Title
Isolating Pulley
Field of the Invention
The invention relates to an isolating pulley, and
more particularly, an isolating pulley comprising a
friction member engaged between the spring carrier and
the hub, the friction member comprising a first multiple
ribbed surface to engage the spring carrier and a second
multiple ribbed surface to engage the hub, each extending
radially from an axis of rotation.
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 application serial
number 2013/0150191 which discloses a drive pulley
structure has a cylindrical pulley member, a hub
structure that is provided inside the pulley member so as
to rotate relative to the pulley member, a coil spring
that is fixed to the hub structure, a tapering which has
a conical round surface as of a cone whose axis is made
up of a rotational axis J of the hub structure, and a
frictionmember that is inserted to be interposed between
the conical round surface of the tapering and the pulley
member, and the coil spring is inserted to be interposed
in place while being compressed in the direction of the
rotational axis of the hub structure, the tapering, the
frictionmember and the pulley member being brought into
press contact with each other by virtue of a restoring
force P of the coil spring.
What is needed is an isolating pulley comprising a
friction member engaged between the spring carrier and
the hub, the friction member comprising a first multiple
ribbed surface to engage the spring carrier and a second
multiple ribbed surface to engage the hub, each extending
radially from an axis of rotation. The present invention
meets this need.
Summary of the Invention
The primary aspect of the invention is an isolating
pulley comprising a friction member engaged between the
spring carrier and the hub, the friction member
comprising a first multiple ribbed surface to engage the
spring carrier and a second multiple ribbed surface to
engage the hub, each extending radially from an axis of
rotation .
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 pulley
comprising a hub, a pulley journalled to the hub, a
spring carrier journalled to the hub, a torsion spring
engaged between the pulley and the spring carrier, a
friction member engaged between the spring carrier and
the hub, the friction member comprising a first multiple
ribbed surface to engage the spring carrier and a second
multiple ribbed surface to engage the hub, and the first
multiple ribbed surface and the second multiple ribbed
surface extending in a radial direction normal to an axis
of rotation A-A.
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 cross-sectional view of the device.
Figure 2 is an exploded view of the device.
Figure 3 is a detail of the friction member.
Detailed Description of the Preferred Embodiment
Figure 1 is a cross-sectional view of the device.
The device comprises a hub 9 . Pulley 4 is journalled to
and thereby rotatable about hub 9 on bush 2 and bush 7 .
Torsion spring 3 is engaged to pulley 4 and spring
carrier 5 . Spring carrier 5 is journalled to and thereby
rotatably engaged with hub 9 through bush 8. Friction
member 6 is frictionally disposed between with hub 9 and
spring carrier 5 . Cap 1 retains pulley 4 on hub 9 .
Pulley 4 directly interfaces with a belt to drive
the device. Power flows from pulley 4 to one end 31 of
torsion spring 3 via an interference fit. Spring 3 is a
biasing member that transmits torque and attenuates
vibration and provides the isolating function of the
device. Spring 3 transmits torque while being driven in
an unwinding direction, but may also transmit torque in
the winding direction in an alternate embodiment.
The other end 32 of spring 3 is connected to spring
carrier 5 . Spring carrier 5 has an interference fit to
receive end 32 of spring 3 . Spring carrier 5 comprises a
ribbed profile 57 on the side opposite the receiving
portion of spring 3 . Spring 3 has a spring rate of
approximately 0.36 Nm/degree.
Spring carrier 5 interfaces with friction member 6
through a ribbed profile portion 57, and thereby
transmits torque through friction. Surfaces 51, 52, 53,
54, 55, and 56 are the surfaces which frictionally engage
spring carrier 5 to friction member 6 . Friction member 6
transmits torque to hub 9 through surfaces 91, 92, 93,
94, 95, and 96.
Friction member 6 comprises surfaces 61, 62, 63, 64,
65, 66 to frictioanlly engage surfaces 51, 52, 53, 54,
55, 56. Friction member 6 comprises surfaces 610, 620,
630, 640, 650, 660 to frictionally engage surfaces 91,
92, 93, 94, 95, 96. Surfaces 91, 92, 93, 94, 95, 96 are
disposed on radially extending flange 97.
The ribbed surfaces on the spring carrier 5 ,
friction member 6 and hub 9 all extend in a radial
direction normal to and outward from the axis of rotation
A-A of hub 9 . Further, the ribbed surfaces of the spring
carrier 5 , friction member 6 and hub 9 each comprise the
form of one or more concentric rings centered about the
axis of rotataion A-A.
Hub 9 is directly connected to drive a driven
component, such as an alternator (not shown) .
Figure 2 is an exploded view of the device.
Figure 3 is a detail of the friction member. It is
known that the rated peak torque of an alternator is
often less than the peak torque observed when starting
the engine. For example, a typical automotive alternator
will have a rated peak torque of 12 Nm, an inertia of
0.00030 kg m2, and an acceleration rate at the alternator
of 100,000 rad/s 2 during engine starting. However, at
engine start-up the device could be exposed to 30 Nm of
torque, but would not receive such a high torque spike
during any other operating conditions.
