Patent ID: 12222018

DESCRIPTION OF EMBODIMENTS

A shock absorber according to an embodiment of the present invention will be described below with reference to the drawings.

A shock absorber10of the present embodiment is a shock absorber that is used in a suspension device of an automobile or a railroad vehicle. As shown inFIG.1, the shock absorber10includes a cylinder11in which a working fluid is enclosed. The cylinder11includes an inner cylinder12having a cylindrical shape and a bottomed cylinder-shaped outer cylinder13having a larger diameter than the inner cylinder12and provided outside the inner cylinder12. A reservoir chamber14is formed between the inner cylinder12and the outer cylinder13. The outer cylinder13has a bottom portion15on one side in an axial direction and an opening portion16on the other side in the axial direction. The opening portion16is an opening portion of the cylinder11.

A piston17is slidably inserted into the inner cylinder12of the cylinder11. The piston17defines the inside of the inner cylinder12of the cylinder11into a one-side chamber18and the other-side chamber19. In the cylinder11, a hydraulic fluid as a working fluid is enclosed in the one-side chamber18and the other-side chamber19, and a hydraulic fluid as a working fluid and a gas are enclosed in the reservoir chamber14. The cylinder11configured of the bottomed cylinder-shaped outer cylinder13and the inner cylinder12disposed inside the outer cylinder13has a bottomed cylinder shape, and the working fluid is enclosed inside the cylinder11.

A piston rod20made of metal is connected to the piston17. In the piston rod20, a base end portion21on one side in the axial direction is inserted into the cylinder11, and a tip portion22on the other side in the axial direction protrudes outward from one end in the axial direction of the cylinder11, that is, one end in the axial direction of each of the inner cylinder12and the outer cylinder13. The piston17is fixed to the base end portion21of the piston rod20by a nut23. The piston17moves integrally with the piston rod20.

An annular rod guide25and an annular seal member26are disposed inside the cylinder11, and a base valve28is provided inside the cylinder11. The annular rod guide25and the annular seal member26are disposed on the opening portion16side of the outer cylinder13, from which the piston rod20protrudes. The base valve28is provided on the bottom portion15side of the outer cylinder13. In the inner cylinder12, the space between the piston17and the rod guide25is the one-side chamber18, and the space between the piston17and the base valve28is the other-side chamber19. Therefore, in the piston17, the one-side chamber18in the axial direction is on the side close to the tip portion22of the piston rod20, and the other-side chamber19in the axial direction is on the side far from the tip portion22of the piston rod20.

The rod guide25is provided on the side opposite to the bottom portion15of the cylinder11. The rod guide25positions an end portion on the opening portion16side in the axial direction of the inner cylinder12with respect to the outer cylinder13, and guides the axial movement of the piston rod20while restricting the radial movement of the piston rod20. The seal member26closes the opening portion16side of one end of the cylinder11and restrains the hydraulic fluid in the inner cylinder12and the gas and the hydraulic fluid in the reservoir chamber14from leaking to the outside.

The base valve28has a base body31. The base body31partitions the other-side chamber19and the reservoir chamber14, and positions an end portion on the bottom portion15side in the axial direction of the inner cylinder12with respect to the outer cylinder13. A liquid passage32and a liquid passage33capable of making the other-side chamber19and the reservoir chamber14communicate with each other are formed in the base body31. A disc valve35and a disc valve36are mounted to the base body31with a rivet37. The disc valve35is capable of opening and closing the liquid passage32on the inner side in the radial direction. The disc valve36is capable of opening and closing the liquid passage33on the outer side in the radial direction.

The disc valve35allows the flow of the hydraulic fluid from the other-side chamber19to the reservoir chamber14while restricting the flow of the hydraulic fluid from the reservoir chamber14to the other-side chamber19through the liquid passage32. The disc valve35is a damping valve that causes the hydraulic fluid to flow from the other-side chamber19to the reservoir chamber14when the piston rod20moves to the contraction side in which the amount of extension hereof from the cylinder11reduces, and generates a damping force at that time.

The disc valve36allows the flow of the hydraulic fluid from the reservoir chamber14to the other-side chamber19while restricting the flow of the hydraulic fluid from the other-side chamber19to the reservoir chamber14through the liquid passage33. The disc valve36is a suction valve that allows the hydraulic fluid to flow from the reservoir chamber14to the other-side chamber19without substantially generating a damping force, when the piston rod20moves to the extension side in which the amount of extension thereof from the cylinder11increases.

The piston17described above and disc valves41and42on both sides thereof are mounted to the piston rod20by a nut23at the base end portion21on the side where the piston rod20is inserted into the inner cylinder12. A liquid passage43and a liquid passage44capable of making the other-side chamber19and the one-side chamber18communicate with each other are formed in the piston17. The disc valve41is capable of opening and closing the liquid passage43. The disc valve42is capable of opening and closing the liquid passage44.

The disc valve41allows the flow of the hydraulic fluid from the other-side chamber19to the one-side chamber18while restricting the flow of the hydraulic fluid from the one-side chamber18to the other-side chamber19through the liquid passage43. The disc valve41is a damping valve that causes the hydraulic fluid to flow from the other-side chamber19to the one-side chamber18when the piston rod20moves to the contraction side, and generates a damping force at that time.

The disc valve42allows the flow of the hydraulic fluid from the one-side chamber18to the other-side chamber19while restricting the flow of the hydraulic fluid from the other-side chamber19to the one-side chamber18through the liquid passage44. The disc valve42is a damping valve that causes the hydraulic fluid to flow from the one-side chamber18to the other-side chamber19when the piston rod20moves to the extension side, and generates a damping force at that time.

A cover member51is mounted on one side of the piston rod20extending from the cylinder11. The cover member51has a circular plate-shaped annular member52and a cylinder-shaped tubular member53. The annular member52is fixed to a midway portion in the axial direction on one side of the piston rod20extending from the cylinder11. The tubular member53is joined to the outer periphery side of the annular member52and extends in the direction of the cylinder11from the annular member52. The tubular member53overlaps the cylinder11in the axial direction. The tubular member53covers the outer peripheral portion of the cylinder11and the portion of the piston rod20protruding from the seal member26.

A mounting eye55is fixed to the outer side of the bottom portion15of the outer cylinder13.

When the shock absorber10is mounted to a vehicle, for example, the tip portion22of the piston rod20is disposed on the upper side and connected to the vehicle body side, and the mounting eye55is disposed on the lower side and connected to the wheel side.

The shock absorber10generates a damping force on the extension side as follows. That is, when the piston rod20moves to the extension side, the piston17moves integrally with the piston rod20in the direction of reducing the volume of the one-side chamber18and increasing the volume of the other-side chamber19. Then, the disc valve42provided in the piston17causes the hydraulic fluid to flow from the one-side chamber18to the other-side chamber19through the liquid passage44, and generates a damping force at that time. At this time, the disc valve36of the base valve28causes the hydraulic fluid to flow from the reservoir chamber14to the other-side chamber19without substantially generating a damping force, thereby supplementing the other-side chamber19with the hydraulic fluid by an amount corresponding to the volume of the piston rod20protruding from the cylinder11.

