JPH11166573A - Shock absorber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a damping force characteristic in a very low speed area of piston speed, substantially a linar characteristic. SOLUTION: A shock absorber has a damping force generating valve 30 provided at a piston 18 on the side of a cylinder lower chamber 22 and imparting flow resistance to oil flowing from a cylinder upper chamber 20 to the cylinder lower chamber 22 through a communicating passage 34, so as to generate damping force. The dampinng force generating valve 30 comprises a valve plate 42 arranged in contact with the piston 18 and having a cutout part 66 communicated with the communicating passage 34, a valve plate 44 arranged in contact with the valve plate 42 and having a cutout part 68 at the outer peripheral part, and a valve plate 46 arranged in contact with the valve plate 44. The cutout parts partition an orifice passage 70, and the height H, width W and length L of the orifice passage 70 are set to the values making a damping force characteristic in a very low speed area of piston speed, substantially a linar characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shock absorber incorporated in a suspension of a vehicle such as an automobile, and more particularly, to a shock absorber having excellent damping force characteristics in a very low speed range.

[0002]

2. Description of the Related Art In general, a shock absorber generally includes a cylinder, a piston which reciprocates with the cylinder and cooperates with the cylinder to define two cylinder chambers, and two cylinder chambers formed in the piston. It has a communication passage for communication and a damping force generating valve provided in the piston and cooperating with the communication passage to generate a damping force.

As one of the damping force generating valves of a shock absorber, for example, as described in Japanese Utility Model Laid-Open Publication No. 63-178646, a first cutout portion having a cutout disposed in contact with a piston and communicating with a communication passage is provided. Including a valve plate, a second valve plate disposed in contact with the first valve plate and having a notch in the outer peripheral portion, and a third valve plate disposed in contact with the second valve plate A damping force generating valve is known in which the notch cooperates with the first and third valve plates to define an orifice passage connecting and connecting the cutout and the corresponding cylinder chamber.

According to the shock absorber having the damping force generating valve, the orifice passage is defined by the notch provided in the second valve plate cooperating with the first and third valve plates. Since the second valve plate does not contact the land of the piston, the shock absorber can be used for a long period of time compared to the structure in which the valve plate defining the orifice passage contacts the land of the piston. It is possible to avoid a change in the effective cross-sectional area of the orifice passage due to abrasion of the valve plate and the like, and to generate an appropriate damping force for a long period of time.

[0005]

However, in the shock absorber described in the above-mentioned publication, what is the optimum value of the width, height and length of the orifice passage is completely taken into consideration. Therefore, the damping force characteristic in the very low speed range of the piston speed becomes a squared characteristic with respect to the piston speed as in the case of many other shock absorbers. Not enough.

In addition, the communication passages for the extension stroke and the contraction stroke connecting the two cylinder chambers communicate with each other at substantially the same radial distance from the axis of the piston. In the shock absorber formed in (1), when the valve plate of the damping force generating valve comprises the first to third valve plates as described in the above-mentioned Japanese Utility Model Application Laid-Open No. 63-178646, As will be described in detail later, a cutout communicating with one of the communication passages must be formed near the inner peripheral edge of the first valve plate.

[0007] Therefore, the radial depth of the notch formed in the second valve plate must be very large, so that the second valve plate is fragile and its durability tends to be reduced. When the barrel processing is performed to improve the durability of the second valve plate, the valve plates are entangled with each other,
Since the valve plate is easily bent, the rotation speed of the barrel processing cannot be increased, and it is difficult to improve the productivity of the second valve plate.

[0008] The present invention has been made in view of the above-mentioned problems in the conventional shock absorber as described above,
A main object of the present invention is to optimize the width, height and length of the orifice passage so that the damping force characteristic in a very low speed range of the piston speed is made substantially linear.

Another main object of the present invention is that the communication passages, particularly for the extension stroke and the contraction stroke, are circumferentially spaced from each other at substantially the same radial distance from the axis of the piston. In the shock absorber formed in the piston in the state, the damping force characteristic in a very low speed range of the piston speed is made substantially linear, and the durability and productivity of the valve plate having the notch portion are improved. It is to improve.

