Note: Descriptions are shown in the official language in which they were submitted.
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Title
Tensioner
Field of the Invention
The invention relates to a tensioner, and more
particularly, to a tensioner having a first pivot arm and
a second pivot arm mounted to a base, a flexible member
trained between the first pivot arm and the second pivot
arm so the pivot arms move in a coordinated manner, and a
tensioner assembly mounted to the base engaging the
flexible member.
Background of the Invention
In most belt drive applications the ability to
maintain proper belt tension is important to ensure power
transmission without slippage of the belt. The
lowest
tension span in a belt drive is commonly referred to as
the slack side span.
Tensioners are traditionally
positioned on the slack side span of a belt drive and are
tasked with maintaining the proper minimum belt tension
in this span.
Using the belt rotation direction as a
guide, this span is the span located just after the power
providing pulley or crankshaft in this case. For
instance, as the crankshaft rotates, the slack side span
will be the span where the belt has just left the
crankshaft pulley and the tight side span will be the
span approaching the crankshaft pulley.
Belt alternator starter (BAS) systems utilize an
alternator that also functions as motor. This is
sometimes referred to as a motor-generator. The
operation of the BAS system is such that when the engine
is running, the alternator primarily behaves in a
traditional manner and the belt is loaded normally with
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the power being provided by the engine crankshaft pulley
and loaded by the alternator. In
BAS systems the drive
is typically arranged to position the alternator as the
next accessory after the belt passes over the crankshaft.
In this arrangement, the belt tensioner should be located
between the crankshaft pulley and the alternator. The
tensioner is located just before the alternator using the
belt rotation direction as a guide.
BAS systems bring a unique problem to the belt
drive. The
alternator acts as both a load on the belt
drive and a power provider for the belt drive. The BAS
system alternator is used to start the engine and the
alternator is used to provide power to the engine. In
start instances, the alternator pulley becomes a power
provider for the drive. This
typically transforms the
location of the slack span in the drive to the span
following the alternator pulley. Additionally, the tight
side span is now the span between the alternator and the
crankshaft. Since a traditional tensioner is designed to
simply maintain a minimum level of slack side tension,
the now high tension in the belt at the tensioner
location causes extreme movement of the tensioner.
Additionally, this situation creates the need for a
second tensioner in a location on the new slack side
span.
The traditional approach to solving this problem is
to create a belt drive with two tensioners. This second
tensioner is typically a tensioner with high resistance
to movement away from the belt. The second tensioner is
often an expensive hydraulic tensioner. This two
tensioner arrangement also requires an excessively long
belt to accommodate the multiple tensioners in the drive.
This often results in an expensive solution.
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Representative of the art is US patent no. 7,494,434
which discloses an accessory drive for an engine with a
belt driven starter generator adapted for driving and
being driven by the engine. In an exemplary embodiment,
the drive includes a first engine drive pulley and a
second starter drive pulley. A drive belt engages the
drive pulleys for driving either pulley from the other. A
dual belt tensioner made as a preassembled unit has a
carrier with a central pivot mounted to the engine and
first and second carrier arms extending radially from the
central pivot. A first tensioner mounted on the first arm
carries a first tensioner pulley biased against a first
belt run adjacent the second drive pulley that is slack
during engine starting. A second tensioner pulley carried
on the second arm is biased against a second belt run
adjacent the second drive pulley that is taut during
engine starting A hydraulic strut connected to the second
arm, and preferably included in the preassembled unit,
provides moderate biasing for the second tensioner pulley
during normal engine operation and velocity sensitive
resistance, to increased belt forces, that limits
reactive movement of the second tensioner pulley during
engine starting and transient engine operation.
What is needed is a tensioner having a first pivot
arm and a second pivot arm mounted to a base, a flexible
member trained between the first pivot arm and the second
pivot arm so the pivot arms move in a coordinated manner,
and a tensioner assembly mounted to the base engaging the
flexible member. The present invention meets this need.
Summary of the Invention
The primary aspect of the invention is to provide a
tensioner having a first pivot arm and a second pivot arm
mounted to a base, a flexible member trained between the
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first pivot arm and the second pivot arm so the pivot
arms move in a coordinated manner, and a tensioner
assembly mounted to the base engaging the flexible
member.
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, a first pivot arm pivotally engaged to the base, a
first pulley journalled to the first pivot arm, a second
pivot arm pivotally engaged to the base, a second pulley
journalled to the second pivot arm, a flexible tensile
member having a toothed engagement with the first pivot
arm and a toothed engagement with the second pivot arm
whereby the first pivot arm and the second pivot arm move
in a coordinated manner, and a tensioner assembly
pivotally engaged to the base and engaged with the
flexible tensile member.
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
together with a description, serve to explain the
principles of the invention.
Figure 1 is a top perspective view of the device.
Figure 2 is a cross-section view of the device.
Figure 3 is an exploded view of the device.
Figure 4 is a detail of a damping assembly.
Figure 5 is an exploded view of the damping assembly
in Figure 4.
Figure 6 is a detail of a damping assembly.
Figure 7 is an exploded view of the damping assembly
in Figure 6.
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Figure 8 is a top perspective view of a synchronous
tensioner assembly.
Figure 9 is an exploded view of the synchronous
tensioner assembly in Figure 8.
Figure 10 is an exploded view of an idler assembly.
Figure 11 is an exploded view of an idler assembly.
Figure 12A is a detail of a pivot arm.
Figure 12B is a detail of a pivot arm.
Figure 13A is a detail of a pivot arm.
Figure 13B is a detail of a pivot arm.
Figure 14 is a top perspective view of the internals
of the device.
Figure 15 is a detail of the device in an operating
position on an engine.
Figure 16 shows the orientation of pivot arm 5 and
pivot arm 55 and the hub load in the at rest position.
Figure 17A is a detail of the pivot arm load
conditions.
Figure 17B is a detail of the pivot arm load
conditions.
Figure 18 shows the orientation of pivot arm 5 and
pivot arm 55 and the hub load in the alternator starting
mode position.
Figure 19 is a detail of a clutch spring.
Figure 20 is a detail of a clutch spring.
Figure 21 is a detail of the base.
Figure 22A illustrates pivot arm position during an
operating condition.
Figure 22B illustrates pivot arm position during an
operating condition.
Figure 22C illustrates pivot arm position during an
operating condition.
