Note: Descriptions are shown in the official language in which they were submitted.
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2. 10 39 6 6 8
This invention relates to a torque limiting clutch
of the type comprising opposed first and second members
mounted for relative rotational and axial movement,
a third member positioned between and mounted for rotational
movement relative to the first and second members and for
axial movement relàtive to at least one of the first and
second members, the third member being provided with a
torque transmitting element receiving aperture, a torque
transmitting rolling element being positioned in the
aperture in the third member~ the first member comprising
a driven member and being provided with a torque transmitt-
ing abutment for torque transmitting engagement with said
torque transmitting element, another of said members
comprising a driving member and being provided with
a torque transmitting abutment for torque transmitting
engagement with said torque transmitting element,
resilient loading means to bias resiliently the first and
second members towards one another and the arrangement
being such that when the clutch is transmitting torque
the torque transmitting element is engaged with a
driving member abutment and a driven member abutment
so as thereb~ to prevent relative rotation between the
driving and driven members and so that, on the torque
to be transmitted exceeding a predetermined value, the
torque transmitting element disengages from the abutment
of at least one of the driving and driven members to
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rotate relative to one another. Such a torque limiting
clutch will be referred to hereinafter as "of the
t~pe de~oribed".
A torque limiting clutch of the type described
may be constructed so that the said first member
comprises the driven member and said second member
comprises the driving member. In this case the third
member comprises only a torque transmitting element
guide member and does itself not transmit torque.
'';
Alternatively an overload clutch of the type
described may be constructed so that said first
member comprises the driven member and said third
member comprises the driving member. In this case the -
third member acts both as a torque transmitting element
guide member and also as the driving member, the
aperture in the third member serving both as a guide
means and as a torque transmitting abutment.
~'',':' .
When a clutch of the type described is subjected ,-
~ to a torque in excess of the predetermined value for
a long period of time performance of the clutch de-
teriorates due to repeated engagement and disengagement
of the torque transmitting elements with the abutments.
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There has been proposed in U.S. patent specifications
Nos. 3,722~644 and 3,744,~20 torque limiting clutches of
the type described provided with spacing key assemblies
arranged to be movable from an inoperative position,
occupied during normal torque transmissions by the clutch,
to an operative position, occupied when the clutch is
disengaged, in which the keys are positioned between the
clutch members to maintain the clutch members spaced
apart, the torque transmitting elements are received in a
receiving means in one of the members and spring means
are provided to continuously urge the torque transmitting
elements out of the receiving means against the other
clutch member for engagement with torque transmitting
abutments thereon in order to permit resetting of the
torque limiter on relative rotation of the clutch elements
in the reverse direction.
The clutches which are described in said U.S.
specifications are relatively difficult to reset due to
the torque required to be applied to the clutch members
during resetting in order to force the clutch members
apart, against spring bias, and to overcome friction
between the relatively sliding balls and clutch member.
Thus an object of the present invention is to
provide a torque limiting clutch of the type described
which can be relatively easily reset.
_ _ . .. . . .... _ . _ . . , . . . ..... . ~ , . . . .
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According to the invention we provide a torque
limiting clutch of the type described including a
spacer element received in an opening in the third member
and positioned between a first track axially located
relative to one of the members and a second track :~
axially located relative to another one of the members,
a spacer element receiving means provided on at least one
of the tracks and of such dimensions as to maintain the
spacer element out of pressure contact with the tracks
during torque transmittal so as to ensure the torque
transmitting element is maintained in pressure contact
with the driven and second members, and a torque transmitt-
ing element receiving means provided on- one of said
driven and second members, whereby on disengagement of the
torque transmitting element from the torque transmitting
abutment on the driven member the third member is caused to
rotate relative to the driven member and hence cause
circumferential movement of the spacer element out of the
spacer element receiving means and subsequently to cause
the torque transmitting element to be engaged and main-
tained within the torque transmitting element receiving
means with the driven and second members spaced apart by
the spacer elements, the torque transmitting element receiv-
ing means being of such dimensions that the torque trans-
mitting element is maintained out of pressure engagement
with the driven and second members and relative rotation
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between the driving and driven members is permitted
when the`torque transmitting element is engaged in th~
torque transmitting element receiving means, and wherein
the spacer element engages at least one of the tracks
through anti-friction means.
The invention will now be described in more detail
by way of example with reference to the accompanying
drawings wherein:
FIGURE la is a diagrammatic fragmentary plan view of
a torque limiting clutch embodying the invention showing
the parts in torque transmitting relationship.
