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1. WO2020158616 - BARRE DE CRÉMAILLÈRE

Document

Description

Title of Invention RACK BAR 0001  

Background Art

0002   0003  

Summary

0004   0005   0006   0007  

Brief Description of Drawings

0008  

Description of Embodiments

0009   0010   0011   0012   0013   0014   0015   0016   0017   0018   0019   0020   0021   0022   0023   0024   0025   0026   0027   0028   0029   0030   0031   0032   0033   0034   0035   0036   0037   0038   0039   0040   0041   0042   0043   0044   0045   0046   0047   0048  

Claims

1   2   3   4   5   6   7   8   9  

Drawings

1   2   3   4   5   6   7   8   9   10   11  

Description

Title of Invention : RACK BAR

Technical Filed

[0001]
The present invention relates to a rack bar.

Background Art

[0002]
As a rack bar used in a rack and pinion steering apparatus and the like, for example, a solid rack bar has been known in which a rack is formed on a solid shaft member. A so-called hollow rack bar has also been known in which a rack is formed on a hollow shaft member for weight reduction.
[0003]
In the steering apparatus, end portions of the rack bars on both axial sides are connected to knuckles that support wheels via tie rods, respectively. The end portion of the rack bar and the tie rod are connected to each other via a ball joint. The ball joint includes a ball stud including a ball and a socket including a spherical seat into which the ball is fitted, and the socket is fixed to the end portion of the rack bar. The socket is typically fixed to the end portion of the rack bar by screw fastening, and the end portion of the rack bar is formed with a female screw (see, for example, JP2006-160113A).

Summary

[0004]
The ball joint fixed to the end portion of the rack bar is relatively standardized. On the other hand, shaft members used for the hollow rack bar vary in inner diameter and outer diameter depending on, for example, specifications of the steering apparatus. Here, a screw diameter of the female screw formed at the end portion of the rack bar is limited by the inner diameter of the shaft member. Therefore, there may be a disadvantage that a standard ball joint cannot be attached.
[0005]
In the rack bar described in JP2006-160113A, a cylindrical core member is press-fitted into an end portion of a hollow rack shaft, and an inner periphery of the core member is formed with the female screw. In this case, it is possible to attach the ball joint when a screw diameter of a male screw of the standard ball joint is smaller than an inner diameter of the rack shaft such that a thickness of the core member sufficient to form the female screw can be secured. However, for example, when the screw diameter of the male screw of the standard ball joint is slightly smaller than the inner diameter of the rack shaft and the thickness of the core member is insufficient to form the female screw or when the thread diameter of the male screw of the standard ball joint is larger than an outer diameter of the rack shaft, the ball joint cannot be attached.
[0006]
Illustrative aspect of the present invention provides a rack bar excellent in versatility.
[0007]
According to an illustrative aspect of the present invention, a rack bar includes a hollow first shaft member including a first rack configured to engage with a first pinion, and a first screw member joined to a first axial end portion of the first shaft member. The first screw member includes an extension portion axially adjacent to the first axial end portion of the first shaft member. The extension portion of the first screw member includes a female screw.

Brief Description of Drawings

[0008]
[fig. 1] Fig. 1 is a cross-sectional view of an example of a steering apparatus according to an embodiment of the present invention.
[fig. 2] Fig. 2 is a cross-sectional view of a rack bar of the steering apparatus in Fig. 1.
[fig. 3] Fig. 3 is a cross-sectional view of a modification of the rack bar in Fig. 2.
[fig. 4] Fig. 4 is a cross-sectional view of another modification of the rack bar in Fig. 2.
[fig. 5] Fig. 5 is a cross-sectional view of another modification of the rack bar in Fig. 2.
[fig. 6] Fig. 6 is a schematic view illustrating a method of manufacturing the rack bar in Fig. 2.
[fig. 7] Fig. 7 is a schematic view illustrating the method of manufacturing the rack bar in Fig. 2.
[fig. 8] Fig. 8 is a schematic view illustrating the method of manufacturing the rack bar in Fig. 2.
[fig. 9] Fig. 9 is a schematic view illustrating the method of manufacturing the rack bar in Fig. 2.
[fig. 10] Fig. 10 is a cross-sectional view of another example of a rack bar according to the embodiment of the present invention.
[fig. 11] Fig. 11 is a cross-sectional view of a modification of the rack bar in Fig. 10.

