JP2003254374A - Hydraulic shock absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To minimize phase lag in damping force with respect to a piston speed while suppressing cavitation, by optimizing burden of damping force of a base portion and a piston portion in a compression stroke, in a hydraulic shock absorber. <P>SOLUTION: A piston 5 connected with a piston rod 6 is fitted in a cylinder 2, and a reservoir 4 is connected with a lower chamber 2B of the cylinder through a base valve 7. In the compression stroke, a compression side damping force generating mechanism 11 of the piston 5 and a damping force generating mechanism 15 of the base valve 7 are set so that a ratio Pp:Pb of differential pressure between upper and lower chambers 2A, 2B of the cylinder (pressure Pp applied to the piston portion) to differential pressure between the lower chamber 2A and the reservoir 4 (pressure Pb applied to the base portion) is 1:1 to 1:2. Therefore, the burden of pressure on the piston portion and base valve portion in the compression stroke can be optimized and the phase lag in the damping force with respect to the piston speed can be minimized. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic shock absorber mounted on a suspension system of vehicles such as automobiles and railway vehicles.

[0002]

2. Description of the Related Art As a general hydraulic shock absorber mounted on a suspension system of a vehicle such as an automobile or a railway vehicle, there is a double-cylinder hydraulic shock absorber. In the double-cylinder type hydraulic shock absorber, the cylinder portion has a double-cylinder structure, and a reservoir in which the oil liquid and gas are sealed is formed around the cylinder in which the oil liquid is sealed.
The cylinder and the reservoir are connected to each other via a base valve provided at the bottom of the cylinder. A piston, to which a piston rod is connected, is slidably fitted in the cylinder, and the interior of the cylinder is divided into two chambers, a cylinder upper chamber and a cylinder lower chamber, by the piston.
The piston is equipped with a damping force generation mechanism that mainly consists of an orifice that generates damping force during the expansion stroke, a disc valve and a check valve, and the base valve has an orifice that generates damping force during the compression stroke, and a disc valve. And a damping force generating mechanism including a check valve and the like.

With this configuration, during the extension stroke, the damping force generating mechanism of the piston controls the flow of the oil liquid from the cylinder upper chamber to the cylinder lower chamber to generate the damping force. At this time, the oil liquid for which the piston rod has withdrawn flows from the reservoir through the check valve of the base valve into the cylinder, and the gas in the reservoir expands to compensate for the volume change in the cylinder.

Further, during the compression stroke, the flow of oil liquid from the cylinder lower chamber to the cylinder upper chamber is controlled by the damping force generation mechanism of the piston portion, and the flow of oil liquid from the cylinder to the reservoir due to the piston rod entering the base is controlled. A damping force is generated by controlling the damping force generation mechanism of the valve. At this time, the gas in the reservoir is compressed to compensate for the volume change in the cylinder.

In the double-cylinder type hydraulic shock absorber, the vertical differential pressure of the damping force generating mechanism of the base valve (the differential pressure between the cylinder chamber and the reservoir) is different from the vertical differential pressure of the damping force generating mechanism of the piston during the compression stroke. If it is smaller than the pressure (the pressure difference between the cylinder upper chamber and the cylinder lower chamber), the cylinder upper chamber becomes negative pressure,
Cavitation may occur and stable damping force (setting damping force) may not be obtained. Therefore, during the compression stroke, the vertical differential pressure of the damping force generation mechanism of the base valve becomes
Cavitation is prevented by setting the piston damping force generation mechanism to be higher than the upper and lower differential pressure and maintaining the cylinder upper chamber at a positive pressure at all times.

[0006]

However, the conventional double-cylinder type hydraulic shock absorber described above has the following problems. In order to prevent the occurrence of cavitation, if the vertical differential pressure of the damping force generating mechanism of the base valve is made excessively higher than the vertical differential pressure of the damping force generating mechanism of the piston, the differential pressure between the cylinder and the reservoir becomes excessive, Due to the volume distortion of each part of the hydraulic shock absorber and the oil liquid, a phase delay of the damping force occurs at the time of switching of the expansion and contraction stroke, or a hysteresis of the damping force, that is, a delay of the response of the damping force to the change of the piston speed becomes large.