Figure 22D illustrates pivot arm position during an
operating condition.
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Figure 23 is an underside view of the tensioner
assembly in Figure 8.
Figure 24 is a detail of a tensioner spring.
Figure 25 is a detail of the base.
Figure 26 is a rear detail of the tensioner mounted
to the alternator.
Figure 27 is a rear top view detail of the tensioner
mounted to the alternator.
Figure 28 is a bottom view of the tensioner arm.
Figure 29 is a perspective view of section 29-29
from Figure 2.
Figure 30 is a perspective view of an alternate
embodiment.
Figure 31 is a plan view of the embodiment in Figure
30.
Figure 32 is an exploded view of the embodiment in
Figure 30.
Figure 33 is cross-sectional view of the embodiment
in Figure 30.
Figure 34 is a side view of an eccentric arm cam.
Figure 35 is a perspective view of the arm in Figure
34.
Figure 35a is a perspective view of the arm in
Figure 34.
Figure 36 is a perspective view of the arm in Figure
37.
Figure 36a is a perspective view of the arm in
Figure 37.
Figure 37 is a side view of an eccentric arm cam.
Figure 38 is a side view of an eccentric upper arm.
Figure 39 is a perspective view of the arm in Figure
38.
Figure 40 is a side view of an eccentric upper arm.
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Figure 41 is a perspective view of the arm in Figure
40.
Figure 42 is a side cross section of the embodiment
in Figure 31.
Figure 43 is a detail of an idler assembly.
Figure 44 is a detail of the damping mechanism for
the embodiment in Figure 30.
Figure 45 is the damping mechanism for the
embodiment in Figure 30.
Figure 46 is a cross section of the embodiment in
Figure 31.
Figure 47 is a detail of the base of the embodiment
in Figure 30.
Figure 48 is a detail of the spring of the
embodiment in Figure 30.
Figure 49 is a detail of the spring of the
embodiment in Figure 30.
Figure 50 is a plan view of the tensioner of the
embodiment in Figure 30.
Figure 51 is a side view of the tensioner in Figure
50.
Figure 52 is a side view of the tensioner in Figure
50.
Figure 53 is a cross section of the tensioner in
Figure 50.
Figure 54 is an exploded view of the tensioner in
Figure 50.
Figure 55 is a detail of the base in Figure 47.
Figure 56 is a detail of the base in Figure 47.
Figure 57 is a detail of the base in Figure 47.
Detailed Description of the Preferred Embodiment
Figure 1 is a top perspective view of the device.
The inventive tensioner 1000 comprises a first tensioner
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assembly 501 and a second tensioner assembly 502 each
pivotally mounted to a base 1.
Figure 2 is a cross-section view of the device.
Extending from base 1 is shaft 2 and shaft 22. Pivot arm
5 is pivotally journalled to shaft 2 through a bushing 6.
The pivot axis of pivot arm 5 is coaxial with shaft 2.
Pivot arm 55 is pivotally journalled to shaft 22 through
a bushing 66. The pivot axis of pivot arm 55 is coaxial
with shaft 22. Shaft
2 and shaft 22 are not coaxial.
The pivot axis of arm 5 is not coaxial with the pivot
axis of arm 55.
Clutch spring 3 is engaged between damping assembly
4 and base 1.
Clutch spring 33 is engaged between
damping assembly 44 and base 1. Pulley 101 is journalled
to pivot arm 55 through bearing 102. Pulley 10 is
journalled to pivot arm 5 through bearing 12.
Clutch
spring 3 and clutch spring 33 are used to activate the
damping function.
Fastener 14 and fastener 144 retain cover 9 on base
1. Arm 5 is retained on base 1 by retaining ring 7.
Tensioner assembly 15 is retained on base 1 by cover 9.
Cover 9 protects the internal components from debris.
Figure 3 is an exploded view of the device. Washer
120 is disposed between retaining ring 7 and bushing 6.
Washer 122 is disposed between retaining ring 77 and
bushing 66. Arm 5
pivots about bushing 6 and bushing
661. Arm
55 pivots about bushing 660 and bushing 66.
Fastener 13 engages arm 5. Fastener 133 engages arm 55.
Figure 4 is a detail of a damping assembly. Figure
5 is an exploded view of the damping assembly in Figure
4.
Damping assembly 4 comprises damping shoe 41 and
damping ring 42. Damping ring 42 is coaxial with damping
shoe 41. Damping ring 42 is cylindrical in shape with a
gap 421 in an axial direction.
Damping ring 42 has a
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plurality of tabs 420 and 430 projecting inwardly for
containing damping shoe 41.
Damping shoe 41 is
cylindrical in shape with a gap 410 in an axial
direction. The outer surface 422 of damping ring 42
frictionally engages inner surface 51 of pivot arm 5.
Figure 6 is a detail of a damping assembly. Figure
7 is an exploded view of the damping assembly in Figure
6. Damping assembly 44 comprises damping shoe 441 and
damping ring 442.
Damping ring 442 is coaxial with
damping shoe 441. Damping ring 442 is cylindrical in
shape with a gap 4440 extending axially.
Damping ring
442 has a plurality of tabs 4420 and tabs 4430 projecting
inward for containing damping shoe 441. Damping shoe 441
is cylindrical in shape with a gap 4410 extending
axially. The
outer surface 4421 of damping ring 442
frictionally engages inner surface 551 of pivot arm 55.
Figure 8 is a top perspective view of a tensioner
assembly. Figure 9 is an exploded view of the tensioner
assembly in Figure 8. Synchronous tensioner assembly 15
comprises a rotatable belt guide 151, fastener 152, arm
153 and spring 154. Belt guide 151 is journalled to arm
153 by shaft 155. Shaft 155 engages hole 1532 in arm 153.
Arm 153 is pivotally attached to base 1 by fastener 152.
Spring 154 is fixedly attached to arm 153 by tab 1530 and
tab 1531, see Figure 28. Spring
154 acts as a biasing
member to apply a torque to arm 153, which then applies
load to belt 8. Figure 23 is an underside view of the
tensioner assembly in Figure 8. Figure 24 is a detail of
a tensioner spring.
Figure 25 is a detail of the base.
Spring end 1540 is engaged between tab 912 and tab 913 in
base 1 which prevents rotation of spring 154 when loaded,
see Figure 21 and Figure 25.
Shaft 2 is fixedly attached to base 1.
