Bush

Abstract

To provide a bush of a novel structure that can stably assemble an outer cylindrical metal fitting to a mounting hole of another member with target press-fit fixing force.SOLUTION: In a bush 10 in which an inner shaft member 12 is connected to an outer cylindrical metal fitting 14 by a body rubber elastic body 16, and the outer cylindrical metal fitting 14 is pressed-fitted and fixed to a mounting hole 34 of another member 32, a cylindrical inclined section 20 which is reduced in diameter toward axially outward at a constant inclination angle of 5 degrees or less is provided at an axial direction end of the outer cylindrical metal fitting 14. In the cylindrical inclined section 20, a half or more in the axial direction is positioned axially outward of an axial direction bottom section 28 of an axial direction end face of the body rubber elastic body 16, and an outer peripheral surface of the cylindrical inclined section 20 has a press-fit surface 22 in which a press-fit margin to the mounting hole 34 is set. An axial direction intermediate section of the outer cylindrical metal fitting 14 is provided with a straight section 18 extending axially with a constant outer diameter dimension. A press-fit fixing surface 40 to the mounting hole 34 is provided only in the straight section 18 outside the press-fit surface 22.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a bushing used, for example, as a suspension bushing for an automobile, and to a method for press-fitting and fixing the bushing into a mounting hole. [Background technology]

[0002] Conventionally, bushes have been known that are used as suspension bushes that connect the suspension arms of automobiles to the vehicle body in a vibration-damping manner. As shown in Japanese Patent No. 5401701 (Patent Document 1), for example, the bush has a structure in which an inner shaft member is inserted into an outer tubular metal member, and the inner shaft member and the outer tubular metal member are connected by a main rubber elastic body. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5401701 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, as shown in Figure 9 of Patent Document 1, bushings are used in a state in which the outer tubular fitting is fixed by being press-fitted into a mounting hole in another member. However, it has been found that with conventional bushings, there is a large variation in the fixing force due to the press-fitting into the other member (press-fit fixing force), in other words, the resistance to coming out of the other member (pull-out resistance force).

[0005] Therefore, the inventors studied conventional bushings and found that, in addition to the fact that it is difficult to avoid dimensional errors between both the outer tubular metal fitting and the mounting hole of the other component, even if the shape, dimensions, metal specifications, etc. of the outer tubular metal fitting are the same, variations in characteristics are unavoidable depending on the manufacturer, manufacturing time, lot, etc., and therefore it was thought that large variations would occur in the press-fit fixing force and pull-out resistance force.

[0006] The inventors conducted further experiments and found that when a simple, straight-shaped outer cylindrical metal fitting was press-fitted into a mounting hole, the outer cylindrical metal fitting of a bushing with a small press-fit fixing force (withdrawal resistance force) had linear scars extending in the press-fit direction on the outer circumferential surface of the outer cylindrical metal fitting. After examining this, they discovered that even if a press-fit allowance (reduction in radial dimension due to press-fitting) was set in calculations so that the outer cylindrical metal fitting would deform within the elastic deformation range, in reality the outer cylindrical metal fitting was plastically deformed locally, which caused uneven contact in the circumferential direction at the press-fit fixing surface of the outer cylindrical metal fitting with the inner surface of the mounting hole, resulting in a decrease in press-fit fixing force.

[0007] An object of the present invention is to provide a bushing of a novel structure that enables an outer tubular fitting to be stably assembled into a mounting hole of another member with a desired press-fitting fixing force.

[0008] Another object of the present invention is to provide a novel method for press-fitting and fixing a bush into a mounting hole, which makes it possible to stably assemble an outer tubular fitting into the mounting hole of another member with the desired press-fitting and fixing force. [Means for solving the problem]

[0009] The following describes preferred embodiments for understanding the present invention, but the embodiments described below are merely examples and may be appropriately combined with one another. Multiple components described in each embodiment may be recognized and employed independently to the greatest extent possible, and may also be appropriately combined with any of the components described in other embodiments. Accordingly, the present invention is not limited to the embodiments described below, and various other embodiments may be realized.

[0010] In a first aspect, in a bushing in which an inner axial member and an outer tubular fitting are connected by a main rubber elastic body, and the outer peripheral surface of the outer tubular fitting is fixed to a mounting hole of another member by press-fitting, at least one axial end of the outer tubular fitting is provided with a cylindrical inclined portion with an outer peripheral surface that reduces in diameter axially outward at a constant inclination angle of 5 degrees or less, and more than half of the axial length of the cylindrical inclined portion is located axially outward from the axial bottom of the axial end face of the main rubber elastic body, the outer peripheral surface of the cylindrical inclined portion is provided with a press-fit surface with a press-fit allowance for the mounting hole, and a straight portion extending axially with a constant outer diameter is provided in an intermediate axial portion of the outer tubular fitting, and a press-fit fixing surface that is press-fitted and fixed to the mounting hole is provided only on the straight portion, away from the press-fit surface.

