JP2000257697A - High surface pressure resisting gear and manufacture therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain pitching generated in a root part by finishing a gear base material to a specified surface roughness or less, and then coating the tooth flank with titanium nitride or titanium carbonic nitride to have its surface roughness in a specified range. SOLUTION: After machining to a designated gear form, carbonitriding hardening is conducted, and the tooth flank of the grinding finished gear base material 2 is further polished by barrel polishing and chemical polishing, thereby finishing the tooth flank to have a surface roughness of Ra 0.12 μm or less. After that, the tooth flank of the gear base material 2 is coated with titanium nitride or titanium carbonic nitride by ion plating to have a surface roughness in a range of Ra 0.02-0.15 μm, thereby coating high bearing pressure titanium nitride to obtain a high bearing pressure gear 1. Thus, pitching generated in the root part can be restrained so as to improve the tooth flank pitching strength of the gear.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gear used as a component of a power transmission device of an automobile or the like, and other various opportunity devices, and particularly to an application requiring excellent surface fatigue strength. The present invention relates to a suitable high surface pressure resistant gear and a method of manufacturing such a high surface pressure resistant gear.

[0002]

For example, power transmission devices used in automobiles tend to be smaller and lighter for the purpose of improving fuel efficiency, and the load on the power transmission gears has been further increased accordingly. Therefore, a gear having more excellent root fracture strength and tooth flank strength has been required.

[0003] Of these, the root strength has been dramatically improved by applying compressive residual stress to the root by employing shot peening, and has reached a level at which there is almost no problem. Accordingly, in recent years, fatigue damage to the tooth surface such as pitching or scoring has become a problem instead of the root fracture fatigue strength.

The cause of pitting and scoring is that in a state where rolling and sliding contact coexist, shear stress and tensile stress act on the inside or near the surface of the tooth surface, resulting in fatigue damage as a result of these generated stresses. Have been done. Based on these, you can increase the pressure angle of the gear,
A method of alleviating one-side contact by forming a tooth surface with a crowning shape and a method of improving lubrication of a contact surface have been adopted.

Japanese Patent Application Laid-Open No. 62-88869 discloses a method of forming a layer having excellent lubricity on the tooth surface by performing low-temperature sulfurizing treatment in the final step. No. 264727 discloses that after surface hardening and shot peening, hexagonal boron nitride (h-B
N) A method of forming a compressive residual stress on the outermost surface by grinding with a grindstone is disclosed.

[0006] However, in the above-described method, although a certain effect can be obtained in a conventional general gear, a sufficient effect can be obtained in a gear in which a larger load is applied than before. Can not.
That is, the lubricating layer formed by the low-temperature sulfurizing treatment as described in JP-A-62-88869 exhibits a lubricating effect only at the beginning of the operation in sliding at a high surface pressure. In addition, there is a problem that the lubricating layer is worn out with the elapse of the sliding time and the effect is lost. Further, as described in Japanese Patent Application Laid-Open No. Hei 1-264727, in a gear having a compressive residual stress applied to a tooth surface by performing shot peening and grinding the tooth surface with a hexagonal boron nitride grindstone. In addition, heat is generated by intense sliding during operation, and the compressive residual stress applied to the tooth surface is released, so that the effect of improving the tooth surface pitching strength cannot be obtained as expected. That is, in gears used under higher surface pressure conditions than before, no effective means for increasing the tooth flank pitching strength has been found at present. Finding and establishing technology has been an issue for high surface pressure gears.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in the conventional high surface pressure gear. For example, in a gear used for a drive transmission device such as a transmission of an automobile, particularly in a tooth root portion. An object of the present invention is to provide a high-surface-pressure resistant gear capable of suppressing the occurrence of pitting and improving the tooth surface pitting strength, and a method of manufacturing such a high-surface-pressure resistant gear.

