WO2019149327A1

WO2019149327A1 - Yaw ring with exchangeable tooth parts

Info

Publication number: WO2019149327A1
Application number: PCT/DK2019/050007
Authority: WO
Inventors: Anton Bech; Aksel PETERSEN
Original assignee: Vestas Wind Systems AS
Current assignee: Vestas Wind Systems AS
Priority date: 2018-02-02
Filing date: 2019-01-09
Publication date: 2019-08-08
Anticipated expiration: 2020-08-02

Abstract

A yaw ring assembly (1) for a yaw gear of a wind turbine is disclosed. The yaw ring assembly (1) comprises a yaw ring (2), and a plurality of independent tooth parts (9) mounted circumferentially on the yaw ring (2). A single tooth part (9) can easily be replaced without dismantling the yaw ring assembly (1) or replacing the entire yaw ring assembly (1). A load distribution among the teeth (9) is obtained which resembles the load distribution in a yaw ring having the teeth formed directly therein.

Description

YAW RI NG W I TH EXCHANGEABLE TOOTH PARTS

FI ELD OF THE I NVENTI ON

The present invention relates to a yaw ring assem bly being provided with a plurality of exchangeable or replaceable tooth parts. The present invention further provides a yaw gear and a wind turbine com prising such a yaw ring assem bly, as well as a method for replacing a tooth part of such a yaw ring assem bly.

BACKGROUND OF THE I NVENTI ON

Wind turbines norm ally comprise a tower and a nacelle, carrying a rotor with a set of wind turbine blades, mounted on top of the tower in such a manner that the nacelle is allowed to rotate relative to the tower in order to allow the wind turbine blades to be directed into the incom ing wind. To this end, a yaw gear is arranged between the tower and the nacelle. Such a yaw gear norm ally com prises a yaw ring with a large toothed rim and one or more drive units, each provided with a gear wheel which engages the teeth of the large toothed rim of the yaw ring. The yaw ring is m ounted on the tower or on the nacelle. I n the case that the yaw ring is mounted on the tower, the drive units are mounted on the nacelle, and in the case that the yaw ring is m ounted on the nacelle, the drive units are mounted on the tower. When the gear wheels of the drive units are rotated, this causes a relative movement between the yaw ring and the drive units, thereby causing the nacelle to rotate relative to the tower.

As the size of wind turbines increases, so does the size of the yaw gear, and thereby the diameter of the yaw ring. Norm ally, the yaw ring is provided as one large toothed ring, i.e. with the teeth form ed directly as an integral part of the yaw ring, and the yaw ring, including the teeth, being m anufactured in one piece. This is in order to ensure sufficient strength of the yaw ring to handle the loads occurring during rotation of the nacelle in the m anner described above.

Providing the yaw ring as one large toothed ring as described above has several disadvantages. Special equipm ent is required in order to manufacture toothed rings with a large diameter. Therefore, for very large yaw rings, the

manufacturing costs are very high. Furtherm ore, the yaw rings need to be transported as one large item , and this requires special transporting equipm ent when the size of the yaw ring reaches a certain lim it, thereby significantly adding to the transporting costs. Finally, the entire yaw ring needs to be replaced if one tooth or a few teeth is/are broken, dam aged or worn out. This is difficult and expensive.

WO 2010/078944 A2 discloses a device for rotatably coupling two ring shaped elements. At least one of the two ring shaped elements com prises a plurality of recesses for receiving one drive pin each, said pins being parallel to the axis of rotation. The pins can be engaged by a drive m echanism driving the relative movement of the two ring shaped elem ents. I n the case that one of the pins is broken, dam aged or worn it can be replaced without replacing the entire ring shaped element.

DESCRI PTI ON OF THE I NVENTI ON It is an object of em bodim ents of the invention to provide a yaw ring which can be manufactured and transported in a cost effective m anner.

It is a further object of em bodim ents of the invention to provide a yaw ring in which the individual teeth can be easily replaced.

It is an even further object of embodiments of the invention to provide a yaw ring in which loads occurring during operation of the yaw ring are distributed am ong several teeth. According to a first aspect the invention provides a yaw ring assembly for a yaw gear of a wind turbine, the yaw ring assembly com prising :

- a yaw ring, and

- a plurality of independent tooth parts mounted circumferentially on the yaw ring.

