JPH05169324A - High strength hypoid gear - Google Patents

Abstract

PURPOSE:To provide a hypoid gear whose fatigue strength is excellent even under high torque. CONSTITUTION:Endrem 10 processing is executed at the large end of the tooth part of either one or both of a driving pinion and a ring gear in a pair of hypoid gears, and after the tooth part is carburizedly quenched, it is shot peened and moreover chemically polished. The movement of a tooth bearing at the time of inputting torque is controlled by the endrem 10 of the large end part 12 to make a local tooth bearing at a heel approach a tooth bearing at a proper position. In addition, since the defective surface layer of the abnormally carburized layer or the like of the tooth part is removed by chemical polishing after the carburized quenching and shot peening of the tooth part, the tooth bearing between the driving pinion and the ring gear turns into a face bearing at a portion being excellent in fatigue strength to sharply improve the fatigue strength of the gears.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reduction gear which is a power transmission device for an automobile, and more particularly to a hypoid gear.

[0002]

2. Description of the Related Art A reduction gear is composed of a drive pinion that receives rotational power from a propeller shaft and a ring gear that crosses at right angles to the drive pinion to reduce the speed. Among them, a hypoid gear is one in which the center of the ring gear and the drive pinion are eccentric. Therefore, it can transmit a large driving force.

These gears for power transmission of automobiles are required to have high strength and are used after being subjected to quenching treatment, particularly carburizing and quenching treatment. As a result, a carburized and quenched layer having high hardness and residual stress of compression is formed, and it is said that the fatigue strength is improved by the action of both of them.

However, with the recent increase in the performance of mechanical devices,
Since the component parts are used under high-speed, high-load and severe conditions, it is required in the industry to increase the strength of the component parts. Particularly in the automobile industry, weight reduction of vehicles for the purpose of improving fuel efficiency has become an important issue.
Therefore, development of technology for strengthening various parts is strongly demanded.

Therefore, in addition to the carburizing and quenching treatment, shot peening treatment is often added to the gear for power transmission of automobiles. Shot peening is a surface treatment method in which relatively spherical spherical iron particles are made to collide with the surface of the component at high speed in order to improve the fatigue strength of the metal component. It is said that this shot peening treatment improves fatigue strength because a large compressive residual stress is applied over 200 to 400 μm below the surface of the steel member.

However, the residual stress generated in the steel member by this shot peening is 10-100 below the surface.
It has a basic characteristic that it has a peak at a position inside μm, and the surface layer has a smaller compressive stress value. In addition, since shot peening causes hard particles to collide at high speed, flaws are likely to occur on the surface of the member.

Further, when the steel member is carburized and quenched,
There is an incompletely hardened layer called a carburized abnormal layer extending from 5 to 50 μm from the surface. Since the abnormal layer of low strength remains without being removed even by the shot peening treatment, it easily becomes a starting point of fatigue fracture along with surface flaws, etc., and it is the actual situation that stable and significant improvement of fatigue strength cannot be expected.

As a method of solving these problems of the prior art, in order to remove the surface layer which hinders the improvement of fatigue strength, a surface hardening treatment is performed followed by shot peening, and further cubic nitriding. Mechanical polishing methods have been proposed, such as "High-strength gear manufacturing method" (Japanese Patent Laid-Open No. 1-264727) in which a boron wheel is ground to finish gear cutting.

[0009]

From the viewpoint of fatigue strength, it is required to remove the surface layer having defects and to make the finished surface as smooth as possible. However, in the mechanical polishing method as proposed above, hardened steel is used. Since the hardness of the member is high, the processing efficiency of grinding finish is very low. In particular, in the case of a component such as a gear having a complicated shape, there is a problem in that the machining efficiency is remarkably lowered if the root portion of the tooth, which is problematic in improving the fatigue strength, is well ground.

In order to solve such a problem, the inventors of the present invention proposed a method for improving the fatigue strength of a steel member in the prior application (Japanese Patent Application No. 2-328190) by chemically polishing the surface of the steel member subjected to shot peening. is doing. In this proposal, since it is based on the chemical dissolving power of the chemical polishing treatment liquid rather than a special external action such as mechanical polishing or electrolytic polishing as in the prior art, Uniform polishing proceeds on the surface of the material to be contacted, regardless of the hardness and shape of the material.

