JPH09144847A - Gear for automobile and its manufacture tehreof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the abrasion resistance, dedendum strength and surface pressure strength to pitching by performing shot peening processing on a gear surface by projecting a shot of a cut wire having a diameter of a specific value range and hardness of a specific value range on the gear surface at speed of a specific value range. SOLUTION: A shot of a cut wire having a diameter of 0.5 to 0.7mm and hardness of 650 to 780Hv is projected on a gear surface at speed of 30 to 60m/s, and shot peening processing is performed on the gear surface. A sphering rate of the shot of the cut wire is set not less than 80%. Therefore, surface roughness of the gear surface containing a round part connecting a bottom and a dedendum becomes roughness by which pitching is not caused as a whole, and high residual stress is caused deeply inside from the gear surface. Therefore, surface pressure strength of a gear, abrasion resistance and dedendum strength are improved, and they can sufficiently cope with realization of high output of an engine. A flaw being a factor of stress concentration is not formed on the gear surface, and therefore, surface roughbess of the gear surface is uniformized as a whole.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle gear and a method for manufacturing the same.

[0002]

2. Description of the Related Art Generally, a vehicle power transmission gear is subjected to high bending stress and high contact stress at the tooth root, and a relative slip occurs on the tooth surface. Therefore, conventionally, the gear material is made of case-hardening steel, and after the gear is processed, carburizing treatment and shot peening treatment are performed to improve the tooth root strength and wear resistance of the gear (JP-A-3-271318). , JP-A-5
-339628 publication).

The above shot peening treatment involves steel shots (steel balls, etc.) of a certain grain size on the surface of the gear.
To make a hardened layer by the collision of shots on the surface layer, and relax the concentration of stress by the compressive residual stress generated in the hardened layer to improve fatigue strength and wear resistance. Therefore, by increasing the shot diameter and increasing the shot projection speed, the shot projection energy can be increased, and the root strength and the wear resistance of the tooth surface can be improved.

[0004]

However, if the diameter of the shot is increased and the projection speed is increased to improve the root strength and wear resistance, the tooth surface may be roughened more than necessary and pitching may occur. There is also a problem that if the R portion connecting the tooth root and the tooth bottom is small, the fatigue strength of this R portion cannot be improved.

Further, the conventional steel shot made of cast steel has a problem that it is easily damaged and has a short life.

An object of the present invention is to provide an automobile gear having high wear resistance, tooth root strength, and surface pressure strength against pitting, and a method for manufacturing the same.

[0007]

A vehicle gear according to claim 1 has a diameter of 0.5 to 0.7 mm and a hardness of 650 to 780.
Hv cut wire shot speed 30-60m / s
It is characterized in that it is projected onto the gear surface with a shot peening treatment on the gear surface.

A vehicle gear according to claim 2 has a diameter of 0.
It is characterized in that a shot of a cut wire having a hardness of 5 to 0.7 mm and a hardness of 650 to 780 Hv is projected on the gear surface to perform shot peening treatment on the gear surface.

A vehicle gear according to a third aspect of the present invention is the first aspect of the present invention.
Alternatively, in the invention described in 2, the spheroidization rate of the shot of the cut wire is 80% or more.

According to a fourth aspect of the present invention, there is provided an automobile gear manufacturing method, wherein the diameter is 0.5 to 0.7 mm and the hardness is 650 to 780 Hv.
The shot of the cut wire of (1) is projected onto the gear surface at a speed of 30 to 60 m / s to perform shot peening treatment on the gear surface. According to a fifth aspect of the present invention, there is provided a method for manufacturing an automobile gear, characterized in that the gear surface is shot peened by shots of a cut wire having a diameter of 0.5 to 0.7 mm and a hardness of 650 to 780 Hv. According to a sixth aspect of the present invention, there is provided the method for producing an automobile gear according to the fourth or fifth aspect, wherein the shot spheroidizing rate of the cut wire is 80% or more.
In the automotive gear according to claim 1, the surface roughness of the gear surface including the R portion connecting the tooth bottom and the tooth root is a roughness that does not cause pitching as a whole, and is highly compressed deep inside the gear surface. Residual stress occurs. Therefore, the surface pressure strength, wear resistance, and tooth root strength of the gear are significantly improved, and it is possible to sufficiently cope with the high output of the engine.

In the automobile gear according to claim 2,
The surface pressure strength against pitting is at least the same as the conventional one, and the compressive residual stress is widely distributed from the surface of the gear to the inner depth. Therefore, it is possible to significantly improve the root strength while preventing pitching.

According to the automotive gear of claim 3,
In the automobile gear according to the first or second aspect of the present invention, scratches that cause stress concentration are not formed on the gear surface, and therefore the surface roughness of the gear surface is made uniform overall.

In the method of manufacturing an automobile gear according to the fourth aspect, it is possible to manufacture an automobile gear having high surface pressure strength against pitching, high wear resistance and high tooth root strength. In addition, the shot life of the cut wire is extended, and the number of shot replacements can be greatly reduced.

