JP5690179B2 - Shock absorber - Google Patents

Description

  The present invention relates to an improvement of a shock absorber.

  Conventionally, in this type of shock absorber, a cylinder, a piston that is slidably inserted into the cylinder and divides the cylinder into an extension side chamber on the piston rod side and a pressure side chamber on the piston side, and the piston are provided. A first channel that communicates the extension side chamber and the pressure side chamber, a second channel that opens from the tip of the piston rod to the side and communicates the extension side chamber and the pressure side chamber, and a pressure chamber connected in the middle of the second channel A free-piston that is slidably inserted into the pressure chamber and divides the pressure chamber into an expansion-side pressure chamber and a compression-side pressure chamber, and an expansion-side pressure chamber and a compression-side pressure chamber And a pair of coil springs for energizing the free piston.

  In the shock absorber configured as described above, the pressure chamber is divided into the expansion side pressure chamber and the pressure side pressure chamber by the free piston, and the expansion side chamber and the pressure side chamber communicate directly with each other via the second flow path. Although not done, the volume ratio between the expansion side pressure chamber and the compression side pressure chamber changes when the free piston moves, and the liquid in the pressure chamber enters and exits the extension side chamber and the compression side chamber according to the amount of movement of the free piston. In addition, the extension side chamber and the pressure side chamber behave as if they are communicated with each other via the second flow path.

  Therefore, this shock absorber can generate a large damping force for low-frequency vibration input, and can generate a small damping force for high-frequency vibration input. It is possible to reliably generate a high damping force in a scene where the input vibration frequency of the vehicle is low, and to reliably generate a low damping force in a scene where the input vibration frequency is high such that the vehicle passes through the unevenness of the road surface. The riding comfort can be improved (see, for example, Patent Documents 1 and 2).

JP 2008-215459 A

  However, in the above shock absorber, the free piston is urged by the pair of coil springs, and the total length of the coil spring is long. Therefore, the total length of the housing is also long because the coil spring is accommodated.

  In this shock absorber, for the convenience of providing the housing at the tip of the piston rod, if the entire length of the housing is lost, the stroke of the shock absorber is sacrificed accordingly. Since the total length of the shock absorber is restricted, depending on the vehicle, if the housing is long, the stroke may be insufficient. As a result, it may be necessary to give up mounting the shock absorber on the vehicle.

  Accordingly, the present invention has been developed to improve the above-described problems, and an object of the present invention is to provide a shock absorber that does not cause a shortage of strokes.

In order to solve the above-described object, the problem-solving means in the present invention includes a cylinder, a partition member that is slidably inserted into the cylinder and divides the cylinder into an extension side chamber and a compression side chamber, and the extension side chamber. A passage communicating with the compression side chamber, a housing forming a pressure chamber therein, and an extension side pressure chamber that is movably inserted into the housing and communicates with the extension side chamber via the extension side channel And a free piston that is partitioned into a pressure side pressure chamber that communicates with the pressure side chamber via a pressure side flow path, and a shock absorber that includes a spring element that generates a biasing force that suppresses displacement of the free piston with respect to the housing. A spring element is housed in the extension side pressure chamber and urges the free piston in a direction to compress the pressure side pressure chamber. The over piston and a second wave washer for biasing in a direction to compress the extension side pressure chamber, when the free piston is displaced to the stroke end, any of the first wave washer and the second wave washer, most It is characterized by being compressed into a flat plate shape .

  According to the shock absorber of the present invention, since the spring elements for biasing the free piston are the first wave washer and the second wave washer, the axial length is maintained while ensuring the stroke length of the free piston rather than using the coil spring. Therefore, the length of the housing can be made compact. As a result, according to the shock absorber of the present invention, it is easy to secure the stroke of the shock absorber, and the shock absorber can be mounted on the vehicle without causing a shortage of the stroke of the shock absorber.

It is a longitudinal cross-sectional view of the shock absorber in one embodiment. It is the figure which showed the damping characteristic with respect to the vibration frequency of the buffering device in one Embodiment.

