Note: Descriptions are shown in the official language in which they were submitted.
1'~'735~0
This invention relates to belt tensioners
and more particularly to improvements in belt
tensioners of the type employed in serpentine belt
systems for automobile engines and the like.
For many years automobile accessories have
been driven from the output shaft of the engine
through the use of a series of V-belts. The u-sual
arrangement was to provide a V-belt for each
accessory and to provide for the proper tensioning
of the belt by adjustably mountin~ the accessory
with respect to the engine itsel~. In recent years
these multiple V-belt assemblies have been replaced
by a sinqle serpentine belt system. In this system
a so-called poly-V belt is utilized instead of the
traditional V-belt. A poly-V belt is one which is
~uch thinner in cross section and is capable o
heing disposed in driving enqagement with a pulley
in a reverse bend ~ashion, a capability which cannot
be accomplished readily with a V-belt. This
capability makes it possible to utilize a sin~le
endless helt which is capable of transmitting the
drive from one pulley to three, four or more
pulleys. Because this single belt system serves to
drive a plurality of different driven pulleys, it
becomes economically feasible to provide a belt
~73S~O
tensioning pulley for the helt which will serve to
maintain a qenerally constant tension on the belt
and to permit all of the other driven pulleys to be
fixed rather than havin~ an adjustable mount.
The provision of a ~elt tensioning pulley
presents the possibility of malfunction of the
system by virtue of the malfunctionin~ of the
tensionin~ pulley. A typical belt tensioning pulley
assembly includes a fixed structure and a pivoted
structure which is mounted on the fixed structure
for pivotal movement about a first axis. The
pivoted structure carries a belt engaqinq pulley
which is mounted thereon for rotational movement
ahout a second axis parallel to the first axis. A
coil spring is connected betweeen the fixed and
pivoted structure to bias the pivoted structure away
from a first limitin~ position toward a second
limitin~ position.
In normal operation, the pivoted structure
may have vibrational movements imparted thereto
through the belt enaagin~ pulley. These vibrational
movements are reflected in the pivotal mounting of
the pivoted structure on the fixed structure. The
bearin~ which is provided for pivotally mountin~ the
pivoted structure on the fixed structure must
therefore he capable of extended operation without
undue wear. The wear characteristics however are
severely affected by the extent of axial offset of
the pulley with respect to the bearin~ for the
pivoted structure.
The helt load which acts upon the pulley
is transmitted to the roller hearin~ assembly which
mounts the pulley on the pivoted structure. The
be~t load applied to the pivoted structure can be
considered to include a tan~ential force component
~Z~
--3--
which tends to move the pivoted structure about its
pivotal axis and is resisted by the spring of the
belt tensioner assembly. The belt load applied to
the pivoted structure also includes a radially
inward force component and it is this force
component which must be resisted ~y the fixed
structure through the bearing which mounts the
pivoted structure on the fixed structure. This
radially inwardly directed force component is
applied to the pivoted structure at the center line
of the bearing which rota-tably supports the
pulley. Where this force is offset axially from the
axial position of the sleeve bearinq, the latter is
unevenly loaded tending to concentrate the force on
a small area so as to present a poor wear
characteristic. Moreover, as wear increases, the
concentration increases and the mounting will become
auite wobbly and unsatisfactory.
