Technical Field of the Invention:
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This invention relates to the improvement of a cam follower having
a sheet-metal rocker arm that is manufactured by press working of metal
plate.
Background Technology
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In reciprocating engines (reciprocating piston engines), except for
some 2-cycle engines, there are air-intake valves and exhaust valves that
open and close in synchronization with the rotation of the crankshaft.
Also, the rocker arm is used in a cam follower which is incorporated in the
valve mechanism of the engine to convert the rotation of the camshaft to
the reciprocating motion of the valve stem (air-intake valve and exhaust
valve). In this kind of reciprocating engine, the camshaft rotates in
synchronization with the rotation of the crankshaft (the rotating speed of
the camshaft is 1/2 that of the crankshaft in the case of a 4-cycle engine),
and the motion of the cam shaft is transmitted to the air-intake valve and
exhaust valve by the rocker arm to move the value stem of the air-intake
valve and exhaust valve in a reciprocating motion in the axial direction.
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In order to secure the strength of the rocker arm inside the valve
mechanism of the engine, while at the same time make it more lightweight,
it has been proposed and put in practice to manufacture the rocker arm by
press working metal plate such as steel plate. Of this kind of cam follower
having a sheet-metal rocker arm developed under such a situation, Figs. 4
through 7 show a cam follower that is disclosed in US Patent No.
5,048,475. This cam follower comprises a sheet-metal rocker arm 1, roller
2 and pivot 3, where the roller 2 is supported by the pivot 3 such that it
rotates freely with respect to the sheet-metal rocker arm 1.
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The cam follower constitutes the cam 9 of the cam shaft and the
lash adjuster as shown in Fig. 7, and associated with the plunger 8 which is
the center of rocking movement of the sheet metal rocker arm 1, and with
the valve stem 7 of the air-intake valve and exhaust valve. The sheet-metal
rocker arm 1 of the cam follower is made from a metal plate such as a 2
mm to 4 mm thick steel plate by a punching process to remove any
unnecessary parts, and plastic-working, such as drawing, for obtaining the
desired shape; and it comprises a pair of side-wall sections 4 and first and
second connecting sections 5, 6 that connect both of these side-wall
sections 4 together, respectively. As shown in Fig. 7, the first connecting
section 5 comes in contact against the base end face of the valve stem 7 and
functions as a pressure portion for displacing the valve stem 7, and the
second connecting section 6 functions as a fulcrum portion for coming in
contact with the tip end face of the plunger 8. Therefore, in the example
shown in the figures, a spherical concave section is formed on one end
surface (lower surface in Fig. 6) of the second connecting section 6.
Construction that differs from that of the example shown in the figure, in
which a screw hole is formed in the section that corresponds to the second
connecting section, so as to threadably receive an adjust screw with a
spherical surface end for fixing, is also conventionally known.
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On the other hand, the roller 2 is located in a space defined by the
pair of connecting sections 5, 6, and the pair of side-wall sections 4 and
supported by the pivot 3 such that it can rotate freely. In order to support
the roller 2 by the pivot 3 in the pair of side-wall sections, both end
sections of the pivot 3 is fitted into the through-holes that are formed at
matching locations in the pair of side-wall sections 4. The outer peripheral
edge of both end surfaces of this pivot 3 is crimped outward toward the
peripheral edge of the respective through-holes (see Fig.10). With this
construction, both end sections of the pivot 3 are attached to the pair of
side-wall sections 4 such that the pivot 3 spans between both of these
side-wall sections 4. The roller 2 fits around the middle section of the pivot
3 that spans between both of these side-wall sections 4 in this way, and is
supported either directly or by way of a radial needle roller bearing such
that it can rotate freely.
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As shown in Fig. 7, when installed in the engine, the base end face
of the valve stem 7 comes in contact with one surface of the first
connecting section 5 (bottom surface in Fig. 7), and the tip end face of the
plunger 8 comes in contact with the spherical concave section on one
surface of the second connecting section 6, and the outer peripheral surface
of the cam 9 securely fastened in the middle section of the cam shaft comes
in contact with the outer peripheral surface of the roller 2. When the engine
is running, as the cam 9 rotates, the sheet-metal rocker arm 1 moves in a
rocking motion with the point of contact between the tip end surface of the
plunger 8 and the spherical concave section as the center (fulcrum), and the
pressure force from the first connecting section 5 and the elastic force of a
return spring 10 moves the valve stem 7 in a reciprocating motion in the
axial direction. Incidentally, a cam follower with a sheet-metal rocker
arm having similar construction is also disclosed in Japanese Patent
Publication No. Tokukou Hei 6-81892, which is not shown in the figures
here.
