GB2613494A

GB2613494A - Multistage fluid pressure cylinder

Info

Publication number: GB2613494A
Application number: GB2303134.7A
Authority: GB
Inventors: Funato Hiroshi; Tanigawa Natsuki
Original assignee: KYB Corp
Current assignee: KYB Corp
Priority date: 2020-08-24
Filing date: 2021-08-12
Publication date: 2023-06-07
Anticipated expiration: 2041-08-12
Also published as: GB2613494B; CN115943261A; WO2022044833A1; JP7177805B2; GB202303134D0; JP2022036748A

Abstract

A multistage fluid pressure cylinder (100) comprises: a cylinder tube (10); a first rod assembly (30) provided with an outside piston portion (32); a third rod assembly (50) provided inside the first rod assembly (30); a first supply-and-exhaust channel (55a) for supplying and exhausting a hydraulic oil to/from a counter-rod-side chamber (5); and a second supply-and-exhaust channel (51a) for supplying and exhausting the hydraulic oil to/from a rod-side chamber (2). The second supply-and-exhaust channel (51a) is provided for the third rod assembly (50), and the third rod assembly (50) is provided with a backflow prevention mechanism (71) that permits only the flow of the hydraulic oil from the second supply-and-exhaust channel (51a) to the counter-rod-side chamber (5).

Description

DESCRIPTION

TITLE OF INVENTION: MULTISTAGE FLUID PRESSURE CYLINDER

TECHNICAL FIELD

[0001] The present invention relates to a multistage fluid pressure cylinder.

BACKGROUND ART

[0002] JP2017-172681A discloses a multistage fluid pressure cylinder including a cylinder tube, a tubular outer rod member, and an inner rod member. The tubular outer rod member is provided with, at an end portion, an outer piston portion sliding along an inner peripheral surface of the cylinder tube. The inner rod member is disposed inside the outer rod member and has a flow passage through which a working fluid is supplied to and discharged from a rod-side chamber and a flow passage through which the working fluid is supplied to and discharged from an anti-rod side chamber.

SUMMARY OF INVENTION

[0003] During extending of the multistage fluid pressure cylinder as described in JP2017-172681A, when an external force for forcibly extending the multistage fluid pressure cylinder at a speed exceeding an extension speed is suddenly applied, the working fluid is not sufficiently supplied to the anti-rod side chamber, and pressure in the anti-rod side chamber decreases or becomes negative, whereas the working fluid is not sufficiently discharged from the rod-side chamber, and pressure in the rod-side chamber increases. When the external force applied to the multistage fluid pressure cylinder is released in a state in which the pressure in the anti-rod side chamber decreases and the pressure in the rod-side chamber increases, the multistage -2 -fluid pressure cylinder is instantaneously slightly contracted. Thereafter, the multistage fluid pressure cylinder is extended and contracted repeatedly to some extent by a rebound, and then returns to the extending again. When the multistage fluid pressure cylinder is extended and contracted repeatedly during a relatively short time in this manner, a device provided with the multistage fluid pressure cylinder may vibrate.

[0004] An object of the present invention is to suppress an instantaneous operation of a multistage fluid pressure cylinder generated by an external force.

[0005] According to one aspect of the present invention, a multistage fluid pressure cylinder includes: a cylinder tube; a tubular outer rod member provided with an outer piston portion at an end portion, the outer piston portion being configured to slide along an inner peripheral surface of the cylinder tube and partition an inside of the cylinder tube into a rod-side chamber and an anti-rod side chamber; an inner rod member provided movably inside the outer rod member in an axial direction of the cylinder tube; a first supply and discharge passage through which a working fluid is supplied to and discharged from the anti-rod side chamber; and a second supply and discharge passage through which the working fluid is supplied to and discharged from the rod-side chamber. The second supply and discharge passage is provided in the inner rod member, and the inner rod member is provided with a backflow prevention mechanism that is configured to allow the working fluid to flow only from the second supply and discharge passage to the anti-rod side chamber.

BRIEF DESCRIPTION OF DRAWINGS

[0006] FIG. 1 is a cross-sectional view of a multistage fluid pressure -3 -cylinder according to a first embodiment of the present invention, and shows a fully contracted state.

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

FIG. 3 is a cross-sectional view showing the multistage fluid pressure cylinder according to the first embodiment of the present invention, and shows a state in which the first rod assembly and the second rod assembly are at the extended position and the third rod assembly is at the contracted position. FIG. 4 is a cross-sectional view showing the multistage fluid pressure cylinder according to the first embodiment of the present invention, and shows a fully extended state.

FIG. 5 is an enlarged view showing a portion A in FIG. 1 in an enlarged manner.

FIG. 6 is a view showing a multistage fluid pressure cylinder according to a second embodiment of the present invention, and shows a portion corresponding to that in FIG. 5.

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

FIG. 7B is a cross-sectional view taken along line B-B in FIG. 7A.

FIG. 8 is a view showing a multistage fluid pressure cylinder according to a third embodiment of the present invention, and shows a portion corresponding to that in FIG. 5.

DESCRIPTION OF EMBODIMENTS

[0007] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0008] <First Embodiment> A multistage fluid pressure cylinder 100 according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 5. Hereinafter, a case in which the multistage fluid pressure cylinder 100 is a multistage hydraulic cylinder 100 (hereinafter, simply referred to as the "hydraulic cylinder 100") that performs drive using hydraulic oil as a working fluid will be described.

[0009] As shown in FIG. 1, the hydraulic cylinder 100 includes a bottomed tubular cylinder tube 10, a first rod assembly 30 as an outer rod member that is slidably inserted into the cylinder tube 10, a third rod assembly 50 as an inner rod member that is movably provided inside the first rod assembly 30 in a central axis direction (hereinafter, simply referred to as the "axial direction") of the cylinder tube 10, and a second rod assembly 40 as an intermediate rod member that is movably provided between the first rod assembly 30 and the third rod assembly 50 in the axial direction. FIG. 1 is a cross-sectional view showing a state in which the hydraulic cylinder 100 is fully contracted.

[0010] The hydraulic cylinder 100 is attached to a drive target device such that the cylinder tube 10 is located on an upper side in a vertical direction and the third rod assembly 50 is located on a lower side in the vertical direction via a first attachment portion 61 and a second attachment portion 62. The first attachment portion 61 is provided at a bottom portion of the cylinder tube 10. The second attachment portion 62 is 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 drive target device such that the first attachment portion 61 is displaced substantially in the vertical direction, that is, in an up-and-down direction with respect to the second attachment portion 62. The direction in which the hydraulic cylinder 100 is attached is not limited thereto. The hydraulic cylinder 100 may be attached such that the cylinder tube 10 is located on the lower side in the vertical direction and the third rod assembly 50 is located on the upper side in the vertical direction. In addition, the hydraulic cylinder 100 may be attached to the drive target device such that the first attachment portion 61 is displaced in a horizontal direction with respect to the second attachment portion 62.

[0011] The first rod assembly 30 includes a tubular outer rod portion 31, an annular outer piston portion 32, and a cylindrical first support portion 33. The annular outer piston portion 32 is provided at one end portion of the outer rod portion 31, slides along an inner peripheral surface 10a of the cylinder tube 10, and partitions an inside of the cylinder tube 10 into a rod-side chamber 2 and an anti-rod side chamber 5. The cylindrical first support portion 33 protrudes radially inward from the other end portion of the outer rod portion 31 and slidably supports the second rod assembly 40.

