Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates generally to
a variable speed transmission of the belt-pulley type
wherein the V groove of the driving pulley is capable
of varying in width to increase or decrease the speed
of the driven pulley, connected to the driving pulley
by the belt, by displacement of the latter in the V groove.
DESCRIPTION OF THE PRIOR ART
In a variable speed transmission of the above
general type, as used on snowmobiles, motorcycles and
other like utilitarian or recreational vehicles, the
pulley comprises a pair of V groove-defining cheeks rota-
table in unison about a common axis and of which one
is axially stationary while the other is axially movable.
2p Located on the side of the pulley away from the stationary
cheek is a reaction cup which is also axially stationary
by being made solid with the said stationary cheek, for
instance. The movable cheek and the reaction cup are
formed with conical cam surfaces converging toward one
another and defining between them a chamber into which
are housed a set of centrifugal weights having the shape
of a isosceles trapezium ~in cross-section. The weights
are free to move radially away from the common axis and
are slidable along their conical cam surfaces. As the
centrifugal force of the weights increases with increasing
speed of the driving pulley, driven by the motor, the
weights move radially outward and force the movable cheek
toward the stationary one to narrow the V groove between
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them, causing the belt to climb in the groove thereby
increasing the speed of rotation of the driven pulley or,
rnore generally, varying the speed ration between the driving
and driven cheeks.
The generating lines of the conical cam surfaces
being rectilinear, the spreading movement of the cheeks is
proportional to the radial displacement of the centrifugal
weights.
The best prior art reference known to Applicant,
with respect to his invention, is French patent application
No. 2,504,635, in the name of Carnot and published on
October 29, 1982. In this application, the centrifugal
weights used are in the form of spheres providing a ponctual
contact between the said spheres and the cam surface of the
reaction cup. In Applicant's tarnsmission, the improved
centrifugal weights and reaction cup are shaped to provide
surface contact between them resulting in reduced and more
evenly distributed wear, as will be seen hereinafter.
Moreover, in the Carnot application, the contact point
between the spheres and the cam surface is always at the
same distance from the center of gravity of the spheres,
because of their shape. In Applicant's transmission, the
distance between the contact point of the weights and their
center of gravity varies as a function of the position of
these weights. As a result, the resultant of the forces
applied by the weights onto 'the cam surface also varies and
may be selected to meet some specific requirement (clutch
response).
Other patents known to Applicant are:
United States Patent Nos.:
2,378,549
2,512,816
3,230,787
3,850,050
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SUMMARY OF THE INVENTION ,,
An important object of the invention lies in a
pulley-type transmission wherein use is made of freely
displaceable centrifugal weights capable of reducing
friction losses in the mechanism as a whole.
Another important object is in the provision of
a transmission of the above type wherein blocks are used
which are molded to the shapes of the sliding planes,
for centrifugal weights, offering a better distribution
of the forces acting between the components of the trans-
mission.
Another object of the present invention is to
provide a pulley-type transmission wherein the cooperating
cam surfaces on the reaction cup and on the centrifugal
weights are designed to cause optimization of the dis-
placement of the belt in the V groove with respect to the
speed of the motor when the latter runs at cruising speed.
From a practical point of view, the above object
is to obtain that the vehicle run faster for a given motor
RPM located between starting up and full speed. In other
words, at medium speed, the motor would run more slowly
for~the same efficiency and would, consequently, wear off
less rapidly and be proportionately more silent.
The above object is made possible, according
to the invention. by making the cam surface of the reac-
tion cup concave, with respect to the rotation axis of
the pulley, while making convex at least a portion of the
end edges of the centrifugal weights riding on the concave
~ cam surface of the cup: the radius of curvature of the
convex end edges being smaller than that of the concave
reaction cup. The end edges may be made convex along the
full radial thickness of the weights or else
-
may be provided, at their center, with round protuberan-
ces or bulges.
Further objects and other advantages of the
invention will become apparent from the description that
follows of preferred embodiment having reference to the
appended drawings.
BRIEF DESCRITPION OF THE DRAWINGS
Figure 1 is an axial cross section of a pulley
type transmission making use of known centrifugal weights;
Figure 2 is an axial cross section of a pulley
type belt transmission making use of a centrifugal weights
and reaction cup arrangement made according to the teach-
ing of the invention; the transmission being in starting-
up position;
Figure 3 is a view like that of Figure 2 but
with the transmission being at running speed;
Figure 4 is a graph showing the speed curves
corresponding to the driving pulley and to the driven
pulley in transmissions using a known centrifugal weights
arrangement and a transmission using a centrifugal weights
arrangement according to the invention; and
Figure 6 is a graph showing the acceleration
curves from starting up of the driven pulley to, respect-
ively, one quarter and full RPM of the driving pulley,
in a known centrifugal weights arrangement and a centri-
fugal weights arrangement according to the invention; and
Figures 6a to 6c are diagrams showing the portion
of the contact points and the various forces acting on the
centrifugal block, in use.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The transmissions shown in Figure 1, on the
one hand and Figures 2 and 3 on the other hand, are basic-
ally the same, being constructed as follows.
