Title: Sheet metal rocker arm, manufacturing method thereof, cam follower with said rocker arm, and assembling method thereof
Abstract: A sheet metal rocker arm manufactured by the steps of punching one metal plate to form a blank having a predetermined contour and through holes, and subjecting this blank to a bending work based on a press work to form a pair of side walls parallel to each other and a connecting portion for connecting the both ends of the side walls in the width direction thereof. This rocker arm is also provided with at least a pair of though holes formed at positions which are aligned with each other on the both side walls and at least one engagement portion provided in a part of the connecting portion. The thickness of at least one engagement portion, is formed to be greater than the thickness of the both side walls.
Patent Number: 6,959,676 Issued on 11/01/2005 to Okubo, et al.
| Inventors:
|
Okubo; Kiyoshi (Maebashi, JP);
Abe; Shoichi (Maebashi, JP);
Kadokawa; Satoshi (Fujisawa, JP);
Iwasa; Hiroshi (Fujisawa, JP)
|
| Assignee:
|
NSK Ltd. (Tokyo, JP)
|
| Appl. No.:
|
702047 |
| Filed:
|
November 6, 2003 |
Foreign Application Priority Data
| Mar 12, 1998[JP] | 10-078556 |
| Aug 07, 1998[JP] | 10-224702 |
| Aug 07, 1998[JP] | 10-224703 |
| Aug 10,
1998[JP] | 10-225661 |
| Aug 10, 1998[JP] | 10-226183 |
| Current U.S. Class: |
123/90.39; 123/90.44; 123/90.45; 74/559 |
| Intern'l Class: |
F01L 001/18 |
| Field of Search: |
123/9039,904.1,904.4,904.5
74/519,559
29/888.2
|
References Cited [Referenced By]
U.S. Patent Documents
| 4727832 | Mar., 1988 | Miyamura et al.
| |
| 4829647 | May., 1989 | Anderson et al.
| |
| 4848180 | Jul., 1989 | Mills.
| |
| 5329891 | Jul., 1994 | Murphy et al.
| |
| 5535641 | Jul., 1996 | Uchida et al.
| |
| 5678305 | Oct., 1997 | Nagano et al.
| |
| 5678459 | Oct., 1997 | Motohashi et al.
| |
| 5720245 | Feb., 1998 | Calka.
| |
| 5799546 | Sep., 1998 | Pryba.
| |
| 5819694 | Oct., 1998 | Trutescu et al.
| |
| 6021750 | Feb., 2000 | Hetrich.
| |
| Foreign Patent Documents |
| 19622888 | Dec., 1997 | DE.
| |
| 19645788 | May., 1998 | DE.
| |
| 3121205 | Jul., 1990 | JP.
| |
| 3172508 | Jul., 1991 | JP.
| |
Primary Examiner: Denion; Thomas
Assistant Examiner: Chang; Ching
Attorney, Agent or Firm: Crowell & Moring LLP
Parent Case Text
This application is a continuation of application Ser. No. 10/342,235, filed
Jan. 15, 2003, now U.S. Pat. No. 6,672,266, which is a continuation of application
Ser. No. 10/101,868, filed Mar. 21, 2002, now U.S. Pat. No. 6,601,555 which is
a continuation of application Ser. No. 09/912,366, filed Jul. 26, 2001, now U.S.
Pat. No. 6,508,215, which is a continuation of application Ser. No. 09/729,111,
filed Dec. 5, 2000, now U.S. Pat. 6,334,416, issued Jan. 1, 2001, which is a division
of Ser. No. 09/265,957, filed Mar. 11, 1999, now U.S. Pat. No. 6,199,527, issued
Mar. 13, 2001.
This application claims the benefits of Japanese Application Nos. 10-078556,
10-224702, 10-224703, 10-225661 and 10-226183 which are hereby incorporated by reference.
Claims
1. A cam follower provided with a sheet metal rocker arm comprising:
a sheet metal rocker arm formed of a metal plate and provided with a pair of
side walls substantially parallel to each other, and a connecting portion connecting
the side walls to each other;
a pivot fixed to bridge over said paired side walls by plastically deforming
both end portions of the pivot to the inner peripheral surfaces of a pair of through
holes formed at positions aligned with each other on the side walls, bridging the
through holes; and
a roller supported rotatably around a middle part of the pivot;
wherein a gap between the portions provided with said through holes on the paired
side walls prior to the plastically deforming of both end portions of said pivot
is made wider than a gap between said portions when both end portions of said pivot
have been plastically deformed, so as to make said paired side walls parallel to
each other when both end portions of the pivot have been plastically deformed.
