Jointed Boots

Abstract

To provide a joint boot which can suppress a bulge of a recess which is formed at a part in a peripheral direction.SOLUTION: A connecting part 40 for connecting a bellows part 33 and a large-diameter cylinder part 32 is formed by connecting a circular arc part 41 in which an external peripheral face with an axial core C as a center is formed at a cross section vertical to the axial core C, and a recessed part 45 which is recessed to the axial core C side with respect to the circular arc part 41 in a peripheral direction. A protrusion 48 protrudes from a center of an external peripheral face of the recessed part 45 at least in the peripheral direction, and an outer radius D2 from the axial core C up to the protrusion 48 and an outer radius D1 of the circular arc part 41 are the same with each other. Therefore, even if a clearance 70 is formed between a metal mold and the external peripheral face of the recessed part 45 at blow-molding, since a tip of the protrusion 48 abuts on the metal mold, and functions as a tension rod, a bulge of the recessed part 45 can be suppressed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a joint boot, and more particularly to a joint boot that can suppress bulging of a recess provided in a portion of its circumferential direction. [Background technology]

[0002] A constant velocity joint used in an automobile drive shaft or propeller shaft is configured by fitting a rolling part provided at the tip of a second transmission shaft into a cylindrical outer case provided at the tip of a first transmission shaft, and a joint boot is attached to the connecting part between the first and second transmission shafts. The joint boot includes a small-diameter cylindrical part into which the second transmission shaft is inserted, a large-diameter cylindrical part into which the outer case is inserted, a cylindrical bellows part extending from the small-diameter cylindrical part to the large-diameter cylindrical part, and a cylindrical connecting part connecting the bellows part and the large-diameter cylindrical part.

[0003] Patent Document 1 discloses a method for manufacturing this joint boot. In Patent Document 1, first, a preform including a small-diameter cylindrical portion, a large-diameter cylindrical portion, a connecting portion, and a tapered portion connecting the large-diameter cylindrical portion and the connecting portion is formed by injection molding. Then, with the outer periphery of the preform covered with a mold, gas is blown into the inner periphery of the preform to plastically deform the tapered portion into a bellows portion.

[0004] Furthermore, in Patent Document 1, due to the shape of the outer case into which the large-diameter cylindrical portion is inserted and the ease of demolding during molding, a portion of the inner peripheral surface of the connecting portion in the circumferential direction is recessed toward the axis of the large-diameter cylindrical portion. Furthermore, to ensure a uniform thickness of the connecting portion in the circumferential direction, taking into account shrinkage during molding, the outer peripheral surface of the connecting portion is formed to conform to the inner peripheral surface. Therefore, the connecting portion includes an arc-shaped portion whose outer peripheral surface is formed in an arc shape centered on the axis of the large-diameter cylindrical portion, and a recessed portion whose outer peripheral surface is recessed toward the axis from the arc-shaped portion. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-168750 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in conventional techniques, the circumferential alignment of the preform relative to the mold during blow molding is omitted, and the portion of the mold where the connecting portion contacts is formed to match the arc-shaped portion along the entire circumference. This results in a gap between the mold and the outer circumferential surface of the recess, which can cause the recess to bulge during blow molding. For example, this bulge can cause a deterioration in the appearance of the joint boot or a decrease in durability due to a partial reduction in thickness near the recess.

[0007] The present invention has been made to solve the above-mentioned problems, and has an object to provide a joint boot that can suppress bulging of a recess provided in a portion of the circumferential direction. [Means for solving the problem]

[0008] In order to achieve this object, the joint boot of the present invention is a cylindrical member made of an elastic body and attached to a constant velocity joint in which a second transmission shaft is fitted into an outer case of a first transmission shaft, and comprises: a small-diameter cylindrical section into which the second transmission shaft is inserted; a large-diameter cylindrical section into which the outer case is inserted; a cylindrical bellows section in which peaks and valleys are formed repeatedly from the small-diameter cylindrical section toward the large-diameter cylindrical section; and a cylindrical connecting section that connects the valleys of the bellows section closest to the large-diameter cylindrical section to the large-diameter cylindrical section, wherein the connecting section, in a cross section perpendicular to the axis of the large-diameter cylindrical section, comprises: an arc-shaped section whose outer peripheral surface is formed in an arc shape centered on the axis; a recess whose outer peripheral surface is recessed toward the axis from the arc-shaped section and connects the arc-shaped sections in the circumferential direction; and a protrusion that protrudes from at least the center in the circumferential direction of the outer peripheral surface of the recess, and the outer radius from the axis to the tip of the protrusion is the same as the outer radius of the arc-shaped section. [Effects of the Invention]

[0009] According to the joint boot of claim 1, the connecting portion connecting the bellows portion and the large-diameter cylindrical portion is formed by connecting, in a circumferential direction, an arc-shaped portion whose outer peripheral surface is formed in an arc shape centered on the axis in a cross section perpendicular to the axis, and a recessed portion recessed toward the axis from the arc-shaped portion. A protrusion protrudes from at least the circumferential center of the outer peripheral surface of this recessed portion, and the outer radius from the axis to the tip of the protrusion is the same as the outer radius of the arc-shaped portion. Therefore, even if a gap occurs between the mold and the outer peripheral surface of the recessed portion during blow molding, the tip of the protrusion comes into contact with the mold and functions as a tension rod, thereby suppressing bulging of the recessed portion.