The present invention has been made in view of the above points, and optimizes the load of the damping force of the base portion and the piston portion during the compression stroke to suppress the cavitation and reduce the damping force with respect to the piston speed. It is an object of the present invention to provide a hydraulic shock absorber capable of suppressing the phase delay of the above.

[0008]

In order to solve the above-mentioned problems, the invention according to claim 1 relates to a cylinder in which an oil liquid is sealed, and a slidably fitted inside of the cylinder. And a piston rod having one end connected to the piston and the other end extending to the outside of the cylinder, and reservoir means communicating with the cylinder chamber via a base valve means. In the hydraulic shock absorber provided with a damping force generating means to the piston and the base valve means, a differential pressure between the two cylinder chambers during the compression stroke of the piston rod,
The ratio of the differential pressure between the cylinder chamber and the reservoir means communicating with each other via the base valve means is 1: 1.
The damping force generating means of the piston and the base valve means are set so that the ratio becomes 1: 2. With this configuration, the pressure load of the damping force generating mechanism of the piston and the base valve means during the compression stroke is optimized. According to a second aspect of the present invention, in the hydraulic shock absorber of the first aspect, the reservoir means is formed between the cylinder and an outer cylinder provided on an outer circumference of the cylinder. And With such a configuration, in the double-cylinder hydraulic shock absorber,
The pressure load of the damping force generating mechanism of the piston and the base valve means during the compression stroke is optimized. The hydraulic shock absorber according to the invention of claim 3 is characterized in that, in the structure of claim 1, the reservoir means includes an oil chamber and a gas chamber formed in the cylinder. With this configuration, in the single-cylinder hydraulic shock absorber,
The pressure load of the damping force generating mechanism of the piston and the base valve means during the compression stroke is optimized.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings. A first embodiment of the present invention will be described with reference to FIGS. 1 to 10. As shown in FIG. 1, the hydraulic shock absorber 1 according to the present embodiment is a double-cylinder hydraulic shock absorber, in which an outer cylinder 3 is provided on the outer periphery of a cylinder 2, and between the cylinder 2 and the outer cylinder 3. It has a double cylinder structure in which the reservoir 4 (reservoir means) is formed. A piston 5 is slidably fitted in the cylinder 2, and the interior of the cylinder 2 is defined by the piston 5 into an upper cylinder chamber 2A and a lower cylinder chamber 2B. One end of a piston rod 6 is connected to the piston 5 by a nut 6A, and the other end side of the piston rod 6 has a rod guide (not shown) and an oil attached to the upper ends of the cylinder 2 and the outer cylinder 3. It is inserted into a seal (not shown) and extended to the outside. Cylinder 2
A base valve 7 (base valve means) that divides the cylinder lower chamber 2B and the reservoir 4 is provided at the lower end of the. The cylinder upper and lower chambers 2A and 2B are filled with oil liquid, and the reservoir 4 is filled with oil liquid and gas.

The piston 5 is provided with extension side and contraction side oil passages 8 and 9 for communicating the cylinder upper and lower chambers 2A and 2B. The expansion-side and contraction-side oil passages 8 and 9 are provided with expansion-side and contraction-side damping force generation mechanisms 10 and 11 each including an orifice and a disc valve that control the flow of the oil liquid to generate a damping force. There is. Also, the base valve 10
The extension side and the contraction side oil passages 12 and 13 that connect the cylinder lower chamber 2B and the reservoir 4 are provided in the. The extension-side oil passage 12 is provided with a check valve 14 that allows only the flow of the oil liquid from the reservoir 4 side to the cylinder lower chamber 2B side.
A compression-side damping force generation mechanism 15 including an orifice and a disc valve that provide resistance to the flow of oil liquid from the cylinder lower chamber 2B side to the reservoir 4 side is provided at 13.

The hydraulic shock absorber 1 has a piston 5 having a diameter D1 of 30 m.
m, the diameter d2 of the piston rod 6 is 12.5 mm. Further, the compression-side damping force generation mechanism 11 (damping force generation means) of the piston 5 and the damping force generation mechanism 15 (damping force generation means) of the base valve 7 are arranged in the cylinder upper and lower chambers 2A during the compression stroke of the piston rod 6. 2B differential pressure (hereinafter referred to as piston burden pressure
Pp) and the differential pressure between the cylinder lower chamber 2A and the reservoir 4 (hereinafter referred to as the base portion bearing pressure Pb) Pp: Pb is 1: 1.
It is set to be from 1: 2.

