The object of the invention is a method for improving the efficiency of a wind or water turbine, in which method the blades are mounted at their base with bearings into a structure with the help of which they are caused to move along a conical surface that opens away from said structure. The typical solution in the utilization of wind energy is a horizontal axis, usually a three-bladed wind turbine (for instance US 6752595 and US 6940185 and the references mentioned therein). This solution has several drawbacks: - The velocity of wind increases under normal circumstances as the height measured from the surface of the earth or the sea increases. It follows from this that the blades of a horizontal-axis turbine in their rotation have to function in a cyclically changing wind velocity. This worsens the efficiency of the energy production and places large demands on the mechanical durability of the blades. The latter will also be challenged by the cyclical torques caused by the weight of the blades.

- In steam and gas turbines a mechanical efficiency of the order of 90 % is attained by means of the medium passing through two or more sets of blades. To accomplish this in a horizontal-axis wind turbine requires two counterrotating rotors. Such solutions are complicated and they suffer from vibration problems (1).

The slowly moving basal parts of the blades of horizontal-axis turbines must be shaped very wide (for example, US 6752595) for them to produce energy, but such blades are heavy and expensive.

The most serious limitation is encountered as one strives towards large turbine structures for reasons of cost . The blades of horizontal-axis wind turbines move in a plane perpendicular to their axis. For reasons of economy the number of blades is usually limited to three, in which case the rotation speed of the turbine has to be kept sufficient, in practice at the level of 40 rev/min, to enable efficient transfer of the wind energy into the turbine.

The rapid growth of aerodynamic drag forces limits the peripheral velocity v of the blade tips of the turbine to values v < 0.6 M, where 1 M is the velocity of sound, ca . 330 m/s . This is reached in a horizontal-axis wind turbine at a rotation speed of 40/min already at a blade length of 21 m. A still more severe limit is caused by the noise created by the blades, which increases approx. according- to the 5 ^th power of the velocity v (2) and which

spreads into the environment as the blades sweep close to the earth's surface and pass the mast of the turbine. For this reason one often has to limit the tip peripheral velocity to values under 65 m/s or v < 0.2 M.

The operation of wind turbines is described with the help of coefficient of power C _P , which expresses how large a fraction of the energy of the air flow passing through the set of blades of the turbine can be transferred to the turbine (3) . The coefficient of power of a horizontal-axis turbine depends on the ratio λ of the peripheral velocity v of the blade tips to the wind velocity u so that the coefficient of power has a maximum when λ ~ 6, from which the coefficient of power decreases to ca . one half of its maximum value at the

values of λ of 4.5 and 8 (4). In typical wind conditions (5,6) the maximum of the wind energy distribution measured over a long time period is located at a wind velocity of ca. 12 m/s. If it is desired to utilize also strong winds, one should' strive to place the maximum of the coefficient of power in

this region of wind velocity. From the condition of λ = 6 follows a peripheral velocity of blade tips of 72 m/s. At a rotation speed of 40/min this is attained already at a blade length of 17 m. The power of a wind turbine with a given geometry and coefficient of power is proportional to the square of the blade length. One can thus substantially raise the power by increasing the blade length assuming that the coefficient of power remains sufficiently high. Solutions have been developed where the maximum of the coefficient of power is attained at a value of λ = 12 (6), which enables the attainment of good efficiency still with blades 34 m long. In the largest wind turbines used nowadays (7) the length of the blades is indeed close to this limiting value.

On the other hand, modern composite materials allow increasing the length of aero-dynamically efficient blades to at least the size class of 50 m. This would double the energy production and bring with it substantial savings in the cost of energy production.

However, the steep worsening of the coefficient of power due to the high peripheral velocities of the blade tips prevents the building of such turbines on the basis of current technology.

The purpose of this invention is to find a solution to this problem, the description of which has to start with the known vertical-axis wind turbines.

The vertical-axis wind turbines often utilize the so-called "scoop and drag" -phenomenon,

where the drag force exerted by the wind on the turbine is not directed at the axis of the turbine, but deviates from it forming a momentum that rotates the turbine. An example of this is the Finnish Savonius rotor (GB244414) .

These solutions have the property that the effective peripheral velocity of the · rotor is in the same class of magnitude as the wind velocity. From this follows their low efficiency,

a substantial improvement of which has not succeeded in spite of many attempts (for instance, US 7008171) .

