JP2008304006A - Fixed type constant velocity universal joint and its outer ring manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixed type constant velocity universal joint having further lighter weight and compacter figure while maintaining basic performance. <P>SOLUTION: The fixed type constant velocity universal joint comprises an outer ring 10 having ball grooves 16 formed in a spherical inner peripheral face 14 at circumferential equal spaces, extending in the axial direction, an inner ring 20 having ball grooves 26 formed in a spherical outer peripheral face 24 at circumferential equal spaces, extending in the axial direction, balls 30 laid between the ball groove 16 of the outer ring and the ball groove 26 of the inner ring, paired with each other, and a cage 40 having pockets 46 formed at circumferential predetermined spaces to store the balls 30. The outer ring 10 is manufactured by cold forging and subjected to tempering treatment. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fixed type constant velocity universal joint and a method for manufacturing the outer ring thereof.

  Constant velocity universal joints used for power transmission devices of automobiles and various industrial machines can be roughly classified into fixed types and sliding types. A sliding type constant velocity universal joint can be displaced not only in an angular displacement but also in an axial direction (plunging), whereas a fixed type constant velocity universal joint can only be angularly displaced, for example, on the wheel side of a drive shaft of an automobile. Used for (outboard side).

  As shown in FIGS. 2 to 4, the main components of the fixed type constant velocity universal joint are an outer ring 10, an inner ring 20, a ball 30, and a cage 40. Elements have been proposed to be smaller and lighter. FIG. 3 shows a fixed type constant velocity universal joint that is lighter and more compact than the fixed type constant velocity universal joint of FIG.

The lighter and more compact fixed type constant velocity universal joint contributes to improving the fuel efficiency of automobiles and the flexibility of drivetrain layout. Therefore, it is desirable to make the fixed type constant velocity universal joint as small as possible while satisfying the required performance. Conventionally, the following proposals have been made to reduce the weight while maintaining the performance of the fixed type constant velocity universal joint.
(1) A special material is used as a measure for fatigue strength (Patent Document 1).
(2) Perform shot peening to improve fatigue strength (Patent Document 2).
(3) A tempering treatment is performed before cold forging to make the material structure uniform, and dimensional accuracy after cold end fabrication and variations in heat treatment are improved. Due to the effect of the tempering treatment, fracture ductility, yield strength, and toughness are improved (Patent Document 3).
JP-A-2005-60724 JP-A-4-104418 JP-A-10-148216

  The outer ring of the fixed type constant velocity universal joint is generally manufactured by cold forging from the viewpoint of cost. As a material for the outer ring, medium carbon steel for machine structure is often adopted from the viewpoint of ease of forging, machinability, heat treatment, economy, strength, and the like. As the fixed constant velocity universal joint becomes lighter and more compact, the outer ring is also thinner. For this reason, the mechanical strength of the outer ring itself is approaching the fatigue limit of medium carbon steel, which is a material, and it has become difficult to further reduce the size and weight.

  As a means for improving the strength, the above proposal (1) uses a special material, which makes it difficult to procure when manufacturing factories are developing globally. Moreover, since an alloy is added to the material, the material cost increases, the workability and cutting performance of cold forging deteriorate, the die life and tool life decrease, and the manufacturing cost increases.

  Even in the proposal (2), the process is increased by adding the shot peening process, and the manufacturing cost is increased. Although effective for fatigue strength, the fracture ductility is not improved, and therefore static failure strength is not improved when the thickness is reduced by compactification.

  In Proposal (3), it is expected that the die life in cold forging may be reduced and forging cracks may occur due to the hardness of the tempering treatment after sub-hot forging.

  Further, when torque is input to the fixed type constant velocity universal joint at an operating angle, the load applied to the track changes depending on the phase. FIG. 5 shows the relationship between the phase angle and the track load in the case of 6 balls. Basically, the same tendency is observed even if the number of balls changes, and the load on the track increases as the operating angle increases. Therefore, when a large torque is instantaneously input, a load is received relatively evenly on each track when the operating angle is small, but the load varies greatly depending on the track when the operating angle increases.

  Since the stress concentrates on a track that receives a heavy load, the strength increases when the tensile strength of the material is improved. In addition, when the operating angle is large and the torque is input for a long time, each track has a phase that receives a large load and a phase that does not receive a load. Cause.

  Accordingly, an object of the present invention is to enable further weight reduction and compactness while maintaining the basic performance of the fixed type constant velocity universal joint.

  The fixed type constant velocity universal joint of the present invention includes an outer ring in which ball grooves extending in the axial direction are formed on the spherical inner peripheral surface at equal intervals in the circumferential direction, and a ball groove extending in the axial direction on the spherical outer peripheral surface. An inner ring formed at equal intervals in the circumferential direction, a ball interposed between a ball groove of a pair of outer rings and a ball groove of the inner ring, and a pocket for accommodating the balls are formed at predetermined intervals in the circumferential direction. The outer ring is manufactured by cold forging and is tempered (Claim 1).

