Traction chain for a series hybrid vehicle comprising an engine (10) which drives an alternator (11), an electric traction motor (21), a inverter which enables the electric traction motor to be operated at a torque set value CC.sub.set, an accelerator available for use by the driver of the vehicle, an actuator (15) which acts on the engine, a controller (3) for the traction chain loaded with a model of the engine's operation and loaded with a program which, from the position of the accelerator, allows a pair (R.sub.th/set, PP.sub.set) of set values to be obtained for the revolution speed R.sub.th of the engine and for the position of the actuator (15), the said controller making it possible to control the position of the said actuator on the basis of the said set value PP.sub.set for the position of the actuator and to calculate a torque set value CC.sub.set for the electric traction motor or motors as a function of the deviation between the measured speed R.sub.th and the set value R.sub.th/set for the revolution speed of the engine.