U.S. patent application number 09/759652 was filed with the patent office on 2001-09-20 for silent chain.
Invention is credited to Fukuda, Shigekazu, Funamoto, Takayuki, Horie, Hiroshi, Iwasaki, Yoshinori, Matsuno, Kazumasa, Onoda, Nobuyuki.
Application Number | 20010023213 09/759652 |
Document ID | / |
Family ID | 18532700 |
Filed Date | 2001-09-20 |
United States Patent
Application |
20010023213 |
Kind Code |
A1 |
Horie, Hiroshi ; et
al. |
September 20, 2001 |
Silent chain
Abstract
A silent chain for use with a sprocket has a plurality of
interleaved rows of link plates connected together in an endless
fashion, each link plate having a pair of teeth. Each of the teeth
has an inside flank and an outside flank surface merging at a tip
of the tooth. The inside flank has a smooth contact surface which
is smaller in width than the smooth contact surface of the outside
flank surface. The point where the link plate starts to move into
contact with the tooth flank of the sprocket is set to locate in an
area having the smooth contact surface at a relatively high rate of
occupancy. With this arrangement, noise occurring at the mesh
between the link plate and the sprocket can be reduced. The point
where the meshing engagement completes is set to locate in an area
having the smooth contact surface at a relatively high rate of
occupancy. This arrangement improves the wear resistance and
fatigue strength of the link plate.
Inventors: |
Horie, Hiroshi; (Osaka,
JP) ; Matsuno, Kazumasa; (Osaka, JP) ; Fukuda,
Shigekazu; (Osaka, JP) ; Funamoto, Takayuki;
(Osaka, JP) ; Iwasaki, Yoshinori; (Osaka, JP)
; Onoda, Nobuyuki; (Osaka, JP) |
Correspondence
Address: |
HOWSON AND HOWSON
ONE SPRING HOUSE CORPORATION CENTER
BOX 457
321 NORRISTOWN ROAD
SPRING HOUSE
PA
19477
US
|
Family ID: |
18532700 |
Appl. No.: |
09/759652 |
Filed: |
January 12, 2001 |
Current U.S.
Class: |
474/213 ;
474/212 |
Current CPC
Class: |
F16G 13/04 20130101 |
Class at
Publication: |
474/213 ;
474/212 |
International
Class: |
F16G 013/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 12, 2000 |
JP |
003820/00 |
Claims
What is claimed is:
1. A silent chain for use with a sprocket, comprising: a plurality
of interleaved rows of link plates connected together in an endless
fashion, each of the link plates having a pair of teeth, each tooth
having a flank surface, a mesh start area at which the tooth starts
to mesh with a tooth flank of the sprocket, and a
power-transmitting area at which the tooth receives power from the
tooth flank of the sprocket, the mesh start area and the
power-transmitting area being located at different positions on the
flank surface; the mesh start area having a smooth contact surface
and a non-contact surface arranged side by side in the widthwise
direction of the link plate, the non-contact surface being set back
from the smooth contact surface, the smooth contact surface being
greater in width than the non-contact surface; and the
power-transmitting area having a smooth contact surface and a
non-contact surface arranged side by side in the widthwise
direction of the link plate, the non-contact surface in the
power-transmitting area being set back from the smooth contact
surface of the power-transmitting area, the smooth contact surface
of the power-transmitting area being greater in width than the
non-contact surface of the power-transmitting area.
2. A silent chain according to claim 1, wherein each of the teeth
has an inside flank surface and an outside flank surface merging at
a tip of the tooth, and the rate of occupancy of the smooth contact
surface in the outside flank surface increases gradually in a
direction from the tip of the tooth toward a base of the tooth.
3. A silent chain according to claim 2, wherein the rate of
occupancy of the smooth contact surface in the inside flank surface
is lower than the rate of occupancy of the smooth contact surface
in the outside flank surface.
4. A silent chain according to claim 3, wherein the rate of
occupancy of the smooth contact surface in the inside flank surface
is uniform throughout the length of the inside flank surface.
5. A silent chain according to claim 4, wherein the smooth contact
surface and the non-contact surface in the outside flank surface
are in phase with the smooth contact surface and the non-contact
surface in the inside flank surface.
