JP2013007425A - Shock absorber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shock absorber that never loses a damping-force reduction effect even when high frequency vibration is continuously input.SOLUTION: The shock absorber D includes: a cylinder 1; a partition member 2 inserted into the cylinder 1 in a freely slidable manner and for dividing the inside of the cylinder 1 into an expanding-side chamber R1 and a pressing-side chamber R2; passages 3a and 3b for communicating between the expanding-side chamber R1 and the pressing-side chamber R2; a pressure chamber R3; and a free piston 9 inserted into the pressure chamber R3 in a freely movable and for dividing the inside of the pressure chamber R3 into an expanding-side pressure chamber 7 and a pressing-side pressure chamber 8. The shock absorber includes a displacement compensation passage 11 for allowing only a flow from the expanding-side pressure chamber 7 toward the pressing-side pressure chamber 8 and giving a resistance to the flow.

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.

Here, on the basis of the pressure in the compression side chamber, P is the differential pressure between the expansion side chamber and the compression side chamber when the shock absorber expands and contracts, Q is the flow rate of the liquid flowing out from the expansion side chamber, and the differential pressure P and the first flow path The coefficient which is the relationship with the flow rate Q1 of the liquid passing through the cylinder is C1, the differential pressure between the compression side chamber and the expansion side pressure chamber is P1, and the difference between the differential pressure P and the differential pressure P1 and the extension side chamber to the extension side pressure chamber The coefficient that is the relationship with the flow rate Q2 of the inflowing liquid is C2, the differential pressure between the pressure side chamber and the pressure side pressure chamber is P2, and the relationship between this differential pressure P2 and the flow rate Q2 of the liquid flowing out from the pressure side pressure chamber to the pressure side chamber Where C is a coefficient, and A is the cross-sectional area that is the pressure receiving area of the free piston, X is the displacement of the free piston with respect to the pressure chamber, K is the spring constant of the coil spring, and the transfer function of the differential pressure P with respect to the flow rate Q is If it calculates | requires, Formula (1) will be obtained. In equation (1), s represents a Laplace operator.

Furthermore, substituting jω for the Laplace operator s in the transfer function shown in the above equation (1) to obtain the absolute value of the frequency transfer function G (jω) yields the following equation (2).

As can be understood from the above equations, the frequency characteristic of the transfer function of the differential pressure P with respect to the flow rate Q in this shock absorber is expressed as Fa = K / {2 · π · A ² as shown in the Bode diagram of FIG. (C1 + C2 + C3)} and Fb = K / {2 · π · A ² · (C2 + C3)}, and in the region of F <Fa, the transfer gain is approximately C1, and Fa ≦ In the region of F ≦ Fb, it changes so as to gradually decrease from C1 to C1 · (C2 + C3) / (C1 + C2 + C3), and is constant in the region of F> Fb. That is, in the frequency characteristic of the transfer function of the differential pressure P with respect to the flow rate Q, the transfer gain increases in the low frequency range, and the transfer gain decreases in the high frequency range.

  Therefore, in this shock absorber, as shown by the damping characteristic in FIG. 9, a large damping force is generated for low-frequency vibration input, while a small damping force is generated for high-frequency vibration input. In a scene where the input vibration frequency is low, such as when the vehicle is turning, a high damping force can be reliably generated, and in a scene where the vehicle has a high input vibration frequency that passes through the unevenness of the road surface. Can reliably generate a low damping force and improve the riding comfort of the vehicle (see, for example, 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 larger than the damping force generated during the compression 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 compression 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 partition member that is slidably inserted into the cylinder and divides the cylinder into an extension side chamber and a compression side chamber, and the extension side chamber. A passage that communicates with the compression side chamber, a pressure chamber, and an extension side pressure chamber that is movably inserted into the pressure chamber and communicates with the extension side chamber via the extension side passage and the pressure side passage. In the shock absorber comprising: a free piston that is divided into a pressure side pressure chamber that communicates with the pressure side chamber; and a spring element that generates a biasing force that suppresses displacement of the free piston with respect to the pressure chamber. A displacement compensation passage is provided which allows only a flow from the pressure side to the pressure side pressure chamber and gives resistance to the flow.

  According to the shock absorber of the present invention, even if high-frequency vibration is continuously input, the displacement of the free piston is not biased. Therefore, it is possible to ensure a stroke margin to the pressure side pressure chamber side of the free piston. Can be prevented from being displaced toward the pressure side pressure chamber. 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 a longitudinal cross-sectional view of the shock absorber 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 a figure which shows the structure of the buffer device of one embodiment actualized. It is a longitudinal cross-sectional view of a part of a free piston of a shock absorber according to a modified example of an embodiment. It is a figure which shows the structure of the buffering device in the other modification of one embodiment which actualized. It is a figure which shows the structure of the buffering device in another modification of one embodiment which actualized. It is the Bode diagram which showed the gain characteristic of the frequency transfer function of the pressure with respect to the flow volume of the conventional shock absorber. It is the figure which showed the damping characteristic with respect to the vibration frequency of the conventional shock absorber.

  Hereinafter, the present invention will be described with reference to the drawings. As shown in FIG. 1, the shock absorber D of the present invention includes a cylinder 1 and a piston 2 as a partition member that is slidably inserted into the cylinder 1 and partitions the cylinder 1 into an expansion side chamber R1 and a compression side chamber R2. The passages 3a and 3b communicating the extension side chamber R1 and the pressure side chamber R2, the pressure chamber R3, and the pressure chamber R3 are movably inserted into the extension side chamber R1 via the extension side channel 5. A free piston 9 that is divided into a communicating side expansion pressure chamber 7 and a pressure side pressure chamber 8 that communicates with the pressure side chamber R2 via the pressure side flow path 6, and an urging force that suppresses displacement of the free piston 9 with respect to the pressure chamber R3. And a displacement compensation passage 11 that allows only the flow from the expansion side pressure chamber 7 to the compression side pressure chamber 8 and that provides resistance to the flow. Generates damping force between them It is intended to 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 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 is connected to one end of a piston rod 4 that is movably inserted into the cylinder 1, and the piston rod 4 protrudes outward from the upper end of the cylinder 1 in the figure. In addition, between the piston rod 4 and the cylinder 1, the inside of the cylinder 1 is in a liquid-tight state with a seal (not shown). Since the shock absorber D is set to a so-called single rod type, the volume of the piston rod 4 that enters and exits the cylinder 1 as the shock absorber D expands and contracts is the volume of the gas in the gas chamber G. The sliding partition 12 is expanded or contracted to be compensated by moving in the vertical direction in FIG. Thus, the shock absorber D is set to a single cylinder type, but instead of installing the sliding partition wall 12 and the gas chamber G, a reservoir is provided on the outer periphery or outside of the cylinder 1, and the piston rod 4 is provided by the reservoir. Volume compensation may be performed. Further, the shock absorber D may be set to a double rod type instead of a single rod type.

