JP2004069044A - Hydraulic shock absorber - Google Patents

Abstract

An object of the present invention is to improve the absorbability of a small disturbance such as a gap on the inner side of a compression stroke in a hydraulic shock absorber.
In a hydraulic shock absorber, a compression-side damping force generator is provided between a piston-side oil chamber and a free piston, and the damper cylinder bypasses the compression-side damping force generator to provide a piston-side oil. A bypass oil passage 80 communicating the chamber 27B with the annular oil chamber 35 is provided. The bypass oil passage 80 communicates the piston side oil chamber 27B with the annular oil chamber 35 when the free piston 34 performs a compression stroke over a certain amount.
[Selection diagram] FIG.

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a hydraulic shock absorber such as a front fork of a motorcycle.
[0002]
[Prior art]
In a front fork of a motorcycle, as described in Patent Document 1, a vehicle body side tube and an axle side tube are slidably fitted to each other, and a damper cylinder and the damper cylinder are provided inside the vehicle body side tube and the axle side tube. A piston that accommodates a damper having a piston rod that slides through a piston provided at a tip portion in a cylinder, and a piston rod-side oil chamber that accommodates the piston rod and a piston that does not accommodate the piston rod in the damper cylinder. A side oil chamber is formed, and the damper cylinder is fixed to one of the vehicle body side tube and the axle side tube, and the piston rod is fixed to the other.
[0003]
[Patent Document 1]
Japanese Patent No. 2666895 (2 pages, FIG. 2)
[0004]
In the front fork of Patent Document 1, a seal member for sealing a piston rod-side oil chamber of the damper cylinder is provided at one end side of the damper cylinder, and an annular free piston is provided on the outer periphery of the damper cylinder. A ring-shaped oil chamber communicating with the piston-side oil chamber is hermetically partitioned around the outer periphery of the damper cylinder, and a pressure-side damping force generator is provided between the piston-side oil chamber and the free piston. Thus, when the front fork is compressed, the compression-side damping force generator generates a compression-side damping force. At the same time, the oil chamber in the damper cylinder is sealed to prevent air bubbles from entering the oil chamber in the damper cylinder, thereby stabilizing the damping force, and the operating oil corresponding to the volume of the piston rod that enters or exits the damper cylinder. Can be compensated for by the displacement of the free piston.
[0005]
Further, in the front fork of Patent Document 1, a suspension spring is interposed between a vehicle body side tube and an axle side tube, and when the front fork is compressed, the suspension spring is bent toward a contraction side to generate spring force of the front fork. The reaction force has been increased and the sinking of the front fork during braking has been suppressed.
[0006]
[Problems to be solved by the invention]
In the related art, the compression-side damping force generator can always generate the compression-side damping force even when the front fork has a compression stroke of a certain degree or more, such as during cornering after braking (during steady turning). For this reason, when the front fork moves over a small disturbance such as a gap on the far side of the compression stroke, the generated damping force makes it difficult for the front fork to expand and contract, thereby deteriorating ride comfort and operability.
[0007]
It is an object of the present invention to improve the absorbability of a small disturbance such as a gap on the inner side of a compression stroke in a hydraulic shock absorber.
[0008]
[Means for Solving the Problems]
According to the invention of claim 1, the vehicle body side tube and the axle side tube are slidably fitted to each other, and a damper cylinder is provided inside the vehicle body side tube and the axle side tube, and the inside of the damper cylinder is provided at a distal end portion. A damper provided with a piston rod that slides through a piston, and a piston rod-side oil chamber that houses the piston rod and a piston-side oil chamber that does not house the piston rod are formed in the damper cylinder; In a hydraulic shock absorber in which a damper cylinder is fixed to one of the body-side tube and the axle-side tube, and the piston rod is fixed to the other, one end of the damper cylinder through which the piston rod passes is provided with the damper cylinder. A seal member for sealing the piston rod side oil chamber is provided, and an annular free piston is provided on the outer periphery of the damper cylinder. An annular oil chamber that communicates with the piston side oil chamber is hermetically sealed around the outer periphery of the damper cylinder by the annular free piston, and a compression damping force is provided between the piston side oil chamber and the annular oil chamber. A damper cylinder, a bypass oil passage that bypasses the pressure damping force generator and communicates the piston side oil chamber and the annular oil chamber, and wherein the bypass oil passage is provided with the free piston. The piston-side oil chamber and the annular oil chamber communicate with each other when a compression stroke exceeds a predetermined value.
