JP2000234141A - Power transmission shaft - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the strength of a power transmission shaft and to attain its lightening. SOLUTION: A power transmission shaft 12 is formed by subjecting carbon steel to induction hardening at 0.25 to 0.50 quench-hardening ratio. As the carbon steel, the one having a compsn. contg., as fundamental components, by weight, 0.39 to 0.49% C, 0.4 to 1.5% Si, 0.4 to 1.0% Mn, <=0.025% S, <=0.02% P and 0.01 to 0.1% Al, and the balance Fe with inevitable impurities is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power transmission shaft used for transmitting torque in automobiles and industrial machines, and more particularly to a power transmission shaft used for a constant velocity universal joint.

[0002]

2. Description of the Related Art In a power transmission shaft, for example, a drive shaft of an automobile, carbon steel is usually used as a material, and the surface is hardened by heat treatment to secure a predetermined strength.

In recent years, it has been desired to further increase the strength of a drive shaft in response to an increase in the output of an automobile or an increase in the weight of a vehicle due to safety. In addition, a demand for a lighter drive shaft has become apparent from the viewpoint of improving fuel efficiency, and in order to achieve this, it is urgently necessary to increase the strength of the drive shaft.

[0004]

In order to improve the load capacity of the shaft, it is general to increase the strength of the material by increasing the carbon concentration of the material. However, in this method, although the strength can be increased in the smooth portion, the cracks and the like are easily generated in the notch portion such as the serration, and the strength may be reduced, and the strength is uneasy. When the fracture mode was analyzed by subjecting the serration axis to a torsional test, the shear plane fracture was observed when the carbon concentration was low, but the principal stress became dominant when the carbon concentration was high, and the principal stress was destroyed (grain boundary fracture surface). Rate increase).
From these results, further strengthening of the grain boundary of the steel structure is desired.

[0005] Higher carbon content also impairs machinability such as forgeability and machinability.

Accordingly, an object of the present invention is to further increase the strength and weight of the power transmission shaft without impairing workability.

[0007]

A power transmission shaft according to the present invention is suitable for a power transmission shaft having a notch portion such as a torque transmission tooth portion, and has a quench hardening ratio of 0.25 to carbon steel.
It is formed by induction hardening at 0.50. As the carbon steel, C: 0.39 to 0.49% by weight, Si:
0.4-1.5%, Mn: 0.4-1.0%, S: 0.
025% or less, P: 0.02% or less, Al: 0.01 to
0.1% is used as a basic component, and the balance consists of Fe and unavoidable impurities.

The quench hardening ratio is represented by the ratio of effective hardened layer depth / shaft radius. If the hardening ratio is less than 0.25, the starting point of damage occurs inside the shaft (core portion), so that the strength is reduced. On the other hand, if it exceeds 0.50, burning cracks will occur in the notches such as serrations.

[0009] Of the above elements, C is less than 0.39%
In some cases, the surface hardness after heat treatment is too low to obtain sufficient strength.
If it exceeds 0.49%, the surface hardness is too high.
This increases the notch sensitivity of the notch, resulting in a decrease in strength.
Figure 3 shows the effect of carbon content on static torsional strength.
Therefore, from this result, if the carbon content is within the above range, it is sufficient.
Good static strength (breakage stress about 1600MPa)
It is thought that.

[0010] Si is further used as a deoxidizer in the steelmaking stage.
Is added for strengthening the grain boundaries. This is less than 0.4%
, The effect of strengthening the grain boundaries cannot be obtained, and exceeds 1.5%.
Then, the cold workability (forgeability, turning property) is significantly reduced.

[0011] Mn fixes and separates sulfur in steel as MnS.
Required to disperse, this is less than 0.4%
Then, hardenability decreases (hardening depth cannot be obtained),
If it exceeds 1.0%, the hardenability is saturated and the cold workability is reduced.
Lower.

[0012] S combines with Mn to form MnS inclusions
Although it is present, it becomes the starting point of crack generation during cold working
0.025% or less. P is a particle in steel.
Precipitates at the boundaries to significantly impair hot workability and material strength
Is significantly reduced, so the content is made 0.02% or less.

[0013] Al is a deoxidizing agent that oxidizes oxygen in steel during steelmaking.
0.03 to adjust the particle size.
1% or more, but too much oxide inclusions cause poor toughness
0.10% as the starting point of cracking during cold working.
% Or less.

