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Abstract

To provide a shock absorber capable of improving ride comfort on a vehicle by changing friction force according to the vibration states of a vehicle body.SOLUTION: A shock absorber D includes a shaft 1 rotatable in the peripheral direction, a first friction disc 2 fixed to the shaft 1, a second friction disc 3 for generating friction force between the first friction disc 2 and itself to suppress the rotation of the shaft 1, a third friction disc 4 for generating friction force between the first friction disc 2 and itself to suppress the rotation of the shaft 1, a first opposite member 5 non-rotatable in the peripheral direction and arranged on the counter first friction disc side of the second friction disc 3 in the axial direction, a second opposite member 6 non-rotatable in the peripheral direction and arranged on the counter first friction disc side of the third friction disc 4 in the axial direction, a first elastic body 7 connected to the first opposite member 5 and the second friction disc 3, and a second elastic body 8 connected to the second opposite member 6 and the third friction disc 4.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a shock absorber. [Background technology]

[0002] Shock absorbers that absorb vibration energy and damp the vibration of the object to be damped include hydraulic shock absorbers that use the viscous resistance of hydraulic oil, as well as shock absorbers that use inertial mass as resistance or frictional force as resistance.

[0003] Generally, hydraulic shock absorbers are widely used in vehicle suspensions, but due to issues with response caused by the compressibility of hydraulic oil, there are attempts to use shock absorbers that utilize frictional force, which has better response, in suspensions.

[0004] Such a shock absorber includes, for example, a cylinder, a rod-shaped piston that is inserted into the cylinder so that it can slide freely, a friction pad that is inserted into the cylinder and restricted from moving axially so that it comes into sliding contact with the side of the piston, and an elastic body that urges the friction pad toward the side of the piston; when the piston moves axially relative to the cylinder, a friction force is generated between the piston and the friction pad, generating a damping force that impedes movement of the piston (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-179198 Summary of the Invention [Problem to be solved by the invention]

[0006] Here, the hydraulic shock absorber used in the suspension has a damping force characteristic that increases the damping force as the extension / retraction speed increases, and suppresses the vibration of the vehicle body according to the vibration conditions of the vehicle body, maintaining a good ride comfort in the vehicle.

[0007] However, although conventional shock absorbers that utilize frictional force are superior to hydraulic shock absorbers in that they can generate damping force with good responsiveness, because the frictional force between the friction pad and the piston is constant, they can only output a constant damping force in response to the stroke of vertical displacement of the vehicle body relative to the wheel.

[0008] Therefore, if the damping force of a conventional shock absorber that uses frictional force is set to a small value to suit the vehicle body vibration when stroking with a small amplitude (small stroke), the shock absorber will not be able to generate the damping force required when stroking with a large amplitude (large stroke), and will not be able to sufficiently suppress the vehicle body vibration.

[0009] However, if the damping force of a conventional shock absorber that uses frictional force is set to a large value to suit vehicle body vibration during large strokes, the damping force generated by the shock absorber during small strokes will be excessive, impairing the ride comfort of the vehicle.

[0010] As described above, conventional shock absorbers that utilize frictional force are unable to generate a damping force that corresponds to the vibration state of the vehicle body, and therefore have the problem of impairing the ride comfort of the vehicle.

[0011] SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a shock absorber that can improve the ride comfort of a vehicle by changing the damping force in accordance with the vibration state of the vehicle body. [Means for solving the problem]

[0012] In order to solve the above-mentioned problems, the shock absorber of the present invention comprises a shaft that can rotate in a circumferential direction, a first friction disc that is fixed to the shaft and can rotate in the circumferential direction together with the shaft, a second friction disc that is unable to rotate in the circumferential direction and that generates a frictional force between it and the first friction disc when it comes into contact with the first friction disc to suppress rotation of the shaft, a third friction disc that is unable to rotate in the circumferential direction and that generates a frictional force between it and the first friction disc when it comes into contact with a side of the first friction disc opposite to the second friction disc to suppress rotation of the shaft, a first opposing member that is unable to rotate in the circumferential direction and is arranged on the side opposite to the first friction disc in the axial direction of the second friction disc, a second opposing member that is unable to rotate in the circumferential direction and is arranged on the side opposite to the first friction disc in the axial direction of the third friction disc, a first elastic body that is arranged between the second friction disc and the first opposing member, and a second elastic body that is arranged between the third friction disc and the second opposing member, and the first opposing member and the second opposing member are configured to move in one axial direction as the shaft rotates in one direction, and move in the other axial direction as the shaft rotates in the other direction.

[0013] In a shock absorber configured in this manner, when the shaft rotates in one direction, the first opposing member and the second opposing member move axially in one direction, and when the shaft rotates in the other direction, the first opposing member and the second opposing member move axially in the other direction.Therefore, when the amount of rotation of the shaft from the neutral position is small, the load on one of the first elastic body and the second elastic body is increased, but the load on the other of the first elastic body and the second elastic body is decreased, thereby reducing the damping force.

[0014] Furthermore, in a shock absorber configured in this manner, when the amount of rotation of the shaft from the neutral position is small, the load on one of the first elastic body and the second elastic body is increased while the load on the other of the first elastic body and the second elastic body is decreased, or both the second friction disc and the third friction disc can be spaced apart from the first friction disc, thereby reducing the damping force. Furthermore, in a shock absorber configured in this manner, when the amount of rotation of the shaft from the neutral position is large, the load on one of the first elastic body or the second elastic body is increased, thereby increasing the damping force.

[0015] Furthermore, the characteristics of the damping force generated when the shaft rotates in one direction from the neutral position may be different from the characteristics of the damping force generated when the shaft rotates in the other direction from the neutral position. With a shock absorber configured in this manner, the characteristics of the damping force on the extension side generated when the vehicle body and the wheel move away from each other and the characteristics of the damping force on the contraction side generated when the vehicle body and the wheel move closer to each other can be optimized, thereby effectively improving the ride comfort of the vehicle.

[0016] Furthermore, the shock absorber may have a shaft provided with a threaded portion on its outer periphery, and the first opposing member and the second opposing member are annular and threaded onto the outer periphery of the threaded portion. With a shock absorber configured in this manner, rotation of the shaft can be easily converted into axial movement of the first opposing member and the second opposing member by using a simple screw mechanism. [Effects of the Invention]

[0017] As described above, the shock absorber of the present invention can change the damping force in accordance with the vibration state of the vehicle body, thereby improving the ride comfort of the vehicle. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 2 is a cross-sectional view of a shock absorber according to an embodiment. [Figure 2] 1 is a diagram showing a shock absorber according to an embodiment in a state where the shock absorber is installed on a vehicle body. [Figure 3] 1 is a side view of a shock absorber according to an embodiment of the present invention, in a state where the shock absorber is installed on a vehicle body. [Figure 4] FIG. 1 is a perspective view of a shock absorber according to an embodiment. [Figure 5] FIG. 4 is a diagram showing the damping force characteristics of the shock absorber according to the embodiment. [Figure 6] FIG. 10 is a diagram showing a first modified example of the damping force characteristics of the shock absorber. [Figure 7] FIG. 10 is a diagram showing a second modified example of the damping force characteristics of the shock absorber. [Figure 8] FIG. 10 is a diagram showing a third modified example of the damping force characteristics of the shock absorber. [Figure 9] FIG. 10 is a diagram showing a fourth modified example of the damping force characteristics of the shock absorber. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, the present invention will be described based on the embodiment shown in the drawings. In this specification, when the term "axial direction" is used simply, it refers to the direction along the axial direction of the shaft 1 in the shock absorber D.

