JP5591138B2 - Hydraulic shock absorber - Google Patents

Description

  The present invention relates to a hydraulic shock absorber suitable for use in a vehicle.

  As a hydraulic shock absorber, a free piston is slidably inserted into the cylinder, the inside of the cylinder is divided into an oil chamber and a gas chamber by this free piston, and a piston fixed to a piston rod that protrudes outside the cylinder into the oil chamber Is slidably inserted. The change in the piston rod entry / exit volume with respect to the cylinder is compensated by the displacement of the free piston in the cylinder.

  In such a hydraulic shock absorber, if the oil in the oil chamber in the cylinder leaks to the outside from the oil seal of the rod guide that supports the piston rod, or leaks from the seal member of the free piston to the gas chamber, the free piston The position of approaches the piston rod. Eventually, the free piston moves until it collides with the piston rod, and the piston rod cannot compress the sealed pressure in the gas chamber behind the free piston, so that the stroke of the piston rod is effectively locked.

  Therefore, in the hydraulic shock absorbers described in Patent Documents 1 and 2, when the tip of the piston rod comes into contact with the free piston, it breaks, and the breakage that forms a through hole that connects the oil chamber and the gas chamber is free. It was provided on the piston. The sealed pressure of the gas chamber behind the free piston is released from the through hole formed in the free piston to the oil chamber, and the piston rod stroke is prevented from locking.

JP 55-17714 JP-A-8-159199

  In the hydraulic shock absorbers described in Patent Documents 1 and 2, a broken portion is provided in a free piston, and a portion where a broken piece is dropped is merely used as a through hole. Therefore, a broken piece generated in the cylinder may flow into the oil chamber side and may bite into the damping force generating portion of the piston, thereby impairing the damper function.

  An object of the present invention is to prevent a broken piece from impairing a damper function in a hydraulic shock absorber having a free piston that is broken when a tip end portion of a piston rod comes into contact therewith.

  According to the first aspect of the present invention, a free piston is slidably fitted into the cylinder, the inside of the cylinder is partitioned into an oil chamber and a gas chamber by the free piston, and a piston rod that protrudes outside the cylinder is formed in the oil chamber. A fixed piston is slidably inserted, and the piston rod breaks when the tip of the piston rod comes into contact with the free piston, and the broken portion that forms a through hole that connects the oil chamber and the gas chamber becomes the free piston. In the provided hydraulic shock absorber, the breaking portion of the free piston that is broken by the tip of the piston rod is such that the breaking size of the portion facing the gas chamber is larger than the breaking size of the portion facing the oil chamber.

  According to a second aspect of the present invention, in the first aspect of the invention, the fracture surface of the rupture portion has a convex root formed on an end surface facing the oil chamber of the free piston, and an end surface facing the gas chamber of the free piston. The ring-shaped fragile portion formed in the shape of the ring is generally conical.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the tip of the piston rod that extends from the fractured portion to the end surface facing the oil chamber of the free piston and contacts the end surface of the free piston. A groove-like communication path that extends over a range larger than the outer diameter of the part is recessed.

  According to a fourth aspect of the present invention, in the first or second aspect of the present invention, the fracture portion further forms a through hole having a larger hole diameter than the outer diameter of the tip portion of the piston rod.

The invention according to claim 5 is the invention according to claim 1, wherein the fracture portion is formed in a groove of an O-ring groove on the outer periphery of the free piston .

(Claim 1)
(a) The size of the broken piece that was broken from the broken portion of the free piston by the tip of the piston rod and pushed into the gas chamber was set to be larger than the diameter of the through hole formed in the free piston. Therefore, the broken piece (size S1) that is broken from the free piston and pushed into the gas chamber cannot pass through the hole diameter S2 (S1> S2) of the through hole formed in the free piston toward the oil chamber. Thereby, the broken piece flows from the gas chamber to the oil chamber and does not impair the damper function due to biting into the damping force generating portion of the piston.