[0008]

Generally, the tooth surface of a gear is
Sliding in a contact state where rolling and sliding are mixed,
At the pitch point of the tooth surface, the ratio of the rolling contact and the sliding contact increases as the distance from the pitch point increases. Therefore, it is known that the relative sliding speed is the highest at the root and the tip and the heat generation is the highest at the root and the tip. In a gear operated under a high load, the feature of the occurrence of the pitching damage often occurs at the tooth root where the direction in which the load applied to the tooth surface moves and the direction in which the tangential force acts are opposite.

From such a viewpoint, as a result of intensive studies to solve the above-mentioned problems, the surface roughness of the gear base material was reduced to Ra.
After finishing to 0.12 μm or less, the tooth surface is coated with titanium nitride or titanium carbonitride so that the surface roughness is in the range of Ra 0.02 to 0.15 μm, so that the relative sliding speed is large. It has been found that friction at the tooth tip and the root can be reduced and the occurrence of pitching at the tooth root can be suppressed.

The present invention is based on such knowledge, and the high surface pressure resistant gear according to claim 1 of the present invention has a tooth surface coated with titanium nitride or titanium carbonitride. Surface roughness is Ra0.02-Ra
The configuration is within a range of 0.15 μm, and such a configuration in the high surface pressure resistant gear is used as means for solving the above-described conventional problem.

[0011] As a preferred embodiment of the high surface pressure resistant gear according to the present invention, in the high surface pressure resistant gear according to the second aspect, the thickness of the coating layer of titanium nitride or titanium carbonitride is 0.1 mm.
5 to 3 μm, and the surface hardness of the coating layer is Hv
In the high surface pressure resistant gear according to claim 3, the carbon steel is formed by coating titanium nitride or titanium carbonitride on a carbonitrided and quenched structural steel or a carburized and quenched alloy steel. In the high surface pressure resistant gear according to claim 4, the amount of droplets on the surface of the coating layer is 700 to 700.
In the high surface pressure resistant gear according to the fifth aspect, the number of droplets at the tooth tip and root at the coating layer surface is 1000 / cm ^2.
cm ² or more, and the amount of droplets near the pitch point is 500 / cm ² or less.

According to a sixth aspect of the present invention, there is provided a method for manufacturing a high-surface-pressure-resistant gear, wherein the surface roughness of the tooth surface of the gear base material is finished to Ra 0.12 μm or less, and then the titanium nitride is added to the tooth surface. Alternatively, the present invention is characterized in that titanium carbonitride is coated, and such a configuration in a method of manufacturing a high surface pressure resistant gear is used as means for solving the above-mentioned conventional problems.

[0013]

The reasons for limiting the numerical values of the present invention will be described below together with the background of the above findings.

First, eight sets of cylindrical flat test pieces Tf and crowned test pieces Tc as shown in Table 1 were prepared.
These flat test pieces Tf were tested by the test apparatus shown in FIG.
And the crowned test piece Tc were slid with each other, and the frictional characteristics at this time were measured.

[0015]

[Table 1]

As shown in FIG. 2A, the test apparatus 20 comprises a flat test piece Tf and a test piece T with crowning.
The main shaft 21 and the driven shaft 22 for mounting the respective members c and c are respectively driven by motors 23 and 24 directly or via a belt 25. Motor 24 and driven shaft 22
Is mounted on the movable base 26 via a bearing, is moved in the direction of arrow A in the figure by an air cylinder (not shown), and a load can be applied between the test pieces Tf and Tc. The reason why the test piece Tc is provided with the crowning is to prevent a hit.

The frictional force generated between the flat test piece Tf and the test piece with crowning Tc is equal to the test piece Tf and the motor 23.
It can be measured by a torque meter 27 installed between the two. As shown in FIG. 2B, the lubricating oil L is placed in the test tank 28 so that the lower ends of the test pieces Tf and Tc are immersed in the lubricating oil L.
The power is supplied to the sliding portion along with the rotation of f and Tc. In the test apparatus 20, since the rotation of the two cylindrical test pieces Tf and Tc can be controlled independently, the sliding conditions at each part of the tooth surface, such as a gear pitch point and a tooth root, are reproduced. I can do it.