6. A silent chain according to claim 4, wherein the smooth contact
surface and the non-contact surface in the outside flank surface
are 180.degree. out of phase with the smooth contact surface and
the non-contact surface in the inside flank surface.
7. A silent chain according to claim 2, wherein the rate of
occupancy of the smooth contact surface in the inside flank surface
increases gradually in a direction from the tip of the tooth toward
the base of the tooth.
8. A silent chain according to claim 7, wherein the smooth contact
surface in the outside flank surface is symmetric to the smooth
contact surface in the inside flank surface with respect to the tip
of the tooth.
9. A silent chain according to claim 8, wherein the smooth contact
surface and the non-contact surface in the outside flank surface
are in phase with the smooth contact surface and the non-contact
surface in the inside flank surface.
10. A silent chain according to claim 8, wherein the smooth contact
surface and the non-contact surface in the outside flank surface
are 180.degree. out of phase with the smooth contact surface and
the non-contact surface in the inside flank surface.
11. A silent chain according to claim 1, wherein the rate of
occupancy of the smooth contact surface in the power-transmitting
area is more than 40%.
12. A silent chain according to claim 1, wherein the rate of
occupancy of the smooth contact surface in the power-transmitting
area is more than 70%.
13. A silent chain according to claim 1, wherein the rate of
occupancy of the smooth contact surface in the mesh start area is
in the range of 7 to 15%.
14. A silent chain according to claim 11, wherein the rate of
occupancy of the smooth contact surface in the mesh start area is
in the range of 7 to 15%.
15. A silent chain according to claim 12, wherein the rate of
occupancy of the smooth contact surface in the mesh start area is
in the range of 7 to 15%.
16. A silent chain according to claim 1, wherein the link plates in
one row and the link plate in another row have different rates of
occupancy of the smooth contact surface.
17. A silent chain according to claim 16, wherein the one row of
link plate and another row of link plates are arranged in a regular
pattern in the longitudinal direction of the silent chain.
18. A silent chain according to claim 16, wherein the one row of
link plate and another row of link plates are arranged in a random
pattern in the longitudinal direction of the silent chain.
19. A silent chain according to claim 1, wherein the link plates in
each row have different rates of occupancy of the smooth contact
surface.
20. A silent chain according to claim 19, wherein the link plates
with different rates of occupancy of the smooth contact surface are
arranged in a regular pattern in the witthwise direction of the
silent chain.
21. A silent chain according to claim 19, wherein the link plates
with different rates of occupancy of the smooth contact surface are
arranged in a random pattern in the witthwise direction of the
silent chain.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a silent chain used in
combination with sprockets, and more particularly to such a silent
chain which is capable of reducing noises and wear produced due to
meshing engagement between the chain and the sprocket.
[0003] 2. Description of the Related Art
[0004] Silent chains include guide link rows and intermediate link
rows alternately connected together in an endless fashion. In a
typical example of such silent chains, the guide link rows each
have a pair of guide plates and at least one link plate disposed
between the guide plates. The guide plates and the link plate each
have a pair of pin holes spaced in the direction of travel of the
silent chain. The intermediate link rows each have two or more link
plates numbering one more than the number of the link plates in
each guide link row. The link plates, like the link plates in the
guide rink rows, each have a pair of spaced pin holes.
[0005] Each of the guide link rows and an adjacent one of the
intermediate link rows are articulately connected together by a
connector pin inserted through the laterally aligned pin holes of
the link plates and guide plates. The connector pin may be a round
pin or a pair of rocker joint pins.
[0006] The silent chain is used for transmitting power between a
driving sprocket and a driven sprocket through meshing engagement
with the sprockets. In a practical application, the silent chain is
wound around a crank sprocket and a cam sprocket of an automobile
engine, or around the output shaft of an automobile transmission
and the input shaft of a transfer unit.
[0007] Consideration will be first given to the method of producing
the link plates and the structure of a surface formed by a punching
operation. The link plates are usually formed by punching a metal
blank into a desired shape and configuration. In the punching or
otherwise blanking operation, a die-cut surface of the link plate
unavoidably has a smooth shear surface and a rough rupture surface.
