GB2330011A

GB2330011A - Rolling rotor motor

Info

Publication number: GB2330011A
Application number: GB9720845A
Authority: GB
Inventors: Michael John Flowerday
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-10-02
Filing date: 1997-10-02
Publication date: 1999-04-07
Also published as: GB9720845D0

Abstract

A radial switched reluctance motor which includes in combination a stator comprised of a circular array of wound rotor poles, a rotor with it's axis of rotation offset from the central axis so that it is made to rotate eccentrically around the central axis by sequential energisation of the stator poles, causing it to 'roll' around the internal diameter of the stator, a means of coupling the eccentric motion of the rotor to an output shaft to provide rotation of it around the central axis, the the whole completed by windings, bearings and end bells designed to co-operate with them. These features may be employed fully or in part in combination with an eccentric gear arrangement within the motor, designed to match the offset of the eccentric rotor, to achieve very high output torques.

Description

IMPROVEMENTS TO A SWITCHED RELUCTANCE MOTOR The present invention relates to a radial pole switched reluctance motor. Such an electric motor is comprised of a stator and a rotor. The salient pole rotor rotates around the axis of rotation centrally within a circular array of wound salient stator poles. The technology covering such devices and their control is well known and is covered by many patents. Maximum torque is created when the reluctance at a stable holding position is minimised, the rotor poles being caused to rotate around the central axis of rotation by sequentially switching the wound stator pole sets or phases to provide such an alignment.

According to the present invention a radial pole switched reluctance motor includes a stator comprised of a circular array of salient or non salient wound poles and a rotor which may be produced with or without poles, salient or non salient. The rotor is caused to rotate eccentrically around the central axis of the stator, the central axis of the rotor being offset from that of the stator. Sequential energisation of adjacent stator poles causes the rotor to 'roll' around the intemal diameter of the stator so as to minimise the reluctance of the energised magnetic circuit. One or more adjacent poles may be energised at the same time to optimise the result.

The eccentric rolling rotation of the rotor may be translated or coupled to the output shaft to produce rotation of it around the central axis. This may be achieved by means of a torque translator or an eccentric gear arrangement within the motor designed to match the offset of the eccentric rotor, or both in combination to achieve very high output torques.

One object of the present invention is to provide a radial pole switched reluctance motor that may achieve a very small rotational movement for a complete switched cycle of all radial poles, thereby providing very low rotational speeds.

A second object is to provide high torques, efficiently, maximising the very short low reluctance magnetic paths that such an eccentric rotor arrangement may provide.

A third object is that by changing the diameter of the rotor, a different speed corresponding to any fixed switched frequency stator pole arrangement may be achieved.

The final objective is to incorporate these features in combination with an eccentric gear arrangement within the motor, designed to match the offset of the eccentric rotor, to achieve very high output torques torques.

In the present invention the attractive force generated by one or more adjacent stator poles attracts the rotor to the position of least reluctance. Unlike in other switched reluctance motors the tangential component of force, required to pull a salient rotor pole into alignment with a particular stator pole, is reduced and the direct radial attractive force is maximised, there being only a small angular rotation, the air gaps being small at all times.

Examples of the present invention will now be described with reference to the accompanying drawings in which: Fig 1. Shows a typical stator / rotor pole arrangement for a conventional switched reluctance motor.

Fig.2 Shows an example of the present invention, illustrating that the axis of rotation of the motor is offset from the central axis of the stator.

Fig.3 Shows the rotor position achieved with pole one only energised.

Figs. 4 - 8 These show the rotor positions achieved by the subsequent sequential energisation of each separate stator pole.

Fig.9 A cross sectional view of one example of the present invention employing torque translators.

Fig. 10 A cross sectional view of an example of the present invention employing eccentric gears and anti rotation devices.

Fig. 11 A cross sectional view of an example employing two torque translators, the rotor being supported, but free to tum on the output shaft, by a concentric bearing arrangement incorporating a freely rotating eccentric sleeve.

Fig. 12 A cross sectional view of an example employing a single torque translator and an eccentric gear arrangement, the rotor being supported, but free to turn on the output shaft, by a concentric bearing arrangement incorporating a freely rotating eccentric sleeve.

Fig. 13 A cross sectional view of an example employing two eccentric gear arrangements, in which the rotor mounted 'internal' gears form elements of anti rotation devices which cause the rotor to oscillate, the rotor being supported by but free to oscillate around the output shaft, by a concentric bearing arrangement incorporating a freely rotating eccentric sleeve.

Fig.14 An example as Fig.13 but employing a single rotor mounted 'internal' gear.

Fig. 15 Shows an example wherein a single torque translator and an eccentric gear arrangement are fitted to the driving end of the motor.