  Further, damping force generation elements 13a and 13b such as orifices and leaf valves are provided in the middle of the passages 3a and 3b, and the flow of liquid passing through the passages 3a and 3b is resisted by the damping force generation elements 13a and 13b. Can be given. Although this damping force generating element 13a is not shown in detail, the passage 3a is set as a one-way passage that allows only the flow of liquid from the extension side chamber R1 to the compression side chamber R2, and the damping force generation element 13b is also Further, the passage 3b is set as a one-way passage that allows only the flow of liquid from the compression side chamber R2 to the extension side chamber R1, and the resistance that the damping force generating element 13a gives to the flow of liquid passing through the passage 3a is attenuated. The force generating element 13b is larger than the resistance given to the flow of the liquid passing through the passage 3b. That is, when the damping device D expands and contracts, considering that a damping force is generated only through the passages 3a and 3b, the liquid passes only through the passage 3a during the expansion operation, and the liquid passes through only the passage 3b during the contraction operation. When the piston speed is the same, the damping force during the extension operation is larger than the damping force during the contraction operation. The damping force generating elements 13a and 13b may have a configuration in which, for example, a well-known orifice and a leaf valve are arranged in parallel. For example, a configuration in which a choke and a leaf valve are arranged in parallel or other configurations may be used. Of course, it can also be adopted.

  In this embodiment, the pressure chamber R3 is formed by a hollow portion 14a provided in the housing 14 that is connected to the lower side of the piston 2 and faces the pressure side chamber R2, and slides on the side wall of the hollow portion 14a. The hollow portion 14a is divided into an extension-side pressure chamber 7 in the upper part of FIG. 1 and a pressure-side pressure chamber 8 in the lower part of FIG. 1 by a free piston 9 that can move in the vertical direction in FIG. Yes. 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 is connected at one end 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, whereby the free piston 9 Is positioned at a predetermined position in the housing 14, and when it is displaced from this predetermined position (hereinafter simply referred to as "free piston neutral position"), an urging force proportional to the displacement amount is applied from the spring element 10. The above-described free piston neutral position 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 intermediate point 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.

  In addition, the inside of the housing 14 is partitioned into an expansion side pressure chamber 7 and a compression side pressure chamber 8 by a free piston 9 up and down, and a vibration direction that the buffer device D expands and contracts and a movement direction of the free piston 9 are illustrated. If the entire shock absorber D vibrates in the vertical direction in FIG. 1 to avoid exciting the vertical vibration of the free piston 9 relative to the housing 14, the movement of the free piston 9 The direction can be set to a direction orthogonal to the expansion / contraction direction of the shock absorber D, that is, the left-right direction in FIG. 1, and the expansion-side pressure chamber 7 and the compression-side pressure chamber 8 can be arranged in the lateral direction in FIG.

  In addition, the housing 14 is provided with a pressure side passage 6 that communicates the pressure side chamber R2 and the pressure side pressure chamber 8, and the pressure side flow path 6 is provided with a throttle 6a. Resistance can be given.

  Further, the extension side chamber R1 and the extension side pressure chamber 7 are opened from the side of the piston rod 4 facing the extension side chamber R1 and communicated with each other via the extension side flow path 5 passing 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 are communicated by the compression side chamber R2, the compression side pressure chamber 8, and the pressure side flow channel 6, and the expansion side pressure chamber 7 and the pressure side pressure chamber are communicated. 8 is changed by the displacement of the free piston 9 in the housing 14, the buffer device D has the above-described extension side flow path 5, extension side pressure chamber 7, pressure side pressure chamber 8, and pressure side flow. A flow path composed of the passage 6 apparently communicates the expansion side chamber R1 and the compression side chamber R2, and the expansion side chamber R1 and the pressure side chamber R2 are also formed by the above-described apparent flow path in addition to the passages 3a and 3b. It will be communicated.

  Further, the housing 14 is provided with a displacement compensation passage 11 that communicates the expansion side pressure chamber 7 and the pressure side pressure chamber 8. This displacement compensation passage 11 is provided in the middle of the communication passage 11 a that connects the expansion side pressure chamber 7 and the pressure side pressure chamber 8, and the flow of liquid from the expansion side pressure chamber 7 toward the pressure side pressure chamber 8. And a compensation check valve 11b that allows only the liquid, and an orifice 11c that is provided in the middle of the communication passage 11a to provide resistance to the flow of liquid. The valve element may be a choke other than the orifice, or may be a leaf valve, a poppet valve, a needle valve, or the like. When the valve element itself also has a function as a check valve, the compensation reverse Of course, the stop valve may be integrated into the valve element. Further, when the valve element and the compensation check valve are provided separately, they may be arranged in series in the communication passage 11a. Although the displacement compensation passage 11 is provided in the housing 14 in the drawing, it may be provided in the free piston 9.

  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. As a result, the compression side liquid in the expansion side chamber R1 and the pressure side chamber R2 includes the passages 3a and 3b, and in addition to this, the expansion side flow path 5, the expansion side pressure chamber 7, the pressure side pressure chamber 8, and the pressure side flow path 6. It moves to the enlargement side of the extension side chamber R1 and the compression side chamber R2 via the apparent flow path.

  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 the 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 passing through the apparent flow path is increased, the flow rate in the passage 3a is decreased, so that the damping force generated by the shock absorber D is smaller than the damping force when the low frequency vibration is input.

  As described above, 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 the same as that shown in FIG. In addition, the damping force characteristic in the shock absorber D indicating the gain of the damping force with respect to the input of the vibration frequency generates a large damping force with respect to the vibration in the low frequency range as shown in FIG. The damping force can be reduced with respect to 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 large damping force is generated for vibrations in the low frequency range, and the damping force is reduced for vibrations in the high frequency range, as in the extension stroke described above. And the change of the damping force of the shock absorber D can be made to depend on the input vibration frequency. 3 is set to a value greater than the value of the sprung resonance frequency of the vehicle and equal to or less than the value of the unsprung resonance frequency of the vehicle, and a larger value is obtained. By setting the frequency Fb to be equal to or lower than the unsprung resonance frequency of the vehicle, the shock absorber D can generate a high damping force with respect to the vibration input of the sprung resonance frequency and stabilize the posture of the vehicle. In addition, it is possible to prevent the passenger from feeling uneasy when the vehicle turns, and a low damping force is always generated when vibration at the unsprung resonance frequency is input. The transmission can be insulated to improve the riding comfort in the vehicle.

  As described above, in the shock absorber D, the flow rate of the liquid passing through the apparent flow path is increased at the time of high-frequency vibration input, but this occurs at the time of compression operation for the purpose of improving the ride comfort in the vehicle. When the damping force generated during the extension operation is made larger than the damping force that is generated, if high-frequency vibration is continuously input, the pressure in the extension side chamber R1 compressed during the extension operation is the pressure side chamber R2 compressed during the compression operation. Therefore, the pressure in the expansion side pressure chamber 7 is higher than the pressure in the pressure side pressure chamber 8.