[0012] An annular recess 30b into which a first snap ring 35 is installed is formed on an inner peripheral surface 30a of the first rod assembly 30 on an outer piston portion 32 side. The first snap ring 35 is a metal wire formed in a substantially annular shape, and has an abutment joint portion that is not shown and that is partially divided. The first snap ring 35 is inserted into the first rod assembly 30 in a diameter-reduced state. An outer diameter side of the first snap ring 35 is pressed against the inner peripheral surface 30a by an elastic force acting in a diameter-expanding direction, and is fitted into the annular recess 30b. In a state in which the first snap ring 35 is assembled to the first rod assembly 30 in this manner, an inner diameter side of the first snap ring 35 protrudes radially inward from the inner peripheral surface 30a of the first rod assembly 30. The first snap ring 35 is installed after the -6 -second rod assembly 40 is inserted into the first rod assembly 30.

[0013] The second rod assembly 40 has the same shape as the first rod assembly 30, and includes a tubular first inner rod portion 41, an annular first inner piston portion 42, and a cylindrical second support portion 43. The tubular first inner rod portion 41 is inserted into the outer rod portion 31.

The annular first inner piston portion 42 is provided at one end portion of the first inner rod portion 41 in a manner of facing the anti-rod side chamber 5 and slides along the inner peripheral surface 30a of the first rod assembly 30. The cylindrical second support portion 43 protrudes radially inward from the other end portion of the first inner rod portion 41 and slidably supports the third rod assembly 50.

[0014] A second annular recess 40b into which a second snap ring 45 is installed is formed on an inner peripheral surface 40a of the second rod assembly 40 on a first inner piston portion 42 side. Similarly to the first snap ring 35, the second snap ring 45 is a metal wire formed in a substantially annular shape, and has an abutment joint portion that is not shown and that is partially divided. The second snap ring 45 is inserted into the second rod assembly 40 in a diameter-reduced state. An outer diameter side of the second snap ring 45 is pressed against the inner peripheral surface 40a by an elastic force acting in the diameter-expanding direction, and is fitted into the second annular recess 40b. In a state in which the second snap ring 45 is assembled to the second rod assembly 40 in this manner, an inner diameter side of the second snap ring 45 protrudes radially inward from the inner peripheral surface 40a of the second rod assembly 40. The second snap ring 45 is installed after the third rod assembly 50 is inserted into the second rod assembly 40.

[0015] The third rod assembly 50 includes a second inner rod portion 51 as -7 -an inner rod portion and an annular second inner piston portion 52 as an inner piston portion. The second inner rod portion 51 is inserted into the first inner rod portion 41. The second inner piston portion 52 is provided at an end portion of the second inner rod portion 51 in a manner of facing the anti-rod 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 the end portion of the second inner rod portion 51 via a plurality of bolts 53.

[0016] In this manner, the three rod members, that is, the first rod assembly 30, the second rod assembly 40, and the third rod assembly 50 are inserted into the cylinder tube 10.

[0017] A cylinder head 11 that slidably supports the outer rod portion 31 of the first rod assembly 30 is provided in an opening portion of the cylinder tube 10. A recess 10b that is recessed toward the first attachment portion 61 is formed in the bottom portion of the cylinder tube 10, which faces each of the piston portions 32, 42, and 52 in the axial direction. An inner diameter of the recess 10b is set to be larger than an inner diameter of the outer piston portion 32 of the first rod assembly 30.

[0018] A fully contracted position of the first rod assembly 30 inserted into the cylinder tube 10 is defined when the outer piston portion 32 abuts on the bottom portion of the cylinder tube 10. A fully extended position is defined when the outer piston portion 32 abuts on the cylinder head 11. A seal member that is not shown and seals a gap between an inner peripheral surface of the cylinder head 11 and an outer peripheral surface of the outer rod portion 31 is provided on the inner peripheral surface of the cylinder head 11 in order to prevent leakage of the hydraulic oil to the outside.

[0019] A fully contracted position of the second rod assembly 40 inserted into the first rod assembly 30 is defined when the first inner piston portion 42 -8 -abuts on the first snap ring 35 that is installed in the first rod assembly 30. A fully extended position is defined when the first inner piston portion 42 abuts on the first support portion 33. The first snap ring 35 restricts movement of the second rod assembly 40 in a contraction direction, and prevents the first rod assembly 30 from dropping out of the cylinder tube 10 when the hydraulic cylinder 100 is contracted.

[0020] A seal member that is not shown and seals a gap between an inner peripheral surface of the first support portion 33 and an 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 hydraulic oil to the outside.

[0021] A fully contracted position of the third rod assembly 50 inserted into the second rod assembly 40 is defined when the second inner piston portion 52 abuts on the second snap ring 45 that is installed in the second rod assembly 40. A fully extended position is defined when the second inner piston portion 52 abuts on the second support portion 43. The second snap ring 45 restricts movement of the third rod assembly 50 in the contraction direction, and prevents the second rod assembly 40 from dropping out of the cylinder tube 10 when the hydraulic cylinder 100 is contracted.

[0022] A seal member that is not shown and seals a gap between an inner peripheral surface of the second support portion 43 and an outer peripheral surface of the second inner rod portion 51 is provided on the inner peripheral surface of the second support portion 43 in order to prevent leakage of the hydraulic oil to the outside. The inner peripheral surface of the second support portion 43 is formed with an annular recess 43a. When the third rod assembly 50 is fully extended, an opening portion of a communication hole 51b that is formed in the second inner rod portion 51 and that will be -9 -described later faces the annular recess 43a. The annular recess 43a is opened to a second inner rod-side chamber 4 that will be described later.

[0023] 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 shapes are inserted is formed with the rod-side chamber 2, a first inner rod-side chamber 3, the second inner rod-side chamber 4, and the anti-rod side chamber 5. The rod-side chamber 2 is defined by the cylinder tube 10, the cylinder head 11, the outer rod portion 31, and the outer piston portion 32. The first inner rod-side chamber 3 is 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. The second inner rod-side chamber 4 is 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. The anti-rod side chamber 5 is defined by the cylinder tube 10, the outer piston portion 32, the first inner piston portion 42, and the second inner piston portion 52.

[0024] 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. Communication between the rod-side chamber 2 and the anti-rod side chamber 5 through a gap between the outer peripheral surface 32a of the outer piston portion 32 and the inner peripheral surface 10a of the cylinder tube 10 is blocked by the first seal member 34.

[0025] A plurality of supply and discharge ports 32b through which the hydraulic oil is supplied to and discharged from the rod-side chamber 2 penetrate the outer piston portion 32 of the first rod assembly 30 in a radial direction.

[0026] 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.

-10 -Communication between the first inner rod-side chamber 3 and the anti-rod side chamber 5 through 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.

[0027] A plurality of inner supply and discharge ports 42b through which the hydraulic oil is supplied to and discharged from the first inner rod-side chamber 3 penetrate the first inner piston portion 42 of the second rod assembly 40 in the radial direction.

[0028] 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. Communication between the second inner rod-side chamber 4 and the anti-rod side chamber 5 through 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.

[0029] The second inner rod portion 51 of the third rod assembly 50 is formed with a second supply and discharge passage 51a and the communication hole 51b. The second supply and discharge passage 51a is connected to an external device that is not shown and supplies and discharges the hydraulic oil to and from the hydraulic cylinder 100. The communication hole 5 lb allows the second supply and discharge passage 51a to communicate with the second inner rod-side chamber 4. The second inner rod portion 51 is formed with a connection passage 51c connecting the second supply and discharge passage 51a and a passage 64 that is formed in the second attachment portion 62.

