Provided is a hydraulic drive apparatus of a work machine capable of reducing a surge pressure. The hydraulic drive apparatus includes a control valve interposed between the hydraulic pump and a hydraulic actuator, an operation device moving the control valve in response to an actuator operation, an unload valve, an unload operation valve changing a pilot pressure of the unload valve in response to an input of an unload operation command, a target pressure calculation part, and an unload operation command part. The target pressure calculation part calculates a target pressure that increases with an increase in the holding pressure of the hydraulic actuator. The unload operation command part inputs an unload operation command to the unload operation valve to make the pump pressure of the hydraulic pump follow the target pressure.

A construction machine that precisely enables derivation of the operation characteristics of hydraulic actuators in a high-velocity area with less calibration operation is provided. A controller (10) has a calibration mode in which the controller (10) derives operation characteristics (α(xs)) representing a relation among a spool position (xs) of a meter-in valve (8a1), an operation velocity (Va) of a hydraulic actuator (4a), and a differential pressure (ΔP) across the meter-in valve (8a1), and is configured to, in a case where the spool position (xs) of the meter-in valve (8a1) has changed in a direction to increase the opening area of the meter-in valve (8a1) in the calibration mode, output a command signal to increase the opening area of a bleed-off valve (8b1) to a bleed-off solenoid proportional pressure-reducing valve (8b2) as a command signal to reduce the differential pressure (ΔP).

A construction machine that precisely enables derivation of the operation characteristics of hydraulic actuators in a high-velocity area with less calibration operation is provided. A controller (10) has a calibration mode in which the controller (10) derives operation characteristics (α(xs)) representing a relation among a spool position (xs) of a meter-in valve (8a1), an operation velocity (Va) of a hydraulic actuator (4a), and a differential pressure (ΔP) across the meter-in valve (8a1), and is configured to, in a case where the spool position (xs) of the meter-in valve (8a1) has changed in a direction to increase the opening area of the meter-in valve (8a1) in the calibration mode, output a command signal to increase the opening area of a bleed-off valve (8b1) to a bleed-off solenoid proportional pressure-reducing valve (8b2) as a command signal to reduce the differential pressure (ΔP).

A hydraulic system includes a hydraulic pump, an output fluid tube connected to the hydraulic pump, an operation fluid tube connected to a hydraulic device, an unload valve connected to the output fluid tube, and having: a supply position in which the operation fluid in the output fluid tube is supplied to the operation fluid tube; and a restrain position in which supply of the operation fluid to the operation fluid tube is restrained, an operation valve connected to the output fluid tube, a control fluid tube connecting the operation valve and the hydraulic device, a warmup fluid tube connecting the control fluid tube and the operation fluid tube, and a check valve provided in the warm-up fluid tube and being for allowing the operation fluid to flow from the control fluid tube side toward the operation fluid tube, and for blocking the operation fluid from flowing side from the operation fluid tube toward the control fluid tube.

A hydraulic system includes a hydraulic pump, an output fluid tube connected to the hydraulic pump, an operation fluid tube connected to a hydraulic device, an unload valve connected to the output fluid tube, and having: a supply position in which the operation fluid in the output fluid tube is supplied to the operation fluid tube; and a restrain position in which supply of the operation fluid to the operation fluid tube is restrained, an operation valve connected to the output fluid tube, a control fluid tube connecting the operation valve and the hydraulic device, a warmup fluid tube connecting the control fluid tube and the operation fluid tube, and a check valve provided in the warm-up fluid tube and being for allowing the operation fluid to flow from the control fluid tube side toward the operation fluid tube, and for blocking the operation fluid from flowing side from the operation fluid tube toward the control fluid tube.

System and methods for a DC powered hydraulic system capable of providing control over pressurized hydraulic fluid delivered to directional valves without the need for a PTO and/or a proportional valve. The hydraulic system controls the output from a battery to a direct current hydraulic pump.

A hydraulic system includes a first system discharge fluid tube that discharges fluid flowing through a first supply fluid tube, a second system discharge fluid tube that discharges fluid, a first control valve, and a second control valve connected to a second supply fluid tube, the first system discharge fluid tube, and the second system discharge fluid tube, configured to be switched between: a supply position that supplies fluid from the second supply fluid tube to the first supply fluid tube; a first stop position that stops supply of fluid from the second to the first supply fluid tube and supplies fluid from the first supply fluid tube to the first system discharge fluid tube; and a second stop position that stops supply of fluid from the second to the first supply fluid tube and supplies fluid from the first supply fluid tube to the second system discharge fluid tube.

A control valve assembly for a load handling vehicle such as forklift comprises a valve body having a bore and a spool located within the bore that is axially movable along the bore between at least two operating configurations. The valve body includes a service port connected to a hydraulic actuator, a pressure port connected to a pump, and a tank port connected to a hydraulic tank reservoir. The valve is reconfigurable between first and second operating configurations. In the first operating configuration the spool defines a fluid pathway connecting the pump port, the service port and the tank port such that in a first flow direction fluid is able to flow from the pressure port to the service port and the tank port, and in a second flow direction fluid is able to flow from the service port to the pressure port and the tank port. The spool is also controllable in the first operating configuration to variably restrict flow to the tank port. In the second operating configuration the spool defines a fluid pathway connecting the pressure port and the actuator port, and is controllable to variably restrict flow between the pressure port and the actuator port.

A control valve assembly for a load handling vehicle such as forklift comprises a valve body having a bore and a spool located within the bore that is axially movable along the bore between at least two operating configurations. The valve body includes a service port connected to a hydraulic actuator, a pressure port connected to a pump, and a tank port connected to a hydraulic tank reservoir. The valve is reconfigurable between first and second operating configurations. In the first operating configuration the spool defines a fluid pathway connecting the pump port, the service port and the tank port such that in a first flow direction fluid is able to flow from the pressure port to the service port and the tank port, and in a second flow direction fluid is able to flow from the service port to the pressure port and the tank port. The spool is also controllable in the first operating configuration to variably restrict flow to the tank port. In the second operating configuration the spool defines a fluid pathway connecting the pressure port and the actuator port, and is controllable to variably restrict flow between the pressure port and the actuator port.

A hydraulic system (1, 50) for a load handling vehicle comprises lifting actuator (2, C1) that operates in a load lifting mode in which a load is induced on the actuator, and a load lowering mode in which the actuator provides hydraulic power PI to the hydraulic system. An auxiliary hydraulic actuator (4, 6, 8, C2) is also provided that has a hydraulic power demand P2. A hydraulic pump (10, 58) directs hydraulic power to the hydraulic lifting actuator and the at least one auxiliary hydraulic actuator. The hydraulic system is configured such that when the hydraulic lifting actuator is in the load lowering mode, it is required to simultaneously actuate the at least one auxiliary hydraulic actuator, and PI is greater than or equal to P2, hydraulic power may be channelled directly to the auxiliary hydraulic actuator from the hydraulic lifting actuator in order that the at least one auxiliary hydraulic actuator is actuated entirely by the hydraulic power from the hydraulic lifting actuator, and without the use of the pump.