Synchronous drive system and method of making the same

The combination of a toothed pulley and a toothed belt and method of making the same are provided. The toothed belt has teeth that serially mesh with cavities of the pulley that are respectively disposed between adjacent teeth thereof and that respectively have bottoms. Each pulley tooth is substantially curvilinear. Each belt tooth has a longitudinal cross-sectional configuration that defines a pair of spaced side faces that respectively have free end portions that are remote from adjacent roots thereof and that are spaced apart from each other by a bottom face of the tooth, each bottom face having a center. The teeth of the pulley and the belt are so constructed and arranged that each belt tooth has a longitudinal substantially trapezoidal cross-sectional configuration that defines the free end portions thereof as a pair of spaced corner means thereof that are remote from said adjacent root means thereof and that each belt tooth would have the pair of free corner means thereof compressed radially outwardly and inwardly toward each other by the respective adjacent pulley teeth while the bottom face thereof has its center spaced from the bottom of the cavity between those respective adjacent pulley teeth if that belt tooth is fully received in the cavity between those respective adjacent pulley teeth and those respective adjacent pulley teeth are just making contact with the land areas of the belt on each side of that belt tooth while being spaced from the respective roots of that belt tooth.

1. Field of the Invention 
This invention relates to an improved synchronous belt and pulley drive 
system and to a method of making such a drive system. 
2. Prior Art Statement 
It is known to provide the combination of a toothed pulley and a toothed 
belt that has the teeth thereof serially mesh with cavities of the pulley 
that are respectively disposed between adjacent teeth thereof each pulley 
tooth being substantially curvilinear and, each belt tooth having a 
longitudinal cross-sectional configuration that defines a pair of spaced 
side face means that respectively have free end portions thereof that are 
remote from adjacent root means thereof. For example, see the U.S. Pat. 
No. 4,403,979 to Wujick; the U.S. Pat. No. 3,756,091 to Miller, and the 
U.S. Pat. No. 3,404,576, to Cicognani et al. 
It is also known to provide a non-conjugate action of the belt teeth with 
the pulley teeth to decrease contact stress. For example, see the U.S. 
Pat. No. 2,987,932 to Szonn; U.S. Pat. No, 3,026,737 to Berg; U.S. Pat. 
No. 3,968,701 to Maruyama; U.S. No. 4,007,644 to Weinberger, and the U.S. 
Pat. No. 4,148,225 to Redmond, Jr. et al. 
SUMMARY OF THE INVENTION 
It is one feature of this invention to provide a combination of a toothed 
pulley and a toothed belt which relieves the high sheer stress at the 
roots of the belt teeth as well as reduces land area slapping. 
In particular, it was found according to the teachings of this invention 
that the belt teeth and the pulley teeth of a synchronous drive system 
could be so constructed and arranged that the free end portions of each 
belt tooth could be compressed radially outwardly and inwardly toward each 
other by the respective adjacent pulley teeth before those adjacent pulley 
teeth make contact with the land areas of the belt on each side of that 
belt tooth while being spaced from the respective root means of that belt 
tooth whereby the resulting pre-stressing and trapping of that belt tooth 
by those adjacent pulley teeth maintain that belt tooth in the pulley 
groove in a manner that is believed to reduce land wear and thereby extend 
the life of the belt. 
