Note: Descriptions are shown in the official language in which they were submitted.
1~3~335
TRACTION BODY CONSTRUCTION FOR
INFINITELY VARIABLE TRANSMISSIONS
This invention relates to torque transmiscion appar-
atus and, more particularly, it concerns improvements in the
construction of torque transmitting traction members by which
normal force loading for the transmission of torque by fric-
tion to or from such members may be supported without object-
ionable deflection of transmission components.
In U.S. Patents No. 4,112,779, No. 4,112,780 and No.
4,152,946 several continuously variable transmission embodi-
ments are disclosed in which three frame supported working
bodies operate to transmit a mechanical power input to a
rotatable output at infinitely or continuously variable speed
ratios within the design range of the particular transmission
embodiment. In the transmissions of this general class, two
of the working bodies are in frictional rolling contact with
each other at two points of contact as a result of one of the
two bodies being of a biconical configuration to define oppos-
itely convergent rolling surfaces of revolution about one axis
and the other of the two bodies taking the form of a rotatably
coupled pair of rings defining complementary rolling surfaces
about another axis inclined with respect to and intersecting
the one axis. The rings are adjustable in a manner to vary
the radius ratio of the contacting rolling surfaces and thus
attain the continuously variable speed ratio for which the
transmission is primarily intended.
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~37335
One preferred way of retaining the engaged rolling
surfaces in contact under normal force loads adequate to
achieve torque transmission by friction has been to provide
the biconical body as an assembly of two conical members on
a common shaft in concentric fashion and to connect the
shaft with a cam system operable to forcibly separate the
cone members along the axis of the shaft in response to a
torque differential between the shaft and the cone members.
By coupling the shaft either directly or indirectly to the
transmission output load, the force by which the cone members
would be urged against the ring-like members could be made
proportional to output load. A major difficulty with this
approach to normal force development is that the nature and
magnitude of the loads imposed on the assembly of cone
members and shaft tend to deflect the shaft relative to the
cone members causing the cone members to bind or otherwise
develop an unwanted path of torque transmission between the
shaft and the cone members. The effectiveness of the cam or
ramp system operative between the shaft and the cone members
is therefore reduced with the result that the normal forces
developed at the points of frictional contact are lower than
that required to handle the output load of the transmission.
This situation, in turn, can result in slippage of the
frictionally engaged surfaces, unequal loading at the two
points of contact and other factors which reduce efficiency
of power transmission and/or cause damage to transmission
components. While various solutions to this problem have
been proposed and demonstrated to be effective, in retrospect,
such prior solutions have entailed structural complexity and
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compromise rather than elimination of potential sources of
power transmitting efficiency losses and mechanical failure.
In accordance with the present invention, a biconi-
cal torque transmiting body is provided for a continuously
variable transmission in which torque is transmitted between
oppositely convergent conical surfaces on said body and a pair
of ring-like surfaces at two diametrically opposite points of
contact, the conical surfaces being the exterior surfaces of
two cone members included in said body which are oriented in
base-to-base relationship and movable axially to vary the
forces under which said surfaces are retained in contact, said
body being adapted for support at opposite ends against tilt-
ing movement under forces applied at said diametrically
opposite points of contact and for rotation on the axis of
said body. The biconical torque transmitting body is further
characterized in that each of said cone members includes a
rigid, integral shaft extension at the small end thereof, said
shaft extensions being cylindrical and coaxial to provide for
freedom of axial movement of both said shaft extensions on the
axis of said biconical body relative to axially fixed radial
bearing supports at opposite ends of said body and whereby
bending stresses imposed on said biconical torque transmitting
body are borne in substantial part directly by said cone
members.
In one embodiment where the cone members are con-
centric with a central shaft and thrusted in opposite axial
directions in response to a torque differential between the
shaft and both cones, the bearing shaft extensions of the
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1~37335
cones are of annular configuration to accommodate the control
shaft. Since the central shaft carries only a small amount of
the bending loads imposed on the torque body, the diameter of
the central shaft may be reduced to that necessary for handl-
ing torque loads only.
In another embodiment the biconical body is constit-
uted by two oppositely convergent cone members interconnected
without a central shaft at the respective base or large dia-
meter ends thereof for relative rotation and axial displace-
ment with respect to each other. The body is resistant to
axial bending as a result of its geometric or biconical con-
figuration and by transmission of bending stresses through a
radial bearing which connects the base ends of the two cones.
