Rotary piston internal combustion engine

A central-axis rotary piston internal combustion engine has a rotor housing closed off by housing covers, has an outer rotor which rotates in the rotor housing with uniform speed, and has an inner rotor which rotates in the interior of the outer rotor with non-uniform speed. The outer rotor has three inwardly pointing pistons rigidly connected to one another and arranged at uniform angular intervals from one another. The inner rotor has a corresponding number of radially outwardly pointing mating pistons which are rigidly connected to one another and which engage between in each case two pistons of the outer rotor so as to delimit in each case two working chambers. Each working chamber is assigned a combustion chamber and each combustion chamber communicates via a control window with stationary inlet and outlet openings.