JP2007211955A - Fixed type constant velocity universal joint - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixed type constant velocity universal joint capable of suppressing early exfoliation caused by hydrogen intruding into steel even when a lubricant or a minute amount of mixed water on a contact surface is decomposed and hydrogen is generated. <P>SOLUTION: The fixed type constant velocity universal joint is equipped with an outside joint member having a track groove 25 formed thereon for rolling of a torque transmission member, and allows only an angle displacement between two shafts. A steel material containing C: 0.45-0.65 wt.%, Si: 0.1-1.0 wt.%, Mn: 0.1-1.5 wt.%, V: 0.05-0.3 wt.% as alloy elements within each range, and Fe and unavoidable impurities as the remainder, is used as the outside joint member. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a fixed type constant velocity universal joint.

  In general, as shown in FIG. 4, the fixed type constant velocity universal joint includes an outer ring 3 as an outer joint member in which a plurality of track grooves 2 are formed along the axial direction at equal intervals in the circumferential direction on the inner spherical surface 1; An inner ring 6 as an inner joint member in which a plurality of track grooves 5 paired with the track grooves 2 of the outer ring 3 are formed in the outer spherical surface 4 along the axial direction at equal intervals in the circumferential direction, and the track grooves 2 of the outer ring 3 A plurality of balls 7 that are interposed between the track grooves 5 of the inner ring 6 and transmit torque, and a cage 8 that is interposed between the inner spherical surface 1 of the outer ring 3 and the outer spherical surface 4 of the inner ring 6 and holds the balls 7. And. A shaft 11 is fitted into the inner ring 6.

  When such a fixed type constant velocity universal joint transmits torque at a constant operating angle, the ball comes into contact with the track groove bottom of the outer ring and the track groove bottom of the inner ring and swings while rolling and sliding. For this reason, medium carbon steel is used for the outer ring, and some of the regions including the track grooves are quenched (for example, induction hardening) (Patent Document 1). On the other hand, carburized steel is generally used for the inner ring, and carburizing and quenching is performed on the entire circumference.

Future technical trends are to reduce resources, save energy, and make compact, so that fixed type constant velocity universal joints are also going to be made more compact and higher in common angle. There is a tendency that, as the load of the load increases, the rocking distance becomes longer and the slip increases.
Japanese Unexamined Patent Publication No. 2000-213553 (5th page, FIG. 3)

  When rolling and sliding contact is performed under high surface pressure, a lubricant or a small amount of mixed water is decomposed on the contact surface to generate hydrogen, which may penetrate into the steel. Hydrogen significantly reduces the fatigue strength of the steel and causes premature delamination. The initial crack in the early peeling is generated by a tensile stress that becomes large at the edge of the contact area when a slip acts. The thing described in the said patent document 1 etc. does not have the tolerance with respect to the early peeling which such hydrogen involves.

In view of the above problems, the present invention can suppress early peeling that occurs when a lubricant or a small amount of mixed water decomposes on the contact surface and hydrogen is generated to enter the steel. A fixed type constant velocity universal joint is provided.

  The fixed type constant velocity universal joint of the present invention includes an outer joint member formed with a track groove for rolling a torque transmission member, and is a fixed type constant velocity universal joint that allows only angular displacement between two axes. C (carbon): 0.45-0.65 wt%, Si (silicon): 0.1-1.0 wt%, Mn (manganese): 0.1-1.5 wt%, V (vanadium): 0.05 A steel material containing ˜0.3 wt% in each range and the balance being Fe (iron) and inevitable impurities is used for at least the outer joint member.

  Fine V carbide is precipitated by tempering after induction hardening. This minute V carbide has good consistency with the substrate, and strongly traps diffusible hydrogen that causes deterioration of tensile fatigue characteristics. For this reason, the deterioration of the tensile fatigue characteristics under hydrogen intrusion can be suppressed small.

  The lower limit of the amount of C is set to 0.45 wt% because it is the minimum necessary to obtain a stable high hardness by induction hardening. On the other hand, the upper limit is set to 0.65 wt%. When the amount is too large, the material hardness increases and the workability is remarkably lowered, and a special heat treatment such as high-temperature diffusion heat treatment or carbide spheroidization for preventing component segregation. This is necessary and leads to cost increase.

  The reason why the lower limit of the amount of Si is set to 0.1 wt% is that Si is originally contained in steel and the significance of reducing it to less than that is rare. On the other hand, the upper limit is set to 1.0 wt%. Si has an effect of suppressing softening due to tempering, and is indispensable for an inexpensive steel material used in high temperature applications. This is because the property decreases.

