U.S. patent number 10,385,927 [Application Number 15/719,871] was granted by the patent office on 2019-08-20 for torque limiter having over-speed protection.
This patent grant is currently assigned to Moog Inc.. The grantee listed for this patent is Moog Inc.. Invention is credited to Lowell Van Lund Larson.
United States Patent |
10,385,927 |
Larson |
August 20, 2019 |
Torque limiter having over-speed protection
Abstract
An apparatus for connecting a rotational drive member to a
rotational driven member brakes rotation when either the torque
transmitted between the members exceeds a predetermined torque
limit or the rotational speed of the drive member exceeds a
predetermined rotational speed limit. The apparatus includes a
torque limiter configured to actuate a braking mechanism or
disconnect transmission when the torque limit is exceeded, and an
over-speed governor configured to trigger the torque limiter when
the rotational speed of the input element exceeds the rotational
speed limit. The over-speed governor may trigger the torque limiter
by reducing the torque limit of the torque limiter, or by
introducing rotational drag in the apparatus to increase
transmitted torque.
Inventors: |
Larson; Lowell Van Lund
(Huntington Beach, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Moog Inc. |
Elma |
NY |
US |
|
|
Assignee: |
Moog Inc. (Elma, NY)
|
Family
ID: |
65896623 |
Appl.
No.: |
15/719,871 |
Filed: |
September 29, 2017 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20190101169 A1 |
Apr 4, 2019 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F16D
43/16 (20130101); F16D 43/216 (20130101); F16D
7/027 (20130101); F16D 43/22 (20130101); F16D
2043/145 (20130101) |
Current International
Class: |
F16D
7/02 (20060101); F16D 43/21 (20060101); F16D
43/22 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hansen; Colby M
Attorney, Agent or Firm: Hodgson Russ LLP
Claims
What is claimed is:
1. An apparatus for connecting a rotational drive member to a
rotational driven member, the apparatus comprising: a structural
ground; an input element rotatable relative to the structural
ground; an output element rotatable relative to the structural
ground; a torque limiter connecting the output element to the input
element for rotation with the input element, wherein the torque
limiter is actuated to brake rotation of the input element and the
output element, or to disconnect the input element from the output
element, when torque transmitted between the input element and the
output element exceeds a torque limit; and an over-speed governor
configured to cause actuation of the torque limiter to brake
rotation of the input element and the output element, or to
disconnect the input element from the output element, when
rotational speed of the input element exceeds a rotational speed
limit.
2. The apparatus according to claim 1, wherein the torque limiter
includes a torque limit setting spring having a preload defining
the torque limit, and the over-speed governor causes actuation of
the torque limiter by reducing the preload of the torque limit
setting spring when the rotational speed limit is exceeded, thereby
reducing the torque limit.
3. The apparatus according to claim 2, wherein the over-speed
governor reduces the torque limit to substantially zero torque when
the rotational speed limit is exceeded.
4. The apparatus according to claim 2, wherein the over-speed
governor includes: a preload setting shaft engaging the torque
limit setting spring, the preload setting shaft being axially
displaceable relative to the structural ground to set the preload
of the torque limit setting spring; at least one fly weight
arranged on the input element to hold the preload setting shaft at
an axial setting position when the rotational speed of the input
element does not exceed the rotational speed limit; wherein the at
least one fly weight moves by centrifugal force when the rotational
speed of the input element exceeds the rotational speed limit to
release the preload setting shaft and permit axial displacement of
the preload setting shaft away from the axial setting position
thereby reducing the preload of the torque limit setting
spring.
5. The apparatus according to claim 4, wherein the at least one fly
weight is pivotally mounted to the input element.
6. The apparatus according to claim 4, wherein the at least one fly
weight directly engages the preload setting shaft to hold the
preload setting shaft at the axial setting position when the
rotational speed of the input element does not exceed the
rotational speed limit.
7. The apparatus according to claim 4, wherein the at least one fly
weight directly indirectly engages the preload setting shaft
through a sear to hold the preload setting shaft at the axial
setting position when the rotational speed of the input element
does not exceed the rotational speed limit.
8. The apparatus according to claim 7, wherein the preload setting
shaft includes a sear groove therein and the input element includes
a radially extending recess, and wherein the sear is partially
received by the sear groove and partially received by a radially
extending recess to hold the preload setting shaft at the axial
setting position when the rotational speed of the input element
does not exceed the rotational speed limit.
