Boot cover and steering device

Abstract

A boot cover (60) according to the present invention is attached to a cylindrical boot (27) having a flexible part (52) that can expand and contract in the axial direction, so as to cover an outer periphery of the cylindrical boot. The boot cover (60) includes a first tubular part (61) which has an open end (60a) and through which the boot (27) is inserted, a second tubular part (62) that is fixed near an end portion of the boot (27) in an axial direction (X2) of the boot cover (60) and that has a smaller diameter than the first tubular part (61), and a tubular linking part (63) that is disposed between the first tubular part (61) and the second tubular part (62) in the axial direction (X2) of the boot cover (60), and that links the first tubular part (61) and the second tubular part (62). The open end (60a) overlaps with the flexible part (52) of the boot (27) in the axial direction (X2) of the boot cover (60).

Description

Boot cover and steering device

[0001] The present disclosure relates to a boot cover and a steering device.

[0002] For example, Patent Document 1 discloses a steering device having a bellows-shaped rack boot for protecting a portion of a rack shaft that is movable in the axial direction and protrudes from a rack housing. The steering device of Patent Document 1 includes a boot cover for protecting the rack boot. Such a boot cover has an end portion on the small-diameter side and an end portion on the large-diameter side, and covers the entire outer periphery in the radial direction of the bellows-shaped structure of the rack boot in a state where the end portion on the small-diameter side faces the tie rod.

[0003] Japanese Patent Application Laid-Open No. 2017-019366

[0004] By the way, the specifications of the axial length of the rack boot are various. In Patent Document 1, since the boot cover is designed according to the axial length of the rack boot, a boot cover is required for each specification of the axial length of the rack boot.

[0005] A boot cover according to one aspect of the present disclosure is a boot cover that is attached to cover the outer periphery of a cylindrical boot having a flexible portion that is axially stretchable. The boot cover has an open end, a first cylindrical portion through which the boot is inserted, a second cylindrical portion that is fixed near an end of the boot in the axial direction of the boot cover and has a smaller diameter than the first cylindrical portion, and a cylindrical connecting portion that is disposed between the first cylindrical portion and the second cylindrical portion in the axial direction of the boot cover and connects the first cylindrical portion and the second cylindrical portion. The open end overlaps the flexible portion of the boot in the axial direction of the boot cover.

[0006] A steering device according to one aspect of the present disclosure comprises a steering shaft, a joint connecting the steering shaft to a steering wheel of a vehicle and configured to be inclined with respect to the axial direction of the steering shaft, a housing that houses the steering shaft with a portion of the steering shaft and the joint exposed, a cylindrical boot having an axially expandable and contractible flexible portion that covers the steering shaft and the joint exposed from the housing, and a boot cover attached to cover the outer circumference of the boot. The boot cover has an open end and a first cylindrical portion through which the boot is inserted, a second cylindrical portion fixed to the outer circumference of the joint in the axial direction of the boot cover and having a smaller diameter than the first cylindrical portion, and a cylindrical connecting portion positioned between the first cylindrical portion and the second cylindrical portion in the axial direction of the boot cover and connecting the first cylindrical portion and the second cylindrical portion. The open end overlaps the flexible portion of the boot in the axial direction of the boot cover.

[0007] This figure shows the configuration of the steering device according to the embodiment. This is a partial cross-sectional view showing the structure of the boot and boot cover in Figure 1. This is a front view showing the configuration of the boot cover in Figure 1. This is a cross-sectional view taken along line IV-IV in Figure 3. This is an enlarged view of section V in Figure 4. This figure illustrates the operation of the steering device in Figure 1.

[0008] The embodiments will be described below with reference to the drawings. <Configuration of the steering device> As shown in Figure 1, the steering device 1 comprises a steering mechanism 4 and an assist mechanism 5. The steering device 1 is mounted on the vehicle. The steering mechanism 4 steers the vehicle's steering wheels 3 based on the driver's operation of the steering wheel 2. The assist mechanism 5 provides the steering mechanism 4 with an assist force to assist in steering operations.

[0009] The steering mechanism 4 comprises a steering shaft 11, a steering shaft 12, and a rack housing 13. The steering shaft 11 is connected to the steering wheel 2. The steering shaft 12 reciprocates axially in accordance with the rotation of the steering shaft 11. The rack housing 13 is a housing through which the steering shaft 12 is inserted so as to be able to reciprocate.

[0010] The steering shaft 11 comprises a column shaft 15, an intermediate shaft 16, and a pinion shaft 17. The upper end of the column shaft 15 is connected to the steering wheel 2. The lower end of the column shaft 15 is connected to the upper end of the intermediate shaft 16. The lower end of the intermediate shaft 16 is connected to the upper end of the pinion shaft 17.