It is an object of the present invention
to alleviate the uneven wear characteristics noted
above so as to prolong the operative life of the
belt tensioning device and, hence, the entire
system. In accordance with the principles of the
present invention, this objective is obtained by
utilizing a frustoconical sleeve bearing as the
bearing means between the pivoted structure and the
fixed structure. The frustoconical sleeve hearing
utilized has a frustoconical exterior surface and a
frustoconical interior surface. The pivoted
structure includes an annular portion having a
frustoconical surface enaaging one of the bearing
frustoconical surfaces for applyin~ the radially
inward force component transmitted to the pivoted
structure to the sleeve bearing. The fixed
structure includes an annular portion havinq a
frustoconical surface engaging the other of the
i2t~3s~0
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bearing frustoconical surfaces for resistin~ the
radially inward force com~onent applied to the
sleeve bearing by the pivoted structure. The
frustoconical surface of one of the annular portions
is formed on the exterior periphery thereof and is
disposed in engagement with the interior bearina
frustoconical surface. The one annular portion has
a load center point disposed on the first axis which
is the axis of pivotal movement of the pivoted
structure with respect to the fixed structure. The
other annular portion has a load center point
disposed on a line disposed within a plane passin~
through the first and second axes corresponding to
the one line of the two lines of intersection of the
bearina frustoconical surface with the plane through
which the radially inward force component
transmitted by the pivoted structure is applied to
the sleeve bearing. The two load center points are
positioned such that the radially inward force
component transmitted by the pivoted structure and
resisted by the fixed structure is transmitted
generally from one load center point to the other
along a line extending between the points which is
perpendicular to and bisects the aforesaid one line
so that the radially inward force component
transmitted by the pivoted structure to the sleeve
bearing is distributed evenly throughout the axial
extent of the sleeve bearing.
The above relationship can be achieved in
situations where the pulley is either co-extensive
with a portion of the sleeve bearinq or has only a
slight amount of offset with respect thereto and the
tensioner assembly does not utilize a radially
inwardly applie~ spring force to achieve damping hy
sliding friction of the bearing as is taught in
commonly assigned U.S. Patent ~o. 4,4731362, ~ -
12~510
In accordance with the principles of the present invention, theutilization of a radially inwardly applied spring force for
damping purposes may also be utilized to e~ualize the bearing
load where the pulley is offset to a considerable extent. In
accordance with the principles of the present invention, the
damping force is provided in such a manner that it has a
significant radially inward force component which acts on the
pivoted structure at a position parallel to the belt load
radially inward force component. Preferably, the damping
radially inward force component is applied at a position so that
it will be transmitted through the sleeve bearing at a position
adjacent the fixed support for the tensioner device. The damping
radially inward force component establishes with the belt load
radially inward force component a combined radially inward force
component which acts in a position between the two radially
inward force components which is proportional to the relative
magnitudes thereof. It is this combined radially inward forced
component which determines the loading of the bearing. In
accordance with the principles of the present invention, the
arrangement is such that the aforesaid load center points are
positioned such that in at least one position of the pivoted
structure between its limiting positions, the combin~d radially
inward force component transmitted by the pivoted structure and
resisted by the fixed structure, is transmitted generally from
one load center point to the other along a line extending between
the points which is perpendicular to and bisects the aforesaid
one line so that the combined radially inward force component
transmitted by the pivoted structure to the sleeve
~2~3S10
--6--
bearinn is distrihuted evenly throuqhout the axial
extent of the sleeve bearing.
Another object of the present invention is
the provision of a helt tensioner of the type
described which is simple in construction, effective
in operation and economical to manufacture.
These and other objects of the present
invention will become more apparent durin~ the
course of the following detailed description and
appended claims.
The invention may ~est he understood with
reference to the accompanying drawings wherein
illustrative e~bodiments are shown.
Figure 1 is a front elevational view of a
serpentine belt system embodying a belt tensioner
constructed in acordance with the principles of the
present invention;
Figure 2 is a front elevational view of
the belt tensioner shown in Figure 1 with the belt
load schematically illustrated as it would be
applied to the pulley axis of the pivoted structure,
the tangential force component and radially inward
force component of the belt load being also
illustrated;
Figure 3 is a sectional view taken along
the line 3-3 of Figure 2 showin~ the application of
the radially inward force component and the
direction which the force is resisted hy the fixed
structure so as to transmit the force component
through the ~earin~ with an even load distri~ution;
Figure 4 is a view similar to Figure 3
illustrating a modified arrangement for pivoting the
pivoted structure on the fixed structure;
1~273510
- 7 -
Figure 5 is a view similar to ~igure 2 illustrating still
another belt tensioner with proportional damping embodying the
principles of the present invention, the belt tensioner being shown
in solid lines in its initial startup position and dotted lines in
its mid or neutral position;
Figure 6 is a sectional Yiew taken along the line 6-6 of
Figure 5 showing schematically both the belt load radially inward
force component and the damping load ~adially inward force component
and the average or combined radially inward force component: -
Figure 7 is a sectional view taken along the line 7-7 of
Figure 5 with the force components illustrated therein.