[0011] In a bushing constructed according to this aspect, the press-fit surface that constitutes the outer peripheral surface of the cylindrical inclined portion of the outer tubular member tapers axially outward at a constant inclination angle. Therefore, when the press-fit surface is press-fitted into the mounting hole of another member, the amount of radial reduction deformation of the outer tubular member gradually increases as the press-fitting progresses. Therefore, compared to when the press-fit end is straight and undergoes sudden, large radial reduction deformation, the outer tubular member is less likely to leave the elastic deformation region. As a result, the outer tubular member within the elastic deformation region is elastically pressed against the inner surface of the mounting hole of the other member over a wide area, providing high press-fitting force and pull-out resistance.

[0012] By setting the inclination angle of the outer peripheral surface of the cylindrical inclined portion including the press-fit surface to 5 degrees or less, the rate of increase in the amount of diameter reduction deformation of the outer tubular fitting as the press-fitting progresses is set to be sufficiently small, making it less likely that the outer tubular fitting will undergo plastic deformation due to sudden diameter reduction, and therefore it is possible to obtain a stable effective press-fit fixing force (pull-out resistance force) for the outer tubular fitting.

[0013] In a second aspect, in the bushing according to the first aspect, the axial length of the press-fit surface of the cylindrical inclined portion is 3 mm or more.

[0014] With a bushing constructed according to this aspect, the press-fit allowance of the outer tubular fitting (the amount of diametrical deformation of the outer tubular fitting due to press-fitting) can be set to a sufficiently large value, which is set to be equal to or less than the difference between the maximum and minimum outer diameters of the press-fitting surface. This makes it possible to obtain a large press-fitting and securing force (pull-out resistance force) for the outer tubular fitting into the mounting hole of another member.

[0015] In a third aspect, in the bushing according to the first or second aspect, the outer peripheral surface of the cylindrical inclined portion serves as the press-fit surface over the entire axial length.

[0016] With a bushing constructed in accordance with this aspect, the axial dimension of the outer tubular member can be reduced while ensuring the press-fitting allowance of the outer tubular member set by the press-fitting surface.

[0017] In a fourth aspect, in the bushing described in any one of the first to third aspects, the press-fit fixing surface is provided partially in the axial direction on the straight portion of the outer tubular member.

[0018] In cases where the press-fit fixing surface is provided only partially in the axial direction on the straight portion of the outer tubular member and the press-fit fixing surface cannot be provided over a sufficient axial length, as in the case of a bushing constructed according to this embodiment, it is necessary to obtain a sufficiently large press-fit fixing force stably from the narrow press-fit fixing surface.Even in such cases, a sufficiently large press-fit fixing force can be obtained by providing a cylindrical inclined portion at the axial end of the outer tubular member and providing a press-fit surface with a predetermined press-fit allowance on the outer peripheral surface of the cylindrical inclined portion.

[0019] A fifth aspect is a bushing described in any one of the first to fourth aspects, wherein the main rubber elastic body has an outer peripheral extension portion that extends axially outward on the outer side of the axial bottom portion, and the outer peripheral extension portion is fixed to the inner peripheral surface of the cylindrical inclined portion.

[0020] With a bushing constructed according to this aspect, the region of the outer tubular member to which the outer peripheral extension of the main rubber elastic body (including, for example, a rubber portion for vulcanization bonding having a fillet radius) is fixed can be configured using a cylindrical inclined portion, thereby reducing or avoiding the increase in size of the outer tubular member that would be caused by providing a cylindrical inclined portion. Additionally, for example, when forming the cylindrical inclined portion by diameter reduction, pre-compression is applied to the axial end of the main rubber elastic body, which is expected to improve not only the press-fit fixing force due to the formation of the cylindrical inclined portion but also the durability of the main rubber elastic body. Furthermore, when the main rubber elastic body is pre-compressed by diameter reduction processing of the outer tubular metal fitting in order to reduce tensile stress due to shrinkage of the main rubber elastic body after molding, the cylindrical inclined portion can also be formed in the outer tubular metal fitting during the pre-compression process of the main rubber elastic body.

[0021] A sixth aspect is a method for press-fitting and fixing a bushing into a mounting hole, comprising the steps of: obtaining a bushing in which an inner axial member and an outer tubular fitting are connected by a main rubber elastic body; forming a cylindrical inclined portion whose diameter is reduced axially outward at an inclination angle of 5 degrees or less by performing diameter reduction processing on at least one axial end portion of the outer tubular fitting of the bushing; and press-fitting the outer tubular fitting of the bushing from the axial end portion where the cylindrical inclined portion is formed into a mounting hole of another member, thereby press-fitting the outer peripheral surface of the outer tubular fitting, including the outer peripheral surface of the cylindrical inclined portion, into the mounting hole of the other member with a press-fitting allowance for the mounting hole of the other member, and passing the cylindrical inclined portion of the outer tubular fitting against the fixed inner peripheral surface of the mounting hole, thereby press-fitting and fixing a straight portion provided in an intermediate portion of the axial direction of the outer tubular fitting to the fixed inner peripheral surface of the mounting hole.

