Damper

Abstract

To provide a damper which can limit a rebound stroke when a stroke speed is high, compared to a case where the stroke speed is low.SOLUTION: A damper 1 includes: a first cylinder which is connected to the wheel side and filled with a working fluid O; a first piston 40 inserted into the first cylinder; a piston valve provided at the first piston; a rod 30 connected to the vehicle body side; a second cylinder 32 fixed to one of the first piston and the rod; a second piston 50 fixed to the other of the first piston and the rod and inserted into the second cylinder; a communication passage 33 which allows communication between a liquid chamber at one side of the second piston in the second cylinder and the interior of the first cylinder and supplies a fluid pressure for pressing the second piston in a direction such that a space between the first piston and the rod can be reduced; and a second piston restriction part 51 which allows relative displacement of the second piston relative to the second cylinder only when a stroke speed is a predetermined value or higher.SELECTED DRAWING: Figure 4

Description

TECHNICAL FIELD

[0001] The present invention relates to a damper provided in a vehicle suspension device. BACKGROUND ART

[0002] As a technology relating to a damper (shock absorber, shock absorbing device) provided as a damping element in a suspension device for a vehicle such as an automobile, Patent Document 1 discloses an arrangement in which a plurality of piston / cylinder type shock absorbers are arranged in series in a space-saving manner. The shock absorber comprises a first shock absorber that consists of a piston, a piston valve, a bottom valve, a hydraulic chamber, and a cylinder and is connected to a vehicle body side via a vehicle body-side mounting bush, and a second shock absorber that consists of a piston, a piston valve, a bottom valve, a hydraulic chamber, and a cylinder and is connected to a wheel side via a wheel-side mounting bush. A shock absorber is described in which these shock absorbers are connected in series, and one of the first and second shock absorbers is housed inside the other. Patent Document 2 describes that in a hydraulic shock absorber, in order to improve insufficient rebound stroke, a first damper and a second damper are arranged in series between a vehicle body and a wheel in a state of being independent of each other, a spring is arranged between the first damper and the vehicle body, the expansion and contraction stroke of the first damper is made longer than that of the second damper, and the damping force of the first damper is set to be higher than that of the second damper. Patent Document 3 describes a shock absorber configured to shorten the mounting distance even when the extension stroke is long, by fitting a large-diameter piston into a large-diameter cylinder tube to form a large-diameter extension chamber and a large-diameter contraction chamber, connecting a small-diameter cylinder tube to the large-diameter piston, and fitting a small-diameter piston with a rod into the small-diameter cylinder tube to form a small-diameter extension chamber and a small-diameter contraction chamber, and connecting the large-diameter extension chamber and the large-diameter contraction chamber through a first orifice, a first base valve that opens due to the negative pressure in the large-diameter extension chamber, and a first communication hole that is opened and closed by a first piston valve that opens due to the high pressure in the large-diameter extension chamber, respectively, and connecting the small-diameter extension chamber and the small-diameter contraction chamber through a second orifice, a second base valve that opens due to the negative pressure in the small-diameter extension chamber, and a second piston valve that opens due to the high pressure in the small-diameter extension chamber, respectively. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-153171 [Patent Document 2] Japanese Patent Publication No. 2005-133800 [Patent Document 3] Japanese Utility Model Publication No. 5-54838 [Overview of the project] [Problems that the invention aims to solve]

[0004] To improve the overall feel of a vehicle while it is in motion, it is necessary to reduce abnormal noises from the suspension system (typically the knocking sound of the rebound stopper) that occur when the vehicle drives over large protrusions such as speed breakers. As a countermeasure, one could consider extending the maximum rebound stroke (maximum damper length on the extension side) of the damper to suppress the stroke speed when the rebound stopper is struck, thereby mitigating the impact when the rebound stopper is struck. Furthermore, extending the rebound stroke of the rear suspension damper is considered effective from the perspective of improving road grip when driving on rough terrain.

[0005] However, if the damper's rebound stroke is made excessively long to an extent that is unnecessary during normal driving, there are concerns that it may negatively affect handling stability during normal driving. Therefore, it is desired that the rebound stroke be made relatively large in the range of slow stroke speeds, and that the rebound stroke be limited in the range of fast stroke speeds. In view of the above-mentioned problems, the object of the present invention is to provide a damper that can limit the rebound stroke when the stroke speed is high compared to when it is low. [Means for solving the problem]

