Title
Isolating Decoupler
Field of the Invention
The invention relates to an isolating decoupler, and
more particularly, to an isolating decoupler comprising a
wrap spring, the wrap spring comprising a variable crosssection
having a first cross sectional dimension and a
second cross sectional dimension.
Background of the Invention
Diesel engine use for passenger car applications is
increasing due to the benefit of better fuel economy.
Further, gasoline engines are increasing compression
ratios to improve the fuel efficiency. As a result,
diesel and gasoline engine accessory drive systems have
to overcome the vibrations of greater magnitude from
crankshafts due to above mentioned changes in engines.
Due to increased crankshaft vibration plus high
acceleration/deceleration rates and high alternator
inertia the engine accessory drive system is often
experiencing belt chirp noise due to belt slip. This will
also reduce the belt operating life.
Crankshaft isolators/decouplers and alternator
decouplers/isolators have been widely used for engines
with high angular vibration to filter out vibration in
engine operation speed range and to also control belt
chirp .
Representative of the art is US patent number
7,153,227 which discloses a decoupler for an alternator
pulley in a serpentine drive system has a resilient,
helical spring member that couples the alternator pulley
with a hub structure through a spring retaining member. A
bushing is disposed between the spring retaining member
and the hub structure to facilitate sliding engagement
therebetween. An annular sleeve member is disposed
between the spring member and the alternator pulley to
facilitate sliding engagement therebetween. The spring
member is connected at one end thereof to the hub
structure and connected at an opposite end thereof to the
spring retaining member. The resilient spring member
transmits the driven rotational movements of the
alternator pulley by the serpentine belt to the hub
structure such that the alternator shaft is rotated in
the same direction as the alternator pulley while being
capable of instantaneous relative resilient movements in
opposite directions with respect to the alternator pulley
during the driven rotational movement.
What is needed is an isolating decoupler comprising
a wrap spring, the wrap spring comprising a variable
cross-section having a first cross sectional dimension
and a second cross sectional dimension. The present
invention meets this need.
Summary of the Invention
The primary aspect of the invention is an isolating
decoupler comprising a wrap spring, the wrap spring
comprising a variable cross-section having a first cross
sectional dimension and a second cross sectional
dimension .
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 an isolating decoupler
comprising a shaft, a pulley journalled to the shaft, a
torsion spring engaged with the pulley, a wrap spring
frictionally engageable with the shaft, the torsion
spring and wrap spring connected in series such that each
is torsionally loaded in a winding direction, the wrap
spring comprising a variable cross-section having a first
cross sectional dimension and a second cross sectional
dimension, and the wrap spring temporarily releasable
from the shaft in an overtorque condition by contact with
the pulley urging the wrap spring in an unwinding
direction .
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.
Fig. 1 is a cross-section view of the device.
Fig. 2 is an exploded view of the device.
Fig. 3 is a perspective detail of the device.
Fig. 4 is a perspective detail of the wrap spring.
Fig. 5 is a perspective view of the torsion spring.
Fig. 6 is a cut away perspective view of Fig. 5 .
Detailed Description of the Preferred Embodiment
Fig. 1 is a cross-section view of the device.
Alternator isolating decoupler 100 comprises a pulley 2 ,
torsion spring 10, shaft 1 , bearing 7 , end cap 5 , thrust
washers 3 , 6 , and 22, and a wrap spring 11. Fig. 2 is an
exploded view of the device.
Shaft 1 comprises a planar end portion 142 which
extends radially from an axis of rotation A-A. Extending
axially parallel to axis A-A from an outer part of
portion 142 is cylindrical member 140. Member 140
engages a cooperating recess 21 in pulley 2 , thereby
forming a labyrinth seal. The labyrinth seal prevents
debris from entering the device.
Pulley 2 is journalled to shaft 1 via a single
needle bearing 7 . Pulley 2 is axially located on shaft 1
between thrust washer 3 and thrust washer 6 . Thrust
washer 6 comprises a gap 61 which extends about a portion
of the washer 6 . Member 24 of pulley 2 extends through
gap 61. Thrust washer 6 bears upon shoulder 15 of shaft
1 . Thrust washer 3 , pulley 2 , bearing 7 , and thrust
washer 6 are held in place on shaft 1 by end cap 5 . End
cap 5 is press fit on shaft 1 .
Pulley 2 comprises an inner cylindrical portion 23
which extends axially parallel to shaft 1 and pulley 2 .
Torsion spring 10 is disposed in part between pulley 2
and portion 23. Portion 23 provides a means by which
pulley 2 engages bearing 7 without unduly extending the
overall length of the device. Portion 23 allows bearing
7 to be disposed within the envelope of pulley 2 while
also allowing room to accommodate torsion spring 10.