Description of Embodiments

[0009]
Fig. 1 illustrates an example of a steering apparatus according to an embodiment of the present invention.
[0010]
The steering apparatus of a vehicle illustrated in Fig. 1 includes a pinion 1 connected to a steering shaft of the vehicle, and a rack bar 10 including a rack 11 configured to engage with the pinion 1.
[0011]
End portions of the rack bar 10 on both axial sides are connected to tie rods 4 via ball joints 3, respectively. The ball joint 3 includes a spherical ball 3a and a socket 3b configured to receive the ball 3a, and the socket 3b is fixed to the end portion of the rack bar 10.
[0012]
The pinion 1 and the rack bar 10 are housed in a casing 5, and a connecting portion between the rack bar 10 and the tie rod 4 which are connected via the ball joint 3 is covered with a bellows-shaped boot 6 extending over the casing 5 and the tie rod 4.
[0013]
Fig. 2 illustrates the rack bar 10.
[0014]
The rack bar 10 includes a hollow shaft member 12, and the rack 11 is formed on a part in circumferential direction of an outer periphery of the shaft member 12. The rack 11 may have a constant gear ratio (CGR) with a constant tooth pitch, or a variable gear ratio (VGR) with a varying tooth pitch. Teeth of the rack 11 may have a tooth width direction orthogonal to an axial direction of the shaft member 12, or may have a tooth width direction oblique to the axial direction of the shaft member 12.
[0015]
The rack bar 10 further includes a pair of screw members 13 joined to end portions 12a, 12b of the shaft member 12 on both axial sides, and the screw members 13 include extension portions 14 axially adjacent to the end portions 12a, 12b of the shaft member 12. The extension portions 14 form end portions of the rack bar 10. The extension portion 14 is formed with a female screw 15. The socket 3b (see Fig. 1) of the ball joint 3 is formed with a male screw, and is fixed to the end portion of the rack bar 10 by screwing the male screw of the socket 3b and the female screw 15 of the extension portion 14 to each other.
[0016]
In an example illustrated in Fig. 2, the screw member 13 is formed of a pipe material. An inner diameter φ1 of the screw member 13 is smaller than an inner diameter φ3 of the shaft member 12, and an outer diameter φ2 of the screw member 13 is larger than the inner diameter φ3 of the shaft member 12. Overlap margins are set on end faces of the screw member 13 and the shaft member 12. The screw members 13 are provided coaxially with the shaft member 12, and are joined to end surfaces of the end portions 12a, 12b of the shaft member 12. In this case, it can be said that the entire screw member 13 is the extension portion 14. The screw member 13 and the shaft member 12 are joined by, for example, welding or friction welding.
[0017]
An inner periphery of the screw member 13 is formed with the female screw 15, and a thread diameter of the female screw 15 is smaller than the inner diameter φ3 of the shaft member 12. Even when the inner diameter φ3 of the shaft member 12 is larger than a screw diameter of the male screw formed in the socket 3b of the standard ball joint 3, the female screw 15 that matches the male screw of the socket 3b can be formed on the inner periphery of the screw member 13. The inner diameter φ1 of the screw member 13 is appropriately set according to the screw diameter of the female screw 15 formed on the inner periphery of the screw member 13. The outer diameter φ2 of the screw member 13 is appropriately set in consideration of the overlap margins of the end surface necessary for securing a joint strength between the screw member 13 and the shaft member 12.
[0018]
Fig. 3 illustrates a modification of the screw member 13. In an example illustrated in Fig. 3, the inner diameter φ1 of the screw member 13 formed of the pipe material is larger than the inner diameter φ3 of the shaft member 12 and is smaller than an outer diameter φ4 of the shaft member 12. The overlap margins are set on the end faces of the screw member 13 and the shaft member 12. The screw members 13 are provided coaxially with the shaft member 12, and are joined to the end surfaces of the end portions 12a, 12b of the shaft member 12. The inner periphery of the screw member 13 is formed with the female screw 15, and the thread diameter of the female screw 15 is larger than the inner diameter φ3 of the shaft member 12. Even when the outer diameter φ4 of the shaft member 12 is larger than the screw diameter of the male screw formed in the socket 3b of the standard ball joint 3, but a difference thereof is slight (a thickness of the shaft member 12 is insufficient to form a female screw on the inner periphery of the shaft member 12), or even when the outer diameter φ4 of the shaft member 12 is smaller than the screw diameter of the male screw formed on the socket 3b, the female screw 15 that matches the male screw of the socket 3b can be formed on the inner periphery of the screw member 13.
