Patent Description:
Modern wind turbines, also called wind motors, wind engines, or wind power plants, are employed to produce electricity. They are often very large structures with blades having a length of more than <NUM> metres, and which are made from fibre-reinforced polymer shells. Today, the blades may even have a length of more than <NUM> metres.

The wind turbines are often provided as so-called horizontal axis wind turbine or HAWTs. Such wind turbines comprise a machine housing on top of a tower and a rotor with a hub and a number of wind turbine blades, preferably two or three, mounted on a substantially horizontal rotor shaft.

Modern wind turbines are often provided with a pitch system to pitch the wind turbine blades to actively change the angle of attack of airflow over the blades. This is preferred over stall-regulated wind turbines as the pitching enables far greater control of the power output from the wind turbine. Further, the pitching may be utilised to change deflection of the blades, whereby collisions between blade tips and the tower may be avoided.

Pitch system may require a pitch limiter or means for calibrating the pitch system in order to ensure optimum functionality of the pitching system,.

<CIT> discloses a wind turbine comprising a pitch blocking mechanism. <CIT> discloses a horizontal axis wind turbine with wind turbine blades. The blade comprises a root end flange. Further, the wind turbine is provided with an adaptor, which is provided between a root end of the blade and a bearing ring of the wind turbine. The adaptor allows the root end to have a smaller diameter than a pitch bearing. The adaptor may be provided in form of a plate member, which provides a continuous mounting surface.

It is an object of the invention to obtain a new wind turbine blade, which overcome or ameliorate at least one of the disadvantages of the prior art or which provide a useful alternative.

This is according to the invention obtained by a wind turbine blade for a horizontal axis wind turbine, wherein the wind turbine blade extends in a longitudinal direction parallel to a longitudinal axis and having a tip end and a root end, and wherein the wind turbine blade further comprises a shell body, and wherein the wind turbine blade further comprises a root end flange at the root end of the blade, the root end flange comprising a ring-shaped body that extends circumferentially along the entire root end, the root end flange preferably made from a metal, such as stainless steel or hot-dip galvanised steel, wherein the root end flange comprises an inwardly extending protrusion with a distal plate part arranged in a distance from the ring body and wherein the root end is configured to be connected to a pitch bearing, the root end flange being separate and distinct from the pitch bearing.

The inwardly extending protrusion extends from the ring-shaped body of the root end flange. The inwardly extending protrusion and distal plate part may thus be utilised as a pitch-position indicator, which in turn can be utilised as a pitch angle limiter or a pitch angle indicator for calibration purposes. Accordingly, they may be utilised to optimise the pitch system of the wind turbine.

The shell body preferably has a profiled contour or aerodynamic surface including a pressure side and a suction side, as well as a leading edge and a trailing edge with a chord having a chord length extending there between, the profiled contour when being impacted by an incident airflow generating a lift.

In a preferred embodiment, the root end flange provides an interface between the root end of the wind turbine blade and a pitch flange provided in a hub of a wind turbine.

In an advantageous embodiment, the root end flange is divided into a plurality of connected root end flange segments. Accordingly, the inwardly extending protrusion and the distal plate part may be provided in one segment, whereas the remainder of the ring-shaped body may be provided as one or more separate segments. Accordingly, the protrusion and plate may more easily be adapted to a particular blade type without having to redesign the entire root end flange.

The root end flange segments may advantageously be interconnected via a mating connection.

In another advantageous embodiment, the inwardly extending protrusion and the distal plate part are integrally formed. Alternatively, the inwardly extending protrusion and the distal plate part may be provided as two or more connected parts.

In principle, the root end flange may comprise a plurality of inwardly extending protrusions and a distal plate parts, e.g. as two pitch limiter devices.

In one embodiment, the distal plate part comprises a taper section at a circumferential end of the distal plate part, advantageously at both circumferential ends of the distal plate part art. The taper section may be adapted to interact with a contact part of a pitch system, the contact part for instance being connected to the hub of the wind turbine.

