Downstream wind turbine

A downstream wind turbine for converting wind energy into electrical energy. In a preferred embodiment the downstream wind turbine adapted to respond to high winds and gyroscopic precession. The downstream wind turbine comprises a support tower; a yaw bearing attached to the support tower; a support frame operably linked to the bearing; at least one swing arm with one end pivotally attached to the support frame; an elongated carry member pivotally attached to the other end of the swing arm; a wind driven energy conversion system balanced on and attached to the carry member so that the carry member is biased to maintain an approximately horizontal orientation with respect to the support frame and in response to wind proportionally swings downstream, and which responds to gyroscopic precession forces by tilting up or down; and a governor device for modifying at least one dynamic characteristic of the turbine.

Not Applicable.

BACKGROUND OF THE INVENTION

This invention relates to a wind turbine for generating electrical power.

Conventional power generating plant, such as coal and oil fired plant, use hydrocarbon fuels to generate electricity. Burning hydrocarbons both uses up valuable non-renewable resources and adds chemical pollutants to the environment. Thus there is a need to harness natural energy for conversion into electrical energy.

Natural energy sources include water, in the form of hydroelectric power, and wind. Hydroelectric power is available in areas with favorable geography such as found in Norway where hydroelectric power makes a significant contribution to Norway's energy needs.

Wind turbines are used to convert wind energy into electrical energy that is typically fed into the grid. However, wind turbines are vulnerable to severe damage caused by high winds. Specifically, in high winds a wind turbine may experience a run-away incident in which the blades of the wind turbine rotate at a destructive rate. Various expensive and complicated design solutions have been applied to wind turbines to avoid run-away incidents.

In one type of wind turbine the rotation rate of rotor blades is monitored and after a predetermined point a control system applies a braking force to the rotor assembly to inhibit or stop the rotation of the rotor blades. Since the brakes are typically applied when the rotor blades are near their maximum permitted rate of revolutions, failure in the braking system can lead to a run-away incident and the destruction of the wind turbine.

The American farm windmill design limits the effect of high winds by using a tail vane which, when triggered by wind speeds exceeding its maximum set point, turns 90 degrees with respect to the turbine shaft in order to rotate the turbine out of the wind. The 4-arm Dutch windmill relies on manual furling of canvas sails to accomplish the same effect. While such design solutions may help to avoid run-away incidents, rotating the turbine completely out of the wind stops the conversion of wind energy into electrical energy.

U.S. Pat. No. 4,333,018 issued Jun. 1, 1982 to Bottrell, describes a downstream wind turbine that converts wind energy into controlled wind turbine torque for generating electrical energy. Like other downstream wind turbines, the '018 wind turbine is normally oriented downwind of the turbine tower, so that wind forces acting on the wind turbine create a drag which keeps the wind turbine directed into the wind, but downstream from the turbine tower. The '018 wind turbine comprises a yaw control vane which is used to partially rotate the wind turbine out of a high wind to maintain a constant turbine torque. Rotating the turbine partially out of the wind creates additional stresses on the wind turbine.

U.S. Pat. No. 4,449,889 issued May 22, 1984 to Belden, describes a windmill having a plurality of blades generally transverse to an upstanding rotor shaft. The blades have an airfoil cross-sectional shape and are oriented with a negative angle of attack, thereby allowing the leading edge of the airfoil to turn into the wind. The windmill preferably has a tilting assembly that tilts the rotor shaft and blades at an angle dependent upon the velocity of the wind. As the wind velocity increases the rotor shaft is automatically tilted into a vertical position by the control tail. This automatic tilting of the windmill provides automatic control of the rotor speed. The rotor blades are preferably pivotally connected to the rotor shaft. Rotating the turbine partially out of the wind creates additional stresses on the wind turbine; rotating the turbine completely out of the wind stops conversion of wind energy into electrical energy.

U.S. Pat. No. 4,352,629 issued Oct. 5, 1982 to Cheney, Jr., describes a wind turbine of the type having an airfoil blade mounted on a flexible beam and a pitch governor which selectively, torsionally twists the flexible beam in response to wind turbine speed thereby setting blade pitch. A limiter restricts unwanted pitch change at operating speeds due to torsional creep of the flexible beam. The limiter allows twisting of the beam by the governor under excessive wind velocity conditions to orient the blades in stall pitch positions, thereby preventing run-away operation of the turbine. In the preferred embodiment, the pitch governor comprises a pendulum which responds to changing rotor speed by pivotal movement, the limiter comprising a resilient member which engages an end of the pendulum to restrict further movement thereof, and in turn restrict beam creep and unwanted blade pitch misadjustment. The '629 solution is complex and relies on twisting a flexible beam, which must be designed to cope with such twisting thereby adding to manufacturing cost.

