Patent Description:
There has been known an extensible member that includes a tubular extensible portion made of a thermoplastic elastomer having an inner peripheral surface and an outer peripheral surface in a bellows shape. For example, <CIT> and <CIT> disclose a bound bumper for automobile and a dust cover, respectively, according to the preamble of claim <NUM>. <CIT> and <CIT> disclose a Stroke-limiting thrust bearing and a jounce bumper, respectively, but does not disclose at least the feature of claim <NUM> that the plurality of first protrusions and the second protrusions are disposed separately in alternation in a circumferential direction on the first contact surfaces and the second contact surfaces contactable with one another. Further, <CIT> (Patent Literature <NUM>) discloses that the extensible member is a bump stopper disposed between a cylinder of a shock absorber and a bracket secured to a piston rod projecting from the cylinder. The bump stopper absorbs an impact of the shock absorber during a large contraction by extension and contraction of an extensible portion. In the extensible member disclosed in Patent Literature <NUM>, roots of an inner peripheral surface of the extensible portion are positioned radially inward of all crests of an outer peripheral surface of the extensible portion. Crests of the inner peripheral surface of the extensible portion are positioned radially inward of all roots of the outer peripheral surface of the extensible portion. This is because to facilitate deformation of the extensible portion made of a thermoplastic elastomer.

However, in the conventional technique, when the extensible portion is contracted and the extensible portion is folded with the roots of the inner peripheral surface and the roots of the outer peripheral surface as fulcrums, two surfaces opposed in an axis direction are brought into close contact. The conventional technique has a problem that air is less likely to enter between the two surfaces in close contact when the two surfaces in close contact are separated at once, and therefore abnormal noise is likely to occur.

The present invention has been made to solve the above-described problem. An object of the present invention is to provide an extensible member that allows abnormal noise during extension and contraction of an extensible portion to be less likely to occur.

The above mentioned object is achieved by the extensible member according to claim <NUM>.

The protrusion includes a plurality of first protrusions that project from the first contact surfaces and a plurality of second protrusions that project from the second contact surfaces. The plurality of respective first protrusions and second protrusions may be disposed at regular intervals around the center axis of the extensible portion. When viewed in the axial direction of the center axis of the extensible portion, all of the first protrusions and the second protrusions may be disposed on an imaginary circle at a predetermined radius around the center axis. The second protrusion may be positioned at a center in a circumferential direction of the first protrusions adjacent in the circumferential direction. The first protrusion may be positioned at a center in the circumferential direction of the second protrusions adjacent in the circumferential direction.

With the extensible member according to claim <NUM>, the inner crests are positioned radially inward of all of the outer roots, and the inner roots are positioned radially inward of all of the outer crests. The extensible portion made of the thermoplastic elastomer is likely to axially contract such that the extensible portion is folded with the inner roots and the outer roots as fulcrums. When the extensible portion is folded, the first contact surfaces attempt to be in close contact with the second contact surfaces. However, since the at least one protrusion is positioned on at least one of the first contact surfaces and the second contact surfaces, the first contact surfaces and the second contact surfaces are less likely to be in close contact around the protrusion. When the first contact surface and the second contact surface are separated at once after being in close contact, the extensible member allows facilitating an entrance of air between the first contact surface and the second contact surface from around the protrusion. The extensible member allows abnormal noise during extension and contraction of the extensible portion to be less likely to occur.

According to the extensible member as defined by claim <NUM>, during the extension and contraction of the extensible portion, a way of deformation of the first contact surface and a way of deformation of the second contact surface can be close to be uniform. The concentration of stress on one of the first contact surface or the second contact surface can be suppressed. The extensible member allows further suppressing the reduction in durability of the extensible portion caused by disposing the protrusions.

According to the extensible member according to claim <NUM>, during the extension and contraction of the extensible portion, an amount of deformation of the outer portion becomes smaller than an amount of deformation of the inner portion. The protrusion is positioned on the outer portion where the amount of deformation is small. Although depending on a size of the protrusion, compared with a case where the protrusion is positioned on the inner portion where the amount of deformation is large, the extensible member allows stress to be less likely to concentrate on the extensible portion around the protrusion during the extension and contraction of the extensible portion. In addition to the effect of claim <NUM>, the extensible member allows suppressing reduction in durability of the extensible portion caused by disposing the protrusion.

The protrusion is positioned on the outer portion at a position separated radially outward from the outer root with respect to the inner portion. The extensible member allows facilitating quick entrance of air between the first contact surface and the second contact surface with the protrusion during the extension and contraction of the extensible portion. The extensible member allows abnormal noise during the extension and contraction of the extensible portion to be more less likely to occur.

According to the extensible member according to claim <NUM>, when the extensible portion extends after the contraction, the perpendicular portions in contact are likely to be separated from radially inward first. Since the protrusion is positioned on the perpendicular portion, air is likely to enter radially inward of the perpendicular portion during the extension of the extensible portion. In addition to the effect of claim <NUM>, the extensible member allows abnormal noise during the extension and contraction of the extensible portion to be more less likely to occur.

In the extensible member according to claim <NUM>, the protrusions are disposed in rotational symmetry with respect to the center axis of the extensible portion. A way of the deformation of the extensible portion is close to be uniform over the circumferential direction. The stress is less likely to concentrate on a part in the circumferential direction of the extensible portion during the extension and contraction. In addition to the effect of any of claims <NUM> to <NUM>, the extensible member allows further suppressing the reduction in durability of the extensible portion caused by disposing the protrusion.

With the extensible member according to claim <NUM>, a circumferential dimension of the protrusion is larger than a radial dimension of the protrusion. During the contraction of the extensible portion, the first contact surfaces and the second contact surfaces are less likely to be in close contact at a further wide range. During the contraction of the extensible portion, the amounts of deformations of the first contact surface and the second contact surface are likely to differ according to radial positions. Compared with a case where the radial dimension of the protrusion is larger than the circumferential dimension of the protrusion, the extensible member allows decreasing the difference in amount of deformation of the protrusions in length directions of the protrusions. The extensible member allows suppressing the concentration of stress around a part of the protrusion in the length direction during the extension and contraction of the extensible portion. In addition to the effect of any of claims <NUM> to <NUM>, the extensible member allows further suppressing the reduction in durability of the extensible portion caused by disposing the protrusions.

Preferred embodiments will be described below with reference to the attached drawings. A stopper unit <NUM> that includes an extensible member <NUM> and a shock absorber <NUM> in a first embodiment will be described with reference to <FIG> and <FIG>. <FIG> is a cross-sectional view that includes a center axis C of a piston rod <NUM> of the shock absorber <NUM> and a cross-sectional view of the stopper unit <NUM> mounted to the shock absorber <NUM>. <FIG> is a partially enlarged cross-sectional view of the stopper unit <NUM> that enlarges a part II of <FIG>.

As illustrated in <FIG> and <FIG>, the shock absorber <NUM> is a part of a suspension that mainly connects a wheel (not illustrated) and a vehicle body (not illustrated). The suspension is to buffer vibrations from the wheel to the vehicle body. The shock absorber <NUM> attenuates vibrations of a coil spring (not illustrated), which absorbs an impact from the wheel, while supporting the vehicle body. The shock absorber <NUM> mainly includes a cylinder <NUM> and the piston rod <NUM>. The cylinder <NUM> is mounted on the wheel side. The piston rod <NUM> projects from an axial end surface <NUM> of the cylinder <NUM>. In the shock absorber <NUM>, in accordance with a load input from the wheel, an amount of projection of the piston rod <NUM> from the cylinder <NUM> changes and extends and contracts to attenuate the vibrations.

