JP3187274B2 - High strength drive shaft for power transmission and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive shaft for power transmission in which a hollow shaft constituting a drive shaft is made of a high-strength steel pipe, and a balance weight for adjusting rotational imbalance is attached. The present invention relates to a drive shaft having excellent strength characteristics and a method for manufacturing the same.

[0002]

2. Description of the Related Art A long drive shaft is used for power transmission in automobiles and industrial machines. Since the drive shaft rotates at a high speed, the drive shaft needs to have excellent rotation balance (balance) characteristics. This is because the vibration generated during rotation increases in proportion to the amount of unbalance, so unless the amount of unbalance is kept below a certain level, not only can cars and industrial machines not operate as designed, but also in the worst case Is a cause of breakdowns and accidents.

[0003] For this reason, in a drive shaft, imbalance during rotation is adjusted. Although there are various methods, a method of electric resistance welding a balance weight to a part of a drive shaft is often used because of its excellent workability and cost.

FIG. 1 is a view showing the shape of a balance weight and a state in which the balance weight is mounted on a drive shaft (hollow shaft). FIG. 4D shows a state in which a balance weight is attached to a part of the hollow shaft 3. The balance weight 2 has a plate thickness of about 1 to 3 mm shown in FIGS. It is manufactured by bending a steel plate into an arc shape having a curvature substantially equal to the outer diameter of the hollow shaft 1. The attachment to the hollow shaft is performed by a method called projection welding.

In the projection welding method, as shown in FIG. 1 (c), one or several projections (projections) 21 are provided inside the curved surface of the balance weight 2, and the projections 21 are pressed against the hollow shaft 3 to energize. And perform welding. At this time, the projections have a diameter of 2.5 to 6.0 mm and a height of about 0.7 to 1.5 mm, and the pressing force per projection is 200 to 500 kgf.
It is common practice to conduct an alternating current of 8 to 20 kA for 10 to 30 cycles (Takao Nakamura, Tokuo Kobayashi, Kazuto Morimoto, "Modern Welding Technology Dai-kei-Resistance Welding" (Sanho Publishing, January 23, 1980) Japanese version)
p.121). In this case, the energization time depends on the power frequency, but is, for example, about 160 to 500 ms at 60 Hz, and the product of the current value and the energization time is 1,280 to 10,000 kA · ms. In recent years, a DC current may be supplied by using a condenser-type electric resistance welding machine. In this case, the welding conditions are approximately the above-described ranges for the pressing force, the current value, and the conduction time.

In recent years, there has been a demand for lower fuel consumption of automobiles and labor saving of industrial machines, and weight reduction of drive shaft materials has been promoted by increasing strength. For example, the hollow tube drive shaft of a motor vehicle, conventionally, a tensile strength of 50 kgf / mm ² class material steel produced in the have been used, recently 70 kg
Attempts are being made to switch to high-strength materials of f / mm ² class or higher, reduce the outer diameter or wall thickness of the tube, and reduce the weight.

[0007]

When a balance weight is attached to a drive shaft made of the above-described high-strength material by the above-described electric resistance welding method, a joint of the balance weight is subjected to a torsional load during driving. The possibility of fatigue cracking due to repetition increases. This phenomenon has not been recognized at all for conventional strength materials, and unless this problem can be solved, it is not possible to increase the strength of the drive shaft.

An object of the present invention is to provide a drive shaft having a long fatigue life even if the drive shaft is made of a steel pipe made of a high-strength material having a tensile strength of 70 kgf / mm ² or more, and such a drive shaft. It is to provide a method of manufacturing the.

[0009]

Means for Solving the Problems In order to solve the above problems, the present inventors have conducted various studies on the effects of the material strength and welding conditions on the metallographic properties and fatigue strength of the welded portion of the balance weight. The following findings were obtained.

(A) Fatigue cracks are generated from the welded joint ends.

(B) Conventional electric resistance (projection)
Under the welding conditions, there is an unwelded portion at the end of the joint, and the unwelded portion acts as an initial defect to generate a fatigue crack.

