JP4192765B2 - Constant velocity joint boots - Google Patents

Description

  The present invention relates to a constant velocity joint boot that is covered by a constant velocity joint used for a drive shaft joint of a front wheel drive vehicle and prevents entry of water and dust into the joint portion of the constant velocity joint. The present invention relates to a boot for a constant velocity joint that has excellent sealing properties for preventing water and dust from entering the portion.

  The joint part of the constant velocity joint used for the drive shaft joint of the front-wheel drive car is covered with a bellows-shaped boot filled with grease, and smooth rotation at a large angle is maintained by preventing water and dust from entering. Has been. Generally, a boot for a constant velocity joint has a large-diameter cylindrical portion fastened to a joint outer race, a small-diameter cylindrical portion fastened to a shaft with a smaller diameter than the large-diameter cylindrical portion, and a large-diameter cylindrical portion and a small-diameter cylindrical portion. It has a substantially cylindrical shape composed of a substantially triangular frustum-shaped bellows portion that is integrally connected. In use, the bellows portion is deformed in accordance with the change in the angle between the joint outer race and the shaft, so that the joint portion can be reliably sealed by the boot even when the angle increases.

  For example, such a constant velocity joint boot is disclosed in Patent Documents 1 and 2.

  In conventional boots for constant velocity joints as shown in Patent Documents 1 and 2, a seal rib portion is provided on the inner periphery of a small diameter cylindrical portion and a large diameter cylindrical portion. A general seal rib part consists of a rib projecting radially inward on the inner peripheral surface of each cylindrical part, and is pressed against the surface of the mating member when assembled to the mating member or the like to ensure sealing performance. Yes.

  Moreover, as shown in Patent Document 1, the fastening portion of the mating member fastened to the large-diameter cylindrical portion of the constant velocity joint boot has a non-circular outer peripheral shape in a tripod type joint, for example. . Therefore, the large-diameter cylindrical portion of the constant velocity joint boot has a shape corresponding to the shape of the mating member, that is, in the circumferential direction in order to provide sufficient sealing performance to reliably prevent water and dust from entering the joint. It is formed in the shape which has a thick part which protrudes to an inner peripheral side partially.

  Such constant velocity joint boots are usually formed of a thermoplastic elastomer having excellent weather resistance and fatigue resistance.

  However, the conventional constant velocity joint boot has problems such as unstable assembling in the large-diameter cylindrical portion and easy leakage of grease.

  Specifically, since the large-diameter cylindrical portion has a thick-walled portion and a thin-walled portion (showing a portion that is not a thick-walled portion of the large-diameter cylindrical portion), the constant velocity joint boot is mated with a circular clamp. When assembled to a member, the contact surface pressure of the large-diameter cylindrical portion against the mating member is not constant, and the assembly of the large-diameter cylindrical portion and the mating member tends to become unstable.

  Further, when the distance between the seal rib part and the bellows part that secures the sealing performance with the mating member of the large diameter cylinder part is short, and the bellows part is deformed so that the axes of the small diameter cylinder part and the large diameter cylinder part are different, In the large-diameter cylindrical portion located on the side where the bellows portion is folded and compressed, the seal portion of the large-diameter cylindrical portion comes to float from the surface of the mating member as the bellows portion is deformed. This will be described with reference to FIG. In FIG. 7, the conventional general constant velocity joint boot 1 is assembled to the mating member 7 having the shaft 7A, and the shaft 7A is inclined so that the small diameter cylindrical portion 2 and the large diameter cylindrical portion 3 have different axes. It is the schematic diagram which showed the state made to do, and there is also a member which is not illustrated.

  As the shaft 7A is inclined, the bellows portion 4 is pulled following the small diameter cylindrical portion 2. At this time, since the large-diameter cylindrical portion 3 is fixed to the counterpart member 7 by the clamp 8, the portion A adjacent to the large-diameter cylindrical portion 3 of the bellows portion 4 is acted on by the force of the arrow a and is pressed against the counterpart member 7. The Further, as the shaft 7A is inclined, the portion B adjacent to the large-diameter cylindrical portion 3 of the bellows portion 4 is crushed toward the large-diameter cylindrical portion 3 and further pushed outward in the radial direction by the inclination of the shaft 7A. To be energized. For this reason, the force of the arrow b which goes to radial direction acts on the site | part B adjacent to the large diameter cylinder part 3, and it deform | transforms in the direction which floats from the other member 7. FIG. Due to this deformation, the seal portion of the large diameter cylindrical portion 3 comes to float.