The shock absorber10generates a damping force on the contraction side as follows. That is, when the piston rod20moves to the contraction side, the piston17moves integrally with the piston rod20in the direction of reducing the volume of the other-side chamber19and increasing the volume of the one-side chamber18. Then, the disc valve41provided in the piston17causes the hydraulic fluid to flow from the other-side chamber19to the one-side chamber18through the liquid passage43, and generates a damping force at that time. Further, at this time, the disc valve35of the base valve28causes the hydraulic fluid to flow from the other-side chamber19to the reservoir chamber14, and generates a damping force at that time.

The piston17is configured of a piston main body61made of metal and a piston hand62made of synthetic resin. The piston main body61is fixed to the base end portion21of the piston rod20. The piston band62is mounted on an outer peripheral portion60of the piston main body61to configure an outer peripheral portion of the piston17. The piston band62is in sliding contact with an inner peripheral portion63of the inner cylinder12of the cylinder11to seal the gap between the piston17and the inner peripheral portion63.

The piston main body61has an annular shape. The base end portion21of the piston rod20is fitted to the inner periphery side of the piston main body61. The liquid passages43and44are formed in the piston main body61.

The configuration on the outer periphery side of the piston17will be further described.

As shown inFIG.2, the outer peripheral portion60of the piston main body61has an outer peripheral main body portion70having a substantially cylindrical shape, and a plurality of (specifically, six) protrusion portions: a protrusion portion71(a first protrusion portion), a protrusion portion72, a protrusion portion73, a protrusion portion74, a protrusion portion75, and a protrusion portion76(a second protrusion portion), arranged in order from the tip portion22side (the upper side inFIG.2) at intervals in the axial direction of the piston main body61. Each of the protrusion portions71to76has an annular shape. Each of the protrusion portions71to76protrudes outward in the radial direction from the outer peripheral main body portion70.

The outer diameter of the protrusion portion71that is on the side closest to the tip portion22in the axial direction of the piston main body61(the upper side inFIG.2), among the protrusion portions71to76, is smaller than the outer diameters of all the other protrusion portions72to76. The outer diameters of the protrusion portions72to76are the same. The outer diameter surface of the protrusion portion71, which is an outer diameter measurement position, has a cylindrical surface shape. Similarly, the outer diameter surface of each of the protrusion portions72to76also has a cylindrical surface shape.

The axial dimension of the protrusion portion71, which is a length in the axial direction oaf the piston main body61, is larger than the axial dimensions of the other protrusion portions72to75. The length of the outer diameter surface of the protrusion portion71in the axial direction of the piston main body61is also longer than the length of the outer diameter surface of each of the other protrusion portions72to75in the axial direction of the piston main body61. The axial dimensions of the protrusion portions72to74are the same, and the axial dimension of the protrusion portion75is smaller than the axial dimensions of the protrusion portions72to74. The length of the outer diameter surface of each of the protrusion portions72to74in the axial direction of the piston main body61is also longer than the length of the outer diameter surface of the protrusion portion75in the axial direction of the piston main body61.

A recess portion91is formed between the protrusion portions71and72adjacent to each other in the axial direction, among the protrusion portions71to76. The recess portion91is annularly recessed inward in the radial direction with respect to the outer diameter surfaces of the protrusion portions71and72. Similarly, a recess portion92is formed between the protrusion portions72and73adjacent to each other in the axial direction. The recess portion92is an recessed inward in the radial direction with respect to the outer diameter surfaces of the protrusion portions72and73. A recess portion93is formed between the protrusion portions73and74adjacent to each other in the axial direction. The recess portion93is recessed inward in the radial direction with respect to the outer diameter surfaces of the protrusion portions73and74. Similarly, a recess portion94is formed between the protrusion portions74and75adjacent to each other in the axial direction. The recess portion94is annularly recessed inward in the radial direction with respect to the outer diameter surfaces of the protrusion portions74and75. A recess portion95is formed between the protrusion portions75and76adjacent to each other in the axial direction. The recess portion95is annularly recessed inward in the radial direction with respect to the outer diameter surfaces of the protrusion portions75and76. The recess portions91to95are also arranged in order from the tip portion22side of the piston main body61(the upper side inFIG.2) at intervals in the axial direction of the piston main body61.

The groove bottom diameter of the recess portion95that is at the position farthest from the tip portion22in the axial direction of the piston main body61(the lower side inFIG.2), among the recess portions91to95, is smaller than the groove bottom diameters of all the other recess portions91to94. The groove bottom diameters of the recess portions91to94are the same. The groove bottom surface of the recess portion91, which is a groove bottom diameter measurement position, has a cylindrical surface shape. Similarly, the groove bottom surface of each of the recess portions92to95also has a cylindrical surface shape. The protrusion height of the protrusion portion71from the groove bottom surfaces of the recess portions91to94is lower than the protrusion heights of the other protrusion portions72to75from the groove bottom surfaces of the recess portions91to94.

A small-diameter surface portion108having a cylindrical surface shape and configured of the outer peripheral surface of the outer peripheral main body portion70is formed on the tip portion22side (the upper side inFIG.2) in the axial direction with respect to the protrusion portion71of the piston main body61. The outer diameter of the small-diameter surface portion108is smaller than the outer diameters of all the protrusion portions71to76. The outer diameter of the small-diameter surface portion108is smaller than the groove bottom diameters of the recess portions91to94and is larger than the groove bottom diameter of the recess portion95. The small-diameter surface portion108, a large-diameter surface portion101which is the outer diameter surface of the protrusion portion71adjacent to the small-diameter surface portion108, and a stepped surface portion102between the small-diameter surface portion108and the large-diameter surface portion101configures a stepped portion103. Therefore, the piston main body61has the stepped portion103at one end on the side close to the tip portion22in the outer peripheral portion60on which the piston band62is mounted. The stepped portion103is configured of the large-diameter surface portion101, the stepped surface portion102, and the small-diameter surface portion108.

As described above, the piston main body61has the plurality of protrusion portions71to76and recess portions91to95at the outer peripheral portion60on which the piston band62is mounted. The protrusion portions71to76and the recess portions91to95are provided alternately along the axial direction, such as the protrusion portion71, the recess portion91, the protrusion portion72, the recess portion92, the protrusion portion73, the recess portion93, the protrusion portion74, the recess portion94, the protrusion portion75, the recess portion95, and the protrusion portion76. The protrusion portion71is formed at one end on the side close to the tip portion22of the piston rod20(the upper side inFIG.2). The protrusion portion76is formed at the other end on the side far from the tip portion22of the piston rod20(the lower side inFIG.2). The small-diameter surface portion108is formed on the side close to the tip portion22of the protrusion portion71.

