KR20240010071A - Drive shaft assay for automobile and its manufacturing method - Google Patents

Abstract

The present invention relates to a drive shaft assembly for an automobile and a method of manufacturing the same, and more specifically, to a shaft and an inner ring. The present invention may include a solid shaft and an inner ring formed integrally with the solid shaft, and the manufacturing method includes forming the inner ring by forging the solid shaft, processing the solid shaft and the inner ring, and processing the processed solid shaft and the inner ring at high frequency. It may include a heat treatment step. The present invention integrates the shaft and the inner ring, thereby reducing the outer diameter of the inner and outer rings, thereby reducing the weight of the drive shaft assembly by 10 to 20%. Additionally, parts manufacturing and management costs can be reduced by omitting spline machining and deleting circlips.

Description

Automotive drive shaft assembly and manufacturing method thereof {DRIVE SHAFT ASSAY FOR AUTOMOBILE AND ITS MANUFACTURING METHOD}

The present invention relates to a drive shaft assembly for an automobile and a method of manufacturing the same, and more specifically, to a shaft and an inner ring.

The drive shaft assembly for automobiles has the function of transmitting the driving force of the engine/transmission to the wheels at a constant speed. Figure 1 is a schematic diagram of a conventional automobile drive shaft assembly. Referring to FIG. 1, a conventional drive shaft assembly for an automobile includes a shaft 11, an inner ring 12, a circlip 13 for fastening and fixing the shaft 11 and the inner ring 12, and a plurality of balls 14. , It is composed of an outer ring 15, splines 16 formed on the outside of the shaft 11, and splines (not shown) formed on the inside of the inner ring 12.

Recently, research and development is underway to reduce the weight of vehicles to improve their fuel efficiency, and if the weight of directly driven parts such as drive shaft assemblies is reduced, the effect of improving fuel efficiency is further increased.

As part of this research and development, Patent Document 1 consists of a shaft made of a pipe material to integrate the inner ring. Typically, six balls are used in automotive driveshaft assemblies. As the number of balls used increases, the diameter of the balls decreases, which not only increases the transmission efficiency of driving force, but also makes the drive shaft assembly for automobiles lighter. However, in Patent Document 1, the number of balls that can be used is three, and there are restrictions on the shape of the inner ring and balls.

Patent Document 2 Additionally, the shaft is made of a pipe material to integrate the inner ring. Unlike Patent Document 1, the number of balls that can be used is 3 to 10. However, there is a limit to the height of the inner ring that can be formed depending on the pipe thickness. This is because the pipe is empty in the middle, which causes bending, etc., so it is technically difficult to form a section that is twice the thickness of one pipe. The thickness of commonly used pipes is 3 to 5 mm, and it is technically difficult to form a pipe section with a pipe thickness of 10 mm within the same pipe, so the height of the inner ring portion is limited to less than 5 mm. Additionally, when the ball diameter is large or the number of balls is large, there are limits to the design of the shaft and inner ring.

Japanese Patent Publication No. 2014-025486 Japanese Patent Publication No. 5410163

The purpose of the present invention is to manufacture a drive shaft assembly in which the shaft and the inner ring are integrated, but are not limited by the height or outer diameter of the inner ring.

In order to achieve the above object, the present invention may include a solid shaft and an inner ring formed integrally with the solid shaft.

Preferably, the outer diameter of the inner ring may be at most three times the outer diameter of the solid shaft.

Preferably, it may contain up to 14 balls.

Preferably, the inner ring may have a constant hardening depth.

Preferably, the solid shaft and inner ring contain 0.45 to 0.60 wt% of carbon (C), 0.2 to 0.6 wt% of chromium (Cr), 0.4 to 0.8 wt% of molybdenum (Mo), and 0.3 to 0.9 wt% of nickel (Ni). ), 0.01 to 0.05 wt% of boron (B), 0.15 to 0.35 wt% of silicon (Si), 0.6 to 0.9 wt% of manganese (Mn), and the remainder of iron (Fe).

Preferably, it may further include copper (Cu) in an amount greater than 0 and less than or equal to 0.3 wt%.

Preferably, it may further include more than 0 and 0.03 wt% or less of phosphorus (P) and more than 0 and 0.035 wt% or less of sulfur (S).

Preferably, the hardening depth of the inner ring may be 2 to 6 mm.

Meanwhile, the present invention may include forming an inner ring by forging a solid shaft, machining the solid shaft and the inner ring, and induction heat treating the machined solid shaft and the inner ring.

