Source: http://www.docstoc.com/docs/55959173/Tension-reducing-Random-Sprocket---Patent-7125356
Timestamp: 2014-12-25 03:50:38
Document Index: 519209161

Matched Legal Cases: ['Application No. 02257611', 'art 5', 'art 40', 'art 40', 'art 60', 'art 60', 'art 52']

Tension-reducing Random Sprocket - Patent 7125356
United States Patent: 7125356
7,125,356
Tension-reducing random sprocket
A sprocket is provided having a plurality of teeth around its
circumference. Adjacent teeth are separated by roots each having a root
radius defined as the distance between the center of the sprocket and a
point along the root closest to the sprocket center in a radial
direction. In one aspect of the invention, the sprocket comprises at
least two different root radii arranged in a pattern effective to
redistribute tensions imparted to a chain by the sprocket at one or more
predetermined sprocket orders.
Todd; Kevin B. (Freeville, NY)
09/993,531
474/152  ; 474/156; 474/160
F16H 55/30&amp;nbsp(20060101); F16H 7/06&amp;nbsp(20060101)
474/152,156,161,162,160,148 74/437
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No. B, pp. 317-320 (English abstract only). cited by other
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Ronbunshu, 1999, vol. 1999, No. A, pp. 443-446 (English abstract only). cited by other
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Japan Society of Mechanical Engineers. C), 2000, vol. 66 No. 645, pp. 1439-1444 (English abstract only). cited by other
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Information Engineers), 200, vol. 44.sup.th pp. 625-626 (English abstract only). cited by other
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Vibration Induced in Driving Mechanism of Photoconductor Drum in Color Laser Printer; Author: Kawamoto Hiroyuki; Watanabe Yosuke; Nippon Kikai Gakkai Kikai Rikigaku, Keisoku Seigyo Koen Ronbunshu, 2000, vol. 2000, No. Pt. 4, pp. 1028-1031(English
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Nonlinear Vibration Analysis of Running Viscoelastic Belts; Author: YS Choi; 5.sup.th Internet Conference on Vibration Engineering; Proc., Nanjing, CN, Sep. 18-20, 2002 (English abstract only). cited by other
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Parametric Instability of Belts: Theory and Experiments; (Authors: F. Pellicano (Reprint); G. Catellani; A. Freglent ( Computers &amp; Structures) 2004, v82, N1 (Jan), pp. 81-91; ISSN: 0045-7949; Jan. 2004 (English abstract only). cited by other.
1.  A chain and sprocket drive system comprising: a chain having a plurality of pairs of links being interconnected by pins;  one or more generally circular sprockets
which operate at varying speeds and the chain having external tensions imparted to it originating from sources other than the sprocket, the sprockets having a plurality of teeth spaced about their periphery, the sprockets having roots located between
pairs of adjacent teeth for receiving the chain pins;  each of the roots having a root radius extending between the center of the sprocket and a point along the root closest to the sprocket center in a radial direction;  at least one of the roots having
a first root radius, and at least one of the roots having a second root radius, at least one of the roots having a third root radius, the second root radius being less than the first root radius, the third root radius being less than the second root
radius;  and the first, second, and third root radii arranged in a pattern which continually repeats itself around the periphery of the sprocket, the repeating pattern effective to redistribute the external tensions imparted to the chain, reducing
maximum tension forces exerted on the chain during operation of the system relative to the maximum tension forces in the system where the sprocket is a straight sprocket.
2.  The chain and sprocket system according to claim 1, wherein the pattern substantially repeats three times.
3.  The chain and sprocket system according to claim 2 wherein the root radii are arranged in a major pattern and a minor pattern.
4.  The chain and sprocket system according to claim 1 wherein the root radii are arranged in a pattern that also reduces noise produced by the interaction of said chain and said sprocket.
5.  The chain and sprocket drive system according to claim 1, wherein the first, second, and third root radii are arranged in a pattern that substantially repeats four times around the sprocket.
6.  A sprocket comprising: a plurality of teeth disposed along a circumference of the sprocket, adjacent teeth having roots therebetween, each of the roots having a root radius defined as the distance between the center of the sprocket and a
point along the root closest to the sprocket center in a radial direction, the sprocket teeth and roots disposed to receive and engage a circular loop of chain which operates at variable speeds;  and at least three different root radii, including a first
root radius, a second root radius and a third root radius, the second radius less than the first and the third less than the second, the at least three different root radii arranged in a sequence which uninterruptedly and continually repeats itself
around the sprocket for distributing the tensions imparted to the chain by the sprocket to one or more preselected orders relative to the rotation of the sprocket, the distributed tensions effective to offset tensions imparted to the chain by forces
external to the sprocket reducing maximum tension forces exerted on the chain relative to maximum tension forces in the system where the sprocket is a straight sprocket.
7.  The sprocket according to claim 6 wherein the root radii are arranged in a plurality of sequences, at least one of which is major sequence and at least one of which is a minor sequence.
8.  The sprocket according to claim 6 wherein the sequence of root radii also is effective to reduce the noise generated by the interaction of the sprocket and a chain.
9.  The sprocket according to claim 6 wherein a preselected order comprises a fourth order.
10.  The sprocket according to claim 6 wherein the sequence repeats three times.
11.  The sprocket according to claim 6 wherein the sequence substantially repeats four times around the sprocket.
12.  A method of distributing tensions imparted to a chain and sprocket system operating at variable speeds, the method comprising: providing a sprocket having a plurality of teeth separated by roots;  providing each root with a root radius
extending between the center of the sprocket and a point along the root closest to the sprocket center in a radial direction;  providing at least three different root radii;  and arranging the different root radii in a pattern which continually repeats
itself at least two times for distributing the tensions imparted to the chain and sprocket system reducing maximum tension forces exerted on the chain relative to maximum tension forces in the system where the sprocket is a straight sprocket.
13.  The method according to claim 12, wherein the pattern repeats three times.
14.  The method according to claim 12 wherein a plurality of root radii patterns are selected, at least one a major pattern and at least one a minor pattern.
