JP2014074443A - Buffer device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a buffer device which does not lose a damping force reduction effect even when high-frequency vibrations are continuously inputted.SOLUTION: A buffer device D includes: a cylinder 1; a piston 2 which is inserted into the cylinder 1 so as to freely slide and divides the interior of the cylinder 1 into an extension side chamber R1 and a pressure side chamber R2; damping passages 3a and 3b which communicate the extension side chamber R1 and the pressure side chamber R2; a pressure chamber R3; a free piston 9 which is inserted freely movably into the pressure chamber R3 and divides the interior of the pressure chamber R3 into an extension side pressure chamber 7 and a pressure side pressure chamber 8; a spring element 10 which generates an energizing force for suppressing a displacement for the pressure chamber R3 of the free piston 9; an extension side channel 5 which communicates the extension side chamber R1 and the extension side pressure chamber 7; and a pressure side channel 6 which communicates the pressure side chamber R2 and the pressure side pressure chamber 8. Therein, when the free piston 9 exists within the prescribed range from a neutral position, a bypass channel 11 which communicates the extension side pressure chamber 7 and the pressure side chamber R2 and gives a resistance to a passing flow is provided.

Description

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

  Conventionally, this type of shock absorber is used between the vehicle body and the axle of the vehicle to suppress vehicle body vibration. For example, a cylinder and a cylinder that is slidably inserted into the cylinder are used. The piston is divided into an extension side chamber on the piston rod side and a pressure side chamber on the piston side, a first flow path communicating with the extension side chamber provided on the piston and the pressure side chamber, and opened from the tip of the piston rod to the side portion to extend. A second flow path communicating with the side chamber and the pressure side chamber; a housing provided with a pressure chamber connected in the middle of the second flow path; and a pressure chamber slidably inserted into the pressure chamber; Is formed of a free piston that divides the pressure side pressure chamber and the pressure side pressure chamber, and a coil spring that biases the free piston. That is, the expansion side pressure chamber is similarly communicated with the expansion side chamber via the second flow path, and the pressure side pressure chamber is communicated with the pressure side chamber via the second flow path.

  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.

  For this reason, this shock absorber can generate a high damping force for low-frequency vibration input, and can generate a low damping force for high-frequency vibration input. It is possible to generate a high damping force in a scene where the input vibration frequency of the vehicle is low, and reliably generate a low damping force in a scene where the input vibration frequency is high such that the vehicle passes through the road surface unevenness. Comfort can be improved (for example, refer patent document 1).

JP 2008-215459 A

  By the way, in the shock absorber interposed between the vehicle body and the axle of the vehicle, for the purpose of improving the riding comfort in the vehicle, the damping force generated during the extension operation is made higher than the damping force generated during the contraction operation. .

  Therefore, in such a shock absorber, the pressure in the expansion side chamber compressed during the expansion operation tends to be higher than the pressure in the compression side chamber compressed during the contraction operation. Since the pressure in the expansion side chamber is propagated to the expansion side pressure chamber and the pressure in the compression side chamber is propagated to the compression side pressure chamber, if the expansion and contraction is repeated at a high frequency, the pressure of the expansion side pressure chamber is reduced. The pressure becomes higher than the pressure in the pressure side pressure chamber, and the free piston is displaced toward the pressure side pressure chamber.

  When the displacement of the free piston is biased in this way, the stroke margin of the free piston toward the pressure side pressure chamber becomes small, and the free piston may come into contact with the housing and cannot be displaced into the pressure side pressure chamber. In particular, in the shock absorber disclosed in Japanese Patent Application Laid-Open No. 2008-215459, when the free piston reaches the stroke end, if the displacement is suddenly hindered, the damping characteristic changes suddenly. When the stroke amount from the neutral position of the free piston increases, consideration is given to making it difficult to displace the free piston by gradually reducing the area of the flow path that connects the pressure side chamber and the pressure side pressure chamber. For this reason, in this shock absorber, when the displacement of the free piston is biased, the area of the flow path is always reduced, so that the free piston must be displaced in a situation where it is difficult to move.

  That is, in the conventional shock absorber, under the situation where high-frequency vibration is continuously input, the displacement of the free piston is biased, and the free piston may be difficult to displace or may reach the stroke end. There is a possibility that the damping force reduction effect cannot be fully exhibited.

  Therefore, the present invention was devised to improve the above-described problems, and the object of the present invention is to provide a shock absorber that does not lose the damping force reduction effect even when high-frequency vibration is continuously input. Is to provide.

  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 compression side chamber, and the extension side chamber and the compression side. A damping passage communicating with the chamber, a pressure chamber, a free piston that is movably inserted into the pressure chamber and divides the pressure chamber into an expansion side pressure chamber and a pressure side pressure chamber, and the free piston is connected to the pressure chamber. A spring element that generates a biasing force that positions the neutral position relative to the free piston and suppresses displacement of the free piston from the neutral position, an expansion-side flow path that communicates the expansion-side chamber and the expansion-side pressure chamber, In a shock absorber provided with a pressure side flow path that communicates the pressure side chamber and the pressure side pressure chamber, the extension side pressure chamber and the pressure side chamber communicate with each other when the free piston is within a predetermined range from the neutral position. Characterized in that a bypass flow path.

  According to the shock absorber of the present invention, since the bypass flow path is provided, an increase in the difference between the pressure in the expansion side pressure chamber and the pressure in the pressure side pressure chamber can be suppressed, and bias in the displacement of the free piston can be suppressed. be able to.