According to a conventional design concept, spacial weight is given
to the way of increasing the proportion of the shear surface with a
view to improve the strength of the silent chain. This is partly
because a high proportion of the rupture surface may cause
cracking, and partly because a narrow shear surface results in an
increased surface pressure on tooth flanks of the link plate,
leading to deterioration of the wear resistance and fatigue
strength of the silent chain.
[0008] Next consideration will be given to the behavior of the
silent chain at the time of meshing with a sprocket. Regardless of
the difference in type of the link rows, meshing starts to occur
between flank surfaces of the link plates and tooth flanks the
sprocket. In one type of silent chain, at the point where the
silent chain starts to engage the sprocket, an outer flank of one
link plate located at the rear side in the travel direction first
comes into contact with a tooth of the sprocket. In another type of
silent chain, at the point where the silent chain starts to engage
the sprocket, an inner flank of one link plate located at the front
side in the travel direction first comes into contact with a tooth
of the sprocket. In any case, when the silent chain starts to mesh
with the sprocket, noises occur due to collision between the flank
surface of each link plate and the tooth flank of the sprocket.
[0009] As discussed above, the rigidity of the link plate increases
with the proportion of the shear surface. However, increasing the
proportion of the shear surface will give rise to a problem that
collision sounds produced by engagement between the link plates and
the sprocket is intensified. In automobile engines and automobile
transmission where the compatibility of the durability with the
silentness is a major requirement, sufficient consideration must be
given to the noise suppressing measure as well as improvements in
the strength.
[0010] Through observations on dynamic behaviors of a silent chain,
the present inventors uncovered the fact that at an area of the
flank surface, which takes part in the improvement in the strength
of the silent chain, is not necessarily the same as an area of the
flank surface, which takes part in the emission of noises from the
silent chain, but these areas are different from each other. Stated
in detail, an area of the outside flank surface of each link plate,
which is located near a chain pitch line, receives power from the
tooth flanks of the sprocket, and an area at which the link plates
start to engage the sprocket is a portion of the inside or the
outside flank surface located near the tip of a tooth of the
sprocket.
[0011] In completing the present invention, account was taken of
the fact that even when the ratio of the shear surface to the
rupture surface is differentiated between the area at which a flank
surface of each link plate starts to engage the surface of a tooth
of the sprocket, and the area at which the flank surface of the
same link plate receives power from the surface of the tooth of the
sprocket, a sufficient chain strength can be maintained provided
that the power-receiving area has a sufficiently large shear
surface.
SUMMARY OF THE INVENTION
[0012] It is accordingly an object of the present invention to
provide a silent chain which is capable of reducing collision
noises occurring between the flank surface of a link plate and the
tooth flank of a sprocket when the silent chain start to engage the
sprocket, and also is able to maintain the desired wear resistance
and fatigue strength of the link plate after completion of meshing
engagement between the silent chain and the sprocket.
[0013] According to the present invention, there is provided a
silent chain for use with a sprocket, comprising: a plurality of
interleaved rows of link plates connected together in an endless
fashion, each of the link plates having a pair of teeth, each tooth
having a flank surface, a mesh start area at which the tooth starts
to mesh with a tooth flank of the sprocket, and a
power-transmitting area at which the tooth receives power from the
tooth flank of the sprocket. The mesh start area and the
power-transmitting area are located at different positions on the
flank surface. The mesh start area has a smooth contact surface and
a non-contact surface arranged side by side in the widthwise
direction of the link plate. The non-contact surface is set back
from the smooth contact surface, and the smooth contact surface is
greater in width than the non-contact surface. The
power-transmitting area has a smooth contact surface and a
non-contact surface arranged side by side in the widthwise
direction of the link plate. In the power-transmitting area, the
non-contact surface is set back from the smooth contact surface,
and the smooth contact surface is greater in width than the
non-contact surface.
[0014] With this arrangement, when the silent chain starts to
engage the sprocket, the inside flank surface or the outside flank
surface first moves into contact with the tooth flank of one tooth
of the sprocket at a position adjacent to the tooth tip. In the
mesh start area at which the inside or outside flank surface start
to move into meshing engagement with the tooth flank of the
sprocket, the rate of occupancy of the smooth contact surface is
relatively low and hence able to reduce collision sound produced
between the smooth contact surface and the tooth flank of the
sprocket. The mesh start area does not take part in the
power-transmitting operation and hence is freed from the problem of
wear.