The stopper unit <NUM> includes a tubular bracket <NUM> and a tubular extensible member (stopper) <NUM>. The piston rod <NUM> is mounted to the bracket <NUM>. The extensible member <NUM> is mounted on the cylinder <NUM> side of the bracket <NUM>. The bracket <NUM> includes a cylinder portion <NUM>, a circular plate portion <NUM>, an elastic portion <NUM>, and a first fixture <NUM> and a second fixture <NUM>. A distal end of the piston rod <NUM> is secured to the cylinder portion <NUM>. The circular plate portion <NUM> projects radially outward from the cylinder portion <NUM>. The elastic portion <NUM> is formed of an elastic body, such as rubber and a thermoplastic elastomer. The elastic portion <NUM> surrounds a peripheral area of the circular plate portion <NUM>. The elastic portion <NUM> is axially sandwiched by the respective first fixture <NUM> and second fixture <NUM>.

The first fixture <NUM> and the second fixture <NUM> are metallic members secured to the vehicle body side. The first fixture <NUM> is a plate material positioned on a side opposite to the cylinder <NUM> with respect to the elastic portion <NUM>. The second fixture <NUM> is a tubular body that surrounds the cylinder <NUM> side and radially outward of the elastic portion <NUM> to support the elastic portion <NUM>.

The second fixture <NUM> includes an annular contact surface <NUM> and a press-fitted surface <NUM>. The contact surface <NUM> is an axial end surface on the cylinder <NUM> side. The contact surface <NUM> is formed to be approximately perpendicular to the center axis C and faces the axial end surface <NUM> of the cylinder <NUM>. The extensible member <NUM> is compressed in the axis direction between the contact surface <NUM> and the axial end surface <NUM>.

The press-fitted surface <NUM> is an inner peripheral surface from an inner peripheral edge of the contact surface <NUM> toward the elastic portion <NUM>. The press-fitted surface <NUM> is formed to be parallel to the center axis C on a cross-sectional surface including the center axis C. That is, the approximately entire press-fitted surface <NUM> is formed to be approximately perpendicular to the contact surface <NUM>. The press-fitted surface <NUM> is concentrically disposed at a predetermined space from the piston rod <NUM> and the cylinder portion <NUM>. To the press-fitted surface <NUM>, a mounting portion <NUM>, which will be described later, of the extensible member <NUM> is press-fitted. A fitting recessed portion <NUM> to which a claw portion <NUM> of the mounting portion <NUM> is fitted is disposed at the approximately center in the axis direction on the press-fitted surface <NUM>.

The extensible member <NUM> is a tubular member disposed between the cylinder <NUM> and the bracket <NUM> so as to surround an outer periphery of the piston rod <NUM>. The extensible member <NUM> is formed in an annular shape around the center axis C on a cross-sectional surface perpendicular to the center axis C. That is, the center axis C of the piston rod <NUM> is also the center axis of the extensible member <NUM>.

The extensible member <NUM> is a member made of a thermoplastic elastomer in which respective portions are integrally formed. A kind of the thermoplastic elastomer forming the extensible member <NUM> is determined according to a hard segment significantly contributing to properties of the thermoplastic elastomer. Examples of the kind of the thermoplastic elastomer include a styrene base, an olefin base, a diene base, a vinyl chloride base, a urethane base, an ester base, an amide base, and a fluorine base. The thermoplastic elastomer of this embodiment is a block copolymer of a hard segment of an ester base (for example, polybutylene terephthalate) and a soft segment of aliphatic polyether (for example, polytetramethylene ether glycol). A commercially available thermoplastic elastomer used for the thermoplastic elastomer of this embodiment includes, for example, "Hytrel" (registered trademark) manufactured by DU PONT-TORAY CO.

With the extensible member <NUM>, the extensible member <NUM> is sandwiched between the axial end surface <NUM> of the cylinder <NUM> and the contact surface <NUM> of the bracket <NUM> during large contraction of the shock absorber <NUM> and compressed in the axis direction to absorb an impact during the compression by an elastic force from the extensible member <NUM>. The extensible member <NUM> includes the approximately cylindrically-shaped mounting portion <NUM>, a tubular extensible portion <NUM>, and a plurality of first protrusions <NUM> and second protrusions <NUM> (see <FIG>). The mounting portion <NUM> is configured to be fitted to the press-fitted surface <NUM> on the second fixture <NUM> by press-fitting. The extensible portion <NUM> is continuous with an end portion in the axis direction on the cylinder <NUM> side of the mounting portion <NUM>. The plurality of first protrusions <NUM> and second protrusions <NUM> project from an outer peripheral surface of the extensible portion <NUM>.

The mounting portion <NUM> includes the claw portion <NUM> that projects radially outward from an outer peripheral surface of a distal end in the axis direction on the side opposite to the extensible portion <NUM>. The claw portion <NUM> is a part discontinuously disposed in a circumferential direction of the mounting portion <NUM>. By fitting the claw portion <NUM> to the fitting recessed portion <NUM> on the press-fitted surface <NUM>, the mounting portion <NUM> is less likely to come off from the bracket <NUM>.

The extensible portion <NUM> is a part axially compressed between the axial end surface <NUM> of the cylinder <NUM> and the contact surface <NUM> of the bracket <NUM> to absorb an impact. The outer peripheral surface and the inner peripheral surface of the extensible portion <NUM> are formed in a bellows shape in which a plurality of mountains and troughs are continuous in the axis direction. The outer peripheral surface of the extensible portion <NUM> is provided with an end surface <NUM> in the axis direction, a pressure receiving surface <NUM>, a plurality of outer crests <NUM> as crests of mountains, a plurality of outer roots <NUM> as bottoms of the troughs, and first contact surfaces <NUM> and second contact surfaces <NUM> between the outer crests <NUM> and the outer roots <NUM>.

The end surface <NUM> is continuous with the outer peripheral surface of the mounting portion <NUM> so as to project radially outward from the mounting portion <NUM>. The end surface <NUM> is a surface pressed against the contact surface <NUM> of the bracket <NUM> during large contraction of the shock absorber <NUM> to be brought into close contact with the contact surface <NUM>. The mounting portion <NUM> axially projects from the end surface <NUM>. The pressure receiving surface <NUM> is a surface that can be in contact with the axial end surface <NUM> of the cylinder <NUM>. The pressure receiving surface <NUM> is a surface that is in surface contact with the axial end surface <NUM> of the cylinder <NUM> during large contraction of the shock absorber <NUM> to be brought into close contact with the axial end surface <NUM>.

The inner peripheral surface of the extensible portion <NUM> includes a plurality of inner crests <NUM> as crests of mountains and a plurality of inner roots <NUM> as bottoms of troughs. The respective inner crests <NUM> are positioned radially inward of all of the outer roots <NUM>. The respective inner roots <NUM> are positioned radially inward of all of the outer crests <NUM>. That is, in an imaginary plane perpendicular to the center axis C, the inner root <NUM> is always positioned on the imaginary plane where the outer crest <NUM> is positioned. The inner crest <NUM> is always positioned on the imaginary plane where the outer root <NUM> is positioned.

According to the positional relationship between the respective parts, the extensible portion <NUM> axially contracts such that the extensible portion <NUM> is folded with the inner roots <NUM> and the outer roots <NUM> as fulcrums. Generally, even when the extensible portion <NUM> is formed with the thermoplastic elastomer harder than rubber and foam synthetic resin, the extensible portion <NUM> is likely to axially contract.

In this embodiment, a distance from the center axis C to the plurality of outer crests <NUM> decreases from the end surface <NUM> side to the pressure receiving surface <NUM> side. A distance from the center axis C to the plurality of outer roots <NUM>, a distance from the center axis C to the plurality of inner crests <NUM>, and a distance from the center axis C to the plurality of inner roots <NUM> each decrease toward the pressure receiving surface <NUM> side.

