Cylindrical vibration damper

Abstract

To provide a cylindrical vibration damper having a new structure, capable of setting a spring ratio between a radial direction in which a bore hole is located and a radial direction deviated from the bore hole to large and attaining low spring characteristics in the prying direction while securing a spring in the radial direction.SOLUTION: In a cylindrical vibration damper 10, an inner shaft member 12 and an outer cylindrical member 14 are coupled by a body rubber elastic body 16. The inner shaft member 12 has a large diameter part 20 having a large outer diameter dimension at an axial intermediate portion. The body rubber elastic body 16 includes a bore hole 30 penetrating in the axial direction and extending by predetermined length in the circumferential direction. An opposing inner surface 38 in the circumferential direction of the bore hole 30 has an inclined surface 40 expanding so that an opposing distance in the circumferential direction gradually becomes larger toward an axial opening part of the bore hole 30.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a cylindrical vibration isolator that is applied to suspension bushes, member mounts, engine mounts, etc. of automobiles. [Background technology]

[0002] Conventionally, a cylindrical vibration isolator has been known as one type of vibration isolator used in automobiles. As disclosed in, for example, Japanese Patent Application Laid-Open No. 2006-153265 (Patent Document 1), a cylindrical vibration isolator has a structure in which an inner shaft member and an outer cylindrical member are connected by a main rubber elastic body. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-153265 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, the cylindrical vibration-damping device described in Patent Document 1 has recessed holes formed on both radial sides of the inner shaft member, penetrating the main rubber elastic body in the axial direction. This allows low spring characteristics to be achieved in the radial direction where the recessed holes are arranged, and high spring characteristics to be achieved in the radial direction where the recessed holes are not arranged. Furthermore, the spring constant in the prying direction is also small in the radial direction where the recessed holes are formed.

[0005] However, in the structure of Patent Document 1, depending on the required spring characteristics, the spring ratio in two orthogonal directions, the radial direction in which the recessed hole is formed and the radial direction perpendicular thereto, may still not be sufficient, and a larger spring ratio may be required. That is, in the cylindrical vibration-damping device of Patent Document 1, if the circumferential length of the recessed hole is lengthened and the spring constant in the axis-perpendicular direction in the radial direction in which the recessed hole is formed is set small, the spring reduction effect of the recessed hole is also exerted in the radial direction perpendicular to the radial direction in which the recessed hole is formed, making it difficult to set a large spring constant in that radial direction, and therefore it was not possible to increase the spring ratio.

[0006] Furthermore, if one attempts to increase the circumferential length of the recessed hole and set the spring constant in the prying direction small in the direction in which the recessed hole is arranged, the spring constant in the direction perpendicular to the axis also becomes small, making it difficult, for example, to set the spring constant in the prying direction small while maintaining the support spring rigidity in the direction perpendicular to the axis.

[0007] The problem to be solved by the present invention is to provide a cylindrical vibration-damping device of a novel structure that makes it possible to set a larger spring ratio between the radial direction in which the recessed hole is located and the radial direction away from the recessed hole, and that can also achieve low spring characteristics in the prying direction while ensuring radial springiness. [Means for solving the problem]

[0008] The following describes preferred embodiments for understanding the present invention, but the embodiments described below are merely illustrative and may be combined with one another as appropriate, and the multiple components described in each embodiment may be recognized and used independently as far as possible, and may also be combined with any of the components described in another embodiment as appropriate. As a result, the present invention is not limited to the embodiments described below, and various other embodiments may be realized.

[0009] The first aspect is a cylindrical vibration-damping device in which an inner shaft member and an outer cylindrical member are connected by a main rubber elastic body, the inner shaft member has a large diameter portion with an increased outer diameter dimension at the axial middle portion, the main rubber elastic body has a recessed hole penetrating in the axial direction and extending a predetermined length in the circumferential direction, and the circumferentially opposing inner surfaces of the recessed hole have inclined surfaces that expand so that the circumferential opposing distance gradually increases toward the axial opening of the recessed hole.

[0010] According to a cylindrical vibration-damping device constructed in accordance with this embodiment, a large diameter portion is provided in the axially middle portion of the inner axial member, and an inclined surface is provided on the circumferentially facing inner surface of the recessed hole, so that the ratio of the radial spring constant where the recessed hole is located to the radial spring constant outside the recessed hole can be set to a larger value.

[0011] In addition, by providing a large diameter portion in the axial middle portion of the inner shaft member and providing an inclined surface on the circumferentially facing inner surface of the recessed hole, it is possible to set the spring constant in the prying direction smaller without excessively reducing the spring constant in the direction perpendicular to the axis.