Preferably, the coil subjected to induction heat treatment may include a curved portion opposing the tooth bottom of the inner ring and a protrusion opposing the tooth bottom of the inner ring along the inner peripheral surface.

Preferably, the frequency range may be Frequency Index (FI) ±5kHz.

The present invention can manufacture a drive shaft assembly in which the shaft and the inner ring are integrated, but are not limited by the height or outer diameter of the inner ring.

The present invention has the advantage of ensuring heat treatability, durability, and economic efficiency by optimizing alloy components.

The present invention can optimize heat treatment conditions and prevent heat treatment defects.

Figure 1 is a schematic diagram of a conventional automobile drive shaft assembly.
Figure 2 is a schematic diagram of the present invention's drive shaft assembly for automobiles.
Figure 3 is a photograph of a shaft and an inner ring formed according to an embodiment of the present invention. Figure 3(a) shows a solid shaft, and Figures 3(b) to (d) show inner rings having outer diameters of about 2.1 times, about 2.6 times, and about 3.0 times the outer diameter of the solid shaft shown in Figure 3(a). .
Figure 4 shows a solid shaft 21, an inner ring 22, and a ball 24 according to an embodiment of the present invention.
Figure 5 is a flowchart showing the manufacturing method of the drive shaft assembly for automobiles according to the present invention.
Figure 6 shows the shape of a coil used for high-frequency heat treatment.
Figure 7(a) and Figure 7(b) are schematic diagrams showing the desired hardening depth of the tooth tooth portion and tooth bottom portion.
Figures 8(a) and 8(b) are schematic diagrams showing insufficient hardening depth as described in the remarks of Table 7.
Figures 9(a) and 9(b) are schematic diagrams showing the hardening depth exceeded in the remarks of Table 7.

Hereinafter, the present invention will be described in detail. However, the present invention is not limited or limited by the exemplary embodiments, and the purpose and effect of the present invention can be naturally understood or become clearer through the following description, and the purpose and effect of the present invention can be realized only by the following description. It is not limited. Additionally, in describing the present invention, if it is determined that a detailed description of known techniques related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description will be omitted.

Figure 2 is a schematic diagram of the present invention's drive shaft assembly for automobiles. Referring to FIG. 2, the present invention may include a solid shaft 21 and an inner ring 22 formed integrally with the solid shaft 21. Since the solid shaft 21 and the inner ring 22 are formed as one body in the present invention, it does not require a circlip for fastening and fixing the shaft and the inner ring, as well as an inner spline formed on the conventional inner ring and an outer spline formed on the conventional shaft. .

In addition, even if the outer diameter of the solid shaft 21 is the same as that of the conventional shaft 11, the weight of the drive shaft assembly for an automobile is reduced as the outer diameters of the inner ring 22 and the outer ring 25 are reduced. According to one embodiment of the present invention, the outer diameter of the inner ring can be reduced from 42mm to 30mm and the outer diameter of the outer ring from 86mm to 74mm, and the total weight of the inner and outer rings can be reduced from 1670g to 1439g (231g saved). Since two inner and outer rings each are used in the driveshaft assembly, a total weight of 462 g can be reduced.

Figure 3 is a photograph of a shaft and an inner ring formed according to an embodiment of the present invention. More specifically, Figure 3(a) shows a solid shaft, and Figures 3(b) to 3(d) show an outer diameter of about 2.1 times, about 2.6 times, and about 3.0 times the outer diameter of the solid shaft shown in Figure 3(a). It represents the inner ring with . Figure 4 shows a solid shaft 21, an inner ring 22, and a ball 24 according to an embodiment of the present invention.

Table 1 shows the maximum number of balls that can be used and the ratio of the outer diameters depending on the outer diameter (C) of the inner ring when the outer diameter (A) of the solid shaft is 30 mm and the diameter of the balls is 10 mm. Table 2 shows the maximum number of balls that can be used and the ratio of the outer diameters depending on the outer diameter (C) of the inner ring when the outer diameter (A) of the solid shaft is 30 mm and the diameter of the balls is 15 mm.

