Note: Descriptions are shown in the official language in which they were submitted.
CA 02248309 2006-02-06
Description
MAGNETIC CENTRIFUGAL CLUTCH
10 Technical Field
This invention relates to mechanical centrifugal clutches which
automatically engage in opposition to a disengaging spring bias responsive to
a
build-up in speed of a power source. The invention also relates to soft start
couplers.
Background of the Invention
Self energizing centrifugal clutches commonly have friction shoes
which move outwardly against a drum on an output shaft responsive to
centrifugal
force resulting from powering an input shaft in a predetermined speed range.
Springs
cause the shoes to retract when the input shaft slows below a prescribed
level. When
the clutch is engaged vibration is transferred between the input and output
shafts via
the clutch and this is more pronounced when the shafts are not perfectly
aligned.
Accordingly, there has been a need for a self-energizing clutch which
will not transfer vibration between the driving and driven components, will
not subject
its parts to wear, and does not require precise alignment between its input
and output
rotary parts.
Couplers with a soft start characteristic require less power for startup
because the full load is not coupled to the driving motor or other power
source until
the motor has accelerated to an adequate rotational velocity to take on the
load.
Although couplers such as disclosed in my prior Patent No. 5,477,094 have soft
start
capabilities when properly matched with a load, there are instances where a
still softer
start is preferred while preserving the other advantages of the coupler.
Summary of the Invention
The present invention meets the foregoing needs in the centrifugal
clutch art by providing a magnetic clutch in which permanent magnets on a
drive rotor
are moved by centrifugal force outwardly in opposition to a spring bias from
an
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inactive position to an active position where they are spaced by an air gap
from an
electroconductive ring on a driven rotor. As a result eddy currents are
induced in the
electroconductive ring, thereby causing the driven rotor to rotate with the
driving
rotor by magnetic action, sometimes referred to as magnetic friction. It is
preferred to
have the driven rotor provided with two spaced electroconductive rings between
which the magnets move with each magnet exposing its poles to respective ones
of the
rings. Each of the magnets has its poles reversed relative to the poles of the
two
adjacent magnets. The magnets are mounted in holders arranged to slide
radially of
the magnet rotor. Springs extend between the holders and the magnet rotor to
bias the
holders inwardly away from the electroconductive ring(s).
Since the magnet rotor and its magnets are always spaced from the
driven rotor and its electroconductive rings, vibration is not transferred
through the
clutch, the rotors need not be in axial alignment, and there is no wear
between the
driving and driven parts.
The clutch of the present invention inherently has a soft start
characteristic. However, the clutch can be used as a soft start coupler with a
superior
soft start characteristic by reversing the starting roles of the magnet rotor
and the
driven rotor, and having the magnets on the magnet rotor arranged to have a
starting
position wherein they are part way overlapped by one or both of the
electroconductive
ring(s). Accordingly, when the rotor with the electroconductive rings is
rotated by a
motor or other power source the magnet rotor starts to rotate by magnetic
friction and
builds up speed as the magnet exposure to the electroconductive rings)
increases due
to outward movement of the magnet holders responsive to the increasing
centrifugal
force.
Brief Description of the Drawings
Fig. 1 is a longitudinal cross-sectional view through a first embodiment
of the invention;
Fig. 2 is a transverse elevational view of the magnet rotor of Fig. 1
taken from the right side of Fig. I and with the hub assembly removed;
Fig. 3 is a perspective view of one of the magnet holder units in the
magnet rotor;
Fig. 4 is a fragmentary elevational view of the hub extension taken as
indicated by line 4-4 in Fig. I ;
Fig. 5 is a sectional view like Fig. 1 showing a second embodiment of
the electroconductive rotor assembly;
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Fig. 6 is a fragmentary elevational view taken as indicated by line 6-6 in
Fig. 5;
Figures 7 and 8 are sectional views taken like Fig. 1 and showing a
third embodiment of the electroconductive rotor assembly and a complementing
second embodiment of the magnet rotor assembly;
Fig. 8A is a fragmentary transverse sectional view taken as indicted by
line 8A-8A in Fig. 8;
Fig. 9 is an elevational view like Fig. 2 and showing a modified spring
arrangement for biasing the magnet holder units;
Fig. 10 is a schematic layout of the drive arrangement for the
refrigeration compressor in a reefer;
Fig. 11 is a sectional view like Fig. 1 showing sheave additions to the
electroconductive rotor assembly; and
Fig. 12 is a sectional view like Fig. 11 showing a modified drive and
takeoff:' arrangement having a stationary shaft.