In addition to run-away issues, gyroscopic precession can cause severe loads on wind turbines. Precession is a phenomenon that effects rotating bodies, wherein an applied force is manifested 90 degrees later in the direction of rotation from where the force was applied. A change in wind direction causes precession, wherein the rotor blades (which form part of the rotor assembly) experience forces that cause them to tilt upward or downward depending on the change in wind direction and direction of rotation of the blades. For example, with respect to a downstream wind turbine, if the rotor blades are rotating clockwise and the wind direction causes the rotor assembly to turn to the right with respect to original wind direction, the rotor blades will want to tilt downwards. If the rotor blades are rotating clockwise and the wind direction causes the rotor assembly to turn to the left with respect to the original wind direction then the rotating blades will want to tilt upwards.

Wind turbines not designed to handle precession risk serious damage. Various solutions have been applied to counter precession. One solution relies on using turbines that always point in one direction. Such design solutions are at best limited in scope and are not suitable for most areas where wind direction is variable.

Some wind turbines are designed to respond slowly to wind direction changes thereby limiting the gyroscopic precession forces. Such systems require gears and drive mechanisms to make controlled slow turns. Such mechanisms add to manufacturing and maintenance costs; in addition, a drive motor might be required to drive the mechanism. Wind turbines fitted with such mechanisms are also less efficient since they are necessarily slow in responding to changes in wind direction.

Some manufacturers of wind turbines deal with precession effects by preventing tilting of the rotor assembly. Such wind turbines still experience the up and down tilt forces in the rotor assembly but incorporate, for example, very strong support towers that are able to withstand the precession forces transmitted to the support tower from the rotating blades. Such wind turbines are very expensive to build since they require a considerable amount of strengthening and use of expensive parts. In addition, the rotator blades will experience severe flexing forces necessitating expensive development and high manufacturing costs.

In another design solution, the rotor attached to the blades is allowed to teeter separately from the rest of the rotor assembly thereby at least partly isolating the support tower from the effects of gyroscopic forces. Teetering blades can strike the support tower destroying the turbine.

None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. Thus a wind turbine solving the aforementioned problems is desired.

SUMMARY OF THE INVENTION

A downstream wind turbine, comprising: a support tower; a yaw bearing attached to the support tower; a support frame operably linked to the bearing; at least one swing arm with one end pivotally attached to the support frame; an elongated carry member pivotally attached to the other end of the swing arm; a wind driven energy conversion system balanced on and attached to the carry member so that the carry member is biased to maintain an approximately horizontal orientation with respect to the support frame and in response impacting on the blades of the turbine proportionally swings downstream; a governor device for modifying at least one dynamic characteristic of the turbine; and a means for measuring the amount of downstream swing experienced by the carry member and simultaneously or nearly simultaneously transmitting this information to the governor device for modifying at least one dynamic characteristic of the turbine.

Accordingly, it is a principal object of the invention to provide a wind turbine.

It is another object of the invention to provide a wind turbine that is responsive to high winds.

It is further object of the invention to provide a wind turbine that is responsive to gyroscopic precession.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to a downstream wind turbine for converting wind energy into electrical energy and, more specifically, to a downstream wind turbine100adapted to respond to high winds and gyroscopic precession.

FIG. 1is side view of a downstream wind turbine100according to the present invention. The downstream wind turbine100is shown operating in ambient wind conditions. Wind condition and direction are represented by alpha-numeral “111a”.

Still referring toFIG. 1, the downstream wind turbine100comprises an approximately vertical support tower120having a top125and bottom130, a yaw bearing140attached to the top125of the tower120, a support frame160, an elongated carry member180pivotally attached to the support frame160, wherein the carry member is free to swing away and downstream from the support tower100or support frame160(seeFIG. 2A), a wind driven energy conversion system200balanced on and firmly attached to the carry member180, a governor device (such as a blade pitch regulator220) for modifying at least one dynamic characteristic of the energy conversion system200, and a downstream swing-monitoring device (such as a pull cable system, discussed below) for measuring the amount of downstream swing experienced by the carry member180and energy conversion system200attached thereto.