(C) Further, under the conventional electric resistance welding conditions, a molten / solidified structure exists in a considerably wide range at the center of the joint. Tensile residual stress is generated in the molten / solidified structure, and the fatigue strength is reduced.

(D) When the drive shaft material has a high strength,
Since the tensile residual stress level of (C) increases in proportion to the increase in strength, the fatigue strength decreases.

(E) When the steel pipe is made of low carbon steel, the hardness difference between the projection welded part and the base steel pipe is reduced, and the hardening of the projection welded part is reduced, so that the notch sensitivity to fatigue is reduced.

(F) When the balance weight is made of a high-strength material, the residual stress value generated on the balance weight side increases, and the residual stress value on the drive shaft side decreases accordingly.

In summary, in order to increase the fatigue strength of the welded portion, it is necessary to reduce the residual stress in the welded portion and to reduce the unwelded portion as much as possible. As a result, it was confirmed that it was desirable to reduce the hardening of the welded portion, and the present invention was completed.

The gist of the present invention resides in the following drive shafts and methods for manufacturing them (see FIGS. 3 and 4).

A power transmission drive shaft in which a balance weight (2) is joined to a part of the hollow shaft (3) constituting the drive shaft (1) by projection welding, wherein the hollow shaft (3) is It is a steel pipe having a tensile strength of 70 kgf / mm ² or more, and a ratio (d / d / d) of the diameter d of the joint to the diameter D of the projection at the joint of the steel pipe and the balance weight (2).
A high-strength drive shaft for power transmission in which D) is 0.6 to 1.0.

A power transmission drive shaft in which a balance weight is joined to a part of a hollow shaft constituting the drive shaft by projection welding, wherein the hollow shaft has a carbon content of 0.05 to 0.12% by weight and a tensile strength. A low-carbon steel pipe having a strength of 70 kgf / mm ² or more, wherein the ratio (d / D) of the diameter d of the joint to the diameter D of the projection at the joint between the steel pipe and the balance weight is 0.6 to 1.0. High strength drive shaft for transmission.

A power transmission drive shaft in which a balance weight is joined to a part of the hollow shaft constituting the drive shaft by projection welding, wherein the hollow shaft has a carbon content of 0.05 to 0.12% by weight and a tensile strength. A low carbon steel pipe having a strength of 70 kgf / mm ² or more, wherein a ratio (d / D) of a diameter d of the joint to a diameter D of the projection at a joint between the steel pipe and the balance weight is 0.6 to 1.0; A high-strength drive shaft for power transmission, wherein the difference (ΔHv) between the maximum Vickers hardness of the joint and the Vickers hardness of the steel pipe is 150 or less.

The above-mentioned balance weight has a tensile strength of 70%.
It is desirable to manufacture with a steel material of kgf / mm ² or more.

The projection provided on the surface of the balance weight to be welded is set to a pressure of 100 to 50 per unit.
0 kgf and pressed against the hollow shaft.
The above or the method for producing a high-strength drive shaft for power transmission, wherein welding is performed at a current per unit of 7 to 30 kA for 1 to 50 ms.

The above pressure is 200 to 400 kgf, and the current is 7 to 20 kgf.
kA, the energization time is preferably 5 to 50 ms, and the product of the current value and the energization time is preferably 100 to 500 kA · ms.
It is desirable to use a DC power supply as the welding power supply.

The above-mentioned "steel pipe having a tensile strength of 70 kgf / mm ² or more" is, for example, a steel pipe containing carbon (C): 0.05 to 0.22% by weight and manganese (Mn): 1.4 to 2.1% by weight. ,
Alternatively, in addition to these components, Mo, Nb, Ti, Cr, Si, or the like is added to the steel pipe to further increase its strength, and is hereinafter simply referred to as “high-strength steel pipe”. In addition, the above-mentioned drive shaft is made of a low carbon steel pipe having a C content of 0.05 to 0.12% by weight, desirably 0.05 to 0.08% by weight (for example, 1.9 to 2.1%).
A steel pipe having a tensile strength of 70 kgf / mm ² or more depending on the weight percent of Mn and other components, and is hereinafter referred to as a “low carbon high strength steel pipe”. ) Is a hollow shaft.

