Abstract: An apparatus for the expansion of pressurized, pulsating exhaust gases comprises at least one expansion chamber (12a, 12b; 40; 68, and 70), a piston (18; 44; and 66) oscillating in the expansion chamber (12a, 12b; 40; 68 and 70) and an output drive (16, 34; 46, 56, 63; 67, 90, 92 and 110) that is connected with the piston (18; 44; and 66) and includes a directional clutch (36; 58; 102, and 104), that is so arranged that it produces a coupling connection in the direction of motion corresponding to exhaust gas expansion. In the case of there being at least two expansion chambers (68 and 70) adapted to receive exhaust gas acting in opposite directions there is preferably a directional clutch (102 and 104) for each direction of expansion, said two directional clutches (102 and 104) being connected together by means of a reversing drive (86, 88, 90, 92 and 110 ) for output drive in the same direction.