9. The apparatus according to claim 4, wherein the at least one fly
weight comprises a plurality of fly weights angularly spaced about
a rotational axis of the input element.
10. The apparatus according to claim 4, further comprising a button
arranged to push the preload setting shaft into the axial setting
position to reset the apparatus after an over-speed event.
11. The apparatus according to claim 4, wherein the preload setting
shaft is adapted for mating with a tool for moving the preload
setting shaft into the axial setting position to reset the
apparatus after an over-speed event.
12. The apparatus according to claim 11, wherein the preload
setting shaft includes a tapped hole for mating with a threaded
tool.
13. The apparatus according to claim 4, wherein the output element
includes a fluid injection port through which pressurized fluid is
injectable into a cavity to force the preload setting shaft into
the axial setting position to reset the apparatus after an
over-speed event.
14. The apparatus according to claim 1, wherein the over-speed
governor causes actuation of the torque limiter by increasing
torque transmitted between the input element and the output element
when the rotational speed limit is exceeded.
15. The apparatus according to claim 14, wherein: the torque
limiter includes a rotatable braking member arranged to transmit
rotational motion from the input member to the output member and a
plurality of disc brakes arranged between the braking member and
the structural ground, the braking member being axially displaced
relative to the structural ground to engage the plurality of disc
brakes when the torque limit is exceeded; and the over-speed
governor includes at least one fly weight arranged on the braking
member, wherein the at least one fly weight moves by centrifugal
force when the rotational speed of the input element exceeds the
rotational speed limit such that the at least one fly weight
applies axially directed force to the plurality of disc brakes to
increase torque transmitted between the input element and the
output element.
16. The apparatus according to claim 15, wherein the at least one
fly weight is pivotally mounted to the braking member.
17. The apparatus according to claim 15, wherein the at least one
fly weight comprises a plurality of fly weights angularly spaced
about a rotational axis of the braking member.
18. The apparatus according to claim 14, wherein the apparatus is
resettable after an over-speed event by commanding reverse rotation
of the rotational drive member to impart reverse rotation to the
input element.
Description
FIELD OF THE INVENTION
The present invention relates generally to torque limiters for
preventing the transmission of torque from a driving element to a
torque responsive element when a predetermined torque limit has
been reached. More specifically, the present invention relates to a
torque limiter configured to lockup when the driving element
experiences a rotational over-speed condition.
BACKGROUND OF THE INVENTION
Torque limiters are used in aircraft flight control systems to
prevent the transmission of excess torque from a drive unit when a
flight control surface actuated by the drive unit becomes jammed.
Flight control surfaces include, for example, a trailing edge flap
on a wing.
A torque limiter commonly includes an input element coupled to an
output element through a braking mechanism responsive to an
over-torque condition, as may be experienced when the output
element is prevented from rotation due to a malfunction. In a
well-known arrangement, the braking mechanism includes an axially
displaceable braking element that transmits rotation from the input
element to the output element during normal operation. The braking
element is spring-biased in an axial direction toward the input
element, and a plurality of angularly spaced balls are received in
opposing recessed pockets in the input element and the braking
element. When a torque limit is exceeded, the balls roll out of the
pockets and axially displace the braking element against the spring
bias into frictional engagement with grounded disc brakes to
frictionally brake rotation of the input and output elements.
While torque limiters of the type described above are effective in
preventing damage to mechanical drive components caused by
over-torque, they do not provide any protection when an over-speed
condition is experienced. In the context of aircraft control
systems, an over-speed condition may occur if a torque tube that
transmits torque to aircraft control surfaces undergoes failure and
load is suddenly removed from the output element, thereby causing
the input and output elements to rotate at a dangerously high
number of revolutions per minute.
What is needed is a torque limiter that is capable of responding to
an over-speed condition.
SUMMARY OF THE INVENTION
The invention provides an apparatus for connecting a rotational
drive member to a rotational driven member, wherein the apparatus
brakes rotation when either the torque transmitted between the
members exceeds a predetermined torque limit or the rotational
speed of the drive member exceeds a predetermined rotational speed
limit. The apparatus generally comprises a structural ground, a
rotatable input element coupled to the drive member and a rotatable
output element coupled to the driven member, a torque limiter
configured to actuate a braking mechanism when the torque limit is
exceeded to brake rotation, and an over-speed governor configured
to trigger the torque limiter braking mechanism when the rotational
speed of the input element exceeds the rotational speed limit.