"The tensile strength used for the balance weight is
The “steel material of 70 kgf / mm ² or more” is a steel material having the same material as that of the drive shaft or a high tensile strength equivalent to or higher than that.

The diameter D of the projection is shown in FIG.
The maximum diameter of the projection 21 (convex portion) formed on the inner surface of the balance weight as shown in FIG. 1 (D = 5.5 mm in the example of FIG. 1B). Further, the diameter d of the joint portion is a diameter of a portion usually called a nugget shown in FIGS. 2 and 3 described later. Note that the diameter D of the projection is usually substantially equal to the diameter D 'of the depression outside the balance weight, so that D' can be regarded as D.

[0027]

The drive shaft of the present invention is characterized in that the ratio (d / D) of the diameter d of the welded portion to the diameter D of the projection at the joint between the steel pipe and the balance weight is as described above.
0.6 to 1.0, using high-strength steel pipe as the steel pipe, or using low-carbon high-strength steel pipe, and the difference between the maximum Vickers hardness of the joint and the Vickers hardness of the steel pipe
(ΔHv) is 150 or less, and the material of the balance weight is a steel material having a tensile strength of 70 kgf / mm ² or more.

FIGS. 2A and 2B are cross-sectional views showing joint sections when a balance weight is joined to a steel pipe by an electric resistance welding method under a conventional condition. FIG. 2A is a microstructure and FIG. 2B is a schematic view. In the figure, the nugget diameter d is considerably larger than the diameter D of the projection (projection). In addition, a molten / solidified structure 11 exists in a central portion of the joint over a considerably wide range, and an unwelded portion 12 exists at a joint end.

The melted / solidified structure 11 is a structure in which the contact portion is melted by the application of heat during welding, and is rapidly cooled and solidified by the conduction of heat to the surroundings at the end of the application of electricity. In iron and steel materials, volume contraction occurs with solidification, so that tensile residual stress is generated in the molten / solidified structure portion 11 and its vicinity, and this value may reach the yield strength of the material.
Tensile residual stress, when a load is repeatedly applied to the material,
It causes a reduction in fatigue strength. Here, when the balance weight is made of a high-strength material, the occurrence of tensile residual stress generated in the steel pipe is reduced, and the fatigue strength can be increased.
The reason will be described later.

In the unwelded portion 12, molten or semi-molten metal generated by energization during welding is extruded into a gap between the hollow shaft 3 (drive shaft 1) and the balance weight 2 by pressurization applied during energization. Since the temperature of the gap is low, the gap remains without being joined. The unwelded portion has the same function as a notch on the surface of the material, and serves as a starting point of a fatigue crack when a load is repeatedly applied to the material.

FIG. 3 shows a joining cross section when joining by an electric resistance welding method under the conditions specified in the present invention.
There are few molten and solidified layers, and the tensile residual stress is reduced. In addition, there is almost no unwelded portion, so that the nugget diameter d is smaller than that of FIG. 2, and d is smaller than D.
As shown in the examples described later, this ratio of d and D (d /
It has been found from a number of test results that when D) is 1.0 or less, the fatigue strength of the joint becomes extremely high. This is because when d / D is greater than 1.0, an unwelded portion is present at the joint end of the joint, which serves as a starting point for fatigue cracking and a high tensile residual stress due to the presence of a wide molten / solidified structure. This causes fatigue strength to decrease. However, when d / D is smaller than 0.6, the area of the joint is too small to obtain a sufficient static joining strength, and there is a risk that the balance weight may be peeled off by centrifugal force or vibration during driving.

From the above, d / D is set as a range in which the static strength of the joint can be secured and the fatigue life can be extended.
It is preferred to be in the range of 0.6 to 1.0.

