JPH0315062B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gear, and more particularly to a surface-hardened gear in which the surface of the teeth is hardened.

In order to improve the fatigue strength of the tooth roots of gears and provide wear resistance to the tooth surfaces, it is effective to harden the tooth surfaces, including the tooth grooves, to an appropriate depth. For example, the hardening treatment method is as follows:
Induction hardening, carburizing, nitriding, soft chambering, etc. are known.

By the way, in conventional surface-hardened gears, the hardening treatment is applied along the tooth profile (outline of the gear) and over the entire width of the tooth, and the peripheral surface of the gear consisting of the tooth surface, tooth top surface, and tooth bottom surface is completely hardened. It was common for hardened areas to form. If such a surface-hardened gear has highly accurate tooth contact (total contact) over almost the entire tooth width when meshing with a mating gear, then it is certainly quenched and tempered without surface hardening treatment. Compared to conventional gears, it is possible to achieve a significant improvement in fatigue strength.

However, in reality, due to errors in gear assembly or load deformation of the rotating shaft that supports the gears, when the gears actually mesh, the teeth at the ends in the tooth width direction may change to a greater or lesser extent. Often, only the surface is in contact with the teeth (partial contact).

When a conventional gear whose entire peripheral surface is surface hardened is used in such conditions,
Since bending stress is concentrated at the root of the tooth end face, fatigue cracks tend to occur from the tooth root, and as a result, the tooth tends to be destroyed quickly. In other words,
The fatigue fracture limit of the root of the tooth for each part was significantly lower than that for the ideal whole part, and as a result, the part was brittle.

On the other hand, in order to bring the meshing of gears closer to the ideal state where almost the entire tooth width is in contact with the teeth, it is necessary to improve the manufacturing and assembly accuracy of the gears, and to strengthen the rigidity of the gear support mechanism. It is difficult to avoid assembly errors, and there is a limit to how rigid the support mechanism can be strengthened.

The present invention was made against the background of the above-mentioned circumstances, with the object of providing a surface-hardened gear that can maintain sufficient fatigue strength even when the teeth of the gear are in contact with each other during meshing. can be,
The gist of this is that the gear circumferential surface, which consists of the tooth surface, tooth top surface, and tooth bottom surface, is located at a point on the tooth tip surface that is within a distance of 5 to 15% of the tooth width from the tooth end surface, and at a point approximately at the pitch on the tooth end surface. If we consider that the tooth is cut diagonally with a nearly planar cut surface that passes through a point on a circle, we will leave the part on the tooth end surface side of the cut surface without hardening, and then be.

In this way, if the surface of the tip of the tooth at the edge in the tooth width direction of the gear circumferential surface is made into a non-hardened part, even if the teeth contact the tooth part during meshing and a large load is locally applied to the tip of the tooth. Since the non-hardened portion of the tooth tip can be compressively deformed, the contact range of the tooth surface can be expanded in the tooth width direction, and the surface pressure of the tooth tip can be lowered. Therefore, the tendency for bending stress to concentrate at the tooth root of the tooth end face is alleviated, and as a result, the fatigue strength (fatigue fracture limit) of the tooth root is increased without significantly decreasing compared to when the tooth face is applied to the entire tooth surface. It is maintained at the same level.

In addition, in the gear according to the present invention, all the root portions of the gear circumference where large stress occurs are hardened, and the compressive stress remaining in the hardened portion improves the fatigue strength and improves the tooth root portion. The effect of extending the life of the gear, which is determined by the occurrence of cracks in the gear, can be obtained in the same way as with a gear whose entire peripheral surface is surface hardened.

In addition, the part that is left unhardened is a limited portion that is truly necessary, and most of the tooth surface is hardened, so the life of the gear based on the wear of the tooth surface is limited to the entire tooth surface. There is almost no difference from hardened gears.

Embodiments of the present invention will be described below based on the drawings. For the sake of clarity, an example will be described in which the present invention is applied to a spur gear, which is the most basic type of gear.

Figure 1 shows the teeth of a spur gear.
The circumferential surface of the gear, that is, the tooth surface, tooth top surface, and tooth bottom surface, except for a portion, is subjected to a surface hardening treatment to form a hardened portion 2 (hardened surface).

The hardening treatment in this example is performed by known induction hardening. That is, a high frequency current is induced on the surface of the steel material, the surface layer is rapidly heated by the resistance heat, and then the surface layer is rapidly cooled with water or oil to harden the surface area. Since induction hardening is used, the base material of gear teeth is generally made of steel suitable for induction hardening (usually steel with a carbon content of about 0.40 to 0.55%, which has been tempered by quenching and tempering, etc.). Carbon steel) is used.