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Since the sheet-metal rocker arm 1 is made by plastic-working of
sheet-metal, the thickness of the sheet-metal rocker arm 1 changes during
the plastic-working process, so if the shape and construction of the other
parts are not designed properly, it may not be possible to secure sufficient
durability. This aspect is explained using Figs. 8 through 10 in addition to
Figs. 4 through 7, mentioned above.
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When a sheet-metal rocker arm 1 like that shown in Figs. 4 to 7 is
manufactured by drawing of a metal plate such as a steel plate, with regard
to both end sections in the width direction (top and bottom direction in Figs.
6 and 7) of the pair of side-wall sections 4, the end sections on the side of
the first and second connecting sections 5, 6 (top side in Figs. 6 and 7)
stretch in the planar direction an amount more than the end sections on the
other side (bottom side in Figs. 6 and 7), and thus the thickness of the
side-wall sections 4 becomes thinner as going upward in Figs. 6 and 7.
Accordingly, the cross-sectional shape in the width direction of both of the
side-wall sections 4 is a wedge shape that is inclined in a direction such
that it becomes thicker moving away from the connecting sections 5, 6 as
shown in Figs. 8, 10. On the other hand, the inner side surfaces of these
side-wall sections 4 must be parallel with each other. The reason for that
is to prevent that only one of these side wall sections 4 comes into contact
with the roller 2 located between these sidewall sections 4, so that the roller
2 can rotate smoothly between the side wall sections 4.
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When the inner side surfaces of these side-wall section 4 having a
wedge-shaped cross-sectional shape are arranged such that they are parallel
with each other, the outer side surface of the side-wall sections 4 are not
parallel with each other as shown in Figs. 8 and 10. That is, the space
between the outer side surfaces of these sidewall sections 4 gradually
becomes large as it goes away from the connecting sections 5, 6 (to the
bottom in Figs. 8 and 10). The space between the outer side surfaces of the
sidewall sections 4 in this way similarly gradually changes in the middle
section in the width direction of these side-wall sections 4 where through
holes 11 are formed for attaching both ends of the pivot 3. For example, in
the results of the tests and measurement performed by the inventors, the
thickness of the side-wall sections 4 was approximately 1 mm along the
edge on the side of the connecting sections 5, 6 (top edge in Figs. 8 and 10),
and was approximately 3 mm along the edge on the opposite side to the
connecting sections 5, 6 (bottom edge in Fig. 8). In this case, the thickness
of the peripheral edge of the through holes 11 was 2.3 mm on the side of
the connecting sections 5, 6 and was 2.9 mm on the opposite side from the
connecting sections 5, 6. The difference in this thickness is the degree that
the outer side surfaces of the side-wall sections 4 are not parallel.
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As mentioned above, the outer peripheral edge of the both end
surfaces of the pivot 3 is crimped out and fixed to the beveled sections 12
formed around the peripheral edges of the openings of each through hole 11.
However, in the state with the outer side surfaces of the sidewall sections 4
are not parallel with each other, it is not possible to uniformly crimp and
fasten both end sections of the pivot 3 all the way around the beveled
sections 12. In other words, since both end surfaces of the pivot 3 are at
right angles with the center axis of the pivot 3, the positional relationship in
the axial direction between both of these end surfaces and the beveled
sections 12 is not uniform in the circumferential direction. In order to
maintain sufficient crimping strength, it is necessary to have a proper
positional relationship in the axial direction between both of the end
surfaces and the beveled sections 12. However, as long as the outer side
surfaces of the side-wall sections 4 are not parallel with each other, it is not
possible to have a proper positional relationship all the way around the
openings. Incidentally, it is unrealistic from the aspect of mass production
to make both end surfaces in the axial direction of the pivot 3 such that they
are not parallel with each other in alignment with the outer side surfaces.
