Vertical axis wind turbine

A vertical axis wind turbine having a plurality of blades around its periphery and a pivotable door associated with each blade. Each door has a pivot axis that is inclined outwardly toward the bottom of the turbine so that gravitational forces will pull the doors toward an open position. The doors are designed to move toward a closed position to at least partially block wind forces from the blades when the rotor rotates at potentially damaging speeds. The turbine has mating coils on the rotor and the support column to generate electrical energy when the rotor rotates.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 This invention relates to wind turbines for generating electrical power,
 particularly to vertical axis wind turbines, and more particularly to such
 turbines having means for preventing catastrophic failures in high winds.
 2. Brief Description of the Prior Art
 Wind Turbines provide a source of electrical power as an alternative to
 fossil fuels to help reduce gaseous emissions and other environmental
 problems. Wind turbines also provide electrical power in remote areas
 where power lines have not been strung. Accordingly, numerous wind
 turbines have been installed in high wind areas in the United States and
 other countries.
 Wind turbines have either horizontal axes or vertical axes of rotation,
 with each type having different advantages and disadvantages. Vertical
 axis turbines have, among other advantages, little or no need for a tower
 on which to mount the turbines. The turbine, gearing electrical generators
 and the like can generally be mounted at ground level.
 Most wind turbines are subject to possible damage from excessively high
 winds. Vertical axis turbines are less vulnerable to damage from high
 winds because such turbines are not usually mounted on towers that can be
 blown over. However, high winds can damage vertical axis turbines by
 causing them to run at excessively high speeds (RPM), which can cause
 catastrophic failure of the rotor, gearing, etc.
 It is known to provide speed limiters or governors for wind turbines to
 reduce the risk of damage from high winds and excessively high speed
 rotation of the turbines. For example, U.S. Pat. No. 5,425,619 to Aglor
 discloses a horizontal axis turbine having spring-loaded gate flaps which
 open responsive to predetermined levels of air pressure to spill air
 through outlets instead of across the air-engaging blades in the turbine.
 U.S. Pat. No. 3,856,432 discloses a vertical axis turbine having leaves
 made of resilient material which are unfolded by centrifugal forces at
 predetermined rotational speeds to interfere with air that would otherwise
 cause the rotor to speed out of control. U.S. Pat. Nos. 591,962; 1,586,914
 and 4,004,861 also disclose systems for controlling the speed of wind
 turbines.
 An improved means is needed for reducing the risk to vertical axis wind
 turbines from high winds.
 A low cost, reliable wind turbine is desired which includes means for
 reducing the possible risk of excessively high speed operation.
 A vertical axis wind turbine is needed that will not destroy itself in high
 winds.
 A wind turbine is also desired that is economical to manufacture.
 SUMMARY OF THE INVENTION
 This invention satisfies all the above needs for an improved wind turbine.
 The invention provides a vertical axis wind turbine having a means for
 automatically maintaining the turbine speed or possibly shutting the
 turbine down if its rotational speed reaches a predetermined RPM in
 excessively high winds. This invention also provides a wind turbine that
 includes electrical power generating means inside the turbine.
 This invention has a rotor with a plurality of blades on the rotor and a
 pivotable door associated with each blade to block or partially block the
 wind from the blade when the rotor rotates at potentially damaging speeds.
 The pivot axis for each door is inclined outwardly with respect to the
 vertical axis of the turbine from the top to the bottom of the turbine so
 gravitational forces on the door pulls it to an open position that permits
 the wind to act on the blade. Each door is also responsive to wind forces
 that push it toward the open position and centrifugal forces that pull it
 toward a closed position. The turbine is designed to balance the three
 forces acting on the doors so that the centrifugal forces exceed the sum
 of the wind forces and gravitational forces when the speed of the rotor
 approaches potentially damaging RPMs. When the rotor slows, the sum of the
 gravitational and wind forces exceed the centrifugal forces so that the
 doors move to or toward the open position to again permit the wind to
 drive the turbine blades. This invention may further have coils in the
 rotor and on the support column within the rotor for generating electrical
 power when the rotor turns in the column.
 Accordingly, an object of this invention is to provide a vertical axis wind
 turbine having a mechanical speed control system.
 Another object is to provide a wind turbine having electrical power
 generating means inside the turbine.