[0006] To solve the above-mentioned problems, the damper of the present invention comprises: a first cylinder connected to one of the wheel side and the vehicle body side and filled with working fluid; a first piston inserted into the inner diameter side of the first cylinder so as to be axially displaceable relative to the first cylinder; a piston valve provided on the first piston that allows the working fluid to pass through in accordance with the relative displacement of the first piston with respect to the first cylinder; a rod connected to the other of the wheel side and the vehicle body side; a second cylinder fixed to one of the first piston and the rod; and a second cylinder fixed to the other of the first piston and the rod. A second piston inserted into the inner diameter side of the second cylinder so as to be axially displaceable relative to the second cylinder; a communication passage that connects the liquid chamber on one side of the second piston inside the second cylinder with the inside of the first cylinder and supplies hydraulic pressure to press the second piston in a direction that shortens the distance between the first piston and the rod; and a second piston restricting section that allows relative displacement of the second piston with respect to the second cylinder only when the relative movement speed between the first cylinder and the rod is greater than or equal to a predetermined value, and restricts relative displacement of the second piston with respect to the second cylinder in other cases. A damper comprising: the second piston restricting section having an auxiliary valve provided on the second piston that opens in accordance with an increase in the relative movement speed between the first cylinder and the rod, and allows the working fluid to pass through in accordance with the relative displacement of the second piston with respect to the second cylinder; the damper comprising: an actuator that opens and closes the auxiliary valve; a driving state detection section that detects the driving state of the vehicle; and an auxiliary valve control section that, based on the output of the driving state detection section, determines that the relative movement speed between the first cylinder and the rod is high, and causes the actuator to open the auxiliary valve; It is further characterized by having the following features. Here, "axial direction" refers to the direction of the extension / retraction axis, which is the relative direction of movement between the first cylinder and the rod when the damper extends or retracts. According to the present invention, when the relative movement speed between the first cylinder and the rod is greater than or equal to a predetermined value, the hydraulic pressure supplied to the inside of the second cylinder causes the second piston to be displaced in a direction that shortens the distance between the first piston and the rod. As a result, the first piston is in close proximity to the rod, which reduces the maximum rebound stroke (typically the extension stroke at which the rebound stopper makes contact) when the first cylinder is displaced in the rebound direction (extension direction). This makes it possible to limit the rebound stroke when the stroke speed is high compared to when it is low. As a result, the rebound stroke when passing over relatively large bumps at low speeds can be extended without affecting the vehicle's performance on smooth roads. This can suppress abnormal noise caused by the rebound stopper hitting when passing over large protrusions such as speed breakers, and improve tire contact when driving on rough roads. Furthermore, according to the present invention, the correlation between the damper's stroke speed and stroke length can be appropriately set by tuning the characteristics of the auxiliary valve. Furthermore, according to the present invention, when it is determined that the damper stroke speed is high according to the vehicle's driving conditions, the auxiliary valve is opened by the actuator, thereby enabling fine-grained control.

[0007] In the present invention, the second piston restricting portion may be configured to have a spring element provided inside the second cylinder that biases the first piston in a direction away from the rod. According to this, the above-mentioned effects can be obtained with a simple configuration.

[0009] In the present invention, the auxiliary valve can be configured as a pressure-sensitive valve that opens in response to an increase in the liquid pressure supplied from the communication passage to the second cylinder. According to this, the above-mentioned effects can be reliably obtained with a simple configuration.

[0010] To solve the above-mentioned problems, the damper of the present invention comprises: a first cylinder connected to one of the wheel side and the vehicle body side and filled with working fluid; a first piston inserted into the inner diameter side of the first cylinder so as to be axially displaceable relative to the first cylinder; a piston valve provided on the first piston that allows the working fluid to pass through in accordance with the relative displacement of the first piston with respect to the first cylinder; a rod connected to the other of the wheel side and the vehicle body side; a second cylinder fixed to the rod; and a second cylinder fixed to the first piston and inserted into the inner diameter side of the second cylinder so as to be axially displaceable relative to the second cylinder. The invention is characterized by comprising: a second piston; a communication passage formed in the second cylinder, which connects a liquid chamber on the side of the second piston to the first piston within the second cylinder with the inside of the first cylinder, and supplies hydraulic pressure to press the second piston in a direction that shortens the distance between the first piston and the rod; and a second piston restricting section that allows relative displacement of the second piston with respect to the second cylinder only when the relative movement speed between the first cylinder and the rod is greater than or equal to a predetermined value, and restricts relative displacement of the second piston with respect to the second cylinder in other cases. To solve the above-mentioned problems, the damper of the present invention comprises: a first cylinder connected to one of the wheel side and the vehicle body side and filled with working fluid; a first piston inserted into the inner diameter side of the first cylinder so as to be axially displaceable relative to the first cylinder; a piston valve provided on the first piston that allows the working fluid to pass through in accordance with the relative displacement of the first piston with respect to the first cylinder; a rod connected to the other of the wheel side and the vehicle body side; a second cylinder fixed to the first piston; and a component fixed to the rod and inserted into the inner diameter side of the second cylinder so as to be axially displaceable relative to the second cylinder. The invention is characterized by comprising: a second piston; a communication passage formed in the second cylinder, which connects a liquid chamber on the rod side of the second piston inside the second cylinder with the inside of the first cylinder, and supplies hydraulic pressure to press the second piston in a direction that shortens the distance between the first piston and the rod; and a second piston restricting section that allows relative displacement of the second piston with respect to the second cylinder only when the relative movement speed between the first cylinder and the rod is greater than or equal to a predetermined value, and restricts relative displacement of the second piston with respect to the second cylinder in other cases. [Effects of the Invention]

