Background of Invention Wind turbine generators, from wind mills used for the milling of grain all the way to the generation of electrical power, rely on blades having an aerofoil design. That is, the blades receive a flow of air from the wind causing rotation of a rotor due to a pressure differential across the blade. Accordingly the rotor blade acts in a similar fashion to the wings of an aircraft or the rotor of a helicopter.

Wind turbine generators may have a horizontal axis about which the rotor rotates or vertical axis with the rotor blades adopting different configurations based upon the different axes. Nevertheless, the function is much the same and categorizes wind turbines as "reaction" turbines in that torque is generated through an interaction between the rotor blades and a change in the pressure of the fluid.

The result is the need for extraordinarily large rotor blades and consequently very tall towers in which to support the rotor. This leads to significant infrastructure costs not to mention the cost of transport from the factory to the site of the wind turbine generator. Statement of Invention

In general terms the invention provides an impulse wind turbine generator comprising a rotor fixed to a shaft said rotor having a plurality of arms, each arm having a wind receiving recess such that an air flow co-planar with and directed towards the rotor is received by the recess.

In a first aspect the invention provides an impulse wind turbine generator comprising a rotor fixed to a shaft said rotor having a plurality of arms, each arm having a wind receiving recess such that an air flow co-planar with and directed towards the rotor is received by the recess a generator coupled to the shaft and a frame supporting said shaft, wherein said frame is arranged to selectively move the shaft vertically. An impulse turbine is defined as a turbine receiving energy from a change in

momentum as a result of a fluid impinging upon an arm of the rotor of said turbine. This differs from the reaction turbine which functions through a change of pressure of said fluid. Conventional wind turbine generators as mentioned are reaction turbines even though a small proportion of impulse is also received. Thus an impulse turbine is defined as that having a substantial proportion of the energy imparted through said change of momentum.

Accordingly, the present invention is an impulse wind turbine generator in that it receives airflow from the wind into recesses of the arms of the rotor. As the wind is caught by the recesses, nevertheless, the energy lost in this change of momentum drives the rotor and consequently produces energy.

An important aspect of an impulse turbine is receiving sufficient fluid bearing upon the rotor. To this end wind guides may be incorporated so as to direct a proportion of a wind driven airflow larger than the area defined by the receiving arms of the rotor. To this end, any such guide may be continuous, or partially continuous, to minimise fluid losses in the guidance of the airflow. Thus by providing an impulse wind turbine generator, the need for manufacturing and transporting extraordinarily large components may be avoided.

The shaft and rotor, or rotors, may be selectively adjustable in the vertical direction so as to raise and lower said shaft and arms to maximize the flow of air into the receiving arms.

In one embodiment there may be a plurality of rotors mounted to the shaft so as to increase the torque applied to the shaft, and subsequently, the power generated by the system.

In one embodiment the shaft and rotors may be mounted to a structure so as to shield the arms on the returning path of the rotor. Said shielding may include mounting the shaft and rotors such that at least the bottom half of the rotor is beneath the ground or within an enclosure preventing the airflow impinging on the returning arms. In a further embodiment the returning arms may be protected by a structure which in addition to shielding also guides the flow of air towards the receiving arms so as to direct a greater flow of air to the rotor. In an alternative arrangement, the wind guide and shield may be separate elements or assemblies, such that the shield is substantially fixed to the structure and the wind guide is movable relative to the structure. In this arrangement, the wind guide may be a relatively light member so as to permit selective movement of the wind guide for optimum use, without the need for significant force, as may be required to move the frame. This movement may be through a hinged connection to provide such function.

In a further embodiment the guide may be pivotally mounted to the frame from a first position resting against the shield, to a position parallel to the incident wind direction. . The guide may further include side panels and/or an upper panel for directing adjacent portions of the wind flow into the path of the receiving arms. Thus, in a further embodiment, the guides may form a wind tunnel, having a relatively large opening, and a profiled tunnel for guiding the airflow in a progressively smaller area until directed onto the rotor.

In a further embodiment the shaft and rotors may be selectively adjustable in the vertical direction so as to raise and lower said shaft and arms to maximize the flow of air into the receiving arms.