15.  A method according to claim 12 comprising selecting the root radii pattern effective also to reduce the noise generated by the interaction of the chain with the sprocket.
16.  The method according to claim 12, comprising concentrating the tensions imparted to the chain by the sprocket at a fourth sprocket order.
17.  The method according to claim 12, comprising selecting the root radii pattern effective to at least partially offset tensions imparted to the chain by sources other than the sprocket to balance the overall tension force imparted to the
system by all tension sources.
18.  The method according to claim 12 wherein the pattern repeats four times.
19.  An automotive timing system comprising: a chain which operates at variable speeds, the chain having a plurality of pairs of links being interconnected by pins;  and a generally circular sprocket mounted on a cam shaft having a plurality of
teeth spaced about the periphery, the sprocket having roots located between pairs of adjacent teeth for receiving the chain pins, each of the roots having a root radius extending between the center of the sprocket and a point along the root closest to
the sprocket center in a radial direction, at least one of the roots having a first root radius, at least one of the roots having a second root radius, and at least one of the roots having a third root radius, the second root radius being less than the
first root radius and the third root radius being less than the second root radius, and the first, second, and third root radii arranged in a sequence which uninterruptedly and continually repeats itself at least two times and which maintains the
distance between the chain pins substantially constant while the chain is engaged around the sprocket and effective to redistribute tensions imparted to the chain reducing maximum tension forces exerted on the chain during operation of the system.
20.  The automotive timing system according to claim 19, wherein the sequence comprises second, third, third, second, first, second, third, third, second, first, second, third, third, second, first, second, third, third, and second root radii.
21.  The automotive timing system according to claim 19 wherein the root radii sequence is effective also to reduce the noise generated by the interaction of the chain and the sprocket.
22.  The automotive timing system according to claim 19, wherein the pattern comprises a sequence of second, third, third, second, first, second, third, third, second, first, second, third, third, second, first, second, third, third, and second
root radii.
23.  An automotive drive system comprising: a chain subject to tension loading sources external to the drive chain, the chain having a plurality of links, each link formed of two or more plates interconnected by pins, each pin having a central
longitudinal axis, and the links providing contact surfaces;  the chain traveling in a loop about at least one sprocket in driving engagement with the chain and at least one sprocket in driven engagement with the chain, each sprocket having a central
axis of rotation and plurality of surfaces spaced about the periphery of the sprocket disposed to engage the chain link contact surfaces;  the sprocket engagement surfaces spaced a distance from the sprocket central axis to position the chain at a pitch
radius defined by the distance between the sprocket central axis and the pin axis of a chain link engaged by the surfaces;  and the engagement surfaces of at least one of the sprockets disposed to engage the chain at least at a first pitch radius, at
least at a second pitch radius, and at least a third pitch radius, the first, second and third pitch radii being different and arranged in a pattern which continually repeats itself, with each rotation of the sprocket and the pattern imparting tensions
to the chain at one or more sprocket orders effective to reduce maximum chain tensions during operation of the system relative to maximum chain tensions of the system where the sprocket is a straight sprocket.
24.  The automotive drive system of claim 23 wherein the system operates at variable speeds, the system speeds where chain tensions are generally at a maximum are the system resonance conditions;  and the pattern of pitch radii are arranged to
impart a maximum tension to the chain at said system resonance speeds.
25.  The automotive drive system of claim 24 wherein the first pitch radius is greater than the second pitch radius and the second pitch radius is larger than the third pitch radius.
26.  The automotive drive system of claim 25 wherein the pattern repeats at least twice with each rotation of the sprocket.
27.  The automotive drive system of claim 23 wherein the pattern repeats at least three times with each rotation of the sprocket.
28.  The automotive drive system of claim 23 wherein the driving sprocket is rotated by an automotive powerplant at varying speeds;  the powerplant operating at one or more speeds that produce substantially maximum chain tensions;  and the pitch
radii patterns of the tension reducing sprockets are effective to reduce said maximum chain tensions relative to maximum chain tensions in a system where the sprocket is a straight sprocket.
29.  The automotive drive system of claim 28 wherein the pitch radii pattern provided by each tension reducing sprocket is effective to produce a maximum chain tension that is substantially equal to or less than the chain tension in a system
where the sprocket is a straight sprocket through the normal operating speed range of the powerplant.
30.  An automotive drive system operable at variable speeds comprising: a chain subject to tension loads in a loop about at least one sprocket in driving engagement with the chain, and at least one sprocket in driven engagement with the chain,
the system operating at one or more speeds where chain tensions reach a peak relative to chain tensions at other system speeds, the system having tensions imparted from sources other than the chain and sprocket, the chain having a plurality of links
formed of two or more plates interconnected by pins, each pin having a central longitudinal axis and the links providing chain contact surfaces, the at least one sprocket having a central axis of rotation and a plurality of teeth end sprocket engagement
surfaces between the teeth, the teeth and the sprocket engagement surfaces spaced about the periphery of the sprocket, the sprocket engagement surfaces disposed to engage the chain link contact surfaces, the sprocket engagement surfaces spaced a distance
from the sprocket central axis to dispose the chain at a pitch radius defined by the distance between the sprocket central axis and the pin axis of a chain link engaged by the surfaces;  and the engagement surfaces of at least one of the sprockets
disposed to engage the chain to provide a sequence of at least a minimum pitch radius, at least a maximum pitch radius, and at least a intermediate pitch radii therebetween, the engagement surfaces maintaining the distance between adjacent pin axes of
links engaged with the sprocket substantially constant, and the pitch radii sequence uninterruptedly and continually repeating itself at least twice with each rotation of the sprocket for imparting tensions to the chain timed with respect to tension
loads imparted to the system from other sources effective to reduce maximum chain tensions at one or more of the peak tension speeds relative to the maximum chain tensions at said peak tension speeds where the sprocket is a straight sprocket.
31.  The automotive system of claim 30 wherein the sequence repeats at least two times with each rotation of the sprocket.
