Note: Descriptions are shown in the official language in which they were submitted.
~2S~3782
BELT TENSIONING DEVICE WIT~
CONSTANT OR VARIABLY PROPORTIONAL DAMPING
This invention relates to belt drive systém~ and more
particularly to improvements in belt tensioners u~ilized in belt
drive systems.
For many years, the automotive industry has used
multiple individual V-belts to drive various rotary devices by
the engine. Such a system of belt driven peripheral devices
typically required the use of a pulley on the engine output shaft
to separately receive multiple V-belts. Each separate V-belt was
then mounted on the pulley and adjusted to drive a single, or in
exceptional cases, two or more rotary devices. Each V belt was
adjusted-and tightened by use of- the adjustable mount of the
peripheral device. A problem arose with this type of system in
that the replacement and adjustment of a belt was very time
consuming and costly.
To help resolve this problem and to gain a generally
more compact peripheral drive system, it has been found desirable
to replace the typical multiple belt system with a system
employing a single belt arranqed in a serpetine fashion to drive
all of the various rotary devices previously driven by separate
belts. Adjustment of such a belt system would not be made by
adjusting the mounts of individual peripheral devices, but
instead a separate belt tensioning device might be commonly
employed to function as an adjustment apparatus.
While belt tensioners have been used in many belt
systems heretofore, the functional requirements placed upon belt
tensioners used in serpetine single belt automotive systems are
particularly stringent. The greater demands placed on a
vehicular belt tensioner are due to the relatively great belt
length and concomitant required take-up capacity. The belt
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tensioner is further sub~ected to operation over an extensive
period of use in which great vibrational loads are imposed.
Damping requirements are essential in order to enable
the system to function over an extended period on a pulsating
macnine without creating resonance. Where an air conditioning
compressor constitutes one of the rotary devices of the system, a
particularly onerous pulsating load is imposed upon the system a~
the compressor operates, and cuts in and out of operation.
The belt tensioner must also compensate for increases in
bèlt length due to wear and other factors. A typical belt
tensioner employs a fixed structure and a pivoted structure in
the form of an arm carrying a belt engaging pulley. A coil
spring biases the pivoted structure toward a position of maximum
take-up so that the spring biasing force decreases as the pivoted
structure moves from the position of minimum take-up to a
position of maximum take-up. Even though the spring force varies
within the ran~e of movement of the pivoted arm, a substantially
constant belt tension is maintained.
In addition to the belt take-up function of the belt
tensioner, the tensioner must also dampen the belt system to
eliminate harmonic spring vibration. Solid elastomeric bodie~
may be used to provide the sprinq force of a belt tensioner (e.g.
U.S. Patent Nos. 3,975,965 and 4,144,722~ causing greater damping
which is inherently provided by such springs as compared to
springs commonly made from steel.
In Thomey et al (U.S. Patent No. 4l473,362), a belt
tensioner with variably proportional damping was described. The
belt tensioner was a steel torsional spring type tensioner
employing twin coils. A separate dampening mechanism was provided
having damping characteristics that are not constant but vary
proportionately with the position of the pivoted structure with
respect to the fixed structure in a manner similar to a spring
force. However, the amount of frictional variability and
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flexability in fine adjustment of this assembly is relatively
limited.
An object of the present invention is to provide a belt
tènsioning device with a damping mechanism that~enables high
flexibility in adjusting damping characteristics of a belt
tensioner to satisfy damping requirements imposed by specific
operational conditions.
