WO2012044791A1

WO2012044791A1 - Magnetic levitation transmission

Info

Publication number: WO2012044791A1
Application number: PCT/US2011/053921
Authority: WO
Inventors: David Chi-Henry Su
Original assignee: David Chi-Henry Su
Priority date: 2010-09-29
Filing date: 2011-09-29
Publication date: 2012-04-05
Also published as: CN201818757U

Abstract

A magnetic-levitation planet gear speed transmission replaces mechanical gears with wheels having magnets around their peripheries. The device includes a ring, a sun wheel rotatably disposed coaxial with the ring, and a plurality of planet wheels located along a radius between the center of the sun wheel and a point on the ring. The ring and planet wheels are of like polarity and create a repulsion force that rotates the planet wheels as they orbit within the ring. Likewise the planet wheels and the sun wheel are of like polarity so that the planet wheels will rotatably drive the sun wheel.

Description

MAGNETIC LEVITATION TRANSMISSION TECHNICAL FIELD

[0001] The present invention relates generally to transmissions for stepping up or stepping down the rotational speed of an input shaft. More specifically, the invention relates to an improved transmission that eliminates toothed gears in favor of closely spaced— but not touching wheels that drive one another by magnetic levitation.

BACKGROUND OF THE INVENTION

[0002] As used herein, the term "transmission" will refer to a device that steps up or steps down the rotational speed of an input shaft.

[0003] Wind turbines for generating electricity employ a transmission in the form of a gearbox comprising many large bearings, gears and castings to step up the relatively slow input shaft speed from the turbine blades to an output shaft speed fast enough to drive a generator to generate electricity. The bearings and gears must be manufactured to very close tolerances from expensive materials. For a two megawatt turbine the gearbox can easily weigh thirty tons. This gearbox needs to be mounted on the top of a pole more than 150 feet (about 45 meters) in the air and to be able to support the turbine blades under full-force wind conditions, [0004] To further complicate matters, a typical gearbox with conventional planet gears may be able to step up the input speed by a ratio of only about 1 :5. Connecting two such stages in series increases the ratio to about 1 :25. It may thus take a three-stage gearbox to achieve a step-up ratio of greater than 1 :100 to drive the generator at the proper speed.

[0005] The most common turbine design today for using wind to generate electricity is a horizontal-axis turbine with a three-blade rotor. For a small 500 kilowatt wind turbine, the rotor will rotate at around 72 rpm. For a larger, two megawatt wind turbine, the rotor will rotate at only around 18-30 rpm in order to keep the blade-tip speed subsonic. However, in either event the output shaft may have to turn at up to 1800 rpm to drive the generator to the speeds needed to generate electricity. A large gearbox is therefore required to step up the rotational speed of the rotor to the rotational speed required by the generator, which may be as much as one hundred times faster than the speed of the rotor.

[0006] Gearboxes are one of the most expensive components of a wind turbine and also among the most prone to failure. While most components of a wind turbine can last for twenty years of service, gearboxes frequently fail within three to four years. Between the down time during which the wind turbine is not generating electricity and the delays and expense associated with obtaining the proper replacement parts, unreliability of conventional gearboxes adds significantly to the cost of generating electricity from wind.

SUMMARY OF THE INVENTION

[0007] Stated generally, the present invention relates to a transmission for changing the rotational speed of an input shaft to a different rotational speed of an output shaft. The transmission includes a ring, a sun wheel, and a plurality of planet wheels. The sun wheel is rotatably mounted coaxially with the ring. A plurality of planet wheels are located between the sun wheel and the ring, each having an axis of rotation located on a radius of the ring. The planet wheels are rotatably mounted to a bracket, which in turn is mounted for relative coaxial rotation with the ring. By the term "relative coaxial rotation," it is not required that either particular one of the bracket and ring be rotatable. The bracket can be fixed and the ring rotatable to create "relative coaxial rotation," or the bracket can be rotatable and the ring fixed.

