JP5831976B2 - 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 (for example, see Patent Document 1).

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 total length of the housing is increased, 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 stroke.

  In order to solve the above-described object, the problem-solving means in the present invention includes a cylinder, a piston that is slidably inserted into the cylinder, and divides the cylinder into an extension side chamber and a pressure side chamber, a hollow housing, An extension-side pressure chamber that is movably inserted into the housing and communicates with the extension-side chamber through the extension-side channel, and a pressure-side pressure chamber that communicates with the compression-side chamber via the pressure-side channel; A free-side piston that is partitioned into an extension-side pressure chamber, an extension-side coil spring that is accommodated in the extension-side pressure chamber, and a compression-side coil spring that is accommodated in the compression-side pressure chamber. In the shock absorber that sandwiches the free piston, the free piston is provided on a bottom plate portion sandwiched between the extension side coil spring and the compression side coil spring, and on an outer periphery of the bottom plate, and A cylindrical sliding contact cylinder in sliding contact with the inner periphery of the ring, wherein the extension side coil spring and the pressure side coil spring are conical springs, and the extension side coil spring includes the free piston in the extension side pressure chamber. When the free side piston is displaced to the stroke end in the direction in which the free piston compresses the compression side pressure chamber, the compression side coil spring is accommodated in the sliding contact tube. It is characterized by being.

  The expansion side coil spring and the compression side coil spring in the shock absorber are conical springs. When the free piston is displaced to the stroke end, the expansion side coil spring or the compression side coil spring is accommodated in the sliding cylinder, so that the stroke of the free piston is reduced. While ensuring, the total length of the housing can be shortened.

  As described above, according to the shock absorber of the present invention, a sufficient stroke can be ensured, and mounting on a vehicle can be improved without causing a shortage of stroke.

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. It is a longitudinal cross-sectional view of the buffer device of one Embodiment in the state which the free piston displaced to the stroke end in the direction which compresses an expansion side pressure chamber. It is a longitudinal cross-sectional view of the buffer device of one Embodiment in the state which the free piston displaced to the stroke end in the direction which compresses a pressure side pressure chamber.

  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, a piston 2 that is slidably inserted into the cylinder 1 and divides the cylinder 1 into an expansion side chamber R1 and a pressure side chamber R2, and a hollow housing. 12, and a pressure side chamber R 2, which is movably inserted into the housing 12 and communicates with the extension side chamber R 1 through the extension side flow channel 5 and the pressure side channel 6. A free piston 9 that is partitioned into a pressure side pressure chamber 8 that communicates with the pressure side pressure chamber 8, an extension side coil spring S 1 that is accommodated in the extension side pressure chamber 7, and a pressure side coil spring S 2 that is accommodated in the pressure side pressure chamber 8. It is interposed between the vehicle body and the axle in 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 side chamber R1, the pressure side chamber R2, and the housing 12 are filled with a liquid such as hydraulic oil. The lower side of the cylinder 1 in the drawing is in sliding contact with the inner periphery of the cylinder 1 (not shown). A sliding partition that partitions the gas chamber is provided below the pressure side chamber R2. In addition, as the fluid filled in the above-described extension side chamber R1, pressure side chamber R2, and housing 12, for example, a liquid other than a liquid such as hydraulic oil, water, and an aqueous solution can be used.

