WO2009050421A1

WO2009050421A1 - A magnetic harmonic gearbox

Info

Publication number: WO2009050421A1
Application number: PCT/GB2008/003136
Authority: WO
Inventors: Paul David Hopewell; Christopher Graham Bright
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2007-10-18
Filing date: 2008-09-16
Publication date: 2009-04-23
Anticipated expiration: 2010-04-18
Also published as: GB0720475D0

Abstract

A magnetic harmonic gearbox (100) comprises a first ferromagnetic member (102) having a plurality of spaced teeth (104), a second ferromagnetic member (106) arranged within the first member (102) and the second member (106) having a plurality of spaced poles (108). Third means (110, 112) are arranged within the second member (106) and the second member (106) is movable relative to the first member (102). The third means (110, 112) is arranged to produce a moving magnetic field and the number of teeth (104) on the first member (102) is different to the number of poles (108) on the second member (106).

Description

A MAGNETIC HARMONIC GEARBOX

The present invention relates to a magnetic gearbox, in particular to a magnetic harmonic gearbox. A mechanical harmonic gearbox is disclosed in US patent US2906143.

The disadvantage of the mechanical harmonic gearbox is that there is physical contact between the meshing gears, leading to wear, noise and energy losses. A magnetic gearbox comprises a first, inner, rotor carrying a . plurality of eircumferentially arranged permanent magnets on its radially outer periphery, a second, outer, rotor carrying a plurality of eircumferentially arranged permanent magnets on its radially inner periphery and a stator carrying a plurality of eircumferentially arranged pole pieces positioned radially between the first rotor and the second rotorl

A combined magnetic gearbox and electrical generator/motor may be produced by providing electrical windings to the magnetic gearbox as disclosed in US patent US6794781.

The disadvantage of the magnetic gearbox is that it has a limited speed ratio, typically 5 to 1 to 20 to 1, and a plurality of magnetic gearboxes arranged in series is needed if a high gear ratio is required.

A magnetic harmonic gearbox has been proposed and is described in "A Novel Magnetic Harmonic Gear" by J Rens, K

Attallah, S D Calverley and D Howe in IEEE International

Electric Machines and Drives Conference, Antalya, Turkey, 3-5 May 2007.

The disadvantage of this magnetic harmonic gearbox is that a flexible rotor carries magnetic poles. This is difficult to manufacture and because most magnetic materials are hard and brittle it would be difficult to secure the magnetic poles to the flexible rotor.

Accordingly the present invention seeks to provide a novel magnetic harmonic gearbox which reduces, preferably overcomes, the above mentioned problem.

Accordingly the present invention provides a magnetic harmonic gearbox comprising a first ferromagnetic member having a plurality of spaced teeth, a second member arranged within the first member, the second member having a plurality of spaced discrete ferromagnetic poles, third means arranged within the second member, the second member being movable relative to the first member, the third means being arranged to produce a moving magnetic field and the number of teeth on the first member being different to the number of poles on the second member or the spacing between the teeth on the first member being different to the spacing between the poles on the second member.

Preferably the third means comprises a third member arranged within the second member, the third member having at least one magnet.

Preferably the first member comprises a stator having a plurality of circumferentially spaced teeth, the second member comprises a rotor arranged coaxially within the first member, the second member having a plurality of circumferentially spaced poles, the poles of the second member being arranged coaxially with the teeth of the first member, the third member comprises a rotor arranged coaxially within the second member.

Alternatively the first member comprises a rotor having a plurality of circumferentially spaced teeth, the second member comprises a stator arranged coaxially within the first member, the second member having a plurality of circumferentially spaced poles, the poles .of the second member being arranged coaxially with the teeth of the first member, the third member comprises a rotor arranged coaxially within the second member.

Alternatively the first member comprises a static member comprising a first limb having a plurality of longitudinally spaced teeth and a second parallel limb having a plurality of longitudinally spaced teeth, the second member comprises a translatable member having a first limb having a plurality of longitudinally spaced poles and a second parallel limb having a plurality of longitudinally spaced poles, the third member is a translatable member.

