JP5156689B2 - Front fork - Google Patents

Description

  The present invention relates to a front fork, and more particularly, to an improvement in a front fork that is a hydraulic shock absorber that absorbs road surface vibration that is input to a front wheel that is mounted on a front wheel side of a two-wheeled vehicle and is suspended at a lower end portion.

  There have been various proposals for a front fork as a hydraulic shock absorber that absorbs road surface vibrations that are input to a front wheel that is mounted on the front wheel side of a motorcycle and is suspended at a lower end portion. In the proposal disclosed in (1), it is possible to boost the internal voltage of the built-in damper.

  That is, the front fork disclosed in Patent Document 1 has a cylindrical damper in the axial center portion of a fork main body composed of a vehicle body side tube and a wheel side tube, and this damper is a working fluid in the bottom end portion of the cylinder body. An attenuating part that allows the reciprocating passage of the motor, a free piston that is disposed downstream of the attenuating part and has a pressure-receiving surface facing the attenuating part, and a free piston that is disposed behind the free piston and that serves as an attenuating part. And an urging spring for urging in the forward direction toward.

  Therefore, in the front fork disclosed in Patent Document 1 described above, the damper in the fork main body has a reaction force that balances the spring force of the urging spring that urges the free piston in the forward direction. The pressure inside the cylinder is increased.

  As a result, for example, in the front fork, it is possible to obtain a ride comfort according to the specifications and traveling conditions of the motorcycle, and the damper has a stable compression-side damping force from the beginning when the damper is reversed from the most extended state and starts to contract. Allows generation.

Japanese Patent Laying-Open No. 2005-30534 (see paragraphs 0036 and 0037 in FIG. 1, FIG. 1)

  However, according to the proposal disclosed in Patent Document 1 described above, a ride comfort according to the specifications and traveling conditions of the motorcycle can be obtained in the front fork, and the contraction operation is started by reversing from the maximum extension state in the damper. Although there is no particular problem in terms of enabling the generation of a stable compression-side damping force from the beginning, it may be pointed out that there is a minor defect when considering the actual use.

  That is, in the above-described front fork, in the damper, the spring force of the biasing spring that biases the free piston in the forward direction and has a reaction force on the damper stops at a strength within the initially set range, The reaction force of the damper cannot be changed in level so as to respond to changes in the running conditions and usage conditions of the motorcycle.

  In other words, for example, in a two-wheeled vehicle that has many opportunities to travel on a flat road surface without riding load increasing unnecessarily, and traveling under increased load due to the presence of a passenger, When the vehicle is used, the reaction force in the damper tends to be insufficient, and the ride comfort is impaired.

  And when a motorcycle that has a lot of opportunities to increase the load is traveling with a small load, or a motorcycle that has a lot of opportunities to travel on rough land is traveling on a flat road surface, the reaction force at the damper becomes too strong. , Make riding in motorcycles worse.

  The present invention was devised in view of such a current situation, and an object of the present invention is to change the reaction force in the damper according to the traveling state and the utilization state of the two-wheeled vehicle and obtain a preferable riding comfort. Thus, it is to provide a front fork that is optimal for expecting improvement in versatility.

  In order to achieve the above-described object, the configuration of the front fork according to the present invention basically includes a damper that serves as a reservoir in the fork body in the fork body composed of a vehicle body side tube and a wheel side tube, A damper that allows the working fluid to reciprocate and a pressure receiving surface that is disposed downstream of the damper and faces the damper and defines a chamber between the damper and the damper. A free piston that retreats due to the fluid pressure action, a communication hole that allows the reservoir to communicate with the reservoir when the free piston retracts, and a free piston that is disposed behind the free piston. In a front fork having a booster spring biased in the forward direction, the fork main body is disposed while being movable in the axial direction of the fork main body. Comprising a adjuster that allows changing the maximum forward-movement position of the free piston in a sliding direction of the free piston.