As a result, various defects that tend to cause fatigue fracture existing after the shot peening process are completely removed by polishing, and a partial residue can be eliminated. Further, since the steel surface after the chemical polishing treatment is significantly smoothed by the chemical polishing action, stress concentration at the starting point of fatigue fracture is relieved, and it is possible to significantly and stably improve the fatigue strength.

As described above, in the above-mentioned proposal that the shot peening is performed after the carburizing treatment and the chemical polishing treatment is further performed, the outermost surface of the steel member has extremely high hardness, high compressive residual stress, and a good surface condition. (Good surface roughness, no abnormal carburizing layer) is obtained, so extremely high fatigue strength is obtained. Therefore, this proposal is considered to be an effective means for designing lightweight parts.

Therefore, the inventors have tried to apply the above-mentioned proposal to a hypoid gear pair, which is a component thereof, in order to enhance the fatigue strength of a differential for an automobile. Table 2 is a comparison of the number of repetitions until a certain torque is input in a vehicle differential unit state, where Conventional Example 1 is carburized and shot peened, and Conventional Example 2 is further chemically polished. It was added.

However, as shown in Table 2, the conventional example 2
Although it is expected that the fatigue strength will be greatly improved by performing chemical polishing after shot peening, the life until damage is 790,000 times in Conventional Example 1 and 50 in Conventional Example 2. However, the fatigue strength was decreased in the durability test in the unit state.

According to the present invention, the hypoid gear pair which is carburized and then shot peened and chemically polished is inferior in fatigue strength to the hypoid gear pair which is carburized and then shot peened. A high-strength hypoid gear that is more excellent in fatigue strength than before by being subjected to carburizing treatment, shot peening, and chemical polishing treatment. The purpose is to provide.

[0016]

Means for Solving the Problems The inventors of the present invention first performed a fatigue strength evaluation in a unit state in order to investigate the reason why the hypoid gear pair subjected to the chemical polishing treatment is inferior in fatigue strength, and a conventional example. The fracture surfaces of the hypoid gear pairs of Example 1 and Conventional Example 2 were observed. FIG. 2 is a copy diagram of the fracture surface of the ring gear of Conventional Example 1, and FIG. 3 is a copy diagram of the fracture surface of the ring gear of Conventional Example 2.

Although it is not easy to identify the primary damage site from these fracture surfaces, the present inventors tried to identify it by macro and micro fractography. As a result, it was possible to identify that the part marked with a circle in FIG. 2 and FIG. 3 was the starting point of the fracture. Note that FIG. 4 is a 1000 × micrograph showing the metal structure at the fracture starting point of FIG. 2, and FIG. 5 shows the metal structure at the fracture starting point of FIG.
It is a micrograph of 00 times, and it is clear that all of them are fatigue fractures.

As shown in FIG. 2, in the conventional example 1, the fatigue fracture starts from the central portion in the tooth trace direction, whereas in the conventional example 2, the fatigue fracture starts from the large edge portion as shown in FIG. It has begun. In both the conventional example 1 and the conventional example 2, the tooth contact is adjusted so as to be located at the central portion in the tooth trace direction in the lapping process, and the difference in the damage state does not occur due to the mere difference in the tooth contact. Therefore, the present inventors made the following hypothesis from the viewpoint of tooth contact movement when torque is input.

As the input torque of the hypoid gear pair increases, the bearing support portion and the case to which the gears are attached are flexed, so that the tooth contact gradually moves to the tooth tip of the large end. The amount of the conventional example 2 was larger than that of the conventional example 1, and the above-mentioned difference in the damaged state was caused. The difference in the tooth contact movement amount with respect to the torque input was considered to be due to the following factors.

Since there is no difference in tooth profile between Conventional Example 1 and Conventional Example 2, they move to the tooth end at the large end in the same manner in response to torque input, but Conventional Example 1 has an abnormal carburized layer on the outermost surface. Since there is a soft layer having a Hv of about 400 to 500, the surface is crushed and comes into contact with the surface. On the other hand, in Conventional Example 2, the abnormal carburizing layer is completely removed by chemical polishing, so that the cushioning action does not occur and the large end tooth It was thought that the tooth contact had already occurred locally, and the actual amount of tooth contact movement increased.