  Hereinafter, the present invention will be described with reference to the drawings. As shown in FIG. 1, the shock absorber D of the present invention includes a cylinder 1 and a piston 2 as a partition member that is slidably inserted into the cylinder 1 and partitions the cylinder 1 into an expansion side chamber R1 and a compression side chamber R2. The passages 3a and 3b communicating the extension side chamber R1 and the pressure side chamber R2, the housing 14 forming the pressure chamber R3 therein, and the pressure chamber R3 through the extension side flow path 5 are movably inserted into the housing 14. A free piston 9 that is divided into an expansion side pressure chamber 7 that communicates with the expansion side chamber R1 via the compression side chamber 6 and a pressure side pressure chamber 8 that communicates with the compression side chamber R2 via the pressure side flow path 6; And a spring element 10 that generates an urging force that suppresses the vibration, and is interposed between the vehicle body and the axle of the vehicle to generate a damping force and suppress the vibration of the vehicle body. The expansion side chamber R1 is a chamber that is compressed when the vehicle body and the axle are separated and the shock absorber D is extended, and the compression side chamber R2 is a state where the vehicle body and the axle are close to each other and the shock absorber D is A chamber that is compressed when contracted.

  The extension chamber R1, the pressure chamber R2, and further the pressure chamber R3 are filled with a liquid such as hydraulic fluid, and the lower chamber R2 is in sliding contact with the inner periphery of the cylinder 1 in the lower portion of the cylinder 1 in the figure. A sliding partition wall 12 that partitions the gas chamber G is provided.

  In addition to the working oil, for example, a liquid such as water or an aqueous solution can be used as the liquid filled in the extension side chamber R1, the pressure side chamber R2, and the pressure chamber R3.

  Hereinafter, each part will be described in detail. The piston 2 is connected to one end of a piston rod 4 that is movably inserted into the cylinder 1, and the piston rod 4 protrudes outward from the upper end of the cylinder 1 in the figure. In addition, between the piston rod 4 and the cylinder 1, the inside of the cylinder 1 is in a liquid-tight state with a seal (not shown). Since the shock absorber D is set to a so-called single rod type, the volume of the piston rod 4 that enters and exits the cylinder 1 as the shock absorber D expands and contracts is the volume of the gas in the gas chamber G. The sliding partition 12 is expanded or contracted to be compensated by moving in the vertical direction in FIG. Thus, the shock absorber D is set to a single cylinder type, but instead of installing the sliding partition wall 12 and the gas chamber G, a reservoir is provided on the outer periphery or outside of the cylinder 1, and the piston rod 4 is provided by the reservoir. Volume compensation may be performed. Further, the shock absorber D may be set to a double rod type instead of a single rod type.

  The piston rod 4 has a small diameter portion 4a formed on the lower end side in FIG. 1, and a screw portion 4b formed on the tip end side of the small diameter portion 4a. The piston rod 4 is formed with an extension-side flow path 5 that opens from the tip of the small diameter portion 4 a and passes through the side of the piston rod 4. In the drawing, a valve serving as a resistance is not provided in the middle of the extension side flow path 5, but a valve such as a throttle may be provided.

  The piston 2 is formed in an annular shape, and the small diameter portion 4a of the piston rod 4 is inserted on the inner peripheral side thereof. Further, the piston 2 is provided with passages 3a and 3b communicating the extension side chamber R1 and the pressure side chamber R2, and the damping force generating element is laminated at the upper end of the passage 3a in FIG. 1 is closed by the laminated leaf valve V1, and the lower end in FIG. 1 of the other passage 3b is also closed by the laminated leaf valve V2, which is a damping force generating element laminated below the piston 2 in FIG.

  The laminated leaf valves V1 and V2 are both formed in an annular shape, and a small diameter portion 4a of the piston rod 4 is inserted on the inner peripheral side. Are stacked.

  The laminated leaf valve V1 is bent by the pressure difference between the compression side chamber R2 and the expansion side chamber R1 during the contraction operation of the shock absorber D, opens the passage 3a, and moves from the pressure side chamber R2 to the expansion side chamber R1. And the passage 3a is closed when the shock absorber D is extended, and the other laminated leaf valve V2 is opposite to the passage 3b when the shock absorber D is extended, as opposed to the laminated leaf valve V1. The passage 3b is closed during the contraction operation. That is, the laminated leaf valve V1 is a damping force generating element that generates a compression side damping force when the shock absorber D is contracted, and the other laminated leaf valve V2 is a stretch side damping force when the shock absorber D is extended. This is a damping force generating element. Even when the passages 3a and 3b are closed by the laminated leaf valves V1 and V2, the extension side chamber R1 and the pressure side chamber R2 are communicated with each other by a well-known orifice (not shown). For example, it is formed by providing a notch on the outer periphery of the laminated leaf valves V1, V2 or providing a recess in the valve seat on which the laminated leaf valves V1, V2 are seated. In addition to the laminated leaf valves V1 and V2 described above, for example, a configuration in which a choke and a leaf valve are arranged in parallel or other configurations can be adopted as the damping force generating element.

