Valve unit for expansion, contraction, and inversion of cylinder

Abstract

To inhibit, with a simple structure, a long time from being taken to switch a position of a spool in a directional control valve to a first position, i.e. an initial position, after a cylinder is contracted, inverted, and expanded one time.SOLUTION: A valve unit for expansion, contraction, and inversion of a cylinder includes a unit body 16, a directional control valve 17, and a sequence valve. The directional control valve 17 includes: a spool 31 which may move in a longitudinal direction within the unit body 16; and a spring 24 which biases the spool 31 toward a first position which is one end of a movable range. The spool 31 moves, based on an oil pressure of an operation chamber 25 formed so as to be located adjacent to the first position of the spool 31, toward a second position which is an end opposite to the first position of the movable range against a biasing force of the spring 24. The spool 31 is formed with: a discharge passage 33 connected to a tank port 21; and a communication part 36 connecting the discharge passage 33 with the operation chamber 25.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a cylinder telescopic reversal valve unit. [Background technology]

[0002] When driving agricultural machinery such as a bottom plow using a hydraulic cylinder equipped with a rod, the cylinder is caused to contract, reverse, and extend once using a hydraulic circuit such as that shown in Patent Document 1. As shown in Figure 7, the hydraulic circuit includes a pump port 81, a tank port 82, a compression passage 83, an extension passage 84, a directional control valve 85, a sequence valve 86, and a pilot check valve 87.

[0003] The cylinder 88, driven by the hydraulic circuit, contracts and extends a rod 91 by supplying and discharging hydraulic oil to a compression pressure chamber 89 and an extension pressure chamber 90. The pump port 81 receives hydraulic oil discharged from the pump. The pump sucks and discharges hydraulic oil accumulated in a tank. The tank port 82 returns hydraulic oil discharged from the cylinder 88 to the tank. The compression passage 83 can be connected to the compression pressure chamber 89 of the cylinder 88. The extension passage 84 can be connected to the extension pressure chamber 90 of the cylinder 88.

[0004] The directional control valve 85 is disposed between the pump port 81 and the tank port 82 and the compression passage 83 and extension passage 84. A pilot check valve 87 is provided in the extension passage 84. The pilot check valve 87 allows hydraulic oil to flow in the extension passage 84 toward the extension pressure chamber 90 of the cylinder 88, while prohibiting hydraulic oil from flowing in the extension passage 84 toward the directional control valve 85. However, when the hydraulic pressure in the compression passage 83 is equal to or higher than a predetermined value, the pilot check valve 87 opens based on the hydraulic pressure, thereby allowing hydraulic oil to flow in the extension passage 84 toward the directional control valve 85.

[0005] The directional control valve 85 is capable of switching its position between a first position A and a second position B. The directional control valve 85 is biased by a spring 93 to the first position A. The directional control valve 85 is capable of switching from the first position A to the second position B against the biasing force of the spring 93 based on the hydraulic pressure in the working chamber 94.

[0006] When the direction switching valve 85 is switched to first position A, hydraulic oil discharged from the pump is supplied to the compression pressure chamber 89 of the cylinder 88 via the pump port 81 and the compression passage 83. At this time, the hydraulic pressure in the compression passage 83 exceeds a specified value, opening the pilot check valve 87. As a result, hydraulic oil discharged from the extension pressure chamber 90 of the cylinder 88 is returned to the tank via the extension passage 84 and the tank port 82.

[0007] When the position of the directional control valve 85 is switched to second position B, hydraulic oil discharged from the pump is supplied to the extension pressure chamber 90 of the cylinder via the pump port 81 and the extension passage 84. At this time, hydraulic oil in the compression pressure chamber 89 of the cylinder 88 is returned to the tank via the compression passage 83 and the tank port 82. At this time, hydraulic oil discharged from the pump also passes through the directional control valve 85 and is then supplied to the working chamber 94 via the working passage 95. As a result, the position of the directional control valve 85 is maintained at second position B based on the hydraulic pressure in the working chamber 94.

[0008] The sequence valve 86 is provided in the middle of an operating passage 97 that connects the compression passage 83 and the operating chamber 94. The sequence valve 86 opens and closes based on the hydraulic pressure in the compression passage 83, the hydraulic pressure in the extension passage 84, and a spring 96, thereby opening and closing the operating passage 97.

[0009] The elastic force of the spring 96 in the sequence valve 86 is set so that the sequence valve 86 closes when hydraulic oil is being supplied from the pump port 81 to the compression-side passage 83 and when hydraulic oil is being discharged from the extension-side passage 84 to the tank-side port 82. The elastic force of the spring 96 is also set so that the sequence valve 86 opens when the hydraulic pressure in the extension-side passage 84 drops to approximately atmospheric pressure after hydraulic oil starts to be discharged from the extension-side passage 84 to the tank-side port 82.

[0010] When the above-described hydraulic circuit is used to cause the cylinder 88 to perform one retraction, reverse rotation, and extension, the pump is driven with the cylinder 88 in its initial state with the rod 91 fully extended and the directional control valve 85 switched to its initial position, first position A. Hydraulic oil discharged from the pump is supplied to the compression pressure chamber 89 of the cylinder 88 via the pump port 81 and the compression passage 83. Meanwhile, hydraulic oil in the extension pressure chamber 90 of the cylinder 88 is returned to the tank via the extension passage 84 and the tank port 82. As a result, the cylinder 88 operates to retract the rod 91.

[0011] At this time, the sequence valve 86 closes based on the hydraulic pressure in the compression passage 83, the hydraulic pressure in the extension passage 84, and the spring 96, thereby blocking the operating passage 97. Therefore, the force based on the hydraulic pressure in the operating chamber 94 does not become greater than the elastic force of the spring 93 in the directional control valve 85. As a result, the position of the directional control valve 85 is maintained at first position A by the spring 93, and the cylinder 88 operates until the rod 91 is fully compressed.

[0012] When the cylinder 88 fully contracts the rod 91, the hydraulic pressure in the extension pressure chamber 90 and the extension passage 84 drops to approximately atmospheric pressure. At this time, the sequence valve 86 opens based on the hydraulic pressure in the compression passage 83, the hydraulic pressure in the extension passage 84, and the spring 96, thereby opening the actuation passage 97. As a result, the hydraulic oil in the compression passage 83 is supplied to the actuation chamber 94 via the actuation passage 97. Then, the force based on the hydraulic pressure in the actuation chamber 94 becomes greater than the elastic force of the spring 93 in the directional control valve 85. As a result, the position of the directional control valve 85 is switched from the first position A to the second position B based on the hydraulic pressure in the actuation chamber 94.