[0010]

SUMMARY OF THE INVENTION According to the present invention, there is provided, in accordance with the present invention, a construction as set forth in claim 1, i.e., a cylinder and a cylinder which is reciprocally fitted into the cylinder and cooperates with the cylinder. A piston defining one cylinder chamber, a communication passage formed in the piston for communicating the two cylinder chambers, and the communication passage provided on the piston on at least one side of the two cylinder chambers. A damping force generating valve that generates a damping force by giving a flow resistance to the working fluid flowing between the two cylinder chambers, and wherein the damping force generating valve is disposed in contact with the piston and the communication passage. A first valve plate having a cut-out portion communicating with the first valve plate, a second valve plate having a cut-out portion on an outer peripheral portion disposed in contact with the first valve plate, and a second valve plate in contact with the second valve plate; Placed A cut-off portion cooperating with the first and third valve plates to define an orifice passage connecting and connecting the cut-out portion and a corresponding cylinder chamber. The orifice passage has a height H, a width W, and a length L that are substantially the same as the thickness of the second valve plate, wherein the height H, the width W, and the length L are minute piston speeds. This is achieved by a shock absorber characterized in that the damping force characteristic in the low-speed range is set to a value that results in a substantially linear characteristic.

According to the present invention, another main object is to provide a structure according to claim 2, namely, a cylinder and two cylinder chambers which are fitted reciprocally in the cylinder and cooperate with the cylinder. A piston defining the piston and an extending stroke formed on the piston at a position substantially at the same radial distance from the axis of the piston and spaced apart from each other in the circumferential direction to communicate and connect the two cylinder chambers. Between the two cylinder chambers via one of the communication passages for the extension stroke and the contraction stroke provided on the piston on at least one side of the two cylinder chambers. A damping force generating valve for generating a damping force by applying a flow resistance to the flowing working fluid, wherein the damping force generating valve is disposed in contact with the piston and communicates with the one communication passage. Department A first valve plate having a second valve plate having a second cutout portion disposed in contact with the first valve plate and communicating with the first cutout portion; A third valve plate that is disposed in contact with the outer peripheral portion and has a cutout portion, and a fourth valve plate that is disposed in contact with the third valve plate, wherein the second cutout portion is The notch extends radially outward with respect to the axis from the first cutout, and the notch cooperates with the second and fourth valve plates to correspond to the cylinder chamber corresponding to the second cutout. And an orifice passage communicating therewith, said orifice passage having a height H, a width W and a length L substantially equal to the thickness of said third valve plate; H, the width W, and the length L are damping force characteristics at a very low piston speed range. There is achieved by a shock absorber, characterized in that it is set to a value that causes a characteristic of the substantially linear.

According to the first and second aspects of the present invention, the height H, width W, and length L of the orifice passage have substantially linear damping force characteristics in a very low piston speed range. Since it is set to a certain value, it is possible to secure sufficient damping force in the very low speed range of the piston speed while avoiding excessive damping force in the medium and high speed range of the piston speed Become.

[0013] In particular, according to the second aspect of the present invention, the second cutout communicates with the first cutout communicating with one of the communication passages, and the second cutout is higher than the first cutout. The notch extends radially outward with respect to the axis of the piston, and the notch cooperates with the second and fourth valve plates to define an orifice passage communicating the second cutout and the corresponding cylinder chamber. Therefore, the radial depth of the cutout portion may be a depth communicating with the second cutout portion.

Therefore, the depth of the notch can be smaller than that required in the case of a structure in which the notch directly communicates with the first cutout without providing the second valve plate. Avoids the weakness of the third valve plate due to the excessively deep part, which reduces its durability, and reduces the possibility of the valve plates becoming entangled during barrel processing. This makes it possible to increase the rotational speed of the barrel processing and improve the productivity of the third valve plate.

[0015]

In general, the flow rate of a viscous liquid such as oil used in a shock absorber is set to Q.
[Mm ³ / sec], the density is ρ [kg / mm ³ ], the kinematic viscosity is ν [mm ² / sec], and the height of the orifice passage is H
[Mm], the width is W [mm], and the length is L [mm], the differential pressure ΔP [kg / mm ² ] generated before and after the viscous liquid passes through the orifice passage when passing through the orifice passage , From Bernoulli's theorem.

