Fluid pressure cylinder

Abstract

To provide a fluid pressure cylinder capable of suppressing generation of high frequency sound even when a cushion mechanism is in operation.SOLUTION: The cushion seal 50 is a cylindrical member, and has an outside radius substantially equal to that of the cushion-seal housing part 43 of the port 40 shown in FIG. 3, and an inside radius substantially equal to the outside radius of the 33A of the protruding portion of the piston 33. Further, a taper 51 is formed in which the inside diameter of the end portion on the side facing the working oil chamber 17A is larger than the outside diameter of the plungers 33, which are the other portions. The angle of the taper 51 is formed to be 8° or more and 12° or less. The cushion-seal storage part 43 is formed to be longer in the axial direction than the cushion seal 50 described later, and the cushion seal 50 is movable inside the cushion-seal storage part 43 along the axial direction in a state of being stored in the cushion-seal storage part 43.SELECTED DRAWING: Figure 6

Description

[Technical Field]

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

[0002] The industrial machine disclosed in FIG. 1 of Patent Document 1 is provided with a rack (rod) that moves linearly by a hydraulic cylinder and a pinion gear fixed to the base of the work machine, as a rotation device for the work machine, as shown in FIG. 2 of the present application. Such a turning device turns the working machine by converting linear motion caused by extension and contraction of a hydraulic cylinder into rotational motion by a rack and pinion gear.

[0003] Incidentally, the above-mentioned slewing device stops operating when the hydraulic cylinder reaches the stroke end. However, if the cylinder end is reached while maintaining the normal operating speed, a strong impact is generated on the hydraulic cylinder due to the inertial forces of the rack and the work machine in addition to the power of the cylinder, which leads to a shortened lifespan of the equipment.

[0004] For this reason, hydraulic cylinders have traditionally been equipped with cushioning mechanisms. A typical cushioning mechanism is one that limits the flow rate of hydraulic oil when the rack (rod) approaches the stroke end by a specified distance, thereby slowing down the operating speed of the rack and reducing the impact when it reaches the stroke end.

[0005] An example of the structure of such a cushion mechanism is one in which a plunger is provided in a cylinder head and a port into which the plunger is inserted is provided in a piston, as shown in Figures 12 and 13 of the present application. The plunger has an internal flow path for hydraulic oil, and is also a component that connects the hydraulic oil chamber with the outside. The port is provided with a cushion seal inside that blocks the flow path between the outer circumferential surface of the plunger and the inner circumferential surface of the port when the plunger is inserted into the port beyond a predetermined length.

[0006] The plunger has a cushion hole formed in the hydraulic oil chamber to connect the hydraulic oil chamber to the flow path inside the plunger while it is inserted into the port. This cushion hole is narrower than the opening at the tip of the plunger and limits the flow rate of hydraulic oil entering the flow path inside the plunger, slowing down the movement of the rack (rod). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2016-114077 Summary of the Invention [Problem to be solved by the invention]

[0008] In a cylinder equipped with the above-described cushion mechanism, a cushion seal housed inside the piston blocks the flow path formed between the outer circumferential surface of the plunger and the inner circumferential surface of the port. However, when the flow path is blocked by such a structure, hydraulic oil leaks between the cushion seal and the surface with which it comes into contact (in this cushion mechanism, the inner circumferential surface of the groove and the outer circumferential surface of the plunger). This causes an oil leak, in which a small amount of hydraulic oil passes through the cushion seal.

[0009] The amount of hydraulic oil passing through an oil leak is extremely small compared to the amount of hydraulic oil flowing in and out of the hydraulic oil chamber through the normal flow path, so it does not affect the operation of the rod. However, the resistance of the hydraulic oil passing through the cushion seal is extremely large, which can generate high-frequency noise that can be observed by operators. This high-frequency noise is often generated especially when the cylinder is retracted.

[0010] The industrial machine disclosed in FIG. 1 of Patent Document 1 includes a cylinder that extends to cause the work machine to turn left, and a cylinder that extends to cause the work machine to turn right. These cylinders retract when the paired cylinder extends. Therefore, whether the work machine turns left or right, one cylinder retracts, which can generate high-frequency noise regardless of the turning direction. High-frequency noise itself does not directly impede work, but it can indirectly impede work by making workers believe that the equipment is malfunctioning or reducing their ability to concentrate while working.