The outer root <NUM> and the inner root <NUM> are point-like on the cross-sectional surface including the center axis C. The first contact surface <NUM> and the second contact surface <NUM> are parts contactable with one another when the extensible portion <NUM> axially contracts. A part continuous with the end surface <NUM> side of the outer root <NUM> is the first contact surface <NUM>. A part continuous with the pressure receiving surface <NUM> side of the outer root <NUM> is the second contact surface <NUM>. The outer crest <NUM> and the inner crest <NUM> are parts not in contact with one another when the extensible portion <NUM> axially contracts and are formed of convex curved lines on the cross-sectional surface including the center axis C.

The first contact surface <NUM> includes an inner portion 35a and an outer portion 35b. The inner portion 35a is continuous with the whole circumference of the outer root <NUM>. The inner portion 35a is formed of a concave curved line on the cross-sectional surface including the center axis C. The outer portion 35b connects the whole circumference of the inner portion 35a and the whole circumference of the outer crest <NUM>. The outer portion 35b is formed of a convex curved line on the cross-sectional surface including the center axis C. A boundary 35c as an inflection point between the inner portion 35a and the outer portion 35b is continuous over the whole circumference of the outer peripheral surface of the first contact surface <NUM>.

Similarly, the second contact surface <NUM> includes an inner portion 36a and an outer portion 36b. The inner portion 36a is continuous with the outer root <NUM> and formed of a concave curved line on the cross-sectional surface including the center axis C. The outer portion 36b connects the inner portion 36a and the outer crest <NUM> and is formed of a convex curved line on the cross-sectional surface including the center axis C. A boundary 36c as an inflection point between the inner portion 36a and the outer portion 36b is continuous over the whole circumference of the outer peripheral surface of the second contact surface <NUM>.

Next, the first protrusions <NUM> and the second protrusions <NUM> will be described with reference to <FIG> and <FIG>. <FIG> is a front view of the extensible member <NUM>. <FIG> is a cross-sectional view of the extensible member <NUM> along the line IV-IV of <FIG> omits the illustration of a part of the extensible portion <NUM> in the axis direction (a part on the pressure receiving surface <NUM> side). <FIG> illustrates the boundaries 35c, 36c by the two-dot chain lines.

As illustrated in <FIG> and <FIG>, the first protrusion <NUM> projects from the outer portion 35b, which is positioned radially outward with respect to the boundary 35c in the first contact surface <NUM>. The second protrusion <NUM> projects from the outer portion 36b, which is positioned radially outward with respect to the boundary 36c in the second contact surface <NUM>. The first protrusions <NUM> and the second protrusions <NUM> are integrally molded with the extensible portion <NUM>. The first protrusion <NUM> and the second protrusion <NUM> are formed in an approximately hemispherical shape having shapes and dimensions same as one another. That is, a diameter L2 of the hemisphere is approximately same as radial dimensions and circumferential dimensions of the first protrusion <NUM> and the second protrusion <NUM>.

The eight first protrusions <NUM> are disposed at regular intervals in the circumferential direction around the center axis C and disposed in rotational symmetry with respect to the center axis C. Similarly, the eight second protrusions <NUM> are disposed at regular intervals in the circumferential direction around the center axis C and disposed in rotational symmetry with respect to the center axis C. The respective first protrusion <NUM> and second protrusion <NUM> have the same radial distance from the center axis C. That is, all of the first protrusions <NUM> and the second protrusions <NUM> are disposed on an imaginary circle at a predetermined radius around the center axis C.

An interval L1 between the first protrusions <NUM> adjacent in the circumferential direction and the interval L1 of the second protrusions <NUM> adjacent in the circumferential direction are same. The second protrusion <NUM> is positioned at the center in the circumferential direction of the first protrusions <NUM> adjacent in the circumferential direction. The first protrusion <NUM> is positioned at the center in the circumferential direction of the second protrusions <NUM> adjacent in the circumferential direction. That is, the first protrusions <NUM> and the second protrusions <NUM> are disposed separately in the circumferential direction in alternation. The intervals of the first protrusions <NUM> and the second protrusions <NUM> adjacent in the circumferential direction are also the same over the whole circumference.

With the extensible member <NUM> as described above, the inner crests <NUM> are positioned radially inward of all of the outer roots <NUM> and the inner roots <NUM> are positioned radially inward of all of the outer crests <NUM>. The extensible portion <NUM> made of a thermoplastic elastomer is likely to axially contract such that the extensible portion <NUM> is folded with the inner roots <NUM> and the outer roots <NUM> as fulcrums. When the extensible portion <NUM> is folded, the first contact surfaces <NUM> attempt to be in close contact with the second contact surfaces <NUM>. When the first contact surfaces <NUM> are separated from the second contact surfaces <NUM> at once after being in close contact, in a case where air is less likely to enter between the first contact surfaces <NUM> and the second contact surfaces <NUM>, abnormal noise is likely to occur in accordance with the extension and contraction of the extensible portion <NUM>.

In this embodiment, the first protrusion <NUM> and the second protrusion <NUM> project from the first contact surface <NUM> and the second contact surface <NUM>, respectively. The first contact surface <NUM> and the second contact surface <NUM> are less likely to be in close contact around the first protrusion <NUM> and the second protrusion <NUM>. When a part of the first contact surface <NUM> and the second contact surface <NUM> are separated at once after being in close contact, the extensible member <NUM> allows facilitating the entrance of air between the first contact surface <NUM> and the second contact surface <NUM> from around the first protrusion <NUM> and the second protrusion <NUM>. The extensible member <NUM> allows abnormal noise during the extension and contraction of the extensible portion <NUM> to be less likely to occur.

Note that, in contrast to the conventional extensible member without the first protrusions <NUM> or the second protrusions <NUM>, stress is likely to concentrate on parts (the first contact surfaces <NUM> and the second contact surfaces <NUM>) between which the first protrusions <NUM> and the second protrusions <NUM> are interposed in the extensible portion <NUM> during the extension and contraction of the extensible portion <NUM> in the extensible member <NUM> in some cases. During the extension and contraction of the extensible portion <NUM>, as an amount of deformation of the parts where the first protrusions <NUM> and the second protrusions <NUM> are disposed becomes large, the first protrusions <NUM> and the second protrusions <NUM> also largely deform. Stress is likely to concentrate on the extensible portion <NUM> around the first protrusions <NUM> and the second protrusions <NUM>.

When the extensible portion <NUM> contracts by being folded with the outer roots <NUM> as the fulcrums, the amount of deformation of the inner portions 35a, 36a formed of the concave curved lines becomes smaller than the amount of deformation of the outer portions 35b, 36b formed of the convex curved lines. In this embodiment, the first protrusion <NUM> and the second protrusion <NUM> are disposed in the outer portions 35b, 36b, respectively. Compared with a case where the first protrusion <NUM> and the second protrusion <NUM> are disposed in the inner portions 35a, 36a where the amount of deformation is large, the extensible member <NUM> can suppress the concentration of stress around the first protrusion <NUM> and the second protrusion <NUM> during the extension and contraction of the extensible portion <NUM>. The extensible member <NUM> allows suppressing reduction in durability of the extensible portion <NUM> caused by disposing the first protrusions <NUM> and the second protrusions <NUM>.

Especially, in the thermoplastic elastomer used in this embodiment, a large strain is likely to remain (plastic deformation is likely to occur) during a contraction for the first time after molding, compared with rubber. After the first contraction of the extensible portion <NUM> made of a thermoplastic elastomer, an amount of plastic deformation of the inner portions 35a, 36a, which easily deform during the extension and contraction, is large and the amount of plastic deformation of the outer portions 35b, 36b, which are less likely to deform during the extension and contraction, is small.

