JP5142971B2 - 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 partitions 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 are provided. A first passage that communicates, a second passage that opens from the tip of the piston rod to the side to communicate the upper chamber and the lower chamber, and a pressure chamber that is connected to the middle of the second passage, There are some which are configured to include an attached housing, 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. That is, one chamber in the pressure chamber communicates with the lower chamber through the first passage, and the other chamber in the pressure chamber communicates with the upper chamber through the second passage.

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３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 differential pressure 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, the differential pressure P and the flow rate Q1 of the liquid passing through the first passage are C1 is the coefficient in the other chamber, P1 is the pressure in the other chamber, C2 is the coefficient in the relationship between the pressure P1 and the flow rate Q2 of the liquid flowing into the other chamber from the upper chamber, and the pressure in the one chamber is P2. The coefficient that is the 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, the cross-sectional area that is the pressure receiving area of the free piston is A, and the displacement of the free piston with respect to the pressure chamber is X. When a transfer function of the differential pressure P with respect to the flow rate Q is obtained with K as the spring constant of the coil spring, 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 where 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 in FIG. 4, this shock absorber generates a large damping force for low frequency vibration input, and generates a small damping force for high frequency vibration input. Therefore, a high damping force can be reliably generated in a scene where the input vibration frequency is low, such as when the vehicle is turning, and a low damping force can be generated in a scene where the input vibration frequency is high such that the vehicle gets over the road surface unevenness. It can be generated reliably and the riding comfort in the vehicle can be improved (see, for example, Patent Document 1).
JP 2006-336816 A (FIG. 2)

  The above-described shock absorber is useful in that it can improve the ride comfort in the vehicle, but has the following problems.

  As described above, the shock absorber can generate a large damping force for low frequency vibration input, and can generate a small damping force for high frequency vibration input. However, when there is an input of vibration that causes the piston speed to be high although the frequency is low, the damping force generated by the shock absorber may be too high, which may impair the riding comfort in the vehicle.

  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 impair riding comfort while exhibiting a damping force depending on the vibration frequency. Is to provide.

  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 A free piston that is partitioned into the other chamber communicated with the other working chamber, and the free piston is sandwiched between a one-side spring element housed in one chamber and the other-side spring element housed in the other chamber, and is neutral In the shock absorber positioned at the position, a bypass path is provided in the housing for communicating between one working chamber and the other chamber and opened and closed by the free piston, and the free piston is located in the middle of the free piston. From position to one chamber side when a predetermined amount displaced set so as to increase the spring constant, free piston is characterized by opening the bypass passage when displaced more than a predetermined amount from the neutral position to one chamber side.

  According to the shock absorber of the present invention, when the extension speed reaches the high speed range, the free piston is displaced by a predetermined amount or more due to the differential pressure between the one chamber and the other chamber, and the bypass passage is opened, Since the chamber and the other working chamber communicate with each other not only through the passage but also through the other chamber and the bypass path, the increase in the generated damping force with respect to the increase in the expansion speed of the shock absorber is suppressed, and the buffer when the expansion speed becomes high is suppressed. It can be avoided that the generated damping force of the device becomes excessive, and the riding comfort in the vehicle can be improved.

  Further, the spring constant of the one side spring element can be kept small until the free piston is displaced by a predetermined amount from the neutral position, i.e., until the bypass path is opened, so until the bypass path is opened, The free piston can be maintained in a state in which it is easily displaced, and the frequency-dependent damping characteristics of the shock absorber are not impaired.

  Therefore, in the shock absorber according to the present invention, the frequency-dependent attenuation characteristic is not impaired, and it is possible to prevent the generated damping force from becoming excessive when the expansion or contraction speed reaches the high speed range. It is possible to achieve both a damping force and an improvement in ride comfort in the vehicle.

  The shock absorber according to the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view of a shock absorber according to an embodiment. FIG. 2 is an enlarged vertical sectional view of a piston portion of the shock absorber according to the embodiment.

