Shock absorber

Provided is a shock absorber that includes a middle chamber formed by a piston, a first damping-force generating device that is provided between an upper chamber and the middle chamber and generates a damping force, a second damping-force generating device that is provided between a lower chamber and the middle chamber and generates a damping force, and a position-based state changing device that changes a state of a passage to a state in which the upper chamber and the lower chamber communicate with each other, a state in which the upper chamber and the middle chamber communicate with each other, or a state in which the lower chamber and the middle chamber communicate with each other depending on a position of the piston.

This application is the U.S. national phase of International Application No. PCT/JP2015/073817 filed on Aug. 25, 2015 which designated the U.S. and claims priority to Japanese Patent Application No. 2014-223501 filed on Oct. 31, 2014, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a shock absorber.

Priority is claimed on Japanese Patent Application No. 2014-223501 filed on Oct. 31, 2014, the content of which is incorporated herein by reference.

BACKGROUND ART

There is a shock absorber in which a damping force is switched depending on a piston position (for example, see Patent Literature 1).

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

It is desired to enhance a degree of freedom in setting a damping force.

The present invention provides a shock absorber capable of enhancing a degree of freedom in setting a damping force.

Solution to Problem

According to a first aspect of the present invention, a shock absorber includes a cylinder in which a working fluid is encapsulated; a piston provided in an inside of the cylinder and configured to divide the inside of the cylinder into an upper chamber and a lower chamber; and a piston rod connected to the pistons and configured to extend outside the cylinder. This shock absorber includes: a middle chamber formed by the piston; a first damping-force generating device provided between the upper chamber and the middle chamber and configured to generate a damping force; a second damping-force generating device provided between the lower chamber and the middle chamber and configured to generate a damping force; and a position-based state changing device configured to change a state of a passage to a state in which the upper chamber and the lower chamber communicate with each other, a state in which the upper chamber and the middle chamber communicate with each other, or a state in which the lower chamber and the middle chamber communicate with each other depending on a position of the piston.

According to a second aspect of the present invention, a shock absorber includes: a cylinder in which a working fluid is encapsulated; first and second pistons, at least one of which is slidably provided in an inside of the cylinder, and which divide the inside of the cylinder into an upper chamber, a middle chamber, and a lower chamber; a piston rod connected to the first and second pistons and configured to extend outside the cylinder; a first passage provided in the first and second pistons and configured to communicate between the upper chamber and the middle chamber and between the middle chamber and the lower chamber such that the working fluid flows; an extension-side damping valve provided on the first and second pistons, configured to restrict a flow of the working fluid flowing along the first passage by movement of the first and second pistons, and configured to generate a damping force; a compression-side damping valve provided on the first and second pistons, configured to restrict a flow of the working fluid flowing along the first passage by movement of the first and second pistons, and configured to generate a damping force; a second passage configured to allow the upper chamber, the middle chamber, and the lower chamber to communicate therethrough in addition to the first passage; a first adjustment section provided on the second passage and configured to adjust a flow passage area of the working fluid between the upper chamber and the middle chamber depending on positions of the first and second pistons; and a second adjustment section that is provided on the second passage and configured to adjust a flow passage area of the working fluid between the lower chamber and the middle chamber depending on the positions of the first and second pistons. The flow passage areas of the first and second adjustment sections are set such that: the flow passage area of the first adjustment section and the flow passage area of the second adjustment section are increased together when the first piston and the second piston are within a first predetermined range including a neutral position; the flow passage area of the first adjustment section is reduced, and the flow passage area of the second adjustment section is increased when the first piston and the second piston exceed the first predetermined range and are within a second predetermined range at a maximum length side; and the flow passage area of the first adjustment section is increased, and the flow passage area of the second adjustment section is reduced when the first piston and the second piston exceed the first predetermined range and are within a third predetermined range at a minimum length side.

According to a third aspect of the present invention, the extension-side damping valve of the first piston and the extension-side damping valve of the second piston may be set such that, when the first piston and the second piston move in an extending direction, the damping force generated by the extension-side damping valve located upstream is smaller than the damping force generated by the extension-side damping valve located downstream. The compression-side damping valve of the first piston and the compression-side damping valve of the second piston may be set such that, when the first piston and the second piston move in a compressing direction, the damping force generated by the compression-side damping valve located upstream is smaller than the damping force generated by the compression-side damping valve located downstream.

According to a fourth aspect of the present invention, in at least one of a case in which the first piston and the second piston exceed the second predetermined range and are located at the maximum length side and a case in which the first piston and the second piston exceed the third predetermined range and are located at the minimum length side, the flow passage area of the first adjustment section and the flow passage area of the second adjustment section may be set to be reduced together.

According to a fifth aspect of the present invention, the flow passage area of the first adjustment section and the flow passage area of the second adjustment section may be adjusted by a metering pin. The metering pin may have a reduced diameter section that extends to be longer than an axial length between the first adjustment section and the second adjustment section, and regulate the first predetermined range.

According to a sixth aspect of the present invention, the flow passage areas of the first and second adjustment sections may be adjusted by an axial groove that is partly formed on an inner circumference of the cylinder. The axial groove may extend to be longer than an axial length between the first adjustment section and the second adjustment section, and regulate the first predetermined range.

Advantageous Effects of Invention

According to the shock absorber, a degree of freedom in setting a damping force can be enhanced.

DESCRIPTION OF EMBODIMENTS

First Embodiment

A first embodiment according to the present invention will be described with reference to the drawings. To facilitate understanding in the following description, a lower side in the drawings is defined as a “lower side,” and an upper side in the drawings is conversely defined as an “upper side.”

A shock absorber1of the first embodiment illustrated inFIG. 1is a position-sensitive adjustable damping force shock absorber. The shock absorber1has a cylinder2in which oil acting as a working fluid is encapsulated, a cover3that covers a first end section of the cylinder2, and a mounting eye4that is fixed to a second end section of the cylinder2. As illustrated inFIG. 2, the shock absorber1is a so-called double cylinder hydraulic shock absorber. The cylinder2has a cylindrical inner cylinder5and a cylindrically bottomed outer cylinder6that has a larger diameter than the inner cylinder5and is concentrically provided to cover the inner cylinder5. A reservoir chamber7is defined between the inner cylinder5and the outer cylinder6.

The outer cylinder6is made up of a substantially cylindrical trunk member8and a bottom member9that is fixedly fitted to a lower portion, which is a first end section, of the trunk member8and blocks a lower-end opening of the trunk member8. As illustrated inFIG. 1, the mounting eye4is mounted on a side of the bottom member9which is opposite to the trunk member8.

As illustrated inFIG. 2, the cover3covers an upper opening of the outer cylinder6. The cover3has a tubular section10and an inner flange section11that extends inward from an upper end of the tubular section10in a radial direction. The cover3is put on an upper-end opening of the trunk member8which is on a side opposite to the bottom member9. As illustrated inFIG. 1, a plurality of concave sections12are formed at the cover3to protrude in the radial direction at intervals in a circumferential direction of the tubular section10. The upper-end opening of the trunk member8is fixedly fitted into the concave sections12.

As illustrated inFIG. 2, two pistons, a first piston15and a second piston16closer to the bottom member9than the first piston, are slidably fitted into the inner cylinder5. The first piston15and the second piston16installed inside the inner cylinder5divide the inside of the inner cylinder5into three chambers, an upper chamber18on a side of the first piston15opposite to the second piston16, a middle chamber19between the first piston15and the second piston16, and a lower chamber20on a side of the second piston16opposite to the first piston15. In other words, the upper chamber18is defined in the inner cylinder5by the first piston15, the middle chamber19is defined in the inner cylinder5by the first piston15and the second piston16, and the lower chamber20is defined in the inner cylinder5by the second piston16. Oil acting as a working fluid is encapsulated in each of the upper chamber18, the middle chamber19, and the lower chamber20in the inner cylinder5. Oil and gas acting as working fluids are encapsulated in the reservoir chamber7between the inner cylinder5and the outer cylinder6.

A first end section of a piston rod21is inserted into the cylinder2. A second end section of the piston rod21extends outside the cylinder2. The first piston15and the second piston16are connected to the first end section of the piston rod21in the cylinder2. The first piston15and the second piston16are moved integrally with the piston rod21. As a result, the middle chamber19between the first piston15and the second piston16in the inner cylinder5are also moved integrally with the piston rod21.

A rod guide22is fitted to one-end openings of the inner cylinder5and the outer cylinder6. A seal member23is mounted on the outer cylinder6on the outside of the cylinder2beyond the rod guide22. Both the rod guide22and the seal member23have annular shapes. The piston rod21is slidably inserted into the rod guide22and the seal member23and extends outside the cylinder2.

The rod guide22movably supports the piston rod21in an axial direction while regulating movement of the piston rod21in the radial direction and guides the movement of the piston rod21. An inner circumferential portion of the seal member23is in slideable contact with an outer circumferential portion of the piston rod21moving in the axial direction. An outer circumferential portion of the seal member23is closely attached to an inner circumferential portion of the outer cylinder6. The seal member23prevents the oil inside the inner cylinder5and a high-pressure gas and the oil of the reservoir chamber7inside the outer cylinder6from leaking to the outside.

The rod guide22has a stepped shape in which an upper portion of an outer circumferential portion of the rod guide22has a larger diameter than a lower portion of the outer circumferential portion of the rod guide22. A lower portion of the rod guide22is fitted to an inner circumferential portion of an upper end of the inner cylinder5, and an upper portion of the rod guide22is fitted to an inner circumferential portion of an upper end of the outer cylinder6. A base valve25defining the lower chamber20and the reservoir chamber7in the inner cylinder5is installed above the bottom member9of the outer cylinder6. An inner circumferential portion of a lower end of the inner cylinder5is fitted to the base valve25. The upper chamber18is provided between the rod guide22and the first piston15. The lower chamber20is provided between the second piston16and the base valve25.

The piston rod21has a rod main body26that is inserted into the rod guide22and the seal member23and extends to the outside, and a tip rod27that is screwed onto an end section of the rod main body26inside the cylinder2and is integrally connected to the rod main body26. An insertion hole28running in then axial direction is formed in the center of the rod main body26in the radial direction from the tip rod27to a midway position around an end section of the rod main body26, which is on a side opposite to the tip rod27. A penetration hole29running in the axial direction is formed in the center of the tip rod27in the radial direction. The insertion hole28and the penetration hole29constitute an insertion hole30formed in the center of the piston rod21in the radial direction. Therefore, the piston rod21has a hollow structure. A metering pin31is inserted into the insertion hole30of the piston rod21. A first end section of the metering pin31is fixed to the base valve25, which is provided closer to the bottom member9of the cylinder2than the metering pin31. A second end section of the metering pin31is inserted into the insertion hole30of the piston rod21. A space between the insertion hole30and the metering pin31forms an intra-rod passage (a second passage)32along which oil can flow in the piston rod21.

An annular stopper35is mounted on an outer circumference of the rod main body26of the piston rod21near the tip rod27in the axial direction. The stopper35comes into contact with the rod guide22at a full extension position thereof at which the piston rod21maximally protrudes from the cylinder2, and regulates protrusion of the piston rod21exceeding the full extension position.