[0011] The rack housing 13 houses the steering shaft 12 and the pinion shaft 17. The rack housing 13 is made of a metal material such as an aluminum alloy. The steering shaft 12 and the pinion shaft 17 are arranged within the rack housing 13 at a predetermined intersection angle. The rack and pinion mechanism 14 is constructed by the meshing of rack teeth 12a formed on the steering shaft 12 and pinion teeth 17a formed on the pinion shaft 17. Both ends of the steering shaft 12 protrude from the open ends 26, which are the axial ends of the rack housing 13. The open ends 26 are stepped cylindrical. A joint 22 is provided at each end of the steering shaft 12. The joint 22 comprises a socket 23 and a ball shaft 24. The socket 23 is fixed to the end of the steering shaft 12. The first end of the ball shaft 24 is tiltably connected to the steering shaft 12 with the socket 23 as a pivot point. The second end of the ball shaft 24 is connected to the first end of the tie rod 30. The second end of the tie rod 30 is connected to a knuckle (not shown) to which the steering wheel 3 is assembled. Therefore, in the steering device 1, the rotation of the steering shaft 11 due to steering operation is converted into axial movement of the steering shaft 12 by the rack and pinion mechanism 14. This axial movement is transmitted to the knuckle via the joint 22 and the tie rod 30, thereby changing the steering angle of the steering wheel 3, i.e., the direction of travel of the vehicle. In this embodiment, the steering shaft 12 and the joint 22 are examples of movable parts. The rack housing 13 is an example of a fixed part.

[0012] The assist mechanism 5 comprises a motor 31, which is a drive source, a transmission mechanism 32, and a conversion mechanism 33. The transmission mechanism 32 transmits the rotation of the motor 31. The conversion mechanism 33 converts the rotation transmitted via the transmission mechanism 32 into reciprocating motion of the steering shaft 12. The assist mechanism 5 transmits the rotation of the motor 31 to the conversion mechanism 33 via the transmission mechanism 32, and the conversion mechanism 33 converts it into reciprocating motion of the steering shaft 12, thereby providing an assist force to the steering mechanism 4. The motor 31 is, for example, a three-phase brushless motor. The transmission mechanism 32 is, for example, a belt reduction mechanism. The conversion mechanism 33 is, for example, a ball screw mechanism.

[0013] Next, the structure of the rack housing 13 and the ball shaft 24 will be described in detail. Since the structure around the open end 26 of the rack housing 13 is identical, the following description will focus on the structure around the left open end 26 in Figure 1. In the following description, the side approaching the rack housing 13, which is an example of a fixed part, will be referred to as the first direction, and the side approaching the steering shaft 12 and joint 22, which are examples of movable parts, will be referred to as the second direction. The first axial direction X1 coincides with the direction along the first axis, which is the axis of the rack housing 13, i.e., the first axis L1, which is the axis of the steering shaft 12.

[0014] As shown in Figure 2, the open end 26 has a mounting portion 41 and a cylindrical portion 42. The cylindrical portion 42 extends from the rack housing 13 toward the tie rod 30 in the second direction. The mounting portion 41 is an annular portion that further extends from the cylindrical portion 42 toward the tie rod 30 in the second direction. The mounting portion 41 has an axial end face 21a perpendicular to the first axial direction X1. A first mounting groove 41a is formed on the outer circumference of the mounting portion 41. The first mounting groove 41a is annular and extends continuously around the entire circumference of the outer surface of the mounting portion 41.

[0015] The ball shaft 24 has an axial portion 24a and a spherical portion 24b at one end of the axial portion 24a on the first direction side. The axial portion 24a extends along the first axial direction X1. The spherical portion 24b fits into the inner circumference of the socket 23. The ball shaft 24 is tiltable with respect to the steering shaft 12, i.e., the first axial direction X1, with the spherical portion 24b, i.e., the socket 23, as a pivot point. In the operating state where the steering wheel 3 of the vehicle equipped with the steering device 1 is in contact with the road surface, the ball shaft 24 extends toward the second direction in a state inclined diagonally downward with respect to the steering shaft 12. A second mounting groove 24c is formed on the outer circumference of the axial portion 24a. The second mounting groove 24c is annular and extends continuously around the entire circumference of the outer surface of the axial portion 24a. A third mounting groove 24d is formed on the outer circumference of the axial portion 24a of the ball shaft 24. The third mounting groove 24d is annular and extends continuously around the entire circumference of the outer surface of the shaft portion 24a. The third mounting groove 24d is located on the second direction side relative to the second mounting groove 24c in the first axial direction X1. The outer diameter of the third mounting groove 24d is smaller than the outer diameter of the second mounting groove 24c.