For example, one embodiment of this invention provides the combination of a 
toothed pulley and a toothed belt that has the teeth thereof serially mesh 
with cavities of the pulley that are respectively disposed between 
adjacent teeth thereof and that respectively have bottoms, each pulley 
tooth being substantially curvilinear and each belt tooth having a 
longitudial cross-sectional configuration that defines a pair of spaced 
side face means that respectively have free end portions thereof that are 
remote from adjacent root means thereof and that are spaced apart from 
each other by a bottom face means of the tooth. Each bottom face means has 
a center. The teeth of the pulley and the belt are so constructed and 
arranged that each belt tooth has a longitudinal substantially trapezoidal 
cross-sectional configuration that defines the free end portions thereof 
as a pair of spaced free corner means thereof that are remote from said 
adjacent root means thereof and that each belt tooth would have the pair 
of free corner means thereof compressed radially outwardly and inwardly 
toward each other by their respective adjacent pulley teeth while the 
bottom face means thereof has its center spaced from the bottom of the 
cavity between those respective adjacent pulley teeth if that belt tooth 
is fully received in the cavity between those respective adjacent pulley 
teeth and those respective adjacent pulley teeth are just making contact 
with the land areas of the belt on each side of that belt tooth while 
being spaced from the respective root means of that belt tooth. 
Accordingly, it is an object of this invention to provide an improved 
combination of a toothed pulley and a toothed belt that has the teeth 
thereof serially mesh with cavities of the pulley that are respectively 
disposed between adjacent teeth thereof, the combination of this invention 
having one or more of the novel features of this invention as set forth 
above or hereinafter shown or described. 
Another object of this invention is to provide a method of making the 
combination of a toothed pulley and a toothed belt that has the teeth 
thereof serially mesh with cavities of the pulley that are respectively 
disposed between adejacent teeth thereof, the method of this invention 
having one or more of the novel features of this invention as set forth 
above or hereinafter shown or described.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
While the various features of this invention are hereinafter illustrated 
and described as providing a synchronous drive system wherein the belt 
teeth are each substantially trapezoidal in their longitudinal 
cross-sectional configurations and the pulley teeth are substantially 
curvilinear in their longitudinal cross-sectional configurations, it is to 
be understood that the various features of this invention can be utilized 
singly or in any combination thereof to provide a synchronous drive system 
wherein the belt teeth and/or the pulley teeth have different longitudinal 
cross-sectional configurations while still providing the improved features 
of this invention. 
Therefore, this invention is not to be limited to only the embodiments 
illustrated in the drawings, because the drawings are merely utilized to 
illustrate one of the wide variety of uses of this invention. 
Referring now to FIG. 1, the improved synchronous drive system or 
combination of a toothed pulley and a toothed belt that has the teeth 
thereof serially mesh with cavities of the pulley that are respectively 
disposed between adjacent teeth thereof is generally indicated by the 
reference numeral 20 and comprises a pair of toothed pulleys 21 and 22 and 
an endless toothed belt 23 cooperating therewith to transmit a driving 
relation between the pulleys 21 and 22 in a manner that is substantially 
conventional in the art, except for the improved features of this 
invention as hereinafter set forth, and such an arrangement is generally 
set forth in the aforementioned seven U.S. Pat. Nos. 3,756,091; 3,404,576; 
2,987,932; 3,026,737; 3,968,701; 4,007,644 and 4,148,225 whereby these 
seven U.S. patents are all being incorporated into this disclosure by this 
reference thereto. 
The pulleys 21 and 22 can be formed of any suitable material, such as 
metallic material, and differ from each other in that the effective 
diameters thereof are different whereby the number of teeth thereon are 
likewise different but the overall configuration of the teeth thereof are 
basically the same. 
However, it is to be understood that the configuration of the teeth of the 
pulleys 21 and 22 could be different as long as at least one of the 
pulleys 21 or 22 has the teeth thereof perform the inventive features of 
this invention with the belt 23 as hereinafter set forth. 
Accordingly, reference is now made to FIGS. 4, 5 and 6 wherein it can be 
seen that the pulley 21 (and/or pulley 22) has a plurality of 
substantially curvilinear pulley teeth 24 extending around the periphery 
thereof with each pair of adjacent teeth 24 defining a cavity therebetween 
that is generally indicated by the reference numeral 25. The longitudinal 
cross-sectional configurations of the pulley teeth 24 define facing 
curvilinear side face means 26 that define the cavity 25 therebetween with 
the side face means 26 of adjacent pulley teeth 24 joining together at the 
bottom 27 of the cavity 25 as illustrated in FIG. 4 and joining with other 
side face means 26 to define outer tips 28 of the pulley teeth 24 that are 
also substantially curvilinear. 