  (b) The breaking size S1 of the part facing the gas chamber is larger than the breaking size S2 of the part facing the oil chamber. Accordingly, the hole diameter of the portion of the through hole formed in the free piston by the fracture of the fracture portion that faces the oil chamber is equal to the fracture size S2 of the portion of the fracture portion that faces the oil chamber and faces the gas chamber at the fracture fragment. Smaller than the breaking size S1 of the part (S1> S2). Therefore, the size S1 of the broken piece that is broken from the broken portion of the free piston by the tip end of the piston rod and is pushed into the gas chamber side and dropped is set to the through hole formed in the free piston as described above (a). It is set to be larger than the hole diameter S2.

(Claim 2)
(c) The fracture surface of the fracture portion provided in the free piston generally connects the root of the convex portion formed on the end surface facing the oil chamber of the free piston and the annular weak portion formed on the end surface facing the gas chamber of the free piston. Conical. Accordingly, the hole diameter of the portion of the conical through hole formed in the free piston by the fracture of the conical rupture portion facing the oil chamber is the rupture size S2 of the portion of the conical rupture portion facing the oil chamber (the root of the convex portion). Is smaller than the fracture size S1 of the portion (annular fragile portion) facing the gas chamber in the conical fracture fragment (S1> S2). Therefore, the size S1 of the cone-shaped broken piece that is broken from the broken portion of the free piston by the tip of the piston rod and pushed into the gas chamber side is set to the size of the through-hole formed in the free piston as described above (a). It is set to be larger than the hole diameter S2.

(Claim 3)
(d) A groove-like communication path extending from the fractured portion to the end face facing the oil chamber of the free piston and extending to a range larger than the outer diameter of the tip end of the piston rod that contacts the end face of the free piston is recessed. did. Therefore, when the tip of the piston rod comes into contact with the free piston and breaks the broken portion of the free piston, a through hole is formed in the free piston to connect the oil chamber and the gas chamber, and the gas behind the free piston is formed. When the sealed pressure in the chamber is released to the oil chamber, if the hole diameter of the through hole is smaller than the outer diameter of the piston rod tip, the piston rod tip pushes the free piston back to its stroke end, and then the piston rod Repeats the stroke, and the tip of the piston rod repeatedly hits the through hole in the end face facing the oil chamber of the free piston at the stroke end. In this case, even if the tip of the piston rod hits the through hole in the end face of the free piston, the groove-shaped communication path recessed around the through hole communicates the oil chamber with the through hole, Keep communicating with the gas chamber. Therefore, it can prevent stably that the stroke of a piston rod locks.

(Claim 4)
(e) A through-hole having a larger diameter than the outer diameter of the tip of the piston rod is formed in the fractured portion provided in the free piston. Therefore, when the tip of the piston rod comes into contact with the free piston and breaks the broken portion of the free piston, a through hole is formed in the free piston to connect the oil chamber and the gas chamber, and the gas behind the free piston is formed. When the sealed pressure in the chamber is released to the oil chamber, the piston rod repeats a stroke extending in and out of a through hole having a larger diameter than the tip. In this case, it is possible to stably prevent the stroke of the piston rod from being locked because the above-described large-diameter through hole of the free piston continues to communicate the oil chamber and the gas chamber. The tip of the piston rod does not hit the end face of the free piston, and no abnormal noise is generated.

(Claim 5)
(f) A fracture portion provided in the free piston was formed in the O-ring groove on the outer periphery of the free piston. A fracture portion is formed in the groove of the O-ring of the free piston, and a portion (upper annular portion) on the oil chamber side from the fracture portion of the O-ring groove remains on the inner periphery of the cylinder together with the O-ring. The portion closer to the gas chamber (lower annular portion) becomes a broken piece. The size S1 of the fracture piece is constituted by the outer diameter S1 of the lower annular portion of the free piston, and the hole diameter S2 of the through hole formed in the free piston by fracture is divided into the upper annular portion (outer diameter S1) and the lower annular portion (outer diameter S1). ) Having a smaller inner diameter S2 (S1> S2). Therefore, the size S1 (outer diameter of the lower annular portion) of the fractured portion that is broken from the broken portion of the free piston by the tip of the piston rod and is pushed into the gas chamber is dropped as shown in (a) above. It is set larger than the hole diameter S2 of the through hole formed in the free piston.

