JP5166334B2 - Shock absorber - Google Patents

Description

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

  Conventionally, in this kind of shock absorber, a cylinder, a piston that is slidably inserted into the cylinder and divides the inside of the cylinder into an upper chamber and a lower chamber, and an upper chamber and a lower chamber provided in the piston communicate with each other. A passage, a flow path that opens from the tip of the piston rod to the side and communicates the upper chamber and the lower chamber, a housing that is attached to the tip of the piston rod with a pressure chamber connected in the middle of the flow path, A free piston that is slidably inserted into the pressure chamber and divides the pressure chamber into one chamber and the other chamber, and a coil spring that biases the free piston are provided. That is, one chamber in the pressure chamber communicates with the lower chamber via the flow path, and the other chamber in the pressure chamber communicates with the upper chamber via the flow path.

さらに、上記式（１）で示された伝達関数中のラプラス演算子ｓにｊωを代入して、周波数伝達関数Ｇ（ｊω）の絶対値を求めると、以下の式（２）が得られる。

上記各式から理解できるように、この緩衝装置における流量Ｑに対する差圧Ｐの伝達関数の周波数特性は、図５のボード線図に示したように、Ｆａ＝Ｋ／｛２・π・Ａ^２・（Ｃ１＋Ｃ２＋Ｃ３）｝とＦｂ＝Ｋ／｛２・π・Ａ^２・（Ｃ２＋Ｃ３）｝の２つの折れ点周波数を持ち、また、Ｆ＜Ｆａの領域においては、伝達ゲインは略Ｃ１となり、Ｆａ≦Ｆ≦Ｆｂの領域においてはＣ１からＣ１・（Ｃ２＋Ｃ３）／（Ｃ１＋Ｃ２＋Ｃ３）まで漸減するように変化して、Ｆ＞Ｆｂの領域においては一定となる。すなわち、流量Ｑに対する差圧Ｐの伝達関数の周波数特性は、低周波数域では伝達ゲインが大きくなり、高周波数域では伝達ゲインが小さくなる。 Here, the pressure difference between the upper chamber and the lower chamber during expansion and contraction of the shock absorber is P, the flow rate of the liquid flowing out from the upper chamber is Q, and the relationship between the differential pressure P and the flow rate Q1 of the liquid passing through the passage. C1 is the coefficient, the pressure in the other chamber is P1, the coefficient that is the relationship between the pressure P1 and the flow rate Q2 of the liquid flowing into the other chamber from the upper chamber is C2, and the pressure in the one chamber is P2. A coefficient that is a relationship between the pressure P2 and the flow rate Q2 of the liquid flowing out from the one chamber to the lower chamber is C3, a cross-sectional area that is a pressure receiving area of the free piston is A, a displacement of the free piston with respect to the pressure chamber is X, a coil spring When the transfer function of the differential pressure P with respect to the flow rate Q is obtained with the spring constant of ## EQU2 ## Equation (1) is 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 becomes 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, as shown by the damping characteristic X in FIG. 6, this shock absorber generates a large damping force for low-frequency vibration input, and on the other hand, small damping for high-frequency vibration input. Because it is possible to generate force, it is possible to reliably generate high damping force in scenes where the input vibration frequency is low, such as when the vehicle is turning, and in situations where the input vibration frequency is high such that the vehicle gets over the road surface unevenness A low damping force can be reliably generated to improve the riding comfort in the vehicle (see, for example, Patent Document 1).

JP 2006-336816 A (FIG. 2)

  As described above, the shock absorber described above can generate a large damping force for low frequency vibration input, and can generate a small damping force for high frequency vibration input. There are the following problems.

  In the above shock absorber, when the damping characteristics of the expansion side and the pressure side of the shock absorber are different, the expansion side passage allowing passage from the upper chamber to the lower chamber and the pressure side passage allowing passage from the lower chamber to the upper chamber are used. The coefficient C1 may be different between the expansion side passage and the compression side passage. However, the maximum value and the minimum value with respect to the frequency of the damping force on the expansion side and the compression side are determined in the flow path. Since it depends on the coefficients C2 and C3, it is necessary to review the coefficients C2 and C3 in the flow path in order to tune the damping characteristics on the expansion side and the compression side of the shock absorber.

  Therefore, when it is desired to tune the damping force of only one of the expansion side and the compression side of the shock absorber, the entire device needs to be reviewed, and tuning may be complicated.