Clutch
spring 3 is fixedly attached to base 6 through tang 31
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which engages slot 911 of base 1, see Figure 19 and
Figure 21. Pivot arm 5 and bushing 6 and bushing 661 are
journalled to shaft 2 through bore 54.
Washer 120 is
coaxial with shaft 2.
Retaining ring 7 is fixedly
located on shaft 2 in groove 21. Damping assembly 4 is
coaxial with pivot arm 5.
Shaft 22 is fixedly attached to base 1.
Clutch
spring 33 is attached to base 1 through tang 331 which
engages slot 910, see Figure 20 and Figure 21. Pivot arm
55 and bushing 66 and bushing 660 are pivotally attached
to shaft 22 through bore 554. Washer 122 is coaxial with
shaft 22. Retaining ring 77 is fixedly located on shaft
22 in groove 221.
Retaining ring 7 retains arm 5 on
shaft 2. Retaining ring 7 is fixedly located on shaft 2
in groove 21. Retaining ring 77 retains arm 55 on shaft
22.
Damping assembly 44 is coaxial with pivot arm 55.
Damping assembly 44 frictionally engages pivot arm
damping surface 551.
Figure 10 is a detail of an idler assembly. Figure
11 is a detail of an idler assembly. Pulley 10 is
journalled to bearing 12.
Bearing 12 is journalled to
pivot arm 5 on surface 53.
Pulley 101 is journalled to
bearing 102.
Bearing 102 is journalled to pivot arm 55
on surface 553.
Figure 12A is a detail of a pivot arm. Figure 12B is
a detail of a pivot arm.
Figure 13A is a detail of a
pivot arm. Figure 13B is a detail of a pivot arm. Pivot
arm bearing mounting surface 53 receives bearing 12 and
is not coaxial with pivot arm bore 54, see bearing axis
(A) and pivot axis (B) respectively. Pivot arm
bearing
mounting surface 553 receives bearing 102 and is not
coaxial with pivot arm bore 554. Bore 54 engages shaft 2
which receives fastener 13. Bore 554 engages shaft 22
which receives fastener 133.
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Pivot arm 5 pivots about the pivot axis (A).
Bearing 12 rotates about the bearing axis (B). Bearing
axis (B) and pivot axis (A) are not coaxial, and instead
are offset from each other by a distance (X).
Pivot arm 55 pivots about the pivot axis (A2).
Bearing 102 rotates about the bearing axis (B2). Bearing
axis (B2) and the pivot axis (A2) are not coaxial, and
instead are offset from each other by a distance (Y).
Belt 8 engages sprocket 52 and sprocket 552 on pivot
arm 5 and pivot arm 55 respectively. Belt 8
may be
toothed, but may also comprise any flexible member
suitable for bearing a tensile load. Sprocket 52 and
sprocket 552 are each toothed to positively engage belt
8.
Figure 14 is a top perspective view of the internals
of the device. Belt
8 engages tensioner assembly 15.
All tensile loads in belt 8 and in belt 200 are imparted
by tensioner assembly 15. Rotation of pivot arm 5 causes
movement of belt 8 which in turn causes movement in a
synchronized or coordinated manner of pivot arm 55 in the
same rotational direction as pivot arm 5.
Rotation of
pivot arm 55 causes movement of belt 8 which in turn
causes movement in a synchronized or coordinated manner
of pivot arm 5 in the same rotational direction as pivot
arm 55, as well. Hence, in operation pivot arm 5 and
pivot arm 55 move substantially simultaneously by action
of belt 8.
A "synchronized" movement may be described as a
movement of pivot arm 5 and pivot arm 55 wherein each
pivot arm rotates at substantially the same time through
substantially the same angle. A
"coordinated" movement
may be described as a movement of pivot arm 5 and pivot
arm 55 wherein each pivot arm rotates at substantially
the same time, but not through an identical angle for
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both pivot arms. Rotation of the pivot arms through non-
identical angles may be caused by stretch of belt 8 for
example, as explained herein, see Figure 22.
Figure 15 is a detail of the device in an operating
position on an engine. In a
typical asynchronous
accessory belt drive system (ABDS) the inventive device
1000 is arranged such as shown in Figure 15.
Tensioner
1000 is mounted to the alternator 203 using fasteners 13
and 133. Belt 200 is routed around a crankshaft pulley
201, alternator pulley 202 and tensioner pulley 10 and
pulley 101. This arrangement disposes the belt spans on
either side of alternator pulley 202. Tension in belt 200
is maintained by operation of tensioner 1000 and the
position of pulley 10 and pulley 101. Belt
200 is
typically a multi-ribbed belt known in the art, namely,
it comprises multiple ribs running in the longitudinal or
endless direction.
The position of pivot arm 5 and thus pulley 10 is
controlled by belt 8. The position of pivot arm 55 and
thus pulley 101 is also controlled by belt 8. Tension in
belt 8 is controlled by the position of pulley 10 and
pulley 101. Tension in belt 8 is maintained by tensioner
assembly 15. The
span of belt 8 that engages tensioner
assembly 15 is the tight side span of belt 8. The
remaining span 81 of belt 8 does not require any
tensioning. The
tension in belt 8 creates torque on
pivot arm 5 and pivot arm 55 through its engagement with
sprocket 52 and sprocket 552 respectively.
Figure 16 shows the orientation of pivot arm 5 and
pivot arm 55 and the hub load in the "at rest" position.
When the engine accessory drive is in the at rest
position, the tension in belt 200 is equalized throughout
the belt.
Tension of belt 200 in this condition is the
initial belt tension and it is established by the
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inventive tensioner.
Pivot arm 5 and pivot arm 55 are
each urged to rotate into belt 200 due to the torque
induced on them by the tension in belt 8 caused by
tensioner assembly 15 bearing on belt 8. The tension in
belt 8 causes pivot arm 5 and pivot arm 55 to rotate
until the torque is opposed equally by the torque created
by the hub load from belt 200. The
belt 200 hub load
acts against pivot arm 5 and pivot arm 55 through the
center axis of bearing 12 and bearing 102 respectively.
This causes a torque to be induced on each pivot arm 5
and pivot arm 55 based on the direction of the load on
the respective arm and the effective arm length. Each
pivot arm 5 and pivot arm 55 will rotate until the hub
load torque is equal and opposite the belt 8 torque on
the respective pivot arm 5 and pivot arm 55.
