JP7733558B2 - Jointed Boots - Google Patents

Description

The present invention relates to a joint boot, and in particular to a joint boot that can suppress bulging of a recess provided in a portion of the circumferential direction.

Constant velocity joints used in automobile drive shafts and propeller shafts are constructed by fitting a rolling element at the tip of a second transmission shaft into a cylindrical outer case at the tip of a first transmission shaft, and a joint boot is attached to the connecting section between the first and second transmission shafts. The joint boot includes 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 extending from the small-diameter cylindrical section to the large-diameter cylindrical section, and a cylindrical connecting section connecting the bellows section to the large-diameter cylindrical section.

Patent Document 1 discloses a method for manufacturing this joint boot. In this document, first, a preform is formed by injection molding, which includes 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. Then, with the outer periphery of the preform covered by a mold, gas is blown into the inner periphery of the preform, which plastically deforms the tapered portion into a bellows portion.

Furthermore, in Patent Document 1, due to the shape of the outer case into which the large-diameter cylindrical portion is inserted and the need for demolding during molding, part of the inner peripheral surface of the connecting portion is recessed toward the axis of the large-diameter cylindrical portion. Also, to ensure that the thickness of the connecting portion is uniform in the circumferential direction and take 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 comprises 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 where the outer peripheral surface is recessed toward the axis from the arc-shaped portion.

Japanese Patent Application Laid-Open No. 2020-168750

However, with conventional technology, the need to circumferentially align the preform with the mold during blow molding is eliminated, and the portion of the mold where the connecting portion comes into contact is formed to fit the arc-shaped portion along its entire circumference. This can result in a gap between the mold and the outer surface of the recess, causing the recess to bulge during blow molding. For example, this bulge can adversely affect the appearance of the joint boot or reduce durability due to a partial reduction in thickness near the recess.

The present invention was made to solve the above-mentioned problems, and aims to provide a joint boot that can suppress bulging of a recess provided in a portion of the circumferential direction.

To achieve this objective, the joint boot of the present invention is a cylindrical member made of an elastic material and attached to a constant velocity joint in which a second transmission shaft is fitted into the outer case of a first transmission shaft. The joint boot 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 alternately formed 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. In a cross section perpendicular to the axis of the large-diameter cylindrical section, the connecting 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, connecting the arc-shaped sections circumferentially; and a protrusion that protrudes from at least the circumferential center 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.

According to the joint boot described in claim 1, the connecting portion connecting the bellows portion and the large-diameter cylindrical portion is formed by circumferentially connecting 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 recess that is 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 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 portion. Therefore, even if a gap occurs between the mold and the outer peripheral surface of the recess during blow molding, the tip of the protrusion comes into contact with the mold and functions as a tension rod, preventing the recess from expanding.

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 identically shaped recesses spaced apart in the circumferential direction, and each of these recesses 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, improving the durability of the joint boot.

The joint boot of claim 3 achieves the following effect in addition to the effect of the joint boot of claim 1 or 2. When a preform having a connecting portion before being blow-molded into a joint boot is injection molded in a mold, the mold that forms the outer surface of the preform is often split in a direction perpendicular to the axis. Because the protrusion is formed to extend circumferentially within the recess, the protrusion does not interfere with demolding when the preform is demolded. This simplifies the manufacturing process for joint boots.

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 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. In this way, by positioning 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.

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 area closer to the small-diameter cylindrical portion than the boundary between this parallel inner surface and the protruding portion is the portion that mainly expands during blow molding, and the protrusion is located closer to the large-diameter cylindrical portion than that boundary. This makes it difficult for the area with the protrusion to undergo plastic deformation, and it is possible to prevent the provision of the protrusion from having an adverse effect on the molding of the bellows portion by blow molding.

In this specification, a specified portion (e.g., a parallel inner surface) is considered parallel to the axis if the inclination of the specified portion relative to the axis is 2° or less. In other words, a draft angle may be set at the specified portion.

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

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 the first transmission shaft 11 and the second transmission shaft 16, and is used in automotive drive shafts, propeller shafts, etc.

The constant velocity joint 10 is a tripod type with an expandable connecting portion. A cylindrical outer case 12 is attached to the tip of the first transmission shaft 11 of the constant velocity joint 10. Three guide grooves 13 are formed along the axial direction on the inner surface of the outer case 12 and are equally spaced circumferentially. The outer surface of the outer case 12 is equipped with a cylindrical convex surface 14 that forms the outer side of the guide grooves 13 and is centered on the axis of the outer case 12, and a concave surface 15 that connects the convex surfaces 14 circumferentially and is recessed toward the axis (radially inward).