ΔP = 12ρ (ν / W) (L / H ³ ) Q + 0.
6ρ {Q / (WH)} ²

In the above equation (1), the first term on the right side is a differential pressure generated by the wall resistance, the second term is a differential pressure generated by the flow velocity, and the former is a first-order term of the flow rate Q. On the other hand, the latter is a square term of the flow rate Q. Therefore, in order to make the pressure difference ΔP as large as possible to the first power of the flow rate Q, the first term must be dominant over the second term, that is, the following inequality expression 2 must be satisfied.

## EQU2 ## 12ρ (ν / W) (L / H ³ ) Q> 0.6ρ
{Q / (WH)} ²

By modifying the above equation (2), the following equation (3) is obtained.

L> (0.05Q / ν) (H / W)

The flow rate Q in the above equation (3) changes according to the piston speed of the shock absorber, and the kinematic viscosity ν changes according to the type of viscous liquid used in the shock absorber and the use condition of the shock absorber. Q is the flow rate when the piston speed of the shock absorber is 0.02 [m / sec], which is a typical value in the very low speed range, and the kinematic viscosity ν is used when a specific viscous liquid is used under standard conditions. In this case, the value of 0.05 Q / ν in Equation 3 can be replaced with a positive constant K. Therefore, Equation 3 can be rewritten as Equation 4 below. If the length L, height H, and width W of the orifice passage are set so as to be established, the damping force characteristic of the shock absorber in a very low piston speed range can be made as linear as possible.

L> KH / W

Therefore, according to a preferred aspect of the present invention, in the configuration of the first or second aspect, the length L, the height H, and the width W of the orifice passage are set so as to satisfy the relationship of the above equation (4). (Preferred embodiment 1).

According to another preferred embodiment of the present invention, in the configuration of the preferred embodiment 1, the piston speed of the shock absorber is 0.02 [m / sec] as a representative value in a very low speed range. The flow rate of the working fluid of the shock absorber passing through the orifice passage at a certain time is Qo [mm
³ / sec], and the kinematic viscosity of the working liquid under standard operating conditions of the shock absorber is νo [mm ² / sec], and K in the above formula 4 is configured to be 0.05 Qo / νo. (Preferred embodiment 2).

According to another preferred aspect of the present invention, in the above-described configuration of the first aspect, the first to third valve plates are configured to have substantially the same outer diameter (preferably). Aspect 3).

According to another preferred embodiment of the present invention, in the configuration of the first aspect, a plurality of communication passages are provided so as to be spaced from each other around the axis of the piston, and the cutout portion is provided. Is configured to extend substantially C-shaped about the axis of the piston (preferred embodiment 4).

According to another preferred embodiment of the present invention, in the configuration of the second aspect, the first to fourth valve plates are configured to have substantially the same outer diameter (preferred). Aspect 5).

According to another preferred embodiment of the present invention, in the configuration of the above-mentioned claim 2, a plurality of communication passages are provided for the extension stroke and the contraction stroke, respectively, and the first cutout portion is a piston. (A preferred embodiment 6).

According to another preferred embodiment of the present invention, in the configuration of the above-mentioned preferred embodiment 6, at least one of the first and second cutouts has a substantially C shape around the axis of the piston. It is configured to extend (preferred mode 7).

[0026]

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail with reference to the accompanying drawings, in which several preferred embodiments are shown.

FIG. 1 is a partial longitudinal sectional view showing a main part of a first embodiment of a shock absorber according to the present invention configured as a twin tube type shock absorber, and FIG. 2 is a first embodiment shown in FIG. It is a top view which shows the 1st valve plate (A) of a form, the 2nd valve plate (B), and the 3rd valve plate (C).

In FIG. 1, reference numerals 10 and 12 denote inner and outer cylinders extending concentrically along an axis 14, both ends of which are closed by end caps (not shown). Have been. The cylinders 10, 12 and the end cap cooperate with each other to define an annular chamber 16. A piston 18 is arranged in the inner cylinder 10 so as to be able to reciprocate along the axis 14. A piston 18 separates the interior of the inner cylinder 10 into an upper cylinder chamber 20 and a lower cylinder chamber 22, and is integrally connected to the main body and extends along the axis 14 through the end cap at the upper end. And a piston rod 26. The piston body 24 is the nut 2
The piston body 24 is fixed to the distal end of the piston rod 26, and the piston body 24 is provided with a damping force generating valve 30 for an extension stroke and a damping force generating valve 32 for a contraction stroke having a known structure, which are constructed according to the present invention. Is provided.

