Object of the invention

The world needs more renewable energy. Ocean waves are currently an unexploited renewable energy resource, holding immense potentials, measured by the amount of energy available for exploitation in the oceans, and by the energy flux density of the waves, which is typically significantly higher than the equivalent for solar and wind in corresponding locations.

Previous attempts at harvesting ocean wave energy have failed. There has been no success in demonstrating ways to deal with extreme waves and the most high- energy sea states and other aspects in challenging maritime environments, to ensure the survival of the wave power installations combined with sufficiently low cost of construction, installation and maintenance and sufficiently high energy production over time, for the technologies to be able to compete economically with established energy sources such as solar, wind power and fossil power.

The invention described herein is based on a solution with an overload protection device described in other presented suggestions mentioned at the beginning of the next section, and solves a problem with frictional heat in those. The invention allows for construction of a more robust wave energy converter, without cost-driving elements, thereby reducing the needs for maintenance and improving survivability in extreme wave conditions.

Background and known technology on which the invention is based

The invention is based on N0325878B1 (inventor: Ingvald Straume), NO329059B1 (inventors: Ingvald Straume and Sivert Straume) and N0329152B1 (inventors: Ingvald Straume, Morten Sandnes and Arne Johannes Mo), and on a winch unit for utilizing wave energy including a mechanical planetary gear slip clutch mechanism built at Tronrud Engineering for Purenco AS in 2012, mentioned and depicted in Ringerikes Blad 8 June 2012 (pp. 1, 2 and 3). The devices in the patents listed above and in said publication of Ringerikes Blad address the challenge of overload protecting winch operated ocean wave energy converters in extreme wave conditions. A yet unresolved problem with all of these is that the overload protection mechanism is based on a mechanical slip clutch device, in which slipping induces friction heat when coping with large waves, causing excess absorbed energy to be dissipated as heat in the adjacent mechanical friction surfaces of the slip clutch device. The current invention solves the problem by replacing the mechanical slip clutch mechanism with a hydraulic device which has the same effect on the winch cable, the float, and the mechanical winch machinery, by providing overload protection in the same way, whilst handling excess energy hydraulically.

The problem of hot run during slipping is thereby reduced or eliminated.

General description

The invention relates to a wave power plant where a float 54 in the sea is moved by ocean waves and absorbs energy mechanically from those waves, so that a cable 1 attached to the float, in one embodiment via a block and tackle suspension as shown in Fig. 7, is pulled out, causing a rotary force movement onto a winch with a winch drum 2. The winch is self-tightening, using a winch tightening motor 25 and associated winch tightening machinery, so that the winch cable 1 is spooled onto the drum 2 when the float moves in any direction which doesn't cause the winch cable to be pulled out, thereby maintaining the tension on the winch cable.

When the float's motion pulls out the winch cable, forcing the winch drum to rotate outwards, mechanical kinetic energy is absorbed and then directed via a power take off pump 28, werein the energy is transformed into hydraulic energy in the form of pressurized flow of fluid, to a power take-off accumulator 32, from which the energy, now in the form of a steady fluid flow, is passed on to a hydraulic motor 33, turbine or equivalent, which powers an electric generator 38 or other machinery to perform useful work. Several winch units, individually associated with their own float, may be connected to a shared generator unit 69 containing a hydraulic motor and generator, as shown in Fig. 9.

When the float is moved by a wave that is too large for the power take-off pump to handle such high speed caused by the wave motion, a machinery containing a brake pump 41, acting as a disengagement mechanism, ensures overload protection by setting an upper threshold for rotational speed or power absorption rate of the power take-off pump, thereby limiting the winch unit's absorption of power from incoming waves. Figures

Fig. 1 shows an example embodiment of the winch unit, without cover, in front view.

Fig. 2 shows the same as Fig. 1, in top view.

Fig. 3a shows one planetary gear embodiment with associated parts, externally.

Fig. 3b shows the same as Fig. 3a, internally.

Fig. 4 shows, by hydraulic symbols, an example embodiment of parts of winch unit.

Fig. 5 shows a section of Fig 1, with mechanical components, in diagonal front view.

Fig. 6 shows the centrifugal governor with connected mechanical parts.

Fig. 7 shows the winch unit connected to the float and pulleys in the sea with cable.

Fig. 8 shows float pulley in detail and connected elements.

