Patent Publication Number: US-2009226320-A1

Title: System for connecting wind generator blade sections

Description:
FIELD OF THE ART  
     The present invention relates to the wind generator blades which are formed by composition by means of two or more longitudinal sections, for the purpose of facilitating the construction and essentially road transport, proposing a system for connecting sections in the constructive formation of the blades, whereby advantageous features for said function are achieved. 
     STATE OF THE ART  
     The worldwide demand for renewable energy in order to deal with climate change and maintain an expectation of power production without depending on non-renewable natural resources involves in a very relevant manner wind energy, which is mostly developed by means of wind generators which are driven by a blade rotor capturing the wind. 
     The development of wind generators and their application to power production by means of using the wind requires, however, wind generators with increasingly greater rated power which are more efficient and have a lower cost per kilowatt of the power produced. 
     The sweep surface of the blades of the rotor receiving the action of the wind, among other aspects, is essential in the power generation by means of said wind generators, such that one of the factors to increase the power generation capacity is the increase in the size of the blades capturing the action of the wind. 
     Exceeding a measurement of the size of the blades of the wind generators entails, however, a series of collateral problems because of the difficulties that arise both in the transport aspect, due to the existing vehicles and highway traffic regulations, and in the aspect of the actual constructive assembly of the wind generator, due to the types of cranes which must be used. 
     Indeed, from 35 meters in length onwards, wind generator blades have large transport difficulties, since they require special transport means, which are very expensive. 
     To solve this problem, the solution of forming blades by means of longitudinal sections is already known, which sections can be independently transported for their connection at the installation site of the wind generator and even in the constructive assembly thereof. 
     This involves an advantage for large blades (between 40 and 60 meters in length) which are already demanded by the wind sector, but also for more traditional blades (between 30 and 40 meters in length), because since they can be made in sections of between 15 and 20 meters in length, they can be transported with normal means, a reduction in the transport cost being achieved which is advantageously greater than the cost of forming the independent sections and connecting them in the constructive assembly of the blades. 
     In this sense, several systems have been developed for connecting the sections making up wind generator blades, which are formed by the connection of longitudinal sections, such as for example the solution of Patent ES 9901177 but the solutions known in such sense generally have deficiencies relating to the difficulty of the assembly and to the efficiency of the securing determining the connection between the sections. 
     OBJECT OF THE INVENTION  
     According to the invention, a system for the connection between the sections making up wind generator blades is proposed, with features which make the performance of the assembly and the effectiveness of the connection advantageous. 
     The system of the invention is essentially provided for blades structurally formed by outer side blades laminated by layers of synthetic fibers, arranged on an inner resistant structure formed by stringers like longitudinal partitions, the aerodynamic profile of the blade being determined by means of outer skins which can extend, they themselves defining the trailing edge of the aerodynamic profile, whereas the formation of the leading edge of said aerodynamic profile is provided by means of a complementary part laminated in turn with synthetic fibers. 
     In the connection of the sections making up the blades there is arranged a ring determining at its front parts channels in which there are fitted with their end edge the inner structural stringers of the blade sections, as well as the edges of the outer skins, which in the area comprised between the inner structural stringers are formed with a section thickened towards the inside, on the inside of which, as well as on the structural stringers there are defined longitudinal holes opening out into respective hollows of the corresponding walls, the securing of the connection being established by means of rods which are inserted through the opposite longitudinal holes of the skins and of the structural stringers of the sections to be connected, passing through the intermediate ring of the connections, which rods are connected in a tension threaded coupling with respect to respective end elements which are housed in the hollows into which the longitudinal holes open out. 
     In the sections which are connected, the hollows into which the longitudinal holes open out are made perpendicularly from the inner part of the corresponding walls, without passing to the outer part, said hollows having a cylindrical shape in one of the sections of the connection, in order to fit therein a corresponding cylindrical element provided with a threaded transverse hole, with respect to which the respective rod of the securing of the connection of the sections is coupled with threading, whereas in the other section of the connection the hollows are oblong, the incorporation of a nut being established therein on the end of the corresponding rod, to carry out the actuation on said nut through the opening of the respective oblong hollow. 
