GB2201469A - Endless belt type wind energy converter - Google Patents

Abstract

Wind energy conversion apparatus comprises vertical endless travelling belt means 27, 28 and a plurality of interspaced hydrodynamic foil members 22 mounted thereon. Passage wind, over the foil members 22 creates lift forces thereon serving to drive the endless belt means about wheels 23, 24. The foil members 22 may have a fixed angle of incidence with respect to the belt runs i.e, between the circulating parts 23, 24 at the top and bottom of the endless belt means; or they may be of variable pitch. In one embodiment the belt means 27, 28 comprises two separate endless belts 27 and 28 respectively, the foils 22 are carried on arms which have pivotal connections at 54 and 55 with both belts; and a tension spring 73 connects the belts 27, 28. The lower wheel 24 is coupled to an electric generator. Aerodynamic lift on the foils 22 drives the belt 27 and, by the spring connection, the belt 28 and the rotary load. The foil angle of incidence is determined by the lift and the spring reaction. A mechanism for causing relative rotation between the wheels of a pair 23 or 24 in response to speed to vary foil pitch is also disclosed (Figs 14, 15 and 16). Devices for pivotally attaching the foils to the belts are also described. The belts may be made from plastics and a wind funnel-like structure (Figs. 4 & 5) may be provided. A wind driven rotor 35 may be selectively engaged to drive the endless belts for starting purposes. <IMAGE>

Description

"Improvements in or Relating to Energy Conversion Apparatus" Background to the Invention This invention relates to energy conversion apparatus and is primarily concerned with energy conversion apparatus operable by a flow of fluid.

The economic viability of any wind energy conversion project is, in common with any other prime source energy conversion project, determined by the ratio of, on the one hand, the capital costs involved in the construction of the wind energy conversion apparatus plus the costs incurred in its maintenance during the productive life thereof, and on the other the total energy produced by the apparatus during that period.

Conventionally, windmills of a wide range of differing forms are employed in wind energy conversion. One might think, at first, that a large windmill would be more cost effective than two smaller ones sweeping an equivalent area. In practice this turns out to be true only up to a certain point, a point determined by other factors notably wind behaviour.

The rate of energy conversion by a windmill is a function of the area swept out by the blades of the windmill; but the dynamics of the windmill is a function of the blade mass, that is to say the cube of the blade dimensions. So the rotor mass increases disproportionately with size to the energy produced.

This translates to disproportionately higher costs to cope with the dynamic loads generated.

It is an object of the present invention to provide wind energy conversion apparatus which may avoid the problems and, hence, the economic limitations of the windmill, as mentioned above, but more generally to provide a novel form of energy conversion apparatus operable by flow of a fluid with respect thereto.

Summaries of the Invention According to one aspect of the invention, energy conversion apparatus operable by a flow of fluid comprises endless travelling belt means and a plurality of inter-spaced hydrodynamic f6il members mounted on the endless belt-means whereby lift forces are generated by passage of fluid over the foil members and are made to drive the endless belt means.

The apparatus may include means controllably varying the angle of incidence of the foil members between a low value obtaining at a low fluid flow velocity and higher values obtaining at higher fluid velocities.

The apparatus may include start-up means to provide an initial movement to the foil members and, hence, of the endless travelling belt means, at low angles of incidence of the foil members i.e. at low fluid velocities. The start-up means may comprise a wind driven rotor coupled to the endless travelling belt means.

