JP2000161349A - Gear shaft support device for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gear shaft support device for vehicle which can secure a long durable life even under a foreign matter mixing condition, and has a small torque loss by friction, and a small heat generation. SOLUTION: While corbonitriding layers 11a, 15a, and 16a with the carbon contining amount not less than 0.80 wt.%, and the Rockwell hardness more than HRC 58, are formed on the part surfaces of an outer ring 11, an inner ring 15, and a tapered roller 16, which are formed of a carbulized bearing steel, the curvature radius R of the large end surface of the tapered roller 16 is made in the value in the scope R/RBASE=0.75 to 0.87, when the distance from the top of the conical angle of the tapered roller 16 to the large flange surface 13 of the inner gear 15 is defined as RBASE. As a result, the durable life of a tapered roller bearing 6 under a foreign matter mixing condition is improved by stably maintaining the carbonitriding layers of the part surfaces in a material with an adequate toughness, and furthermore, a torque loss and heat generation owing to the sliding friction between the large flange surface 13 of the inner ring 15, and the large end face 18 of the tapered roller 16, are reduced, so as to prevent the generation of a seizure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a support device for rotatably supporting a gear shaft in a power transmission device for a vehicle or the like.

[0002]

2. Description of the Related Art Tapered roller bearings are suitable for bearing radial loads, axial loads, and their combined loads, and have a large load capacity. Therefore, tapered roller bearings such as differentials and transmissions for vehicles such as automobiles and construction machines are used. In a power transmission device, a support device in which a gear shaft is supported by tapered roller bearings is used.

FIG. 1 shows a differential of an automobile using a gear shaft supporting device according to an embodiment of the present invention. The differential includes a drive pinion 4 rotatably supported by two tapered roller bearings 2 and 3 on a housing 1.
And a ring gear 5 meshing with the drive pinion 4
A differential gear case 7 to which the ring gear 5 is attached and rotatably supported by the housing 1 by a pair of tapered roller bearings 6; a pinion 8 disposed in the differential gear case 7; A pair of side gears 9 meshing with 8
And these are housed in a housing 1 in which gear oil is sealed. This gear oil also serves as lubricating oil for the tapered roller bearings 2, 3, and 6.

Next, a basic configuration and a basic design standard of the tapered roller bearing will be described with reference to FIGS. 2A and 3 which are examples of the embodiment of the present invention. The tapered roller bearing is shown in FIG.
As shown in the figure, an outer race 11 having a conical raceway surface 10
And an inner ring 15 having a conical raceway surface 12 having a large flange surface 13 on the large diameter side and a small flange surface 14 on the small diameter side of the raceway surface 12, and each raceway surface of the outer ring 11 and the inner ring 15. It comprises a plurality of conical rollers 16 arranged to be able to roll freely between 10, 12 and a retainer 17 for holding the conical rollers 16 at predetermined intervals in the circumferential direction.

[0005] The tapered roller 16 comprises an outer ring 11 and an inner ring 15.
Line contact with each of the raceway surfaces 10 and 12, as shown in FIG.
The tapered rollers 16 and the respective cone angle vertices of the raceway surfaces 10 and 12 are designed to coincide at a point O on the center line of the tapered roller bearing. Thereby, the tapered roller 16 can roll along each of the raceway surfaces 10 and 12.

In the tapered roller bearing, each of the raceway surfaces 1
Since the cone angles 0 and 12 are different, the resultant force of the loads applied to the tapered rollers 16 from the respective raceway surfaces 10 and 12 acts in a direction to push the tapered rollers 16 toward the large collar surface 13 of the inner ring 15. For this reason, the large end face 18 of the tapered roller 16 is
, And is brought into sliding contact with the large brim surface 13.

[0007]

Since the above-mentioned power transmission device such as a differential has a meshing portion of many gears and a sliding portion of a rotating member, foreign matters such as metal abrasion powder generated at these portions are not provided in the housing. Mixed into the gear oil enclosed in These abrasion powders enter the tapered roller bearing that supports the gear shaft rotating under a high load, and may cause a problem in terms of the durability life.