The length of the moment arm from belt 8 acting on
pivot arm 5 is equal to the
pitch diameter of sprocket
52 (for example, 26.3mm). The
length of the moment arm
acting on pivot arm 5 from the belt 200 hub load is equal
to the arm length times the sine of the angle of the
force to the pivot arm 5 which is referred to as the
effective arm length. Figure 17A is a detail of the pivot
arm load conditions. Figure 17B is a detail of the pivot
arm load conditions.
The length of the moment arm of belt 8 acting on
pivot arm 55 is equal to 1. the pitch diameter of sprocket
552 (for example, 26.3mm). The length of the moment arm
acting on pivot arm 55 from the belt 200 hub load is
equal to the arm length times the sine of the angle of
the force to the pivot arm 55 which is also referred to
as the effective arm length.
In a belt drive, when the torsion angle of a belt
around a pulley is 60 degrees the hub load created by the
tension in the belt is roughly equal to the tension in
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the belt. For instance, if the tension in each span of
the belt is 100N, then the hub load on a pivot arm 5
would equal 100N when the torsion angle is 60 degrees.
The torque created in pivot arm 5 is then the hub
load 100N times the effective arm length. If the
effective arm length is 7mm, then the torque on pivot arm
5 from the hub load is 100N x 0.007m = 0.70 Nm.
The tension in belt 8 would then need to be 0.7
Nm/0.0263m = 26.6N to create an equal and opposite torque
on pivot arm 5 and pivot arm 55.
As can be seen from the previous example, the
tension in belt 8 need only be roughly 'K,1 that of the belt
200 slack side tension. This
is the ratio of the
effective arm length to the radius of sprocket 52 and
sprocket 552.
Figure 18 shows the orientation of pivot arm 5 and
pivot arm 55 and the hub load in the alternator starting
mode position. During a starting event in which the
alternator becomes the driver pulley in the system
instead of the crankshaft, the upper span (C) in Figure
18 becomes the slack side span and the lower belt span
(D) the tight side span. If the alternator supplies 60Nm
of torque for a starting event, the tight side tension
must rise to a level capable of supporting this level of
power transmission. During
a start event, the lower
pivot arm 55 is forced to rotate by the increased tension
in belt 200. The
tension in belt 200 rises to a level
that is sufficient to start the engine rotating, that is,
driving the crankshaft.
In belt drives, the ratio of the tight side tension
to the slack side tension about a pulley is known as the
tension ratio. To
maintain proper belt function in an
ABDS drive, it is necessary that the tension ratio be
approximately 5.
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For a starting event requiring 60Nm torque supplied
by the alternator, the difference in tension about the
alternator pulley required to create 60Nm torque is:
Torque = r *AT = r(T2-T1) (Eq. 1)
Where T2 = tight side tension
Ti = slack side tension
R = pulley radius = 0.030m
solving for AT:
AT = Torque/r = 60/0.030 = 2000N
It is known that the slack side tension must be such
that a tension ratio of 5 is maintained for proper ABDS
system funtion. So:
T2/T1 = 5 (Eq. 2)
It is known that
AT = T2-T1 (Eq.3)
Solving for T2 in Eq. 3
T2 = AT+T1
Substituting into Eq. 2 and solving for Ti
(AT+T1)/T1 = 5
AT+T1 = 5T1
AT = 4T1
AT/4 = Ti
2000/4 = Ti
Ti = 500N
Substituting back into Eq. 2
T2/T1 = 5
T2/500 = 5
T2 = 2500N
The high tension in the tight side span (T2) (see
(D) Figure 18) during the starting event causes the hub
load acting on pivot arm 55 to create a torque that
causes the arm to rotate to a position where the arm
direction is essentially parallel with the direction of
the hub load, see Figure 18. This has the effect of
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temporarily transforming tensioner assembly 502 into a
fixed idler. The
amount of rotation of tensioner
assembly 502 pivot arm 55 is approximately 65 degrees.
The arrangement of pivot arm 5 and pivot arm 55 is
such that as each rotates toward belt 200 the movement of
pulley 10 and pulley 101 respectively toward the belt 200
per degree of rotation is greater than when each pivot
arm rotates away from belt 200. This
requires that the
angle of rotation of the slack side tensioner assembly
501 be less than that moved by the tight side tensioner
assembly 502 in order to maintain the same belt length.
Table 1 shows the amount of rotation of each pivot arm 5
and pivot arm 55 during a starting event with no belt
stretch.
Tablel
Position Belt length A angle Top Arm 5 A angle Bottom Arm
Nominal (no load) 884.2mm
Alternator starting 884.2mm 2.5 65
Since belt 200 stretches due to loading, the slack
side pivot arm 5 must compensate for this stretch.
Assuming the amount of belt stretch due to loading is 3
mm, the slack side tensioner must rotate an additional 30
20 degrees to take up this additional belt length. Table 2
shows the amount of rotation of each pivot arm 5 and
pivot arm 55 during a starting event and includes the
information taking belt stretch into account.
Table2
Position Belt length A angle Top Arm 5 A angle Bottom Arm
Nominal (no load) 884.2mm
Alternator start (no stretch) 884.2mm 25 65
Alternator start (with stretch) 887.2mm 55 65
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As can be seen in Table 2, the slack side tensioner
pivot arm 5 must rotate an additional 30 degrees to
account for the stretch of belt 200.
Figure 22A
illustrates pivot arm position during an operating
condition. Figure 22B illustrates pivot arm position
during an operating condition. Figure 22C illustrates
pivot arm position during an operating condition. Figure
22D illustrates pivot arm position during an operating
condition.
Additionally, the arrangement is such that the slack
side pivot arm 5 effective arm length is reduced as it
moves toward belt 200. This
reduction in effective arm
length enables the inventive device to increase slack
side tension and thus increase the overall belt 200
tension during events such as alternator starting. This
is accomplished because the tension in belt 8 is
controlled via the tensioner assembly 15.
Tensioner
assembly 15 induces a torque on pivot arm 5 that must be
opposed by the hub load of belt 200 as previously
described. Fifty-
Five degrees of rotation of the slack
side pivot arm 5 reduces its effective arm length from
7mm to 4.2mm.
Since tensioner assembly 15 controls the tension in
belt 8 and thereby belt 200, it controls the torque in
pivot arm 5. The rotation angle of pivot arm 5 is less
than the rotation angle of pivot arm 55 by 10 degrees.
