U.S. patent application number 09/759768 was filed with the patent office on 2002-07-18 for twin clutch automated transaxle.
Invention is credited to Bowen, Thomas C..
Application Number | 20020092372 09/759768 |
Document ID | / |
Family ID | 25056875 |
Filed Date | 2002-07-18 |
United States Patent
Application |
20020092372 |
Kind Code |
A1 |
Bowen, Thomas C. |
July 18, 2002 |
TWIN CLUTCH AUTOMATED TRANSAXLE
Abstract
An automated twin-clutch multi-speed transmission adapted to
transfer power from the engine to one or more drivelines of a motor
vehicle. The transmission includes a first engine clutch operable
to establish a releasable drive connection between the engine and a
first input shaft, a second engine clutch operable to establish a
releasable drive connection between the engine and a second input
shaft, an output shaft adapted to transfer power to the driveline,
and a geartrain for selectively establishing a plurality of forward
and reverse speed ratio drive connections between the input shafts
and the output shaft. The transmission further includes
power-operated dog clutches for selectively engaging constant-mesh
gearsets associated with the geartrain, and a transmission
controller for controlling coordinated actuation of the first and
second engine clutches and the power-operated dog clutches to
permit non-power interrupted ("powershift") sequential gear changes
automatically without input from the vehicle operator. A clutch
control system includes a first hydraulic pump driven by the first
input shaft for delivering high-pressure fluid to a first control
valve associated with the first engine clutch, a second hydraulic
pump driven by the second input shaft for delivering high-pressure
fluid to a second control valve associated with the second engine
clutch, and flow control valving for controlling fluid flow between
the first and second pumps. When shifting under power between gear
ratios, one engine clutch is released such that the pump associated
with the driven input shaft supplies fluid to the pump associated
with released input shaft for causing acceleration/deceleration of
the released input shaft into synchronization with the output
shaft.
Inventors: |
Bowen, Thomas C.; (Rochester
Hills, MI) |
Correspondence
Address: |
Philip E. Rettig
Harness, Dickey & Pierce, P.L.C.
P. O. Box 828
Bloomfield Hills
MI
48303
US
|
Family ID: |
25056875 |
Appl. No.: |
09/759768 |
Filed: |
January 12, 2001 |
Current U.S.
Class: |
74/339 ; 74/340;
74/730.1 |
Current CPC
Class: |
F16H 3/091 20130101;
F16H 2200/0052 20130101; F16H 2003/0811 20130101; Y10T 74/19149
20150115; Y10T 74/19233 20150115; F16H 3/006 20130101; F16H
2061/0422 20130101; F16H 61/688 20130101; Y10T 74/1926 20150115;
F16H 61/0025 20130101; Y10T 74/19284 20150115; Y10T 74/19288
20150115; F16H 2306/48 20130101 |
Class at
Publication: |
74/339 ; 74/340;
74/730.1 |
International
Class: |
F16H 003/12 |
Claims
What is claimed is:
1. A twin-clutch transmission for use in a motor vehicle having an
engine and a driveline, comprising: an output shaft adapated for
connection to the driveline and having an output gear fixed
thereto; a first input shaft rotatably supporting a first speed
gear meshed with said output gear; a first engine clutch operable
for establishing a releasable drive connection between the engine
and said first input shaft; a first shift clutch operable for
releaseably coupling said first speed gear to said first input
shaft to establish a drive connection between said first input
shaft and said output shaft; a second input shaft rotatably
supporting a second speed gear meshed with said output gear; a
second engine clutch operable for establishing a releasable drive
connection between the engine and said second input shaft; a second
shift clutch operable for releasably coupling said second speed
gear to said second input shaft to establish a drive connection
between said second input shaft and said output shaft; a first
fluid pump driven by said first input shaft; a second fluid pump
driven by said second input shaft; and a flow path connecting said
first fluid pump to said second fluid pump such that when said
first engine clutch and first shaft clutch are engaged and said
second engine clutch and second shift clutch are released, driven
rotation of said first input shaft causes high pressure fluid to be
transferred through said flow path to said second pump for
synchronizing the rotary speed of said released second input shaft
with that of said output shaft.
