Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVEMENTS IN OR RELATING TO TRANSMISSIONS
OF THE TORODIAL-RACE ROLLING-TRACTION TYPE
This invention relates to continuously-variable-ratio
transmissions (Which will be referred to as CVT~s) of the
toroidal-race, rolling-traction type, and it relates in
particular to CVT~s as described in the specification of
Canadian patent application No. 2,003,334, which was filed on
20th November, 1989 and which claims priority under the
International Convention from UK Patent Application No.
8827140, filed 21st November, 1988.
The present invention relates to a roller control system
for a CVT of the toroidal-race, rolling-traction type in which
a roller is mounted to spin in a carriage and transmits
traction between coaxial rotatable discs presenting input and
output races conforming to different parts of the surface of a
single imaginary torus and is free to rotate about a diameter
and so to change the transmitted ratio, in which an operating
mechanism is reciprocable over a predetermined stroke of
operating movement and is operable to apply a predetermined
control force to the carriage, and in which the operating
mechanism and roller assembly seek an equilibrium position and
ratio in which the resultant of the control force and of the
traction forces experienced by the roller assembly in a plane
at right angles to the axis of the discs is zero. Such a
roller control system Will now be referred to as a roller
control system of the kind described. While the prior art
teaches and the invention will be described With relation to
toruses of circular cross-section, the invention includes CVT~s
in which the torus is generated by rotating any closed figure,
of generally curved outline, about a generator line.
According to one aspect of the present invention, in a
roller control system of the kind described, the operating
mechanism includes a first piston moveable within a first
cylinder, this piston and cylinder combination is single-acting
and capable of
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exerting a force in a first direction, a second piston and
cylinder are provided capable of exerting a force in a second and
substantially opposite direction) and the second piston and
carriage are separate items which abut each other in use in a
05 non-interlocking manner. Preferably the second piston and
cylinder are so disposed, relative to the carriage) that
depression of the second piston within its cylinder facilitates
the assembly of the carriage and roller within the CVT) by
allowing easy access of the first piston into its cylinder) and
easy introduction of the roller into contact with the discs
between: which it is to transmit traction. Once assembly is
complete) and the second cylinder is pressurised when the CVT is
brought into use, the second piston will be driven out of its
cylinder and into working abutment with the carriage.
According to another aspect of the present invention the
operating mechanism of a roller control system of the kind
described includes a single-acting first piston moveable within a
first cylinder which determines the motion of the roller
carriage. The cylinder is in communication with a hydraulic
operating circuit, and the cross-section of the connexion between
the cylinder and that circuit is large in comparison with the
cross-section of conventional hydraulic inlet and outlet ports.
An important consequence of this enhanced-area connexion is less
resistance to fluid flow into and out of the cylinder when the
piston moves suddenly in response to sudden changes in operating
conditions - for instance a crash stop or a quick change from
normal to icy road surface when the CVT is fitted to a road
vehicle - and thus less tendency for the pressure within the
cylinder to take up a spurious value because fluid cannot enter
or leave the cylinder quickly enough. Preferably the full bore
of the back end of the cylinder is in communication with the
circuit. The part of the circuit conduit with which the cylinder
bore communicates may be a gallery formed within the CVT casing,
and the gallery may be ring-like in shape) and coaxial with the
main CVT axis. Preferably the gallery conforms to the shape of
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only an incomplete ring, the break in the ring allowing access
for other components to pass through the CVT casing. Where a
second piston and cylinder are provided to exert a force in a
second and substantially opposite direction upon the roller
05 carriage, the second cylinder may be in communication with a
second gallery, with like effect. Where a plurality of rollers -
typically three - transmit traction between coaxial rotatable
discs in a CVT of the toroidal-race) rolling-traction type, the
first and second galleries may be common to the first and second
cylinders of the operating mechanisms of all three such rollers.
In a so-called "double-ended" CVT of the toroidal-race, rolling-
traction type) as shown for instance in patent specification
US-A-4297918, having two separate but symmetrically-arranged sets
of torque-transmitting rollers, both sets of rollers may have
first and second galleries, the first galleries of the two sets
may be connected so that the fluid pressures within them are
equal, and the second galleries may be similarly connected.