[0011] As described above, according to the present invention, it is possible to provide a damper capable of limiting rebound stroke when the stroke speed is high compared to when the stroke speed is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view of a first embodiment of a damper to which the present invention is applied, taken along a plane including an expansion-contraction axis. [Figure 2] FIG. 2 is a diagram illustrating an example of state changes of the damper according to the first embodiment during a low-speed stroke, shown in chronological order. [Figure 3] FIG. 3 is a diagram illustrating an example of state changes of the damper according to the first embodiment during a high-speed stroke, shown in chronological order. [Figure 4] FIG. 4 is a diagram illustrating the difference in rebound stroke between low-speed stroke and high-speed stroke in the damper according to the first embodiment. [Figure 5] FIG. 5 is a diagram showing the configuration of a control system of a third embodiment of a damper to which the present invention is applied. [Figure 6] FIG. 6 is a schematic cross-sectional view of a fourth embodiment of a damper to which the present invention is applied, taken along a plane including an expansion-contraction axis. MODE FOR CARRYING OUT THE INVENTION

[0013] <First Embodiment> Hereinafter, a first embodiment of a damper to which the present invention is applied will be described. The damper of the first embodiment is a damping element (shock absorber, hydraulic buffer) that is provided in parallel with a spring element in a suspension device of a vehicle such as an automobile, for example, and generates a damping force corresponding to the stroke speed.

[0014] FIG. 1 is a schematic cross-sectional view of the damper according to the first embodiment, taken along a plane including the expansion-contraction axis. FIG. 1 shows, for example, the 1G state (initial state / neutral state) of the vehicle. (The same applies to FIG. 6 described later) The damper 1 of the first embodiment is used, for example, in a double wishbone type suspension for the rear wheels of a vehicle. The damper 1 includes an inner cylinder 10, an outer cylinder 20, a first rod 30, a first piston 40, a second piston 50, a second rod 60, a rebound stopper 70, a base valve 80, and the like. Here, the expansion axis refers to a straight line along the central axis of the inner cylinder 10, the outer cylinder 20, and the first rod 30. In damper 1, the main cylindrical part consisting of an inner cylinder 10 and an outer cylinder 20 and the first rod 30 are displaced relative to each other in the direction of expansion and contraction along this expansion and contraction axis.

[0015] The inner cylinder 10 and outer cylinder 20 are cylindrical members that are concentric with the expansion / contraction axis. The inner cylinder 10 and the outer cylinder 20 constitute the main body cylinder of the damper 1, which is a twin-tube hydraulic shock absorber. The inner diameter side of the inner cylinder 10 is into which the first piston 40 is inserted, and functions as the first cylinder of the present invention. The inner diameter side of the inner cylinder 10 is filled with oil O, which is the working fluid for the damper 1. The inner cylinder 10 is inserted into the inner diameter side of the outer cylinder 20.

[0016] The outer cylinder 20 is provided on the outer diameter side of the inner cylinder 10 and is a component that forms part of the outer surface of the damper 1. A gap S is provided between the inner circumferential surface of the outer cylinder 20 and the outer circumferential surface of the inner cylinder 10. The upper and lower ends of the outer cylinder 20 are closed by end faces 21 and 22. At the bottom of the void S, oil O that has flowed in through the base valve 80 is stored. The upper part of the void S (the area other than the oil O) is filled with gas G. The lower part of the outer cylinder 20 is connected, for example, to an unsprung component (typically a suspension link) of a suspension device (not shown) via an elastic body such as a rubber bushing.

[0017] The first rod 30 is a cylindrical member whose lower part is inserted into the inner cylinder 10 through an opening formed in the end face 21, and whose upper part protrudes from the inner cylinder 10. The upper part of the first rod 30 is connected to a vehicle body or a vehicle body side member such as a subframe via an elastic bushing or the like (not shown). The first rod 30 is capable of relative displacement with respect to the inner cylinder 10 in the direction of its telescopic axis. The end face 31 of the first rod 30 on the side of the first piston 40 is positioned opposite the disc portion 71 of the rebound stopper 70, which will be described later.

[0018] A cylinder 32 is formed near the end of the first rod 30 on the side of the first piston 40 (the lower end in Figure 1). The cylinder 32 is a hollow section having a cylindrical shape that is concentric with the extension axis of the damper 1. Cylinder 32 functions as the second cylinder of the present invention. A second piston 50 is inserted into the inner diameter side of cylinder 32. The first rod 30 is split at a point not shown in the diagram to allow for the installation of the second piston 50 and other components, thereby providing access to the inside of the cylinder 32.

[0019] The first rod 30 further has a communication hole 33. The communication hole 33 is an oil passage formed to penetrate from the outer circumferential surface of the first rod 30 to the inner circumferential surface of the cylinder 32. The communication hole 33 connects the inside of the inner cylinder 10 (first cylinder) to the inside of the cylinder 32. The position of the through-hole 33 in the extension axis direction of the first rod 30 is located on the side of the first piston 40 (downward in the case of Figure 1) relative to the second piston 50.

[0020] The first piston 40 is a component inserted into the inner diameter side of the inner cylinder 10 in a manner that allows for relative displacement along the expansion / contraction axis direction relative to the inner cylinder 10. The first piston 40 is equipped with a piston valve that allows oil to pass through and generates damping force through flow resistance when the damper 1 strokes. The piston valve of the first piston 40 generates the damping force of the damper 1, primarily on the rebound side.