[0030] The second supply and discharge passage 51a communicates with the second inner rod-side chamber 4 through the communication hole 51b, communicates with the first inner rod-side chamber 3 through the inner -11 -supply and discharge ports 42b and the communication hole 51b, and communicates with the rod-side chamber 2 through the supply and discharge ports 32h, the inner supply and discharge ports 42b, and the communication hole 51b.

[0031] That is, the hydraulic oil is supplied to and discharged from the rod-side chamber 2, the first inner rod-side chamber 3, and the second inner rod-side chamber 4 through the second supply and discharge passage 51a formed in the second inner rod portion 51.

[0032] The second inner rod portion 51 is provided with a pipe-shaped supply and discharge pipe 55 which is formed with, inside thereof, a first supply and discharge passage 55a connected to the external device that supplies and discharges the hydraulic oil to and from the hydraulic cylinder 100. The supply and discharge pipe 55 is assembled in the second inner rod portion Si such that one end of the supply and discharge pipe 55 faces the anti-rod side chamber 5 and is opened. Specifically, the supply and discharge pipe 55 is joined to the second inner rod portion 51 in a manner of passing through the second supply and discharge passage 51a in the axial direction. The second inner rod portion Si is formed with a connection passage 51d connecting the other end of the supply and discharge pipe 55 and a passage 63 that is formed in the second attachment portion 62.

[0033] Since the supply and discharge pipe 55 is provided such that one end is opened to the anti-rod side chamber 5 in this manner, the hydraulic oil is supplied to and discharged from the anti-rod side chamber 5 through the first supply and discharge passage 55a in the supply and discharge pipe 55.

[0034] Next, an operation of the hydraulic cylinder 100 will be described with reference to FIGS. 1 to 4. In the following description, a case will be described in which the hydraulic cylinder 100 is attached to the drive target -12 -device 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.

[0035] When the hydraulic cylinder 100 is extended, the hydraulic oil is supplied from a hydraulic source such as a pump, which is not shown, to the anti-rod side chamber 5 through the first supply and discharge passage 55a in the supply and discharge pipe 55, and the hydraulic oil in the rod-side chamber 2, the first inner rod-side chamber 3, and the second inner rod-side chamber 4 is discharged to a tank that is not shown through the second supply and discharge passage 51a.

[0036] When the hydraulic cylinder 100 is extended from a fully contracted state shown in FIG. 1, the hydraulic oil is supplied to the anti-rod side chamber 5 through the first supply and discharge passage 55a. Here, a pressure receiving area for receiving pressure in the anti-rod side chamber 5 is the largest when the first rod assembly 30 is extended, and is the smallest when the third rod assembly 50 is extended. Therefore, when the hydraulic cylinder 100 is extended from the fully contracted state, the cylinder tube 10 first moves relative to the first rod assembly 30. Specifically, as shown in FIG. 2, the cylinder tube 10 moves upward (toward the upper side in FIG. 2) with respect to the first rod assembly 30. Since the inner diameter of the recess 10b formed in the bottom portion of the cylinder tube 10 is larger than the inner diameter of the outer piston portion 32 of the first rod assembly 30, the pressure of the hydraulic oil guided to the anti-rod side chamber 5 acts on the outer piston portion 32 through the recess 10b.

[0037] When the cylinder tube 10 moves relative to the first rod assembly 30, the hydraulic oil in the rod-side chamber 2 is guided to the second supply and discharge passage 51a through the supply and discharge ports 32b, the -13 -inner supply and discharge ports 42b, and the communication hole 51b, and is discharged to the outside.

[0038] Then, as shown in FIG. 2, when the cylinder tube 10 is fully extended with respect to the first rod assembly 30, that is, when the cylinder tube 10 moves upward until the cylinder head 11 abuts on the outer piston portion 32 of the first rod assembly 30, the cylinder tube 10 and the first rod assembly 30 move relative to the second rod assembly 40 by the pressure in the anti-rod side chamber 5. Specifically, as shown in FIG. 3, the cylinder tube 10 and the first rod assembly 30 move upward (toward the upper side in FIG. 3) with respect to the second rod assembly 40.

[0039] When the first rod assembly 30 moves relative to the second rod assembly 40, the hydraulic oil in the first inner rod-side chamber 3 is guided to the second supply and discharge passage 51a through the inner supply and discharge ports 42b and the communication hole 51b, and is discharged to the outside.

[0040] Then, as shown in FIG. 3, when the first rod assembly 30 is fully extended with respect to the second rod assembly 40, that is, when the cylinder tube 10 and the first rod assembly 30 move upward until the first support portion 33 of the first rod assembly 30 abuts on the first inner piston portion 42 of the second rod assembly 40, the cylinder tube 10, the first rod assembly 30, and the second rod assembly 40 move relative to the third rod assembly 50 by the pressure in the anti-rod side chamber 5. Specifically, as shown in FIG. 4, the cylinder tube 10, the first rod assembly 30, and the second rod assembly 40 move upward (toward the upper side in FIG. 4) with respect to the third rod assembly 50.

[0041] When the second rod assembly 40 moves relative to the third rod assembly 50, the hydraulic oil in the second inner rod-side chamber 4 is -14 -guided to the second supply and discharge passage 51a through the communication hole 51b, and is discharged to the outside.

[0042] Then, as shown in FIG. 4, the hydraulic cylinder 100 is in a fully extended state when the second rod assembly 40 is fully extended 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 move upward until the second support portion 43 of the second rod assembly 40 abuts on the second inner piston portion 52 of the third rod assembly 50.

[0043] In contrast, when the hydraulic cylinder 100 is contracted, the hydraulic oil is supplied from the hydraulic source to the rod-side chamber 2, the first inner rod-side chamber 3, and the second inner rod-side chamber 4 through the second supply and discharge passage 51a, and the hydraulic oil in the anti-rod side chamber 5 is discharged to the tank through the first supply and discharge passage 55a. The hydraulic cylinder 100 may be contracted by an own weight of the drive target device coupled to the first attachment portion 61. In this case, it is not necessary to supply the hydraulic oil to the rod-side chamber 2, the first inner rod-side chamber 3, and the second inner rod-side chamber 4, and the hydraulic oil is suctioned from the tank into the rod-side chamber 2, the first inner rod-side chamber 3, and the second inner rod-side chamber 4.

[0044] When the hydraulic cylinder 100 is contracted from the fully extended state, first, the cylinder tube 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. Then, the cylinder tube 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 moves relative to the first rod assembly 30 from the state shown in -15 -FIG. 2 to the state shown in FIG. 1, and accordingly, the hydraulic cylinder 100 is in the fully contracted state.

[0045] Here, during the extending of the hydraulic cylinder 100 having the above configuration, when an external force for forcibly extending the hydraulic cylinder 100 having the above configuration at a speed exceeding an extension speed is suddenly applied, the hydraulic oil is not sufficiently supplied to the anti-rod side chamber 5 whose volume is increased, and the pressure in the anti-rod side chamber 5 decreases or becomes negative, whereas the hydraulic oil is not sufficiently discharged from each of the rod-side chambers 2, 3, and 4 whose volume is being reduced, and pressure in each of the rod-side chambers 2, 3, and 4 increases.

[0046] When the external force applied to the hydraulic cylinder 100 is released in a state in which the pressure in the anti-rod side chamber 5 decreases and the pressure in each of the rod-side chambers 2, 3, and 4 increases, the hydraulic cylinder 100 is instantaneously slightly contracted. Thereafter, the hydraulic cylinder 100 is extended and contracted repeatedly to some extent by a rebound, and then returns to the extending again. When the hydraulic cylinder 100 is extended and contracted repeatedly during a relatively short time in this manner, a device provided with the hydraulic cylinder 100, for example, a vehicle on which the hydraulic cylinder 100 is mounted may vibrate.