  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 or contracts is expanded or the volume of the gas in the gas chamber is expanded. The sliding partition wall is shrunk and compensated by moving up and down in FIG. Thus, the shock absorber D is set to a single cylinder type, but instead of providing a sliding partition to partition the gas chamber, a reservoir is provided on the outer periphery or outside of the cylinder 1 and the piston is used by the reservoir. Volume compensation of the rod 4 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 at one end as a lower end in FIG. 1, and a screw portion 4b formed at the distal end side of the small diameter portion 4a. The piston 2 is connected to the small-diameter portion 4a that is one end of the piston rod 4, and the other end of the piston rod 4 protrudes outward from the upper end of the cylinder 1, although not shown. In addition, 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 ports 3a and 3b for communicating the expansion side chamber R1 and the pressure side chamber R2, and the damping force generating element in which the upper end of the port 3a in FIG. 1 is closed by the laminated leaf valve V1, and the lower end of the other port 3b in FIG. 1 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. The laminated leaf valves V1 and V2 are attached to the piston 2 together with an annular valve stopper 11 that regulates the amount of deflection of the laminated leaf valve V1. 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 port 3a, and moves from the pressure side chamber R2 to the expansion side chamber R1. And the port 3a is closed when the shock absorber D is extended, and the other laminated leaf valve V2 is connected to the port 3b when the shock absorber D is extended, opposite to the laminated leaf valve V1. Open and close the port 3b during 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 ports 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 small diameter portion 4a of the piston rod 4, and the small diameter portion 4a is formed from below the laminated leaf valve V2. The housing 12 forming the pressure chamber R3 is screwed to the screw portion 4b. Thus, by screwing the housing 12 to the piston rod 4, the piston 2, the laminated leaf valves V <b> 1 and V <b> 2, and the valve stopper 11 are fixed to the piston rod 4. Thus, the housing 12 plays not only the role of forming the pressure chamber R3 therein, but also the role of fixing the piston 2 to the piston rod 4.

  The housing 12 has a cylindrical shape and is screwed into the screw portion 4 b of the piston rod 4, a lid portion 17 that is attached to the opening end of the case 13 and closes the opening end, and the case 13. And a gripping portion 16 that is provided on the outer periphery and can be gripped by a fastening tool (not shown).

  More specifically, the case 13 includes a small-diameter portion 14 formed with the upper side in FIG. 1 as a small diameter, and a large-diameter portion 15 having an inner and outer diameter larger than the small-diameter portion 14. The inner diameter of the small-diameter portion 14 is provided with a female screw, which is screwed into a screw portion 4b provided on the small-diameter portion 4a of the piston rod 4 so that the housing 12 is connected to the small-diameter portion of the piston rod 4. It can be screwed to 4a.

  A disk-shaped lid 17 is fixed to the opening end of the large diameter portion 15 at the lower end in FIG. 1, and the case 13 and the lid portion 17 are secured by caulking the opening end of the large diameter portion 15 inward. Are integrated. The housing 12 configured in this way is hollow inside and forms a pressure chamber R3 partitioned from the pressure side chamber R2. The large-diameter portion 15 is provided with variable orifices 22 and 23 that communicate the inside and outside of the housing 12, that is, the pressure chamber R3 communicates with the pressure-side chamber R2, and the lid portion 17 includes the pressure-side chamber inside the housing 12. A fixed orifice 21 communicating with R2 is provided.

  The outer periphery of the lower end in FIG. 1 of the large-diameter portion 15 has a shape other than a perfect circle, for example, a shape with a part cut away, a hexagon, or the like so that it can be gripped with a tightening tool (not shown). Thus, a gripping portion 16 is formed. The gripping portion 16 may be provided at a position other than the lower end of the large diameter portion 15 of the case 13. The housing 12 can be firmly screwed onto the piston rod 4 by gripping the grip 16 with a tightening tool (not shown) and applying a torque to the case 13. In this case, the gripping portion 16 is provided in the case 13, and no torque acts on the lid portion 17 fixed to the inner periphery of the case 13 by caulking when the housing 12 is screwed onto the piston rod 4. . Therefore, due to the action of torque when the housing 12 is screwed onto the piston rod 4, problems such as the lid portion 17 falling off from the case 13 or rattling between the case 13 and the lid portion 17 are caused. There is nothing. In addition, when integrating the case 13 and the cover part 17, methods, such as screw fastening and welding other than caulking, can also be utilized.

  A free piston 9 is slidably inserted into the housing 12 formed as described above, and the pressure chamber R3 is located below the extension side pressure chamber 7 in FIG. It is divided into a pressure side pressure chamber 8 on the side.

The free piston 9 has a bottom plate portion 24 sandwiched between the extension side coil spring S <b> 1 and the compression side coil spring S <b> 2, and a cylindrical shape that is provided on the outer periphery of the bottom plate portion 24 and is in sliding contact with the inner periphery of the large diameter portion 15 of the housing 12. Slidable contact tube 25, an annular groove 26 provided on the outer periphery of the slidable contact tube 25 along the circumferential direction, and a through hole that opens from the inner periphery facing the pressure side pressure chamber 8 of the slidable contact tube 25 and communicates with the annular groove 26. 27.

