Note: Descriptions are shown in the official language in which they were submitted.
--1--
De_cription
"TIMING BELT WITH CONTROLLED
FRIC~ION BACKSIDE RIBS"
Technical Field
This inventionrelates tobelts andin particular
to timing belts.
Back~ound A~t
In one conventional form of timing belt
having longitudinally spaced teeth on the inner
section thereof, longitudinally extending ribs
are provided in the outer, or tension, section
of the belt adapted to have engagement with an
idler pulley or the like.
A problem arises in the use of such ribbed
timing belts in that such ribs limit the contact-
ing angle with the pulley as they restrict the
bendability of the belt. Thus, while such ribs
provide a large contacting area with the pulley
so as to provide high power transmission therebe-
tween, because of the limitation on the contacting
angle heretofore required to provide the necessary
bendability of the belt, high power transmission
in such belts has been restric~ed heretofore.
Disclosure of Invention
The present invention comprehends the provi-
sion of a novel timing belt wherein the backside
ribs are provided with longitudinally spaced,
transversely extending grooves so as to define
a series of longitudinally spaced cogs, the side
faces of which engage the complementary pulley
groove surfaces in transmitting power between
the belt and pulley.
The provision of the transversely extending
grooves in the backside ribs provides for improved
bendability of the belt while yet, at the same
time, the use of the backside cogged ribs provides
for desired high power transmission as a result
of the friction between the side faces of the
cogs and the confronting surfaces of the pulley
grooves.
The invention comprehends providing the
outer section of the belt defined by the longi~u-
dinally spaced cog side faces to have a predeter-
mined friction which is a function not only of
the frictional characteristics of the material
making up the cogged ribs, but also the ratio
of the area of the side faces of the cogs to
the coplanar area of the grooves between ~he
cogs.
Thus, in broad aspect, the invention compre-
hends providing a timing belt provided with back-
side ribs which are discontinuous in such a manner
as to provide a preselected frictional engagement
between the ribs and the cooperating pulley,
thereby providing for preselected high power
transmission with concurrent desired bendability
of the belt.
More specifically, the invention comprehends
the provision in a timing belt having an outer
section, an inner toothed section, and an inter-
mediate section provided with a plurality of
longitudinally extending tensile cords, the outer
section being provided with transversely spaced
ribs having longitudinally spaced transverse
grooves defining therebetween a series of cogs
having side faces, the effective coefficient
of friction ~ of the side of the ribs being
~ = C x ~
where C= coefficient oE friction of the rib mater-
ial, Ag = area of the portion of the side of
the ribs defined by said grooves, and Ac = area
of the side of the cogs, of preselecting Ag and
Ac to cause ~ to be less than approximately 0.90
where C = approximately 0.35.
More specifically, in the illustrated inven-
tion, the coefficient of friction of the rib
material is approximately 0.35.
Further more specifically, in the present
invention, the values of Ag and Ac are preselected
to cause ~ to be in the range of approximately
0.15 to approximately 0.90.
In the illustrated embodiment, the side
faces of the cogs are inclined at less than 90
to the transverse extent of ~he belt, whereby
the cogs define a trapezoidal transverse cross
section.
The side faces of the cogs comprise raw
edge surfaces of the outer section of the belt
and the ribs are provided with a cover fabric.
In the illustrated embodiment, the ribs
are formed of rubber which may comprise rubber
similar to the rubber of which the other sections
of the belt are formed.
In the illustrated embodiment, the cogs
are aligned with -the teeth of the inner section
of the belt.
The tensile cords are located at the pitch
9~
line of the belt in the illustrated embodiment.
The timing belt of the present invention
is extremely simple and economical of construction
while yet providing the highly desirable features
discussed above.
Brief Description of the Drawing
Other features and advantages of the invention
will be apparent from the following description
taken in connection with the accompanying drawing
wherein:
FIGURE 1 is a fragmentary perspective view
of a timing belt embodying the invention;
FIGURE 2 is a fragmentary vertical section
taken substantially along the line 2-2 of Figure
1; and
FIGURE 3 is a fragmentary longitudinal section
taken substantially along the line 3-3 of Figure
2.
Best Mode for Carryin~ Out the Invention
In the illustrative embodiment of the invention
as disclosed in the drawing 9 a timing belt generally
designated 10 includes an outer tension section
generally designated 11, an inner toothed compres-
sion section generally designated 12, and an
intermediate section generally designated 13
provided with a plurality of longitudinally extend-
ing transversely spaced tensile cords 14.
