Abstract: A construction machine includes a bidirectionally tiltable type hydraulic pump 2, a hydraulic cylinder 1 having a cap chamber 1e and a rod chamber 1f, a first flow path 11 connecting the hydraulic pump 2 and the cap chamber 1e, a second flow path 12 connecting the hydraulic pump 2 and the rod chamber 1f, a discharge flow path 16 branched from the first flow path 11, a discharge valve 32 that is disposed in the discharge flow path 16 and controls a discharge rate of hydraulic working oil from the cap chamber 1e to the discharge flow path 16, an operation device 54 that instructs an action of the hydraulic cylinder 1, and a controller 56.

Abstract: A construction machine incorporates a hydraulic closed circuit system capable of suppressing, even where a selector valve is stuck in an open state by a failure of the selector valve or a control system therefor, unintended operation of a hydraulic actuator and continuing operation of a machine body. The construction machine includes first sensors that detect open-closed states of a plurality of switching valves, first compulsory valve closing devices that change over the plurality of switching valves to a closed position irrespective of open-close control by a machine body controller, and a valve device controller that controls, when it is detected based on the open-closed states of the plurality of selector values detected by the first sensors that one of the plurality of selector values is stuck in an open state, the first compulsory valve closing device such that other selector valve connected to one of the plurality of closed circuit pumps to which the one selector valve is connected is closed.

Abstract: To provide a work machine capable of efficiently regenerating the energy owned by hydraulic fluid during a swing deceleration.

Abstract: This construction machine includes a first hydraulic drive device that is driven by a first prime mover and a second hydraulic drive device that is driven by a second prime mover. The first hydraulic drive device has a first closed circuit that connects a first hydraulic actuator and a first closed-circuit pump and a first assist flow path that connects the first closed circuit and a first open-circuit pump and that supplies pressure oil from the first open-circuit pump to the first closed circuit. The second hydraulic drive device is provided with a second closed circuit that connects a second hydraulic actuator and a second closed-circuit pump. The present invention also includes a first emergency flow path that branches from the first assist flow path and connects to the second closed circuit and that supplies pressure oil from the first open-circuit pump to the second closed circuit.

Abstract: Provided is a construction machine capable of detecting a stuck-open state of a surplus flow control valve in real time during operation without involving a reduction in the operational speed.

Abstract: Closed circuit lines (33, 43, 53, 63) for connecting hydraulic cylinders (17, 18, 19) and closed circuit pumps (31, 41, 51, 61) are provided with a charge pressure adjustment apparatus (75) via a charge line (72) to variably adjust the pressure in the charge line (72). An operating device (12) for operating the hydraulic cylinders (17, 18, 19) and the charge pressure adjustment apparatus (75) are connected to a control device (81). In the case of extending the hydraulic cylinders (17, 18, 19), the control device (81) increases a set pressure of the charge pressure adjustment apparatus (75) to be high to increase the pressure in the bottom side of the hydraulic cylinders (17, 18, 19) in accordance with an operating amount of the operating device (12).

Abstract: A work machine includes a closed circuit system in which there is provided a flushing valve.

Abstract: To provide a hydraulic driving device configured to smoothly extend a hydraulic cylinder. The present invention includes the open circuit E, the closed circuit A, a control device 57, and a control lever 56a. The open circuit E is provided with a flow passage 202 for connecting an outlet port of the open circuit pump 13 and a head chamber 1a of the boom cylinder 1, a selector valve 44a provided in the flow passage 202, a discharge flow passage 404 for connecting a hydraulic fluid tank 25 and a flow passage 200, and a bleed-off valve 64 provided in the discharge flow passage 404. The control device 57 is configured in such a manner that when a manipulate signal for extending the boom cylinder 1 is input from the control lever 56a, the bleed-off valve 64 is closed, the selector valve 44a is subsequently opened, and the open circuit pump 13 is controlled.

Abstract: There is provided a driving device for a work machine, having a closed hydraulic circuit system for driving cylinders with hydraulic pumps, the driving device making the speed of operation substantially the same in both directions of piston rod extension and contraction.