It is essential that the d / D be in the range of 0.6 to 1.0 as described above, irrespective of the material, as long as the steel pipe forming the hollow shaft is a high-strength steel pipe of 70 kgf / mm ² or more. However, if the hollow shaft is a low-strength steel pipe, the problems to be solved by the present invention are not inevitable. Therefore, the steel pipe is limited to a high-strength material having a tensile strength of 70 kgf / mm ² or more.

By setting the d / D to be in the range of 0.6 to 1.0 and making the hollow shaft a low-carbon high-strength steel pipe having C of 0.05 to 0.12% by weight, the fatigue strength is further improved. This is because notch susceptibility to fatigue is reduced by reducing the hardness of the projection welded portion by using low carbon steel. That is, when projection welding is performed on a general high-strength steel pipe, the difference (ΔHv) between the maximum Vickers hardness of the joint and the Vickers hardness of the steel pipe usually exceeds 200, but is suppressed to 200 or less for a low-carbon high-strength steel pipe. And the hardening of the joint can be reduced, so that the fatigue strength is improved.

This effect becomes more remarkable when ΔHv is 150 or less, and the fatigue life is further improved.

When bonding is performed in a very short time as described below,
By making the material of the balance weight a high-strength steel material equal to or greater than that of the drive shaft, the fatigue life of the joint can be extended. The reason is considered as follows. Tensile residual stress due to joining occurs on the drive shaft side and the balance weight side. Therefore, when the material of the balance weight is made of a high strength, the residual stress value generated on the balance weight side increases, and the residual stress value on the drive shaft side decreases correspondingly.

The drive shaft of the present invention can be manufactured by the following method (the above-described method). The most significant features of this method are that the welding pressure and welding current during welding are increased, the energization time is shortened, and the product of the current value and the energization time is regulated. By applying a very short period of time,
By adjusting d / D to a preferable range, it is possible to reduce a portion having a melted / solidified structure at a central portion of the joint and substantially eliminate an unwelded portion at a joint end.

The difference in the cross section of the joint between the welding under the conventional conditions as shown in FIGS. 2 and 3 and the welding according to the present invention is essentially due to the difference in the volume (amount) of the metal that is melted when energized. However, what should be noted here is that the melting amount does not change linearly in proportion to the energization time. In the initial stage of energization, heat is generated due to contact electric resistance between the tip of the projection (projection) 21 of the balance weight 2 and the surface of the hollow shaft 3, and only the surface layer is melted. However, when current is further supplied in this state, the melted portion has no contact resistance, and current is concentrated in this portion and heat is generated by Joule heat, so that the amount of fusion increases dramatically.

Conventional welding conditions have focused on lowering the pressing force and welding current, increasing the energizing time, melting the material with Joule heat, and joining. On the other hand, in the method of the present invention, the pressing force and the welding current are increased, and the energization time is shortened. The upper limit of 50 ms for the energization time is set as the limit of change from contact resistance heating to Joule heating. As a result, the amount of fusion can be extremely reduced, the tensile residual stress generated by solidification and shrinkage after the current is applied is reduced, and the unwelded portion 12 extruded into the gap between the drive shaft 1 and the balance weight 2 becomes small. The energization may be performed in a very short time because only a small amount of melting may occur in the contact portion. Therefore, the lower limit is set to 1 ms, more preferably 5 ms in consideration of the stability of energization.

The current value is 7 to 30 kA, which is higher than the conventional welding conditions. Thereby, the bonding can be stabilized. If the welding current is less than 7 kA, the welding heat input is insufficient, and the interface of the contact portion does not melt near the lower limit of the pressing force described later.
In some cases, good bonding cannot be obtained, or d / D is too small even when bonding is performed, and the static strength of the bonded portion cannot be obtained. On the other hand, if the welding current exceeds 30 kA, the amount of melting increases near the upper limit of the energizing time, and the d / D becomes too large.
In addition, dust may occur and defects such as voids may occur at the joint. In order to make the junction more stable, the current value should be 10 ~
It is preferably 20 kA.