The present invention comprises a belt tensioning device
having a fixed structure, a pivoted structure mounted with
respect to the fixed structure for pivotal movement about a first
axis between first and second limiting positions, a belt engaging
pulley rotatably carried by the pivoted structure for rotational
movement about a rotatational axis parallel with the pivotal
axis, a spring act;ng between the fixed and pivoted structures
or resiliently biasing the'pivoted structure to move in a
direction away from the first limiting position toward the second
limiting position so as to tension a belt engaged by the pulley,
and a damping mechanism for damping the pivotal movements of the
pivoted structure about the pivotal axis; the improvement which
comprises the damping mechanism includes: 1) a stack of damping
elements having interengaging pairs of surfaces disposed
transversely with respect to the pivotal axis so as to be
slidable with respect to one another in spaced planes of
revolution about the pivotal axis; 2) the stack including a f irst
plurality of damping elements and a second plurality of damping
elements which are disposed within the stack in alternate
positions with respect to the damping elements of the first
plurality; 3) a mechanism for connecting the first plurality of
damping elements with the fixed structure, (a) against movement
in the rotational planes of the interengaging surfaces thereof
and (b) for movement relative to one another in the axial
direction of the pivotal axis; 4) a mechanism for connecting the
second plurality of damping elements (a) for movement with the
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pivoted structure about the pivotal axis so that the
interengaging surfaces thereof will move in the rotational planes
thereof with the pivoted structure and (b) for movement relative
to one another in the axial direction of the pivotal axis; and
5) a mechanism for supporting one end element of the stack
against movement in an axial direction away from the stack so
that an axial force component acting in the direction applied to
the opposite end element of the stack will cause the pairs of
interengaging surfaces of the stack elements to move together and
create a predetermined sliding friction therebetween when the
pivoted structure is moved with respect to the fixed structure
about the pivotal axis so as to provide a predetermined damping
of such movement.
In accordance with the principles of the present
invention the objective of providing a damping mechanism with
highly flexible adjustment, is obtained by providing at least a
major part of the damping of the belt tensioning device by means
of a separate damping mechanism which employs a number of
frictionally slidable elements which upon application of a
compression force increases friction between the elements and
thereby creates an increased damping effect. The compression
force may be constant or may be variably proportional to the
pivot movement of the belt tensioner arm. Where the nvrmal
operating characteristics of the system are such that a
relatively high amount of damping is req~ired and the vibrational
amplitudes encountered are relatively low, it. is desirable to
form the damping elements of an elastomeric material or other
high friction material. Such a material may provide a high
degree of internal deformation with an attendant high degree of
solid damping. These characteristics combine to perform
sequential actions which are desirable in a system having high
frequency - low amplitude vibrational characteristics. The
damping elements may be composed of different materials which may
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be mixed to provide a spectrum of damping characteristicS. At
the low friction end of the dampening material spectrum, a low
friction material such as Zytel or metal may be used when the
belt tensioning system does not require a large amount of damping
but nevertheless requires damping of high am~litudes. In such a
situation little internal deformation would occur but
substantially all of the damping requirements would be met by
sliding friction. Where a system presents both high frequency
and high amplitude conditions, damping elements havinq a
predominantly sliding friction damping action is preferred
because solid damping-sliding friction damping as with an
elastomeric material results in more rapid wear which is
exacerbated by excess heat conditions.
The flexibility of adjusting damping characteristics by
providing frictionally slidable elements is enhanced by not only
the ability to use slidable elements composed of material~ having
different coefficients of friction as describea above, but
elements of varying thicknesses as well. The amount of surface
area of each damping element is generally relatively large
compared to the thickness of the element. This feature enables
each element to have a significant damping effect. Varying the
thickness of the damping elements varies the surface area which
in turn alters the amount of surface friction and resulting
damping effect. Thicker elements which are formed from
elastomeric materials may dampen by internal deformation.
Another object of the present invention is to provide a
belt tensioning device of the type described which is simple in
construction, economical to manufacture and e~fective in
operation.
These and other objects of the present invention will
become more apparent during the course of the following detailed
description and appended claims.
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The invention may best be understood with reference to
the accompanying drawings, wherein two illustrative embodiments
are shown.
. . .
BRIEF DESCRIPTION OF THE DRAWINGS
.
FIG. 1 is a front elevational view of an automotive
serpentine belt system embodying a belt tensioning device
constructed in accordance with the principals of.the present
invention:
FIG. 2 is a cross-sectional view of a first embodiment
taken along the line 2-2 of FIG. l;
-
FIG. 3 is a cross-sectional view of the pivoted and
fixed structures of the first embodiment taken along the line A-A
of FIG. 2;
FIG. 4 is a cross-sectional view of a dampening body o~
the first embodiment taken along the line B-B of FIG. 2;
FIG. 5 is a cross-sectional view of a second embodiment
taken along the line 2-2 of FIG. l; and
FIG. 6 is a cross-sectional view of a dampening body of
: a second embodiment-taken along the line 4-4 of FIG. 3.
