FIELD OF THE INVENTION

The present invention relates to a power transmission arrangement in a wave energy converter described in the preamble of claim 1 .

The power transmission arrangement according to the invention is suited very well for instance to be used in a wave energy conversion apparatus comprising a reciprocating panel or flap or essentially plate-like wing element, hereafter called a panel, which panel is hinged at its lower edge to enable a reciprocating movement caused by wave energy or tidal energy of seawater as shown, for example, in a patent publication No. WO2017029425 (A1 ). The wave energy or tidal energy captured is further converted with a conversion unit to electric energy, for instance.

BACKGROUND OF THE INVENTION

According to prior art, there are various types of wave energy conversion (WEC) apparatuses that comprise reciprocating panels rotating with ocean waves, which apparatuses convert the wave energy to electricity by harvesting the energy of the oscillatory motion using hydraulic systems for power take-off (PTO).

In these types of WEC apparatuses the rotational movement is changed to linear movement before transmitting the movement to a power unit of the PTO. These apparatuses are, however, not as efficient as possible. For example, in the systems presented in patent publications W02006100436 (A1) and WO2011026173 (A1 ), there have been attempts to connect the power take-off cylinders directly to the oscillating part. This drastically reduces the lifetime of the hydraulic system components as the solutions do not always include a way to compensate for the installation tolerances, small misalignments, and any unwanted load components in operation, e.g., axial forces to the PTO from the panel.

AIM OF THE INVENTION

The aim of the present invention is to eliminate the drawbacks described above and to achieve a wave energy converter power transmission arrangement that is simple, reliable, cost-effective, energy efficient and durable by creating a system that changes the alternat- ing rotational movement from the panel to linear movement to the power unit with minimal amount of energy losses. Another aim of the invention is to create a power transmission arrangement where the panel bearings are not directly involved in the power transmission. The power transmission arrangement according to the invention is characterized by what is presented in the characterization part of claim 1 . Other embodiments of the invention are characterized by what is presented in the other claims.

BRIEF DESRCRIPTION OF THE INVENTION

An aspect of the invention is to provide a power transmission arrangement in a wave energy converter that comprises at least a reciprocating panel with a pivot shaft, one or more power take-off (PTO) units with one or more power units, and a connection mechanism, which is arranged to transfer the panel movement to said one or more PTO units. Advantageously the power transmission arrangement comprises a chain drive system equipped with a cylindrical power transmission drum, which is connected to the connection mechanism in order to rotate along with the reciprocating panel, and with a chain for each power unit, which chain is arranged to transfer the rotational motion of the power transmission drum to linear motion in the power unit.

ADVANTAGES OF THE INVENTION

The main advantages of the power transmission arrangement according to the invention are smaller energy losses and thus significantly higher efficiency compared to prior art solutions. In addition, the power transmission arrangement according to the invention comprises mechanically smaller parts, which simplifies assembly and maintenance. Another advantage of the arrangement according to the invention is that the panel bearings are not involved in the power transmission, which makes it possible to separate systems. Both the panel and the PTO unit can be assembled and maintained with as little interference as possible. The arrangement is designed to increase the robustness of the complete device. In many areas the required tolerances can be made easier to achieve.

Other advantages of the present invention include:

- the chain drive system changes the alternating rotational movement of the panel to linear movement that is used to push hydraulic cylinders of the PTO in a reliable, efficient and cost-effective manner; the hydraulic cylinders of the PTO are immovable, which increases reliability; - a lever arm system of the power transmission arrangement transfers the panel movement to the PTO in such a way that as much as possible only the rotational component is included;

- the system does not transmit any axial movement of the panel; the effective radius of the power transmission drum is constant and, in this way, allows for more efficient energy capture;

- all the components have simple interfaces so the maintenance of the parts that experience wear can be easily arranged;

- alignment of different areas (inside the PTO and between the foundation, panel and PTO) is simple;

- the required accuracy in assembly and operation phases is reduced;

- the internal alignment of the PTO cylinder pack does not have to be very accurate;

- panel bearings can be simple and identical structures, which makes it possible to design the bearings more independently;

- the panel bearing wear is not that critical and the bearings are easy to replace;

- the lifetime of the wave energy converter and its components can be increased.

LIST OF FIGURES

In the following, the invention will be described in detail by the aid of examples by referring to the attached simplified and diagrammatic drawings, wherein

Fig. 1 presents in a perspective view a wave energy converter according to the arrangement of one preferred embodiment of the invention,

Fig. 2 presents the wave energy converter according to Figure 1 in a front view,

Fig. 3 presents in a side view a part of the chain drive system of the power transmission arrangement of the wave energy converter according to the invention,

Fig. 4 presents a part of the chain drive system according to Figure 3 in a perspective view,

Fig. 5 presents a part of the chain drive system according to Figure 3 in a top view,

Fig. 6 presents a part of the chain drive system according to Figure 3 in a bottom view,

Fig. 7 presents in a perspective view a part of the power transmission arrangement connection mechanism according to the invention,

Fig. 8 presents the part of the power transmission arrangement connection mechanism according to Figure 7 in a side view, Fig. 9 presents a push rod according to the arrangement of the invention partially cross-sectioned.

