A first piston connected to a first shaft and a second piston connected to a second shaft are supported within a housing by using a first leaf-spring unit and a second leaf-spring unit, respectively. Therefore, axial movement of the first shaft or the second shaft can be allowed, while circumferential...http://www.google.com.au/patents/US6945202?utm_source=gb-gplus-sharePatent US6945202 - Free piston engine and power generation system therewith
