Cylinder driving device

TECHNICAL FIELD

The present invention relates to a cylinder driving device.

BACKGROUND ART

JP2006-250311A discloses a hydraulic driving unit that includes a hydraulic pump that is driven by an electric motor, a hydraulic cylinder that is operated with working oil from the hydraulic pump, and an operation check valve that controls a flow of the working oil between the hydraulic pump and the hydraulic cylinder.

SUMMARY OF INVENTION

A cylinder driving device including the operation check valve or a control valve having the same function as the operation check valve may experience a hunting phenomenon in which the hydraulic cylinder is repeatedly operated and stopped even during the operation of the pump. The hunting phenomenon is caused when an the external force due to a load is exerted to the hydraulic cylinder, and the hydraulic cylinder is forced to function as a pump and sucks the working oil in a passage.

In the hydraulic driving unit disclosed in JP2006-250311A, in order to prevent the occurrence of the hunting phenomenon, a slow return valve is provided in a pipe channel between the hydraulic cylinder and the operation check valve. Because the flow of the working oil that is discharged from the hydraulic cylinder to the pipe channel is restricted by the slow return valve, the working oil in the passage is not sucked to the hydraulic cylinder, and the hunting phenomenon is prevented.

However, with the slow return valve disclosed in JP2006-250311A, an opening area of the restrictor is constant. Even in a condition in which the hunting phenomenon does not occur, the flow of the working oil flowing out from the hydraulic cylinder is restricted in a similar manner as in the case in which the hunting phenomenon occurs. Therefore, a large amount of energy is always required to operate the hydraulic cylinder, and the electric power consumption of the electric motor is increased.

An object of the present invention is to reduce an electric power consumption of an electric motor and to prevent the occurrence of a hunting phenomenon.

According to one aspect of the present invention, a cylinder driving device includes: an electric motor; a pump configured to be driven by the electric motor and discharge working fluid; a first passage and a second passage respectively connected to the pump, the first passage and the second passage being configured to selectively guide the working fluid from the pump; a fluid pressure cylinder connected to the first passage and the second passage, the fluid pressure cylinder being configured to be operated by the working fluid supplied from one of the first passage and the second passage, the fluid pressure cylinder being configured to discharge the working fluid to the other of the first passage and the second passage when operated; a control valve provided in the second passage, the control valve being configured to allow a flow of the working fluid directed from the fluid pressure cylinder to the pump in response to an increase in a pressure in the first passage while allowing a flow of the working fluid directed from the pump to the fluid pressure cylinder; and a restriction valve provided between the fluid pressure cylinder and the control valve in the second passage, the restriction valve being configured to restrict a flow of the working fluid directed from the fluid pressure cylinder to the control valve. An opening area of the restriction valve is reduced in response to an increase in a flow rate of the working fluid discharged from the fluid pressure cylinder to the second passage.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of a rotating device provided with a cylinder driving device according to an embodiment of the present invention;

FIG. 2 shows a state in which a hydraulic cylinder shown in FIG. 1 is extended;

FIG. 3 shows a state in which the hydraulic cylinder shown in FIG. 2 is extended further;

FIG. 4 is a circuit diagram of the cylinder driving device according to the embodiment of the present invention;

FIG. 5 is a schematic sectional view of a restriction valve shown in FIG. 4;

FIG. 6 is a circuit diagram of the cylinder driving device according to the embodiment of the present invention and shows a state in which an the external force due to a load is exerted to a fluid pressure cylinder in the contracting direction and in which a pump is operated such that the fluid pressure cylinder is extended;

FIG. 7 is a schematic view of the restriction valve shown in FIG. 6;

FIG. 8 is a circuit diagram of the cylinder driving device according to the embodiment of the present invention, and shows a state in which the external force due to the load is exerted to the fluid pressure cylinder in the extending direction and in which the pump is operated such that the fluid pressure cylinder is extended;

FIG. 9 is a schematic view of the restriction valve shown in FIG. 8;

FIG. 10 is a circuit diagram of the cylinder driving device according to a modification of the embodiment of the present invention; and

FIG. 11 is a circuit diagram of the cylinder driving device according to a comparative example.

DESCRIPTION OF EMBODIMENT

A cylinder driving device 100 according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic view of a rotating device 1000 provided with the cylinder driving device 100. The cylinder driving device 100 is provided with a hydraulic cylinder 10 that extends/contracts by a pressure of working oil. The rotating device 1000 rotates a target object W by the extension/contraction of the hydraulic cylinder 10.

As shown in FIG. 1, the rotating device 1000 is provided with a base member 1 and an arm member 2 linked to the base member 1. The arm member 2 is formed to have a rod shape. The target object W is attached to an end portion 2a of the arm member 2.

An end portion 2b of the arm member 2 is formed with a hole 2c. The hole 2c penetrates through the end portion 2b in the direction perpendicular to the longitudinal direction of the arm member 2. A pin 1b formed on the base member 1 is inserted into the hole 2c.

The pin 1b of the base member 1 projects out from a main body portion 1a of the base member 1 in the horizontal direction. The outer diameter of the pin 1b is equal to or less than the inner diameter of the hole 2c of the arm member 2, and the end portion 2b of the arm member 2 is rotatably supported by the pin 1b. As described above, the arm member 2 is linked to the base member 1 so as to be freely rotatable about the pin 1b (about the horizontal axis).

The hydraulic cylinder 10 is provided with a cylinder 11 and a piston rod 13 that extends out from the cylinder 11. The piston rod 13 is capable of advancing/retracting with respect to the cylinder 11. As the piston rod 13 retracts out from the cylinder 11, the hydraulic cylinder 10 is extended. As the piston rod 13 advances into the cylinder 11, the hydraulic cylinder 10 is contracted.

The cylinder 11 is provided with a linkage portion 10a by which the hydraulic cylinder 10 is linked to the base member 1. The linkage portion 10a is formed with a hole 10c that penetrates through the linkage portion 10a in the direction perpendicular to the extending direction of the hydraulic cylinder 10. A pin 1c formed on the base member 1 is inserted into the hole 10c.

The pin 1c of the base member 1 projects out from the main body portion 1a of the base member 1 in the same direction as the projecting direction of the pin 1b. The outer diameter of the pin 1c is equal to or less than the inner diameter of the hole 10c of the hydraulic cylinder 10, and the linkage portion 10a of the hydraulic cylinder 10 is rotatably supported by the pin 1c. As described above, the hydraulic cylinder 10 is linked to the base member 1 so as to be freely rotatable about the pin 1c (about the horizontal axis).

The piston rod 13 is provided with a linkage portion 10b by which the hydraulic cylinder 10 is linked to the arm member 2. The linkage portion 10b is formed with a hole 10d that penetrates the linkage portion 10b in the same direction as the penetrating direction of the hole 10c of the hydraulic cylinder 10. A pin 2d formed on the arm member 2 is inserted into the hole 10d.

The pin 2d of the arm member 2 is provided on a middle portion 2e that is formed between the end portions 2a and 2b. The projecting direction of the pin 2d corresponds to the projecting direction of the pin 1b and the pin 1c of the base member 1. The outer diameter of the pin 2d is equal to or less than the inner diameter of the hole 10d of the hydraulic cylinder 10, and the linkage portion 10b of the hydraulic cylinder 10 is rotatably supported by the pin 2d. As described above, the hydraulic cylinder 10 is linked to the arm member 2 so as to be freely rotatable about the pin 2d (about the horizontal axis).