The first protrusion <NUM> and the second protrusion <NUM> are disposed in the outer portions 35b, 36b, respectively, where the amount of plastic deformation is small. The way of deformation of the extensible portion <NUM> after the plastic deformation is less likely to change according to the presence/absence of the first protrusion <NUM> and the second protrusion <NUM>. A buffering property and durability of the extensible portion <NUM> according to the way of deformation become approximately similar between the cases where the first protrusions <NUM> and the second protrusions <NUM> are present and absent. Using the extensible portion <NUM> designed for the conventional extensible member in which the first protrusions <NUM> and the second protrusions <NUM> are absent, the buffering property and durability of the extensible portion <NUM> of the extensible member <NUM> including the first protrusions <NUM> and the second protrusions <NUM> can be easily set.

The outer portions 35b, 36b are positioned separately from the outer root <NUM> outward in the radial direction. When the extensible portion <NUM> extends after contraction, the first contact surface <NUM> is separated from the second contact surface <NUM> in the order from radially outward in many cases. That is, the first contact surface <NUM> is separated from the second contact surface <NUM> in the order from the outer portions 35b, 36b and the inner portions 35a, 36a in many cases. By providing the first protrusions <NUM> and the second protrusions <NUM> in the outer portions 35b, 36b, air is likely to quickly enter between the first contact surfaces <NUM> and the second contact surfaces <NUM> by the first protrusions <NUM> and the second protrusions <NUM>. The extensible member <NUM> allows abnormal noise during the extension and contraction of the extensible portion <NUM> to be more less likely to occur.

In the extensible member <NUM>, the respective first protrusions <NUM> and second protrusions <NUM> are disposed in rotational symmetry with respect to the center axis C. The way of deformation of the extensible portion <NUM> during the extension and contraction is close to be uniform over the circumferential direction. The concentration of stress at a part of the extensible portion <NUM> in the circumferential direction during the extension and contraction can be suppressed. The extensible member <NUM> allows further suppressing the reduction in durability of the extensible portion <NUM> caused by disposing the first protrusions <NUM> and the second protrusions <NUM>.

The respective radial distances from the center axis C to the plurality of first protrusions <NUM> and second protrusions <NUM> are same. The extensible member <NUM> allows the way of deformation of the extensible portion <NUM> to be further close to be uniform over the circumferential direction. The plurality of respective first protrusions <NUM> and second protrusions <NUM> are disposed at regular intervals in the circumferential direction. The extensible member <NUM> allows the way of deformation of the extensible portion <NUM> to be further close to be uniform over the circumferential direction.

The plurality of first protrusions <NUM> and second protrusions <NUM> are disposed separately in the circumferential direction in alternation in the first contact surfaces <NUM> and the second contact surfaces <NUM> contactable with one another. During the extension and contraction of the extensible portion <NUM>, the way of deformation of the first contact surface <NUM> and the way of deformation of the second contact surface <NUM> are close to be uniform. The concentration of stress on one of the first contact surface <NUM> or the second contact surface <NUM> can be suppressed. The extensible member <NUM> allows further suppressing the reduction in durability of the extensible portion <NUM> caused by disposing the first protrusions <NUM> and the second protrusions <NUM>.

In the extensible member <NUM>, the interval L1 between the first protrusions <NUM> is the same as the interval L1 between the second protrusions <NUM>. The way of deformation of the first contact surface <NUM> and the way of deformation of the second contact surface <NUM> during the extension and contraction of the extensible portion <NUM> are further close to be uniform. The first protrusion <NUM> and the second protrusion <NUM> have the shapes and dimensions same as one another. With the extensible member <NUM>, the way of deformation of the first contact surface <NUM> and the way of deformation of the second contact surface <NUM> during the extension and contraction of the extensible portion <NUM> can be further close to be uniform.

The radial distances from the center axis C to all of the first protrusions <NUM> and the second protrusions <NUM> are same, and the intervals between the first protrusions <NUM> and the second protrusions <NUM> are same over the whole circumference. With the extensible member <NUM>, the way of deformation of the first contact surfaces <NUM> and the way of deformation of the second contact surfaces <NUM> during the extension and contraction of the extensible portion <NUM> can be close to be uniform over the circumferential direction.

The first protrusion <NUM> and the second protrusion <NUM> are formed in the approximately hemispherical shape in which the circumferential dimensions L2 and the radial dimensions L2 are same. In the extensible member <NUM>, compared with a case where the first protrusion <NUM> and the second protrusion <NUM> have the circumferential dimensions greater than the radial dimensions, when the first protrusion <NUM> and the second protrusion <NUM> are separated from the first contact surface <NUM> and the second contact surface <NUM> at once after being in close contact, air can quickly enter between the first contact surface <NUM> and the second contact surface <NUM>. This is because that air goes around both sides in the circumferential direction of the first protrusion <NUM> and the second protrusion <NUM> and quickly enters between the first contact surface <NUM> and the second contact surface <NUM> in the center axis C side of the first protrusion <NUM> and the second protrusion <NUM>. The extensible member <NUM> allows abnormal noise during the extension and contraction to be more less likely to occur.

A second embodiment will be described with reference to <FIG>, <FIG>. In the first embodiment, the case where the first protrusion <NUM> and the second protrusion <NUM> have the approximately hemispherical shape has been described. In the second embodiment, a case where a circumferential dimension L3 of a first protrusion <NUM> and a second protrusion <NUM> is formed larger than the radial dimension L2 of the first protrusion <NUM> and the second protrusion <NUM> will be described. Same reference numerals are given to parts same as those of the first embodiment and the description thereof will be omitted.

<FIG> is a partial cross-sectional view of an extensible member <NUM> in the second embodiment. In <FIG>, the right side with respect to the center axis C in the paper is the cross-sectional view of the extensible member <NUM> and the left side with respect to the center axis C in the paper is a front view of the extensible member <NUM>. <FIG> is a cross-sectional view of the extensible member <NUM> along the line VIa-VIa of <FIG>. <FIG> is a cross-sectional view of the extensible member <NUM> along the line VIb-VIb of <FIG> illustrates a first contact surface <NUM> at a part from which the first protrusion <NUM> projects by the two-dot chain line.

As illustrated in <FIG>, the extensible member <NUM> includes the mounting portion <NUM>, a tubular extensible portion <NUM> continuous with the end portion in the axis direction of the mounting portion <NUM>, and the plurality of first protrusions <NUM> and second protrusions <NUM> projecting from an outer peripheral surface of the extensible portion <NUM>. The extensible member <NUM> is a member made of a thermoplastic elastomer in which respective portions are integrally formed. The extensible member <NUM> is sandwiched between the axial end surface <NUM> of the cylinder <NUM> and the contact surface <NUM> of the bracket <NUM> and compressed in the axis direction to absorb an impact during compression by an elastic force from the extensible member <NUM>.

An outer peripheral surface of the extensible portion <NUM> is provided with the end surface <NUM>, the pressure receiving surface <NUM>, the outer crests <NUM>, the outer roots <NUM>, and first contact surfaces <NUM> and second contact surfaces <NUM> that connect the outer crests <NUM> and the outer roots <NUM>. An inner peripheral surface of the extensible portion <NUM> is provided with the inner crests <NUM> and the inner roots <NUM>. The first contact surface <NUM> and the second contact surface <NUM> are parts contactable with one another when the extensible portion <NUM> axially contracts. A part continuous with the end surface <NUM> side of the outer root <NUM> is the first contact surface <NUM>. A part continuous with the pressure receiving surface <NUM> side of the outer root <NUM> is the second contact surface <NUM>.

