CA2466205A1 - Hydraulic shock absorber - Google Patents
Hydraulic shock absorber Download PDFInfo
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- CA2466205A1 CA2466205A1 CA 2466205 CA2466205A CA2466205A1 CA 2466205 A1 CA2466205 A1 CA 2466205A1 CA 2466205 CA2466205 CA 2466205 CA 2466205 A CA2466205 A CA 2466205A CA 2466205 A1 CA2466205 A1 CA 2466205A1
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- piston
- cylinder
- chamber
- fluid chamber
- shock absorber
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- 239000006096 absorbing agent Substances 0.000 title claims abstract description 43
- 230000035939 shock Effects 0.000 title claims abstract description 43
- 239000012530 fluid Substances 0.000 claims abstract description 100
- 230000037361 pathway Effects 0.000 claims abstract description 19
- 238000013016 damping Methods 0.000 claims description 39
- 230000006835 compression Effects 0.000 claims description 20
- 238000007906 compression Methods 0.000 claims description 20
- 239000007789 gas Substances 0.000 description 29
- 238000007789 sealing Methods 0.000 description 4
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 1
- 230000008602 contraction Effects 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- 239000000428 dust Substances 0.000 description 1
- 238000005192 partition Methods 0.000 description 1
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- Fluid-Damping Devices (AREA)
- Axle Suspensions And Sidecars For Cycles (AREA)
Abstract
A hydraulic shock absorber including: a cylinder 20; a piston 30 slidably housed in the cylinder; a piston rod 31 connected to the piston; a piston rod side fluid chamber 2 and piston side fluid chamber 3 being partitioned off within the cylinder on both sides of the piston; an outer shell 10 that is disposed coaxially with the cylinder in the outer side of the cylinder; a bypass pathway 4 formed between the cylinder and the outer shell; a plurality of connection holes 21,22 formed in different locations in a piston stroke direction of the cylinder, the plurality of connection holes connecting the bypass pathway with the piston rod side fluid chamber and the piston side fluid chamber; an extension portion 17 of the outer shell that extends further in an axial direction than an end portion of the cylinder; a free piston 52 disposed slidably within the extension portion; a fluid reservoir chamber 5 and a gas chamber 6 being partitioned off on both sides of the free piston.
Description
HYDRAULIC SHOCK ABSORBER
BACKGROUND OF THE INVENTION
Field of the Invention [OOOI] The present invention relates to a hydraulic shock absorber of a vehicle. In particular, the present invention relates to a hydraulic shock absorber that is used as a reaction unit in an automatic two wheel vehicle.
Description of the Related Art [0002] A hydraulic shock absorber in which a damping force generated by the hydraulic shock absorber changes depending upon a piston stroke position is already known, as in JP 2000-145870 A.
BACKGROUND OF THE INVENTION
Field of the Invention [OOOI] The present invention relates to a hydraulic shock absorber of a vehicle. In particular, the present invention relates to a hydraulic shock absorber that is used as a reaction unit in an automatic two wheel vehicle.
Description of the Related Art [0002] A hydraulic shock absorber in which a damping force generated by the hydraulic shock absorber changes depending upon a piston stroke position is already known, as in JP 2000-145870 A.
[0003] In this hydraulic shock absorber, a working fluid and a gas within a cylinder are separated by a free piston that is disposed freely slidably within the cylinder. The free piston moves while compressing the gas according to the pressure of an inner portion of the hydraulic shock absorber.
[0004] The free piston is disposed within the cylinder, making it unnecessary to dispose a separate gas chamber in an outer side of the hydraulic shock absorber and resulting in a simple structure .
There is a problem, however, in that the length in an axial direction of the hydraulic shock absorber becomes longer in order to ensure an amount for the free piston to move within the cylinder, and a I
large space is necessary for mounting the hydraulic shock absorber to an automatic two wheeled vehicle.
SUMMARY OF THE INVENTION
There is a problem, however, in that the length in an axial direction of the hydraulic shock absorber becomes longer in order to ensure an amount for the free piston to move within the cylinder, and a I
large space is necessary for mounting the hydraulic shock absorber to an automatic two wheeled vehicle.
SUMMARY OF THE INVENTION
[0005] Therefore, an obj ect of the present invention is to make a length of the hydraulic shock absorber in an axial direction thereof as short as possible without losing a simple structure of the hydraulic shock absorber.
[00061 According to the present invention, there is provided a hydraulic shock absorber including: a cylinder having an inner side and an outer side;
a piston that is slidably housed in the inner side of the cylinder;
a piston rod that is connected to the piston: a piston rod side fluid chamber that is partitioned off within the cylinder on one side of the piston; a piston side fluid chamber that is partitioned off within the cylinder on another side of the piston; an outer shell that is disposed coaxially with the cylinder in the outer side of the cylinder, the outer shell having a larger diameter than the diameter of the cylinder; a bypass pathway that is formed between the cylinder and the outer shell; a plurality of connection holes formed in different locations in a piston stroke direction of the cylinder, the plurality of connection holes connect:Lng the bypass pathway with the piston rod side fluid chamber and the piston side fluid chamber; an extension portion of the outer shell that extends further in an axial direction than an end portion of the cylinder: a free piston that is slidably disposed within the extension portion; a fluid reservoir chamber that is connected to the piston side fluid chamber, the fluid reservoir chamber being partitioned off on one side of the free piston; and a gas chamber in which a gas is enclosed, the gas chamber being partitioned off on another side of the free piston.
