Audible
Conventional automatics tend to be very smooth in operation—both upon starting from a stop and in gear changes—but lose some efficiency (and thus fuel economy) due to the slight “slip” of the fluid-filled torque converter and driving the hydraulic pump that operates the clutch packs.
Automated manuals are often used in performance cars today because they’re more efficient than a conventional automatic transmission, and can handle much more power than a CVT.
Automatic transmissions have gone through many changes since being introduced by
Oldsmobile for 1940. There are four types of Automatic transmission.
1. Torque converter(Conventional automatic)
2.Continuously variable transmission(CVT)
3.Automated manual
4.Dual-clutch automated manual(DSG)
1. Torque converter(Conventional automatic)
2.Continuously variable transmission(CVT)
3.Automated manual
4.Dual-clutch automated manual(DSG)
Torque converter(Conventional
automatic)
The current
generation of conventional automatics use a torque converter to transfer power
from the engine to the transmission. The transmission itself typically contains
several sets of gears, and the different “speeds” are chosen by engaging
electronically controlled, hydraulically operated clutch packs. Most earlier
automatics worked much the same way but didn’t have as many speeds and lacked
electronic controls.
Conventional automatics tend to be very smooth in operation—both upon starting from a stop and in gear changes—but lose some efficiency (and thus fuel economy) due to the slight “slip” of the fluid-filled torque converter and driving the hydraulic pump that operates the clutch packs.
Continuously variable transmission(CVT)
Rather than sets
of gears, CVTs use a belt that runs between two variable-diameter pulleys to
give a wide range of ratios and a smooth transition between them. In automotive
applications, some CVTs use a fluid-filled torque converter (as with a
conventional automatic) to transfer power from the engine to the transmission,
others a clutch similar to that used for a manual transmission, but with
automatic activation (there is no clutch pedal).
The advantage of
a CVT is that the engine can be kept at its most efficient speed while the
transmission adjusts to changes in load or road speed. Under brisk
acceleration, for example, the engine revs up to where it produces the most
power and is held there as the transmission constantly adjusts to the
increasing speed of the car. Under cruise conditions, the transmission can
adjust for small changes in road speed while the engine is kept at a consistent
rpm for best fuel economy. A limiting factor is that because CVTs rely on
friction between the belt and the pulleys, they haven’t yet been designed to
handle a lot of power.
Automated manual
There
are two types of automated manual transmissions in use, with the more modern one
(which is now far more common) being called a “Dual Clutch Automated Manual”;
it’s described below. Both are essentially manual transmissions where the
clutch and shift actions are carried out by computer-controlled, electronically
activated mechanisms, so they work without driver interaction, just like a
conventional automatic transmission. However, they can also be shifted manually
(though still without the driver using a clutch) via a conventional gear lever
or steering-column-mounted “paddles.”
Automated
manuals are more efficient than conventional automatics because there’s no
“slip” of a torque converter and no losses from driving an internal hydraulic
pump. The earliest versions – which were found primarily in European
performance cars – were based on a conventional manual transmission with a
single clutch, but the only car still using this kind is the very
non-performance-oriented Smart ForTwo.
Dual-clutch automated manual(DSG)
It
gets its name from the fact that there are two gear shafts – one for the
odd-numbered gears (1, 3, 5, 7), another for the even-numbered gears (2, 4, 6)
– each having its own clutch. When the car moves off from a stop, 1st gear is
already selected, and the “odd” clutch is engaged to start the car moving.
While this is going on, the computer puts the other gear shaft into 2nd gear.
When it comes time to shift to second, the “odd” clutch disengages and the
“even” clutch engages, and presto; you’re in second gear. It does the same with
the higher gears, which are “preselected” before the clutch for that shaft is
engaged. This results in much quicker – and usually much smoother – gear
changes than with a “single clutch” automated manual.
Automated manuals are often used in performance cars today because they’re more efficient than a conventional automatic transmission, and can handle much more power than a CVT.
Branded
examples of dual-clutch automated manual transmissions include Ford’s
“PowerShift” available in the Fiesta and Focus, and Porsche’s “PDK” available
in several of the maker’s vehicles
Conclusion
Although
the four types of automatic transmissions —conventional, CVT, automated manual,
and dual clutch automated manual — all operate without a clutch pedal and can
be set to shift for themselves, they each exhibit slightly different driving
characteristics. You’re probably already familiar with how a conventional
automatic “feels,” so we’ll compare the others to that.
Closest
in terms of perception to a conventional automatic is the dual clutch automated
manual. One difference can often be felt when you’re barely moving. If you’re
stopped on a slight upward incline, a conventional automatic will “hold” you
there without having your foot on the brake; likewise, your car will creep
forward on level ground if you are stopped and take your foot off the brake.
Automated manuals often won’t hold you on an upward incline, and may not creep
forward on flat ground quite as smoothly as a conventional automatic does. This
is most noticed in stop-and-go traffic.
Many
automated manuals also feel different if you floor the throttle, either from a
stop or when cruising down the road. From a stop, they sometimes lurch a bit
where a conventional automatic is smoother. If you’re cruising down the road
and floor the throttle to pass, an automated manual can often be felt “stepping
down” one gear at a time rather than dropping from, say, sixth gear straight
down to second. As a result, the time that passes between flooring the throttle
and the car actually accelerating is sometimes a bit longer.
These
all sound like negative traits, so why do some manufacturers use automated
manuals? Efficiency. Automated manuals are often credited with about a
10-percent increase in fuel economy. And they’re usually better from a
performance standpoint, as there’s less power loss through an automated manual,
and under hard acceleration, they are often quicker to upshift into the next
gear.
A
CVT exhibits even more of a difference, notably under acceleration. The
objective of a CVT is to have the transmission make most of the adjustments
necessary to maintain different road speeds while letting the engine turn at a
fairly constant speed—which results in about 10 percent better fuel economy.
Under even moderate throttle applications from a stop, however, a CVT maximizes
engine power by letting the engine quickly rev up to where it makes more power
and then holds it there while the transmission adjusts to the car’s increasing
road speed. This means the engine is held at a steady, high-revving speed where
it usually makes a lot of noise and sometimes is rather ragged, and this is
what is most obvious — and annoying — to many drivers.
It
used to be that nearly every car that offered both a manual and an automatic
transmission scored significantly better EPA fuel-economy numbers with the
manual. Not anymore. Although there are a few examples where the manual is
still thriftier, many of today’s cars score better with an automatic. Part of
this is due to the greater number of “speeds” now used even in conventional
automatics — which allow the engine to run more efficiently at any given road
speed — and to the use of automated manuals and CVTs.
Currently,
most manufacturers still rely on conventional automatic transmissions, but the
use of CVTs and particularly dual clutch automated manuals is growing. In their
best applications, CVTs and dual clutch automated manuals behave much the same
as conventional automatics in everyday driving, and the goal is to make them
nearly indistinguishable — except for a noticeable boost in fuel economy.
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