The shock absorber1is used in a suspension system of a vehicle such as an automobile or a railroad vehicle. For example, a first end section of the shock absorber1is supported by a vehicle body, and a second end section of the shock absorber1is connected to a wheel section. To be specific, the shock absorber1is connected to the vehicle body by the piston rod21, and the mounting eye4that is illustrated inFIG. 1on a side opposite to a protruding side of the piston rod21of the cylinder2is connected to the wheel section. Conversely, the second end section of the shock absorber1may be supported by the vehicle body, and the first end section of the shock absorber1may be connected to the wheel section. In the shock absorber1, when the vehicle body is moved up relative to a wheel, the piston rod21protrudes from the cylinder2. Conversely, when the vehicle body is moved down relative to the wheel, the piston rod21enters the cylinder2. A direction in which the piston rod21protrudes from the cylinder2may be referred to as an “extension side” and a “maximum length side.” A direction in which the piston rod21enters the cylinder2may be referred to as a “compression side” and a “minimum length side.”

When the wheel vibrates during traveling, positions of the cylinder2and the piston rod21vary relatively along with the vibration. This variation is suppressed by fluid resistance of the intra-rod passage32formed in the piston rod21. As will be described below, the fluid resistance of the intra-rod passage32formed in the piston rod21is made different depending on a speed or an amplitude of the vibration to suppress the vibration so that riding comfort is improved. In addition to the vibration generated by the wheel, an inertial force or a centrifugal force occurring at the vehicle body during the traveling of the vehicle also acts between the cylinder2and the piston rod21. For example, as a traveling direction is changed by operating a steering wheel, a centrifugal force occurs at the vehicle body and a force based on the centrifugal force acts between the cylinder2and the piston rod21. As will be described below, the shock absorber1of the present embodiment has an excellent characteristic with respect to vibration based on a force occurring at the vehicle body during the traveling of the vehicle, and obtains high stability during the traveling of the vehicle.

As illustrated inFIG. 3, a screw hole43having a larger diameter than the insertion hole28is formed in an end section of the rod main body26which is close to the tip rod27. A passage hole44, which is orthogonal to the insertion hole28and passes through the rod main body26in the radial direction, is formed near the screw hole43of the rod main body26. The passage hole44also constitutes the intra-rod passage32along with the insertion hole28. The passage hole44is formed between the stopper35and the tip rod27in the rod main body26.

A screw shaft section45is formed at a first end section of the tip rod27. The screw shaft section45is screwed into the screw hole43of the rod main body26to integrally connect the tip rod27to the rod main body26. The penetration hole29formed in the intra-rod passage32of the tip rod27is made up of a main hole section47that constitutes almost the entirety of the penetration hole29, and a small diameter hole section48that is formed at an intermediate portion of the main hole section47which is on a side opposite to the screw shaft section45in the axial direction and has a smaller diameter than the main hole section47. A passage hole50which is orthogonal to the penetration hole29and passes through the tip rod27in the radial direction is formed in the tip rod27at a position on a side of the small diameter hole section48opposite to the screw shaft section45at the main hole section47. The passage hole50also constitutes the intra-rod passage32.

The tip rod27has the screw shaft section45, a flange section56, and a holding shaft section57in order from the rod main body26side in the axial direction. An outer diameter of the flange section56is larger than an outer diameter of the screw shaft section45and an outer diameter of the rod main body26. As described above, the tip rod27is screwed into the screw hole43of the rod main body26at the screw shaft section45. On this occasion, the flange section56comes into contact with the rod main body26. The holding shaft section57has a smaller diameter than the flange section56. A male screw58is formed at a portion of the holding shaft section57on a side opposite to the flange section56in the axial direction. The passage hole50is formed between the male screw58of the holding shaft section57and the flange section56.

One regulating member61, one abutting disc62, one disc63, a disc valve64made up of a plurality of discs, the first piston15, a disc valve65made up of a plurality of discs, one disc66, one abutting disc67, one regulating member68, one abutting disc69, one disc70, a disc valve71made up of a plurality of discs, the second piston16, one passage forming disc72, a plurality of discs73, a disc valve74made up of a plurality of discs, one disc75, one abutting disc76, and one regulating member77are sequentially arranged at the holding shaft section57of the tip rod27from the flange section56side and are sandwiched by the flange section56and a nut78screwed to the male screw58.

The first piston15is constituted of a piston main body95that is supported by the tip rod27and is formed of a metal, and a sliding member96that is mounted on an outer circumferential surface of the piston main body95, slides in the inner cylinder5, and is formed of a synthetic resin in an annular shape.

The piston main body95includes a plurality of passages (first passages)101(only one of which is shown becauseFIG. 3is a sectional view) which allows the upper chamber18and the middle chamber19to communicate with each other and out of which oil flows from the middle chamber19toward the upper chamber18in a process of a movement of the first piston15toward the middle chamber19side, that is in a compression stroke, and a plurality of passages (first passages)102(only one of which is shown becauseFIG. 3is a sectional view) out of which oil flows from the upper chamber18toward the middle chamber19in a process of a movement of the first piston15toward the upper chamber18side, that is in an extension stroke. That is, the plurality of passages101and the plurality of passages102are provided on the first piston15and allow the upper chamber18and the middle chamber19to communicate with each other such that the oil, which is the working fluid, flows between the upper chamber18and the middle chamber19depending on the movement of the first piston15.

The passages101are formed at equal pitches in the circumferential direction with one passage102sandwiched between two neighboring passages101. First end sections (the lower side ofFIG. 3) of the passages101in the axial direction of the first piston15are open to the outside in the radial direction. Second end sections (the upper side ofFIG. 3) of the passages101in the axial direction of the first piston15are open to the inside in the radial direction. The disc valve64is provided on half of the passages101and102, particularly the passages101. The disc valve64is disposed close to the upper chamber18, which is at the second end section of the first piston15in the axial direction. The passages101constitute a compression-side passage through which oil flows when the first piston15is moved toward the compression side at which the piston rod21enters the cylinder2. The disc valve64provided on the passages101constitutes a compression-side damping valve103that restricts a flow of oil of the compression-side passages101to generate a damping force.

The passages102corresponding to the remaining half of the passages101and102are formed at equal pitches in the circumferential direction with one passage101sandwiched between two neighboring passages102. Second end sections (the upper side ofFIG. 3) of the passages102in the axial direction of the first piston15are open to the outside in the radial direction. First end sections (the lower side ofFIG. 3) of the passages102in the axial direction of the first piston15are open to the inside in the radial direction. The disc valve65is provided on the passages102corresponding to the remaining half of the passages101and102. The disc valve65is disposed near the middle chamber19, which is at the first end section of the first piston15in the axial direction, in a direction of an axis. The passages102constitute an extension-side passage through which oil flows when the first piston15is moved toward the extension side at which the piston rod21extends outside the cylinder2. The disc valve65provided on the passages102constitutes an extension-side damping valve104that restricts a flow of oil of the extension-side passages102to generate a damping force.

The compression-side damping valve103including the disc valve64and the extension-side damping valve104including the disc valve65constitute a first damping-force generating device105that is provided between the upper chamber18and the middle chamber19and generates a damping force.

The piston main body95of the first piston15has a substantially disc shape. An insertion hole106, which penetrates into the piston main body95in the axial direction so that the holding shaft section57of the tip rod27is inserted therein, is formed in the center of the piston main body95. A seat section107is formed at an end section of the piston main body95which is close to the upper chamber18in an annular shape beyond positions of one-end openings of the compression-side passages101. A seat section108is formed at an end section of the piston main body95which is close to the middle chamber19in an annular shape on the outside of positions of one-end openings of the extension-side passages102.

A portion of the seat section107which is on a side opposite to the insertion hole106in the piston main body95has a stepped shape in which a height is lower than the seat section107in the direction of the axis. Second ends of the extension-side passages102are open at this step-shaped portion. When an outer circumferential portion of the disc valve64is seated on the seat section107, the disc valve64closes the compression-side passages101inside the seat section107. When the outer circumferential portion of the disc valve64is separated from the seat section107, the disc valve64opens the passages101. That is, the disc valve64and the seat section107constitute the compression-side damping valve103that restricts the flow of the oil of the compression-side passages101to generate the damping force.

The disc valve64is made up of a plurality of discs, each of which is formed of a metal and has a perforated disc shape. One of two discs that overlap each other in the axial direction, which is far from the seat section107, has an outer diameter that is smaller than or equal to that of the other which is close to the seat section107. The disc63is formed of a metal and has a perforated disc shape. An outer diameter of the disc63is smaller than that of the smallest diameter disc that constitutes the disc valve64. The abutting disc62is formed of a metal and has a perforated disc shape. An outer diameter of the abutting disc62is larger than that of the smallest diameter disc that constitutes the disc valve64, and is smaller than that of the largest diameter disc that constitutes the disc valve64. The regulating member61is formed of a metal and has a perforated disc shape, and has higher rigidity than the disc valve64. An outer diameter of the regulating member61is smaller than that of the abutting disc62, and is smaller than that of the flange section56. The abutting disc62comes into contact with the disc valve64when the disc valve64is deformed in an opening direction, and regulates deformation of the disc valve64which is higher than or equal to a prescribed level along with the regulating member61.

A side of the seat section108, which is opposite to the insertion hole106, in the piston main body95has a stepped shape in which a height is lower than the seat section108in the direction of the axis. Second ends of the compression-side passages101are open at this step-shaped portion. When an outer circumferential portion of the disc valve65is seated on the seat section108, the disc valve65closes the extension-side passages102inside the seat section108. When the outer circumferential portion of the disc valve65is separated from the seat section108, the disc valve65opens the passages102. That is, the disc valve65and the seat section108constitute the extension-side damping valve104that restricts the flow of the oil of the extension-side passages102to generate the damping force.

The disc valve65is made up of a plurality of discs, each of which is formed of a metal and has a perforated disc shape. One of two discs that overlap each other in the axial direction, which is far from the seat section108, has an outer diameter that is smaller than or equal to that of the other which is close to the seat section108. The disc66is formed of a metal and has a perforated disc shape. An outer diameter of the disc63is smaller than that of the smallest diameter disc that constitutes the disc valve65. The abutting disc67is formed of a metal and has a perforated disc shape. An outer diameter of the abutting disc67is larger than that of the smallest diameter disc that constitutes the disc valve65and is smaller than that of the largest diameter disc that constitutes the disc valve65. The regulating member68is formed of a metal and has a perforated disc shape and has higher rigidity than the disc valve65. An outer diameter of the regulating member68is smaller than that of the abutting disc67. The abutting disc67comes into contact with the disc valve65when the disc valve65is deformed in an opening direction, and regulates deformation of the disc valve65which is higher than or equal to a prescribed level along with the regulating member68. The disc valve65has lower rigidity than the disc valve64and is more easily opened than the disc valve64.

The second piston16is made up of a piston main body111that is supported by the tip rod27and is formed of a metal, and a sliding member112that is mounted on an outer circumferential surface of the piston main body111, slides in the inner cylinder5, and is formed of a synthetic resin in an annular shape.