[0047] When the pressure in the rod-side chambers 2, 3, and 4 rapidly increases, the seal members that seal the rod-side chambers 2, 3, and 4 may be detached, the cylinder tube 10 may be expanded, and accordingly the hydraulic cylinder 100 may be damaged.

[0048] In response to this, in the hydraulic cylinder 100 according to the present embodiment, as shown in FIG. 5, the third rod assembly 50 is provided -16 -with a backflow prevention mechanism 71 that blocks the hydraulic oil from flowing from the anti-rod side chamber 5 to the second supply and discharge passage 51a and allows the hydraulic oil to flow only from the second supply and discharge passage 51a to the anti-rod side chamber 5. FIG. 5 is an enlarged view of a portion surrounded by a broken line indicated by an arrow A in FIG. 1 that shows the hydraulic cylinder 100 in the fully contracted state.

[0049] The backflow prevention mechanism 71 shown in FIG. 5 is a check valve 72 provided in a through hole that penetrates through the second inner piston portion 52 in the axial direction and that has one end opened to the second supply and discharge passage 51a and the other end opened to the anti-rod side chamber 5.

[0050] The check valve 72 includes a valve body 72a and a spring 72b that biases the valve body 72a. The check valve 72 operates to block the hydraulic oil from flowing from the anti-rod side chamber 5 to the second supply and discharge passage 51a and to allow the hydraulic oil to flow from the second supply and discharge passage 51a to the anti-rod side chamber 5 when a pressure in the second supply and discharge passage 51a is larger than the pressure in the anti-rod side chamber 5.

[0051] When the first rod assembly 30 is extended, the second supply and discharge passage 51a provided in the third rod assembly 50 communicates with the second inner rod-side chamber 4 through the communication hole 51b, communicates with the first inner rod-side chamber 3 through the inner supply and discharge ports 42b and the communication hole 51b, and communicates with the rod-side chamber 2 through the supply and discharge ports 32b, the inner supply and discharge ports 42b, and the communication hole 51b. When the second rod assembly 40 is extended, the second supply and discharge passage 51a communicates with the second inner rod-side -17 -chamber 4 through the communication hole 51b, and communicates with the first inner rod-side chamber 3 through the inner supply and discharge ports 42b and the communication hole 51b. When the third rod assembly 50 is extended, the second supply and discharge passage 51a communicates with the second inner rod-side chamber 4 through the communication hole 51b.

[0052] Therefore, the check valve 72 provided in the third rod assembly 50 can allow the hydraulic oil to flow from the second supply and discharge passage 51a to the anti-rod side chamber 5 when the pressure in each of the rod-side chambers 2, 3, and 4 is larger than the pressure in the anti-rod side chamber 5 while the hydraulic cylinder 100 is in an extended state.

[0053] In other words, for example, when the check valve that allows the hydraulic oil to flow from the rod-side chamber 2 to the anti-rod side chamber is provided in the first rod assembly 30, during the extending of the first rod assembly 30, the hydraulic oil can flow to the anti-rod side chamber 5 through the check valve when the pressure in the first inner rod-side chamber 3 and the second inner rod-side chamber 4 is larger than the pressure in the anti-rod side chamber 5. The first inner rod-side chamber 3 and the second inner rod-side chamber 4 communicate with the rod-side chamber 2 through the supply and discharge ports 32b. However, when the second rod assembly 40 is extended, the hydraulic oil cannot flow to the anti-rod side chamber 5 through the check valve provided in the first rod assembly 30 even when the pressure in the first inner rod-side chamber 3 and the second inner rod-side chamber 4 is larger than the pressure in the anti-rod side chamber 5, since the first inner rod-side chamber 3 and the second inner rod-side chamber 4 do not communicate with the rod-side chamber 2.

[0054] Similarly, for example, also when the check valve that allows the hydraulic oil to flow from the first inner rod-side chamber 3 to the anti-rod side -18 -chamber 5 is provided in the second rod assembly 40, when the third rod assembly 50 is extended, the hydraulic oil cannot flow to the anti-rod side chamber 5 through the check valve provided in the second rod assembly 40 even when the pressure in the second inner rod-side chamber 4 is larger than the pressure in the anti-rod side chamber 5, since the first inner rod-side chamber 3 and the second inner rod-side chamber 4 do not communicate with each other.

[0055] In contrast, by the check valve 72 having the above configuration provided in the third rod assembly 50, the hydraulic oil can flow to the anti-rod side chamber 5 through the check valve 72 when the pressure in any one of the rod-side chamber 2, the first inner rod-side chamber 3, and the second inner rod-side chamber 4 is larger than the pressure in the anti-rod side chamber 5 during the extending of the first rod assembly 30, when the pressure in any one of the first inner rod-side chamber 3 and the second inner rod-side chamber 4 is larger than the pressure in the anti-rod side chamber 5 during the extending of the second rod assembly 40, and when the pressure in the second inner rod-side chamber 4 is larger than the pressure in the anti-rod side chamber 5 during the extending of the third rod assembly 50.

[0056] In this manner, by providing, in the third rod assembly 50, the check valve 72 that allows the hydraulic oil to flow only from the second supply and discharge passage 51a to the anti-rod side chamber 5, the hydraulic oil quickly flows from the second supply and discharge passage 51a to the anti-rod side chamber 5 through the check valve 72 when the external force for forcibly extending the hydraulic cylinder 100 at the speed exceeding the extension speed is suddenly applied and the pressure in any one of the rod-side chambers 2, 3, and 4 is larger than the pressure in the anti-rod side chamber 5 during the extending of the hydraulic cylinder 100.

-19 - [0057] Accordingly, since the pressure in each of the rod-side chambers 2, 3, and 4 is less likely to be maintained larger than the pressure in the anti-rod side chamber 5, and the hydraulic oil is supplied from the rod-side chambers 2, 3, and 4 to the anti-rod side chamber 5 to suppress the pressure in the anti-rod side chamber 5 from being negative, the hydraulic cylinder 100 returns to the extending relatively smoothly again without being instantaneously contracted even when the external force applied to the hydraulic cylinder 100 is released.

[0058] In this manner, it is possible to prevent the device provided with the hydraulic cylinder 100 from vibrating by suppressing the instantaneous extending and contracting of the hydraulic cylinder 100 caused by the external force. In addition, since the rapid increase in the pressure in each of the rod-side chambers 2, 3, and 4 whose volume is being reduced is also suppressed, it is possible to prevent the seal members that seal the rod-side chambers 2, 3, and 4 from being detached and the cylinder tube 10 from being expanded.

[0059] The check valve 72 is provided in the third rod assembly 50 provided with the first supply and discharge passage 55a and the second supply and discharge passage 51a, that is, in a rod member disposed in the innermost side among the rod members provided in the cylinder tube 10. A cross-sectional shape of a pressure receiving surface of the third rod assembly disposed on the innermost side is not an annular shape but a circular shape. Therefore, a space in which the check valve 72 is disposed can be easily secured without increasing an outer diameter of the rod member when compared with a case in which the check valve 72 is provided in the first rod assembly 30 or the second rod assembly 40 whose pressure receiving surface has an annular cross-sectional shape.

-20 - [0060] As shown in FIG. 5, the through hole in which the check valve 72 is provided includes a first through hole 51e that is formed in the second inner rod portion 51 and a second through hole 52b as an insertion hole that is formed in the second inner piston portion 52. 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 the bolts 53 as fastening members used for assembling the second inner piston portion 52 to the second inner rod portion 51 are inserted.

