CN115943261A

CN115943261A - Multi-stage fluid pressure cylinder

Info

Publication number: CN115943261A
Application number: CN202180052327.1A
Authority: CN
Inventors: 船户泰志; 谷川夏树
Original assignee: KYB Corp
Current assignee: KYB Corp
Priority date: 2020-08-24
Filing date: 2021-08-12
Publication date: 2023-04-07
Also published as: GB202303134D0; JP2022036748A; JP7177805B2; GB2613494A; WO2022044833A1; GB2613494B

Abstract

A multi-stage fluid pressure cylinder (100) is provided with: a cylinder (10); a first rod assembly (30) provided with an outer piston portion (32); a third rod assembly (50) disposed inside the first rod assembly (30); a first supply/discharge passage (55 a) for supplying/discharging working oil to/from the rod opposite side chamber (5); and a second supply/discharge passage (51 a) for supplying/discharging the working oil to/from the rod-side chamber (2), wherein the second supply/discharge passage (51 a) is provided in the third rod assembly (50), and the third rod assembly (50) is provided with a backflow prevention mechanism (71) that allows only the flow of the working oil from the second supply/discharge passage (51 a) to the rod-opposite-side chamber (5).

Description

Multi-stage fluid pressure cylinder

Technical Field

The present invention relates to a multistage fluid pressure cylinder.

Background

Japanese patent laying-open No. JP2017-172681A discloses a multistage fluid pressure cylinder including: a cylinder barrel; a cylindrical outer rod member having an outer piston portion at an end thereof, the outer piston portion sliding along an inner peripheral surface of the cylinder; and an inner rod member disposed inside the outer rod member and having a flow path for supplying and discharging the working fluid to and from the rod-side chamber and a flow path for supplying and discharging the working fluid to and from the rod-opposite chamber.

Disclosure of Invention

In the case where an external force such as forcibly extending the multi-stage fluid pressure cylinder exceeding the extension speed is suddenly applied during the extension operation of the multi-stage fluid pressure cylinder described in japanese patent application laid-open No. JP2017-172681A, the supply of the working fluid to the rod side chamber is not followed, and the pressure in the rod side chamber is reduced or becomes negative, while the discharge of the working fluid from the rod side chamber is not followed, and the pressure in the rod side chamber is increased. When the external force acting on the multi-stage fluid pressure cylinder is released in a state where the pressure of the rod side chamber is increased while the pressure of the opposite-rod side chamber is decreased, the multi-stage fluid pressure cylinder contracts slightly instantaneously, repeats expansion and contraction to some extent by a reaction thereof, and then returns to the expansion operation again. When the multistage fluid pressure cylinder is repeatedly expanded and contracted in such a relatively short period of time, there is a possibility that the apparatus in which the multistage fluid pressure cylinder is installed may vibrate.

The purpose of the present invention is to suppress transient operation of a multistage fluid pressure cylinder caused by external force.

According to one aspect of the present invention, a multistage fluid pressure cylinder includes: a cylinder barrel; a cylindrical outer rod member having an outer piston portion provided at an end thereof, the outer piston portion sliding along an inner peripheral surface of the cylinder tube and dividing the inside of the cylinder tube into a rod side chamber and a rod opposite side chamber; an inner rod member provided inside the outer rod member so as to be movable in an axial direction of the cylinder tube; a first supply/discharge passage that supplies and discharges a working fluid to and from the rod opposite side chamber; and a second supply/discharge passage that supplies/discharges the working fluid to/from the rod-side chamber, wherein the second supply/discharge passage is provided in the inner rod member, and the inner rod member is provided with a backflow prevention mechanism that allows only a flow of the working fluid from the second supply/discharge passage to the rod-opposite-side chamber.

Drawings

Fig. 1 is a sectional view of a multistage fluid pressure cylinder according to a first embodiment of the present invention, which is a view showing a most contracted state.

Fig. 2 is a sectional view showing the multistage fluid pressure cylinder according to the first embodiment of the present invention, in which the first rod assembly is in an extended position, and the second rod assembly and the third rod assembly are in a contracted position.

Fig. 3 is a sectional view of the multistage fluid pressure cylinder according to the first embodiment of the present invention, showing a state in which the first rod assembly and the second rod assembly are in the extended position and the third rod assembly is in the retracted position.

Fig. 4 is a sectional view showing a multistage fluid pressure cylinder according to a first embodiment of the present invention, which is a view showing the most extended state.

Fig. 5 is an enlarged view showing an enlarged portion a of fig. 1.

Fig. 6 is a view showing a multistage fluid pressure cylinder according to a second embodiment of the present invention, which is a view showing a portion corresponding to fig. 5.

Fig. 7A is a plan view of a check seal of a multistage fluid pressure cylinder according to a second embodiment of the present invention.

Fig. 7B is a sectional view showing a section along the line B-B of fig. 7A.

Fig. 8 is a view showing a multistage fluid pressure cylinder according to a third embodiment of the present invention, which is a view showing a portion corresponding to fig. 5.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

< first embodiment >

A multistage fluid pressure cylinder 100 according to a first embodiment of the present invention will be described with reference to fig. 1 to 5. Hereinafter, a case where the multi-stage fluid pressure cylinder 100 is a multi-stage fluid pressure cylinder 100 (hereinafter, simply referred to as "fluid pressure cylinder 100") that drives the hydraulic fluid as the working fluid will be described.

As shown in fig. 1, the hydraulic cylinder 100 includes: a bottomed cylindrical cylinder tube 10; a first rod assembly 30 as an outer rod member inserted into the cylinder 10 so as to be slidable; a third rod assembly 50 as an inner rod member provided inside the first rod assembly 30 so as to be movable in a central axis direction (hereinafter simply referred to as an "axial direction") of the cylinder 10; a second rod assembly 40, which is an intermediate rod member, is disposed between the first rod assembly 30 and the third rod assembly 50 in a manner freely movable in the axial direction. Fig. 1 is a cross-sectional view showing a most contracted state of the hydraulic cylinder 100.

The hydraulic cylinder 100 is attached to the drive target apparatus such that the cylinder tube 10 is positioned on the upper side in the vertical direction and the third rod assembly 50 is positioned on the lower side in the vertical direction, by a first attachment portion 61 provided at the bottom of the cylinder tube 10 and a second attachment portion 62 provided at an end portion of the third rod assembly 50 protruding from the cylinder tube 10. That is, the hydraulic cylinder 100 is attached to the driving target equipment such that the first attachment portion 61 is displaced in a substantially vertical direction, that is, in the vertical direction, with respect to the second attachment portion 62. The direction in which the hydraulic cylinder 100 is attached is not limited to this, and may be attached such that the cylinder tube 10 is positioned on the vertically lower side and the third cylinder assembly 50 is positioned on the vertically upper side. The hydraulic cylinder 100 may be attached to the driving target equipment such that the first attachment portion 61 is displaced in the horizontal direction with respect to the second attachment portion 62.

The first rod assembly 30 has: a cylindrical outer rod portion 31; an annular outer piston portion 32 provided at one end of the outer rod portion 31 and sliding along the inner circumferential surface 10a of the cylinder 10 to divide the inside of the cylinder 10 into a rod side chamber 2 and a rod opposite side chamber 5; and a cylindrical first support portion 33 formed to protrude radially inward from the other end portion of the outer rod portion 31, and supporting the second rod assembly 40 to be slidable.