According to this aspect of the invention- it is also advantageous
that the same hydraulic circuit should generate the appropriate
contact forces between the rollers and the discs by exerting an
end load on the discs, and that the parts of the circuit in
communication with the end- load and roller control cylinders
should be separated by no substantial resistance, so that
substantially equal pressures exist in these two parts of the
circuit at all times. The requirement to put the input and
output discs under an appropriate end load, that is to say an
axially load urging them together and into the appropriate
reaction with the rollers between them, is well understood in the
art. Many prior patent specifications) for instance US-A-4297918
and US-A-4524641) describe and illustrate the generation of the
end load by hydraulic means.
According to another aspect of the present invention, the
operating mechanism of a roller control system of the kind
described includes pistons moveable within cylinders in
communication with a hydraulic operating circuit. The geometry
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of the pistons and their cylinders may be such that whenever a
piston approaches the end of its permitted stroke (thus
indicating an "overload" or other emergency condition of the
transmission), it creates an obstruction within the circuit and
causes a rise in fluid pressure upstream of the obstruction
which acts to oppose further overshoot. Where a sat of rollers
- typically three - transmit traction between two discs, and
especially where two related such sets of rollers are used as
in a "double-ended" CVT, the cylinders of all the rollers may
be connected in parallel to the same hydraulic circuit, so that
the pressure rise is generated at the pistons associated with
only one or two of the rollers, but acts upon the operating
mechanisms of the others.
The invention may be summarized, according to one aspect
as a CVT of the toroidal race, rolling traction type in which a
roller assembly comprises a carriage, bearings mounted on the
carriage and a roller defining a roller centre and supported by
the bearings, for rotation about a roller axis, in which the
roller contacts and transmits traction forces between coaxial
rotatable discs, presenting input and output races conforming
to different parts of the surface of a single torus and is
subjected to traction forces at disc/roller contacts, and a
double-acting operating mechanism having a fixed part and a
moveable part, the moveable part being reciprocal over a
predetermined stroke of operating movement and operable to
apply a control force to the carriage, and in Which the
operating mechanism and carriage seek an equilibrium position
in which the resultant of the control force and of the traction
forces experienced by the roller assembly is zero, wherein: the
single torus defines a mid-planet the carriage includes a rigid
structure relative to which the roller axis and the roller
centre are fixedf the operating mechanism includes constraint
means defining a single point of constraint which constrains
the operating mechanism to the application of the control force
along a force application axis passing through the constraint
point and the roller centref the constraint point and the
disc/roller contacts form a constant triangular relationship
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the equilibrium position of the roller assembly is determined
by only the two disc/roller contacts and the position of the
constraint pointy and the roller is free to rotate about the
force application axis.
According to another aspect the invention provides a CVT
of the toroidal race rolling traction type in Which a roller
assembly comprises a carriage, bearings mounted on the carriage
and a roller defining a roller centre supported by the
bearings, for rotation about a roller axis, in which the roller
contacts and transmits traction forces between coaxial
rotatable discs, presenting input and output races conforming
to different parts of the surface of a single torus defining a
mid-plane and in so doing are subjected to traction forces at
disc/roller contacts, and an operating mechanism having a fixed
part and a movable part, the movable part being reciprocal over
a stroke of operating movement and operable to apply a
predetermined control force to a location on the carriage, with
the control force acting solely along an axis including both
the location on the carriage and the roller centre and in which
the operating mechanism and carriage seek an equilibrium
position in which the resultant of the control force and of the
traction forces experienced by the roller assembly is zero When
resolved in the same direction in a plane normal to the axis of
the discs, wherein: the carriage includes a rigid structure
relative to Which the roller axis and the roller centre are
fixedt the operating mechanism includes means capable of
effecting translational movement of the roller centre back and
forth along a path dictated by the two disc/roller contactst
means allowing the roller freedom to rotate about a diameter
thereof so as to change the transmitted ratio of the CVT~ the
axis and the roller centre are fixed relative to the carriages
the roller centre is positioned to impose no loads on the
carriage nor on the operating mechanism other than to produce
the balance between the control force and the traction forces
experienced by the roller assembly, in the plane normal to the
axis of the discs and the two disc/roller contacts and the
location at which the control force is applied to the roller
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assembly define a triangular relationship establishing a
triangle of forces acting in the same plane.