Bearing 7 is located at a midportion "M" of the load
bearing portion "L" of the pulley, which engages a multiribbed
belt (not shown) . Bearing 7 is the only means by
which pulley 2 is journalled to shaft 1 , which
arrangement eliminates the need for two bearings, one at
each end of the pulley. Shaft 1 and end cap 5 can be
installed on an alternator shaft (not shown) .
One end of torsion spring 10 is connected to pulley
2 . The other end of torsion spring 10 is connected to
wrap spring 11. Wrap spring 11 is frictionally engaged
with shaft 1 . Torsion spring 10 and wrap spring 11 are
connected in series.
In operation wrap spring 11 is wound about shaft 1 .
Wrap spring 11 is disposed radially inward of the torsion
spring 10 with respect to axis A-A. When loaded in the
winding direction the diameter of the wrap spring
decreases, which causes wrap spring 11 to frictionally
grip shaft 1 . During a torque reversal shaft 1 will
slightly overrotate with respect to pulley 2 given the
inertia of a connected load such as an alternator. Given
the frictional engagement between the wrap spring 11 and
shaft 1 , wrap spring 11 will slightly unwind thereby
increasing its diameter, which causes wrap spring 11 to
partially or fully release the frictional grip on shaft
1 . This will allow shaft 1 to continue to over-rotate as
pulley 2 slows. In this way wrap spring 11 operates in a
manner similar to a one-way clutch.
For a typical alternator a maximum torque is in the
range of approximately 16 Nm to 2 0 Nm. This torque is
delivered to shaft 1 from pulley 2 by torsion spring 10
through wrap spring 11 in the direction of rotation of
pulley 2 . Torsion spring 10 is loaded in the winding
direction as torque is transmitted to shaft 1 .
Fig. 3 is a perspective detail of the device.
Torsion spring 10 is omitted from this view. In an overtorque
condition wrap spring 11 is also releasable from
shaft 1 . As torque increases pulley 2 will incrementally
advance in relative relation to shaft 1 . As pulley 2
continues to advance, member 24 of portion 23 will engage
member 85 of wrap spring 11. Member 85 projects in a
radially outward direction from the end of wrap spring
11. Member 24 extends axially from portion 23. In a
normal torque condition member 24 does not engage member
85. As the transmitted torque increases member 24 will
first contact and then press member 85 in an unwinding
direction for wrap spring 11. This will in turn cause
wrap spring 11 to partially unwind, thereby increasing
the diameter of wrap spring 11. The increase in diameter
will partially or fully release the frictional grip of
wrap spring 11 from shaft 1 , thereby allowing pulley 2 to
over-rotate shaft 1 during the over-torque condition.
This feature protects the device from damage during an
over-torque condition.
Fig. 4 is a perspective detail of the wrap spring.
Wrap spring 11 is a machined spring and is permanently
connected to torsion spring 10. Torsion spring 10 is a
machined spring as well. Wrap spring 11 has a variable
cross-section along the length of its body. Wrap spring
11 comprises three portions: the constant cross-section
portion 110, the variable cross-section portion 120, and
the hub 130 .
"Machined" refers to any manufacturing process
performed on the spring in addition to winding, and can
refer to cutting diagonal slots in a homogenous cylinder
to form the spring, for example. It can also refer to
machining the inner and outer surface of the cylinder to
a preferred OD and ID dimension, or to machining each
volute in the spring to vary a cross-sectional size and
shape. Machined can generally refer to adjusting or
altering one or more physical characteristics of the
spring in order to determine its operating
characteristics .
Hub 130 of wrap spring 11 is attached to an end of
torsion spring 10. In particular, hub 130 is press fit
into an annular end 150 of torsion spring 10. Wrap
spring 11 comprises two variable cross-section portions.
Portion 120 has a cross-section of 2.4mm x 1.2mm at its
connection 121 to hub 130 and a second cross-section of
0.6mm x 1.2mm at the connection 1210 with constant crosssection
portion 110. Hub 130 does not comprise spring
volutes or windings, although it is an integral part of
the wrap spring 11. Member 85 extends from an end of
portion 110.
All numeric dimensions contained herein are provided
solely for the purpose of illustrating the invention and
are not intended to limit the breadth or scope of the
invention in any way.
At the connection 121 between hub 130 and variable
cross-section portion 120 tension in the wrap spring will
generate 16-20 Nm torque. At the connection 1210 between
variable cross-section portion 120 and the constant
cross-section portion 110 tension in the wrap spring
generates torque that is approximately 6.5 to 10 times
less than the maximum torque delivered by the torsion
spring or 2-3 Nm. This is because friction between the
variable cross-section portion 120 and shaft 1 will
generate about 17 Nm to 18 Nm torque on shaft 1 . The
constant cross-section portion 110 accommodates this
torque range. The cross-section of portion 110 is about
0.6mm x 1.2mm. Wrap spring portion 110 has about 9 to 10
coils .
