The present disclosure relates to a hydraulic control circuit for crane slewing gear having directional valves arranged in work lines and controllable separately for the inflow and outflow to the hydraulic motor for the carrying out of a rotational movement of the slewing gear, wherein an inflow valve serves the control of the oil inflow from a hydraulic pump via the work line to the hydraulic motor and an outflow valve is provided via which the hydraulic motor can be relieved to the tank, wherein the work lines are each connected via at least one check valve to a common inlet of the outflow valve to relieve the hydraulic motor independently of the direction of rotation of the slewing gear via an outflow valve into the tank.

The present disclosure relates to a hydraulic control circuit for crane slewing gear having directional valves arranged in work lines and controllable separately for the inflow and outflow to the hydraulic motor for the carrying out of a rotational movement of the slewing gear, wherein an inflow valve serves the control of the oil inflow from a hydraulic pump via the work line to the hydraulic motor and an outflow valve is provided via which the hydraulic motor can be relieved to the tank, wherein the work lines are each connected via at least one check valve to a common inlet of the outflow valve to relieve the hydraulic motor independently of the direction of rotation of the slewing gear via an outflow valve into the tank.

A hydraulic system (600) and method for reducing boom dynamics of a boom (30), while providing counter-balance valve protection, includes a hydraulic actuator (110), first and second counter-balance valves (300, 400), first and second independent control valves (700, 800), and first and second blocking valves (350, 450). The actuator includes first and second corresponding chambers. In a first mode, the second counter-balance valve is opened by the first control valve, and the first counter-balance valve is opened by the second control valve. In a second mode, at least one of the counter-balance valves is closed. A meter-out control valve (800, 700) may be operated in a flow control mode, and/or a meter-in control valve (700, 800) may be operated in a pressure control mode. Boom dynamics reduction may occur while the boom is in motion (e.g., about a worksite). By opening the counter-balance valves, sensors at the control valves may be used to characterize external loads. The control valves may respond to the external loads and at least partially cancel unwanted boom dynamics. The system may further detecting faults in actuators with counter-balance valves and prevent any single point fault from causing a boom falling event and/or mitigate such faults.

To provide a construction machine that can highly precisely control branch flows from a hydraulic pump to a plurality of hydraulic actuators without being affected by load conditions. A controller (100) has a meter-out valve control section (140) configured to calculate a target opening area of a second meter-out valve (65a) (65b) according to a pressure difference between a supply pressure and a second meter-in pressure, or calculate a target opening area of a first meter-out valve (55a) (55b) according to a pressure difference between the supply pressure and the first meter-in pressure.

To provide a construction machine that can highly precisely control branch flows from a hydraulic pump to a plurality of hydraulic actuators without being affected by load conditions. A controller (100) has a meter-out valve control section (140) configured to calculate a target opening area of a second meter-out valve (65a) (65b) according to a pressure difference between a supply pressure and a second meter-in pressure, or calculate a target opening area of a first meter-out valve (55a) (55b) according to a pressure difference between the supply pressure and the first meter-in pressure.

A flow controller that changes the flow rate of air exhausted from an air cylinder in mid-stroke includes a first switching valve displaced from a first position to a second position under the effect of pilot air, and causing one port of the air cylinder to communicate with a first channel at the first position, exhausting air exhausted from the one port of the air cylinder while reducing the flow rate of the air using a first regulating valve at the second position. Since the pilot air is taken into the first switching valve from a second channel in a system different from the system of the first channel, a second regulating valve can be adjusted without being affected by the degree of opening of the first regulating valve.

A flow controller that changes the flow rate of air exhausted from an air cylinder in mid-stroke includes a first switching valve displaced from a first position to a second position under the effect of pilot air, and causing one port of the air cylinder to communicate with a first channel at the first position, exhausting air exhausted from the one port of the air cylinder while reducing the flow rate of the air using a first regulating valve at the second position. Since the pilot air is taken into the first switching valve from a second channel in a system different from the system of the first channel, a second regulating valve can be adjusted without being affected by the degree of opening of the first regulating valve.

A hydraulic system (600) and method for reducing boom dynamics of a boom (30), while providing counter-balance valve protection, includes a hydraulic cylinder (110), first and second counter-balance valves (300, 400), and first and second control valves (700, 800). A net load (90) is supported by a first chamber (116, 118) of the hydraulic cylinder, and a second chamber (118, 116) of the hydraulic cylinder may receive fluctuating hydraulic fluid flow from the second control valve to produce a vibratory response (950) that counters environmental vibrations (960) on the boom. The first control valve may apply a holding pressure and thereby hold the first counter-balance valve closed and the second counter-balance valve open.

A control system for construction machinery includes a hydraulic cylinder operable by a working oil discharged from a hydraulic pump, a control valve arranged between the hydraulic pump and the hydraulic cylinder to control an operation of the hydraulic cylinder according to a position of a spool therein, the control valve having a first spool position for draining the working oil discharged from a chamber of the hydraulic cylinder to a drain tank, and a pressure compensated valve installed in a return hydraulic line through which the working oil discharged from the control valve at the first spool position is drained to the drain tank, the pressure compensated valve being configured to control a flow rate of the working oil passing through the pressure compensated valve according to a pressure difference between a front end and a rear end of the control valve.

The disclosure relates to a method for operating a hydraulic drive which comprises a hydraulic consumer with a positionable piston in a cylinder which is connected to a tank at one connection via a pump of variable rotational speed and at another connection via a proportional valve, wherein a position of the piston is controlled using a model-based control in which a rotational speed of the pump is used as a manipulated variable and in which a position of the proportional valve is preset.