JPH10184804A - Driving shaft having excellent torsional fatigue characteristics - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automotive driving shaft capable of manufacturing without needing big change in conventional manufacturing processes, in which resistance to torsional fatigue of a welded part of a balance weight is high, and in which the fatigue strength is in well balanced with the joining strength of the balance weight. SOLUTION: In a driving shaft for transmitting automobile engine driving force to an axle, to which a balance weight for reducing rotational whirling is mounted by projection welding, the diameter (a) of a welded joint part at which the balance weight is welded to the shaft, and the thickness (d) of the balance weight at the welded part satisfy the following equations: a+4d<=10mm, 1.5mm<=(a)<=4.5mm, 0.5mm<=(d)<=2.0mm. Thus, a driving shaft having excellent torsional fatigue strength characteristics can be obtained. Further, when the number of welding points at which the balance weight is welded to the shaft is set to be three or more, and the arrangement of the welding points is to be a row in the circumferential direction of the shaft, a driving shaft which is excellent in the joining strength of the balance weight and in the torsional fatigue characteristic, can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive shaft, such as a propeller shaft or a drive shaft, for transmitting the engine propulsion force of each vehicle belonging to a so-called automobile such as a car, truck or tractor. The present invention relates to an automobile drive shaft that has improved fatigue characteristics compared to conventional products and can be reduced in weight by reducing the size.

[0002]

2. Description of the Related Art As described in the Automobile Technology Handbook (Vol. 4, Production, Quality, and Maintenance, p. 233, The Automobile Manufacturers Association, 1991), it is important for the driving shaft of an automobile to have low vibration during high-speed rotation. One. As a countermeasure, as shown in the external view of the driving parts in FIG.
The balance weight 2 is attached to the, and the weight balance adjustment in the circumferential direction is performed.

[0003] Resistance welding is used as a method of mounting the balance weight, and there are two types, (a) spot welding and (b) projection welding shown in FIG. 2. In either case, the driving force is repeatedly transmitted. When a torsional fatigue test corresponding to the above is performed, a fatigue crack 6 from the welded portion of the balance weight may be recognized as shown in FIG. In the case of a fatigue test of a low-strength material having a tensile strength of less than 500 MPa, the characteristics are determined by the fatigue crack 7 from the joint part 3 of the joint as shown in FIG. As shown in FIG. 3A, when the weight of the drive shaft is reduced by increasing the material strength and reducing the cross-sectional area of the drive shaft, the fatigue fracture is caused by fatigue cracks 6 from the balance weight weld as shown in FIG. It became dominant, and the torsional fatigue properties deteriorated, which was a major obstacle for weight reduction.

[0004] The main causes of fatigue cracking from a balance weight weld are stress concentration due to the geometrical shape of the weld, changes in the metal structure due to rapid heating and rapid cooling during welding, and the like.
Welding residual stress can be considered. In order to solve these problems, for example, Japanese Unexamined Patent Application Publication No. 6-246440 discloses a manufacturing method in which the fatigue characteristics are improved by heating a balance weight mounting portion. Further, Japanese Patent Laid-Open No. 6-2
Japanese Patent No. 46439 discloses an automobile drive shaft excellent in torsional fatigue characteristics in which a balance weight is mounted by using arc welding without using conventional spot welding or projection welding as a mounting method. Discloses an automobile drive shaft having excellent torsional fatigue characteristics, to which a balance weight is attached using an adhesive.
However, in these inventions, the productivity is reduced in the conventional balance weight mounting process, and the equipment and process need to be changed or newly installed, which has a disadvantage in terms of economy.

[0005] In a general balance weight mounting, first, a balance weight mounting position is calculated by a balancer.
A balance weight is attached by spot welding or projection welding, and then the balancer is used again to check whether the rotational center of gravity of the drive shaft is at a predetermined position. For example, Japanese Patent Laid-Open No. 6-24644
In order to apply the manufacturing method disclosed in Japanese Patent Application Publication No. 0-204, it is necessary to newly provide a heating line, and to apply the invention disclosed in Japanese Patent Application Laid-Open No. 6-246439, it is necessary to change the welding machine.
In applying the invention of Japanese Patent Application Laid-Open No. 6-249291, it is necessary to wait for the adhesive to dry in order to confirm the position of the center of gravity of rotation after the balance weight is attached, and there is a problem that the productivity is reduced. .