[000?j Preferably, the hydraulic shock absorber includes a base valve that is provided in the end portion of the cylinder, interposed between the piston side fluid chamber and the fluid reservoir chamber.
[OOO8j Further, the base valve is provided with a compression side damping valve that imparts resistance to a flow of a working fluid that flows out from the piston side fluid chamber to the fluid reservoir chamber.
BRIEF DESCRIPTION OF THE DRAWING
[0009] FIG. 1 is a cross sectional view of a hydraulic shock absorber that shows an embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[OOlOj A preferred embodiment of the present invention is explained below based on the appended drawing.
[0011] Referring to FIG. 2, a hydraulic shock absorber 1 is used as a reaction unit of a two wheeled vehicle, for example. The hydraulic shock absorber 1 operates in compression and extension according to upward and downward motion of a vehicle wheel with respect to a vehicle body, thus damping vibrations of the vehicle wheel.
[0012) The hydraulic shock absorber 1 is provided with an upper eye bracket 32 and a lower eye bracket 11. The eye brackets 32 and 11 are connected to the vehicle body and the vehicle wheel, respectively. It should be noted that a position of the hydraulic shock absorber 1 when it is mounted to the vehicle is not limited to that shown in FIG. 1.
[0013] The hydraulic shock absorber 1 is provided with an outer shell 10, and a cylinder 20 that is disposed coaxially in an inner side of the outer shell 10.
[0014] A piston 30 is slidably disposed in an inner side of the cylinder 20, and a piston rod 31 is connected to the piston 30.
An upper fluid chamber 2 and a lower fluid chamber 3 are partitioned off by a piston 30 within the cylinder 20. The upper fluid chamber 2 means a piston rod side fluid chamber, and the lower fluid chamber 3 means a piston side fluid chamber here.
[0015] An upper end portion of the cylinder 20 is supported by the outer shell 10, through a seal case 60. A lower end portion of the cylinder 20 is supported by the outer she11~10 through support cylinder 70 that mates to an outer side of the cylinder 20.
[0016] The upper end of the outer shell 10 and the upper end of the cylinder 20 are closed off by the seal case 60. The piston rod 31 passes through the seal case 60, and the eye bracket 32 is provided in an upper portion of the piston rod 31. An oil seal F~1 and a dust seal 62 are provided to the seal case 60, thus sealing so that oil does not leak from pass through regions of the piston rod 31.
[001?] The support cylinder 70 has an outer circumferential flange portion 71 that annularly projects out from an outer circumferential surface of the support cylinder 70. On the other hand, an annular step portion I2 is provided to an inner wall 13 of the outer shell 10. The outer circumferential flange portion 71 of the support cylinder 70 contacts the step portion 12.
Positioning of the support cylinder ?0 with respect to the outer shell 10 is thus performed.
[0018) The lower end portion of the cylinder 20 is inserted to an inner circumferential surface of the support cylinder 70. The support cylinder 70 has an inner circumferential flange portion 72 that projects out annularly from the inner circumferential surface of the support 70.
[0019] Ports 33 and 34 are provided passing through the piston 30, which slides within the cylinder, in a vertical direction. One port, the port 33, is opened and closed by a compression side damping valve 35, while the other port, the port 34, is opened and closed by an extension side damping valve 36. The compression side damping valve 35 opens when the piston 30 moves in a direction toward which the piston rod 31 pushes in, thus imparting a resistance to the flow of the working fluid from the piston side fluid chamber 3 to the piston rod side fluid chamber 2. In contrast, the extension side damping valve 36 opens when the piston 30 moves in a direction toward which the piston rod 3I extends out, thus imparting a resistance to the flow of the working fluid from the piston rod side fluid chamber 2 to the piston side fluid chamber 3. It should be noted that the compression side damping valve 35 is set to make a restriction resistance larger than the extension side damping valve 36.
[0020] An annular bypass passage 4 is provided between the cylinder 20 and the outer shell 10. An upper end of the bypass passage 4 is closed off by the seal case 60, and further, a lower end of the bypass passage 4 is closed off by the support cylinder 70. The cross sectional area of the bypass pathway 4 is determined according to the difference between the outer diameter of the cylinder 20 and the inner diameter of the outer shell 10.
[0021] First and second connection holes 21 and 22 are provided along a wall of the cylinder 20 at a predetermined spacing in an axial direction. The first and the second connection holes 21 and 22 connect the bypass pathway 4 with the piston rod side fluid chamber 2 or the piston side fluid chamber 3, depending upon the stroke position of the piston 30.