Detailed Description of the Invention
Referring to the first embodiment of the invention (Figs. 1-4), input and
output shafts 10-1 I are connected by couplings 12-13 to a magnet rotor unit
14 and
electroconductive rotor unit 15. The electroconductive rotor unit presents two
axially-spaced flat rings (continuous bands) 16-17 having good
electroconductive
characteristics such, for example, as copper or aluminum. Ring 16 is mounted
on a
ferrous backing ring 18 and ring 17 is mounted on a circular ferrous backing
plate 19
which is in turn mounted on a hub 20 as by bolts 21. Spacers in the form of
sleeves 22
separate the electroconductive rings 16-17 and they are held by bolts 23
passing
through the electroconductive rings I 6-17, the backing ring 18 and backing
plate I 9.
The magnet rotor 14 unit includes a disc 24 having sets 2b of
permanent magnets 26a-26b slide-mounted for radial movement relative to the
center
of the disc. This can be accomplished by providing radial cutouts 28 in the
disc 24
each having two parallel sides formed with central tracks 30 therealong for
slidably
receiving generally rectangular magnet holders 32. The tracks 30 may take the
form
of elongated lands which fit into longitudinal grooves 34 in the side edges of
the
magnet holders 32 so that the holders 32 and disc 24 have a tongue and groove
sliding
interfit.
Each holder 32 has a square cutout in which a set 26 of the magnets is
mounted. The magnets 26a-26b in each set 26 are arranged so that the poles of
each
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magnet 26a have their polarity reversed relative to like facing poles of each
magnet
26b. Hence, the magnet poles facing the electroconductive ring 16 alternate in
polarity around the magnet rotor 14, and the same is true of the magnet poles
facing
the electroconductive ring 17. Furthermore, as indicated in Fig. 2, the
longitudinal
side faces of the magnets in each set 26 which face one another define a
neutral plane
36 therebetween which extends radially from the rotary axis 37 of the shaft 10
for
maximum performance of the magnets.
The tracks 30 have sufficient length (a) to give the magnet holders 32
an inner retracted position at which the sets of magnets 26a-26b are located
radially
inward with respect to the electroconductive rings 16-17, i.c~., the magnets
26a-26b
are not overlapped by the orbits of the rings 16-17, and (b) to give the
magnet holders
32 an outward expanded position at which the sets of magnets 26a-26b are
completely
overlapped by the electroconductive rings 16-17 and are separated by air gaps
38-39
therefrom.
. 15 The magnet holders 32 are biased toward their retracted position as by
tension springs 40 which are connected to projecting portions of respective
inner and
outer pins 42-43 which are preferably stainless steel and project in the
direction of the
input shaft 10 from the body of the disc 24 and from an inner end portion of
the
magnet holders 32, respectively. The springs 40 are enclosed by a hub
extension
housing 45 which is connected by bolts 46 to a hub 47 and has outwardly
extending
mounting flanges 45a which are mounted by screws 48 on the body of the disc 24
between the cutouts 28. Adeduate clearance is provided between the rim of the
housing 45 and the magnet holders 32 at the cutouts 28 so that the magnet
holders 32
are free to slide on the tracks 30. The magnet holders 32, disc 24, housing
45, and
hubs 20, 47 are preferably aluminum and the backing ring 18 and backing plate
19 are
preferably mild steel. The couplings 12-13 are preferably wedge-type units in
which
split rings with complementing wedge faces are axially pulled together by
tightening
bolts to expand the outer ring against the surrounding hub and contract the
inner ring
against the surrounded shaft. It will be understood that instead of providing
couplings
12-13, the hubs 47 and 20 may be key-connected to the shafts 10-1 I .