1 is a cross-sectional view showing a hydraulic shock absorber according to a first embodiment. FIG. 2 is an enlarged cross-sectional view of the main part of FIG. FIG. 3 shows a free piston, (A) is a cross-sectional view, (B) is a plan view, and (C) is an enlarged view of a main part. FIG. 4 is a schematic view showing a breaking state of the free piston. FIG. 5 is a schematic view showing a breaking process of the free piston in the hydraulic shock absorber. 6A and 6B show a free piston used in the hydraulic shock absorber according to the second embodiment, where FIG. 6A is a cross-sectional view, FIG. 6B is a plan view, FIG. 6C is a perspective view, and FIG. FIG. 7 is a schematic view showing a breaking state of the free piston. FIG. 8 shows a modification of the free piston, (A) is a sectional view, and (B) is a perspective view. FIG. 9 is a schematic diagram illustrating a fracture state of a free piston used in the hydraulic shock absorber according to the third embodiment.

Example 1 (FIGS. 1 to 5)
A hydraulic shock absorber 10 for a vehicle is a separate pressure damper, and as shown in FIGS. 1 and 2, through a rod guide 12 provided at an upper end opening of a bottomed cylindrical cylinder 11, an oil seal 13 and the like. The piston rod 14 is inserted into the cylinder 11. A piston 15 is inserted into the tip of the piston rod 14 inserted into the cylinder 11, and the piston 15 is fixed by a nut 14 </ b> A so that the piston 15 can slide on the inner periphery of the cylinder 11. An axle side mounting portion 17A is provided on the outer surface of the bottom of the cylinder 11, and a vehicle body side mounting member 17B is provided on the projecting end of the piston rod 14 to the outside of the cylinder 11.

  In the hydraulic shock absorber 10, a free piston 20 (FIG. 3) is slidably fitted on the bottom side of the piston 15 inside the cylinder 11, and the inside of the cylinder 11 is fixed to the oil chamber 18 by the free piston 20 with a certain amount. It is partitioned into a gas chamber 19 in which gas pressure is enclosed. A piston 15 fixed to the piston rod 14 is slidably fitted into the oil chamber 18. The free piston 20 is in sliding contact with the inner periphery of the cylinder 11 via an O-ring 22 fitted in an O-ring groove 21 provided on the outer periphery.

  The piston 15 divides the interior of the oil chamber 18 into a rod-side oil chamber 18A and a piston-side oil chamber 18B, and an extension-side damping valve 16A is provided in the extension-side flow passage 15A that communicates both the oil chambers 18A and 18B. A pressure side damping valve 16B is provided in the pressure side flow path 15B communicating with the chambers 18A and 18B. The damping force generators of these damping valves 16A and 16B generate an extension side damping force and a compression side damping force.

  In such a hydraulic shock absorber 10, the oil in the oil chamber 18 in the cylinder 11 leaks to the outside from the oil seal 13 of the rod guide 12 that supports the piston rod 14, or gas from the O-ring 22 of the free piston 20. When leaking into the chamber 19, the position of the free piston 20 approaches the piston rod 14. Eventually, the free piston 20 moves until it collides with the piston rod 14, the piston rod 14 cannot compress the enclosed pressure of the gas chamber 19 behind the free piston 20, and the stroke of the piston rod 14 is effectively locked. There is a risk that.

  Therefore, as shown in FIGS. 3 and 4, the hydraulic shock absorber 10 is broken when the tip of the piston rod 14 comes into contact with the free piston 20, and the through hole 30 that communicates the oil chamber 18 and the gas chamber 19. A breaking portion 23 (FIG. 3C) forming (FIG. 4) is provided in the free piston 20.

