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Abstract

Provided is a shock absorber that can achieve damping force characteristics in which the above-spring portion of a vehicle is stable regardless of road surface. This shock absorber comprises an inner cylinder, a piston, a first oil passage, a piston extension-side valve, a second oil passage, and a piston contraction-side valve. Among the piston extension-side valve and the piston contraction-side valve, the valve having the more frequency-dependent damping force is configured so as to match the valve having the less frequency-dependent damping force. In order to do so, for example, among the piston extension-side valve and the piston contraction-side valve, the valve (e.g., the piston extension-side valve) with the higher valve opening pressure is provided with a valve opening promotion mechanism so as to match the valve opening timing of the valve (for example, the piston contraction-side valve) with the lower valve opening pressure.

Description

[Technical Field]

[0001] The present disclosure relates to a shock absorber that reduces vibrations in a vehicle, such as an automobile. [Background technology]

[0002] Vehicles such as four-wheeled automobiles are provided with shock absorbers (dampers) between the vehicle body (sprung mass) and each wheel (unsprung mass). The shock absorber described in Patent Document 1 has disc valves on both the lower and upper surfaces of the piston. The disc valve on the lower surface of the piston opens based on an increase in the differential pressure between the piston lower oil chamber and the piston upper oil chamber when the rod moves in the extension direction. The disc valve on the upper surface of the piston opens based on an increase in the differential pressure between the piston lower oil chamber and the piston upper oil chamber when the rod moves in the contraction direction. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-34068 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, when shock absorbers are installed (introduced or adopted) in a vehicle, they must be adapted to that vehicle. That is, the damping force of the shock absorber is adjusted (tuned) so that the desired ride comfort can be obtained for the vehicle on which it is installed. In this case, the desired ride comfort is approached by mainly adjusting the damping force relative to the piston speed on the extension side and the compression side. However, simply adjusting the damping force relative to the piston speed on the extension side and the compression side may result in a deterioration of ride comfort depending on the road surface condition, and there is a possibility that the road surfaces on which the shock absorber can be driven comfortably may be limited.

[0005] An object of the present invention is to provide a shock absorber that can obtain damping force characteristics that stabilize the sprung mass of a vehicle regardless of the road surface. [Means for solving the problem]

[0006] The present invention is preferably a shock absorber comprising: an inner cylinder filled with hydraulic fluid; a piston slidably provided within the inner cylinder and dividing the interior of the inner cylinder into a first chamber and a second chamber; a first passage provided in the piston; a first valve that opens and closes the first passage; a second passage provided in the piston; and a second valve that opens and closes the second passage, wherein the valve having a higher valve opening pressure out of the first valve and the second valve is provided with a valve opening promotion mechanism that synchronizes the opening timing of the valve having a lower valve opening pressure.

[0007] Furthermore, the present invention preferably provides a shock absorber comprising: an inner cylinder filled with hydraulic fluid; a piston slidably disposed within the inner cylinder and dividing the interior of the inner cylinder into a first chamber and a second chamber; a first passage disposed in the piston; a first valve for opening and closing the first passage; a second passage disposed in the piston; and a second valve for opening and closing the second passage, wherein the frequency characteristics of the valve having a damping force that is more frequency-dependent of the first valve or the second valve are configured to match the frequency characteristics of the valve having a damping force that is less frequency-dependent.

[0008] Furthermore, the present invention is preferably a shock absorber comprising: an inner cylinder filled with hydraulic fluid; a piston slidably provided within the inner cylinder and dividing the interior of the inner cylinder into a first chamber and a second chamber; a first passage provided in the piston; a first valve for opening and closing the first passage; a second passage provided in the piston; and a second valve for opening and closing the second passage, wherein the valve having a higher valve opening pressure out of the first valve or the second valve has a smaller biasing force than the valve having a lower valve opening pressure, and a low-speed valve is provided which opens the first passage or the second passage when the piston speed is low.

[0009] Furthermore, the present invention preferably includes an inner cylinder filled with hydraulic fluid, a piston slidably provided within the inner cylinder and dividing the interior of the inner cylinder into a first chamber and a second chamber, an outer cylinder provided outside the inner cylinder and forming a reservoir chamber between the inner cylinder and the outer cylinder, a valve body provided between the reservoir chamber and the second chamber, a first passage provided in the piston, a first valve (e.g., a piston extension valve) that opens and closes the first passage, a first orifice provided in the first passage, a second passage provided in the piston, and a second valve (e.g., a piston retraction valve) that opens and closes the second passage. a third passage provided in the valve body, a third valve (e.g., a suction valve) that opens and closes the third passage, a fourth passage provided in the valve body, a fourth valve (e.g., a body contraction valve) that opens and closes the fourth passage, and a second orifice provided in the fourth passage, wherein a valve opening promotion mechanism is provided for the valve having a higher valve opening pressure between the first valve and the fourth valve to match the opening timing of the valve having a lower valve opening pressure (for example, when the valve opening pressure of the first valve is higher than that of the fourth valve, the opening timing of the first valve is matched to that of the second valve).

[0010] According to one embodiment of the present invention, it is possible to obtain damping force characteristics that stabilize the sprung mass of a vehicle regardless of the road surface. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a vertical cross-sectional view showing a shock absorber according to a first embodiment. [Figure 2] FIG. 2 is an enlarged cross-sectional view showing the piston, the first valve, and the second valve in FIG. 1. [Figure 3] FIG. 3 is an enlarged view of part (III) in FIG. [Figure 4] FIG. 2 is an exploded perspective view showing a piston, a first valve, etc. [Figure 5] FIG. 4 is a characteristic diagram showing the relationship between piston speed and damping force when low-frequency vibration is applied according to the first embodiment. [Figure 6] 4 is a characteristic diagram showing the relationship between the expansion / compression ratio (expansion / compression ratio) of the damping force and frequency according to the first embodiment. FIG. [Figure 7] FIG. 4 is a cross-sectional view taken from the same position as in FIG. 3, showing a piston, a first valve, and the like according to a modified example. [Figure 8] FIG. 4 is a cross-sectional view taken from the same position as in FIG. 3, showing a piston, a first valve, and the like according to a second embodiment. [Figure 9] FIG. 10 is an exploded perspective view showing a piston, a first valve, etc. according to a second embodiment. [Figure 10] FIG. 10 is a characteristic diagram showing the relationship between piston speed and damping force when low-frequency vibration is applied according to the second embodiment. [Figure 11] FIG. 10 is a characteristic diagram showing the relationship between the expansion / compression ratio (expansion / compression ratio) of the damping force and the frequency according to the second embodiment. [Figure 12] FIG. 4 is a characteristic diagram showing the relationship between the damping force of the orifice area and frequency. [Figure 13] FIG. 4 is a characteristic diagram showing the relationship between the damping force of the valve region and frequency. [Figure 14] FIG. 10 is a characteristic diagram showing the relationship between piston speed and damping force according to a comparative example. [Figure 15] FIG. 10 is a characteristic diagram showing the relationship between the expansion / compression ratio (expansion / compression ratio) of the damping force and the frequency according to the comparative example. [Figure 16] This is a hydraulic circuit diagram of a monotube shock absorber and a twin-tube shock absorber. [Figure 17] FIG. 2 is an explanatory diagram for explaining ride comfort (vehicle behavior) in an ideal state. [Figure 18] FIG. 1 is an explanatory diagram for explaining a ride comfort (vehicle behavior) that is desired to be improved. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, a shock absorber according to an embodiment will be described with reference to the accompanying drawings, taking as an example a case where the shock absorber is used as a hydraulic shock absorber to be installed in a vehicle such as a four-wheeled automobile.

[0013] 1 to 6 show a first embodiment. In FIG. 1, shock absorber 1 is, for example, a hydraulic shock absorber for a vehicle such as an automobile. Shock absorber 1 constitutes a vehicle suspension device together with, for example, a suspension spring (not shown) made of a coil spring. In the following description, one axial end of shock absorber 1 will be referred to as the "lower end" side, and the other axial end will be referred to as the "upper end" side; however, one axial end of shock absorber 1 may also be referred to as the "upper end" side, and the other axial end may also be referred to as the "lower end" side.