[0011] In view of the above circumstances, an object of the present invention is to provide a fluid pressure cylinder that can suppress the generation of high frequency noise even when the cushion mechanism is in operation. [Means for solving the problem]

[0012] A first invention is a fluid pressure cylinder equipped with a cushion mechanism that reduces the operating speed of a piston by restricting the flow rate of working fluid flowing out of a working fluid chamber, wherein the cushion mechanism includes a plunger and a port into which the plunger is inserted, the plunger is provided on one of the piston or the cylinder head so as to protrude into the working fluid chamber, and the port is provided on the other of the piston or the cylinder head, a cushion seal accommodating portion is formed inside the port and a cylindrical cushion seal is accommodated inside the cushion seal, and the cushion seal is tapered so that the inner diameter of the end on the working fluid chamber side is larger than other portions.

[0013] A second invention provides the cylinder head according to the first invention, wherein the piston includes the port and an in-piston flow path formed therein, the plunger includes an in-plunger flow path inside the plunger that connects the inside of the working fluid chamber to the outside, an opening of the plunger flow path in the working fluid chamber is formed at a tip end of the plunger and at a circumferential surface of the plunger, the opening at the circumferential surface having an area smaller than that of the opening at the tip end, the cushion seal accommodating portion is formed axially longer than the cushion seal and accommodates the cushion seal movably along its axial direction, and the in-piston flow path is formed inside the working fluid chamber of its own a surface of the cushion seal housing facing the piston communicates with an end of the cushion seal housing on a side farther from the cylinder head; when the plunger passes the taper of the cushion seal and is inserted into the port, the cushion seal moves to the side of the cushion seal housing farther from the cylinder head to block the flow path within the piston, with the opening in the circumferential surface of the plunger becoming the dominant opening; and when the plunger is pulled out of the port, the cushion seal moves to the cylinder head side of the cushion seal housing to connect the flow path within the piston, with the opening in the tip of the plunger becoming the dominant opening.

[0014] A third invention is the fluid pressure cylinder according to the first or second invention, characterized in that the taper angle is equal to or greater than 1° and equal to or less than 20°.

[0015] A fourth invention is a fluid pressure cylinder characterized in that the piston according to the first invention is configured by combining a first piston member having a surface facing the working fluid chamber and a second piston member arranged on the side of the first piston member farther from the cylinder head, the port is formed coaxially in the first piston member and the second piston member, and the cushion seal accommodating portion is formed in only one of the first piston member or the second piston member from one end face of the first piston member or the second piston member, with a portion having approximately the same diameter as the cushion seal.

[0016] A fifth invention is a fluid pressure cylinder in which the piston according to the first invention is configured by combining a first piston member having a surface facing the working fluid chamber with a second piston member arranged on the side of the first piston member farther from the cylinder head, and an outer circumferential seal accommodating portion is formed on the outer periphery of the first piston member having a smaller diameter than other portions, and the outer circumferential seal accommodating portion is formed such that only one of the first piston member or the second piston member has a smaller diameter from one end face of the first piston member or the second piston member. [Effects of the Invention]

[0017] By using the fluid pressure cylinder according to the present invention, it is possible to provide a fluid pressure cylinder that can suppress the generation of high frequency noise even when the cushion mechanism is in operation. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a side view of a forwarder equipped with a cushion mechanism according to an embodiment of the present invention. [Figure 2] 2 is a diagram showing a turning device provided in the forwarder shown in FIG. 1. FIG. [Figure 3] FIG. 3 is an enlarged view of a portion I surrounded by a dashed dotted line shown in FIG. [Figure 4] 1A is a front view of a cushion seal according to an embodiment of the present invention, FIG. 1B is a cross-sectional view taken along line AA, and FIG. 1C is a rear view. [Figure 5] FIG. 1A is a front view of a conventional cushion seal, and FIG. 1B is a cross-sectional view taken along line BB. [Figure 6] FIG. 4 is an enlarged view of a portion II surrounded by a dashed dotted line in FIG. 3. [Figure 7] 3 is an enlarged view of a portion I indicated by a dashed dotted line in FIG. 2 when the first stage of the cushion mechanism is activated. [Figure 8] 8 is an enlarged view of a portion III surrounded by a dashed dotted line shown in FIG. 7. [Figure 9] 3 is an enlarged view of a portion indicated by a dashed dotted line I in FIG. 2 when the second stage of the cushion mechanism is activated and the piston reaches the stroke end on the contraction side. FIG. [Figure 10] 10 is an enlarged view of a portion IV surrounded by a dashed dotted line shown in FIG. 9. [Figure 11] 10 is an enlarged view of a portion indicated by a dashed dotted line IV in FIG. 9 when the rod starts to extend from the shortened stroke end. [Figure 12] FIG. 1 is a diagram showing a cushion mechanism portion of a hydraulic cylinder equipped with a conventional cushion seal. [Figure 13] FIG. 13 is an enlarged view of a portion V in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0019] A hydraulic cylinder according to one embodiment of the present invention will be described below with reference to the drawings, using a forwarder, a type of forestry work machine, as an example. It should be noted that the drawings are schematic. Therefore, it should be noted that the relationships and ratios between thickness and planar dimensions may differ from those in reality, and the drawings may also include portions where the relationships and ratios between dimensions differ. Furthermore, the embodiments shown below are merely examples of devices and methods that embody the technical concept of the present invention, and the technical concept of the present invention is not limited to the following embodiments in terms of the materials, shapes, structures, arrangements, etc. of the components.

