Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02540226 2001-03-15
CENTRIFUGAL CLUTCH
This is a divisional application of Canadian Patent Application Serial No.
2,401,765 filed on March 15, 2001.
The present invention relates to a centrifugal clutch for coupling a drive
shaft to a driven member.
It should be understood that the expression "the invention" and the like
encompasses the subject-matter of both the parent and the divisional
applications.
Centrifugal clutches are required for example in latch arrangements
for automotive doors, as disclosed in W098/27301, where an electric drive
motor
has to be decoupled from the latch, which is the driven member, to allow
manual
actuators to operate the latch, so as to avoid jamming particularly on power
failure_
Centrifugal clutches are of course available in many different forms. The
purpose of the present invention is to provide a centrifugal clutch with the
minimum
number of component pieces, capable of easy assembly at a minimum cost. Such
considerations are of prime importance in automotive manufacture, where
lightness
in weight is also extremely important.
Accordingly, the present invention provides a centrifugal clutch for coupling
a
drive shaft to a driven member at rotary speeds above a predetermined
threshold,
comprising:
a centrifugal slider with a massive enlargement at one end and a first
coupling formation;
a frame formed to carry the centrifugal slider on formations to constrain it
to
sliding motion between an extended radial position and a retracted radial
position,
and to fit fixedly on the drive shaft to be driven by it, with the shaft at
right-angles to
the axis of sliding motion of the frame;
an output drive member mountable for free rotation on the drive shaft and
formed for driving engagement with the driven member in use. and formed With a
second coupling formation which connects drivingly with the first only when
the
centrifugal slider is at its extended posifion;
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and means, located wholly within a recess in the centrifiugal slider, for
biasing the centrifugal slider towards its retracted position;
whereby rotation of the centrifugal slider and frame causes the massive
enlargement to pull the centrifugal slider radially from its retracted to its
extended
radial position to cause the frst and second coupling arrangements to
interengage
and thus to transmit rotary drive from the drive shaft to the driven member,
but the
biasing means causes disengagement when the rotation ceases, so as to decouple
the drive shaft from the driven member.
Recessing the biasing means allows the clutch to be extremely compact in
the axial direction, and by thus shortening the shaft the eccentric vibration
of the
output drive member is minimised, giving a stable structure with long life.
Preferably, the first coupling formation is at the other end of the
centrifugal
slider. This balances the impulsive forces upon engagement of the clutch. It
is also
advantageous that the coupling formation is then at a substantially shorter
radius
than the massive enlargement, at the point of engagement, because a Larger
impulsive force is then given as a "kick° to the output drive, freeing
any possible jam
or excessive friction.
The invention also provides a centrifugal clutch for coupling a drive shaft to
a
driven member at rotary speeds above a predetermined threshold, comprising:
a centrifugal slider with a massive enlargement at one end and a first
coupling formation;
a frame formed to carry the centrifugal slider on formations to constrain it
to
sliding motion between an extended radial position and a retracted radial
position,
and to fit fixedly on the drive shaft to be driven by it, with the shaft at
right-angles to
the axis of sliding motion of the frame;
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an output drive member mountable for free rotation on the drive shaft and
formed for driving engagement with the driven member in use, and formed with a
second coupling formation which connects drivingly with the first only when
the
centrifugal slider is at its extended position;
and a return spring acting on the centrifugal slider, and also bearing
directly
on the drive shaft in use, to bias the centrifugal slider toward its retracted
position;
whereby rotation of the centrifugal slider and frame causes the massive
enlargement to pull the centrifugal slider radially from its retracted to its
extended
radial position to cause the first and second coupling arrangements to
interengage
and thus to transmit rotary drive from the drive shaft to the driven member,
but the
spring causes disengagement when the rotation ceases, so as to decouple the
drive
shaft from the driven member.
With the spring bearing directly on the drive shaft, the arrangement is
particularly compact, with the minimum number of parts, and the simplest
construction.