A two-dot chain line in FIG. 1 shows an imaginary line L that extends in the vertical direction through the pin 1b. In FIG. 1, a state in which the hydraulic cylinder 10 is contracted to the utmost extents is shown. In this state, the centers of gravity of the target object W and the arm member 2 are positioned at positions higher than the pin 1b in the vertical direction and at positions on the pin 1c side of the imaginary line L. Gravity acting on the target object W and the arm member 2 acts as the load on the piston rod 13 in the direction in which the hydraulic cylinder 10 is contracted.

FIG. 2 shows a state in which the hydraulic cylinder 10 is extended from the state shown in FIG. 1. As the hydraulic cylinder 10 is extended, the arm member 2 is rotated about the pin 1b with respect to the base member 1. Along with the rotation of the arm member 2, the target object W is also rotated with respect to the base member 1.

As described above, the rotating device 1000 rotates the target object W by the extension/contraction of the hydraulic cylinder 10.

In the state shown in FIG. 2, similarly to the state shown in FIG. 1, the centers of gravity of the target object W and the arm member 2 are positioned at positions higher than the pin 1b in the vertical direction and at positions on the pin 1c side of the imaginary line L. Gravity acting on the target object W and the arm member 2 acts as the load on the piston rod 13 in the direction in which the hydraulic cylinder 10 is contracted.

FIG. 3 shows a state in which the hydraulic cylinder 10 is further extended from the state shown in FIG. 2. In the state shown in FIG. 3, the centers of gravity of the target object W and the arm member 2 are positioned at positions higher than the pin 1b in the vertical direction and at positions on the opposite side of the pin 1c with respect to the imaginary line L. Gravity acting on the target object W and the arm member 2 acts as the load on the piston rod 13 in the direction in which the hydraulic cylinder 10 is extended.

As described above, with the rotating device 1000, along with the operation of the hydraulic cylinder 10, the direction in which the load acts on the piston rod 13 of the hydraulic cylinder 10 is reversed.

As shown in FIG. 4, the hydraulic cylinder 10 is further provided with a piston 12 that is slidably accommodated in the cylinder 11. The piston rod 13 is connected to the piston 12. The interior of the cylinder 11 is partitioned into a counter rod side chamber 11a and a rod side chamber 11b by the piston 12.

The counter rod side chamber 11a and the rod side chamber 11b are filled with the working oil. The piston 12 is moved with respect to the cylinder 11 by the working oil that is selectively supplied to the counter rod side chamber 11a and the rod side chamber 11b. As the piston 12 is moved, the piston rod 13 advances/retracts with respect to the cylinder 11, and the hydraulic cylinder 10 is extended/contracted.

More specifically, when the working oil is supplied to the counter rod side chamber 11a, the piston 12 is moved in the direction in which the size of the counter rod side chamber 11a is increased and the size of the rod side chamber 11b is reduced. As the piston 12 is moved, the piston rod 13 retracts out from the cylinder 11. As a result, the hydraulic cylinder 10 is extended. At this time, as the size of the rod side chamber 11b is reduced, the working oil in the rod side chamber 11b is discharged to the outside of the hydraulic cylinder 10.

When the working oil is supplied to the rod side chamber 11b, the piston 12 is moved in the direction in which the size of the rod side chamber 11b is increased and the size of the counter rod side chamber 11a is reduced. As the piston 12 is moved, the piston rod 13 advances into the cylinder 11. As a result, the hydraulic cylinder 10 is contracted. At this time, as the size of the counter rod side chamber 11a is reduced, the working oil in the counter rod side chamber 11a is discharged to the outside of the hydraulic cylinder 10.

The cylinder driving device 100 is provided with a pump 20 that supplies the working oil to the hydraulic cylinder 10 and an electric motor 30 that drives the pump 20. The electric motor 30 is electrically connected to a power source (not shown) and is operated by the electrical power supplied from the power source.

The pump 20 is connected to an output shaft 31 of the electric motor 30 and is driven by a rotational driving force from the electric motor 30. The pump 20 is formed with a first port 21a and a second port 21b, and the working oil is discharged from the first port 21a and the second port 21b selectively.

When the output shaft 31 of the electric motor 30 is rotated in a forward direction R1, the pump 20 sucks the working oil from the second port 21b and discharges the working oil from the first port 21a. When the output shaft 31 of the electric motor 30 is rotated in a reverse direction R2, the pump 20 sucks the working oil from the first port 21a and discharges the working oil from the second port 21b.

As described above, the discharge direction of the pump 20 is switched depending on the rotation direction of the electric motor 30. As the pump 20, for example, a gear pump can be used.

A main passage 80a is connected to the first port 21a of the pump 20, and a main passage 80b is connected to the second port 21b of the pump 20. The working oil is selectively guided from the pump 20 to the main passage 80a and the main passage 80b.

The main passage 80a is connected to the counter rod side chamber 11a of the hydraulic cylinder 10, and the main passage 80b is connected to the rod side chamber 11b of the hydraulic cylinder 10. The main passage 80a is provided with an operation check valve (control valve) 60a that controls the flow of the working oil, and the main passage 80b is provided with an operation check valve (control valve) 60b that controls the flow of the working oil. A restriction valve 70a is provided between the operation check valve 60a in the main passage 80a and the counter rod side chamber 11a. A restriction valve 70b is provided between the operation check valve 60b in the main passage 80b and the rod side chamber 11b.

In the following description, a portion between the first port 21a of the pump 20 and the operation check valve 60a in the main passage 80a is referred to as “a passage portion 81a”. A portion between the second port 21b of the pump 20 and the operation check valve 60b in the main passage 80b is referred to as “a passage portion 81b”. A portion between the operation check valve 60a and the restriction valve 70a in the main passage 80a is referred to as “a passage portion 82a”, and a portion between the operation check valve 60b and the restriction valve 70b in the main passage 80b is referred to as “a passage portion 82b”. A portion between the restriction valve 70a in the main passage 80a and the counter rod side chamber 11a is referred to as “a passage portion 83a”, and a portion between the restriction valve 70b in the main passage 80b and the rod side chamber 11b is referred to as “a passage portion 83b”.

The operation check valve 60a allows the flow of the working oil discharged from the first port 21a of the pump 20 and directed to the counter rod side chamber 11a of the hydraulic cylinder 10 through the main passage 80a. In addition, the operation check valve 60a has a back-pressure chamber (not shown). When the pressure in the back-pressure chamber reaches a valve opening pressure, the operation check valve 60a is opened to allow the flow of the working oil in the main passage 80a.

The back-pressure chamber of the operation check valve 60a is connected to the passage portion 81b of the main passage 80b via a pilot passage 86b. When the pressure in the passage portion 81b is increased, the pressure in the back-pressure chamber of the operation check valve 60a is increased, and the operation check valve 60a is opened. In other words, in response to the increase in the pressure in the passage portion 81b, the operation check valve 60a allows the flow of the working oil from the counter rod side chamber 11a of the hydraulic cylinder 10 to the first port 21a of the pump 20 through the main passage 80a.

