Abstract: A hydraulic excavator drive system includes: a first pump that supplies hydraulic oil to a boom cylinder via a boom control valve, and supplies the hydraulic oil to a bucket cylinder via a first bucket control valve; a second pump that supplies the hydraulic oil to an arm cylinder via an arm control valve; a third pump that supplies the hydraulic oil to a slewing motor via a slewing control valve, and supplies the hydraulic oil to the bucket cylinder via a second bucket control valve; and a controller that moves one of the first bucket control valve and the second bucket control valve when a bucket excavating operation or a bucket dumping operation is performed concurrently with another operation, and moves both the first bucket control valve and the second bucket control valve when a bucket excavating operation is performed alone.

Abstract: A hydraulic drive system of construction machine including: turning motor; turning operation device that outputs turning operation signal corresponding to inclination angle of operating lever; turning direction switching valve including spool and driver, driver receiving command current and driving spool, turning direction switching valve increasing amount of hydraulic liquid supplied to turning motor and amount of hydraulic liquid discharged from turning motor with increase in command current; controller that feeds command current to turning direction switching valve, wherein command current increases in accordance with increase in turning operation signal; and pressure sensor that detects outflow pressure of turning motor.

Abstract: A hydraulic excavator drive system includes: a first pump that supplies hydraulic oil to a boom cylinder via a boom control valve, and supplies the hydraulic oil to a bucket cylinder via a first bucket control valve; a second pump that supplies the hydraulic oil to an arm cylinder via an arm control valve; a third pump that supplies the hydraulic oil to a slewing motor via a slewing control valve, and supplies the hydraulic oil to the bucket cylinder via a second bucket control valve; and a controller that moves one of the first bucket control valve and the second bucket control valve when a bucket excavating operation or a bucket dumping operation is performed concurrently with another operation, and moves both the first bucket control valve and the second bucket control valve when a bucket excavating operation is performed alone.

Abstract: A hydraulic drive system of construction machine including: turning motor; turning operation device that outputs turning operation signal corresponding to inclination angle of operating lever; turning direction switching valve including spool and driver, driver receiving command current and driving spool, turning direction switching valve increasing amount of hydraulic liquid supplied to turning motor and amount of hydraulic liquid discharged from turning motor with increase in command current; controller that feeds command current to turning direction switching valve, wherein command current increases in accordance with increase in turning operation signal; and pressure sensor that detects outflow pressure of turning motor.