Fig.16 & 17 These show in simplified cross section, taken at A-A, the motor illustrated in Fig.15, showing the disposition of the concentric bearing arrangement and eccentric sleeve relative to the other parts, Fig.16 with pole 1 energised and Fig.17 with pole 2 energised.

Fig.18 This shows an example wherein the rotor is supported by bearings mounted eccentrically on the output shaft.

Fig. 19 This shows a cross section, taken at A-A, of the motor illustrated in Fig.18.

A comparison of Fig. 1, an example of conventional radial pole switched reluctance motor, with Fig.2, an example of the present invention, shows clearly one of the inventive steps.

The rotor of the conventional motor, 21, Fig. 1 has salient poles arranged to be aligned by sequential energisation of the pole sets on the stator 22. Such energisation causing the rotor, mounted within bearings, to tum on the central axis of rotation 23. In this case the diametrically opposite poles 1" are aligned with the salient North and South poles of phase 1'. The magnetic paths 24 may be seen to extend around and within the circumference of the stator and diametrically across the rotor.

In contrast the eccentric rotor, 31, Fig.2 of the present invention is shown without poles, it rotates around an axis of rotation 35 offset from the central axis 33. Movement is caused by the attraction of the rotor 31 towards the energised pole 1 on the stator 32. The magnetic paths 34 are completed by the two adjacent unwound poles. It can be seen that the magnetic path length is much shorter.

Figures 3 to 8 show the rotation of the eccentric rotor as each wound pole is sequentially energised, the previously energised pole being de-energised. It can be seen that the rotation of the rotor 31, from the position shown with pole 1 energised, Fig.3, to that with pole 2 energised, Fig.4 provides, at all times, air gaps 36, between the relevant pole faces which are very much smaller and the magnetic path lengths shorter than those that would be associated with the rotation of a conventional rotor as shown in Fig.1. At all times the complete pole faces of the next poles to be switched are in close proximity to the rotor face.

It can be seen that with the example shown illustrated ,Figs. 3 - 8, employing a rotor with a radius of 49 mm., 1 mm. less than the 50 mm. internal radius of the stator, produces an angular rotation of 1.20 per switched step, around the axis of rotation of the rotor. A full cycle of six switched steps would produce, as shown in Fig.8, a rotation of the rotor of 7.20 . In contrast a complete cyclic energisation of the pole sets in the conventional motor shown in Fig. 1 would create a rotation of 60.0 As in the case of the conventional motor, the number of stator poles may be varied and the sequential energisation of adjacent stator poles may be partially coincidental. The wave form of the current applied to each coil may be processed by one of many different techniques known to those skilled in the art, and shaped to provide maximum performance and or efficiency.

Fig. 9 shows a simplified cross sectional view of an example of the present invention.

Assuming a pole layout as shown in Fig.3 with pole 1 energised, the rotor 43 is shown pulled towards pole 1, 42. Coil 1, 49, is shown around pole 1. The rotor is shown coupled to the output shaft 41, by means of a torque translator, this, as illustrated is similar to a hollow Oldham Coupling, comprised of one part secured to the rotor 46, the coupling disc 47, and the output element of the coupling 48, being secured to the output shaft.

The output shaft rotating in bearings 44 forms a stiff assembly preventing translation of the eccentric rotation of the rotor to it.

The rotor, 43, may be allowed to eccentrically rotate freely, rolling around the inside diameter of the stator. Bearings and or other devices or finishes may be employed to maintain a small air gap between the rotor and the stator poles, as may be seen in later examples.

Fig. 10 shows an alternative example of the present invention. Here again pole 1, 42, is assumed energised attracting the rotor 43 towards it. In this case the internal diameter of the rotor encloses or may be fixed to an 'internal' gear 56, or another non or minimum slip surface. This surface is made to engage or interfere with an extemal spur type gear 57, or suitable minimum slip surface, so that the attraction of the energised pole pulls the gear into engagement or the surfaces in contact, the one with the other at a position diametrically opposite to the energised pole or the position of minimum reluctance.

An anti rotational device 58 is fitted to prevent the rotor rotating. This is again a device similar to a hollow Oldham Coupling, but in this case one side of the coupling is secured to the eccentric rotor 43, the other is fixed to the stator end bells. This anti rotation device or coupling disc 58 causes an oscillatory motion of the rotor to take place, the subsequent rotation of the gear mounted on to the output shaft transferring the torque to the shaft.

Employing a pole arrangement and offset as shown in Figs 3 - 8, the magnification of the torque produced to eccentrically tum the rotor will be in the order of the ratio of the intemal radius of the stator divided by the difference between the internal radius of the stator and the external diameter of the eccentric rotor. As each pole is energised the rotor 43 and gear 56 are oscillated and the rotor mounted gear 56 is pulled into engagement with the extemal spur gear 57 on the output shaft. It is possible to have the stator poles made to provide an integral ' intemal' gear.