  As a result, sufficient sealing performance between the large-diameter cylindrical portion and the mating member is not ensured, and grease leakage occurs.

  Patent Document 2 discloses a method of manufacturing a hollow body that can manufacture a constant velocity joint boot. In the manufacturing method described in Patent Document 2, the small-diameter cylindrical portion is formed by injection molding, and then the bellows portion is formed by blow molding. At this time, the large diameter cylindrical portion is in a molten state up to the bellows portion. And since the part connected to the bellows part from the large diameter cylinder part is manufactured by pulling up the neck mold that formed the small diameter cylinder part and pulling out the parison, the reduced diameter shape from the large diameter cylinder part side toward the bellows part side A part is made. For this reason, the shape of the thick-walled portion is such that the portion of the connecting portion from the large-diameter cylindrical portion to the bellows portion is visible on the left side in FIG. This shape is considered to have been formed with consideration for the core die not to be undercut with respect to the large-diameter cylindrical portion having the thick portion. Further, in the constant velocity joint boot manufactured in Patent Document 2, as shown on the right side in FIG. 4A in Patent Document 2, the portion connected from the large diameter cylindrical portion to the bellows portion is inclined. Is formed.

The manufacturing method described in Patent Document 2 is a manufacturing method for manufacturing a constant velocity joint boot having the same shape as the constant velocity joint boot described in Patent Document 1. There was a problem like this.
JP 2002-13546 A JP 2002-361715 A

  The present invention has been made in view of the above circumstances, and provides a constant-velocity joint boot excellent in sealing performance in which a large-diameter cylindrical portion does not lift from a mating member even if deformation occurs in a bellows portion. Let it be an issue.

A constant velocity joint boot according to the present invention for solving the above-described problems includes a small-diameter cylindrical portion held by a shaft, and a large-diameter cylindrical portion that is coaxially disposed apart from the small-diameter cylindrical portion and has a larger diameter than the small-diameter cylindrical portion. And a bellows portion integrally connecting the small diameter cylindrical portion and the large diameter cylindrical portion, a small diameter seal rib provided on a surface in contact with the shaft of the small diameter cylindrical portion, and a surface in contact with the mating member of the large diameter cylindrical portion in the circumferential direction. In the constant-velocity joint boot having a large-diameter seal rib portion, the bellows portion includes a first valley portion, a first peak portion, a second valley portion, a second peak portion,. · And a plurality of valleys and peaks are alternately continuous, and between the first valley and the large-diameter cylinder, a fold leading to the straight part extending from the large-diameter cylinder and the first valley and a part, the large-diameter cylindrical portion is molded by injection molding, the thick portion protruding to the inner circumferential side circumferential direction partially and thick section And a thin portion connecting, folding portion of provided phase of the thick portion, boot for a constant velocity joint, characterized in that it is enlarged radially outward.

  The constant velocity joint boot of the present invention has a straight portion, whereby the rigidity of the large-diameter cylindrical portion is increased, and when the bellows portion is deformed, deformation due to the force from the bellows portion is difficult to occur. For this reason, it is difficult for the large-diameter cylindrical portion to lift from the counterpart member.

  Moreover, since the distance between the bellows portion and the large-diameter seal rib portion is sufficiently secured by the straight portion, the sealing performance at the seal portion is secured even if the bellows portion is deformed. For this reason, grease leakage does not occur.

  The boot for constant velocity joints of the present invention has a bent portion that connects the straight portion and the first valley portion. When the bent portion connects the straight portion and the first valley portion, when the bellows portion is deformed, it is a portion that prevents the deformation and the force generated by the deformation from being transmitted to the straight portion.

  In the constant velocity joint boot of the present invention, the above effect can be obtained when the length of the straight portion is 0.18 to 0.37 times as long as the distance to the small-diameter seal rib portion. When the length of the straight portion is shorter than the above range, the large-diameter cylindrical portion is easily lifted from the mating member when the bellows portion is deformed, and when the length of the straight portion is longer than the above range, it occupies the entire length of the constant velocity joint boot. The length of the bellows portion may be shortened, and the durability as a constant velocity joint boot may be reduced.

  It is preferable that each seal rib part of a large diameter cylinder part and a small diameter cylinder part consists of a rib protruded to each internal peripheral surface of a large diameter cylinder part and a small diameter cylinder part. When each seal rib portion is composed of a plurality of ribs arranged in the axial direction of each cylindrical portion, the length of the straight portion is determined using the center in the axial direction of the plurality of ribs as a reference (seal point). .