This effectively shortens the span of belt 8 acting upon
tensioner assembly 15, thereby causing rotation of
tensioner assembly 15. The
rotation of tensioner
assembly 15 causes the tension in belt 8 to increase.
Increasing tension in belt 8 increases the torque on
pivot arm 5 and pivot arm 55. The
hub load force
creating the opposing torque on pivot arm 5 and pivot arm
55 must increase to reach equilibrium.
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To calculate the tension on belt 200 which is
approximately equal to the hub load as previously shown,
one simply divides the torque on pivot arm 5 from belt 8
by the new effective arm length. The new tension in belt
5 8 is 81N. The torque on pivot
arm 5 from belt 8 is
2.13Nm. The
tension in belt 200 is 2.13Nm/0.0042m =
507N. This
tension is above the minimum slack side
tension (Ti) calculated earlier and creates the proper
overall belt tension. The inventive device's ability to
increase slack side tension is advantageous in that it
allows overall initial tensions to be reduced which is
beneficial for belt life and accessory life.
Hence, for a 60Nm starting event, the inventive
device provides the minimum 500N slack side tension. For
a 60Nm regenerative braking event, the inventive device
provides the minimum 500N slack side tension. For no load
situations, the inventive device provides reduced slack
side tension of 100N. For medium load situations such as
20Nm alternator load, the inventive device provides the
necessary slack side tension of 167N.
Please note that all numeric values used in this
description are only examples used for the purpose of
illustration and are not intended to limit the scope of
the invention.
Damping belt vibration is also an important function
of tensioners. Damping is most often accomplished by
creating resistance to movement in the tensioner pivot
arm. It is generally considered advantageous to have
asymmetric damping in ABDS tensioners.
Asymmetric
damping is a condition where resistance to tensioner arm
movement differs depending on the direction of tensioner
pivot arm movement.
Figure 19 is a detail of a clutch spring. Figure 20
is a detail of a clutch spring. Damping in the inventive
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tensioner is created through the interaction of damping
assembly 4 with clutch spring 3 and pivot arm 5, and by
interaction of damping assembly 44 with clutch spring 33
and pivot arm 55. Clutch spring 3 is a right hand wind
and clutch spring 33 is a left hand wind. Clutch spring
3 is attached to base 1 through the engagement of tang 31
into slot 911. Clutch spring 33 is attached to base 1
through the engagement of tang 331 into slot 910, see
Figure 21. Figure 21 is a detail of the base.
Clutch spring 3 acts as a one way clutch against
damping assembly 4. Clutch spring 3 limits damping
assembly 4 so it will only rotate freely in the direction
in which the pivot arm 5 rotates toward the belt 200.
Damping assembly 4 is configured such that damping shoe
41 creates outward pressure on damping ring 42 which in
turn is forced outward into contact with damping surface
51 of pivot arm 5. The normal force created by this
outward pressure combines with the friction coefficient
of damping ring 42 on the pivot arm 5 to create a
frictional force resisting movement between damping
assembly 4 and pivot arm 5. The
friction force causes
damping assembly 4 to urge pivot arm 5 to rotate whenever
damping assembly 4 rotates.
Clutch spring 33 acts as a one way clutch against
damping assembly 44. Clutch
spring 33 limits damping
assembly 44 so it will only rotate freely in the
direction in which pivot arm 55 rotates toward the belt
200. Damping assembly 44 is configured such that damping
shoe 441 creates outward pressure on damping ring 442
which in turn is forced outward into contact with damping
surface 551 of pivot arm 55. The normal force created by
this outward pressure combines with the friction
coefficient of damping ring 442 on pivot arm 55 to create
a frictional force resisting movement between the damping
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assembly 44 and pivot arm 55. The friction force causes
damping assembly 44 to cause pivot arm 55 to rotate
whenever damping assembly 44 rotates.
During vehicle operation in which the tight span of
belt 200 is engaged with tensioner assembly 15, as belt
200 tension increases, the torque exerted by the hub load
on pivot arm 5 increases causing pivot arm 5 to rotate
away from belt 200. During this movement away from belt
200, clutch spring 3 locks against damping assembly 4
eliminating the ability of damping ring 4 to rotate with
pivot arm 5, which stops pivot arm 5 from rotating.
Pivot arm 5 can then only rotate after the torque caused
by the increasing hub load exceeds the resistance from
damping assembly 4. In
addition, the tension in the
slack side span of belt 200 drops and the respective
pivot arm 55 moves into belt 200.
Since in this
direction of rotation the clutch spring 33 clutch
releases, pivot arm 55 freely rotates and thereby
maintains proper slack span belt tension.
During vehicle operation in which the tight span is
against tensioner assembly 502, as belt 200 tension
increases, the torque exerted by the hub load on pivot
arm 55 increases causing the arm to rotate away from belt
200.
During this movement away from belt 200, clutch
spring 33 locks against damping assembly 44 eliminating
the ability of damping assembly 44 to rotate with pivot
arm 55, thereby stopping pivot arm 55. Pivot arm 55 can
only rotate after the torque caused by the increasing hub
load exceeds the resistance from damping assembly 44. In
addition, the tension in the slack side span of belt 200
drops and the respective pivot arm 5 moves into belt 200.
Since in this direction of rotation the clutch spring 3
clutch releases pivot arm 5, pivot arm 5 freely rotates
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and thereby maintains proper slack span belt tension in
belt 200.
The rotational resistance of pivot arm 5 caused by
damping assembly 4 acting with clutch spring 3 creates a
greater resistance to movement in one direction than the
other. The unequal resistance to rotation creates
asymmetric damping in tensioner assembly 501.
The rotational resistance of pivot arm 55 caused by
damping assembly 44 acting with clutch spring 33 creates
greater resistance to movement in one direction than the
other. This unequal resistance to rotation creates
asymmetric damping in tensioner assembly 502.
BAS systems also operate in normal modes in which
the alternator loads the crankshaft pulley through belt
200, for example, when the alternator is generating
electrical power.
BAS systems also operate in modes in which the
alternator is used to highly load the crankshaft pulley
and in turn assist vehicle breaking, also referred to as
regenerative braking. In regenerative braking events the
loading of the belt is opposite of that described above
in the alternator starting event. In this case the
function of the inventive tensioner is merely switched
such that the tight span of belt 200 bears on tensioner
assembly 501 and the slack side span of belt 200 bears on
tensioner assembly 502.