  As a result, according to the shock absorber of the present invention, even if high-frequency vibration is continuously input, the stroke margin of the free piston is ensured, so that the damping force reduction effect is not lost.

It is the longitudinal cross-sectional view shown notionally of the shock absorber in one embodiment. It is the longitudinal cross-sectional view which showed concretely the buffering device in one Embodiment. It is a Bode diagram which showed the gain characteristic of the frequency transfer function of the pressure to the flow rate. It is the figure which showed the damping characteristic with respect to the vibration frequency of a buffering device. It is the longitudinal cross-sectional view which showed notionally the shock absorber in other embodiment. It is the longitudinal cross-sectional view which showed concretely the buffering device in other 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, a piston 2 that is slidably inserted into the cylinder 1 and divides the cylinder 1 into an extension side chamber R <b> 1 and a compression side chamber R <b> 2, and an extension side chamber The expansion side attenuation passage 3a and the pressure side attenuation passage 3b serving as attenuation passages for communicating R1 and the pressure side chamber R2, the pressure chamber R3, and the pressure chamber R3 are movably inserted into the expansion side pressure chamber 7 so as to be movable. And a free piston 9 that is divided into a pressure side pressure chamber 8 and a spring that generates an urging force that positions the free piston 9 in a neutral position with respect to the pressure chamber R3 and suppresses displacement from the neutral position of the free piston 9 The element 10, the expansion side flow path 5 that communicates the expansion side chamber R1 and the expansion side pressure chamber 7, the pressure side flow path 6 that communicates the pressure side chamber R2 and the pressure side pressure chamber 8, and the free piston 9 are predetermined from the neutral position. Stretching side pressure is within the range Configured and 7 and the compression side chamber R2 and a bypass passage 11 communicating, is to suppress the vibration of the vehicle body is interposed and generates a damping force between the vehicle body and an axle of the vehicle. 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 further the pressure chamber R3 are filled with liquid such as hydraulic oil, and the pressure side chamber R2 is in sliding contact with the inner periphery of the cylinder 1 in the lower part 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.

  The piston 2 has an annular shape and is attached to the outer periphery of one end of a piston rod 4 that is movably inserted into the cylinder 1. The piston rod 4 projects outward from the upper end of the cylinder 1 in the figure. Has been. The piston rod 4 and the cylinder 1 are sealed with a seal (not shown), and the inside of the cylinder 1 is in a liquid-tight state. 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.

  For compensation of the volume by which the piston rod 4 advances and retreats to and from the cylinder 1, in addition to providing the gas chamber G in the cylinder 1, a reservoir may be provided in the cylinder 1 or outside the cylinder 1. In this case, an outer cylinder that covers the outer periphery of the cylinder 1 is provided to form a double cylinder type shock absorber that forms a reservoir between the cylinder 1 and the outer cylinder, and a tank is provided separately from the cylinder 1 A reservoir may be formed. In addition, in order to increase the pressure of the pressure side chamber R2 during the contraction operation of the shock absorber D, a partition member that partitions the pressure side chamber R2 and the reservoir, and a resistance provided to a liquid flow that is provided in the partition member and travels from the pressure side chamber R2 to the reservoir A base valve for providing the above may be provided. Further, the shock absorber D may be set to a double rod type instead of a single rod type.

  Further, the extension side damping passage 3a and the pressure side damping passage 3b are provided in the piston 2 in this embodiment, and a damping force generating element comprising a leaf valve stacked on the piston 2 is provided at the outlet end thereof. 13a and 13b are provided so that the damping force generating elements 13a and 13b can give resistance to the flow of the liquid passing through the expansion side attenuation passage 3a and the compression side attenuation passage 3b. The damping force generation element 13a sets the expansion side attenuation passage 3a as a one-way passage that allows only the flow of liquid from the expansion side chamber R1 to the compression side chamber R2, and the damping force generation element 13b also includes the compression side attenuation passage. 3b is set as a one-way passage that allows only the flow of liquid from the compression side chamber R2 to the expansion side chamber R1, and the resistance that the damping force generating element 13a gives to the flow of liquid that passes through the expansion side attenuation passage 3a is attenuated. The force generating element 13b is larger than the resistance given to the flow of the liquid passing through the compression side attenuation passage 3b. That is, when the damping device D expands and contracts, considering that a damping force is generated only through the extension side damping passage 3a and the compression side damping passage 3b, the liquid passes only through the extension side damping passage 3a during the extension operation. In the contraction operation, the liquid passes only through the compression side damping passage 3b. When the piston speed is the same, the damping force during the extension operation is higher than the damping force during the contraction operation. The damping force generating elements 13a and 13b may be other valves such as well-known orifices, chokes, poppet valves, etc., in addition to the leaf valves, for example, and are configured such that the orifices and chokes are arranged in parallel with the leaf valves. May be. Further, since the damping passage only needs to communicate the expansion side chamber R1 and the pressure side chamber R2, the expansion side attenuation passage 3a and the pressure side attenuation passage 3b can be provided in addition to the piston 2, for example, the piston rod 4 It can also be provided outside the cylinder 1.

