A working vehicle provided with a fixed-capacity hydraulic pump driven by power from an engine and a working hydraulic actuator driven by working oil pumped from the fixed-capacity hydraulic pump is a rotary working vehicle which is provided with an electromagnetic relief valve for modifying the pressure of working oil from the fixed-capacity hydraulic pump, and the rotary working vehicle is such that if the actual number of revolutions (N) of the engine is reduced by a set number of revolutions (Ns) as the load on the engine increases, then the electromagnetic relief valve operates in accordance with the deviation (e) between the actual number of revolutions (N) of the engine and the specified number of revolutions (Ns), and the pressure of the working oil from the fixed-capacity hydraulic pump is modified.

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. The driving device includes: a first hydraulic pump that has flow rate control device for controlling the flow rate and direction of hydraulic fluid to be delivered; a single rod hydraulic cylinder that is driven with the hydraulic fluid to drive one of work members of a work device on the work machine; a closed hydraulic circuit that connects the first hydraulic pump with the single rod hydraulic cylinder to form a closed circuit using flow lines through which the hydraulic fluid flows; a branch line that branches from the flow line between the first hydraulic pump and the single rod hydraulic cylinder; a first flow line of which one end is connected to the branch line; a tank to which the other end of the first flow line is connected; and a hydraulic fluid flow rate control device attached to the first flow line to control the flow rate of the hydraulic fluid flowing from the branch line to the tank or from the tank to the branch line.

A hydraulic fluid flowpath includes a first flowpath and a second flowpath. The first flowpath connects a first pump port and a first chamber in a hydraulic cylinder. The second flowpath connects a second pump port and a second chamber in the hydraulic cylinder. The hydraulic fluid flowpath forms a closed circuit between a hydraulic pump and the hydraulic cylinder. A bleed-off flowpath bleeds off a portion of the hydraulic fluid from the second flowpath. A control valve connects the second flowpath to the bleed-off flowpath via a throttle when an operation amount of an operating member for lowering a work implement is less than a predetermined operation amount so that a hydraulic pressure in second flowpath is maintained at less than a relief pressure. The predetermined operation amount is less than or equal to the maximum operation amount for lowering the work implement.

A work machine includes: a hydraulic actuator that is driven by a hydraulic fluid from a hydraulic pump; an open-center directional control valve that is arranged on a center bypass line, and controls a flow of the hydraulic fluid to be supplied to the hydraulic actuator; a CB cut valve arranged between a directional control valve and a hydraulic working fluid tank on the center bypass line; and a machine controller that controls an opening of the CB cut valve. The machine controller restricts the opening of the CB cut valve when operation on the hydraulic actuator is in a fine operation state in which the operation on the hydraulic actuator is within a predetermined range representing a region of fine operation, and the fine operation state is continued longer than a predetermined period, and fully opens the CB cut valve otherwise.

An over-pressure protection system includes a main body housing defining a main body chamber configured to receive a fluid therein, wherein the main body housing comprises a spring, the main body housing configurable in a collapsed configuration and an expanded configuration; and a pressure sensor configured to measure a fluid pressure of the fluid, the pressure sensor configurable in an activated mode and a deactivated mode; wherein, in the collapsed configuration, the spring biases main body housing inward at an intermediate point of the main body housing such that the main body housing defines a substantially hourglass shape.

A hydraulic control system for linear actuation that provides a bypass flow during startup of a lifting command, provides a split flow between a cylinder and a reservoir once a minimum operating speed of a pump has been reached, and provides complete flow to a cylinder after the minimum operating speed of the pump has been reached. This is achieved through control of a flow control valve and a proportional flow control valve by a processor.

A fixed displacement hydraulic pump match flow demand control system that includes a spool valve, a plurality of fixed displacement pumps and a control valve is provided. The spool valve includes a spool. The spool is configured to shuttle within a chamber of a housing based at least in part on a pressure difference between a first end and the second end of the chamber. A fluid flow from each fixed displacement pump of the plurality of fixed displacement pumps is in fluid communication with an associated input port to the spool valve. At least one output port of the spool valve is in fluid communication with a hydraulically operated device and at least one of another output port is in fluid communication with a return. The control valve is configured to adjust the location of the spool in the chamber to regulate fluid flow to the hydraulically operated device.

A hydraulic system is provided for controlling one or more piston-cylinders of an implement. An implement valve includes at least one spool operable to transition between a neutral position and an open position. A variable displacement pump is operable to move a fluid from a reservoir into a supply conduit and to the at least one spool. A flow control valve, distinct and separate from the at least one spool is located in-line with the supply conduit between the variable displacement pump and the at least one spool, and is operable to simultaneously provide the fluid to the implement valve and to a bypass pathway. The bypass pathway extends from the flow control valve to the reservoir without intervening valving. Each of the at least one spool is operable to permit increased fluid flow to a corresponding piston cylinder of the implement when in the open position. The variable displacement pump is operable to vary a flow rate to maintain a predetermined pump margin across the flow control valve.

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 hydraulic system for a construction machine having a protection device is disclosed, which can limit a flow rate of hydraulic fluid that is discharged from a hydraulic pump in accordance with a hydraulic fluid temperature and notify an operator of information on the hydraulic fluid temperature. The hydraulic system for a construction machine includes a hydraulic actuator operated by hydraulic fluid that is supplied from a hydraulic pump; a control valve installed in a flow path between the hydraulic pump and the hydraulic actuator to control a flow rate of the hydraulic fluid that is supplied from the hydraulic pump to the hydraulic actuator; an oil cooler installed in a return flow path from the control valve to an hydraulic fluid tank to cool the hydraulic fluid; a hydraulic fluid temperature sensor detecting in real time a hydraulic fluid temperature of the hydraulic fluid tank; a hydraulic pump regulator controlling a discharge flow rate of the hydraulic pump through adjustment of an inclination angle of a swash plate of the hydraulic pump; and a controller comparing the hydraulic fluid temperature detected by the hydraulic fluid temperature sensor with a predetermined hydraulic fluid temperature, and outputting a control signal to the hydraulic pump regulator so as to limit the discharge flow rate of the hydraulic pump to or below a predetermined flow rate if the detected hydraulic fluid temperature is equal to or lower than a predetermined lower limit value, or equal to or higher than a predetermined upper limit value.