GB2094408A - Wave-powered orbital electrical generator - Google Patents

Abstract

An electrical generator apparatus is provided for installation on a floating structure to extract useful energy from the action of waves on the structure. The apparatus comprises a weight 15 mounted for rotation about a vertical shaft 2 with its centre of gravity offset therefrom whereby any non-vertical motion of the floating structure causes orbital movement of the weight 15 about the shaft 2. Coupling means 18 serve to transmit movement of the weight 15 to the rotor 8 of the electrical generating part of the apparatus. These coupling means 18 may, for example, comprise a lost- motion coupling or an hydraulic circuit. Energy storage means can be provided to smooth the flow of energy from the orbital weight to the rotor 8. <IMAGE>

Description

SPECIFICATION Wave-powered orbital electrical generator The present invention relates to a wavepowered electrical generator for use, for example, on board a sea-going vessel for continuously recharging the vessel's battery.

Sea-going vessels and other floating structures undergo complex motions due to the action of the sea thereupon. For a sailing vessel, the motion of the vessel will include components such as elliptical motion of the vessel's centre of gravity in a vertical plane due to normal wave motion, rotation of the vessel about its centre of gravity in a manner dependent on its buoyance distribution (affected by the angle of heel of the vessel) and the heading of the vessel relative to the wave direction, and movements caused by the action of the wind on the sails in combination with the effect of keel reaction. The pattern of the waves themselves will generally also be a compound one.

The actual displacements experienced at a particular point on a vessel will generally be proportional to the distance from the vessel's centre of gravity. For a typical sea-going sailing boat of 10 metres length, a beam roll of 100 may produce a lateral or rotational deck velocity of 11 km/h at its maximum in moderate seas.

It is well recognised that a considerable amount of energy is available for extraction from the motion of the sea and a number of proposals have been made in the past for utilising this energy for the generation of on-board electrical power.

However, known wave-powered electrical generators generally exhibit one or more of the following drawbacks, namely, technical complexity, undue size, lack of responsiveness to gentle sea swells, high initial and maintenance costs, and difficulty of installation.

It is an object of the present invention to provide a wave-powered electrical generator which is economic, simple in form and easy to install.

According to the present invention, there is provided, a wave-powered orbital electrical generator for installation on a floating structure subject to the action of wave motion, said generator comprising: a support structure; an electric machine including a stator fixedly mounted on said support structure, and a rotor mounted for rotation relative to the stator; a weight mounted for rotation about an axis with its centre of gravity offset therefrom, said support structure being intended for secural to said floating structure such that said axis extends substantially vertically in the absence of any wave motion, whereby in use of the generator, any nonvertical motion of the floating structure is effective to cause orbital movement of the weight around the axis; and coupling means coupling the said weight and rotor such as to enable movement of the weight to be transmitted to the rotor.

In the presence of waves, the floating structure exhibits complex motion which results in continually-reversing orbital movement of the weight about the said axis. Even a simple tilt motion of the structure will result in the weight oscillating like a pendulum. The movement of the weight is transmitted to the rotor as a result of which electrical power is generated.

In one embodiment of the orbital generator, the rotor is carried on a shaft coaxial with said axis, the weight being also supported on said shaft.

However, it is also possible to arrange for the weight and rotor to rotate on separate non-coaxial shafts.

Advantageously, the said coupling means comprise an arcuate lost-motion coupling. The use of a lost-motion coupling increases the efficiency of the generator by minimising the dwell time of the weight and rotor at a top dead centre position and by improving their acceleration away from such a position; reversal of the direction of rotation is also facilitated.

Where a lost-motion coupling is employed and the rotor and weight are supported on a common shaft, the weight can be carried at one end of an arm which is centrally rotatably mounted on the shaft. The other end of the arm is provided with a pin which engages in an arcuate slot formed in the body of the rotor. Of course, the location of the slot and pin can be reversed so that the pin is carried by the rotor and the slot is formed in the arm. Whichever of these two arrangemenis is adopted, the arcuate length of the slot is preferably made adjustable and is set in accordance with the motion characteristics of the floating structure mounting the generator.

In order to cause the rotor to be more smoothly driven from the orbital weight, the coupling means can comprise energy storage means arranged to receive the random energy inputs from the weight while outputting a more constant flow of energy to drive the rotor. These energy storage means may take the form of a coil or torsion bar spring arrangement together with means for converting bi-directional movement of the weight into unidirectional movement winding up the spring arrangement.

