JP2010038173A - Hydraulic shock absorber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To release hydraulic oil that has entered a cylinder tube from a reservoir and hydraulic oil that has entered a gas chamber behind a free piston to a reservoir in a hydraulic shock absorber.
In the hydraulic shock absorber 10, when the free piston 60 is on the lower end to the normal upper end side, the gas chamber 73 behind the free piston 60 is blocked from the gas chamber 32 of the reservoir 30, and the free piston The sub-tank chamber 53 communicates with the reservoir 30 via the gas chamber 73 behind the free piston 60 when 60 normally exceeds the rising end.
[Selection] Figure 5

Description

  The present invention relates to a hydraulic shock absorber such as a front fork for a motorcycle.

  As a hydraulic shock absorber used for a front fork for a motorcycle, as disclosed in Patent Document 1, an axle side tube is slidably inserted into a vehicle body side tube, and a damper connected to the vehicle body side tube inside the vehicle body side tube is used. A main piston provided on a piston rod connected to the axle side tube inside the axle side tube is slidably inserted into the cylinder tube, and the inside of the cylinder tube is inserted into the piston side oil chamber and the rod side oil chamber by the main piston. The expansion side damping valve is provided in the flow path connecting the piston side oil chamber and the rod side oil chamber of the main piston, and the sub piston facing the main piston is provided above the main piston inside the cylinder tube, With this sub piston, the sub tank chamber is partitioned above the piston side oil chamber inside the cylinder tube, A compression-side damping valve is provided in the flow path that allows the piston-side oil chamber and sub-tank chamber to communicate with each other, and a free piston facing the sub-piston is movably provided above the sub-piston inside the cylinder tube. Some have a pressure spring biased toward the sub-piston.

  In this hydraulic shock absorber, the gas chamber behind the free piston is blocked from the gas chamber of the reservoir. As a result, the free piston provided inside the cylinder tube of the damper has a spring force that increases in proportion to the stroke amount of the pressure spring and a gas spring that increases in proportion to the volume change of the gas chamber behind the free piston. Energized by force. Therefore, the inside of the cylinder tube of the damper is always pressurized by the free piston, and a predetermined damping force is generated by the compression side damping valve from the beginning when the damper starts the compression operation from the maximum extension state.

Further, in this hydraulic shock absorber, the gas spring force depending on the volume change of the gas chamber of the reservoir is not exerted on the free piston inside the cylinder tube of the damper. Therefore, by appropriately exerting the gas spring force of the gas chamber behind the free piston, the spring force of the pressure spring can be reduced, and riding comfort can be improved.
JP2005-30534

  In the hydraulic shock absorber described in Patent Document 1, the free piston rises to the highest rise end caused by the high pressure surplus oil of the hydraulic oil that has entered the cylinder tube of the damper from the reservoir, exceeding the normal rise end caused by the expansion / contraction stroke of the damper. In this case, the sub tank chamber between the free piston and the sub piston is directly communicated with the reservoir without passing through the gas chamber behind the free piston. The high pressure surplus oil that has entered the cylinder tube from the reservoir is released directly from the sub-tank chamber to the reservoir to avoid high pressure in the cylinder tube.

  However, in the hydraulic shock absorber described in Patent Document 1, when the free piston repeatedly moves, the hydraulic oil in the sub tank chamber may be scooped up by the free piston and enter the gas chamber behind the free piston. Since the gas chamber behind the free piston is always blocked from the reservoir gas chamber, the pressure is gradually increased by the hydraulic oil that has entered the sub tank chamber. This may impair the sealing function of the sealing member that is sealed.

  An object of the present invention is to release hydraulic oil that has entered the cylinder tube from the reservoir and hydraulic oil that has entered the gas chamber behind the free piston to the reservoir in the hydraulic shock absorber.

