WO2011067633A1

WO2011067633A1 - Gear tooth profile for a wind turbine

Info

Publication number: WO2011067633A1
Application number: PCT/IB2010/001626
Authority: WO
Inventors: Edwin C. Hahlbeck; Frank Klein; Amir S. Mikhail; Anthony Chobot
Original assignee: Clipper Windpower LLC
Current assignee: Clipper Windpower LLC
Priority date: 2009-12-01
Filing date: 2010-07-02
Publication date: 2011-06-09
Anticipated expiration: 2012-06-01

Abstract

The invention relates to an electric power-generating device that converts fluid flow to electricity. The electric power- generating device comprises a rotor having blades that rotate in response to fluid flow; a main power input shaft coupled to said rotor; and at least one gear stage, coupled to the main power input shaft. The gears (210, 220, 230) comprise an asymmetric gear tooth profile with high and low pressure angle flanks (212, 213, 222, 223, 232, 233; 336, 337, 346, 347, 356, 357) whereas the high pressure angle flank has a pressure angle (β₂) which is greater than the pressure angle (β₁) of the low pressure angle flank.

Description

GEAR TOOTH PROFILE FOR A WIND TURBINE

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to gearing apparatus for distributing a source of energy to one or more multiple rotational devices, and more particularly to a specific gear tooth profile of a planetary gear stage to increase the capacity of a loaded planetary gear stage .

Description of the Prior Art

As turbines grow in size, the size and weight of individual components grow as well. In order to transmit considerable power in confined spaces, epicyclic gear systems, often called

planetary systems, are used in wind turbines. In its most basic form an epicyclic gear stage comprises planet gears, a sun gear and a ring gear located around the sun gear. The planet gears are located between the sun and ring gears . Further, in an epicyclic gear stage planet gear teeth are loaded in both directions since one side engages the sun gear and the opposite side engages the ring gear. The sun gear is generally a much smaller external gear and rotates at a higher speed, thus it not only has lower strength capacity (relative to the larger internal ring gear) but also accumulates more fatigue cycles .

A typical gear tooth profile designed to accommodate the load scenario at the sun mesh and the ring mesh would be

necessarily overdesigned, contributing to the weight of the gears .

Therefore, it is an object of the present invention to provide a planetary gear stage that overcomes the drawbacks known from the state of the art. It is a further object of the present invention to increase the capacity of a loaded planetary gear stage. SUMMARY OF THE INVENTION

The above mentioned objects of the invention are solved by an electric power-generating device that converts fluid flow to electricity. The device comprises a rotor having blades that rotate in response to fluid flow, a main power input shaft coupled to said rotor, and one or more gear stage, coupled to the main power input shaft. The gears of the at least one gear stage comprise an asymmetric gear tooth profile with high and low pressure angle flanks, whereas the high pressure flank has a pressure angle which is greater than the pressure angle of the low pressure angle flank.

Accordingly, the invention pertains to a novel gear tooth profile for high torque gears such as those used in wind

turbines. The invention uses an asymmetric gear tooth-profile on the gears of at least one planetary gear stage. The tooth profile is such that the pressure angle is intentionally

different on opposite sides of the gear tooth. The asymmetrical gearing allows for more design freedom in view of larger radii that can be created in the roots of the teeth, thus allowing for a greater rated strength capacity. Further, the differing pressure angles on both sides of each tooth reduce gear tooth stress when loaded on the higher pressure angle side than the other side. The invention provides a solution to the aspect that opposite flanks (profiles) of the gear tooth are functionally different for most gears. The work-load on one profile is significantly higher and/or is applied for longer periods of time than on the opposite one. The asymmetric tooth shape accommodates this functional difference. The design intent of asymmetric teeth is to improve performance of main contacting profiles (driven tooth flank) by sacrificing performance on the opposite profiles (coast tooth flank) . These opposite profiles (coast tooth flank) are unloaded or lightly loaded, and usually work for a relatively short period compared to the highly loaded driven tooth flank. The improved performance could mean

increasing load capacity or reducing weight, noise, vibration and contact stress .

According to a preferred embodiment of the invention, the at least one gear stage is a planetary gear stage which

comprises a sun gear located along a central axis, a ring gear located around the sun gear and centered with respect to the central axis, and multiple planet gears located between and engaged with the sun and ring gears . Such a planetary gear stage or epicyclic gear system provides the advantages of high power density, large reduction in a small volume, multiple kinematic combinations, pure torsional reactions, and coaxial shafting.

