An object to reduce a relief amount at the start of turning. A hydraulic drive system of a construction machine includes: a turning control valve disposed on a first circulation line extending from a first pump; a boom control valve disposed on a second circulation line extending from a second pump; first and second regulators, which change tilting angles of the first and second pumps; and a controller, which controls one or more solenoid proportional valves, which output a secondary pressure to the first and second regulators. While a turning operation is being performed, if a discharge pressure of the first pump is higher than a first setting value and a discharge pressure of the second pump is lower than a second setting value, the controller lowers first and second horsepower control lines that restrict discharge flow rates of the first and second pumps.

A hydraulic system is provided to selectively and independently route pressurized fluid to one or more operational systems of a machine. The hydraulic system is capable of switching fluid flow in operation from one of the operational systems to another of the operational systems in the event of hydraulic drive power being required by the latter one of the operational systems. The hydraulic system is also configured to continue supplying a nominal amount of fluid to support one or more auxiliary functions, for example, a lubrication system for bearings associated with the former one of the operational systems while routing the pressurized fluid to the latter one of the operational systems. A recirculation and anti-cavitation arrangement is also provided to allow recirculation of fluid to a hydraulic motor in the former one of the operational systems when pressurized fluid is being routed to the latter one of the operational systems.

A hydraulic system includes a first hydraulic device, a second hydraulic device, a first control valve to control the first hydraulic device, a second control valve disposed on a downstream side of the first control valve and configured to control the second hydraulic device, a communication tube connecting the first hydraulic device to the first control valve, a supply fluid tube connecting the first control valve to the second control valve, a connection fluid tube disposed on the first control valve, the connection fluid tube connecting the communication tube to the supply fluid tube, a discharge fluid tube connected to the first control valve, a setting portion disposed on the discharge fluid tube and configured to increase a pressure in the discharge fluid tube, a branching fluid tube branched from the connection fluid tube and connected to the discharge fluid tube, and a throttle disposed on the branching fluid tube.

A multi-actuation system includes a first electrohydraulic servo valve and a first actuator. A first fluid line fluidically connects the first electrohydraulic servo valve to the first actuator. The multi-actuation system also includes a second electrohydraulic servo valve and a second actuator. A second fluid line fluidically connects the second electrohydraulic servo valve to the second actuator. A ring fluidically connects the first fluid line with the second fluid line.

According to an embodiment, a variable pressure device includes a channel constituting unit and a switch valve mechanism. The channel constituting unit constitutes a channel including a first regulator and second regulators that are arranged in series to the first regulator and are in parallel to one another. The switch valve mechanism selectively connects the second regulators to the first regulator. Opening areas of the second regulators are different from one another.

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. The construction machine is equipped with: a surplus flow control valve control section configured to output a closing command to a first surplus flow control valve at the operation start when an operation amount signal of an operation lever device is detected; a pump delivery control section configured to output a delivery flow rate command to an adjustment section of an open circuit pump; an assist valve control section configured to continue to output a closing command from before to an assist valve; a sticking detection determination section configured to compare a pressure signal with a previously set threshold value and determining that the surplus flow control valve is in a stuck-open state when the pressure signal is less than the threshold value and determining that the surplus flow control valve is normal when the pressure signal exceeds the threshold value; and a stop signal generating section configured to input therein a sticking determination signal, output in the case of a stuck-open state a control signal maintaining a closed state of the assist valve to the assist valve control section, and output in the case of a normal state a control signal causing the assist valve to perform an opening operation to the assist valve control section.

The invention relates to a valve unit for the exclusive hydraulic actuation of the locking means of a mechanical quick-changer for attachments of a construction machine, wherein the valve unit comprises a feed pressure connector for applying the feed pressure, a first valve unit outlet for connecting an unlocking pressure line, a second valve unit outlet for connecting a locking pressure line, at least one discharge to the tank, and at least two switchable directional valves, with the feed pressure connector being connected or connectable to the second valve unit outlet via a serial connection of the at least two switchable directional valves.

A valve subassembly includes a pump connection location, a tank connection location, and two constantly adjustable direction control valves each with first and second operating connection locations and an input connection location. A first valve group includes one direction control valve whose input is connected in parallel to two separate pump lines such that pressurized fluid is directed exclusively from the two pump lines to the control connection location. The two pump lines include a maximum of a first pump line and each remaining pump line is a second pump line. The maximum one first pump line is directly connected to the pump connection location in fluid terms, and a separate constantly adjustable pump valve is associated with each second pump line. Pressurized fluid is directed from the pump connection location via the pump valve into the associated second pump line.

Sod harvesters can have hydraulic systems that are configured to actuate components with precise timing. The hydraulic system of a sod harvester can be configured to maintain the temperature of hydraulic fluid both during harvesting and while harvesting is paused to thereby eliminate or minimize the occurrence of periods of variation in the timing of actuation of the components that the hydraulic fluid drives. As a result, these components can be consistently actuated with precise timing even after harvesting has been paused. Additionally, such configurations can minimize the amount of time required to warm the hydraulic fluid to a steady operational temperature.

A hydraulic switching assembly for a motor vehicle, having a hydraulic pump (1) which guides a hydraulic medium from a reservoir (2) via hydraulic lines (3) and at least one magnetic valve assembly (4) including a magnetically actuatable switching valve (5), to a switching element (6) in order to hydraulically actuate the switching element (6) between two switching positions. A pressure accumulator (7) and a first check valve (8a) are mounted in a supply line (3a) upstream of the switching valve (5) in order to realize a reliable temporary supply of oil pressure to the switching element (6).