JPS6288869A - Manufacture of high fatigue strength gear - Google Patents

Abstract

PURPOSE:To improve fatigue strength by performing low temperature sulfurization in the final process. CONSTITUTION:A drive pinion 1 and a ring gear 2 are hobbed and then carburized and quenched. Then they are finished with, low temperature sulfurizing process. With this constitution, fatigue strength is improved because a ferrous sulfide layer on the surface of teeth absorbs stresses even when there is abnormal contact of the teeth.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a gear having high fatigue strength, and particularly to a method of manufacturing a final reduction gear such as a hypoid gear or a final gear.

(Prior art) For example, the
・As shown in Fig. 2, the warp gear consists of a gear pair consisting of a drive pinion 1 and a ring gear 2, and is usually made of case-hardened steel, which is carburized or carbo-nitrided and quenched after gear cutting. Manufactured by lapping and adjusting the tooth contact position to the center of the tooth width.

(Problem to be Solved by the Invention) By the way, if the above-mentioned void gear for automobiles uses a differential assembly with strength and capacity that matches the vehicle type and engine output, even if a large load is applied during operation. Also, the tooth contact surface of the large end 811j is allowed. However, when a larger load is applied, if the gear box including the bearing support system is not sufficiently rigid,
As the teeth of the drive pinion 1 and the edge of the large end of the ring gear 2 come into contact with each other, the lubricating oil film breaks due to increased surface pressure at the area where the interference occurs, causing metal contact. This causes micro-cracks due to fatigue to be induced there. As a result, as shown in FIG. 5, the ring gear 2 suffered a process in which destruction progressed as indicated by the arrow starting from the large end portion 2a, and the life of the gear was significantly reduced.

Conventionally, countermeasures to this problem include changing the design specifications (adjusting the tooth thickness, increasing the tooth root fillet R, and machining the large end diameter), or changing the material or heat treatment conditions. However, no definitive solution has been reached in either case, and for this reason, even if the car is the same model, some models are equipped with high-output engines (with turbo equipment, 4-pulp, etc.), and parts are designed to match that. , tedious procedures such as installing a new differential assembly one rank higher were required.

The present invention has been made in view of the above-mentioned conventional problems.
The object of the present invention is to provide a method for manufacturing gears that can fully improve fatigue strength without changing design specifications, materials, or heat treatment conditions, thereby expanding the range of use as much as possible.

(Means for solving the problem) For this reason, the present invention performs surface hardening treatment after gear cutting,
It is characterized in that it is then wrapped and finished by performing low-temperature sulfurization treatment in the final step.

Surface hardening treatments include carburizing and quenching, and carbonitriding and quenching.

In addition, low-temperature sulfurization treatment is performed by adding 160 to 19 ft of sodium sulfide A (Na, So) to an alkali metal salt bath.
A two-pet method is used in which the temperature is maintained at 0° C. and electricity is applied for 10 to 20 minutes using the object to be treated (gear) as an anode and the treatment tank as a cathode.

(Function) In the method for manufacturing a gear having the above configuration, iron sulfide is generated on the surface of the gear by performing the final low-temperature sulfurization treatment.

This iron sulfide has a hexagonal crystal structure, has a small coefficient of friction, and is easy to plastically flow. This plastic flow causes the porous soft layer to increase the actual contact surface, and as a result, metal contact with the abnormal tooth contact is avoided, susceptibility to microcracks is alleviated, and fatigue strength is improved.

(Example) Examples of the present invention will be explained below in comparison with comparative examples.

Example 1 Using JIS 80M420H case hardening steel, the drive pinion (1) and ring gear (2) shown in FIG. The drive pinion is then finished by lapping, and the ring gear is finished by lapping.
Finished with low temperature sulfurization treatment. Low-temperature sulfurization treatment involves adding sodium sulfide to an alkali metal salt solution and heating it at 180°C.
with the ring gear as the anode and the treatment tank as the cathode.
I turned on the electricity and went.

The gear pair (hypoid gear) of the drive pinion and ring gear obtained as described above was assembled into a differential assembly and subjected to a bench simulation test.
An SN curve was obtained.

Example 2 A drive pinion and a ring gear were obtained under basically the same conditions as in Example 1, and the drive pinion was subjected to shot peening after carburizing and quenching. In addition, Example 1
It was subjected to the same bench simulation test.

Example 3 JIS 80M420H case hardened steel was used, and only the drive pinion was carburized and quenched, and then the tooth bottom was machined.

The ring gear was manufactured under basically the same conditions as in Example 1. Both samples were also subjected to the same bench simulation test as in Example 1.

Comparative Example Using JIS 80M420H case hardening steel, the same drive pinion and ring gear as in Example 1 and t W+, both 9
Carburizing and quenching was performed at 30°C for 250 minutes and finished with lapping. Further, both were subjected to the same bench simulation test as in Example 1.

The test results are summarized in the table below and Figure 1.

Note that the fatigue limit ratio is expressed as a ratio when the fatigue limit of the comparative example is set to 100.

From this, it is clear that Examples 1 to 5 according to the present invention, in which the ring gear was subjected to the final low-temperature sulfurizing treatment, all have higher fatigue limits than the comparative example, which is a combination of carburizing and quenching. became.

In addition, when combining a drive pinion with a ring gear that has been subjected to low-temperature sulfurizing treatment, it is better to combine a drive pinion that has been carburized and quenched and then sit-peeled than when it is combined with a drive pinion that has been simply carburized and quenched. The fatigue limit is extremely high, and the carburized and quenched layer is made of carbide tools (CB).
It was found that when a drive pinion with tooth bottom cutting performed in N) is combined, the fatigue limit becomes even larger than in 1. Furthermore, in the combination of carburizing and quenching (comparative example), fatigue failure occurred due to ring gear screaming, whereas in this example, all fatigue failure occurred on the drive pinion side, and the fatigue strength of low-temperature sulfurization treatment It can be seen that the improvement effect is large.

It has been confirmed that iron sulfide produced by low-temperature sulfurization has a small friction coefficient and is effective in seizure resistance and wear resistance. Incidentally, ring gears were conventionally treated with manganese phosphate (Luprite) for the purpose of initial break-in, but when a seizure test was conducted using a mechanical testing laboratory-type test machine, it was found that the ring gears that had been subjected to low-temperature sulfurization treatment were The seizure life was 5 to 4 times longer than that which had been completely treated with manganese phosphate.

In the above embodiments, all examples were shown in which the ring gear was subjected to low-temperature sulfurization treatment, but the present invention is not limited thereto. It may also be subjected to low temperature sulfurization treatment.

(Effects of the Invention) As explained above in detail, the present invention finishes the gear by performing the final low-temperature sulfurization treatment, so even if there is abnormal tooth contact, the iron sulfide generated on the gear surface will be removed. It has an absorbing effect and is effective in improving fatigue strength as much as possible.

Furthermore, the above-mentioned improvement in fatigue strength makes it possible to expand the range of use without changing design specifications, materials, or heat treatment conditions, which has a significant effect.

[Brief explanation of drawings]

Figure 1 is an S-N diagram showing the fatigue test results of hypoid gears obtained by the manufacturing method of the present invention in comparison with comparative examples;
The figure is a perspective view schematically showing the appearance of a hypoid gear.
The figure is an explanatory diagram showing the failure mode of a conventional hypoid gear. Figure 1 Figure 2 Figure 30

Claims (1)

[Claims] (1) A method for manufacturing a high fatigue strength gear, which comprises performing a surface hardening treatment after gear cutting, followed by lapping, and finishing by performing a low-temperature sulfurization treatment in the final step.