An annular recess 30b to which the first snap ring 35 is attached is formed in an inner peripheral surface 30a of the first rod assembly 30 on the outer piston portion 32 side. The first snap ring 35 is a metal wire formed in a substantially annular shape, and has a mouthpiece portion, not shown, which is partially divided. The first snap ring 35 is inserted into the first rod assembly 30 in a state of being reduced in diameter, and is fitted into the annular recess 30b by being pressed on the outer diameter side by the inner peripheral surface 30a by an elastic force acting in the diameter expansion direction. In this way, in a state where the first snap ring 35 is assembled to the first rod assembly 30, the inner diameter side of the first snap ring 35 is in a state of protruding radially inward from the inner peripheral surface 30a of the first rod assembly 30. In addition, the installation of the first snap ring 35 is performed after the second rod assembly 40 is inserted into the first rod assembly 30.

The second rod assembly 40 has the same shape as the first rod assembly 30, and has: a first cylindrical inner rod 41 inserted into the outer rod 31; an annular first inner piston portion 42 that is provided at one end of the first inner rod portion 41 so as to face the rod-opposite-side chamber 5, and that slides along the inner peripheral surface 30a of the first rod assembly 30; and a cylindrical second support portion 43 formed so as to protrude radially inward from the other end portion of the first inner rod portion 41, and supporting the third rod assembly 50 so as to be slidable.

A second annular recess 40b to which a second snap ring 45 is attached is formed in an inner peripheral surface 40a of the second rod assembly 40 on the first inner piston portion 42 side. The second snap ring 45 is a metal wire formed in a substantially annular shape, similarly to the first snap ring 35, and has a mouthpiece portion, not shown, which is partially divided. The second snap ring 45 is inserted into the second rod assembly 40 in a reduced diameter state, and is fitted into the second annular recess 40b by being pressed on the outer diameter side by the inner peripheral surface 40a by an elastic force acting in the diameter expansion direction. In this way, in a state where the second snap ring 45 is assembled to the second rod assembly 40, the inner diameter side of the second snap ring 45 is in a state of protruding radially inward from the inner peripheral surface 40a of the second rod assembly 40. Additionally, installation of second snap ring 45 is performed after third rod assembly 50 is inserted into second rod assembly 40.

The third lever assembly 50 has: a second inner lever portion 51 as an inner lever portion inserted into the first inner lever portion 41; an annular second inner piston portion 52 as an inner piston portion is provided at an end of the second inner rod portion 51 so as to face the rod-opposite-side chamber 5, and slides along the inner peripheral surface 40a of the second rod assembly 40. The second inner piston portion 52 is coupled to one end portion of the second inner rod portion 51 by a plurality of bolts 53.

Thus, three rod members, i.e., the first rod assembly 30, the second rod assembly 40, and the third rod assembly 50, are inserted into the cylinder 10.

A cylinder head 11 that slidably supports the outer rod portion 31 of the first rod assembly 30 is provided at an opening portion of the cylinder tube 10, and a recess 10b that is recessed toward the first mounting portion 61 is formed at a bottom portion of the cylinder tube 10 that axially faces the

respective piston portions

32, 42, and 52. The inner diameter of the recess 10b is set to be larger than the inner diameter of the outer piston portion 32 of the first rod assembly 30.

The most contracted position of the first rod assembly 30 inserted into the cylinder tube 10 is defined by the outer piston portion 32 abutting against the bottom of the cylinder tube 10, and the most expanded position is defined by the outer piston portion 32 abutting against the cylinder head 11. Further, a seal member, not shown, that closes a gap between the inner peripheral surface of the cylinder head 11 and the outer peripheral surface of the outer rod portion 31 is provided on the inner peripheral surface of the cylinder head 11 to prevent leakage of the hydraulic oil to the outside.

The most contracted position of the second rod assembly 40 inserted into the first rod assembly 30 is defined by the first inner piston portion 42 abutting against the first snap ring 35 attached to the first rod assembly 30, and the most extended position is defined by the first inner piston portion 42 abutting against the first support portion 33. In addition, the first snap ring 35 restricts the movement of the second rod assembly 40 in the retraction direction, and prevents the first rod assembly 30 from being detached from the cylinder tube 10 when the hydraulic cylinder 10 is retracted.

Further, a seal member, not shown, that closes a gap between the inner peripheral surface of the first support portion 33 and the outer peripheral surface of the first inner rod portion 41 is provided on the inner peripheral surface of the first support portion 33 in order to prevent leakage of the working oil to the outside.

The most contracted position of the third rod assembly 50 inserted into the second rod assembly 40 is defined by the second inner piston portion 52 abutting against the second snap ring 45 attached to the second rod assembly 40, and the most extended position is defined by the second inner piston portion 52 abutting against the second support portion 43. In addition, the second snap ring 45 restricts the movement of the third rod assembly 50 in the retraction direction, and prevents the second rod assembly 40 from being detached from the cylinder tube 10 when the hydraulic cylinder 100 is retracted.

Further, a seal member, not shown, that closes a gap between the inner peripheral surface of the second support portion 43 and the outer peripheral surface of the second inner rod portion 51 is provided on the inner peripheral surface of the second support portion 43 to prevent leakage of the working oil to the outside. Further, an annular recess 43a, which is faced by an opening of a communication hole 51b, which will be described later, formed in the second inner rod portion 51 when the third rod assembly 50 is maximally extended, is formed in the inner peripheral surface of the second support portion 43. The annular recess 43a is formed to open into a second inside rod side chamber 4 described later.

Further, in the cylinder tube 10 into which the first rod assembly 30, the second rod assembly 40, and the third rod assembly 50 having the above-described shapes are inserted, a rod side chamber 2 defined by the cylinder tube 10, the cylinder head 11, the outer rod portion 31, and the outer piston portion 32, a first inner side chamber 3 defined by the outer rod portion 31, the first support portion 33, the first inner rod portion 41, and the first inner piston portion 42, a second inner side chamber 4 defined by the first inner rod portion 41, the second support portion 43, the second inner rod portion 51, and the second inner piston portion 52, and a rod opposite side chamber 5 defined by the cylinder tube 10, the outer piston portion 32, the first inner piston portion 42, and the second inner piston portion 52 are formed.

A first seal member 34 is provided on an outer peripheral surface 32a of the outer piston portion 32 of the first rod assembly 30, and communication between the rod side chamber 2 and the rod opposite side chamber 5 via a gap between the outer peripheral surface 32a of the outer piston portion 32 and the inner peripheral surface 10a of the cylinder 10 is blocked by the first seal member 34.

Further, a plurality of supply/discharge ports 32b for supplying/discharging the working oil to/from the rod side chamber 2 are formed in the outer piston portion 32 of the first rod assembly 30 so as to penetrate in the radial direction.

A second seal member 44 is provided on an outer peripheral surface 42a of the first inner piston portion 42 of the second rod assembly 40, and communication between the first inner rod side chamber 3 and the rod opposite side chamber 5 via a gap between the outer peripheral surface 42a of the first inner piston portion 42 and the inner peripheral surface 30a of the first rod assembly 30 is blocked by the second seal member 44.

Further, a plurality of inner supply/discharge ports 42b for supplying/discharging the working oil to/from the first inner side rod side chamber 3 are formed in the first inner piston portion 42 of the second rod assembly 40 so as to penetrate in the radial direction.

A third seal member 54 is provided on an outer peripheral surface 52a of the second inner piston portion 52 of the third rod assembly 50, and communication between the second inner rod side chamber 4 and the rod opposite side chamber 5 via a gap between the outer peripheral surface 52a of the second inner piston portion 52 and the inner peripheral surface 40a of the second rod assembly 40 is blocked by the third seal member 54.