[0019]
Accordingly, the screw diameter of the female screw 15 can be freely set by joining the screw member 13 to the end portions 12a, 12b of the hollow shaft member 12, providing the extension portions 14 axially adjacent to the end portions 12a, 12b, and forming the female screw 15 on the extension portion 14. Accordingly, versatility of the rack bar 10 can be improved.
[0020]
In the examples illustrated in Figs. 2 and 3, the screw member 13 is formed of the pipe material. However, as illustrated in Fig. 4, the screw member 13 may be formed of a bar material, in other words, the screw member 13 is at least partially solid. A cross-sectional shape of the bar material forming the screw member 13 is not particularly limited, and is, for example, a circular shape. When the screw members 13 are formed of the bar material, the screw members 13 may include fitting portions 17 configured to be fitted inside the end portions 12a, 12b of the shaft member 12 as illustrated in Fig. 4, or may include fitting portions 18 configured to be fitted outside the end portions 12a, 12b of the shaft member 12 as illustrated in Fig. 5. The joint strength between the screw member 13 and the shaft member 12 is increased by providing the fitting portion 17 or the fitting portion 18.
[0021]
The rack bar 10 is manufactured, for example, as follows. First, the rack 11 is formed on the shaft member 12, and the screw member 13 is joined to both axial end portions of the shaft member 12 on which the rack 11 is formed. Then, the female screw 15 is formed on the extension portion 14 of the screw member 13 joined to the shaft member 12. This will be described in order below.
[0022]
The shaft member 12 is a hollow shaft member formed of steel which is, for example, JIS-S45C. As illustrated in Fig. 6, the outer periphery of the circumferential part of the shaft member 12 is flattened by pressing to form a flattened portion 16 extending on the shaft member 12 in the axial direction. Thereafter, if necessary, a chemical conversion treatment is performed to form a phosphate film on an outer peripheral surface of the shaft member 12 including the flattened portion 16.
[0023]
Next, as illustrated in Fig. 7, a part of the shaft member 12 including the flattened portion 16 is held by a die 20. The die 20 includes an upper die 21 and a lower die 22. The upper die 21 and the lower die 22 are opened and closed by a mold clamping mechanism (not illustrated) to sandwich the shaft member 12 in an upper-lower direction and hold an outer periphery of the shaft member 12. A rack tooth forming die 23 is detachably attached to the upper die 21, and the rack tooth form 23 is fixed to abut on a substantially flat outer surface of the flattened portion 16. A forming surface 24 of the rack tooth forming die 23 abutting on the outer surface of the flattened portion 16 is provided with a plurality of tooth grooves configured to mold the rack 11.
[0024]
While the rack tooth forming die 23 abuts on the flattened portion 16, a mandrel 30 is inserted into the shaft member 12 through an opening on one end of the shaft member 12, and is press-fitted into the flattened portion 16 by a push rod 31. Then, the press-fitted mandrel 30 is pushed back by a push rod 32 inserted from an opening on the other end of the shaft member 12, and is discharged from the shaft member 12. In a process in which the mandrel 30 is reciprocated over an entire length of the flattened portion 16, a material of the flattened portion 16 is squeezed by the mandrel 30 to plastically flow toward the rack tooth forming die 23. As the mandrel 30 is gradually changed to a larger one and the press-fitting of the mandrel 30 is repeated, the material of the flattened portion 16 gradually enters into the tooth grooves of the forming surface 24 of the rack tooth forming die 23, and a shape of the forming surface 24 is transferred to the flattened portion 16. Accordingly, the rack 11 is formed on the flattened portion 16.
[0025]
If necessary, the shaft member 12 on which the rack 11 is formed is subjected to processing which is bending correction accompanying tooth molding, grinding of the outer peripheral surface, quenching to increase hardness of the rack 11, or the like. Heating during the quenching of the shaft member 12 can be performed by, for example, high frequency induction heating, but is not limited to the high frequency induction heating.
[0026]
Then, as illustrated in Fig. 8, the screw member 13 is joined to the end portions 12a, 12b of the shaft member 12 on both axial sides, and as illustrated in Fig. 9, the female screw 15 is formed on the extension portion 14 of the screw member 13. As described above, the shaft member 12 and the screw member 13 are joined by welding, friction welding, or the like. A material of the screw member 13 may be the same as or different from a material of the shaft member 12. Considering that hardness of the shaft member 12 is increased by quenching, the material of the screw member 13 may have higher hardness than that of the material of the shaft member 12.
