Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TENSIONER ASSEMBLY WITH ELECTRONICALLY CONTROLLED
VIBRATION CLUTCH ASSEMBLY
Field of the Invention
[0001] The invention relates to tensioners for belt drive systems, and more
particularly to
tensioners for belt drive systems capable of actuation to various positions.
Description of the Related Art
[0002] Typical belt tensioners are known in the art for use in automotive
applications and are
utilized to apply a steady uniform load to the belt or chain to maintain the
applied belt tension
on a slack slide of the belt drive above a minimum value required to drive
various
components attached to the belt system. Additionally, belt tensioners are
utilized in a non-
synchronized belt drive system to prevent belt slippage and power transmission
loss.
Tensioners are commonly utilized in accessory drive systems, and timing belt
or timing chain
systems of an automobile.
[0003] Typical belt tensioners include a tensioner arm, which is fitted with
an idler pulley
that is applied to the belt. A radial bearing operably connects the idler
pulley to the tensioner
arm. The tensioner arm is rotatably mounted on a pivot pin that is fixedly
mounted to the
engine. The axis of rotation of the idler pulley is offset from the axis of
rotation of the
tensioner arm. A bushing is disposed about the pivot pin. A rotary spring is
wrapped
coaxially around the bearing pin and bushing for pretensioning the tensioner
arm enabling the
idler pulley to exert a predetermined force on the belt. In this manner, the
force of the rotary
spring applies a load to the belt to take up slack due to changes in the
length of the belt or
chain.
[0004] In a typical belt drive system, a primary drive pulley, such as an
engine crankshaft
pulley rotates to drive various accessory components associated with the belt
system, for
example, an alternator, water pump, power steering pump or air conditioning
compressor. As
the belt stretches under load, the coil spring must drive the tensioner arm
farther into the belt
to compensate for the longer belt length.
[0005] Variations in the belt tension occur when the driving pulley suddenly
decelerates from
a steady state condition while the other components continue rotating due to
their own
inherent inertia. In this situation, the accessory components become the
primary drivers
within the system resulting in changes in the tension within the belt. During
this transitional
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maximum travel position. This backward motion continues to a point
corresponding to the
tensioner arm position at which the torque output applied by the coil springs
inside the
tensioner equals or exceeds the equivalent load applied to the tensioner arm
by the belt span.
If the torque output of the spring is significantly lower than the load
applied by the belt span,
the tensioner arm continues to travel until it reaches its mechanical load
stop, possibly
overstressing the coil spring inside the tensioner. Additionally, fluctuations
in the tension
within the belt can lead to belt flutter or belt skip resulting in damage to
the other components
of the belt drive system.
[0006] A tensioner has been proposed in WO 03/048606 wherein a clutch spring
and a
frictional brake are utilized to provide a travel limit for the tensioner arm.
This tensioner has
a relatively large range of travel to take up a significant degree of belt
flutter. However, the
tensioner passively responds to belt movement to enable the braking or locking
function.
[0007] Another tensioner is commercially available on an Alfa Romero 3.01 24
valve engine.
This tensioner provides a clutch spring that is operably connected between a
bi-metallic strip
and a tensioner arm. As the.temperature varies, the length of the strip varies
proportionally.
This movement is coupled to the clutch spring to engage and disengage the
spring. As the
engine temperature increases, the clutch spring allows a greater degree of
travel of the
tensioner arm to take up the slack in the belt as it stretches with increasing
temperature. The
tensioner passively responds temperature to effect the braking or locking
function.
[0008] There is therefore a need in the art for a tensioner capable of dynamic
actuation or
adjustment to various positions in response to transitional loading in the
belt drive system,
providing stability to the belt drive system.
Summary Of The Invention
[0009] A tensioner for use in a belt or chain drive system includes a base and
a tensioner arm
pivotally mounted to the base and movable between a load stop position and a
free stop
position. A spring biases the tensioner arm to move towards the free arm stop
position. A
clutch spring is associated with the base and tensioner arm. An electronic
actuator,
preferably an actuator comprising a shape memory alloy, is associated with the
clutch spring
for engaging and disengaging the clutch spring in relation to the base,
whereby a stop
position of the tensioner arm can be selectively fixed upon selective
activation of the
electronic actuator.