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Therefore, conventionally, the positional relationship in the axial
direction between the beveled sections 12 formed around the peripheral
edges of the through holes 11 and both end surfaces of the pivot 3 is made
to be proper on the opposite side from the connecting sections 5, 6 (lower
side in Fig. 8), as shown in Fig. 8. Also, as shown by the dot-dash line α
in Fig. 9, a crimping tool (punch) is pressed on a portion of the end surfaces
of the pivot 3 from the middle to the side opposite to the connecting
sections 5, 6, so that the edge of the portion from the middle to the side
opposite to the connecting sections 5, 6 is crimped outward in the radial
direction. Therefore, as shown in Fig. 10, the outer peripheral surface
around the end section of the pivot 3 comes in contact with the inner
peripheral surfaces of the through holes 11 at a section on the side closer to
the connecting sections 5, 6 (on the upper side in Fig. 10). On the sides
where the crimped sections 13 are formed, or in other words, on the sides
opposite from the connecting sections 5, 6 (on the lower side in Fig. 10),
there is a clearance 14 between the outer peripheral surface around the both
end sections of the pivot 3 and the inner peripheral surface of the through
holes 11.
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In the state where there is a clearance 14 between the outer
peripheral surface around the both end sections of the pivot 3 and the inner
peripheral surface of the through holes 11 on the opposite side from the
first and second connecting section 5, 6 as shown in Fig. 10, the crimped
sections 13 formed on the both ends of the pivot 3 support the load applied
to the pivot 3 from the cam 9 shown in Fig. 7 by way of the roller 2 (further
by way of the radial needle roller bearing). In other words, when the engine
is running, a load is applied to pivot 3 from the top side toward the bottom
side in Fig. 10 (in balance with the elastic force of the return spring 10).
Since there is a clearance 14 between the outer peripheral surface around
the both end sections of the pivot 3 and the inner peripheral surface of the
through holes 11 in the direction where the load is applied, the crimped
section 13 supports the load, and the load is not directly transmitted from
the outer peripheral surface around the both end sections of the pivot 3 to
the inner peripheral surface of the through holes 11.
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However, the area of contact between the crimped sections 13 and
the beveled sections 12 is small, and since the crimped sections 13 are
formed just by plastically deforming the ends of the pivot 3, it is easy for
them to become plastically deformed. Therefore, after a long period of use,
the crimped sections 13 plastically deform inward in the radial direction,
and there is a possibility that the contact pressure between the crimped
sections 13 and the beveled sections 12 will decrease. When the contact
pressure decreases in this way, the pivot 3 and the roller 2 that is supported
around the middle section of the pivot 3 are lashed with respect to the
sheet-metal rocker arm 1, and thus vibration and noise occur so largely
while the engine is running, which is not desirable.
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The cam follower of this invention was invented taking the
aforementioned problems into consideration.
Disclosure of the Invention
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The cam follower of this invention comprises a sheet-metal rocker
arm, pivot and roller.
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The sheet-metal rocker arm is manufactured by plastic-working of a
metal plate such as steel plate, and comprises a pair of side-wall sections,
and connecting sections that connect this pair of side-wall sections.
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There is a pair of through holes formed at locations in alignment
with each other in these sidewall sections. By crimping and opening up the
outer peripheral edges around the opposite end surfaces of the pivot toward
the inner peripheral surface of the pair of through holes, the pivot is
attached to the pair of side-wall sections such that it extends between the
pair of side-wall sections.
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Also, the roller is rotatably supported around the middle section of
the pivot directly, or through a rolling bearing such as radial needle roller
bearing, or through a sliding bearing.
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The thickness of the respective side-wall sections of the sheet-metal
rocker arm gradually changes in the width direction, specifically from the
thin portion located near the connecting sections to the thick portion
located remote from the connecting sections.
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The space between the outer side surfaces of the pair of the
side-wall sections becomes large going away from the connecting sections.
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During use, a load is applied to the pivot from the side of the
connecting sections.
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Particularly, in the cam follower provided with the sheet-metal
rocker arm of the present invention, the outer peripheral edges around both
end surfaces in the axial direction of the pivot are crimped around half of
the peripheral edges of the through holes on the side near the connecting
sections. In addition, the outer peripheral surfaces of both end sections of
the pivot come in contact with the inner peripheral surfaces of the
respective through holes on the side away from the connecting sections.