Although not shown in FIG. 1, a base valve assembly is provided below the inner cylinder 10, and each of the base valve assemblies has a damping force generating valve 30 for an extension stroke. Force generating valve 32 for compression and contraction
A damping force generating valve for a contraction stroke and a damping force generating valve for an extension stroke, which are configured in the same manner as described above, are provided. The cylinder upper chamber 20, the cylinder lower chamber 22, and a part of the annular chamber 16 are filled with oil as a working liquid, and the upper part of the annular chamber 16 is filled with high-pressure gas. Although not shown in FIG. 1, the upper end of the piston rod 26 is connected to a vehicle body as a sprung body, and the outer cylinder 12 or the end cap at the lower end is connected to a suspension member as a unsprung body not shown in the figure. It is supposed to be.

The piston body 24 is equally spaced around the axis 14 from the cylinder upper chamber 20 and the cylinder lower chamber 2.
2 and a plurality of communication passages 34 for the extension stroke connecting and connecting
And a plurality of communication passages 36 for the contraction stroke are formed, and the communication passages 36 for the contraction stroke are located radially outwardly of the communication passages 34 for the extension stroke and between the communication passages 34 in the circumferential direction. Position. The upper and lower surfaces of the piston main body 24 are provided with annular ports 38A and 38B communicating with the upper and lower ends of the communication passage 34 and extending annularly around the axis 14, respectively. An annular port 40 </ b> A is provided which communicates with the upper end of the passage 36 and extends annularly around the axis 14.

The damping force generating valve 30 for the extension stroke has a first valve plate 42 disposed in contact with the piston body 24 on the side of the cylinder lower chamber 22 and a first valve plate 42 disposed in contact with the valve plate 42. It includes a second valve plate 44 and a third valve plate 46 disposed in contact with the valve plate 44. In the illustrated embodiment, the first through third valve plates 42-46 have substantially the same outer diameter and thickness H as one another.
And has a hole that fits into the lower end of the piston rod 26 and is fixed to the piston body 24 by a nut 28 via a spacer 48.

Also, the first to third valve plates 42 to 46
Is formed of an elastically deformable material, and a compression coil spring 52 is elastically mounted between a spring seat member 50 fitted to the nut 28 so as to be able to reciprocate along the axis 14 and a spring seat portion 28A of the nut 28. Thus, the first to third valve plates are biased to the illustrated valve closing position where the first valve plate 42 contacts the lower surface of the piston body 24.

On the other hand, the damping force generating valve 32 for the contraction stroke includes a valve plate 54 disposed in contact with the piston main body 24 on the side of the upper cylinder chamber 20, and the valve plate 54 is formed by the cylinder upper chamber 20 and the annular port 38A. Are connected to each other. A disc spring 62 is clamped between a stopper 58 disposed in contact with the shoulder of the piston rod 26 and a spacer 60 disposed in contact with the valve plate 54, and the disc spring 62 is disposed radially outward. A plurality of arm portions extending to the upper surface of the piston main body 24, the valve plate abutting against the upper surface of the piston body 24 at the arm portions to cut off the communication between the cylinder upper chamber 20 and the communication passage 36. It is biased to the valve closing position.

In the first embodiment shown in FIG.
As shown in detail in (A), the first valve plate 42 of the damping force generating valve 30 for the extension stroke has a cutout 66 extending annularly around the axis 14 so as to be substantially C-shaped. have. The cutout portion 66 is provided at a radial position that is always in communication with the annular port 38B so that oil can freely flow, and the outer peripheral edge of the cutout portion 66 is radially inward from the outer peripheral edge of the valve plate 42 by a distance L. Are spaced apart.

As also shown in detail in FIG. 2B, the second valve plate 44 has three notches 68 equally spaced about the axis 14. Each notch 68 has an arcuate portion 68A extending in an arc around the axis 14 and an inner end connected to the arcuate portion 68A and having a substantially outer diameter opening at the outer end to the outer peripheral edge of the valve plate 44. And a linear portion 68B extending in the direction. The arc portion 68A is provided at a radial position overlapping the cutout portion 66 so that oil can freely flow, and the outer peripheral edge of the arc portion 68A is spaced radially inward by a distance L from the outer peripheral edge of the valve plate 44. The straight portion 68B has a width W.

