Piston arrangement and internal combustion engine

1. A piston arrangement comprising: a piston, a first chamber, a second chamber and a power transfer assembly; wherein the piston comprises a first head movable within the first chamber and a second head movable within the second chamber; wherein, in operation, the piston follows a linear path in reciprocating motion along a first axis; wherein the power transfer assembly comprises a shaft rotatably coupled to a shuttle bearing and arranged to convert the reciprocating motion of the piston to rotary motion of the shaft; wherein the shuttle bearing moves relative to the piston in reciprocating motion along a second axis substantially transverse to the first axis; and wherein the shuttle bearing is coupled to the piston via a non-planar bearing surface thereby allowing rotation of the shuttle bearing.

2. A piston arrangement according to claim 1 , wherein the non-planar bearing surface is arranged to allow rotation of the shuttle bearing about the second axis and/or about a third axis which is substantially transverse to the first and second axes.

3. A piston arrangement according to claim 1 , wherein the shuttle bearing comprises one or more convex bearing surfaces.

4. A piston arrangement according to claim 3 , wherein the piston comprises one or more concave bearing surfaces corresponding to the one or more convex bearing surfaces of the shuttle bearing.

5. A piston arrangement according to claim 1 , wherein the interface between the piston and the shuttle bearing appears circular or part circular when viewed in the direction of the second axis.

6. A piston arrangement according to claim 1 , wherein the interface between the piston and the shuttle bearing is cylindrical or part cylindrical or spherical or part spherical.

7. A piston arrangement according to claim 1 , wherein the piston comprises a bore extending through its thickness in a direction substantially parallel to the second axis, and wherein the shuttle bearing is received in the bore.

8. A piston arrangement according to claim 1 , wherein the piston comprises a slot extending through its thickness in a direction substantially perpendicular to the second axis, and wherein the shaft is received in the slot.

9. A piston arrangement according to claim 1 , wherein the shuttle bearing is substantially cylindrical or part-cylindrical and has a longitudinal axis parallel to the second axis.

10. A piston arrangement according to claim 1 , wherein at least one bearing surface of the piston and/or shuttle bearing comprises one or more grooves formed in the bearing surface.

11. A piston arrangement according to claim 1 , wherein the shaft is rotatably coupled to the shuttle bearing at an eccentric portion of the shaft.

12. A piston arrangement according to claim 1 , wherein the second head has the same or a different outer diameter to that of the first head.

13. A piston arrangement according to claim 1 , wherein the second head is rigidly held in fixed relation to the first head.

14. A piston arrangement according to claim 1 , wherein the second head is integrally formed with the first head.

15. A piston arrangement according to claim 1 , wherein the first head and the second head face away from each other in opposite directions.

16. A piston arrangement according to claim 1 , wherein the first head and the second head are both centered on the first axis and each move in reciprocating motion along the first axis.

17. A piston arrangement according to claim 1 , wherein the shuttle bearing directly or indirectly engages the piston.

18. A piston arrangement according to claim 1 , wherein the shuttle bearing contacts a reverse face of the first and/or the second piston head.

19. An internal combustion engine comprising a piston arrangement according to claim 1 , wherein the first chamber is a combustion chamber.

20. An internal combustion engine according to claim 19 , wherein the internal combustion engine is a two-stroke or four-stroke engine.

21. An internal combustion engine according to claim 19 , wherein the second chamber is a supercharging chamber arranged to supply inlet air to the combustion chamber.

22. An internal combustion engine according to claim 21 , further comprising a transfer port extending between the supercharging chamber and the combustion chamber, wherein the transfer port has an outlet at the combustion chamber which is opened and closed by the reciprocating motion of the first head.

23. An internal combustion engine according to claim 22 , further comprising an oil seal mounted to a cylinder wall of the first chamber.

24. An internal combustion engine according to claim 23 , wherein the oil seal is mounted to the cylinder wall on the opposite side of the transfer port to the combustion chamber.

25. An internal combustion engine according to claim 24 , wherein the first head comprises an extended piston skirt which remains in continuous contact with the oil seal during reciprocating movement of the piston.

26. An internal combustion engine according to claim 22 , further comprising a gas seal mounted to the first head.

27. An internal combustion engine according to claim 26 , wherein the gas seal is positioned such that it passes the outlet of the transfer port during operation of the engine.

28. An internal combustion engine according to claim 19 , wherein the power transfer assembly is housed within an intermediate chamber located between the first and second chambers.

29. An internal combustion engine according to claim 28 , wherein the intermediate chamber is sealed to substantially prevent the passage of fluid past the first and/or second head into or out of the first and/or second chambers.