Alternatively the first member comprises a translatable member comprising a first limb having a plurality of longitudinally spaced teeth and a second parallel limb having a plurality of longitudinally spaced teeth, the second member comprises a static member having a first limb having a plurality of longitudinally spaced poles and a second parallel limb having a plurality of longitudinally spaced poles, the third member is a translatable member.

Preferably the first member and teeth of the first member comprise steel, e.g. electrical steel.

Preferably the first member and teeth of the first member are laminated. Preferably the poles of the second member comprise steel, e.g. electrical steel.

Preferably the poles of the second member are laminated.

Preferably the third member is cylindrical. Preferably the third member has a plurality of magnets.

Preferably the third member has at least one permanent magnet . Preferably the third member is movable relative to the first and second members.

Alternatively the third means comprises at least one electromagnet . Alternatively the third means is static and means to modulate the current supplied to the at least one electromagnet to produce a moving magnetic field.

The third member may be movable and the third member has electrical coils and means to transfer electric power to or from the electrical coils on the third member.

The means to transfer electrical power may comprise slip rings, commutators or a brushless excitation system.

The first member may comprise a stator having a plurality of circumferentially spaced teeth, the second member comprises a rotor arranged coaxially within the first member, the second member having a plurality of circumferentially spaced poles, the poles of the second member being arranged coaxially with the teeth of the first member, the third means comprises a plurality of circumferentially arranged electromagnets within the second member .

The first member may comprise a rotor having a plurality of circumferentially spaced teeth, the second member comprises a stator arranged coaxially within the first member, the second member having a plurality of circumferentially spaced poles, the poles of the second member being arranged coaxially with the teeth of the first member, the third means comprises a plurality of circumferentially arranged electromagnets within the second member.

The first member may comprise a static member comprising a first limb having a plurality of longitudinally spaced teeth and a second parallel limb having a plurality of longitudinally spaced teeth, the second member comprises a translatable member having a first limb having a plurality of longitudinally spaced poles and a second parallel limb having a plurality of longitudinally spaced poles, the third means comprises a plurality of longitudinally spaced electromagnets.

The first member may comprise a translatable member comprising a first limb having a plurality of longitudinally spaced teeth and a second parallel limb having a plurality of longitudinally spaced teeth, the second member comprises a static member having a first limb having a plurality of longitudinally spaced poles and a second parallel limb having a plurality of longitudinally spaced poles, the third means comprises a plurality of longitudinally spaced electromagnets. The present invention will be more fully described by way of example with reference to the accompanying drawings in which :-

Figure 1 is a cross-sectional view through a prior art magnetic gearbox. Figure 2 is a cross-sectional view through a prior art magnetic harmonic gearbox.

Figure 3 is a cross-sectional view through a magnetic harmonic gearbox according to the present invention.

Figure 4 is a cross-sectional view through the magnetic harmonic gearbox shown in figure 3 with the rotors in different positions.

Figure 5 is a cross-sectional view through an alternative magnetic harmonic gearbox according to the present invention. Figure 6 is a cross-sectional view through another magnetic harmonic gearbox according to the present invention. Figure 7 is a cross-sectional view through a further magnetic harmonic gearbox according to the present invention.

Figure 8 is a cross-sectional view through an alternative magnetic harmonic gearbox according to the present invention.

Figure 9 is a cross-sectional view through another magnetic harmonic gearbox according to the present invention. Figure 10 is a cross-sectional view through a further magnetic harmonic gearbox according to the present invention.

Figure 11 is a cross-sectional view through the first member of figures 3 to 7. Figure 12 is a cross-sectional view through the second member of figures 3 to 7.

Figure 13 is a further enlarged cross-sectional view of the second member.

Figure 14 is a further enlarged alternative cross- sectional view of the second member.

A prior art magnetic gearbox 10, as shown in figure 1, comprises a first, inner, rotor 12 carrying a plurality of circumferentially arranged permanent magnets 14 on its radially outer periphery, a second, outer, rotor 16 carrying a plurality of circumferentially arranged permanent magnets 18 on its radially inner periphery and a stator 20 carrying a plurality • of circumferentially arranged pole pieces 22 positioned radially between the first rotor 12 and the second rotor 16. The first rotor 12, second rotor 16 and stator 20 are arranged coaxially. Adjacent magnets 14 on the first rotor 12 have opposite polarity and adjacent magnets 18 on the second rotor 16 have opposite polarity. The first rotor 12 is rotated at a predetermined input speed and the second rotor 16 rotates at a lower speed.