[0009]
According to the invention of claim 2, the axle-side tube is slidably fitted in the vehicle-body-side tube, a damper cylinder is erected in the axle-side tube, and a piston is provided at the distal end in the damper cylinder. A piston rod is slidably inserted, and a piston rod-side oil chamber that houses the piston rod and a piston-side oil chamber that does not house the piston rod are formed in the damper cylinder. In a hydraulic shock absorber provided with an oil reservoir serving as a gas chamber, a seal member for sealing a piston rod side oil chamber in the damper cylinder is provided at one end side of the damper cylinder through which the piston rod is inserted. An annular free piston biased by a spring is slidably provided on the outer periphery of the damper cylinder. An annular oil chamber communicating with the piston-side oil chamber is hermetically partitioned around the circumference, and a compression-side damping force generator is provided between the piston-side oil chamber and the annular oil chamber. A bypass oil passage that bypasses the damping force generator and communicates the piston-side oil chamber with the annular oil chamber; The chamber communicates with the annular oil chamber.
[0010]
According to a third aspect of the present invention, in the first or second aspect, an intermediate cylinder is further provided between the outer periphery of the damper cylinder and the inner periphery of the axle side tube via an annular gap. The annular free piston is provided between the damper cylinders.
[0011]
According to a fourth aspect of the present invention, in the first aspect of the present invention, the bypass oil passage is formed of a long hole along an axial direction of the damper cylinder.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
1 is a sectional view showing the entire hydraulic shock absorber, FIG. 2 is a lower sectional view of FIG. 1, and FIG. 3 is an enlarged view of a main part of FIG.
[0013]
The front fork 10 (hydraulic shock absorber) is used as a front fork of a motorcycle, and as shown in FIGS. 1 and 2, a vehicle body side tube 11 and an axle side tube 12 are slidably fitted in a liquid-tight manner. It is composed. A bush 13 is provided on the inner circumference of the lower end of the body-side tube 11, and a bush 14 is provided on the inner circumference of the upper end of the body-side tube 11.
[0014]
The vehicle body side tube 11 is provided with a cap 16 in a detachable manner in a liquid-tight manner in an opening 15 at an upper end portion, and the vehicle body side tube 11 is provided with a vehicle body side mounting portion. The axle-side tube 12 has a bottom bracket 18 fixed to the lower end in a liquid-tight manner, and the bottom bracket 18 includes an axle-side mounting portion 19.
[0015]
The front fork 10 accommodates a damper cylinder 21 and a piston rod 24 that constitute a damper 20 in a body-side tube 11 and an axle-side tube 12. That is, the front fork 10 has the damper cylinder 21 fixed inside the bottom bracket 18 erected inside the axle side tube 12. The damper cylinder 21 is fixed by a center bolt 22 inserted into the bottom of the bottom bracket 18. In the front fork 10, a spring load adjusting sleeve 23 is screwed to the center of the cap 16 in a liquid-tight manner, and a hollow piston rod 24 is fixedly attached to the lower end of the spring load adjusting sleeve 23 inserted into the body side tube 11. To support. The piston rod 24 is slidably penetrated through a rod guide 25 provided at the upper end of the damper cylinder 21 and inserted into the oil chamber 27 inside the damper cylinder 21. 26. The piston 26 slides up and down on the inner surface of the damper cylinder 21. The oil chamber 27 is partitioned by the piston 26 into a piston rod-side oil chamber 27A on the side where the piston rod 24 is inserted and a piston-side oil chamber 27B on the side where the piston rod 24 is not inserted.
[0016]
The front fork 10 has a rod guide 25 provided at the upper end of the damper cylinder 21 provided with a seal member 25A made of an oil seal that is in close contact with the outer periphery of the piston rod 24, and seals the piston rod side oil chamber 27A of the damper cylinder 21. .
[0017]
The front fork 10 has a space around the damper cylinder 21 between the vehicle body side tube 11 and the axle side tube 12 as an oil storage chamber 28, and an upper part of the oil storage chamber 28 as a gas chamber (air chamber) 29. 29A is an air valve provided on a damping force adjusting rod 54 described later.