  Thus, when the pressure in the expansion side pressure chamber 7 becomes higher than the pressure in the pressure side pressure chamber 8, the free piston 9 tends to be displaced toward the pressure side pressure chamber 8, but the compensation check in the displacement compensation passage 11. The valve 11b opens and the expansion side pressure chamber 7 and the pressure side pressure chamber 8 communicate with each other through the communication passage 11a, and the pressure in the expansion side pressure chamber 7 is released to the pressure side pressure chamber 8. Therefore, the difference between the pressure in the extension side pressure chamber 7 and the pressure in the pressure side pressure chamber 8 is reduced. When the pressure side pressure chamber 8 exceeds the pressure in the expansion side pressure chamber 7, the compensation check valve 11 is closed and the pressure in the pressure side pressure chamber 8 rapidly rises during the contraction operation of the shock absorber D during vibration. Since the pressure exceeds the pressure in the expansion side pressure chamber 7, the free piston 9 can be urged toward the expansion side pressure chamber 7 to displace the expansion side pressure chamber 7 in the compressing direction.

  Therefore, in the shock absorber D of the present invention, even when high-frequency vibration is continuously input and the pressure in the expansion side pressure chamber 7 becomes higher than the pressure in the pressure side pressure chamber 8, the displacement compensation passage 11 is used. Thus, since the pressure in the expansion side pressure chamber 7 can be released to the pressure side pressure chamber 8, the free piston 9 can be prevented from being displaced from the neutral position of the free piston toward the pressure side pressure chamber 8 side. In addition, since the orifice 11c is provided as the valve element even if the compensation check valve 11b is opened in this way, the pressure in the extension side pressure chamber 7 and the pressure in the pressure side pressure chamber 8 are provided. Therefore, during the expansion operation of the shock absorber D, there is no difference between the pressures of the expansion side pressure chamber 7 and the pressure side pressure chamber 8, and the free piston 9 does not operate and the apparent flow path is passed through. There is no possibility that the liquid can move from the extension side chamber R1 to the compression side chamber R2. That is, the bias of the free piston 9 toward the pressure side pressure chamber 8 can be prevented without impairing the basic operation of the shock absorber D.

  Therefore, 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 a stroke margin of the free piston 9 toward the pressure side pressure chamber 8 is ensured. 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.

  When the displacement compensation passage 11 is provided in the free piston 9, the shock absorber D can be made compact by reducing the size of the housing 14 as compared with the case of providing the displacement compensation passage 11 in the housing 14.

  The basic structure of the shock absorber D has been described above. Hereinafter, the shock absorber D1 with a more specific structure will be described.

  As shown in FIG. 4, the specific shock absorber D1 basically includes a cylinder 21, an extension side chamber R4 and a pressure side chamber which are slidably inserted into the cylinder 21 and have two working chambers. Piston 22 as a partition member partitioned into R5, piston rod 23 having one end connected to piston 22, passages 22a and 22b communicating with extension side chamber R4 and pressure side chamber R5 formed in piston 22, and piston rod 23 A housing 24 which is fixed to the distal end of the housing and forms a pressure chamber R6 therein, and an extension side pressure which is movably inserted into the housing 24 and communicates with the extension side chamber R4 via the extension side channel 25. A free piston 29 that is partitioned into a chamber 27 and a pressure-side pressure chamber 28 that communicates with the pressure-side chamber R5 via the pressure-side channel 26, and the displacement of the free piston 29 relative to the housing 24 Coil springs 51 and 52 as spring elements that generate a biasing force to be controlled, and a displacement compensation passage 30 that allows only a flow from the extension side pressure chamber 27 to the pressure side pressure chamber 28 and that provides resistance to the flow. It is configured. Although not shown in the drawing, similarly to the shock absorber D shown in FIG. 1, a sliding partition is provided below the cylinder 21 and a gas chamber is provided.

  Hereinafter, each part will be described in detail. The piston rod 23 has a small-diameter portion 23a formed at the lower end side in FIG. 4 and a screw portion 23b formed at the distal end side of the small-diameter portion 23a.

  The piston rod 23 is formed with an extension-side flow passage 25 that opens from the tip of the small diameter portion 23 a and passes through the side of the piston rod 23. In the drawing, a valve serving as a resistance is not provided in the middle of the extension side flow path 25, but a valve such as a throttle may be provided.

  The piston 22 is formed in an annular shape, and a small diameter portion 23a of the piston rod 23 is inserted on the inner peripheral side thereof. Further, the piston 22 is provided with passages 22a and 22b communicating with the expansion side chamber R4 and the pressure side chamber R5, and the damping force generating element in which the upper end of the passage 22a in FIG. 4 is closed by the laminated leaf valve V1, and the lower end in FIG. 4 of the other passage 22b is also closed by the laminated leaf valve V2 which is a damping force generating element laminated below the piston 22 in FIG.

  The laminated leaf valves V1 and V2 are both formed in an annular shape, and a small-diameter portion 23a of the piston rod 23 is inserted on the inner peripheral side. The laminated leaf valves V1 and V2 are attached to the piston 22 together with an annular valve stopper 31 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 pressure side chamber R5 and the expansion side chamber R4 during the contraction operation of the shock absorber D1, opens the passage 22a, and moves from the pressure side chamber R5 to the expansion side chamber R4. And the passage 22a is closed when the shock absorber D1 is extended, and the other laminated leaf valve V2 is opposite to the passage 22b when the shock absorber D1 is extended opposite to the laminated leaf valve V1. Open and close the passage 22b during contraction. That is, the laminated leaf valve V1 is a damping force generating element that generates a compression-side damping force when the shock absorber D1 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. Further, even when the passages 22a and 22b are closed by the laminated leaf valves V1 and V2, the extension side chamber R4 and the pressure side chamber R5 are communicated with each other by a 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. When the piston speed of the shock absorber D1 is the same, the laminated leaf valve V2 has a greater resistance to the liquid flow than the laminated leaf valve V1.

  The above-described valve stopper 31, laminated leaf valve V1, piston 22, and laminated leaf valve V2 are sequentially assembled to the screw portion 23b of the piston rod 23, and a pressure chamber R6 is formed from below the laminated leaf valve V2. The housing 24 is screwed. The housing 24 fixes the piston 22, the laminated leaf valves V 1 and V 2, and the valve stopper 31 to the piston rod 23. As described above, the housing 24 not only forms the pressure chamber R <b> 5 inside, but also plays a role of fixing the piston 22 to the piston rod 23.

  The housing 24 has a bottomed cylindrical shape integrated with a nut portion 32 with a flange 33 screwed to the screw portion 23b of the piston rod 23, and an opening is crimped on the outer periphery of the flange 33 in the nut portion 32. An outer cylinder 35 is provided. The nut portion 32 and the outer cylinder 35 define a pressure chamber R6 in the pressure side chamber R5. In addition, when integrating the nut part 32 and the outer cylinder 35, it is also possible to employ | adopt other methods, such as welding other than the said caulking process.

