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.

A cooling flow circuit is provided and includes a main line having first and second sections ported to piston extend and return sides of the gas turbine engine actuator, respectively, an orifice disposed along the main line between the first and second sections, a bypass line and a bypass valve. The bypass line is fluidly coupled to the first and second sections at opposite ends thereof, respectively. The bypass valve is disposed along the bypass line between the opposite ends thereof. The bypass valve has a variable flow area which is responsive to a pressure differential between the first and second sections.

A hydraulic system is disclosed. The hydraulic system may include a source of pressurized fluid; a tank; a hydraulic actuator including a first chamber and a second chamber; a first independent metering valve disposed between and fluidly connected to the source, the tank, and the first chamber of the hydraulic actuator; and a second independent metering valve disposed between and fluidly connected to the source, the tank, and the second chamber of the hydraulic actuator. Each of the first independent metering valve and the second independent metering valve may include a spool and a valve actuator disposed on one side of the spool. The valve actuator may include a push coil, a pull coil, and a force feedback mechanism configured to balance a force of the push coil and the pull coil.

When hydraulic fluid discharged from a hydraulic actuator is to be recovered for driving a different hydraulic actuator, the recovery frequency is increased to achieve further energy saving. To this end, a pressure increasing circuit 36 is provided in which a communication pressure increasing valve 12 is disposed in a communication passage 26 that connects a bottom side line 23 of and a rod side line 24 a boom cylinder 4. A recovery control valve 11 is controlled such that, when a first operation unit 5 is operated in a boom lowering direction (own weight falling direction of the boom) and a second operation unit 6 is operated simultaneously, only if the pressure at the bottom side of the boom cylinder 4 is higher than the pressure at the arm cylinder side that is a recovery destination of hydraulic fluid, the recovery control valve 11 is opened to recover the flow rate discharged from the bottom side of the boom cylinder 4 to the arm cylinder side.

To provide a hydraulic drive system for a work machine capable of securing a favorable operability in the case where hydraulic fluid discharged from a hydraulic actuator is regenerated for driving other hydraulic actuator. The hydraulic drive system for a work machine includes: a regeneration line that connects a bottom-side hydraulic chamber of a hydraulic cylinder to a portion between a hydraulic pump and a second hydraulic actuator; a regeneration flow rate adjustment device that supplies at least part of the hydraulic fluid discharged from the bottom-side hydraulic chamber to a portion between the hydraulic pump and the second hydraulic actuator through the regeneration line; a differential pressure calculating section that reads a pressure in the bottom-side hydraulic chamber of the hydraulic cylinder detected by a first pressure sensor and a pressure between the hydraulic pump and the second hydraulic actuator detected by a second pressure sensor, and calculates a differential pressure, or a differential pressure sensor; and a control unit that controls the regeneration flow rate adjustment device such as to gradually increase the flow rate of the hydraulic fluid flowing through the regeneration line according to an increase in the differential pressure calculated by the differential pressure calculation section or in the differential pressure detected by the differential pressure sensor.

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.

A cooling flow circuit is provided and includes a main line having first and second sections ported to piston extend and return sides of the gas turbine engine actuator, respectively, an orifice disposed along the main line between the first and second sections, a bypass line and a bypass valve. The bypass line is fluidly coupled to the first and second sections at opposite ends thereof, respectively. The bypass valve is disposed along the bypass line between the opposite ends thereof. The bypass valve has a variable flow area which is responsive to a pressure differential between the first and second sections.

A hydraulic system is disclosed. The hydraulic system may include a source of pressurized fluid; a tank; a hydraulic actuator including a first chamber and a second chamber; a first independent metering valve disposed between and fluidly connected to the source, the tank, and the first chamber of the hydraulic actuator; and a second independent metering valve disposed between and fluidly connected to the source, the tank, and the second chamber of the hydraulic actuator. Each of the first independent metering valve and the second independent metering valve may include a spool and a valve actuator disposed on one side of the spool. The valve actuator may include a push coil, a pull coil, and a force feedback mechanism configured to balance a force of the push coil and the pull coil.

A hydraulic system for a machine is disclosed. The system may have a pump and a motor driven by pressurized fluid from the pump. An accumulator is configured to receive fluid discharged from the motor and to discharge fluid to the motor. The system may include a first valve to selectively communicate the higher pressure of conduits coupled between the pump and motor to the accumulator. A second valve and a third valve can be used to facilitate charging and discharging of the accumulator. The system may include a controller configured to implement a plurality of modes of operation, which each mode of operation may include a different combination of motor deceleration and motor acceleration segments during which the accumulator receives and discharges fluid, respectively. An input may be used to determine the segment of the work cycle.

During boom-midair lowering operation in which a front work implement 130 can be turned under the self-weight of a boom 131, a hydraulic pump/motor 7 is operated as a motor to operate a generator/electric motor 10 as a generator. Power generation operation is performed by the hydraulic fluid discharged from a bottom-side chamber 5b of a boom cylinder 5 to recover positional energy. During jack-up in which the front work implement 130 cannot be turned under the self-weight of the boom 131, the generator/electric motor 10 is operated as an electric motor to operate the hydraulic pump/motor 7 as a pump. The jack-up is performed by supplying the hydraulic fluid from the bottom-side chamber 5b to rod-side chamber 5a of the boom cylinder 5 without supplying the hydraulic fluid from the main pump 2 to the rod-side chamber 5a of the boom cylinder 5.