[0010] The joint boot of claim 2 achieves the following effect in addition to the effect of the joint boot of claim 1. The connecting portion has a plurality of recesses of the same shape spaced apart in the circumferential direction, and each recess is provided with a protrusion of the same shape. This makes it possible to make the recesses less likely to expand during blow molding and to make the rigidity of the joint boot near the recesses uniform in the circumferential direction. As a result, stress is less likely to concentrate in certain circumferential areas, such as low-rigidity areas, and the durability of the joint boot can be improved.

[0011] The joint boot of claim 3 achieves the following effect in addition to the effect achieved by the joint boot of claim 1 or 2. When a preform having a connecting portion before being blow-molded into a joint boot is molded by injection molding or the like in a mold, the mold for forming the outer peripheral surface of the preform is often split in a direction perpendicular to the axis. Since the protrusion is formed extending in the entire circumferential direction within the recess, the protrusion does not interfere with demolding when the preform is demolded. This simplifies the manufacturing process of the joint boot.

[0012] The joint boot of claim 4 achieves the following effect in addition to the effect achieved by the joint boot of any one of claims 1 to 3. The arc-shaped portion has a parallel surface portion whose outer circumferential surface is parallel to the axis. The protrusion is located closer to the small-diameter cylindrical portion (bellows portion) than the axial center of the parallel surface portion. In this way, by bringing the protrusion closer to the bellows portion, which expands during blow molding, the protrusion can make it even more difficult for the recess to expand.

[0013] The joint boot of claim 5 achieves the following effect in addition to the effect achieved by the joint boot of any one of claims 1 to 4. The inner peripheral surface of the recess has a parallel inner surface parallel to the axis and a protruding portion that is connected to the end of the parallel inner surface on the small-diameter cylindrical portion side and protrudes from the parallel inner surface toward the axis. The portion that bulges mainly during blow molding is closer to the small-diameter cylindrical portion than the boundary between the parallel inner surface and the protruding portion, and the protrusion is located closer to the large-diameter cylindrical portion than that boundary. This makes it possible to prevent the protrusion from adversely affecting the molding of the bellows portion by blow molding, such as making the portion with the protrusion less susceptible to plastic deformation.

[0014] In this specification, a predetermined portion (for example, a parallel inner surface) is parallel to the axis when the inclination of the predetermined portion with respect to the axis is 2° or less. In other words, a draft may be set at the predetermined portion. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view of a constant velocity joint equipped with a joint boot according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view of one side of the joint boot. [Figure 3] 3 is a bottom view of the joint boot as seen from the direction of arrow III in FIG. 2. FIG. [Figure 4] FIG. 4 is a cross-sectional view of the joint boot taken along line IV-IV in FIG. 2. [Figure 5] FIG. 2 is a cross-sectional view of a preform and a mold during blow molding. [Figure 6] 10 is a cross-sectional view of a joint boot showing a modified example of the protrusion. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] Preferred embodiments will now be described with reference to the accompanying drawings. Figure 1 is a cross-sectional view of a constant velocity joint 10 fitted with a joint boot 30 in one embodiment. The constant velocity joint 10 transmits rotational force at a constant speed while changing the angle at the connection between a first transmission shaft 11 and a second transmission shaft 16, and is used in automobile drive shafts, propeller shafts, etc.

[0017] Constant velocity joint 10 is a tripod type in which the connecting portion is extendable and contractible. A cylindrical outer case 12 is provided at the tip of first transmission shaft 11 of constant velocity joint 10. Three guide grooves 13 are formed along the axial direction on the inner peripheral surface of outer case 12 and are arranged at equal intervals in the circumferential direction. The outer peripheral surface of outer case 12 is provided with a cylindrical convex surface 14 that forms the outer peripheral side of guide grooves 13 and is centered on the axis of outer case 12, and a concave surface 15 that connects convex surfaces 14 in the circumferential direction and is concave toward the axis center (radially inward).

[0018] A tripod 19 is provided at the tip of the second transmission shaft 16. The tripod 19 is configured by three trunnions 18 with rollers 17 protruding from the second transmission shaft 16. The first transmission shaft 11 and the second transmission shaft 16 are connected by fitting the tripod 19 into the outer case 12 so that the rollers 17 roll within the guide grooves 13 of the outer case 12.