  The reason why the lower limit of the amount of Mn is set to 0.1 wt% is that it is combined with Mn and precipitated as MnS in order to prevent S contained in a trace amount as an impurity from segregating at the grain boundary. On the other hand, the upper limit was set to 1.5 wt%, but Mn is an effective element that improves hardenability, but it replaces Fe atoms in cementite to form composite carbides, increasing the material hardness. If too much is added, workability and machinability are lowered.

  Since V has a strong affinity for C, it exists in the form of a carbide in which both are bonded before quenching. In order to precipitate fine V carbide having good consistency with the substrate by tempering, it is necessary to once dissolve V into the substrate during quenching heating. The reason why the lower limit of the amount of V is set to 0.05 wt% is to dissolve the minimum necessary V into the substrate at an induction hardening heating temperature of about 1000 ° C. On the other hand, V significantly increases the hardness of the material in the non-tempered state, so if too much is added, workability and formability are impaired. Therefore, the upper limit was set to 0.3 wt%.

  For this reason, this outer joint member has a small decrease in tensile fatigue strength even when hydrogen enters, and can obtain high hardness, and is excellent in hardenability and workability.

  The predicted value of the hardness of the outer joint member based on the alloy component amount is preferably 23 ≦ HRC ≦ 30.

By the way, the steel material which comprises an outer joint member will be in a non-tempered state in the state cooled by air after forging. If the hardness in this non-tempered state is too high, subsequent machining becomes difficult. On the other hand, if it is too soft, the fatigue strength of the non-quenched hardened portion cannot be obtained sufficiently. For this reason, it is desirable to suppress to HRC30 or less from the viewpoint of workability. In addition, the fatigue strength of the non-quenched hardened portion is 300 MPa on average with respect to the conventional medium carbon steel S53C, so that 400 MPa or more is necessary. There is a relationship of σ _Wb = 1.54 HV between the rotational bending fatigue limit σ _Wb and the hardness (HV). When σ _Wb = 400 MPa is substituted into this equation to obtain the required hardness, HRC23 is obtained. Therefore, it is desirable that it is HRC23 or more from the surface of the fatigue strength of a non-hardening hardening part.

  The fixed type constant velocity universal joint of the present invention uses a steel with a small decrease in tensile fatigue strength even when hydrogen enters the outer joint member, so that rolling and sliding contact conditions become severe with downsizing, etc. Even if a lubricant or a small amount of mixed water is decomposed on the contact surface and hydrogen is generated, it is possible to suppress early peeling that occurs when the hydrogen penetrates into the steel. Further, the outer joint member can obtain a high hardness and can exhibit a stable strength. And it is excellent in hardenability, workability, etc., and can reduce manufacturing cost.

  In particular, when the predicted value of the hardness of the outer joint member satisfies 23 ≦ HRC ≦ 30, the outer joint member is excellent in workability and strength.

  Embodiments of the present invention will be described below with reference to FIGS.

  As shown in FIG. 1, the fixed type constant velocity universal joint includes an outer ring 23 as an outer joint member in which a plurality of track grooves 22 are formed in the inner spherical surface 21 at equal intervals in the circumferential direction, and an outer ring 23. An inner ring 26 as an inner joint member in which a plurality of track grooves 25 paired with the track grooves 22 of the outer ring 23 are formed on the spherical surface 24 along the axial direction at equal intervals in the circumferential direction, and the track grooves 22 and the inner rings of the outer ring 23 are formed. A plurality of balls 27 that transmit torque by being interposed between the 26 track grooves 25, and a cage 28 that holds the balls 27 by being interposed between the inner spherical surface 21 of the outer ring 23 and the outer spherical surface 24 of the inner ring 26. It has. The plurality of balls 27 are accommodated in pockets 29 formed in the cage 28 and arranged at equal intervals in the circumferential direction.

  The center of curvature O1 of the track groove 22 of the outer ring 23 and the center of curvature of the track groove 25 of the inner ring 6 are provided so that the contact point between the track grooves 22 and 26 and the ball 27 can take a large operating angle without being detached from the tracks 22 and 26. O2 is offset in the axial direction by an equal distance from the joint center O in the opposite direction. That is, the center of curvature O1 of the track groove 22 of the outer ring 23 is on the opening side, and the center of curvature O2 of the track groove 5 of the inner ring 26 is on the back side. As a result, each of the track grooves 22 and 25 is shallow on the outer ring bottom side (back side) from the axial center and deep on the outer ring opening side, and as a result, from the bottom side (back side) of the outer ring 23. A wedge-shaped ball track in which the radial interval gradually increases toward the opening side is formed.