Fig. 9 shows five floats and five winch units connected to a shared generator unit.

Fig. 10 shows winch tightening motor, power take-off pump and centrifugal governor etc.

Detailed description

Absorbed power from ocean waves is transferred mechanically via cable 1 to a winch drum 2, when the cable powered by wave energy is pulled out, whereby the winch drum rotates outwards. The thereby generated rotary force movement from the winch drum is captured by a winch shaft 3 to which said winch drum is attached and rotates about, and transferred further from this one to a planetary carrier shaft 5.

The winch may be connected to the planetary carrier shaft via a coupling 4 or several, and the coupling(s) may have built-in elasticity that provides for shock absorption. Or the winch shaft 3 and the planetary carrier shaft 5 may be fixed to each other, in which case they constitute one and the same shaft. Rotation of the winch drum causes rotation of the planetary carrier shaft. The planetary carrier shaft is fixed to a planetary carrier 12, so that the planetary carrier also rotates dependently on the winch drum. Rotary force movement, i.e. mechanical power in the form of rotational speed and torque, is transferred inside the planetary gear 6 from the planetary carrier 12 via two or more planetary wheels, on Fig. 3b shown as three planetary wheels 13a, 13b, 13c, to the planetary gear annulus 15 or to the centric solar wheel 14 and the solar wheel shaft 11, or distributed among these, through which the power gear level is varied by altering the rotational speed to torque ratio in the gear mechanism. Mechanical power exiting through the solar wheel shaft 11 has a higher rotational speed and correspondingly lower torque than the incoming power from the winch shaft.

During normal operation, that is, when the waves are not too violent, the planetary gear annulus 15 is static, due to it being connected to a brake pump shaft 39 that powers a brake pump 41, whereby the annulus is prevented from rotating when the brake pump is prevented from rotating. The annulus of the planetary gear is connected to a belt pulley 7 attached to the planetary gear in such a way that the annulus 15 and belt pulley 7 rotate interdependently. The belt pulley 7 is connected via a suitable transfer mechanism that transfers the belt pulley's torque and rotation, optionally with a gearing ratio, to the brake pump shaft 39. In figures 1 to 5, one embodiment of this transfer mechanism is shown, where the belt pulley 7 is connected via a drive belt 8 to a belt pulley 9 on a belt pulley shaft 10. The belt pulley shaft 10 may be connected to the brake pump shaft via a coupling 40, which may be a flexible one, or the belt pulley shaft 10 and the brake pump shaft may be fixed to each other, in which case they constitute one and the same shaft. This assembly causes the brake pump shaft to rotate dependently on the annulus 15, thus preventing the annulus from rotating if the brake pump shaft is held, whether embodied as shown in figures 1 to 5 or in other correspondingly functioning embodiments. The brake pump shaft's degree of motion resistance depends on the rotational speed of the power take-off pump shaft 21. As long as the rotational speed of the power take-off pump shaft is below a certain lower threshold value, the brake pump 41 and thus the brake pump shaft 39 will be prevented from rotating, by a pilot valve 45 being closed, blocking the fluid outlet 62 from the brake pump. When the speed of the power take-off pump shaft exceeds said lower threshold value, a device associated with the power take-off pump shaft ensures that the pilot valve is gradually opened, as a function of the degree of exceedance above the threshold value. At an upper threshold value for the power take-off pump shaft's speed, the pilot valve is fully open, allowing fluid from the brake pump to flow through it unimpeded.

A freewheel 42 may have one run attached to a mounting bracket 43 on the winch unit's frame or bottom plate, and the other run attached to the belt pulley shaft 10, whereby reverse rotation of the brake pump 41 becomes impossible.