According to yet another aspect the invention provides a
CVT of the toroidal race, rolling traction type in Which a
roller assembly comprises a carriage, bearings mounted on the
carriage and a roller defining a roller centre supported by the
bearings, for rotation about a roller axis, in which the roller
contacts and transmits traction forces between coaxial
rotatable discs, presenting input and output races conforming
to different parts of the surface of a single torus defining a
mid-plane and in so doing are subjected to traction forces at
disc/roller contacts, wherein: the roller assembly is supported
at three points only, namely the two contacts of the roller
with the discs and a single point of support defined by a
supported operating mechanism that applies a control force to
the assembly at the point of support, the single point of
support permitting the roller centre to freely follow a path
dictated by the two disc/roller contacts when the roller
assembly is moved by the control force while constraining the
application of the control force to a control axis passing
through the single point of support and the roller centre
the operating mechanism and carriage seek an equilibrium
position in which the resultant of the control force and of the
traction forces experienced by the roller assembly is zero when
resolved in the same direction in a plane normal to the axis of
the discs the roller is free to rotate about the control axis.
According to still another aspect the invention provides a
CVT of the toroidal race, rolling traction type in which a
roller assembly comprises a carriage, bearings mounted on the
carriage and a roller defining a roller centre supported by the
bearings, for rotation about a roller axis, in which the roller
contacts and transmits traction force between coaxial rotatable
discs, presenting input and output races conforming to
different parts of the surface of a single torus defining a
mid-plane and in so doing are subjected to traction forces at
disc/roller contacts wherein: a supported operating mechanism
has means for applying a control force to a roller assembly
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always along a control axis, passing through a single point of
constraint defined by the mechanism and the roller centre,
means at the constraint point allowing the roller centre
freedom to follow a path dictated by the two disc/roller
contacts when the roller assembly is moved by the control
force, the roller being located by only three points, namely
the constraint point and the two disc/roller contacts the
operating mechanism and carriage seek an equilibrium position
in which the resultant of the control force and of the traction
forces experienced by the roller assembly is zero when resolved
in the same direction in a plane normal to the axis of the
discsl the roller is free to rotate about the control axis.
The present invention will now be described, by way of
example, with reference to the accompanying diagrammatic
drawings in whichs-
Figure 1 shows a roller, its carriage and operating
mechanism, partly in elevation and partly in a section taken in
a direction generally at right angles to the axis of the discs
Figure 2 shows a piston of another operating mechanism
Figure 3 shows a hydraulic circuit for use in connection
with the operating mechanism of Figure 2, and
Figure 4 shows part of an alternative hydraulic circuit.
In Figure 1, a roller 60 transmits traction between the
part-toroidal race 85 of an input disc 61 and the corresponding
part-toroidal race 87 of an output disc 62, and is mounted in a
carriage 67 fixed rigidly at one and to a piston 71, the centre
82 of which is constrained to follow the axis 84 of the
cylinder 150 in which it moves. It will be appreciated that
while races 85 and 87 are of part-toroidal shape, as just
stated, the surfaces indicated by references 85 and 87 in
Figure 1 are straight because that part of the Figure is a
section taken in the diametral plane of the roller 60.
According to one aspect of the present invention the opposite
and of carriage 67 is formed as a spherical face 151 which in
use abuts the flat working face 152 of a separate piston 153
moveable within a cylinder 154.
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Carriage 67 and piston 153 are thus not only separate, but also
without any interlock in use, and are therefore to be contrasted
wi th des i gns where there i s , say, a bal 1-i n-socket joi nt between
the carriage and the piston. The construction of Figure 1 of the
05 present application has the advantage that roller 60 can be put
in place between discs 61 and 62 by the following succession of
simple steps
1. With fluid power disconnected, depress piston 153 within
cylinder 154;
2. Insert piston 71 into cylinder 150) and introduce roller
60 between discs 61 and 62 until the crown of face 151 is
substantially aligned with the axis of piston 153;
3. Release piston 153. Then, when the CVT starts to
operate, and input disc 61 rotates and pistons 71 and 153 are
exposed to fluid pressure) roller 60 will take up the correct
orientation and working face 152 will abut spherical face 151
to exert the restoring force which single-acting piston 71
itself cannot exert.
According to another aspect of the present invention) the
inner ends of cylinders 150, 154 are not closed, but the full
bores of these cylinders are in communication with part-annular
galleries 160, 161 formed within the casing 63 of the CVT.