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Brief Description Of The Drawings
[0010] Figure 1 is schematic representation of an accessory drive system
including alternator
and air conditioning pulleys;
[0011] Figure 2 is a perspective assembly view of a first embodiment of a
tensioner having
an electronic actuator;
[0012] Figure 3 is a perspective view of a first embodiment of a tensioner
having an
electronic actuator;
[0013] Figure 4 are side views detailing the tensioner of the first embodiment
in various
positions;
[0014] Figure 5 is a schematic representation of an accessory drive system
including an
alternator that is utilized as a starter for an engine;
[0015] Figure 6 is a schematic representation of the accessory drive system
when the
alternator is starting the engine resulting in a reversal of the tension
within the belt;
[0016] Figure 7 is a side sectional view a second embodiment of a tensioner
having an
electronic actuator;
[0017] Figure 8 is a side sectional view of a third embodiment of a tensioner
having an
electronic actuator;
[0018] Figure 9 is a perspective view of a fourth embodiment of a tensioner
having an
electronic actuator;
[0019] Figure 10 is a perspective view of a fifth embodiment of a tensioner
having an
electronic actuator;
[0020] Figure 11 is a side sectional view of the clutch mechanism of the
electronic actuator
according to the embodiment disclosed in Figure 10;
[0021] Figure 12 is a schematic representation of a open loop control of the
tensioner of the
present invention;
[0022] Figure 13 is a schematic representation of a closed loop control of the
tensioner of the
present invention;
[0023] Figure 14 is a perspective view of a fifth embodiment of the tensioner
of the present
invention; and
[0024] Figure 15 is a side elevational view of a sixth embodiment of the
present invention.
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Detailed Description Of The Preferred Embodiments
[0025] Referring to Figure 1, there is shown a schematic representation of an
accessory drive
system 2 including a crankshaft pulley 5, alternator pulley 10, air
conditioner pulley 15, and a
tensioner 20 disposed between the crankshaft pulley 5 and alternator pulley
10. A belt 17 is
wrapped about the pulleys for transferring rotational force between the
pulleys. Such a
representation is generic with respect to an accessory drive and may include
other
components commonly associated with accessory drive systems of automobiles.
[0026] As can be seen in Figure 1, the tensioner 20 is rotatable about a first
axis of rotation
from a free arm stop position 25 corresponding to the maximum inward position
with respect .
to the belt 17. The tensioner 20 also includes a load stop position 30 at the
opposite extreme
of the tensioner travel denoting the maximum position the tensioner may move
away with
respect to the belt 17. Between the two extremes of the free arm stop 25 and
load stop 30
positions is a nominal belt position 35 indicating the position of the
tensioner 20 with respect
to the belt 17 under steady state conditions.
[0027] Referring to Figures 2 and 3, there is shown a first embodiment of a
tensioner 220
= having an electronic actuator 210, preferably a shape memory alloy
actuator, according to the
present invention. As can be seen, the tensioner 220 includes a body or base
205 having a
circular ring or drum portion 215 extending there from. A spindle or pivot
shaft 225 extends
from the base 205 centrally or coaxially within the drum 215. A tensioner arm
230 and
bushing 235 are disposed about the pivot shaft 225 and include a tensioner
spring 240
disposed between the spring support 235 and tensioner arm 230. A clutch spring
245 is
= staked or attached to the tensioner arm 230 at a first end 247 of the
clutch spring 245 and
retained by the drum 215 at a second end 249 of the clutch spring 245. The
clutch spring 245
is disposed about the shaft 225 and drum 215. An inner surface 255 of the
clutch spring 245
may engage an outer surface 260 of the drum 215 to prevent movement of the
tensioner 220
by locking it in a desired position.
[0028] A pulley 265 is rotatably mounted about tensioner arm 230 and engages
the belt or
chain of a belt system. Pulley 265 rotates about a second axis that is
parallel to and offset
from the first axis of rotation of the tensioner arm 230.
[0029] Attached to the body or base 205 is a T-shaped pivot member or arm 270
disposed
about a pivot pin 275 for pivotal movement between an engaged position and a
disengaged
position. The second end 249 of the clutch spring 245 is attached or staked to
,a first branch
277 of the pivot member 270. A return spring 257 is attached to a second
branch 279 of the
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arm 270 for biasing the clutch spring 245 to a disengaged position relative to
the drum 215,
as will be discussed in more detail below. A third branch 281 of the arm 270
includes the
electronic actuator 210 of the present invention. The electronic actuator 210
comprises a
shape memory alloy wire 212 attached at a first end 214 to the third branch
281 of the arm
270 and a second end 216 attached to the body portion 205 of the tensioner
220.