[0008] The planet wheels do not physically contact either the ring or the sun wheel. Instead, a small gap is left between the various components, and magnetic levitation drives the components of the transmission. The ring has a plurality of magnets, each magnet being mounted along a radius of the ring and extending toward the inner surface of the ring. The sun wheel and the planet wheels each have at least one magnet located along its radius and extending toward the outer surface of the wheel. The magnets of the ring and of the planet wheels have like poles that generate a repulsion force such that the ring drives the planet wheel to rotate. Similarly, the magnets on the planet wheel and the sun wheel have like poles that generate a repulsion force such that the planet wheel drives the sun wheel to rotate.

[0009] A first shaft is coaxially mounted to the ring and rotatable therewith. A second shaft is operatively associated with the sun wheel and rotatable therewith. A rotational force applied to one of the shafts will result in the other shaft rotating at a different speed than the first shaft.

In one disclosed embodiment, two or more such transmissions are mounted in series, the output shaft of the first transmission serving as, or being coupled to, the input shaft of the second transmission. In turn, the output shaft of the second transmission serves as, or is coupled to, the input shaft of the third transmission. With each successive transmission, the speed of the input shaft is increased or decreased by a greater extent than if only a single transmission were used.

In another disclosed embodiment, the transmission is used in place of a conventional gearbox on a wind turbine. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a schematic front view of a transmission retention bracket according to a disclosed embodiment.

[0011 ] FIG. 2 is a schematic side view of the bracket of FIG. 1.

[0012] FIG. 3 is a schematic front view of a ring positioned within the bracket of FIGS. 1 and 2.

[0013] FIG. 4 is a schematic side cutaway view of the ring and bracket of FIG. 3.

[0014] FIG. 5 is an isometric view of a bracket for retaining a sun wheel and four planet wheels of the transmission of the disclosed embodiment.

[0015] FIG. 6 is an isometric view of a planet wheel of the disclosed embodiment.

[0016] FIG. 7 is an isometric view of a sun wheel of the disclosed embodiment.

[0017] FIG. 8 is an isometric view of an assembly of four planet wheels and a sun wheel exploded away from a mounting bracket.

[0018] FIG. 9 is an isometric view showing the planet wheels and sun wheel mounted to the bracket. [0019] FIG. 10 is a schematic front view showing the planet wheel, sun wheel, and bracket assembly of FIG. 9 mounted within the ring of FIG. 3.

[0020] FIG. 11 is a side cutaway view as seen along line 11-11 of FIG. 10.

[0021] FIG. 12 is a front view of the transmission of FIG. 10 with the mounting bracket removed to show interior detail.

[0022] FIG. 13 is a schematic front view of the transmission of FIG. 1 showing magnetic flux lines emanating from the magnets of the various components.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS

[0023] Reference will now be made to the drawings, in which like numerals indicate like elements throughout the several views.

[0024] The magnetic- levitation planet gear speed transmission of the disclosed embodiment has a number of moving and interactive parts. The relationships among the various components can perhaps best be understood by introducing each part in the order one might assemble the transmission. Referring first to FIGS. 1 and 2, the transmission includes a circular bracket 10 with upstanding side walls 12 and a closed back 13. An input shaft 14 driven by a rotor 16 extends through a hole 18 in the bracket. [0025] Looking next at FIGS. 3 and 4, a ring 20 having a closed back wall 22 and an open front 23 fits within the circular bracket 10. The input shaft 14 couples to the ring 20 so that as the input shaft 14 rotates, the ring 20 rotates with it.

[0026] With further reference to FIGS. 3 and 4, the inner surface of the ring 20 has a plurality of notches (fourteen in the disclosed embodiment), each of which contains one of a first set 24 of magnets. The magnets 24 are evenly distributed around the inner surface of the ring 20.

[0027] FIG. 5 depicts a planet wheel bracket 28. In the disclosed embodiment, to save material the bracket 28 has four arms 30. There is a through hole 32 formed in the end of each arm 30 and another through hole 34 formed at the center of the intersection of the four arms.

[0028] FIG. 6 depicts a planet wheel 36. The planet wheel 36 is formed of iron and has five notches equidistantly spaced around the periphery of the wheel. One of a second set 38 of magnets is mounted within each notch.