  In the case of this embodiment, the pressure chamber R3 is formed by a hollow portion 14a that is connected to the lower side of the piston 2 and provided in the housing 14 facing the pressure side chamber R2 as shown in FIG. Yes. The housing 14 has a bottomed cylindrical shape including a cylindrical portion 14b and a bottom portion 14c, and is screwed to the tip of the piston rod 4 and below the piston 2 in FIG. 1 to form a pressure chamber R3. In addition, it functions as a piston nut for fastening the piston 2 to the piston rod 4.

  In the hollow portion 14a of the housing 14, there is a free piston 9 that is slidably in contact with the side wall of the hollow portion 14a, that is, the inner periphery of the cylindrical portion 14b, and is movable in the vertical direction in FIG. The hollow portion 14a is partitioned by the free piston 9 into an extension side pressure chamber 7 at the upper side in FIG. 1 and a pressure side pressure chamber 8 at the lower side in FIG. That is, the free piston 9 is slidably inserted into the housing 14 and can be displaced in the vertical direction in FIG.

  The free piston 9 has one end connected to the lower end of the hollow portion 14a forming the pressure chamber R3 and is connected to the other end of the spring element 10 accommodated in the pressure-side pressure chamber 8. The piston 9 is positioned at a predetermined neutral position in the housing 14. When the free piston 9 is displaced from this neutral position, the spring element 10 generates an urging force in a direction to return the free piston 9 to the neutral position in accordance with the amount of displacement. The neutral position described above is a position where the free piston 9 is positioned by the spring element 10 with respect to the pressure chamber R3, and does not necessarily have to be set at the midpoint in the vertical direction of the hollow portion 14a. The spring element 10 may be accommodated in the expansion side pressure chamber 7, and the spring element 10 is constituted by two springs accommodated in each of the expansion side pressure chamber 7 and the compression side pressure chamber 8, and these springs are free pistons. 9 may be clamped and positioned to the neutral position.

  The housing 14 is divided into an expansion side pressure chamber 7 and a compression side pressure chamber 8 up and down by the free piston 9 and the vibration direction in which the shock absorber D expands and contracts and the movement direction of the free piston 9 coincide with each other. When it is desired to avoid the vibration of the free piston 9 in the vertical direction relative to the housing 14 caused by the entire shock absorber D vibrating in the vertical direction in FIG. 1, the movement direction of the free piston 9 is buffered. It is also possible to set the expansion direction pressure chamber 7 and the pressure side pressure chamber 8 in the lateral direction in FIG.

  Further, the housing 14 is provided with a pressure-side flow path 6 that communicates the pressure-side chamber R2 and the pressure-side pressure chamber 8, and in this case, the pressure-side flow path 6 is in parallel with the variable throttle passage 6a. And a fixed restricting passage 6b, which can provide resistance to the flow of liquid passing through the fixed restricting passage 6b. The variable throttle passage 6a is a variable throttle that reduces the opening area as the free piston 9 is displaced from the neutral position. The free piston 9 abuts on the upper end of the housing 14 or the spring element 10 is in the most compressed state. As the stroke end approaches, the displacement speed of the free piston 9 can be reduced.

  For example, as shown in FIG. 2, the variable throttle passage 6 a communicates between the pressure side communication passage 9 a provided in the free piston 9 and opening from the surface facing the pressure side pressure chamber 8 to the outer periphery, and the inside and outside of the housing 14. When the free piston 9 is in the neutral position, the pressure side through hole 14d of the housing 14 is fully opened opposite to the opening on the outer periphery of the free piston 9 of the pressure side communication passage 9a. When the free piston 9 is displaced from the neutral position, the opposed area of the pressure side through hole 14d and the pressure side communication passage 9a is gradually reduced so that the flow area of the variable throttle passage 6a decreases with the displacement of the free piston 9. As shown in FIG. 2, it may be set to be blocked when the displacement from the neutral position of the free piston 9 advances. In this case, in order to function as the variable throttle passage 6a, a throttle may be provided in one or both of the pressure side communication passage 9a and the pressure side through hole 14d. As shown in FIG. 2, by making the free piston 9 into a bottomed cylindrical shape, it is possible to ensure the stroke length of the free piston 9 and the axial direction of the housing 14 while avoiding interference with the tip of the piston rod 4. Miniaturization can be achieved. The spring element 10 can be easily realized by configuring the free piston 9 with a pair of springs 10a and 10b arranged up and down in FIG.

  Further, as shown in FIG. 2, an annular groove 9b is provided at the outer peripheral side opening end of the free piston 9 of the pressure side communication passage 9a, or an annular groove is provided at the inner peripheral side opening end of the pressure side through hole 14d on the inner periphery of the housing 14. If the free piston 9 is displaced in the circumferential direction with respect to the housing 14, the pressure side communication passage 9a and the pressure side through hole 14d can be reliably communicated with each other. Thus, when the variable throttle passage 6a is provided in the pressure side passage 6, the flow passage area of the variable throttle passage 6a decreases with the displacement of the free piston 9, and a structure for making the flow passage area variable is added separately. Therefore, the variable throttle passage 6a can be formed, and the labor and cost of installing the variable throttle passage 6a are reduced. In the illustrated case, the variable throttle passage 6a is blocked, but the fixed throttle passage 6b is always open, and the pressure side channel 6 is not blocked even if the channel area is reduced. However, if the variable throttle passage 6a is not completely blocked regardless of the displacement of the free piston 9, the fixed throttle passage 6b may be eliminated, or the variable throttle passage 6a may be eliminated and the fixed throttle passage 6b. It is also possible to configure the pressure-side flow path 6 with only the above.

