Patent Application
20160377055
This invention relates to a vertical axis wind turbine. More particularly, the invention relates to a vertical axis wind turbine with a dual cam cyclic pitch control.
Wind turbines have been in use tor many centuries to perform various tasks. But there has been an increased interest in them for power generation in the last decade because of factors like global warming and the need to shift to greener power generation methods. Many different wind turbine designs exist today. The major classification of wind turbines is based on the position of the axis of rotation of the blades with respect to the wind flow direction. Wind turbines with their axes parallel to the flow are called horizontal axis wind turbines (HAWT) and they occupy a majority of the present share of commercial wind turbines. Their blades' cross sections resemble an airfoil and produce lift and drag forces while wind blows over them. The lift forces generate torque and rotate the blades when wind velocity is sufficient.
Unlike HAWTs, vertical axis wind turbines (VAWT) have blades with the axis of rotation perpendicular to the wind direction. Hence, they are also called cross flow turbines. Popular VAWTs include the Darrius Turbine and the Savonius Turbine. Different Damns Turbine configurations exist and in most cases they are not self-starting. They use the lift forces on their airfoil blades to generate the required torque.
Savonius Turbines on the other hand are drag based turbines. Most of them have two buckets with an “S” shaped cross section and rotate about a symmetrical vertical axis. The shape of the turbine causes it to experience more drag in the down wind direction than that in the upwind direction and tits net drag forces the turbine to rotate. They are simple to construct, have cheaper maintenance and work independent of wind direction. The efficiency of these turbines drops very quickly with increase in rotational speed as it adversely alters the relative velocity between the wind and the buckets. Modifications to the Savonius turbine were made to minimize the upstream drag and increase efficiency which resulted in adverse inertial effects of moving parts at high speeds, in order to increase such a turbine's efficiency, it is necessary to maximize live aiding downstream drag and minimize the adverse upstream drag simultaneously.
A similar mechanism is found in a helicopter which uses a device called swash plate. It has two circular discs which can be tilted about any planar axis passing through their center. The lower disc only tilts while the upper disc also rotates along with the blades of the helicopter. The upper disc has levers connected to the blades through a crank. When these discs are tilted, one half on their surface is elevated while the other half is lowered. The levers on the elevated side of the discs move up rotating the crank which results in having an increased pitch on those blades while the blades on the lower side experience decreased pitch by the same amount. So each blade experiences a reversal of the pitch about a mean position when it moves from the elevated side to the lowered side i.e. for every 180 degrees of rotation in a cyclic manner. The blades with increased pitch produce more thrust than the blades with reduced pitch and this difference in thrust is the reason a helicopter can pitch forward or backwards and roll to the left or right according to the input from the pilot. And the maximum pitch angle attained by each of the blades m each cycle is proportional to the angle by which the discs are tilted. The swash plate can also be moved up or down without tilting which would change the collective pitch resulting in increasing or decreasing the altitude of the helicopter.
A swash plate converts linear input into rotary output which is the gradual continuous pitch variations spread uniformly over 360 degrees of rotation of a blade. But since, the turbine of the present invention benefits from quicker rotations which must happen when the blade is changing from upstream to downstream location and vice versa, an improved system is desired.
In at least one embodiment, the present disclosure describes a dual cam pitch turbine assembly in which the turbine blades are rotated or pitched cyclically by means of a dual cam to obtain maximum differential drag between the drive stroke and the recovery stroke of the turbine cycle to maximize the efficiency and/or power output from a VAWT. This is analogous to the motion of an oar blade in the sport of shell rowing. The water is pushed backwards by an oar blade held perpendicular to the water surface during the drive stroke, and then the blade is rotated parallel to the water surface and pulled back to the initial position during the recovery. The drive stroke force and hence the work done is much larger during the recovery stroke, and net positive work is done on the system.
The system regains its initial state after completing one cycle. During this cycle, a small portion of work generated during the drive stroke is used to complete the recovery. Thus, the system can work independently and generate net positive work while capturing energy from the fluid flow.
In at least one embodiment, the present disclosure provides turbine blades that each rotate by 90 degrees twice in one cycle i.e. once each at the end of the drive stroke and then recovery stroke by means of a dual mechanical cam. The rotation can either be in the same direction or m the opposite as it would not have any effect on the resulting state. This is because rotating a blade by 90 degrees twice and rotating by 90 degrees in a certain direction and then rotating it back by 90 degrees results in a similar configuration.
In at least one embodiment, the present disclosure provides a dual cam combining two concentric end cams with a sharp rise and a sharp fall of the outer end cam aligned with a sharp fall and sharp rise respectively of the inner end cam. Followers which move over the end cams slide on the cams and rotate by 90 degrees whenever they move over the rise/fall of the end cams. The 90 degree rotation of the followers result in pitching motions of blades attached thereto. Where most mechanical cams convert input rotary motion of a shaft into a controlled linear or radial motion which can either be sudden or gradual based on requirements, linear cams convert linear motion into a modified still linear motion but in a direction perpendicular to the direction of initial motion. The dual cam of the present disclosure modifies the cam mechanism to output rotary motion from an input rotary motion.
In at least one embodiment, the present disclosure provides a dual cam cyclic pitch system with three turbine blades. Three blades are found to keep at least one blade in the drive stroke at all times, provides a compromise between simplicity and uniformity in power output However, it is understood that more or fewer blades may be utilized based on other design preferences.