Further the invention provides a drive assembly comprising a drive shaft
coupled to the frame of a centrifugal clutch for coupling a drive shaft to a
driven
member at rotary speeds above a predetermined threshold, comprising.
a centrifugal slider with a massive enlargement at one end and a first
coupling formation;
a frame formed to carry the centrifugal slider on formations to constrain it
to
sliding motion between an extended radial position and a retracted radial
position,
and to frt fixedly on the drive shaft to be driven by it, with the shaft at
right-angles to
the axis of sliding motion of the frame;
an output drive member mountable for free rotation on the drive shaft and
formed for driving engagement with the driven member in use, and formed with a
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second coupling formation which connects drivingly with the first only when
the
centrifugal slider is at its extended position;
and means for biasing the centrifugal slider towards its retracted position;
whereby rotation of the centrifugal slider and frame causes the massive
enlargement to pull the centrifugal slider radially from its retracted to its
extended
radial position to cause the first and second coupling arrangements to
interengage
and thus to transmit rotary drive from the drive shaft to the driven member,
but the
biasing means causes disengagement when the rotation ceases, so as to decouple
the drive shaft from the driven member;
in which the drive shaft projects through the frame and the slider.
Extending the drive shaft through the whole clutch gives optimum stability,
and ease of assembly.
Further, the invention provides a centrifugal clutch comprising driving and
driven coaxial members, the radially inner member having a slider constrained
to
slide between an extended radial position at which it engages a tooth on the
radially
outer member and drivingly couples the members, and a retracted radial
position at
which it allows free rotary relative movement of the members;
a spring biasing the slider to its retracted position;
and a centrifugal crank lever, pivotally mounted on the radial inner member
on an axis parallel to that of the members and spaced therefrom, having a
massive
enlargement at one end and pivotally connected to the slider at its other end
such
that rotation of the inner member causes the massive enlargement to turn the
crank
lever to drive the slider against the spring bias to its extended position,
but the
spring causes the slider to return to its retracted position when the clutch
ceases
rotation.
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A method of assembly of a drive arrangement, according to the invention,
comprises pre-assembling a centrifugal clutch and then mounting the pre-
assembled clutch over a drive shaft to effect a push fit;
the clutch comprising a centrifugal slider carried by a frame, a gear for
conveying rotary drive from the slider to an external driven member in use,
and a
spring biasing the slider to a radial position when it is out of driving
engagement with
the gear, the slider being formed so as to slide under centrifugal action
against the
spring bias into driving engagement with the gear when the clutch is rotated;
and the pre-assembled clutch having an axial opening, extending through
the slider and the frame and axially into the gear, for receiving the drive
shaft.
By retaining the spring in the slider such that there is still an opening for
the
free axial passage of the motor drive shaft through it, it is possible to use
a stronger
spring than if it were necessary 1o compress the spring during assembly. The
use of
a strong spring gives improved efficiency in disengaging the clutch in use. By
carrying the spring wholly within the slider, the arrangement can be made more
compact and its assembly can be simplified_
In another aspect; the invention provides a centrifugal clutch for coupling a
drive shaft to a driven member at rotary speeds above a pre-determined
threshold;
the clutch comprising a centrifugal slider with a massive enlargement at one
end
and a first coupling arrangement, a frame formed to carry the centrifugal
slider on
formations to constrain it to sliding motion between an extended radial
position and
a retracted radial position, and to fit fixedly on the drive shaft to be
driven by it, with
the shaft at right-angles to the axis of sliding motion of the frame, an
output drive
member mountable for free rotation on the drive shaft and formed for driving
engagement with the driven member in use, and formed with a second coupling
arrangement which connects drivingly with the first only when the centrifugal
slider
is at its extended position, and a return spring acting on the centrifugal
slider, and
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also bearing directly on the drive shaft in use, to bias the centrifugal
slider towards
its retracted position, whereby rotation of the centrifugal slider and frame
causes
the massive enlargement to pull the centrifugal slider radially from its
retracted to its
extended radial position to cause the first and second coupling arrangements
to
interengage and thus to transmit rotary drive from the drive shaft to the
driven
member, but the spring causes disengagement when the rotation ceases, so as to
decouple the drive shaft from the driven member.