  Therefore, in the front fork according to the present invention, the damper in the fork main body has a reaction force that balances the spring force of the booster spring that biases the free piston from behind, so that the cylinder body can be maintained in a boosting tendency. Therefore, when the damper in the most extended state is reversed to start the contracting operation, it is possible to generate a stable damping force by the compression side damping valve from the beginning.

  In the front fork according to the present invention, the spring force of the booster spring that urges the free piston from the back by rotating the adjuster can be changed to be stronger or stronger than the initial set value, and the reaction force of the damper can be increased accordingly. It can be strong and weak, and it is possible to obtain a favorable riding comfort according to the running situation and usage situation of the motorcycle.

It is a figure which shows in principle the front fork by this invention. It is a fragmentary longitudinal cross-section which shows embodiment which actualized the upper end side part of the front fork shown in FIG.

  Hereinafter, the present invention will be described based on the illustrated embodiment. A front fork according to the present invention is a fluid that absorbs road surface vibrations that are input to a front wheel that is mounted on the front wheel side of a two-wheeled vehicle and is suspended at a lower end. It functions as a hydraulic shock absorber as a pressure shock absorber.

  The front fork has a fork main body that suspends a front wheel (not shown) at the lower end while the upper end is coupled to a handle (not shown), and a fork main body that is housed in the fork main body. And a damper that generates a predetermined damping force by expanding and contracting in synchronization with the operation.

  As shown in FIG. 1, which is a principle diagram, the fork main body includes a vehicle body side tube 1 composed of a large-diameter outer tube whose upper end side is coupled to a handle side (not shown) of a two-wheeled vehicle (not shown), The tube 1 has a wheel-side tube 2 formed of a small-diameter inner tube that suspends a front wheel (not shown) of a two-wheeled vehicle at the lower end while the upper end is inserted into the lower end of the tube 1 so as to be retractable. .

  Incidentally, the fork main body shown in the figure is set upside down, but from the point that the present invention intends, instead of this, although not shown, the large-diameter outer tube is used as the wheel-side tube 1 and the small-diameter inner tube is formed. The tube may be set to an upright type in which the vehicle body side tube 2 is used.

  The fork main body accommodates a suspension spring S therein, and is biased in an extending direction, which is a direction in which the wheel side tube 2 comes out of the vehicle body side tube 1 by the biasing force of the suspension spring S.

  Incidentally, the suspension spring S is supported by a head end (not shown) which is a lower end in the drawing in a cylinder body 3 which constitutes a damper which will be described later, and a distal end which is not shown in the drawing. Is locked to the bottom portion (not shown) of the wheel-side tube 2.

  In addition, the fork main body has a reservoir R that is inside of the fork main body and is outside a damper, which will be described later, and the reservoir R has an air chamber A with the liquid level O of the working fluid as a boundary. The air chamber A exhibits a spring force due to its expansion and contraction.

  As shown in the figure, the damper is set to be an inverted type in which the cylinder body 3 that contains the working fluid as the working fluid is an upper end side member and the rod body 4 is a lower end side member, and the cylinder body 3 is connected to the vehicle body side tube 1. It is coupled and is suspended from the shaft core portion of the vehicle body side tube 1, and the rod body 4 is coupled to the wheel side tube 2 and is standing on the shaft core portion of the wheel side tube 2 while being at the top end in the figure. The side is inserted into the cylinder body 3 so as to be able to appear and retract.

  Incidentally, the damper shown in the figure is set upside down. However, from the point that the present invention intends, instead of this, the cylinder body 3 is used as the lower end side member and the rod body 4 is used as the upper end side. It can be said that the member may be set upright.

  However, daringly speaking, in the present invention, as will be described later, the spring force of the booster spring 71 that biases the free piston 7 by the turning operation of the adjuster 10 performed by the rider of the two-wheeled vehicle is adjustable. Therefore, since it is advantageous in terms of operation that the adjuster 10 is located at the upper end rather than the lower end of the fork main body, the damper is preferably set in an inverted type.

