Field of the Invention
The invention relates to a tensioner, and more
particularly, to a rotary tensioner having a rotary arm pivotally engaged with a base, a center of rotation of the rotary arm aligned with a base aperture center, a swing arm pivotally engaged with the rotary arm about a
shaft, the shaft and swing arm each having a cooperating frustoconical portion, a bushing having a frustoconical portion in frictional engagement with the swing arm frustoconical portion.
Background of the Invention
Most internal combustion engines comprise
accessories such as power steering, an alternator and air
conditioning to name a few. These accessories are
20 typically driven by a belt. A tensioner is typically used
to apply a preload to the belt in order to prevent
slippage. The tensioner can be mounted to an engine
mounting surface
The engine may further comprise a start-stop system
25 whereby the engine will shut down when the vehicle is not
in motion, and when a driver command is received to
proceed the engine will restart.
The start-stop function will tend to reverse loading
on the belt. Hence, tensioners are available to
30 accommodate belt load reversals. The tensioner may
comprise one or more components which independently pivot
in order to properly apply a required belt preload force
in both belt drive directions. The tensioner may also be
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mounted directly to an accessory such as an alternator in
order to save space in the engine bay.
Representative of the art is WO2014/100894 which
discloses a tensioner for tensioning an endless drive
5 member that is engaged with a rotary drive member on a
shaft of a motive device. The tensioner includes a base
that is mountable to the motive device, a ring that is
rotatably supported by the base in surrounding
relationship with the shaft of the motive device and
10 which is rotatable about a ring axis, a tensioner arm
pivotally mounted to the ring for pivotal movement about
an arm pivot axis, and first and second tensioner
pulleys. The first tensioner pulley is rotatably mounted
to the tensioner arm. The tensioner arm is biased towards
15 a first span of the endless drive member on one side of
the rotary drive member. The second tensioner pulley is
rotatably mounted at least indirectly to the ring and is
biased towards a second span of the endless drive member
on another side of the rotary drive member. The ring is
20 rotatable in response to hub loads in the first and
second tensioner pulleys that result from engagement with
the first and second spans of the endless drive member.
What is needed is a tensioner having a rotary arm
pivotally engaged with a base, a center of rotation of
25 the rotary arm aligned with a base aperture center, a
swing arm pivotally engaged with the rotary arm about a
shaft, the shaft and swing arm each having a cooperating
frustoconical portion, a bushing having a frustoconical
portion in frictional engagement with the swing arm
30 frustoconical portion. The present invention meets this
need.
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Summary of the Invention
The primary aspect of the invention is to provide a
tensioner having a rotary arm pivotally engaged with a
base, a center of rotation of the rotary arm aligned with
5 a base aperture center, a swing arm pivotally engaged
with the rotary arm about a shaft, the shaft and swing
arm each having a cooperating frustoconical portion, a
bushing having a frustoconical portion in frictional
engagement with the swing arm frustoconical portion.
10 Other aspects of the invention will be pointed out
or made obvious by the following description of the
invention and the accompanying drawings.
The invention comprises a tensioner comprising a
base having a base aperture, the base aperture disposed
15 to receive a driven component, a rotary arm pivotally
engaged with the base, an axis of rotation of the rotary
arm aligned with a base aperture center, a first pulley
journalled to the rotary arm, a swing arm pivotally
engaged with the rotary arm about a shaft, the shaft and
20 swing arm each having cooperating frustoconical portions,
a torsion spring biasing the pivot arm, a second pulley
journalled to the swing arm, a bushing having a
frustoconical portion in frictional engagement with the
swing arm f rustoconical portion, the bushing in fixed
25 relation to the shaft or pivot arm, and a first damping
ring frictionally engaged between the rotary arm and the
base, a Belleville spring in pressing engagement whereby
a normal force is applied to the first damping ring.
30 Brief Description of the Drawings
The accompanying drawings, which are incorporated in
and form a part of the specification, illustrate
preferred embodiments of the present invention, and
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together with a description, serve to
principles of the invention.