[0019] A joint boot 30 is attached to the connecting portion of this constant velocity joint 10. The joint boot 30 is designed to contain the grease required to lubricate the connecting portion of the constant velocity joint 10 and to prevent foreign matter such as water and mud from entering the connecting portion. The joint boot 30 is integrally molded from an elastic body, specifically from a thermoplastic resin (such as polyester or polyurethane, including thermoplastic elastomers).

[0020] The joint boot 30 includes a small-diameter cylindrical portion 31 into which the second transmission shaft 16 is inserted, a large-diameter cylindrical portion 32 into which the outer case 12 is inserted, a cylindrical bellows portion 33 extending from the small-diameter cylindrical portion 31 toward the large-diameter cylindrical portion 32, and a cylindrical connecting portion 40 connecting the bellows portion 33 and the large-diameter cylindrical portion 32. The outer diameter of the large-diameter cylindrical portion 32 is larger than the outer diameter of the small-diameter cylindrical portion 31. The small-diameter cylindrical portion 31 and the large-diameter cylindrical portion 32 are each fastened from the outer periphery by a band 20, and are fixed to the second transmission shaft 16 and the outer case 12, respectively.

[0021] 2 is a half-sectional view of the joint boot 30 taken along the axis C of the large-diameter cylindrical portion 32. The bellows portion 33 is a portion in which peaks and valleys are repeatedly formed, and the cross section perpendicular to the axis C is formed in an annular shape. The bellows portion 33 is expandable in the direction of the axis C, and the peaks and valleys each increase in diameter as they move away from the small-diameter cylindrical portion 31. The internal space formed by this bellows portion 33 is mainly a space for enclosing grease.

[0022] The small diameter cylindrical portion 31 is a substantially cylindrical portion, and has a fastening groove 31a on its outer circumferential surface into which the band 20 fits. A plurality of (two in this embodiment) annular seal lips 31b are formed continuously around the entire periphery inside the fastening groove 31a to seal between the inner circumferential surface of the small diameter cylindrical portion 31 and the second transmission shaft 16.

[0023] Similarly, a fastening groove 32a into which the band 20 fits is provided on the outer peripheral surface of the large-diameter cylindrical portion 32. A plurality of (three in this embodiment) annular seal lips 32b for sealing between the inner peripheral surface of the large-diameter cylindrical portion 32 and the outer peripheral surface of the outer case 12 are continuously formed around the entire periphery inside this fastening groove 32a.

[0024] Figure 3 is a bottom view of the joint boot 30 as seen from the direction of arrow III in Figure 2. Line II-II in Figure 3 is a cutting line of the cross-sectional view in Figure 2. The large diameter cylindrical portion 32 is formed to have a circular outer shape. The inner peripheral surface of the large diameter cylindrical portion 32 is formed with an uneven shape corresponding to the convex surfaces 14 and concave surfaces 15 on the outer peripheral surface of the outer case 12, and is formed so as to be able to closely contact the outer peripheral surface of the outer case 12 and not be able to rotate relative to the outer case 12.

[0025] The large-diameter cylindrical portion 32 includes three cylindrical portions 35 whose inner circumferential surfaces 35a are formed along the convex surface 14, three convex portions 36 whose inner circumferential surfaces 36a are formed along the concave surface 15, and three abutment portions 32c that protrude from the end of the cylindrical portion 35 on the small-diameter cylindrical portion 31 side toward the axis C. The abutment portions 32c are areas that come into contact with the tip of the outer case 12 inserted into the large-diameter cylindrical portion 32, and rise approximately perpendicularly from the cylindrical portion 35 toward the axis C. The inner circumferential surfaces 35a, 36a are formed parallel to the axis C in a cross section including the axis C, except for the seal lip 32b.

[0026] The cylindrical portion 35 is a part of a cylinder centered on the axis C, and forms part of the circumference of the large-diameter cylindrical portion 32. In a cross section perpendicular to the axis C, both the outer peripheral surface and the inner peripheral surface 35a of the cylindrical portion 35 are arc-shaped with the axis C as the center, and the thickness (radial dimension) is approximately constant over the entire circumferential length.

[0027] The protrusions 36 are portions that connect the cylindrical portions 35 in the circumferential direction, and the inner peripheral surfaces 36a bulge radially inward relative to the inner peripheral surfaces 35a of the cylindrical portions 35. In a cross section perpendicular to the axis C, the radial dimension of the protrusions 36 from the arc-shaped outer peripheral surface centered on the axis C to the inner peripheral surface 36a gradually increases toward the circumferential center. The point where the radial dimension of the protrusions 36 is greatest (the apex of the inner peripheral surface 36a) is located on a radial line centered on the axis C.

[0028] The protrusion 36 has a lightening hole 36c formed in the end face opposite to the small-diameter cylindrical portion 31. The larger the volume of this lightening hole 36c, the lighter the protrusion 36 can be. Furthermore, the lightening hole 36c makes it possible to uniform the cooling rate of the entire protrusion 36 and the amount of shrinkage of the protrusion 36 when molding the joint boot 30, thereby enabling the protrusion 36 to be molded with high precision.