In a first embodiment, the torque limiter includes a torque limit
setting spring having a preload which defines the torque limit, and
the over-speed governor acts to reduce the preload of the torque
limit setting spring when the rotational speed limit is exceeded,
thereby reducing the torque limit needed to trigger the torque
limiter so that actuation of the torque limiter is caused by any
applied torque. In the first embodiment, the over-speed governor
may include a preload setting shaft engaging the torque limit
setting spring, wherein the preload setting shaft is axially
displaceable relative to a structural ground to set the preload of
the torque limit setting spring. The over-speed governor of the
first embodiment may also include at least one fly weight arranged
on the input element for releasably holding the preload setting
shaft in an axial setting position relative to the structural
ground. The fly weight may directly engage the preload setting
shaft in the manner of a sear, or it may radially confine a
separate sear element for maintaining the preload setting shaft in
its axial setting position. When the rotational speed of the input
element exceeds the rotational speed limit, each fly weight moves
radially outward by centrifugal force, thereby releasing the
preload setting shaft to permit axial displacement of the preload
setting shaft relative to the structural ground. The preload
setting shaft is displaced by the torque limit setting spring
relative to the structural ground, thereby reducing the preload.
All or substantially all of the preload on the torque limit setting
spring may be removed such that the over-speed governor reduces the
torque limit to substantially zero torque and the torque limiter
will be triggered by any transmitted torque.
The first embodiment may include means for resetting the torque
limiter and over-speed governor for continued operation. The
preload setting shaft may be urged back into its axial setting
position against the bias of the torque limit setting spring by
pressing an axially movable push button engaging an end of the
preload setting shaft, inserting a puller tool into a tapped hole
at an opposite end of the preload setting shaft and pulling the
preload setting shaft, and/or introducing pressurized fluid into a
cavity between the output element and the end of the preload
setting shaft. The fly weights of the over-speed governor may be
spring-biased to return to a radially inward position for holding
the preload setting shaft upon its return to the axial setting
position.
In a second embodiment, the over-speed governor is configured to
add drag torque to the grounding brake of the torque limiter when
the rotational speed limit is exceeded, thereby triggering the
torque limiter to fully brake rotation. The over-speed governor of
the second embodiment may include at least one fly weight arranged
on a rotatable braking member of the torque limiter that is coupled
to the input element. The at least one fly weight moves by
centrifugal force when the rotational speed of the input element
and coupled braking element exceed the rotational speed limit such
that the fly weight applies axially directed force to disc brakes
of the torque limiter to increase torque transmitted between the
input and output elements. As a result, the torque limit is exceed
and the torque limiter responds in the known manner to stop
rotation. The over-speed governor of the second embodiment is
resettable after an over-speed event by commanding reverse rotation
of the drive member to impart reverse rotation to the input
element.
The input element and output element are reversible in function,
i.e. the input element may be used as an output element and the
output element may be used as an input element.
BRIEF DESCRIPTION OF THE DRAWING VIEWS
The nature and mode of operation of the present invention will now
be more fully described in the following detailed description of
the invention taken with the accompanying drawing figures, in
which:
FIG. 1 is a cross-sectional view illustrating a torque limiter
apparatus having over-speed protection in accordance with a first
embodiment of the present invention, wherein the apparatus is shown
in its normal operating condition;
FIG. 2 is a sectional view taken generally along the line 2-2 in
FIG. 1;
FIG. 3 is a cross-sectional view similar to that of FIG. 1, wherein
the apparatus is shown in an over-speed condition triggering an
over-speed governor of the apparatus;
FIG. 4 is a sectional view taken generally along the line 4-4 in
FIG. 3;
FIG. 5 is a cross-sectional view similar to that of FIG. 3, wherein
the apparatus is shown having means for resetting the apparatus
after the apparatus has been triggered by an over-speed
condition;
FIG. 6 is an enlarged view of region A in FIG. 5 illustrating
biasing of a fly weight of the over-speed governor;
FIG. 7 is a view similar to that of FIG. 6, wherein the apparatus
has been reset;
FIG. 8 is a cross-sectional view similar to that of FIG. 5, wherein
the apparatus is shown having alternative means for resetting the
apparatus;
FIG. 9 is an enlarged view showing an alternative configuration of
a fly weight in which the fly weight itself acts as a sear;
FIG. 10 is a cross-sectional view illustrating a torque limiter
apparatus having over-speed protection in accordance with a second
embodiment of the present invention, wherein the apparatus is shown
in its normal operating condition;
FIG. 11 is a cross-sectional view similar to that of FIG. 5,
wherein the apparatus is shown in an over-speed condition
triggering an over-speed governor of the apparatus.