DETAILED DESRCRIPTION OF THE INVENTION

Figure 1 presents a wave energy converter according to the arrangement of one preferred embodiment of the invention viewed obliquely from above and Figure 2 presents the wave energy converter according to Figure 1 viewed from the front. The wave energy converter comprises a foundation 1 , a panel 2 reciprocating about its pivot shaft 2a, which is attached to the foundation 1 by its bearings 2b, and one or more PTO units. Each PTO unit comprises one or more power units 4 and a chain drive system 5. The chain drive system 5 comprises at least a base 3 and a cylindrical power transmission drum 5a. The central axis of the power transmission drum 5a is substantially parallel with the pivot shaft 2a of the panel 2.

The panel 2 is attached from its one side edge to the power transmission drum 5a by a connection mechanism 6 at a distance from the pivot shaft 2a. The power transmission drum 5a is arranged to rotate along with the reciprocating panel 2 by means of the connection mechanism 6. The power transmission drum 5a comprises bearings to keep it in place in radial and axial direction and to allow it to rotate. The chain drive system 5 and the power units 4 comprise sealed casings to keep seawater out. Advantageously, the bearings of the power transmission drum 5a also comprise a sealing system.

Figures 3-6 present the chain drive system 5 of the power transmission arrangement of the wave energy converter according to one preferred embodiment of the invention. For the sake of clarity, the protective casings of the arrangement, among other things, are not presented in the figures. The chain drive system 5 comprises at least one chain 5b being attached from its first end onto the outer circumference of the power transmission drum 5a and from its second end to a motion element 8. The chain 5b is arranged to transfer the rotational movement of the power transmission drum 5a to the linear movement of the motion element 8. Further, the motion element 8 is arranged to transfer its linear movement to the power unit 4, which comprises one or more energy capturing units 7, such as hydraulic cylinder packs 7 each comprising one or more hydraulic cylinders. Advantageously, the motion element 8 is arranged to be moved linearly back and forth along its guide rail 9. For that purpose, the motion element 8 comprises preferably two slide guides 9a attached to the bottom of the motion element 8 which slide guides 9a are arranged to slide along the guide rail 9 that is preferably beneath the motion element 8.

The power transmission arrangement may comprise only one PTO unit, which is placed at one side of the panel 2, or the power transmission arrangement may comprise two PTO units placed at both sides of the panel 2. The power transmission arrangement may also comprise even more than two PTO units.

Preferably, each PTO unit comprises the chain drive system 5 and two power units 4. In that case, the chain drive system 5 of the power transmission arrangement comprises two chains 5b (one for each power unit 4) and two motion elements 8 on their own guide rails 9 as presented in the solution of Figures 3-6. The power units 4 are advantageously placed on opposite sides of the power transmission drum 5a, the first power unit being placed at the first end of the base 3 and the second power unit being placed at the second end of the base 3. The chains 5b are attached in parallel on the outer surface of the power transmission drum 5a in such a way that the chains are wound on the outer surface of the power transmission drum 5a from opposite directions, and the attachment points are on the opposite sides of the circumference of the power transmission drum 5a.

Each motion element 8 is advantageously connected to a third guide rail 10 between the guide rails 9 to prevent the motion elements 8 from tilting to either side. The chain drive system 5 preferably comprises two grip members 12, the first grip member 12 being fastened to the first motion element 8 and arranged to slide along the third guide rail 10. The second grip member 12 is fastened to the second motion element 8 and is also arranged to slide along the third guide rail 10.

Advantageously, the length of each chain 5b is essentially about a half of the circumference of the outer surface of the power transmission drum 5a. Each chain 5b comprises at least three joints, suitably 3-9 joints and advantageously 5-7 joints. The first end of the first chain is attached on the outer surface of the power transmission drum 5a near the first end E1 of the drum, the chain traveling around the drum clockwise, for example, and is attached from its second end to the first end of the first motion element 8 placed below the power transmission drum 5a. The first end of the second chain is attached on the outer surface of the power transmission drum 5a near the second end E2 of the drum and on opposite side of the drum than the attachment point of the first chain, the second chain traveling around the drum in opposite direction compared to the first chain, i.e., counter-clockwise in this case. The second chain is attached from its second end to the first end of the second motion element 8 placed below the power transmission drum 5a. The first ends of the adjacent motion elements 8 are in mutually opposite directions.

The positions of the attachment points of the chains 5b on the surface of the power transmission drum 5a and the length of the chains 5b are selected so that when the panel 2 is in its vertical position the motion elements 8 are in their middle position below the power transmission drum 5a and substantially symmetrically in both sides of the drum. When the panel 2 rotates in a first direction the motion elements 8 move in a second direction opposite to the first direction.

The motion elements 8 pulled by the chains 5b are arranged to push the pistons of the cylinders inside the cylinder packs 7. Advantageously, the piston rods 7a are attached to a common plate 7b and the outer end 8a at the second end of the motion elements 8 is arranged to hit the common plate 7b and push the piston rods 7a with pistons into the cylinders of the cylinder packs 7.