[0018]
The front fork 10 has an intermediate cylinder 31 erected around the other end of the damper cylinder 21 via an annular gap with the inner periphery of the axle tube 12. The intermediate cylinder 31 has the base flange portion 31A seated on a stepped seat portion provided on the bottom bracket 18, and is sandwiched between the bottom bracket 18 and the other end surface of the axle-side tube 12 screwed to the bottom bracket 18. An O-ring 32 is provided between the axle-side tube 12 and the bottom bracket 18, and an O-ring 33 is provided between the axle-side tube 12 and the intermediate cylinder 31.
[0019]
An annular free piston 34 is slidably provided between the inner periphery of the intermediate cylinder 31 and the outer periphery of the damper cylinder 21 (101 is a bush), and oil passages 44A and 45A of the bottom bracket 18 are provided below the free piston 34. An annular oil chamber 35 communicating with the piston-side oil chamber 27B via 43 oil chambers 44 and 45 is defined.
[0020]
The free piston 34 has an O-ring 36 fitted in the outer ring groove and an O-ring 37 fitted in the inner ring groove. The free piston 34 is moved from the lowermost position shown by a broken line in the right half of FIGS. The annular oil chamber 35 between the damper cylinder 31 and the damper cylinder 21 is moved upward as shown by the solid line in the left half and the solid line in the right half of FIGS. The O-ring 37 slides on the outer periphery of the damper cylinder 21 in the normal movement range (movement range of the free piston 34 corresponding to the maximum compression stroke of the front fork 10) excluding the upper end portion of the entire movement range while sliding on the inner periphery. Touch The free piston 34 seals the piston-side oil chamber 27B with respect to the oil reservoir 28 via the annular oil chamber 35 in the above-described normal movement range.
[0021]
When the O-ring 37 reaches the reduced-diameter communication portion 39 provided on the outer periphery of the damper cylinder 21 at the upper end (sliding end) beyond the above-described normal movement range, the free piston 34 communicates with the O-ring 37. Between 39, an oil release passage from the annular oil chamber 35 to the oil reservoir 28 is formed. Seal member 25A at the upper end of damper cylinder 21 (seal member 25A completely prevents oil from leaking from piston rod side oil chamber 27A to oil sump chamber 28, but from oil sump chamber 28 to piston rod side oil chamber 27). When the hydraulic oil that has entered the damper cylinder 21 from the one-way seal member that does not completely prevent the oil from entering the damper cylinder 21 increases to a certain amount or more, the free piston 34 moves up to the above-mentioned sliding end, and the damper The oil in the cylinder 21 escapes to the oil reservoir 28 outside the damper cylinder 21.
[0022]
The front fork 10 urges the free piston 34 toward the annular oil chamber 35 between a spring seat 41 screwed around the outer periphery of the damper cylinder 21 and a spring seat 34A provided at the upper end of the free piston 34. Further, a coil spring 42 for pressurizing the oil chamber 27 of the damper cylinder 21 is provided. The spring seat 41 has an annular portion 41A, and the annular portion 41A is fitted on the inner periphery of the upper end of the intermediate cylinder 31. The space for accommodating the spring 42 between the damper cylinder 21 and the intermediate cylinder 31 forms a part of the oil hole 28 via the oil hole 31B provided in the intermediate cylinder 31 and the oil hole 41B provided in the spring seat 41. .
[0023]
The front fork 10 has a sub-tank 43 connected to the bottom bracket 18 fixed to the lower end of the axle-side tube 12, and connects the piston-side oil chamber 27 B of the damper cylinder 21 and the lower oil chamber 44 of the sub-tank 43 to the center bolt 22. The provided oil passage 22A communicates with an oil passage 44A provided in the bottom bracket 18, and the lower annular oil chamber 35 of the free piston 34 communicates with the upper oil chamber 45 of the sub tank 43 via an oil passage 45A provided in the bottom bracket 18. ing.
[0024]
The front fork 10 has a spring collar 47 composed of a combination of a plurality of members supported by the above-mentioned spring load adjusting sleeve 23 provided on the cap 16 and moving up and down, and an upper spring seat 48A backed up by the spring collar 47; A suspension spring 49 is interposed between the lower spring seat 48B fixed to the outer periphery of the rod guide 25.
[0025]
The front fork 10 buffers an impact force received from a road surface when the vehicle is traveling by a spring reaction force of the suspension spring 49 and a spring reaction force of the air spring of the air chamber 29.