A prior art magnetic^' harmonic gearbox 30, as shown in figure 2, comprises a stator 32 carrying a plurality of circumferentially arranged permanent magnets 34 on its radially inner periphery, a first, outer, rotor 36 carrying a plurality of permanent magnets 38 on its outer periphery and a second, inner, rotor 40. The stator 32 comprises a back iron ring. The first rotor 36 comprises a flexible back iron. The first rotor 36 is positioned radially between the stator 32 and the second rotor 40. The first rotor 36 is mounted on the second rotor 40 by a bearing 42. The stator 32, first rotor 36 and second rotor 40 are arranged coaxially. The second rotor 40 is oval or other suitable non-circular shape in cross-section. Adjacent magnets 34 on the stator 32 have opposite polarity and adjacent magnets 38 on the first rotor 36 have opposite polarity.

The second rotor 40 is rotated at a predetermined input speed and the second rotor 40 deforms the flexible first rotor 36 by the sliding contact such that the flexible first rotor 36 assumes the same profile as the second rotor 40 while rotating independently. Due to the non-circular shape of the second rotor 40 and hence the first rotor 36, there is a variable gap, or clearance, between the stator 32 and the first rotor 36 and thus the magnetic field produced by the magnets 34 and 38 on the stator 30 and first rotor 36 is modulated such that the asynchronous space harmonics generated by one set of magnets 34 have the same number of poles as the other set of magnets 38 and visa-versa.

A magnetic harmonic gearbox 100 according to the present invention is shown in figure 3 and comprises a first member, an annular stator 102, having a plurality of integral circumferentially spaced teeth 104 extending radially inwardly from its inner periphery. A second member, a rotor, 106 is arranged coaxially within the first member, the annular stator, 102 and the second member, rotor, 106 has a plurality of circumferentially spaced discrete magnetically conductive poles 108. A third member, a rotor, 110 is arranged coaxially within the second member, rotor, 106 and the third member, rotor, 110 comprises a bar magnet with opposite poles, north and south poles 112.

The first member, annular stator, 102, the teeth 104 and the poles 108 are made from a ferromagnetic material, e.g. electrical steel or similar magnetically conductive material, and the first member, annular stator, 102 and the teeth 104 are laminated or otherwise constructed to reduce eddy current losses and magnetic hysteresis losses. The poles 108 are supported on the second member 106 but are separated by magnetically non-conductive material.

The number of poles 108 on the second member, rotor 106, is different to the number of teeth 104 on the first member, annular stator, 102 and this difference results in operation as a magnetic harmonic gearbox 100. As shown in figure 3 the difference in the number of teeth 104 on the first member, stator, 102 and poles 108 on the second member, rotor, 106 has the result that the majority of teeth 104 on the first member, stator, 102 and the poles 108 on the second member, rotor, 106 are misaligned but in two diametrically opposite positions A and B a tooth 104A, 104B on the first member, stator, 102 is aligned with a pole 108A, 108B on the second member, rotor, 106. At positions A and B a low reluctance magnetic path via the first member, stator, 102 and the opposite poles 112 of the bar magnet of the first member, rotor, 110 tend to align with these aligned teeth 104 and poles 108 at positions A and B.

In figure 4 the second member, rotor-, 106 of the magnetic harmonic gearbox 100 has rotated slightly in an anti-clockwise direction. The effect of this movement is to move the two diametrically opposite positions where a tooth 104C, 104D on the first member, stator, 102 is aligned with a pole 108C, 108D on the second member, rotor, 106 to positions C .and D. The positions C and D are moved slightly in a clockwise direction relative to the positions A and B. It is to be noted that the slight anti-clockwise, angular, movement of the second member, rotor, 106 produces a much larger clockwise, angular, movement of the third member, rotor, 110. Thus as described above the second member, rotor, 106 is rotated at a predetermined input speed and the third member, rotor, 110 is then rotated at a higher speed.