FIGURE lb is a similar plan view of the torque
limiting clutch of Figure 1 but showing the parts after
disengagement.
~ IGURE 2 is a diagrammatic cross-sectional view on the
line 2-Z of Figure la.
FIGURE 3 is a diagrammatic cross-sectional view on
the line 3-3 of Figure lb.
.
FIGURE 4 is a plan view of a driven clutch member of
the clutch of Figure 1.
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FIGURE 4a is a developed longitudinal section on the
line 4a - 4a of Figure 4.
FIGURE 5 is a section on the line 5-5 of Figure 4.
FIGURE 6 is a plan view of a driving clutch member
of the clutch of Figure la.
FIGURE 7 is a section on the line 7-7 of Figure 6.
FIGURE 8 is a plan view of the ball guide member
of the clutch of Figure 1.
FIGURE 9 is a section on the line 9-9 of Figure 8,
FIGURE 10 is a plan view of a ball guide member of
another embodiment of the invention.
FIGURE 11 is a diagrammatic sectional view through
another torque limiting clutch embodying the invention,
with parts omitted for clarity, the left hand half
showing the parts in torque transmitting relationship and
the right hand half showing the parts after disengagement.
FIGURE 12 is a fragmentary cross-sectional view through
part of another embodiment of the invention.
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1039668
FIGURE 13 is a plan view of one of the clutch
members of the clutch of Figure 12.
FIGURE 14 is a section on the line 14-14 of Figure 13.
FIGURE 15 is a plan view of the other clutch member of
the clutch of Figure 12.
FIGURE 16 is a section on the line 16-16 of Figure 15.
FIGURE 17 is a plan view of a track member of the clutch
of Figure 12.
FIGURE 18 is a section on the line 18-18 of Figure 17.
FIGURE 19 is a section on the line 19-19 of Figure
20 taken through another embodiment of the invention.
FIGURE 20 is a section on the line 20-20 of
Figure 19.
FIGURE 21 is a diagrammatic half-cross sectional view
through another embodiment of the invention taken on a
line similar to that of Figure 2 and showing the parts in
torque transmitting relationship, and
FIGURE 22 is a half-cross-sectional view similar to
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that of Figure 21 but taken on a section similar -to that
of Figure 6 and showing the parts after disengagement.
Referring to Figures 1 to 9 of the drawings there is -
illustrated a -torque limiting clutch comprising drive
transmitting members 10 and 17. In this example the member
10 will be described as a driving member and the member 17
as a driven member but it should be understood that if
desired the member 17 may be the driving member and the
member 10 would then be a driven member. The interchange-
ability of these terms should be appreciated throughout
this specification and claims.
The driving member 10 comprises in this example a
belt pulley adapted to be driven by a belt drive from a
prime mover, not shown, in conventional manner. The
driving member 10 is connected by means of bolts 11 and a
clamping washer 12 to a body 13 of the torque limiting
clutch which is attached, by bolts 14, to a second or
driving clutch member 15.
Rotatably mounted within the body 13 by means of a
suitable bearing sleeve 16 is an output member 17 which
constitutes a driven member of the clutch. A suitable
thrust race 18 is interposed between a flange 19 on the
output member 17 and the clamping washer 12.
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10 .
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Splined to the output member 17 is a first or driven
clutch member 20 for axially sliding and non-rotating move-
ment relative to the output member 17. A nu-t 22 is thread-
edly engaged with the outer end 23 of the output member 17
and a coil compression spring 24 is interposed between the
nut 22 and the driven clutch member 20 to urge the clutch
member 20 towards the driving clutch member 15.
Interposed between the driving and driven clutch
member 15,20 respectively are a plurality (in the present
example three) of tor~ue transmitting elements in the form
of spherical hardened steel balls 25. The balls 25 are
received in cylindrical bores 27 formed in a third or
ball guide member 28.
For a reason hereinafter to be described, there
may be provided a ball control means, comprising a coil
compression spring 27a received with a cylindrical bore
27b which extends radially from each bore 27, (see Figure 8)
to act on the ball 25 therewithin in a direction radial
to the axis of rotation of the clutch and thus to urge the
ball lightly against one side of its associated bore 27
thereby to restrain the ball from axial movement in the
disengaged condition of the clutch as hereafter described.