[0016] A boot 27 is provided at each of the open ends 26 of the rack housing 13. The first-direction end of the boot 27 is fixed to the open end 26 of the rack housing 13. The second-direction end of the boot 27 is fixed to the ball shaft 24 of the joint 22. The boot 27 protects the portion of the steering shaft 12 that is exposed from the rack housing 13, including the portion to which the socket 23 is fixed, and a portion of the joint 22, including the portion to which the socket 23 and the ball shaft 24 are connected, from foreign matter such as dust and rainwater. A boot cover 60 is provided on the outer circumference of each boot 27. The boot cover 60 covers a portion of the outer circumference of the boot 27 with a gap between it and the boot 27. The first-direction end of the boot cover 60 is an open end 60a that opens toward the rack housing 13. The second-direction end of the boot cover 60 is a fixed end 60b that is fixed to the ball shaft 24 of the joint 22. The boot cover 60 protects a portion of the boot 27 from contact with foreign objects such as ice and mud or with vehicle parts. Details of the boot 27 and boot cover 60 will be described later.

[0017] <About the Boot> As shown in Figure 2, the boot 27 is cylindrical and made of a resin material. The resin material is, for example, thermoplastic elastomer (TPE). The boot 27 is manufactured, for example, by injection molding using a mold. The boot 27 has a flexible portion 52, a small diameter end 53, and a large diameter end 54.

[0018] The annular small-diameter end 53 is fitted into the second mounting groove 24c of the shaft-shaped portion 24a. The inner diameter of the small-diameter end 53 is approximately the same as the outer diameter of the second mounting groove 24c. The annular large-diameter end 54 is fitted into the first mounting groove 41a of the mounting portion 41. The inner diameter of the large-diameter end 54 is approximately the same as the outer diameter of the first mounting groove 41a. In other words, the inner diameter of the large-diameter end 54 is larger than the inner diameter of the small-diameter end 53. The flexible portion 52 is a cylindrical part that connects the small-diameter end 53 and the large-diameter end 54, and is formed in a bellows shape. The flexible portion 52 is expandable and contractible in the first axial direction X1. In the boot 27, the portion from the small-diameter end 53 to near the middle portion is a tapered portion 52a that expands in diameter toward the large-diameter end 54. The tapered portion 52a exists in the range from the second mounting groove 24c of the ball shaft 24 to the position corresponding to the spherical portion 24b. In the boot 27, the portion between the tapered portion 52a and the large-diameter end portion 54 maintains the same diameter along the first axial direction X1.

[0019] The boot 27 is fixed to the ball shaft 24 via its shaft portion 24a by the small diameter end 53 being tightened from the outside by a first band member 55. The boot 27 is fixed to the open end 26 via its mounting portion 41 by the large diameter end 54 being tightened from the outside by a second band member 56. With the small diameter end 53 fixed to the ball shaft 24 and the large diameter end 54 fixed to the open end 26, the boot 27 can deform to conform to the tilting state of the ball shaft 24 relative to the steering shaft 12 by the bending deformation of the flexible portion 52.

[0020] <About the structure of the boot cover> Next, the structure of the boot cover 60 will be explained. The second axial direction X2 coincides with the direction along the second axis L2 of the boot cover 60. The second circumferential direction R2 coincides with the direction around the second axis L2.

[0021] As shown in Figures 3-5, the boot cover 60 is a tubular body with a frustoconical shape. The boot cover 60 is made of a resin material. The resin material of the boot cover 60 is, for example, a thermoplastic elastomer (TPE), which is the same type of resin material as the boot 27. In this case, the hardness of the boot cover 60 and the hardness of the boot 27 are the same. The boot cover 60 is manufactured, for example, by injection molding using a mold.

[0022] The boot cover 60 has a first cylindrical portion 61, a second cylindrical portion 62, and a connecting portion 63. The inner diameter of the second cylindrical portion 62 is smaller than the inner diameter of the first cylindrical portion 61. The connecting portion 63 connects the first cylindrical portion 61 and the second cylindrical portion 62.