[0012] In the second aspect, in the cylindrical vibration-damping device described in the first aspect, the distance between the circumferentially opposing inner surfaces of the recessed hole is smallest in the axial central portion and gradually increases toward both sides in the axial direction.

[0013] In a cylindrical vibration isolator constructed according to this embodiment, the provision of inclined surfaces on both axial sides makes it easier to set a larger ratio between the radial spring constant where the recessed hole is located and the radial spring constant away from the recessed hole. It is also possible to more advantageously achieve low spring in the prying direction while maintaining spring in the axis-perpendicular direction.

[0014] In a third aspect, in the cylindrical vibration-damping device described in the first or second aspect, at the axial position where the distance between the circumferentially opposing surfaces of the circumferentially opposing inner surfaces in the recessed hole is minimum, the distance between the circumferentially opposing surfaces of the circumferentially opposing inner surfaces is made smaller than the outer diameter of the inner shaft member.

[0015] In a cylindrical vibration-damping device constructed according to this embodiment, at the axial position where the distance between the circumferentially opposing inner surfaces of the recessed hole is minimum, the compression spring component in the radial direction where the recessed hole is located is secured on the circumferential outside of the recessed hole, so that the spring constant in the radial direction can be prevented from becoming excessively small. Also, the shear spring component that affects the axial spring constant in the radial direction outside the recessed hole is secured in the axial middle, so that the axial spring constant in the radial direction outside the recessed hole can be set large.

[0016] A fourth aspect is a cylindrical vibration-damping device as described in the third aspect, in which the distance between the circumferentially opposing inclined surfaces on the circumferentially opposing inner surfaces of the recessed hole is smaller than the outer diameter of the inner shaft member.

[0017] In a cylindrical vibration-damping device constructed in accordance with this embodiment, the distance between the circumferentially opposing surfaces of the inclined surfaces is set to be smaller than the outer diameter of the inner axial member, thereby further reducing the effect of the recessed hole on the radial spring constant outside the recessed hole, and the radial spring constant outside the recessed hole can be set larger.

[0018] A fifth aspect is a cylindrical vibration-damping device described in any one of the first to fourth aspects, wherein the recessed hole does not overlap with the inner shaft member when projected perpendicular to the axis from the side.

[0019] With a cylindrical vibration-damping device constructed in accordance with this embodiment, in the axial projection direction where the recessed hole is located away from the inner axial member without overlapping with it, the rubber compressed between the inner axial member and the outer tubular member can be prevented from being reduced due to the formation of the recessed hole, and the spring constant in that axial projection direction can be set to a large value.

[0020] A sixth aspect is a cylindrical vibration-damping device described in any one of the first to fifth aspects, in which the main rubber elastic body has a pair of recessed holes on both sides of a first radial direction relative to the inner axial member, and has a solid structure in a second radial direction perpendicular to the first radial direction.

[0021] With a cylindrical vibration-damping device constructed according to this aspect, the ratio of the spring constant in the first radial direction in which the pair of recesses are located to the spring constant in the second radial direction perpendicular to the first radial direction can be set to a larger value. Also, by forming a pair of recesses in the main rubber elastic body, the prying spring constant in the first radial direction can be set to a smaller value.

[0022] In a seventh aspect, in the cylindrical vibration-damping device according to any one of the first to sixth aspects, the radially opposing inner surfaces of the recessed hole have a constant distance therebetween.

[0023] With a cylindrical vibration-damping device constructed in accordance with this embodiment, the axial spring constant and the prying spring constant in the radial direction where the recessed hole is located can be set small, while the axial spring constant in the radial direction outside the recessed hole can be secured.

[0024] The eighth aspect is a cylindrical vibration-damping device described in any one of the first to seventh aspects, wherein the thickness dimension of the portion of the main rubber elastic body located on the inner side of the recessed hole is constant in the circumferential direction.

[0025] In a cylindrical vibration-isolating device constructed according to this embodiment, stress concentration on the inner periphery of the recessed hole during deformation of the main rubber elastic body is suppressed, thereby improving durability, etc. Effect of the Invention

[0026] According to the present invention, in a cylindrical vibration-damping device, it is possible to set a larger spring ratio between the radial direction in which the recessed hole is located and the radial direction away from the recessed hole, and it is also possible to achieve low spring characteristics in the prying direction while ensuring radial springiness. [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 is a perspective view showing a suspension bush according to a first embodiment of the present invention; [Diagram 2] Front view of the suspension bush shown in Figure 1 [Diagram 3] III-III cross section of Figure 2 [Figure 4] IV-IV cross section of Figure 2 [Diagram 5] A table showing the results of measurements of the axial spring characteristics in the vertical and horizontal directions for the cylindrical vibration isolator according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0029] 1 to 3 show a suspension bushing 10 for an automobile as a first embodiment of a cylindrical vibration-damping device constructed according to the present invention. The suspension bushing 10 has a structure in which an inner shaft member 12 and an outer cylindrical member 14 are connected by a main rubber elastic body 16. In the following description, in principle, the up-down direction refers to the up-down direction in Fig. 2 which is the first radial direction, the left-right direction refers to the left-right direction in Fig. 2 which is the second radial direction, and the front-rear direction refers to the left-right direction in Fig. 3 which is the axial direction.