The weight of the rotors may be arranged so as to act as a flywheel. That is, once rotation commences, momentum of the rotors may be such that a more uniform torque is achieved. The weight of the rotors may be achieved through a relatively large rotor. Alternatively, the rotor may have a substantial proportion of weight located proximate to the extreme ends, or peripheral end, of the arms, so as to best maximise torque. In a further embodiment, the weight may be achieved by a plurality of relatively light rotors, mounted to the shaft, and so providing a substantial weight cumulatively.

In a still further embodiment, a proportion of the weight of the rotor may be selectively movable along the axis of the arms. Such a weight distribution system may be achieved through a rotatable screw threaded rod mounted on each arm, having one or more weighted objects in screw threaded engagement with the rod, but fixed from rotation. On activation of the rod, the weights may then selectively move along the rod.

Such a system may be operator controlled, or part of the control system to automatically move the weights to the desired to position on the arms. For instance, the generator may include a coupling system to manage power transmission to maintain power output across a range of wind speeds. In this way the coupling is able to absorb fluctuations in wind speed to provide an optimal power output.

Such adjustment may include adjustment of the weight distribution system which in turn may increase or decrease applied torque.

Alternatively, or in combination, such a coupling may include a differential gear arrangement positioned within a drive train of the generator, and arranged to vary the transmission ratio to the generator. Operation of the coupling system, and therefore either or both the transmission ratio or weight distribution system, may be a function of instantaneous and/or average wind speed, variability of wind speed, required power output or other parameters. This is not an exhaustive list of parameters, with the possibility of other internal and external parameters also providing an influence.

With regard to the weight distribution system, the movement of the weights, and so adjustment of the torque applied to the shaft, may be a function of the wind speed, rated load of the system, grid capacity etc. For an automatic control system, the parameters may be received from an appropriate sensor, than the control system activate the weight distribution system in a closed loop arrangement, or accept some or total operator input.

It will be appreciated that the impulse wind turbine generator according to the present invention may be constructed using a vertical axis rather than a horizontal axis. The limitations on the length of blades for conventional wind turbines are avoided due to the shorter required length of an arm according to the present invention compared to the very long blades of the conventional type. In a second aspect, the invention provides an impulse wind turbine generator comprising a rotor fixed to a shaft; said rotor having a plurality of arms, each arm having a wind receiving member mounted at a distal end of said arm such that an air flow co-planar with and directed towards the rotor is received by the member; a generator coupled to thø shaft and; wherein the member is in pivotal engagement with said arm.

In a further embodiment, the arms of the wind turbine generator may include a member at the extreme, or distal, end to receive the wind load. The member may be sized to maximise the wind receiving area, and so transmit an optimised force to generate a torque. As the member is pivotally engaged, the area exposed to an incident air flow from the wind may bear on as much of the full face of the member as possible. As the pressure imparted to the member is defined by the area perpendicular to the air flow, if the member can be pivoted to a position perpendicular to the air flow during the portion of the turbine rotation, then it follows that the maximum pressure will be imparted.

In a further embodiment, the portion of rotation of the generator may be from 0° to 90°, and so the first quarter rotation. To do this the member must pivot at a rate

corresponding to the rotation of the turbine. One such way of achieving this is to include weights on the member, so that gravity swings the member to the vertical position.

Alternatively, an assembly may be used to bias, or force, the member to the vertical position, or other such position depending upon the direction of wind generated air flow. That is, the angle between the wind receiving members and the supporting arms vary as the arms rotate.

In a further embodiment, a bearing assembly may be used to bias the members into a perpendicular position to the wind/air flow. In a further embodiment, the shaft supporting the one or more rotors may be connected to generators at each ends. Further, the generators may be different in that, for low wind flow, such as less than 2 m/s, a low torque generator may be used. At the opposed end, a high torque generator may be used for when the wind speed exceeds this limit. It will be appreciated that the specific 'change over" wind speed may depend upon the application, location of the wind turbine and so may be more or less than 2 m/s.

