JPH10331898A - Shock absorber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adjust clamping force characteristics in a range of low displacement speed for a piston rod. SOLUTION: A sub piston 30 and a main piston 32 are fixed to a piston rod 16. The sub piston 30 is provided with passages 62 and 66, and with relief valves 50 and 54. And the main piston 32 is provided with passages 96 and 98, and with relief valves 82 and 88. The valve opening pressure of the relief valves 50 and 54 is so set up as to be sufficiently lower as compared with that of the relief valves 82 and 86. A bypass passage bypassing the sub piston 30, is provided for the inside of the piston rod 16. The opening of the bypass passage is adjusted by an adjusting rod 42.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a shock absorber, and more particularly to a shock absorber suitable for changing a damping force characteristic according to a displacement speed of a piston rod.

[0002]

2. Description of the Related Art Conventionally, for example, Japanese Patent Application Laid-Open No. Hei.
No. 8 discloses a known shock absorber. The conventional shock absorber includes a first piston and a second piston fixed to a piston rod and slidably disposed in a cylinder. The first and second pistons have first and second damping force generating mechanisms, respectively.

Each of the first and second damping force generating mechanisms is composed of an orifice and a valve mechanism, and generates a damping force due to a flow resistance when the working fluid flows through the orifice and the valve mechanism. The sum of the damping forces generated by the first and second damping force generating mechanisms is the total damping force generated by the shock absorber. In a region where the displacement speed of the piston rod is equal to or lower than a predetermined speed (hereinafter, referred to as a valve opening speed), the valve mechanisms of the first and second damping force generating mechanisms are both closed. In this case, when the working fluid flows only through the orifice, a large damping force is generated by the first and second damping force generating mechanisms. On the other hand, when the piston rod is displaced at a speed exceeding the valve opening speed, the valve mechanisms are both opened. In this case, since the working fluid flows through the valve mechanism, the magnitude of the damping force generated by the first and second damping force generating mechanisms is suppressed. Therefore, according to the above conventional shock absorber, in the relationship of the damping force to the displacement speed of the piston rod, the increasing gradient of the damping force becomes large in a region where the displacement speed is equal to or less than the valve opening speed, and the displacement speed exceeds the valve opening speed. In such a region, characteristics such that the increasing gradient of the damping force is suppressed are obtained. The characteristic indicating the relationship between the displacement speed of the piston rod and the damping force is hereinafter referred to as damping force characteristic.

[0004] In order to ensure good riding comfort of the vehicle, it is preferable that the damping force be small in a region where the displacement speed of the piston rod is low. On the other hand, in order to ensure good steering stability of the vehicle, it is desirable that the damping force be large in a region where the displacement speed of the piston rod is high. In general, it is known that when the displacement speed of the piston rod exceeds 0.1 to 0.3 m / s, both the riding comfort and the steering stability can be achieved by reducing the gradient of the damping force characteristic. ing.
Therefore, in the above-mentioned conventional shock absorber, by setting the valve opening speed to 0.1 to 0.3 m / s, it is possible to realize good ride comfort and good steering stability.

[0005] The above conventional shock absorber also has
A bypass passage is provided to bypass the first damping force generating mechanism. The bypass passage is configured to open and close according to the height of the vehicle. In a state where the bypass passage is opened, the working fluid flows by bypassing the first damping force generating mechanism, so that the damping force is not generated by the first damping force generating mechanism. Therefore, according to the conventional shock absorber, the damping force characteristics can be changed not only by the displacement speed of the piston rod but also by the height of the vehicle.

[0006]

According to experiments conducted by the inventor of the present invention, the riding comfort and steering stability of a vehicle are limited in a region where the piston rod displacement speed is extremely low (for example, 0.02 m / s or less). Region; hereinafter, referred to as an ultra-low speed region). Therefore, in order to optimally set the riding comfort and the driving stability of the vehicle, it is desirable to be able to adjust the damping force characteristics in such a very low speed range. However, depending on the damping force characteristics in the ultra-low speed range, the ride comfort and steering stability of the vehicle are largely changed.
It has not been recognized, and even in the conventional shock absorber described above, no consideration is given to changing the damping force characteristics in a very low speed range.

