WO2007125844A1

WO2007125844A1 - Constant velocity universal joint

Info

Publication number: WO2007125844A1
Application number: PCT/JP2007/058698
Authority: WO
Inventors: Kisao Yamazaki; Shintaro Suzuki
Original assignee: Ntn Corporation
Priority date: 2006-04-27
Filing date: 2007-04-23
Publication date: 2007-11-08
Also published as: JP2007298058A

Abstract

A constant velocity universal joint that allows skipping of any grinding operation for intergranular oxide layer to thereby attain cost reduction, and that excels in strength and enables prolongation of rolling life duration (life duration of track groove). There is provided a constant velocity universal joint wherein forge finished hardened layer (35) of 1 μm or less intergranular oxide layer is disposed on at least the surface of track groove (25) of inside joint member.

Description

Specification

Constant velocity universal joint

Technical field

[0001] The present invention relates to a fixed or sliding constant velocity universal joint used in a power transmission system of an automobile or various industrial machines, for example, incorporated in a drive shaft or a propeller shaft used in a 4WD vehicle or an FR vehicle. .

Background art

[0002] For example, a fixed type constant velocity universal joint (Tweeper type constant velocity universal joint: BJ) used as a coupling joint for an automobile drive shaft or the like has a plurality of inner surfaces 1 as shown in FIG. The outer ring 3 as an outer joint member in which the track grooves 2 are formed along the axial direction at equal intervals in the circumferential direction, and a plurality of track grooves 5 paired with the track grooves 2 of the outer ring 3 on the outer diameter surface 4 are circumferential. An inner ring 6 as an inner joint member formed along the axial direction at equal intervals in the direction, and a plurality of balls 7 interposed between the track groove 2 of the outer ring 3 and the track groove 5 of the inner ring 6 to transmit torque. And a cage 8 for holding the ball 7 interposed between the inner diameter surface 1 of the outer ring 3 and the outer diameter surface 4 of the inner ring 6.

Further, a spline portion 9 is provided on the inner peripheral surface of the center hole of the inner ring 6, and the spline portion 11 of the shaft 10 inserted into the center hole of the inner ring 6 is engaged. A concave circumferential groove 12 is formed at the end of the spline portion 11 of the shaft 10, and a retaining ring 13 for retaining the shaft is fitted into the concave circumferential groove 12.

[0004] The track groove 2 of the outer ring 3 has its center of curvature O shifted to the opening side of the outer ring 3 in the axial direction of the joint center O force, and the track groove 5 of the inner ring 6 has its center of curvature O of the joint center O force axis. Direction

2

Are provided at an equal distance f on the far side opposite to the center of curvature O of the track groove 2 of the outer ring 3.

[0005] The inner ring 6 used in such a constant velocity universal joint has a hardened layer formed on the surface thereof. This hardened layer is generally formed by carburizing and quenching. Carburizing and quenching is a heat treatment technique suitable for a relatively complicated shape such as the inner ring 6. However, it takes time to carburize, so the productivity is bad. In carburizing and quenching, The deeper the carburized hardened layer depth, the longer the processing time and the higher the cost. For this reason, when forming a deep carburized layer required for large inner rings, there are significant disadvantages in terms of cycle time and cost. Here, the cycle time is the time from the start to the end of a job, and includes not only the operation time but also the waiting time. In other words, if carburizing was performed, it took time for the heat treatment, and it was difficult to in-line due to the batch processing of the furnace.

Further, when carburizing and quenching is performed, crystal grain boundaries are clearly formed as shown in FIG. Here, a crystal grain boundary is an interface between crystals, and eutectic having a low melting point is likely to collect impurities, and therefore, is more easily corroded than other parts, resulting in grain boundary oxidation. In other words, the power of gas carburizing is known as a carburizing method. The gas used in this process contains trace amounts of oxidizing components such as H 2 O and CO. Therefore, during carburizing

twenty two

At the austenite grain boundary, Cr, Mn, etc., which has a higher affinity for oxygen than Fe, are preferentially oxidized, and Cr, Mn, etc. within the grain boundary are also diffused and oxidized at the grain boundary, so the alloy elements on the surface part Decreases and grain boundary acid is generated. When grain boundary oxidation occurs, the hardenability deteriorates, and a hardened layer with the required hardness cannot be obtained, and the rolling life is reduced due to the notch effect due to the oxide.

[0007] For this reason, in the constant velocity universal joint, if a grain boundary oxide layer is formed in the hardened layer of the track groove to form a grain boundary oxide layer, the rolling life (track groove life) is reduced. Therefore, it was necessary to remove the grain boundary acid layer. However, if this grain boundary oxide layer is removed by grinding or the like, the thin hardened layer will be scraped off, so that the hardened layer will be thicker in anticipation of processing allowance. It is necessary to extend the carburizing time. Moreover, the additional cost of the grinding process increases the cost!