  At this time, in the hydraulic shock absorber 10, the size S1 of the broken piece 24 (FIG. 4) that is broken from the broken portion 23 of the free piston 20 by the tip portion of the piston rod 14 and pushed into the gas chamber 19 side, It is set larger than the hole diameter S2 of the through hole 30 formed in the free piston 20 (S1> S2).

  In this embodiment, the breaking portion 23 provided in the free piston 20 has a breaking size S1 at a portion facing the gas chamber 19 larger than a breaking size S2 at a portion facing the oil chamber 18 (S1> S2).

  And the fracture | rupture surface of the fracture | rupture part 23 provided in the free piston 20 is formed in the end surface which faces the oil chamber 18 of the free piston 20 as shown in FIG. The rod-shaped convex portion 25 having a diameter S2 base 25A and a ring-shaped weak portion 26 having a diameter S1 formed on the end face of the free piston 20 facing the gas chamber 19 are generally conical in a wedge shape (even in the shape of a pyramid). Yes). The annular fragile portion 26 is on the end surface facing the gas chamber 19 of the free piston 20, and the intersection angle between the thinnest portion between the end surfaces facing the oil chamber 18 and the gas chamber 19 and the thick portion on the side thereof. It is formed at the part.

  Further, as shown in FIG. 3, the end surface of the free piston 20 facing the oil chamber 18 extends from a fracture portion 23 formed by the base 25 </ b> A of the convex portion 25, and is in contact with the end surface of the free piston 20. A groove-like communication path 27 extending in a larger range (B in FIG. 2) than the outer diameter (A in FIG. 2) of the front end of each was recessed. The groove-like communication path 27 of this embodiment includes a circular groove 27A around the base 25A of the convex portion 25 and a cross groove 27B extending around the circular groove 27A.

  Therefore, in the hydraulic shock absorber 10, when the oil in the oil chamber 18 in the cylinder 11 leaks to the outside of the cylinder 11 or the gas chamber 19 as described above and the position of the free piston 20 approaches the piston rod 14, Specifically, as shown in FIG. 5A, the tip of the piston rod 14 collides with the projection 25 of the free piston 20 (the projection may be formed at the tip of the piston rod 14). When the tip of the piston rod 14 contacts the convex portion 25 of the free piston 20 in this way, the fracture portion 23 of the free piston 20 breaks, and as shown in FIG. 5B, the oil chamber 18 and the gas chamber 19 Through hole 30 is formed. As a result, the sealed pressure in the gas chamber 19 behind the free piston 20 is released from the through hole 30 to the oil chamber 18, and the tip of the piston rod 14 pushes the free piston 20 back to the pressure side stroke end, and then the piston rod 14 repeats the expansion / contraction stroke. The broken piece 24 broken at the broken portion 23 of the free piston 20 is pushed into the gas chamber 19 by the tip of the piston rod 14 and dropped off as shown in FIG.

According to the present embodiment, the following operational effects can be obtained.
(a) A broken piece 24 (size S1) that is broken from the free piston 20 and pushed into the gas chamber 19 side is changed from the hole diameter S2 (S1> S2) of the through hole 30 formed in the free piston 20 to the oil chamber 18. I can't get through to the side. As a result, the broken piece 24 flows from the gas chamber 19 to the oil chamber 18 and does not impair the damper function by biting into the damping force generating portion of the piston 15.

  (b) The fractured portion 23 provided in the free piston 20 has the fracture size S1 at the part facing the gas chamber 19 larger than the fracture size S2 at the part facing the oil chamber 18. Therefore, the hole diameter S2 of the portion facing the oil chamber 18 of the through hole 30 formed in the free piston 20 due to the breakage of the breakage portion 23 is equal to the breakage size S2 of the portion of the breakage portion 23 facing the oil chamber 18, and 24 is smaller than the fracture size S1 of the portion facing the gas chamber 19 (S1> S2). Therefore, the size S1 of the broken piece 24 that is broken from the broken portion 23 of the free piston 20 by the tip of the piston rod 14 and is pushed into the gas chamber 19 and dropped is set as shown in FIG. It is set to be larger than the hole diameter S2 of the through-hole 30 formed in.