Japanese Unexamined Patent Publication No. 7-317844 discloses a drive shaft in which the fatigue strength is increased by limiting the diameter of the projection projection of the balance weight and the diameter of the welded joint in a projection welded portion to a certain ratio. However, this focuses only on the diameter of the joint, and control of only the diameter of the joint does not provide a sufficient improvement in fatigue strength. Was impossible to balance in a high dimension.

[0007]

SUMMARY OF THE INVENTION In view of the above situation, the present invention provides a balance weight weld having a high torsional fatigue resistance and a high fatigue strength, which can be manufactured without a major change in the conventional manufacturing process. The purpose of the present invention is to obtain an automobile drive shaft that is excellent in the balance between the joining strength of the balance weight and the balance weight.

[0008]

Means for Solving the Problems The present inventors have conducted various studies on the above-mentioned problems, and as a result, by adjusting the diameter and thickness of the welded portion between the balance weight and the shaft to predetermined sizes. It has been found that torsional fatigue strength is improved and high fatigue strength is obtained. In addition, by setting the diameter and thickness of the welded joint to a predetermined size and increasing the number of points while considering the arrangement of the welding points, the fatigue strength and the joining strength of the balance weight can be balanced at a high level. succeeded in.

That is, the gist of the present invention is as follows. (1) In a drive shaft that transmits the engine propulsion force of a car to wheels by mounting a balance weight for reducing rotational whirling by projection welding, the diameter a of the weld joint of the balance weight and the shaft and the balance of the weld joint A drive shaft having excellent torsional fatigue characteristics, wherein the thickness d of the weight is within a range satisfying a + 4d ≦ 10 mm 1.5 mm ≦ a ≦ 4.5 mm 0.5 mm ≦ d ≦ 2.0 mm.

(2) A balance weight for reducing rotational whirling is attached by projection welding.
In the drive shaft transmitting the engine propulsion force of the vehicle to the wheels, the number of welding points between the balance weight and the shaft is three or more, and the arrangement of each welding point is arranged in a row in the circumferential direction of the shaft. And the thickness d of the balance weight of the weld joint at each welding point is within a range satisfying a + 4d ≦ 10 mm 1.5 mm ≦ a ≦ 4.5 mm 0.5 mm ≦ d ≦ 2.0 mm. A drive shaft with excellent balance weight joint strength and torsional fatigue characteristics.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the main causes of fatigue cracking from a balance weight weld are stress concentration due to the geometrical shape of the weld, and changes in the metal structure due to rapid heating and quenching during welding. And welding residual stress. Further, since the balance weight is usually fixed to the shaft at a plurality of welding points, a force is generated between the welding points when the shaft is torsionally deformed. The inventors of the present invention have conceived that, among these factors, the one having the greatest effect on the fatigue properties of the balance weight weld is and. In order to reduce stress concentration by optimizing the welding force, we examined how to optimize the arrangement of welding points and reduce the binding force between welding points.

In the case of projection welding, the weld between the balance weight and the shaft generally has a shape as shown in FIG. When subjected to torsional alternating stress, stress concentration occurs in the welded portion due to this shape, and fatigue characteristics deteriorate.
The present inventors focused on the relationship between the stress concentration and the diameter and thickness of the welded joint, and reduced the occurrence of stress concentration by controlling both the diameter and the thickness of the welded joint, and improved the fatigue characteristics. We considered that we planned. As a result, it has been found that reducing the diameter of the welded joint and reducing the thickness are effective in improving the fatigue strength.