[0030] The shape memory alloy wire 212 contracts or lengthens in response to a
change in
temperature. In a preferred aspect, the shape memory alloy wire 212 contracts
in response to
a change in temperature. In a preferred aspect, a current may be applied to
the shape memory
alloy wire 212 rapidly raising the temperature of the wire 212 causing
actuation or movement
of the Arm 270 about the pivot pin 275. In this manner, the second end 249 of
the clutch
spring 245 is manipulated to cause engagement of the inner surface 255 of the
clutch spring
245 with the outer surface 260 of the drum 215. The coils or wraps of the
clutch spring
contract increasing frictional engagement thereby, preventing movement of the
tensioner 220
and locking it in a desired position.
[0031] Also included in the first embodiment is a stop or pin 285 positioned
adjacent to the
arm 270 preventing movement of the arm 270 beyond a desired position.
[0032] In a preferred aspect of the present invention, the shape memory alloy
wire 212 may
comprise nitinol or flexinol SMA materials. Typical SMA materials contract or
expand when
undergoing a phase transformation, resulting in a length change of from 4 to
10 percent at the
transition temperature of the SMA material. However, a specified wire 212 of a
given
composition and shape can contract or expand to a specified distance within
tight tolerance
controls. Preferably, flexinol is utilized by the present invention as it has
advantageous
fatigue properties allowing for greater numbers of cycles to be performed
before failure of a
wire. Preferably, the flexinol wire does not undergo a phase change causing
contraction of
the wire below a temperature of 200 C. In this manner, the wire 212 will not
be affected by
ambient temperature changes under the hood of an engine compartment.
[0033] While the electronic actuator. 210 has been described as comprising an
element of
wire, it is to be understood that other elements such as strips, bars, or
tubes may also be
utilized by the present invention. The temperature of the shape memory alloy
wire 212 can
be kept within a designated range to prevent overheating of the wire 212.
[0034] A hall effect sensor (not shown) may be positioned proximate the shape
memory alloy
wire 212 to monitor the current within the wire 212. The current can be
associated with a
temperature, such that adjustment of the current will maintain the temperature
within a
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desired range. The hall effect sensor may be integrated with a connector
associated with the
shape memory alloy wire 212 or positioned in proximity to the wire 212.
[00351 Referring to Figure 4, in operation, the tensioner 220, as shown in
Figure 4a, is
generally in an open or movable position in which the clutch spring 245 does
not contact the
outer surface 260 of the drum 215 significantly allowing the tensioner 220 to
move and
operate in a normal condition, as shown in Figure 4b. In Figures 4a and b, the
return spring
257 biases the clutch spring 245 to the open position. Referring to Figure 4c,
when the
electronic actuator 210 is engaged by applying a current from an energy
source, preferably
through a controller, the wire 212 contracts, pivoting the arm 270 about its
pivot pin 275
against the biasing force of the return spring 257. The second end 249 of the
clutch wire 212
is then moved, contracting the coils of the clutch spring 245 to engage the
outer surface 260
of the drum 215. When the clutch spring 245 engages the outer surface 260, the
tensioner
220 is locked to prevent movement of the tensioner 220 away from or towards a
belt or chain
in a drive system.
100361 The element of shape memory alloy wire 212 of actuator 210 may be
controlled by
various techniques, including open and closed loop systems, shown in Figures
12 and 13,
respectively. One property of the electronic actuator 210 advantageous for
rapid control is its
rapid response to a signal input comprising an electrical current, thereby
rapidly changing the
length of the wire 212. In this manner, the electronic actuator 210 acts as a
digital on/off
switch, as opposed to an analog switch, which changes over time in response to
an input.
100371 The electronic actuator 210 may be controlled by open loop mapping
various
conditions of known instability in the belt system, by an engine control unit
231. For
example, various conditions can be monitored within an engine, such as engine
speed (RPM)
that would trigger application of a current to the shape memory alloy wire
212. Other
conditions present in the components of the belt system can also be monitored
and utilized as
an indication that impending resonance or instabilities are present or about
to occur, thereby,
triggering the electronic actuator 210. In this manner, a system can be
analyzed to
preprogram actuation of the electronic actuator, when certain conditions
exist.
[0038] Alternatively, a position sensor 232 may be utilized to determine a
position of the
tensioner arm. By monitoring the relative position of the tensioner arm 230,
an engine
control unit 231 can determine when oscillations are sufficient to justify
activation of the
electronic actuator 210 to lock the tensioner arm 230 in position. A feedback
loop including
the positional sensor incorporated above and the electronic actuator 210 can
provide for real
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time adjustment of the position of the tensioner 220 such that the tensioner
220 can be locked
and unlocked in response to various parameters.