[0030] The inner shaft member 12 is a highly rigid member made of metal such as iron or aluminum alloy, or fiber-reinforced synthetic resin, and has a small diameter and approximately cylindrical shape. As shown in Fig. 3, the inner shaft member 12 has small diameter sections 18 at both axial ends that extend in the axial direction with a substantially constant cross section, and a large diameter section 20 at the center in the axial direction that has an outer diameter larger than that of the small diameter section 18.

[0031] More specifically, the large diameter section 20 has a straight section 22 that extends axially with a substantially constant outer diameter at its axial center, and tapered sections 24 on both axial sides of the straight section 22, the outer diameter of which gradually decreases axially outward. However, the large diameter section 20 is not limited to a shape including the straight section 22 and the tapered section 24, and may have a tapered shape in which the outer diameter dimension changes over the entire axial direction, and may be, for example, substantially semicircular in vertical cross section.

[0032] The inner diameter dimension of the large diameter portion 20 in this embodiment is approximately constant over its entire length, but the inner diameter dimension may also be changed in the axial direction in response to changes in the outer diameter dimension, for example, to form an inner axial member 12 having an approximately constant radial thickness dimension over its entire axial length.

[0033] The axial length dimension of the large diameter portion 20 is desirably within a range of 1 / 5 to 1 / 2 of the axial length dimension of the entire inner shaft member 12. The difference in the radial dimensions of the large diameter portion 20 and the small diameter portion 18 is not particularly limited, but is set to be approximately the same as or smaller than the thickness dimension of the small diameter portion 18.

[0034] The outer cylindrical member 14 is made of a high-rigidity material similar to the inner axial member 12, and has a generally cylindrical shape that is thinner and has a larger diameter than the inner axial member 12. The outer cylindrical member 14 has generally constant inner and outer diameters over the entire axial length.

[0035] One axial end of the outer tubular member 14 (the right end in FIG. 3) is tapered in a C-chamfered shape on the outer circumferential surface so that the diameter decreases toward the edge, and can serve as a guide surface for press fitting, etc. The other axial end of the outer tubular member 14 is integrally formed with an outer flange portion 26 in the shape of a circular ring plate that bends and widens toward the outer circumferential side.

[0036] 1 to 3, the inner shaft member 12 is inserted into the inner periphery of the outer cylindrical member 14, and a main rubber elastic body 16 is disposed radially between the inner shaft member 12 and the outer cylindrical member 14. The main rubber elastic body 16 has a thick-walled, generally cylindrical shape overall, and its inner periphery is vulcanization bonded to the outer periphery of the inner shaft member 12, and its outer periphery is vulcanization bonded to the inner periphery of the outer cylindrical member 14.

[0037] The main rubber elastic body 16 is fixed to the axial middle parts of the inner shaft member 12 and the outer cylindrical member 14, and the inner shaft member 12 and the outer cylindrical member 14 protrude axially outward from the main rubber elastic body 16. In this embodiment, the inner shaft member 12 is longer in the axial direction than the outer cylindrical member 14, and the inner shaft member 12 protrudes axially outward from the outer cylindrical member 14. The amount of protrusion of the inner shaft member 12 axially outward from the main rubber elastic body 16 and the amount of protrusion of the outer cylindrical member 14 axially outward from the main rubber elastic body 16 are approximately the same, and the inner peripheral end of the main rubber elastic body 16 is located axially outward from the outer peripheral end. The inner peripheral end of the main rubber elastic body 16 extends axially outward beyond the large diameter portion 20 of the inner shaft member 12, and is fixed to not only the large diameter portion 20 but also the small diameter portions 18, 18.

[0038] The axial end face of the main rubber elastic body 16 is a curved end face 28 with a concave cross section that opens axially outward. The curved end face 28 has its deepest part, located axially innermost, set at the radial center, and in this embodiment, set at a position biased toward the outer periphery from the radial center.

