Patent Application
20130017085
1. Field of the Invention
The present invention relates to wind turbines. More particularly, the present invention relates to wind turbines that can self-orient themselves in response to drastic changes in wind velocity or direction using only natural forces.
2. The Prior Art
Wind turbines are known in the prior art. Wind turbine design strategies are typically focused on overcoming one or two of three common design challenges. First, a small minority of prior designs have attempted to achieve the aerodynamic characteristics needed to harness meaningful amounts of energy from low velocity winds—winds that cover over 85% of the surface of the earth. Second, some designs have strived to implement governing mechanisms that automatically protect the turbine from extremely high velocity winds—winds that place massive stress on the structural integrity of a turbine—without sacrificing the ability to deliver a constant power output. Every wind turbine that utilizes rotor blades has a rotor shaft. A vertically governed wind turbine moves the axis of rotation of its rotor shaft from a horizontal to vertical orientation. A horizontally governed wind turbine moves the axis of rotation of its rotor shaft within a horizontal plane. Lastly, some designs have sought to limit the gyroscopic movements arising from drastic changes in wind velocity or direction that disorient a turbine and ultimately disrupt its power output efficiency by horizontally orienting the axis of its rotor shaft. Although no single prior design has provided optimal solutions to all three problems, many have attempted to incorporate solutions to one or two of these issues at a time.
Foremost, most previously known wind turbines lack the aerodynamic characteristics needed to harness meaningful amounts of energy from low velocity winds. Accordingly, nearly all existing commercial wind turbines are designed for use in the few geographic regions around the globe that regularly experience high velocity winds. U.S. Pat. Nos. 4,449,889 and 5,295,793 constitute a small minority of patents that disclose wind turbines that are specifically suited for use in low velocity winds. As discussed later in further detail, the present invention improves significantly on these prior designs.
Additionally, it has been suggested that the aerodynamic deficiency issues may be solved by applying vortex generating technologies to rotor blade design. U.S. Pat. No. 7,832,689 discloses a system of passive fluid jet vortex generating outlets. Although effective, such outlets impose constraints on rotor blade design. Because they rely on generating swirling vortices, the outlets only function when spaced close enough to interact with one another, but not so close as to interfere with one another.
Moreover, such outlets are best suited for enhancing the lift properties of rotor blades that are already rotating rather than for obtaining start-up momentum in low velocity winds. Specifically, they run from edge to edge in a direction parallel to the plane of the blade. Because a wind turbine needs to capture as much wind as possible to obtain any meaningful rotational speed in low velocity winds, it must expose as much rotor blade surface area to the wind as possible. Given that the outlets disclosed in U.S. Pat. No. 7,832,689 run from edge to edge, their inlets are optimized for receiving incoming wind when the rotor blades have already picked up rotational speed and are slightly angled rather than when resting perpendicular to the ground.
Other vortex generating technologies are also generally known in the art. For example, U.S. Pat. No. 4,455,045 discloses a set of vortex generating channels that rely on the sharp edges of “V-shaped” ramps to create swirling vortices. Such generators are optimized for reducing drag in automobile designs.
In addition to addressing aerodynamic deficiencies, some prior wind turbine designs have attempted to quell the excessive stress forces that high velocity winds place on the structural integrity of a wind turbine. The force placed on a wind turbine increases in proportion to the area of the rotor blades multiplied by the wind velocity cubed. As a result, assuming that the area of the rotor blades exposed to the wind remains constant, a 60 mph gust subjects a turbine to eight times the force than that imposed by a 30 mph gust. Such forces can drive movable components beyond their design limits and result in mechanical breakdown.
In response to such issues, prior designs have incorporated governing mechanisms that automatically reduce the exposed rotor blade area when the wind exceeds a certain velocity. Some designs reduce rotor blade exposure by allowing the rotor assembly to tilt vertically. Examples of such designs are disclosed in U.S. Pat. Nos. 4,449,889 and 5,295,793. The present invention improves significantly on these prior designs by adding additional safety mechanisms.