[0008] Therefore, in recent years, there is one in which a hardened layer is formed by induction hardening (Patent Document 1). Here, induction hardening means that an induction current is generated in the surface portion of the derivative (a body to be processed) by flowing a high frequency to generate heat, and the surface of the object to be processed is rapidly heated by this heat for quenching. How to do it. In the device described in Patent Document 1, the fatigue strength is improved by utilizing the property that the hardened layer depth of high-frequency quenching can be controlled relatively freely. That is, the thickness of the hardened layer is different between the thin portion and the non-thin portion, and the thin layer-side hardened layer is made thinner than the non-thin portion. Is.

[0009] For this reason, in the device described in Patent Document 1, the balance of the ratio between the hardened layer and the non-hardened layer in the thin portion is maintained, the toughness of the thin portion is improved, and the torque transmission ball is rotated. It is intended to improve fatigue strength against repeated tensile stress caused by motion.

Patent Document 1: Japanese Patent Laid-Open No. 2000-227123

Disclosure of the invention

Problems to be solved by the invention

[0010] However, in the above-mentioned Patent Document 1, the properties of the formed hardened layer and the like are not known in the formed hardened layer, which does not describe the grain boundary oxide layer and the crystal grain boundary. For this reason

In some cases, it is necessary to perform finishing such as grinding after induction hardening.

[0011] In view of the above-mentioned problems, the present invention can reduce the cost by reducing the grinding process of the grain boundary acid layer, and has excellent strength and rolling life (track groove life). Provide a constant velocity universal joint that can be extended.

Means for solving the problem

[0012] The constant velocity universal joint of the present invention includes an outer joint member having a plurality of track grooves formed on the inner diameter surface, an inner joint member having a plurality of track grooves formed on the outer diameter surface, and the outer joint member. A plurality of balls that are interposed between the track groove and the track groove of the inner joint member and transmit torque, and a ball that is interposed between the inner diameter surface of the outer joint member and the outer diameter surface of the inner joint member. A constant velocity universal joint provided with a holding cage is provided with a forged finish hardened layer having a grain boundary oxide layer of 1 μm or less on at least the surface of the track groove of the inner joint member. Here, the forged finish hardened layer is a surface layer that leaves the forged skin as it is, and is a layer that is not subjected to a finishing force such as grinding.

[0013] In the constant velocity universal joint of the present invention, since the grain boundary acid layer of the hardened layer is 1 m or less, the rolling life can be reduced without removing the grain boundary acid layer. rare.

[0014] The hardened layer is an induction-hardened hardened layer formed on the groove surface of the track groove and the outer diameter surface of the inner joint member between the track grooves. It was clear. [0015] The inner joint member is preferably made of steel containing 0.4 wt% or more of carbon. The invention's effect

[0016] In the present invention, it is not necessary to perform grinding or the like to remove the grain boundary oxide layer, so that productivity can be improved and costs can be reduced. In addition, since there is no grain boundary oxide layer, there is no decrease in rolling life, and a constant velocity universal joint with excellent durability can be achieved, resulting in a long life.

[0017] Since the prior austenite grain boundaries in the surface portion of the hardened layer are obscured, grain boundary oxidation and corrosion can be prevented, and the life can be further increased. In addition, induction hardening has the advantage that cycle time can be reduced compared to carburizing and quenching.

BEST MODE FOR CARRYING OUT THE INVENTION

[0018] An embodiment of a constant velocity universal joint according to the present invention will be described with reference to Figs.

As shown in FIG. 1, the constant velocity universal joint includes an outer ring 23 as an outer joint member in which a plurality of track grooves 22 are formed on the inner diameter surface 21 at equal intervals in the circumferential direction along the axial direction. 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 outer diameter surface 24 along the axial direction at equal intervals in the circumferential direction, and the track grooves 22 of the outer ring 23 Between the inner ring 26 and the track groove 25 of the inner ring 26 to transmit torque, and between the inner diameter surface 21 of the outer ring 23 and the outer diameter surface 24 of the inner ring 26, Holding cage 28. The ball 27 is held in the pocket 28a of the cage 28.

Further, a spline portion 29 is provided on the inner peripheral surface of the center hole 34 of the inner ring 26, and the spline portion 31 of the shaft 30 inserted into the center hole of the inner ring 26 is engaged. A concave circumferential groove 32 is formed at the end of the spline portion 31 of the shaft 30, and a retaining ring 33 for retaining the shaft is fitted into the concave circumferential groove 32.

[0021] The track groove 22 of the outer ring 23 has its center of curvature O shifted from the joint center O in the axial direction to the opening side of the outer ring 23, and the track groove 25 of the inner ring 26 has its center of curvature O away from the joint center O.

2

In the axial direction, the outer ring 23 is provided at an equal distance f on the back side opposite to the center of curvature O of the track groove 22 of the outer ring 23.

