C2 DE 19904269 C2,Michael Ruppel,"Heißluftmotor - Heat engine has a simplified design with combined piston and valve and with alternate sides of the piston vented in either limits of the piston movement",published 2000-11-9,issued 2001-6-5
GBapplication 2554458A,Christopher Guise,"Improvement to Manson engine",published 2000-11-09