  Here, the core part of the outer ring means a part excluding the spherical inner peripheral surface of the outer ring, the ball groove, and the hardened surface layer formed on the stem part (Claim 5). Since the inner peripheral surface of the outer ring is in spherical contact with the cage, the ball groove is the rolling surface of the ball, and the stem portion is a portion that fits serrations (or splines, the same applies hereinafter). A surface hardened layer is formed by applying a heat treatment comprising quenching and tempering.

It is preferable that the hardness of the core portion of the outer ring is set to Vickers hardness HV320 or more by the tempering treatment (Claim 2).
The tempering is a kind of tempering, and after cold forging, it is heated to 800 to 900 ° C. and then rapidly cooled, and reheated to 450 to 650 ° C. to obtain a desired tempered structure (Claim 3). . Specifically, when the iron metal structure is made sorbite or troostite by tempering treatment, the iron metal structure has to be martensite once, and therefore, the steel is heated to 800 to 900 ° C. where martensitic transformation occurs. And it cools from 450-650 degreeC in order to temper and to make a sorbite structure after rapid cooling.
In addition, the material becomes hard in the tempering before cold forging, and there is a possibility of forging die life and molding cracking, whereas in the tempering treatment after cold forging, the conventional cold forging process becomes possible, It is not necessary to change the equipment and mold in consideration of the mold life.

  Since the heat treatment as described above is performed, a medium carbon steel containing 0.40 to 0.60 wt% of carbon is preferable as the material of the outer ring. This carbon content range corresponds to S48C to S55C in carbon steel for machine structures generally used for constant velocity universal joints. If the amount of carbon is lower than this range, it is not possible to sufficiently quench the part that requires hardness, and conversely if the amount of carbon is higher than this range, the forging formability and workability deteriorate, and the cost increases. It tends to lead to processing defects.

  The method of manufacturing the outer ring of the fixed type constant velocity universal joint of the present invention is to perform preforming from a steel material to a substantially predetermined dimension by sub-hot forging or warm forging, and after finish forming by cold forging, tempering treatment is performed. (Claim 6).

  According to the present invention, the core portion of the outer ring subjected to the tempering treatment has a troustite or sorbite structure in which carbides are spheroidized, and is refined and increased in hardness compared to the ferrite pearlite structure of the material before tempering. is doing. Therefore, the tensile strength of the outer ring is improved and the breaking strength is improved. Even when repeated stress is input, the fatigue strength is improved by the increase in the strength of the core and the refinement of the structure. As a result of improving the strength of the outer ring in this way, it becomes possible to reduce the wall thickness of the outer ring compared to the cold forged outer ring, and it is possible to further reduce the weight and size compared to conventional fixed type constant velocity universal joints. Can be achieved.

Embodiments of the present invention will be described below with reference to the drawings.
First, the basic configuration of the fixed type constant velocity universal joint will be described. As shown in FIGS. 2 to 4, the fixed type constant velocity universal joint includes an outer ring 10 as an outer joint member, an inner ring 20 as an inner joint member, a ball 30 as a torque transmission element, and a cage for holding the ball. 40 is a main component.

  The outer ring 10 includes a mouse portion 12 and a stem portion 18, and is connected to one of two shafts to be coupled by a spline (or serration, hereinafter the same) shaft portion of the stem portion 18 so that torque can be transmitted. ing. Here, the mouth portion 12 is bell-shaped and has a spherical inner peripheral surface 14, and ball grooves 16 extending in the axial direction are formed at equal intervals in the circumferential direction of the spherical inner peripheral surface 14.

  The inner ring 20 is connected to the other of the two shafts to be coupled by a spline hole 22 formed in the shaft center portion so as to be able to transmit torque. The inner ring 20 has a spherical outer peripheral surface 24, and ball grooves 26 extending in the axial direction are formed at equal intervals in the circumferential direction of the spherical outer peripheral surface 24.

  The ball groove 16 of the outer ring 10 and the ball groove 26 of the inner ring 20 form a pair, and one ball 30 is incorporated between each pair of ball grooves 16 and 26. All the balls 30 are held in the same plane by the cage 40. In general, six or eight balls 30 are used, but the number of balls is not particularly limited here.

  The cage 40 is interposed between the inner peripheral surface 14 of the outer ring 10 and the outer peripheral surface 24 of the inner ring 20. The outer peripheral surface 42 of the cage 40 is in spherical contact with the inner peripheral surface 14 of the outer ring 10, and the inner peripheral surface 44 of the cage 40 is in spherical contact with the outer peripheral surface 24 of the inner ring 20. In the cage 40, pockets 46 for accommodating the balls 30 are formed at predetermined intervals in the circumferential direction.

  The center of the ball groove 16 of the outer ring 10 and the center of the ball groove 26 of the inner ring 20 are offset in the axial direction by equal distances from the joint center in opposite directions. Therefore, the ball track formed by the ball groove 16 of the outer ring 10 and the ball groove 26 of the inner ring 20 that form a pair has a wedge shape that becomes gradually narrower from one to the other in the axial direction. When the joint takes an operating angle, the ball 30 is held in the biaxial bisector, and the lengths of the perpendiculars extending from the center of the ball 30 to the respective axes become equal. Therefore, the two axes always rotate at an equiangular speed.