Each clutch member 15 20 is also formed with a
corresponding number (in the present example three) of
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torque transmitting abutments 29, 30 respectively each
taking the form, as best shown in Figures 4 to 7 of a
generally frusto-conical recess.
The torque transmitting abutments 29, 30 and bores 27
are arranged so as to be mutually registerable so that the
balls 25 can be received in the bores 27 and engage both the
driven and driving abutment 29, 30 to permi-t the trans-
mission of torque as hereinafter to be described in more
detail and as shown in Figures la and 2.
The driven clutch member Z0 is also formed with a
plurality (in the present example three) of torque trans-
mitting element receiving means 31, each comprising an
arcuate depression 32a extending over an arc of approxi
mately 60 , of par-t circular cross-section and having
inclined end faces 32b see Figure 4a. If desired the
receiving means may be of a different shape, for example,
a recess of shallow frusto-conical configuration, the half
angle of the cone may be, for example 80 , so that the
surface of the cone is inclined to the surface of the clutch
member 20 at an angle of 10 . Alternatively they may
be of identical shape to the torque transmitting abutments
30. The dimensions of the receiving means 31 are such, as
best shown in Fi~re 3, that the balls 25 have a slight
clearance between the receiving means 31 and the surface
of the driving clutch member 15, in the region inter-
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l2'1039668
mediate the reces.ses 29, whereby no pressure is imposed
between the balls 25 and the surface of the member 15
whilst the balls are within the receiving means 31.
The ball guide member 28 is also formed with three
spacer element receiving bores 33 withill which are
received spherical spacer elements or balls 34.
The driven clutch member 20 is provided with three
spacer element receiving means 35 each of frusto-conical
configuration, as best shown in Figures 4 and 5.
A first track for the spacer elements 34 is provided
by means of an annular member 36 received in a rebate 17a
formed in the output member 17. In order to permit free
rotation of the track 36 relative to the output member 17
a relatively friction-free bearing is provided between
the track and the out-put member. The bearing is pref-
erably in the form of a crowded race 37 although any
other suitable relatively friction free bearing may
be used.
Restraining means are-provided to limit
rotation of the ball guide member 28 relative to the out- -~
put member 17 and hence relative to the driven clutch
member 20. In the present example the restraining means
comprises at least one peg 38 shown in dottten line in Figure
8 extending radially outwardly of the member 17 and
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and received in an annular cut-out 39 (or cut-outs if .
more than one peg is provided) in the guide membeF 28.
The, or each peg is arranged to engage one end of the
cut-out 39 within which it is received when the torque
transmitting balls are aligned with the central part of
the receiving means 31.
The ball guide member is prevented from axial
movement in the direction away from the driving clutch
member 15 by means of a circlip 40.
Formed in the ball guide member 28 are three radial
slots 41 whilst in the body 13 are formed three cylindrical
recesses 42 for a purpose hereinafter to be described. :-
In use, during torque transmittal the balls 25 are
engaged in the torque transmitting abutments 29, 30 and
are prevented from moving out of engagement therewith as
a result of the force applied to the driven clutch member -. .
20 by the coil compression spring 24. The torque trans-
mitted from the driving member 10 to the driven or out-
put member 17 through the balls produces an axially
directed reaction force between the balls and the driving
and driven members proportional to the transmitted torque
which, when the torque exceeds a predetermined value,
is sufficient to overcome the pressure exerted by the
spring 24. Thus, the drivell clutch member 20 commences
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to move axial:Ly away from the driving clutch members
15 and simultaneously each ball 25 commences to roll
in the direction of rotation of the driving clutch
member 15 on t~lat part of each driving and driven clutch
member recess edge which is respectively rearmost and
foremost in the direction of rotation. Therefore, the
balls 25 now commence to move out of torque transmitting
engagement with the recesses 29 and 30 by a simple
rolling movement permitted by the engagement between
the balls and the edges of the recesses 29 and 30. As
the balls rotate they also move circumferentially relative
to the driving and driven clutch members 15 and 20 thereby
causing the ball guide member 28 to also move circum-
ferentially relative thereto.
This causes the spacer elements 34 to move out of
their recesses 35 onto the planar parts of the clutch ~ -
member 20 between the recesses. These planar pa ts
comprise a second track. As shown in Figures 2 and 3,
the surface of the track 36 is very slightly below the
level of the planar part of the clutch member 15 and
hence at this stagel the spacer elements 34 are
maintained out of pressure engagement with the track 36
and the clutch member 20.