However, it is equally possible for the third member, rotor, 110 to be rotated at a predetermined input speed and the second member, rotor, 106 or the first member 102 may rotate at a slower speed. As the third member, rotor, 110 is rotated it magnetises the adjacent poles 108 of the second member, rotor, 106 and the adjacent teeth 104 of the first member, stator, 102 tends to draw the poles 108 and teeth 104 into alignment. Thus, as shown in figure 3, at two diametrically opposite positions A and B a tooth 104 on the first member, stator, 102 is aligned with a pole 108 on the second member, rotor, 106. If the third member, rotor, 110 is moved in a clockwise direction the effect of this movement is to move the two diametrically opposite positions where a tooth 104 on the first member, stator, 102 is aligned with a pole 108 on the second member, rotor, 106 to positions C and D. The positions C and D are moved slightly in a clockwise direction relative to the positions A and B. It is to be noted that the slight clockwise, angular, movement of the third member, rotor, 110 produces a much smaller anti-clockwise, angular, movement of the second member, rotor, 106. Thus as described above the third member, rotor, 110 is rotated at a predetermined speed and the second member, rotor, 106 is then rotated at a lower speed.

This alignment of teeth 104 of the first member, stator 102 and the poles 108 of the second member, rotor 106, travels as a "wave" at the same speed as the third member, rotor, 110 and the action therefore is directly analogous to that of a mechanical harmonic gearbox.

In figures 3 and 4 the bar magnet of the third member, rotor, 110 is wide enough such that each pole 112 of the bar magnet only interacts with one pole 108 of the second member, rotor, 106 and one tooth 104 of the first member, stator, 102.

An alternative magnetic harmonic gearbox 200 according to the present invention is shown in figure 5. The magnetic harmonic gearbox 200 is similar to that shown in figure 3 and like parts are denoted by like numerals. In the arrangement in figure 5 the bar magnet is made wider such that each pole 112 of bar magnet interacts with several poles 108 of the second member, rotor, 106 and several teeth of the first member, stator, 102. It is to be noted from figure 3 that although there is only perfect alignment between one tooth 104 of the first member, stator, 102 and one pole 108 of the second member, rotor, 106 at each of positions A and B, there is a reasonable amount of alignment between the teeth 104 and poles 108 at both sides of the fully aligned tooth 104 and pole 108 and these other teeth 104 and poles 108 provide a reasonably low reluctance path. The wider bar magnet is wide enough to interact with three pairs of teeth 104 and poles 108 at one side of the third member, rotor, 110 and with three pairs of teeth 104 and poles 108 at the diametrically opposite side of the third member, rotor, 110.

A further magnetic harmonic gearbox 300 according to the present invention is shown in figure 6. The magnetic harmonic gearbox 300 is similar to that shown in figure 3 and like parts are denoted by like numerals. In the arrangement in figure 6 the third member, rotor, 110 is cylindrical to minimise windage losses. The third member, rotor, 110 again has one magnetic north pole and one magnetic south pole. The third member, rotor, 110 may be designed according to known synchronous and/or permanent magnet generator and/or motors in which the rotor is a cylindrical permanent magnet or an electromagnet. In the case of an electromagnet, the electromagnet may be supplied with DC or AC power by slip-rings, commutators or known brushless excitation means. If AC power is used, the third member, rotor, may be made of electrical steel, or similar material, which is laminated or otherwise constructed to reduce eddy current losses and magnetic hysteresis losses.