  The bottom plate portion 24 has a disk shape, and is provided with convex portions 24a and 24b that protrude to the extension side pressure chamber 7 side and the pressure side pressure chamber 8 side, respectively. The inside of the sliding contact cylinder 25 is closed by the bottom plate portion 24 at the center in the axial direction, and the thickness gradually decreases from the center toward the upper and lower ends. Further, the inner peripheral surface 25b facing the pressure side pressure chamber 8 side of the slidable contact tube 25 is such that the inner diameter of the slidable contact tube 25 becomes smaller toward the bottom plate portion 24 by making the lower end side thinner than the center side. It becomes the taper surface which becomes. And the through-hole 27 which leads to the annular groove 26 from the inner peripheral surface 25b used as this taper surface is opening, By making the said inner peripheral surface 25b into a taper surface, the through-hole 27 is made into the axis line of the free piston 9. The processing when drilling in a direction inclined with respect to the surface is easy.

  In addition, the inner peripheral surface 25a facing the extension side pressure chamber 7 side of the sliding contact tube 25 on the opposite side is also made such that the thickness of the sliding contact tube 25 is thinner at the upper end side than the center side, so that the bottom plate portion 24 is provided. The taper surface is such that the inner diameter becomes smaller as it goes toward. Further, an annular recess 29 is formed by removing the boundary between the expansion side pressure chamber 7 side of the sliding contact cylinder 25 of the free piston 9 and the expansion side pressure chamber 7 side of the bottom plate portion 24, and freeing by this thinning. The piston 9 is lightened.

  When the free piston 9 is inserted into the housing 12, the inside of the housing 12 is partitioned into the extension side pressure chamber 7 and the pressure side pressure chamber 8 as described above. In this case, an annular groove 26 provided on the outer periphery of the free piston 9 can be opposed to the variable orifices 22 and 23, and when the annular groove 26 and the variable orifices 22 and 23 are opposed, the pressure side via the through hole 27. The pressure chamber 8 and the pressure side chamber R2 are in communication. When the free piston 9 strokes in the housing 12 and the annular groove 26 does not face the variable orifices 22 and 23, the pressure side pressure chamber 8 through the variable orifices 22 and 23, the annular groove 26 and the through hole 27. And communication with the pressure side chamber R2 are cut off.

  A seal ring 28 is mounted on the lower side in FIG. 1 with respect to the annular groove 26 of the sliding contact cylinder 25, and the space between the free piston 9 and the housing 12 is sealed by the seal ring 28. Even if the free piston 9 strokes in the housing 12, the seal ring 28 does not get over the variable orifices 22 and 23, so that the seal ring 28 is inserted when the free piston 9 is inserted into the housing 12. It is considered that the seal ring 28 is not damaged by interfering with the openings of the variable orifices 22 and 23 by inserting the annular groove 26 before the side.

  Subsequently, the expansion side pressure chamber 7 accommodates the expansion side coil spring S1, and this expansion side coil spring S1 is an intermediate portion 18 connecting the small diameter portion 14 and the large diameter portion 15 in the case 13 of the housing 12. And a bottom plate portion 24 of the free piston 9 are interposed in a compressed state. The extension side coil spring S <b> 1 is a conical spring, and the small diameter side faces the bottom plate portion 24 of the free piston 9. A convex portion 24a provided on the bottom plate portion 24 is inserted inwardly on the small-diameter side of the extension side coil spring S1 and positioned in the radial direction. Further, the large-diameter side of the extension side coil spring S1 is positioned in the radial direction by fitting in the step portion 19 provided in the intermediate portion 18 between the small-diameter portion 14 and the large-diameter portion 15 of the case 13 of the housing 12. Yes. Therefore, the extension side coil spring S1 is positioned in the radial direction with respect to the housing 12 and the free piston 9 and is stably biased toward the direction in which the compression side pressure chamber 8 is compressed with respect to the free piston 9. Can be demonstrated.