[0029] The protrusion 36 is provided with an outer wall portion 37 that forms the outer peripheral surface of the protrusion 36 due to the lightening holes 36c, and an inner wall portion 38 that is spaced radially from the outer wall portion 37 and forms the inner peripheral surface 36a of the protrusion 36. The outer wall portion 37 is a portion that extends the cylindrical portion 35 in the circumferential direction, and the outer wall portion 37 and the cylindrical portion 35 form a cylinder centered on the axis C.

[0030] In a cross section perpendicular to the axis C that intersects with the inner circumferential surface 36a and the fastening groove 32a at a position where the seal lip 32b is not present, the thickness of the outer wall portion 37 and the thickness of the inner wall portion 38 are substantially the same, and the thicknesses of the outer wall portion 37 and the inner wall portion 38 are substantially the same as the thickness of the cylindrical portion 35. This makes it possible to make the amount of shrinkage during molding of the large-diameter cylindrical portion 32 uniform in each portion, thereby improving the moldability of the large-diameter cylindrical portion 32.

[0031] A plurality of ribs 39 are arranged in the lightening holes 36c, connecting the outer wall portion 37 and the inner wall portion 38. This ensures the rigidity of the protrusions 36 in which the lightening holes 36c are formed, thereby ensuring the surface pressure between the protrusions 36 fastened by the band 20 and the recessed surface 15 of the outer case 12. As a result, the sealing performance between the protrusions 36 and the recessed surface 15 can be improved.

[0032] 2, the connecting portion 40 is a cylindrical portion that connects the valley portion 33a of the bellows portion 33 closest to the large-diameter cylindrical portion 32 to the large-diameter cylindrical portion 32. Therefore, the connecting portion of the connecting portion 40 with the valley portion 33a is formed in an annular shape centered on the axis C. On the other hand, the connecting portion of the connecting portion 40 with the large-diameter cylindrical portion 32 is formed along the unevenness formed by the tip of the abutting portion 32c that has an arc shape centered on the axis C and the inner circumferential surface 36a of the protrusion 36 that protrudes toward the axis C beyond the tip.

[0033] The description will be made with reference to Figure 4 in addition to Figures 1 and 2. Figure 4 is a cross-sectional view of the joint boot 30 taken along line IV-IV in Figure 2. In this cross-section perpendicular to the axis C, the connecting portion 40 includes an arc-shaped portion 41 whose outer and inner peripheral surfaces are formed in an arc shape centered on the axis C, a recess 45 whose outer and inner peripheral surfaces are recessed toward the axis C relative to the arc-shaped portion 41 and connects the arc-shaped portion 41 in the circumferential direction, and a protrusion 48 protruding from the outer peripheral surface of the recess 45. The arc-shaped portion 41 and the recess 45 are formed to have a substantially constant thickness (radial dimension) in the circumferential direction in order to make the amount of shrinkage during molding of the joint boot 30 uniform in the circumferential direction.

[0034] The arc-shaped portion 41 is a portion that connects to the tip of the abutting portion 32c on the axis C side. The arc-shaped portion 41 includes a parallel surface portion 42 that rises vertically from the tip of the abutting portion 32c, and an inclined surface portion 43 that connects the end of the parallel surface portion 42 on the small-diameter cylindrical portion 31 side to the valley portion 33a. The parallel surface portion 42 has inner and outer circumferential surfaces that are parallel to the axis C, i.e., the inner and outer radii D1 (see FIG. 4) are constant. The inner and outer circumferential surfaces of the inclined surface portion 43 incline toward the axis C as they approach the valley portion 33a, i.e., the inner and outer radii decrease in diameter as they approach the valley portion 33a.

[0035] The recesses 45 are portions where the inner wall portion 38 of the protrusion 36 is extended toward the small diameter cylindrical portion 31, and are formed at three equally spaced locations in the circumferential direction. The inner peripheral surface of the recesses 45 includes a parallel inner surface 46 that extends the inner peripheral surface 36a of the protrusion 36 toward the small diameter cylindrical portion 31 and is parallel to the axis C, and a protruding portion 47 that is connected to the end of the parallel inner surface 46 on the small diameter cylindrical portion 31 side and protrudes from the parallel inner surface 46 toward the axis C. The outer peripheral surface of the recesses 45 is similarly formed along the inner peripheral surface of the recesses 45.

[0036] The protrusions 48 are portions that make it difficult for the recesses 45 to expand during blow molding, which will be described later. The thickness (axial dimension) of the protrusions 48 gradually decreases from the base end (the end on the axis C side) to the tip end (the radially outer end). This makes it easier to remove the protrusions 48 from the mold when they are molded.