To assist in the connection between the shaft and generators, gear boxes having appropriate gear differential may be used. In a further embodiment, there may be a control system for switching between the generators. Said control system may receive an input on torque from the wind turbine, and switching based upon a threshold torque. Alternatively, the control system may switch based upon a threshold rotational speed of the shaft. Further still, the control system may be connected to an anemometer, or other wind speed measuring device, and switch based upon direct wind speed input.

Brief Description of Drawings

It will be convenient to further describe the present invention with respect to the accompanying drawings that illustrate possible arrangements of the invention. Other arrangements of the invention are possible and consequently the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention. ^" Figure 1 is an elevation, view of the impulse wind turbine generator according to one embodiment of the present invention;

Figure 2 is an elevation view of the impulse wind turbine generator according to Figure 1;

Figure 3 is an exploded view of a rotor mountable to a shaft according to a further embodiment of the present invention; Figure 4 is a sectional view of an arm of a rotor according to further embodiment of the present invention;

Figure 5 is an elevation view of a wind turbine according to a futher embodiment of the present invention, and;

Figure 6 is a plan view of a wind turbine according to a further embodiment of the present invention.

Detailed Description

Figures 1 and 2 show an impulse wind turbine generator 1 according to one embodiment of the present invention. Here a rotor 5 is mounted to a shaft 20 which in turn is coupled to a generator 25. Rotation of the rotor 5 defines a plane parallel to the direction of the incident wind direction, whereupon the rotor 5 is arranged to receive airflow 30 from the wind which contacts the arms 10 of the rotor 5 to rotate 35 the rotor in a clock wise direction. Unlike a reaction wind turbine generator, the airflow 30 is received within recesses (not shown), imparting the wind energy to the rotor 5 through a change of momentum of said airflow 30.

The shaft 20 is mounted to a frame 50 and in particular, upon a platform 70 so as to maintain the rotor 5 above the ground, which avoids turbulence and a reduced input capacity through boundary effects with the ground. In this embodiment the frame 50 is in fact a parallelogram linkage of members with an actuator 55 mounted thereto. On activation of the actuator 55, the ram extends or retracts 60 causing rotation 65 of the linkage members so as to lift or lower the platform 70, and consequently the rotor 5. This permits the operator to selectively position the rotor 5 at the optimum height so as to receive the optimum torque. The selective adjustment of height may be used for initialising the system when established at a new site or maybe in conditions where height adjustment may be necessary due to differential airflow conditions at the site.

It will be appreciated that with an impulse wind turbine generator such as that shown in Figures 1 and 2, one half of the rotor will have receiving arms 10 and the other half will have returning arms 15. The returning arms 15 would normally travel into the wind and so counter the wind generated rotation 35. In this embodiment the frame 50 further includes a barrier 45 which prevents wind contacting the returning arms 15. And further, in this embodiment, a wind guide 46 adjacent to the barrier 45 acts to guide the a portion of the airflow, 31 towards the receiving arm 10 and so enhance the efficiency of the wind turbine 1 by maximizing airflow 30, 31 to the receiving arms 10. Said wind guide 46 may be selectively movable 47 so as to direct wind 31 based on a signal from a control system 64 to an actuator 48. The control system may include a coupling for receiving parameters such as wind speed etc and control transmission ratio or the wind guide based on optimising the power output from the wind generator. Such parameters may be received from strategically placed sensors for wind speed, torque of the shaft etc. Whilst the embodiment in Figures 1 and 2 show one rotor only mounted to the shaft 20, in fact several rotors may be mounted to a single shaft so as to benefit from the airflow. In this way a greater torque will be applied to the shaft and thus further increase power generation. Further still, with only one wind guide shown in Figures 1 and 2, in fact other wind guides could be possible such as from the side or above the rotor and so direct a greater volume of airflow into the rotors to again increase torque for the increase in power generation. A plurality or assembly of guides may be used to create a wind tunnel for directing airflow to the rotors.