[0023] More specifically, the end of the first cylindrical portion 61 is the open end 60a of the boot cover 60. The inner diameter of the first cylindrical portion 61 decreases from the open end 60a toward the connecting portion 63 adjacent to the first connecting end 61c on the opposite side of the open end 60a. In other words, the inner diameter of the open end 60a is the largest in the boot cover 60. The first cylindrical portion 61 has a gradient C with respect to the second axis L2. The gradient C is the draft angle when using a mold in the manufacture of the boot cover 60. The first cylindrical portion 61 has a plurality of slits 61b. The number of slits 61b is, for example, 12. The slits 61b open at the open end 60a and extend in a straight line from the open end 60a toward the connecting portion 63. The ends of the slits 61b do not reach the connecting portion 63. The width of the slits 61b in the second circumferential direction R2, i.e., the slit width D, decreases from the open end 60a toward the connecting portion 63. In other words, as shown in Figure 5, the slit width D1 at the open end 60a of the slit 61b is larger than the slit width D2 at the end of the slit 61b. Therefore, the circumferential length of the portion of the first cylindrical portion 61 between two adjacent slits 61b decreases as it approaches the open end 60a. Also, the wall thickness of the first cylindrical portion 61 is smaller than the wall thickness of the second cylindrical portion 62 and the connecting portion 63.

[0024] The end of the second cylindrical portion 62 is the fixed end 60b of the boot cover 60. The inner diameter of the second cylindrical portion 62 is the same from the fixed end 60b toward the connecting portion 63 adjacent to the second connecting end 62c on the opposite side of the fixed end 60b. The inner diameter of the second cylindrical portion 62 is approximately the same size as the outer diameter of the axial portion 24a of the joint 22. A boot cover locking portion 62b is formed on the inner circumference of the second cylindrical portion 62. The boot cover locking portion 62b protrudes radially inward from the inner circumferential surface of the second cylindrical portion 62. The boot cover locking portion 62b is annular and extends continuously around the entire circumference of the inner circumferential surface of the second cylindrical portion 62.

[0025] The connecting portion 63 has a first enlarged diameter portion 63a, an intermediate portion 63b, a second enlarged diameter portion 63c, and a connecting portion 63d. The inner diameter of the first enlarged diameter portion 63a decreases from the first end of the first enlarged diameter portion 63a connected to the first cylindrical portion 61 toward the second cylindrical portion 62. The inner diameter of the intermediate portion 63b is constant. The inner diameter of the second enlarged diameter portion 63c increases from the first end of the second enlarged diameter portion 63c connected to the second cylindrical portion 62 toward the first cylindrical portion 61. The connecting portion 63d is the portion to which the first enlarged diameter portion 63a and the intermediate portion 63b are connected.

[0026] The boot cover 60 has a hollow frustoconical shape in which the inner diameter of the second cylindrical portion 62 is smaller than the inner diameter of the first cylindrical portion 61, and the open end 60a and the fixed end 60b are open in the second axial direction X2.

[0027] The connecting portion 63 has a plurality of ribs 64 and a plurality of through holes 65. The number of ribs 64 is, for example, six. The number of through holes 65 is, for example, the same as the number of ribs 64, i.e., six. The ribs 64 are formed on the outer circumferential surface of the connecting portion 63. The ribs 64 are formed to span the first enlarged diameter portion 63a, the intermediate portion 63b, and the connecting portion 63d. The ribs 64 are rhombic in shape when viewed from the radial direction. The ribs 64 protrude radially outward from the outer circumferential surface of the connecting portion 63. The through holes 65 are formed in the first enlarged diameter portion 63a. The through holes 65 are circular in shape when viewed from the second axial direction X2. The through holes 65 connect the inside and outside of the first enlarged diameter portion 63a.

[0028] <Arrangement of slits, ribs, and through holes> As shown in Figure 3, the multiple slits 61b are arranged at equal angular intervals in the second circumferential direction R2. The multiple ribs 64 are arranged at equal angular intervals in the second circumferential direction R2. The multiple through holes 65 are arranged at equal angular intervals in the second circumferential direction R2. The multiple ribs 64 and the multiple through holes 65 are arranged alternately at equal angular intervals in the second circumferential direction R2. Each of the multiple slits 61b is located between adjacent ribs 64 and through holes 65.

[0029] For example, the six ribs 64 and the six through holes 65 are arranged at equal angular intervals in the second circumferential direction R2. The twelve slits 61b are arranged so that one slit 61b is located between adjacent ribs 64 and through holes 65 in the second circumferential direction R2. In other words, the boot cover 60 is arranged to have rotational symmetry in which the slits 61b, ribs 64, and through holes 65 appear regularly at 15-degree intervals in the second circumferential direction R2.