  Therefore, the present invention has been developed to improve the above-described problems, and an object of the present invention is to provide a shock absorber capable of simplifying the tuning of the attenuation characteristics.

  In order to solve the above-described object, the problem solving means in the present invention communicates a cylinder, a partition member slidably inserted into the cylinder and partitioning the cylinder into two working chambers, and the two working chambers. A passage, a housing that forms a pressure chamber, and a chamber that is slidably inserted into the housing and communicates with the one working chamber via the one-side flow path and the one-side flow path In a shock absorber provided with a free piston partitioned into the other chamber communicated with the other working chamber and a spring element that generates a biasing force that suppresses displacement of the free piston with respect to the housing, an elastic ring is provided on the outer periphery of the free piston. It is mounted, and the pressure in the other chamber is applied to the inner periphery of the elastic ring.

  According to the shock absorber of the present invention, it is possible to make the attenuation characteristic of the expansion pressure different by the elastic ring without changing the resistance setting in the passage, so that the attenuation characteristic of only the expansion side or only the compression side can be changed. This makes it possible to easily tune the attenuation characteristics.

It is a longitudinal cross-sectional view of the shock absorber in one embodiment. It is an expansion longitudinal cross-sectional view of the piston part of the buffer 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 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.

  The shock absorber according to the present invention will be described below with reference to the drawings. As shown in FIG. 1 and FIG. 2, the shock absorber D in one embodiment basically includes a cylinder 1 and two working chambers that are slidably inserted into the cylinder 1. Piston 2, which is a partition member that divides the chamber R1 and the lower chamber R2, a piston rod 15 having one end connected to the piston 2, and passages 2a and 2b that are formed in the piston 2 and communicate with the upper chamber R1 and the lower chamber R2. The housing 4 is fixed to the tip of the piston rod 15 to form a pressure chamber R3, and is slidably inserted into the housing 4 so that the pressure chamber R3 passes through the one-side flow path 5 as one working chamber. A free piston 9 that divides into one chamber 7 that communicates with the chamber R2 and another chamber 8 that communicates with the upper chamber R1 that is the other working chamber via the other-side flow path 6, and the inside of the one chamber 7 and the other chamber 8 Each housed in a free A pair of coil springs 18 and 19 that elastically support the stone 9 from both sides are configured, and the upper chamber R1, the lower chamber R2, and the pressure chamber R3 are filled with a liquid such as hydraulic oil. In the case of the shock absorber D, a sliding partition 30 that slidably contacts the inner periphery of the cylinder 1 and divides the lower chamber R2 and the gas chamber G is provided below the cylinder 1 in the figure. That is, in the case of this shock absorber D, the piston rod 15 penetrates the inside of the upper chamber R1 as the other working chamber and is connected to the piston 2 as the partition member. The upper chamber R1 is set to be compressed.

  The upper end of the cylinder 1 is sealed with a head member (not shown) that slidably supports the piston rod 15, and the lower end of the cylinder 1 is also sealed with a bottom member (not shown).

  Hereinafter, each part will be described in detail. The piston rod 15 has a small-diameter portion 15a formed on the lower end side in FIG. 2, and a screw portion 15b formed on the distal end side of the small-diameter portion 15a.

  The piston rod 15 is formed with the other-side flow path 6 that opens from the tip of the small diameter portion 15 a and passes through the side of the piston rod 15. In the figure, a valve that serves as a resistor is not provided in the middle of the other-side flow path 6, but a valve such as a throttle may be provided.

  The piston 2 is formed in an annular shape, and a small diameter portion 15a of the piston rod 15 is inserted on the inner peripheral side thereof. The piston 2 is provided with passages 2a and 2b communicating the upper chamber R1 and the lower chamber R2, and the upper end of the passage 2a in the figure is closed by a laminated leaf valve V1 that is a damping force generating element. The lower end of the passage 2b in the figure is also closed by a laminated leaf valve V2 which is a damping force generating element.

  The laminated leaf valves V1 and V2 are both formed in an annular shape, and a small-diameter portion 15a of the piston rod 15 is inserted on the inner peripheral side, and annular valve stoppers 16 for restricting the amount of deflection of the laminated leaf valves V1 and V2, respectively. 17 and the piston 2 are laminated together.

