Constant velocity joint boots

Abstract

To provide a constant velocity joint boot that can suppress the deterioration of sealing performance. [Solution] A differential-side constant velocity joint 50 is provided with an outer race 54 that is rotatable about a first axis C1 and whose outer peripheral surface 54o of the opening 54b in view in the direction of the first axis C1 is non-circular, and a boot 56 is fixed by a clamp 72 so as to cover the outer peripheral surface 54o, wherein (a) the boot 56 has a cylindrical fixing part 62 that is fixed so as to cover the outer peripheral surface 54o, (b) in a cross-section perpendicular to the first axis C1, the inner peripheral surface 62i of the fixing part 62 has a corner portion 62t that is recessed toward the outer peripheral side, with a shape corresponding to the shape of the outer peripheral surface 54o, and (c) in the state before the fixing part 62 is fixed by the clamp 72, the fixing part 62 has a thickness-reinforcing part 62g of a predetermined shape in which the outer peripheral surface 62o of the fixing part 62 protrudes toward the outer peripheral side at a position corresponding to the corner portion 62t in the circumferential direction in a cross-section perpendicular to the first axis C1.

Description

Technical Field

[0001] The present invention relates to a constant velocity joint boot that is fixed so as to cover the outer peripheral surface of an opening portion by a clamp in a constant velocity joint including an outer race having a non-circular outer peripheral surface of the opening portion when viewed in the direction of the rotation center line.

Background Art

[0002] In a constant velocity joint including an outer race that is rotatable about a rotation center line and has a non-circular outer peripheral surface of an opening portion when viewed in the direction of the rotation center line, a constant velocity joint boot that is fixed so as to cover the outer peripheral surface of the opening portion by a clamp is known. For example, the constant velocity joint boot described in Patent Document 1 is such a boot. The constant velocity joint boot described in FIGS. 15 and 16 of Patent Document 1 has a cylindrical fixing portion that is fixed so as to cover the outer peripheral surface of the opening portion of the outer race by a clamp. In a cross-sectional plane perpendicular to the axis of the constant velocity joint boot, the inner peripheral surface of the fixing portion has a shape corresponding to the shape of the outer peripheral surface of the opening portion. On the other hand, when viewed in the axial direction of the constant velocity joint boot, the outer peripheral surface of the fixing portion is substantially circular, and a wall thickness supplement portion that is thickened on the outer peripheral side with respect to the circumcircle of the thin wall portion is formed at the boundary between the thick wall portion and the thin wall portion. Thereby, when the wall thickness supplement portion is tightened by a clamp, the wall thickness supplement portion partially increases the tightening pressure at which the fixing portion at the boundary between the thick wall portion and the thin wall portion presses the outer peripheral surface of the outer race to a high pressure.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Incidentally, as described in Patent Document 1, even if a thickness-reinforcement portion is formed on the outer circumferential surface of the fixing portion of the constant velocity joint boot, depending on its shape, the sealing performance of the constant velocity joint boot may be reduced.

[0005] This invention was made against the above circumstances, and its objective is to provide a constant velocity joint boot that can suppress a decrease in sealing performance. [Means for solving the problem]

[0006] The gist of the present invention is a constant velocity joint comprising an outer race that is rotatable about a rotational centerline and whose outer peripheral surface of the opening in view in the direction of the rotational centerline is non-circular, wherein the constant velocity joint boot is fixed by a clamp so as to cover the outer peripheral surface of the opening, and (a) the constant velocity joint boot has a cylindrical fixing portion that is fixed so as to cover the outer peripheral surface of the opening, (b) in a cross-section perpendicular to the axis of the constant velocity joint boot, the inner peripheral surface of the fixing portion has a corner portion that is recessed toward the outer peripheral side, with a shape corresponding to the shape of the outer peripheral surface of the opening, and (c) in the state before the fixing portion is fixed by the clamp, the fixing portion has a thickness-reinforcing portion of a predetermined shape that protrudes toward the outer peripheral side of the outer peripheral surface of the fixing portion at a position corresponding to the corner portion in the circumferential direction of the cross-section. [Effects of the Invention]