  In addition, the cylinder body 3 is connected to a cap member 11 that closes the upper end opening of the vehicle body side tube 1 at the bottom end (not shown) of the bottom end portion 3a of the cylinder body 3 in the drawing. By doing so, it is suspended from the shaft core portion of the vehicle body side tube 1.

  On the other hand, in this damper, the rod side chamber R1 and the piston side chamber R2 are provided in the cylinder body 3 while being slidably accommodated in the cylinder body 3 and connected to the tip which is the upper end in the figure of the rod body 4. A piston body 5 is defined.

  Further, in this damper, the rod side chamber R1 and the piston side chamber R2 in the cylinder body 3 can be communicated with each other via a damping valve 5a provided in the piston body 5, and the damping valve 5a is checked. Valves 5b are arranged in parallel.

  Incidentally, the check valve 5b prevents the hydraulic oil in the rod side chamber R1 from passing toward the piston side chamber R2, but conversely allows the hydraulic oil in the piston side chamber R2 to pass toward the rod side chamber R1. To do.

  Therefore, in this damper, an amount of hydraulic oil corresponding to the intrusion rod volume that becomes redundant in the piston side chamber R2 during the contraction operation in which the rod body 4 is immersed in the cylinder body 3 passes through the damping section 6 described later. As a result, the piston side chamber R2 flows out.

  Then, the amount of hydraulic oil corresponding to the withdrawal rod volume integral that is insufficient in the piston side chamber R2 during the extension operation in which the rod body 4 projects from the cylinder body 3 flows into the piston side chamber R2 through the damping portion 6 as well. .

  By the way, in this damper, it has the damping part 6 in the bottom end part 3a used as the upper end part in the figure of the cylinder body 3, and the free piston 7 arrange | positioned in the downstream of this damping part 6. It becomes.

  Although not shown, the attenuating portion 6 corresponds to a base valve portion in a hydraulic shock absorber formed in a double cylinder type and upright, and in the drawing, is accommodated in a bottom end portion 3a of the cylinder body 3. The piston side chamber R2 in the cylinder body 3 and the oil chamber R3, which is a container chamber upstream of the free piston 7, are defined.

  The damping section 6 includes a damping valve 6a that allows communication between the piston side chamber R2 and the oil chamber R3, and a check valve 6b that is arranged in parallel with the damping valve 6a. The check valve 6b is connected to the piston side chamber R2. The hydraulic oil is prevented from flowing out into the oil chamber R3, but the hydraulic oil from the oil chamber R3 is allowed to flow into the piston-side chamber R2.

  Incidentally, it is sufficient that the damping part 6 is accommodated in the bottom end part 3a of the cylinder body 3 and the oil chamber R3 is defined between the damping part 6 and the free piston 7, so in principle, this is the bottom end part 3a. It may be arranged in a fixed state inside.

  However, the damping portion 6 of the illustrated embodiment is slidably accommodated in the bottom end portion 3a, and the base end serving as the upper end in the drawing is attached to the vehicle body side tube 1 as will be described later. The guide rod 61 to be connected is held at the tip which is the lower end in the figure.

  The free piston 7 is located in the bottom end portion 3a and is slidably disposed on the downstream side, which is the upper side in the drawing of the damping portion 6, and includes the oil chamber R3, the rear air chamber A1, and the like. And is urged in a forward direction, which is a downward direction in the figure, by a booster spring 71 accommodated in the rear air chamber A1, that is, disposed behind.

  Incidentally, the rear side air chamber A1 is separated from the reservoir R outside the damper as shown in the figure, and therefore, this rear side air chamber A1 has a sealed pressure as a unique pressure that is not influenced by the pressure of the reservoir R. .

  The free piston 7 is slidably accommodated in the bottom end portion 3a while being formed in an annular shape through which the guide rod 61 penetrates the shaft core portion. Generation | occurrence | production of the malfunction which inclines with respect to the edge part 3a is avoided beforehand.