Thus, the first aspect of the invention provides a yaw ring assembly for a yaw gear of a wind turbine. As described above, the yaw gear of a wind turbine is a part which is arranged between the tower and the nacelle of the wind turbine, and which allows the nacelle to rotate relative to the tower in order to arrange the wind turbine blades in the direction of the incom ing wind.

The yaw ring assembly com prises a yaw ring and a plurality of independent tooth parts m ounted circumferentially on the yaw ring. Accordingly, the yaw ring with the plurality of tooth parts m ounted thereon form a full toothed gear ring which can be used as a yaw ring in a yaw gear, i.e. the teeth are arranged to engage teeth of a rotatable drive part used for driving the yawing m ovement of the nacelle.

I n the present context the term‘tooth’ should be interpreted to mean an object having the shape of a conventional gear tooth. For instance, the tooth comprises two surfaces arranged on opposite sides of the tooth. The surfaces may have an involute shape, or any other suitable shape. The surfaces are arranged to contact a driving or driven object, e.g. in the form of a gear tooth arranged on another gear wheel, in order to transfer torque there between. The surfaces m ay be connected via a top land.

However, since the teeth are m ounted on the yaw ring, rather than form ing an integral part thereof, it is possible to replace a single tooth part without dismantling the yaw gear and/or replacing the entire yaw ring. Furthermore, this can be done in a very easy m anner, since it only requires rem oving one of the independent tooth parts and m ounting another corresponding tooth part on the yaw ring.

I n a first embodiment, a tooth part m ay comprise no m ore than one tooth, i.e. a single tooth. I n other embodiments, a tooth part m ay comprise two or m ore teeth being m anufactured in one piece and m ounted as such on the yaw ring.

Furtherm ore, the yaw ring can be manufactured without the need for large equipment for form ing the teeth directly on the yaw ring. Finally, the yaw ring may be m anufactured in a segmented m anner, m aking it easier to m anufacture and transport the yaw ring. I n this case the yaw ring can be assembled and the teeth mounted thereon at the site where the wind turbine in which the yaw gear is to be arranged is positioned.

Providing the yaw ring with a plurality of independent teeth instead of a plurality of pins as described in WO 2010/078944 A2 ensures that the resulting yaw ring assem bly functions in the sam e manner as a conventional yaw ring having the teeth form ed directly in the yaw ring. This m eans, inter alia, that the load distribution in the yaw ring assem bly is essentially as in a conventional yaw ring. For instance, when a tooth of a rotatable drive part engages a tooth of the yaw ring assem bly, the load transferred from the drive part to the tooth part of the yaw ring assem bly is partly transferred to the neighbouring tooth part of the yaw ring assem bly. This reduces the risk of excessive wear on the teeth of the yaw ring assem bly.

It should be noted that the plurality of tooth parts m ay be m ounted along an outer circumference or along an inner circumference of the yaw ring.

The teeth m ay be arranged to transfer loads from one tooth part to a

neighbouring tooth part without transferring the loads via the yaw ring. Thereby loads can be transferred directly between the tooth parts, and this allows for an efficient load distribution am ong the tooth parts, without loading the yaw ring or the connections between the tooth parts and the yaw ring. This m ay be obtained by positioning the tooth parts in abutment with each other or by arranging the tooth parts in abutment with intermediate parts, such as pins, which are in turn arranged in abutm ent with a neighbouring tooth part. This will be described in further detail below.

The yaw ring assem bly m ay further com prise a plurality of pins m ounted circumferentially on the yaw ring, interleaved with the tooth parts. According to this em bodiment, a plurality of tooth parts and pins are m ounted alternatingly along the circumference of the yaw ring. The pins m ay be used for fixating the tooth parts with respect to the yaw ring, thereby preventing the tooth parts from falling out during operation. Furthermore, according to this em bodim ent, when loads are transferred from one tooth part to a neighbouring tooth part, this takes place via a pin.

At least one of the tooth parts m ay be provided with at least one recess arranged to receive a pin arranged adjacent to the tooth part. According to this em bodiment, the tooth parts may be m ounted on the yaw ring along a substantially radial direction, and the pins may subsequently be m ounted between the tooth parts along a direction which is substantially parallel to an axis of rotational sym metry defined by the yaw ring, i.e. substantially

perpendicularly to the radial direction along which the tooth parts were mounted. Since the pins are received in the recesses of the tooth parts, they prevent the tooth parts from accidentally falling out of the yaw ring along the radial direction, i.e. the tooth parts are fixed in the yaw ring. This allows the yaw ring assem bly to be m anufactured with very little play between the tooth parts without requiring high m anufacturing tolerances on the tooth parts or the yaw ring.