The present invention has been made in view of the above points, and has as its object to provide a shock absorber capable of adjusting a damping force characteristic in a region where the displacement speed of a piston rod is low.

[0008]

The above object is achieved by the present invention.
A main piston connected to a piston rod and slidably disposed in a cylinder, a sub-piston connected to the piston rod and slidably disposed in the cylinder, A first flow path that passes through the main piston in the axial direction, a first valve mechanism that is provided in the first flow path, that opens with a first valve opening pressure, and that the valve mechanism is closed. A first damping force generating mechanism including an orifice for conducting the first flow path, a second flow path axially penetrating the sub-piston, and a second flow path provided in the second flow path; A second valve mechanism that opens with a second valve opening pressure that is smaller than the first valve opening pressure, a second damping force generation mechanism that includes a bypass passage that bypasses the second flow path, Opening adjustment means for adjusting the opening of the bypass passage. It is achieved by the absorber.

In the present invention, the first damping force generating mechanism includes a first flow path axially penetrating the main piston,
A first valve mechanism is provided in the first flow path and opens at a first valve opening pressure, and comprises an orifice for conducting the flow path when the first valve mechanism is closed. The displacement speed of the piston rod is low and the differential pressure acting on the first valve mechanism is
Is lower than the valve opening pressure, the first valve mechanism is in the valve closed state. In this case, when the working fluid flows through the orifice, the damping force generated by the first damping force generating mechanism rises rapidly as the displacement speed increases. When the displacement speed of the piston rod increases until the differential pressure acting on the first valve mechanism reaches the first valve opening pressure, the first valve mechanism opens. In this case, the working fluid flows through the first flow path, and an increase in the damping force is suppressed. Hereinafter, the displacement speed of the piston rod when the first valve mechanism opens the valve is referred to as a main valve opening speed.

[0010] The second damping force generating mechanism is provided in the second flow passage penetrating the sub-piston in the axial direction and the second flow passage, and the second damping force generation mechanism is opened by the second valve opening pressure. Of the valve mechanism,
It comprises a bypass passage which bypasses the second flow passage. In a state where the displacement speed of the piston rod is low and the differential pressure acting on the second valve mechanism is lower than the second valve opening pressure, the second valve mechanism is closed. In this case, since the working fluid flows only through the bypass passage, the damping force generated by the second damping force generating mechanism rises rapidly with the increase in the displacement speed. On the other hand, when the displacement speed of the piston rod increases until the differential pressure acting on the second valve mechanism exceeds the second valve opening pressure, the second valve mechanism opens. in this case,
The working fluid also flows through the second flow path, and an increase in the damping force is suppressed. The displacement speed of the piston rod when the second valve mechanism opens is hereinafter referred to as a sub-valve opening speed.

The damping force generated by the shock absorber is:
It is the sum of the damping force generated by the first damping force generation mechanism and the damping force generated by the second damping force generation mechanism. Also, the second
Is smaller than the first valve opening pressure, the sub valve opening speed is lower than the main valve opening speed. Therefore, as the displacement speed of the piston rod transitions from a region at or below the sub-valve opening speed to a region between the sub-valve opening speed and the main valve opening speed, and further to a region exceeding the main valve opening speed. Thus, the gradient of the damping force characteristic of the shock absorber decreases.

When the opening degree of the bypass passage is changed by the opening degree adjusting means, the damping force generated when the working fluid flows through the bypass passage changes. In this case, when the differential pressure acting on the second valve mechanism changes with respect to the constant displacement speed of the piston rod, the sub-valve opening speed changes. Accordingly, the damping force characteristic of the shock absorber is changed in a region where the displacement speed of the piston rod is equal to or less than the sub-valve opening speed by changing the opening degree of the bypass passage.

[0013]

FIG. 1 is a sectional view of a shock absorber 10 according to an embodiment of the present invention. As shown in FIG. 1, the shock absorber 10 includes a piston rod 16
And an outer cylinder 18. Inside the outer cylinder 18, an inner cylinder 20 is disposed coaxially with the outer cylinder 18. An annular chamber 21 is formed between the outer cylinder 18 and the inner cylinder 20.