[0021] The second piston 50 is a component inserted into the inner diameter side of the cylinder 32 of the first rod 30 in a manner that allows for relative displacement along the extension axis direction relative to the first rod 30. The second piston 50 is provided with a piston valve that allows oil to pass through and generates a damping force through flow resistance when the second piston 50 is displaced relative to the first rod 30. A spring 51 is provided between the end face of the cylinder 32 on the side opposite to the first piston 40 (the upper side in the case of Figure 1) and the face of the second piston 50 that faces this end face. The spring 51 is a spring element, such as a compression coil spring, that biases the second piston 50 toward the first piston 40.

[0022] The spring 51 is a spring element that applies a predetermined preset load P (see Figure 2, etc.) to the second piston 50. The second piston 50 is constrained by the spring 51 from relative displacement with respect to the cylinder 32 until the pressure difference between the upper and lower liquid chambers of the second piston 50 within the cylinder 32 exceeds a predetermined value (the stroke speed of the damper 1 exceeds a predetermined value). Furthermore, once this pressure difference exceeds a predetermined value, the spring 51 begins to compress and deform. At this time, the second piston 50 is displaced relative to the cylinder 32 in a direction that shortens the first rod 30 and the first piston 40.

[0023] The second rod 60 is a cylindrical (or axial) member that connects the first piston 40 and the second piston 50. The second rod 60 has a small diameter portion 61 and a large diameter portion 62 that are formed integrally. The small-diameter portion 61 is the part of the second rod 60 that is on the side of the second piston 50 (the upper part in Figure 1). A portion of the small-diameter section 61 (the upper part in Figure 1) is inserted into the cylinder 32 through an opening formed in the end face 31 of the first rod 30. The second piston 50 is fixed to the tip of the small-diameter portion 61 (the upper end in Figure 1).

[0024] The large-diameter portion 62 is the part of the second rod 60 that is on the side of the first piston 40 (the lower part in Figure 1). A stepped portion, which is widened in a stepped shape, is provided at the boundary between the large-diameter portion 62 and the small-diameter portion 61. The first piston 40 is fixed to the tip of the large-diameter portion 62 (the lower end in Figure 1).

[0025] The rebound stopper 70 restricts the maximum stroke of the damper 1 in the rebound (extension) direction. The rebound stopper 70 is composed of a base portion 71, a cylindrical portion 72, a stopper member 73, and the like.

[0026] The base portion 71 is attached to the stepped portion between the small-diameter portion 61 and the large-diameter portion 62 of the second rod 60. The base portion 71 is formed, for example, in the shape of a disc with an opening in the center. The small-diameter portion 61 of the second rod 60 is inserted into the opening of the base portion 71. The cylindrical portion 72 extends from the outer peripheral edge of the base portion 71 toward the end face 21 side (upward in Figure 1). The cylindrical portion 72 is positioned concentrically with the expansion and contraction axis of the damper 1. The stopper member 73 is an elastic body attached to the end of the cylindrical portion 72 on the end face 21 side. The stopper member 73 is positioned opposite the end face 21 at a distance from it, except when the damper 1 is fully extended in the rebound direction. Furthermore, when the damper 1 is fully extended in the rebound direction, the stopper member 73 comes into contact with the end face 21.

[0027] The base valve 80 is located at the end of the inner cylinder 10 opposite to the first rod 30 side. The base valve 80, when the damper 1 strokes, allows oil to pass from inside the inner cylinder 10 to the space between the inner cylinder 10 and the outer cylinder 20, and generates a damping force due to the flow resistance. The base valve 80 generates damping force primarily on the rebound (bump) side of the damper 1.

[0028] The operation of the damper 1 in the first embodiment during stroke will be described below. Figure 2 is a time-series diagram showing an example of the state change of the damper in the first embodiment during low-speed stroke. The lower part of Figure 2 shows the time-series change in the stroke of damper 1, while the upper part shows the state of damper 1 at each point in time. The time-series changes in stroke shown in the lower section are for illustrative purposes only and do not accurately represent the actual stroke amounts. The time-series change of the stroke first shows the displacement from the initial state (neutral state) to the rebound side (compression side), then to the extension side, and finally beyond the initial state to the rebound side (extension side), until the rebound stopper is reached. (The same applies to Figure 3 described later.) Figure 2 shows a situation where the stroke speed of damper 1 is relatively slow and the road surface is uneven, such as when a vehicle passes over a speed breaker (a protrusion on the road surface to slow down a vehicle) at a low speed, or when passing over a rough road with relatively large period and amplitude irregularities (a so-called mogul road, etc.).

[0029] As shown in Figure 2(b), from the initial state shown in Figure 2(a), when the inner cylinder 10 and outer cylinder 20 rise relative to the first rod 30 and displacement toward the bound side begins, a pressure difference is created above and below the first piston 40 inside the inner cylinder 10, and the oil moves from below to above through the piston valve of the first piston 40. At this time, the piston valve generates a damping force corresponding to the stroke speed of the damper 1. Furthermore, as the insertion depth of the first rod 30 into the inner cylinder 10 increases, the volume in which oil can be stored within the inner cylinder 10 decreases, causing some of the oil to pass through the base valve 80 and move into the space between the inner cylinder 10 and the outer cylinder 20.