Referring now more particularly to the drawings, there is
shown in Figure 1 thereof an automotive ~erpentine belt ~ystem,
generally indicated at lO, which includes a relatively large endless
poly-v belt 12, a drivè pulley 14 connected to the output shaft 16 of
the automobile en~ine, four driven pulleys 18, 20, 22 and 24 and a
belt tensioner, generally indicated at 26 which embodies the
principles of the present invention. The system 10, as shown, is
exemplary of the type of system described in the paper entitled
"Serpentine-Extended ~ife Accessory Drive" by R. C. Cassidy et al
given at a meeting of the Society of Automotive Engineers, referred
to as Passenger Car Meeting, at Dearborn, Michigan on June 11 - 15,
1979.
In the arrangement shown, driven pulley 18 may b~
operatively connected with a shaft 28 for a cooling fan, driving
pulley 20 may be mounted on a ~haft 32 which forms a part of an
alternator or the like and driven pulley 24 is mounted on a shaft 34
which forms a part of ~he air conditioning compressor. It will be
understood that
,
.
~273S~.O
the belt 12 is trained about the various pulleys in
the manner indicated in the drawings and the belt
tensioner 26 is mounted in operative relation with
the helt so as to be capable of moving into a
position enabling the ~elt to be mounted on the
other instrumentalities and then released to provide
a desired tension to the belt in normal operative
condition. The belt tensioner 26 also provides for
the application of a substantially constant tension
to the belt 12 of the system 10 over an extended
period of time during which the helt tends to hecome
lon~er. For example, the solid line position of the
belt tensioner illustrates the initial condition of
the belt with the best tensioner 26 in a minimu~
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 particularly to Figures
2-6 of the drawings, the belt tensioner 26 of the
present invention includes a fixed structure 36
which is ada~ted to be secured to a bracket plate 38
or the like in a stationary position with respect to
the engine hlock. The belt tensioner 26 also
includes a pivoted structure 40 which is mounted
with resPeCt to the fixed structure 36 for pivotal
movement about a fixed axis between first and second
limitinq positions. The pivoted structure 40
carries a belt enqaging pulley 42 for rotational
movement about a second axis parallel with the first
fixed axis. As shown, a ball bearinq assembly 44
serves to journal the pulley 42 on the pivoted
structure. A coil spring 46 is mounted between the
fixed structure 36 and pivoted structure 40 for
resiliently biasing the latter to ~ove in a
direction away fro~ the first limitinq position
12735il~ '
~-9 - `
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 26 corresponds
generally with the dotted line position shown in
Figure 1.
In accordance with the principles of the
present invention the pivoted structure 40 is
mounted on the fixed structure 36 for pivotal
movement about the aforesaid first axis by a
frustoconical bearing, generally indicated at 48.
The angular slope of the frustoconical bearing is
chos~en in accordance with the principles hereinafter
enunciated so as to distribute the load transmitted
therethrough from the pivoted structure 40 to the
fixed structure 36 evenly throughout the
longitudinal extent of the bearing.
The fixed structure 36 in the embodiment
shown in Figures 1-3 includes a main casting part
providing a disk shaped mounting portion 50 having a
central annular core portion 52 extending axially
outwardly therefrom. The mounting portion 50 and
core portion 52 are centrally apertured to receive a
mounti~g bolt 54 therethrough which is threadedly
engaged within the bracket 38. Bracket 38 is formed
with a spaced recess for receiving a lug S6 formed
integrally on the bracket engaging surface of the
mountin~ portion S0. The engagement of the lug 56
within the bracket recess serves to locate the fixed
structure in a predetermined angular relationship
with respect to the axis of the bolt 54.