Further embodiments include, but are not limited to,
sprocket 52 and sprocket 552 are each individually or in
combination, non-circular in shape. Each sprocket 52 and
sprocket 552 can be non-coaxial with pivot arm 5 and
pivot arm 55 pivot axis respectively.
Sprocket 52 and
sprocket 552 can be eccentric to pivot arm 5 and pivot
arm 55 and each can have a different offset respectively.
Pivot arm 5 can have a different eccentric offset from
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pivot arm 55.
Sprocket 52 and sprocket 552 can be
different diameter. Belt
8 need not be an endless
plurality of evenly spaced teeth, namely, belt 8 can have
ends wherein span 81 is not present. Belt 8 need not be
an endless plurality of evenly spaced teeth but rather
only needs to be toothed at the interface with sprocket
52 and sprocket 552. Belt 8 can be a flexible endless
member such as a flat belt, strap, rope or cable capable
of carrying a tensile load. Belt
8 can be a rigid bar
hinged near tensioner assembly 15. Belt 8
can be
replaced by a compressible member representing span 81 of
belt 8.
Figure 26 is a rear detail of the tensioner mounted
to the alternator. Fastener 13 and fastener 133 are used
to attach the tensioner 1000 to an alternator 203.
Figure 27 is a rear top view detail of the tensioner
mounted to the alternator.
Figure 28 is a bottom view of the tensioner arm.
End 1541 of spring 154 engages between tab 1530 and tab
1531 on pivot arm 153.
Figure 29 is a perspective view of section 29-29 in
Figure 2. Damping assembly 4 frictionally engages surface
51 of pivot arm 5. Damping assembly 44 frictionally
engages surface 551 of pivot arm 55.
Clutch spring 3
frictionally engages damping shoe 41. Clutch
spring 33
frictionally engages damping shoe 441.
Clutch spring 3
and clutch spring 33 are each loaded in the unwinding
direction, which means the diameter of each expands as
the imparted load increases. Expansion of clutch spring
3 presses damping shoe 41 against damping ring 42 which
in turn presses against surface 51, which slows or stops
rotation of pivot arm 5. Expansion of clutch spring 33
presses damping shoe 441 against damping ring 442 which
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in turn presses against surface 551, which slows or stops
rotation of pivot arm 55.
For example, if belt 8 moves in direction (M1),
clutch spring 3 will be loaded in the winding direction
and therefore will not resist rotation of pivot arm 5.
However, clutch spring 33 will be loaded in the unwinding
direction and therefore damping assembly 44 will resist
rotation of pivot arm 55.
If belt 8 moves in direction (M2), clutch spring 3
will be loaded in the unwinding direction and therefore
will resist rotation of pivot arm 5.
However, clutch
spring 33 will be loaded in the winding direction and
therefore damping assembly 44 will not resist rotation of
pivot arm 55.
Tensioner assembly 15 will maintain load in belt 8
regardless of the direction of movement of belt 8.
Tensioner assembly 15 will maintain load in belt 200
through each pivot arm 5 and pivot arm 55 regardless of
the direction of movement of belt 200.
Figure 30 is a perspective view of an alternate
embodiment. The
alternate embodiment comprises idler
assembly 100 and idler assembly 200, each pivotally
engaged with base 300.
Tensioner assembly 340 is
pivotally mounted to base 300.
Adjuster 35 is used to
adjust a position of tensioner assembly 340. Each idler
assembly 100, 200 pivots eccentrically about its
respective pivot axis. The pivot axis for idler assembly
100 is post 3310. The pivot axis for idler assembly 200
is post 3315, see Figure 47.
Figure 31 is a plan view of the embodiment in Figure
30.
Figure 32 is an exploded view of the embodiment in
Figure 30. Adjuster member 35 adjusts the load by which
tensioner 340 engages belt 315. Each retainer 355 holds
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each respective idler assembly 100, 200 in its proper
position. Damping mechanism 140 is disposed between
assembly 100 and base 300. Damping mechanism 240 is
disposed between assembly 200 and base 300. A
torsion
spring 320, 360 is engaged between each respective idler
assembly 100, 200 and base 300. Each
spring 320, 360
acts as a one-way clutch engaging damping mechanism 140,
240 and base 300.
Bushing 368 is engaged between each retainer 355 and
assembly 100 and 200.
Fasteners 18, 19, 20, 25 and 30
attach cover 375 to base 300.
Bushing 370 is engaged
between the base 300 and each assembly 100, 200.
Flexible member 315 does not comprise an endless
length, meaning, it has discrete ends. Each
end of
member 315 is attached to a lower eccentric arm 130, 230,
respectively.
Figure 33 is cross-sectional view of the embodiment
in Figure 31.
Eccentric idler assembly 100 comprises
upper eccentric arm 110, fastener 115, idler assembly
120, dust shield 125, lower eccentric arm 130, spring
320, and damping mechanism 140. Fastener 115 connects
upper arm 110 to lower arm 130.
Bushing 368 engages
upper arm 110. Bushing 370 engages lower arm 130.
Idler assembly 120 and dust shield 125 are coaxial
with eccentric axis 1320. Damping
mechanism 140 is
coaxial with pivot axis 1310. Eccentric axis 1120 is
coaxial with eccentric axis 1320.
Pivot axis 1110 is
coaxial with pivot axis 1310.
Figure 34 is a side view of an eccentric arm cam.
The idler assembly comprises a lower eccentric arm 130.
Arm 130 comprises a pivot axis 1310, an eccentric axis
1320, toothed portion 1340, cam portion 1350 and tang
1360.
Eccentric axis 1320 and pivot axis 1310 are not
coaxial and instead are offset by distance 1330. Portion
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1370 engages bearing 121. The
radius R1 of toothed
portion 1340 is less than the radius R2 of the cam
portion 1350. Belt 315 is progressively engagable with
cam portion 1350 as arm 130 pivots.
Figure 35 is a perspective view of the arm in Figure
34. Arm 130 comprises tang 1360. One end of belt 315 is
captured with tang 1360. Threaded hole 1380 receives
fastener 115.
Figure 36 is a perspective view of the arm in Figure
37. Lower arm 230 comprises tang 2360. The other end of
belt 315 is engaged with tang 2360. Portion 2370 engages
bearing 221. Threaded hole 2380 receives fastener 215.