  Returning, the expansion side chamber R1 and the expansion side pressure chamber 7 open from the side facing the expansion side chamber R1 of the piston rod 4 and communicate with each other via the expansion side flow path 5 through the piston 2 and the housing 14. In this way, the expansion side chamber R1 and the expansion side pressure chamber 7 are communicated by the expansion side flow channel 5, and the compression side chamber R2 and the compression side pressure chamber 8 are communicated by the compression side flow channel 6, and the expansion side pressure chamber 7 and the pressure side pressure are communicated. Since the volume of the chamber 8 changes as the free piston 9 is displaced in the housing 14, the shock absorber D has the above-described extension side flow path 5, extension side pressure chamber 7, pressure side pressure chamber 8 and pressure side. The flow channel 6 apparently communicates the expansion side chamber R1 and the pressure side chamber R2, and the expansion side chamber R1 and the pressure side chamber R2 are described above in addition to the expansion side attenuation passage 3a and the pressure side attenuation passage 3b. It is also communicated by the apparent flow path.

  In addition, the housing 14 is provided with a bypass channel 11 that communicates the expansion side pressure chamber 7 and the pressure side chamber R2. The bypass channel 11 is provided with a throttle 11a as a valve element in the middle, and provides resistance to the flow of liquid flowing through the bypass channel 11. Further, an on-off valve 15 that opens and closes the bypass passage 11 in conjunction with the free piston 9 is provided in the middle of the bypass passage 11. The on-off valve 15 includes a valve body 15a that is provided in the middle of the bypass passage 11 with a communication position 15b and two blocking positions 15c and 15d, and a lever 15e that connects the valve body 15a to the free piston 9. If the free piston 9 is displaced, the position is changed. Specifically, when the amount of displacement from the neutral position of the free piston 9 is within a predetermined range, the on-off valve 15 adopts a communication position 15b that opens the bypass passage 11 and extends from the neutral position of the free piston 9 to the extended side. When the pressure chamber 7 is displaced in the compressing direction and the free piston 9 exceeds the predetermined range, a blocking position 15d for blocking the bypass passage 11 is taken, and the compression side pressure chamber 8 is compressed from the neutral position of the free piston 9. When the free piston 9 is displaced and exceeds the predetermined range, a blocking position 15c for blocking the bypass flow path 11 is adopted. That is, the on-off valve 15 opens the bypass passage 11 only when the free piston 9 is within a predetermined range from the neutral position.

  Since the bypass flow path 11 communicates the expansion side pressure chamber 7 and the pressure side chamber R2 and is arranged in parallel with the free piston 9, the liquid passes through the bypass flow path 11 when the bypass flow path 11 is opened. As a result, the flow rate flowing through the apparent flow path is reduced, and the amount of displacement of the free piston 9 is suppressed as compared with the conventional shock absorber. In the case of this embodiment, the bypass channel 11 uses the throttle 11a to provide resistance to the liquid flow, but other valve elements such as an orifice and a choke that make the channel area variable. It is also possible to use. In addition, the bypass flow path 11 is provided in the housing 14 in this case, but may be provided over the free piston 9 and the housing 14.

  The on-off valve 15 is interlocked with the free piston 9 as described above. For example, as shown in FIG. 2, the on-off valve 15 is opened from the surface facing the expansion side pressure chamber 7 as shown in FIG. An extension side communication passage 9c communicating with the outer periphery is provided, and a through hole 14e communicating with the inside and the outside is provided in the housing 14, thereby forming the bypass flow path 11, and when the free piston 9 is within a predetermined range from the neutral position, the housing If the opening of the through-hole 14e on the outer periphery of the free piston 9 is opposed to the opening on the outer periphery of the free piston 9 of the expansion side communication passage 9c, the bypass flow path when the free piston 9 is displaced outside the predetermined range. 11 is cut off, so that the free piston 9 and the housing 14 can function as an on-off valve, saving labor and cost of providing an on-off valve separately. Kill. In this case, one or both of the expansion side communication passage 9c and the through hole 14e may function as the restrictor 11a. Further, as shown in FIG. 2, an annular groove 9d is provided at the outer peripheral side opening end of the free piston 9 of the extension side communication passage 9c, or an annular groove is provided at the inner peripheral side opening end of the through hole 14e on the inner periphery of the housing 14. If the free piston 9 is displaced in the circumferential direction with respect to the housing 14, the expansion side communication passage 9 c and the through hole 14 e can be reliably communicated to function as the on-off valve 15. .

  Next, the basic operation of the shock absorber D will be described. When the shock absorber D performs an expansion / contraction operation in which the piston 2 moves up and down in FIG. 1 with respect to the cylinder 1, one of the expansion side chamber R1 and the compression side chamber R2 is compressed by the piston 2, and the other of the expansion side chamber R1 and the compression side chamber R2 Since the pressure of the expansion side chamber R1 and the compression side chamber R2 that is compressed increases, the pressure of the expansion side chamber R1 and the compression side chamber R2 that expands the volume decreases and the pressure difference between the two increases. Arise. Then, the compression side liquid in the expansion side chamber R1 and the compression side chamber R2 is one of the expansion side attenuation passage 3a and the compression side attenuation passage 3b, and in addition to this, the expansion side flow channel 5, the expansion side pressure chamber 7, the pressure side pressure. It moves to the expansion side of the expansion side chamber R1 and the pressure side chamber R2 via an apparent flow path consisting of the chamber 8 and the pressure side flow path 6.