In at least one embodiment the present disclosure provides for blade shapes as thin, rectangular plates. Though a rectangle may not be the optimal shape for the blades, rectangular plates are being used for simplicity and ease of analysis and comparison with other drag based VAWTs. However, the present disclosure recommends the use of a variety of known blade shapes including airfoils, variable pitch blades, oar shaped blades and the like.
The dual cam pitch turbine assembly disclosed herein is not limited to VAWT applications, or to tidal energy systems, but may be utilized in turbines of various applications such as wind turbines, propellers, and industrial turbines.
The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate the presently preferred embodiments of the invention, and, together with the general description given above and the detailed description given below, serve to explain the features of the invention. In the drawings:
In the drawings, like numerals indicate like elements throughout. Certain terminology is used herein for convenience only and is not to be taken as a limitation on the present invention. The following describes preferred embodiments of the present invention. However, it should be understood, based on this disclosure, that the invention is not limited by the preferred embodiments described herein, or to the particular systems, devices and methods described, as these can vary.
Referring to
The inner cam 21 and the outer 23 cam of the dual cam 20 are uniformly molded, each having a lower surface area 26, 27 respectively, a raised surface area 28, 29 respectively, and a pair of sloping rises 22, 24 each respectively, rite inner and outer cams 21, 23 used in conjunction with the inner and outer lobes 101, 102 of a follower shaft 103 act as mechanical switches which are activated when a fluid flow moves the turbine blades 10, causing the inner and outer lobes 101, 102 to rotatingly interact with sloping rises 22, 24 of the inner and outer cams 21, 23, thereby changing the pitch of the turbine blades 10 with respect to the fluid by 90 degrees with each interaction. With continued movement of the follower shaft 103, the inner and outer lobes 101, 102 continue to interact with the sloping rises 22, 24, so that the turbine blades 10 undergo another rotation of 90 degrees back to their initial pitched profile positions. These changes in pitch occur in continuous cycles.
Referring to
The dual cam 20 design allows for the inner and outer lobes 101, 102 of a follower shaft 103 to rotate twice in the same direction whenever the lobes move over one of the sloping rises 22, 24 of one of the inner or outer lobes 101, 102, which coincides the sloping rises 22, 24 of the opposing toner or outer cam 21, 23. The sloping rises 22, 24 are positioned such that they are typically 180 degrees apart but can be as little as 60 degrees apart. A turbine blade 10 connected to a follower shaft 103 rotates when the inner or outer lobe 101, 102 interacts with the sloping rise 22, 24 of the inner or outer cam 21, 23 respectively. The turbine blade 10 remains in the rotated position for the next 60 to 180 degrees of follower shaft 103 rotation and then again rotates by 90 degrees when the inner or outer lobe 101, 102 interacts with the opposite sloping rise 22, 24 of the inner or outer cam 21, 23 respectively, and then remains in that position for the next 60 to 180 degrees. The rotation of the turbine blades 10 is not abrupt, and is not preferred, as rotating the turbine blade 10 sharply might result in vibrations and might require more energy because the fluid around the turbine blade 10 would be displaced at a rate proportional to the speed of rotation of the follower shaft 103.
Still referring again to
The turbine blade 10 is connected to the follower shaft 103 and rotates along with the follower shaft 103. The follower shaft 103 is connected to the dual cam turbine blade assembly 100 through a roller bearing to the hub 90 of the assembly 100 to which all the power is transferred. A drive shaft 98 is connected to the hub 90 and is concentric to the dual cam 20 and rotates through a roller bearing about a vertical axis whenever the turbine blades 10 rotate about the same axis.
Referring now to
As shown in
Lobe bearings 60 for the reduction of friction are secured within the follower 50 in compression by the bolt 30 and securing out 38 in between the first bearing lobe 50 find an upper surface 72 of the crisscross lobe connector 70, as well as in between the lower surface 74 of the crisscross lobe connector 70 and the second bearing lobe 80.
Still referring to
The second bearing lobe 80 has second lobe pins 82 at one end and turbine blade prongs 84 at an opposite end. The second lobe pins 82 are cylindrical and pass through bearing cams 60 then rotatingly engage with annular holes 78 in a lower flange 74 of the crisscross lobe connector 70 which is uniformly molded with a cylindrically shaped middle 76 connecting the upper flange 72 to the lower flange 74. The turbine blade prongs 84 each include a hole 86 for attaching a turbine blade 10 using a pair of standard nuts and bolts 11.
When comparing the invention herein with other drag based VAWTs, it is apparent that since the adverse drag force, which reduces the power output by a large amount, is considerably reduced it results in better efficiency.
These and other advantages of the present invention will be apparent to those skilled in the art from the foregoing specification. Accordingly, it will be recognized by those skilled in the art that changes or modifications may be made to the above-described embodiments without departing from the broad inventive concepts of the invention. It should therefore be understood that this invention is not limited to the particular embodiments described herein, but is intended to include ail changes and modifications that are within the scope and spirit of the invention as defined in the claims.
This application is entitled to the benefit of and incorporates by reference subject matter disclosed in Provisional Patent Application No. 62/183,980 tiled on Jun. 24,2015.
| Number | Date | Country | |
|---|---|---|---|
| 62183980 | Jun 2015 | US |
