JP2010276044A - Telescopic hydraulic shock absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a telescopic hydraulic shock absorber capable of imparting excellent cushion performance in compression. <P>SOLUTION: A fork bolt side sleeve 94 and a free piston side sleeve 67 form a communicating passage for blowing surplus oil in a sub-tank chamber 53 to an outer cylinder chamber 27, by communicating the outer cylinder chamber 27 with the sub-tank chamber 53. An end surface 67a in the axial direction of the free piston side sleeve 67 as a back pressure receiving part facing the communicating passage, is formed on the volume compensating chamber side of a free piston 61, and the pressure receiving area of the end surface 67a in the axial direction is smaller than the pressure receiving area on the sub-tank chamber side of the free piston 61. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a telescopic hydraulic shock absorber applied to a front fork or the like of a saddle-ride type vehicle.

  As a conventional front fork, there is disclosed a structure in which a blow hole is provided in a damper cylinder that defines a gas chamber (volume compensation chamber) behind a free piston (see, for example, Patent Document 1). In this case, when the hydraulic pressure in the sub tank reaches a predetermined pressure, the free piston slides, and the oil is blown into the outer cylinder chamber formed between the vehicle body side tube and the damper cylinder through this blow hole, and the damper cylinder The high pressure inside is avoided.

JP-A-11-280826

  By the way, in the front fork described in Patent Document 1, the air pressure in the outer cylinder chamber increases during compression, and the air flows backward from the blow hole. The back pressure is applied to the entire surface of the free piston on the gas chamber side, and the cushion performance may become hard.

  This invention is made | formed in view of the said situation, The objective is to provide the telescopic type hydraulic shock absorber which can give a favorable cushion performance at the time of compression.

The invention according to claim 1 which solves the above-mentioned problem is
A vehicle body side tube and a wheel side tube which are slidably fitted to each other;
A damper cylinder provided in the vehicle body side tube so as to extend downward from the upper end side of the vehicle body side tube;
A piston rod provided in the wheel side tube so as to extend upward from the lower end side of the wheel side tube;
A main piston that is provided at an upper end of the piston rod and is slidably attached to the inside of the damper cylinder, and divides the inside of the damper cylinder into a piston-side oil chamber and a rod-side oil chamber;
A sub-piston that is attached to the damper cylinder on the upper end side of the vehicle body side tube from the main piston, divides the interior of the damper cylinder into the piston-side oil chamber and a sub-tank chamber, and has a damping force generator;
It is slidably attached to the inside of the damper cylinder on the upper end side of the vehicle body side tube from the sub piston, and slidably contacts the inner peripheral surface of the damper cylinder so that the inside of the damper cylinder becomes the sub tank chamber and the gas chamber. Free piston to partition,
A free piston spring that is provided in the gas chamber and presses the free piston;
A guide rod that is provided inside the damper cylinder in a state in which the free piston is extrapolated, and guides the sliding of the free piston;
In the telescopic hydraulic shock absorber with
When the free piston slides and the volume of the sub tank chamber reaches a predetermined value or more, the outer cylinder chamber formed between the vehicle body side tube and the damper cylinder communicates with the sub tank chamber, A communication passage for blowing surplus oil in the sub tank chamber to the outer cylinder chamber is formed between the free piston and the guide rod and is cut off from the gas chamber.

In addition to the structure of Claim 1, the invention of Claim 2 is
A back pressure receiving portion facing the communication passage is formed on the gas chamber side of the free piston, and the back pressure receiving portion has a pressure receiving area smaller than a pressure receiving area on the sub tank chamber side of the free piston. It is formed in this.

In addition to the structure of Claim 1, the invention of Claim 3 is
Fork bolt having a fork bolt body that closes one end opening of the vehicle body side tube, and a fork bolt side sleeve that extends downward concentrically with the guide rod and includes a portion smaller in diameter than the inner diameter of the damper cylinder. Further comprising
The free piston extends upward concentrically with the guide rod, and includes a free piston side sleeve having an outer diameter smaller than the fork bolt side sleeve and an inner diameter larger than the guide rod.
The free piston side sleeve is slidably fitted in the fork bolt side sleeve,
The fork bolt side sleeve above the sliding area of the free piston side sleeve is formed with a communication hole communicating with the outer cylinder chamber.

In addition to the structure of Claim 3, the invention of Claim 4 is
A back pressure receiving portion facing the communication path is formed at an upper end of the free piston side sleeve, and the back pressure receiving portion has a pressure receiving area smaller than a pressure receiving area on the sub tank chamber side of the free piston. It is formed.

