U.S. patent application number 10/210442 was filed with the patent office on 2004-02-05 for magnetic brake actuated spring clutch.
Invention is credited to Webber, James L..
Application Number | 20040020737 10/210442 |
Document ID | / |
Family ID | 31187328 |
Filed Date | 2004-02-05 |
United States Patent
Application |
20040020737 |
Kind Code |
A1 |
Webber, James L. |
February 5, 2004 |
MAGNETIC BRAKE ACTUATED SPRING CLUTCH
Abstract
A magnetic brake actuated spring clutch has an input shaft that
is rotatably mounted in a housing, a coaxial output shaft that is
rotatably mounted in the housing for rotation relative to the input
shaft, and a coil spring surrounding a portion of the output shaft.
The coil spring has one end attached to the input shaft and an
opposite end attached to a rotor of a magnetic brake. The rotor is
journalled on the output shaft, and the magnetic brake further
includes a stator that is secured in the housing. The stator
includes a permanent magnet and the rotor includes a copper plate
that is juxtaposed the permanent magnet. The coil spring has a
first part that is wound in one direction and a coaxial second part
that is wound in an opposite direction so that the input shaft
drives the output shaft in either direction when the spring clutch
is engaged by input shaft via the magnetic brake. Alternatively,
the stator may include a pair of spaced opposed magnets that are
juxtaposed either side of the copper plate. A simple coil spring
wound in one direction can be used to provide a one-way magnetic
brake actuated spring clutch.
Inventors: |
Webber, James L.; (Shelby
TWP., MI) |
Correspondence
Address: |
REISING, ETHINGTON, BARNES, KISSELLE, P.C.
P O BOX 4390
TROY
MI
48099-4390
US
|
Family ID: |
31187328 |
Appl. No.: |
10/210442 |
Filed: |
August 1, 2002 |
Current U.S.
Class: |
192/35 ;
192/75 |
Current CPC
Class: |
F16D 13/12 20130101;
F16D 41/206 20130101; F16D 27/105 20130101 |
Class at
Publication: |
192/35 ;
192/75 |
International
Class: |
F16D 013/12 |
Claims
1. A magnetic brake actuated spring clutch comprising: an input
shaft that is rotatably mounted in a housing, the input shaft
having a bore at one end that receives the end of an output shaft
for rotation relative to the input shaft, a coil spring wound from
flat wire disposed in the bore and surrounding the end of the
output shaft that is in the bore, the coil spring having an inboard
part that is wound in one direction and a coaxial outboard part
that is wound in an opposite direction, the inboard part having an
inboard end that is attached the to input shaft, the outboard part
having an outboard end that is attached to a rotor of a magnetic
brake, the rotor being journalled on the output shaft and including
a sleeve that surrounds the outboard part of the coil spring, the
input shaft having a counterbore that surrounds the sleeve, and the
magnetic brake further including a stator that is secured in the
housing.
2. The magnetic brake actuated spring clutch as defined in claim 1
wherein one of the stator and the rotor includes at least one
permanent magnet and another of the stator and the rotor includes a
plate of electrically conductive, non-magnetic metal disposed
adjacent the at least one permanent magnet.
3. The magnetic brake actuated spring clutch as defined in claim 1
wherein the stator holds at least one permanent magnet and is made
of a ferro-magnetic material, and the rotor includes a plate of
electrically conductive, non-magnetic metal that is juxtaposed the
magnet.
4. The magnetic brake actuator spring clutch as defined in claim 1
wherein the stator holds spaced opposed permanent magnets and the
rotor includes a plate of electrically conductive, non-magnetic
metal that is disposed between the spaced opposed permanent
magnets.
5. A magnetic brake actuated spring clutch comprising: an input
shaft that is rotatably mounted in a housing, a coaxial output
shaft that is rotatably mounted in the housing for rotation
relative to the input shaft, a compound coil spring surrounding a
portion of the output shaft, the coil spring having a first part
that is wound in one direction and a coaxial second part that is
wound in an opposite direction, the first part being attached the
to input shaft and the second part being attached to a rotor of a
magnetic brake, and the magnetic brake further including a stator
that is secured in the housing.
6. The magnetic brake actuated spring clutch as defined in claim 5
wherein one of the stator and the rotor includes at least one
magnet and another of the stator and the rotor includes at least
one plate of electrically conductive, non-magnetic metal that is
disposed adjacent the at least one magnet.
7. The magnetic brake actuated spring clutch as defined in claim 5
wherein the stator holds at least one magnet and the rotor includes
a plate of electrically conductive, non-metallic metal that is
juxtaposed the magnet.
8. The magnetic brake actuated spring clutch as defined in claim 5
wherein the stator holds two spaced opposed magnets and the rotor
includes a plate of electrically conductive, non-metallic metal
that is disposed between the two spaced opposed magnets.