[0008] As described above, the tapered roller bearing is
Because the large end surface of the tapered roller makes sliding contact with the large collar surface of the inner ring,
When used to support a gear shaft such as a differential that rotates at high speed and high load, the friction torque due to this sliding friction increases, and the temperature of the bearing part rises due to the frictional heat and the viscosity of the gear oil as lubricating oil decreases. Shortages can cause problems.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a gear shaft support device for a vehicle, which can secure a long durable life even when foreign matters are mixed therein and generate little torque loss and heat generation due to friction.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a vehicle gear shaft support device in which a gear shaft is rotatably supported by a tapered roller bearing in a housing filled with gear oil. In the above, the tapered roller bearing has an outer race having a conical raceway surface, an inner race having a conical raceway surface, and a large flange surface provided on a large diameter side of the raceway surface, and a raceway surface of the outer race. A plurality of tapered rollers arranged rotatably between the raceway surface of the inner ring and a retainer for holding the tapered rollers at a predetermined circumferential interval, each surface of the outer ring, the inner ring and the tapered rollers, A carbonitrided layer having a carbon content of 0.80% by weight or more and a Rockwell hardness of HRC 58 or more is formed, the radius of curvature of the large end face of the tapered roller is R, and the inner ring large flange from the vertex of the cone angle of the tapered roller. The distance to the surface is R
_{When BASE} was used, a configuration in which R / R _BASE was in the range of 0.75 to 0.87 was adopted.

The carbonitrided layers were formed on the surfaces of the outer ring, inner ring and tapered rollers for the following reasons. The residual austenite of the carburized layer obtained by normal carburizing and quenching has high toughness and work hardening characteristics, and by including this moderately, secures the hardness of the carburized layer and suppresses the occurrence and propagation of cracks Works, but has the disadvantage of being unstable to heat. On the other hand, when nitriding treatment is performed under appropriate conditions,
Nitrogen atoms form a solid solution in the retained austenite and serve to stabilize the retained austenite against heat, so that the material of the carbonitrided layer can be appropriately maintained against a temperature rise due to heat generation in the bearing portion. The carbonitrided layer obtained by this nitriding treatment has a larger residual compressive stress than the normal carburized layer, so that the fatigue strength can be further increased.

The structure of the carbonitrided layer as described above can be formed by the following processing steps. That is, after the carbon potential in the carburizing atmosphere is kept at 0.8% or more and heated and held for a predetermined time, it is cooled in oil to perform carburizing and quenching, and then heated and held in an ammonia gas for a predetermined time to perform a nitriding treatment. Do. It is also possible to adopt a method of performing a nitriding treatment simultaneously during the carburizing step.

The ratio R / R _BASE between the radius of curvature R of the large end face of the tapered roller and the distance R _BASE from the apex of the cone angle of the tapered roller to the inner ring large flange surface is in the range of 0.75 to 0.87. This is for the following reasons.

FIG. 4 shows the result of calculating the oil film thickness t formed between the inner ring large flange surface and the tapered roller large end surface using Karna's formula. The vertical axis indicates the ratio t / t ₀ to the oil film thickness t ₀ when R / R _BASE = 0.76. The oil film thickness t becomes maximum when R / R _BASE = 0.76, and R / R
_{When BASE} exceeds 0.9, it decreases sharply.

FIG. 5 shows the result of calculating the maximum Hertz stress p between the inner ring large collar surface and the tapered roller large end surface. The vertical axis is shown in FIG.
Similarly to the above, it is indicated by the ratio p / p ₀ to the maximum Hertz stress p ₀ when R / R _BASE = 0.76. Maximum Hertz stress p
Decreases monotonically with increasing R / R _BASE .

In order to reduce torque loss and heat generation due to sliding friction between the inner ring large flange surface and the tapered roller large end surface, it is desirable to increase the oil film thickness t and reduce the maximum Hertz stress p. The present inventors referred to the calculation results of FIGS. 4 and 5, and based on the seizure resistance test results shown in Table 1 below,
The appropriate range of R / R _BASE was determined to be 0.75 to 0.87. In the conventional tapered roller bearing, the value of R / R _BASE is designed in the range of 0.90 to 0.97.

Further, by forming a surface roughness R _a of the inner ring large rib surface in the range of 0.05～0.20Myuemu,
Due to the relationship between the oil film thickness t between the inner ring large flange surface and the tapered roller large end surface, the lubrication state between these surfaces can be maintained in an appropriate state.

The reason for setting the surface roughness _Ra to 0.05 μm or more is as follows. When installing the tapered roller bearing in the shaft, said Describing the tapered roller bearing 6 as an example, as shown in FIG. 6, axial load F _a on the end face of the inner ring 15
While rotating the shaft at a low speed of about 50 to 100 rpm, the tapered roller 16 is moved toward the large flange surface 13 of the inner ring 15, and the large end surface 18 of the tapered roller 16 is moved to the large flange surface 13 at a predetermined pressure. I try to preload. This preload prevents the tapered roller 16 from moving in the axial direction during use of the bearing.
Is performed to make stable line contact with the raceway surfaces 10 and 12 of the outer ring 11 and the inner ring 15. The management of the preload is performed by measuring the shaft torque. When the shaft torque reaches a predetermined value, the preload operation is completed.