  Therefore, in the illustrated damper, the free piston 7 is urged in the forward direction by the booster spring 71 from behind, so that the pressure in the cylinder body 3 is maintained even when it is in the most extended state. It becomes high to balance with the spring force of 71.

  As a result, compared with the case where the free piston 7 does not have the booster spring 71 behind, the inside of the cylinder body 3 tends to be boosted. For example, from the beginning when the damper in the most extended state starts contracting operation, A stable compression-side damping force can be generated without exhibiting a phenomenon of so-called “damping force sabotage” in which the generation of damping force is delayed due to expansion and contraction of bubbles contained therein.

  By the way, the lower end of the booster spring 71 for urging the free piston 7 is locked to the back surface of the free piston 7, but the base end of the upper end in the drawing is a guide in the drawing. It is carried by a spring receiver 72 formed in a flange shape connected to the rod 61.

  The spring receiver 72 is rotated in the axial direction of the cap member 11 that closes the upper end opening of the vehicle body side tube 1. In the illustrated state, the spring receiver 72 moves forward in the downward direction in the figure. , And moves backward in the ascending direction in the drawing to return to the old state by a reverse rotation operation with respect to the adjuster 10.

  Therefore, with the advancement and retraction of the spring receiver 72, the base end position of the booster spring 71 moves in the vertical direction in the figure. At this time, the tip of the booster spring 71 is not forcibly blocked from moving, so that It moves up and down in the figure so as to move the piston 7.

  When the free piston 7 moves as the distal end advances as the base end of the booster spring 71 moves forward, the inside of the cylinder body 3 is further increased by the amount of movement of the free piston 7. To increase the reaction force in the damper.

  Further, since the tip position of the free piston 7 when the free piston 7 moves forward is changed by the amount of movement of the free piston 7, the amount of reverse stroke when the relief operation of the free piston 7 described later is changed.

  Therefore, in the damper of the present invention, the reaction force can be adjusted up and down so as to correspond to the load acting on the damper, and the fork main body that accommodates the damper, that is, the front fork, It realizes the optimal riding comfort that generates damping force according to the specifications and running conditions of the mounted motorcycle.

  Since the adjuster 10 is also provided on the cap member 11 that closes the upper end opening of the vehicle body side tube 1, the adjuster 10 can be rotated while the rider is in the posture of riding the motorcycle. The desired control can be practiced.

  In the present invention, the tip position of the free piston 7 can be changed by rotating the adjuster 10 to increase or decrease the spring force of the booster spring 71. The tip position of the free piston 7 can be changed. This can be realized, for example, by changing the pressure in the rear side air chamber A1 defined by the free piston 7, that is, the sealing pressure.

  However, in the present invention, in order to make it possible to change the tip position of the free piston 7, the configuration for changing the sealing pressure in the back side air chamber A1 was not adopted because of the change in the sealing pressure, particularly the sealing. When the pressure is increased, there is a problem that a sealing operation using a predetermined device is essential.

  In addition, the enclosing operation using the predetermined equipment can be practiced only in a specific place such as a so-called workstation, and cannot satisfy the request to change the reaction force of the damper on the spot, so-called convenience. Considering the deterioration of the property, the configuration cannot be adopted.

  The front fork thus formed according to the present invention has the following considerations as shown in the figure, and this consideration will be described a little.

  That is, first, the bottom end portion 3a of the cylinder body 3 in which the above-described free piston 7 is accommodated has a communication hole 3b closed by the free piston 7 in the drawing.

  That is, the bottom end portion 3a of the cylinder body 3 has a communication hole 3b that allows internal and external communication, and the hydraulic oil in the oil chamber R3 flows out to the reservoir R through the communication hole 3b. to enable.

  Incidentally, since the communication hole 3b is closed by the free piston 7, the back side air chamber A1 defined in the bottom end portion 3a by the free piston 7 becomes an independent air chamber A1 separated from the reservoir R. And demonstrate independent spring force.