According to the invention, the pressure angle that

corresponds to a lower stress situation is engaged on the sun gear mesh while the pressure angle that corresponds to a higher stress situation is engaged on the ring gear mesh. According to an embodiment of the invention, the pressure angle of each high pressure angle flank is set to greater than 24°. According to a further embodiment of the invention, the pressure angle of each low pressure angle flank is set to less than 21°. In order to achieve a better mechanical efficiency, in operation of the device under forward load conditions, the high pressure angle flanks of the teeth of the sun and planet gears and the low pressure angle flanks of the teeth of the ring and planet gears mesh. Alternatively or additionally, according to a further embodiment of the present invention, in operation of the device under reverse load conditions, the low pressure angle flanks of the teeth of the sun and planet gears and the high pressure angle flanks of the teeth of the ring and planet gears mesh, resulting also in a better mechanical efficiency. In regard to a further advantageously embodiment of the present invention, the root radius of each tooth of the gears is in the range of R/5<R<R*5. According to another aspect of the present invention, the ring, planet and sun gears may be helical gears, thus leading to a better running smoothness and lower noise emission.

In order to provide a high compact drive train, a second gear stage is arranged between the main power input shaft and the first gear stage. The second gear stage is a planetary gear stage and comprises ring, planet and sun gears, wherein the ring gear of the first planetary gear stage is coupled to the main power input shaft and the sun gear of the first planetary gear stage is coupled to the ring gear of the second planetary gear stage .

According to an aspect of the further embodiment, the planet gears of the second planetary gear stage are coupled to the main power input shaft. In this regard, the planetary gear stages or epicyclic stages are interconnected and form a two stage device operating in a differential (coupled) configuration.

Finally, according to another aspect of the invention, the electric power-generating device may be used in a wind turbine gearbox .

The advantage of this invention is that the planetary stage or stages is such that the pressure angle that corresponds to a lower stress situation is engaged on the sun gear mesh, whereas the pressure angle that corresponds to a higher stress situation is engaged on the ring gear mesh.

The invention avoids the drawback of a typical symmetric gear tooth profile that is designed to accommodate the load scenario at the sun mesh and the ring gear mesh which results in an overdesigned gear system. A further advantage of the invention is that gearbox efficiency is improved since the lower pressure angle gear mesh inherently has a better mechanical efficiency.

The present invention is uniquely suitable for wind turbine application because the gears are predominantly loaded in one direction, newer megawatt turbines have to contend with

unprecedented levels of torque, and a compact lightweight gearbox design is critical to a cost competitive turbine since the structures are highly dependent on tower top mass .

This invention has the advantage that it increases the gear- torque capacity rating relative to size and weight of the planetary gear stages. This enables the most optimal lightweight, compact and high efficiency design.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in detail with reference to the drawings in which:

FIGURE 1 is a schematic view of a planetary gear stage;

FIGURE 2 is a detail view of the meshing of sun, planet and ring gear of the planetary gear stage shown in FIGURE 1;

FIGURE 3 is a detail view of the gear meshing according to the invention,

FIGURE 4 shows a comparison of symmetrical and asymmetrical tooth profiles,

FIGURE 5 is a schematic representation of a two-stage gearing apparatus,

FIGURE 6a is a perspective view of a ring gear of the two- stage gearing apparatus shown in FIGURE 5, FIGURE 6b shows details of the tooth profile of the ring gear, FIGURE 7a is a perspective view of a planet gear of the two- stage gearing apparatus,

FIGURE 7b shows details of the tooth profile of the planet gear,

FIGURE 8a is a perspective view of a sun gear of the two- stage gearing apparatus shown in FIGURE 5 , and

FIGURE 8b shows details of the tooth profile of the sun gear.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A wind turbine is a rotating machine, which converts the energy in wind into electrical energy. Rotor blades are

connected via a main power input shaft to a gearbox, which turns the slow rotation of the blades into a faster rotation that is more suitable to drive electrical generators. The gearbox steps up the rotation of the rotor blades to drive one ore more generators .