The first contact surface <NUM> includes the inner portion 35a continuous with the whole circumference of the outer root <NUM> and an outer portion 52b that connects the whole circumference of the inner portion 35a and the whole circumference of the outer crest <NUM>. The outer portion 52b includes a planar portion 52d continuous with the inner portion 35a and a convex surface portion 52e that connects the planar portion 52d and the outer crest <NUM>. The planar portion 52d is formed of a straight line on the cross-sectional surface including the center axis C. The convex surface portion 52e is formed of a convex curved line on the cross-sectional surface including the center axis C.

The second contact surface <NUM> includes the inner portion 36a continuous with the whole circumference of the outer root <NUM> and an outer portion 53b that connects the whole circumference of the inner portion 36a and the whole circumference of the outer crest <NUM>. The outer portion 53b includes a planar portion 53d continuous with the inner portion 36a and a convex surface portion 53e that connects the planar portion 53d and the outer crest <NUM>. The planar portion 53d is formed of a straight line on the cross-sectional surface including the center axis C. The convex surface portion 53e is formed of a convex curved line on the cross-sectional surface including the center axis C. Boundaries 52c, 53c between the inner portions 35a, 36a and the outer portions 52b, 53b are continuous over the whole circumference of the outer peripheral surface of the extensible portion <NUM> and indicated by the two-dot chain lines in <FIG>.

The first protrusion <NUM> projects from the planar portion 52d in the outer portion 52b of the first contact surface <NUM>. The second protrusion <NUM> projects from the planar portion 53d in the outer portion 53b of the second contact surface <NUM>. The first protrusions <NUM> and the second protrusions <NUM> are integrally molded with the extensible portion <NUM>.

As illustrated in <FIG>, the first protrusions <NUM> are arc-shaped parts around the center axis C. Specifically, the first protrusion <NUM> is formed by extending the hemispherical first protrusion <NUM> of the first embodiment in the circumferential direction with the radial dimension L2 of the first protrusion <NUM> maintained. The four first protrusions <NUM> are disposed at regular intervals in the circumferential direction around the center axis C and disposed in rotational symmetry with respect to the center axis C. Respective radial distances from the center axis C to the plurality of first protrusions <NUM> are same.

As illustrated in <FIG>, the second protrusion <NUM> is disposed at the center in the circumferential direction of the first protrusions <NUM> adjacent in the circumferential direction. Similarly to the first protrusions <NUM>, the second protrusions <NUM> are formed in an arc shape around the center axis C. The four second protrusions <NUM> are disposed at regular intervals in the circumferential direction around the center axis C and disposed in rotational symmetry with respect to the center axis C. Respective radial distances from the center axis C to the plurality of second protrusions <NUM> are same.

The radial distance from the center axis C to the first protrusion <NUM> and the radial distance from the center axis C to the second protrusion <NUM> are mutually same. An interval between the first protrusions <NUM> adjacent in the circumferential direction and an interval between the second protrusions <NUM> adjacent in the circumferential direction are same. The first protrusions <NUM> and the second protrusions <NUM> are disposed to be separated in the circumferential direction in alternation. The intervals of the first protrusions <NUM> and the second protrusions <NUM> adjacent in the circumferential direction are also the same over the whole circumference.

The first protrusion <NUM> and the second protrusion <NUM> project from the outer portions 52b, 53b where the amount of deformation during the extension and contraction of the extensible portion <NUM> is small, respectively. Similarly to the first embodiment, the extensible member <NUM> allows abnormal noise during the extension and contraction to be less likely to occur with the first protrusions <NUM> and the second protrusions <NUM> and allows suppressing the reduction in durability of the extensible portion <NUM> caused by disposing the first protrusions <NUM> and the second protrusions <NUM>.

Since the planar portions 52d, 53d are the straight lines on the cross-sectional surface including the center axis C, the planar portion 52d and the planar portion 53d are likely to be in close contact during the contraction of the extensible portion <NUM>. By disposing the first protrusion <NUM> and the second protrusion <NUM> in the planar portions 52d, 53d, the planar portions 52d, 53d are less likely to be in close contact during the contraction of the extensible portion <NUM>. The extensible member <NUM> allows abnormal noise during the extension and contraction to be more less likely to occur.

The shape and dimensions of the first protrusion <NUM> will be described in further detail with reference to <FIG>. Since the shape and the dimensions of the second protrusion <NUM> are same as the shape and the dimensions of the first protrusion <NUM>, a part of the description of the shape and the dimensions of the second protrusion <NUM> will be omitted.

As illustrated in <FIG>, the arc-shaped first protrusion <NUM> around the center axis C has the circumferential dimension L3 larger than the radial dimension L2. During the contraction of the extensible portion <NUM>, the first contact surfaces <NUM> and the second contact surfaces <NUM> are less likely to be in close contact at a further wide range. In the extensible member <NUM>, compared with the hemispherical first protrusions <NUM> and second protrusions <NUM> as in the first embodiment, abnormal noise during the extension and contraction of the extensible portion <NUM> can be sufficiently less likely to occur while the numbers of the first protrusions <NUM> and the second protrusions <NUM> are reduced.

In the first embodiment, a local load is applied by point from the first protrusion <NUM> and the second protrusion <NUM> to the first contact surface <NUM> and the second contact surface <NUM>. In the extensible member <NUM> of the second embodiment, a linear load is applied from the first protrusion <NUM> and the second protrusion <NUM> to the first contact surface <NUM> and the second contact surface <NUM>. The extensible member <NUM> allows facilitating a dispersion of the load applied from the first protrusion <NUM> and the second protrusion <NUM> to the first contact surface <NUM> and the second contact surface <NUM>. That is, concentration of stress on the extensible portion <NUM> around the first protrusions <NUM> and the second protrusions <NUM> can be suppressed. The extensible member <NUM> can ensure the durability of the extensible portion <NUM>.

During the extension and contraction of the extensible portion <NUM>, amounts of deformation of the first contact surface <NUM> and the second contact surface <NUM> are likely to differ according to radial positions from the center axis C. When the radial dimensions L2 of the first protrusion <NUM> and the second protrusion <NUM> are larger than the circumferential dimensions L3 of the first protrusion <NUM> and the second protrusion <NUM>, the amounts of deformation of the first protrusion <NUM> and the second protrusion <NUM> are likely to differ according to positions in length directions of the first protrusion <NUM> and the second protrusion <NUM>. Stress is likely to concentrate on the extensible portion <NUM> around the part where the amount of deformation is large among the first protrusion <NUM> and the second protrusion <NUM>, and the durability of the extensible portion <NUM> is reduced. Plastic deformation of the extensible portion <NUM> in accordance with cyclic deformation becomes large from the peripheral area of the part where the amount of deformation is large among the first protrusion <NUM> and the second protrusion <NUM>. The durability of the extensible portion <NUM> is reduced and the buffering property is deteriorated.

In this embodiment, the circumferential dimension L3 of the first protrusion <NUM> and the second protrusion <NUM> is larger than the radial dimension L2 of the first protrusion <NUM> and the second protrusion <NUM>. Compared with the case where the radial dimension L2 is larger than the circumferential dimension L3, a difference in amount of deformation between the first protrusion <NUM> and the second protrusion <NUM> in the length direction decreases. Since the first protrusions <NUM> and the second protrusions <NUM> are formed in the arc shape around the center axis C, the difference in amount of deformation between the first protrusion <NUM> and the second protrusion <NUM> in the length direction further decreases. The extensible member <NUM> allows suppressing the concentration of stress around a part of the first protrusion <NUM> and the second protrusion <NUM> in the length direction during the extension and contraction of the extensible portion <NUM>. The extensible member <NUM> allows suppressing the reduction in durability and deterioration of the buffering property of the extensible portion <NUM>.