DETAILED DESCRIPTION OF THE INVENTION
Reference is made initially to FIGS. 1-4, wherein a torque limiter
apparatus formed in accordance with a first embodiment of the
invention is shown and identified generally by reference numeral
10. Apparatus 10 comprises a structural ground in the form of
housing members 12 and 14, an input element 16 rotatable about a
rotational axis 11 relative to the structural ground by virtue of a
rotary bearing 18, and an output element 20 rotatable relative to
the structural ground by virtue of another rotary bearing 22.
Apparatus 10 further comprises a torque limiter 24 and an
over-speed governor 26 described in greater detail below. As will
be understood, apparatus 10 is useful for connecting a rotational
drive member (not shown) to a rotational driven member (not shown)
by coupling the drive member to input element 16 and by coupling
the driven member to output element 20. Coupling of the drive
member to input element 16 may be achieved by a splined connection
to a spline 28 of input element 16, and coupling of the driven
member to output element 20 may be achieved by a splined connection
to a spline 30 of output element 20. While splined couplings are
shown, other types of couplings that provide transmission of
rotational motion may be used. The connection provided by apparatus
10 provides both over-torque and over-speed protections in the
transmission of rotational motion from the drive member to the
driven member.
As mentioned above, housing members 12 and 14 act as a structural
ground relative to which the input element 16 and the output
element 20 rotate. Housing member 12 may be an axially elongated
housing member surrounding the torque limiter 24 and the over-speed
governor 26, and housing member 14 may be an end plate threadably
coupled to housing member 12 and secured against rotation relative
to housing member 12 by threaded fasteners 32. In the illustrated
embodiment, rotary bearing 18 is nested in an annular recess of
housing member 14 and rotatably supports input element 16, and
rotary bearing 22 is nested in an annular recess of housing member
12 and rotatably supports output element 20.
Torque limiter 24 connects output element 20 to input element 16
for coupled rotation with the input element at the same rotational
speed. Torque limiter 24 is actuated to brake rotation of input
element 16 and output element 20 when torque transmitted between
input element 16 and output element 20 exceeds a predetermined
torque limit.
A torque limiter is a mechanical design element, used in the
transmission system, to protect downstream components from
excessive torque levels. A torque limiter either releases or locks
to ground if the predetermined torque limit has been exceeded.
There are three general types of torque limiters: sacrificial weak
element, slip clutch, and torque brake.
The sacrificial weak element type is one that fractures and/or
fully disconnects from the transmission drive line if the maximum
design torque is exceeded. This type of torque limiter must be
replaced or reset to transmit torque and return to operation after
it is triggered. Examples of the sacrificial weak element type are
shear and clear shafts, or ball or roller elements that snap over
into a tripped condition and do not transmit any more torque.
The slip clutch type introduces slippage or losses into the system
rig or the rotary relationship between the input and output shafts
of the torque limiter if the torque limit has been exceeded. A slip
clutch torque limiter may include spring-loaded brake plates or
ball detents between input and output shafts. If the torque limit
has been exceeded, the slip clutch torque limiter simply lets the
output shaft slip at a different speed relative to the input shaft.
Unlike the sacrificial weak element type, the slip clutch type
transmits nearly the same maximum torque during a slip event and it
automatically resets itself after the slip event.
The torque brake type maintains the system rig or the rotary
relationship of the input and output shaft of the torque limiter,
even if the torque limit has been exceeded. The torque brake type
protects its output shaft from the excess torque at the input shaft
by applying braking torque from the input shaft directly to the
ground. The input torque is measured by a spring-loaded axial or
radial ball ramp or cam, which applies force to brake plates or
shoes, causing the brake plates or shoes to directly engage a
grounded structure if the torque limit is exceeded. To reset or
release the locked shaft, the input torque must be lowered to zero,
and in some cases, the input shaft might need to back-up axially to
release the brakes.
