Fluid reaction surfaces (i.e. – impellers) – Method of operation
Reexamination Certificate
2001-04-16
2003-08-26
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Method of operation
C416S155000, C415S004300, C415S908000
Reexamination Certificate
active
06609889
ABSTRACT:
The present invention relates in a broad aspect to a device and a method for adjusting the pitch of a wind turbine and for stopping the rotation of the blades of a wind turbine.
BACKGROUND OF THE INVENTION AND INTRODUCTION TO THE INVENTION
In one aspect, the present invention relates to a method of adjusting the angular position of at least one blade of a wind turbine, the said wind turbine comprising a bevel gear and a motor for the rotation of a drive wheel of the bevel gear and drive pinions of the bevel gear for turning at least one blade at an angle, this at least one blade being turned at an angle by the drive pinions, the said drive pinions being rotated by the drive wheel, and the drive wheel being rotated by the motor relative to the main shaft. The invention also relates to a mechanism for controlling the pitch of at least one blade of a wind turbine relative to a wind direction parallel to a longitudinal main shaft of the wind turbine, the said mechanism comprising a motor for rotating drive wheels in the bevel gear around a longitudinal blade shaft via drive wheels of a bevel gear. Furthermore the invention relates to a wind turbine having such a mechanism.
In another aspect, the present invention relates to a method of stopping the complete rotation of the main shaft of a wind turbine comprising a motor to rotate a drive pinion of a bevel gear via a drive wheel of the said bevel gear, the said drive pinion being meant to turn at least one blade of the wind turbine around its longitudinal axis. The invention also relates to a mechanism for stopping the complete turning of a main shaft of a wind turbine comprising a motor to rotate a drive pinion in a bevel gear via a drive wheel, the said bevel gear being meant to pitch at least one blade around a longitudinal axis. Furthermore the invention relates to a wind turbine provided with such a mechanism.
DE 42 21 783 describes a device for setting the pitch angle of wind turbine blades. The device comprises an electrical motor mounted inside a fixed bearing. Surrounding the fixed bearing a longitudinal axis of rotation has been installed. On the rotational shaft blades have been installed which can be set at an angle relative to the main shaft and relative to a wind direction parallel to the longitudinal main shaft. The motor adjusts the pitch of the blades through a bevel gear. The longitudinal main shaft rotating and the pitch of the blades being correct, the motor must rotate at the same speed of rotation as the main shaft to maintain the correct pitch of the blades.
This is a major disadvantage. First, it requires very accurate control of the dynamic relations between motor and main shaft, i.e. the rotational speed of the motor in relation to the rotational speed of the main shaft. Second, the motor has to operate continuously to maintain the correct blade pitch. This results in extensive wear of the motor and entails large energy consumption for operating the motor. Furthermore it is necessary to control the speed of rotation variably and continuously relative to the variations in the speed of rotation of the main shaft, and the motor control risks being constantly somewhat behind compared with the main shaft, and consequently an optimal pitch angle of the blades cannot always be obtained.
Furthermore, the device is not capable of stopping or limiting the rotation of the main shaft in a controlled manner in case the motor cannot rotate because of e.g. current failure of the motor shaft rotation. The main shaft will, however, stop rotating after a while, since the blades once the motor no longer rotates synchroneously with the main shaft will soon be pitched at angular positions which are not optimal for the main shaft rotation. The blades will then reach a stable pitch characterized by the main shaft not rotating at the said pitch.
EP 0.094.106 describes a pitch controlling device according to the above. Thus, the device has a pitch motor for controlling the pitch of the blades in an operational situation of the wind turbine. A synchronizing shaft is connected to the blades through a bevel gear and the synchronizing shaft may be rotated by the pitch motor. In order for the pitch motor to rotate the synchronizing shaft, an electromagnetic clutch must be activated because the synchronizing shaft is journalled by means of bearings in the rotatable main shaft of the blades and the pitch motor is fastened to a stationary part of the wind turbine in relation to the main shaft.
However, the need for a clutch or other means of coupling the pitch motor and the synchronizing shaft by means of a disengagable coupling means is a disadvantage. The clutch may be worn or may even failure, which makes it impossible to control the pitch of the blades. If the pitch of the blades cannot be controlled then the wind turbine is not able to produce the maximum amount of effect or may even not be able to produce effect at all. If the clutch is worn or has a failure, then it is furthermore necessary to stop the wind turbine and to repair the clutch or exchange the clutch with a new one. This is time consuming which decreases the overall efficiency of the wind turbine. Furthermore it involves costs of a technician and the costs of spare parts. Lastly using a clutch or other disengagable coupling means may delay controlling of the pitch of the blades when as example a clutch has to be activated before controlling of the pitch of the blades can take place. Accordingly, the use of a clutch involves many disadvantages.
DE 196 34 059 and other prior art wind turbines achieve stopping the rotation of the main shaft by pitching the blades by means of individual motors at each blade. Pitching the blades in this way may have the same technical effect as the above-mentioned procedure and the main shaft stops so that the main shaft either effects no rotation at all or only rotates very slowly in its positive direction of rotation. However, this prior art necessitates the use of a pitch motor for each of the blades. Furthermore, an individual control of the pitch motors as well as a mutual control of the pitch motors will be necessary in order to assure that each blade of the wind turbine is having the same pitch as the other blades.
The object of the present invention is to provide a mechanism which does not suffer from the above mentioned disadvantages, and which will thus to a larger extent be able to establish and maintain the correct pitch of the blades, whether the control is sufficiently precise or not, and without major wear to the gear motor and the pitch motor, or high energy consumption for operating the pitch motor and without the risk of being the method and the mechanism being delimited in the controlling of the pitch because of sudden failure or ordinary wear of coupling means between the pitch altering means and the pitch motor.
The present object is in one embodiment of the invention achieved by a method characterised by the rotation of a drive wheel relative to the main shaft being brought to a standstill once the blades have reached the correct pitch, said drive wheel establishing a permanent coupling between the pitch motor and the synchronizing shaft.
Bringing the rotation of the pitch motor to a standstill relative to the main shaft while the said main shaft is rotating under normal operational conditions provides several advantages. Firstly, the wear of the pitch motor will be substantially reduced compared with a method continuing the rotation of the pitch motor rotation shaft also under normal operational conditions when correct pitch of the blades has been established.
Furthermore, continuously monitoring the speed of rotation of the pitch motor relative to the speed of rotation of the main shaft is no longer necessary. Finally, the pitch motor is used exclusively for controlling the pitch of the blades and is not used simultaneously for maintaining a speed of rotation of the drive wheel relative to the speed of rotation of the main shaft, a function which entails further technical control difficulties.
A mechanism for use in
Edgar Richard A.
NEG Micon A/S
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