Internal-combustion engines – Poppet valve operating mechanism – Rocker
Reexamination Certificate
1999-03-11
2001-03-13
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Rocker
C123S090430, C123S090510, C123S090390, C074S559000, C029S888200
Reexamination Certificate
active
06199527
ABSTRACT:
This application claims the benefits of Japanese Application Nos. 10-078556, 10-224702, 10-224703, 10225661 and 10-226183 which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a rocker arm made of sheet metal which is manufactured by a press work from a metal plate, out of rocker arms incorporated in a valve driving mechanism of an engine for converting a rotation of a cam shaft to a reciprocating motion of a valve unit (including a suction valve and an exhaust valve), as well as an improvement in a manufacturing method thereof.
The present invention also relates to a cam follower provided with a sheet metal rocker arm and an improvement in an assembling method thereof.
A reciprocating engine (reciprocating piston engine) is provided with a suction valve and an exhaust valve which opens and closes in synchronism with a rotation of a crank shaft, except a two-cycle engine provided in certain types. In such a reciprocating engine, a motion of a cam shaft which rotates in synchronism with a rotation of the crank shaft (at a rotation speed of ½ in case of a four-cycle engine) is transmitted to the intake valve and the exhaust valve by use of a rocker arm, and the intake valve and the exhaust valve are reciprocated along the axial direction.
Conventionally, such a rocker arm incorporated in the valve driving mechanism of the engine is generally formed by casting (as a cast iron or aluminum die cast product). However, a cast product is too weighty (in case of an iron cast) or bulky (in case of an aluminum die cast) for maintaining a sufficient strength. In addition, since the rocker arm is generally manufactured by a lost wax method, the manufacturing cost is unavoidably increased. For this reason, it is recently considered to manufacture such rocker arm by a press work from a metal plate such as a steel plate, which is partially realized.
A conventional manufacturing method of a sheet metal rocker arm considering such circumstances is disclosed in, for example, Japanese Patent Application Laid-Open No. 3-172506.
FIGS. 19
to
22
show the manufacturing method of a sheet metal rocker arm disclosed in this application. According to this conventional method, first a metal plate (such as a carbon steel plate having the thickness of 2 to 4 mm) as blank is punched by the press work, so as to form a blank
1
having a shape as shown in FIG.
19
A and the thickness of t
1
, as shown in FIG.
19
B.
Next, this blank
1
is subjected to a bending work by press to form a first intermediate blank
2
as shown in
FIGS. 20A and 20B
. This first intermediate material
2
comprises a pair of side walls
3
,
3
parallel to each other, a connecting portion
4
for connecting the edges of the both side walls
3
,
3
in the width direction, a roller receiving recess
5
formed in a middle part of a space surrounded in three directions by the both side walls
3
,
3
, and the connecting portion
4
, and a pivot portion
6
as a spherical concave surface formed in a middle part at a position nearer one end of the connecting portion
4
.
Subsequently, a through hole
7
which has a Japanese hand drum shape when seen from the side parallel to the side walls
3
,
3
, as shown in
FIGS. 21A and 21B
, is formed in a portion which is a part of the connecting portion
4
for forming the first intermediate blank
2
as described above and is corresponding to the roller receiving recess
5
, as a second intermediate blank
8
; Arched protrusions
9
,
9
which are part of the second intermediate blank
8
are provided to sandwich this through hole
7
from the both sides thereof in the width direction (the up-and-down direction in
FIG. 21A
) in a state that the protruding edges of both of the protrusions
9
,
9
are placed opposite to each other. The through hole
7
has a narrower width W
7
at the center thereof, compared with the width at a part nearer either of the ends thereof.
When a part surrounding the though hole
7
of the second intermediate blank
8
as described above is subjected to burring and ironing, a third intermediate blank
10
as shown in
FIG. 22
is obtained. In this third intermediate blank
10
, the through hole
7
becomes an opening
11
which has a rectangular shape when seen from the side parallel to the side walls
3
,
3
, and the shape of the other end portion of the connecting portion
4
is adjusted to become a valve engagement portion
12
for abutting on the base end portion of the valve unit constituting the intake valve or the exhaust valve. At the subsequent step, in the third intermediate blank
10
as described above, circular holes for supporting the both ends of a support shaft for supporting to allow free rotation a roller which is engaged with the cam are formed at positions aligned with each other on both of the side walls
3
,
3
, thereby completing a sheet metal rocker arm. Then, in a state that such sheet metal rocker arm is assembled in the engine, the outer peripheral surface of the roller which is supported by the roller receiving portion
5
in a rotating manner is brought into contact with the outer peripheral surface of the cam, the leading end portion of a lash adjuster is caused to abut upon the pivot portion
6
, and the base end surface of the suction valve or the exhaust valve is caused to abut upon the valve engagement portion
12
.
The thickness t
3
of each of the laterally paired side walls
3
,
3
for constituting the sheet metal rocker arm manufactured in the manner described above is substantially equal to the thickness t
1
of the blank
1
(
FIG. 19B
) (t
3
≈t
1
). The thickness t
3
of each of the both side walls
3
,
3
and the thickness t
4
of the connecting portion
4
including the pivot portion
6
and the valve engagement portion
12
. (
FIG. 22B
) are also substantially equal to the thickness t
1
of the blank
1
(t
1
≈t
3
≈t
4
).
More specifically, since formed of one metal plate in a unitary structure mainly by the press work, the conventional sheet metal rocker arm mentioned above has substantially a uniform thickness over the entire surface thereof except a part of the pivot portion
6
and a part followed by a part of the metal plate. Also, in case of a conventional technology other than Japanese Patent Application Laid-Open No. 3-172506 mentioned above, a sheet metal rocker arm which is formed of one metal plate in a unitary structure mainly by the press work has substantially a uniform thickness over the entire surface thereof.
On the other hand, there is conventionally known a structure of a rocker arm in which two or three members respectively formed by the press work of a metal plate are connected and fixed to each other by welding. In case of a sheet metal rocker arm which is formed by combining plural members as stated, the thickness of the connecting portion including the pivot portion and the valve engagement portion is formed greater than the thickness of each of the side walls.
According to the conventional technology described above, inconveniences as stated below will be brought about. First, according to the technology disclosed in Japanese Patent Application Laid-Open No. 3-172506 for forming a sheet metal rocker arm from one metal plate in a unitary structure, the thickness of the formed sheet metal rocker arm is uniform substantially over the entire surface thereof. On the other hand, when the rocker arm is in use, a stress acting on the connecting portion
4
, specially that acting in the vicinity of the valve engagement portion
12
, is greater, compared with that stress acting on another portion such as the side walls
3
,
3
. For this reason, when the thickness is uniform, the connecting portion
4
, specially in the vicinity of the valve engagement portion
12
, is disadvantageous in terms of the strength, compared with other portions, and the rigidity also may be lowered in some cases. In case of the conventional technology, the thickness of the metal plate for forming the sheet metal rocker arm is made to be great in order to s
Abe Shoichi
Iwasa Hiroshi
Kadokawa Satoshi
Okubo Kiyoshi
Evenson, McKeown, Edwards & Lenahan P.L.L.C.
Lo Weilun
NSK Ltd.
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