[0014] The shock absorber 1 includes an outer cylinder 2, an inner cylinder 4, a piston 5, a piston rod 10, and a valve body 12. The outer cylinder 2 is provided on the outside of the inner cylinder 4. The outer cylinder 2 is formed in a cylindrical shape with a bottom and constitutes the outer shell of the shock absorber 1. The lower end of the outer cylinder 2 is closed by welding a bottom cap 3 to it, and the upper end of the outer cylinder 2 is open. The upper end of the outer cylinder 2 is provided with a plurality of crimped portions 2A that are bent radially inward by, for example, crimping. The upper end opening of the outer cylinder 2 is closed by a rod guide 8 and a rod seal 9.

[0015] The inner cylinder 4 is provided coaxially within the outer cylinder 2. The inner cylinder 4, together with the outer cylinder 2, constitute a twin-cylinder shock absorber (cylinder device). An oil liquid (hydraulic oil) is sealed inside the inner cylinder 4 and the outer cylinder 2 as a working fluid (hydraulic liquid). The oil liquid as the working fluid is not limited to oil, and may be, for example, water mixed with an additive. The lower end of the inner cylinder 4 is fitted onto the outer periphery of the valve body 12 and is closed off at the upper end by a rod guide 8.

[0016] The inner cylinder 4 defines (defines) an annular reservoir chamber A between itself and the outer cylinder 2. Conversely, the outer cylinder 2 defines the reservoir chamber A between itself and the inner cylinder 4. Gas is sealed in the reservoir chamber A together with hydraulic fluid. This gas may be, for example, air at atmospheric pressure or compressed nitrogen gas. The reservoir chamber A functions as a reservoir and compensates for the advancement and retreat of the piston rod 10. The valve body 12 is located at the lower end of the inner cylinder 4 and is provided between the bottom cap 3 and the inner cylinder 4.

[0017] The piston 5 is slidably provided within the inner cylinder 4. The piston 5 divides (defines) the inner cylinder 4 into two chambers, namely, a rod-side oil chamber B serving as a first chamber and a bottom-side oil chamber C serving as a second chamber. The piston 5 is provided with a plurality of oil passages 5A, 5B that allow communication between the rod-side oil chamber B and the bottom-side oil chamber C. Of the plurality of oil passages 5A, 5B, the first oil passage 5A serving as a first passage is shown in FIGS. 1 to 4, and the second oil passage 5B serving as a second passage is shown in FIG. 4.

[0018] The oil passages 5A and 5B constitute passages that allow the working fluid (oil) to flow from one of the oil chambers B and C inside the inner cylinder 4 to the other as the piston 5 moves. That is, the first oil passage 5A as a first passage and the second oil passage 5B as a second passage communicate the rod-side oil chamber B, which is the first chamber, with the bottom-side oil chamber C, which is the second chamber, as the piston 5 moves. The first oil passage 5A and the second oil passage 5B are flow paths through which the flow of the working fluid (oil) occurs as the piston 5 moves.

[0019] The piston 5 is provided with a valve 6, which is configured to include, for example, one or more discs (disc valves). That is, the valve 6, which serves as an extension-side damping valve, is provided on the underside of the piston 5. The extension-side valve 6 (hereinafter referred to as the piston extension-side valve 6) applies resistance to the oil flowing through the first oil passage 5A from the rod-side oil chamber B to the bottom-side oil chamber C when the piston 5 slides upward along the inner cylinder 4 during the extension stroke of the piston rod 10. This generates a predetermined damping force during the extension stroke of the piston rod 10.

[0020] That is, the piston extension side valve 6 generates a damping force by controlling the flow of working fluid (oil) caused by the sliding of the piston 5 inside the inner cylinder 4. The piston extension side valve 6 corresponds to a first valve that opens and closes a first oil passage 5A serving as a first passage. As shown in FIG. 16 , which will be described later, a piston extension side orifice 52 that serves as a throttle (opening) is provided in the first oil passage 5A as necessary. The piston extension side orifice 52, which corresponds to the first orifice, may be provided in the piston extension side valve 6 or on the seat side (piston 5 side).

[0021] The piston 5 is provided with a valve 7, which is configured to include, for example, one or more disks (disk valves), in addition to the piston extension valve 6. That is, the valve 7, which serves as a contraction-side damping valve, is provided on the upper surface of the piston 5. The contraction-side valve 7 (hereinafter referred to as the piston compression-side valve 7) applies resistance to the oil flowing through the second oil passage 5B from the bottom-side oil chamber C toward the rod-side oil chamber B when the piston 5 slides downward along the inner cylinder 4 during the contraction stroke of the piston rod 10. This generates a predetermined damping force during the contraction stroke of the piston rod 10.

[0022] That is, the piston compression valve 7 generates a damping force by controlling the flow of working fluid (oil) caused by the sliding of the piston 5 inside the inner cylinder 4. The piston compression valve 7 corresponds to a second valve that opens and closes a second oil passage 5B serving as a second passage. As shown in FIG. 16 , which will be described later, a piston compression orifice 53 that acts as a throttle (opening) is provided in the second oil passage 5B as needed. The piston compression orifice 53, which corresponds to the third orifice, may be provided in the piston compression valve 7 or on the seat side (piston 5 side).

[0023] The upper end sides (open end sides) of the outer cylinder 2 and the inner cylinder 4 are closed by a rod guide 8 and a rod seal 9. The rod guide 8 is a guide member that slidably guides the piston rod 10 so that it does not move in the axial direction. The rod guide 8 is formed as a cylindrical body of a predetermined shape by subjecting, for example, a metal material or a hard resin material to molding or cutting, and is provided by fitting into the upper end sides (open end sides) of the outer cylinder 2 and the inner cylinder 4.

[0024] The rod seal 9 is provided between the upper surface of the rod guide 8 and the crimped portion 2A of the outer cylinder 2. The rod seal 9 has a metallic annular plate 9A as a core metal. An elastic sealing material such as rubber is integrally molded onto the annular plate 9A by, for example, baking. The rod seal 9 has its inner periphery in sliding contact with the outer periphery of the piston rod 10, thereby providing a liquid-tight and airtight seal between the outer cylinder 2 and the piston rod 10.

[0025] The piston rod 10 has its lower end, or base end, inserted into the inner cylinder 4, and its upper end, or tip end, protruding outside the inner cylinder 4 via a rod guide 8. That is, the piston rod 10 is connected to the piston 5 and extends outside the inner cylinder 4. The piston 5, piston compression valve 7, and piston extension valve 6 are attached to the lower end of the piston rod 10. For this purpose, the lower end of the piston rod 10 is provided with a small-diameter section 10A that is smaller in diameter than the other sections. The end of the small-diameter section 10A is provided with a male thread section 10B onto which a nut 11 is threadedly attached to secure the piston 5, piston compression valve 7, and piston extension valve 6 to the piston rod 10.

[0026] A valve body 12 is provided at the lower end of the inner cylinder 4, and is located between the inner cylinder 4 and the bottom cap 3, forming the bottom body. The valve body 12 is provided on the body side (cylinder side) of the shock absorber 1. The valve body 12 separates (divides) the reservoir chamber A and the bottom-side oil chamber C between the bottom cap 3 and the inner cylinder 4. As a result, the valve body 12 is provided between the reservoir chamber A and the bottom-side oil chamber C. The valve body 12 is provided with a plurality of oil passages 12A, 12B that allow communication between the reservoir chamber A and the bottom-side oil chamber C.

[0027] The oil passages 12A and 12B constitute passages that allow the working fluid (oil) to flow from one of the bottom-side oil chamber C in the inner cylinder 4 and the reservoir chamber A in the outer cylinder 2 to the other chamber as the piston 5 moves. That is, the third oil passage 12A as a third passage and the fourth oil passage 12B as a fourth passage communicate the bottom-side oil chamber C, which becomes the second chamber, with the reservoir chamber A, which becomes the third chamber, as the piston 5 moves. The oil passages 12A and 12B are flow paths through which the flow of the working fluid (oil) occurs as the piston 5 moves.

[0028] The valve body 12 is provided with a valve 13, which is formed of, for example, one or more discs (disc valves). That is, the valve 13, which serves as an extension-side damping valve, is provided on the upper surface of the valve body 12. The extension-side valve 13 (hereinafter referred to as the body extension-side valve 13) applies resistance to the oil flowing through the third oil passage 12A from the reservoir chamber A side toward the bottom-side oil chamber C when the piston 5 slides upward during the extension stroke of the piston rod 10.

[0029] The body extension-side valve 13 corresponds to a third valve that opens and closes a third oil passage 12A serving as a third passage. As shown in Fig. 16 (described later), a body extension-side orifice 56 that serves as a throttle (opening) is provided in the third oil passage 12A as needed. The body extension-side orifice 56, which corresponds to the fourth orifice, may be provided in the body extension-side valve 13 or on the seat side (valve body 12 side).