[0030] At this time, the force F exerted by the oil to push up the first piston 40 is less than the preset load P of the spring 51. In this state, the second piston 50 is constrained by the preset load of the spring 51 and does not undergo relative displacement with respect to the first rod 30. Therefore, as shown in Figure 2(c), even if the inner cylinder 10 strokes further toward the bounding side relative to the first rod 30, the relative position of the first piston 40 with respect to the first rod 30 remains unchanged.

[0031] Subsequently, when the inner cylinder 10 and outer cylinder 20 begin to descend relative to the first rod 30 (starting a stroke toward the rebound), the relative position of the first piston 40 with respect to the first rod 30 remains unchanged, while the inner cylinder 10 and outer cylinder 20 descend relative to the first rod 30 and the first piston 40. Ultimately, as shown in Figure 2(d), the rebound stroke is restricted when the stopper member 73 comes into contact with the end face 21 (stopper contact).

[0032] Figure 3 is a time-series diagram showing an example of the state change of the damper in the first embodiment during high-speed stroke. As shown in Figure 3(b), from the initial state in Figure 3(a), when the inner cylinder 10 and outer cylinder 20 rise relative to the first rod 30 and displacement toward the bound side begins, a pressure difference is created above and below the first piston 40 inside the inner cylinder 10, similar to the low-speed stroke, and the oil moves from bottom to top through the piston valve of the first piston 40. At this time, the piston valve generates a damping force corresponding to the stroke speed of the damper 1. Furthermore, as the insertion depth of the first rod 30 into the inner cylinder 10 increases, the volume in which oil can be stored within the inner cylinder 10 decreases, causing some of the oil to pass through the base valve 80 and move into the space between the inner cylinder 10 and the outer cylinder 20.

[0033] Here, during high-speed strokes where the stroke speed of damper 1 exceeds a predetermined value, the force F exerted by the oil to push up the first piston 40 becomes greater than or equal to the preset load P of spring 51. In this state, the force acting from the oil on the first piston 40 compresses the spring 51, causing the second piston 50 to be displaced in a direction that pushes it against the rod 32 (in a direction that brings the first piston 40 closer to the first rod 30).

[0034] Therefore, as shown in Figure 3(c), even if the inner cylinder 10 and outer cylinder 20 stroke further toward the bounding side relative to the first rod 30, the first piston 40 is maintained in a state closer to the first rod 30 than in the initial state (a state in which the first piston 40 and the first rod 30 are shortened).

[0035] Subsequently, even when the inner cylinder 10 begins to descend relative to the first rod 30 (starting its stroke toward the rebound), the pressure of the oil supplied into the cylinder 32 from the communication hole 33 does not decrease. Therefore, the inner cylinder 10 and outer cylinder 20 descend relative to the first rod 30 and the first piston 40 while the first piston 40 remains in close proximity to the first rod 30. Ultimately, as shown in Figure 3(d), the rebound stroke is restricted when the stopper member 73 comes into contact with the end face 21 (stopper contact).

[0036] Figure 4 shows the difference in rebound stroke between low-speed and high-speed strokes in the damper of the first embodiment. As described above, during high-speed stroke, the second piston 50 is displaced relative to the cylinder 32 so that the first piston 40 approaches the first rod 30. As a result, the amount of downward movement (rebound stroke) of the inner cylinder 10 and outer cylinder 20 when contact occurs with the end face 21 of the stopper member 73 is reduced by the stroke difference ΔS shown in Figure 4 compared to the low-speed stroke.

[0037] According to the first embodiment described above, the following effects can be obtained. (1) When the relative movement speed (stroke speed) between the inner cylinder 10, the outer cylinder 20 and the first rod 30 is greater than or equal to a predetermined value, the pressure of the oil O supplied into the inside of the cylinder 32 causes the second piston 50 to be displaced in a direction that shortens the distance between the first piston 40 and the first rod 30. Therefore, as the first piston 40 is in close proximity to the first rod 30, the stroke required for the damper 1 to fully extend (rebound stopper contact) when the inner cylinder 10 and outer cylinder 20 are displaced in the rebound direction (extension direction) becomes smaller. This makes it possible to limit the rebound stroke when the stroke speed is high compared to when it is low. As a result, the rebound stroke when passing over relatively large bumps at low speeds can be extended without affecting the vehicle's performance on smooth roads. This can suppress abnormal noise caused by the rebound stopper hitting when passing over large protrusions such as speed breakers, and improve tire contact when driving on rough roads. (2) By restricting the movement of the second piston 50 during low-speed strokes using a spring 51 provided inside the cylinder 32, the above-mentioned effects can be obtained with a simple configuration. (3) During high-speed stroke, damping force can also be obtained from the flow resistance of the oil as it passes through the piston valve of the second piston 50, thereby improving the damping force of the damper 1 as a whole and suppressing excessive changes in the vehicle's posture when driving at high speeds on good roads.