2. A method of assembling a cam follower provided with a sheet metal rocker arm,
which is formed of a metal plate and comprises a pair of side walls and a connecting
portion connecting the side walls to each other and in which a pair of through
holes are formed at positions aligned to each other on both side walls, comprising
the steps of:
inserting a pivot into a roller and said paired side walls such that the roller
is disposed between said paired side walls, thereafter plastically deforming both
end portions of the pivot toward the inner peripheral surfaces of the paired through
holes, whereby the pivot is fixed to bridge over the paired side walls;
wherein a gap between the portions provided with the paired through holes on
the paired side walls, prior to the plastically deforming of both end portions
of said pivot is made wider than a gap between said portions when both end portions
of said pivot have been plastically deformed, and the gap between the portions
with said through holes formed therein is narrowed upon plastically deforming both
end portion of the pivot, thereby making the paired side walls parallel to each other.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a rocker arm made of sheet metal which is manufactured
by pressing from a metal plate, out of rocker arms incorporated in a valve driving
mechanism of an engine for converting 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 reciprocate 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 heavy (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 pressing 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 a thickness of 2 to 4
mm) as a blank is punched by pressing, so as to form a blank
1 having a
shape as shown in FIG. 19A and a thickness of t
1, as shown in FIG.
19B.
Next, this blank
1 is subjected to bending by pressing 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 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 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 suction valve or the exhaust
valve. At the subsequent step, in the third intermediate blank
10 as described
above, circular holes for supporting 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, when 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≈1). The thickness t
3 of each of the
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 pressing, 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 pressing 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 pressing 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, especially 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 large in order to secure a sufficient strength
and rigidity of a portion in the vicinity of the valve engagement portion
12.
Consequently, the thickness of the other portions such as the side walls
3,
3 is greater than that originally required, so that the size and the weight
of the sheet metal rocker arm can not be sufficiently reduced. In addition, the
cost of materials is increased.
In case of the sheet metal rocker arm in which two or three members respectively
formed of a metal plate by pressing are connected and fixed to each other by welding,
the thickness of the connecting portion including the valve engagement portion
can be made greater than the thickness of another portion such as the side wall.
On the other hand, however, after plural members are formed separately, these members
are required to be combined with each other and bonded together by welding. Consequently,
the number of processing steps increases and extra labor is required for controlling
the constituent parts. Since complicated and precise equipment is required for
positioning the respective members when they are assembled, it is unavoidable to
increase the cost, as well as to increase the number of processing steps and to
require extra labor for controlling the parts. Moreover, the quality of the obtained
sheet metal rocker arm (precision) is often inferior to that of the rocker arm
formed in a unitary structure.
Though having a superior toughness to the cast-type rocker arm, the sheet
metal rocker arm may be elastically deformed more easily depending on the direction
of action of the force. That is, since each of the paired walls
3,
3
for bridging both ends of a pivot for supporting the roller takes a flat-plate
shape, if a force in a right-angled direction is applied on the side walls
3,
3, the side walls
3,
3 are elastically deformed comparatively
easily. On the other hand, when both ends of the pivot are plastically deformed
toward the inner peripheral surfaces of both of the through holes for connecting
and fixing both ends of the pivot to each other, a force is applied onto portions
which are provided on the side walls
3,
3 with the through holes
formed thereon in a direction in which both portions come toward each other. Then,
the side walls
3,
3 are elastically deformed on the basis of this force.
In case of the conventional sheet metal rocker arm, the paired side walls
3,
3 are formed to be parallel to each other prior to when both ends of the
pivot are plastically deformed. For this reason, when both ends of the pivot are
plastically deformed toward the inner peripheral surfaces of the through holes,
the paired side walls
3,
3 are formed to be non-parallel to each
other. Accordingly, the inner side surfaces (the side surfaces opposite to each
other) of the side walls
3,
3 and both end surfaces in the axial
direction of the roller supported in a middle part of the pivot in a rotating manner
are formed to be non-parallel to each other. As a result, a so-called edge abutment
is brought about in which the inner side surfaces of the side walls
3,
3
and both end surfaces of the roller in the axial direction are not brought into
contact with each other in a uniformly wide area, but may be brought into contact
with each other in a very narrow area, or the edges of the side walls
3,
3 and both end surfaces of the roller in the axial direction are brought
into contact with each other.
In such a state, it is difficult to satisfactorily form an oil film between the
inner side surfaces of the side walls
3,
3 and the respective both
end surfaces of the roller in the axial direction for decreasing friction between
these both surfaces. This is not preferable since a resistance required for a rotation
of the roller may be increased, or an amount of abrasion of the roller or the sheet
metal rocker arm may be increased.
When the cam follower with the sheet metal rocker arm is in use, the roller
is rotated inside the roller receiving recess
5, which is provided on this
sheet metal rocker arm. When this roller is displaced in the axial direction with
respect to the pivot which is supported on and fixed to the sheet metal rocker
arm, the end surface of the roller in the axial direction and the inner side surface
of one of the side walls
3 rub against each other. Accordingly, it is required
to decrease a frictional resistance of a contact portion between these end surfaces
of the roller in the axial direction and the inner side surfaces of the side walls
3,
3 for reducing a rotational resistance of the roller and for reducing
abrasion of this roller and the sheet metal rocker arm.
However, in case of the cam follower provided with the conventional sheet
metal rocker arm, such requirements are not always taken into consideration.
SUMMARY OF THE INVENTION
A sheet metal rocker arm according to the present invention and a method of such
rocker arm have been conceived to solve any of the above-described inconveniences.
