Hybrid construction machine

A hybrid construction machine, comprising:

• a main pump;
• a first hydraulic motor;
• a first hydraulic passage that drives the first hydraulic motor using a discharge pressure of the main pump;
• a second hydraulic motor that varies a motor capacity according to a tilt angle thereof;
• a power generator connected to the second hydraulic motor;
• a hydraulic control circuit that controls a flow in the first hydraulic passage, the hydraulic control circuit comprising a plurality of valves all of which are switched to a neutral position upon input of a braking command of the first hydraulic motor;
• a brake circuit that is activated when all of the plurality of valves are switched to the neutral position and causes the first hydraulic motor in rotation to act as a hydraulic pump;
• a second hydraulic passage that supplies a discharge pressure of the first hydraulic motor acting as a hydraulic pump to the second hydraulic motor;
• a safety valve that regulates a flow resistance in the second hydraulic passage system;
• a pressure sensor that detects the discharge pressure of the first hydraulic motor acting as a hydraulic pump;
• a neutral position detecting sensor detecting that all of the plurality of valves are in the neutral position;
• and
• a programmable control unit programmed to:
• control the safety valve to decrease the flow resistance in the second hydraulic passage when and a detected pressure of the pressure sensor has reached a predetermined pressure in a state where all of the plurality of valves are in the neutral position;
• control the tilt angle of the second hydraulic motor to compensate for a pressure drop in the second hydraulic passage when the safety valve has decreased the flow resistance in the second hydraulic passage.