2. The twin-clutch transmission of claim 1 further comprising: a
second output gear fixed to said output shaft; a third speed gear
rotatably supported on said first input shaft and meshed with said
second output gear; and a fourth speed gear rotatably supported on
said second input shaft and meshed with said second output gear;
wherein said first shift clutch is operable for releasably coupling
said third speed gear to said first input shaft, and said second
shift clutch is operable for releasably coupling said fourth speed
gear to said second input shaft.
3. The twin-clutch transmission of claim 1 wherein the driveline is
a front driveline and said output shaft drives a final drive unit
including a differential and left and right front axleshafts.
4. The twin-clutch transmission of claim 1 wherein said first and
second engine clutches and said first and second shift clutches are
power-operated devices controlled by a transmission controller for
automatically shifting between a first gear ratio established by
said first speed gear and a second gear ratio established by said
second speed gear.
5. The twin-clutch transmission of claim 4 wherein said first and
second shift clutches are electrically-actuated dog clutches.
6. The twin-clutch transmission of claim 4 wherein said first and
second engine clutches are hydraulically-actuated by first and
second electronically-controlled control valves respectively
supplied with fluid by said first and second fluid pumps.
7. The twin-clutch transmission of claim 1 further comprising a
transfer shaft releasably driven by said first engine clutch, and a
power transfer assembly coupling said transfer shaft to said first
input shaft.
8. The twin-clutch transmission of claim 7 wherein said power
transfer assembly includes a first sprocket fixed to said first
input shaft, a second sprocket fixed to said transfer shaft, and a
chain meshed with said first and second sprockets.
9. A twin-clutch transmission for use in a motor vehicle having an
engine and a driveline, comprising: an output shaft adapted for
connection to the driveline; a first input shaft; a second input
shaft; a first engine clutch operable for establishing a releasable
drive connection between the engine and said first input shaft; a
second engine clutch operable for establishing a releasable drive
connection between the engine and said second input shaft; a
geartrain including first and second output gears fixed to said
output shaft, a first speed gear supported on said first input
shaft and meshed with said first output gear, a second speed gear
supported on said second input shaft and meshed with said first
output gear, a third speed gear supported on said first input shaft
and meshed with said second output gear, and a fourth speed gear
supported on said second input shaft and meshed with said second
output gear; a first shift clutch operable for releasable coupling
said first and third speed gears to said first input shaft; a
second shift clutch operable for releasably coupling said second
and fourth speed gears to said second input shaft; a first fluid
pump driven by said first input shaft; a second fluid pump driven
by said second input shaft; a control valve permitting fluid flow
between said first and second fluid pumps; and a transmission
control system for controlling coordinated actuation of said first
and second engine clutches to cause powershift sequential gear
shifts, such that when one of said first and second input shafts is
released from driven connection with the engine, said fluid pump
associated with the driven one of said first and second input
shafts supplies high pressure fluid through said control valving to
said fluid pump associated with the released one of said first and
second input shafts to synchronize the rotary speed of the released
one of said first and second input shaft to said output shaft.
10. The twin-clutch transmission of claim 9 wherein the driveline
is a front driveline and said output shaft drives a final drive
unit including a differential and left and right front
axleshafts.
11. The twin-clutch transmission of claim 9 wherein said first and
second engine clutches and said first and second shift clutches are
power-operated devices controlled by a transmission controller for
automatically shifting between a first gear ratio established by
said first speed gear, a second gear ratio established by said
second speed gear, a third gear ratio established by said third
speed gear, and a fourth gear ratio established by said fourth
speed gear.
12. The twin-clutch transmission of claim 11 wherein said first and
second shift clutches are electrically-actuated dog clutches.
13. The twin-clutch transmission of claim 11 wherein said first and
second engine clutches are hydraulically-actuated by first and
second control valves controlled by said transmission controller
and which are supplied with high pressure fluid by said first and
second fluid pumps.
14. An automated twin-clutch transmission adapted to transfer power
from the engine to a driveline of a motor vehicle, comprising: a
first engine clutch operable to establish a releasable drive
connection between the engine and a first input shaft; a second
engine clutch operable to establish a releasable drive connection
between the engine and a second input shaft; an output shaft
adapted to transfer power to the driveline; first and second
constant-mesh gearsets interconnecting said first and second input
shafts to said output shaft; first and second power-operated dog
clutches for selecting engaging said first and second gearsets; a
transmission controller for controlling coordinated actuation of
said first and second engine clutches and said first and second dog
clutches; and a clutch control system including a first hydraulic
pump driven by said first input shaft for delivering high pressure
fluid to a first control valve for selectively releasing said first
engine clutch, a second hydraulic pump driven by said second input
shaft for delivering high pressure fluid to a second control valve
for selectively releasing said second engine clutch, and flow
control valving for controlling fluid flow between said first and
second fluid pumps in response to release of the drive connection
between one of said first and second input shafts and the
engine.