[0020] As shown in FIGS. 1 to 3 , a shock absorber D in one embodiment includes: a shaft 1 rotatably inserted in a cylindrical case 9; a first friction disc 2 fixed to the shaft 1 and rotatable in the circumferential direction together with the shaft 1; a second friction disc 3 that generates a frictional force between the first friction disc 2 and the second friction disc 2 when it comes into contact with the first friction disc 2 to suppress rotation of the shaft 1; a third friction disc 4 that generates a frictional force between the first friction disc 2 and the third friction disc 4 when it comes into contact with the first friction disc 2 to suppress rotation of the shaft 1; a first opposing member 5 that is unable to rotate in the circumferential direction and is arranged on the opposite side of the second friction disc 3 in the axial direction; a second opposing member 6 that is unable to rotate in the circumferential direction and is arranged on the opposite side of the third friction disc 4 in the axial direction; a first elastic body 7 that is arranged between the first opposing member 5 and the second friction disc 3; and a second elastic body 8 that is arranged between the second opposing member 6 and the third friction disc 4. The shock absorber D is interposed between the vehicle body B and the wheel W, with the case 9 attached to the vehicle body B and the shaft 1 connected to an axle A supporting a wheel W of the vehicle via arms 10a, 10b attached to both ends of the shaft 1. When the vehicle body B and the wheel W approach or move away from each other in the vertical direction, the shock absorber D rotates the shaft 1 to generate frictional forces that suppress the rotation of the shaft 1 between the first friction disc 2 and the second friction disc 3, and between the first friction disc 2 and the third friction disc 4, thereby exerting a damping force that suppresses relative displacement between the vehicle body B and the wheel W.

[0021] Each part of the shock absorber D will be described in detail below. As shown in Figures 1 to 4, the case 9 is cylindrical and has eight key grooves 9a formed along the axial direction on the inner periphery. Annular caps 11 and 12 are attached to the left and right ends of the case 9 in Figure 1, respectively.

[0022] Both ends of shaft 1 protrude outside case 9 through the inner peripheries of caps 11 and 12, and shaft 1 is supported in a state where rotation in the circumferential direction is permitted by bearings 13 and 14 provided on the inner peripheries of caps 11 and 12. An annular first friction disc 2 is fixedly attached to the outer periphery of the center of shaft 1, and screw portions 1a and 1b with screw grooves are provided on both sides of the outer periphery of shaft 1 that sandwich first friction disc 2.

[0023] The first friction disc 2 is annular and has friction surfaces 2a and 2b with high friction resistance on both sides in the axial direction of the shaft 1. The outer diameter of the first friction disc 2 is smaller than the inner diameter of the case 9, and is rotatable together with the shaft 1 in the circumferential direction relative to the case 9.

[0024] The second friction disc 3 is annular, and is disposed so as to face the friction surface 2a of the first friction disc 2 on the right side in Fig. 1 in the axial direction, and is held by an annular holder 15, which restricts rotation in the circumferential direction but allows movement in the axial direction, and is therefore able to move toward and away from the first friction disc 2 in the axial direction. When the second friction disc 3 comes into contact with the friction surface 2a, which is the second friction disc side surface of the first friction disc 2, a friction force is generated between the second friction disc 3 and the first friction disc 2 that restricts rotation of the shaft 1.

[0025] The holder 15 is annular, and has the second friction disc 3 attached to its left end in FIG. 1. The holder 15 also has eight keys 15a that are evenly spaced around its outer periphery and inserted into the key grooves 9a of the case 9, and an annular ridge 15b that protrudes in the axial direction from its right end in FIG. 1, which is the end opposite the second friction disc.

[0026] The inner diameters of the second friction disc 3 and the holder 15 are larger than the outer diameter of the shaft 1, and the shaft 1 is inserted through the inner peripheries of the second friction disc 3 and the holder 15. When the holder 15 is housed in the case 9, the key 15a is slidably inserted into the key groove 9a, so that the holder 15 is prevented from rotating in the circumferential direction relative to the case 9 but is allowed to move in the axial direction. Thus, the second friction disc 3 is restricted from rotating in the circumferential direction relative to the case 9 but is allowed to move in the axial direction, and the shaft 1 can rotate in the circumferential direction within the case 9 without interfering with the inner periphery of the second friction disc 3 and the inner periphery of the holder 15. In this embodiment, the second friction disc 3 is held in the holder 15, and the key 15a and the key groove 9a restrict the rotation of the second friction disc 3 relative to the case 9. However, the circumferential rotation of the second friction disc 3 may be restricted by other means, and the holder 15 may be omitted if the circumferential rotation of the second friction disc 3 can be suppressed. Furthermore, the number of keys 15a and key grooves 9a can be changed arbitrarily as long as it allows the second friction disc 3 to move in the axial direction while preventing rotation in the circumferential direction.

[0027] The third friction disc 4 is annular, and is disposed so as to face the friction surface 2b of the first friction disc 2 on the left side in Fig. 1 in the axial direction, and is held by an annular holder 16, which restricts rotation in the circumferential direction but allows movement in the axial direction, and is therefore able to move toward and away from the first friction disc 2 in the axial direction. When the third friction disc 4 comes into contact with the friction surface 2b, which is the third friction disc side surface of the first friction disc 2, a friction force is generated between the third friction disc 4 and the first friction disc 2 that restricts rotation of the shaft 1.

[0028] The holder 16 is annular, and has the third friction disc 4 attached to its right end in FIG. 1. The holder 16 also has eight keys 16a that are evenly spaced around its outer periphery and inserted into key grooves 9a in the case 9, and an annular ridge 16b that protrudes in the axial direction from its left end in FIG. 1, which is the end opposite the third friction disc.