As previously stated, the longitudinal cross-sectional configuration of the 
pulley teeth 24 can be any suitable configuration which will produce the 
improved results of this invention as hereinafter set forth. However, in 
the embodiment illustrated in FIGS. 4-6, the configuration of the pulley 
teeth 24 and, thus, of the pulley 21 is substantially the same as the 
pulley illustrated in FIG. 3 of the aforementioned U.S. Pat. No. 3,756,091 
to Miller, whereby further details of the pulley 21 need not be set forth. 
The belt 23 of this invention is best illustrated in FIGS. 2 and 3 and 
comprises a conventional tensile means 30 having a plurality of teeth 31 
extending from the inner side 32 thereof and a backing member 33 extending 
from the outer side 34 thereof, the teeth 31 and backing member 33 being 
mainly formed from any suitable fiber loaded or unloaded polymeric 
material or materials and being formed in any suitable manner, such as in 
the manner set forth in the U.S. Pat. No. 3,078,206 to Skura, the U.S. 
Pat. No. 4,343,666, to Wetzel, the co-pending U.S. patent application of 
Marsh et al, Ser. No. 502,777, filed June 9, 1983, the co-pending U.S. 
patent application of Wetzel et al, Ser. No. 658,832, filed Oct. 9, 1984, 
the co-pending U.S. patent application of Whitt, Ser. No. 659,159, filed 
Oct. 9,1984, etc., whereby these two U.S. patents and three U.S. 
co-pending patent applications are all being incorporated into this 
disclosure by this reference thereto. 
Therefore, it can be seen that the particular method of making the belt 
construction 23 of this invention is not to be a limitation on this 
invention as this invention is directed to the feature of forming the belt 
teeth 31 and the pulley teeth 24 to cooperate in a unique manner as 
hereinafter set forth. 
If desired, a conventional fabric layer 35 can cover the outer surface of 
the teeth 31 as well as the land areas 36 of the belt 23 that are disposed 
between adjacent teeth 31 in a conventional manner. 
Each belt tooth 31 has a longitudinal cross-sectional configuration that is 
substantially trapezoidal and defines opposed side face means 37 that 
respectively join with a substantially flat bottom face means 38 and 
substantially curvilinear root means 39, each side face 37 having a 
substantially flat or straight section 40 and an arcuate section 41 with 
the arcuate section 41 being defined by a radius 42 having its center 43 
disposed intermediate the opposed side face means 37 of the respective 
tooth 31. Each arcuate root means 39 of each belt tooth 31 is defined by a 
radius 44 having its center 45 disposed outboard of the respective side 
face means 37. The flat section 40 of each side face means 37 of each belt 
tooth 31 joins with its respective arcuate root means 39 and with its 
arcuate section 41 while that arcuate section 41 joins with the flat 
bottom face means 38, the flat section 40 of each side face means 37 being 
disposed at an angle 46 relative to a line 47 which is substantially 
parallel to the transverse center line 48 of that respective belt tooth 
31. 
The arcuate section 41 of each side face means 37 of each belt tooth 31 
defines at least part of a free end portion or corner means of the belt 
tooth 31 that is generally indicated by the reference numeral 49 and is 
disposed remote from the respective root means 39 of that belt tooth 31. 
The size of the belt teeth 31 relative to the cavities 25 of the pulley 21 
(and/or pulley 22) is so selected that when a particular belt tooth 31 of 
the belt 23 as illustrated in FIG. 4 is initially received in the cavity 
25 between an adjacent pair of pulley teeth 24, with the pulley 21 and 
belt 23 both rotating in a counterclockwise direction in FIG. 4, the 
left-hand land means 36 of the belt 23 makes contact with the tip 28 of 
the left-hand pulley tooth 24 while the corner means 49 of that belt tooth 
31 initially and respectively make contact with the opposed side faces 26 
of the adjacent belt teeth 24. 