[0061] In this manner, by using the through hole formed as the insertion hole through which the bolt 53 is inserted as the through hole in which the check valve 72 is provided, manufacturing cost of the hydraulic cylinder 100 can be reduced and the check valve 72 can be disposed in a compact manner, as compared with a case in which the through hole is separately formed.

[0062] The check valve 72 may be provided in the bolt 53 that fastens the second inner piston portion 52 and the second inner rod portion 51, and in this case, it is possible to secure a sufficient fastening force for fastening the second inner piston portion 52 and the second inner rod portion 51.

[0063] When the hydraulic cylinder 100 is contracted by the own weight of the drive target device coupled to the first attachment portion 61, the pressure in the anti-rod side chamber 5 is always larger than the pressure in each of the rod-side chambers 2, 3, and 4 if no external force is applied to the hydraulic cylinder 100, and thus the operation of the hydraulic cylinder 100 is not affected even when the backflow prevention mechanism 71 is simply the check valve 72. However, when the hydraulic cylinder 100 is contracted by supplying the pressurized hydraulic oil to each of the rod-side chambers 2, 3, and 4, the pressure in the anti-rod side chamber 5 is smaller than the pressure in each of the rod-side chambers 2, 3, and 4, and the hydraulic cylinder 100 -21 -may not be contracted when the backflow prevention mechanism 71 is simply the check valve 72.

[0064] Therefore, in such a 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 larger than the pressure in the anti-rod side chamber 5 by a predetermined value or more so that the hydraulic oil does not flow from the second supply and discharge passage 51a to the anti-rod side chamber 5 through the backflow prevention mechanism 71 during the contracting. Specifically, a valve opening pressure of the valve body 72a can be changed by appropriately changing a load of the spring 72b that biases the valve body 72a. In this manner, even when the backflow prevention mechanism 71 is the relief valve, the hydraulic oil quickly flows from the second supply and discharge passage 51a to the anti-rod side chamber 5 through the relief valve when the pressure in each of the rod-side chambers 2, 3, and 4 is abnormally larger than the pressure in the anti-rod side chamber 5, and thus the same effect as the case in which the backflow prevention mechanism 71 is the check valve 72 is achieved. Therefore, a relief valve may be used as the backflow prevention mechanism 71 for the hydraulic cylinder 100 that is contracted by the own weight of the drive target device coupled to the first attachment portion 61.

[0065] According to the first embodiment described above, the following effects are achieved.

[0066] In the hydraulic cylinder 100 having the above configuration, the check valve 72 as the backflow prevention mechanism 71 that allows the hydraulic oil to flow only from the second supply and discharge passage 51a to the anti-rod side chamber 5 is provided in the third rod assembly 50 having the first supply and discharge passage 55a and the second supply and discharge passage 51a, that is, in the rod member disposed on the innermost -22 -side among the rod members provided in the cylinder tube 10.

[0067] In this manner, by providing the check valve 72 that allows the hydraulic oil to flow only from the second supply and discharge passage 51a to the anti-rod side chamber 5, the hydraulic oil quickly flows from the second supply and discharge passage 51a to the anti-rod side chamber 5 through the check valve 72, for example, when the external force for forcibly extending the hydraulic cylinder 100 at the speed exceeding the extension speed is suddenly applied and the pressure in any one of the rod-side chambers 2, 3, and 4 is larger than the pressure in the anti-rod side chamber 5 during the extending of the hydraulic cylinder 100.

[0068] Accordingly, since the pressure in each of the rod-side chambers 2, 3, and 4 is less likely to be maintained larger than the pressure in the anti-rod side chamber 5, and the hydraulic oil is supplied from the rod-side chambers 2, 3, and 4 to the anti-rod side chamber 5 to suppress the pressure in the anti-rod side chamber 5 from being negative, the hydraulic cylinder 100 returns to the extending relatively smoothly again without being instantaneously contracted even when the external force applied to the hydraulic cylinder 100 is released.

[0069] In this manner, it is possible to suppress the instantaneous extending and contracting of the hydraulic cylinder 100 caused by the external force, by providing the backflow prevention mechanism 71 that allows the hydraulic oil to flow only from the second supply and discharge passage 51a to the anti-rod side chamber 5 in the third rod assembly 50 having the first supply and discharge passage 55a and the second supply and discharge passage 51a. In addition, since the rapid increase in the pressure in each of the rod-side chambers 2, 3, and 4 is suppressed, it is possible to prevent the seal members that seal the rod-side chambers 2, 3, and 4 from being detached -23 -and the cylinder tube 10 from being expanded.

[0070] The cross-sectional shape of the pressure receiving surface of the third rod assembly 50 disposed on the innermost side among the rod members provided in the cylinder tube 10 is not the annular shape but the circular shape. Therefore, the space in which the check valve 72 is disposed can be easily secured without increasing the outer diameter of the rod member when compared with the case in which the check valve 72 is provided in the first rod assembly 30 or the second rod assembly 40 whose pressure receiving surface has the annular cross-sectional shape.

[0071] <Second Embodiment> Next, a multistage fluid pressure cylinder 200 (hereinafter, referred to as the "hydraulic cylinder 200") according to the second embodiment of the present invention will be described with reference to FIG. 6. Hereinafter, points different from the first embodiment will be mainly described, and the same configurations as those in the first embodiment will be denoted by the same reference numerals, and description thereof will be omitted.

[0072] The two embodiments are different in that the backflow prevention mechanism 71 of the hydraulic cylinder 100 according to the first embodiment is the check valve 72 provided in the through hole that penetrates through the inside of the second inner piston portion 52 in the axial direction, whereas a backflow prevention mechanism 171 of the hydraulic cylinder 200 is a check seal 172 provided between an outer periphery of the supply and discharge pipe 55 as a tubular member and an inner periphery of a through hole 51f as shown in FIG. 6. FIG. 6 is a view showing the hydraulic cylinder 200 according to the second embodiment, and shows a portion corresponding to that in FIG. 5. Basic configurations and operations of the hydraulic cylinder 200 are the same as those of the hydraulic cylinder 100 according to the first embodiment, and -24 -

thus the description thereof will be omitted.

[0073] As shown in FIG. 6, the through hole 51f is a hole that penetrates through the inside of the second inner piston portion 52 in the axial direction and that has one end opened to the second supply and discharge passage 51a and the other end opened to the anti-rod side chamber 5, and is provided at the end portion of the second inner rod portion 51 to which the second inner piston portion 52 is coupled. One end of the supply and discharge pipe 55 is inserted into the through hole 51f via a predetermined gap. The check seal 172 that slides along an 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 51f. In order to accommodate the check seal 172, the through hole 51f is provided with an accommodation groove 51g that is recessed radially outward.

[0074] The check seal 172 is an annular member made of a material having elasticity such as a resin material (for example, rubber) or a metal. As shown in FIGS. 7A and 7B, the check seal 172 has an inner peripheral surface 172a that is in contact with the outer peripheral surface 55b of the supply and discharge pipe 55, an outer peripheral surface 172b that faces a bottom surface of the accommodation groove 51g, a flow surface 172d that is formed with a plurality of notch grooves 172c notched in the radial direction, a flat seal surface 172e, and an abutment joint portion 172f that is partially divided in a circumferential direction. FIG. 7A is a plan view of the check seal 172, and FIG. 7B is a cross-sectional view taken along line B-B in FIG. 7A.