  On the other hand, the pressure side pressure chamber 8 accommodates a pressure side coil spring S2, and this pressure side coil spring S2 is interposed between the lid portion 17 of the housing 12 and the bottom plate portion 24 of the free piston 9 in a compressed state. Has been. The compression side coil spring S2 is a conical spring, and the small diameter side faces the bottom plate portion 24 of the free piston 9. A convex portion 24b provided on the bottom plate portion 24 is inserted inside the compression-side coil spring S2 on the small-diameter side and positioned in the radial direction. Further, the large diameter side of the compression side coil spring S <b> 2 is positioned in the radial direction by fitting into the step portion 20 provided in the lid portion 17 of the housing 12. Therefore, the compression side coil spring S2 is positioned in the radial direction with respect to the housing 12 and the free piston 9 and is stable in the direction of compressing the expansion side pressure chamber 7 with respect to the free piston 9. Can be demonstrated.

  Thus, both the extension side coil spring S1 and the pressure side coil spring S2 hold the free piston 9 in a compressed state, and no pressure or biasing force other than the extension side coil spring S1 and the compression side coil spring S2 acts. Then, the position where the urging forces of the extension side coil spring S1 and the compression side coil spring S2 are balanced is set as a neutral position, and the free piston 9 is positioned at this neutral position.

  When the free piston 9 is in the neutral position, the annular groove 26 always faces the variable orifices 22 and 23 to communicate the pressure side pressure chamber 8 and the pressure side chamber R2, and the free piston 9 is displaced to the stroke end. The variable orifices 22 and 23 are completely wrapped and closed on the outer periphery of the free piston 9. That is, the pressure side flow path 6 includes an annular groove 26, variable orifices 22 and 23, a through hole 27, and a fixed orifice 21. Two variable orifices 22 and 23 are provided, but the number thereof is arbitrary.

  Therefore, in the case of this shock absorber D, when the displacement amount from the neutral position of the free piston 9 becomes a predetermined displacement amount, the variable pistons 22 and 23 are all opened from the situation in which the openings of the variable orifices 22 and 23 face the annular groove 26. The situation starts to face the outer periphery, the flow area of the variable orifices 22 and 23 begins to decrease gradually, and the flow resistance in the pressure side flow path 6 gradually increases. In this embodiment, the flow areas of the variable orifices 22 and 23 gradually decrease as the displacement of the free piston 9 increases, and when the free piston 9 reaches the stroke end, the variable orifices 22 and 23 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 21.

In this case, if in Figure 1 the upper end of the sliding tube 25 of the free piston 9 abuts against the intermediate part 18 of the casing 13, moving to more upward relative to the housing 12 of the-free piston 9, ie, Shin Movement in the direction of compressing the side pressure chamber 7 is hindered, so that the upper stroke end of the free piston 9 is set. As described above, when the free piston 9 strokes in the direction of compressing the expansion side pressure chamber 7 to the stroke end, the expansion side coil spring S1 is compressed and completely accommodated in the sliding contact tube 25.

In contrast, if in Figure 1 the lower end of the sliding tube 25 of the free piston 9 abuts on the lid part 17, moving to more downward relative to the housing 12 of the-free piston 9, ie, the compression side pressure chamber 8 Is prevented from moving in the direction in which the free piston 9 is compressed, whereby the lower stroke end of the free piston 9 is set. Thus, when the free piston 9 is stroked to the stroke end in the direction of compressing the pressure side pressure chamber 8, the pressure side coil spring S <b> 2 is compressed and completely accommodated in the sliding contact cylinder 25.

  The shock absorber D is configured as described above. Next, the operation of the shock absorber D will be described. First, the operation of the shock absorber D when the amount of displacement from the neutral position in the free piston 9 is in a range where the variable orifices 22 and 23 do not begin to close will be described.

  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 22 and 23 do not begin to close.

  When the amplitude of the free piston 9 increases in the above range, the biasing force received by the free piston 9 from the extension side coil spring S1 and the compression side coil spring S2 increases, and when the shock absorber D extends, the pressure in the compression side pressure chamber 8 increases. Is smaller than the pressure in the expansion side pressure chamber 7 by the urging force of the expansion side coil spring S1 and the compression side coil spring S2, and conversely, when the shock absorber D contracts, The pressure is smaller than the pressure in the compression side pressure chamber 8 by the urging force of the extension side coil spring S1 and the compression side coil spring S2.