In the present disclosure, torque limiter 24 is embodied as a
torque brake type torque limiter. However, torque limiter 24 may be
embodied as another type of torque limiter, for example a
sacrificial weak element type torque limiter or a slip clutch type
torque limiter, without straying from the present invention.
In the illustrated embodiment, torque limiter 24 may include a
braking member 34 arranged to transmit rotational motion from input
element 16 to output element 20 during normal operation of
apparatus 10 (i.e. when there is no over-torque or over-speed
condition present). Braking member 34 may be coupled to input
element 16 by a plurality of angularly spaced balls 36 received
within opposing recessed pockets 38, 40 in input element 16 and
braking member 34, respectively. Braking member 34 may be coupled
to output element 20 by a splined connection 41 allowing braking
member 34 to transmit rotational motion to output member 20 and to
slide axially relative to output element 20. Thus, under normal
operation, braking member 34 rotates with input element 16 and
output element 20 at the same rotational speed. Torque limiter 24
may further include a torque limit setting spring 42 arranged to
bias braking member 34 in an axial direction toward input element
16 to retain the balls 36 within corresponding opposing pockets 38,
40. In the illustrated embodiment, torque limit setting spring 42
has a first end operatively engaging an inner radial shelf of
braking member 34 and a second end operatively engaging a flange 44
fixed at an axial location on a preload setting shaft 46. Torque
limiter 24 may further include a plurality of disc brakes 48
arranged between braking member 34 and structural ground defined by
an inner surface of housing member 12.
Under normal operating conditions, the preload setting shaft 46 may
be held at a predetermined axial setting position relative to input
element 16 and structural ground members 12, 14 by one or more
sears 50 partially received by a corresponding sear groove 52 in
preload setting shaft 46 and partially received by a respective
radially extending recess 54 in input element 16. As shown in FIG.
2, sear groove 52 may be part of a continuous circumferential
groove about preload setting shaft 46. Alternatively, sear groove
52 may be a local notch or indentation arranged to receive a
respective sear 50. The axial setting position of preload setting
shaft 46 determines the preload applied to torque limit setting
spring 42, which in turn determines the torque limit above which
torque limiter 24 is triggered. When the torque limit is exceeded,
balls 36 will roll out of pockets 38, 40 and displace braking
member 34 in an axial direction relative to structural ground 12,
14 against the force of spring 42. As a result, braking member 34
is pushed axially into engagement with disc brakes 48, thereby
increasing friction and causing the rotating input and output
elements 16 and 20 to lock-up and stop rotating. When the preload
on torque limit setting spring 42 is relatively low, balls 36 are
not held as tightly within pockets 38, 40 and the balls will roll
out of pockets 38, 40 at a lower torque threshold to actuate
braking. Conversely, when the preload on torque limit setting
spring 42 is relatively high, balls 36 are held more tightly within
pockets 38, 40 and a higher torque threshold must be exceeded
before balls 36 are caused to roll out of pockets 38, 40 to actuate
braking.
Over-speed governor 26 is configured to cause actuation of torque
limiter 24 to brake rotation of input element 16 and output element
20 when rotational speed of input element 16 exceeds a rotational
speed limit. In the first embodiment depicted in FIGS. 1-4,
over-speed governor 26 causes actuation of torque limiter 24 by
reducing the preload of torque limit setting spring 42 when the
rotational speed limit is exceeded, thereby reducing the torque
limit. In the configuration of over-speed governor 26 shown in
FIGS. 1-4 and described below, over-speed governor 26 reduces the
torque limit to substantially zero torque by removing all or
substantially all preload from torque limit setting spring 42.
Consequently, as a result of an over-speed event, any torque will
trigger torque limiter 24.
Over-speed governor 26 may include preload setting shaft 46, one or
more sears 50, and at least one fly weight 56. As described above,
preload setting shaft 46 engages an end of the torque limit setting
spring 42, is axially displaceable relative to structural ground
12, 14 to set the preload of torque limit setting spring 42, and
has one or more sear grooves 52. Each sear 50 may be a ball
partially received by a corresponding sear groove 52 and partially
received by a corresponding radially extending recess 54 in input
element 16 to maintain an axial setting position of preload setting
shaft 46 relative to structural ground 12, 14 during normal
operation when the rotational speed of input element 16 does not
exceed the rotational speed limit. The normal operating condition
is shown in FIGS. 1-2. Each fly weight 56 may be arranged on input
element 16 to retain a respective sear 50 partially in sear groove
52 of preload setting shaft 46 when the rotational speed of input
element 16 does not exceed the rotational speed limit.
