Note: Descriptions are shown in the official language in which they were submitted.
~'~t32266
BELT TENSIONER
TECHNICAL FIELD
This invention relates to belt tensioning devices and in
particular to spring biased belt tensioner for use with
endless drive belts of the drive system for vehicle acces-
sories. More particularly, the invention relates to a simple
and inexpensive belt tensioner operated by a torsional spring
in which an improved damping ring reduces undesirable
vibration by retarding movement of the pulley mounting lever
by using one end of the spring as a lever arm which moves
about a fulcrum to move the damping ring into frictional
engagement with a stationary mounting bracket.
BACKGROUND ART
There is a trend today in the automobile industry to
operate the various vehicle accessories, such as the power
steering pump, oil and air pumps, air conditioning and alter-
nator, by a single endless belt driven by a pulley connected
to the engine crankshaft. This system is referred to as a
"serpentine" drive belt system. To ensure optimum operating
efficiency for these various accessories, it is necessary
that the driven belt be maintained at a predetermined tension
to assure efficient performance of the accessories as well as
satisfactory service life for the belt. Due to the relative-
ly greater length for the single drive belt which replaces
the heretofore plurality of smaller belts, there is a greater
tendency for the belt to stretch which will affect the
operating characteristics of the driven accessories.
Therefore, it is desirable that a belt tensioning device be
used for these endless belts to provide reliable service over
an extended period of time and to maintain a constant amount
of tension on the belt regardless of the amount of belt
stretch.
Numerous devices have been proposed and used to ac-
.
1'~8`~266
complish this purpose. One type of tensioner uses a bushingformed of an elastomeric material which is placed in compres-
sion by some mechanical means for continuously exerting a
tensioning force on the belt. Examples of these construc-
tions are shown in U. S. Patent Numbers 3,975,965 and
4,144,772. These tensioning constructions have the disad-
vantage that the bushing must serve as the spring, provide
the required damping and also maintain the alignment of the
arm and all of these functions are therefore compromised.
The spring rate compromise results in belt tensioner varia-
tion and the damping compromise results in a lack of motion
control. Also, the bushing softness allows the arm to
deflect resulting in less alignment control of the arm and
pulley.
Numerous other types of belt tensioning devices use coil
springs which are either in compression or tension, for
applying and maintaining the tensioning force on a belt-
engaging idler pulley or chain-engaging sprocket. Some
examples of these types of constructions are shown in U.S.
Patent Numbers 2,703,019; 2,893,255; 3,413,866; 3,483,763;
3,631,734; 3,768,324; 3,812,733; 3,924,483; 3,965,768 and
4,108,013. Some of these various coil spring-actuated
devices use the biasing force of a spring in combination with
hydraulic-actuated members for regulating the amount of
tensioning force applied to the belt, depending on whether
the engine is running or shut off. Examples of these
combination spring and hydraulic belt tensioners are shown in
U.S. Patent Numbers 2,051,488; 3,142,193; and 4,077,272.
Other known belt tensioner constructions, such as shown
in U.S. Patent Number 3,924,483, use a torsional spring for
pivotally moving one of the vehicle accessories to achieve
the desired tensioning force. Other constructions, such as
shown in U.S. Patent Numbers 3,136,170; 3,483,763;
3,834,246; and 4,285,676, use a torsional coil spring for
pivotally moving a lever and idler pulley into belt tension-
266
ing engagement which provides a relatively simple, economicaland compact unit. U.S. Patent Number 4,473,362 shows still
another belt tensioner which uses a torsional coil spring to
provide a variable damping force by applying the radial
forces exerted by the volutes of the spring against an
internal elastomeric bushing.
It is desirable that a belt tensioner be provided with
some type of damping means to prevent excessive oscillation
from occurring in the spring tensioning member, and which
will absorb sudden shocks to prevent a whipping action from
occurring in the tensioner and drive belt. This damping
action is especially critical when a coil spring is used for
applying the belt tensioning force since coil springs are
highly susceptible to developing natural oscillating frequen-
cies when the counter force, which is exerted thereon by thebelt, fluctuates during acceleration action. Such fluctua-
tions effect the efficiency of the tensioning force applied
to the belt by the coil spring and reduces belt life.