[0027]
Fig. 10 illustrates another example of a rack bar according to the embodiment of the present invention.
[0028]
A rack bar 110 illustrated in Fig. 10 is used in a steering apparatus including an assist mechanism, and includes a first rack 111 configured to engage with a steering pinion connected to the steering shaft and a second rack 112 configured to engage with an auxiliary pinion of the assist mechanism.
[0029]
The steering pinion is rotated by rotation operation of a steering wheel, and the rack bar 110 that engages with the steering pinion by the first rack 111 is moved in the axial direction. A driving force of a motor of the assist mechanism controlled in accordance with a steering force of the steering wheel is transmitted to the rack bar 110 via the auxiliary pinion that engages with the second rack 112, and a movement of the rack bar 110 by the rotation operation of the steering wheel is assisted.
[0030]
The rack bar 110 includes a hollow first shaft member 113 and a solid second shaft member 114, and a second end portion 113a of the first shaft member 113 on one axial side and a first end portion 114a of the second shaft member 114 on one axial side are joined by, for example, welding or friction welding. The first rack 111 is formed on an outer periphery of a circumferential part of the first shaft member 113, and the second rack 112 is formed on an outer periphery of a circumferential part of the second shaft member 114. A rotation angle difference around a center axis of the rack bar 110 is appropriately set between the first rack 111 and the second rack 112 according to a positional relationship between the steering shaft and the assist mechanism.
[0031]
The first rack 111 is formed on the hollow first shaft member 113 in the same manner as the above-described rack 11 formed on the hollow shaft member 12 of the rack bar 10. The second rack 112 is formed on the solid second shaft member 114 by, for example, cutting. The first rack 111 is formed in advance on the first shaft member 113 before the first shaft member 113 and the second shaft member 114 are joined. On the other hand, the second rack 112 may be formed in advance on the second shaft member 114 before the first shaft member 113 and the second shaft member 114 are joined, or may be formed on the second shaft member 114 after the first shaft member 113 and the second shaft member 114 have been joined.
[0032]
The rack bar 110 further includes a screw member 115 joined to a first end portion 113b of the first shaft member 113, and the screw member 115 includes an extension portion 116 axially adjacent to the first end portion 113b of the first shaft member 113. The extension portion 116 forms an end portion of the rack bar 110 on one axial side, and is formed with a female screw 117. The female screw 117 is screwed to the male screw of the socket 3b (see Fig. 1) of the ball joint 3. Accordingly, the socket 3b is fixed to the end portion of the rack bar 110 on a first shaft member 113 side.
[0033]
The screw member 115 may be configured in a similar manner as the above-described screw member 13 of the rack bar 10. As illustrated in Fig. 10, the screw member 115 may be formed of the pipe material, or may be formed of the bar material. A screw diameter of the female screw 117 can be freely set by joining the screw member 115 to the first end portion 113b of the hollow first shaft member 113, providing the extension portion 116 axially adjacent to the first end portion 113b, and forming the female screw 117 on the extension portion 116. Accordingly, versatility of the rack bar 110 can be improved.
[0034]
On the other hand, an end portion of the rack bar 110 on a second shaft member 114 side is formed by a second end portion 114b of the solid second shaft member 114, and a female screw 118 is formed on the second end portion 114b of the second shaft member 114. The female screw 118 is also screwed to the male screw of the socket 3b (see Fig. 1) of the ball joint 3. Accordingly, the socket 3b is fixed to the end portion of the rack bar 110 on the second shaft member 114 side. When an outer diameter of the second shaft member 114 is smaller than the screw diameter of the male screw formed in the socket 3b of the standard ball joint 3, the outer diameter of the second end portion 114b of the second shaft member 114 may be increased by, for example, upsetting forging.
[0035]