The piston main body111includes a plurality of passages (first passages)116(only one of which is shown becauseFIG. 3is a sectional view) which allow the middle chamber19and the lower chamber20to communicate with each other and out of which oil flows from the lower chamber20toward the middle chamber19in a process of a movement of the second piston16toward the lower chamber20side, that is in the compression stroke, and a plurality of passages (first passages)117(only one of which is shown becauseFIG. 3is a sectional view) out of which oil flows from the middle chamber19toward the lower chamber20in a process of a movement of the second piston16toward the middle chamber19side, that is in the extension stroke. That is, the plurality of passages116and the plurality of passages117are provided on the second piston16and allow the middle chamber19and the lower chamber20to communicate with each other such that the oil, which is the working fluid, flows between the middle chamber19and the lower chamber20depending on the movement of the second piston16.

The passages116are formed at equal pitches in the circumferential direction with one passage117sandwiched between two neighboring passages116. First end sections (the lower side ofFIG. 3) of the passages116in the axial direction of the second piston16are open to the outside in the radial direction. Second end sections (the upper side ofFIG. 3) of the passages116in the axial direction of the second piston16are open to the inside in the radial direction. The disc valve71is provided on half of the passages116and117, particularly the passages116. The disc valve71is disposed near the middle chamber19, which is at one end of the second piston16in the axial direction. The passages116constitute a compression-side passage through which oil flows when the second piston16is moved toward the compression side at which the piston rod21enters the cylinder2. The disc valve71provided on the passages116constitutes a compression-side damping valve118that restricts a flow of the oil of the compression-side passages116to generate a damping force.

The passages117corresponding to the remaining half of the passages116and117are formed at equal pitches in the circumferential direction with one passage116sandwiched between two neighboring passages117. Second end sections (the upper side ofFIG. 3) of the passages117in the axial direction of the second piston16are open to the outside in the radial direction. First end sections (the lower side ofFIG. 3) of the passages117in the axial direction of the second piston16are open to the inside in the radial direction. The disc valve74generating a damping force is provided on the passages117corresponding to the remaining half of the passages116and117. The disc valve74is disposed close to the lower chamber20, which is at the first end section of the second piston16in the axial direction, in the direction of the axis. The passages117constitute an extension-side passage through which oil flows when the second piston16is moved toward the extension side at which the piston rod21extends outside the cylinder2. The disc valve74provided with respect to the passages117constitutes an extension-side damping valve119that restricts a flow of the oil of the extension-side passages117to generate a damping force.

The compression-side damping valve118including the disc valve71and the extension-side damping valve119including the disc valve74constitute a second damping-force generating device120that is provided between the middle chamber19and the lower chamber20and generates a damping force.

The piston main body111of the second piston16has a substantially disc shape. An insertion hole126, which penetrates into the piston main body111in the axial direction so that the holding shaft section57of the tip rod27is inserted therein, is formed in the center of the piston main body111. The insertion hole126is made up of a fitting hole section124that the holding shaft section57fits into and is close to the middle chamber19, and a passage forming hole section125that has a larger diameter than the fitting hole section124and is close to the lower chamber20. A gap between the passage forming hole section125and the holding shaft section57communicates with the passage hole50of the tip rod27. A seat section127is formed at an end section of the piston main body111which is close to the middle chamber19in an annular shape beyond positions of one-end openings of the compression-side passages116. A seat section128is formed at an end section of the piston main body111which is close to the lower chamber20in an annular shape on the outside of positions of one-end openings of the extension-side passages117.

A side of the seat section127, which is opposite to the insertion hole126, in the piston main body111has a stepped shape in which a height is lower than the seat section127in the direction of the axis. Second ends of the extension-side passages117are open at this step-shaped portion. When an outer circumferential portion of the disc valve71is seated on the seat section127, the disc valve71closes the compression-side passages116inside the seat section127. When the outer circumferential portion of the disc valve71is separated from the seat section127, the disc valve71opens the passages116. That is, the disc valve71and the seat section127constitute the compression-side damping valve118that restricts the flow of the oil of the compression-side passages116to generate the damping force.

The disc valve71is made up of a plurality of discs, each of which is formed of a metal and has a perforated disc shape. These discs have the same outer diameters. The disc70is formed of a metal and has a perforated disc shape. An outer diameter of the disc70is smaller than that of the disc valve71. The abutting disc69is formed of a metal and has a perforated disc shape. An outer diameter of the abutting disc69is smaller than that of the disc valve71and is larger than that of the regulating member68. The abutting disc69comes into contact with the disc valve71when the disc valve71is deformed in an opening direction, and regulates deformation of the disc valve71which is greater than or equal to a prescribed level along with the regulating member68.

A side of the seat section128, which is opposite to the insertion hole106, in the piston main body111has a stepped shape in which a height is lower than the seat section128in the direction of the axis. Second ends of the compression-side passages116are open at this step-shaped portion. When an outer circumferential portion of the disc valve74is seated on the seat section128, the disc valve74closes the extension-side passages117inside the seat section128. When the outer circumferential portion of the disc valve74is separated from the seat section128, the disc valve74opens the passages117. That is, the disc valve74and the seat section128constitute the extension-side damping valve119that restricts the flow of the oil of the extension-side passages117to generate the damping force.

The disc valve74is made up of a plurality of discs, each of which is formed of a metal and has a perforated disc shape. These discs have the same outer diameters. The discs73are formed of a metal. The discs73have perforated disc shapes. An outer diameter of each of the discs73is smaller than that of the disc valve74. The passage forming disc72is formed of a metal. The passage forming disc72has a perforated disc shape. An outer diameter of the passage forming disc72is larger than that of each of the discs73and is smaller than that of the disc valve74. A passage groove131is formed in the passage forming disc72. The passages117and the inside of the passage forming hole section125communicate with each other due to the passage groove131. Accordingly, the passages117communicate with the intra-rod passage32in the passage hole50. The passage groove131and the inside of the passage forming hole section125constitute a communication passage (a second passage)132that allows the passages117and the intra-rod passage32to communicate with each other at normal times.

The disc75is formed of a metal. The disc75has a perforated disc shape. An outer diameter of the disc75is smaller than that of the disc valve74. The disc76is formed of a metal. The disc76has a perforated disc shape. An outer diameter of the disc76is smaller than that of the disc valve74and is larger than that of the disc75. The regulating member77is formed of a metal. The regulating member77has a perforated disc shape and has higher rigidity than the disc valve74. An outer diameter of the regulating member77is smaller than that of the disc76. The disc76comes into contact with the disc valve74when the disc valve74is deformed in an opening direction, and regulates deformation of the disc valve74which is higher than or equal to a prescribed level along with the regulating member77. The disc valve74has lower rigidity than the disc valve71and is more difficult to open than the disc valve71.

The passages101and102provided on the first piston15and the passages116and117provided on the second piston16allow the upper chamber18and the middle chamber19to communicate with each other and the middle chamber19and the lower chamber20to communicate with each other such that the oil, which is the working fluid, flows between the upper chamber18and the middle chamber19and between the middle chamber19and the lower chamber20.

The extension-side damping valves104and119are provided on the first and second pistons15and16, and restrict the flow of the oil flowing along the passages102and117to generate a damping force due to the movement of the first and second pistons15and16in an extending direction. In the extension stroke, the passages102are upstream (that is, the upper chamber18side) from the flow of the oil, and the passages117are downstream (that is, the lower chamber20side). In the extension stroke, the extension-side damping valve104of the extension-side damping valves104and119is upstream (that is, the upper chamber18side), and the extension-side damping valve119is downstream (that is, the lower chamber20side).

The disc valves65and74are configured such that the disc valve65of the first piston15has lower rigidity than the disc valve74of the second piston16and is more easily opened than the disc valve74of the second piston16. As a result, the disc valves65and74are configured such that the damping force generated by the disc valve65located upstream from the flow of the oil in the extension stroke in which the first piston15and the second piston16are moved in the extending direction is set to be weaker and softer than that generated by the disc valve74located downstream.

The compression-side damping valves103and118are provided on the first and second pistons15and16and restrict the flow of the oil flowing along the passages101and116to generate a damping force due to the movement of the first and second pistons15and16in a compressing direction. In the compression stroke, the passages116are upstream (that is, the lower chamber20side) from the flow of the oil, and the passages101are downstream (that is, the upper chamber18side). In the compression stroke, the compression-side damping valve118of the compression-side damping valves103and118is upstream (that is, the lower chamber20side), and the compression-side damping valve103is downstream (that is, the upper chamber18side).

The disc valves64and71are configured such that the disc valve64of the first piston15has higher rigidity than the disc valve71of the second piston16and is more difficult to open than the disc valve71of the second piston16. As a result, the compression-side damping valves103and118are configured such that the damping force generated by the compression-side damping valve118located upstream from the flow of the oil in the compression stroke in which the first piston15and the second piston16are moved in the compressing direction is set to be weaker and softer than that generated by the compression-side damping valve103located downstream.

A screw hole section136, in which a female screw135screwed onto the male screw58of the tip rod27is formed, and a small diameter hole section137, which has a smaller diameter than the screw hole section136, are formed at the nut78. The nut78constitutes the piston rod21along with the rod main body26and the tip rod27. The inside of the nut78constitutes the intra-rod passage32. The metering pin31is inserted inside the small diameter hole section137of the nut78. The small diameter hole section137also constitutes the insertion hole30into which the metering pin31is inserted. An inner diameter of the small diameter hole section137is identical to that of the small diameter hole section48. The small diameter hole section137is formed at an end section of the intra-rod passage32.

In a state in which the nut78is fastened to the tip rod27, an inner circumferential portion of the disc valve64is clamped by the disc63and the first piston15. An inner circumferential portion of the disc valve65is clamped by the disc66and the first piston15. An inner circumferential portion of the disc valve71is clamped by the disc70and the second piston16. An inner circumferential portion of the disc valve74is clamped by the disc75and the discs73. Thereby, an outer circumferential portion of each of the disc valves64,65,71, and74can be deformed.

As illustrated inFIG. 1, the base valve25is provided between the bottom member9of the outer cylinder6and the inner cylinder5. The base valve25has a base valve member141that partitions the lower chamber20and the reservoir chamber7, a disc142that is provided a lower side of the base valve member141, that is, close to the reservoir chamber7, a disc143that is provided an upper side of the base valve member14, that is, close to the lower chamber20, a bolt member144that mounts the disc142on the base valve member141, a nut member145that mounts the disc143on the base valve member141, a locking member146that is mounted on an outer circumferential portion of the base valve member141, and a support plate147that supports a support flange section161(to be described below) of the metering pin31. The bolt member144and the nut member145sandwich central portions of the disc142and the disc143in the radial direction along with the base valve member141.

The base valve member141has an annular shape. The bolt member144is inserted into the base valve member141. A plurality of passage holes149that circulate oil between the lower chamber20and the reservoir chamber7and a plurality of passage holes150that circulate oil between the lower chamber20and the reservoir chamber7on the outside of the passage holes149in the radial direction are formed in the base valve member141. The disc142close to the reservoir chamber7allows the oil flowing from the lower chamber20to flow toward the reservoir chamber7via the passage holes149. On the other hand, the disc142restricts the flow of the oil from the reservoir chamber7toward the lower chamber20via the inside passage holes149. The disc143allows the oil flowing from the reservoir chamber7to flow toward the lower chamber20via the passage holes150. On the other hand, the disc143restricts the flow of the oil from the lower chamber20toward the reservoir chamber7via the outside passage holes150.