[0029] The inner diameters of the third friction disc 4 and the holder 16 are larger than the outer diameter of the shaft 1, and the shaft 1 is inserted through the inner peripheries of the third friction disc 4 and the holder 16. When the holder 16 is housed in the case 9, the key 16a is slidably inserted into the key groove 9a, so that the holder 16 is prevented from rotating in the circumferential direction relative to the case 9 but is allowed to move in the axial direction. Thus, the third friction disc 4 is restricted from rotating in the circumferential direction relative to the case 9 but is allowed to move in the axial direction, and the shaft 1 can rotate in the circumferential direction within the case 9 without interfering with the inner periphery of the third friction disc 4 and the inner periphery of the holder 16. Note that in this embodiment, the third friction disc 4 is held by the holder 16, and the key 16a and the key groove 9a restrict the rotation of the third friction disc 4 relative to the case 9. However, the circumferential rotation of the third friction disc 4 may be restricted by other means, and the holder 16 may be omitted if the circumferential rotation of the third friction disc 4 can be suppressed. Furthermore, the number of keys 16a and key grooves 9a can be changed arbitrarily as long as it allows the third friction disc 4 to move in the axial direction while preventing rotation in the circumferential direction.

[0030] The first opposing member 5 is disposed at a position spaced apart from the second friction disc 3 in the axial direction, and faces the right side surface of the second friction disc 3 in FIG. 1, which is the side surface opposite the first friction disc. The first opposing member 5 is annular, and includes a threaded portion 5a provided on its inner periphery and an annular ridge 5b protruding from the end on the second friction disc side, and is threadedly engaged with the outer periphery of the threaded portion 1a of the shaft 1.

[0031] The outer periphery of the first opposing member 5 is provided with eight keys 5c that are inserted into key grooves 9a of the case 9. When the first opposing member 5 is housed in the case 9, the keys 5c are slidably inserted into the key grooves 9a, preventing the first opposing member 5 from rotating in the circumferential direction relative to the case 9, but allowing movement in the axial direction. Therefore, when the shaft 1 rotates clockwise as viewed from the left in FIG. 1, the first opposing member 5 moves axially toward the first friction disk, which is to the left in FIG. 1, relative to the shaft 1 and the case 9. Conversely, when the shaft 1 rotates counterclockwise as viewed from the left in FIG. 1, the first opposing member 5 moves axially toward the opposite side of the first friction disk, which is to the right in FIG. 1, relative to the shaft 1 and the case 9. In this way, when the shaft 1 rotates in one circumferential direction, the first opposing member 5 moves in one axial direction on the shaft 1, and when the shaft 1 rotates in the other circumferential direction, the first opposing member 5 moves in the other axial direction on the shaft 1.

[0032] Next, in the shock absorber D of this embodiment, the first elastic body 7 is a coil spring, and one end, which is the left end in FIG. 1 , is fitted into the inner periphery of a protrusion 15b provided on a holder 15 that holds the second friction disc 3, thereby connecting the second friction disc 3, and the other end, which is the right end in FIG. 1 , is fitted into the inner periphery of a protrusion 5b of the first opposing member 5, thereby connecting the first opposing member 5, and is disposed between the first opposing member 5 and the second friction disc 3. In this way, the first elastic body 7 is connected to the second friction disc 3 and the first opposing member 5 and interposed between them. Note that it is sufficient that the first elastic body 7 is disposed between the first opposing member 5 and the second friction disc 3 in a manner that prevents it from falling off at least one of the first opposing member 5 and the holder 15.

[0033] When the second friction disc 3 is in contact with the first friction disc 2 and the axial distance between the second friction disc 3 and the first opposing member 5 becomes shorter than the natural length of the first elastic body 7, the first elastic body 7 is compressed to exert a resilient force and press the second friction disc 3 against the first friction disc 2. On the other hand, when the second friction disc 3 is separated from the first friction disc 2, the first elastic body 7 fully extends to its natural length. In this case, the first elastic body 7 is at its natural length and the second friction disc 3 is also separated from the first friction disc 2, so no load is applied to the second friction disc 3 and the first friction disc 2.

[0034] One end of the first elastic body 7 is positioned radially by the rib protrusion 15b of the holder 15, and the other end of the first elastic body 7 is positioned radially by the rib protrusion 5b of the first opposing member 5. This prevents the load applied by the first elastic body 7 to the first friction disc 2 and the second friction disc 3 from being eccentric relative to the axis when compressed. Therefore, the first elastic body 7 can apply a stable load to the first friction disc 2 and the second friction disc 3 when compressed. The first elastic body 7 may be radially positioned by fitting the rib protrusion 15b of the holder 15 to the inner periphery of the end of the first elastic body 7 and fitting the rib protrusion 5b of the first opposing member 5 to the inner periphery of the end of the first elastic body 7. The structure connecting the first elastic body 7 to the second friction disc 3 and the first opposing member 5 may be a structure other than the structure using the ribs 15b, 5b described above.

[0035] The second opposing member 6 is disposed at a position spaced apart from the third friction disc 4 in the axial direction, and faces the left side surface of the third friction disc 4 in FIG. 1, which is the side surface opposite the first friction disc. The second opposing member 6 is annular, and includes a threaded portion 6a provided on its inner periphery and an annular ridge 6b protruding from the end on the third friction disc side, and is threadedly engaged with the outer periphery of the threaded portion 1b of the shaft 1.

[0036] Furthermore, eight keys 6c are provided on the outer periphery of the second opposing member 6 to be inserted into key grooves 9a of the case 9. When the second opposing member 6 is housed in the case 9, the keys 6c are slidably inserted into the key grooves 9a, so that the second opposing member 6 cannot rotate in the circumferential direction relative to the case 9 but is allowed to move in the axial direction. Therefore, when the shaft 1 rotates clockwise as viewed from the left in FIG. 1, the second opposing member 6 moves axially to the left in FIG. 1 relative to the shaft 1 and the case 9, and is displaced so as to move axially away from the third friction disc 4. Conversely, when the shaft 1 rotates counterclockwise as viewed from the left in FIG. 1, the second opposing member 6 moves axially to the right in FIG. 1 relative to the shaft 1 and the case 9, and approaches the third friction disc 4 in the axial direction. In this way, when the shaft 1 rotates in one circumferential direction, the second opposing member 6 moves on the shaft 1 in one axial direction, which is the same direction as the first opposing member 5, and when the shaft 1 rotates in the other circumferential direction, the second opposing member 6 moves on the shaft 1 in the other axial direction, which is the same direction as the first opposing member 5.

[0037] Next, in the shock absorber D of this embodiment, the second elastic body 8 is a coil spring, and one end, which is the right end in FIG. 1 , is fitted into the inner periphery of a protrusion 16 b provided on a holder 16 that holds the third friction disc 4, thereby connecting the third friction disc 4, and the other end, which is the left end in FIG. 1 , is fitted into the inner periphery of a protrusion 6 b of the second opposing member 6, thereby connecting the second opposing member 6, and is thus arranged between the second opposing member 6 and the third friction disc 4. In this way, the second elastic body 8 is connected to the third friction disc 4 and the second opposing member 6 and interposed between them. Note that it is sufficient that the second elastic body 8 is arranged between the second opposing member 6 and the third friction disc 4 in a manner that prevents it from falling off at least one of the second opposing member 6 and the holder 16.