The invention shown in FIGURES l-8b relates to an electric power-generating device that converts fluid to electricity. In particular, the invention relates to a multi-stage gearing apparatus for distributing a source of energy to multiple rotational devices. The device comprises a rotor with blades rotating in response to fluid flow, a main power input shaft coupled to the rotor and at least one epicyclic or planetary gear stage . In its most basic form, shown in FIGURES 1, 2 and 3, such an epicyclic or planetary gear stage 200 comprises at least one planet gear 210, a sun gear 220 and a ring gear 230 located around the sun gear 220. The sun gear 220 is the central gear which is located along a central axis 205 and comprises sun gear teeth 221 around an outer circumference of the sun gear 220. The planet gears 210 are located between the sun gear 220 and the ring gear 230 and engage both. The planet gears 210 comprise planet gear teeth 211 around an outer circumference of each planet gear 210 and rotate about pins that establish axes that are offset from the central axis. The pins form part of a planet carrier 240 that likewise share the central axis 205. In this respect, the planet carrier 240 holds peripheral the planet gears 210, all of the same size, that mesh with the sun gear 220. The planet gears 210 are mounted on the planet carrier 240. The ring gear 230 is an outer ring gear or annulus which is centered with respect to the central axis and comprises ring gear teeth 231 around an inner circumference of said ring gear 230. The inward-facing ring gear teeth 231 mesh with the planet gears 210.

According to one embodiment of the invention, the planetary carrier 240 is held stationary and the ring gear 230 is used as input, the stationary planet gears 210 rotate about their own axes at a rate determined by the number of teeth in each gear. This rotation of the planet gears 210 in turn drive the sun gear

220 shown in FIGURES 1 and 2, which rotates at a higher speed than the input shaft. Alternatively, the planetary carrier 240 can be used as an input shaft which may be connected to the rotor blade shaft and will rotate with the rotor blade shaft.

Refer to FIGURE 3, which is a detail of the planetary gear stage shown in FIGURES 1 and 2. With respect to FIGURE 3, one face (the high pressure angle flank 222) of each sun gear tooth

221 comprises a pressure angle β₂ which is greater than the opposite flank pressure angle βι . The opposite face (the low pressure angle flank 223) comprises a pressure angle βι which is less than the opposite flank pressure angle β₂ , so that the gear tooth profile of the sun gear 220 comprises an asymmetric gear tooth profile. Further, one face (the low pressure angle flank 232) of the ring gear tooth 231 comprises a pressure angle βι which is less than the opposite flank pressure angle β₂. The opposite face (the high pressure angle flank 233) comprises a pressure angle β₂ which is greater than the opposite flank pressure angle piso that the gear tooth profile of the ring gear 230 comprises also an asymmetric gear tooth profile.

With respect to FIGURE 3, each of the planet gear teeth 211 comprises an asymmetric gear tooth profile with differing pressure angles βι and β₂ on its opposite side faces or flanks

212 and 213. In operation of the apparatus or of the planetary gear stage 200, the planet gear teeth 211 are loaded on both faces or flanks 212 and 213, since one face or flank 212 of the planet gear tooth 211 engages the sun gear 220 and the opposite side face 213 of the planet gear tooth 211 engages the ring gear 230. In operation under forward load conditions, the high pressure angle flanks 222, 212 of the teeth 221, 211 of the sun and planet gears 220, 210 and the low pressure angle flanks 233,

213 of the teeth 231, 211 of the ring and planet gears 230, 210 mesh. According to one embodiment of the invention, the pressure angle β₂ of the face 222 of each of the sun gear teeth 221 interacting with the planet gear teeth 211 is set to 27°, and the pressure angle β₂ of the face 233 of each of the ring gear teeth 231 interacting with the planet gear teeth 211 is set to 17°.

On the other hand, in operation under reverse load

conditions, the low pressure angle flanks 223, 213 of the teeth of the sun and planet gears 221, 211 and the high pressure angle flanks 232, 212 of the teeth of the ring and planet gears 230, 210 mesh.

In a particular embodiment of the invention, the asymmetric gear tooth profile shows a sun gear 220, a planet gear 210 and a ring gear 230 with 17-degree and 27-degree pressure angles.