[0030] The body extension valve 13, which serves as the third valve, can be configured, for example, as a suction valve that primarily functions as a check valve and generates almost no damping force. That is, the body extension valve 13 can be configured as a check valve that opens when the piston 5 slides upward during the extension stroke of the piston rod 10 and closes at other times. The body extension valve 13, which functions as such a check valve, allows oil in the reservoir chamber A to flow through the oil passage 12A toward the bottom-side oil chamber C and prevents oil from flowing in the opposite direction.

[0031] The valve body 12 is provided with a valve 14, which is configured, for example, by one or more discs (disc valves), in addition to the body extension-side valve 13. That is, the valve 14, which serves as a compression-side damping valve, is provided on the underside of the valve body 12. The compression-side valve 14 (hereinafter referred to as the body compression-side valve 14) applies resistance to the oil flowing through the fourth oil passage 12B from the bottom-side oil chamber C toward the reservoir chamber A when the piston 5 slides downward during the compression stroke of the piston rod 10.

[0032] The body compression valve 14 corresponds to a fourth valve that opens and closes a fourth oil passage 12B serving as a fourth passage. As shown in Fig. 16, which will be described later, a body compression orifice 57 that serves as a throttle (opening) is provided in the fourth oil passage 12B as needed. The body compression orifice 57, which corresponds to the second orifice, may be provided in the body compression valve 14 or on the seat side (the valve body 12 side).

[0033] Automobiles travel at various speeds on roads with various road surface conditions. Therefore, the vehicle body is subjected to various inputs from the road surface. It is desirable to maintain a ride quality that gives occupants a sense of stability under such various driving conditions. In a typical hydraulic shock absorber, the magnitude of the damping force relative to the piston speed is adjusted mainly on the compression side and the extension side to achieve a desired ride quality. Generally, such damping force adjustment is performed based on the characteristics in a low-frequency band with a relatively large amplitude.

[0034] However, hydraulic damping force exhibits frequency dependency. Therefore, simply adjusting the magnitude of the damping force relative to the piston speed based on the characteristics in the low frequency band where the amplitude is relatively large on the compression and extension sides may not be able to generate an appropriate damping force when the input frequency varies widely. For example, simply adjusting the damping force may result in a stiff feeling as shown in Figure 18(A). Furthermore, simply adjusting the damping force may result in a bumpy feeling as shown in Figure 18(B). As a result, during actual driving, good behavior may not be achieved depending on the road surface, which may impair the stability felt by the occupants.

[0035] As mentioned above, a vehicle body receives various inputs from the road surface while traveling. Furthermore, the size of the road surface undulations and the spacing between the bumps and recesses vary. Therefore, it is important to optimize not only the damping force relative to the piston speed but also the damping force relative to the input frequency. In particular, to obtain a stable ride comfort under various driving conditions, it is desirable to reduce the frequency dependency of the damping force. However, reducing the frequency dependency is difficult, for example, because of delays in the damping force caused by the compressibility of the hydraulic oil.

[0036] On the other hand, even if the extension side damping force and the compression side damping force each exhibit frequency dependency, if the ratio between them does not change with respect to the input frequency, or if the change is small, the balance of the sprung up and down movement will not change significantly even if the road surface condition changes. In other words, as shown in Figure 17, a consistently flat feeling (ideal state) can be achieved, reducing the sense of discomfort while driving. Therefore, in this embodiment, the above problem is solved by reducing the frequency dependency of the ratio between the extension side damping force and the compression side damping force (hereinafter referred to as the "damping force extension / compression ratio").

[0037] The following describes the factors that cause the frequency dependency of the extension / compression ratio of the damping force (= extension side damping force / compression side damping force) and methods for reducing this dependency.

[0038] A typical hydraulic shock absorber, which applies damping force by stacking valves, has a high-pressure oil chamber (high-pressure side chamber) and a low-pressure oil chamber (low-pressure side chamber) filled with hydraulic oil. A flow path is provided through which the hydraulic oil moves between these oil chambers, and the differential pressure is adjusted by the area of ​​this flow path to obtain the desired damping force. The flow path through which the hydraulic oil moves is generally divided into two types. One of these is an orifice that is always connected with a constant area regardless of the differential pressure between the oil chambers. The other is a valve composed of a valve body made of stacked disc valves.

[0039] The valve closes the flow path by closing until the differential pressure between the upstream and downstream oil chambers of the flow path reaches a set value. When the differential pressure exceeds the set value, the valve opens, connecting the upstream and downstream oil chambers. Therefore, when the stroke speed (piston speed) of the hydraulic shock absorber is low, the differential pressure is also low, so the valve closes and hydraulic oil passes only through the orifice. As the piston speed increases from this state, the differential pressure increases. When the load caused by this differential pressure exceeds the preset closing load on the valve, the valve opens. From this point on, the valve opening increases as the differential pressure increases, expanding the flow path area.

[0040] Here, the region where a pressure difference occurs due to the orifice when the valve is closed is defined as the "orifice region," and the region where the valve is open is defined as the "valve region." In this case, the frequency characteristics of the damping force differ between the orifice region and the valve region. Specifically, as shown in Figure 12, in the orifice region, the flow path area is small and constant, so it is difficult to obtain a flow rate in response to an increase in the pressure difference, and the pressure is easily converted not only into inflow and outflow but also into volumetric deformation of the hydraulic oil, resulting in a large response delay and a decrease in damping force as the frequency increases. In contrast, as shown in Figure 13, in the valve region, the response delay is easily alleviated and almost no change in damping force due to frequency is observed.

[0041] Generally, damping force characteristics of dampers (shoe buffers) used in automobiles are often given different characteristics on the extension and compression sides. To achieve such characteristics, it is necessary to use different orifice areas on the extension and compression sides, as well as different valve opening pressures and valve opening heights for the extension and compression valves depending on their respective stiffness and presets. As a result, differences occur in the valve opening characteristics of the extension and compression sides, that is, the timing at which the valves open. Depending on the piston speed, one of the extension and compression sides may be in the orifice region and the other in the valve region. This difference in frequency characteristics between the orifice region and the valve region mentioned above causes the extension-pressure ratio of the damping force to be frequency-dependent.

[0042] For example, Figure 14 shows an example of the relationship between piston speed and damping force when a significantly higher valve opening pressure is applied to the extension valve than to the compression valve. In this case, the extension valve exhibits orifice region characteristics up to a higher piston speed than the compression valve, and the extension damping force in this region decreases as the frequency increases. On the other hand, the compression valve shifts to the valve region at a lower piston speed than the extension valve, so the decrease in damping force with frequency is small.

[0043] These differences in characteristics result in frequency dependency of the extension / compression ratio of the damping force. FIG. 15 shows an example of the relationship between the extension / compression ratio of the damping force (extension-side damping force / compression-side damping force) and frequency in a case similar to that of FIG. 14, i.e., when a significantly higher valve opening pressure is applied to the extension valve than to the compression valve. In this case, characteristic line 101 in FIG. 15 shows the change in the extension / compression ratio of the damping force with respect to frequency at "piston speed a" in FIG. 14. Similarly, characteristic line 102 in FIG. 15 shows the change in the extension / compression ratio of the damping force with respect to frequency at "piston speed b" in FIG. 14, and characteristic line 103 shows the change in the extension / compression ratio of the damping force with respect to frequency at "piston speed c" in FIG. 14.

[0044] As shown in Figure 15, for example, at "piston speed b," the change in the extension / compression ratio of the damping force with respect to frequency is greater than at "piston speed a" and "piston speed c." In such a case, as mentioned above, the sense of stability felt by the occupant decreases. Therefore, by shortening the opening timing of the extension and compression valves, it is possible to reduce the frequency dependency of the extension / compression ratio.

[0045] However, with the typical disc valve stacking method, if you try to slow down the valve opening timing on the high damping side (the extension side in this example) in order to bring the valve opening timing of the extension and compression sides closer together, it becomes necessary to reduce the rigidity of the valve on the high damping side and lower the valve opening pressure, which reduces the damping force after the valve opens and there is a risk that the damping force in the medium to high speed range that is actually needed to suppress sprung resonance, etc. will not be sufficient.