Under normal operation conditions, when the planetary gear annulus 15 is not moving, in small and medium waves, all rotation from the winch drum will be directed to the solar wheel shaft 11, geared up by the planetary gear 6 to a higher rotational speed and correspondingly lower torque. When an external force pulls out the winch cable, causing the winch drum to rotate outwards, a force movement is generated, powering a power take-off pump 28 and a winch tightening motor 25, now the winch tightening motor functioning as a pump. The power take-off pump and the winch tightening motor are both connected to the same belt pulley shaft 22, which in one embodiment is connected to the solar wheel shaft 11 via a coupling 16. The coupling 16 may be omitted, so that the solar wheel shaft 11 and the belt pulley shaft 22 become one and the same shaft. The belt pulley shaft 22 may be connected to the winch tightening motor shaft 24 and the winch tightening motor 25 via a coupling 23. Or the coupling 23 may be omitted, so that the belt pulley shaft 22 and the winch tightening motor shaft 24 become one and the same shaft. Thus, the winch tightening motor shaft rotates dependently on the winch drum in both directions, through which the tightening motor 25 acts as a pump when an external force pulls the winch cable out forcing the winch drum to rotate outwards. Thus, when the winch tightening motor acts as a pump, it will extract fluid from a fluid reservoir 50 and pump this fluid under pressure into a winch tightening accumulator 26. Oppositely, at the moment when the force that pulled the winch cable out decreases sufficiently, pressurized fluid from the winch tightening accumulator will flow in the reverse direction back to the fluid reservoir through the winch tightening motor — now acting as a motor — , powering it, thereby forcing connected shafts 24, 22, 11, couplings 23, 16 and gear device 6 to rotate in the direction which spools the cable in onto the winch drum. In this way, the winch tightening motor causes the winch drum to rotate inwards and spool in the cable, keeping it tight when the cable is not pulled out by external force.

In one embodiment, the power take-off pump is powered 28 by force movement from a belt pulley 18, via a belt transfer 19 to a belt pulley 20. The belt pulley 18 is connected to the belt pulley shaft 22. The belt pulley 20 is connected to the belt pulley shaft 30, which is further connected to and powers the power take-off pump. The power take-off pump is activated only when the cable is pulled out and is at rest when the winch is spooled in, provided by a freewheel 17 interfacing the belt pulley shaft 22 and the belt pulley 18. The freewheel disengages the belt pulley 18 from the belt pulley shaft 22 when the latter rotates in the winch cable rewinding direction. When the power take-off pump is activated, it drains fluid from reservoir 50 and pumps it under pressure into a power take-off accumulator 32. A check valve 29 in the hydraulic passage from the power take-off pump to the power take-off accumulator ensures that fluid cannot flow in the reverse direction from accumulator to pump. Each time the winch cable is pulled out, a surplus of pressurized fluid accumulates in the accumulator 32. This surplus means energy. Normally this energy is extracted by means of the fluid flowing from the accumulator 32 to the hydraulic motor 33 powering a generator 38. Also, one or more safety valves, which are not further described here and not plotted in the figures, but which a professional engineer may find appropriate to arrange, may ensure that fluid is passed on and returned to reservoir 50 by-pass the motor 33 when the pressure in the accumulator(s) or other parts of the hydraulic system becomes too high. The motor 33 may be connected to the generator 38 directly via a generator shaft 37, or it may, as shown in Fig. 4, be connected via a motor shaft 34, connected to the generator shaft via a coupling 35. A flywheel 36 may be mounted on the generator shaft, to contribute to stabilizing the rotary speed of the generator. In other embodiments, the fluid channel 67 leading to the motor and fluid cannel 68 leading from the motor back to the reservoir 50 may be connected with corresponding hydraulic channels from other winch units whereby they together drive a shared motor and electric generator in a shared generator unit 69, as shown in Fig. 9.

The electric generator may be replaced with machinery that performs other useful work, powered by the rotary force movement from the generator shaft. For example, the generator shaft can, instead of or in addition to operating a generator, power a pump that pressurizes seawater for desalination through the process known as reverse osmosis, in a wave powered freshwater production facility.

In figures 1, 2, 5 and 6, the motors 25 and 33 and pumps 28 and 41 are depicted as displacement motors and pumps. These will inevitably have some volumetric fluid leakage, which is collected and returned to the fluid reservoir 50 via drainage channels 65. For the winch tightening accumulator 26, such fluid leakage, however small, will lead to a decline in the pressure inside the accumulator, and thus a weakening of the tension on the cable from the winch tightening motor 25. In that case, a hydraulic passage 66 connected to the passage of the power take-off accumulator 32 ensures that a sufficient amount of fluid under pressure is supplied to the winch tightening accumulator from the power take-off accumulator. A check valve 27 ensures that fluid cannot flow in the opposite direction from the winch tightening accumulator through the passage 66 to the power take-off accumulator.