Galleries 160) 161 are each in communication with a fluid source
comprising twin pumps 175 and 176, are associated with control
valve means 43) and also communicate with return line s 162 and
163 as customary. By using valve means 43 to vary the fluid
pressure within gallery 160, piston 71 imparts tangential shift
to carr i age 67 wh i ch wi 11 , as i s we l 1 known i n the art ) have the
effect of causing the carriage and its roller 60 to tilt about
axis 84, so changing the transmitted ratio. If carriage 67 makes
a sudden axial movement in use due to some emergency such as a
crash stop or a change in road surface from normal to icy for
example, the large cross-section of the access between the
galleries 160, 161 and the cylinders facilitates a speedy entry
of fluid into cylinder 150 and exit of fluid from cylinder 154)
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or vice versa. Such a rapid entry or exit of fluid could be
impossible, and give rise to undesirable back pressures, if the
cylinders were blind-ended) and connected to the pressure fluid
circuit by way only of the normal small-bore inlet and outlet
05 ports.
In practice there will be not just one roller 60, but
typically a set of three such rollers transmitting traction
between discs 61 and 62, the rollers being spaced at equal
intervals around the common axis of the discs. The same
galleries 160) 161 may conveniently communicate with the
corresponding pistons 71) 153 of all rollers in the set. Where
there are two such sets of three rollers used together in a
double-ended CVT having two inwardly-facing input discs and a
single double-faced output disc between them, as shown for
instance in Figure 1 of patent specification US-A-4297918)
galleries 160) 161 may communicate with the pistons of one set
and galleries 160a and 161a also formed within casing 63 may
communicate with the pistons of the other set. Galleries 160,
160a are connected by a conduit 177 so that the pressures
existing within them are equal) galleries 161) 161a are connected
to like effect by a conduit 178) and in the example of the
invention shown in Figure 1 the control valve means 43 are
located on the downstream side of galleries 160a) 161a and
therefore communicate with the galleries 160, 161 of the first
set of pistons by way of conduits 177, 178.
The galleries 160, 160a) 161 and 161a are preferably each
only part-annular in shape, the annuli being coaxial with the
discs 61 and 62, so as to leave a sector of the casing 63 that is
free of the galleries and that can therefore be formed with
apertures allowing access to the casing interior.
Piston 71, moving within cylinder 150 in Figure 2 of the
drawings) is modified by an extension 165, the end face 166 of
which meets the side wall 167 at a smoothly curved edge 168. The
edge of return line 162) where it enters gallery 160) is formed
with an angled face at 170. If in use of the CVT an
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overload/abuse condition develops and is reflected in an extreme
axial movement (leftwards) as in Figure 2> of piston 71) surfaces
168 and 170 will approach, so imposing an extra resistance on the
normal flow of fluid out of gallery 160 into return line 162.
05 Pressure in galleries 160 and 160a will therefore rise) and since
the pressure in those galleries operates on all the other pistons
71, all those other pistons will be subjected to an enhanced
force which opposes them as they approach the corresponding
extremes of their ranges of axial movement. A "hydraulic end
stop" effect is therefore set up. Figure 3 diagrammatically
shows one possible practical embodiment in which the fluid source
again comprises twin pumps 175, 176 connected to the galleries
160) 160a, 161) 161a feeding the operating cylinders 150) 154 of
the two sets of cylinders (20, 25> of a double-ended CVT of the
toroidal-race) rolling-traction type. The return lines 162, 163
of the hydraulic circuit connect with the cylinders of only one
roller (60a)) which acts as the "master" for all the other
rollers. Piston 71 of the carriage 67 of this roller carries an
extension 165) which exercises an "end stop" action as already
described) when piston 71 tends to overshoot within cylinder 150)
and piston 153 of that same roller carries a seal 180 which
exercises a similar end stop effect) by approaching cylinder end
wal 1 181 and obstructi ng outl et port 182 ) when that pi ston tends
to overshoot within cylinder 154. It should also be noted that
the end load cylinder 183, which generates the end load force
urging discs 61, 62 into contact with rollers 60) is connected to
a part of the hydraulic circuit which is close to the galleries
and to the roller operating mechanisms, with no substantial
resistance intervening, so that equal pressures exist in the
galleries and cylinder 183 at all times.
Generating the end stop effect by means of the principal
piston (71> of the roller operating mechanism may require
accurate machining of the edge 168 (Figure 2>, which must conform
to part of the surface of a sphere with centre 82. Figure 4
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shows part of an alternative design in which the simpler "second
piston" 153 of one roller (60b) carries a ring seal 180 and
generates the end stop effect in the left-hand side of the
hydraulic circuit when that piston tends to overshoot. The
05 adjacent roller 60c is arranged the other way round so that its
"second" piston 153 is on the right-hand side of the circuit
(corresponding to galleries 161, 161a>, and generates the end
stop effect on that side of the circuit by means of a similar
ring seal 180 when it overshoots.