According to the present invention, there is provided a sheet metal rocker
arm manufactured by the steps of punching one metal material to form a blank having
a predetermined contour and through holes, and subjecting this blank to bending
by pressing to form a pair of side walls parallel to each other and a connecting
portion for connecting both ends of both side walls in the width direction thereof.
This rocker arm is also provided with at least a pair of through holes formed at
positions which are aligned with each other on both side walls and at least one
engagement portion provided in a part of the connecting portion. The thickness
of the part in which at least one engagement portion is provided, out of this connecting
portion, is formed to be greater than the thickness of both side walls by increasing
the thickness of the part in which at least one engagement portion is provided,
out of this connecting portion, by pressing.
According to the method of manufacturing a sheet metal rocker arm of the
present invention, when the sheet metal rocker arm as described above is manufactured,
the blank is subjected to bending to form both of the side walls, and a portion
corresponding to the connecting portion is curved to have an arched section, thereby
forming the curved portion. Then, pressing is conducted to strongly press this
curved portion to be plastically deformed. Thus, the thickness of this curved portion
is increased and an engagement portion is formed in this curved portion.
According to the sheet metal rocker arm of the present invention having
the above-mentioned structure and the manufacturing method of such rocker arm,
though the rocker arm is formed from one metal plate in a unitary structure having
a uniform thickness, the thickness of the connecting portion including the valve
engagement portion can be made greater than the thickness of the paired side walls.
Consequently, it is possible to reduce stress acting on the connecting portion
including this valve engagement portion to secure the strength and a rigidity of
the sheet metal rocker arm without unnecessarily increasing the weight of the rocker
arm. It is sufficient if the thickness of the side walls is great enough to secure
the strength and the rigidity required for these side walls, and the thickness
is not be unnecessarily great. Thus, it is possible to reduce the width of the
sheet metal rocker arm, which is a distance between the outer side surfaces of
both side walls, so that a design incorporating this sheet metal rocker arm into
a limited space inside the engine becomes easier.
Moreover, since the whole sheet metal rocker arm is formed from one metal
plate in a unitary integral structure, extra labor for connecting plural members
separately manufactured is not necessary, thereby decreasing the number of the
processing steps and preventing an increase in manufacturing cost as well as deterioration
in precision. In addition, it is possible to save a complicated mechanism for assembly
and positioning, so as to manufacture a sheet metal rocker arm with high quality
at a low cost. Further, it is possible to increase the thickness of the connecting
portion only by pressing without introducing special equipment. For this reason,
it is possible to suppress investment in equipment and to realize a sheet metal
rocker arm with a high quality at a low cost by saving labor with automated manufacturing steps.
The present invention has been designed to further reduce the size and the weight
of the sheet metal rocker arm. More specifically, when the sheet metal rocker arm
is used, a stress is generated in each part based on a load applied from the valve
unit and the lash adjuster. Unless the shape and the size of each constituent part
are selected in relation to this load, the magnitude of this stress is in the respective
parts. Naturally, in order to secure a sufficient durability of the sheet metal
rocker arm, the rigidity of even a part in which a stress with the greatest magnitude
is generated is secured so that the rigidity of this part does not exceed the allowed
value. In such a case, however, a rigidity in other parts becomes excessive. The
excessive rigidity hinders reduction of the size and the weight of the sheet metal
rocker arm and is not preferred.
The sheet metal rocker arm of the present invention has been designed considering
the above-mentioned circumstances.
The sheet metal rocker arm of the present invention is manufactured by subjecting
one metal plate to punching and bending. The sheet metal rocker arm is provided
with a pair of side walls which are substantially parallel to each other, a connecting
portion for connecting the respective end edges of both of the side walls in the
width direction, a pair of through holes formed at positions aligned with each
other on the side walls, a first engagement portion provided in a part of the connecting
portion to abut upon the base end portion of a valve unit, and a second engagement
portion provided in another part of this connecting portion to abut upon the leading
end portion of a rush adjuster.
Especially, in the sheet metal rocker arm of the present invention, the
thickness of the first engagement portion is formed to be greater than that of
the side wall. Both of the side walls when they stand up from the connecting portion,
are not formed over the entire edge portions of the both sides of these first and
second engagement portions. The forms and the sizes of the respective parts are
restricted so that a ratio of the maximum value to the minimum value of the stress
generated in the first and second engagement portion is within five, based on the
load applied to the first and second engagement portions from the valve unit and
the rush adjuster.
According to the sheet metal rocker arm of the present invention having
such structure as described above, though the rocker arm is formed of one metal
plate having a uniform thickness in a unitary integral structure, the thickness
of the connecting portion for constituting the first engagement portion is formed
to be greater than that of the paired side walls. Accordingly, it is possible to
secure the strength and the rigidity of the sheet metal rocker arm by decreasing
stress acting on the first engagement portion, without unnecessarily increasing
the weight of the rocker arm. It is sufficient if the thickness of the side walls
is enough to maintain the strength and the rigidity required for these side walls
and is not required to be unnecessarily large. Consequently, it is possible to
reduce the width of the sheet metal rocker arm, which is the distance between the
outer side surfaces of the side walls so that it becomes easier to incorporate
this rocker arm within a limited space inside the engine.