Similarly, horizontally governed wind turbines reduce rotor blade exposure by allowing the rotor assembly to rotate horizontally. Notably, however, because horizontally governed turbines—unlike those that are vertically governed—do not directly oppose gravity, they typically experience difficulty re-orienting back into the wind. Some previously known turbines rotate so much that they must be manually reset after effectively shutting down in order to save the machine Because such turbines experience time periods in which the rotor shaft is not spinning at a constant angular velocity, they struggle to deliver a consistent power output.
Some horizontally governed wind turbines known in the prior art have attempted to solve such efficiency problems by biasing the horizontal axis of the rotor assembly in some way. For example, U.S. Pat. No. 5,746,576 discloses a wind turbine design in which the rotor assembly is slightly inclined and swivels on a mechanical pivot point. Similarly, U.S. Pat. No. 7,915,751 discloses a design in which the rotor assembly flexes to the side on an elastic rod. Although horizontal governing mechanisms reduce rotor blade exposure, they generally cannot do so as effectively as vertical governing mechanisms. Specifically, while a vertically governed turbine can reduce rotor blade exposure nearly to zero by lifting the surface of its blades parallel to an oncoming airstream, a horizontally governed turbine cannot rotate enough to achieve such an effect without sacrificing its ability to re-orient.
Additionally, vertically governed wind turbine designs are optimized for using supplemental safety mechanisms like blade tip winglets. Blade tip winglets are generally known in the prior art. For example, U.S. Pat. No. 7,931,444 B2 discloses an inclined winglet at the outer edges of the blades that can be used to improve overall turbine performance and reduce noise emissions. The height of these winglets is significant and they are best suited for reducing tip drag in designs in which the rotor blades are always perpendicular to the ground.
Notably, however, because a vertically governed turbine functions by lifting the exposed surface area of its rotor blades parallel to the oncoming airstream, such blade tip winglets are less suited for use in such turbines. Specifically, when such a turbine that has blades that are equipped with such winglets is titled such that its blades are parallel to the airstream, the blade tip winglets present too much surface area perpendicular to the wind, thus tending to rotate the blades out of their nominal plane of rotation. On the one hand, if the winglets are nearly perpendicular, they can interfere with the ability of a turbine to provide lift to its rotor blades in response to dangerously high velocity winds. On the other hand, if the winglets are less sharply inclined, their excessive height can create excessive lift and risk hyper-extending the rotor assembly.
Furthermore, prior wind turbine designs have also attempted to limit gyroscopic movements arising from drastic changes in wind velocity or direction that disorient the turbine and ultimately disrupt its power efficiency. When the wind velocity abruptly drops or the wind suddenly changes direction, a vertically governed wind turbine experiences a destabilizing gyroscopic torque that stems from the rapidly slowing yet still rotating rotor blades. Such torque causes the entire structure to precess and turn away from the wind. Previously known vertically governed wind turbines lack mechanisms for preventing such movement. Accordingly, rather than preventing the precession in the first place, they require that the turbine wait until the wind changes directions in such a way that it passively re-orients the machine back into the wind. Such movements ultimately reduce power output efficiencies.
Moreover, prior known designs like those disclosed in U.S. Pat. Nos. 6,974,307 B2, 5,746,576 and 7,915,751 have attempted to address this issue by utilizing a horizontal governing mechanism that is not susceptible to precession around a vertical axis. As previously mentioned, however, such mechanisms limit the ability of a wind turbine to reduce rotor blade exposure to nearly zero. In short, no previously existing designs have successfully combined the ability of a vertically governed wind turbine to reduce rotor blade surface area with the anti-rotational benefits of a horizontally governed turbine.
According to a first aspect of the present invention, a wind turbine includes a base and a support member mounted to the base. The support member is mounted such that it rotates horizontally around the axis of the base. An elongate body with a first and second end is mounted to the distal end of the support member at a pivot point. The body is mounted such that it tilts vertically in a position offset from the axis of the base.
