the air gaps because of the strengthening or weakening of the magnetic fields.In the case of axial movements of the rotor or tilting movements of the rotor about the axes perpendicular to the axis of rotation restoring forces or moments act so that a passive rotor stabilization takes place.

The invention seeks to create a flywheel having a small expenditure, which can ensure exact and safe stabilization of the rotor and can fulfill the requirements space technology.

According to the invention there is provided a flywheel comprising a rotor with an annular flywheel mass, a magnetic bearing device with controllable electrical coils for mounting the rotor free of contact, wherein on the stator, the magnetic bearing device has two pole plates arranged in radial planes and between which at least one permanent magnet is arranged, and at least two electrical coils wherein a rotor ring is connected to the flywheel mass to provide annual radial air gaps between the pole surfaces of the rotor ring and the pole surfaces of the stator pole plates and wherein a mechanical auxiliary bearing is provided, the stator parts of which at least partially encircle the associated rotor parts.

The flywheel in accordance with the invention may have a simple design construction, may be manufactured without any special expenditure to the required precision and can have a very high ratio of moment of inertia to total mass. The formation of the magnetic bearing device, which causes an actively controlled stabilization in radial directions and a sufficiently rigid stabilization of the rotor in the axial direction as well as about the spatial axes may be of special advantage. The bearing device, and more particularly the rotor ring, may have a small constructional width in the direction of the axis of rotation so that the rotor may also be constructed to be correspondingly flat and may have a high moment of inertia about the main inertia axis.A definite housing and fixing of all of the stator components of the flywheel may be ensured in an advantageous manner with the aid of the flat baseplate, whereby the required rigidity and strength may be achieved with a small weight without any special difficulties.

The magnetic bearing device may contain rings having attachments onto which the coils are placed and with which sector-shaped pole shoes are associated. An exact alignment of the pole shoes or of their pole surfaces with respect to the pole surfaces of the rotor ring may be achieved with the aid of a support ring. An axially magnetized permanent magnet ring or several axially magnetized square permanent magnets may be located between the pole shoes so that a largely homogeneous magnetic field is achieved between the pole surfaces of the pole shoes and the rotor ring. The permanent magnets are preferably arranged radially on the outside in the front of the coils.

The flywheel mass may be arranged at the outer periphery of the rotor and is preferably connected by spokes to a hub accommodating the rotor ring. Since the magnetic field lines of the permanent magnets and coils penetrate the soft magnetic rotor ring largely in the radial and axial direction i.e. not in a peripheral direction-the rotor ring may have a small cross-section and a small mass. Furthermore, with regard to providing a high moment of inertia of the rotor, the rotor ring or the flywheel mass may encircle the remaining parts of the bearing device and thus have a large spacing with respect to the axis of rotation.

In a preferred embodiment, the support ring and the rotor ring or a component connected thereto may be so constructed that a mechanical emergency bearing is provided or a limit of rotor movements achieved. The associated surface of the support ring or the rotor component may thus be manufactured from materials having good sliding properties or suitable ball or roller bearings may be provided. The same effect may be achieved with ball bearings between the hub, or a rotor part connected to the hub, and the stator or the baseplate.

This type of emergency bearing or auxiliary bearing may be of particular importance in the case of faults in the bearing device and also, in the case of rotor movements in an axial direction or tilting movements of the rotor. The essential point in the case of this bearing is that the stator parts of the auxiliary mounting, more particularly the support ring, may encircle or engage around the rotor or the said rotor component. As a result, it can be guaranteed that with mutual contact of the opposite surfaces or bearing parts of the rotor and the stator, stabilizing forces or moments are applied to the rotor, these forces or moments being opposed to the said movements, so as to have a tendency to guide the rotor back into its desired position.

In a preferred embodiment, damping rings made from electrically conductive material may be provided in the region of the pole surfaces either on the rotor ring and/or on the pole shoes in order to damp particularly tilting movements of the rotor about axes perpendicular to the axis of rotation.