Inner ring outer diameter
(C, mm) cheek
maximum number 40 6 1.3 50 7 1.7 60 9 2.0 70 11 2.3 80 12 2.7 90 14 3.0

Inner ring outer diameter
(C, mm) cheek
maximum number 40 4 1.3 50 5 1.7 60 6 2.0 70 7 2.3 80 8 2.7 90 9 3.0

Referring to Figures 3 and 4, Table 1 and Table 2, the present invention forms the inner ring 22 by forging the solid shaft 21, so that the outer diameter C of the inner ring is up to 3 times the outer diameter A of the solid shaft. It can be doubled. The outer diameter of the inner ring (C) may exceed 3 times the outer diameter of the solid shaft (A), but not only is it not a suitable shape for use as an automobile drive shaft assembly, but the weight of the drive shaft assembly increases, so the outer diameter of the inner ring (C) is preferably at most 3 times the solid shaft outer diameter (A). As the outer diameter (C) of the inner ring increases, the maximum number of balls that can be used increases. For example, if the outer diameter (C) of the inner ring is 3 times the outer diameter (A) of the solid shaft, that is, if the outer diameter (C) of the inner ring is 90 mm and the outer diameter (A) of the solid shaft is 30 mm, a maximum of 14 balls with a diameter of 10 mm can be used. You can use it.

According to the present invention, the inner ring 22 can have a constant hardening depth. The hardening depth of the inner ring 22 defined in this specification refers to the average value of the hardening depth of the tooth portion 221 and the hardening depth of the tooth bottom portion 222. As will be described in detail later, in order to improve dimensional accuracy by uniformly hardening the entire tooth section, it is desirable for the inner ring to have a hardening depth of 2 to 6 mm.

Material C Cr Mo Ni B Si Mn Cu P S shaft
(conventional) 0.35
~0.41 0.3
Max - - 0.05
Max 0.15
~0.35 0.6
~0.9 0.3
Max 0.030
Max 0.035
Max Inner ring (conventional) 0.17
~0.23 0.8
~1.3 0.1
~0.4 0.3
Max - 0.15
~0.35 0.5
~0.9 0.3
Max 0.030
Max 0.035
Max this invention 0.45
~0.60 0.2
~0.6 0.4
~0.8 0.3
~0.9 0.01
~0.05 0.15
~0.35 0.6
~0.9 0.3
Max 0.03
Max 0.035
Max

Table 3 is a table summarizing the composition of the conventional shaft, inner ring, and the present invention. Referring to Table 3, the solid shaft 21 and the inner ring 22 of the present invention contain 0.45 to 0.60 wt% of carbon (C), 0.2 to 0.6 wt% of chromium (Cr), and 0.4 to 0.8 wt% of molybdenum (Mo). ), 0.3 to 0.9 wt% of nickel (Ni), 0.01 to 0.05 wt% of boron (B), 0.15 to 0.35 wt% of silicon (Si), 0.6 to 0.9 wt% of manganese (Mn), and the balance of iron. (Fe) may be included. The solid shaft 21 and the inner ring 22 of the present invention may further include 0.3 wt% or less of copper (Cu), 0.03 wt% or less of phosphorus (P), and 0.035 wt% or less of sulfur (S).

Comparing the composition of the conventional shaft, the inner ring, and the present invention, the amount of carbon added in the present invention is greater than that in the conventional shaft and inner ring, and the amount of chromium added in the present invention overlaps to some extent the amount of chromium added selectively to the conventional shaft, but compared to the amount of carbon added to the conventional shaft and inner ring. It is less than the amount of chrome added to the inner ring.

*Molybdenum and nickel, which were not added to the conventional shaft, are added to the solid shaft of the present invention, and the amount of molybdenum and nickel added in the present invention is greater than the amount of molybdenum and nickel added to the conventional inner ring. Boron, which was not added to the conventional inner ring, is added to the inner ring of the present invention, and unlike the case where boron was selectively added to the conventional shaft, boron is essentially added to the inner ring and shaft of the present invention. Hereinafter, the amount of each component added to the present invention will be described in detail.

(1) 0.45~0.60wt% of carbon (C)

Carbon is added to increase the strength of the material. If less than 0.45 wt% of carbon is added, the desired strength cannot be obtained, and if more than 0.60 wt% of carbon is added, processing and formability become disadvantageous, so it is preferable to add 0.45 to 0.60 wt% of carbon.

(2) 0.2~0.6wt% of chromium (Cr)

Chromium is added to increase the strength of the material. If less than 0.2 wt% of chromium is added, the desired strength cannot be obtained, and if more than 0.6 wt% of chromium is added, toughness decreases, so it is preferable to add 0.2 to 0.6 wt% of chromium.