A further magnetic harmonic gearbox 400 according to the present invention is shown in figure 7. The magnetic harmonic gearbox 400 is similar to that shown in figure 6 and like parts are denoted by like numerals. In the arrangement in figure 7 the third member, rotor, 110 is again cylindrical to minimise windage losses, but the third member, rotor, 110 has four magnetic poles, e.g. two magnetic north poles and two magnetic south poles. All four magnetic poles tend to align themselves with poles 108 on the second member, rotor, 106 and teeth 104 on the first member, stator, 102 that are well aligned. It may also be possible to use a third member, rotor, with six magnetic poles, eight magnetic poles or other even number of magnetic poles. As an example a rotary magnetic harmonic gearbox with a gear ratio of 100:1 may comprise a ferromagnetic stator with two hundred and two teeth, a rotor with four hundred ferromagnetic poles and a rotor with a bar magnet with two magnetic poles. Such a rotary magnetic harmonic gearbox may have a diameter of 400mm and thus the teeth on the stator and slots between the teeth would be about 3mm wide. The stator may be produced from steel lamination produced by stamping. However, if any attempt were made to make a magnetic gearbox with a gear ratio of 100:1 and a design similar to that in figure 1, the ferromagnetic stator would require over 400 magnets each about 3mm wide. The handling and fixing of such a large number of small, but strong, magnets would be difficult and time consuming compared with the stamping and assembly of steel laminations.

In the magnetic harmonic gearboxes according to the present invention there are two "air-gaps" a first air gap is between the magnet and the poles 108 and the second air gap is between the poles 108 and the teeth 104. In these magnetic harmonic gearboxes it is possible to provide the poles 108 _. in a hermetically sealed assembly, with mechanical output power taken from the teeth 104 and first member, rotor, 102, to transmit mechanical power through a hermetically sealed assembly obviating the need for rotating seals and eliminating a cause of leakage and potential unreliability.

Another magnetic harmonic gearbox 500 according to the present invention is shown in figure 8. The magnetic harmonic gearbox 500 is similar to that shown in figure 3 and like parts are denoted by like numerals. In the arrangement in figure 8 the third member, rotor, and the bar magnet are replaced by a plurality of static circumferentially spaced electrical coils 502. This arrangement produces a combined electric motor and magnetic harmonic gearbox or a combined electric generator and magnetic harmonic gearbox. The electrical coils 502 may be supplied with an alternating current (AC) or direct current (DC) for various electromagnetic effects. The electrical supply may be via slip rings, commutators or brushless excitation systems. If used as a combined electric motor and magnetic harmonic gearbox, the current to the electrical coils 502 is modulated to produce a rotating magnetic field which imparts a differential torque between the teeth 104 on the first member, stator, 102 and the poles 108 on the second member, rotor, 106 due to the reluctance effect.

In another alternative it may be possible to arrange for the teeth 104 to be provided on a first member, rotor, 102 and the poles 108 to be provided on a second member, stator, 106. In this arrangement there is only one "air gap" between the teeth 104 and the poles 108. Again it is possible to provide the poles 108 in a hermetically sealed assembly, with mechanical output power taken from the teeth 104 and first member, rotor, 102, to transmit mechanical power through a hermetically sealed assembly obviating the need for rotating seals and eliminating a cause of leakage and potential unreliability. A combined electric motor and magnetic harmonic gearbox of this type is suitable for use as a pump.

If used as a combined magnetic harmonic gearbox and electrical generator, the teeth 104 are provided on a first member, rotor, 102 and the poles 108 are provided on a second member, stator, 106 and the first member, rotor, 102 is driven so that a suitable modulation^' of the magnetic currents in the electrical coils 502 will allow the extraction of electrical power from the electrical coils 502. This combines the advantages of a compact high speed electric generator and a compact speed increasing gearbox and is applicable to many applications, including wind turbines where the mechanical input power is at slow speed, particularly to offshore wind turbines, where reliability is of paramount importance.

It is possible in the magnetic harmonic gearboxes 100, 200, 300, 400 and 500 to arrange for the slots between the teeth 105 of the first member, annular stator 102, to contain and be filled with a magnetically non-conductive material 105 so that the stator bore, the radially inner surface, of the first member, annular stator 102, has a smooth surface to reduce windage losses as shown in Figure 11. Preferably the non-conductive material 105 in the slots between the teeth of the first member, annular stator 102, is also an electrical insulator.