The test piece Tc with crowning has the same grinding finish as that of a normal gear tooth surface, and the flat test piece Tf has been finished to various surface roughnesses only by grinding or further superfinishing, and then ionized. The coating treatment of titanium nitride or titanium carbonitride was performed by a plating method, the surface roughness of the coating layer was measured, and the number of droplets per unit area on the surface was roughly estimated by microscopic observation. Note that the droplet means a projection made of titanium fine particles which are scattered in a molten state from a titanium target and adhere to the coating layer during ion plating.

Then, as shown in Table 1, the coefficient of friction when each test piece was combined was measured using the test apparatus 20 described above. The test conditions were as follows: surface pressure: 1.5 GPa, lubricating oil temperature: 60 ° C., relative sliding speed 1.25 m / sec.
It measured about the case of 0% of slip rates, and the case of 20-60%. In addition, the combination with the flat test piece Tf not coated (No. 1 and No. 1).
2) was also measured for comparison. In this case, no.
1 corresponds to the combination of the surface roughness by the conventional gear.

FIGS. 3 and 4 show an example of the measurement results. FIG. 3 shows the friction coefficient when the slip ratio is 0%.
FIG. 4 shows the coefficient of friction when the slip ratio is 60%. As shown in FIG. 3, when the slip ratio is 0% (pure rolling), that is, with respect to the friction coefficient corresponding to the condition at the pitch point of the gear tooth surface, No. 1 having the smallest surface roughness of the coating layer. The combination of 5 is the smallest. On the other hand, as shown in FIG. 4, when the slip ratio is 60%, that is, with respect to the friction coefficient corresponding to the sliding condition near the tooth root, the base surface before coating is super-finished, and after coating, No. 2 was a combination with a flat test piece Tf having a small surface roughness and a relatively small amount of droplets on the surface of the coating layer. 4 and no. The value of 8 was lower than the others.

FIG. 5 shows a flat test piece Tf in FIG.
FIG. 6 shows the surface roughness of the test piece with crowning Tc before and after the test. As is apparent from FIG. 6, the coated flat test piece T
f (No. 3 to 8) has the effect of reducing the surface roughness of the mating test piece, that is, the test piece Tc with crowning, as compared to the flat test piece Tf (No. 1, 2) without coating. You can see that. This is because when a titanium nitride (TiN) or titanium carbonitride (TiCN) layer is formed by an ion plating method, grains formed on the surface, which are called droplets, protrude from the surface, and a test piece with crowning, which is a mating test piece. This is because the surface of Tc is polished. In addition, the combination No. 1 with the flat test piece Tf coated without superfinishing after the grinding process. 3 and No. 3 In No. 7, the mating test piece Tc is polished to reduce the surface roughness, but the flat test piece Tf itself has a surface roughness of Ra 0.1 μm or less, although the droplets fall off the surface of the coating layer to reduce the surface roughness. No, the combination of surface roughness No. A coefficient of friction not different from 1 is shown.

After the substrate surface is super-finished, N is combined with a coated flat specimen Tf.
o. 4 and no. 8, the flat test piece Tf
Polished the surface of the counterpart test piece Tc and also had a small surface roughness. 1
It has a lower coefficient of friction than that. In addition, in combination with the test piece Tf having an extremely small amount of droplets on the surface of the coating layer (No. 5), the combination with the test piece Tf having an extremely large amount of droplets due to insufficient polishing action on the counterpart test piece Tc. In (No. 6), the aggressiveness to the mating test piece Tc is high and the polishing action is not sufficient, the surface roughness of the flat test piece Tf itself does not become small, and a sufficient friction reducing effect cannot be obtained. confirmed.