A rotor blade assembly is coupled to a rotor shaft. The rotor shaft is mounted to the top of the body such that it rotates around its own axis. The rotor blade assembly includes a plurality of blades and is oriented to rotate when exposed to an airstream generated by wind. An alternator is coupled to the rotor shaft. The power output of the alternator varies as a function of the angular velocity of the rotor shaft.
A tail assembly is mounted to the second end of the body. The tail assembly includes both an airfoil section oriented perpendicular to the rotor shaft and at least one upright vane. The vane passively rotates the body into the direction of the wind in response to an airstream. The vane features an angular rudder offset to generate wind-induced torque in a direction opposite to the gyroscopic torque generated by rotation of the rotor blade assembly.
The pivot point is located at a position along the length of the body such that the turbine achieves a particular weight balance. According to such balance, when an airstream exerts a force on the airfoil section of the tail assembly, the body tilts about the pivot point and effectively changes the cross-sectional area of the rotor blades exposed to the airstream such that the rotor shaft rotates at a substantially constant angular velocity.
An annular ratchet is mounted to the top of the base. The ratchet includes a plurality of ratchet teeth, each of which has a flat side and a slanted side. A flag assembly is pivotally coupled to a proximal end of the support member such that it can rotate around the axis of the base in two directions: a restricted direction and an unrestricted direction. The flag assembly includes a control vane mounted to a distal end of an angled extension shaft and a pawl mounted to a proximal end of the extension shaft. The control vane has a front-side and a back-side and is sized as a function of the scale of the overall turbine such that the vane can capture enough wind to engage or disengage the pawl with the flat side of the ratchet teeth.
When the wind rotates the body in the restricted direction, the pawl is stopped by the flat side of the ratchet teeth unless the pawl is disengaged from the ratchet. When the wind rotates the body in the unrestricted direction, the pawl passes freely over the slanted sides of the successive ratchet teeth. The flag assembly, support member, and ratchet function together as a self-regulated anti-rotational locking mechanism that prevents the body from precessing like a top and ultimately turning away from the wind in response to an abrupt change in wind velocity or direction.
According to a second aspect of the present invention, the rotor blade assembly includes at least two rotor blades that have one or more tapered bores running between their top and bottom surfaces. Such bores effectively serve as thrust channels. Each bore is oriented at an angle such that it independently creates a thrust tending to rotate the blade by passively compressing the airstream as it passes through the blade in a straight line.
According to a third aspect of the present invention, each rotor blade features a short inclined distal region that effectively serves as a blade tip winglet. Namely, the inclined distal region provides additional lift when the turbine tilts its rotor blades parallel to the ground in response to high velocity winds.
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Persons of ordinary skill in the art will realize that the following description of the present invention is illustrative only and not in any way limiting. Other embodiments of the invention will readily suggest themselves to such skilled persons.
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A rotor blade assembly 24 is coupled to a rotor shaft 26. The rotor shaft 26 is mounted to the top of the body 16 such that it rotates around its own axis. The rotor blade assembly 24 includes a plurality of blades 28 and is oriented to rotate when exposed to an airstream generated by wind. Each rotor blade 28 is mounted at a negative angle of attack. In an exemplary embodiment, the outer blade-to-blade angle is between about 180° to about 185°. In other embodiments, other blade-to-blade angles above about 180° may be used. Moreover, in an exemplary embodiment, the number of blades 28 may be three. In other embodiments, other numbers of blades 28 may be employed. An alternator 30 is coupled to the rotor shaft 26. The power output of the alternator 30 varies as a function of the angular velocity of the shaft 26.
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While embodiments and applications of this invention have been shown and described, it would be apparent to those skilled in the art that many more modifications than mentioned above are possible without departing from the inventive concepts herein. The invention, therefore, is not to be restricted except in the spirit of the appended claims.