(3) 0.4 to 0.8 wt% of molybdenum (Mo)

During high-frequency heat treatment of materials, molybdenum is added to ensure heat treatability, that is, hardening depth. If less than 0.4 wt% of molybdenum is added, the heat treatability of the material cannot be secured, and if more than 0.8 wt% of molybdenum is added, durability is reduced due to segregation, so it is preferable to add 0.4 to 0.8 wt% of molybdenum.

(4) 0.3 to 0.9 wt% of nickel (Ni)

Nickel is added to improve the durability and toughness of the material. If less than 0.3 wt% of nickel is added, the effect of improving toughness cannot be obtained, and if more than 0.9 wt% of nickel is added, the cost-effectiveness decreases, so it is preferable to add 0.3 to 0.9 wt% of nickel.

(5) 0.01 to 0.05 wt% of boron (B)

During high-frequency heat treatment of materials, boron is added to ensure heat treatability, that is, hardening depth. If less than 0.01 wt% of boron is added, the effect of improving heat treatability cannot be obtained, and if more than 0.05 wt% of boron is added, segregation and related problems may occur, so it is preferable to add 0.01 to 0.05 wt% of boron. .

(6) 0.15 to 0.35 wt% of silicon (Si)

Silicon is added to suppress the formation of harmful carbides. If less than 0.15 wt% of silicon is added, the formation of harmful carbides cannot be effectively suppressed, and if more than 0.35 wt% of silicon is added, segregation occurs, so it is preferable to add 0.15 to 0.35 wt% of silicon.

(7) 0.6 to 0.9 wt% of manganese (Mn)

Manganese is added to increase the strength of the material. If less than 0.6 wt% of manganese is added, the effect of improving the strength of the material cannot be achieved, and if more than 0.9 wt% of manganese is added, toughness and machinability deteriorate, so it is preferable to add 0.6 to 0.9 wt% of manganese. .

In the present invention, copper, phosphorus, and sulfur are added in amounts of 0.3 wt% or less, 0.03 wt% or less, and 0.035 wt% or less, respectively, to prevent quality degradation due to segregation and inclusion formation.

Figure 5 is a flowchart showing the manufacturing method of the drive shaft assembly for automobiles according to the present invention. Referring to FIG. 5, the present invention includes the steps of forging a solid shaft to form an inner ring (S101), processing the solid shaft and the inner ring (S102), and high-frequency heat treating the machined solid shaft and the inner ring (S103). It can be included.

The conventional shaft was manufactured by processing the raw material of the shaft (including the formation of the outer spline) and then high-frequency heat treatment (using a circular coil, 3 ≤ frequency f (kHZ) ≤ 30), and the conventional inner ring was manufactured by forging and processing the raw material (inner spline). (including the formation of) and then carburized heat treatment. The reason why the conventional inner ring was carburized heat treated rather than induction heat treated is because the amount of carbon added to the conventional inner ring was small, so even if the conventional inner ring was induction heat treated, the surface hardness of the inner ring was only HV500, whereas when carburized heat treated, the surface hardness of the inner ring was HV770. This is because it increases. Unlike the conventional method of improving the surface hardness of the inner ring by carburizing the inner ring, the present invention is different in that the surface hardness of the inner ring is improved by induction heat treatment.

Meanwhile, in the present invention, since the solid shaft and the inner ring are formed as one piece, if the solid shaft and the inner ring are separately subjected to high-frequency heat treatment, a portion of the heat treatment overlaps and cracks may occur in that portion. Therefore, it is desirable to heat treat the solid shaft and the inner ring all at once.

Figure 6 shows the shape of a coil used for high-frequency heat treatment. Referring to FIG. 6, the inside of the coil 27 includes a curved portion 271 facing the tooth bottom 221 of the inner ring and a protrusion 272 facing the tooth bottom 222 of the inner ring, and the curved portion 271 and The protrusions 272 may be formed alternately along the inner peripheral surface of the coil.

When a circular coil without the curved portion 271 and the protruding portion 272 is used during the induction heat treatment of the present invention in which the solid shaft and the inner ring are formed integrally, the toothed portion 221 of the inner ring is adjacent to the circular coil, so the grooved portion of the inner ring is Sufficient heat treatment can be applied to (221). However, since the tooth bottom portion 222 of the inner ring and the solid shaft are not adjacent to the circular coil compared to the tooth portion 221 of the inner ring, sufficient heat treatment cannot be applied to the tooth bottom portion 222 of the inner ring and the solid shaft. Therefore, when using the coil 27 of the present invention, sufficient heat treatment can be applied to the tooth portion 221 of the inner ring as well as the tooth bottom portion 222 of the inner ring and the solid shaft, thereby solving the above-mentioned problems.