Now, the hardened area of the gear's circumferential surface,
In other words, in the hardening pattern, as is clear from the example shown in Fig. 1, the surface of the tooth tips at both ends in the tooth width direction is left unhardened and becomes a non-hardened portion 4 (non-hardened surface). On the other hand, the entire peripheral surface of the gear other than that portion is hardened to form the hardened portion 2. The part that should be left without surface hardening is the tooth tip part of the gear peripheral surface consisting of the tooth surface, tooth top surface, and tooth bottom surface, and surface hardening is applied to both end surfaces of the gear including the tooth ends. It doesn't matter whether you are allowed to do it or not. In this example, since the surface hardening is performed by induction hardening using a coil placed around the outer circumference of the gear, the surface of both end faces of the gear is hardly hardened, but the surface of the end face adjacent to the bottom face of the gear is hardly hardened. Small areas are surface hardened. It is desirable that this small portion be surface hardened from the viewpoint of improving the fatigue strength of the tooth base.

The hardened portion 2 improves the wear resistance of the tooth and strengthens the fatigue strength of the tooth due to compressive stress remaining on the surface, while the non-hardened portion 4 is compressively deformed to reduce contact with the tooth. It has a relaxing function. Therefore, the area balance between the non-hardened portion 4 and the hardened portion 2 becomes important. If the non-hardened portion 4 is expanded in the tooth width direction so as to extend far beyond the tooth end face, or if the non-hardened portion 4 extends too far near the root of the tooth in the tooth thickness direction, the wear resistance of the tooth may deteriorate. This is because the fatigue strength of the root of the tooth end surface is likely to be reduced, and on the other hand, if the range of the non-hardened portion 4 is too narrow, the effect of alleviating tooth part contact will be reduced.

Therefore, the range of the non-hardened portion 4 passes through a point A on the tooth tip surface that is located inside by a distance L of 5 to 15% of the tooth width W from the tooth end surface, and a point B on the tooth end surface that is approximately on the pitch circle P. When a tooth is cut diagonally with a substantially planar cut surface, it is set to be the surface portion on the tooth tip side from the cut surface. It is most preferable to make the unhardened portion 4 within this range in view of the wear resistance of the teeth and the like.

In addition, in order to harden the surface of the tooth so that the surface in such a range remains as the unhardened portion 4, the coil through which the high-frequency current is passed is placed in the direction of the tooth width so as to avoid the tips of the tooth at both ends. It is sufficient that the induction heating effect is not applied to the surface that is to become the non-hardened portion 4. The portion that is not subjected to the heating action is naturally not hardened and becomes a non-hardened portion 4 in which the surface of the tooth base material remains almost as it is.

According to induction hardening, it is possible to easily harden only the surface that should become the hardened part 2 while leaving the surface that should become the unhardened part 4, and the time required for the hardening process is short and mass production is good. . In addition, the hardening depth, that is, the depth of the hardened portion 2, is set to the most appropriate depth depending on the material, shape, and size of the teeth, the rotational torque during engagement, etc., and the depth adjustment can also be done by changing the cycle. This can be easily achieved by appropriately setting the number or the energization time.

Now, when a gear with the above hardened portion 2 and non-hardened portion 4 on the tooth surface participates in meshing, there are times when the tooth surface of the tooth does not contact the tooth over the entire length of the tooth width (total contact). be. In fact, it is normal for the situation to be more or less like that. Even if it doesn't hit all the way, it won't be much of a problem as long as it has a certain width in the tooth width direction.
If only the tip of the tooth at the end in the tooth width direction is brought into contact with the tooth, a load is concentrated on the tip of the tooth, resulting in concentration of bending stress at the root of the tooth end surface. However, in the gear of this embodiment, the circumferential surface of the tooth tip portion, which has a high degree of hardness and is brought into local tooth contact, becomes a non-hardened portion 4 that has not been hardened (the base material of the tooth remains as it is). Therefore, even if there is a partial contact, the non-hardened portion 4 is plastically deformed to some extent in the direction in which the load acts, or is worn out, and the range of tooth contact can be expanded in the tooth width direction. As a result, the occurrence of large bending stress at the root of the tooth end surface is prevented or alleviated, and the occurrence and growth of fatigue cracks at the root of the tooth are suppressed. It is maintained at a high level without being affected much by the condition.

In other words, due to the presence of the non-hardened portion 4, manufacturing or assembly errors of the gear can be corrected to the extent that it does not place a large burden on the root of the tooth end surface, although it may not be corrected on the entire gear. It will become.

Incidentally, the situation in which teeth partially touch each other is actually delicate, and it is difficult to predict which side of the tooth end in the tooth width direction will make contact with the tooth. Therefore, as in this example, both ends in the tooth width direction It is desirable that the surface of the tip of the tooth be the non-hardened portion 4.

It has been confirmed through the experiments described below that the above-mentioned effects can be obtained due to the presence of the non-hardened portion 4, and furthermore, the experimental data has revealed that the effects are very large.