  A free piston 29 is slidably inserted into the pressure chamber R6 formed as described above, and the pressure chamber R6 includes an upper side expansion pressure chamber 27 and a lower side pressure side pressure in FIG. It is divided into chambers 28.

  Further, the nut portion 32 is provided with the flange 33 on the side as described above, and a cylindrical screw portion 34 is formed on the inner periphery thereof, and the screw portion 34 is screwed to the screw portion 23 b of the piston rod 23. Thus, the housing 24 can be fixed to the small diameter portion 23 a of the piston rod 23. Therefore, the engaging portion 35b is formed with a cross-sectional shape of the outer periphery of the lower end of the outer cylinder 35 being a shape other than a perfect circle, for example, a shape with a part cut away or a hexagonal shape, and the engaging portion 35b. The operation of screwing the housing 24 onto the piston rod 23 using a tool that engages the outer periphery of the piston rod 23 is facilitated. Note that the entire outer peripheral shape of the outer cylinder 35 may be set to a shape other than a perfect circle.

  The outer cylinder 35 has a bottomed cylindrical shape, and a fixed orifice 36 that constitutes a part of the pressure side flow path 26 is provided in the outer cylinder bottom portion 35a, and a pressure side chamber R5 is provided in a side portion of the outer cylinder 35. Two variable orifices 37 and 38 communicating with the inside of the housing 24 are provided.

  On the other hand, the free piston 29 is provided on the bottomed tubular free piston main body 40 and the bottom portion 40a of the free piston main body 40 so as to penetrate from the extension side pressure chamber side end to the pressure side pressure chamber side end of the bottom portion 40a. The provided through hole 40b and a spool 41 that is slidably inserted into the through hole 40b are provided.

  The free piston main body 40 has a bottomed cylindrical shape, and includes a through hole 40b in the bottom portion 40a. The bottom portion 40a faces downward in FIG. 4 so that the outer periphery of the cylindrical portion 40c is the inner periphery of the outer cylinder 35 in the housing 24. It is inserted into the housing 24 in sliding contact. A spool 41 is slidably inserted into the through hole 40b of the free piston body 40, and the free piston 29 extends in the pressure chamber R6 when slidably inserted into the housing 24 as described above. The pressure chamber 27 is divided into a pressure chamber 27 and a pressure chamber 28. In addition, by accommodating the bottom part 40a of the free piston main body 40 in the housing 24 facing downward in FIG. 4, interference with the nut part 32 of the free piston 29 can be avoided. Furthermore, in the case of this embodiment, the free piston main body 40 includes an annular groove 40d on the outer periphery of the cylindrical portion 40c and a hole 40e that communicates from the bottom 40a of the free piston main body 40 to the annular groove 40d.

  In addition, coil springs 51 and 52 as spring elements are provided between the bottom portion 40a of the free piston body 40 and the nut portion 32 and between the bottom portion 40a and the outer cylinder bottom portion 35a of the outer cylinder 35, respectively. It is intervened. These coil springs 51 and 52 are elastically supported by sandwiching the free piston 29, and an urging force that suppresses the displacement is applied according to the amount of displacement of the free piston 29 with respect to the pressure chamber R6. The piston 29 is positioned at the neutral position in the pressure chamber R6. As the spring element, it is sufficient if the free piston 29 can be elastically supported, and other elements than the coil springs 51 and 52 may be employed. For example, the free piston 29 is elastically supported using an elastic body such as a disc spring. You may do it.

  The annular groove 40d is always opposed to the variable orifices 37 and 38 when the free piston 29 is elastically supported by the coil springs 51 and 52 as spring elements and is in the neutral position, and the pressure side pressure chamber 28 and the pressure side chamber R5. When the free piston 29 is displaced until the stroke end, that is, until it contacts the flange 33 of the nut portion 32 or the stepped portion 35c provided on the inner periphery of the outer cylinder 35, the outer periphery of the free piston 29 is completely removed. It is wrapped and blocked. That is, the pressure side flow path 26 includes an annular groove 40d, a hole 40e, variable orifices 37 and 38, and a fixed orifice 36. Two variable orifices 37 and 38 are provided, but the number is arbitrary.

  That is, in the case of this specific shock absorber D1, when the amount of displacement from the neutral position of the free piston 29 increases, all the openings of the variable orifices 37 and 38 face the annular groove 40d. The situation starts to face the outer periphery, the flow area of the variable orifices 37 and 38 begins to decrease gradually, and the flow resistance in the pressure side flow path 26 gradually increases. In this embodiment, as the amount of displacement of the free piston 29 increases, the flow area of the variable orifices 37 and 38 gradually decreases, and when the free piston 29 reaches the stroke end, the variable orifices 37 and 38 It is completely closed at the outer periphery of the free piston 29, the flow path resistance in the pressure side flow path 26 is maximized, and the pressure side pressure chamber 28 is communicated with the pressure side chamber R5 only by the fixed orifice 36.

  Subsequently, the spool 41 includes a cylindrical spool body 41a that is slidably inserted into the through hole 40b, a flange 41b provided at the pressure side pressure chamber side end of the spool body 41a, and an expansion side pressure of the spool body 41a. An annular stopper 41c provided on the outer periphery of the chamber side end, a vertical hole 41d opened from the end of the extension side pressure chamber of the spool body 41a, and a side portion of the spool body 41a, which is above the flange 41b in FIG. A horizontal hole 41e that opens from the expansion side pressure chamber side and communicates with the vertical hole 41d is provided.

  The axial length of the spool 41 is longer than the axial length of the bottom portion 40a of the free piston main body 40, and the length between the stopper 41c and the flange 41b is also longer than the axial length of the bottom portion 40a of the free piston main body 40. .

  In the spool 41, the pressure receiving area where the pressure in the expansion side pressure chamber 27 acts is equal to the pressure receiving area where the pressure in the compression side pressure chamber 28 acts, and the pressure in the expansion side pressure chamber 27 is higher than the pressure in the pressure side pressure chamber 28. When the pressure in the pressure side pressure chamber 28 is higher than the pressure in the expansion side pressure chamber 27, the pressure side pressure chamber 28 is pressed in the direction of the expansion side pressure chamber. Thus, the stroke is made upward and the state shown in FIG. 4 is obtained. In addition, although each said pressure receiving area is made equal, it is not limited to this, For example, the pressure receiving area where the pressure of the pressure side pressure chamber 28 acts rather than the pressure receiving area where the pressure of the expansion side pressure chamber 27 acts It is also possible to set so that the spool 41 strokes in the direction of the pressure side pressure chamber when the pressure in the extension side pressure chamber 27 exceeds the pressure in the pressure side pressure chamber 28 by a predetermined value.