According to a fifth aspect of the present invention, there is provided a method for manufacturing an automobile gear, which has a surface pressure strength at least equal to that of a conventional one against pitching, and has significantly higher wear resistance and tooth root strength than the conventional one. Gears can be manufactured. In addition, the number of shot exchanges can be significantly reduced as compared with the conventional steel shot.

According to a sixth aspect of the present invention, there is provided a method for manufacturing an automobile gear according to the fourth or fifth aspect, wherein
It is possible to manufacture an automobile gear having a uniform surface roughness by preventing generation of scratches by a cut wire.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below.

(Embodiment 1) First, hardness 650-780H
v wire (SWRH42A to SWRH82A) is cut to have a length of 0.5 to 0.7 mm and hardness of 650 to 780H
Make a v cut wire.

Thereafter, the cut wire is made to collide with a metal plate or the like, or is subjected to a polishing machine to obtain a shot of the cut wire having a spheroidization rate of 80%, which is used as a shot for shot peening the automobile gear.

The reason why the shot of the cut wire is used for the shot peening treatment of the automobile gear is that the shot of the cut wire has less wear and cracks and has a long life as compared with the steel shot made of cast steel. Further, the reason why the spheroidization rate of the shot of the cut wire is set to 80% or more is that if it is less than 80%, the shot of the cut wire may cause scratches that cause stress concentration and pitching on the gear surface. Because.

For shot peening of car gears (for example, transmission gears) after carburizing,
For example, a pneumatic nozzle that shoots a shot by the pressure of compressed air, or an impeller type that projects a shot by the centrifugal force of a rotary blade is used, and the shot speed of the shot of the cut wire is set to 30 to 60 m / s. The shot of the cut wire projected from the nozzle is the tooth surface of the transmission gear, the tooth root, the tooth bottom, the R portion connecting the tooth root and the tooth bottom,
It collides with the gear surface such as the side surface of the gear and forms a hardened layer having a constant surface roughness on the surface.

The shot diameter of the cut wire is 0.5 to
The reason for setting 0.7 mm is that shot peening can be applied to the R portion for connecting the root and the root to eliminate stress concentration.

The hardness of the shot of the cut wire is 650 to
780 Hv is used to reliably transfer the energy held by the shot of the cut wire from the gear surface of the automobile gear to the inner depth, so that the compressive residual stress can be generated deep inside the automobile gear. This is because

The projection speed of the cut wire is 30-60 m /
The reason for setting s is that in the shot peening treatment using the shot of the above-mentioned cut wire, the surface roughness of the gear surface is such that pitching does not occur and a high compressive residual stress is generated deep inside the gear surface. This is also because the life of the cut wire, which has a longer life than that of steel shot, is further extended and the number of times of shot replacement is significantly reduced.

Therefore, the automotive gear according to the present embodiment is greatly improved in tooth contact pressure strength, wear resistance and tooth root strength, and can sufficiently cope with high engine output.

(Embodiment 2) First, similarly to the above embodiment, a wire having a hardness of 650 to 780 Hv (SWRH42A to
SWRH82A) is cut and length is 0.5-0.7m
A cut wire having a hardness of 650 to 780 Hv and a hardness of 650 to 780 Hv is produced. Thereafter, the cut wire is collided with a metal plate or the like to form a shot of the cut wire having a spheroidization rate of 80%.

The projection speed of the cut wire is not set to 30 to 60 m / s as in the above embodiment, but the projection speed is set to the high speed side.
For example, it is set to 70 m / s, 80 m / s, and 90 m / s. That is, the diameter of the shot of the cut wire is 0.5 to
0.7mm, hardness of shot of cut wire is 650
If it is set to 780 Hv, the compressive residual stress will be 6
A compressive residual stress can be generated deeper than in the case of 0 m / s, and the root strength can be dramatically improved.

The shot peening process using the above cut wire under each of the above projection conditions is not limited to automobile gears, but can be applied to various industrial machines driven by heavy load and high speed rotation. It is a thing.

[0028]

EXAMPLES Examples of the present invention will be described below.

First, case-hardening steel (SCM420H, SCr4
20H, SNCM420H, etc.) is carburized to form a test gear, and the wire material of SWRH42A to SWRH82A is cut and spheroidized to a spheroidization rate of 80% or more. , A shot of a cut wire having a hardness of 700 Hv is formed, and a shot speed of this shot of the cut wire is 50 m /
The test gears were shot peening at s and 90 m / s respectively.

As a comparative example, shot peening treatment was performed in which a shot of a steel ball having a hardness of 550 Hv and a diameter of 0.8 (steel shot) was projected onto another test gear at a projection speed of 90 m / s.