The range of frequency that can be used in the high-frequency heat treatment step (S103) of the present invention is Frequency Index (FI) ±5 kHz, and the frequency index refers to Equation 1 below.

[Equation 1]

Gap (mm) means B - A (where B ≥ A) and Height (mm) means C - B (where C > B), where A is the outer diameter of the solid shaft, B is the inner diameter of the inner ring, and C is the outer diameter of the solid shaft. It refers to the outer diameter of the inner ring.

The frequency conditions need to be changed depending on the difference in dimensions between the outer diameter of the solid shaft and the inner and outer diameters of the inner ring. Since the frequency index can be used as a standard for adjusting heat treatment conditions according to the shape of the solid shaft and inner ring during high-frequency heat treatment, the present invention can prevent heat treatment defects through preliminary quality control through optimization of high-frequency heat treatment conditions.

division A (mm) B (mm) C (mm) Gap Height F.I. One 30 30 50 0 20 27.1 2 30 30 40 0 10 25.0 3 30 30 90 0 60 32.2 4 30 33 53 3 20 22.3 5 30 33 43 3 10 20.2 6 28 28 48 0 20 27.1 7 28 28 38 0 10 25.0 8 28 33 50 5 17 18.5 9 28 33 40 5 7 16.2

Table 4 is a table summarizing the frequency index according to the outer diameter of the solid shaft (A), the inner diameter of the inner ring (B), and the outer diameter of the inner ring (C). The solid shaft and inner ring of categories 1 to 9 had the same chemical composition as that of Example 1, which will be described later. Referring to division 1 as an example in Table 4, if the outer diameter (A) of the solid shaft is 30 mm, the inner diameter (B) of the inner ring is 30 mm, and the outer diameter (C) of the inner ring is 50 mm, the outer diameter (A) of the solid shaft and The difference between the inner diameter (B) of the inner ring is 0 (Gap=0) and the difference between the outer diameter (C) of the inner ring and the inner diameter (B) of the inner ring is 20 (Height=20). By substituting Gap=0 and Height=20 into Equation 1, the frequency index becomes 27.1kHz. Ultimately, the frequency (f) used during high-frequency heat treatment is selected from 22.1 ≤ f ≤ 32.1. Even if the solid shaft and inner ring are heat treated in batches, considering that the outer diameter of the solid shaft is smaller than the outer diameter of the inner ring, the frequency index is used. Therefore, even if the high-frequency heat treatment conditions are optimized, sufficient surface hardness and hardening depth cannot be secured because the distance from the solid shaft to the coil is relatively long. Therefore, reinforcement of components that can compensate for this is necessary, which has already been described above.

Hereinafter, specific embodiments of the present invention will be described in detail. However, the examples described below are only for illustrating or explaining the present invention in detail, and the present invention is not limited thereto.

division Chemical composition (wt%) C Si Mn Cr Mo Ni B shaft
(conventional) 0.38 0.2 0.7 - - - - Inner ring (conventional) 0.2 0.25 0.7 1.0 0.2 - - Example 1 0.5 0.25 0.7 0.3 0.6 0.6 0.03 Comparative Example 1 0.42 0.25 0.7 0.3 0.6 0.6 0.03 Comparative example 2 0.65 0.25 0.7 0.3 0.6 0.6 0.03 Comparative Example 3 0.5 0.25 0.7 0.05 0.6 0.6 0.03 Comparative Example 4 0.5 0.25 0.7 0.8 0.6 0.6 0.03 Comparative Example 5 0.5 0.25 0.7 0.3 0.04 0.6 0.03 Comparative Example 6 0.5 0.25 0.7 0.3 1.0 0.6 0.03 Comparative Example 7 0.5 0.25 0.7 0.3 0.6 0.1 0.03 Comparative example 8 0.5 0.25 0.7 0.3 0.6 0.6 - Comparative Example 9 0.5 0.25 0.7 0.3 0.6 0.6 0.07

