In a hydraulic driving system, a plurality of loading-line driving devices adjust a flow rate of an operating liquid flowing from a loading-line pump to a loading-line actuator, and a steering-line driving device adjusts a flow rate of the operating liquid flowing from the steering-line pump to the steering actuator. When one of a plurality of loading-line actuators is driving, a switching valve device connects a loading-side passage and a steering-side passage. When any of the plurality of loading-line actuators is not driving, the switching valve device disconnects the loading-side passage and the steering-side passage.

A pneumatic unit for a hydropneumatic pressure booster has a system line that leads from a compressed air inlet to a compressed air outlet. A bypass line runs parallel to the system line and it is connected to the system line via first and second compressed air switches. A compressed air reservoir is connected in the bypass line, and a pressure intensifier is connected in the region between the first compressed air switch and the compressed air reservoir. The pneumatic unit makes available to the pressure booster a sufficiently high pneumatic pressure for carrying out at least one operational step of a connected hydraulic tool, even in the case of a pressure decrease or pressure failure in the supplying pneumatic line. For that purpose, the second compressed air switch is configured for switching the compressed air flow between the system line and the bypass line.

There is provided a hydraulic driving device for working machine having operability handling a change in burden weight in a front working device due to a loaded burden and the like when the working machine that accumulates energy in an accumulator and recovers and regenerates the energy performs an operation of lowering the front working device. A hydraulic driving device 5 includes a main pump 101, a boom cylinder 3, a tank 20, a flow rate control valve 6, an accumulator 300, a first differential pressure control valve 201, and a second differential pressure control valve 202. The first differential pressure control valve 201 is located between the boom cylinder 3 and the accumulator 300. The first differential pressure control valve 201 performs control on discharge oil from the boom cylinder 3 such that a differential pressure between before and after the flow rate control valve 6 becomes a target differential pressure. The second differential pressure control valve 202 is located between the accumulator 300 and the tank 20. The second differential pressure control valve 202 performs control on the discharge oil such that a differential pressure between an upstream pressure and a downstream pressure of the flow rate control valve 6 and the first differential pressure control valve 201 becomes the target differential pressure. The first and the second differential pressure control valves 201 and 202 are configured such that the target differential pressure increases according to an increase in pressure of the discharge oil.

A hydraulic system for a working machine is a load sensing system and includes a hydraulic actuator for movement of an implement and a control valve having an inlet valve and an outlet valve for controlling the flow of hydraulic fluid from a pump to the hydraulic actuator and for draining hydraulic fluid from the hydraulic actuator, respectively. The hydraulic system also includes an arrangement for determining the load on the hydraulic actuator. The hydraulic system further includes a valve for disconnecting the flow of hydraulic fluid from the pump to the hydraulic actuator, while allowing another flow of hydraulic fluid to the hydraulic actuator, provided that the determined load on the hydraulic actuator exceeds a threshold value.

A pressure compensation unit includes: a control valve controlling hydraulic fluid supply and discharge to and from an actuator, the control valve including a pump port, a pair of relay and supply/discharge ports, and a tank port; a pressure compensation valve connected to the relay ports by an upstream and downstream-side relay lines, the pressure compensation valve moving in accordance with a pressure difference between upstream-side relay line and signal pressure; a load pressure detection line branching from the downstream-side relay line; a relief line connected to the downstream-side relay line and having a relief valve; and a switching valve leading: a maximum load pressure to the pressure compensation valve as the signal pressure when the hydraulic fluid does not flow through the relief line; and a pump pressure to the pressure compensation valve as the signal pressure when the hydraulic fluid flows through the relief line.

A dual pressure margin priority circuit and method for controlling flow from a pump to steering valve and low priority inlets. A steering pressure valve controls flow from pump to steering valve inlets, and provides a steering valve load sense pressure. A priority valve controls flow from pump to low priority inlets. A load sense cutoff valve has a first inlet receiving the steering valve load sense pressure. The load sense cutoff valve controls flow through the priority valve based on steering valve load sense pressure at the first cutoff valve inlet. The cutoff valve can include a second inlet coupled to tank, and a load sense input coupled to the steering valve load sense pressure. The cutoff valve can be a pressure limiter valve. The priority and steering pressure valves can be 2-way proportional flow spool valves with bias springs, and contributing and opposing load sense inputs.

A control system includes: a first hydraulic pump and a second hydraulic pump; a passage connecting the first hydraulic pump and the second hydraulic pump with each other; an opening/closing device provided in the passage and configured to open and close the passage; a control device configured to control the opening/closing device to switch between a split-flow state in which the passage is closed and a connected state in which the passage is open; a first actuator to which hydraulic fluid discharged from the first hydraulic pump is supplied in the split-flow state; and a second actuator to which hydraulic fluid discharged from the second hydraulic pump is supplied in the split-flow state. In the connected state, the control device controls the opening/closing device so that the connected state is maintained even when either one of the first actuator and the second actuator is brought into a driven state.

A hydraulic system for a working machine is a load sensing (LS) system and includes a first hydraulic actuator and a first control valve for controlling the flow of hydraulic fluid from a pump to the first hydraulic actuator and for draining hydraulic fluid from the first hydraulic actuator, respectively, and a second hydraulic actuator and a second control valve for controlling the flow of hydraulic fluid from the pump to the second hydraulic actuator and for draining hydraulic fluid from the second hydraulic actuator, respectively. The hydraulic system further includes a first hydraulic circuit for providing an LS pressure for the first actuator and a second hydraulic circuit for providing an LS pressure for the second actuator. At least one of the first and second hydraulic circuits includes an offset valve for changing the LS pressure before providing the LS pressure to the pump.

A dual pressure margin priority circuit and method for controlling flow from a pump to steering valve and low priority inlets. A steering pressure valve controls flow from pump to steering valve inlets, and provides a steering valve load sense pressure. A priority valve controls flow from pump to low priority inlets. A load sense cutoff valve has a first inlet receiving the steering valve load sense pressure. The load sense cutoff valve controls flow through the priority valve based on steering valve load sense pressure at the first cutoff valve inlet. The cutoff valve can include a second inlet coupled to tank, and a load sense input coupled to the steering valve load sense pressure. The cutoff valve can be a pressure limiter valve. The priority and steering pressure valves can be 2-way proportional flow spool valves with bias springs, and contributing and opposing load sense inputs.

In a hydraulic driving system, a plurality of loading-line driving devices adjust a flow rate of an operating liquid flowing from a loading-line pump to a loading-line actuator, and a steering-line driving device adjusts a flow rate of the operating liquid flowing from the steering-line pump to the steering actuator. When one of a plurality of loading-line actuators is driving, a switching valve device connects a loading-side passage and a steering-side passage. When any of the plurality of loading-line actuators is not driving, the switching valve device disconnects the loading-side passage and the steering-side passage.