  On the other hand, the free piston 7 slides within the bottom end portion 3a except when the predetermined stroke is retracted to open the communication hole 3b, that is, the communication hole 3b is closed.

  When the sliding of the free piston 7 is repeated, the pressure is further increased by the volume expansion of the hydraulic oil in the cylinder body 3 as the oil temperature rises. At this time, the free piston 7 has a predetermined stroke due to the pressure increase. Retreat, open the communication hole 3b, and release the high pressure in the cylinder body 3 to the reservoir R.

  Accordingly, the free piston 7 exhibits a relief function for maintaining the hydraulic pressure in the cylinder body 3 in a so-called initial state in addition to enabling the pressure increase in the cylinder body 3 described above.

  Therefore, in the illustrated front fork, when the spring force of the booster spring 71 that biases the free piston 7 is raised or lowered, the reaction force in the damper is raised or lowered as described above, and the free piston 7 Since the tip position also changes, the relief point of the free piston 7 is also changed accordingly.

  Next, the attenuating portion 6 disposed in the bottom end portion 3a of the cylinder body 3 is connected to a cap member 11 that closes the upper end opening of the vehicle body side tube 1 as illustrated. The guide rod 61 is connected to the bottom end 3a so as to be slidable.

  By the way, as described above, according to the present invention, the spring force of the booster spring 71 that biases the free piston 7 can be adjusted by the turning operation of the adjuster 10. Although the position is changed according to the change of the spring force of 71, it is not essential that the damping part 6 moves in accordance with this.

  That is, it is unavoidable to change to the position of the free piston 7 by changing the spring force of the booster spring 71, but it is not necessary to change to the position of the damping unit 6.

  However, since the damping part 6 is held at the lower end of the guide rod 61 in the drawing as shown in the figure, the damping part 6 also moves up and down when the guide rod 61 moves up and down by the turning operation of the adjuster 10.

  Therefore, in the illustrated embodiment, when the spring force of the booster spring 71 is increased and the free piston 7 moves, there is no need to worry about the free piston 7 interfering with the damping portion 6.

  As a result, in this embodiment, the spring force adjustment of the booster spring 71 can be realized as set, and the free piston 7 can be moved according to the spring force of the booster spring 71 changed.

  FIG. 2 shows an embodiment in which the front fork shown in FIG. 1 is embodied, and particularly shows an upper end side portion of the front fork, which will be described below a little.

  Incidentally, in addition to the wheel side tube 2 (see FIG. 1), in addition to the wheel side tube 2 (see FIG. 1), the cylinder body 3 in the damper has the piston body 5 and the rod body 4 that protrudes and retracts from the cylinder body 3 (see FIG. 1). ) Is omitted.

  In addition, in the place shown in FIG. 2, the same configuration as that shown in FIG. 1 described above will be described using the same reference numerals as they are, without being described again.

  First, in the place shown in FIG. 2, the bottom end 3a (see FIG. 1) of the cylinder body 3 is formed by the cylinder 31, and the upper end 31a formed relatively thick of the cylinder 31 is the vehicle body side. The tube 1 is screwed inside the upper end portion 1a, and the cap member 11 is screwed inside the upper end portion 31a to close the upper end opening of the vehicle body side tube 1.

  Then, the lower end portion 31b having a reduced diameter of the cylindrical body 31 is screwed to a bottom portion (not shown) which is the upper end portion in the drawing of the cylinder body 3, and integration with the cylinder body 3 is achieved.

  Therefore, when the bottom end portion 3a of the cylinder body 3 is formed by the cylindrical body 31, the wheel side tube 2 (ascending along the inner periphery of the vehicle body side tube 1 at the time of the most contraction operation of the fork body) As long as the inner circumference of the virtual line diagram in FIG. 2 does not interfere, the size of the pressure receiving surface of the damping unit 6 and the free piston 7 can be arbitrarily changed by selecting the diameter of the cylindrical body 31.