If the ferrite grain size in the steel structure is too large, the susceptibility to quenching cracking increases significantly. Therefore, the ferrite grain size number (defined in JIS) of carbon steel is set to 7 or more.
The measurement of the crystal grain size can be performed at, for example, a shaft core portion which is not affected by heat due to induction hardening.

The carbon steel is B: 0.001-0.
004%, Ti: 0.02-0.05%, and N:
It should contain 0.008% or less and the Ti / N ratio should be 3.4 or more.

B is added for the purpose of improving hardenability, strengthening grain boundaries, and reducing susceptibility to quenching. If the content is less than 0.001%, these effects cannot be sufficiently obtained, and
If it exceeds 4%, BC is generated at the grain boundary, which causes a decrease in strength. Ti is added in order to fix N by generating TiN and to prevent generation of BN. B is less than 0.02%
The generation of N cannot be prevented, and if it exceeds 0.05%, the cleanliness is impaired and the strength is reduced. N is contained in steel as an impurity, but if it exceeds 0.008%, BN is generated and the effect of adding B is diminished. The Ti / N ratio is a weight ratio of Ti to N and indicates how much N is fixed by Ti. The larger this is, the smaller the amount of BN generated. T
If the i / N ratio is less than 3.4, it becomes difficult to secure effective B.

If a carbon steel containing Mo: 0.4% by weight or less is used, the hardenability is improved. 0.4
%, The effect of improving hardenability is saturated.

If the carbon steel contains one or more of Nb, V and Zr, the toughness is improved by the refinement of the crystal grains, so that more severe use conditions are expected. This is effective when If these proportions are less than 0.01% by weight, the effect of improving toughness is insufficient, and if they exceed 0.3% by weight, on the contrary, toughness decreases.

The compressive residual stress on the surface after induction hardening is 6
When it is 0 kgf / mm ² or more, improvement in fatigue strength is achieved. If the compressive residual stress on the surface is set to 100 kgf / mm ² or more by shot peening after induction hardening, the fatigue strength can be further improved.

[0020]

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

FIG. 1 shows a Zepper type constant velocity universal joint (ball fixed joint) as an example of a constant velocity universal joint. This constant velocity universal joint includes an outer member 1 (outer ring) having a plurality of (usually six) curved guide grooves 1b formed in the axial direction on a spherical inner surface 1a and a spherical outer surface 2a. An inner member 2 (inner ring) in which a plurality (usually six) of curved guide grooves 2b are formed in the axial direction, and a guide groove 1b of the outer member 1 and a guide groove 2b of the inner member 2 are formed in cooperation. A plurality of (usually six) torque transmitting balls 3 arranged on a ball track to be formed and a retainer 4 for holding the torque transmitting balls 3.

The center A of the guide groove 1b of the outer member 1 and the center B of the guide groove 2b of the inner member 2 are opposite to each other by an equal distance in the axial direction with respect to the joint center plane O including the center of the torque transmitting ball 3. Therefore, the ball track has a wide opening side and a shape (wedge shape) gradually reduced toward the back side. The center of the spherical surface of the outer diameter surface 1a of the outer member 1 and the outer diameter surface 2a of the inner member 2 that serve as the guide surfaces of the retainer 4 coincide with the joint center plane O. When the outer member 1 and the inner member 2 are angularly displaced by the angle θ, the torque transmitting ball 3 guided by the retainer 4 always stays within the bisecting plane (θ / 2) of the angle θ at any operating angle θ. It is maintained and the constant velocity of the joint is ensured.

At the bottom of the mouse of the outer member 1, a first shaft 1
1 is formed integrally, or a separate shaft portion is joined by an appropriate means. Further, a second shaft portion 12 is coupled to an inner peripheral portion of the inner member 2 via a torque transmitting tooth portion 13 such as a serration. Either of the two shaft portions 11 and 12 serves as a driving shaft, and the power is transmitted to the other shaft portion serving as a driven shaft via a torque transmission ball 3.

A second serration connected to the inner member 2
As a material of the shaft portion 12, C: 0.39 to 0.49%,
Si: 0.4 to 1.5%, Mn: 0.4 to 1.0%,
S: 0.025% or less, P: 0.02% or less, Al:
0.01 to 0.1% (all by weight) as a basic component,
Carbon steel (medium carbon steel) whose balance is composed of Fe and unavoidable impurities is used.