In one embodiment, fluid that is led back to the reservoir 50 from the hydraulic drainage passages 65 (a-d), 68, and any other passages, such as safety valve runs, pass through a return line filter 49 mounted on the reservoir. Several return line filters may also be arranged in the hydraulic system, wherever a professional engineer will find it appropriate.

Said device which act to open the pilot valve 45 gradually as a function of the power take-off pump shaft speed exceeding the specified lower threshold value, may be designed in many different ways, by means and procedures well known to professional engineers, for example by using hydraulic or electrical components or electronics. Figures 1, 5, 6 and 10 show an embodiment in which the device is a mechanical centrifugal governor 46, whose rotor shaft is connected via transfer gearwheels 63, 64 and a flexible coupling 47 to the belt pulley shaft 30 and further via a flexible coupling 31 to the power take-off pump shaft 21, so that the centrifugal governor and the power take-off pump shaft rotates interdependently. Couplings 47 and 31 may be omitted, in which case the belt pulley shaft 30 and the power take-off pump shaft 21 constitute one and the same shaft, directly connected to the transfer gearwheel 64 and the power take-off pump 28. Transfer gearwheels 63, 64 may also be omitted or replaced with another kind of mechanical transmission, such as a belt drive. When the speed of the centrifugal governor exceeds a certain lower threshold value, the centrifugal forces act to gradually move a valve control rod 48 by which the pilot valve 45 connected to the valve control rod, gradually opens. Oppositely, as the centrifugal governor's speed decreases, the valve control rod will move back, gradually closing the pilot valve, and causing it to be fully closed at the moment when the centrifugal governor's speed drops below the lower threshold value. The arrangement with a centrifugal governor rotating dependently on the power take-off pump shaft 21 and controlling whether and to what extent fluid is allowed to flow through the pilot valve 45, constitutes a feedback mechanism. It works in the same way as the centrifugal governor of James Watt's original steam engine, where rotational speed over a certain pre-calibrated value activated a mechanism which opened a safety valve through which the pressure in the boiler was reduced to protect the rotating parts of the steam engine from overload in the form of excessive speed. Together, the centrifugal governor 46 and the brake pump 41 ensure that the rotary speed of the power take-off pump shaft 21 cannot exceed a certain threshold speed. As the threshold speed is reached, the centrifugal governor ensures that the pilot valve 45 is kept just sufficiently open to direct all excess speed from the winch drum via the planetary gear annulus 15 to the brake pump 41, keeping the speed of the power take-off pump shaft below or at the threshold speed.

In alternative embodiments, the device which regulates whether and to what extent the brake pump is allowed to rotate, may be governed by one or more electrical, electronic, optical or hydraulic sensors, or other means suitable for the purpose, well known to professional engineers. By such means, the degree of speed limiting on the power take-off pump shaft may also be determined by acceleration, force or torque acting on different parts of the mechanical system, frequency of change in direction of winch drum rotation, fluid current, pressure or temperature in different parts of the hydraulic system, or the amount of fluid accumulated in the accumulators. Optionally, speed limiting may be governed by external agency, automatically, autonomously or remotely, or manually.

When the pilot valve 45 is in a partially open state and fluid under pressure flows through it, heat will be generated. Cooling is provided for by having hot fluid from the pilot valve outlet led through a cooling coil 44, before passed on to the accumulator 32. Figures 1 and 2 show one embodiment of a cooling coil device, having a fan 70 powered by a belt transfer 71 connected to the brake pump shaft 39, which ensure that an external cooling fluid medium, which may be atmospheric air, flows past the cooling coil when the shaft 10 rotates. The belt transfer 71 may be connected to the shaft 10 via a coupling 72 or several.

In an alternative design, the belt pulley 7 and the winch drum 2 have switched places, so that the transmission of power in the form of force movement during normal operation is directed from the winch drum via the planetary gear annulus 15 and then via the planetary wheels 13 to the solar wheel 14 and the solar wheel shaft 11, while the transmission of excess speed to the brake pump 41 when the waves are too violent is directed from the annulus via the planetary wheels and the planetary carrier 12 to the planetary carrier shaft 5.