[0039] A pair of recessed holes 30, 30 are formed in the main rubber elastic body 16. The recessed holes 30 are through holes that pass through the main rubber elastic body 16 in the axial direction. The pair of recessed holes 30, 30 are disposed on both sides of the inner shaft member 12 in the up-down direction, which is the first radial direction. The recessed holes 30 extend a predetermined length in the circumferential direction, and have a hole cross-sectional shape that is curved in the circumferential direction so as to fit along the outer tubular member 14. The circumferential length of the recessed holes 30 is preferably ⅓ of the circumference or less, and more preferably ¼ of the circumference or less.

[0040] The radial width w of the hollow hole 30, which is the distance between the radially opposing inner surfaces 32, 32 of the hollow hole 30, is constant in the circumferential direction as shown in Fig. 2 (a degree of dimensional change due to reasons such as manufacturing and precision is permitted, and is within a substantially constant range in appearance, the same applies below), and is also constant in the axial direction as shown in Fig. 3. The inner circumferential rubber 34 located on the inner circumferential side of the hollow hole 30 in the main rubber elastic body 16 has a constant thickness in the circumferential direction, and in this embodiment, extends in the circumferential direction with a constant cross section. The outer circumferential rubber 36 located on the outer circumferential side of the hollow hole 30 in the main rubber elastic body 16 has a constant thickness in the circumferential direction, and in this embodiment, extends in the circumferential direction with a constant cross section.

[0041] In this embodiment, the pair of recessed holes 30, 30 have the same shape (symmetrical shape) as each other. Also, the circumferentially facing inner surfaces 38, 38 on both circumferential sides of the recessed hole 30 have the same shape (symmetrical shape) as each other. However, the shapes of the pair of recessed holes 30, 30 and the shapes of the circumferentially facing inner surfaces 38, 38 of each recessed hole 30 are not limited to being symmetrical to each other.

[0042] 4, the circumferentially facing inner surfaces 38 of the recessed hole 30 are provided with inclined surfaces 40, 40. The inclined surfaces 40 are inclined so as to widen outward in the circumferential direction from the axial center portion toward the axially outer side (the axial opening of the recessed hole 30). Therefore, the recessed hole 30 has a circumferential length dimension that changes in the axial direction, and has an expanding shape in which the circumferential length increases toward the axially outer side.

[0043] The circumferentially facing inner surfaces 38 of the recessed hole 30 have inclined surfaces 40, 40 inclined at a substantially constant inclination angle α in the axial middle portion with respect to the axial direction. In other words, in this embodiment, the circumferentially facing inner surfaces 38 have inclined surfaces 40, 40 in the middle portion excluding the central portion and both end portions in the axial direction where the inclination angle changes in the axial direction.

[0044] In this embodiment, the circumferential length of the recessed hole 30 changes in the axial direction in both the region closer to the axial center than the inclined surface 40 of the middle portion and the region closer to the axial end portion, and the recessed hole 30 has an expanding shape in which the circumferential length increases toward the axial outside. The region closer to the axial center than the inclined surface 40 of the middle portion has a smaller inclination angle than the inclined surface 40, while the region closer to the axial end portion has a larger inclination angle than the inclined surface 40.

[0045] The inclination angle of the inclined surface 40 does not necessarily have to be constant, and may change gradually or stepwise in the axial direction. When the inclination angle of the inclined surface 40 changes in the axial direction, the inclination angle α of the inclined surface 40 is, for example, the average value or median value of the inclination angle. The magnitude of the inclination angle α of the inclined surface 40 is not particularly limited, but is set, for example, within a range of 1 to 30°, and more preferably within a range of 5 to 20°.

[0046] The distance between the circumferentially opposed inner surfaces 38, 38 in the recessed hole 30 is minimum at the axial center and maximum at the axial end. The distance (maximum distance) d1 (straight-line distance in FIG. 2) between the circumferentially opposed inner surfaces 38, 38 at the axial end of the main rubber elastic body 16 is preferably set within a range of 1.2 to 2 times, and more preferably within a range of 1.4 to 1.8 times, the distance (maximum distance) d2 between the circumferentially opposed inner surfaces 38, 38 at the axial center of the main rubber elastic body 16. The distance (maximum distance) d3 between the circumferentially opposed inner surfaces 38, 38 at the axial end of the inclined surface 40 is smaller than the distance d1 between the circumferentially opposed surfaces of the circumferentially opposed inner surfaces 38, 38 at the axial end of the main rubber elastic body 16 and is larger than the distance d2 between the circumferentially opposed surfaces of the circumferentially opposed inner surfaces 38, 38 at the axial center of the main rubber elastic body 16. It is preferable that the distance d3 is within a range of 1.1 to 1.6 times the distance d2.