[0013] When the position of the directional control valve 85 is switched to the second position B, the hydraulic oil discharged from the pump is supplied to the extension pressure chamber 90 of the cylinder 88 via the pump port 81 and the extension passage 84. Meanwhile, the hydraulic oil in the compression pressure chamber 89 of the cylinder 88 is returned to the tank via the compression passage 83 and the tank port 82. As a result, the cylinder 88 operates to extend the rod 91.

[0014] At this time, the sequence valve 86 closes based on the hydraulic pressure in the compression passage 83, the hydraulic pressure in the extension passage 84, and the spring 96, thereby blocking the actuation passage 97. However, because the hydraulic oil discharged from the pump passes through the pump port 81 and the directional control valve 85 and is then supplied to the actuation chamber 94 via the actuation passage 95, the force based on the hydraulic pressure in the actuation chamber 94 becomes greater than the elastic force of the spring 93. As a result, the force based on the hydraulic pressure in the actuation chamber 94 holds the position of the directional control valve 85 at second position B, and the cylinder 88 operates until the rod 91 reaches its maximum extension state.

[0015] When the cylinder 88 extends the rod 91 to its maximum extent, the discharge of hydraulic oil from the pump is stopped. After the discharge of hydraulic oil from the pump is stopped, the direction switching valve 85 switches from the second position B to the first position A based on the spring 93. More specifically, the switching of the position of the direction switching valve 85 is performed based on the hydraulic oil in the working chamber 94 flowing to the tank port 82 through a gap in the direction switching valve 85 (shown as an oil passage 98 in FIG. 7) due to the elastic force of the spring 93. In this way, the direction switching valve 85 is switched to the first position A, which is its initial position. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-318810 Summary of the Invention [Problem to be solved by the invention]

[0017] When the above-described hydraulic circuit is used to cause the cylinder 88 to contract, reverse, and extend once, it takes a relatively long time from when the discharge of hydraulic oil from the pump is stopped until the directional control valve 85 switches to its initial position, first position A. This is because the switching of the directional control valve 85 to the first position A is performed based on the hydraulic oil in the working chamber 94 flowing to the tank port 82 through a gap in the directional control valve 85 (shown as oil passage 98 in FIG. 7) due to the elastic force of the spring 93. In other words, since it takes a long time for the hydraulic oil to flow from the working chamber 94 as described above, it takes a long time from when the discharge of hydraulic oil from the pump is stopped until the directional control valve 85 switches to first position A.

[0018] Furthermore, in order to shorten the time from when the discharge of hydraulic oil from the pump is stopped until the directional control valve 85 switches to first position A, Patent Document 1 employs the following configuration. Specifically, an oil passage 99 for hydraulically biasing the position of the directional control valve 85 toward second position B is connected to the tank port 82. Then, after the discharge of hydraulic oil from the pump is stopped as described above, the destination of the hydraulic oil from the pump is switched to the tank port 82 using a directional control valve or the like, and the pump is then driven to discharge the hydraulic oil from the pump to the tank port 82. In this way, after the discharge of hydraulic oil from the pump is stopped, the directional control valve 85 quickly switches to first position A. However, the configuration of the cylinder extension / reversal valve unit becomes more complex because it requires the provision of the oil passage 99 and a mechanism for switching the destination of the hydraulic oil from the pump between the pump port 81 and the tank port 82.

[0019] It is also possible to make the cylinder 88 retract, reverse, and extend once by setting the rod 91 of the cylinder 88 in its fully retracted state as the initial state, fully extending the rod 91 of the cylinder 88, and then returning the cylinder to its fully retracted state. This type of operation of the cylinder 88 can be achieved by reversing the connection relationship between the compression-side passage 83 and the extension-side passage 84 of the hydraulic circuit and the compression-side pressure chamber 89 and the extension-side pressure chamber 90 of the cylinder 88 from the connection relationship shown in Figure 7. When operating the cylinder 88 in this way, the above-mentioned problems are generally the same. [Means for solving the problem]

[0020] The means for solving the above problems and their effects will be described below. A cylinder retraction / reversal valve unit that solves the above problem can be installed between a cylinder equipped with a rod, a pump, and a tank. The cylinder retraction / reversal valve unit supplies hydraulic oil discharged from the pump to one of the compression pressure chamber and the extension pressure chamber in the cylinder, and returns hydraulic oil discharged from the other chamber to the tank, thereby causing the cylinder to perform a single retraction, reversal, and extension. The cylinder retraction / reversal valve unit includes a unit body, a directional control valve, and a sequence valve. The unit body is formed with a pump port that receives hydraulic oil discharged from the pump, a tank port that returns hydraulic oil discharged from the cylinder to the tank, a compression passage that can be connected to the compression pressure chamber of the cylinder, and an extension passage that can be connected to the extension pressure chamber of the cylinder. The directional control valve includes a spool that can move longitudinally within the unit body and a spring that biases the spool toward a first position, which is one end of its range of movement. The spool moves against the biasing force of a spring in the directional control valve toward a second position, which is the opposite end of its range of movement from the first position, based on hydraulic pressure in an actuation chamber formed in the unit body adjacent to the spool's first position. The unit body and the spool are configured to communicate the pump port with one of the compression-side passage and the extension-side passage when the spool is in the first position, and to communicate the other of the compression-side passage and the extension-side passage with the tank port when the spool is in the second position. The unit body and the spool are configured to communicate the pump port with the other passage and to communicate the one passage with the tank port when the spool is in the second position. The sequence valve is located in the actuation passage connecting the one passage and the actuation chamber, and opens or closes based on the hydraulic pressure in the one passage, the hydraulic pressure in the other passage, and a spring, to open or close the actuation passage. The elastic force of the spring in the sequence valve is set so that the sequence valve closes when hydraulic oil is supplied from the pump port to one of the passages and hydraulic oil is being discharged from the other passage to the tank port, and so that the sequence valve opens when the oil pressure in the other passage drops after hydraulic oil has started to be discharged from the other passage to the tank port.The working chamber is formed to communicate with the other passage when the spool is in the second position. The spool is formed with a discharge passage connected to the tank port and a communication part connecting the discharge passage to the working chamber of the unit body. The discharge passage is formed to communicate with the other passage when the spool is in the first position and to be cut off from the other passage when the spool is in the second position.