Core portion 52 is formed with a
frustoconical exterior surface 58 which engages an
interior frustoconical surface 60 of the bearing
lZ73S~
--10--
48. While the engagement between the frustoconical
surfaces 58 and 60 may be a sliding engagement,
preferably, the two surfaces are bonded together as
by adhesive, glue or the like. Alternatively,
another preferred construction would be to lock the
two surfaces together by a key and slot
arrangement. For example, the bearing 48 may be
molded with an integral key portion (not shown)
extending inwardly from its interior surface 60 at
an angular position corresponding with the an~ular
position of engagement of the belt 12 with the
pulley 42. This key position would extend
substantially throughout the axial extent of the
bearing and would engage within a corresponding
recess in the surface 58 of the portion 52. The key
portion would have a rectangular cross-section which
may taper to provide an interference type mechanical
lode.
The small end of the frustoconical core
portion 52 defines an outwardly facing shoulder 62
at the end of surface 58 and a deformable free end
portion 64 of square cross-sectional configuration
extends axially outwardly of the shoulder 62. A
circular plate 66 forming a part of the fixed
structure 36 has a correspondinqly shaped central
aperture fitted over the square end portion 64. The
portion 64 is swagged or otherwise deformed over the
exterior surface of the plate 66 to secure its
opposite surface in engagement with shoulder 62.
The inwardly facing outer marginal surface
of the plate 66 engages a damping washer 68 which in
turn, engages a cooperating damping surface 70
formed on the pivoted structure 40. The pivoted
structure 40 includes a central annular portion 72
which is disposed axially inwardly of the surface
lZ735i(:~
70. Annular portion 72 includes an interior
frustoconical surface 74 which engages an exterior
frustoconical surface 76 of the bearing 48.
Coil spring 46 is mounted over the
exterior of the annular porti.on 72 of the pivoted
structure 40 and includes a first bent end 78 which
is positioned to extend outwardly throug`h an openinq
in an outer peripheral wall portion 80 forming an
integral part of the pivoted st.ructure 40 in
outwardly surrounding coaxial relation with respect
to the central portion 72 thereof. The fixed
structure includes a similar integral peripheral
wall portion 82 which likewise is apertured to
receive a second outwardly bent end 84 of the coil
sprinq 46. As shown, the fixed structure 36 also
includes an inner shorter annular wall portion 86
disposed within the adjacent portion of the coil
spring 46.
The pivoted structure 40 includes an
arcuate face portion extending laterally outwardly
with respect to the exterior periphery of the
damping surface 70 which includes spaced ends 88 and
90. A stop tab 92 extends radially from the plate
66 outwardly between the ends 88 and 90. The
connection of the ends 78 and 84 of the spring 46 is
such that the surface of end 88 on the pivoted
structure 40 is biased to engage the adjacent
surface of the stop tab 92 when the pivoted member
has been fully extended into its second limitin~
position. When the spring 46 is stressed to its
maximum extent the surface of end 90 engages the
adjacent surface of stop tab 92 and the pivoted
structure 40 is disposed in its first limiting
position.
~27~ 0
-12-
The pivoted structure 40 also includes a
radially outwardly extending arm portion 94.
Extending axially inwardly from the outer end of the
arm portion 94 is an integral shouldered shaft
portion 96. Ball bearing assembly 44 has its inner
race seated on the shouldered shaft portion 96 and
its outer race seated within the interior periphery
of pulley 42. While pulley 42 may be formed of any
suitable construction, as shown, it is formed of two
circular plates 98 fixed together in face-to-face
abutting relation along their central annular
portions as by rivets 100. The inner annular
portions of the plates are bent outwardly and
downwardly to form the bearing seat and the outer
annular portions are bent outwardly, as indicated at
102, to form the belt engaging periphery.