[0021] Therefore, the inventors of the present invention, by controlling the above-mentioned amount of tooth contact movement to bring it closer to the correct contact from the heel contact, it is possible to achieve surface contact at a portion having excellent carburizing fatigue strength and excellent fatigue strength. We thought that it would be possible to improve the tooth movement, and conducted intensive studies on measures to control the amount of tooth contact movement. As a result, the inventors arrived at the present invention while actually trial-producing and evaluating the idea of performing an appropriate endrem processing on the hypoid gear pair.

The high-strength hypoid gear of the present invention has end teeth processing on the tooth ends of one or both of the drive pinion and the ring gear of the hypoid gear pair, and after carburizing and quenching the teeth, shot peening treatment is performed. The point is that chemical polishing is further performed.

The endrem processing applied to the large end of the tooth portion may be performed on either one of the drive pinion or the ring gear of the hypoid gear pair, or both. The point is that the amount of tooth contact movement of the drive pinion and the ring gear should be properly controlled.

Regarding the amount of end rem, for example, when it is applied only to the ring gear, as shown in FIG.
The length L of 0 is 1/1 of the distance from the large end 12 to the small end 14.
It is preferable that the height is 5 to 1/4 and the height x is 0.02 to 0.3 mm. If the length L of the end rem is less than 1/15, the effect of suppressing the amount of tooth contact movement is not sufficient, and good strength characteristics cannot be obtained. If it exceeds 1/4, the actual meshing ratio decreases and vibration and noise levels are reduced. Since it rapidly increases, the distance is limited to 1/15 to 1/4 of the distance from the large end to the small end.
Regarding the endrem height x, if it is less than 0.02 mm, the effect of suppressing the amount of tooth contact movement is not sufficient, and good strength characteristics cannot be obtained, and if it exceeds 0.3 mm, the edge effect rapidly becomes remarkable. Since pitching occurs remarkably, the pitch is limited to 0.02 to 0.3 mm.

For the carburizing and quenching, a case-hardening steel such as Cr steel, Cr-Mo steel or Ni-Cr-Mo steel is used, and a solid carburizing method of contacting with a solid carburizing agent to heat it, or heating in a carburizing atmosphere gas There is no particular limitation such as a gas carburizing method or a liquid carburizing method of immersing in a carburizing salt bath.

A conventional device can be used for the shot peening. As the shot projection device, either a centrifugal projection device that is accelerated by the wing of a rotating impeller or a pneumatic spray projection device that uses the air velocity when compressed air is jetted from a nozzle can be used. ..

As the shot material, in order to obtain a large peening effect, one having a relatively large density such as steel is preferable. When the shot material is steel, it may have a Vickers hardness (Hv) of approximately 450 to 600, but it is 600 to 8 in order to enhance the fatigue strength effect.
It is preferably about 00.

The strength of shot peening is
When expressed in terms of arc height, it is good to set it to 0.1 mm or more.
If the arc height is less than 0.1 mm, it becomes difficult to obtain the peening effect. Further, the coverage is preferably 100% or more so that the peening effect can be given to the entire shot projection surface. The speed of projection particles is 30 to 7
A shot time of 0.5 to 10 minutes at 0 m / sec is preferable.

The chemical polishing liquid used in the chemical polishing treatment step may be a general one composed of an acid and an oxidizing agent. In the present invention, hydrofluoric acid is used as the acid and hydrogen peroxide is used as the oxidizing agent. The one used is preferable.
The hydrofluoric acid acts as a normal acid to chemically remove the steel surface. Further, hydrogen peroxide, in addition to its strong oxidizing power, fixes iron ions as a complex, thus suppressing the decomposition action of hydrogen peroxide and enabling stable treatment for a long time.

[0030]

In the high-strength hypoid gear of the present invention, the tooth contact movement amount at the time of torque input is controlled because the toothed ends of one or both of the drive pinion and the ring gear of the hypoid gear pair are subjected to the endrem processing. It is possible to get close to a proper tooth contact from the local contact at the heel. Further, the surface defect layer such as the abnormal carburizing layer was removed after the carburizing and quenching treatment and the shot peening treatment of the tooth portion, so that it was possible to make the surface contact with the portion having excellent fatigue strength, and the fatigue strength was remarkably improved.