32.  The automotive system of claim 30 wherein the sequence repeats at least three times with each rotation of the sprocket.
33.  The automotive system of claim 32 wherein an automotive power plant rotates the driving sprocket, the automotive power plant imparting periodic tension loads on the chain, the system reaching resonance conditions at powerplant speeds where
the chain tensions reach their approximate maximum, and the sequence of pitch radii and the timing of the tensions provided by the pitch radii relative to the power plant tension loads are effective to reduce maximum chain tensions during operation of
the system at said resonance conditions relative to the system where the sprocket is a straight sprocket operating at resonance conditions.
34.  The automotive system, of claim 30 wherein the sequence substantially repeats at least four times with each rotation of the sprocket.
35.  A tension reducing sprocket for an automotive drive system having a continuous loop chain in driving engagement with a driving sprocket and a driven sprocket, the chain formed of two or more plates interconnected by pins, each pin having a
central longitudinal axis, and the links providing contact surfaces disposed to engage the sprocket, the sprocket comprising: a sprocket body and a central rotational axis, the sprocket body provided with engagement surfaces about its periphery, the
engagement surfaces disposed to receive the chain link contact surfaces in a driving relation, the engagement surfaces spaced a distance from the sprocket central axis to position the chain link received thereon at a pitch radius defined by the distance
between the sprocket central axis and the chain link pin axis;  and the engagement surfaces providing a repeating sequence of at least, three different pitch radii which uninterruptedly and continually repeats itself with each rotation of the sprocket,
the sequence of the pitch radii effective to reduce maximum chain tensions during operation of the drive system relative to the system where the sprocket is a straight sprocket.
36.  The tension reducing sprocket of claim 35 wherein at least the first and second pitch radii are selected and disposed to impose tension events on the chain timed with respect to torque loads imposed on the chain from other sources effective
to reduce the maximum chain tensions during operation of the drive system relative to a system where the sprocket is a straight sprocket.
37.  The tension reducing sprocket of claim 35 wherein the engagement surfaces of the tension reducing sprocket are disposed to provide a repeating sequence of pitch radii having a minimum pitch radius, a plurality of pitch radii increasing to a
maximum pitch radius, and a plurality radii decreasing to the minimum pitch radius.
38.  A chain and sprocket drive system comprising: a chain having a plurality of pairs of links being interconnected by pins;  one or more generally circular sprockets having a plurality of teeth spaced about their periphery, the sprocket having
roots located between pairs of adjacent teeth for receiving the chain pins;  each of the roots having a root radius extending between the center of the sprocket and a point along the root closest to the sprocket center in a radial direction;  at least
one of the roots having a first root radius, and at least one of the roots having a second root radius, at least one of the roots having a third root radius, the second root radius being less than the first root radius, the third root radius being less
than the second root radius;  and the first, second and third root radii arranged in a pattern that substantially continually repeats itself four times around the sprocket, the pattern effective to redistribute tensions imparted to the chain, reducing
39.  A sprocket comprising: a plurality of teeth disposed along a circumference of the sprocket, adjacent teeth having roots therebetween, each of the roots having a root radius defined as the distance between the center of the sprocket and a
point along the root closest to the sprocket center in a radial direction, the sprocket teeth and roots disposed to receive and engage a circular loop of chain;  and at least three different root radii, the second radius being less than the first radius
and the third radius being less than the second radius, the at least three different root radii arranged in a pattern around the sprocket that substantially continually repeats itself four times around the sprocket arranged in a pattern distributing the
tensions imparted to the chain by the sprocket to one or more preselected orders relative to the rotation of the sprocket, the distributed tensions effective to offset tensions imparted to the chain by other tension sources reducing maximum tension
forces exerted on the chain relative to maximum tension forces in the system where the sprocket is a straight sprocket.  Description
Chain and sprocket systems are often used in automotive engine systems to transmit rotational forces between shafts.  For example, a sprocket on a driven shaft may be connected via a chain to a sprocket on an idler shaft.  In such a chain and
sprocket system, rotation of the driven shaft and driven sprocket will cause the rotation of the idler shaft and idler sprocket via the chain.  In an automotive engine system, sprockets on the crankshaft may be used, for example, to drive one or more cam
shaft sprockets.
The chains used in chain and sprocket systems typically comprise a plurality of intermeshing link plates connected with pins or rollers.  The sprockets typically comprise a circular plate having a plurality of teeth disposed around the
circumference thereof.  Located between adjacent teeth are roots having generally arcuate or semi-circular profiles for receiving the pins or rollers of the chain.  Each root has a root radius, defined as the distance from the center of the sprocket to a
point on the root closest to the sprocket center.
In a &quot;straight&quot; sprocket the root radii are all substantially equal.  However, it has been found that as a chain rotates around a straight sprocket, audible sound frequencies creating undesirable noise are often generated as the pins or rollers
connecting the links of the chain contact the sprocket teeth and impact the roots disposed between adjacent teeth of the sprockets.
The sound frequencies and volume of such noise typically varies depending on the chain and sprocket designs, chain rotational speed, and other sound or noise sources in the operating environment.  In the design of chain and sprocket systems, it
can be desirable to reduce the noise levels generated as the rollers of a chain engage roots of a sprocket.
&quot;Random&quot; sprockets have been developed to help reduce the radiated noise levels generated by the engagement of the chains with the sprockets.  Random sprockets may be characterized by having a plurality of different root radii.  The different
root radii can be arranged in a pattern around the sprocket circumference to modulate the sound frequencies generated by the engagement of the chain rollers or pins with sprocket teeth and roots.  By modulating these sound frequencies, the noise
generated as the chain rotates around the sprocket may be reduced.
In addition to minimizing noise generated by engagement between a chain and sprocket, it is also desirable to reduce the tensions imparted to the chain by the sprocket.  Reduced chain tensions can be advantageous because they may result in
decreased wear of the chain, thus increasing the life cycle of the chain.  Furthermore, reduced chain tensions may also result in less wear to the sprocket, thereby also increasing the life cycle of the sprocket.