Various damping devices have been used with belt
tensioners to eliminate or reduce this problem of coil spring
oscillation. One type of construction uses a hydraulic fluid
as the damping means, such as shown in U.S. Patent Numbers
2,893,255; 3,964,311 and 3,986,407. U.S. Patent Number
3,710,634 shows a belt tensioner which uses an eccentrically
mounted mechanical pinion and rack arrangement which is
spring biased by a leaf spring for absorbing an excessive
amount of shock as opposed to providing a damping action for
spring-biased belt tensioning plunger.
It also is highly desirable when developing a belt
tensioner intended primarily for use on an automobile to
devise a construction which can be produced as inexpensively
as possible without sacrificing durability and efficiency
since a savings of only part of a dollar would amount to a
sufficient overall savings when considering the millions of
vehicles that are produced by the various vehicle manufac-
~L~8~266
turers on which such belt tensioners will be mounted.
Many of these problems have been overcome by the belttensioner which is the subject of applicant's Canadian Patent
No. 1,232,157, granted February 21, 1988. In the belt
tensioner of this Canadian Patent, a damping ring is biased
into frictional engagement with the lever arm on which an
idler pulley is mounted by the same torsional coil spring
which provides the tensioning force on the lever arm. Such
an arrangement insures that the amount of damping is propor-
tional to the torque of the spring. Although the device ofthis Canadian Patent solves many of the problems, it is
desirable to form the damping ring of a material suitable to
achieve the most efficient frictional engagement between the
pivotal movable lever arm and a stationary part of the
bracket while in addition to providing a damping band of a
material able to withstand the various forces exerted thereon
by the biasing force of the torsional spring. Furthermore, it
is desirable that the amount of damping force applied by the
damping band from the torsional coil spring be changeable
without materially changing the component parts of the
tensioner.
Therefore, the need has existed for such a belt ten-
sioner having an improved damping arrangement which uses a
damping band formed out of the most satisfactory and effi-
cient friction material; in which the damping band is movedinto damping engagement by the torsional spring which
provides the belt tensioning force; in which the damping band
is of such a material which is able to better withstand the
forces exerted thereon by the coil spring; and in which the
amount of tension exerted by the torsional spring on the
damping band can be varied without materially affecting the
biasing force exerted by the spring on the idler pulley lever
arm.
Objectives of the invention include providing an
improved device for tensioning the drive belt for vehicle
~8~266
accessories which maintains a generally constant predeter-
mined tensioning force on the belt throughout the life of the
belt regardless of whether the engine is on or off or
operating at various speeds and conditions, and regardless of
the tensioning position of the bel.t engaging idler pulley in
its tensioning movement range.
These objectives and advantages are obtained by the
improved belt tensioner construction of the invention which
automatically tensions an endless drive belt of a drive
system for vehicle engine accessories, the general nature of
which may be stated as including a housing adapted to be
mounted on a vehicle adjacent the belt drive; lever means
pivotally mounted on the bracket for movement toward and away
from the drive belt; pulley means rotatably mounted on the
lever means and engageable with the drive belt for applying a
tensioning force on said belt when the lever means is biased
in a belt-tensioning direction toward the drive belt; spring
means acting between the housing and lever means for biasing
the lever means in the belt tensioning direction; brake means
mounted on the lever means for frictional engagement with the
hou~ing for retarding pivotal movement of the lever means
with respect to the housing; and fulcrum means formed on the
lever means and engaged by the spring means for directing a
first end of the spring means into engagement with the brake
means biasing the brake means into frictional engagement with
the housing as the spring means biases the lever means in the
belt tensioning direction.
A feature of a specific embodiment of the invention is
to provide such a tensioning device which is of a relatively
inexpensive design which may be formed of lightweight sheet
or cast metal components which can be mass produced by simple
metal working procedures and then assembled with a usual
pulley and torsional spring; and in which the radial center-
line of the belt engaging idler pulley groove is aligned with
the radial centerline of the bushing on which the idler
~3'2266
pulley lever mounting arm is pivotally mounted thereby
reducing the unbalanced frictional force components heretof-
ore exerted on the pivot bushing to increase the life and
operating efficiency of the tensioner.