In addition to the structure of Claim 3 or 4, the invention of Claim 5 is
The free piston includes a free piston body that is in sliding contact with an inner peripheral surface of the damper cylinder, and the free piston side sleeve,
A first seal member that seals between the outer peripheral surface of the free piston main body and the damper cylinder is provided on the outer peripheral surface of the free piston main body,
A second seal member that seals between the inner peripheral surface of the free piston main body and the outer peripheral surface of the guide rod is provided on the inner peripheral surface of the free piston main body,
The outer peripheral surface of the free piston side sleeve is provided with a third seal member for sealing between the outer peripheral surface of the free piston side sleeve and the inner peripheral surface of the fork bolt side sleeve.

In addition to the structure of Claim 5, the invention of Claim 6 is
The guide rod has a reduced diameter portion on an outer peripheral surface at an axial position facing the second seal member when the free piston moves by a predetermined amount.

  According to the first aspect of the present invention, when the free piston slides and the volume of the sub tank chamber exceeds a predetermined value, the outer cylinder chamber communicates with the sub tank chamber, and excess oil in the sub tank chamber is removed from the outer cylinder. A communication passage for blowing into the chamber is formed between the free piston and the guide rod and is cut off from the gas chamber. As a result, when the hydraulic shock absorber is compressed, when the rising air pressure in the outer cylinder chamber operates as a back pressure on the free piston, the back pressure can be set small, preventing the cushion performance from becoming hard, and good cushion performance Can be given.

  According to the second aspect of the present invention, the back pressure receiving portion formed on the gas chamber side of the free piston is formed so that its pressure receiving area is smaller than the pressure receiving area on the sub tank chamber side of the free piston. Therefore, the back pressure received by the free piston can be set small by changing the pressure receiving areas of the free pistons on the gas chamber side and the sub tank chamber side.

  According to the third aspect of the present invention, the fork bolt includes a fork bolt side sleeve that extends downward concentrically with the guide rod and includes a portion having a smaller diameter than the inner diameter of the damper cylinder. It has a free piston side sleeve that extends concentrically upward and has an outer diameter smaller than that of the fork bolt side sleeve and an inner diameter larger than that of the guide rod. The free piston side sleeve is slidable within the fork bolt side sleeve. The fork bolt side sleeve is fitted to the free piston side sleeve, and a communication hole communicating with the outer cylinder chamber is formed in the fork bolt side sleeve. Thereby, the said back pressure which a free piston receives can be set small with the comparatively simple structure of a fork bolt and a free piston.

  According to the fourth aspect of the present invention, the back pressure receiving portion formed at the upper end of the free piston side sleeve is formed so that its pressure receiving area is smaller than the pressure receiving area on the sub tank chamber side of the free piston. Therefore, the back pressure received by the free piston can be set small by changing the pressure receiving areas of the free piston on the gas chamber side and the sub tank chamber side by the back pressure receiving portion formed on the free piston side sleeve.

  According to the fifth aspect of the present invention, the first seal member for sealing between the outer peripheral surface of the free piston main body and the damper cylinder is provided on the outer peripheral surface of the free piston main body. A second seal member is provided for sealing between the inner peripheral surface of the free piston main body and the outer peripheral surface of the guide rod. The outer peripheral surface of the free piston side sleeve is provided with the outer peripheral surface of the free piston side sleeve and the fork bolt side sleeve. A third seal member is provided for sealing between the inner peripheral surface of the first seal member and the inner peripheral surface. As a result, air is prevented from being released into the sub tank chamber and the gas chamber during compression, and an appropriate back pressure is applied to the back pressure receiving portion of the free piston.

  According to the invention described in claim 6, the guide rod has the reduced diameter portion on the outer peripheral surface at the axial position facing the second seal member when the free piston moves by a predetermined amount. As a result, when the amount of oil in the sub tank chamber reaches a predetermined amount, the free piston moves by a predetermined amount, the second seal member reaches the reduced diameter portion, and excess oil passes through the reduced diameter portion from the sub tank chamber to the guide rod. It passes through the gap between the outer peripheral surface and the inner peripheral surface of the free piston sleeve, and is blown into the outer cylinder chamber through the communication hole. Therefore, surplus oil can be blown into the outer cylinder chamber while taking a structure in which the back pressure can be set small.

1 is a side view showing a motorcycle to which a front fork of the present invention is applied. It is sectional drawing which fractures | ruptures and shows the front fork of one Embodiment of this invention. FIG. 3 is an enlarged cross-sectional view of a main part of the front fork of FIG. 2. FIG. 4 is an enlarged cross-sectional view of a main part corresponding to FIG. 3, showing a state where the free piston is raised and oil in the sub tank chamber is blown into the outer cylinder chamber.

