Hydraulic circuit, energy recovery device, and hydraulic circuit for work machine

An energy recovery device comprising:

• a hydraulic actuator adapted to be driven by hydraulic fluid supplied from a pump;
• an energy recovery motor adapted to be driven by energy contained in return fluid discharged from the hydraulic actuator;
• a motor generator adapted to be driven by the energy recovery motor so as to function as a generator for feeding electric power to an electric power storage device as well as be driven by electric power fed from the electric power storage device so as to function as an electric motor;
• and
• a clutch that serves to transmit power from the motor generator to the pump when the motor generator is functioning as an electric motor, and disengage the motor generator from the pump when the motor generator is functioning as a generator.

A hydraulic circuit for a work machine provided with a work equipment comprising a boom, a stick, and a bucket sequentially connected to one another;

• the boom being adapted to be pivoted by a boom cylinder, which is adapted to receive hydraulic fluid from a plurality of main pumps comprising a first main pump and a second main pump;
• the stick adapted to be pivoted by a stick cylinder;
• and the bucket adapted to be pivoted by a bucket cylinder;
• wherein the hydraulic circuit comprises:
• a boom cylinder hydraulic fluid feeding passage for feeding hydraulic fluid from the first main pump to the boom cylinder;
• a bucket cylinder hydraulic fluid feeding passage that branches off the boom cylinder hydraulic fluid feeding passage and serves to feed hydraulic fluid to the bucket cylinder;
• a stick cylinder hydraulic fluid feeding passage for feeding hydraulic fluid from the second main pump to the stick cylinder;
• a boom assist pump that, together with the first main pump, serves to feed hydraulic fluid to the boom cylinder hydraulic fluid feeding passage;
• a solenoid valve between bucket and boom disposed in the boom cylinder hydraulic fluid feeding passage, at a location between a point at which the bucket cylinder hydraulic fluid feeding passage branches off and a point at which a passage from the boom assist pump joins the boom cylinder hydraulic fluid feeding passage, the solenoid valve between bucket and boom being adapted to shift between a position for enabling the hydraulic fluid that would otherwise be fed to the bucket cylinder to be fed to the boom cylinder in a one-way direction and a position for interrupting the flow of fluid;
• a circuit-to-circuit communicating passage between stick and boom for providing fluid communication from the stick cylinder hydraulic fluid feeding passage to a head-side of the boom cylinder;
• and
• a solenoid valve between stick and boom that is disposed in the circuit-to-circuit communicating passage between stick and boom and adapted to shift between a position for enabling the hydraulic fluid that would otherwise be fed to the stick cylinder to be fed to the head-side of the boom cylinder in a one-way direction and a position for interrupting the flow of fluid.

A hydraulic circuit for a work machine provided with a work equipment having a boom to be pivoted by a boom cylinder, which is adapted to receive hydraulic fluid from a plurality of main pumps comprising a first main pump and a second main pump, wherein the hydraulic circuit comprises:

• a boom cylinder hydraulic fluid feeding passage for feeding hydraulic fluid from the first main pump to the boom cylinder;
• a boom assist pump that, together with the first main pump, serves to feed hydraulic fluid to the boom cylinder hydraulic fluid feeding passage;
• a solenoid valve adapted to shift between a communicating position for enabling hydraulic fluid discharged from the boom assist pump to merge with hydraulic fluid discharged from the first main pump, and a position for interrupting the flow of fluid;
• another solenoid valve adapted to shift between a communicating position for enabling hydraulic fluid discharged from the first main pump to merge with hydraulic fluid discharged from the second main pump, and a position for interrupting the flow of fluid;
• a pair of travel motors for traveling;
• and
• a straight travel valve disposed in a passage that enables the first and second main pumps to communicate with the pair of travel motors, the straight travel valve being adapted to shift between:
• a high-speed travel position for enabling, when the solenoid valves are at their respective communicating positions, supplementary fluid received from the boom assist pump through the solenoid valves to merge with hydraulic fluid fed from the first main pump and the second main pump to the pair of travel motors, and
• a straight travel position for feeding equally divided volume of hydraulic fluid from either the first main pump or the second main pump to the pair of travel motors.