The disc142constitutes a compression-side damping valve152that is opened in the compression stroke by the base valve member141, makes oil flow from the lower chamber20to the reservoir chamber7, and generates a damping force. The disc143constitutes a suction valve153that is opened in the extension stroke of the shock absorber1by the base valve member141and makes oil flow from the reservoir chamber7into the lower chamber20. The suction valve153mainly serves to make oil flow from the reservoir chamber7to the lower chamber20to make up for shortage of oil which is caused by the extension of the piston rod21from the cylinder2without substantially generating a damping force.

The locking member146has a tubular shape. An upper portion of the base valve member141is fitted inside the locking member146. The base valve member141is fitted to an inner circumferential portion of the lower end of the inner cylinder5via the locking member146. An end section of the locking member146, which is close to the pistons15and16, extends inward in the radial direction, and the support plate147is locked on this extending portion at an outer circumferential portion of the support plate147. An inner circumferential portion of the support plate147locks the support flange section161of the metering pin31near the pistons15and16. Thereby, the locking member146and the support plate147maintain contact between the support flange section161of the metering pin31and the bolt member144.

The metering pin31has the support flange section161that is supported by the base valve25, a first large diameter section162that has a smaller diameter than the support flange section161and extends from the support flange section161in the axial direction, a first tapered section163that extends from a side of the first large diameter section162which faces the support flange section161in the axial direction and is illustrated inFIG. 3, and a reduced diameter section164that extends from a side of the first tapered section163, which is opposite to the first large diameter section162, and has a smaller diameter than the first large diameter section162. The metering pin31has a second tapered section165that extends in the axial direction from a side of the reduced diameter section164, which is opposite to the first tapered section163, and a second large diameter section166that extends in the axial direction from a side of the second tapered section165, which is opposite to the reduced diameter section164.

The first large diameter section162has a constant diameter. The reduced diameter section164has a constant diameter that is smaller than the first large diameter section162. The first tapered section163is continuous with the first large diameter section162and the reduced diameter section164and has a tapered shape that is reduced in diameter as it approaches the reduced diameter section164. The second large diameter section166has a constant diameter that is identical to the first large diameter section162. The second tapered section165is continuous with the reduced diameter section164and the second large diameter section166and has a tapered shape that is reduced in diameter as it approaches the reduced diameter section164.

The metering pin31is inserted into the insertion hole30of the piston rod21. The intra-rod passage32is formed between the metering pin31and the insertion hole30of the piston rod21. Due to the movement of the pistons15and16, the intra-rod passage32communicates between the upper chamber18and the lower chamber20such that the oil flows. In addition to the passages101,102,116and117, the intra-rod passage32and the communication passage132allow the upper chamber18, the middle chamber19, and the lower chamber20to communicate with one another.

The small diameter hole section48located at the middle portion of the piston rod21in the axial direction is provided between the upper chamber18and the communication passage132that always communicates with the middle chamber19in the intra-rod passage32. Therefore, the small diameter hole section48and the metering pin31constitute a first adjustment section171that adjusts a flow passage area of a flow passage interposing the intra-rod passage32between the upper chamber18and the middle chamber19according to a position of the piston rod21, that is, according to positions of the first piston15and the second piston16. When the small diameter hole section48aligns an axial position thereof with the first and second large diameter sections162and166of the metering pin31, the first adjustment section171minimizes a flow passage area between the upper chamber18and the middle chamber19. When the small diameter hole section48aligns a position thereof with the reduced diameter section164of the metering pin31, the first adjustment section171maximizes the flow passage area between the upper chamber18and the middle chamber19. That is, the first adjustment section171constitutes a variable orifice. A flow passage area in the variable orifice is adjusted by the metering pin31.

The small diameter hole section137of the nut78located at the end section of the piston rod21in the axial direction is provided between the lower chamber20and the communication passage132that always communicates with the middle chamber19in the intra-rod passage32. Therefore, the small diameter hole section137and the metering pin31constitute a second adjustment section172that adjusts a flow passage area of a flow passage interposing the intra-rod passage32of the oil between the middle chamber19and the lower chamber20according to the position of the piston rod21, that is, according to the positions of the first piston15and the second piston16.

When the small diameter hole section137aligns an axial position thereof with the first and second large diameter sections162and166of the metering pin31, the second adjustment section172minimizes a flow passage area between the middle chamber19and the lower chamber20. When the small diameter hole section137aligns a position thereof with the reduced diameter section164of the metering pin31, the second adjustment section172maximizes the flow passage area between the middle chamber19and the lower chamber20. The second adjustment section172also constitutes a variable orifice. A flow passage area in the variable orifice is adjusted by the metering pin31.

Thereby, in view of a hydraulic circuit, as illustrated inFIG. 4, the passages101on which the compression-side damping valve103is arranged, the passages102on which the extension-side damping valve104is arranged, and the first adjustment section171are arranged in parallel between the upper chamber18and the middle chamber19. The passages101and102, the first damping-force generating device105made up of the compression-side damping valve103and the extension-side damping valve104, and the first adjustment section171constitute a first piston section110. In addition, the passages116on which the compression-side damping valve118is arranged, the passages117on which the extension-side damping valve119is arranged, and the second adjustment section172are arranged in parallel between the middle chamber19and the lower chamber20. The passages116and117, the second damping-force generating device120made up of the compression-side damping valve118and the extension-side damping valve119, and the second adjustment section172constitute a second piston section121.

As illustrated inFIG. 3, the reduced diameter section164of the metering pin31extends to be longer than an axial length between the small diameter hole section48of the piston rod21constituting the first adjustment section171and the small diameter hole section137of the nut78constituting the second adjustment section172. Thereby, the reduced diameter section164of the metering pin31can overlap the axial positions of both the small diameter hole section48and the small diameter hole section137with each other at the same time. In this state, a flow passage area of the first end section of the intra-rod passage32has a maximum value regulated by flow passage areas of the small diameter hole section48and the reduced diameter section164of the first adjustment section171, and a flow passage area of the second end section of the intra-rod passage32has a maximum value regulated by flow passage areas of the small diameter hole section137and the reduced diameter section164of the second adjustment section172so that the intra-rod passage32maintains the communication between the upper chamber18and the lower chamber20.

A solid line U1ofFIG. 5(a)represents a change in the flow passage area of the first adjustment section171of the first piston section110according to stroke positions of the first piston15and the second piston16. A broken line U2ofFIG. 5(a)represents a change in the flow passage area of the second adjustment section172of the second piston section121according to the stroke positions of the first piston15and the second piston16. A solid line V1ofFIG. 5(b)represents a relation between a stroke position and a damping force when the first piston15and the second piston16are moved in the extending direction. A broken line V2ofFIG. 5(b)represents a relation between a stroke position and a damping force when the first piston15and the second piston16are moved in the compressing direction.

In the shock absorber1, when the stroke positions of the first piston15and the second piston16are within a first given range from S4to S5that includes a neutral position (a position of 1G (a position at which a vehicle body stopped at a horizontal position is supported)) and is shown inFIG. 5(a), both the small diameter hole section48and the small diameter hole section137of the piston rod21simultaneously overlap axial positions thereof with the reduced diameter section164of the metering pin31. In other words, the first given range from S4to S5is a range in which a flow passage area is regulated by the reduced diameter section164of the metering pin31. In the first given range from S4to S5, the flow passage area of the first adjustment section171represented inFIG. 5(a)by the solid line U1and the flow passage area of the second adjustment section172represented inFIG. 5(a)by the broken line U2have the same maximum values. Therefore, the communication between the upper chamber18and the lower chamber20is maintained with a maximum flow passage area of the intra-rod passage32.

When the first piston15and the second piston16are within the first given range from S4to S5, the oil of the upper chamber18flows to the lower chamber20via the intra-rod passage32having the maximum flow passage area in the extension stroke in which the pistons are moved toward the upper chamber18side. Therefore, as represented by the solid line V1ofFIG. 5(b), a damping force enters into a soft state.

When the first piston15and the second piston16are within the first given range from S4to S5, the oil of the lower chamber20flows to the upper chamber18via the intra-rod passage32having the maximum flow passage area in the compression stroke in which the pistons are moved toward the lower chamber20side. Therefore, as represented by the broken line V2ofFIG. 5(b), a damping force enters into the soft state.

In the shock absorber1, when the stroke positions of the first piston15and the second piston16exceed the first given range from S4to S5and are within a second given range from S6to S7that is shown inFIG. 5(a)at a maximum length side at which the shock absorber1is set to a maximum length, the first adjustment section171aligns the axial positions of the small diameter hole section48and the second large diameter section166of the metering pin31, and the second adjustment section172aligns the axial positions of the small diameter hole section137and the reduced diameter section164of the metering pin31. In the second given range from S6to S7, the flow passage area of the first adjustment section171made up of the small diameter hole section48and the second large diameter section166has the maximum value as represented by the solid line U1ofFIG. 5(a)and nearly closes the upper chamber18side, and the flow passage area of the second adjustment section172made up of the small diameter hole section137and the reduced diameter section164has the maximum value as represented by the broken line U2ofFIG. 5(a)so that the intra-rod passage32and the communication passage132maintain the communication between the lower chamber20and the middle chamber19with the flow passage area regulated by this maximum value.

When the first piston15and the second piston16are within the second given range from S6to S7, the first adjustment section171narrows the intra-rod passage32in the extension stroke in which the first piston15and the second piston16are moved toward the upper chamber18side. For this reason, entry of the oil of the upper chamber18into the intra-rod passage32is restricted, and the oil passes through the passages102of the first piston15and flows into the middle chamber19by opening the extension-side damping valve104having a soft damping force property. The second adjustment section172opens the intra-rod passage32with the maximum flow passage area. For this reason, the oil of the middle chamber19flows from the middle chamber19to the lower chamber20via the communication passage132and the intra-rod passage32having the maximum flow passage area. Therefore, as represented by the solid line V1ofFIG. 5(b), the damping force is maintained in the soft state while entering into a slightly harder state than the first given range from S4to S5.

When the first piston15and the second piston16are within the second given range from S6to S7, the second adjustment section172opens the intra-rod passage32with the maximum flow passage area in the compression stroke in which the first piston15and the second piston16are moved toward the lower chamber20side, and the first adjustment section171nearly closes the intra-rod passage32. For this reason, the oil of the lower chamber20flows toward the middle chamber19via the intra-rod passage32and the communication passage132, passes through the passages101of the first piston15, and flows to the upper chamber18by opening the compression-side damping valve103having a hard damping force property. Therefore, as represented by the broken line V2ofFIG. 5(b), the damping force enters into a softer state than the first given range from S4to S5and a third given range from S2to S3(to be described below).