According to the invention also energy conversion means comprises: a rigid frame structure; first and second endless travelling belt circulating parts supported for rotation about a first axis defined in the said frame structure; third and fourth endless travelling belt circulating parts supported for rotation about a second axis defined in the said frame structure; a first endless travelling belt engaging the said first and third said circulating parts; a second endless travelling belt engaging the said second and fourth said circulating parts; a multiplicity of arm members distributed at intervals along the said endless belts, being each pivotally connected-to the said belts at spaced apart positions along the arm members; a multiplicity of hydrodynamic surfaces respectively supported by the said arm members; spring means linking the said endless belts; and a load in the form of a rotary member adapted to be driven by rotation of the said fourth wheel; the arrangement being such that lift forces acting on the said hydrodynamic surfaces, as a result of passaage of fluid over the said surfaces, causes the said arm members to pivot against the action of the said spring means, under the load of the said rotary member, about their connections with the said belts, thereby to cause the hydrodynamic surfaces to adopt an angle of incidence determined by the velocity of the fluid over the said surfaces and the lift velocity of the hydrodynamic surfaces.

The said spring means may link two belt circulating parts sharing the same axis. The said axis may be shared by the first and second said belt circulating parts.

The apparatus may comprise means operable in response to variation in fluid flow direction to orientate the hydrodynamic surfaces so as to maximise the lift forces developed thereon.

This aspect of the invention may be used to generate electricity, to pump water, or to propel a ship by coupling the endless belt means to a water-screw propeller.

According to another aspect of the invention, energy conversion apparatus operable on fluid comprises endless belt means, a plurality of inter-spaced foil members mounted on the endless belt means such that, when the endless belt means are driven, lift forces are generated by movement of the foil members through the fluid.

Means are preferably provided whereby the pitch of the foil members may be varied.

This alternative aspect of the invention may be used to propel a ship by disposing the foil members in water.

As used herein, the term "endless belt means" includes, ropes, cables, chains and like endless driven or drive means.

The invention also comprises any novel subject matter or combination including novel subject matter herein disclosed.

Brief Description of the Drawings Embodiments of the invention will now be described by way of-example only with reference to the accompanying drawings, wherein: Figure 1 is a side view, in section, of energy conversion apparatus, Figures 2 and 3 are side and front views of the apparatus, Figure 4 is a front view of a modified form of apparatus, Figure 5 is a section, taken on the lines D - D of Figure 4, Figures 6 and 7. illustrate the principle of operation of the arrangement, Figures 8 and 9 illustrate how pitch of a foil member is varied, Figures 10 and 11 illustrate details of the endless cable means, Figures 12 to 16 illustrate details of the yoke wheels and pitch control mechanism used by the apparatus, and Figures 17 to 20 collectively illustrate an alternative construction of the endless belt and associated circulating parts.

Detailed Descriptions of the Preferred Embodiments With reference to Figures 1 to 3, energy conversion apparatus 20 operable by a flow of fluid (wind) comprises a rigid frame structure S, endless travelling belt means 21 supported by the frame structure S, and a plurality of interspaced aerodynamic surfaces of foil members 22 mounted on the endless belt means 21 so that lift forces are generated by passage of wind over the foil members 22 and are made to drive the endless belt means 21. The foil members 22 are, in lateral cross-section, high speed aerofoils. The bights of the endless belt means 21, which is disposed substantially vertically, extend around belt circulating parts, being upper and lower parts of yoke wheels 23, 24. The frame S of the apparatus 20 incorporates a pillar 25 by which the apparatus is supported above the ground.

The endless belt means 21 comprises two endless cables 27, 28 arranged for movement in respective parallel planes, the cables extending round the upper and lower yoke wheels 23, 24 respectively mounted for rotation on horizontal shafts 29, 30.

The shaft 30 is connected to an electric generator 31 by way of a belt (32) and pulley (33) system, as well as a magnetic clutch 34. Tension springs are provided, (see Figures 8 and 13), which, acting through the endless belt means 21, serve to keep the foil members 22 thereof in a start-up condition, until the twin opposing forces of lift and reaction, (i.e. the load developed by the generator 31), cause the springs to stretch to the limits imposed by mechanical restraints of the linkage.

This is the maximum lift and maximum speed mode of the apparatus 20.

Thereafter when lift or reaction are absent the springs will return the foil members 22 to their original, i.e. startup positions.

Rotation of shaft 30 results in the production of useful electric power from generator 31.

