Bearing device assembly

A bearing device assembly includes a water pump shaft supported by a rolling bearing, and a plulley seat press fitted to one end of the water pump shaft. A recess or recesses in the form of a ring-shaped groove, a spiral-shaped groove, and a groove extending in the axial direction of the shaft, or the like are formed in at least one of the peripheral surface of the one end portion of the water pump shaft and the inner surface of the pulley seat. The recess prevents formation of an oil film on the fitting surface between the water pump shaft and the pulley seat at the time of press fitting the pulley seat, and also allows the remaining oil on the fitting surface to flow into the recess.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a bearing device assembly, and, in 
particular, to an improved bearing device assembly wherein the fixing 
force of a rotary member mounting seat which is press fitted onto a shaft 
member of the bearing device assembly is enhanced. 
2. Description of the Relevant Art 
Prior art bearing device assemblies are those in which a rotary member 
mounting seat is press fitted onto one axial end of a shaft member having 
a rolling bearing assembled thereto. an example of this type of bearing 
device assembly is a cooling water pump shaft of a water-cooled engine. 
FIG. 1 shows an assembled water pump shaft comprising a rolling bearing 10 
having an outer ring 11, mounted on an intermediate portion of a water 
pump shaft 12. The bearing 10 is fitted in a housing 31 of a water pump 
30. The bearing may be of the ball or roller type. The water pump shaft 12 
rotates and serves and the inner bearing ring. 
A vane 32 is secured to one axial end 13 of the water pump shaft 12, and a 
pulley seat 20, for mounting a rotary member, is press fitted to the other 
axial end 14 of the water pump shaft 12. A driving pulley 40, which is the 
rotary member, and a cooling fan 42 are secured by bolts 43 to the pulley 
seat 20. By driving the driving pulley 40 through a belt 44, the vane 32 
and the cooling fan 42 are rotated as a unit, using the water pump shaft 
12 as a common shaft. 
The pulley seat 20 is press fitted to the one axial end 14 of the water 
pump shaft 12 with an interference clearance of minus 30-70 micrometers. 
However, in order to fit the pulley seat 20 in proper alignment with the 
center of the water pump shaft 12, it is necessary to insure a high 
fitting accuracy. Therefore, the surface of the one axial end 14 of the 
water pump shaft 12 is highly finished with the chamfering or bevelling 
angle and the shape of the end face of the end 14 configured so that the 
smooth fitting can be achieved. Also, it is necessary to prevent drag from 
being caused on the fitting surface. 
The fixing force of the pulley seat 20, which is press fitted to the water 
pump shaft 12, is affected by such conditions as the viscosity and the 
amount of rust resisting oil remaining on the fitting surface of the water 
pump shaft 12 or pulley seat 20, the roughness of the fitting surface, the 
chamfered shape of the end face of the water pump shaft at which the 
pulley seat is press fitted, and the speed at which press fitting occurs. 
For this reason, if these conditions are not appropriate, the fixing force 
of the pulley seat will be reduced to a great extent. 
When the pulley seat fixing force between the pulley seat 20 and the pump 
shaft 12 is reduced, the pulley seat will move in the axial direction, or 
slip off of the water pump shaft causing damage to the cooling fan, or a 
radiator attached to the front side of the cooling fan. 
The inventors of the present application found that the main cause of the 
reduced fixing force between the pulley seat 20 and the pump shaft 12, 
which results in displacement of the pulley seat 20 along the water pump 
shaft 12 or the slipping off of the pulley seat 20, is due to the 
formation of an oil film 52, as shown in FIG. 2, on the fitting surfaces 
of the pulley seat 20 and water pump shaft 12. Consequently, a boundary 
friction condition is caused wherein the frictional coefficient of the 
fitting surface is decreased. In this case, the aforementioned oil film 52 
is formed when a rust resisting oil 50 which has been coated on the outer 
surface of the end portion 14 of the water pump shaft 12 remains on the 
fitting surface at the time of force fitting the pulley seat 20. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a bearing device 
assembly having a mechanism which enables press fitting of a rotary member 
mounting seat to a shaft member without allowing a rust resisting oil to 
remain on the fitting surface of one end of the shaft member and the 
rotary member mounting seat. 
A bearing device assembly in accordance with the present invention is 
provided with recesses in at least one of the outer surface of one axial 
end of a shaft member on which surface a rust resisting oil remains or the 
inner surface of a rotary member mounting seat which is fixed by press 
fitting to the one axial end of the shaft member, or both. Owing to these 
recesses, when the rotary member mounting seat is press fitted to the one 
axial end of the shaft member, an oil film is interrupted by the recesses 
when the end face of the rotary member mounting seat or the end face of 
the shaft member passes across a recess. Moreover, once the rotary member 
mounting seat is press fitted past the edges of a recess, the subsequent 
formation of an oil film is made difficult, and any rust resisting oil 
remaining on the fitting surface flows into the recess and is stored 
therein. 
