JP2008298270A - Fixed type constant velocity universal joint - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To give the strength of more than the same as that a cold forging article to an outer ring of a fixed type constant velocity universal joint manufactured by hot forging and cutting without changing its shape. <P>SOLUTION: This fixed type constant velocity universal joint has: an outer ring 10 forming ball grooves 16 extending in the axial direction on a spherical inner peripheral surface 14 with constant intervals in the circumferential direction; an inner ring 20 forming ball grooves 26 extending in the axial direction on a spherical outer peripheral surface 24 with constant intervals in the circumferential direction; balls 30 interposed between the ball grooves 16 of the outer ring and the ball grooves 26 of the inner ring making pairs; and a cage 40 forming pockets 46 to store the balls 30 with prescribed intervals in the circumferential direction. The outer ring 10 is manufactured by cold forging or cutting and is subjected to a refining process. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fixed type constant velocity universal joint, and can be used for a power transmission device of an automobile or various industrial machines.

  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).

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 that the fixed type constant velocity universal joint satisfies the required performance and is made as small as possible. 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. Element size and weight reduction have been proposed (see, for example, Patent Document 1 and Patent Document 2). 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.
Japanese Patent No. 3460107 JP-A-9-317784

Conventionally, the outer ring of a 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.
On the other hand, in the case of fixed type constant velocity universal joints used in automobile drive shafts, the shape of the outer ring varies depending on the vehicle model. Depending on the number of products produced, the cost of cold forging (die cost and forging equipment costs) is taken into account. In some cases, it is manufactured by hot forging, which can share several types of outer ring shapes, or by turning from a bar material such as round steel bar by turning.

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.
When the strength of a fixed type constant velocity universal joint is evaluated by using a hot forged product or turning product on the outer ring of such a compact fixed type constant velocity universal joint, a cold forged product is used. It tends to be slightly weaker than that. The reason is considered as follows. That is, the cold forged product has a fine structure due to the effect of cold working, the hardness of the material is increased by work hardening, and there is no metal flow cutting. Therefore, the tensile strength of the outer ring material is improved, and the strength is higher than that of a hot forged product or a turned product from a steel bar.

  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 provide an outer ring of a fixed type constant velocity universal joint manufactured by hot forging or turning to have a strength equal to or higher than that of a cold forged product without changing its shape.

  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 hot forging and tempered (Claim 1).

  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 extending in the axial direction on the spherical outer peripheral surface. An inner ring having grooves formed at equal intervals in the circumferential direction, a ball interposed between a pair of outer ring ball grooves and a ball groove of the inner ring, and pockets for containing the balls at predetermined intervals in the circumferential direction. And the outer ring is manufactured from a steel bar by turning and is tempered (Claim 2).

  It is preferable that the hardness of the core portion of the outer ring is HV 270 to 350 by the tempering treatment (Claim 3). When the hardness of the core part is less than HV270, the strength is reduced as compared with the cold forged product. If it exceeds HV350, the strength increases, but there is a problem that thermal deformation increases. The fatigue strength of the fixed type constant velocity universal joint is improved by increasing the material hardness and making the structure finer. The material hardness of the hot forged outer ring and turning outer ring is increased, and the tempering treatment is performed to refine the structure, and the structure of the core part is refined with troostite or sorbite to increase the hardness of the material.

  Here, the core part of the outer ring means a part excluding the hardened surface layer (Claim 6) formed on the inner peripheral surface of the outer ring, the ball groove, and the stem part. Since the ball groove is a rolling surface of the ball, the inner peripheral surface is in spherical contact with the cage, and the stem portion is a portion that fits serrations (or splines, the same applies hereinafter). A surface hardened layer is formed by performing a heat treatment comprising tempering.

  The tempering process is a kind of tempering, and after heating to 800 to 900 ° C, it is rapidly cooled and reheated to 450 to 650 ° C to obtain a desired tempered structure (claim 4). 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.

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 (Claim 5). 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.

According to the present invention, the core of the outer ring subjected to the tempering treatment (the part not subjected to high-frequency heat treatment) becomes a troostite or sorbite structure and is refined, and the hardness is further increased. The tensile strength of the part is improved and the breaking strength is improved.
Even when a repeated stress is input, the fatigue strength is improved by increasing the strength of the core and refining the structure.
Thus, the same strength as a fixed type constant velocity universal joint using an outer ring manufactured by cold forging can be obtained.
Therefore, in this invention, because the number of production is small, considering the cost, the outer ring must be manufactured by hot forging or turning. Thus, it is particularly suitable for a fixed type constant velocity universal joint that can be manufactured only by hot forging or turning.

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 the two shafts to be connected by a serration (or spline, 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 serration 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. Accordingly, the 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 side to the other side 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 the manufacturing method of the outer ring 10, hot forging or turning is adopted. In any case, a hardened surface layer is formed on the inner peripheral surface 14, the ball groove 16, and the stem portion 18 by an induction heat treatment including normal induction hardening and tempering. Since the ball groove 16 becomes a rolling surface of the ball 30, the inner peripheral surface 14 becomes a spherical fitting portion with the cage 40, and the stem portion 18 becomes a spline fitting portion with the hub wheel, therefore, high-frequency heat treatment is performed, The rolling durability of the running surface, the durability against rubbing of the cage fitting, the strength and durability of the spline fitting, and the stem strength are ensured.

  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 hot forging, the forging finish is usually left, but if machining accuracy is required, further turning may be performed. Although this turning is performed after the tempering treatment, the turning may be performed before the tempering treatment in consideration of the ease of machining.

  The hardness of the core portion of the outer ring manufactured by cold forging is about Vickers hardness HV270-340. On the other hand, in the outer ring manufactured by hot forging or turning, the hardness of the core part is about HV180 to 250. Therefore, the hardness of the core part is equal to or higher than that of the cold forging outer ring by tempering treatment, for example, HV270 to 350. . By the tempering treatment, the structure of the core portion of the outer ring 10 is changed from a general structure mixed with ferrite to a troostite or sorbite structure to refine the structure and increase the hardness.

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, a hardened surface layer is locally formed on 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.

  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 fixed type 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 Serration 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 in which pockets for accommodating balls are formed at predetermined intervals in the circumferential direction, and wherein the outer ring is manufactured by hot forging and subjected to a tempering treatment. 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 in which pockets for accommodating balls are formed at predetermined intervals in the circumferential direction, wherein the outer ring is manufactured by turning from steel bar and is subjected to a tempering treatment.   The fixed constant velocity universal joint according to claim 1 or 2, wherein the hardness of the core portion of the outer ring is HV270 to 350.   The fixed constant velocity universal joint according to claim 3, 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 4, wherein the outer ring is made of medium carbon steel containing carbon of 0.40 to 0.60 wt%. The fixed constant velocity universal joint according to claim 5, wherein a locally hardened layer is formed on the inner peripheral surface of the outer ring, the ball groove, and the stem portion.

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