Wheel bearing device

Details Wheel bearing device Wheel bearing device

1999-09-14

2001-05-01

Footland, Lenard A. (Department: 3682)

Bearings

Rotary bearing

Antifriction bearing

C384S589000, C384S912000, C384S913000, C384S625000

Reexamination Certificate

active

06224266

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a wheel bearing device for supporting a wheel on an axle through tapered roller bearings.
Tapered roller bearings are bearings suited to bear radial load, axial load and their combined load. Due to their large load capacity, they are used to support axles of automobiles.
FIG. 5
shows an example of a wheel bearing device for a non-driven wheel of a truck. This wheel bearing device has a double-row tapered roller bearing
22
having a pair of inner rings
23
mounted on an axle
21
. A hub
26
and a brake rotor
27
are fixed by bolts
28
to an outwardly extending flange
25
provided at one end of an outer ring
24
. The inner rings
23
are prevented from coming out by a nut
29
. A hub
26
carries wheel mounting bolts
30
.
On the inner-periphery of the outer ring
24
, two rows of raceways
31
are formed. Opposite the raceways
31
, the pair of inner rings
23
are formed each with rows of raceways
32
, respectively. Between these pairs of opposed raceways
31
and
32
, a plurality of tapered rollers
33
are provided in two rows. The tapered rollers
33
roll with their large-diameter ends
34
abutting with flanges
35
provided at outer ends of the pair of inner rings
23
, respectively.
Thus, the hub
26
and the brake rotor
27
fixed to the outer ring
24
are supported so as to be rotatable relative to the axle
21
.
A contact type rubber seal
36
is provided at the inner end, that is, the end near the center of the axle
21
, of an annular space in which the tapered rollers
33
are arranged in two rows. A cap
37
covers the outer end, i.e. the end near the end of the axle
21
together with the end of the axle on which is mounted the nut
29
to prevent scattering of lubricating grease in the bearing and entry of dust and water from outside.
The bearing portion of such a wheel bearing device as described above is periodically greased and maintained. With increasing horsepower and loading capacity of modern cars, higher resistance to high loading and high temperature during high-speed cruising are required for wheel bearing devices. Long-term maintenance-freedom is also desired. Under high-load, high-temperature conditions, grease sealed in the bearing portion of a wheel bearing device tends to deteriorate quickly. Thus a highly heat-resistant, long-life grease is desired. Also, it is required to maintain long life of bearing members under high-load, high-temperature conditions.
As mentioned above, since tapered rollers of a tapered roller bearing roll with their large-diameter ends abutting with the flanges of the inner rings, heat is produced at the sliding portions between the roller ends and the flanges. The higher the load, the higher the contact pressure between the roller ends and the flange, and thus the greater the heat produced.
Heretofore, for the inner circumferential surface shape of the outer ring
24
, the portion between the pair of raceways
31
was made straight and no measure for reducing weight has been taken. Also, one of the factors that influence the bearing life is whether the lubricating condition is good or bad. The amount of lubricating grease sealed depends on the volume of the internal space of the bearing. But heretofore, it was not structured taking into account the amount of sealed grease, so that there was a limit on the amount of grease.
An object of this invention is to provide a wheel bearing device which assures long life even under high-load, high-temperature conditions.
Another object of this invention is to reduce the weight of a wheel bearing device for an axle and to increase its life.
SUMMARY OF THE INVENTION
According to this invention, there is provided a wheel bearing device comprising a tapered roller bearing for rotatably supporting a wheel on an axle, the tapered roller bearing including an outer ring having a raceway formed on an inner periphery thereof, an inner ring having a raceway on an outer periphery thereof so as to be opposed to the raceway of the outer ring, and a plurality of tapered rollers disposed between the opposed raceways, characterized in that carburized and nitrided layers containing 0.80 wt or more carbon and having a Rockwell hardness of 58 or over are formed on the surfaces of the inner ring or the tapered rollers, the carburized and nitrided layers having a residual austenite content of 25-35 vol %.
Carburized and nitrided layers are formed on the inner rings and tapered rollers for the following reasons. The residual austenite in a carburized layer obtained by ordinary carburizing hardening is high in toughness and work-hardening characteristics. Thus, if it is contained in a suitable amount, it would suppress the development and progression of cracks while maintaining required hardness of the carburized layer. But it is unstable to heat. In contrast, if they are subjected to nitriding treatment under suitable conditions, nitrogen atoms will melt into the residual austenite in a solid state, thus making the residual austenite stable against heat. In a carburized and nitrided layer obtained by nitriding treatment, a greater compressive residual stress is formed than in a carburized layer, so that it is possible to further improve fatigue strength.
The carburized and nitrided layers should contain 0.80 wt % or more carbon and have a Rockwell hardness HRC of 58 or over to reduce friction at sliding portions between the larger ends of the tapered rollers and the flanges of the inner rings. The residual austenite content should be 25-35 vol % to give suitable toughness to the carburized and nitrided layer and to relieve excessive increase in stress due to biting of abrasion powder produced from e.g. the sliding portions and contained in grease. That is to say, if the residual austenite content is less than 25 vol %, toughness is insufficient. If over 35 vol %, the hardness would decrease excessively, resulting in the deterioration of surface roughness due to plastic deformation.
The carburized and nitrided layers as described above can be formed by the following treatment steps. That is, it is heated and held for a predetermined time period while keeping the carbon potential in a carburizing atmosphere at 0.8% or over, and then subjected to carburizing hardening by cooling in oil. It is then heated and held for a predetermined time period in ammonia gas for nitrizing. Nitriding may be carried out during carburizing. In order to adjust the residual austenite content, sub-zero treatment or annealing may be carried out.
To achieve the second object, according to the present invention, the internal space of the bearing is increased by forming an annular recess in the inner periphery of the outer ring at a portion between the rows of the raceways of the outer ring.
Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which:


REFERENCES:
patent: 3937535 (1976-02-01), Ladin
patent: 4179167 (1979-12-01), Lura et al.
patent: 5037214 (1991-08-01), Dougherty
patent: 5259676 (1993-11-01), Marti
patent: 2374172 (1978-07-01), None
patent: 2117459 (1983-10-01), None

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