15. The automated twin-clutch transmission of claim 14 wherein when
said first engine clutch and said first dog clutch are engaged and
said second engine clutch and said second dog clutch are released,
driven rotation of said first input shaft cause fluid to be
transferred from said first fluid pump to said second fluid pump
which acts to modify the rotary speed of said second input shaft to
match with the rotary speed of said output shaft.
16. The automated twin-clutch transmission of claim 14 wherein said
first and second dog clutches are electronically-actuated dog
clutches.
17. The automated twin-clutch transmission of claim 14 wherein said
first and second engine clutches are hydraulically-actuated by
first and second electrically-actuated control valves that are
supplied with high pressure fluid by said first and second fluid
pumps.
18. The automated twin-clutch transmission of claim 14 further
comprising a transfer shaft releasably driven by said first engine
clutch, and a power transfer assembly coupling said transfer shaft
to said first input shaft, said transfer shaft coaxially supporting
said second input shaft.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to transmissions for
use in motor vehicles and, more particularly, to a twin-clutch
automated transmission applicable for use in front-wheel drive and
rear-wheel drive vehicles.
BACKGROUND OF THE INVENTION
[0002] Automobile manufacturers continuously strive to improve fuel
efficiency. This effort to improve fuel efficiency, however, is
typically offset by the need to provide enhanced comfort and
convenience to the vehicle operator. For example, it is well known
that manual transmissions are more fuel efficient than automatic
transmissions, yet a majority of all passenger vehicles are
equipped with automatic transmissions due to the increased
convenience they provide.
[0003] More recently, "automated" variants of conventional manual
transmissions have been developed which shift automatically without
any input from the vehicle operator. Such automated transmissions
typically include a plurality of power-operated actuators that are
controlled by a transmission controller to shift traditional
synchronized dog clutches. However, such automated transmissions
have the disadvantage that there is a power interruption in the
drive connection between the input shaft and the output shaft
during sequential gear shifting. Power interrupted shifting results
in a harsh shift feel which is generally considered to be
unacceptable when compared to smooth shift feel associated with
most automatic transmissions. To overcome this problem, automated
twin-clutch transmissions have been developed which can be
powershifted to permit gearshifts to be made under load. Examples
of such automated manual transmissions are shown in U.S. Pat. Nos.
5,966,989 and 5,890,392. While such powershift twin-clutch
transmissions overcome several drawbacks associated with
conventional single-clutch automated transmissions, a need exists
to develop simpler and more robust transmissions which advance the
automotive transmission technology.
SUMMARY OF THE INVENTION
[0004] Accordingly, it is an object of the present invention to
provide a twin-clutch transmission and a control system for
permitting automatic shifting of the twin-clutch transmission.
[0005] As a related object, the twin-clutch automated transmission
of the present invention has a compact split-path geartrain
applicable for use as a transaxle in front-wheel drive
vehicles.
[0006] As a further object, the twin-clutch automated transmission
of the present invention is also applicable for use in rear-wheel
drive vehicles.
[0007] These and other objects of the present invention are met by
providing an automated twin-clutch multi-speed transmission adapted
to transfer power from the engine to one or more drivelines of a
motor vehicle. The transmission includes a first engine clutch
operable to establish a releasable drive connection between the
engine and a first input shaft, a second engine clutch operable to
establish a releasable drive connection between the engine and a
second input shaft, an output shaft adapted to transfer power to
the driveline, and a geartrain for selectively establishing a
plurality of forward and reverse speed ratio drive connections
between the input shafts and the output shaft. The transmission
further includes power-operated dog clutches for selectively
engaging constant-mesh gearsets associated with the geartrain, and
a transmission controller for controlling coordinated actuation of
the first and second engine clutches and the power-operated dog
clutches to permit non-power interrupted ("powershift") sequential
gear changes automatically without input from the vehicle operator.