A rod guide 22 is fitted into the upper end of the outer cylinder 18. The rod guide 22 is a columnar rigid member having a large diameter portion 22a and a small diameter portion 22b. The outer peripheral surface of the small diameter portion 22b engages with the inner peripheral surface of the inner cylinder 20, and the large diameter portion 2
The outer peripheral surface of 2 a is engaged with the inner peripheral surface of the outer cylinder 18. The rod guide 22 has a through hole at the center thereof. The piston rod 16 is slidably inserted through the through hole in a liquid-tight manner. A cap 24 is fixed to the upper end of the outer cylinder 18 so that the piston rod 16 passes through the center of the cap 24.

The piston rod 16 is a columnar member having a large diameter portion 16a and a small diameter portion 16b. The piston rod 16 is arranged such that the small diameter portion 16 b is accommodated inside the inner cylinder 20. A rebound stopper 26 and a rebound stopper plate 28 are mounted on the large-diameter portion 16 a of the piston rod 16 at a position accommodated inside the inner cylinder 20.

The rebound stopper plate 28 is an annular rigid member, and is fixed to the outer periphery of the large diameter portion 16a of the piston rod 16. Also, the rebound stopper 26
Is an annular member having elasticity, which is mounted on the upper part of the rebound stopper plate 28. Piston rod 1
6 is displaced upward by a predetermined distance, the rebound stopper 2
6 comes into contact with the rod guide 22, and further displacement of the piston rod 16 is restricted.

A sub-piston 30 and a main piston 32 are fixed to the small-diameter portion 16b of the piston rod 16 in this order from the upper side. The inner space of the inner cylinder 20 includes an upper chamber 34 above the sub piston 30 by the sub piston 30 and the main piston 32, an intermediate chamber 36 between the sub piston 30 and the main piston 32, and a main piston 3
The lower chamber 36 is divided into a lower chamber 36 below the lower chamber 2.

Sub piston 30 and main piston 32
Are provided with orifices and valve mechanisms that allow fluid to flow between the upper chamber 34 and the middle chamber 36 and between the middle chamber 34 and the lower chamber 38, respectively. A damping force is generated according to. Details of the configuration of the sub piston 30 and the main piston 32 will be described later.

Inside the piston rod 16, there is provided a passage 40 penetrating in the axial direction. Passage 40
A large-diameter portion 40a and a small-diameter portion 4 extending below the large-diameter portion 40a
0b. The step 40c between the large-diameter portion 40a and the small-diameter portion 40b of the passage 40 is arranged above the step between the large-diameter portion 16a and the small-diameter portion 16b of the piston rod 16. Large diameter portion 40a of passage 40
The adjustment rod 42 is inserted into the.

A base valve 44 is fixed to a lower end of the outer cylinder 18. The base valve 44 is configured to allow a fluid to flow between the lower chamber 38 and the annular chamber 21. The working fluid is contained inside the outer cylinder 18 so as to fill the inner space of the inner cylinder 20 and fill the annular chamber 21 to a predetermined height. Next, the configuration of the sub-piston 30, the main piston 32, and peripheral portions thereof will be described with reference to FIG. FIG. 2 shows the sub piston 3
FIG. 2 is an enlarged view of a main piston 32 and a peripheral portion thereof. The left half of FIG. 2 includes the lower chamber 3 from the upper chamber 34 side.
The component that allows the fluid to flow to the side 8 is shown in FIG.
In the right half of the figure, components that allow the fluid to flow from the lower chamber 38 side to the upper chamber 34 side are shown.

As shown in FIG. 2, the adjusting rod 42 has a small-diameter portion 42a having an outer diameter smaller than the inner diameter of the large-diameter portion 40a of the passage 40, and a conical portion formed at the lower end of the small-diameter portion 42a in FIG. 42b. The adjustment rod 42 is arranged such that the tip of the conical portion 42b enters the small diameter portion 40b of the passage 40. A clearance C is formed between the outer peripheral surface of the conical portion 42b and the step 40c of the passage 40.