At this time, it can be seen that a relatively wide gap or area 50 is 
provided between the left-hand root means 39 of that belt tooth 31 and the 
adjacent surface or face means 26 of the left-hand pulley tooth 24 so that 
no stress is being placed on that root means 39. 
Further rotation of the pulley means 21 and belt means 23 in a 
counterclockwise direction from the position illustrated in FIG. 4 to the 
position illustrated in FIG. 5 causes the tooth 31 to be compressed in the 
left-hand corner means 49 thereof, as represented by the dash-dotted line 
51 in FIG. 5, before the left-hand root means 39 makes contact with the 
side face means 26 of the left-hand tooth 24, the line 51 being the normal 
outline profile of the belt tooth 31. In this manner, the left-hand corner 
means 49 of the belt tooth 31 is compressed radially outwardly and 
inwardly to the right by the amount represented by the area 52 in FIG. 5 
that is bordered by the line 51 and the side face means 26 of the 
left-hand tooth 24 as illustrated in FIG. 5 and this compression takes up 
a considerable force in the belt tooth 31 at a point therein that is 
remote from the left-hand root means 39 before any force would be placed 
on the left-hand root area 39 of the belt 23. 
It is believed that providing such compression area 52 in the belt tooth 31 
remote from its respective root means 39 enhances the life of the belt 
means 23 by removing as much stress or strain in the root areas 39 of the 
belt teeth 31 as possible during their driving or driven operation with 
the pulley 21. 
The configurations and arrangement of the belt teeth 31 and pulley teeth 24 
are such that if the respective belt tooth 31 could be theoretically fully 
and uniformly received in the cavity 25 between the adjacent pulley teeth 
24 in the manner illustrated in FIG. 6, the corner means 49 of the belt 
tooth 31 would be radially outwardly and inwardly compressed toward each 
other by the amount represented by the areas 53 in FIG. 6 that is bounded 
by the surface means 26 of the adjacent pulley teeth 24 and the normal 
profile outline of the belt tooth 31 represented by the dash-dotted lines 
54 in FIG. 6 at the time the pulley teeth 24 have the tips 28 thereof just 
engaging the adjacent land areas 36 of the belt 23 on each side of that 
belt tooth 31 while the side face means 26 of the adjacent pulley teeth 24 
are respectively spaced from the adjacent root means 39 of the belt tooth 
31 by the large gaps 50' illustrated in FIG. 6 whereby theoretically no 
force or stress is being imposed on the root means 39 or land areas 36 at 
this time. 
In this manner, it can be seen that each belt tooth 31 of the belt 23 of 
this invention cooperates with its receiving cavity 25 between adjacent 
pulley teeth 24 by having both of the corner means 49 thereof compressed 
radially outwardly and inwardly toward each other through the trapping 
effect of the side face means 26 of the adjacent pulley teeth 24 which 
produces both a radial and horizontal pre-stressing of the belt tooth 31 
before the root means 39 and land areas 36 of the belt 23 are subsequently 
stressed by further action between the respective belt tooth 31 and pulley 
teeth 24 through the normal work load being imposed thereon and it is 
believed that this pre-stressing effect results in increased belt life and 
reduced noise by relieving the high sheer stress at the root means 39 of 
each belt tooth 31 and a reduced land area slapping by the land areas 36 
engaging the tips 28 of the teeth 24. 
While the invention is not to be limited to any particular configurations 
or dimensions, one belt 23 of this invention that has been utilized in 
pulleys 21 and 22 formed similar to the aforementioned U.S. Pat. No. 