The illustrated embodiment of the invention is a
tensioning device having an improved damping mechanism
consisting of a split ring of plastic material which is
attached to a pivotally mounted lever arm and located
adjacent the wall of an annular housing fixed to the engine;
and in which the damping ring is moved into frictional
engagement with the housing by a torsional spring acting
through a backing shoe mounted on, or formed as part of the
damping ring adjacent the area where the majority of the
damping force i9 applied between the damping band and
lS housing. A further objective is to provide such a tensioning
device in which the damping band can be formed of the most
efficient friction material and the backing shoe formed of a
different material thereby enabling the shoe to be formed out
of a stiffer and more durable material which is able to
absorb the forces exerted thereon by the torsional spring
more efficiently thereby enabling the damping device to be
formed of two different materials utilizing the best charac-
teristics of both materials.
More specifically the present invention may include a
tensioning device having an improved damping mechanism in
which one end of the torsional spring is biased radially
outwardly about a fulcrum formed on the lever arm and into
engagement with the damping band backing shoe to satisfac-
torily transmit the biasing force of the torsional spring
against the damping band, and in wbich the directional angle
of the shoe engaging spring end can be changed easily to
adjust the amount of tension exerted radially outwardly by
the spring against the damping band which determines the
amount of the friction force exerted by the damping band
between the lever arm and housing.
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X66
The backing shoe maybe mounted on the damping band by an
angled tab which also forms one side of an opening into which
a complementary shaped projection that is formed on the lever
arm is inserted for mounting the damping band on the lever
arm; and in which a force component exerted by the torsional
spring against the backing shoe assists in clamping the
angled tab against the mounting projection to secure the
damping band on the lever arm and to prevent it from rotating
thereon.
According to another specific feature of the invention
there is provided an improved belt tensioner in which the
damping band also provides a seal between the lever arm and
housing to reduce dirt and debris from entering the housing
and affecting the operation of the lever arm pivot shaft and
torsional spring which are located within the housing.
An object of the invention is to provide a belt ten-
sioner which achieves the stated characteristics in a simple,
effective, rugged and relatively inexpensive manner and which
solves problems and satisfies needs existing in the art.
BRIEF DESCRIPTION OF THE DRAWINGS
A preferred embodiment of the invention, illustrative of
the best mode in which applicants have contemplated applying
the principles, iB set forth in the following description and
is shown in the accompanying drawings, and is particularly
and distinctly pointed out and set forth in the appended
claim~.
FIG. 1 is a diagrammatic view looking toward the front
of an engine ill~strating an endless drive belt operatively
connected to and driving the vehicle accessories with the
improved belt tensioner engaged with the belt;
FIG. 2 is an enlarged plan view of the belt tensioner of
FIG. 1 removed from engagement with the endless belt drive;
FIG. 3 is a fragmentary end elevational view of the
improved belt tensioner looking in the direction of Arrows
~'~8~66
3--3, FIG. 2;
FIG. 4 is an enlarged fragmentary sectional view taken
on line 4-4, FIG. 2;
FIG. 5 is a sectional view with portions broken away,
taken on line 5-5, FIG. 4;
FIG. 6 is an enlarged fragmentary sectional view taken
on line 6-6, FIG. 5;
FIG. 7 is a fragmentary sectional view taken on line 7-
7, FIG. 4;
FIG. 8 is an enlarged fraqmentary sectional view with
portions broken away, taken on line 8-8, FIG. 2;
FIG. 9 is a plan view of the backing shoe of the damping
band component of the improved belt tensioner;
FIG. 10 is a sectional view taken on line 10-10, FIG. 9;
FIG. 11 is a plan view of the improved damping band;
FIG. 12 is an enlarged sectional view taken on line
12-12, FIG. 11:
FIG. 13 is an enlarged sectional view taken on line 13-
13, FIG. 11:
FIG. 14 is an enlarged fragmentary sectional view taken
on line 14-14, FIG. 2; and
FIG. 15 is a top plan view of the lever arm component of
the improved belt tensioner.