[0022] According to the method of press-fitting and fixing a bushing into a mounting hole according to this aspect, a cylindrical inclined portion that improves the force with which the outer tubular fitting is press-fit and fixed into the mounting hole of another member can be easily obtained by reducing the diameter of the axial end of the outer tubular fitting. [Effects of the Invention]

[0023] According to the present invention, it is possible to stably assemble the outer tubular fitting of the bush into the mounting hole of another member with the desired press-fitting fixing force. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a cross-sectional view showing a bushing according to a first embodiment of the present invention; [Figure 2] FIG. 2 is a cross-sectional view of the bush shown in FIG. 1, showing the state before the cylindrical inclined portion is formed. [Figure 3] Cross-sectional view showing the bushing of Figure 1 attached to the suspension arm [Figure 4] A partial cross-sectional view showing the process of press-fitting the bushing of Figure 1 into the mounting hole of the suspension arm. [Figure 5] Graph showing the results of measuring the press-fitting fixing force between the bushing of FIG. 1 and a bushing of a comparative example. [Figure 6] Graph showing the results of measuring the pull-out resistance of the bushing of FIG. 1 and a bushing of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0026] Figure 1 shows a bushing 10 as a first embodiment of the present invention. The bushing 10 has a structure in which an inner shaft member 12 and an outer cylindrical fitting 14 are connected by a main rubber elastic body 16. In the following description, the axial direction generally refers to the up-down direction in Figure 1.

[0027] The inner shaft member 12 has a thick, small-diameter, and generally cylindrical shape. The inner shaft member 12 is a hard member formed of metal such as iron or aluminum alloy, or fiber-reinforced synthetic resin reinforced with glass fiber or the like.

[0028] The outer tubular member 14 has a generally cylindrical shape that is thin-walled and large in diameter compared to the inner axial member 12. The outer tubular member 14 of this embodiment has a smaller axial length dimension than the inner axial member 12. The outer tubular member 14 is formed from a metal such as iron or an aluminum alloy. An axially intermediate portion of the outer tubular member 14 is provided with a straight portion 18 that has a generally constant outer diameter dimension and extends non-inclined in the axial direction. The straight portion 18 of this embodiment also has a generally constant inner diameter dimension in the axial direction, and a generally constant radial thickness dimension in the axial direction. The axial length dimension of the straight portion 18 is at least half the axial length dimension of the outer tubular member 14.

[0029] A cylindrical inclined portion 20 is formed at the axial end of the outer tubular member 14. The cylindrical inclined portion 20 is inclined so that its diameter decreases axially outward. The outer peripheral surface of the cylindrical inclined portion 20 decreases axially outward at a substantially constant inclination angle α. The inclination angle α of the outer peripheral surface of the cylindrical inclined portion 20 is 5 degrees or less. The inclination angle α of the outer peripheral surface of the cylindrical inclined portion 20 is preferably 0.5 degrees or greater, and more preferably 1 degree or greater. The inclination angle α of the outer peripheral surface of the cylindrical inclined portion 20 (press-fit surface 22 described below) only needs to be substantially constant, and can be considered constant by ignoring variations of, for example, 0.2 degrees or less. The cylindrical inclined portion 20 of this embodiment has a substantially constant thickness, and the inner peripheral surface is inclined at the same inclination angle as the outer peripheral surface.

[0030] The axial length L of the cylindrical inclined portion 20 is preferably 3 mm or more, and more preferably 4 mm or more. The axial length L of the cylindrical inclined portion 20 is preferably 10 mm or less, and more preferably 7 mm or less.

[0031] The outer peripheral surface of the cylindrical inclined portion 20 serves as a press-fit surface 22 having a set press-fit allowance for a mounting hole 34 of a suspension arm 32, which will be described later. In this embodiment, the minimum outer diameter of the cylindrical inclined portion 20 is smaller than the minimum inner diameter of the mounting hole 34, and the outer peripheral surface of the cylindrical inclined portion 20 serves as the press-fit surface 22 over its entire axial length. Therefore, the axial length of the press-fit surface 22 and the axial length of the cylindrical inclined portion 20 are approximately the same. Furthermore, the inclination angle of the press-fit surface 22 is approximately the same as the inclination angle of the cylindrical inclined portion 20.

[0032] A guide portion 24 is provided on the outer tubular fitting 14 axially outward of the cylindrical inclined portion 20. The inner peripheral surface of the guide portion 24 has a diameter that tapers axially outward at approximately the same inclination angle as the inner peripheral surface of the cylindrical inclined portion 20. The outer peripheral surface of the guide portion 24 forms a guide surface 26 that tapers axially outward. The inclination angle of the guide surface 26 is greater than 5 degrees. Due to the provision of the guide surface 26, the inclination angle of the guide portion 24 is greater than the inclination angle α of the cylindrical inclined portion 20, and is therefore greater than 5 degrees. The minimum outer diameter of the guide portion 24 is smaller than the minimum inner diameter of the mounting hole 34 of the suspension arm 32, which will be described later. The maximum outer diameter of the guide portion 24 is the same as the minimum outer diameter of the cylindrical inclined portion 20. The guide surface 26 is formed by chamfering, such as by cutting, which prevents defects caused by crushed edges of the outer tubular fitting 14. The inclination angle of the guide portion 24 may vary in the axial direction.