Figure 37 is a side view of an eccentric arm cam.
The idler assembly comprises a lower eccentric arm 230.
Arm 230 comprises a pivot axis 2310, an eccentric axis
2320, toothed portion 2340, cam portion 2350 and tang
2360.
Eccentric axis 2320 and pivot axis 2310 are not
coaxial and instead are offset by distance 2330. Radius
R1 of toothed portion 2340 is less than radius R2 of the
cam portion 2350. Belt 315 is progressively engagable
with cam portion 2350 as arm 230 pivots.
Figure 38 is a side view of an eccentric upper arm.
Upper eccentric arm 110 comprises a pivot axis 1110 and
eccentric axis 1120. Axis 1110 and 1120 are not coaxial
and instead are offset by distance 1130. Portion 1140
pivotally engages retainer 355 through busing 368.
Figure 39 is a perspective view of the arm in Figure
38. Recess 1150 receives fastener 115.
Figure 40 is a side view of an eccentric upper arm.
Upper eccentric arm 210 comprises a pivot axis 2110 and
eccentric axis 2120. Axis 2110 and 2120 are not coaxial
and are offset by distance 2130. Portion 2140 pivotally
engages retainer 355 through bushing 368.
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Figure 41 is a perspective view of the arm in Figure
40. Recess 2150 receives fastener 215.
Figure 42 is a side cross section of the embodiment
in Figure 31. Eccentric idler assembly 200 comprises
upper eccentric arm 210, fastener 215, idler assembly
120, dust shield 225, lower eccentric arm 230, damping
mechanism 240 and spring 360. Fastener 215 connects arm
210 to arm 230. Upper arm 210 engages retainer 355
through bushing 368.
Idler assembly 220 and dust shield 225 are coaxial
with eccentric axis 2320.
Damping mechanism 240 is
coaxial with pivot axis 2310.
Eccentric axis 2120 is
coaxial with eccentric axis 2320.
Pivot axis 2110 is
coaxial with pivot axis 2310.
Figure 43 is a detail of an idler assembly. Idler
assembly 120 comprises bearing 121 and idler 122.
Idler
assembly 220 comprises bearing 221 and idler 222.
Idler
assembly 120 and 220 are identical in form and function.
Figure 44 is a detail of the damping mechanism for
the embodiment in Figure 30. Damping mechanism 140
comprises transfer ring 141, damping shoe 142 and damping
ring 143. Transfer ring 141 is cylindrical with an inner
surface 1410, slot 1411, face 1412 and face 1413, see
Figure 45.
Damping shoe 142 is cylindrical with a gap
1425 running axially and tab 1424 protruding axially. Tab
1424 comprises face 1422 opposing face 1423. Damping ring
143 is cylindrical with a gap 1430 running axially.
Damping ring 143 and damping shoe 142 are coaxial with
transfer ring 141. Face 1413 opposes face 1423. Face 1412
opposes face 1422.
Face 1410 frictionally engages spring 320. Outward
surface 1431 of damping ring 143 frictionally engages
inward surface 1390 of lower eccentric arm 130, see
Figure 35a.
Damping shoe 142 acts in a spring like
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manner pushing outside surface 1441 outward against
inward surface 1442 and thus forces surface 1431 outward
against surface 1390. The
outward spring force creates
the normal force for frictional engagement of damping
mechanism 140 to arm 142. When arm 142 rotates into the
belt 200, spring 320 clutches and disengages damping
mechanism 140. Arm
142 is free to rotate toward belt
200. When arm 142 rotates away from belt 200, the outer
surface of spring 320 radially expands in the unwinding
direction thereby clutching and engaging surface 1410 of
damping mechanism 140.
Rotation of arm 142 is resisted
by the frictional engagement of damping mechanism 140
with arm 142.
Damping mechanism 240 is identical in form and
function to damping mechanism 140. The corresponding
numbers for damping mechanism 240 are noted in
parenthesis in Figure 44.
Transfer ring 241 is
cylindrical in shape with an inner surface 2410, slot
2411, face 2412 and face 2413. Damping shoe 242 is
cylindrical in shape with a gap running axially and tab
2424 protruding axially. Tab 2423 has face 2422 opposing
face 2423. Damping ring 243 is cylindrical in shape with
a gap running axially. Damping mechanism 240 comprises
transfer ring 241, damping shoe 242 and damping ring 243.
Damping ring 234 and damping shoe 242 are coaxial with
transfer ring 241, face 2413 opposes face 2423. Face
2412 opposes face 2422.
Face 2410 frictionally engages spring 360. Outward
surface 2431 of damping ring 243 frictionally engages
surface 2390 of lower eccentric arm 230, see Figure 36a.
Damping shoe 242 acts in a spring like manner pushing
outside surface 2441 outward against inside surface 2442
and thus forces surface 2431 outward against surface
2390. The outward spring force creates the normal force
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for frictional engagement of damping mechanism 240 to arm
242. When
arm 242 rotates into belt 200, spring 360
clutches and disengages damping mechanism 240. Arm 242
is free to rotate toward belt 200. When arm 242 rotates
away from belt 200, the outer surface of spring 360
radially expands in the unwinding direction thereby
clutching and engaging surface 2410 of damping mechanism
240.
Rotation of arm 242 is resisted by the frictional
engagement of damping mechanism 240 with arm 242.
Figure 45 is the damping mechanism for the
embodiment in Figure 30.
Figure 46 is a cross section of the embodiment in
Figure 31. Base assembly 300 comprises retainers 355,
receivers 310, belt 315, spring 320, bushings 370, base
330, spring 360, cover 375, idler 335, idler 345, and
tensioner assembly 340. Belt
315 is a toothed or
synchronous belt. Belt 315 engages sprocket 1340 and
sprocket 2340 of each arm 130 and 230 respectively. Belt
315 is attached to sprocket 1340 by tang 1360. Belt 315
is attached to sprocket 2340 by tang 2360. Each
idler
335 and 345 has a smooth surface for engaging the back
side of belt 315.
Arm 3200 of spring 320 resides within pocket 3320.
Arm 3600 of spring 360 resides within pocket 3325.
Tensioner assembly 340 is pivotally attached to post 3345
by fastener 20.
Cover 375 is attached to base 300 by
fastener 30 and fastener 25.