[0021] According to the above configuration, when the cylinder is caused to perform one cycle of contraction, reverse rotation, and extension, the pump is driven with the spool of the directional control valve in the first position. Hydraulic oil discharged from the pump is supplied to one of the compression pressure chambers and the extension pressure chamber in the cylinder, connected to the one of the compression pressure chambers and the extension pressure chamber, via the pump port and one of the compression passage and the extension passage. At this time, the hydraulic oil in the other of the compression pressure chambers and the extension pressure chamber in the cylinder is returned to the tank via the other of the compression passage and the extension passage and the tank port. As a result, the cylinder operates to expand and contract toward one end in the extension / contraction direction.

[0022] At this time, the sequence valve closes based on the hydraulic pressure in the compression passage, the hydraulic pressure in the extension passage, and the spring, thereby blocking the working passage. Therefore, the force based on the hydraulic pressure in the working chamber never becomes greater than the biasing force of the spring in the directional control valve. As a result, the spring holds the position of the spool in the directional control valve in the first position, so the cylinder operates to extend and retract to one end of the extension / retraction direction.

[0023] When the cylinder reaches one end of the extension / retraction direction, the hydraulic pressure in the other pressure chamber and the other passage drops to approximately atmospheric pressure. At this time, the sequence valve opens based on the hydraulic pressure in the compression passage, the hydraulic pressure in the extension passage, and the spring, thereby opening the working passage. This allows hydraulic oil in the one passage to be supplied to the working chamber via the working passage. The force based on the hydraulic pressure in the working chamber then becomes greater than the biasing force of the spring in the directional control valve. As a result, the position of the spool in the directional control valve is switched from the first position to the second position based on the hydraulic pressure in the working chamber.

[0024] When the position of the spool in the directional control valve is switched to the second position, hydraulic oil discharged from the pump is supplied to the other pressure chamber in the cylinder via the pump port and the other passage. Meanwhile, hydraulic oil in the one pressure chamber in the cylinder is returned to the tank via the one passage and the tank port. As a result, the cylinder operates to expand and contract toward the other end in the expansion / contraction direction.

[0025] At this time, hydraulic oil discharged from the pump flows into the other passage, causing the hydraulic oil in the other passage to rise. Then, because the working chamber receives the hydraulic pressure from the other passage, the force based on the hydraulic pressure in the working chamber becomes greater than the biasing force of the spring in the directional control valve. As a result, the force based on the hydraulic pressure in the working chamber holds the position of the spool in the directional control valve in the second position, causing the cylinder to extend and retract to the other end in the extension / retraction direction.

[0026] When the cylinder extends to the other end in the extension / retraction direction, the discharge of hydraulic oil from the pump is stopped. After the discharge of hydraulic oil from the pump is stopped, the spool of the directional control valve switches from the second position to the first position based on the spring of the directional control valve. Specifically, the switching of the spool position is performed based on the hydraulic oil in the working chamber quickly flowing to the tank port through the communication portion and discharge passage in the spool of the directional control valve due to the biasing force of the spring. Therefore, as described above, it does not take a long time for the hydraulic oil to flow. Therefore, it is possible to prevent the long time it takes for the spool of the directional control valve to switch to the first position, which is the initial position, due to the long time it takes for the hydraulic oil to flow. Furthermore, since it is only necessary to provide a discharge passage and a communication portion in the spool of the directional control valve to achieve this, the configuration does not become complicated.

[0027] In the cylinder extension / retraction reversal valve unit, the spool of the directional control valve moves between a first position and a second position within a hole formed in the unit body, with the outer peripheral surface of the spool in contact with the inner peripheral surface of the hole. The compression-side passage and the extension-side passage open at the inner peripheral surface of the hole. The discharge passage opens at the outer peripheral surface of the spool. The communication portion is formed between the opening of the discharge passage and the working chamber by making the gap between the outer peripheral surface of the spool and the inner peripheral surface of the hole, which come into contact with each other when the spool moves, larger at a location on the outer peripheral surface that is located between the opening of the discharge passage and the working chamber than at other locations.

[0028] According to the above configuration, of the gaps between the outer peripheral surface of the spool and the inner peripheral surface of the hole, which come into contact with each other when the spool moves, the gap at a location on the outer peripheral surface between the opening of the discharge passage and the working chamber is made larger than the gaps at other locations. This forms a communication portion connecting the opening of the discharge passage and the working chamber. In this case, it is easy to increase the flow cross-sectional area of the hydraulic oil in the communication portion, so that when the position of the spool of the directional control valve is switched from the second position to the first position, the hydraulic oil in the working chamber flows quickly to the tank port via the communication portion and the discharge passage.

[0029] In the cylinder extension / retraction reversal valve unit, among the gaps between the outer peripheral surface of the spool and the inner peripheral surface of the hole, which come into contact with each other when the spool moves, making the gap between the opening of the discharge passage and the working chamber on the outer peripheral surface larger than the gaps at other locations can be achieved by making the diameter of the part of the outer peripheral surface of the spool that is located between the opening of the discharge passage and the working chamber smaller than the diameter of the other parts.

[0030] According to the above configuration, the gap between the outer peripheral surface of the spool and the inner peripheral surface of the hole, which come into contact with each other when the spool moves, at the point on the outer peripheral surface located between the opening of the discharge passage and the working chamber can easily be made larger than the gap at other points.

[0031] In the cylinder telescopic reversal valve unit, the other of the compression-side passage and the extension-side passage may branch into a main passage and a sub-passage, each opening at the inner circumferential surface of the hole. The unit body and the spool are configured to connect the main passage and the sub-passage to the tank port when the spool is in a first position. The communication portion is configured to be located between the outer circumferential surface of the spool and the inner circumferential surface of the hole, and between the sub-passage and the working chamber when the spool is in the first position. A throttle is formed in the sub-passage to reduce the cross-sectional area of hydraulic oil flow.

[0032] According to the above configuration, when the spool of the directional control valve is in the first position, hydraulic oil discharged from the pump is supplied via the pump port and the one passage to one pressure chamber in the cylinder connected to the one passage. The hydraulic oil in the other of the compression pressure chamber and the extension pressure chamber in the cylinder is returned to the tank via the main passage, the sub-passage, and the tank port in the other passage. If a large flow of hydraulic oil flows through the sub-passage, the hydraulic pressure in the working chamber connected to the sub-passage through the communication part increases. This hydraulic pressure could move the spool from the first position to the second position against the spring of the directional control valve. Such spool movement could adversely affect stable hydraulic operation of the cylinder. However, because the sub-passage has a restriction formed to reduce the cross-sectional area of hydraulic oil flow, a large flow of hydraulic oil does not flow through the sub-passage. Therefore, as described above, when the hydraulic pressure in the working chamber connected to the sub-passage via the communication portion increases, the spool is prevented from moving from the first position to the second position against the spring of the directional control valve due to the hydraulic pressure, which in turn prevents the movement of the spool from adversely affecting the stable operation of the cylinder due to the hydraulic pressure.

