Electronically Shifted Manual
Transmission
Many modern manual transmissions operate without
a clutch pedal. Electronically operated devices control
clutch operation and gear selection. The driver moves a
shifter, or “paddle,” that sends signals to an onboard com-
puter. The computer controls solenoids or motors to shift
gears and also applies and releases the clutch. On some
vehicles with this type of transmission, the clutch pedal is
used only to start moving the vehicle from rest. Other vehi-
cles with electronically shifted manual transmissions have
no clutch pedal at all.
The transmission controls now in use can be con-
nected to the engine and anti-lock brake computers. The
computers could provide fully automatic shifting. Some
manufacturers are working on automatic versions of man-
ual transmissions. A few of these designs are being used in
large trucks, usually with a torque converter replacing the
manual clutch.
Dual Clutch Transmission
One type of electronically shifted manual transmission
that may replace the planetary-type automatic transmission
on some vehicles is the dual clutch transmission, or DCT.
It can be thought of as two manual transmissions, each with
its own clutch, in one housing, Figure 1-42. In a five-speed
DCT, one transmission contains the odd-numbered gears
(first, third, and fifth) and the other transmission contains
even-numbered gears (second and fourth). A reverse gear
is built into one of the transmissions. To save space, the
two transmissions and clutches are combined into a single
unit. Hollow shafts allow each transmission to transfer
power without interfering with the other transmission.
Operation depends on alternately applying and releasing
the clutches, and engaging gears before the clutch is
applied. For instance, when the vehicle is accelerating in
first, power flows through the clutch and first gear of the
odd-gear transmission. While power is traveling through
the odd-gear transmission, second gear of the even-gear
transmission has been engaged, but is not yet delivering
power. To shift to second, the odd-gear transmission clutch
disengages and the even-gear transmission clutch engages.
Power then flows through the clutch and second gear of the
even-gear transmission. Meanwhile, third gear of the
odd-gear transmission is engaged for the next shift.
The vehicle powertrain computer controls gear selection
and clutch application sequence. This results in fast, smooth
shifts, with no gear clash or interruption in power flow. The
powertrain module is programmed to give the best shift
pattern at various throttle openings. DCT fuel efficiency is
about 15% better than that of a torque converter automatic.
32 Automatic Transmissions and Transaxles
Figure 1-41. Infinitely variable transmissions (IVTs), like the
one shown here, are currently being used in Asia. In this IVT, a
planetary gearset provides reverse. (NSK)
Figure 1-40. This motor-generator is installed between the
engine and transmission. Note the stator, rotor, and control
module. (ZF)
Figure 1-42. The clutches can be seen in this cutaway of a dual
clutch transmission. Note the oil pump and cooler used to cool
the oil in the wet clutch.They are the only hydraulic components
in the transmission. (ZF)