[0029] FIG. 7 depicts a sun wheel 40. The sun wheel 40 is formed of iron and has four notches equidistantly spaced around the periphery of the wheel. One of a third set 42 of magnets is mounted within each notch. [0030] FIGS. 8 and 9 illustrate the assembly of the sun wheel 40 and four planet wheels 36 onto the planet wheel bracket 28. Each planet wheel 36 has a shaft 46 that fits into a through hole 32 formed at the end of an arm 30 to rotatably mount the planet wheel to the bracket. The sun wheel 40 has a longer shaft 48 that fits through the hole 34 in the center of the bracket 28. The sun wheel is rotatable with respect to the bracket 28, and the portion of the shaft 48 that extends beyond the bracket serves as the output shaft 50.

[0031] Referring now to FIGS. 10 and 1 1, the planet wheels and sun wheel assembly 54 are inserted into the ring 20 to form a transmission 60. In FIG. 12 the transmission 60 is shown with the brackets 10 and 28 removed to show interior detail. With the ring and the wheels thus positioned, the sun wheel 40 is mounted for rotation coaxially with the ring 20. Each of the plurality of planet wheels 36 has an axis of rotation generally parallel to the axes of the ring 20 and sun wheel 40. The axis of rotation of each planet wheel 36 lies on a radial line between the sun wheel 16 and the coaxial ring 12.

[0032] None of the planet wheels 36 touch the ring 20, and the sun wheel 40 does not touch any of the planet wheels 36. Instead, the magnets on the various elements interact to magnetically couple the ring and wheels. There is a small gap between the various elements, the exact dimensions of which are not critical but rather depend upon the strength of the magnets and the torque required of the transmission, among other factors.

[0033] With further reference to FIG. 12, iron sheets 62 are positioned between adjacent planet wheels 36 to block magnetic interference.

[0034] Operation of the transmission 60 will now be explained with reference to FIG. 12. As the turbine rotor is driven by the wind, the input shaft 14 causes the ring 20 to rotate in a counterclockwise direction. This rotation causes the first magnets 24 on the ring 20 to pass the planet wheels 36 in a counterclockwise direction. The magnets 24 on the ring and the magnets 38 on each planet wheel 36 are of like polarity and hence create a repulsive force when brought within the vicinity of one another. This magnetic repulsive force causes the planet wheels 36 to rotate in a counterclockwise direction. Similarly, the magnets 38 on the planet wheels 36 and the magnets 42 on the sun wheel 40 are of like polarity and also create a repulsive force. This force causes the sun wheel 40 to rotate in a clockwise direction as the planet wheels orbit around it. As a result, the output shaft 50 that is coupled to the sun wheel 40 is driven in a clockwise direction, which is the direction opposite the input shaft 14. [0035] In the disclosed embodiment the ring 20 has a total of fourteen magnets 24 spaced equidistant around the ring and directed radially inward (FIG. 3). Each planet wheel 36 has a total of five magnets 38 directed radially outward and evenly spaced around the periphery of the planet wheel (FIG. 6). The sun wheel 40 has a total of four magnets 42 (FIG. 7) directed radially outward and evenly spaced around the periphery of the sun wheel. In the disclosed embodiment grooves are formed at the desired locations for the magnets, and the magnets are secured within the grooves. The magnets 24, 38, and 42 can be manufactured from a rare-earth permanent magnet, an iron block, or a copper block.

[0036] The magnets 24 of the ring 20 and the magnets 38 of the planet wheels 36 are of like polarity and create a repulsive force between them. Likewise, the magnets 38 of the planet wheels 36 and the magnets 42 of the sun wheel 40 are of like polarity and create a repulsive force between them.

