Abstract: Problem to be solved: To provide a hydraulic circuit for the construction machine which enables to use the relief valve of low capacity in the work tool circuit. Solution: The hydraulic circuit 2 for a construction machine has: a hydraulic pump 4 of variable capacity, a work tool 6 operated by hydraulic oil delivered by the hydraulic pump 4, a work tool operating device 10 to output a signal for operating the work tool 6, a control valve 14 allowing the hydraulic pump 4 to supply the hydraulic oil to the work tool 6 based on the signal output from the work tool operating device 10, a tool's relief valve 44 to release the hydraulic oil flowing between the control valve 14 and the work tool 6, a pressure sensor 46 to detect a pressure of hydraulic oil flowing into the work tool 6, and a controller 48 to reduce a delivery rate from the hydraulic pump 4 when the pressure detected by the pressure sensor 46 exceeds a predetermined value.

Abstract: Problem to be solved: To provide a hydraulic circuit for the construction machine which enables to use the relief valve of low capacity in the work tool circuit. Solution: The hydraulic circuit 2 for a construction machine has: a hydraulic pump 4 of variable capacity, a work tool 6 operated by hydraulic oil delivered by the hydraulic pump 4, a work tool operating device 10 to output a signal for operating the work tool 6, a control valve 14 allowing the hydraulic pump 4 to supply the hydraulic oil to the work tool 6 based on the signal output from the work tool operating device 10, a tool's relief valve 44 to release the hydraulic oil flowing between the control valve 14 and the work tool 6, a pressure sensor 46 to detect a pressure of hydraulic oil flowing into the work tool 6, and a controller 48 to reduce a delivery rate from the hydraulic pump 4 when the pressure detected by the pressure sensor 46 exceeds a predetermined value.

Abstract: Provided are a hydraulic circuit and a work machine capable of improving an initial motion speed of a hydraulic cylinder during a contraction of the hydraulic cylinder and securing a necessary pump flow rate while hydraulic fluid is being accumulated in an accumulator. Hydraulic oil from a head side of a second boom cylinder is regenerated in a first boom cylinder and the second boom cylinder through a second control valve of a regeneration circuit. At the same time, oil from the head side of the first boom cylinder is accumulated to a first accumulator by a pressure accumulating circuit through a first control valve. The hydraulic oil supplied under pressure from a main pump is fed to a rod side of the first boom cylinder by a boom control valve. A bleed-off valve of a bleed-off circuit communicates the first control valve to a tank at the time of initial operation of the first control valve, thereby releasing hydraulic oil from the head end of the first boom cylinder to improve an initial motion speed.

Abstract: In a control device, a pilot-operated first check valve connects a solenoid-operated first directional control valve to a lock side chamber of a lock cylinder installed in a quick coupler. A pilot-operated second check valve is connected to the lock cylinder unlock side chamber, a solenoid-operated second directional control valve connected between the second check valve and the first directional control valve. The first and second directional control valves are controlled by a controller with processed signals input from a mode selector switch, first sensor detecting a buck closing pilot pressure, and second sensor detecting a bucket closing working pressure.

Abstract: Provided are a hydraulic circuit and a work machine capable of improving an initial motion speed of a hydraulic cylinder during a contraction of the hydraulic cylinder and securing a necessary pump flow rate while hydraulic fluid is being accumulated in an accumulator. Hydraulic oil from a head side of a second boom cylinder is regenerated in a first boom cylinder and the second boom cylinder through a second control valve of a regeneration circuit. At the same time, oil from the head side of the first boom cylinder is accumulated to a first accumulator by a pressure accumulating circuit through a first control valve. The hydraulic oil supplied under pressure from a main pump is fed to a rod side of the first boom cylinder by a boom control valve. A bleed-off valve of a bleed-off circuit communicates the first control valve to a tank at the time of initial operation of the first control valve, thereby releasing hydraulic oil from the head end of the first boom cylinder to improve an initial motion speed.