The second inner rod portion 51 of the third rod assembly 50 is formed with a second supply/discharge passage 51a for supplying/discharging hydraulic oil to/from the hydraulic cylinder 100 and connecting to an external device not shown, and a communication hole 51b for communicating the second supply/discharge passage 51a with the second inner rod side chamber 4. In addition, the second inner lever portion 51 is formed with a connection passage 51c that connects the passage 64 formed in the second mounting portion 62 and the second supply/discharge passage 51 a.

The second supply/discharge passage 51a communicates with the second inside rod side chamber 4 via the communication hole 51b, communicates with the first inside rod side chamber 3 via the inside supply/discharge port 42b and the communication hole 51b, and communicates with the rod side chamber 2 via the supply/discharge port 32b, the inside supply/discharge port 42b, and the communication hole 51b.

That is, the supply of the working oil to the rod side chamber 2, the first inside chamber 3, and the second inside chamber 4, and the discharge of the working oil from the rod side chamber 2, the first inside chamber 3, and the second inside chamber 4 are performed via the second supply/discharge passage 51a formed in the second inside rod 51.

Further, a pipe-shaped supply/discharge pipe 55 is provided in the second inner lever portion 51, and a first supply/discharge passage 55a for supplying/discharging hydraulic oil to/from the hydraulic cylinder 100 and connecting to an external device is formed in the supply/discharge pipe 55. The supply and discharge pipe 55 is assembled to the second inner rod 51 so that one end thereof opens into the rod-opposite-side chamber 5, and specifically, is joined to the second inner rod 51 so as to axially penetrate the second supply and discharge passage 51 a. The second inner lever portion 51 is formed with a connection passage 51d that connects the passage 63 formed in the second attachment portion 62 and the other end of the supply/discharge pipe 55.

Since the supply/discharge pipe 55 is provided so that one end thereof opens into the rod side opposite chamber 5, the supply of the hydraulic oil to the rod side opposite chamber 5 and the discharge of the hydraulic oil from the rod side opposite chamber 5 are performed through the first supply/discharge passage 55a in the supply/discharge pipe 55.

Next, the operation of the hydraulic cylinder 100 will be described with reference to fig. 1 to 4. Hereinafter, a case will be described in which the hydraulic cylinder 100 is attached to the driving target equipment such that the first attachment portion 61 is located on the upper side in the vertical direction and the second attachment portion 62 is located on the lower side in the vertical direction.

When the hydraulic cylinder 100 is extended, hydraulic oil is supplied to the rod-side opposite chamber 5 from a hydraulic source such as a pump not shown via the first supply/discharge passage 55a in the supply/discharge pipe 55, and the hydraulic oil in the rod-side chamber 2, the first inside rod-side chamber 3, and the second inside rod-side chamber 4 is discharged to a tank not shown via the second supply/discharge passage 51 a.

When the hydraulic cylinder 100 performs an extension operation from the most contracted state shown in fig. 1, hydraulic oil is supplied to the rod opposite side chamber 5 via the first supply/discharge passage 55a. Here, the pressure receiving area of the chamber 5 on the opposite side of the rod, which receives the pressure, is largest when the first rod assembly 30 is elongated, and smallest when the third rod assembly 50 is elongated. Thus, when the hydraulic cylinder 100 performs an extension operation from the most contracted state, first, the cylinder tube 10 moves relative to the first rod assembly 30. Specifically, as shown in fig. 2, the cylinder 10 moves upward (upward in fig. 2) with respect to the first rod assembly 30. Further, since the recess 10b formed in the bottom of the cylinder tube 10 has an inner diameter larger than that of the outer piston portion 32 of the first rod assembly 30, the pressure of the working oil guided to the rod opposing side chamber 5 acts on the outer piston portion 32 via the recess 10b.

When the cylinder 10 moves relative to the first rod assembly 30, the hydraulic oil in the rod side chamber 2 is guided to the second supply/discharge passage 51a via the supply/discharge port 32b, the inner supply/discharge port 42b, and the communication hole 51b, and is discharged to the outside.

As shown in fig. 2, when the cylinder 10 is in the most extended state with respect to the first rod assembly 30, that is, the cylinder 10 is moved upward until the cylinder head 11 comes into contact with the outer piston portion 32 of the first rod assembly 30, the cylinder 10 and the first rod assembly 30 are moved relative to the second rod assembly 40 by the pressure of the rod opposing side chamber 5. Specifically, as shown in fig. 3, the cylinder 10 and the first rod assembly 30 move upward (upward in fig. 3) with respect to the second rod assembly 40.

When the first rod assembly 30 moves relative to the second rod assembly 40, the hydraulic oil in the first inside rod side chamber 3 is guided to the second supply/discharge passage 51a via the inside supply/discharge port 42b and the communication hole 51b, and is discharged to the outside.

Further, as shown in fig. 3, when the first rod assembly 30 is in a state of being most extended with respect to the second rod assembly 40, that is, the cylinder 10 and the first rod assembly 30 are moved upward until the first support portion 33 of the first rod assembly 30 comes into contact with the first inner piston portion 42 of the second rod assembly 40, the cylinder 10, the first rod assembly 30, and the second rod assembly 40 are relatively moved with respect to the third rod assembly 50 by the pressure of the rod opposing side chamber 5. Specifically, as shown in fig. 4, the cylinder 10, the first rod assembly 30, and the second rod assembly 40 move upward (upward in fig. 4) with respect to the third rod assembly 50.

When the second rod assembly 40 moves relative to the third rod assembly 50, the hydraulic oil in the second inside rod-side chamber 4 is guided to the second supply/discharge passage 51a via the communication hole 51b and discharged to the outside.

As shown in fig. 4, when the second rod assembly 40 is in the most extended state with respect to the third rod assembly 50, that is, when the cylinder tube 10, the first rod assembly 30, and the second rod assembly 40 are moved upward until the second support portion 43 of the second rod assembly 40 comes into contact with the second inner piston portion 52 of the third rod assembly 50, the hydraulic cylinder 100 is in the most extended state.

On the other hand, when the hydraulic cylinder 100 performs the contraction operation, the hydraulic oil is supplied from the hydraulic pressure source to the rod side chamber 2, the first inside rod side chamber 3, and the second inside rod side chamber 4 via the second supply/discharge passage 51a, and the hydraulic oil in the rod opposite side chamber 5 is discharged to the tank via the first supply/discharge passage 55a. The retraction operation of the hydraulic cylinder 100 may be performed by the weight of the driving target equipment connected to the first attachment portion 61. In this case, the working oil does not need to be supplied to the rod side chamber 2, the first inside side chamber 3, and the second inside side chamber 4, and the working oil is sucked from the tank into the rod side chamber 2, the first inside side chamber 3, and the second inside side chamber 4.

When the hydraulic cylinder 100 performs a retracting operation from the most extended state, first, the cylinder 10, the first rod assembly 30, and the second rod assembly 40 move relative to the third rod assembly 50 from the state shown in fig. 4 to the state shown in fig. 3, and then, the cylinder 10 and the first rod assembly 30 move relative to the second rod assembly 40 from the state shown in fig. 3 to the state shown in fig. 2. Further, the cylinder tube 10 is moved relative to the first rod assembly 30 from the state shown in fig. 2 to the state shown in fig. 1, whereby the hydraulic cylinder 100 is brought into the most contracted state.

Here, when an external force such as forcibly extending the hydraulic cylinder 100 of the above-described configuration is suddenly applied while the hydraulic cylinder 100 of the above-described configuration is performing the generating operation, the supply of the hydraulic oil to the rod side chamber 5 whose volume is increased does not follow up, and the pressure in the rod side chamber 5 is reduced or becomes a negative pressure, while the discharge of the hydraulic oil from the

rod side chambers

2, 3, 4 whose volumes are reduced does not follow up, and the pressures in the

rod side chambers

2, 3, 4 are increased.