[0022] When the piston 30 is positioned between the first connection hole 21 and the second connection hole 22, the bypass pathway 4 communicates with the piston rod side fluid chamber 2 and the piston side fluid chamber 3. The flow of the working fluid from the piston rod side fluid chamber 2 to the piston side fluid chamber 3, or in the reverse direction, via the first arid the second connection holes 21 and 22 is thus permitted by movement of the piston 30. Accordingly, the amount of the working fluid passing through the compression side damping valve 35 or the extension side damping valve 36 of the piston 30 drops, and the generated damping force becomes relatively weaker.
[0023] In contrast, when the piston 30 is positioned lower than the second connection hole 22, communication between the piston side fluid chamber 3 and the bypass pathway 4 is cut off.
Accordingly, when the piston 30 moves further downward, the working fluid flows from the piston side fluid chamber 3 to the piston rod side fluid chamber 2 only through the compression side damping valve 35. The damping force thus becomes relatively larger.
[0024] Further, when the piston 30 is positioned higher than the first connection hole 21, communication between the piston rod side fluid chamber 2 and the bypass pathway 4 is cut off. Accordingly, when the piston 30 moves further upward, all of the working fluid that flows out from the piston rod side fluid chamber 2 to the piston side fluid chamber 3 passes through the extension side damping valve 36. The damping force thus becomes relatively larger.
[0025] The hydraulic shock absorber 1 thus demonstrates that the generated damping force changes depending upon the position of the piston stroke. That is, compared to when the piston 30 is in an intermediate position, the extension side damping force increases in the vicinity of the maximum extension in a stroke where the piston rod 31 extends out, and the compression side damping force increases in the vicinity of the maximum compression in a stroke where the piston rod 31 retracts.
[0026) An outer shell extension portion 17 that extends lower than the lower end portion of the cylinder 20 is provided to the outer shell 10. A free piston 50 is freely slidably disposed in an inner side of the extension portion 17, which has a larger diameter than the outer diameter of the cylinder 20. A fluid reservoir chamber 5 is partitioned off above the free piston 50, and a gas chamber 6 is partitioned off below the free piston 50.
[0027) The fluid reservoir chamber 5 is connected to the piston side fluid chamber 3 within the cylinder thraugh a base valve 40 that is provided to the lower end of the cylinder 20.
j0028] An oil seal 51 is provided in an outer circumference of the free piston 50, sealing the outer shell 10 so that oil does not leak from sliding contact portion to the .gas chamber 6 side.
[0029] An inner diameter D1 of the extension portion 17 in sliding contact with the free piston 50 is formed larger than an inner diameter D2 of the cylinder 20. The cross sectional area of the fluid reservoir chamber 5 and the gas chamber 6 is thus formed larger than the cross sectional area of the piston rod side fluid chamber 2 and the piston side fluid chamber 3 by an amount equal to the cross sectional area of the support cylinder 70. A large capacity can therefore be ensured for the fluid reservoir chamber and the gas chamber 6, even if the distance in a movement direction of the piston 50 is small.
[0030] The thickness of a lower portion of the extension portion 17 of the outer shell 10 becomes larger than an upper portion of the annular step portion 12. A lower end of the extension portion 17 is closed by a bottom portion 14. The eye bracket 11 is formed integrally with the bottom portion 14, thus ensuring rigidity.
[0031] A gas sealing inlet 15 is provided in the outer shell 10.
Nitrogen gas sent from a pressurized gas source that is not shown fills the gas chamber 6 from the gas sealing inlet 15, and is sealed in. Gas spring characteristics of the hydraulic shock absorber change according to the pressure of the gas enclosed in the gas chamber 6. The higher the gas pressure, the higher a repulsive force of the hydraulic shock absorber becomes.
[0032] A concave portion 52 is formed in an upper portion of the free piston 50. Interference between the free piston 50 and the base valve 40 thus does riot occur when the free piston 50 rises to its highest position.
(0033] The base valve 40 is supported by the lower portion of the cylinder 20 through a flange portion 41 of the base valve 40 being sandwiched between the lower end of the cylinder 20 and the inner circumference flange portion 72 of the support cylinder 70.
[0034] Ports 43 and 44 are provided passing through the base valve 40 in an axial direction. One of the ports, the port 43, is opened and closed by a compression side damping valve 45, while the other port, the port 44, is opened and closed by an extension side damping valve 46. When the piston 30 moves in a direction toward which the piston rod 31 pushes in, an amount of the working fluid corresponding to the volume that the piston rod 31 enters into the cylinder pushes open the compression side damping valve 45, flowing from the piston side fluid chamber 3 to the fluid reservoir chamber 5. In contrast, when the piston 31 moves in a direction toward which the piston rod 31 extends out, an amount of the working fluid corresponding to the volume that the piston rod 31 pulls out from the cylinder pushes open the extension side damping valve 4C, flowing from the fluid reservoir chamber 5 to the piston side fluid chamber 3.
[0035) It should be noted that a constriction resistance due to the extension side damping valve 46 is set to be smaller than the constriction resistance due to the compression side damping valve 45. The working fluid thus flows swiftly within the cylinder when the piston 30 moves to the piston rod extension side, preventing negative pressurization.