The taper section may have a taper angle in the interval from <NUM> to <NUM> degrees, advantageously in the interval <NUM> to <NUM> degrees, and more advantageously in the interval <NUM> to <NUM> degrees, e.g. around <NUM> degrees.

The distal plate part may extend along <NUM> to <NUM> degrees of a circumference of the root end flange, advantageously along <NUM> to <NUM> degrees of the circumference, more advantageously along <NUM> to <NUM> degrees of the circumference, e.g. around <NUM> degrees (or <NUM>/<NUM> of the entire circumference). Accordingly, it is seen that the plate part only extends along a limited part of the entire root end flange.

In one advantageous embodiment, the distal plate part is arranged with a spacing to a radial inner part of the ring-shaped body. Accordingly, a clearing is provided for the sensor for detecting the position of the plate part, such that the blade itself does not interfere with the sensor.

In another advantageous embodiment, the distal plate part is centered at an offset angle of <NUM> to <NUM> degrees from a zero twist angle of the wind turbine blade, advantageously <NUM> to <NUM> from the zero twist angle, more advantageously <NUM> to <NUM> from the zero twist angle, e.g. approximately <NUM> degrees from the zero twist angle.

The distal plate part may advantageously be arranged substantial flush with an inboard part of the root end flange. Accordingly, the plate part is arranged near the hub.

The invention also provides a wind turbine blade pitch system comprising a blade according to any of the aforementioned embodiments and a pitch bearing, wherein the distal plate part is utilised as a pitch limiter or a pitch angle indicator. The plate part may for instance be utilised to indicate a zero pitch angle point for continuous calibration of the pitch system.

The invention further provides a wind turbine comprising a rotor including a number of wind turbine blades according to any of the aforementioned embodiments and a hub, from which the blade or blades extend substantially in a radial direction, wherein the wind turbine is provided with a sensor to detect a location of the distal plate part of the root end flange.

Accordingly, the sensor may be utilised to identify the pitch position of the wind turbine blade.

The wind turbine preferably comprises a substantially horizontal rotor shaft, i.e. the wind turbine being a horizontal axis wind turbine (HAWT). The wind turbine preferably comprises a machine housing on top of a tower and has a rotor with a hub and a number of wind turbine blades, preferably two or three, mounted on a substantially horizontal rotor shaft.

In one advantageous embodiment, the sensor is mounted to a stationary part of the hub.

In a highly advantageous embodiment, the wind turbine comprises at least two sensors arranged so as to be able to detect a direction of pitching. The sensors may for instance be arranged at two different circumferential positions relative to the plate part of the root end flange. Accordingly, the sensors may be arranged such that a first sensor detects the plate part at a first pitch angle and the second sensor detects the plate part at a second pitch angle.

In a first advantageous embodiment, the sensor is a contact sensor, which is adapted to contact the distal plate part of the root end flange.

In a second advantageous embodiment, the sensor is an optical sensor. In a third advantageous embodiment, the sensor is a capacitive sensor. In a fourth advantageous embodiment, the sensor is an inductive sensor.

In princle, it is also possible to provide a pitch limiter or a pitch angle indicator as a separate device that extends from an inner blade wall of the wind turbine instead of the root end flange. The pitch limiter or pitch angle indicator may still advantageously be arranged close to the root end of the flange and may have a form corresponding to any of the aforementioned embodiments.

<FIG> illustrates a conventional modern upwind wind turbine according to the so-called "Danish concept" with a tower <NUM>, a nacelle <NUM> and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub <NUM> and three blades <NUM> extending radially from the hub <NUM>, each having a blade root <NUM> nearest the hub and a blade tip <NUM> farthest from the hub <NUM>.

<FIG> shows a schematic view of a first embodiment of a wind turbine blade <NUM> according to the invention. The wind turbine blade <NUM> has the shape of a conventional wind turbine blade and comprises a root region <NUM> closest to the hub, a profiled or an airfoil region <NUM> farthest away from the hub and a transition region <NUM> between the root region <NUM> and the airfoil region <NUM>.