[0038] <Second Embodiment> Next, a second embodiment of a damper to which the present invention is applied will be described. In each embodiment described below, parts common to previous embodiments are denoted by the same reference numerals and their descriptions are omitted; the differences will be explained primarily. In the second embodiment, the piston valve provided on the second piston 50 is a pressure-sensitive valve that opens when the pressure of the oil O introduced into the cylinder 32 from the communication hole 33 exceeds a predetermined value. The piston valve of the second piston 50 opens due to the pressure of the oil O corresponding to the increase in the relative movement speed between the inner cylinder 10, outer cylinder 20 and the first rod 30, and functions as an auxiliary valve (second piston restrictor) that allows the oil O to pass through in accordance with the relative displacement of the second piston 50 with respect to the cylinder 32. In this case, the spring constant of the spring 51 does not need to take into account the preset load P as in the first embodiment, and should be set to such an extent that it is possible to return the second piston 50 to its initial position in the neutral state where no hydraulic pressure acts on the second piston 50.

[0039] According to the second embodiment described above, in addition to the effects similar to those of the first embodiment described above, the correlation between the stroke speed and stroke length of the damper 1 can be appropriately set by tuning the characteristics of the piston valve of the second piston 50. Furthermore, by making the piston valve a pressure-sensitive valve that opens in response to an increase in the oil pressure supplied to the cylinder 32, the above-mentioned effects can be reliably obtained with a simple configuration.

[0040] <Third Embodiment> Next, a third embodiment of a damper to which the present invention is applied will be described. In the third embodiment, a valve that can be opened and closed by an actuator (for example, a solenoid) is used as the piston valve of the second piston 50 in the second embodiment, and the opening and closing of the valve is controlled according to the vehicle's driving conditions. In the third embodiment, as in the second embodiment, the piston valve of the second piston 50 functions as the second piston restrictor.

[0041] Figure 5 shows the configuration of the damper control system according to the third embodiment. The control system 200 includes a damper control unit 210, an environment recognition unit 220, a driving mode control unit 230, and the like. Each unit can be configured as a microcomputer having, for example, an information processing unit such as a CPU, a storage unit such as RAM or ROM, an input / output interface, and a bus to connect these. Furthermore, each unit is connected in a way that allows communication, either via an in-vehicle LAN such as a CAN communication system, or directly.

[0042] The damper control unit 210 is an auxiliary valve control unit that controls and drives the solenoid 211, which is an actuator that opens and closes the piston valve (auxiliary valve in this invention) of the second piston 50. A damper stroke sensor 212 is connected to the damper control unit 210. The damper stroke sensor 212 has a position encoder that detects the stroke of the damper 1 (the relative position of the inner cylinder 10 with respect to the first rod 30). The damper control unit 210 calculates the stroke velocity of the damper 1 (the relative velocity of the inner cylinder 10 with respect to the first rod 30) by differentiating the stroke detected by the damper stroke sensor 212 with respect to time.

[0043] The environmental recognition unit 220 recognizes the environment in front of the vehicle and other surrounding areas using various sensors. The environmental recognition unit 220 is connected to a stereo camera device 221, which is an example of a sensor. The stereo camera device 221 is arranged horizontally separated by a predetermined baseline length and includes a pair of cameras whose imaging range is in front of the vehicle, and an image processing unit that performs stereo camera processing on the images captured by these cameras to recognize objects and calculate the relative position of objects to the vehicle. The environmental recognition unit 220 can recognize obstacles such as speed breakers and large-amplitude uneven roads that are located in front of the vehicle and are expected to be passed by the vehicle, in accordance with information from the stereo camera device 221.

[0044] The driving mode control unit 230 changes the vehicle's driving mode in response to the operation of the driving mode selection switch 231 by the driver or other occupant. Driving modes include, for example, a normal mode used for driving on good roads and a rough road mode used for driving on rough roads. The driving mode control unit 230 modifies the characteristics of the driving power source such as the engine, the shift control in the transmission, the fastening force control of the AWD transfer case, and the LSD control which prevents some wheels from slipping by utilizing the braking force of each wheel, according to the selected driving mode. The environmental recognition unit 220 and the driving mode control unit 230 function as the driving state detection unit of the present invention.

[0045] The damper control unit 210, for example, if at least one of the following conditions is met, causes the second piston valve solenoid 211 to close the piston valve of the second piston 50, thereby making the rebound stroke of the damper 1 relatively long, and otherwise opens the piston valve, thereby limiting the rebound stroke of the damper 1. (1) The stroke speed of the damper 1 detected by the damper stroke sensor 212 is less than or equal to a predetermined value. (2) The environmental recognition unit 220 recognizes protrusions such as speed breakers or rough roads. (3) Select rough road mode in the driving mode control unit 230 In other words, when the damper control unit 210 determines that the relative movement speed between the inner cylinder 10, outer casing 20, and rod 30 is high, it causes the solenoid 211 to open the piston valve (auxiliary valve) of the second piston 50.

[0046] According to the third embodiment described above, when it is determined that the stroke speed of the damper 1 is high according to the vehicle's driving conditions, the piston valve of the second piston 50 is opened by the solenoid 211, thereby enabling fine-grained control.

[0047] <Fourth Embodiment> Next, a third embodiment of a damper to which the present invention is applied will be described. Figure 6 is a schematic cross-sectional view of the damper of the fourth embodiment, as seen when it is cut through a plane containing the expansion axis. The damper 1A of the fourth embodiment is used, for example, in a MacPherson strut type suspension for the front wheels of a vehicle.