Also a pilot cone, rigidly connected at its base to the base
end of one of the cone members, extends to and is journalled
concentrically within the small end of the other of the two
cone members and thus further stabilizes the body against the
forces which act thereon.
To develop normal force components by which rolling
or traction surfaces on the cone members are pressed into
engagement with complementing rolling or traction surfaces of
revolution about an axis inclined with respect to and inter-
secting the axis of the biconical body, the two cone members
of the latter embodiment are in axial abutment with each other
through complementing cam or ramp surfaces preferably, but not
necessarily, located at the concentric small ends of the pilot
cone and the other one of the two cone members. The cam or
ramp surfaces operate to convert torque acting between the
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1137335
cone members to an axial force or thrust acting to separate
the cone members on the axis of the biconical body. In
addition, an adjustable preload force may be imposed on the
cone members by a set screw arrangement acting between them.
The following is a description of certain embodi-
ments of the present invention, reference being had to the
accompanying drawings in which:
Fig. 1 is a longitudinal cross-section of an
infinitely variable transmission incorporating one embodiment
of the present invention;
Fig. 2 is a longitudinal cross-section through
another continuously variable torque transmission incorpor-
ating an alternative embodiment of the invention;
Fig. 3 is an enlarged fragmentary cross-section in
the same cutting plane as Fig. 2;
Fig. 4 is an enlarged fragmentary section similar to
Fig. 3 but illustrating components in a different orientation;
Fig. 5 is an exploded side elevation illustrating
components shown in Figs. 2-4; and
Fig. 6 is an end view as seen on line 6-6 of Fig. 5.
In Fig. 1, one exemplary embodiment of an infinitely
variable transmission unit incorporating the present invention
is generally designated by the reference numeral 10 and shown
to include a casing or frame 12 from which working components
of bodies of the transmission are supported. In this
transmission embodiment, a supporting body 14 is mounted
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at opposite ends by axle-like extensions 16 and 18 in casing
end walls 20 and 22 to be generally concentric with a
primary or first axis 24. The extensions 16 and 18 and thus
the body 14 are retained against rotation on the axis 24 by
interlocking spline sets 26 and 28, for example. A generally
cylindrical body 30 is supported from the extensions 16 and
18 and thus from the frame 12 to be rotatable about the
first axis 24 by bearings 32 and 34. The body 30 carries a
pair of axially spaced rings 36 and 38 defining internal
traction surfaces 40 of revolution about the first axis 24.
The rings rotate with the body 30 and are axially adjustable
toward and away from each other by appropriate control means
such as one or more, preferably three oppositely pitched
threaded screws 42 adapted to be driven in rotation on their
respective axes by means (not shown)~
A biconical body, generally designated by the
reference numeral 44, is supported by the body 14 for
rotation about a second axis 46 which is inclined with
respect to the first axis 24 and intersects the first axis
at a point S of axes intersection. Although the body 44
functions as a unit, it is comprised of separate components
in the embodiment of Fig. 1, such components including a
pair of oppositely convergent cone members 4% and 50 defining
conical traction surfaces 52 of revolution about the axis
46. The conical surfaces 52 converge at an apex angle which
is twice the angle at which the axes 24 and 46 intersect.
In light of this configuration, the traction surfaces 52 on
the cones 48 and 50 may be in continuous contact with the
1137335
traction surfaces 40 on the rings 36 and 38 throughout all
axial positions of the rings.
Separating the base ends of the conical members 48
and 50 is a ball/ramp assembly 54 including a pair of plate
members 56 and 58 biased away from each other under a spring
preload developed by a Belleville spring washer set 60. The
plates 56 and 58 as well as the base ends of the conical
members 48 and 50 are formed having complementing ramp
surfaces to engage two pairs of balls 62 and 64 which operate
to force the cone members 48 and 50 in opposite directions
away from the point S of axes intersection in a manner to be
described in more detail below.
