A hydraulic system is provided for a working machine that includes a hydraulic cylinder for raising and lowering an implement. The hydraulic system includes a sensor for measuring a pressure in the hydraulic cylinder; and a control unit for controlling the movement of the hydraulic cylinder; wherein the control unit is configured to compare a pressure value measured by the sensor with a preset target pressure level range and to control the pressure in the hydraulic cylinder to be within the preset target pressure level range by adding or draining hydraulic fluid to/from a pressure side of the hydraulic cylinder for maintaining a substantially constant ground contact force between the implement and the ground.

A fluid pressure system includes an actuator, an operating valve, and a spool valve. The spool valve is connected to a pressure source and a tank by a pressure source line and a tank line, respectively, and connected to the actuator by a first movement line and a second movement line. The spool valve moves from a neutral position to a movement position by a moving amount corresponding to a pilot pressure outputted from the operating valve, the movement position being a position at which the spool valve allows the pressure source line to communicate with the first movement line and allows the second movement line to communicate with the tank line. A relief line branches off from the second movement line, and the relief line connects to a tank. A variable throttle valve is provided on the relief line.

A liquid seal energy-accumulator and hydraulic system thereof based on liquid-collector and sandwich piston is provided. The liquid seal energy-accumulator includes a piston cylinder (HSG) and a high pressure gas-tank (QTG). When a piston (HS) moves to a top of the piston cylinder, the leaked pressure liquid accumulated on the top of the piston flows into the gas-tank through a gas-liquid-pipe (TD), so as to timely clean up the pressure liquid accumulated on the top of the piston. The pressure liquid collected at the bottom of the gas-tank is increased for upwardly moving a buoy (FT), when the buoy presses a collection-liquid sensor (JYG), a signal is sent for opening an electronically-controlled-valve (DKF), the leaked pressure liquid flows from the liquid leakage pipe (LYG) back to the liquid-container (SYT).

A first case accommodating a first check valve of a switching valve switching a flow of hydraulic fluid to one of a first chamber and a second chamber of a cylinder device, an inside of which is segmented into the first chamber and the second chamber by a piston, and a second case which is stacked on the first case and in which a first actuation valve of the switching valve is accommodated to be displaced in a direction of stacking the first case are provided. A first valve chamber, accommodating the first actuation valve, of the second case has a pressure receiving surface on which pressure of hydraulic fluid that acts on the first valve chamber acts toward the first case.

One 3-position selector valve is used as a main control valve that controls hoist cylinders. A control valve is provided for supplying hydraulic oil from a low-pressure hydraulic pressure source to rod chambers of the hoist cylinders upon lowering a vessel. Provided between the rod chambers of the hoist cylinders and an oil tank is a check valve that enables to supply hydraulic oil from the oil tank to the rod chambers upon a vessel FLOAT operation. When an operation command from a control device is a vessel-lowering command, a controller switches the main control valve to a FLOAT position, and also switches the vessel LOWER operation control valve and supplies hydraulic oil of a low pressure from the low-pressure hydraulic pressure source to the rod chambers of the hoist cylinders.

A work machine has a controller which has an area limiting control section correcting the pilot pressures of pilot lines, a regeneration control section adjusting the flow rate of the hydraulic fluid caused to flow from a tank side line of an arm cylinder into a pump side line thereof between zero and a predetermined upper limit value, and a regeneration control switching section that issues an order to the regeneration control section to set the predetermined upper limit value to a first set value when the function of the area limiting control section is invalid and that issues an order to the regeneration control section to set the predetermined upper limit value to a second set value that is smaller than the first set value when the function of the area limiting control section is effective.

A hydraulic system in of a work machine includes a hydraulic pump to supply pilot hydraulic oil in a hydraulic oil reservoir. A travel pump is to drive a travel motor according to a pilot pressure of the pilot hydraulic oil. A target pilot pressure of the pilot hydraulic oil is input through a travel operation device to control, according to the target pilot pressure, the pilot pressure supplied from the hydraulic pump to the travel pump. A pilot oil path connects the travel operation device and the travel pump to supply the pilot pressure to the travel pump. A drain oil path is divided from the pilot oil path. A pressure adjustment valve is provided in the drain oil path to adjust the pilot pressure to be less than the target pilot pressure when a condition is satisfied.

A spool for a hydraulic valve includes a cylindrical body having a first end, a second end disposed opposite the first end, and an annular wall defined by an internal surface of the cylindrical body and an external surface of the cylindrical body. The annular wall defines a plurality of holes therethrough. The internal surface defines a first chamber, a second chamber, and a slot chamber within the cylindrical body, the second chamber being in fluid communication with the plurality of holes via the first chamber, the slot chamber being located between the second chamber and the second end of the cylindrical body. The annular wall defines a slot therethrough, the slot extending from the second end of the cylindrical body toward the first end of the cylindrical body along the longitudinal direction, the slot being open at the second end of the cylindrical body along the longitudinal direction.

A refuse vehicle includes a chassis and a vehicle body. A variable displacement pump is positioned within the vehicle body and is configured to pump hydraulic fluid from a hydraulic fluid reservoir into a high pressure line of a hydraulic circuit. A lifting system on the vehicle includes at least one actuator in fluid communication with the variable displacement pump, which delivers pressurized hydraulic fluid from the hydraulic fluid reservoir to the actuator through the high pressure line to adjust a position of the actuator. A valve is positioned downstream of the variable displacement pump. In a first valve position, the valve restricts flow outward from the high pressure line. In a second valve position, the valve directs fluid from the high pressure line into a lower pressure line to reduce a hydraulic pressure within the high pressure line and adjust an output parameter of the variable displacement pump.

A hydraulic energy regeneration system for a work machine for boosting a pressure of a return hydraulic fluid of a hydraulic cylinder and regenerating the hydraulic fluid, prevents a bottom pressure from reaching an overload relief set pressure and suppresses a changeover shock to ensure favorable operability.

The hydraulic energy regeneration system for the work machine, includes: a communication pressure boost passage that can boost a pressure of a discharge-side hydraulic fluid by communicating a discharge side and a suction side of the hydraulic cylinder with each other during an own weight fall of a driven body; a communication pressure boost valve that is disposed in the communication pressure boost passage and that can regulate one of or both of a pressure and a flow rate of the communication pressure boost passage; a reuse-side line and a reuse control valve or a regeneration-side line and a regeneration control valve that can regenerate a hydraulic fluid discharged from the hydraulic cylinder during the own weight fall of the driven body; and a controller. The controller is configured to reduce an opening degree of the communication pressure boost valve in response to an increase of the discharge-side pressure of the hydraulic cylinder right after the discharge-side pressure reaches a preset high load set pressure, and gradually reduces the opening degree of the communication pressure boost valve with passage of time.