A start-up propeller 35 is provided.

Figures 6 and 7 illustrate the principle of lift-force generation by a foil member 22. In Figure 6, a cantilevered arm 53 is disposed so that the leading edge of the foil member 22 it supports faces into the wind. The wind direction is indicated by arrow 45. The lift force acting on the foil member 22 is indicated by the arrow 47.

A component of the lift force 47 will act along the cable 28, and, as the belt means 21 begins to move along its path, the apparent wind direction changes and increases in velocity.

In response to these changes, the foil member 22 has to tilt toward the new apparent wind direction (45a - see Figure 7), and to the desired angle of incidence to it. Lift increases in proportion to the square of the velocity and continues to cause the cables 27, 28 to travel faster, reaching an optimum power condition when the lift force approaches an angle of approximately 82 to the cable, as shown in Figure 7. Beyond this point the now very large lift force would begin to lose effectiveness as its direction approaches one which is normal to its most desired direction, having zero effect at 850 or 860 and rapidly increasing negative influence from thereon. In comparison, the conventional windmill blade sees a changing speed along its length which reaches the maximum efficiency element but goes right on past it to the zero effect point mentioned above.The foil members 22 however, can be at or near this maximum efficiency setting over their entire lengths, giving an advantage over the windmill blade on an area-to-area basis of up to 6:1, in the case of a high speed aerofoil.

R.A.F. No. 15 is an example of such an aerofoil.

The apparatus 20 includes an upright, elongate rigid structure 50 (Figure 2) which also serves as a directional stabilizer structure. The structure 50 is in the form of a sheet metal, aerodynamic mast which is acted on by the wind so as to rotate the structure 50 and foil members 22 so that the foil members face into the wind as the wind direction changes.

As is seen in Figure 8, each foil member 22 is pivotally connected to cable 27 at one end of a cantilever arm 53 by pivot structure 54, and is pivotally connected intermediate the ends of arm 53 to cable 28 by pivot structure 55. The arm 53 is connected to the foil member 22 generally mid-way along the foil member and mid-way across the foil member. Movement of cable 27 relative to cable 28 will move the arm 53 so that the foil member 22 can move from a start, low-lift, position shown in chain-dotted lines, to a full-lift position shown in continuous lines. The tension springs described above bias the foil members to their start-up positions until lift fqrces generated by the wind flowing overcomes the spring force and can move the arm 53 until it meets a stop. All the arms 53 are moved together when cable 27 moves relative to cable 28.

Figures 10 and 11 illustrate another form of pivot structure 54 or 55. Stainless steel or "KEVLAR" (Registered Trade Mark) cable 27 has ends received on slotted eyelets 60 through which extend lugs 61 formed on connecting spaced plates 62 (stainless steel or titanium) which clamp between them a trunnion 63. The trunnion 63, in respect of the forward cable 28, is part of the arm 53, and, in respect of the aft cable 27, provides a pivot for the end of the arm 53. Snap rings (or "CIRCLIPS") 64 secure the end of arm 53 and both trunnions 63.

Rotation of the arm 53 in a trunnion 63 takes place whenever either of the couplings 54 or 55 precedes the other, either on to, or off of, the associated yoke wheel.

With cables 27, 28 in sections connected by the couplings 54, 55 assembly and replacement of parts is relatively easy and the size of the unit can be changed by adding or removing sections. Spacing of the foil members 22 is fixed.

Because the foil members 22 are spaced forward of the cables on arms 53, drag and turbulence in the region of the foil members is reduced.

The bias springs return the foil members 22 to their start-up or datum positions when the wind speed is too low to generate useful power.

The pitch of the foil members 22 is variable for two reasons: 1. Windmill/wind belt blades/foils are designed to operate at a certain speed relationship to the wind speed.

when that relationship is in the order of 9 to 1, the blade tip/foil chord (pitch) angle is close to being at right angles to the wind --(850).