From the above, for example, by superfinishing the tooth surface of the gear base material, the surface roughness of the tooth surface is reduced to Ra0.
After processing to 12 μm or less, the tooth surface is coated with titanium nitride or titanium carbonitride, and the surface roughness of the coating layer is set to a range of Ra 0.02 to Ra 0.15 μm. As a result, the generation of frictional heat and excessive stress on the tooth surface are suppressed, and the occurrence of pitting damage is suppressed. That is, when the surface roughness of the coating layer is less than Ra 0.02, the function of polishing the tooth surface of the mating gear is reduced, and the effect of reducing the frictional force cannot be obtained.
If it exceeds m, the friction increases and the desired low friction performance cannot be obtained.

The surface roughness of the coating layer follows the surface roughness of the gear base material as the base and changes depending on the amount of droplets (the larger the amount of droplets, the greater the surface roughness). By adjusting these, a desired surface roughness can be obtained.

At this time, from the viewpoint of stably forming a coating layer having abrasion resistance, the coating layer of titanium nitride or titanium carbonitride has a thickness of 0.5 μm to 3 μm. It is desirable that the surface hardness is Hv900 or more. In other words, to make the coating layer thinner, the coating time must be shortened or the coating speed must be reduced,
If the thickness is less than 0.5 μm, it is difficult to obtain a coating layer having stable performance. If the thickness exceeds 3 μm, the stress in the layer caused by the difference in thermal expansion from the underlying gear base material increases, and the This is because the strength of the layer tends to decrease. When the surface hardness of the coating layer is less than Hv900, the wear resistance is insufficient, and the coating layer is easily worn. Note that the surface hardness of the coating layer can be changed by the amount of nitrogen contained in the coating layer, and can be adjusted by coating conditions such as gas pressure, applied voltage, and film formation rate during ion plating.

As the gear base material, from the viewpoint of preventing softening due to temperature rise during ion plating,
As described in claim 3, it is desirable to use carbonitrided and quenched structural steel or carburized and quenched alloy steel.

Further, the amount of droplets present on the surface of the coating layer is desirably in the range of 700 to 3000 droplets / cm ² . This means that the amount of droplets is 700 / cm ²
If it is less than 3,000, it is difficult to obtain the function of grinding the mating gear to reduce the surface roughness of the tooth surface.
If m ² is exceeded, seizure tends to occur easily with the mating gear. Further, under severe conditions, at a pitch point where there is no slip, the droplet is difficult to fall off and has a high surface pressure. Therefore, from the viewpoint of suppressing the generation of friction and high stress, as described in claim 5, It is also desirable that the amount of droplets on the surface of the coating layer at the tip and the root of the tooth is 1000 / cm ² or more, and the amount of droplets on the surface of the coating layer near the pitch point is 500 / cm ² or less, if necessary. . That is, since the relative sliding speed with the mating gear is high at the root and the tip of the tooth surface and the efficiency of polishing the tooth surface of the mating gear is high, the droplet amount is particularly 1000 pieces / c.
By setting m ² or more, the polishing effect on the mating gear becomes remarkable. Contrary to this, rolling contact occurs at the pitch point, almost no slippage occurs, and it is difficult for the droplets to smooth the mating tooth surface and the own tooth surface. In order to reduce the change in the tooth surface roughness and reduce the frictional force, it is preferable to reduce the surface roughness by setting the amount of droplets at the corresponding portion to 500 or less / cm ² . Note that, in the present invention, the vicinity of the pitch point refers to a region of one third of the tooth surface around the pitch point.

In the method of manufacturing a high surface pressure resistant gear according to claim 6 of the present invention, the tooth base surface roughness of the gear base material is set to Ra.
After finishing to 0.12 μm or less, the tooth surface is coated with titanium nitride or titanium carbonitride. The surface roughness of the base material tooth surface is Ra0.
When it exceeds 12 μm, the surface roughness of the coating layer is increased due to the influence of the surface roughness after coating, and it is difficult to make the range preferable for a high surface pressure resistant gear, and the adhesion to the coating layer is reduced. It tends to be.