[0075] The check seal 172 having the above shape is attached to the outer peripheral surface 55b of the supply and discharge pipe 55 in a manner of expanding a gap of the abutment joint portion 17211 The inner peripheral surface 172a is slightly pressed against the outer peripheral surface 55b of the -25 -supply and discharge pipe 55 by an elastic force acting in a diameter-reduced direction, and the check seal 172 is in a state of being slidable along the outer peripheral surface 55b of the supply and discharge pipe 55 in the axial direction. In this state, an outer diameter of the check seal 172 is set such that a gap having a predetermined size is formed between the outer peripheral surface 172b and the bottom surface of the accommodation groove 51g. The abutment joint portion 172f shown in FIG. 7A is cut stepwise so as to have overlapping portions in the axial direction, but a shape of the abutment joint portion 172f is not limited thereto, and may be a shape cut at a right angle or obliquely with respect to the circumferential direction of the check seal 172.

[0076] The check seal 172 is accommodated in the accommodation groove 51g such that the flow surface 172d is located on an anti-rod side chamber 5 side and the seal surface 172e is located on a second supply and discharge passage 51a side.

[0077] By providing the check seal 172 in this manner, when the pressure in the second supply and discharge passage 51a, that is, the pressure in each of the rod-side chambers 2, 3, and 4 is larger than the pressure in the anti-rod side chamber 5, the check seal 172 is in a state in which the flow surface 172d is pressed against a side surface of the accommodation groove 51g. In this state, the working fluid can flow from the second supply and discharge passage 51a to the anti-rod side chamber 5 through the gap that is formed between the outer peripheral surface 172b of the check seal 172 and the bottom surface of the accommodation groove Mg and the notch grooves 172c that are formed in the flow surface 172d.

[0078] In contrast, when the pressure in the second supply and discharge passage 51a, that is, the pressure in each of the rod-side chambers 2, 3, and 4 is smaller than the pressure in the anti-rod side chamber 5, the check seal 172 -26 -is in a state in which the flat seal surface 172e is pressed against a side surface of the accommodation groove 51g. In this state, a gap through which the hydraulic oil can flow is not formed, and the hydraulic oil is prevented from flowing from the anti-rod side chamber 5 to the second supply and discharge passage 51a.

[0079] In this manner, by disposing the check seal 172, which allows the hydraulic oil to flow only from the second supply and discharge passage 51a to the anti-rod side chamber 5, on a flow passage formed between the outer peripheral surface 55b of the supply and discharge pipe 55 and the through hole 51f, the hydraulic oil can quickly flow to the anti-rod side chamber 5 through the check seal 172 when the pressure in any one of the rod-side chambers 2, 3, and 4 is larger than the pressure in the anti-rod side chamber 5. The flow passage allows the second supply and discharge passage 51a to communicate with the anti-rod side chamber 5.

[0080] Therefore, also in the hydraulic cylinder 200, similarly to the first embodiment, it is possible to suppress the instantaneous extending and contracting of the hydraulic cylinder 200 caused by the external force. 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 and discharge pipe 55 inserted into the through hole 51f, it is not necessary to join the supply and discharge pipe 55 to the second inner rod portion 51 by welding. Therefore, it is not necessary to take measures to prevent the hydraulic oil from leaking from the anti-rod side chamber 5 to the second supply and discharge passage 51a due to breakage of a welded portion that is caused by expansion and contraction of the supply and discharge pipe 55 due to temperature change.

[0081] According to the second embodiment described above, the following -27 -effects are achieved.

[0082] In the hydraulic cylinder 200 having the above configuration, the check seal 172 as the backflow prevention mechanism 171 that allows the hydraulic oil to flow only from the second supply and discharge passage 51a to the anti-rod side chamber 5 is provided in the third rod assembly 50 having the first supply and discharge passage 55a and the second supply and discharge passage 51a, that is, in the rod member disposed on the innermost side among the rod members provided in the cylinder tube 10.

[0083] In this manner, similarly to the first embodiment, it is possible to suppress the instantaneous extending and contracting of the hydraulic cylinder 200 caused by the external force, by providing the backflow prevention mechanism 171 that allows the hydraulic oil to flow only from the second supply and discharge passage 51a to the anti-rod side chamber 5 in the third rod assembly 50 having the first supply and discharge passage 55a and the second supply and discharge passage 51a. In addition, since the rapid increase in the pressure in each of the rod-side chambers 2, 3, and 4 is suppressed, it is possible to prevent the seal members that seal the rod-side chambers 2, 3, and 4 from being detached and the cylinder tube 10 from being expanded.

[0084] <Third Embodiment> Next, a multistage fluid pressure cylinder 300 (hereinafter, referred to as the "hydraulic cylinder 300) according to the third embodiment of the present invention will be described with reference to FIG. 8. Hereinafter, points different from the first embodiment will be mainly described, and the same configurations as those in the first embodiment will be denoted by the same reference numerals, and description thereof will be omitted.

[0085] The two embodiments are different in that the backflow prevention -28 -mechanism 71 of the hydraulic cylinder 100 according to the first embodiment is the check valve 72 provided in the through hole that penetrates through the inside of the second inner piston portion 52 in the axial direction, whereas a backflow prevention mechanism 271 of the hydraulic cylinder 300 is the check seal 172 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 view showing the hydraulic cylinder 300 according to the third embodiment, and shows a portion corresponding to that in FIG. 5. Basic configurations and operations of the hydraulic cylinder 300 are the same as those of the hydraulic cylinder 100 according to the first embodiment, and thus the description thereof will be omitted. The check seal 172 used in the hydraulic cylinder 300 is different from the check seal 172 used in the hydraulic cylinder 200 according to the second embodiment only in a size in the radial direction, and thus a detailed description thereof will be omitted.

[0086] The check seal 172 used in the hydraulic cylinder 300 is slidably provided along the inner peripheral surface 40a of the second rod assembly 40. In order to accommodate the check seal 172, the outer peripheral surface 52a of the second inner piston portion 52 is provided with an accommodation groove 52c that is recessed radially inward.

[0087] The check seal 172 is attached to the inner peripheral surface 40a of the second rod assembly 40 in a manner of narrowing the gap of the abutment joint portion 172f. 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-expanding direction, and the check seal 172 is in a state of being slidable along the inner peripheral surface 40a of the second rod assembly 40 in the axial direction. In this state, an inner diameter -29 -of the check seal 172 is set such that a gap having a predetermined size is formed between the inner peripheral surface 172a and a bottom surface of the accommodation groove 52c.

[0088] The check seal 172 is provided in the accommodation groove 52c such that the flow surface 172d is located on the anti-rod side chamber 5 side and the seal surface 172e is located on a second inner rod-side chamber 4 side.

[0089] By providing the check seal 172 in this manner, when the pressure in each of the second inner rod-side chamber 4, and the second supply and discharge passage 51a and the rod-side chambers 2 and 3 that communicate with the second inner rod-side chamber 4 is larger than the pressure in the anti-rod side chamber 5, the check seal 172 is in a state in which the flow surface 172d is pressed against a side surface of the accommodation groove 52c. In this state, the working fluid can flow from the second inner rod-side chamber 4 to the anti-rod side chamber 5 through the gap that is formed between the inner peripheral surface 172a of the check seal 172 and the bottom surface of the accommodation groove 52c and the notch grooves 172c that are formed in the flow surface 172d.

[0090] In contrast, when the pressure in each of the second inner rod-side chamber 4 and the second supply and discharge passage 51a and the rod-side chambers 2 and 3 that communicate with the second inner rod-side chamber 4 is smaller than the pressure in the anti-rod side chamber 5, the check seal 172 is in a state in which the flat seal surface 172e is pressed against a side surface of the accommodation groove 52c. In this state, a gap through which the hydraulic oil can flow is not formed, and the hydraulic oil is prevented from flowing from the anti-rod side chamber 5 to the second inner rod-side chamber 4.