Table 5 is a table summarizing the compositions of conventional shafts and inner rings, and the compositions of examples and comparative examples of the present invention. 0.3 wt% copper, 0.03 wt% phosphorus, and 0.035 wt% sulfur were added to each composition. Referring to Table 5, comparing the composition of Example 1 and the conventional shaft and inner ring, 0.5 wt% of carbon, which is more than the carbon addition amount of 0.38 wt% and 0.2 wt% of the conventional shaft and inner ring, was added to Example 1 to increase surface hardness. added. 0.3 wt% of chromium, which is less than the 1.0 wt% of chromium added to the conventional inner ring and not added to the conventional shaft, was added in Example 1, and 0.6 wt% of chromium, which is more than the 0.2 wt% of molybdenum added to the conventional inner ring and not added to the conventional shaft, was added in Example 1. Molybdenum was added in Example 1. 0.6 wt% of nickel and 0.03 wt% of boron, which were not previously added to the shaft and inner ring, were added in Example 1.

Comparative Examples 1 and 2 are comparative examples in which 0.42 wt% of carbon and 0.65 wt% of carbon, which are not included in the carbon addition amount (0.45 to 0.60 wt%) of the present invention, were added, and Comparative Examples 3 and 4 are comparative examples in which chromium of the present invention was added. This is a comparative example in which 0.05 wt% of chromium and 0.8 wt% of chromium, which are not included in the addition amount (0.2 to 0.6 wt%), were added.

Comparative Examples 5 and 6 are comparative examples in which 0.04 wt% of molybdenum and 1.0 wt% of molybdenum, which are not included in the molybdenum addition amount (0.4 to 0.8 wt%) of the present invention, were added, and Comparative Example 7 is a comparative example in which nickel addition amount (0.4 to 0.8 wt%) of the present invention was added. This is a comparative example in which 0.1 wt% of nickel, which is not included in 0.3 to 0.9 wt%, was added. Comparative Example 8 is a comparative example in which boron was not added, and Comparative Example 9 is a comparative example in which 0.07 wt% of boron was added, which exceeds the boron addition amount (0.01 to 0.05 wt%) of the present invention.

division shape High frequency conditions A
(mm) B
(mm) C
(mm) frequency index
(kHz) result
(kHz) shaft
(conventional) 30 - - 19.1 20 inner ring
(conventional) - 35 55 - - Example 1 and Comparative Examples 1 to 9 30 30 50 27.1 27

Table 6 is a table summarizing the frequency index and frequency results calculated according to the shape of the solid shaft and inner ring. The inner and outer diameter dimensions of the conventional inner ring were used to calculate the frequency index, and the conventional inner ring was carburized heat treated, unlike the conventional shaft. Since Example 1 and Comparative Examples 1 to 9 have the same high frequency conditions, the effects depending on the composition of the shaft and inner ring can be compared.

evaluation division surface hardness
(HV) Hardening depth
(mm) robbery
(MPa) durability
(number) note shaft
(conventional) 680 3 105 510,000 - inner ring
(conventional) 770 One Example 1 750 4.0 115 560,000 OK Comparative Example 1 635 2.5 86 380,000 Insufficient surface hardness Comparative example 2 790 7.1 87 450,000 Exceeding hardening depth Comparative example 3 715 1.5 98 410,000 Hardening depth not reached Comparative example 4 770 6.9 87 470,000 Exceeding hardening depth Comparative Example 5 720 1.8 91 390,000 Hardening depth not reached Comparative Example 6 745 8.5 85 460,000 Exceeding hardening depth Comparative example 7 748 3.9 103 400,000 Lack of durability Comparative Example 8 748 1.8 95 410,000 Insufficient hardening depth, insufficient strength,
Lack of durability Comparative Example 9 750 4.0 110 490,000 Lack of durability

Table 7 is a table summarizing the surface hardness, hardening depth, strength, and durability measured after induction heat treatment of the conventional shaft and inner ring, Example 1 of the present invention, and Comparative Examples 1 to 9 under the high frequency conditions of Table 6. The desired physical properties are surface hardness of HV700 or more, hardening depth of 2 to 6 mm, strength of 100 MPa or more, and durability of 500,000 or more. Figures 7(a) and 7(b) show the desired hardening depth of tooth base and tooth base. This is a schematic diagram. Figures 8(a) and 8(b) are schematic diagrams showing insufficient hardening depth as described in the remarks of Table 7. Figures 9(a) and 9(b) are schematic diagrams showing the hardening depth exceeded in the remarks of Table 7.