In the magnetic harmonic gearboxes 100, 200, 300, 400 and 500 the second member, the rotor, 106 comprises a plurality of circumferentially spaced discrete magnetically conductive poles 108 and a plurality of circumferentially spaced magnetically non-conductive members 109. The poles

108 and magnetically non-conductive members 109 are arranged, alternately circumferentially around the second member, rotor 106 as shown in Figure 12. Preferably the magnetically non-conductive members 109 are electrical insulators. Thus, the magnetically non-conductive members

109 provide mechanical support and strength to the poles 108 and to the second member, rotor 106 generally. Thus, the use of the circumferentially alternate poles 108 and magnetically non-conductive members 109 forms the hermetically sealed assembly as discussed earlier. The radially inner and radially outer surfaces of the second member, rotor, 106, the hermetically sealed assembly, have smooth surfaces to reduce windage losses. The magnetically non-conductive members 109 and the poles 108 are arranged to provide a mechanically strong structure for the second member 106. Each magnetically non-conductive member 109 and each pole 108 is provided with a tongue on one abutting face and a groove on the other abutting face such that the tongue on each pole 108 locates in a groove on an adjacent magnetically nonconducting member 109 and a tongue on each magnetically non-conducting member 109 locates in a groove on an adjacent pole 108, as shown in Figure 13. The tongues and grooves are dovetail shape in cross-section but other suitable shapes may be used.

In an alternative arrangement as shown in Figure 14 each magnetically non-conducting member 109 and each pole 108 is provided with grooves on both its abutting faces and a locking member fits into the grooves. The grooves are dovetail shaped in cross-section but other suitable shapes may be used. The locking members may be magnetically conducting or magnetically non-conducting. The use of a plurality of circumferentially spaced poles 108 on the second member, 106 prevents magnetic flux flowing in a short circuit circumferentially between the north and south poles 112 on the third member, 110 via the poles 108. Instead the magnetic flux from the north pole 112 must flow through the first member 1.02, eg the magnetic flux must flow through the poles 108 to the teeth 104 on the first member 102 and then back through the teeth 104, the pole 108 to the south pole 112. This increases the torque transmission of the magnetic harmonic gearbox. The teeth 104 are integral with and form part of the first member 102.

Another magnetic harmonic gearbox 600 according to the present invention is shown in figure 9. The magnetic harmonic gearbox 600 is a translating gearbox rather than a rotary gearbox. The magnetic harmonic gearbox 600 comprises a first member 602, which has a pair of parallel limbs 603. Each limb 603 of the first member 602 has a plurality of integral longitudinally spaced teeth 604 which extend inwardly from its inner periphery towards the other limb 603. A second member 606 is arranged within, between, the limbs 603 of the first member 602 and the second member 606 has a pair of parallel limbs 607. Each limb 607 of the second member 606 has a plurality of longitudinally spaced discrete magnetically conductive poles 608 on its outer periphery. A third member 610 is arranged within, between, the limbs 607 of the second member 606 and the third member 610 comprises a bar magnet with opposite poles 612.

The first member 602, the teeth 604, and the poles 608 are made from a ferromagnetic material, e.g. electrical steel or similar magnetically conductive material, and the first member 602 and teeth 604 are laminated or otherwise constructed to reduce eddy current losses and magnetic hysteresis losses. The poles 608 are supported on the second member 606 but separated by magnetically non- conductive material.

The number of poles 608 on the second member 606 is different to the number of teeth 604 on the first member 602 and this difference results in operation as a magnetic harmonic gearbox 600. In general, the pitch between the teeth 604 on the first member 602 must be different to the pitch between the poles 608 on the second member 606, the number of teeth 604 and poles 608 may or may not be the same . This magnetic harmonic gearbox 600 may be arranged such that the first member 602 is a static member and the second member 606 is a movable, translatable, member and the third member 610 is movable, translatable. In this arrangement the third member 610 and bar magnet are moved relative to the first member 602 to produce movement of the second member 606 in particular movement of the third member 610 at high speed with low force is transformed to movement of the second member 606 at a lower speed with a larger force.

Alternatively this magnetic harmonic gearbox 600 may be arranged such that the first member 602 is a movable, translatable, member and the second member 606 is a static member and the third member 610 is movable, translatable. In this arrangement the third member 610 'and bar magnet are moved relative to the first member 602 to produce movement of the first member 602 in particular movement of the third member 610 at high speed with low force is transformed to movement of the first member 602 at a lower speed with a larger force.

