Dual Cam Cylic Pitch Turbine

This invention relates to a novel turbine design that increases turbine efficiency whereby turbine blades experience cyclic pitch variations while rotating about the blade axis which is accomplished by means of a concentric end cam double follower mechanism. This mechanism rotates the blades by 90 degrees about a horizontal axis which allows the blades rotating upstream and downstream to be oriented horizontally and vertically so minimum drag and maximum drag are obtained respectively. Since the aiding downstream drag is at a maximum, and the adverse upstream drag is at a minimum, this configuration allows for higher power output compared to conventional vertical axis wind turbines.

FIELD OF THE INVENTION

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.

BACKGROUND OF THE INVENTION

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.

SUMMARY OF THE INVENTION

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.

DETAILED DESCRIPTION OF THE INVENTION

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 toFIGS. 1-7, the present disclosure relates to a dual cam turbine blade assembly100in which a disk shaped dual cam20is configured with an inner cylindrical end cam21concentric to a cylindrical outer end cam23on an upper surface, and a bottom surface18that has an annular neck19for affixation to a drive shaft98, The dual cam20is designed to interact with a moving follower shaft103so that under a fluid force the rotational interaction between the dual cam20and follower shaft103cause a turbine blade10affixed at one end of the follower shaft103to undergo a cyclical pitch motion by means of an inner lobe101and an outer lobe102which are located on the follower shaft103at locations that will interact with the inner cam21and outer cam23of the dual cam20.

The inner cam21and the outer23cam of the dual cam20are uniformly molded, each having a lower surface area26,27respectively, a raised surface area28,29respectively, and a pair of sloping rises22,24each respectively, rite inner and outer cams21,23used in conjunction with the inner and outer lobes101,102of a follower shaft103act as mechanical switches which are activated when a fluid flow moves the turbine blades10, causing the inner and outer lobes101,102to rotatingly interact with sloping rises22,24of the inner and outer cams21,23, thereby changing the pitch of the turbine blades10with respect to the fluid by 90 degrees with each interaction. With continued movement of the follower shaft103, the inner and outer lobes101,102continue to interact with the sloping rises22,24, so that the turbine blades10undergo another rotation of 90 degrees back to their initial pitched profile positions. These changes in pitch occur in continuous cycles.

Referring toFIGS. 3-7. the position of the sloping rises24of the outer cam23with respect to the sloping rises22of the inner cam21of the dual cam20determines whether the inner and outer lobes101,102of the follower shaft103rotate continuously in one direction or rotate back and forth in each successive pitching motion. The inner cam21is typically out of phase with respect to the outer cam23by 90 degrees, The sloping rises22of the inner cam21typically also coincide with the opposite sloping rises24of the outer cam23, and vice versa which allows the inner and outer lobes101,102to rotating roll without interference.

The dual cam20design allows for the inner and outer lobes101,102of a follower shaft103to rotate twice in the same direction whenever the lobes move over one of the sloping rises22,24of one of the inner or outer lobes101,102, which coincides the sloping rises22,24of the opposing toner or outer cam21,23. The sloping rises22,24are positioned such that they are typically 180 degrees apart but can be as little as 60 degrees apart. A turbine blade10connected to a follower shaft103rotates when the inner or outer lobe101,102interacts with the sloping rise22,24of the inner or outer cam21,23respectively. The turbine blade10remains in the rotated position for the next 60 to 180 degrees of follower shaft103rotation and then again rotates by 90 degrees when the inner or outer lobe101,102interacts with the opposite sloping rise22,24of the inner or outer cam21,23respectively, and then remains in that position for the next 60 to 180 degrees. The rotation of the turbine blades10is not abrupt, and is not preferred, as rotating the turbine blade10sharply might result in vibrations and might require more energy because the fluid around the turbine blade10would be displaced at a rate proportional to the speed of rotation of the follower shaft103.

Still referring again toFIGS. 1-7, the inner and outer lobes101,102are typically positioned out of phase with respect to each other by 180 degrees. The inner lobe101interacts with the inner cam21. and the outer lobe102interacts with the outer cam23of the dual cam20. While the inner lobe is active and is undergoing rotation over either of the sloping rises22or24of the inner cam21, the outer lobe is passive and vice versa. And this happens alternatively for the pitching motion to be occur continuously. The inner and outer cams21,23can be modified to obtain any number rotations of the follower shaft103by having the corresponding number of rises22,24on the inner and outer cams21,23.

The turbine blade10is connected to the follower shaft103and rotates along with the follower shaft103. The follower shaft103is connected to the dual cam turbine blade assembly100through a roller bearing to the hub90of the assembly100to which all the power is transferred. A drive shaft98is connected to the hub90and is concentric to the dual cam20and rotates through a roller bearing about a vertical axis whenever the turbine blades10rotate about the same axis.

Referring now toFIGS. 8-16, a second embodiment of a dual cam turbine blade assembly150is disclosed. Each of a plurality of turbine blades10and followers50work in conjunction with the dual cam20to provide cyclical pitch to the turbine blades10upon interaction with fluid forces with reduced friction by incorporation of rotatable bearings,60of suitable material.

As shown inFIGS. 8-16, each follower50is comprised of a plurality of interlocking parts to form cam lobes which are fastened together by means of a bolt30whose bolt shaft34passes through the open centers of the plurality of parts starting at erne distal end and threadingly attaches with a threaded section36to a securing nut38. The bolt head32is secured within a central hub90along with a washer40and a hub bearing42, through which the bolt shaft34passes when the hub cover94cut outs97are snapped over and affixed to the hub apertures92. The hub90is affixed at a lower distal end to a drive shaft98. Extending outwardly from the hub90, the bolt shaft34passes through the central openings of a first bearing lobe50, a crisscross uniformly molded lobe connector70, a second bearing lobe80and the nut38. The adjacent affixation of the first bearing lobe50, the crisscross lobe connector70, and the second bearing lobe80form orthogonal parts that interact with the dual cam20to create the cyclic pitch motion of the turbine blade10.

Lobe bearings60for the reduction of friction are secured within the follower50in compression by the bolt30and securing out38in between the first bearing lobe50find an upper surface72of the crisscross lobe connector70, as well as in between the lower surface74of the crisscross lobe connector70and the second bearing lobe80.

Still referring toFIGS. 8-16, the first bearing lobe50includes a flange56, a neck extending outwardly front the flange56in a first direction, and a pair of first lobe pins54, extending outwardly from the flange56in an opposite direction. The first lobe pins54are cylindrical and formed to pass through the cam bearing60then to rotatingly engage with annular holes78in an upper flange72of the crisscross lobe connector70.

The second bearing lobe80has second lobe pins82at one end and turbine blade prongs84at an opposite end. The second lobe pins82are cylindrical and pass through bearing cams60then rotatingly engage with annular holes78in a lower flange74of the crisscross lobe connector70which is uniformly molded with a cylindrically shaped middle76connecting the upper flange72to the lower flange74. The turbine blade prongs84each include a hole86for attaching a turbine blade10using a pair of standard nuts and bolts11.

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.