As shown, the arm portion 94 is formed
with an integral annular wall portion 104 which
extends axially outwardly so that its inner end
overlaps the adjacent side of the bearing seat
portion of the pulley 42. A bearinq shield plate
106, having a similar peripheral wall portion 108
disposed in overlapping relation with the opposite
side of the bearing seat portion of the pulley 42,
is fixed to the shaft portion 96 as by a bolt 110.
~olt 110 is threadedly engaqed within a central
opening extending through th~ shaft portion the
opposite end of which is ormed with a square cross-
sectional configuration, as indicat.ed at 112, to
receive a tool capable of pivotinq the pivoted
structure 40 into its first limiting position
against the bias of spring 46 to facilitate the
initial installation of belt 12 in the system 10.
With reference to Figures 1 and 2, it will
be noted that the mountinq of the spring 46 between
1273S10
-13-
the fixed structure 36 and pivoted structure 40 is
such as to bias the pivoted stucture 40 into a
second limiting position shown in phantom lines in
Figure 1 or in a position wherein end surface 88 on
the pivoted structure 40 engages the adjacent
surface of the stop lug 92 of the fixed structure
36. In assembling the serpentine belt system 10, a
tool (not shown) is inserted within the square
shaped opening 112 and the pivoted structure 40 is
moved in a counterclockwise direction, as viewed in
Figure 2, into a first limiting position wherein the
end surface 90 of the;pivoted structure 40 engages
the adjacent surface of the stop lug 92 of the fixed
structure 36. In this first limitinq position the
belt 12 can be trained about all of the other
pulleys of the serpentine system 10 since the
tensioner is not applying tension to the belt.
After the belt has been installed, the pivoted
structure 40 is released bv manipulation of the
aforesaid tool allowing the spring 46 to bias the
pivoted structure 40 in a clockwise direction, as
viewed in Figure 1 or 2, into a position wherein the
belt is tensioned to a desired load.
The tensioning load of the belt is
transmitted to the tensioner pulley 42 in a
direction which bisects the wrap angle of the belt
with respect to the pulley 42. The belt load force
and the direction in which it acts is illustrated by
the arrow designated by the numeral 114 in Figure
2. The belt load force 114 is transmitted through
the pulley 42 and its bearing assembly 44 to the
pivoted structure 40. The belt tension load 114 as
it is transmitted to the pivoted structure 40 can be
broken down into two force components, (1) a
tangential force component designated by an arrow
116 in Figure 2 which acts at the axis of rotation
~273S1o
-14-
of the pulley 42 in a direction perpendicular to a
line extending from the axis to the pivotal axis of
the pivoted structure 40 and (2) a radially inward
force component designated by the arrow 118 which
acts on the rotational axis of the pulley 42 in a
direction toward the pivotal axis of the pivoted
structure 40. In Figure 3 the radially inward force
component 118 is shown applied to the pivoted
structure 40 at the rotational axis of the pulley 4
in a position symmetrical with respect to the ball
bearing assembly 44. The force component 118 is
transmitted by the pivoted structure 40 to the
frustoconical bearing 48 in an aligned position as
indicated by an arrow 120, shown in Figure 3.
It is noted that Figure 3 is a cross-
sectional view taken along the line 3-3 of Figure 2
which extends through both the rotational axis of
the pulley 42 and the pivotal axis of the pivoted
structure 40. The cross-sectional view illustrated
by Figure 3 is therefore a view of the structure in
a plane passing through both of the aforesaid
axes. It will be noted that this plane intersects
the exterior surface 76 of the frustoconical bearing
48 along two lines. Since the force component 120
is transmitted to the bearing in only one direction,
it is appropriate to designate the application of
that force only along one of the aforesaid two lines
appearing in Figure 3.
In accordance with the principles of the
present invention it is important in order to
achieve a uniform distrihution of the force
component 120 along the axial extent of the
frustoconical bearing 48, to insure that the load
transmittal through the bearing is from the load
center point 122 to a load center point 124 of the
lZ735~ ~
15- :
fixed structure along a force path indicated-by the
double-headed arrow 126 which is perpendicular to
the line on which the point 122 occurs. The point
122 constitutes the axial midpoint of the aforesaid
line on which it occurs. The force component 120
will be distributed evenly along the entire axial
extent of the frustoconical bearing 48 as long as
the above force transmittal relationship exists.