Figure 47 is a detail of the base of the embodiment
in Figure 30. Base 300 comprises cylindrical post 3310,
cylindrical post 3315, cylindrical post 3330, cylindrical
post 3335, cylindrical post 3345, receiver 3340, pocket
3320 and pocket 3325. Pocket 3320 receives arm 3200.
Pocket 3325 receives arm 3600.
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Idler 335 is journalled to post 3330.
Idler 345 is
journalled to post 3335. Bushing 325 is coaxial with post
3310. Bushing 370 is coaxial with post 3315. Pivot axis
1310 is coaxial with post 3310.
Pivot axis 2310 is
coaxial with post 3315. Adjuster 35 engages receiver
3340.
Figure 48 is a detail of the spring of the
embodiment in Figure 30.
Spring 320 comprises arm 3200
at one end. Arm 3200 engages pocket 3320, thereby
anchoring arm 3200.
Figure 49 is a detail of the spring of the
embodiment in Figure 30.
Spring 360 comprises arm 3600
at one end. Arm 3600 engages pocket 3325, thereby
anchoring arm 3600.
Figure 50 is a plan view of the tensioner of the
embodiment in Figure 30. Fastener 20 engages hole 3471.
Figure 51 is a side view of the tensioner in Figure
50.
Figure 52 is a side view of the tensioner in Figure
50. Each pin 3510 and 3511 bears upon and locates
tensioner 340 in base 300. Pins
3510 and 3511 provide
clearance for idler 3500.
Figure 53 is a cross section of the tensioner in
Figure 50.
Tensioner assembly 340 comprises cover 3410,
pivot pin 3420, bushing 3430, torsion spring 3440,
bushing 3450, arm 3460, base 3470, pin 3480, bushing
3490, and idler 3500. Bushing 3430 and bushing 3450 are
coaxial with arm 3460.
Spring 3340 is coaxial with arm
3460 and engaged between arm 3460 and cover 3410. Pivot
pin 3420 is coaxial with arm 3460 and fixedly attached to
base 3470. Pin
3480 is coaxial with bushing 3490 and
fixedly attached to arm 3460. Idler 3500 is coaxial with
bushing 3490. Tensioner assembly 340 is known in the art
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of automatic belt tensioners found commonly in automotive
and industrial applications.
Figure 54 is an exploded view of the tensioner in
Figure 50. Hole 3471 engages post 3345.
Figure 55 is a detail of the base in Figure 47.
Tensioner 340 pivots about post 3345.
Adjuster 35
adjusts the position of tensioner 340 relative to belt
315, thereby adjusting the load imparted to belt 315.
Figure 56 is a detail of the base in Figure 47.
Tensioner assembly 340 is installed such that its
position is adjustable. Adjuster 35 is threadably
engaged with base 3300. The
position of adjuster 35
determines the position tensioner assembly 340. The
extended position of adjuster 35 is the initial
installation position. Screwing
in adjuster 35 causes
tensioner 340 to pivot about post 3345 thereby applying a
load to belt 315. This
transitions the device to the
contracted position (Figure 57) which progressively
increases the tension in ABDS belt 200. The
belt 200
tension is adjusted in this manner for proper system
performance.
Figure 57 is a detail of the base in Figure 47.
Adjuster 35 is shown in the "screwed in" position which
represents the position of maximum tension for belt 315
and belt 200, see Figure 15.
This alternate embodiment incorporates cam 1350 and
cam 2350. Cam
1350 and cam 2350 each engage belt 315.
Given the engagement with belt 315 the angular motion of
lower eccentric arm 130 and lower eccentric arm 230 are
the same as long as arm 3460 of tensioner assembly 340
remains stationary.
It is desirous to raise the tension in the slack
side of belt 200 during certain operating events as
explained elsewhere in this specification, see Fig. 15.
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This is achieved by deflecting arm 3460, which deflects
spring 3440 thereby raising the torque in arm 3460. The
torque in arm 3460 is opposed by the tension in belt 315
in the form of the hub load on idler 3500.
Deflecting
arm 3460 away from belt 315 increases the torque in arm
3460. This causes the tension in belt 315 to increase
and thus the tension in the slack side span of belt 200.
When lower eccentric arms 130 and 230 each rotate
clockwise as seen in Figure 56, cam 2350 engages belt 315
while cam 1350 rotates away from belt 315. This
increases the take up of belt 315 causing arm 3460 to
deflect, which raises tension in belt 315. This
increases the tension in belt 200. Conversely, if lower
eccentric arm 130 and 230 rotate counterclockwise as seen
in Figure 56, cam 1350 engages belt 315 while cam 2350
rotates away from belt 315. This
increases take up of
belt 315 causing arm 3460 to deflect raising tension in
belt 315. This
increases the tension in the slack side
span of belt 200.
In operation each cam profile 1350, 2350 enables
additional take up of belt 315. The additional take up
of belt 315 has two advantages. It increases deflection
of the tensioner 340 which increases movement of the
slack side arm (idler 100) attached to the end of belt
315. The increased deflection of tensioner 340 gives an
additional level of tension control to the overall
device. The shape of the cam profiles can dramatically
change the slack side tension of belt 200, namely, radius
R2 can be varied. The
increased movement of the slack
side tensioner arm is such that in an increasing
accessory belt 200 load situation the arm is moving into
the belt at a greater rate with the cam than without it.
This raises slack side tension of belt 200 at an
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increased rate. This
provides the ability to further
tune the tensioner to the desired application.
The alternate embodiment adds the transfer ring 141,
241 to each damping mechanism 140, 240. Transfer ring
141, 241
absorbs the pressure from each clutch spring
320, 360 and separates it from the respective damping
shoe 142, 242. Each
damping shoe is rotationally fixed
to each transfer ring 141, 241 enabling clutching and
enabling control of the normal force on the damping ring
by the damping shoe.
The tensioner assembly 340 is a miniature Z-style
tensioner known in the art. The tensioner occupies
otherwise unused space within the plane of the belt 200.
Tensioner 340 is mounted such that its position is
adjustable. The position of fastener 35 determines the
position of tensioner assembly 240. This enables one to
control the installation tension in 200 by simply
adjusting fastener 35. Moving tensioner assembly 340
into the belt 315 raises the belt tension thus raising
the accessory belt 200 tension.
Although forms of the invention have 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.
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