[0038] When the third friction disc 4 is in contact with the first friction disc 2 and the axial distance between the third friction disc 4 and the second opposing member 6 becomes shorter than the natural length of the second elastic body 8, the second elastic body 8 is compressed to exert a resilient force and press the third friction disc 4 against the first friction disc 2. On the other hand, when the third friction disc 4 is separated from the first friction disc 2, the second elastic body 8 fully extends to its natural length. In this case, the second elastic body 8 is at its natural length and the third friction disc 4 is also separated from the first friction disc 2, so no load is applied to the third friction disc 4 and the first friction disc 2.

[0039] One end of the second elastic body 8 is positioned radially by the rib protrusion 16b of the holder 16, and the other end of the second elastic body 8 is positioned radially by the rib protrusion 6b of the second opposing member 6. This prevents the load applied by the second elastic body 8 to the first friction disc 2 and the third friction disc 4 from being eccentric relative to the axis when compressed. Therefore, the second elastic body 8 can apply a stable load to the first friction disc 2 and the third friction disc 4 when compressed. The second elastic body 8 may be radially positioned by fitting the rib protrusion 16b of the holder 16 to the inner periphery of the end of the second elastic body 8 and fitting the rib protrusion 6b of the second opposing member 6 to the inner periphery of the end of the second elastic body 8. The structure connecting the second elastic body 8 to the third friction disc 4 and the second opposing member 6 may be a structure other than the structure using the ribs 16b, 6b described above.

[0040] In addition, in the shock absorber D of this embodiment, the second friction disc 3 and the third friction disc 4 have the same thickness (axial length), the first elastic body 7 and the second elastic body 8 are coil springs with the same natural length and spring constant, and the threaded portions 1a and 1b of the shaft 1 have the same winding direction and pitch. Furthermore, in the shock absorber D of this embodiment, the friction coefficient between the first friction disc 2 and the second friction disc 3 is made equal to the friction coefficient between the first friction disc 2 and the third friction disc 4. The amount of rotation of the shaft 1 is proportional to the relative stroke between the vehicle body B and the wheel W, and can therefore be considered the stroke amount in a direct-acting shock absorber. In the shock absorber D of this embodiment, the stroke range is the range within which the shaft 1 can rotate in the circumferential direction relative to the case 9, and the position where the rotation position of the shaft 1 is in the center of this stroke range is considered the neutral position of the shaft 1.

[0041] Furthermore, when the shaft 1 is in the neutral position, the axial distance from the first opposing member 5 to the first friction disc 2 is shorter than the sum of the thickness (axial length) of the second friction disc 3 and the natural length of the first elastic body 7, and the first elastic body 7 is compressed to exert a resilient force, thereby applying a load to the first friction disc 2 and the second friction disc 3. Furthermore, when the shaft 1 is in the neutral position, the axial distance from the second opposing member 6 to the first friction disc 2 is shorter than the sum of the thickness (axial length) of the third friction disc 4 and the natural length of the second elastic body 8, and the second elastic body 8 is compressed to exert a resilient force, thereby applying a load to the first friction disc 2 and the third friction disc 4. Furthermore, when the shaft 1 is in the neutral position, the axial distance from the first opposing member 5 to the first friction disc 2 and the axial distance from the second opposing member 6 to the first friction disc 2 are both equal.

[0042] Therefore, when the shaft 1 is in the neutral position, the first friction disc 2 and the second friction disc 3 come into contact with each other, causing the first elastic body 7 to be compressed, and a load from the first elastic body 7 acts on the first friction disc 2 and the second friction disc 3, and the first friction disc 2 and the third friction disc 4 come into contact with each other, causing the second elastic body 8 to be compressed, and a load from the second elastic body 8 acts on the first friction disc 2 and the third friction disc 4. Therefore, when the shaft 1 is in the neutral position, the shock absorber D generates a damping force that suppresses rotation of the shaft 1 by the friction forces generated between the first friction disc 2 and the second friction disc 3 and between the first friction disc 2 and the third friction disc 4, regardless of whether the shaft 1 rotates clockwise or counterclockwise as viewed from the left in FIG.

[0043] The shock absorber D is configured as described above, and operation of the shock absorber D will be described below. In the shock absorber D, the case 9 is attached to the vehicle body B, and the shaft 1 is connected to the axle A that supports the wheel W via arms 10a, 10b attached to both ends, and the shock absorber D is interposed in parallel with the suspension spring S between the vehicle body B and the wheel W. As described above, the case 9 is used to hold the caps 11, 12 that support the shaft 1 and to restrict circumferential rotation of the second friction disc 3, the third friction disc 4, the first opposing member 5, and the second opposing member 6, but the circumferential rotation of the second friction disc 3, the third friction disc 4, the first opposing member 5, and the second opposing member 6 may be restricted by using something other than the case 9. The cylindrical shape of the case 9 protects the components of the shock absorber D housed within the case 9, but the caps 11 and 12 may be connected by a connecting rod or the like instead of the case 9, and the connecting rod may be used to restrict the circumferential rotation of the second friction disc 3, the third friction disc 4, the first opposing member 5, and the second opposing member 6. Also, a reducer may be provided between the arms 10a, 10b and the shaft 1.

[0044] The suspension spring S is compressed by the weight of the vehicle body B, generating a resilient force that supports the vehicle body B, thereby elastically supporting the vehicle body B, and maintaining the vehicle height at a predetermined height when the vehicle body B is not vibrating. The shock absorber D of this embodiment is installed on the vehicle so that the shaft 1 is located in the neutral position described above when the vehicle height is maintained at a predetermined height by the suspension spring S.

[0045] When the vehicle is traveling and the wheels W travel over uneven road surfaces, causing a relative displacement between the vehicle body B and the wheels W in the vertical direction, the shock absorber D generates a damping force that suppresses vertical vibration of the vehicle body B and the wheels W by suppressing the rotation of the shaft 1 with the sum of the friction force between the first friction disc 2 and the second friction disc 3 and the friction force between the first friction disc 2 and the third friction disc 4 when the shaft 1 rotates from its neutral position relative to the case 9.

[0046] Specifically, when the vehicle travels and the wheel W travels over an uneven road surface, the vehicle body B and the wheel W move apart in the vertical direction, causing the shaft 1 to rotate clockwise relative to the case 9 from a neutral position as viewed from the left in FIG. 1. As the shaft 1 rotates clockwise from the neutral position, the first opposing member 5 moves axially toward the first friction disc 2 provided at the center of the shaft 1, and the second opposing member 6 moves axially away from the first friction disc 2 provided at the center of the shaft 1. As described above, because the winding direction and pitch of the threaded portions 1a and 1b are the same, when the shaft 1 rotates clockwise, the first opposing member 5 and the second opposing member 6 are displaced axially to the left in FIG. 1 by an equal distance.