 The above and other objects and advantages of this invention will be more
 fully understood by reference to the following description and the
 drawings attached hereto.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
 FIG. 1 shows a preferred embodiment of a wind turbine 10 of this invention
 as including a support column 12, a rotor 14 on the column, and a cap 15
 on the rotor and support column. In the preferred embodiment, the column
 12 is stationary or non-rotating, and the rotor 14 rotates or turns on the
 stationary column. This embodiment includes coils 16 and 18 (FIGS. 2 and
 3), for generating electrical power as the rotor 14 turns. As an
 alternative, the rotor could be fixedly secured to the support column and
 turn the column, which would drive a separate generator at the base of the
 column. In the embodiment of FIG. 1, the support column 12 is securely
 mounted on a base, not shown, to hold the turbine 10 in position. The base
 can either be on the ground or secured to the top of another structure
 such as a building or tower.
 As shown in FIG. 2, the rotor 14 includes an inner cylindrical liner 17, a
 disc-shaped base 19 with an open center for the column 12, and a top cap
 15 that covers the rotor and the central column. The top cap 15 and the
 base 19 may have air spaces in them or could be filled with vibration
 dampening material. The base 19 could also be flat instead of convex
 downwardly. The rotor further has several blades 38 and doors 40 spaced
 around its periphery as is best seen in FIGS. 1 and 3. The blades 38 are
 responsive to wind forces on them to rotate the rotor 14 around the
 stationary column 12. The doors 40 provide an automatic blocking of at
 least a portion of wind to the blades of the turbine in high winds, as is
 described below. As is also described below, it is important to this
 invention that the rotor 14, including the blades 38 and doors 40 on the
 rotor, has a generally frustoconical shape with a smaller diameter at the
 top of the rotor than at its bottom, and the doors are hinged at an angle
 to vertical.
 The rotor 14 of the wind turbine 10 is mounted to rotate on the column 12
 by upper and lower bearings, not shown. The bearings may be conventional
 type bearings which support the rotor 14 on the column 12, and permit it
 to rotate on it with minimal friction. The turbine 10 may also include
 magnetic stabilizers for helping to stabilize the rotor 14 against
 vibrations and oscillation that might be caused by the wind or by
 out-of-balance of the rotor on the column 12. The stabilizers comprise a
 plurality of opposed magnets 20-22, 24-26, and 28-30 that stabilize the
 rotor 14 both vertically and horizontally on the column 12 during rotation
 of the rotor on the column.
 As stated above, the turbine 10 preferably includes coils 16, 18 for
 generating electrical power when the rotor 14 turns on the column 12. Such
 coils 16, 18 are well known in the art. Coil 16 is on the inside of the
 rotor 14, and coil 18 is on the stationary support column 12. Electrical
 wires or cables, not shown, connect the coils 16, 18 to an electrical
 utility line or to electrical equipment for drawing off the electrical
 power generated by the turbine.
 Turbine 10, including the column 12 and rotor 14, is manufactured from
 conventional materials such as steel or aluminum sheet or cast materials.
 The doors 40 can be made of a variety of materials such as metal plate,
 sheet metal, plastic or the like, to provide sufficient weight for
 effective balancing of forces as is described below.
 FIGS. 3 and 4 show the blades 38 and doors 40 on the rotor 14 of this
 invention. The embodiment selected for illustration has eight blades 38
 projecting outwardly from the center portion 42 of the rotor 14, but may
 have any number of blades 38 on it. The blades 38 preferably extend for
 substantially the full height of the rotor 14 (FIG. 1) and are equally
 spaced around the rotor. Each blade 38 has a concavely curved windward
 surface 32 for catching wind energy and a leeward surface 34 on the
 opposite face of the blade. The blades 38 and doors 40 are wider at the
 bottom of the rotor than at the top since the rotor has a frustoconical
 outer diameter and a cylindrical inner liner 17.
 Each of the doors 40 is pivotally connected to the rotor at a pivot axis 36
 at or near the outer periphery of the rotor 14 for pivoting of the door
 from an open position (FIG. 3) in which the windward surface 32 of the
 adjacent blade 38 is exposed to the wind, to a closed position (FIG. 4 and
 in ghost in FIG. 3) in which the windward surface 32 of the adjacent blade
 is shielded from, or closed to, the wind. The pivot axis 36 can be in the
 form of a piano hinge, pivot pin or the like on the outer edge of each of
 the blades 38. The doors 40 are preferably outwardly convex and have a
 radius of curvature approximately the same radius as the rotor 14 at the
 same height on the rotor so the rotor will have a substantially round
 exterior, in horizontal cross-section when the doors 40 are closed. The
 radius of curvature of the doors preferably increases from the top to the
 bottom of the rotor 14 since the rotor tapers outwardly from top to bottom
 (frustoconical).
 The rotor 14 further has a stop 44 for each of the doors 40 to stop the
 doors from pivoting outwardly any further than the end of the adjacent
 blades 38. The stop 44 may comprise mating edges 46, 48 on the doors 40
 and blades 38 as seen in FIG. 4. The stops 44 may further include rubber,
 plastic or other resilient material to cushion the impact of a door edge
 48 against the blade edge 46 when the door 40 pivots outwardly. Resilient
 means, not shown, may also be provided to cushion the impact of the doors
 40 against the blades 38 when the doors pivot inwardly to the closed
 position.