Moreover, since the whole sheet metal rocker arm is formed of one metal
plate in a unitary integral structure, problems with connecting the plural constituent
members that are separately manufactured to each other, is eliminated, which results
in a reduced number of processing steps to prevent an increase of the manufacturing
cost and deterioration in accuracy. It is also possible to manufacture the sheet
metal rocker arm with a high quality at a low cost without providing unnecessary
complicated equipment for the assembly and positioning.
Out of the side walls to which a large stress is not applied when the rocker
arm is in use, both side edge portions of the first and second engagement portions
are partially omitted except a part required for supporting the pivot for supporting
the roller. Further, since the forms and the sizes of the respective parts are
restricted in such a manner that a ratio of the maximum value to the minimum value
of a stress generated in these first and second engagement portions is within five,
there is no part having excessive rigidity. Thus, the effect of reducing the weight
of the sheet metal rocker arm as a whole becomes better.
A cam follower which is provided with the sheet metal rocker arm of the present
invention and an assembling method thereof have been devised to solve problems
as described above.
Out of the cam follower provided with the sheet metal rocker arm of the present
invention and the assembling method thereof, the cam follower provided with a sheet
metal rocker arm comprises a sheet metal rocker arm provided with a pair of side
walls which are formed of a metal plate to be substantially parallel to each other
and a connecting portion for connecting these side walls to each other, a pivot
which is fixed to bridge over the paired side walls by plastically deforming both
ends thereof toward the inner peripheral surfaces of a pair of through holes when
the pivot bridges over the paired through holes formed at positions aligned with
each other on the side walls, and a roller supported rotatably around a middle
part of this pivot.
Especially, in the cam follower provided with the sheet metal rocker
arm of the present invention, it is preferable to make the paired side walls to
be parallel to each other when both ends of this pivot are plastically deformed,
by forming a gap between the portions at which the through holes are formed, out
of the paired side walls, prior to when both ends of the pivot are plastically
deformed, to be wider than this gap when both ends of the pivot have been plastically deformed.
Especially, in the assembling method of the cam follower which is provided
with the sheet metal rocker arm of the present invention, a gap between the portions
at which the through holes are formed, out of the pair of side walls, prior to
the plastically deforming both ends of the pivot, are formed to be wider than this
gap when both ends of this pivot have been plastically deformed. Then, it is preferable
to form the paired side walls to be parallel to each other by reducing the gap
between the portions at which the through holes are formed on the paired side walls,
upon the plastically deforming of both ends of this pivot.
According to the cam follower provided with the sheet metal rocker arm
of the present invention having the structure as mentioned above and the assembling
method thereof, when the sheet metal rocker arm, the roller, and the pivot are
combined with each other and both ends of this pivot are connected and fixed to
the paired side walls for constituting this sheet metal rocker arm, both of these
side walls and both end surfaces of the roller in the axial direction can be formed
to be parallel to each other. Consequently, it is possible to sufficiently form
an oil film between the inner side surfaces of the side walls and the both end
surfaces of the roller in the axial direction for reducing friction between these
surfaces, thereby reducing the resistance required for rotating the roller and
reducing an amount of abrasion of the roller and the sheet metal rocker arm.
The cam follower provided with the sheet metal rocker arm of the present invention
has been designed considering these circumstances to reduce frictional resistance
in a contact portion between the end surfaces of the roller in the axial direction
and the inner side surfaces of the side walls.
Any cam follower provided with the sheet metal rocker arm of the present invention
comprises a pair of side walls which are formed of a metal plate to be parallel
to each other, a sheet metal rocker arm provided with a connecting portion for
connecting these side walls; a pivot fixed to bridge over the paired side walls
by supporting both end portions thereof at a pair of through holes formed at positions
aligned with each other on both side walls, and a roller supported rotatably around
a middle part of this pivot.
In the cam follower provided with the sheet metal rocker arm, a recess for receiving
lubricating oil is preferably formed on the inner side surface of at least one
side walls out of the paired side walls in such a manner that one end thereof is
open at the outer edge of said side wall and the recess is inclined in a direction
which becomes shallower toward the opposite end.
In the cam follower provided with the sheet metal rocker arm, the degree of flatness
of the inner side surface of each of the side walls is preferably not more than
10 μm, and the surface roughness thereof not more than 0.3 μRa.
Also, in the cam follower provided with the sheet metal rocker arm, it is preferable
to conduct a solid lubricating film coating or soft nitriding at least on the inner
side surface of the side walls to reduce the coefficient of friction of this inner
side surface.
Further, in the cam follower provided with the sheet metal rocker arm, it
is preferable to provide washers rotatably around the pivot between the inner side
surfaces of the side walls and the both end surfaces of the roller in the axial
direction or the both end surfaces of a needle for constituting a radial needle
bearing provided on the inner diameter side of this roller.
According to any cam follower provided with the sheet metal rocker arm
of the present invention having a structure as mentioned above, it is possible
to reduce frictional resistance between the end surfaces of the roller in the axial
direction and the inner side surface of the side walls to reduce rotational resistance
of this roller, and to reduce abrasion of this roller and the sheet metal rocker arm.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a sheet metal rocker arm according to a first
embodiment of the present invention.