As described above, as the carbon steel, B:
0.001-0.004%, Ti: 0.02-0.05
% And N: not more than 0.008%, and Ti / N
A ratio of 3.4 or more is desirable, and a ferrite grain size number of 7 or more is desirable. In addition, if necessary, Mo: 0.4% by weight or less may be added, Nb,
Any one or more of V and Zr are 0.01
~ 0.3% by weight may be added.

This carbon steel is forged into a predetermined shape and then quenched.
Induction hardened at a curing ratio of 0.25 to 0.50, surface pressure
Shrinkage residual stress is 60kgf / mm^TwoCured until
It is. This compressive residual stress value adjusted the tempering temperature
Change or adjust the quenching coolant (water, oil, etc.)
Can be achieved by Furthermore, high frequency
Surface compression residual stress by shot peening after quenching
Force 100kgf / mm ^TwoIncreased to above, further fatigue strength
It is desirable to improve the degree. This compressive residual stress value is
For example, by performing shot peening twice
Can be done. Shot peening is performed on the torque transmitting tooth 1
3, but the other smoothing portions 12a
May be applied.

While the above description has been made with respect to the second shaft portion 12, when the first shaft portion 11 is formed separately from the outer member 1, the above structure is applied to the first shaft portion. be able to. Further, the present invention can be widely applied to not only the shaft portions 11 and 12 but also a power transmission shaft connected to and coupled to a constant velocity universal joint such as a pressure welding stub or a welding stub, and the shaft shape may be hollow or solid. . FIG. 2 exemplifies a pressure contact stub, in which a torque transmission tooth portion 13 (serration) for coupling to the inner member 2 or the like is provided at one end, and a flange portion 14 for press-fixing the steel pipe at the other end. Is provided.

The power transmission shaft according to the present invention is not limited to the Zepper type constant velocity universal joint shown in FIG. 1, but may be applied to other types of constant velocity universal joints such as a double offset type constant velocity universal joint and a tripod type constant velocity universal joint. Can also be widely used.

[0029]

As described above, according to the present invention, a power transmission shaft having higher strength than conventional products can be provided, and as a result, the load capacity can be increased and the weight can be reduced. Further, since carbon steel is used, the cost is low. Furthermore, there is no need to increase the carbon for higher strength, and there is no loss in machinability.

[Brief description of the drawings]

FIG. 1 (a) is a longitudinal sectional view of a Zepper type constant velocity universal joint (CC section in FIG. 1 (b)), and FIG. 1 (b) is a transverse sectional view thereof.

FIG. 2 is a side view of a pressure contact stub.

FIG. 3 is a diagram showing the effect of carbon content on static torsional strength.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Outer member 1b Guide groove 2 Inner member 2b Guide groove 3 Torque transmitting ball 4 Cage 11 Shaft portion 12 Shaft portion 13 Torque transmitting tooth portion

Continuation of the front page (72) Inventor Akira Wakita 1578 Higashikaizuka, Iwata-shi, Shizuoka F-term in NTN Corporation (reference) 3J033 AA01 AB03 AC01 BA15 BA20

Claims (7)

[Claims] 1. A power transmission shaft used for a constant velocity universal joint, wherein the power transmission shaft is formed by induction hardening carbon steel at a quench hardening ratio of 0.25 to 0.50. :
0.39 to 0.49%, Si: 0.4 to 1.5%, M
n: 0.4 to 1.0%, S: 0.025% or less, P:
A power transmission shaft characterized by having 0.02% or less, Al: 0.01 to 0.1% as a basic component, and the balance being Fe and unavoidable impurities. 2. The power transmission shaft according to claim 1, wherein the ferrite grain size number of the carbon steel is 7 or more. 3. The carbon steel in weight%, B: 0.001
-0.004%, Ti: 0.02-0.05%, and N: 0.008% or less, and the Ti / N ratio is 3.4.
The power transmission shaft according to claim 1 or 2, which is as described above. 4. The power transmission shaft according to claim 1, wherein the carbon steel contains Mo: 0.4% by weight or less. 5. The power transmission shaft according to claim 1, wherein the carbon steel contains 0.01 to 0.3% by weight of one or more of Nb, V, and Zr. 6. A compressive residual stress on a surface of 60 kgf / mm.
The power transmission shaft according to claim 1, wherein the number is ^two or more. 7. The constant velocity universal joint according to claim 1, wherein the compressive residual stress on the surface is increased to 100 kgf / mm ² or more by shot peening.