  Hereinafter, a front fork according to an embodiment of the telescopic hydraulic shock absorber of the present invention will be described with reference to FIGS.

  As shown in FIG. 1, a motorcycle 110 to which the present invention is applied includes a body frame 111, a head pipe 112 provided at the front end, a pair of left and right main frames 113 extending downward from the head pipe 112, and a main frame. 113 a pair of left and right center frames 114 connected to the rear end of 113 and extending downward, a cross member 115 connecting the lower ends of the pair of left and right center frames 114 in the vehicle width direction, and a pair of left and right extending downward from the head pipe 112. Connected to the down frame 116, a pair of left and right reinforcing frames 117 that extend downward from the middle portion of the main frame 113 and are respectively connected to the lower ends of the down frames 116, and the lower frames 116 and the lower ends of the reinforcing frames 117 And a down tube 118 to be formed. An engine 150 is suspended from the main frame 113, the cross member 115, and the down tube 118. A skid plate 160 that covers the lower side of the engine 150 is attached to the center frame 114, the lower end portion, and the lower end portion of the down tube 118.

  The motorcycle 110 also includes a front fork 10 that is steerably supported by the head pipe 112, a front wheel WF that is rotatably supported by the lower end portion of the front fork 10, and steering that is attached to the upper end portion of the front fork 10. And a handle 22 for use. The front fork 10 is provided with a front fender 123, and the front fender 123 covers the upper side of the front wheel WF. The motorcycle 110 includes a rear fork 124 that is swingably supported between a center frame 114 via a pivot shaft (not shown), and a rear wheel WR that is rotatably supported at a rear end portion of the rear fork 124. . Note that a fuel tank 125 is mounted on the main frame 113, and a vehicle body cover 126 with a rear fender 127 integrally formed thereon is attached thereto.

  The engine 150 is a water-cooled single-cylinder engine, and its outer shell is mainly attached to the crankcase 151, the cylinder block 152 attached to the front upper end of the crankcase 151, and the upper end of the cylinder block 152. Cylinder head 153, a cylinder head cover 154 covering the upper opening of the cylinder head 153, an ACG (generator) cover 155 covering the opening on the left side of the crankcase 151, and an opening on the right side of the crankcase 151 (not shown) And a clutch cover.

  Further, as shown in FIG. 1, a throttle body 192 is connected to an intake port (not shown) of the cylinder head 153 via an intake pipe 191, and an upstream end of the throttle body 192 is connected via a connection pipe 193. An air cleaner 194 is connected. A muffler 196 is connected to an exhaust port (not shown) of the cylinder head 153 via an exhaust pipe 195.

As shown in FIG. 2, in the front fork 10, a wheel side tube (inner tube) 12 is slidably inserted into a vehicle body side tube (outer tube) 11, and a suspension spring 13 is inserted between the tubes 11, 12. While interposing, the single cylinder type damper 14 is turned upside down.

  A bushing 15 slidably contacting the outer peripheral portion of the wheel side tube 12 is fitted to the inner peripheral portion of the lower end of the vehicle body side tube 11, and a bushing of the inner peripheral portion of the vehicle body side tube 11 is slidably contacting the upper outer peripheral portion of the wheel side tube 12. 16 is fitted.

  The vehicle body side tube 11 is supported on the vehicle body side via an upper bracket 17A and a lower bracket 17B, and the wheel side tube 12 is coupled to the axle via an axle bracket 18.

  A fork bolt main body 91 of the fork bolt 19 is screwed to the upper end portion of the vehicle body side tube 11 via an O-ring. Further, the upper end portion of the damper cylinder 21 (upper cylinder tube 21 </ b> A) of the damper 14 is screwed into the fork bolt 19, and the upper end opening of the upper cylinder tube 21 </ b> A is closed by the fork bolt 19. The damper cylinder 21 of the damper 14 is divided into two upper and lower cylinder tubes 21A and 21B, and a joined body thereof. Therefore, the damper cylinder 21 is provided in the vehicle body side tube 11 so as to extend downward from the upper end portion side of the vehicle body side tube 11.

  An oil lock collar 23 is fitted on the inner periphery of the lower end of the wheel side tube 12 via an O-ring. The oil lock collar 23 is fixed to the axle bracket 18 with an O-ring via a O-ring. It is. Further, a base end portion of a piston rod (hollow rod) 22 of the damper 14 is screwed to the bottom bolt 24 and locked by a lock nut 24A, and a tip end portion of the piston rod 22 is inserted into the damper cylinder 21. . The piston rod 22 is provided in the wheel side tube 12 so as to extend upward from the lower end side of the wheel side tube 12.

