U.S. patent application number 09/759883 was filed with the patent office on 2002-07-18 for dual mode, geared neutral continuously variable transmission.
Invention is credited to Haka, Raymond James.
Application Number | 20020094911 09/759883 |
Document ID | / |
Family ID | 25057310 |
Filed Date | 2002-07-18 |
United States Patent
Application |
20020094911 |
Kind Code |
A1 |
Haka, Raymond James |
July 18, 2002 |
DUAL MODE, GEARED NEUTRAL CONTINUOUSLY VARIABLE TRANSMISSION
Abstract
A powertrain has a continuously variable transmission that
incorporates a continuously variable unit in the form of a belt
drive, a summing differential gearing assembly in the form of a
planetary gear set and a plurality of torque transmitting
mechanisms. A continuous mechanical input path is provided between
an engine and one member of the summing differential gearing
assembly. One of the torque transmitting mechanisms are selectively
engaged to provide a low continuously variable reverse range,
neutral condition and a continuously variable low forward range
between the transmission input and output shafts. Another of the
torque transmitting mechanisms is selectively engaged to establish
a continuously variable high forward range between the transmission
input and output shafts. A third torque transmitting mechanism is
selectively engaged to establish a fixed mechanical ratio drive
path between the transmission input and output shafts. The fixed
mechanical ratio may be utilized during the high forward range if
desired to provide an efficient operating ratio.
Inventors: |
Haka, Raymond James;
(Brighton, MI) |
Correspondence
Address: |
General Motors Corporation
Legal Staff
Mail Code 482-C23-B21
P.O. Box 300
Detroit
MI
48265-3000
US
|
Family ID: |
25057310 |
Appl. No.: |
09/759883 |
Filed: |
January 16, 2001 |
Current U.S.
Class: |
477/211 |
Current CPC
Class: |
F16H 37/0846 20130101;
F16H 2037/088 20130101; F16H 61/66254 20130101 |
Class at
Publication: |
477/211 |
International
Class: |
F16H 037/02 |
Claims
1. A powertrain having a continuously variable transmission, said
transmission comprising: an input shaft connected to receive power
from an engine; an output shaft connected to deliver power from
said transmission; a continuously variable unit having a CVU input
member continuously connected with said input shaft and a CVU
output member; a summing differential gearing assembly having a
first differential input member continuously connected for common
rotation with said input shaft to provide a continuous fixed ratio
input drive to said summing differential gearing assembly, a second
differential input member, and a differential output member
continuously connected for common rotation with said output shaft;
a first torque transmitting mechanism operatively connectable
between said CVU output member and said second differential input
member to deliver a variable ratio input drive to said summing
differential gearing assembly in a rotational direction opposite
the rotational direction of said fixed ratio input drive; a second
torque transmitting mechanism operatively connectable between said
CVU output member and said output shaft to deliver a variable ratio
drive between said input shaft and said output shaft in bypassing
relation to said summing differential gearing assembly; and said
continuously variable unit being adjustable to deliver drive ratios
within a range of values including a maximum overdrive ratio and a
maximum underdrive ratio.
2. The transmission defined in claim 1 further comprising: a third
torque transmitting mechanism selectively operatively connectable
between said input shaft and said output shaft to provide a fixed
mechanical ratio therebetween.
3. The transmission defined in claim 2 further comprising: said
fixed mechanical ratio having a value within said range of values
including said maximum underdrive ratio and said maximum overdrive
ratio.
4. The transmission defined in claim 2 further comprising: said
third torque transmitting mechanism being disposed in bypass power
flow relation with said summing differential gearing assembly.
5. The transmission defined in claim 1 further comprising: said
summing differential gearing assembly comprising a planetary gear
set having at least a sun gear member and a planet carrier assembly
member and a third member, said first differential input member
being the sun gear member.
6. The transmission defined in claim 5 further comprising: said
planet carrier assembly being either said second differential input
member or said differential output member and said third member
being the other of said second differential input member and said
differential output member.