Rotation of the guide member 28 continues until the
torque transmitting balls 25 enter their respective
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receiving means 31, as shown in ~igure 3. As the balls
25 enter the receiving means 31. they move out of pre~sure
engagement with the member 20 and 15 and hence the whole of
the load imposed by the spring 24 on the member 20 is taken
by the spacer members 34 which are engaged with the track
36 and with planar parts of the clutch member 20 between
the recesses 35.
When the balls 25 have entered the receiving means 31
and hence no longer drive the guide member 28 any continu-
ing rotation of the guide member 28 due to inertia is
arrested by the hereinbefore described restraining means
38 and 39 and hence the balls 25 are maintained within
their receiving means 31.
Because of the fact that the torque transmitting
elements 25 are maintained completely unloaded after dis-
engagement of the torque transmitting connection no
damage or wear will occur to the torque transmitting
parts of the torque limiter if the driving member is
continued to be rotated after the torque limiter has
disengaged.
Because there is no pressure engagement between the
balls 25 and the member 15 the torque limiting clutch
can operate without the provision of the springs 27a
as if the balls 25 should enter into and out of engage-
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1039668
ment with the recesses 29 under unloaded conditions thiswould not cause any significant wear of the parts. More-
over, in practice, the balls 25 would only enter into and
out of engagement with the recesses 29 on relatively few
occasions as there is nothing to force them out of the
recesses 31.
If desired, however, the springs 27a may be provided
to retain the balls in the receiving means 31 and thus
prevent any chatter and so make the clutch quieter in
operation.
Instead of the springs 27a other ball control means
may be provided. In appropriate circumstances there may
be provided a frusto-conically shaped bore in the ball
guide member with its wide end adjacent the member 20.
In the case where the member 17 is the driven member then
the balls will be urged, as a result of centrifugal force,
towards the wide end of the balls and hence away from the
clutch member 15. In the case where the member 17 is the
driven member and the axis of rotation of the clutch is
hori~ontal then the action of gravity will cause the
balls to run towards the wide end of the balls and hence
away from the member 15.
Alternatively, the balls may be engaged by spring
fingers provided on circlips engaged with the bores 27
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~039668
in the ball g~lide member 28 so as to bias the balls in
the direction away from the member 15 under unloaded
conditions but permitting engagement of the balls within
the recesses 29 of the member 15 when the torque limiter
is in torque transmitting engagement and also during
resetting of the torque limiter.
In the above example the track 36 is mounted on the
crowded race 37 and the means for restraining continued
rotation of the guide member 28 comprises at least one peg
38 and recess 39. In appropriate circumstances, as
described hereinafter, the restraining means may be provided
by arranging that the track 36 instead of being mounted
by a relatively friction free bearing is in frictional
engagement with the output member 17 to a controlled
extent, for example, by providing one or more friction
pads between the clutch member 20 and ball guide member
28, the friction being arranged so as to provide just
sufficient friction to prevent rotation of the ball guide
member sufflciently far to cause disengagement of the
torque transmitting elements from their receiving means
whilst not causing sufficient friction to unduly affect
resetting. Alternatively the restraint to rotation of
the track 36 could be arranged to be rendered inoperative
when it is desired to reset the torque limiter.
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1039668
It has been found that where the clutch is to
transmit a relatively large torque, and hence the force
applied by the spring 24 is relatively high, when it was
desired to reset the clutch it was necessary to apply
a relatively large torque to the clutch in order to over- :
come the friction created on resetting as a result of
sliding engagement between the track 36, member 17,
spacer balls 34 and driver clutch member 20.
The force necessary to overcome this friction has
been found to be unacceptably high, particularly for the
larger sizes of clutch. It is-accordingly referred, at
- least for the larger size of clutch, to mount the track on
a relatively friction free bearing.
In order to reset the torque limiter it is necessary
to move the torque transmitting balls 25 out of the
receiving means 31 and into the torque transmitting
recesses 29, 30.
This is achieved by moving the balls 25 relative to at
least one of the clutch members 15, 20 by means of the guide
- 20 member 28. Dy utilising the guide member 28 to effect the
relative movement there is avoided the use of springs or
other biasing means, to continuously urge the balls 15
so as to be in a position to be engaged by the torque
transmitting recesses of the member 15 on resetting
: '' ' ' ~ "' ' ' ' ' ~ '' . '. .- ' '
~0396~8
movement of the torque limiter. Hence in the clutch
of this invention the torque transmitting balls are
maintained in completely unloaded condition, at least in -~
a direction towards the member 15, when the torque trans-
mitting connection has been disengaged.