[0037] The base end of the protrusion 48 is located closer to the large-diameter cylindrical portion 32 than the boundary B1 between the parallel inner surface 46 of the recess 45 and the protruding portion 47. The tip of the protrusion 48 is located closer to the small-diameter cylindrical portion 31 than the axial center of the parallel surface portion 42 of the arc-shaped portion 41. In particular, in this embodiment, the corner of the tip of the protrusion 48 is located at the boundary B2 between the parallel surface portion 42 and the inclined surface portion 43.

[0038] The protrusion 48 is formed to extend circumferentially throughout the recess 45. An outer radius D2 from the axis C to the tip of the protrusion 48 is the same as an outer radius D1 of the parallel surface portion 42 of the arc-shaped portion 41. In other words, when viewed from the direction of the axis C, the tip of the protrusion 48 and the outer peripheral surface of the parallel surface portion 42 form a circle with the axis C as its center.

[0039] Next, a manufacturing method of the joint boot 30 and the function of the protrusions 48 will be described with reference to Fig. 5. Fig. 5 is a cross-sectional view of a preform 50 and a mold 60 of the joint boot 30. The joint boot 30 is manufactured by first molding the preform 50 by injection molding, and then subjecting the preform 50 to blow molding.

[0040] The preform 50 includes a small diameter cylindrical portion 31, a large diameter cylindrical portion 32, a connecting portion 40, and a tapered portion 51 connecting the connecting portion 40 and the small diameter cylindrical portion 31. The tapered portion 51 is a cylindrical portion that is plastically deformed into a bellows portion 33 by blow molding, and its diameter is increased in a tapered manner from the small diameter cylindrical portion 31 toward the connecting portion 40.

[0041] Furthermore, in the preform 50, a closing portion 52 that closes the small-diameter cylindrical portion 31 is connected to the axial end face of the small-diameter cylindrical portion 31 opposite the large-diameter cylindrical portion 32. In the preform 50, an annular portion 54 is connected to the axial end face of the large-diameter cylindrical portion 32 opposite the small-diameter cylindrical portion 31 via an annular thin-walled portion 53. The thickness (radial dimension) of the annular portion 54 is greater than the minimum thickness portion of the large-diameter cylindrical portion 32 (the portion where the fastening groove 32a of the cylindrical portion 35 is provided). The thickness (radial dimension) of the thin-walled portion 53 is smaller than the minimum thickness portion of the large-diameter cylindrical portion 32 and the thickness of the annular portion 54.

[0042] In injection molding, a thermoplastic resin is filled into a cavity between an outer mold that molds the outer periphery of the preform 50 and a core mold that molds the inner periphery of the preform 50, and the thermoplastic resin is cured to form the preform 50. The small diameter cylindrical portion 31, large diameter cylindrical portion 32, and connecting portion 40 of the molded preform 50 are molded into the final product shape (joint boot 30). Therefore, the cross-sectional view of the joint boot 30 shown in FIG. 4 is also a cross-sectional view of the preform 50.

[0043] As shown in FIG. 4, when viewed in the direction of the axis C, the outer mold is split into two halves on either side of an imaginary line 56 passing through the axis C (in a direction perpendicular to the axis C). To prevent the recesses 45 from having an undercut shape, the imaginary line 56 is set perpendicular to an imaginary line connecting the circumferential center of one of the three recesses 45 to the axis C. Note that a portion of the outer mold at the top of the page in FIG. 4 extends beyond the imaginary line 56 to form the entire recesses 45 on both the left and right sides, thereby preventing the formation of an undercut shape. A parting line along the imaginary line 56 is formed on the outer peripheral surface of the preform 50 released from this outer mold, and the parting line may remain in the final product shape.

[0044] 6(a), in a modified preform (joint boot) in which the protrusions 48a protruding from the recess 45 of the connecting part 40 are provided only at the circumferential center of the recess 45, some of the protrusions 48a spread outward as they move away from the imaginary straight line 56, resulting in an undercut shape. In this case, the protrusions 48a become an obstacle when the preform is demolded, so a slide core or the like must be provided separately in the outer mold.

[0045] In contrast, as shown in Figure 4, the protrusions 48 of the preform 50 (joint boot 30) of this embodiment are formed to extend in the entire circumferential direction within the recess 45, so the protrusions 48 do not spread outward as they move away from the imaginary line 56, and no undercut shape is formed by the protrusions 48. Therefore, in this embodiment, it is possible to prevent the protrusions 48 from interfering with demolding when demolding the preform 50. Furthermore, the thickness (dimension in the direction of the axis C) of the protrusions 48 becomes smaller toward the tip, forming a draft slope, which makes it easier to demold the protrusions 48.

[0046] After the preform 50 is demolded, it is heated to facilitate plastic deformation of the tapered portion 51, and then blow molding is performed using a mold 60 shown in Fig. 5. The mold 60 includes a support 61 that supports the preform 50, and an outer mold 67 that covers the outer periphery of the support 61.