DET~ILED DESCRIPTION OF THE DRAWINGS
_ _ _ _
Referring now more particularly to the drawings, there
is shown in FIG. 1, an automotive serpentine belt system,
generally indicated at 20, which includes a relatively large
endless poly-v belt 22, a drive pulley 24 connected to the output
shaft 26 of the automobile engine, four driven pulleys 28, 30, 32
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and 34 and a belt tensioner generally indicated at 36 which
embodies the principals of the present invention. The system 20
as shown is exemplary of the type of system described in the
previously identified patent, Thomey et al. (U.S. Patent No.
4,473,362). In the arrangement shown in FIG. 1, driven pulley 28
may be operatively connected with a shaft 38 for a cooling fan,
driven pulley 30 may be mounted on a shaft 42 which forms a part
of an alternator or the like, and driven pulley 34 is mounted on
a shaft 44 which forms a part of an air conditioning
compressor. It will be understood that the belt 22 is trained
about the various pulleys in the manner indicated in the drawings
and the belt tensioner 36 is mounted in operatlve relation with
the belt so as to be capable of moving into a position enabling
the belt to be mounted on the other rotary devices and then
release to provide a desired tension to the belt in normal
operative condition. The belt tensioner 36 also provides the
application of a substantially constant tension to the belt ~2 of
the system 20 over an extended period of time during which the
belt tends to become longer. For example, the solid line
position of the belt tensioner illustrates the initial condition
o the belt with the belt tensioner 36 in a minimum belt take-up
position whereas the dotted line position illustrates a maximum
belt take-up position which may occur after extended use and the
belt has been elongated.
Referring now more particular to FIG. 2 of the drawings
the belt tensioner 36 includes a bracket plate 110 which is
secured in a stationary position with respect to the engine
block. The belt tensioner also includes a pivoted structure 140
which is mounted with respect to the bracket plate 110 for a
pivotal movement about a fixed axis between the first and second
limiting positions. The pivoted structure 140 carries a belt
engaging pulley 142 for rotational movement about a second axis
parallel with the first axis. The pulley 142 may ~or example, be
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formed from mild steel sheet metal. The free end of the arm
portion 178 of the pivoted structure 140 has a bolt shaft 180
which the pulley 142 is journalled, as by a ball bearing 182 or
the like. The arm 178 may for example, be formed from die cast
aluminium. A coil spring 144 is mounted between the fixed
bracket plate 110 and pivoted structure 140 for resiliently
biasing the latter to move in a direction away from the first
limiting position toward the second limiting position with a
spring force which decreases as the pivoted structure is moved in
a direction away from the first position toward the second
position. The coil spring 144 may for example be formed from
0.250 inch to 0.285 inch diameter spring steel. The second
position of the belt tensioner 36 corresponds generally with the
dotted line position shown in FIG. 1.
In accordance with the principals of the present
invention, belt tensioner 36 also includes a damping mechanism,
generally indicated at 56, which serves in operation to provide
damping by a damping force which decreases as the pivoted
structure 140 is moved in a direction away from its first
position toward the second position thereof. The damping
mechanism 56 is shown to consist of a plurality of damping
elements 212 which for example may be of a disk shape. The
damping elements are frictionally slidable with one another and
include a first plurality thereof, having elements attached
alternately, respectively, to the outer housing 220 and interior
shaft 215 by peripheral means for engagement including splines,
which are fixed for example by complementary splines formed in
the housing 220 and interior shaftO The damping element~ 212 may
also be alternately fixed interiorally by circular or elongated
holes or arms fixed by rigid perpendicular pins (not shown) to at
least one of the damping body retaining ring 225 and interior
support member 230 of the spring housing structure 220. The
damping body retaining ring 225 is rigidly fixed to an interior
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tlxed shaft 215 which is in turn rigidly fixed to the ~ixed
bracket plate 110. The interior shaft 215 has a central opening
230 which is a threaded or thru hole, for receiving a bolt or the
like for fastening the tensioning device 36 fro~ either side to
an engine mount or the like. A tang or hole (not shown) in
retaining ring 225 or bracket 110 is provided to ensure positive
location and prevent rotation of the tensioner 36. The interior
shaft 215 may for exam~le be formed from a steel forging integral
with the retaining ring 225, or the shaft 215 and retaining ring
225 may be securely "staked" or welded together. At the axial
periphery of the interior shaft 215 are bearings 240 separated by
a bearing spacer 245. The bearings 240, may for example be two
steel needle bearings or a combination of one needle bearing and
one nylon (Zytel) bearinq. The bearing spacer 245 may for
example be a carbon steel sleeve. The spring housing 220 rotates
about the interior shaft 215 using the bearings 240 to reduce
friction therebetween. When the pivoted structure 140 is moved
to a second position the spring 144 tightens and axially
contracts to consequently elongate the spring. Thus, where a
first end 250 of the spring presses against the fixed bracket
plate 110 and the second end 255 of the spring presses against
the interior support member 230 of the housing, the interior
support member 230 in turn presses against the stack of damping
elements 212 compressing them and upon sufficient pivoting action
causing the damping elements to frictionally slide upon one
another causing a damping of the pivoting movement. As the
pivoting movement of the pivoted structure 140 becomes greater,
the contraction and consequent elongation of the spring 144
becomes proportionately greater causinq proportionately greater
compression of the damping elements 212. Thus, in the embodiment
oE the present invention shown in FIG. 2 the damping effect on
the pivoting movement is variably proportional to the amount of
pivoting movement by the pivoted structure 140.