Then, as shown in FIGS. 2 and 3, a forged finish hardened layer 35 is formed on the entire outer peripheral surface of the inner ring 26. In this case, use steel containing 0.4 wt% or more of carbon for the inner ring 26. The track grooves 25 are formed by forging (cold forging), and then induction hardening is performed on the entire outer periphery of the inner ring 26. Therefore, a forged finish hardened layer 35 is formed on at least the surface of the track groove 25 of the inner ring 26. In other words, the forged finish hardened layer is a surface layer that leaves the forged skin as it is, and is a layer that is not subjected to finishing such as grinding. Here, induction hardening means that an induction current is generated on the surface portion of the derivative (workpiece) by flowing a high frequency to generate heat, and the surface of the work piece is rapidly heated by this heat for quenching. Is the method. In this case, the high-frequency heating temperature is preferably 900 ° C or higher and 1100 ° C or lower. In FIG. 3, the illustration of the spline portion 29 formed in the center hole 34 of the inner ring 26 is omitted.

In this case, the grain boundary oxide layer of the hardened layer 35 to be formed is 1 m or less by this induction hardening. It is possible to set the heating temperature as described above in order to make the grain boundary oxide layer: L m or less. The thickness of the hardened layer 35 varies depending on internal dimensions such as the ball diameter and track PCD diameter used in the constant velocity universal joint.

[0024] Further, the surface portion of the hardened layer 35 is subjected to induction hardening as described above, so that the prior austenite grain boundaries do not appear clearly and become unclear as shown in FIG.

[0025] According to the present invention, since the grain boundary oxide layer of the hardened layer is 1 µm or less, the rolling life is not reduced even in this state. For this reason, it is not necessary to perform a grinding process for removing the grain boundary oxide layer, and it is possible to improve productivity and reduce costs. If the grain boundary oxide layer exceeds: m, the rolling life (the groove life of the track groove) may be reduced unless the grain boundary oxide layer is removed.

[0026] Further, since the prior austenite crystal grain boundaries in the surface portion of the hardened layer 35 are obscured, the grain boundary oxidation and corrosion can be prevented, and the lifetime can be further increased. In addition, induction hardening can reduce cycle time compared to carburizing and quenching.

[0027] In particular, steel containing 0.4 wt% or more of carbon is an optimal material for induction hardening that can suppress the grain boundary oxide layer to 1 μm or less. The forged finish hardened layer 35 having a grain boundary oxide layer of 1 m or less can be reliably formed.

As described above, the embodiment of the present invention has been described. However, the present invention is not limited to the embodiment, and various modifications are possible. For example, in the embodiment, the track groove of the inner ring 26 The hardened layer 35 is formed on the groove surface of 25 and the outer diameter surface of the inner ring 26 (outer diameter surface other than the track groove 25), but the hardened layer 35 may be formed at least on the groove surface of the track groove 25. This is also the force by which the ball 27 rolls in the track groove 25.

[0029] As the constant velocity universal joint, in the above embodiment, the force exemplified by the fixed type (Tweeper type) constant velocity universal joint (BJ) Other constant velocity universal joints, for example, the fixed type (undercut free type) constant velocity It may be a universal joint (UJ), sliding (cross group type) constant velocity universal joint (LJ), sliding type (double offset type) constant velocity universal joint (DOJ), etc.

Brief Description of Drawings

FIG. 1 is a cross-sectional view of a main part of a constant velocity universal joint showing an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of an inner ring of the constant velocity universal joint.

FIG. 3 is a cross-sectional view of the constant velocity universal joint.

FIG. 4 is an enlarged view of a hardened layer when induction hardening is performed.

FIG. 5 is an enlarged view of a hardened layer when carburizing and quenching is performed.

FIG. 6 is a cross-sectional view of a main part of a conventional constant velocity universal joint.

Claims

The scope of the claims

[1] An outer joint member having a plurality of track grooves formed on the inner diameter surface, an inner joint member having a plurality of track grooves formed on the outer diameter surface, a track groove of the outer joint member, and a track groove of the inner joint member And a cage for holding the balls interposed between the inner diameter surface of the outer joint member and the outer diameter surface of the inner joint member. In the joint,

A constant velocity universal joint characterized in that at least the surface of the track groove of the inner joint member is provided with a forged finish hardened layer having a grain boundary oxide layer of: m or less.

[2] The hardened layer is an induction-hardened hardened layer formed on the groove surface of the track groove and the outer diameter surface of the inner joint member between the track grooves, and the former austenite crystal grain boundary on the surface portion of the hardened layer is removed. 2. The constant velocity universal joint according to claim 1, wherein the constant velocity universal joint is obscure.

[3] The constant velocity universal joint according to claim 1 or 2, wherein the inner joint member is steel containing carbon of 0.4 wt% or more.