[0046] Therefore, in this embodiment, the valve with the higher valve opening pressure, either the extension or compression side, is provided with a valve opening promotion mechanism (sub-valve) that matches the piston speed at which the valve with the lower valve opening pressure opens. This valve opening promotion mechanism makes it possible to suppress a decrease in valve opening pressure while slowing down the valve opening timing compared to the stacking method of a typical disc valve. Therefore, by slowing down the valve opening timing to match the opening timing of the valve with the lower valve opening pressure, it is possible to suppress a decrease in damping force while reducing the frequency dependency of the extension / compression ratio of the damping force.

[0047] That is, in this embodiment, by providing a valve opening promotion mechanism (sub-valve), it is possible to shift the valve opening timing to a slower speed while maintaining the valve opening pressure of the valve with the higher valve opening pressure between the extension and compression sides. This allows the valve opening timing of the extension and compression sides to be synchronized while ensuring the degree of freedom in adjusting the damping force (of the valve with the higher valve opening pressure), thereby reducing the frequency dependency of the extension-pressure ratio of the damping force. As a result, compared to conventional technology, it is possible to achieve a ride comfort that is more robust against changes in road surface conditions and gives the occupant a sense of stability. The configuration that achieves this is described in detail below.

[0048] First, the valves to be equipped with the valve opening promotion mechanism are defined according to the structure of the damper (shock absorber).

[0049] FIG. 16A shows the hydraulic circuit of a monotube damper 51, which is a single-tube shock absorber. As shown in FIG. 16A, the monotube damper 51 generates a damping force using two valves 6 and 7 provided on the piston 5. That is, in the monotube damper 51, a piston compression-side valve 7 (piston compression valve) and a piston extension-side valve 6 (piston extension valve) are provided on the piston 5. In this case, a piston extension-side orifice 52 (piston extension orifice) and / or a piston compression-side orifice 53 (piston compression orifice) may be provided between the rod-side oil chamber B, which serves as the chamber above the piston, and the bottom-side oil chamber C, which serves as the chamber below the piston, as necessary. In the case of such a monotube damper 51, a valve-opening promotion mechanism may be provided in the valve with the higher valve-opening pressure of the two valves 6 and 7 of the piston 5 (for example, the piston extension-side valve 6).

[0050] FIG. 16(B) shows the hydraulic circuit of a twin-tube damper 54, which is a twin-tube shock absorber. The shock absorber 1 of the embodiment corresponds to the twin-tube damper 54. As shown in FIG. 16(B), the twin-tube damper 54 is provided with four valves 6, 7, 13, and 14 on the piston 5 side and on the body 55 side. That is, the twin-tube damper 54 is provided with a piston compression-side valve 7 (piston compression valve) that contributes to the compression-side damping force and a piston extension-side valve 6 (piston extension valve) that contributes to the extension-side damping force on the piston 5 side. In this case, a piston extension-side orifice 52 (piston extension orifice) and / or a piston compression-side orifice 53 (piston compression orifice) is provided, as necessary, between the rod-side oil chamber B, which is the piston upper chamber, and the bottom-side oil chamber C, which is the piston lower chamber.

[0051] Furthermore, the twin-tube damper 54 is provided with a body extension valve 13 (body extension valve) that contributes to extension-side damping force and a body compression valve 14 (body compression valve) that contributes to compression-side damping force on the body 55 (valve body 12) side. In this case, a body extension orifice 56 (body extension orifice) and / or a body compression orifice 57 (body compression orifice) is provided between the bottom-side oil chamber C, which serves as the piston lower chamber, and the reservoir chamber A, as necessary.

[0052] To reduce the frequency dependency of the damping force extension / pressure ratio, it would be sufficient to synchronize the valve opening timing (piston speed) of all valves. However, this is not practical because the stiffness (valve stiffness) of each valve varies greatly. Therefore, the damping force extension / pressure ratio can be efficiently reduced by synchronizing the valve opening timing of the valves that primarily contribute to the generation of damping force. To achieve this, body extension valve 13, which primarily functions as a check valve and is a suction valve that generates almost no damping force, is ignored because its contribution to the damping force characteristics is small. The opening timing of the remaining three valves 6, 7, and 14 is adjusted using the following concept.

[0053] First, the frequency dependency of damping force is due to a decrease in responsiveness in the orifice area. For this reason, frequency dependency becomes more pronounced in valves where the valve opening pressure is high and the orifice area persists up to higher piston speeds. Therefore, a valve opening acceleration mechanism is installed for the valve with the highest opening pressure of the three valves 6, 7, and 14, to bring its opening timing closer to that of the valve with lower opening pressure and lower rigidity. Specifically, the valve opening pressures of the piston compression valve 7 and body compression valve 14, which contribute to compression damping force, and the piston extension valve 6, which contributes to extension damping force, are compared.

[0054] For example, when the extension-side damping force is greater than the compression-side damping force, i.e., when the valve opening pressure of the piston extension-side valve 6 is the greatest, a valve-opening promotion mechanism is provided to the piston extension-side valve 6. This causes the opening timing of the piston extension-side valve 6 to approach the opening timing of the valve with the lower valve opening pressure between the piston compression-side valve 7 and the body compression-side valve 14, which contribute to the compression-side damping force (in principle, this would be the piston compression-side valve 7 due to the pressure balance relationship). Next, when the compression-side damping force is greater than the extension-side damping force, i.e., when the valve opening pressure of the body compression-side valve 14 is the greatest, a valve-opening promotion mechanism is provided to the body compression-side valve 14. This causes the opening timing of the body compression-side valve 14 to approach the opening timing of the piston extension-side valve 6.

[0055] Next, a valve-opening promotion mechanism 21 according to a first embodiment will be described with reference to Figures 2 to 4 in addition to Figure 1. In the first embodiment, the valve-opening promotion mechanism 21 is provided in the piston extension-side valve 6.

[0056] The piston extension valve 6 includes a low-speed valve 22 and a second-stage valve 24 serving as a main valve. The valve-opening promotion mechanism 21 is configured with the low-speed valve 22. The low-speed valve 22 includes a low-speed disc 22A corresponding to the low-speed valve-opening valve and a small-diameter disc 22B corresponding to the small-diameter valve. The low-speed disc 22A contacts a seat portion 5C provided at the opening of the first oil passage 5A of the piston 5. The low-speed disc 22A is formed as an annular plate with an insertion hole formed on the inside. The low-speed disc 22A constituting the low-speed valve 22 is seated on and lifted from a seat pressure-receiving surface 5C1 of the seat portion 5C. As shown in FIG. 4, the seat portion 5C is not annular but has a seat shape with a variable diameter. Although not shown, a recess (gap) that serves as an orifice can be formed in the seat portion 5C by coining (pressing or pressing) if necessary.

[0057] A small-diameter disc 22B, whose outer diameter is smaller than that of the seat portion 5C of the piston 5, is disposed on the rear side (lower side) of the low-speed disc 22A. The small-diameter disc 22B has an outer diameter smaller than that of the low-speed disc 22A. The small-diameter disc 22B is also formed as an annular plate with an insertion hole formed on the inside. A second-stage valve 24 is disposed on the rear side (lower surface) of the small-diameter disc 22B. The second-stage valve 24 has an outer diameter that is the same as that of the low-speed disc 22A of the low-speed valve 22. The second-stage valve 24 is formed by stacking three discs 24A, 24B, and 24C, each formed as an annular plate. A retainer 25 and a washer 26 are disposed on the rear side of the second-stage valve 24. The low-speed valve 22 (low-speed disc 22A, small-diameter disc 22B), the second-stage valve 24 (disks 24A, 24B, 24C), the retainer 25 and the washer 26 are fastened to the piston rod 10 by a nut 11.

[0058] As described above, in the first embodiment, the small diameter disc 22B is disposed between the low speed disc 22A and the second stage valve 24. As a result, a gap 27 is provided between the low speed disc 22A and the second stage valve 24 by the small diameter disc 22B. Therefore, this gap 27 can reduce the stiffness of the low speed valve 22 (low speed disc 22A) when it is initially opened. In other words, the gap 27 can encourage the low speed valve 22 (low speed disc 22A) to open at a lower piston speed.

[0059] As a result, in the piston extension side valve 6, only the low-speed valve 22 (low-speed disc 22A) functions as a valve element in the low piston speed range at the beginning of valve opening, allowing for low valve stiffness. Furthermore, in the medium-to-high speed range where the low-speed valve 22 (low-speed disc 22A) comes into contact with the second-stage valve 24, the second-stage valve 24 also functions as a valve element, increasing valve stiffness. This nonlinear valve stiffness characteristic is a feature of this configuration. The stiffness of the low-speed valve 22 is primarily determined by the thickness of the low-speed disc 22A and the outer diameter of the small-diameter disc 22B. Therefore, two parameters (i.e., the thickness of the low-speed disc 22A and the outer diameter of the small-diameter disc 22B) are adjusted so that the opening timing of the piston extension side valve 6 (i.e., the opening timing of the low-speed valve 22) is the desired timing.