[0015] As the silent chain further advances along the periphery of
the sprocket, the same tooth flank of the sprocket comes into
contact with a different portion of the tooth flank than the
portion including the mesh start area. When the silent chain has
established complete mesh with the sprocket, the tooth flank of the
sprocket is in contact with a power-transmitting area completely
different from the mesh start area and thus transmits power to the
power-transmitting area. In the power-transmitting area, the
occupancy rate of the smooth contact surface is relatively high, so
that the power-transmitting area is able to perform a
power-transmitting operation without involving undue surface
pressure. The power-transmitting area has high wear resistance and
fatigue strength, which leads to a long service life of the silent
chain.
[0016] In one preferred form of the invention, each of the teeth
has an inside flank surface and an outside flank surface merging at
a tip of the tooth, and the rate of occupancy of the smooth contact
surface in the outside flank surface increases gradually in a
direction from the tip of the tooth toward a base of the tooth.
This arrangement is particularly useful when embodied in a silent
chain of the type wherein the mesh start area and the
power-transmitting area are both provided on the outside flank
surface.
[0017] The rate of occupancy of the smooth contact surface in the
inside flank surface may be lower than the rate of occupancy of the
smooth contact surface in the outside flank surface. This
arrangement is particularly useful when applied in a silent chain
of the type wherein the inside flank surface first comes into
contact with the tooth flank of the sprocket, and the outside flank
surface is then engaged in the power transmitting operation. The
inside flank surface, which is not engaged in the power
transmitting operation, has the smooth contact surface at a low
occupancy rate and, hence, is able to reduce noise and has improved
degree of durability and fatigue strength. The rate of occupancy of
the smooth contact surface in the inside flank surface may uniform
throughout the length of the inside flank surface in which instance
the smooth contact surface and the non-contact surface in the
outside flank surface may be in phase with, or 180.degree. out of
phase with the smooth contact surface and the non-contact surface
in the inside flank surface. Alternatively, the rate of occupancy
of the smooth contact surface in the inside flank surface may
increase gradually in a direction from the tip of the tooth toward
the base of the tooth. The smooth contact surface in the outside
flank surface may be symmetric to the smooth contact surface in the
inside flank surface with respect to the tip of the tooth, in which
instance the smooth contact surface and the non-contact surface in
the outside flank surface may be in phase with, or 180.degree. out
of phase with the smooth contact surface and the non-contact
surface in the inside flank surface.
[0018] The rate of occupancy of the smooth contact surface in the
power-transmitting area may be more than 40%, and preferably more
than 70%. The rate of occupancy of the smooth contact surface in
the mesh start area is preferably in the range of 7 to 15%.
[0019] The link plates in one row and the link plate in another row
may have different rates of occupancy of the smooth contact
surface. These rows of link plates may be arranged either in a
regular pattern or in a random pattern in the longitudinal
direction of the silent chain. This arrangement is highly effective
in reducing noise caused by resonance of periodic sounds.
[0020] Similarly, the link plates in each row may different rates
of occupancy of the smooth contact surface. The link plates with
different rates of occupancy of the smooth contact surface may be
arranged either regularly or at random in the witthwise direction
of the silent chain. This arrangement adds to the reduction of
noise.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] A preferred embodiment of the present invention will now be
described in detail, by way of example only, with reference to the
accompanying drawings, in which:
[0022] FIG. 1 is a fragmentary plan view, partly in cross section,
of a silent chain according to an embodiment of the present
invention;
[0023] FIG. 2 is a front elevational view of the silent chain;
[0024] FIG. 3 is an enlarged perspective view of a link plate of
the silent chain;
[0025] FIG. 3A is a bottom view of a portion of the link plate;
[0026] FIGS. 3B to 3D are views similar to FIG. 3A, but showing
modifications according to the present invention;
[0027] FIG. 4 is a cross-sectional view of a portion the link plate
including an area having a relatively large proportion of a smooth
contact surface;
[0028] FIG. 5 is a cross-sectional view of a portion the link plate
including an area having a relatively small proportion of the
smooth contact surface;
[0029] FIG. 6 is a diagrammatical view showing the manner in which
one link plate of the silent chain starts to engage with a
sprocket; and
[0030] FIG. 7 is a diagrammatical view illustrative of the
condition in which the link plate has completed engagement with the
sprocket.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0031] The following description is merely exemplary in nature and
is in no way intended to limit the invention or its application or
uses.
[0032] Referring now to the drawings and FIGS. 1 and 2 in
particular, there is shown a silent chain 10 embodying the present
invention. The silent chain 10 includes guide link rows 12 and
intermediate link rows 14 arranged alternately in the longitudinal
direction of the chain and articulately connected together in an
endless fashion. The guide link rows 12 each have a pair of guide
plates 16 and at least one link plate 18 (five link plates being
shown) disposed between the guide plates 16. The guide plates 16
each have a pair of pin holes (not designated) spaced in the
longitudinal direction of the chain 10. Similarly, the link plates
18 each have a pair of pin holes (not designated) spaced in the
longitudinal direction of the chain 10. The intermediate link rows
14 each have link plates 20 numbering one more than the number of
the link plates 20 in each of the guide link rows 12. In the
illustrated embodiment, each of the intermediate link rows 14 has
six link plates 20. The link plates 20, like the guide and link
plates 16 and 18, have a pair of pin holes (not designated) spaced
in the longitudinal direction of the chain 10.
[0033] The guide plates 16 and the link plates 18 in one guide link
row 12 and the link plates 20 in the adjacent intermediate link row
14 are articulately connected together by a connector pin (not
designated) inserted through respective pin holes of the plates 16,
18 and 20. The connector pin may be comprised of a cooperating pair
of rocker joint pins such as shown in the illustrated embodiment,
or a round pin (not shown).
[0034] The guide plates 16, when the silent chain 16 is in mesh
with the tooth flanks of a sprocket S (see FIG. 6), is guided by
the opposite side surfaces of the sprocket S so that the silent
chain 10 is prevented from displacing off the sprocket S in a
lateral direction. Since each guide link row 12 have a greater
number of plates 16, 18 than each intermediate link row 14, the
link plates 20 in the intermediate row 14 may be made thicker than
the guide plates 16 and link plates 18 of the guide link row 12. As
an alternative, the thickness of the guide plates 16 may be
reduced. In the illustrated embodiment, the link plates 18 in the
guide link rows 12 and the link plates 20 in the intermediate link
rows 14 have the same contour or profile.
[0035] FIG. 3 is a perspective view showing the link plate 18 (20)
of each link row 12 (14) As shown in this figure, one side of the
link plate 18 (20) is bifurcated so as to form a pair of spaced
tooth 22. Each tooth 22 has an inside flank surface 24 and an
outside flank surface 26. The respective inside flank surfaces 24
of the teeth 22 are blended together at concavely arcuate crotch
28. The inside flank surface 24 and the outside flank surface 26
marge together at a tip 30 of the tooth 22. In such a typical
silent chain 10 as shown in FIGS. 1 and 2, an area of the outside
flank surface 26 of each tooth 22, which is located in and around a
outside flank pitch line (not shown), is used for meshing
engagement with the tooth flanks of the sprocket S (see FIG. 6) for
achieving a power transmitting operation. The term "outside flank
pitch line" used herein represents a line passing parallel to a
chain pitch line over the outside flank 26 at points where the
distance between these points becomes 3/2 of the chain pitch. The
term "chain pitch line" used herein represents a line
interconnecting the centers of the pin accommodating holes (not
designated) of the link plate.
[0036] According to the present invention, the link plate 18 (20)
has an outside surface (peripheral surface) configured to have a
unique structure, as will be described below. FIG. 3A shows one
tooth 22 of the link plate 18 (20) as viewed from the tooth tip 30
side. For purposes of illustration, a smooth contract surface 32 is
indicated by hatching. In the illustrated embodiment, in the inside
flank surface 24, the rate occupancy of the smooth contact surface
32 is uniform and smaller than that of a non-contact surface 34. In
the outside flank surface 26, the rate of occupancy of the smooth
contact surface 32 increases gradually in a direction form the
tooth tip 30 toward the outside flank pitch line (namely, toward a
base of the tooth 22 shown in FIG. 3). The occupancy rate of the
smooth contact surface 32 becomes maximum at an area where the
outside flanks surface 26 comes in complete mesh with the tooth
flank of the sprocket.