The operation of the present embodiment having the above-described structure will be described below. During the expansion stroke of the piston rod 6, as the piston 5 in the cylinder 2 slides, the oil liquid in the cylinder upper chamber 2A flows through the expansion side oil passage 8 of the piston 5 to the cylinder lower chamber 2B, and the expansion side damping force. The differential pressure generated between the cylinder upper and lower chambers 2A and 2B due to the flow resistance of the generating mechanism 10 causes the pressure receiving area S1 of the piston 5 (the cross-sectional area of the piston 5 and the piston rod 6
(Difference with the cross-sectional area S2 of), a damping force is generated. At this time, the oil liquid corresponding to the piston rod 6 withdrawing from the cylinder 2 is returned from the reservoir 4 to the check valve of the base valve 7.
14 is opened to flow into the lower cylinder chamber 2B, and the gas in the reservoir 4 expands to compensate for the volume change in the cylinder 2.

During the compression stroke, the piston 5 in the cylinder 2
The oil in the lower chamber 2B of the cylinder contracts with the sliding of the
It flows through the upper chamber 2A of the cylinder through 9 and the upper and lower chambers 2A, 2A
The differential pressure generated between B acts on the pressure receiving area S1 of the piston 5 to generate a damping force, and when the piston rod 6 enters the cylinder 2, the cylinder lower chamber 2B
Oil flows to the reservoir 4 through the contraction side oil passage 13 of the base valve 7, and the differential pressure generated between the cylinder lower chamber 2B and the reservoir 4 due to the flow resistance of the damping force generating mechanism 15 is received by the piston rod 6. A damping force is generated by acting on the area S2, and the total of these damping forces becomes the damping force at the time of the compression stroke. At this time, the gas in the reservoir 4 is compressed by the amount of the piston rod 6 entering the cylinder 2 to compensate for the volume change in the cylinder.

Next, when the ratio Pp: Pb of the piston portion bearing pressure Pp and the base portion bearing pressure Pb during the above-described compression stroke is different, the hysteresis force of the damping force and the damping force with respect to the actual change of the piston speed are measured. The phase delay of will be described with reference to FIGS.

Piston speed when the damping force characteristics on the extension side and the contraction side are kept constant and the ratio Pp: Pb of the piston portion bearing pressure Pp and the base portion bearing pressure Pb is set to 3: 1 Fig. 6 shows the damping force diagram for the ratio Pp: P
Fig. 7 shows a diagram of damping force with respect to piston speed when b is set to 1: 1, and Fig. 8 shows a diagram of damping force with respect to piston speed when the ratio Pp: Pb is set to 1: 2. FIG. 9 shows a diagram of the damping force with respect to the piston speed when the ratio Pp: Pb is set to 1: 5.

Base part bearing pressure Pb piston part bearing pressure
Figure 10 shows the relationship between the ratio Pb / Pp to Pp and the phase delay of the damping force during the extension stroke and the contraction stroke. 6 to 10
Therefore, the larger the hysteresis of the damping force with respect to the change of the piston speed, the larger the phase delay of the damping force.As the base part bearing pressure Pb increases, the hysteresis of the damping force decreases and the phase delay also increases during the extension stroke. Although it becomes smaller, it can be seen that the hysteresis increases and the phase delay also increases during the contraction stroke. If the piston bearing pressure Pp is greater than the base bearing pressure Pb (Pb / P
It can be seen that the hysteresis is increased and the phase delay is increased during both the expansion stroke and the contraction stroke (p <1.0).

From the above, by optimizing the ratio Pp: Pb between the piston portion bearing pressure Pp and the base portion bearing pressure Pb from 1: 1 to 1: 2, both the hysteresis of the damping force and the phase delay are reduced to optimize Can be achieved. In the first embodiment, during the compression stroke of the piston rod 6, the ratio Pp: Pb of the piston portion bearing pressure Pp and the base portion bearing pressure Pb is
Since the damping force characteristics of the compression side damping force generation mechanism 11 of the piston 5 and the damping force generation mechanism 15 of the base valve 7 are set so as to be from 1: 1 to 1: 2, while suppressing the occurrence of cavitation. It is possible to obtain a stable damping force by optimizing both the hysteresis and the phase delay of the damping force, and to improve the running stability and riding comfort of the vehicle.