[0013] The smaller the diameter of the welded joint, the higher the fatigue strength. However, if the diameter is too small, the joint strength between the balance weight and the shaft is insufficient, and the balance weight separates from the shaft when the drive shaft is used. Therefore, the lower limit of the diameter of the welded joint is set to 1.5 mm. Like the diameter of the welded joint, the smaller the thickness, the higher the fatigue strength. However, if it is too small, the balance weight is torn off when the drive shaft is used, and there is a disadvantage that the drive shaft is separated from the shaft.

Regarding the upper limit of the diameter and thickness of the welded joint,
According to the study by the present inventors, as shown in FIG. 5, when the diameter is a and the thickness is d, good fatigue strength is obtained if a + 4d ≦ 10 mm. However, if the diameter a exceeds 4.5 mm, sufficient fatigue strength cannot be obtained even if a and d are within the range of the above formula. Further, when the thickness d exceeds 2.0 mm, sufficient fatigue strength cannot be obtained even if a and d are within the range of the above formula. As described above, in the present invention, the diameter a and the thickness d are limited to the range of a + 4d ≦ 10 mm 1.5 mm ≦ a ≦ 4.5 mm 0.5 mm ≦ d ≦ 2.0 mm.

As a method of controlling the diameter of the welded joint,
For example, there are a method of changing the size of the diameter of the projection protrusion of the balance weight, a method of controlling welding heat input during projection welding, and the like. As for the thickness of the welded joint, there are a method of controlling the heat input similarly and a method of changing the thickness of the projection protrusion of the balance weight. When the thickness of the projection protrusion is changed, the thickness of only the projection protrusion or only the vicinity thereof may be changed depending on the weight required for the balance weight and the productivity and economy in producing the balance weight. Alternatively, the thickness of the entire balance weight may be changed.

As described above, various methods for controlling the diameter and thickness of the welded joint can be considered, but whichever method is used, the object of the present invention is the essence of the present invention. This does not depart from the scope of the present invention, as long as the diameter and thickness of the joint are controlled within a certain range. The balance weight is usually welded to the shaft at two points.
This is because if the number of welding points is large, the fatigue strength is deteriorated due to the restraining force. From the viewpoint of fatigue strength, one welding point is ideal, but one-point welding may result in insufficient joint strength of the balance weight, causing a disadvantage that the drive shaft is separated from the shaft when used. There are cases. Therefore, conventionally, two-point welding has been generally used from the balance between joining strength and fatigue strength.

If there is a margin in the joint strength in the light of the operating conditions of the drive shaft, controlling the diameter and thickness of the welded joint within the range of the present invention ensures sufficient joint strength while maintaining the fatigue strength. Can be improved. However, if the joint strength is not sufficient, the conventional two-point welding is not sufficient if the diameter and thickness of the weld joint are reduced to improve the fatigue strength. However, it is necessary to increase the welding strength by increasing the number of welding points. In order to solve this contradictory problem, the present inventors have studied the arrangement of welding points when multiple points are used, and the balance between fatigue strength and bonding strength.

When the drive shaft is deformed by torsion, the relative positions of the welding points of the balance weight and the shaft change,
As a result, the balance weight is deformed. At this time,
Each welding point receives a reaction force of the deformation of the balance weight. When the number of welding points is one, the deformation of the balance weight does not occur. On the other hand, when there are a plurality of welding points, the welding point receives a large stress by the deformation reaction force of the balance weight. Therefore, increasing the number of welding points results in deterioration of fatigue strength.

However, the present inventors have paid attention to the fact that the deformation of the drive shaft is torsional deformation, and if the arrangement of the welding points is devised, the deterioration of the fatigue strength is minimized and the high joining strength is obtained. Thought it could be. Based on this idea,
When the welding points are arranged in the axial direction of the drive shaft as shown in FIG. 6 (a), when the welding points are arranged in the circumferential direction as shown in FIG. 6 (b), the shaft as shown in FIG. 6 (c) The case where they were arranged in a cross in the direction and the circumferential direction was examined. FIG. 8 shows the results of the study. In contrast to the conventional general two-point welding in the circumferential direction, the number of welding points is increased in any of four-point welding in the circumferential direction, four-point welding in the axial direction, and four-point welding in the cross direction. Although the fatigue strength decreases as the joining strength increases, the fatigue strength deterioration is least in the circumferential arrangement.