[0048] The damper 1A of the fourth embodiment has a rod 130, a second piston 150, a second rod 160, and a rebound stopper 170, which are described below, instead of the first rod 30, second piston 50, second rod 60, and rebound stopper 70 of the first embodiment.

[0049] The rod 130 is a cylindrical member whose lower part is inserted into the inner cylinder 10 through an opening formed in the end face 21, and whose upper part protrudes from the inner cylinder 10. The upper part of the rod 130 is connected to a vehicle body or a vehicle body side member such as a subframe via an elastic bushing or the like (not shown). The rod 130 is capable of relative displacement in the direction of its telescopic axis with respect to the inner cylinder 10. The end of the rod 130 on the side of the first piston 40 is connected to the upper part of the second piston 50.

[0050] The second piston 150 is a disc-shaped member connected to the end of the rod 130 on the side of the first piston 40 (the lower end in Figure 6). The second piston 150 is inserted into a cylinder 162 (second cylinder) formed inside the second rod 160, in a manner that allows for relative displacement along the extension axis direction relative to the second rod 160. The second piston 150 is provided with a piston valve that allows oil to pass through and generates a damping force through flow resistance when the second piston 150 is displaced relative to the second rod 160.

[0051] The second rod 160 is a cylindrical member that protrudes from the first piston 40 toward the rod 130 side (upward side). An opening is formed on the end face 161 of the second rod 160 on the side opposite to the first piston 40 (upper side), into which the lower end of the rod 130 is inserted into the cylinder 162. A cylinder 162 is formed inside the second rod 160. The cylinder 162 is a hollow section having a cylindrical shape that is concentric with the extension axis of the damper 1. Cylinder 162 functions as the second cylinder of the present invention. A second piston 150 is inserted into the inner diameter side of cylinder 162. The second rod 160 is split at a point not shown in the diagram to allow for the installation of the second piston 150 and other components, thereby providing access to the inside of the cylinder 162.

[0052] Inside the cylinder 162, there is a spring 151 that biases the second piston 150 toward the opposite side from the first piston 40 (upwards in Figure 6). The spring 151 is a compression coil spring, for example, provided between the face of the second piston 150 on the side of the first piston 40 and the end (end face) of the cylinder 162 on the side of the first piston. The spring 151 is a second piston restricting unit that generates a predetermined preset load P and restricts the relative displacement of the second piston 150 with respect to the second rod 160 during the low-speed stroke of the damper 1.

[0053] The second rod 160 further has a communication hole 163. The communication hole 163 is an oil passage formed to penetrate from the outer circumferential surface of the second rod 160 to the inner circumferential surface of the cylinder 162. The communication hole 163 connects the inside of the inner cylinder 10 (first cylinder) to the inside of the cylinder 162. The through-hole 163 of the second rod 160, in the direction of its extension and retraction axis, is located on the opposite side of the second piston 150 from the first piston 40 side (upper side in the case of Figure 6).

[0054] The rebound stopper 170 restricts the maximum stroke of the damper 1A in the rebound (extension) direction. The rebound stopper 170 is configured to include a disc portion 171, a stopper member 172, and the like.

[0055] The disc portion 171 is a disc-shaped member that is concentric with the expansion and contraction axis of the damper 1A. An opening is formed in the center of the disc portion 171 through which the rod 130 is inserted. The disc portion 171 is fixed to the end of the second rod 160 opposite to the first piston 40 side (upper side). The disc portion 171 moves relative to the rod 130 in accordance with the relative displacement of the second rod 160 with respect to the rod 130. The stopper member 172 is an elastic body attached to the surface of the disc portion 171 that faces the end face 21. The stopper member 172 is positioned opposite the end face 21 at a distance from it, except when the damper 1A is fully extended in the rebound direction. Furthermore, when the damper 1A is fully extended in the rebound direction, the stopper member 172 comes into contact with the end face 21.

[0056] In the fourth embodiment, during the low-speed stroke of the damper 1A, the relative displacement of the second piston 150 with respect to the second rod 160 is restricted by the preset load P of the spring 151. On the other hand, during high-speed strokes of the damper 1A, the pressure of the oil introduced into the cylinder 162 from the communication hole 163 overcomes the preset load P, causing the second piston 150 to be displaced in a direction that brings it closer to the first piston 40. As a result, the rebound stroke amount of damper 1A is limited (shortened) compared to that during low-speed stroke.

[0057] According to the fourth embodiment described above, in addition to the effects similar to those of the first embodiment described above, the present invention can also be applied to dampers with relatively small rod diameters, such as those used in MacPherson strut type suspensions. Furthermore, in the configuration of the damper 1A of the fourth embodiment, similar to the second embodiment, the piston valve of the second piston 150 can be made a pressure-sensitive valve and used as a second piston restrictor. Also, similar to the third embodiment, the piston valve of the second piston 150 can be opened and closed by an actuator such as a solenoid.