[0007] According to the constant velocity joint boot of the present invention, (a) the constant velocity joint boot has a cylindrical fixing portion that is fixed so as to cover the outer circumferential surface of the opening, (b) in a cross-section perpendicular to the axis of the constant velocity joint boot, the inner circumferential surface of the fixing portion has a corner portion that is recessed toward the outer circumferential side, with a shape corresponding to the shape of the outer circumferential surface of the opening, and (c) in the state before the fixing portion is fixed by the clamp, the fixing portion has a thickness-reinforcing portion of a predetermined shape in which the outer circumferential surface of the fixing portion protrudes toward the outer circumferential side at a position corresponding to the corner portion in the circumferential direction of the cross-section. In the state before the fixing portion of the constant velocity joint boot is fixed by the clamp, if the fixing portion has a thickness-reinforcing portion of a predetermined shape in which the outer circumferential surface of the fixing portion protrudes toward the outer circumferential side at a position corresponding to the corner portion in the circumferential direction, the localized reduction of the clamping pressure in the region near the corner portion is suppressed compared to the case where it is not. As a result, the reduction in the sealing performance of the constant velocity joint boot due to a localized decrease in clamping pressure is suppressed. [Brief explanation of the drawing]

[0008] [Figure 1] This diagram illustrates the schematic configuration of a differential-side constant velocity joint to which the present invention is applied. [Figure 2] This is a cross-sectional view of the boot fixing portion according to Example 1, taken by cutting it with a plane perpendicular to the first axis. [Figure 3] Figure 2 illustrates the local decrease in the clamping pressure exerted by the boot's fixing portion against the outer surface of the outer race when the boot shown in Figure 2 is secured by a clamp. (a) is an enlarged view of the region enclosed by the dashed line in Figure 2, and (b) is a diagram illustrating the relationship between each position of the fixing portion and the stress. [Figure 4] This is a cross-sectional view of the boot fixing portion according to Example 2, taken by cutting it with a plane perpendicular to the first axis. [Modes for carrying out the invention]

[0009] Hereinafter, each embodiment of the present invention will be described in detail with reference to the drawings. Note that in each embodiment, the drawings have been simplified or modified as appropriate, and the dimensional ratios and shapes of each part are not necessarily depicted accurately. In this specification, "circumferential direction" refers to the circumferential direction centered on the first axis C1, and "radial direction" refers to the radial direction centered on the first axis C1. [Examples]

[0010] Figure 1 is a diagram illustrating the schematic configuration of a differential-side constant velocity joint 50 to which the present invention is applied.

[0011] The drive shaft 10 comprises a shaft body 20, a differential-side connecting shaft 30, a wheel-side connecting shaft 40, a differential-side constant velocity joint 50, and a wheel-side constant velocity joint 80. The shaft body 20 is rotatable around the first axis C1. The differential-side connecting shaft 30 is connected to the side gear of a differential gear (not shown). The differential-side connecting shaft 30 is rotatable around the second axis C2. The wheel-side connecting shaft 40 is connected to a drive wheel (not shown). The differential-side constant velocity joint 50 connects the shaft body 20 and the differential-side connecting shaft 30. The wheel-side constant velocity joint 80 connects the shaft body 20 and the wheel-side connecting shaft 40.

[0012] The differential-side constant velocity joint 50 is, for example, a tripod-type sliding constant velocity universal joint that has an extension and contraction function in the longitudinal direction of the drive shaft 10. The wheel-side constant velocity joint 80 is, for example, a Barfield-type fixed constant velocity universal joint that does not have an extension and contraction function in the longitudinal direction of the drive shaft 10, and is a well-known configuration. The differential-side constant velocity joint 50 corresponds to the "constant velocity joint" in the present invention.

[0013] The differential-side constant velocity joint 50 comprises a tripod 52, an outer race 54, and a boot 56.

[0014] The tripod 52 is a well-known configuration in which three trunnions 52a are fixed to the differential gear side end of the shaft body 20 and protrude outward at equal angular intervals.

[0015] The outer race 54 is rotatable about the second axis C2 and has an opening 54b at one end in the direction of the second axis C2. The outer race 54 has three guide grooves 54a for guiding the three trunnions 52a and is a bottomed cylindrical member that houses the tripod 52 so that it is not rotatable relative to it and is movable in the direction of the second axis C2, and is a well known configuration. The second axis C2 corresponds to the "rotation centerline" in this invention.