The piston band62is made of a low friction material such as fluororesin. Specifically, the piston band62is made of PTFE (polytetrafluoroethylene). The piston band62has an annular band-shaped band main body portion110and a plurality of (specifically, five) inner periphery-side projecting portions111,112,113,114, and115provided at the band main body portion110, in a state of being mounted on the outer peripheral portion60of the piston main body61. The inner periphery-side projecting portions111,112,113,114, and115are arranged in order from the tip portion22side (the upper side inFIG.2) at intervals in the axial direction of the band main body portion110. Each of the inner periphery-side projecting portions111to115has an annular shape that protrudes inward in the radial direction from the band main body portion110. The inner diameter surface of the inner periphery-side projecting portion111, which is an inner diameter measurement position, has a cylindrical surface shape. Similarly, the inner diameter surface of each of the inner periphery-side projecting portions112to115also has a cylindrical surface shape.

An inner periphery-side groove portion121is formed between the inner periphery-side projecting portion111and the inner periphery-side projecting portion112adjacent to each other in the axial direction. The inner periphery-side groove portion121is annularly recessed outward in the radial direction with respect to the inner diameter surfaces of the inner periphery-side projecting portion111and the inner periphery-side projecting portion112. Similarly, an inner periphery-side groove portion122is formed between the inner periphery-side projecting portion112and the inner periphery-side projecting portion113. The inner periphery-side groove portion122is annularly recessed outward in the radial direction with respect to the inner diameter surfaces of the inner periphery-side projecting portion112and the inner periphery-side projecting portion113. An inner periphery-side groove portion123is formed between the inner periphery-side projecting portion113and the inner periphery-side projecting portion114. The inner periphery-side groove portion123is annularly recessed outward in the radial direction with respect to the inner diameter surfaces of the inner periphery-side projecting portion113and the inner periphery-side projecting portion114. Similarly, an inner periphery-side groove portion124is formed between the inner periphery-side projecting portion114and the inner periphery-side projecting portion115. The inner periphery-side groove portion124is annularly recessed outward in the radial direction with respect to the inner diameter surfaces of the inner periphery-side projecting portion114and the inner periphery-side projecting portion115. The plurality of inner periphery-side groove portions121to124are arranged at intervals in the axial direction of the piston band62. The groove bottom surface of the inner periphery-side groove portion121, which is a groove bottom diameter measurement position, has a cylindrical surface shape. Similarly, the groove bottom surface of each of the inner periphery-side groove portions122to124also has a cylindrical surface shape.

In a state where the piston band62is mounted on the piston main body61, the inner periphery-side projecting portion111is completely fitted the recess portion91without any gap, the inner periphery-side projecting portion112is completely fitted to the recess portion92without any gap, the inner periphery-side projecting portion113is completely fitted to the recess portion93without any gap, the inner periphery-side projecting portion114is completely fitted to the recess portion94without any gap, and the inner periphery-side projecting portion115is completely fitted to the recess portion95without any gap. Further, the inner periphery-side groove portion121is completely fitted to the protrusion portion72without any gap, the inner periphery-side groove portion122is completely fitted to the protrusion portion73without any gap, the inner periphery-side groove portion123is completely fitted to the protrusion portion74without any gap, and the inner periphery-side groove portion124is completely fitted to the protrusion portion75without any gap. InFIG.2, the complete fitting without any gap is shown. However, there may be a portion having a partial gap, that is, a partially separated portion, between each protrusion portion or each recess portion and the piston band62.

The piston band62that is in a state of being mounted on the piston main body61, as shown inFIG.2, and in a natural state before being disposed in the cylinder11will be further described.

The piston band62has a fixed portion131and an extended portion132. The fixed portion131is fixed to the piston main body61including the inner periphery-side projecting portions111to115and the inner periphery-side groove portions121to124. The extended portion132is an end portion on one end side in the axial direction of the piston band62. The fixed portion131is fitted and fixed to the piston main body61in the radial direction and the axial direction. The fixed portion131includes portions having axial positions overlapping the inner periphery-side projecting portions111to115and the inner periphery-side groove portions121to124of the band main body portion110. The extended portion132is disposed on the side close to the tip portion22of the piston band62(the upper side inFIG.2). The extended portion132is not fitted and fixed to the piston main body61in the axial direction. In other words, the extended portion132extends from the end portion on the tip portion22side of the fixed portion131toward the tip portion22side. The extended portion132is a portion which does not have an axial positions overlapping the inner periphery-side projecting portions111to115and the inner periphery-side groove portions121to124in the band main body portion110.

The extended portion132includes a contact portion135and a projecting portion136. The contact portion135comes into contact with the outer diameter surface of the protrusion portion71at the end portion on the side closest to the tip portion22of the piston main body61(the upper side inFIG.2). The projecting portion136protrudes from the contact portion135toward the tip portion22side in the axial direction. The projecting portion136protrudes in a substantially tapered shape such that the diameter becomes smaller toward the tip portion22, from the contact portion135to the tip portion22side in the axial direction with respect to the protrusion portion71with which the contact portion135comes into contact. In other words, the projecting portion136has a reduced diameter shape in which the diameter becomes smaller toward the protruding tip side.

An outer peripheral surface140facing the outside in the radial direction, of an outer peripheral portion139of the piston band62, has a first outer peripheral surface portion141, a second outer peripheral surface portion142, a third outer peripheral surface portion143, a fourth outer peripheral surface portion144, a fifth outer peripheral surface portion145, a sixth outer peripheral surface portion146, and a seventh outer peripheral surface portion147(an outer peripheral surface) in order from the side close to the tip portion22of the piston rod20(the upper side inFIG.2). The first outer peripheral surface portion141has a diameter that becomes larger as the axial distance from the tip portion22increases. The second outer peripheral surface has a cylindrical surface shape or a curved surface shape. The third outer peripheral surface portion143has a diameter that becomes smaller as the axial distance from the tip portion22increases. The fourth outer peripheral surface portion144has a cylindrical surface shape or a curved surface shape. The fifth outer peripheral surface portion145has a diameter that becomes larger as the axial distance from the tip portion22increases. The sixth outer peripheral surface portion146has a cylindrical surface shape or a curved surface shape. The seventh outer peripheral surface portion147(the outer peripheral surface) has a diameter that becomes smaller as the axial distance from the tip portion22increases. The diameter of the sixth outer peripheral surface portion146is smaller than the diameter of the second outer peripheral surface portion142and larger than the diameter of the fourth outer peripheral surface portion144.

