阅读说明：本技术 能实现淘汰用于扭杆的过程的设计改变 (Design change enabling elimination of process for torsion bar ) 是由 E·D·帕托克 A·J·阿米塔奇 于 2015-11-26 设计创作，主要内容包括：本申请涉及能实现淘汰用于扭杆的过程的设计改变。本发明的一方面在于提供了扭杆组件。所述组件包括具有第一钻孔的第一轴、具有第二钻孔的第二轴,以及放置在所述第一和第二钻孔之内的扭杆,所述第二轴操作地联接到所述第一轴。所述扭杆包括具有第一直径的花键第一端部,具有第二直径的花键第二端部,以及在所述花键第一端部和所述花键第二端部之间延伸的有效直径。所述第一端部延伸至具有与所述第一直径大体上相同的直径的第一端部面,所述第二端部延伸至具有与所述第二直径大体上相同的直径的第二端部面。所述扭杆是由具有大于C分度表示的洛氏硬度45的硬度的材料制造的。(The present application relates to design changes that enable elimination of processes for torsion bars. One aspect of the present invention is to provide a torsion bar assembly. The assembly includes a first shaft having a first bore, a second shaft having a second bore, and a torsion bar positioned within the first and second bores, the second shaft operatively coupled to the first shaft. The torsion bar includes a splined first end portion having a first diameter, a splined second end portion having a second diameter, and an effective diameter extending between the splined first end portion and the splined second end portion. The first end extends to a first end face having a diameter substantially the same as the first diameter, and the second end extends to a second end face having a diameter substantially the same as the second diameter. The torsion bar is made of a material having a hardness greater than rockwell hardness 45 expressed by C-scale.)

1. A method of manufacturing a torsion bar having a first end portion and a second end portion, the method comprising:

performing a shearing operation on the torsion bar;

performing a hobbing operation on the first and second ends to form a splined first end and a splined second end, the first splined end having a minor diameter that is less than an effective diameter extending between the splined first end and the splined second end;

a hardening process is performed on the torsion bar, which hardens the torsion bar to a hardness between rockwell hardnesses 48 and 55, expressed in C-scale.

2. The method of claim 1, wherein no peening process is performed on the torsion bar.

3. The method of claim 1, wherein no contour grinding process is performed on the torsion bar.

4. The method of claim 1, further comprising performing a washing and oiling process on the torsion bar after the hardening process.

5. The method of claim 1, further comprising performing a centerless grinding process on the torsion bar prior to the hardening process.

6. The method of claim 5, wherein the centerless grinding process includes feeding the torsion bar through a grinding machine.

7. The method of claim 1, further comprising performing a washing process on the torsion bar prior to the hardening process.

8. The method of claim 7, wherein the washing process comprises flooding the torsion bar with a lubricant.

9. The method of claim 1, wherein the hardening process includes placing the torsion bar in a furnace heated to about 1500 ° F and then quenching the torsion bar.

10. The method of claim 1, wherein the spline first end includes a first major diameter extending to a first end face and the spline second end includes a second major diameter extending to a second end face.

Technical Field

The present invention relates to a torsion bar, and more particularly, to a torsion bar for a power steering assembly. The scheme is a divisional application, the application number of a parent application is 201510835688.X, the application date is 2015, 11 and 26, and the invention is named as 'design change capable of realizing the process of eliminating torsion bars'.

Background

The power steering assembly of a vehicle may include a power assist device that assists the vehicle operator in turning the steering wheel. In order to achieve the power steering function, it may be necessary to provide a torsion bar. However, the process required to manufacture the torsion bar to a specified grade can be expensive and time consuming, especially if it includes a profile grinding cycle process. In addition, it has historically been thought that torsion bars need to be made of relatively soft materials, with little or no hardening of the material, as the assembly process typically involves drilling and reaming which shortens the life of the tool. Thus, the torsion bar is not hardened to improve tool life. The second function of the torsion bar is to regain the original neutral position of the steering wheel after it has been turned and to release torque thereafter, which is commonly referred to as hysteresis. This results in a long torsion bar which requires multiple processing steps in the manufacturing process. It is therefore desirable to provide a torsion bar having a shorter length, lower hysteresis, and which undergoes fewer manufacturing processes.