3,756,091, to Miller, wherein generally the radius of curvature of each 
cavity 25 is approximately 0.103 of an inch and the cavity depth is 
approximately 0.142 of an inch, had the pitch of the belt teeth 31 thereof 
approximately 0.31496 of an inch, the number of belt teeth being 120, the 
belt pitch length being approximately 37.795275 inches and the belt pitch 
diameter being approximately 12.030609 inches. The belt teeth 31 of such 
belt 23 each had an overall height along the center line 48 from the 
bottom surface face 38 to approximately the inner side 32 of the tensile 
means 30 of approximately 0.130 of an inch with the distance between the 
corner means 49 thereof being approximately 0.182 of an inch, each radius 
42 thereof being approximately 0.060 of an inch, each radius 44 thereof 
being approximately 0.031 of an inch and the flat sections 40 thereof 
making an included angle of approximately 9.degree.. 
Such a belt provided the gross interference during engagement with the 
pulley as previously described and this actually increased belt life as 
well as provided a quieter drive system. For example, the prior known belt 
for such system had a belt life of approximately 122.7 hours whereas the 
life of the belt 23 of this invention was approximately 193.6 hours. 
As previously stated, the particular configurations of the pulley teeth 24 
and belt teeth 31 cooperating therewith in the unique manner provided by 
this invention can be provided by other configurations than those 
illustrated in the drawings and previously described. 
For example, reference is now made to FIGS. 7 and 8 wherein another 
synchronous drive system of this invention is generally indicated by the 
reference numeral 20A and parts thereof similar to the drive system 20 
previously described are indicated by like reference numerals followed by 
the reference letter "A." 
As illustrated in FIGS. 7 and 8, the pulley 21A has the teeth 24A thereof 
so constructed and arranged that the same provide a substantially 
trapezoidal cavity 25A between adjacent pulley teeth 24A that is defined 
by substantially flat side face means 26A even though the tips 28A of the 
teeth 24A are rounded as illustrated. However, the bottom 27A of each 
cavity 25A is substantially flat as illustrated. 
In contrast, the longitudinal cross-sectional configuration of each belt 
tooth 31A of the belt 23A of this invention is substantially the same as 
the configurations set forth in FIG. 2 of the aforementioned U.S. Pat. No. 
3,756,091, to Miller and would theoretically have the opposed free end 
portions 49A of the opposed side face means 37A thereof compressed 
radially outwardly and inwardly toward each other by the amount of areas 
53A represented in FIG. 8 as the area bordered by the side faces 26A of 
the pulley teeth 24A and the dash-dotted lines 54A that depict the normal 
profile of the tooth 31A when that tooth 31A is fully and uniformly 
received in the cavity 25A and has the tips 28A of the pulley teeth 24A 
just engaging the land areas 36A on each side of that tooth 31A as 
illustrated in FIG. 8. At this time, it can be seen in FIG. 8 that the 
root means 39A of the belt tooth 31A are fully spaced from the sides 26A 
of the adjacent pulley teeth 24A in the same manner as the root means 39 
of the teeth 31 in the cavities 25 as previously described whereby it is 
believed the belt 23A and pulley 21A will function in the manner 
previously set forth to extend the life of the belt 23A through 
prestressing thereof as well as reduce the noise of operation thereof 
through reduced land slapping thereof. 
Therefore, it can be seen that this invention not only provides an improved 
synchronous drive system or combination of a toothed pulley and a toothed 
belt, but also this invention provides an improved method of making such a 
drive system or combination. 
While the forms and methods of this invention now preferred have been 
illustrated and described as required by the Patent Statute, it is to be 
understood that other forms and method steps can be utilized and still 
fall within the scope of the appended claims wherein each claim sets forth 
what is believed to be known in each claim prior to this invention in the 
portion of each claim that is disposed before the terms "the improvement" 
and sets forth what is believed to be new in each claim according to this 
invention in the portion of each claim that is disposed after the terms 
"the improvement" whereby it is believed that each claim sets forth a 
novel, useful and unobvious invention within the purview of the patent 
statute.