Still referring toFIG. 1, the bottom130of tower120is optionally attached to a hinge135and hence to the ground for lowering and raising the wind turbine100. The optional hinge135may be firmly attached to a base or firm ground such as a layer of stable concrete. Optional guy cables138may be used to stabilize the tower120as shown inFIG. 1.

The energy conversion system200comprises an electric generator or alternator280, a low speed shaft300, a high speed shaft310, a transmission system320, and a rotor head340attached to at least two aerofoil blades360. It will be understood that the component parts found in the energy conversion system200may vary in order listed or type of components as is well understood in the art of electric power generation from wind energy. The energy conversion system200is balanced on and firmly attached to the carry member180so that the carry member.180is biased to maintain an approximately horizontal orientation with respect to the support frame160. It will be understood by persons of ordinary skill in the art that the component parts, and arrangement thereof, that make up the energy conversion system200can vary; for example, the transmission320may be placed at a different position relative to the generator280or the carry member180thereby impacting on the lengths of the shafts300and310.

FIGS. 2A and 2Bare side views of downstream wind turbine100according to the present invention. The downstream wind turbine100is shown operating in high wind conditions. Wind direction represented by numeral “111b”. High winds111bincident on the aerofoil blades360are transmitted to the carry member180(and energy conversion system200attached to the carry member180) and cause the carry member180to swing downstream from the support frame160or tower120as shown inFIG. 2A, and summarized inFIG. 6. The degree of downstream swing is proportional to the ferocity of the wind incident on the aerofoil blades360.

The downstream swing, as depicted inFIG. 2A, occurs simultaneously or almost simultaneously and in synchrony with the high wind incident on the aerofoil blades360. When the wind subsides the force of gravity returns the carry member back to its normal operating position as depicted inFIG. 1. Thus, the force of gravity constantly counteracts the amount of downstream swing such that the downstream swing is proportional to the power of the wind111bincident on the aerofoil blades360.

For convenience herein, the support frame160is labeled with a top portion162and a bottom portion164(seeFIG. 3A). The bottom164is operably linked to the yaw bearing140such that the support frame160is free to yaw about a horizontal axis. The top162need not be continuous; for example, the support frame160can resemble a generally planar U-shape as shown inFIG. 3A. As will be understood the exact form of the support frame160may vary.

At least one swing arm380(shown as swing arm members380aand380binFIGS. 3A and 3B) is pivotally attached by means of at least one pivot point165(shown as pivot points165aand165binFIG. 3A) to the support frame160. The pivot points165aand165bmay form part of a first bearing shaft167as depicted in, for example,FIGS. 3A and 11. More specifically, each at least one swing arms380has first400and second420opposite ends (shown as400a/400b, and420a/420b, respectively, inFIG. 3B), the first opposite end400is pivotally attached at pivot point165(or pivot points165aand165b) to the support frame160such that the at least one swing arm380is free to swing downstream and back at a perpendicular angle with respect to the support frame160. The second opposite end420is pivotally attached at pivot point168(shown as pivot points168aand168binFIGS. 3A and 3B) to the carrier member180. The pivot points168aand168bmay form part of a second bearing shaft169as depicted inFIG. 3A.

The carry member180is at least partly accommodated inside at a perpendicular angle with respect to the support frame160(see, e.g.,FIGS. 1 and 3A). It is preferred that there are two swing arms380, but the number of swing arms may vary. For example, a single swing arm380may suffice as shown inFIG. 3C.

InFIG. 3C, the carry member180is shown comprising a bottom185, and opposite lateral sides190aand190b. The energy conversion system200is attached to the bottom185. However, it should be understood that the carry member180might vary in form and structure.

The energy conversion system200is balanced on and firmly attached to the carry member180so that in ambient or ordinary wind conditions111athe carry member180is biased to maintain a substantially horizontal orientation with respect to the support frame160(seeFIG. 1). However, in high wind conditions111b, wherein the high wind111bis incident on the blades360, the carrier member180responds to the wind111bby proportionally swinging and holding a position downstream from the support frame160and tower120(seeFIG. 2A).