[0016] The boot 56 is a cylindrical member. The boot 56 comprises a fixing portion 58, a bellows portion 60, and a fixing portion 62. The fixing portion 58 is a cylindrical portion that covers the outer circumferential surface of the differential gear end of the shaft body 20 and is fixed to the shaft body 20 by a clamp 70. The fixing portion 62 is a cylindrical member that covers the outer circumferential surface 54o of the opening 54b of the outer race 54 and is fixed to the outer race 54 by a clamp 72. That is, the clamp 72 presses the outer circumferential surface 62o of the fixing portion 62, causing the inner circumferential surface 62i of the fixing portion 62 to press the outer circumferential surface 54o of the opening 54b of the outer race 54. The fixing portion 62 corresponds to the "fixing portion" in this invention. The bellows portion 60 is a bellows-shaped cylindrical portion located between the fixing portion 58 and the fixing portion 62, and holds high-viscosity grease inside. The boot 56 is made of an oil-resistant, weather-resistant, and elastically deformable material, such as rubber, and the composition of the boot 56, especially the fixing portion 62, is constant and homogeneous. The boot 56 absorbs the change in relative movement in the direction of the first axis C1 between the differential gear end of the shaft body 20 and the outer race 54, and also absorbs the change in relative movement in the rotational direction between the shaft body 20 and the outer race 54 when the first axis C1 and the second axis C2 intersect. The boot 56 corresponds to the "constant velocity joint boot" in this invention.

[0017] Figure 2 is a cross-sectional view of the fixing portion 62 of the boot 56 according to Embodiment 1, taken from a cross-section perpendicular to the first axis C1 (hereinafter simply referred to as the "C1 perpendicular cross-section"). The first axis C1 corresponds to the "axis" in the present invention. Figure 2 shows a state in which the first axis C1 and the second axis C2 do not intersect, that is, a state in which the first axis C1 and the second axis C2 overlap. The fixing portion 62 before tightening by the clamp 72 is shown by a solid line, and the outer race 54 is shown by a dashed line. The clamping surface 72r, which is the outer circumferential surface 62o after tightening by the clamp 72, is shown by a dashed line for reference. The clamp 72 tightens the fixing portion 62 in a circular shape in the C1 perpendicular cross-section. Even if the fixing portion 62 is deformed to the dashed line by the clamp 72, the deformation is elastic deformation.

[0018] In a cross-section perpendicular to the second axis C2 (hereinafter simply referred to as the "C2 perpendicular cross-section"), the shape of the outer circumferential surface 54o is non-circular. Therefore, in the C1 perpendicular cross-section, the inner circumferential surface 62i of the fixing portion 62 has a shape corresponding to the shape of the outer circumferential surface 54o and is non-circular. On the other hand, in the C1 perpendicular cross-section, the outer circumferential surface 62o has fewer radial irregularities compared to the inner circumferential surface 62i, so that approximately uniform pressure is applied to the outer circumferential surface 62o when tightened by the clamp 72. Therefore, in the part where the inner circumferential surface 62i is greatly recessed inward, the fixing portion 62 has a relatively thicker wall portion 62a, and in the part where the inner circumferential surface 62i is not so recessed inward, the fixing portion 62 has a relatively thin wall portion 62b. In the vertical cross-section of C1, the inner circumferential surface 62i has corners 62t that are recessed toward the outer circumferential side at the boundary between the thick-walled portion 62a and the thin-walled portion 62b.

[0019] Before the fixing part 62 is fixed by the clamp 72, the fixing part 62 has a wall thickness replenishing part 62g of a predetermined shape in which the outer peripheral surface 62o of the fixing part 62 protrudes to the outer peripheral side at a position corresponding to the corner part 62t in the circumferential direction in the C1 vertical cutting plane. The tightening pressure PRf will be described later. In the present embodiment, the wall thickness replenishing part 62g is provided at positions corresponding to the corner parts 62t present at both ends of the thin wall part 62b in the circumferential direction and at a position corresponding to the central part of the thin wall part 62b. The wall thickness replenishing part 62g has a greater thickness at a position corresponding to the central part of the thin wall part 62b than at a position corresponding to the corner part 62t.