Each of the first outer peripheral surface portion141, the third outer peripheral surface portion143, and the fifth outer peripheral surface portion145has a curved surface shape. The seventh outer peripheral surface portion147has a tapered surface shape. The first outer peripheral surface portion141is formed on the projecting portion136. The first outer peripheral surface portion141has an axial position overlapping the small-diameter surface portion108. The second outer peripheral surface portion142is formed on the contact portion135. The second outer peripheral surface portion142has an axial position overlapping the protrusion portion71. The third outer peripheral surface portion143is formed on the fixed portion131. The third outer peripheral surface portion143has axial positions overlapping the recess portion91, the protrusion portion72, the inner periphery-side projecting portion111, and the inner periphery-side groove portion121. The fourth outer peripheral surface portion144is formed on the fixed portion131. The fourth outer peripheral surface portion144has axial positions which overlap the protrusion portions73and74, the recess portions92and93, the inner periphery-side groove portions122and123, and the inner periphery-side projecting portions112and113. The fifth outer peripheral surface portion145is formed on the fixed portion131. The fifth outer peripheral surface portion145has axial positions overlapping the recess portion94and the inner periphery-side projecting portion114. The sixth outer peripheral surface portion146is formed on the fixed portion131. The sixth outer peripheral surface portion146has axial positions overlapping the protrusion portion75and the inner periphery-side groove portion124. The seventh outer peripheral surface portion147is formed on the fixed portion131. The seventh outer peripheral surface portion147has axial positions overlapping the recess portion95and the inner periphery-side projecting portion115. The seventh outer peripheral surface portion147has the entire axial position overlapping the recess portion95and the inner periphery-side projecting portion115.

Therefore, the fixed portion131includes the third outer peripheral surface portion143, the fourth outer peripheral surface portion144, the fifth outer periphery surface portion145, the sixth outer peripheral surface portion146, and the seventh outer peripheral surface portion147. The extended portion132includes the first outer peripheral surface portion141and the second outer peripheral surface portion142.

In the piston main body61, the small-diameter surface portion108, the protrusion portions71to75, and the recess portions91to95have axial positions overlapping the piston band62. The outer diameter surface of the protrusion portion76does not have an axial position overlapping the piston hand62.

The first outer peripheral surface portion141, the second outer peripheral surface portion142, and the third outer peripheral surface portion143configure an outer peripheral surface of an annular first bulging portion151having a shape that bulges outward in the radial direction in the piston band62. The second outer peripheral surface portion142forms the position of the maximum diameter in the first bulging portion151. The portion including the second outer peripheral surface portion142of the piston band62forms a large diameter portion152(a first projecting portion). The first bulging portion151and the large diameter portion152which is a part thereof configure the outer peripheral surface140of the piston band62. The second outer peripheral surface portion142of the large diameter portion152has the maximum outer diameter on the outer peripheral surface140. The first bulging portion151is configured of an outer peripheral portion of the extended portion132and an outer peripheral portion of the end portion on the extended portion132side of the fixed portion131.

The fifth outer peripheral surface portion145, the sixth outer peripheral surface portion146, and the seventh outer peripheral surface portion147configure an outer peripheral surface of an annular second bulging portion155having a shape that bulges outward in the radial direction in the piston band62. The sixth outer peripheral surface portion146forms the position of the maximum diameter in the second bulging portion155. The portion including the sixth outer peripheral surface portion146of the piston band62forms a medium diameter portion156(a second projecting portion). The second bulging portion155and the medium diameter portion156which is a part thereof configure the outer peripheral surface140of the piston hand62. The sixth outer peripheral surface portion146of the medium diameter portion156has a diameter different from that of the second outer peripheral surface portion142of the large diameter portion152. That is, the sixth outer peripheral surface portion146has a smaller diameter than the second outer peripheral surface portion142. Therefore, the outer diameter of the medium diameter portion156is smaller than the outer diameter of the large diameter portion152. In the piston hand62, the large diameter portion152and the medium diameter portion156are provided to be separated from each other in the axial direction. The second bulging portion155is configured of an outer peripheral portion of an end portion on the side opposite to the extended portion132in the axial direction of the fixed portion131.

The third outer peripheral surface portion143, the fourth outer peripheral surface portion144, and the fifth outer peripheral surface portion145configure the outer peripheral surface of an annular concave portion161having a shape that is concave inward in the radial direction in the piston band62. The fourth outer peripheral surface portion144forms the position of the minimum diameter of the concave portion161. The portion that includes the fourth outer peripheral surface portion144forms a s diameter portion162. The concave portion161and the small diameter portion162which is a part thereof configure the outer peripheral surface140of the piston band62. The fourth outer peripheral surface portion144of the small diameter portion162. has a diameter different from the diameters of the second outer peripheral surface portion142of the large diameter portion152and the sixth outer peripheral surface portion146of the medium diameter portion156. That is, the fourth outer peripheral surface portion144has a smaller diameter than the second outer peripheral surface portion142and the sixth outer peripheral surface portion146. Therefore, the outer diameter of the small diameter portion162is smaller than the outer diameters of the large diameter portion152and the mediums diameter portion156. The large diameter portion152and the medium diameter portion156are provided to protrude outward in the radial direction with respect to the small diameter portion162. The small diameter portion162is provided to be axially separated from the medium diameter portion156and the large diameter portion152. The small diameter portion162is configured of an outer peripheral portion at an intermediate position in the axial direction of the fixed portion131.

The outer peripheral surface of the extended portion132is configured of the first outer peripheral surface portion141and the second outer peripheral surface portion142. The inner peripheral surface of the extended portion132has a contact surface portion171having a cylindrical surface shape, an extended surface portion172(an inner peripheral surface), and a tip surface portion173. The contact surface portion171comes into surface contact with the outer diameter surface of the protrusion portion71. The extended surface portion172extends from the contact surface portion171to the tip portion22side in the axial direction (the upper side inFIG.2). The tip surface portion173connects the end edge portions on the tip portion22side in the axial direction, of the extended surface portion172and the first outer peripheral surface portion141. In contrast, the fixed portion131has the third outer peripheral surface portion143, the fourth outer peripheral surface portion144, the fifth outer peripheral surface portion145, the sixth outer peripheral surface portion146, and the seventh outer peripheral surface portion147.

The boundary between the extended surface portion172and the tip surface portion173forms an annular inner peripheral surface end175. The boundary between the first outer peripheral surface portion141and the tip surface portion173forms an annular outer peripheral surface end176. Both the inner peripheral surface end175and the outer peripheral surface end176are separated in the radial direction from the small-diameter surface portion108.FIG.2shows that both the inner peripheral surface end175and the outer peripheral surface end176are separated in the radial direction from the small-diameter surface portion108. However, only the inner peripheral surface end175may be in contact with the small-diameter surface portion108. Further, both the inner peripheral surface end175and the outer peripheral surface end176may be in contact with the small-diameter surface portion108.

The extended surface portion172is inclined so as to approach the small-diameter surface portion108from the outer diameter surface of the protrusion portion71at a position separated from the protrusion portion71. In other words, the extended surface portion172is inclined such that a diameter decrease toward the side close to the tip portion22of the piston rod20(the upper side inFIG.2). The extended surface portion172has a tapered shape. Therefore, the extended surface portion172, which is the inner peripheral surface of the extended portion132is inclined from the protrusion portion71toward the small-diameter surface portion108. At one end on the side close to the tip portion22of the piston band62, the extended surface portion172is inclined toward the piston main body61side from the large-diameter surface portion104to the small-diameter surface portion108of the stepped portion103. At one end on the side close to the tip portion22of the piston band62, the extended surface portion172is inclined from the large-diameter surface portion101toward the small-diameter surface portion108of the stepped portion103. The extended surface portion172is separated from the stepped surface102of the stepped portion103.