Figure 3 shows one embodiment of the mounting of the rotor 5 to the shaft 20. Here the shaft 20 is a modular construction whereby the rotor 5 includes a hub 75 to which the arm 10 is mounted. The hub 75 acts as a portion of the shaft allowing a bolted connection to the shaft 20 to shaft flanges 80A and 80B. Such a modular construction of the shaft allows the removal and replacement of a damaged rotor without having to dismantle the entire wind turbine generator and so reducing maintenance costs and maximizing online capacity of the power generation. It also permits the modular construction of a wind turbine generator by allowing the shaft/rotor assembly to be constructed for a plurality of rotors, without the need for different materials. Accordingly, a customised approach may be used with such a modular construction. A characteristic of the impulse wind turbine generator according to the present invention is having arms 85 with wind receiving recesses 90 as shown in Figure 4. In order to receive the airflow, the arms must include a recess so as to ensure the

"impulse" from the change in momentum of the airflow is captured and converted to kinetic energy of the rotor.

Figure 4 shows one embodiment of the recess 90 maximizing the size of the recess 90 by including the full length of the arm 85.

To reduce windage losses, the opposed face 95 of the arm 85 has been shaped so as to reduce rotational air dredge. In this case the arm is triangular shaped which reduces the coefficient of drag Ca of each arm. It will be appreciated that the arms may further be shaped to reduce cross sectional area which is also a factor in rotational air drag. The reduction in area of the arm will of course be balanced against maximising the size of the recess 90 and so balance capturing the change in momentum of the airflow against the reduction of rotational air dredge through a large cross sectional area of each arm 85.

In a further embodiment shown in Figure 4 to permit escape of the airflow 105, a vent 100 is provided adjacent to the hub 75 of the rotor 5. In this case the airflow 105 is received within the recess 90 and permitted to escape through the vent 100 into the hub 75 and allowed to exit through a hallow shaft 20. Thus momentum transfer is maximised without creating a high pressure zone within the recess 90 which may hinder the efficiency of the airflow capture.

In a further embodiment, the recess 90 may further be profiled so as to provide a continuous internal surface of the recess and so reduce losses during the transfer of momentum. In a further embodiment, the arm may further include a weight distribution system whereby weight may be selectively distributed along the arm so as to maximum torque subject to strength of the airflow impinging on the wind turbine generator. For instance, in very high wind conditions, weight may be redistributed to the periphery of the rotor, i.e. the extreme end of each arm and so turn the rotor into a hybrid flywheel.

Figure 5 shows a further embodiment the wind turbine generator 500. The rotor 501 is mounted to a horizontal shaft 520 which in turn is coupled to generators (not shown) at both ends. Rotation of the rotor 501 shows when the wind flow directing at 0°the rotor turns counter-clockwise direction. On the other hand, when the wind flow at 180°, as the wind direction indicator will track and turn the wind mill to the incident wind directly.

Figure 5 shows the rotor 501 turns clock wise with respect to the previous direction. The blades, or members 502, are engaged through by a moveable item, for example, bearing 503 which is mounted to the support arms 504. The limits of the blades are set by the limiters 505 which provide the angle of contact to the incident wind flow.

The balancers 506 & 507 are mounted at each side of the blades. The first balancer, which maybe weights 506 provide the blades laying positions after 90°. The weights 506 ensure the blades are in up right (vertical) position and make direct contact to the incident wind. The second balancer 507 at the other side of the blades serves to turn the blades after 180°position. The weights from the blades 502, the balancers 506 & 507 form a balance assembly. The balance assembly times the length of the supporting arms 504 will be the amount of the torque generation to the mill.

Figure 6 shows a wind turbine 600 according to a further embodiment. Here the wind turbine 600 includes a plurality of rotors 605 mounted to a shaft 610. At each end of the shaft there are located two generators 615 A, B, which are in communication with a control system 620.

The generators are of different form whereby the first generator 615 A is a low torque generator arranged to operate under very low wind speeds, such as 2 m/s. The control system may be connected to an anemometer (not shown) which provides direct wind speed data to the control system. When the wind speed falls below this threshold, the control system switches operation from the primary generator 615B to the low speed generator 615A so as to maintain a power output over a much wider range of conditions. Subject to the application or location, the threshold may be arranged at a higher or lower level so as to optimize the extended wind speed range over which the wind turbine can operate. For instance, in conditions where wind speed undergoes very wide variation, a third or more generator(s) may be used to extend the operable range further.