Abstract:
A wind turbine for generating electrical power, the turbine having a rotor assembly comprising a hub, a rim and a plurality of blade members extending between the hub and rim, and at least two anemometers mounted at stationary locations relative to the rotor assembly or on the rotor assembly itself, wherein the pitch of individual blade members is adjustable in response to differences in wind speed detected by the anemometers as the rotor assembly rotates.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates generally to the field of fluid driven turbines, such as wind turbines, wherein electrical power is generated from airflow across rotor blades. More particularly, the invention relates to such turbines wherein the blades extend from a central rotating hub or shaft member to an annular rotating ring or rim member. Even more particularly, the invention relates to mechanisms and methods for adjusting the pitch of the blades to maximize efficiency. 
     Wind turbines, also known as windmills, wind generators, wind machines or the like, are well known devices for producing energy, typically electrical energy, by harnessing the power of wind. Typical wind turbines are very large structures, standing hundreds of feet tall and having rotor blades extending hundreds of feet, the rotor blades being mounted to a central hub or shaft. Large elongated blades are required since the area of blade sweep is proportional to the power that can be produced by a given wind turbine. This size creates a problem, in that each blade must act as a cantilever that can support the elongated blade and the blades must be increasingly massive toward the central hub in order to preclude the blade from breaking during use. Even with the use of high tech composites, carbon fibers and the like, a practical limit has been reached. For example, most large wind turbines have three blades, as this has been found to be the most efficient design. The desire to increase blade length in order to capture more wind is offset by the accompanying reduction in shaft revolutions per minute (rpm). Reduced rpm&#39;s require larger reduction gearboxes, which is undesirable. Decreasing blade pitch in order to increase the rpm&#39;s reduces torque, which is undesirable. In addition, repair or replacement of these giant blades is difficult and can be extremely expensive. The cost of upkeep and repair reduces the overall benefits of energy production using wind technology. Thus, known wind turbine designs always have to make sacrifices in order to balance these competing factors. 
     An alternative type of wind turbine incorporates an outer, annular ring or rim that is joined to the blades, such that the blade tips are no longer self-supporting and thereby allowing the blades to be lighter and/or longer, easier to manufacture and repair, etc. The blades extend from the central rotating hub or shaft to the annular rim and are therefore supported at both ends. In this embodiment, it is also known to utilize the rotational energy from the rotating annular rim rather than the central hub, since the annular rim travels at much faster speed. Rollers, wheels, gears, magnets or the like are used to transfer the rotational energy from the rim to one or more generator mechanisms or the like. Examples of such turbines are shown in U.S. Pat. No. 4,319,865 to Richard, U.S. Pat. No. 4,330,714 to Smith, U.S. Pat. No. 4,350,895 to Cook, U.S. Pat. No. 4,545,729 to Storm, U.S. Pat. No. 4,729,716 to Schmidt, and U.S. Pat. No. 6,664,655 to Vann. Such wind turbines are often of smaller size and utilize sail-like blades rather than complicated blade structures in order to increase the number of wind catching elements, since the weight of the annular rim adds structural problems to the design. 
     It is important in wind turbines to maintain a relatively steady rotation rate, since this allows for simpler gearbox or other rotation transfer mechanisms. Since wind speed will vary, it is known to provide mechanisms and methods for adjusting the pitch of the blades to account for stronger or weaker winds. This can be accomplished by measuring the wind speed directly or by measuring the rate of rotation of the rotor assembly and then adjusting the blade pitch as required to keep the rotation rate within desired parameters. While this addresses the problem on a macro scale, the known solutions do not take into account localized variations in wind speed striking the rotor assembly at different locations. For example, especially with large diameter wind turbines, the wind speed at the top of the rotor assembly may be significantly greater than the wind speed at the bottom of the rotor assembly. This variation in wind speed also negatively stresses the rotor assembly, which can damage the wind turbine. 