  (c) The fracture surface of the fracture portion 23 provided in the free piston 20 is formed on the root 25A of the convex portion 25 formed on the end surface facing the oil chamber 18 of the free piston 20 and the end surface facing the gas chamber 19 of the free piston 20 The ring-shaped fragile portion 26 is generally conical. Therefore, the hole diameter S2 of the portion facing the oil chamber 18 of the conical through hole 30 formed in the free piston 20 by the breakage of the conical break portion 23 is the portion (convex portion) facing the oil chamber 18 of the conical break portion 23. 25 is equal to the fracture size S2 of the root 25A) and is smaller than the fracture size S1 of the portion (annular fragile portion 26) facing the gas chamber 19 in the conical fracture piece 24 (S1> S2). Therefore, the size S1 of the cone-shaped broken piece 24 that is broken from the broken portion 23 of the free piston 20 by the tip portion of the piston rod 14 and pushed into the gas chamber 19 side is set to the free piston 20 as described above (a). It is set to be larger than the hole diameter S2 of the formed through hole 30.

  (d) A groove shape extending from the fractured portion 23 to the end surface of the free piston 20 facing the oil chamber 18 and extending over a range larger than the outer diameter of the tip of the piston rod 14 that contacts the end surface of the free piston 20. The communication path 27 was recessed. Therefore, when the tip of the piston rod 14 comes into contact with the free piston 20 and breaks the fractured portion 23 of the free piston 20, a through hole 30 is formed in the free piston 20 to communicate the oil chamber 18 and the gas chamber 19. When the sealed pressure of the gas chamber 19 behind the free piston 20 is released to the oil chamber 18, if the hole diameter S2 of the through hole 30 is smaller than the outer diameter of the tip of the piston rod 14, the tip of the piston rod 14 Pushes the free piston 20 back to its stroke end, and then the piston rod 14 repeats the stroke, and the tip of the piston rod 14 repeats around the through hole 30 at the end face facing the oil chamber 18 of the free piston 20 at the stroke end. You will win. In this case, even if the tip of the piston rod 14 hits the through hole 30 on the end surface of the free piston 20, the groove-shaped communication path 27 recessed around the through hole 30 allows the oil chamber 18 to pass through the through hole 30. The oil chamber 18 and the gas chamber 19 are kept in communication with each other. Therefore, it can prevent stably that the stroke of piston rod 14 locks.

Example 2 (FIGS. 6 and 7)
The second embodiment employs a free piston 40 as shown in FIG.

  The free piston 40 includes an O-ring groove 41 and an O-ring 42 that are the same as the O-ring groove 21 and the O-ring 22 in the free piston 20 of the first embodiment, and also includes a fracture portion 43 that replaces the fracture portion 23 of the free piston 20. .

  That is, as shown in FIGS. 6 and 7, the hydraulic shock absorber 10 is broken when the tip portion of the piston rod 14 comes into contact with the free piston 20, and the through hole 50 communicates the oil chamber 18 and the gas chamber 19. The fracture | rupture part 43 (FIG.6 (D)) which forms (FIG. 7) is provided in the free piston 40. FIG.

  At this time, in the hydraulic shock absorber 10, the size S1 of the fracture piece 44 (FIG. 7) that is fractured from the fracture portion 43 of the free piston 40 by the tip of the piston rod 14 and pushed into the gas chamber 19 side, It is set to be larger than the hole diameter S2 of the through hole 50 formed in the free piston 40 (S1> S2).

  In this embodiment, the breaking portion 43 provided in the free piston 40 has a breaking size S1 at a portion facing the gas chamber 19 larger than a breaking size S2 at a portion facing the oil chamber 18 (S1> S2).