The tip surface portion173is inclined such that a diameter becomes larger toward the side close to the tip portion22of the piston rod20(the upper side inFIG.2). The tip surface portion173has a tapered shape.

The seventh outer peripheral surface portion147is provided at a fitting end portion181which is the end portion on the side opposite to the extended portion132of the fixed portion131. The fitting end portion181is provided at the other end on the side far from the tip portion22(the lower side inFIG.2), which is opposite to the extended portion132provided at one end on the side close to the tip portion22in the piston band62. The seventh outer peripheral surface portion147, which is the outer peripheral surface of the fitting end portion181, extends toward the protrusion portion76. An inner peripheral surface182of the fitting end portion181is in contact with the recess portion95adjacent to the protrusion portion76. Therefore, at the other end on the side far from the tip portion22of the piston band62, the seventh outer peripheral surface portion147is inclined toward the protrusion portion76, and the inner peripheral surface182is in contact with the recess portion95adjacent to the protrusion portion76.

As described above, the outer peripheral portion139of the piston hand62has the first bulging portion151, the concave portion161, and the second bulging portion155in order from the side close to the tip portion22of the piston rod20(the upper side inFIG.2). Further, the piston band62has the large diameter portion152, the medium diameter portion156, and the small diameter portion162at the outer peripheral portion in a natural state before being disposed in the cylinder11. The large diameter portion152is formed on the side close to the tip portion22of the piston rod20. The medium diameter portion156is formed on the side far from the tip portion22so as to have a smaller diameter than the large diameter portion152. The small diameter portion162is formed between the large diameter portion152and the medium diameter portion156so as to have a smaller diameter than the medium diameter portion156. In the natural state, the outer diameter of the large diameter portion152is larger than the inner diameter of the inner cylinder12of the cylinder11, and the outer diameter of the medium diameter portion156is smaller than the inner diameter of the inner cylinder12of the cylinder11. Therefore, the outer diameter of the small diameter portion162is also smaller than the inner diameter of the inner cylinder12of the cylinder11.

In other words, the piston band62has the small diameter portion162, the large diameter portion152, and the medium diameter portion156at the outer peripheral portion139in a state before being disposed in the cylinder11. The large diameter portion152is provided to protrude outward in the radial direction from the small diameter portion162on the side close to the tip portion22of the piston rod20with respect to the small diameter portion162. The medium diameter portion156is provided to protrude outward in the radial direction from the small diameter portion162on the side far from the tip portion22with respect to the small diameter portion162. The amount of protrusion of the large diameter portion152from the small diameter portion162is larger than the amount of protrusion of the medium diameter portion156from the small diameter portion162. The piston band62made of synthetic resin is formed in the above shape by controlling a temperature at the time of molding, a molding time, or the like.

In a case where the piston band62made of synthetic resin is mounted on the piston main body61made of metal, a perforated circular plate-shaped band material having a constant thickness, which will become the piston band62later, is prepared. This band material has an inner diameter smaller than the outer diameter of the piston main body61. This band material is deformed into a tapered shape while expanding the inner diameter with a conical jig, and finally deformed into a substantially cylindrical shape to cover the outer peripheral portion60of the piston main body61.

In this state, one end portion in the axial direction of the band material is heated and crimped to form the fitting end portion181that is fitted into the recess portion95. In this way, one end in the axial direction of the band material is fixed to the piston main body61. The seventh outer peripheral surface portion147is formed in a tapered shape by a jig at the time of the crimping. The second bulging portion155that includes the seventh outer peripheral surface portion147, the sixth outer peripheral surface portion146, and the fifth outer peripheral surface portion145is formed mainly due to the thickness portion of the band material fitted to the protrusion portion75side by the crimping being raised outward in the radial direction due to the protrusion portion75.

In a state where one end in the axial direction of the band material is fixed to the piston main body61in this way, these are inserted into a cylindrical tunnel of a heating chamber, the cylindrical tunnel having substantially the same inner diameter as the, inner diameter of the inner cylinder12. In this way, the band material is heated and deformed to form the inner periphery-side projecting portions111to114that are fitted into the recess portions91to94, so that the portion to become the fixed portion131later is generally formed. Then, the outer diameter of the band material is reduced due to the thickness portions to become the inner periphery-side projecting portions111to114entering the recess portions91to94, so that the portion to become the concave portion161later is generally formed.

At this time, the piston main body61has the small-diameter surface portion108having a shape in which the portion on the side opposite to the protrusion portions72to76with respect to the protrusion portion71extends outward in the axial direction. Therefore, in the band material, the portion to become the extended portion132later is not constrained on the side opposite to the fitting end portion181in the axial direction, and extends without limitation in the axial direction. At this time, the axial dimension of the protrusion portion71is larger than the axial dimensions of the protrusion portions72to75, and the amount of protrusion of the protrusion portion71from the groove bottom surfaces of the recess portions91to94becomes smaller than those of the protrusion portions72to75. Therefore, the portion to become the extended portion132later is easily tilted inward in the radial direction following the protrusion portion71.

Next, by cooling in a water cooling chamber, the band material is cooled to become the piston band62. Due to this cooling, the band material contracts in a state where the radial inside of the portion that is not fitted to the piston main body61in the axial direction and will become the extended portion132later is constrained by the protrusion portion71. As a result, the first bulging portion151that includes the first outer peripheral surface portion141, the second outer peripheral surface portion142, and the third outer peripheral surface portion143is formed, and the extended portion132including the contact portion135and the projecting portion136having a reduced diameter shape is formed.

When the piston17including the piston main body61and the piston band62is fitted into the inner peripheral portion63of the inner cylinder12made of metal, the extended portion132of the piston band62is disposed at the end portion on the rod guide25side. In this state, since the outer diameter of the large diameter portion152is larger than the inner diameter of the inner cylinder12of the cylinder11, the first bulging portion151that includes the large diameter portion152, of the piston band62, is elastically deformed inward in the radial direction to come into close contact with the cylindrical inner peripheral portion63of the inner cylinder12, as shown inFIG.3. At this time, since the outer diameter of the medium diameter portion156is smaller than the inner diameter of the inner cylinder12of the cylinder11, unless a radial external force, a so-called lateral force, is applied to the piston rod20, the second bulging portion155that includes the medium diameter portion156, of the piston band62, does not come into contact with the inner peripheral portion63of the inner cylinder12and has a radial gap between itself and the inner peripheral portion63of the inner cylinder12. At this time, the small diameter portion162also has a radial gap between itself and the inner peripheral portion63of the inner cylinder12. It is preferable that the second bulging portion155that includes the medium diameter portion156, of the piston band62, does not come into contact with the inner peripheral portion63of the inner cylinder12and has a radial gap between itself and the inner peripheral portion63of the inner cylinder12. However, slight contact may be made in a state where a lateral force is not applied.