  In the first aspect of the present invention, the axle side tube is slidably inserted into the vehicle body side tube, and the cylinder tube of the damper connected to the vehicle body side tube inside the vehicle body side tube is connected to the axle side inside the axle side tube. A main piston provided on a piston rod connected to the tube is slidably inserted, and the inside of the cylinder tube is partitioned into a piston side oil chamber and a rod side oil chamber by this main piston, and the piston side oil chamber and rod of the main piston are divided. The expansion side damping valve is provided in the flow path connecting the side oil chambers, and the sub-piston facing the main piston is provided above the main piston inside the cylinder tube, and the piston-side oil chamber inside the cylinder tube is provided by this sub-piston. A subtank chamber is defined above the pipe to enable communication between the piston side oil chamber of the subpiston and the subtank chamber. A compression-side damping valve is provided in the cylinder tube, and a free piston facing the sub-piston is movably provided above the sub-piston inside the cylinder tube. The free piston exceeds the normal rising end caused by the expansion / contraction stroke of the damper, and the cylinder of the damper When the hydraulic oil that has entered the tube from the reservoir rises to the highest end due to the high-pressure surplus oil, the sub tank chamber between the free piston and the sub piston is connected to the reservoir outside the cylinder tube, and the free piston is In a hydraulic shock absorber having a pressure spring that urges toward the piston side, when the free piston is on the lower end to the normal upper end side, the gas chamber behind the free piston becomes the gas chamber of the reservoir. When the free piston exceeds the rising end, the sub tank chamber It is obtained so as to communicate with the reservoir through the gas chamber behind tons.

  According to a second aspect of the present invention, in the first aspect of the present invention, the free piston has a bottomed cylindrical body, the bottom portion of the free piston is disposed near the sub piston, and the lower outer periphery and the upper outer periphery of the free piston. The upper and lower seal members that are always in sliding contact with the inner periphery of the cylinder tube are provided on each of the cylinders, and when the free piston normally exceeds the rising end, the sub-tank chamber is sandwiched between the upper and lower seal members of the free piston. Are connected to the reservoir via a gas chamber behind the through hole, a through hole penetrating the tube wall of the cylinder tube inward and outward, and a through hole penetrating the cylindrical wall of the free piston inward and outward.

  According to a third aspect of the present invention, in the second aspect of the present invention, the free piston is movable in an annular space between the inner periphery of the cylinder tube and the outer periphery of the support shaft attached to the upper end of the vehicle body side tube. An intermediate seal member that is sandwiched between upper and lower seal members and slidably contacts the inner periphery of the cylinder tube is provided on the outer periphery of the intermediate portion of the free piston. A seal member is provided, and the through hole provided in the cylindrical wall of the free piston is opened between the lower seal member and the intermediate seal member on the outer peripheral side of the free piston, and the upper portion of the inner peripheral seal member on the inner peripheral side of the free piston. When the free piston normally exceeds the rising end, the intermediate seal member reaches the enlarged diameter portion of the inner periphery of the cylinder tube and is separated from the inner periphery. It is obtained by away from the outer peripheral reaching the perimeter of the reduced diameter portion.

(Claim 1)
(a) When the free piston is at the lower end to the normal ascending end (the position immediately before reaching the normal ascending end or the position at which the ordinary ascending end is reached), the gas chamber behind the free piston Is blocked. As a result, the free piston provided inside the cylinder tube of the damper has a spring force that increases in proportion to the stroke amount of the pressure spring and a gas spring that increases in proportion to the volume change of the gas chamber behind the free piston. Energized by force. Therefore, the inside of the cylinder tube of the damper is always pressurized by the free piston, and a predetermined damping force is generated by the compression side damping valve from the beginning when the damper starts the compression operation from the maximum extension state.

  Further, the gas spring force depending on the volume change of the gas chamber of the reservoir is not exerted on the free piston inside the cylinder tube of the damper. Therefore, by appropriately exerting the gas spring force of the gas chamber behind the free piston, the spring force of the pressure spring can be reduced, and riding comfort can be improved.

  However, the range of movement of the free piston that blocks the gas chamber behind the free piston from the gas chamber of the reservoir may extend from the lower end of the free piston to the position where the free piston has normally reached the upper end. However, it can also be limited to the position immediately before reaching the lower end of the free piston to the normal upper end of the free piston. In this case, when the free piston further rises from a position just before reaching the rising end, the gas chamber behind the free piston communicates with the gas chamber of the reservoir. According to this, a gas spring force depending on a large volume change of the gas chamber of the reservoir is introduced into the gas chamber behind the free piston, and the shock is absorbed at the rising end of the compression stroke where a large reaction force is required. Necessary reaction force can be generated and shock absorbing ability can be secured.