  The laminated leaf valve V1 is bent by the pressure difference between the lower chamber R2 and the upper chamber R1 when the shock absorber D is contracted to open the passage 2a, and the liquid flow moves from the lower chamber R2 to the upper chamber R1. In addition to providing resistance, the passage 2a is closed when the shock absorber D is extended, and the other laminated leaf valve V2 opens the passage 2b when the shock absorber D is extended, as opposed to the laminated leaf valve V1. During contraction, the passage 2b is closed. That is, the laminated leaf valve V1 is a damping force generating element that generates a compression side damping force when the shock absorber D is contracted, and the other laminated leaf valve V2 generates an extension side damping force when the shock absorber D is extended. It is a damping force generating element. As described above, when the passage is one-way, the passages 2a and 2b may be provided as in the shock absorber D so that the liquid passes only when the shock absorber D is extended or contracted. Also, if the passage allows bidirectional flow, only one may be provided.

  A housing 4 that forms a pressure chamber R3 is screwed to the screw portion 15b of the piston rod 15 from below the valve stopper 17, and the piston 2, the laminated leaf valves V1 and V2, and the valve are formed by the housing 4. Stoppers 16 and 17 are fixed to the piston rod 15. Thus, the housing 4 not only forms the pressure chamber R3 inside, but also plays a role of fixing the piston 2 to the piston rod 15.

  The housing 4 will be described. The housing 4 includes an inner cylinder 21 with a flange 22 that is screwed into the screw portion 15 b of the piston rod 15, and a bottomed cylindrical outer cylinder 23. The upper cylinder 23 and the inner cylinder 21 are integrated by caulking the upper end opening in FIG. 2 toward the outer periphery of the flange 22, and the inner cylinder 21 and the outer cylinder 23 define a pressure chamber R3 in the lower chamber R2. It is made. In addition, when integrating the inner cylinder 21 and the outer cylinder 23, it is also possible to employ | adopt other methods, such as welding other than the said crimping process.

  The inner cylinder 21 includes the flange 22 as described above, and a screw portion 21a is formed on the inner periphery thereof. By screwing the screw portion 21a to the screw portion 15b of the piston rod 15, the housing 4 is fixed. The piston rod 15 can be fixed to the small diameter portion 15a. Therefore, if the cross-sectional shape of the outer periphery of the outer cylinder 23 is a shape other than a perfect circle, for example, a shape with a part cut away or a hexagonal shape, the operation of screwing the housing 4 to the tip of the piston rod 15 is performed. It becomes easy.

  Further, the outer cylinder 23 has a small diameter at the lower end in FIG. 1 and a step portion 23b is formed in the cylinder portion 23a, and a fixed orifice constituting a part of the one-side flow path 5 at the bottom portion 23c. 13 is provided.

  A free piston 9 is slidably inserted into the pressure chamber R3 formed by the inner cylinder 21 and the outer cylinder 23, and the pressure chamber R3 is slid by the other side flow path 6 by the free piston 9. The other chamber 8 communicated with the upper chamber R1 and the one chamber 7 communicated with the lower chamber R2 by the fixed orifice 13 are partitioned.

  The free piston 9 is formed in a bottomed cylindrical shape, and is provided at the bottom portion 9c of the cylindrical portion 9a, the bottom portion 9b closing one end of the cylindrical portion 9a, and the bottom portion 9b in FIG. A projecting portion 9c that protrudes toward the outside, an annular groove 9d formed on the outer periphery of the cylindrical portion 9a, and a through hole 9e that opens from the inner periphery of the cylindrical portion 9a and communicates with the annular groove 9d. The cylindrical portion 9a is slidably contacted with the inner periphery of the outer cylinder 23 toward the inner cylinder 21, and is inserted into the pressure chamber R3, thereby dividing the pressure chamber R3 into one chamber 7 and the other chamber 8.

  The annular groove 9d of the free piston 9 is fitted with a rubber square ring 20 as an elastic ring, and the square ring 20 is introduced into the other chamber 8 guided into the annular groove 9d through the through hole 9e. The pressure is urged in the diameter-expanding direction, and the contact surface pressure with the outer cylinder 23 increases according to the pressure in the other chamber 8 to increase the frictional force generated between the outer cylinder 23 and the outer cylinder 23. Note that the upper and lower surfaces of the square ring 20 in FIG. 2 are in close contact with the side wall of the annular groove 9 d so that the through hole 9 e does not communicate with the one chamber 7. The square ring 20 functions to suppress the movement of the free piston 9 relative to the outer cylinder 23 with a frictional force according to the pressure in the other chamber 8, and in this case, the elastic ring is a rubber-made square ring 20 Therefore, the square ring 20 seals between the free piston 9 and the outer cylinder 23 and communicates between the one chamber 7 and the other chamber 8 by a sliding gap between the free piston 9 and the outer cylinder 23. Is refused.