Further, the product of the current value and the energizing time is 100 to 500
kA · ms. If the product of the current value and the conduction time is 100 kA · ms or less, stable bonding cannot be obtained or even if bonding is performed, d / D
In some cases, it is not possible to obtain a static joining strength sufficient to attach the balance weight to the drive shaft. On the other hand, if it exceeds 500 kA · ms, the d / D becomes close to 1.0, a melt-solidified structure and tensile residual stress are generated, and the effect of extending the fatigue life is reduced. From the above, it is preferable that the product of the current value and the conduction time is 100 to 500 kA · ms in order to obtain a sound bond and extend the fatigue life.

As the welding power source, a capacitor type or inverter-controlled DC power source can be used in addition to a general-purpose single-phase AC welding power source. When a DC power supply is used, the heat generation efficiency at the interface between the drive shaft and the balance weight is improved, and good bonding can be obtained even in a short time. For this reason, when selecting welding conditions near the lower limit from the range specified in the present invention, it is preferable to use a DC power supply.

The pressing of the balance weight against the hollow shaft is performed so that the pressing force per projection is 100 to 500 kgf. Increasing the pressing force in this manner has the effect of preventing the projection from moving during welding. If the applied pressure is less than 100 kgf,
Since the current cannot be concentrated on the projections, good bonding may not be obtained. On the other hand, if it exceeds 500 kgf, the amount of melting becomes too large when the current value and the energizing time are selected near the upper limit. In order to make the joining more stable, it is preferable that the pressure is 200 to 400 kgf. It is to be noted that by increasing the pressing force two to three times immediately after energization and applying a so-called forging force, the joining strength of the welded portion can be further improved.

As described above, the energizing time, the current value and the pressing force affect each other, so that they are adjusted within the respective preferable ranges so as to be correlated with each other. It is desirable to select a lower value.

There is no particular limitation on the shape of the projection (projection). Any shape can be used as long as the current can be concentrated at the time of energization, and a conventionally used shape may be used.

According to the method of the present invention, by increasing the pressing force and the welding current and setting the energizing time to 1 to 50 ms, the tensile residual stress which adversely affects the fatigue strength is reduced, and the unwelded portion acting as a defect is reduced. Thus, the fatigue strength of the balance weight joint can be greatly improved.

[0047]

EXAMPLES Hereinafter, the effects of the present invention will be described more specifically with reference to examples.

Example 1 The static strength of a joint welded by projection welding using an 80 kgf / mm ² class steel pipe for machine structure shown in Table 1 and a balance weight of a 40 kgf / mm ² class hot rolled steel sheet was examined. .

FIG. 1 is a view showing the shape of a balance weight and a state in which the balance weight is attached to a hollow shaft 3 (steel pipe). FIG.
Pressing a steel ball with a diameter of 6 mm on two places of a mild steel plate (40 kgf / mm class ² ) having a length of 40 mm, a width of 25 mm, and a thickness of 2.6 mm as shown in (a), the diameter as shown in Fig. 1 (b) 5.5mm, 1.1mm high protrusion
21 was formed in two places, and then this was bent into an arc shape with a radius of 50 mm as shown in (c) to produce a balance weight.

The balance weight was brought into contact with the hollow shaft 3 (steel pipe) as shown in FIG.
Was changed to 0.35 to 1.20 to produce seven test pieces.

FIG. 4 is a view showing a state in which a load is applied to check the static joining strength of the balance weight.
Is a view from above, and (b) is a front view.

As shown in FIG. 4, the test piece used in this test had a hole 5 (load rod insertion hole, diameter 14 mm) penetrating in the diameter direction in the steel pipe 3 in advance by machining, and the center of one hole was formed. The balance weight was set so that the center of the balance weight 2 coincided with the center of the balance weight 2, and projection welding was performed by the method shown in FIG.

As shown in FIG. 4, in the test of the static joining strength of the balance weight, the test piece (steel pipe 3) is supported by the support 7 and the other hole 5 to which the balance weight is not joined is used.
Then, a force for pushing the balance weight from the steel pipe was applied to the balance weight, and the maximum load (N) at which the balance weight was peeled was measured. The results are shown in Table 2.