The guide member 28 may be used to cause the above
mentioned relative movement in a number of ways.
For example the ball guide member 28 is rotated
relative to the driven clutch member 20 in the reverse
direction to that in which the member 28 moves on dis-
engagement of the clutch, until the torque transmitting
balls 25 are in a position where they engage the inclined
end face 32b of the ball receiving means 31 and simul-
taneously engage the planar face of the driving member 15.
This movement of the ball guide member 28 is permitted
without sliding between the spacer elements 34 and the
driven clutch member 20 as a result of rotation of the
track 36 relative to the clutch member 20 which permits
rotation of the spacer elernents 34. If the track 36 is
not freely rotatable relative to the member 17 -then slid-
ing between the elements 34 and the member 2Q occurs but
as the annular extent of rotation is relatively small this
sliding movement is possible, particularly if a suitable
tool is engaged with one of the slots 41 in the guide member
28,
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When the torque transmitting balls 25 have been moved
into this position, a suitable tool is engaged in one of the
recesses 42 in the body 13 and the body 13 is rotated
thereby (with rotation still being applied if necessary,
to the guide member 28 to maintain the balls 25 in simul-
taneous engagement with the faces 32b and the planar face
of the driving clutch member 15) in a direction to cause
relative rotation between the clutch member 15 and the
clutch member 20 so that the balls roll up the faces
32b of the ball receiving means 31 and onto the planar
part of the driven clutch member 20 with consequent move-
ment of the member 20 away from the member 15 and oom-
pression of the spring 24. If necessary the member 20 may
be held against rotation if it is not held sufficiently
by the apparatus to which it is connected.
The body 13 is then further rotated with the balls 25
rolling between the planar faces of the clutch members 15
and 20 and, depending upon the angular orientation of the
.. ...
member 15 relative to the member 20 when the guide member
28 is rotated to move the balls so that they simul-
taneously engage the faces 32b and the planar face of the
member 15, the balls 25 will nex-t either enter the torque
transmitting recesses 29 or the torque transmitting
recesses 30.
If the balls first enter the recesses 29, the
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driven member 20 moves towards the driving member 15 so
that it is spaced from the driving member 15 by the spacer
balls 34 and hence the ;balls 25 are not subject to any
pressure from the spring 24. During further rotation of
the body 13, the cage 28 moves with the driving member
15. When the track 36 is freely rotatably mounted,
relative movement between the cage 28 and the driven member -
20 is permitted without sliding movement between the
spacer balls 34 and the track 36 or the driven member 20
as a result of rotation of the balls 34 .,ogether with
rotation of the track 36. Because the balls 25 are not
subject to pressure they are not in sliding engagement with
the valves 15 and 20 and so do not afford any resistance
- to the further relative rotation.
This further rotation continues until the balls 25
re-enter the torque transmitting abutment 30 and simul-
taneously the spacer balls re-enter the three spacer
element receiving means 25.
.
The clutch is now again ready for use.
20 . If the balls 25 enter the torque transmitting abut-
ments 30 first, this is accompanied by simultaneously
re-entry of the spacer balls 34 into the spacer element
receiving means 35. The members 15 and 20 are than held
apart by the balls 25 with these balls 25 engaging the
, .
. .. ! , . ' . . ' :. . :
- .. '............... ~ ~ . - t
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abutments 30 and the planar face of the driving member
15. The body 13 is now further rotated, and the balls
25 slide on the planar face of the member 15 until they
re-enter the torque transmitting abutments 29. The
clutch is now again ready for use.
It should be noted that in the above described method
of re-engagement the original angular relationship between
~he driven and driving members is not necessarily pre-
served. The clutch will re-engage as the sets of abut-
ments 29 and 30 which are most closely adjacent at the
beginning of resetting move into alignment.
The method of resetting hereinbefore described
suffers from a number of disadvan ages arising from
friction between relatively sliding parts and the com- -
pression of the spring 24 when the balls 25 force -the
members 15 and 20 apart. In order to overcome these
disadvantages further arrangements of resetting have been
-develoled as will now be described.
In a preferred re-setting arrangement referring to
Figures 19 and 20, a ratchet pawl 500 is provided on the
body part 13 which engages a pawl recess 501 on the guide -
member 28.