From the foregoing description it is seen that the magnet rotor unit
comprises hub 47, hub extension housing 45, disc 24, magnet holders 32, and
magnet
set 26, and that the electroconductive rotor unit comprises hub 20, backing
plate 19,
backing ring 18, spacers 22, bolts 23, and electroconductive rings 16-17.
The operation of the first embodiment will now be described. When
the input shaft 10 is rotated the magnet holders 32 and associated sets 26 of
magnets
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are urged to slide outwardly by centrifugal force in opposition to the bias of
the
springs 40. As the magnets move outwardly between the electroconductive rings
16-
17 their magnetic fields induce eddy currents in the rights 16-17 thereby
causing the
electroconductive rotor unit to start rotating at a lower speed. When the
rotational
S speed of the input shaft 10 reaches a predetermined level the magnet holders
reach
their outer level of travel established by engagement of the outer pins 43
with the
housing 45 as a stop, or by any other suitable stop arrangement. With the
magnet
holders 32 at their outer limit of travel the magnets 26a, 26b are completely
located
between the orbits of the electroconductive rings 16-17 and maximum torque
output is
achieved at which the output shaft 20 is driven via the clutch with some slip
relative to
the input shaft 10. If the load on the output shaft becomes excess the amount
of slip
will responsively increase.
The described centrifugal clutch assembly can also be used as a soft
start coupler by connecting the shaft 11 to the power source and connecting
the shaft
10 to the load so that the shaft 11 becomes the input shaft and the shaft 10
becomes
the load shaft. Also, the retracted position of the magnet holders 32 is
changed so that
the magnets 26a-26b are slightly overlapped by the orbits of the
electroconductive
rings 16-17 when the magnet holders 32 are fully retracted. This initial
overlap is
made adequate to cause the magnet rotor 14 to start to rotate responsive to
the
rotation of shaft 11. As the magnet rotor 14 picks up speed its magnet holders
32 and
sets of magnets move outwardly thereby increasing the exposure of the
electroconductive rings 16-17 to the fields of the magnets and a resulting
pick up in
speed of the magnet rotor until the shaft 10 reaches a speed of minimum slip
relative
to the shaft 11. Instead of having a slight overlap of the magnets 26a-26b
with both
electroconductive rings 16-17 when the magnet holders are fully retracted, one
of the
rings 16-17 may be made wider by reducing its inner radius so that the widened
inner
portion will be overlapped by the magnets when the magnet holders are in
retracted
position.
An alternative electroconductive rotor unit 15' is shown in Figure 5
wherein the ferrous backing 18-19 for the electroconductive rings 16-17, and
the
electroconductive rings 16-17, are mounted on an aluminum support ring 50 and
support plate 51. In this rotor unit 15' the electroconductive rings are
designated
16'-17' and their ferrous backing comprises mild steel rings designated 18'-
19',
respectively. The support members 50-51 are each formed with like annular
recesses
SOa-Sla of a thickness to receive respective of the backing rings 18'-19' and
electroconductive rings 16'-17' in stacked relation. It is preferred to have
the mouth of
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the recesses SOa-S 1 a countersunk with a pattern of indentations 52 (Fig. 6)
matching
lobes 16a'-17a' provided on an expanded outer border portion of the
electroconductive
rings 16'-17' which extends beyond the outer marginal edge of the support
rings 18'-
19'. Mounting screws 53 extend through the lobes 16a'-17a' into the support
members
50-51. The latter are held in spaced relation by spacer sleeves 22' and bolts
23'. Bolts
21' anchor the support plate 51 to the hub 20,
In a further embodiment of the invention (Figs. 7 & 8) an
electroconductive rotor unit 15" is provided like the rotor unit 15', but
having an
intermediate support ring 54 added which has recesses like recess 51 a on its
opposite
sides receiving electroconductive rings 16", 17" and ferrous backing rings
18", 19".