Similarly, the operation check valve 60b allows the flow of the working oil discharged from the second port 21b of the pump 20 and directed to the rod side chamber 11b of the hydraulic cylinder 10 through the main passage 80b. The back-pressure chamber (not shown) of the operation check valve 60b is connected to the passage portion 81a of the main passage 80a via a pilot passage 86a. In response to the increase in the pressure in the passage portion 81a, the operation check valve 60a allows the flow of the working oil from the rod side chamber 11b of the hydraulic cylinder 10 to the second port 21b of the pump 20 through the main passage 80b.

When the working oil is discharged from the first port 21a by the pump 20, the working oil from the first port 21a pushes the operation check valve 60a open. At this time, the pressure in the passage portion 81a of the main passage 80a is increased, and the operation check valve 60b is opened. The working oil from the first port 21a is supplied to the counter rod side chamber 11a of the hydraulic cylinder 10 through the main passage 80a, and the working oil in the rod side chamber 11b is discharged to the main passage 80b and guided to the second port 21b of the pump 20. The hydraulic cylinder 10 is extended by the supply of the working oil to the counter rod side chamber 11a and by the discharge of the working oil in the rod side chamber 11b.

When the working oil is discharged from the second port 21b by the pump 20, the working oil from the second port 21b pushes the operation check valve 60b open. At this time, the pressure in the passage portion 81b of the main passage 80b is increased, and the operation check valve 60a is opened. The working oil from the second port 21b is supplied to the rod side chamber 11b of the hydraulic cylinder 10 through the main passage 80b, and the working oil in the counter rod side chamber 11a is discharged to the main passage 80a and guided to the first port 21a of the pump 20. The hydraulic cylinder 10 is contracted by the supply of the working oil to the rod side chamber 11b and by the discharge of the working oil in the counter rod side chamber 11a.

When the pump 20 is being stopped, the pressure in the passage portion 81a of the main passage 80a and the pressure in the passage portion 81b of the main passage 80b are not increased. The operation check valve 60a and the operation check valve 60b are closed, and the flow of the working oil in the main passage 80a and the main passage 80b is shut off. The working oil in the counter rod side chamber 11a and the rod side chamber 11b of the hydraulic cylinder 10 is not discharged to the main passage 80a and the main passage 80b, and the hydraulic cylinder 10 is not operated. In other words, when the pump 20 is being stopped, the hydraulic cylinder 10 is maintained in a stationary state by the operation check valve 60a and the operation check valve 60b.

In the hydraulic cylinder 10, although the piston rod 13 is inserted through the rod side chamber 11b, the piston rod 13 is not inserted through the counter rod side chamber 11a. When the piston 12 is moved by the operation of the hydraulic cylinder 10, the flow rate of the working oil flowing between the rod side chamber 11b and the main passage 80b is less than the flow rate of the working oil flowing between the counter rod side chamber 11a and the main passage 80a. The volume change caused by the piston rod 13 being advanced/retracted with respect to the cylinder 11 is compensated by a tank 40 connected to the pump 20. The compensation of the volume change will be described more specifically.

The cylinder driving device 100 is provided with a control valve 50 that controls the flow of the working oil between the pump 20 and the tank 40. The tank 40 stores the working oil in a closed space.

The control valve 50 is a three-port-three-position switching valve. A first port of the control valve 50 is connected to a branch passage 91a that is branched from the passage portion 81a of the main passage 80a. A second port of the control valve 50 is connected to a branch passage 91b that is branched from the passage portion 81b of the main passage 80b. A third port of the control valve 50 is connected to a tank passage 91c that is connected to the tank 40.

When the control valve 50 is positioned at a first position 50a, the communication between the tank passage 91c and the branch passage 91a is shut off, and the tank passage 91c is allowed to communicate with the branch passage 91b. When the control valve 50 is positioned at a second position 50b, the tank passage 91c is allowed to communicate with the branch passage 91a, and the communication between the tank passage 91c and the branch passage 91b is shut off. When the control valve 50 is positioned at a third position 50c, the communication between the tank passage 91c and the branch passage 91a is shut off, and the communication between the tank passage 91c and the branch passage 91b is shut off.

The position of the control valve 50 is switched by the pressure in the branch passage 91a and the branch passage 91b. When the pump 20 is being stopped and when the pressure in the branch passage 91a and the branch passage 91b has not been increased, the control valve 50 is positioned at the third position 50c to shut off the communication between the tank passage 91c and the branch passage 91a and to shut off the communication between the tank passage 91c and the branch passage 91b.

When the working oil is discharged from the first port 21a by the pump 20, as described above, the hydraulic cylinder 10 is extended. At this time, the pressure in the branch passage 91a is increased, and the control valve 50 is switched to the first position 50a. Then, the tank passage 91c is allowed to communicate with the branch passage 91b, and thereby, the working oil is allowed to flow between the tank 40 and the passage portion 81b of the main passage 80b. Because the communication between the tank passage 91c and the branch passage 91a is shut off, the working oil from the first port 21a is supplied to the counter rod side chamber 11a of the hydraulic cylinder 10 without flowing into the tank 40.

When the hydraulic cylinder 10 is extended, the flow rate of the working oil discharged from the rod side chamber 11b to the main passage 80b is less than the flow rate of the working oil supplied from the main passage 80a to the counter rod side chamber 11a by an amount corresponding to the volume of the piston rod 13 retracting out from the rod side chamber 11b. The working oil is supplied from the tank 40 to the passage portion 81b of the main passage 80b through the tank passage 91c and the branch passage 91b by the amount corresponding to the volume of the piston rod 13 retracting out from the rod side chamber 11b. Therefore, the pump 20 can suck the working oil from the second port 21b at the same flow rate as the flow rate of the working oil discharged from the first port 21a.

When the working oil is discharged from the second port 21b by the pump 20, as described above, the hydraulic cylinder 10 is contracted. At this time, the pressure in the branch passage 91b is increased, and the control valve 50 is switched to the second position 50b. Then, the tank passage 91c is allowed to communicate with the branch passage 91a, and thereby, the working oil is allowed to flow between the tank 40 and the passage portion 81a of the main passage 80a. Because the communication between the tank passage 91c and the branch passage 91b is shut off, the working oil from the second port 21b is supplied to the rod side chamber 11b of the hydraulic cylinder 10 without flowing into the tank 40.

When the hydraulic cylinder 10 is contracted, the flow rate of the working oil discharged from the counter rod side chamber 11a to the main passage 80a is greater than the flow rate of the working oil supplied from the main passage 80b to the rod side chamber 11b by an amount corresponding to the volume of the piston rod 13 advancing into the rod side chamber 11b. The amount of the working oil corresponding to the volume of the piston rod 13 advancing into the rod side chamber 11b is discharged from the passage portion 81a of the main passage 80a to the tank 40 through the branch passage 91a and the tank passage 91c. Therefore, the pump 20 can suck the working oil from the first port 21a at the same flow rate as the flow rate of the working oil discharged from the second port 21b.