Next, as a second embodiment of the present invention, a case where the present invention is applied to a suspension strut will be described with reference to FIGS. 11 and 12. In addition, the above
Similar parts to the first embodiment are designated by the same reference numerals, and only different parts will be described in detail.

As shown in FIG. 11, the suspension strut 16 uses a hydraulic shock absorber as a link member of the suspension, enhances the strength of the outer cylinder 3, and
The diameter D2 of the piston rod 6 is increased. Therefore, the diameter D1 of the piston 5 is 32 mm, the diameter D2 of the piston rod 6 is 22 mm, the cross-sectional area S2 of the piston rod 6 is large, compared to the first embodiment,
The pressure receiving area S1 of the piston 5 is small.

FIG. 12 shows the relationship between the ratio Pb / Pp of the base portion bearing pressure Pb to the piston portion bearing pressure Pp and the phase delay of the damping force during the extension stroke and the contraction stroke in this case. As can be seen from FIG. 12, even if the ratio of the diameters of the piston 5 and the piston rod 6 changes, the piston portion bearing pressure Pp and the base portion bearing pressure Pb are the same as in the case of the first embodiment.
So that the ratio Pp: Pb with is from 1: 1 to 1: 2
By setting the damping force of the contraction-side damping force generation mechanism 11 of 5 and the damping force generation mechanism 15 of the base valve 7, while suppressing the occurrence of cavitation, the hysteresis and phase delay of the damping force are optimized and stabilized. A damping force can be obtained.

Next, as a third embodiment of the present invention, a case where the present invention is applied to a single-cylinder type hydraulic shock absorber will be described with reference to FIG.
Will be described with reference to. Note that the same parts as those of the first embodiment are designated by the same reference numerals, and only different parts will be described in detail.

As shown in FIG. 13, in the single-cylinder hydraulic shock absorber 17, the outer cylinder, the reservoir and the base valve are omitted from the double-cylinder hydraulic shock absorber, instead, a free piston is provided in the cylinder 2. 18 is slidably fitted and cylinder 2
Gas chamber 19 (reservoir means) with high-pressure gas sealed at the bottom of
Are formed. Further, in the cylinder 2, a partition member 20 (base valve means) is fitted and fixed between the piston 5 and the free piston 18, and an oil chamber 21 (between the partition member 20 and the free piston 18 ( (Reservoir means) is formed. The partition member 20 includes a cylinder lower chamber 2A and an oil chamber 21.
An orifice passage 22 (damping force generating means) is provided for communicating the and.

With this structure, the extension side damping force generating mechanism 10 of the piston 5 generates a damping force during the extension stroke of the piston rod 6. During the compression stroke, the compression side damping force generating mechanism 11 of the piston 5 generates a damping force, and the partition member 20 functions in the same manner as the base valve of the double-cylinder type hydraulic shock absorber, so that the orifice passage 22 is located below the cylinder. Room 2A
Control the flow of oil liquid from the oil chamber 21 to generate a damping force,
The sum of these damping forces is the shrinking side damping force. In addition,
The volume change in the cylinder 2 due to the intrusion and retreat of the piston rod 6 is compensated by the compression and expansion of the high pressure gas in the gas chamber 19.

Therefore, also in the case of the single-cylinder type hydraulic shock absorber 17, the ratio Pp: Pb between the piston portion bearing pressure Pp and the base portion bearing pressure Pb is from 1: 1 as in the case of the first embodiment.
Damping force generation mechanism 1 on the compression side of piston 5 so that it becomes 1: 2
By setting the damping force by the orifice passage 22 of 1 and the partition member 20, it is possible to suppress the occurrence of cavitation, optimize the hysteresis and phase delay of the damping force, and obtain a stable damping force.

