초록 ▼

An actuator unit includes two chambers defined in the cylinder; a supply passage allowing a working fluid discharged from the pump to be supplied to the two chambers; a discharge passage allowing the two chambers to communicate with the tank; a direction control valve configured to selectively commu

An actuator unit includes two chambers defined in the cylinder; a supply passage allowing a working fluid discharged from the pump to be supplied to the two chambers; a discharge passage allowing the two chambers to communicate with the tank; a direction control valve configured to selectively communicate each of the two chambers with one of the pump and the tank; a control passage that branches from the supply passage on a side of the pump rather than the direction control valve so as to communicate the pump with the tank; a variable relief valve provided on the control passage, the variable relief valve opening so as to allow the working fluid to flow from the supply passage toward the tank when a pressure in the supply passage reaches the valve opening pressure; and a center passage that communicates the tank with an interior of the cylinder.

대표청구항 ▼

1. An actuator unit, comprising: a cylinder;a piston slidably inserted into the cylinder, the piston defining two chambers in the cylinder;a rod inserted into the cylinder and coupled to the piston;a tank;a pump;a supply passage provided between the pump and each of the two chambers so as to allow a

1. An actuator unit, comprising: a cylinder;a piston slidably inserted into the cylinder, the piston defining two chambers in the cylinder;a rod inserted into the cylinder and coupled to the piston;a tank;a pump;a supply passage provided between the pump and each of the two chambers so as to allow a working fluid discharged from the pump to be supplied to the two chambers;a discharge passage provided between each of the two chambers and the tank so as to allow the two chambers to communicate with the tank;a direction control valve configured to selectively communicate each of the two chambers with one of the pump and the tank by allowing and blocking communication between the corresponding chambers and one of the supply passage and the discharge passage;a control passage that branches from the supply passage between the pump and the direction control valve so as to communicate the pump with the tank;a variable relief valve provided on the control passage, the variable relief valve being configured to have a varied valve opening pressure, the variable relief valve opening so as to allow the working fluid to flow from the supply passage toward the tank when a pressure in the supply passage reaches the valve opening pressure; anda center passage that communicates the tank with an interior of the cylinder via a through hole through the cylinder,wherein a length of the through hole in an axial direction of the cylinder is smaller than a length of the piston facing an inner surface of the cylinder in the axial direction of the cylinder, and the through hole is closed by the piston when the piston moves on the through hole,wherein the center passage opens onto the cylinder only at the through hole aligned with a stroke center of the piston,wherein the two chambers include a rod-side chamber and a piston-side chamber, andwherein the cylinder, the center passage, and an opening/closing valve are configured such that thrust is provided only in a direction for returning the piston to the stroke center side both when the piston is leftward and rightward of the stroke center. 2. The actuator unit according to claim 1, wherein the supply passage includes: a common passage that communicates with a discharge port of the pump;a first branch passage that branches from the common passage so as to communicate with one of the two chambers; anda second branch passage that branches from the common passage so as to communicate with the other of the two chambers,wherein the direction control valve includes: a first direction control valve provided on the first branch passage; anda second direction control valve provided in the second branch passage, wherein the discharge passage includes:a first discharge passage connected to the first direction control valve so as to communicate one of the two chambers with the tank; anda second discharge passage connected to the second direction control valve so as to communicate the other of the two chambers with the tank,wherein the first direction control valve has a first position and a second position so as to be capable of switching between the first position and the second position, communication between the first branch passage being opened and the first discharge passage being closed at the first position, the first branch passage being closed and the first discharge passage being opened at the second position,wherein the second direction control valve has a first position and a second position so as to be capable of switching between the first position and the second position, the second branch passage being opened and the second discharge passage being closed at the first position, the second branch passage being closed and the second discharge passage being opened at the second position, andwherein check valves allowing the working fluid to flow only from the pump toward the cylinder are respectively provided on the first branch passage and the second branch passage between the pump and the first and second direction control valves. 3. The actuator unit according to claim 1, wherein the supply passage includes: a common passage that communicates with a discharge port of the pump;a first branch passage that branches from the common passage so as to communicate with one of the two chambers; anda second branch passage that branches from the common passage so as to communicate with the other of the two chambers,wherein the direction control valve is provided in a bifurcating part of the supply passage, and the discharge passage communicating with the tank is connected to the direction control valve, andwherein the direction control valve has a first communication position, a blocking position, and a second communication position so as to be capable of switching among the first communication position, the blocking position, and the second communication position, the common passage communicating with the first branch passage and the discharge passage communicating with the second branch passage at the first communication position, none of the passages communicating with each other at the blocking position, the common passage communicating with the second branch passage and the discharge passage communicating with the first branch passage at the second position. 4. The actuator unit according to claim 1, further comprising: a contraction side intake passage that communicates the tank with a rod side chamber of the two chambers, the rod side chamber expanding when the actuator unit contracts;an expansion side intake passage that communicates the tank with a piston side chamber of the two chambers, the piston side chamber expanding when the actuator unit expands;a check valve provided on the contraction side intake passage to allow the working fluid to pass only from the tank toward the rod side chamber;a check valve provided on the expansion side intake passage to allow the working fluid to pass only from the tank toward the piston side chamber;an expansion side relief passage and a contraction side relief passage each of which communicates the rod side chamber with the piston side chamber;an expansion side relief valve provided on the expansion side relief passage so as to open when a pressure in the rod side chamber exceeds a pressure in the piston side chamber by a predetermined amount; anda contraction side relief valve provided on the contraction side relief passage so as to open when the pressure in the piston side chamber exceeds the pressure in the rod side chamber by a predetermined amount. 5. The actuator unit according to claim 1, wherein the center passage opens onto the cylinder at a position aligning with a stroke center of the piston. 6. The actuator unit according to claim 1, wherein an opening/closing valve is provided on the center passage to open and close the center passage. 7. The actuator unit according to claim 1, wherein the thrust is provided only in the direction for returning the piston to the stroke center side regardless of whether the actuator unit functions as an actuator or a damper. 8. An actuator unit, comprising: a cylinder;a piston slidably inserted into the cylinder, the piston defining two chambers in the cylinder;a rod inserted into the cylinder and coupled to the piston;a tank;a pump;a supply passage provided between the pump and each of the two chambers so as to allow a working fluid discharged from the pump to be supplied to the two chambers;a discharge passage provided between each of the two chambers and the tank so as to allow the two chambers to communicate with the tank; a direction control valve configured to selectively communicate each of the two chambers with one of the pump and the tank by allowing and blocking communication between the corresponding chambers and one of the supply passage and the discharge passage; a control passage that branches from the supply passage between the pump and the direction control valve so as to communicate the pump with the tank;a variable relief valve provided on the control passage, the variable relief valve being configured to have a varied valve opening pressure, the variable relief valve opening so as to allow the working fluid to flow from the supply passage toward the tank when a pressure in the supply passage reaches the valve opening pressure; anda center passage that communicates the tank with an interior of the cylinder via an only one through hole through the cylinder,wherein a length of the only one through hole in an axial direction of the cylinder is smaller than a length of the piston facing an inner surface of the cylinder in the axial direction of the cylinder, and the only one through hole is closed by the piston when the piston moves on the only one through hole.