According to the invention, pressure angle β₂ of each high pressure angle flank 212, 222, 232 is set to greater than 24°, whereas the pressure angle β_χ of each low pressure angle flank 213, 223, 233 is set to less than 21°. The invention uses an asymmetric gear tooth-profile on the gears of a planetary gear stage. The tooth profile is such that the pressure angle is intentionally different on opposite sides of the gear teeth of the sun, planet and ring gears. The advantage of an asymmetric gear tooth profile with the differing pressure angles on both sides of the tooth is that the gear tooth stress is reduced when loaded in one direction (the higher pressure angle flank or drive side flank) than the other (the low pressure angle flank or coast side flank) .

Planet gear teeth are loaded in both directions since one side engages the sun gear and the opposite side engages the ring gear. The sun gear is generally a much smaller external gear and rotates at a higher speed, thus it not only has lower strength capacity (relative to the larger internal ring gear) but also accumulates more fatigue cycles. The arrangement shown in FIGURE 3 reduces operating stress or conversely enables a higher torque load capacity for a given size gear net.

FIGURE 4 shows a comparison of a symmetrical tooth profile 100 (dotted line) with a pressure angle of 20° and an asymmetrical tooth profile 110 (continuous line) with differing pressure angles. According to the invention, the planetary stage employs asymmetrical tooth forms. A high pressure angle form 111

(pressure angle of approx. 27°) is used for the planet to sun mesh, and a lower pressure angle form 112 (pressure angle of approx. 17°) is used at the planet to ring/annulus mesh. The asymmetrical gear tooth form configuration allows use of a larger root fillet and stronger tooth shape as shown in FIGURE 4. The planet to annulus mesh inheriently has greater strength and lower contact stress and the asymmetrical tooth form concept trades this "extra" capacity for increasing the load limiting sun to planet mesh. This effect is depicted in Figure 4. The asymmetrical tooth^' form may be further enhanced by forming the root fillet with a non-generating cutter (gashing) to allow more control over the critical tooth root shape .

FIGURE 5 is a schematic representation of a two- stage gearing apparatus or gearbox 300, in which the present invention may be embodied. The gearing apparatus or gearbox 300 consists of two epicyclic or planetary gear stages, namely a first planetary gear stage 310 and a second planetary gear stage 320. The two-stage gearing apparatus 300 is at least part of an electric power-generating device that converts fluid flow to electricity. The first planetary gear stage 310 comprises a sun gear 311, a ring gear 312 located around the sun gear 311 and multiple planet gears 313 located between and engaged with the sun gear 311 and the ring gear or annulus 312. Further, the second planetary gear stage 320 comprises also a sun gear 321, a ring gear 322 located around the sun gear 321 and multiple planet gears 323 located between and engaged with the sun gear 321 and the ring gear or annulus 322. It should be noted that the number of planet gears in each stage of the gear train 300 can be changed according to specific design and/or load

requirements. The two planetary gear stages 310, 320 operate in a differential (coupled) configuration. The numerical values used in subscripts refer to the stage number. The epicyclic gear elements are named S for sun, P for planet and A for annulus (ring) and combined in subscripts using the stage number.

The loads of the gearing apparatus or gearbox 300 are based on rotor torques and speeds transmitted via a main power input shaft ("INPUT" in FIGURE 5) . In accordance with the differential (coupled) configuration of the two planetary gear stages 310, 320, the main power input shaft ("INPUT") powers the ring gear or annulus 312 of the first planetary gear stage 310 so that the ring gear 312 will rotate with the main power input shaft.

Additionally, the main power input shaft powers the planet gears 323 of the second planetary gear stage 320 so that the input is divided in the second planetary gear stage 320. As discussed in connection with FIGURES 3 and 4, the gears have tooth flank modifications to improve loaded mesh conditions to compensate for deflections and alignment errors due to manufacturing tolerances. These attributes are considered in a 3D mesh analysis that predicts the peak stress / mean stress ratio to be used in power rating.

FIGURE 6a is a perspective view of the ring gear 312 of the first planetary gear stage 310 in FIGURE 5. The ring gear 312 is located around the sun gear 311 and comprises a ring gear tooth profile 330 around its inner circumference. FIGURE 6b shows a detailed view of the fillet between neighbouring teeth. In

FIGURE 6b, reference numeral 331 denotes the starting points of the fillet between two neighbouring teeth, whereas the nominal depth 332 of the ring gear tooth is measured from the ground of the fillet to the tooth tip. Further, the reference numerals 333, 334 and 335 denote root radii, which can be optimized to achieve a lower stress in the tooth root relative to a gear with symmetric tooth profiles. In one embodiment of the invention, the radii 333 and 335 are set to R=20mm and the root radius 334 is set to approx. R=8mm. Furthermore, as can be seen from FIGURE 6b, the tooth form leads to an asymmetrical profile comprising a high pressure angle flank 336 which in one embodiment may have a pressure angle of approx. 27° and a low pressure angle flank 337 with a pressure angle of approx. 17°.