[0047] Here, the distance that the first opposing member 5 and the second opposing member 6 move in the axial direction when the shaft 1 rotates clockwise as viewed from the left in Fig. 1 from a state in which the shaft 1 is in the neutral position is referred to as the movement distance, and the amount of compression of the first elastic body 7 and the second elastic body 8 when the shaft 1 is in the neutral position is referred to as the initial compression amount. When the movement distance is equal to or less than the initial compression amount, the first opposing member 5 approaches the first friction disc 2, so the first elastic body 7 is compressed while the first friction disc 2 and the second friction disc 3 remain in contact with each other, and even when the second opposing member 6 moves away from the first friction disc 2 by the movement distance, the second elastic body 8 only extends by a length equal to or less than its natural length, so the first friction disc 2 and the third friction disc 4 remain in contact with each other.

[0048] In this case, the first elastic body 7 between the second friction disc 3 and the first opposing member 5 contracts by an amount equal to the movement distance, and the load that the first elastic body 7 applies to the first friction disc 2 and the second friction disc 3 increases, while the second elastic body 8 between the third friction disc 4 and the second opposing member 6 expands by an amount equal to the movement distance, and the load that the second elastic body 8 applies to the first friction disc 2 and the third friction disc 4 decreases.

[0049] As described above, in the shock absorber D of this embodiment, the natural lengths and spring constants of the first elastic body 7 and the second elastic body 8 are the same, so when the movement distance of the first opposing member 5 and the second opposing member 6 due to rotation of the shaft 1 from the neutral position is equal to or less than the initial compression amount, the increase in the load applied by the first elastic body 7 and the decrease in the load applied by the second elastic body 8 are balanced. As described above, the shock absorber D generates a damping force that suppresses vertical vibration of the vehicle body B and the wheels W by suppressing the rotation of the shaft 1 with the sum of the friction force between the first friction disc 2 and the second friction disc 3 and the friction force between the first friction disc 2 and the third friction disc 4.

[0050] In the shock absorber D of this embodiment, the coefficient of friction between the first friction disc 2 and the second friction disc 3 is equal to the coefficient of friction between the first friction disc 2 and the third friction disc 4, and the load increase of the first elastic body 7 is equal to the load decrease of the second elastic body 8. Therefore, when the shaft 1 rotates with the movement distance equal to or less than the initial compression amount, the sum of the friction force between the first friction disc 2 and the second friction disc 3 and the friction force between the first friction disc 2 and the third friction disc 4 does not change from the sum of the respective friction forces when the shaft 1 starts to rotate from a state in which it is in the neutral position.

[0051] Therefore, even if the vehicle body B and the wheel W are displaced so as to separate from each other in the vertical direction, if the amount of rotation of the shaft 1 is small and the movement distance is equal to or less than the initial compression amount, the damping force generated by the shock absorber D will not change, will be constant, and will be at a minimum, as shown by the solid line in Fig. 5. In Fig. 5, the horizontal axis indicates the stroke of the vehicle body B relative to the wheel W, and the state in which the shaft 1 is in the neutral position is set to 0. In addition, the range to the right of the vertical axis in Fig. 5 indicates the damping force exerted by the shock absorber D when the rotational position of the shaft 1 is clockwise from the neutral position, and the range to the left of the vertical axis in Fig. 5 indicates the damping force exerted by the shock absorber D when the rotational position of the shaft 1 is counterclockwise from the neutral position.

[0052] Conversely, when the vehicle body B and the wheel W are displaced so as to approach each other in the vertical direction and the shaft 1 rotates counterclockwise as viewed from the left in Fig. 1, the counterclockwise rotation of the shaft 1 from the neutral position causes the first opposing member 5 to move in the axial direction away from the first friction disc 2 provided at the center of the shaft 1, and the second opposing member 6 to move in the axial direction toward the first friction disc 2 provided at the center of the shaft 1. As described above, since the winding direction and pitch of the threaded portions 1a and 1b are the same, when the shaft 1 rotates counterclockwise, the first opposing member 5 and the second opposing member 6 are displaced in the axial direction to the right in Fig. 1 by an equal distance.

[0053] If the movement distance when the shaft 1 rotates counterclockwise from the neutral position is less than the initial compression amount, the decrease in the load applied by the first elastic body 7 and the increase in the load applied by the second elastic body 8 are balanced, just as when the shaft 1 rotates clockwise from the neutral position.

[0054] Therefore, even if the vehicle body B and the wheel W are displaced so as to approach each other in the vertical direction, if the amount of rotation of the shaft 1 is small and the movement distance when the shaft 1 rotates from the neutral position is equal to or less than the initial compression amount, the damping force generated by the shock absorber D will not change, will be constant, and will be at a minimum, as shown in Figure 5.

[0055] On the other hand, if the amount of rotation of the shaft 1 when it rotates clockwise from the neutral position is large and the movement distance exceeds the initial compression amount, the amount of compression of the first elastic body 7 increases as the first opposing member 5 approaches the first friction disc 2, while the second opposing member 6 moves away from the first friction disc 2, causing the second elastic body 8 to fully stretch and causing the third friction disc 4 to move away from the first friction disc 2.

[0056] In this situation, because the third friction disc 4 is separated from the first friction disc 2, the amount of compression of the first elastic body 7 increases in response to the clockwise rotation of the shaft 1, and the friction force generated between the first friction disc 2 and the second friction disc 3 simply increases. Therefore, if the amount of rotation of the shaft 1 when it rotates clockwise from the neutral position is large and the movement distance exceeds the initial compression amount, the damping force generated by the shock absorber D increases in response to the clockwise rotation of the shaft 1.

[0057] Furthermore, after the shaft 1 rotates clockwise and the movement distance exceeds the initial compression amount, when the shaft 1 rotates counterclockwise toward the neutral position, the damping force generated by the shock absorber D decreases in accordance with the counterclockwise rotation of the shaft 1 until the movement distance becomes equal to the initial compression amount.

[0058] Furthermore, if the amount of rotation of the shaft 1 when it rotates counterclockwise from the neutral position is large and the movement distance exceeds the initial compression amount, the amount of compression of the second elastic body 8 increases as the second opposing member 6 approaches the first friction disc 2, while the first opposing member 5 moves away from the first friction disc 2, causing the first elastic body 7 to fully stretch, and the second friction disc 3 to move away from the first friction disc 2.