[0030] For example, as shown in Figure 3, when viewed from the second axial direction X2, the angle θ1 between the first imaginary line V1 passing through the second axis L2 and the vertex T of the rib 64, and the second imaginary line V2 passing through the second axis L2 and the center O of the through hole 65, is 30 degrees. The angle θ2 between the third imaginary line V3 passing through the second axis L2 and the center M of the width of the slit 61b, and the first imaginary line V1, is 15 degrees. Also, the angle θ3 between the third imaginary line V3 and the second imaginary line V2 is 15 degrees. In this way, the multiple slits 61b, multiple ribs 64, and multiple through holes 65 are arranged such that their positions in the second circumferential direction R2 are different from each other. In the above example, when viewed from the second axial direction X2, the slits 61b, ribs 64, and through holes 65 are arranged so as to have symmetry with respect to a 60-degree rotation.

[0031] Furthermore, in the above example, let the number of ribs 64 be "N1", the number of through holes 65 be "N2", and the number of slits 61b be "N3". However, "N1" and "N2" are equivalent and are divisors of 360. "N3" is determined such that "N3" = "N1" + "N2". As a result, the ribs 64 and through holes 65 are arranged alternately in the second circumferential direction R2 with a spacing of "360 / N3" degrees, which is obtained by dividing 360 by "N3". Also, the slits 61b are arranged in the second circumferential direction R2 with a spacing of "360 / N3" degrees, with one slit between each adjacent rib 64 and through hole 65. For example, if "N1" and "N2" are "6", then "N3" is "12". In this case, the ribs 64 and through holes 65 are arranged alternately at 30-degree intervals in the second circumferential direction R2. The slits 61b are arranged at 30-degree intervals so that one slit 61b is located between each adjacent rib 64 and through hole 65 in the second circumferential direction R2.

[0032] <About the mounting structure of the boot cover> Next, the mounting structure for attaching the boot cover 60 to the boot 27 will be described. As shown in Figure 2, the boot cover locking portion 62b of the second cylindrical portion 62 is fitted into the third mounting groove 24d of the axial portion 24a. The boot cover 60 is fixed to the ball shaft 24 via the axial portion 24a by the second cylindrical portion 62 being tightened from the outside by the third band member 70. When the second cylindrical portion 62 is fixed to the ball shaft 24, the boot cover 60 is open such that the open end 60a faces the opening end 26 which is on the first direction side. The open end 60a includes a portion that reaches the spherical portion 24b of the ball shaft 24 in the first axial direction X1 when the ball shaft 24 is tilted relative to the steering shaft 12. That is, when the ball shaft 24 is tilted relative to the steering shaft 12, the open end 60a overlaps with the flexible portion 52 of the boot 27 in the first axial direction X1. In other words, the open end 60a overlaps with the flexible portion 52 of the boot 27 in the second axial direction X2. As a result, the boot cover 60 extends to a range that includes the portion of the boot 27 from the small diameter end 53 to the tapered portion 52a. The open end 60a does not come into contact with the outer circumference of the boot 27 when the ball shaft 24 is tilted relative to the steering shaft 12.

[0033] In this embodiment, the fixing position of the boot cover 60 is on the second direction side of the fixing position of the boot 27. Therefore, for example, if the open end 60a reaches the first direction side with respect to the pivot point of the tilt, the open end 60a is more likely to come into contact with the flexible portion 52 of the boot 27 when the flexible portion 52 of the boot 27 expands and contracts. On the other hand, if the open end 60a does not reach the pivot point of the tilt, the function of the boot cover 60 in protecting the boot 27 is reduced. Therefore, the total length of the boot cover 60 in the second axial direction X2 of this embodiment is such that the open end 60a reaches the spherical portion 24b of the ball shaft 24, more specifically, it reaches the spherical portion 24b but does not extend beyond the spherical portion 24b in the first direction, and the open end 60a does not come into contact with the outer circumference of the boot 27. In this case, the gap between the inner surface of the boot cover 60 and the outer surface of the boot 27 is such that the boot cover 60 and the boot 27 do not come into contact with each other when the ball shaft 24 is tilted relative to the steering shaft 12.

[0034] <Operation and Effects of this Embodiment> The boot cover 60 is designed so that its open end 60a overlaps with the flexible portion 52 of the boot 27 in the second axial direction X2. That is, the open end 60a does not reach the large-diameter end 54, which is the fixed end that secures the boot 27 to the rack housing 13. Therefore, for example, when the flexible portion 52 of the boot 27 is compressed in the axial direction, the boot cover 60 will not interfere with the rack housing 13. As a result, the design of the boot cover 60 can be reused even if the specifications for the axial length of the boot 27 are different. Therefore, even if the specifications for the axial length of the boot 27 are different for each vehicle model on which the steering device 1 is installed, a common boot cover 60 can be used.

