Transmission for heavy construction equipment

A transmission for heavy construction equipment having an upper turning body, a lower traveling body and a turning joint for coupling the upper turning body to the lower traveling body so as to turn the upper turning body with respect to the lower traveling body, comprising:

• a control unit disposed in the upper turning body, said control unit comprising a pilot pump, and a solenoid valve switchable between different oil path communication positions and adapted to control the direction of oil discharged from the pilot pump;
• a charging pump disposed in the upper turning body;
• a power shift motor disposed in the lower traveling body and adapted to be to be actuated by oil fed from the charging pump;
• a power shift pump disposed in the lower traveling body and adapted to be actuated by the power shift motor;
• and
• a gear box disposed in the lower traveling body and provided with clutches for at least two speed change stages, the gear box performing a speed change operation by means of oil fed from the power shift pump, the gear box having a pilot valve communicating with the power shift pump and provided with a spool movable by the switching operation of the solenoid valve to be switched between different oil path communication positions, a gear shifting valve communicating with the power shift pump and provided with a spool movable by the switching operation of the pilot valve to be switched between different oil path communication positions respectively for feeding the oil discharged from the power shift pump to corresponding ones of the clutches, and a modulation valve communicating with the power shift pump and adapted to feed lubrication oil to the clutches.