Abstract: An inexpensive engine assist device capable of performing stable energy regeneration from an accumulator and a working machine on which the engine assist device is mounted are provided. A variable capacity type main pump and a variable capacity type assist pump are directly connected to an engine. A return pressure oil flowing out from a fluid pressure actuator is temporarily accumulated by a sub-accumulator and is supplied to an inlet of the assist pump, and the assist pump pressurizes the return fluid pressure oil and supplies the return fluid pressure oil to a main accumulator. A controller calculates and controls an assist pump swash plate angle, and assist starting torque or charge starting torque, and introduces a pressure-accumulated fluid discharged from the main accumulator to the inlet of the assist pump or introduces a pressurized fluid discharged from an outlet of the assist pump into the main accumulator.

Abstract: In a control device, a pilot-operated first check valve connects a solenoid-operated first directional control valve to a lock side chamber of a lock cylinder installed in a quick coupler. A pilot-operated second check valve is connected to the lock cylinder unlock side chamber, a solenoid-operated second directional control valve connected between the second check valve and the first directional control valve. The first and second directional control valves are controlled by a controller with processed signals input from a mode selector switch, first sensor detecting a buck closing pilot pressure, and second sensor detecting a bucket closing working pressure.

Abstract: Provided is a hydraulic circuit capable of saving a pump flow rate while hydraulic fluid is being accumulated in an accumulator. The hydraulic circuit has: a couple of boom cylinders that simultaneously operate the same operation by the hydraulic oil supplied under pressure from main pumps; an accumulator in which pressure of the hydraulic oil is accumulated; a pressure accumulating circuit that accumulates the pressure of the hydraulic oil extruded from one boom cylinder in the accumulator; and a regenerating circuit that regenerates the hydraulic oil extruded from the other boom cylinder to the boom cylinders.

Abstract: In order to avoid cavitation in a boom cylinder head end at the beginning of a dig cycle, fluid from an alternate source is supplied to the head end before or in addition to fluid supplied by the main boom-up hydraulic circuit. In one embodiment, an electronic hydraulic valve, related sensors, and control system determines the beginning of a dig operation and uses fluid at an intermediate pressure to rapidly provide fluid to a boom head end cylinder to prevent voiding or cavitation before fluid under high pressure from the main pump can be brought to the cylinder. An on/off fluid switch is activated early in a dig operation to address low pressure at the boom cylinder head end and provide an alternate path for fluid into the cylinder in reaction to the boom being lifted by a motion of the stick and bucket in contact with the work surface.

Abstract: An object of the present invention is to solve such problems associated with installing of a spool-type regenerative valve, in that an overall installation space of a hydraulic valve increases and processing that requires accuracy becomes complex. A regenerative circuit includes: a regenerative oil path provided in a valve body of a direction switching valve so as to connect a supply oil path connected to one side of a hydraulic actuator and a discharge oil path connected to the other side; and a regenerative valve which is a poppet-type flow regulating valve that is screwed into and attached to the valve body so as to control the flow of oil in the regenerative oil path according to an operation state of the direction switching valve.

Abstract: An object of the present invention is to solve such problems associated with a merging circuit using a pair of spool-type direction switching valves, in that the installation space of a hydraulic valve device increases and the processing that requires accuracy becomes complex. A merging circuit includes a direction switching valve that merges oil discharged from first and second pumps to supply the oil to an actuator; and a controller. The direction switching valve includes a central bypass oil path connected to the discharge oil paths of the first and second pumps, a first parallel supply oil path connected to the discharge oil path of the first pump, and a second parallel supply oil path connected to the discharge oil path of the second pump and connected to a first parallel oil path via a poppet-type flow regulating valve. The poppet-type flow regulating valve regulates the flow rate to a predetermined magnitude according to a signal of the controller.

Abstract: A pressure loss reducing circuit reduces a pressure loss of oil returning from an actuator to a direction switching valve with a simple configuration while suppressing an increase in the manufacturing cost and substantially eliminating the need of an additional installation space. The pressure loss reducing circuit includes a bypass valve disposed between an actuator oil path and a tank oil path of a direction switching valve, and opened and closed according to a signal from a controller, and moreover screwed into and attached to the direction switching valve. According to an operation signal of a switching spool when oil returning from an actuator is caused to flow to the actuator oil path, the controller opens the bypass valve so that the actuator oil path and the tank oil path communicate with each other and supplies the returning oil to the switching spool and the bypass valve to reduce a pressure loss.

