The present invention relates to a hybrid system that comprises: a multifunctional hybrid motor system with pistons, wheels, and associated means including in combination two motor cycles complementary in terms of technology and temperature, one defining an internal combustion engine (A) with at least three cylinders (c1, c2,c3) with pistons (p1,p2,p3), and the other defining a so-called external combustion engine (B) with at least three cylinders (c4,c5,c6) with pistons (p4,p5,p6) driven by the expansion of an active fluid, said hybrid motor system being formed so as to include at least three cylinder/piston pairs, wherein the internal combustion engine (A) operates according to a 4-stroke cycle while the external combustion engine (B) operates according to a 2-stroke cycle, said engine (B) does not include any valves, the pistons (p1,p2,p3, etc) of the internal combustion engine (A) and the at least three pistons (p4,p5,p6, etc) are arranged so that the energy resulting from the consecutive expansion of the active fluid in the at least three cylinders (c4,c5,c6 ) of the external combustion engine (B) acts consecutively on said pistons of said 4-stroke internal combustion engine (A) during the compression and exhaust phases. This technical solution makes it possible to recover a portion of the thermal energy discharged by the exhaust gases of the internal combustion engine in order to convert the same into mechanical energy in the external combustion engine.