[0047] The support body 61 comprises a disk-shaped base portion 62 to which the end face of the annular portion 54 of the preform 50 in the direction of the axis C is in close contact around the entire circumference, a circular wall portion 63 that rises from the outer peripheral edge of the base portion 62 and restricts the radial movement of the annular portion 54, a shaft 64 that protrudes axially from the center of the base portion 62, and a cylindrical tip portion 65 that is arranged at the tip of the shaft 64.

[0048] The tip portion 65 is covered with the small diameter cylindrical portion 31 and the closed portion 52 of the preform 50. The support body 61 is also used during heating before blow molding. Specifically, the support body 61 supporting the preform 50 is rotated by a rotation device 66 while the tapered portion 51 is heated by a heater. After this heating, with the preform 50 still supported by the support body 61, an outer mold 67 is clamped to cover the preform 50.

[0049] Outer mold 67 is a metal mold for molding bellows portion 33 (see FIG. 2), and is divided into two parts like the outer mold for molding preform 50. The inner surface of outer mold 67 is provided with a bellows molding surface 68 for molding bellows portion 33, and a connecting contact surface 69 that continues to the support body 61 side of bellows molding surface 68. Bellows molding surface 68 surrounds the outer periphery of tapered portion 51 when the mold is clamped.

[0050] The connecting contact surface 69 is formed over the entire circumference in the same shape as the outer peripheral surface of the arc-shaped portion 41 of the connecting part 40. That is, when the mold is clamped, the connecting contact surface 69 comes into close contact with the arc-shaped portion 41 (the parallel surface portion 42 and the inclined surface portion 43) of the connecting part 40, but a gap 70 is formed between the connecting contact surface 69 and the recessed portion 45 of the connecting part 40. The connecting contact surface 69 also includes a parallel contact surface 69a that is parallel to the axis C along the parallel surface portion 42, and an inclined contact surface 69b that is inclined with respect to the axis C along the inclined surface portion 43.

[0051] Here, if a convex portion is provided on a part of the connecting contact surface 69 in the circumferential direction so as to come into close contact with the concave portion 45, it becomes necessary to rotate the support 61 and the preform 50 with the rotation device 66 when heating the tapered portion 51, and then align the convex portion of the connecting contact surface 69 with the concave portion 45 when clamping the mold. In contrast, in this embodiment, the connecting contact surface 69 does not have a convex portion, so the work of aligning the convex portion with the concave portion 45 when clamping the mold is not necessary.

[0052] In blow molding using the mold 60, the outer mold 67 is clamped, and with the space between the base portion 62 of the support body 61 and the annular portion 54 airtight, gas is injected into the inside of the preform 50 from holes 62a that penetrate the base portion 62 in the thickness direction. This causes the tapered portion 51 to expand radially outward, and the bellows portion 33 (see FIG. 2) is formed by the outer mold 67. After removal from the mold 60, the thin-walled portion 53 is cut all around to separate the annular portion 54 from the large-diameter cylindrical portion 32, and similarly, the closing portion 52 is separated from the small-diameter cylindrical portion 31, thereby obtaining the joint boot 30.

[0053] During this blow molding, the gap 70 may cause the recess 45 to bulge toward the connecting contact surface 69. If the recess 45 bulges, the appearance of the joint boot 30 may deteriorate, or the thickness near the recess 45 may be partially reduced, reducing the durability of the joint boot 30.

[0054] However, in this embodiment, the dimensions of the protrusion 48 are set so that the tip of the protrusion 48 protruding from the recess 45 comes into contact with the connecting contact surface 69. Therefore, even if a gap 70 is formed between the recess 45 and the connecting contact surface 69, the protrusion 48 functions as a tension rod during blow molding, thereby preventing the recess 45 from expanding. Therefore, deterioration in the appearance and durability of the joint boot 30 due to the expansion of the recess 45 can be prevented.

[0055] Boundary B3 between bellows molding surface 68 and inclined contact surface 69b of connecting contact surface 69 is the portion that forms valley portion 33a of bellows portion 33 closest to large-diameter cylindrical portion 32. When the mold is clamped, part of tapered portion 51 extends beyond boundary B3 toward support body 61, and the corner between recess 45 and tapered portion 51 comes into contact with inclined contact surface 69b. This makes it possible to prevent the vicinity of the corner between recess 45 and tapered portion 51 from expanding toward bellows molding surface 68 during blow molding.

[0056] Furthermore, during blow molding, the protruding portion 47 on the small-diameter cylindrical portion 31 side of the boundary B1 (see FIG. 2) located inside the corner between the recess 45 and the tapered portion 51 bulges (stretches and deforms) as the bellows portion 33 is formed. On the other hand, the parallel inner surface 46 on the large-diameter cylindrical portion 32 side of the boundary B1 hardly undergoes plastic deformation during blow molding. Because the base end of the protrusion 48 is located on the large-diameter cylindrical portion 32 side of the boundary B1, it is possible to prevent the provision of the protrusion 48 from adversely affecting the formation of the bellows portion 33 by blow molding, such as making the portion where the protrusion 48 is provided less susceptible to plastic deformation.