[0020] The "predetermined shape" of the thickness reinforcement portion 62g is set, for example, by simulation or experiment using an electronic computer, so that when the boot 56 is fixed by the clamp 72, the clamping pressure PRf does not locally decrease at the position corresponding to the corner portion 62t in the circumferential direction. For example, the finite element method is used for the simulation. In the simulation, the stress Fint at each position of the inner circumferential surface 62i of the boot 56 when the boot 56 is tightened by the clamp 72 is calculated, using the shape of the part of the boot 56 corresponding to the corner portion 62t (such as the shape of the rate of change of thickness in the circumferential direction and the compression ratio of the fixing portion 62 by the clamp 72) as parameters. Through this simulation, the predetermined shape is calculated so that the inner circumferential surface 62i does not lift away from the outer circumferential surface 54o in the vicinity region 62n on the thickened portion 62a side of the corner portion 62t, as described later. Specifically, the simulation is performed so that the force ΔF [Pa] based on the difference in circumferential stress Fint at the corner 62t is less than or equal to a predetermined judgment value, assuming that the inner circumferential surface 62i does not lift away from the outer circumferential surface 54o in the nearby region 62n. For example, in the experiment, various shapes of the thickness-reinforced portion 62g are prepared, and when they are tightened by the clamp 72, it is observed whether the inner circumferential surface 62i in the nearby region 62n shifts from the thin-walled portion 62b side to the thick-walled portion 62a side. This allows the shape of the portion of the boot 56 corresponding to the corner 62t to be determined as a predetermined shape when the tightening pressure PRf does not decrease locally. The "circumscribed circle 62a1" shown in Figure 2 is the outer circumferential surface 62o when there is no thickness-reinforced portion 62g, and is a circle that circumscribes the portion where the thickness is maximum in each thick-walled portion 62a in the C1 vertical cross-section.

[0021] FIG. 3 is a diagram for explaining a local decrease in the tightening pressure PRf at which the fixing portion 62 of the boot 56 presses the outer peripheral surface 54o of the outer race 54 when the boot 56 shown in FIG. 2 is fixed by the clamp 72. (a) is an enlarged view of a region A surrounded by the two-dot chain line shown in FIG. 2, and (b) is a diagram for explaining the relationship between each position of the fixing portion 62 and the stress Fint. In FIG. 3(b), the stress Fint according to the present embodiment having the thickness compensation portion 62g is shown by a solid line, and the stress Fint according to a comparative example not having the thickness compensation portion 62g is shown by a broken line. In addition, in the portion of the fixing portion 62 tightened by the clamp 72, the shape of the opening 54b in the view in the direction of the first axis C1 and the shape of the fixing portion 62 in the view in the direction of the first axis C1 are shapes that are maintained and extend in the direction of the first axis C1.

[0022] Hereinafter, for the sake of easy understanding of the invention, when the fixing portion 62 is tightened by the clamp 72, the pressure applied to the outer peripheral surface 62o of the fixing portion 62 will be described as acting only in the direction toward the inner peripheral side in the radial direction. However, strictly speaking, due to the unevenness of the outer peripheral surface 62o, it may act slightly deviated in the circumferential direction from the direction toward the inner peripheral side in the radial direction.

[0023] Here, in the radial direction, the ratio obtained by dividing the thickness of the fixing portion 62 after tightening by the clamp 72 by the thickness of the fixing portion 62 before tightening is referred to as the "collapse amount ratio α". In elastic deformation, the stress Fint [Pa], which is the force generated inside the object, is proportional to the collapse amount ratio α. Materials such as rubber have isotropy with respect to the direction in which the stress Fint acts. On the inner peripheral surface 62i, the stress Fint acts toward the inner peripheral side. When the inner peripheral surface 62i of the fixing portion 62 is in contact with the outer peripheral surface 54o of the outer race 54, the stress Fint acting on this inner peripheral surface 62i acts as a tightening pressure PRf for tightening the outer peripheral surface 54o by the inner peripheral surface 62i.

[0024] First, the comparative example will be described. In the comparative example, in the C1 vertical cross-section, the outer peripheral surface 62o of the fixing portion 62 is the same as the circumscribed circle 62a1.