  When the spool 41 is stroked downward in FIG. 4 in the direction of the pressure side pressure chamber and the stopper 41c comes into contact with the upper surface in FIG. 4 of the bottom 40a of the free piston main body 40, the spool 41 is further in the pressure side pressure side direction. The stroke to is regulated. Thus, in a state where the stopper 41c is in contact with the bottom portion 40a of the free piston main body 40, at least the lateral hole 41e faces the pressure side pressure chamber 28, and the pressure side pressure chamber 28 is connected to the pressure side pressure chamber 28 via the lateral hole 41e and the vertical hole 41d. The extension side pressure chamber 27 is communicated with the extension side pressure chamber 27. Thus, the vertical hole 41d and the horizontal hole 41e form a communication passage. The cross-sectional area in the vertical hole 41d is set so that resistance can be given to the flow of liquid passing through the vertical hole 41d, and functions as a valve element. In this embodiment, the vertical hole 41d is used as a valve element, but the horizontal hole 41e may be used as a valve element, and both the vertical hole 41d and the horizontal hole 41e may function as a valve element as well as a communication passage. Further, a throttle such as an orifice may be provided in the vertical hole 41d or the horizontal hole 41e, and this may be used as a valve element. From the above, when the pressure in the expansion side pressure chamber 27 is larger than the pressure in the compression side pressure chamber 28, the spool 41 moves downward in FIG. 4 and is extended by the communication passage formed by the vertical hole 41d and the horizontal hole 41e. The pressure chamber 27 and the pressure side pressure chamber 28 communicate with each other. However, since the vertical hole 41d functions as a valve element, a difference occurs between the pressure in the expansion side pressure chamber 27 and the pressure in the pressure side pressure chamber 28. In accordance with the pressure, the coil spring 52 contracts and the free piston 29 moves downward in FIG.

  Further, when the spool 41 strokes upward in the direction of the extension side pressure chamber and the flange 41b comes into contact with the lower surface in FIG. 4 of the bottom 40a of the free piston main body 40 as shown in FIG. The stroke toward the extension side pressure chamber is restricted. Thus, in a state where the flange 41b is in contact with the bottom portion 40a of the free piston main body 40, at least the lateral hole 41e is closed so as to face the inner periphery of the through hole 40b of the free piston main body 40, and The communication between the pressure side pressure chamber 28 and the extension side pressure chamber 27 through the hole 41d is cut off. Therefore, in this embodiment, the spool 41 functions as a compensation check valve. From the above, when the pressure in the pressure side pressure chamber 28 is larger than the pressure in the extension side pressure chamber 27, the spool 41 moves upward in FIG. 4 and the communication passage formed by the vertical hole 41d and the horizontal hole 41e is blocked. In accordance with the differential pressure between the pressure in the extension side pressure chamber 27 and the pressure in the pressure side pressure chamber 28, the coil spring 51 contracts and the free piston 29 moves upward in FIG.

  Note that the stopper 41c and the flange 41b also function as a stopper to prevent the spool 41 from coming out of the through hole 40b. When the spool 41 moves in the direction of the extension side pressure chamber and the lateral hole 41e completely faces the inner periphery of the through hole 40b, the communication passage is blocked. Therefore, the restriction of the movement of the spool 41 is not the annular flange 41b. This can be done with a pin or other parts that can come into contact with the bottom 40a, and the same applies to the stopper 41c. However, since the spool 41 includes the annular flange 41b on the outer periphery, the pressure in the compression side pressure chamber 28 is higher than the pressure in the expansion side pressure chamber 27, and the spool 41 is pressed upward in FIG. By closely contacting the bottom 40a of the free piston main body 40, the communication passage can be tightly blocked.

  Further, in the above description, the longitudinal passage 41d and the lateral hole 41e provided in the spool 41 form a communication passage and a valve element, and the spool 41 functions as a compensation check valve. Is embodied in the spool 41 of the free piston 29. As shown in FIG. 5, a communication passage 53 also serving as a valve element is provided at the bottom 40a of the free piston main body 40, and the flange 41b of the spool 41 opens and closes the pressure side pressure chamber side end of the communication passage 53. A compensation check valve may be configured. In this case, the communication passage also serving as a valve element can be formed by a notch groove continuous with the through hole 40b as shown by a broken line in FIG.

  Now, although the shock absorber D1 is configured as described above, the operation of the shock absorber D1 will be described next.

  (A) Operation in the shock absorber D1 when the amount of displacement of the free piston 29 from the neutral position is within a range where the variable orifices 37 and 38 do not begin to close.

  In this case, the free piston 29 can be displaced without changing the resistance of the pressure side flow path 26. Then, when considering the condition that the piston speed is the same when the vibration frequency input to the shock absorber D1 is low and high, first, when the input frequency is low, the amplitude of the input vibration increases. The amplitude of the free piston 29 also increases within a range where the variable orifices 37 and 38 do not begin to close.

  When the amplitude of the free piston 29 increases in the above range, the urging force that the free piston 29 receives from the coil springs 51 and 52 increases, and when the shock absorber D1 extends, the pressure in the compression side pressure chamber 28 is increased by the expansion side pressure. If the pressure of the coil springs 51 and 52 is smaller than the pressure in the chamber 27 and conversely, the shock absorber D1 contracts, the pressure in the expansion side pressure chamber 28 is increased in the pressure side pressure chamber 27. It becomes smaller than the pressure by the urging force of the coil springs 51 and 52.

  As described above, when the shock absorber D1 exhibits low frequency vibration, a differential pressure corresponding to the urging force of the coil springs 51 and 52 is generated in the expansion side pressure chamber 27 and the compression side pressure chamber 28. Therefore, the expansion side chamber R4 and the expansion side The differential pressure in the pressure chamber 27 and the differential pressure between the pressure side chamber R5 and the pressure side pressure chamber 28 become smaller, and an apparent flow path composed of the expansion side flow path 25, the pressure side flow path 26, the expansion side pressure chamber 27, and the pressure side pressure chamber 28. The flow rate passing through is small. Since the flow rate of the passages 22a and 22b is increased by the small flow rate passing through the apparent flow path, the damping force generated by the shock absorber D1 is maintained high.

  On the other hand, when the input frequency to the shock absorber D1 is high, the amplitude of the input vibration becomes small and the amplitude of the free piston 29 becomes smaller. When the amplitude of the free piston 29 is reduced, the urging force received by the free piston 29 from the coil springs 51 and 52 is reduced, so that the shock absorber D1 in the extension side pressure chamber 27 is in the extension stroke or the contraction stroke. The pressure and the pressure in the pressure side pressure chamber 28 are substantially equal. Then, since the differential pressure between the expansion side chamber R4 and the expansion side pressure chamber 27 and the differential pressure between the compression side chamber R5 and the compression side pressure chamber 28 increase, the flow rate passing through the expansion side flow channel 25 and the pressure side flow channel 26 also increases.