  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 is partitioned into one chamber 7 that communicates with the chamber R2 and the other chamber 8 that communicates with the upper chamber R1 that is the other working chamber via the other-side flow path 6, and is accommodated in the one chamber 7. Free piston 9 on top in Fig. 1 One side spring element 18 urged to the side, the other side spring element 19 accommodated in the other chamber 9 to urge the free piston 9 downward in FIG. 1, and the housing 4 are provided as one working chamber. The lower chamber R2 and the other chamber 8 communicate with each other and include a bypass passage 17 that is opened and closed by the free piston 4. The free piston 9 is sandwiched between the one side spring element 18 and the other side spring element 19. Thus, it is positioned at a neutral position with respect to the housing 4.

  Further, in the shock absorber D, the upper chamber R1, the lower chamber R2, and the pressure chamber R3 are filled with a liquid such as hydraulic oil. Is provided with a sliding partition wall 30 that slidably contacts the inner periphery of the cylinder 1 and partitions the lower chamber R2 and the gas chamber G.

  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. Laminated.

  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. A stopper 16 is 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. And a convex portion 9c that protrudes toward the inner cylinder 21, and is inserted into the pressure chamber R3 with the cylindrical portion 9a slidingly contacting the inner periphery of the outer cylinder 23. It is divided into the chamber 7 and the other chamber 8.

  Further, the one-side spring element 18 is accommodated in the one chamber 7, and the other-side spring element 19 is accommodated in the other chamber 8, and the free piston 9 is sandwiched and elastically supported by these spring elements 18, 19. In this state, the free piston 9 is positioned at a predetermined neutral position in the pressure chamber R3. The neutral position does not necessarily have to be set at the stroke center of the free piston 9 in the pressure chamber 3, and is determined by the balance between the one side spring element 18 and the other side spring element 19.

  Specifically, the one side spring element 18 is in the one chamber 7 between the bottom 23c of the outer cylinder 23 and the outside of the bottom 9b of the free piston 9, and the other side spring element 19 is in the other chamber 8. It is interposed between the flange 22 of the inner cylinder 21 and the inside of the bottom portion 9 b of the free piston 9.

  In this embodiment, the one-side spring element 18 includes a coil spring 18a having a small spring constant and a coil spring 18b having a spring constant larger than the coil spring 18a arranged in series. When a predetermined amount is displaced downward in FIG. 2 from the position toward the one chamber 7 side, the coil spring 18a having a small spring constant is in the most compressed state, and with respect to any further displacement of the free piston 9 toward the one chamber 7 side. Only the coil spring 18b having a large spring constant is contracted. That is, the apparent spring constant of the one-side spring element 18 increases for further compression with the free piston 9 displaced by a predetermined amount from the neutral position. A washer 18c is interposed between the coil springs 18a and 18b to prevent the ends of the coil springs 18a and 18b from directly interfering with each other, thereby realizing smooth expansion and contraction of the coil springs 18a and 18b. Yes.

  The other side spring element 19 is shown as a coil spring in the drawing, but it is only necessary to be able to elastically support the free piston 9, and other elements than the coil spring may be employed. For example, an elastic body such as a disc spring is used. The free piston 9 may be elastically supported. The same applies to the coil springs 18a and 18b in the one-side spring element 18. As described above, when the free piston 9 is displaced from the neutral position to the one chamber 7 side by a predetermined amount, the spring constant is set to be large. If possible, it is also possible to employ other than the coil spring.

  The lower end of the coil spring as the other side spring element 19 in the drawing is fitted to the innermost periphery of the deepest part of the cylindrical portion 9a of the free piston 9, and is positioned in the radial direction. The coil spring 18a in the one side spring element 18 is a coil spring 18a. The free piston 9 is centered by inserting the convex portion 9c of the free piston 9 into the inner periphery thereof, thereby preventing the displacement of the free piston 9 so that a biasing force can be applied to the free piston 9 stably. It is possible.

  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 as the other side spring element 19 is compressed and the winding diameter is expanded. The wire material of the coil spring is not rubbed against the inner periphery of the cylindrical portion 9a, thereby preventing the occurrence of contamination.