After stopping due to lost wind, such an arrangement will not start up again for a light wind because the foil members will not develop enough lift whilst almost flat on to the wind.

The foil members must be partially feathered to start up or power must be applied through the generator 31 to get it moving.

2. Excessive winds will destroy the machine, so a means must be employed to limit the speed at which it may run. One way to accomplish this is to reduce the pitch angle so .that the foil members now run at a lower speed relationship to the wind.

In the case of the present invention, the pitch angle of a foil member can be reduced to zero, causing it to stop completely, if desired.

Three methods can, for example, provide the desired control. Feathering for start-up is achieved by resisting the lift leverage forces of a cantilever 53 with a spring. When there is little or no lift, the spring will return the foil member to a "start-up" position. When the wind picks up and lift forces cause the endless belt means 21 to start moving, increasing speed and lift will continue-to stretch the springs until the foil members 22 reach their maximum setting, when stop means arrest movement.

The pitch change system will maintain the foil members 22 at that setting, where they will run at a substantially constant ratio to the wind speed up to a certain maximum speed, as determined by the forces to be dealt with. At that point, a governor will commence to reduce the differential between the yoke wheel pairs 23, 24, thereby reducing the foil chord angle and the relative speed ratio to the wind.

Lift-generating attitudes are assumed during both forward and reverse runs of the endless belt means 21.

The yoke wheels 23, 24 are designed so as to accommodate relative vertical movement between the endless cables 27, 28.

With reference first to Figure 12, a wheel 24 is of spoked form, each of the spokes 70 thereof carries a pair of spacedapart studs 71, 72 to which the ends of tension springs 73 (Figure 13) are anchored. Each stud 71 is disposed on the far side of the wheel 24, whereas each stud 72 is disposed on the near side thereof.

Referring now to Figure 13, each pair of yoke wheels 24 (and similarly wheels 23) are coupled by the tension springs 73 which are disposed between the wheels. The springs 73 bias the wheels to positions whereby their spokes 70 are non-aligned as shown in phantom, i.e. zero pitch position of the foil members 22.

The front or drive wheel 24 is fixed to the shaft 30 and therefore will resist rotation through the magnetic particle clutch 34 and generator 31. This resistance enables foils 22 to enact a leverage through cantilevers 53 as shown in Figure 8, and in accordance with the force of lift being applied, will stretch the springs 73, permitting the drive (front) wheel to move ahead of the rear wheel, thereby changing the foil pitch.

Figures 14, 15 and 16 illustrate how (Figures 14, 15) the wheels of a yoke wheel pair 24 (or 23) can move relative to each other both axially and angularly on their common support shaft 30 and how (Figure 16) original settings of the wheels can be made.

With reference first to Figures 14 and 15, this apparatus acts to reverse the previously described pitch change when the wind speed exceeds a certain predetermined speed. Weights 81 are attached to force transposer wheels 82 which are mounted to the front yoke wheel 24. 'G' forces on the weights 81 tend to rotate the force transposer wheels which, through links 83, in turn tend to rotate the sleeve 84 and the clamp ring 85 clamped to it in an adjustable manner through ring adjuster 86.

Referring now to Figure 16, rollers 87 on the clamp ring 85 push against pins 88 extending from the rear yoke wheel 24, which is free to rotate and slide on the shaft 30 as the pitch of the foils 22 is reduced as wind speed increases further.

Referring to Figure 15, a spring ring 89 serves to retain the inner link pins 90 whilst set into a groove in sleeve 84.

A second groove set back from the first, allows pins to be extracted to link 83 release position but retains the pins in place.

As shown in Figures 1 to 3, a maintenance/safety platform 120 is secured below the upper end of the pillar 25. The platform 120 can be folded (as in Figures 2 and 3).

On start-up of the apparatus 1, the propeller 35 is turned by the wind. A centrifugal clutch 36 (Figure 1) is used to couple the propeller 35 with endless belt means 21 as soon as propeller speed allows. The clutch 36 can then be disconnected.