[00391 Referring to Figures 7 and 8, there are shown second and third
embodiments of the
tensioner similar to that of the first embodiment. The second and third
embodiments also
utilize an element of shape memory alloy wire 212 with various minor
differences. In Figure
7, the shape memory alloy wire 212 is wound around a pivot 300 prior to
attachment to the
pawl or arm 270. In this manner, various mechanical advantages and layouts can
be
accommodated. Also, in Figure 5, the return spring 257 is replaced with a
spring clip 305 for
biasing the arm 270 to maintain the clutch spring 245 in an open position.
While the
preferred embodiments of the tensioner have been described as having the
clutch spring 245
in the open position under steady state conditions, the clutch spring could be
locked under
normal conditions such that the shape memory alloy actuator 210 must be
triggered to
disengage the clutch spring 245 allowing movement of the tensioner with
respect to the belt.
100401 With reference to Figure 8, the shape memory alloy wire 212 is shown
pivoting about
a different pivot point 300 than the second embodiment of Figure 7 prior to
engagement with
the arm 270. The return spring of the third embodiment is a clock spring 310
as opposed to
the coil spring 257 and spring clip 305 of the first and second embodiments.
100411 Figure 9 details a fourth embodiment of the present invention, in which
the electronic
actuator 210 comprises the tensioner spring 240'. In this embodiment, the
tensioner spring
240' is made out of a shape memory alloy material, which contracts in response
to a change
in temperature, preferably caused, by a current passed through the wire. In
this embodiment,
the tensioner spring 240' can change its overall length to engage the bushing
235 thereby
preventing movement of the tensioner 220 with respect to a belt drive system.
Alternatively,
the clutch spring 245, as shown in Figure 4, may be made of a shape memory
alloy material,
such that the length of the clutch spring can be changed upon the application
of current to the
wire 212.
[0042] Referring to Figures 10, 11 and 14, there is shown a fifth embodiment
of a tensioner
520 having an electronic actuator, preferably a shape memory alloy actuator
510, of the
present invention. A pivot member 505 is rotatably mounted and has a tab 507
extending
there from is disposed about a shaft 525. The electronic actuator 510
comprises a shape
memory alloy wire 512 wrapped around the rotational member 505, such that
application of a
current over the wire directly moves the rotational member 505 to various
positions. A clutch
spring 545 is associated with the tab 509 of the rotational member 505.
Movement of the
rotational member 505 causes the tab 509 to interact with the clutch spring
545 to engage and
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disengage the clutch spring 545, as previously described with respect to the
first embodiment.
Another tab 507 is attached to the rotational member for preventing movement
of the
tensioner beyond a desired distance. A return spring 537 comprising a clock
spring biases the
rotational member 505 such that the clutch spring 545 is biased towards an
open position.
100431 In this embodiment, the shape memory alloy wire 512 contracts,
shortening its overall
length, causing rotation of the rotational member 505, which in turn causes
movement of the
clutch spring 545 to lock the tensioner 520 in a desired position. The
rotational member 505
may include screws or channels 550 formed on the outer surface 555 of the
rotational
member 505. The shape memory alloy wire 512 is disposed within the channel 550
and
wrapped around the rotational member 505 providing additional engagement of
the wire 512
with the outer surface 555 of rotational member 505, as well as preventing
damage to the
wire 512.
[00441 Referring to Figure 15, a sixth embodiment of the present invention is
illustrated. In
this embodiment, the electronic actuator 610 is preferably a solenoid, the
length of which can
be selectively controlled by applying predetermined amounts of electricity.
100451 Through the use of an electronic actuator, the tensioner 20 can be
selectively fixed or
locked to any position between the free arm stop 25 and load stop positions 30
and locked
into position. By locking the tensioner 20 in a specific position, the
tensioner 20 would act as
fixed idler pulley providing a set tension to the belt 17 of the belt drive
system 2. The fixed
position allows the belt drive system 2 to maintain stability during
transitional periods
produced by oscillations in belt tension.