-30 - [0091] In this manner, by disposing the check seal 172, which allows the hydraulic oil to flow only from the second supply and discharge passage 51a to the anti-rod side chamber 5 through the second inner rod-side chamber 4, on a 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, the hydraulic oil can quickly flow to the anti-rod side chamber 5 through the check seal 172 when the pressure in any one of the rod-side chambers 2, 3, and 4 is larger than the pressure in the anti-rod side chamber 5. The flow passage allows the second supply and discharge passage 51a to communicate with the anti-rod side chamber 5.

[0092] Therefore, also in the hydraulic cylinder 300, similarly to the first embodiment, it is possible to suppress the instantaneous extending and contracting of the hydraulic cylinder 300 caused by the external force. 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 is originally a sliding surface, and the inner peripheral surface 40a of the second rod assembly 40, changes in design and additional processing are not required. Therefore, it is possible to suppress an increase in manufacturing cost of the hydraulic cylinder 300 provided with the backflow prevention mechanism 271. The check seal 172 may be provided in place of the third seal member 54, or may be provided together with the third seal member 54.

[0093] According to the third embodiment described above, the following effects are achieved.

[0094] In the hydraulic cylinder 300 having the above configuration, the check seal 172 as the backflow prevention mechanism 271 that allows the hydraulic oil to flow only from the second supply and discharge passage 51a to -31 -the anti-rod side chamber 5 is provided in the third rod assembly 50 having the first supply and discharge passage 55a and the second supply and discharge passage 51a, that is, in the rod member disposed on the innermost side among the rod members provided in the cylinder tube 10.

[0095] In this manner, similarly to the first embodiment, it is possible to suppress the instantaneous extending and contracting of the hydraulic cylinder 300 caused by the external force, by providing the backflow prevention mechanism 271 that allows the hydraulic oil to flow only from the second supply and discharge passage 51a to the anti-rod side chamber 5 in the third rod assembly 50 having the first supply and discharge passage 55a and the second supply and discharge passage 51a. In addition, since the rapid increase in the pressure in each of the rod-side chambers 2, 3, and 4 is suppressed, it is possible to prevent the seal members that seal the rod-side chambers 2, 3, and 4 from being detached and the cylinder tube 10 from being expanded.

[0096] The following modifications are also within the scope of the present invention. It is also possible to combine a configuration described in the modifications and a configuration described in the above embodiments, or combine configurations described in the above embodiments.

[0097] In the first embodiment and the third embodiment, the first supply and discharge passage 55a through which the hydraulic oil is supplied to and discharged from the anti-rod side chamber 5 is provided in the third rod assembly 50. Instead of this, the first supply and discharge passage 55a may be provided in the cylinder tube 10. In this case, the hydraulic oil is directly supplied to and discharged from the anti-rod side chamber 5 formed in the cylinder tube 10 through the first supply and discharge passage 55a that is opened in the inner peripheral surface 10a of the cylinder tube 10, for -32 -

example.

[0098] In the above embodiments, the hydraulic cylinders 100, 200, and 300 are three-stage hydraulic cylinders 100, 200, and 300 in which the three rod members (the first rod assembly 30, the second rod assembly 40, and the third rod assembly 50) overlap each other in the radial direction in the cylinder tube 10. One second rod assembly 40 as the intermediate rod member is provided between the first rod assembly 30 as the outer rod member and the third rod assembly 50 as the inner rod member. Instead of this, 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 fluid pressure cylinders in which the second rod assembly 40 as the intermediate rod member is not provided and only the third rod assembly 50 as the inner rod member is provided inside the first rod assembly 30 as the outer rod member.

[0099] Hereinafter, configurations, functions, and effects according to the embodiments of the present invention will be collectively described.

[0100] Each of the hydraulic cylinders 100, 200, and 300 includes the cylinder tube 10, the tubular first rod assembly 30, the third rod assembly 50, the first supply and discharge passage 55a through which hydraulic oil is supplied to and discharged from the anti-rod side chamber 5, and the second supply and discharge passage 51a through which the hydraulic oil is supplied to and discharged from the rod-side chamber 2. The tubular first rod assembly 30 is provided with, at an end portion, the outer piston portion 32 sliding along the inner peripheral surface 10a of the cylinder tube 10 and partitioning an inside of the cylinder tube 10 into the rod-side chamber 2 and the anti-rod side chamber 5. The third rod assembly 50 is movably provided inside the first rod assembly 30 in an axial direction of the cylinder tube 10.

-33 -The second supply and discharge passage 51a is provided in the third rod assembly 50. The third rod assembly 50 is provided with one of the backflow prevention mechanisms 71, 171, and 271 that allow the hydraulic oil to flow only from the second supply and discharge passage 51a to the anti-rod side chamber 5.

[0101] In this configuration, one of the backflow prevention mechanisms 71, 171, and 271 that allow the hydraulic oil to flow only from the second supply and discharge passage 51a to the anti-rod side chamber 5 is provided in the third rod assembly 50 provided with the second supply and discharge passage 51a, that is, in the third rod assembly 50 disposed on the innermost side among rod members provided in the cylinder tube 10. In this manner, by providing the one of the backflow prevention mechanisms 71, 171, and 271 in the third rod assembly 50, the hydraulic oil quickly flows from the second supply and discharge passage 51a to the anti-rod side chamber 5 through the one of the backflow prevention mechanisms 71, 171, and 271, for example, when an external force for forcibly extending each of the hydraulic cylinders 100, 200, and 300 at a speed exceeding an extension speed is suddenly applied and pressure in any one of the rod-side chambers 2, 3, and 4 is larger than pressure in the anti-rod side chamber 5 during the extending of each of the hydraulic cylinders 100, 200, and 300. Accordingly, since the pressure in each of the rod-side chambers 2, 3, and 4 is less likely to be maintained larger than the pressure in the anti-rod side chamber 5, and the hydraulic oil is supplied from the rod-side chambers 2, 3, and 4 to the anti-rod side chamber 5 to suppress the pressure in the anti-rod side chamber 5 from being negative, each of the hydraulic cylinders 100, 200, and 300 returns to the extending relatively smoothly again without being instantaneously contracted even when the external force applied to each of the hydraulic cylinders 100, 200, and 300 -34 -is released. As a result, it is possible to suppress the instantaneous extending and contracting of each of the hydraulic cylinders 100, 200, and 300 caused by the external force. In addition, since the rapid increase in the pressure in each of the rod-side chambers 2, 3, and 4 is suppressed, it is possible to prevent the seal members that seal the rod-side chambers 2, 3, and 4 from being detached and the cylinder tube 10 from being expanded.

[0102] Further, a cross-sectional shape of a pressure receiving surface of the third rod assembly 50 disposed on the innermost side among the rod members provided in the cylinder tube 10 is not an annular shape but a circular shape. Therefore, a space in which one of the backflow prevention mechanisms 71, 171, and 271 is disposed can be easily secured without increasing an outer diameter of the rod member when compared with a case in which the one of the backflow prevention mechanisms 71, 171, and 271 is provided in the first rod assembly 30 or the second rod assembly 40 whose pressure receiving surface has an annular cross-sectional shape.

[0103] The third rod assembly 50 includes: the second inner rod portion 51 in which the second supply and discharge passage 51a is formed; the second inner piston portion 52 that is provided at an end portion of the second inner rod portion 51 and faces the anti-rod side chamber 5; and the through hole 51e, 52b that penetrates the second inner piston portion 52 in the axial direction and has one end opened to the second supply and discharge passage 51a and the other end opened to the anti-rod side chamber 5. The backflow prevention mechanism 71 is the check valve 72 provided in the through holes 51e, 52b.