[0026]
The front fork 10 has a piston valve device (extension-side damping force generator) 50 and a bottom valve device (compression-side damping force generator) 60 for damping expansion and contraction vibration of the suspension spring 49 and the air spring of the air chamber 29. have.
[0027]
The piston valve device 50 includes an expansion-side flow path 51 (not shown) and a pressure-side flow path 52 that allow the piston rod-side oil chamber 27A and the piston-side oil chamber 27B to communicate with the piston 26 that slides on the inner surface of the damper cylinder 21. The expansion side flow path 51 can be opened and closed by the expansion side attenuation valve 51A, and the compression side flow path 52 can be opened and closed by the compression side attenuation valve 52A. The compression side damping valve 52A is backed up and supported by a valve spring 52C locked to the piston rod 24 via a spring receiver 52B. In addition, the piston valve device 50 has a bypass passage 53 that allows the piston rod-side oil chamber 27A and the piston-side oil chamber 27B to communicate with each other by bypassing the piston 26, and the bypass passage 53 can be opened and closed by a needle valve 53A. And At this time, a damping force adjusting rod 54 is screwed into the center of the spring load adjusting sleeve 23 provided on the cap 16, the damping force adjusting rod 54 is inserted into the hollow portion of the piston rod 24, and the above-described needle valve 53A is inserted into the insertion end. Is provided.
[0028]
The bottom valve device 60 is housed in the sub tank 43 installed as described above between the piston side oil chamber 27B of the damper cylinder 21 and the annular oil chamber 35 below the free piston 34. The bottom valve device 60 has a cap 62 screwed into the opening 61 of the sub-tank 43, a support bolt 63 screwed onto the upper end surface of the cap 62 facing the lower oil chamber 44 of the sub-tank 43, and a tip end of the support bolt 63. A bypass bolt 64 is screwed on, and a bottom piece 65 is fixed to an intermediate portion of the bypass bolt 64. The bottom piece 65 partitions the lower oil chamber 44 and the upper oil chamber 45. The bottom piece 65 has a compression-side flow path 66 and an expansion-side flow path 67 that allow the lower oil chamber 44 and the upper oil chamber 45 to communicate with each other. The compression-side flow path 66 can be opened and closed by a compression-side damping valve 66A. The passage 67 can be opened and closed by a check valve 67A. Further, the bottom valve device 60 has a bypass oil passage 68 in the bolts 63 and 64 for allowing the lower oil chamber 44 and the upper oil chamber 45 to communicate with each other by bypassing the bottom piece 65, and the bypass oil passage 68 is connected to the needle valve 68A. And can be opened and closed by the plate valve 68B. At this time, the damping force adjusting rod 69 is screwed into the cap 62, the damping force adjusting rod 69 is inserted into the center of the cap 62, and the above-described needle valve 68A is provided at the insertion end.
[0029]
The sub tank 43 has a supply / discharge port 71 for hydraulic oil that opens into the upper oil chamber 45, and the supply / discharge port 71 can be opened and closed by a plug 72 screwed into a screw hole of the sub tank 43. When the plug 42 is loosened and the supply / drain opening 71 is opened, hydraulic oil can be supplied / discharged through the supply / drain hole 72 </ b> A of the plug 72. Reference numeral 73 denotes a cap for the supply / discharge hole 72A attached to the plug 72.
[0030]
The front fork 10 is buffered at the time of maximum extension by a rebound spring 55 interposed between the rod guide 25 and the piston bolt 24A inside the damper cylinder 21.
[0031]
In addition, the front fork 10 abuts a stopper rubber 56 fixed to the outer periphery of the piston rod 24 against the rod guide 25 outside the damper cylinder 21 so as to buffer the most compression.
[0032]
Further, the front fork 10 is provided with the following configuration in order to improve the absorbability of small disturbances such as gaps entering the wheels on the inner side of the compression stroke (the side of the maximum compression stroke).
[0033]
The front fork 10 connects the piston side oil chamber 27 </ b> B and the annular oil chamber 35 below the free piston 34 to the lower end side of the damper cylinder 21, bypassing the pressure side damping force generator 60 built in the sub tank 43. A hole-shaped bypass oil passage 80 is formed. The bypass oil passage 80 communicates the piston-side oil chamber 27B with the annular oil chamber 35 when the free piston 34 performs a compression stroke of a certain degree or more within the above-described normal movement range on the far side of the compression stroke of the front fork 10; As a result, the generation of the compression-side damping force by the compression-side damping force generator 60 is stopped, and only the lower compression-side damping force based on the passage resistance of the bypass oil passage 80 is generated, and the generated damping force of the front fork 10 is reduced. Improves the absorption of small disturbances such as gaps entering the wheels.