The invention will now be described in greater detail, by way of the example with reference to the drawings, in which: Figure 1 shows an axial section through a flywheel, the sectional planes of the left-hand and right-hand halves of the drawing being offset with respect to each other by approximately 450; Figure 2 shows a crosssection through the stator parts of the magnetic bearing device along the iine Il-Il in Figure 1; Figures 3 and 4 show partial axial sections of mechanical emergency bearings between the rotor ring and the support ring; Figure 5 shows a partial axial section of a flywheel having ball bearings of small diameter at its hub, and Figure 6 shows a partial axial section of a flywheel having an emergency bearing inside a bore in an axle.

The flywheel contains an annular flywheel mass 1 at its outer periphery as shown in Figure 1, the flywheel mass 1 being arranged about an axis of rotation 2 for rotation with respect to a stator 3. The flywheel mass 1 is connected by spoke 4 to a hub 5 lying radially inwardly of the mass, the diameter of the hub 5 being approximately half as the large as that of the flywheel mass 1. A rotor 7 constructed in this way contains a rotor ring 6, which is arranged on the inner surface of the hub 5. The rotor ring 6 has radially directed limbs 8, 9 and pole surfaces 10, 11. The rotor ring 6 comprises a soft magnetic material and has a generally u-shaped crosssection. The rotor ring may also contain an axially magnetized permanent magnet ring (not shown) between its limbs. Furthermore, the rotor ring 6 may be arranged directly on the inner surface of the flywheel mass 1.On the inside, pole plates 14, 15 of a magnetic bearing device are associated with the pole ring 6. The pole plates are arranged in two radial planes and contain a ring 1 6, 17 in each case having radially directed attachments 1 8, 1 9 and sector-shaped pole shoes 20, 21. These pole shoes 20, 21 have annular pole surfaces 22, 23. As can be seen from Figure 2, in each case, four attachments 18, 19 and four pole shoes 20, 21 are provided offset by 900 in a peripheral direction whereby annular radial air gaps 28, 29 are present between the pole surfaces. In each case, a rectangular axially magnetized permanent magnet 24 is located between the pole shoes 20, 21 as well as a support ring 25.The attachments 1 8, 1 9 have a rectangular cross-section as seen in the radial direction and a coil 26, 27 is positioned on each of them. A very accurate alignment of the associated pole surfaces 10, 11 and 22, 23 is ensured by the support ring 25. The magnetic flow of the permanent magnets 24 penetrates the pole shoes 20, 21, air gaps 28, 29 in which largely homogeneous magnetic fields are present and the limbs 8, 9 of the rotor ring 6. The magnetic flow in the rotor ring 6 passes in an axial direction between the limbs 8, 9 so that the rotor ring has a small cross-section and thus a small mass. Magnetic tension forces directed radially are thus applied to the rotor ring 6.The pole surfaces 10, 11 and 22, 23 are constructed so as to be narrow in an axial direction so that opposite resetting forces or moments arise with movements of the rotor in an axial direction and in the case of tilting movements about the space axes perpendicular to the axis of rotation 2 passive rotor stabilization is effected to this extent. The coils 26, 27 which may be controlled by means of suitable control devices, depending on the signals of radial sensors 28, serve to actively stabilize the rotor ring 6 and the flywheel mass 1 in the radial direction. At least two of these sensors 38 are provided in the two radial directions which are orthogonal with respect to the axis of rotation 2 and with respect to each other.If the rotor in Figure 1 moves towards the right, for example, then a magnetic flux is produced by the coils 26, 27, which flux is superimposed on the magnetic flux of the permanent magnets 24 in the air gaps 28, 29 in a sense to increase the flux so that an increased force directed radially and oppositely of the rotor movement is applied to the rotor. The diametrally opposite coils are thus so controlled that a weakening of the tension forces takes place there.