[0033] The inner shaft member 12 is inserted into the outer tubular metal fitting 14, and a main rubber elastic body 16 is disposed radially between the inner shaft member 12 and the outer tubular metal fitting 14. The main rubber elastic body 16 is substantially cylindrical in shape, and its inner peripheral surface is vulcanization bonded to the outer peripheral surface of the inner shaft member 12, and its outer peripheral surface is vulcanization bonded to the inner peripheral surface of the outer tubular metal fitting 14. The main rubber elastic body 16 is formed as an integrally vulcanization molded product comprising the inner shaft member 12 and the outer tubular metal fitting 14.

[0034] The axial length of the main rubber elastic body 16 is greater at its inner peripheral end than at its outer peripheral end. Therefore, the axial end face of the main rubber elastic body 16 has a tapered shape that slopes axially outward toward the inner periphery as a whole. The axial end face of the main rubber elastic body 16 is configured as a curved surface that curves in the radial direction, with the angle of inclination varying radially. In this embodiment, the axial end face of the main rubber elastic body 16 has a concave cross section as shown in FIG. 1 , with the outer peripheral portion sloped axially inward toward the inner periphery and the inner peripheral portion sloped axially outward toward the inner periphery. Furthermore, the axially innermost portion of the axial end face of the main rubber elastic body 16 with a concave cross section is defined as the axial bottom portion 28.

[0035] The outer peripheral end of the main rubber elastic body 16 is provided with an outer peripheral extension 30 that extends axially outward on the outer peripheral side of the axial bottom 28. The outer peripheral extension 30 is formed with a substantially constant cross-sectional shape around its entire circumference, and its outer peripheral surface is fixed to the inner peripheral surface of the cylindrical inclined portion 20 of the outer tubular fitting 14. In this embodiment, the outer peripheral extension 30 is a thin-walled, rounded fillet extending axially from the outer peripheral edge of the axial end face of the main rubber elastic body 16. This portion reduces deformation and stress during load input, ensuring a sufficient adhesive area to the outer tubular fitting 14, thereby improving the durability and load-bearing capacity of the adhesive surface. Furthermore, by fixing this outer peripheral extension 30 to the cylindrical inclined portion 20 of the outer tubular fitting 14, it is possible to realize the cylindrical inclined portion 20 without excessively increasing the axial size of the outer tubular fitting 14.

[0036] In this embodiment, the axially outer end of the outer peripheral extending portion 30 extends axially outward beyond the cylindrical inclined portion 20 and is fixed to the inner peripheral surface of the guide portion 24. The axially outer bottom portion 28 of the main rubber elastic body 16 is located axially outward beyond the straight portion 18 of the outer tubular metal fitting 14, and the axially inner end of the outer peripheral extending portion 30 is located on the inner periphery of the cylindrical inclined portion 20. Note that more than half of the axial length of the cylindrical inclined portion 20 of the outer tubular metal fitting 14 is located axially outward beyond the axial bottom portion 28 of the main rubber elastic body 16.

[0037] The bushing 10 according to this embodiment can be obtained as follows. First, the inner axial member 12 and the outer tubular member 14' are prepared. The inner axial member 12 and the outer tubular member 14' can be obtained by cutting a metal pipe of a certain inner and outer diameter obtained by, for example, extrusion or welding, to a predetermined length. As shown in FIG. 2, the outer tubular member 14' has a generally straight cylindrical shape overall, and does not have a cylindrical inclined portion 20 or a guide portion 24. In addition, a guide surface 26 is formed on the outer peripheral surface of the axial end of the outer tubular member 14'.

[0038] Next, the inner shaft member 12 and the outer tubular metal fitting 14' are set in a mold for molding the main rubber elastic body 16, and the main rubber elastic body 16 is vulcanization molded. This results in a bushing 10' as an integrally vulcanization molded product of the main rubber elastic body 16, as shown in Figure 2.

[0039] Next, the axial end of the outer tubular member 14' of the bushing 10' is subjected to diameter reduction processing to form a cylindrical inclined portion 20 that is tapered axially outward at a constant inclination angle of 5 degrees or less, thereby obtaining the bushing 10 equipped with the outer tubular member 14. In this embodiment, a cylindrical inclined portion 20 is formed at each of both axial end portions of the outer tubular member 14. The cylindrical inclined portions 20 on both axial sides can also be formed simultaneously by a single diameter reduction process. Note that in this embodiment, when forming the cylindrical inclined portion 20 by diameter reduction processing, the portion provided with the guide surface 26 is also reduced in diameter, so that the guide portion 24 located axially outward of the cylindrical inclined portion 20 also has a shape that is inclined axially outward and inward. Furthermore, when forming the cylindrical inclined portion 20 by diameter reduction processing, the straight portion 18 of the outer tubular member 14 is also reduced in diameter, and the main rubber elastic body 16 is pre-compressed in the radial direction.