     It is an object of this invention to provide a system and a method that measures localized wind speed at various points on the wind turbine or the rotor assembly, such that the blade pitch of each individual blade can be more precisely adjusted in response to the actual wind speed being encountered as the blade rotates about the central hub. 
     SUMMARY OF THE INVENTION 
     The invention is a wind turbine for generating electrical power, the wind turbine comprising a rotating rotor assembly comprising a rotating central hub member and a rotating annular rim member, the rim member joined to the hub by a plurality of blade members. The blade members are mounted to the hub and rim such that the pitch of each blade can be adjusted independently of the other blades and while the rotor assembly is rotating. In order to maintain the rotation rate within desired parameters, the pitch of the blades are reduced in low winds and increased in high winds. The invention is a system and method that accounts for variations in wind speed at different points relative to the wind turbine, such as at the bottom and top of the rotor assembly, such that the pitch of each blade is adjusted in response to the encountered wind speed at predetermined locations or at any location as the rotor assembly rotates. 
     In one embodiment, means for measuring wind speed, such as a wind gauges or anemometers, are provided at stationary, fixed positions on the wind turbine, such as for example adjacent the top and the bottom of the rotor assembly. Wind speed measurements at each location are then utilized to adjust the pitch of each blade as it moves through a full rotation. For example, if the wind speed at the top of the rotor assembly is greater than at the bottom of the rotor assembly, the pitch of each upwardly moving blade will be increased to account for the higher wind speed. After it passes the top and begins downward movement, the pitch will be decreased to account for the lower wind speed occurring at the bottom of the rotor assembly. 
     In an alternative embodiment, a plurality of means for measuring wind speed are mounted onto the annular rim member at spaced intervals such that the means for measuring wind speed rotate with the rotor assembly. In one embodiment, each blade will have a corresponding or dedicated means for measuring wind speed. If necessary, rotational effects that may alter the wind speed measurement will be accounted for by software or shielding means such that a true wind speed reading is obtained. The means for measuring wind speed may be located at or on the rim itself, or they may be positioned between the rim and the hub using struts, extended arm members or the like. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simple illustration of a wind turbine consisting of a rotating hub, a rotating annular outer rim and a plurality of blades extending from the hub to the rim, with stationary means for measuring wind speed. 
         FIG. 2  is partial view showing a blade mounted onto the rim, with means for adjusting the pitch of the blade and means for measuring wind speed mounted onto the rim. 
         FIG. 3  is a partial view showing a rotor assembly having a plurality of means for measuring wind speed located at points between the rim and the hub. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the drawings, the invention will now be described in detail with regard for the best mode and the preferred embodiment. In a broad sense, the invention is a fluid powered turbine, such as a wind turbine, where airflow rotates a rotor assembly on a central shaft or hub member, whereby electrical power or the like is generated by the rotational energy, and wherein the rotor element comprises a plurality of blade members extending from the rotating central hub member to a rotating annular rim member. 
     As shown in  FIG. 1 , a typical turbine  10  comprises a rotor assembly  11  mounted onto a fixed support means, such as a base  15  and tower  16 , whereby the rotor assembly  11  is positioned to have a generally horizontal axis of rotation in order to capture wind passing across the ground surface. The turbine may be of any size, and the structure as described herein is suitable for relatively large turbines, wherein the diameter of the rotor assembly  11  may be hundreds of feet. 
     The rotor assembly  11  comprises a central rotating hub or shaft member  12 , which is mounted in suitable manner to a tower  16  such that the rotor assembly  11  can rotate relative to the fixed support means. The rotor assembly  11  further comprises an outer or peripheral annular ring or rim member  13 , with a plurality of blade members  14  extending between the rim member  13  and the central hub member  12 , the blade members  14  being the means to capture the energy of the wind and translate that energy into rotational movement. 
