JPH0694100A - Gear - Google Patents

Abstract

PURPOSE:To provide a gear lighter in weight and high in load carrying capacity by installing a coating layer, consisting of a cemented carbide material, on the surface of a fillet curved part of a dedendum. CONSTITUTION:A coating layer consisting of cemented carbide material is applied on at least one side surface of a dedendum fillet curved part and a meshing plane. In addition, thickness t1 of this coating layer at the fillet curved part is set to t1>=0.03m in relation to a gear module (m), or thickness t2 of the coating layer on the meshing plane is set to t1>=0.15m in relation to the gear module. On the basis of transfer torque, a maximum bending stress to be produced on the surface of one side dedendum of the gear can be supported by such a cemented carbide material as high in a Young's modulus, so even in the case where the transfer torque attributable to the bending stress is large enough, sufficient strength is appliable to a gear tooth. Therefore such a gear as lighter in weight and larger in transfer torque is securable. Likewise, the surface of a contact plane is covered with the cemented carbide material, through which wear resistance and surface pressure strength are well improvable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gear used for, for example, a transmission mechanism or a differential mechanism of an automobile.

[0002]

2. Description of the Related Art In gears used for the above applications,
There are contradictory requirements for high load capacity and light weight and miniaturization.To meet these requirements, heat treatment such as carburizing, carburizing and nitriding, nitriding, nitrocarburizing, quenching and tempering, Abrasion resistance and surface pressure strength are increased.

In addition to the above heat treatment, as disclosed in, for example, Japanese Patent Application Laid-Open No. 4-17658, after carburizing, TiC is further formed by CVD (chemical vapor deposition).
Surface coating of hard materials such as

[0004]

However, all of the above treatments are merely to provide a hard layer on the surface, and therefore, although abrasion resistance can be increased,
It was not intended to significantly improve the breakage strength and surface pressure strength of the teeth themselves, which directly affect the transmission torque of the gear. The present invention has been made in view of the above circumstances, and provides a light-weight and high-load capacity gear by improving not only the wear resistance or surface pressure strength of the surface but also the breakage strength and surface pressure strength of the teeth themselves. The purpose is.

[0005]

In order to achieve the above object, the present invention provides a coating layer made of a superhard material on at least one of the fillet curved portion of the tooth root and the meshing surface. is there. Further, the thickness t1 of the coating layer at the fillet curve portion is set to t1 ≧ 0.03 m for the gear module m, or the thickness t2 of the meshing surface coating layer is set to t2 ≧ for the gear module m. It is set to 0.15 m.

[0006]

Since the surface of the fillet curved portion is formed of the superhard material, the bending stress generated on one surface of the tooth root portion of the gear based on the transmission torque can be supported by the superhard material. Further, by coating the surface of the contact surface with a superhard material, wear resistance and surface pressure strength of this portion can be enhanced. The thickness of the portion formed of this superhard material is defined by a certain ratio because the contact surface shape and the Hertzian stress are determined substantially uniformly in comparison with the module.

[0007]

EXAMPLES Examples of the present invention will be described below. 1st Example Module m = 3.78 mm Pressure angle 22 ° 30 ′ Tooth profile Standard tooth profile Tooth fillet R = 0.5 mm Tooth width of 18 mm A bevel gear of SCM418H round bar billet is hot forged by the thickness of the sprayed metal. Manufactured with small dimensions. After carburizing and quenching this gear, cemented carbide with a predetermined thickness (powder of WC and Co powder mixed in a ratio of 9: 1)
Was sprayed and then coined or ground to obtain a gear with a predetermined accuracy.

By the above processing, a gear having JIS class 2 accuracy could be obtained. A torque was applied to this gear to perform a static fracture strength test of the single body. In addition, an operation test was performed while increasing the load, and the critical average surface pressure that caused spalling was determined.

As shown in FIG. 1, as the ratio t / m between the coating thickness t and the module m increases, the static fracture strength [kgf · m] and the allowable surface pressure [kgf / mm ² ] are Also increases once, then decreases, then increases again. Regarding the allowable surface pressure, when t / m ≧ 0.15, a value exceeding the maximum allowable surface pressure in the preceding stage (before the allowable surface pressure once decreases) could be obtained. For static fracture strength, t / m
When ≧ 0.03, it was possible to obtain a value exceeding the maximum static fracture strength in the previous stage (before the static fracture strength once decreased).