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The pulley 1 comprises an outer axially stationary
cheek 3 driven by a motor (not shown) and an inner axially
movable cheek 5 rotatable in unison about a common axis and
defining between them a V groove 7 into which is received a
flexible drive belt 9. The cheek 5 is freely mounted
through axial bearings 21 onto an axial tubular central hub
11 having one end 27 passing through a hole 31 provided at
the center of the cheek 3. A bolt 25 integrally extends the
other free end of the hub 11. A reaction cup 13 (Figure 1)
or 15 (Figures 2 and 3) is removably secured to the hub 11
by means of a nut and lock washer assembly 17 screwed onto
the bolt 25. The one end 27 or the hub 11 is rigidly fixed
into the hole 31 of the cheek and retained by a stop plate
29. By this connection, the cup 13 or 15 is made solid and
rotatable in unison with the cheek 3.
A sleeve 19 integral to the cheek 5 is mounted
over the hub 11. The sleeve 19 which is coaxial with the
hub 11 extends at the center of the cheek 5.
A plug 23 is screwed onto the free end of the
sleeve 19. This plug which is free to rotate relative to
the hub thanks to an axial bearing 26, is shaped to define
an annular blind bore 33 into which is received one end of a
coil spring 35 mounted about the hub 11 inside the sleeve
19. This one end of the coil spring 35 bears against the
bottom of the bore while its other end bears against a
radial shoulder 37 held by a flange 38 attached to the hub
11. The spring 35 is intended to resist cheek 5 from
closing in on cheek 3, as can be gathered from Figures 2 and
3.
The reaction cup 13 and the movable cheek 5, in
Figure 1, are formed with frusto-conical cams surfaces 39,
41, of equal inclination, extending around the axis 24 and
converging toward one another to define a chamber 43 between
them. A set of at least two centrifugal inertia weights 45,
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having the shape of an elongated isosceles trapezium in
cross-section, are housed in this chamber and are seized so
that their end edges 47, 49 are constantly flatly applied
against their respective cam surfaces 39, 41, by the bias of
the spring 35.
With the above arrangement iii mind and as the
driving pulley 3 picks up speed, throucfh its attachment to
the stub shaft 29, the centrifugal weights 45 are thrown
outward in the chamber 43 forcing the movable cheek 5
rightward and climbing of the belt 9 in the groove 7. The
generating lines of the cam surfaces 39, 41, being
rectilinear, movement of the cheek 5 is proportional to the
.radial displacement of the weights 45.
The curve A in Figure 4 shows the stabilized RPM
of the driven pulley for different RPM's of the driving
pulley. When use is made of the prior art transmission
shown in Fig. 1 it is seen that the curve bends first
slightly upwards as the speed of the motor increases and
then tapers off as the motor speeds reaches its maximum.
In order to guide the weights 45, properly, in
their radial displacement, they are made to slide freely in
guide channels defined by pairs of parallel spaced ribs 51
projecting perpendicularly from the cam surface 41 of the
movable cheek 5.
Figures 2 and 3 show the basic improvement of the
invention as applied to essentially the same pulley
structure 1 as in Figure 1.
According to the improved arrangement, the cam
surface 53 of the axially stationary modified reaction cup
15 is concave with respect to the common axis 24 while the
end edges 55 of the modified centrifugal inertia blocks or
weights 57 are convex on at least a portion of their radial
fitness. According to the invention, the radius of
curvature of the cam surface 53 of the reaction cup is
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longer than that of the convex portion of the weights 57 so
that the latter bear on the surface 53 along a very limited
length thereof.
Preferably, the end edges 55 are convex along the
full radial thickness of the weights 57 but the convex
portion may also be in the form of rounded protuberances or
bulges at the center of the end edges.
It will be noted that the opposite end edges 49 of
the weights and the cooperating cam surface 41 of the
movable cheek 5 have the same configuration as in the pulley
structure of Figure 1.
Tf desired, rims 59 may be fixed by rivet or
otherwise to the cup 15, to keep the weights equally
distributed in channels all around the cup and guide these
wrights during their radial displacement.