  Here, the piston speed in the expansion stroke of the shock absorber D is the same regardless of whether the vibration frequency input to the shock absorber D, that is, the vibration frequency in the expansion / contraction direction of the shock absorber D is low or high. In this case, the amplitude of the shock absorber D at the time of low frequency vibration input is larger than the amplitude of the shock absorber D at the time of high frequency vibration input. Thus, when the frequency of the vibration input to the shock absorber D is low, the amplitude is large, so that the flow rate of the liquid flowing between the expansion side chamber R1 and the compression side chamber R2 increases in one expansion / contraction cycle. Although the displacement of the free piston 9 increases substantially in proportion to the flow rate, the free piston 9 is biased by the spring element 10, so that when the displacement of the free piston 9 increases, the spring element received by the free piston 9 The urging force from 10 also increases, and accordingly, a differential pressure is generated between the pressure in the expansion side pressure chamber 7 and the pressure in the compression side pressure chamber 8, and the differential pressure between the expansion side chamber R1 and the expansion side pressure chamber 7 and the pressure side chamber R2 The differential pressure in the pressure side pressure chamber 8 is reduced, and the flow rate passing through the apparent flow path is reduced. Since the flow rate passing through this apparent flow path is small, the flow rate of the passage 3a is increased, so that the damping force generated by the shock absorber D is maintained high.

  Conversely, when high-frequency vibration is input to the shock absorber D, the amplitude is smaller than when low-frequency vibration is input, so the flow rate of the liquid flowing between the expansion-side chamber R1 and the compression-side chamber R2 in one expansion / contraction cycle is small, and the free piston 9 The moving displacement is also reduced. Then, the biasing force is also reduced from the spring element 10 received by the free piston 9. Accordingly, the pressure in the expansion side pressure chamber 7 and the pressure in the compression side pressure chamber 8 become substantially equal, and 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 are low frequency. It becomes larger than that at the time of vibration input, and the flow rate passing through the above apparent flow path is increased compared to that at the time of low frequency vibration input. Since the flow rate through the apparent flow path increases, the flow rate of the expansion side attenuation passage 3a decreases. Therefore, the damping force generated by the shock absorber D is more than the damping force at the time of low frequency vibration input. Lower.

  In this way, when the piston speed is low, the gain characteristic with respect to the frequency of the frequency transfer function of the differential pressure with respect to the flow rate is as shown in FIG. It becomes the characteristic. In addition, the damping force characteristic in the shock absorber D that indicates the gain of the damping force with respect to the input of the vibration frequency generates a high damping force for the vibration in the low frequency range as shown in FIG. The damping force can be lowered with respect to the vibration, and the change in the damping force of the shock absorber D can be made dependent on the input vibration frequency. Even in the contraction stroke of the shock absorber D, a high damping force is generated for vibrations in the low frequency range and a damping force is low for vibrations in the high frequency range, as in the above-described expansion stroke. And the change of the damping force of the shock absorber D can be made to depend on the input vibration frequency. In the damping characteristic of FIG. 4, by adjusting the breakpoint frequency, the shock absorber D can generate a high damping force with respect to the vibration input of the sprung resonance frequency, and the vehicle posture is stabilized. Therefore, it is possible to prevent the passenger from feeling uneasy when turning the vehicle, and when the vibration of the unsprung resonance frequency is input, the damping force becomes low, and the transmission of the vibration on the axle side to the vehicle body side is insulated. The riding comfort in the vehicle can be made favorable. The damping characteristic of the shock absorber D can be arbitrarily set by setting each part as disclosed in Japanese Patent Application Laid-Open No. 2008-215459.

  Further, in this shock absorber D, the flow area of the pressure side flow path 6 is reduced as the amount of displacement from the neutral position of the free piston 9 increases. The movement speed to the stroke end side is reduced, and the amount of liquid movement through the apparent flow path is also reduced, and the amount of liquid passing through the expansion side attenuation passage 3a or the pressure side attenuation passage 3b is increased accordingly. Therefore, the generated damping force of the shock absorber D1 gradually increases. When the free piston 9 reaches the stroke end, the liquid no longer moves through the apparent flow path, and the liquid does not move until the shock absorber D rotates in the expansion / contraction direction. Only the passage 3b is passed, and the shock absorber D generates a damping force with the maximum damping coefficient. That is, when a vibration having a high frequency and a large amplitude that causes the free piston 9 to be displaced to the stroke end is input to the shock absorber D, the pressure side flow path is increased with respect to an increase in the amount of displacement from the neutral position of the free piston 9. 6, the damping force generated by the shock absorber D gradually increases, so that the low damping force exerted by the shock absorber D against high-frequency vibrations suddenly changes to a high damping force. Disappears. That is, when the free piston 9 reaches the stroke end and the alternating current between the extension side chamber R1 and the pressure side chamber R2 cannot be exchanged via the pressure chamber R3, the damping force does not change suddenly. The damping force change to high damping force becomes gentle. Further, 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, a structure is adopted in which the flow passage area of the pressure side flow passage 6 gradually decreases in accordance with the displacement from the neutral position of the free piston 9, so that the amplitude is high at a high frequency. Even if vibration is input, the generated damping force changes smoothly, so that it is possible to improve the ride comfort in the vehicle without having the passenger perceive shock due to the change in the damping force. A situation in which the vehicle body vibrates due to a change in the damping force and the bonnet resonates to generate abnormal noise can be prevented, and in this respect as well, the riding comfort in the vehicle can be improved.