  As the material of the outer ring 10, medium carbon steel containing 0.40 to 0.60 wt% of carbon is adopted, and as a method for manufacturing the outer ring 10, cold forging is adopted. Then, a hardened surface layer is formed on the spherical inner peripheral surface 14, the ball groove 16, and the stem portion 18 by an induction heat treatment including normal induction hardening and tempering. The inner peripheral surface 14 becomes a spherical fitting portion with the cage 40, the ball groove 16 becomes a rolling surface of the ball 30, and the stem portion 18 becomes a spline fitting portion with the hub wheel. The site is the main organization, ensuring the rolling durability of the ball rolling surface, the durability against scuffing of the cage fitting, the strength and durability of the spline fitting, and the stem strength.

  Prior to the above-described high-frequency heat treatment, the following tempering treatment is performed, and the portion where the surface hardened layer is not formed is referred to as a core portion. FIG. 1 is a partially broken cross section of the outer ring 10. A narrow parallel oblique line indicates a hardened surface layer, and a wide parallel oblique line indicates a core part.

  In the case of cold forging, the forging finish is usually left, but turning may be further performed if machining accuracy is required. The tempering process may be performed before the turning process, or the tempering process may be performed after the turning process in consideration of ease of processing.

  By the tempering treatment, the structure of the outer ring 10 is changed from a general structure mixed with ferrite to a troostite or sorbite structure, the structure is refined and the hardness is increased. Specifically, the hardness of the outer ring manufactured by cold forging is about Vickers hardness HV270 to 340, but the hardness is set to HV320 or more by applying a tempering treatment.

The tempering process is a kind of tempering, which is heated to 800 to 900 ° C., then rapidly cooled (quenched), and reheated to 450 to 650 ° C. (tempered) to obtain a desired tempered structure.
A specific example of the tempering process is as follows.
Quenching is performed in a batch-type quenching furnace at a quenching temperature of 850 ° C. for about 1.5 hours, and then rapidly cooled using a cooling liquid (eg, Cosmo Quench A212). The furnace atmosphere is CP (carbon potential) 0.5%.
Tempering is carried out in a tempering furnace at a tempering temperature of 500 to 550 ° C. for about 2 hours and then air-cooled.

  The structure of the tempered outer ring 10 becomes troostite or sorbite and is refined, and the hardness is further increased, so that the tensile strength of the outer ring 10 is improved and the breakage strength is improved. In addition, the fatigue strength can be improved by increasing the strength and refining the structure against repeated stress.

  The outer ring 10 that has been subjected to the tempering treatment is subjected to high-frequency heat treatment. That is, as already described, the inner peripheral surface 14 in contact with the cage 40, the ball groove 16 in contact with the ball 30, and the stem portion 18 are subjected to induction hardening locally to form a surface hardened layer made of a martensite structure. Let it form.

  The undercut-free type constant velocity universal joint (UJ) has been described as an example, but the present invention can also be applied to other constant velocity universal joints such as a barfield type (BJ).

It is a partially broken front view of the outer ring of a fixed type constant velocity universal joint. It is a longitudinal cross-sectional view of a general fixed type constant velocity universal joint. It is a longitudinal section of a fixed type constant velocity universal joint made compact. It is an end view of a fixed type constant velocity universal joint. It is a diagram which shows the relationship between a phase angle and a track load.

Explanation of symbols

10 Outer ring (outer joint member)
12 Mouse part 14 Inner peripheral surface 16 Ball groove 18 Stem part 20 Inner ring (inner joint member)
22 spline hole 24 outer peripheral surface 26 ball groove 30 ball (torque transmission element)
40 Cage 42 Outer peripheral surface 44 Inner peripheral surface 46 Pocket

Claims (6)

An outer ring in which ball grooves extending in the axial direction are formed at equal intervals in the circumferential direction on a spherical inner peripheral surface;
An inner ring in which ball grooves extending in the axial direction are formed at equal intervals in the circumferential direction on a spherical outer peripheral surface;
A ball interposed between the ball groove of the outer ring and the ball groove of the inner ring,
A fixed type constant velocity universal joint having a cage for accommodating balls to be formed at predetermined intervals in the circumferential direction, wherein the outer ring is manufactured by cold forging and is subjected to a tempering treatment.   The fixed constant velocity universal joint according to claim 1, wherein the hardness of the core portion of the outer ring is HV320 or more.   The fixed constant velocity universal joint according to claim 1 or 2, wherein the tempering treatment is performed at a quenching temperature of 800 to 900 ° C and a tempering temperature of 450 to 650 ° C.   The fixed outer constant velocity universal joint according to any one of claims 1 to 3, wherein the outer ring is made of medium carbon steel containing 0.40 to 0.60 wt% of carbon.   The fixed type constant velocity universal joint according to claim 4, wherein a locally hardened layer is formed on the inner peripheral surface of the outer ring, the ball groove, and the stem portion.   In manufacturing the outer ring of the fixed type constant velocity universal joint according to claim 1, after pre-forming from steel material to approximately a predetermined size by sub-hot forging or warm forging, and after finish forming by cold forging, tempering treatment A method for manufacturing an outer ring of a fixed type constant velocity universal joint.

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