[0033] In the above-mentioned cylinder extension / retraction reversal valve unit, the unit body and the spool may be configured so that when the spool is in a first position, the pump port is connected to the compression-side passage and the extension-side passage is connected to the tank port, and when the spool is in a second position, the pump port is connected to the extension-side passage and the compression-side passage is connected to the tank port. The extension-side passage branches into the main passage and the sub-passage. An opening of the discharge passage on the outer peripheral surface of the spool is configured so as to be connected to the sub-passage when the spool is in the first position and to be separated from the sub-passage when the spool is in the second position.

[0034] When the above-described cylinder is used to drive agricultural machinery, the rod is extended, which is the initial position of the cylinder. In this state, a load based on the weight of the agricultural machinery often acts on the cylinder rod in the retracting direction. As a result, when hydraulic oil discharged from the pump is supplied to the compression pressure chamber of the cylinder via the pump port and the compression passage with the spool of the directional control valve in the first position, hydraulic oil in the extension pressure chamber of the cylinder tends to flow at a high flow rate into the extension passage. However, with the above-described configuration, the throttle formed in the sub-passage prevents a large flow of hydraulic oil from flowing into the sub-passage of the extension passage. Therefore, as a large flow of hydraulic oil flows into the sub-passage, the hydraulic pressure in the working chamber connected to the sub-passage via the communication part increases, and this hydraulic pressure prevents the spool from moving from the first position to the second position against the spring of the directional control valve. [Brief explanation of the drawings]

[0035] [Figure 1] FIG. 1 is a circuit diagram showing a hydraulic circuit to which a cylinder extension / retraction reversal valve unit is applied. [Figure 2] 2 is an enlarged cross-sectional view showing a directional control valve in the cylinder extension / retraction reversal valve unit of FIG. 1. FIG. [Figure 3] FIG. 2 is a cross-sectional view showing the cylinder extension / retraction reversal valve unit of FIG. 1. [Figure 4]FIG. 2 is a cross-sectional view showing the cylinder extension / retraction reversal valve unit of FIG. 1. [Figure 5] FIG. 2 is a cross-sectional view showing the cylinder extension / retraction reversal valve unit of FIG. 1. [Figure 6] FIG. 2 is a cross-sectional view showing the cylinder extension / retraction reversal valve unit of FIG. 1. [Figure 7] FIG. 1 is a circuit diagram showing a conventional example of a hydraulic circuit that causes a cylinder to contract, reverse, and extend once. DETAILED DESCRIPTION OF THE INVENTION

[0036] Hereinafter, one embodiment of a cylinder extension / retraction reversal valve unit will be described with reference to FIGS. A cylinder 11 shown in FIG. 1 drives agricultural machinery such as a bottom plow by extending and retracting a rod 12. A cylinder telescopic / reversing valve unit 13 can be provided between the cylinder 11, the pump, and a tank in a hydraulic circuit for driving the cylinder 11. The cylinder telescopic / reversing valve unit 13 supplies hydraulic oil discharged from the pump to one of a compression pressure chamber 14 and an extension pressure chamber 15 in the cylinder 11, and returns hydraulic oil discharged from the other chamber to the tank. The cylinder telescopic / reversing valve unit 13 supplies and discharges hydraulic oil to and from the cylinder 11, causing the cylinder 11 to perform a single retraction, reversal, and extension to drive an agricultural machinery such as a bottom plow.

[0037] The cylinder extension / reversal valve unit 13 includes a unit body 16, a directional control valve 17, a sequence valve 18, and a pilot check valve 19. The unit body 16 is formed with a pump port 20 and a tank port 21. The pump port 20 is for receiving hydraulic oil discharged from the pump. The tank port 21 is for returning hydraulic oil discharged from the cylinder 11 to the tank. The unit body 16 also has a compression side passage 22 and an extension side passage 23. The compression side passage 22 can be connected to the compression side pressure chamber 14 of the cylinder 11. The extension side passage 23 can be connected to the extension side pressure chamber 15 of the cylinder 11.

[0038] The directional control valve 17 is disposed between the pump port 20 and the tank port 21 and the compression passage 22 and extension passage 23. A pilot check valve 19 is provided in the extension passage 23. The pilot check valve 19 allows hydraulic oil to flow through the extension passage 23 toward the extension pressure chamber 15 of the cylinder 11, while prohibiting hydraulic oil from flowing through the extension passage 23 toward the directional control valve 17. However, when the hydraulic pressure in the compression passage 22 is equal to or higher than a predetermined value, the pilot check valve 19 opens based on the hydraulic pressure, allowing hydraulic oil to flow through the extension passage 23 toward the directional control valve 17. The extension passage 23 is branched into a main passage 23a and a sub-passage 23b and is connected to the directional control valve 17.

[0039] The directional control valve 17 is switched between a first position A and a second position B by moving the spool. The switching of the directional control valve 17 between the first position A and the second position B is performed based on the biasing force of the spring 24 and the hydraulic pressure in the working chamber 25. That is, the directional control valve 17 is biased by the spring 24 to the first position A, which is its initial position. When the force based on the hydraulic pressure in the working chamber 25 becomes larger than the biasing force of the spring 24, the directional control valve 17 is switched from the first position A to the second position B. Furthermore, when the force based on the hydraulic pressure in the working chamber 25 becomes smaller than the biasing force of the spring 24 under this condition, the directional control valve 17 is switched from the second position B to the first position A.

[0040] When the direction switching valve 17 is switched to first position A, hydraulic oil discharged from the pump is supplied to the compression pressure chamber 14 of the cylinder 11 via the pump port 20 and the compression passage 22. At this time, the hydraulic pressure in the compression passage 22 is equal to or higher than a specified value, so the pilot check valve 19 opens. As a result, hydraulic oil discharged from the extension pressure chamber 15 of the cylinder 11 is returned to the tank via the extension passage 23 and the tank port 21. When the direction switching valve 17 is switched to second position B, hydraulic oil discharged from the pump is supplied to the extension pressure chamber 15 of the cylinder 11 via the pump port 20 and the extension passage 23. At this time, hydraulic oil in the compression pressure chamber 14 of the cylinder 11 is returned to the tank via the compression passage 22 and the tank port 21.