In the bearing device assembly of the present invention, since recesses are 
provided in at least one of the fixing surfaces of the axial end portion 
of the shaft member on which surface a rust resisting oil is remaining or 
the inner surface of the rotary member mounting seat, the formation of the 
oil film on the fitting surface is hindered, and at the same time, the 
rust resisting oil remaining on the fitting surface is allowed to flow 
into the recess. As a result, the formation of the oil film of rust 
resisting oil on the fitting surface is substantially decreased and the 
rotary member mounting seat, which is force fitted, is secured with an 
increased fixing force. Moreover, the securing force on the fitting 
surface between the shaft member and the rotary member mounting seat is 
enhanced with the lapse of time after press fitting, as any remaining oil 
flows into the recesses. Accordingly, in the present invention, it is 
possible to prevent an accident in which the rotary member mounting seat 
moves in the axial direction or slips off of the shaft member during 
rotation of the shaft member. Thus, a bearing device assembly having 
stable and reliable properties can be obtained. 
Other objects and features of the invention will become apparent by 
reference to the following specification and to the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The embodiments of the present invention applied to a bearing device 
assembly for a water pump will be described with reference to the 
drawings. 
FIG. 3 shows an axial end portion 14 of a water pump shaft on which a 
pulley is force fitted, having a recess or groove 15, having a 
semi-circular cross section, formed continuously around the peripheral 
surface of the axial end portion 14 to form a ring shape. 
FIG. 4 shows a pulley seat 20 in the present invention, with a recess or 
groove 25, having a semi-circular cross section, formed continuously and 
circumferentially around an inner surface of a cylindrical through hole 
25a, in pulley seat 20, in which the axial end portion 14 is fitted. 
Either one or both of the recess or groove 15 of the axial end portion 14 
of the water pump shaft or the recess or groove 25 of the pulley seat 20 
may be provided. 
FIGS. 5 and 6 are enlarged sectional views of an upper half portion of the 
one axial end portion 14 and the pulley seat 20 for illustrating a change 
in condition of an oil film during press fitting of the pulley seat 20, 
and after the press fitting of the pulley seat 20, respectively. 
In FIG. 5, when the pulley seat 20 is press fitted to the one axial end 14 
of the water pump shaft in the direction of the arrow, and until the front 
face 21 of the pulley seat 20 reaches the recess 15 of the one axial end 
14 of the water pump shaft, most of a rest resisting oil 50 coated on the 
outer surface of the one axial end portion 14 is scraped down, leaving 
only a part of the rust resisting oil 50 to remain on the fitting surface 
to form an oil film 52. However, when the front face of the pulley seat 20 
passes over recess 15, the oil film 52 is cut and separated between the 
inner surface 21 of the pulley seat 20 and the recess 15. Specifically, 
when the front face of the pulley seat 20 passes over an inside edge or 
shoulder 16 of the recess 15, the connection of the oil film 52 with 
remaining rust resisting oil 53 in the recess 15 is cut. As the press 
fitting of the pulley seat 20 is continued, as shown in FIG. 6, the rust 
resisting oil 50 on the one axial end 14 of the water pump shaft is 
scraped off by the front face of the pulley seat 20 in the direction of 
press fitting and pushed forwardly. As a result, substantially no oil film 
is formed on the fitting surface at an axially inside portion thereof with 
respect to the recess 15. 
Furthermore, the oil film 52 formed on the fitting surface at a position 
axially outside of the recess 15 of the one axial end 14, at the beginning 
of the press fitting of the pulley seat 20, is gradually pulled towards 
the remaining rust resisting oil 53 in the recess 15. At this position, 
the surface pressure is low due to a surface pressure difference between 
the inner surface of the pulley seat 20 and the peripheral surface of the 
one axial end portion 14 of the water pump. Thus, the oil film 52 flows 
into the recess 15 and is stored therein. Additionally, the oil film 
formed on the fitting surface at a position axially inside of the recess 
15 of the one axial end portion 14 of the water pump, similarly due to the 
surface pressure difference, flows into the recess 15, leaving no rust 
resisting oil remaining on the fitting surface, excepting the recess 15. 
Also, in cases in which the recess 25 is formed in the pulley seat 20, or 
both the recess 15 of the one axial end 14 of the water pump shaft and the 
recess 25 of the pulley seat are provided, it is possible to prevent the 
formation of the oil film on the fitting surface by entirely similar 
action as described above. 
FIGS. 7 to 13 show additional embodiments of the present invention. 