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In the damping body 56, the damping elements 212 may
have one alternately fixed set of elements composed of one
material and the second set of alternately fixed elements
composed of a second material or any combination of materials in
both sets of dampening elements. Of the damping elements 212,
one set of alternately fixed damping elements may be of one
thickness and the second set of alternately fixed elements may be
of a second thickness. The damping elements 212 may be of
diEerent thicknesses throughout the stack of said elements. The
chosen materials and thickness of the damping elements 212 are
selected in accordance with the principals of the present
invention to suit the vibrational and pivotal movement
characteristics of the system within which the belt tensioner 36
~s used. When the system provides high frequency low amplitude
vibrations it is preferable to employ an elastomeric material
such as, elastomeric urethane, for example Type II Black
urethane. While the durometer value of the urethane may vary, an
exemplary durometer value is 90. Where an elastomeric material
is employed and the damping elements are sufficiently thick, the
operation of the damping body 56 is such as to provide two
different sequential damping actions: first, a solid damping
action or internal material displacement damping action: and
second, a sliding friction damping action. The two types of
damping actions ta~e place sequentially in that solid da~ping
only occurs where the amplitude of the vibration is below a
threshold amplitude, while sliding friction dampiny will occur
only after the threshold amplitude has been reached. It is
important to note that the sliding friction damping action varies
proportionately as aforesaid and that the threshold amplitude
likewise varies proportionately.
Where the system has relatively low frequency but high
amplitude vibrational characteristics, a preferred material for
the damping elements 212 is Zytel 103HSL (nylon made by
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DuPont) Where Zytel is utilized as the material for the damping
-elements 212, the damping action provided is essentially all
sliding friction damping with the amount of solid damping by
internal displacement being relatively insignificantly.
Alternatively, it may be considered that there is some sequential
solid dampening action provided but with a threshold amplitude
very close to zero. Since the operation with the elastomeric
urethane material includes both the same type of operation as the
Zytel material plus another type of operation in se~uence
therebefore, the prior description oE the operation with urethane
should suffice to give an understanding of both.
Where the system has both high frequency and high
amplitude vibrational characteristics, the Zytel material is
preferred over the elastomeric urethane material, although the
provision of other damping means within the system sufficient to
reduce either the frequency or amplitude, may be in order. For
example, it may be desirable to utilize a pulley having an
elastomeric hub either on the main engine drive shaft or the
compressor shaft or both. Note that in using non-ela~tomeric
materials that the combination of damping elements may be for
example of steel and Zytel, steel and bronze, steel and fiber or
many other materials. Note also that friction produced by the
damping body may be increased or decreased by the number o~
damping elements used in the damping body 56.
FIG. 3 shows by another cross-sectional view oE the
first embodiment, the pivoted structure 140,;with the pully 142
at one end. The pulley 142 is mounted on the bolt shaft 180 and
is journalled by ball bearings 182. The pivoted structure 140 is
connected to the housing 220. The damping mechanism is shown
generally at 56 with damping elements 212 having one plurality of
damping elements attached by splines 500 to the outer housing 220
in alternate fashion with a second plurality of damping elements
Eixed interiorly by splines 505 to the interior shaft 215.
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~ IG. 4 is a cross-sectional view of the first embodiment
showing the coil spring 144 which biases the pivoted structure
140 (see FIG. 2 and 3). The coil spring 144 is within an outer
housing 220, and surrounds the interior shaft 215.