<FIG> illustrates a cross-sectional surface along the first protrusion <NUM> and a cross-sectional surface perpendicular to the first contact surface <NUM> of a part where the first protrusion <NUM> is disposed. In the cross-sectional surface of <FIG>, the first protrusion <NUM> includes a center portion <NUM> where a thickness T of the first protrusion <NUM> (a distance from the first contact surface <NUM> to a distal end of the first protrusion <NUM>) is approximately constant. The center portion <NUM> is disposed at the center portion in the circumferential direction of the first protrusion <NUM> and has a circumferential dimension formed to be sufficiently larger than the radial dimension L2 of the first protrusion <NUM>. Similarly, the second protrusion <NUM> also includes the center portion <NUM>.

An approximately uniform load is applied on the first contact surface <NUM> and the second contact surface <NUM> between which the center portion <NUM> is sandwiched from the center portion <NUM> over the circumferential direction during the extension and contraction of the extensible portion <NUM>. Since the extensible member <NUM> allows further facilitating the dispersion of the load applied from the center portion <NUM> to the first contact surface <NUM> and the second contact surface <NUM>, the durability of the extensible portion <NUM> can be improved.

An example will be described with reference to <FIG>. In the first and second embodiments, the cases where the first protrusions <NUM>, <NUM> and the second protrusions <NUM>, <NUM> project from the first contact surfaces <NUM>, <NUM> and the second contact surfaces <NUM>, <NUM>, respectively, have been described. In the example, a case where protrusions <NUM> project from only first contact surfaces <NUM> will be described. Same reference numerals are given to parts same as those of the first embodiment and the description thereof will be omitted.

<FIG> is a partial cross-sectional view of an extensible member <NUM> of the example. In <FIG>, the right side with respect to the center axis C in the paper is the cross-sectional view of the extensible member <NUM> and the left side with respect to the center axis C in the paper is a front view of the extensible member <NUM>. <FIG> is cross-sectional view of the extensible member <NUM> perpendicular to a first contact surface <NUM> as a part where the protrusion <NUM> is disposed and taken along the protrusion <NUM>. <FIG> illustrates the first contact surface <NUM> as the part from which the protrusion <NUM> projects by the two-dot chain line.

As illustrated in <FIG>, the extensible member <NUM> includes the mounting portion <NUM>, a tubular extensible portion <NUM> continuous with the end portion in the axis direction of the mounting portion <NUM>, and the plurality of protrusions <NUM> projecting from an outer peripheral surface of the extensible portion <NUM>. The extensible member <NUM> is a member made of a thermoplastic elastomer in which respective portions are integrally formed. The extensible member <NUM> is sandwiched between the axial end surface <NUM> of the cylinder <NUM> and the contact surface <NUM> of the bracket <NUM> and compressed in the axis direction to absorb an impact during compression by an elastic force from the extensible member <NUM>.

An outer peripheral surface of the extensible portion <NUM> is provided with the end surface <NUM>, the pressure receiving surface <NUM>, the outer crests <NUM>, the outer roots <NUM>, and the first contact surfaces <NUM> and second contact surfaces <NUM> that connect the outer crests <NUM> and the outer roots <NUM>. An inner peripheral surface of the extensible portion <NUM> is provided with the inner crests <NUM> and the inner roots <NUM>. The first contact surface <NUM> and the second contact surface <NUM> are parts contactable with one another when the extensible portion <NUM> axially contracts. A part continuous with the end surface <NUM> side of the outer root <NUM> is the first contact surface <NUM>. A part continuous with the pressure receiving surface <NUM> side of the outer root <NUM> is the second contact surface <NUM>.

The first contact surface <NUM> includes the inner portion 35a continuous with the whole circumference of the outer root <NUM> and an outer portion 62b that connects the whole circumference of the inner portion 35a and the whole circumference of the outer crest <NUM>. The outer portion 62b includes a perpendicular portion 62d continuous with the inner portion 35a and a convex surface portion 62e that connects the perpendicular portion 62d and the outer crest <NUM>. The perpendicular portion 62d is formed of a straight line perpendicular to the center axis C on the cross-sectional surface including the center axis C. The convex surface portion 62e is formed of a convex curved line on the cross-sectional surface including the center axis C.

The second contact surface <NUM> includes the inner portion 36a continuous with the whole circumference of the outer root <NUM> and an outer portion 63b that connects the whole circumference of the inner portion 36a and the whole circumference of the outer crest <NUM>. The outer portion 63b includes a perpendicular portion 63d continuous with the inner portion 35a and a convex surface portion 63e that connects the perpendicular portion 63d and the outer crest <NUM>. The perpendicular portion 63d is formed of a straight line perpendicular to the center axis C on the cross-sectional surface including the center axis C. The convex surface portion 63e is formed of a convex curved line on the cross-sectional surface including the center axis C. Boundaries 62c, 63c between the inner portions 35a, 36a and the outer portions 62b, 63b are continuous over the whole circumference of the outer peripheral surface of the extensible portion <NUM>.

The protrusion <NUM> projects from the perpendicular portion 62d in the outer portion 62b of the first contact surface <NUM> and is integrally molded with the extensible portion <NUM>. The protrusions <NUM> are disposed similarly to the first protrusions <NUM> of the second embodiment illustrated in <FIG>. The protrusions <NUM> are arc-shaped parts around the center axis C. The four protrusions <NUM> are disposed at regular intervals in the circumferential direction around the center axis C and disposed in rotational symmetry with respect to the center axis C. Respective radial distances from the center axis C to the plurality of protrusions <NUM> are same.

Since the protrusions <NUM> project from the first contact surfaces <NUM>, similarly to the first and second embodiments, the extensible member <NUM> allows the first contact surfaces <NUM> and the second contact surfaces <NUM> to be less likely to be in close contact around the protrusions <NUM> during the extension and contraction of the extensible portion <NUM>. When the first contact surface <NUM> and the second contact surface <NUM> are separated at once after being in close contact, air is likely to enter between the first contact surface <NUM> and the second contact surface <NUM> from around the protrusion <NUM>. The extensible member <NUM> allows abnormal noise during the extension and contraction to be less likely to occur. Similarly to the first and second embodiments, the protrusion <NUM> projects from the outer portion 62b where the amount of deformation during the extension and contraction of the extensible portion <NUM> is small in the extensible member <NUM>. The extensible member <NUM> allows suppressing the reduction in durability of the extensible portion <NUM> caused by disposing the protrusions <NUM>.

The perpendicular portions 62d, 63d are straight lines perpendicular to the center axis C on the cross-sectional surface including the center axis C. When the perpendicular portions 62d, 63d are mutually in contact during the contraction of the extensible portion <NUM> and then separated, the insides in the radial direction of the mutual perpendicular portions 62d, 63d are likely to be separated first. Since the protrusions <NUM> are disposed on the perpendicular portions 62d, 63d, air is likely to enter the insides in the radial direction of the perpendicular portions 62d, 63d during the extension of the extensible portion <NUM>. The extensible member <NUM> allows abnormal noise during the extension and contraction of the extensible portion <NUM> to be more less likely to occur.

The protrusion <NUM> has a radial dimension same as the radial dimension L2 of the first protrusion <NUM> of the second embodiment. As illustrated in <FIG>, a circumferential dimension L4 of the protrusion <NUM> is formed larger than the radial dimension L2 of the protrusion <NUM>. Similarly to the second embodiment, the extensible member <NUM> allows abnormal noise during the extension and contraction of the extensible portion <NUM> to be less likely to occur sufficiently with the reduced number of protrusions <NUM> and also allows suppressing the reduction in durability and deterioration of the buffering property of the extensible portion <NUM>.