When the surface roughness _Ra is less than 0.05 μm, the lubrication state between the large flange surface 13 of the inner race 15 and the large end surface 18 of the tapered roller 16 during the low-speed rotation of the preloading operation is determined by fluid lubrication ( Since complete lubrication) and boundary lubrication are mixed, the coefficient of friction fluctuates greatly, the fluctuation of the measured shaft torque becomes large, and the accuracy of preload control deteriorates. R _a
Is 0.05 μm or more, the lubricated state becomes boundary lubrication, the friction coefficient is stabilized, and accurate preload management can be performed. At a rotational speed under normal bearing use conditions exceeding 100 rpm, a sufficient oil film is formed between the large flange surface 13 and the large end surface 18, and the lubrication state between these two surfaces is fluid lubrication (complete lubrication). The coefficient of friction decreases.

[0020] was not more than 0.20 [mu] m the surface roughness R _a, when R _a is more than 0.20 [mu] m, when the bearing unit is increased temperatures, lubricating oil was reduced viscosity at a high speed rotation region,
This is because the oil film thickness t becomes insufficient and seizure easily occurs.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a differential of an automobile, as described above, and the drive pinion 4.
The gear shaft supporting device using the tapered roller bearings 2, 3, and 6 of the embodiment is adopted to support the shaft of the differential gear case 7 to which the ring gear 5 is attached, and the shaft of the differential gear case 7.

FIG. 2A is an enlarged view of the tapered roller bearing 6 as a representative example. As described above, the tapered roller bearing 6 includes the outer ring 11, the inner ring 15, the tapered rollers 16, and the retainer 17, and the outer ring 11, the inner ring 15, and the tapered rollers 16 are all carburized bearing steel SCr435. It is formed with. FIG. 2 (b) shows the surface of each of these components.
As shown in the figure, the carbonitrided layers 11a, 15 having a carbon content of 0.80% by weight or more and a Rockwell hardness of HRC 58 or more.
a, 16a are formed.

As shown in FIG. 3, the tapered rollers 16
The vertices of the cone angles of the raceway surfaces 10 and 12 of the outer ring 11 and the inner ring 15 coincide at one point O on the center line of the tapered roller bearing 6, and the radius of curvature R of the large end surface 18 of the tapered roller 16 and the point O to the inner ring 15 ratio R / R to the distance R _BASE to the large brim 13
_BASE is manufactured in the range of 0.75 to 0.87. The large flange surface 13 is ground to _a surface roughness Ra of 0.12 μm.

Although not shown, the tapered roller bearings 2 and 3 are manufactured with the same configuration and specifications.

In this embodiment, the SCr 435 is used as the material of each component.
CM435, SCr430, SCr420, SCM42
0, SAE5130, SAE8620 and the like. Further, the present invention can be applied to various types of tapered roller bearings. For example, the present invention can also be applied to a double row tapered roller bearing in which two or more rows of tapered rollers are arranged.

Examples and comparative examples will be described below.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Carburized bearing steel SCr shown in FIGS.
435 outer ring, inner ring and tapered roller components have a carbon content of 0.80% by weight or more, Rockwell hardness HR
C58 or carbonitrided layer is formed, the radius of curvature R of the large end faces of tapered rollers, wherein R / R _BASE = from 0.75 to 0.87
It enters the range of the surface roughness R _a of the large rib surface of the inner ring is 0.12
μm tapered roller bearings (Examples 1 to 4 in Table 1) were prepared. The bearing dimensions are 40 mm inside diameter and 68 m outside diameter.
m.

[0028]

[Comparative Example] On the surface of each of the outer ring, inner ring and tapered roller parts made of carburized bearing steel SCr435, a carbon content of 0.80% by weight or more and a Rockwell hardness HRC58, as in the example,
Tapered roller bearings in which the above carbonitrided layer is formed and the value of R / R _BASE is out of the range of the present application (Comparative Examples 1 to 1 in Table 1)
3) and heat treatment is only normal carburizing and quenching, and R / R _{BA SE}
A tapered roller bearing (Comparative Example 4 in Table 1) having a value out of the range of the present application was prepared. The dimensions of each bearing are the same as in the embodiment.

For the tapered roller bearings of the above-described Examples and Comparative Examples, a life test with foreign substances attached to a rotating shaft in an oil bath containing foreign substances, and a seizure resistance test using a rotation tester were performed.