[0060] The size of the gap 27 between the low-speed valve 22 (low-speed disc 22A) and the second-stage valve 24 controls the timing (piston speed) at which the low-speed valve 22 (low-speed disc 22A) comes into contact with the second-stage valve 24. Therefore, the size of the gap 27 (the distance between the low-speed disc 22A and the second-stage valve 24) determines the range in which the low-speed valve 22 (low-speed disc 22A) is effective.

[0061] Therefore, it affects the damping force in the medium to high speed range. Furthermore, the rigidity of the second-stage valve 24 is a factor that governs the damping force in the medium to high speed range. Therefore, the rigidity of the second-stage valve 24 is adjusted so that the desired damping force is obtained. The second-stage valve 24 may be structured to impart initial deflection to the piston extension side valve 6. Furthermore, the outer diameter of the second-stage valve 24 may be changed midway. In other words, the discs 24A, 24B, and 24C that make up the second-stage valve 24 may have different outer diameters.

[0062] In either case, in the first embodiment, the piston extension-side valve 6 is provided with a low-speed valve 22 (low-speed disc 22A and small-diameter disc 22B) that serves as a valve-opening promotion mechanism 21. The valve-opening promotion mechanism 21 matches the frequency characteristics of the damping force generated by the piston extension-side valve 6 with the frequency characteristics of the damping force generated by the piston compression-side valve 7, thereby reducing the frequency dependency of the extension-pressure ratio of the damping force. The valve-opening promotion mechanism 21 (low-speed valve 22) matches the frequency characteristics of the damping force of the piston extension-side valve 6 with the frequency characteristics of the damping force of the piston compression-side valve 7. In this case, the low-speed valve 22 (low-speed disc 22A) opens at a piston speed lower than the piston speed at which the piston compression-side valve 7 opens. As a result, the piston extension-side valve 6 opens at a lower piston speed than the piston compression-side valve 7. Preferably, the piston compression-side valve 7 and the piston extension-side valve 6 are adjusted to open simultaneously.

[0063] FIG. 5 shows the relationship between the piston speed and the damping force of the shock absorber 1 of the first embodiment, i.e., the characteristics of the damping force versus the piston speed at low frequencies for the shock absorber 1 in which the valve-opening promotion mechanism 21 is provided in the piston extension valve 6. FIG. 6 shows the relationship between the expansion-pressure ratio of the damping force and the frequency, i.e., the change in the expansion-pressure ratio of the damping force versus the frequency at three different "piston speeds a," "piston speeds b," and "piston speeds c" in FIG. 5. In this case, characteristic line 31 in FIG. 6 shows the change in the expansion-pressure ratio of the damping force versus the frequency at "piston speed a" in FIG. 5. Similarly, characteristic line 32 in FIG. 6 shows the change in the expansion-pressure ratio of the damping force versus the frequency at "piston speed b" in FIG. 5, and characteristic line 33 shows the change in the expansion-pressure ratio of the damping force versus the frequency at "piston speed c" in FIG. 5. As is clear from comparing FIG. 6 with the aforementioned FIG. 15, the provision of the valve-opening promotion mechanism 21 significantly reduces the change in the expansion-pressure ratio of the damping force versus the frequency. As a result, compared to a configuration that does not include the valve opening promotion mechanism 21 (low-speed valve 22), it is possible to achieve a ride that is more robust against changes in road surface conditions and gives the occupant a sense of stability.

[0064] As described above, the shock absorber 1 of the first embodiment includes the inner cylinder 4, the piston 5, the first oil passage 5A as a first passage, the piston extension-side valve 6 as a first valve, the second oil passage 5B as a second passage, and the piston compression-side valve 7 as a second valve. The shock absorber 1 also includes the outer cylinder 2 and the valve body 12. The shock absorber 1 further includes a piston extension-side orifice 52 (see FIG. 16) as a first orifice provided in the first oil passage 5A of the piston 5, a third oil passage 12A as a third passage, the body extension-side valve 13 as a third valve, the fourth oil passage 12B as a fourth passage, the body compression-side valve 14, and a body compression-side orifice 57 (see FIG. 16) as a second orifice provided in the fourth oil passage 12B of the valve body 12.

[0065] Furthermore, the frequency characteristics of the valve (e.g., piston extension valve 6) whose damping force is more frequency-dependent, out of the piston extension valve 6 and the piston compression valve 7 (or body compression valve 14), are configured to match the frequency characteristics of the valve (e.g., piston compression valve 7) whose damping force is less frequency-dependent. For this reason, the valve (e.g., piston extension valve 6) between the piston extension valve 6 and the piston compression valve 7 whose valve opening pressure is higher, is provided with a valve-opening acceleration mechanism 21 that synchronizes the opening timing of the valve (e.g., piston compression valve 7) whose valve opening pressure is lower. In addition, the valve (e.g., piston extension valve 6) between the piston extension valve 6 and the body compression valve 14 whose valve opening pressure is higher, is provided with a valve-opening acceleration mechanism 21 that synchronizes the opening timing of the valve (e.g., piston compression valve 7) whose valve opening pressure is lower.

[0066] In this case, of the piston extension valve 6 and the piston compression valve 7, the valve with the higher valve opening pressure (e.g., the piston extension valve 6) opens when the piston speed is slower than the valve with the lower valve opening pressure (e.g., the piston compression valve 7). Also, of the piston extension valve 6 and the body compression valve 14, the valve with the higher valve opening pressure (e.g., the piston extension valve 6) opens when the piston speed is slower than the valve with the lower valve opening pressure (e.g., the body compression valve 14). In other words, the valve-opening promotion mechanism 21 opens the valve with the higher valve opening pressure (e.g., the piston extension valve 6) when the piston speed is slower than the valve with the lower valve opening pressure (e.g., the piston compression valve 7 and / or the body compression valve 14).

[0067] Valve-opening promotion mechanism 21 is configured, for example, with low-speed valve 22 (low-speed disc 22A and small-diameter disc 22B). That is, between piston extension valve 6 and piston compression valve 7, the valve with a higher valve-opening pressure (e.g., piston extension valve 6) is provided with low-speed valve 22 having a smaller biasing force (deformation resistance force, deformation resistance force, valve-closing force, force to maintain the valve closed) than the valve with a lower valve-opening pressure (e.g., piston compression valve 7 and / or body compression valve 14). For example, when low-speed valve 22 is provided in piston extension valve 6, low-speed valve 22 opens first oil passage 5A when the piston speed is low. For example, when low-speed valve 22 is provided in piston compression valve 7, low-speed valve 22 opens second oil passage 5B when the piston speed is low. As shown in FIGS. 2 and 3, a gap 27 is formed between the low-speed valve 22 and the valve stacked on this low-speed valve 22 (ie, the second-stage valve 24).

[0068] The shock absorber 1 according to the first embodiment has the above-described configuration, and its operation will now be described.

[0069] In the shock absorber 1, for example, the tip end (upper end) of the piston rod 10 is attached to the body of the vehicle (automobile), and the bottom cap 3, which is the base end (lower end) of the outer cylinder 2, is attached to the wheel side (axle side) of the vehicle. As a result, when vibrations occur while the vehicle is running, the piston rod 10 is extended and retracted, and a damping force is generated by the valves 6, 7 of the piston 5, etc., to damp the vibrations.

[0070] That is, when the piston rod 10 is in the contraction stroke, the bottom-side oil chamber C is under higher pressure than the rod-side oil chamber B. Then, the oil (pressure oil) in the bottom-side oil chamber C flows into the rod-side oil chamber B via the second oil passage 5B of the piston 5 and the piston retraction-side valve 7, generating a damping force. At this time, an amount of oil equivalent to the volume of the piston rod 10 entering the inner cylinder 4 flows from the bottom-side oil chamber C into the reservoir chamber A via the fourth oil passage 12B of the valve body 12 and the body retraction-side valve 14. In the reservoir chamber A, the gas sealed inside is compressed, absorbing the volume of the piston rod 10 entering.