After the shot peening treatment, the surface of the test gear was inspected for scratches. As a result, no scratch was found on each test gear due to the shot of the cut wire and the shot of the steel ball. After this, a fatigue test in which a constant contact pressure is repeatedly applied to the specific tooth surface of each test gear to measure the number of repetitions until the tooth breaks, and to the specific root of each test gear A fatigue test was carried out by repeatedly applying a constant load and measuring the number of repetitions until the tooth was broken, and the surface pressure strength and the root stress of these test gears were evaluated.

The results of the surface pressure-repetition number fatigue test are shown in FIG.
As shown in FIG. 5, the test gear subjected to the shot peening treatment by the shot of the above-mentioned cut wire under the shot condition of the projection speed of 50 m / s was found to be broken at the number of repetitions about 3 times that of the comparative example, Also, projection speed 90m
The test gear subjected to shot peening treatment with a shot of a cut wire under a projection condition of / s is about 2 of the comparative example.
It was confirmed that pitching occurred at twice the number of repetitions. As shown in FIG. 2, the tooth root stress-repetition number fatigue test result shows that the test gear subjected to the shot peening treatment with the shot of the cut wire under the shot condition of the projection speed of 50 m / s was about 8 of the comparative example. The test gear was found to break at a repetition rate of more than twice, and the test gear that was shot peened by shots of a cut wire under a projection condition of a projection speed of 90 m / s had a repetition rate about 6 times that of the comparative example. It was confirmed that the material fractured at.

Further, shot peening treatment was applied to each of the test gears while changing the shot projection speed of the cut wire to 50 m / s, 70 m / s and 90 m / s, and the magnitude of the compressive residual stress with respect to the projection speed and its magnitude. I checked the depth.

The results, as shown in FIG. 3, the peak value of compressive residual stress is approximately -120K ^g in each blasting speed /
It was confirmed to be constant at cm2, and the depth became deeper as the projection speed increased.

Therefore, in order to increase the compressive residual stress of the test gear and the root strength by using the above-mentioned cut wire,
The higher the projection speed, the better.

Further, in order to evaluate the life of the shot of the cut wire and the shot of the steel ball, the shot peening treatment is repeated for a certain time, and the usable shot is 100 parts by weight (Wt%) to 40 parts by weight (Wt).
%) Was measured.

In this test, the shot of the cut wire had a diameter of 0.6 and a hardness of 700 Hv.
Cut wire projection speed is 50m / s, 70m / s, 9
The projection speed of the shot of the steel ball was 90 m / s.

As a result, as shown in FIG. 4, it was confirmed that the shot of the cut wire has a life of more than twice as long as the shot of the steel ball. It was also found that even with the same shot of the cut wire, the life of the shot was dramatically extended if the projection speed was lowered.

[0039]

As is apparent from the above description, according to the present invention, the following excellent effects are exhibited.

(1) It is possible to provide an automobile gear having high surface pressure strength, wear resistance and tooth root strength (claims 1 and 4).

(2) The shot life of the cut wire can be remarkably extended, and the number of times of exchanging the cut wire can be greatly reduced (claims 1 and 4).

(3) It is possible to provide a gear for an automobile which has wear resistance and surface pressure strength against pitting which are at least as good as conventional ones and whose root fatigue strength is much higher than before (claims 2 and 5).

(4) It is possible to prevent the formation of scratches that cause stress concentration on the gear surface and to make the surface roughness of the gear surface uniform throughout (claims 3 and 6).

[Brief description of the drawings]

FIG. 1 is a diagram showing the results of a fatigue test on the surface pressure-repetition number of an automotive gear that has been shot peened by a shot of a cut wire and a shot of a steel ball.

FIG. 2 is a diagram showing the results of a fatigue test on root stress-repetition number of an automotive gear that has been shot peened by a shot of a cut wire and a shot of a steel ball.

FIG. 3 is a view showing a change in compressive residual stress and a distribution of the compressive residual stress with respect to a projection speed of an automobile gear which has been shot peened by shots of a cut wire.

FIG. 4 is a view showing changes in shot life of shots of a cut wire and conventional steel balls.

Claims (6)

[Claims] 1. A diameter of 0.5 to 0.7 mm and a hardness of 650.
780 Hv cut wire shot speed 30-60
A gear for an automobile, characterized in that the gear surface is shot at a speed of m / s for shot peening. 2. A diameter of 0.5 to 0.7 mm and a hardness of 650.
An automotive gear, characterized in that a shot of a 780 Hv cut wire is projected onto the gear surface and shot peening is applied to the gear surface. 3. The automobile gear according to claim 1, wherein the shot spheroidization rate of the cut wire is 80% or more. 4. A diameter of 0.5 to 0.7 mm and a hardness of 650.
780 Hv cut wire shot speed 30-60
A method for manufacturing an automobile gear, characterized in that the gear surface is projected at m / s for shot peening treatment. 5. A diameter of 0.5 to 0.7 mm and a hardness of 650.
A method of manufacturing an automobile gear, characterized in that the gear surface is shot peened by shots of a 780 Hv cut wire. 6. The method of manufacturing an automobile gear according to claim 4, wherein the shot spheroidizing rate of the cut wire is 80% or more.