In the shock absorber1, when the stroke positions of the first piston15and the second piston16exceed the first given range from S4to S5and are within the third given range from S2to S3that is shown inFIG. 5(a)at a minimum length side at which the shock absorber1is set to a minimum length, the first adjustment section171aligns the axial positions of the small diameter hole section48and the reduced diameter section164of the metering pin31, and the second adjustment section172aligns the axial positions of the small diameter hole section137and the first large diameter section162of the metering pin31. In the third given range from S2to S3, the flow passage area of the second adjustment section172made up of the small diameter hole section137and the first large diameter section162has the maximum value as represented by the broken line U2ofFIG. 5(a)and nearly closes the intra-rod passage32close to the lower chamber20, and the flow passage area of the first adjustment section171made up of the small diameter hole section48and the reduced diameter section164has the maximum value as represented by the solid line U1ofFIG. 5(a)so that the intra-rod passage32and the communication passage132maintain the communication between the upper chamber18and the middle chamber19with the flow passage area regulated by this maximum value.

When the first piston15and the second piston16are within the third given range from S2to S3, the first adjustment section171opens the intra-rod passage32with the maximum flow passage area in the extension stroke in which the pistons are moved toward the upper chamber18side, and the second adjustment section172nearly closes the intra-rod passage32. For this reason, the oil of the upper chamber18flows to the passages117via the intra-rod passage32and the communication passage132, is introduced to the middle chamber19, and flows to the lower chamber20by opening the extension-side damping valve119having a soft damping force property. Therefore, as represented by the solid line V1ofFIG. 5(b), the damping force enters into a harder state than the second given range from S6to S7.

When the first piston15and the second piston16are within the third given range from S2to S3, the second adjustment section172narrows the intra-rod passage32in the compression stroke in which the pistons are moved toward the lower chamber20side. For this reason, entry of the oil of the lower chamber20into the intra-rod passage32is restricted and the oil passes through the passages116of the second piston16and flows to the middle chamber19by opening the compression-side damping valve118having a soft damping force property. Since the first adjustment section171opens the intra-rod passage32with the maximum flow passage area, the oil of the middle chamber19flows from the passages117to the upper chamber18via the communication passage132and the intra-rod passage32having the maximum flow passage area. Therefore, as represented by the broken line V2ofFIG. 5(b), the damping force is maintained in the soft state while entering into a slightly harder state than the first given range from S4to S5.

In the shock absorber1, when the stroke positions of the first piston15and the second piston16exceed the second given range from S6to S7and are within a fourth given range from S8to S9up to a full extension position S9at a maximum length side, the first adjustment section171and the second adjustment section172align the axial positions of the small diameter hole sections48and137with that of the second large diameter section166of the metering pin31. In the fourth given range from S8to S9, the flow passage area of the first adjustment section171made up of the small diameter hole section48and the second large diameter section166has the minimum value as represented by the solid line U1ofFIG. 5(a)and nearly closes the intra-rod passage32close to the upper chamber18, and the flow passage area of the second adjustment section172made up of the small diameter hole section137and the second large diameter section166has the minimum value as represented by the broken line U2ofFIG. 5(a)and nearly closes the intra-rod passage32close to the lower chamber20so that the restriction of the communication between the upper chamber18, the middle chamber19, and the lower chamber20by the intra-rod passage32is maintained.

When the first piston15and the second piston16are within the fourth given range from S8to S9, the first adjustment section171and the second adjustment section172nearly close the intra-rod passage32in the extension stroke in which the first piston15and the second piston16are moved toward the upper chamber18side. For this reason, the oil of the upper chamber18passes through the passages102, flows to the middle chamber19by opening the extension-side damping valve104having a soft damping force property, passes through the passages117, and flows to the lower chamber20by opening the extension-side damping valve119having a hard damping force property. Therefore, as represented by the solid line V1ofFIG. 5(b), the damping force enters into the soft state like the third given range from S2to S3. Thereby, in the event of full extension, the damping force enters into a hard state and suppression of abnormal noises and improvement of riding comfort can be ensured.

When the first piston15and the second piston16are within the fourth given range from S8to S9, the first adjustment section171and the second adjustment section172nearly close the intra-rod passage32in the compression stroke in which the first piston15and the second piston16are moved toward the lower chamber20side. For this reason, the oil of the lower chamber20passes through the passages116, flows to the middle chamber19by opening the compression-side damping valve118having a soft damping force property, passes through the passages101, and flows to the upper chamber18by opening the compression-side damping valve103having a hard damping force property. Therefore, as represented by the broken line V2ofFIG. 5(b), the damping force enters into the hard state like the second given range from S6to S7.

In the shock absorber1, when the stroke positions of the first piston15and the second piston16exceed the third given range from S2to S3and are within a fifth given range from S0to S1up to a full compression position S0at a minimum length side, the first adjustment section171and the second adjustment section172align the axial positions of both of the small diameter hole sections48and137with that of the first large diameter section162of the metering pin31. In the fifth given range, the flow passage area of the first adjustment section171made up of the small diameter hole section48and the first large diameter section162has the minimum value as represented by the solid line U1ofFIG. 5(a)and nearly closes the intra-rod passage32close to the upper chamber18, and the flow passage area of the second adjustment section172made up of the small diameter hole section137and the first large diameter section162has the minimum value as represented by the broken line U2ofFIG. 5(a)and nearly closes the intra-rod passage32close to the lower chamber20so that the restriction of the communication between the upper chamber18, the middle chamber19, and the lower chamber20by the intra-rod passage32is maintained.

When the first piston15and the second piston16are within the fifth given range from S0to S1, the first adjustment section171and the second adjustment section172nearly close the intra-rod passage32in the extension stroke in which the first piston15and the second piston16are moved toward the upper chamber18side. For this reason, the oil of the upper chamber18passes the passages102, flows to the middle chamber19by opening the extension-side damping valve104having a soft damping force property, passes the passages117, and flows to the upper chamber18by opening the extension-side damping valve119having a hard damping force property. Therefore, as represented by the solid line V1ofFIG. 5(b), the damping force enters into the hard state like the third given range from S2to S3.

When the first piston15and the second piston16are within the fifth given range from S0to S1, the first adjustment section171and the second adjustment section172nearly close the intra-rod passage32in the compression stroke in which the first piston15and the second piston16are moved toward the lower chamber20side. For this reason, the oil of the lower chamber20passes the passages116, flows to the middle chamber19by opening the compression-side damping valve118having a soft damping force property, passes the passages101, and flows to the upper chamber18by opening the compression-side damping valve103having a hard damping force property. Therefore, as represented by the broken line V2ofFIG. 5(b), the damping force enters into the hard state like the second given range from S6to S7. Thereby, in the event of full compression, the damping force enters into the hard state and the suppression of abnormal noises and the improvement of riding comfort can be ensured.

That is, the first adjustment section171and the second adjustment section172constitute a position-based state changing device175that changes a state of the intra-rod passage32depending on a position of the piston rod21having the small diameter hole sections48and137and positions of the first and second pistons15and16connected to the piston rod21. The position-based state changing device175changes the state of the intra-rod passage32to a state in which the upper chamber18, the middle chamber19, and the lower chamber20communicate with one another with the maximum flow passage area, a state in which the upper chamber18and the middle chamber19communicate with each other with the maximum flow passage area and the communication between the upper chamber18, the middle chamber19, and the lower chamber20is restricted, a state in which the lower chamber20and the middle chamber19communicate with each other with the maximum flow passage area and the communication between the lower chamber20and the middle chamber19and between the lower chamber20and the upper chamber18is restricted, and a state in which the communication between the upper chamber18, the middle chamber19, and the lower chamber20is restricted depending on the positions of the first and second pistons15and16.

Thereby, in the shock absorber1, as illustrated inFIG. 5, when the first piston15and the second piston16are within the first given range from S4to S5including the neutral position, damping forces of both a movement in the extending direction and a movement in the compressing direction enter into the soft state. In the shock absorber1, when the first piston15and the second piston16are within the second given range from S6to S7at the maximum length side, a damping force of a movement in the extending direction enters into the soft state, and a damping force of a movement in the compressing direction enters into the hard state. In the shock absorber1, when the first piston15and the second piston16are within the third given range from S2to S3at the minimum length side, a damping force of a movement in the extending direction enters into the hard state, and a damping force of a movement in the compressing direction enters into the soft state. Further, in the shock absorber1, when the first piston15and the second piston16are within the fourth given range from S8to S9at the maximum length side and within the fifth given range from S0to S1at the minimum length side, damping forces of a movement in the extending direction and a movement in the compressing direction enter into the hard state together. That is, the shock absorber1has inversion-type position-sensitive damping force change characteristics in which a relation between the hard state and the soft state of the movement in the extending direction and the movement in the compressing direction is inverted within the second given range from S6to S7at the maximum length side and the third given range from S2to S3at the minimum length side.

FIG. 6shows results of simulation of a damping force property to a piston speed of the shock absorber1.

As can be seen inFIG. 6, a damping force property (a solid line W1ofFIG. 6) during movement in the extending direction when the first piston15and the second piston16are within the first given range from S4to S5and a damping force property (a broken line W2ofFIG. 6) during movement in the compressing direction when the first piston15and the second piston16are within the second given range from S6to S7enter into the soft state in the full range of a piston speed in substantially the same way. In contrast, a damping force property (a solid line W3ofFIG. 6) during movement in the extending direction when the first piston15and the second piston16are within the third given range from S2to S3and a damping force property (a broken line W4ofFIG. 6) during movement in the extending direction when the first piston15and the second piston16are within the fourth given range from S8to S9and the fifth given range from S0to S1enter into the hard state in the full range of the piston speed in substantially the same way. In any damping force property, as the piston speed increases, the damping force enters into the hard state.

A damping force property (a solid line W5ofFIG. 6) during movement in the compressing direction when the first piston15and the second piston16are within the first given range from S4to S5and a damping force property (a broken line W6ofFIG. 6) during movement in the compressing direction when the first piston15and the second piston16are within the third given range from S2to S3enters into the soft state in the full range of the piston speed in substantially the same way. In contrast, a damping force property (a solid line W7ofFIG. 6) during movement in the compressing direction when the first piston15and the second piston16are within the second given range from S6to S7and a damping force property (a broken line W8ofFIG. 6) during movement in the compressing direction when the first piston15and the second piston16are within the fourth given range from S8to S9and the fifth given range from S0to S1enter into the hard state in the full range of the piston speed in substantially the same way.

FIG. 7shows result of simulation of a damping force property according to the stroke positions of the first piston15and the second piston16of each piston speed of the shock absorber1. In any one among during the movement in the extending direction when a piston speed represented inFIG. 7by X1is a high speed (particularly, 0.6 m/s), during the movement in the extending direction when a piston speed represented inFIG. 7by X2is an intermediate speed (particularly, 0.3 m/s), during the movement in the extending direction when a piston speed represented inFIG. 7by X3is a low speed (particularly, 0.1 m/s), and during the movement in the extending direction when a piston speed represented inFIG. 7by X4is an extremely low speed (particularly, 0.05 m/s), the damping forces of the third given range from S2to S3, the fourth given range from S8to S9, and the fifth given range from S0to S1enter into a harder state than the damping forces of the first given range from S4to S5and the second given range from S6to S7. However, as the piston speed becomes high while maintaining this relation, the damping force enters into the hard state.