[0037] The non-contact surface 34 forms a part of the peripheral
surface of the link plate 18, 20 excluding the smooth contact
surface 32. The non-contact surface 34 is set back from the smooth
contact surface 32.
[0038] As discussed previously, the link plates 18 (20) are
produced by punching out or blanking a metal sheet into a desired
shape and configuration. In the punching process, formation of a
shear surface and a rupture surface is unavoidable. The shear
surface is smooth and hence can be used as the above-mentioned
smooth contact surface 32. As an alternative, the shear surface may
be subjected to a shaving process to form a smooth contact surface
32. The rupture surface can be used as the above-mentioned
non-contact surface 34. By using the shear and rupture surfaces
unavoidably formed as a result of the punching operation, it
becomes possible to control the occupancy rate or proportion of the
smooth contact surface to the inside or the outside flank surface
depending on the proportion of the shear surface to the rupture
surface.
[0039] FIG. 4 is a cross-sectional view of an area of the outside
flank surface 26 which is engaged in the power transmission between
the link plate 18 (20) and the sprocket. The power-transmitting
area is formed by a shear drop d, a shear surface s and a rupture
surface b arranged in the order named as viewed in the punching or
die-cutting direction. The occupancy rate of the shear surface
(smooth contact surface) s, which is represented by the ratio of
the shear length (length of the shear surface s) hs to the
thickness t of the link plate 18 (20), is above 40%. It is
desirable that the occupancy rate of the smooth contact surface
(shear surface s) is as high as possible, and preferably more than
70%.
[0040] FIG. 5 is a cross-sectional view of an area of the inside
flank surface 26 at which the link plate 18 (29) first starts to
mesh with a tooth flank of the sprocket. It is to be noted however
that in another type of silent chain, the outside flank surface 26
(FIG. 3) first starts to come into meshing engagement witrh the
tooth flank of the sprocket. In the latter case, the outside flank
surface 26 is configured to have the same area as shown in FIG. 5.
The mesh start area shown in FIG. 5 is formed by a shear drop d, a
shear surface s and a rupture surface b arranged in the order named
as viewed in the punching or die-cutting direction. The rate of
occupancy of the shear surface s (smooth contact surface 32), which
is represented by the ratio of the shear length hs to the thickness
t of the link plate 18 (20) is in the range of 7 to 15%.
[0041] Turning back to FIGS. 3B, 3C and 3D, there are shown
modifications according to the present invention.
[0042] In the first modification shown in FIG. 3B, the occupancy
rate of the smooth contact surface 32 in the inside flank surface
24 increases gradually in a direction from the tooth tip 30 (see
FIG. 3) toward an inside flank pitch line side (namely, toward the
crock 28 shown in FIG. 3). The smooth contact surface 32 in the
inside flank surface 24 and the smooth contact surface 32 in the
outside flanks surface 26 vary symmetrically with each other about
the tooth tip 30 (FIG. 3). Since the occupancy rate of the smooth
contact surface 32 is made maximum at the crotch 28, the crotch 28
is highly resistant to cracking.
[0043] In the modification shown in FIG. 3C, the positional
relation established in the outside flank surface 26 (see FIG. 3A)
between the smooth contact surface 32 and the non-contact surface
34 is reversed in the inside flank surface 24 (see FIG. 3A). The
inside and outside flank surfaces 24, 26 of the link plate can be
produced by a two-stage punching process. In the first punching
stage, the outside flank surface 26 and the tooth tip 30 are
punched out in one direction from the above to the bottom of FIG.
3C, and in the second or subsequent punching stage, the tooth tip
30 and the inside flank surface 24 are punched out in the opposite
direction from the bottom to the above of FIG. 3C.
[0044] In the modification shown in FIG. 3D, the smooth contact
surface 32 in the outside flank surface 26 (see FIG. 3A) is nearly
180.degree. out of phase with the smooth contact surface 32 in the
inside flank surface 24 (see FIG. 3A). The link plate with inside
and outside flank surfaces shown in FIG. 3D, like the one shown in
FIG. 3C, can be produced by the two-stage punching process. In the
first punching stage, the outside flank surface 26 and the tooth
tip 30 are punched out in one direction from the above to the
bottom of FIG. 3D, and in the second or subsequent punching stage,
the tooth tip 30 and the inside flank surface 24 are punched out in
the opposite direction from the bottom to the above of FIG. 3D. In
the inside flank surface 24, the occupancy rate of the smooth
contact surface 32 increases gradually in a direction from the
tooth tip 30 toward the crotch 28 (see FIG. 3A). Thus, the crotch
28 is highly resistant to cracking.