From the above experiment, it is understood that the bending strength can be effectively increased by setting the coating thickness t of the cemented carbide material at the fillet portion of the tooth root to t ≧ 0.03 m. That is, since a superhard material such as WC-Co has a Young's modulus twice or more that of a steel material, it can support the maximum bending stress generated on the surface of the tooth root portion. Further, since the tooth tip displacement is reduced due to the large Young's modulus, the tooth engagement rate is increased, and thus the noise during operation is reduced.

Further, in the tooth surface portion, t ≧ 0.
By setting the length to 15 m, it is possible to further prevent damage to the meshing surface of the teeth. That is, when the coating of the superhard material is thinner than this range, a large number of pits (dents) are generated on the tooth surface due to the peeling of the coating layer due to the shearing force generated at the interface between the coating layer and the base material (steel). .

When t ≧ 0.15 m, the adhesion area decreases due to the presence of the outer skin layer and the outer skin material stress increases, but the peak stress due to Hertzian contact completely exists in the outer skin layer and reduces the stress of the base material. At the same time, the shearing force at the joint interface is greatly reduced, and the risk of peeling is reduced. Therefore, it is possible to obtain a gear that is significantly superior in bending strength and surface pressure strength to the conventional gear.
Further, in the range of t ≧ 0.25, the increase in the surface pressure strength reaches a peak and the ratio of the cemented carbide material having a higher density than steel to the entire gear becomes large, so that the weight of the gear and the moment of inertia of the gear are increased. Grows larger. Therefore,
From the standpoints of gear efficiency and manufacturing cost, it is desirable that the coating thickness t be 0.25 m or less.

As described above, the bending strength and the surface pressure strength of the gear could be increased by coating the surface of the steel gear with the cemented carbide material having a predetermined ratio of thickness with respect to the module.

The above effect is that the stress of the surface layer having a high Young's modulus relaxes the stress of the inner surface layer, and both the bending and the surface pressure strength have a certain layer thickness ratio (t / m) as a boundary. Since it is based on the finding that it rapidly grows, the same effect can be obtained even when the carburized layer is not formed on the surface of steel. Further, the combination of the outer skin material and the core material is not limited to the steel and the cemented carbide of the above-mentioned embodiment, but ceramic and Fe, Fe and Al, Fe.
Needless to say, it can be applied to various combinations of plastic and plastic.

[0015]

As is apparent from the above description, the present invention is
A coating layer made of a cemented carbide material is applied to at least one of the fillet curve portion of the tooth root and the meshing surface, and the thickness t1 of the coating layer of the fillet curve portion is set to the module m of the gear. With respect to t1 ≧ 0.03
m or the thickness t2 of the coating layer on the meshing surface is t2 ≧ 0.15 m with respect to the gear module m, the following effects are achieved.

Since the surface of the fillet curve portion is formed of a superhard material, the maximum bending stress generated on the surface of one of the roots of the gear on the basis of the transmission torque is determined by the superhard material having a Young's modulus higher than that of steel. It can be supported, and the teeth can have sufficient strength even when the transmission torque that causes the bending stress is large. Therefore, it is possible to obtain a gear that is lightweight and has a large transmission torque.

Further, by coating the surface of the contact surface with a superhard material, wear resistance and surface pressure strength of this portion can be enhanced. From this point as well, a gear which is lighter in weight than the allowable transmission torque can be obtained. Obtainable.

[Brief description of drawings]

FIG. 1 is a table showing changes in static fracture strength and allowable surface pressure with respect to t / m.

Claims (6)

[Claims] 1. A gear having a coating layer made of a superhard material provided on the surface of the fillet curve portion of the tooth base. 2. The gear according to claim 1, wherein the thickness t1 of the coating layer is t1 ≧ 0.03 m with respect to the module m of the gear. 3. A gear having a coating layer made of a superhard material on the surface of the meshing surface. 4. The gear according to claim 3, wherein the thickness t2 of the coating layer is t2 ≧ 0.15 m with respect to the module m of the gear. 5. A gear having a coating layer made of a superhard material provided on the surface of the fillet curve portion of the tooth root and the surface of the meshing surface. 6. The thickness t1 of the coating layer of the fillet curve portion is t1 ≧ 0.03 m with respect to the gear module m.
The gear according to claim 5, wherein: