JPH0968261A - Cast iron gear and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gear which blocks a relict ferrite after an induction hardening along the tooth surface of a tooth form, has a large damping function to a vibration and a noise, and has sufficient toughness and hardness, so as to be suitable as a high load and a high rotation frequency gear such as a timing gear or the like. SOLUTION: When a gear which consists of a cast iron material is manufactured, at first a quenching and tempering process 2 is applied to a gear raw material 1, and after that, a gear cutting process is carried out. Then, an induction hardening process 4 is applied to the tooth surface, so as to prevent the including of a ferrite to the basic structure of an induction hardening layer, and a cast iron gear improving the bending fatigue strength can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to cast iron gears applied to engine timing gears, etc., and more particularly to spheroidal graphite cast iron gears and a method for manufacturing the same.

[0002]

The timing gear of a high-speed engine such as an automobile engine is used under a high load and a high rotation, and one-sided contact during gear meshing is likely to occur.
Since it is used under severe conditions, a gear is generally used in which the surface of carbon steel or alloy steel is subjected to surface hardening treatment such as nitriding, soft nitriding, or carburizing and quenching.

However, in recent years, there has been an increasing demand for engine noise reduction, and as a timing gear corresponding to this, cast iron gears having a large vibration and noise damping characteristic, that is, a small Young's modulus E (a steel material Young Rate E = 2
E = 1700 for cast iron compared to around 1000 kgf / mm ^2.
0 kgf / mm ² ) has been proposed.

As the cast iron gear, spheroidal graphite cast iron (so-called ductile cast iron, hereinafter referred to as such) is preferable because of its strength and hardness. However, as one of the means for obtaining strength comparable to that of a steel gear whose surface is hardened with this ductile cast iron material, there is a means for subjecting the tooth profile of the gear that has been gear-cut from the ductile cast iron material to induction hardening. It is provided.

Regarding this induction hardening, since the entire tooth profile is hardened and the toughness is remarkably deteriorated by the usual hardening method, the induction hardening technique for steel materials is applied to the ductile cast iron material, and the hardening along the tooth profile surface is performed. A method of applying is being proposed.

[0006] In this technique, a gear tooth-cut from a ductile cast iron (for example, JIS.FCD700) material is induction-hardened along the surface of the tooth profile. Since the time is 1 second or less, which is very short, the ferrite around the graphite remains even after induction hardening and there is a problem that the desired hardness cannot be obtained.

The object of the present invention is to prevent induction of ferrite after the quenching in a gear made of ductile cast iron by induction hardening along the tooth flank of the tooth profile and to have a large vibration and noise damping function, and a sufficient damping function. An object of the present invention is to provide a gear having hardness and suitable as a high-load, high-rotation gear such as a timing gear.

[0008]

Means for Solving the Problems The present invention is intended to solve the above problems, and a first means thereof is a gear made of a cast iron material containing spheroidal graphite cast iron, the tooth surface of which is
An induction hardening layer is formed along the tooth profile, and the matrix structure of the hardening layer is a structure that does not substantially contain ferrite.

In the first means, the matrix structure is a sorbite structure of spheroidal graphite cast iron, and the induction hardening layer has a thickness of 0.3 mm to 0.6 mm.
It is also two forms of the present invention.

Further, according to the method of the present invention, in manufacturing the cast iron gear having the above-mentioned structure, the gear material is hardened and tempered, then gear cutting is performed, and then the tooth surface is induction hardened. Especially.

Since the cast iron gear and the method for manufacturing the same according to the present invention are configured as described above, the gear material before induction hardening is subjected to normal quenching to eliminate ferrite, and then toughness is obtained by tempering. Since induction hardening is performed after the restoration, the matrix structure of the hardening layer does not include ferrite, and the induction hardening layer having a sufficient hardness along the surface is formed on the tooth profile.

As a result, a gear having sufficient vibration and noise damping functions and strength as a high-load, high-rotation gear can be obtained.