FIG. 2A is a plan view of the sheet metal rocker arm of the first embodiment,
FIG. 2B is a cross-sectional view taken along a—a in FIG. 2A, FIG. 2C is
a cross-sectional view taken along b—b in FIG. 2A, and FIG. 2D is a crosssectional
view taken along c—c in FIG. 2A.
FIGS. 3A to 3D show a first blank obtained by a first step when the
sheet metal rocker arm is manufactured, in which FIG. 3A is a plan view of the
first blank, FIG. 3B is a cross-sectional view taken along a—a in FIG. 3A,
FIG. 3C is a cross-sectional view taken along b—b in FIG. 3A, and FIG. 3D
is a crosssectional view taken along c—c in FIG. 3A.
FIGS. 4A to 4D show a second blank obtained by a second step in the
same manner, in which FIG. 4A is a plan view of the second blank, FIG. 4B is a
cross-sectional view taken along a—a in FIG. 4A, FIG. 4C is a cross-sectional
view taken along b—b in FIG. 4A, and FIG. 4D is a cross-sectional view taken
along c—c in FIG. 4C.
FIGS. 5A to 5D show a first intermediate blank obtained by a third step
in the same manner, in which FIG. 5A is a plan view of the first intermediate blank,
FIG. 5B is a cross-sectional view taken along a—a in FIG. 5A, FIG. 5C is
a cross-sectional view taken along b—b in FIG. 5A, and FIG. 5D is a cross-sectional
view taken along c—c in FIG. 5D.
FIGS. 6A to 6D show a second intermediate blank obtained by a fourth
step in the same manner, in which FIG. 6A is a plan view of the second intermediate
blank, FIG. 6B is a cross-sectional view taken along a—a in FIG. 6A, FIG.
6C is a cross-sectional view taken along b—b in FIG. 6A, and FIG. 6D is a
cross-sectional view taken along c—c in FIG. 6C.
FIGS. 7A and 7B show Uthe progress of the fourth step, in which FIG. 7A is
a partially-enlarged cross sectional view for showing the condition prior to urging
of a curved portion, and FIG. 7B is a partially-enlarged cross sectional view for
showing when the curved portions are urged to become a connecting portion, respectively.
FIGS. 8A to 8D show a third intermediate blank obtained by a fifth step
in the same manner, in which FIG. 8A is a plan view of the third intermediate blank,
FIG. 8B is a cross-sectional view taken along a—a in FIG. 8A, FIG. 8C is
a cross-sectional view taken along b—b in FIG. 8A, and FIG. 8D is a cross-sectional
view taken along c—c in FIG. 8C.
FIGS. 9A to 9D show an auxiliary intermediate blank manufactured by
an auxiliary urging step in a second example of the manufacturing method of a sheet
metal rocker arm of the present invention, in which FIG. 9A is a plan view of the
auxiliary intermediate blank, FIG. 9B is a cross-sectional view taken along a—a
in FIG. 9A, FIG. 9C is a cross-sectional view taken along b—b in FIG. 9A,
and FIG. 9D is a cross-sectional view taken along c—c in FIG. 9C.
FIGS. 10A and 10B show a progress of the auxiliary pressing step, in which
FIG. 10A is a partially enlarged cross sectional view for showing the condition
prior to the pressing of a curved portion, and FIG. 10B is a partially-enlarged
cross sectional view for showing when the curved portions are pressed, respectively.
FIGS. 11A to 11D show the second blank manufactured through a second
step according to a third embodiment of the present invention, in which FIG. 11A
is a plan view of the second blank, FIG. 11B is a cross-sectional view taken along
a—a in FIG. 11A, FIG. 11C is a cross-sectional view taken along b—b
in FIG. 11A, and FIG. 11D is a cross-sectional view taken along c—c in FIG. 11C.
FIG. 12A and FIG. 12B show a first embodiment of a cam follower provided
with a sheet metal rocker arm according to the present invention. FIG. 12A illustrates
the condition prior to plastically deforming both end portions of a pivot, and
FIG. 12B illustrates the condition after plastically deforming these portions, respectively.
FIG. 13 is a partial schematic cross sectional view of a sheet metal rocker
arm according to a second embodiment of the present invention.
FIG. 14 is a cross sectional view for showing a third embodiment of a cam follower
provided with a sheet metal rocker arm according to the present invention.
FIG. 15 is a view for showing an inner side surface of a side wall according
to the third embodiment.
FIG. 16 is a cross sectional view for showing a fourth embodiment of a cam follower
provided with a sheet metal rocker arm according to the present invention.
FIG. 17 is a cross sectional view for showing a fifth embodiment of this cam follower.
FIG. 18 is a cross sectional view for showing a sixth embodiment of this cam follower.
FIG. 19A and FIG. 19B show a blank which is manufactured by the first
step when a conventional sheet metal rocker arm is manufactured. FIG. 19A is a
plan view of the blank, and FIG. 19B is a cross-sectional view taken along a—a
in FIG. 19A.