[0020] In the following explanations and drawings, the direction in which the forwarder moves forward (the direction in which the forwarder moves forward as seen from the driver in the driver's seat) may be referred to as "forward." Similarly, in the following explanations and drawings, the direction in which the forwarder moves backward may be referred to as "rear." In addition, the left-hand side when the driver is sitting in the driver's seat will be referred to as the "left side," and the right-hand side when the driver is sitting in the driver's seat will be referred to as the "right side." Therefore, in the following explanations and drawings, expressions such as "front side of the vehicle," "rear side of the vehicle," "right side of the vehicle," "left side of the vehicle," "outer side in the vehicle width direction," and "inner side in the vehicle width direction" may be used in accordance with these definitions.

[0021] <Forwarder structure> The structure of the forwarder 1 will be described with reference to FIG. The forwarder 1 is equipped with a self-propelled crawler-type traveling device 3 at the bottom of a chassis frame 2. A driver's seat 4 is provided at the front of the vehicle and a loading platform 5 is provided at the rear of the vehicle above the chassis frame 2. A work machine 6 for loading and unloading lumber from the loading platform 5 is mounted on the chassis frame 2 between the driver's seat 4 and the loading platform 5. The hydraulic cylinder according to the present invention is provided in the swing device 10 of the work machine 6. Therefore, hereinafter, only the swing device 10 portion will be described, and descriptions of other portions will be omitted or only briefly described.

[0022] <Structure of the swivel device> The structure of the swivel device 10 will be described with reference to FIG. The slewing device 10 is configured approximately symmetrically with respect to the center of the vehicle in the left-right direction, and includes a gear housing 11, a slewing gear 12, a left front cylinder 13, a right front cylinder 14, a front rack 15, a left rear cylinder 16, a right rear cylinder 17, and a rear rack 18.

[0023] The gear housing 11 is located in the center of the slewing device 10, with its lower part fixed to the chassis frame 2 shown in FIG. 1, and the working machine 6 being mounted on its upper part. The swivel gear 12 is accommodated in the center of the interior of the gear housing 11 so as to be rotatable around an axis extending in the vertical direction of the vehicle. The left front cylinder 13 and the right front cylinder 14 are single-acting cylinders fixed coaxially to the front side of the gear housing 11 so that their axial directions run along the left-right direction of the vehicle, and share a front rack 15 . The left rear cylinder 16 and the right rear cylinder 17 are single-acting cylinders fixed coaxially to the rear side of the gear housing 11 so that their axial directions run along the left-right direction of the vehicle, and share a rear rack 18 .

[0024] The front rack 15 and the rear rack 18 are rods that are long in the left-right direction of the vehicle, and have gear teeth formed thereon to mesh with the turning gear 12, with the front rack 15 meshing with the turning gear 12 from the front side of the vehicle and the rear rack 18 meshing with the turning gear 12 from the rear side of the vehicle. In addition, pistons 20A to 20D are fixed to both end portions of the front rack 15 and the rear rack 18. Hereinafter, the spaces divided by the pistons 20A to 20D and filled with hydraulic oil in the cylinders 13, 14, 16, and 17 will be referred to as hydraulic oil chambers 13A, 14A, 16A, and 17A (the hydraulic oil chambers 13A and 17A are not shown in FIG. 2).