The yaw ring m ay be provided with a plurality of holes, each being arranged for receiving a pin. According to this em bodim ent, the plurality of pins are mounted on the yaw ring by inserting each of them into one or m ore of the holes.

Alternatively, or additionally, the tooth parts m ay be mounted on the yaw ring in abutment with each other. I n this case loads are transferred directly from one tooth part to a neighbouring tooth part. The tooth parts m ay, in this case, be fixed to the yaw ring in an alternative m anner, e.g. by m eans of protrusions on the tooth parts and corresponding recesses in the yaw ring, and retaining means arranged for retaining the protrusions in the recesses.

The yaw ring m ay define a U-shaped recess, and the tooth parts m ay be at least partially accom m odated in the U-shaped recess. According to this embodim ent, the yaw ring com prises an upper ring and a lower ring. The upper ring and the lower ring are interconnected by a peripheral ring, form ing a‘bottom’ of the U- shape. I n the case that the tooth parts are mounted along an outer

circumference of the yaw ring, the peripheral ring form s an inner circumference of the yaw ring, and in the case that the tooth parts are m ounted along an inner circumference of the yaw ring, the peripheral ring form s an outer circumference of the yaw ring. Thereby the tooth parts can be inserted between the upper ring and the lower ring along a radial direction, and are at least partially

accom m odated there. It is not ruled out that a sm all part of each tooth part extends beyond the U-shaped recess, thereby form ing the actual toothed rim of the yaw ring.

At least one of the tooth parts m ay com prise a protruding portion being arranged to be received in a corresponding recess formed in the yaw ring in order to mount the tooth parts on the yaw ring. I n the case that the yaw ring defines a U-shaped recess as described above, the recess m ay be formed in the upper ring and/or in the lower ring. I n this case, the protruding portion of the tooth parts m ay extend along a direction which is substantially perpendicular to the radial direction.

Thus, at least one of the protruding portion(s) m ay extend along a direction which is substantially parallel to an axial direction defined by the yaw ring assem bly. I n the present context, the term‘axial direction’ should be interpreted to mean a direction which is defined by an axis of rotation of the yaw ring assem bly. This axis also constitutes an axis of rotational sym m etry of the yaw ring assem bly. Alternatively or additionally, one or m ore recesses m ay be form ed in the ‘bottom’ part of the U-shaped recess, and a corresponding radially extending protrusion may be formed on one or more of the tooth parts. I n this case the tooth parts can be positioned accurately relative to each other along the circumference of the yaw ring, since a given tooth part m ust be positioned in such a m anner that its radially protruding portion is received in one of the recesses form ed in the‘bottom’ of the U-shaped recess.

The tooth parts may com prise two or more protruding portions, e.g. a radially extending protruding portion as well as one or more axially extending protruding portions.

A portion of at least one of the tooth parts may protrude outwards from an outer or an inner diameter defined by the yaw ring. According to this embodiment, the portion of the tooth parts which protrudes outwards from the yaw ring form a toothed rim of the yaw ring. As an alternative, the tooth parts may be

com pletely accom m odated in the yaw ring.

The yaw ring m ay comprise two or m ore yaw ring segm ents connected to each other to form the yaw ring. According to this em bodiment, the yaw ring is manufactured in sm aller segm ents which are subsequently assembled to form the yaw ring. Thereby even very large yaw rings can be m anufactured without the requirem ent of large and specially designed equipm ent, and thereby the manufacturing costs of the yaw ring are reduced. Furthermore, the segm ents can be transported individually to a relevant operating site, and the yaw ring can be assem bled on site. Thereby special transporting equipm ent is not required, and this provides a considerable reduction of the transporting costs.

For instance, the yaw ring may com prise an upper ring, a lower ring and a peripheral ring, as described above, and these three parts may be manufactured separately and subsequently assem bled. Furtherm ore, each of the upper ring, the lower ring and the peripheral ring may comprise two or m ore segments. I n this case the segments of the upper ring, the lower ring and the peripheral ring may advantageously be assem bled in such a manner that the joints between segm ents of the rings are not coinciding. Thereby weak points of the resulting yaw ring assem bly are avoided, and the strength of the yaw ring assembly is im proved.