The support frame160and at least one swing arm380respectively possess central longitudinal axes: a–a′ and b–b′ (seeFIG. 2B). The angle of downstream swing is represented by the alpha labels “α” and as “α′” and “α”, i.e. the angle between longitudinal mid-axes a–a′ and b–b′. As discussed above, the downstream position and degree of downstream swing varies with the power of the wind111b. When the high power wind111bis very severe, the at least one swing arm380swings downstream until it is approximately horizontal with an α angle of about 90° (inFIG. 2A, the swing arm380is at a downstream angle of about 45° with respect to the planar support frame160). Thus, the degree of downstream swing is represented by the degree of swing experienced by the swing arm380, which varies between a starting point at an approximately vertical orientation (i.e., an α angle of about 0°) with no wind or very low wind conditions and an approximately horizontal orientation (i.e., an α angle of about 90°) in very severe wind conditions. Thus, the swing arm380can swing downstream through an angle range of about 0° to about 90°. However, it should be understood that the swing arm380might be configured to swing between different starting and end points and through a different swing angle.

The amount of downstream swing experienced by the swing arm380is synonymous with the amount of downstream swing experienced by the carrier member180. Thus, monitoring the swing arm380(i.e. α angle) would provide downstream swing data on the carrier member180. Monitoring the downstream swing provides a basis for adjusting a dynamic characteristic of the wind turbine100.

The amount of downstream swing experienced by the carry member180(or swing arm380) is monitored by a downstream swing monitoring device, which transmits or operably communicates the degree of downstream swing to a governor device for modifying at least one dynamic characteristic of the downstream wind turbine100. The form of the monitoring device may vary and take the form of an electronic device or a mechanical device, or a combination of an electronic device and a mechanical device to measure the downstream swing action of the carry member180. The form of the governor device may vary and take the form of an electronic device or a mechanical device, or a combination of an electronic device and a mechanical device to control one or more dynamic characteristics of the wind turbine100.

InFIG. 2A, the downstream swing-monitoring device takes the form of a pull cable system that comprises a pull cable440attached to a control lever460. Part of the cable440is encased in a cable guide tube480. More specifically, the pull cable440has two opposite ends445and450, end445is attached to a fixed guide arm500and the other end450is attached to the control lever460. The control lever460is attached to a governor device, which in this example is a blade pitch regulator220. The pitch regulator220is attached to part of the energy conversion system200at a point near the rotor head340.

Pitch regulators and blades capable of varying blade pitch are well known in the art. For example, U.S. Pat. No. 4,352,629 (Cheney, Jr., issued Oct. 5, 1982) describes a wind turbine blade mounted on a flexible beam and a pitch governor or regulator that selectively twists the flexible beam to vary pitch. The Cheney '629 patent is herein incorporated by reference in its entirety.

The cable end450pulls on the control lever460when the carry member180swings out from the support frame160. The control lever460controls the pitch regulator220(seeFIG. 2A). The pitch regulator220controls the pitch of the at least two blades360. Thus, the governor device shown inFIG. 2Ais a pitch regulator220that controls a dynamic characteristic of the wind turbine100, namely the pitch of the blades360.

When the carry member180swings downstream this causes tension in the pull cable440. Thus, the amount of swing is monitored mechanically and in real time and this information is inherently transmitted via the cable440to the governor device, which in the exemplary example discussed here is in the form of control lever460attached to pitch regulator220. The pitch regulator220alters the pitch of the blades360almost simultaneously and in proportion to the downstream swing of the carry member180.

In normal wind conditions the pull cable440is in a relaxed mode and does not pull on the control lever460(seeFIG. 1); in this condition the pitch regulator220does not alter the pitch of the blades, allowing them to remain in their most efficient pitch configuration in which the maximum amount of wind energy is captured to rotate the blades360. In high winds the pull cable440pulls on the control lever460and causes the pitch regulator220to alter the pitch of the blades360to their least efficient configuration with respect to capturing the wind energy, thus limiting the rotation of the blades360in a high wind condition thereby preventing a run-away condition.

The governor device could be a braking device to regulate the rotation rate of the blades360. For example, applying a brake to the transmission system320. Alternatively, the governor device could be a blade tip pitch control device comprising an hydraulic actuator operably coupled to blade tips that are pivotable to a position in which they act as brakes to slow the wind turbine down (see, for example, U.S. Pat. No. 4,575,309 (Brown, issued Mar. 11, 1986; the Brown '309 is herein incorporated by reference in its entirety).

The governor device could be a mechanical device that causes the blades360to be moved out of the direction of a high wind by moving the blades on a horizontal axis or by causing the blades360to be moved vertically out of the wind as described in U.S. Pat. No. 4,449,889 (Belden, issued May 22, 1984; the Belden '889 is incorporated herein by reference in its entirety). Thus, it will be understood that the governor device could be any type of governor device that can alter a dynamic characteristic of the wind turbine such as blade pitch, blade tip pitch, and any form of device capable of creating drag such as a spoiler flap attached to a wind turbine blade as described in U.S. Pat. No. 5,570,859 issued Nov. 5, 1996 to Quandt; the Quandt '859 reference is herein incorporated by reference in its entirety. A governor device may incorporate or be operatively coupled to a brake that is in turn operably coupled to the rotor head340, transmission system320or shafts300/310; alternatively, a governor device may be coupled to a mechanism to move the blades360out of a high wind and so on.