  Then, as shown in FIG. 6D, the fracture surface of the fracture portion 43 provided in the free piston 40 is formed on the end face of the free piston 40 that faces the oil chamber 18 and protrudes in the axial direction on the oil chamber 18 side. The base 45A of the dome-shaped convex portion 45 having a diameter S2 and the annular fragile portion 46 having a diameter S1 formed on the end face of the free piston 40 facing the gas chamber 19 are formed in a substantially conical shape. The annular fragile portion 46 is formed on the end surface facing the gas chamber 19 of the free piston 40 and is formed by an annular groove provided at the thinnest portion between the end surfaces facing the oil chamber 18 and the gas chamber 19.

  Further, the breaking portion 43 provided in the free piston 40 has a hole diameter S2 larger than the outer diameter of the tip end portion of the piston rod 14 (in this embodiment, a hole diameter S2 larger than the outer diameter of the nut 14A provided at the tip end portion of the piston rod 14). The through-hole 50 is formed.

  Further, the free piston 40 is provided with intermittent protrusions 47 at a plurality of positions at regular intervals in the circumferential direction of the outer edge portion surrounding the dome-shaped convex portion 45 on the end face facing the oil chamber 19. When the nut 14 </ b> A at the tip of the piston rod 14 enters the through hole 50 of the free piston 40, even if the end surface of the piston 15 comes into contact with each protrusion 47 on the end surface facing the oil chamber 18 of the free piston 40, The flow path for connecting the oil chamber 18 to the through hole 50 is to be secured.

  Therefore, in the hydraulic shock absorber 10, when the oil in the oil chamber 18 in the cylinder 11 leaks to the outside of the cylinder 11 or the gas chamber 19 as described above and the position of the free piston 40 approaches the piston rod 14, Specifically, the leading end portion of the piston rod 14 collides with the convex portion 45 of the free piston 40 (the convex portion may be formed at the leading end portion of the piston rod 14). When the tip end portion of the piston rod 14 abuts against the convex portion 45 of the free piston 40 in this way, the fracture portion 43 of the free piston 40 is broken, and the oil chamber 18 and the gas chamber 19 are communicated as shown in FIG. Thus, a through hole 50 having a larger hole diameter than the tip of the piston rod 14 is formed. As a result, the sealed pressure of the gas chamber 19 behind the free piston 40 is released from the through hole 50 to the oil chamber 18, the tip of the piston rod 14 enters the through hole 50 of the free piston 40, and then the piston rod 14 Repeats the expansion / contraction stroke. The broken piece 44 broken at the broken portion 43 of the free piston 40 is pushed into the gas chamber 19 by the tip of the piston rod 14 and falls off.

According to the present embodiment, the following operational effects can be obtained.
(a) The broken piece 44 (size S1) that has been broken from the free piston 40 and pushed into the gas chamber 19 side has the diameter S2 (S1> S2) of the through hole 50 formed in the free piston 40 as the oil chamber 18. I can't get through to the side. As a result, the broken piece 44 flows from the gas chamber 19 toward the oil chamber 18 and does not impair the damper function by biting into the damping force generating portion of the piston 15.

  (b) The fractured portion 43 provided in the free piston 40 has the fracture size S1 at the part facing the gas chamber 19 larger than the fracture size S2 at the part facing the oil chamber 18. Therefore, the hole diameter S2 of the portion facing the oil chamber 18 of the through hole 50 formed in the free piston 40 by the breakage of the breakage portion 43 is equal to the breakage size S2 of the portion of the breakage portion 43 facing the oil chamber 18, and 44 is smaller than the fracture size S1 of the portion facing the gas chamber 19 (S1> S2). Therefore, the size S1 of the broken piece 44 that is broken from the broken portion 43 of the free piston 40 by the tip end of the piston rod 14 and is pushed into the gas chamber 19 and dropped is set as shown in FIG. It is set to be larger than the hole diameter S2 of the through-hole 50 formed in.