Fig. 11 shows in cross section a detailed example of the type of device illustrated in Fig.9, wherein the rotor 43 is mounted on to a split dual translator sleeve 46, this providing the rotor drive element of the torque translator. The sleeve mounted rotor 43 is supported on a concentric bearing system 50 incorporating a freely rotating eccentric 51. The eccentric rotation of the rotor is created by the sequential switching of the poles 42, the rotor 43 maintaining a position close to the stator pole faces by means of the supporting concentric bearing system 50 and the eccentric 51.

Another arrangement is shown in Fig.12 wherein a single torque translator 46,47 and 48 is employed. The rotor drive element 46 being incorporated in one half of the split rotor support sleeve. The other half of this split sleeve supporting and driving an external spur gear 62. This spur gear 62 being rotated eccentrically meshing with a fixed internal gear 63.

The rotor 43 being supported by the concentric bearing arrangement 50 incorporating the eccentric sleeve 51 means that at all times the gears 62 and 63 are substantially in mesh and the full torque advantage afforded by the eccentric rotation of the rotor 43 and the gear 62 is available at the output shaft 41. Such torque being translated into circular rotation of the output shaft 43 by means of the torque translator made up of the support sleeve 46, the disc 47 and the integral shaft output member 48.

Typical examples of the device simply illustrated in Fig.10 are shown in Fig.13 and Fig.14.

Fig.13 employs a rotor 43 mounted on a split sleeve 40 which is used to connect the rotor 43 to internal gears 53 which also form the moving element of the anti rotation devices completed by the ring 55 and the fixed element 54 at each end of the rotor 43.

The rotor 43 and the split sleeve 40 are supported by concentric bearing arrangement 50 incorporating a freely rotating eccentric 51.

This arrangement Fig. 13 employing combined intemal gear cum anti rotation elements 53 in co-operation with the coupling rings 55 and the fixed elements 54 cause what would otherwise be the eccentric rotation of the rotor 43 to be an eccentric oscillation of the rotor around the inside of the stator poles 42, around and in mesh with the output shaft mounted spur gears 52 causing the output shaft 41 to rotate. The torque advantage provided by such an eccentric speed reducer arrangement, Patent application No 9712136.2, is in keeping with such a device. The fact that the torque is available from the rotor being pulled directly towards the stator provides yet more torque to the output shaft.

Fig. 14 shows a single combined anti rotation device cum internal gear arrangement 53 in co-operation with a single output shaft mounted spur gear 52. All other details are as in Fig.13.

The device shown in Fig.15 is an example wherein a single torque translator is comprised in part of a rotor mounted spur gear 64, specially made to incorporate the rotor drive element to co-operate with the disc 47 and the integral shaft output element 48. The torque is transmitted from the rotor 43 via the split sleeve 40 to the gear 64.

The rotor is again shown supported by a concentric bearing arrangement 50 incorporating a freely rotating eccentric 51. This device employing an eccentrically rotating spur gear 64 can be further refined by enabling the coupling disc 47 and the output member 48 to be housed within the confines of the gear 64, not shown, making a very small assembly.

Fig.16 and Fig.17 show in simplified cross sections of Fig.15 taken at a-a, the general disposition of the bearings 74 and 75 which comprise the concentric bearing arrangement 50, and the freely rotating eccentric sleeve 51. Fig. 16 shows the relationship with pole 1 energised and Fig. 17 with pole 2 energised. The sectioned coil windings 49 have been omitted for clarity.

In each of the above examples Figs. 11 to 15 employ the concentric bearing arrangement 50 in co-operation with the freely rotating eccentric 51 to maintain the position of the rotor 43 closely adjacent to the operative stator pole 42 and maintaining the gears in mesh where appropriate. This enables the full torque of the devices to be realised at all times and with the use of the gears substantially prevents the device from being reverse turned via the output shaft. Without this support of the concentric bearing arrangement 50 in co-operation with the eccentric sleeve 51, the torque translators where used may pull the rotor gears out of mesh.

Another example is shown in Fig.18 and Fig.19 wherein a bearing arrangement 83 is employed to support the rotor 43 and split mounting sleeve 40. The bearings are in turn mounted onto an eccentrically turned section of the output shaft 41.

In this case the sequential energisation of poles 1-6 causes the rotor to rotate eccentrically, indirectly causing the shaft 41 to rotate by the repositioning of the eccentric 81 to allow the rotor 43 to take up its position of minimum reluctance. In this case the speed of the shaft 41 is determined solely by the frequency and the number of poles. The eccentric 81 and therefore the shaft 41 rotating a complete revolution for each completed pole cycle. Again the rolling action of the eccentric rotor 43 provides for substantial smooth torque generation.