  (b) Due to the high pressure surplus of hydraulic oil that has entered the cylinder tube from the reservoir, the sub tank chamber communicates with the reservoir via the gas chamber behind the free piston when the free piston normally exceeds the rising end. As a result, the high-pressure hydraulic oil that has entered the cylinder tube from the reservoir is released from the sub tank chamber in the cylinder tube to the reservoir through the gas chamber behind the free piston, and also enters the gas chamber behind the free piston from the sub tank chamber. The hydraulic oil thus discharged is also discharged to the reservoir. Therefore, the oil chamber and the sub tank chamber inside the cylinder tube and the gas chamber behind the free piston can be prevented from being pressurized, and the sealing function of the sealing member sealing the inside of the cylinder tube to the outside can be impaired. Absent.

(Claim 2)
(c) When the free piston exceeds the normal rising end, the sub tank chamber penetrates the gas chamber behind the free piston and the tube wall of the cylinder tube in and out while being sandwiched between the upper and lower seal members of the free piston. The above-described (b) can be realized by communicating with the reservoir through the through-holes that pass through and the through-holes that pass through the cylindrical wall of the free piston.

(Claim 3)
(d) The upper and lower seal members and the intermediate seal member are provided on the outer periphery of the free piston, the inner periphery seal member is provided on the inner periphery of the free piston, and the intermediate seal member is the cylinder tube when the free piston exceeds the normally rising end. The above-mentioned (c) can be realized by reaching the enlarged diameter portion of the inner circumference and leaving the inner circumference, and the inner circumference sealing member reaching the reduced diameter portion of the outer circumference of the support shaft and away from the outer circumference.

  1 is an overall sectional view showing a hydraulic shock absorber, FIG. 2 is a lower sectional view of FIG. 1, FIG. 3 is an upper sectional view of FIG. 1, FIG. 4 is an enlarged sectional view of an essential part of FIG. It is principal part expanded sectional drawing, sectional drawing which shows the falling end of a free piston, FIG. 6: is sectional drawing which shows the normal raising end of a free piston.

  As shown in FIGS. 1 to 4, the front fork 10 (hydraulic shock absorber) has an axle side tube (inner tube) 12 slidably inserted into a vehicle body side tube (outer tube) 11. A suspension spring 13 is interposed therebetween, and the single cylinder damper 14 is inverted and is internally provided.

The vehicle body side tube 11 is supported on the vehicle body side, and the axle side tube 12 is coupled to the axle.
The upper end portion of the cylinder tube 16 (upper cylinder tube 16A) of the damper 14 is screwed to the upper end portion of the vehicle body side tube 11 via an O-ring, and the upper open end of the cylinder tube 16 is closed by a fork bolt 15. The fork bolt 15 is inserted and screwed into the inner periphery of the upper cylinder tube 16A via an O-ring.

  An axle bracket 19 is screwed to the lower end portion of the axle side tube 12, and the base end portion of the oil lock collar 17 is sandwiched between the axle side tube 12 and the axle bracket 19. The oil lock collar 17 is liquid-tightly fitted to the inner periphery of the lower end portion of the axle tube 12 via an O-ring, and seated liquid-tightly on the bottom surface inside the axle bracket 19 via the O-ring. . Further, a bottom bolt 18 is screwed to the axle bracket 19 from the outside via an O-ring. A base end portion of a piston rod (hollow rod) 20 of the damper 14 is screwed to the bottom bolt 18 and is locked by a lock nut 18 </ b> A, and a tip end portion of the piston rod 20 is inserted into the cylinder tube 16. The piston rod 20 is supported by a bush 21A of a rod guide 21 screwed into an opening on the lower end side of the cylinder tube 16 (lower cylinder tube 16B), and is inserted into the cylinder tube 16 through the seal member 21B. Yes. The seal member 21 </ b> B has a unidirectional sealing function that seals an oil chamber 43 </ b> B (described later) of the cylinder tube 16 and prevents oil in the oil chamber 43 </ b> B from escaping out of the cylinder tube 16. An oil lock collar 22 is provided on the outer periphery of the rod guide 21. A rebound spring 23 is supported on the inner end face of the rod guide 21. The cylinder tubes 16A and 16B are connected and locked by a pipe nut 16C.