An O-ring 43 is mounted on the outer periphery of the adjusting rod 42 above the small-diameter portion 42a. The O-ring 43 defines an annular communication space 44 between the outer periphery of the small diameter portion 42 a of the adjustment rod 42 and the inner periphery of the large diameter portion 40 a of the passage 40. The communication space 44 communicates with the internal space of the small diameter portion 40b of the passage 40 via the clearance C.

The adjusting rod 42 extends in the radial direction,
A communication passage 46 that connects the upper chamber 34 and the communication space 44 is provided. Further, the adjusting rod 42 is provided with a communication passage 47 extending in the radial direction and communicating the internal space of the small diameter portion 40 b of the passage 40 and the external space of the small diameter portion 16 b of the piston rod 16. The adjusting rod 42 is screwed with a large diameter portion 40a of the passage 40 at a screw portion (not shown),
The upper end reaches near the upper end of the piston rod 16. Therefore, by rotating the upper end of the adjusting rod 42 from above the piston rod 16 and thereby changing the vertical position of the adjusting rod, the clearance C is increased.
Can be adjusted.

On the outer periphery of the small diameter portion 16b of the piston rod 16, the stopper plate 4
8, leaf seat 49, leaf valve 50, sub-piston 30, leaf valve 54, and leaf seat 56 are fitted. The leaf valves 50 and 54 are members made of a thin plate and having low bending rigidity. The upper end face and the lower end face of the sub piston 30 have annular grooves 5 respectively.
8 and 60 are provided. Leaf valves 50 and 5
4 are disposed so as to close the annular grooves 58 and 60, respectively. The sub-piston 30 also has a through passage 62 that communicates the inner space of the annular groove 58 with the middle chamber 36,
In addition, a through passage 64 that communicates the internal space of the annular groove 60 with the upper chamber 34 is provided.

The leaf valve 50 opens by flexing and deforming when the hydraulic pressure of the middle chamber 36 becomes higher than the hydraulic pressure of the upper chamber 34 by a predetermined valve opening pressure P _1. The flow of the working fluid from 36 toward the upper chamber 34 is allowed. Further, the leaf valve 54 is opened by resiliently deformed when compared to the hydraulic pressure of the upper chamber 34 of the hydraulic pressure medium chamber 36 reaches a predetermined valve opening pressure P ₂ only high pressure, the upper chamber 34 To the middle chamber 36 from the working fluid.

A piston ring 66 is mounted on the outer periphery of the sub piston 30. The seal between the sub-piston 30 and the inner cylinder 20 is ensured by the piston ring 66. On the outer periphery of the small diameter portion 16b of the piston rod 16, further below the leaf sheet 56, in order from the upper side,
The passage member 68, the leaf seat 70, the spacer 72, the spring seat 74, and the spacer 76 are fitted.

The communication member 68 has a communication passage 77 penetrating in the radial direction and communicating with the communication passage 47 of the adjustment rod 42. A spring seat 78 is fitted on the outer periphery of the spacer 76 so as to be slidable in the axial direction. A spring 80 is provided between the spring seat 74 and the spring seat 78. On the outer periphery of the small diameter portion 16b of the piston rod 16, further below the sleeve 76,
In order from the top, the leaf valve 82, the main piston 3
2, and the leaf valve 86 is fitted. A plurality of seat surfaces 92 are provided on the upper end surface of the main piston 32. Also, on the lower end surface of the main piston 32,
A plurality of sheet surfaces 94 are provided at positions not corresponding to the sheet surface 92. The leaf valves 82 and 86 are members formed by stacking a plurality of thin plate members,
2 and 94 are arranged so as to contact the top surfaces. A piston ring 95 is provided on the outer periphery of the main piston 32.
Is installed. The seal between the main piston 32 and the inner cylinder 20 is ensured by the piston ring 95.

The main piston 32 is also provided with through passages 96 and 98 penetrating in the axial direction.
The through-passage 96 is configured to open at a concave portion between the seat surfaces 92 at an upper end thereof, and to open at a top surface of the seat surface 94 at a lower end thereof. In addition, the through passage 9
Numeral 8 is configured to open at the top of the seat surface 92 at its upper end and to open into the recess between the seat surfaces 94 at its lower end.