  As described above, basically, the shock absorber D generates a high damping force for vibrations in the low frequency range and a damping force for vibrations in the high frequency range, as in the conventional shock absorbing device. Although it can be lowered, the shock absorber D of the present invention includes a bypass passage 11 that is opened when the free piston 9 is within a predetermined range from the neutral position. Therefore, in addition to the above basic operation, in the shock absorber D of the present invention, while the bypass channel 11 is open, the liquid also flows through the bypass channel 11 and therefore flows through the apparent channel. Since the flow rate of the liquid is reduced and the increase in the pressure difference between the expansion side pressure chamber 7 and the pressure side pressure chamber 8 is suppressed, the displacement amount of the free piston 9 can be suppressed as compared with the conventional shock absorber.

  Further, when the free piston 9 is displaced from the neutral position to outside the predetermined range, the bypass flow path 11 is blocked. In this way, when the free piston 9 is located in the vicinity of the neutral position, the free piston 9 is difficult to move, and when the free piston 9 is displaced from the neutral position to outside the predetermined range, the bypass flow path 11 is blocked. A difference in the pressure between the extension side pressure chamber 7 and the pressure side pressure chamber 8 is likely to occur, and the displacement of the free piston 9 is promoted. Then, at the time of large amplitude input, it is possible to obtain a damping force reduction effect that is comparable to that of a conventional shock absorber. If the flow area of the bypass flow path 11 is set to gradually decrease when the free piston 9 reaches outside the predetermined range and the bypass flow path 11 is blocked, the displacement of the free piston 9 The speed does not change abruptly, and a sudden change in damping force does not cause abnormal noise due to vibrations applied to the vehicle body. If the amount of displacement from the neutral position of the free piston 9 is within a predetermined range, the bypass flow path 11 is opened, but the predetermined range can be arbitrarily set.

  Further, when the free piston 9 is displaced from the neutral position in the direction of compressing the expansion side pressure chamber 7, a predetermined range of expansion side limit, and when the free piston 9 is displaced from the neutral position in the direction of compressing the compression side pressure chamber 8. The distance between the neutral position and the extension limit may be different from the distance between the neutral position and the pressure limit, that is, the predetermined range is not necessarily centered on the neutral position. It is not necessary to have a range limit at the same distance on both sides of the displacement direction.

  As described above, in the shock absorber D of the present invention, since the displacement from the neutral position of the free piston 9 can be suppressed, the free piston 9 is moved from the neutral position to the pressure side pressure chamber even if high frequency vibration is continuously input. It is less likely to be displaced toward the 8 side, and the operation of reducing the damping force is not impaired during the high frequency vibration that is the basic operation of the shock absorber D.

  Further, in the shock absorber D of the present invention, even if high-frequency vibration is continuously input, the displacement of the free piston 9 is not biased, so that it is possible to ensure a stroke margin of the free piston 9 toward the pressure side pressure chamber 8. It is possible to prevent the free piston 9 from coming into contact with the housing 14 and being unable to be displaced into the pressure side pressure chamber 8.

  As a result, according to the shock absorber D of the present invention, even if high-frequency vibration is continuously input, the stroke margin of the free piston 9 is ensured, so that the damping force reduction effect is not lost.

  In addition, in this shock absorber D, even if high-frequency vibration is continuously input, the damping force reduction effect can be exhibited, so even when the vehicle travels on a rough road or a bumpy road, A good ride can be achieved.

  Further, in this shock absorber D1, the differential pressure between the expansion side pressure chamber 7 and the pressure side pressure chamber 8 when the bypass flow channel 11 is open is determined by the resistance that the throttle 11a gives to the liquid flow and the pressure side flow channel 6 The displacement amount of the free piston 9 can be tuned with respect to the expansion / contraction speed of the shock absorber D by the ratio to the resistance applied to the liquid flow.

  Next, the shock absorber D1 of another embodiment shown in FIG. 5 will be described. The shock absorber D1 is different from the shock absorber D described above in that the bypass channel 16 is also communicated with the pressure side pressure chamber 8. Since the other configuration is the same as that of the shock absorber D, the shock absorber D1 will be described in detail below about the members different from the shock absorber D, and the same members will be described with the same reference numerals because the description is redundant. Detailed description will be omitted.

  Specifically, the bypass channel 16 communicates the expansion side pressure chamber 7 with the compression side chamber R2, and includes a throttle 16a as a valve element in the middle. The pressure side chamber R2 side of the throttle 16a as the valve element of the bypass flow channel 16 is also communicated with the pressure side pressure chamber 8 via the branch passage 18. Thus, in the shock absorber D1, the expansion-side pressure chamber 7 and the compression-side pressure chamber 8 are placed in communication with each other by the bypass flow path 16, but the throttle 16a as a valve element is provided. A differential pressure is generated between the extension-side pressure chamber 7 and the compression-side pressure chamber 8. As the valve element, for example, a valve element such as an orifice or a choke can be used.

