Field of the Invention
The invention relates to an isolating decoupler, and
more particularly, to an isolating decoupler having a
torsion spring with a diameter greater than a diameter of
a belt bearing surface.
Background of the Invention
This invention relates to alternator tuning devices,
particularly to isolating decouplers using a torsion
spring for isolation. The function and utility of
isolating decoupler tuning devices is commonly known. A
typical device comprises mutiple components including an
isolating spring, one way clutch, bearing (s), a pulley
and other ancillary parts. The need for each of these
components typically requires the overall diameter of the
device to exceed what the industry desires. Decreasing
automotive engine sizes and ever increasing fuel
efficiency requirements indicate that isolating decoupler
diameters can be an engine develoment limiting factor.
A size limiting relationship is that between the
pulley and a torsion spring. In the prior art devices
the torsion spring is typically in a radial "stack"
disposed between the shaft and the pulley. This
arrangement tends to increase the diameter of the pulley
depending upon the spring rate of the torsion spring.
Representative of the art is US 6 , 083, 130, which
discloses a serpentine belt drive system for an
automotive vehicle comprising a drive assembly including
an internal combustion engine having an output shaft with
a driving pulley thereon rotatable about a driving pulley
axis. A sequence of driven assemblies each has a driven
pulley rotatable about an axis parallel with the driving
pulley axis and a serpentine belt mounted in cooperating
relation with the driving pulley and with the driven
pulleys in a sequence which corresponds with the sequence
of the driven assemblies when related to the direction of
movement of the belt to cause said driven pulleys to
rotate in response to the rotation of the driving pulley.
The sequence of driven assemblies includes an alternator
assembly including an alternator shaft mounted for
rotation about a shaft axis. A hub structure is fixedly
carried by the alternator shaft for rotation therewith
about the shaft axis. A spring and one-way clutch
mechanism couples the alternator pulley with the hub
structure. The spring and one-way clutch mechanism
comprises a resilient spring member separately formed
from and connected in series with a one-way clutch
member. The resilient spring member is constructed and
arranged to transmit 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 thereof. The one
way clutch member is constructed and arranged to allow
the hub structure and hence the alternator shaft to
rotate at a speed in excess of the rotational speed of
the alternator pulley when the speed of the engine output
shaft is decelerated to an extent sufficient to establish
the torque between the alternator pulley and the hub
structure at a predetermined negative level.
What is needed is an isolating decoupler having a
torsion spring with a diameter greater than a diameter of
a belt bearing surface. The present invention meets this
need .
Summary of the Invention
The primary aspect of the invention is an isolating
decoupler having a torsion spring with a diameter greater
than a diameter of a belt bearing surface.
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 and
having a belt bearing surface, the belt bearing surface
having a diameter over balls not greater than 2A, a oneway
clutch mounted to the shaft, a clutch carrier mounted
to the one-way clutch, a torsion spring engaged between
the clutch carrier and the pulley, the torsion spring
loadable in the unwinding direction, the torsion spring
having a diameter not less than 2B, and the torsion
spring diameter 2B is greater than the belt bearing
surface diameter over balls 2A.
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 perspective cross section view.
Figure 2 is a cross section view.
Figure 3 is an exploded view.
Figure 4 is a diagram of an engine belt drive
system.
Figure 5 is a partial cross-sectional view of the
spring .
Figure 6 is a partial exploded view of the spring
assembly .
Detailed Description of the Preferred Embodiment
Figure 1 is a perspective cross section view. The
inventive isolating decoupler device 14 comprises a
pulley 4 , bearing 2 and bearing 5 , torsion spring 3 , oneway
clutch 7 , shaft 1 , thrust bushing 6 , clutch carrier
9 , spring retainer 8 and a slinger 10.
Pulley 4 is journalled to shaft 1 on bearing 2 .
Spring retainer 8 is journalled to shaft 1 on bearing 5 .
Spring retainer 8 is press fit into pulley 4 , hence
pulley 4 is journalled to shaft 1 on bearing 2 and
bearing 5 . Torsion spring 3 is contained in its entirety
within pulley portion 42. Portion 42 is concave toward
shaft 1 . Portion 42 is axially adjacent to belt bearing
surface 41. A belt 30 engages belt bearing surface 41.
Clutch carrier 9 is mounted to one-way clutch 7 .