[0025] When the outer circumferential surface 62o is compressed to the clamping surface 72r by the clamp 72, the deformation ratio α in the thick-walled section 62a is smaller than the deformation ratio α in the thin-walled section 62b. Therefore, even if pressure is applied uniformly from the clamp 72 to the inner circumference of the outer circumferential surface 62o, the stress Fint due to elastic deformation is smaller in the thick-walled section 62a compared to the thin-walled section 62b. Thus, assuming that the deformation ratio α and the stress Fint are proportional, the relationship between the position P1 on the thick-walled section 62a side, the corner 62t, the position P2 on the thin-walled section 62b side of the inner circumferential surface 62i shown in Figure 3(a), and the stress Fint at each of these positions is as shown by the dashed line in Figure 3(b). In particular, at the corner 62t, which is the boundary between the thick-walled section 62a and the thin-walled section 62b, the force ΔFref[Pa] based on the difference in stress Fint in the circumferential direction becomes large, and a large force acts in the direction of the dashed white arrow. This force ΔFref causes the inner circumferential surface 62i to shift from the thin-walled portion 62b to the thick-walled portion 62a, lifting the inner circumferential surface 62i away from the outer circumferential surface 54o in the vicinity region 62n. As a result, the clamping pressure PRf in the vicinity region 62n becomes locally smaller, leading to a decrease in sealing performance.

[0026] Next, this embodiment will be described. In this embodiment, in the vertical cross-section of C1, the outer peripheral surface 62o of the fixing portion 62 is provided with a thickness-reinforcing portion 62g of a predetermined shape at a position corresponding to the corner portion 62t in the circumferential direction with respect to the circumscribed circle 62a1 of the thickened portion 62a.

[0027] When the outer surface 62o is compressed to the clamping surface 72r by the clamp 72, the deformation ratio α increases in proportion to the thickness of the thickness-reinforced portion 62g compared to the comparative example. The relationship between the position P1 on the thick-walled portion 62a side, the corner 62t, the position P2 on the thin-walled portion 62b side on the inner surface 62i, and the stress Fint at each of these positions is shown by the solid line in Figure 3(b). Thus, due to the provision of the thickness-reinforced portion 62g, the stress Fint increases near the thin-walled portion 62b and the corner 62t compared to the comparative example. At the corner 62t, the force ΔFemb [Pa] based on the difference in stress Fint in the circumferential direction is smaller compared to the comparative example, and only a small force acts in the direction of the solid white arrow. With this force ΔFemb, the inner circumferential surface 62i is prevented from shifting from the thin-walled portion 62b to the thick-walled portion 62a, thereby maintaining the pressure on the outer circumferential surface 54o of the outer race 54 by the inner circumferential surface 62i of the fixing portion 62 in the vicinity region 62n. This suppresses a local decrease in the clamping pressure PRf in the vicinity region 62n, thereby suppressing a decrease in sealing performance. Furthermore, even if the difference in circumferential stress Fint is larger in areas other than the vicinity region 62n than in the comparative example, the inner circumferential surface 62i is less likely to lift away from the outer circumferential surface 54o compared to the vicinity region 62n, so the sealing performance does not decrease.

[0028] According to this embodiment, (a) the boot 56 has a cylindrical fixing portion 62 that is fixed so as to cover the outer peripheral surface 54o of the opening 54b, (b) in the vertical cross-section of C1, the inner peripheral surface 62i of the fixing portion 62 has a corner portion 62t that is recessed toward the outer peripheral side, as the shape corresponds to the shape of the outer peripheral surface 54o, and (c) in the state before the fixing portion 62 is fixed by the clamp 72, the fixing portion 62 has a thickness-reinforcing portion 62g of a predetermined shape in which the outer peripheral surface 62o of the fixing portion 62 protrudes toward the outer peripheral side at a position corresponding to the corner portion 62t in the circumferential direction of the vertical cross-section of C1. In the state before the fixing portion 62 of the boot 56 is fixed by the clamp 72, if the fixing portion 62 has a thickness-reinforcing portion 62g of a predetermined shape in which the outer peripheral surface 62o of the fixing portion 62 protrudes toward the outer peripheral side at a position corresponding to the corner portion 62t in the circumferential direction, then the localized reduction of the clamping pressure PRf in the nearby region 62n is suppressed compared to the case where it is not. This suppresses the decrease in the sealing performance of the boot 56 due to a localized decrease in the tightening pressure PRf. [Examples]