It has been observed in chain tension measurements that certain chain tensions in a particular system may vary on a periodic or repeating basis, which often can be correlated to tension inducing events.  For example, in automotive timing chain
systems, it has been observed from chain tension measurements that the engagement and disengagement of each sprocket tooth and/or root with the chain pins often results in repeating tension changes.  These chain tension changes may be correlated with
potentially tension inducing events, such as the firing of piston cylinders, transmission engagements, etc.
A useful approach to analyzing such tension events is to observe the number of events that occur relative to a reference time period, as well as the amount of the tension change for each event.  For example, in an automotive timing chain system,
one may observe the number or frequency of tension changes in the chain relative to rotations of a sprocket or a crankshaft, as well as the magnitude of the tension change in the chain.
In such a system, for example, a tensioning event that occurs once per shaft or sprocket rotation may be considered a &quot;first&quot; order event, and an event occurring four times for each shaft or sprocket rotation may be considered a &quot;fourth&quot; order
event.  Depending on the system and the relative reference period, i.e., rotations of the crankshaft or the sprocket (or another reference), there may be multiple &quot;orders&quot; of events in a crankshaft or sprocket rotation in such a system originating from
one or more tension sources.  Similarly, a particular order of the sprocket rotation may include or reflect the cumulative effect of more than one tensioning event.  As used herein, such orders of tensioning events occurring during a sprocket (or
crankshaft) rotation also may be referred to as the orders of a sprocket (or crankshaft) and/or sprocket orders (or crankshaft orders).
In straight sprockets, measurable tensions typically are imparted to the chain at a sprocket order corresponding to the number of teeth on the sprocket, also known as the pitch order.  Thus, in a sprocket with nineteen teeth, tensions would be
imparted to the chain at the nineteenth or pitch order, i.e., nineteen times per revolution of the sprocket.  Depending on the sprocket design, the order in a straight sprocket would typically occur at equal intervals relative to the sprocket rotation,
with a generally equal tension change or amplitude.
Random sprockets, in contrast, typically have different tensioning characteristics when compared to straight sprockets due to the different root radii.  As the chain rotates around the random sprocket, each of the different root radii typically
imparts a different tensioning event to the chain.  For instance, as a roller of the chain engages a root having a first root radius, the chain may be imparted with a tension different from when a roller of the chain engages a root having a second root
radius larger than the first root radius.  Tension changes, in addition, may also be imparted to the chain by a random sprocket due to the relative positioning of the different root radii.  A roller moving between adjacent roots having the same root
radii may result in different chain tension changes than a roller moving between adjacent roots having different radii.
The change in chain tensions imparted by random sprockets may be further accentuated when the sprocket has more than two different root radii.  In a random sprocket having first, second, and third successively larger root radii, the tension
imparted to the chain may be greater when a chain roller moves from a root having a first root radii to a root having a third root radii than when a chain roller moves from a root having a first root radii to a root having a second root radii.
Thus, random sprockets designed principally for noise reduction often cause increases in chain tensions and tension changes as compared to the maximum tensions imparted to the chain by straight sprockets.  For example, a random sprocket design
may reduce chain noise or chain whine by reducing the pitch order of the sprocket.  However, reducing the pitch order of a sprocket may result in redistributing or concentrating the tensional forces imparted to the chain by the sprocket over the lower
orders of the sprocket.  This often results in increased chain tensions corresponding to the lower orders of the random sprocket.
The increased chain tensions at the lower sprocket orders frequently cause the overall maximum chain tension force exerted on the chain and sprocket to increase.  As a consequence, a chain and sprocket system subjected to such tensions typically
will experience greater wear and increased opportunities for failure, as well as others adverse effects, due to the concentration of the tensional forces in the lower orders.
Accordingly, there remains a need for a sprocket design and method of designing sprockets that incorporates the noise reduction properties of random sprockets without the increased maximum chain tensions associated therewith.  In addition, there
is a need for a sprocket design and method for designing sprockets to provide the flexibility to shift tensional forces to different sprocket (or other) orders to enhance the performance, durability, and efficiency of a chain and sprocket system or other
comparable systems.
In accordance with one aspect of the invention, a sprocket is provided that has a root pattern and root radii selected to concentrate the maximum chain tensions at a predetermined order or at multiple predetermined orders relative to the sprocket
rotation or another reference, such as, for example, the rotation of a crankshaft in automatic timing chain applications.  In this aspect, a sprocket is provided that promotes reduced or controlled chain tensions and may also simultaneously reduce chain
In another important aspect, the order or orders of the sprocket having the concentrated chain tensions may be chosen to at least partially cancel or add to corresponding tensions imparted to the chain from sources external to the sprocket.  By
coordinating the maximum tensions imparted to the chain by the sprocket with the maximum or minimum tensions imparted to the chain by sources external to the sprocket, the overall maximum tensions in the system may be reduced or redistributed in a
beneficial way.
In another important aspect of the invention, a sprocket is provided that has a random tooth pattern and root radii that are selected to concentrate the maximum chain tensions at a predetermined order of the sprocket (or other reference).  The
sprocket comprises a plurality of radially extending teeth arranged around the circumference of the sprocket.  Roots are defined between adjacent teeth and have a generally concave or semi-circular profile for engagement with roller or pin connecting
links of the chain.  The roots each have a root radius measured from the center of the sprocket to a point along the root closest to the sprocket center in the radial direction.
In accordance with another aspect of the invention, the tooth pattern of the random sprocket may comprise two or more different root radii between adjacent teeth arranged in a predetermined pattern around the circumference of the sprocket
effective to reduce the sound frequencies generated as the rollers of the chain engage the sprocket teeth and roots, and the overall tension forces in the chain and sprocket system.  In another important aspect of the invention, three different root
radii may be arranged in a pattern around the circumference of the sprocket.  The use of three different root radii to vary the depth of the spaces between adjacent teeth may further reduce the sound frequencies and overall tension forces exerted on the
The root radii pattern according to the sprocket of another aspect of the invention also may be selected to redistribute the first, second, third, and fourth order tensions imparted to the chain by the sprocket to a fourth order of the sprocket
revolution.  In yet another aspect of the invention, a sprocket is provided that reduces chain tensions and chain noise, as compared to typical random sprockets designed principally for noise reduction.