To avoid use of torsion spring that can handle a
elevated starting torque, the inventive device uses a
friction member clutch to protect torsion spring 3 from
receiving a torque spike in excess of a predetermined
level. Friction member 6 is pressed or biased by axial
compression of torsion spring 3 against hub flange 97,
thereby inparting a normal force "F" which enables
transmission of torque from pulley 4 to hub 9 . Normal
force "F" is in the range of approximately 100N to 200N.
The embodiment described herein comprises a force "F" of
approxiamtely 140N by way of example.
The use of ribbed surfaces on friction member 6
maximizes the number of surfaces and thereby surface area
which eliminates the need for multiple friction disks or
a radially larger engaging surface. Rib angle Q ensures
that the friction member 6 smoothly engages and
disengages to avoid "grabbing" or stick-slip.
The ribbed profiles can also wedge lock in a manner
similar to a cone clutch as shown in Equation 1 . The
advantage is that it is impractical to use more than one
surface with a cone clutch and cone clutches tend to
"grab" and often need a mechanism to disengage the
clutch. On the other hand a ribbed profile with a
relatively large wedge (rib) angle Q of approximately 20°
and multiple rib surfaces has the ability to smoothly
engage, disengage, and permit gross slip between the
spring carrier 5 , friction member 6 , and hub 9 when
required. Rib angle Q may be in the range of
approximately 18° to 22°.
Equation 1: T =
m Coefficient of friction
F Applied normal force
r Outer radius
r Inner radius
q : Wedge angle
Friction member 6 may comprise any suitable
frictional material, including plastic, composites,
paper, resin bonded materials, elestomeric materials, and
sintered materials. The coefficient of friction between
friction member 6 and spring carrier 5 is greater than
approximately 0.17. The instant embodiment having a
coefficient of friction of approximately 0.50. The
coefficient of friction between the friction member 6 and
hub 9 is greater than approximately 0.17. The instant
embodiment having a coefficient of friction of
approximately 0.50.
An example comprises:
Assumptions
Ustatic = 0.5
Applied force (F) from spring: 140N
Ribbed profile with six 6 conical surfaces
e of friction member 6
The equation is for one surface, for example,
surface 61. Slip occurs when TInput > T r t o Member .
Example variables are noted in the Table below.
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
We claim:
1 . An isolating pulley comprising:
a hub ;
a pulley journalled to the hub;
a spring carrier journalled to the hub;
a torsion spring engaged between the pulley and the
spring carrier;
a friction member engaged between the spring carrier
and the hub, the friction member comprising a first
multiple ribbed surface to engage the spring carrier and
a second multiple ribbed surface to engage the hub; and
the first multiple ribbed surface and the second
multiple ribbed surface extending in a radial direction
normal to an axis of rotation A-A.
2 . The isolating pulley as in claim 1 , wherein each of
the first multiple ribbed surface and the second multiple
ribbed surface comprises one or more rings concentric
about an axis of rotation A-A.
3 . The isolating pulley as in claim 2 , wherein the
torsion spring is axially compressed between the pulley
and hub .
4 . The isolating pulley as in claim 3 , wherein the
torsion spring is loaded in an unwinding direction.
5 . An isolating pulley comprising:
a hub ;
a pulley journalled to the hub;
a spring carrier journalled to the hub;
a torsion spring engaged between the pulley and the
spring carrier;
a friction member engaged between the spring carrier
and the hub, the friction member comprising a multiple
ribbed surface to engage a spring carrier multiple ribbed
surface; and
the multiple ribbed surface extending in a radial
direction normal to an axis of rotation A-A.
6 . The isolating pulley as in claim 5 , wherein the
multiple ribbed surface comprises one or more rings
concentric about an axis of rotation A-A.
7 . The isolating pulley as in claim 6 , wherein the
torsion spring is axially compressed between the pulley
and hub .
8 . The isolating pulley as in claim 7 , wherein the
torsion spring is loaded in an unwinding direction.
9 . An isolating pulley comprising:
a hub ;
a pulley journalled to the hub;
a spring carrier journalled to the hub;
a torsion spring engaged between the pulley and the
spring carrier;
a friction member engaged between the spring carrier
and the hub, the friction member comprising a multiple
ribbed surface to engage a hub multiple ribbed surface;
and
the multiple ribbed surface extending in a radial
direction normal to an axis of rotation A-A.
10. The isolating pulley as in claim 9 , wherein the
multiple ribbed surface comprises one or more rings
concentric about an axis of rotation A-A.
11. The isolating pulley as in claim 10, wherein the
torsion spring is axially compressed between the pulley
and hub .
12. The isolating pulley as in claim 11, wherein the
torsion spring is loaded in an unwinding direction.