Control system for construction machine

1. A control system for a construction machine, comprising:

a boom cylinder partitioned into a piston side chamber and a rod side chamber by a piston, the boom cylinder operating so as to be extended and contracted by supplying a working fluid to the piston side chamber or the rod side chamber, thereby driving a boom;

a boom switching valve adapted to adjust a supply amount of the working fluid to be supplied to the piston side chamber or the rod side chamber by means of a stroke of a spool;

a fluid pressure motor adapted to drive a motor generator by being rotated by means of a return fluid guided from the piston side chamber;

a regeneration control valve adapted to communicate the piston side chamber with the boom switching valve and the fluid pressure motor, the regeneration control valve being adapted to adjust a first supply amount and a second supply amount, the first supply amount serving as a supply amount of the working fluid supplied from the piston side chamber to the boom switching valve, the second supply amount serving as a supply amount of the working fluid supplied from the piston side chamber to the fluid pressure motor; and

a controller adapted to control the regeneration control valve so that the second supply amount becomes smaller than the first supply amount in response to a determination that a stroke amount of the spool becomes an upper limit value or more.

2. A control system for a construction machine, comprising:

a boom cylinder in which a piston side chamber and a rod side chamber are formed by a piston, the boom cylinder operating so as to be extended and contracted by supplying a working fluid to the piston side chamber or the rod side chamber, thereby driving a boom;

a boom switching valve adapted to adjust a supply amount of the working fluid to be supplied to the piston side chamber or the rod side chamber by means of a stroke of a spool;

a fluid pressure motor adapted to drive a motor generator by being rotated by means of a return fluid guided from the piston side chamber;

a regeneration control valve adapted to communicate the piston side chamber with the boom switching valve and the fluid pressure motor, the regeneration control valve being adapted to adjust a supply amount of the working fluid supplied from the piston side chamber to the boom switching valve and a supply amount of the working fluid supplied from the piston side chamber to the fluid pressure motor;

a bleed-off valve provided on a passage connecting the regeneration control valve to the fluid pressure motor, the bleed-off valve communicating or blocking between the piston side chamber and a tank at a drain side; and

a controller adapted to, in a case where a stroke amount of the spool becomes an upper limit value or more, control an opening degree of the bleed-off valve in accordance with the stroke amount to communicate the piston side chamber with the tank.

3. The control system for the construction machine according to claim 1 , wherein the regeneration control valve includes:

a pilot chamber connected to a pilot pressure source via a proportional solenoid valve; and

a spring provided on the opposite side of the pilot chamber, the spring being adapted to exert spring force for pressing the spool toward the side of the pilot chamber, and

wherein the controller controls the opening degree of the regeneration control valve by controlling the proportional solenoid valve to apply pilot pressure to the pilot chamber.

4. The control system for the construction machine according to claim 1 , wherein

the upper limit value is set up on the basis of rated power of the motor generator.