[0040] The outer cylindrical fitting 14 has a cylindrical inclined portion 20 and a guide portion 24 at both axial ends, and is shaped as plane symmetry with respect to a plane perpendicular to the axis that passes through the center of the axial direction. In this embodiment, the inner shaft member 12 and the main rubber elastic body 16 also have plane symmetry with respect to the outer cylindrical fitting 14, and the entire bushing 10 has plane symmetry with respect to a plane perpendicular to the axis that passes through the center of the axial direction. In addition, the bushing 10 is rotationally symmetric about the central axis.

[0041] As shown in FIG. 3 , the bushing 10 according to this embodiment is fixed by press-fitting the outer peripheral surface of the outer tubular member 14 into a mounting hole 34 of a suspension arm 32, which serves as another member. The inner peripheral surface of the mounting hole 34 in the suspension arm 32 has one axial end formed as a cylindrical fixed inner peripheral surface 36 that extends straight, and the other axial end formed as a tapered guide surface 38 that widens as it moves away from the fixed inner peripheral surface 36. The inner diameter of the fixed inner peripheral surface 36 is smaller than the minimum outer diameter of the cylindrical inclined portion 20 of the outer tubular member 14 and larger than the minimum outer diameter of the guide portion 24 of the outer tubular member 14. The axial length of the fixed inner peripheral surface 36 is smaller than the axial length of the straight portion 18 of the outer tubular member 14. The maximum inner diameter of the guide surface 38 is larger than the maximum outer diameter of the outer tubular member 14. 3 shows the portion of the suspension arm 32 where the bushing 10 is press-fitted and fixed, but the suspension arm 32 extends in a direction intersecting the plane of the paper on which FIG. 3 is drawn, for example.

[0042] The straight portion 18 of the outer tubular fitting 14 is fixed by press fitting into the mounting hole 34 of the suspension arm 32, and so a press-fit fixing surface 40 that is press-fitted and fixed into the mounting hole 34 is provided on the outer peripheral surface of the straight portion 18. The outer tubular fitting 14 is press-fitted and fixed into the mounting hole 34 at a position that is offset axially inward from the cylindrical inclined portion 20, and so the press-fit fixing surface 40 is provided only on the straight portion 18, not on the cylindrical inclined portion 20. In this embodiment, the axial length of the straight portion 18 is greater than the axial length of the mounting hole 34 in the suspension arm 32, and part of the axial length of the straight portion 18 is press-fitted and fixed into the mounting hole 34, so the press-fit fixing surface 40 is set partially in the axial direction on the straight portion 18.

[0043] 4, the outer tubular fitting 14 is press-fit into the mounting hole 34 of the suspension arm 32 from the axial end side where the guide surface 38 is formed. As a result, the axial end of the outer tubular fitting 14 abuts against the guide surface 38 and is guided onto the same center axis as the mounting hole 34, making it easy to position the outer tubular fitting 14 with respect to the mounting hole 34.

[0044] The outer tubular fitting 14 is press-fitted into the mounting hole 34 of the suspension arm 32 from one axial end (the lower end in FIG. 1 ) where the cylindrical inclined portion 20 and the guide portion 24 are provided. The minimum outer diameter of the guide portion 24 provided at the press-fitting tip of the outer tubular fitting 14 is smaller than the minimum inner diameter of the fixed inner circumferential surface 36 of the mounting hole 34, so that the outer tubular fitting 14 can be easily inserted into the mounting hole 34. In particular, the inner circumferential surface of the opening end of the mounting hole 34 on the side that receives the outer tubular fitting 14 has a flared shape, making it even easier to insert the outer tubular fitting 14 into the mounting hole 34. In this embodiment, the cylindrical inclined portion 20 and the guide portion 24 are provided at both axial ends of the outer tubular fitting 14, so that the press-fitting tip of the outer tubular fitting 14 may be at either axial end.

[0045] Because the minimum outer diameter of the cylindrical inclined portion 20 is larger than the minimum inner diameter of the fixed inner peripheral surface 36 of the mounting hole 34, the outer peripheral surface of the outer tubular fitting 14, including the cylindrical inclined portion 20, is press-fit into the mounting hole 34 of the suspension arm 32 with a press-fit allowance. Note that even when a chamfered guide surface 26 is employed, the minimum inner diameter of the mounting hole 34 (the inner diameter of the fixed inner peripheral surface 36) is desirably designed taking into account the outer diameter of the imaginary outer peripheral edge of the outer tubular fitting 14 in the absence of the guide surface 26. For example, the minimum inner diameter of the mounting hole 34 is made larger than the outer diameter of the imaginary outer peripheral edge of the outer tubular fitting 14 without the guide surface 26. However, regardless of the presence or absence of a chamfered guide surface 26, the outer diameter (minimum outer diameter) of the press-fit tip of the cylindrical inclined portion 20 may be designed to be the same as the minimum inner diameter of the mounting hole 34.