A tripod 19 is provided at the tip of the second transmission shaft 16. The tripod 19 is composed of three trunnions 18 with rollers 17 protruding from the second transmission shaft 16. The first transmission shaft 11 and 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.

A joint boot 30 is attached to the connecting portion of this constant velocity joint 10. The joint boot 30 seals in the grease necessary to lubricate the connecting portion of the constant velocity joint 10 and prevents foreign matter such as water and mud from entering the connecting portion. The joint boot 30 is integrally molded from an elastic material, specifically a thermoplastic resin (such as polyester or polyurethane, including thermoplastic elastomers).

The joint boot 30 comprises 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 to 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.

Figure 2 is a cross-sectional view of one side of the joint boot 30, taken along the axis C of the large-diameter cylindrical portion 32. The bellows portion 33 is a portion formed by repeated peaks and valleys, and its 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 primarily the space for sealing in grease.

The small-diameter cylindrical portion 31 is a generally cylindrical portion, and its outer surface is provided with a fastening groove 31a into which the band 20 fits. Inside this fastening groove 31a, multiple (two in this embodiment) annular seal lips 31b are formed continuously around the entire circumference to seal between the inner surface of the small-diameter cylindrical portion 31 and the second transmission shaft 16.

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. Multiple (three in this embodiment) annular seal lips 32b are continuously formed around the entire periphery inside this fastening groove 32a to seal between the inner peripheral surface of the large-diameter cylindrical portion 32 and the outer peripheral surface of the outer case 12.

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 has 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 that it can adhere closely to the outer peripheral surface of the outer case 12 and cannot rotate relative to the outer case 12.

The large-diameter cylindrical portion 32 has 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 the 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. Note that 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.

The cylindrical portion 35 is 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 and inner surfaces 35a of the cylindrical portion 35 are arc-shaped and centered on the axis C, and the thickness (radial dimension) is approximately constant over the entire circumferential length.

The convex portions 36 are portions that connect the cylindrical portions 35 circumferentially, and the inner peripheral surface 36a bulges radially inward relative to the inner peripheral surface 35a of the cylindrical portions 35. In a cross section perpendicular to the axis C, the radial dimension of the convex portions 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 convex portions 36 is greatest (the apex of the inner peripheral surface 36a) is located on a radial line centered on the axis C.

The protrusion 36 has a lightening hole 36c that opens to the end face opposite 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.

The lightening holes 36c define the protrusion 36, which includes an outer wall portion 37 that forms the outer peripheral surface of the protrusion 36, and an inner wall portion 38 that is radially spaced 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.

In a cross section perpendicular to the axis C that intersects with the inner circumferential surface 36a and fastening groove 32a where there is no seal lip 32b, the thickness of the outer wall portion 37 and the thickness of the inner wall portion 38 are approximately the same, and the thicknesses of the outer wall portion 37 and the inner wall portion 38 are approximately the same as the thickness of the cylindrical portion 35. This allows the amount of shrinkage during molding of the large-diameter cylindrical portion 32 to be uniform across each portion, improving the moldability of the large-diameter cylindrical portion 32.

A number 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 protrusion 36 in which the lightening holes 36c are formed, thereby ensuring sufficient surface pressure between the protrusion 36, which is fastened by the band 20, and the concave surface 15 of the outer case 12. As a result, the seal between the protrusion 36 and the concave surface 15 can be improved.

As shown in FIG. 2, the connecting portion 40 is a cylindrical section 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 created by the tip of the abutment portion 32c, which is arc-shaped about the axis C, and the inner circumferential surface 36a of the protrusion 36 that protrudes toward the axis C beyond the tip.

The following description will refer 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 comprises 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. Note that 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.

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 inner and outer circumferential surfaces of the parallel surface portion 42 are formed parallel to the axis C, i.e., the inner and outer radii D1 (see Figure 4) are constant. The inclined surface portion 43 inclines toward the axis C as the inner and outer circumferential surfaces approach the valley portion 33a, i.e., the inner and outer radii decrease in diameter as they approach the valley portion 33a.

The recesses 45 are formed by extending the inner wall portion 38 of the protrusion 36 toward the small-diameter cylindrical portion 31, and are formed at three equally spaced locations around the circumference. The inner surface of the recesses 45 includes a parallel inner surface 46 that extends the inner surface 36a of the protrusion 36 toward the small-diameter cylindrical portion 31 and is parallel to the axis C, and a protrusion 47 that connects 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 surface of the recesses 45 is similarly formed along the inner surface of the recesses 45.

The protrusions 48 are designed to prevent the recesses 45 from expanding during blow molding, as described below. The thickness (axial dimension) of the protrusions 48 gradually decreases from the base end (the end on the axis C side) to the tip (the radially outer end). This makes it easier to remove the protrusions 48 from the mold when they are being molded.