As described above, the volume change caused by the piston rod 13 being advanced/retracted with respect to the cylinder 11 is compensated by the tank 40 connected to the pump 20.

The cylinder driving device 100 is further provided with a relief valve 96a, a relief valve 96b, a relief valve 97a, and a relief valve 97b. The relief valve 96a is provided in a relief passage 92a that is branched from the passage portion 81a of the main passage 80a and that is connected to the tank 40. The relief valve 96a is opened when the pressure in the passage portion 81a reaches the valve opening pressure of the relief valve 96a, and the working oil in the passage portion 81a is discharged to the tank 40 through the relief passage 92a. By providing the relief valve 96a, the pressure in the passage portion 81a is restricted to a pressure equal to or less than the valve opening pressure of the relief valve 96a.

Similarly, the relief valve 96b is provided in a relief passage 92b that is branched from the passage portion 81b of the main passage 80b and that is connected to the tank 40, and thereby, the pressure in the passage portion 81b is restricted to a pressure equal to or less than the valve opening pressure of the relief valve 96b. The relief valve 97a is provided in a relief passage 93a that is branched from the passage portion 82a of the main passage 80a and that is connected to the tank 40, and thereby, the pressure in the passage portion 82a is restricted to a pressure equal to or less than the valve opening pressure of the relief valve 97a. The relief valve 97b is provided in a relief passage 93b that is branched from the passage portion 82b of the main passage 80b and that is connected to the tank 40, and thereby, the pressure in the passage portion 82b is restricted to a pressure equal to or less than the valve opening pressure of the relief valve 97b.

The cylinder driving device 100 is provided with a switching valve 98 that enables a manual operation of the hydraulic cylinder 10. The switching valve 98 is a three-port-two-position switching valve. A first port of the switching valve 98 is connected to a branch passage 94a that is branched from the passage portion 82a of the main passage 80a. A second port of the switching valve 98 is connected to a branch passage 94b that is branched from the passage portion 82b of the main passage 80b. A third port of the switching valve 98 is connected to a tank passage 94c that is connected to the tank 40.

When the switching valve 98 is positioned at a first position 98a, the communication between the tank passage 94c and the branch passage 94a is shut off, the communication between the tank passage 94c and the branch passage 94b is shut off, and the communication between the branch passage 94a and the branch passage 94b is shut off. When the switching valve 98 is positioned at a second position 98b, the tank passage 94c is allowed to communicate with the branch passage 94a, the tank passage 94c is allowed to communicate with the branch passage 94b, and the branch passage 94a is allowed to communicate with the branch passage 94b. The position of the switching valve 98 is switched by manually operating the switching valve 98.

When the switching valve 98 is switched to the second position 98b, the counter rod side chamber 11a and the rod side chamber 11b of the hydraulic cylinder 10 are connected to the tank 40 by bypassing the operation check valves 60a and 60b, and the control valve 50. The hydraulic cylinder 10 can be extended/contracted by the manual operation.

The restriction valve 70b restricts the flow of the working oil in the main passage 80b. The flow of the working oil in the restriction valve 70b is restricted in accordance with the opening area of the restriction valve 70b. Therefore, the flow rate of the working oil discharged from the rod side chamber 11b to the main passage 80b is restricted, and thereby, it is possible to prevent a hunting phenomenon during the extending operation of the hydraulic cylinder 10.

In this description, the hunting phenomenon means a phenomenon in which the hydraulic cylinder 10 is repeatedly operated and stopped even during the operation of the pump 20. The hunting phenomenon will be described in detail with reference to FIG. 11.

FIG. 11 is a circuit diagram of a cylinder driving device 300 according to a comparative example. Configurations that are the same as those of the cylinder driving device 100 are assigned the same reference signs, and descriptions thereof shall be omitted. The cylinder driving device 300 differs from the cylinder driving device 100 in that the restriction valve 70a and the restriction valve 70b are not provided (see FIG. 4).

An operation of the cylinder driving device 300 under a condition in which the hunting phenomenon does not occur will be described first. More specifically, a description will be given of the operation of the cylinder driving device 300 when the hydraulic cylinder 10 is extended in a state in which the piston rod 13 is receiving an the external force due to the load in the contracting direction (a state shown in FIG. 2).

Because the external force due to the load is exerted to the piston 12 in the contracting direction via the piston rod 13, the piston 12 does not move in the extending direction with this external force. The working oil supplied to the counter rod side chamber 11a causes the piston 12 to move in the extending direction against the external force.

The pressure in the main passage 80a is kept at a high state by the working oil discharged from the first port 21a of the pump 20, and so, the operation check valve 60b is kept in the opened state. Therefore, the working oil in the rod side chamber 11b is continued to be discharged to the main passage 80b, and the hydraulic cylinder 10 is continued to be extended without being stopped.

As described above, when the hydraulic cylinder 10 is extended in a state in which the piston rod 13 is receiving the external force due to the load in the contracting direction (a state shown in FIG. 2), the hydraulic cylinder 10 is continued to be extended.

Similarly, also when the hydraulic cylinder 10 is contracted in a state in which the piston rod 13 is receiving the external force due to the load in the extending direction (a state shown in FIG. 3), the hydraulic cylinder 10 is continued to be contracted without being stopped. In other words, the hunting phenomenon does not occur if the direction in which the external force due to the load is exerted to the piston rod 13 does not match the operating direction of the hydraulic cylinder 10.

Next, the operation of the cylinder driving device 300 under the condition in which the hunting phenomenon occurs will be described. More specifically, a description will be given of the operation of the cylinder driving device 300 when the hydraulic cylinder 10 is extended in a state in which the piston rod 13 is receiving the external force due to the load in the extending direction (a state shown in FIG. 3).

Soon after the working oil is discharged from the first port 21a by the pump 20, the working oil from the first port 21a pushes the operation check valve 60a open and is supplied to the counter rod side chamber 11a of the hydraulic cylinder 10. At this time, the pressure in the passage portion 81a of the main passage 80a is increased, and the operation check valve 60b is opened. The working oil in the rod side chamber 11b is discharged to the main passage 80b, and the hydraulic cylinder 10 starts to extend.

Because the external force due to the load is exerted to the piston 12 in the extending direction via the piston rod 13, the piston 12 is moved in the extending direction by receiving the external force in addition to the pressure of the working oil supplied to the counter rod side chamber 11a. The larger the external force due to the load is, the faster the moving speed of the piston 12 is, and the greater the flow rate of the working oil discharged from the rod side chamber 11b to the main passage 80b becomes.

As the piston 12 is moved at high speed in the direction in which the hydraulic cylinder 10 is extended, the working oil in the main passage 80a is sucked to the counter rod side chamber 11a by the piston 12. In other words, with the external force due to the load, the hydraulic cylinder 10 functions as a pump and sucks the working oil in the main passage 80a.

When the flow rate of the working oil sucked from the main passage 80a by the hydraulic cylinder 10 exceeds the maximum discharge flow rate of the pump 20, the pump 20 can no longer increase the pressure in the main passage 80a, and the pressure in the passage portion 81a of the main passage 80a is decreased. Thereby, the operation check valve 60b is closed, and the discharge of the working oil from the rod side chamber 11b to the main passage 80b is stopped. The piston 12 is stopped, and the hydraulic cylinder 10 is stopped.