Similar numerals refer to similar parts throughout the
drawings.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring to FIG. 1 of the drawings, the improved belt
tensioner construction is indicated generally at 1, and is
shown in tensioning engagement with an endless drive belt 2
of a power transmission belt drive system which is shown
diagramatically looking toward the front of an engine. The
accessory drive system consists of a plurality of belt
pulleys or sheaves having configurations and diameters
determined by their association with the engine accessories
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and their locations relative to each other. The various
pulleys are supported on their respective engine components
which in turn are mounted on an engine (not shown) in a usual
manner known in the art. Belt 2 preferably operates in a
single vertical plane to eliminate binding and skewing of the
belt.
The particular engine accessories drive system shown in
FIG. 1 consists of a main driving pulley 3 which is opera-
tively connected to the main drive shaft of the engine, a
pulley 4 which is operatively connected to the engine air
pump, a pulley 5 which is operatively connected to an
alternator 6 which provides electrical power for the engine,
a pulley 7 which is operatively connected to the vehicle
power steering unit, and a pulley 8 which is operatively
connected to the engine water pump.
Improved belt tensioner 1 includes an engine mounting
bracket indicated generally at 10, Which preferably is
formed of an aluminum casting. Bracket 10 is provided with a
plurality of mounting holes 11, five of which are shown on
the particular bracket configuration of the drawings for
mounting the bracket onto the vehicle engine. Bracket 10
further includes an annular-shaped housing indicated general-
ly at 12 (FIGS. 4 and 7), which includes a generally cylindr-
ical wall 13 which extends upwardly from a base surface 14.
Cylindrical wall 13 includes a top circular edge 15 which
defines the opening into the interior of housing 12.
Tensioner 1 need not have a mounting bracket such as bracket
10 for certain applications. Likewise, bracket 10 may be
used to support an accessory or may be used to attach ten-
sioner housing 12 to the vehicle engine or another bracket.
Referring to FIGS. 7 and 14, an annular-shaped projec-
tion 16 is formed integrally with base surface 14 and
projects upwardly within the opening of housing 12. Projec-
tion 16 has an opening 17 at one location on its periphery
for receiving the bent end 18 of a torsional coil spring
~'~8~266
indicated generally at 20. A hub 21 is formed integrally
with base surface 14 and projects upwardly within the housing
interior concentric with annular projection 16 and cylindri-
cal wall 13. Hub 21 is formed with a threaded bore 24 which
preferably is cast without threads with the threads subse-
quently being formed therein by a pivot shaft 26 as it is
driven into the bore, FIG. 4. A pair of stops 22 and 23 may
be formed integrally with hub 21 or as separate components
and extend generally radially outward]y therefrom terminating
at annular projection 16. Stops 22 and 23 form an included
angle which is approximately 90 for the particular embodiment
shown in the drawings. Bracket 10 also may include an anchor
post 28 ~FIGS. 4, 5 and 8), on which is mounted a strip of
spring steel which forms a retention clip 29, the purpose of
which is described in greater detail below.
Tensioner 1 further includes a lever arm indicated
generally at 30 ~FIG. 15), which is pivotally mounted on
bracket 10 by shaft 26 (FIG. 4). Lever arm 30 includes a
disc-shaped plate 31 formed with an upstanding central boss
32 having an opening 33 in which a bearing sleeve 34 is press
fitted and having a top sealing o-ring 35. A raised arm 36
is formed integrally with plate 31 and extends radially
outwardly from central boss 32 and terminates in an upwardly
extending stub shaft 37. Stub shaft has a bore 38, the axis
39 of which i8 parallel with the axis 40 of central boss 32.
Referring to FIG. 5, a generally semi-circular shaped
projection 42 is formed on bottom surface 43 of plate 31 and
terminates in a pair of end projections 44 and 45. Another
projection 46 is formed on bottom plate surface 43 and is
located generally between projections 44 and 45. Projections
44 and 45 may be formed integrally with projection 42 as
shown in the drawings or as separate free standing com-
ponents. Lever arm 30 preferably is an integral one-piece
aluminum casting with the various projections and bosses
being formed as an integral part thereof providing a sturdy,
.:
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~: '
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~'~82266
11
durable and lightweight one-piece component. Lever arm 30 is
pivotally mounted on bracket lO by shaft 26 as shown in FIG.
4 which includes a second o-ring 47 located between head 48
of shaft 26 and bearing sleeve 34.
