Abstract: A spool valve capable of suppressing deterioration of position controllability of a spool due to misalignment includes: a housing including a spool hole; a spool inserted into the spool hole of the housing so as to be movable in an axial direction; and an electric actuator configured to move the spool in the axial direction. The electric actuator includes: an electric motor configured to rotate an output shaft; a linear-motion converting mechanism including a linear-motion member configured to be linearly movable, the linear-motion converting mechanism being configured to convert a rotational motion of the output shaft into a linear motion of the linear-motion member; and a coupling member coupling the linear-motion member and the spool moves in accordance with the linear motion of the linear-motion member. The coupling member allows one of tilt and eccentricity of an axis of the spool relative to an axis of the linear-motion member.

Abstract: A spool valve capable of suppressing deterioration of position controllability of a spool due to misalignment includes: a housing including a spool hole; a spool inserted into the spool hole of the housing so as to be movable in an axial direction; and an electric actuator configured to move the spool in the axial direction. The electric actuator includes: an electric motor configured to rotate an output shaft; a linear-motion converting mechanism including a linear-motion member configured to be linearly movable, the linear-motion converting mechanism being configured to convert a rotational motion of the output shaft into a linear motion of the linear-motion member; and a coupling member coupling the linear-motion member and the spool moves in accordance with the linear motion of the linear-motion member. The coupling member allows one of tilt and eccentricity of an axis of the spool relative to an axis of the linear-motion member.

Abstract: A hydraulic excavator drive system includes: first and second pumps; arm cylinder; arm first control valve connected to the cylinder by an arm crowding supply line and arm pushing supply line; arm second control valve connected to the supply lines by a first and second replenishment line; and arm operation device that outputs an operation signal corresponding to an inclination angle of an operating lever. The arm second control valve is configured so, when performing an arm crowding operation, an opening area at a meter-in side changes in accordance with the operation signal, and an opening area at a meter-out side is: kept to zero when a predetermined condition is not satisfied; and kept to zero until the operation signal becomes a setting value or greater, and when the operation signal has become the setting value or greater, increases to a maximum value when the predetermined condition is satisfied.

Abstract: A hydraulic excavator drive system includes: first and second pumps; arm cylinder; arm first control valve connected to the cylinder by an arm crowding supply line and arm pushing supply line; arm second control valve connected to the supply lines by a first and second replenishment line; and arm operation device that outputs an operation signal corresponding to an inclination angle of an operating lever. The arm second control valve is configured so, when performing an arm crowding operation, an opening area at a meter-in side changes in accordance with the operation signal, and an opening area at a meter-out side is: kept to zero when a predetermined condition is not satisfied; and kept to zero until the operation signal becomes a setting value or greater, and when the operation signal has become the setting value or greater, increases to a maximum value when the predetermined condition is satisfied.

Abstract: 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.

Abstract: A hydraulic excavator drive system includes: a cylinder that drives a moving part that is an arm or a bucket. Hydraulic oil is supplied from a hydraulic pump to the cylinder via a control valve. A bypass line branches off from a rod-side supply/discharge line. The bypass line is blocked and opened by a restrictor. The restrictor is controlled by a controller such that, when the hydraulic oil is supplied to the cylinder through a head-side supply/discharge line, the restrictor blocks the bypass line if a pressure detected by a load detector is lower than a predetermined value, and opens the bypass line if the pressure detected by the load detector is higher than or equal to the predetermined value.

Abstract: A tilting angle control device includes pressure sensors. Each of the pressure sensors outputs to a control unit a pressure command signal corresponding to an operation amount. The control unit outputs to an electromagnetic proportional control valve a pressure control signal corresponding to the pressure command signal, and the electromagnetic proportional control valve outputs to a tilt adjustment mechanism pilot pressure corresponding to the pressure control signal. The tilt adjustment mechanism adjusts a tilting angle of a variable displacement pump such that the tilting angle becomes an angle corresponding to the pilot pressure. A pilot pressure sensor detects the pilot pressure to output a pressure feedback signal to the control unit. The control unit calculates the pressure control signal based on the pressure feedback signal and the pressure command signal and performs feedback control of the pilot pressure.