Figure 4 depicts a modification of the
belt tensioner 26, which illustrates essentially a
reversal of the pivotal mount of the pivoted
structure on the fixed structure. As shown, in
Figure 4, the modified belt tensioner is designated
by the numeral 226 and the corresponding parts
thereof are designated by correspondinqly changing
reference numerals. The significantly changed
relationships are that the frustoconical bearing
engaging surface 258 of fixed structure 236
constitutes an interior surface rather than an
exterior surface and the frustoconical bearing
engaging surface 274 of the pivoted structure 240
constitutes an exterior surface rather than an
interior surface. The interior surface 258 of the
fixed structure therefore engages the exterior
frustoconical surface 276,of the bearing 248 and the
exterior surface 274 of the pivoted structure
engages the interior frustoconical surface 260 of
the bearinq 248.
With the reverse mount arrangement as
described above and illustrated in Figure 4, the
force transmittal of the pivoted structure 240 to
the bearing 248 is along the line of bearing surface
260 farthest frorn the pulley 240 rather than
nearest, as before. As before uniform load
transmittal requires that the force component
1~73X10
transmitted by the pivoted structure be app]ied at a
load center 322 which is midway along the line. The
reverse mount also establishes that the center load
point 324 which lies on the pivotal axis of the
pivoted structure 240 to be a load center point of
the pivoted structure rather than the fixed
structure, as before. With the above in mind, the
radially inwardly belt force component 318 is
illustrated as being translated to the load center
324. As before, the double arrow line 326 between
the two center load points 322 and 324 is
perpendicular to the line within which the load
center point 322 is contained.
In connection with the uniform loadinq of
the frustoconical bearing 48 in the manner indicated
above, it is contemplated by the present invention
to manufacture the frustoconical bearing 48 or 248
so that the radius of the surface 76 or 260 in any
given plane within the portions thereof extending
80 on opposite sides of the line on which point 122
or 322 occurs is slightly greater than the radius of
the remaining arcuate extent. A relief of
approximately 0.025 inches is sufficient to
compensate for any expansion that may occur as a
result of temperature changes. Moreover, it will be
understood that the term frustoconical as herein
applied with respect to the bearing 48 or 248
contemplates frustoconical bearings which are
segmental. That is, it is possible to not only
relieve the hearin~ as indicated but to actually cut
off the relieved portion of the bearing, although
this is not preferred.
With both of the arrangements shown,
damping can be provided by virtue of the sliding
friction contact between the surface 74 or 274 of
1273510
the pivoted structure 40 or 240 and the surface 76
or 276 of the frustoconical bearing 48 or 248 as
well as the friction sliding surface contact between
the damping washer 68 or 268 and the surface 70 or
270 of the pivoted structure 40 or 270. In the
embodiments shown in Figures 1-3 and in Figure 4 no
particular arrangement has been provided for varying
the force components effecting the aforesaid sliding
surface frictional contact such as the proportional
arrangement described in U.S. Patent No.
4,473,362. Moreover, it will be noted that since
the frictional contact between the dampin~ washer 68
or 268 and the pivoted structure 40 or 240 is
perpendicular to the force component 120 or 320 the
latter is uneffected by the force components which
act between the damping washer 68 or 268 and the
surface 70 or 270 of the pivoted structure 40 or
240.
Similarly, while the spring load 114
remains generally constant as the operating position
of the belt tensioner 26 moves from the solid line
position shown in Figure 1 to the dotted line
position thereof, the relative magnitudes of the
force components 116 and 118 will change, the
directions in which they act remain the same and
hence the point 122 at which the radially inwardly
component 120 is transmitted to the bearing 48
remains the same. Consequently, with the
arrangement as depicted in Figures 1-3, a force
transmittal presenting an even load distribution to
the bearing 48 is retained throuqhout the operating
extent of the belt tensioner 26. The same is also
true with the reverse mount arrangement of Figure 4.