[0059] In this situation, because the second friction disc 3 is separated from the first friction disc 2, the amount of compression of the second elastic body 8 increases in response to the counterclockwise rotation of the shaft 1, and the friction force generated between the first friction disc 2 and the third friction disc 4 simply increases. Therefore, if the amount of rotation of the shaft 1 when it rotates counterclockwise from the neutral position is large and the movement distance exceeds the initial compression amount, the damping force generated by the shock absorber D increases in response to the counterclockwise rotation of the shaft 1.

[0060] Furthermore, after the shaft 1 rotates counterclockwise and the movement distance exceeds the initial compression amount, when the shaft 1 rotates clockwise toward the neutral position, the damping force generated by the shock absorber D decreases in accordance with the clockwise rotation of the shaft 1 until the movement distance becomes equal to the initial compression amount.

[0061] Therefore, when the shaft 1 rotates from the neutral position and the movement distance is in a range that exceeds the initial compression amount, as shown in Figure 5, the damping force of the shock absorber D increases or decreases in proportion to the amount of rotation of the shaft 1 from the neutral position.

[0062] As can be understood from the above, the shock absorber D generates a constant, minimum damping force until the movement distance of the first opposing member 5 and the second opposing member 6 as the shaft 1 rotates clockwise or counterclockwise from a state in which the shaft 1 is in the neutral position exceeds the initial compression amount of the first elastic body 7 and the second elastic body 8, and once the movement distance exceeds the initial compression amount, the shock absorber D increases or decreases the damping force in proportion to the rotation amount of the shaft 1. The initial compression amount of the first elastic body 7 and the second elastic body 8 can be adjusted by setting the distance between the first opposing member 5 and the first friction disc 2 and the distance between the second opposing member 6 and the first friction disc 2 when the shaft 1 is in the neutral position. Therefore, if the initial compression amounts of the first elastic body 7 and the second elastic body 8 are reduced, the stroke range (amount of rotation from the neutral position of the shaft 1) over which the damping force exerted by the shock absorber D is constant and at its minimum can be reduced, as shown by the dashed line in Fig. 5, and if the initial compression amounts of the first elastic body 7 and the second elastic body 8 are increased, the stroke range (amount of rotation from the neutral position of the shaft 1) over which the damping force exerted by the shock absorber D is constant and at its minimum can be increased, as shown by the dashed line in Fig. 5. Furthermore, if the first friction disc 2 and the second friction disc 3 are exactly in contact with each other and the first friction disc 2 and the third friction disc 4 are also exactly in contact with each other when the shaft 1 is in the neutral position, and the initial compression amounts of the first elastic body 7 and the second elastic body 8 are set to 0, then as the shaft 1 rotates from the neutral position, the damping force of the shock absorber D increases from 0 in proportion to the amount of rotation of the shaft 1, as shown by the dashed line in Fig. 5.

[0063] Furthermore, if the second friction disc 3 and the third friction disc 4 are spaced apart from the first friction disc 2 when the shaft 1 is in the neutral position, the shaft 1 can rotate freely without being restricted by frictional force until the shaft 1 rotates from the neutral position and the first friction disc 2 comes into contact with the second friction disc 3 or the third friction disc 4. Therefore, in this case, as shown in Fig. 6, the shock absorber D does not exert a damping force when the amount of rotation of the shaft 1 from the neutral position is small, but when the amount of rotation of the shaft 1 from the neutral position increases and the first friction disc 2 comes into contact with the second friction disc 3 or the third friction disc 4, the first elastic body 7 or the second elastic body 8 contracts, generating a frictional force between the second friction disc 3 or the third friction disc 4 and the first friction disc 2, and therefore exerts a damping force according to the amount of rotation of the shaft 1.

[0064] When the shaft 1 is in the neutral position, if the axial distance between the first opposing member 5 and the first friction disc 2 is made shorter than the axial distance between the second opposing member 6 and the first friction disc 2, the range in which the damping force of the shock absorber D is constant at a minimum can be offset to the left as shown by the solid line in Fig. 7, compared to the damping force characteristics when both distances are the same, as shown by the dashed line in Fig. 7. Note that when the shaft 1 is in the neutral position, if the axial distance between the first opposing member 5 and the first friction disc 2 is made longer than the axial distance between the second opposing member 6 and the first friction disc 2, the range in which the damping force of the shock absorber D is constant at a minimum can be offset to the right, compared to the damping force characteristics when both distances are the same. Note that by making the natural length of the second elastic body 8 longer than the natural length of the first elastic body 7 and making the axial distance between the first opposing member 5 and the first friction disc 2 the same as the axial distance between the second opposing member 6 and the first friction disc 2 when the shaft 1 is in the neutral position, the range in which the damping force of the shock absorber D is constant at its lowest can be offset to the left in FIG. 7 compared to the damping force characteristics when the natural lengths of the first elastic body 7 and the second elastic body 8 are the same. Conversely, by making the natural length of the second elastic body 8 longer than the natural length of the first elastic body 7, the range in which the damping force of the shock absorber D is constant at its lowest can be offset to the right in FIG. 7. In this way, the initial positions of the first opposing member 5 and the second opposing member 6 and the natural lengths of the first elastic body 7 and the second elastic body 8 are tuning elements for setting the damping force characteristics of the shock absorber D.

[0065] In the configuration of the shock absorber D described above, if the spring constant of the first elastic body 7 and the spring constant of the second elastic body 8 are different, the damping force characteristic line can be set to have a slope in the range where the movement distance is equal to or less than the initial compression amount, and the rate of increase in the damping force relative to the amount of rotation of the shaft 1 can be set to differ depending on the direction of rotation of the shaft 1 in the range where the movement distance exceeds the initial compression amount. If the spring constant of the first elastic body 7 is set to be greater than the spring constant of the second elastic body 8, the damping force characteristic line in the range where the movement distance is equal to or less than the initial compression amount will rise to the right, as shown by line A in Fig. 8, and in the range where the movement distance exceeds the initial compression amount, the rate of increase in the damping force of the shock absorber D relative to the amount of rotation of the shaft 1 when the rotation position of the shaft 1 is clockwise from the neutral position will be greater than the rate of increase in the damping force of the shock absorber D relative to the amount of rotation of the shaft 1 when the rotation position of the shaft 1 is counterclockwise from the neutral position. If the spring constant of the first elastic body 7 is made smaller than the spring constant of the second elastic body 8, the damping force characteristics of the shock absorber D will be the opposite of what has been described above, as shown by line B in Fig. 8, where the damping force characteristic line rises to the left in the range where the movement distance is equal to or less than the initial compression amount, and in the range where the movement distance exceeds the initial compression amount, the rate of increase in the damping force of the shock absorber D relative to the amount of rotation of the shaft 1 when the rotation position of the shaft 1 is clockwise from the neutral position will be smaller than the rate of increase in the damping force of the shock absorber D relative to the amount of rotation of the shaft 1 when the rotation position of the shaft 1 is counterclockwise from the neutral position. In this way, the spring constants of the first elastic body 7 and the second elastic body 8 are tuning elements for setting the damping force characteristics of the shock absorber D.