The conical members 48 and 50 are provided with
through-bores 66 and 68 concentric with the axis 46 to fit
the external dimensions of a central shaft 70. The shaft 70
includes splines 72 positioned centrally along its length to
effect a rotational coupling of the ball/ramp plates 56 and
58 with the shaft 70. Also, the shaft 70 makes a close
rotatable and sliding fit at opposite end portions of each
of the cone members 48 and 50 in a manner permitting relative
rotation and axial movement of the cone members 48 and 50
and the shaft 70. At least one end of the shaft 70 is keyed
with a bevel gear 74 which, in the illustrated embodiment,
is in direct meshing engagement with a gear 76 on a shaft 78
journalled in part by a bearing 80 to be independently
rotatable with respect to the body 14. A thrust bearing
represented by a ball 81 in the drawing is positioned
between one end of the shaft 70 and a bracket 82 fixed to
1137335
the supporting body 14. The opposite end of the shaft 70 is
similarly constrained by a washer 83 abutting a portion of
the body 14. In this way, axial movement of the shaft by
reaction to the gears is prevented.
In the embodiment illustrated in Fig. 1, the
cylindrical body 30 carries a gear or sprocket 84 by which
the body 30 may be driven in rotation about the axis 24.
Although input and output power to and from the transmission
may be alternated between the gear 84 and the shaft 78, if
it is assumed that the body 30 is driven in rotation by a
power input to the gear 84, the driving torque will be
transmitted from the traction surfaces 40 by friction to the
traction surfaces 52 on the cone members 48 and 50. Torque
in the conical members will then be transferred through the
balls 62 and 64 to the plates 56 and 58 and to the shaft 70.
Torque is then transmitted as output torque to the shaft 78
through the gears 74 and 76.
The torque differential between the conical members
48 and 50 and the shaft 70 is through the balls 62 and 64
which, because of the ramp surfaces in which they are situated,
will develop an axial separating force on the conical members
48 and 50 proportional to the torque differential. As a
result, the traction surfaces 52 on the conical members will
be urged into engagement with the traction surfaces 40 under
normal force loading proportional to the output load on the
shaft 80 in the example given. Because the points Pl and P2
of contact between the surfaces 40 and 52 are diametrically
opposite from each other, the normal force loading will
1~3733S
develop a rocking couple in a direction which, if unopposed,
would reduce the angle at which the axes 24 and 46 intersect
each other. Because the body 14 is fixed in the embodiment
under discussion and movement of the biconical body 44 is in
simple rotation about the axis 46, the rocking couple is
opposed exclusively by bearings 86 and 88 by which opposite
ends of the body 44 are supported rotatably in the body
14.
Because of the different moment arms in the rocking
couple resulting from normal force loading and the reaction
couple developed by the bearings 86 and 88 there is a tendency
for the biconical body 44 and the shaft 70 thereof to be
deflected into an S-shaped curve in which the axis 46, when
so curved, would intersect the point S and two points centered
with the bearings 86 and 88. Such deflection is the result
of bending stresses which are substantially equal and opposite
along each half-length of the shaft between the respective
bearings and the point S.
In accordance with the present invention, deflection
in the biconical body 44 between the point S and the bearings
86 and 88 is substantially avoided by providing each of the
cone members 48 and 50 with integral shaft extensions 90 and
92 from the small diameter ends of the conical traction
surfaces 52. Because the shaft 70 is reduced to a diameter
capable of handling exclusively the torque and shear loading
on the shaft 70, the shaft extensions 88 and 90 are increased
in radial thickness. Resistance to biconical body deflection
as a result of the normal force loading of the traction
1~3733~;
surfaces 52 is borne entirely by the cone members 48 and 50.
Because the conical members are formed of high strength
materials of the type used for bearing rollers, and also
because of the increased diameter of these members and of
the shaft extensions 90 and 92, deflection along the axis 46
is substantially avoided.
The bearings 86 and 88 are preferably hydrodynamic
bearings having an inner race defined directly by the shaft
extensions 88 and 90 and an outer race or bushing 96 seated
in the body 14. The cylindrical interface between the races
94 and 96 is supplied with a lubricant under high pressure
supplied by external piping 98 through internal passageways
99 and 100 in the body 14 and the shaft 70, repsectively.