[0035] As described above, the embodiment provides the following additional benefits. (1-1) For example, as shown in Figure 6, when the steering shaft 12 and joint 22 move in the first direction along the first axial direction X1, the boot cover 60 moves in the first direction in conjunction with them to approach the rack housing 13. Also, if foreign matter 100 is present between the first cylindrical portion 61 of the boot cover 60 and the rack housing 13, the first cylindrical portion 61 of the boot cover 60 moving in the first direction toward the rack housing 13 may come into contact with the foreign matter 100. In this case, the foreign matter 100 acts as resistance when the boot cover 60 moves. If the boot cover 60 moves further toward the rack housing 13 from a state where the foreign matter 100 is in contact with the first cylindrical portion 61, the boot cover 60 may be pressed by the foreign matter 100 and the entire boot cover may be peeled off from the first cylindrical portion 61.

[0036] In view of this, the boot cover 60 of this embodiment has a plurality of slits 61b in the first cylindrical portion 61 that extend from the open end 60a toward the first connecting end 61c. In the above example, as shown in Figure 6, even if the boot cover 60 moves toward the rack housing 13 in the first direction and the first cylindrical portion 61 comes into contact with the foreign object 100, causing the foreign object 100 to act as resistance, the first cylindrical portion 61 having the slits 61b deforms radially outward. In this case, the effect of resistance due to contact with the foreign object 100 can be less likely to be transmitted to the connecting portion 63 and the second cylindrical portion 62. Therefore, for example, even if the boot cover 60 is peeled back by the foreign object 100, only a part of the first cylindrical portion 61 having the slits 61b will deform, and the connecting portion 63 and the second cylindrical portion 62 will not be easily peeled back. Thus, the boot cover 60 can be less likely to reduce its effect of protecting the boot 27.

[0037] (1-2) The inner diameter of the first cylindrical portion 61 decreases in the second axial direction X2 from the open end 60a towards the first connecting end 61c. In other words, the rigidity of the first cylindrical portion 61 when it deforms radially decreases as it approaches the open end 60a. As a result, the first cylindrical portion 61 is more easily deformed when foreign matter acts as resistance as it approaches the open end 60a. This is effective in promoting radial deformation of the first cylindrical portion 61 and in realizing a configuration that makes it difficult for the effects of this deformation to be transmitted to the connecting portion 63 and the second cylindrical portion 62.

[0038] (1-3) The slit width D of the slit 61b decreases in the second axial direction X2 from the open end 60a towards the first connecting end 61c. In other words, the circumferential length of the portion between the slits 61b decreases as you get closer to the open end 60a, so the rigidity of the first cylindrical portion 61 when it deforms radially decreases. As a result, the first cylindrical portion 61 is more easily deformed when foreign matter acts as resistance as it approaches the open end 60a. This is effective in promoting radial deformation of the first cylindrical portion 61 and in realizing a configuration that makes it difficult for the effects of this deformation to be transmitted to the connecting portion 63 and the second cylindrical portion 62.

[0039] (1-4) The wall thickness of the first cylindrical portion 61 is smaller than that of the connecting portion 63. As a result, the first cylindrical portion 61 is more easily deformed than the connecting portion 63 when foreign matter acts as resistance. This is effective in promoting radial deformation of the first cylindrical portion 61 and in achieving a configuration that makes it difficult for the effects of this deformation to be transmitted to the connecting portion 63 and the second cylindrical portion 62.

[0040] (1-5) The connecting portion 63 is reinforced by having multiple ribs 64. In other words, the connecting portion 63 is less likely to deform than the first cylindrical portion 61 when foreign matter acts as resistance. This is effective in preventing the connecting portion 63 from being peeled off, even if the first cylindrical portion 61 deforms due to foreign matter acting as resistance.

[0041] (1-6) The connecting portion 63 has multiple through holes 65, which allows for radial communication between the inside and outside. In other words, the connecting portion 63 can easily discharge foreign matter that has entered the gap between the boot cover 60 and the boot 27, i.e., the inner circumferential surface side of the boot cover 60, to the outside of the boot cover 60.

[0042] (1-7) The plurality of slits 61b, the plurality of ribs 64, and the plurality of through-holes 65 are arranged at different positions from each other in the second circumferential direction R2. This is effective in suppressing the increase in the overall length of the boot cover 60 as compared with, for example, the case where the plurality of slits 61b, the plurality of ribs 64, and the plurality of through-holes 65 of the boot cover 60 are arranged at overlapping positions in the second circumferential direction R2.