Abstract: An inexpensive engine assist device capable of performing stable energy regeneration from an accumulator and a working machine on which the engine assist device is mounted are provided. A variable capacity type main pump and a variable capacity type assist pump having a motor function and a pump function are directly connected to an engine. A return pressure oil flowing out from a fluid pressure actuator is temporarily accumulated by a sub-accumulator and is supplied to an inlet of the assist pump, and the assist pump pressurizes the return fluid pressure oil and supplies the return fluid pressure oil to a main accumulator.

Abstract: In a work machine including a hydraulic pump (1), a swing motor (2), and swing relief valves (3a and 3b), the amount of the swing operation (P1) related to the swing motion of the swing motor (2) is detected, and the hydraulic pressure (P2) supplied from the hydraulic pump (1) to the swing motor is also detected. Additionally, the required flow rate (FR) of hydraulic oil required for the swing motor (1) is set based on the amount of the swing operation (P1). In addition, the volume of relief (FE) is estimated from the hydraulic pressure (P2) based on the override characteristics of the swing relief valves (3a and 3b). The discharge flow rate of the hydraulic pump (1) is controlled based on the value obtained by subtracting the volume of relief (FE) from the required flow rate (FR).

Abstract: In order to avoid cavitation in a boom cylinder head end at the beginning of a dig cycle, fluid from an alternate source is supplied to the head end before or in addition to fluid supplied by the main boom-up hydraulic circuit. In one embodiment, an electronic hydraulic valve, related sensors, and control system determines the beginning of a dig operation and uses fluid at an intermediate pressure to rapidly provide fluid to a boom head end cylinder to prevent voiding or cavitation before fluid under high pressure from the main pump can be brought to the cylinder. An on/off fluid switch is activated early in a dig operation to address low pressure at the boom cylinder head end and provide an alternate path for fluid into the cylinder in reaction to the boom being lifted by a motion of the stick and bucket in contact with the work surface.

Abstract: The present invention is intended to provide a technology that can utilize the advantages of both a load sensing control and a regeneration circuit without causing any problem. A regeneration circuit is added to a hydraulic circuit provided with a hydraulic pressure signal line for detecting a hydraulic pressure value of a circuit and controlling a volume of hydraulic fluid to a cylinder 1 with reference to the detected value. A pressure reducing valve 6 that outputs a reduced pressure as an operating signal to a pump 2, and subsequently the controlling means 5 causes the pressure reducing valve 6 to output a pressure reduction command to a pump 2 and thus to reduce a discharge rate from the pump 2, when the regeneration circuit is in a regeneration state.

Abstract: In a work machine including a hydraulic pump (1), a swing motor (2), and swing relief valves (3a and 3b), the amount of the swing operation (P1) related to the swing motion of the swing motor (2) is detected, and the hydraulic pressure (P2) supplied from the hydraulic pump (1) to the swing motor is also detected. Additionally, the required flow rate (FR) of hydraulic oil required for the swing motor (1) is set based on the amount of the swing operation (P1). In addition, the volume of relief (FE) is estimated from the hydraulic pressure (P2) based on the override characteristics of the swing relief valves (3a and 3b). The discharge flow rate of the hydraulic pump (1) is controlled based on the value obtained by subtracting the volume of relief (FE) from the required flow rate (FR).

Abstract: The present invention is intended to provide a technology that can utilize the advantages of both a load sensing control and a regeneration circuit without causing any problem. A regeneration circuit is added to a hydraulic circuit provided with a hydraulic pressure signal line for detecting a hydraulic pressure value of a circuit and controlling a volume of hydraulic fluid to a cylinder 1 with reference to the detected value. A pressure reducing valve 6 that outputs a reduced pressure as an operating signal to a pump 2, and subsequently the controlling means 5 causes the pressure reducing valve 6 to output a pressure reduction command to a pump 2 and thus to reduce a discharge rate from the pump 2, when the regeneration circuit is in a regeneration state.