When the piston 12 is stopped, the suction of the working oil from the main passage 80a to the counter rod side chamber 11a by the piston 12 is stopped. The pressure in the main passage 80a is increased by the pump 20, and the operation check valve 60b is opened. The working oil in the rod side chamber 11b is discharged to the main passage 80b, and the hydraulic cylinder 10 starts to extend again.

The piston 12 is moved in the extending direction by receiving the external force due to the load in addition to the pressure of the working oil supplied to the counter rod side chamber 11a. The working oil in the main passage 80a is sucked to the counter rod side chamber 11a by the piston 12, and the pressure in the passage portion 81a of the main passage 80a is decreased. The operation check valve 60b is closed, and the discharge of the working oil from the rod side chamber 11b to the main passage 80b is stopped. The piston 12 is stopped, and the hydraulic cylinder 10 is stopped again.

As described above, with the cylinder driving device 300, the hydraulic cylinder 10 is repeatedly extended and stopped when the hydraulic cylinder 10 is extended in a state in which the piston rod 13 is receiving the large external force due to the load in the extending direction (a state shown in FIG. 3).

Similarly, the hydraulic cylinder 10 is also repeatedly contracted and stopped even when the hydraulic cylinder 10 is contracted in a state in which the piston rod 13 is receiving the large external force due to the load in the contracting direction (a state shown in FIG. 2). In other words, with the cylinder driving device 300, the hunting phenomenon is caused when the direction in which the external force due to the load is exerted to the piston rod 13 matches the operating direction of the hydraulic cylinder 10.

When referring to FIG. 4, with the cylinder driving device 100, the flow of the working oil discharged from the rod side chamber 11b to the main passage 80b is restricted by the restriction valve 70b. Even when the hydraulic cylinder 10 is extended in a state in which the external force due to the load is exerted to the piston rod 13 in the extending direction, the increase in the flow rate of the working oil discharged from the rod side chamber 11b of the hydraulic cylinder 10 to the main passage 80b is restricted. It is possible to prevent the suction of the working oil from the main passage 80a to the counter rod side chamber 11a by the piston 12 and to prevent the decrease in the pressure in the main passage 80a. Therefore, it is possible to prevent the occurrence of the hunting phenomenon during the extending operation of the hydraulic cylinder 10.

Similarly, the flow of the working oil discharged from the counter rod side chamber 11a to the main passage 80a is restricted by the restriction valve 70a. The increase in the flow rate of the working oil discharged from the counter rod side chamber 11a of the hydraulic cylinder 10 to the main passage 80a is restricted. It is possible to prevent the decrease in the pressure in the main passage 80b and to prevent the occurrence of the hunting phenomenon during the contracting operation of the hydraulic cylinder 10.

The restriction valve 70b is formed such that the opening area of the restriction valve 70b is reduced in response to the increase in the flow rate of the working oil discharged from the rod side chamber 11b of the hydraulic cylinder 10 to the main passage 80b.

FIG. 5 is a schematic sectional view of the restriction valve 70b. The restriction valve 70b has a first port 71a that is connected to the passage portion 83b of the main passage 80b, a second port 72a that is connected to the passage portion 82b of the main passage 80b, and a flow passage 73 through which the first port 71a is communicated with the second port 72a. The first port 71a is formed by a circular hole that is formed in a first housing 71. The second port 72a is formed by a circular hole that is formed in a second housing 72.

The second housing 72 has an opposing surface 72b that opposes the first housing 71. The opposing surface 72b is formed with a hollow portion 72c. The first port 71a is in communication with the hollow portion 72c.

The second housing 72 is formed with a hole 72d that opens at a bottom surface of the hollow portion 72c. The inner diameter of the hole 72d is larger than the inner diameter of the second port 72a, and the second port 72a opens at a bottom surface 72e of the hole 72d. The flow passage 73 is formed by the hollow portion 72c and the hole 72d. An annular valve seat 72f is formed by the bottom surface 72e of the hole 72d and an inner circumferential surface of the second port 72a.

The restriction valve 70b has a valve body 74 that is provided in the flow passage 73 and a spring (a biasing member) 75 that biases the valve body 74 in the direction in which the valve body 74 is separated from the valve seat 72f. The spring 75 is, for example, a coil spring.

The valve body 74 has a large-diameter portion 74a that has the outer diameter that is substantially the same as the inner diameter of the hole 72d and a small-diameter portion 74b that has the outer diameter smaller than the outer diameter of the large-diameter portion 74a. The large-diameter portion 74a is slidably accommodated in the hole 72d.

The small-diameter portion 74b projects from the large-diameter portion 74a towards the second port 72a. A step portion 74c is formed between the large-diameter portion 74a and the small-diameter portion 74b.

The outer diameter of a proximal end portion of the small-diameter portion 74b (a portion that continued from the large-diameter portion 74a) is larger than the inner diameter of the second port 72a. The outer diameter of a distal end surface of the small-diameter portion 74b is smaller than the inner diameter of the second port 72a. A distal end portion of the small-diameter portion 74b is formed to have a tapered shape. When the valve body 74 is seated on the valve seat 72f, the distal end surface of the small-diameter portion 74b enters the second port 72a, and the distal end portion of the small-diameter portion 74b is brought into contact with the valve seat 72f.

The spring 75 is provided between the step portion 74c of the valve body 74 and the bottom surface 72e of the hole 72d in a compressed state. The valve body 74 is biased in the direction in which the valve body 74 is separated from the valve seat 72f by a restoring force of the spring 75. The movement of the valve body 74 in the direction in which the valve body 74 is separated from the valve seat 72f is restricted by the first housing 71.

The valve body 74 is formed with a hole 74d that opens at an end surface of the large-diameter portion 74a and that is formed so as to extend from the large-diameter portion 74a to the small-diameter portion 74b. The end surface of the large-diameter portion 74a is formed with a groove 74e that extends from an inner circumferential surface of the hole 74d to an outer circumferential surface of the large-diameter portion 74a. Through the groove 74e, the hole 74d is communicated with the hollow portion 72c even in a state in which the valve body 74 is pushed against the first housing 71.

The small-diameter portion 74b is formed with a restriction hole (first restriction portion) 74f that penetrates between a bottom surface of the hole 74d and the distal end surface of the small-diameter portion 74b. The small-diameter portion 74b is formed with a restriction hole (second restriction portion) 74g that penetrates between the inner circumferential surface of the hole 74d and an outer circumferential surface of the small-diameter portion 74b. In a state in which the valve body 74 is seated on the valve seat 72f, the working oil flows between the second port 72a and the hole 74d only through the restriction hole 74f and not through the restriction hole 74g.

In a state in which the pump 20 is stopped, the pressure of the working oil does not act on the valve body 74, and the valve body 74 is separated from the valve seat 72f by the biasing force exerted by the spring 75. When the working oil is discharged from the second port 21b by the pump 20, the valve body 74 is separated from the valve seat 72f by the pressure of the working oil directed from the second port 72a to the first port 71a through the flow passage 73 and by the biasing force exerted by the spring 75.