Disclosure of Invention

These and other advantages and features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.

One aspect of the present invention is to provide a torsion bar for a steering column assembly. The torsion bar includes a splined first end portion having a first diameter, a splined second end portion having a second diameter, and an effective diameter extending between the splined first end portion and the splined second end portion. The first end extends to a first end face having a diameter substantially the same as the first diameter, and the second end extends to a second end face having a diameter substantially the same as the second diameter.

Another aspect of the present invention is to provide a torsion bar assembly for a steering column assembly. The torsion bar assembly includes a first shaft having a first bore, a second shaft having a second bore, the second shaft operatively coupled to the first shaft, and a torsion bar disposed within the first and second bores. The torsion bar includes a splined first end portion having a first diameter, a splined second end portion having a second diameter, and an effective diameter extending between the splined first end portion and the splined second end portion. The first end extends to a first end face having a diameter substantially the same as the first diameter, and the second end extends to a second end face having a diameter substantially the same as the second diameter.

It is a further aspect of the present invention to provide a method of manufacturing a torsion bar having a first end portion and a second end portion. The method includes performing a shearing operation on the torsion bar, performing a hobbing operation on the first and second end portions, and performing a hardening process on the torsion bar that hardens the torsion bar to a rockwell hardness, expressed in C-scale, of between 48 and 55.

Drawings

The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic illustration of a comparison of a prior art torsion bar and an exemplary torsion bar according to the present invention;

FIG. 2 is a cross-sectional view of a comparison of a prior art torsion bar assembly and an exemplary torsion bar assembly in accordance with the present invention;

FIG. 3 is a cross-sectional view of a comparison of the shaft of the prior art assembly shown in FIG. 2 and the shaft of the exemplary assembly shown in FIG. 2;

FIG. 4 is a schematic illustration of an exemplary manufacturing process according to the present invention;

FIG. 5 is a chart of a design improvement of one of the exemplary torsion bars shown in FIG. 1;

FIG. 6 is an enlarged side view of a portion of one of the exemplary torsion bars shown in FIG. 1; and

FIG. 7 is a chart of a design improvement of one of the exemplary torsion bars shown in FIG. 1.

Detailed Description

Described herein are systems and methods for manufacturing reduced length torsion bars with lower hysteresis and fewer processing steps than previously known torsion bars. For example, the torsion bars described herein undergo more hardening that facilitates production of shorter torsion bars but which do not require processing steps such as water washing, contour grinding, or shot peening.

Reference will now be made to the accompanying drawings, in which the invention will be described with reference to specific embodiments, but the invention is not limited thereto. Fig. 1 illustrates a prior art torsion bar 10 for a steering column assembly, an exemplary torsion bar 100 for a steering column assembly according to the present invention, and another exemplary torsion bar 200 for a steering column assembly according to the present invention. FIG. 2 illustrates a prior art torsion bar assembly 12, an exemplary torsion bar assembly 102 according to the present invention, and another exemplary torsion bar assembly 202 according to the present invention.

As shown in fig. 1, a prior art torsion bar 10 includes a bullet 14, a press ramp 16, a splined major diameter 18, a blend 20, and an effective diameter 22. As shown in fig. 2 and 3, torsion bar assembly 12 includes a first shaft 24, a second shaft 26, and a prior art torsion bar 10. The second shaft 26 includes a clearance bore 28 drilled to maintain clearance from the effective diameter 22, a press bore 30 to engage the splined major diameter 18, and a pre-drilled bore 32.