[0058] (modified version) The present invention is not limited to the embodiments described above, and various modifications and changes are possible, all of which fall within the technical scope of the present invention. For example, the shape, structure, material, manufacturing method, number, arrangement, etc., of each component constituting the damper can be changed as appropriate, without being limited to the embodiments described above. For example, the dampers in each embodiment are of the twin-tube type, having an inner cylinder and an outer cylinder as the main body cylinder, but the present invention can also be applied to a single-tube type damper in which an oil chamber and a gas chamber are arranged in series via a free piston. Furthermore, the type and layout of the suspension system in which the dampers are installed, as well as the configuration of the vehicle, are not particularly limited. [Explanation of Symbols]

[0059] 1 Damper (First Embodiment) 1A Damper (Fourth Embodiment) 10 Inner cylinder 20 Outer cylinder 21,22 End face 30 First rod 31 End face 32 Cylinder 33 Connecting holes 40 First piston 50 Second piston 51 Spring 60 Second rod 61 Small diameter section 62 Large diameter section 70 Rebound stopper 71 Base 72 Cylindrical part 73 Stopper member 80 Base valve 130 Rod 150 Second Piston 151 Spring 160 Second Rod 161 End face 162 Cylinder 163 Connecting holes 170 Rebound stopper 171 Disc section 172 Stopper member 200 Control System (Third Embodiment) 210 Damper control unit 211 Solenoid 212 Damper stroke sensor 220 Environmental recognition unit 221 Stereo camera device 230 Driving mode control unit 231 Driving mode selection switch

Claims

1. A first cylinder connected to either the wheel side or the vehicle body side and filled with working fluid, A first piston is inserted into the inner diameter side of the first cylinder so as to be axially displaceable relative to the first cylinder, A piston valve provided on the first piston allows the working fluid to pass through in accordance with the relative displacement of the first piston with respect to the first cylinder, A rod connected to the other side of the wheel side and the vehicle body side, A second cylinder fixed to either the first piston or the rod, A second piston is fixed to the other end of the first piston and the rod and inserted into the inner diameter side of the second cylinder so as to be axially displaceable relative to the second cylinder, A communication passage is provided to connect the liquid chamber on one side of the second piston inside the second cylinder with the inside of the first cylinder, supplying hydraulic pressure to press the second piston in a direction that shortens the distance between the first piston and the rod, A second piston restricting unit that allows relative displacement of the second piston relative to the second cylinder only when the relative movement speed between the first cylinder and the rod is greater than or equal to a predetermined value, and restricts relative displacement of the second piston relative to the second cylinder in other cases, A damper equipped with, The second piston restricting section has an auxiliary valve provided on the second piston that opens in accordance with an increase in the relative movement speed between the first cylinder and the rod, and allows the working fluid to pass through in accordance with the relative displacement of the second piston with respect to the second cylinder. The aforementioned damper, An actuator for opening and closing the auxiliary valve, A driving state detection unit that detects the driving state of the vehicle, Based on the output of the driving state detection unit, if it is determined that the relative movement speed between the first cylinder and the rod is high, the auxiliary valve control unit causes the actuator to open the auxiliary valve, A damper characterized by having additional features.

2. The second piston restricting portion is provided inside the second cylinder and has a spring element that biases the first piston in a direction away from the rod. The damper according to claim 1, characterized by the following:

3. The auxiliary valve is a pressure-sensitive valve that opens in response to an increase in the fluid pressure supplied from the communication passage to the second cylinder. The damper according to claim 2, characterized by the following:

4. A first cylinder connected to either the wheel side or the vehicle body side and filled with working fluid, A first piston is inserted into the inner diameter side of the first cylinder so as to be axially displaceable relative to the first cylinder, A piston valve provided on the first piston allows the working fluid to pass through in accordance with the relative displacement of the first piston with respect to the first cylinder, A rod connected to the other side of the wheel side and the vehicle body side, A second cylinder fixed to the aforementioned rod, A second piston is fixed to the first piston and inserted into the inner diameter side of the second cylinder so as to be axially displaceable relative to the second cylinder, A communication passage formed in the second cylinder, which connects the liquid chamber on the first piston side of the second piston inside the second cylinder with the inside of the first cylinder, and supplies a liquid pressure that presses the second piston in a direction that shortens the distance between the first piston and the rod, A second piston restricting unit that allows relative displacement of the second piston relative to the second cylinder only when the relative movement speed between the first cylinder and the rod is greater than or equal to a predetermined value, and restricts relative displacement of the second piston relative to the second cylinder in other cases, A damper characterized by having the following features.

5. A first cylinder connected to either the wheel side or the vehicle body side and filled with working fluid, A first piston is inserted into the inner diameter side of the first cylinder so as to be axially displaceable relative to the first cylinder, A piston valve provided on the first piston allows the working fluid to pass through in accordance with the relative displacement of the first piston with respect to the first cylinder, A rod connected to the other side of the wheel side and the vehicle body side, A second cylinder fixed to the first piston, A second piston is fixed to the rod and inserted into the inner diameter side of the second cylinder so as to be axially displaceable relative to the second cylinder, A communication passage formed in the second cylinder, which connects the liquid chamber on the rod side of the second piston inside the second cylinder with the inside of the first cylinder, and supplies a liquid pressure that presses the second piston in a direction that shortens the distance between the first piston and the rod, A second piston restricting unit that allows relative displacement of the second piston relative to the second cylinder only when the relative movement speed between the first cylinder and the rod is greater than or equal to a predetermined value, and restricts relative displacement of the second piston relative to the second cylinder in other cases, A damper characterized by having the following features.

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