As shown in detail in FIG. 2C, the third valve plate 46 includes a cutout 66 and a cutout 6.
It does not have a cutout portion or a notch portion as shown in FIG. Therefore, as shown in detail in FIGS.
Is a cutout portion 66 even when the damping force generating valve 30 is closed.
And the lower cylinder 22 in communication with each other.
Linear portion 68B cooperates with the first valve plate 42 and the third valve plate 46 to define an orifice passage 70 having a length L, a height H, and a width W.

The length L [mm], the height H [mm], and the width W [mm] of the orifice passage 70 are 0.02 [m / sec] as a representative value of the piston speed in a very low speed range. When the flow rate of the oil passing through the orifice passage 70 is Qo [mm ³
/ Sec], and the kinematic viscosity of the oil under standard operating conditions of the shock absorber is νo [mm ² / sec].

L> (0.05Qo / νo) (H / W)

In the extension stroke of the first embodiment configured as described above, that is, in the stroke in which the piston 18 moves relatively upward with respect to the inner cylinder 10, the cylinder upper chamber 2
As the pressure in the cylinder upper chamber 20 increases, the pressure in the cylinder lower chamber 22 decreases, and due to the pressure difference between the cylinder upper chamber 20 and the cylinder lower chamber 22, the oil in the cylinder upper chamber becomes the damping force generating valve 3.
It tries to move to the lower chamber of the cylinder via 0.

In this case, in a very low speed range where the piston speed is smaller than a predetermined value, the valve plate force is smaller than the valve opening force on the damping force generating valve 30 due to the pressure difference between the upper cylinder chamber 20 and the lower cylinder chamber 22. Since the sum of the spring force of the elasticity of 42 to 46 and the spring force of the compression coil spring 52 is higher, the damping force generating valve 30 is maintained in the closed state. Therefore, the oil in the cylinder upper chamber 20 flows into the communication passage 34 through the hole 56 and the annular port 38A, and also flows into the cylinder lower chamber 22 from the communication passage 34 through the annular port 38B, the cutout 66, and the notch 68. .

Accordingly, a damping force is generated by the flow resistance when the oil passes through the orifice passage 70, and the damping force characteristic is substantially linear as shown by the straight line of the characteristic curve shown by the solid line in FIG. Thus, a sufficient damping force can be secured even in a very low speed range of the piston speed Vp.

In FIG. 4, the characteristic curve shown by the broken line shows the characteristic of a conventional general shock absorber.
The characteristic curve indicated by the dashed line indicates the characteristic of a conventional shock absorber of the type in which the damping force generating valve opens even in the very low speed range of the piston speed Vp. In the case of the former shock absorber, the damping force characteristic in a very low speed region of the piston speed Vp is a characteristic of the square of the piston speed, and the damping force in the very low speed region tends to be insufficient. In the case of the latter shock absorber, the damping force characteristic is a characteristic of 0.6 to the piston speed over the entire region of the piston speed Vp, and the damping force in the very low speed region tends to be excessive.

On the other hand, according to the first embodiment shown in the drawings, the damping force characteristic in the very low speed range of the piston speed Vp is substantially linear, so that the damping force in the middle and high speed range is small. While avoiding excess or shortage,
It is possible to optimize the damping force in a very low piston speed range.

In the middle / high speed range where the piston speed is higher than a predetermined value, the cylinder upper chamber 20 and the cylinder lower chamber 22
Is higher than the sum of the spring force due to the elasticity of the valve plates 42 to 46 and the spring force of the compression coil spring 52, and the damping force generation valve 30 is opened. Therefore, the oil in the cylinder upper chamber 20 can pass not only through the orifice passage 70 but also through the damping force generating valve 30 in the open state, and mainly the oil is supplied to the damping force generating valve 30 in the open state.
A damping force is generated by the flow resistance when passing through the piston, so that the damping force characteristic in the medium to high speed region of the piston speed Vp becomes a characteristic as shown by a solid curve in FIG. The rate of increase of the damping force with the increase in speed becomes smaller than in the case of a very low speed range.

In the contraction stroke in which the piston 18 moves relatively downward with respect to the inner cylinder 10, the base is not shown in the drawing at any of the very low speed range and the middle high speed range of the piston speed. The damping force is generated by the damping force generating valve for the contraction stroke of the valve assembly in the same manner as the damping force generating valve 30.