Referring to fig. 1-3, torsion bar 10 is pressed into bore 28 and includes bullet 14 to seat on bit point cone 34 of bore 28. Historically, the pressure load in a pressing operation was kept as low as possible. Typically, the press interference and therefore the tolerances of the spline and the press bore diameter are kept small. The close tolerances necessitate a reaming operation which creates a bore 30 in the shafts 24, 26 and a grinding operation on the ends of the splines 18 of the torsion bar 10. A pre-drilling operation is performed to remove most of the material before reaming can take place, as precise reaming depends on only slight material removal. Thus, after drilling bore 28, a pre-drilling operation is required to establish bore 32 from bit 30 to the end location of clearance bore 28. The reamer is then used to create the swage hole 36 and produce tighter tolerances. However, due to variations in bit size, reamer size and actual location of the borehole, the shoulder 38 (fig. 3) established by the reamer is not large enough to act as a final stop for the axial pressing operation of torsion bar 10. This may result in the following situation: the torsion bar 10 has large variations in its bottom load and axial compression position. To alleviate the shoulder 38 problem that may occur, a bullet 14 is added to prior art torsion bar 10 to produce a certain measurable bottom load change by contacting the bit 30. However, the bullet 14 increases the length of the torsion bar 10, which requires the bore 28 to have an additional bore depth.

The addition of the pressure ramp 16 to the prior art torsion bar 10 not only minimizes pressure loading but also reduces seizure events. The effective diameter 22 has historically been designed at the upper limit of allowable torsional stress required for fatigue life and hysteresis. Large diameter feature 18 provides sufficient material to transmit torque from torsion bar 10 to mating shafts 24, 26 by increasing to a diameter larger than effective diameter 22. Without this additional material, the combination of torsional stresses and stresses from the interface between torsion bar 10 and shafts 24, 26 would reduce fatigue life and add hysteresis.

A blend 20 is added to the torsion bar 10 to prevent stress concentrations from being added as the diameter increases from the effective diameter 22 to the major diameter 18. Due to the tight tolerances required for the effective diameter 22 or twist rate and at the interface major diameter 18, a contour grinding process is used in the manufacture of the torsion bar 10 to reduce press interference. Warhead 14, press bevel 16, and blend 20 are additionally created during the contour grinding process to reduce the number of machining steps. However, the contour grinding process can be time consuming and expensive. In addition, the long torsion bar 10 requires more material, which may be costly, and the shafts 24 and/or 26 may require time consuming and more costly drilling, reaming and/or securing steps to be configured to the longer torsion bar.

As shown in fig. 1 and 2, the torsion bar 100 is a cylindrical torsion bar having a circular cross-section, said torsion bar 100 comprising a splined first end portion 108, a splined second end portion 110, a major diameter 118, a blend portion 120, and an effective diameter 122. The splined first end 108 extends to a first end face 109, and the first end face 109 has a diameter substantially the same as the diameter of the splined first end 108. As used herein, the term "substantially the same" means the same diameter or a difference in diameter that occurs naturally or is only expediently formed to facilitate assembly, as will be described further herein. The splined second end 110 extends to a second end face 111, and the second end face 111 has a diameter substantially the same as the diameter of the splined second end 110. The effective diameter 122 has a diameter that is less than the major diameter 118 of the splined first and second ends 108, 110.

The length "L1" of torsion bar 100 is less than the length "L" of prior art torsion bar 10. For example, in one embodiment, length "L" is about 126mm and length "L1" is between 90mm and 110mm or between about 90mm and about 110 mm. In another embodiment, "L1" is between 95mm and 105mm or between about 95mm and about 105 mm. In yet another embodiment, "L1" is between 100mm and 104mm or between about 100mm and about 104 mm.

As shown in FIG. 2, the torsion bar assembly 102 includes a first shaft 124, a second shaft 126, and a bore 128. However, the depth "D1" of the bore 128 is less than the depth "D" of the prior art bore 28 (fig. 3), and the bore 128 does not include the enlarged hole 30 or the shoulder 38. Thus, torsion bar 100 requires less material and shorter drilling time for drilling holes 128 than prior art torsion bar 10. In one embodiment, the depth "D1" is 20mm to 30mm shorter or about 20mm to about 30mm shorter than the depth "D". In another embodiment, the depth "D1" is about 25mm to 27mm shorter than the depth "D" or about 25mm to 27mm shorter than the depth "D".