One-way clutch 7 is mounted to shaft 1 . Thrust bushing 6
is disposed between pulley 4 and clutch carrier 9 . One
way clutch 7 axially locates clutch carrier 9 on shaft 1 .
Pulley 4 is axially located between bearing 2 and thrust
bushing 6.
Spring 3 is engaged between clutch carrier 9 and
spring retainer 8 . End 31 engages clutch carrier 9 and
end 32 engages spring retainer 8.
A driven alternator posesses significant inertia.
In an overrun condition or during an engine speed
decrease, due to inertia the alternator shaft 120 will
try to spin faster that it is being driven by the belt,
in effect driving the engine through the crankshaft.
This is not desirable. To avoid this problem one-way
clutch 7 will temporarily disengage thereby allowing
alternator shaft 120 to spin down at its own rate. A s
the rotational speed of shaft 120 decreases to that of
the belt input, one-way clutch 7 will re-engage.
In operation torque is transmitted from pulley 4 to
spring retainer 8 through torsion spring 3 to clutch
carrier 9 to one-way clutch 7 and to shaft 1. One-way
clutch 7 in this device can be of any known kind, for
example, a roller type or sprague style.
Figure 2 is a cross section view. An inventive
aspect of this device is related to the location of
torsion spring 3 in relationship to pulley 4 . Due to
axial length constraints on the device a spring 3 is
typically disposed between the shaft 1 and belt bearing
surface 41. In the inventive device spring 3 is not
disposed between belt bearing surface 41 and shaft 1 ,
thereby allowing improved packaging of the components and
a smaller diameter over balls for belt bearing surface
41. Instead, spring 3 is axially adjacent to the belt
bearing surface. Spring 3 and belt bearing surface 41 do
not axially overlap.
It is known in the art that pulley diameters are
measured using the method referred to as "diameter over
balls". This may also be referred to as radius over
balls in this specification. For a description see
paragraph 4.1 of SAE Surface Vehicle Standard J1459 for
V-ribbed belts and pulleys.
Radius B of torsion spring 3 is greater than the
radius A over balls of belt bearing surface 41 of pulley
4 . The diameter (2 x radius A ) of surface 41 is not
greater than 2A. In the relaxed state torsion spring 3
comprises a cylindrical form, hence the diameter of
torsion spring 3 is constant in an axial direction X-X.
The entirety of the cylindrical form of torsion spring 3
comprises an inside diameter (ID) of not less than 2B.
The entirety of torsion spring 3 is located radially
outward of the pulley belt bearing surface 41 since: B >
A . This allows the pulley belt bearing surface diameter
over balls 2A to be as small as may be required by a user
application. It also allows greater control over the
design and operating characteristics of the device since
spring 3 has a uniform diameter 2B along its entire
length instead of spiraling radially outward from a
shaft. It also results in the overall diameter D of the
inventive device being typically less than an overall
diameter compared to a device using a spring which
spirals radially outward from a hub. For a prior art
example see Fig. 13A of US 6,083,130 which discloses a
torsion wire spring having a circular cross-sectional
configuration that is spirally wound about an annular
hub. A radially inner end of the spring is fixed in any
conventional fashion to the hub. The radially outer end
portion of the torsion spring is fixed to a carrier plate
which is radially outward of the spring.
By way of example the pulley belt bearing surface
diameter over balls A for surface 41 can be as small as
45mm. "A" and "B" are each measured in relation to axis
of rotation X-X. In an alternate embodiment B > A .
A further characteristic of the inventive device is
the spring rate of the torsion spring 3 . Spring rate
values are typcially in the range of approxiamtely
0.24Nm/degree to approximately 0.45Nm/degree . Torsion
spring 3 used in an unwinding loading application can
have the following characteristics:
• Nominal diameter = ID = 51.5mm = 2B
• Wire width = 4 .0mm
• Wire height = 5.48mm
• Spring length = 16mm to 26mm
• Spring rate = 0.24Nm/degree to 0.45Nm/degree
These numbers are by way of example only and are not
intended to limit the scope of the invention. Unwinding
loading refers to loading the torsion spring 3 in the
unwinding direction whereby the spring coils radially
expand as they are loaded when the device is in use
transmitting torque.
The end to end length of a device using the noted
spring 3 will be acceptable for most applications.
Axially displacing torsion spring 3 from the belt bearing
surface 41 causes the axial length of the device to
extend in a direction x2 . The axial space within portion
42 can accommodate a torsion spring with a greater spring
rate if desired. It can also accommodate a torsion spring
with a greater overall length of wire in the event a
greater given diameter is needed for a desired number of
coils .