  Further, in the shock absorber D1, an on-off valve 17 is provided in the middle of the bypass flow path 16 and closer to the pressure side chamber R2 than the branch passage 18. This on-off valve 17 opens and closes the bypass flow path 16 in conjunction with the free piston 9, and includes a communication position 17b and two blocking positions 17c and 17d and is provided in the middle of the bypass flow path 16. A body 17a and a lever 17e for connecting the valve body 17a to the free piston 9 are provided, and the position changes when the free piston 9 is displaced. Specifically, when the displacement from the neutral position of the free piston 9 is within a predetermined range, the on-off valve 17 adopts a communication position 17b that opens the bypass passage 16 and extends from the neutral position of the free piston 9 to the extended side. When the pressure chamber 7 is displaced in the direction of compression and the free piston 9 exceeds the predetermined range, a blocking position 17d for blocking the bypass flow path 16 is adopted, and the compression side pressure chamber 8 is compressed from the neutral position of the free piston 9. When the free piston 9 is displaced and exceeds the predetermined range, a blocking position 17c for blocking the bypass channel 16 is adopted. That is, the on-off valve 17 opens the bypass passage 16 only when the free piston 9 is within a predetermined range from the neutral position.

  In the shock absorber D1 of this embodiment, the variable throttle 16b is provided on the pressure side chamber R2 side of the branch passage 18 of the bypass passage 16. In this case, since the variable throttle 16b is disposed between the pressure side pressure chamber 8 and the pressure side chamber R2, the branch passage 18 and the portion where the branch passage 18 of the bypass passage 16 is connected to the pressure side chamber R2. Then, the variable throttle 16b is formed in the shock absorber D by the variable throttle 16b, and a part of the bypass channel 16 also functions as the pressure side channel 6. In the shock absorber D1 of this embodiment, a part of the bypass flow path 16 also functions as the variable throttle passage 6a, so that the variable throttle passage 6a is also opened and closed by the opening / closing valve 17.

  In the shock absorber D1, basically, like the shock absorber D, the free piston 9 is displaced so that the liquid moves back and forth between the extension side chamber R1 and the pressure side chamber R2 via the apparent flow path. A high damping force can be generated for vibrations in the low frequency range, and a damping force can be lowered for vibrations in the high frequency range.

  And the buffering device D1 of this invention is equipped with the bypass flow path 16 opened like the buffering device D, when the free piston 9 exists in a predetermined range from a neutral position. Therefore, in addition to the basic operation described above, even in the shock absorber D1 of the present invention, the extension-side pressure chamber 7 is communicated with the compression-side chamber R2 while the bypass channel 16 is open. Of the flow rate of the liquid flowing through the flow path, the flow rate of the liquid flowing through the bypass flow path 16 does not contribute to the displacement of the free piston 9 and suppresses an increase in the pressure difference between the expansion side pressure chamber 7 and the pressure side pressure chamber 8. Therefore, the displacement amount of the free piston 9 can be suppressed as compared with the conventional shock absorber.

  Further, when the free piston 9 is displaced from the neutral position to outside the predetermined range, the bypass flow path 16 is blocked. In this way, when the free piston 9 is positioned in the vicinity of the neutral position, the free piston 9 is difficult to move, and when the free piston 9 is displaced from the neutral position to outside the predetermined range, the bypass flow path 16 is blocked. A difference in the pressure between the extension side pressure chamber 7 and the pressure side pressure chamber 8 is likely to occur, and the displacement of the free piston 9 is promoted. Then, at the time of inputting a large amplitude, it is possible to obtain a damping force reduction effect that is comparable to that of a conventional shock absorber with respect to high-frequency vibration. If the flow passage area of the bypass flow passage 16 is set to gradually decrease when the free piston 9 reaches outside the predetermined range and the bypass flow passage 16 is blocked, the displacement of the free piston 9 The speed does not change abruptly, and a sudden change in damping force does not cause abnormal noise due to vibrations applied to the vehicle body. If the amount of displacement from the neutral position of the free piston 9 is within a predetermined range, the bypass flow path 16 is opened. However, the predetermined range can be arbitrarily set with the shock absorber D. It is the same.

  As described above, in the shock absorber D1 of the present invention, since the displacement from the neutral position of the free piston 9 can be suppressed, the free piston 9 is moved from the neutral position to the pressure side pressure chamber even if high frequency vibration is continuously input. It is less likely to be displaced toward the 8 side, and the operation of reducing the damping force is not impaired during the high frequency vibration that is the basic operation of the shock absorber D1.

  Further, in the shock absorber D1 of the present invention, even if high-frequency vibration is continuously input, the displacement of the free piston 9 is not biased, so that it is possible to ensure a stroke margin of the free piston 9 toward the pressure side pressure chamber 8 side. It is possible to prevent the free piston 9 from coming into contact with the housing 14 and being unable to be displaced into the pressure side pressure chamber 8.

  As a result, according to the shock absorber D1 of the present invention, even if high-frequency vibration is continuously input, the stroke margin of the free piston 9 is ensured, so that the damping force reduction effect is not lost.

  Further, in this shock absorber D1, even if high-frequency vibration is continuously input, the damping force reduction effect can be exhibited, so even when the vehicle travels on a rough road or a bumpy road, A good ride can be achieved.

  Further, even in the shock absorber D1, the differential pressure between the expansion side pressure chamber 7 and the pressure side pressure chamber 8 when the bypass flow path 16 is open is a valve element between the expansion side pressure chamber 7 and the pressure side pressure chamber 8. The displacement amount of the free piston 9 can be tuned with respect to the expansion / contraction speed of the shock absorber D1 by the ratio of the resistance that the restriction 16a gives to the liquid flow and the resistance that the pressure side flow path 6 gives to the liquid flow. .