[0025] When piston 20A located inside left front cylinder 13 is located at the stroke end on the shortening side of left front cylinder 13 (the end on the left side of the vehicle), piston 20B located inside right front cylinder 14 is located at the stroke end on the extending side of right front cylinder 14 (the end on the gear housing 11 side). At this time, piston 20C located inside left rear cylinder 16 is located at the stroke end on the extension side of left rear cylinder 16 (the end on the gear housing 11 side), and piston 20D located inside right rear cylinder 17 is located at the stroke end on the shortening side of right rear cylinder 17 (the end on the right side of the vehicle).

[0026] Since the swivel device 10 has the above-described structure, when the swivel gear 12 is rotated, the cylinders located at symmetrical positions across the swivel gear are operated. As an example, when rotating the swing gear 12 clockwise from the state shown in Fig. 2, pressure oil is supplied to the hydraulic oil chambers 13A, 17A of the left front cylinder 13 and the right rear cylinder 17, and the front rack 15 is moved to the right side of the vehicle and the rear rack 18 is moved to the left side of the vehicle. At this time, hydraulic oil is pushed out of the hydraulic oil chamber 14A of the right front cylinder 14 and the hydraulic oil chamber 16A of the left rear cylinder 16, which are already filled with hydraulic oil, by the pressure of the front rack 15 and the rear rack 18.

[0027] <Hydraulic cylinder structure> Next, the structure of the hydraulic cylinder will be explained with reference to Figure 3. However, since each hydraulic cylinder of the swing device 10 has the same structure, the right rear cylinder 17 will be explained as an example, and explanations of the other cylinders will be omitted. In the following description, when specifying directions, the left side of the drawing may be referred to as the "housing side" and the right side of the drawing as the "cylinder head side." The "housing side" is the "side farther from the cylinder head" in the claims. Moreover, the outline arrows shown in the drawing indicate the direction of movement of the piston 20D, and the thin arrows indicate the flow of hydraulic oil.

[0028] (overview) The right rear cylinder 17 is configured by fixing a cylinder head 32, which serves as a lid, to the outer end of a cylindrical cylinder tube 31 in the vehicle width direction, and accommodating a piston 20D, to which the right end of the rear rack 18 is fixed, in the inner peripheral portion of the cylinder tube 31. Inside the right rear cylinder 17, a plunger 33 is provided in the cylinder head 32 as a cushioning mechanism that limits the flow rate of hydraulic oil flowing out of the hydraulic oil chamber 17A when the piston 20D moves toward the stroke end on the cylinder head side, thereby decelerating the piston 20D, and a port 40 is provided inside the piston 20D to accommodate the plunger 33. A groove 32A is formed on the surface of the cylinder head 32 facing the hydraulic oil chamber 17A as a flow path for hydraulic oil when the piston 20D reaches the stroke end.

[0029] (Plunger structure) The plunger 33 has a protruding portion 33A, half of whose length protrudes into the hydraulic oil chamber 17A, and a tapered tip portion is formed so that the outer diameter is smaller than the outer diameter of the remaining portion of the protruding portion 33A. A fixing screw portion is formed on one-quarter of the protruding portion 33A toward the outside of the hydraulic oil chamber 17A, and a joint portion is formed on the remaining one-quarter for attaching a hose, etc. Inside the plunger 33, an internal plunger flow path 34 is formed to connect the hydraulic oil chamber 17A to the outside.

[0030] An opening 34A having the same diameter as the plunger internal flow path 34 is formed at the tip of the protruding portion 33A. Two through holes are formed in the protruding portion 33A along the radial direction, spaced apart in the axial direction. Hereinafter, the through hole formed on the tip side of the plunger 33 will be referred to as a first cushion hole 35, and the through hole formed on the cylinder head 32 side will be referred to as a second cushion hole 36. The first cushion hole 35 and the second cushion hole 36 penetrate from the outer peripheral surface of the plunger 33 through the axis to the opposite outer peripheral surface, and connect the hydraulic oil chamber 17A to the plunger internal flow path 34. The first cushion hole 35 and the second cushion hole 36 have a smaller diameter than the opening 34A, and therefore function as a throttle.