In another aspect, the invention provides a drive assembly comprising a
drive shaft coupled to the frame of a centrifugal clutch for coupling a drive
shaft to a
driven member at rotary speeds above a predetermined threshold, the drive
assembly comprising a centrifugal slider with a massive enlargement at one end
and a first coupling arrangement, a frame formed to carry the centrifugal
slider on
formations to constrain it to sliding motion between an extended radial
position and
a retracted radial position, and to fit fixedly on the drive shaft to be
driven by it, with
the shaft at right-angles to the axis of sliding motion of the centrifugal
slider, an
output drive member mountable for free rotation on the drive shaft and formed
for
driving engagement with the driven member in use, and formed with a second
coupling arrangement which connects drivingly with the first only when the
centrifugal slider is at its extended position, and means for biasing the
centrifugal
slider towards its retracted position, whereby rotation of the centrifugal
slider and
frame causes the massive enlargement to pull the centrifugal slider radially
from its
retracted to its extended radial position to cause the first and second
coupling
arrangements to interengage and thus to transmit rotary drive from the drive
shaft
to the driven member, but the biasing means causes disengagement when the
rotation ceases, so as to decouple the drive shaft from the driven member, in
which
the drive shaft projects through the frame and the slider.
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In another aspect, the invention provides a centrifugal clutch comprising
driving and driven coaxial members, a radially inner member having a slider
constrained to slide between an extended radial position at which it engages a
tooth
on a radially outer member and drivingly couples the members, and a retracted
radial position at which it allows free rotary relative movement of the
members, a
spring biasing the slider to its retracted position, and a centrifugal crank
lever,
pivotally mounted on the radial inner member on an axis parallel to that of
the
members and spaced therefrom, having a massive enlargement at one end and
pivotally connected to the slider at its other end such that rotation of the
inner
member causes the massive enlargement to turn the crank lever to drive the
slider
against the spring bias to its extended position, but the spring causes the
slider to
return to its retracted position when the clutch ceases rotation.
In another aspect, the invention provides a method of assembly of a drive
arrangement, the method comprising pre-assembling a centrifugal clutch and
then
mounting the pre-assembled clutch over a drive shaft to effect a push fit, the
clutch
comprising a centrifugal slider carried by a frame, a gear for conveying
rotary drive
from the slider to an external driven member in use, and a spring which abuts
against the drive shaft and biases the slider to a radial position when it is
out of
driving engagement with the gear, the slider being formed so as to slide under
centrifugal action against the spring bias into driving engagement with the
gear
when the clutch is rotated, and the pre-assembled clutch having an axial
opening,
extending through the slider and the frame and axially into the gear, for
receiving
the shaft.
In another aspect, the invention provides a centrifugal clutch for coupling a
drive shaft to a driven member at rotary speeds above a predetermined
threshold,
the clutch comprising a centrifugal slider with a massive enlargement at one
end
and a first coupling arrangement, a frame formed to carry the centrifugal
slider on
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formations to constrain it to sliding motion between an extended radial
position and
a retracted radial position, and to fit fixedly on the drive shaft to be
driven by it, with
the shaft at right-angles to the axis of sliding motion of the frame, an
output drive
member mountable for free rotation on the drive shaft and formed for drive
engagement with the driven member in use, and formed with a second coupling
arrangement which connects drivingly with the first only when the centrifugal
slider
is at its extended position, and means, located wholly within a recess in the
centrifugal slider, for biasing the centrifugal slider towards its retracted
position,
whereby rotation of the centrifugal slider and frame causes the massive
enlargement to pull the centrifugal slider radially from its retracted to its
extended
radial position to cause the first and second coupling arrangements to
interengage
and thus to transmit rotary drive from the drive shaft to the driven member,
but the
biasing means causes disengagement when the rotation causes, so as to decouple
the drive shaft from the driven member.
1 S In another aspect, the invention provides a method of assembly of a drive
arrangement, the method comprising preassembling a centrifugal clutch and then
mounting the pre-assembled clutch over a drive shaft to effect a push fit, the
clutch
comprising a centrifugal slider carried by a frame, a gear for conveying
rotary drive
from the slider to an external driven member in use, and a spring biasing the
slider
to a radial position when it is out of driving engagement with the gear, the
slider
being formed so as to slide under centrifugal action against the spring bias
into
driving engagement with the gear when the clutch is rotated, and the pre-
assembled clutch having an axial opening, extending through the slider and the
frame and axially into the gear, for receiving the drive shaft.