A first orifice (see FIG. 4) for connecting the through passage 98 to the middle chamber 36 in a state where the leaf valve 82 is in contact with the seat surface 92 is formed in the thin plate material closest to the main piston 32 constituting the leaf valve 82. (Not shown). A spacer 98 is fitted on the outer periphery of the small diameter portion 16b of the piston rod 16 and further below the leaf valve 86. A screw portion 16c is formed at the lower end of the small diameter portion 16b of the piston rod 16.
A spring seat 100 is screwed to 6c.
A spring seat 102 is fitted on the outer periphery of the sleeve 98 so as to be slidable in the axial direction. Spring seat 10
2 and the spring seat 100
4 are provided.

At the lower end of the small diameter portion 16b of the piston rod 16, a screw 105 for closing the passage 40 is mounted. Therefore, communication between the passage 40 and the lower chamber 38 is interrupted, and the passage 40 communicates only with the upper chamber 34 and the middle chamber 36. The above member arranged on the outer periphery of the small diameter portion 16b of the piston rod 16 is
By being pressed toward the step surface at the boundary between the large diameter portion 16a and the small diameter portion 16b, it is integrally fixed to the piston rod 16.

The leaf valves 82 and 86 are respectively
The urging force of the springs 80 and 104 presses the main piston 32 toward the top surfaces of the seat surfaces 92 and 94. Leaf valve 82, by fluid pressure in the lower chamber 38 when a predetermined valve opening pressure P ₃ or more high pressure than the fluid pressure in the middle chamber 36, upward deflection deformed against the urging force of the spring 80 The valve is opened to allow the flow of the working fluid from the lower chamber 38 to the middle chamber 36. The leaf valve 86 has a predetermined valve opening pressure P that is higher than the hydraulic pressure of the middle chamber 36 compared to the hydraulic pressure of the lower chamber 38.
_{When the} pressure becomes ₄ or more, the valve opens by flexing and deforming downward against the urging force of the spring 104, and allows the flow of the working fluid from the middle chamber 36 to the lower chamber 38.

In this embodiment, since the leaf valves 50 and 54 are made of low-rigidity thin plate members, their valve opening pressures P ₁ and P ₂ are set to very small values. On the other hand, since the leaf valves 82 and 86 are pressed by the springs 80 and 104, respectively, the valve opening pressures P ₃ and P ₄ are set to relatively large values.

Next, the operation of the shock absorber 10 will be described with reference to FIG. 3 together with FIG. 1 and FIG. FIG.
Indicates a damping force characteristic realized by the shock absorber 10. 3, the horizontal axis represents the displacement speed V of the piston rod 16, and the vertical axis represents the shock absorber 10
Indicates the damping force F generated. In FIG. 3, the direction in which the piston rod 16 retreats from the inner cylinder 20,
That is, the damping force F when displacing in the extension direction is shown as positive.

When the piston rod 16 is displaced in the extension direction, the volume of the upper chamber 34 decreases and the volume of the lower chamber 38 increases. To compensate for these volume changes, working fluid flows from the upper chamber 34 through the middle chamber 36 to the lower chamber 38. Further, when the piston rod 16 retreats from the inner cylinder 20, the volume of the inner cylinder 20 increases. In order to compensate for the increase in the volume of the inner cylinder 20, the working fluid flows from the annular chamber 21 into the lower chamber 38 via the base valve 40.

When the displacement speed V of the piston rod 16 is sufficiently low, the differential pressure between the upper chamber 34 and the middle chamber 36 and the differential pressure between the middle chamber 36 and the lower chamber 38 are small. Both the leaf valve 54 and the leaf valve 86 are kept in a closed state. For this reason, the absorber fluid in the upper chamber 34 is connected to the communication passage 46 of the piston rod 16 and the communication space 4.
4, flows into the intermediate chamber 36 through a flow path (hereinafter, referred to as a bypass path) including the clearance C, the small diameter portion 40b of the path 40, the communication path 47, and the communication path 77 of the path member 68. The absorber fluid in the middle chamber 36 flows into the lower chamber 38 through the through passage 96 of the main piston 32 and the second orifice.

