Motors: expansible chamber type – With correlated control of motive fluid and locking means
Reexamination Certificate
1999-01-08
2001-12-11
Ryznic, John E. (Department: 3745)
Motors: expansible chamber type
With correlated control of motive fluid and locking means
C416S159000
Reexamination Certificate
active
06327957
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention is concerned with wind-driven electric generators of the downwind type having flexible blades capable of downwind coning and pitch control by a collective pitch mechanism.
Wind-driven electric generators, commonly referred to as “wind turbines,” have proved their ability to generate substantial amounts of electricity in proper operating environments. However, most wind turbines presently in use are heavy machines with rigid blades and are expensive to manufacture and maintain. Because of their rigidity, structural loads tend to be very high, and the entire wind turbine must be heavy enough and strong enough to withstand such loads.
Structural loads can be reduced by designing flexibility or compliance in the wind turbine rotor.
Examples of downwind wind turbines with flexible blades are described in U.S. Pat. No. 5,178,518 issued Jan. 12, 1993 to Carter, Sr., U.S. Pat. No. 4,431,375 issued Feb. 14, 1984 to Carter, Jr. et al, and U.S. Pat. No. 4,366,387 issued Dec. 28, 1982 to Carter, Jr., et al, all of which are incorporated herein by reference.
It is desirable that the wind turbine be constructed in a manner that takes maximum benefit of blade flexibility and weight reduction, while providing high strength and reduced manufacturing and maintenance costs. Also, it is desirable that the wind turbine be constructed to run only when operating conditions are appropriate. The present invention provides such wind turbines.
BRIEF DESCRIPTION OF THE INVENTION
In accordance with one aspect of the invention, flexible, oppositely disposed rotor blades are mounted on a hub of a drive shaft by means of a flexible spar that is attached to the hub and that extends therefrom into hollow interior portions of the blade shells, the ends of the flexible spar being attached to the blades by ball joints. In a preferred embodiment, each blade has a root-rib with an opening through which the spar extends freely, and the root-rib has a blade pitch pivot with a stub shaft that is slidable in a ball joint mounted on the hub. The root-ribs are coupled to a pitch-changing mechanism by which the pitch of the blades is changed, collectively rather than individually, between run and stall positions.
In a preferred embodiment, the collective pitch mechanism comprises a pitch beam extending transversely of the drive shaft and having linkages at opposite ends thereof that couple the-pitch beam to the root-ribs. Each linkage includes a tie-rod, one end of which is connected to an end of the pitch beam by a clevis, and the other end of which is connected to the root-rib by a ball joint. The pitch beam has a shaft portion that reciprocates within the drive shaft of the wind turbine to change the pitch of the blades.
In a preferred embodiment, a nacelle cover of the wind turbine head defines an airflow path through the head, and an airflow responsive device, such as a swing door inside the nacelle cover, controls the movement of the pitch beam. By virtue of this arrangement, predetermined airflow conditions, based on desired run and non-run conditions of the wind turbine, determine whether the rotor blades are in the run or stall position.
The flexible rotor blades are designed to cone in a downwind direction. In a preferred embodiment, to minimize the risk of a blade striking a tower of the wind turbine, the ability of the blades to cone reversely, i.e., in the upwind direction when the rotor is downwind, or in the downwind direction when the rotor is upwind, is limited. Such limitation may be provided by a stiff spar mounted on the hub behind the flexible spar.
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Miles & Stockbridge P.C.
Ryznic John E.
Wind Eagle Joint Venture
LandOfFree
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