Automatic pitch control for horizontal axis wind turbines

Abstract

A self setting and self powered system for adjusting the blade angles of a wind turbine such that they have a high angle of attack when parked to promote early start up, move to their ideal setting angle for normal running, can respond to gusts and lulls with appropriate changes, and feathers the blades to limit the rpm and reduce loads in storm conditions. The system balances the thrust loads on the turbine against centripetal forces generated by masses reacting to the rpm, increasing the blade pitch with gusts to increase torque and hence rotational acceleration and reducing blade pitch in lulls to conserve rotational momentum, and uses springs to establish the starting position and the rpm limit appropriate for the generator mechanism.

1 . A self powered automatic pitch adjustment system for a turbine that includes a shaft and at least one blade characterized by a blade pitch angle, the system comprising: a mechanism for adjusting said blade pitch angle, said mechanism coupled with the shaft; an element for generating a centripetal force when the turbine rotates and for resolving said force axially along the shaft, wherein an axial wind force on the turbine is balanced against the axially resolved centripetal force, said element coupled with said mechanism, such that when the wind force builds faster than the centripetal force the blade pitch angle is increased and when the wind force reduces faster than the centripetal force the pitch blade angle is reduced. 
     
     
         2 . The system of  claim 1 , wherein the mechanism comprises a hub holding the at least one blade, wherein the hub is displaced alone the shaft in a rearward direction in response to an increasing wind force but is displaced along the shaft in a forward direction in response to an increasing centripetal force so that it results in a displacement that determines the blade pitch angle. 
     
     
         3 . The system of  claim 1 , wherein the mechanism further comprises a spring force member adapted to act along the shaft to augment the wind force so as to return the at least one blades to a high blade pitch angle when both wind force and speed of rotation of the turbine are low. 
     
     
         4 . The system of  claim 2 , wherein the mechanism further comprises a preload device adapted to enable the hub to be displaceable along the shaft in said rearward direction, when a wind force is above a defined level, irrespective of the centripetal force. 
     
     
         5 . The system of  claim 2 , wherein: the element for generating a centripetal force comprises one or more masses mounted on lever arms to swing radially outward, the mechanism comprises means for transforming radial movement of the masses into movement in said forward and rearward directions. 
     
     
         6 . The system of  claim 1  wherein the centripetal force is generated by a plurality of masses constrained to move out radially from the shaft with a means to transform the radial displacement into an axial displacement along the shaft. 
     
     
         7 . The system of  claim 2 , wherein the mechanism further comprises:
 a cam coupled with the at least one blade; and   one or more rollers fixed to the shaft and coupled with the cam;   wherein displacement of the hub causes said cam to be proportionately rotated by said one or more rollers.   
     
     
         8 . The system of  claim 1 , wherein the centripetal forces are generated by allowing the blades to move out radially and where such motion is translated into an axial force to oppose the wind force. 
     
     
         9 . The system of  claim 2 , wherein the at least one blade comprises an axle, and wherein the mechanism further comprises a pulley on said axle and a belt attached to the hub and running around said pulley so that the net displacement of the hub causes the belt to rotate the at least one blade about the axles proportionally to said net displacement. 
     
     
         10 . The system of  claim 2 , wherein the at least one blade comprises an axle, and wherein the mechanism further comprises a crank attached to said axle and a push rods running from a fixed point on the hub to said cranks so that the net displacement of the hub causes the push rods to rotate the blades about the axles proportionally to said net displacement. 
     
     
         11 . The system of  claim 5 , wherein the means for transforming includes a belt or a chain attached to the hub. 
     
     
         12 . The system of  claim 5 , wherein the means for transforming includes:
 a cam attached to the hub, the cam having a profile; and   a roller attached to the element for generating a centripetal force and adapted to act against the profile when the element undergoes said radial movement.   
     
     
         13 . The system of  claim 5 , wherein the means for transforming has at least one characteristic that is selected to optimize a balance between the axial wind force and the axially resolved centripetal force. 
     
     
         14 . The system of  claim 9 , wherein at least one end of the belt is attached to the hub via a spring force member. 
     
     
         15 . The system of  claim 14 , wherein the spring force member is adapted to act along the shaft to augment the wind force so as to return the at least one blade to a high blade pitch angle when both wind force and speed of rotation of the turbine are low. 
     
     
         16 . A wind turbine comprising:
 a shaft;   a hub rotatably mounted on the shaft and moveable along the shaft;   at least two blades mounted on the hub, wherein a wind force on the blades causes the blades to rotate about the shaft and to be forced in a first direction along the shaft;   a centripetal element rotatable with the blades around the shaft, generating a centripetal force towards the shaft;   a coupling mechanism for balancing the centripetal force with a force on the hub in a second direction along the shaft opposite to the first direction; and   a mechanism for adjusting a pitch angle for each blade in response to movement of the hub in the first and second directions.   
     
     
         17 . The turbine of  claim 16 , wherein the mechanism adjusts the pitch angle to a relatively steep pitch angle with movement in the first direction and a relatively shallow pitch angle with movement in the second direction. 
     
     
         18 . The turbine of  claim 16 , wherein the centripetal element comprises a plurality of centripetal masses and wherein the coupling mechanism comprises lever arms that on which the centripetal masses are constrained to move out radially from the shaft whereby the lever arms transform radial displacement into axial displacement.