This hydraulic drive system includes: first and second circuit systems; first and second hydraulic pumps; a merge valve that opens and closes a merge passage connecting the hydraulic pumps; an operation device that outputs an operation command corresponding to an amount of operation specifying an amount of actuation of first and second hydraulic actuators; and a control device that controls the merge valve according to the operation command from the operation device. The first circuit system includes: a first meter-in control valve that controls a meter-in flow rate of the working fluid that flows to the first hydraulic actuator; and a first meter-out control valve that controls a meter-out flow rate of the working fluid that is drained from the first hydraulic actuator into a tank. The control device controls an opening degree of the first meter-in control valve and an opening degree of the first meter-out control valve.

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.

In a fluid circuit for an air cylinder connected to a switching valve provided with exhaust ports, a head-side pressure chamber is connected to the switching valve by a first pipe, and a rod-side pressure chamber is connected to the switching valve by a second pipe. A first restrictor is disposed at a connection point between the first pipe and the switching valve or in the vicinity of a first output port of the switching valve, and a second restrictor is disposed at a connection point between the second pipe and the switching valve or in the vicinity of a second output port of the switching valve.

A hydraulic system, mining machine and method of controlling a hydraulic actuator. The hydraulic system (HS) is provided with a control valve (23) for controlling movement direction and speed of a hydraulic actuator (HA) connected to the system. Generated force of the hydraulic actuator is controlled independently relative to the control valve by means of counterbalance valves (Cb1, Cb2) and servo valves (Sv1, Sv2) controlling their opening pressure. The counterbalance valves and the servo valves operate as a meter-out control assembly which controls flow of hydraulic fluid discharged from working pressure spaces (16a, 16b) of the hydraulic actuator. The disclosed system may be implemented to control a mining boom (3) of a mining machine (1).

A work vehicle includes: an operation tool that is operated by an operator; and a controller that determines a target flow rate for hydraulic oil fed to a hydraulic device on a basis of the amount of operation of the operation tool. The controller calculates a bleed-off target flow rate on a basis of the flow rate of hydraulic oil fed from a hydraulic oil pump and the target flow rate for hydraulic oil fed to the hydraulic device, calculates a bleed-off throttle differential pressure on a basis of a pressure of hydraulic oil fed from the hydraulic oil pump and a pressure of hydraulic oil in a hydraulic oil tank, calculates a bleed-off target opening area on a basis of the bleed-off target flow rate and the bleed-off throttle differential pressure, and controls a hydraulic oil control valve such that the bleed-off target opening area is achieved.

A work vehicle includes: an operation tool that is operated by an operator; and a controller that determines a target flow rate for hydraulic oil fed to a hydraulic device on a basis of the amount of operation of the operation tool. The controller calculates a bleed-off target flow rate on a basis of the flow rate of hydraulic oil fed from a hydraulic oil pump and the target flow rate for hydraulic oil fed to the hydraulic device, calculates a bleed-off throttle differential pressure on a basis of a pressure of hydraulic oil fed from the hydraulic oil pump and a pressure of hydraulic oil in a hydraulic oil tank, calculates a bleed-off target opening area on a basis of the bleed-off target flow rate and the bleed-off throttle differential pressure, and controls a hydraulic oil control valve such that the bleed-off target opening area is achieved.

The present disclosure relates to systems that use a single proportional valve to control raising and lowering of a load. The present disclosure also relates to proportional valves that provide proportional flow control in first and second opposite flow directions through the proportional valve.

The present invention relates to a mobile work machine, in particular to a wheeled loader, having a hydraulic circuit, having a pump for conveying a hydraulic medium through the hydraulic circuit, and having at least one control block having an inflow control edge and an outflow control edge for controlling the flow of the hydraulic medium, wherein the work machine has a working tool and a cylinder for actuating the working tool and wherein the cylinder has an outflow and in inflow for the hydraulic medium, and wherein the outflow is in fluid communication with the outflow control edge and the inflow is in fluid communication with the inflow control edge, and wherein the inflow control edge does not have any or has fewer fine control notches than the outflow control edge and thus works in a largely unrestricted manner, while the outflow control edge is equipped with one or more fine control notches so that with a pulling load at the working tool, the outflow control edge restricts the outflow amount through the outflow of the cylinder.

An electro-hydraulic actuator system includes a fixed-displacement hydraulic pump and a variable speed electric motor configured in combination to constitute an individual electro-hydraulic unit that is coupled to an actuator, and a bypass valve in parallel to the actuator. The system is configured to enable the actuator to be operated at actuation speeds that are higher than a maximum actuation capability of the pump at the maximum flow capability thereof, and at actuation speeds that are lower than a minimum actuation capability of the pump at the minimum flow capability thereof. The actuation velocity of the actuator may be controlled by controlling the speed of the electro-hydraulic unit and a size of an opening of the bypass valve.

A hydraulic system includes a hydraulic pump, a first hydraulic actuator, a second hydraulic actuator, a first control valve to control the first hydraulic actuator, a second control valve to control the second hydraulic actuator, a pressure increasing portion to increasing a pressure of the operation fluid, a first discharge fluid tube connected to any one of the first control valve and the second control valve and connected to the pressure increasing portion, a second discharge fluid tube connected to the first discharge fluid tube and configured to discharge the operation fluid, a float switching valve having an allowance position, a prevention position, and a float position, the allowance position blocking the second discharge fluid tube and allowing the operation fluid to flow to the pressure increasing portion, the prevention position unblocking the second discharge fluid tube and preventing the operation fluid from flowing to the pressure increasing portion.