Another magnetic harmonic gearbox may have either the first member 602 or the second member 606 as a low speed, high force, input and the third member 610 as a high speed, low force, output. Again it is possible to provide the poles 608 in a hermetically sealed assembly, with mechanical output power taken from the teeth 604^' and first member 602, to transmit mechanical power through a hermetically sealed assembly obviating the need for seals and eliminating a cause of leakage and potential unreliability.

Another magnetic harmonic gearbox 700 according to the ■ present invention is shown in figure 10. The magnetic harmonic gearbox 700 is similar to the translating gearbox shown in figure 9 and like parts are denoted by like numerals. In the arrangement in figure 10 the third member and the bar magnet are replaced by a plurality of static longitudinally spaced electrical coils 702. This arrangement produces a combined electric motor, e.g. a linear electric actuator, and magnetic harmonic gearbox or a combined electric generator and magnetic harmonic gearbox. If used as a combined electric motor and magnetic harmonic gearbox, the current to the electrical coils 702 is modulated to produce a moving magnetic field which imparts a differential force between the teeth 604 on the first member 602 and the poles 608 on the second member 606 due to the reluctance effect and if one of the first and second members 602 and 606 is fixed the other of the second and first members 606 and 602 will move. Thus, either the first member 602 is a static member and the second member 606 is a movable member or the first member 602 is a movable member and the second member 606 is a static member. Thus, this may be used as an electro-magnetic ram with a built-in high ratio reduction gear. The present invention exploits the reluctance and cogging effects on adjacent ferro-magnetic assemblies having poles and teeth with different angular spacing, in the case of a rotary device, or different linear spacing, in the case of a linearly translating device, when under the influence of a moving magnetic field, whether produced by a moving magnet or a modulated electro-magnet. The present invention provides a high ratio mechanical speed changing gearbox in a single stage utilising magnetism as an interface between an input and an output without contacting parts. The present invention provides a rotary gearbox or a translating gearbox, with step-up or step-down according to the placement of the magnets with respect to the ferromagnetic poles and teeth. The present invention may provide modulated fixed current windings in a rotary gearbox instead of a rotating magnet to provide an electric motor with an inbuilt high reduction ratio, without any contacting parts, or alternatively an electric generator with an inbuilt high speed increasing ratio. The present invention may provide modulated fixed current windings in a linear gearbox instead of a translating magnet to provide an electro-magnetic ram with an inbuilt high reduction ratio, without any contacting parts, or alternatively a linear electric generator with inbuilt high speed increasing ratio. The present invention enables the transmission of mechanical power through a hermetically sealed boundary without the need for moving seals or deformation of surfaces. The present invention enables high over-speed tolerance in the case of the electrical machines because of the simple construction of the moving poles. The present invention has the advantage of simplicity over any attempt to make a magnetic gear with a high gear ratio.

Thus, in the present invention in the case of rotary motion the number of teeth on the first member is different to the number of poles on the second member whereas in the case of linear motion the spacing between the teeth on the first member is different to the spacing between the poles on the second member.

Claims

1. A magnetic harmonic gearbox comprising a first ferromagnetic member having a plurality of spaced teeth, a second member arranged within the first member, the second member having a plurality of spaced discrete ferromagnetic poles, third means arranged within the second member, the second member being movable relative to the first member, the third means being arranged to produce a moving magnetic field and the number of teeth on the first member being different to the number of poles on the second member or the spacing between the teeth on the first member being different to the spacing between the poles on the second member .

2. A magnetic harmonic gearbox as claimed in claim 1 wherein the third means comprises a third member arranged within the second member, the third member having at least one magnet .

3. A magnetic harmonic gearbox as claimed in claim 2 wherein the first member comprises a stator having a plurality of circumferentially spaced teeth, the second member comprises a rotor arranged coaxially within the first member, the second member having a plurality of circumferentially spaced poles, the poles of the second member being arranged coaxially with the teeth of the first member, the third member comprises a rotor arranged coaxially within the second member.

4. A magnetic harmonic gearbox as claimed in claim 2 wherein the first member comprises a rotor having a plurality of circumferentially spaced teeth, the second member comprises a stator arranged coaxially within the first member, the second member having a plurality of circumferentially spaced poles, the poles of the second member being arranged coaxially with the teeth of the first member, the third member comprises a rotor arranged coaxially within the second member.