     A securing for the connection between the blade sections is thus obtained which allows determining a resistant fastening with complete precision by means of tightening the nuts which are arranged on the rods of the connection, the assembly being very easy to carry out, since the securing rods are incorporated before the coupling in one of the sections to be connected, such that it is then only necessary to couple by insertion the second section and tighten the tension nuts for the securing on the second end of the securing rods. 
     The incorporation of the intermediate ring in the connection further determines a protection preventing the defibration of the layers of fiber in the connection edge of the outer skins of the blade sections, which prevents, in the application work of the formed blade, the force of the wind from being able to cause a progressive deterioration of defibration of the skins forming the aerodynamic profile. 
     In addition, making the hollows for housing the outer coupling elements of the securing rods of the connecting, at the inner part of the walls of the sections and without passing to the outside, means that said walls of the sections which are connected are not very weakened, and furthermore the outer surface remains continuous, such that the efficiency of the aerodynamic profile for the performance of the blade is not affected. 
     Due to the foregoing, the system of the invention has truly advantageous features, acquiring its own identity and a preferred character for the securing function of the sections making up wind generator blades, compared to the already known solutions for said function. 
    
    
     
       DESCRIPTION OF THE DRAWINGS  
         FIG. 1  shows an exploded perspective view of the structural assembly of a wind generator blade which is made up of two longitudinal sections, with the connection of said sections according to the invention. 
         FIG. 2  is a perspective view of the blade of the previous figure in its assembled form. 
         FIG. 3  is a detailed perspective view of a partial section of the previous blade, the arrangement of the structural elements of its formation being observed. 
         FIG. 4  is an enlarged detail of area IV indicated in  FIG. 2 , corresponding to the root of the blade. 
         FIG. 5  is an enlarged detail of area V indicated in  FIG. 2 , corresponding to the connection between the sections making up the blade. 
         FIG. 6  is an exploded perspective view of said connection area of the sections making up the blade. 
         FIG. 7  is a perspective view of the same connection area of the sections making up the blade, with the outer skins being transparent to observe the elements of the inside. 
         FIG. 8  is a detail according to segment VIII-VIII indicated in  FIG. 5 , the arrangement of a securing rod of the connection between the sections making up the blade being observed. 
         FIG. 9  is a perspective view of the structural formation of the inner framework of the sections making up the blade. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     The object of the invention relates to a system intended to establish the securing for the connection between the sections making up the wind generator blades which are formed by independent longitudinal sections which can be separately transported, for the connection thereof at the constructive assembly site of the application wind generator. 
     The system of the invention is provided essentially, but without a limiting character, for blades structurally formed by two outer side skins ( 3 ) which are arranged on an inner structure formed by stringers ( 4 ) like longitudinal partitions, such that the outer skins ( 3 ) determine the aerodynamic profile of the blade, together with a complementary part ( 5 ) defining the leading edge, the actual skins ( 3 ) forming the trailing edge by means of their prolongation until being connected in this edge, as observed in  FIG. 3 , whereas the inner stringers ( 4 ) form a framework determining, together with the skins ( 3 ) a structural box along the formation of the blade, the stringers ( 4 ) being connected on the inside by means of supports ( 4 . 1 ), as observed in  FIG. 9 . The blades thus formed can be longitudinally unitary, but with the same structural concept of the constructive formation, they can be formed by two or more longitudinal sections intended to be connected in the constructive assembly of the corresponding wind generator. 
     According to the system of the invention, the connection between two sections ( 1 ,  2 ) making up a blade is established by incorporating an intermediate ring ( 6 ) determining on its front faces grooves ( 6 . 1 ) in which the outer skins ( 3 ) and the inner stringers ( 4 ) of the sections ( 1 ,  2 ) to be connected are fitted with their end edge, as observed in  FIGS. 6 to 8 . 