The test conditions are as follows. (Foreign matter mixing life test) Load load: 11.76 kN Rotational speed: 1500 rpm Lubricating oil: Turbine VG56 (oil bath) Foreign matter: Gas atomized metal powder (particle size: 100 to 180)
μm, hardness HV700-800, mixing amount 1 g / l) (seizure resistance test) Load: 19.61 kN Rotational speed: 1000-3500 rpm Lubricating oil: Turbine VG56 (lubricating amount 40 ml / min, lubricating temperature 40 ° C ± 3 ° C) )

[0031]

[Table 1]

Table 1 shows the test results. The durability life in the foreign matter contamination life test was evaluated based on L10 life (90% of the bearings can be used without being damaged). The life ratio was based on the durability life of Comparative Example 4 as a reference value. Further, the seizure in the seizure resistance test occurred between the large flange surface of the inner ring and the large end surface of the tapered rollers.

Each of the tapered roller bearings of the examples exhibits an excellent durability life with a life ratio of 4 times or more in a foreign matter mixing life test, and has a limit rotation speed of 2700 rpm or more in the occurrence of seizure in an anti-seizure test. You can see that there is.
On the other hand, Comparative Examples 1 to 3 in which the carbonitrided layer is formed but the value of R / R _BASE is out of the range of the present application have an excellent life ratio, but have a limit rotation speed of seizure generation of 2500 rpm or less. Value, and the possibility of seizure under normal use conditions such as differential is high. Surface roughness R _a rough Comparative Example 3 of the large rib surface shows a low Seizure limit speed than Comparative Example 2 having the same radius of curvature R. In Comparative Example 4 in which the heat treatment was only normal carburizing and quenching, and R / R _BASE was also a conventional value, all the test results were inferior.

[0034]

As described above, the tapered roller bearing of the present invention has a carbon content of 0.80% by weight or more and a Rockwell hardness H on the surface of each of the outer ring, inner ring and tapered roller components.
While forming a carbonitrided layer of RC58 or more, the radius of curvature R of the large end face of the tapered roller is determined by the aforementioned R / _RBASE = 0.75.
The value is in the range of ~ 0.87, so the carbonitrided layer on the surface of the component can be stably maintained in a material having appropriate toughness, the durability life can be remarkably improved even when foreign substances are mixed, and the inner ring large flange surface and cone Torque loss and heat generation due to sliding friction between the large roller end faces can be reduced to prevent seizure.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a differential into which a gear shaft support device according to an embodiment is incorporated.

2A is a longitudinal sectional view showing the tapered roller bearing of FIG. 1, and FIG. 2B is an enlarged sectional view of a main part of a.

FIG. 3 is a sectional view for explaining the design specifications of the tapered roller bearing of FIG. 1;

FIG. 4 is a graph showing a relationship between a radius of curvature of a tapered roller large end face and an oil film thickness.

FIG. 5 is a graph showing the relationship between the radius of curvature of the tapered roller large end face and the maximum Hertz stress;

FIG. 6 is a cross-sectional view illustrating a preload operation of the tapered roller bearing.

[Explanation of symbols]

 Reference Signs List 1 housing 2, 3 tapered roller bearing 4 drive pinion 5 ring gear 6 tapered roller bearing 7 differential gear case 8 pinion 9 side gear 10 raceway surface 11 outer ring 12 raceway surface 13 large flange surface 14 small flange surface 15 inner ring 16 tapered roller 17 retainer 18 Large end face 11a, 15a, 16a Carbonitrided layer

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 3J101 AA16 AA25 AA32 AA42 AA54 AA62 AA75 AA82 BA05 BA53 BA54 DA02 EA78 FA31 GA11 4K028 AA03 AB06

Claims (2)

[Claims] 1. A vehicle gear shaft support device in which a gear shaft is rotatably supported by a tapered roller bearing in a housing in which gear oil is sealed, wherein the tapered roller bearing comprises:
An outer ring having a conical raceway surface, an inner ring having a conical raceway surface, and a large flange surface provided on a large diameter side of the raceway surface;
A plurality of tapered rollers arranged rotatably between a raceway surface of an outer ring and a raceway surface of an inner ring; and a retainer for holding the tapered rollers at predetermined circumferential intervals. The outer ring, the inner ring, and the tapered rollers A carbonitrided layer having a carbon content of 0.80% by weight or more and a Rockwell hardness of HRC 58 or more is formed on each surface of the surface roller, the radius of curvature of the large end face of the tapered roller is R, and the apex of the cone angle of the tapered roller. R / R _BASE is in the range of 0.75 to 0.87, where R _BASE is the distance from the inner ring to the large collar surface. Wherein the surface roughness R _a of the inner ring large rib surface 0.0
2. The gear shaft support device for a vehicle according to claim 1, wherein the device is formed in a range of 5 to 0.20 [mu] m.