DESCRIPTION

AN EOLIAN TOWER WITH A BIROTOR

The subject of this invention is an eolian tower, namely a high structure which carries at its upper end a rotating system that is actuated by the wind and operates an electric generator, this installation being intended for use in the conversion of the eolian energy.

Different systems of rotating systems have been used in the known eolian towers, but in the practice the most used systems consist of a blade screw having an about horizontal axis, which by means of various devices may be oriented with respect to the wind direction in order to attain the best operating conditions. Due to different reasons, the efficiency in the conversion of the eolian energy is rather small. One of these reasons resides in the interaction among the different screw blades, which perturbs the operation and therefore reduces the efficiency. Another reason consists in the fact that the forces applied to the screw blades by the air flow has some components that are not useful for producing the screw rotation. The blade screw does not attain the rotational speed which could be produced by the actual wind, and therefore it does not produce the maximum possible power.

The object of this invention is to improve the efficiency of the rotating system of an eolian tower by eliminating or reducing some reasons for the reduction in the rotational speed and in the efficiency of these rotating systems. The principle of the invention is to replace for the usual blade screw a birotor formed by two parallel coaxial and counter-rotating blade rotors. Thanks to the counter-rotation of the two blade rotors, the detrimental inter- actions among the different blades are partially compensated between the two blade rotors, and the forces applied to the blades by the wind are, in their whole, reduced to the only forces useful for producing the rotation. As a consequence, the same wind can produce a more rapid rotation of the rotating system and thus can cause the conversion of a greater energy quantity. Therefore, the subject of the invention is an eolian tower comprising a high fixed load bearing structure which carries at its upper end a rotating system that is actuated by the wind and operates an electric generator, this installation being intended for use in the conversion of the eolian energy, characterized in that said rotating system comprises a birotor including two

parallel coaxial and counter-rotating blade rotors whose axis is at least nearly horizontal, each blade rotor comprising a hub and a number of blades fixed to the hub, the blades of the two blade rotors being fixed to the corresponding hub according to opposite inclination angles, whereby under the action of a wind flow the two blade rotors take opposite directions of rotation.

Both blade rotors forming the birotor may be substantially identical to each other, except for the opposite inclination angles according to which the blades are fixed to the corresponding hubs, or else some slight differences may be foreseen between the two blade rotors, in order to attain in the whole the best operation conditions.

Preferably a synchronization device or movement inversion device is provided for operating between the hubs of the two blade rotors of the birotor, in order that the rotational movements of the two blade rotors take place with angular speeds opposite in direction but having the same value. In this way, to the unavoidable interactions among the various blades of each blade rotor is added an opposite interaction among the blades of the two blade rotors forming the birotor, whereby the detrimental effects of these interactions on the rotational speed impressed to the blade rotors and on the efficiency in the energy conversion are reduced in a noticeable measure. A synchronization device or movement inversion device may be inserted directly between the two hubs of the blade rotors, whereby the power output of the birotor takes place on a single output motor shaft, or else each blade rotor can be provided with its own output motor shaft, both output motor shafts being coaxial. In this latter case, a synchronization device or movement inversion device can be inserted between the two output motor shafts, or else the rotation of the two output motor shafts can be applied to two different electric generators, or to two mutually cooperating component parts of a single electric generator.

The number of blades used for forming each blade rotor of the bi- rotor may vary according to the needs of each local application. In most cases it is advantageous to foresee the use of four blades for each blade rotor of the birotor.

Of course, devices similar or identical to those usually employed in the known eolian towers can be used in the eolian tower according to the in-

vention, in order to orientate the direction of the rotational axis of the birotor as a function of the wind direction.

These and other features, objects and advantages of the subject of this invention will appear more clearly from the description which follows of a non-limiting example of embodiment, with reference to the accompanying drawing, wherein the sole figure shows in a very diagrammatic perspective view an eolian tower embodied according to the invention.

The eolian tower represented in the drawing comprises a high fixed structure 1 forming the proper tower. This structure can be provided in any known manner and it does not require any modification for the application of the invention. Therefore, it is also possible to replace, for the rotating system with a simple blade screw of an existing eolian tower, a rotating system with a birotor according to the invention.

The rotating system is provided at the upper end of the tower struc- ture 1 , and it should be equipped with orientation means that can also be similar or identical to the .orientation means usually employed in these application; for this reason the orientation means have not been represented. In an existing eolian tower subjected to modification by the application of the rotating system according to the invention, the existing orientation means may be conserved without changes.

The rotating system according to the invention comprises a first blade rotor 2-3 including a hub 2 and a number of blades 3 fixed onto the hub 2, and a second blade rotor 4-5 including a hub 4 and a number of blades 5 fixed onto the hub 4. Both blade rotors 2-3 and 4-5 forming the birotor are coaxial and, therefore, the blades 3 and the blades 5 are lying in two respective mutually parallel planes. The blades 3 and 5 are plane and they are not shaped as dihedrons.

The blades 5 of the second blade rotor 4-5 are fixed onto the respective hub 4 with an inclination opposite the inclination with which the blades 3 of the first blade rotor 2-3 are fixed onto the respective hub 2, as it clearly appears from the drawing. As a consequence, the two rotors 2-3 and 4-5 which form the birotor 2-5 are put in rotation, by the same wind acting thereon, in opposite directions. Moreover, if both blade rotors are substantially identical to each other except for the opposite inclination with which the

respective blades are fixed to the hubs, both blade rotors have the tendency to rotate with angular speeds that are opposite but have values nearly equal. It is the whole of these conditions that establishes the increase in the useful speed and in the efficiency, to which aims the invention. Of course, in view of the possible inequality of interactions to which the two blade rotors can generate, due to the fact that one of them is stricken by the wind before the other, some slight differences can be introduced between the two blade rotors, in order to attain in the whole the best possible operation conditions. When this is considered suitable, a synchronization device or movement inversion device 6 can be provided between the two hubs 2 and 4 of the blade rotors 2-3 and 4-5. In this case the rotating system with birotor has a single output motor shaft to be coupled with an electric generator diagram- matically shown at 7. Otherwise one can foresee that the hub 4 is provided with an output motor shaft 6 directed towards the electric generator 7, and that the hub 2 is provided with a tubular output shaft 6' also directed towards the electric generator 7; the output motor shaft 6 of hub 4 passes inside the tubular output motor shaft 6" of hub 2. In this case, the synchronization device or movement inversion device can be provided between the two output motor shafts 6 and 6' of the hubs 4 and 2, in order to operate with a single resulting output motor shaft the electric generator 7.

If it is not intended to make use of a synchronization device or movement inversion device, both output motor shafts 6 and 6 ¹ of the hubs 4 and 2 can operate two separate electric generators, or two separate cooperating component parts of a single electric generator.

In the diagrammatic representation of the drawing, the electric generator 7 is shown as coaxial with the birotor 2-5, however it is of course possible to make use of a per se known arrangement, according to which the electric generator is installed with vertical axis inside the tower structure 1 and is connected to the output motor shaft of the rotating system by means of an angular transmission device. In these cases, when an existing eolian tower is improved by the application of the invention, the existing electric generator does not require to be replaced.

It is to be understood that the invention is not limited to the embodiment shown and described. Several possible modifications have been stated in the description, and others are within the capacity of the skilled persons. These modifications and others can be applied to what has been described and shown, without departing from the spirit of the invention and the scope of this Patent, as specified by the Claims.