In this case, when the working fluid flows through the bypass passage and the second orifice, a damping force is generated due to the flow resistance. Damping force F the shock absorber 10 is exerted, the damping force F _a that the working fluid is generated in accordance with the flow resistance R ₁ when flowing from the upper chamber 34 into the middle chamber 36,
Consisting working fluid medium chamber 36 and the sum of the damping force F _b generated in accordance with the flow resistance R ₂ at the time of flowing into the lower chamber 38. Thus, as indicated at A ₁ in FIG. 3, the damping force F rises in large gradient with increasing displacement velocity V.

When the flow resistance R ₁ when the working fluid flows from the upper chamber 34 to the middle chamber 36 increases, the upper chamber 34 and the middle chamber 36
And the pressure difference between them rises. Further, when the flow resistance R ₂ when the working fluid flows from the middle chamber 36 to the lower chamber 38 increases,
The pressure difference between the middle chamber 36 and the lower chamber 38 increases. And
Until the pressure difference between the upper chamber 34 and Chushitsu 36 reaches the valve opening pressure P ₂ of the leaf valve 54, the displacement speed V is increased, the leaf valve 54 is opened. Hereinafter, the displacement speed V of the piston rod 16 when the leaf valve 54 opens, and
The damping force F generated by the shock absorber 10 is referred to as a first valve opening speed V ₁ and a first valve opening damping force F ₁ , respectively. As described above, in the present embodiment, the first opening damping force F ₁ is very small value, for example, such that a 3 to 5 kgf, and the valve opening pressure P ₂ of the leaf valve 54 is set sufficiently small I have. Thus, the valve opening pressure P of the leaf valve 54
_{If 2} is set, the first opening speed V ₁ was 0.02 m /
s or less.

When the leaf valve 54 is opened, the upper chamber 34
The movement of the fluid from the inner chamber 36 to the inner chamber 36 is performed through the through passage 64 together with the bypass passage. For this reason,
The working fluid flow resistance R ₁ when flowing toward the upper chamber 34 into the middle chamber 36 is reduced. Then, as the flow resistance R ₁ decreases, as shown by reference numeral A _{2 in} FIG. 3, in the region where the displacement speed V exceeds the first valve opening speed V ₁ , the damping force F
Increase slope decreases.

The displacement speed V is further increased, the differential pressure between the middle chamber 36 and lower chamber 38 reaches the valve opening pressure P ₄ of the leaf valve 86, the leaf valve 86 is opened. Hereinafter, the displacement speed V and the damping force F when the leaf valve 86 is opened are referred to as the second valve opening speed V ₂ and the second valve opening damping force F _{2, respectively.}
Called. In the present embodiment, as the second valve opening damping force F ₂ is, for example, about 50 kgf, the leaf valve 86
It has set the valve opening pressure P _2. In this case, the second opening speed V ₂ is a value of about 0.2 m / s.

When the leaf valve 86 is opened, the middle chamber 36
By increasing the flow passage area of the flow passage from the lower chamber 38 to the lower chamber 38,
Flow resistance R ₂ when flowing toward the lower chamber 38 from the working fluid medium chamber 36 is reduced. Therefore, code A ₃ in FIG. 3
As shown, the displacement velocity V is in the region above the second opening speed V _2, the increase gradient of the damping force F is further reduced. on the other hand,
When the piston rod 16 is displaced in the direction in which it enters the inner cylinder 20, that is, in the contraction direction, the volume of the upper chamber 34 increases and the volume of the lower chamber 38 decreases. To compensate for these volume changes, the working fluid is
It flows into the upper chamber 34 via the middle chamber 36. In addition, as the piston rod 16 enters the inner cylinder 20, the volume of the inner cylinder 20 decreases. In order to compensate for such a decrease in the volume of the inner cylinder 20, the working fluid flows out from the lower chamber 38 to the annular chamber 21 via the base valve 40.