When the external force acting on the hydraulic cylinder 100 is removed in a state where the pressure of the opposite-rod side chamber 5 is decreased and the pressure of the

rod side chambers

2, 3, and 4 is increased, the hydraulic cylinder 100 contracts slightly instantaneously, repeats expansion and contraction to some extent by reaction thereof, and then returns to the expansion operation again. When the hydraulic cylinder 100 repeatedly expands and contracts in such a relatively short time, a device provided in the hydraulic cylinder 100, for example, a vehicle on which the hydraulic cylinder 100 is mounted may vibrate.

When the pressure in the

rod side chambers

2, 3, and 4 rises sharply, the seal members that seal the

rod side chambers

2, 3, and 4 are disengaged, or the cylinder tube 10 expands, and the hydraulic cylinder 100 may be damaged.

In contrast, in the hydraulic cylinder 100 of the present embodiment, as shown in fig. 5, the backflow prevention mechanism 71 that blocks the flow of the hydraulic oil from the rod side chamber 5 toward the second supply/discharge passage 51a and allows only the flow of the hydraulic oil from the second supply/discharge passage 51a toward the rod side chamber 5 is provided in the third rod assembly 50. Fig. 5 is an enlarged view of a portion enclosed by a broken line indicated by an arrow a in fig. 1 showing the hydraulic cylinder 100 in the most contracted state.

The backflow prevention mechanism 71 shown in fig. 5 is a check valve 72 provided in a through-hole that penetrates the inside of the second inner piston portion 52 in the axial direction, one end of which opens into the second supply/discharge passage 51a, and the other end of which opens into the rod-opposite side chamber 5.

The check valve 72 includes a valve body 72a and a spring 72b that biases the valve body 72a, and is operated so as to block the flow of the working oil from the rod opposite side chamber 5 toward the second supply/discharge passage 51a and to allow the flow of the working oil from the second supply/discharge passage 51a toward the rod opposite side chamber 5 when the pressure of the second supply/discharge passage 51a is greater than the pressure of the rod opposite side chamber 5.

Here, when the first rod assembly 30 is extended, the second supply/discharge passage 51a provided in the third rod assembly 50 communicates with the second inside rod side chamber 4 via the communication hole 51b, communicates with the first inside rod side chamber 3 via the inside supply/discharge port 42b and the communication hole 51b, and communicates with the rod side chamber 2 via the supply/discharge port 32b, the inside supply/discharge port 42b, and the communication hole 51b. When the second rod assembly 40 extends, it communicates with the second inside rod chamber 4 via the communication hole 51b, and communicates with the first inside rod chamber 3 via the inside supply/discharge port 42b and the communication hole 51b. When the second rod assembly 50 extends, it communicates with the second inside rod chamber 4 via the communication hole 51b.

Therefore, the check valve 72 provided in the third rod assembly 50 can allow the flow of the hydraulic oil from the second supply/discharge passage 51a to the rod-side chamber 5 when the pressure in each of the rod-

side chambers

2, 3, 4 is greater than the pressure in the rod-side chamber 5 while the hydraulic cylinder 100 is in the extended state.

In other words, for example, when a check valve that allows the flow of working oil from the rod side chamber 2 to the rod side opposite chamber 5 is provided in the first rod assembly 30, when the pressure in the first inside rod side chamber 3 and the second inside rod side chamber 4 that communicate via the supply/discharge port 32b is higher than the pressure in the rod side opposite chamber 5 while the first rod assembly 30 is extended, the working oil can be caused to flow into the rod side opposite chamber 5 via the check valve. However, when the second rod assembly 40 is extended, the first inside rod chamber 3, the second inside rod chamber 4, and the rod chamber 2 are not in communication with each other, and therefore, even if the pressure in the first inside rod chamber 3 and the second inside rod chamber 4 is higher than the pressure in the rod opposite chamber 5, the working oil cannot flow into the rod opposite chamber 5 through the check valve provided in the first rod assembly 30.

Similarly, for example, when a check valve that allows the flow of working oil from the first inside chamber 3 to the rod side opposite chamber 5 is provided in the second rod assembly 40, the first inside chamber 3 and the second inside chamber 4 are not in communication when the third rod assembly 50 is extended, and therefore, even if the pressure in the second inside chamber 4 is higher than the pressure in the rod side opposite chamber 5, the working oil cannot flow into the rod side opposite chamber 5 through the check valve provided in the second rod assembly 40.

On the other hand, in the check valve 72 provided in the third rod assembly 50 and having the above-described configuration, when the pressure of any one of the

rod side chamber

2, 3, 4 among the rod side chamber 2, the first inside rod side chamber 3, and the second inside rod side chamber 4 is higher than the pressure of the rod opposite side chamber 5 during extension of the first rod assembly 30, the working oil can be caused to flow into the rod opposite side chamber 5 via the check valve 72, when the pressure of any one of the

rod side chambers

3, 4 among the first inside rod side chamber 3 and the second inside rod side chamber 4 is higher than the pressure of the rod opposite side chamber 5 during extension of the second rod assembly 40, the working oil can be caused to flow into the rod opposite side chamber 5 via the check valve 72, and when the pressure of the second inside rod side chamber 4 is higher than the pressure of the rod opposite side chamber 5 during extension of the third rod assembly 50, the working oil can be caused to flow into the rod opposite side chamber 5 via the check valve 72.

As described above, by providing the check valve 72 that allows only the flow of the hydraulic oil from the second supply/discharge passage 51a to the rod-side opposite chamber 5 in the third rod assembly 50, as described above, an external force that exceeds the extension speed and forcibly extends the hydraulic cylinder 100 acts abruptly during the extension operation of the hydraulic cylinder 100, and when the pressure in any one of the rod-

side chambers

2, 3, 4 is higher than the pressure in the rod-side opposite chamber 5, the hydraulic oil flows rapidly from the second supply/discharge passage 51a into the rod-side opposite chamber 5 via the check valve 72.

Accordingly, the pressure of the

rod side chamber

2, 3, 4 is hardly maintained in a state higher than the pressure of the rod side chamber 5, and the working oil is supplied from the

rod side chamber

2, 3, 4 to the rod side chamber 5, and the pressure of the rod side chamber 5 is suppressed from becoming negative pressure, so that even if the external force acting on the hydraulic cylinder 100 is released, the hydraulic cylinder 100 does not contract instantaneously and returns to the extension operation smoothly again.

Thus, the instantaneous expansion and contraction operation of the hydraulic cylinder 100 due to the external force is suppressed, and the vibration of the device provided in the hydraulic cylinder 100 can be prevented. Further, since the pressure in the

rod side chambers

2, 3, and 4 whose volumes are being reduced is also suppressed from rising rapidly, it is possible to prevent the seal members that seal the

rod side chambers

2, 3, and 4 from coming off, or the cylinder 10 from expanding.

The check valve 72 is provided in the third rod assembly 50 in which the first supply/discharge passage 55a and the second supply/discharge passage 51a are provided, that is, in the rod member disposed on the innermost side among the rod members provided in the cylinder 10. The cross-sectional shape of the pressure receiving surface of the third rod assembly 50 disposed on the innermost side is not circular, but circular. Therefore, as compared with the case where the check valve 72 is provided in the first rod assembly 30 and the second rod assembly 40 having annular pressure receiving surfaces in cross section, a space for disposing the check valve 72 can be easily secured without increasing the outer diameter of the rod member.