Where the coupling means comprises an hydraulic circuit including a pump driven by the weight and a motor driving the rotor of the electric machine, the energy storage means can advantageously be provided in the form of an hydraulic accumulator inserted in the hydraulic circuit between the pump and the motor.

Advantageously, the generator is provided with an auxiliary weight pivotally supported for outward radial movement at the end of an arm mounted for joint rotation with the main weight.

The auxiliary weight swings outwards as the arm rotates and serves as an energy store from which energy is supplied to assist the rotation of the arm and the main weight during periods of deceleration. The auxiliary weight can be carried at the end of its mounting arm by a universal joint permitting both radial and tangential motion of the auxiliary weight. Preferably, the angular position of the auxiliary weight about said axis is made adjustable relative to the position of the main weight, whereby to enable the generator to be at least partially tuned to the motion characteristics of the floating structure provided with the generator.

Various other novel aspects and features of the invention will become apparent from the following description, given by way of example, of four embodiments of a wave-powered orbital electrical generator, reference being made to the accompanying diagrammatic drawings, in which: Figure 1 is a plan view of a first embodiment of the generator; Figure 2 is a side elevation of the Figure 1 generator; Figure 3 is a section on line Ill-Ill of Figure 1; Figure 4 is a voltage-time graph of the output of the Figure 1 generator; Figures 5 and 6 respectively show second and third embodiments of the generator each incorporating a different form of energy storage means; Figures 7 and 8 are plan and elevational views respectively of a fourth embodiment of the generator provided with an auxiliary weight; and Figure 9 shows a spring-resisted lost motion coupling connecting the main weight of the generator of Figures 7 and 8 to an arm carrying the auxiliary weight.

The orbital electrical generator shown in Figure 1 comprises a circular base 1 carrying an upstanding shaft 2. The base 1 is intended to be mounted on a vessel or other floating structure such that the axis of the shaft 2 extends substantially vertically when the floating structure is motionless.

The shaft 2 is rigidly secured to the base 1 with a frusto-conical portion 3 of the shaft 2 locating in a central frusto-conical aperture 4 of the base 1. A nut 5 threadedly engages a screw-threaded end portion 6 of the shaft 2 and is tightened up against the underside of the base 1 to firmly engage the frusto-conical portion 3 with the walls of the aperture 4.

The stator 7 of an alternator is mounted on the base 1 concentric with the shaft 2. The rotor 8 of the alternator is rotatably mounted on the shaft 2 by means of a ball bearing 9. The rotor 8 carries a plurality of permanent magnets 10 arranged to cooperate with windings 11 of the stator 7 to form a multi-pole alternator. Preferably the pole spacing is approximately three degrees of arc and the windings 11 are arranged as three-phase windings. The body of the rotor 8 is formed with a circular array of ventilation apertures 12.

Above the rotor 8, the shaft 2 rotatably mounts an arm 13 by means of a pair of ball bearings 14. The arm 13 extends on both sides of the shaft 2 and is rigidly connected at one end to a massive weight 1 5 by bolts 1 6 and a iocating pin 1 7. The opposite end of the arm 13 is coupled to the rotor 8 by an arcuate lost-motion coupling 1 8 which is constituted by a pin 1 9 rigid with the arm 13 and extending parallel to the shaft 2, and an arcuate slot 20 formed in the upper surface of the body of the rotor 8.

The arcuate length of the slot 20 is made adjustable by means of an arrangement comprising a movabie end stop 21, and a bolt 22 extending through the walis of the slot 20 in threaded engagement therewith. The end stop 21 is captively mounted at the end of the bolt 22 located within the slot 20. The position of the stop 21 within the slot 20 is adjusted by rotation of the bolt 22. A lock nut 23 serves to lock the bolt 22 in place once the desired position for the stop 21 has been reached.

The stator windings 11 are connected to a fullwave rectifier unit (not shown) to provide a D.C.

electrical output. The alternator and rectifier unit are preferably enclosed within a water-tight housing to protect them from the elements.

Operation of the orbital generator will now be described.

The generator is, for example, secured to the deck of a sea-going sailing boat for the purpose of automatically recharging the boat's battery. As discussed previously, the deck of a sea-going vessel undergoes very complex motion. The present generator is arranged to convert components of this motion into rotation of the alternator rotor 8 by means of the rotatably mounted eccentric weight 1 5 which is alternately accelerated and decelerated in lagging phase relation with respect to the lateral deck motion.