Additional spacer sleeves 22" are provided in alignment with the spacer
sleeves 22'.
The bolts 23" passing through the spacers 22', 22" and through registering
openings in
the outer and intermediate support rings 50, 54 and support plate S I hold the
support
rings and plate together as a unit.
1 S A complementing magnet rotor unit 14" with a pair of magnet carrying
discs 24, 24' is provided for use with the electroconductive unit 15". The
discs 24, 24'
are spaced apart by a cylindrical brass spacer 56 and are tied together by
bolts 46'.
Each of the discs 24, 24' has radial cutouts with side tracks 30 therealong
for slidably
receiving magnet holders 32 grooved along their longitudinal side edges and
containing pairs 26 of magnets with reversed poles as before. The magnet
holders on
disc 24' are designated 32'.
Instead of using tension springs to bias the holders 32, 32' inwardly, the
biasing is performed by compression springs 60 seating at their outer ends
against the
inside face of the spacing cylinder 56. Extending longitudinally through the
compression springs 60 are pull pins 62 which project inwardly from weld
connections
to cross-pins 64 each of which has opposite end portions fitting into
respective holes
in two of the magnet holders 32, 32' near the inner end thereof The pull pins
62 slide
freely through radial holes 56a in the spacing cylinder 56. Adjacent their
inner ends
the pull pins have axially extending through-bores for receiving cotter keys
66 on
which the inner ends of the springs 60 are seated.
Each cross-pin 64 and the related pull pins 62 are manufactured as a
pin unit 65. Initially these pin units 65 are positioned with their pull pins
62
registering with respective of the radial holes 56a in the spacing cylinder
56. As each
pin unit is introduced to the spacing cylinder a pair of compression springs
60 are
placed endwise over the pull pins 62 of the unit. A single cotter key 66 is
then
inserted through the aligned holes near the inner end of the pull pins. After
the pin
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units 65 and compression springs 62 have been installed with the spacing
cylinder 56
as a pin/spacer unit, this unit is positioned over the disc 24' when its
magnet holders
32 are positioned at the inner end of their tracks. This positions the pin
holes in the
holders 32' in proper position to receive one end of all of the cross-pins 64
of the
S pin/spacer unit. The intermediate support ring 54 with its electroconductive
rings 16",
17" and ferrous backing rings 18", 19" installed is then positioned over the
magnet
rotor disc 24'. Then the other magnet rotor disc 24 with a hub 47' mounted
thereon by
bolts 46', and with its magnet holders 32 also at the inner end of their
tracks is
positioned so that the magnet rotor disc 24 can be lowered and have the cross-
pins 64
register with the pin holes in its magnet holders 32. The discs 24, 24' are
then tied
together against the ends of the spacing cylinder 56 by the bolts 57. With the
described arrangement it is seen that outward movement of the magnet holders
32, 32'
in the pair of coacting magnet rotor discs 24, 24' is yieldingly opposed by
the
compression springs 60. The magnet rotor unit 14" and the intermediate support
ring
54 with its electroconductive rings 16", 17" and ferrous backing rings 18",
19"
attached, can then be assembled with the remainder of the electroconductive
rotor unit
1 S" by use of the tie bolts 23" and sets of spacers 22' and 22".
In the embodiments described previously the magnet holders and their
magnets are loaded into the magnet rotor through the outer ends of the cutouts
28
which extend radially outward to the periphery of the magnet rotor. As shown
in
Figure 9 the radial cutouts, designated 28', may be open at their inner ends
rather than
their outer ends, in which case a central portion of the magnet rotor is open
to an
extent permitting each magnet holder 32 to be positioned in the open central
portion
and introduced endwise to the tracks 30 of the respective cutout.