A clutch control system includes a first hydraulic pump driven by
the first input shaft for delivering high-pressure fluid to a first
control valve associated with the first engine clutch, a second
hydraulic pump driven by the second input shaft for delivering
high-pressure fluid to a second control valve associated with the
second engine clutch, and flow control valving for controlling
fluid flow between the first and second pumps. When shifting under
power between gear ratios, one engine clutch is released such that
the pump associated with the driven input shaft supplies fluid to
the pump associated with released input shaft for causing
acceleration/deceleration of the released input shaft into
synchronization with the output shaft. Following completion of
speed synchronization, the dog clutch for the selected gearset on
the released input shaft is actuated and thereafter the released
engine clutch is re-engaged and the engaged engine clutch is
released.
[0008] In accordance with an alternative arrangement, the clutch
control system can include a single control valve in conjunction
with an engine clutch assembly operable for selectively
establishing drive connections between the engine and each of the
first and second input shafts.
[0009] Further areas of applicability of the present invention will
become apparent from the detailed description provided hereinafter.
It should be understood that the detailed description and specific
examples, while indicating preferred embodiments of the invention,
are intended for purposes of illustration only, since various
changes and modifications within the scope of this invention will
become apparent to those skilled in the art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic view of a twin-clutch automated
transmission according to the principles of the present
invention;
[0011] FIG. 2 is a diagrammatically illustration of the
transmission control system adapted for use with the twin-clutch
automated transmission shown in FIG. 1;
[0012] FIG. 3 is a schematic view of a twin-clutch automated
transmission according to an alternative embodiment of the present
invention;
[0013] FIG. 4 is a schematic view of a twin-clutch automated
transmission according to another alternative embodiment of the
present invention; and
[0014] FIG. 5 is a diagram of the transmission control system
adapted for use with the twin-clutch automated transmission shown
in FIG. 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] With reference to FIGS. 1 and 2 of the accompanying
drawings, a twin-clutch automated transmission, hereinafter
referred to as transaxle 10, will now be described. Transaxle 10 is
driven by the output of an engine 12 and generally includes a first
engine clutch 14, a second engine clutch 16, a first input shaft
18, a second input shaft 20, a split-path geartrain 22, an output
shaft 24, a final drive unit 26, a clutch control system 28, and a
shift control system 30.
[0016] First engine clutch 14 is a hydraulically-actuated
spring-apply plate-type clutch which is normally operable in its
engaged state to establish a drive connection between the output of
engine 12 and a transfer shaft 32. Likewise, second engine clutch
16 is a hydraulically-actuated spring-apply plate-type clutch
normally operable in its engaged state to establish a drive
connection between the output of engine 12 and second input shaft
20. First engine clutch 14 includes a drive plate 34 fixed to the
output of engine 12, a friction clutch plate 36 fixed to transfer
shaft 32, an apply plate 38, and a spring-biased release mechanism
40 acting on apply plate 38. Release mechanism 40 is moveable to
engage and release the drive connection between drive plate 34 and
friction clutch plate 36. An actuator 41 is provided to control
movement of release mechanism 40. Preferably, actuator 41 is a
hydraulically-actuated device that controls the position of release
mechanism 40 (and thus the magnitude of engagement of first engine
clutch 14) in response to the fluid pressure provided thereto.
[0017] Second engine clutch 16 includes a drive plate 42 fixed to
drive plate 34, a friction clutch plate 44 fixed to second input
shaft 20, an apply plate 46, and a spring-biased release mechanism
48 acting on apply plate 46. Release mechanism 48 is moveable to
engage and release the drive connection between drive plate 42 and
friction clutch plate 44. Similarly, an actuator 49 is provided to
control movement of release mechanism 48. Actuator 49 is a
hydraulically-actuated device that controls the position of release
mechanism 48 (and thus the magnitude of engagement of second engine
clutch 16) in response to the fluid pressure provided thereto. As
will be detailed, clutch control system 28 is operable to control
actuators 41 and 49 and, in turn, the engagement and release of
engine clutches 14 and 16. Second input shaft 20 is tubular and is
concentrically supported on transfer shaft 32. As seen from the
unrolled schematic view shown in FIG. 1, first input shaft 18 is
offset from transfer shaft 32. However, a chain 50 meshed between a
first sprocket 52 fixed to transfer shaft 32 and a second sprocket
54 fixed to first input shaft 18 provides a direct drive connection
between transfer shaft 32 and first input shaft 18.