In a state in which the external force due to the load is exerted to the piston rod 13 in the contracting direction (a state shown in FIG. 2), when the working oil is discharged from the first port 21a by the pump 20, the hydraulic cylinder 10 is extended against the external force due to the load by the pump 20 (see FIG. 6). At this time, the flow rate of the working oil discharged from the rod side chamber 11b to the main passage 80b is low.

As shown in FIG. 7, the working oil supplied from the first port 71a of the restriction valve 70b causes the valve body 74 to approach the valve seat 72f against the biasing force exerted by the spring 75. However, because the flow rate of the working oil supplied from the first port 71a of the restriction valve 70b is low, the pressure difference between the first port 71a and the second port 72a is small. Thus, the movement of the valve body 74 is restricted by the biasing force exerted by the spring 75, and the valve body 74 does not seat on the valve seat 72f. In other words, the valve body 74 is kept in a state in which it is separated from the valve seat 72f.

The first port 71a of the restriction valve 70b is communicated with the second port 72a through both of the restriction hole 74f and the restriction hole 74g. In other words, the opening area of the restriction valve 70b corresponds to a total sum of the opening area of the restriction hole 74f and the opening area of the restriction hole 74g. The opening area of the restriction valve 70b is large, and so, a resistance imparted to the flow of the working oil by the restriction valve 70b in the main passage 80b is small. Therefore, it is possible to reduce the load on the electric motor 30 and to reduce the electric power consumption of the electric motor 30.

In addition, because the load on the electric motor 30 is made small, the low power electric motor 30 can be used. Thus, a cost for the electric motor 30 and electric equipment for supplying electrical power to the electric motor 30 can be reduced.

Furthermore, because a resistance imparted to the flow of the working oil by the restriction valve 70b in the main passage 80b is small, it is possible to increase the speed of the operation of the hydraulic cylinder 10 without increasing the power of the electric motor 30.

At this time, because the external force due to the load is not exerted in the direction in which the hydraulic cylinder 10 is extended, the hydraulic cylinder 10 is prevented from functioning as a pump to suck the working oil in the main passage 80a. Thus, the pressure in the main passage 80a is increased by the pump 20, and the operation check valve 60b is kept in the opened state. Therefore, the hunting phenomenon does not occur.

In a state in which the external force due to the load is exerted to the piston rod 13 in the extending direction (a state shown in FIG. 3), when the working oil is discharged from the first port 21a by the pump 20, the hydraulic cylinder 10 is extended by the pump 20 together with the external force due to the load (see FIG. 8). Thus, the flow rate of the working oil discharged from the rod side chamber 11b to the main passage 80b is increased.

As shown in FIG. 9, the working oil supplied from the first port 71a of the restriction valve 70b causes the valve body 74 to approach the valve seat 72f against the biasing force exerted by the spring 75. Because the flow rate of the working oil supplied from the first port 71a of the restriction valve 70b is high, the pressure difference between the first port 71a and the second port 72a is large. Thus, the valve body 74 is made to seat on the valve seat 72f against the biasing force exerted by the spring 75.

The first port 71a of the restriction valve 70b is communicated with the second port 72a only through the restriction hole 74f, and the first port 71a is not communicated with the second port 72a through the restriction hole 74g. In other words, the opening area of the restriction valve 70b corresponds to the opening area of the restriction hole 74f.

At this time, the opening area of the restriction valve 70b is small, and the flow of the working oil in the main passage 80b is restricted by the restriction valve 70b to a greater extent. Thus, the increase in the flow rate of the working oil in the main passage 80b is restricted, and it is possible to prevent the hydraulic cylinder 10 from functioning as a pump to suck the working oil in the main passage 80a. Therefore, the pressure in the main passage 80a can be increased by the pump 20, and it is possible to keep the operation check valve 60b in the opened state. Thus, it is possible to prevent the occurrence of the hunting phenomenon.

At this time, because the external force due to the load is exerted in the direction in which the hydraulic cylinder 10 is extended, the load of the pump 20 is made small. Therefore, it is possible to reduce the load on the electric motor 30 and to reduce the electric power consumption of the electric motor 30.

As described above, in the cylinder driving device 100, the opening area of the restriction valve 70b is changed between a case in which the external force is exerted to the hydraulic cylinder 10 such that the hunting phenomenon is caused and a case in which the external force is exerted to the hydraulic cylinder 10 such that the hunting phenomenon is not caused. Therefore, during the extending operation of the hydraulic cylinder 10, it is possible to reduce the electric power consumption of the electric motor 30 and to prevent the occurrence of the hunting phenomenon.

Similarly to the restriction valve 70b, the restriction valve 70a is formed such that the opening area of the restriction valve 70a is reduced in response to the increase in the flow rate of the working oil discharged from the counter rod side chamber 11a of the hydraulic cylinder 10 to the main passage 80a. Therefore, during the contracting operation of the hydraulic cylinder 10, it is possible to reduce the electric power consumption of the electric motor 30 and to prevent the occurrence of the hunting phenomenon.

The configuration of the restriction valve 70a is substantially the same as the configuration of the restriction valve 70b, and so, a description thereof shall be omitted.

The restriction valve 70b is set such that the opening area of the restriction valve 70b is reduced when the flow rate of the working oil sucked from the main passage 80a by the hydraulic cylinder 10 reaches the maximum discharge flow rate of the pump 20.

Until the flow rate of the working oil sucked from the main passage 80a by the hydraulic cylinder 10 reaches the maximum discharge flow rate of the pump 20, the opening area of the restriction valve 70b is large. Therefore, the load on the electric motor 30 is small, and so, it is possible to reduce the electric power consumption of the electric motor 30.

When the flow rate of the working oil sucked from the main passage 80a by the hydraulic cylinder 10 reaches the maximum discharge flow rate of the pump 20, the opening area of the restriction valve 70b is decreased, and the restriction valve 70b restricts the increase in the flow rate. Therefore, it is possible to prevent the hydraulic cylinder 10 from functioning as a pump to suck the working oil in the main passage 80a, and it is possible to prevent the occurrence of the hunting phenomenon.

The settings of the restriction valve 70b can be changed by changing a spring constant of the spring 75, the opening area of the restriction hole 74f, and the opening area of the restriction hole 74g.

Similarly to the restriction valve 70b, the restriction valve 70a is set such that the opening area of the restriction valve 70a is reduced when the flow rate of the working oil sucked from the main passage 80b by the hydraulic cylinder 10 reaches the maximum discharge flow rate of the pump 20.

The opening area of the restriction hole 74g is larger than the opening area of the restriction hole 74f. Thus, a difference between the opening area of the restriction valve 70b in a case in which both of the restriction hole 74f and the restriction hole 74g allow the communication between the first port 71a and the second port 72a, and the opening area of the restriction valve 70b in a case in which only the restriction hole 74f allows the communication between the first port 71a and the second port 72a is increased. Therefore, it is possible to further reduce the opening area of the restriction valve 70b in response to the increase in the flow rate of the working oil discharged from the rod side chamber 11b of the hydraulic cylinder 10 to the main passage 80b.

The hydraulic cylinder 10, the pump 20, the electric motor 30, the tank 40, various passages, and various valves form one unit (see FIG. 1). Thus, the hydraulic cylinder 10 can be operated only by supplying the electrical power to the electric motor 30 without connecting pipes, etc. to the hydraulic cylinder 10. Therefore, the operability of the cylinder driving device 100 is improved.