[0031] (Piston structure) The piston 20D is formed by combining a first piston member 41 having a surface facing the hydraulic oil chamber 17A with a second piston member 42 that is disposed closer to the housing than the first piston member 41. Specifically, a fitting recess 41A is formed on the housing side of the first piston member 41, and a fitting protrusion 42A is formed on the cylinder head 32 side of the second piston member 42. The piston 20D is assembled by fitting the fitting protrusion 42A into the fitting recess 41A and fixing the first piston member 41 and the second piston member 42 together. The end face of the first piston member 41 on the cylinder head side is the face facing the hydraulic oil chamber 17A, and the right end of the rear rack 18 is fixed to the housing side of the second piston member .

[0032] The ports 40 are formed coaxially from the first piston member 41 to the second piston member 42. Hereinafter, when it is necessary to distinguish between them, the port formed on the first piston member 41 side will be referred to as the "first port 40A," and the port formed on the second piston member 42 side will be referred to as the "second port 40B."

[0033] The first port 40A is formed, from the cylinder head side, with a portion having a diameter larger than the outer diameter of the plunger 33 and an even larger diameter cushion seal accommodating portion 43. The entire second port 40B is formed to have the same diameter as the portion of the first port 40A that is not the cushion seal accommodating portion 43. Because the cushion seal accommodating portion 43 is formed up to the housing side end face of the first piston member 41, the end face of the second piston member 42 is exposed on the housing side of the cushion seal accommodating portion 43. The cushion seal accommodating portion 43 is formed to be longer in the axial direction than the cushion seal 50 described later, and the cushion seal 50 is movable in the axial direction while being accommodated in the cushion seal accommodating portion 43.

[0034] In addition, the first piston member 41 has an in-piston flow path 44 formed in a position that is axially parallel to the port 40 and partially overlaps with the cushion seal accommodating portion 43, from the end face on the cylinder head side to the end face on the housing side. Although only one internal piston flow passage 44 is shown in the figure, three passages are formed on a concentric circle centered on the axis of the port 40 so that the total flow passage area is equal to or greater than the flow passage area of ​​the opening 34 of the plunger 33.

[0035] The fitting protrusion 42A is formed to be longer than the fitting recess 41A. That is, the second piston member 42 is formed with an outer circumferential seal accommodating portion 45, which is continuous with the fitting protrusion 42A and has a smaller diameter than the other portions. Therefore, when the first piston member 41 and the second piston member 42 are combined to form the piston 20D, a groove is formed in the outer circumferential portion. A dust seal 46, which is harder than an oil seal, is attached to the outer circumferential seal accommodating portion 45 to prevent foreign matter from entering the hydraulic oil chamber 17A.

[0036] <Cushion sticker> The structure of the cushion seal 50 will be described with reference to FIG. The cushion seal 50 is a cylindrical member provided to block the second port 40B from the hydraulic oil chamber 17A at a predetermined time, and has an outer diameter slightly smaller than the inner diameter of the cushion seal housing portion 43 of the port 40 shown in Figure 3, and an inner diameter substantially the same as the outer diameter of the protruding portion 33A of the plunger 33. Therefore, the cushion seal 50 is movable radially inside the cushion seal housing portion 43. The inner diameter of the end on the cylinder head side is larger than that of the other portions, forming a taper 51. The angle of the taper 51 is formed to be equal to or greater than 8° and equal to or less than 12°.

[0037] A conventional cushion seal 60 will be described with reference to FIG. Conventionally used cushion seals 60 do not have a tapered interior, and the overall inner diameter is approximately equal to the outer diameter of the protruding portion 33A of the plunger 33. That is, the cushion seal 50 according to the present invention differs from the conventional cushion seal 60 in that it has a tapered portion on its inner periphery.

[0038] <Cushion mechanism operation> The operation of the cushion mechanism will be described with reference to FIGS. 3 and 6 to 11. FIG. 3 shows the inside of the hydraulic oil chamber 17A when the cushion mechanism is not operating. At this time, the protruding portion 33A of the plunger 33 is positioned outside the port 40. When the piston 20D moves toward the cylinder head, hydraulic oil in the hydraulic oil chamber 13A flows into the plunger internal flow path 34 from the opening 34A. At the same time, hydraulic oil also flows into the plunger internal flow path 34 from the first cushion hole 35 and the second cushion hole 36. However, because the flow path areas of these holes are much smaller than the opening 34A, the opening 34A becomes the dominant flow path, and the piston 20D does not decelerate. In this way, the operating speed of the piston 20D while the plunger 33 is not housed in the port 40 may hereinafter be referred to as the "normal speed."