[00361 The configuration is as described above. Operation is explained next.
[0037) When operating in the extension direction of the hydraulic shock absorber 1, the piston 30 moves upward within the cylinder 20. The working fluid of the compressed piston rod side fluid chamber 2 flows into the expanded piston side fluid chamber 3. When the piston 30 is in an intermediate position between the first and the second connection holes 21 and 22, the bypass pathway 4 opens, and the working fluid flows through the bypass pathway 4 and the extension side damping valve 36 of the piston 30. In contrast, the first connection hole ~21 is closed by the piston 30 when the piston 30 moves upward, exceeding the intermediate position, and the flow of the working fluid from the piston rod side fluid chamber 2 to the bypass pathway 4 is cut off. The damping force generated therefore relatively increases when the piston 30 exceeds the intermediate position.
[0038] Further., an amount of the working fluid corresponding to the volume that the piston rod 31 pulls out from the cylinder 20 flows from the fluid reservoir chamber 5, through the extension side damping valve 46, to the piston side fluid chamber 3 during extension operation of the hydraulic shock absorber 1.
[0039] When operating in the compression direction of the hydraulic shock absorber l, the piston 30 moves downward within the cylinder 20. The working fluid of the compressed piston side fluid chamber 3 flows into the expanded piston rod side fluid chamber 2. When the piston 30 is in an intermediate position between the first and the second connection holes 21 and 22, the bypass pathway 4 opens, and the working fluid flows through the bypass pathway 4 and the compression side damping valve 35 of the piston 30. In contrast, the second connection hole 22 is closed by the piston 30 when the piston 30 moves downward, exceeding the intermediate position, and the flow of the working fluid through.the bypass pathway 4 is cut off. The damping force generated therefore relatively increases when the piston 30 exceeds the intermediate position.
[0040] Further, an amount of the working fluid corresponding to the volume that the piston rod 31 enters into the cylinder 20 flows from the piston side fluid chamber 3, through the compression side damping valve 45 of the base valve 40, to the fluid reservoir chamber 5 during compression operation of the hydraulic shock absorber 1.
(0041] The bypass pathway 4 is thus open when the hydraulic shock absorber 1 strokes in the intermediate position, and the damping force that is generated by the extension side damping valve 36 or the compression side damping valve 35 is kept low. In contrast, the bypass pathway 4 is cut off when the hydraulic shock absorber 1 strokes in a position that exceeds the intermediate position, and the damping force that is generated by the extension side damping valve 36 or the compression side damping valve 35 increases, [0042] There is a possibility of cavitation being generated if the pressure of the expanded piston rod side fluid chamber 2 drops too much when the hydraulic shock absorber 1 operates rapidly in contraction. In order to prevent cavitation, the pressure of the gas that fills the gas chamber 6 may be increased, and the pressure of the piston side fluid chamber 3 may be made relatively higher.
However, if the pressure of the gas chamber 6 is too high, the reactive force normally working on the piston rod 31 will become relatively larger, and the riding comfort of the vehicle will suffer .
[0043] According to the present invention, the pressure of the piston side fluid chamber 3 is increased by the compression side damping valve 45 provided to the base valve 40 imparting a resistance to the flow of the working fluid that flows out from the piston side fluid chamber 3 to the fluid reservoir chamber 5. The working fluid thus flows smoothly from the piston side fluid chamber 3 to the expanded piston rod side chamber 2, even when the hydraulic shock absorber 1 is suddenly compressed. Excessive reduction in the pressure of the piston rod side chamber 2 is suppressed, and the generation of cavitation can be prevented. It thus becomes possible to set the pressure of the gas chamber 6 low, making the reaction force that normally works on the piston rod 31 smaller.
That is, it becomes possible to maintain a smaller spring constant of the gas spring, and the riding comfort of the vehicle can be improved.
[0044] The hydraulic shock absorber 1 employs a structure in which the fluid reservoir chamber 5 and the gas chamber 6 are provided within the outer shell 10. Accordingly, it is unnecessary to provide a tank or the like separate to the shock absorber, and the structure can be simplified. It should be noted that the hydraulic shock absorber 1 is structured by providing the gas chamber 6 extending in the axial direction of the cylinder 20. The basic length in the axial direction of the shock absorber thus increases compared to a structure in which the gas chamber is provided within a separate tank.
[0045) However, this is a structure in which the free piston 50 that partitions off the gas chamber 6 is housed within the extension portion 17 of the outer shell 10, not within the cylinder. It thus becomes possible to make the outer diameter D1 of th.e free piston 50 larger than the outer diameter D2 of the piston 3a within the cylinder. That is, the cross sectional area of the fluid reservoir chamber 5 and the gas chamber 6 becomes larger than the cross sectional area within the cylinder 20 by the amount that the inner diameter D1 of the outer shell extension portion 17 is larger than the inner diameter D2 of the cylinder 20.
(0046] The amount that the free piston 50 moves can thus be made smaller for cases where the surface area of the fluid reservoir chamber 5 and the gas chamber 6 are the same. The basic length of the hydraulic shock absorber 1 in the axial direction is shortened compared to a conventional structure in which the free piston is housed within the cylinder, and the space needed for mounting the hydraulic shock absorber 1 to a vehicle can be made smaller.
(0047) The present invention is not limited to the embodiment described above . It is clear that various changes can be made within the scope of the technical concepts of the present invention.
[00061 According to the present invention, there is provided a hydraulic shock absorber including: a cylinder having an inner side and an outer side;
a piston that is slidably housed in the inner side of the cylinder;
a piston rod that is connected to the piston: a piston rod side fluid chamber that is partitioned off within the cylinder on one side of the piston; a piston side fluid chamber that is partitioned off within the cylinder on another side of the piston; an outer shell that is disposed coaxially with the cylinder in the outer side of the cylinder, the outer shell having a larger diameter than the diameter of the cylinder; a bypass pathway that is formed between the cylinder and the outer shell; a plurality of connection holes formed in different locations in a piston stroke direction of the cylinder, the plurality of connection holes connect:Lng the bypass pathway with the piston rod side fluid chamber and the piston side fluid chamber; an extension portion of the outer shell that extends further in an axial direction than an end portion of the cylinder: a free piston that is slidably disposed within the extension portion; a fluid reservoir chamber that is connected to the piston side fluid chamber, the fluid reservoir chamber being partitioned off on one side of the free piston; and a gas chamber in which a gas is enclosed, the gas chamber being partitioned off on another side of the free piston.
[000?j Preferably, the hydraulic shock absorber includes a base valve that is provided in the end portion of the cylinder, interposed between the piston side fluid chamber and the fluid reservoir chamber.
[OOO8j Further, the base valve is provided with a compression side damping valve that imparts resistance to a flow of a working fluid that flows out from the piston side fluid chamber to the fluid reservoir chamber.
BRIEF DESCRIPTION OF THE DRAWING
[0009] FIG. 1 is a cross sectional view of a hydraulic shock absorber that shows an embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[OOlOj A preferred embodiment of the present invention is explained below based on the appended drawing.
[0011] Referring to FIG. 2, a hydraulic shock absorber 1 is used as a reaction unit of a two wheeled vehicle, for example. The hydraulic shock absorber 1 operates in compression and extension according to upward and downward motion of a vehicle wheel with respect to a vehicle body, thus damping vibrations of the vehicle wheel.
[0012) The hydraulic shock absorber 1 is provided with an upper eye bracket 32 and a lower eye bracket 11. The eye brackets 32 and 11 are connected to the vehicle body and the vehicle wheel, respectively. It should be noted that a position of the hydraulic shock absorber 1 when it is mounted to the vehicle is not limited to that shown in FIG. 1.
[0013] The hydraulic shock absorber 1 is provided with an outer shell 10, and a cylinder 20 that is disposed coaxially in an inner side of the outer shell 10.
[0014] A piston 30 is slidably disposed in an inner side of the cylinder 20, and a piston rod 31 is connected to the piston 30.
An upper fluid chamber 2 and a lower fluid chamber 3 are partitioned off by a piston 30 within the cylinder 20. The upper fluid chamber 2 means a piston rod side fluid chamber, and the lower fluid chamber 3 means a piston side fluid chamber here.
[0015] An upper end portion of the cylinder 20 is supported by the outer shell 10, through a seal case 60. A lower end portion of the cylinder 20 is supported by the outer she11~10 through support cylinder 70 that mates to an outer side of the cylinder 20.
[0016] The upper end of the outer shell 10 and the upper end of the cylinder 20 are closed off by the seal case 60. The piston rod 31 passes through the seal case 60, and the eye bracket 32 is provided in an upper portion of the piston rod 31. An oil seal F~1 and a dust seal 62 are provided to the seal case 60, thus sealing so that oil does not leak from pass through regions of the piston rod 31.
[001?] The support cylinder 70 has an outer circumferential flange portion 71 that annularly projects out from an outer circumferential surface of the support cylinder 70. On the other hand, an annular step portion I2 is provided to an inner wall 13 of the outer shell 10. The outer circumferential flange portion 71 of the support cylinder 70 contacts the step portion 12.
Positioning of the support cylinder ?0 with respect to the outer shell 10 is thus performed.
[0018) The lower end portion of the cylinder 20 is inserted to an inner circumferential surface of the support cylinder 70. The support cylinder 70 has an inner circumferential flange portion 72 that projects out annularly from the inner circumferential surface of the support 70.
[0019] Ports 33 and 34 are provided passing through the piston 30, which slides within the cylinder, in a vertical direction. One port, the port 33, is opened and closed by a compression side damping valve 35, while the other port, the port 34, is opened and closed by an extension side damping valve 36. The compression side damping valve 35 opens when the piston 30 moves in a direction toward which the piston rod 31 pushes in, thus imparting a resistance to the flow of the working fluid from the piston side fluid chamber 3 to the piston rod side fluid chamber 2. In contrast, the extension side damping valve 36 opens when the piston 30 moves in a direction toward which the piston rod 3I extends out, thus imparting a resistance to the flow of the working fluid from the piston rod side fluid chamber 2 to the piston side fluid chamber 3. It should be noted that the compression side damping valve 35 is set to make a restriction resistance larger than the extension side damping valve 36.
[0020] An annular bypass passage 4 is provided between the cylinder 20 and the outer shell 10. An upper end of the bypass passage 4 is closed off by the seal case 60, and further, a lower end of the bypass passage 4 is closed off by the support cylinder 70. The cross sectional area of the bypass pathway 4 is determined according to the difference between the outer diameter of the cylinder 20 and the inner diameter of the outer shell 10.
[0021] First and second connection holes 21 and 22 are provided along a wall of the cylinder 20 at a predetermined spacing in an axial direction. The first and the second connection holes 21 and 22 connect the bypass pathway 4 with the piston rod side fluid chamber 2 or the piston side fluid chamber 3, depending upon the stroke position of the piston 30.
[0022] When the piston 30 is positioned between the first connection hole 21 and the second connection hole 22, the bypass pathway 4 communicates with the piston rod side fluid chamber 2 and the piston side fluid chamber 3. The flow of the working fluid from the piston rod side fluid chamber 2 to the piston side fluid chamber 3, or in the reverse direction, via the first arid the second connection holes 21 and 22 is thus permitted by movement of the piston 30. Accordingly, the amount of the working fluid passing through the compression side damping valve 35 or the extension side damping valve 36 of the piston 30 drops, and the generated damping force becomes relatively weaker.
[0023] In contrast, when the piston 30 is positioned lower than the second connection hole 22, communication between the piston side fluid chamber 3 and the bypass pathway 4 is cut off.
Accordingly, when the piston 30 moves further downward, the working fluid flows from the piston side fluid chamber 3 to the piston rod side fluid chamber 2 only through the compression side damping valve 35. The damping force thus becomes relatively larger.
[0024] Further, when the piston 30 is positioned higher than the first connection hole 21, communication between the piston rod side fluid chamber 2 and the bypass pathway 4 is cut off. Accordingly, when the piston 30 moves further upward, all of the working fluid that flows out from the piston rod side fluid chamber 2 to the piston side fluid chamber 3 passes through the extension side damping valve 36. The damping force thus becomes relatively larger.
[0025] The hydraulic shock absorber 1 thus demonstrates that the generated damping force changes depending upon the position of the piston stroke. That is, compared to when the piston 30 is in an intermediate position, the extension side damping force increases in the vicinity of the maximum extension in a stroke where the piston rod 31 extends out, and the compression side damping force increases in the vicinity of the maximum compression in a stroke where the piston rod 31 retracts.
[0026) An outer shell extension portion 17 that extends lower than the lower end portion of the cylinder 20 is provided to the outer shell 10. A free piston 50 is freely slidably disposed in an inner side of the extension portion 17, which has a larger diameter than the outer diameter of the cylinder 20. A fluid reservoir chamber 5 is partitioned off above the free piston 50, and a gas chamber 6 is partitioned off below the free piston 50.
[0027) The fluid reservoir chamber 5 is connected to the piston side fluid chamber 3 within the cylinder thraugh a base valve 40 that is provided to the lower end of the cylinder 20.
j0028] An oil seal 51 is provided in an outer circumference of the free piston 50, sealing the outer shell 10 so that oil does not leak from sliding contact portion to the .gas chamber 6 side.
[0029] An inner diameter D1 of the extension portion 17 in sliding contact with the free piston 50 is formed larger than an inner diameter D2 of the cylinder 20. The cross sectional area of the fluid reservoir chamber 5 and the gas chamber 6 is thus formed larger than the cross sectional area of the piston rod side fluid chamber 2 and the piston side fluid chamber 3 by an amount equal to the cross sectional area of the support cylinder 70. A large capacity can therefore be ensured for the fluid reservoir chamber and the gas chamber 6, even if the distance in a movement direction of the piston 50 is small.
[0030] The thickness of a lower portion of the extension portion 17 of the outer shell 10 becomes larger than an upper portion of the annular step portion 12. A lower end of the extension portion 17 is closed by a bottom portion 14. The eye bracket 11 is formed integrally with the bottom portion 14, thus ensuring rigidity.
[0031] A gas sealing inlet 15 is provided in the outer shell 10.
Nitrogen gas sent from a pressurized gas source that is not shown fills the gas chamber 6 from the gas sealing inlet 15, and is sealed in. Gas spring characteristics of the hydraulic shock absorber change according to the pressure of the gas enclosed in the gas chamber 6. The higher the gas pressure, the higher a repulsive force of the hydraulic shock absorber becomes.
[0032] A concave portion 52 is formed in an upper portion of the free piston 50. Interference between the free piston 50 and the base valve 40 thus does riot occur when the free piston 50 rises to its highest position.
(0033] The base valve 40 is supported by the lower portion of the cylinder 20 through a flange portion 41 of the base valve 40 being sandwiched between the lower end of the cylinder 20 and the inner circumference flange portion 72 of the support cylinder 70.