FIG. 5 is a partial longitudinal sectional view showing a main part of a second embodiment of a shock absorber according to the present invention configured as a twin tube type shock absorber, and FIG. 6 is a part taken along line VI-VI of FIG. It is a plane sectional view. In FIGS. 5 and 6, members corresponding to those shown in FIG.
Are given the same reference numerals as in FIG.

Also in the second embodiment, the piston body 24 has a plurality of extending strokes equally spaced around the axis 14 for connecting the upper cylinder chamber 20 and the lower cylinder chamber 22 to each other. A plurality of communication passages 34 and a plurality of communication passages 36 for a contraction stroke are formed. As can be seen from FIG. 6, the communication passages 34 and 36 are formed at substantially the same radial distance from the axis 14. ing.

In particular, in the illustrated second embodiment, four communication passages 34 and 36 are respectively formed, and the annular ports 38B and 4 at the lower ends of these communication passages are formed.
OBs are separated from each other by lands 72. The land 72 has an outer circular arc portion 72A extending radially outward from the communication passage 34 in an arc shape and an inner circular arc portion 72B extending radially inward from the communication passage 36 in an arc shape.
And an outer circular arc portion 72A extending substantially linearly in the radial direction.
And a connecting portion 72C connecting the inner circular portion 72B to the inner circular portion 72B.

Further, the damping force generating valve 30 for the extension stroke is disposed on the side of the cylinder lower chamber 22 in contact with the piston body 24, and is disposed in contact with the valve plate 74. The second valve plate 76 and the valve plate 7
6 and a fourth valve plate 80 abutting against the valve plate 78
And Also in the second embodiment shown, the first to fourth valve plates 74 to 80 have substantially the same outer diameter and thickness H as one another, and fit into the lower end of the piston rod 26. Nut 2 through a spacer 48
8 is fixed to the piston main body 24.

The first to fourth valve plates 74 to 80
Is formed of an elastically deformable material, and a compression coil spring 52 is provided between a spring seat member 50 fitted to the nut 28 so as to reciprocate along the axis 14 and a spring seat portion (28A) of the nut 28. The first to fourth valve plates are biased to the illustrated valve closing position where the first valve plate 74 abuts against the lower surface of the piston main body 24.

A land 73 similar to the land 72 of the damping force generating valve 30 is also provided on the damping force generating valve 32 for the contraction stroke provided on the piston 18. Although not shown in the drawings, the base valve assembly includes a damping force generation valve 32 for a contraction stroke and a damping force generation valve 30 for an extension stroke of this embodiment, respectively. A damping force generating valve and a damping force generating valve for a contraction stroke are provided.

In the second embodiment shown in FIG.
As shown in detail in (A), the first valve plate 74 of the damping force generating valve 30 for the extension stroke extends substantially semi-circularly about the axis 14 near its inner periphery. And a pair of cutouts 82 to be formed. The cutout 82 is provided at a radial position close to the inner peripheral edge of the valve plate 74 so as to always communicate with the annular port 38B.

As shown in detail in FIG. 7 (B), the second valve plate 76 is substantially the same as the first valve plate 42 of the first embodiment.
Has a cut-out portion 84 extending annularly around. The cutout portion 84 has a larger radial width and outer diameter than the cutout portion 82, and is provided at a radial position that is always in communication with the cutout portion 82 so that free flow of oil is possible.
Although the distance between the outer peripheral edge of the cutout portion 84 and the outer peripheral edge of the valve plate 76 is set to be larger than L, this distance may be set to L.

Also, as shown in detail in FIG. 7C, the third valve plates 78 are equally spaced from each other about the axis 14, similarly to the second valve plate 44 of the first embodiment. It has three notched portions 86. Each notch 86 has an arc portion 86A extending in an arc around the axis 14.
And a linear portion 86B that is connected to the arc portion 86A at the inner end and extends substantially in the radial direction so as to open to the outer peripheral edge of the valve plate 78 at the outer end. The arc portion 86A is provided at a radial position overlapping the cutout portion 84 so that oil can flow freely, and the outer peripheral edge of the arc portion 86A is spaced radially inward by a distance L from the outer peripheral edge of the valve plate 78. The straight portion 86B has a width W.