In this method, in order to re-set the output member
~039668
17 is rotated in the reverse direction with the ball
guide member 28, and hence the balls 25 rotating there-
with until the ratchet pawl 500 on the body 13 engages
the pawl recess 501 on the guide member 28. The pawl
recess 501 is so positioned that at this stage the abut-
ments 29 in the member 15 will be aligned with the ball
receiving recesses 27 in the cage 28.
On further rotation of the hub 17 the ball cage 28
is held stationary relative to the member 15 by the pawl
lo 500 and the balls 25 are urged into the abutments 29 by the
resultant of the forces imposed on the balls 25 by the
end faces 32b of the recesses 31 and the edges of the
apertures 27 in the guide member 28. The members 15 and 20
are then held apart by the spacér elements 34. Thus,
during this stage, the ball guide member 28 rotates re-
lative to -the member 20, this being permitted by rolling
engagement of the spacer element 34 with a planar face of
the member 20 and the rotatable track 36.
This rotation will continue until the balls 25 are
in register with the abutment 30 and the spacer balls 34
are in register with their receiving means 35 at which
stage the balls 25 re-enter the abutments 30 and simul-
taneously the balls 34 re-enter their receiving means 35.
The clutch is now again ready for use.
24.
~0~668
This method of re-set has considerable advantages
over that described hereinbefore. This method is com-
pletely automatic and if only a single pawl and recess are
used the original angular orientation of the driving and
driven members is maintained.
Further in this method of re-set as the balls 25
first re-enter the abutments 29 they do not have to be
forced along the end faces 32b of the recesses 31 into
rolling engagement between the planar faces of the members
15 and 20 and so the high torque which was needed to achieve
this in the methods hereinbefore described is not needed
in this method. A further result of the balls re-entering
the abutments 29 first is that they will not slide along
the planar face of the member 20 so the high torque which
was necessary for the final stage of re-set in the methods
hereinbefore described is avoided in this method.
If it is desired to operate the clutch so as to
transmit drive in the reverse direction it is merely
necessary to reverse the effective direction of operation
of the pawl i.e. by engaging the ball with a recess 502
shown in dotted line in Figure 20.
Alternatively the above described sequence of events
can be performed manually by manually rotating the members
15, 20 and 28 to the above described positions. This can
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10396~8
be done conveniently by providing a generally "C" shaped
spanner having one fixed tooth for engagement with a
recess in the driving member 15 and one spring tooth for
engagement with a recess in the guide member 28. The
spanner is used initially ~to rotate the driving member
15 relative to the driven member 20 until the balls 25
are engaged in the drive transmitting abutments 29 of the
member 15 whereupon the spring loaded tooth enters the
recess on the periphery of the guide member 28. On fur-
ther rotation of the spanner the driving member 15 and the
guide member 28 are rotated together until the balls 25 and
the spacer elements 34 are received respectively in the
abutments 30 and receiving means 35.
This method of resetting has all the advan-tages
discussed with reference to the previously described re-
setting arrangement except that this method is not auto-
matic. However, this method may be used for a clutch
capable of driving in ei-ther direction, it merely being
necessary manually to rotate the parts in the respective
reverse direction of rotation.
It will be seen from tl~e above tha-t a torque limi-ting
clutch embodying the invention when reset by either
of the last two described arrangements, because of
the provision of rotatable spacer elements together
with a track which is rotatable relative to the driven
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103~668
clutch member 20, upon reset-ting of the torque limiter
no sliding movement takes place between the spacer elements
34 and the parts of the clutch into which they are urged
into pressure engagement by the spring 24 i . e. the member
20 and the track 36. Upon re-setting there occurs only
rolling engagement between the spacer elements 34, driven
clutch member 20 and track 36 and in addition as the
members 15 and 20 are not forced apart by the balls 25
the torque required to reset is maintained rela-tively
small, compared with that which would be required to reset
if sliding movement of the spacer occurred. The torque
limiting clutch of the present invention can therefore be
reset easily either manually or au-tomatically and, if
desired, the initial angular orientation between the
driven and driving members can be maintained.
As a result of providing a fric-tion free bearing
means such as the race 37, when the clutch disengages there
is a tendency for the ball guide member 28 and the balls
25 and 34 therewithin to continue to rotate as a result
of their inertia, there being little or no braking of the
ball guide member 28 and balls 25, 34 as a result of
engagement between the track 36 and the balls 34 due to
the fact that the track 36 is itself free to rotate.
