This is pretty interesting invention from the Germans. Toyota is taking the opportunity to do more research on this design where the piston movement produces electric charge. Genius in design but we’ll see if it ever comes to full concept.
Another illustration video (Different design from the two opposed piston that bang each other. See what I did there? Bang each other.)
http://green.autoblog.com/2014/05/01/toyota-randd-shows-off-free-piston-engine-linear-generator-for-fut/
http://www.greencarreports.com/news/1091794_toyota-describes-combustion-engine-that-generates-electricity-directly
http://www.foxnews.com/leisure/2014/05/02/toyota-developing-free-piston-engine-linear-generator-for-hybrid-cars/