In the shock absorber10having the piston17disposed in the inner cylinder12of the cylinder11in this manner, the piston17moves with respect to the cylinder11together with the piston rod20. At that time, if the lateral force that the piston rod20receives is less than a first predetermined value including 0, even if there is a case where the piston rod20is tilted with respect to the cylinder11with the rod guide25as a fulcrum, the piston17moves in the axial direction with only the first bulging portion151that includes the large diameter portion152coming into contact with the inner peripheral portion63of the inner cylinder12, as shown inFIG.4. The surface pressure distribution at this time is shown in a two-dot chain line Z1inFIG.4.

Further, if the piston rod20receives a lateral force equal to or larger than the first predetermined value and smaller than a second predetermined value, the amount of tilting of the piston rod20with respect to the cylinder11with the rod guide25as a fulcrum becomes larger than the above. In this way, the piston17moves in the axial direction with the first bulging portion151that includes the large diameter portion152and the second bulging portion155that includes the medium diameter portion156coming into contact with the inner peripheral portion63of the inner cylinder12, as shown inFIG.5. At this time, the small diameter portion162of the concave portion161does not come into contact with the inner peripheral portion63of the inner cylinder12. The contact area of the piston band62with the inner peripheral portion63at this time becomes larger than that in the above state where the contact is made only at the first bulging portion151. Therefore, the surface pressure that the piston band62receives becomes low. The surface pressure distributions at this time are as shown in two-dot chain lines Z2and Z3inFIG.5, and the surface pressure becomes lower than that in the case shown in the two-dot chain line Z1inFIG.4. The contact area between the piston band62and the inner peripheral portion63of the cylinder11becomes larger when a radial force acts on the piston rod20than when the radial force does not act on the piston rod20.

Here, PTFE is a material having a surface pressure dependence in which when the surface pressure (SP) is high, the friction coefficient (FC) is low, and when the surface pressure (SP) is low, the friction coefficient (EC) is high, as shown inFIG.6. Since the piston band62made of PTFE has a high friction coefficient when the surface pressure is low in this way, as shown by a solid line X1inFIG.7, the frictional force (FF) that is generated on the contact surface between the piston17and the cylinder11becomes larger in a case where the first bulging portion151and the second bulging portion155come into contact with the inner peripheral portion63of the inner cylinder12, so that the lateral force (LF) is large and the surface pressure is low, than in a case where only the first bulging portion151comes into contact with the inner peripheral portion63of the inner cylinder12, so that the lateral force (LF) is small and the surface pressure is high.

Further, if the piston rod20receives the lateral force (LF) equal to or larger than the second predetermined value, the amount of tilting of the piston rod20with respect to the cylinder11with the rod guide25as a fulcrum becomes even larger than the above. Then, the piston17moves in the axial direction with the first bulging portion151, the second bulging portion155, and the concave portion161coining into contact with the inner peripheral portion63of the inner cylinder12. The contact area of the piston band62with the inner peripheral portion63at this time becomes larger than that in the above state where the contact is made only at the first bulging portion151and the second bulging portion155, and the surface pressure (SP) becomes lower. Since the friction coefficient (FC) of the piston band62becomes high when the surface pressure (SP) is low, the frictional force that is generated on the contact surface between the piston17and the cylinder11becomes even larger, as shown by the solid line X1inFIG.7, than in a case where the contact with the inner peripheral portion63of the inner cylinder12is made only at the first bulging portion151and the second bulging portion155.

Patent Document 1 described above discloses a structure in which a piston band62athat is mounted on an outer peripheral portion of a piston main body61ahas an annular protrusion portion151a,which bulges outward in the radial direction with respect to a main body portion200a,only on one end side of the piston band62a(the rod guide (not shown) side), as shown inFIG.8A. When such a structure is defined as Comparative Example 1, in Comparative Example 1, in a state where the lateral force that the piston rod receives is small including 0, the annular protrusion portion151aon one side of the piston band62acomes into sliding contact with the inner peripheral portion63aof a cylinder11awith a high surface pressure, and therefore, the frictional force that is generated by the piston band62acan be suppressed to a small value, as shown by a two-dot chain line Xa inFIG.7. If the lateral force increases from this state and becomes relatively large, the frictional force that is generated by the piston band62aincreases due to the sliding contact with the inner peripheral portion of the cylinder11abeing made even at the other end portion of the piston band62ain addition to the annular protrusion portion151a.At this time, unless the lateral force becomes relatively large, the other end portion of the piston band62adoes not come into sliding contact with the inner peripheral portion63aof the cylinder11a,and therefore, the ratio of an increase in the frictional force of the piston band62ato an increase in the lateral force is low.

Further, Patent Document 1 discloses a structure in which a piston band62bthat is mounted on an outer peripheral portion of a piston main body61bhas annular protrusion portions151b,which bulge outward in the radial direction from a main body portion200band have the same outer diameter, at both end portions of the piston band62b,as shown inFIG.8B. When such a structure is defined as Comparative Example 2, in Comparative Example 2, as shown inFIG.8B, even in a state where the lateral force that the piston rod receives is small including 0, the annular protrusion portions151bon both sides of the piston band62bcome into sliding contact with an inner peripheral portion63bof a cylinder11b.Therefore, as shown by a broken line Xb inFIG.7, even in a state where the lateral force is small including 0, the surface pressure is low and the frictional force that is generated by the piston band62bbecomes large. If the lateral force increases from this state, although the frictional force that is generated by the piston band62bbecomes larger, the ratio of an increase of the frictional force is low because the annular protrusion portions151bon both sides are in sliding contact with the inner peripheral portion63bof the cylinder11bfrom the beginning.

In contrast, in the present embodiment, the piston band62has the large diameter portion152, the medium diameter portion156, and the small diameter portion162at the outer peripheral portion thereof in a natural state before being disposed in the cylinder11. The large diameter portion152is formed on the side close to the tip portion22of the piston rod20. The medium diameter portion156is formed on the side far from the tip portion22so as to have a smaller diameter than the large diameter portion152. The small diameter portion162is formed between the large diameter portion152and the medium diameter portion156so as to have a smaller diameter than the medium diameter portion156. In other words, the piston band62has the small diameter portion162, the large diameter portion152, and the medium diameter portion156at the outer peripheral portion thereof in a natural state before being disposed in the cylinder11. The large diameter portion152is provided to protrude outward in the radial direction from the small diameter portion162on the side close to the tip portion22of the piston rod20with respect to the small diameter portion162. The medium diameter portion156is provided to protrude outward in the radial direction from the small diameter portion162on the side far from the tip portion22with respect to the small diameter portion162. The amount of protrusion of the large diameter portion152in the radial direction from the small diameter portion162is larger than the amount of protrusion of the medium diameter portion156in the radial direction from the small diameter portion162.

Therefore, in a state where the lateral force that the piston rod20receives is small including 0, the first bulging portion151that includes the large diameter portion152comes into contact with the inner peripheral portion63of the inner cylinder12. If the lateral force becomes larger than this, the first bulging portion151that includes the large diameter portion152and the second bulging portion155that includes the medium diameter portion156is capable of coming into contact with the inner peripheral portion63of the inner cylinder12. Further, if the lateral force becomes larger than this, it becomes possible to increase the contact area with the inner peripheral portion63of the inner cylinder12of the concave portion161in addition to the first bulging portion151that includes the large diameter portion152and the second bulging portion155that includes the medium diameter portion156.