[0047] At the axial center where the circumferential length of the recessed hole 30 is the shortest, the distance d2 between the circumferentially opposing inner surfaces 38, 38 is smaller than the outer diameter dimension R of the inner shaft member 12 (small diameter portion 18), and the circumferentially opposing inner surfaces 38, 38 overlap with the inner shaft member 12 in the vertical projection. In this embodiment, even at the axial outer end of the inclined surface 40, the distance d3 between the circumferentially opposing surfaces of the circumferentially opposing inner surfaces 38, 38 (inclined surfaces 40, 40) is smaller than the outer diameter dimension R of the inner shaft member 12 (small diameter portion 18), and the circumferentially opposing inner surfaces 38, 38 overlap with the inner shaft member 12 in the vertical projection. Each inclined surface 40 of the recessed hole 30, 30 is provided at a position where the entirety overlaps with the inner shaft member 12 in the vertical projection. In this embodiment, the distance d1 between the circumferentially opposing inner surfaces 38, 38 at the axial end of the main rubber elastic body 16 is larger than the outer diameter dimension R of the inner axial member 12 (small diameter portion 18), but may also be smaller than the outer diameter dimension R of the inner axial member 12, for example.

[0048] The recessed holes 30, 30 do not overlap with the inner shaft member 12 in a lateral projection in the left-right direction. Preferably, the entire recessed holes 30, 30 are spaced apart from the inner shaft member 12 in the up-down direction. In the left and right side portions of the main rubber elastic body 16 that overlap with the inner shaft member 12 in a left-right projection, at least the central portion in the axial direction is solid, and extends continuously in the radial direction between the radially opposing surfaces of the inner shaft member 12 and the outer tubular member 14. In this way, the main rubber elastic body 16 has a pair of recessed holes 30, 30 formed therethrough on both sides in the up-down direction, which is the first radial direction, and has a solid structure on both sides in the left-right direction, which is the second radial direction, to continuously connect the inner shaft member 12 and the outer tubular member 14 in the radial direction.

[0049] The suspension bush 10 constructed in this manner, for example, has the inner shaft member 12 attached to a suspension member (not shown) on the vehicle body side, and the outer cylindrical member 14 attached to a suspension arm (not shown) on the wheel side, thereby providing a vibration-proof connection between the suspension arm and the suspension member.

[0050] When vibrations are input between the inner shaft member 12 and the outer tubular member 14 while the suspension bush 10 is mounted on a vehicle, the main rubber elastic body 16 exhibits a vibration damping effect due to internal friction and the like as it deforms.

[0051] The suspension bushing 10 has a spring constant in the vertical direction smaller than the spring constant in the horizontal direction by forming a pair of recessed holes 30, 30 in the main rubber elastic body 16. Therefore, softer spring characteristics are exhibited when an axially direct input is applied in the vertical direction than when an axially direct input is applied in the horizontal direction. As a result, when an axially direct input is applied in the vertical direction due to, for example, an uneven road surface, a good ride comfort is realized due to the soft spring characteristics, and when an axially direct input is applied in the horizontal direction during cornering, the hard spring characteristics provide excellent driving stability.

[0052] In order to effectively satisfy both the required characteristics for input in the vertical direction and the required characteristics for input in the horizontal direction, it is desirable to set the ratio of the spring constant in the horizontal direction to the spring constant in the vertical direction large. In particular, the spring constant in the horizontal direction, which affects the running performance, needs to satisfy the required value of the vehicle characteristics, and it is desirable to set the ratio of the spring constant in the horizontal direction to the spring constant in the vertical direction large while satisfying the required value of the spring constant in the horizontal direction. In short, there are cases where it is necessary to set the spring constant in the vertical direction small while preventing a decrease in the spring constant in the horizontal direction.

[0053] Therefore, in the suspension bushing 10 of this embodiment, a large diameter portion 20 is provided in the axial center portion of the inner shaft member 12, and inclined surfaces 40, 40 that incline circumferentially outward as they approach the axially outward are provided on each of the circumferentially opposing inner surfaces 38 of the recessed hole 30. This makes it possible to set the spring constant in the vertical direction small while suppressing a decrease in the spring constant in the horizontal direction, thereby making it possible to set a larger ratio of the spring constant in the horizontal direction to the spring constant in the vertical direction.

[0054] In other words, in the axial central portion where the large diameter portion 20 is provided in the inner axial member 12, the main rubber elastomer 16 is made thin in the radial direction, and since the shear spring component of the main rubber elastomer 16 in this portion affects the spring constant in the left-right direction, the circumferential length dimension of the recessed hole 30 is set small, thereby suppressing the decrease in the spring constant in the left-right direction due to the formation of the recessed hole 30.