  The above-described valve stopper 11, laminated leaf valve V1, piston 2, and laminated leaf valve V2 are sequentially assembled to the screw portion 4b of the piston rod 4, and a pressure chamber R3 is formed from below the laminated leaf valve V2. The housing 14 is screwed. The housing 2 fixes the piston 2, the laminated leaf valves V <b> 1 and V <b> 2, and the valve stopper 11 to the piston rod 4. Thus, the housing 14 not only forms the pressure chamber R3 inside, but also plays a role of fixing the piston 2 to the piston rod 4.

  The housing 14 has a nut portion 15 with a flange 16 that is screwed into the screw portion 4b of the piston rod 4 and a bottomed cylindrical shape that is integrated by tightening an opening on the outer periphery of the flange 16 in the nut portion 15. A cylindrical portion 17 is provided. The nut portion 15 and the tubular portion 17 define a pressure chamber R3 in the pressure side chamber R2. In addition, when integrating the nut part 15 and the cylinder part 17, other methods, such as welding, can also be employ | adopted besides the said caulking process.

  A free piston 9 is slidably inserted into the pressure chamber R3 formed as described above, and the pressure chamber R3 includes an upper side expansion pressure chamber 7 and a lower side pressure side pressure in FIG. It is divided into a chamber 8.

  Further, the nut portion 15 is provided with the flange 16 on the side as described above, and a cylindrical screw portion 18 is formed on the inner periphery thereof, and the screw portion 18 is screwed to the screw portion 4 b of the piston rod 4. As a result, the housing 14 can be fixed to the small diameter portion 4 a of the piston rod 4. In addition, the cross-sectional shape of the outer periphery of the cylindrical portion 17 is a shape other than a perfect circle, for example, a shape with a part cut away, a hexagonal shape, etc., so that the housing 14 can be used with a tool that engages with the outer periphery. The operation of screwing onto the piston rod 4 can be facilitated.

  The cylindrical portion 17 has a bottomed cylindrical shape, and a fixed orifice 19 that constitutes a part of the pressure side flow path 6 is provided at the bottom, and the pressure side chamber R <b> 2 enters the housing 14 at the side of the cylindrical portion 17. Two variable orifices 20 and 21 communicating with each other are provided.

  On the other hand, the free piston 9 has a bottomed cylindrical shape, and is inserted into the housing 14 with the bottom portion 9a facing downward in FIG. 1 and the outer periphery of the cylindrical portion 9b slidably contacting the inner periphery of the cylindrical portion 17. Yes. When the free piston 9 is slidably inserted into the housing 14 as described above, the pressure chamber R3 is partitioned into the expansion side pressure chamber 7 and the pressure side pressure chamber 8. In addition, by accommodating the bottom portion 9a of the free piston 9 in the housing 14 facing downward in FIG. 1, interference with the screw portion 18 in the nut portion 15 of the free piston 9 can be avoided. Furthermore, in the case of this embodiment, the free piston 9 includes an annular groove 9c on the outer periphery of the cylindrical portion 9b, and a hole 9d that communicates from the bottom 9a of the free piston 9 to the annular groove 9c.

  The free piston 9 is provided with a spring element 10 that applies a biasing force that suppresses the displacement of the free piston 9 with respect to the housing 14 according to the amount of displacement of the free piston 9. 1 between the flange 16 of the nut portion 15 and the upper end in FIG. 1 of the cylindrical portion 9b of the free piston 9, and in the compression side pressure chamber 8 and the bottom portion of the cylindrical portion 17 and the bottom portion 9a of the free piston 9. Between the first wave washer 22 and the second wave washer 23.