[0025]

As described above in detail, according to the hydraulic shock absorber according to the invention of claim 1, the ratio Pp: Pb of the pressure applied to the piston portion and the pressure applied to the base portion is changed from 1: 1 to 1: 2. By doing so, it is possible to optimize the damping force load of the piston portion and the base valve portion during the compression stroke, and it is possible to minimize the phase delay of the damping force with respect to the piston speed while suppressing the occurrence of cavitation. . According to the hydraulic shock absorber according to the invention of claim 2, in the double-cylinder hydraulic shock absorber, it is possible to optimize the pressure load of the piston portion and the base valve portion during the compression stroke, and obtain a stable damping force. be able to. Further, according to the hydraulic shock absorber according to the invention of claim 3, in the single-cylinder hydraulic shock absorber, it is possible to optimize the pressure load of the piston portion and the base valve portion during the compression stroke, and stabilize the damping force. Can be obtained.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a main part of a hydraulic shock absorber according to a first embodiment of the present invention.

FIG. 2 is a diagram showing these pressures with respect to the piston speed in the hydraulic shock absorber shown in FIG. 1 when the ratio of the piston portion bearing pressure and the base portion bearing pressure is 3: 1.

FIG. 3 is a diagram showing these pressures with respect to the piston speed when the ratio of the piston portion bearing pressure and the base portion bearing pressure is 1: 1 in the hydraulic shock absorber shown in FIG. 1.

FIG. 4 is a diagram showing these pressures with respect to the piston speed when the ratio of the piston portion bearing pressure and the base portion bearing pressure is 1: 2 in the hydraulic shock absorber shown in FIG. 1.

5 is a diagram showing these pressures relative to the piston speed when the ratio of the piston bearing pressure and the base bearing pressure is 1: 5 in the hydraulic shock absorber shown in FIG.

FIG. 6 is a damping force diagram with respect to the piston speed when the ratio of the piston bearing pressure and the base bearing pressure is 3: 1 in the hydraulic shock absorber shown in FIG. 1.

FIG. 7 is a damping force diagram with respect to the piston speed when the ratio of the piston bearing pressure and the base bearing pressure is 1: 1 in the hydraulic shock absorber shown in FIG. 1.

8 is a damping force diagram with respect to the piston speed when the ratio of the piston bearing pressure and the base bearing pressure is 1: 2 in the hydraulic shock absorber shown in FIG. 1.

9 is a damping force diagram with respect to the piston speed when the ratio of the piston bearing pressure and the base bearing pressure is 1: 5 in the hydraulic shock absorber shown in FIG.

10 is a graph showing the relationship between the ratio of the piston portion bearing pressure to the base portion bearing pressure in the hydraulic shock absorber shown in FIG. 1 and the phase delay of the damping force during the extension stroke and the contraction stroke.

FIG. 11 is a vertical cross-sectional view of a main part of a suspension strut according to a second embodiment of the present invention.

12 is a graph showing the relationship between the ratio of the piston bearing pressure to the base bearing pressure in the suspension strut shown in FIG. 11 and the phase delay of the damping force during the extension stroke and the contraction stroke.

FIG. 13 is a vertical cross-sectional view of a main part of a hydraulic shock absorber according to a third embodiment of the present invention.

[Explanation of symbols]

1,17 hydraulic shock absorber 2 cylinder 3 outer cylinder 4 Reservoir (reservoir means) 5 pistons 6 piston rod 7 Base valve (base valve means) 11 Contraction side damping force generation mechanism (damping force generation means) 15 Damping force generation mechanism (damping force generation means) 19 gas chamber 21 oil chamber

Claims (3)

[Claims] 1. A cylinder in which an oil liquid is sealed, a piston slidably fitted in the cylinder to define two cylinder chambers in the cylinder, one end of which is connected to the piston, and the other. A hydraulic buffer provided with a piston rod whose end extends to the outside of the cylinder and a reservoir means communicating with the cylinder chamber via a base valve means, and a damping force generating means provided on the piston and the base valve means. In the container, the ratio of the differential pressure between the two cylinder chambers during the compression stroke of the piston rod and the differential pressure between the cylinder chamber and the reservoir means communicating with each other via the base valve means is 1 The hydraulic shock absorber, wherein the damping force generating means of the piston and the base valve means is set so as to be from 1: 1 to 1: 2. 2. The reservoir means includes the cylinder,
2. The hydraulic shock absorber according to claim 1, which is formed between the cylinder and an outer cylinder provided on the outer periphery of the cylinder. 3. The hydraulic shock absorber according to claim 1, wherein the reservoir means comprises an oil chamber and a gas chamber formed in the cylinder.