A rack bar 210 illustrated in Fig. 11 includes a first shaft member 213 formed with a first rack 211 configured to engage with the steering pinion connected to the steering shaft, and a second shaft member 214 formed with a second rack 212 configured to engage with the auxiliary pinion of the assist mechanism. The first shaft member 213 and the second shaft member 214 are both hollow shaft members. A second end portion 213a of the first shaft member 213 on one axial side and a first end portion 214a of the second shaft member 214 on one axial side are joined by, for example, welding or friction welding.
[0036]
The first rack 211 is formed on the hollow first shaft member 213 in the same manner as the above-described rack 11 formed on the hollow shaft member 12 of the rack bar 10, and the second rack 212 is also formed on the hollow second shaft member 214 in the same manner as the above-described rack 11 formed on the hollow shaft member 12 of the rack bar 10. The first rack 211 and the second rack 212 are formed in advance on the first shaft member 213 and the second shaft member 214 before the first shaft member 213 and the second shaft member 214 are joined.
[0037]
The rack bar 210 further includes a pair of screw members 215 joined to a first end portion 213b of the first shaft member 213 and a second end portion 214b of the second shaft member 214, and the screw members 215 include extension portions 216 axially adjacent to the first end portion 213b of the first shaft member 213 and the second end portion 214b of the second shaft member 214. The extension portions 216 form end portions of the rack bar 210, and are formed with female screws 217. The female screw 217 is screwed to the male screw of the socket 3b (see Fig. 1) of the ball joint 3. Accordingly, the socket 3b is fixed to the end portion of the rack bar 210.
[0038]
The screw member 215 may be configured in a similar manner as the above-described screw member 13 of the rack bar 10. As illustrated in Fig. 11, the screw member 215 may be formed of the pipe material, or may be formed of the bar material. A screw diameter of the female screw 217 can be freely set by joining the screw members 215 to the first end portion 213b of the hollow first shaft member 213 and the second end portion 214b of the hollow second shaft member 214, providing the extension portions 216 axially adjacent to the first end portions 213b and the second end portion 214b, and forming the female screw 217 on the extension portion 216. Accordingly, versatility of the rack bar 210 can be improved.
[0039]
As described above, according to an illustrative aspect of the present invention, a rack bar includes a hollow first shaft member including a first rack configured to engage with a first pinion, a first screw member joined to a first axial end portion of the first shaft member. The first screw member includes an extension portion axially adjacent to the first axial end portion of the first shaft member. The extension portion of the first screw member includes a female screw.
[0040]
The first screw member may be joined to an end surface of the first axial end portion of the first shaft member.
[0041]
The first screw member may further include a fitting portion fitted inside or outside the first axial end portion of the first shaft member.
[0042]
The rack bar may further include a second screw member joined to a second axial end portion of the first shaft member. The second screw member may include an extension portion axially adjacent to the second axial end portion of the first shaft member. The extension portion of the second screw member may include a female screw.
[0043]
The second screw member may be joined to an end surface of the second axial end portion of the first shaft member.
[0044]
The second screw member may further include a fitting portion fitted inside or outside the second axial end portion of the first shaft member.
[0045]
The rack bar may further include a second shaft member joined to a second axial end portion of the first shaft member. The second shaft member may include a second rack configured to engage with a second pinion.
[0046]
The second shaft member may be solid. A first axial end portion of the second shaft member may be joined to the first shaft member. A second axial end portion of the second shaft member may include a female screw.
[0047]
The second shaft member may be hollow. A first axial end portion of the second shaft member may be joined to the first shaft member. The rack bar may further comprise a second screw member joined to a second axial end portion of the second shaft member. The second screw member may include an extension portion axially adjacent to the second axial end portion of the second shaft member. The extension portion of the second screw member may include a female screw.
[0048]
This application claims priority to Japanese Patent Application No. 2019-017145 filed on February 1, 2019, the entire content of which is incorporated herein by reference.