  Incidentally, the cap member 11 has an enclosing plug 11a, and makes it possible to inject gas into the air chamber A in the reservoir R and adjust the amount of injected gas using the enclosing plug 11a.

  The adjuster 10 is disposed on the shaft core portion of the cap member 11, and the inner adjuster 20 is further disposed on the shaft core portion of the adjuster 10. The inner adjuster 20 is connected to the sub valve 62 provided in the damping portion 6. The flow rate of hydraulic oil passing through the communicating oil passage, that is, the bypass passage is controlled.

  That is, the damping unit 6 basically has a partition wall 63 serving as a valve seat member, and a pressure-side damping valve 64 that closes and opens the downstream end of the pressure-side port 63a for opening in the partition 63. Similarly, the partition wall 63 has a suction valve 65 that closes the downstream end of the opening side port 63b for opening and closing.

  2 constitutes the damping valve 6a in the damping unit 6 shown in FIG. 1, and the suction valve 65 in the damping unit 6 is also the check valve 6b in the damping unit 6. Configure.

  Therefore, in the damping section 6 shown in FIG. 2, when hydraulic oil from the piston side chamber R2 flows out to the oil chamber R3 via the pressure side damping valve 64, a predetermined pressure side damping force is generated.

  On the other hand, the damping section 6 has a bypass passage (not shown) as an oil passage that bypasses the compression side damping valve 64, and a control valve 21 made of a needle valve body is provided in the bypass passage. The control valve 21 controls the flow rate of the hydraulic oil passing through the bypass passage by the turning operation of the inner adjuster 20 described above.

  Incidentally, a through-hole (not shown) is opened in the shaft core portion of the guide rod 61, and the control rod 22 is accommodated in the through-hole so as to be movable up and down. The tip of the control valve 21 is brought into contact with the rear end which is the upper end in the drawing of the control valve 21, and the base end which is the upper end of the control rod 22 in the drawing is the tip which is the lower end of the inner adjuster 20 in the drawing. Locked.

  The lower end portion 10a of the adjuster 10 is screwed to the base end portion 61a which is the upper end portion in the drawing of the guide rod 61, and is integrated with each other. A tip member 66 is screwed to the tip portion 61b to be integrated with each other.

  By the way, the bypass path is provided in the tip member 66, and one end opens to the piston side chamber R2, and the other end opens to the so-called back side of the sub valve 62 described above.

  Incidentally, the sub-valve 62 closes the bypass path from the oil chamber R3 side so as to be openable and closable, and prevents the hydraulic oil from flowing into the bypass path from the oil chamber R3, but the hydraulic oil chamber from the bypass path Allow inflow to R3.

  Therefore, when the above bypass path is fully opened and the hydraulic oil passes freely, the hydraulic oil from the piston side chamber R2 flows into the oil chamber R3 almost without passing through the compression side damping valve 64, The compression side damping valve 64 generates an extremely low compression side damping force.

  Then, as the flow rate of hydraulic fluid passing through the bypass passage is suppressed by the control valve 21, the flow rate of hydraulic fluid passing through the pressure side damping valve 64 from the piston side chamber R2 increases. In other words, a high compression side damping force is generated.

  Next, the free piston 7 is shown in the figure and is formed in a bottomed cylindrical shape having a square U-shaped cross section, and the bottom portion 7a is formed in an annular shape and penetrates the guide rod 61 described above in the shaft core portion. The cylindrical portion 7b is disposed along the inner periphery of the cylindrical body 31 described above.

  At this time, the cylindrical body 31 has a main body 31b that slides the outer periphery of the bottom 7a of the free piston 7 under the arrangement of the seal 73 and the bush 74, and extends upward from the upper end of the main body 31b. An inclined portion 31c that gradually inclines toward the side and gradually increases in diameter, and extends upward from the upper end of the inclined portion 31c and has an upper end portion (not shown) of the cylindrical portion 7b of the free piston 7 that is enlarged in diameter. A diameter-expanding portion 31d that is in sliding contact with the seal 75 and the bush 76 is provided, and the communication portion 3b is provided in the inclined portion 31c.