Further, according to the above-mentioned method of the present invention, only a very simple working step of adding the step of subjecting the gear material to the usual quenching and tempering treatment before the induction hardening is added, so that the substantial manufacturing is performed. It is possible to obtain the cast iron gear having a large effect of damping vibration and noise and high strength as described above, while suppressing the cost increase of the process to the minimum.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to FIGS. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, and are merely illustrative examples. It's just

FIG. 5 shows an example of an engine timing gear device to which a gear made of spheroidal graphite cast iron (hereinafter referred to as ductile cast iron) according to an embodiment of the present invention is applied.
In the figure, 10 is a crankcase, 11 is a crank gear fixed to a crankshaft, 12 is a cam gear, 13 is an oil pump gear for driving an oil pump, 14 is an idler gear, 15 is an injection pump gear for driving a fuel injection pump, 1
6 is a power steering pump gear.

The metal composition of the ductile cast iron gear used for the above timing gear is JIS. FCD700
It is equivalent to a material and has no additional components to be noted, but the content and process of heat treatment and surface hardening treatment are different from those of the conventional gears of this type.

FIG. 1 shows a manufacturing process of such a ductile cast iron gear. In FIG. 1, the base material 1 has JIS. A casting material made of ductile cast iron corresponding to FCD700 is used.

The matrix structure of the FCD700 material is pearlite + slightly ferrite structure, and causes transformation when heated to a temperature above the transformation temperature range. Regarding the improvement of the matrix structure by this transformation, the structure generated differs depending on the heating temperature and the cooling method.

Next, in the quenching (Q) and tempering (T) step 2, the above-mentioned ductile cast iron material is subjected to a quenching treatment in which it is heated to about 800 to 900 ° C. above the A1 transformation point and then rapidly cooled, and subsequently, below the A1 transformation point. After that, a tempering treatment is performed in which the material is heated to the above temperature and gradually cooled.

The above-mentioned quenching and tempering treatments are carried out by the usual methods. The base structure becomes a sorbite structure by this quenching and tempering treatment.

Next, in the mechanical finishing step 3, the material subjected to the tempering treatment of quenching and tempering is subjected to cutting and gear cutting to form a tooth profile. Furthermore, the surface of the tooth profile is shaving finished to finish the tooth profile with high accuracy.

Next, in the induction hardening step 4,
The tooth profile of the gear finished to the specified dimensions is induction hardened by the usual method.

As described above, the heating time at the time of induction hardening is very short. Therefore, in the case of the conventional method, the ferrite remained after the induction hardening. As described above, since the base material was subjected to quenching and tempering treatment to form a sorbite structure in the base, there is no ferrite remaining after induction hardening.

The quenching conditions for the induction hardening are set as follows. FIG. 2 shows a hardening pattern of the tooth profile 1 of the gear that has been induction hardened. As is clear from FIG.
The hardened layer 2 after induction hardening has a deep tooth tip 4 and a tooth root 5
Becomes shallow.

However, since the bending fatigue of the tooth profile 1 becomes maximum at the tooth tip portion 4, in order to increase the bending fatigue strength of that portion, Hv ≧
Increasing the effective hardened layer depth H with 500 is required.

However, when the heating time for induction hardening is increased to increase the depth of the hardened layer of the tooth root portion 5, H, and when this is set to 0.7 mm or more, the hardening depth is higher than that of the tooth root portion 5 as described above. In the tooth tip portion 4 in which the tooth gap becomes larger, the tooth tip side than the pitch circle portion is entirely a hardened layer, and it becomes impossible to maintain the required toughness.

On the other hand, when the hardened layer depth H is 0.2 mm or less, the hardened layer is thin and the required fatigue strength cannot be obtained.
Therefore, the depth H of hardened layer after induction hardening is 0.3mm
0.6 mm is the most appropriate value in consideration of the bending fatigue strength in the tooth profile 1 and the hardness distribution characteristics as described above, and the induction hardening conditions, especially the heating time, are such that the depth of the hardening layer is within this range. Set to.