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It is desirable that the portion of the middle section of the pivot on
the radially inner side of the roller is quench hardened, while the portions at
the both ends of the pivot to be crimped and opened are left as it is without
being quench hardened.
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It is desirable that of the openings at the both ends of the through
holes, the peripheral edge of the opening on the outer side surface of the
both side wall sections is beveled, and the outer peripheral edge at the
axially opposite end surfaces of the pivot is crimped, such that the outer
peripheral surface of the crimped portion comes into contact with the
beveled portion around the opening.
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In the case of the cam follower provided with the sheet-metal rocker
arm constructed as mentioned above, the side where the load is supported,
or in other words, in the load-support section, the outer peripheral surfaces
around both ends of the pivot come in contact with the inner peripheral
surfaces of the respective through holes over a large area. Moreover, in this
load-support section, the outer peripheral surface sections around both ends
of the pivot that come in contact with the inner peripheral surfaces of the
respective through holes are not plastically deformed as are the crimped
sections, so they are not easily plastically deformed even when large
surface pressure is applied to them. Therefore, even when used for a long
period of time, lost motion does not easily occur in the support sections on
both ends of the pivot with respect to the side-wall sections of the
sheet-metal rocker arm.
Brief Explanation of the Drawings
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- Fig. 1 is a view, similar to the cross section taken along the line I-I
in Fig. 6, to show one example of the embodiment of the present invention
in the state before both ends of the pivot are crimped, where the thickness
of the side-wall sections and the clearance between the outer peripheral
surface of the both ends of the pivot and the inner peripheral surface of the
through hole are exaggerated.
- Fig. 2 is a view as seen from the direction II in Fig. 1, to show the
position where the crimping tool is pressed in order to crimp the both ends
of the pivot.
- Fig. 3 is a view, similar to that of Fig. 1, to show the state after both
ends of the pivot are crimped.
- Fig. 4 is a perspective view showing an example of a cam follower
having a sheet-metal rocker arm conventionally known in the art.
- Fig. 5 is a top plan view as seen from above in Fig. 4.
- Fig. 6 is a cross-sectional view taken along the line VI-VI in Fig. 5.
- Fig. 7 is a cross-sectional view of part of the engine showing the
state in which the cam follower is installed in the engine.
- Fig. 8 is a view, similar to Fig. 1, to show a conventional structure.
- Fig. 9 is a view as seen from the direction IX in Fig. 8 and shows
the position where the crimping tool is pressed to crimp both ends of the
pivot.
- Fig. 10 is a view, similar to Fig. 1, to show the both ends of the
pivot which have been crimped.
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Best Mode of the Invention for Working
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A first example of the embodiment of the invention is shown in Figs.
1 to 3. The feature of this invention resides in the construction of a pair of
side-wall sections 4 which have a wedge-shaped cross section such that the
outer side surfaces of the side-wall sections 4 are not parallel to each other,
and specifically of the part to support both ends of a pivot 3 with respect to
the pair of side-wall sections 4. The overall construction and function of the
cam follower with sheet-metal rocker arm is substantially the same as the
conventionally well-known construction, including the construction
disclosed in US Patent No. 5,048,475, and Japanese Patent Publication No.
Tokukou Hei 6-81892, so drawings and explanations are either omitted or
simplified, and this explanation will center only on the features of this
invention. Throughout all of the drawings, the same reference numbers are
used for like parts.
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Similar to the prior art cam followers, the cam follower of this
example comprises a sheet-metal rocker arm 1, roller 2 and pivot 3.
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The sheet-metal rocker arm 1 is manufactured by plastic-working,
specifically drawing of metal plate such as steel plate, and comprises: a pair
of side-wall sections 4, and first and second connecting sections that
connect the pair of side-wall sections 4 (for example, the first and second
connecting sections 5, 6 as shown in Figs. 4 to 7). There are through holes
11 formed at locations in alignment with each other in the middle sections
of each of the pair of side-wall sections 4, and both ends of the pivot 3 fit
inside and are supported by these through holes 11 such that this pivot 3
extends between the sidewall sections 4. The outer peripheral surface of the
middle portion of the pivot 3 is subjected to induction hardening to form a
quench-hardened layer 15 generally in the circumference.