As shown in detail in FIG. 7D, the fourth valve plate 80 has cutouts 84 and 86 and a cutout 86 as in the third plate 46 of the first embodiment.
It does not have a cutout portion or a notch portion as described above. Therefore, as shown in detail in FIGS. 5 and 7, the notch 86 is formed by the cutout 84 even when the damping force generating valve 30 is closed.
86 and the cylinder lower chamber 22 are communicated with each other, and the straight portion 86B of the notch 86 cooperates with the second valve plate 76 and the fourth valve plate 80 to have a length L, a height H, and a width W. Orifice passage 88 is defined.

As in the case of the first embodiment, the length L [mm], the height H [mm], and the width W [mm] of the orifice passage 88.
Indicates that the piston speed is set to 0.
When the flow rate is 02 [m / sec], the flow rate of the oil passing through the orifice passage 88 is Qo [mm ³ / sec], and the kinematic viscosity of the oil under standard operating conditions of the shock absorber is νo [mm ² / Sec] is set to a dimension that satisfies the relationship of Equation 5 above.

Therefore, according to the second embodiment, similarly to the first embodiment, the damping force characteristic becomes the characteristic shown by the solid line in FIG. 4, and particularly, when the piston speed Vp is very low. The characteristic in the region becomes substantially linear as shown by the linear portion of the characteristic curve, and a sufficient damping force is ensured even in a very low speed region of the piston speed Vp.

FIGS. 8A to 8C show that the communication path 34 for the extension stroke and the plurality of communication paths 36 for the contraction stroke are substantially the same as the axis 14 as shown in FIGS. In the shock absorber formed at a position at a radial distance of the first to third embodiments, the damping force generating valve 30 for the extension stroke is constituted by the same three valve plates as in the first embodiment. Shown are third valve plates 42-46.

When the number of valve plates constituting the damping force generating valve 30 is three, the cutout portion 66 is provided close to the inner peripheral edge of the first valve plate 42, so that the arc portion 68A is formed.
The straight portion 68 of the notch 68 communicating with the cutout 66
B must be long, so the second valve plate 4
4 is fragile and its durability is liable to decrease, and when the barrel processing is performed to improve the durability of the second valve plate, the valve plates are entangled with each other and the valve plate is easily bent. The rotation speed of the processing cannot be increased, and it is difficult to improve the productivity of the second valve plate.

On the other hand, according to the illustrated second embodiment, the damping force generating valve 30 is constituted by four valve plates, and the arc portion 86 A of each notch 86 is formed by the second valve plate 76. What is necessary is just to communicate with the cutout part 82 via the cutout part 84, and since the length of the straight part 86B of each notch part 86 may be short, the above-mentioned various problems can be surely solved.

In the above, the present invention has been described in detail with respect to two embodiments. However, the present invention is not limited to these embodiments, and various other embodiments are within the scope of the present invention. It will be apparent to those skilled in the art that forms are possible.

For example, in the above two embodiments, each valve plate has the same outer diameter and thickness, but each valve plate has a different outer diameter or thickness. You may.

The cutout 66 of the first valve plate 42 in the first embodiment and the cutout 84 of the second valve plate 76 in the second embodiment are substantially C
The cutout 82 of the first valve plate 74 in the second embodiment extends substantially annularly around the axis 14 so as to form. However, these cutouts may have any shape as long as they always communicate with the corresponding annular port of the communication passage so that the oil can freely flow.

Although the above two embodiments are configured as twin tube type shock absorbers, the shock absorber of the present invention is provided with a damping force generating valve provided on the piston in both the extension stroke and the contraction stroke. The shock absorber may be configured as a monotube type shock absorber in which a damping force is generated.

[0064]

As apparent from the above description, according to the first and second aspects of the present invention, the damping force characteristic in a very low speed range of the piston speed is made substantially linear. As a result, it is possible to secure a sufficient damping force in a very low speed range of the piston speed while avoiding an excessive damping force in the medium speed region of the piston speed.

In particular, according to the second aspect of the present invention, the communication passages for the extension stroke and the contraction stroke are circumferentially spaced from each other at substantially the same radial distance from the axis of the piston. In the shock absorber formed in the piston in the state in which the third valve plate is provided, the radial depth of the notch provided with the third valve plate can be reduced to the depth communicating with the second cutout.