[0041] The sequence valve 18 is located in an actuating passage 26 that connects the compression passage 22 and the actuating chamber 25. The actuating chamber 25 is also connected to a sub-passage 23b of the extension passage 23 via an actuating passage 28. The sequence valve 18 opens and closes based on the hydraulic pressure in the compression passage 22, the hydraulic pressure at a location in the extension passage 23 closer to the cylinder 11 than the pilot check valve 19, and the elastic force of a spring 27. The sequence valve 18 opens and closes the actuating passage 26 through such opening and closing. The elastic force of the spring 27 in the sequence valve 18 is set to achieve the following (a) and (b): (a) The sequence valve 18 closes when hydraulic oil is supplied from the pump port 20 to the compression passage 22 and when hydraulic oil is discharged from the extension passage 23 to the tank port 21. (b) After the hydraulic oil starts to be discharged from the extension passage 23 to the tank port 21, the sequence valve 18 opens when the hydraulic pressure in the extension passage 23 drops to approximately atmospheric pressure.

[0042] When the cylinder 11 is caused to retract, reverse, and extend once, the directional control valve 17 and the sequence valve 18 are operated as follows: With the cylinder 11 fully extended and the directional control valve 17 switched to first position A, which is its initial position, hydraulic oil discharged from the pump is supplied to the compression pressure chamber 14 of the cylinder 11 via the pump port 20 and the compression passage 22. This causes the cylinder 11 to retract. As a result, hydraulic oil discharged from the extension pressure chamber 15 of the cylinder 11 is returned to the tank via the extension passage 23 and the tank port 21.

[0043] At this time, the sequence valve 18 closes based on the oil pressure in the compression-side passage 22, the oil pressure in the extension-side passage 23 closer to the cylinder 11 than the pilot check valve 19, and the elastic force of the spring 27, thereby blocking the operating passage 26. Therefore, the oil pressure in the operating chamber 25 does not rise, and the force based on that oil pressure does not exceed the biasing force of the spring 24 in the directional control valve 17. As a result, the spring 24 holds the directional control valve 17 in the first position A, so that the cylinder 11 operates to be in its most compressed state.

[0044] When the cylinder 11 is fully compressed, the hydraulic pressure in the extension pressure chamber 15 and the extension passage 23 drops to approximately atmospheric pressure. At this time, the sequence valve 18 opens based on the hydraulic pressure in the compression passage 22, the hydraulic pressure at a location in the extension passage 23 closer to the cylinder 11 than the pilot check valve 19, and the elastic force of the spring 27, thereby opening the working passage 26. As a result, the hydraulic oil in the compression passage 22 is supplied to the working chamber 25 via the working passage 26. Then, the force based on the hydraulic pressure in the working chamber 25 becomes greater than the biasing force of the spring 24 in the directional control valve 17. As a result, the hydraulic pressure in the working chamber 25 switches the directional control valve 17 from the first position A to the second position B.

[0045] When the directional control valve 17 is switched to the second position B, the hydraulic oil discharged from the pump is supplied to the extension pressure chamber 15 of the cylinder 11 via the pump port 20 and the extension passage 23. This causes the cylinder 11 to reverse from its contracted state and extend. Meanwhile, the hydraulic oil in the compression pressure chamber 14 of the cylinder 11 is returned to the tank via the compression passage 22 and the tank port 21. As a result, the cylinder 11 extends.

[0046] At this time, hydraulic oil discharged from the pump is also supplied to the working chamber 25 via the sub-passage 23b of the extension-side passage 23 and the working passage 28, so that the force based on the hydraulic pressure in the working chamber 25 becomes greater than the biasing force of the spring 24 in the directional control valve 17. As a result, the force based on the hydraulic pressure in the working chamber 25 holds the directional control valve 17 at the second position B, so that the cylinder 11 operates to be in the most extended state.

[0047] <Detailed structure of directional control valve 17> As shown in Fig. 2, the directional control valve 17 includes a spool 31 that is movable in the longitudinal direction inside the unit body 16, and the spring 24 that biases the spool 31 toward one end of its range of movement. The directional control valve 17 is switched between the first position A and the second position B by moving the spool 31 between one end and the other end of the range of movement. That is, when the spool 31 moves to the first position A, which is one end of the range of movement, the directional control valve 17 is switched to the first position A in Fig. 1. When the spool 31 moves to the second position B, which is the other end of the range of movement, the directional control valve 17 is switched to the second position B in Fig. 1.

[0048] 2 and 3 show a state in which the spool 31 has moved to the first position A. FIGS. 4 and 5 show a state in which the spool 31 is between the first position A and the second position B. FIG. 6 shows a state in which the spool 31 has moved to the second position B. As can be seen from these figures, the spool 31 moves between the first position A and the second position B within the hole 32 formed in the unit body 16 while the outer circumferential surface of the spool 31 contacts the inner circumferential surface of the hole 32.

[0049] As shown in FIG. 2, the unit body 16 is formed with the working chamber 25 adjacent to the first position A of the spool 31. The working chamber 25 is located on the opposite side of the spring 24 in the unit body 16 with the spool 31 in between. The working chamber 25 is formed by extending the hole 32 in the opposite direction from the spring 24. The working chamber 25 is connected to the working passage 26 formed in the unit body 16. The spool 31 is biased toward the first position A by the biasing force of the spring 24. Furthermore, the spool 31 can move toward the second position B against the biasing force of the spring 24 based on the hydraulic pressure in the working chamber 25.

[0050] The hole 32 of the unit body 16 is connected to the tank port 21. A discharge passage 33 connected to the tank port 21 is formed in the spool 31. The discharge passage 33 extends inside the spool 31 along the center line of the spool 31 and is formed to extend from the center line toward the outer circumferential surface. As a result, an opening 33a of the discharge passage 33 opens on the outer circumferential surface of the spool 31. The opening 33a extends in an annular shape along the outer circumferential surface of the spool 31.

[0051] A groove 34 is formed on the outer peripheral surface of the spool 31, at a position closer to the spring 24 than the opening 33a of the discharge passage 33. The groove 34 is formed to extend in an annular shape along the outer peripheral surface of the spool 31. The width of the groove 34 in the direction of the center line of the spool 31 is wider than the opening 33a of the discharge passage 33. A supply passage 35 formed in the unit body 16 is connected to the groove 34. The supply passage 35 is connected to the pump port 20 and opens to the inner peripheral surface of the hole 32 in the unit body 16 so as to connect to the groove 34. Because the width of the groove 34 is wide, the groove 34 and the opening 35a of the supply passage 35 are always connected when the spool 31 is moved between the first position A and the second position B.