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In the example illustrated, the axial length of the quench-hardened
layer 15 is a little longer than the space between the inner side surfaces of
the both side-wall section 4. Accordingly, the both ends of the
quench-hardened layer 15 enter the both through holes 11. The outer
peripheral surface of the middle portion of the pivot 3 functions as the inner
raceway of the radial needle roller bearing for supporting the roller 2 (see
Figs. 4 to 7). The both end sections of the pivot 3, however, are kept as it is
without undergoing quench hardening, so that the both end sections of the
pivot 3 may easily be processed to form the crimped portion 13a to fix the
both end sections with respect to the respective through holes 11.
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The both side-wall sections 4 have a wedge-shaped cross section in
the width direction (up and down direction in Figs. 1 and 3), and the
thickness of the side-wall sections 4 generally changes in the width
direction such that it is thinner on the side closer to the connecting sections
(upper side in Figs. 1 and 3) and thicker on the side remote from the
connecting sections. The inner side surfaces 16 of the both side-wall
sections 4 are parallel to each other at least in the width direction, while the
space between the outer side surfaces 17 of the both side-wall sections 4
becomes larger going remote from the connecting sections. During use, a
load is applied to the pivot 3 from the side of the connecting sections,
specifically from the upper side to the lower side in Figs. 1 and 3.
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Particularly, in the cam follower of the present invention, the outer
peripheral edge of the both axial end surfaces of the pivot 3 are crimped
onto the half on the side near the connecting sections (top half in Figs. 1 to
3) of the peripheral edge of the respective through holes 11. In order to do
this, as shown in Fig. 2 with the dot-chain line β, a crimping tool is pressed
to part in the circumferential direction of each end surface of the pivot 3
from the middle section to the side near the connecting sections to form a
crimped section 13a. When performing this crimping, the outer peripheral
surfaces around the both end portions of the pivot 3 come in contact with
the inner peripheral surfaces of the through holes 11 on the side away from
the connecting sections (lower side in Figs. 1 to 3). In this illustrated case,
with the openings at the opposite ends of the respective through holes 11, a
beveled section 21 is formed along the peripheral edge of the opening on
the side of the outer side surface 17 of the respective side-wall sections 4,
the outer peripheral surfaces around the crimped sections 13a formed along
the outer peripheral edge of the axial opposite end surfaces of the pivot 3
come in contact with the beveled sections 21. Also, due to processing of
these crimped sections 13a, the opposite ends of the pivot 3 are strongly
pressed toward the side away from the connecting sections so that the outer
peripheral surfaces around the opposite ends of the pivot 3 and the inner
peripheral surfaces of the respective through holes 11 come in strong
contact with each other on the side away from the connecting sections
(lower side in Figs. 1 to 3).
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As clearly shown in Figs. 1 and 3, in the present invention, the
space between the outer side surfaces 17 of the both side-wall sections 4 at
the portions to be abutted by the crimped portion 13a is smaller than the
space between the outer side surfaces at the portions to be abutted by the
crimped portion 13 in the conventional structure shown in Figs. 8 to 10.
Accordingly, the axial length of the pivot 3 of the cam follower in the
present invention is a little shorter than the axial length of the pivot 3 of the
conventional structure.
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In the case of the cam follower of this invention having the
construction as mentioned above, on the side where the load is supported,
or in other words, in the load-support section, the outer peripheral surfaces
around the both end sections of the pivot 3 come in contact with the inner
peripheral surfaces of the through holes 11 over a wide area. Also, in this
load-support section, the portion of the outer peripheral surface of the ends
of the pivot 3 that come in contact with the inner peripheral surfaces of the
through holes 11 did not undergo plastical deformation like the crimped
sections 13a, so they do not easily deform plastically even when large
pressure is applied. Particularly, in the example shown in the figures,
there is a quench hardened layer 15 on part of the outer peripheral surfaces
around the both end sections of the pivot 3 that come in contact with the
inner peripheral surfaces of the through holes 11. This quench hardened
layer 15 is hard and very difficult to deform. Therefore, even when used
for a long period of time, it is difficult for lost motion to occur in the
support sections of the both ends of the pivot 3 with respect to the side-wall
sections 4 of the sheet-metal rocker arm 1.
Industrial Applicability
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This invention is constructed and functions as described above and
is capable of improving the durability of a cam follower having a
lightweight and produced at low-cost.