In an exemplary embodiment, torsion bar 100 is subjected to a hardening step to increase the stiffness of torsion bar 100, such that said torsion bar 100 is stiffer than prior art torsion bar 10. This allows the torsion bar 100 to be manufactured with a length "L1" that is shorter than the prior art length "L" and reduces hysteresis (e.g., by about 50%). Although the prior art torsion bar 10 may be subjected to a slight hardening process, this is only to reduce seizure during the pressing operation, and the upper limit to which the bar 10 is hardened is only rockwell hardness 40, expressed in C-scale. Thus, prior art torsion bar 10 is still considered a "soft" torsion bar.

In contrast, the torsion bar 100 is subjected to a hardening process and hardened to be higher than or equal to rockwell hardness 45 expressed in C-scale. In one embodiment, the torsion bar 100 is hardened to a hardness between rockwell hardnesses 48 and 55 on the C scale or between about 48 and about 55 on the C scale. Torsion bar 100 has a higher stiffness than torsion bar 10, which can have a reduced length "L1" while providing reduced hysteresis. In addition, the increased stiffness allows for more press interference, which allows for more dimensional tolerance to be given to both the press bore 128 and the major diameter of the spline.

Due to the increased stiffness of the torsion bar 100, it does not have to undergo a shot peening process as in the prior art torsion bar 10. The peening process is one process required for soft torsion bar 10 in order to increase the fatigue life of torsion bar 10. Thus, the torsion bar 100 does not require a peening step because the higher hardness significantly increases the yield point, and the reduction of the maximum twist angle reduces the stress. That is, torsional stress is a function of applied torque, diameter, and twist angle, and reducing the twist angle reduces the stress.

As previously described, the warhead 14 is included in the torsion bar 10 so as to reach near the shoulder 38 established at the interface between the pre-drilled hole and the counterboring feature. This is to ensure that the shank 10 is minimized to lie on the bit cone 34 so that the pressure versus displacement curve is easier to read and predict. However, for torsion bar 100, the elimination of the reaming operation allows for the elimination of the bullet, which increases the life of the grinding wheel (not shown) due to the fact that it is the deepest grinding portion of the shaft and further reduces costs.

Fig. 4 illustrates a manufacturing process 104 for a torsion bar 100 that includes a shearing step 140, a centerless grinding step 142, a hobbing step 144, a washing step 146, a hardening step 148, a washing step 150, a profile grinding step 152, and a washing and oiling step 154. The shearing step 140 may include cutting the torsion bar blank to the correct length, the centerless grinding step 142 may include feeding through a grinder, and the hobbing step 144 may include forming splines in the torsion bar 100. In a washing step 146, the torsion bar may be flooded and washed with lubricant, in a hardening step 148, the torsion bar 100 may be placed in an oven and heated (e.g., to about 1500 °) and then quenched, and in a washing step 150, the torsion bar 100 may be washed to remove quenching oil. In the wash and oil step 154, dirt (e.g., iron powder) may be washed off the torsion bar 100 and the torsion bar 100 is given a rust-inhibiting oil coating.

As shown, process 104 eliminates the peening process 156 as compared to prior art manufacturing processes due to the increased stiffness of the torsion bar 100, as previously described.

As shown in fig. 5, the design change or improvement of torsion bar 100 compared to prior art torsion bar 10 provides the following properties shown in graph 106. In an exemplary embodiment, (1) the elimination of the bullet 160 facilitates the elimination of the reaming operation 162; (2) the increased torsion bar stiffness 164 facilitates increasing the torsion bar yield stress 166, which facilitates eliminating the peening process 168, increasing the maximum allowable press interference 170 (along with increasing press load capacity 172), and decreasing the torsion bar length 174. The increased maximum allowable press interference 170 facilitates an increased spline outer diameter tolerance 176 and an increased press bore tolerance 178, the increased press bore tolerance 178 facilitates elimination of the reaming operation 162; (3) reduced maximum angle twist 184 reduces torsion bar torsional stress 186 and facilitates reducing torsion bar length 174; and (4) the reduced torsion bar length 174 facilitates reducing the bore depth 188 in the shafts 124, 126. Thus, as shown, design improvements 160, 164, 174, 178, and 184 facilitate manufacturing improvements 162, 168, 176, and 188.