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.

The protrusion 48 is formed to extend circumferentially throughout the recess 45. The outer radius D2 from the axis C to the tip of the protrusion 48 is the same as the 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 centered on the axis C.

Next, the manufacturing method of the joint boot 30 and the function of the protrusions 48 will be explained with reference to Figure 5. Figure 5 is a cross-sectional view of the preform 50 and 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.

The preform 50 comprises 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 increases in a tapered manner from the small-diameter cylindrical portion 31 toward the connecting portion 40.

Furthermore, the preform 50 has a closing portion 52 that closes the small-diameter cylindrical portion 31 connected to the axial end face of the small-diameter cylindrical portion 31 opposite the large-diameter cylindrical portion 32. The preform 50 has a circular annular portion 54 connected to the axial end face of the large-diameter cylindrical portion 32 opposite the small-diameter cylindrical portion 31 via a circular annular thin-walled portion 53. The thickness (radial dimension) of the annular portion 54 is greater than the minimum thickness 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 of the large-diameter cylindrical portion 32 and the thickness of the annular portion 54.

In injection molding, the cavity between an outer mold that forms the outer periphery of the preform 50 and a core mold that forms the inner periphery of the preform 50 is filled with thermoplastic resin, and the thermoplastic resin is then hardened 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 Figure 4 is also a cross-sectional view of the preform 50.

As shown in Figure 4, when viewed from the direction of axis C, the outer mold is split into two halves on either side of an imaginary line 56 passing through axis C (perpendicular to axis C). To prevent the recesses 45 from having an undercut shape, imaginary line 56 is set perpendicular to an imaginary line connecting the circumferential center of one of the three recesses 45 to axis C. Note that the portion of the outer mold at the top of Figure 4 extends beyond 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 imaginary line 56 is formed on the outer peripheral surface of the preform 50 released from this outer mold, and this parting line may remain in the final product shape.

As shown in Figure 6(a), in a modified preform (joint boot) in which the protrusions 48a protruding from the recess 45 of the connecting portion 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, creating an undercut shape. In this case, the protrusions 48a interfere with demolding of the preform, so a separate slide core or similar must be provided in the outer mold.

In contrast, as shown in Figure 4, the protrusions 48 of the preform 50 (joint boot 30) of this embodiment are formed to extend circumferentially throughout the recess 45. Therefore, the protrusions 48 do not spread outward as they move away from the imaginary line 56, and an undercut shape cannot be formed by the protrusions 48. Therefore, this embodiment prevents the protrusions 48 from interfering with demolding of the preform 50. Furthermore, the thickness (dimension in the direction of the axis C) of the protrusions 48 decreases toward the tip, forming a draft gradient, making it easier to demold the protrusions 48.

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 the mold 60 shown in Figure 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.

The support body 61 comprises a disk-shaped base portion 62 against which the end face of the annular portion 54 of the preform 50 in the direction of the axis C comes into close contact over the entire circumference, an annular wall portion 63 that rises from the outer edge of the base portion 62 and restricts 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 located at the tip of the shaft 64.

The tip portion 65 is covered by the small-diameter cylindrical portion 31 and 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, the outer mold 67 is clamped while the preform 50 remains supported by the support body 61, and the outer mold 67 covers the preform 50.

The outer mold 67 is a mold for forming the bellows portion 33 (see Figure 2) and is divided into two parts, just like the outer mold for forming the preform 50. The inner surface of the outer mold 67 has a bellows forming surface 68 for forming the bellows portion 33 and a connecting contact surface 69 that connects to the bellows forming surface 68 on the support body 61 side. The bellows forming surface 68 surrounds the outer periphery of the tapered portion 51 when the mold is clamped.

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 of the connecting part 40 (the parallel surface portion 42 and the inclined surface portion 43), but a gap 70 is formed between the connecting contact surface 69 and the recess 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.

If a convex portion is provided on a portion of the connecting contact surface 69 in the circumferential direction so as to fit closely to the concave portion 45, it would be necessary to rotate the support 61 and 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 this eliminates the need to align the convex portion with the concave portion 45 when clamping the mold.

During blow molding using the mold 60, the outer mold 67 is clamped, creating an airtight seal between the base portion 62 of the support body 61 and the annular portion 54. Gas is then 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 outer mold 67 forms the bellows portion 33 (see Figure 2). After removal from the mold 60, the thin-walled portion 53 is cut all the way around to separate the annular portion 54 from the large-diameter cylindrical portion 32, and similarly, the closure portion 52 is separated from the small-diameter cylindrical portion 31, thereby obtaining the joint boot 30.