In this embodiment, when the leaf valve 50 is opened.
Valve pressure P₁Is the valve opening pressure P of the leaf valve 54_TwoAlmost matches
It is provided to be. Therefore, the displacement speed V
1 Valve opening speed V₁V approximately equal to₁And the damping force F
1 Valve opening damping force F₁F approximately equal to₁At the time
The leaf valve 54 opens. In addition, the leaf valve 82
Valve opening pressure P_ThreeIs the valve opening pressure P of the leaf valve 86_FourCompared to
It is provided to be slightly smaller. Because of this, the displacement
The speed V is equal to the second valve opening speed V_TwoLess v_Two(For example, 0.
15 m / s), and the damping force F becomes the second valve opening damping force F
_TwoLess than f _Two(For example, about 30kgf)
At this point, leaf valve 82 opens. In the following, Lee
Piston rod 1 when valves 50 and 82 open
V, the displacement speed of 6.₁And v_Two, Also the first open
Referred to as a valve speed and a second valve opening speed.
F and 0 are damping forces F when the valve is opened.₁And f_Two
Respectively, the first valve opening damping force and the second valve opening damping force.
Called.

Accordingly, even when the piston rod 16 is displaced in the contracting direction, similarly to the case where the piston rod 16 is displaced in the extending direction, the displacement speed V of the piston rod 16 reaches the first valve opening speed v _1. , as shown by reference numeral B ₁ in FIG. 3, the damping force F rises relatively large gradient. When the displacement speed V reaches the first opening speed v _1, by the leaf valve 50 is opened, as shown by reference numeral B ₂ in FIG. 3, an increase gradient of the damping force F is reduced. Further, when the displacement speed V reaches the second valve opening speed v ₂ , the leaf valve 86 is opened, and the symbol B in FIG.
_As indicated by ₃ , the increasing gradient of the damping force F further decreases.

As described above, according to the shock absorber 10 of the present embodiment, the displacement speed V of the piston rod 16 is
From an extremely low speed range (a region where the first valve opening speed V ₁ , v ₁ or less)
To a low speed region (a region between the first valve opening speeds V ₁ and v ₁ and the second valve opening speeds V ₂ and v ₂ ) and further to a high speed region (a region exceeding the second valve opening speeds V ₂ and v ₂ ). , The damping force characteristic such that the increasing gradient of the damping force F decreases sequentially is realized.

Incidentally, the opening degree of the bypass passage changes according to the size of the clearance C. As the opening degree of the bypass passage increases, the flow resistance of the working fluid flowing through the bypass passage decreases. When the flow resistance when flowing through the bypass passage decreases, the differential pressure between the upper chamber 34 and the middle chamber 36 generated for a constant displacement speed V decreases. Therefore, when the clearance C increases, the upper chamber 34 and the middle chamber 3
6, the displacement speed V at which the differential pressure between the pressures V.6 and V.6 becomes equal to the valve opening pressures P ₁ and P ₂ of the leaf valves 50 and 54, that is,
The first valve opening speeds V ₁ and v ₁ increase.

On the other hand, the damping force generated as the working fluid moves between the upper chamber 34 and the middle chamber 36 has a magnitude corresponding to the pressure difference between the upper chamber 34 and the middle chamber 36. The leaf valves 50 and 54 open when the differential pressure between the upper chamber 34 and the middle chamber 36 reaches the valve opening pressures P ₁ and P ₂ irrespective of the degree of opening of the bypass passage. Therefore, even if the clearance C changes, the first valve opening damping forces F ₁ and f ₁ do not change.

As described above, when the clearance C increases, the first valve opening speeds V ₁ and v ₁ increase, while the first valve opening damping forces F ₁ and f ₁ are kept constant. For this reason, when the clearance C increases, the displacement velocity V becomes the first as shown by the broken lines with a ₁ and b ₁ in FIG.
In the region where the valve opening speeds are V ₁ and v ₁ or less, the gradient of the damping force characteristic becomes small.

As the clearance C increases, the first valve opening speed
Degree V₁, V₁Rises, the symbol a in FIG._Two, A_Three
And b_Two, B_ThreeAs shown by the broken line
Means that the displacement speed V is equal to the first valve opening speed V₁, V₁In the above area
The first valve opening speed V₁, V ₁Only in proportion to the increase
It has shifted in the positive direction. However, as mentioned above,
First valve opening speed V₁, V₁Is the second valve opening speed V_Two, V_TwoTo
The value is set to a sufficiently small value. Therefore, the first
Valve opening speed V₁, V₁Is changed by the second opening
Valve speed V_Two, V_TwoNegligibly small for
2 Valve opening speed V_Two, V_TwoThe damping force characteristics in the region near
And has little effect.

