The present invention relates to wind-turbines, and more particularly to wind-turbines having but few blades, mounted on a horizontal shaft. More specifically, the invention relates to means for regulating the position and rotation of the blades of such wind-turbines or wind¬ mills.

With respect to the degree of freedom of blade move¬ ment relative to the shaf , attachment of the blades to the shaft can be divided into four main groups, these being:

1. Rigid hub with fixed blades, in which the blades are mounted on the turbine shaft so as to be totally immovable relative to a vertical axis. This kind of attachment can only be used with "small" windmills, since it results in the occurrence of very large blade-forces which cannot be controlled.

2. Rigid hub with twistable blades, in which the blades are mounted on the turbine shaft in a manner which renders said blades resistant to torsional forces around said shaft and around an axis at right angles to the blades, but which enables the blades to twist about their own axes. Twisting of a blade about its own axis, some¬ times known as feathering, enables the attitude of the blade to change in response to prevailing wind conditions, thereby enabling the blade to be held under a certain amount of control. Feathering can be controlled by the wind forces, a control system, or by a combination of the two.

3. Rocking hub with twistable blades (this method of attachment can only be applied with two-bladed wind¬ mills) in which the blades are connected together in a torsion-resistant manner to form a blade-pair which is mounted on the turbine shaft in a manner which renders said blade-pair resistant to torsion forces around the turbine shaft, but capable of rotating about an axis

extending at right angles to said shaft and at right angles, or substantially at right angles to the blade- pair. The blades are also coupled in a manner such that they can twist about their own axes, either indivi- dually or in concert. Rocking about the axis at right angles to, or substantially at right angles to the blade- pair is normally a free movement, while feathering is controlled to varying degrees by the co-action of a control system, the wind-forces and rocking. 4. Flapping hub with twistable blades, each of whi is attached to the turbine shaft in a manner to render said blade torsion-resistant around said shaft, but rotatable about an axis perpendicular to the turbine shaf and perpendicular or substantially perpendicular to the blade. The blades are either coupled so that they can be twisted together, or are individually twistable about their respective axes. Rotation of the blades about the axis extending at right angles to the turbine shaft - flapping - is generally free, while feathering is con- trolled to varying degrees through the co-action of a control system, windforces and flapping.

The four main methods of attachment afford in a rising numerical sequence reduction of forces and torque at the blade attachment point and the turbine shaft, since the wind-forces on the blade are balanced by inerti forces to a large extent. Problems of a structural nature increase, however, primarily due to increased requirements of damping and of restricting the limit positions of blade movement. An object of the invention is to provide a wind- turbine of the aforedescribed kind in which all the advantages of a flapping hub from the power aspect are retained, while all the disadvantages associated with uncontrolled flapping movement are avoided. Accordingly this invention consists in a wind- turbine or windmill having a substantially horizontal shaft and a flapping hub carrying the turbine blades,

characterized in that the flap angle of the turbine blade is adjustable by means of the position of the piston of a double-acting piston-cylinder drive means, and in that the two chambers of the piston-cylinder drive means are connected to one another over a regulatable throttle valve. By means of the inven¬ tion the flapping movement can be caused to act against a damping force having a varying degree of damping, so that freedom of blade movement can be varied continously between a state in which the blades 'can move completely freely and a state in which said blades are firmly held against movement. Damping can also be superimposed by a control pulse, so that rotation of -the blades can be caused to take place about a desired centre position and locking take place in any desired position.

The invention will now be described in more detail with reference to the accompanying schematic drawings , in which

Figure 1 is a side view of a wind-turbine and illustrates the flapping movement.

Figure 2 illustrates detail A shown in Figure 1 in larger scale.

Figure 2 also illustrates the principle structure and function of the invention. A turbine blade 1 is rotatably mounted in a bearing housing 2. The bearing in the illustrated embodiment is a single-plane bearing 3 , although said bearing can also be a two-plane bearing, depending upon the size of the turbine and upon considerations irrelevant to the inven- tion.

The bearing housing 2 is journalled in a bracket structure 5 through a bearing 4, said bracket structure being fixedly connected to a turbine shaft 6. The axis of rotation of the bearing 4 is perpendicular or approxi- mately perpendicular to blade 1 and turbine shaft 6.

The bearing housing 2 is pivotally connected by means of a pivot 7 to the piston rod 8 of a double-acting

hydraulic piston-cylinder drive means 9 , which in turn is pivotally connected to the turbine shaft 6 at a pivot 10, said pivot 7 being excentrically located relative to the bearing 4. The piston rod 8 extends through the hydrauli cylinder 9 in a manner such that the total volume of the chambers on both sides of hte piston is constant. The cylinder can be provided with limit-position braking mean and bottom-stroke damping means of hydraulic or mechanica construction, or of a combination thereof, illustrated symbolically in the figure by springs 11.

Extending from the two chambers 17 and 18 from the cylinder 9 are oil lines between which a regulatable throttle valve 12 and a regulatable pump 13 are coupled in parallel. The system is also provided with pressure-limiting valves 14 for avoiding an overpressure in the system, and a low-pressure pump 15 which feeds the system over check valves 16, to avoid cavitation.

By co-regulating the throttle valve 12 and the pump 13, the blade 1 can be permitted to swing freely about - the shaft 4 with the degree of damping afforded by a completely open valve, or can be damped so as to rotate about a desired centre position, or can be damped to an extent such that the blade is locked in a desired positio In this way any tendency to wide oscillations at revolu¬ tions lower than normal working revolutions , found with flapping hubs, are avoided, while at the same time the favourable properties of the flapping hub with respect to force-distribution are maintained. The system, as a result of its properties, affords considerably improved conditions with respect to starting and stopping the windmill, and also enables production runs to be made at a wide variation of speed, which enabl flapping hubs to be used without disadvantage, in systems having varying gearing between turbine and generator, and therewith a wide variation in turbine speed.

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