5. A magnetic harmonic gearbox as claimed in claim 2 wherein the first member comprises a static member comprising a first limb having a plurality of longitudinally spaced teeth and a second parallel limb having a plurality of longitudinally spaced teeth, the second member comprises a translatable member having a first limb having a plurality of longitudinally spaced poles and a second parallel limb having a plurality of longitudinally spaced poles, the third member is a translatable member.

6. A magnetic harmonic gearbox as claimed in claim 2 wherein the first member comprises a translatable member comprising a first limb having a plurality of longitudinally spaced teeth and a second parallel limb having a plurality of longitudinally spaced teeth, the second member comprises a static member having a first limb having a plurality of longitudinally spaced poles and a second parallel limb having a plurality of longitudinally spaced poles, the third member is a translatable member.

7. A magnetic harmonic gearbox as claimed in any of claims 1 to 6 wherein the first member and teeth of the first member comprise steel.

8. A magnetic harmonic gearbox as claimed in any of claims 1 to 7 wherein the first member and teeth of the first member are laminated.

9. A magnetic harmonic gearbox as claimed in any of claims 1 to 8 wherein the poles of the second member comprise steel.

10. A magnetic harmonic gearbox as claimed in any of claims 1 to 9 wherein the poles of the second member are laminated.

11. A magnetic harmonic gearbox as claimed in claim 3 or claim 4 wherein the third member is cylindrical.

12. A magnetic harmonic gearbox as claimed in any of claims 1 to 11 wherein the third member has a plurality of magnets.

13. A magnetic harmonic gearbox as claimed in any of claims 1 to 12 wherein the third member has at least one permanent magnet .

14. A magnetic harmonic gearbox as claimed in any of claims 1 to 14 wherein the third member is movable relative to the first and second members.

15. A magnetic harmonic gearbox as claimed in claim 1 wherein the third means comprises at least one electromagnet .

16. A magnetic harmonic gearbox as claimed in claim 15 wherein the third means is static and means to modulate the current supplied to the at least one electromagnet to produce a moving magnetic field.

17. A magnetic harmonic gearbox as claimed in claim 14 wherein the third member is movable and the third member has electrical coils and means to transfer electric power to, or from, the electrical coils on the third member.

18. A magnetic harmonic gearbox as claimed in claim 17 wherein the means to transfer electrical power comprises slip rings, commutators or a brushless excitation system.

19. A magnetic harmonic gearbox as claimed in claim 15 wherein the first member comprises a stator having a plurality of circumferentially spaced teeth, the second member comprises a rotor arranged coaxially within the first member, the second member having a plurality of circumferentially spaced poles, the poles of the second member being arranged coaxially with the teeth of the first member, the third means comprises a plurality of circumferentially arranged electromagnets within the second member .

20. A magnetic harmonic gearbox as claimed in claim 15 wherein the first member comprises a rotor having a plurality of circumferentially spaced teeth, the second member comprises a stator arranged coaxially within the first member, the second member having a plurality of circumferentially spaced poles, the poles of the second member being arranged coaxially with the teeth of the first member, the third means comprises a plurality of circumferentially arranged electromagnets within the second member.

21. A magnetic harmonic gearbox as claimed in claim 15 wherein the first member comprises a static member comprising a first limb having a plurality of longitudinally spaced teeth and a second parallel limb having a plurality of longitudinally spaced teeth, the second member comprises a translatable member having a first limb having a plurality of longitudinally spaced poles and a second parallel limb having a plurality of longitudinally spaced poles, the third means comprises a plurality of longitudinally spaced electromagnets.

22. A magnetic harmonic gearbox as claimed in claim 2 wherein the first member comprises a translatable member comprising a first limb having a plurality of longitudinally spaced teeth and a second parallel limb having a plurality of longitudinally spaced teeth, the second member comprises a static member having a first limb having a plurality of longitudinally spaced poles and a second parallel limb having a plurality of longitudinally spaced poles, the third means comprises a plurality of longitudinally spaced electromagnets.