9. A magnetic brake actuated spring clutch comprising: a spring
clutch having an input shaft that is rotatably mounted in a
housing, a coaxial output shaft that is rotatably mounted in the
housing for rotation relative to the input shaft, a coil spring
surrounding a portion of the output shaft, the coil spring being
attached to the input shaft at one end and attached to a rotor of a
magnetic brake at another end, the magnetic brake further including
a stator that is secured in the housing, one of the stator and the
rotor including at least one magnet, and another of the stator and
the rotor including at least one plate of electrically conductive,
non-magnetic metal that is disposed adjacent the at least one
magnet.
10. The magnetic brake actuated spring clutch as defined in claim 9
wherein the stator includes a pair of spaced permanent magnets and
the rotor includes a plate of electrically conductive, non-magnetic
metal that is disposed between the pair of permanent magnets.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to clutches and more
particularly to spring clutches that include a coil spring that is
wound tightly around a shaft to transfer toque to the shaft.
BACKGROUND OF THE INVENTION
[0002] Devices such as automotive lift gates, side doors, deck lids
and latches are often power operated by a drive mechanism that has
an electric motor as the prime mover. With such devices it is
desirable to provide for manual operation of the device in the
event of power failure. Ideally, manual operation of the device
does not take any more effort than an installation without the
drive mechanism.
[0003] Some power operated devices, such as power operated lift
gates and side doors include an electromagnetic clutch in the drive
mechanism. The magnetic clutch allows the drive mechanism to
operate the power operated device in either direction, for example
to raise or lower the lift gate, or to open or close the side door.
However, the electromagnetic clutch also automatically disengages
the electric motor from the power operated device at the end of the
power operation. Thus in the event of power failure the manual
operating effort is reduced substantially by eliminating the
requirement for back driving the electric motor. While such drive
mechanisms are successful in reducing the manual operating effort,
drive mechanisms incorporating electromagnetic clutches are complex
and costly due in large part to the electrical operation of the
electromagnetic clutch.
SUMMARY OF THE INVENTION
[0004] This invention provides a spring clutch that can have all
the capabilities of an electromagnetic clutch with respect to
driving a power operated device in either direction and
automatically disengaging at the end of the power operation so that
the device can be operated manually with a reduced effort.
[0005] In one aspect, the invention provides a spring clutch that
is actuated by a magnetic brake so that an input shaft drives an
output shaft in at least one direction and the spring clutch
automatically disengages at the end of the driving operation so
that the output shaft rotates freely in either direction.
[0006] In another aspect, the invention provides a bidirectional
spring clutch actuated by a magnetic brake. Here, an input shaft
that drives an output shaft in either direction and the spring
clutch automatically disengages at the end of the driving operation
so that the output shaft rotates freely in either direction.
[0007] In either aspect, the spring clutch includes a magnetic
brake that operates on the Lorenz principle. As a conductive,
non-magnetic metal, such as copper, is moved past a magnet, an
opposing or drag force is generated by eddy currents set up in the
conductive, non-magnetic metal. The drag force is proportional to
the speed of the movement until magnetic saturation occurs at which
time, the drag force becomes constant. This drag force is produced
in response rotation of an input shaft and when sufficient engages
a spring clutch that couples the input shaft to an output shaft for
torque transfer. When speed of the input shaft drops below a
predetermined value, the drag force is overcome by the spring force
and the spring clutch disengages automatically. Thus when the input
shaft stops, the output shaft can be rotated freely in either
direction. Since the drag force is created without any contact as
in the case of friction produced drag force, there is not any wear
and the spring clutch will operate with consistent long term
performance.
[0008] The spring clutch contains a coil spring that is attached to
the input shaft at one end and to a rotor of the magnetic brake at
the other end. The coil spring is wound around the output shaft and
wound down tight onto the output shaft by the magnetic brake
resulting is torque transfer in one direction in the case of a
one-way spring clutch. The bi-directional spring clutch operates by
using two springs wound in opposite directions. The two springs can
be connected by a collar or wound from a single piece of wire.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a longitudinal section of a magnetic brake
actuated spring clutch of the invention showing the spring clutch
disengaged;
[0010] FIG. 2 is a section taken along the line 2-2 of FIG. 1
looking in the direction of the arrows;
[0011] FIG. 3 is fragmentary view showing details of the spring
clutch; and
[0012] FIG. 4 is a longitudinal section of an alternate magnetic
brake actuated spring clutch of FIG. 1 showing the spring clutch
engaged.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
[0013] Referring now to the drawing, the magnetic brake actuated
spring clutch 10 comprises a spring clutch 11 having an input shaft
12 that is rotatably mounted in a housing 14. The input shaft 12
has a bore 16 at one end that receives an end portion of an output
shaft 18. The terminus 20 of the output shaft 18 is journalled in a
sleeve 22 that is non-rotatably attached to input shaft 12.