It is necessary to improve dimensional accuracy by uniformly hardening the entire tooth profile, and for this purpose, it is desirable to form a hardening depth of 2 to 6 mm on the inner ring. More specifically, the desired hardening depths of the tooth base and tooth base are 2 to 8 mm and 2 to 4 mm, respectively. If the hardening depth of the tooth bottom is less than 2 mm, the strength required for the drive shaft assembly cannot be met. If the hardening depth of the tooth base exceeds 8 mm, that is, if the hardening depth of the inner ring exceeds 6 mm, the dimensional accuracy may be damaged due to distortion due to overheating of the tooth. deteriorates.

Durability evaluation is based on torsional fatigue testing of the driveshaft assembly. The torsional fatigue test involves fixing one side of the drive shaft assembly to a test equipment and repeatedly applying a torsional load to the other side to check the point of fracture.

Referring to Tables 5 to 7 and Figures 7 to 9, except that the surface hardness of the conventional inner ring subjected to carburizing heat treatment is higher than that of Example 1, Example 1 has surface hardness, strength, and It can be seen that durability is excellent.

As 0.42 wt% of carbon, which is less than the minimum carbon addition amount of 0.45 wt% of the present invention, was added to Comparative Example 1, the surface hardness of Comparative Example 1 was lower than that of Example 1 and lower than the desired surface hardness of HV700. . On the other hand, as 0.65 wt% of carbon, which is more than the maximum carbon addition amount of 0.60 wt% of the present invention, was added to Comparative Example 2, the surface hardness of Comparative Example 2 was higher than that of Example 1, but the hardening depth of the inner ring was exceeded 6 mm.

In Comparative Example 3, as 0.05 wt% of chromium was added, which is less than the minimum chromium addition amount of 0.2 wt% of the present invention, the hardening depth of the inner ring was less than 2 mm, and in Comparative Example 4, 0.8 wt more than the maximum chromium addition of 0.6 wt% of the present invention. As % of chromium was added, the hardening depth of the inner ring exceeded 6mm.

As 0.04 wt% of molybdenum, which is less than the minimum addition amount of molybdenum of the present invention of 0.4 wt%, was added in Comparative Example 5, the hardening depth of the inner ring was less than 2 mm, and in Comparative Example 6, the hardening depth of the inner ring was 1.0 wt%, which is more than the maximum addition amount of molybdenum of the present invention of 0.8 wt%. As wt% molybdenum was added, the hardening depth of the inner ring exceeded 6mm.

As 0.1 wt% of nickel, which is less than the minimum nickel addition amount of 0.3 wt% of the present invention, was added to Comparative Example 7, the durability was measured at 400,000 cycles, which is lower than the desired durability of 500,000 cycles. In Comparative Example 8, although the addition amount of the remaining elements except boron was the same as Example 1, the hardening depth of the inner ring was less than 2 mm as boron was not added, and the strength was less than 100 MPa and the durability was less than 500,000 times. Comparative Example 9 showed a durability of less than 500,000 as 0.07 wt% of boron was added, which is more than the boron addition amount of the present invention (0.01 to 0.05 wt%).

division shape High frequency conditions A
(mm) B
(mm) C
(mm) frequency index
(kHz) result
(kHz) Example 1 30 30 50 27.1 27 Comparative Example 10 20 Comparative Example 11 35 Example 2 30 33 42 20.2 20 Comparative Example 12 10 Comparative Example 13 30 Example 3 28 33 40 16.2 12 Example 4 20 Example 5 30 30 90 32.2 32

division evaluation note surface hardness
(HV) Hardening depth
(mm) robbery
(MPa) durability
(number) Example 1 750 4.0 115 560,000 OK Comparative Example 10 633 3.2 85 430,000 Insufficient surface hardness Comparative Example 11 711 1.5 90 400,000 Hardening depth not reached Example 2 751 4.0 113 550,000 OK Comparative Example 12 628 3.0 84 410,000 Insufficient surface hardness Comparative Example 13 719 1.7 92 400,000 Hardening depth not reached Example 3 748 4.1 114 550,000 OK Example 4 749 4.0 112 540,000 OK Example 5 749 4.1 113 530,000 OK