In still another aspect of the invention, the maximum tensions imparted to the chain by the sprocket may be concentrated at the fourth order of the sprocket rotation.  Accordingly, a peak in the chain tension imparted by the sprocket occurs four
times for every rotation of the sprocket.
According to another aspect of the invention, the sprocket may be used in a chain and sprocket system where tension is imparted to the chain from sources external to the sprocket.  When the maximum tensions imparted to the chain from sources
external to the sprocket occur at generally predetermined orders of the sprocket rotation, the arrangement of the sprocket root radii may be selected to at least partially offset, disperse, compensate for, or add to the tensions imparted to the chain
originating from external sources.
In another aspect of the invention, a random sprocket may be comprise a plurality of different pitch radii, as measured from the center of the sprocket to a chain joint when the chain is seated in the sprocket.  The plurality of different pitch
radii may be arranged in a pattern effective to distribute chain tensions at one or more predetermined orders of the sprocket revolution, such as for silent chains wherein teeth of the chain contact teeth of the sprocket.
FIG. 4 is a detail view of section 4--4 of FIG. 3 showing pins of a chain in sprocket roots;
FIG. 7 is a graph comparing the maximum chain tensions of the sprockets of FIGS. 1 3 with the speed of an engine; and
The invention in one important aspect is embodied in a random sprocket for use in an automotive chain and sprocket system, such as used in an engine timing system.  In this aspect of the invention, the sprocket root radii and patterns are
selected, and are effective, to redistribute chain tensions to one or more predetermined orders of the sprocket revolution.  In another important aspect, the random sprocket has a plurality of different root radii arranged in a pattern effective to
reduce tensions imparted to the chain by the sprocket.  In yet another aspect, the root radii and pattern is selected to reduce tensions important to the chain and to reduce noise generated as the chain contacts the sprocket.
FIG. 1 illustrates a typical prior art sprocket 10.  The sprocket 10 has nineteen radially extending teeth 12 disposed about its circumference for engaging links 82 of a chain 80, such as the chain 80 illustrated in FIG. 8.  Such sprockets 10 may
have a variety of sizes, and, for example, may have an outer radius of approximately 3.0915 cm, as measured from the center of the sprocket 10 to tips of the teeth 12.
Sprocket roots 14 are defined between adjacent teeth 12 for receiving pins or rollers 84 that connect the links 82 of the chain 80.  The roots 14 have a generally arcuate profile to facilitate engagement with the pins 84 of the chain.  Each root
14 has a root radius RR, defined as the distance from the center of the sprocket 10 to a point along the root 14 closest to the sprocket center.  In the illustrated sprocket 10, the root radius RR is approximately 2.57685 cm, as measured from the center
of the sprocket 10 to the innermost point along the root 14.  The sprocket 10 of FIG. 1 has all of its root radii RR equal to each other, and is generally known as a &quot;straight&quot; sprocket.  Thus, the depths of each root 12 are the same, as indicated with
reference numeral 1, corresponding to the first (and only) root radius RR for this type of sprocket 10.
Different tensioning events of the chain 80 may be repeated on a periodic basis during each rotation of the sprocket 10.  As mentioned above, the number of times a given tensioning event is repeated in one rotation of the sprocket 10 may be
referred to as an &quot;order&quot; relative to the sprocket 10 rotation.  For example, a tensioning event of the chain 80 that occurs once during each rotation of the sprocket 10 may be termed a first order event, events occurring twice during one sprocket
revolution may be termed second order events, etc.
When the tension in the chain 80 is observed during operation of the system, increases in the tension of the chain 80 may occur at certain orders of the sprocket 10 revolution.  In a straight sprocket, such as the sprocket 10 of FIG. 1, the only
significant peak in the chain tension may occur at the order of the sprocket 10 corresponding to the number of teeth 12 on the sprocket 10, also known as the pitch order as mentioned above.
Thus, a chain rotating about the sprocket 10, having nineteen teeth 12, will have a peak in the tension imparted to the chain 80 by the sprocket at the nineteenth order of the sprocket revolution, or nineteen times for every revolution of the
sprocket 10.  Peaks in the tension imparted to a chain 80 by a sprocket 10 may also be due to other factors besides the number of sprocket teeth 12.  For example, a sprocket 10 that is not rotating about its exact center may impart a tension to the chain
80 at the first sprocket order, or once for every rotation of the sprocket 10, due to the eccentric rotation of the sprocket 10.
In order to reduce noise generated by contact between pins or rollers 84 of a chain 80, and roots 14 and teeth 12 of a sprocket 10, &quot;random&quot; sprockets have been developed with plurality of different root radii.  For example, a random sprocket may
have two different root radii arranged in a predetermined pattern selected to decrease noise.  A random sprocket may also be designed to incorporate three different root radii arranged in a predetermined pattern to further reduce noise generated by
engagement of the chain 80 with the sprocket.  The root radii may vary based on the particular system and sprocket design.
The random sprocket 20 illustrated in FIG. 2 is designed to reduce noise generated by engagement of the chain 80 with the sprocket 20.  The random sprocket 20 is similar to the straight sprocket 10 of FIG. 1, but has three different root radii
R1, R2, and R3 and thus three different root depths 1 3.  In the sprocket 20 illustrated in FIG. 2, the first root radii R1 is approximately 2.54685 cm, the second root radii R2 is approximately 2.57685 cm, and the third root radii R3 is approximately
2.60685 cm, as measured from the center of the sprocket 20 to the innermost points of the roots 24.
