POWER TRANSMISSION SYSTEM FOR A WIND TURBINE

Title of the Invention

[0001] Power Transmission System for a Wind Turbine

Cross-Reference to Related Applications

[0002] The present patent application claims the benefits of priority of commonly assigned Canadian Patent Application No. 2,587,354 entitled "Power Transmission System for a Wind Turbine" and filed at the OPIC on May 4, 2007.

Field of the Invention

[0003] The present invention generally relates to electric power generating systems, and more particularly, to wind powered generating systems.

Background of the Invention

[0004] The goal of a wind turbine power transmission system is to converts the kinetic energy of wind to drive a generator, resulting in the conversion of the wind force to electrical energy, or other mechanical devices, directly using the kinetic energy. Conventionally, for vertical axis wind turbines, a gear assembly, or a planetary gear system, is interposed between a rotor and a generator such that the input shaft of the gear assembly is connected to the rotating shaft of the wind turbine rotor, and by adjusting the gear ratio of this gear assembly, the rotational speed of the output shaft of the gear assembly which is connected to the rotating shaft of the generator is controlled to be within a predetermined range of rotational speeds. A main disadvantage of a gear assembly is the high maintenance time and cost because of the quantity of gears needed to modify the gear ratio, which increases the probability of failure.

Objects of the Invention

[0005] A first object of the present invention is to provide a simpler power transmission system for a wind turbine.

[0006] A further object of the present invention is to provide a power transmission system allowing the installation of a plurality of independent power generation subsystems on the same wind turbine rotor.

[0007] Another object of the present invention is to provide a power transmission system allowing the installation of more than one independent generator on the same wind turbine rotor.

[0008] A still further object of the present invention is to provide a power transmission system which can be disconnected from the wind turbine rotor without stopping the wind turbine.

[0009] Other and further objects and advantages of the present invention will be obvious upon an understanding of the illustrative embodiments about to be described or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.

Summary of the Invention

[0010] The present invention provides a system for transmitting torque from a wind turbine rotor having a base to a power generator. The system comprises a driving surface attached to said base and a means drivingly connecting the driving surface to the generator.

[0011] The present invention is described for a wind turbine rotor having a plurality of blades disposed between two circular plates, a top plate and a base plate. The blades are preferably located at the circumference of the plates. The torque is transmitted to the generator via a drive system that is driven by the wind turbine rotor through a

driving surface. In the present document, the driving surface refers to the surface on which a first gear or a first wheel is in contact with and from which the torque is transmitted from the wind turbine rotor to a generator.

[0012] A main advantage of the system described herein is that the configuration needs fewer parts compared to conventional power transmission systems that use a planetary gear system. Furthermore, a plurality of sub-systems may be connected to the same wind turbine rotor. This invention allows each sub-system generator system to be disengaged independently. Finally, the fabrication costs are significantly reduced because the system is conceived to be tolerant to minor construction faults, misalignments, and other faults thus reducing the precision required during the manufacturing process.

[0013] In the present invention, a first friction wheel, a first gear, a first ribbed wheel or other similar known means, is in contact with the driving surface and is driven by the driving surface. Typically, the first wheel is drivingly connected to the generator by an axle but it may be any other known means which is able to transmit a torque.

The driving surface is located on a surface of the base plate of the wind turbine rotor

(top edge, side edge or underside) or on a surface of a ridge which is itself attached to the wind turbine rotor. The driving surface may be horizontal or vertical.

[0014] In another embodiment, the torque may be transmitted to the generator through a second axle. The second axle is driven by a belt (or any other known means to transmit a torque) connected to the first axle. The belt may be connected to both axles or through a second and a third ribbed wheels (or a friction wheel, a gear or other similar known means), attached to the first and second axle, respectively. Obviously, the belt may comprise tooth to engage gears or ribbed wheels.

[0015] Means are preferably used to maintain the first wheel, gear or other similar means biased against the driving surface. In all cases, a disengaging means is preferably used to selectively disengage the driving means.

[0016] In a first embodiment, the driving surface is the surface under the base plate, sometimes referred to as the outside surface. In a second embodiment, an annular ridge

may be attached under the base plate of the wind turbine and the horizontal or vertical (internal or external) surfaces of the annular ridge may be used as the driving surface. As stated above, the driving means is preferably biased towards the driving surface. To disengage the driving means, the bias is released and the driving means is displaced so as to no longer be in contact with the driving surface. It is to be noted that it is possible to have electronically disengaging means (electronically deactivate the generator) instead of mechanical disengaging means.