  The suspension spring 13 includes an outer peripheral step surface of the base end portion of the oil lock collar 17 and a perforated spring collar 25 (a large number of communication holes 25A) that are externally attached to the cylinder tube 16 (lower cylinder tube 16B) and locked in the axial direction. ) Is interposed between the spring receiver 26 fixed to the tip end portion. Also, an oil chamber 31 and a gas chamber 32 constituting a reservoir 30 are provided inside the vehicle body side tube 11 and the axle side tube 12 and outside the damper 14, and the oil chamber 31 and the gas chamber 32 form a free interface. The gas that is in contact with each other and trapped in the gas chamber 32 constitutes a gas spring. The elastic force of the suspension spring 13 and the gas spring absorbs the impact force that the vehicle receives from the road surface.

  The damper 14 has a main valve device (extension side damping valve device) 40 and a sub valve device (pressure side damping valve device) 50. The damper 14 suppresses the expansion and contraction vibration of the vehicle body side tube 11 and the axle side tube 12 due to the absorption of the impact force by the suspension spring 13 and the gas spring by the damping force generated by the main valve device 40 and the sub valve device 50.

(Main valve device 40)
The main valve device 40 has a piston holder 41 attached to the tip of the piston rod 20 and a main piston 42 attached to the piston holder 41. The main piston 42 partitions the inside of the cylinder tube 16 into a piston-side oil chamber 43A in which the piston rod 20 is not accommodated and a rod-side oil chamber 43B in which the piston rod 20 is accommodated, and slides in the cylinder tube 16. . The main piston 42 is provided with an extension side damping valve 44A and is provided with an extension side flow path 44 capable of connecting the piston side oil chamber 43A and the rod side oil chamber 43B, and a pressure side damping valve (check valve) 45A. The pressure side flow path 45 which enables communication between the oil chamber 43A and the rod side oil chamber 43B is provided.

  Further, the main valve device 40 is provided with an adjuster 46 that can be rotated from the outside to the aforementioned bottom bolt 18 that is screwed to the axle bracket 19. The main valve device 40 passes a damping force adjusting rod 47 coupled to an adjuster 46 through a hollow portion of the piston rod 20 and is moved by a needle 47A at the tip of the damping force adjusting rod 47 that advances and retreats in the axial direction when the adjuster 46 rotates. The flow passage area of the bypass passage 48 between the piston-side oil chamber 43A and the rod-side oil chamber 43B provided in the piston holder 41 can be adjusted.

(Sub-valve device 50)
The sub-valve device 50 has a guide pipe 51 (support shaft) screwed to the fork bolt 15 screwed to the upper end of the upper cylinder tube 16A, and is locked by a lock nut 15A. A piston holder 51A is screwed to the piston holder 51A, and the sub-piston 52 is held on the piston holder 51A by a nut 51B or the like. The sub-piston 52 is disposed relative to the main piston 42 inside the cylinder tube 16, is in fluid-tight contact with the inner peripheral portion of the upper cylinder tube 16A, and defines a sub-tank chamber 53 above the piston-side oil chamber 43A. The sub-piston 52 is provided with a pressure-side damping valve 54A to allow the piston-side oil chamber 43A and the sub-tank chamber 53 to communicate with each other, and the extension-side damping valve 55A is provided with a piston-side oil chamber 43A and the sub-tank chamber 53. Is provided with an extension-side flow channel 55 (not shown). The piston holder 51 </ b> A includes a bypass path 56 that bypasses the pressure side flow path 54 and the extension side flow path 55 to allow the piston side oil chamber 43 </ b> A and the sub tank chamber 53 to communicate with each other.

  The damping force adjustment rod 58 screwed into the fork bolt 15 includes an adjuster 59 and is inserted into the guide pipe 51 and is flown through the bypass flow path 56 by a needle 58A at the tip which is advanced and retracted in the axial direction by the rotation operation of the adjuster 59. The road area can be adjusted. The fork bolt 15 has an adjuster 59 and its holder 59A embedded in the center of the end face of the head.