As shown in fig. 5, the through hole in which the check valve 72 is provided is composed of a first through hole 51e formed in the second inner rod portion 51 and a second through hole 52b formed in the second inner piston portion 52 as an insertion hole. The second through-hole 52b formed in the second inner piston portion 52 is one of a plurality of second through-holes 52b formed as insertion holes through which bolts 53 are inserted, and the bolt 53 is a fastening member used to assemble the second inner piston portion 52 to the second inner rod portion 51.

By using the through-hole formed as the insertion hole through which the bolt 53 is inserted as the through-hole through which the check valve 72 is provided, the manufacturing cost of the hydraulic cylinder 100 can be reduced and the check valve 72 can be arranged compactly, as compared with a case where a separate through-hole is formed.

In addition, the check valve 72 may be incorporated in the bolt 53 that fastens the second inner piston portion 52 and the second inner rod portion 51, and in this case, sufficient fastening force for fastening the second inner piston portion 52 and the second inner rod portion 51 can be ensured.

In addition, when the contraction operation of the hydraulic cylinder 100 is performed by the weight of the driving target equipment connected to the first mounting portion 61, if an external force is not applied to the hydraulic cylinder 100, the pressure of the opposite-rod side chamber 5 is in a state of being extremely higher than the pressure of each of the

rod side chambers

2, 3, and 4, and therefore, even if the backflow prevention mechanism 71 is a simple check valve 72, the operation of the hydraulic cylinder 100 is not affected. However, when the pressurized hydraulic oil is applied to the

rod side chambers

2, 3, and 4 to contract the hydraulic cylinder 100, the pressure of the rod side chamber 5 is lower than the pressure of the

rod side chambers

2, 3, and 4, and if the backflow prevention mechanism 71 is a simple check valve 72, the hydraulic cylinder 100 may not be contracted.

Therefore, in this case, the backflow prevention mechanism 71 may be a relief valve that opens only when the pressure in each of the

rod side chambers

2, 3, and 4 is greater than or equal to a predetermined value than the pressure in the rod side chamber 5 so that the hydraulic oil does not flow from the second supply/discharge passage 51a to the rod side chamber 5 via the backflow prevention mechanism 71 during the contraction operation. Specifically, the valve opening pressure of the valve body 72a can be changed by appropriately changing the load of the spring 72b that biases the valve body 72 a. Even in the case where the backflow prevention mechanism 71 is a backflow valve as described above, when the pressure of the

rod side chambers

2, 3, 4 is abnormally higher than the pressure of the rod side chamber 5, the working oil flows into the rod side chamber 5 from the second supply/discharge passage 51a quickly via the relief valve, and therefore, the same effect as that in the case where the backflow prevention mechanism 71 is a check valve 72 is exhibited. Therefore, a return valve may be employed as the backflow prevention mechanism 71 in the hydraulic cylinder 100 of the type that performs the contraction operation by the weight of the driving target equipment coupled to the first mounting portion 61.

According to the first embodiment described above, the following effects are obtained.

In the hydraulic cylinder 100 having the above-described configuration, only the check valve 72 serving as the backflow prevention mechanism 71 that allows the flow of the hydraulic oil from the second supply/discharge passage 51a to the rod-opposite-side chamber 5 is provided in the third rod assembly 50 having the first supply/discharge passage 55a and the second supply/discharge passage 51a, that is, in the innermost rod member of the rod members provided in the cylinder tube 10.

By providing the check valve 72 that allows only the flow of the hydraulic oil from the second supply/discharge passage 51a to the rod side opposite chamber 5 in this way, for example, an external force that exceeds the extension speed and forcibly extends the hydraulic cylinder 100 acts abruptly during the extension operation of the hydraulic cylinder 100, and when the pressure in any one of the

rod side chambers

2, 3, 4 is higher than the pressure in the rod side opposite chamber 5, the hydraulic oil flows rapidly from the second supply/discharge passage 51a into the rod side opposite chamber 5 via the check valve 72.

Accordingly, the pressure of the

rod side chambers

2, 3, 4 to the rod side chamber 5, and the pressure of the rod side chamber 5 is suppressed from becoming negative, so that even if the external force acting on the hydraulic cylinder 100 is released, the hydraulic cylinder 100 does not contract instantaneously and returns to the extension operation smoothly again.

By providing the backflow prevention mechanism 71 that allows only the flow of the hydraulic oil from the second supply/discharge passage 51a to the rod-opposite-side chamber 5 in the third rod assembly 50 having the first supply/discharge passage 55a and the second supply/discharge passage 51a in this manner, the instantaneous expansion and contraction operation of the hydraulic cylinder 100 due to the external force can be suppressed. Further, since the rapid rise of the pressure in the

rod side chambers

2, 3, 4 is suppressed, it is possible to prevent the seal members that seal the

rod side chambers

2, 3, 4 from coming off, or the cylinder 10 from expanding.

Further, of the rod members provided in the cylinder tube 10, the pressure receiving surface of the third rod assembly 50 disposed on the innermost side has a circular cross-sectional shape, not an annular shape. Therefore, as compared with the case where the check valve 72 is provided in the first rod assembly 30 and the second rod assembly 40 having annular pressure receiving surfaces in cross section, a space for disposing the check valve 72 can be easily secured without increasing the outer diameter of the rod member.

< second embodiment >

Next, a multi-stage fluid pressure cylinder 200 (hereinafter, referred to as a "hydraulic cylinder 200") according to a second embodiment of the present invention will be described with reference to fig. 6. Hereinafter, the description will be given centering on differences from the first embodiment, and the same components as those of the first embodiment will be given the same reference numerals and will not be described.

The backflow prevention mechanism 71 of the hydraulic cylinder 100 according to the first embodiment is a check valve 72 provided in a through-hole formed so as to axially penetrate the inside of the second inner piston portion 52, and the backflow prevention mechanism 171 of the hydraulic cylinder 200 differs in that a check seal (check seal) 172 is provided between the outer periphery of the supply/discharge pipe 55, which is a tubular member, and the inner periphery of the through-hole 51f, as shown in fig. 6. Fig. 6 is a diagram showing a hydraulic cylinder 200 according to a second embodiment, and is a diagram showing a portion corresponding to fig. 5. The basic configuration and operation of the hydraulic cylinder 200 are the same as those of the hydraulic cylinder 100 according to the first embodiment, and therefore, the description thereof is omitted.

As shown in fig. 6, the through-hole 51f is a hole formed to penetrate the inside of the second inner piston portion 52 in the axial direction, one end of which opens to the second supply/discharge passage 51a and the other end of which opens to the rod-opposite-side chamber 5, and the through-hole 51f is provided at the end of the second inner rod portion 51 coupled to the second inner piston portion 52. One end of the supply and discharge pipe 55 is inserted into the through hole 51f with a predetermined gap therebetween, and a check seal 172 that slides along the outer peripheral surface 55b of the supply and discharge pipe 55 is provided on the outer periphery of the supply and discharge pipe 55 inserted into the through hole 51 f. The through-hole 51f is provided with a receiving groove 51g formed so as to be recessed radially outward for receiving the check seal 172.

The check seal 172 is an annular member formed of a resin material such as rubber or an elastic material such as metal, and as shown in fig. 7A and 7B, includes: an inner peripheral surface 172a contacting the outer peripheral surface 55b of the supply/discharge pipe 55; an outer peripheral surface 172b facing the bottom surface of the storage groove 51 g; a flow surface 172d formed with a plurality of cutout grooves 172c cut out in the radial direction; a sealing surface 172e formed flat; the closing portion 172f is partially divided in the circumferential direction. Fig. 7A is a plan view of the backup seal 172, and fig. 7B is a sectional view showing a section taken along line B-B of fig. 7A.