[0071] On the other hand, when the piston rod 10 is in the extension stroke, the rod-side oil chamber B is under higher pressure than the bottom-side oil chamber C. Then, the oil (pressure oil) in the rod-side oil chamber B flows into the bottom-side oil chamber C via the first oil passage 5A of the piston 5 and the piston extension-side valve 6, generating a damping force. At this time, an amount of oil equivalent to the advanced (retracted) volume of the piston rod 10 advancing (retracting) from the inner cylinder 4 flows from the reservoir chamber A into the bottom-side oil chamber C via the third oil passage 12A of the valve body 12 and the body extension-side valve 13 (check valve).

[0072] According to the first embodiment, the piston extension valve 6, which has the second-stage valve 24 (the valve with the higher valve-opening pressure) of the piston extension valve 6 and the piston compression valve 7, is provided with a valve-opening facilitation mechanism 21 that synchronizes the opening timing of the piston extension valve 6 with the opening timing of the piston compression valve 7 (the valve with the lower valve-opening pressure). Therefore, for example, (compared to a conventional configuration without the valve-opening facilitation mechanism 21), the low-speed valve 22 of the piston extension valve 6 opens at a low piston speed, while the second-stage valve 24 increases the piston speed even further (compared to a conventional configuration without the valve-opening facilitation mechanism 21). This reduces the frequency dependency of the extension-pressure ratio of the damping force, while ensuring sufficient damping force in the medium-to-high speed range of the extension side. Therefore, compared to the conventional technology (configuration without the valve-opening facilitation mechanism 21), this configuration is more robust to changes in road surface conditions and provides a ride comfort that gives the occupant a sense of stability. In other words, it is possible to obtain damping force characteristics that stabilize the vehicle's sprung mass regardless of the road surface, allowing the occupant to continue riding the vehicle without discomfort.

[0073] According to the first embodiment, the piston extension valve 6 is configured so that the frequency dependence of the damping force is equivalent to that of the piston compression valve 7. That is, the piston extension valve 6, which is the valve whose damping force has a greater frequency dependence, is configured to match the piston compression valve 7, which is the valve whose damping force has a lesser frequency dependence. This reduces the frequency dependence of the damping force extension / pressure ratio. This makes it possible to achieve a ride that is more robust against changes in road surface conditions and gives the occupants a sense of stability. In other words, it is possible to obtain damping force characteristics that stabilize the sprung mass of the vehicle regardless of the road surface, allowing the occupants to continue riding the vehicle without any discomfort.

[0074] According to the first embodiment, the piston extension valve 6, which is the valve with a higher valve opening pressure, opens at a slower piston speed than the piston compression valve 7, which is the valve with a lower valve opening pressure. Therefore, while the piston extension valve 6 opens at a low piston speed, valve stiffness in the medium to high speed range can be increased to obtain a large pressure difference, thereby suppressing a decrease in the damping force of the piston extension valve 6 and opening the piston extension valve 6 at a low piston speed, thereby reducing the frequency dependency of the extension-pressure ratio of the damping force.

[0075] According to the first embodiment, the piston extension-side valve 6 is provided with a low-speed valve 22 that has a smaller biasing force than the piston compression-side valve 7 and opens the first oil passage 5A when the piston speed is low. This allows the initial valve opening characteristics of the piston extension-side valve 6 and the stiffness in the medium to high speed range to be adjusted independently, thereby reducing the frequency dependency of the extension-pressure ratio of the damping force and ensuring flexibility in adjusting the extension-side damping force.

[0076] According to the first embodiment, a gap 27 is formed between the low-speed valve 22 (low-speed disc 22A) and the second-stage valve 24. Therefore, the low-speed valve 22 (low-speed disc 22A) is easily displaced (deformed) toward the gap 27. This allows the low-speed valve 22 to be opened when the piston speed is low.

[0077] According to the first embodiment, the piston extension valve 6, which has a higher valve opening pressure than the body compression valve 14, is provided with a valve-opening promotion mechanism 21 that synchronizes the opening timing of the piston extension valve 6 with the opening timing of the piston compression valve 7, which has a lower valve-opening pressure. This allows the piston extension valve 6 to open at a low piston speed while maintaining high rigidity in the medium-to-high speed range. This reduces the frequency dependency of the extension-pressure ratio of the damping force and ensures sufficient damping force in the medium-to-high speed range on the extension side. This results in a more robust ride that provides a sense of stability to occupants compared to the prior art (a configuration without the valve-opening promotion mechanism 21). In other words, this configuration achieves damping force characteristics that stabilize the vehicle's sprung mass regardless of the road surface, allowing occupants to continue riding the vehicle without discomfort.

[0078] In the low-speed valve 22 of the first embodiment, the size of the gap 27 between the low-speed disc 22A and the second-stage valve 24 is determined by the thickness of the small-diameter disc 22B. By reducing the gap 27 between the small-diameter disc 22B and the second-stage valve 24, the piston extension-side valve 6 transitions to a region with high valve stiffness from an earlier timing (piston speed), making it possible to generate a large damping force. However, from the standpoints of mass productivity and strength, it is difficult to make the thickness of the small-diameter disc 22B thinner than a certain level, which may restrict the degree of freedom in generating the damping force.

[0079] Therefore, in the modified example shown in FIG. 7 , the low-speed valve 41 is provided with a gap adjustment disk 42 between the small-diameter disk 22B and the second-stage valve 24, which makes the size of the gap 27 different between the inner diameter side and the outer diameter side. The gap adjustment disk 42 makes the size of the gap 27 larger on the inner diameter side and smaller on the outer diameter side. That is, in this modified example, the low-speed valve 41 includes the gap adjustment disk 42 as a fifth valve (gap adjustment valve) and the small-diameter disk 22B. The gap adjustment disk 42 has a protruding portion 42A that protrudes toward the low-speed disk 22A of the piston extension side valve 6 and has a larger axial width than other portions. The small-diameter disk 22B is provided between the low-speed disk 22A of the piston extension side valve 6 and the gap adjustment disk 42. The small-diameter disk 22B has a smaller diameter than the low-speed disk 22A and the gap adjustment disk 42.

[0080] In this way, in this modification, a gap adjustment disk 42 with a varying radially outer thickness is provided between the small diameter disk 22B and the second-stage valve 24. This makes it possible to set a small gap 27 between the low speed disk 22A and the second-stage valve 24 even if the thickness of the small diameter disk 22B is increased. Therefore, it is possible to improve the degree of freedom in generating damping force while setting the thickness of the small diameter disk 22B to a thickness that ensures mass productivity and strength.

[0081] That is, the modified low speed valve 41 includes a gap adjustment disc 42 in addition to the low speed disc 22A and the small diameter disc 22B. The gap adjustment disc 42 has a protrusion 42A that protrudes toward the low speed disc 22A. This makes it possible to reduce the gap 27 between the low speed disc 22A of the piston extension side valve 6 and the gap adjustment disc 42 (protrusion 42A) while increasing the thickness of the small diameter disc 22B. This makes it possible to both "ensure the mass productivity and strength of the small diameter disc 22B" and "ensure the degree of freedom in adjusting the damping force of the piston extension side valve 6."

[0082] In the modified example, a configuration in which the gap adjustment disk 42 is provided with a protrusion 42A has been described. However, this is not limiting, and the gap adjustment disk may have different thicknesses at its inner diameter portion and outer diameter portion, for example. That is, the thickness of the outer diameter portion of the gap adjustment disk may be greater than the thickness of the inner diameter portion. Furthermore, the protrusion may be formed integrally with the disk by press working, or may be formed integrally with the disk by welding a separate member to the portion corresponding to the protrusion.

[0083] 8 to 11 show a second embodiment. The second embodiment is characterized by a configuration in which a first seat portion on which the low-speed valve is seated and unseated and a second seat portion on which the main valve (second-stage valve) is seated and unseated are provided. In the second embodiment, the same components as those in the first embodiment described above are denoted by the same reference numerals, and their description will be omitted.

[0084] In the second embodiment, the piston extension valve 6 includes a low-speed valve 61 and a second-stage valve 62 serving as a main valve. The valve-opening promotion mechanism 21 is made up of the low-speed valve 61. That is, the piston extension valve 6 includes the low-speed valve 61, which has low valve rigidity and contributes to damping force in the low-speed range in which the valve opens from low speeds, and the second-stage valve 62, which has higher rigidity than the low-speed valve 61 and contributes to damping force in the medium to high speed ranges. The low-speed valve 61 and the second-stage valve 62 are arranged in series in the hydraulic circuit.