[0055] At the axially outer portion deviating axially outward from the maximum outer diameter portion of the large diameter section 20, the main rubber elastic body 16 is made thicker in the radial direction, and the shear spring component of the main rubber elastic body 16 at this portion has little effect on the spring constant in the left-right direction. Therefore, by providing inclined surfaces 40, 40 on each of the circumferentially opposing inner surfaces 38 of the recessed hole 30 and setting the circumferential length dimension of the recessed hole 30 to increase axially outward, it is possible to effectively reduce the spring constant in the up-down direction by reducing the compression spring component, while suppressing a decrease in the spring constant in the left-right direction.

[0056] Thus, according to the suspension bush 10 of this embodiment, the large diameter portion 20 of the inner axial member 12 provided in the axial middle portion and the shape of the circumferentially opposing inner surfaces 38, 38 of each recessed hole 30 make it possible to set a large spring ratio between the vertical spring constant and the horizontal spring constant while ensuring a sufficiently large spring constant in the horizontal direction.

[0057] The suspension bushing 10 of this embodiment has a pair of recessed holes 30, 30 provided on both the top and bottom of the inner shaft member 12, and has a solid structure in which the main rubber elastic body 16 is continuous in the radial direction in the left-right direction. This makes it possible to set a larger spring ratio between the spring constant in the up-down direction and the spring constant in the left-right direction.

[0058] In this embodiment, the distance between the opposing circumferential inner surfaces 38, 38 is minimum at the axial center of the recessed hole 30, and inclined surfaces 40, 40 are provided on both axial sides. This makes it possible to set the spring ratio between the spring constant in the vertical direction and the spring constant in the horizontal direction larger more efficiently than when the inclined surface 40 is provided on only one side.

[0059] The distance d1 between the circumferentially opposing inner surfaces 38, 38 of the recessed hole 30 at the axial center is made smaller than the outer diameter R of the inner shaft member 12. This reduces the effect of the recessed hole 30 on the axially perpendicular spring constant at the axial center of the main rubber elastic body 16, making it possible to obtain a large axially perpendicular spring constant in the lateral direction.

[0060] Furthermore, at the axial outer ends of the inclined surfaces 40, 40, the distance d2 between the circumferentially opposing inner surfaces 38, 38 of the recessed hole 30 is made smaller than the outer diameter dimension R of the inner axial member 12. This further reduces the effect of the recessed hole 30 on the axial spring constant in the left-right direction, making it possible to obtain a large axial spring constant in the left-right direction.

[0061] In left-right projection, the recessed holes 30 are spaced apart from the inner shank member 12 on both the top and bottom outer sides and do not overlap with the inner shank member 12. This makes it possible to prevent the recessed holes 30 from reducing the left-right compression spring component of the main rubber elastic body 16, and suppresses the effect of the recessed holes 30 on the axial spring constant in the left-right direction.

[0062] Furthermore, the main rubber elastic body 16 of the suspension bushing 10 is set to have a small spring constant in the prying direction in which the inner shaft member 12 and the outer tubular member 14 tilt relatively in the up-down direction due to the formation of the recessed hole 30. The recessed hole 30 has an increased circumferential length at its axially outer portion due to the inclined surfaces 40, 40 provided on the circumferentially opposing inner surfaces 38, and the rubber at the axially outer end portion, which becomes a compression spring component or a tension spring component when the inner shaft member 12 and the outer tubular member 14 are displaced by prying in the up-down direction, is reduced, effectively reducing the spring constant against prying input in the up-down direction.

[0063] In particular, in the axial center portion, which has a large effect on the axial spring constant in the vertical direction and a small effect on the torsion spring constant, the circumferential length of the recessed hole 30 is shortened and the rubber connecting the inner shaft member 12 and the outer cylindrical member 14 in the vertical direction is secured, so that the torsion spring constant can be efficiently reduced while securing the necessary axial spring constant in the vertical direction. Moreover, since the large diameter portion 20 is provided in the axial center portion of the inner shaft member 12, the compression spring component and the tension spring component are reduced during torsion displacement of the inner shaft member 12 and the outer cylindrical member 14, so that it is possible to set the torsion spring constant smaller while securing the axial spring constant.

[0064] The recessed hole 30 has a constant radial distance w between the radially opposing inner surfaces 32, 32, which does not become large in any part. This makes it easy to ensure a large axial spring constant in the left-right direction of the suspension bushing 10 while setting a small pry spring constant in the up-down direction by forming the recessed hole 30.