The circumferential dimension L4 of the protrusion <NUM> is formed larger than the circumferential dimension L3 of the first protrusion <NUM> and the second protrusion <NUM> of the second embodiment. The circumferential dimension L4 of the protrusion <NUM> is about twice the circumferential dimension L3 of the first protrusion <NUM> and the second protrusion <NUM>. In contrast to the second embodiment in which the first protrusions <NUM> and the second protrusions <NUM> are disposed in the first contact surfaces <NUM> and the second contact surfaces <NUM>, respectively, even when the protrusions <NUM> are disposed only in the first contact surfaces <NUM> in the example, the first contact surfaces <NUM> and the second contact surfaces <NUM> are less likely to be in close contact sufficiently during the contraction of the extensible portion <NUM> with the protrusions <NUM>. The extensible member <NUM> allows abnormal noise during the extension and contraction of the extensible portion <NUM> to be less likely to occur sufficiently.

<FIG> illustrates a cross-sectional surface along the protrusion <NUM> and a cross-sectional surface perpendicular to the first contact surface <NUM> as the part where the protrusion <NUM> is disposed. On the cross-sectional surface of <FIG>, in the protrusion <NUM>, the distance from the first contact surface <NUM> to the distal end of the protrusion <NUM> (thickness of the protrusion <NUM>) gradually shortens from the center in the circumferential direction to both ends in the circumferential direction.

When the first contact surface <NUM> and the second contact surface <NUM> are separated at once after being in close contact during the extension and contraction of the extensible portion <NUM>, the protrusion <NUM> is gradually separated from the second contact surface <NUM> from both ends in the circumferential direction to the center in the circumferential direction of the protrusion <NUM>. In the extensible member <NUM>, air passes through a clearance where the protrusion <NUM> is separated from the second contact surface <NUM> and can quickly enter between the first contact surface <NUM> and the second contact surface <NUM> in the center axis C side of the protrusion <NUM>. That is, the air quickly enters between the first contact surface <NUM> and the second contact surface <NUM> without the air coming around from both ends in the circumferential direction of the protrusion <NUM>. The extensible member <NUM> allows abnormal noise during the extension and contraction of the extensible portion <NUM> to be more less likely to occur.

A further example will be described with reference to <FIG> and <FIG>. In the first, and second embodiments and the example, the cases where the plurality of first protrusions <NUM>, <NUM>, second protrusions <NUM>, <NUM>, and protrusions <NUM> are disposed in the circumferential direction have been described. In the further example, a case where a protrusion <NUM> is formed continuously over the whole circumference in the circumferential direction will be described. Same reference numerals are given to parts same as those of the first embodiment and the description thereof will be omitted. <FIG> is a front view of an extensible member <NUM> of the further example. <FIG> is a cross-sectional view of the extensible member <NUM> along the line IX-IX of <FIG>.

As illustrated in <FIG> and <FIG>, the extensible member <NUM> includes the mounting portion <NUM>, the extensible portion <NUM>, and the protrusion <NUM> projecting from the outer portion 35b in the first contact surface <NUM> of the extensible portion <NUM>. The extensible member <NUM> is a member made of a thermoplastic elastomer in which respective portions are integrally formed. The extensible member <NUM> is sandwiched between the axial end surface <NUM> of the cylinder <NUM> and the contact surface <NUM> of the bracket <NUM> and compressed in the axis direction to absorb an impact during compression by an elastic force from the extensible member <NUM>.

The protrusion <NUM> projects from the outer portion 35b where the amount of deformation during the extension and contraction of the extensible portion <NUM> is small. Similarly to the first, and second embodiments and the example, the extensible member <NUM> allows abnormal noise during the extension and contraction of the extensible portion <NUM> to be less likely to occur with the protrusion <NUM> and also allows suppressing the reduction in durability of the extensible portion <NUM> caused by disposing the protrusion <NUM>.

The protrusion <NUM> is a strip-shaped part formed continuously over the whole circumference around the center axis C. Since this allows the first contact surface <NUM> and the second contact surface <NUM> to be less likely to be in close contact at the further wide range during the contraction of the extensible portion <NUM>, the extensible member <NUM> allows abnormal noise during the extension and contraction of the extensible portion <NUM> to be more less likely to occur.

The protrusion <NUM> smoothly changes its radial distance to the center axis C along the circumferential direction. Specifically, in the protrusion <NUM>, a part where the radial distance from the center axis C becomes a maximum value L5 and a part where the radial distance from the center axis C becomes a minimum value L6 are provided in alternation at regular intervals in the circumferential direction. Viewing from the axis direction of the center axis C, the part with the maximum value L5 in the protrusion <NUM> is formed in a convex curved line shape to outside in the radial direction. Viewing from the axis direction of the center axis C, the part with the minimum value L6 in the protrusion <NUM> is formed in a convex curved line shape to inside in the radial direction. The respective convex curved lines are smoothly connected to one another.

During the extension and contraction of the extensible portion <NUM>, after the first contact surfaces <NUM> are in close contact with the second contact surfaces <NUM>, the first contact surfaces <NUM> and the second contact surfaces <NUM> are gradually separated mainly from radially outward. After the whole circumference of the protrusion <NUM> is in close contact with the second contact surfaces <NUM>, the protrusion <NUM> is gradually separated from the second contact surfaces <NUM> from the part with the maximum value L5, which is positioned outermost in the circumferential direction in the protrusion <NUM>, to the part with the minimum value L6. The extensible member <NUM> allows reducing the separation of the protrusion <NUM> from the second contact surfaces <NUM> at once. The extensible member <NUM> allows suppressing abnormal noise caused by the close contact of the protrusion <NUM> with the second contact surfaces <NUM>.

The parts with the maximum value L5 and the parts with the minimum value L6 are disposed in alternation at regular intervals in the protrusion <NUM>. When the protrusion <NUM> is gradually separated from the second contact surfaces <NUM>, the extensible member <NUM> allows disposing the positions where the protrusion <NUM> has already been separated from the second contact surfaces <NUM> and the positions where the protrusion <NUM> is in still close contact with the second contact surfaces <NUM> to be approximately uniform over the circumferential direction. This allows suppressing the change in the way of deformation of the extensible portion <NUM> in the circumferential direction caused by, for example, a pressure of air passing through the part where the protrusion <NUM> has already been separated from the second contact surface <NUM>. The extensible member <NUM> allows the way of deformation of the extensible portion <NUM> to be close to uniform over the circumferential direction. The extensible member <NUM> allows suppressing the reduction in durability of the extensible portion <NUM> caused by disposing the protrusion <NUM>.

In the protrusion <NUM>, the parts with the maximum value L5 and the parts with the minimum value L6 are formed in the curved line shape, and the radial distance from the center axis C to the protrusion <NUM> smoothly changes along the circumferential direction. This suppresses the concentration of stress on the parts with the maximum value L5 and the parts with the minimum value L6 during the extension and contraction of the extensible portion <NUM>, compared with a case where the parts with the maximum value L5 and the parts with the minimum value L6 form squares in the protrusion <NUM>. The extensible member <NUM> allows suppressing the reduction in durability of the protrusion <NUM> and the extensible portion <NUM>.