[0057] The tip of the protrusion 48 is located closer to the small-diameter cylindrical portion 31 than the axial center of the parallel surface portion 42 of the arc-shaped portion 41, and contacts the small-diameter cylindrical portion 31 than the axial center of the parallel contact surface 69a of the connecting contact surface 69. This allows the protrusion 48 to be brought closer to the tapered portion 51 (bellows portion 33) that expands during blow molding.

[0058] When tapered portion 51 is heated and softened before blow molding, a heat shield or the like is used to prevent connecting portion 40, including recessed portion 45, from also being heated and softened. However, because connecting portion 40 is more likely to soften the closer it is to tapered portion 51 due to heat conduction from tapered portion 51, recessed portion 45 is more likely to bulge the closer it is to tapered portion 51 during blow molding. In this embodiment, protrusions 48 are brought closer to tapered portion 51 and are positioned in recessed portion 45 at a location where bulging is more likely, so protrusions 48 can make recessed portion 45 even less likely to bulge.

[0059] Furthermore, it is preferable that the tip of the protrusion 48 is located closer to the large-diameter cylindrical portion 32 than the boundary B2 (see FIG. 2) between the parallel surface portion 42 (parallel contact surface 69a) and the inclined surface portion 43 (inclined contact surface 69b). In other words, it is preferable that the tip of the protrusion 48 does not come into contact with the inclined contact surface 69b.

[0060] If the tip of the protrusion 48 comes into contact with the inclined contact surface 69b, the radial load that tries to expand the recess 45 during blow molding may cause the tip of the protrusion 48 to slide along the inclined contact surface 69b toward the large-diameter cylindrical portion 32, potentially resulting in buckling of the protrusion 48. This may make it difficult for the protrusion 48 to function as a tension rod during blow molding, and may make the recess 45 more likely to expand. In contrast, by not having the tip of the protrusion 48 come into contact with the inclined contact surface 69b, the protrusion 48 is less likely to buckle, making it even more difficult for the protrusion 48 to expand the recess 45.

[0061] As a result, the closer the tip of the protrusion 48 is to the boundary B2 between the parallel surface portion 42 (parallel contact surface 69a) and the inclined surface portion 43 (inclined contact surface 69b), the more effectively the protrusion 48 suppresses the bulging of the recess 45. In particular, in this embodiment, the corner of the tip of the protrusion 48 is located at the boundary B2 between the parallel surface portion 42 and the inclined surface portion 43, so the protrusion 48 can make the recess 45 even less likely to bulge.

[0062] Furthermore, the protrusions 48 are formed to extend circumferentially throughout the recess 45, and the entire circumferential length of the base ends of the protrusions 48 is connected to the outer peripheral surface of the recess 45, thereby improving the rigidity of the protrusions 48. This makes it difficult for the protrusions 48 to buckle during blow molding, and makes it even more difficult for the recess 45 to bulge due to the protrusions 48.

[0063] The thickness of the protrusions 48 (dimension in the direction of the axis C) is preferably 0.5 to 1.2 times the thickness (radial dimension) of the recesses 45. If the thickness of the protrusions 48 is less than 0.5 times the thickness of the recesses 45, the protrusions 48 may be prone to buckling during blow molding. If the thickness of the protrusions 48 is more than 1.2 times the thickness of the recesses 45, it may be difficult to control the amount of shrinkage of the protrusions 48 during molding of the preform 50, and it may be difficult to bring the tips of the protrusions 48 into contact with the parallel contact surfaces 69a during blow molding.

[0064] In contrast, by making the thickness of the protrusions 48 0.5 to 1.2 times the thickness of the recesses 45, the protrusions 48 are less likely to buckle during blow molding, and the amount of shrinkage of the protrusions 48 is easier to control, making it easier to bring the tips of the protrusions 48 into contact with the parallel contact surface 69a. As a result, the recesses 45 are less likely to bulge due to the protrusions 48 during blow molding.

[0065] The connecting portion 40 has a plurality of recesses 45 of the same shape arranged at intervals in the circumferential direction, and each recess 45 is provided with a protrusion 48 of the same shape. This makes it possible to make the recesses 45 less likely to expand during blow molding and to make the rigidity of the joint boot 30 near the recesses 45 uniform in the circumferential direction. As a result, it is possible to prevent a portion of the connecting portion 40 in the circumferential direction from becoming a low rigidity and becoming a starting point for cracks, and the durability of the joint boot 30 can be improved.