[0031]

EXAMPLES Examples of the present invention will be described in comparison with a conventional example to clarify the effects of the present invention. As an example of the present invention, JI
A rough shaped material of a hypoid gear pair was manufactured from S SCM420 steel material by hot forging, and gear cutting was performed with a helix form after blank processing. At that time, the length L of the end rem shown in FIG. 1 is 6 mm and the height of the end rem x is 0.1.
In order to attach a large end rem of mm, the lead cam was changed from a normal one and processed. The main specifications of the hypoid gear pair are as shown in Table 1.

[0032]

[Table 1]

After that, carburizing and quenching were performed aiming at an effective hardening depth of 1.0 mm and a surface carbon concentration of 0.8%, and an average grain size of 0.
Projection speed of 50m with shot particles of 8mm and hardness Hv700
/ Sec, shot peening with a coverage of 600% was performed. The arc height value at that time was 0.67 mm.

Next, the carburized abnormal layer was completely removed by immersing it in a HF-H ₂ O ₂ -based chemical polishing liquid for 3 minutes to make the surface mirror-finished. When the surface roughness at that time was measured on the tooth surface, R
It was z-1.5 micrometers. Then, after undergoing the wrapping and assembling steps of the gear kit, the fatigue evaluation in the unit state was performed. For comparison, in the comparative example in which end lam processing was applied to the same large end as in this example, and chemical polishing after carburizing and shot peening was omitted, the number of repetitions until failure was measured under the same conditions. did. The obtained results are collectively shown in Table 2 together with the conventional example 1 and the conventional example 2 which were not subjected to the endrem processing.

[0035]

[Table 2]

As is clear from Table 2, the conventional example 1 in which the endless processing and the chemical polishing were not performed on the large end was 790,000 times, while the conventional example 2 in which the chemical polishing was performed on this was a tooth contact movement amount. There is a lot of local contact at the heel, so life is 5
As described above, the fatigue strength was inferior even if it was 0,000 times. However, the comparative example in which the end end was processed at the large end and there was no chemical polishing had a narrow tooth width, so the life was 550,000 times. Therefore, the life was not improved. On the contrary,
In this example, it was confirmed that the life was 16.10 million times by controlling the tooth contact movement amount by the endrem processing, and the fatigue strength was significantly improved by the present invention.

[0037]

As described above in detail, the high-strength hypoid gear of the present invention has end teeth processing applied to the tooth ends of either or both of the drive pinion and the ring gear of the hypoid gear pair, and the teeth are carburized and quenched. After that, shot peening is performed and chemical polishing is further applied.The end rem of the large end controls the amount of tooth contact movement at the time of torque input, and from the local contact at the heel to the proper position. You can get close to the tooth contact. Further, since the surface defect layer such as the abnormal carburizing layer is removed by chemical polishing after the carburizing and quenching treatment and the shot peening treatment of the tooth portion, the tooth contact between the drive pinion and the ring gear becomes a surface contact at a portion excellent in fatigue strength, Fatigue strength can be significantly improved.

[Brief description of drawings]

FIG. 1 is a partial perspective view of a tooth portion of a ring carrier having a large end portion endremed.

FIG. 2 is a copy drawing of a damaged portion of a conventional ring gear that has not been chemically polished.

FIG. 3 is a copy of a damaged portion of a conventional ring gear that has been chemically polished.

FIG. 4 is a diagram 1 showing the metallographic structure of the damage starting point of the conventional example of FIG.
It is a microscope photograph of 000 times.

FIG. 5 shows a metallographic structure of a starting point of damage of the conventional example of FIG.
It is a microscope photograph of 000 times.

[Explanation of symbols]

 10 Endrem 12 Large end 14 Small end

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masasumi Onishi 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Co., Ltd. (72) Inventor Yasuyuki Suzuki 1, Toyota Town, Aichi Prefecture, Toyota Motor Co., Ltd. (72) Inventor Kenichi Suzuki, 41, Nagachote, Nagachite-cho, Aichi-gun, Aichi Prefecture, 1st in Yokota Central Research Institute Co., Ltd. Toyota Central Research Institute Co., Ltd. (72) Inventor Fumio Shimizu 1 of 41, Yokomichi Nagakute-cho, Aichi-gun, Aichi Prefecture Toyota Central Research Institute

Claims (1)

[Claims] 1. A drive pinion of a pair of hypoid gears or a ring gear, one or both of which has a tooth end having a large end portion subjected to endrem processing, the tooth portion being carburized and quenched, then shot peened, and chemically polished. High-strength hypoid gear characterized by.