As described above, in this embodiment, by adjusting the clearance C, the damping force in the region where the displacement speed V of the piston rod 16 is higher than the second valve opening speeds V ₂ , v ₂ , that is, in the high speed region. The first valve opening speeds V ₁ and v ₁ can be changed while maintaining the characteristics substantially constant. As described above, the first valve opening speeds V ₁ and v ₁ are 0.02 m
/ S or less. Therefore, according to the shock absorber 10 of the present embodiment, by changing the clearance C, only the damping force characteristic in the ultra-low speed range of 0.02 m / s or less is not affected without affecting the damping force characteristic in the high speed range. Can be adjusted.

According to an experiment conducted by the present inventor using the shock absorber 10 of the present embodiment, the ride comfort and the steering stability of the vehicle greatly change depending on the damping force characteristics in a very low speed range. I know. For example, when the clearance C is decreased to increase the gradient of the damping force characteristic in the ultra-low speed range, the steering assist force at the time of cornering increases, and the feeling of steering response increases. In addition, the responsiveness of the rolling speed of the vehicle during turning and the responsiveness of the yawing change of the vehicle during steering are sensitive to changes in the damping force characteristics in a very low speed range. Therefore, according to the shock absorber 10 of the present embodiment, by adjusting the clearance C and changing the damping force characteristic in the ultra-low speed range, it is possible to obtain more optimal riding comfort and steering stability.

As described above, the adjustment of the clearance C by the adjusting rod 42 can be performed by rotating the adjusting rod 42 from above the piston rod 16. Therefore, according to the present embodiment, it is possible to easily adjust the damping force characteristics without disassembling the shock absorber 10 in a state where the shock absorber 10 is mounted on the vehicle.

In the above embodiment, the adjustment of the adjusting rod 42 is performed manually.
2 may be driven by a motor. Adjustment rod 4
When the motor drive unit 2 is configured to be driven by a motor, the driver can adjust the damping force characteristics from the vehicle interior by providing the motor operation unit in the vehicle interior. Therefore, according to such a configuration, it is possible to realize more appropriate damping force characteristics according to the driver's preference.

In the above embodiment, the through passage 9
6 and 98 are provided with the leaf valve 8 in the first flow path.
6 and 92 are provided in the first valve mechanism.
And 64 are provided in the above-mentioned second flow path,
Reference numeral 4 corresponds to the above-described second valve mechanism, and the adjustment rod 42 corresponds to the above-described opening adjustment means.

[0053]

As described above, according to the shock absorber according to the present invention, the damping force characteristic can be adjusted in a region where the displacement speed of the piston rod is low.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a shock absorber that is an embodiment of the present invention.

FIG. 2 is an enlarged view of a sub-piston, a main piston, and peripheral portions shown in FIG.

FIG. 3 is a diagram showing damping force characteristics realized by the shock absorber of the present embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Shock absorber 30 Sub piston 32 Main piston 40 Passage 42 Adjustment rod 46, 47, 77 Communication passage 50, 54, 82, 86 Leaf valve 64, 66, 96, 98 Through passage

Claims (1)

[Claims] A main piston connected to a piston rod and slidably disposed in a cylinder; a sub-piston connected to the piston rod and slidably disposed in the cylinder; A first flow path axially penetrating the main piston;
A first valve that is provided in the first flow path and opens at a first valve opening pressure;
And a first valve mechanism in a state where the valve mechanism is closed.
A first damping force generating mechanism including an orifice for conducting the flow path of the first piston, a second flow path penetrating the sub-piston in the axial direction, and a first opening provided in the second flow path. A second damping force generating mechanism including a second valve mechanism that opens with a second valve opening pressure smaller than the valve pressure, a bypass passage that bypasses the second flow path, and the bypass passage And an opening adjusting means for adjusting the opening of the shock absorber.