[0066] While the present invention has been described above based on the embodiments, it is not limited to the above embodiments, and various improvements and modifications are possible without departing from the spirit and scope of the present invention. For example, the shapes and dimensions of the small-diameter cylindrical portion 31, the large-diameter cylindrical portion 32, the bellows portion 33, the outer case 12, etc. may be changed as appropriate. The protrusions 36 and the recesses 45 are not limited to being formed at three equally spaced locations in the circumferential direction, and the number and arrangement of the protrusions 36 and the recesses 45 may be changed as appropriate. Furthermore, the number of seal lips 31b, 32b may be changed as appropriate.

[0067] In the above embodiment, the constant velocity joint 10 to which the joint boot 30 is attached is of a tripod type, but this is not limiting. The joint boot 30 may be attached to a sliding type constant velocity joint other than a tripod type that expands and contracts at the connecting portion between the first transmission shaft 11 and the second transmission shaft 16, or may be attached to a fixed type constant velocity joint that does not expand and contract at the connecting portion.

[0068] In the above embodiment, the protrusion 48 is formed to extend over the entire circumferential direction within the recess 45, but this is not limited to this. If the protrusion protrudes from at least the circumferential center of the outer peripheral surface of the recess 45, the recess 45 will be less likely to expand due to the protrusion during blow molding. For example, as shown in FIG. 6(a), the protrusion 48a may protrude only from the circumferential center of the outer peripheral surface of the recess 45. In this case, there is almost no need to consider shrinkage of the protrusion 48a during molding of the preform, and therefore the product shape of the joint boot having the protrusion 48a can be less likely to vary.

[0069] 6(b), a portion of the protrusion 48 may be cut out to provide a protrusion 48b partially in the circumferential direction within the recess 45. In this case, by cutting out the protrusion 48b between the portion away from the imaginary line 56 indicating the parting position of the mold for molding the preform and the outer peripheral surface of the recess 45, an undercut shape is not formed by the protrusion 48b, making it easier to remove the protrusion 48b from the mold.

[0070] Furthermore, although not specifically shown, the protrusion 48a may extend in the direction of the axis C. Also, a cross-shaped protrusion may be formed by combining the protrusions 48, 48b extending in the circumferential direction with a protrusion extending in the direction of the axis C. Also, multiple protrusions may be arranged in the recess 45. The shapes of the protrusions arranged in each of the multiple recesses 45 may be different. [Explanation of symbols]

[0071] 10 Constant velocity joint 11 First transmission shaft 12 outer case 16 Second transmission shaft 30 Jointed Boots 31 Small diameter cylinder part 32 Large diameter cylinder 33 Bellows 33a Tanibe 40 Connection part 41 Arc-shaped part 42 Parallel surface section 45 recess 46 Parallel inner surface 47 Overhang 48,48a,48b protrusion C axis center

Claims

1. A cylindrical joint boot made of an elastic body is attached to a constant velocity joint in which a second transmission shaft is fitted into an outer case of a first transmission shaft, a small-diameter cylindrical portion into which the second transmission shaft is inserted; a large-diameter cylindrical portion into which the outer case is inserted; a cylindrical bellows portion in which peaks and valleys are repeatedly formed from the small diameter cylindrical portion to the large diameter cylindrical portion; a cylindrical connecting portion that connects a valley portion of the bellows portion closest to the large diameter cylindrical portion and the large diameter cylindrical portion, the connecting portion has an arc-shaped portion whose outer circumferential surface is formed in an arc shape centered on the axis of the large-diameter cylindrical portion in a cross section perpendicular to the axis of the large-diameter cylindrical portion; a recessed portion whose outer circumferential surface is recessed toward the axis center with respect to the arc-shaped portion and connects the arc-shaped portion in a circumferential direction; a protrusion protruding from at least the center in the circumferential direction of the outer peripheral surface of the recess, A joint boot characterized in that the outer radius from the axis center to the tip of the projection is the same as the outer radius of the arc-shaped portion.

2. The connecting portion has a plurality of recesses of the same shape arranged at intervals in the circumferential direction, 2. The joint boot according to claim 1, wherein the projections are provided for each of the plurality of recesses and are formed in the same shape as each other.

3. 3. The joint boot according to claim 1, wherein the protrusion is formed so as to extend over the entire circumferential direction of the recess.

4. the arc-shaped portion has a parallel surface portion whose outer circumferential surface is parallel to the axis, 4. The joint boot according to claim 1, wherein the projection is located closer to the small-diameter cylindrical portion than the axial center of the parallel surface portion.

5. The inner peripheral surface of the recess has a parallel inner surface parallel to the axis, a protruding portion that is continuous with an end portion of the parallel inner surface on the side of the small-diameter cylindrical portion and protrudes from the parallel inner surface toward the axis center, 5. The joint boot according to claim 1, wherein the projection is located closer to the large-diameter cylindrical portion than the boundary between the parallel inner surface and the protruding portion.

Images