The brake pump 41 may be a fixed displacement pump, as shown by the symbol in Fig. 4. However, in one embodiment, it is replaced with a variable displacement pump, where the centrifugal governor 46 and valve control rod 48 govern the pump's displacement in such a way that the displacement gradually decreases when the centrifugal governor's speed exceeds a certain lower threshold value. 'Displacement' is defined as the amount of fluid displaced per full rotation of the pump shaft. Thereby the pilot valve 45 is redundant. Since the torque of the pump shaft 39 is a function of displacement and pressure in the brake pump 41, where the pressure is the same as the pressure in the accumulator 32, and the torque increases with increasing displacement, such an arrangement will work correspondingly to the aforementioned arrangement with a centrifugal governor- controlled pilot valve, apart from the fact that now the majority amount of energy per time unit absorbed by the brake pump, is channeled as hydraulic power in the form of pressurized fluid directed to the accumulator 32 and motor 33, instead of being dissipated as heat. Thus, the cooling coil 44 and associated cooling machinery become redundant. In the embodiment of the wave energy converter shown in Figure 7, the winch cable 1 connects a float 54 in the sea to the winch drum 2 on land in such a way that the winch drum is forced to rotate when the wave forces move the float in the winch cable's longitudinal direction. Here, the end of the winch cable is connected to the float via a shock absorber 61 attached to the float pulley 52 under the float via a becket 60 attached to the float's pulley wheel shaft 56, where the float's pulley wheel fork 57 connects the float's pulley wheel shaft to the float. The cable runs over the pulley wheel 55. On each side where the winch cable extends from the pulley wheel, it is led through a guide tube 59 (a, b) arranged on a bracket 58 (a, b) attached to the pulley wheel shaft 56. Each of the brackets 58a, 58b has a degree of freedom to rotate in the pulley wheel plane about the pulley wheel shaft 56. The seabed pulleys 51 and 53 function and are built likewise, but without the becket. From the end attachment point of the shock absorber 61, the winch cable 1 runs down to the seabed pulley 53 and over its pulley wheel, then back up to the float pulley 52 and over its pulley wheel 55, then down to the seabed pulley 51 and over its pulley wheel, before running diagonally upwards through the water to shore where it is wound on the winch drum 2. In total, this arrangement constitutes a block and tackle suspension which gears up the absorbed mechanical power of the ocean waves, so that the part of the cable that winds onto the winch drum, moves faster, yet with less force than the float. The seabed pulleys 51 and 53 are both attached to the seabed, separated by some distance, to prevent the block and tackle suspension from tangling.

In other embodiments, the winch drum and associated machinery may be located at the seabed, embedded inside the float, or submerged in the pelagic zone, and the block and tackle suspension may include more or fewer pulleys and pulley wheels.

Figure names

1. Winch cable 37. Generator shaft

2. Winch drum 38. Generator

3. Winching 39. Brake pump shaft

4. Coupling 40. Coupling

5. Planetary carrier shaft 41. Brake pump

6. Planetary gear 42. Freewheel

7. Belt pulley 43. Freewheel mounting bracket

8. Belt 44. Cooling coil

9. Belt pulley 45. Pilot valve

10. Belt pulley shaft 46. Centrifugal governor

11. Solar wheel shaft 47. Coupling

12. Planetary carrier 48. Valve control rod

13. Planetary wheel (a, b, c) 49. Return line filter

14. Solar wheel 50. Fluid reservoir

15. Annulus 51. Seabed pulley

16. Coupling 52. Float trim

17. Freewheel 53. Seabed pulley

18. Belt pulley 54. Float

19. Belt 55. Pulley wheel

20. Belt pulley 56. Pulley wheel shaft

21. Power take-off pump shaft 57. Pulley wheel fork

22. Belt pulley shaft 58. Bracket (a, b)

23. Coupling 59. Guide tube (a, b)

24. Winch tightening motor shaft 60. Becket

25. Winch tightening motor 61. Shock absorber

26. Winch tightening accumulator 62. Fluid outlet

27. Check valve 63. Transfer gearwheel

28. Power take-off pump 64. Transfer gearwheel

29. Check valve 65. Drainage (a, b, c, d)

30. Belt pulley shaft 66. Hyd raulic passage

31. Coupling 67. Fluid channel

32. Power take-off accumulator 68. Return fluid channel

33. Motor 69. Generator unit

34. Motor shaft 70. Fan

35. Coupling 71. Belt transfer

36. Flywheel 72. Coupling