Further, FIGURE 7a is a perspective view of one of the planet gears 313 of the two-stage gearing apparatus 300, whereas FIGURE 7b shows the tooth profile 340 of the planet gear 313 shown in FIGURE 7a. The teeth of the planet gear 313 engage with the teeth of both the sun gear 311 and the ring gear 312. In FIGURE 7b, reference numeral 341 denotes the starting points of the fillet between two neighbouring teeth, whereas the nominal depth 342 of the planet gear tooth is measured from the ground of the fillet to the tooth tip. Further, the reference numerals 343, 344 and 345 denote root radii, which can be optimized to achieve a lower stress in the tooth root relative to a gear with symmetric tooth profile. According to an embodiment of the invention, the radii 343 and 345 are set to R=20mm and the root radius 344 is set to approx. R=8mm. Furthermore, as can be seen from FIGURE 7b, the tooth form leads to the asymmetrical profile comprising a high pressure angle flank 346 which in one

embodiment may have a pressure angle of approx. 27° and a low pressure angle flank 347 with a pressure angle of approx. 17°.

Furthermore, FIGURE 8a is a perspective view of the sun gear 311 of the two-stage gearing apparatus shown in FIGURE 5, whereas FIGURE 8b shows the tooth profile 350 of the sun gear 311. The teeth of the sun gear 311 engage with the teeth of the planet gears 313. In FIGURE 8b, reference numeral 351 denotes the starting points of the fillet between two neighbouring teeth, whereas the nominal depth 352 of the planet gear tooth is measured from the ground of the fillet to the tooth tip.

Further, the reference numerals 353, 354 and 355 denote root radii, which can be optimized to achieve a lower stress in the tooth root relative to a gear with symmetric tooth profile.

According to an exemplary embodiment of the present invention, the radii 353 and 355 may set to R=20mm and the root radius 354 may set to approx. R=8mm. Furthermore, as can be seen from

FIGURE 8b, the tooth form leads to the asymmetrical profile comprising a high pressure angle flank 356 which in one

embodiment may have a pressure angle of approx. 27° and a low pressure angle flank 357 with a pressure angle of approx. 17°.

In summary, according to the present invention, a high input torque of a rotor is distributed between one or multiple

generators via a torque-dividing gearbox. The sum of the power producing capacities of the generators is equal to the maximum power delivered by the main shaft.

Those skilled in the art will understand that the gears shown in the drawings may be replaced by any machine component consisting of a wheel attached to a rotating shaft that operate in pairs to transmit and modify rotary motion and torque

(turning force) without slip.

The invention has been described with reference to a

planetary gear system. Those skilled in the art will understand that the main power input shaft may be fitted directly onto a circular gear, or the main shaft may be indirectly linked to the circular gear. For example, a reciprocating main shaft may impart rotational motion to the circular gear or the main shaft may be combined with other gears or linkages to impart

rotational motion to the circular gear.

The invention has been described with reference to a gearing apparatus in which a main shaft is connected to a prime mover input (a source of energy) through intermediate gears to one or multiple output shafts connected to rotational devices. Those skilled in the art will understand that the same gearing

arrangement can have the input and output reversed. That is, the "input" becomes the output , the "output" becomes the input , and intermediate remains the same. In this reversed configuration, the rotational devices become prime movers, and the main shaft is connected to a driven machine .