  And in this outer ring | wheel 23, C (carbon): 0.45-0.65 wt%, Si (silicon): 0.1-1.0 wt%, Mn (manganese): 0.1-1. A steel material containing 5 wt%, V (vanadium): 0.05 to 0.3 wt% in the respective ranges, and the balance of Fe (iron) and inevitable impurities is used.

  In the outer ring 23, the region including the track groove is induction hardened to form a hardened portion. Here, induction hardening is performed by heating only the surface of the processed material utilizing skin hardening by high frequency. In addition, when forming a hardening part, you may carry out by metal heat processing other than induction hardening.

  The lower limit of the amount of C is set to 0.45 wt% because it is the minimum necessary to obtain a stable high hardness by induction hardening. On the other hand, the upper limit of the amount of C is 0.65 wt%, if too much, the material hardness increases and the workability is remarkably reduced, and high temperature diffusion heat treatment for preventing component segregation and spheroidization of carbide, This is because a special heat treatment is necessary, leading to an increase in cost.

  The reason why the lower limit of the amount of Si is set to 0.1 wt% is that Si is originally contained in steel and the significance of reducing it to less than that is rare. On the other hand, the upper limit of Si amount is 1.0 wt%, Si has an effect of suppressing softening due to tempering, and is indispensable for inexpensive steel materials used in high temperature applications, but if too much, cold workability, This is because hot workability is lowered.

  The reason why the lower limit of the amount of Mn is set to 0.1 wt% is that it is combined with Mn and precipitated as MnS in order to prevent S contained in a trace amount as an impurity from segregating at the grain boundary. On the other hand, the upper limit was set to 1.5 wt%, but Mn is an effective element that improves hardenability, but it replaces Fe atoms in cementite to form composite carbides, increasing the material hardness. If too much is added, workability and machinability are lowered.

  Since V has a strong affinity for C, it exists in the form of a carbide in which both are bonded before quenching. In order to precipitate fine V carbide having good consistency with the substrate by tempering, it is necessary to once dissolve V into the substrate during quenching heating. The reason why the lower limit of the amount of V is set to 0.05 wt% is to dissolve the minimum necessary V into the substrate at an induction hardening heating temperature of about 1000 ° C. On the other hand, V significantly increases the hardness of the material in the non-tempered state, so if too much is added, workability and formability are impaired. Therefore, the upper limit of the V amount is set to 0.3 wt%.

  The hardness of the outer ring 23 is set so that the predicted value of hardness based on the amount of alloy components satisfies 23 ≦ HRC (Rockwell hardness) ≦ 30. If the amount of alloy components is known, the material hardness can be predicted with high accuracy. Actually, it can be obtained by substituting each alloy component amount into the following equation (1).

  By the way, the steel material which comprises the outer ring | wheel 23 will be in a non-tempered state in the state cooled by air after forging. If the hardness in this non-tempered state is too high, subsequent machining becomes difficult. On the other hand, if it is too soft, the fatigue strength of the non-quenched hardened portion cannot be obtained sufficiently. Considering that, in the future, due to downsizing and the like, a large load will be applied to the non-hardened and hardened portion, the fatigue strength of the non-hardened and hardened portion as well as the hardened and hardened portion will be important. For this reason, it is desirable to suppress to HRC30 or less from the viewpoint of workability.

In addition, the fatigue strength of the non-quenched hardened portion is 300 MPa on average with respect to the conventional medium carbon steel S53C, so that 400 MPa or more is necessary. Conventionally, a relationship of σ _Wb = 1.54 HV is known between the rotational bending fatigue limit σ _Wb and the hardness (HV). Substituting σ _Wb = 400 MPa into this equation yields the required hardness, resulting in HRC23. Therefore, it is desirable that it is HRC23 or more from the surface of the fatigue strength of a non-hardening hardening part.

  Thus, since the outer ring 23 using the steel material as described above contains 0.05 wt% or more of V in the alloy element, the decrease in tensile fatigue strength is small even when hydrogen enters. This is because fine V carbide is precipitated by tempering after induction hardening, and this fine V carbide has good consistency with the substrate and strongly traps diffusible hydrogen that causes deterioration of tensile fatigue characteristics. It is. For this reason, rolling and sliding contact conditions become stricter with downsizing, and even if the contact surface is decomposed and a small amount of water is decomposed and hydrogen is generated, it is an early stage that occurs when it enters into steel. Peeling can be suppressed. Further, the outer joint member can obtain a high hardness and can exhibit a stable strength. And it is excellent in hardenability, workability, etc., and can reduce manufacturing cost.

  In particular, when the predicted value of the hardness of the outer joint member satisfies 23 ≦ HRC ≦ 30, the outer joint member is excellent in workability and strength.