[0052] An opening 22a of the compression-side passage 22 is open on the inner peripheral surface of the hole 32 in the unit body 16, and an opening 24a of the main passage 23a and an opening 24b of the sub-passage 23b of the extension-side passage 23 are open on the inner peripheral surface of the hole 32. The opening 24a of the main passage 23a is located closer to the spring 24 than the opening 35a of the supply passage 35. The opening 24b of the sub-passage 23b is located closer to the working chamber 25 than the opening 35a of the supply passage 35. The unit body 16 and the spool 31 are formed so that the positions of the openings 22a, 24a, 24b, and 35a on the inner peripheral surface of the hole 32 and the positions of the groove 34 and the opening 33a of the discharge passage 33 on the outer peripheral surface of the spool 31 are connected as follows:

[0053] That is, when the spool 31 is in the first position A, the groove 34 is connected to the opening 22a of the compression-side passage 22. Furthermore, the opening 24a of the main passage 23a is open to the tank port 21, and the opening 24b of the sub-passage 23b is connected to the opening 33a of the discharge passage 33. As a result, when the spool 31 is in the first position A, the pump port 20 and the supply passage 35 are connected to the compression-side passage 22, and the extension-side passage 23 is connected to the tank port 21.

[0054] 6, when the spool 31 is in the second position B, the groove 34 is connected to the opening 24a of the main passage 23a in the extension-side passage 23. Furthermore, the opening 22a of the compression-side passage 22 is connected to the opening 33a of the discharge passage 33. As a result, when the spool 31 is in the second position B, the pump port 20 is connected to the main passage 23a in the extension-side passage 23, and the compression-side passage 22 is connected to the tank port 21. In this state, the opening 33a of the discharge passage 33 is blocked from the opening 24a of the main passage 23a and the opening 24b of the sub-passage 23b in the extension-side passage 23. This is achieved by positioning the opening 33a of the discharge passage 33 away from the opening 24a of the main passage 23a and the opening 24b of the sub-passage 23b.

[0055] Furthermore, at this time, the opening 24b of the sub-passage 23b in the extension-side passage 23 is connected to the working chamber 25. That is, when the spool 31 is in the second position B, the working chamber 25 is formed to communicate with the opening 24b of the sub-passage 23b. The working passage 28 in FIG. 1 shows the connection state when the sub-passage 23b and the working chamber 25 are connected in this manner.

[0056] <Operation of the spool 31 in the directional control valve 17> To cause the cylinder 11 to retract, reverse, and extend once, the spool 31 of the directional control valve 17 is operated as follows. That is, to retract the cylinder 11 from its fully extended state, the pump is driven with the spool 31 of the directional control valve 17 in first position A, as shown in Figures 2 and 3. As a result, hydraulic oil discharged from the pump is supplied to the compression pressure chamber 14 of the cylinder 11 via the pump port 20 and the compression passage 22. Furthermore, hydraulic oil discharged from the extension pressure chamber 15 of the cylinder 11 is returned to the tank via the main passage 23a and sub-passage 23b of the extension passage 23 and the tank port 21. As a result, the cylinder 11 retracts.

[0057] When the cylinder 11 is fully compressed, the hydraulic pressure in the working chamber 25 increases due to the operation of the sequence valve 18, which is based on a decrease in hydraulic pressure in the extension passage 23 upstream of the pilot check valve 19. As the hydraulic pressure in the working chamber 25 increases, the spool 31, as shown in FIGS. 4 and 5, gradually approaches second position B shown in FIG. 6. When the spool 31 moves to second position B as shown in FIG. 6, hydraulic oil discharged from the pump is supplied to the extension pressure chamber 15 in the cylinder 11 via the pump port 20 and the main passage 23a of the extension passage 23. Furthermore, hydraulic oil in the compression pressure chamber 14 in the cylinder 11 is returned to the tank via the compression passage 22 and the tank port 21. As a result, the cylinder 11 reverses from the contracted state and extends.

[0058] While the cylinder 11 is extended, i.e., while the spool 31 is at the second position B, the sub-passage 23b of the extension-side passage 23 is connected to the working chamber 25. Therefore, the hydraulic pressure of the extension-side passage 23 is received by the working chamber 25 via the sub-passage 23b. As a result, the force based on the hydraulic pressure of the working chamber 25 becomes greater than the biasing force of the spring 24, so the spool 31 is held at the second position B. Then, when the cylinder 11 is fully extended, the pump is stopped. This also stops the pump from discharging hydraulic oil to the extension-side passage 23.

[0059] After the discharge of hydraulic oil from the pump is stopped, the spool 31 moves from the second position B to the first position A, which is its initial position, based on the biasing force of the spring 24. More specifically, the spool 31 is pushed toward the first position A by the biasing force of the spring 24. When the spool 31 is pushed by the biasing force of the spring 24 in this manner, the hydraulic oil in the working chamber 25 flows between the outer peripheral surface of the spool 31 and the inner peripheral surface of the hole 32 and into the opening 33a of the discharge passage 33. This causes the spool 31 to move from the second position B to the first position A, which is its initial position.

[0060] However, if the hydraulic oil in the working chamber 25 does not easily flow to the opening 33a of the discharge passage 33, it takes time to discharge the hydraulic oil from the working chamber 25 to the discharge passage 33. In this case, it takes a long time for the spool 31 to return from the second position B to the initial position, the first position A, after the pump is stopped. To address this issue, the cylinder extension / reversal valve unit 13 is formed with a communication part 36 that connects the opening 33a of the discharge passage 33 to the working chamber 25.

[0061] 2, the communication section 36 is formed by making the gap between the outer peripheral surface of the spool 31 and the inner peripheral surface of the hole 32, which come into contact with each other when the spool 31 moves, larger than the gap at other locations on the outer peripheral surface at a location located between the opening 33a of the discharge passage 33 and the working chamber 25. More specifically, the communication section 36 is realized by making the diameter of the portion of the outer peripheral surface of the spool 31 located between the opening 33a of the discharge passage 33 and the working chamber 25 smaller than the diameter of the other portions.

[0062] The communication portion 36 connects the opening 33a of the discharge passage 33 to the working chamber 25 when the spool 31 is in the first position A, the second position B, or any position therebetween. Figures 2 and 3 show the communication portion 36 when the spool 31 is in the first position A. Figures 4 and 5 show the communication portion 36 when the spool 31 is between the first position A and the second position B. Figure 6 shows the communication portion 36 when the spool 31 is in the second position B.