FIG. 20A and FIG. 20B show the first intermediate blank manufactured
by the second step in the same manner. FIG. 20A is a plan view of the first intermediate
embodiment, and FIG. 20B is a cross-sectional view taken along a—a in FIG. 20A.
FIG. 21A and FIG. 21B show the second intermediate blank manufactured
by the third step in the same manner, in which FIG. 21A is a plan view of the second
intermediate blank, and FIG. 21B is a cross-sectional view taken along a—a
in FIG. 21A.
FIG. 22A and FIG. 22B show the third intermediate embodiment manufactured
by the fourth step in the same manner, in which FIG. 22A is a plan view of the
third intermediate blank, and FIG. 22B is a cross-sectional view taken along a—a
in FIG. 22A.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a first embodiment of the present invention. Referring to FIG.
1, a sheet metal rocker arm
31 is manufactured in a unitary structure by
conducting punching and bending based on pressing one metal plate such as a low
carbon carburizing steel plate. This sheet metal rocker arm
31 is provided
with a pair of side walls
22,
22 which are substantially parallel
to each other, connecting portions
24,
24 for connecting the edge
ends of the both side walls
22,
22 in the width direction thereof,
and a pair of through holes
18,
18 formed at positions in a middle
part of the side wall, aligned with each other.
At one end portion of the connecting portions
24 (the right end portion
in FIGS.
2A and
2B), there is formed a first engagement portion
28
for abutting on the base end portion of a valve unit when it is incorporated in
the engine. Of this first engagement portion
28, a middle part in the width
direction (the up-and-down direction in FIGS. 2A and 2B) at one end portion of
the connecting portions
24 is depressed to become a curved surface which
is concave along the width direction and the length direction (the lateral direction
in FIGS.
2A and
2B). On the other hand, at the other end (the left
end portion in FIGS. 2A and 2B) of the connecting portions
24, there is
formed a second engagement portion
29 for abutting on the leading edge of
a rush adjuster when it is incorporated in the engine. This second engagement portion
29 is formed as a curved surface by depressing the center of the above other
end of the connecting portion
24 in a spherical form.
The thickness T
24 of the connecting portions
24 with the first
engagement portion
28 and the second engagement portion
29 thus formed
thereon is set to be greater than the thickness T
22 of the side walls
22,
22 (T
24≧T
22). In each connecting portion
24,
both side walls
22,
22 which stand up from the connecting portion
24 exist partly but do not cover the entire edge portions on the both side
edges of the first and second engagement portions
28 and
29. More
specifically, the side walls
22,
22 are widest at the centers thereof
in the length direction at which the through holes
18,
18 are formed,
and gradually become narrower toward both end portions in the length direction
at which they are connected to the respective connecting portions
24. The
thickness of the side walls at these end portions is substantially equal to the
thickness T
24 of this connecting portions
24. Consequently, on the
connecting portions
24, the side walls
22,
22 are formed only
partially on both side edge portions of the first and second engagement portions
28 and
29.
The forms and the sizes of the respective members are restricted such that a
ratio of the maximum value to the minimum value of the stress generated in these
first and second engagement portions
28 and
29 based on loads applied
onto the first and second engagement portions
28 and
29 from the
unshown valve unit and lash adjuster incorporated into the engine is not more than
5. That is, when the rocker arm is incorporated into the engine, the base
end portion of the valve unit (not shown) is caused to abut on the first engagement
portion
28 and the leading edge of the unrepresented lash adjuster on the
second engagement portion
29, respectively. When the engine is driven, the
valve unit or the lash adjuster strongly urges the first engagement portion
28
or the second engagement portion
29, thereby generating a stress in the
first or second engagement portion
28 or
29, in the sheet metal rocker
arm
31. Naturally, the rigidity of such portion is secured such that a sufficient
durability can be secured even in a portion in which a stress is easily generated,
based on the above-mentioned load. However, a ratio of the maximum value to the
minimum value of a stress generated in each portion is kept within 5 by setting
the rigidity of a portion in which a stress is difficult to be generated not to
be excessive.
Despite the sheet metal rocker arm
31 of the present invention being
formed of one metal plate having a uniform thickness as a unitary integral unit
as described above, the thickness of the connecting portion
24 for constituting
the first engagement portion
28 in which a large stress tends to be generated
is formed to be greater than the thickness of the paired side walls
22,
22 in which a large stress is seldom generated. Consequently, it is possible
to secure sufficient strength and rigidity of the sheet metal rocker arm
31
by reducing a stress acting on the first and second engagement portions
28
and
29 without unnecessarily increasing the weight thereof. On the other
hand, the thickness of the side walls
22,
22 suffices if it can secure
the strength and rigidity required for the side walls
22,
22, and
is not required to be unnecessarily great. Consequently it is possible not only
to reduce the width of the sheet metal rocker arm
31, which is a gap between
the outer side surfaces of the both side walls
22,
22, thereby reducing
the weight of the rocker arm, but to design more easily to incorporate this sheet
metal rocker arm
31 in a limited space inside the engine.