7. A powertrain having a continuously variable transmission, said
continuously variable transmission comprising: an input shaft for
receiving power from a prime mover; an output shaft for delivering
power from said continuously variable transmission; a continuously
variable ratio unit comprising a first selectively variable
diameter pulley, a second selectively variable diameter pulley, and
a flexible drive transmitter engaging said first and second
pulleys, said input shaft being continuously connected with said
first pulley, said pulleys being controllable to provide a
continuously variable ratio between said input shaft and said
second pulley within a predetermined range; a summing differential
gearing assembly having a first input member continuously connected
with said input shaft to establish a mechanical drive path thereto,
a second input member, and a third member being continuously
connected with said output shaft; a first torque transmitting
mechanism selectively, operatively connectable between said second
pulley and said second input member for establishing a variable
ratio path thereto; a second torque transmitting mechanism
selectively operatively connectable between said second pulley and
said output shaft for establishing a variable ratio path thereto in
bypassing relation to said summing differential gearing assembly;
and a third torque transmitting mechanism selectively operatively
connectable between said mechanical drive path and said output
shaft to establish a discrete drive ratio therebetween at a value
encompassed by said predetermined range.
8. The continuously variable transmission defined in claim 7
further comprising: said first variable diameter pulley being
continuously rotatable with said mechanical drive path; and said
first input member of said summing differential gearing assembly
being a sun gear member, said second input member of said summing
differential gearing assembly being one of a sun gear member and a
planet carrier assembly member, and said third member of said
summing differential gearing assembly being a planet carrier
assembly member when said second member of said summing
differential gearing assembly is a sun gear member and being a ring
gear member when said second member of said summing differential
gearing assembly is a planet carrier assembly member.
9. The continuously variable transmission defined in claim 7
further wherein: power delivered to said mechanical path
continuously rotates said first input member of said summing
differential gearing assembly in a first directional sense, and
power delivered to said variable ratio path rotates said second
input member of said summing differential gearing assembly in an
opposite directional sense when said first torque transmitting
mechanism is operative and rotates said output shaft in said first
directional sense when said second torque transmitting mechanism is
operative, and said power delivered to mechanical path rotates said
output shaft in said first directional sense.
10. The continuously variable transmission defined in claim 9
further wherein: said second torque transmitting mechanism and said
third torque transmitting mechanism are simultaneously operative
when the variable ratio path and the discrete ratio are rotating
said output shaft at substantially the same speed.
11. The continuously variable transmission defined in claim 9
further wherein: said second torque transmitting mechanism and said
third torque transmitting mechanism are simultaneously operative
when the variable ratio path and said mechanical path operating at
the discrete ratio are rotating said output shaft at substantially
the same speed, and said third torque transmitting mechanism being
selectively inoperative when the ratio of the variable ratio path
is adjusted upward from said discrete ratio.
12. The continuously variable transmission defined in claim 9
further wherein: said second torque transmitting mechanism and said
third torque transmitting mechanism are simultaneously operative
when the variable ratio path and said mechanical path operating at
the discrete ratio are rotating said output shaft at substantially
the same speed, and said third torque transmitting mechanism being
selectively inoperative when the ratio of the variable ratio path
is adjusted downward from said discrete ratio.
Description
TECHNICAL FIELD
[0001] This invention relates to continuously variable
transmissions (CVT) with a geared neutral condition.
BACKGROUND OF THE INVENTION
[0002] Continuously variable transmissions generally employ a
continuously variable unit (CVU) such as a belt and sheave
mechanism, electric motor/generator systems, or hydraulic
pump/motor systems. The electrical and hydraulic units can achieve
a neutral condition by simply not supplying energy to the drive
unit (i.e. the motor). Belt and sheave mechanisms however, must
incorporate either a clutch mechanism or a summing differential
gearing assembly that will permit the output speed to be zero while
the input speed is not zero.
[0003] One such unit can be found in U.S. Pat. No. 4,644,820 issued
to Macey and Vahabzadeh (Macey et al.) on Feb. 24, 1987. This
patent incorporates two selectively engageable friction clutches
and one one-way clutch, in the mechanical power path, between the
input shaft, driven by a prime mover, and an input member of the
summing differential gearing assembly. The CVU output is
continuously connected with another input member of the summing
differential gearing assembly. To achieve a high ratio drive
through the CVU, the input clutches in the mechanical power path
must be disengaged.
[0004] The Macey et al. patent does not permit a mechanical high
range drive condition. Thus, the efficiency loss of the CVU is
always present during the operation of the CVT. The incorporation
of two friction clutches and a oneway clutch adds to the complexity
of the transmission without additional benefit from the mechanical
power path. Also this patent requires a total of three selectively
engageable clutches and a one-way clutch to establish a low range
and a high range of operation.