[0066] Furthermore, in the configuration of shock absorber D described above, if the pitch of threaded portion 1a and the pitch of threaded portion 1b are different, a difference may occur in the distance traveled by first opposing member 5 and second opposing member 6 per rotation of shaft 1. If the pitch of threaded portion 1a is made larger than the pitch of threaded portion 1b, the characteristic line of the damping force of shock absorber D will trace a locus similar to that obtained by offsetting the characteristic shown by the solid line in Fig. 5 to the right and rotating counterclockwise, as shown by line A in Fig. 8. In this case, within a range in which the travel distance exceeds the initial compression amount, the rate of increase in the damping force of shock absorber D relative to the amount of rotation of shaft 1 when the rotational position of shaft 1 is clockwise from the neutral position will be greater than the rate of increase in the damping force of shock absorber D relative to the amount of rotation of shaft 1 when the rotational position of shaft 1 is counterclockwise from the neutral position.

[0067] If the pitch of thread portion 1a is made smaller than the pitch of thread portion 1b, the damping force characteristics of shock absorber D will be the opposite of what has been described above, as shown by line B in Fig. 8, where the characteristic line of the damping force of shock absorber D traces a locus that resembles the characteristic shown by the solid line in Fig. 5 offset to the left and rotated clockwise. In this case, within a range in which the movement distance exceeds the initial compression amount, the rate of increase in the damping force of shock absorber D relative to the amount of rotation of shaft 1 when the rotation position of shaft 1 is clockwise from the neutral position will be smaller than the rate of increase in the damping force of shock absorber D relative to the amount of rotation of shaft 1 when the rotation position of shaft 1 is counterclockwise from the neutral position. In this way, the pitch of thread portions 1a and 1b is a tuning element for setting the damping force characteristics of shock absorber D.

[0068] Furthermore, in the configuration of the shock absorber D described above, when the friction coefficient between the first friction disc 2 and the second friction disc 3 and the friction coefficient between the first friction disc 2 and the third friction disc 4 are different, the damping force characteristic line can be set to have a slope in the range where the movement distance is equal to or less than the initial compression amount, and the rate of increase in the damping force relative to the amount of rotation of the shaft 1 can be set to differ depending on the direction of rotation of the shaft 1 in the range where the movement distance exceeds the initial compression amount. Note that if the friction coefficient between the first friction disc 2 and the second friction disc 3 is made larger than that between the first friction disc 2 and the third friction disc 4, the damping force characteristic line will rise to the right in the range where the movement distance is equal to or less than the initial compression amount, as shown by line C in Fig. 9 , and in the range where the movement distance exceeds the initial compression amount, the rate of increase in the damping force of the shock absorber D relative to the amount of rotation of the shaft 1 when the rotation position of the shaft 1 is clockwise from the neutral position will be larger than the rate of increase in the damping force of the shock absorber D relative to the amount of rotation of the shaft 1 when the rotation position of the shaft 1 is counterclockwise from the neutral position.

[0069] If the friction coefficient between the first friction disc 2 and the second friction disc 3 is made smaller than the friction coefficient between the first friction disc 2 and the third friction disc 4, the damping force characteristics of the shock absorber D will, contrary to what has been described above, become such that the damping force characteristic line rises to the left in a range in which the movement distance is equal to or less than the initial compression amount, as shown by line D in Fig. 9 , and in a range in which the movement distance exceeds the initial compression amount, the rate of increase in the damping force of the shock absorber D relative to the amount of rotation of the shaft 1 when the rotation position of the shaft 1 is clockwise from the neutral position will be smaller than the rate of increase in the damping force of the shock absorber D relative to the amount of rotation of the shaft 1 when the rotation position of the shaft 1 is counterclockwise from the neutral position. In this way, the friction coefficient between the first friction disc 2 and the second friction disc 3 and the friction coefficient between the first friction disc 2 and the third friction disc 4 are tuning elements for setting the damping force characteristics of the shock absorber D.

[0070] As mentioned above, there are many tuning factors for the damping force characteristics of the shock absorber D of this embodiment, but tuning the damping force characteristics becomes easier if the spring constants of the first elastic body 7 and the second elastic body 8 are made the same. This is because, by making the spring constants of the first elastic body 7 and the second elastic body 8 the same, the damping force characteristics can be easily adjusted by the axial positions of the first elastic body 7 and the second elastic body 8 when the shaft 1 is in the neutral position.

[0071] In the case of shock absorber D of this embodiment, the range in which shaft 1 is allowed to rotate circumferentially relative to case 9 is defined as the stroke range, and the position where shaft 1's rotation position is at the center of this stroke range is defined as the neutral position of shaft 1. However, the neutral position can be changed arbitrarily, and the neutral position may also be the position where shaft 1 is positioned circumferentially relative to case 9 when vehicle body B is stationary and maintained at a constant vehicle height by suspension spring S.

[0072] As described above, the shock absorber D of this embodiment comprises the shaft 1 that is rotatable in the circumferential direction, the first friction disc 2 that is fixed to the shaft 1 and is rotatable in the circumferential direction together with the shaft 1, the second friction disc 3 that is unable to rotate in the circumferential direction and that generates a frictional force between the first friction disc 2 and the second friction disc 2 when it comes into contact with the first friction disc 2 to suppress the rotation of the shaft 1, the third friction disc 4 that is unable to rotate in the circumferential direction and that generates a frictional force between the first friction disc 2 and the first friction disc 2 when it comes into contact with the side of the first friction disc 2 opposite to the second friction disc, and the third friction disc 4 that is unable to rotate in the circumferential direction and that generates a frictional force between the first friction disc 2 and the second friction disc 2 when it comes into contact with the side of the first friction disc 2 opposite to the second friction disc, a first opposing member 5 arranged on the opposite side of the third friction disc 4 to the first friction disc in the axial direction; a second opposing member 6 which is unable to rotate in the circumferential direction and is arranged on the opposite side of the third friction disc 4 to the first friction disc in the axial direction; a first elastic body 7 which has one end connected to the second friction disc 3 and the other end connected to the first opposing member 5; and a second elastic body 8 which has one end connected to the third friction disc 4 and the other end connected to the second opposing member 6. The first opposing member 5 and the second opposing member 6 are configured to move in one axial direction as the shaft 1 rotates in one direction, and to move in the other axial direction as the shaft 1 rotates in the other direction.