  The sub-valve device 50 is provided inside the upper cylinder tube 16A so as to be movable in an annular space between the upper cylinder tube 16A and the guide pipe 51, and between the free piston 60 and the fork bolt 15. There is a pressure spring 70 interposed therebetween. The pressure spring 70 is a compression coil spring and biases the free piston 60 toward the sub-piston 52 side.

  At this time, the free piston 60 has a bottomed cylindrical body, and the bottom 61 of the free piston 60 is disposed near the sub-piston 52, and the lower piston ring 63L is disposed on the outer periphery of the bottom 61 to the cylinder 62 of the free piston 60. A lower seal member 64L such as an oil seal is provided, and an upper piston ring 63U and an upper seal member 64U such as an oil seal are provided on the outer periphery of the upper portion of the cylindrical portion 62 of the free piston 60. Further, the free piston 60 is provided with an inner peripheral seal member 65 such as an oil seal in an inner peripheral concave portion of the bottom 61 of the free piston 60. The annular space between the upper cylinder tube 16A and the guide pipe 51 is lowered as shown in FIG. 5 in order to compensate for the volume of the piston rod 20 that the free piston 60 enters and leaves the cylinder tube 16 with the expansion / contraction stroke of the damper 14. The lower piston ring 63L and the lower seal member 64L slide on the lower inner diameter portion 71 on the lower side of the upper cylinder tube 16A in the normal movement region that moves between the end and the normal rising end shown in FIG. 6, and the upper piston ring 63U. The upper seal member 64U slides on the large inner diameter portion 72 (expanded diameter portion) on the upper side of the upper cylinder tube 16A, and the inner peripheral seal member 65 slides on the straight outer periphery of the guide pipe 51. In the free piston 60, the seal members 64L and 64U slide in a liquid-tight manner on the small inner diameter portion 71 and the large inner diameter portion 72 of the upper cylinder tube 16A, and the inner peripheral seal member 65 is the guide pipe 51. By sliding liquid-tightly on the outer periphery, a sub-tank chamber 53 communicating with the piston-side oil chamber 43A on the sub-piston 52 side and a gas chamber (volume compensation chamber) 73 behind the free piston 60 are partitioned. .

  However, when the sub-valve device 50 is on the free piston 60 from the lower end (FIG. 5) to the normal ascending end (in the present embodiment, the position immediately before entering the narrow movement range immediately before the free piston 60 reaches the normal ascent end). The gas chamber 73 behind the free piston 60 is blocked from the gas chamber 32 of the reservoir 30. Thereby, in the normal movement region of the compression stroke of the damper 14, the gas spring force of the gas chamber 32 of the reservoir 30 is not introduced into the gas chamber 73 behind the free piston 60, and the gas spring force of the gas chamber 73 is moderately adjusted. By exhibiting the above, the spring force of the pressure spring 70 can be reduced, and riding comfort can be improved.

  As shown in FIG. 6, when the free piston 60 is in a narrow moving range immediately before reaching the normal rising end to the normal rising end position (further, the highest rising end position due to high pressure surplus oil described later), the free piston A gas chamber 73 behind 60 communicates with the gas chamber 32 of the reservoir 30. According to this, a gas spring force depending on a large volume change of the gas chamber 32 of the reservoir 30 is introduced into the gas chamber 73 behind the free piston 60, and an impact is applied at the rising end of the compression stroke where a large reaction force is required. The reaction force necessary to absorb the pressure can be generated, and the shock absorbing ability can be secured.

  In the present invention, the sub-valve device 50 uses the gas chamber 73 behind the free piston 60 in the reservoir 30 throughout the normal movement range where the free piston 60 is located at the lower end (FIG. 5) to the normal upper end (FIG. 6). The gas chamber 32 may be shut off.