[0037] As an alternative, the input shaft can be coupled to the sun wheel 38. When the input shaft causes the sun wheel 38 to rotate counterclockwise, the planet wheels 36 are driven to rotate counterclockwise, and non-contact magnetic torque is delivered to the magnet 38 on the planet wheel 36. Magnetic torque is generated because of the fact that a magnetic flux line passes through an air gap between the first magnet 38 and the second magnet 38 (as shown in FIG. 13). The ring 20 in turn is rotated counterclockwise. According to this arrangement, the speed transmission is in a step-down magnetic transmission process, that is, the sun wheel 38 and the ring 20 are reverse in rotation directions, and the sun wheel rotates 3.5 times the rotation speed of the inner gear ring. Through this design, a valid magnetic air gap between the driving inner gear ring and the driven sun wheel is greatly reduced, the number of the planet wheels is increased, the torque is proportionally increased accordingly, and each planet wheel can share torque loads borne by the inner gear ring and the sun wheel, or the total torque can also be improved by proportionally increasing the number of the magnets on the planet wheel.

[0038] Referring again to its original variation, the output shaft 50 of the transmission is coupled to the sun wheel 40. Because the sun wheel 40 turns several times faster than the ring 20, the output shaft 50 rotates correspondingly faster than the input shaft 16. The input to output ratio can be calculated as follows: the number of the magnets 42 on the sun wheel 40 to the number of magnets 24 on the ring 20. Using the number of magnets in this embodiment as an example, the input to output ratio is 4:14, or 1 :3.5. [0039] It is common in wind turbine applications to require the speed of the input shaft to be stepped up 50 to 100 times to drive a generator to the speed necessary to generate electricity. This effect can be accomplished by arranging a plurality of transmissions in series, so that the output shaft of the upstream transmission becomes the input shaft for the next transmission. At a ratio of 1 :3.5, two transmissions arranged in series will step up the input to output speed ratio to 1 : 14, and three transmissions in series can step up the input to output speed ratio to almost 1 :53.

[0040] The invention described herein is by no means limited to fourteen magnets on the ring, five magnets on the planet wheels, and four magnets on the sun wheel. A greater or lesser number of magnets can be used, with a larger number of magnets supplying more torque. In the disclosed embodiment, the number of magnets 26 on the ring 12 is equal to the number of magnets 30 on the sun wheel 16 + 2* (number of magnets 28 on a planet wheel 14. The number of magnets on the sun wheel is 4, the number of magnets on the planet wheel is 5. 4 + 5*2 = 14.

[0041 ] Because there are no gears, the disclosed embodiment eliminates the problem of wear and possible breakage of gear teeth and also the expensive requirement of manufacturing gears to exacting specifications from expensive material. Measures must be adopted to ensure that an air gap between magnetic poles of the driving rotor and the driven rotor is small so that an interactive magnetism between the driving rotor and the driven rotor is sufficient. Strong magnetism must ensure that coupling occurs between the rotors. Strength of a magnetic field does not cause glide and stall, and does not affect synchronism between the driving rotor and the driven rotor. If a smaller rotator is arranged in a circle center of a larger rotator and the two rotators are concentric, air gaps, possibly of different sizes, between magnetic poles of the driven rotator and the driving rotator must be reduced as much as possible, thereby avoiding a harmful effect.

[0042] As an intermediate rotator of the speed transmission, the planet wheel functions to deliver the moment of force between the inner gear ring used as the driving body and the sun wheel used as the driven body. Torque between the ring and the sun wheel can be shared by adding to the group of intermediate rotators, or the total torque may also be increased by proportionally increasing the number of the magnets on the planet wheel.

[0043] Second, compared with a parallel axes structure, the planet structure increases interactive points between the magnets during transmission and increases the delivered torque. When the same torque force needs to be delivered, the transmission through parallel axes facilitates reducing the sizes and the number of the used magnets, thereby saving the materials. Since mutual interference exists between the magnets mounted on the planet wheels, the interference between the magnetic blocks can be isolated by mounting iron plates between the planet wheels. The rare-earth permanent magnet may be used to ensure the normal operation of the planet structure under the operating temperature up to 200°C. Gap fit occurs between the inner gear ring and the planet wheel, and between the planet wheel and the sun wheel, in which the smaller the gap is, the greater the driving torque is. When the planet speed transmission operates at a high speed, magnetic lines of like poles of two corresponding magnets become flat, which easily causes a stall. On the contrary, an attractive force of other two like poles of the two corresponding magnets facing far away from each other can prevent the stall.