[0063] By forming the communication portion 36 in the cylinder extension / retraction reversal valve unit 13, the hydraulic oil in the working chamber 25 can easily flow to the opening 33a of the discharge passage 33 when the spool 31 is moved from the second position B to the first position A, which is the initial position, as described above. In other words, when the spool 31 is pushed toward the first position A by the biasing force of the spring 24, the hydraulic oil in the working chamber 25 quickly flows to the opening 33a of the discharge passage 33 via the communication portion 36. The working passage 38 in FIG. 1 represents the flow path of the hydraulic oil when the hydraulic oil in the working chamber 25 flows to the opening 33a of the discharge passage 33 via the communication portion 36 in this way.

[0064] As described above, the hydraulic oil in the working chamber 25 flows quickly to the opening 33a of the discharge passage 33 via the communication portion 36, so that it does not take long for the hydraulic oil to be discharged from the working chamber 25 to the discharge passage 33. Furthermore, since it does not take long for the hydraulic oil to be discharged, it also prevents the spool 31 from taking a long time to return from the second position B to the first position A, which is the initial position, after the pump is stopped.

[0065] <Details of the sub-passage 23b in the extension-side passage 23> 2, when the spool 31 is in the first position A, the opening 24b of the sub-passage 23b in the extension-side passage 23 is connected to the opening 33a of the discharge passage 33. Therefore, when the spool 31 is in the first position A, the communication portion 36 is located between the outer peripheral surface of the spool 31 and the inner peripheral surface of the hole 32, and between the opening 24b of the sub-passage 23b and the working chamber 25. In other words, the communication portion 36 is formed to be located in such a position.

[0066] In this case, the following occurs when the cylinder 11 is contracted during a single cycle of contraction, reversal, and extension: When the cylinder 11 is contracted, hydraulic oil in the extension pressure chamber 15 of the cylinder 11 is returned to the tank via the main passage 23a and sub-passage 23b of the extension passage 23 and the tank port 21. If a large flow of hydraulic oil flows through the sub-passage 23b at this time, the hydraulic pressure in the working chamber 25 connected to the sub-passage 23b via the communication portion 36 increases, and this hydraulic pressure may cause the spool 31 to move from the first position A toward the second position B against the spring 24. This movement of the spool 31 may adversely affect the stable operation of the cylinder 11 by hydraulic pressure.

[0067] To address this issue, as shown in Figure 1, a throttle 37 is formed in the sub-passage 23b to reduce the cross-sectional area of hydraulic oil flow. By forming the throttle 37 in the sub-passage 23b in this manner, a large flow rate of hydraulic oil does not flow through the sub-passage 23b. Therefore, as described above, when the hydraulic pressure in the working chamber 25 connected to the sub-passage 23b via the communication portion 36 increases, the spool 31 is prevented from moving from the first position A toward the second position B against the spring 24 due to the increased hydraulic pressure. As a result, the movement of the spool 31 is prevented from adversely affecting the stable operation of the cylinder 11 by the hydraulic pressure.

[0068] Next, the operation and effect of the cylinder extension / retraction reversal valve unit of this embodiment will be described. (1) After the cylinder 11 has been contracted, reversed, and extended once, the spool 31 of the directional control valve 17 in the cylinder extension / reversal valve unit 13 is returned from the second position B to the first position A, which is its initial position. By forming the communication portion 36 in the cylinder extension / reversal valve unit 13, when the spool 31 is moved from the second position B to the first position A after the pump is stopped, the hydraulic oil in the working chamber 25 easily flows to the opening 33a of the discharge passage 33. As a result, it is no longer necessary for the hydraulic oil to be discharged from the working chamber 25 to the discharge passage 33. This prevents the spool 31 from returning from the second position B to the first position A after the pump is stopped from taking a long time. Furthermore, since this can be achieved by simply providing the discharge passage 33 and the communication portion 36 in the spool 31 of the directional control valve 17, the configuration does not become complicated.

[0069] (2) Of the gaps between the outer peripheral surface of the spool 31 and the inner peripheral surface of the hole 32, which come into contact with each other when the spool 31 moves, the gap at a location on the outer peripheral surface between the opening 33a of the discharge passage 33 and the working chamber 25 is made larger than the gaps at other locations. As a result, a communication portion 36 is formed between the opening 33a of the discharge passage 33 and the working chamber 25, connecting the two. In this case, it is easy to increase the flow cross-sectional area of the hydraulic oil in the communication portion 36, so that when the position of the spool 31 is switched from the second position B to the first position A, the hydraulic oil in the working chamber 25 flows quickly to the tank port 21 via the communication portion 36 and the discharge passage 33.

[0070] (3) The above (2) is achieved by making the diameter of the portion of the outer circumferential surface of the spool 31 that is located between the opening 33a of the discharge passage 33 and the working chamber 25 smaller than that of the other portions. In this case, of the gaps between the outer circumferential surface of the spool 31 and the inner circumferential surface of the hole 32 that come into contact with each other when the spool 31 moves, the gap at the portion of the outer circumferential surface that is located between the opening 33a of the discharge passage 33 and the working chamber 25 can be easily made larger than the gaps at other portions.

[0071] (4) A throttle 37 is formed in the sub-passage 23b to reduce the cross-sectional area of hydraulic oil flow. Therefore, when the cylinder 11 is contracted to perform a single contraction, reversal, and extension, a large flow rate of hydraulic oil does not flow through the sub-passage 23b, and the hydraulic pressure in the working chamber 25 connected to the sub-passage 23b via the communication portion 36 does not increase accordingly. This prevents the spool 31 from moving from the first position A toward the second position B against the spring 24, which would otherwise be caused by a sudden increase in the hydraulic pressure in the working chamber 25. As a result, the movement of the spool 31 is prevented from adversely affecting the stable operation of the cylinder 11 by hydraulic pressure.

[0072] (5) When driving an agricultural implement using the cylinder 11, the rod 12 is extended, which is the initial position of the cylinder 11. In this state, a load based on the weight of the agricultural implement often acts on the rod 12 of the cylinder 11 in the retracting direction. As a result, when the spool 31 of the directional control valve 17 is in first position A and hydraulic oil discharged from the pump is supplied to the compression pressure chamber 14 of the cylinder 11 via the pump port 20 and the compression passage 22, a large amount of hydraulic oil in the extension pressure chamber 15 of the cylinder 11 tends to flow into the extension passage 23. However, the flow of a large amount of hydraulic oil into the sub-passage 23b of the extension passage 23 is suppressed by the throttle 37 formed in the sub-passage 23b.