The results of tests carried with the improved
transmission of Figures 2 and 3 is illustrated by curves B,
in Figures 4 and 5. The show that the RPM of the driven
pulley is directly proportional to that of the motor or
driving pulley. It follows that for a given speed of the
motor, the driven pulley runs faster when a curved cam and
curved weight edges, are used; the latter having a lesser
radius of curvature.
From the acceleration curves in Figure 5, plotted
from starting-up of the driven pulley to, respectively, one
quater driving RPM and full RPM of the motor, it is seen
that the improved transmission makes it possible to use the
full power of the motor when the latter runs at full speed.
The tests have also shown that, with the improved
clutch transmission and after several hours of operation,
there was hardly any change in the coefficient of friction
between the curved components.
The cam surface of the reaction cup.
The cam surface of the reaction cup must be given
a concave shape such that it tends to stabilize the '
resultant of the forces acting on the driving belt. There
is a precise shape for each type of motor (diesel, gasoline,
electric...etc). The calculations that follow resume the
mathematical developments that make it possible to design a
proper reaction cup capable of stabilizing the resultant of
the forces acting on the driving belt.
Reference is now made to Figure 6a in order to
establish from the following mathematical developments, the
position of the contact point C between the centrifugal
block and the cam surface, with respect to the center of
gravity of the block.
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List of variables:
C : Point of contact between the centrifugal block
and the cup.
C.G.: Center of gravity of the centrifugal block.
R : Center of the radius of curvature of the block.
r : Radius of curvature of the block.
a : Angle at the point of contact C.
'~ + a
1. Equation of the circle of center R, as a function
r, a,
x2 + y2 - r2
x = r cos a + xR
y = r sin a+ yR
2. Equation of the tangent at C;
equation of the type Y1 = Axl + B
where A is the slope of the tangent and B the point
of intersection of the tangent with the axis of the
center of gravity of the block.
A = - tg a
g = y + ootg a
yl = _xl tg a + y + x cotg a
3. Equation of the point of contact C as a function
of the position of the radius of the block and of
the angle of contact
yC = =xCtg a + r sin a + YR + cotg a L r cos a + xR )
~ ar~_3 ~.4:~
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4. Fquation of the point of contact C with respect to
the center of gravity Vof the block, _ ,_
yR yCG yRCG
where: yRCG is the distance in y between the position
of the radius and of the center of gravity
xR = xCG - xRCG
where: xRCG is the distance in x between the position
of the radius and of the center of gravity.
yC = - xC tg a + r sin a + yCG YRCG + cotg a
(r cos a + xCG - xRCG~
Figure 5b gives a geometrical study of the cen-
trifugal block from which may be drawn the following
mathematical telations.
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~y - ~ x - + ~ x - ~X ( 1 + 1 )
tg al tg a2 t9 al tg a2
~x = 1 - ~ y
-1 1
Ctg a 1 tg a 2
1 _ 1 _ 1
tg a ~x/4y tg a2
1
tgal - 1 _ 1
~x/~y tg a2
-1 1
al - tg p 1
_ t g a2
where:
al is the complementary angle of the per-
pendicular at the point of contact
between the block and the cam surface
of the racting cup;
a2 is the complementary angle of the per-
pendicular at the point of contact
between the block and the inclined
plane (fixed angle);
~y is the variation in the position of
px
the center of gravity as a function
of the speed of rotation of the motor.
11 - 2013~~45
Figure 6c gives the diagram of the block of
the forces acting on the radially free centrifugal block
~.aherein the variables shown are defined as follows:
FR: Force acting on the belt (resultant)
FC: Centrifugal force = - 3~l~ZR where
R = x + ~x
0
Ni: Reaction of the centrifugal forces at
the points of contact
ai: Angle at the point of contact.
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a . Coefficient o.f friction on the
sliding plane.
It is by the modification of the shape of the
sliding planes (cam surfaces) that a rough adjustment may
be carried out for the type of motor connected with the
application under consideration (electric or gazoline
motor or diesel motor).
By changing, in accordance with the above
mathematical considerations, the mass of the movable
center, it is possible to obtain an adjustment of the
transmission which is directly related to the power of
the motor. This is what makes adjustments of a trans-
mission made according to the invention simple.
It should be noted here that calculating, in
the manner shown above, the cam surface of the reaction
cup and the shape of the end edges of the centrifugal
blocks, the latter is made to slide along a surface
portion that increases from start-up to cruising speed
of the transmission, as can be seen in Figures 2 and 3.