The weight 1 5 effectively acts as an orbital pendulum executing a continually reversing orbital motion relative to the shaft 2; this motion is transmitted to the rotor 8 via the lost-motion coupling 18. Considering the typical situation of a sailing boat (or, indeed, a moored buoy), heeled over in the wind at a substantial angle, the weight 15 will move to the leeward side of the shaft 2 and swing fore and aft like a simple pendulum in response to pitching and other movements of the boat.

The coupling 1 8 acts to minimise the dwell time of the rotor 8 and weight 1 5 at the metastable top-dead-centre position, the stability of which is aided by the rotor-stator drag; due to the presence of the lost-motion coupling 18, the weight is free to move from the top-dead-centre position under its own momentum and to thereafter re-engage the rotor 8 for continued joint rotation. The overall resulting effect on the generator output of the provision of the lostmotion coupling can best be appreciated by reference to Figure 4 which is a graph of generator output against time for the situation where the weight 15 is moving off from a top-dead-centre position.

In Figure 4, the curves X and Y both represent the rise in generator output from zero as the weight 1 5 and rotor 8 accelerate from rest starting at T,. The dashed curve Y corresponds to the case where the weight and rotor are rigidly connected to each other. As can be seen, in this case the output voltage increases only slowly due to the slow acceleration of the rotor and weight; maximum output voltage is achieved after time T3 from the start of movement from top-dead-centre position. The continuous curve X corresponds to the case where the weight and rotor are coupled by a lost-motion coupling such as shown in Figures 1 to 3; in this case, the weight 1 5 accelerates free of the rotor 7 until it re-engages with the latter at time T,.The momentum of the weight 1 5 causes a rapid acceleration of the rotor 7 and thus a rapid increase in the generator output voltage which reaches its maximum at time T2.

The area A lying between the two curves X and Y is representative of the additional electrical energy extracted from the wave motion due to the provision of the lost-motion coupling 1 8.

The arcuate length of the slot 20 of the coupling 1 8 is adjusted in accordance with the motion characteristics of the vessel mounting the generator.

It will be appreciated that the rotor 8 will rotate at widely varying speeds with random reversal of its rotational sense. Unless corrective steps are taken, the output of the rectifier unit will also vary widely; in order to render the output of the unit more suitable for use in battery recharging, the rectifier unit is preferably provided with voltage limiting circuitry. Furthermore, the stator 7 can be provided with a neutralizing winding on the lines of a compound D.C. dynamo electrical machine in order to suppress output peaks and also: i) to remove peak loading on the weight 1 5 and consequent absorption and waste of power and irregular rotation; ii) to assist reversal of rotation; and iii) to enable the mass of the weight 1 5 to be minimised.

A light duty "trickle charge" winding and circuit can be incorporated for light sea or sheltered mooring conditions.

From the foregoing it can be seen that the Figure 1 generator is of a simple, rugged construction with only two moving parts. A generator of this form is thus easy to install and maintain which is highly desirable for generators intended to be used on sea-going vessels and other floating structures (such as beacons and buoys). The Figure 1 generator is substantially silent in operation and produces no significant destabilising effects on the floating structure to which it is secured.

Although the provision of the lost-motion coupling 1 8 is advantageous, the weight and rotor can be rigidly connected if so desired.

In order to enable better control of the generator output voltage, the coupling means coupling the weight 1 5 to the alternator rotor 7 may include energy storage means for smoothing the energy flow from the randomly moving weight 1 5 to the rotor 7. These energy storage means preferably incorporate control means for governing the output of energy to the rotor 7 such that the alternator output voltage is maintained between minimum and maximum limits when the alternator is operating.

Figures 5 and 6 show two embodiments of the orbital generator each provided with a different form of energy storage means incorporated in the coupling means between the weight 1 5 and the alternator (for the sake of clarity, the weight 1 5 and its carrying arm 13 are only shown dashed in Figures 5 and 6). It will be noted that in these embodiments of the generator, the alternator is arranged with its axis offset from that of the shaft 2 rotatably supporting the weight.