  The large-diameter cylindrical portion of the tripod type joint has a thick portion that protrudes partially inward in the circumferential direction and a thin portion that connects the thick portions. Since the large-diameter cylindrical portion has a thick portion and a thin portion, the constant velocity joint boot of the present invention can be assembled to a mating member having a non-circular outer peripheral shape such as a tripod type joint. This non-circular outer peripheral shape is usually a shape in which a circular shape is indented from several predetermined positions. In the present invention, the thin-walled portion of the large-diameter cylindrical portion is in contact with the circular portion of the counterpart material, and the thick-walled portion is in contact with the indented portion of the counterpart material. Therefore, it is preferable that the shape of the thin portion is substantially cylindrical, and the shape of the thick portion is a shape corresponding to the indented portion of the counterpart material. Further, the position where the thick portion is provided and the number of the thick portions are also adapted to the shape of the mating member.

  The constant velocity joint boot according to the present invention includes a small-diameter cylindrical portion that is held by a shaft, a large-diameter cylindrical portion that is coaxially arranged apart from the small-diameter cylindrical portion, and has a larger diameter than the small-diameter cylindrical portion, a small-diameter cylindrical portion, and a large-diameter cylindrical portion. Between the bellows part integrally connecting the diameter cylinder part, each seal rib part provided on the contact surface of the shaft of the small diameter cylinder part and the large diameter cylinder part or the mating member, and between the large diameter cylinder part and the bellows part It is preferable that the straight portion is formed, and the small diameter cylindrical portion, the bellows portion, each seal rib portion and the straight portion are integrally formed by blow molding, and the large diameter cylindrical portion is integrally formed by injection molding. Moreover, you may shape | mold by injection blow molding.

  The constant velocity joint boot of the present invention uses an injection mold having a ring-shaped cavity for molding a large-diameter cylindrical portion and a donut disk-shaped runner portion extending radially inward from the ring-shaped cavity. An injection molding process in which molten resin is injected into the ring-shaped cavity through a disc-shaped runner portion to form a large-diameter cylindrical portion, and the molten resin is continuously supplied to the injection mold while holding the large-diameter cylindrical portion. The injection mold is pulled away from the nozzle mold, and the parison forming process to draw the molten resin from the nozzle mold to form the parison extending from the large-diameter cylindrical part, and the parison is sandwiched by the blow mold from the side and pressurized in the parison It is preferable that the molding is performed by a molding method in which gas is introduced and a bellows part is molded in this order.

  The constant velocity joint boot of the present invention is formed by a molding method in which an injection molding process, a parison formation process, and a blow molding process are performed in this order, thereby forming an integrally molded product, which eliminates the need for secondary processing such as joining and increases productivity. Since it improves and man-hours are reduced, it becomes inexpensive. Further, since this molding method can prevent sinking of the thick portion of the large-diameter cylindrical portion, the sealing performance is improved. In addition, the parison is prevented from being caught by the mold, the occurrence of defective products during molding is reduced, the cost increase due to the occurrence of defective products is suppressed, and it becomes a low-cost constant velocity joint boot. Yes.

  The constant velocity joint boot of the present invention can be formed of a general material having elasticity, and is preferably formed of a thermoplastic elastomer.

  The constant velocity joint boot of the present invention has a straight portion between the large-diameter seal rib portion and the bellows portion. In the boot for a constant velocity joint according to the present invention, the straight portion increases the rigidity of the large-diameter cylindrical portion and prevents the large-diameter cylindrical portion from being deformed due to the deformation of the bellows portion. As a result, the constant velocity joint boot of the present invention is a constant velocity joint boot excellent in sealing performance with the mating member.

  In order to further clarify the configuration and operation of the present invention described above, preferred embodiments of the present invention will be described below.

  FIG. 1 is a sectional view of a constant velocity joint boot according to the present invention. FIG. 2 is a view showing an end face of the large-diameter cylindrical portion of the constant velocity joint boot. 3 and 4 are enlarged cross-sectional views of a thick part and a thin part of the large-diameter cylindrical part, respectively.

  In FIG. 1, the constant velocity joint boot is manufactured by using TPEE or TPO, which is a thermoplastic elastomer, as a material and molding the thermoplastic elastomer by blow molding.