Figure 1 is a top perspective view.
Figure 2 is a bottom perspective view.
5 Figure 3 is an exploded view.
Figure 4 is a cross-sectional view.
Figure 5 is a detail of Figure 1.
Figure 6 is a perspective view of the
to a driven component.
10
Detailed Description of the Preferred Embodiment
Figure 1 is a top perspective view. Rotary
tensioner 1000 comprises a base 100, rotary arm 202, and
swing arm tensioner 300.
15 Base 100 comprises holes 101 for attaching the
tensioner to a mounting surface such as an engine
alternator (not shown). Each hole 101 receives a
fastener such as a bolt (not shown) . Base 100 comprises
an aperture 102. Aperture 102 has a large enough diameter
20 to accommodate and encircle a driven component such as an
alternator pulley (not shown). A drive belt (not shown)
engages the driven component, see Figure 6.
Rotary arm 202 comprises a first radial projection
210 and a second radial projection 211. Rotary arm 202
25 further comprises an aperture 209. Aperture 209 is a
large enough diameter to accommodate a driven component
such as an alternator pulley (not shown). Aperture 102
and aperture 209 are coaxial. Rotary arm 202 pivots
about base 100 and thereby aperture 102, namely, rotary
30 arm 202 has an axis of rotation A-A that is aligned with
the center (B) of the base aperture 102. The rotary arm
axis of rotation also aligns with the axis of rotation of
a driven pulley, such as an alternator pulley (not
shown).
explain the
device mounted
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Pulley 201 is journalled to rotary arm 202 on
projection 210 by a bearing 207. Pulley 201 engages a
drive belt (not shown) which drives a driven engine
accessory, for example, an alternator pulley. Bolt 208
5 secures bearing 207 to projection 210. Dust cover 212
prevents debris from entering bearing 207.
Tensioner 300 comprises a swing arm 301. Swing arm
301 pivots about shaft 304. Shaft 304 can be press fit
or threaded into projection 211 on pivot arm 301. Shaft
10 304 is disposed radially outward from the base aperture.
Pulley 302 is journalled to swing arm 301 on bearing 310.
Pulley 302 engages a drive belt (not shown). Torsion
spring 303 urges swing arm 301 into contact with the
drive belt (not shown), thereby applying a belt load. A
15 belt load is advantageous to prevent belt slippage, wear
and noise during operation. Pivotal movement of swing
arm 301 is coordinated with rotary movement of rotary arm
202.
In operation swing arm 301 presses on a drive belt
20 thereby applying a belt load. The swing arm load also
causes a reaction whereby pulley 201 presses on the drive
belt by pivotal movement of rotary arm 202. Movement of
swing arm 301 and rotary arm 202 allows the inventive
device to accommodate various system and belt operating
25 characteristics. Pulley 201 and pulley 302 are coplanar
with a driven pulley (not shown).
Figure 2 is a bottom perspective view. In operation
a drive belt (not shown) engages a driven pulley such as
an alternator pulley that projects through aperture 209.
30 The drive belt also engages pulleys 201 and 302.
Figure 3 is an exploded view. Shaft 304 comprises a
frustoconical portion 304a. Bushing 305 is disposed
between shaft 304 and swing arm 301. Bushing 305
comprises a frustoconical portion 305a.
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Bushing 305 is held in fixed relation to shaft 304
by tabs 305b on bushing 305 which engage slots 304b in
shaft 304. Swing arm 301 pivots about shaft 304 on
bushing 305. A frictional relation between bushing 305
5 and swing arm 301 acts to damp pivotal movement of swing
arm 301. In an alternate embodiment bushing 305 is held
in fixed relation to the pivot arm. In yet another
embodiment bushing 305 is not held in fixed relation to
either the pivot arm or the shaft.