[0034]
The free piston 34 is a skirt portion 81 extending downward from the inner periphery in sliding contact with the outer periphery of the damper cylinder 21, and the skirt portion 81 closes the bypass oil passage 80 in a range excluding the far side of the compression stroke of the front fork 10. 1 to 3 (the free piston 34 shown by a solid line in the left half and the free piston 34 shown by a broken line in the right half). The path 80 is opened (the free piston 34 indicated by a solid line in the right half of FIGS. 1 to 3).
[0035]
Therefore, the front fork 10 operates as follows.
(Compression process)
When the front fork 10 is compressed, one of the vehicle body side tube 11 and the axle side tube 12 is relatively compressed with respect to the other, and the suspension spring 49 is compressed. Further, the piston rod 24 enters the damper cylinder 21, and the hydraulic oil in the piston-side oil chamber 27B passes through the bypass passage 53 of the piston 26 at low speed, and the compression-side damping valve of the compression-side passage 52 of the piston 26 at medium and high speeds. It flows to the piston rod side oil chamber 27A through 52A. In addition, at the time of low speed, the operating oil corresponding to the entering volume of the piston rod 24 flows into the lower oil chamber 35 of the free piston 34 through the bypass passage 68 that bypasses the bottom piece 65, and at the time of middle and high speed, the pressure side flow passage of the bottom piece 65. It flows to the lower oil chamber 35 of the free piston 34 through the pressure side damping valve 66A of 66.
[0036]
During this compression, the free piston 34 moves upward to compress the spring 42. Thus, at low speed, the oil in the piston-side oil chamber 27B flows through the bypass passage 53 of the piston 26 to the piston-rod-side oil chamber 27A, and the compression resistance is obtained by the throttle resistance of the needle valve 53A during this time. At the same time, oil corresponding to the volume of the piston rod 24 that enters the damper cylinder 21 enters the lower oil chamber 44 of the sub tank 43 from the piston-side oil chamber 27B, and further passes through the bypass passage 68 of the bottom piece 65 to the upper oil chamber 45. During the flow, a compression damping force is obtained by the throttle resistance of the needle valve 68A and the bending resistance of the plate valve 68B. The oil in the piston-side oil chamber 27B flows from the minute flow path formed by lifting up the pressure-side damping valve 52A through the pressure-side flow path 52 of the piston 26 to the piston rod-side oil chamber 27A. Get damping force. At medium and high speeds, oil corresponding to the volume of the piston rod 24 entering the damper cylinder 21 enters the lower oil chamber 44 of the sub tank 43 from the piston side oil chamber 27B and further passes through the pressure side flow path 66 of the bottom piece 65 to the upper oil chamber. 45, and a compression-side damping force is obtained by the bending resistance of the compression-side damping valve 66A during this time. The oil in the piston-side oil chamber 27B flows through the pressure-side flow path 52 of the piston 26 into the piston-rod-side oil chamber 27A in a state of bending and deforming the compression-side damping valve 52A. Get damping force. The suspension spring 49 and the spring 42 buffer the impact during compression, and the compression damping force controls the compression speed of the suspension spring 49 and the spring 42.
[0037]
(A) During the compression stroke of the front fork 10, the suspension spring 49 is compressed by the compression stroke of the vehicle body side tube 11 with respect to the axle side tube 12. Further, since the piston rod 24 enters the damper cylinder 21, the operating oil corresponding to the volume of the entered piston rod 24 flows into the lower oil chamber 35 of the free piston 34 to move the free piston 34 upward, and the spring 42 Compress.
[0038]
That is, at the time of compression, in addition to the suspension spring 49 flexing to the contraction side, the spring 42 biasing the free piston 34 is increased by the amount that the piston rod 24 enters the damper cylinder 21 and the free piston 34 moves upward. Deflected to the contraction side. As a result, the spring reaction force of the front fork 10 increases, and the sinking of the front fork 10 can be suppressed by a large spring reaction force during braking.