SUMMARY OF THE INVENTION
[0005] It is an object of the present invention to provide an
improved continuously variable transmission.
[0006] In one aspect of the present invention, a variable ratio
belt drive path, a direct mechanical drive path, and a planetary
gear set are disposed in a power path between an input shaft and an
output shaft to provide a geared neutral condition, a forward
continuously variable range and a reverse continuously variable
range. In another aspect of the present invention, the planetary
gear set operates as a summing differential gearing assembly or
unit during a low forward range and a reverse range and is bypassed
during a continuously variable high forward range during which only
the variable ratio belt drive path is active.
[0007] In yet another aspect of the present invention, a discrete
mechanical path is provided between the input shaft and the output
shaft in bypassing relation with the summing differential gearing
assembly. In still another aspect of the present invention, the
discrete mechanical path provides a discrete ratio at a point
within the continuously variable high forward range or at the upper
end of the continuously variable high forward range to thereby
establish an efficient operating point in the power path.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a schematic representation of an embodiment of a
CVT incorporating the present invention.
[0009] FIG. 2 is a schematic representation of another embodiment
of a CVT incorporating the present invention.
[0010] FIG. 3 is a plot of engine speed and vehicle speed for a
plurality of throttle settings which describe some of the operating
characteristics of the CVT described in FIG. 2.
[0011] FIG. 4 is a schematic representation of yet another
embodiment of a CVT incorporating the present invention.
DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0012] A powertrain 10, illustrated in FIG. 1, has an engine 12, a
continuously variable transmission (CVT) 14, and a final drive 16.
The engine 12 and final drive 16 are conventional mechanical
assemblies that are wellknown as to construction and operation. The
CVT 14 includes an input shaft 18, an output shaft 20, a
continuously variable unit (CVU) 22 and a summing differential
gearing assembly 24. The input shaft 18 is connected with the
engine 12 for common rotation therewith, and the output shaft 20 is
connected with the final drive 16 to provide input rotation
thereto.
[0013] The CVU 22 is a conventional friction drive or traction unit
such as a belt and sheave mechanism having an input sheave or
pulley 26, an output sheave or pulley 28 and a flexible belt 30
rotatably interconnecting the pulleys 26 and 28. The construction
and operation of the CVU is well-known. The relative axial
positions of the half sheaves of each of the pulleys 26 and 28 is
controlled by a hydraulic pressure and spring in a well-known
manner. The drive ratio between the pulleys 26 and 28 is determined
by the effective radius at which the belt 30 and the pulleys 26 and
28 are in frictional contact. As the axial spacing of the half
sheaves of the pulley 26 is widened, the spacing between the half
sheaves of the pulley 28 will be reduced which results in a
reduction of the speed ratio between the pulleys 26 and 28. A
maximum underdrive ratio is established when the axial spacing in
the pulley 26 is at a maximum and the axial spacing of the pulley
28 is at a minimum, and a maximum overdrive ratio is established
when the axial spacing of the pulley 26 is at a minimum and the
axial spacing of the pulley 28 is at a maximum. In order to provide
the maximum torque capacity for the CVU, the belt 30 is preferably
constructed with a plurality of metal blocks secured in a
continuous loop by a plurality of metal bands. This is a well-known
construction.
[0014] The input pulley 26 is continuously connected with the input
shaft 18 through a pair of meshing transfer gears 32 and 34. The
input pulley 26 rotates in a direction opposite the engine
rotation. For the purpose of this disclosure, the engine rotary
direction will be considered to be clockwise (CW) and the speed
value will be considered to be unity. Thus the input pulley 26 will
rotate counterclockwise (CCW). The output pulley 28 will also
rotate CCW.
[0015] A shaft 36 is connected with the output pulley 28 and with a
sprocket 38 which in turn is connected by a chain 40 to a sprocket
42. The sprocket 38 is operatively connected with a selectively
engageable, fluid operated rotatable torque transmitting mechanism
(clutch) 44 and the sprocket 42 is operatively connected with a
selectively engageable, fluid operated rotatable torque
transmitting mechanism (clutch) 46. The torque transmitting
mechanisms 44 and 46 are conventional mechanisms that are
controlled in engaged and disengaged conditions by a conventional
electro-hydraulic control system, not shown, which includes a
programmable digital computer. The electro-hydraulic control also
provides the pulleys 26 and 28 with pressurized hydraulic fluid to
control the axial spacing of the half sheaves thereof. The torque
transmitting mechanism 44 is also operatively connected with a
transfer gear 48 that is disposed in meshing relation with a
transfer gear 50 which is continuously connected with the output
shaft 20. The torque transmitting mechanism 46 is operatively
connected with a sleeve shaft 52 which is continuously connected
with a sun gear member 54, a component of the summing differential
gearing assembly 24.