There is no or a very small ID interference between
the variable cross-section portion 120 and shaft 1 . Wrap
spring portion 110 comprises an ID interference fit with
shaft 1 sufficient to transmit approximately 2 to 3 Nm of
torque to shaft 1 . Once hub 130 is pulled by torsion
spring 10 the variable cross-section portion 120 is
pulled as well and so too portion 110.
Fig. 5 is a perspective view of the torsion spring.
Torsion spring 10 comprises projecting member 150 which
projects radially inward. Hub 130 of wrap spring 11 is
press fit into projecting annular member 150, thereby
connecting and axially locating wrap spring 11 within
torsion spring 10. Unlike the prior art the instant
device has no spring carrier disposed between the torsion
spring and the wrap spring. Fig. 6 is a cut away
perspective view of Fig. 5 .
Advantages of the device include a smaller size one
way clutch (wrap spring 11) particularly in the axial
direction, a smaller overall length due to the central
location of bearing 7 , a substantially smaller
interference and friction torque requirement to lock the
wrap spring, a substantially smaller drag torque during
overrun, and a lower operating temperature due to lower
friction between the wrap spring and the shaft.
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 without departing from the spirit and
scope of the invention described herein.
Claims
I claim:
1 . An isolating decoupler comprising:
a shaft (1);
a pulley (2) journalled to the shaft;
a torsion spring (10) engaged with the pulley;
a wrap spring (11) frictionally engageable with the
shaft ;
the torsion spring and wrap spring connected in
series such that each is torsionally loaded in a winding
direction;
the wrap spring comprising a variable cross-section
(120) having a first cross sectional dimension and a
second cross sectional dimension; and
the wrap spring temporarily releasable from the
shaft in an overtorque condition by contact with the
pulley urging the wrap spring in an unwinding direction.
2 . The isolating decoupler as in claim 1 , wherein the
wrap spring is disposed radially inward of the torsion
spring .
3 . The isolating decoupler as in claim 1 , wherein the
torsion spring comprises a radially inward projecting
member for engaging the wrap spring.
4 . The isolating decoupler as in claim 1 , wherein the
wrap spring comprises a member for temporarily engaging
the pulley.
5 . The isolating decoupler as in claim 1 , wherein:
the pulley comprises an inner cylindrical portion
extending in an axial direction, the inner cylindrical
portion engaging a bearing; and
the torsion spring disposed radially outward of the
inner cylindrical portion.
6 . The isolating decoupler as in claim 5 , wherein the
bearing is disposed at a midpoint of a pulley load
bearing portion.
7 . An isolating decoupler comprising:
a shaft;
a pulley journalled to the shaft on a bearing
disposed at a midpoint of the pulley load bearing
portion;
a torsion spring engaged with the pulley;
a wrap spring frictionally engageable with the
shaft;
the torsion spring and wrap spring connected in
series such that each is torsionally loaded in a winding
direction;
the wrap spring comprising a variable cross-section
having a first cross sectional dimension and a second
cross sectional dimension; and
the wrap spring temporarily releasable from the
shaft in an overtorque condition by contact with the
pulley urging the wrap spring in an unwinding direction.
8 . An isolating decoupler comprising:
a shaft;
a pulley journalled to the shaft on a bearing
disposed at a midpoint of a pulley load bearing portion;
a torsion spring engaged with the pulley;
a wrap spring disposed radially inward of the
torsion spring, the wrap spring frictionally engageable
with the shaft in a loaded condition;
the torsion spring and wrap spring connected in
series such that each is torsionally loaded in a winding
direction;
the wrap spring comprising a variable cross-section
having a first cross sectional dimension and a second
cross sectional dimension; and
the wrap spring temporarily releasable from the
shaft in an overtorque condition by contact with the
pulley urging the wrap spring in an unwinding direction.
9 . The isolating decoupler as in claim 8 , wherein:
the pulley comprises an inner cylindrical portion
extending in an axial direction, the inner cylindrical
portion engaging the bearing; and
the torsion spring disposed radially outward of the
inner cylindrical portion.
10. The isolating decoupler as in claim 8 , wherein the
torsion spring comprises a radially inward projecting
annular member for engaging the wrap spring.
11. The isolating decoupler as in claim 8 , wherein the
wrap spring comprises a member for temporarily engaging
the pulley in the overtorque condition.