  Further, in order to apply an urging force to the free piston 9 in proportion to the amount of displacement of the free piston 9 relative to the housing 4, the flange 22 of the inner cylinder 21 and the free piston 9 are located in the other chamber 8. Coil springs 18 and 19 are interposed as spring elements between the inside of the bottom portion 9b of the outer cylinder 23 and between the bottom portion 23c of the outer cylinder 23 and the outside of the bottom portion 9b of the free piston 9, respectively. The free piston 9 is sandwiched from above and below by the spring elements of these coil springs 18 and 19, and is elastically supported after being positioned at a predetermined neutral position in the pressure chamber R3.

  As the spring element, it is sufficient that the free piston 9 can be elastically supported, and other elements than the coil springs 18 and 19 may be employed. For example, the free piston 9 may be elastically supported using an elastic body such as a disc spring. It may be. When a single spring element whose one end is connected to the free piston 9 is used, the other end may be fixed to the inner cylinder 21 or the outer cylinder 23.

  The lower end of the coil spring 18 in the drawing is fitted to the inner periphery of the deepest portion of the cylindrical portion 9 a of the free piston 9 and is positioned in the radial direction. The coil spring 19 has a convex portion 9 c of the free piston 9 on the inner periphery of the coil spring 19. By being inserted, it is centered to prevent positional displacement with respect to the free piston 9, thereby enabling an urging force to act on the free piston 9 stably.

  Note that the inner circumference of the cylindrical portion 9a of the free piston 9 is expanded in diameter compared to the deepest portion thereof, so that when the coil spring 18 is compressed and the winding diameter is expanded, the wire of the coil spring 18 is cylindrical. There is no rubbing against the inner periphery of the portion 9a, thereby preventing the occurrence of contamination.

  Further, as described above, the convex portion 9c has a function of centering the coil spring 19, and its height (length in the vertical direction in FIG. 2) is set to a height that can sufficiently prevent the coil spring 19 from climbing up. Has been.

  Subsequently, in the case of this embodiment, the above-described free piston 9 includes, in addition to the above-described configuration, an annular recess 9f provided at a position that does not interfere with the annular groove 9d on the outer periphery of the cylindrical portion 9a, A hole 9g that passes through the thickness of the free piston 9 and communicates with the annular recess 9f and the one chamber 7 is provided.

  Further, two variable orifices 11 and 12 communicating with the lower chamber R2 and the inside of the outer cylinder 23 are provided in the cylinder portion 23a of the outer cylinder 23. In the variable orifices 11 and 12, the free piston 9 is a coil spring 18. , 19 is in the neutral position and is always in the neutral position so that the one chamber 7 communicates with the lower chamber R2 while facing the annular recess 9f, and the free piston 9 is displaced to the stroke end, that is, the inner cylinder 21 In FIG. 1, when it is displaced until it comes into contact with the lower end or the step portion 23 b of the outer cylinder 23, it is completely overlapped with the outer periphery of the cylinder portion 9 a of the free piston 9 to be closed. That is, in this case, the one-side flow path 5 is configured by the annular recess 9f, the variable orifices 11 and 12, the hole 9g, and the fixed orifice 13. Two variable orifices 11 and 12 are provided, but the number thereof is arbitrary.

  In other words, in the case of the shock absorber D, when the displacement amount from the neutral position of the free piston 9 becomes an arbitrary displacement amount, the opening of the variable orifices 11 and 12 faces the annular recess 9f from the situation where the cylindrical portion 9a The situation starts to face the outer periphery and the flow area of the variable orifices 11 and 12 begins to decrease gradually, and the flow resistance in the one-side flow path 5 gradually increases. Therefore, the above-mentioned arbitrary amount of displacement is set by setting the vertical width in the figure of the annular recess 9f and the opening position of the variable orifices 11 and 12 on the inner peripheral side of the outer cylinder 23. In this embodiment, as the displacement amount of the free piston 9 increases, the flow area of the variable orifices 11 and 12 gradually decreases, and when the free piston 9 reaches the stroke end, the variable orifices 11 and 12 It is completely closed so as to face the cylinder portion 9a, and the flow resistance in the one-side flow path 5 is maximized so that the one chamber 7 is communicated with the lower chamber R2 only by the fixed orifice 13.