[0065] In addition, the thickness dimension of the inner circumferential rubber 34 located on the inner periphery of the recessed hole 30 is made approximately constant in the circumferential direction. This makes it difficult for stress concentration to occur in the inner circumferential rubber 34 when the inner circumferential rubber 34 elastically deforms in the circumferential direction, and the durability can be improved by dispersing the stress.

[0066] The inventors prepared a suspension bushing using an inner shaft member 12 with a large diameter portion 20 and a suspension bushing using a straight-shaped inner shaft member without a large diameter portion 20, and conducted a test to measure their spring characteristics. The test results are shown in FIG. 5. The table in FIG. 5 shows the results of measuring the vertical axial spring characteristics, the horizontal axial spring characteristics, and the ratio of the vertical and horizontal axial spring constants for a suspension bushing with a large diameter portion 20 when the inclination angle α (see FIG. 4) of the inclined surface 40 is set to 0°, 5°, 10°, 15°, and 20°. The table in FIG. 5 also shows the results of measuring the vertical axial spring characteristics, the horizontal axial spring characteristics, and the ratio of the vertical and horizontal axial spring constants for a suspension bushing without a large diameter portion 20 when the inclination angle α of the inclined surface 40 is set to 0°. The vertical spring characteristics and horizontal spring characteristics in FIG. 5 are shown as ratios of the vertical and horizontal spring constants to the vertical spring constant when the inclination angle α of the inclined surface 40 is 0°.

[0067] 5, the suspension bush 10 with the large diameter portion 20 has a vertical spring constant that is approximately 1.5 times larger and a horizontal spring constant that is approximately 1.6 times larger than a suspension bush without the large diameter portion 20. In this way, by employing the inner shaft member 12 with the large diameter portion 20, it is possible to obtain a large axial spring constant, and it was confirmed by measurement tests that it is possible to set a large spring constant in the radial direction (horizontal direction) outside the recessed holes 30, 30 where high spring characteristics are required.

[0068] 5, in a suspension bushing having a large diameter portion 20, within the range of the inclination angle α of the inclined surface 40 from 0° to 20°, the spring ratio increases as the inclination angle α increases, and it was also confirmed that the spring ratio is greater when the inclined surface 40 is provided (α=5, 10, 15, 20) than when the inclined surface 40 is not provided (α=0). Thus, the actual measurement results also clarified that by providing the large diameter portion 20 of the inner shaft member 12 and the inclined surface 40 of the hollow hole 30, it is possible to set a large ratio of the spring constants in the vertical direction and the horizontal direction.

[0069] Although the embodiment of the present invention has been described in detail above, the present invention is not limited to the specific description. For example, in the above embodiment, a pair of recessed holes 30, 30 is provided on both radial sides of the inner shaft member 12, but the recessed holes 30 may be provided only one at one location in the circumferential direction, or three or more recessed holes may be provided. In addition, when a plurality of recessed holes 30 are formed, the inclined surface 40 of the circumferentially facing inner surface 38 needs only to be provided in at least one of the plurality of recessed holes 30, and does not need to be provided in all of the recessed holes 30.

[0070] The inclination angle of the inclined surface 40 does not necessarily have to be constant over the entirety, but may vary gradually or stepwise in the axial direction over at least a portion of the axial direction.

[0071] The inclined surfaces 40 do not necessarily have to be provided on both axial sides, but may be provided on only one axial side. In addition, when the inclined surfaces 40, 40 are provided on both axial sides, the inclined surfaces 40, 40 may differ from each other in inclination angle, axial length, vertical cross-sectional shape, etc.

[0072] The inclined surface 40 does not necessarily have to be provided on both of the circumferentially facing inner surfaces 38, 38 of the recessed hole 30, but may be provided on only one of the circumferentially facing inner surfaces 38. As can be seen from this, the circumferentially facing inner surfaces 38, 38 of the recessed hole 30 may have mutually different shapes.

[0073] The axial end of the inclined surface 40 of the recessed hole 30 may be positioned laterally (outside in the left and right direction) away from the inner shank member 12 in a radial (up-down) projection where the recessed hole 30 is located. Furthermore, a portion of the circumferentially opposing inner surfaces 38, 38 of the recessed hole 30 where the circumferential inter-surface distance is minimum may be positioned laterally away from the inner shank member 12 in a radial projection where the recessed hole 30 is located. Moreover, the recessed hole 30 may be provided at a position overlapping with the inner shank member 12 in a lateral projection (left-right projection).