The above-described shaped check seal 172 is attached to the outer peripheral surface 55b of the supply/discharge pipe 55 so as to widen the gap of the closing portion 172f, and the inner peripheral surface 172a is slightly pressed against the outer peripheral surface 55b of the supply/discharge pipe 55 by the elastic force acting in the diameter reduction direction, so that the check seal is slidable in the axial direction on the outer peripheral surface 55b of the supply/discharge pipe 55. In this state, the outer diameter of the check seal 172 is set to a predetermined size so as to form a gap between the outer peripheral surface 172b and the bottom surface of the housing groove 51g. Although the fitting portion 172f shown in fig. 7A is cut in a step shape so as to have an overlapping portion in the axial direction, the shape of the fitting portion 172f is not limited thereto, and may be cut at a right angle or obliquely with respect to the circumferential direction of the check seal 172.

The check seal 172 is housed in the housing groove 51g such that the flow surface 172d is located on the rod-opposite-side chamber 5 side and the seal surface 172e is located on the second supply/discharge passage 51a side.

The check seal 172 is provided in such a manner that when the pressure of the second supply/discharge passage 51a, that is, the pressure of the

rod side chamber

2, 3, 4 is higher than the pressure of the rod opposite side chamber 5, the check seal 172 is in a state in which the flow surface 172d is pressed against the side surface of the housing groove 51g. In this state, the working fluid can flow from the second supply/discharge passage 51a to the rod-opposite-side chamber 5 through the gap formed between the outer peripheral surface 172b of the check seal 172 and the bottom surface of the housing groove 51g and the notch groove 172c formed in the flow surface 172 d.

On the other hand, when the pressure of the second supply/discharge passage 51a, that is, the pressure of the rod-

side chambers

2, 3, and 4 is lower than the pressure of the rod-opposite-side chamber 5, the check seal 172 is in a state in which the seal surface 172e, which is a flat surface, is pressed against the side surface of the housing groove 51g. In this state, no gap through which the working oil can flow is formed, and the flow of the working oil from the rod-opposite-side chamber 5 to the second supply/discharge passage 51a is blocked.

By disposing the check seal 172 that allows only the flow of the hydraulic oil from the second supply/discharge passage 51a to the rod opposite side chamber 5 in the flow passage formed between the through hole 51f that enables the second supply/discharge passage 51a and the rod opposite side chamber 5 to communicate with each other and the outer peripheral surface 55b of the supply/discharge pipe 55 in this way, the hydraulic oil can flow into the rod opposite side chamber 5 quickly through the check seal 172 when the pressure in any one of the

rod side chambers

2, 3, 4 is higher than the pressure in the rod opposite side chamber 5.

Therefore, in the hydraulic cylinder 200, as in the first embodiment, the instantaneous expansion and contraction operations of the hydraulic cylinder 200 due to the external force can be suppressed. In addition, in the hydraulic cylinder 200, since the check seal 172 is provided between the through hole 51f formed in the second inner rod portion 51 and the supply/discharge pipe 55 inserted into the through hole 51f, it is not necessary to weld the supply/discharge pipe 55 to the second inner rod portion 51. Therefore, it is not necessary to take measures against the case where the welded portion is cracked and the working oil leaks from the rod side chamber 5 to the second supply/discharge passage 51a due to the expansion or contraction of the supply/discharge pipe 55 caused by the temperature change.

According to the second embodiment described above, the following effects are obtained.

In the hydraulic cylinder 200 configured as described above, the check seal 172 serving as the backflow prevention mechanism 171 that permits only the flow of the hydraulic oil from the second supply/discharge passage 51a to the rod opposite side chamber 5 is provided in the third rod assembly 50 having the first supply/discharge passage 55a and the second supply/discharge passage 51a, that is, in the innermost rod member of the rod members provided in the cylinder tube 10.

By providing the backflow prevention mechanism 171 that allows only the flow of the hydraulic oil from the second supply/discharge passage 51a to the rod-opposite-side chamber 5 in the third rod assembly 50 having the first supply/discharge passage 55a and the second supply/discharge passage 51a in this way, the instantaneous expansion and contraction operation of the hydraulic cylinder 200 due to the external force can be suppressed as in the first embodiment. Further, since the rapid rise of the pressure in the

rod side chambers

2, 3, 4 is suppressed, it is possible to prevent the seal members that seal the

rod side chambers

2, 3, 4 from coming off, or the cylinder 10 from expanding.

< third embodiment >

Next, a multistage fluid pressure cylinder 300 (hereinafter, referred to as a "hydraulic cylinder 300") according to a third embodiment of the present invention will be described with reference to fig. 8. Hereinafter, description will be given mainly on differences from the first embodiment, and the same components as those of the first embodiment will be given the same reference numerals and omitted.

The backflow prevention mechanism 71 of the hydraulic cylinder 100 according to the first embodiment is a check valve 72 provided in a through-hole formed so as to axially penetrate the inside of the second inner piston portion 52, whereas the backflow prevention mechanism 271 of the hydraulic cylinder 300 is different in that a check seal 172 is provided between the outer peripheral surface 52a of the second inner piston portion 52 of the third rod assembly 50 and the inner peripheral surface 40a of the second rod assembly 40, as shown in fig. 8. Fig. 8 is a diagram showing a hydraulic cylinder 300 according to a third embodiment, and is a diagram showing a portion corresponding to fig. 5. The basic configuration and operation of the hydraulic cylinder 300 are the same as those of the hydraulic cylinder 100 according to the first embodiment, and therefore, the description thereof is omitted. Further, since the check seal 172 used in the hydraulic cylinder 300 is different only in size in the radial direction from the check seal 172 used in the hydraulic cylinder 200 according to the second embodiment, detailed description thereof will be omitted.

The check seal 172 used in the hydraulic cylinder 300 is provided so as to be slidable along the inner peripheral surface 40a of the second rod assembly 40, and a receiving groove 52c formed so as to be recessed radially inward is provided in the outer peripheral surface 52a of the second inner piston portion 52 so as to receive the check seal 172.

The check seal 172 is attached to the inner peripheral surface 40a of the second rod assembly 40 so as to reduce the gap of the closing portion 172f, and the outer peripheral surface 172b is slightly pressed against the inner peripheral surface 40a of the second rod assembly 40 by an elastic force acting in the diameter expansion direction, so that the check seal is slidable in the axial direction on the inner peripheral surface 40a of the second rod assembly 40. In this state, the inner diameter of the check seal 172 is set to a predetermined size so as to form a gap between the inner circumferential surface 172a and the bottom surface of the housing groove 52c.

The check seal 172 is provided in the housing groove 52c such that the flow surface 172d is located on the rod-opposite-side chamber 5 side and the seal surface 172e is located on the second inner rod-side chamber 4 side.

By providing the check seal 172 in this manner, when the pressure in the second inside rod side chamber 4 and the second supply/discharge passage 51a and the

rod side chambers

2 and 3 communicating with the second inside rod side chamber 4 becomes higher than the pressure in the rod opposite side chamber 5, the check seal 172 is in a state in which the flow surface 172d is pressed against the side surface of the housing groove 52c. In this state, the working fluid can flow from the second inside rod side chamber 4 to the rod side chamber 5 through the gap formed between the inner peripheral surface 172a of the check seal 172 and the bottom surface of the housing groove 52c and the cutout groove 172c formed in the flow surface 172 d.

On the other hand, when the pressure in the second inner rod side chamber 4 and the second supply/discharge passage 51a and the

rod side chambers

2 and 3 communicating with the second inner rod side chamber 4 becomes lower than the pressure in the rod opposite side chamber 5, the check seal 172 is in a state in which the seal surface 172e, which is a flat surface, is pressed against the side surface of the housing groove 52c. In this state, no gap through which the working oil can flow is formed, and the flow of the working oil from the rod-opposite-side chamber 5 to the second inside-side chamber 4 is blocked.