Claims

[Claim 1]
A rack bar comprising:
a hollow first shaft member including a first rack configured to engage with a first pinion; and
a first screw member joined to a first axial end portion of the first shaft member,
wherein the first screw member includes an extension portion axially adjacent to the first axial end portion of the first shaft member, and
wherein the extension portion of the first screw member includes a female screw.
[Claim 2]
The rack bar according to claim 1, wherein the first screw member is joined to an end surface of the first axial end portion of the first shaft member.
[Claim 3]
The rack bar according to claim 1 or 2, wherein the first screw member further includes a fitting portion fitted inside or outside the first axial end portion of the first shaft member.
[Claim 4]
The rack bar according to any one of claims 1 to 3, further comprises a second screw member joined to a second axial end portion of the first shaft member,
wherein the second screw member includes an extension portion axially adjacent to the second axial end portion of the first shaft member, and
wherein the extension portion of the second screw member includes a female screw.
[Claim 5]
The rack bar according to claim 4, wherein the second screw member is joined to an end surface of the second axial end portion of the first shaft member.
[Claim 6]
The rack bar according to claim 4 or 5, wherein the second screw member further includes a fitting portion fitted inside or outside the second axial end portion of the first shaft member.
[Claim 7]
The rack bar according to claim 1, further comprises a second shaft member joined to a second axial end portion of the first shaft member,
wherein the second shaft member includes a second rack configured to engage with a second pinion.
[Claim 8]
The rack bar according to claim 7, wherein the second shaft member is solid,
wherein a first axial end portion of the second shaft member is joined to the first shaft member, and
wherein a second axial end portion of the second shaft member includes a female screw.
[Claim 9]
The rack bar according to claim 7, wherein the second shaft member is hollow,
wherein a first axial end portion of the second shaft member is joined to the first shaft member,
wherein the rack bar further comprises a second screw member joined to a second axial end portion of the second shaft member,
wherein the second screw member includes an extension portion axially adjacent to the second axial end portion of the second shaft member, and
wherein the extension portion of the second screw member includes a female screw.

Drawings

[ Fig. 1]

[ Fig. 2]

[ Fig. 3]

[ Fig. 4]

[ Fig. 5]

[ Fig. 6]

[ Fig. 7]

[ Fig. 8]

[ Fig. 9]

[ Fig. 10]

[ Fig. 11]