Table 8 is a table that summarizes the high-frequency conditions according to the shape of the solid shaft and inner ring, which has the same composition as that of Example 1, and Table 9 is a table that summarizes the surface hardness, depth of hardening, strength, and durability after high-frequency heat treatment. . Referring to Table 8 and Table 9, Examples 1 to 5 were subjected to high-frequency heat treatment at 27kHz, 20kHz, 12kHz, 20kHz, and 32kHz, which are within the ±5kHz range of each frequency index (FI) of 27.1kHz, 20.2kHz, 16.2kHz, and 32.2kHz. Therefore, the desired surface hardness, hardening depth, strength, and durability were obtained. In contrast, Comparative Examples 10 and 12 were subjected to high-frequency heat treatment at 20kHz and 10kHz, which are outside the -5kHz range of the frequency index (FI) of 27.1kHz and 20.2kHz. In one comparative example, the surface hardness did not reach HV700, and Comparative Examples 11 and 13 were comparative examples in which high-frequency heat treatment was performed at 35kHz and 30kHz, which are outside the +5kHz range of each frequency index (FI) of 27.1kHz and 20.2kHz, and hardening of the inner ring was achieved. It can be seen that the depth was less than 2mm.

Although the present invention has been described in detail above through representative embodiments, those skilled in the art will understand that various modifications can be made to the above-described embodiments without departing from the scope of the present invention. will be. Therefore, the scope of rights of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the patent claims described later, but also by all changes or modified forms derived from the scope of the patent claims and the concept of equivalents.

11: shaft 12: inner ring
13: Circlip 14: Ball
15: Outer ring 16: Spline
21: shaft 22: inner ring
24: ball 25: paddle
221: Chigobu 222: Tooth base
S101: Forging of solid shaft and formation of inner ring
S102: Machining steps for solid shaft and inner ring
S103: Induction heat treatment step of solid shaft and inner ring
271: indentation 272: protrusion
A: Outer diameter of solid shaft
B: Inner diameter of the inner ring
C: Outer diameter of inner ring

Claims (7)

A drive shaft assembly for an automobile comprising a solid shaft and an inner ring formed integrally with the solid shaft, wherein the outer diameter of the inner ring is larger than the outer diameter of the solid shaft and includes a plurality of balls,
The solid shaft and inner ring include 0.45 to 0.60 wt% of carbon (C), 0.2 to 0.6 wt% of chromium (Cr), 0.4 to 0.8 wt% of molybdenum (Mo), 0.3 to 0.9 wt% of nickel (Ni), A drive shaft for an automobile, characterized in that it contains 0.01 to 0.05 wt% of boron (B), 0.15 to 0.35 wt% of silicon (Si), 0.6 to 0.9 wt% of manganese (Mn), and the balance of iron (Fe). Assey. According to clause 1,
A drive shaft assembly for an automobile, wherein the inner ring has a constant hardening depth. According to clause 1,
Automotive driveshaft assembly further containing 0.3 wt% or less of copper (Cu). According to clause 1,
A drive shaft assembly for an automobile further comprising 0.03 wt% or less of phosphorus (P) and 0.035 wt% or less of sulfur (S). According to clause 1,
A drive shaft assembly for an automobile, characterized in that the hardening depth of the inner ring is 2 to 6 mm. Forming an inner ring by forging a solid shaft;
Processing the solid shaft and inner ring; and
High-frequency heat treatment of the processed solid shaft and inner ring; and
The coil subjected to high-frequency heat treatment includes a curved portion facing the toothed portion of the inner ring along the inner peripheral surface; And a protrusion opposing the tooth bottom of the inner ring; - A method of manufacturing a drive shaft assembly for an automobile including,
The frequency range that can be used in the high-frequency heat treatment step is Frequency Index (FI) ±5kHz,
A method of manufacturing a drive shaft assembly for an automobile, wherein the frequency index is expressed in Equation 1 below.
[Equation 1]

Gap(mm) = B - A (however, B ≥ A)
height(mm) = C - B (where C > B)
A: Outer diameter of solid shaft, B: Inner diameter of inner ring, C: Outer diameter of inner ring
According to claim 6,
The solid shaft and inner ring include 0.45 to 0.60 wt% of carbon (C), 0.2 to 0.6 wt% of chromium (Cr), 0.4 to 0.8 wt% of molybdenum (Mo), 0.3 to 0.9 wt% of nickel (Ni), A drive shaft for an automobile, characterized in that it contains 0.01 to 0.05 wt% of boron (B), 0.15 to 0.35 wt% of silicon (Si), 0.6 to 0.9 wt% of manganese (Mn), and the balance of iron (Fe). Assay manufacturing method.