[0039]
(B) Then, when the compression stroke of the front fork 10 reaches a certain value or more (the depth side of the compression stroke), as during cornering after breaking, the piston rod 24 enters the damper cylinder 21 for a certain length or more. As a result, the free piston 34 moves upward by a certain length or more, the skirt portion 81 of the free piston 34 opens the bypass oil passage 80 provided in the damper cylinder 21, and the above-described compression-side damping force generator 60 (compression-side damping valve 66A, needle The generation of the compression damping force by the valve 68A and the plate valve 68B) is stopped as described above. The front fork 10 only generates a low pressure-side damping force based on the passage resistance of the bypass oil passage 80, and reduces the generated damping force so that fine disturbances such as gaps entering the wheels can be well absorbed, and the vehicle is in a stable running state. Can be secured.
[0040]
(Extension process)
When the front fork 10 is extended, one of the body-side tube 11 and the axle-side tube 12 extends relatively to the other, and the suspension spring 49 extends. Further, the piston rod 24 retreats from the damper cylinder 21, and the hydraulic oil in the piston rod side oil chamber 27A passes through the bypass flow path 53 of the piston 26 at low speed, and passes through the extension flow path 51 of the piston 26 at medium / high speed. It flows to the piston side oil chamber 27B through the extension side damping valve 51A. Further, the hydraulic oil corresponding to the volume from which the piston rod 24 has retreated enters the upper oil chamber 45 of the sub-tank 43 from the lower oil chamber 35 of the free piston 34, and passes through the check valve 67 A of the extension side flow passage 67 of the bottom piece 65. It returns to the piston side oil chamber 27B.
[0041]
Then, the free piston 34 moves down by the urging force of the spring 42, and the spring 42 extends.
[0042]
Thus, at low speed, the oil in the piston rod-side oil chamber 27A flows into the piston-side oil chamber 27B through the bypass passage 53 of the piston 26, and the expansion resistance is obtained by the throttle resistance of the needle valve 53A during this time. At medium to high speeds, the oil in the piston rod side oil chamber 27A flows through the expansion side flow path 51 of the piston 26 to the piston side oil chamber 27B, and the expansion side damping force is obtained by the bending resistance of the expansion side damping valve 51A during this time. The extension-side damping force prevents the suspension spring 49 and the spring 42 from resonating.
[0043]
(A) By the way, when moving from the compression stroke to the extension stroke, the suspension spring 49 extends by an amount corresponding to the stroke of the vehicle body side tube 11 with respect to the axle side tube 12. Further, since the piston rod 24 retreats from the damper cylinder 21, the lower oil chamber 35 of the free piston 34 is depressurized, and the free piston 34 is moved down by the urging force of the spring 42.
[0044]
That is, when a transition is made from the compression stroke to the extension stroke, the suspension spring 49 bends to the extension side, and the free piston 34 is urged to the extent that the piston rod 24 withdraws from the damper cylinder 21 and the free piston 34 moves downward. The spring 42 which is bent bends to the extension side. As a result, the spring reaction force of the front fork 10 is reduced, and the front fork 10 is prevented from extending during acceleration during cornering, thereby suppressing understeering.
[0045]
(B) When the front fork 10 further extends, the free piston 34 bottoms on the stopper portion 38 of the intermediate cylinder 31 and does not move down any further. From the time when the free piston 34 bottoms out, only the spring reaction force of the suspension spring 49 is generated, the spring reaction force of the front fork 10 rapidly decreases, and the suspension spring 49 returns to the most extended state.
[0046]
According to the present embodiment, the following operations are provided.
(Action corresponding to claim 1)
{Circle around (1)} When the front fork 10 is compressed, the suspension spring 49 is compressed, the piston rod 24 enters the damper cylinder 21, and the oil in the piston side oil chamber 27 B passes through the compression side damping force generator 60 and the free piston 34. Into the annular oil chamber 35 at the lower portion of the cylinder, and obtains the compression side damping force generated by the compression side damping force generator 60 during this time. The compression damping force controls the compression speed of the suspension spring 49.
[0047]
(2) When the compression stroke of the front fork 10 advances and reaches a compression stroke equal to or greater than a certain value, the piston-side oil chamber 27 </ b> B is connected to the annular oil chamber below the free piston 34 by the bypass oil passage 80 that bypasses the compression-side damping force generator 60. It communicates with 35. As a result, the generation of the compression side damping force by the compression side damping force generator 60 is stopped during the compression stroke equal to or more than a certain value.