[0034] Ports 43 and 44 are provided passing through the base valve 40 in an axial direction. One of the ports, the port 43, is opened and closed by a compression side damping valve 45, while the other port, the port 44, is opened and closed by an extension side damping valve 46. When the piston 30 moves in a direction toward which the piston rod 31 pushes in, an amount of the working fluid corresponding to the volume that the piston rod 31 enters into the cylinder pushes open the compression side damping valve 45, flowing from the piston side fluid chamber 3 to the fluid reservoir chamber 5. In contrast, when the piston 31 moves in a direction toward which the piston rod 31 extends out, an amount of the working fluid corresponding to the volume that the piston rod 31 pulls out from the cylinder pushes open the extension side damping valve 4C, flowing from the fluid reservoir chamber 5 to the piston side fluid chamber 3.
[0035) It should be noted that a constriction resistance due to the extension side damping valve 46 is set to be smaller than the constriction resistance due to the compression side damping valve 45. The working fluid thus flows swiftly within the cylinder when the piston 30 moves to the piston rod extension side, preventing negative pressurization.
[00361 The configuration is as described above. Operation is explained next.
[0037) When operating in the extension direction of the hydraulic shock absorber 1, the piston 30 moves upward within the cylinder 20. The working fluid of the compressed piston rod side fluid chamber 2 flows into the expanded piston side fluid chamber 3. When the piston 30 is in an intermediate position between the first and the second connection holes 21 and 22, the bypass pathway 4 opens, and the working fluid flows through the bypass pathway 4 and the extension side damping valve 36 of the piston 30. In contrast, the first connection hole ~21 is closed by the piston 30 when the piston 30 moves upward, exceeding the intermediate position, and the flow of the working fluid from the piston rod side fluid chamber 2 to the bypass pathway 4 is cut off. The damping force generated therefore relatively increases when the piston 30 exceeds the intermediate position.
[0038] Further., an amount of the working fluid corresponding to the volume that the piston rod 31 pulls out from the cylinder 20 flows from the fluid reservoir chamber 5, through the extension side damping valve 46, to the piston side fluid chamber 3 during extension operation of the hydraulic shock absorber 1.
[0039] When operating in the compression direction of the hydraulic shock absorber l, the piston 30 moves downward within the cylinder 20. The working fluid of the compressed piston side fluid chamber 3 flows into the expanded piston rod side fluid chamber 2. When the piston 30 is in an intermediate position between the first and the second connection holes 21 and 22, the bypass pathway 4 opens, and the working fluid flows through the bypass pathway 4 and the compression side damping valve 35 of the piston 30. In contrast, the second connection hole 22 is closed by the piston 30 when the piston 30 moves downward, exceeding the intermediate position, and the flow of the working fluid through.the bypass pathway 4 is cut off. The damping force generated therefore relatively increases when the piston 30 exceeds the intermediate position.
[0040] Further, an amount of the working fluid corresponding to the volume that the piston rod 31 enters into the cylinder 20 flows from the piston side fluid chamber 3, through the compression side damping valve 45 of the base valve 40, to the fluid reservoir chamber 5 during compression operation of the hydraulic shock absorber 1.
(0041] The bypass pathway 4 is thus open when the hydraulic shock absorber 1 strokes in the intermediate position, and the damping force that is generated by the extension side damping valve 36 or the compression side damping valve 35 is kept low. In contrast, the bypass pathway 4 is cut off when the hydraulic shock absorber 1 strokes in a position that exceeds the intermediate position, and the damping force that is generated by the extension side damping valve 36 or the compression side damping valve 35 increases, [0042] There is a possibility of cavitation being generated if the pressure of the expanded piston rod side fluid chamber 2 drops too much when the hydraulic shock absorber 1 operates rapidly in contraction. In order to prevent cavitation, the pressure of the gas that fills the gas chamber 6 may be increased, and the pressure of the piston side fluid chamber 3 may be made relatively higher.
However, if the pressure of the gas chamber 6 is too high, the reactive force normally working on the piston rod 31 will become relatively larger, and the riding comfort of the vehicle will suffer .
[0043] According to the present invention, the pressure of the piston side fluid chamber 3 is increased by the compression side damping valve 45 provided to the base valve 40 imparting a resistance to the flow of the working fluid that flows out from the piston side fluid chamber 3 to the fluid reservoir chamber 5. The working fluid thus flows smoothly from the piston side fluid chamber 3 to the expanded piston rod side chamber 2, even when the hydraulic shock absorber 1 is suddenly compressed. Excessive reduction in the pressure of the piston rod side chamber 2 is suppressed, and the generation of cavitation can be prevented. It thus becomes possible to set the pressure of the gas chamber 6 low, making the reaction force that normally works on the piston rod 31 smaller.
That is, it becomes possible to maintain a smaller spring constant of the gas spring, and the riding comfort of the vehicle can be improved.