[0043] (1-8) The plurality of slits 61b, the plurality of ribs 64, and the plurality of through-holes 65 are arranged so as to have symmetry with respect to a 60-degree rotation around the second axis L2. Therefore, the heat dissipation path when the boot cover 60 exposed to heat dissipates the heat has symmetry. Thus, for example, even if the boot cover 60 is affected by heat, the heat can be evenly dispersed. This is particularly effective when the boot cover 60 is made of a resin material.

[0044] (1-9) The boot 27 and the boot cover 60 are made of the same type of resin material. Therefore, the hardness of the boot cover 60 is the same as the hardness of the boot 27. Thus, for example, even if the boot cover 60 contacts the boot 27, the damage to the boot 27 is reduced.

[0045] (1-10) The open end 60a of the boot cover 60 is configured not to contact the outer circumference of the boot 27 in the tilted state of the ball shaft 24 with respect to the steering shaft 12. Also, the gap between the inner circumferential surface of the boot cover 60 and the outer circumferential surface of the boot 27 has a size such that the boot cover 60 and the boot 27 do not contact each other in the tilted state of the ball shaft 24 with respect to the steering shaft 12. That is, the boot cover 60 does not contact the boot 27 in the tilted state of the ball shaft 24 with respect to the steering shaft 12. Therefore, the contact between the boot cover 60 and the boot 27 is suppressed in the usage state of the vehicle.

[0046] (1-11) For example, when the joint 22 is tiltable about the spherical portion 24b as a center fulcrum, when the open end 60a reaches the first direction side with respect to the fulcrum of the tilting, when the flexible portion 52 of the boot 27 expands and contracts, the open end 60a is likely to come into contact with the flexible portion 52. On the other hand, when the open end 60a does not reach the fulcrum of the tilting, the function of the boot cover 60 for protecting the boot 27 is reduced. In contrast, the open end 60a of the boot cover 60 of the present embodiment includes a portion that reaches the spherical portion 24b of the ball shaft 24 in the first axial direction X1 in the tilting state of the ball shaft 24 with respect to the steering shaft 12. Thus, the boot cover 60 of the present embodiment can achieve both damage prevention of the boot 27 and protection of the boot 27. Further, by designing the boot cover 60 based on the spherical portion 24b, it is possible to suitably suppress the boot cover 60 and the boot 27 from coming into contact with each other at the portion corresponding to the spherical portion 24b regardless of the specifications of the vehicle.

[0047] <Other Embodiments> The above embodiment may be modified as follows. Also, the following other embodiments can be combined with each other within a technically non - conflicting range.

[0048] - The method of applying the assist force in the steering device 1 is not limited to the method of applying the assist force to the steering shaft 12 via the transmission mechanism 32 and the conversion mechanism 33. For example, the method of applying the assist force may be a method of applying the assist force to the steering shaft 12 via a worm and wheel mechanism. Also, the method of applying the assist force is not limited to the method of applying the assist force to the steering shaft 12, and may be a method of applying the assist force to the column shaft 15 or an additional pinion shaft. Also, the steering device 1 may be configured not to include the assist mechanism 5.

[0049] - The steering device 1 may be a steer-by-wire type in which the power transmission path between the reaction force unit and the steering unit is mechanically separated at all times or can be separated. - The inner diameter of the first cylindrical portion 61 may be constant from the open end 60a toward the first connecting end 61c. That is, the first cylindrical portion 61 does not have to have a gradient C with respect to the second axis L2.

[0050] - The slit width D in the second circumferential direction R2 of the slit 61b may be constant from the open end 60a toward the first connecting end 61c. - Multiple slits 61b may extend all the way to just before the connecting portion 63, or some of the multiple slits 61b may reach the connecting portion 63.

[0051] - The wall thickness of the first cylindrical portion 61 may be the same as the wall thickness of the second cylindrical portion 62 and the connecting portion 63. Alternatively, the wall thickness of only the portion of the first cylindrical portion 61 from the open end 60a to the end of the slit 61b may be smaller than the wall thickness of the second cylindrical portion 62 and the connecting portion 63.

[0052] - It is not essential that the connecting portion 63 has ribs 64 and through holes 65. The connecting portion 63 may have either ribs 64 or through holes 65. - The number of slits 61b, ribs 64, and through holes 65 can be changed as appropriate.

[0053] - It is not essential that the slit 61b, rib 64, and through hole 65 are positioned at different locations in the second circumferential direction R2. Furthermore, it is not essential that the slit 61b, rib 64, and through hole 65 are positioned to have rotational symmetry when viewed from the second axial direction X2.