[0048]
(3) At the time of braking, the suspension spring 49 contracts greatly due to the large compression stroke of the front fork 10, and the spring reaction force thereby suppresses the sinking of the front fork 10.
[0049]
(4) During the cornering after braking (during steady turning), the front fork 10 may still be further compressed by the above (3), or may be slightly extended from the above (3) by the cancellation of the brake, but still have the compressed stroke. The bypass oil passage 80 is set to be in the open state as described in (2) above, and the generation of the compression side damping force by the compression side damping force generator 60 is stopped. As a result, the front fork 10 well absorbs small disturbances such as gaps entering the wheels on the far side of the compression stroke, facilitates expansion and contraction operations, and improves ride comfort and operability.
[0050]
(Action corresponding to claim 2)
(5) Since the spring 42 is attached to the free piston 34, when the hydraulic oil corresponding to the volume of the piston rod 24 entering the damper cylinder 21 moves the free piston 34 upward when the front fork 10 is compressed, the spring 42 is attached. It will be compressed. Thus, the spring reaction force of the front fork 10 is such that the compression amount of the spring 42 is added to the compression amount of the suspension spring 49, and the sinking of the front fork 10 is suppressed by a large spring reaction force during braking.
[0051]
{Circle around (6)} Since the free piston 34 pressurizes the oil chamber 27 in the damper cylinder 21 with the spring force of the spring 42, generation of bubbles (cavitation) in the hydraulic oil in the damper cylinder 21 is prevented, and the damping force is stabilized. Secure.
[0052]
(Action corresponding to claim 3)
{Circle around (7)} In the front fork 10, the intermediate cylinder 31 is provided inside the axle-side tube 12 through an annular gap, and the free piston 34 is provided between the intermediate cylinder 31 and the damper cylinder 21. Even if the surface bends in an elliptical shape, it is not affected by the bending. Accordingly, smooth sliding of the free piston 34 can be ensured.
[0053]
FIG. 4 is a modified example of the front fork 10 of FIGS. 1 to 3, in which the hole-shaped bypass oil passage 80 of FIGS. The bypass oil passage 90 is formed along the axial direction on the lower end side of the damper cylinder 21, bypasses the pressure-side damping force generator 60 built in the sub-tank 43, and bypasses the lower part of the piston-side oil chamber 27 </ b> B and the lower part of the free piston 34. The annular oil chamber 35 is communicated.
[0054]
According to the long hole bypass oil passage 90, when the hole area of the bypass oil passage 90 is made equal to the hole area of the bypass oil passage 80, the free piston 34 performs a compression stroke on the back side of the compression stroke of the front fork 10. As it goes, the bypass oil passage 90 gradually opens from one end side of the long hole, in other words, gradually communicates the piston side oil chamber 27 </ b> B and the annular oil chamber 35, and as a result, the compression side damping force generated by the compression side damping force generator 60 is reduced. The generation is gradually stopped, and a transition is made to a state in which the generated damping force of the front fork 10 that only generates a lower pressure-side damping force based on the passage resistance of the bypass oil passage 90 is gradually reduced. Therefore, a sudden change in the compression damping force of the front fork 10 due to the opening of the bypass oil passage 90 on the far side of the compression stroke of the front fork 10 is alleviated, and fine disturbance such as a gap entering the wheel can be well absorbed. Thus, the running state of the vehicle can be further stabilized.
[0055]
In the front fork 10, the spring 42 attached to the free piston 34 is formed separately from the suspension spring 49. However, in the front fork 10 of the present invention, the free piston 34 may be biased by the suspension spring 49 without using the spring 42.
[0056]
Further, the front fork 10 is of an inverted type in which the body-side tube 11 is an outer tube, and the axle-side tube 12 is an inner tube inserted into the body-side tube 11. However, the front fork 10 of the present invention may be an upright type in which the vehicle body side tube 11 is an inner tube and the axle side tube is an outer tube.
[0057]
In the front fork 10, the damper cylinder 21 is fixed to the axle tube 12 and the piston rod 24 is fixed to the vehicle body tube 11. However, in the front fork 10 of the present invention, the damper cylinder 21 may be fixed to the vehicle body side tube 11 and the piston rod 24 may be fixed to the axle side tube 12.