During this blow molding process, 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.

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, preventing the recess 45 from expanding. This prevents the joint boot 30 from deteriorating in appearance or durability due to the expansion of the recess 45.

The boundary B3 between the bellows molding surface 68 and the inclined contact surface 69b of the connecting contact surface 69 forms the valley portion 33a of the bellows portion 33 closest to the large-diameter cylindrical portion 32. When the mold is clamped, part of the tapered portion 51 extends beyond boundary B3 toward the support body 61, and the corner between the recess 45 and the tapered portion 51 comes into contact with the inclined contact surface 69b. This prevents the area near the corner between the recess 45 and the tapered portion 51 from bulging toward the bellows molding surface 68 during blow molding.

Furthermore, during blow molding, the protruding portion 47 on the small-diameter cylindrical portion 31 side of the boundary B1 (see Figure 2), which is located inside the corner between the recess 45 and the tapered portion 51, expands (expands 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 this boundary B1, the portion where the protrusion 48 is provided is less susceptible to plastic deformation, and other adverse effects on the formation of the bellows portion 33 by blow molding due to the presence of the protrusion 48 can be suppressed.

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 closer to the tapered portion 51 (bellows portion 33), which expands during blow molding.

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

Furthermore, it is preferable that the tip of the protrusion 48 be located closer to the large-diameter cylindrical portion 32 than the boundary B2 (see Figure 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.

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 could make it difficult for the protrusion 48 to function as a tension rod during blow molding, and could 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 recess 45 to expand due to the protrusion 48.

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 makes it even more difficult for the recess 45 to bulge.

In addition, the protrusion 48 is formed to extend circumferentially within the recess 45, and the entire circumferential length of the base end of the protrusion 48 is connected to the outer peripheral surface of the recess 45, thereby improving the rigidity of the protrusion 48. This makes the protrusion 48 less likely to buckle during blow molding, and the protrusion 48 makes it even more difficult for the recess 45 to bulge.

The thickness of the protrusions 48 (dimension in the direction of the axis C) is preferably 0.5 to 1.2 times the thickness of the recesses 45 (radial dimension). 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. Furthermore, 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 surface 69a during blow molding.

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.

The connecting portion 40 has multiple recesses 45 of the same shape spaced apart 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 parts of the connecting portion 40 in the circumferential direction from becoming low rigid and becoming the starting point for cracks, improving the durability of the joint boot 30.

The present invention has been described above based on an embodiment, but it is not limited to the above embodiment, and it is readily apparent that various improvements and modifications are possible without departing from the spirit of the present invention. For example, the shape and dimensions of each part, such as the small-diameter cylindrical portion 31, the large-diameter cylindrical portion 32, the bellows portion 33, and the outer case 12, may be modified as appropriate. The protrusions 36 and recesses 45 are not limited to being formed at three equally spaced locations around the circumference, and the number and arrangement of the protrusions 36 and recesses 45 may be modified as appropriate. The number of seal lips 31b, 32b may also be modified as appropriate.

In the above embodiment, the constant velocity joint 10 to which the joint boot 30 is attached is described as being of a tripod type, but this is not limited to this. The joint boot 30 may also 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 to a fixed type constant velocity joint that does not expand and contract at the connecting portion.

In the above embodiment, the protrusion 48 is formed to extend circumferentially throughout 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 bulge due to the protrusion during blow molding. For example, as shown in Figure 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 little need to consider shrinkage of the protrusion 48a during molding of the preform, which reduces variation in the product shape of the joint boot having the protrusion 48a.

Alternatively, a portion of the protrusion 48 may be cut away to provide a protrusion 48b in a circumferential direction within the recess 45, as shown in Figure 6(b). 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 used to mold 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.

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 circumferentially extending protrusions 48, 48b with a protrusion extending in the direction of the axis C. Furthermore, multiple protrusions may be arranged within the recess 45. The shapes of the protrusions arranged in each of the multiple recesses 45 may be different.

REFERENCE SIGNS LIST 10 Constant velocity joint 11 First transmission shaft 12 Outer case 16 Second transmission shaft 30 Joint boot 31 Small diameter cylindrical portion 32 Large diameter cylindrical portion 33 Bellows portion 33a Root portion 40 Connecting portion 41 Arc-shaped portion 42 Parallel surface portion 45 Recessed portion 46 Parallel inner surface 47 Protruding portion 48, 48a, 48b Protrusion C Axis center

Claims (5)

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. 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. A joint boot as described in claim 1 or 2, characterized in that the protrusion is formed to extend circumferentially throughout the recess. 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. 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.