As shown in fig. 1 and 2, the torsion bar 200 is a cylindrical torsion bar having a circular cross section, said torsion bar 200 comprising first and second splined end portions 208 and 210. The splined first end 208 extends to a first end face 209 and the first end face 109 has a diameter substantially the same as the diameter of the splined first end 208. As used herein, the term "substantially the same" means the same diameter or a difference in diameters that occurs naturally or is only expediently formed to facilitate assembly. The splined second end 210 extends to a second end face 211, and the second end face 211 has a diameter that is substantially the same as the diameter of the splined second end 210.

The length "L2" of torsion bar 200 is less than the length "L" of prior art torsion bar 10. For example, in one embodiment, the length "L" is about 126 mm; the length "L2" is between 90mm and 110mm or between about 90mm and about 110 mm. In another embodiment, length "L2" is between 95mm and 105mm or between about 95mm and about 105 mm. In yet another embodiment, length "L2" is between 100mm and 104mm or between about 100mm and about 104 mm.

As shown in FIG. 2, torsion bar assembly 202 includes a first shaft 224, a second shaft 226, and a bore 228. However, the depth "D2" of the bore 228 is less than the depth "D" of the prior art bore 28 (fig. 3), and the bore 228 does not include the enlarged hole 30 or the shoulder 38. Additionally, the torsion bar 200 does not require a bullet, a tapered surface, a large diameter, an intersection, or a profile grinding step. Thus, torsion bar 100 requires less material and shorter drilling time for drilling 228 than prior art torsion bar 10. In one embodiment, the depth "D2" is 20mm to 30mm shorter or about 20mm to about 30mm shorter than the depth "D". In another embodiment, the depth "D2" is about 25mm to 27mm shorter or about 25mm to 27mm shorter.

In an exemplary embodiment, the torsion bar 200 is subjected to a hardening step to increase the stiffness of the torsion bar 200, such that said torsion bar 200 is stiffer than the prior art torsion bar 10. This allows the torsion bar 20 to be manufactured with a length "L2" that is shorter than the prior art length "L" and reduces hysteresis (e.g., by about 50%). Although the prior art torsion bar 10 may be subjected to a slight hardening process, this is only to reduce seizure during the pressing operation, and the upper limit to which the bar 10 is hardened is only rockwell hardness 40, expressed in C-scale. Thus, prior art torsion bar 10 is still considered a "soft" torsion bar.

In contrast, the torsion bar 200 is subjected to a hardening process and hardened to greater than or equal to rockwell hardness 45 expressed in C-scale. In one embodiment, the torsion bar 200 is hardened to a hardness between rockwell hardnesses 48 and 55 on the C scale or between about 48 and about 55 on the C scale. Torsion bar 200 has a higher stiffness than torsion bar 10, which can have a reduced length "L2" while providing reduced hysteresis. In addition, the increased stiffness allows for more press interference, which allows for more dimensional tolerance to be given to both the press bore 228 and the major diameter of the spline.

Due to the increased stiffness of the torsion bar 200, it does not have to undergo a shot peening process as in the prior art torsion bar 10. The peening process is one process required in the soft torsion bar 10 for the drilling/reaming/pinning system, for example, to increase the fatigue life of the torsion bar 10. Thus, the torsion bar 200 does not require a peening step because its higher hardness significantly increases the yield point, and reducing the maximum twist angle reduces the stress.

As previously described, the warhead 14 is included in the torsion bar 10 so as to reach near the shoulder 38, the shoulder 38 being established at the interface between the pre-drilled hole and the counterboring feature. This is to ensure that the shank 10 bottoms out on the bit cone 34 so that the pressure versus displacement curve is easier to read and predict. However, the elimination of the reaming operation allows for the elimination of a bullet for torsion bar 200, which increases the life of the grinding wheel (not shown) and further reduces costs.

The large diameter 18 is included in the torsion bar 10 in order to provide sufficient material to transmit torque without twisting the torsion bar, which may result in reduced life and hysteresis. However, the level of hardness of the torsion bar 10 is limited because drilling holes in the hardened material reduces tool life and necessitates frequent replacement of the drill bit. In contrast, torsion bar 200 no longer requires the large diameter shape and eliminates the manufacturing process after the teeth are added.