The facility for the use of hydrodynamic bearings
in the support of the biconical body 44 is important not
only from the standpoint of accommodating the loads imposed
at the gears and the indefinite life characteristics of
hydrodynamic bearings, but also, such bearings will enable
the necessary slight degree of axial movement in the cone
members 52 resulting from elasticity of the material from
which the cone members 48 and 50 as well as the rings 36 and
38 are formed. Also, the avoidance of loads on the shaft 70
which tend to cause a relative deflection between the shaft
70 and the cone members 48 and 50 is important from the
standpoint of avoiding a direct torque differential between
the cone members and the shaft. In particular, any direct
transfer of torque from the shaft 70 to the cone members
would reduce torque seen by the balls 62 and 64 and reduce
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the effective normal force loading of the surfaces 40 and 52
to below that which is necessary to transmit a given output
torque load on the shaft 80.
In this latter respect, it is to be noted that the
bending stresses imposed on the biconical body 44, as a
whole, are transmitted to the shaft 70 only at the base ends
of the cone members where deflection of the shaft is minimal.
Also, the moment of direct torque transmission by friction
between the shaft and at the inner or base ends of the cone
members is small relative to the moment arm of torque
transmitted by the balls 62 and 64 and the moment arm of
torque transmitted at the traction surfaces 52. Therefore,
the magnitude of any unwanted torque differential between
the cone members 48 and 50 and the longitudinally central
portion of the shaft 70 is small relative to operating
torques and required normal force loading which create the
unwanted cone-shaft friction forces in this region. Further-
more, the relative torque arm lengths when the rings 36 and
38 are positioned at the base or large ends of the cone
members reduce the effect of the unwanted cone-shaft friction
because less normal force development by the ball/ramp
assembly 54 is needed for the transmission of a given torque
at the base end of the cones than is needed for the trans-
mission of the same torque at the small ends of the cones.
In other words, a lower efficiency of ball/ramp operation
can be tolerated under conditions of transmission operation
when friction between the central region of the shaft 70 and
the cone members is maximum.
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~37335
At the small ends of the cones, where the arm of
the unwanted cone-shaft friction approaches in length, the
arm of torque transmission at the traction surfaces 52, the
entire reaction to normal force loading on the cone members
is borne through the bearings 86 and 88 directly by the cone
members and integral shaft extensions 90 and 92. Hence,
there is no normal force acting between the shaft extensions
and the shaft 70 by which torque can be transmitted by
friction between the shaft extensions 92 and 90 and the
shaft 70. As a result of this structural organization, the
ball/ramp assembly is fully effective to develop the normal
force loading of the cone members against the rings 36 and
38 substantially proportional to the torque load on the
shaft 70.
In Fig. 2 of the drawings, an alternative embodi-
ment of the biconical torque transmitting body of the present
invention, generally designated by the reference numeral
lla, is shown incorporated in a slightly different continuously
variable transmission unit having a frame 112, an input
shaft 114 and an output shaft 116. The input shaft 114 is
connected as an integral shaft extension with a body 118
supported in the frame 112 by bearings 120 and 122 for
rotation about a first axis 124. It will be noted that the
body 118 is similar to the body 14 in the transmission of
Fig. 1 but, in this instance, is rotatable as a cranking
body. The biconical body 110, in turn, is supported directly
from the cranking body 118 by bearings 126 and 128 to be
rotatable on a second axis 130 inclined with respect to and
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li3733S
intersecting the first axis 124 at a point S of axes intersection.
Supported by and coupled against rotation with respect to
the frame 112 are a pair of rings 132 and 134 which are
capable of axial adjustment toward and away from the point S
of axes intersection. In the embodiment described in Fig.
2, such axial adjustment of the rings 132 and 134 is effected
by one or more oppositely pitched screws 136 rotatable by an
external control (not shown) through gears 138 and 140 which
are rotatable on axes fixed with respect to the frame 112.
An additional control gear 142, rotatable with respect to
the frame 112, is shown and in practice is used to synchronize
rotation of the gear 140 with corresponding gears for additional
sets of double pitched screws (not shown). A pinion gear
144, connected directly to the biconical body 110 in a
manner which will be described in more detail below, meshes
with a ring gear 146 coupled directly with the output shaft
116.