A substantially better efficiency can be attained with appropriately formed blade structures that move around a vertical axis and in which the blade velocity under normal circumstances is higher than the velocity of the wind. The principle was presented by Darrieus already in 1931 (US1835018) .

At the velocities found in practice (v « 1 M) the function of the formed blades is most efficient when their profile is unsymmetrical . This can be accomplished by equipping the blades with adjustable flaps, as has been described in several publications . Analogous blade structures, "cycloidal propellers", have also been proposed for the motive power of vessels in several publications, for instance US 3134443, US 6065935 , and US 6109875. These solutions have not attained favor because of their complexity and also because their blades operate close to the hull of the vessel in a water flow disturbed by it.

In Publication US 4428712 is described the use of a _, blade structure to capture the energy of flowing water with a device attached underneath a barge anchored in place.

The majority of the' vertical-axis wind turbine . structures presented in the literature describe either the above mentioned Darrieus type, in which curved blades are attached at both ends to a vertical axis, or solutions in which rigid vertical blades are attached at both ends to a rotating frame, for instance US 5503525. The velocity of wind, and also that of, for instance, tidal currents of the oceans, increases as one moves higher above the earth' s surface or correspondingly from the bottom of the sea. For this reason it is advantageous to arrange the blades of a vertical-axis turbine to move along a conical surface that opens upwards, so that the peripheral velocity of a blade rotating at a given speed also increases with increasing height. The matching of the peripheral velocity of the blade, to the velocity of the medium at different heights improves the transfer of energy into the set of blades and increases the amount of energy that can be obtained with blades of a given length. This is accomplished in the wind turbine of Publication -US 4168439, where (Fig. la) blades set at an opening angle of 45° with respect to the vertical axis of the turbine are attached to a horizontal ring that is mounted with bearings so that it can rotate. The blades are mounted on bearings on the ring so that their pitch angle with respect to the air flow meeting them can be controlled. An analogous solution where blades set at a fixed opening angle are also used is presented in Publication US 4355956.

The orbital motion of the blade of Fig. la is shown schematically in Fig. lb. The orbit has been divided into four sectors so that most of the energy production takes place in Sectors 1 and 3. Sector 1 deflects the airflow according to the arrows and Sector 3 restores the flow approximately into its original direction. In Sectors 2 and 4 the blades are nearly "feathered" so that the force acting on them mostly consists of drag of the air flow. Compared to ordinary horizontal-axis turbines the vertical- axis turbines have the advantage that their blades capture energy from the medium flow that passes through a sector that opens away from the machinery of the turbine that is not disturbed by other structures of the turbine. In horizontal- axis turbines the blades cover a surface in the shape of a circle, one half of which is situated below the axis of the turbine, and where the flow meeting its central part has to be utilized at a poor value of the coefficient of performance. In vertical-axis turbines the blades pass through the flow of the medium twice, but in horizontal-axis turbines only once. From this follows that in vertical-axis turbines better coefficients of performance are attained. In them it is also possible to use longer blades than in horizontal-axis turbines, which together with the degrees of freedom described below enables increasing the power of the turbines.

In Publication GB2175350 are presented several arrangements in which the blades of a vertical-axis turbine are articulated onto the axis of the turbine so that the opening angle of the cone of motion of the blades can be adjusted. In the blades are also employed shrouds, which carry the central forces arising as the blades rotate. Solutions using articulated blades are also presented in US5584655 and JP2003222069.

A limitation of this technique is that although the opening angle of the cone of motion of the blades can be adjusted, the orbit of motion of the blades is a circle in the cross section. From this follows that the blades spend one half of the time in Sectors 2 and 4 in Fig. lb, where they produce very little energy. Further, the direction of motion of the blades in a large part of Sectors 1 and 3 is not close to the geometry of optimal energy production.

The objective of this invention is to provide an improvement in a wind or water turbine. The characteristic features of the method according to this invention are presented in Claim 1 and the corresponding turbine in Claim 10.