The root depths 1 3 are arranged in a pattern selected to modulate the engagement frequency between the pins 84 of the chain 80 and roots 24 between adjacent teeth 22 of the sprocket 20 in order to reduce noise generation.  As the pins 84 of the
chain 80 move between adjacent roots 24 of the sprocket 22, the radial position at which the pins 84 seat varies between a maximum radius, a nominal radius, and a minimum radius.  In the noise reducing sprocket 20 of FIG. 2, the pattern of root 24
depths, beginning at the timing mark T, is 2, 2, 3, 3, 2, 1, 1, 2, 2, 3, 2, 1, 1, 2, 1, 2, 1, 1, 1.
The sprocket 20 was mounted on a shaft and used to drive a chain 80.  A tension measuring device was placed in contact with the chain 80 to measure the tension as the chain 80 was driven by the sprocket 20.  FIG. 5 includes a chart 40 comparing
maximum chain tensions with corresponding orders of the rotation of the shaft on which the random sprocket 20 of FIG. 2 was mounted.  Thus, in this example, the rotational speed of the sprocket 10 is the same as the rotational speed of the shaft, and the
sprocket 20 therefore has the same relative order numbers as the shaft.  If the sprocket under consideration is a driven sprocket, the rotational speed and orders relative to the shaft may differ from the example, depending upon the size of the driven
sprocket and the relative number of rotations the driven sprocket makes compared to the driving sprocket 20.
FIG. 5, in addition, includes a table 42 listing the maximum chain tensions corresponding to the first nineteen orders of the revolution of the shaft and random sprocket 20.  As shown in chart 40 and the table 42, the greatest chain tensions
occur at the sixteenth and nineteenth orders, but the lowest sprocket orders also have relatively high corresponding maximum chain tensions.  For example, the first, second, third, and fourth sprocket orders have corresponding chain tensions which are
considerably greater than the chain tensions occurring at the fifth through thirteenth orders of the sprocket.
Thus, in the random sprocket 20 having three different root radii arranged in pattern selected for noise reduction, illustrated in FIG. 2, the first, second, third, and fourth sprocket orders may impart relatively large tensions to the chain 80
as compared to the remaining sprocket orders.  This increase in chain tensions corresponding to lower sprocket orders may have the undesirable effect of increasing the overall maximum chain tensions, creating an imbalance in chain tensions, and reducing
the overall life of the chain and/or sprockets.
In order to reduce the chain tensions resulting from random sprockets such as in Example 1, the tensions imparted to the chain 80 by a sprocket utilizing one aspect of the invention may be redistributed among select sprocket orders or
concentrated at a predetermined sprocket order.  In this aspect, a plurality of different root radii are used and those root radii are arranged in one or more patterns that are effective to redistribute chain tensions occurring at one or more sprocket
orders to other sprocket orders.  The root radii and patterns also may be selected to reduce chain noise or whine without the disadvantages of random sprockets such as those discussed above and in Example 1.
In this aspect, the sprocket root radii are selected relative to a maximum radius and a minimum root radius as determined from the chain link size and configuration; the chain connecting pin size and spacing; and/or the number of sprocket teeth,
tooth configuration and sprockets size.  The root radii also may be selected relative to a nominal root radius which typically is the mid-point between the maximum and minimum root radii, and often is analogous to the root radii selected for a similar
straight sprocket.
The selection of varying root radii allows for the distribution of the pitch tensions generated by the chain to sprocket tooth/root contact.  It is believed that this is due to the contact of the chain pins (or equivalent chain elements) with the
sprocket teeth/roots at different times and at different tension levels as a result of the varying depths of the sprocket roots.
The root radii further are arranged in a pattern that repeats around the sprocket circumference.  This pattern typically includes one or more sets or multiple, non-uniform or random root radii.  Each set typically includes the same number of root
radii having the same length and arranged in the same order.  Different sets of root radii may have radii of different lengths, number and arrangement.
The use of such patterns of sets of otherwise random root radii repeated along the circumference of the sprocket permits the shifting of those tensions to specific sprocket orders (or other orders based on the applicable reference).  In doing so,
the cumulative effect of shifting the tension forces permits the planned reduction or increase in the amount of chain tension is incorporated to the system by the sprocket at specific sprocket orders (or other reference orders).
The selection of the patterns of non-uniform or random root radii, and the lengths of those radii further permits the use of major and minor patterns or sub-patterns of root radii.  Such major and minor patterns are effective to redistribute the
tensions imparted to the chain (and overall system) to multiple sprocket orders (or other applicable orders) and at different magnitudes.  This provides the additional flexibility in the selection of the sprocket root radii and patterns to offset
multiple tension sources in the system and/or to balance the overall tensions on the chain and sprocket regardless of other sources of the tensional forces.
Moreover, the selection of such root radii and patterns permits the design of a sprocket and chain system that provides reduced levels of chain noise with the proper selection of the root radii within a set of radii, without unduly increasing
overall chain or system tensions.  Similarly, such a design is capable of providing reduced chain noise life and durability of the chain and a balance of tensional forces extending the sprocket system.
The following Example 2 illustrates several important aspects of the invention.  Other variations and applications of the invention also are discussed below.
FIG. 3 illustrates a sprocket 30 according to an aspect of the invention wherein a random sprocket 30 is provided for both redistributing chain tensions at a predetermined sprocket orders and reducing noise generated by engagement of the chain 80
with the sprocket 30.  Similar to the straight sprocket 10 of FIG. 1 and the random sprocket 20 designed principally for noise reduction of FIG. 2, the sprocket 30 has a plurality of radially extending teeth 32 disposed about its circumference for
engaging the pins 84 of the chain 80.  Roots 34 are defined between adjacent teeth 32 for receiving the pins 84 that connect the links 82 of the chain 80.
The sprocket 30 of FIG. 3 has a maximum root radius R3, a nominal root radius R2, and a minimum root radius R1.  As mentioned above, the maximum and minimum root radii are dependent on the link size and pin spacing, the shape of the sprocket
teeth, etc. The root pattern of the sprocket 30 of FIG. 3 is different from the root pattern of the sprocket 20 of FIG. 2.