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In another aspect, the invention provides a centrifugal clutch for coupling a
drive shaft to a driven member at rotary speeds above a predetermined
threshold, the clutch comprising a centrifugal slider with a massive
enlargement
at one end and a first coupling formation, a frame formed to carry the
centrifugal
slider on formations to constrain it to sliding motion between an extended
radial
position and a retracted radial position, and to fit fixedly on the drive
shaft to be
driven by it, with the shaft at right-angles to the axis of sliding motion of
the
slider, an output drive member mountable for free rotation on the drive shaft
and
formed for drive engagement with the driven member in use, and formed with a
second coupling formation which connects drivingly with the first coupling
formation only when the centrifugal slider is at its extended position, and
means,
located wholly within a recess in the centrifugal slider, for biasing the
centrifugal
slider towards its retracted position, whereby rotation of the centrifugal
slider and
frame causes the massive enlargement to pull the centrifugal slider radially
from
its retracted to its extended radial position to cause the first and second
coupling
formations to interengage and thus to transmit rotary drive from the drive
shaft to
the driven member, but the biasing means causes disengagement when the
rotation causes, so as to decouple the drive shaft from the driven member.
In another aspect, the invention provides a drive assembly comprising a
drive shaft coupled to a frame of a centrifugal clutch for coupling the drive
shaft
to a driven member at rotary speeds above a predetermined threshold, the drive
assembly comprising a centrifugal slider with a massive enlargement at one end
and a first coupling formation, a frame formed to carry the centrifugal slider
on
formations to constrain it to sliding motion between an extended radial
position
and a retracted radial position, and to fit fixedly on the drive shaft to be
driven by
it, with the shaft at right-angles to the axis of sliding motion of the
slider, an
output drive member mountable for free rotation on the drive shaft and formed
for
drive engagement with the driven member in use, and formed with a second
coupling formation which connects drivingly with the first coupling formation
only
when the centrifugal slider is at its extended position, and means, located
wholly
within a recess in the centrifugal slider, for biasing the centrifugal slider
towards
its retracted position, whereby rotation of the centrifugal slider and frame
causes
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the massive enlargement to pull the centrifugal slider radially from its
retracted to
its extended radial position to cause the first and second coupling formations
to
interengage and thus to transmit rotary drive from the drive shaft to the
driven
member, but the biasing means causes disengagement when the rotation
causes, so as to decouple the drive shaft from the driven member.
In another aspect, the invention provides a method of assembly of a drive
arrangement, the method comprising pre-assembling a centrifugal clutch and
then mounting the pre-assembled clutch over a drive shaft to effect a push
fit,
wherein the clutch includes a centrifugal slider carried by a frame, a gear
for
conveying rotary drive from the slider to an external driven member in use,
and a
spring which abuts against the drive shaft and biases the slider to a radial
position when it is out of driving engagement with the gear, the slider being
formed so as to slide under centrifugal action against the spring bias into
driving
engagement with the gear when the clutch is rotated, and a recess in the
centrifugal slider, the spring being located wholly within the recess.
In order that the invention may be better understood, two embodiments will
now be described, by way of example only, with reference to the accompanying
diagrammatic drawings, in which:
Figure 1 is an exploded perspective view from the motor drive side of a
centrifugal clutch embodying the invention and part of an electric drive
motor;
Figure 2 is a perspective view from the motor side of the assembled
centrifugal clutch of Figure 1, with the centrifugal slider in its retracted
position;
Figure 3 is a perspective view corresponding to Figure 2 but with the
centrifugal slider in its extended position;
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Figure 4 is a perspective view from the driven member side of the assembly
of Figures 1 and 2;
Figures 5 and 6 are plan views of a centrifugal clutch according to a second
embodiment of the invention, with the centrifugal slider respectively extended
and
retracted. ,
A first embodiment will be described with reference to Figures 1 to 4.
A centrifugal clutch comprises a centrifugal slider 15, a spring 16, a frame
12
for connection to the drive shaft 11 of an electric motor 10, and an output
drive
member 13 which is a single toothed gear in this example.
The frame 12 is generally planar and rectangular, but is cut away at 12fi to
accommodate part of the centrifugal slider 15. Four flanges 121,122,123,124
extending parallel to the plane of the frame 12 but spaced axially from it,
are
arranged in a rectangle to guide the centrifugal slider 15 and to constrain it
to sliding
motion transverse to the axis of the motor spindle 11. An integral bush 125
projecting axially from the centre of the frame 12 coincides with an aperture
through
the frame, for accommodating the motor spindle 11. The motor spindle 11 is
knurled (not shown) to provide rough projections for engagement against the
inner
surface of the bush 125, to form a push-fit when the clutch pre-assembly is
pushed
over the motor spindle 11.