It is to overcome this problem that a restraining
means such as the peg and recesses 38, 39 are provided.
...
`. . , '. ' , ' . ' ': ', " ,, ' '~ '. . ' ": ~ '
27.
103966Ei~
However, if desired, where the clutch is to be
operated at suitably slow speeds of rotation, so that the
inertial forces are relatively small, the ball receiving
means 31 of the present invention are of sufficiently
long angular extent, as described hereinbefore, in order
to accommodate this rela-tively great angular movement of
the ball guide member 28 and balls 25 upon disengagement
of the clutch without the provision of a restraining means
there being sufficient residual friction in the relatively
friction free bearing means, such as the race ~37, to
arrest and maintain the balls 25 within the relatively long
receiving means 31.
However, if the conditions of use of the clutch are
such that the provision of the relatively long ball
receiving means 31 does not avoid this problem there is
provided either instead of a relatively long ball receiving
means 31 i.e. by providing only a relatively short ball
receiving means 31, or in addition thereto, a restraining
means to limit relative rotation between the torque trans-
mitting elements 25 and the driven clutch member 20 on
disengagement of the clutch whereby the torque transmitting
elements 25 are permitted to enter their respective ball
receiving means 31 and are maintained therewithin. Such
means may comprise the hereinbefore described peg and
recess 38 and 39 or other suitable means.
.. . : , ................................................ .
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~8.
1039668
One such alternative restraining means may com;,rise,
referring to Figure 10, a two part guide member 228
instead of the guide member 28 described hereinbefore.
In this embodiment the guide member comprises an outer part
229 and an inner part 230 which is splined to the output rnember
17. The outer member 229 is of basically similar config-
uration to the member 28 except that there is a central
opening 231 of a radius equal to the radial distance of
the centre of each spacer element receiving opening 233
from the axis of the clutch. The inner member 230 is
provided with three abutment parts 234 which are adapted
to abut the spacer elements 34 in the openings 233. The
member 230 is splined to the member 17 so that the abutment
parts are symmetrically located relative to the spacer element
receiving means in the driven clutch member 20.
In use, when the parts of the clutch are in torque
transmitting relationship the abutment parts 234 of the
inner member 230 are located intermediate the spacer
elements 34. When overload occurs continued rotation of the
outer cage member between the spacer elements 34 engaged in
the openings 233 therein and the abutment parts 234 of
the inner cage part 230. Thus rotation of the torque
transmitting elements to a position in which they can be
dis-engaged from their respective receiving means is
prevented.
.
29.
1039668
Alternatively the inner member 230 of the ball guide
member 228 may be formed integrally with the drive or
output member 17 instead of being formed as a separate
element splined thereto.
Further alternatively at leas-t one spring loaded
detent may be provided between the clutch member 20 and
the ball guide member 28 so as to prevent relative
rotation therebetween after the ball guide member has
moved an appropriate distance. The strength of the or each
spring loadèd detent may be overcome upon resetting of the
torque limiter in either direction.
Referring now to Figure 11 there is illustrated a
further embodiment of the present invention which is
basically similar to the embodiment described with
reference to Figures 1 to 9 hereof and the same reference
numerals are usual to refer to corresponding parts.
In the embodiment of Figure 11 the torque transmitt-
ing elements comprise cylindrical rollers 325 whilst the
spacer elements likewise comprise cylindircal rollers 334.
The track 36 is supported on a crowded race of balls 37
and the driving clutch plate 15 is rotatably mounted on the
driven member 17 through the intermediary of a further
crowded race of balls 318.
; ~ . . . .. , . ... , . :. .. ., . . :
~3o.~
~039668
The torque transmit-ting abutments comprise prismatic
notches 329 and 330 and the torque transmitting element
and spacer element receiving means comprise part annular
surfaces 331 and 335 respectively lie slightly below the
general planar surface of the driver clutch member 20. In
other respects and manner of operation the clutch of this
embodiment is as described in connection with the first
embodiment.
By providing the torque transmitting and spacer
elements in the form of rollers a considerably smaller
size of roller can be used compared with the size of
ball required to transmit the same torque. Thus the
overall dimensions of the torque limiting clutch can be
reduced. The diameter can be reduced because rollers
of shorter length than the diameter of the balls which would
be required to transmit the same torque can be used. A
shorter spring 24 can be used as the distance through which
the clutch member 20 is displaced axially is reduced
because a smaller diameter of roller can be used. The
crowded race 318 to support the clutch member 15 permits
the greatest possible area of the undersurface 315 of the
element 15 to be available for the attachment of a drive
applying means.