[0104] In this configuration, the backflow prevention mechanism 71 is the check valve 72 provided in the through holes 51e, 52b that are formed in the third rod assembly 50. By adding the simple configuration of the check valve -35 - 72 to the third rod assembly 50 in this manner, it is possible to suppress the instantaneous extending and contracting of the hydraulic cylinder 100 caused by the external force. Since the cross-sectional shape of the pressure receiving surface, which faces the anti-rod side chamber 5, of the third rod assembly 50 disposed on the innermost side among the rod members provided in the cylinder tube 10 is not the annular shape but the circular shape, it is possible to easily lay out 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.

[0105] The plurality of second through holes 52b through which the bolts 53 are insertable are formed in the second inner piston portion 52 in a manner of penetrating through the second inner piston portion 52 in the axial direction. The bolts 53 are configured to assemble the second inner piston portion 52 to the second inner rod portion 51. One of the plurality of second through holes 52b constitutes a part of the through hole 51e, 52b.

[0106] In this configuration, one of the plurality of second through holes 52b through which the bolt 53 are insertable constitutes a part of the through hole 51e, 52b in which the check valve 72 is provided. In this manner, by processing a part of the through holes 51e, 52b in which the check valve 72 is provided similarly to the insertion hole through which the bolt 53 is inserted, it is possible to suppress an increase in manufacturing cost of the hydraulic cylinder 100 provided with the backflow prevention mechanism 71.

[0107] The first supply and discharge passage 55a is provided in the third rod assembly 50. The third rod assembly 50 includes: the second inner rod portion 51 in which the second supply and discharge passage 51a is formed; the second inner piston portion 52 that is provided at the end portion of the second inner rod portion 51 and faces the anti-rod side chamber 5; the -36 -through hole 51f that penetrates through the second inner piston portion 52 in the axial direction and has one end opened to the second supply and discharge passage 51a and the other end opened to the anti-rod side chamber 5; and the supply and discharge pipe 55 that is inserted through the through hole 51f and in which the first supply and discharge passage 55a is formed. The backflow prevention mechanism 171 is the check seal 172 provided between an outer periphery of the supply and discharge pipe 55 and an inner periphery of the through hole 51f.

[0108] In this configuration, the backflow prevention mechanism 171 is the check seal 172 provided between the outer periphery of the supply and discharge pipe 55 and the inner periphery of the through hole 51f. By adding the simple configuration of the check seal 172 to the third rod assembly 50 in this manner, it is possible to suppress the instantaneous extending and contracting of the hydraulic cylinder 200 caused by the external force. Since the check seal 172 is provided between the through hole 51f formed in the second inner rod portion 51 and the supply and discharge pipe 55 inserted into the through hole 51f, it is not necessary to join the supply and discharge pipe 55 to the second inner rod portion 51 by welding. Therefore, it is not necessary to take measures to prevent the hydraulic oil from leaking from the anti-rod side chamber 5 to the second supply and discharge passage 51a due to breakage of a welded portion that is caused by expansion and contraction of the supply and discharge pipe 55 due to temperature change. As a result, it is possible to suppress an increase in manufacturing cost of the hydraulic cylinder 200 provided with the backflow prevention mechanism 171.

[0109] The third rod assembly 50 includes the second inner rod portion 51 in which the second supply and discharge passage 51a is formed, and the second inner piston portion 52 that is provided at the end portion of the second -37 -inner rod portion 51 and faces the anti-rod side chamber 5. The second inner piston portion 52 slides along the inner peripheral surface 40a of the second rod assembly 40 provided between the first rod assembly 30 and the third rod assembly 50, or along the inner peripheral surface 30a of the first rod assembly 30. The backflow prevention mechanism 271 is the check seal 172 provided between the second inner piston portion 52 and the second rod assembly 40 or the first rod assembly 30 with which the second inner piston portion 52 is in sliding contact.

[0110] In this configuration, the backflow prevention mechanism 271 is the check seal 172 provided between the second inner piston portion 52 and the second rod assembly 40 or the first rod assembly 30 with which the second inner piston portion 52 is in sliding contact. By adding the simple configuration of the check seal 172 to the third rod assembly 50 in this manner, it is possible to suppress the instantaneous extending and contracting of the hydraulic cylinder 300 caused by the external force. In this configuration, since the check seal 172 may be provided in place of or together with the third seal member 54 originally provided in the outer peripheral surface 52a of the second inner piston portion 52, a change in design and additional processing are not required. Therefore, it is possible to suppress an increase in manufacturing cost of the hydraulic cylinder 300 provided with the backflow prevention mechanism 271.

[0111] 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.

[0112] This application claims priority based on Japanese Patent Application No. 2020-141116 filed with the Japan Patent Office on August 24, -38 - 2020, the entire contents of which are incorporated into this specification by reference.

Claims

-39 -CLAIMS1. A multistage fluid pressure cylinder comprising: a cylinder tube; a tubular outer rod member provided with an outer piston portion at an end portion, the outer piston portion being configured to slide along an inner peripheral surface of the cylinder tube and partition an inside of the cylinder tube into a rod-side chamber and an anti-rod side chamber; an inner rod member provided movably inside the outer rod member in an axial direction of the cylinder tube; a first supply and discharge passage through which a working fluid is supplied to and discharged from the anti-rod side chamber; and a second supply and discharge passage through which the working fluid is supplied to and discharged from the rod-side chamber, wherein the second supply and discharge passage is provided in the inner rod member, and the inner rod member is provided with a backflow prevention mechanism that is configured to allow the working fluid to flow only from the second supply and discharge passage to the anti-rod side chamber.
2. The multistage fluid pressure cylinder according to claim 1, wherein the inner rod member has an inner rod portion in which the second supply and discharge passage is formed, an inner piston portion that is provided at an end portion of the inner rod portion and faces the anti-rod side chamber, and a through hole that penetrates through the inner piston portion in -40 -the axial direction and has one end opened to the second supply and discharge passage and the other end opened to the anti-rod side chamber, and the backflow prevention mechanism is a check valve or a relief valve provided in the through hole.
3. The multistage fluid pressure cylinder according to claim 2, wherein a plurality of insertion holes through which fastening members are insertable are formed in the inner piston portion in a manner of penetrating through the inner piston portion in the axial direction, the fastening members being configured to assemble the inner piston portion to the inner rod portion, and one of the plurality of insertion holes constitutes a part of the through hole.
4. The multistage fluid pressure cylinder according to claim 1, wherein the first supply and discharge passage is formed in the inner rod member, the inner rod member has an inner rod portion in which the second supply and discharge passage is formed, an inner piston portion that is provided at an end portion of the inner rod portion and faces the anti-rod side chamber, a through hole that penetrates through the inner piston portion in the axial direction and has one end opened to the second supply and discharge passage and the other end opened to the anti-rod side chamber, and a tubular member that is inserted through the through hole and in which the first supply and discharge passage is formed, and the backflow prevention mechanism is a check seal provided between an -41 -outer periphery of the tubular member and an inner periphery of the through hole.
5. The multistage fluid pressure cylinder according to claim 1, wherein the inner rod member has an inner rod portion in which the second supply and discharge passage is formed, and an inner piston portion that is provided at an end portion of the inner rod portion and faces the anti-rod side chamber, the inner piston portion slides along an inner peripheral surface of an intermediate rod member provided between the outer rod member and the inner rod member, or along an inner peripheral surface of the outer rod member, and the backflow prevention mechanism is a check seal provided between the inner piston portion and the intermediate rod member or the outer rod member with which the inner piston portion is in sliding contact.