The hydraulic cylinder 10, the pump 20, the electric motor 30, the tank 40, the various passages, and the various valves may not form a unit. For example, the pump 20 may be installed at a position separated from the hydraulic cylinder 10, and the pump 20 may be connected to the hydraulic cylinder 10 through pipes

Next, operations of the cylinder driving device 100 and the rotating device 1000 will be described with reference to FIGS. 1 to 9.

When the output shaft 31 of the electric motor 30 is rotated in the forward direction R1, the pump 20 discharges the working oil from the first port 21a. The working oil from the pump 20 pushes the operation check valve 60a open and is guided to the restriction valve 70a.

The valve body of the restriction valve 70a receives a force from the working oil in the direction in which the valve body is separated from the valve seat, and thereby, a state in which the valve body is separated from the valve seat is maintained. In the restriction valve 70a, the passage portion 82a of the main passage 80a is communicated with the passage portion 83a through the restriction hole 74f and the restriction hole 74g. The working oil in the passage portion 82a of the main passage 80a is supplied to the counter rod side chamber 11a of the hydraulic cylinder 10 through the restriction hole 74f and the restriction hole 74g of the restriction valve 70a.

At this time, the opening area of the restriction valve 70a corresponds to a total sum of the opening area of the restriction hole 74f and the opening area of the restriction hole 74g, and the resistance imparted to the flow of the working oil in the main passage 80a by the restriction valve 70a is small.

In addition, the pressure in the passage portion 81a of the main passage 80a is increased, and the operation check valve 60b is opened. The working oil in the rod side chamber 11b of the hydraulic cylinder 10 is discharged to the main passage 80b, and thereby, the hydraulic cylinder 10 is extended. The working oil that has been discharged to the main passage 80b is guided to the second port 21b of the pump 20.

In a state in which the external force due to the load is exerted to the piston rod 13 in the contracting direction (a state shown in FIGS. 1 and 2), the piston 12 is not moved in the extending direction by the external force. The flow rate of the working oil discharged from the rod side chamber 11b to the main passage 80b is low, and so, the valve body 74 of the restriction valve 70b is kept in a state in which it is separated from the valve seat 72f (see FIGS. 6 and 7). The working oil in the passage portion 83b of the main passage 80b is guided to the passage portion 82b of the main passage 80b through the restriction hole 74f and the restriction hole 74g of the restriction valve 70b.

In the restriction valve 70b, because the passage portion 83b of the main passage 80b is communicated with the passage portion 82b through the restriction hole 74f and the restriction hole 74g, the opening area of the restriction valve 70b is large, and so, a resistance imparted to the flow of the working oil by the restriction valve 70b in the main passage 80b is small.

Because the resistance imparted to the flow of the working oil in the main passage 80a and the main passage 80b is small, it is possible to reduce the load on the electric motor 30. Therefore, it is possible to reduce the electric power consumption of the electric motor 30.

Because the external force due to the load is not exerted in the direction in which the hydraulic cylinder 10 is extended, even when the opening area of the restriction valve 70b is large, the hunting phenomenon does not occur.

As the hydraulic cylinder 10 is extended, the external force due to the load starts to be exerted to the piston rod 13 in the extending direction (see FIG. 3). The piston 12 is moved in the extending direction also by this external force. The flow rate of the working oil discharged from the rod side chamber 11b to the main passage 80b is increased, and the valve body 74 of the restriction valve 70b is made to seat on the valve seat 72f against the biasing force exerted by the spring 75 (see FIGS. 8 and 9).

In the restriction valve 70b, the passage portion 83b of the main passage 80b is communicated with the passage portion 82b only through the restriction hole 74f. The opening area of the restriction valve 70b corresponds to the opening area of the restriction hole 74f, and the flow of the working oil in the main passage 80b is restricted by the restriction valve 70b.

The increase in the flow rate of the working oil in the main passage 80b is restricted, and it is possible to prevent the hydraulic cylinder 10 from functioning as a pump to suck the working oil in the main passage 80a. The pressure in the main passage 80a can be increased by the pump 20, and it is possible to keep the operation check valve 60b in the opened state. Therefore, it is possible to prevent the occurrence of the hunting phenomenon.

At this time, because the external force due to the load is exerted in direction in which the hydraulic cylinder 10 is extended, the load of the pump 20 is made small. Therefore, it is possible to reduce the load on the electric motor 30 and to reduce the electric power consumption of the electric motor 30.

As described above, with the cylinder driving device 100, it is possible to reduce the electric power consumption of the electric motor 30 and to prevent the occurrence of the hunting phenomenon.

The contracting operation of the hydraulic cylinder 10 is substantially the same as the extending operation, and so, a description thereof shall be omitted.

FIG. 10 is a circuit diagram of a cylinder driving device 200 according to a modification. The cylinder driving device 200 differs from the cylinder driving device 100 mainly in that the operation check valve 60a and the restriction valve 70a are not provided (see FIG. 4). Also with the cylinder driving device 200, it is possible to prevent the occurrence of the hunting phenomenon during the extending operation.

Although an illustration is omitted, the cylinder driving device is provided with the operation check valve 60a and the restriction valve 70a (see FIG. 4), but may not be provided with the operation check valve 60b and the restriction valve 70b. In this case, it is possible to prevent the occurrence of the hunting phenomenon during the contracted operation.

In the following, configurations, actions, and effects of the embodiment of the present invention will be described collectively.

In this embodiment, the cylinder driving device (100, 200) includes: the electric motor 30; the pump 20 configured to be driven by the electric motor 30 and discharge the working oil; the main passage 80a and the main passage 80b respectively connected to the pump 20, the main passage 80a and the main passage 80b being configured to selectively guide the working oil from the pump 20; the hydraulic cylinder 10 connected to the main passage 80a and the main passage 80b, the hydraulic cylinder 10 being configured to be operated by the working oil supplied from the one of the main passage 80a and the main passage 80b, the hydraulic cylinder 10 being configured to discharge the working oil to the other of the main passage 80a and the main passage 80b when operated; the operation check valve 60b and the operation check valve 60a respectively provided in the main passage 80b and the main passage 80a, the operation check valve 60b and the operation check valve 60a being configured to allow the flow of the working oil directed from the hydraulic cylinder 10 to the pump 20 in response to the increase in the pressure in the main passage 80a and the main passage 80b while allowing the flow of the working oil directed from the pump 20 to the hydraulic cylinder 10; and the restriction valve 70b and the restriction valve 70a respectively provided between the hydraulic cylinder 10 and the operation check valves 60b and 60a in the main passage 80b and the main passage 80a, the restriction valve 70b and the restriction valve 70a being configured to restrict the flow of the working oil directed from the hydraulic cylinder 10 to the operation check valve 60b and the operation check valve 60a, wherein the opening areas of the restriction valve 70b and the restriction valve 70a are reduced in response to the increase in the flow rate of the working oil discharged from the hydraulic cylinder 10 to the main passage 80b and the main passage 80a.