Figure 3 is an exploded view. Slinger 10, press fit
to shaft 1 , is used to eject debris from the device.
Surface 41 accommodates a multi-ribbed belt.
Figure 4 is a diagram of an engine belt drive
system. In this example arrangement, a multi-ribbed belt
30 is trained between the pulleys for the power steering
pump 20, water pump 22, engine crankshaft 24, alternator
12 and air conditioner compressor 18. A tensioner 2 8
maintains a preload on belt 30 to avoid belt slip. Idler
16 further routes belt 30 and ensures proper engagement
with the pulley on inventive device 14 and pulley 24.
Isolating decoupler 14 is attached to a shaft 120 of
alternator 12. The described components, excluding the
specific inventive device 14, comprise a typical
accessory drive system as found on most vehicle engines.
The accessories drive or comprise various known engine
and vehicle systems including cooling, air conditioning,
electrical, and hydraulic for steering.
Crankshaft 24 drives belt 30, which in turn drives
alternator 12 and the other accessories. Each of the
accessories is typically mounted to the front of a
vehicle internal combustion engine (not shown) . In an
overrun condition or during engine deceleration the
inventive device 14 will disengage the alternator from
the accessory drive system.
Figure 5 is a partial cross-sectional view of the
spring. Spring 3 comprises an end 31 and an end 32. End
31 engages receiving portion 91 in clutch carrier 9 . End
32 engages receiving portion 81 in spring retainer 8 .
This lockingly engages each end of the spring to the
clutch carrier and the spring retainer. The locking
engagement of each end 31, 32 allows spring 3 to be
loaded in either the winding or unwinding direction.
Figure 6 is a partial exploded view of the spring
assembly. Spring 3 is contained between clutch carrier 9
and spring retainer 8 .
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 (4) journalled to the shaft and having a
belt bearing surface (41), the belt bearing surface
having a diameter over balls not greater than 2A;
a one-way clutch (7) mounted to the shaft;
a clutch carrier (9) mounted to the one-way clutch;
a torsion spring (3) engaged between the clutch
carrier and the pulley, the torsion spring loadable in
the unwinding direction;
the torsion spring having a diameter not less than
2B; and
the torsion spring diameter 2B is greater than the
belt bearing surface diameter over balls 2A.
2 . The isolating decoupler as in claim 1 mounted to a
driven device.
3 . The isolating decoupler as in claim 1 , wherein the
torsion spring diameter is constant along an axial
length .
4 . The isolating decoupler as in claim 1 , wherein the
pulley further comprises a concave portion disposed
adjacent to the belt bearing surface for receiving the
torsion spring.
5 . The isolating decoupler as in claim 1 , wherein the
belt bearing surface comprises a multiple ribbed surface.
6 . The isolating decoupler as in claim 1 , wherein the
torsion spring further comprises a first end and a second
end for lockingly engaging the clutch carrier and the
shaft .
An belt drive system comprising:
an isolating decoupler comprising;
a shaft;
a pulley journalled to the shaft and having a
pulley belt bearing surface, the pulley belt bearing
surface having a diameter over balls not greater
than 2A;
a one-way clutch mounted to the shaft;
a clutch carrier mounted to the one-way clutch;
a torsion spring engaged between the clutch
carrier and the pulley, the torsion spring loaded in
the unwinding direction;
the torsion spring having a diameter not less
than 2B;
the torsion spring diameter 2B is greater than
the pulley belt bearing surface diameter over balls
2A ;
the isolating decoupler mounted to a driven
load; and
the driven load driven by a belt.
8 . An isolating decoupler comprising:
a shaft;
a pulley journalled to the shaft and having a belt
bearing surface, the belt bearing surface having a
diameter over balls not greater than 2A;
a one-way clutch mounted to the shaft;
a clutch carrier mounted to the one-way clutch;
a torsion spring engaged between the clutch carrier
and the pulley;
the pulley comprises a portion disposed adjacent to
the belt bearing surface for receiving the torsion
spring;
the torsion spring having a constant diameter not
less than 2B; and
the torsion spring diameter 2B is greater than the
belt bearing surface diameter over balls 2A.
9 . The isolating decoupler as in claim 8 , wherein:
the torsion spring further comprises a first end for
lockingly engaging the clutch carrier and a second end
for lockingly engaging the shaft.