In the Figure 5 embodiment, the energy storage means comprises a coil spring housed within a spring drum 50. One end of the spring is connected to the spring drum 50 while the other end is connected via a ratchet mechanism 61 to the shaft 2 which rigidly mounts the arm 13. The ratchet mechanism 61 is a double-acting ratchet arrangement which converts the bi-directional oscillating movement of the arm 1 3 into movement in one rotational sense only; as a result, the random movement of the weight 1 5 is harnessed to wind up the coil spring. The spring drum 50 rigidly mounts a toothed gear 52 which meshes with a gear 53 carried on a shaft 54. The shaft 54 also carries a second gear 55 which is fast for rotation with the gear 53 and meshes with a pinion 56 rigidly mounted on the rotor shaft of the alternator 57.Unwinding movement of the coil spring is thus transmitted via the drum 50, the gears 52, 53, and 55, and the pinion 56 to the alternator 57. The maximum speed of rotation of the alternator (and therefore its maximum output voltage) is controlled by a centrifugal governor 58 which is driven from the shaft 54 via a worm wheel and gear arrangement 59. Mechanical means (not shown) can be provided which in response to the coil spring expanding to a certain diameter (corresponding to a particular degree of unwinding) is operative to lock the drum 50 against rotation until the spring has been further wound up; by such means, the alternator voltage can be prevented from falling below a given value during driving of the alternator.

It would, of course, be possible to use torsion bar springs for storing energy rather than coil springs. Thus, for example, three parallel, side-byside torsion bars could be drivingly connected in series by pairs of meshing gears with one end of the bar series being coupled to the shaft 2 carrying the weight 1 5 and the other end to the alternator.

Preferably the coupling between the torsion bars and shaft 2 is such that bi-directional movement of the weight 1 5 and shaft 2 is converted into unidirectional rotational movement of the bars, a double-acting ratchet mechanism being suitable for this purpose. In operation, energy is input into the torsion bars from the randomly moving weight 1 5 via the ratchet mechanism. This energy is then output to drive the alternator, the maximum rotational speed of which is controlled by a governor. Control means can be provided wtiich, in response to the alternator speed or output voltage falling below a certain minimum value, operate a brake to halt the alternator, the brake only being released when the torque exerted thereupon reaches a certain value.

The embodiment of Figure 6 differs from those previously described in that the oscillating weight 1 5 is coupled to the alternator of the generator via an hydraulic circuit rather than by a mechanical transmission. As a result, the provision of energy storage means is readily effected using an hydraulic accumulator.

Referring in detail now to Figure 6, the shaft 2 which rigidly mounts the arm 13 and weight 15, is connected to the input shaft of an hydraulic pump 70. The pump 70 communicates on its inlet side with an hydraulic fluid reservoir 71 and on its outlet side with an hydraulic accumulator 72 in the form of a pressure vessel containing a predetermined amount of a compressible fluid (for example, a gas insoluble in the hydraulic fluid).

The pump 70 is of such a form that fluid is pumped from the pump inlet to the pump outlet by rotation of the input shaft in either sense. The hydraulic accumulator 72 communicates via a control valve 75 with an hydraulic motor 73 and, via a pressure-relief valve 74, with the reservoir 71. After passage through the motor 73, the hydraulic fluid is returned to the reservoir 71. The motor 73 is arranged coaxially with the alternator 57 and is coupled to the rotor of the latter.

In operation of the Figure 6 embodiment, the random movement of the weight 1 5 serves to drive the pump 70 and cause a build up of fluid under pressure in the accumulator 72. Upon a certain minimum pressure being established in the accumulator 72, the control valve 75 opens to permit fluid to flow therethrough to the hydraulic motor 73; as a result the motor 73 rotates and drives the alternator 57. The build up of excessive pressures in the accumulator is prevented by the pressure relief valve 74.

The Figure 6 orbital generator is very robust and reliable and is therefore suitable for powering navigational buoys.

The embodiment of the generator shown in Figures 7 and 8 is similar to that of Figures 1 to 3 in that it comprises a weight 1 5 carried by an arm 13 mounted on a shaft 2, the arm 1 3 being coupled by coupling 18 to the rotor of an alternator 57 which is arranged coaxially with the shaft 2. However, unlike the Figure 1 embodiment, the Figure 7 embodiment further includes an auxiliary weight 81 connected to the radially outer end of an arm 80 arranged to rotate with the arm 13.

The manner of connection of the arm 80 to the arm 1 3 is such as to permit angular adjustment of the position of the auxiliary weight 81 relative to that of the weight 1 5. Since varying the angular position of the weight 81 relative to that of the weight 1 5 will effectively vary the resultant moment of inertia presented by the two weights 1 5 and 81, adjustment of the arm 80 enables the kinematic characteristics of the generator to be tuned, at least to some degree, to the motion characteristics of the structure mounting the generator.