  Both the first wave washer 22 and the second wave washer 23 are annular and curved so that a waveform appears in the circumferential direction. When the first wave washer 22 and the second wave washer 23 are compressed by pressing in the axial direction, the first wave washer 22 and the second wave washer 23 are resistant to the compression force. It has come to show the power to do. Unlike the coil spring, the first wave washer 22 and the second wave washer 23 are flat at the time of the most compression, so the axial length at the time of the most compression is equal to the plate thickness. Mostly contributes to the stroke length of the free piston 9. Therefore, even if the stroke length of the free piston 9 is set to be the same, the axial length is much shorter when the first wave washer 22 and the second wave washer 23 are used than when the coil spring is used. Can do.

  The first wave washer 22 is accommodated in the expansion side pressure chamber 7 in a compressed state, and urges the free piston 9 in the direction in which the compression side pressure chamber 8 is compressed. The other second wave washer 23 is housed in the compression side pressure chamber 8 in a compressed state, and urges the free piston 9 in the direction of compressing the expansion side pressure chamber 7. Therefore, the free piston 9 has the urging forces of the first wave washer 22 and the second wave washer 23 in the housing 14 in a state where no pressure or urging force other than the first wave washer 22 and the second wave washer 23 acts. The balanced position is set to the neutral position as the neutral position.

  When the free piston 9 is in the neutral position, the annular groove 9c always communicates the pressure side pressure chamber 8 and the pressure side chamber R2 so as to face the variable orifices 20 and 21, and the free piston 9 is displaced to the stroke end. That is, when either the first wave washer 22 or the second wave washer 23 is displaced until it is compressed to the maximum, the variable orifices 20 and 21 are completely wrapped around the free piston 9 and closed. . That is, the pressure side flow path 6 includes an annular groove 9 c, variable orifices 20 and 21, a hole 9 d and a fixed orifice 19. Although two variable orifices 20 and 21 are provided, the number is arbitrary.

  That is, in the case of this specific shock absorber D, when the displacement amount from the neutral position of the free piston 9 becomes a predetermined displacement amount, the opening of the variable orifices 20 and 21 is free from the situation where it faces the annular groove 9c. Shifting to a situation where the piston 9 starts to face the outer periphery, the flow area of the variable orifices 20 and 21 begins to decrease gradually, and the flow resistance in the pressure side flow path 6 gradually increases. In this embodiment, as the displacement amount of the free piston 9 increases, the flow area of the variable orifices 20 and 21 gradually decreases, and when the free piston 9 reaches the stroke end, the variable orifices 20 and 21 It is completely closed at the outer periphery of the free piston 9 so that the flow path resistance in the pressure side flow path 6 is maximized and the pressure side pressure chamber 8 is communicated with the pressure side chamber R2 only by the fixed orifice 19. A plurality of arc-shaped protrusions 9e are provided on the outer periphery of the lower end in FIG. 1 of the bottom 9a of the free piston 9 so as to avoid the opening of the hole 9d, and the second wave washer 23 is compressed most. Even if it is flat, the hole 9d is not blocked. In addition, by providing the protrusions 9e as described above, even when the second wave washer 23 is compressed to a flat plate shape, the contact area with the free piston 9 can be reduced, and the surface adsorption force can be reduced. . The protrusion may be provided on the second wave washer 23 instead of being provided on the free piston 9. Further, such a protrusion may be provided at the upper end of the cylindrical portion 9b of the free piston 9 in FIG. 1 to reduce the surface adsorption force with the first wave washer 22, and the protrusion is attached to the first wave washer 22. You may make it provide.

  The shock absorber D is configured as described above. Next, the operation of the shock absorber D will be described.

  (A) Operation in the shock absorber D when the amount of displacement of the free piston 9 from the neutral position is within a range where the variable orifices 20 and 21 do not begin to close.

  In this case, the free piston 9 can be displaced without changing the resistance of the pressure side flow path 6. Then, when considering the condition that the piston speed is the same when the vibration frequency input to the shock absorber D is low and high, first, when the input frequency is low, the amplitude of the input vibration increases, The amplitude of the free piston 9 also increases within a range where the variable orifices 20 and 21 do not begin to close.

  When the amplitude of the free piston 9 increases in the above range, the urging force that the free piston 9 receives from the first wave washer 22 and the second wave washer 23 increases, and when the shock absorber D extends, the pressure in the pressure side pressure chamber 8 is increased. The pressure is smaller than the pressure in the expansion side pressure chamber 7 by the urging force of the first wave washer 22 and the second wave washer 23. Conversely, when the shock absorber D contracts, the expansion side pressure chamber 8 The internal pressure becomes smaller than the pressure in the compression side pressure chamber 7 by the urging force of the first wave washer 22 and the second wave washer 23.