[0039] As shown in Figure 7, when the piston 20D moves closer to the cylinder head 32 from the position shown in Figure 3 and the protruding portion 33A of the plunger 33 passes over the taper 51 of the cushion seal 50 and is accommodated in the port 40, the outer surface of the protruding portion 33A and the inner surface of the cushion seal 50 come into close contact with each other, blocking the flow path between the second port 40B and the hydraulic oil chamber 17A. As the plunger 33 is inserted into the cushion seal 50, the tapered tip of the protruding portion 33A comes into contact with the inner surface of the cushion seal 50, and the cushion seal 50 is moved radially within the cushion seal accommodating portion 43 to be aligned to a coaxial position. This centering function reduces the radial load acting on both the cushion seal 50 and the plunger 33, making it possible to prevent wear and scuffing of the cushion seal 50 and the plunger 33, as well as bending deformation of the plunger 33. Furthermore, the centering function allows the cushion seal 50 to be accommodated in the cushion seal accommodating portion 43 in the correct orientation, so that the sealing function described in the next paragraph is stably exhibited.

[0040] Furthermore, the cushion seal 50 moves toward the housing due to friction with the plunger 33 and the hydraulic oil pressure in the hydraulic oil chamber 17A and is pressed against the end face of the second piston member 42, blocking the flow path from the second port 40B to the intra-piston flow path 44. Therefore, the flow path between the opening 34A of the plunger 33 and the hydraulic oil chamber 17A is blocked. By blocking this flow path, communication between the cushion seal housing 43 and the second port 40B is blocked, even when the cushion seal 50 has a smaller diameter than the cushion seal housing 43. At this time, as shown in Fig. 8, the hydraulic oil in the hydraulic oil chamber 17A flows into the plunger internal flow path 34 from the first cushion hole 35 and the second cushion hole 36. Because the first cushion hole 35 and the second cushion hole 36 are throttles, the flow rate of the hydraulic oil flowing into the plunger internal flow path 34 is restricted, and the piston 20D slows down from its normal speed.

[0041] However, even at this time, the opening 34A is not completely blocked from the hydraulic oil chamber 17A, and a very small amount of hydraulic oil leaks from the portion blocked by the cushion seal 50, flows from the hydraulic oil chamber 17A into the second port 40B, and then flows from the opening 34A into the plunger internal flow path 34. The leaked hydraulic oil causes high-frequency noise, which will be described later.

[0042] As shown in FIGS. 9 and 10, when the piston 20D approaches the cylinder head 32 further from the position shown in FIG. Therefore, thereafter, only the second cushion hole 36 becomes the dominant flow path for the hydraulic oil until the piston 20D hits the cylinder head 32, and the movement of the piston 20D further decelerates. During this time, hydraulic oil continues to leak from the portion blocked by the cushion seal 50.

[0043] In this way, as the piston 20D approaches the cylinder head 32, the piston 20D operates at a normal speed until the opening 34A at the tip of the plunger 33 passes over the taper 51 of the cushion seal 50 and is accommodated in the port 40, after which the piston 20D is decelerated in two stages by the first cushion hole 35 and the second cushion hole 36. This deceleration reduces the impact when the piston 20D hits the cylinder head 32, thereby providing a cushioning function.

[0044] Thereafter, when the piston 20D is moved toward the housing, hydraulic oil flows into the port 40 from the opening 34A at the tip of the plunger 33, and as a result, the cushion seal 50 moves toward the cylinder head due to the hydraulic oil pressure inside the port 40, as shown in Fig. 11. This forms a gap between the housing-side end face of the cushion seal 50 and the cylinder-head-side end face of the second piston member 42. Therefore, a hydraulic oil flow path is established from the intra-plunger flow path 34 to the groove 32A in the cylinder head 32 via the opening 34A, the gap between the housing-side end face of the cushion seal 50 and the cylinder-head-side end face of the second piston member 42, and the intra-piston flow path 44.

[0045] After the hydraulic oil flows into the groove 32A, the piston 20D moves toward the housing and transits to the position shown in FIG. 3 via the position shown in FIG. During this time, until the piston 20D moves and the plunger 33 is pulled out to a position where the protruding portion 33A and the cushion seal 50 are separated, the in-piston flow path 44 functions as a dominant flow path. Furthermore, since the total flow path area of ​​the piston internal flow path 44 is greater than or equal to the flow path area of ​​the opening 34A as described above, even when the piston starts moving from the stroke end on the cylinder head 32 side, it is possible to supply hydraulic oil pressure and flow rate to the hydraulic oil chamber 17A that are equivalent to when the opening 34A is located inside the hydraulic oil chamber 17A.