  (c) The fracture surface of the fracture portion 43 provided on the free piston 40 is formed on the base 45A of the convex portion 45 formed on the end surface facing the oil chamber 18 of the free piston 40 and the end surface facing the gas chamber 19 of the free piston 40. The ring-shaped fragile portion 46 is generally conically connected. Therefore, the hole diameter S2 of the portion of the conical through hole 50 that faces the oil chamber 18 formed in the free piston 40 by the breakage of the conical rupture portion 43 is the portion (convex portion) of the conical rupture portion 43 that faces the oil chamber 18. It is equal to the fracture size S2 of the root 45A) of 45 and is smaller than the fracture size S1 of the portion (annular weakened portion 46) facing the gas chamber 19 in the conical fracture piece 44 (S1> S2). Therefore, the size S1 of the cone-shaped broken piece 44 that is broken from the broken portion 43 of the free piston 40 by the tip of the piston rod 14 and pushed into the gas chamber 19 side is set to the free piston 40 as described above (a). It is set to be larger than the hole diameter S2 of the formed through hole 50.

  (d) The broken portion 43 provided in the free piston 40 forms a through hole 50 having a larger hole diameter S2 than the outer diameter of the tip of the piston rod 14. Therefore, when the tip of the piston rod 14 abuts on the free piston 40 and breaks the fractured portion 43 of the free piston 40, a through hole 50 for communicating the oil chamber 18 and the gas chamber 19 is formed in the free piston 40. When the sealed pressure in the gas chamber 19 behind the free piston 40 is released to the oil chamber 18, the piston rod 14 repeats a stroke extending in and out of the through hole 50 having a larger diameter S2 than the tip. In this case, it is possible to stably prevent the stroke of the piston rod 14 from being locked because the through hole 50 of the free piston 40 having the large hole diameter S2 continues to communicate with the oil chamber 18 and the gas chamber 19. The tip of the piston rod 14 does not hit the end face of the free piston 40, and no abnormal noise is generated.

  FIG. 8 shows a free piston 40A according to a modification. The free piston 40 </ b> A has substantially the same configuration as the free piston 40, and includes reinforcing ribs 48 that extend radially from the center portion of the end face that faces the gas chamber 19 in the portion that becomes the broken piece 44. In order to reduce the weight of the free piston 40A, the portion that becomes the broken piece 44 is formed into a thin plate shape and is reinforced by the reinforcing rib 48. The presence of the reinforcing rib 48 keeps the broken piece 44 of the broken portion in a single lump and avoids this fragmentation.

Example 3 (FIG. 9)
The third embodiment employs a free piston 60 as shown in FIG.
The free piston 60 has an O-ring groove 41 and an O-ring 62 similar to the O-ring groove 41 and the O-ring 42 in the free piston 40 of the second embodiment, and also has a breaking portion 63 instead of the breaking portion 43 of the free piston 40. .

  That is, the hydraulic shock absorber 10 is broken when the tip of the piston rod 14 comes into contact with the free piston 60 and forms a through hole 70 (FIG. 9) that connects the oil chamber 18 and the gas chamber 19. 63 is provided on the free piston 60.

  At this time, in the hydraulic shock absorber 10, the size S1 of the broken piece 64 (FIG. 9) that is broken from the broken portion 63 of the free piston 60 by the tip of the piston rod 14 and is pushed into the gas chamber 19 side, It is set larger than the hole diameter S2 of the through hole 70 formed in the free piston 60 (S1> S2).

  In the present embodiment, the breaking portion 63 provided in the free piston 60 is formed in the groove of the O-ring groove 61 on the outer periphery of the free piston 60. And the fracture | rupture surface of the fracture | rupture part 63 provided in the free piston 60 is the outer peripheral annular groove 65A of the dome-shaped convex part 65 formed in the end surface which faces the oil chamber 18, and protruding in the axial direction by the side of the oil chamber 18. The O-ring groove 61 has a substantially cylindrical or conical shape connecting the groove side surface and the intersection corner portion 66 of the groove bottom surface. The conical fracture portion 63 has a diameter-expanded shape from the upper annular portion 60U side of the free piston 60 toward the lower annular portion 60D side.