[0054] - It is not necessary for the resin material of the boot cover 60 and the resin material of the boot 27 to be of the same type. For example, the hardness of the resin material of the boot cover 60 may be less than or equal to the hardness of the resin material of the boot 27. By determining the resin materials of the boot cover 60 and the boot 27 to have such a hardness relationship, the same effects as those described above (1-9) can be achieved.

[0055] The overall length of the boot cover 60 can be changed as appropriate. For example, the overall length of the boot cover 60 in the first axial direction X1 may be shorter than the length at which the open end 60a reaches the spherical portion 24b of the ball shaft 24.

[0056] The first band member 55 and the second band member 56 may be integrally formed with the boot 27 by insert molding, vulcanization bonding, or the like. The third band member 70 may also be integrally formed with the boot cover 60 by insert molding, vulcanization bonding, or the like.

[0057] - Instead of the first band member 55, the second band member 56, and the third band member 70, adhesive may be used, for example, to fix the boot 27 and the boot cover 60. - The boot cover 60 of the above embodiment is not limited to the configuration applied to the steering device 1, but is applicable to boots configured to protect a part of a movable part that is exposed from a fixed part and is configured to be displaceable. For example, the movable part may be a piston rod housed in a cylinder which is a fixed part that constitutes a damper for a vehicle. A damper for a vehicle includes, for example, an air suspension. In this case, the boot is assumed to be a dust boot that protects the piston rod.

Claims

1. A boot cover that is attached to cover the outer circumference of a cylindrical boot having a flexible portion that is expandable and contractible in the axial direction, wherein the boot cover has: a first cylindrical portion having an open end through which the boot is inserted; a second cylindrical portion fixed near the end of the boot in the axial direction of the boot cover and having a smaller diameter than the first cylindrical portion; and a cylindrical connecting portion positioned between the first cylindrical portion and the second cylindrical portion in the axial direction of the boot cover and connecting the first cylindrical portion and the second cylindrical portion, wherein the open end overlaps with the flexible portion of the boot in the axial direction of the boot cover.

2. The boot cover according to claim 1, having a plurality of slits extending axially from the open end of the boot cover.

3. The boot cover according to claim 1, wherein the inner diameter of the first cylindrical portion decreases in the axial direction of the boot cover as it approaches the connecting portion.

4. The boot cover according to claim 2, wherein the width of the slit decreases in the axial direction of the boot cover as it approaches the connecting portion.

5. The boot cover according to claim 1, wherein the first cylindrical portion includes a portion with a smaller wall thickness compared to the connecting portion.

6. The boot cover according to claim 1, wherein the connecting portion has a rib extending in the axial direction of the boot cover.

7. The boot cover according to claim 1, wherein the connecting portion has a through hole.

8. The boot cover according to claim 2, wherein the connecting portion has a plurality of ribs and a plurality of through holes extending in the axial direction of the boot cover, and the plurality of slits, the plurality of ribs and the plurality of through holes are arranged at different positions from each other in the circumferential direction of the boot cover.

9. The boot cover according to claim 8, wherein the plurality of ribs and the plurality of through holes are alternately arranged at equal angular intervals in the circumferential direction of the boot cover, and the positions of the plurality of slits in the circumferential direction of the boot cover are between adjacent ribs and through holes in the circumferential direction of the boot cover, and are arranged at equal angular intervals in the circumferential direction of the boot cover.

10. The boot cover according to claim 1, wherein the boot is made of a resin material, the boot cover is made of a resin material, and the resin material of the boot cover is of the same type as the resin material of the boot.

11. A steering device comprising: a steering shaft; a joint connecting the steering shaft to the steering wheel of a vehicle and configured to be inclined with respect to the axial direction of the steering shaft; a housing that houses the steering shaft with a portion of the steering shaft and the joint exposed; a cylindrical boot having an axially expandable and contractible flexible portion that covers the steering shaft and the joint exposed from the housing; and a boot cover attached to cover the outer circumference of the boot, wherein the boot cover has an open end and a first cylindrical portion through which the boot is inserted; a second cylindrical portion fixed to the outer circumference of the joint in the axial direction of the boot cover and having a smaller diameter than the first cylindrical portion; and a cylindrical connecting portion positioned between the first cylindrical portion and the second cylindrical portion in the axial direction of the boot cover and connecting the first cylindrical portion and the second cylindrical portion, the open end overlapping the flexible portion of the boot in the axial direction of the boot cover.

12. The steering device according to claim 11, wherein the open end is positioned so that the boot cover does not come into contact with the boot when the joint is tilted.

13. The steering device according to claim 12, wherein the joint has a spherical portion and is configured to be inclined about the spherical portion, and the open end is positioned to overlap with the spherical portion in the axial direction of the steering shaft.

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