[0045] FIGS. 6 and 7 show the state of meshing engagement between
the silent chain 10 and a sprocket S wherein link plates 18 (20)
used to form the silent chain 10 have inside and outside flank
surfaces 24, 26 shown in FIG. 3A. For purposes of illustration,
description given below with reference to FIGS. 6 and 6 will be
limited to the behavior of only one link plate designated by 18
(20).
[0046] Firstly, at the point A which is located near the tooth tip
30, the tooth flank T of each tooth of the sprocket S starts to
mesh with the inside flank surface 24 of one tooth 22 located at
the front side in the travel direction of the chain 10. It is to be
noted however that in another type of silent chain, meshing
engagement starts at the point B which is located on the outside
flank surface 26 adjacent the tooth tip 30. In any case, in an area
(hereinafter referred to as "mesh start area") of the inside or
outside flank surface 24 or 26 including the point A or the point
B, the occupancy rate of the smooth contact surface 32 (FIGS.
3A-3D) is made relatively low. By thus starting the meshing
engagement between the sprocket S and the link plate 18 (20) at the
mesh start area having a relatively low occupancy rate of the
smooth contact surface 32, noise occurring at the collision between
the link plate 18 (20) and the sprocket S can be reduced to a
greater extent. In this instance, since the tooth flank T of the
sprocket S has a pressure surface inclined toward the rear side in
the chain travel direction, the mesh start area has little
contribution to the transmission of power. Thus, the engagement
start area is freed from the problem of wear and fatigue.
[0047] As the silent chain 10 further advances around the sprocket
S, the tooth flank T of the next tooth of the sprocket S, as shown
in FIG. 7, comes in mesh with the outside flank surface 26 of the
other tooth 22 located at the rear side in the travel direction and
thus transmits power to the outside flank surface 26 at the point C
which is located in and around the outside flank pitch line. The
area (hereinafter referred to as "power-transmitting area") of the
outside flank surface 26 including the point C has a smooth contact
surface at a high occupancy rate, as shown in FIG. 3A, and hence
the surface pressure on the power-transmitting area is considerably
low. Thus, power-transmitting area of the outside flank surface 26
has a high wear resistance. In this instance, the tooth flank T of
the sprocket S is held out of contact with the mesh start area of
the inside flank surface 24. Accordingly, no consideration can be
given to wear and fatigue of the mesh start area even though the
occupancy rate of the smooth contact surface 32 is relatively low
in the mesh start area.
[0048] It is preferable that plural different sorts of link plates
are prepared and the link plates are then arrange either at random
or in a predetermined pattern to assemble a silent chain. For
instance, link plates 18 (FIG. 1) in each guide link row 12
designed to have a mesh start area including a smooth contact
surface 32 (FIGS. 3A to 3D) at a occupancy rate of 7%, and link
plates 20 (FIG. 1) in each intermediate link row 14 are designed to
have a mesh start area including the smooth contact surface 32
(FIGS. 3A to 3D) at a occupancy rate of 15%. By using the link
plates 18, 20 of different smooth contact surface occupancy rates,
it becomes possible to prevent the resonance of periodic noises,
thereby suppressing magnification of the noise.
[0049] Alternatively, the link plates 18, 20 differentiated from
each other by the occupancy rate of the smooth contact surface 32
are arranged in a random order in the longitudinal direction of the
silent chain. This arrangement can also suppress noises caused by
resonance.
[0050] Furthermore, link plates 18, 20 with different smooth
contact surface occupancy rates either may be arranged in each
individual link row (guide link row 12 or intermediate link row 14)
either in a regular pattern or in a random pattern. This
arrangement is also contributive to the reduction of noise caused
by resonance.
[0051] Obviously, various minor changes and modifications of the
present invention are possible in the light of the above teaching.
It is therefore to be understood that within the scope of the
appended claims, the present invention may be practiced otherwise
than as specifically described.
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