  In this way, when the shock absorber D exhibits low frequency vibration, a differential pressure corresponding to the urging force of the extension side coil spring S1 and the compression side coil spring S2 is generated in the extension side pressure chamber 7 and the compression side pressure chamber 8, so that the extension side chamber R1. The pressure difference between the pressure side chamber 7 and the pressure side chamber R2 and the pressure side pressure chamber 8 are reduced, and the apparent pressure formed by the stretch side flow channel 5, the pressure side flow channel 6, the stretch side pressure chamber 7 and the pressure side pressure chamber 8 is apparent. The flow rate passing through the channel is small. Since the flow rate passing through the apparent flow path is small, the flow rate of the ports 3a and 3b is large, so that the damping force generated by the shock absorber D is kept large.

  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 biasing force that the free piston 9 receives from the extension side coil spring S1 and the compression side coil spring S2 is reduced. The pressure in the 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 speeds are 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 of the ports 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 D, the change of the damping force can be made to depend on the input vibration frequency, and the vehicle posture can be changed by generating a high damping force for 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.

  Next, the operation of the shock absorber D when the amount of displacement from the neutral position of the free piston 9 falls within the range in which the flow path resistance of the pressure side flow path 6 is increased will be described. The variable orifices 22 and 23 are configured so that the free piston 9 is displaced from the neutral position regardless of whether the shock absorber D is extended or contracted, and the flow passage area is gradually reduced according to the amount of displacement. As shown in FIG. 4, when the free piston 9 reaches one of the upper and lower stroke ends, the free piston 9 is completely closed, and the flow passage area becomes the same as the flow passage area of the fixed orifice 21.

  That is, after the free piston 9 starts to close the variable orifices 22 and 23, 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 22 and 23. However, when the free piston 9 is displaced beyond the position where the variable orifices 22 and 23 begin 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 ports 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 does not move any more through the apparent flow path, and the fluid flows 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. The movement is performed only through the ports 3a and 3b until the expansion / contraction direction of the shock absorber D is changed, and the shock absorber D generates a damping force with a 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 9 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.

  And the extension side coil spring S1 and the pressure side coil spring S2 in the shock absorber D of the present invention are conical springs, and the conical spring has a compression length compared to the same coil spring over the entire length. Can be very short. In addition to this, in the shock absorber D of the present invention, when the free piston 9 is displaced to the stroke end in the direction of compressing the expansion side pressure chamber 7, the expansion side coil spring S <b> 1 is compressed and moved into the sliding contact cylinder 25. When the free piston 9 is displaced to the stroke end in the direction in which the compression side pressure chamber 8 is compressed, the compression side coil spring S2 is accommodated in the sliding cylinder 25. As a result, according to the shock absorber D of the present invention, the entire length of the housing 12 can be shortened while ensuring the stroke of the free piston 9, and the stroke of the shock absorber D can be sufficiently secured, so that it can be mounted on a vehicle. Improves. In addition, since the extension side coil spring S1 or the compression side coil spring S2 is stored in the sliding cylinder 25, the length of the sliding cylinder 25 of the free piston 9 in the axial direction is shortened while shortening the overall length of the housing 12. Therefore, the slidability of the free piston 9 is not impaired.

  Further, according to the shock absorber D of the present invention, the housing 12 is screwed to the tip end side of the piston rod 4 and the cylindrical case 13 in which the sliding contact cylinder 25 is slidably contacted on the inner periphery is attached to the opening end of the case 13. The lid portion 17 that closes the open end and the grip portion 16 that can be gripped by a tightening tool provided on the outer periphery of the case 13 are provided. Therefore, when the housing 12 is screwed to the piston rod 4, the case No torque acts on the lid portion 17 provided on the inner periphery of the case 13, and even when the housing 13 and the lid portion 17 are integrated by caulking or screw fastening, the housing 12 is screwed onto the piston rod 4. The problem that the lid portion 17 falls off from the case 13 or looseness occurs between the case 13 and the lid portion 17 due to the action of the torque is not caused. Thereby, the freedom degree of design at the time of integration of case 13 and lid part 17 improves.

  Furthermore, according to the shock absorber D of the present invention, the inner peripheral surface 25b facing the pressure side pressure chamber 8 side in the sliding cylinder 25 of the free piston 9 is a tapered surface whose inner diameter becomes smaller toward the bottom plate portion 24, Since the through hole 27 is opened from the taper surface, it is easy to drill the through hole 27 into the free piston 9.