     In the end part corresponding to the connection, the outer skins ( 3 ) of the sections ( 1 ,  2 ) are formed, in the area comprised between the inner stringers ( 4 ), with a thickening ( 7 ) towards the inside, longitudinal holes ( 8 ) being defined in said thickening ( 7 ), as well as in the stringers ( 4 ), which holes correspond to one another in an opposite manner in both sections ( 1 ,  2 ) and which also correspond with respective through holes in the intermediate ring ( 6 ). 
     The longitudinal holes ( 8 ) open out into corresponding sections ( 1 ,  2 ) in respective hollows ( 9 ,  10 ) made perpendicularly at the inner part of the walls in which said longitudinal holes ( 8 ) are defined. 
     In one of the blade sections, for example, the section ( 1 ), the hollows ( 9 ) into which the longitudinal holes ( 8 ) open out are cylindrical and therein there are fitted corresponding cylindrical elements ( 11 ) provided with a threaded transverse hole ( 11 . 1 ) for the threaded coupling of the end of a rod ( 12 ) which is inserted through the respective longitudinal hole ( 8 ). 
     In the other blade section, in this case the section ( 2 ), the hollows ( 10 ) into which the longitudinal holes ( 8 ) open out are oblong, a stop washer ( 13 ) and a nut ( 14 ) which is incorporated on the other end of the rod ( 12 ) passing through the respective longitudinal hole ( 8 ) being housed in each of such hollows, such that said nut ( 14 ) can be actuated through the opening of the oblong hollow ( 10 ), to thereby tighten the tension of the rod ( 12 ). 
     In such conditions, to establish the securing for the connection between the sections ( 1 ,  2 ), first the cylindrical elements ( 11 ) are inserted in the hollows ( 9 ) of the section ( 1 ) and respective rods ( 12 ) are introduced through the corresponding longitudinal holes ( 8 ), which rods are coupled by threading on the mentioned cylindrical elements ( 11 ), whereby said rods ( 12 ) are fixed with respect to the section ( 1 ), axially projecting from the longitudinal holes ( 8 ). 
     Once so, the intermediate ring ( 6 ) is inserted, making the rods ( 12 ) pass through the holes of said ring ( 6 ), which is taken in until abutting against the section ( 1 ), and in this arrangement, in order to establish the connection of the section ( 2 ), both parts are inserted in relation to one another, making the rods ( 12 ) be introduced through the longitudinal holes ( 8 ) of said section ( 2 ), up to the oblong hollows ( 10 ) thereof, wherein the washers ( 13 ) and the corresponding nuts ( 14 ) are incorporated on the end of the rods ( 12 ), such that by tightening the nuts ( 14 ) a tension of the rods ( 12 ) ensuring the connection between the sections ( 1 ) and ( 2 ) is obtained, as depicted in  FIG. 8 . 
     The hollows ( 9 ,  10 ) into which the longitudinal holes ( 8 ) of the sections ( 1 ,  2 ) open out do not pass to the outside of the outer skins ( 3 ) of the sections ( 1 ,  2 ), such that the aerodynamic profile of the blade is not affected by the securing of the connection and furthermore, the structural weakening due to the mentioned hollows ( 9 ,  10 ) does not affect the resistance of the blade for its function. The actuation on the tightening nuts ( 14 ) for the securing of the connection is in any case practicable from inside the blade, since the connection of the sections ( 1 ,  2 ) is established in a mid-area of the blade, wherein the inner space is sufficient for the entrance of an operator. 
     The incorporation of the intermediate ring ( 6 ) in the connection determines in turn a protection on the edge of the outer skins ( 3 ) of the sections ( 1 ,  2 ) which are connected, preventing the defibration of said skins from their edges by the action of the wind in the function of the application work of the blade.