It may be seen that, if necessary, more than or fewer than the total of eight coils 26, 27 shown in this embodiment may be provided; however there is at least one coil for each of the radial directions.

This embodiment provides a high functional safety since it is quite easy to provide redundant control circuits.

The stator 3 comprises a flat baseplate 30 with a short axle 31 at the centre on which the pole plates 14, 1 5 are positioned. The baseplate 30 is provided with a number of reinforcing or stiffening ribs 32 and housing elements 34 to 37 so that an arrangement which is particularly suitable to its function is achieved. In particular the pole plates 14, 1 5, the support ring 25, the position sensors 38 and an electrical winding 41 are achieved with a low weight and space requirement.Above all, the immediate fixing of the support ring 25 to several housing elements 34, peripherally separated ensures defined alignment of the pole plates 14, 1 5. The support ring, as shown in Figure 2 is provided, in regions between the sector-shaped pole shoes 20, 21, with boreholes 39 and is screwed onto the housing elements 34.

The sensors 38 for detecting the rotor position are connected to the housing element 35 so that they can be very easily aligned. An ironless stator ring 40 is connected to the housing element 36, on which a multi-phase winding 41 of the motorgenerator unit is arranged.

Opposite the winding 41,42, peripherally adjacent, radially magnetized permanent magnets are oppositely magnetized in each case. They are arranged on the inner surface of the annular flywheel mass 1 opposite the winding 41. This unit is operated in a known manner as a brushless direct current machine, whereby the angular position signals required for commutation of the currents in the winding phases are produced by sensors 43, arranged on housing elements 37 of the base plate 30. A unit of this type may operate with a suitable control and in both motor operation and generator operation so that appropriate torques or reaction moments are brought about or a conversion of electrical energy into kinetic energy or vice versa is achieved.The electronics required to control the motor/generator unit and the magnetic bearing device are arranged on plate bars 46, 47 on the underside of the baseplate 30 so that only relatively short electrical connecting lines (not shown) are necessary for the sensors 38, 43, coils 26,27 and windings 41.

The support ring 25 contains an annular groove 50 into which a component 51 connected to the rotor ring 6 projects at least partially. The support ring 25 and the component 51, or upper surfaces opposite each other in the annular groove 50, comprise materials having good sliding properties so that a mechanical auxiliary bearing is formed by means of which excessive rotor movements are limited. Since the support ring 25 is arranged directly on the housing elements 34, it is not possible to damage the magnetic bearing device. The decisive feature is that the stator support ring 25 surrounds the component 51 in an axial direction.In this way, stabilizing forces and moments become effective, if the component 51 contacts the support ring 25 as a result of axial movements or tilting movements of the rotor, the rotor being guided back into the desired position shown by the stabilizing forces or moments. At the same time a socalled caging mechanism is used with an auxiliary bearing of this type, in order to enable locking of the rotor with respect to the stator, particularly in the case of the high accelerations during initial positioning of a satellite, so that damage to the flywheel is avoided. Furthermore, damping rings 52, 53 made from electrical conductive material are provided for the purpose of damping the said movements, these damping rings being inserted into annular grooves on the outside of the support ring 25. Because of induced eddy currents in the damping rings 52, 53 an effective damping is achieved.The same effect is achieved if damping rings are arranged on the pole shoes 20, 21 or on the rotor ring 6, in fact as near as possible to the pole surfaces 10, 11 or 22, 23.

In Figure 3 a preferred embodiment of a combined auxiliary bearing and caging mechanism is shown cut away. The support ring 25 has annular extensions 56, 57 between the pole shoes 20, 21, which extensions project partially into the U-shaped rotor ring 6, whereby an annular groove 58 is formed between the extensions 56, 57. The component 51 has a Tshaped cross-section and its limb 59 projects into the annular groove 58 whereby the opposite surfaces, in a radial or axial direction, of limbs 59 and annular groove 58 comprise materials with good sliding properties or have inserts 60 made from these materials. The support ring 25 and the rotor ring 6 are constructed from separate parts in the manner shown in order to ensure simple mounting.