  As described above, when the shock absorber D exhibits low frequency vibration, a differential pressure corresponding to the urging force of the first wave washer 22 and the second wave washer 23 is generated in the expansion side pressure chamber 7 and the compression side pressure chamber 8. The differential pressure between R1 and the expansion side pressure chamber 7 and the differential pressure between the pressure side chamber R2 and the compression side pressure chamber 8 are reduced, and the apparent pressure formed by the expansion side flow path 5, the pressure side flow path 6, the expansion side pressure chamber 7, and the pressure side pressure chamber 8 The flow rate through the upper channel is small. Since the flow rate passing through the apparent flow path is small, the flow rate of the passages 3a and 3b is increased, so that the damping force generated by the shock absorber D is maintained high.

  On the other hand, when the input frequency to the shock absorber D is high, the amplitude of the input vibration becomes small and the amplitude of the free piston 9 becomes smaller. When the amplitude of the free piston 9 is reduced, the urging force that the free piston 9 receives from the first wave washer 22 and the second wave washer 23 is reduced, and the expansion is performed regardless of whether the shock absorber D is in the expansion stroke or the contraction stroke. The pressure in the side pressure chamber 7 and the pressure in the pressure side pressure chamber 8 are substantially equal. Then, since the differential pressure between the expansion side chamber R1 and the expansion side pressure chamber 7 and the differential pressure between the compression side chamber R2 and the compression side pressure chamber 8 increase, the flow rate passing through the expansion side flow channel 5 and the pressure side flow channel 6 also increases.

  When the frequency of vibration input to the shock absorber D is low, the flow rate that passes through the apparent flow path is small, and when the input frequency is high, the flow rate that passes through the apparent flow path increases. If the speed is the same, the flow rate flowing from the expansion side chamber R1 to the compression side chamber R2 or from the compression side chamber R2 to the expansion side chamber R1 must be equal regardless of the input frequency, so the laminated leaf valves V1, V2 in the passages 3a, 3b. When the input frequency is low, the flow rate passing through is increased and the damping force is high. Conversely, when the input frequency is high, the flow rate is decreased and the damping force is low. Therefore, the damping characteristic of the shock absorber D changes as shown in FIG.

  Therefore, in this shock absorber D1, the change of the damping force can be made to depend on the input vibration frequency, and the posture of the vehicle can be changed by generating a high damping force with respect to the vibration input of the sprung resonance frequency. It is possible to stabilize and prevent the passenger from feeling uneasy when turning the vehicle, and when a vibration at the unsprung resonance frequency is input, a low damping force is always generated to transmit the vibration on the axle side to the vehicle body side. Insulation can improve the ride comfort in the vehicle.

(B) Operation in the shock absorber D when the amount of displacement from the neutral position of the free piston 9 is within the range of increasing the flow path resistance of the pressure side flow path 6 The variable orifices 20 and 21 Even if it contracts, the free piston 9 is displaced from the neutral position, and the flow passage area is gradually reduced in accordance with the amount of displacement. When the free piston 9 reaches one of the upper and lower stroke ends, it is completely blocked. Thus, the flow path area becomes the same as the flow path area of the fixed orifice 19 and is minimized.

  That is, after the free piston 9 begins to close the variable orifices 20 and 21, the flow resistance of the pressure side flow path 6 is gradually increased according to the amount of displacement, and when the free piston 9 reaches the stroke end, the flow resistance is reduced. Maximum.

  Here, the free piston 9 is displaced to the stroke end when the amount of liquid flowing into and out of the expansion side pressure chamber 7 or the pressure side pressure chamber 8 is large. Is the case.

  When the vibration frequency input to the shock absorber D is relatively high, the shock absorber D generates a relatively low damping force until the free piston 9 is displaced to a position where it begins to close the variable orifices 20 and 21. However, when the free piston 9 is displaced beyond the position where the variable orifices 20 and 21 start to be closed, the flow resistance of the pressure side flow path 6 gradually increases. The movement speed to the stroke end side is reduced, the amount of liquid movement through the apparent flow path is also reduced, and the amount of liquid passing through the passages 3a and 3b is increased accordingly. The generated damping force of D gradually increases.

