Control device for hybrid construction machine

1. A control device for a hybrid construction machine, comprising:

a variable volume pump;

a plurality of operation valves that control a flow of a working oil led to respective actuators from the variable volume pump;

a neutral flow passage that leads the oil discharged from the variable volume pump to a tank when the operation valves are in a neutral position;

a pilot pressure generating throttle provided in the neutral flow passage on a downstream side of the operation valves;

a first pilot flow passage to which a pressure generated on an upstream side of the pilot pressure generating throttle is led;

a regulator that performs control such that a tilt angle of the variable volume pump increases as an exerted pilot pressure decreases;

an operating condition detector that detects an operating condition of the operation valves;

a regenerative hydraulic motor rotated by the oil discharged from the variable volume pump;

a power generator connected to the hydraulic motor;

a main switch valve that leads the working oil discharged from the variable volume pump selectively to the operation valves or the hydraulic motor;

a second pilot flow passage that leads a pilot pressure oil supplied from a pilot pressure source to the regulator;

a pilot selection valve that connects the first pilot flow passage or the second pilot flow passage to the regulator selectively;

a solenoid variable pressure reducing valve that is provided in the second pilot flow passage to be capable of variably controlling a pilot pressure led from the pilot pressure source and exerted on the regulator; and

a controller that switches the main switch valve such that the oil discharged from the variable volume pump is led to the hydraulic motor and switches the pilot selection valve such that the second pilot flow passage communicates with the regulator when all of the operation valves are determined to be in the neutral position on the basis of a detection result from the operating condition detector.

2. The control device for a hybrid construction machine as defined in claim 1 , wherein the main switch valve is a pilot operated valve switched by the pilot pressure oil supplied from the pilot pressure source,

the control device further comprises:

a third pilot flow passage that leads the pilot pressure oil supplied from the pilot pressure source to a pilot chamber of the main switch valve; and

a pilot solenoid switch valve that is provided in the third pilot flow passage and switched to a blocking position or a communicating position on the basis of an output signal from the controller, and

the controller switches the main switch valve by setting the pilot solenoid switch valve to the communicating position when all of the operation valves are determined to be in the neutral position.

3. The control device for a hybrid construction machine as defined in claim 1 , wherein the solenoid variable pressure reducing valve is capable of controlling the pilot pressure exerted on the regulator from a pressure for keeping the variable volume pump at a minimum tilt angle to a pressure for keeping the variable volume pump at a maximum tilt angle on the basis of an output signal from the controller.

4. The control device for a hybrid construction machine as defined in claim 1 , further comprising:

a prime mover that drives the variable volume pump; and

a rotation speed detector that detects a rotation speed of the prime mover,

wherein, the controller controls a secondary pressure of the solenoid variable pressure reducing valve such that a displacement amount per revolution of the variable volume pump reaches a minimum when all of the operation valves are determined to be in the neutral position and the rotation speed detected by the rotation speed detector exceeds a predetermined set rotation speed.

5. The control device for a hybrid construction machine as defined in claim 1 , further comprising a battery that is charged with power generated as the hydraulic motor rotates,

wherein the controller calculates a required amount of charge on the basis of a amount of charge of the battery, determines a discharge flow of the variable volume pump corresponding to the calculated required amount of charge, and controls the secondary pressure of the solenoid variable pressure reducing valve such that the discharge flow of the variable volume pump matches the determined discharge flow when all of the operation valves are determined to be in the neutral position.