Abstract:
The invention relates to a wind turbine tower comprising a tower foundation, and at least two tower sections connected by numerous sets of connecting means positioned in close proximity of each other. The connecting means comprising at least one nut with at least one assembly opening for interacting with an assembly tool. 
     The invention also relates to a method for assembling a wind turbine tower and a method for manufacturing a nut of connection means for fixating a wind turbine tower including at least two tower sections.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of pending International patent application PCT/DK2005/000756, filed Nov. 24, 2005, which designates the United States, the content of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a wind turbine tower comprising a tower foundation, and at least two tower sections connected by connecting means positioned in close proximity of each other, connection means for assembling a wind turbine tower comprising a bolt with a threaded part, and a nut with an internal threaded part corresponding to the thread of said bolt, method for assembling a wind turbine tower comprising at least two tower sections at a wind turbine site, said method comprising the steps of establishing a foundation, positioning a first tower section on the foundation and fixating said first tower section to the foundation by sets of connection means, positioning a further tower section on the first tower section and fixating said further tower section to the first tower section by sets of connection means, and so on until the tower is established, and method of manufacturing a nut of the connection means for fixating a wind turbine tower. 
     BACKGROUND OF THE INVENTION 
     A wind turbine known in the art typically comprises a wind turbine tower positioned on a foundation and with a wind turbine nacelle positioned on top of the tower. A wind turbine rotor, comprising three wind turbine blades, is connected to the nacelle through a low speed shaft, which extends out of the nacelle front as illustrated on  FIG. 1 . 
     The wind turbine tower typically comprises a number of round tower rings mounted on top of each other, where each tower ring is made of a steel plate rolled into a circular shape and welded to constitute a closed ring. 
     When the different sections, that constitute the wind turbine tower, have been transported to the site at which the tower is to be erected, the sections are connected by flanged joints. The flanges are provided with an array of through going holes which allow a large number of bolts and corresponding nuts to connect a tower section with the foundation or the next section. 
     A way to assemble sections of a wind turbine tower by using bolts and nuts is disclosed in international patent application No. WO-A 03/100268. 
     However, the height of wind turbine towers has increased significantly in the recent years and has increased the strength requirements of the flange joint connections. The number of bolts and corresponding nuts used in the flange joint connections has consequently also increased significantly. 
     The object of the present invention is to provide a technique which allows higher strength of the flange joint connections to be established with the same or less flange material to be used. 
     SUMMARY OF THE INVENTION 
     The invention provides for a wind turbine tower wherein connecting means comprises at least one nut with at least one assembly opening for interacting with an assembly tool. 
     Hereby it is possible to position a nut in close proximity of the surrounding nuts of an array as well as closer to the inner surface of the tower side. Consequently, more sets of connection means in more favourable positions may be used in the flanged joint and thus establish a higher strength connection. 
     The length and thickness of the flanges may also be decreased as a result of the higher strength connection i.e. less flange material is used. Alternatively, flanges with the same amount of flange material may be used but with flange material of a lower strength and thus a lower cost price. 
     The term “assembly tool” should be understood as a tool which may be used in an assembling or disassembling operation in connection with the invention. 
     In an aspect of the invention, said nut with a bolt form a set of connection means. Hereby an advantageous embodiment of the invention achieved. 
     The term “bolt” should be understood as a headed fastener having an external thread that may meet an exacting, uniform bolt thread specification such that it can accept a nontapered nut. 
     In an aspect of the invention, the lower part of the nut comprises an opening with an internal thread corresponding to the thread and length of the bolt in the set. By establishing sets of nuts and bolts corresponding in size, the assembly process is enhanced even further and thus the total time of assembling the wind turbine tower is decreased. 
     In an aspect of the invention, said nut comprises one assembly opening for interacting with an assembly tool. 
     In an aspect of the invention, said one opening is positioned in the upper part of the nut and is shaped as a slot, square, penta, hex, cross, Torx or any similar shaped socket for interacting with the assembly tool. 
     By using the said opening shaped in one of the said ways, it is possible to use an already developed tool, instead of a special developed assembly tool, as an assembly tool needed in these couplings is already present. A further advantage is that the experiences drawn from the aforementioned coupling methods can be used in connection with this unit. 
     In an aspect of the invention, the size Xb of the opening with an internal thread is larger than the size Xa of the assembly opening. Hereby it is possible to manufacture an assembly opening through the nut and subsequently manufacture the opening with an internal thread in a part of the nut i.e. a more efficient way of manufacturing of the nut. 
     In an aspect of the invention, said nut comprises more than one assembly opening e.g. two or three assembly openings for interacting with one assembly tool. Hereby it is possible to use small openings but—all together—with a large surface in the openings to meet the assembly tool. 