In this invention one controls, in addition to the pitch angle of the blades, also the opening angle of the blades with respect to the vertical axis of the turbine, advantageously with a mechanical or hydraulic arrangement directed by a processor. Changing the opening angle provides a degree of freedom for adapting the turbine to operate under different conditions of the flow of the medium, for instance, under a changing force of the wind. Upon reducing the opening angle from the 45° used in the known art the blades will reach higher and have access to higher velocities of wind or sea current. As a reduction of the opening angle reduces the peripheral velocity of the blade tips of the turbine, it enables an increase of the length of the blades.

In this invention the blades are arranged to move along a flattened conical surface, the horizontal cross section of which is an oval. The conical surface is oriented so that the major axis of the oval is nearly at right angles to the direction of the wind (Fig. 2a and 2b) . A flattened orbit of motion is more advantageous for the production of energy than the circular orbit of known technology shown in Fig. lb, for in it a larger portion of the orbit is directed sideways to the wind and a correspondingly smaller part against and with the wind.

A flattened orbit of motion is created by cyclically changing the angle between the blades and the axis of the turbine as the turbine rotates. The blades are articulated at their base to the rotating base plate of the turbine, so that their base parts move along circular orbits, whereas the other parts move ■ along orbits that are the more elliptical, the higher one ascends along the blade. This enables the efficient utilization of the stronger winds blowing at higher elevations.

If there are two cycles of change during each revolution of the turbine, the orbit of the blade is symmetrical with respect to the axis of the turbine (Fig. 2a) . If there is only one cycle per revolution, the blade moves along an eccentric orbit according to Fig. 2b. The eccentricity of the orbit reduces the moment of the drag forces acting on the blade as it moves against the wind in Sector 4 so that the energy efficiency of the turbine improves. In the cyclical adjustment of the orbit of the blades it is possible to utilize aerodynamic forces and the orbit can be controlled mechanically or hydraulically, as will be explained in the Embodiments .

In the above mentioned publication US5584655 there is a mention of "the undesirable flapping motions" of the blades moving in a circular orbit ("undesirable "flapping", i.e. cyclic changes in the angle 214 on a short time scale", Column 4, lines 14-15). Here the motions with which the oval orbits are created in this invention are rejected as "undesirable".

In this invention the operation of the turbine can be optimized by adjusting the following parameters with, e.g., the help of a processor: -the average opening angle β of the cone of motion of the blades,

-the amplitude γ of the cyclical motion of the blades,

-the orientation z of the major axis of the cone of motion , -the pitch angle φ of the blades, which changes cyclically as the turbine rotates,

-the rotation speed of the turbine.

Of these the first three can be combined in the control automation to the instantaneous opening angle a _n of the blade, which is the angle between the axis of Blade n and the axis of the turbine. The a' s change cyclically as the turbine rotates (except when γ = 0) . The opening angles are adjusted with a control mechanism situated in the middle of the turbine. The changes can be assisted with aerodynamical forces by changing the momentary pitch angles φ _η of the blades, which angles can be controlled during the rotation of the turbine with servo or other mechanisms connected to the blades. The turbine is preferably equipped with a syncronizing mechanism to control all blades or bladepairs dependently with respect to one another.

The modes of application of this invention ^' are extremely manifold and are not limited to the embodiments presented here .

The invention will be described in the following with the help of Embodiments with reference to the Figures appended.

Fig. la shows a wind turbine representing known technology of

Publication US4168439.

Fig. lb shows the orbit of blades and the flow of air in the blades of the said turbine.

Figs 2a and b show some flattened orbits of the blades of a turbine according to the present invention.

Fig. 3a shows schematically the turbine described in

Embodiment 1.

Fig. 3b shows a mechanical coupling of the blade cradles of the said turbine.

Fig. 3c shows a hydraulic coupling of the blade cradles of the said turbine.

Fig. 4 shows schematically the turbine described in

Embodiment 2.

Fig. 5a shows a sectional view of a turbine equipped with a particular mechanism for the control of the blades.

Fig. 5b shows the turbine of Fig. 5a with the blades in an opened position. Fig. 6 shows some applications of a water turbine according to this invention.

Embodiment 1

In this Embodiment (Fig. 3a) there are four blades 11 and the center of their orbit ellipse is on the axis of the turbine. The opposite blades 1 and 3 as well as 2 and 4 are in the same phase of the pendulum motion, so that cii = a ₃ and a ₂ = a ₄ , that is, the blades of a pair open and close together as the turbine rotates. Each a has two maxima and two minima during each revolution of the turbine so that the phase difference between the motions of two adjacent blades is 180° and

cci + a ₂ = a ₃ + a ₄ = 2 β.

