Provided is a hydraulic circuit, for a construction machine, which drives an actuator by merging pressure oil from a fixed-volume pump into a center bypass oil path from a variable-volume pump to an oil tank, wherein the flow rate of flow from the fixed-volume pump to the center bypass oil path can be controlled in accordance with a requested flow rate of the actuator. A distribution direction-switching valve, which has a first oil path from a fixed-volume pump to an oil tank and a second oil path from the fixed-volume pump to a first center bypass oil path, has a first signal reception unit which causes a spool to slide in a direction in which the first oil path is formed, and a second signal reception unit which causes a spool to slide in a direction in which the second oil path is formed, and determines a distribution ratio of pressure oil flowing to the first oil path and the second oil path in accordance with the difference in size of the signals received by the first signal reception unit and the second signal reception unit, the first signal reception unit receiving a signal based on a negative control signal.

A direction control valve group for a construction machine that controls an amount of pressure oil supplied to a hydraulic actuator from a hydraulic pump that discharges the pressure oil is provided. The direction control valve includes a cylinder port that supplies the pressure oil to the hydraulic actuator, a bridge passage that is switchably connected and disconnected to the cylinder port according to a change in position of a first spool, and an internal passage that supplies the pressure oil discharged from the hydraulic pump to the bridge passage. The first spool is provided in the internal passage.

A hydraulic apparatus comprises first and second manifolds each of which is connected to a plurality of actuators via corresponding actuator valves connected in parallel and operated responsive to inputs to regulate the flow of fluid to the actuators. A plurality of working chambers are connectable to either the first or second manifold and have a net flow which is controlled responsive to a negative feedback signal. The negative feedback signal is determined in response to a calculated pressure or flow rate in virtual fluid flow paths extending from the first and second manifolds.

A hydraulic system of a construction machine includes: control valves interposed between a variable displacement main pump and hydraulic actuators; and first solenoid proportional valves connected to pilot ports of the control valves. The hydraulic system further includes: a regulator that changes a displacement of the main pump; and a second solenoid proportional valve connected to an auxiliary pump by a primary pressure line, the second solenoid proportional valve outputting a secondary pressure to the regulator through a secondary pressure line. A switching valve is interposed between the auxiliary pump and the first solenoid proportional valves, and includes a pilot port that is connected to the secondary pressure line by a pilot line.

A hydraulic system for a rear gate of a baler implement includes a fluid circuit having a first portion connected to and disposed in fluid communication with a first fluid port of a hydraulic cylinder. A flow bypass assembly is disposed in the first portion of the fluid circuit. The flow bypass assembly includes a flow rate control valve selectively moveable between a first position allowing fluid communication therethrough at a first flow rate, and a second position blocking fluid communication therethrough. The flow bypass assembly further includes a bypass passageway for circulating the fluid when the flow rate control valve is closed. A flow restriction is disposed within the bypass passageway to provide a second flow rate that is less than the first flow rate.

A hydraulic system includes: a slewing motor; a mechanical brake; and a slewing control valve interposed between a main pump and the slewing motor. A first pilot port of the slewing control valve is connected to a first solenoid proportional valve by a pilot line. A second pilot port of the slewing control valve is connected to a second solenoid proportional valve by a second pilot line. The first solenoid proportional valve and the second solenoid proportional valve are connected to an auxiliary pump by a primary pressure line. A switching valve is interposed between the auxiliary pump and the mechanical brake. The switching valve includes a pilot port that is connected to the first pilot line by a switching pilot line. The valve switches from a closed to an open position when a pilot pressure led to the pilot port becomes higher than or equal to a setting value.

A hydraulic machine is provided. A boom actuator includes a large chamber and a small chamber. A recovery unit receives fluid discharged from the large chamber and then recovers energy. A recovery line connects the large chamber and the recovery unit. An accumulator is connected to the recovery line. A jack-up assist line connects the accumulator and the small chamber. A jack-up assist valve is disposed on the jack-up assist line to block flow of fluid from the accumulator to the small chamber in a first position and allow the flow of fluid from the accumulator to the small chamber in a second position. A controller controls movement of the jack-up assist valve. The controller may determine whether or not the hydraulic machine is in a jack-up condition, and when the hydraulic machine is determined to be in the jack-up condition, moves the jack-up assist valve to the second position.

A hydraulic machine. A boom actuator includes a large chamber and a small chamber. A recovery unit receives fluid discharged from the large chamber and then recovers energy. A recovery line connects the large chamber and the recovery unit. An accumulator is connected to a first point on the recovery line. A discharge valve is disposed on the recovery line between the first point and the recovery unit. A first sensor measures a pressure in the accumulator. A controller controls opening and closing of the discharge valve. The controller performs anti-bouncing control of: determining a target pressure in the accumulator corresponding to a load pressure applied to fluid in the large chamber by a load according to a predetermined correspondence; and controlling the opening and closing of the discharge valve such that the pressure in the accumulator measured by the first sensor reaches the target pressure.

A hydraulic drive apparatus includes a flow-path selector valve and a flow-path switching control unit that operates the valve. The flow-path selector valve has a first position for a single operation state and a second position for a combined operation state, configured to, at the first position, form a first flow path connected to a first pump, a second flow path connected to a second pump, and a connecting flow path providing communication between the first flow path and the second flow path. When a driving state of a work actuator is deviated from an allowable range in the combined operation state, the flow-path switching control unit reduces an opening area of the connecting flow path as compared with that when the driving state is within the allowable range.

Disclosed is a hydraulic control apparatus including a flow-path selector valve that switches a supply flow path and a flow-path switching control unit that operates the same, a regeneration valve and a regeneration release valve capable of the regenerative operation, and a regeneration control unit that operates the same. The flow-path switching control unit makes the flow-path selector valve form a flow-path providing communication between first and second pumps in a combined operation state. The regeneration control unit judges the propriety of the regenerative operation on the basis of the second pump pressure which is the discharge pressure of the second pump in a single operation state and judges the propriety of the regenerative operation on the basis of whether or not the driving state of the work actuator is within an allowable range corresponding to the target work operation amount in the combined operation state.