Consistent with the several transmission embodiments
disclosed in the aforementioned U.S. patents, the biconical
body 110 in the illustrated embodiment defines a pair of
external conical surfaces 148 and 150 of revolution about
the axis 130 and which function as rolling or traction
surfaces. The surfaces 148 and 150 engage complementing
internal traction surfaces on the rings 132 and 134 at two
diametrically opposite points of contact Pl and P2. As a
result of this frictional contact between the biconical body
110 and the rings 132 and 134, the rotational speed of the
output shaft 116 in this instance, is the product of both
rotation of the cranking body 118 on the first axis 124,
causing orbital or planetary movement of the pinion gear
144, and rotation of the pinion gear with the biconical body
110 on the axis 130. Thus, where ~ is the rotational
speed of the cranking body 118 about the axis 124; ~ is
the speed of rotation in the output shaft 116; ~ is the
ratio of the traction surface radius on the rings 132 and
134 to the radii of the conical surfaces 148 and 150 at the
contact points Pl and P2; and k is the diametric ratio of
the pinion gear 144 to the ring gear 146, the output/input
speed ratio of the transmission is determined by the equation:
~ kp.
It is to be noted that in the embodiment illustrated
in Fig. 2 the biconical member 110 undergoes a nutational
movement as a result of its being supported on the second
axis 130 by the cranking body 118. In other forms of the
same basic transmission and as disclosed in U.S. Patent No.
4,152,946, the biconical body 110 may be concentric with the
first axis 124 and coupled directly with an output shaft
whereas the rings 132 and 134 are concentric with the second
axis 130 and, as such, carried in nutation by the equivalent
of the cranking body 118. As will be apparent from the
description to follow, the structure and function of the
biconical body 110 is equally applicable to either form of
transmission in this general class.
As may be seen in Fig. 2, the conical surfaces 148
and 150 are the external surfaces of two cone members 152
and 154, respectively. Both cone members 152 and 154 are
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1137335
hollow and extend at their small ends as cylindrical inner
race portions 156 and 158 for rotatable support by the
respective bearings 126 and 128. Each of the two cones has
a relatively large diameter or base end 160, 162 shaped to
define telescopic journal formations 164 and 166, which define
respectively, outer and inner races of a radial bearing 167.
As a result of the journal formations and the bearing 167,
the cone members 152 and 154 may rotate relative to each
other and also slide longitudinally along the axis 130 in
relation to each other.
As mentioned above, the pinion gear 144 by which
torque is transmitted from the biconical body 110 to a
driven load through the output shaft 116 is coupled for
rotation with the body 110. In the embodiment under discussion,
the sole direct connection of the pinion gear 144 to the
body 110 is with the cone member 154. Thus, the gear 144 is
formed as an integral extension at the small end of the cone
rnember 154.
To establish a torque path from the cone member
152 to the pinion gear 144 as well as to stabilize the
assembly of the two cones 152 and 154 on the axis 130, the
base end 162 of the cone member 154 is secured, such as by
welding, to the base end 168 of a pilot cone 170, the small
end 172 of which is rotatably and slidably supported by a
radial bearing 173 formed between the exterior of the end
172 and the interior of the bearing race portion 156 at the
small end of the cone member 152. A cam or ramp assembly
174 operates as the sole torque transmitting coupling
~ 13733~i
between the cone member 152 and the pinion gear 144 through
the pilot cone 170 and the cone member 154 in a manner to be
described in more detail below.
The cam assembly 174 is located within the bearing
race portion 156 at the small end of the cone member 152.
As shown most clearly in Figs. 3-6 of the drawings, the
assembly 174 includes a thrust plate or plug 176 threadably
or otherwise anchored against axial displacement with respect
to the cone member 152, a cylindrical cam member 178 coupled
by splines 180 for direct rotation with the cone member 152
and a complementing cylindrical cam portion 182 integral
with or otherwise nonrotatably fixed at the small end 172 of
the pilot cone 170. A set screw 184 is threadably received
in the thrust plate 176 and is in abutting relationship with
the cam member 178. As may be seen by comparing the illustra-
tions in Figs. 3 and 4, the splines 180 are of a length
sufficient to enable the cam 178 to be adjustably positioned
axially in the race portion 156 of the cone member 152 by
appropriate adjustment of the set screw 184.
