Micro speed changer for passenger car

The invention belongs to the technical field of speed changers, and particularly relates to a micro speed changer for a passenger car. A main body structure comprises a clutch shell, a speed changer shell, a clutch, a gear selecting and shifting mechanism, an oil discharging screw plug, a shifting fork shaft assembly, an input shaft, an output shaft, a middle shaft, a separation bearing, an input shaft sheath, a gear-III and gear-IV synchronizer component, a gear-III gear assembly, a gear-II gear assembly, a gear-I and gear-II synchronizer component, a gear-I gear assembly, an intermediate supporting bearing, a reverse-gear gear assembly, a gear-V and reverse-gear synchronizer component, a gear-V gear assembly, a rear supporting bearing, an odometer driving gear, an output shaft sheath, a left supporting bearing, a right supporting bearing, an idle pulley shaft, a gear, a compression nut, a connecting bearing and an idle pulley gear, wherein the clutch shell and the speed changer shell are aluminum die castin