An idler pulley indicated generaIly at 50 ~FIG. 4) is
rotatably mounted on stub shaft 37 by a bearing ring 51, a
dust cap 49 and a mounting bolt 53 which preferably includes
a flanged head 52. Idler pulley 50 and its mounting arrange-
ment on bracket 10 is similar to that shown in Patent No.
4,551,120. Pulley 50 includes an outer annular belt engaging
wall 54 and has an inverted U-shaped cross sectional con-
figuration formed with a ring-like opening 55 located between
outer annular wall 54 and an inner annular wall 56. Pulley
50 is mounted on stub shaft 37 so that pivot shaft 26 is
located within the periphery of pulley 50 and preferably
extends into ring-like opening 55. This pulley mounting
arrangement provides a relatively large circumferential belt
wrap with a short moment arm between the idler pulley
mounting shaft and the pivot shaft on which the idler pulley
lever arm is pivotally mounting. Furthermore, as shown in
FIG. 4, the frictional forces which are exerted against lever
arm pivot bushing 34 and shaft 26 are reduced considerably by
the location of pivot shaft 26 within the periphery of belt
engaging surface 54. Likewise, the radial centerline of belt
engaging idler pulley surface 54 is aligned generally with
the center line of bearing sleeve 34 on which lever arm 30 is
pivotally mounted thereby reducing the unbalanced frictional
force component heretofore exerted on the pivot bushing.
In accordance with one of the main features of the
invention, an improved brake means indicated generally at 60,
is mounted on lever arm 30 and frictionally engages housing
12, and in particular frictionally engages housing wall 13
thereof to provide damping for the movement of lever arm 30
with respect to housing 12. Brake means 60 (FIG. 9 - 13)
includes an annular brake band indicated generally at 61, and
.
'' . '' ,`''' '' '
~- . .
2~6
12
a backing shoe indicated generally at 62. sand 61 has a
generally ring-like annular configuration preferably having a
split 63 at one location on its periphery and has a generally
z-shaped configuration provided by an annular wall 64 and a
pair of opposed flanges 65 and 66 which extend outwardly in
opposite directions from the ends of wall 64 as shown in FIG.
12.
Brake band 61 further includes an arcuate shaped
friction surface 68 formed along one portion of annular wall
64 (FIGS. 5, 6, 11 and 13) which frictionally engages an
inner portion of annular wall 13 of housing 12. A plurality
of axially extending slots 69 may be formed in surface 68 and
69 may contain a lubricating grease and provides an area for
dirt to collect to reduce its harmful effect on the friction-
al engagement between surface 68 and a portion of the innersurface of housing wall 13. Brake band 61 further includes a
generally radially inwardly extending shoe mounting tab 70
located on the inside surface of friction surface 68. Tab 70
is adapted to be inserted into a complementary shaped groove
71 (FIG. 13. formed in an outer convex arcuate surface 72 of
backing shoe 62. Brake band 61 further includes an angled
generally inwardly extending tab 73 which forms a pocket 74
with a projection 75 formed at the junction of sealing flange
66 and arcuate friction surface 68, the purpose of which is
described in greater detail below. A shoulder 76 formed at
the junction of sealing flange 66 and the opposite end of
friction surface 68 provides an abutment for engagement with
end 78 of backing shoe 62 for retention during assembly.
Backing shoe 62 is removably mounted on brake band 61 by
~ 30 engagement of shoe mounting tab 70 in shoe groove 71 and the
:: abutment of shoe edge 78 with shoulder 76 and the abutting
engagement between angled tab 73 and a complementary shaped
~: flat edge surface 79 of backing shoe 62. Thus, backing shoe
; 62 i8 removably mounted on brake band 60 adjacent the inside
~ 35 surface of friction surface 68 by tabs 70 and 73 and shoulder
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- '. . ' - ' '
: , - .