It is considered that the deterioration in fatigue strength when the number of points is increased in the circumferential arrangement is due to the following reasons. In torsional deformation, the movement of each point on the drive shaft has only a circumferential component and no axial component. Therefore, there is no change in the relative position between the welding points arranged in the circumferential direction.
On the other hand, when the welding points are arranged in the axial direction, the relative positions change because the welding points have circumferential movement components having different magnitudes depending on the positions on the axis. Therefore, in the circumferential arrangement, the balance weight is not deformed due to a change in the relative position of the welding point, whereas in the axial arrangement, the balance weight is deformed and a reaction force acts on the welding point. From the above, it is considered that the circumferential arrangement has little fatigue strength deterioration.

From the viewpoint of the balance between the joint strength and the fatigue strength, the joint strength is increased by increasing the number of welding points.
Although it rises almost proportionally regardless of the arrangement of the welding points, the circumferential arrangement is less deteriorated in fatigue strength than other arrangement methods, so that the balance between joining strength and fatigue strength is excellent. From the above study, the present inventors succeeded in increasing the balance between the joint strength and the fatigue strength by increasing the number of welding points in the circumferential arrangement.

When the balance weight is actually welded to the drive shaft, the arrangement of the welding points is limited to the circumferential component only due to the positioning accuracy of the balance weight at the time of projection projection processing and the positioning accuracy of the balance weight at the time of welding. And may have an axial component, albeit small. If the welding point arrangement has an axial component, the fatigue strength is deteriorated for the reasons described above. Therefore, it is preferable to eliminate the axial component as much as possible by accurate positioning. However, according to the study of the present inventors, there is no influence on the fatigue strength as long as it is within the range of the positioning accuracy at the time of ordinary machining or projection welding. When the angle θ between the line connecting the adjacent welding points shown in FIG. 7 and the circumferential direction of the shaft is arranged within 15 degrees, the deterioration of the fatigue strength is not so remarkable. When the welding points are arranged in the circumferential direction, it can be considered that they are arranged in a line in the circumferential direction according to the present invention.

With respect to the number of welding points in the circumferential arrangement, as shown in FIG. 8, three points have already improved the joint strength-fatigue strength balance compared to the conventional two-point fixing.
The number of welding points is more preferably three or more. In the present invention, the upper limit of the number of welding points is not particularly limited,
When actually performing projection welding, the larger the number of welding points, the higher the projection height of the balance weight when projecting the projection, and the accuracy of the R processing for aligning the balance weight along the outer periphery of the shaft. In addition, it becomes difficult to uniformly apply the projections to the shaft, which causes a problem in production that the welding quality at each welding point varies. Therefore, the number of welding points may be selected in consideration of the joint strength-fatigue strength balance required for the drive shaft and the above-mentioned production problems. In the study of the present inventors, if the operating conditions of the drive shaft that is normally used, the joint strength-fatigue strength balance is often sufficient at 6 points or less,
The above production problem can also be solved by means of accurate balance weight processing and welding.

[0024]

EXAMPLE A balance weight was attached to a drive shaft having an outer diameter of 114.3 mm, a wall thickness of 4.0 mm, and a high-strength steel pipe having a tensile strength of 735 MPa class by projection welding, and a torsional fatigue test was performed. Balance weights have two projection projections in the circumferential direction, four projection projections in the axial direction,
Various types of projections with four projection projections in the cross and four projection projections in the circumferential direction are prepared, and the diameter and thickness of the projection projections and welding conditions are changed to obtain the joint diameter and the junction. The thickness was changed.
Various drive shafts produced in this manner were subjected to a torsional fatigue test at a torsional torque of ± 7 kNm. The diameter and thickness of the welded joint were measured by cutting out the welded joint after the fatigue test. For the joint strength measurement, a test piece was prepared by welding a balance weight under the same conditions as the drive shaft used for the fatigue test, and the load required for peeling the balance weight was measured.