[0085] The low-speed valve 61 is composed of two low-speed discs 61A and 61B and a retainer 61C. The second-stage valve 62 is composed of four discs 62A, 62B, 62C, and 62D. The retainer 61C is provided between the low-speed disc 61B, which is disposed on the rear side (lower side), and the disc 62A of the second-stage valve 62. In the second embodiment, the low-speed valve 61 and the second-stage valve 62 have different seat portions 63, 64. That is, the piston 5 is provided with an inner seat portion 63 as a first seat portion on which the low-speed valve 61 is seated and released, and an outer seat portion 64 located radially outward of the inner seat portion 63 and serving as a second seat portion on which the second-stage valve 62 is seated and released. The inner seat portion 63, which comes into contact with the low-speed valve 61, is located on the inner diameter side of the outer seat portion 64, which comes into contact with the second-stage valve 62. The inner sheet portion 63 and the outer sheet portion 64 are both formed in an annular sheet shape.

[0086] The low-speed valve 61 is provided so that the extension-side valve 6 opens at a lower speed. Therefore, it is desirable that the height between the seat surface 63A of the inner seat portion 63 on which the low-speed valve 61 is seated and the support surface 65A of the support portion 65 against which the inner diameter side of the low-speed valve 61 abuts be as small as possible within manufacturing tolerances. Furthermore, the support surface 65A against which the inner diameter side of the low-speed valve 61 abuts is also used as a support for the inner diameter side of the second-stage valve 62. The low-speed valve 61 is first stacked on the support surface 65A, and then the second-stage valve 62 is placed behind the low-speed valve 61. Therefore, a height difference, or step H, is provided between the support surface 65A and the seat surface 64A of the outer seat portion 64.

[0087] Furthermore, the second-stage valve 62 may be preset (preloaded, preset load). In this case, the size of the step H between the support surface 65A and the seat surface 64A of the outer seat portion 64 is set to be equal to or greater than the thickness of the low-speed valve 61 (two low-speed discs 61A, 61B and retainer 61C). Of the two low-speed discs 61A, 61B that make up the low-speed valve 61, the low-speed disc 61A that contacts the inner seat portion 63 is a slit disc with a pair of notches 61A1 on its outer periphery. The notches 61A1 correspond to the first orifice (piston extension side orifice). The low-speed valve 61 contributes to the characteristics in the low-speed range.

[0088] Note that, depending on the vehicle requirements, it may not be necessary to provide a slit disc (low-speed disc 61A). Also, although not shown, a disc having the same diameter as the low-speed valve 61 (low-speed disc 61A, 61B) or a valve having different thicknesses between its inner diameter portion and outer diameter portion (for example, gap adjustment disc 42 in FIG. 7) may be arranged on the back surface (lower surface) of retainer 61C in order to regulate the lift amount of the low-speed valve 61 (low-speed disc 61A, 61B).

[0089] It is desirable to increase the contribution of the damping force generated by the low-speed valve 61 to the damping force of the piston extension valve 6 in the low-speed range. For this reason, of the four discs 62A, 62B, 62C, and 62D that make up the second-stage valve 62, the disc 62A that comes into contact with the outer seat portion 64 is a slit disc with a pair of notches 62A1 on its outer periphery. In this case, the second-stage valve 62 ensures a sufficient orifice area by using the disc 62A (slit disc), thereby reducing the contribution of the second-stage valve 62 to the generation of damping force in the low-speed range.

[0090] The second-stage valve 62 has the role of generating damping force in the medium to high speed range of the piston extension valve 6. For this reason, the rigidity of the second-stage valve 62 is adjusted by parameters such as the number of stacked discs 62A, 62B, 62C, and 62D, the plate thickness, and the diameter of the retainer 25 on the back side. Also, the second-stage valve 62 may be given a set step to impart preload, thereby adjusting to obtain desired characteristics. Note that the inner seat portion 63 on which the low-speed valve 61 sits and unseats is not limited to an annular seat shape, and may have a seat shape with a different diameter depending on the desired low-speed characteristics.

[0091] The second embodiment includes the low-speed valve 61 and second-stage valve 62 as described above, and its basic operation is not significantly different from that of the first embodiment. That is, like the first embodiment, the second embodiment can also achieve damping force characteristics that stabilize the sprung mass of the vehicle regardless of the road surface. FIG. 10 shows the damping force characteristics versus piston speed according to the second embodiment. FIG. 11 shows the change in the damping force extension / pressure ratio versus frequency for three different piston speeds (piston speed a, piston speed b, and piston speed c) in FIG. 10. Comparing FIG. 11 with the aforementioned FIG. 15 makes it clear that the provision of the valve-opening promotion mechanism 21 significantly reduces the change in the damping force extension / pressure ratio versus frequency. As a result, compared to a configuration without the valve-opening promotion mechanism 21 (low-speed valve 61), a ride that is more robust to changes in road surface conditions and provides a sense of stability to the occupant can be achieved.

[0092] It is not possible to accurately determine the valve opening point from the "damping force-piston velocity diagram" shown in FIG. 5 and FIG. 10. That is, even if the break point of the extension-side damping force and the break point of the compression-side damping force appear to coincide on the "damping force-piston velocity diagram," this does not necessarily mean that the valve opening timing coincides. For example, the valve opening promotion mechanism 21 of the first embodiment has a characteristic in which the valve stiffness is nonlinear, reducing the valve stiffness only in the low-speed range and increasing the stiffness in the medium- to high-speed range. Therefore, no clear valve opening point appears on the damping force-piston velocity diagram. Furthermore, in a configuration in which the low-speed valve 61 and the second-stage valve 62 are arranged in series, as in the second embodiment, the valve opening point of the second-stage valve 62, which has a higher valve opening pressure, appears on the diagram, but the valve opening point of the low-speed valve 61 does not appear clearly. Therefore, it is difficult to determine the valve opening point from a "damping force-piston speed diagram," and to determine the valve opening point, it is necessary to either calculate it from the orifice, valve pressure-receiving area, and valve stiffness, or to determine the valve opening point by measuring the frequency characteristics at each piston speed.In other words, because the valve opening timing (piston speed) is determined by the differential pressure acting between the upstream and downstream of the valve, valve stiffness, set load, pressure-receiving area, and valve seat shape, it must be determined by calculation, not from a "damping force-piston speed diagram."

[0093] In the first embodiment, the piston extension valve 6 is the first valve and the piston compression valve 7 is the second valve. However, this is not limiting, and for example, the piston extension valve may be the second valve and the piston compression valve may be the first valve. This also applies to the second embodiment and the modified example.

[0094] In the first embodiment, the body extension-side valve 13 is the third valve and the body compression-side valve 14 is the fourth valve. However, this is not limiting, and for example, the body extension-side valve may be the fourth valve and the body compression-side valve may be the third valve. This also applies to the second embodiment and the modified example.

[0095] In the first embodiment, an example has been described in which the piston extension valve 6 below the piston 5 applies resistance to the hydraulic fluid (working fluid) to generate a damping force during the extension stroke of the piston rod 10, and the piston compression valve 7 above the piston 5 applies resistance to the hydraulic fluid (working fluid) to generate a damping force during the retraction stroke of the piston rod 10. However, the present invention is not limited to this. For example, the piston extension valve above the piston may be a check valve, and a body compression valve serving as a fourth valve provided in the valve body may generate a damping force during the retraction stroke of the piston rod. This also applies to the second embodiment and its modified example.

[0096] In the first embodiment, the piston extension valve 6, which has the higher valve-opening pressure of the piston extension valve 6 and the body compression valve 14, is provided with a valve-opening promotion mechanism 21 that synchronizes the opening timing of the piston compression valve 7, which has the lower valve-opening pressure. However, this is not limiting. For example, if the body compression valve has the higher valve-opening pressure of the piston extension valve and the body compression valve, the body compression valve may be provided with a valve-opening promotion mechanism that synchronizes the opening timing of the piston extension valve, which has the lower valve-opening pressure. This also applies to the second embodiment and its modified example.

[0097] In the first embodiment, a twin-cylinder shock absorber 1 consisting of an outer cylinder 2 and an inner cylinder 4 has been described as an example. However, the present invention is not limited to this, and may be applied to a shock absorber consisting of a single-cylinder member (cylinder). In this case, the valve-opening promotion mechanism can be provided to the valve having the higher rigidity between the first valve and the second valve provided on the piston. This also applies to the second embodiment and the modified example.