[0016] The summing differential gearing assembly 24 also includes a
sun gear member 56 and a planet carrier assembly member 58. The sun
gear member 56 is continuously connected with the input shaft 18
and therefore rotates in a CW direction with the engine 12. The
planet carrier assembly member 58 includes a carrier 60 that
rotatably supports a plurality of short pinion gear members 62 and
a plurality of long pinion gear members 64. The short pinion gear
members 62 and the long pinion gear members 64 are disposed in
intermeshing relation. The short pinion gear members 62 also mesh
with the sun gear member 54. The long pinion gear members 64 also
mesh with the sun gear member 56. The sun gear member 54 rotates in
unison with the sprocket 42 when the torque transmitting mechanism
46 is engaged. The direction of rotation of the sun gear member 54
is CCW when the torque transmitting mechanism 46 is engaged which
is the direction of rotation of the pulley 28. The planet carrier
assembly member 58 is continuously connected with the output shaft
20. The direction of rotation of the carrier 60 of the planet
carrier assembly member 58 is determined by the rotary speed and
tooth ratio of the sun gear members 54 and 56.
[0017] Since the speed of the sun gear member 56 and the input
pulley 26 are fixed, relative to the input shaft 18, the carrier 60
can be made to rotate both forward (engine direction) and backward.
Therefore, the output shaft 20 has a forward range and a reverse
range depending on the speed ratio of the CVU 22. The speed ratio
of the CVU 22 is controllable between a maximum underdrive and a
maximum overdrive. At the maximum overdrive ratio, the sun gear
member 54 will rotate CCW at its fastest speed and the output shaft
20 will rotate CCW at the maximum speed of the reverse range when
the torque transmitting mechanism 46 is engaged and the torque
transmitting mechanism 44 is disengaged. During the ratio change in
the CVU 22 from the maximum underdrive to the maximum overdrive,
the rotation of the output shaft 20 will change from forward to
reverse. This is a geared neutral condition. Both sun gear members
54 and 56 are rotating but the carrier 60 and output shaft 20 are
stationary.
[0018] At the maximum underdrive condition in the CVU 22, the
transfer gear 48 is rotating at the same speed as the transfer gear
38. Therefore, the torque transmitting mechanism 44 can be engaged
without slippage (synchronous engagement) and the torque
transmitting mechanism 44 is simultaneously disengaged. This will
effectively disconnect the power flow through the summing
differential gearing assembly 24 and connect the power flow path
through the transfer gears 48 and 50. When the torque transmitting
mechanism swap is completed, the ratio of the CVU 22 can be
manipulated toward the maximum overdrive condition to further
increase the speed of the output shaft 20. This is the high forward
range. All of the power flow is directed through the CVU 22 during
this range.
[0019] A powertrain 100, shown in FIG. 2, includes a conventional
engine 102, a CVT 104, and a conventional final drive gearing 106.
The CVT 104 has an input shaft 108, an output shaft 110, a CVU 112
and a summing differential gearing assembly 114. The CVU 112 is a
conventional friction or traction drive which is illustrated as
being a belt and pulley mechanism. The CVU 112 has an input pulley
116, an output pulley 118 and a flexible belt 120 that frictionally
engages the pulleys 116 and 118. The pulleys 116 and 118 have
sheave halves that are axially adjustable to vary the drive ratio
therebetween with hydraulic power supplied by a conventional
electro-hydraulic control, not shown.
[0020] The input shaft 108 is continuously connected with a
transfer gear 122 and a sun gear member 124 of the summing
differential gearing assembly 114. The transfer gear 122 meshes
with a transfer gear 126 that is drivingly connected with a
transfer shaft 128 which is continuously connected with the input
pulley 116 and operatively connected with a fluid operated,
selectively engageable torque transmitting mechanism 130. The
torque transmitting mechanism 130 is also operatively connected
with a transfer gear 132 such that when, the torque transmitting
mechanism 130 is engaged, the transfer gear 132 will rotate with
the transfer shaft 128 at a speed proportional to the speed of the
input shaft 108. The transfer gear 132 meshes with a transfer gear
134 that is fixed for common rotation with the output shaft
110.