[0046] As the press-fitting of the outer tubular fitting 14 into the mounting hole 34 progresses, the fixed inner circumferential surface 36 of the mounting hole 34 in the suspension arm 32 moves axially inward along the outer periphery of the cylindrical inclined portion 20 while pressing the press-fit surface 22 that constitutes the outer periphery of the cylindrical inclined portion 20 inward. Because the diameter of the press-fit surface 22 increases axially inward, the press-fit allowance between the press-fit surface 22 of the cylindrical inclined portion 20 and the fixed inner circumferential surface 36 of the mounting hole 34 gradually increases as the press-fitting progresses. This prevents a sudden increase in the amount of radial reduction and deformation of the outer tubular fitting 14 that accompanies press-fitting into the mounting hole 34, and prevents the outer tubular fitting 14 from leaving its elastic deformation range and becoming plastically deformed. As a result, when the outer tubular fitting 14 is press-fit and fixed into the mounting hole 34 of the suspension arm 32, the press-fit fixing surface 40 of the outer tubular fitting 14 is effectively pressed against the fixed inner surface 36 of the mounting hole 34 by the elasticity of the outer tubular fitting 14, thereby obtaining a large press-fit fixing force for the outer tubular fitting 14 into the mounting hole 34.

[0047] In this way, by providing the cylindrical inclined portion 20 at the axial end portion of the outer tubular fitting 14, the outer tubular fitting 14 is less likely to undergo plastic deformation outside of its elastic deformation range when press-fitted. This prevents the occurrence of plastic deformation of the outer tubular fitting 14 due to, for example, variations in press-fit allowance caused by dimensional errors in the outer tubular fitting 14 and suspension arm 32, or variations in characteristics caused by differences in the manufacturer, manufacturing date, lot, etc. of the outer tubular fitting 14, making it possible to obtain a stable press-fitting and fixing force.

[0048] In particular, because the inclination angle α of the press-fit surface 22 is 5 degrees or less, the rate of change in the amount of radial reduction deformation of the outer tubular fitting 14 as press-fitting progresses is kept sufficiently small, making it possible to reliably prevent a decrease in the press-fit fixing force due to plastic deformation of the outer tubular fitting 14. Furthermore, if the inclination angle α of the press-fit surface 22 is 0.5 degrees or more, it is possible to ensure a press-fit allowance between the outer tubular fitting 14 and the mounting hole 34 without making the outer tubular fitting 14 longer than necessary.

[0049] Because the inclination angle α of the press-fit surface 22 is set to a substantially constant value in the axial direction, the rate of change in the amount of radial reduction deformation of the outer tubular fitting 14 as press-fitting progresses is substantially constant. This effectively prevents sudden deformation of the outer tubular fitting 14, allowing the outer tubular fitting 14 to stably deform elastically within the elastic deformation range.

[0050] The axial length dimension L of the cylindrical inclined portion 20 having the press-fit surface 22 is set to 3 mm or more. As a result, even if the inclination angle α of the cylindrical inclined portion 20 is set to a small value of 5 degrees or less, a sufficient press-fit allowance (amount of radial reduction deformation of the outer cylindrical fitting 14 due to press-fitting) between the outer cylindrical fitting 14 and the mounting hole 34 is ensured. In particular, in this embodiment, the press-fit surface 22 that is press-fitted into the mounting hole 34 is provided over the entire axial length of the cylindrical inclined portion 20, so that it is possible to more efficiently ensure the press-fit allowance between the outer cylindrical fitting 14 and the mounting hole 34 and to more efficiently reduce the size of the outer cylindrical fitting 14 in the axial direction. Note that if the axial length dimension L of the cylindrical inclined portion 20 is set to 10 mm or less, it is possible to prevent the outer cylindrical fitting 14 from becoming unnecessarily long while ensuring the press-fit allowance between the outer cylindrical fitting 14 and the mounting hole 34.

[0051] The cylindrical inclined portion 20 of the outer tubular fitting 14 is passed over the fixed inner circumferential surface 36 of the mounting hole 34, and the straight portion 18 of the outer tubular fitting 14 is press-fitted and fixed against the fixed inner circumferential surface 36, thereby attaching the bushing 10 to the suspension arm 32 with the outer tubular fitting 14 fixed thereto. This completes the process of press-fitting and fixing the outer tubular fitting 14 into the mounting hole 34.

[0052] The bushing 10 of this embodiment can stably obtain a large force for press-fitting and fixing into the mounting hole 34 of the outer tubular member 14. Therefore, even if the press-fit fixing surface 40, which is press-fitted and fixed into the fixed inner circumferential surface 36 of the mounting hole 34 of the suspension arm 32, is provided partially in the axial direction with respect to the straight portion 18 of the outer tubular member 14, and the axial length of the press-fit fixing surface 40 is reduced, the bushing 10 can be attached to the suspension arm 32 with sufficient pull-out resistance.

[0053] In the outer tubular member 14, the press-fit fixing surface 40 for the mounting hole 34 of the suspension arm 32 is set only on the straight portion 18, and not on the cylindrical inclined portion 20. This makes it possible to reduce the axial length dimension of the mounting hole 34, for example, to make the suspension arm 32 more compact, while also enabling a stable design and setting of the press-fit fixing force.

[0054] Incidentally, it has been confirmed by measurements that the bush 10 constructed according to this embodiment exerts a high press-fitting fixing force.