     The blade members  14  are mounted to the hub  12  and rim  13  by suitable mechanical means for retaining the blades  14  therebetween. The blades  14  are be joined to the hub  12  and rim  13  in a manner that allows at least one of the blade ends to be adjusted so as to alter the pitch of the blade  14 . Preferably the interior ends of the blades  14  are mounted to the hub  12  in fixed manner, preferably at an angle of about five to ten degrees off the main hub axis, and the exterior ends are mounted to the rim  13  in a manner that allows the exterior ends to be pivoted, such as for example utilizing a mounting shaft, as shown in  FIG. 2 . 
     Means  22  for adjusting the blade pitch are provided such that the pitch of each blade  14  can be individually adjusted to increase or decrease the pitch in response to the encountered localized wind speed. Any suitable powered mechanism or assembly, such as servo motors or the like, may be utilized to alter the blade pitch, typically by pivoting the exterior end of the blade  14  about the shaft  18 . 
     The wind turbine  10  further comprises at least two means  21  for measuring wind speed, such as an anemometer or wind gauge, whereby the measured localized wind speed is utilized to determine the proper blade pitch at a given blade location. In one embodiment, the means  21  for measuring wind speed are provided in stationary, fixed locations relative to the wind turbine  10  and rotor assembly  11 , as shown in  FIG. 1 . In the illustration, a first means  21  for measuring wind speed is positioned on a mounting arm member  17  such that it is located at or near the top of the rotor assembly  11 , while a second means  21  for measuring wind speed is positioned near the bottom of the rotor assembly  11 . This set-up addresses the most common occurrence of wind speed variation, wherein the upper winds are of greater velocity than the lower winds nearer the ground surface. 
     In this manner, the wind speed at the top and at the bottom of the rotor assembly  11  is measured. As an individual blade member  14  rotates upwardly toward the top means  21  for measuring wind speed, the measured wind speed information from this detector is provided to the operating system of the means  22  for adjusting the blade pitch, many such operating systems being known and typically including a computer processor. The pitch of the blade  14  is then adjusted to the optimum value for the wind speed measured at the top of the rotor assembly  11 . As the blade  14  passes the apex and begins downward rotation toward the bottom means  21  for measuring wind speed, the measured wind speed information from this detector is now provided to the operating system of the means  22  for adjusting the blade pitch. The pitch of the blade  14  is then adjusted to the optimum value for this measured wind speed, which is very likely different from the wind speed at the top of the rotor assembly  11 , and thus the optimum pitch will now differ. In like manner, the pitch for all blade members  14  are adjusted as they rotate about the central hub  12  depending on their position at any given moment. The sensitivity of the system can be increased by increasing the number of means  21  for measuring wind speed. 
     In an alternate embodiment shown in  FIG. 2 , a plurality of means  21  for measuring wind speed are mounted onto the annular rim  13 . A given means  21  for measuring wind speed may control the means  22  for adjusting blade pitch of several blade members  14  simultaneously, but preferably there is an equal number of means  21  for measuring wind speed and blades  14 , such that each blade  14  has a dedicated means  21  for measuring wind speed controlling its means  22  for adjusting blade pitch. With this structure, the localized variation in wind speed during the entire rotation can be accounted for. Inaccuracies in measurement of wind speed resulting from the rotation of the means  21  for measuring wind speed can be corrected through software programming or by providing shielding structures as necessary. In another alternative embodiment, as shown in  FIG. 3 , the means  21  for measuring wind speed can be positioned between the hub  12  and rim  13  by mounting them on a strut or mounting arm  17 . 
     With the non-stationary means  21  for measuring wind speed, precise control of the blade pitch and immediate response can be obtained, thereby maximizing the efficiency of the wind turbine  10 . By adjusting the blade pitch, the desired speed of rotation is easily maintained. In addition, immediate adjustment of the blade pitch in response to wind speed variation reduces the wind force stresses on the rotor assembly  11 , thereby increasing the longevity of the wind turbine  10 . 
     It is understood that equivalents and substitutions for certain elements set forth above may be obvious to those skilled in the art, and therefore the true scope and definition of the invention is to be as set forth in the following claims.