The induction hardened gear made of ductile cast iron which has undergone the above steps has a hardness Hv of the hardened layer along the surface of the tooth profile 1.
It is possible to obtain 500 to 700 and a depth of 0.3 mm to 0.6 mm. The above description has been given by taking the gears of the module 3 and below as an example.

The induction-hardened gear that has been subjected to the above-mentioned procedure is subjected to a final finishing step 5 such as grinding and shot peening, if necessary, to obtain a finished product.

[0030]

[Example] According to JIS. In the above process, the FCD700 ductile cast iron gear was subjected to quenching, tempering → machining (machining, gear cutting, shaving) → induction hardening, and was applied to an engine timing gear. The experiment as shown in (2) was conducted.

(1) Essential points of helical gear made of ductile cast iron for experiments Tooth profile: Regular tooth module: 2.0 Number of teeth: 63 Pressure angle: 20 ° Twist angle: 19.5 °

(2) Noise measurement test FIG. 3 shows the result of measuring the noise at the idle speed on the engine stand. As is clear from FIG. 3, the FCD700 material induction hardened gear, which is a product of the present invention, has a noise reduction effect of 1.1 dB compared to the conventional S58C material soft nitrided gear. This is because, as described above, the cast iron material has a smaller Young's modulus E than the steel material, so that the meshing impact force is small and the damping characteristics are excellent.

(3) Bending Fatigue Test A fatigue limit diagram obtained by measuring the bending fatigue limit of the tooth root portion 5 by applying a sine wave unidirectional repeated bending load to the tooth profile 1 is shown in FIG.
Shown in From FIG. 4, the bending fatigue limit of the test ductile cast iron gear is about 10 KN, which is a practically sufficient value.

[0034]

As described above, according to the present invention, it is only necessary to add a very simple working step of adding the steps of normal quenching and tempering to the gear material before the induction hardening, so that it is practical. It is possible to obtain a cast iron gear having a large effect of damping vibration and noise and having sufficient bending fatigue strength while suppressing the cost increase of various manufacturing processes to the minimum.

When the depth of the induction hardening layer is set as in the third aspect of the invention, the surface effect is evenly applied over the entire tooth profile from the tooth tip to the tooth root, and a stable quality gear is obtained. .

[Brief description of drawings]

FIG. 1 is a block diagram showing a manufacturing procedure of a ductile cast iron gear according to an embodiment of the present invention.

FIG. 2 is a partially enlarged view showing a hardened state of the tooth profile of the gear according to the above embodiment.

FIG. 3 is a diagram showing a noise test result of a ductile cast iron gear according to an embodiment of the present invention.

FIG. 4 is a bending fatigue limit diagram in the above embodiment.

FIG. 5 is a front view of a main portion of a timing gear device for an automobile engine.

[Explanation of symbols]

 1 Tooth profile 2 Hardened layer 3 Material 4 Tooth tip 5 Tooth root 11 Crank gear 12 Cam gear

Claims (5)

[Claims] 1. An induction hardened layer formed of a cast iron material containing spheroidal graphite cast iron along a tooth profile is formed on a tooth surface, and the matrix structure of the hardened layer is a structure substantially free of ferrite. Features cast iron gears. 2. The cast iron gear according to claim 1, wherein the matrix structure is a sorbite structure of spheroidal graphite cast iron. 3. The induction hardened layer has a thickness of 0.3 mm.
The cast iron gear according to claim 1 or 2, wherein the cast iron gear has a diameter of 0.6 mm to 0.6 mm. 4. When manufacturing a gear made of a cast iron material containing spheroidal graphite cast iron, the gear material is hardened and tempered, then subjected to gear cutting, and then the tooth surface is subjected to induction hardening treatment. Method for manufacturing cast iron gears. 5. A cast iron gear applied to a timing gear of an engine, wherein the gear is made of a cast iron material containing spheroidal graphite cast iron, and an induction hardened layer is formed on a tooth surface along a tooth profile. The cast iron gear characterized in that the matrix structure of is a structure that does not substantially contain ferrite.