[0055] 5 is a graph showing the results of measuring the press-fitting force required to press-fit an outer tubular fitting into a mounting hole in another member. In the graph of Fig. 5, the horizontal axis represents the amount of relative displacement between the outer tubular fitting and the other member in the press-fitting direction, and the vertical axis represents the press-fitting force.

[0056] Moreover, Figure 6 is a graph showing the results of measuring the pull-out force required to axially pull out the outer tubular fitting, which has been press-fitted into the mounting hole 34 of the other member 32, from the mounting hole 34. In the graph of Figure 6, the horizontal axis represents the amount of relative displacement between the outer tubular fitting and the other member 32 in the pulling-out direction, which is opposite to the press-fitting direction, and the vertical axis represents the pulling-out force.

[0057] 5 and 6, the measurement results for the bushing 10 according to this embodiment are shown by solid lines, and the measurement results for the bushing of the comparative example are shown by dashed lines. The bushing of the comparative example employs an outer tubular fitting 14' that does not have the cylindrical inclined portion 20 instead of the outer tubular fitting 14.

[0058] According to the measurement results shown in FIG. 5 , the bushing 10 according to this embodiment has a low press-fitting force in a region where the press-fit displacement is less than 2 mm, but the press-fitting force gradually increases at a substantially constant rate of change across a press-fit displacement range of approximately 2 mm to 7 mm. Furthermore, when the press-fit displacement exceeds 4 mm, the press-fitting force becomes larger than that of the bushing of the comparative example, demonstrating a higher press-fitting and fixing force. Furthermore, when the press-fit displacement exceeds 7 mm, although there are some fluctuations, a stable press-fitting and fixing force is exerted up to approximately 14.5 mm. On the other hand, the bushing of the comparative example exhibits a sudden increase in press-fitting force when the press-fit displacement is only in a range of approximately 1 mm to 2 mm, and a sudden decrease in press-fitting force in a range of approximately 2 mm to 3 mm. This is thought to indicate that the outer cylindrical metal member is forced to undergo a sudden diameter reduction deformation due to press-fitting into the mounting hole in the early stages of press-fitting, causing plastic deformation of the outer cylindrical metal member. When the press-fit displacement exceeds 3 mm, the press-fitting force is stable, but is lower than that of the bushing 10 according to this embodiment, resulting in insufficient press-fitting and fixing force.

[0059] For this reason, when the bushing of the comparative example is press-fitted into the mounting hole 34 with a short axial length, strain tends to concentrate in the circumferential direction due to variations in the contact surface in the circumferential direction caused by component dimensional errors, etc., and plastic deformation such as localized buckling occurs on the outer peripheral surface, which tends to result in large variations in press-fit fixing force. To address this problem, the bushing 10 of this embodiment has a cylindrical inclined portion 20 with a small inclination angle of 5 degrees or less, which is barely noticeable from the outside. This allows for gradual press-fit deformation, allowing for the outer tubular member 14 to be press-fitted gradually and gradually, thereby adjusting the deformation pattern in the initial press-fit stage so that the amount of diametrical contraction deformation of the outer tubular member 14 is dispersed and adapted to the new shape. This allows the outer tubular member 14 to be deformed stably within the elastic deformation range over the entire circumferential direction, resulting in an advantageous and stable attainment of the desired press-fit fixing force.

[0060] The measurement results in Figure 6 show that the bushing 10 according to this embodiment provides a large resistance force that prevents the outer tubular metal member 14 from coming out of the mounting hole 34. In particular, measurements confirmed that the bushing 10 provides a significantly higher pull-out resistance force than the bushing of the comparative example in the region where the pull-out displacement is 8 mm or less. Similar to the difference in press-fit fixing force, this difference in pull-out resistance force is thought to be achieved by preventing plastic deformation of the outer tubular metal member during press-fitting.

[0061] Furthermore, when the outer fitting of the comparative example was observed after it had actually been pulled out of the mounting hole 34, linear scars extending in the press-fitting direction were observed on the outer peripheral surface, confirming that strain had concentrated locally in the circumferential direction, resulting in plastic deformation of the outer tubular fitting in a buckling manner.

[0062] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the specific description. For example, the inner shaft member is not limited to a straight cylindrical shape, and may have a bulge-like portion protruding toward the outer periphery in the axially middle portion. The bulge-like portion may be formed, for example, by partially expanding the diameter of the inner shaft member, or by attaching a separate annular member to the outer periphery of the inner shaft member.

[0063] The cylindrical inclined portion 20 is preferably provided at both axial ends of the outer tubular fitting 14 to prevent the direction of press-fitting of the outer tubular fitting 14 into the mounting hole 34 from being limited. However, it may be provided, for example, at only one axial end that is the press-fitting tip side.