In any of during the movement in the compressing direction when a piston speed represented inFIG. 7by X5is a high speed (particularly, 0.6 m/s), during the movement in the compressing direction when a piston speed represented inFIG. 7by X6is an intermediate speed (particularly, 0.3 m/s), during the movement in the compressing direction when a piston speed represented inFIG. 7by X7is a low speed (particularly, 0.1 m/s), and during the movement in the compressing direction when a piston speed represented inFIG. 7by X8is an extremely low speed (particularly, 0.05 m/s), the damping forces of the second given range from S6to S7, the fourth given range from S8to S9, and the fifth given range from S0to S1enters into a harder state than the damping forces of the first given range from S4to S5and the third given range from S2to S3. However, as the piston speed becomes high while maintaining this relation, the damping force enters into the hard state.

The damping force change characteristics described above are obtained, and thereby a force used to vibrate a spring can be reduced (i.e., soft), and a force used to damp a spring can be increased (i.e., hard). A high-quality riding comfort such as skyhook control is obtained without electronic control.FIG. 8shows a sprung acceleration for illustrating an effect of riding comfort during traveling on a bad road of the vehicle on which the shock absorber1is mounted.FIG. 8shows results of simulation of the sprung acceleration during traveling on a long waveform road at a speed of 60 km per hour. According to the shock absorber1of the present embodiment which has a position sensitive function represented inFIG. 8by a solid line Y2with respect to a case in which there is no position sensitive function represented inFIG. 8by a dashed-dotted line Y1, it is understood that the sprung acceleration during traveling on the bad rod is sharply reduced. This shows that sprung movement is reduced and that the riding comfort during traveling on the bad rod is improved. The same performance as an expensive and electronically controlled semi-active suspension represented inFIG. 8by a broken line Y3is obtained.

FIG. 9shows results of simulation of a yaw rate at the time of double lane change during traveling of the vehicle on which the shock absorber1is mounted at a speed of 80 km per hour. A dashed-dotted line Z0ofFIG. 9is a steering angle. The shock absorber1of the present embodiment which has a position sensitive function represented inFIG. 9by a solid line Z2with respect to a case in which there is no position sensitive function represented inFIG. 9by a broken line Z1has a great turn-over yaw rate and high steering responsivenesss. The turn-over yaw rate up to the same level as the expensive and electronically controlled semi-active suspension represented inFIG. 9by a dashed-two dotted line Z3can be increased, and the steering responsivenesss is high.

The shock absorber described in Patent Literature 1 above is configured to provide two pistons, each of which has a damping valve, and switch a state in which the damping valve of the piston located upstream is bypassed and a damping force is generated by the damping valve of the piston located downstream and a state in which a hard damping force is generated by the damping valves of the two pistons without bypassing the damping valve of the piston located upstream depending on positions of the pistons. On the other hand, it is expected that a degree of freedom in setting the damping force is enhanced.

In the shock absorber1according to the first embodiment, the position-based state changing device175changes the state of the passage to the state in which the upper chamber18and the lower chamber20communicate with each other, the state in which the upper chamber18and the middle chamber19communicate with each other, and the state in which the lower chamber20and the middle chamber19communicate with each other. For this reason, the shock absorber1can communicate between the upper chamber18and the lower chamber20to make the damping force in the soft state, communicate between the upper chamber18and the middle chamber19to generate the damping force using the second damping-force generating device120provided between the middle chamber19and the lower chamber20, or communicate between the lower chamber20and the middle chamber19to generate the damping force using the first damping-force generating device105provided between the middle chamber19and the upper chamber18.

Therefore, the degree of freedom in setting the damping force is enhanced.

To be more specific, aside from the passages101,102,116and117that are provided on the first piston15and the second piston16and communicate between the upper chamber18and the middle chamber19and between the middle chamber19and the lower chamber20such that the oil flows, the intra-rod passage32is provided, and the first adjustment section171that adjusts the flow passage area of the oil between the upper chamber18and the middle chamber19depending on the positions of the first piston15and the second piston16and the second adjustment section172that adjusts the flow passage area of the oil between the lower chamber20and the middle chamber19depending on the positions of the first piston15and the second piston16are provided in the intra-rod passage32. When the first piston15and the second piston16are within the first given range from S4to S5including the neutral position, the flow passage areas of the first adjustment section171and the second adjustment section172are increased together, and communicate between the upper chamber18and the lower chamber20to make the damping force in the soft state.

When the first piston15and the second piston16exceed the first given range from S4to S5and are within the second given range from S6to S7at the maximum length side, the flow passage area of the first adjustment section171is reduced, and the flow passage area of the second adjustment section172is increased. Therefore, in the extension stroke, the oil of the upper chamber18can flow to the lower chamber20via the middle chamber19and the second adjustment section172while passing through the extension-side damping valve104of the first piston15. In addition, in the compression stroke, the oil of the lower chamber20can flow to the upper chamber18while flowing from the second adjustment section172to the middle chamber19to pass through the compression-side damping valve103of the first piston15.

When the first piston15and the second piston16exceed the first given range from S4to S5and are within the third given range from S2to S3at the minimum length side, the flow passage area of the first adjustment section171is increased, and the flow passage area of the second adjustment section172is reduced. Therefore, in the extension stroke, the oil of the upper chamber18can flow to the lower chamber20while being introduced to the middle chamber19via the first adjustment section171and passing through the extension-side damping valve119of the second piston16. In addition, in the compression stroke, the oil of the lower chamber20can pass through the compression-side damping valve118of the second piston16to flow to the middle chamber19, and flow to the upper chamber18via the first adjustment section171. Therefore, the degree of freedom in setting the damping force is enhanced.

The extension-side damping valve104of the first piston15of the extension-side damping valve119of the second piston16are set such that, when the first piston15and the second piston16move in the extending direction, the damping force generated by the extension-side damping valve104located upstream is smaller than the damping force generated by the extension-side damping valve119located downstream. For this reason, the damping force can be made soft due to the flow of the oil passing through the extension-side damping valve104in the extension stroke when the pistons are within the second given range from S6to S7, and the damping force can be made hard due to the flow of the oil passing through the extension-side damping valve119in the extension stroke when the pistons are within the third given range from S2to S3.

The compression-side damping valve103of the first piston15and the compression-side damping valve118of the second piston16are set such that, when the first piston15and the second piston16move in the compressing direction, the damping force generated by the compression-side damping valve118located upstream is smaller than the damping force generated by the compression-side damping valve103located downstream. For this reason, the damping force can be made soft due to the flow of the oil passing through the compression-side damping valve118in the compression stroke when the pistons are within the third given range from S2to S3, and the damping force can be made hard due to the flow of the oil passing through the compression-side damping valve103in the compression stroke when the pistons are within the second given range from S6to S7.

When the first piston15and the second piston16exceed the second given range from S6to S7and are within the fourth given range from S8to S9located at the maximum length side and when the first piston15and the second piston16exceed the third given range from S2to S3and are within the fifth given range from S0to S1located at the minimum length side, the flow passage area of the first adjustment section171and the flow passage area of the second adjustment section172are reduced together. Therefore, since the intra-rod passage32is kept restricting any communication between the upper chamber18, the middle chamber19, and the lower chamber20, the damping forces of the extension stroke and the compression stroke are increased together. Thereby, the damping forces during the full extension and full compression can be increased, and the suppression of abnormal noises and the improvement of riding comfort can be ensured.

Since the metering pin31having the reduced diameter section164that extends to be longer than the axial length between the first adjustment section171and the second adjustment section172and regulates the first given range from S4to S5is used, the shock absorber1can be made in a simple structure.

In the first embodiment, relations between lengths of the first large diameter section162, the reduced diameter section164, and the second large diameter section166of the metering pin31and a length between the small diameter hole section48of the first adjustment section171and the small diameter hole section137of the second adjustment section172may be changed such that up to the full extension position S9, the first adjustment section171may align the axial positions of the small diameter hole section48and the second large diameter section166of the metering pin31, and the second adjustment section172may align the axial positions of the small diameter hole section137and the reduced diameter section164of the metering pin31. That is, the second given range from S6to S7meeting these relations may extend up to the full extension position S9. Likewise, up to the full compression position S0, the first adjustment section171may align the axial positions of the small diameter hole section48and the reduced diameter section164of the metering pin31, and the second adjustment section172may align the axial positions of the small diameter hole section137and the first large diameter section162of the metering pin31. The third given range from S2to S3meeting these relations may extend up to the full compression position S0.

Among these changes, the change of only any one of the extension side and compression side may be adopted. Preferably, in at least any one of the case in which the first piston15and the second piston16exceed the second given range from S6to S7and are located at the maximum length side and the case in which the first piston15and the second piston16exceed the third given range from S2to S3and are located at the minimum length side, the flow passage areas of the first adjustment section171and the second adjustment section172may be set to be reduced together. More preferably, in both the cases, the flow passage areas of the first adjustment section171and the second adjustment section172may be set to be reduced together.

A portion having a much larger diameter than the first large diameter section162and the second large diameter section166may be provided at a side of at least one of the first and second large diameter sections162and166of the metering pin31which is opposite to the reduced diameter section164, and the damping force may be further enhanced in at least one of the vicinity of the first large diameter section162and the vicinity of the second large diameter section166. In this case, since the damping force can be further enhanced at the full extension position and the full compression position, the stopper35that can protect the piston or the base valve during the full extension or during the full compression and improve the riding comfort can be removed.

Therefore, an improvement in productivity by reducing the number of components and miniaturization by reducing the axial length can be ensured.

The first embodiment is not limited to the double cylinder shock absorber, and may be applied to a single cylinder shock absorber. In this case, a free-piston is provided in the cylinder at a side of the second piston which is opposite to the extension side of the piston rod, and an intermediate member fixed to the cylinder is provided between the free-piston and the second piston and supports the metering pin.

Second Embodiment

Next, a second embodiment will be mainly described with reference toFIGS. 10 to 12based on portions different from those of the first embodiment. Sections that are in common with those of the first embodiment are expressed with the same names and reference signs.

In a shock absorber1A of the second embodiment shown inFIG. 10, a cylinder2A that is partly different from the cylinder2is used, and particularly an inner cylinder5A that is partly different from the inner cylinder5is used.

An axial groove200extending in an axial direction as illustrated inFIG. 11is partly formed in an inner circumferential portion of the inner cylinder5A as illustrated inFIG. 12. As illustrated inFIG. 10, in the shock absorber1A, the metering pin31of the first embodiment is not provided, and a base valve25A partly different from the base valve25is used. A locking member146and a support plate147for mounting the metering pin31are not provided in the base valve25A. A base valve member141A, an outer diameter of an upper portion of which is different from that of the base valve member141is used for the base valve25A. The upper portion of the base valve member141A is directly fitted with the inner cylinder5A.

In the second embodiment, a piston rod21A partly different from the piston rod21is used. The piston rod21A has a rod main body26A that is partly different from the rod main body26and the tip rod27, and a nut78A that is partly different from the nut78.