As illustrated in FIG. 3 was prepared with root radii R1, R2, and R3 of approximately 2.54685 cm, 2.57685 cm, and approximately 2.60685 cm, respectively.  The pattern of root depths, beginning at the timing mark T, is 2, 3, 3, 2, 1, 2, 3, 3, 2,
1, 2, 3, 3, 2, 1, 2, 3, 3, 2.  The root radii pattern of the sprocket 30 contains a sequence, i.e., 2, 3, 3, 2, 1, that is substantially repeated four times around the circumference of the sprocket 30.
Thus, the use of a random pattern of root radii grouped in sets of radii in this example provide a repeating pattern may be used to effectively shift and concentrate the lower order tensions of the chain 80 at the fourth order of the sprocket 30,
thereby reducing the overall maximum tensions imparted to the chain 80 by the sprocket 30.  Such use of a combination of random root radii and repeating root radii patterns that shifts tensions imparted to the chain 80 by the sprocket 30 also provides
benefits in that the overall maximum chain tensions may be reduced, while also reducing chain noise or whine.
As illustrated in FIG. 4, showing a detailed view of a portion of the sprocket 30 of FIG. 3, the sprocket has three different root radii R1, R2, and R3, and thus three different root depths 1 3.  FIG. 4 also shows arcs A1, A2, and A3 through the
centers of chain pins 84 that correspond to the maximum seating radius R3, the minimum seating radius R1 and the nominal seating radius R2.  The different root depths 1 3 are arranged in a pattern about the circumference of the sprocket 30 that is
selected to concentrate the tensions imparted to the chain 80 by the sprocket 30 at a predetermined sprocket order.
The arrangement of the root radii may be selected by substantially repeating the root radii pattern a number of times equal to the sprocket order at which it is desired to concentrate the chain tensions.  For instance, to concentrate the tensions
imparted to the chain 80 by the sprocket 30 of the invention at the fourth sprocket order, the arrangement of the root radii may comprise a pattern that substantially repeats four times around the sprocket 30.
FIG. 6 includes a chart 60, similar to the chart of FIG. 5, comparing the expected maximum chain tensions with corresponding orders of the revolution of a shaft on which the random sprocket 30 is mounted.  Thus, the orders of the sprocket 30
directly correspond to the orders of the shaft.  In a table 62 of FIG. 6, the maximum chain tensions expected to correspond to the first nineteen orders of the sprocket revolution are listed.
As shown in the chart 60 and the table 62, the sprocket 30 of FIG. 3 is expected to have reduced chain tensions corresponding to the lower sprocket orders, as compared to the lower orders of the sprocket 20 of FIG. 2, as shown in chart 52 of FIG.
5.  Unlike the sprocket 20 of FIG. 2 designed only for noise reduction, the sprocket 30 of FIG. 3 is configured to concentrate the maximum chain tensions at the fourth and nineteenth orders of the sprocket revolution, while reducing the maximum chain
tensions corresponding to the lower sprocket orders.
For example, the first, second, and third sprocket orders for the sprocket 30 of FIG. 3 are expected to have corresponding chain tensions reduced by about 76%, 73%, and 30%, respectively, as compared to the sprocket 20 of FIG. 2.  The sprocket 30
redistributes those tensions from the lower orders to the fourth order, which is expected to have a corresponding maximum chain tension nearly 400% larger than the random sprocket 20 of FIG. 2, designed principally for noise reduction.
As mentioned above, the random and repeating root radii pattern can provide the benefit of reducing the overall maximum tensions imparted to the chain 80 by the sprocket 30, while also reducing noise generated by contact between the sprocket 30
and the chain 80.  The expected overall maximum tension reducing effects of the random sprocket 30 of the invention are illustrated in FIG. 7.  The maximum tensions expected to be imparted to a chain by the sprockets 10, 20, and 30 of FIGS. 1 3 are
compared with corresponding engine speeds in FIG. 7.
As illustrated in FIG. 7, the straight sprocket 10 of FIG. 1 imparts significantly lower maximum tensions to the chain 80 throughout the various engine speeds relative to a random sprocket 20 designed only for noise reduction.  In particular, it
is expected that the maximum tensions imparted to the chain 80 by the random sprocket 20, designed principally for noise reduction, are higher near engine speeds of 4000 rpm, while the straight sprocket 10 would impart much lower maximum tensions to the
chain for the same engine speed.
The maximum tensions imparted to the chain 80 by the random sprocket 30 designed for both noise reduction and reduced maximum chain tensions are expected to be significantly lower than for the random sprocket 20 designed principally to reduce
noise.  In fact, the tension reducing sprocket 30 may impart comparable, and in some instances, lower maximum tensions to the chain 80 than the straight sprocket 10 at engine speeds reflected in FIG. 7.  Thus, FIG. 7 illustrates that the improved random
sprocket design 30 of the invention is expected to provide for reduction of maximum overall chain tensions, an effect that is not available with prior random sprocket designs.
Although the fourth order was selected in the aspect of the invention illustrated in FIG. 3, chain tensions may also be concentrated at other orders of the sprocket revolution.  For example, a root radii pattern may be selected that is effective
to concentrate chain tensions at the third order of the sprocket revolution.  Such a pattern may include a root radii sequence that is substantially repeated three times around the circumference of the sprocket.  For example, a root depth pattern for
concentrating chain tensions at the third sprocket order may be 1, 2, 3, 3, 3, 2, 1, 2, 3, 3, 3, 2, 1, 2, 3, 3, 3, 2, 1, where a root depth pattern, i.e., 1, 2, 3, 3, 2, 1, is substantially repeated three times for each revolution of the sprocket.
In addition, the tensions imparted to the chain 80 by the sprocket may be concentrated at more than one sprocket order.  For example, a root radii pattern may be selected that has a major root radii sequence repeating twice for each revolution of
the sprocket and a minor sequence that repeats twice within each major sequence.  Thus, in this aspect of the invention, the major and minor radii are provided by having the minor pattern repeating within the major repeating pattern.  A benefit of having
both major and minor repeating patterns is the ability to further redistribute the sprocket orders at which tensions imparted to the chain 80 by the sprocket occur.