The diameter (or the chord) of the root region <NUM> is typically constant along the entire root area <NUM>. The transition region <NUM> has a transitional profile <NUM> gradually changing from the circular or elliptical shape <NUM> of the root region <NUM> to the airfoil profile <NUM> of the airfoil region <NUM>. The width of the transition region <NUM> typically increases substantially linearly with increasing distance r from the hub.

The airfoil region <NUM> has an airfoil profile <NUM> with a chord extending between the leading edge <NUM> and the trailing edge <NUM> of the blade <NUM>.

The chords of different sections of the blade normally do not lie in a common plane, since the blade may be twisted and/or curved (i.e. pre-bent), thus providing the chord plane with a correspondingly twisted and/or curved course, this being most often the case in order to compensate for the local velocity of the blade being dependent on the radius from the hub.

The wind turbine blade <NUM> comprises a shell body <NUM>, which is made of a fibre-reinforced polymer material, e.g. a polymer matrix reinforced with glass fibres and/or carbon fibres and is further provided with a root end flange <NUM> connected to a root end of the wind turbine blade <NUM>. The root end flange <NUM> is provided with an inwardly extending protrusion <NUM> having a distal plate part <NUM>. The protrusion <NUM> and plate <NUM> may for instance be arranged such that a proximal end of the plate part <NUM> is arranged at approximately a <NUM> degree angle compared to a zero pitch angle of the blade.

The shell body <NUM> is often made of an upwind blade shell part and a downwind blade shell part, which are bonded to each other near the leading edge <NUM> and the trailing edge <NUM> of the blade <NUM>. The zero pitch angle of the blade is located close to the bond lines of the shell parts.

<FIG> shows a longitudinal sectional view through a root section of a first embodiment of the wind turbine blade according to the invention connected to the hub <NUM> of the rotor of the wind turbine <NUM>.

In the embodiment according to the invention shown in <FIG>, the blade <NUM> comprises a root end flange <NUM> forming part of a hub to root connection between the root of the blade and a pitch bearing <NUM> of the hub. The pitch bearing <NUM> comprises an outer ring <NUM> and an inner ring <NUM>. The inner ring <NUM> is connected to the blade via the root end flange <NUM> and a plurality of fastening elements <NUM> for instance in form of a bushing and bolt connection, e.g. with a plurality of bushings embedded in the shell body <NUM> of the blade and connected to the inner ring <NUM> of the pitch bearing <NUM> via a plurality of corresponding stay bolts. The number of bushings and bolts may e.g. be <NUM>-<NUM>.

The outer ring <NUM> of the pitch bearing <NUM> is stationary mounted to the hub <NUM> of the wind turbine, which can also be obtained by a plurality of fasteners <NUM>, such as bolts. The inner ring <NUM> and the outer ring <NUM> of the pitch bearing <NUM> may be rotated relative to each other via a plurality of ball bearings <NUM> such that the blade <NUM> may be pitched relative to the hub <NUM>.

The bolts and bushings <NUM> as well as the root end flange <NUM> and the inner and outer rings <NUM>, <NUM> of the pitch bearing <NUM> are preferable made of a metal, such as stainless steel. It is also possible to attach the blades in other ways, e.g. by use of T-bolts and barrel nuts.

As shown in <FIG>, the pitch bearing <NUM> is advantageously a ball bearing. The pitch bearing <NUM> could, however, also be any kind of bearing, including a roller bearing or a combination of a roller bearing and a ball bearing.

According to the invention, the root end flange <NUM> is provided with an inwardly extending protrusion <NUM> having a distal plate part <NUM>.

The hub <NUM> of the wind turbine <NUM> comprises a pitch sensor <NUM>, which can detect the position of the distal plate part <NUM>. The pitch sensor <NUM> is stationary mounted to the hub <NUM> and may be provided with a contact <NUM>, which is adapted to interact with the distal plate part <NUM> of the root end flange <NUM>, when the blade <NUM> is pitched to an angle, where the blade sensor <NUM> and the distal plate part <NUM> are positioned in the same angular position. Accordingly, the inwardly extending protrusion <NUM> and the plate part <NUM> may be used as a pitch limiter or pitch angle indicator.

