Hydraulic control device and operating machine having the same

1. A hydraulic control device, comprising:

a hydraulic pump that is driven by rotation of an output shaft of an engine;

at least one hydraulic actuator that is activated by a supply of hydraulic fluid from the hydraulic pump and includes a regenerative actuator, a part of return oil to be derived from the regenerative actuator being used for regeneration;

a recovery oil passage for recovering, into a tank, the hydraulic fluid derived from the at least one hydraulic actuator and the hydraulic pump;

a regenerative motor that rotates the output shaft of the engine in response to the supply of the hydraulic fluid and is driven to rotate by rotation of the output shaft of the engine;

a regenerative oil passage for guiding the return oil from the regenerative actuator to the regenerative motor without passing the return oil through the recovery oil passage;

a coupling oil passage that couples the recovery oil passage and the regenerative oil passage to each other;

a regeneration-side check valve that is provided on the coupling oil passage, allows the hydraulic fluid to flow from the recovery oil passage toward the regenerative motor through the coupling oil passage, and prevents the hydraulic fluid from flowing from the regenerative motor toward the recovery oil passage through the coupling oil passage,

a recovery-side check valve that is provided in a position of the recovery oil passage between the tank and a recovery connection between the recovery oil passage and the coupling oil passage, and that is closed normally, and moreover allows the hydraulic fluid to flow from the recovery connection side toward the tank side when a pressure on the recovery connection side is equal to or greater than a set pressure; and

a regeneration valve that is provided in a position of the regenerative oil passage located upstream of a regeneration connection between the regenerative oil passage and the coupling oil passage and can be switched between an allowing state for allowing the return oil to flow through the regenerative oil passage and a restricting state for restricting the flow of the return oil through the regenerative oil passage, and that is a two-port valve;

wherein the regeneration-side check valve is opened at a pressure equivalent to or lower than the set pressure of the recovery-side check valve.

2. The hydraulic control device according to claim 1 , further comprising:

a control unit that switches the regeneration valve to the allowing state during a regeneration period in which the return oil from the regenerative actuator can be regenerated, and switches the regeneration valve to the restricting state during a period other than the regeneration period.

3. The hydraulic control device according to claim 1 , further comprising:

a discharge oil passage that couples the recovery oil passage to a position of the regenerative oil passage located upstream of a regeneration connection between the regenerative oil passage and the coupling oil passage; and

a discharge valve for guiding, to the recovery oil passage, return oil other than the return oil to be supplied to the regenerative motor out of return oil from the regenerative actuator, the discharge valve provided on the discharge oil passage.

4. An operating machine, comprising:

a base machine;

a boom attached to the base machine so as to be raised and lowered with respect to the base machine;

a boom cylinder that raises and lowers the boom with respect to the base machine; and

the hydraulic control device according to claim 1 ,

wherein the hydraulic control device includes the boom cylinder as the regenerative actuator.