Abstract: To provide a driving device capable of improving the operability of a plurality of single rod hydraulic cylinders. The present invention takes a construction provided with a closed circuit A in which first and third hydraulic pumps 12, 14 and a boom cylinder 1 are connected through selector valves 43a, 45a in a closed-circuit fashion, a plurality of open circuits E, F provided with second and fourth hydraulic pumps 13, 15 and selector valves 44a, 46a that switch the supply destinations of hydraulic oils flowing out from the second and fourth hydraulic pumps 13, 15, and a connection passage 301 connected to sides of the selector valves 44a, 46a from which sides hydraulic oil flows out, and connected to the closed circuit A.

Abstract: A hydraulic closed circuit system using a single rod type hydraulic cylinder prevents the hunting of a flushing valve due to a delay in response of the flushing valve and circuit pressure pulsations, thereby preventing a decrease in operability of the hydraulic cylinder. A single rod type hydraulic cylinder is connected to a hydraulic pump via two hydraulic lines. A flushing valve is connected between the hydraulic lines and a tank; and a control unit is configured to add a predetermined control parameter to a pressure in a lower-pressure hydraulic line of the two hydraulic lines. The magnitude of a pressure in the higher-pressure hydraulic line of the two hydraulic lines is compared with the magnitude of a compensation pressure to which the control parameter has been added, and the flushing valve is switched when the compensation pressure and the higher-pressure hydraulic line pressure are found to be reversed in magnitude.

Abstract: To provide a work machine capable of efficiently regenerating the energy owned by hydraulic fluid during a swing deceleration.

Abstract: Closed circuit lines (33, 43, 53, 63) for connecting hydraulic cylinders (17, 18, 19) and closed circuit pumps (31, 41, 51, 61) are provided with a charge pressure adjustment apparatus (75) via a charge line (72) to variably adjust the pressure in the charge line (72). An operating device (12) for operating the hydraulic cylinders (17, 18, 19) and the charge pressure adjustment apparatus (75) are connected to a control device (81). In the case of extending the hydraulic cylinders (17, 18, 19), the control device (81) increases a set pressure of the charge pressure adjustment apparatus (75) to be high to increase the pressure in the bottom side of the hydraulic cylinders (17, 18, 19) in accordance with an operating amount of the operating device (12).

Abstract: To provide a driving device capable of improving the operability of a plurality of single rod hydraulic cylinders. The present invention takes a construction provided with a closed circuit A in which first and third hydraulic pumps 12, 14 and a boom cylinder 1 are connected through selector valves 43a, 45a in a closed-circuit fashion, a plurality of open circuits E, F provided with second and fourth hydraulic pumps 13, 15 and selector valves 44a, 46a that switch the supply destinations of hydraulic oils flowing out from the second and fourth hydraulic pumps 13, 15, and a connection passage 301 connected to sides of the selector valves 44a, 46a from which sides hydraulic oil flows out, and connected to the closed circuit A.

Abstract: To provide a hydraulic driving device configured to smoothly extend a hydraulic cylinder. The present invention includes the open circuit E, the closed circuit A, a control device 57, and a control lever 56a. The open circuit E is provided with a flow passage 202 for connecting an outlet port of the open circuit pump 13 and a head chamber 1a of the boom cylinder 1, a selector valve 44a provided in the flow passage 202, a discharge flow passage 404 for connecting a hydraulic fluid tank 25 and a flow passage 200, and a bleed-off valve 64 provided in the discharge flow passage 404. The control device 57 is configured in such a manner that when a manipulate signal for extending the boom cylinder 1 is input from the control lever 56a, the bleed-off valve 64 is closed, the selector valve 44a is subsequently opened, and the open circuit pump 13 is controlled.

Abstract: There is provided a driving device for a work machine, having a closed hydraulic circuit system for driving cylinders with hydraulic pumps, the driving device making the speed of operation substantially the same in both directions of piston rod extension and contraction.

Abstract: A hydraulic closed circuit system using a single rod type hydraulic cylinder prevents hunting of a flushing valve due to a delay in response of the flushing valve and circuit pressure pulsations, thereby preventing a decreasein operability of the hydraulic cylinder. A single rod type hydraulic cylinder is connected to a hydraulic pump via two hydraulic lines. A flushing valve is connected between the hydraulic lines and a tank; and a control unit is configured to add a predetermined control parameter to a pressure in a lower-pressure hydraulic line of the two hydraulic lines. The magnitude of a pressure in the higher-pressure hydraulic line of the two hydraulic lines is compared with the magnitude of a compensation pressure to which the control parameter has been added, and the flushing valve is switched when the compensation pressure and the higher-pressure hydraulic line pressure are found to be reversed in magnitude.