In the depicted embodiment, each fly weight 56 is pivotally mounted
to input element 16 by a pivot pin or pivot axle 58. As shown in
FIG. 2, a plurality of fly weights 56 may be angularly spaced about
rotational axis 11 of input element 16, and a plurality of sears 50
may be respectively received within a plurality of radially
extending recesses 54 angularly spaced about rotational axis 11 of
input element 16. The illustrated embodiment provides three sears
50 and three fly weights 56 spaced at regular angular intervals of
120.degree. about rotational axis 11 for balanced operation. It
will be understood that more or fewer sears 50 and fly weights 56
may be used.
Referring specifically now to FIGS. 3 and 4, operation of apparatus
10 during an over-speed event is shown. When the rotational speed
of the input element 16 exceeds the rotational speed limit,
centrifugal force causes each fly weight 56 to pivot about its
associated pivot pin 58 in a direction away from the corresponding
sear 50 (e.g. clockwise in FIG. 3), and centrifugal force causes
each sear 50 to move radially outward such that the sear 50
withdraws completely from sear groove 52 to permit axial
displacement of preload setting shaft 46 relative to structural
ground 12, 14. As a result, preload setting shaft 46 is displaced
by torque limit setting spring 42 relative to structural ground 12,
14, thereby reducing the preload applied to torque limit setting
spring 42. As best seen in FIG. 3, the permitted displacement of
preload setting shaft 46 may be sufficient to remove all or
substantially all preload in torque limit setting spring 42 so as
to reduce the torque limit to essentially zero torque.
Consequently, torque limiter 24 is actuated as described above to
brake rotation of input element 16 and output element 20.
As may be understood, the rotational speed limit above which
over-speed governor 26 is triggered may be determined by designing
the mass and center of gravity of the at least one fly weight 56
such that a predetermined rotational speed of input element 16 is
required before pivoting of the at least one fly weight occurs.
Additionally, each fly weight 56 may be spring-loaded toward a
non-triggered position, wherein the preload must be overcome by
centrifugal force. Over-speed governor 26 may be balanced and
calibrated as known in the art such that all sears 50 are released
and travel radially outward simultaneously. Once over-speed
governor 26 is triggered and the preload on torque limit setting
spring 42 is discharged, apparatus 10 will remain stopped and
resetting the apparatus is not possible without disassembly.
FIGS. 5-8 illustrate modifications to the apparatus 10 enabling the
apparatus to be reset after an over-speed event. In the variant
shown in FIG. 5, apparatus 10 is adapted to allow a user to axially
push or pull preload setting shaft 46 back into its original
preload setting position without disassembly. A push button 47 may
be axially slidable through a passage in output element 20 to exert
force on an end of preload setting shaft 46 to push the preload
setting shaft back into the predetermined preload setting position
against the bias of torque limit setting spring 42. In addition to
push button 47, or as an alternative to the push button, an
opposite end of preload setting shaft 46 may be adapted to
releasably mate with a puller tool (not shown) so that a user may
pull preload setting shaft 46 back into the predetermined preload
setting position against the bias of torque limit setting spring
42. For example, a tapped hole 49 may be provided at the opposite
end of preload setting shaft 46 to mate with a threaded tip of a
puller tool inserted through a passage in input element 16. As
shown in FIGS. 6 and 7, each fly weight 56 may be biased by a
spring 59 toward a non-triggered position, whereby the fly weight
will return to a position for holding preload setting shaft 46 in
the axial setting position as preload setting shaft 46 reaches the
axial setting position during reset. FIG. 8 shows another
modification wherein the output element 20 is provided with a
nipple or sealable port 51 through which pressurized fluid, for
example grease from a grease gun, may be injected into a cavity
between output element 20 and the end of preload setting shaft 46
to force preload setting shaft 46 back into its axial setting
position.