In ~igures 12 to 18 there is shown diagrammatically
a clutch which is basically similar to that of the first
. , , . . , . .. ~ .
1039668
embodiment described hereinbefore and again the same
reference numerals have been used to refer to the
corresponding parts.
In this embodiment, as can be seed from Figures
12 to 18, the torque transmitting, spacer and crowded
race elements are spherical balls and the parts o~ the clutch
engaged by these elements are formed with tracks of arcuate
cross-section of a diameter equal to that of their re-
spective element. In other respects the clutch of the
present embodiment is similar to that of the first
embodiment. With this arrangement there is a relatively
large area of the ball in contact with its associate clutch
member thereby reducing the pressure acting between the
ball and the member compared with the pressure which would
act if the ball engaged a planar surface. Whilst it is
preferred that the grooves are of the same diameter as the
ball engaged therewith a similar, though less advantageous
effect is achieved by utilising a groove of slightly greater
diameter than its associated ball.
Referring now to Figures 21 and 22 there is illustrated
an alternative embodiment in which a first drive transmitting
member 620~is connected by bolts 614 to a hub 617 connected
to an output shaft 616. A ball guide member 628, which
~onstitutes a third member, is connected by a bolt 611
to a sleeve 613 as is a flange member 612 which is
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32- .
103966B
connected by means of a bolt 607 to an input shaft
606.
In this embodiment of the invention, the first
member 620 comprises a driver member and the third member
628 comprises a driving member but, as explained in
connection with the first embodiment these functions
may be reversed.
Interposed between the flange member 612 and the
clutch member 620 is an anti-friction thrust bearing 618
10 and a plain journal bearing 610.
The gllide member 628 is provided with two sets of
three apertures 627 and 633 within which are received torque
transmitting balls 625 and spacer elements 634 respectively.
A ball race 637 is provided in the flange member 612
and one part 636 thereof constitutes a first track for
the spacer elements 634. Rotatably mounted on the sleeve
613 is a pressure plate 609 which constitutes a second
member, which is forced towards the member 620 by means
of a spring 624 engaged between a nut 622 on the sleeve
613 and a ball race 608. The driven clutch member 620 is
provided with three conical torque transmitting abutments
630 whilst the pressure plate 609 is provided with three
torque transmitting element receiving means 631 and spacer
element receiving means 635. The planar parts of the member
, . , , , . . .. ...... . . _ .. . _ .. .. . _ . . _ _ _ .. . _ .. _ . _ _
. ., : . .
:' .' , : .''' : , ' . '
33 -
~0~966~
609 facing the part 636 of the ball race 637 comprise
a second track for the spacer element 634.
The clutch of the present invention operates in the
basically similar manner to the embodiments previously
described. That i.s to say, during torque transmittall, the
parts are in the position shown in Figure 21, the torque
transmitting balls 625 within the bores 627 are maintained
by the pressure plate 609 in engagement with the abutments
630 so that drive imparted to the member 628 is transmitted
through the balls 625 and abutments 630 to the driven.
member 620. In this condition the spacer elements 634 are
received within their receiving means 635 which, as shown
in Figure 21, are of such dimension as to provide a
clearance for the balls 634.
When the torque to be transmitted exceeds a pre- :
determined value the balls 625 leave the abutments 630
in the member 620 thus causing movement of the pressure
plate 609 away from the member 620 and permitting the :
balls 630 to roll on the planar parts of the members 620
and 609 causing consequent relative rotation between the :
members 628 and 620 so that the balls 625 roll until they
are aligned with their receiving means 631 and causing the
spacer balls 634 to be rolled out oP alignment with their
receiving means 635 into the position shown in Fig~lre 22.
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3'~ -
~039668 ~
In all other respects the clutch of the present
embodiment is similar to that of the embodiments
described hereinbefore.
In order to reset the torque limiting clutch of the
present embodiment, initially, relative rotation is
caused between the ball guide member 628 and the member 620
so that the balls 625 are aligned with the abutments
630. There is then caused relative ro-tation be-tween the
pressure member 609 and the aligned members 620, 628
until the spacer elements 634 enter their receiving means
635 whereupon the clutch is again ready to transmit
torque.
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