[0014] A compound coil spring 24 wound from flat wire is disposed
in the bore 16 and surrounds the end of the output shaft 18 that is
in bore 16. Coil spring 24 has an inboard part 24a that is wound in
one direction, e.g. clockwise, and a coaxial outboard part 24b that
is wound in the opposite direction, e.g. counter-clockwise. The
inboard end 26 of the inboard part 24a is attached to input shaft
12 via sleeve 22 while the outboard end 27 of outboard part 24b is
attached to a rotatable member or rotor 28 of magnetic brake 30 as
best shown in FIG. 3. (Magnetic brake 30 is sometimes referred to
as an eddy current brake or an eddy current damper). While the
compound spring 24 is wound from a single piece of flat wire, it is
also possible to wind two separate springs in opposite directions
and connect the two separate springs by a collar.
[0015] Rotor 28 is journalled on output shaft 18 and includes a
sleeve 32 that surrounds the outboard part 24b of coil spring 24.
Sleeve 32 is journalled in a counterbore 33 of input shaft 12 and
retained by collar 35 secured to output shaft 18. Magnetic brake 30
further includes a stationary U-shaped holder or stator 34 that is
secured in housing 14. Stator 34 holds a permanent magnet 36 while
the rotor 28 includes a plate 38 of electrically conductive,
non-magnetic metal that is attached to sleeve 32 and disposed in
the slot of U-shaped stator 34 adjacent the permanent magnet 36.
Stator 34 is a suitable ferromagnetic material, such as steel and
rotor 28 or at least plate 38 is preferably copper. While holder 34
and magnet 36 are stationary and plate 38 is rotatable, it is also
possible to have holder 34 and magnet 36 attached to sleeve 32 for
rotation by the input shaft 12 and to have a stationary plate of
electrically conductive, non-magnetic metal.
[0016] Magnetic brake actuated spring clutch 10 operates as
follows. When input shaft 12 is stationary, spring clutch 11 is
disengaged as shown in FIG. 1, and output shaft 18 can be rotated
freely in either direction without any back drive to input shaft
12. However, spring clutch 11 is engaged whenever input shaft 12 is
rotated above a predetermined speed, driving the output shaft
18.
[0017] When input shaft 12 is rotated clockwise, rotor 28 is also
rotated clockwise by compound coil spring 24. This produces eddy
currents in the copper plate 38 which produce a drag force on
copper plate 38 that increases with the speed of the input shaft 12
until magnetic saturation occurs. Rotor 28 lags behind rotating
input shaft 12 and twists coil spring 24 in the counter-clockwise
direction, winding the clockwise wound, inboard spring part 24a
down into tight gripping engagement with output shaft 18 while
expanding the counter-clockwise wound outboard part 24b against
sleeve 32 (as shown in FIG. 4 in connection with an alternate
embodiment described below). Output shaft 18 is then driven
clockwise by input shaft 12. When input shaft 12 stops or drops
below some predetermined speed, the drag force acting on rotor 24
is overcome by the spring force of twisted coil spring 24 releasing
the grip of inboard spring part 24a on output shaft 18. Output
shaft 18 is then free to rotate in either direction.
[0018] When input shaft 12 is rotated counter-clockwise, rotor 28
is also rotated counter-clockwise by compound coil spring 24. This
also produces eddy currents in the copper plate 38 which produce a
drag force on the copper plate 38. Rotor 28 now lags behind
rotating input shaft 12 and twists coil spring 24 in the clockwise
direction 24 winding outboard spring part 24b down into tight
gripping engagement with output shaft 18 while expanding the
clockwise wound inboard spring part 24a against bore 16 of input
shaft 12. Output shaft 18 is then driven counterclockwise by input
shaft 12. When input shaft 12 stops or drops below a predetermined
speed, the drag force acting on rotor 24 diminishes releasing the
grip of outboard spring part 24b and output shaft 18 is then free
to rotate in either direction.
[0019] FIG. 4 shows an alternate embodiment wherein the U-shaped
holder 34a holds opposing magnets 36a and 36b that are spaced apart
to provide a gap for plate 38. This eliminates the need for a
holder of ferro-magnetic material. In most instances a single
magnet 36 or a pair of opposing magnets are sufficient to actuate
the spring clutch. However, a plurality of circumferentially spaced
magnets or pairs of magnets can be used if the drag force is kept
to a reasonable level.
[0020] Thus the invention provides a simple and inexpensive spring
clutch that allows free rotation of the output member when
disengaged, that is engaged in either direction of rotation of the
input member and that is automatically disengaged when the input
member stops.
[0021] While bidirectional spring clutches have been disclosed as
the preferred embodiments, the principles of the invention are also
applicable to a one way spring clutch in which the spring clutch is
engaged in one direction only. The one-way spring clutch of the
invention still requires a magnetic brake but does not require two
coil springs or a compound coil spring with two coil spring parts.
A simple coil spring wound in a single direction will do. In other
words, many modifications and variations of the present invention
are possible in light of the above teachings. It is, therefore, to
be understood that within the scope of the appended claims, the
invention may be practiced otherwise than as specifically
described.
* * * * *