The centrifugal slider 15 is also generally planar and rectangular, with a
length similar to that of the frame 12, but narrower in width so as to be
accommodated within the guides 121 to 124. The slider 15 has a massive
enlargement 155 at one end, projecting axially both above and below the plane
of
the slider- The radial exterior surface of the enlargement 155 is part-
cylindrical,
with its centre of curvature on the axis. The slider 15 has an oval stot 152
at its
centre, through which the motor spindle 11 extends when assembled, such as to
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allow the slider 15 to slide radially between a retracted position as shown in
Figure 2
and an extended position as shown in Figure 3.
The slider 15 is resiliently biased towards its retracted position as shown in
Figure 2 by means of a fiat zig-zag steel spring 16 which is accommodated
wholly
within a shallow recess 151 in the surface of the slider 15. The spring 16
fits into the
recess, with one end abutting against a pair of shoulders 153,154 positioned
about
halfway along the opening 152, which still leaves an unobstructed opening
equal to
or slightly greater than the outer diameter of the spindle 11. This allows for
automatic assembly of the clutch over the spindle 11, since it is not
necessary to
compress further the spring 16 during insertion of the clutch pre-assembly
12,13,15
over the spindle 11.
The output drive member comprises, in this example, a single-toothed gear
13 formed integrally with a multiply-toothed gear 14. The single tooth 131 of
the first
gear 13 projects radially beyond the teeth of the second gear 14. An axial
opening
132, broader than the outer diameter of the motor spindle 11, allows the gears
13
and 14 to be accommodated on the spindle 11 but to rotate freely relative to
the
spindle 11. In use, the teeth on the second gear 14 convey motor drive to a
driven
member (not shown), when and only when the centrifugal slider 15 is in its
extended
position shown in Figure 3, at which the single tooth 131 engages a tooth 156
(Figure 4) on the centrifugal slider 15, projecting axially from the slider,
away from
the motor 10, and located at the end of the slider opposite to that of the
massive
enlargement 155.
The centrifugal clutch is assembled as follows. As shown in Figure 1, the
spring 16 is inserted into the recess 151, and the slider 15 is then slotted
into the
frame 12 until the unobstructed opening 152 is in register with the axial
opening 125
in the frame 12. The spring is thus fully supported, and is carried wholly
within the
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slider 15. The pre-assembled three components 12,15,16 are then pushed axially
over the motor spindle 11 until a permanent push-fit is achieved, with part of
the
spindle 11 projecting from the clutch pre-assembly. The gears 13,14 are then
mounted over the projecting spindle 11, as shown more clearly in Figure 4, and
the
combination of the motor, clutch and gear 14 is then assembled into the door
latch
(or aitemative receiving assembly) for engagement with the driven member, as
appropriate. This assembly can be fully automated, using pick-and-place
action, as
it is particularly simple and straight forward.
Whilst in this example the gears 13 and 14 are formed integrally, this is not
essential: they could be formed as separate components, for example with a
push
fit together.
In this example, the frame 12 and gears 13 and 14 are all plastics
injection mouldings. The slider 15 can be of metal or plastic with a metal
insert, to
give it a sufficient mass for the centrifugal action and sufficient smoothness
of sliding
operation.
An important feature of this example is that the tooth 156 for engaging the
gear pinion 13 is diametrically opposite the massive enlargement 155. Thus the
clutch coupling arrangement is separated from the centrifugal mass
arrangement,
allowing for a more efficient power transfer in operation, and greater
simplicity in
construction. In the clutch disclosed for example in W095124534 (Rockwell),
the
massive enlargement functions itself as the coupling between the clutch
halves, i.e.
both are on the same radial side of the axis, and the coupling has to take
place at
the same extreme radial position. With the preferred feature, the coupling
tooth 156
is diametrically opposite the enlargement 155, and the point of engagement of
the
tooth 156 and the gear tooth 131 is much closer to the axis, e.g. at half the
radius of
the enlargement 155. Thus the gear 13 can be smaller, and the power coupling
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more efficient. Firstly, the spindle acts as a pivot, and contributes to the
dynamic
stability of the clutch.