[0098] In addition, in each embodiment and modified example, a shock absorber attached to an automobile has been described as a representative example of a shock absorber. However, the present invention is not limited to this, and may be applied to a shock absorber attached to a railway vehicle, for example. Furthermore, the present invention is not limited to vehicles such as automobiles and railway vehicles, and may be applied to various types of shock absorbers used in various machines, structures, buildings, etc. that are sources of vibration.

[0099] Furthermore, each embodiment and modification is merely an example, and it goes without saying that partial substitution or combination of the configurations shown in different embodiments and modifications is possible.

[0100] According to the above-described embodiment and / or modified example (hereinafter simply referred to as "embodiment"), the first valve or the second valve, whichever has a higher valve opening pressure, is provided with a valve-opening promotion mechanism that synchronizes the opening timing of the valve with the lower valve opening pressure. This allows the valve with the higher valve opening pressure to open at a lower piston speed while increasing stiffness in the medium-to-high speed range. This reduces the frequency dependency of the extension-to-pressure ratio of the damping force, and ensures the damping force in the medium-to-high speed range of the valve with the higher valve opening pressure. This makes it possible to achieve a ride that is more robust against changes in road surface conditions and gives occupants a sense of stability, compared to a configuration that does not have a valve-opening promotion mechanism. In other words, it is possible to obtain damping force characteristics that stabilize the sprung mass of the vehicle regardless of the road surface, allowing occupants to continue riding the vehicle without any discomfort.

[0101] According to the embodiment, the frequency characteristics of the first valve or the second valve, whichever has a greater frequency dependency of the damping force, are configured to match the frequency characteristics of the valve whose damping force has a lesser frequency dependency. This reduces the frequency dependency of the extension / pressure ratio of the damping force. This makes it possible to achieve a ride that is more robust to changes in road surface conditions and gives occupants a sense of stability. In other words, it is possible to obtain damping force characteristics that stabilize the sprung mass of the vehicle regardless of the road surface, allowing occupants to continue riding the vehicle without any discomfort.

[0102] According to this embodiment, of the first and second valves, the valve with the higher valve opening pressure opens at a slower piston speed than the valve with the lower valve opening pressure. This allows the valve with the higher valve opening pressure to increase stiffness in the mid- to high-speed range while opening at a lower piston speed. This reduces the frequency dependency of the extension-pressure ratio of the damping force, while ensuring the damping force of the valve with the higher valve opening pressure in the mid- to high-speed range.

[0103] According to this embodiment, the valve with a higher valve opening pressure, either the first or second valve, is provided with a low-speed valve that has a smaller biasing force than the valve with a lower valve opening pressure and opens the first or second passage when the piston speed is low. This allows the valve with a higher valve opening pressure to increase rigidity in the medium to high speed range while opening at a lower piston speed. This allows the valve with a higher valve opening pressure to maintain flexibility in the medium to high speed range damping force while reducing the frequency dependency of the extension / pressure ratio of the damping force.

[0104] According to the embodiment, a gap is formed between the "low-speed valve" and the "valve stacked on the low-speed valve." This makes it easier for the low-speed valve to displace (deform) toward the gap. This allows the low-speed valve to open when the piston speed is low.

[0105] According to this embodiment, the low-speed valve includes a fifth valve having a protruding portion that protrudes toward the second valve and has a larger axial width than other portions, and a small-diameter disc between the second valve and the fifth valve. This allows the thickness of the small-diameter disc to be increased while reducing the gap between the second valve and the fifth valve (protruding portion). This allows both "ensuring the mass productivity and strength of the small-diameter disc" and "ensuring the freedom to adjust the damping force."

[0106] According to this embodiment, the valve with the higher valve opening pressure, either the first or fourth valve, is provided with a valve-opening promotion mechanism that synchronizes the opening timing of the valve with the lower valve opening pressure. This allows the valve with the higher valve opening pressure to increase stiffness in the medium- to high-speed range while opening at a lower piston speed. This reduces the frequency dependency of the damping force extension / pressure ratio, while ensuring the damping force of the valve with the higher valve opening pressure in the medium- to high-speed range. This allows for a more robust ride that provides a sense of stability to occupants compared to a configuration without a valve-opening promotion mechanism, achieving a damping force characteristic that stabilizes the vehicle's sprung mass regardless of the road surface, allowing occupants to continue riding the vehicle without discomfort.

[0107] This application claims priority to Japanese Patent Application No. 2022-156052, filed September 29, 2022. The entire disclosure of Japanese Patent Application No. 2022-156052, filed September 29, 2022, including the specification, claims, drawings, and abstract, is incorporated herein by reference in its entirety. [Explanation of symbols]

[0108] 1:Buffer 2: Outer cylinder 4: Inner cylinder 5: Piston 5A: 1st oil passage (1st passage) 5B: 2nd oil passage (2nd passage) 6: Piston extension valve (first valve) 7: Piston retraction valve (second valve) 12: Valve body 12A: 3rd oil passage (3rd passage) 12B: 4th oil passage (4th passage) 13: Body extension valve (third valve) 14: Body retraction valve (4th valve) 21: Valve opening promotion mechanism 22, 41, 61: Low speed valve 22B, small diameter disc 42: Gap adjustment disc (5th valve) 42A:Protrusion 52: Piston extension side orifice (first orifice) 57: Body contraction side orifice (second orifice) A: Reservoir chamber B: Rod side oil chamber (1st chamber) C: Bottom oil chamber (second chamber)

Claims

1. A shock absorber, the shock absorber comprising: an inner cylinder in which a hydraulic fluid is sealed; a piston slidably provided within the inner cylinder, dividing the inner cylinder into a first chamber and a second chamber; a first passage provided in the piston; a first valve that opens and closes the first passage; a second passage provided in the piston; a second valve that opens and closes the second passage, A shock absorber in which the valve with the higher valve opening pressure out of the first valve and the second valve is provided with a valve opening promotion mechanism that synchronizes the opening timing of the valve with the lower valve opening pressure.

2. A shock absorber, the shock absorber comprising: an inner cylinder in which a hydraulic fluid is sealed; a piston slidably provided within the inner cylinder, dividing the inner cylinder into a first chamber and a second chamber; a first passage provided in the piston; a first valve that opens and closes the first passage; a second passage provided in the piston; a second valve that opens and closes the second passage, A shock absorber configured so that the frequency characteristics of the valve whose damping force is more frequency-dependent, out of the first valve and the second valve, are matched to the frequency characteristics of the valve whose damping force is less frequency-dependent.

3. 2. The shock absorber according to claim 1, A shock absorber in which one of the first valve and the second valve, which has a higher valve opening pressure, opens when the piston speed is lower than the valve which has a lower valve opening pressure.

4. A shock absorber, the shock absorber comprising: an inner cylinder in which a hydraulic fluid is sealed; a piston slidably provided within the inner cylinder, dividing the inner cylinder into a first chamber and a second chamber; a first passage provided in the piston; a first valve that opens and closes the first passage; a second passage provided in the piston; a second valve that opens and closes the second passage, The shock absorber is provided with a low-speed valve, which has a smaller biasing force than the valve having a lower valve-opening pressure, of the first valve and the second valve, and which opens the first passage or the second passage when the piston speed is low.

5. 5. The shock absorber according to claim 4, A shock absorber in which a gap is formed between the low-speed valve and a valve stacked on the low-speed valve.

6. 5. The shock absorber according to claim 4, The low-speed valve is a shock absorber comprising: a fifth valve having a protruding portion that protrudes toward the second valve and has a larger axial width than other portions; and a small-diameter disk between the second valve and the fifth valve, the small-diameter disk having a smaller diameter than the second valve and the fifth valve.

7. A shock absorber, the shock absorber comprising: an inner cylinder in which a hydraulic fluid is sealed; a piston slidably provided within the inner cylinder, dividing the inner cylinder into a first chamber and a second chamber; an outer cylinder provided outside the inner cylinder and forming a reservoir chamber between the outer cylinder and the inner cylinder; a valve body provided between the reservoir chamber and the second chamber; a first passage provided in the piston; a first valve that opens and closes the first passage; a first orifice provided in the first passage; a second passage provided in the piston; a second valve that opens and closes the second passage; a third passage provided in the valve body; a third valve that opens and closes the third passage; a fourth passage provided in the valve body; a fourth valve that opens and closes the fourth passage; a second orifice provided in the fourth passage; A shock absorber in which the valve having a higher valve opening pressure out of the first valve and the fourth valve is provided with a valve opening promotion mechanism that synchronizes the opening timing of the valve having a lower valve opening pressure.

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