Moreover, since the whole sheet metal rocker arm
31 is integrally
formed of one sheet of metal plate, a problem in connecting plural constituent
members which are manufactured separately from each other is not required and the
number of the manufacturing steps can be reduced. At the same time, it is possible
to prevent an increase of the manufacturing cost and deterioration in an accuracy,
whereby the sheet metal rocker arm
31 with high quality can be manufactured
at a low cost without complicated equipment for assembling and positioning.
Out of both side walls
22,
22 to which a large stress is not applied
when the rocker arm is in use, both side edge portions of the connecting portions
24 provided respectively with the first and second engagement portions
28
and
29 are partially omitted except the central portion in the length direction
which is required for supporting a pivot for supporting a roller. Further, the
forms and the sizes of the respective members are restricted such that a ratio
between the maximum value and the minimum value of a stress generated in the first
and second engagement portions
28 and
29 is kept within 5. For this
reason, there exists no portion which has an excessive rigidity, compared with
the generated stress. With these arrangements, the weight of the whole sheet metal
rocker arm
13 can be reduced more effectively.
In the conventional rocker arm, it is required to provide side walls all over
the engagement portions to secure the rigidity. However, in the sheet metal rocker
arm of the present invention, it is possible to secure the rigidity by increasing
the plate thickness of the engagement portions even if the side walls are not provided
all over the engagement portions. That is, even if an area for the side walls is
decreased, compared with that of the conventional rocker arm, the performance of
the rocker arm does not become inferior to that of the conventional one. Further,
the weight of this rocker arm may be reduced corresponding to the reduced area
for the side walls.
Next, an example of a method of manufacturing a sheet metal rocker arm as mentioned
above will be described with reference to FIGS. 3 to
8.
When a sheet metal rocker arm of the present invention is to be manufactured
by the manufacturing method of the present invention, a first blank
13 as
shown in FIGS. 3A to
3D is prepared at a first step. More specifically,
at this first step, a metal plate (a flat plate blank or a coil blank) having a
sufficient rigidity, such as a carbon steel having a thickness of, for example,
3 mm to 4 mm is placed between a punch and a counterpunch of a pressing machine
(not shown) to prepare the first blank
13 by punching.
This first blank
13 has, as shown in FIG. 3A, a lozenge shape with round
corners and having a cut-away part at one end in the length direction thereof (the
right end portion in FIG.
3A), and a thickness t
13 (FIG.
3B).
A portion having the width W
14 located slightly inside two chain lines α,α
shown in FIG. 3A (a portion nearer the center in the width direction) in a central
part in the width direction (the up-and-down direction in FIG. 3A) of the first
blank
13 is called the base portion
14 which is connected to the
length direction (the lateral direction in FIG. 3A) of the first blank
13.
Then, on both sides of this base portion
14 in the width direction, a pair
of wing-shaped portions
15,
15 each having a substantial triangular
shape are formed. The outer periphery of the base portion
14 and the outer
peripheries of these wing-shaped portions
15,
15 are smoothly connected
to each other in a straight line or a curved line. In other words, there is formed
no pointed part in which a stress is easily concentrated. Note that the shape of
the base portion
14 is not necessarily limited to that shown in the drawings.
The base portion
14 may take a suitable shape in accordance with a finished
shape of a sheet metal rocker arm to be manufactured.
In the central part of the first blank
13 described above, there is formed
a through hole
16 at a subsequent second step, as shown in FIG. 4A, to form
a second blank
20. This through hole
16 takes a substantial Japanese
hand drum shape having a pair of flap portions which are partial arched parts respectively
projecting toward each other in the central part in the length direction of the
both side edges in the width direction. These flap portions
17,
17
are provided to form circular holes
18,
18 (see FIGS. 1 and 2) for
respectively supporting both ends of a support shaft for supporting rotatably a
roller (which is described later). At the four corners of the through hole
16,
there are formed cut-away portions
19,
19 each taking a substantial
semi-circular shape. These cut-away portions
19,
19 are formed to
facilitate the bending to be carried out at a next third step in which a curved
portion
21 (see FIGS. 5A to
5D) is formed by bending the base portion
14 to have an arched section.
The second blank
20 as described above is formed by placing the first
blank
13 between the piercing punch and the piercing die of the pressing
machine incorporated in a press processing machine (not shown), and then punching
the through hole
16 between the punch and the counterpunch. Note that the
width W
14 of the base portion
14 of the first blank
13 as
well as the second blank
20 is formed greater than the width W
23
of a first intermediate blank
23 (see FIGS. 5C and 5D) which is a space
between the outer side surfaces of the paired side walls manufactured at the third
step described next (W
14>W
23). Since the width W
14 of
the base portion
14 is formed greater than the width W
23 of the first
intermediate portion
23 in this manner, a distance D
17 between the
paired flap portions
17,
17 mentioned above is formed greater than
the width W
7 of the central portion of the through hole
7 which is
formed by the prior art described before (see FIG. 21A) (D
17>W
7).