The plurality of tooth parts may form a full toothed rim of the yaw ring assem bly. The toothed rim m ay be arranged along an outer circumference or along an inner circumference of the yaw ring.

According to a second aspect the invention provides a yaw gear for a wind turbine, the yaw gear com prising:

- a yaw ring assembly according to the first aspect of the invention, and

- a rotatable drive part arranged to engage the teeth m ounted on the yaw ring of the yaw ring assembly in order to cause a relative m ovem ent between the yaw ring assem bly and the drive part, via the teeth.

The yaw gear according to the second aspect of the invention comprises a yaw ring assem bly according to the first aspect of the invention. The remarks set forth above are therefore equally applicable here.

The yaw gear according to the second aspect of the invention further com prises a rotatable drive part arranged to engage the teeth mounted on the yaw ring of the yaw ring assem bly. The drive part may, e.g. , include a yaw m otor driving a rotatable gear wheel. When the rotatable drive part rotates, a relative movement between the yaw ring assem bly and a com ponent or part on which the drive part is arranged takes place. For instance, the yaw ring assem bly may be mounted on an upper part of a wind turbine tower, while the drive part may be mounted on a nacelle of the wind turbine. I n this case rotation of the rotatable drive part causes the nacelle to rotate relative to the yaw ring assem bly, and thereby relative to the tower. Alternatively, the yaw ring assem bly m ay be m ounted on the nacelle, while the drive part may be m ounted on an upper part of the wind turbine tower. I n this case rotation of the rotatable drive part causes the yaw ring, and thereby the nacelle, to rotate relative to the tower.

According to a third aspect the invention provides a wind turbine com prising a tower, a nacelle and a yaw gear according to the second aspect of the invention arranged between the tower and the nacelle.

According to a fourth aspect the invention provides a method for replacing a tooth part of a yaw ring assembly, the yaw ring assem bly comprising a yaw ring and a plurality of independent tooth parts m ounted circumferentially on the yaw ring, the method comprising the steps of:

- rem oving a tooth part to be replaced from the yaw ring, and

- mounting a new tooth part on the yaw ring at the position of the rem oved tooth part.

The m ethod according to the fourth aspect of the invention is a method for replacing a tooth part of a yaw ring assem bly according to the first aspect of the invention. Accordingly, the remarks set forth above are equally applicable here. As described above, a single tooth part or a few tooth parts can easily be replaced without dism antling the yaw ring assem bly or replacing the entire yaw ring assem bly.

The yaw ring assem bly m ay further com prise a plurality of pins m ounted circumferentially on the yaw ring, interleaved with the teeth, and the m ethod may further comprise the steps of rem oving at least one pin arranged adjacent to the tooth part to be replaced, from the yaw ring, prior to rem oving the tooth part, and rem ounting the pin on the yaw ring, after the new tooth part has been mounted on the yaw ring.

According to this em bodiment, the tooth parts are fixated relative to the yaw ring by m eans of the pins, as described above. Thereby, rem oving one or more pins arranged adjacent to the tooth part to be replaced removes this fixation, and thereby the tooth part is allowed to be rem oved from the yaw ring along a radial direction. When the new tooth part has been m ounted on the yaw ring, the pin(s) is/ are rem ounted on the yaw ring in order to fixate the new tooth part relative to the yaw ring. The tooth parts may be provided with at least one protruding portion extending along a direction being substantially parallel to an axial direction defined by the yaw ring assem bly, and the step of removing a tooth to be replaced m ay com prise m oving the protruding portion(s) out of one or more recesses formed in the yaw ring, along a radial direction defined by the yaw ring assem bly, and the step of m ounting a new tooth part may com prise inserting the protruding portion(s) into the recess(es) .

According to this em bodiment, one or m ore protruding portions form ed on the tooth parts are arranged in engagem ent with recesses form ed in the yaw ring, and the tooth parts are removed from and mounted on the yaw ring by m oving the protruding portion(s) out of and into the recesses along a radial direction.

BRI EF DESCRI PTI ON OF THE DRAWI NGS

The invention will now be described in further detail with reference to the accompanying drawings in which

Figs. 1 -8 illustrate a yaw ring assembly according to a first embodim ent of the invention,

Figs. 9 and 10 are perspective views of a tooth part for the yaw ring assembly of Figs. 1 -8,

Fig. 1 1 is a perspective view of a pin for the yaw ring assem bly of Figs. 1 -8,

Figs. 12- 17 illustrate a yaw ring assembly according to a second em bodiment of the invention, and Figs. 18 and 19 are perspective views of a tooth part for the yaw ring assem bly of Figs. 12- 17.