[0073] In the shock absorber D configured in this manner, when the shaft 1 rotates in one direction (clockwise), the first opposing member 5 and the second opposing member 6 move in one axial direction, and when the shaft 1 rotates in the other direction (counterclockwise), the first opposing member 5 and the second opposing member 6 move in the other axial direction. Therefore, when the amount of rotation of the shaft 1 from the neutral position is small, the shock absorber D increases the load on one of the first elastic body 7 and the second elastic body 8 while decreasing the load on the other of the first elastic body 7 and the second elastic body 8, or can space both the second friction disc 3 and the third friction disc 4 from the first friction disc 2, thereby reducing the damping force. Furthermore, in the shock absorber D configured in this manner, when the amount of rotation of the shaft 1 from the neutral position is large, the load on one of the first elastic body 7 or the second elastic body 8 increases, thereby increasing the damping force.

[0074] Therefore, when the vehicle body B is displaced vertically relative to the wheel W around the vehicle height, the shock absorber D configured in this manner generates a damping force sufficient to suppress the displacement of the vehicle body B, since the amount of rotation of the shaft 1 from the neutral position is small if the amount of displacement is small. On the other hand, when the vehicle body B vibrates significantly relative to the wheel W, the amount of rotation of the shaft 1 from the neutral position becomes large, and a high damping force is exerted according to the stroke of the vehicle body B.

[0075] Therefore, the shock absorber D of this embodiment can not only exert a low damping force suitable for suppressing vibration of the vehicle body B when the vehicle body B vibrates with a small stroke, but also generate a high damping force required when the vehicle body B vibrates with a large stroke, and can generate an appropriate damping force according to the vibration conditions of the vehicle body B. In this way, the shock absorber D of this embodiment can change the damping force according to the vibration conditions of the vehicle body B, thereby improving the ride comfort of the vehicle.

[0076] Furthermore, in the shock absorber D of this embodiment, the spring constants of the first elastic body 7 and the second elastic body 8 are the same. With the shock absorber D configured in this manner, by making the spring constants of the first elastic body 7 and the second elastic body 8 the same, it is possible to easily adjust the damping force characteristics by changing the axial positions of the first elastic body 7 and the second elastic body 8 when the shaft 1 is in the neutral position.

[0077] Furthermore, if the characteristics of the damping force generated when the shaft 1 rotates from the neutral position to one side are different from the characteristics of the damping force generated when the shaft 1 rotates from the neutral position to the other side, the ride comfort of the vehicle can be effectively improved by optimizing the characteristics of the extension side damping force generated when the shock absorber D separates the vehicle body B and the wheel W, and the characteristics of the contraction side damping force generated when the vehicle body B and the wheel W approach each other.

[0078] Furthermore, in the shock absorber D of this embodiment, the shaft 1 is provided with threaded portions 1a and 1b on its outer periphery, and the first opposing member 5 and the second opposing member 6 are annular and are threadedly engaged with the outer peripheries of the threaded portions 1a and 1b. With the shock absorber D configured in this manner, it is possible to easily convert rotation of the shaft 1 into axial movement of the first opposing member 5 and the second opposing member 6 using a simple screw mechanism. Note that if the first opposing member 5 and the second opposing member 6 are provided with ball nuts on their inner peripheries, it is possible to smoothly convert rotational movement of the shaft 1 into axial linear movement of the first opposing member 5 and the second opposing member 6, which makes it possible to suppress damping force that is not attributable to the frictional force between the first friction disc 2 and the second friction disc 3 and the frictional force between the first friction disc 2 and the third friction disc 4, and it becomes easier to set the damping force characteristics of the shock absorber D.

[0079] In the shock absorber D of this embodiment, the first elastic body 7 and the second elastic body 8 are coil springs, but it is also possible to use elastic bodies other than coil springs, such as disc springs, spring washers, gas springs, rubber, synthetic resins, etc.

[0080] The first elastic body 7 and the second elastic body 8 may be coil springs whose pitch changes along the way. In the shock absorber D configured in this way, the spring constant changes when the narrow-pitch portion becomes the solid length due to compression of the first elastic body 7 and the second elastic body 8, so the damping coefficient of the shock absorber D can be set to change along the way.

[0081] In the shock absorber D of this embodiment, a first friction force generating unit consisting of a second friction disc 3, a first elastic body 7, and a first opposing member 5 is provided on one axial side of the first friction disc 2, and a second friction force generating unit consisting of a third friction disc 4, a second elastic body 8, and a second opposing member 6 is provided on the other axial side of the first friction disc 2, but multiple sets of the first friction disc 2 and the first friction force generating unit may be provided in the axial direction of the shaft 1, or multiple sets of the first friction disc 2, the first friction force generating unit, and the second friction force generating unit may be provided in the axial direction of the shaft 1.

[0082] In the description of this embodiment, the shock absorber D is interposed between the vehicle body B and the wheels W to be used for vibration control of the vehicle body B, but the shock absorber D can also be used for vibration control of civil engineering structures, buildings, various machines and equipment in addition to vehicle vibration control applications.

[0083] Although the preferred embodiment of the present invention has been described in detail, modifications, variations and changes can be made thereto without departing from the scope of the appended claims. [Explanation of symbols]

[0084] REFERENCE SIGNS LIST 1 shaft, 1a, 1b screw portion, 2 first friction disc, 3 second friction disc, 4 third friction disc, 5 first opposing member, 6 second opposing member, 7 first elastic body, 8 second elastic body, D shock absorber

Claims

1. a shaft that is rotatable in a circumferential direction; a first friction disk fixed to the shaft and rotatable in a circumferential direction together with the shaft; a second friction disc that is unable to rotate in a circumferential direction and that generates a friction force between the first friction disc and the second friction disc when the second friction disc abuts against the first friction disc to suppress rotation of the shaft; a third friction disc that is unable to rotate in a circumferential direction and that generates a frictional force between the first friction disc and the third friction disc when the third friction disc abuts against a side surface of the first friction disc opposite to the second friction disc, thereby suppressing rotation of the shaft; a first opposing member that is unable to rotate in a circumferential direction and is disposed on the opposite side of the second friction disc in the axial direction from the first friction disc; a second opposing member that is unable to rotate in a circumferential direction and is disposed on the opposite side of the third friction disc in the axial direction from the first friction disc; a first elastic body having one end connected to the second friction disc and the other end disposed between the first opposing member and the first elastic body; a second elastic body having one end connected to the third friction disc and the other end disposed between the second friction disc and the second opposing member; The first opposing member and the second opposing member move in one axial direction as the shaft rotates in one direction, and move in the other axial direction as the shaft rotates in the other direction. A shock absorber characterized by:

2. The characteristics of the damping force generated when the shaft rotates in one direction from the neutral position are different from the characteristics of the damping force generated when the shaft rotates in the other direction from the neutral position.

2. The shock absorber according to claim 1.

3. The shaft has a threaded portion on its outer periphery, The first opposing member and the second opposing member are annular and are threaded onto the outer periphery of the screw portion.

3. The shock absorber according to claim 1 or 2.

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