Each blade is mounted with bearings into a "cradle" 13 so that they can be turned about their longitudinal axis for adjusting their pitch angle φ. The cradles are mounted with bearings onto the base plate 14 of the turbine and they and the blades are approximately balanced with counterweights 16.

The pairs of cradles with their blades perform a pendulum motion in two planes 21 and 22 (Fig. 3b) at right angles to each other. They are coupled together with levers 23 that form a quadrangle which binds the movements of the cradles together so that opposite cradles always move in opposite directions and oil + a ₂ = a ₃ + a ₄ . The pendulum motion can be controlled independently of the aerodynamic forces with hydraulic cylinders 24.

In Fig. 3c is schematically presented a variation where the blades are connected together hydraulically with the help of doubly acting cylinders 61 - 64. The cylinders can also be used in active control of the motion of the blades (not shown) .

The base plate 14 rests on pedestal 32 supported by bearing 31. The energy produced by the turbine is transferred with a planetary transmission formed by gear ring 33 and gears 34 and 35 to generator 37. In the middle of base plate 14 is the control unit of the turbine blades 38 and mast 39, in which are the sensors for the wind direction and strength. The required electrical energy is brought to the rotating structure of the turbine with slip rings placed underneath control unit 38, to which the energy is brought through the hollow shafts of gears 34 (not shown) . Adjustment of the opening angle β of the orbital cone of the blades is used in known technology. In this invention the opening angle can be reduced in a strong wind even to negative values, in which case the central forces acting on the blades are reduced and the rotation speed of the turbine can be increased. In addition, the amplitude γ of the pendulum motion of the blades can be reduced or the pendulum motion can be stopped. These measures enable the production of energy in winds in which the present turbines have to be feathered. This requires generators with a variable rotation speed together with frequency converters.

Embodiment 2

In this Embodiment (Fig. 4) the turbine blades 11 perform only one cycle of pendulum motion during each revolution of the turbine. The base plate 14 of the turbine is coupled directly to the hollow axis 36 of generator 37. Inside the axis is a nonrotating inner axis 51, onto which is attached an adjustable eccentric or crank 52. In the Figure the blades are in the middle position of their pendulum motion, i.e., in the sectors 1 and 3 of Fig. 2b. The cradle of each blade is connected to the eccentric with levers 53 in which there are joints 54. The coupling transforms the sinusoidal motion of the eccentric into an a symmetrical one so that the sine of the opening angle a of the blades increases as the blades move from Sector 1 to Sector 2 more than it decreases as they move from Sector 3 to Sector 4. This produces the ellipticity of the orbit of the blades, which can be adjusted by changing the eccentricity of the eccentric 52.

The control unit 38 and mast 39 are similar to those in the previous Embodiment. The electrical energy required for the control is brought with an induction coil 40 (for instance, US 7352929) .

The long blades of high-power wind turbines have to endure the aerodynamical and central forces directed into them in strong wind. The rigidity of the blades against flexure can be substantially increased with shrouds. By prestressing the blades so that they curve away from the rotation axis of the turbine when free, one can use shrouds 41 only on the side of the rotation axis of the turbine to carry the central forces arising as the turbine rotates. This - affords thin and light blade profiles, which allow high blade velocities without excessive drag or central forces. Such blade constructions offer an advantageous opportunity to use carbon nanotube plastics that contain covalent bonds (hybtonite®) . Together with the possibilities of control described in the previous Embodiment these structures enable an increase of the rotation velocity of the turbine in strong winds, in which a generator possessing a given torque is able to generate more energy. In the previous Embodiment a planetary gear with a low gear ratio is used between the turbine and the generator, and ^' in this Embodiment they are directly coupled together. Turbines of this kind adapt flexibly to wind gusts, unlike the commonly used structures, whose high gear ratio and a generator coupled to the frequency of the grid prevent such adaptation and often cause breakdowns. Embodiment 3