In this regard, it will be understood that
it would be possible to mount the ends 78 and 80 of
lZ~3510
-18-
the spring 45 in such a way that the damping
provided by the damping washer 68 is significantly
greater than the damping provided by the bearing
48. This could be accomplished, for example, by
choosing the material of the bearing 48 to have a
relatively low coefficient of friction and the
material of the damping washer 68 to have a
relatively high coefficient of friction. Under
these circumstances the operation of the damping
washer 6~ (or 268) would be such that a generally
proportional damping in accordance with the
teachings contained in U.S. Patent No. 4,473,362
could be obtained.
It is preferred, however, to utilize the
proportional damping arrangement depicted in the
aforesaid patent which is achieved by variation in a
radial spring provided damping force component since
this force component may be utilized to help bring
the belt load forces transmitted by the pivoted
structure to the bearing into a more uniform
relationship, especially where the pulley is carried
by the pivoted structure in a more severe offset
relation than that illustrated in Figures 1-4.
Figures 5-7 illustrate a belt tensioner 426 similar
to the belt tensioner 226 except that it embodies a
more severe offset and proportional damping. Here
again, rather than to repeat the description of all
of the construction, corresponding parts are
designated by numerals related as 426 is to 26.
The first hasic difference embodied in the
belt tensioner 426 is that the arm portion 494 of
the pivoted structure 440 is shorter than the arm
portion 40 or 240 and the shouldered shaft portion
296 extends axially outwardly beyond the fixed plate
466. This changed relationship enables the pulley
442 to be mounted entirely in an outwardly axially
1~73S10
--19--
offset relation to the plate 466 of the fixed
structure 436 so that it can lap the same radially
to accommodate the shorter distance bewtween the
pivotal axis of the pivoted structure 440 and the
rotational axis of the pulley 442.
The second basic difference lies in the
manner in which the spring 446 is mounted between
the fixed structure 436 and pivoted structure 440 so
as to achieve proportional damping. The pivoted
structure includes an intermediate tubular wall
portion 526 disposed between the outer peripheral
wall portion 480 and the central frustoconical
portion 472. The intermediate tubular portion 526
extends almost entirely within all the coils or
volutes of the spring coil spring 446 so that its
free end is disposed closely adjacent the mounting
portion 450 of the fixed .structure 436. Disposed in
surrounding abutting relation to the free end of the
intermediate tubular portion 526 is an annular
spring support, generally indicated at 528. Spring
support 528 is in the form of a ring of L-shaped
cross-section including a cylindrical leg portion
530 which is engaged interiorly by the free end of
the intermediate tubular portion 526 and exteriorly
by the first coil or volute of the spring 446
extending from the end 478 thereof disposed within
the aperture in the wall portion 482 of the fixed
structure 436. The spring support 528 also includes
a leg portion 532 extending radially outwardly from
the leg portion 530 in a position to engage between
the mounting portion 450 of the fixed structure 436
and the aforesaid first coil of the spring 446.
The arrangement of the spring support 528
is such that the tensioning of the spring 446
applies a radially inward force component to the leg
~273510
-20-
portion 530 of the spring support. This force
component is illustrated in Figure 6 as an arrow 534
and it will be noted that it is transmitted from the
spring support to the free end of the intermediate
tubular portion 526 of the pivoted structure at an
axial position which bisects the adjacent volute and
the leg portion 530. This axially inwardly directed
force component 534 is applied to the pivoted
structure 440 at a position closely adjacent the
support 438 for the fixed structure 436.
The belt tension load which is represented
by the force arrow 514 in Figure 5 can be considered
transmitted to the pivoted structure 440 with a
tangential force component 516 and a radially inward
force component 518. As best shown in Figure 6, the
radially inward force component acts on the pivoted
structure at a position axially offset from the
axial extent of the bearing 448. The two radially
inwardly directed force components 518 and 534 which
act upon the pivoted structure 440 at different
locations can be represented by a combined force
component represented by the arrow 536 in Figure
6. As shown in Figure 6, the combined radially
inward force component 536 has a magnitude equal to
the combined magnitudes of the force components 518
and 534. The position at which the combined force
component 536 acts is inbetween the two force
components 518 and 534 at a position which is
determined by the proportion of their ma~nitudes.