  When the frequency of vibration input to the shock absorber D1 is low, the flow rate passing through the apparent flow path is small, and when the input frequency is high, the flow rate passing through the apparent flow path is large, and the input If the speeds are the same, the flow rate flowing from the expansion side chamber R4 to the compression side chamber R5 or from the compression side chamber R5 to the expansion side chamber R4 must be equal regardless of the input frequency. Therefore, the laminated leaf valves V1, V2 in the passages 22a, 22b 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 D1 changes as shown in FIG.

  Therefore, even in the shock absorber D1, the change in 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 with respect to the vibration input at 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.

  When the pressure in the expansion side pressure chamber 27 becomes higher than the pressure in the pressure side pressure chamber 28, the free piston 29 tends to be displaced toward the pressure side pressure chamber 28, but the spool 41 functioning as a compensation check valve is provided. 4, the communication passage formed by the vertical hole 41 d and the horizontal hole 41 e is opened, and the expansion side pressure chamber 27 and the compression side pressure chamber 28 communicate with each other via the displacement compensation passage 30. Can be released to the pressure side pressure chamber 28. Therefore, the difference between the pressure in the extension side pressure chamber 27 and the pressure in the pressure side pressure chamber 28 is reduced. When the pressure-side pressure chamber 28 exceeds the pressure in the expansion-side pressure chamber 27, the spool 41 functioning as a compensation check valve moves upward in FIG. 4 to close the connecting passage and vibrate the shock absorber D1 in vibration. During the contraction operation, the pressure in the compression side pressure chamber 28 quickly rises and exceeds the pressure in the expansion side pressure chamber 27, so that the free piston 29 is urged toward the expansion side pressure chamber 27 to compress the expansion side pressure chamber 27. It can be displaced in the direction of

  Therefore, in the shock absorber D1 of the present invention, even when high-frequency vibration is continuously input and the pressure in the extension side pressure chamber 27 becomes higher than the pressure in the pressure side pressure chamber 28, the displacement compensation passage 30 is used. Thus, the pressure in the expansion side pressure chamber 27 can be released to the pressure side pressure chamber 28, so that the free piston 29 can be prevented from being displaced from the neutral position of the free piston toward the pressure side pressure chamber 28. Since the vertical hole 41d, which is the communication passage, functions as a valve element, a difference occurs between the pressure in the expansion side pressure chamber 27 and the pressure in the pressure side pressure chamber 28. Therefore, during the expansion operation of the shock absorber D1, The difference between the pressures of the side pressure chamber 27 and the pressure side pressure chamber 28 no longer occurs, the free piston 29 does not operate, and the liquid cannot be moved from the expansion side chamber R4 to the pressure side chamber R5 through the apparent flow path. There is nothing. That is, it is possible to prevent the free piston 29 from being biased toward the pressure side pressure chamber 8 without impairing the basic operation of the shock absorber D1.

  Therefore, in the shock absorber D1 of the present invention, even if high-frequency vibration is continuously input, the displacement of the free piston 29 is not biased, so that a stroke margin of the free piston 29 toward the pressure side pressure chamber 28 is ensured. It is possible to prevent the free piston 29 from coming into contact with the housing 24 and being unable to be displaced into the pressure side pressure chamber 28. As a result, according to the shock absorber D1 of the present invention, even when high-frequency vibration is continuously input, the stroke margin of the free piston 29 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.

  In addition, since the displacement compensation passage 30 is provided in the free piston 29, the housing 24 can be downsized and the shock absorber D1 can be made compact as compared with the case where the displacement compensation passage is provided in the housing 24.

  Further, in this case, since the flange 41b is provided on the outer periphery of the spool 41 and the communication passage can be tightly closed by the flange 41b, the pressure in the pressure side pressure chamber 28 is higher than the pressure in the extension side pressure chamber 27. In addition, the pressure in the pressure side pressure chamber 28 does not leak to the expansion side pressure chamber 27, and the free piston 29 can be quickly returned to the neutral position.

(B) Operation in the shock absorber D1 when the amount of displacement from the neutral position of the free piston 29 is within the range of increasing the flow path resistance of the pressure side flow path 26 The variable orifices 37 and 38 are expanded by the shock absorber D1. Even if contracted, the free piston 29 is displaced from the neutral position, and the flow passage area is gradually reduced in accordance with the amount of displacement. When the free piston 29 reaches one of the upper and lower stroke ends, it is completely blocked. Thus, the flow path area is made the same as the flow path area of the fixed orifice 36 to minimize the flow path area.

  That is, after the free piston 29 starts to close the variable orifices 37 and 38, the flow resistance of the pressure side flow path 26 is gradually increased according to the amount of displacement, and when the free piston 29 reaches the stroke end, the flow resistance is reduced. Maximum.

  Here, the free piston 29 is displaced to the stroke end when there is a large amount of liquid flowing into and out of the expansion side pressure chamber 27 or the compression side pressure chamber 28. Specifically, the expansion / contraction amplitude of the shock absorber D1. Is the case.

  When the vibration frequency input to the shock absorber D1 is relatively high, the shock absorber D1 generates a relatively low damping force until the free piston 29 is displaced to a position at which the variable orifices 37 and 38 begin to close. However, when the free piston 29 is displaced beyond the position where the variable orifices 37 and 38 start to close, the flow resistance of the pressure side flow passage 26 gradually increases, so that the free piston 29 and beyond. The movement speed to the stroke end side is reduced, the amount of liquid movement through the apparent flow path is also reduced, and the amount of liquid passing through the passages 22a and 22b is increased accordingly. The generated damping force of D1 gradually increases.

  When the free piston 29 reaches the stroke end, the liquid no longer moves through the apparent flow path, and the liquid passes only through the passages 22a and 22b until the expansion / contraction direction of the shock absorber D1 is changed. Therefore, the shock absorber D1 generates a damping force with the maximum damping coefficient.

  That is, even if a high-frequency and large-amplitude vibration that causes the free piston 29 to be displaced to the stroke end is input to the shock absorber D1, the amount of displacement from the neutral position of the free piston 29 exceeds an arbitrary amount of displacement. Since the shock absorber D1 gradually increases the generated damping force until the free piston 29 reaches the stroke end, there is no sudden change from a low damping force to a high damping force. That is, when the free piston 29 reaches the stroke end and the liquid in the extension side chamber R4 and the pressure side chamber R5 cannot be exchanged via the pressure chamber R6, the magnitude of the damping force does not change abruptly. The damping force change from the damping force to the high damping force becomes gentle. Furthermore, since the generated damping force is gradually increased when the free piston 29 reaches the stroke ends at both ends in the pressure chamber R6, the function of suppressing a sudden change in the damping force is the function of the pressure expansion of the shock absorber D1. Demonstrated in both strokes.

  Therefore, in this shock absorber D1, even if a vibration having a high frequency and a large amplitude is input, the generated damping force changes gently, so that 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.