[0029] Figure 4 is a cross-sectional view of the fixing portion 162 of the boot 156 according to Embodiment 2, cut by a plane perpendicular to the first axis C1. The boot 156 according to this embodiment has substantially the same configuration as the boot 56 according to Embodiment 1 described above, but the shape of the outer peripheral surface 154o of the opening of the outer lace 154 of the fixing portion 162 is different from the outer peripheral surface 54o described above. In this embodiment, we will mainly explain the parts that differ from Embodiment 1 described above, and the explanation of parts that are substantially common will be omitted as appropriate.

[0030] The boot 156 comprises a fixing portion 58, a bellows portion 60, and a fixing portion 162. The fixing portion 162 corresponds to the fixing portion 62 of the boot 56 according to Embodiment 1. The boot 156 corresponds to the "constant velocity joint boot" in the present invention.

[0031] The fixing portion 162 has a thick portion 62a and a thin portion 162b, depending on the shape of the outer peripheral surface 154o. In the vertical cross-section C1, the inner peripheral surface 162i of the fixing portion 162 has corner portions 62t that are recessed toward the outer peripheral side at the boundary between the thick portion 62a and the thin portion 162b. Compared to the above-described embodiment 1, the thickness of the thin portion 162b relative to the circumscribed circle 62a1 is slightly thicker than that of the thick portion 62a in embodiment 1 at both corner portions 62t in the circumferential direction and at the center of the corner portion 62t.

[0032] To prevent a localized decrease in clamping pressure PRf [Pa] at positions corresponding to the corners 62t in the circumferential direction, the fixing portion 162 has a thickness-reinforcing portion 162g of a predetermined shape in which the outer peripheral surface 162o protrudes outward. Specifically, in the circumferential direction, a thickness-reinforcing portion 162g with a larger thickness is provided at positions corresponding to the corners 62t, and a thickness-reinforcing portion with a smaller thickness is provided at positions corresponding to the central portion.

[0033] According to this embodiment, similar to Embodiment 1 described above, when the boot 156 has a thickness-reinforcement portion 162g of a predetermined shape, the local decrease in the tightening pressure PRf in the vicinity region 62n is suppressed compared to the case where it does not. This suppresses the decrease in the sealing performance of the boot 156 due to the local decrease in the tightening pressure PRf.

[0034] The above-described examples are embodiments of the present invention, and the present invention can be implemented in various modified and improved forms based on the knowledge of those skilled in the art, without departing from its spirit.

[0035] In the above-described embodiment, the "constant velocity joint" in the present invention was a differential-side constant velocity joint 50, but the present invention is also applicable to a wheel-side constant velocity joint 80. [Explanation of Symbols]

[0036] 50: Differential side constant velocity joint (constant velocity joint), 54: Outer race, 54b, 154b: Opening, 54o, 154o: Outer surface (outer surface of the opening), 56, 156: Boot (boot for constant velocity joint), 62, 162: Fixing part (fixing part), 62g, 162g: Wall thickness replenishment part, 62i, 162i: Inner surface, 62o, 162o: Outer surface (outer surface of the fixing part), 62t, 162t: Corner part, 72: Clamp, C1: First axis (axis), C2: Second axis (rotation centerline), PRf: Clamping pressure

Claims

[Claim 1] A constant velocity joint comprising an outer race that is rotatable about a rotational centerline and whose outer circumferential surface of the opening in the direction of the rotational centerline is non-circular, wherein a constant velocity joint boot is fixed by a clamp so as to cover the outer circumferential surface of the opening, The constant velocity joint boot has a cylindrical fixing portion that is fixed so as to cover the outer circumferential surface of the opening, In the cross-section perpendicular to the axis of the constant velocity joint boot, the inner circumferential surface of the fixing portion is shaped to match the shape of the outer circumferential surface of the opening, and has a corner that is recessed on the outer side. Before the fixing portion is secured by the clamp, the fixing portion has a predetermined thickness-reinforcing portion at a position corresponding to the corner in the circumferential direction of the cut surface, where the outer surface of the fixing portion protrudes outward. A constant velocity joint boot characterized by the following features.

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