As previously indicated, the root end flange comprises a ring-shaped body and an inwardly extending protrusion having a connected plate part. The root end flange may further be divided into a number of separate segments.

<FIG> shows a first embodiment of a root end flange segment <NUM> according to the invention. The root end flange segment <NUM> as shown comprises an inwardly extending protrusion <NUM> having a distal plate part <NUM>. The distal plate part comprises a first taper section <NUM> at a first circumferential end of the plate part <NUM> and a second taper section <NUM> at a second circumferential end of the plate part <NUM>. In the shown embodiment, the ring-shaped part of the root end flange segment <NUM>, the inwardly extending protrusion <NUM> and the distal plate part <NUM> are integrally formed as a single unit.

The root end flange segment <NUM> comprises mating connections at circumferential ends of the ring-shaped part of the root end flange segment <NUM>, thereby being adapted to form a mating connection with one or more additional root end flange segments completing the ring-shaped part of the root end flange. The additional root end flange segments may also be provided with inwardly extending protrusions and distal plate parts. But in general, a single protrusion and plate are sufficient for the invention.

<FIG> shows a second embodiment of a root end flange segment <NUM> according to the invention. The root end flange segment <NUM> comprises an inwardly extending protrusion <NUM>. Instead of having an integrally formed plate part, the inwardly extending protrusion <NUM> is provided with mounting holes <NUM> for connecting a plate part. Further, the root end flange segment <NUM> is provided with an alignment marker <NUM>, which may be utilised to ensure correct arrangement on the root end of the wind turbine blade compared to for instance a zero-pitch position of the blade. The embodiment shown in <FIG> may of course also be provided with such a marker.

<FIG> show further details of the second embodiment of the root end flange segment <NUM> according to the invention. <FIG> shows a cross-sectional view of a plate <NUM>, which is adapted to be connected to the inwardly extending protrusion <NUM> of the root end flange segment <NUM>. <FIG> shows a top view of the plate <NUM> and <FIG> shows a perspective view of the plate <NUM>. It is seen that the plate <NUM> is provided with a number of mounting holes <NUM>, such that the plate <NUM> may be connected to the corresponding mounting holes <NUM> of the protrusion <NUM>. Further, the plate <NUM> comprises a first taper section <NUM> at a first circumferential end of the plate <NUM> and a second taper section <NUM> at a second circumferential end of the plate part <NUM>.

<FIG> shows a perspective view of the plate <NUM> mounted to the protrusion <NUM> of the root end flange segment <NUM>. The plate <NUM> and the protrusion <NUM> may advantageously be connected via a number of screws (not shown). As shown, the mounting holes <NUM> of the protrusion <NUM> may be provided with a countersink. The mounting holes of the plate <NUM> may be threaded in order to provide a connection. Alternatively, the hole may be through-going and nuts may be utilised to provide the connection between the plate <NUM> and the protrusion <NUM>.

In the shown embodiment, the plate <NUM> and protrusion <NUM> are each provided with two mounting holes. The two mounting holes may have different diameters, such that it is ensured that the mounting plate <NUM> may only be arranged in one orientation relative to the protrusion <NUM>.

<FIG> shows a first sensor system embodiment for detecting a pitch angle of a wind turbine blade. The sensor system embodiment comprises a plate part <NUM>, which is attached to a root end flange of a pitchable wind turbine blade. The sensor system comprises a sensor <NUM>, which is stationary mounted to the hub of the wind turbine. The sensor <NUM> is provided with a contact <NUM>, which may be provided in form of a linearly actuated switch or an angular switch. When the blade is pitched, the plate part <NUM> may thus be brought into contact with the contact <NUM>. If the plate part <NUM> as depicted is provided with tapered end sections, pitching of the blade will bring the taper section into contact with the contact <NUM> and thus push the contact <NUM> towards the hub. Accordingly, the sensor system may be utilised as a pitch limiter for the wind turbine or as a pitch angle indicator, e.g. for continuous calibration of the pitch system of the wind turbine.