  A seal cap 29 is screwed into the opening on the lower end side of the damper cylinder 21, and an oil lock piece 30 is loosely fitted on the outer peripheral portion of the lower end portion of the seal cap 29. A guide bush 49 is inserted between the piston rod 22 and the seal cap 29.

  The suspension spring 13 is interposed between a spring receiver 25 attached to the outer peripheral surface of the base end portion of the oil lock collar 23 and a spring receiver 26 fixed to the outer peripheral surface of the intermediate portion of the damper cylinder 21 (lower cylinder tube 21B). Has been. Further, an oil chamber 27A and an air chamber 27B are provided in the outer cylinder chamber 27 formed inside the vehicle body side tube 11 and the wheel side tube 12, that is, between the vehicle body side tube 11 and the wheel side tube 12, and the damper cylinder 21. The gas confined in the air chamber 27B constitutes a gas spring. The elastic force of the suspension spring 13 and the gas spring absorbs the impact force that the vehicle receives from the road surface.

  The damper 14 has a piston valve device 40 and a base valve device 50. The damper 14 suppresses expansion and contraction vibration of the vehicle body side tube 11 and the wheel side tube 12 by the damping force generated by the piston valve device 40 and the base valve device 50.

  The piston valve device 40 has a piston holder 41 attached to the tip (upper end) of the piston rod 22 and a main piston 42 attached to the piston holder 41. The main piston 42 slidably contacts the inside of the damper cylinder 21B, and divides the inside of the damper cylinder 21B into a piston side oil chamber 43A in which the piston rod 22 is not accommodated and a rod side oil chamber 43B in which the piston rod 22 is accommodated. The main piston 42 is provided with an expansion side valve 44A so that the piston side oil chamber 43A and the rod side oil chamber 43B can communicate with each other, and a pressure side valve 45A is provided with the piston side oil chamber 43A and the rod side. The pressure side flow path 45 which enables communication with the oil chamber 43B is provided.

  Further, the piston valve device 40 passes the damping force adjustment rod 47 coupled to the adjuster 46 pivotally supported by the bottom bolt 24 through the hollow portion of the piston rod 22, and the damping that advances and retreats in the axial direction by the rotation operation of the adjuster 46. The flow passage area of the bypass passage 48 between the piston-side oil chamber 43A and the rod-side oil chamber 43B provided in the piston holder 41 can be adjusted by the needle 47A at the tip of the force adjusting rod 47.

  As shown in FIG. 3, the base valve device 50 has a guide rod 51 screwed onto the fork bolt 19 described above, and a sub-piston 52 held by a nut 51 </ b> B at the tip of the guide rod 51. The sub piston 52 is in liquid-tight contact with the inner peripheral portion of the upper cylinder tube 21A on the upper end side of the vehicle body side tube 11 with respect to the main piston 42, and forms a sub tank chamber 53 above the piston side oil chamber 43A. . The sub-piston 52 includes a pressure-side valve 54A so that the piston-side oil chamber 43A and the sub-tank chamber 53 can communicate with each other, and a sub-piston 52 includes an expansion-side valve 55A that connects the piston-side oil chamber 43A and the sub-tank chamber 53. And an extension-side flow channel 55 that enables communication. The housing holder 51 </ b> A includes a bypass channel 56 that bypasses the pressure side channel 54 and the extension side channel 55 to allow the piston side oil chamber 43 </ b> A and the sub tank chamber 53 to communicate with each other.

  The damping force adjusting rod 58 provided in the fork bolt 19 is provided with an adjuster 59 and is inserted into the guide rod 51, and the flow of the bypass channel 56 by the needle 58A at the tip which moves forward and backward in the axial direction by the rotation operation of the adjuster 59. The road area can be adjusted. The fork bolt 19 has an adjuster 59 and its holder 59A embedded in the center of the end face of the head.

  The base valve device 50 is externally inserted into the guide rod 51 inside the upper cylinder tube 21 </ b> A on the upper end side of the vehicle body side tube 11 with respect to the sub piston 52, and the liquid is moved along the upper cylinder tube 21 </ b> A and the guide rod 51. A free piston 61 that slides closely is provided. The free piston 61 includes a free piston main body 66 that is in sliding contact with the upper cylinder tube 21 </ b> A, and a free piston side sleeve 67 that is slidably fitted in a fork bolt side sleeve 94 formed on the fork bolt 19. The free piston side sleeve 67 extends upward from the free piston main body 66 concentrically with the guide rod 51, the outer diameter D 1 is set smaller than the inner diameter D 7 of the fork bolt side sleeve 93, and the inner diameter D 2 is equal to the guide rod 51. It is larger than the outer diameter D3 and is formed uniformly with the inner diameter of the free piston main body 66.