In the embodiment in accordance with Figure 4, a ball bearing 64 is provided as an auxiliary bearing. The inner bearing race 65 is located between the pole shoes 20, 21 so that the support ring 25 has a correspondingly smaller outer diameter in comparison with the previous embodiments. Outer bearing race 66 is arranged inside the U-shaped rotor ring 6 such that axial and radial air gaps 68, 69 are formed. The ball bearing 64 has very little radial and axial play so that the outer bearing race retains the position shown. The bearing races comprise a nonferromagnetic material so that the magnetic flux of the permanent magnets 24 or the coils 26, 27 may flow unchanged through the rotor ring 6.

Since the outer bearing ring 66 is not fixed in the rotor ring, but only abuts the rotor ring in the case of movements which are too large, the rotor mass is not unnecessarily increased. Instead of the ball bearing 64, a four-point ball bearing may be provided so that tilting of the outer bearing race is prevented. Moreover, it is advantageous to provide the running surfaces for the balls or roller elements directly in the support ring 25 and in the rotor ring 6. Finally, reference is made additionally to the combination of the auxiliary mountings described by way of Figures 3 and 4 i.e. sliding bearings and ball bearings.Thus the balls are arranged in the support ring with the aid of a crown cage having cone-shaped pockets, the said support ring projecting in accordance with Figure 3, into the rotor ring in order to bring about the radial auxiliary mounting of the rotor ring or of the flywheel mass. Axial auxiliary mounting takes place with the aid of the surfaces of the support ring and rotor ring which are axially opposite. In the case of all of the embodiments of the auxiliary bearing, it is advantageous to manufacture the balls and/or the bearing races which may be provided from a non-ferromagnetic material, more particularly from oxide ceramics, which have a very fine crystal size and are largely homogeneous and pore-free so that lubricants are not necessary' for the auxiliary bearing.

The partial axial section in accordance with Figure 5 shows a further embodiment of the auxiliary bearing having ball bearings 73 at the outer surface of the hub 5. Thus three ball bearings 73 of small diameter are arranged distributed over the periphery on the baseplate 30 with the aid of resilient pins. The inner race 71 of the bearing is connected to a pin 76 and the outer race 72 of the bearing provides an air gap 74 at the outer surface of the hub 5. The hub 5 furthermore contains rings 77, 78, whereby air gaps 79 are provided in an axial direction between the outer bearing ring 72 and the rings 77, 78. If the rotor and thus the hub 5 perform movements which exceed the extent prescribed by the size of the air gaps 74, 79, then the rotor is retained by this auxiliary mounting.Large sudden loads are prevented because of the resilient pins 76. A single ball bearing or roller bearing with a diameter which is greater than the outer diameter of the hub 5 may be arranged on housing parts of the baseplate 30 instead of the three ball bearings 73 of small diameter which are shown.

Furthermore, damping rings 54, 55 made from electrically conductive material are arranged on the rotor ring 6 for the purpose of damping oscillation.

In an embodiment in accordance with Figure 6 the central axle 31 of the baseplate 30 has an axial bore 80. A cylindrical rotor part 81 projects into the bore 80 and is connected by spokes 82 to the hub 5 or to the flywheel mass 1. A ball bearing 83 is provided between the rotor part 81 and the inner wall of the axial bore 80, whereby a radial air gap 84 is provided between the inner bearing race 86 and the rotor part 81. The outer bearing race 85 is connected to the inner wall of the bore 80. Since the rotor part 81 is arranged inside the bore or the bearing 83 encircles the rotor part 81, then in the case of movements of the rotor, which bring the rotor part 81 into engagement with the inner bearing race 86, stabilizing forces or moments are formed in an advantageous manner in order to guide the rotor back into the desired position shown. The inner bearing race 86 and thus the bearing 83 may be connected to the rotor part 81 in an alternative embodiment (not shown) and a radial air gap may be provided between the outer bearing ring and the inner wall of the bore 80.