Abstract: A hydraulic driving system includes first to third liquid-pressure pumps and control valves. The first boom control valve is connected to the first hydraulic pump, and the second arm control valve and the first bucket control valve are connected to the second liquid-pressure pump. Further, the turning control valve and the second bucket control valve are connected to the third hydraulic pump. When a pilot pressure XAk0 is output from a bucket operating device while a turning operation is performed, a command switching device outputs a pilot pressure XAk1 to the first bucket control valve. When the pilot pressure XAk0 is output from the bucket operating device while the turning operation is performed, the command switching device outputs a pilot pressure XAk2 to a second bucket control valve.

Abstract: A hydraulic excavator drive system includes: a first hydraulic pump and a second hydraulic pump, whose respective tilting angles are controllable independently of each other; an arm main control valve and an arm auxiliary control valve each for controlling supply of hydraulic oil to an arm cylinder; and a boom main control valve and a boom auxiliary control valve each for controlling supply of the hydraulic oil to a boom cylinder. An arm operation valve outputs a pilot pressure to the arm main control valve. A boom operation valve outputs a pilot pressure to the boom main control valve. A pair of arm-side regulating valves outputs no pilot pressure to the arm auxiliary control valve and a boom-side regulating valve outputs no pilot pressure to the boom auxiliary control valve when an arm crowding operation and a boom raising operation are performed concurrently.

Abstract: A hydraulic control device includes: a hydraulic pump connected in parallel to steering and boom cylinders; a steering control valve that controls the direction of operating oil flowing through the steering cylinders; a boom control valve that connects the hydraulic pump to a tank when the valve is at a neutral position and controls the direction of the oil flowing through the boom cylinders when the valve is at an offset position; a meter-in pressure compensator that increases flow rate of the oil flowing through a variable restrictor of the steering control valve in accordance with pressure in front of and behind the restrictor; and a bleed-off pressure compensator that decreases flow rate of the oil flowing through the boom control valve in accordance with the increase in pressure of the oil flowing through the steering cylinders to maintain the predetermined pressure of the oil in the steering control circuit.

Abstract: A hydraulic excavator drive system includes: a cylinder that drives a moving part that is an arm or a bucket. Hydraulic oil is supplied from a hydraulic pump to the cylinder via a control valve. A bypass line branches off from a rod-side supply/discharge line. The bypass line is blocked and opened by a restrictor. The restrictor is controlled by a controller such that, when the hydraulic oil is supplied to the cylinder through a head-side supply/discharge line, the restrictor blocks the bypass line if a pressure detected by a load detector is lower than a predetermined value, and opens the bypass line if the pressure detected by the load detector is higher than or equal to the predetermined value.

Abstract: A hydraulic driving system includes first to third liquid-pressure pumps and control valves. The first boom control valve is connected to the first hydraulic pump, and the second arm control valve and the first bucket control valve are connected to the second liquid-pressure pump. Further, the turning control valve and the second bucket control valve are connected to the third hydraulic pump. When a pilot pressure XAk0 is output from a bucket operating device while a turning operation is performed, a command switching device outputs a pilot pressure XAk1 to the first bucket control valve. When the pilot pressure XAk0 is output from the bucket operating device while the turning operation is performed, the command switching device outputs a pilot pressure XAk2 to a second bucket control valve.

Abstract: 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.

Abstract: A hydraulic drive system of a construction machine includes: a first hydraulic pump and a second hydraulic pump, whose respective tilting angles are adjustable independently of each other; a turning control valve for controlling supply of hydraulic oil to a turning motor; and a boom main control valve and a boom auxiliary control valve each for controlling supply of the hydraulic oil to a boom cylinder. The turning control valve and the boom auxiliary control valve are disposed on a first bleed line, and the boom main control valve is disposed on a second bleed line. A turning operation valve outputs a pilot pressure to the turning control valve, and a boom operation valve outputs a pilot pressure to the boom main control valve. A boom-side regulating valve outputs no pilot pressure to the boom auxiliary control valve when a turning operation and a boom raising operation are performed concurrently.