[0021] The output pulley 118 is secured to a transfer shaft 136
that is continuously connected with a transfer sprocket 138 and
operatively connected with a fluid operated, selectively engageable
torque transmitting mechanism 140 which is operatively connected
with a transfer gear 142. When the torque transmitting mechanism
140 is engaged, the transfer gear 142 will rotate in unison with
the output pulley 118. The transfer gear 142 is disposed in meshing
relation with the transfer gear 134.
[0022] The transfer sprocket 138 is connected by a chain 144 with a
transfer sprocket 146 that is operatively connected with a fluid
operated, selectively engageable torque transmitting mechanism 148
which is operatively connectable with a planet carrier assembly
member 150 of the summing differential gearing assembly 114. When
the torque transmitting mechanism 148 is engaged, the planet
carrier assembly member 150 will rotate in unison with the sprocket
146 at a speed proportional to the speed of the output pulley 118.
The planet carrier assembly member 150 includes a carrier member
152 that rotatably supports a plurality of intermeshing pinion gear
members 154 and 156 that mesh, respectively, with the sun gear
member 124 and a ring gear member 158. The ring gear member 158 is
continuously connected with the output shaft 110.
[0023] The sun gear member 124 rotates in the same direction as the
input shaft 108 and at a speed equal to the speed of the input
shaft 108. The input pulley 116 rotates in a direction opposite to
the input shaft 108 and at a speed proportional to the speed of the
input shaft 108 as determined by the tooth ratio of the transfer
gears 122 and 126. The output pulley 118 rotates in the same
direction as the input pulley 116 at a speed proportional thereto
as determined by the ratio of the effective diameters of the
pulleys 116 and 118. This ratio is variable between a maximum
underdrive ratio and a maximum overdrive ratio.
[0024] The sun gear member 124 rotates in the same direction as the
engine 102 and the input shaft 108. When the torque transmitting
mechanism 148 is engaged, the carrier 152 member rotates in the
opposite direction. The ring gear member 158 rotates in a direction
as determined by the speed of the sun gear member 124, the carrier
member 152 and the tooth ratio of the ring gear member 158 and the
sun gear member 124. The ring gear member 158 can rotate forwardly
(engine direction) or reversely (CVU direction). As with the CVT
14, the CVT 104 has a geared neutral condition at which the sun
gear member 124 (engine speed/unity) and the carrier member 152
(CVU ratio) are rotated at speeds that permit the speed of the ring
gear member 158 to be zero.
[0025] When the ratio of the CVU 114 is adjusted from the neutral
condition toward the maximum overdrive condition, the output shaft
110 will rotate opposite to the rotational direction of the input
shaft 108. When the ratio of the CVU 114 is adjusted toward the
maximum underdrive ratio, the output shaft 110 will rotate in the
same direction, at a reduced ratio, as the input shaft 108.
[0026] When the ratio of the CVU 114 is at the maximum underdrive
ratio, the shaft 136 and the transfer gear 142 are rotating at the
same speed which permits a synchronous engagement of the torque
transmitting mechanism 104 while the torque transmitting mechanism
148 is disengaged. The output shaft speed will remain constant
through the torque transmitting mechanism interchange. After the
interchange, the ratio of the CVU 114 is adjusted toward the
maximum overdrive ratio to increase the speed of the output shaft
110 up to the maximum vehicle speed.
[0027] The transfer gear 132 is rotated at a speed proportional to
the speed of the input shaft 108 when the torque transmitting
mechanism 130 is engaged. This will establish a fixed mechanical
ratio between the engine 102 20 and the output shaft 110. This
fixed ratio is determined by the tooth ratio of the transfer gears
122 and 126 and the tooth ratio of the transfer gears 132 and
134.
[0028] The fixed mechanical ratio is preferably designed to occur
between the limits of the ratio range of the CVU 114. This will
permit a mechanical power path, consisting of the transfer gears
122, 126, 132, and 134, to be established during 25 the operation
of the vehicle to provide an efficient operating ratio during the
forward high range. The fixed mechanical ratio and the ratio of the
CVU power path are equal at some point during the forward high
range. At this point the torque transmitting mechanism 130 is
engaged and the torque transmitting mechanism 140 can remain
engaged. To permit extended operation at the fixed 30 mechanical
ratio, the CVU ratio is decreased to match the fixed mechanical
ratio, the vehicle is then permitted to accelerate along the fixed
ratio path for a brief interval, and the CVU ratio is then
re-established at the higher vehicle speed.