[0058]
In the front fork 10, the space around the outer periphery of the damper cylinder 21 is an oil reservoir 28. However, in the front fork 10 of the present invention, the outer periphery of the damper cylinder 21 may be a gas chamber (air chamber).
[0059]
As described above, the embodiment of the present invention has been described with reference to the drawings. However, the specific configuration of the present invention is not limited to this embodiment, Are also included in the present invention.
[0060]
【The invention's effect】
As described above, according to the present invention, in the hydraulic shock absorber, it is possible to improve the absorbability of a small disturbance such as a gap on the inner side of the compression stroke.
[Brief description of the drawings]
FIG. 1 is a sectional view showing the entire hydraulic shock absorber.
FIG. 2 is a lower sectional view of FIG. 1;
FIG. 3 is an enlarged view of a main part of FIG. 2;
FIG. 4 is an enlarged view of a main part showing a modification of the hydraulic shock absorber.
[Explanation of symbols]
10 Front fork (hydraulic shock absorber)
11 Body side tube 12 Axle side tube 20 Damper 21 Damper cylinder 24 Piston rod 25A Seal member 26 Piston 27 Oil chamber 27A Piston rod oil chamber 27B Piston oil chamber 28 Oil storage chamber 29 Gas chamber 31 Intermediate cylinder 34 Free piston 35 Ring Oil chamber 42 Spring 60 Pressure side damping force generator 80, 90 Bypass oil passage

Claims (4)

The body side tube and the axle side tube are slidably fitted,
Inside the body side tube and the axle side tube, a damper cylinder, and a damper including a piston rod that slides through a piston provided at a tip end portion of the damper cylinder, are housed,
In the damper cylinder, a piston rod-side oil chamber that houses the piston rod and a piston-side oil chamber that does not house the piston rod are formed,
In a hydraulic shock absorber in which the damper cylinder is fixed to one of the vehicle body-side tube and the axle-side tube, and the piston rod is fixed to the other,
On one end side of the damper cylinder through which the piston rod is inserted, a seal member for sealing a piston rod side oil chamber of the damper cylinder is provided,
An annular free piston is provided on the outer periphery of the damper cylinder, and the annular free piston hermetically partitions an annular oil chamber communicating with the piston side oil chamber on the outer periphery of the damper cylinder.
A pressure-side damping force generator is provided between the piston-side oil chamber and the annular oil chamber, and the damper cylinder bypasses the pressure-damping force generator, and the piston-side oil chamber and the annular oil chamber are provided. A bypass oil passage that communicates with the
The hydraulic shock absorber, wherein the bypass oil passage communicates the piston side oil chamber with the annular oil chamber when the free piston makes a compression stroke of a certain amount or more. The axle side tube is slidably fitted in the body side tube,
A damper cylinder is erected in the axle side tube, and a piston rod provided with a piston at a tip end is slidably inserted into the damper cylinder,
In the damper cylinder, a piston rod-side oil chamber that houses the piston rod and a piston-side oil chamber that does not house the piston rod are formed,
In a hydraulic shock absorber provided with an oil reservoir having an upper portion as a gas chamber on an outer periphery of the damper cylinder,
On one end side of the damper cylinder through which the piston rod is inserted, a seal member for sealing a piston rod-side oil chamber in the damper cylinder is provided.
An annular free piston urged by a spring is slidably provided on the outer periphery of the damper cylinder,
In the annular free piston, an annular oil chamber communicating with the piston-side oil chamber is hermetically partitioned on the outer periphery of the damper cylinder,
A compression-side damping force generator is provided between the piston-side oil chamber and the annular oil chamber, and the damper cylinder bypasses the compression-side damping force generator, and the piston-side oil chamber and the annular oil chamber are provided. A bypass oil passage that communicates with the
The hydraulic shock absorber, wherein the bypass oil passage communicates the piston side oil chamber with the annular oil chamber when the free piston makes a compression stroke of a certain amount or more. An intermediate cylinder is provided through an annular gap between the outer periphery of the damper cylinder and the inner periphery of the axle tube,
3. The hydraulic shock absorber according to claim 1, wherein the annular free piston is provided between the intermediate cylinder and the damper cylinder. The hydraulic shock absorber according to any one of claims 1 to 3, wherein the bypass oil passage is formed by a long hole along an axial direction of the damper cylinder.

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