The joint d was measured by polishing and etching the cross section of the test piece subjected to projection welding under the same conditions as shown in FIGS. The diameter (D ') of the depression was measured and regarded as the diameter D of the projection (projection). Table 2 shows the results.

[0055]

[Table 1]

[0056]

[Table 2]

FIG. 5 is a diagram showing the relationship between the d / D of the balance weight joint and the static joint strength (peel strength) based on these results. As can be seen in the figure, d / D is 0.6
The maximum load (peel strength) drops sharply below
When D is 0.6 or more, it becomes substantially constant and saturates. This is d /
If D is less than 0.6, the joint will peel off, whereas d / D will be
This is because if it exceeds 0.6, the joint does not peel off but breaks at the balance weight. That is, the balance weight destruction mode is different from 0.6.

Therefore, from the viewpoint of the static joint strength of the balance weight, it is necessary to set the joint d / D to 0.6 or more.

Example 2 Based on the results of Example 1, a full-scale fatigue test was conducted in which balance weights were joined under welding conditions such that the d / D of the joint was 0.6 or more.

FIG. 6 is a diagram showing a drive shaft model manufactured to confirm the fatigue life of the drive shaft of the present invention. The drive shaft 1 is manufactured by joining a cross joint 4 by arc welding to both ends of a hollow shaft 3 forming a main body of the drive shaft. And
The balance weight 2 is attached to a part of the hollow shaft 3.

The hollow shaft 3 has an outer diameter of 101.6 mm, a thickness of 4.0 mm,
Length 600 mm, are made by the tensile strength of 80 kgf / mm ² grade and 70 kgf / mm ² class machine structural use steel pipes. These steel pipes are medium-carbon steel pipes generally used as high-strength steel pipes, as shown in Table 1, as in Example 1.

The shape of the balance weight and the hollow shaft 3
The method of attaching to the (steel pipe) is the same as in Example 1 (see FIG. 1), and the welding conditions are as shown in Table 3. A drive shaft model as shown in FIG. 6 was manufactured from such a test piece, and an electrohydraulic torsional fatigue tester was used.
A torsional fatigue test was performed at 00 kgf · m. The results are shown in Table 3.

[0063]

[Table 3]

As is clear from Table 3, the test pieces A to D and a to c of the present invention broke at the arc welded portions where the cruciform joints were welded, and the balance weight joints showed a decrease in fatigue strength. I can't.

On the other hand, all of the test pieces E to H and d and e of the comparative examples were broken at the joint of the balance weight, had a short fatigue life, and were not practical. That is, the specimen E welded under the conventional conditions had a d / D of 1.05 and broke at the balance weight joint at 150,000 times. Specimen F had a d / D of 1.20 because the pressure was increased to 600 kgf.
And it broke at the balance weight joint at 109,000 times. Specimen G had a high welding current of 35 kA and an energizing time of 67 ms, which was too long, resulting in a large d / D of 1.30, and 1340
It was broken at the balance weight joint at 00 times. Examination of the joint revealed the occurrence of dust. The specimen H
The energization time was too long, 333 ms, and d / D increased to 1.10, and it broke at the balance weight joint after 113,000 times.

Further, since the welding current of the test piece d was too high, 32 kA, the d / D increased to 1.20, and the test piece d broke at the balance weight joint after 105,000 times. Also, since the welding time of specimen e was as long as 200 ms, d / D was as large as 1.25,
It broke at the balance weight joint at 000 times.

[0067] Example 3 To investigate the relationship between the material and d / D of the steel pipe, 80 kgf / mm ² grade and 70 kgf / mm ² as shown in Table 4
Specimens were prepared in the same manner as in Example 2 using grade-grade steel pipes (the chemical components are shown only for C and Mn), and a fatigue test and measurement of d and D of the joint were performed in the same manner. However, in the fatigue test of the present example, the load torque was set to 1400 kgf · m, and those fractured at the arc welded portion of the cruciform joint were re-welded and tested until fractured at the balance weight portion.

Table 4 collectively shows the results of the test piece manufacturing conditions (welding conditions), the joint investigation and the fatigue test.