     In an aspect of the invention, said more than one opening are positioned in the upper part of the nut and are circular shaped sockets such as “snake eyes” for interacting with the assembly tool. The circular shaped sockets are particularly easy assembly openings to manufacture. 
     In an aspect of the invention, said tower sections are connected in a flanged joint with one or more arrays of sets of connection means. 
     In aspects of the invention, the nuts of said sets of connection means are tightened by said assembly tool. Further, bolts of said sets of connection means comprise means for interacting with a holding tool. 
     Hereby it is possible to hold the bolt with a holding tool wherein a holding procedure does not require any significant work space. Consequently, the bolt may also have an internal assembly opening or a standard head such as hex head adapted to be held by a standard wrench while the nut is being tightened by the assembly tool. 
     The assembly procedure of a set of connection means such as a bolt and a corresponding nut requires at least one means being tightened e.g. one being tightened and one being held in place. A normal procedure may involve the nut being tightened and the bolt being held in place as the opposite procedure may result in an overturning of the bolt head. 
     In an aspect of the invention, the length Lb of the shaft of said bolt is prechosen to correspond substantially to the sum of the size Tf of said flanged joint and the length Ln 2  of the internal thread part of said nut. Hereby it is possible to design the set of connection in the jointed flange with a minimal distance between the bolt tip and the assembly tool i.e. allowing a preferred force transfer during the assembly. 
     The invention also relates to connection means wherein the nut further comprises at least one assembly opening for interacting with an assembly tool. 
     Further, the invention relates to a method for assembling a wind turbine tower where a fixating is initiated by an assembly tool tightening a set of connection means by entering at least one assembly opening in a nut of said set of connection means. Hereby it is possible to decrease the assembly time as the positioning and use of the assembly tool in relation to the nut is less demanding and requires less precision. 
     Even further, the invention relates to a method for manufacturing a nut of the connection means for fixating wind turbine tower including at least two tower sections, said method comprising the steps of, establishing a through going hole in said nut, establishing an assembly opening in the nut, and establishing an internal thread in the lower part of the hole whereby the size of the internal thread is larger than the size of the assembly opening. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in the following with reference to the figures in which 
         FIG. 1 . illustrates a large modern wind turbine, 
         FIG. 2  illustrates a part of a flanged joint in between wind turbine tower sections according to the invention, 
         FIG. 3  illustrates a cross view of the flanged joint shown in  FIG. 2 , 
         FIGS. 4   a  and  4   b  illustrates a preferred embodiment of a connection set comprising a bolt and nut, and 
         FIG. 5  illustrates a method step in assembling a wind turbine tower according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a modern wind turbine  1  mounted on a foundation  6 . The wind turbine comprises a tower  2 , including a number of tower sections such as tower rings, and a wind turbine nacelle  3  positioned on top of the tower  2 . The wind turbine rotor  4 , comprising three wind turbine blades  5 , is connected to the nacelle through the low speed shaft which extends out of the nacelle front. 
     The different components of a wind turbine are usually transported separately to the site of mounting and assembled there e.g. the different tower sections, the nacelle and the wind turbine blades. 
       FIG. 2  illustrates a part of a flanged joint in between two wind turbine tower sections according to the invention. 
     The tower flange usually establishes a full circle with the tower section but may also be divided into a number of flange sections which together form a full circle corresponding to the tower section. 
     The figure especially illustrates a part of an upper tower section  2  which at its lower edge is connected to a first flange  8   a  in a welding seam  14 . The flange  8   a  has a first and second arm wherein the arms together form a substantially perpendicular angle. The first arm is vertically connected to the upper tower section and the second arm extends horizontally into the interior of the tower. 
     A lower tower section is connected to a second flange  8   b  in a welding seam (not illustrated on the figure). The second flange  8   b  also has a first and second arm wherein the arms together form a substantially perpendicular angle. The first arm is vertically connected to the lower tower section and the second arm extends horizontally into the interior of the tower. The second flange is—more or less—a mirror image of the first flange about a horizontal line. 
     The first and second flange  8   a ,  8   b  meet by the arms extending horizontally into the interior of the tower. Each flange comprises a number of through going holes in one or more arrays e.g. one array of holes spaced apart by the same distance in the full length of the flange. The flanges are fixed to each other by an array  17  of sets of connection means penetrating the flanges through the flange holes and hereby establishing the flanged joint between the two wind turbine tower sections. 
     The figure especially illustrates a number of nuts  9  which are part of sets of connection means. Each nut is provided with an assembly opening  13  in the top surface of the nut. The opening allows an assembly tool to be entered from above and tighten or loosen the nut as a part of a set of connection means. 