As described above, by disposing the check seal 172 that allows only the flow of the working oil from the second supply/discharge passage 51a to the rod opposite side chamber 5 via the second inner rod side chamber 4 on the flow passage formed between the outer peripheral surface 52a of the second inner piston portion 52 and the inner peripheral surface 40a of the second rod assembly 40, which can communicate the second supply/discharge passage 51a and the rod opposite side chamber 5, the working oil can flow into the rod opposite side chamber 5 quickly via the check seal 172 when the pressure of any one of the

rod side chambers

2, 3, 4 is higher than the pressure of the rod opposite side chamber 5.

Therefore, in the hydraulic cylinder 300, as in the first embodiment, the instantaneous expansion and contraction operations of the hydraulic cylinder 300 due to the external force can be suppressed. Further, in the hydraulic cylinder 300, since the check seal 172 is provided between the outer peripheral surface 52a of the second inner piston portion 52 of the third rod assembly 50, which conventionally becomes a sliding surface, and the inner peripheral surface 40a of the second rod assembly 40, a change in design and additional processing are hardly required, and therefore, an increase in manufacturing cost of the hydraulic cylinder 300 in which the backflow prevention mechanism 271 is provided can be suppressed. In addition, the check seal 172 may be provided either in place of the third sealing member 54 or together with the third sealing member 54.

According to the third embodiment described above, the following effects are obtained.

In the hydraulic cylinder 300 having the above-described configuration, the check seal 172 serving as the backflow prevention means 271 that allows only the flow of the hydraulic oil from the second supply/discharge passage 51a to the rod-opposite-side chamber 5 is provided in the third rod assembly 50 having the first supply/discharge passage 55a and the second supply/discharge passage 51a, that is, in the innermost rod member of the rod members provided in the cylinder tube 10.

As described above, by providing the backflow prevention mechanism 271 that allows only the flow of the hydraulic oil from the second supply/discharge passage 51a to the rod-opposite-side chamber 5 to the third rod assembly 50 having the first supply/discharge passage 55a and the second supply/discharge passage 51a, the instantaneous expansion and contraction operation of the hydraulic cylinder 300 due to the external force can be suppressed as in the first embodiment. Further, since the rapid rise of the pressure in the

rod side chambers

2, 3, 4 is suppressed, it is possible to prevent the seal members that seal the

rod side chambers

2, 3, 4 from coming off, or the cylinder 10 from expanding.

In addition, the following modifications are also within the scope of the present invention, and the configurations described in the modifications and the configurations described in the above embodiments may be combined or the configurations described in the following embodiments may be combined with each other.

In the first and third embodiments, the first supply/discharge passage 55a for supplying/discharging the working oil to/from the rod opposite side chamber 5 is provided in the third rod assembly 50. In addition, the first supply/discharge passage 55a may be provided in the cylinder 10, and in this case, the working oil is directly supplied to the rod-opposite-side chamber 5 formed in the cylinder 10, for example, via the first supply/discharge passage 55a that opens in the inner peripheral surface 10a of the cylinder 10.

In each of the above embodiments, the

hydraulic cylinders

100, 200, and 300 are three-stage

hydraulic cylinders

100, 200, and 300 provided such that three rod members (the first rod assembly 30, the second rod assembly 40, and the third rod assembly 50) overlap in the radial direction in the cylinder tube 10, and one second rod assembly 40 as an intermediate rod member is provided between the first rod assembly 30 as an outer rod member and the third rod assembly 50 as an inner rod member. In addition, two or more second rod assemblies 40 as intermediate rod members may be provided between the first rod assembly 30 and the third rod assembly 50. The

hydraulic cylinders

100, 200, and 300 may be two-stage hydraulic cylinders in which the second rod assembly 40 is not provided as the intermediate rod member, and only the third rod assembly 50 is provided as the inner rod member inside the first rod assembly 30 as the outer rod member.

Hereinafter, the structure, operation, and effects of the embodiments of the present invention will be summarized.

The

hydraulic cylinders

100, 200, and 300 include: a cylinder barrel 10; a first cylindrical rod assembly 30 having an outer piston 32 provided at an end thereof, the outer piston 32 sliding along an inner peripheral surface 10a of the cylinder 10 to divide the inside of the cylinder 10 into a rod side chamber 2 and a rod opposite side chamber 5; a third rod assembly 50 provided inside the first rod assembly 30 so as to be movable in the axial direction of the cylinder 10; a first supply/discharge passage 55a for supplying/discharging the working oil to/from the rod opposite side chamber 5; and a second supply/discharge passage 51a for supplying/discharging the hydraulic oil to/from the rod-side chamber 2, wherein the second supply/discharge passage 51a is provided in the third rod assembly 50, and the third rod assembly 50 is provided with backflow prevention means 71, 171, 271 for allowing only the flow of the hydraulic oil from the second supply/discharge passage 51a to the rod-opposite-side chamber 5.

In this configuration, the

backflow prevention mechanisms

71, 171, and 271 that allow only the flow of the working oil from the second oil supply/discharge passage 51a to the rod-opposite-side chamber 5 are provided in the third rod assembly 50 in which the second oil supply/discharge passage 51a is provided, that is, the third rod assembly 50 disposed innermost in the rod member provided in the cylinder 10. By providing the

backflow prevention mechanisms

71, 171, and 271 in the third rod assembly 50 in this way, for example, when an external force that forcibly extends the

hydraulic cylinders

100, 200, and 300 beyond the extension speed acts abruptly during the extension operation of the

hydraulic cylinders

100, 200, and 300, and when the pressure in any one of the

rod side chambers

2, 3, and 4 is higher than the pressure in the rod side chamber 5, the hydraulic oil flows rapidly from the second supply/discharge passage 51a into the rod side chamber 5 via the

backflow prevention mechanisms

17, 171, and 271. Accordingly, since the pressure of the

rod side chamber

2, 3, 4 to the rod side chamber 5, and the pressure of the rod side chamber 5 is suppressed from becoming negative, even if the external force acting on the

hydraulic cylinders

100, 200, 300 is released, the

hydraulic cylinders

100, 200, 300 do not contract instantaneously and return to the extension operation smoothly again, and as a result, the instantaneous extension and retraction operation of the

hydraulic cylinders

100, 200, 300 due to the external force can be suppressed. Further, since the rapid rise of the pressure in the

rod side chambers

2, 3, 4 is suppressed, it is possible to prevent the seal members for sealing the

rod side chambers

2, 3, 4 from coming off or the cylinder 10 from expanding.

Further, the cross-sectional shape of the pressure receiving surface of the third rod assembly 50 disposed innermost among the rod members provided in the cylinder 10 is not circular, but circular. Therefore, as compared with the case where the

backflow prevention mechanisms

71, 171, and 271 are provided in the first rod assembly 30 and the second rod assembly 40 having annular pressure receiving surfaces in cross section, a space for disposing the

backflow prevention mechanisms

71, 171, and 271 can be easily secured without increasing the outer diameter of the rod member.

In addition, the third lever assembly 50 has: a second inner rod part 51 having a second supply/discharge passage 51a formed therein; a second inner piston portion 52 provided at an end of the second inner rod portion 51 and disposed so as to face the rod-opposite-side chamber 5; and through

holes

51e and 52b formed to axially penetrate the second inner piston portion 52, one end of each of which opens into the second supply/discharge passage 51a and the other end of each of which opens into the rod-side chamber 5, and the backflow prevention mechanism 71 is a check valve 72 provided in the through

holes

51e and 52b.