In the embodiment of FIG. 7, two continuous recesses or grooves, in the 
form of two rings 15a, are provided in the peripheral surface of the one 
axial end portion 14 of the water pump shaft. The grooves 15a are spaced 
from each other by a suitable distance. Each of the recesses 15a has a 
shape similar to the recess 15 in FIG. 3. 
In the embodiment of FIG. 8, a recess or groove 15b is formed in a spiral 
shape in the peripheral surface of one axial end portion 14 of the water 
pump shaft. 
In the embodiment of FIG. 9, a recess 15c, having a plurality of parallel 
narrow channels 15cc intersecting one another to form a mesh shape, is 
provided in the peripheral surface of one axial end portion 14 of the 
water pump shaft. The recess 15c is continuous around the peripheral 
surface of the one axial end portion 14 to form a circular band and 
extends in the axial direction to a suitable width. 
In the embodiment of FIGS. 10A and 10B, a recess or groove 15d having a 
semi-circular cross section is formed in the peripheral surface of one 
axial end portion 14 of the water pump shaft so that the recess 15d 
extends axially inwardly from the end face of the end portion 14. 
In the embodiment of FIGS. 11A and 11B, four recesses or grooves 15e having 
semi-circular cross-sections are formed in the peripheral surface of one 
axial end portion 14 of the water pump shaft. The four recesses 15e extend 
axially in a parallel relation to one another from the end face of the 
axial end portion 14 inwardly therefrom. The four recesses 15e are spaced 
at equal intervals along the circumference of the peripheral surface of 
the axial end portion 14. 
In the embodiment of FIGS. 12A and 12B, four circular recesses 15f are 
formed in the peripheral surface of one end portion 14 of the water pump 
shaft along the circumference of the peripheral surface in equally spaced 
intervals. 
In the embodiment of FIGS. 13A and 13B, two slit-like recesses 15g are 
formed at both sides of a vertical center line (a center line in the cross 
section) which passes through the shaft center of the water pump shaft and 
intersects the center axial line by notching the peripheral surface of one 
end portion 14 of the water pump shaft. 
The recesses or grooves in the embodiments of FIGS. 7 through 13 may also 
be provided in the inner surface of the pulley seat 20, or may be provided 
in both the peripheral surface of one end portion 14 of the water pump 
shaft and the inner surface of the pulley seat 20. 
The cross sectional and plane shapes of the recesses or grooves in the 
above embodiments are not limited to the shapes shown in the FIGURES, but 
other arbitrary shapes such as a triangular shape, polygonal shape, 
elliptical shape, or other suitable shapes may be selected. 
Next, the results of a test of the drawing-out force for a pulley seat, 
conducted as to samples of the bearing device assembly of the present 
invention, are shown in FIG. 14 in comparison with samples of the prior 
art. 
The samples of the present invention used in the test include a sample 
having a shaft member formed with one recess or groove having a 
semicircular cross section and extending along the circumference, and the 
other sample having a shaft member formed with one recess or groove having 
a triangular cross section and extending along the circumference. Each 
sample of the present invention was coated with a rust resisting oil on 
the peripheral surface of the shaft member. The samples were left to stand 
for one week after which a pulley seat was press fitted at a speed of 1.5 
mm/s. 
The samples of the prior art used in the test include a sample having a 
pulley seat force fitted under the same condition as mentioned above, and 
another sample in which, after the rust resisting oil was coated on the 
peripheral surface of the shaft member, the rust resisting oil was removed 
when a pulley seat was force fitted. 
For each of the samples, the roughness of the peripheral surface of the 
shaft member, the chamfering angle, the shape of the end portion of the 
shaft member to which the pulley seat is force fitted, and the kind of 
rust resisting oil were set the same as the prior art specification. 
As shown in FIG. 14, the samples of the present invention require a higher 
drawing-out force than the samples of the prior art; the drawing-out force 
being comparable to that of the sample in which the rust resisting oil is 
removed. 
The frictional coefficient was calculated using the test results. According 
to the calculations, the frictional coefficient of the samples of the 
present invention, and the samples having the rust resisting oil removed, 
was about 0.16 which is in a dry frictional region. In contrast to this, 
the frictional coefficient of the samples having the rust resisting oil 
coated thereon was about 0.06 which is in a boundary frictional region, 
showing that an oil film is formed on the fitting surface. 
In the above embodiments, the bearing device assembly for the water pump is 
described. However, the present invention is not limited to the above 
embodiments but the present invention is also applicable to other bearing 
assemblies which are assembled by force fitting a rotary member mounting 
seat to one axial end portion of a shaft member. 
While certain embodiments of the invention have been described in detail 
above in relation to a bearing device assembly, it will be apparent to 
those skilled in the art that the disclosed embodiment may be modified. 
Therefore, the foregoing description is to be considered exemplary rather 
than limiting, and the true scope of the invention is that defined in the 
following claims.