With this configuration, the opening areas of the restriction valve 70b and the restriction valve 70a are reduced in response to the increase in the flow rate of the working oil discharged from the hydraulic cylinder 10 to the main passage 80b and the main passage 80a. When the external force due to the load is exerted to the hydraulic cylinder 10 such that the hunting phenomenon is not caused, the flow rate of the working oil discharged from the hydraulic cylinder 10 to the main passage 80b and the main passage 80a is low. Thus, the opening areas of the restriction valve 70b and the restriction valve 70a are large, and so, it is possible to reduce the load on the electric motor 30. When the external force due to the load is exerted to the hydraulic cylinder 10 such that the hunting phenomenon is caused, the flow rate of the working oil discharged from the hydraulic cylinder 10 to the main passage 80b and the main passage 80a is increased, while the opening areas of the restriction valve 70b and the restriction valve 70a are reduced. The increase in the flow rate of the working oil in the main passage 80b and the main passage 80a is restricted, and so, it is possible to prevent the hydraulic cylinder 10 from functioning as the pump 20. Therefore, it is possible to reduce the electrical power of the electric motor 30 and to prevent the occurrence of the hunting phenomenon.

In addition, in this embodiment, the restriction valve 70b and the restriction valve 70a are set such that the opening areas are reduced when the flow rate of the working oil sucked from the main passage 80a and the main passage 80b by the hydraulic cylinder 10 reaches the maximum discharge flow rate of the pump 20.

With this configuration, the opening areas of the restriction valve 70b and the restriction valve 70a are reduced when the flow rate of the working oil sucked from the main passage 80a and the main passage 80b by the hydraulic cylinder 10 reaches the maximum discharge flow rate of the pump 20. Until the flow rate of the working oil sucked from the main passage 80a and the main passage 80b by the hydraulic cylinder 10 reaches the maximum discharge flow rate of the pump 20, the opening areas of the restriction valve 70b and the restriction valve 70a are large. Therefore, the load on the electric motor 30 is small, and so, it is possible to reduce the electric power consumption of the electric motor 30. In addition, when the flow rate of the working oil sucked from the main passage 80a and the main passage 80b by the hydraulic cylinder 10 reaches the maximum discharge flow rate of the pump 20, the opening areas of the restriction valve 70b and the restriction valve 70a are reduced, and the increase in the flow rate is restricted. Therefore, it is possible to prevent the hydraulic cylinder 10 from functioning as the pump 20 and to prevent the occurrence of the hunting phenomenon.

In addition, in this embodiment, the cylinder driving device (100, 200) is characterized in that the restriction valve 70b and the restriction valve 70a have: the first port 71a connected to the hydraulic cylinder 10; the second port 72a connected to the operation check valve 60b and the operation check valve 60a; the flow passage 73 through which the first port 71a is communicated with the second port 72a; the valve seat 72f provided in the flow passage 73; the valve body 74 provided in the flow passage 73, the valve body 74 being configured to be separated from and seated on the valve seat 72f; the spring 75 configured to bias the valve body 74 in the direction in which the valve body 74 is separated from the valve seat 72f; the restriction hole 74f formed in the valve body 74, the restriction hole 74f being configured to allow communication between the first port 71a and the second port 72a; the restriction hole 74g formed in the valve body 74, the restriction hole 74g being configured to allow the communication between the first port 71a and the second port 72a in a state in which the valve body 74 is separated from the valve seat 72f, the restriction hole 74g being configured to shut off the communication between the first port 71a and the second port 72a in a state in which the valve body 74 is seated on the valve seat 72f.

With this configuration, the restriction valve 70b and the restriction valve 70a each has the restriction hole 74f and the restriction hole 74g. While the restriction hole 74f always allows the communication between the first port 71a and the second port 72a, the restriction hole 74g allows the communication between the first port 71a and the second port 72a in a state in which the valve body 74 is separated from the valve seat 72f, and the restriction hole 74g shuts off the communication between the first port 71a and the second port 72a in a state in which the valve body 74 is seated on the valve seat 72f. Because each of the opening areas of the restriction valve 70b and the restriction valve 70a corresponds to a total sum of the opening area of the restriction hole 74f and the opening area of the restriction hole 74g, the opening areas of the restriction valve 70b and the restriction valve 70a are changed in accordance with a state of the valve body 74. Because the spring 75 biases the valve body 74 in the direction in which the valve body 74 is separated from the valve seat 72f, the valve body 74 is separated from and seated on the valve seat 72f in accordance with the flow rate of the working oil directed from the first port 71a to the second port 72a. Therefore, it is possible to reduce the opening areas of the restriction valve 70b and the restriction valve 70a in response to the increase in the flow rate of the working oil discharged from the hydraulic cylinder 10 to the main passage 80b and the main passage 80a.

In this embodiment, the opening area of the restriction hole 74g is larger than the opening area of the restriction hole 74f.

With this configuration, the opening area of the restriction hole 74g is larger than the opening area of the restriction hole 74f. The respective differences between: the opening area of the restriction valve 70b or the restriction valve 70a in a case in which both of the restriction hole 74g and the restriction hole 74f allow the communication between the first port 71a and the second port 72a; and the opening area of the restriction valve 70b or the restriction valve 70a in a case in which only the restriction hole 74f allows the communication between the first port 71a and the second port 72a are large. Therefore, it is possible to reduce the opening areas of the restriction valve 70b and the restriction valve 70a in response to the increase in the flow rate of the working oil discharged from the hydraulic cylinder 10 to the main passage 80b and the main passage 80a to a greater extent.

Embodiments of the present invention were described above, but the above embodiments are merely examples of applications of the present invention, and the technical scope of the present invention is not limited to the specific constitutions of the above embodiments.

(1) In the cylinder driving device (100, 200) according to the above-mentioned embodiment, although the working oil is used as working fluid, non-compressive fluid such as water, aqueous liquid, and so forth may be used instead of the working oil.

(2) In the rotating device 1000, the target object W is attached to the end portion 2a of the arm member 2. The arm member 2 may be a rotating target object. In addition, instead of the arm member 2, a plate member such as a flat panel may be rotated.

(3) In the cylinder driving device (100, 200) according to the above-mentioned embodiment, as the operation check valve 60b, it may be possible to use a switching valve that switches on and off of the flow of the working oil in the main passage 80b by a pilot pressure. In this case, the switching valve allows the flow of the working oil in the main passage 80b in response to the increase in the pressure in the passage portion 81b of the main passage 80b or the main passage 80a and shuts off the flow of the working oil in the main passage 80b in response to the drop in the pressures in both thereof. In the cylinder driving device 100, similarly to the operation check valve 60b, it may be possible to use, as the operation check valve 60a, a switching valve that switches on and off of the flow of the working oil in the main passage 80a by the pilot pressure.

This application claims priority based on Japanese Patent Application No. 2016-130544 filed with the Japan Patent Office on Jun. 30, 2016, the entire contents of which are incorporated into this specification by reference.

Number	Name	Date	Kind
20060242957	Sakai et al.	Nov 2006	A1
20160091004	Gomm	Mar 2016	A1

Number	Date	Country
S53-152225	Nov 1978	JP
2006-250311	Sep 2006	JP
2008-309212	Dec 2008	JP

Cylinder driving device

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