[0029]

According to the high surface pressure resistant gear according to the first aspect of the present invention, the tooth surface has a surface roughness of Ra0.02 to Ra0.15μ.
Since it is provided with a coating layer composed of titanium nitride or titanium carbonitride, the pitching generated at the root of the tooth can be suppressed and the tooth surface pitting strength of the gear can be improved even in operation under high surface pressure conditions. This is an extremely excellent effect of being able to do so.

In a high-pressure bearing gear according to a second aspect of the present invention, the coating layer has a thickness of 0.5 to 3 μm and a surface hardness of Hv900. As described above, a coating layer having excellent wear resistance can be stably formed. Similarly, in the high surface pressure resistant gear according to the third aspect, carbonitriding and quenching and quenching are performed as the gear substrate. Since the coated structural steel or the carburized and quenched alloy steel is coated, it is possible to prevent the base material from softening due to a rise in temperature during ion plating. For gears, the amount of droplets on the surface of the coating layer is 700 to 3000 / cm2.
Therefore, it is possible to reduce the surface roughness by polishing the mating tooth surface without causing seizure with the mating gear, and in the high surface pressure resistant gear according to claim 5 as an embodiment, The amount of droplets at the tooth tip and root at the coating layer surface is 1000 / cm ² or more, and the amount of droplets near the pitch point is 5
Since it is not more than 00 pieces / cm ^2, it is possible to enhance the polishing effect at the tooth tip portion and the root portion where the sliding speed relative to the mating gear is large, and to reduce the frictional force at the pitch point where slip does not occur.

Further, in the method for manufacturing a high surface pressure resistant gear according to claim 6 of the present invention, the tooth base surface of the gear base material as a base is finished to Ra 0.12 μm or less, and then the tooth surface is Is coated with titanium nitride or titanium carbonitride to prevent stress concentration due to roughness projections, improve the adhesion of the coating layer, and reduce the surface roughness of the coating layer to reduce friction. A very good effect that the force can be reduced is brought about.

[0032]

EXAMPLES The present invention will be described below more specifically based on examples. Example 1 First, structural steel SC specified in JIS G 4052
After machining into a predetermined gear shape using M420H,
The tooth surface of the gear base material 2 that has been subjected to carbonitriding and quenching and quenching is further polished by subjecting the tooth surface of the gear base material 2 to barrel polishing and chemical polishing to reduce the tooth surface roughness to Ra.
Finished to 0.070 μm. Next, a titanium nitride (Ti) is formed on the tooth surface of the gear base 2 by an ion plating method.
By coating N), a high surface pressure gear 1 as shown in FIG. 1 was obtained. At this time, the coating layer 3 had a thickness of 1.0 μm, a surface hardness of Hv 1800, a surface roughness of Ra 0.082 μm, and a surface droplet amount of 225.
It was 0 / cm ² . Example 2 At 2 % by weight, C: 0.18%, Si: 0.48%, Mn:
0.34%, P: 0.009%, S: 0.013%, C
r: 2.63%, Al: 0.025%, N: 0.012
Carbide-hardened alloy steel containing 0.3%
gear base material 2 having a carbon concentration of 0.9 to 1.5%, a mean particle size and area ratio of precipitated carbides of 0.2 to 0.5 μm and 2 to 20%, respectively, and a residual austenite amount of 25%. Was prepared, and the tooth surface, which had been ground and finished in the same manner as in Example 1, was polished and finished by barrel polishing and chemical polishing to finish the surface roughness of the tooth surface to Ra 0.060 μm.
Next, the tooth surface of the gear base 2 was coated with titanium nitride (TiN) by an ion plating method to obtain a high surface pressure gear 1 as shown in FIG.