[0029] An alternative operating schedule is also possible with the
present invention. During this alternate schedule, the fixed
mechanical ratio is engaged (torque transmitting mechanism 130
engaged) at a first throttle setting (20%) and the CVU power path
is disconnected (torque transmitting mechanism 140 released). The
throttle setting is then increased to permit increased vehicle
speed using the mechanical power path for improved fuel efficiency.
At a higher throttle setting (i.e. 50%), the CVU power path is
re-established (torque transmitting mechanism 140 engaged) and the
mechanical power path is released (torque transmitting mechanism
130 disengaged). The ratio of the CVU 112 will be the same before
and after the use of the fixed mechanical ratio. By way of example,
the CVU ratio can vary to establish an overall ratio from 0.30
underdrive to 1.80 overdrive. The fixed mechanical ratio can be
designed to be equal to an overall ratio of 1.40. Thus, whenever
the overall ratio is to pass through the 1.40 ratio, the mechanical
power path can be utilized to improve the operating efficiency of
the vehicle.
[0030] This operation is depicted in the plot of operating
characteristics shown in FIG. 3. The engine throttle is adjusted
along the maximum underdrive ratio to increase the vehicle speed.
When a desired throttle setting is achieved, as shown at line 160,
the CVU ratio is adjusted toward the maximum overdrive ratio. The
CVU ratio is continuously varied until the ratio is slightly
greater than the fixed mechanical ratio at which point the torque
transmitting mechanism 130 is engaged and all of the engine power
passes through the mechanical power path. Due to the increase in
overall efficiency, the vehicle speed will increase along the fixed
mechanical ratio between the points 162 and 164 at which time the
torque transmitting mechanism 130 will be disengaged and the CVU
power path will be re-established.
[0031] An alternative operating process is also available. During
this operating sequence, the torque transmitting mechanism 130 is
engaged and the torque transmitting mechanism 140 is disengaged at
the throttle setting represented by the line 160. The engine
throttle is then increased until a throttle setting represented by
the line 166 is reached and the torque transmitting mechanisms 130
and 140 are interchanged at the point and the CVU ratio is adjusted
toward the maximum overdrive ratio along the throttle line 166. It
should be noted that the vehicle speed was increased from point 162
to point 168 during this procedure by a change in throttle position
only. The high efficiency of the mechanical power path is employed
during this speed change. As is well-known, the CVU 112 undergoes
some slippage of the belt 120 at the pulleys 116 and 118 which
accounts for the efficiency loss. For this reason, the CVU ratio is
slightly higher than the fixed mechanical ratio during the
interchanges. The slight ratio change necessary is accommodated by
the torque transmitting mechanisms 130 and 140.
[0032] A powertrain 200, shown in FIG. 4, includes a conventional
engine 202, a CVT 204 and a conventional final drive gearing 206.
The CVT 204 has an input shaft 208, an output shaft 210, a CVU 212
and a summing differential gearing assembly 214. The CVU 212 is
comprised of an input pulley 216, an output pulley 218 and a
flexible belt 220 that interconnects the pulleys 216 and 218 to
transmit power therebetween. The pulleys 216 and 218 have sheaves
that can be adjusted in the axial direction to change the drive
ratio therebetween. The input shaft 208 is drivingly connected with
the engine 202 and a sprocket 222. The sprocket 222 is connected
with a sprocket 224 through a chain 226. Both sprockets 222 and 224
rotate in the same direction as the engine 202.
[0033] The sprocket 224 is connected with a shaft 228 that is also
drivingly connected with the input pulley 216 and a sprocket 230.
The sprocket 230 is drivingly connected with a sprocket 232 by a
chain 234. The sprocket 232 is connected for continuous co-rotation
with a shaft 236. The input pulley 216, output pulley 218, sprocket
230, sprocket 232 and shaft 236 all rotate in the same direction as
the engine 202.
[0034] The shaft 236 is continuously drivingly connected with a sun
gear member 238 of the summing differential gearing assembly 214.