Secondly coupling takes place between facing surfaces of the gear tooth 131
and the tooth 156 at a smaller radius than that of the massive enlargement,
e.g. at
half the radius, which means a correspondingly greater force on the opposed
surfaces; this means the contact area can be reduced, and this in turn reduces
the
likelihood of frictional resistance preventing retraction of the slider.
Thirdly, with the
coupling at a smaller radius, the gear 13, and the slider 15 and frame 12, can
be
made sufficiently rigid to reduce substantially their tendency to bend about
the axis
at the time of impact as the clutch engages, when there is an angular
impulsive
force.
A further novel feature of this arrangement is that the centrifugal slider 15
is
spring biased against the motor spindle shaft 11, by direct contact between
the
spring 16 and the spindle 11. This allows for a reduction in the number of
component parts.
Typically, when compared with conventional centrifugal clutches, the number
of component parts has been reduced from nine down to four. This makes a
significant saving in material costs and in assembly costs and the simplicity
of the
arrangement with reduced stresses gives it a longer life-cycle. Smaller
housings
may be used, leading to further savings, and greater adaptability to a variety
of
applications.
The invention also allows the motor drive spindle 11 to be shorter than with
other conventional clutches, and this further assists in making the housing
smaller.
As an alternative to the use of a spring, it would be possible to use a
magnetic bias between the slider 15 and the other components. This could
involve
a permanent magnet acting on magnetic metallic parts of the components, with
the
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force of the magnet balancing the centrifugal force at a predetermined speed
of
rotation.
An alternative arrangement, as a second embodiment of the invention, is
shown in Figures 5 and 6.
A centrifugal clutch comprises a driving cylinder 512 and coaxial driven ,
cylinder 514. The radially inner, driving cylinder 512 is fixed to the motor
drive
spindle 11, and has a slider 515 constrained by pins 26,27 and 30 on the inner
cylinder to slide between an extended radial position, shown in Figure 5, at
which it
engages a tooth 513 on the radially outer cylinder and drivingly couples the
cylinders, and a retracted radial position, shown in Figure 6, at which it
allows free
rotary relative movement of the cylinders. A coil spring 22, mounted over a
pin 29,
has one end 25 coupled to the rim of the inner cylinder 512, and the other end
in
engagement with a centrifugal crank lever 21 _which is mounted pivotally on
the
same pin 29 on the inner cylinder 512_ The crank lever 21 has a massive
enlargement 20 at one end, at the end of a tong radius arm; the other arm of
the
crank lever, which is shorter to provide leverage and a mechanical advantage,
is
coupled pivotally at 23 to the end of the centrifugal slider 24. Another pin
28 on the
inner cylinder acts as an end stop to limit the anti-clockwise rotation of the
crank
lever 21 to the position shown in Figure 5. At this limit position, the
massive
enlargement 20 does not interfere with the motion of the driven coaxial
cylinder 514_
In this example, although it is not essential, the slider 24 also has a
massive
enlargement 515 at its radially outer end, opposite to that of the pivot point
23. This
assists in the centrifugal action.
In use, when the motor spindle 11 is stationary, the spring 22 drives the
crank lever 21 clockwise as shown in Figures 5 and 6, towards the position
shown in
Figure 6, at which the slider 24 is retracted, and the clutch is disengaged.
Once the
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motor speed has increased to a particular predetermined speed, the centrifugal
force on the massive enlargement 515, combined with the centrifugal force on
the
massive enlargement 20, in combination overcome the spring bias, and drive the
slider 24 to its extended position as shown in Figure 5_ When the rotation
decelerates once again, the spring will eventually overcome the centrifugal
forces
and return the slider to its retracted position, to disengage the clutch.
It will be understood that alternative mechanical arrangements are possible
for example to have a spring acting on the slider 24 instead of, or in
addition to, the
spring 21 acting on the crank lever. The centre of mass of the slider 24, in
the
example given, is displaced radiaify a considerable distance from the axis of
the
motor spindle 11, because of the massive enlargement 515, but in some examples
this may not be necessary, depending upon the centrifugal force available from
the
enlargement 20 on the crank lever and the mechanical advantage provided by the
crank lever, together with an allowance made for the frictional losses in the
assembly.
The driving and driven "cylinders" need not be perfectly cylindrical, and
could
have less regular shapes, provided they are basically coaxial.
11