[0046] <High-frequency noise suppression effect> (conventional hydraulic cylinder) The effect of suppressing high frequency noise when the cushion seal 50 according to the present invention is used will be described. First, the structure of a hydraulic cylinder 100 equipped with a cushion mechanism having a conventional cushion seal 60, which serves as a comparison object, will be described with reference to FIGS. 5, 12 and 13. FIG.

[0047] A conventional hydraulic cylinder 100 also has a cylinder head 102 fixed to the end of a cylindrical cylinder tube 101. A plunger 103 of the same shape as that used in the present invention is fixed to the cylinder head 102. The conventional piston 110 is made up of a single member, and the port 120 is formed with a cushion seal receiving portion 111 and an in-piston flow path 112 . The port 120 provided in a conventional piston has approximately the same shape as the port 40 described above, but is formed in the same shape as the cushion seal accommodating portion 111, except for the end face on the cylinder head side to the end of the cushion seal accommodating portion 111. Therefore, after accommodating the cushion seal 60, the sleeve 113 is inserted and the front rack 15 is fixed from above.

[0048] Although there are differences as described above between the structure of the right rear cylinder 17 according to the present invention and the structure of the conventional hydraulic cylinder 100, there is no difference in that the cushion seals 50, 60 move to switch the communication state of the flow path, and there is no difference in their function as cushion mechanisms.

[0049] (Comparative experiment results) Table 1 shows the results of an experiment comparing the generation of high frequency noise while the cushion mechanisms of the conventional hydraulic cylinder 100 and the right rear cylinder 17 according to the present invention are in operation. The high-frequency sound refers to noise in a frequency band that is higher in frequency than the sound generated by the engine of the forwarder 1 and the work equipment 6 while the work equipment 6 is turning, and that can be clearly recognized by an observer. The observer stood at a position about 2 m away from the slewing device 10, spun the work implement 6, and observed the high-frequency sound from the time the slewing speed decreased until the piston reached the cylinder end and the slewing stopped. The experiment was conducted while changing the oil temperature and flow rate. In each condition, if the observer was able to hear the high-frequency sound, an X was recorded, and if they were unable to hear it, an O was recorded.

[0050] [Table 1]

[0051] As a result of the experiment, no high frequency sounds were observed in the hydraulic cylinder according to the present invention under any of the conditions under which high frequency sounds were generated in the conventional hydraulic cylinder 100. Therefore, by using a hydraulic cylinder equipped with a cushion seal in which a taper 51 is formed so that the inner diameter of the end on the hydraulic oil chamber side is larger than the other parts, it is possible to suppress the generation of high frequency noise.

[0052] <Other effects> Furthermore, since the piston 20D provided in the hydraulic cylinder according to the present invention is configured by combining the first piston member 41 and the second piston member 42, it is easy to form the cushion seal accommodating portion 43 only in the first piston member 41 by machining, and the sleeve 113 is not required, which enables reduction in manufacturing costs.

[0053] Furthermore, by providing an outer circumferential seal accommodating portion with a small diameter portion formed in only one of the first piston member 41 or the second piston member 42, it is possible to reduce the effort required to attach a seal to the outer circumferential portion of the piston. For example, the dust seal shown in the embodiment is made of a harder material than the seal used to prevent hydraulic oil leakage. Therefore, it takes a lot of effort to deform the seal to expand its inner diameter and attach it to the piston. Reducing this effort can improve productivity. It can also reduce the possibility of unintentionally damaging the seal when deforming it.

[0054] <Modification> In the embodiment, the hydraulic cylinder in which the plunger 33 is provided in the cylinder head 32 and the port 40 is provided in the piston 20D has been described as an example, but the application of the present invention is not limited to such a hydraulic cylinder. The present invention can also be applied to a hydraulic cylinder in which the plunger 33 is provided on the piston and the port 40 is provided on the cylinder head, as long as the cushion seal 50 is housed inside the port 40 in which the plunger 33 is housed.

[0055] In the embodiment, the taper 51 of the cushion seal 50 is formed at an angle of 8° or more and 12° or less, but the angle of the taper 51 may be formed at an angle of 1° or more and 20° or less, and even in that case, the effect of suppressing high-frequency noise is still achieved.