Therefore, as shown by the solid line X1inFIG.7, it becomes possible to obtain a frictional characteristic in which the frictional force (FF) that is generated by the piston band62is reduced when the lateral force (LF) is small, the frictional force (FF) that is generated by the piston band62is increased when the lateral force (LF) is large, and the ratio of the increase at that time is high. Therefore, the axial force of the piston rod20when the lateral force (LF) is small is suppressed to a small value, and when the lateral force (LF) is large, the axial force of the piston rod20can be increased.

In a state where the piston rod20does not receive a radial force, the medium diameter portion156of the piston band62has a radial gap between itself and the inner peripheral portion63of the cylinder11. Therefore, a frictional characteristic becomes more remarkable in which the frictional force that is generated by the piston band62is reduced when the lateral force is small, the frictional force that is generated by the piston band62is increased when the lateral force is large, and the ratio of the increase at that time is high. When the frictional force between the medium diameter portion156and the cylinder11in a state where the piston rod20does not receive a radial force is small, the medium diameter portion156may be in contact with the inner peripheral portion63of the cylinder11without a radial gap therebetwen.

The extended surface portion172, which is the inner peripheral surface at one end of the piston hand62, is inclined from the protrusion portion71toward the small-diameter surface portion108. The seventh outer peripheral surface portion147, which is the outer peripheral surface at the other end of the piston band62, is inclined toward the protrusion portion76. The inner peripheral surface182at the other end of the piston band62is in contact with the recess portion95adjacent to the protrusion portion76. In this way, in a step of mounting the piston band62on the piston60, the position of the piston band62with respect to the piston60can be restricted by the fitting end portion181. Further, the deformation of the piston hand62can be restricted at the fitting end portion181in the axial direction, and the side opposite to the fitting end portion181in the axial direction is not constrained and is capable of extending in the axial direction without limitation.

In the projecting portion136at one end of the piston band62, both the inner peripheral surface end175and the outer peripheral surface end176are separated from the small-diameter surface portion108. In this way, the projecting portion136at one end of the piston band62is not constrained by the small-diameter surface portion108, and therefore, the projecting portion136can be easily deformed into a reduced diameter shape having a smaller diameter toward the protruding tip side.

The protrusion height of the protrusion portion71of the piston main body, which comes into contact with the extended portion132of the piston hand62, is lower than the protrusion heights of the other protrusion portions72to76. In this way, it is possible to promote the deformation of the extended portion132of the piston band62into a reduced diameter shape of the projecting portion136.

The protrusion portion71of the piston main body61, which comes into contact with the extended portion132of the piston band62, has an axial dimension larger than the axial dimensions of all the protrusion portions72to75in which the piston band62comes into contact with the outer diameter surfaces thereof. In this way, the amount of radial bulging of the first bulging portion151that is formed when the piston band62is cooled can be increased. In other words, the large diameter portion152can be easily made larger than the medium diameter portion156.

The piston band62is formed of a material that is a low friction material and has a characteristic in which the friction coefficient increases when the surface pressure is low. Therefore, the piston band62has a frictional characteristic in which when the lateral force is small, the contact area with the cylinder11is small, and the surface pressure is high, the frictional force becomes small, and when the lateral force is large, the contact area with the cylinder11is large, and the surface pressure is low, the frictional force becomes large.

The piston band62has the medium diameter portion156haying a radial gap between itself and the inner peripheral portion63of the cylinder11in a state where the piston rod20does not receive a radial force. Therefore, the contact area between the piston hand62and the inner peripheral portion63of the cylinder11becomes larger when a radial force acts on the piston rod20than when a radial force does not act on the piston rod20. Therefore, a frictional characteristic become more remarkable in which when the lateral force is small, the contact area with the cylinder11is small, and the surface pressure is high, the frictional force becomes small, when the lateral force is large, the contact area with the cylinder11is large, the frictional force becomes large, and the surface pressure is low, and the ratio of the increase in frictional force is high.

Here, a frictional force characteristic that is generated by the shock absorber is important for creating a stable posture of a vehicle when the vehicle turns. In particular, the axial force of the shock absorber in a low piston speed region is important. In this region, the contribution of the frictional force that is generated between the piston band and the cylinder is high. If the frictional force that is generated between the piston band and the cylinder is small, although the riding comfort performance can be improved, the vehicle tends to be unstable when the vehicle turns.

In contrast, when the shock absorber10of the present embodiment is used for a suspension device of a vehicle, as described above, the frictional force that is generated by the piston band62can be reduced during normal traveling when the lateral force is small, and therefore, good riding comfort can be obtained. That is, in a situation where the lateral force that is applied to the shock absorber10is small, such as traveling in a straight line or the like, by bringing only the first bulging portion151on the rod guide25side of the piston band62into contact with the cylinder11, it is possible to reduce the frictional force of the shock absorber10, and therefore, it becomes possible to improve the riding comfort performance.

Further, when the vehicle turns with a large lateral force, since it is possible to increase the frictional force that is generated by the piston band62, the posture of the vehicle is stabilized. That is, in a situation where the lateral force that is applied to the shock absorber10is large, such as turning or the like, it is possible to increase the frictional force of the shock absorber10by bringing the second bulging portion155on the bottom portion15side of the cylinder11into contact with the cylinder11, in addition to the first bulging portion154on the rod guide25side of the piston band62. When the lateral force is further increased, it is possible to further increase the frictional force of the shock absorber10by bringing the concave portion161between the first bulging portion151and the second bulging portion155into contact with the cylinder11, so that it becomes possible to improve steering stability. Therefore, it is possible to achieve both improvement in riding comfort performance and improvement in steering stability.

In the embodiment described above, a configuration is made in which each of the large diameter portion152, the medium diameter portion156, and the small diameter portion162is formed in an annular shape with a constant diameter over the entire periphery of the outer peripheral surface140of the piston band62. However, at least one of the large diameter portion152and the medium diameter portion156protruding in the radial direction from the small diameter portion162may be partially formed in the circumferential direction. Further, portions having different diameters may be partially formed in three or more steps in the circumferential direction. In either case, the contact area between the piston band62and the inner peripheral portion63of the cylinder11becomes larger when a radial force acts on the piston rod20than when a radial force does not act on the piston rod20.

Further, in the embodiment described above, the plurality of protrusion portions71to76and recess portions91to95are provided on the outer periphery of the piston main body61. The protrusion portions71to76and the recess portions91to95are provided alternately along the axial direction, such as the protrusion portion71, the recess portion91, the protrusion portion72, the recess portion92, the protrusion portion73, the recess portion93, the protrusion portion74, the recess portion94, the protrusion portion75, the recess portion95, and the protrusion portion76. The protrusion portion71is formed at one end on the side close to the tip portion22of the piston rod20(the upper side inFIG.2). The protrusion portion76is formed at the other end on the side far from the tip portion22of the piston rod20(the lower side inFIG.2). The small-diameter surface portion108is formed on the side close to the tip portion22, of the protrusion portion71. However, one protrusion portion or only one recess portion may be formed on the outer periphery of the piston body61.