  A first seal member 81 having an O-ring is provided on the outer peripheral surface of the free piston main body 66, and seals between the outer peripheral surface of the free piston main body 66 and the upper cylinder tube 21A. A second seal member 82 having an O-ring is provided on the inner peripheral surface of the free piston main body 66 to seal between the inner peripheral surface of the free piston main body 66 and the outer peripheral surface of the guide rod 51. A third seal member 83 having an O-ring is provided on the outer peripheral surface of the free piston side sleeve 67, and seals between the outer peripheral surface of the free piston side sleeve 67 and the inner peripheral surface of the fork bolt side sleeve 93.

  Thereby, the free piston 61 partitions the sub tank chamber 53 communicating with the piston side oil chamber 43A on the sub piston 52 side, and the volume compensation chamber (gas chamber) 53B on the fork bolt 19 side in which air is accommodated. . A free piston spring 62 is interposed between the free piston 61 and the fork bolt 19 so as to have a predetermined pressure load.

  The free piston 61 moves up and down to compensate for the oil amount change in the damper cylinder 21 corresponding to the volume of the piston rod 22 entering and exiting when the piston rod 22 enters and exits the damper cylinder 21. When the piston rod 22 enters the damper cylinder 21 and is compressed, the spring 62 contracts, and the oil chamber in the damper cylinder 21 is pressurized by the spring force of the spring 62 at this time.

  Here, the fork bolt 19 is screwed to the vehicle body side tube 11 to close the one end opening of the vehicle body side tube 11 and the fork bolt concentric with the guide rod 51 and extending downward from the fork bolt body 91. Side sleeve 94. The fork bolt side sleeve 94 has a cylinder mounting portion 93 into which the damper cylinder 21 is screwed on the outer peripheral surface, and the outer diameter D4 of the straight portion 94a below the cylinder mounting portion 93 is smaller than the inner diameter D5 of the damper cylinder 21. Formed. The portion 92 above the cylinder mounting portion 93 of the fork bolt side sleeve 94 has an outer diameter D6 larger than the cylinder mounting portion 93 and smaller than the fork bolt main body 91 (that is, smaller than the inner diameter D8 of the vehicle body side tube 11). A plurality of communication holes 92a extending in the radial direction are formed. Therefore, the fork bolt 19 has a plurality of steps so that the outer diameter of the fork bolt main body 91, the portion 92 where the communication hole 92a is formed, the cylinder mounting portion 93, and the straight portion 94a become smaller in order. It is formed in a cylindrical shape.

  The inner peripheral surface of the fork bolt-side sleeve 94 has a uniform inner diameter D7 so as to accommodate the free piston-side sleeve 67 that slides between the outer peripheral surface of the guide rod 51 and the outer peripheral surface of the guide rod 51. An annular space 68 is defined between them. Therefore, the annular space 68 forms a sliding region where the free piston side sleeve 67 slides, but the annular space 68 is formed longer than the sliding region of the free piston side sleeve 67 (FIG. 3). reference.). Accordingly, the communication hole 92 a opens to the inner peripheral surface of the fork bolt side sleeve 94 above the sliding region, and is defined between the inner peripheral surface of the fork bolt side sleeve 94 and the outer peripheral surface of the guide rod 51. The annular space 68 to be communicated with the outer cylinder chamber 27.

  Although not shown, the fork bolt 19 includes an exhaust plug for discharging air that has entered the outer cylinder chamber 27 from the sliding portion of the vehicle body side tube 11 and the wheel side tube 12 due to the expansion and contraction of the front fork 10, and a volume. An adjustment plug for adjusting the pressure in the compensation chamber 53B and the amount of oil is provided.

Further, the guide rod 51 has a reduced diameter portion 51C whose outer diameter is smaller than the remaining portion on the outer peripheral surface at the axial position where the second seal member 82 faces when the free piston 61 moves by a predetermined amount. Then, when the excess oil accumulated in the damper cylinder 21 increases and the oil amount in the sub tank chamber 53 reaches a predetermined amount, the free piston 61 moves by a predetermined amount as shown in FIG. 82 reaches the reduced diameter portion 51C. As a result, a gap is formed between the second seal member 82 and the reduced diameter portion 51C, and surplus oil passes from the sub tank chamber 53 through the reduced diameter portion 51C to the outer peripheral surface of the guide rod 51 and the free piston side sleeve 67. It passes through the gap g between the peripheral surface and blown into the outer cylinder chamber 27 through the annular space 68 and the communication hole 92a.
For this reason, in the present embodiment, the communication path includes the reduced diameter portion 51C, the gap g between the outer peripheral surface of the guide rod 51 and the inner peripheral surface of the free piston side sleeve 67, and the inner peripheral surface of the fork bolt side sleeve 94. An annular space 68 defined between the outer periphery of the guide rod 51 and a communication hole 92 is included. Further, the axial end surface 67a of the free piston-side sleeve 67 facing the annular space 68 constituting the communication path constitutes a back pressure receiving portion that receives air pressure from the outer cylinder chamber 27 that flows in through the communication hole 92a during compression. To do.