Abstract: A hydraulic excavator drive system includes: a first hydraulic pump and a second hydraulic pump, whose respective tilting angles are controllable independently of each other; an arm main control valve and an arm auxiliary control valve each for controlling supply of hydraulic oil to an arm cylinder; and a boom main control valve and a boom auxiliary control valve each for controlling supply of the hydraulic oil to a boom cylinder. An arm operation valve outputs a pilot pressure to the arm main control valve. A boom operation valve outputs a pilot pressure to the boom main control valve. A pair of arm-side regulating valves outputs no pilot pressure to the arm auxiliary control valve and a boom-side regulating valve outputs no pilot pressure to the boom auxiliary control valve when an arm crowding operation and a boom raising operation are performed concurrently.

Abstract: A construction machine energy regeneration apparatus includes: a movable weight provided in a construction machine and movable vertically; and a power-transmitting hydraulic circuit, which moves the movable weight upward by utilizing energy that is generated when a boom, an arm, or a bucket moves in a gravitational direction or energy that is generated when a brake is applied to bring a turning unit or a running unit to a stop, and utilizes potential energy of the movable weight as energy for driving the boom or the arm.

Abstract: A liquid-pressure control device includes a switching valve, a manipulation valve, a first back pressure output mechanism, and a second shuttle valve. When a manipulation lever is manipulated, the manipulation valve outputs a first output pressure corresponding to a manipulation amount of the manipulation lever. When a predetermined operation state is satisfied, the first back pressure output mechanism outputs a first back pressure. The first output pressure is input as a first pilot pressure to the switching valve, and the first back pressure is input as a second pilot pressure to the switching valve. The switching valve supplies a liquid pressure to a boom cylinder at a flow rate corresponding to a differential pressure between the first and second pilot pressures.

Abstract: A tilting angle control device includes pressure sensors. Each of the pressure sensors outputs to a control unit a pressure command signal corresponding to an operation amount. The control unit outputs to an electromagnetic proportional control valve a pressure control signal corresponding to the pressure command signal, and the electromagnetic proportional control valve outputs to a tilt adjustment mechanism pilot pressure corresponding to the pressure control signal. The tilt adjustment mechanism adjusts a tilting angle of a variable displacement pump such that the tilting angle becomes an angle corresponding to the pilot pressure. A pilot pressure sensor detects the pilot pressure to output a pressure feedback signal to the control unit. The control unit calculates the pressure control signal based on the pressure feedback signal and the pressure command signal and performs feedback control of the pilot pressure.

Abstract: A hydraulic control device includes: a hydraulic pump connected in parallel to steering and boom cylinders; a steering control valve that controls the direction of operating oil flowing through the steering cylinders; a boom control valve that connects the hydraulic pump to a tank when the valve is at a neutral position and controls the direction of the oil flowing through the boom cylinders when the valve is at an offset position; a meter-in pressure compensator that increases flow rate of the oil flowing through a variable restrictor of the steering control valve in accordance with pressure in front of and behind the restrictor; and a bleed-off pressure compensator that decreases flow rate of the oil flowing through the boom control valve in accordance with the increase in pressure of the oil flowing through the steering cylinders to maintain the predetermined pressure of the oil in the steering control circuit.

Abstract: A cushion valve device includes a valve block that includes first, second and first discharge passages. The first passage is disposed between a first supply/discharge passage of an operating valve and a first pilot passage of a switching valve, and includes a first throttle. The second passage is between a second supply/discharge passage of the operating valve and a second pilot passage of the switching valve. The first discharge passage connects to the first passage and a tank. A first check valve is provided on the first discharge passage. The first check valve includes: a poppet valve element configured to be seated on a valve seat portion, thereby closing the first discharge passage; and a piston configured to move the poppet valve element when the pressure of pilot oil in the second supply/discharge passage has become higher than or equal to a predetermined pressure, thereby opening the first discharge passage.