Stirling Machine
A Stirling machine comprising a reciprocating power piston with a power magnet, and a stator having a coil electromagnetically coupled to the power magnet. At least one spring magnet is arranged to provide an axial centring force on the piston. The spring magnet is fixed with respect to the stator.
1 . A Stirling machine comprising a reciprocating power piston with a power magnet; a stator having a coil electromagnetically coupled to the power magnet; and at least one spring magnet arranged to provide an axial centring force on the piston, the spring magnet being fixed with respect to the stator.
2 . A machine according to claim 1 , wherein there is a spring magnet at each axial end of the stator.
3 . A machine according to claim 1 , wherein the power piston includes a hollow drum on which the power magnet is mounted, and the stator comprises an annular gap in which the drum and power magnet reciprocate.
4 . A machine according to claim 3 , wherein the spring magnet is positioned on a inner stator element.
5 . A machine according to claim 3 , wherein the spring magnet is positioned on an outer stator element.
6 . A machine according to claim 2 , wherein the axial spacing between the spring magnets is greater than the overall axial length of the power magnet.
7 . A machine according to claim 6 , wherein the axial spacing between the spring magnets is at least 10% greater than the overall axial length of the power magnet.
8 . A machine according to claim 6 , wherein the spacing between the spring magnets is at least 20% greater than the length of the power magnet.
9 . A machine according to claim 1 , wherein at least one of the spring magnets is comprised of two or more spring magnet sections spaced apart in the direction of reciprocation.
10 . A machine according to claim 1 , wherein at least one of the spring magnets is radially spaced from the reciprocating power piston.
11 . A machine according to claim 1 , wherein at least one of the spring magnets is axially spaced from the power piston such that the power piston reciprocates towards and away from the spring magnet in use.
12 . A machine according to claim 11 , wherein the axially spaced spring magnet is provided with a resilient cushion between the spring magnet and the power piston.
13 . A machine according to claim 1 , wherein at least one of the spring magnets is associated with a respective auxiliary magnet positioned on the power piston and is arranged to co-operate with its associated spring magnet to generate a centring force on the piston.