  Further, as described above, the convex portion 9c has a function of centering the coil spring 18a, and its height (vertical length in FIG. 2) is set to a height that can sufficiently prevent the coil spring 18a 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 groove 9d provided on the outer periphery of the cylindrical portion 9a, and further, an annular groove that passes through the inside of the wall thickness of the free piston 9. 9d and the hole 9e which connects the one chamber 7 are provided.

  In addition, the cylinder portion 23a of the outer cylinder 23 is provided with two variable orifices 11 and 12 communicating with the lower chamber R2 and the outer cylinder 23. The variable orifices 11 and 12 are offset with respect to the axial direction. When the free piston 9 is elastically supported by the coil springs 18 and 19 and is in the neutral position, the one chamber 7 and the lower chamber R2 are communicated with each other so as to face the annular groove 9d. When the free piston 9 is displaced from the neutral position toward the one chamber 7 to the stroke end, that is, when the free piston 9 is displaced until it abuts against the step portion 23b of the outer cylinder 23, the variable orifice 11 is When the free piston 9 is displaced from the neutral position to the other chamber 8 side to the stroke end, that is, the free piston 9 is closed. When the variable orifice 12 is displaced until it comes into contact with the lower end in FIG. 2, the variable orifice 12 is closed first and then the variable orifice 11 is also closed.

  In the case of the shock absorber D of this embodiment, the one-side flow path 5 is composed of an annular groove 9d, variable orifices 11 and 12, a hole 9e, and a fixed orifice 13, from the neutral position of the free piston 9. When the displacement amount becomes an arbitrary displacement amount, the variable orifices 11 and 12 are gradually shifted from the state in which all the openings of the variable orifices 11 and 12 face the annular groove 9d to the state in which they start to face the outer periphery of the cylindrical portion 9a. The flow path area of the one-side flow path 5 gradually increases. Therefore, the above-mentioned arbitrary displacement amount is set by setting the vertical width in the figure of the annular groove 9d 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.

  Further, in this shock absorber D, a bypass passage 17 that communicates the other chamber 8 and the lower chamber R2 that is one working chamber is provided in the cylindrical portion 23a of the outer cylinder 23. When the free piston 9 is in the neutral position in the pressure chamber R3, the outer periphery of the cylindrical portion 9a is opposed to be cut off, and the communication between the other chamber 8 and the lower chamber R2 is cut off. When the free piston 9 is displaced from the neutral position to the one chamber 7 by a predetermined amount or more, the upper end in FIG. 2 of the cylindrical portion 9a of the free piston 9 is disposed below the upper end in FIG. The bypass passage 17 is opened, and the other chamber 8 and the lower chamber R2 communicate with each other bypassing the passages 2a and 2b.

  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.

  First, the case where the amount of displacement from the neutral position in the free piston 9 is a predetermined amount or less will be described. In this case, when the shock absorber D is in the expansion stroke, the free piston 9 is pressed toward the one chamber 7 with the pressure in the other chamber 8 exceeding the pressure in the one chamber 7, but the free piston 9 is displaced by a predetermined amount or more. Therefore, the bypass path 17 is not opened, and the spring constant of the one-side spring element 18 is not changed because the small coil spring 18a is not in the most compressed state and the spring constant remains small.

  In the shock absorber D incorporated between the vehicle body and the axle of the vehicle, the differential pressure between the one chamber 7 and the other chamber 8 is generally reduced when the expansion speed of the shock absorber D is low. Further, the frequency of the stretching vibration of the shock absorber D is also lowered. On the other hand, when the frequency of the expansion and contraction vibration of the shock absorber D is high, the expansion and contraction speed of the shock absorber D becomes high, and the differential pressure between the one chamber 7 and the other chamber 8 becomes large.

  From the above, when the frequency of the expansion and contraction vibration of the shock absorber D is low, the differential pressure between the one chamber 7 and the other chamber 8 is small, and the free piston 9 is not displaced much with respect to the housing 4 and In order not to change the volume of the other chamber 8 so much, the shock absorber D causes the liquid to mainly pass through the passages 2a and 2b and move back and forth between the upper chamber R1 and the lower chamber R2, and the laminated leaf valves V1 and V2 are mainly used for this liquid. Damping force is generated by resistance applied to the flow.

