Control system for hybrid construction machine

1. A control system for construction machine, comprising:

a pair of first and second main pumps which are variable-displacement pumps;

first and second circuit systems connected to the first and second main pumps and including a plurality of control valves;

main switching valves provided between the first and second circuit systems and the first and second main pumps;

a hydraulic motor for power generation connected to the first and second main pumps via the main switching valves;

a generator coupled to the hydraulic motor for power generation; and

a battery for storing power generated by the generator;

wherein when at least the main switching valve connected to one circuit system is at a position to cause one main pump connected thereto to communicate with the hydraulic motor for power generation, the main switching valve connected to the other circuit system causes the other main pump to communicate with the other circuit system.

2. The control system according to claim 1 , wherein:

one of the main switching valves causes one of the first and second main pumps to communicate with one of the first and second circuit systems connected thereto via a throttle passage in the one main switching valve when at a position to connect the main pump to the hydraulic motor for power generation.

3. The control system according to claim 1 , wherein:

one of the main switching valves connected to one of the first and second circuit systems opens a main passage for connecting one of the first and second main pumps to the one circuit system connected thereto and a joint passage for causing oil discharged from an assist pump to join the one main pump via a check valve when at a normal position, and opens the main passage and closes the joint passage when at a switch position.