~'~8`Z266
13
76. Shoulder 76 is angled slightly towards backing shoe 62
to provide a clamping action therewith to assist in securing
the brake shoe on brake band 61.
srake means 60 which includes brake band 61 and backing
shoe 62, is removably mounted on lever arm 30 by insertion of
a projection 80 which is formed on surface 43 of disc-shaped
plate 31 (FIG. 5) into a complementary-shaped pocket 74 of
brake band 61. When brake means 60 is mounted on lever arm
30, sealing flange 66 will engage the outer periphery of
lever arm plate surface 43 (FIG. 14) and the inner surface of
annular wall 64 will abut against circular edge 81 of lever
arm plate 31. When lever arm 30 is mounted on bracket 10 by
shaft 26, outwardly extending sealing flange 65 will abut and
lie along the top circular edge 15 of housing wall 13 as
shown in FlG. 14. Furthermore, when brake means 60 is
mounted on lever arm 30, arcuate friction surface 68 lies in
abutment with a portion of the inner surface of housing wall
13 as shown particularly in FIG. 5.
In accordance with another of the main features of the
invention, arcuate surface 72 of backing shoe 62 lies against
a complementary shaped inner arcuate surface 83 of brake band
61 and a projection 84 which extends outwardly from body 85
of shoe 62 has a groove 86 formed therein providing a seat
for spring end 87 which is engaged therewith.
Referring to FIG. 5, spring end 87 is a generally
straight section extending inwardly from the circular
convolutions 88 which form spring 20. Straight spring end 87
extends inwardly from the end most convolution across
projection 44 and is engaged in groove 86 of backing shoe 62.
Projection 44 forms a fulcrum for spring end 87 which biases
backing shoe 62 and correspondingly, brake band friction
surface 68 into frictional damping engagement with the
interior surface of housing wall 13 in the general direction
of arrow A (FIG. 5). Projection 46 assists in maintaining
spring end 87 in engagement with backing shoe 62.
~Z82266
14
Lever arm projection 45 engages projections 22 and 23
formed on housing 12 and functions as a stop to limit the
pivotal movement of lever arm 30 between the minimum and
maximum belt tensioning positions. As shown in FIG. 5, lever
arm 30 is in a generally intermediate tensioning position
wherein stop projection 45 is located between projections 22
and 23.
The two piece construction of brake means 60 enables
brake band 61 to be formed out of a material which provides
the desired frictional characteristics for arcuate friction
surface 68 while enabling backing shoe 62 to have the desired
strength and rigidity for transferring the biasing force of
spring end 87 through shoe 62 for forcing friction surface 68
against housing wall 13.
A shoulder 90 ~FIG. 5) is formed on the underside
surface of a circular base 91 on which stub shaft 37 is
formed. Spring retention clip 29 (FIG. 8) is formed with a
shoulder 92 which engages shoulder 90 of lever arm 30 upon
rotation of the lever arm and manual inward movement of
spring clip 29 toward circular base 91. Spring clip 29 is
shown in disengaged position with shoulder 90 in FIG. 8.
Spring clip 29 is used only at the time of installation
of belt tensioner 1 on an engine. Spring 20 biases lever arm
30 in the direction of arrow B (FIG. 5) which when clip 29 is
forced manually inwardly will enable shoulder 90 of the lever
arm to abut against shoulder 92 on the spring clip maintain-
ing the lever arm in the engaged position with the spring
clip. When in this position idler pulley 50 will be located
between mounting holes 11 of bracket 10 somewhat similar to
that shown in FIG. 2, thereby completely exposing all of
mounting holes 11 enabling an automatic tool to simulataneou-
sly insert five bolts through holes 11 and into the engine
block or other engine component on which the bracket will be
mounted. After tensioner 1 is mounted on an engine, the
biasing force of spring 20 forces spring clip 29 to remain in
8a~ 66
the notch at the end of the lever arm. When the lever arm is
manually rotated in the direction opposite to the biasing
force of spring 20 the notch in the lever arm leaves the
spring clip whereupon the biasing force of the spring clip
which is in a direction away from the arm, moves the clip
from the lever arm allowing the arm to be returned by spring
20 to the position shown in FIG. 2.
Clip 29 is a feature used only at the time of installa-
tion of tensioner 1 on a vehicle engine to facilitate the use
of automatic mounting equipment and does not assist or affect
the tensioning and damping ability of the improved belt ten-
sioner.