  As described above, when the piston speed is high and the flow path resistance in the fixed orifice 36 and the variable orifices 37 and 38 does not become too large, the specific shock absorber D1 includes the above (A) and As described in (B), the damping force depending on the input vibration frequency is exhibited, and when the free piston 29 is displaced to the stroke end, the damping force is gradually increased to decrease the damping. It is possible to suppress a change in damping force such that the force suddenly increases.

  In the shock absorber D1, the displacement compensation passage 30 releases the pressure in the expansion side pressure chamber 27 to the compression side pressure chamber 28 when the pressure in the expansion side pressure chamber 27 is higher than the pressure in the compression side pressure chamber 28. Since the high pressure of the side pressure chamber 27 can be suppressed and the free piston 29 can be quickly returned to the neutral position, even if the free piston 29 is displaced to the stroke end, the return delay of the free piston 29 is not caused. Therefore, in this shock absorber D1, the state where the variable orifices 37 and 38 are not fully opened does not occur for a long time, and the damping force can be prevented from staying high for a long time. .

  In this way, in the specific shock absorber D1, even if a situation occurs in which the free piston 29 is displaced to the stroke end, it is possible to prevent the damping force from staying high, so that vibration is transmitted from the axle to the vehicle body. The problem that the effect of insulating the vehicle disappears can be solved, and the riding comfort in the vehicle can be further improved.

  In addition, you may comprise the displacement compensation channel | path 60 like the buffering device D2 in the modification of the concrete buffering device shown in FIG. The displacement compensation passage 60 is provided in the free piston 61, and the shock absorber D2 differs from the shock absorber D1 only in the configuration of the free piston 61.

  As shown in FIG. 6, the free piston 61 in the shock absorber D <b> 2 has a bottomed cylindrical shape, and opens and closes the communication passage 62 provided in the bottom portion 61 a and the communication passage 62 on the pressure side pressure chamber side of the bottom portion 61 a. It comprises a valve element and a leaf valve 63 that functions as a compensation check valve. The displacement compensation passage 60 includes the communication passage 62 and the leaf valve 63 described above.

  The free piston 61 has a bottom 61a and a cylindrical portion 61b continuous to the outer periphery of the bottom 61a. The free piston 61 has a bottomed cylindrical shape, and an annular groove 61c is provided on the outer periphery of the cylindrical portion 61b. A hole 61d is provided. The annular groove 61c and the hole 61d correspond to the annular groove 40d and the hole 40e in the free piston 29 in the above-described shock absorber D1, respectively, and exhibit functions similar to these.

  A rod insertion hole 61e is provided at the center of the bottom 61a of the free piston 61, and a guide bolt 64 for fixing the leaf valve 63 to the bottom 61a of the free piston 61 is provided in the bolt insertion hole 61e. It is inserted.

  The guide bolt 64 includes a shaft portion 64a having a screw portion 64b formed at the tip, and a flange-shaped head portion 64c provided at the base end of the shaft portion 64a. The leaf valve 63 is annular, and is mounted on the outer periphery of the shaft portion 64 a of the guide bolt 64 together with the annular shim 65. When the shaft portion 64a of the guide bolt 64 is inserted into the bolt insertion hole 61e of the free piston 61 and the nut 66 is screwed onto the screw portion 64b, the leaf valve 63 is sandwiched between the nut 66 and the head portion 64c. And fixed to the bottom 61 a of the free piston 61. Therefore, the free piston 61 is stacked on the pressure side pressure chamber side of the bottom 61 a of the free piston 61 in a state where the outer periphery is allowed to be bent, and closes the opening end of the communication passage 62. Therefore, when the pressure in the extension side pressure chamber 27 exceeds the pressure in the pressure side pressure chamber 28 and the outer periphery of the leaf valve 63 is bent, the outer periphery of the leaf valve 63 is separated from the bottom 61a, and the communication passage 62 is opened. The extension-side pressure chamber 27 and the compression-side pressure chamber 28 are communicated with each other.

  In the state where the leaf valve 63 is stacked on the bottom 61a and the communication passage 62 is closed, when the leaf valve 63 is bent to give the leaf valve 63 initial deflection, depending on the amount of initial deflection. The valve opening pressure (the differential pressure between the expansion side pressure chamber 27 and the pressure side pressure chamber 28) when the leaf valve 63 is bent to open the communication passage 62 can be set. The leaf valve 63 may be a laminated leaf valve configured by laminating a plurality of annular plates.

  By configuring the displacement compensation passage 60 as described above, when the pressure in the expansion side pressure chamber 27 becomes higher than the pressure in the compression side pressure chamber 28, the leaf valve 63 is bent to open the communication passage 62, and the expansion side pressure chamber is opened. 27 pressure can be released to the pressure side pressure chamber 28. When the pressure side pressure chamber 28 exceeds the pressure in the extension side pressure chamber 27, the leaf valve 63 blocks the communication passage 62.

  Accordingly, in the shock absorber D2, as in the shock absorber D1, the high frequency vibration is continuously input, and the pressure in the expansion side pressure chamber 27 becomes higher than the pressure in the pressure side pressure chamber 28. The pressure in the extension side pressure chamber 27 can be released to the pressure side pressure chamber 28 via the displacement compensation passage 60, and the free piston 61 is displaced from the neutral position of the free piston toward the pressure side pressure chamber 28. Can be suppressed. Since the leaf valve 63 functions as a valve element to provide resistance to the flow of liquid passing through the communication passage 62, the pressure difference between the expansion side pressure chamber 27 and the pressure side pressure chamber 28 is different during the expansion operation of the shock absorber D2. The free piston 61 does not operate and the liquid does not move from the expansion side chamber R4 to the pressure side chamber R5 through the apparent flow path. That is, it is possible to prevent the free piston 61 from being biased toward the pressure side pressure chamber 8 without impairing the basic operation of the shock absorber D2.

  Therefore, according to the shock absorber D2, the displacement of the free piston 61 is not biased even if high-frequency vibration is continuously input. Therefore, it is possible to ensure a stroke margin of the free piston 61 toward the pressure side pressure chamber 28. It is possible to prevent the free piston 61 from coming into contact with the housing 24 and being unable to be displaced into the pressure side pressure chamber 28. As a result, according to the shock absorber D2, even if high-frequency vibration is continuously input, the stroke margin of the free piston 61 is ensured, so that the damping force reduction effect is not lost.

  Further, in this shock absorber D2, 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.

  Since the displacement compensation passage 60 is provided in the free piston 61, the housing 24 can be reduced in size and the shock absorber D2 can be made compact as compared with the case where the displacement compensation passage is provided in the housing 24.