  As described above, the embodiment of the present invention has been described. However, the present invention is not limited to the above-described embodiment, and various modifications are possible. For example, only the outer ring 23 of the fixed type constant velocity universal joint is used as an alloy element. C: 0.45-0.65 wt%, Si: 0.1-1.0 wt%, Mn: 0.1-1.5 wt%, V: 0.05-0.3 wt% within each range And although the steel material which the remainder consists of Fe and an unavoidable impurity was used, you may use this steel material for the inner ring | wheel 26 (inner joint member). Moreover, as the fixed type constant velocity universal joint, the bar field type (BJ) is shown in the above embodiment, but the fixed type constant velocity universal joint of the undercut free type (UJ) having a straight bottom parallel to the axial direction is also shown. Applicable. Furthermore, the present invention can also be applied to other fixed type constant velocity universal joints having track groove shapes other than these bar field type and undercut free type.

  C-1 to C-10 test products (implemented products) and C-11 to C-17 test products (comparative products) having chemical components shown in Table 1 were manufactured and subjected to an axial load fatigue test. Each test article is an hourglass-like body having a minimum diameter of 4 mm and a length of about 80 mm. In order to cure uniformly to the center of the minimum diameter portion, induction hardening was performed at a heating temperature of 1000 ° C., and then tempering was performed at 170 ° C. The comparative product C-11 is S53C.

  Prior to the fatigue test, the test product was charged with hydrogen by a cathodic electrolysis method. For hydrogen charging, a 0.05 mol / L dilute sulfuric acid aqueous solution to which 1.4 g / L thiourea was added was used. The diffusion rate of hydrogen differs depending on the steel type, and the hydrogen concentration on the surface differs even at the same current density. After obtaining them in advance, the current density and the charge time were adjusted so that the diffusible hydrogen concentration was uniformly 3 wt-ppm up to the center of the minimum diameter portion. Here, the diffusible hydrogen concentration refers to the fraction of the weight of hydrogen released from room temperature to 350 ° C. when the sample is heated at 180 ° C./h with respect to the sample weight.

Immediately after hydrogen charging the test article, a fatigue test was performed in a room temperature atmosphere. The stress ratio in the test is R = -1, and the load frequency is 20 kHz. Even if the number of loadings reached 10 ⁸ times, the test was terminated if it was not broken. In addition, the diffusible hydrogen introduced into the test sample diffuses in the steel even at room temperature and dissipates over time. However, the tests conducted this time are extremely fast loads, and the number of loads reaches 10 ⁸ in a very short time, so there is no room for diffusible hydrogen to dissipate. Therefore, the influence of diffusible hydrogen on fatigue strength can be rationally evaluated.

Table regression of S / N diagram obtained in 2 to fatigue test shows the fatigue strength at 10 ⁷ times was determined. The product containing 0.05 wt% or more of V had higher fatigue strength than the comparative product that was not. This is presumably because the minute V carbide that precipitates by tempering after induction hardening and has good consistency with the substrate strongly traps diffusible hydrogen that causes deterioration of tensile fatigue characteristics. The comparative products C-14 and 15 also contain a small amount of V, but their fatigue strength was low because the V carbides precipitated by tempering were insufficient.

The maximum contact surface pressure acting on the rolling / sliding contact portion of the outer ring 23 is about 4 GPa when high estimation is made in consideration of severe use conditions in the future. In this case, the tensile stress that repeatedly acts on the contact edge is about 600 MPa in terms of calculation by estimating the friction. Moreover, in this fatigue test, 3 wt-ppm diffusible hydrogen was forcibly introduced and the effect was observed. However, in reality, it is considered rare that a large amount of hydrogen penetrates. In other words, if the fatigue strength at 10 ⁷ times is 600 MPa or more, it is considered that the fatigue strength can sufficiently be put into practical use. Looking at the fatigue strength at 10 ⁷ times Table 2 in products from this viewpoint, it is both 600MPa or more. Therefore, it can be said that it is a necessary condition for suppressing a decrease in fatigue strength under hydrogen penetration by containing at least 0.05 wt% or more of V as an alloy element and precipitating V carbide by tempering after induction hardening.