[0018] Geartrain 22 includes a first set of speed gears rotatably
supported on first input shaft 18 and a second set of speed gears
rotatably supported on second input shaft 20, both of which are in
constant mesh with a set of output gears fixed to output shaft 24.
The first set of speed gears include a first speed gear 60 which is
meshed with a first output gear 62, a third speed gear 64 which is
meshed with a second output gear 66, and a fifth speed gear 68
which is meshed with a third output gear 70. Similarly, the second
set of speed gears includes a second speed gear 72 which is meshed
with first output gear 62, a fourth speed gear 74 which is meshed
with second output gear 66, and a sixth speed gear 76 which is
meshed with third output gear 70. Geartrain 22 also includes a
third sprocket 78 rotatably supported on output shaft 24 and which
is also driven by chain 50.
[0019] Shift control system 30 includes a plurality of shift
clutches which are operable for selectively coupling a selected
speed gear to its corresponding input shaft for establishing six
forward and one reverse speed ratio drive connections with output
shaft 24. Preferably, these shift clutches are
electrically-actuated dog clutches which include a first dog clutch
80 operable for selectively coupling/releasing first speed gear 60
and third speed gear 64 to/from first output shaft 18, a second dog
clutch 82 operable for selectively coupling/releasing second speed
gear 72 and fourth speed gear 74 to/from second output shaft 20, a
third dog clutch 84 operable for selectively coupling/releasing
fifth speed gear 68 to first input shaft 18. Shift control system
30 also include a fourth dog clutch 86 operable for selectively
coupling/releasing sixth speed gear 76 to/from second input shaft
20, and a fifth dog clutch 88 operable for selectively
coupling/releasing third sprocket 78 to/from output shaft 24. Each
dog clutch includes a sliding sleeve (denoted by the suffix "A")
which is splined for rotation with and axial movement on a clutch
hub which, in turn, is fixed to a corresponding one of input shafts
18 and 20. As is conventional, axial movement of the sliding
sleeves from the neutral uncoupled positions shown results in
clutched engagement with the adjacent speed gear. Preferably, each
dog clutch is of the electromagnetic type having a coil (denoted by
suffix "B") adjacent to and facing a radial armature plate segment
of each sliding sleeve. Electrical power delivered to the coils
causes controlled axial movement of the shift sleeves. Since first
clutch 80 and second clutch 82 are of the double-acting variety, a
pair of coils are provided therewith. It is to be understood that
any other type of power-operated device capable of moving each
sliding sleeve between its uncoupled and coupled positions is
within the scope of this invention.
[0020] Clutch control system 28 includes a first hydraulic pump 100
driven by first input shaft 18, a second hydraulic pump 102 driven
by second input shaft 20, and flow control valving 104
interconnecting first pump 100 and second pump 102. Preferably
pumps 100 and 102 are shaft-driven pumps, such as gerotor pumps,
but can optionally be electrically controlled if desired. As
schematically shown pumps 100 and 102 draw fluid from a sump 106
internal to transaxle 10. As best seen from FIG. 2, clutch control
system 28 further includes a first electrically-actuated control
valve 108 in fluid communication between actuator 41 and first pump
100, and a second electrically-actuated control valve 110 in fluid
communication between actuator 49 and second pump 102. First
control valve 108 is operable to deliver/vent fluid to/from a
pressure chamber within which a piston associated with first
actuator 41 is located. The position of this piston controls
release mechanism 40 which, as noted, controls the magnitude of
frictional clutch engagement between drive plate 34 and clutch
plate 36, thereby controlling the drive connection between transfer
shaft 32 and engine 12. Likewise, second control valve 110 is
operable to deliver/vent fluid to/from a pressure chamber within
which a piston associated with second actuator 49 is located. The
position of this piston controls release mechanism 48 which
controls the magnitude of frictional clutch engagement between
drive plate 42 and clutch plate 44, thereby controlling the drive
connection between second input shaft 20 and engine 12. Thus, first
and second control valves 108 and 110 are capable of providing
variable pressure control and, preferably, are pulse-width
modulated (PWM) valves.