[0044] And third, during transmission the magnets radially interact with one another to generate a driving torque force. If the torque force is intended to be increased, the number of axial magnetic rings may be increased along a planet shaft or a solar shaft to increase the torque force without changing the sizes of the magnets. The ring may also be designed to be rotatable. In such a case the inner gear ring is connected to an automatic control system to implement infinite speed variation. When an output rotation speed needs to be constant, a rotation speed of the inner gear ring may be adjusted to implement the infinite speed variation.

[0045] The speed transmission of this design is disclosed herein with respect to its use in a wind turbine. If an output mode of the speed transmission has no specific requirements, the speed transmission may also be used in other apparatuses, such as a water turbine or a steam turbine. If a reducer is intended to be produced, local adjustment only needs to be performed on the design according to the operating conditions and speed-down requirements to output reversely to form the reducer. This design can be used to produce the reducer according to the principle scheme, and the designed reducer may be applied to the use scope of the reducer.

[0046] In the disclosed embodiment, the planet wheel with the magnets is adopted to deliver the torque between the magnets on the ring and the magnetic blocks on the sun wheel, thereby effectively reducing an entire size of the magnetic -levitation transmission structure, reducing the air gap between the inner gear ring used as the driving body and the sun wheel used as the driven body, and ensuring the stability of magnetic torque delivering, the use security of the speed transmission, the stability of torque delivering, and long service life of the speed transmission. [0047] The first, second, and third magnets 24, 38 and 42, may be the same or different and adopt rare-earth permanent magnets or iron blocks. Gap fit occurs between the ring 20 and the planet wheels 36, and between the planet wheels 36 and the sun wheel 40, in which the smaller the gap is, the better the effect of torque delivering is.

[0048] Finally, it will be understood that the preferred embodiment has been disclosed by way of example, and that other modifications may occur to those skilled in the art without departing from the scope and spirit of the appended claims.

Claims

What is claimed is: 1. A transmission for converting the rotational speed of an input shaft to a different rotational speed of an output shaft, comprising: a ring having an inner surface and a central axis;

a sun wheel having an axis of rotation and being rotatably mounted coaxially with the ring;

a plurality of planet wheels each having an axis of rotation located on a radius between the ring and the sun wheel;

each of the plurality of planet wheels being rotatably mounted to a bracket, and the bracket and ring being arranged to permit relative rotation between the planet wheels and the ring; each planet wheel being spaced apart from the adjacent surface of the ring, and each planet wheel being spaced apart from the adjacent surface of the sun wheel;

a first shaft being mounted to the ring and rotatable therewith;

a second shaft being operatively associated with the sun wheel and rotatable therewith; wherein the ring has a plurality of magnets associated therewith, each magnet being mounted along a radius of the ring and extending toward the inner surface of the ring;

wherein the sun wheel and the planet wheels each have at least one magnet located along a radius of the corresponding wheel and extending toward the outer surface of the wheel,

wherein the magnets of the ring and the planet wheels have like poles that generate a repulsion force such that the ring drives the planet wheel to rotate, and

wherein the magnets on the planet wheel and the sun wheel have like poles that generate a repulsion force such that the planet wheel drives the sun wheel to rotate;

whereby a rotational force applied to a first one of the first and second shafts will result in the other of the first and second shafts rotating at a different speed than the first one of the first and second shafts.

2. The transmission of Claim 1 , wherein the input shaft is connected to the ring such that rotation of the input shaft causes the ring to rotate;

wherein the bracket to which the sun wheel and planet wheels are rotatably mounted is fixed; and wherein the rotation of the ring moves the magnets on the ring past the planet wheels so as to magnetically drive the planet wheels; and

wherein the rotation of the planet wheels creates a magnetic field that rotates the sun wheel, thereby rotating an output shaft.

3. The transmission of Claim 1, further comprising a bracketunting the ring for rotational movement with respect thereto.