As the endless belt means 21 moves the foil members 22 take up "full-pitch" positions, against their tension spring loads. Angular movement between the wheels of wheel pairs 23, 24 then takes place, which movement is accommodated as explained above.

Figures 4 and 5 illustrate a modification provided with wind force booster means 100, comprising a funnel-like structure, (when viewed in plan), which causes the wind to increase speed over the foil members 22.

Referring, next, to Figures 17 to 20, in an alternative construction of the energy conversion apparatus, an endless travelling belt comprises a strong plastic belt 101 of e.g.

KEVLAR (Registered Trade Mark). The belt 101 has a multiplicity of thrust receiving portions 103 distributed at intervals therealong. Each thrust receiving portion 103 comprises two closely spaced transverse rib portions, 107a, 107b, respectively, integral with the main body 105 of the belt 101.

The belt 101 may support fixed pitch aerodynamic foils as 109t or it may support variable pitch foils as 111.

Fixed pitch foils, as 109, are bonded to side surfaces, as 113, of the belt 101 at right angles to the plane of the belt.

Variable pitch foils, as 111, are angularly displaceable about a hinge axis defined in the belt 101 at right angles to the plane of the belt.

In the arrangement of Figures 17 to 20 variable pitch foils 111 each carry a control vane 115 operable to vary the incidence of the associated foil 111, in dependence upon wind velocity. In Figures 17 and 18 the foil l11a is shown in the start-up position, and the foil lllb at maximum speed pitch.

Figures 19 and 20 contain a representation of the belt the circulating parts employed in connection with the belt of Figures 17 and 18. Here the circulating parts each comprise a spider shaped wheel 117. There is a hub portion 119 from which radiate the several legs 121 of the wheel. Each leg 121 has first and second portions 123a, 123b, secured to the hub portion 119 and each having a radial component of direction; and a longitudinally extending portion 125, integral with the outer extremities of the radial portions 123a, 123b, of a length equal substantially to the length of the thrust receiving portions 103 of the belt 101. The chordal distance between the portions 125 is equal to the spacings between the thrust receiving portions 103 of the belt 101.

In operation, the spider wheels 117 are driven by progressive engagement of the portions 125 between the transverse rib portions 107a, , 107b.

The foils, as 109, may be curved in cross-section and may have weakened portions 127 permitting the foils to snap fold in damaging winds.

Some of the advantages of the present invention, compared with the conventional windmill, are as follows: (a) An electrical generator can be disposed at the bottom of the apparatus instead of having to be at the top, reducing structural loading and simplifying maintenance.

(b) Area for area, a foil member 22 is several times as efficient as a windmill blade.

(c) Being able to reduce the total foil surface to about one sixth of that required for a conventional windmill blade sweeping an equivalent area, reduces the total foil member volume and mass to about a fourteenth. This mass is furthermore broken down into a greater number of foil components so that the sort of dynamic loading associated with a conventional windmill simply will not apply. Additional mass reduction will result from being able to fabricate the much lower stressed foil members with their non-catastrophic failure character, out of the lighter materials.

(d) Foil member pitch control allows the invention to operate in much higher wind speeds than can a conventional windmill.

(e) Because of the much simpler aspect of straight rather than circular deflectors, the invention is particularly suited to wind enhancement techniques. By channelling the adjacent wind outward behind the foil members, (using structure 100), a low-pressure area is created in the centre which speeds up the airflow-over the foil membe-rs. In-its most efficient arrangement, the means 100 could be expected to increase power in the same ratio that intersected area is increased.

Thus an increase in power can be obtained without additional dynamic components. Also, because all wind speeds are increased, the minimum effective wind speed instead of being about seven m.p.h., might now be lowered to perhaps 5 m.p.h. enhanced to 7 m.p.h.