       FIGS. 3 and 5  illustrate a cross view of a preferred embodiment of a set of connection means in the flanged joint. 
     The two flanges  8   a ,  8   b  are illustrated with the welding seams  14   a ,  14   b  to the lower and the upper tower section, respectively. However, the connection may also be between the foundation with foundation bolts and a first tower section with an initial flange and nuts according to the invention. 
     Further, the two flanges  8   a ,  8   b  are illustrated with their arms making full contact and with a through going hole  18 . The hole is occupied by the rod of a bolt  10  connected to a nut  9  at one surface of the flanges and with the bolt head  10   a  at the opposite surface, said bolt and nut establishing a set of connection means  15  of the jointed flange  7 . 
     The assembly opening  13  of the nut is illustrated with a size Xa e.g. the length from one internal surface to the opposite in a hex shaped socket. The threaded part of the nut is illustrated with a size Xb corresponding to the thread diameter. The nut is finally illustrated with an outer size Xc wherein the outer shape of the nut may be round, hex or any other suitable shape. 
     Further,  FIG. 5  illustrates a method step in assembling or disassembling a wind turbine tower according to the present invention. 
     The assembly tool  16  is illustrated as wrench with a hex head  16   a  and a handle  16   b . The hex head corresponds to the assembly opening  13  of the nut  9  i.e. the nut of the present embodiment comprises a hex shaped socket. 
     The socket part of the nut  9  has a depth Ln 1  that extends from a top surface of the nut and in to the beginning of the threaded part of the nut. The inner surface of the socket part may interact with the head of the assembly tool and thus allow the nut to be tightened from above instead of from the side. 
     The threaded part  12  of the nut  9  has a depth Ln 2  that extends from a top surface of the nut and in to the beginning of the socket part of the nut. The depth Ln 2  at least corresponds to length of the bolt rod  10   b  extending out of the flange hole  18 . 
     The depths of Ln 1  and Ln 2  may be chosen freely but are preferably similar in size. 
     The bolt rod  10   b  including a threaded part  10   c  has a length L b that allows the bolt to extend the necessary distance out of the flange hole  18  in order to establish a threaded connection with the nut  9 . 
       FIG. 3  illustrates the nut with a size Xa being smaller than the size Xb and  FIG. 5  illustrates the opposite relationship between the two. 
       FIGS. 4   a  and  4   b  illustrate in perspective views a preferred embodiment of a connection set  15  comprising a bolt  10  and a nut  9 . 
     The internal threaded part  12  of the nut  9  is illustrated as in direct connection with the part comprising assembly opening  13 . However, the two parts may also be divided from each other by a wall e.g. to control the entrance of the head of the assembly tool. 
     The sets of connection means are preferably positioned inside a wind turbine tower but may also be used in flanged joints on the outside of the tower or other types of joints involving a set of connection means such as a bolt and a nut. Further, a set of connection means may involve two nuts and a threaded shaft instead of a bolt and a nut. 
     In assembling the wind turbine tower it is preferred that the nut is tightened from above i.e. the nut is positioned above the joint e.g. as illustrated in  FIG. 2 . However, the nut may also be positioned below the joint and thus be tightened from below. 
     LIST 
     
         
           1 . Wind turbine 
           2 . Wind turbine tower including at least two tower sections 
           2   a ,  2   b . Tower sections such as tower rings 
           3 . Wind turbine nacelle 
           4 . Wind turbine hub 
           5 . Wind turbine blade 
           6 . Foundation for the wind turbine tower 
           7 . Flanged joint of tower sections 
           8   a ,  8   b . Upper and lower flange of a tower section, respectively 
           9 . Nut for connecting tower sections or a tower section to the foundation 
           10 . Bolt 
           10   a . Bolt head 
           10   b . Bolt rod 
           10   c . Threaded part of the bolt shaft 
           11 ,  11   a ,  11   b . Lock washer 
           12 . Internal threaded part of the nut 
           13 . Assembly opening of the nut 
           14 ,  14   a ,  14   b . Welded connection between a tower section and a flange 
           15 . Set of connection means 
           16 . Assembly tools such as a wrench 
           16   a . Hex head of the wrench 
           16   b . Handle of the wrench 
           17 . Array of sets of connection means 
           18 . Hole in the upper and lower flange 
         Lb Length of the bolt rod 
         Lf Length of the flange into the interior of the tower 
         Ln 1  Length/depth of the part of the nut comprising an assembly opening 
         Ln 2  Length/depth of the threaded part of the nut 
         Tf Total thickness of the two flange arms extending into the interior of the tower 
         Xa Size of the assembly opening of the nut 
         Xb Size of the threaded opening of the nut 
         Xc Outer size of the nut