As shown, the combined force component 536 when
translated to the pivotal axis of the pivoted
structure 440 is spaced axially inwardly from the
load center point 524. The force component
application shown in Figure 6 corresponds with the
operating position of the belt tensioner 426 when
the same is initially installed in the system 10.
3~10
-21-
With reference to Figure 1, the belt tensioner 426
would replace the belt tensioner 26 shown therein
and the position of the unit, shown in solid lines
in Figure 5 and in Figure 6, coresponds with the
solid line showing of Figure l. It is noted,
however, that the uniform bearing load relationship
wherein the radially inward force component acts at
the center load point 524 and in the direction of
the double arrowed line 526 to the load point 522 of
the frustoconical bearing 448 does not quite hold
true.
Figure 7 illustrates a situation where
this uniform loading does occur and it represents an
operating position of the belt tensioner 426 which
is near the mid-point between the irst and second
limiting positions thereof, a posil:ion which is
slightly beyond the initial operating position in a
direction toward the second limitinq position. This
mid position is illustrated in phantom lines in
Figure 5 and it will be noted that the belt load
force represented by the force arrow 538 is applied
in generally the same direction to the pulley 442
with a generally similar magnitude as the belt load
514. However, because of the changed position of
the axls of rotation of the pulley, the tangential
force component 540 acting on the pivoted structure
440 is of a reduced magnitude as compared;with the
tangential force component 516. This reduction in
the tangential force component is commensurate with
the reduction in the spring force component which
opposes it due to the slightly extended position of
the spring 446. By the same token, the radially
inward force component represented by the arrow 542
has increased in magnitude compared with the force
component 518. The radially inward force component
of the constant belt load thus increases throughout
:~Z735~0
-22-
the operative range of the movement of the belt
tensioner as the pulley 442 thereof moves away from
its first limiting position toward its second
limiting position. In contrast, because the spring
446 is extending and the damping force applied
thereby is diminishing the radially inwardly
directed spring damping force component 534
descreases as the pivoted structure 440 moves toward
its second limiting position.
In Figure 7, the radially inwardly
directed spring damping force component is
represented by a force arrow 544 which is of reduced
magnitude in comparison with the force component 534
and yet acts in exactly the same position. Still
with reference to Figure 7, it can be seen that when
the reduced damping force component 544 is combined
with the increased belt load force component 542,
the resultant combined force component 546 now acts
in a position intermediate the position in which the
~wo force components act which coincides with the
load center point 522 when translated to the pivotal
axis of the pivoted structure 440.
It can thus be seen that the uniform load
relationship depicted in Figure 7 is a relationship
which will be achieved only at one operating
position of the belt tensioner 426. While it is
within the contemplation of the present invention to
have this one position occur in any desired
operating position, the position chosen is
preferred since it is closer to the initial
operating position than the final operating position
or second limiting position. In the normal
operating life of the belt tensioner 426, the same
will operate at a substantially greater period of
time during its life at a position near the initial
lZ73~10
-23- :
operating position than at the final operating
position. While the arrangement as depicted in
Figures 5-7 does not provide for uniform loading
throughout the operating life of the bearing 448, it
does provide for uniform loading at one position
which occurs for an extended period of time
throughout the total lifetime period. Moreover, a
substantial uniform loading situation, such as
indicated in Figure 6, will occur through
substantially the entire operating life of the belt
tensioner. The arrangement is clearly preferable in
a severe pulley offset situation, to the severe non
uniform loading which would occur when only the belt
load radially inward force component is transmitted
through the bearing.
It thus will be seen that the objects of
this invention have been fully and effectively
accomplished. It will be realized, however, that
the foregoing preferred specific embodiment has 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.