(f) Deploying the invention in å "wind farm" situation would make better utilisation of the available acreage because its vertical disposition would allow it to intersect a greater cross-section of the wind, given the same spacing and the same width of sweep as blade diameter for the conventional windmill.

The actual extent of the improvement would be determined by the maximum height to width ratio to which the invention can be economically built.

(g) The invention is expected to be more responsive to wind direction changes without inducing high stresses due to blade precession.

(h) The apparatus 1 could throw (i.e. lose) a foil member 22 with no more effect than reduced power.

(i) Pitch control is automatic partly through the spring versus lift force arrangement.

(j) Expansion of an apparatus 1 is possible up to some maximum height as determined by future tests.

(k) Start-up is automatic partly through the multibladed, coarse pitch, start up rotor.

(1) The maintenance/safety platform 120 together with the lighter nature of components in general will ease construction and maintenance.

The invention is not confined to the conversion of wind energy, or indeed air as a driving fluid. In a modified form, it may be driven for example, by river water flow or by tidal streams.

It may also be "reversed" by driving the endless belt means whereby the apparatus may be used for propulsion.

Claims (11)

1. Energy conversion apparatus operable by a flow of fluid comprises endless travelling belt means and a plurality of inter-spaced hydrodynamic foil members mounted on the endless belt means whereby lift forces are generated by passage of fluid over the foil members and are made to drive the endless belt means.

2. Energy conversion apparatus as claimed in claim 1 comprising means controllably varying the angle of incidence of the foil members between a low value obtaining at a low fluid flow velocity and higher values obtaining at higher fluid velocities.

3. Energy conversion apparatus as claimed in claim 2 including start-up means to provide an initial movement to the foil members and, hence, of the endless travelling belt means, at low angles of incidence of the foil members i.e. at low fluid velocities.

4. Energy conversion apparatus as claimed in claim 3 in which the start-up means comprises a wind driven rotor coupled to the endless travelling belt means.

5. Energy conversion apparatus which comprises: a rigid frame structure; first and second endless travelling belt circulating parts supported for rotation about a first axis defined in the said frame structure; third and fourth endless travelling belt circulating parts supported for rotation about a second axis defined in the said frame structure; a first endless travelling belt engaging the said first and third said circulating parts; a second endless travelling belt engaging the said second and fourth said circulating parts; a multiplicity of arm members distributed at intervals along the said endless belts, being each pivotally connected to the said belts at spaced apart positions along the arm members; a multiplicity of hydrodynamic surfaces respectively supported by the said arm members; spring means linking the said endless belts; and a load in the form of a rotary member adapted to be driven by rotation of the said fourth wheel; the arrangement being such that lift forces acting on the said hydrodynamic surfaces, as a result of passaage of fluid over the said surfaces, causes the said arm members to pivot against the action of the said spring means, under the load of the said rotary member, about their connections with the said belts, thereby to cause the hydrodynamic surfaces to adopt an angle of incidence determined by the velocity of the fluid over the said surfaces and the lift velocity of the hydrodynamic surfaces.

6. Energy conversion means as claimed in claim 5 in which the said spring means links two belt circulating parts sharing the same axis.

7. Energy conversion means as claimed in claim 6 in which the said axis is the axis shared by the first and second said belt circulating parts.

8. Energy conversion apparatus as claimed in any of claims 5 to 7 which comprises means operable in response to variation in fluid flow direction to orientate the hydrodynamic surfaces so as to maximise the lift forces developed thereon.

9. Energy conversion apparatus operable on fluid comprises endless belt means, a plurality of inter-spaced foil members mounted on the endless belt means such that, when the endless belt means are driven, lift forces are generated by movement of the foil members through the fluid.

10. Energy conversion apparatus as claimed in any of claims 1 to 4 substantially as hereinbefore described with reference to Figs. 1 to 7 or with reference to Figs. 1 to 7 and Figs. 17 to 20.

11. Energy conversion apparatus substantially as hereinbefore described with reference to the accompanying drawings.