In the illustrated embodiment, the outer
section 11 is defined by a plurality of longitudi-
nally extending discontinuous ribs generally
designated 15 defined by a series of longitudinally
al~ernating cogs 16 and grooves 17. As seen
in Figure 1, a plurality of the discontinuous
ribs 15 are provided in transversely side-by-side
spaced relationship. In the illustrated embodi-
ment, cogs 16 are aligned with the longitudinally
spaced teeth 18 of the inner section 12.
In the illustrated embodiment, ribs 15 are
provided with an outer fabric cover 19 and teeth
18 are provided with an inner fabric cover 20.
As shown in Figure 1, the side faces 21 of the
cogs are raw edge, i.e. not covered with fabric.
In the illustrated embodiment, the tensile
cords are formed of low elongated, high strength
material, such as polyester resin, polyamide
resin, aromatic polyamide resin, rayon, glass
fibers, carbon fibers, and the like. Intermediate
section 13 is defined by a layer of rubber inter-
mediate the inner and outer sections, and in
the illustrated embodiment, rubber layer 13 is
formed of a stretchable rubber, such as natural
rubber, chloroprene rubber, nitrile rubber, butyl
rubber, styrene-butadiene rubber, chlorosulfonated
polyethylene, hydrogenated nitrile rubber, etc.,
or a blend thereof.
In the illustrated embodiment, the inner
section 12 and the outer section 11 are formed
of similar rubber and, thus, may be molded inte-
grally in the formation of the belt.
The tooth covering fabric 20 may comprise
conventional stretchable fabric, such as canvas
with one or more plies of rubber woven with warps
of crimped polyamide iber, aromatic polyamide
fiber, etc., and wefts of conventional nonstretch~
able yarns.
The fabric 19 may comprise one or more plies
~ 3~
of bias canvas fabric, a wide angle canvas fabric
made of wefts and warps of cotton yarns, polyester
resin, polyamide resin, aromatic polyamide resin,
or a mixture thereof. The cover fabric 19 may
be applied with layers of rubber similarly as
fabric 20.
As shown in Figure 1, the side faces of
the tee~h 18 and ribs 15 comprise raw edge
surfaces.
The coefficient of friction of the rubber
utilized defining the cogs 16, in the illustrated
embodiment, is approximately 0.35. The invention
comprehends causing the discontinuity in the
ribs 15 to be such as to reduce the total area
of the side faces of the ribs engaging the pulley
surfaces a preselected amount by ~he provision
of the grooves 17. More specifically, the inven-
tion comprehends causing the reduction in the
side area of the ribs to cause the effective
coefficient of friction of the side faces 21
of the cogs with the pulley to meet the following
requirements: A
0 35 ~ A - ~ < 0 90
~5 where Ag = the area of the portion of the side of
the ribs defined by the grooves and Ac = the area
of the side of the cogs, and the coefEicient of
friction of the cover material = 0.35.
As will be obvious to those skilled in the
art, the desirable range of ~ may be achieved
with materials having coefficients of friction
differing from the 0.35 coefficient by suitably
varying the side areas of the cogs relative to
the effective side area of the grooves.
Thus, the invention comprehends reducing
" : .
the coefficient of friction of the rubber material
of the ribs by effectively reducing the total
area of the ribs by suitably proportioning the
size of the grooves to the size of the cogs.
It is contemplated that the coefficient of fric-
tion of the cog material is higher than the min-
imum value of .15, as set out in the formula,
and that the use of the transverse grooves provid-
ing the reduced area of the cogs defining the
discontinuous ribs provide the desired reduced
frictional coefficient.
The provision of the longitudinally spaced
cogs 16 in the backside of the belt permits the
belt further to be utilized as a double timing
belt wherein the cogs serve as teeth in cooper-
ation with a toothed pulley, when desired. Thus,
the belt of the present invention has the univer-
sal characteristic of being adapted for use in
high power transmission wi~h ribbed pulleys,
as well as synchronous timing functioning with
front and backside toothed pulleys. The improved
bendability of the belt provides for extended
usefulness in a wide range of applications, such
as in the automotive field.
The invention comprehends, as discussed
above, providing a ratio of the side area of
the grooves to the side area of the ribs in the
range of approximately -1 to approximately 2~
times where the coefficient of friction of the
cog material is approximately 0.35.
As illustrated in Figure 2, the respective
ribs effectively define discontinuous V-ribs
having a trapezoidal cross section. The ribs
are disposed in conLiguous side-by-side relation-
ship in the illustrated embodiment.
Theforegoingdisclosureof specificembodiments
is illustrative of the broad inventive concepts
comprehended by the invention.