Further, by processing only the vicinity of the pitch point of the tooth surface with wrapping tape, the surface roughness near the pitch point and the amount of droplets on the surface are set to Ra 0.063 μm and 480 pieces / cm ² , respectively. Ra 0.078 μm and 2750 particles /
cm ² . Comparative Example In order to compare with the high surface pressure gear 1 according to Examples 1 and 2 above, the SC which is generally used as a gear material was used.
A carbon gear was subjected to carbonitriding and quenching using M420H to produce an uncoated gear. At this time, the surface roughness of the tooth surface was finished to Ra 0.24 μm by grinding. Life Test The gears obtained in the above Examples and Comparative Examples were subjected to a life test to compare and evaluate the life in which pitting damage occurred. In the life test, a gear pitting tester of a power circulation type was used, and the gears of Examples 1 and 2 and Comparative Example were subjected to a test as small gears. The mating gear is made in the same manner as the gear of the first embodiment. Test conditions are as follows: rotational torque: 34 kg-m and 28 kg-m, lubricating oil: automatic transmission oil (ATF), oil temperature: 120 ° C., rotation speed: 2000 rpm. It was adopted. The pitting life was defined as the cumulative number of revolutions at the time when the value obtained by dividing the peeling area due to pitting damage generated on the tooth surface of the small gear (test gear) by the effective meshing area of all gears exceeded 3%. Table 3 shows the results.

[0034]

[Table 2]

As is clear from the results in Table 2, Example 1
And, in the high surface pressure resistant gear according to Example 2, even when the cumulative number of rotations is 2 × 10 ⁷ , no pitching occurs,
It was confirmed that the pitting life was significantly improved. Also, almost no wear occurred. On the other hand, in the comparative example, when the rotational torque is 34 kg-m, the cumulative rotation speed is 3.1 × 10 ⁶ , not only pitching occurs at the tooth root portion, but also the amount of wear at the tooth root portion is large. It was confirmed that the vibration generated from the gears increased accordingly.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing a shape of a high surface pressure resistant gear according to the present invention.

FIGS. 2A and 2B are schematic explanatory views showing the structure of a two-cylinder test apparatus used for measuring a coefficient of friction in the present invention.

FIG. 3 is a graph showing a measurement result of a friction coefficient when a slip ratio is 0%.

FIG. 4 is a graph showing measurement results of a coefficient of friction when the slip ratio is 60%.

FIG. 5 is a graph showing a change in surface roughness of a cylindrical flat test piece before and after the test.

FIG. 6 is a graph showing a change in surface roughness of a cylindrical test piece with crowning before and after the test.

[Explanation of symbols]

 1 High surface pressure resistant gear 2 Gear base material 3 Coating layer

Claims (6)

[Claims] 1. A high surface pressure resistant gear having a tooth surface coated with titanium nitride or titanium carbonitride and having a coating layer having a surface roughness of Ra 0.02 to Ra 0.15 μm. 2. The high withstand pressure according to claim 1, wherein the thickness of the coating layer of titanium nitride or titanium carbonitride is 0.5 to 3 μm, and the surface hardness of the coating layer is Hv900 or more. Surface pressure gear. 3. The high-resistance steel according to claim 1, wherein the carbonitrided and quenched structural steel or the carbonized and quenched alloy steel is coated with titanium nitride or titanium carbonitride. Surface pressure gear. 4. The high surface pressure resistant gear according to claim 1, wherein the amount of droplets on the surface of the coating layer is 700 to 3000 / cm ² . 5. The amount of droplets at the tooth tip and root at the coating layer surface is 1000 / cm ² or more, and the amount of droplets near the pitch point is 5
The high surface pressure resistant gear according to any one of claims 1 to 3, wherein the number is not more than 00 pieces / cm ² . 6. The surface roughness of a tooth surface of a gear base material is Ra.
6. The method according to claim 1, wherein the tooth surface is coated with titanium nitride or titanium carbonitride after finishing to 0.12 [mu] m or less.