[0069]

[Table 4]

The test specimens (IM, fi) of the examples of the present invention
In each case, the d / D is 1.0 or less, the number of repetitions up to break is 400,000 or more, and the fatigue life is about 1.7 times or more longer than the comparative example in which the d / D exceeds 1.0.

FIG. 7 is a diagram showing the relationship between the C content of the steel pipe and the fatigue life from Table 4. From the same figure and Table 4, the fatigue life is prolonged by reducing the carbon material of the steel pipe (C content is 0.12% by weight or less), and the C content is further reduced by 0.08%.
It can be seen that the fatigue life is prolonged by setting the difference in hardness ΔHv of the welded portion to 150% or less by weight% or less.

On the other hand, in the comparative example (specimens N to P and j to l (ell)), the conventional welding conditions (the energization time was as long as 250 ms)
D / D is 1.0 due to projection welding
Therefore, the steel pipe material was reduced to low carbon (specimen M,
k), the fatigue life is short even though the hardness difference ΔHv of the weld is 150 or less (specimen P, 1 (ell)). That is, the effect of improving the fatigue life cannot be obtained simply by reducing the carbon material of the steel pipe, but d / D can be reduced to 1.0 or less by joining under the welding conditions specified in the present invention. The effect is obtained.

Example 4 Here, a test of the material of the balance weight, the welding current value × the energizing time, and the welding power source was performed.

A steel pipe for machine structural use having a tensile strength of 80 kgf / mm ² (0.
Using 10% C, 1.90% Mn, outer diameter 101.6 mm, wall thickness 4.0 mm, length 600 mm), use the same method as in Example 2 except that a 90 kg class hot rolled steel sheet is used as the balance weight. Mainly used) test specimens were prepared. In the fatigue test, the same test machine as in Example 2 was used, the load torque was 1400 kgf · m, and those fractured at the cruciform joint were re-welded and tested until fractured at the balance weight part. Table 5 summarizes the test body manufacturing conditions (welding conditions) and test results.

[0075]

[Table 5]

Regarding the material of the balance weight: Comparing the test pieces Q and R, the fatigue life of the test piece R using a 90 kg class high strength steel sheet as the balance weight is longer than Q using a 40 kg class steel sheet.

About welding current value × energization time: Specimen R
Comparing ~ W, welding current value x energizing time increases and d / D increases, and welding current value x energizing time increases.
For R, U, V and W in the range of 102-495 kA · ms
A fatigue life of more than 650,000 times was obtained. In comparison, specimens S and T with welding current value × conduction time of 1000 and 750 kA · ms
In this case, d / D was near the upper limit of 1.0 of the range defined by the invention, and the fatigue life was slightly shortened.

Regarding the welding power source: It was found that the effect of the welding power source was noticeable in a range where welding current value × power-on time was small. That is, when the welding current value × the energizing time is equal to 102 kA · ms, which is the lower limit of the preferable range defined in the present invention (specimen W: inverter DC: 883,000 times and specimen X: single-phase alternating current:
870,000 times), the fatigue life is almost the same between AC power supply and DC power supply, but with AC power supply, d / D is as small as 0.40, and the static bonding strength is poor.

However, welding current value × energization time is 255 kA ·
ms and within the preferred range defined by the present invention (specimen R: inverter; 895,000 times and specimen Z: condenser; 859000 times and specimen Y: single-phase alternating current: 857000 times) There is almost no difference in fatigue life.

[0080]

The high-strength drive shaft of the present invention has a long fatigue life at the joint of the balance weight, even if the drive shaft is made of high-strength steel of 70 kgf / mm ² class or higher. This drive shaft can be manufactured by performing projection welding under the aforementioned welding conditions. INDUSTRIAL APPLICABILITY The present invention greatly contributes to reducing fuel consumption of automobiles by reducing the weight of drive shafts and saving labor for industrial machines.

[Brief description of the drawings]

FIG. 1 is a view showing a balance weight attached to a part of a hollow shaft of a drive shaft and a state where the balance weight is attached.