When the distance D
17 between the paired flap portions
17,
17
is formed greater as stated above, the service life of the punch for punching the
through hole
16 can be secured. That is, if the width W
7 of the central
portion of the through hole
7 is small, as in the conventional example,
a load applied on the punch for punching the through hole
7 becomes great,
and the service life of this punch is shortened. On the other hand, according to
the present invention, since the distance D
17 between the paired flap portions
17,
17 is formed great, a load applied on the punch for forming the
through hole
16 is decreased so that the durability of this punch can be
secured to reduce the manufacturing cost.
For forming the second blank
20, a punching of the through hole
16,
which is to be conducted at the above-described second step, may be conducted first,
and a punching of the base portion
14 and the wing-shaped portions
15,
15 which is to be conducted at the above-described first step may be conducted
thereafter. Further, the second blank
20 as shown in FIG. 2 may be formed
directly of metal plate material if the piercing punch and the piercing die can
be processed and the pressing machine has a sufficient capacity.
In any case, the second blank
20 processed into a form as shown in FIGS.
4A to
4D is formed into the first intermediate blank
23 as shown
in FIGS. 5A to
5D at the next third step. At this third step, the second
blank
20 is placed between the punch and the die of the pressing machine
(not shown) and is pressed strongly, and the base portion
14 of the second
blank
20 and the wing-shaped portions are subjected to the bending work.
Then, the second blank
20 is formed into the first intermediate blank
23
which is comprised of the pair of side walls
22,
22 laterally provided
with respect to the width direction and curved portion
21 for connecting
the edges of these side walls
22 in the width direction (in the lateral
direction in FIGS. 5A and 5D) to each other. This curved portion
21 is formed
in a semi-cylindrical shape which is discontinuous at a portion corresponding to
the through hole
16 in a middle part of this first intermediate blank
23
in the length direction thereof (the lateral direction in FIG.
5A). In this
manner, out of the curved portion
21 which is divided into two parts by
the through hole
16, one end side thereof (the right end side in FIGS. 5A
and 5B) becomes the first engagement portion
28 (see FIGS. 2 and 8) for
abutting on the base unit of the valve unit, and the other end side thereof (the
left end side in FIGS. 5A and 5B) becomes the second engagement portion
29
(see FIGS. 2 and 8) for abutting on the leading end of the rush adjuster.
As described above, the width W
23 of the first intermediate blank
23
which is a distance between the outer side surfaces of the paired side walls
22,
22 is formed smaller than the width W
14 of the base portion
14
of the first and second blanks
13 and
20 mentioned above. That is,
as one of the characteristics of the present invention, in the first intermediate
blank
23, the curved portion
21 serving as a connecting portion for
connecting the edges of the paired side walls
22,
22 in the width
direction thereof is formed in a substantially semi-cylindrical shape, as shown
in FIGS. 5C and 5D. Since the substantially semi-cylindrical curved portion
21
is thus formed and the width of this curved portion
21 is formed smaller
than the width W
14 of the flat-shaped base portion
14 described above
which serves as the base of the curved portion
21, the width W
14
of this base portion
14 can be made greater than the width W
23 of
the first intermediate blank
23 which is the distance between the paired
side walls
22,
22 provided laterally in the first intermediate blank
23 (W
14>W
23), and the distance D
17 between the
above-described flap portions
17,
17 can be formed great. The thickness
t
21 of the curved portion
21 for constituting the first intermediate
blank
23 as shown in FIGS. 5A to
5D is substantially equal to the
thickness t
13 of the first blank
13 (t
21≈t
13).
Note that, out of the curved portion
21, at least the end side portion
for constituting the first engagement portion
28 for abutting upon the base
portion of the valve unit is subjected to pressing at a fourth step which is described
later, thereby making the thickness thereof greater. In this case, for obtaining
a desired thickness of the portion after pressing, it is required to restrict the
shape and the size of the curved portion
21. That is, the thickness of the
end side portion in the pressing is determined by the selected shape and size of
this curved portion
21. On the first intermediate blank
23, when
the curved portion
21 is formed, the lateral pair of side walls
22,
22 are also formed simultaneously. That is, upon formation of the curved
portion
21, the wingshaped portions
15,
15 formed at the both
end portions in the width direction of the first and second blanks
13 and
20 and the flap portions
17,
17 provided on the inner side
edges of the through hole
16 in the central portion (see FIGS. 3 and 4)
are raised to form the paired side walls
22,
22 which are substantially
parallel to each other.
The curved portion
21 of the first intermediate blank
23 thus arranged
is subjected to pressing at the next fourth step, thereby preparing a second intermediate
blank
25 as shown in FIGS. 6A to
6D. More specifically, at the fourth
step, the curved portion
21 is processed into a flat shape and the thickness
thereof is increased, thereby forming the connecting portion
24 which has
a thickness t
24 greater than the thickness t
13 of the first blank
13 (see FIG. 3B) (t
13 <t
24). Note that in an example
shown in the drawings, the base portion
14 (FIGS. 3 and 4) is subjected
to bending until it is formed into a substantial semi-cylindrical shape at the
above-mentioned third step, to obtain the curved portion
21 (FIG.
5).
However, this curved portion
21 may not always take a semicylindrical shape,
but may take an elongated semi-cylindrical shape or an elliptical semi-cylindrical
shape so long as it is curv