As shown in Figs. 5 and 6, cam members 178 and 182
are each provided with complementing annular end camming
faces 186 and 188, respectively. These surfaces define a
ramp angle by which an angular or rotational force (i.e.
torque) is resolved into an axial component of force operating
to separate the cam members 178 and 182 axially. The axial
separating force is, therefore, proportional to torque
transmitted between the cam members 178 and 182 and the
magnitude of that axial force for a given torque wlll be
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- ` 1~3 733~
determined by the ramp angle of the engaged camming surfaces
186 and 188. The camming surfaces 186 and 188 are, moreover,
bidirectional in the sense that the same axial component of
force will be developed irrespective of the relative direction
of torque transfer between the cam members 178 and 182.
Because of the direct torque path between the cam
member 178 and the cone member 152 and between the cam
member 182 and the cone member 154 through the pilot cone
170, the torque transmitted by the camming surfaces 186 and
188 will be approximately one half the torque load at the
pinion gear 144. The development of this torque and its
effect on the operation of the overall transmission in which
the biconical body 110 is designed for use will now be explained.
As above mentioned, in the operation of the
transmission illustrated in Fig. 2, torque transmission from
the input shaft 114 and the cranking body 118 to the biconical
body 110 is by friction between the rings 132, 134 and the
cone members 152, 154 at the two points of contact Pl and
P2. Assuming that the two points Pl and P2 are maintained
in symmetry with respect to the point S of axes intersection
during operation by appropriate adjustment of the rings 132
and 134, the torque transmitted at the points Pl and P2 will
be equal, in the same direction and, as such, represent an
equal division or splitting of torque delivered to the
pinion gear 144. Assuming further that the set screw 184
has been adjusted to preload the conical surfaces 148 and
150 into engagement with the inner surfaces of the rings 132
and 134, no relative movement between the cone members 152
1~37335
and 154 will occur at torque loads on the output shaft until
the normal force required at the point P2 exceeds that
developed by the set screw preload. When the torque load on
the output shaft 116 exceeds the normal force preload at the
point P2, a measure of slippage will occur between the
traction surface 150 and the complementing traction surface
on the interior of the ring 134. Because the cone member
152 is not connected directly to the pinion gear 144, however,
the same tendency for slippage will not exist at the point
Pl except as a result of torque transmitted through the cam
assembly 174. Since any torque at the cam assembly 174 will
be resolved into an axial separation of the cone members 152
and 154, the normal force development at both points Pl and
P2 will increase in proportion to the load on the output
shaft 116. The magnitude of torque transmitted by the cam
assembly 176 will be only one-half the magnitude of the torque
load at the gear 144 because it is the torque carried only
by the cone member 152. The magnitude of the axial force
component developed by the cam assembly 176, however, and
the resulting normal force loading at the contact points Pl
and P2 will be a function of the ramp angle of the engaged
camming surfaces 186 and 188. By design of the ramp angle,
therefore, the normal force loading of the conical surfaces
148 and 150 against the rings 132 and 134 may be made
proportional to torque loads on the output shaft.
Thus it will be seen that as a result of the
present invention, an improved torque transmitting body
structure is provided for continuously variable torque
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113733S
transmissions of the type exemplified in the drawings. In
both embodiments, the integral extension of the cone members
to provide substantially the complete support of the biconical
body takes maximum advantage of the biconical geometry of
the body as well as the materials used in the cones to
resist bending loads imposed on the body. The embodiment of
Figs. 2-6 further demonstrates such additional characteristics
as simplicity and adaptability of the structure either to a
hollow construction as shown or to a solid cone construction
at least of the cone 154 and pilot cone 170. This latter
characteristic also paves the way to consideration of
materials other than high strength bearing alloys for use in
the cones, such as less expensive steels and synthetic
resinous or plastic materials, particularly in transmissions
designed for power transmitting capacities which, though
lower than the demonstrated power transmitting capacity of
existing prototypes of the general class of transmissions
under consideration, would have wide application in many
fields.
Modifications and/or changes in the illustrated
embodiment are, therefore, contemplated and thus will be
apparent to those skilled in the art from the preceding
description. Accordingly, it is expressly intended that the
foregoing description and accompanying drawing illustrations
are of preferred embodiments only, not limiting, and that
the true spirit and scope of the present invention be determined
by reference to the appended claims.
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