In the turbine of this Embodiment (Figs. 5a and 5b) the blades of the turbine travel along a flattened conical surface, the opening angle of which can be adjusted during the operation of the turbine while the pitch angle of the blades with respect to the flow of the medium meeting them is adjusted in the manner presented in the classic publication by Darrieus in 1931 (8). The concave formed blades 11 are mounted with bearings onto blade supports 16 so that they can be turned around their longitudinal axis to adjust the pitch angle of the blades. In the same way as in the Darrieus patent (8) mentioned above, an eccentric 71 on the axis of the turbine, from which control rods 72 transmit the adjusting motion to blades 11, is used in the adjustment. The blade supports 16 are mounted with bearings 15 onto the rotating base plate 14 of the turbine so that the supports and the blades can be turned in order to change the opening angle of the cone of motion of the blades. In order to minimize the disturbance that this change causes to the adjustment of the pitch angle, the control rods 72 are connected to the blades 11 with ball joints placed on the axis of bearings 15. The opening angle of the cone of motion of the blades is controlled by two mechanisms, of which the first one comprises, situated on the axis of the turbine, a bearing 73 that can be moved in the vertical direction and that is connected with control rods 74 to summing levers . 75. From these the control motions are transmitted via joints 76 to the lower part of blade supports 16. This mechanism is used to control the opening angle of the cone of motion of the blades so that in light winds the power of the turbine is increased by using a large opening angle and in strong winds the opening angle is reduced to reduce the stress directed to the blades.

In the second mechanism of controlling the opening angle of the cone of motion of the blades there is a gear ring 81 attached to the nonrotating body of the turbine that drives four gears 82 with a gear ratio of 1:2. Gears 82 have cranks 83 that are connected with rods 84 equipped with ball joints to the lower end of summing levers 75. This control mechanism causes the blades to move out- and inwards twice during each revolution of the turbine. Due to this motion each point of the blades will describe an orbit that is the more flattened, the higher the point concerned is in the blade. In Fig. 5a the bearing 73 that controls the opening angle of the cone of motion of the blades is at its lowest position and cranks in the gears 83 are at their outermost position. In this case the blades 11 are in a vertical position and as close as possible to the axis of rotation of the turbine, while the other pair of blades that is only partially visible in the Figure is somewhat farther from the axis. The turbine is in the position used in strong winds. In light winds the bearing 73 is moved higher (Fig. 5b) , while the second control mechanism keeps the cone of motion of the blades flattened, but its average opening angle increases and the turbine captures a larger moving mass of air.

Embodiment 4

A water turbine intended for the utilization of tidal and other water currents is presented schematically in Fig. 6. The turbine and its machinery are attached to a base plate 31 made of, e.g. concrete, which is placed on the bottom of a body of water of suitable depth. Several turbines can be placed in rows or fields in suitable locations. Turbines can also be placed in other positions, for instance, on the side of artificial islands, barrier structures, canals, or river banks (Fig. 6) .

Other versions The invention can be applied also in the context of closed blade structures such as a wind and water mill of exactly the Darrieus type. In the case of a wind mill the blades are articulated to a vertical axis at both bottom and top, and by cyclically varying the vertical articulation distance of these the mentioned flattened conical surface, or in the context of a Darrieus rotor, a flattened ellipsoidal surface is attained. In a Darrieus rotor the blades are elastic so that that they can be bent to different radii of curvature. Rigid blades are instead made of two parts and they have an intermediate joint at the outermost point of their circumference. Into the rigid blades it is possible in this case to arrange for an adjustment of the blade angle. A closed blade structure easily enables equipping the central axis with shrouds also above the blades, which substantially lightens the structure.

In connection with the upper or lower joint, or both, of each blade there are associated means for providing a cyclical axial motion, which implements a radial motion (not shown) .

References :

1. Wikipedia: "Wind Turbine", p.3.

2. Burton et al., Wind Energy Handbook, Sec. 6.4.4, Wiley & Sons (2001) .

3. Ibid., Ch. 4.1

4. Ibid., Fig. 3.15

5. Wikipedia: "Wind Power", p. 3

6. P. Mutschler, IEEE 33rd Annual PESC Conference Vol.1 pp.6- 11 (2002).

7. P. Lampola, TKK-DISS-1418 Acta Polytech. Scand. El ISSN 0001-6845;101 (2000) .

8. Darrieus, US 183501