  The constant velocity joint boot 1 includes a small-diameter cylindrical portion 2 held by a shaft, a large-diameter cylindrical portion 3 that is coaxially disposed apart from the small-diameter cylindrical portion 2 and has a larger diameter than the small-diameter cylindrical portion 2, and a small-diameter cylindrical portion. 2, a bellows portion 4 that integrally connects the large diameter cylindrical portion 3, a small diameter seal rib portion provided on a surface that contacts the shaft of the small diameter cylindrical portion 2, and a circumferential direction on a surface that contacts the mating member of the large diameter cylindrical portion 3. A large-diameter seal rib portion 30, a straight portion 5 extending from the large-diameter cylindrical portion 3, and a fold portion 6 that connects the straight portion 5 and the bellows portion 4.

  The small diameter cylindrical portion 2 has a substantially cylindrical shape, and an inner peripheral surface thereof is held in contact with the shaft. Two small-diameter seal ribs 20, 20 projecting radially inward are provided on the inner peripheral surface of the small-diameter cylindrical portion 2. The small-diameter seal rib 20 ensures the sealing performance of the constant velocity joint boot by being pressed against the outer peripheral surface of the shaft when the small-diameter cylindrical portion 2 is held on the shaft and causing elastic deformation. The small-diameter cylindrical portion 2 has two small-diameter seal ribs 20 and 20, and the center of the two small-diameter seal ribs 20 and 20 is used as a seal point in the small-diameter cylindrical portion 2.

  The large-diameter cylindrical portion 3 has a substantially cylindrical shape, and an inner peripheral surface thereof is held in contact with a mating member. Two large-diameter seal ribs 30, 30 ′ projecting radially inward are provided on the inner peripheral surface of the large-diameter cylindrical portion 3. The large-diameter seal ribs 30 and 30 ′ are pressure-bonded to the outer peripheral surface of the shaft and elastically deformed when the large-diameter cylindrical portion 3 is held by the mating member, thereby ensuring the sealing performance of the constant velocity joint boot. The large-diameter cylindrical portion 3 has two large-diameter seal ribs 30 and 30 ′, and the center of the two large-diameter seal ribs 30 and 30 ′ is a seal point in the large-diameter cylindrical portion 3.

  The large-diameter cylindrical portion 3 has a shape in which thick portions 3A and thin portions 3B are alternately arranged in the circumferential direction. Three thick portions 3A and three thin portions 3B are provided. When viewed from the end face of the large-diameter cylindrical portion 3, the thick-walled portion 3A has a substantially convex shape and a shape protruding radially inward.

  The bellows portion 4 integrally connects the small diameter cylindrical portion 2 and the large diameter cylindrical portion 3. In addition, the bellows portion 4 includes a first valley portion, a first mountain portion, a second valley portion, a second mountain portion, ... and a plurality of valley portions and mountain portions alternately in order from the large-diameter cylindrical portion 3 side. It is made. In the bellows portion 4, the inner diameter is reduced as the first valley portion, the second valley portion, the third valley portion,. Similarly, in the peak portion, the inner diameter is reduced as the first peak portion, the second peak portion, the third peak portion,. Since each crest and trough are gradually reduced in diameter, the large-diameter cylindrical portion 3 and the inner-diameter cylindrical portion 2 having different diameters are integrally connected.

  The straight part 5 extends from the large-diameter cylindrical part 3. The straight portion 5 is provided between the large-diameter seal rib 30 located on the small-diameter cylindrical portion 2 side and the bellows portion 4 of the two large-diameter seal ribs 30 and 30 ′. The straight portion 5 has the same inner diameter as the portion of the large-diameter cylindrical portion 3 where the large-diameter seal ribs 30 and 30 ′ are not provided.

  In the constant velocity joint boot 1, when the length of the straight portion 5 is B and the length between the seal points of the small diameter cylindrical portion 2 and the large diameter cylindrical portion 3 is A, B / A = 0. The straight part 5 is formed so that it may become 18-0.37. Moreover, it is preferable that the length of the straight part 5 is 12 mm or more.

  The bent portion 6 is provided so as to connect the straight portion 5 and the first valley portion of the bellows portion 4. The bent portion 6 is provided at the end portion of the straight portion 5 on the bellows portion 4 side. In the present embodiment, the inner diameter changes from the bellows part 4 side of the folded part 6. In the present embodiment, the folded portion 6 in the phase where the thick portion 3A is formed is the same as the portion where the inner circumference reduced in diameter by the thick portion 3A is not reduced in diameter as shown in the lower part of FIG. The diameter is expanded to be the inner circumference.

