Title
Dual Arm Tensioner
Field of the Invention
The invention relates to a tensioner, and more
particularly, to a dual arm tensioner having a first
pivot arm having a first pulley journalled thereto and
engagable with a mounting surface through a first pivot
axis, a second pivot arm having a second pulley
journalled thereto, the second pivot arm pivotally
engaged to the first pivot arm through a second pivot
axis, the second pivot axis disposed from the first pivot
axis .
Background of the Invention
Tensioners are used to apply a preload to belts used
in engine accessory drives. A tensioner will typically
comprise a pivot arm mounted to a base. A spring between
the pivot arm and base urges the pivot arm, and a pulley
journalled thereto, into engagement with a belt. This
will apply a preload to the belt which assures proper
power transmission from the belt to a driven accessory
such as an alternator.
Belt alternator starter (BAS) systems for hybrid
vehicles differ from conventional accessory drive belt
systems in that the torque to turn the system is not
always generated from the crankshaft. During normal
operation the engine crankshaft provides torque for
rotating a motor generator (MG) unit, or starter
generator, generally providing taut and slack sides of
the belt on opposite sides of the MG pulley. During
engine starting, the MG unit drives the system causing
the slack side of the belt to switch to the opposite side
of the MG unit. Accordingly, two belt tensioners are
generally required in such systems, engaging the belt on
opposite sides of the MG pulley.
During normal engine driven operation of the
generator and other accessories, the loads placed on the
belt drive are determined by the power required to drive
the accessories, including the MG unit. These accessory
drive loads are relatively light and accordingly require
belt tensioning only at a moderate low level.
Contrariwise, during engine starting, the motor generator
unit is required to provide power to rotate the engine as
well as the connected accessories. This requires a higher
level of belt tensioning to control motion on the slack
side of the belt and assure that the belt will not slip.
But the higher belt tension may put excessive tensioning
loads on the belt and bearings of the system components
during normal engine operation, which occupies the vast
majority of operating time of the belt drive system.
Also, because of packaging requirements it is usually
necessary to provide separate tensioner arms with
different pivot locations on each side of the MG unit to
attain the necessary tensioner arm geometry. An improved
accessory drive system, and belt tensioner are
accordingly desired.
Representative of the art is US patent no. 7494434
which discloses an accessory drive for an engine has 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 dual arm tensioner having a
first pivot arm having a first pulley journalled thereto
and engagable with a mounting surface through a first
pivot axis, a second pivot arm having a second pulley
journalled thereto, the second pivot arm pivotally
engaged to the first pivot arm through a second pivot
axis, the second pivot axis disposed from the first pivot
axis. The present invention meets this need.
Summary of the Invention
The primary aspect of the invention is to provide a
dual arm tensioner having a first pivot arm having a
first pulley journalled thereto and engagable with a
mounting surface through a first pivot axis, a second
pivot arm having a second pulley journalled thereto, the
second pivot arm pivotally engaged to the first pivot arm
through a second pivot axis, the second pivot axis
disposed from the first pivot axis.
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
first pivot arm having a first pulley journalled thereto
and engagable with a mounting surface through a first
pivot axis, a second pivot arm having a second pulley
journalled thereto, the second pivot arm pivotally
engaged to the first pivot arm through a second pivot
axis, the second pivot axis disposed from the first pivot
axis, a biasing member engaged between the first pivot
arm and the second pivot arm urging the first pulley
toward the second pulley, and the second pivot axis is
between the first pulley and the first pivot axis.
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 tensioner.
Figure 2 is a bottom perspective view of the
tensioner .
Figure 3 is a bottom perspective view of the
tensioner .
Figure 4 is a top perspective view of the tensioner.
Figure 5 is a system schematic view of the
tensioner .
Detailed Description of the Preferred Embodiment
Figure 1 is a top perspective view of the tensioner.
Tensioner 100 comprises a first arm 10 and a second arm
20. Coil spring 30 urges first arm 10 toward second arm
20, which urges pulley 22 toward pulley 12.
First arm 10 pivots about pivot 11. Second arm 20
pivots about pivot 21. Pulley 12 is journalled to first
arm 10. Pulley 22 is journalled to second arm 20.