The rod main body26A has a solid structure. The rod main body26A has a main shaft section201that is slidably inserted inside each of a rod guide22and a seal member23and extends outside the cylinder2, and a holding shaft section57A inside the cylinder2A. The holding shaft section57A has a smaller diameter than the main shaft section201. A male screw58A is formed on an outer circumference of an end section of the holding shaft section57A which is on the opposite side of the main shaft section201.

In the second embodiment, as illustrated inFIG. 11, a second piston16A that is partly different from the second piston16is used. To be specific, a piston main body111A that is partly different from the piston main body111is used. A passage forming hole section125is not formed in the piston main body111A, and an insertion hole126A having a constant diameter is formed in the piston main body111A. The piston main body111A fits the holding shaft section57A of the piston rod21A with the insertion hole126A.

One regulating member61, one abutting disc62, one disc63, a disc valve64made up of a plurality of discs, a first piston15, a disc valve65made up of a plurality of discs, one disc66, and one abutting disc67, all of which are the same as in the first embodiment, are mounted on the holding shaft section57A in this order and in addition, one regulating member68A whose thickness is different from that of the first embodiment is mounted on the holding shaft section57A. Further, one abutting disc69, one disc70, and a disc valve71made up of a plurality of discs, all of which are the same as in the first embodiment, are mounted on the holding shaft section57A in this order and in addition, a second piston16A and a disc72A that is different from the passage forming disc72of the first embodiment in that passage groove131is not formed are mounted on the holding shaft section57A in this order. Further, a plurality of discs73, a disc valve74made up of a plurality of discs, one disc75, one abutting disc76, and one regulating member77, all of which are the same as in the first embodiment, are mounted on the holding shaft section57A in this order. These members mounted on the holding shaft section57A are sandwich by the general-purpose nut78A screwed to the male screw58A without a small diameter hole section137and an end face of the main shaft section201which is close to the holding shaft section57A. The stopper35of the first embodiment is not provided.

The axial groove200of the inner cylinder5A has a length that can cross both of the first piston15and the second piston16in the axial direction at the same time. That is, the axial groove200extends to be longer than an axial length between the first piston15and the second piston16(a maximum distance between sliding members96and112).

In a state in which the entire axial groove200is located at a side of the first piston15which is opposite to the second piston16and in a state in which the entire axial groove200is located at a side of the second piston16which is opposite to the first piston15, the axial groove200does not cross both the first piston15and the second piston16in the axial direction, and does not allow all of an upper chamber18, a middle chamber19, and a lower chamber20to communicate with one another. In a state in which the axial groove200does not cross only the first piston15in the axial direction, the axial groove200allows the upper chamber18and the middle chamber19to communicate with each other with a wall passage (a second passage)202inside the first piston15, but does not allow the middle chamber19and the lower chamber20to communicate with each other. In a state in which the axial groove200crosses only the second piston16in the axial direction, the axial groove200allows the middle chamber19and the lower chamber20to communicate with each other with the wall passage202of the second piston16, but does not allow the upper chamber18and the middle chamber19to communicate with each other. In the state in which the axial groove200crosses both the first piston15and the second piston16in the axial direction at the same time, the axial groove200allows all of the upper chamber18, the middle chamber19, and the lower chamber20to communicate with one another with the wall passage202of the first piston15and the second piston16. Therefore, in addition to passages101,102,116and117, the wall passage202allows the upper chamber18, the middle chamber19, and the lower chamber20to communicate with one another.

Thereby, the first piston15and the axial groove200constitute a first adjustment section171A that is provided with respect to the wall passage202and adjusts a flow passage area of oil between the upper chamber18and the middle chamber19depending on positions of the first piston15and the second piston16. The second piston16and the axial groove200constitute a second adjustment section172A that is provided with respect to the wall passage202and adjusts a flow passage area of oil between the middle chamber19and the lower chamber20depending on the positions of the first piston15and the second piston16. In other words, the flow passage areas of the first adjustment section171A and the second adjustment section172A are adjusted by the axial groove200that is partly formed in the inner circumference of the inner cylinder5of the cylinder2.

In the shock absorber1A, when stroke positions of the first piston15and the second piston16are within a first given range from S4to S5that includes a neutral position (a position of 1G (a position at which a vehicle body stopped at a horizontal position is supported)) and is shown inFIG. 5(a), the axial groove200crosses both the first piston15and the second piston16in the axial direction at the same time, and allows the upper chamber18, the middle chamber19, and the lower chamber20to communicate with one another using the flow passage area of the wall passage202. In other words, the first given range from S4to S5is a range regulated by the axial groove200. In the first given range from S4to S5, the flow passage area of the wall passage202surrounded by the first piston15and the axial groove200of the first adjustment section171A and the flow passage area of the wall passage202surrounded by the second piston16and the axial groove200of the second adjustment section172A have the same maximum values as represented by the solid lines U1and U2ofFIG. 5(a), and the communication between the upper chamber18and the lower chamber20is maintained with flow passage area of the wall passage202.

When the first piston15and the second piston16are within the first given range from S4to S5, the oil of the upper chamber18flows to the lower chamber20via the wall passage202in an extension stroke in which the first piston15and the second piston16move to the upper chamber18side. Therefore, as represented by the solid line V1ofFIG. 5(b), a damping force enters into a soft state.

When the first piston15and the second piston16are within the first given range from S4to S5, the oil of the lower chamber20flows to the upper chamber18via the wall passage202in a compression stroke in which the first piston15and the second piston16move to the lower chamber20side. Therefore, as represented by the broken line V2ofFIG. 5(b), the damping force enters into a soft state.

In the shock absorber1A, when the stroke positions of the first piston15and the second piston16exceed the first given range from S4to S5and are within a second given range from S6to S7that is shown inFIG. 5(a)at a maximum length side at which the shock absorber1is set to a maximum length, the first piston15of the first adjustment section171A interrupts the communication between the upper chamber18and the middle chamber19due to the wall passage202so that the flow passage area is made to the minimum value as represented by the solid line U1ofFIG. 5(a), and the first piston15of the second adjustment section172A communicates between the middle chamber19and the lower chamber20due to the wall passage202so that the flow passage area is made to the maximum value as represented by the broken line U2ofFIG. 5(a).

When the first piston15and the second piston16are within the second given range from S6to S7, the first adjustment section171A interrupts the communication between the upper chamber18and the middle chamber19due to the wall passage202in the extension stroke in which the first piston15and the second piston16move to the upper chamber18side. For this reason, entry of the oil of the upper chamber18into the wall passage202is restricted, the oil passes through the passages102of the first piston15, and flows to the middle chamber19by opening the extension-side damping valve104having a soft damping force property. Since the second adjustment section172A communicates between the middle chamber19and the lower chamber20with the wall passage202, the oil of the middle chamber19flows from the middle chamber19to the lower chamber20via the wall passage202. Therefore, as represented by the solid line V1ofFIG. 5(b), the damping force is maintained in a soft state while becoming a slightly harder state than the first given range from S4to S5.

When the first piston15and the second piston16are within the second given range from S6to S7, the second adjustment section172A communicates between the middle chamber19and the lower chamber20due to the wall passage202in the compression stroke in which the first piston15and the second piston16move to the lower chamber20side, and the first adjustment section171A interrupts the communication between the upper chamber18and the middle chamber19due to the wall passage202. For this reason, the oil of the lower chamber20flows to the middle chamber19side via the wall passage202, passes the passages101of the first piston15, and flows to the upper chamber18by opening the compression-side damping valve103having a hard damping force property. Therefore, as represented by the broken line V2ofFIG. 5(b), the damping force enters into a harder state than the first given range from S4to S5and a third given range from S2to S3(to be described below).

In the shock absorber1A, when the stroke positions of the first piston15and the second piston16exceed the first given range from S4to S5and are within the third given range from S2to S3that is shown inFIG. 5(a)at a minimum length side at which the shock absorber1A is set to a minimum length, the first adjustment section171A communicates between the upper chamber18and the middle chamber19due to the wall passage202so that the flow passage area is made to the maximum value as represented by the solid line U1ofFIG. 5(a), and the second adjustment section172A interrupts the communication between the middle chamber19and the lower chamber20due to the wall passage202so that the flow passage area is made to the minimum value as represented by the broken line U2ofFIG. 5(a).

When the first piston15and the second piston16are within the third given range from S2to S3, the first adjustment section171A communicates between the upper chamber18and the middle chamber19due to the wall passage202in the extension stroke in which the first piston15and the second piston16move to the upper chamber18side, and the second adjustment section172A interrupts the communication between the middle chamber19and the lower chamber20with the wall passage202. For this reason, the oil of the upper chamber18is introduced to the middle chamber19via the wall passage202, and flows to the lower chamber20by opening the extension-side damping valve119having a hard damping force property. Therefore, as represented by the solid line V1ofFIG. 5(b), the damping force enters into a harder state than the second given range from S6to S7.

When the first piston15and the second piston16are within the third given range from S2to S3, the second adjustment section172A interrupts the communication between the middle chamber19and the lower chamber20due to the wall passage202in the compression stroke in which the first piston15and the second piston16move to the lower chamber20side. For this reason, the oil of the lower chamber20passes the passages116of the second piston16, and flows to the middle chamber19by opening the compression-side damping valve118having a soft damping force property. Since the first adjustment section171A communicates between the upper chamber18and the middle chamber19with the wall passage202, the oil of the middle chamber19flows from the upper chamber18via the wall passage202. Therefore, as represented by the broken line V2ofFIG. 5(b), the damping force is maintained in a soft state while becoming a slightly harder state than the first given range from S4to S5.

In the shock absorber1A, when the stroke positions of the first piston15and the second piston16exceed the second given range from S6to S7and are within a fourth given range from S8to S9up to a full extension position S9at the minimum length side, the first adjustment section171A interrupts the communication between the upper chamber18and the middle chamber19due to the wall passage202so that the flow passage area is made to the minimum value as represented by the solid line U1of FIG.5(a), and the second adjustment section172A interrupts the communication between the middle chamber19and the lower chamber20due to the wall passage202so that the flow passage area is made to the minimum value as represented by the broken line U2ofFIG. 5(a).

When the first piston15and the second piston16are within the third given range from S2to S3, the first adjustment section171A interrupts the communication between the upper chamber18and the middle chamber19due to the wall passage202in the extension stroke in which the first piston15and the second piston16move to the upper chamber18side, and the second adjustment section172A interrupts the communication between the middle chamber19and the lower chamber20due to the wall passage202. For this reason, the oil of the upper chamber18passes the passages102, flows to the middle chamber19by opening the extension-side damping valve104having a soft damping force property, passes the passages117, and flows to the lower chamber20by opening the extension-side damping valve119having a hard damping force property. Therefore, as represented by the solid line V1ofFIG. 5(b), the damping force enters into a hard state like the third given range from S2to S3. Thereby, the damping force during the full extension enters into a hard state, and the suppression of abnormal noises and the improvement of riding comfort can be ensured.