  The sliding partition wall 30 has a recess on the lower chamber R2 side, and when the shock absorber D is contracted to the minimum, the lower end in FIG. 1 that is the tip of the outer cylinder 23 of the housing 4 enters the recess. The loss of the stroke length due to the provision of the housing 4 at the tip of the piston rod 15 in the shock absorber D configured as a single cylinder is caused by the shape of the outer cylinder 23 and the sliding partition wall 30. It will be relieved by the recess.

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

(A) When the displacement amount from the neutral position in the free piston 9 is within a range where the variable orifices 11 and 12 do not begin to be closed. In this case, the free piston 9 is displaced without changing the resistance of the one-side flow path 5. It is possible.

  First, when the shock absorber D is in the compression stroke, the pressure in the other chamber 8 acting on the inner periphery of the square ring 20 is small in the entire compression stroke, and the friction generated between the square ring 20 and the outer cylinder 23 is small. Since the force is small, the free piston 9 is freely displaced with respect to the housing 4 in accordance with the differential pressure between the one chamber 7 and the other chamber 8. Therefore, the gain characteristic with respect to the frequency of the frequency transfer function of the differential pressure with respect to the flow rate in the shock absorber D in the compression stroke is the same as the gain characteristic of the conventional shock absorber shown in FIG.

  On the other hand, when the shock absorber D is in the extension stroke, the free piston 9 is equipped with a square ring 20 as an elastic ring on the outer periphery, but when the pressure in the other chamber 8 is small, the square ring 20 20 is small in contact surface pressure with respect to the outer cylinder 23, the frictional force generated between the square ring 20 and the outer cylinder 23 is small, and the free piston 9 has a differential pressure between the one chamber 7 and the other chamber 8 with respect to the housing 4. Accordingly, it can be displaced relatively freely. On the other hand, when the pressure in the other chamber 8 increases, the contact surface pressure of the square ring 20 to the outer cylinder 23 increases, and the free piston 9 is applied to the housing 4 by the frictional force generated between the square ring 20 and the outer cylinder 23. On the other hand, it becomes difficult to displace.

  In the shock absorber D incorporated between the vehicle body and the axle of the vehicle, the shock absorber D incorporated between the vehicle body and the axle of the vehicle is in the extension stroke, and the pressure in the other chamber 8 is reduced. This is generally the case when the frequency of vibration toward the expansion side of the shock absorber D is low. On the other hand, when the frequency of the vibration toward the extension side of the shock absorber D is high, the extension speed of the shock absorber D becomes high and the pressure in the other chamber 8 increases.

  That is, when the shock absorber D is in the expansion stroke and the vibration frequency is low and the pressure in the other chamber 8 is small, the displacement of the free piston 9 with respect to the housing 4 is not suppressed, and the differential pressure with respect to the flow rate in the shock absorber D As shown in FIG. 3, the gain characteristic Y with respect to the frequency of the frequency transfer function substantially coincides with the gain characteristic of the conventional shock absorber, but is free when the vibration frequency increases and the pressure in the other chamber 8 increases. Even if the displacement of the piston 9 with respect to the housing 4 is suppressed, the degree of gain drop is smaller than the gain characteristic of the conventional shock absorber, and the resistances in the laminated leaf valves V1 and V2 are set to be the same, the shock absorber As shown in FIG. 4, D has a higher damping force on the extension side than a damping force on the compression side with respect to high-frequency vibration. Since the flow rate per unit time depends on the vibration amplitude per unit time of the shock absorber D, the frequency characteristic of the damping characteristic of FIG. 4 is obtained from the gain characteristic shown in FIG. 3 and the pressure receiving area of the piston 2. This attenuation characteristic follows the same locus as the gain characteristic of FIG.

  In the above description, one of the pressure chambers disposed below the free piston 9 in FIG. 2 is defined as one chamber 7 and the chamber disposed above the free piston 9 in FIG. 2, the chamber disposed above the free piston 9 in FIG. 2 is defined as one chamber, the chamber disposed below the free piston 9 in FIG. 2 is defined as the other chamber, and the free piston 9 is reversed to the pressure chamber. It is also possible to adopt a configuration in which the pressure of the room connected to the lower chamber R2 is applied to the elastic ring so as to be inserted. In this case, the piston rod 15 penetrates the upper chamber R1 set in one of the working chambers, and the damping force with respect to the vibration frequency on the pressure side of the shock absorber D can be increased.