[0021] In operation, rotation of first input shaft 18 causes first
pump 100 to draw fluid from internal sump 106 and supply high
pressure fluid to first control valve 108. Likewise, rotation of
second input shaft 20 causes second pump 102 to supply pressure
fluid to second control valve 110. In addition, flow control
valving 104 functions to regulate the transfer of high-pressure
fluid between hydraulic pumps 100 and 102 such that the pump
associated with the released (i.e. non-driven) one of input shafts
18 and 20 acts as a motor/brake for advancing/retarding the speed
of the non-driven input shaft into speed synchronization with the
uncoupled gearsets of geartrain 22 that are driven by output shaft
24. Thus, pumps 100 and 102 act as hydraulic synchronizers which
function to synchronize the speed of output shaft 24 to the input
shafts prior to actuation of any of the electrically-actuated dog
clutches.
[0022] Geartrain 22 is shown in FIG. 1 to further include an output
pinion 116 fixed to output shaft 24 which is meshed with a ring
gear 118 fixed to final drive unit 26. Final drive unit 26 is a
differential having a carrier 120 to which ring gear 118 is fixed,
and a gearset 122 for transferring drive torque from carrier 120 to
a pair of axle half-shaft 124 and 126. Gearset 122 allows speed
differentiation between half-shafts 124 and 126 and carrier 120. A
parking pawl wheel 130 is also fixed to output shaft 24 and can be
engaged by a parking pawl 131 for releasably locking output shaft
24 to a stationary member (i.e. the housing of transaxle 10) to
selectively prevent rotation of output shaft 24. Parking pawl 131
is operable to release output shaft 24 when the gearshift lever is
moved out of its PARK position and lock output shaft 24 when the
gearshift lever is returned to its PARK position.
[0023] In addition to the above, transaxle 10 includes a
transmission controller 140 which receives various sensor input
signals, denoted diagrammatically by block 142. Transmission
controller 140 is an electronically-controlled unit capable of
receiving data from the vehicle sensors and generating output
signals in response to the sensor input signals. The input signals
delivered to controller 140 can include, without limitation, engine
speed, throttle position, brake status, input shaft speeds and
output shaft speed. Controller 140 is operable to coordinate and
monitor actuation of all the electrically-controlled devices
associated with clutch control system 28 and shift control system
30, so as to permit powershifted sequential gear changes
automatically without any input from the vehicle operator. As such,
automated transaxle 10 is capable of being smoothly shifted without
power interruption. If desired, a manually-operable mode selector
switch 144 can be provided to shift transaxle 10 from its automatic
shift mode to a manual shift mode. Mode switch 144 would, when
actuated, allow the vehicle operator to shift the gearshift lever
manually to effect sequential gear shifts (without use of a clutch
pedal). However, controller 140 would only permit the selected
gearshift to be completed if the current vehicle characteristics
(i.e. engine speed, vehicle speed, etc.) permit completion of the
requested shift.
[0024] When it is desired to operate the vehicle, engine 12 is
started with the gearshift lever in its PARK position and both
engine clutches 14 and 16 engaged such that both input shafts 18
and 20 are in drive connection with the output of engine 12.
However, all of the electrically-actuated dog clutches are released
with each shift sleeve located in its neutral uncoupled position,
whereby no drive torque is delivered through geartrain 22 to output
shaft 24. When the vehicle operator moves the gearshift lever from
the PARK position to the DRIVE position, parking pawl 131 is
released from engagement with parking wheel 130 and first engine
clutch 14 is also released. In particular, controller 140 actuates
first control valve 108 to move actuator 41 for releasing first
engine clutch 14, whereby the drive connection between engine 12
and first input shaft 18 is released. However since second engine
clutch 16 is still engaged, driven rotation of second input shaft
20 causes second pump 102 to supply pressurized fluid through flow
control valving 104 to first pump 100 which then acts as a brake to
stop rotation of first input shaft 18. Thereafter, first dog clutch
80 is actuated by controller 140 sending an electrical signal to
coil 80B for moving sliding sleeve 80A into clutched engagement
with first speed gear 60. As such, first speed gear 60 is coupled
for rotation with first input shaft 18, whereby the first forward
speed ratio drive connection is established between first input
shaft 18 and output shaft 24. First engine clutch 14 is then
gradually engaged to accelerate the vehicle.