100461 In another aspect of the present invention, a tensioner 20 having an
electronic actuator
may be utilized in a belt drive system using an alternator as a starter for an
engine. In this
application, as shown in Figure 5, the accessory drive system may be utilized
as a starter for
an engine, negating the need for a separate starter motor. As can be seen in
Figure 5, the
accessory drive system 102 includes a crankshaft pulley 105, a starter
/alternator pulley 110,
a power steering pulley 115, an idler pulley 122, and an air conditioner
pulley 125. A belt
117 is positioned around the pulleys for transferring torque from the
crankshaft pulley 105 to
the accessory pulleys. A belt tensioner 120 is positioned on the slack side
140 of the belt 117
between the starter/alternator 110 and crankshaft 105 pulleys. The belt
tensioner 120 is
movable from a free arm stop position 145 to a load stop 150 position. Under
normal
operation, the crankshaft pulley 105 operates as the driving member of the
accessory drive
system 102 providing torque to the various accessory pulleys. During normal
operation, the
tight side 142 of the belt 117 is positioned between the air compressor pulley
125 and
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crankshaft pulley 105 with a slack side 140 of the belt 117 being positioned
between the
alternator/starter 110 and the crankshaft 105 pulleys. However, when the
alternator is
utilized as a starter, as shown in Figure 6, the alternator pulley 110 would
become the
primary drive pulley resulting in a reversal of the tension within the belt
spans wherein the
span between the crankshaft 105 and alternator/starter 110 pulleys would
become the tight
sPan 142 and the span between the alternator/starter 110 and power steering
115 pulleys
would become the slack span 140. Under such a load condition, the tensioner
120 would
normally move in a direction away from the belt 117 towards its load stop
position 150.
However, through the use of an electronic actuator, the belt tensioner 120 can
be adjusted or
locked in position towards its free stop position 145 to provide a constant
tension on the belt
117 to prevent slack in the belt from causing oscillations within the system
or uncontrolled
belt slippage and belt traction loss, potentially causing damage to the
system. In this manner,
the belt tensioner 120 provides stability to the system against oscillations
and belt slippage
generated by the reversal of the tight and slack spans. In a preferred aspect
of the present
invention, the tensioner 120 will move towards the free arm stop position 145
prior to
engaging the alternator/starter assuring maintenance of sufficient belt
tension to absorb belt
stretch and torsional oscillations within the system. Once the engine has
started running, the
tensioner is released and allowed to operate normally.
10047] A tensioner 20 having an electronic actuator may also be utilized by
the present
invention as an anti-belt tooth skip mechanism. Belt tooth skip typically
occurs when a belt
or chain of a belt system becomes too long for the drive system, allowing the
tooth profile of
the belt or chain to rise to a sufficient height to escape the corresponding
pocket or recess
within the sprocket or pulley designed to hold the belt captive. Under normal
operating
conditions, the function of a tensioner 20 of a timing belt or timing chain
system is to apply
sufficient load to a slack side of the belt or chain so as to prevent rise of
the belt teeth above a
certain threshold of the tooth profile of the sprocket or pulley. However, in
situations where
the belt rises above the profile, belt tooth skip can occur such that the belt
or chain loses grip
and skips backward a tooth on the drive pulley relative to its correct
position. In such a
situation, severe damage to various components can occur. Again, a tensioner
20 having an
electronic actuator can be utilized to move the tensioner 20 with respect to
the belt or
otherwise lock the tensioner 20 into position thereby taking up the slack
within a belt or chain
to prevent belt tooth skip.
[0048] In another aspect of the present invention, a tensioner 20 having an
electronic
actuator, preferably a shape memory alloy actuator, can be utilized to prevent
ratcheting
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. .
within a tensioner 20. Accessory drive tensioners and timing belt tensioners
are often
equipped with pneumatic or hydraulic dampers or springs to provide resistance
to tensioner
arm motion when the tensioner arm is forced away from the belt during high
periods of
torsional activity and system inertia. Pneumatic and hydraulic dampers
generally dissipate
significantly more energy than frictional tensioners. The primary disadvantage
of pneumatic
and hydraulic tensioners, however, is their tendency to get permanently
"pumped up" over
time as they are forced in a direction away from the belt, in response to
transitional loads
within the belt span. As the tensioner load "pumps up", or ratchets upward,
the resulting
tension applied to the belt increases as a result. As a result of the
increased tension, the
applied load to the various components within the system increases reducing
the overall life
of the belt, as well as pulleys, bearings, and other mechanisms within the
system. However,
the increased belt tension can be utilized to provide stability to the system
under transitional
loads. Again, a tensioner 20 having an electronic actuator could be utilized
to adjust the
tensioner 20 or lock the tensioner 20 in a fixed position preventing movement
away from the
belt. Such an adjustment would allow for movement of the tensioner arm towards
the free
arm position into the belt in response to various belt inputs, but would
prevent movement of
the tensioner arm away from the belt. In this manner, the tensioner having the
electronic
actuator allows the tensioner to take advantage of the high belt loads induced
by the natural
ratcheting action of the tensioner arm against the locked position. However,
unlike prior art
tensioners, the higher belt loads can be released upon command by an engine
control
computer to prevent buildup of applied tension within the belt when a higher
belt system
tension is no longer required to provide stability to the system in response
to a disturbance or
period of high torsional activity.
