Crankshaft holding structure for internal combustion engine

Details Crankshaft holding structure for internal combustion engine Crankshaft holding structure for internal combustion engine

2001-05-09

2003-03-11

Wolfe, Willis R. (Department: 3747)

Internal-combustion engines

Frame construction

Horizontal cylinder

C123S197100

Reexamination Certificate

active

06530353

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a crankshaft holding structure for use in an internal combustion engine, and more particularly to a crankshaft holding structure for absorbing axial elongation and deformation of a crankshaft.
2. Description of the Background Art
Crankshafts of internal combustion engines suffer from axial elongation and deformation due to thermal expansion. However, there are crankshaft holding structures for absorbing axial elongation and deformation of a crankshaft. For example, one crankshaft holding structure is shown in Japanese Patent Laid-open No. 60-179597 entitled “Crankshaft Holding Structure for Internal Combustion Engine.”
This type of crankshaft holding structure includes a resilient member which is placed in a gap between an end face of a bearing and a crankcase. When a crankshaft is installed in the crankcase with bearings, the resilient member serves to absorb axial elongation and deformation of the crankshaft.
However, the resilient member required in this type of arrangement to absorb axial elongation and deformation of the crankshaft presents an obstacle to any efforts to cut down the cost of the crankshaft holding structure.
There is also a technique in the background art for absorbing axial elongation and deformation of a crankshaft without the use of a resilient member. Such a technique will be described below with reference to FIG.
4
and FIG.
5
.
FIG. 4
of the accompanying drawings is a cross-sectional view of a conventional crankshaft holding structure for use in an internal combustion engine. In
FIG. 4
, the terms “front” and “rear” are used to indicate front and rear sides of the holding structure.
A crankshaft holding structure
60
for use in an internal combustion engine has a rear bushing
65
of cast iron that is cast in a rear wall
62
(shown in the rear side in
FIG. 4
) of a crankcase
61
. A radial ball bearing
70
has an outer race
71
press-fitted in the rear bushing
65
and an inner race
72
with a rear crankshaft
76
interference-fitted therein.
The crankshaft holding structure
60
also has a front bushing
66
of cast iron that is cast in a front wall
63
(shown in the front side in
FIG. 4
) of the crankcase
61
. A radial roller bearing
73
has an outer race
74
press-fitted in the front bushing
66
and an inner race
75
with a front crankshaft
77
clearance-fitted therein. A connecting rod
79
is coupled by a connecting rod pin
78
to a counterweight
76
a
of the rear crankshaft
76
and a counterweight
77
a
of the front crankshaft
77
.
Since the front crankshaft
77
is clearance-fitted in the inner race
75
of the radial roller bearing
73
, axial elongation and deformation of the crankshafts
76
,
77
can be accomodated in the direction toward the radial roller bearing
73
as indicated by the arrow “a.”
FIG. 5
of the accompanying drawings is an enlarged view of an encircled area
5
shown in FIG.
4
. The counterweight
77
a
of the front crankshaft
77
has a land
77
b
confronting the front bushing
66
and spaced from an end face
66
a
thereof by a gap L
5
. The gap L
5
is set to a value smaller than a gap L
6
between an inner side surface
75
a
of the inner race
75
and a stepped wall surface
77
c
of the counterweight
77
a.
When the elongation or deformation of the rear crankshaft
76
and the front crankshaft
77
increases, the land
77
b
abuts against the end face
66
a
of the front bushing
66
before the stepped wall surface
77
c
of the counterweight
77
abuts against the inner race
75
of the radial roller bearing
73
. This limits crankshaft elongation and deformation due to thermal expansion of the crankshafts.
Therefore, since no axial load is applied to the inner race
75
of the radial roller bearing
73
, rollers
73
a
of the radial roller bearing
73
, for example, are prevented from being locally worn.
In order to make the gap L
5
between the land
77
b
and the end face
66
a
of the front bushing
66
smaller than the gap L
6
, it is necessary that the front bushing
66
projects from the front wall
63
of the crankcase. Since the front bushing
66
thus projecting from the front wall
63
has an increased width W
5
, the front bushing
66
has a relatively larger shape.
In addition, in order to keep the land
77
b
in uniform abutment against the end face
66
a
of the front bushing
66
, the end face
66
a
of the front bushing
66
needs to be machined in its entirety to a flat surface. However, it is time-consuming to machine the end face
66
a
as it is normally annular in shape. Therefore, the machining process inhibits attempts to further reduce the cost of the front bushing
66
and the crankshaft holding structure.
Furthermore, in order to satisfy the dimension of the gap L
5
, the extent to which the end face
66
a
of the front bushing
66
projects needs to fall within an allowable range. However, since the front bushing
66
is cast in the front wall
63
of the crankcase
61
, dimensional errors tend to be large.
It is tedious and time-consuming to manage gap dimensions so as to keep the extent of projection of the front bushing
66
within this allowable range. The tedious and time-consuming process of dimensional management also obstructs efforts to minimize the cost of the structure.
As much as the front bushing
66
projects from the front wall
63
of the crankcase, the width W
5
of the front bushing
66
is correspondingly larger. Therefore, this increase in size of the front brushing
66
virtually eliminates the ability to use the front bushing
66
and the rear bushing
65
(see
FIG. 4
) as common parts, e.g. interchangeably. Accordingly, it becomes necessary to manage and store different types of bushings. However, there is a demand for using the front and rear bushings as common parts that is further complicated by the aforementioned arrangement of the background art.
SUMMARY OF THE INVENTION
The present invention overcomes the shortcomings associated with the background art and achieves other advantages not realized by the background art.
It is an aspect of the present invention to provide a crankshaft holding structure for use in an internal combustion engine that includes a simplified structure.
It is an aspect of the present invention to provide a crankshaft holding structure having bushings with bearings press-fitted therein.
It is an additional aspect of the present invention to provide a crankshaft holding structure permitting bushings to be used as common parts.
These and other aspects of the present invention are accomplished by a crankshaft holding structure for an internal combustion engine, the crankshaft holding structure comprising a crankcase; a plurality of bearings including at least one radial roller bearing having an outer race, the outer race fixed to the crankcase; and a crankshaft having a side surface, the side surface of the crankshaft abutting against a side surface of the outer race of the radial roller bearing and limiting an axial elongation and a deformation of the crankshaft.
The outer face of the radial roller bearing is mounted on the crankcase so as not to be axially displaced when the side surface of the crankshaft abuts against the outer face of the radial roller bearing. In view of this arrangement, the side surface of the crankshaft is held in abutment against the side surface of the outer race of the radial roller bearing for thereby limiting axial elongation and deformation of the crankshaft. Since the outer race of the radial roller bearing is not axially displaced, rollers of the radial roller bearing are prevented from becoming locally worn.
The side surface of the outer race of the radial roller bearing against which the side surface of the crankshaft abuts is machined to a flat finish in advance. Therefore, any process of subsequently machining the side surface of the outer race to a flat finish can be dispensed with. In addition, because the radial roller bearing is press-fitted in the crankcase while being positioned highly

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