An apparatus includes a hydraulic circuit that is configured to selectively open fluid communication between one portion of the hydraulic circuit and another portion of the hydraulic circuit, such as a reservoir, based on the flow of the hydraulic fluid in the one portion. When the flow of hydraulic fluid exceeds a selected threshold in the one portion of the hydraulic circuit, the flow of fluid urges the opening of a hydraulic component of the hydraulic circuit to allow fluid communication between the one portion and the reservoir to discharge fluid from the one portion.

A prime mover and hydraulic actuators, a hydraulic machine having a rotatable shaft engaged with the prime mover and having a plurality of working chambers, a hydraulic circuit extending between a group of working chambers of the hydraulic machine and the hydraulic actuators, each working chamber of the hydraulic machine having a low-pressure and a high-pressure valve regulating the flow of hydraulic fluid between the working chamber and a corresponding low-pressure manifold and a high-pressure manifold. The hydraulic machine controlling the low-pressure valves of the group of working chambers to select the net displacement of hydraulic fluid by each working chamber on each cycle of working chamber volume, and thereby the net displacement of hydraulic fluid by the group of working chambers, responsive to a demand signal, the apparatus further having a controller calculating the demand signal responsive to a measured property of the hydraulic circuit or an actuator.

To make it possible to control supply, discharge, and recycled flow rates independently of each other for the boom cylinder in a construction machine comprising first and second boom spool valves respectively connected to first and second hydraulic pumps. When the boom cylinder is contracted, the first boom spool valve is configured to control the recycled flow rate from head side oil chamber to rod side oil chamber, the second boom spool valve is configured to control the discharge flow rate from head side oil chamber to oil tank, and both first and second boom spool valves are configured not to supply pressure oil from first and second hydraulic pumps to the boom cylinder.

A control valve of hydraulic system for a working machine is provided, which includes a main body and a spool. The main body includes first, second, third, fourth and fifth ports, and first second, third, fourth and fifth inner fluid paths connected to the first, second, third, fourth and fifth ports, respectively. The spool is configured to move between a neutral position and a communicating position allowing fluid communication between the second inner fluid path and the fifth inner fluid path or between the first inner fluid path and the fifth inner fluid path. The spool includes a communicating hole configured to allow the fluid communication between the second port and the fourth port, or between the first port and the fourth port, when the spool is in a position between the communicating position and the neutral position.

To achieve reduction of fuel consumption and enhancement of operability, in a hydraulic control circuit provided with a bypass oil passage formed by being branched from a discharge line of a hydraulic pump and extending to an oil tank, and a bypass valve having variable opening area for controlling a flow rate of the bypass oil passage, and to accurately perform pump pressure control through opening area control of the bypass valve without being affected by a condition of each time. The hydraulic control circuit is configured to perform closed-loop control of the opening area of the bypass valve so that the pump pressure is maintained at a set pressure, during nonoperation of the operation lever; on the other hand, to perform open-loop control for reducing the opening area of the bypass valve depending on the operation input of the operation lever, during an operation of the operation lever, and further configured to correct on the basis of the opening area of the bypass valve during the closed-loop control, the correspondence relationship between the operation input of the operation lever and the opening area of the bypass valve during the open-loop control.

Provided is a construction machine which can promptly adjust the rotational speed of a swing motor to a target rotational speed. A controller calculates a target rotational speed of the swing motor based on input from an operation device, calculates a degree of deviation of a rotational speed detected by a rotational speed sensor from the target rotational speed, sets a target driving pressure of the swing motor according to a moment of inertia about a swing axis of a swing structure and a work device and controls a pressure adjusting device in such a manner as to reduce a difference between a driving pressure detected by a pressure sensor and the target driving pressure, when the degree of deviation is larger than a predetermined value, and controls the pressure adjusting device in such a manner as to reduce a difference between the rotational speed detected by the rotational speed sensor and the target rotational speed, when the degree of deviation is equal to or smaller than the predetermined value.

There is provided a construction machine that is capable of measuring a minute leakage flow rate of a one-sided tilting variable displacement hydraulic pump. The construction machine includes a pressure sensor that detects a pressure of a hydraulic pump, a bleed-off adjusting device that is enabled to adjust a bleed-off flow rate of the hydraulic pump, and an input device that gives an instruction for measurement of a leakage flow rate of the hydraulic pump. The controller is configured to measure, when the controller determines that the operation device is in a non-operated state and when a measuring command is inputted from the input device, a pressure of the hydraulic pump while changing a control command value for the bleed-off adjusting device in a state in which a flow rate of the hydraulic pump is maintained, and calculate the leakage flow rate of the hydraulic pump on the basis of the control command value for the bleed-off adjusting device at the time that the pressure of the hydraulic pump is stabilized at a predetermined pressure.

To achieve reduction of fuel consumption and enhancement of operability, in a hydraulic control circuit provided with a bypass oil passage formed by being branched from a discharge line of a hydraulic pump and extending to an oil tank, and a bypass valve having variable opening area for controlling a flow rate of the bypass oil passage, and to accurately perform pump pressure control through opening area control of the bypass valve without being affected by a condition of each time. The hydraulic control circuit is configured to perform closed-loop control of the opening area of the bypass valve so that the pump pressure is maintained at a set pressure, during nonoperation of the operation lever; on the other hand, to perform open-loop control for reducing the opening area of the bypass valve depending on the operation input of the operation lever, during an operation of the operation lever, and further configured to correct on the basis of the opening area of the bypass valve during the closed-loop control, the correspondence relationship between the operation input of the operation lever and the opening area of the bypass valve during the open-loop control.

A hydraulic-pump flow-rate calibration system includes: a variable capacitance type hydraulic pump that supplies an operating fluid to a hydraulic actuator; a regulator that changes the dispense flow rate of the hydraulic pump according to a flow rate command signal; a flow rate detection device that detects the flow rate of the operating fluid; a control device that outputs the flow rate command signal to the regulator to control the regulator; and a calibration device that calculates an actual measurement characteristic of the dispense flow rate for the flow rate command signal, and performs, on a preset reference characteristic, calibration based on the actual measurement characteristic. The actual measurement characteristic is calculated as a result of the flow rate of the operating fluid being detected by the flow rate detection device during output of a predetermined flow rate command signal from the control device to the regulator.

A hydraulic system for a working machine includes hydraulic actuators actuated with hydraulic fluid delivered from a hydraulic pump, and control valves each of which is shiftable among shift positions to control a flowrate of hydraulic fluid flowing to the corresponding hydraulic actuator. Each control valve includes an input port, an output port, and a flowrate reduction section. When the control valve is shifted to a reduction position, the flowrate reduction section reduces a flowrate of the hydraulic fluid entering the input port and outputs the flowrate-reduced hydraulic fluid to the output port. At least one of the control valves includes a flowrate increase section. When the control valve is shifted to an increase position, the flowrate increase section outputs the hydraulic fluid having entered the input port to the output port at a flowrate larger than that of hydraulic fluid output by the flowrate reduction section.