Therefore, the depth of the notch may be smaller than the depth required in the case of a structure in which the notch directly communicates with the first cutout without providing the second valve plate, so that the orifice passage is provided. Excessive damping force at very low piston speeds due to excessively long length can be avoided, and the third valve plate having the second cutout becomes brittle. It is possible to avoid a decrease in the durability of the third valve plate by further increasing the rotation speed of the barrel processing by reducing the risk that the valve plates are entangled during the barrel processing. , The durability of the shock absorber can be improved, and the manufacturing cost of the shock absorber can be reduced.

[Brief description of the drawings]

FIG. 1 is a partial longitudinal sectional view showing a main part of a first embodiment of a shock absorber according to the present invention configured as a twin tube type shock absorber.

FIG. 2 is a plan view showing a first valve plate (A), a second valve plate (B), and a third valve plate (C) of the first embodiment.

FIG. 3 is an exploded perspective view showing an orifice passage of the first embodiment.

FIG. 4 is a graph showing the damping force characteristics of the first embodiment in comparison with the damping force characteristics of a conventional shock absorber.

FIG. 5 is a partial longitudinal sectional view showing a main part of a second embodiment of a shock absorber according to the present invention configured as a twin tube type shock absorber.

FIG. 6 is a partial plan sectional view taken along line VI-VI in FIG. 5;

FIG. 7 is a plan view showing a first valve plate (A), a second valve plate (B), a third valve plate (C), and a fourth valve plate (D) of the second embodiment. is there.

FIG. 8 is a plan view showing each valve plate in a case where the damping force generating valve has three valve plates in the structure of the piston shown in FIGS. 5 and 6.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Inner cylinder 12 ... Outer cylinder 18 ... Piston 20 ... Cylinder upper chamber 22 ... Cylinder lower chamber 24 ... Piston body 26 ... Piston rod 30 ... Damping force generating valve for extension stroke 32 ... Damping force generation valve for contraction stroke 34 36, communication passages 42-46, valve plate 66, cutout 68, cutout 70, orifice passage 74-80, valve plate 82, 84, cutout 86, cutout 88, orifice passage

Claims (2)

[Claims] A cylinder, a piston reciprocatingly fitted to the cylinder and cooperating with the cylinder to define two cylinder chambers, and communicating the two cylinder chambers formed in the piston. At least one side of the communication passage and the two cylinder chambers is provided in the piston, and a damping force is generated by applying a flow resistance to the working fluid flowing between the two cylinder chambers via the communication passage. A first valve plate having a cut-out portion disposed in contact with the piston and communicating with the communication passage; and a damping force generating valve disposed in contact with the first valve plate. A second valve plate having a notch in the outer peripheral portion thereof, and a third valve plate disposed in contact with the second valve plate, wherein the notch is formed by the first and third valves. With valve plate And has KakuJo the orifice passage connecting communication between the cylinder chamber corresponding to the cut-out portion,
The orifice passage has a height H, a width W, and a length L substantially equal to the thickness of the second valve plate, wherein the height H, the width W, and the length L are different from the piston speed. A shock absorber characterized in that the damping force characteristic in a very low speed range is set to a value that becomes substantially linear. 2. A cylinder, a piston reciprocatingly fitted to said cylinder and cooperating with said cylinder to define two cylinder chambers, wherein said piston has substantially the same radial distance from an axis of said piston. A communication passage for an extension stroke and a contraction stroke formed in the piston in a state of being spaced apart from each other in the circumferential direction at a position and communicating with the two cylinder chambers; and at least one side of the two cylinder chambers. A damping force generating valve that is provided in the piston and that provides a flow resistance to the working fluid flowing between the two cylinder chambers through one of the communication paths for the expansion stroke and the contraction stroke to generate a damping force. A first valve plate having a first cutout portion disposed in contact with the piston and communicating with the one communication passage; and a damping force generating valve disposed in contact with the first valve plate. Sa A second valve plate having a second cutout communicating with the first cutout, a third valve plate disposed in contact with the second valve plate and having a cutout in an outer peripheral portion, A fourth valve plate disposed in contact with the third valve plate, wherein the second cutout extends radially outward with respect to the axis from the first cutout, The notch cooperates with the second and fourth valve plates to define an orifice passage communicating and connecting the second cutout to a corresponding cylinder chamber, and the orifice passage is substantially The height H, the width W, and the length L are the same as the thickness of the third valve plate, and the height H, the width W, and the length L are within a very low piston speed range. The damping force characteristic is set to a value that results in a substantially linear characteristic. Kkuabusoba.