  Further, in the shock absorber D2, the volume of the expansion side pressure chamber 27 and the pressure side pressure chamber 28 hardly fluctuates even if the leaf valve 63 is bent, so that the free piston 61 operates even when a fine amplitude vibration is input. Thus, a damping force depending on the frequency can be exhibited. In the shock absorber D1, when the spool 41 moves relative to the free piston 29, the spool 41 protrudes into one of the expansion side pressure chamber 27 and the compression side pressure chamber 28 and then retreats from the other. The volume of the pressure side pressure chamber 28 changes. Thus, the movement of the spool 41 changes the volumes of the extension-side pressure chamber 27 and the compression-side pressure chamber 28. This means that the movement of the spool 41 moves the liquid corresponding to the volume change even if the free piston 29 does not move. However, it is possible to go back and forth between the extension side chamber R4 and the compression side chamber R5 through the apparent flow path. That is, in the shock absorber D1, the free piston 29 does not operate until the spool 41 strokes to the movement limit, and the operation of the free piston 29 is delayed with respect to the vibration input, or the vibration with a small amplitude is detected. The movement of the spool 41 may cause the liquid to pass through the apparent flow path, and the damping force may be too small to exhibit the frequency-dependent damping force. On the other hand, in the shock absorber D2, as described above, when the leaf valve 63 opens and closes the communication passage 62, the volumes of the extension side pressure chamber 27 and the pressure side pressure chamber 28 are hardly changed. Therefore, the operation delay of the free piston 61 does not occur, and the damping force depending on the frequency can be exhibited without the damping force becoming too small even for the input of the minute amplitude vibration.

  Further, the inner periphery of the leaf valve 63 is not fixedly supported by the guide bolt 64, and the leaf valve 63 is mounted on the outer periphery of the shaft portion 64a so as to be movable in the axial direction as in the shock absorber D3 shown in FIG. And you may make it interpose the coil spring 67 as a valve | bulb urging | biasing element between the head 64c and the leaf valve 63. FIG. In this case, the leaf valve 63 is pressed against the bottom 61 a of the free piston 61 by the urging force generated by the coil spring 67, and the pressure in the expansion side pressure chamber 27 exceeds the pressure in the compression side pressure chamber 28. When the urging force of the coil spring 67 is overcome, the communication passage 62 is opened away from the bottom 61a. That is, the valve opening pressure of the leaf valve 63 is set by the urging force of the coil spring 67, and when the differential pressure between the expansion side pressure chamber 27 and the pressure side pressure chamber 28 reaches the valve opening pressure, the leaf valve 63 is released from the bottom 61a. The communication passage 62 is opened after being separated, and the expansion-side pressure chamber 27 and the compression-side pressure chamber 28 are communicated with each other so that the pressure in the expansion-side pressure chamber 27 is released to the compression-side pressure chamber 28. In the drawing, the valve urging element is a coil spring, but any element that exerts an urging force against the compression of a disc spring, rubber or the like may be used.

  The shock absorber D3 can exhibit the same operation and effect as the shock absorber D2 by exhibiting the same operation as the shock absorber D2. In the shock absorber D3, the opening pressure of the leaf valve 63 can be easily set by providing the coil spring 67 as a valve urging element. When the piston speed of the shock absorber D3 is low, the leaf valve 63 is By setting the valve opening pressure so that it does not open, it becomes easy to obtain a damping force that depends on the frequency, and the piston speed also increases for high-frequency vibrations, so the leaf valve 63 opens and is free. The function of suppressing the bias of the piston 61 toward the pressure side pressure chamber 28 can be exhibited. Even in the shock absorber D2, the valve opening pressure can be adjusted by giving initial deflection to the leaf valve 63, so that the valve opening pressure can be set in the same manner as in the shock absorber D3.

  Further, the position at which the coil spring 67 presses the leaf valve 63 may be the inner circumference of the leaf valve 63. In this case, the leaf valve 63 may bend the outer circumference to open the communication passage 62. Although it is possible, depending on the setting of the urging force of the coil spring 67, the outer periphery is bent with a lower differential pressure than the leaf valve 63 contracts the coil spring 67 and separates from the bottom 61a, thereby opening the communication passage 62. You can also. In this way, the characteristic given to the flow of the liquid of the valve element is the valve characteristic by the leaf valve 63 when the communication passage 62 starts to open, and the coil spring 67 is contracted and the entire leaf valve 63 is separated from the bottom 61a. It can be changed to a port characteristic determined by the setting of the cross-sectional area and length of the communication passage 62, the degree of freedom of tuning of the characteristic of the valve element is improved, and the damping force characteristic of the shock absorber D3 is more suitable for the vehicle. It can be set as a damping force characteristic.

  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.

1, 21 Cylinder 2, 22 Bulkhead members 2a, 2b, 22a, 22b Passage 5, 25 Stretch side flow path 6, 26 Pressure side flow path 7, 27 Stretch side pressure chamber 8, 28 Pressure side pressure chamber 9, 29, 61 Free piston DESCRIPTION OF SYMBOLS 10 Spring element 11, 30, 60 Displacement compensation passage 11a, 62 Communication path 11b Compensation check valve 11c Orifice 40 as valve element Free piston main body 40b Through-hole 41 Spool 51, 52 Coil spring 63 as spring element Leaf valve 67 Coil springs D, D1, D2, and D3 as valve urging elements Buffer R1, R4 Extension side chamber R2, R5 Pressure side chamber R3, R6 Pressure chamber

Claims (6)

A cylinder, a partition member which is slidably inserted into the cylinder and partitions the cylinder into an extension side chamber and a pressure side chamber, a passage communicating the extension side chamber and the pressure side chamber, a pressure chamber, and the pressure chamber A free piston that is movably inserted and divides the pressure chamber into an extension side pressure chamber that communicates with the extension side chamber via the extension side channel and a pressure side pressure chamber that communicates with the pressure side chamber via the pressure side channel; A shock absorber including a spring element that generates a biasing force that suppresses displacement of the free piston with respect to the pressure chamber, and allows only a flow from the extension side pressure chamber to the pressure side pressure chamber and resists the flow. A shock absorber provided with a displacement compensation path for providing The displacement compensation passage is a communication passage that communicates the extension side pressure chamber and the pressure side pressure chamber, and a compensation that is provided in the middle of the communication passage and allows only a flow from the extension side pressure chamber to the pressure side pressure chamber. The shock absorber according to claim 1, further comprising a check valve for use and a valve element that is provided in the middle of the communication passage to provide resistance to the flow. The shock absorber according to claim 1, wherein the displacement compensation passage is provided in the free piston. The free piston includes a free piston main body, a through-hole penetrating from the expansion-side pressure chamber side end of the free piston main body to the pressure-side pressure chamber side end, and a spool slidably inserted into the through-hole. 4. The shock absorber according to claim 2, wherein the communication passage is provided in the spool or free piston main body together with the valve element, and the compensation check valve is formed by the spool. The communication passage is provided in the free piston, and a leaf valve functioning as the valve element and the compensation check valve is provided by opening and closing the communication passage on the pressure side pressure chamber side of the free piston. Item 4. The shock absorber according to Item 2 or 3. 6. The shock absorber according to claim 5, wherein the leaf valve is provided so as to be separated from the free piston and includes a valve urging element that urges the leaf valve toward the free piston.

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