  Further, in the constant velocity joint boot 1 of the present embodiment, the bent portion 6 does not transmit the force generated by the deformation of the bellows portion 4 during use to the straight portion 5.

  When assembling the constant velocity joint boot 1 of the present embodiment to the mating member, as shown in FIG. 5, even if it is assembled in a state of contacting the mating member 7 up to the inner peripheral surface of the straight portion 5, it is shown in FIG. As described above, the large-diameter cylindrical portion 3 may be assembled in a state where the inner peripheral surface does not contact the counterpart member 7. Preferably, it is in a state of contacting the mating member 7 up to the inner peripheral surface of the straight portion 5. In addition, when assembling the boot for constant velocity joint 1 of the present embodiment to the mating member 7, the large-diameter cylindrical portion 3 is pressed against the mating member 7 by a biasing means (not shown). Then, as shown in FIG. 5, when the mating member 7 is assembled in contact with the inner peripheral surface of the straight portion 5, the biasing means is also provided in the straight portion 5 so that the straight portion 5 Separation from the mating member 7 can be suppressed.

  The constant velocity joint boot of this embodiment is assembled to the mating member 7 as shown in FIGS. Here, FIGS. 5 and 6 each show only the vicinity of the large-diameter cylindrical portion 3, and the outer periphery of the shaft 7 </ b> A and the inner periphery of the small-diameter cylindrical portion 2 are pressure-bonded also at the end on the small-diameter cylindrical portion 2 side. Has been assembled. In both figures, the large diameter cylindrical portion 3 and the small diameter cylindrical portion 2 are in a coaxial state.

  And when the axis | shaft of the large diameter cylinder part 3 and the small diameter cylinder part 2 comes to be different (shaft 7A inclines), in bellows part 4 (depending on the direction in which shaft 7A inclines), the space | interval of a trough part and a peak part And a portion where the interval between the valley and the peak is reduced occurs.

  When the shaft 7A is inclined, a part of the bellows part 4 is pulled following the small-diameter cylindrical part 2, and the interval between the valley part and the peak part is widened. At this time, since the large-diameter cylindrical portion 3 is fixed, a part of the large-diameter cylindrical portion 3 is pressed against the mating member 7 (shaft 7A). Here, the part of the large-diameter cylindrical portion 3 that is press-contacted to the large-diameter cylindrical portion 3 is a portion that is located in the same phase in the circumferential direction as the portion in the bellows portion 4 where the interval between the valley and the ridge is widened.

  When the shaft 7A is inclined, another part of the bellows portion 4 is crushed toward the large-diameter cylindrical portion 3, the space between the valley portion and the mountain portion is reduced, and further, the shaft 7A is pushed outward in the radial direction by the inclination of the shaft 7A. Biased in the direction. For this reason, a radially outward force is applied to a portion adjacent to the large-diameter cylindrical portion 3, and the portion is deformed in the direction of lifting from the counterpart member 7 (shaft 7A). This deformation tends to lift the seal portion of the large diameter cylindrical portion 3 from the surface of the counterpart member 7.

  In the constant velocity joint boot 1 of the present embodiment, the bellows portion 4 and the straight portion 5 are connected by the bent portion 6, so that the large diameter cylindrical portion 3 and the small diameter cylindrical portion 2 are displaced so that their axes are different. Even if the bellows portion 4 is deformed, the bent portion 6 is prevented from transmitting the deformation generated in the bellows portion 4 to the straight portion 5.

  Furthermore, since the constant velocity joint boot 1 of this embodiment has a sufficient distance between the bellows portion 4 and the seal point of the large-diameter cylindrical portion 3 by the straight portion 5, the large-diameter cylindrical portion 3 and the small-diameter cylinder are secured. Even if the portion 2 is displaced so that its axis is different and the bellows portion 4 is deformed, the straight portion 5 buffers the stress due to the deformation, and the large diameter cylindrical portion 3 is difficult to transmit the stress.

  As a result, in the constant velocity joint boot of the present embodiment, the large-diameter cylindrical portion 3 does not float from the mating member 6 (no peeling occurs).

  Moreover, in the constant velocity joint boot 1 of this embodiment, the rigidity of the large diameter cylindrical portion 3 itself is increased by having the straight portion 5, and the large diameter cylindrical portion 3 is less likely to be deformed. That is, the constant velocity joint boot 1 of the present embodiment has a large rigidity of the large-diameter cylindrical portion 3 itself and is less likely to transmit stress due to deformation of the bellows portion 4 to the large-diameter cylindrical portion 3.