FIGS. 2A and 2Bshow the approximately horizontal swing movement of the carry member180, wherein the energy conversion system200acts as balancing ballast for maintaining the carry member180in an approximately horizontal orientation in the absence of gyroscopic precession forces. The energy conversion system200is balanced on and firmly attached to the carry member180so that the carry member is biased to maintain an approximately horizontal orientation with respect to the support frame160and in response to wind incident on the blades360proportionally swings downstream from the support frame160. Gyroscopic forces are transferred from the rotating blades360to the carry member180via the rotor head340, low speed shaft300, and transmission system320. The carrier member180tilts down or up in response to gyroscopic forces as shown respectively inFIGS. 4 and 5, and summarized inFIG. 7.

FIGS. 5 and 6show how the at least one swing arm380and pivot points165and168also permit the carry member180to tilt up or down in response to gyroscopic forces transmitted from the blades360in response to changes in wind direction. For example, if the blades360are rotating clockwise with respect to the wind incident on the blades360, and the wind changes direction to the right with respect to the rotating blades360, the carrier member180will tilt downwards as the support frame160yaws to the right on the yaw bearing140to realign the energy conversion system200with the new wind direction thus assuring optimum conversion of wind energy into electrical energy.

FIG. 6shows a side view of the carry member180in different positions during a downstream swing.

FIG. 7shows a side view of the carry member180in different positions during a gyroscopic precession event, i.e. the carry member180is able to tilt up or down in response to a change in wind direction incident on the rotors360.

FIG. 8shows an alternative embodiment of the carry member180(represented by the alpha-numeric label “180a”). The carry member180acomprises a curved glide540in operable contact with a roller560. The curved glide540and roller560work in unison to limit the downward tilt of the carry member180a; a stop580, in the form of an extension of the bottom600of the carry member180, prevents over-tilting of the carry member180in response to precession forces. The stop580abuts against the roller560at a predetermined maximum angle of downward tilt of the carry member180. The predetermined maximum angle of downward tilt is selected to ensure that there is no contact between the blades360and the tower120.

FIG. 9is another embodiment of the carry member180(represented by the alpha-numeric label “180b”). The carry member180bcomprises a damper shock620that helps to dampen tilt movements of the carry member180b. The damper shock620is shown connected between an extended swing-arm380cand the bottom600of the carry member180. Thus, the exact form of the carry member180can vary; any type of carry member180can be employed providing the member180is pivotally attached to a support frame in such a manner that the carry member180can tilt and perform a downstream swinging action.

It should be understood that support frame160is not limited to a particular shape and can vary in structure. For example, inFIG. 10support frame160(represented by alpha-numeral “160b”) takes the form of a single generally elongated structure with ends162and164. End162includes a hollow bore to accommodate shaft167as shown inFIG. 11, which shows a top view of the wind turbine ofFIG. 10. The support frame160bsits inside a modified version of carrier180((represented by alpha-numeral “180c” inFIGS. 10 and 11). Carrier member180ccomprises a structure that defines an empty central portion197. Support frame160bsits in the empty central portion197such that the carrier180ccan swing freely with respect to the support arm160b; however the dimensions of empty central portion197limit the degree of swing of member180c; i.e., the downstream swing angle α must be limited to avoid clashes between the ends of carrier member180c(and components connected to the ends of the carrier member180csuch as generator280) and the support frame160b. In addition, the overall shape of support frame160bis designed to accommodate shaft310; specifically, support arm160bhas a middle portion163defined by support arms162and164, middle portion163is set back sufficiently to avoid contact with shaft310(seeFIG. 10). Limiting the downstream swing angle α can be achieved by any suitable means such as limiting the amount of play or stretch in cable440(shown inFIG. 2A).

With respect toFIGS. 12 and 13, the support frame160is in the form of an upright U-shaped bracket represented by alpha-numeral “160c”. Support frame160cshould be positioned to avoid touching shaft310.FIG. 13shows a side-view of the wind turbine ofFIG. 12. Carrier member180is represented by alpha-numeral “180d”.