In a second embodiment of the present invention shown in
FIG. 5 the damping of pivotal movement is constant rather than
variably proportionate which was the case in the first embodiment
of the present invention. As shown in FIG. 5 of the drawings,
the belt tensioner 436 includes a fixed bracket plate 438 in a
stationary position with respect to the engine block. The belt
tensioner also includes a pivoted structure 440 which i5 mounted
with respect to the fixed bracket plate 438 and associated
structures for a pivotal movement about a fixed axis between the
first and second limiting positions. The pivoted structure 440
carries a belt engaging pulley 442 for rotational movement about
a second axis parallel with the first axis. A coil spring 444 is
mounted between the fixed bracket plate 438 and pivoted structure
440 for resilîently biasing the latter to move in a direction
away from the first limiting position thereof toward the second
limiting position with a spring force which decreases as the
pivoted structure is moved in a direction away from the first
position toward the second position. The second position of the
belt tensioner 436 corresponds generally with the dotted line
position shown in FIG. 1.
In accordance with the principals of the present
invention, the belt tensioner 436 also includes a damping body
generally located at 456 which serves in operation to provide
damping by a damping force which is constant.
The arm 478 connected to the pivoted structure 440 forms
an integral part of the spring housing 420. The spring 444 may
for example, be a torsion spring. The spring housing 420 is an
integral part of the damping body housing 460. The pivoting arm
478, spring housing 420, and damping body housing 460 all rotate
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and pivot about a center shaft 415 which is rigidly connected to
the ~ixed bracket plate 438. The center shaft 415 may for
example, be formed from steel, or cast as one piece with the
fixed bracket plate 438 and hard anodized. ~he pivoted
structured 440 which ultimately rotates and pivots about the
center shaft 415 has a sleeve type bearing 465 which may for
example, be a Garlock bearing and for example, be formed of steel
backed with teflon, lead, brass or the like.
The damping body 456 includes two sets of ~rictionally
slidable elements 412 each set of which has the dampinq elements
412 alternately fixed. A first set of damping elements is fixed
to the pivoted structure 440 via the pivoted arm structure 478
and a second set of damping elements is fixed to the fixed
bracket plate structure 438. The peripheral means for engagement
include ~or example, splines fixed by complementary splineq. The
damping elements may also be ixed by interior means including
for example, circular or elongated holes, or arms, fixed by rigid
perpendicular pins (not shown). The first set of damping
elements may be composed of one material and the second set of
damping elements may be composed of a second material; or the
damping elements may be of different materials throughout the
damping body 456. The damping elements may be made from
materials including for example, nylon, steel, bronze or fiber.
One set of damping elements may be of one thickness and the
second set of damping elements may be of a second thickness, or
the damping elements may be of different thicknesses throughout
the damping body 456. Constant pressure is applied to the
damping elements by means of a spring 480 which may be or
example, a Bellville washer or symmetrically disposed coil
springs.
The spring 444 operates to keep the pivoted structure
440 in a tensioned state and upon the application of a stress on
the pivoted structure 440, the spring 444 contracts to create
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greater spring force on the pivoted structure 440. The damping
body spring 480 applies a constant pressure to the damping
elements providing a constant damping force on the pivoted
structure 440. The interaction of the damping elements where the
damping elements are made of a high frictlon material such as
elastomeric urethane or a low friction material such as Zytel has
been previously discussed with regard to the first embodimént of
the present invention. The utilization of a damping body which
uses a stack of frictionally slidable elements is highly flexible
by enabling fine adjustment of damping the pivoted structure 440
under various system operational circumstances.
FIG. 6 shows a cross-sectional of, generally, the
damping body 456, including damping elements 412. The damping
elements 412 include a first plurality fixed by splines 600 to
the pivoted arm structure 478. A second plurality of damping
elements 412 is shown to be fixed by splines 605, interiorly, to
the fixed bracket plate structure 438. A spring 480 applies
constant pressure to the damping elements 412 to provide a
~rictional force.
While the present invention has been described in
relation to the above exemplary embodiments it will be understood
that various modifications may be made within the spirit and
scope of the invention. While the objects of the present
invention have been fully and effectively accomplished, it will
be realized, however, that the foregoing exemplary embodiments
have been shown and described for the purpose of illustrating the
functional and structural principles of this invention and is
subject to change without departure from such principles.
Therefore, this invention includes all modifications encompassed
within the spirit and scope of the following claims.
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