  Further, as described above, the inner diameter of the free piston side sleeve 67 and the inner diameter of the free piston main body 66 are uniform, while the outer diameter of the free piston side sleeve 67 is smaller than the outer diameter of the free piston main body 66. Yes. Accordingly, the pressure receiving area of the axial end surface 67a of the free piston side sleeve 67 is smaller than the pressure receiving area of the free piston main body 66 on the sub tank chamber side.

  The front fork 10 thus configured performs a damping action as follows.

  When the front fork 10 is compressed, in the base valve device 50, a compression side damping force is generated by the oil flowing through the needle 58A of the sub piston 52 or the compression side valve 54A. Specifically, the oil corresponding to the volume of the piston rod 22 that has entered the damper cylinder 21 is discharged from the piston side oil chamber 43 </ b> A to the sub tank chamber 53 through the bypass flow path 56 of the sub piston 52 or the pressure side flow path 54. Is done. At this time, when the relative speed between the damper cylinder 21 and the piston rod 22 is low, a compression-side damping force is obtained by the throttle resistance by the needle 58A provided in the bypass flow path 56. This damping force is adjusted by adjusting the position of the needle 58A by the adjuster 59. Further, when the relative speed between the damper cylinder 21 and the piston rod 22 is medium to high, the oil passing through the pressure side flow path 54 from the piston side oil chamber 43A is deflected and deformed by the pressure side valve 54A and guided to the sub tank chamber 53, and the pressure side damping is performed. Produce power. On the other hand, in the piston valve device 40, the oil in the piston-side oil chamber 43A passes through the pressure-side flow path 45, opens the pressure-side valve 45A and is guided to the rod-side oil chamber 43B, and generates a pressure-side damping force set as necessary.

  When the front fork 10 is extended, an extension side damping force is generated in the piston valve device 40 by the oil flowing through the needle 47A of the main piston 42 or the extension side valve 44A. Specifically, when the relative speed between the damper cylinder 21 and the piston rod 22 is low, the oil in the rod-side oil chamber 43B is guided to the piston-side oil chamber 43A through the bypass passage 48 with the needle 47A, and the needle between these The expansion side damping force is generated by the diaphragm resistance of 47A. This damping force is adjusted by adjusting the position of the needle 47A by the adjuster 46. When the relative speed between the damper cylinder 21 and the piston rod 22 is medium to high, the oil in the rod side oil chamber 43B passes through the extension side flow path 44 to bend and deform the extension side valve 44A and is guided to the piston side oil chamber 43A. Side damping force is generated. On the other hand, in the base valve device 50, the oil corresponding to the retraction volume of the piston rod 22 retreating from the damper cylinder 21 passes from the sub tank chamber 53 to the piston side oil chamber 43A through the extension side flow passage 55 of the sub piston 52. Reflux to generate the desired damping force.

  The damping force on the compression side and the extension side suppresses the stretching vibration of the front fork 10.

  When the front fork 10 is most compressed, the oil lock piece 30 at the lower end portion of the lower cylinder tube 21B of the damper cylinder 21 is fitted to the oil lock collar 23 provided at the lower end portion of the wheel side tube 12, The oil compressed between them causes an oil lock action and prevents the damper 20 from bottoming.

  Further, when the front fork 10 is extended to the maximum, the lower end surface of the piston holder 41 provided on the piston rod 22 abuts on the rebound spring 32 supported by the seal cap 29, thereby achieving a fully buffering action.

  Here, when the front fork 10 is compressed, the air pressure in the outer cylinder chamber 27 rises, so that air flows back into the annular space 68 through the communication hole 92 a and flows to the axial end surface 67 a of the free piston side sleeve 67. Back pressure is applied. For this reason, the pressing force of the free piston 61 when the front fork 10 is compressed can add the spring force of the air pressure in the outer cylinder chamber 27 to the spring force of the free piston spring 62. However, since the communication passage is formed between the free piston 61 and the guide rod 51 so as to be cut off from the volume expansion chamber 53B, back pressure is applied to the surface of the free piston body 66 facing the volume expansion chamber 53B. As described above, the back pressure is applied to the axial end surface 67 a of the free piston side sleeve 67. Since the pressure receiving area of the axial end surface 67a of the free piston side sleeve 67 is smaller than the pressure receiving area of the free piston main body 66 on the sub tank chamber side, the back pressure can be set small and the cushion performance can be improved.