  The sub-valve device 50 removes the oil in the oil chamber 31 adhering to the outer peripheral surface of the piston rod 20 from the seal member 21B of the rod guide portion 21 to the inside of the cylinder tube 16 every time the piston rod 20 of the front fork 10 strokes. Bring it in. As a result, the hydraulic oil in the oil chambers 43A, 43B, 53 inside the cylinder tube 16 gradually increases to become high-pressure surplus oil, the hydraulic pressure in these oil chambers 43A, 43B, 53 is increased, and the free piston 60 Exceeds the normal rising end of the above-mentioned normal moving range and further rises to the highest rising end, which is a predetermined position above, the sub tank chamber 53 between the free piston 60 and the sub piston 52 becomes a reservoir outside the cylinder tube 16. Communicate to 30. In this embodiment, the sub tank chamber 53 communicates with the reservoir 30 via the gas chamber 73 behind the free piston 60. As a result, surplus oil and high pressure in the damper 14 are discharged from the sub tank chamber 53 to the reservoir 30 outside the cylinder tube 16 via the gas chamber 73 behind the free piston 60 and released.

  In this embodiment, when the free piston 60 exceeds the normal rising end, the sub tank chamber 53 is sandwiched between the upper and lower seal members 64U, 64L of the free piston 60 and the gas chamber 73 behind the free piston 60 A through hole 81 that opens through the tube wall of the upper cylinder tube 16A inward and outward and opens toward the lower end of the large inner diameter portion 72 (a tapered portion connected to the small inner diameter portion 71 within the range of the large inner diameter portion 72), and a free piston 60 The gas chamber 32 of the reservoir 30 is passed through a through hole 82 that penetrates the cylindrical wall of the cylindrical portion 62 inward and outward, and a sliding gap 83 (FIG. 6) between the outer periphery of the free piston 60 and the inner periphery of the upper cylinder tube 16A. Communicate.

  Specifically, an intermediate seal member 64M is provided on the outer periphery of the intermediate portion of the free piston 60 so as to be slidably contacted with the lower inner diameter portion 71 on the lower side of the upper cylinder tube 16A between the upper and lower seal members 64U and 64L. The through hole 82 provided in the cylindrical wall of the cylindrical portion 62 of the free piston 60 is opened between the lower seal member 64L and the intermediate seal member 64M on the outer peripheral side of the free piston 60, and the inner peripheral side of the free piston 60 Then, it opens to the upper part of the inner peripheral seal member 65. Accordingly, the following (1) to (3) are realized by the compression stroke of the damper 14.

  (1) When the free piston 60 enters a narrow movement range immediately before reaching the rising end (FIG. 6), the intermediate seal member 64M of the free piston 60 is increased from the small inner diameter portion 71 on the inner periphery of the upper cylinder tube 16A. It reaches the inner diameter portion 72 and leaves the inner periphery (the gas chamber 73 behind the free piston 60 communicates with the gas chamber 32 of the reservoir 30 through the through holes 81 and 82).

  (2) Subsequent to the above (1), the inner peripheral seal member 65 of the free piston 60 reaches the reduced diameter portion 74 having a reduced diameter on the straight outer periphery of the guide pipe 51 and leaves the outer periphery (the high pressure surplus in the sub tank chamber 53). Oil flows into the gas chamber 73 behind the free piston 60).

  (3) The high-pressure surplus oil in the sub tank chamber 53 that has flowed into the gas chamber 73 behind the free piston 60 according to the above (2), together with the oil remaining in the gas chamber 73 behind the free piston 60, The gas is discharged into the gas chamber 32 of the reservoir 30 through the through hole 82, the sliding gap 83, and the through hole 81 of the upper cylinder tube 16A.

  In the front fork 10, the expansion and contraction of the front fork 10 enters the gas chamber 32 of the reservoir 30 and the gas chamber 73 behind the free piston 60 from the sliding portions of the vehicle body side tube 11 and the axle side tube 12. Fork bolts 15 are provided with exhaust plugs 33 and 34 for discharging the air.