DETAI LED DESCRI PTI ON OF THE DRAWI NGS

Figs. 1 -8 illustrate a yaw ring assem bly 1 according to a first embodiment of the invention. Fig. 1 is a perspective view of a yaw ring 2 without tooth parts mounted thereon, and Fig. 2 shows a detail of the yaw ring 2 of Fig. 1 . The yaw ring 2 com prises an upper ring 3 and a lower ring 4 interconnected by an inner peripheral ring 5. Thereby the yaw ring 2 defines a U-shaped recess in which a plurality of teeth can be received, the U-shaped recess having its open end arranged along an outer periphery of the yaw ring 2. This will be described in further detail below.

A plurality of recesses 6 are formed in the peripheral ring 5. Each of these recesses 6 is arranged to receive a protruding portion of a tooth part in order to accurately position a plurality of teeth in the U-shaped recess. This will be described in further detail below.

Furthermore, a plurality of holes 7 are formed in the upper ring 3 and a plurality of holes 8 are form ed in the lower ring 4. This allows a plurality of pins to be mounted on the yaw ring 2 in order to fixate the plurality of teeth with respect to the yaw ring 2. This will be described in further detail below. The yaw ring 2 m ay be manufactured in a single piece. Alternatively, the upper ring 3, the lower ring 4 and the inner peripheral ring 5 m ay be manufactured as separate parts and subsequently assembled to form the yaw ring 2.

Furtherm ore, each of the upper ring 3, the lower ring 4 and the inner peripheral ring 5 may be assem bled from two or more segm ents. I n this case the joints between the segm ents of the rings 3, 4, 5 may advantageously be displaced with respect to each other in order to avoid weak spots in the yaw ring 2.

As m entioned above in the sum mary, a tooth part may comprise only a single tooth or it may comprise two or m ore teeth. Preferred embodiments include that each tooth part comprises exactly one tooth, exactly two teeth, or exactly three teeth. For simplicity, in the figures and the following description, tooth parts com prising exactly one tooth is shown, and consequently, these will often be referred to simply as‘tooth’ to ease reading. Fig. 3 shows the yaw ring 2 of Figs. 1 and 2 with one tooth 9 and one pin 10 mounted thereon. The tooth 9 has been arranged with a protruding portion (not shown) being received in one of the recesses 6 form ed in the peripheral ring 5. Thereby the position of the tooth 9 relative to the yaw ring 2 is defined by the position of the recess 6 in which the protruding portion of the tooth 9 has been received.

The pin 10 has been mounted on the yaw ring 2 along a direction which is substantially perpendicular to a radial direction defined by the yaw ring 2. The pin 10 has been passed through one of the holes 7 form ed in the upper ring 3 of the yaw ring 2 and through one of the holes 8 form ed in the lower ring 4.

Thereby the position of the pin 10 relative to the yaw ring 2 is defined by the positions of the hole 7, 8, respectively, in which the pin 10 has been positioned.

Accordingly, the relative position of the tooth 9 and the pin 10 is determ ined by the positions of the relevant recess 6 and the relevant holes 7, 8 relative to the yaw ring 2. Thereby the tooth 9 and the pin 10 are positioned accurately relative to each other, and a firm abutment between the tooth 9 and the pin 1 0 is ensured. This allows appropriate load transfer to take place between the tooth 9 and the pin 10.

The pin 10 is arranged along a groove or recess (not shown) formed in the tooth 9. Thereby, once a plurality of teeth 9 and pins 10 have been m ounted circumferentially on the yaw ring 2 in the U-shaped recess, the pin 10 prevents the tooth 9 from accidentally leaving the U-shaped recess.

Figs. 4 and 5 are cross sectional views of a yaw ring assembly 1 comprising the yaw ring 2 of Figs. 1 -3. I n Figs. 4 and 5 a plurality of teeth 9 and a plurality of pins 10 have been circumferentially mounted on the yaw ring 2 in an interleaved manner, i.e. in such a m anner that the teeth 9 and the pins 10 are arranged alternatingly along the outer circumference of the yaw ring 2. Thereby the plurality of teeth 9 forms a complete toothed rim of the yaw ring assembly 1 . A small portion of each tooth 9 protrudes outwards from the U-shaped recess, thereby form ing the toothed rim of the yaw ring assem bly 1 in a region which exceeds the yaw ring 2 along an outward radial direction.

The cross section illustrated in Fig. 4 goes through one of the teeth 9. Thereby it can be seen that the tooth 9 has a protruding portion 1 1 which is received in one of the recesses 6 form ed in the inner peripheral ring 5. The cross section illustrated in Fig. 5 goes through one of the pins 1 0. Thereby it can be seen how the pin 10 passes through the holes 7, 8 form ed in the upper ring 3 and the lower ring 8, respectively.

Fig. 6 is a perspective view of the yaw ring assem bly 1 of Figs. 4 and 5, Fig. 7 is a detail of the yaw ring assem bly 1 of Fig. 6, and Fig. 8 is a cross sectional view of the yaw ring assem bly 1 of Fig. 6.

I n Fig. 6 it can be seen that the teeth 9 and the pins 1 0 have been m ounted along the entire outer circumference of the yaw ring 2, thereby form ing a toothed rim of the yaw ring assem bly 1 . The toothed rim and the interleaved arrangement of the teeth 9 and the pins 10 can also be clearly seen in Figs. 7 and 8. As shown here, there are m any tooth parts 9, such as around 90.

Flowever, the num ber of tooth parts may vary in different em bodim ents, but it is preferred to have at least five tooth parts, such as at least 10, or even at least 20.

Since the teeth 9 and the pins 10 are mounted individually on the yaw ring 2, a single tooth 9 can easily be replaced, e.g. in the case of dam age or wear on the tooth 9, without dism antling the entire yaw ring assem bly 1 , and without replacing the entire yaw ring assem bly 1 . This can sim ply be done by rem oving the pins 10 arranged adjacent to the tooth 9 to be replaced, removing the tooth 9, inserting a new tooth 9 and reintroducing the pins 10. Simultaneously, since the teeth 9 and the pins 10 are mounted accurately and in firm abutment along the circumference of the yaw ring 2, a load distribution among the teeth 9 during operation is obtained which resembles the load distribution in a yaw ring in which the teeth form an integral part of the yaw ring. This is obtained without the disadvantages involved with manufacturing the yaw ring with the teeth directly therein.

It should be noted that the yaw ring 2 could, alternatively, be designed with an outer peripheral ring instead of the inner peripheral ring 5. In this case the yaw ring 2 would define a U-shaped recess having its open end arranged along an inner periphery of the yaw ring 2. Thereby a plurality of teeth 9 mounted in the U-shaped recess essentially in the manner described above would form a toothed rim along the inner circumference of the yaw ring 2 rather than along the outer circumference of the yaw ring 2.

Figs.9 and 10 are perspective views of a tooth 9 for use in the yaw ring assembly 1 illustrated in Figs. 1-8, seen from two different angles. The

protruding portion 11 being arranged to be received in a recess formed in the inner peripheral ring of a yaw ring is clearly seen. Furthermore, the tooth 9 is provided with a recess or groove 12 in which a pin can be received in the manner described above with reference to Fig.3. Fig. 11 is a perspective view of a pin 10 for use in the yaw ring assembly 1 illustrated in Figs.1-8.

Figs. 12-17 illustrate a yaw ring assembly 1 according to a second embodiment of the invention. The yaw ring assembly 1 according to the second embodiment of the invention is very similar to the yaw ring assembly 1 according to the first embodiment of the invention illustrated in Figs. 1-8 and described above, and it will therefore not be described in detail here.

Fig. 12 is a perspective view of a yaw ring 2 without any teeth mounted thereon, the yaw ring 2 comprising an upper ring 3, a lower ring 4 and an inner

peripheral ring 5, essentially as described above with reference to Figs. 1 and 2. However, instead of the holes 7, 8 form ed in the upper ring 3 and the lower ring 4, respectively, the yaw ring 2 of Fig. 12 is provided with a plurality of recesses 13 formed in the upper ring 3 and a plurality of recesses 14 formed in the lower ring 4. The recesses 13, 14 are each arranged to receive a protruding portion form ed on a tooth being inserted into the U-shaped recess along a radial direction. This will be described in further detail below.

Fig. 13 is a detail of the yaw ring 2 of Fig. 12 having a single tooth 9 m ounted in the U-shaped recess thereof. The tooth 9 comprises two protruding portions 15, 16. Protruding portion 15 has been received in one of the recesses 13 formed in the upper ring 3 and protruding portion 1 6 has been received in one of the recesses 14 formed in the lower ring 4. Furthermore, an additional protruding portion (not shown) has been received in one of the recesses 6 form ed in the inner peripheral ring 5, essentially in the manner described above with reference to Figs. 1 -8. Accordingly, the position of the tooth 9 relative to the yaw ring 2 is defined by the positions of the relevant recesses 6, 13, 14. Thereby teeth 9 can be mounted on the yaw ring 2 in a very precise m anner with respect to the yaw ring 2 and with respect to each other. Retaining pins 17 have been mounted on the yaw ring 2 in order to prevent the tooth 9 from accidentally leaving the U- shaped recess. Fig. 14 is a perspective view of a part of a yaw ring assembly 1 comprising the yaw ring 2 of Figs. 12 and 13. A plurality of teeth 9 have been mounted on the yaw ring 2, thereby form ing a complete toothed rim of the yaw ring assembly 1 , essentially as described above with reference to Figs. 1 -8. The teeth 9 are arranged in abutm ent with each other. Figs. 15 and 1 6 are cross sectional views of the yaw ring assem bly 1 of Fig. 14.

The cross section illustrated in Fig. 15 goes through one of the teeth 9. Thereby it can be seen that the tooth 9 has a protruding portion 1 1 which is received in one of the recesses 6 formed in the inner peripheral ring 5. Furtherm ore, it can be seen that the protruding portion 15 is received in one of the recesses 13 form ed in the upper ring 3, and the protruding portion 16 is received in one of the recesses 14 form ed in the lower ring 4.

The cross section illustrated in Fig. 16 goes through a part of the yaw ring 2 between two of the teeth 9. Fig. 17 is a perspective view of the yaw ring assembly 1 according to the second em bodiment of the invention. I t is clearly seen that the teeth 9 form a complete toothed rim of the yaw ring assembly 1 .

Due to the precise positioning of the teeth 9 relative to the yaw ring 2 and relative to each other provided by the cooperation of the protruding portions 1 1 , 15, 16 of the teeth 9 and the recesses 6, 13, 14 of the yaw ring 2, and because the teeth 9 are arranged in abutm ent with each other, a load distribution among the teeth 9 during operation is obtained which resem bles the load distribution in a yaw ring in which the teeth form an integral part of the yaw ring. I n particular, loads applied to one tooth 9 during operation can be partly transferred directly to adjacent tooth 9, since the teeth 9 are arranged in abutm ent with each other. This is obtained without the disadvantages involved with m anufacturing the yaw ring with the teeth directly therein.

Furtherm ore, a single tooth 9 can easily be replaced, essentially for the reasons set forth above with reference to Figs. 1 -8. As compared to the first em bodim ent illustrated in Figs. 1 -8, in the em bodim ent of the second em bodim ent illustrated in Figs. 12- 17, the pins 10 have been om itted, and the teeth 9 are instead provided with protruding portions 15, 1 6 being received in recesses 13, 14 form ed in the yaw ring 2, and arranged in abutment with each other. Flowever, this design also ensures that the teeth 9 are kept firm ly in place during operation, and that an appropriate load

distribution am ong the teeth 9 is obtained.

Figs. 18 and 19 are perspective views of a tooth 9 for use in the yaw ring assem bly 1 illustrated in Figs. 12- 1 7, seen from two different angles. The protruding portions 1 1 , 15, 16 being arranged to be received in respective recesses form ed in the yaw ring are clearly seen.

It should again be emphasized that the invention should not be lim ited by the illustrated exam ples. I n particular that a tooth part 9 may com prise only a single tooth as illustrated, or it m ay comprise two or m ore teeth, such as exactly two teeth or exactly three teeth. I n such variations, each tooth part m ay be fixed as shown for individual teeth, i.e. have a single protruding portion 1 1 , be mounted via a single recess 6, etc. as shown. However, variations to this could still be possible within the scope of the following claim s.

Claims

1. A yaw ring assembly (1 ) for a yaw gear of a wind turbine, the yaw ring assembly (1) comprising:

- a yaw ring (2), and - a plurality of independent tooth parts (9) mounted circumferentially on the yaw ring (2).