<FIG> shows a second sensor system embodiment for detecting a pitch angle of a wind turbine blade. The sensor system embodiment comprises a plate part <NUM>, which is attached to a root end flange of a pitchable wind turbine blade. The sensor system comprises a sensor <NUM>, which is stationary mounted to the hub of the wind turbine. The sensor <NUM> is provided with a first contact <NUM> and a second contact <NUM>', which may be provided in form of a linearly actuated switch. When the blade is pitched, the plate part <NUM> may thus be brought into contact with the contacts <NUM>, <NUM>'. If the plate part <NUM> as depicted is provided with tapered end sections, pitching of the blade will bring the taper section into contact with one of the contacts <NUM>, <NUM>' and thus push the contact <NUM>, <NUM>' towards the hub. Depending on the direction of pitching, either the first contact <NUM> or the second contact <NUM>' will first come into contact (or out of contact) with the plate part <NUM>. Accordingly, it is seen that the use of two sensor parts or contacts <NUM>, <NUM>' provides a simple solution to also derive the direction of pitching.

Contact or switch solutions as shown in <FIG> and <FIG> are preferred according to the invention, but in principle, it is also possible to utilise other sensor types as will be shown in the following.

<FIG> shows a third sensor system embodiment for detecting a pitch angle of a wind turbine blade, which utilise a capacitive sensor <NUM>. The plate part <NUM> of the root end flange of the blade may be formed such that the distance between the plate part <NUM> and the capacitive sensor varies as a function of the pitch angle. Accordingly, the capacitance changes, which in turn can be utilised to determine the pitch angle of the blade.

<FIG> shows a fourth sensor system embodiment for detecting a pitch angle of a wind turbine blade, where optical sensing is utilised to determine the pitch angle of the blade. In the shown embodiment, an optical source <NUM>, such as a light emitting diode or a laser diode, is use for the sensor system. In the shown embodiment, the plate part <NUM> of the root end flange is provided with a number of apertures and a photo sensor array is arranged behind the apertures. Thus, only a limited number of the photo sensors detects the emitted light from the light source <NUM> depending on the particular blade pitch angle. In the shown embodiment, the photo sensor array is arranged behind apertures in the plate <NUM>. However, in principle, the photo sensor array may also be arranged in front of the plate <NUM>. Further, the setup may be reversed, such that the light source is arranged on the plate part <NUM> and the photo sensor array is arranged stationary to the hub.

<FIG> shows a fifth sensor system embodiment for detecting a pitch angle of a wind turbine blade. In this setup the sensor <NUM> houses both a light emitter and a receiver, and the sensor system is based on backscattered light from the plate part <NUM> of the root end flange. The plate <NUM> may be shaped so as to be able to derive the exact position of the plate <NUM> relative to the sensor <NUM> and/or the light source may be modulated.

The invention is not limited to the embodiment described herein, and may be modified or adapted without departing from the scope of the present invention.

Claim 1:
A wind turbine blade (<NUM>) for a horizontal axis wind turbine (<NUM>), wherein the wind turbine blade (<NUM>) extends in a longitudinal direction parallel to a longitudinal axis and having a tip end (<NUM>) and a root end (<NUM>), and wherein the wind turbine blade (<NUM>) further comprises a shell body (<NUM>), and wherein the wind turbine blade (<NUM>) further comprises a root end flange (<NUM>, <NUM>, <NUM>) at the root end (<NUM>) of the blade (<NUM>) and which comprises a ring-shaped body that extends circumferentially along the entire root end (<NUM>), the root end flange (<NUM>, <NUM>, <NUM>) preferably made from a metal, such as stainless steel, characterised in that the root end flange (<NUM>, <NUM>, <NUM>) comprises an inwardly extending protrusion (<NUM>, <NUM>) with a distal plate part (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) arranged in a distance from the ring body, wherein the root end (<NUM>) is configured to be connected to a pitch bearing, the root end flange (<NUM>, <NUM>, <NUM>) being separate and distinct from the pitch bearing.