The motion elements 8 are not fixedly connected to the cylinder packs 7 to allow disconnecting the movement from the hydraulic system in case of a storm or system failure. The motion elements 8 are elongated, upwards open cases, having a room for chains 5b. The motion elements 8 are arranged to move below the power transmission drum 5a longitudinally, perpendicular to the central axis of the power transmission drum 5a. The motion elements 8 are arranged to move back and forth in parallel. Each chain 5b is arranged in turn to pull into one direction the motion element 8 to which it is attached. The two adjacent chains 5b pull the motion elements 8 to which they are attached into opposite directions in relation to each other.

The chain drive system 5 also comprises a tensioning means 11 with at least an actuator 13 and a pressure accumulator 18. The actuator 13, such as a hydraulic cylinder assembly, is connected to the motion elements 8. Preferably, the tensioning means 11 is arranged to automatically remove the free play between the chains 5b to keep the chains taut relative to each other by pushing the motion elements 8 in opposite directions in longitudinal direction, that is, in their motion direction, and to act as shock absorber as the chain movement is by nature somewhat pulsating.

The actuator 13 may be connected to the motion elements 8 through the grip members 12. It may be connected at least to one of the grip members 12 and is arranged to increase the distance between the grip members 12 powered by the pressure accumulator 18 in order to remove free play between the chains 5b.

In addition, with this arrangement, the return movement of the motion element 8 in the free shift is carried out by the motion element 8 in the working shift. The chain 5b itself comprises bearings between the rotating parts of the chain units, and thus the wear and the friction resistance of the chain 5b is minimized and the components’ lifetime can be estimated better.

The chain drive system 5 is connected through a connection mechanism 6 to one side edge of the panel 2, which connection mechanism 6 is arranged to transfer the reciprocating panel movement to the chain drive system 5 by rotating the power transmission drum 5a. The connection mechanism 6 comprises at least a lever arm 6a attached to the power transmission drum 5a, a first coupling unit 14, such as a hole in the free end of the lever arm 6a, and a second coupling unit 6c, such as a dowel or a corresponding structure at one side edge of the panel 2.

According to one preferred embodiment of the invention, the connection mechanism 6 comprises a push rod 6b, which connects the lever arm 6a to the second coupling unit 6c, which coupling unit 6c extends outwards from the side edge of the panel 2 at a distance towards the top edge of the panel 2 from the pivot shaft 2a. At the end where the coupling unit 6c extends outwards from the panel 2 end, the coupling unit 6c comprises a coupling element 15, such as a hole, into which the first end of the push rod 6b is arranged to be fitted. The second end of the push rod 6b is arranged to be attached to the upper, i.e., the free end of the lever arm 6a via the hole 14.

Advantageously, the lever arm 6a is substantially V-shaped, opening towards the power transmission drum 5a, as can be seen in Figures 7 and 8. Preferably, the central axis of the push rod 6b is substantially perpendicular to the central axis of the power transmission drum 5a.

Panel movement is arranged to move the push rod 6b, which is in turn arranged to move the lever arm 6a, which is attached from its lower end to the second end E2 of the power transmission drum 5a.

The push rod 6b is presented in detail and partially cross-sectioned in Figure 9. Advantageously, the push rod 6b comprises spherical bearings 16 on its both ends, which bearings 16 are pretensioned with e.g., spring plates 17 to compensate any misalignment between the panel 2 and rotational centers of rotational parts of the PTO. The angular misalignment a oscillates suitably from 0° to approximately 4°, advantageously from 0° to approximately 2° for compensating manufacturing and assembly misalignment and a few degrees during the operation. The bearings 16 and spring plates 17 of the push rod 6b are advantageously sealed from seawater.

According to the arrangement of the invention, the chain drive system 5 is arranged to act as separate intermediate mechanism between the panel 2 and the power units 4. This enables an easy and fast removal and installation of the power units 4.

The power transmission drum 5a may be closed from seawater at least on its one end, advantageously on both ends E1 , E2.

It is obvious to the person skilled in the art that the invention is not restricted to the examples described above but that it may be varied within the scope of the claims presented below. Thus, for example, the structure and position of the power unit can be different from what is presented. For example, instead of hydraulic cylinder systems it may comprise water pumps or linear generators.

In addition, it is obvious to a person skilled in the art that the chains may comprise different number of joints than mentioned above. Also, the chains may be different types of power transmission elements, such as belts, wire ropes or rods. It is also obvious to a person skilled in the art that the chain drive system may be connected to the panel through a different kind of means than the connection mechanism described above. It is yet obvious to a person skilled in the art that the power transmission drum can be hollow and open to seawater to reduce movement of the drum caused by waves. This feature requires double sealing so that the drum is sealed from both ends to the casing of the chain drive system. It is also yet obvious to a person skilled in the art that the return movement of the motion elements may be arranged also in some other way as described above. For instance, it may be performed by the piston rods of the double-acting hydraulic cylinders of the cylinder packs.