(Experiment) A gear equipped with the non-hardened portion 4 in this example (main gear) and a conventional gear whose entire peripheral surface was hardened (conventional gear) were prepared as samples, and the gears were tested for normal use. For conventional gears, we intentionally set the situation for each part of the tooth that would occur when In the case of a hit, it was also measured.

Note that both of the above two types of sample gears were surface hardened under the following induction hardening conditions. However, the form of the heating coil is naturally slightly different.

〔preheat〕

600℃×10 seconds [Main heating] Number of cycles: 4000Hz Power density: 4000W/ ^cm2Heating time: 0.5sec Gear rotation: 100rpm [Cooling] Cooling water amount: 150/min Return.

In the graph of Figure 2 showing the above experimental results,
The solid line C1 and the broken line C2 indicate the fatigue fracture limit of the root of the tooth when the conventional gear is brought into contact with the entire part and when it is brought into contact with the part, that is, the extent to which the tooth can withstand the bending stress that is repeatedly applied to the tooth root. Graph D, which is a dot-dash line, shows the fatigue fracture limit of the root of the gear in a state where it is in contact with a portion of the gear.

As is clear from this, in conventional gears, while sufficient fatigue strength is maintained when the entire gear is brought into contact, the fatigue strength is significantly reduced when it is brought into a state where the part is brought into contact. (Dotted line C2) On the other hand, in the case of the gear according to the present invention, as shown by the dashed line D, it exhibits much higher fatigue strength than the conventional gear even when it is partially hit. This is almost the same as when the whole gear is hit by a conventional gear.

Moreover, in order to obtain such an effect, a special material is not used as the base material of the gear, and no complicated surface hardening treatment is performed. By leaving a part of the peripheral surface of the gear to be surface-treated as a non-hardened part 4, which is almost cost-effective compared to the conventional method, it is possible to significantly improve the fatigue fracture limit of the tooth root at the time of partial contact, and thus the life of the tooth. It is.

Next, another embodiment is shown in FIG.

An example of this is carburizing, a process in which carbon is diffused into the surface layer of the steel by heating the steel in a carburizing agent (for example, a solid carburizing agent is a mixture of hard charcoal grains and carbonate). Therefore, the hardened portion 8 is formed by hardening the surface of the tooth of the gear, while leaving a non-hardened portion 6 in the same area as in the previous embodiment. Identical parts are indicated by the same reference numerals and explanations will be omitted.

However, the boundary line between the non-hardened portion 6 and the hardened portion 8 on the tooth surface of the tooth tip has an almost circular arc shape that is concave toward the tooth end surface, in other words, the virtual cut surface in the above example. is set in an almost cylindrical shape.

In order to obtain the non-hardened portion 6 as shown in FIG. 3, it is sufficient to prevent carburization of the tooth surface that should become the non-hardened portion with copper plating or the like prior to carburizing treatment. As shown in FIG. 3, the root side of the tooth end face is also surface hardened.

In addition, when the carburizing method is adopted as described above, it is desirable to use low carbon steel, low carbon alloy steel, etc., which are generally suitable as case hardening steel, as the base material of the gear (teeth).

This embodiment also provides substantially the same effects as those of the previous embodiment, which have also been confirmed through experiments. The graph shown in FIG. 4 compares the fatigue strength of a gear with and without a carburized non-hardened portion 8, as described above, and compares the fatigue strength of a gear with and without a carburized non-hardened portion 8. Results similar to the data are obtained. Although the same reference numerals are given to the graph in FIG. 4 and the explanation thereof is omitted, it can be seen from this result that there is no relationship between the treatment method employed for surface hardening and the effect of the unhardened portion.

It should be noted that the present invention is by no means to be construed as being limited to the embodiments described in detail above.

For example, it goes without saying that the present invention is applicable not only to spur gears but also to various gears such as helical gears, racks, bevel gears, and internal gears.

Furthermore, in addition to induction hardening and carburizing, which are shown as typical methods, almost any surface hardening method can be used, such as nitriding, as long as the surface of the tooth can be hardened while leaving unhardened parts. It is possible.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a main part of a gear showing an embodiment of the present invention, and FIG. 2 is a graph showing the root fatigue fracture limit of the gear in comparison with a conventional gear. 3 is a diagram corresponding to FIG. 1 showing another embodiment of the present invention, and FIG. 4 is a graph corresponding to FIG. 2 showing the effect of the gear in FIG. 3. 2, 6: hardened portion, 4, 8: non-hardened portion.

Claims (1)

[Claims] 1 The gear peripheral surface consisting of tooth surface, tooth top surface and tooth bottom surface is 5 to 15% of the tooth width from the tooth end surface on the tooth top surface.
If we consider that the tooth is cut diagonally with a nearly planar cut surface that passes through a point inside the distance of A surface hardened gear characterized by being surface hardened without being left behind.