  When the free piston 9 reaches the stroke end, the liquid no longer moves through the apparent flow path, and the liquid passes only through the passages 3a and 3b until the expansion / contraction direction of the shock absorber D1 is changed. Therefore, the shock absorber D generates a damping force with the maximum damping coefficient.

  That is, even if a high-frequency and large-amplitude vibration that causes the free piston 9 to be displaced to the stroke end is input to the shock absorber D, the amount of displacement from the neutral position of the free piston 9 exceeds an arbitrary amount of displacement. Since the shock absorbing device D gradually increases the generated damping force until the free piston 29 reaches the stroke end, there is no sudden change from a low damping force to a high damping force. That is, when the free piston 9 reaches the stroke end and the liquid in the extension side chamber R1 and the pressure side chamber R2 cannot be exchanged through the pressure chamber R3, the magnitude of the damping force does not change suddenly. The damping force change from low damping force to high damping force becomes gentle. Furthermore, since the generated damping force is gradually increased when the free piston 9 reaches the stroke ends on both ends in the pressure chamber R3, the function of suppressing a sudden change in the damping force is Demonstrated in both strokes.

  Therefore, in this shock absorber D, even if a vibration with a high frequency and a large amplitude is input, the generated damping force changes gently, and the passenger does not perceive a shock due to the change in the damping force. It is possible to improve the ride comfort in the vehicle, and in particular, it is possible to prevent a situation in which the vehicle body vibrates due to a sudden change in damping force and the bonnet resonates and abnormal noise is generated. Can be improved.

  According to the shock absorber D of the present invention, since the first wave washer 22 and the second wave washer 23 are used as the spring element 10 for urging the free piston 9, the stroke length of the free piston 9 is used rather than using a coil spring. As a result, the axial length of the housing 14 can be shortened, and the axial length of the housing 14 in the vertical direction in FIG. As a result, according to the shock absorber D of the present invention, the stroke of the shock absorber D can be easily ensured, and the shock absorber D can be mounted on the vehicle without causing a shortage of the stroke of the shock absorber D.

  This is the end of the description of the embodiment of the present invention, but the scope of the present invention is of course not limited to the details shown or described.

  The shock absorber of the present invention can be used for vehicle vibration control.

DESCRIPTION OF SYMBOLS 1 Cylinder 2 Piston 3a, 3b as a partition member Passage 5 Extension side flow path 6 Pressure side flow path 7 Extension side pressure chamber 8 Pressure side pressure chamber 9 Free piston 10 Spring element 14 Housing 22 First wave washer 23 Second wave washer D Buffer Apparatus R1 Extension side chamber R2 Pressure side chamber R3 Pressure chamber

Claims (3)

A cylinder,
A partition member which is slidably inserted into the cylinder and divides the cylinder into an extension side chamber and a pressure side chamber;
A passage communicating the extension side chamber and the compression side chamber;
A housing forming a pressure chamber therein;
And the compression side pressure chamber communicated with the pressure side chamber through the extension side pressure chamber and the compression side flow path communicates with the expansion side chamber through the extension side flow path inserted in the pressure chamber movably in the housing A free piston that divides into
A shock absorber comprising a spring element that generates a biasing force that suppresses displacement of the free piston with respect to the housing.
A first wave washer housed in the extension side pressure chamber and energizing the free piston in a direction to compress the pressure side pressure chamber;
A second wave washer housed in the pressure side pressure chamber and biasing the free piston in a direction to compress the extension side pressure chamber ;
When the free piston is displaced to the stroke end, one of the first wave washer and the second wave washer is compressed most and becomes a flat plate . 2. The shock absorber according to claim 1, wherein a plurality of protrusions are provided on at least one side of the free piston on the extension side pressure chamber side and the pressure side pressure chamber side. The pressure side channel is
A variable orifice provided on the outer periphery of the housing;
An annular groove provided on the outer periphery of the free piston that communicates the pressure side pressure chamber and the pressure side chamber so as to face the variable orifice when the free piston is in a neutral position;
A hole leading to the annular groove opening at the bottom of the free piston;
A fixed orifice that communicates the pressure side pressure chamber and the pressure side chamber provided at the bottom of the housing;
3. The shock absorber according to claim 2, wherein the plurality of protrusions provided on the free piston are provided so as to avoid the opening of the hole.

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