[0073] The above embodiment can be modified as follows, for example: The above embodiment and the following modifications can be combined and implemented within the scope of technical compatibility. When the cylinder 11 is caused to retract, reverse, and extend once, the rod 12 of the cylinder 11 may be set to the most retracted state as the initial state, and the rod 12 of the cylinder 11 may be fully extended before the cylinder is returned to the most retracted state. Depending on the agricultural implement driven by the cylinder 11, it may also be possible to operate the cylinder 11 as described above. In this case, the above operation of the cylinder 11 can be achieved by reversing the connection relationship between the compression-side passage 22 and the extension-side passage 23 and the compression-side pressure chamber 14 and the extension-side pressure chamber 15 of the cylinder 11 from the relationship shown in FIG. 1.

[0074] The aperture 37 does not necessarily have to be provided. The communication section 36 does not necessarily have to be realized by making the portion of the outer circumferential surface of the spool 31 located between the opening 33a of the discharge passage 33 and the working chamber 25 smaller in diameter than the other portions. For example, the communication section 36 may be realized by forming a groove in the portion of the outer circumferential surface of the spool 31 located between the opening 33a of the discharge passage 33 and the working chamber 25, connecting the opening 33a and the working chamber 25. [Explanation of symbols]

[0075] 11...Cylinder 12...Rod 13...Cylinder extension / reversal valve unit 14...Compression side pressure chamber 15...Extension pressure chamber 16...Unit body 17...Directional switching valve 18...Sequence valve 19...Pilot check valve 20...Pump port 21...Tank port 22...Contraction side passage 22a...Opening 23...Extension side passage 23a...Main passage 23b...Sub-passage 24a, 24b...opening 24...Spring 25...Operating chamber 26...Operating passage 31...Spool 32...hole 33…Discharge passage 33a...Opening 34...Groove 35…Supply passage 35a...Opening 36…Communication part

Claims

1. A cylinder retraction / extension valve unit can be installed between a cylinder having a rod, a pump, and a tank, and causes the cylinder to perform one contraction, reversal, and extension by supplying hydraulic oil discharged from the pump to one of a compression-side pressure chamber and an extension-side pressure chamber in the cylinder and returning hydraulic oil discharged from the other chamber to the tank, The device comprises a unit body, a directional control valve, and a sequence valve, The unit body is formed with a pump port for receiving hydraulic oil discharged from the pump, a tank port for returning hydraulic oil discharged from the cylinder to the tank, a compression side passage connectable to the compression side pressure chamber of the cylinder, and an extension side passage connectable to the extension side pressure chamber of the cylinder, the directional control valve includes a spool that is movable in a longitudinal direction inside the unit body, and a spring that biases the spool toward a first position that is one end of a movable range of the spool; the spool moves against the biasing force of the spring of the directional control valve toward a second position, which is an end of the movement range opposite to the first position, based on hydraulic pressure in an actuation chamber formed in the unit body so as to be adjacent to the first position of the spool, the unit body and the spool are formed so that, when the spool is in the first position, the pump port is communicated with one of the compression side passage and the extension side passage, and the other of the compression side passage and the extension side passage is communicated with the tank port; the unit body and the spool are formed so as to communicate the pump port with the other passage and to communicate the one passage with the tank port when the spool is in the second position; the sequence valve is provided in the middle of an actuation passage connecting the one passage and the actuation chamber, and opens or closes the actuation passage by opening or closing based on the oil pressure of the one passage, the oil pressure of the other passage, and a spring; an elastic force of the spring in the sequence valve is set so that the sequence valve closes when hydraulic oil is supplied from the pump port to one of the passages and hydraulic oil is being discharged from the other passage to the tank port, and so that the sequence valve opens when hydraulic oil pressure in the other passage drops after hydraulic oil starts to be discharged from the other passage to the tank port, the operating chamber is formed to communicate with the other passage when the spool is in the second position; The spool is formed with a discharge passage connected to the tank port and a communication portion connecting the discharge passage to the working chamber of the unit body, The exhaust passage is connected to the other passage when the spool is in the first position, and is disconnected from the other passage when the spool is in the second position.

2. the spool of the directional control valve moves between the first position and the second position by moving within a hole formed in the unit body while the outer peripheral surface of the spool contacts the inner peripheral surface of the hole, the compression-side passage and the extension-side passage open at an inner circumferential surface of the hole, The discharge passage opens at the outer peripheral surface of the spool, 2. The cylinder telescopic reversal valve unit according to claim 1, wherein the communication portion is formed between the opening of the discharge passage and the working chamber by making the gap between the outer peripheral surface of the spool and the inner peripheral surface of the hole, which come into contact with each other when the spool moves, larger than the gaps at other locations on the outer peripheral surface that are located between the opening of the discharge passage and the working chamber.

3. 3. A cylinder telescopic reversal valve unit according to claim 2, wherein the gap between the outer peripheral surface of the spool and the inner peripheral surface of the hole, which come into contact with each other when the spool moves, at a portion of the outer peripheral surface located between the opening of the discharge passage and the working chamber is made larger than the gap at other portions by making the diameter of the portion of the outer peripheral surface of the spool located between the opening of the discharge passage and the working chamber smaller than the diameter of the other portions.

4. the other of the compression-side passage and the extension-side passage branches into a main passage and a sub-passage, each of which opens at an inner circumferential surface of the hole, the unit body and the spool are formed to communicate the main passage and the sub-passage with the tank port when the spool is in the first position; the communication portion is formed to be located between an outer peripheral surface of the spool and an inner peripheral surface of the hole, and between the sub-passage and the working chamber, when the spool is in the first position; 4. The cylinder extension / retraction reversal valve unit according to claim 2, wherein a throttle is formed in the sub-passage to reduce a cross-sectional area of the hydraulic oil flow.

5. the unit body and the spool are formed so that, when the spool is in the first position, the pump port is communicated with the compression-side passage and the extension-side passage is communicated with the tank port, and, when the spool is in the second position, the pump port is communicated with the extension-side passage and the compression-side passage is communicated with the tank port, The extension-side passage branches into the main passage and the sub-passage, 5. The cylinder telescopic reversal valve unit according to claim 4, wherein an opening of the discharge passage on the outer peripheral surface of the spool is formed so as to be connected to the sub-passage when the spool is in the first position and so as to be separated from the sub-passage when the spool is in the second position.

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