[0044] The hydraulic shock absorber 1 employs a structure in which the fluid reservoir chamber 5 and the gas chamber 6 are provided within the outer shell 10. Accordingly, it is unnecessary to provide a tank or the like separate to the shock absorber, and the structure can be simplified. It should be noted that the hydraulic shock absorber 1 is structured by providing the gas chamber 6 extending in the axial direction of the cylinder 20. The basic length in the axial direction of the shock absorber thus increases compared to a structure in which the gas chamber is provided within a separate tank.
[0045) However, this is a structure in which the free piston 50 that partitions off the gas chamber 6 is housed within the extension portion 17 of the outer shell 10, not within the cylinder. It thus becomes possible to make the outer diameter D1 of th.e free piston 50 larger than the outer diameter D2 of the piston 3a within the cylinder. That is, the cross sectional area of the fluid reservoir chamber 5 and the gas chamber 6 becomes larger than the cross sectional area within the cylinder 20 by the amount that the inner diameter D1 of the outer shell extension portion 17 is larger than the inner diameter D2 of the cylinder 20.
(0046] The amount that the free piston 50 moves can thus be made smaller for cases where the surface area of the fluid reservoir chamber 5 and the gas chamber 6 are the same. The basic length of the hydraulic shock absorber 1 in the axial direction is shortened compared to a conventional structure in which the free piston is housed within the cylinder, and the space needed for mounting the hydraulic shock absorber 1 to a vehicle can be made smaller.
(0047) The present invention is not limited to the embodiment described above . It is clear that various changes can be made within the scope of the technical concepts of the present invention.
Claims (4)
1. A hydraulic shock absorber comprising:
a cylinder having an inner side and an outer side;
a piston that is slidably housed in the inner side of the cylinder;
a piston rod that is connected to the piston;
a piston rod side fluid chamber that is partitioned off within the cylinder on one side of the piston;
a piston side fluid chamber that is partitioned off within the cylinder on another side of the piston;
an outer shell that is disposed coaxially with the cylinder in the outer side of the cylinder, the outer shell having a larger diameter than the diameter of the cylinder;
a bypass pathway that is formed between the cylinder and the outer shell;
a plurality of connection holes formed in different locations in a piston stroke direction of the cylinder, the plurality of connection holes connecting the bypass pathway with the piston rod side fluid chamber arid the piston side fluid chamber;
an extension portion of the outer shell that extends further in an axial direction than an end portion of the cylinder;
a free piston that is slidably disposed within the extension portion;
a fluid reservoir chamber that is connected to the piston side fluid chamber, the fluid reservoir chamber being partitioned off on one side of the free piston; and a gas chamber in which a gas is enclosed, the gas chamber being partitioned off on another side of the free piston.
a cylinder having an inner side and an outer side;
a piston that is slidably housed in the inner side of the cylinder;
a piston rod that is connected to the piston;
a piston rod side fluid chamber that is partitioned off within the cylinder on one side of the piston;
a piston side fluid chamber that is partitioned off within the cylinder on another side of the piston;
an outer shell that is disposed coaxially with the cylinder in the outer side of the cylinder, the outer shell having a larger diameter than the diameter of the cylinder;
a bypass pathway that is formed between the cylinder and the outer shell;
a plurality of connection holes formed in different locations in a piston stroke direction of the cylinder, the plurality of connection holes connecting the bypass pathway with the piston rod side fluid chamber arid the piston side fluid chamber;
an extension portion of the outer shell that extends further in an axial direction than an end portion of the cylinder;
a free piston that is slidably disposed within the extension portion;
a fluid reservoir chamber that is connected to the piston side fluid chamber, the fluid reservoir chamber being partitioned off on one side of the free piston; and a gas chamber in which a gas is enclosed, the gas chamber being partitioned off on another side of the free piston.
2. The hydraulic shock absorber according to claim 1, further comprising a base valve that is provided in the end portion of the cylinder, interposed between the piston side fluid chamber and the fluid reservoir chamber.
3. The hydraulic shock absorber according to claim 2, further comprising a compression side damping valve that imparts resistance to a flow of a working fluid that flows out from the piston side fluid chamber to the fluid reservoir chamber.
4. The hydraulic shock absorber according to claim 2, further comprising:
a support cylindrical member that supports the end portion of the cylinder at an inner circumferential portion of the outer shell;
wherein the base valve is supported by being sandwiched between the support cylindrical member and the cylinder.
a support cylindrical member that supports the end portion of the cylinder at an inner circumferential portion of the outer shell;
wherein the base valve is supported by being sandwiched between the support cylindrical member and the cylinder.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2003131292A JP2004332860A (en) | 2003-05-09 | 2003-05-09 | Hydraulic shock absorber |
| JP2003-131292 | 2003-05-09 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2466205A1 true CA2466205A1 (en) | 2004-11-09 |
Family
ID=33432124
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2466205 Abandoned CA2466205A1 (en) | 2003-05-09 | 2004-05-03 | Hydraulic shock absorber |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JP2004332860A (en) |
| CA (1) | CA2466205A1 (en) |
-
2003
- 2003-05-09 JP JP2003131292A patent/JP2004332860A/en active Pending
-
2004
- 2004-05-03 CA CA 2466205 patent/CA2466205A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| JP2004332860A (en) | 2004-11-25 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Dead |