10 Damping ring 203 is disposed between base 100 and
rotary arm 202. Damping ring 204 is disposed opposite
damping ring 203. Member 205 holds damping ring 204 to
base 100. Belleville spring 206 applies a compressive
normal force to member 205 which in turn applies a normal
15 force to each damping ring 203, 204. The normal force
multiplied by the frictional coefficient between the
damping rings and the base creates a frictional force
which in turn damps movement of rotary arm 202.
Belleville spring 206 is held in a compressed state due
20 to a material deformation based assembly process applied
to base 100, which in turn holds the tensioner together.
Each tab 203a engages a receiving portion 213 of
rotary arm 202. Each tab 204a also engages receiving
portion 213 of rotary arm 202. Therefore, each damping
25 ring 203 and 204 move in fixed relation to rotary arm
202. Surface 203c frictionally engages surface 104 of
base 100. Surface 205a frictionally engages surface
204c.
Pin 308 engages rotary arm portion 214 and pivot arm
30 301. Pin 308 holds pivot arm 301 in a predetermined
position in order to facilitate installation of a drive
belt (not shown) . Pin 308 is then removed once
installation of the tensioner and belt are complete and
the system is put into operation.
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Figure 4 is a cross-sectional view. Shaft 304
comprises a frustoconical portion 304a. A conical angle
9 is in the range of >0 degrees to <90 degrees. By way
of example, the instant embodiment comprises a conical
5 angle 9 of approximately 30 degrees.
Bushing portion 305a has a frustoconical shape to
cooperatively match the form of portion 304a. Bushing
305 is disposed between pivot arm 301 and shaft 304.
Pivot arm 301 pivots on bushing 305. Cap 309 is affixed
10 to pivot arm 301 and acts as a seal to prevent debris
from entering between bushing 305 and pivot arm 301.
In operation torsion spring 303 is in axial
compression which creates an axial spring force Fspr. The
axial spring force presses surface 305c of bushing 305
15 into surface 301b of pivot arm 301. The resulting
frictional force between surface 301b and surface 305c
damps pivotal movement of pivot arm 301. Depending on
the axial spring force and the shape of the frustoconical
portion, the damping torque can have a wide range for
20 example, +/-1 to +20Nm. The preferred range is
approximately INm to approximately 8Nm. By way of
example, a 850N axial spring force and 30 degree conical
angle with a 3 6mm maximum and 16mm minimum diameter of
portion 305a and a coefficient of friction of 0.16 gives
25 a damping torque of approximately +/- 3.7Nm. Numbers
provided herein are by way of example and are not
intended to limit the scope of the invention.
The apex of angle A of the f rustoconical portion
305a projects in the direction opposite the axial spring
30 force vector Fspr. This orientation firmly engages the
pivot arm frustoconical portion 301b with the shaft
conical portion 304a. This in turn is the basis of the
reaction force Fcr, a normal of which to surface 305c
causes the frictional damping force between the bushing
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305 and surface 301b. For example, in this embodiment the
apex angle A is 60°. Apex angle A = 2 x 9.
The frustoconical form enhances damping durability
due to the enlarged surface area of the bushing portion
5 305a as compared to a purely cylindrical bushing. It also
optimizes the use of axial force due to the wedge effect:
Fn = Fspr(sin 9) . Fn is the normal force on surface 305c.
Fspr is the spring force. It also provides improved
alignment of pivot arm 301 on shaft 304 which in turn
10 results in improved alignment of pulley 302 with a drive
belt.
Figure 5 is a detail of Figure 1. Bolt 306 secures
bearing 310 to swing arm 301. Dust shield 307 protects
bearing 310 from debris. Each tab 305b engages a slot
15 304b to prevent movement of bushing 305.
Figure 6 is a perspective view of the device mounted
to a driven component. Tensioner 1000 is mounted to a
driven component DC. Driven component DC comprises a
pulley P. Driven component DC may comprise an
20 alternator, starter-generator, or other vehicle engine
component. Fasteners F fix tensioner 1000 to the driven
component. A belt (not shown) engages pulley 201,
pulley 302 and pulley P. The belt drives component DC
through pulley P.