Further, the pre-hobbing diameter of the splined ends 208, 210 is equal or substantially equal to the effective diameter 222 (FIG. 1). As such, after the hobbing process, the minimum diameter of the teeth is less than the diameter of the effective diameter 222.

In addition, torsion bar 200 has a smaller spline diameter and fewer teeth than prior art torsion bar 10 by reducing the maximum twist angle allowed in torsion bar 200. In order to achieve said reduction of the maximum torsion angle allowed in the torsion bar 200, a new torsion bar centering machine is provided which maintains better tolerances during the centering process. This reduction in centering then enables the maximum twist angle to be reduced.

In an exemplary embodiment, torsion bar 200 eliminates press ramps 16. However, as shown in fig. 6, since the end of the torsion bar 200 is unconstrained, a natural blend 234 occurs. Thus, during hobbing, the metal follows the path of least resistance resulting in axial growth at the outer edge 236 of the torsion bar 200. This results in an unfilled state in the mould, which can then be used as a lead-in ramp/merge for the pressing operation. It is noted that the natural blend 234 occurs naturally, however, a special process is used to form the press-slanted surface 16 and the blend 20 in the torsion bar 10.

Fig. 4 shows a manufacturing process 204 for a torsion bar 200 comprising a shearing step 240, a centerless grinding step 242, a hobbing step 244, a washing step 246, a hardening step 248, and a washing and oiling step 254. As shown, process 204 eliminates the washing step 250, the profile grinding step 252, and the peening process 256 as compared to prior art manufacturing processes, the elimination of peening process 256 being due to increased stiffness of the torsion bar 100, as discussed above.

As shown in fig. 7, the design change or improvement of torsion bar 200 compared to torsion bar 10 of the prior art provides the following properties shown in graph 206. In an exemplary embodiment, (1) the elimination of the bullet 260 facilitates the elimination of the reaming operation 262; (2) the increase in torsion bar hardness 264 facilitates increasing torsion bar yield stress 266, which facilitates eliminating the peening process 268, increasing the maximum allowable pressure interference 270 (while increasing the press load capacity 272), and decreasing the torsion bar length 274. The increased maximum allowable press interference 270 facilitates an increased spline outer diameter tolerance 276 and an increased press bore tolerance 278, the increased press bore tolerance 278 facilitates elimination of the reaming operation 262; (3) the reduced maximum angle twist 284 reduces the torsion bar torsional stress 286. The reduced torsional stress 286 facilitates reducing the torsion bar length 274 and eliminates the major diameter or any diameter (diameter greater than the effective diameter) shape 290, which eliminates the major diameter or any diameter (diameter greater than the effective diameter) shape 290 facilitates eliminating the profile grinding step 292. The increased spline outer diameter tolerance 276 also facilitates eliminating the profile grinding step 292; (4) the reduced torsion bar length 274 facilitates reducing the bore depth 288 in the shafts 124, 126; and (5) eliminating the profile grind 292 facilitates production of a pointed spline tip 294 that promotes side-to-side (non-radial) deformation 296 of the void-pressing material. The deformation of the hole-pressing material from side to side (non-radially) facilitates increasing the maximum allowable press interference 270. Thus, as shown, design improvements 260, 264, 274, 276, 278, 284, and 290 facilitate manufacturing improvements 262, 268, 288, and 292.

Described herein are systems and methods for improving the manufacture of torsion bars. By making design improvements in the manufacture of the torsion bar, a number of processes previously required can be reduced or eliminated. For example, the torsion bar may undergo a hardening process, which enables the torsion bar to be shorter than previous torsion bar designs. As such, the warhead, large diameter, and ramp that were once required for the torsion bar can now be eliminated. In addition, machining steps such as shot peening, reaming, contour grinding, and the like may be eliminated. Accordingly, the improved torsion bar described herein provides the same functionality as previous torsion bars, but with reduced cost and processing time.

While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description.