[0056] In the embodiment, the piston 20D is configured by combining the first piston member 41 and the second piston member 42, but in the application of the present invention, this structure is not necessarily required, and a structure such as that of a conventional piston 110 may be selected. Even with the conventional piston 110, if the cushion seal 50 having the taper 51 is housed, it is possible to suppress the generation of high frequency noise. When the conventional piston 110 is used, it is only necessary to adjust the lengths of the in-piston flow path 112 and the sleeve 113, and the existing manufacturing processes for the other parts including the dust seal 46 can be used. [Explanation of symbols]

[0057] 1... forwarder (industrial machine), 6... work machine, 10... swivel device, 11... gear housing, 12... swivel gear, 13... left front cylinder, 14... right front cylinder, 16... left rear cylinder, 17... right rear cylinder, 15... front rack, 18... rear rack, 13A, 14A, 16A, 17A... hydraulic oil chamber, 20A, 20B, 20C, 20D... piston, 31... cylinder tube, 32... cylinder head, 33... plunger, 33A... protruding portion, 34... flow path inside plunger , 34A...Opening, 35...First cushion hole, 36...Second cushion hole, 40...Port, 40A...First port, 40B...Second port, 41...First piston member, 42...Second piston member, 43...Cushion seal accommodating portion, 45...Outer circumferential seal accommodating portion, 46...Dust seal, 50...Cushion seal, 51...Taper, 60...Cushion seal (conventional type), 100...Hydraulic cylinder (conventional type), 110...(conventional type), 120...Port (conventional type)

Claims

1. A fluid pressure cylinder equipped with a cushion mechanism that reduces the operating speed of a piston by restricting the flow rate of a working fluid flowing out of a working fluid chamber, The cushion mechanism includes a plunger and a port into which the plunger is inserted, the plunger is provided on one of the piston and the cylinder head so as to protrude into the working fluid chamber, the port is provided in the other of the piston or the cylinder head; A cushion seal receiving portion is formed inside the port, and a cylindrical cushion seal is received inside the cushion seal receiving portion. a cushion seal having a taper formed therein such that the inner diameter of the end portion on the working fluid chamber side is larger than that of other portions;

2. the cylinder head includes the plunger, the piston includes the port and an internal piston flow path formed therein; the plunger includes an internal plunger flow path that communicates the inside and outside of the working fluid chamber; The opening of the plunger internal flow path in the working fluid chamber is formed at the tip end of the plunger and at the circumferential surface of the plunger, The opening in the peripheral surface of the plunger has an area smaller than that of the opening in the tip portion, the cushion seal accommodating portion is formed to be longer in the axial direction than the cushion seal and accommodates the cushion seal so as to be movable along the axial direction of the cushion seal; the piston internal flow path communicates a surface of the piston facing the working fluid chamber with an end of the cushion seal receiving portion on a side farther from the cylinder head, 2. The fluid pressure cylinder according to claim 1, wherein, when the plunger passes over the taper of the cushion seal and is inserted into the port, the cushion seal moves to a side of the cushion seal housing that is farther from the cylinder head and blocks the intra-piston flow path, so that an opening in the circumferential surface of the plunger becomes a dominant opening, and when the plunger is pulled out of the port, the cushion seal moves to a cylinder head side of the cushion seal housing that opens the intra-piston flow path, so that an opening in the tip end of the plunger becomes a dominant opening.

3. 3. The fluid pressure cylinder according to claim 1, wherein the taper angle is equal to or greater than 1° and equal to or less than 20°.

4. the piston is configured by combining a first piston member having a surface facing the working fluid chamber and a second piston member disposed on a side of the first piston member farther from the cylinder head, the port is coaxially formed in the first piston member and the second piston member; 2. The fluid pressure cylinder according to claim 1, wherein the cushion seal accommodating portion is formed with a portion having approximately the same diameter as the cushion seal from one end face of the first piston member or the second piston member only on the one end face of the first piston member or the second piston member.

5. the piston is configured by combining a first piston member having a surface facing the working fluid chamber with a second piston member disposed on the side of the first piston member farther from the cylinder head, and has an outer circumferential seal accommodating portion formed on an outer circumferential portion of the piston, the outer circumferential portion having a smaller diameter than other portions; 2. The fluid pressure cylinder according to claim 1, wherein the outer circumferential seal accommodating portion is formed such that only one of the first piston member and the second piston member has a small diameter from an end face of the first piston member or the second piston member.

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