  As shown in FIG. 6, the bypass flow path 16 communicates between the inside and outside of the housing 14 and the extension side communication path 9 e that is provided in the free piston 9 and opens from the surface facing the extension side pressure chamber 7 and communicates with the outer periphery. The through-hole 14f that opens, and the pressure-side communication passage 9f that opens from the pressure-side pressure chamber 8 and communicates with the expansion-side communication passage 9e can be formed. In this case, the expansion side communication path 9e itself may function as a throttle, or a throttle may be provided in the middle. Further, as shown in FIG. 6, since the annular groove 9g is provided at the outer peripheral opening end of the free piston 9 of the extension side communication passage 9c, the extension side communication passage 9c and the through hole 14f are displaced in the circumferential direction. However, the function as the on-off valve 17 can be exhibited while ensuring communication between the two.

  When the free piston 9 is within a predetermined range from the neutral position, the opening in the outer periphery of the free piston 9 of the through hole 14f of the housing 14 is opposed to the annular groove 9g that communicates with the expansion side communication passage 9e. When the flow path 16 is opened and the free piston 9 is displaced outside the predetermined range, the through hole 14f is closed at the outer periphery of the free piston 9 and the bypass flow path 16 is blocked, so that the free piston 9 and the housing 14 are opened and closed. It can be made to function as the valve 17, and the trouble and cost of providing an on-off valve can be saved separately.

  Further, in this case, as shown in FIG. 6, the expansion side communication passage 9e is communicated with the pressure side communication passage 9f, and the variable throttle passage is formed by the pressure side communication passage 9d and the through hole 14f communicating with the inside and the outside of the housing 14. 6a is formed. The extension side communication passage 9c and the pressure side communication passage 9d are communicated with each other through an annular groove 9g, and the processing for communicating both is easy. In this case, a throttle may be provided in one or both of the pressure side communication path 9f and the through hole 14f. When the free piston 9 is in the neutral position, the variable throttle passage 6a is gradually opened when the through hole 14f of the housing 14 is fully opened facing the annular groove 9d and the free piston 9 is displaced from the neutral position. Since the opposed area between the hole 14f and the annular groove 9g is reduced, the flow area of the variable throttle passage 6a is reduced with the displacement of the free piston 9, and is blocked when the displacement from the neutral position of the free piston 9 proceeds. Is done. In this way, the variable throttle passage 6a can be formed without adding a structure that makes the flow path area variable, and the labor and cost of installing the variable throttle passage 6a are reduced.

  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 The expansion | extension side attenuation | damping channel | path 3b as an attenuation | damping channel | path Pressure side attenuation | damping channel | path 4 as an attenuation | damping channel | path 4 Piston rod 5 Extinction side channel | channel 6 Pressure side channel | channel 6b Fixed throttle channel | , 9f Pressure side communication path 9c, 9e Extension side communication path 10 Spring element 11, 16 Bypass flow path 14 Housing 14d Pressure side through hole 14e, 14f Through hole 15, 17 Open / close valve 16a Restrictor 22 as valve element Guide rod D, D1 Buffer Apparatus R1 Extension side chamber R2 Pressure side chamber R3 Pressure chamber

Claims (7)

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 damping passage that communicates the extension side chamber and the pressure side chamber, a pressure chamber, and a pressure chamber A free piston that is movably inserted and divides the pressure chamber into an expansion side pressure chamber and a pressure side pressure chamber, and positions the free piston in a neutral position with respect to the pressure chamber and from the neutral position of the free piston A spring element that generates an urging force that suppresses the displacement of the gas, an extension-side passage that communicates the extension-side chamber and the extension-side pressure chamber, and a pressure-side passage that communicates the compression-side chamber and the pressure-side pressure chamber. In the shock absorber provided, when the free piston is within a predetermined range from the neutral position, a bypass flow path is provided which communicates the extension side pressure chamber and the pressure side chamber and gives resistance to the passing flow. Buffer and wherein the door. The said bypass flow path is provided with the valve element which gives resistance to the flow which passes in the middle, The pressure side chamber side is connected to the said pressure side pressure chamber rather than the valve element of the said bypass flow path. Shock absorber. The bypass flow path includes an on-off valve interlocked with the free piston in the middle, and the on-off valve opens only when the free piston is within a predetermined range from a neutral position. The shock absorber according to 1 or 2. The shock absorber according to any one of claims 1 to 3, wherein the free piston functions as the on-off valve. A hollow housing that forms the pressure chamber, the free piston is slidably inserted into the housing, and the housing is partitioned into the extension side pressure chamber and the pressure side pressure chamber; Is formed by an extension side communication passage provided in the free piston and communicating the extension side pressure chamber with the outer periphery of the free piston, and a through hole provided in the housing and communicating the pressure side chamber in the housing. 5. When the free piston is in the neutral position, the extension side communication path and the through hole are communicated to open the bypass flow path. The shock absorber described. The pressure side flow path is provided in the free piston and communicates the pressure side pressure chamber with the outer periphery of the free piston. The pressure side flow path is provided in the housing and the pressure side communication path when the free piston is in a neutral position. A pressure side through hole that communicates the pressure side pressure chamber with the pressure side chamber and a fixed throttle passage that is provided in the housing and communicates the pressure side chamber with the pressure side pressure chamber. The shock absorber according to any one of 1 to 5. The shock absorber according to claim 6, wherein the pressure side communication path is communicated with the extension side communication path.

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