 It is a feature of this invention that the pivot axis 36 for each of the
 doors 40 is inclined outwardly with respect to the center of the column
 toward the bottom of the door as is illustrated in FIGS. 1 and 2. Each
 pivot axis 36 is also preferably in a plane extending through the center
 axis of the rotor. Such incline of the pivot axis 36 to vertical produces
 a gravitation force on the door 40 that pulls the door toward the closed
 position. The magnitude of such gravitational force depends primarily on
 the weight of the door 40 and the angle of the incline. The greater the
 angle of the pivot axis 36 to vertical, the greater the gravitational
 force will be on the doors 40. The angle of incline is preferably in a
 range of about 2-10.degree. but may be more or less depending on the
 weight of the doors 40, diameter of the rotor 14 and the design speed for
 the turbine, among other factors. The top and bottom edges of the doors
 may also have a similar small angle to horizontal or may be substantially
 horizontal as illustrated. In accordance with this invention, the rotor 14
 is designed to have a gravitational force sufficient to move the doors 40
 to the open position when the winds acting on the turbine 10 are not
 excessive to the point of possibly causing the turbine 10 to be damaged.
 In the operation of a turbine 10, the doors 40 are responsive to wind
 energy acting on the outer surfaces of the doors to push them toward the
 open position. The higher the wind speed, the greater the force. The doors
 40 are also responsive to centrifugal force produced by rotation of the
 rotor 14. Such centrifuged forces pull the doors 40 outwardly toward the
 closed position. The centrifugal forces increase with increases on the
 rotational speeds (RPM) which result from higher wind speeds. The doors 40
 are also responsive to the gravitational forces discussed above that pull
 the doors toward the open position. The gravitational forces are
 essentially constant regardless of the speed of the rotation and wind
 speeds.
 Turbines of the invention are designed such that the sum of the wind forces
 and gravitational forces on the doors 40 exceed the centrifugal forces on
 the doors when the rotational speed (RPM) of the turbine is safely below a
 RPM that might damage the turbine (safe RPM), and that the centrifugal
 forces are greater than the sum of the wind forces and gravitational
 forces when the turbine speed exceeds the safe RPM. The safe RPM will vary
 from turbine-to-turbine depending on a number of factors such as materials
 of construction, bearings, base construction, etc. Balancing of the three
 above-described forces acting on the doors 40 is also dependent on several
 factors including size of the doors, weight of the doors, angle of incline
 of the pivot axis of the doors, diameter of the rotor 14 and loci of the
 pivot axes around the turbine axis, among others. The balance of forces
 can be determined mathematically and/or empirically by trial and error to
 produce the desired opening and closing of the doors in accordance with
 the invention.
 In the operation of a wind turbine 10, the doors 40 may pivot between the
 closed positions to their open positions or to any position therebetween
 depending on the rotational speed of the turbine. The doors 40 can
 therefore act as a governor that maintains the rotational speed at a safe
 level rather than completely shutting the turbine down. As the speed of
 the turbine approaches a potentially damaging RPM, the doors 40 can
 partially close so that the speed does not increase beyond a safe RPM, but
 may not fully close to shut the wind completely from the turbine blades.
 The doors will further close or open again as the turbine turns faster or
 slower. The doors 40 may fully close if the speed of the rotor is
 excessively high.
 FIG. 5 shows an alternative embodiment of the invention in which a
 plurality of rotors 50 are mounted one on top of another (stacked) on a
 rotor 52. The rotors 50 are all substantially the same as the rotor 14
 shown in FIGS. 1-4 with a plurality of blades and hinged doors on each
 rotor. The angle of incline on the outer edges of the rotors 50 is
 exaggerated in the illustration in FIG. 5. As stated above with respect to
 FIGS. 1 and 2, the angle of incline is preferably about 2-10.degree. to
 vertical. The rotors 50 in FIG. 5 are stacked to provide a more consistent
 outer diameter for the system for a substantial height. If a single rotor
 were to have the same vertical height as the multiple rotors of FIG. 5,
 the top of the rotor would have a much smaller outer diameter than does
 the top rotor 50 in FIG. 5.
 It is therefore seen that this invention provides an improved wind turbine
 that has an automatic governor means to prevent high wind speeds from
 possibly damaging the turbine. It will be apparent to those skilled in the
 art that numerous modifications can be made to the preferred embodiment
 without departing from this invention or the scope of the claims appended
 hereto.