[0017] The first friction wheel, the gear or the ribbed wheel (also referred as the "driving means") is installed at a radius R from the center of the wind turbine. The radius R is chosen in regard of the appropriate ratio R/r for the generator(s) installed with the wind turbine. The multiplier ratio of the present invention is R/r, where R is the radius of the position of the driving means on the driving surface from the center of the base plate, and r is the radius of the driving means.

[0018] Because R is preferably large in relation to r, it would be very costly to machine a driving surface having little or neither no deformation nor construction fault. Such deformation may cause the driving means to momentarily cease to be in driving contact with the driving surface therefore causing an interruption of power.

[0019] Biasing means are used to allow the driving means to follow the imperfections and remain in driving contact with the driving surface.

[0020] The contact between the driving means and the driving surface must be such that the driving surface will transfer the torque generated by the wind turbine to the driving means. High friction surfaces, a gear and a rack or a ribbed wheel and a ribbed ring are preferably used.

[0021] The features of the present invention which are believed to be novel are set forth with particularity in the appended claims.

Brief Description of the Drawings

[0022] The above and other objects, features and advantages of the invention will become more readily apparent from the following description, reference being made to the accompanying drawings in which:

[0023] Figures Ia is a cross-section side view of a first embodiment of the present invention.

[0024] Figure Ib is a perspective view showing a larger view of a wheel and a support of Figure Ia.

[0025] Figure Ic is a perspective view showing another embodiment of a support for the wheel.

[0026] Figure 2a is a cross-section side view showing the base of a wind turbine rotor with a second embodiment of the present invention.

[0027] Figure 2b is a magnified area of the cross-section view of the Figure 2a.

[0028] Figure 2c an elevation view of the Figure 2b.

[0029] Figure 3a and 3b are a front view and an elevation view of another embodiment of the present invention.

[0030] Figure 4 is a schematic view showing a possible configuration for drivingly connecting a plurality of sub-system generators on the same wind turbine rotor.

[0031] Figure 5 is perspective view showing an embodiment of the power transmission system of the present invention as installed on a wind turbine.

[0032] Figure 6 is a side view of an embodiment of the power transmission system.

[0033] Figures 7a and 7b are a side view and a top perspective view of the power transmission system.

Detailed Description of the Preferred Embodiments

[0034] A novel power transmission system for a wind turbine will be described hereinafter. Although the invention is described in terms of specific illustrative embodiment(s), it is to be understood that the embodiment(s) described herein are by way of example only and that the scope of the invention is not intended to be limited thereby.

[0035] A first embodiment is shown in Figures Ia, Ib and Ic, in which the underneath surface 165 (also referred as the driving surface) of the base plate 160 of a wind turbine rotor (not shown) is used to transmit the torque generated by the rotational movement of the wind turbine rotor to the generators 115 and 130. As shown in Figure Ia, the first friction wheels 105 and 120 are in driving contact with the driving surface 165 and with the cylindrical supports 140 and 145. When the base plate 160 rotates under the action of the wind, the first friction wheels 105 and 120 rotate and cause axles 110 and 125 to turn such that torque is transmitted to the generators 115 and 130. It is to be noted that the number of generators may vary as is necessary or desired. Figure Ib shows a more detailed view of the first friction wheel 120 and support 145 assembly of Figure Ia. The support 145 is driven by the first friction wheel 120 and it rotates about a horizontal axis of the structure 180. The supports 140 and 145 maintain the vertical position of the wheel and thus maintain the contact between the driving surface 165 and the first friction wheels 105 and 120. The first friction wheels 105 and 120 are positioned at a distance R from the center of the base plate and have a radius r. The multiplier ratio is thus RJr. It is possible to install as many generators as needed, the only limitation being the space available under the wind turbine rotor, the space needed between each power generation system and the torque generated by the wind turbine rotor. It is to be noted that the driving surface is not necessarily the underneath surface or the base plate, it may be an intermediary surface which rotates with the wind turbine rotor.