2. A yaw ring assembly (1) according to claim 1 comprising at least five independent tooth parts (9) mounted circumferentially on the yaw ring (2).

3. A yaw ring assembly (1) according to claim 1 or 2, wherein at least one of said plurality of independent tooth parts (9) comprises no more than one tooth.

4. A yaw ring assembly (1 ) according to any of the preceding claims, wherein at least one of said plurality of independent tooth parts (9) comprises two or more teeth.

5. A yaw ring assembly (1) according to any of the preceding claims, wherein the plurality of tooth parts (9) form a full toothed rim of the yaw ring assembly

(1)·

6. A yaw ring assembly (1) according to any of the preceding claims, wherein the tooth parts (9) are arranged to transfer loads from one tooth part (9) to a neighbouring tooth part (9) without transferring the loads via the yaw ring (2).

7. A yaw ring assembly (1) according to any of the preceding claims, further comprising a plurality of pins (10) mounted circumferentially on the yaw ring (2), interleaved with the tooth parts (9).

8. A yaw ring assembly (1) according to claim 7, wherein at least one of the tooth parts (9) is provided with at least one recess (12) arranged to receive a pin (10) arranged adjacent to the tooth part (9).

9. A yaw ring assembly (1) according to claim 7 or 8, wherein the yaw ring (2) is provided with a plurality of holes (7, 8), each being arranged for receiving a pin (10).

10. A yaw ring assembly (1 ) according to any of the preceding claims, wherein the yaw ring (2) defines a U-shaped recess, and wherein the tooth parts (9) are at least partially accommodated in the U-shaped recess.

11. A yaw ring assembly (1 ) according to any of the preceding claims, wherein at least one of the tooth parts (9) comprises at least one protruding portion (11 , 15, 16) being arranged to be received in a corresponding recess (6, 13, 14) formed in the yaw ring (2) in order to mount the tooth parts (9) on the yaw ring (2).

12. A yaw ring assembly (1 ) according to claim 11 , wherein at least one of the protruding portion(s) (15, 16) extends along a direction which is substantially parallel to an axial direction defined by the yaw ring assembly (1).

13. A yaw ring assembly (1 ) according to any of the preceding claims, wherein a portion of at least one of the tooth parts (9) protrudes outwards from an outer or an inner diameter defined by the yaw ring (2).

14. A yaw ring assembly (1) according to any of the preceding claims, wherein the yaw ring (2) comprises two or more yaw ring segments connected to each other to form the yaw ring (2).

15. A yaw gear for a wind turbine, the yaw gear comprising:

- a yaw ring assembly (1) according to any of the preceding claims, and

- a rotatable drive part arranged to engage the tooth parts (9) mounted on the yaw ring (2) of the yaw ring assembly (1) in order to cause a relative movement between the yaw ring assembly (1) and the drive part, via the tooth parts (9).

16. A wind turbine comprising a tower, a nacelle and a yaw gear according to claim 15 arranged between the tower and the nacelle.

17. A method for replacing a tooth part (9) of a yaw ring assembly (1), the yaw ring assembly (1) comprising a yaw ring (2) and a plurality of independent tooth parts (9) mounted circumferentially on the yaw ring (2), the method comprising the steps of:

- removing a tooth part (9) to be replaced from the yaw ring (2), and

- mounting a new tooth part (9) on the yaw ring (2) at the position of the removed tooth part (9).

18. A method according to claim 17, wherein the yaw ring assembly (1) further comprises a plurality of pins (10) mounted circumferentially on the yaw ring (2), interleaved with the tooth parts (9), and wherein the method further comprises the steps of removing at least one pin (10) arranged adjacent to the tooth part (9) to be replaced, from the yaw ring (2), prior to removing the tooth part (9), and remounting the pin (10) on the yaw ring (2), after the new tooth part (9) has been mounted on the yaw ring (2).

19. A method according to claim 17, wherein the tooth parts (9) are provided with at least one protruding portion (15, 16) extending along a direction being substantially parallel to an axial direction defined by the yaw ring assembly (1), and wherein the step of removing a tooth part (9) to be replaced comprises moving the protruding portion(s) (15, 16) out of one or more recesses (13, 14) formed in the yaw ring (2), along a radial direction defined by the yaw ring assembly (1), and the step of mounting a new tooth part (9) comprises inserting the protruding portion(s) into the recess(es) (13, 14).