Other arrangements employing the present invention in co-operation with gears, couplings and or anti rotation devices, separately or in combination may be achieved.

The materials used to produce motors in accordance with the present invention may be traditional, such as stamped or cut laminations in co-operation with bearings. gears and other parts. The couplings and anti rotational devices may be similar to a hollow Oldham Coupling, or different, integral or separated from the main rotor. In the future other materials and processes may be employed to achieve the same switched reluctance motor with an eccentric rotor.

Patent application number 9712136.2 covers the use of eccentric gears and or coated wheels of various geometries which may be used integrally with other types of motor, either within or without the motor frame, but in each case the driving force is rotational, ie. The input shaft to the system or the rotor driving the eccentric has to revolve at a speed much greater than that of the output shaft. In this invention there is no direct high speed rotation of an input shaft.

Only Fig.18 and Fig.19 illustrate a device with a more traditional output, where there is no torque amplification at the expense of speed.

The concentric bearing arrangements, where used, incorporating a freely rotating eccentric sleeve may be replace by one special composite bearing. The split sleeves may also be repaced by other devices or ommited as appropriate. More than one stator and rotor may be employed to drive the same output shaft.

In all cases care must be taken to balance the critical assemblies to prevent excessive vibration. Special bearings and or wheels of various geometries and or coatings and materials may be used both to replace the gears and or the coupling used, as is clearly illustrated in patent number 9712136.2, in co-operation with the other features described above to provide alternative constructions of these motors.

Claims

Claims 1. A radial switched reluctance motor which includes in combination a stator comprised of a circular array of wound rotor poles, a rotor with it's axis of rotation offset from the central axis so that it is made to rotate eccentrically around the central axis by sequential energisation of the stator poles, causing it to 'roll' around the internal diameter of the stator, a means of coupling the eccentric motion of the rotor to an output shaft to provide rotation of it around the central axis, a concentric bearing arrangement incorporating a freely rotating eccentric sleeve and a spur gear or gears made to rotate eccentrically in co-operation with the rotor meshing with a fixed 'intemal gear or gears, the whole completed by windings, shaft, bearings and end bells designed to co-operate with them.
2. a radial switched reluctance motor which includes in combination a stator corr4rised of a circular array of wound rotor poles, a rotor with it's axis of 'rotation' offset from the central axis, an anti rotation device or devices fitted to prevent the rotor from rotating so that it is made to oscillate eccentrically around the central axis by sequential energisation of the stator poles, causing it to 'oscillate' around the internal diameter of the stator, an 'internal' gear or gears directly or indirectly fixed to the rotor being made to follow the same oscillatory eccentric path meshing with a spur gear or gears mounted onto the output shaft, a concentric bearing arrangement incorporating a freely rotating eccentric sleeve, the whole completed by windings, shaft, bearings and end bells designed to co-operate with them.
3. A radial switched reluctance motor as in claim 1 wherein the spur gear or gears and the fixed internal gear or gears are omitted.
4. A radial switched reluctance motor as in claim 1 wherein the spur gear or gears, the fixed internal gear or gears and the concentric bearing arrangement incorporating a freely rotating eccentric sleeve are omitted.
5. A radial switched reluctance motor as in claim 2 wherein the concentric bearing arrangement incorporating a freely rotating eccentric sleeve is omitted.
6. A radial switched reluctance motor as in any of claims 1, 3 and 4 wherein the means of coupling the rotor to the output shaft is a suitably modified Oldham Coupling or another coupling capable of accepting the offset generated by the eccentric motion of the rotor.
7. A radial switched reluctance motor as in either of claim 2 or 5 wherein the anti rotation device takes the form of a suitably modified hollow Oldham Coupling or another coupling capable of accepting the offset generated by the eccentric oscillation of the rotor.
8. A radial switched reluctance motor as in claim 1 wherein the means of coupling the rotor to an output shaft is omitted, such eccentric drive being taken directly from the rotor.
9. A radial switched reluctance motor which includes in combination a stator comprised of a circular array of wound rotor poles, a rotor with it's axis of rotation offset from the central axis so that it is made to rotate eccentrically around the central axis by sequential energisation of the stator poles, causing it to 'roll' around the intemal diameter of the stator, the rotor being mounted on a bearing or bearings which is in turn mounted eccentrically on the output shaft, the whole completed by windings, shaft support bearings and end bells designed to co-operate with them.
10. A radial switched reluctance motor as in claims 1,2,3 and 6 wherein a single bearing complete with concentric ball races or rollers and an intermediate eccentric sleeve is employed to replace the individual parts.