  Furthermore, according to the shock absorber D of the present invention, the boundary between the expansion side pressure chamber 7 side of the sliding contact cylinder 25 of the free piston 9 and the expansion side pressure chamber 7 side of the bottom plate portion 24 is thinned. Since the inertial mass of the free piston 9 is reduced, the displacement of the free piston 9 other than the action of pressure due to the acceleration input from the outside to the shock absorber D can be suppressed. Attenuation characteristics can be realized.

  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 4 Piston rod 5 Stretch side flow path 6 Pressure side flow path 7 Stretch side pressure chamber 8 Pressure side pressure chamber 9 Free piston 12 Housing 13 Case 16 Grasping part 17 Lid part 21 Fixed orifice 22, 23 Variable orifice 24 Bottom plate part 25 Sliding contact cylinders 25a, 25b Inner circumferential surface 26 of sliding contact cylinders, annular groove 27, through hole D, shock absorber R1, expansion side chamber R2, compression side chamber S1, expansion side coil spring S2, compression side coil spring

Claims (9)

A cylinder, a piston that is slidably inserted into the cylinder, a piston that divides the cylinder into an extension side chamber and a pressure side chamber, a hollow housing, and a slidably inserted into the housing so as to extend through the housing. A free piston that divides into an extension side pressure chamber that communicates with the extension side chamber via a passage and a pressure side pressure chamber that communicates with the compression side chamber via a pressure side flow path, and an extension accommodated in the extension side pressure chamber. A shock absorber comprising: a side coil spring; and a pressure side coil spring housed in the pressure side pressure chamber, wherein the free piston is sandwiched between the extension side coil spring and the pressure side coil spring.
The free piston includes a bottom plate portion sandwiched between the extension side coil spring and the compression side coil spring, and a cylindrical sliding contact tube provided on the outer periphery of the bottom plate portion and in sliding contact with the inner periphery of the housing. ,
The extension side coil spring and the compression side coil spring are conical springs,
The extension side coil spring is accommodated in the sliding contact cylinder when the free piston is displaced to the stroke end in the direction of compressing the extension side pressure chamber,
The shock absorber according to claim 1, wherein the pressure side coil spring is accommodated in the sliding cylinder when the free piston is displaced to the stroke end in a direction in which the pressure side pressure chamber is compressed. The shock absorber according to claim 1, wherein a large diameter side of the extension side coil spring is fitted into a step portion of the housing on the extension side pressure chamber side. The shock absorber according to claim 1 or 2, wherein a large-diameter side of the compression side coil spring is fitted into a step portion on the compression side pressure chamber side of the housing. Comprising a piston rod movably inserted into the cylinder,
The housing is screwed to the front end side of the piston of the piston rod so that the sliding contact cylinder is in sliding contact with the inner periphery thereof, and is attached to the opening end of the case to close the opening end. The shock absorber according to any one of claims 1 to 3, further comprising a lid and a gripper that can be gripped by a tightening tool provided on an outer periphery of the case. The shock absorber according to claim 4, wherein the grip portion is formed in a shape other than a perfect circle. The case includes a small-diameter portion that is screwed to the piston rod, and a large-diameter portion that has a larger inner and outer diameter than the small-diameter portion,
The shock absorber according to claim 4 or 5, wherein an outer diameter of the grip portion is larger than an outer diameter of the large diameter portion. The free piston includes an annular groove provided on the outer periphery of the sliding contact tube along the circumferential direction, and a through hole that opens from an inner periphery facing the pressure side pressure chamber of the sliding contact tube and communicates with the annular groove. ,
The compression side flow path, and the through hole, and the annular groove, and the opposite, variable orifice to the annular groove provided on the case of the housing communicates the housing inside and outside, provided in the lid portion of the housing shock absorber according to any one of claims 1 to 6, characterized in that it is formed by the fixed orifice which communicates to the pressure side chamber the pressure side pressure chambers Te. An inner peripheral surface facing the pressure side pressure chamber side of the sliding contact cylinder of the free piston is a tapered surface whose inner diameter becomes smaller toward the bottom plate portion, and the through hole is opened from the tapered surface. The shock absorber according to claim 7 . Shock absorber according to claim 7 or 8, characterized in that the extension side pressure chamber side of the boundary of the extension side pressure chamber side and the bottom plate portion and lightening the sliding cylinder of the free piston.

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