FIGS. 2A and 2B are a cross-sectional structure (a) and a schematic diagram (b) of a joint portion where a balance weight of a drive shaft according to the present invention is mounted.

FIG. 3 is a cross-sectional structure (a) and a schematic diagram (b) of a joint portion where a conventional drive shaft balance weight is mounted.

FIG. 4 is a view showing a state where a load is applied to check the static joining strength of the balance weight, where (a) is a view from above and (b) is a front view.

FIG. 5 is a diagram showing a relationship between d / D of a balance weight and static bonding strength (peel strength).

FIG. 6 is a diagram showing a drive shaft model subjected to a fatigue test.

FIG. 7 is a diagram showing the relationship between the C content of the drive shaft and the fatigue life.

[Explanation of symbols]

1: drive shaft, 2: balance weight, 3: hollow shaft, 4: cruciform joint, 5: load rod insertion hole, 6: load rod
7: Support 11: Fused / solidified structure, 12: Unwelded part, 21: Projection (projection)

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-50-2620 (JP, A) JP-A-5-186821 (JP, A) JP-A-6-246439 (JP, A) JP-A-4- 270076 (JP, A) JP-A-7-35200 (JP, A) JP-A-63-290691 (JP, A) JP-A 5-94555 (JP, U) JP-A 3-112159 (JP, U) Japanese Utility Model Application Hei 3-91552 (JP, U) Japanese Utility Model Application Heisei 12-124949 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F16F 15/32-15/34 B23K 11/14 B60B 35/12 F16C 3/02

Claims (7)

(57) [Claims] 1. A power transmission drive shaft in which a balance weight is joined to a part of a hollow shaft constituting the drive shaft by projection welding, wherein the hollow shaft has a tensile strength of 70 kgf / mm ² or more. A high-power drive shaft for power transmission, wherein the ratio (d / D) of the diameter d of the joint to the diameter D of the projection at the joint between the steel pipe and the balance weight is 0.6 to 1.0. 2. A power transmission drive shaft in which a balance weight is joined to a part of a hollow shaft constituting the drive shaft by projection welding, wherein the hollow shaft has a carbon content of 0.05 to 0.12% by weight. , tensile strength is 70 kgf / mm ² or more steel, power transmission ratio of the diameter d of the joint portion to the diameter D of the projection at the junction between the steel pipe and the balance weight (d / D) is 0.6 to 1.0 For high strength drive shaft. 3. A power transmission drive shaft in which a balance weight is joined to a part of the hollow shaft constituting the drive shaft by projection welding, wherein the hollow shaft has a carbon content of 0.05 to 0.12% by weight. A steel pipe having a tensile strength of 70 kgf / mm ² or more, wherein the ratio (d / D) of the diameter d of the joint to the diameter D of the projection at the joint between the steel pipe and the balance weight is 0.6 to 1.0, and Difference between the maximum Vickers hardness of the joint and the Vickers hardness of the steel pipe
High strength drive shaft for power transmission with (ΔHv) of 150 or less. 4. The high-strength drive shaft for power transmission according to claim 1, wherein the material of the balance weight is a steel material having a tensile strength of 70 kgf / mm ² or more. 5. A projection provided on a surface of a balance weight to be welded, wherein a pressure per one of the projections is 100 to 500.
The high-strength drive shaft for power transmission according to any one of claims 1 to 4, wherein the welding is carried out in a time of 1 to 50 ms with the current per projection being 7 to 30 kA by pressing the hollow shaft as kgf. Manufacturing method. 6. A projection provided on a surface of the balance weight to be welded, the pressure per unit of which is 200 to 400.
kgf and pressed against the hollow shaft, the current per projection is 7-20 kA, and the energizing time is 5-50 ms
And the product of the current value and the conduction time is 100 to 500 kA
The method for producing a high-strength drive shaft for power transmission according to any one of claims 1 to 4, wherein welding is performed with ms. 7. A method for manufacturing a high-strength drive shaft for power transmission according to claim 5, wherein said welding is electric resistance welding by direct current.