Thus, for every revolution of a sprocket having such a pattern, the major root radii sequence may impart two tensioning events, while the minor root radii sequence may impart four tensioning events.  The tensioning events imparted by the minor
root radii sequence may be of a lesser magnitude than the tensioning events imparted by the major root radii sequence.
Chain tensions, in addition, may be imparted to the chain 80 by various parts of the automotive engine system external to the sprockets, such as the shaft, the pistons, and/or chain tensioners.  Chain tensions further may vary according to the
operating temperature of the system.  For example, when the ambient temperature of the engine decreases, the chain 80 may tend to cool and then contract, resulting in an increased chain tension.  Conversely, when the ambient temperature of the engine
increase, the chain 80 may tent to expand, thereby decreasing the tension in the chain 80.  These external sources may impart tension events to the chain 80 in addition to those imparted to the chain 80 by the sprockets 20 and 30 of the above examples.
These external tensioning events may occur at intervals that correspond to orders of the sprocket revolution.
In order to reduce overall chain tensions in the chain and sprocket system, the tensions imparted to the chain 80 by the improved random and repeating root radii pattern of the invention, such as those of sprocket 30, may be selected to at least
partially offset tensions imposed on the chain 80 by such sources external to the sprocket 30 and chain 80.  In one aspect of the invention, the orders of the sprocket revolution corresponding to peaks in the chain tension due to external sources, as
well as those due to the sprocket 30, are determined.  The sprocket 30 is then configured to concentrate chain tensions at a sprocket order at which the chain tensions due to external sources are at a minimum.  This provides the potential to reduce the
overall tensions in the chain 80, such as may occur if both the chain tension due to the sprocket 30 and the chain tension due to external sources are at their maximums.
In another aspect of the invention, the sprocket 30 is configured to impart maximum tensions to the chain 80 at orders that add to tensions imparted by external sources.  This provides the ability to concentrate the maximum chain tensions due to
both the sprocket 30 and the external sources at a predetermined sprocket order.
For example, when the external tensions occur four times for every rotation of the sprocket 30, the root radii of the sprocket 30 may be arranged to concentrate the maximum tensions imparted to the chain 80 by the sprocket 30 at sprocket orders
phased to at least partially cancel the external tensions imparted to the chain.  In this manner, the external tensions in the chain 80 may be at least partially offset by the sprocket tensions in the chain 80 to reduce the overall tension in the chain
80 and increase the life cycle of both the chain 80 and the sprocket 30.
In another aspect of the invention, the sprocket 30 is configured to impart increased chain tensions at one or more predetermined orders to generate low order tension fluctuations.  The low order fluctuations may be used to help actuate a
variable cam timing unit.
FIG. 8 illustrates a sprocket 100 according to an aspect of the invention for use with a silent chain 90.  The silent chain 90 comprises a plurality of link plates 92, each having one or more teeth 96, pivotable relative to each other about
joints 94.  As the silent chain 90 rotates around the sprocket 100, the teeth 96 of the chain 90 engage teeth 102 of the sprocket 100.  The sprocket 100 has three different pitch radii PR1, PR2, and PR3, as measured from the center of the sprocket 100 to
joints 94 between link plates 92 having teeth 96 seated between teeth 102 of the sprocket 100.  FIG. 8 illustrates arcs PA1, PA2, and PA3 through the centers of chain joints 94 that correspond to the pitch radii R1, R2 and R3.  The pitch radii PR1, PR2,
and PR3 are arranged in a pattern effective to distribute tensions imparted to the chain 90 by the sprocket 100 at one or more predetermined orders of the revolution of the sprocket 100.
From the foregoing, it will be appreciated that the invention provides a method and apparatus for reducing noise generated by the engagement between a chain and a sprocket, while reducing the tensions imparted to the chain by the sprocket.  While
the figures are illustrative of aspects of the invention, the invention is not limited to the aspects illustrated in the figures.  Furthermore, the invention is not limited to the aspects described herein above or to any particular aspects.
Tension-reducing random sprocket, Todd, Kevin B. Todd, Application number 09 993-531, Endless Belt Power Transmission Systems Or Components, sprocket teeth, Patent Application, chain and sprocket, Patent Search, patent applications, Power transmission, BELT POWER, Classification tree, tree browser, Patent Documents
The invention relates generally to a sprocket, and particularly to a sprocket for reducing chain tensions.BACKGROUND OF THE INVENTIONChain and sprocket systems are often used in automotive engine systems to transmit rotational forces between shafts. For example, a sprocket on a driven shaft may be connected via a chain to a sprocket on an idler shaft. In such a chain andsprocket system, rotation of the driven shaft and driven sprocket will cause the rotation of the idler shaft and idler sprocket via the chain. In an automotive engine system, sprockets on the crankshaft may be used, for example, to drive one or more camshaft sprockets.The chains used in chain and sprocket systems typically comprise a plurality of intermeshing link plates connected with pins or rollers. The sprockets typically comprise a circular plate having a plurality of teeth disposed around thecircumference thereof. Located between adjacent teeth are roots having generally arcuate or semi-circular profiles for receiving the pins or rollers of the chain. Each root has a root radius, defined as the distance from the center of the sprocket to apoint on the root closest to the sprocket center.In a "straight" sprocket the root radii are all substantially equal. However, it has been found that as a chain rotates around a straight sprocket, audible sound frequencies creating undesirable noise are often generated as the pins or rollersconnecting the links of the chain contact the sprocket teeth and impact the roots disposed between adjacent teeth of the sprockets.The sound frequencies and volume of such noise typically varies depending on the chain and sprocket designs, chain rotational speed, and other sound or noise sources in the operating environment. In the design of chain and sprocket systems, itcan be desirable to reduce the noise levels generated as the rollers of a chain engage roots of a sprocket."Random" sprockets have been developed to help reduce the radiated noise levels generated b
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