[0025] Thereafter, when the vehicle operating parameters indicate a
need to shift into the second forward gear ratio, controller 140
actuates second control valve 110 to move actuator 49 for releasing
second engine clutch 16, whereby the drive connection between
engine 12 and second input shaft 20 is released. Since first engine
clutch 14 is engaged, first pump 100 delivers fluid to second pump
102 which then acts to retard rotation of second input shaft 20 so
as to synchronize its rotary speed to that of second speed gear 72
which is driven by output gear 62 on output shaft 24. When
controller 140 determines that speed synchronization is complete,
second dog clutch 82 is activated by controller 140 for moving
sliding sleeve 82A such that second speed gear 72 is coupled to
second input shaft 20. Thereafter, controller 140 coordinates the
release of first engine clutch 14 and the re-engagement of second
engine clutch 16. Once first engine clutch 14 is released
completely, controller 140 causes first dog clutch 80 to return
sliding sleeve 80A to its neutral position for uncoupling first
speed gear 60 from first input shaft 18.
[0026] To automatically establish the third forward gear ratio,
driven rotation of second input shaft 20 causes second pump 102 to
deliver pressurized fluid through valving 104 to first pump 100. As
a result, first pump 100 causes the rotary speed of non-driven
first input shaft 18 to be synchronized with that of third speed
gear 64 which is driven by output gear 66 on output shaft 24. Upon
completion of synchronization, controller 140 actuates first dog
clutch 80 for moving sleeve 80A into clutched engagement with third
speed gear 64. Thereafter, controller 140 coordinates the release
of second engine clutch 16 and the engagement of first engine
clutch 14. Once second engine clutch 16 is released, second dog
clutch 82 is caused to return sleeve 82A to its neutral position
for releasing second speed gear 72 from clutched engagement with
second input shaft 20. As will be appreciated, this upshift process
continues through each of the other forward speed gear ratios and
likewise works in reverse for downshifts. When the gearshift lever
is shifted into its REVERSE position, fifth dog clutch 88 is
actuated by controller 140 for moving sleeve 88A into clutched
engagement with third sprocket 78. With this powershift
methodology, transaxle 10 shifts between engine clutches in a
power-on shift strategy (i.e. no power interruption).
[0027] Referring now to FIG. 3, a rear-wheel drive version of the
automated transmission is shown and identified by reference numeral
200. As seen, final drive unit 26 and output pinion 116 have been
eliminated with output shaft 24 adapted for direct connection to
the rear driveline of the motor vehicle. The automatic shifting
function of six-speed twin-clutch transmission 200 is identical to
six-speed twin clutch transaxle 10.
[0028] Referring now to FIGS. 4 and 5, a modified version of
transaxle 10 is shown and identified by reference numeral 10A. As
seen, transaxle 10A is substantially identical to transaxle 10 with
the exception that first pump 100 is now connected to transfer shat
32 instead of first input shaft 18, dog clutch 88 is now shown
outboard of third sprocket 78, and an engine clutch assembly 202
replaces first and second engine clutches 14 and 16.
[0029] In general, engine clutch assembly 202 includes a primary
clutch 204 that is operable for selectively establishing a drive
connection with second input shaft 20, and a secondary clutch 206
that is operable for selectively establishing a drive connection
with transfer shaft 32. Primary clutch 204 and secondary clutch 206
are disposed within a clutch housing 208 that is fixed to the
output of engine 12. A spring-loaded piston 210 normally functions
to clamp friction clutch plate 44 to clutch housing 208 for
establishing a spring-apply drive connection between engine 12 and
second input shaft 20. Concurrently, piston 210 is displaced from
engagement with friction clutch plate 36 so as to normally release
transfer shaft 32 from driven connection with engine 12. However,
the delivery of high pressure fluid to a pressure chamber 212
within housing functions to overcome the biasing force of spring
214 and move piston 210 to a position whereat friction plate 44 is
released from frictional engagement with clutch housing 208 and
friction plate 36 is frictionally clamped to clutch housing 208. As
such, the drive connection between engine 12 and second input shaft
20 is released while the drive connection between engine 12 and
transfer shaft 32 is established. Primary clutch 204 is arranged to
drive second input shaft 20 since the highest forward gear (i.e.,
6.sup.th gear) is established by coupling speed gear 76 to second
input shaft 20. Thus, the spring-apply function in 6.sup.th gear
eliminates the need for hydraulic pressure at cruise speeds,
thereby reducing parasitic losses.
[0030] As shown in FIG. 5, a single control valve 218 is supplied
with fluid from one of fluid pumps 120 and 122. Actuation of
control valve 218 is controlled by controller 140 for selectively
supplying or venting high pressure fluid to/from pressure chamber
212 so as to control actuation of engine clutch assembly 202.
* * * * *