  For this reason, the constant velocity joint boot 1 of the present embodiment ensures the sealing performance in the large-diameter cylindrical portion 3, and grease leakage does not occur in the large-diameter cylindrical portion 3.

  The constant velocity joint boot 1 of the present embodiment was manufactured by the manufacturing method according to claim 4.

  That is, an injection mold having a ring-shaped cavity for molding a large-diameter cylindrical portion and a donut disk-shaped runner portion extending radially inward from the ring-shaped cavity is used, and from the nozzle mold to the donut disk-shaped runner portion. An injection molding process in which molten resin is injected into the ring-shaped cavity to form a large-diameter cylindrical portion, and the injection-molding die is held in a state where the large-diameter cylindrical portion is held in the injection mold and the molten resin is continuously supplied. A parison forming step of pulling the molten resin from the nozzle mold and forming a parison extending from the large-diameter cylindrical portion, and inserting the pressurized gas into the parison by sandwiching the parison from the side with the blow mold, Molding was performed by performing a blow molding process for molding in this order.

It is sectional drawing of the boot for constant velocity joints of an Example. It is the figure which showed the end surface of the large diameter cylinder part of the boot for constant velocity joints of an Example. It is sectional drawing of the thin part of the boot for constant velocity joints of an Example. It is sectional drawing of the thick part of the boot for constant velocity joints of an Example. It is sectional drawing of the large diameter cylinder part vicinity when the large diameter cylinder part of the boot for constant velocity joints of an Example is assembled | attached to the other member. It is sectional drawing of the large diameter cylinder part vicinity when the large diameter cylinder part of the boot for constant velocity joints of the Example of another form is assembled | attached to the other member. FIG. 6 is a cross-sectional view of a conventional constant velocity joint boot in a state where a floating from a mating member occurs in a large diameter cylindrical portion.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Boot for constant velocity joints 2 ... Small diameter cylinder part 20 ... Small diameter seal rib 3 ... Large diameter cylinder part 30, 30 '... Large diameter seal rib 3A ... Thick part 3B ... Thin part 4 ... Bellows part 5 ... Straight part 6 ... Folding Part 7 ... Counterpart 7A ... Shaft 8 ... Clamp

Claims (3)

A small-diameter cylindrical portion held by the shaft, a large-diameter cylindrical portion that is coaxially disposed apart from the small-diameter cylindrical portion, and has a larger diameter than the small-diameter cylindrical portion, and the small-diameter cylindrical portion and the large-diameter cylindrical portion are integrated. A bellows portion connected to the shaft, a small-diameter seal rib portion provided on a surface of the small-diameter cylindrical portion in contact with the shaft, and a large-diameter seal rib portion provided in a circumferential direction on a surface in contact with the mating member of the large-diameter cylindrical portion; In the constant velocity joint boot having
In the bellows portion, the first trough portion, the first crest portion, the second trough portion, the second crest portion, and a plurality of trough portions and crest portions are alternately arranged in order from the large-diameter cylindrical portion side. A straight portion extending from the large-diameter cylinder portion and a fold portion connected to the first valley portion between the first valley portion and the large-diameter cylinder portion ;
The large-diameter cylindrical portion is formed by injection molding, and has a thick portion that protrudes partially inward in the circumferential direction and a thin portion that connects the thick portions,
The boot for a constant velocity joint , wherein the bent portion in the phase where the thick-walled portion is formed has a diameter expanded radially outward . 2. The constant velocity joint boot according to claim 1, wherein the straight portion is formed with a length of 0.18 to 0.37 times the distance from the large-diameter seal rib portion to the small-diameter seal rib portion. An injection mold having a ring-shaped cavity for molding the large-diameter cylindrical portion and a donut disk-shaped runner portion extending radially inward from the ring-shaped cavity is used, and from the nozzle mold to the donut disk-shaped runner portion. Injection molding step of injecting molten resin into the ring-shaped cavity to mold the large-diameter cylindrical portion;
The injection mold is pulled away from the nozzle mold in a state where the large diameter cylindrical portion is held in the injection mold and the molten resin is continuously supplied, and the molten resin is pulled out from the nozzle mold to be removed from the large diameter cylindrical portion. A parison formation process for forming an extended parison;
A blow molding step of molding the bellows part by sandwiching the parison from the side with a blow mold and introducing a pressurized gas into the parison;
The constant velocity joint boot according to claim 1, wherein the boot is formed by a forming method in which the steps are performed in this order.

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