[0074] The distance between the radially opposing inner surfaces 32, 32 of the hollow hole 30 may vary in at least one of the circumferential and axial directions, and for example, it is possible to provide a stopper projection that protrudes radially into the hollow hole 30. Furthermore, the inner circumferential rubber 34 provided on the inner side of the hollow hole 30 may vary in thickness in the circumferential direction, and the cross-sectional shape may not be constant in the circumferential direction.

[0075] In the above embodiment, the large diameter portion 20 is integrally formed in the inner shaft member 12. However, for example, the inner shaft member having the large diameter portion can be formed by combining two parts, the inner shaft member and the annular member, by fixing an annular member formed separately from the inner shaft member in an outer-inserted state to the straight-shaped inner shaft member extending with a substantially constant cross section. In this case, it is also possible to make the inner shaft member and the annular member different in material, for example, by forming the inner shaft member from metal and the annular member from synthetic resin. For example, if the annular member is directly formed on the outer peripheral surface of the inner shaft member, the work of attaching the annular member to the inner shaft member can be omitted. The inner shaft member (inner shaft member) is not necessarily limited to a hollow cylinder shape, and may be, for example, a solid rod shape.

[0076] When the inclined surfaces 40, 40 are provided on both axial sides of the recessed hole 30, a non-inclined surface that is not inclined with respect to the axial direction may be provided between the inclined surfaces 40, 40. However, when such a non-inclined surface is provided in the approximate center portion in the axial direction, the axial length of the non-inclined surface is desirably 30% or less of the total axial length of the recessed hole 30, and more preferably 20% or less.

[0077] Also, the inclined surface 40 may be provided at an axial position offset axially outward from the large diameter portion 20 of the inner shaft member 12, with the entire inclined surface 40 being located on the outer periphery of the small diameter portion 18. However, it is desirable that the inclined surface 40 extend over a bulge portion (both axial side portions of the large diameter portion 20) that has a diameter slightly larger than the small diameter portion 18 of the inner shaft member 12, and at least a portion of the inclined surface 40 overlaps with the large diameter portion 20 when projected perpendicular to the axis. [Explanation of symbols]

[0078] 10 Suspension bush (first embodiment, cylindrical vibration isolator) 12 Inner shaft member 14 Outer cylindrical member 16 Main rubber elastic body 18 Small diameter section 20 Large diameter section 22 Straight section 24 Tapered section 26 Outer flange 28 Curved End Face 30. Curly Hole 32 radially opposed inner surface 34 Inner rubber 36 Outer rubber 38 Circumferentially facing inner surface 40 Slope

Claims

1. A cylindrical vibration-damping device in which an inner shaft member and an outer cylindrical member are connected by a main rubber elastic body, The inner shaft member is provided with a large diameter portion in an axially intermediate portion, the large diameter portion having an increased outer diameter. The main rubber elastic body is provided with a recessed hole penetrating the main rubber elastic body in the axial direction and extending a predetermined length in the circumferential direction, The cylindrical vibration-damping device has circumferentially opposing inner surfaces of the recessed hole having inclined surfaces which widen so that the circumferentially opposing distance between them gradually increases toward the axial opening of the recessed hole.

2. 2. A cylindrical vibration-damping device according to claim 1, wherein a distance between the circumferentially opposing inner surfaces of the recessed hole is smallest in an axial center portion and gradually increases toward both axial sides.

3. 3. A cylindrical vibration-damping device as described in claim 1 or 2, wherein at the axial position where the distance between the circumferentially opposing inner surfaces of the circumferentially opposing inner surfaces in the recessed hole is smallest, the distance between the circumferentially opposing surfaces of the circumferentially opposing inner surfaces is smaller than the outer diameter of the inner shaft member.

4. 4. The cylindrical vibration-damping device according to claim 3, wherein a distance between the circumferentially opposing inclined surfaces on the circumferentially opposing inner surfaces of the recessed hole is smaller than an outer diameter of the inner shaft member.

5. 3. The cylindrical vibration-isolating device according to claim 1, wherein the recessed hole does not overlap with the inner shaft member when projected from the side in the direction perpendicular to the axis.

6. A cylindrical vibration-damping device as described in claim 1 or 2, wherein the main rubber elastic body has a pair of recessed holes on both sides in a first radial direction relative to the inner shaft member, and has a solid structure in a second radial direction perpendicular to the first radial direction.

7. 3. A cylindrical vibration isolating device according to claim 1, wherein a distance between diametrically opposed inner surfaces of said recessed hole is constant.

8. 3. A cylindrical vibration-damping device according to claim 1, wherein a thickness dimension of said main rubber elastic body at a portion located on an inner periphery side of said recessed hole is constant in the circumferential direction.

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