For the outer ring 23, the non-tempered state is a state of being air-cooled after forging. If the hardness in that state is too high, subsequent machining becomes difficult. On the other hand, if it is too soft, the fatigue strength of the non-quenched hardened portion cannot be obtained sufficiently. Considering that, in the future, due to downsizing and the like, a large load will be applied to the non-hardened and hardened portion, the fatigue strength of the non-hardened and hardened portion as well as the hardened and hardened portion will be important. Specifically, it is desirable to suppress to HRC30 or less from the viewpoint of workability. On the other hand, as the fatigue strength of the non-quenched hardened portion, it is 300 MPa on average with respect to the conventional medium carbon steel S53C, so that 400 MPa or more is necessary. Conventionally, a relationship of σ _Wb = 1.54 HV is known between the rotational bending fatigue limit σ _Wb and the hardness (HV). Substituting σ _Wb = 400 MPa into this equation yields the required hardness, resulting in HRC23. Therefore, it is desirable that it is HRC23 or more from the surface of the fatigue strength of a non-hardening hardening part.

  C-1a to C-10a test products (implemented products) and C-11a to C-17a test products (comparative products) were manufactured, and the material hardness in an untempered state was examined. The results are shown in Table 3. The chemical composition of each test product is as follows: C-1a corresponds to C-1, C-2a corresponds to C-2, C-3a corresponds to C-3, and C-4a corresponds to C-4. C-5a corresponds to C-5, C-6a corresponds to C-6, C-7a corresponds to C-7, C-8a corresponds to C-8, C-9a Corresponds to C-9, C-10a corresponds to C-10, C-11a corresponds to C-11, C-12a corresponds to C-12, C-13a corresponds to C-13 , C-14a corresponds to C-14, C-15a corresponds to C-15, C-16a corresponds to C-16, and C-17a corresponds to C-17.

各試験品は、直径３０ｍｍ、長さ３０ｍｍの中実体とした。各試験品を９００℃で１時間保持した後、直ちに自然空冷し、試験品の中心付近の硬度を測定した。その結果、表３に示す結果を得た。実施品の硬度は２３≦ＨＲＣ≦３０の範囲にある。一方、比較品はＣ−１６ａを除きＨＲＣ２３未満である。ここで、合金元素Ｃ、Ｓｉ、Ｍｎ、Ｖの各量を従属変数とし、硬度を目的変数として重回帰分析を行った結果、前記数１の式を得た。表３中に示した硬度の予測値とは、各合金成分量を数１の式に代入して求めた値である。図３に硬度の実測値と予測値の関係を示すように、両者にはよい相関が見られる。すなわち、合金成分量がわかれば、素材硬度を高精度で予測可能であることを意味している。したがって、今回の実施品の合金成分Ｃ、Ｓｉ、Ｍｎ、Ｖの構成だけでなく、前記数１の式から求まる硬度の予測値が２３≦ＨＲＣ≦３０の条件を満たすような構成であればよいといえる。

Each test article was solid with a diameter of 30 mm and a length of 30 mm. Each test specimen was held at 900 ° C. for 1 hour, and then immediately cooled with natural air, and the hardness near the center of the specimen was measured. As a result, the results shown in Table 3 were obtained. The hardness of the product is in the range of 23 ≦ HRC ≦ 30. On the other hand, comparative products are less than HRC23 except for C-16a. Here, as a result of performing multiple regression analysis using the respective amounts of the alloy elements C, Si, Mn, and V as dependent variables and the hardness as an objective variable, the above equation 1 was obtained. The predicted value of hardness shown in Table 3 is a value obtained by substituting each alloy component amount into the formula (1). As shown in FIG. 3 showing the relationship between the actually measured value of hardness and the predicted value, there is a good correlation between the two. That is, if the alloy component amount is known, it means that the material hardness can be predicted with high accuracy. Therefore, not only the structure of the alloy components C, Si, Mn, and V of the present embodiment product but also the structure in which the predicted value of hardness obtained from the formula 1 satisfies the condition of 23 ≦ HRC ≦ 30. It can be said.

It is a longitudinal cross-sectional view of the fixed type constant velocity universal joint which shows embodiment of this invention. It is the sectional view on the AA line of the said FIG. It is a graph which shows the relationship between the measured value of hardness, and a predicted value. It is a longitudinal cross-sectional view of the conventional fixed type constant velocity universal joint.

Explanation of symbols

22 Track groove

Claims (2)

  In a fixed type constant velocity universal joint having an outer joint member formed with a track groove for rolling a torque transmission member and allowing only angular displacement between two axes, C: 0.45 to 0.65 wt% as an alloy element , Si: 0.1 to 1.0 wt%, Mn: 0.1 to 1.5 wt%, V: 0.05 to 0.3 wt% within the respective ranges, the balance from Fe and inevitable impurities A fixed type constant velocity universal joint characterized in that a steel material is used for at least the outer joint member.   2. The fixed type constant velocity universal joint according to claim 1, wherein a predicted value of the hardness of the outer joint member based on the alloy component amount is 23 ≦ HRC ≦ 30.

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