Further, the shapes of the other ends of the piston main body61and the piston band62are not limited to the shapes in the embodiment described above, and the inner peripheral surface182may not be in contact with the recess portion95adjacent to the protrusion portion76.

According to the first aspect of the present invention described above, the shock absorber includes: a bottomed cylinder-shaped cylinder in which a working fluid is enclosed; a piston rod having a base end portion that is inserted into the cylinder, and a tip portion that protrudes out of the cylinder; a piston that is fixed to the base end portion side of the piston rod and defines an inside of the cylinder into a one-side chamber and an other-side chamber; and a rod guide provided on a side opposite to a bottom portion of the cylinder to guide the piston rod. The piston includes a piston main body that is fixed to the piston rod, and a piston band that is provided on an outer peripheral portion of the piston body and is in sliding contact with an inner peripheral portion of the cylinder. The piston main body has a stepped portion including a large-diameter surface portion, a stepped surface portion, and a small-diameter surface portion, at one end on the side close to the tip portion of the piston rod, of the outer peripheral portion on which the piston hand is mounted. The piston band has, at an outer peripheral portion thereof, a large diameter portion that is formed on the side close to the tip portion of the piston rod, a medium diameter portion that is formed on the side far from the tip portion so as to have a smaller diameter than the large diameter portion, and a small diameter portion that is formed between the large diameter portion and the medium diameter portion so as to have a smaller diameter than the medium diameter portion, in a state before being disposed in the cylinder. At the one end on the side close to the tip portion of the piston rod, an inner peripheral surface is inclined toward the piston main body side from the large-diameter surface portion to the small-diameter surface portion of the stepped portion. In this way, it becomes possible to increase the ratio of an increase in the frictional force between the piston and the cylinder to an increase in the radial force that is applied to the piston rod.

According to a second aspect, in the first aspect, an inner peripheral surface at one end of the piston band is separated from a stepped surface of the stepped portion.

According to a third aspect, in the first or second aspect, at one end of the piston band, both an inner peripheral surface end and an outer peripheral surface end are separated from the small-diameter surface portion.

According to a fourth aspect, in any one of the first to third aspects, the piston main body includes a protrusion portion and a recess portion provided along the axial direction at the outer peripheral portion on which the piston band is mounted, a first protrusion portion is formed at one end on the side dose to the tip portion of the piston rod, and the small-diameter surface portion is formed on the side dose to the tip portion of the piston rod, of the first protrusion portion, and at one end of the piston band, an inner peripheral surface is inclined from the first protrusion portion toward the small-diameter surface portion.

According to a fifth aspect, in the fourth aspect, a second protrusion portion is formed at the other end on the side far from the tip portion, and at the other end of the piston hand, an outer peripheral surface is inclined toward the second protrusion portion, and an inner peripheral surface is in contact with the recess portion adjacent to the second protrusion portion.

According to a sixth aspect, in the fourth or fifth aspect, the first protrusion portion has a protrusion height lower than protrusion heights of other protrusion portions.

According to a seventh aspect, in any one of the fourth to sixth aspects, the first protrusion portion has an axial dimension larger than axial dimensions of other protrusion portions.

According to an eighth aspect, in any one of the first to seventh aspects, the piston band is formed of a material that is a low friction material and has a characteristic in which a friction coefficient increases when a surface pressure is low.

According to a ninth aspect, the shock absorber includes: a bottomed cylinder-shaped cylinder in which a working fluid is enclosed; a piston rod having a base end portion that is inserted into the cylinder, and a tip portion that protrudes out of the cylinder; a piston that is fixed to a base end portion side of the piston rod and defines an inside of the cylinder into a one-side chamber and an other-side chamber; and a rod guide provided on a side opposite to a bottom portion of the cylinder to guide the piston rod. The piston includes a piston main body that is fixed to the piston rod, and a piston band that is provided on an outer peripheral portion of the piston main body and is in sliding contact with an inner peripheral portion of the cylinder. The piston main body has a stepped portion including a large-diameter surface portion, a stepped surface portion, and a small-diameter surface portion, at one end on the side close to a tip portion of the piston rod, of an outer peripheral portion on which the piston hand is mounted. The piston band has, at an outer peripheral portion thereof, a small diameter portion, a first projecting portion that is provided to protrude from the small diameter portion on the side close to the tip portion of the piston rod with respect to the small diameter portion, and a second projecting portion that is provided to protrude from the small diameter portion on the side far from the tip portion with respect to the small diameter portion, and is smaller than the first projecting portion, in a state before being disposed in the cylinder. At one end of the piston band on the side close to the tip portion of the piston rod, an inner peripheral surface is inclined from the large-diameter surface portion toward the small-diameter surface portion. In this way, it becomes possible to increase the ratio of an increase in frictional force between the piston and the cylinder to an increase in the radial force that is applied to the piston rod.

According to a tenth aspect, in the ninth aspect, the piston main body includes a protrusion portion and a recess portion provided along the axial direction at the outer peripheral portion on which the piston band is mounted, and a first protrusion portion is formed at one end on the side close to the tip portion of the piston rod, and at one end of the piston band, the inner peripheral surface is inclined from the first protrusion portion toward the small-diameter surface portion.

According to an eleventh aspect, in the tenth aspect, a second protrusion portion is formed at the other end on the side far from the tip portion, the small-diameter surface portion is formed on the side close to the tip portion of the piston rod, of the first protrusion portion, and at the other end of the piston band, an outer peripheral surface is inclined toward the second protrusion portion, and an inner peripheral surface is in contact with the recess portion adjacent to the second protrusion portion.

According to a twelfth aspect, in any one of the first to eleventh aspects, a contact area between the piston band and the inner peripheral portion of the cylinder becomes larger when a radial force acts on the piston rod than when a radial force does not act on the piston rod.

INDUSTRIAL APPLICABILITY

According to the shock absorber described above, it is possible to increase the ratio of are increase in the frictional force between the piston and the cylinder to an increase in the radial force that is applied to the piston rod.

REFERENCE SIGNS LIST

10: Shock absorber11: Cylinder15: Bottom portion17: Piston18: One-side chamber19: Other-side chamber20: Piston rod21: Base end portion22: Tip portion25: Rod guide60: Outer peripheral portion61: Piston main body62: Piston band63: Inner peripheral portion71: Protrusion portion (first protrusion portion)72to75: Protrusion portion76: Protrusion portion (second protrusion portion)91to95: Recess portion101: Large-diameter surface portion102: Stepped surface portion103: Stepped portion108: Small-diameter surface portion139: Outer peripheral portion147: Seventh outer peripheral surface portion (outer peripheral surface)152: Large diameter portion (first projecting portion)156: Medium diameter portion (second projecting portion)162: Small diameter portion172: Extended surface portion (inner peripheral surface)175: Inner peripheral surface end176: Outer peripheral surface end187: inner peripheral surface