FIG. 9 illustrates a fly weight 66 according to an alternative
design which avoids the use of a separate sear element such as
balls 50. Similar to fly weight 56 described above, fly weight 66
is pivotally mounted to input element 16 by a pivot pin or pivot
axle 68. Fly weight 66 directly engages preload setting shaft 46 in
the manner of a sear for maintaining the preload setting shaft in
its axial setting position, and moves out of engagement to release
preload setting shaft 46 when the rotational speed limit is
exceeded. In the illustrated design, fly weight 66 includes a
latching edge 64 arranged to engage a radial shoulder 74 of preload
setting shaft 46. When the rotational speed limit is exceeded, the
center of gravity 70 of fly weight 66 is forced radially outward,
causing fly weight 66 to pivot clockwise in the view of FIG. 9
against the bias of resetting spring 72 to disengage latching edge
64 from radial shoulder 74 and release preload setting shaft 46.
When this happens, preload on torque limit setting spring 42 forces
preload setting shaft 46 to the left in FIG. 9 thereby discharging
the preload so that torque limiter 24 is triggered by any torque
transmission.
FIGS. 10 and 11 illustrate a torque limiter apparatus 110 having
over-speed protection in accordance with a second embodiment of the
present invention. The second embodiment differs from the first
embodiment described above in that the over-speed governor of the
second embodiment acts to add drag torque to the grounding brake of
the torque limiter when the rotational speed limit is exceeded,
thereby triggering the torque limiter.
FIG. 10 shows apparatus 110 during a normal operating condition,
whereas FIG. 11 shows apparatus 110 in an over-speed condition
triggering an over-speed governor 126 of the apparatus. In contrast
to over-speed governor 26 of the first embodiment, over-speed
governor 126 of the second embodiment does not change the preset
torque limit of torque limiter 24 when the rotational speed limit
is exceeded, but merely adds drag to the system to trigger torque
limiter 24. By operating in this manner, over-speed governor 126 of
the second embodiment allows torque limiter 24 to be reset by
commanding reverse rotation of the drive member to rotate input
element 16 in an opposite rotational direction, and disassembly or
manual intervention is not required to reset apparatus 110.
Apparatus 110 of the second embodiment is similar to apparatus 10
of the first embodiment in that it comprises torque limiter 24,
described above. Torque limiter 24 may include rotatable braking
member 34 arranged to transmit rotational motion from the input
member 16 to output member 20, and disc brakes 48 arranged between
braking member 34 and structural ground 12, 14. As in the first
embodiment, braking member 34 is axially displaced relative to
structural ground 12, 14 to engage disc brakes 48 when the torque
limit is exceeded. Preload setting shaft 46 may be integrally
formed with input element 16.
Over-speed governor 126 includes at least one fly weight 156
arranged on braking member 34. Each fly weight 156 may be pivotally
mounted to braking member 34 by a pivot pin or pivot axle 158.
Similar to the first embodiment, a plurality of fly weights 156 may
be angularly spaced about rotational axis 11 of input element 16,
which corresponds to the rotational axis of braking member 34. For
example, three fly weights 156 may be spaced at regular angular
intervals of 120.degree. about rotational axis 11 for balanced
operation. It will be understood that more or fewer fly weights 156
may be used.
As shown in FIG. 11, when input element 16 exceeds the rotational
speed limit, each fly weight 156 moves by centrifugal force such
that it applies axially directed force to disc brakes 48. As
illustrated in FIG. 11, movement of each fly weight 156 may be
pivotal movement about corresponding pivot pin or pivot axle 158.
The application of force to disc brakes 48 by each fly weight 156
increases frictional resistance to rotation, thereby increasing
torque transmitted between input element 16 and output element 20.
As a result, the predetermined torque limit is exceeded in an
over-speed condition causing actuation of torque limiter 24.
Following actuation, torque limiter 24 may be reset by commanding
reverse rotation of the drive element to rotate input element 16 in
an opposite rotational direction, thereby causing balls 36 to roll
back into pockets 38, 40.
With respect to the embodiments described above, those skilled in
the art will realize that input element 16 and output element 20
are reversible in function, i.e. input element 16 may be used as an
output element coupled to an external driven member, and output
element 20 may be used as an input element to which an external
drive member is coupled. In such an arrangement, element 20 is
considered an "input element" and element 16 is considered an
"output element."
The invention improves safety by providing an over-speed governor
configured to cooperate with a torque limiter apparatus. The
invention utilizes the existing capability of the torque limiter
during an over-speed event, thereby avoiding additional braking or
torque limiting components and external controls.
While the invention has been described in connection with exemplary
embodiments, the detailed description is not intended to limit the
scope of the invention to the particular forms set forth. The
invention is intended to cover such alternatives, modifications and
equivalents of the described embodiment as may be included within
the scope of the claims.
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