Claims

1. A flywheel comprising a rotor with an annular flywheel mass, a magnetic bearing device with controllable electrical coils for mounting the rotor free of contact, wherein on the stator, the magnetic bearing device has two pole plates arranged in radial planes, and between which at least one permanent magnet is arranged, and at least two electrical coils; wherein a rotor ring is connected to the flywheel mass to provide annular radial air gaps between the pole surfaces of the rotor ring and the pole surfaces of the stator pole plates; and wherein a mechanical auxiliary bearings provided, the stator parts of which at least partially encircle the associated rotor parts.

2. A flywheel according to Claim 1, wherein the rotor ring is U-shaped.

3. A flywheel according to Claim 1 or 2, wherein a support ring with an annular groove is arranged between the pole plates and cooperating component connected to the rotor projects at least partially into the annular groove.

4. A flywheel according to Claim 3, wherein the opposite surfaces of the support ring and/or cooperating component or parts thereof are manufactured from materials having good sliding properties.

5. A flywheel according to Claim 3 or 4, wherein a roller or ball bearing is provided between the support ring and rotor ring, whereby running surfaces for the rollers or balls are arranged in the rotor ring or the support ring and/or in the bearing races.

6. A flywheel according to Claim 5, wherein the roller elements and/or the bearing races are manufactured from non-ferromagnetic materials.

7. A flywheel according to Claim 5, wherein the roller elements and/or the bearing races are manufactured from oxide ceramics.

8. A flywheel according to Claim 1 or 2, wherein the rotor has a hub which is surrounded by at least one ball or roller bearing on the stator.

9. A flywheel according to Claim 8, wherein three ball bearings are arranged distributed over the periphery of the hub at a small diameter and wherein the inner bearing races are located on the stator with the aid of the resilient pin.

10. A flywheel according to Claim 1 or 2, wherein the stator has an axial bore into which a rotor part projects and a roller or ball bearing is provided between the rotor part and the inner wall of the bore.

11. A flywheel according to Claim 10, wherein the rotor part is connected by spokes to the hub of the rotor and/or to the flywheel mass.

12. A flywheel according to Claim 10 or 11, wherein an air gap is present between the inner bearing race and the rotor part.

13. A flywheel according to any one of Claims 1 to 12, wherein active stabilization of the rotor is carried out in two directions perpendicular to the axis of rotation by means of the coils and the stator has a baseplate to which the stator parts of the magnetic bearing device and of a motor/generator unit are connected.

14. A flywheel according to Claim 1 3 when appended directly or indirectly to Claim 3, wherein the baseplate has an axle in the region of the rotation axis to which are attached pole plates and radial outer receiving elements for the support ring, for position sensors and the winding of the motor/generator unit.

1 5. A flywheel according to Claim 3, wherein the pole plates each have a ring with radially directed attachments and sector-shaped pole shoes associated therewith; the coils are located on the attachments and square permanent magnets and the support ring are arranged axially between the pole shoes.

1 6. A flywheel according to Claim 15, wherein the pole shoes are inclined or bent towards the rotor ring and the pole surfaces of the pole shoes have a small axial spacing than the pole plates in the region of the coils.

1 7. A flywheel according to Claim 12, characterized in that the rings of the pole plates each have four attachments offset peripherally by 900; a coil is associated with each attachment; and the pole shoes are arranged axially between the attachments.

18. A flywheel according to Claim 3 or any claim appended directly or indirectly thereto, wherein pole shoes having small spacings with respect to each other in a peripheral direction are provided in the region of the pole surfaces; these spacings extend towards the axis of rotation; and the support ring is provided there with axial bores.

19. A flywheel according to any one of the preceding Claims, wherein damping rings made from electrically conductive material are arranged in the region of the pole surfaces of the rotor ring and/or the stator.

20. A flywheel substantially as described herein with reference to the drawings.