According to the present embodiment, the following operational effects can be obtained.
(a) When the free piston 60 is on the lower end to the normal ascending end side (a position immediately before reaching the normal ascending end or a position reaching the normal ascending end), the gas chamber 73 behind the free piston 60 The gas chamber 32 is blocked. Thus, the free piston 60 provided inside the cylinder tube 16 of the damper 14 is proportional to the spring force that increases in proportion to the stroke amount of the pressure spring 70 and the volume change of the gas chamber 73 behind the free piston 60. It is energized by a gas spring force that increases. Accordingly, the inside of the cylinder tube 16 of the damper 14 is constantly pressurized by the free piston 60, and a predetermined damping force is generated by the compression side damping valve 54A from the beginning when the damper 14 starts the compression operation from the maximum extension state.

  Further, the gas spring force depending on the volume change of the gas chamber 32 of the reservoir 30 is not exerted on the free piston 60 inside the cylinder tube 16 of the damper 14. Accordingly, by appropriately exerting the gas spring force of the gas chamber 73 behind the free piston 60, the spring force of the pressurizing spring 70 can be reduced, and riding comfort can be improved.

  However, the range of movement of the free piston 60 that blocks the gas chamber 73 behind the free piston 60 from the gas chamber 32 of the reservoir 30 is the position where the free piston 60 reaches its normally raised end. Although it may cross, it can also be limited to the position immediately before reaching the lower end of the free piston 60 to the normal upper end of the free piston 60. In this case, the gas chamber 73 behind the free piston 60 communicates with the gas chamber 32 of the reservoir 30 when the free piston 60 further rises from a position immediately before reaching the normal rising end. According to this, a gas spring force depending on a large volume change of the gas chamber 32 of the reservoir 30 is introduced into the gas chamber 73 behind the free piston 60, and an impact is applied at the rising end of the compression stroke where a large reaction force is required. The reaction force necessary to absorb the pressure can be generated, and the shock absorbing ability can be secured.

  (b) When the free piston 60 normally exceeds the rising end due to the high-pressure surplus hydraulic oil that has entered the cylinder tube 16 from the reservoir 30, the sub tank chamber 53 passes through the gas chamber 73 behind the free piston 60. It communicates with the reservoir 30. As a result, the high-pressure hydraulic oil that has entered the cylinder tube 16 from the reservoir 30 is released from the sub tank chamber 53 in the cylinder tube 16 to the reservoir 30 via the gas chamber 73 behind the free piston 60 and free from the sub tank chamber 53. The hydraulic oil that has entered the gas chamber 73 behind the piston 60 is also discharged to the reservoir 30. Therefore, the pressure of the oil chambers 43A, 43B and the sub tank chamber 53 inside the cylinder tube 16 and the gas chamber 73 behind the free piston 60 is avoided, and the seal that seals the inside of the cylinder tube 16 from the outside. The sealing function of the members (the O-ring of the fork bolt 15, the seal member 21B of the rod guide 21, etc.) is not impaired.

  (c) While the sub-tank chamber 53 is sandwiched between the upper and lower seal members 64U and 64L of the free piston 60 when the free piston 60 exceeds the normal rising end, the gas chamber 73 and the cylinder behind the free piston 60 The above-described (b) can be realized by communicating with the reservoir 30 through a through-hole 81 that penetrates the tube wall of the tube 16 inward and outward and a through-hole 82 that penetrates the cylindrical wall of the free piston 60 inward and outward.

  (d) When the upper and lower seal members 64U and 64L and the intermediate seal member 64M are provided on the outer periphery of the free piston 60, and the inner periphery seal member 65 is provided on the inner periphery of the free piston 60. Furthermore, the intermediate seal member 64M reaches the large inner diameter portion 72 (expanded diameter portion) on the inner periphery of the cylinder tube 16 and leaves the inner periphery, and the inner periphery seal member 65 reaches the reduced diameter portion 74 on the outer periphery of the guide pipe 51. Thus, by separating from the outer periphery, the above (c) can be realized.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration of the present invention is not limited to this embodiment, and even if there is a design change or the like without departing from the gist of the present invention. It is included in the present invention. Note that the seal member of the present invention may be an oil seal, an O-ring, or the like.

FIG. 1 is an overall cross-sectional view showing a hydraulic shock absorber. FIG. 2 is a lower cross-sectional view of FIG. FIG. 3 is a top sectional view of FIG. 4 is an enlarged cross-sectional view of the main part of FIG. FIG. 5 is an enlarged cross-sectional view of the main part of FIG. 3 and is a cross-sectional view showing the descending end of the free piston. FIG. 6 is a cross-sectional view showing the normal rising end of the free piston.