The hub extension housing 45 has its mounting flanges bolted to the
magnet rotor as before and presents spring mounting pins 42' adjacent the
center of
the hub, one opposite the inner end of each cutout 28'. These pins 42' project
far
enough to receive the inner ends of dual tension springs 40', 40" having their
other
ends looped around complementing mounting pins 43' on the inner end portions
of the
magnet holders.
When the tension springs 40', 40" are in a non-loaded condition the
magnet holders 32 are retracted such that the magnet sets 26 are located
radially
inward of the electroconductive element orbits. When the tension springs 40',
40" are
tensioned responsive to centrifugal force on the holders and their magnets
responsive
to rotation of the magnet rotor, the magnet holders slide radially to the
outer ends of
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the tracks where the portion 24a of the magnet rotor outwardly of the outer
ends of
the radial cutouts 28' serve as stops.
As indicated in Fig. 10, the refrigeration plant for "reefer" trucks or
trailers commonly has a compressor 80 aligned with an internal combustion
engine 81
and side-by-side with an electric motor 82. The input shaft of the compressor
is
continuously connected to the output shaft of the motor 82 by a belt 83
extending
between sheaves 80a and 82a on the shafts of the compressor and motor. The
output
shaft of the engine 81 is connected to the input shaft of the compressor by a
centrifugal mechanical clutch 84 located between the sheave 80a and the
engine.
When the reefer is underway the engine 81 is used to power the compressor and
when
the reefer is at a loading dock where electricity is available, normally the
motor 82 is
used to drive the compressor. Heretofore, when the compressor has been driven
by
the engine the engine vibration has transferred through the clutch 84 to the
compressor and the related bearings. However, when one of the centrifugal
clutches
of the present invention is used rather than a mechanical centrifugal clutch
no engine
vibration is transferred via the clutch.
Referring to Fig. 11, to enable a particularly compact drive
arrangement between the engine 81 and compressor 80 in a reefer refrigeration
system
like that shown in Fig. 10 utilizing a centrifugal clutch like that in Fig. 5,
for example,
the electroconductive rotor 15' may be provided with a double sheave 90 in
place of
the spacers 22 with the bolts 23 passing through the sheave. Also, one or more
sheaves 92 can be mounted on the hub 20 as shown.
Referring to Fig. 12, there is shown an arrangement in which a
stationary stepped stub shaft 98 projecting from a flange 99 mounted by bolts
100, has
the inner races of three bearing units 101-103 mounted thereon. Bearing 101
provides
journal support for the hub 20' of a double sheave 92' connected to the
electroconductive rotor unit 15 in place of the hub 20, and bearings 102-103
provide
journal support for the magnet rotor unit 14 which has a modified hub 47' to
receive a
double sheave 104'. A sheave 90' may also be provided in the manner of sheave
90 in
Figure l 1. Spacers 108-109 are provided on the shaft 98 between the inner
races of
the bearings 102-103 and between the inner race of bearing 102 and the plate
19 to
maintain edual air gaps 38, 39. The assembly is retained on the shaft 98 by a
nut 110.
With this stub shaft arrangement the magnet rotor 14 may be driven by a belt
drive to
the sheave 92 from a power source, and a power takeoff can be taken by belts
from
the sheaves 104 or 90' on the electroconductive rotor unit 15.
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Although coil springs have been illustrated and described as the means
, for biasing the magnet holders inwardly in opposition to centrifugal force,
it will be
appreciated that other biasing means would be suitable such, for example, as
air
springs. It will be appreciated that the sheaves shown in Figures 11-12 can be
sprockets for chain drives rather than having belt drives.
From the foregoing it will be appreciated that, although specific
embodiments of the invention have been described herein for purposes of
illustration,
various modifications may be made without deviating from the spirit and scope
of the
invention. Accordingly, the invention is not limited except as by the appended
claims.