  On the other hand, when the frequency of the expansion and contraction vibration of the shock absorber D is high, the expansion and contraction speed of the shock absorber D is slightly increased to reach the middle speed range, and the differential pressure between the one chamber 7 and the other chamber 8 becomes large, and the free piston 9 is displaced according to the differential pressure, and the volume of the one chamber 7 and the other chamber 8 is changed to reduce the flow rate of the liquid passing through the passages 2a and 2b. Therefore, the generated damping force of the shock absorber D is reduced. .

  That is, until the differential pressure between the one chamber 7 and the other chamber 8 increases to some extent and the free piston 9 starts to move, 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 is the same as that of the conventional shock absorber. Similarly, as shown in FIG. 3, there is no constant drop, and therefore the damping characteristic in the shock absorber D showing the gain of the damping force with respect to the vibration frequency remains constant and high as shown in FIG. 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.

  When the differential pressure between the one chamber 7 and the other chamber 8 is increased to some extent and the free piston 9 starts to move, 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 is shown in FIG. Thus, it gradually decreases and becomes constant in the high frequency range, and the damping characteristic in the shock absorber D also changes as shown in FIG.

  Thus, when the amount of displacement from the neutral position in the free piston 9 is a predetermined amount or less, the damping characteristic that is the relationship of the damping force generated with respect to the vibration frequency of the shock absorber D is the same as that of the conventional shock absorber. It changes so as to exhibit a large damping force for low frequency vibrations and a small damping force for high frequency vibrations.

  If the amplitude increases even in the case of low frequency vibration, the expansion / contraction speed increases, and if the low speed is exceeded and the medium speed range is reached, the differential pressure between the one chamber 7 and the other chamber 8 becomes larger than the above, and free The piston 9 begins to close the variable orifices 11 and 12, the flow resistance of the one-side flow path 5 increases, the displacement speed of the free piston 9 in the same direction is reduced, and the free piston 9 is in the neutral position. As long as the amount of displacement is less than a predetermined amount and the bypass passage 17 is not opened, the amount of liquid movement between the upper chamber R1 and the lower chamber R2 via the pressure chamber R3 also decreases, and passes through the passages 2a and 2b accordingly. The amount of liquid to be increased increases, and the damping force generated by the shock absorber D gradually increases.

  As described above, in the shock absorber D, even if the vibration is low frequency, when the expansion / contraction speed is high to some extent and the vibration amplitude is large, the generated damping force can be gradually increased to firmly attenuate the vibration.

  Further, when the amplitude increases and the extension speed increases beyond the medium speed range, if the damping force is increased as it is, the ride comfort in the vehicle is impaired. For this reason, in this shock absorber D, when the operation is performed such that the extension speed reaches the high speed region in the extension stroke, the free piston 9 is displaced by a predetermined amount or more due to the differential pressure between the one chamber 7 and the other chamber 8, and the bypass passage 17 The upper chamber R1 and the lower chamber R2 communicate with each other not only through the passage 2b but also through the other chamber 8 and the bypass passage 17.

  Then, the liquid moves from the upper chamber R1 to the lower chamber R2 through the bypass passage 17 in addition to the passage 2b, and suppresses the increase in the generated damping force with respect to the increase in the expansion speed of the shock absorber D, thereby reducing the generated damping force. Make it cap.

  Thereby, it is possible to avoid an excessively generated damping force of the shock absorber D when the extension speed becomes high, and to improve the riding comfort in the vehicle. If the pressure chamber R3 is installed in the upper chamber R1 or outside the cylinder 1 and the bypass passage is communicated with the one chamber 7 and the upper chamber R1, the occurrence when the shock absorber D contracts. An increase in the damping force can be suppressed.

  Further, the spring constant of the one side spring element 18 can be kept small until the free piston 9 is displaced from the neutral position by a predetermined amount, that is, until the bypass path 17 is opened. Until this is done, the free piston 9 can be maintained in a state of being easily displaced, and the frequency-dependent damping characteristics of the shock absorber D are not impaired.