Explanation of symbols

10 Front fork (hydraulic shock absorber)
11 Car body side tube 12 Axle side tube 14 Damper 16, 16A, 16B Cylinder tube 20 Piston rod 30 Reservoir 32 Gas chamber 42 Main piston 43A Piston side oil chamber 43B Rod side oil chamber 44 Extension side flow path 44A Extension side damping valve 51 Guide Pipe (support shaft)
52 Sub piston 53 Sub tank chamber 54 Pressure side flow path 54A Pressure side damping valve 60 Free piston 64L Lower seal member 64U Upper seal member 64M Intermediate seal member 65 Inner peripheral seal member 70 Pressure spring 71 Small inner diameter portion 72 Large inner diameter portion (expanded diameter portion) )
73 Gas chamber 74 Reduced diameter portion 81 Through hole 82 Through hole 83 Sliding gap

Claims (3)

Insert the axle side tube slidably into the body side tube,
A main piston provided on a piston rod connected to the axle side tube inside the axle side tube is slidably inserted into a cylinder tube of a damper connected to the body side tube inside the body side tube. The inside of the cylinder tube is partitioned into a piston-side oil chamber and a rod-side oil chamber, and an extension-side damping valve is provided in the flow path connecting the piston-side oil chamber and the rod-side oil chamber of the main piston,
A sub-piston facing the main piston is provided above the main piston inside the cylinder tube, and the sub-piston chamber is defined above the piston-side oil chamber inside the cylinder tube by the sub-piston. A pressure-side damping valve is provided in the flow path that enables communication between the sub tank chamber and
A free piston facing the sub-piston is movably provided above the sub-piston inside the cylinder tube.
When the free piston exceeds the normal rising end due to the expansion / contraction stroke of the damper and rises to the highest rising end due to the high pressure surplus of hydraulic oil that has entered the cylinder tube of the damper from the reservoir, it is between the free piston and the sub piston. The subtank chamber to the reservoir outside the cylinder tube,
In the hydraulic shock absorber having a pressure spring that biases the free piston toward the sub-piston side,
When the free piston is on the lower end to the normal upper end side, the gas chamber behind the free piston is blocked from the gas chamber of the reservoir,
A hydraulic shock absorber characterized in that, when the free piston normally exceeds the rising end, the sub tank chamber communicates with the reservoir through a gas chamber behind the free piston. The free piston forms a cylindrical body with a bottom, and the bottom of the free piston is arranged near the sub-piston, and the upper and lower seals are always in sliding contact with the inner periphery of the cylinder tube on the lower outer periphery and the upper outer periphery of the free piston. A member,
A through-hole that penetrates the gas chamber behind the free piston and the tube wall of the cylinder tube in and out while the sub-tank chamber is sandwiched between the upper and lower sealing members of the free piston when the free piston exceeds the rising end The hydraulic shock absorber according to claim 1, wherein the hydraulic shock absorber communicates with the reservoir through a through-hole penetrating the cylindrical wall of the free piston. The free piston is movably provided in an annular space between the inner periphery of the cylinder tube and the outer periphery of the support shaft attached to the upper end of the vehicle body side tube,
Provided on the outer periphery of the intermediate part of the free piston is an intermediate seal member that is sandwiched between upper and lower seal members and slidably contacts the inner periphery of the cylinder tube,
On the inner periphery of the free piston, an inner periphery seal member that is in sliding contact with the outer periphery of the support shaft is provided
The through hole provided in the cylindrical wall of the free piston is opened between the lower seal member and the intermediate seal member on the outer peripheral side of the free piston, and is opened on the upper portion of the inner peripheral seal member on the inner peripheral side of the free piston.
When the free piston normally exceeds the rising end, the intermediate seal member reaches the enlarged diameter portion of the inner circumference of the cylinder tube and is separated from the inner circumference, and the inner circumference seal member reaches the reduced diameter portion of the outer circumference of the support shaft. The hydraulic shock absorber according to claim 2, which is separated from the outer periphery.

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