  In addition, the oil seal 35 removes hydraulic oil attached to the outer peripheral surface of the piston rod 22 located in the oil chamber 27 inside the vehicle body side tube 11 and the wheel side tube 12 every time the front fork 10 strokes. Bring it inside. Accordingly, the hydraulic oil in the oil chambers 43A and 43B and the sub tank chamber 53 inside the damper cylinder 21 gradually increases due to long-term use, and the free piston 61 moves upward due to the increase. Here, when the second seal member 82 provided on the free piston 61 rises to a position facing the reduced diameter portion 51C due to excess oil accumulated over time, as shown by an arrow in FIG. Oil can be blown into the outer cylinder chamber 27 through the portion 51C, the gap g, the annular space 68, and the communication hole 92a, and the amount of oil and pressure in the damper cylinder 21 can be adjusted.

  Therefore, according to the present embodiment, when the free piston 61 slides and the volume of the sub tank chamber 53 exceeds a predetermined value, the outer cylinder chamber 27 and the sub tank chamber 53 communicate with each other, and the surplus in the sub tank chamber 53 is obtained. A communication path for blowing oil into the outer cylinder chamber 27 is formed between the free piston 61 and the guide rod 51 and is cut off from the volume compensation chamber 53B. As a result, when the front fork 10 is compressed, the rising air pressure in the outer cylinder chamber 27 operates as a back pressure on the free piston 61 via the communication path, but the communication path is blocked from the volume compensation chamber 53B. The back pressure can be set small, and good cushion performance can be given.

  An axial end surface 67a of a free piston side sleeve 67 as a back pressure receiving portion facing the communication path is formed at the volume compensation chamber side of the free piston 61, that is, at the upper end of the free piston side sleeve. The pressure receiving area is formed to be smaller than the pressure receiving area of the free piston 61 on the sub tank chamber side. Therefore, the back pressure received by the free piston 61 can be set small by changing the pressure receiving area of the free piston 61 on the volume compensation chamber side and the sub tank chamber side.

  The fork bolt 19 includes a fork bolt side sleeve 94 that extends downward concentrically with the guide rod 51 and includes a straight portion 94 a that is smaller than the inner diameter D 5 of the damper cylinder 21. And a free piston side sleeve 67 having an outer diameter D1 smaller than the fork bolt side sleeve and an inner diameter D2 larger than the guide rod 51. The free piston side sleeve 67 is a fork bolt side sleeve. A fork bolt side sleeve 94 that is slidably fitted in the inner side 94 and is above the sliding area of the free piston side sleeve 67 is formed with a communication hole 92 a that communicates with the outer cylinder chamber 27. As a result, the back pressure received by the free piston 61 can be set small by a relatively simple structure of the fork bolt 19 and the free piston 67.

  Further, a first seal member 81 that seals between the outer peripheral surface of the free piston main body 66 and the damper cylinder 21 is provided on the outer peripheral surface of the free piston main body 66. A second seal member 82 is provided for sealing between the inner peripheral surface of 66 and the outer peripheral surface of the guide rod 51, and the outer peripheral surface of the free piston side sleeve 67 is connected to the outer peripheral surface of the free piston side sleeve 67 and the fork bolt side. A third seal member 83 is provided for sealing between the inner peripheral surface of the sleeve 94. Accordingly, air is prevented from being released into the sub tank chamber 53 and the volume compensation chamber 53B during compression, and an appropriate back pressure is applied to the axial end surface 67a of the free piston 61.

  Further, the guide rod 51 has a reduced diameter portion 51C on the outer peripheral surface at the axial position facing the second seal member 82 when the free piston 61 moves by a predetermined amount. Accordingly, when the amount of oil in the sub tank chamber 53 reaches a predetermined amount, the free piston 61 moves by a predetermined amount, the second seal member 82 reaches the reduced diameter portion 51C, and excess oil is reduced in diameter from the sub tank chamber 53. It passes through a gap g between the outer peripheral surface of the guide rod 51 and the inner peripheral surface of the free piston side sleeve 67 via the portion 51C, and is blown into the outer cylinder chamber 27 through the communication hole 92a. Therefore, surplus oil can be blown into the outer cylinder chamber 27 while taking a structure in which the back pressure can be set small.

  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 there are design changes and the like without departing from the gist of the present invention. Is included in the present invention.