As described above, while the present invention has been described based on the above-mentioned embodiments, the present invention is not limited to the embodiments by any means. It can be easily inferred that various improvements and modifications are possible within a scope as defined by the claims. For example, the shapes and the dimensions of the respective portions of the bracket <NUM> and the extensible members <NUM>, <NUM>, <NUM>, <NUM> may be changed as necessary. The respective radial distances from the center axis C to the plurality of outer crests <NUM> may be set to be the same. Similarly to the plurality of outer roots <NUM>, inner crests <NUM>, and inner roots <NUM>, the distances from the center axis C may be set to be the same. The convex surface portions 52e, 53e, 62e, 63e may be omitted, and outer portions may be formed by the planar portions 52d or the perpendicular portions 62d formed of straight lines on the cross-sectional surface including the center axis C. The outer crests <NUM> may be formed by straight lines approximately parallel to the center axis C on the cross-sectional surface including the center axis C.

The first protrusions <NUM>, <NUM>, the second protrusions <NUM>, <NUM>, and the protrusions <NUM>, <NUM> may be disposed on the convex surface portions 52e, 53e, 62e, 63e in the outer portions 52b, 53b, 62b, 63b. During the extension and contraction of the extensible portions <NUM>, <NUM>, the first contact surfaces <NUM>, <NUM> are separated from the second contact surfaces <NUM>, <NUM> in the order from radially outward in many cases. By disposing the first protrusions <NUM>, <NUM>, the second protrusions <NUM>, <NUM>, and the protrusions <NUM>, <NUM> on the convex surface portions 52e, 53e, 62e, 63e, air is likely to enter quickly between the first contact surfaces <NUM>, <NUM> and the second contact surfaces <NUM>, <NUM>. Abnormal noise during the extension and contraction of the extensible portions <NUM>, <NUM> is less likely to occur.

In the embodiments, while the extensible members <NUM>, <NUM>, <NUM>, <NUM> as the stoppers sandwiched between the axial end surface <NUM> of the cylinder <NUM> and the contact surface <NUM> of the bracket <NUM> have been described, the present invention is not necessarily limited to the embodiments. The extensible member only needs to be a member that includes the extensible portion <NUM>, <NUM>, <NUM> having the outer peripheral surface and the inner peripheral surface in the bellows shape in which the mountains and the troughs are continuous in the axis direction and extends and contracts in the axis direction. For example, the extensible member may be, for example, a dust cover that covers the outer periphery of the shock absorber <NUM>. However, the present invention is preferably applied to the extensible member as the stopper. Since the first contact surfaces <NUM>, <NUM>, <NUM> and the second contact surfaces <NUM>, <NUM>, <NUM> are in instantaneously close contact and then separated in the stopper that absorbs an impact by extension and contraction of the extensible member in the axis direction, abnormal noise during the extension and contraction of the extensible member tends to be a problem. By disposing the first protrusions <NUM>, <NUM>, the second protrusions <NUM>, <NUM>, and the protrusions <NUM>, <NUM> in the extensible member that absorbs an impact, abnormal noise during the extension and contraction of the extensible member, which tends to be problem, is suppressed.

While the cases where the first protrusions <NUM>, <NUM> and the second protrusions <NUM>, <NUM> are disposed separately in alternation in the circumferential direction have been described in the first and second embodiments, the present invention is not necessarily limited to the embodiments. The first protrusions <NUM>, <NUM>, the second protrusions <NUM>, <NUM>, and the protrusions <NUM>, <NUM> may be randomly disposed. The fine first protrusions <NUM>, <NUM>, second protrusions <NUM>, <NUM>, and protrusions <NUM>, <NUM> may be formed with unevennesses formed on a mold for forming the first contact surfaces <NUM>, <NUM>, <NUM> and the second contact surfaces <NUM>, <NUM>, <NUM> by, for example, etching, sand-blasting, and shot-blasting.

During the extension and contraction of the extensible portions <NUM>, <NUM>, <NUM>, stress is less likely to concentrate on the extensible portions <NUM>, <NUM>, <NUM> around the fine first protrusions <NUM>, <NUM>, second protrusions <NUM>, <NUM>, and protrusions <NUM>, <NUM>. Even when the fine first protrusions <NUM>, <NUM>, second protrusions <NUM>, <NUM>, and protrusions <NUM>, <NUM> are disposed on the inner portions 35a, 36a, the durability of the extensible portions <NUM>, <NUM>, <NUM> is ensured. In other words, by disposing the first protrusions <NUM>, <NUM>, the second protrusions <NUM>, <NUM>, and the protrusions <NUM>, <NUM> only in the outer portions 35b, 36b, 52b, 53b, 62b, 63b, even when the first protrusions <NUM>, <NUM>, the second protrusions <NUM>, <NUM>, and the protrusions <NUM>, <NUM> are increased in size, the durability of the extensible portions <NUM>, <NUM>, <NUM> is ensured.

Instead of the first contact surfaces <NUM>, <NUM>, <NUM>, the protrusions <NUM>, <NUM> of the examples may project only from the second contact surfaces <NUM>, <NUM>, <NUM>. As in the first and second embodiments, while the protrusions (first protrusions) <NUM> project from the first contact surfaces <NUM>, <NUM>, <NUM>, the protrusions (second protrusions) <NUM> may project from the second contact surfaces <NUM>, <NUM>, <NUM>.

As in the first and second embodiments, while the protrusion (first protrusion) <NUM> projects from the first contact surfaces <NUM>, <NUM>, <NUM>, the protrusion (second protrusion) <NUM> may project from the second contact surfaces <NUM>, <NUM>, <NUM>. The part with the maximum value L5 in the first protrusion <NUM> and the part with the maximum value L5 in the second protrusion <NUM> are preferably disposed separately in the circumferential direction. During the extension and contraction of the extensible portions <NUM>, <NUM>, <NUM>, the way of deformation of the first contact surfaces <NUM>, <NUM>, <NUM> and the way of deformation of the second contact surfaces <NUM>, <NUM>, <NUM> are close to be uniform.

Claim 1:
An extensible member (<NUM>, <NUM>, <NUM>) comprising:
a tubular extensible portion (<NUM>, <NUM>, <NUM>) made of a thermoplastic elastomer that has an inner peripheral surface and an outer peripheral surface in a bellows shape in which mountains and troughs are continuous in an axis direction; and
at least one protrusion (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) that projects from the outer peripheral surface,
wherein the outer peripheral surface includes:
outer crests (<NUM>) as crests of mountains;
outer roots (<NUM>) as bottoms of troughs; and
first contact surfaces (<NUM>, <NUM>, <NUM>) and second contact surfaces (<NUM>, <NUM>, <NUM>) between the outer crests (<NUM>) and the outer roots (<NUM>) that are positioned to be contactable with one another when the extensible portion (<NUM>, <NUM>, <NUM>) axially contracts,
the inner peripheral surface includes:
inner crests (<NUM>) as crests of mountains; and
inner roots (<NUM>) as bottoms of troughs,
the inner crests (<NUM>) are positioned radially inward of all of the outer roots (<NUM>), and the inner roots (<NUM>) are positioned radially inward of all of the outer crests (<NUM>),
the protrusion (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) is positioned on at least one of the first contact surfaces (<NUM>, <NUM>, <NUM>) and the second contact surfaces (<NUM>, <NUM>, <NUM>), and
the protrusion includes a plurality of first protrusions (<NUM>, <NUM>) that project from the first contact surfaces (<NUM>, <NUM>), characterized in that
the protrusion further includes a plurality of second protrusions (<NUM>, <NUM>) that project from the second contact surfaces (<NUM>, <NUM>), and
the plurality of first protrusions (<NUM>, <NUM>) and the second protrusions (<NUM>, <NUM>) are disposed separately in alternation in a circumferential direction on the first contact surfaces (<NUM>, <NUM>) and the second contact surfaces (<NUM>, <NUM>) contactable with one another.