25 Although a form of the invention has been described
herein, it will be obvious to those skilled in the art
that variations may be made in the construction and
relation of parts and method without departing from the
spirit and scope of the invention described herein.

Claims
We claim:
1. A tensioner comprising:
a base having a base aperture, the base aperture
5 disposed to receive a driven component;
a rotary arm pivotally engaged with the base, an
axis of rotation of the rotary arm aligned with a base
aperture center, a first pulley journalled to the rotary
arm;
10 a swing arm pivotally engaged with the rotary arm
about a shaft, the shaft and swing arm each having
cooperating frustoconical portions, a torsion spring
biasing the pivot arm, a second pulley journalled to the
swing arm;
15 a bushing having a frustoconical portion in
frictional engagement with the swing arm frustoconical
portion, the bushing in fixed relation to the shaft or
pivot arm; and
a first damping ring frictionally engaged between
20 the rotary arm and the base, a Belleville spring in
pressing engagement whereby a normal force is applied to
the first damping ring.
2. The tensioner as in claim 1, wherein the shaft
25 frustoconical portion comprises an apex angle A which
projects in the direction opposite a torsion spring axial
spring force vector Fspr.
3. The tensioner as in claim 1 further comprising a
30 second damping ring frictionally engaged between the
rotary arm and the base, the second damping ring disposed
opposite the first damping ring relative to a base
frictional surface.
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4. The tensioner as in claim 1, wherein the rotary arm
comprises a rotary arm aperture aligned with the base
aperture.
5 5. The tensioner as in claim 1, wherein the bushing is
held in fixed relation to the shaft.
6. The tensioner as in claim 1, wherein the bushing is
held in fixed relation to the pivot arm.
10
7. The tensioner as in claim 1, wherein the first
damping ring is held in fixed relation to the rotary arm.
8. The tensioner as in claim 3, wherein the second
15 damping ring is held in fixed relation to the rotary arm.
9. The tensioner as in claim 1, wherein the first
damping ring is held in fixed relation to the base.
20 10. The tensioner as in claim 3, wherein the second
damping ring is held in fixed relation to the base.
11. A tensioner comprising:
a base having a base aperture, the base aperture
25 disposed to encircle a driven component;
a rotary arm pivotally engaged with the base, an
axis of rotation of the rotary arm aligned with a base
aperture center, a first pulley journalled to the rotary
arm, the rotary arm comprises a rotary arm aperture
30 aligned with the base aperture;
a swing arm pivotally engaged with the rotary arm
about a shaft, the shaft and the swing arm each having
cooperating frustoconical portions, a torsion spring
biasing the pivot arm, a second pulley journalled to the
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swing arm, the shaft frustoconical portion comprises an
apex angle A which projects in the direction opposite a
torsion spring axial spring force vector Fspr;
a bushing having a frustoconical portion in
5 frictional engagement with the swing arm frustoconical
portion, the bushing in fixed relation to the shaft; and
a first damping ring frictionally engaged between
the rotary arm and the base, a Belleville spring in
pressing engagement whereby a normal force is applied to
10 the first damping ring.
12. A tensioner comprising:
a base having a base aperture;
a rotary arm pivotally engaged with the base, an
15 axis of rotation of the rotary arm aligned with a base
aperture center, a first pulley journalled to the rotary
arm, the rotary arm comprises a rotary arm aperture
aligned with the base aperture;
a swing arm pivotally engaged with the rotary arm
20 about a shaft, the shaft and swing arm each having
cooperating frustoconical portions, a torsion spring
biasing the pivot arm, a second pulley journalled to the
swing arm, the shaft frustoconical portion comprises an
apex angle A which projects in the direction opposite a torsion spring axial spring force vector Fspr; a bushing having a frustoconical portion in frictional engagement with the swing arm frustoconical portion, the bushing having a fixed relation to the shaft; and a first damping ring frictionally engaged between the rotary arm and the base, a Belleville spring in pressing engagement to apply a normal force to the first
damping ring.