  Therefore, in this free piston 7, in the normal state described above, the communication hole 3b is positioned between the bottom portion 7a and the upper end portion of the cylindrical portion 7b, and therefore the communication of the oil chamber R3 to the reservoir R is established. Stop.

  And in this free piston 7, when it reverse | retreats so that it may raise in a figure and the outer periphery of the bottom part 7a reaches | attains said inclination part 31c and opens the communicating hole 3b, oil chamber R3 is made into the reservoir | reserver R. The fluid is communicated to allow the hydraulic oil in the oil chamber R3 to flow out to the reservoir R, that is, release the high pressure in the cylinder body 3 described above.

  In addition, since the free piston 7 has the cylindrical portion 7b and increases the total length in the sliding direction, there is no need to worry about the occurrence of the twisting phenomenon with respect to the cylindrical body 31 due to the booster spring 71 formed of a coil spring. .

  As described above, the motorcycle in which the front fork according to the present invention is mounted on the front wheel side is not particularly mentioned, but in many cases, the motorcycle will be a motorcycle.

  However, from the point of view of the present invention, the two-wheeled vehicle need not be limited to the two-wheeled motor vehicle. Of course, the two-wheeled vehicle may be a bicycle, and the function and effect in this case are not different. It is.

  It is suitable for the realization of a hydraulic shock absorber that absorbs road surface vibration that is input to the front wheel that is mounted on the front wheel side of the motorcycle and is suspended at the lower end.

DESCRIPTION OF SYMBOLS 1 Car body side tube 2 Wheel side tube 3 Cylinder body 3a Bottom end part 3b Communication hole 4 Rod body 6 Damping part 7 Free piston 10 Adjuster 31 Cylindrical body 71 Booster spring

Claims (5)

  A fork main body composed of a vehicle body side tube and a wheel side tube has a damper that serves as a reservoir in the fork main body, a damper that allows the working fluid to reciprocate, and a downstream side of the damper. A free piston which is disposed and opposes the damping portion and retreats by a fluid pressure action on a pressure receiving surface defining an oil chamber between the damping portion and the oil chamber when the free piston is retracted In the front fork comprising a communication hole that allows communication to the reservoir and a booster spring that is disposed behind the free piston and urges the free piston in the forward direction, the fork body includes: While the fork body is arranged so as to be movable in the axial direction, the position of the most advanced forward movement of the free piston can be changed to the sliding direction of the free piston during the movement. Front fork and characterized by having an adjuster.   The front fork according to claim 1, wherein the booster spring has the rear end engaged with the adjuster while the front end is in contact with the back surface of the free piston.   The adjuster is disposed on the shaft core portion of the cap member that closes the upper end opening of the vehicle body side tube, and a guide rod is connected to the adjuster, and the attenuation portion is held by the guide rod. The front fork according to claim 1 or 2, wherein the free piston is interposed.   A rod body in which the damper is disposed in the shaft core portion of the fork main body, and a cylinder body constituting the damper is suspended from the shaft core portion of the vehicle body side tube so that the tip portion protrudes and retracts in the cylinder body. The above-mentioned damping part, free piston and booster spring are housed in the bottom end part of this cylinder body which stands up at the shaft core part of the above-mentioned wheel side tube and connects the above cylinder body to the above-mentioned vehicle body side tube. The front fork according to claim 1, 2 or 3.   The bottom end portion of the cylinder body is formed of a cylindrical body that connects the upper end portion to the inner periphery of the upper end portion of the vehicle body side tube, and the damping portion and the free piston are accommodated in the cylindrical body. 5. A piston according to claim 4, wherein a piston is formed in the cylindrical body to prevent an oil chamber between the damping portion and the free piston from communicating with the reservoir outside the cylindrical body. Front fork.

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