The summing differential gearing assembly 214 also includes a ring
gear member 240 and a planet carrier assembly member 242 that has a
planet carrier 244 on which is rotatably mounted a plurality of
pinion gear members 246 that mesh with both the sun gear member 238
and the ring gear member 240. The planet carrier 244 is
continuously connected with the output shaft 210 and operatively
connected with a torque transmitting mechanism 248 which is also
operatively connected with the sprocket 232 and sun gear member 238
through the shaft 236. The torque transmitting mechanism 248 is a
conventional fluid operated, selectively engageable mechanism that,
when engaged, will cause the sun gear member 238 and the planet
carrier 244 to rotate in unison with the output shaft 210.
[0035] The output pulley 218 is continuously connected for common
rotation with a shaft 250 that is operatively connected with a pair
of conventional fluid operated, selectively engageable torque
transmitting mechanisms 252 and 254. The torque transmitting
mechanism 252 is operatively connected with a transfer gear 256
that meshes with a transfer gear 258 which in turn is continuously
drivingly connected with the ring gear member 240 through a hub
260. When the torque transmitting mechanism 252 is engaged, the
ring gear member 240 will rotate at a speed proportional to the
output pulley 218 but in a direction opposite thereto. The drive
ratio between the output pulley 218 and the ring gear member 240 is
determined by the tooth ratio of the transfer gears 256 and
258.
[0036] The torque transmitting mechanism 254 is operatively
connected with a sprocket 262 which is continuously connected with
a sprocket 264 through a chain 266. The sprocket 264 is
continuously connected with the output shaft 210. When the torque
transmitting mechanism 254 is engaged, the output pulley 218 and
the output shaft 210 will rotate in unison. The drive ratio between
the output pulley 218 and the output shaft 210 is determined by the
tooth ratio of the sprockets 262 and 264. The output shaft 210 will
rotate in the same direction as the engine 202 when the torque
transmitting mechanism 254 is engaged. The overall ratio between
the engine 202 and the output shaft 210 is determined by the ratio
of the CVU 212 and the tooth ratio of the sprockets 222 and 224 and
the tooth ratio of the sprockets 262 and 264.
[0037] When the torque transmitting mechanism 252 is engaged, the
CVT 204 is conditioned to provide a reverse range, a geared neutral
condition, and a low forward range. During the engagement of the
torque transmitting mechanism 252, the sun gear member 238 and the
ring gear member 240 are rotating in opposite directions. The sun
gear member 238 rotates in the same direction as the engine 202 at
a ratio relative thereto that is determined by the tooth ratio of
the sprockets 222 and 224 and the tooth ratio of the sprockets 230
and 232. The ring gear member 240 rotates opposite the direction of
the engine 202 at a ratio determined by the tooth ratio of the
sprockets 222 and 224 and the drive ratio of the CVU 212. Thus the
speed of the ring gear member 240 can be varied within the range of
the CVU ratio which is adjustable between a maximum underdrive and
a maximum overdrive. Since the speed and direction of the planet
carrier 244 of the planet carrier assembly member 242 is determined
by the tooth ratio of the ring gear member 240 and the sun gear
member 238 and the speed and direction of the sun gear member 238
and the ring gear member 240, the speed of the planet carrier 244
and therefore output shaft 210 is variable. The planet carrier can
be rotated at a maximum reverse speed when the CVU ratio is at a
maximum overdrive ratio and at a maximum low forward range speed
when the CVU ratio is at a maximum underdrive ratio. At a
predetermined ratio of the CVU between these maximum extremes, the
planet carrier 244 and the output shaft 210 will be stationary
(geared neutral).
[0038] When the maximum underdrive ratio is set at the CVU 212, the
sprocket 262 will be rotating at the same speed as the output
pulley 218 and the shaft 250. When this condition is achieved, the
torque transmitting mechanisms 252 and 254 are synchronously
interchanged and the CVT 204 is conditioned for a high forward
range. During the high forward range, the CVU ratio is varied from
the maximum underdrive ratio toward the maximum overdrive ratio to
increase the speed of the output shaft 210. During this forward
range, the torque transmitting mechanism 248 can be engaged at a
specific predetermined overall ratio of the CVT 204. As described
above for the CVT 104 of FIG. 2, with reference to the operating
characteristics described in FIG. 3, a mechanical drive path is
established which increases the operating efficiency of the
CVT.
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