DESCRIPTION OF SYMBOLS 10 Front fork 11 Car body side tube 12 Wheel side tube 19 Fork bolt 21 Damper cylinder 22 Piston rod 27 Outer cylinder chamber 29 Seal cap 32 Rebound spring 35 Oil seal 40 Piston valve device 42 Main piston 43A Piston side oil chamber 43B Rod side oil chamber 50 Base valve device 51 Guide rod 51C Reduced diameter portion 52 Sub piston 53 Sub tank chamber 53B Volume compensation chamber (gas chamber)
61 Free piston 62 Free piston spring 66 Free piston body 67 Free piston side sleeve 81 First seal member 82 Second seal member 83 Third seal member 91 Fork bolt body 92a Communication hole 94 Fork bolt side sleeve

Claims (6)

A vehicle body side tube and a wheel side tube which are slidably fitted to each other;
A damper cylinder provided in the vehicle body side tube so as to extend downward from the upper end side of the vehicle body side tube;
A piston rod provided in the wheel side tube so as to extend upward from the lower end side of the wheel side tube;
A main piston that is provided at an upper end of the piston rod and is slidably attached to the inside of the damper cylinder, and divides the inside of the damper cylinder into a piston-side oil chamber and a rod-side oil chamber;
A sub-piston that is attached to the damper cylinder on the upper end side of the vehicle body side tube from the main piston, divides the interior of the damper cylinder into the piston-side oil chamber and a sub-tank chamber, and has a damping force generator;
It is slidably attached to the inside of the damper cylinder on the upper end side of the vehicle body side tube from the sub piston, and slidably contacts the inner peripheral surface of the damper cylinder so that the inside of the damper cylinder becomes the sub tank chamber and the gas chamber. Free piston to partition,
A free piston spring that is provided in the gas chamber and presses the free piston;
A guide rod that is provided inside the damper cylinder in a state in which the free piston is extrapolated, and guides the sliding of the free piston;
In the telescopic hydraulic shock absorber with
When the free piston slides and the volume of the sub tank chamber reaches a predetermined value or more, the outer cylinder chamber formed between the vehicle body side tube and the damper cylinder communicates with the sub tank chamber, A telescopic hydraulic buffer characterized in that a communication passage for blowing excess oil in the sub tank chamber to the outer cylinder chamber is formed between the free piston and the guide rod, and is cut off from the gas chamber. vessel.   A back pressure receiving portion facing the communication passage is formed on the gas chamber side of the free piston, and the back pressure receiving portion has a pressure receiving area smaller than a pressure receiving area on the sub tank chamber side of the free piston. The telescopic hydraulic shock absorber according to claim 1, wherein the telescopic hydraulic shock absorber is formed as follows. Fork bolt having a fork bolt body that closes one end opening of the vehicle body side tube, and a fork bolt side sleeve that extends downward concentrically with the guide rod and includes a portion smaller in diameter than the inner diameter of the damper cylinder. Further comprising
The free piston extends upward concentrically with the guide rod, and includes a free piston side sleeve having an outer diameter smaller than the fork bolt side sleeve and an inner diameter larger than the guide rod.
The free piston side sleeve is slidably fitted in the fork bolt side sleeve,
2. The telescopic hydraulic shock absorber according to claim 1, wherein a communication hole communicating with the outer cylinder chamber is formed in the fork bolt side sleeve above the sliding region of the free piston side sleeve.   A back pressure receiving portion facing the communication path is formed at an upper end of the free piston side sleeve, and the back pressure receiving portion has a pressure receiving area smaller than a pressure receiving area on the sub tank chamber side of the free piston. The telescopic hydraulic shock absorber according to claim 3, wherein the telescopic hydraulic shock absorber is formed. The free piston includes a free piston body that is in sliding contact with an inner peripheral surface of the damper cylinder, and the free piston side sleeve,
A first seal member that seals between the outer peripheral surface of the free piston main body and the damper cylinder is provided on the outer peripheral surface of the free piston main body,
A second seal member that seals between the inner peripheral surface of the free piston main body and the outer peripheral surface of the guide rod is provided on the inner peripheral surface of the free piston main body,
5. The third seal member for sealing between the outer peripheral surface of the free piston side sleeve and the inner peripheral surface of the fork bolt side sleeve is provided on the outer peripheral surface of the free piston side sleeve. The telescopic hydraulic shock absorber described in 1.   The telescopic hydraulic pressure according to claim 5, wherein the guide rod has a reduced diameter portion on an outer peripheral surface at an axial position facing the second seal member when the free piston moves by a predetermined amount. Shock absorber.

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