The results are shown in Tables 1 and 2 (continued from Table 1). In the circumferential two-point welding, Examples 1 to 4 of the present invention in which the diameter a and the thickness d of the welded joint are within the range of the present invention have excellent fatigue strength, while as shown in FIG. 1
Fatigue strength of Comparative Examples 12, 14 and 14 exceeding 0 mm is significantly reduced.

As shown in FIG. 8, Examples 5 to 11 of the present invention, in which the number of welding points is three or more and arranged in the circumferential direction, are more excellent in joint strength-fatigue strength balance than circumferential two-point welding. However, the angle θ between the line connecting the adjacent welding points and the circumferential direction of the shaft
In Comparative Examples 15 and 15 in which the welding point arrangement is greater than 15 degrees, and in Comparative Examples 16 and 17 in which the welding points are arranged in the axial direction or in a cross shape, there is no superiority in the joint strength-fatigue strength balance with respect to two-point welding.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

According to the present invention, in an automobile drive shaft to which a balance weight for reducing rotational whirling is attached by projection welding, the occurrence of fatigue fracture from the balance weight attachment portion, which has reduced the torsional fatigue characteristics, is reduced. In addition to being able to be delayed, it is possible to secure the bonding strength of the balance weight. as a result,
The actual working stress can be increased, which contributes to a reduction in the weight of the drive shaft of an automobile.

[Brief description of the drawings]

FIG. 1 is a diagram showing the structure of a typical automobile drive shaft.

FIG. 2 is a diagram showing an outline of spot welding (a) for attaching a balance weight to a drive shaft and projection welding (b).

FIGS. 3 (a) and 3 (b) are diagrams showing fatigue fracture occurrence positions when a torsional fatigue test, which is a main performance evaluation, is performed on a drive shaft.

FIG. 4 is a view showing a cross-sectional shape of a projection welding portion between a balance weight and a drive shaft.

FIG. 5 is a diagram showing a relationship between a projection weld joint diameter a, a weld joint thickness d, and fatigue strength.

FIG. 6 is a diagram showing an arrangement of projection welding points;
(A) shows an axial arrangement, (b) shows a circumferential arrangement, and (c) shows a cross arrangement.

FIG. 7 is a diagram showing an angle θ between a line connecting adjacent welding points and a circumferential direction of a drive shaft.

FIG. 8 is a diagram showing the number and arrangement of projection welding points and the balance between joint strength and fatigue strength.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Steel pipe 2 Balance weight 3 Joint part joint part 4 Joint part 5 Electrode chip 6 Fatigue crack from balance weight weld part 7 Fatigue crack from joint part joint part 8 Projection of balance weight (projection) a Weld joint diameter d Weld joint Part thickness 9 Unwelded part 10 Projection welding point θ Angle between the line connecting the adjacent welding points and the circumferential direction of the drive shaft

Claims (2)

[Claims] 1. A drive shaft for transmitting an engine propulsion force of an automobile to a wheel, to which a balance weight for reducing rotational whirling is attached by projection welding, wherein a diameter a of a weld joint between the balance weight and the shaft and a weld joint are provided. Wherein the thickness d of the balance weight is within a range satisfying a + 4d ≦ 10 mm 1.5 mm ≦ a ≦ 4.5 mm 0.5 mm ≦ d ≦ 2.0 mm. 2. A drive shaft for transmitting engine propulsion force of an automobile to a wheel, wherein a balance weight for reducing rotational whirling is attached by projection welding, wherein the number of welding points between the balance weight and the shaft is three or more. hand,
In addition, the arrangement of each welding point is arranged in a line in the circumferential direction of the shaft, and further,
The diameter a of the welding joint at each welding point and the thickness d of the balance weight of the welding joint at each welding point satisfy the following condition: a + 4d ≦ 10 mm 1.5 mm ≦ a ≦ 4.5 mm 0.5 mm ≦ d ≦ 2.0 mm A drive shaft with excellent bonding strength and torsional fatigue characteristics of the balance weight, characterized by being within the range.