The operation of improved belt tensioner 1 is described
below with particular reference to FIGS. 4, 5 and 7 of the
drawings. End 18 of spring 20 is attached to housing 12 and
opposite straight spring end 87 is engaged with fulcrum 44 of
lever arm 30 and is engaged with backing shoe 62. Spring 20
when operatively engaged with housing 12 and lever arm 30 is
placed in tension whereby spring end 87 will attempt to move
outwardly in the direction of arrow A (FIG. 5). The force
exerted by spring 20 provides the belt tensioning force since
it will bias lever arm 30 in a counter-clockwise direction
when viewing FIGS. 1 and 2 and will use projection 44 as a
fulcrum to move arcuate friction surface 68 into frictional
engagement with housing wall 13 by transmission of the spring
biasing force through backing shoe 62. The outward force
exerted by spring end 87 will result in a generally equal
opposite force against fulcrum projection 44, which outward
force is exerted against the stationary wall of housing 12
through friction surface 68 providing the desired damping to
the belt tensioner. Thus spring 20 provides both the belt
tensioning biasing force and the damping force.
Since torsional spring 20 provides both the tensioning
force for pivotally moving lever arm 30 in the belt tension-
ing direction and the force for moving brake means 60 into
8;:ZG6
16
frictional engagement with housing wall 13 this insures thatthe amount of damping is proportional to the belt tensioning
force providing a uniform damping throughout the tensioning
range of the tensioning spring. Also, the amount of damping
provided by brake means 60 can be adjusted easily to cor-
respond to the particular engine on which tensioner 1 is
mounted by merely changing the angle that spring end 87 forms
with the convolutions of the spring and correspondingly the
angle that it engages backing shoe 62 or by changing the
distance between fulcrum projection 44 and shoe projection 84
as shown in FIG. 5. Referring to FIG. 5, it is seen that the
angle at which spring end 87 extends with respect to fulcrum
44 will determine the force component exerted against backing
shoe 62 and correspondingly the amount of force exerted by
arcuate friction surface 68 against housing wall 13.
Another main advantage by improved belt tensioner 1 is
that the two piece construction of brake means 60 enables
the most efficient results to be achieved by both of the
components namely, brake band 61 and backing shoe 62. This
construction enables the desired frictional characteristics
to be achieved by brake band 61 and the desired strength and
rigidity to be achieved by backing shoe 62. Another ad-
vantage achieved by improved belt tensioner 1 is that the z-
shaped configuration of brake band 61 and in particular
flanges 65 and 66 as shown in FIG. 12 and 14, provides a
sealing engagement with lever arm 30 and housing 12 to
prevent dust, dirt and other debris from entering housing 12
and affecting the operation of pivot shaft 26 and bearing 34.
Also, it has been found that the placement of a lubricating
grease in grooves 69 of friction surface 68 prevents salt
water from effecting the frictional engagement of surface 68
with the interior surface of housing wall 13.
Furthermore, the particular mounting arrangement of
backing shoe 62 on brake band 61 achieved by tabs 70 and 73
and shoulder 76 provides a clamping action against backing
1 28"2Z66
17
shoe 62 to retain it in position on tab 70. Likewise, the
shaped pocket 74 of brake band 61 securely mounts brake means
60 on lever arm 30 preventing any sliding or rotational
movement therebetween to insure that the biasing force
exerted by spring end 87 is transferred through backing shoe
62 and frictional surface 68 and against housing wall 13.
Also, spring clip 29 provides a means of enabling idler
pulley 50 to be maintained in a position on bracket 10 so
that all of the bracket mounting holes 11 are exposed for use
of automatic installation equipment when mounting improved
belt tensioner 1 on a vehicle engine.
Accordingly, the improved belt tensioner construction is
simplified, provides an effective, safe, inexpensive, and
efficient device which achieves all the enumerated objec-
tives, provides for eliminating difficulties encountered withprior constructions, and solves problems and obtains new
results in the art.
In the foregoing description certain terms have been
used for brevity, clearness and understanding; but no
unnecessary limitations are to be implied therefrom beyond
the requirements of the prior art, because such terms are
used for descriptive purposes and are intended to be broadly
construed.
Moreover, the description and illustration of the
invention is by way of example, and the scope of the inven-
tlon i8 not limited to the exact details shown or described.
Having now described the features, discoveries, and
principles of the invention, the manner in which the improved
belt tensioner is constructed and used, the characteristics
of the construction, and the advantageous, new and useful
results obtained; the new and useful structures, devices,
elements, arrangements~ parts, and combinations, are set
forth in the appended claims.