When the first piston15and the second piston16are within the fourth given range from S8to S9, the first adjustment section171A interrupts the communication between the upper chamber18and the middle chamber19due to the wall passage202in the compression stroke in which the first piston15and the second piston16move to the lower chamber20side, and the second adjustment section172A interrupts the communication between the middle chamber19and the lower chamber20due to the wall passage202. For this reason, the oil of the lower chamber20passes the passages116, flows to the middle chamber19by opening the compression-side damping valve118having a soft damping force property, passes the passages101, and flows to the upper chamber18by opening the compression-side damping valve103having a hard damping force property. Therefore, as represented by the broken line V2ofFIG. 5(b), the damping force enters into a hard state like the second given range from S6to S7.

In the shock absorber1A, when the stroke positions of the first piston15and the second piston16exceed the third given range from S2to S3and are within a fifth given range from S0to S1up to a full compression position S0at the minimum length side, the first adjustment section171A interrupts the communication between the upper chamber18and the middle chamber19due to the wall passage202so that the flow passage area is made to the minimum value as represented by the solid line U1ofFIG. 5(a), and the second adjustment section172A interrupts the communication between the middle chamber19and the lower chamber20due to the wall passage202so that the flow passage area is made to the minimum value as represented by the broken line U2ofFIG. 5(a).

When the first piston15and the second piston16are within the fifth given range from S0to S1, the first adjustment section171A interrupts the communication between the upper chamber18and the middle chamber19due to the wall passage202in the extension stroke in which the first piston15and the second piston16move to the upper chamber18side, and the second adjustment section172A interrupts the communication between the middle chamber19and the lower chamber20due to the wall passage202. For this reason, the oil of the upper chamber18passes the passages102, flows to the middle chamber19by opening the extension-side damping valve104having a soft damping force property, passes the passages117, and flows to the lower chamber20by opening the extension-side damping valve119having a hard damping force property. Therefore, as represented by the solid line V1ofFIG. 5(b), the damping force enters into a hard state like the third given range from S2to S3.

When the first piston15and the second piston16are within the fifth given range from S0to S1, the first adjustment section171A interrupts the communication between the upper chamber18and the middle chamber19due to the wall passage202in the compression stroke in which the first piston15and the second piston16move to the lower chamber20side, and the second adjustment section172A interrupts the communication between the middle chamber19and the lower chamber20due to the wall passage202. For this reason, the oil of the lower chamber20passes the passages116, flows to the middle chamber19by opening the compression-side damping valve118having a soft damping force property, passes the passages101, and flows to the upper chamber18by opening the compression-side damping valve103having a hard damping force property. Therefore, as represented by the broken line V2ofFIG. 5(b), the damping force enters into a hard state like the second given range from S6to S7, and the suppression of abnormal noises and the improvement of riding comfort can be ensured.

That is, the first adjustment section171A and the second adjustment section172A constitute a position-based state changing device175A that changes a state of the wall passage202depending on positions of the first piston15and the second piston16. The position-based state changing device175A changes the state of the passage to the state in which the upper chamber18and the lower chamber20communicate with each other via the middle chamber19with a maximum flow passage area, the state in which the upper chamber18and the middle chamber19communicate with each other with a maximum flow passage area and the communication between the upper chamber18and the middle chamber19and the communication between the upper chamber18and the lower chamber20are interrupted, the state in which the lower chamber20and the middle chamber19communicate with each other with a maximum flow passage area and the communication between the lower chamber20and the middle chamber19and the communication between the lower chamber20and the upper chamber18are interrupted, and the state in which all the communications between the upper chamber18, the middle chamber19, and the lower chamber20are interrupted depending the positions of the first piston15and the second piston16.

Thereby, in the shock absorber1A, when the first piston15and the second piston16are within the first given range from S4to S5including the neutral position, the damping forces of both the movement in the extending direction and the movement in the compressing direction enter into the soft state. In the shock absorber1A, when the first piston15and the second piston16are within the second given range from S6to S7at the maximum length side, the damping force of the movement in the extending direction enters into the soft state, and the damping force of the movement in the compressing direction enters into the hard state. In the shock absorber1A, when the first piston15and the second piston16are within the third given range from S2to S3at the minimum length side, the damping force of the movement in the extending direction enters into the hard state, and the damping force of the movement in the compressing direction enters into the soft state. Further, in the shock absorber1A, when the first piston15and the second piston16are within the fourth given range from S8to S9at the maximum length side and within the fifth given range from S0to S1at the minimum length side, the damping forces of the movement in the extending direction and the movement in the compressing direction enter into the hard state together. That is, the shock absorber1A has inversion-type position-sensitive damping force change characteristics in which a relation between the hard state and the soft state of the movement in the extending direction and the movement in the compressing direction is inverted within the second given range from S6to S7at the maximum length side and the third given range from S2to S3at the minimum length side.

In the second embodiment, a relation between a length of the axial groove200and a length between the first piston15constituting the first adjustment section171A and the second piston16constituting the second adjustment section172A may be changed such that up to the full extension position S9, the first adjustment section171A may interrupt the communication between the upper chamber18and the middle chamber19, and the second adjustment section172A may allow the middle chamber19and the lower chamber20to communicate with each other. That is, the second given range from S6to S7meeting these relations may extend up to the full extension position S9. Likewise, up to the full compression position S0, the first adjustment section171A may allow the upper chamber18and the middle chamber19to communicate with each other, and the second adjustment section172A may interrupt the communication between the middle chamber19and the lower chamber20. The third given range from S2to S3meeting these relations may extend up to the full compression position S0.

Among these changes, the change of only any one of the extension side and compression side may be adopted. Preferably, in at least any one of the case in which the first piston15and the second piston16exceed the second given range from S6to S7and are located at the maximum length side and the case in which the first piston15and the second piston16exceed the third given range from S2to S3and are located at the minimum length side, the flow passage areas of the first adjustment section171A and the second adjustment section172A may be set to be reduced together. More preferably, in both the cases, the flow passage areas of the first adjustment section171A and the second adjustment section172A may be set to be reduced together.

According to the second embodiment described above, since the axial groove200that extends to be longer than the axial length between the first adjustment section171A and the second adjustment section172A and regulates the first given range from S4to S5may be formed, the shock absorber1A can be made in a simple structure.

In the first and second embodiments described above, the middle chamber19may be provided inside the first piston15and the second piston16without any one of the first piston15and the second piston16sliding in the inner cylinder5. In addition, a tubular body joining the first piston15and the second piston16may be provided at outer circumference sides of the first piston15and the second piston16, and the middle chamber may be formed inside the tubular body.

The damping force properties of the compression-side damping valves103and118and the extension-side damping valves104and119may be all made different, and at least two thereof may be the same damping force properties. For example, the damping force properties may be changed in such a manner that the two properties are set as a medium property between soft and hard properties, one remaining property is set as a soft property, and the other remaining property is set as a hard property.

The second embodiment is also not limited to the double cylinder shock absorber, and may be applied to a single cylinder shock absorber.

The shock absorber of the present embodiment is a shock absorber having a cylinder in which a working fluid is encapsulated, a piston that is provided in an inside of the cylinder and divides the inside of the cylinder into an upper chamber and a lower chamber, and a piston rod that is connected to the pistons and extends outside the cylinder, and includes a middle chamber that is formed by the piston, a first damping-force generating device that is provided between the upper chamber and the middle chamber and generates a damping force, a second damping-force generating device that is provided between the lower chamber and the middle chamber and generates a damping force, and a position-based state changing device that changes a state of a passage to a state in which the upper chamber and the lower chamber communicate with each other, a state in which the upper chamber and the middle chamber communicate with each other, or a state in which the lower chamber and the middle chamber communicate with each other depending on the position of the piston. Thereby, a degree of freedom in setting the damping force can be enhanced.

The shock absorber includes: a cylinder in which a working fluid is encapsulated; first and second pistons, at least one of which is slidably provided in an inside of the cylinder and which divide the inside of the cylinder into an upper chamber, a middle chamber, and a lower chamber; a piston rod connected to the first and second pistons and extending outside the cylinder; a first passage that is provided in the first and second pistons and communicates between the upper chamber and the middle chamber and between the middle chamber and the lower chamber such that the working fluid flows; extension-side and compression-side damping valves that are provided on the first and second pistons, restrict a flow of the working fluid flowing along the first passage by movement of the first and second pistons, and generate damping forces; a second passage that communicates the upper chamber, the middle chamber, and the lower chamber with one another aside from the first passage; a first adjustment section that is provided with respect to the second passage and adjusts a flow passage area of the working fluid between the upper chamber and the middle chamber depending on positions of the first and second pistons; and a second adjustment section that is provided with respect to the second passage and adjusts a flow passage area of the working fluid between the lower chamber and the middle chamber depending on the positions of the first and second pistons. The flow passage areas of the first and second adjustment sections are set such that: the flow passage area of the first adjustment section and the flow passage area of the second adjustment section are increased together when the first piston and the second piston are within a first given range including a neutral position; the flow passage area of the first adjustment section is reduced, and the flow passage area of the second adjustment section is increased when the first piston and the second piston exceed the first given range and are within a second given range at a maximum length side; and the flow passage area of the first adjustment section is increased, and the flow passage area of the second adjustment section is reduced when the first piston and the second piston exceed the first given range and are within a third given range at a minimum length side. Thereby, a degree of freedom in setting the damping force can be enhanced.

The extension-side damping valve of the first piston and the extension-side damping valve of the second piston is set such that, when the first piston and the second piston move in an extending direction, the damping force generated by the extension-side damping valve located upstream is smaller than the damping force generated by the extension-side damping valve located downstream. The compression-side damping valve of the first piston and the compression-side damping valve of the second piston is set such that, when the first piston and the second piston move in a compressing direction, the damping force generated by the compression-side damping valve located upstream is smaller than the damping force generated by the compression-side damping valve located downstream. Thereby, the damping force can be made soft by the flow of the oil passing through the extension-side damping valve in the extension stroke when the first and second pistons are within the second given range. The damping force can be made hard by the flow of the oil passing through the extension-side damping valve in the extension stroke when the first and second pistons are within the third given range. The damping force can be made soft by the flow of the oil passing through the compression-side damping valve in the compression stroke when the first and second pistons are within the third given range. The damping force can be made hard by the flow of the oil passing through the compression-side damping valve in the compression stroke when the first and second pistons are within the second given range.

In at least one of the case in which the first piston and the second piston exceed the second given range and are located at the maximum length side and the case in which the first piston and the second piston exceed the third given range and are located at the minimum length side, the flow passage area of the first adjustment section and the flow passage area of the second adjustment section are set to be reduced together. Thereby, the damping forces during the full extension and full compression can be increased, and the suppression of abnormal noises and the improvement of riding comfort can be ensured.

The flow passage area of the first adjustment section and the flow passage area of the second adjustment section are adjusted by a metering pin. The metering pin has a reduced diameter section that extends to be longer than an axial length between the first adjustment section and the second adjustment section, and regulates the first given range. Thereby, the shock absorber can be made in a simple structure.

The flow passage areas of the first and second adjustment sections are adjusted by an axial groove that is partly formed on an inner circumference of the cylinder. The axial groove extends to be longer than the axial length between the first adjustment section and the second adjustment section, and regulates the first given range. Thereby, the shock absorber can be made in a simple structure.

INDUSTRIAL APPLICABILITY

According to the shock absorber, a degree of freedom in setting a damping force can be enhanced.