  As a result, when the tip of the piston rod 14 collides with the dome-shaped convex portion 65 facing the oil chamber 18 of the free piston 60, and a broken piece 64 is generated, the through hole 70 communicating with the oil chamber 18 and the gas chamber 19 is formed. It is formed.

  At this time, a rupture portion is formed in the groove of the O-ring 62 of the free piston 60, and the portion closer to the oil chamber 18 than the rupture portion of the O-ring groove 61 (upper annular portion 60 U) together with the O-ring 62 inside the cylinder 11. The part (lower annular part 60 </ b> D) on the gas chamber 19 side from the broken part of the O-ring groove 61 becomes a broken piece 64. The size S1 of the fracture piece 64 is constituted by the outer diameter S1 of the lower annular portion 60D of the free piston 60, and the hole diameter S2 of the through hole 70 formed in the free piston 60 by fracture is lower than the upper annular portion 60U (outer diameter S1). The inner portion S2 is smaller than the annular portion 60D (outer diameter S1) (S1> S2). Therefore, the size S1 (outer diameter of the lower annular portion 60D) of the fractured piece 64 that is fractured from the fractured portion 63 of the free piston 60 by the tip of the piston rod 14 and is pushed into the gas chamber 19 and dropped is shown in the embodiment. As shown in FIG. 2, it is set to be larger than the hole diameter S2 of the through hole 70 formed in the free piston 60.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration of the present invention is not limited to this embodiment, and even if there is a design change or the like without departing from the gist of the present invention. It is included in the present invention.

  According to the present invention, in the hydraulic shock absorber, the breaking portion of the free piston that is broken by the tip portion of the piston rod is larger in the breaking size of the portion facing the gas chamber than the breaking size of the portion facing the oil chamber. Thereby, in the hydraulic shock absorber having a free piston that is broken when the tip end portion of the piston rod comes into contact, the broken piece can be prevented from impairing the damper function.

DESCRIPTION OF SYMBOLS 10 Hydraulic buffer 11 Cylinder 14 Piston rod 15 Piston 18 Oil chamber 19 Gas chamber 20, 40, 40A, 60 Free piston 23, 43, 63 Breaking parts 24, 44, 64 Broken fragments 25, 45, 65 Convex parts 26, 46 Annular weak part 27 Groove-shaped communication path 30, 50, 70 Through hole 61 O-ring groove

Claims (5)

A free piston is slidably inserted into the cylinder, the inside of the cylinder is partitioned into an oil chamber and a gas chamber by this free piston, and a piston fixed to a piston rod that protrudes outside the cylinder can be slid into the oil chamber. Inserted,
In the hydraulic shock absorber in which the free piston is provided with a break portion that breaks when the tip of the piston rod comes into contact with the free piston and forms a through hole that connects the oil chamber and the gas chamber.
A hydraulic shock absorber in which a broken portion of a free piston, which is broken by a tip portion of a piston rod, has a larger broken size of a portion facing the gas chamber than a broken size of a portion facing the oil chamber.   2. The fracture surface of the fracture portion has a generally conical shape connecting a root of a convex portion formed on an end surface facing the oil chamber of the free piston and an annular weak portion formed on an end surface facing the gas chamber of the free piston. Hydraulic shock absorber as described in.   A groove-shaped communication path extending from the fractured portion to the end surface facing the oil chamber of the free piston and extending over a range larger than the outer diameter of the tip portion of the piston rod that contacts the end surface of the free piston is recessed. Item 3. The hydraulic shock absorber according to Item 1 or 2.   The hydraulic shock absorber according to claim 1 or 2, wherein the fracture portion forms a through hole having a larger hole diameter than an outer diameter of a tip portion of the piston rod. The hydraulic shock absorber according to claim 1, wherein the fracture portion is formed in a groove of an O-ring groove on an outer periphery of the free piston .

Images