  In the description of this embodiment, the frequency range is divided into a low frequency range and a high frequency range. However, the frequency range is used to explain the change in gain and damping force with respect to the change in frequency. The boundary between the heights can be arbitrarily set according to the weight and personality of the vehicle.

  As described above, in the shock absorber D, the damping characteristics of the tension increase can be obtained by the angular ring 20 which is an elastic ring without changing the setting of the laminated leaf valves V1 and V2 which become resistances in the passages 2a and 2b. Since they can be made different, it is possible to change the damping characteristic only on the extension side or only on the compression side, and the tuning of the damping characteristic becomes easy.

  Furthermore, in the case of this embodiment, the piston rod 15 passes through the upper chamber R1 as the other chamber, and the angular ring 20 as an elastic ring suppresses the displacement of the free piston 9 with respect to the housing 4 because of the shock absorber. Since D is in the extension stroke, the damping force on the extension side of the shock absorber D can be increased, and the shock absorber D is optimal for a vehicle application in which it is normal to set a large damping force on the extension side. Become.

  Further, when the pressure in the other chamber 8 is small, the square ring 20 that is an elastic ring does not suppress the displacement of the free piston 9 with respect to the housing 4, so that the free piston 9 is moved to the neutral position positioned by the coil springs 18 and 19. Do not disturb the return.

  Therefore, according to this shock absorber D, the damping force on the extension side and the compression side can be easily tuned and made different, so that the optimum damping characteristic for the vehicle can be realized and the riding comfort in the vehicle can be improved. it can.

  Further, in this embodiment, since the elastic ring is a square ring 20 and seals between the free piston 9 and the outer cylinder 23, the one chamber 7 and the other chamber 8 are connected to the free piston 9 and the outer cylinder 23. Can be prevented from communicating through the sliding clearance between the two, and it is difficult to be affected by the dimensional tolerances of the free piston 9 and the outer cylinder 23. As a result, it is possible to prevent a situation in which the damping characteristic changes during traveling.

  When there is no need to always seal between the free piston 9 and the outer cylinder 23, or when it is desired to smoothly displace the free piston 9 with respect to the housing 4 at the time of low frequency vibration, the elastic ring The outer peripheral diameter may be set smaller than the inner diameter of the outer cylinder 23 so that the elastic ring does not contact the inner periphery of the outer cylinder 23 unless the pressure in the other chamber 8 rises to some extent.

(B) Operation in the case where the amount of displacement from the neutral position of the free piston 9 is within the range of increasing the channel resistance of the one-side channel 5 In turn, the amount of displacement from the neutral position of the free piston 9 is variable orifice 11 The operation of the shock absorber D when the flow resistance of the one-side flow path 5 is increased by starting to close both of the first and second flow paths 12 and 12 will be described.

  In this case, the variable orifices 11 and 12 gradually reduce the flow passage area in accordance with the amount of displacement of the free piston 9, and are completely closed when the free piston 9 reaches the stroke end so that the flow passage area is fixed to the fixed orifice 13. This is the same as the flow path area.

  That is, after the free piston 9 starts to close the variable orifices 11 and 12, the flow resistance of the one-side flow path 5 is gradually increased according to the amount of displacement, and when the free piston 9 reaches the stroke end, the flow resistance Is the maximum.

  Here, the free piston 9 is displaced to the stroke end when the amount of liquid flowing into and out of the one chamber 7 or the other chamber 8 is large. Specifically, when the vibration amplitude of the shock absorber D is large. It is.

  When the vibration frequency of the shock absorber D is relatively high, the shock absorber D generates a relatively low damping force until the free piston 9 is displaced to a position where the free piston 9 begins to close the variable orifices 11 and 12. When the piston 9 is displaced beyond the position where the variable orifices 11 and 12 begin to close, the flow resistance of the one-side flow path 5 gradually increases, so that the stroke beyond that of the free piston 9 increases. The moving speed to the end side is reduced, the amount of liquid movement between the upper chamber R1 and the lower chamber R2 via the pressure chamber R3 is also reduced, and the amount of liquid passing through the passages 2a and 2b is increased accordingly. Thus, the generated damping force of the shock absorber D gradually increases.