Preferably the weight 81 is pivotally connected to the arm 80 to enable the weight 81 to swing out at least in a radial direction. By this arrangement, the weight 81 serves to store up energy (by increasing its angular momentum as it swings out) during periods of acceleration of the weights 1 5 and 81 this energy being returned to the system during periods of deceleration. The effect of the weight 81 is thus to facilitate movement of the weight 1 5 past its top-deadcentre position to execute uni-directional orbital motion rather than pendulum type motion.

Advantageously, the weight 81 is connected to the arm 80 by a universal joint enabling the weight 81 to swing out in any direction. During periods of deceleration, the weight 81 will thus swing out forward of the arm 80 (considered relative to the direction of rotation), the actual angle made with the arm depending on the degree of deceleration and the instantaneous angular velocity (this latter factor determining the amount by which the weight 81 swings out radially).

Instead of the arm 80 being rigidly connected to the arm 13, a spring-resisted lost motion coupling 82 (Figure 9) can be interposed between the arms 13 and 80. In this arrangement, a mount 83 is rigidly (but angularly adjustably) secured to the arm 13 and engages the arm 80 via two springs 84 acting in opposition. The arm 80 as well as being engaged by the springs 84, is also rotatably mounted on the shaft 2. The arm 80 can thus move with increasing resistance in either direction away from a neutral position defined by the springs 84, the maximum extent of this movement being limited by arms 85 of the mount 83.

Claims (13)

1. A wave-powered orbital electrical generator for installation on a floating structure subject to the action of wave motion, said generator comprising: a support structure, an electric machine including a stator fixedly mounted on said support structure, and a rotor mounted for rotation relative to the stator; a weight mounted for rotation about an axis with its centre of gravity offset therefrom, said support structure being intended for secural to said floating structure such that said axis extends substantially vertically in the absence of any wave motion, whereby in use of the generator, any nonvertical motion of the floating structure is effective to cause orbital movement of the weight around the axis, and coupling means coupling the said weight and rotor such as to enable movement of the weight to be transmitted to the rotor.

2. A generator according to Claim 1, wherein the rotor is carried on a shaft coaxial with said axis, the weight being also supported on said shaft.

3. A generator according to Claim 2, wherein said coupling means comprises a lost-motion coupling.

4. A generator according to Claim 3, wherein the extent of relative movement permitted between the cooperating parts of the lost-motion coupling is adjustable.

5. A generator according to any one of the preceding claims, wherein the coupling means includes energy storage means arranged to receive the energy inputs from the weight while outputting a more constant flow of energy to drive the rotor.

6. A generator according to Claim 5, wherein said energy storage means takes the form of a coil or torsion-bar spring arrangement with means for converting bi-directional movement of the weight into uni-directional movement winding up the spring arrangement.

7. A generator according to Claim 5, wherein said coupling means comprises an hydraulic circuit including a pump driven by the weight and a motor driving the rotor of the electric machine, the energy storage means being in the form of an hydraulic accumulator disposed in the hydraulic circuit between the pump and the motor.

8. A generator according to any one of the preceding claims, including an auxiliary weight mounted for rotation about said axis with its centre of gravity offset therefrom, the auxiliary weight being arranged to rotate jointly with the first-mentioned weight and being so mounted as to enable adjustment of its angular position relative to that of the first-mentioned weight.

9. A generator according to any one of Claims 1 to 7, including an auxiliary weight mounted for rotation about said axis with its centre of gravity offset therefrom, the auxiliary weight being arranged to rotate jointly with the first-mentioned weight and the manner of mounting of the auxiliary weight being such as to permit its outward radial displacement from an at-rest position under the action of the centrifugal forces experienced thereby during rotation about said axis.

10. A generator according to Claim 10, wherein the angular position of the auxiliary weight about said axis is adjustable relative to that of the firstmentioned weight.

11. A generator according to Claim 9 or Claim 10, wherein the auxiliary weight is connected by a universal joint to a mounting arm rotatably about said axis.

1 2. A wave-powered orbital electrical generator, substantially as hereinbefore described with reference to Figures 1 to 3, of the accompanying drawings.

13. A wave-powered orbital electrical generator, substantially as hereinbefore described with reference to Figures 1 to 3 as modified by Figure 5, Figure 6, or Figures 7 and 8 of the accompanying drawings.