Pivot 2 1 is disposed on first arm 10 between pivot
11 and pulley 12. Second pulley 22 is a greater radial
distance than the first pulley 12 from the first pivot
axis A-A when the tensioner is in the unloaded condition.
The radial relationship of the first pulley and second
pulley with respect to the first pivot axis may change
according to the angular relationship of the first arm to
the second arm in the unloaded condition.
The length of pivot arm 10 and pivot arm 20 may vary
according to system requirements.
Figure 2 is a bottom perspective view of the
tensioner. Pivot 11 receives a fastener (not shown)
through bore 14 for mounting the first arm 10 to a
mounting surface (not shown) . The mounting surface may
comprise a case for an engine alternator, or a startergenerator,
or other engine surface. Pivot 11 operates
about axis A-A.
Figure 3 is a bottom perspective view of the
tensioner. First arm 10 is shown with an arcuate form
15, but any suitable shape will suffice. For example,
linear or having an angular bend in addition to arcuate.
The first arm is concave toward the second arm. The
relationship of the first arm concave portion to the
second arm may be changed or reversed according to the
needs of a user.
Figure 4 is a top perspective view of the tensioner.
Second arm 20 pivots about axis B-B. Second arm 20 is
shown with an arcuate form 23, but any suitable shape
will suffice. For example, linear or having an angular
bend in addition to being arcuate. The second arm is
concave toward the first arm. The relationship of the
second arm concave portion to the first arm may be
changed or reversed according to the needs of a user.
In an alternate embodiment the second pulley is a
greater distance than the first pulley from the first
pivot axis A-A in the unloaded condition. In yet another
embodiment the first pulley is a greater distance than
the second pulley from the second pivot axis B-B in the
unloaded condition. In yet another embodiment the second
pulley is a greater distance than the first pulley from
the second pivot axis B-B in the unloaded condition.
Figure 5 is a system schematic view of the
tensioner. Tensioner 100 is mounted to an alternator A .
Belt B is routed about and engages a pulley mounted to
each of alternator A , air conditioner compressor A-C,
crankshaft CRK, and idler ID. Pulley 22 and pulley 12
bear upon belt B , thereby imparting a belt load. The
belt load allows torque transmission to occur between the
crankshaft and the noted components without slipping
between the belt and the pulleys.
A tensioner comprising a first pivot arm having a
first pulley journalled thereto and engagable with a
mounting surface through a first pivot axis, a second
pivot arm having a second pulley journalled thereto, the
second pivot arm pivotally engaged to the first pivot arm
through a second pivot axis, the second pivot axis
disposed from the first pivot axis, a biasing member
engaged between the first pivot arm and the second pivot
arm urging the first pulley toward the second pulley, and
the second pivot axis is between the first pulley and the
first pivot axis.
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 first pivot arm having a first pulley journalled
thereto and engagable with a mounting surface through a
first pivot axis;
a second pivot arm having a second pulley journalled
thereto ;
the second pivot arm pivotally engaged to the first
pivot arm through a second pivot axis, the second pivot
axis disposed from the first pivot axis;
a biasing member engaged between the first pivot arm
and the second pivot arm urging the first pulley toward
the second pulley; and
the second pivot axis is between the first pulley
and the first pivot axis.
2 . The tensioner as in claim 1 , wherein the first pivot
arm has an arcuate form.
3 . The tensioner as in claim 1 , wherein the second pivot
arm has an arcuate form.
4 . The tensioner as in claim 2 , wherein the first pivot
arm is concave toward the second pivot arm.
5 . The tensioner as in claim 3 , wherein the second pivot
arm is concave toward the first pivot arm.
6 . The tensioner as in claim 1 , wherein the first pulley
is a greater distance than the second pulley from the
first pivot axis in the unloaded condition.
7 . The tensioner as in claim 1 , wherein the second
pulley is a greater distance than the first pulley from
the first pivot axis in the unloaded condition.
8 . The tensioner as in claim 1 , wherein the first pulley
is a greater distance than the second pulley from the
second pivot axis in the unloaded condition.
9 . The tensioner as in claim 1 , wherein the second
pulley is a greater distance than the first pulley from
the second pivot axis in the unloaded condition.