  When the free piston 9 reaches the stroke end, the liquid no longer moves between the upper chamber R1 and the lower chamber R2 via the pressure chamber R3, and the liquid passes through the passage 2a until the expansion / contraction direction of the shock absorber D is changed. , 2b, the shock absorber D generates a damping force with the maximum damping coefficient.

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

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

  Further, in this shock absorber D, since the urging force for returning the free piston 5 to the neutral position is acting on the free piston 9 by the coil springs 18 and 19, the sudden change in the damping force is suppressed when necessary. It is possible to avoid a situation where the function cannot be performed.

  Further, in this shock absorber D, when the free piston 9 reaches the stroke ends on both ends in the pressure chamber R3, the flow resistance of the one-side flow path 5 is gradually changed to increase, so The function of suppressing a sudden change in damping force does not fluctuate each time the device expands and contracts, and the passenger does not feel uncomfortable.

  In addition, although the shock absorber in each embodiment is configured as a so-called single cylinder type shock absorber, this is a double cylinder type provided with an annular reservoir formed to cover the cylinder outside the cylinder. The shock absorber may be configured as a shock absorber, or may be configured as a shock absorber provided with a completely separate reservoir tank outside the cylinder.

  Moreover, in each embodiment, although the pressure chamber is formed in the cylinder, it can also be provided outside the cylinder.

  Further, the use of the square ring 20 as the elastic ring is advantageous in that the communication between the through hole 9e and the one chamber 7 can be reliably prevented, but the elastic ring is set in the other chamber of the pressure chambers. As long as the pressure in the room increases the contact surface pressure with the housing 4 to increase the frictional force and suppress the displacement of the free piston 9 with respect to the housing 4, the rubber other than the rubber square ring 20 is used. Other synthetic resins or metallic rings may be used, or an elastic ring may be configured by combining a plurality of rings.

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.

DESCRIPTION OF SYMBOLS 1 Cylinder 2 Piston 2a, 2b Passage 4 Housing 5 One side flow path 6 Other side flow path 7 One chamber 8 Other chamber 9 Free piston 9a The cylinder part 9b in a free piston The bottom part 9c in a free piston The convex part 9d in a free piston Annular groove 9e Through hole 9f in free piston Annular recess 9g in free piston Holes 11 and 12 in free piston Variable orifice 13 Fixed orifice 15 Piston rod 15a Small diameter portion 15b in piston rod Screw portions 16 and 17 in piston rod Valve stoppers 18 and 19 Coil spring 20 Square ring 21 that is an elastic ring Inner cylinder 21a in the housing Screw part 22 in the inner cylinder 22 A collar 23 in the inner cylinder Outer cylinder 23a in the housing Cylinder part 23c in the outer cylinder In the outer cylinder Bottom 30 sliding bulkhead D dampener G gas chamber R1 other working chamber serving the upper chamber R2 one of the working chambers serving lower chamber R3 pressure chamber V1 in the step portion 23c outer cylinder, V2 laminated leaf valve

Claims (5)

A cylinder, a partition member that is slidably inserted into the cylinder and divides the inside of the cylinder into two working chambers, a passage communicating the two working chambers, a housing that forms a pressure chamber, and a slide within the housing A free piston that is freely inserted and divides the pressure chamber into one chamber that communicates with one working chamber via one channel and the other chamber that communicates with the other working chamber via the other channel; In a shock absorber provided with a spring element that generates a biasing force that suppresses displacement of the free piston with respect to the housing, an elastic ring is attached to the outer periphery of the free piston, and the pressure in the other chamber is applied to the inner periphery of the elastic ring. A shock absorber characterized by. The shock absorber according to claim 1, wherein an annular groove communicating with the other chamber is formed on an outer periphery of the free piston, and an elastic ring is attached to the annular groove. The shock absorber according to claim 1 or 2, wherein the elastic ring is always in sliding contact with the housing to seal between the free piston and the housing. The shock absorber according to any one of claims 1 to 3, further comprising a piston rod connected to the partition wall member, the piston rod penetrating the other working chamber. The housing includes a flanged inner cylinder that fixes to the piston rod a partition wall member that is screwed to the piston rod and is fitted to the piston rod, and a bottomed cylindrical outer cylinder that extends from the outer periphery of the flange. A pressure chamber is formed, and the pressure chamber is partitioned into one chamber and the other chamber by a free piston that is in sliding contact with the inner periphery of the outer cylinder. Shock absorber.

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