Those skilled in the art will understand that whereas the invention is described with reference to wind or water current sources of power driving generators to generate electricity, other sources of power may be utilized to impart torque to the main shaft. Also the invention has been described with reference to electric generators being driven by the multi- stage gearing disclosed. Those skilled in the art will understand that any rotational device or devices may be driven by the gearing. The sources of power and respective appropriate rotational devices driven by the gearing include, but are not limited to (1) fossil fuels, such as diesel motor-generator sets and gas turbines; (2) nuclear fuels, such as steam turbines for nuclear power plants; (3) solar energy; (4) bio-energy technologies, such as making use of renewable plant material animal wastes and industrial waste; (5) thermal energy; (6) automotive energy, such as electric cars; (7) tunnel boring equipment; (8) mining

equipment; (9) micro-turbines , such as those using natural gas, gas from landfills or digester gas; (10) marine drives; and (11) other heavy equipment with a low speed drive, such as rotating cement mixers and earth moving equipment. Likewise, the role of generators may be replaced by prime movers, such as motors, to create a reduction gearbox to drive machines requiring high torque and slow speeds.

While the invention has been particularly shown and

described with reference to preferred embodiments thereof, those skilled in the art will understand that the foregoing and other changes in form and detail may be made therein without departing from the scope of the invention.

Claims

1. An electric power-generating device that converts fluid flow to electricity, comprising:

a rotor having blades that rotate in response to fluid flow;

a main power input shaft coupled to said rotor; and at least one gear stage, coupled to the main power input shaft;

characterized in that the gears (210, 220, 230) comprise an asymmetric gear tooth profile with high and low pressure angle flanks (212, 213, 222, 223, 232, 233; 336, 337, 346, 347, 356, 357) whereas the high pressure angle flank has a pressure angle (β₂) which is greater than the pressure angle (βι) of the low pressure angle flank.

2. The electric power-generating device according to claim 1, characterized in that at least one gear stage is a

planetary gear (200; 310) stage which comprises a sun gear (220; 311) located along a central axis (205), a ring gear

(230; 312) located around the sun gear (220; 311) and centered with respect to the central axis (205), and planet gears (210; 313) located between and engaged with the sun and ring gears (220, 230; 311, 312) .

3. The electric power-generating device according to claim 1 or 2, characterized in that the pressure angle (β₂) of each high pressure angle flank (212, 222, 232; 336, 346, 356) is set to greater than 24°.

3. The electric power-generating device according to claim 3, characterized in that the pressure angle (βι) of each low pressure angle flank (213, 223, 233; 337, 347, 357) is set to less than 21° .

4. The electric power-generating device according to claim 2 or 3 , characterized in that, in operation of the device under forward load conditions, the high pressure angle flanks (212, 222, 232; 336, 346, 356) of the teeth of the sun and planet gears (220, 210; 313, 311; 323, 321) and the low pressure angle flanks (213, 223, 233; 337, 347, 357) of the teeth of the ring and planet gears (230, 210; 312, 313; 322, 323) mesh.

5. The electric power-generating device according to any of the claims 2-4, characterized in that, in operation of the device under reverse load conditions, the low pressure angle flanks (213, 223, 233; 337, 347, 357) of the teeth of the sun and planet gears (220, 210; 313, 311; 323, 321) and the high pressure angle flanks (212, 222, 232; 336, 346, 356) of the teeth of the ring and planet gears (230, 210; 312, 313; 322, 323) mesh.

6. The electric power-generating device according to any of the preceding claims, characterized in that the root radius (334, 344, 354) of each tooth of the gears is in the range of R/5 < R < R*5.

7. The electric power-generating device according to any of the claims 2-6, characterized in that the ring, planet and sun gears (210, 220, 230; 311, 312, 313) are helical gears.

8. The electric power-generating device according to any of the preceding claims, characterized in that a second gear stage (320) is arranged between the main power input shaft and the first gear stage (310) , wherein the second gear stage (320) is a planetary gear stage comprising ring, planet and sun gears (322, 323, 321), and wherein the ring gear (312) of the first planetary gear stage is coupled to the main power input shaft and the sun gear (313) of the first planetary gear stage (310) is coupled to the ring gear (322) of the second planetary gear stage (320) .

9. The electric power-generating device according to claim 8, characterized in that the planet gears (323) of the second planetary gear stage (320) are coupled to the main power input shaft.

10. The electric power-generating device according to any of the preceding claims, characterized in that the differing pressure angles (β_Χ/ β₂) on both sides of each tooth reduce gear tooth stress when loaded on the higher pressure angle flank (212, 222, 232; 336, 346, 356) than the other flank (213, 223, 233; 337, 347, 357).

11. The electric power-generating device according to any of the preceding claims, characterized in that the device is used in a wind turbine gearbox.