  That is, in this shock absorber D, the frequency-dependent attenuation characteristics are not impaired, and it is possible to prevent the generated damping force from becoming excessive when the expansion or contraction speed reaches a high speed range. It is possible to achieve both strength and improvement in ride comfort in the vehicle.

  In the present embodiment, in order to explain the change of the damping characteristic, the piston speed is provided with sections of low speed, medium speed, and high speed, but the speed of the boundary between these sections is arbitrarily set. be able to.

  Further, in the above-described embodiment, the variable orifices 11 and 12 that make the flow path resistance of the one-side flow path 5 variable are provided, but even if this is omitted, the operation of the present invention. There is no loss of effectiveness.

  Further, the one-side spring element 18 may be configured to include a portion having a small spring constant and a portion having a large spring constant connected in series to the portion having the small spring constant, and the free piston 9 is moved from the neutral position to the one chamber. If a portion with a small spring constant is set to the most compressed state when a predetermined amount of displacement is made to the 7 side, the above-mentioned operation and effect can be obtained. Therefore, springs and elastic bodies having different spring constants are arranged in series. In addition to the above, for example, the one-side spring element 18 is a coil spring having a small pitch portion and a large pitch portion, and when the piston 9 is displaced from the neutral position to the one chamber 7 side by a predetermined amount, a small pitch portion is provided. You may comprise so that it may be compressed most.

  Further, in this embodiment, the washer 18c is interposed between the coil springs 18a and 18b of the one-side spring element 18, but this may be omitted, and the one-side flow path 5 defines the one chamber 7. Since the fixed orifice 13 and the variable orifices 11 and 12 are connected in parallel to the lower chamber R2 as one working chamber, the washer 18c is not a ring but a disk, and the one chamber 7 is divided by a disk. May be adopted.

  Further, the shock absorber D in the present embodiment is configured as a so-called single cylinder shock absorber, and is provided with an annular reservoir formed so as to cover the cylinder 1 outside the cylinder 1. It may be configured as a double cylinder type shock absorber, or may be configured as a shock absorber provided with a completely separate reservoir tank outside the cylinder 1. In addition, although the pressure chamber R3 is formed in the cylinder 1, it can also be provided outside the cylinder 1.

 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.

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 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.

Explanation of symbols

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 Holes 11 and 12 in free piston Variable orifice 13 Fixed orifice 15 Piston rod 15a Small diameter portion 15b in piston rod Screw portion 16 in piston rod Valve stopper 17 Bypass path 18 One side spring element 18a Coil spring 18b having a small spring constant Spring constant Large coil spring 18c washer 19 other side spring element 21 inner cylinder 21a in housing screw part 22 in inner cylinder flange 23 in inner cylinder outer cylinder 23a in housing cylindrical part 23 in outer cylinder c Step portion 23c in outer cylinder Bottom 30 in outer cylinder Sliding partition wall D Shock absorber G Gas chamber R1 Upper chamber R2 as the other working chamber R3 Lower chamber R3 as one working chamber Pressure chambers V1, V2 Stacked leaf valve

Claims (3)

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; And a free piston is sandwiched between one spring element housed in one chamber and the other spring element housed in the other chamber and positioned in a neutral position. A bypass path is provided in the housing that communicates and is opened and closed by the free piston. When the free piston is displaced by a predetermined amount from the neutral position to the one chamber side, the spring constant is increased. Set free piston shock absorber, characterized in that opening the bypass passage when displaced more than a predetermined amount from the neutral position to one chamber side. The one-side spring element is configured to include a portion having a small spring constant and a portion having a large spring constant in series with the portion having the small spring constant, and when the free piston is displaced from the neutral position to the one chamber side by a predetermined amount, The shock absorber according to claim 1, wherein a portion having a small constant is in a most compressed state. The housing includes a nut with a hook for fixing a partition wall member screwed to the piston rod and fitted to the piston rod, and a bottomed cylindrical outer cylinder extending from the outer periphery of the flange. The shock absorber according to claim 1 or 2, wherein a pressure chamber is formed and the pressure chamber is partitioned into a first chamber and a second chamber by a free piston slidingly contacting the inner periphery of the outer cylinder.

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