In this configuration, the backflow prevention mechanism 71 is a check valve 72 provided in through-

holes

51e, 52b formed in the third rod assembly 50. By adding a simple structure such as the check valve 72 to the third rod assembly 50 in this way, the instantaneous expansion and contraction operation of the hydraulic cylinder 100 due to external force can be suppressed. Further, since the cross-sectional shape of the pressure receiving surface facing the rod-opposite-side chamber 5 of the third rod assembly 50 disposed innermost among the rod members provided in the cylinder 10 is not circular, the check valve 72 functioning as the backflow prevention mechanism 71 and the through-

holes

51e, 52b in which the check valve 72 is provided can be easily laid out.

Further, a plurality of second through-holes 52b through which bolts 53 are inserted are formed in the second inner piston portion 52 so as to axially penetrate, the bolts 53 being used to assemble the second inner piston portion 52 to the second inner rod portion 51, and one of the plurality of second through-holes 52b constitutes a part of the through-

holes

51e and 52b.

In this configuration, one of the second through-holes 52b through which the bolt 53 can be inserted constitutes a part of the through-

holes

51e and 52b in which the check valve 72 is provided. By processing a part of the through-

holes

51e and 52b in which the check valves 72 are provided in the same manner as the insertion holes through which the bolts 53 are inserted, an increase in the manufacturing cost of the hydraulic cylinder 100 in which the backflow prevention mechanism 71 is provided can be suppressed.

Further, the first supply/discharge passage 55a is provided in the third rod assembly 50, and the third rod assembly 50 includes: a second inner rod part 51 having a second supply/discharge passage 51a formed therein; a second inner piston portion 52 provided at an end of the second inner rod portion 51 and disposed so as to face the rod-opposite-side chamber 5; a through hole 51f formed so as to axially penetrate the second inner piston portion 52, one end of which opens to the second supply/discharge passage 51a and the other end of which opens to the rod-opposite-side chamber 5; and a supply/discharge pipe 55 inserted into the through-hole 51f and having a first supply/discharge passage 55a formed therein, wherein the backflow prevention mechanism 171 is a check seal 172 provided between an outer periphery of the supply/discharge pipe 55 and an inner periphery of the through-hole 51 f.

In this configuration, the backflow prevention mechanism 171 is a check seal 172 provided between the outer periphery of the supply and discharge pipe 55 and the inner periphery of the through-hole 51 f. By adding a simple structure such as the check seal 172 to the third rod assembly 50 in this way, the instantaneous expansion and contraction operation of the hydraulic cylinder 200 due to external force can be suppressed. Further, since the check seal 172 is provided between the through hole 51f formed in the second inner rod portion 51 and the supply/discharge pipe 55 inserted into the through hole 51f, it is not necessary to weld the supply/discharge pipe 55 to the second inner rod portion 51. Therefore, it is not necessary to take measures against the case where the welded portion is cracked due to expansion or contraction of the supply/discharge pipe 55 due to a temperature change and the hydraulic oil leaks from the rod side chamber 5 to the second supply/discharge passage 51a, and as a result, an increase in the manufacturing cost of the hydraulic cylinder 200 provided in the supply/return prevention mechanism 171 can be suppressed.

In addition, the third lever assembly 50 has: a second inner rod part 51 having a second supply/discharge passage 51a formed therein; and a second inner piston part 52 provided at an end of the second inner rod part 51 and disposed so as to face the rod opposite side chamber 5, the second inner piston part 52 sliding along an inner peripheral surface 40a of the second rod assembly 40 provided between the first rod assembly 30 and the third rod assembly 50 or an inner peripheral surface 30a of the first rod assembly 30, and the backflow prevention means 271 being a backflow prevention seal 172 provided between the second rod assembly 40 or the first rod assembly 30, with which the second inner piston part 52 is in sliding contact, and the second inner piston part 52.

In this structure, the backflow prevention mechanism 271 is a check seal 172 provided between the second rod assembly 40 or the first rod assembly 30, which is in sliding contact with the second inner piston portion 52, and the second inner piston portion 52. By adding a simple structure such as the check seal 172 to the third rod assembly 50 in this manner, instantaneous expansion and contraction operations of the hydraulic cylinder 300 due to external force can be suppressed. In addition, in this configuration, since the check seal 172 may be provided instead of the third seal member 54 that is conventionally provided on the outer peripheral surface 52a of the second inner piston portion 52, or the check seal 172 may be provided together with the second seal member 54, design changes and additional processing are hardly required, and therefore, an increase in the manufacturing cost of the hydraulic cylinder 300 in which the backflow prevention mechanism 271 is provided can be suppressed.

Although the embodiments of the present invention have been described above, the above embodiments are merely some of application examples of the present invention, and the technical scope of the present invention is not limited to the specific configurations of the above embodiments.

This application claims priority based on Japanese patent application No. 2020-141116 filed on the sun on 24/8/2020 and is incorporated by reference in its entirety in this specification.

Claims

1. A multi-stage fluid pressure cylinder is provided with:

a cylinder barrel;

a cylindrical outer rod member having an outer piston portion at an end thereof, the outer piston portion sliding along an inner peripheral surface of the cylinder and dividing the inside of the cylinder into a rod side chamber and a rod opposite side chamber;

an inner rod member provided inside the outer rod member so as to be movable in an axial direction of the cylinder tube;

a first supply/discharge passage for supplying/discharging a working fluid to/from the rod opposite side chamber;

a second supply/discharge passage for supplying/discharging a working fluid to/from the rod side chamber,

the second supply and discharge passage is provided to the inner rod member,

a backflow prevention mechanism that allows only a flow of the working fluid from the second supply and discharge passage toward the rod opposite side chamber is provided on the inner rod member.

2. The multi-stage fluid pressure cylinder of claim 1,

the inner rod member includes:

the inner side rod part is internally provided with the second supply and discharge channel;

an inner piston part provided at an end of the inner rod part and disposed to face the opposite-rod-side chamber;

a through hole formed so as to penetrate the inner piston portion in the axial direction, one end of the through hole being open to the second supply/discharge passage, and the other end of the through hole being open to the rod-opposite side chamber,

the backflow prevention mechanism is a check valve or an overflow valve provided in the through hole.

3. The multiple stage fluid pressure cylinder as claimed in claim 2,

a plurality of insertion holes are formed in the inner piston part so as to penetrate in the axial direction, and a fastening member for assembling the inner piston part to the inner rod part is inserted through the insertion holes,

one of the plurality of insertion holes constitutes a part of the through-hole.

4. The multi-stage fluid pressure cylinder of claim 1,

the first supply and discharge passage is provided to the inner rod member,

the inner rod member includes:

a through hole formed so as to penetrate the inner piston portion in the axial direction, one end of the through hole being open to the second supply/discharge passage, and the other end of the through hole being open to the rod-opposite-side chamber;

a tubular member inserted through the through-hole and having the first supply/discharge passage formed therein,

the backflow prevention mechanism is a non-return seal provided between an outer periphery of the tubular member and an inner periphery of the through-hole.

5. The multiple stage fluid pressure cylinder as claimed in claim 1,

the inner rod member includes:

an inner piston part provided at an end of the inner rod part and disposed to face the chamber on the opposite side of the rod,

the inner piston part slides along an inner peripheral surface of an intermediate rod member provided between the outer rod member and the inner rod member or an inner peripheral surface of the outer rod member,

the backflow prevention means is a check seal provided between the intermediate rod member or the outer rod member, which is in sliding contact with the inner piston portion, and the inner piston portion.