[0064] The press-fit surface 22 can also be set partially in the axial direction on the outer peripheral surface of the cylindrical inclined portion 20. Specifically, for example, if the outer peripheral surface of the cylindrical inclined portion 20 has a smaller diameter at its axially outer end than the mounting hole 34, the outer peripheral surface of the axially outer end portion of the cylindrical inclined portion 20 that is not press-fitted into the mounting hole 34 does not become the press-fit surface, but the outer peripheral surface of the axially inner end portion of the cylindrical inclined portion 20 that is press-fitted into the mounting hole 34 becomes the press-fit surface 22. Note that if the minimum outer diameter dimension of the axial tip side of the cylindrical inclined portion 20 or the guide portion 26 is smaller than the inner diameter dimension of the mounting hole 34, there is no need to provide the guide surface 38 on the suspension arm 32.

[0065] The cylindrical inclined portion 20 may be formed by subjecting the outer tubular fitting 14' to diameter reduction processing after the main rubber elastic body 16 has been vulcanized, but, for example, the outer tubular fitting 14' in a standalone state before the main rubber elastic body 16 is vulcanized may be subjected to diameter reduction processing to form the cylindrical inclined portion 20, and then the main rubber elastic body 16 may be vulcanized. In short, the outer tubular fitting set in the mold for molding the main rubber elastic body 16 may be the outer tubular fitting 14' without the cylindrical inclined portion 20, or it may be the outer tubular fitting 14 provided with the cylindrical inclined portion 20.

[0066] The outer tubular fitting 14 may have the entire straight portion 18 press-fitted into the mounting hole 34 , in which case the entire outer circumferential surface of the straight portion 18 serves as the press-fit fixing surface 40 .

[0067] The main rubber elastic body may be provided with a recessed hole for the purpose of tuning spring characteristics, etc. The recessed hole may be provided so as to pass through the main rubber elastic body in the axial direction, or may be provided so as to extend in the circumferential direction without passing through.

[0068] The bushing 10 according to the present invention is not limited to a suspension bushing in which the outer tubular member 14 is press-fitted and fixed into the mounting hole 34 of the suspension arm 32. Specifically, the present invention can also be applied to power unit mounts such as engine mounts and motor mounts, torque rod bushings, subframe mounts, etc. [Explanation of symbols]

[0069] 10 Bush (first embodiment) 10´ Bush 12 Inner shaft member 14 Outer cylindrical fitting 14´ outer tube fitting 16 Main body rubber elastic body 18 Straight section 20 cylindrical inclined section 22 Press-fit surface 24 Guide section 26 Guide surface 28 Axial bottom 30 Peripheral extension 32 Suspension arm (other parts) 34 Mounting hole 36 Fixed inner surface 38 Guide surface 40 Press-fit fixing surface L Axial length dimension of the cylindrical inclined portion and press-fit surface α: Inclination angle of the cylindrical inclined portion and the press-fit surface

Claims

1. In a bushing in which an inner shaft member and an outer tubular metal member are connected by a main rubber elastic body, and the outer peripheral surface of the outer tubular metal member is fixed to a mounting hole of another member by press-fitting, a cylindrical inclined portion having an outer circumferential surface whose diameter decreases axially outward at a constant inclination angle of 5 degrees or less is provided on at least one axial end of the outer tubular member, a portion of at least half of the cylindrical inclined portion in the axial direction is located axially outward from an axial bottom portion of an axial end surface of the main rubber elastic body, an outer peripheral surface of the cylindrical inclined portion includes a press-fit surface having a press-fitting margin set for the mounting hole; A straight section extending in the axial direction with a constant outer diameter is provided in the axially intermediate portion of the outer tubular fitting, and a press-fitting surface that is press-fitted and fixed into the mounting hole is provided only on this straight section, away from the press-fitting surface.

2. 2. The bushing according to claim 1, wherein the axial length of the press-fit surface of the cylindrical inclined portion is 3 mm or more.

3. 3. The bushing according to claim 1, wherein the outer peripheral surface of the cylindrical inclined portion is the press-fit surface over the entire axial length.

4. 3. The bushing according to claim 1, wherein the press-fitted fixing surface is provided partially in the axial direction on the straight portion of the outer tubular member.

5. A bushing as described in claim 1 or 2, wherein the main rubber elastic body has an outer peripheral extension portion that extends axially outward on the outer side of the axial bottom portion, and the outer peripheral extension portion is fixed to the inner peripheral surface of the cylindrical inclined portion.

6. a step of obtaining a bushing in which an inner shaft member and an outer tubular member are connected by a main rubber elastic body; a step of performing a diameter reduction process on at least one axial end portion of the outer tubular member of the bushing to form a cylindrical inclined portion whose diameter is reduced axially outward at an inclination angle of 5 degrees or less; a step of press-fitting the outer tubular fitting of the bushing from the axial end portion on which the cylindrical inclined portion is formed into a mounting hole of another member, thereby press-fitting the outer peripheral surface of the outer tubular fitting, including the outer peripheral surface of the cylindrical inclined portion, into the mounting hole of the other member with a press-fitting allowance for the mounting hole, and passing the cylindrical inclined portion of the outer tubular fitting against the fixed inner peripheral surface of the mounting hole to press-fit and fix a straight portion provided in an axial intermediate portion of the outer tubular fitting to the fixed inner peripheral surface of the mounting hole; A method of press-fitting a bush into a mounting hole.

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