A hybrid power train having an epicyclic gear set that serves as a clutch device, said hybrid power train coupling an engine and at least one electric machine, comprising: a rocker arm; a controllable brake device, for locking and releasing said rocker arm; an epicyclic gear set including at least one epicyclic wheel, an input wheel, and an output wheel, wherein said at least one epicyclic wheel, input wheel, and output wheel are bevel gears or bevel friction wheels, said at least one epicyclic wheel engaging both said input wheel and output wheel; a first rotation shaft connected to and rotatable with the input wheel; a second rotation shaft connected to and rotatable with the output wheel; an external input/out shaft rotatably coupled to an input/output side of at least one electrical machine; and a cylindrical rotation shaft extending from said rocker arm and coaxial with said first rotation shaft, said cylindrical rotation shaft being engaged by said controllable brake device to prevent rotation of said rocker arm, wherein the epicyclic wheel is rotatably mounted on the rocker arm such that when the controllable brake device locks said rocker arm to prevent rotation thereof, said epicyclic wheel couples said input wheel to said output wheel, and when said controllable brake device releases said rocker arm, rotation of said input wheel or said output wheel causes said rocker arm to rotate, at least partially decoupling said input wheel from said output wheel, said epicyclic gear set thereby serving as a releasable clutch controlled by said controllable brake device to control transmission of power between said first rotation shaft and said second rotation shaft, wherein said first rotation shaft is rotatably coupled to an engine and said second rotation shaft is rotatably coupled to said at least one electrical machine, wherein said electrical machine serves primarily as a motor for converting input electrical power into rotary mechanical energy to drive said external input/output shaft, whereby when said electrical machine is driven as a motor and said controllable brake device engages said cylindrical rotation shaft to prevent rotation of said rocker arm, said engine and the electrical machine are coupled through said epicyclic gear set to jointly drive the external input/output shaft, and whereby when said controllable brake device releases said cylindrical rotation shaft (AS 101), said engine is decoupled from said at least one electrical machine. a rocker arm; a controllable brake device, for locking and releasing said rocker arm; an epicyclic gear set including at least one epicyclic wheel, an input wheel, and an output wheel, wherein said at least one epicyclic wheel, input wheel, and output wheel are bevel gears or bevel friction wheels, said at least one epicyclic wheel engaging both said input wheel and output wheel; a first rotation shaft connected to and rotatable with the input wheel; a second rotation shaft connected to and rotatable with the output wheel; an external input/out shaft rotatably coupled to an input/output side of at least one electrical machine; and a cylindrical rotation shaft extending from said rocker arm and coaxial with said first rotation shaft, said cylindrical rotation shaft being engaged by said controllable brake device to prevent rotation of said rocker arm, wherein the epicyclic wheel is rotatably mounted on the rocker arm such that when the controllable brake device locks said rocker arm to prevent rotation thereof, said epicyclic wheel couples said input wheel to said output wheel, and when said controllable brake device releases said rocker arm, rotation of said input wheel or said output wheel causes said rocker arm to rotate, at least partially decoupling said input wheel from said output wheel, said epicyclic gear set thereby serving as a releasable clutch controlled by said controllable brake device to control transmission of power between said first rotation shaft and said second rotation shaft, wherein said first rotation shaft is rotatably coupled to an engine and said second rotation shaft is rotatably coupled to said at least one electrical machine, wherein said electrical machine serves primarily as a motor for converting input electrical power into rotary mechanical energy to drive said external input/output shaft, whereby when said electrical machine is driven as a motor and said controllable brake device engages said cylindrical rotation shaft to prevent rotation of said rocker arm, said engine and the electrical machine are coupled through said epicyclic gear set to jointly drive the external input/output shaft, and whereby when said controllable brake device releases said cylindrical rotation shaft (AS 101), said engine is decoupled from said at least one electrical machine.