[0036] Figure Ic shows another embodiment to support the first friction wheel 120. A first bearing 190 and a second bearing 195 are mounted on the axle 125 and are all fixed on the support structure 185. The position of the support structure is controlled by the disengaging means 175, which may comprise, for example, a spring, a pneumatic drive, a worm drive or any other actuator. Thus the first friction wheel 120 may be pressed against the base plate 160 and may be disengaged when the support structure 185 is pulled down by the disengaging means 175. It is to be noted that even if the support structure 185 is shown with two axel supports, it is possible to have only one or more than two such supports.

[0037] Figure 2a shows a second embodiment of the present invention comprising a base plate 260 of a wind turbine rotor (not shown) and an annular ridge 235 is fixed under the base plate 260. A rack or ribbed ring 230 having a radius R is fixed on the vertical internal surface, or driving surface, of the annular ridge 235. The first gear or the first ribbed wheel 210 having a radius r is shown on the magnified area of Figure 2b and in Figure 2c. The first gear 210 is biased with the disengaging means 255 towards the rack 230 by a spring 250 or other known means to maintain the first gear 210 in engagement with the rack 230, as shown in Figure 2c. The bias is applied to the first gear 210 through the elongated members 240 and 245 which also retain the biasing wheel 215. As for the first embodiment, the ribbed ring 230 preferably has the highest radius R to increase the multiplier ratio RJr. Like in the previous embodiment, it is possible to install as many generators as needed, the only limitation being the space available under the wind turbine rotor, the space needed between each power generation system and the available torque. In both embodiments, even if one has been described with a wheel and the other with a gear, the wheel and the gear may be interchanged with proper modifications.

[0038] Figure 3 shows another embodiment of the present invention. There is the wheel 315 and the gear 310, and between them the space 350 where the annular ridge and the rack are normally located. A bias is applied by the disengaging means 355 with a sliding part 330 which is comprised in the guiding part 335. The sliding part 330 is biased towards the rack by a spring, a pneumatic drive, a worm drive or any other known means. The bias maintains the engagement between the rack and the gear or ribbed ring 310. It also allows the disengagement of the wheel or ribbed ring 310

from the rack with no need to stop the wind turbine rotor. To control the motion of the sliding part 330, a controlled actuator may be used instead of a spring, such as a pneumatic drive, a worm drive, or any other actuator. Thus, when the gear or the ribbed ring 330 is disengaged, the wheel 315 continues to rotate with the annular portion, but the generator is no longer connected to the wind turbine rotor.

[0039] Figure 4 is a schematic view showing the possibility of installing more than one generation sub-system. The circle 490 represents the driving surface of a base plate similar to the one shown as element 165 in Figure Ia and each generation sub- system 410, 412, 414 and 416 comprise a generator (415, 425, 435, 445), a wheel (412, 422, 432, 442) and a shaft (schematically shown in Figure 4 as 417, 427, 437, 447). In this embodiment, four generation sub-systems are shown but it is possible to install more or less than four generation sub-systems.

[0040] In Figure 5, the power transmission system is shown as installed on a wind turbine. The surface 540 is the underside of the base plate of a wind turbine on which is attached an annular ridge 510. The annular ridge 510 is schematically represented by a planar surface in Figure 5. In reality, the annular ridge would be thicker and it would have a ribbed surface to drive the ribbed wheel 520.

[0041] In the embodiment of the Figure 6, the rotation is transmitted to the generator (not shown) with a axle 660. The axle 660 is driven by the third ribbed wheel 650 which is in turn driven by a belt (not shown). The belt is driven by the second ribbed wheel 640 which is attached to the same axle than the first ribbed wheel 620 which is driven by the driving surface (not shown). The driving surface is to be placed between the ribbed wheel 620 and the biasing wheel 630.

[0042] In Figures 7a and 7b, it is possible to see in another perspective the power transmission system of the Figures 5 and 6. The driving surface (not shown) is to be placed between the ribbed wheel 720 and the biasing wheel 730. The generator 770 is driven by the axle 760.

[0043] While illustrative and presently preferred embodiment(s) of the invention have been described in detail hereinabove, it is to be understood that the inventive concepts

may be otherwise variously embodied and employed and that the appended claims are intended to be construed to include such variations except insofar as limited by the prior art.