Page 128 - How It Works - Book Of Amazing Answers To Curious Questions, Volume 05-15

How do twin-clutch

gearboxes work?

Even gears
When the gear change
They are a common feature in today’s supercars and here’s why happens, the clutches are
quickly swapped and the
new gear is called into
action – all in the space of
s supercars get faster and faster, with Inside a twin-clutch gearbox 100 milliseconds.
0-100-kilometre (0-62-mile)-per-hour
Atimes of less than three seconds, Here’s how a twin-clutch gearbox works in a semi-automatic
manufacturers are now looking at ways of Porsche 911
making gains for their cars to cover even more
ground in even less time. An area that has been
developed a lot in supercars in recent years are
gearboxes, where a lightning-quick gear
change is absolutely essential if the car is to
maintain linear power delivery when
accelerating to 100 kilometres (62 miles) per
hour and far beyond.
To provide this super-quick shift,
manufactures such as Porsche, Audi and
Lamborghini have produced a complex yet
exquisite ‘double-clutch’ semi-automatic Drivetrain
gearbox that substantially reduces the time it Power is transferred Input and output Clutches
takes to shift up or down a gear. This through the gearbox shafts These concentrically mounted
technology works by effectively splitting the and on to the car’s Each shaft is connected to wet clutches are connected to
two separate input shafts, one
gearbox in two, with a concentrically mounted drivetrain a set of gears. The odd for the solid inner shaft and
gears are connected to the
clutch on the end of two separate input shafts. components, which outer shaft, and the even one for the hollow outer shaft.
turns the wheels of
The odd gears are on one shaft and the even the car, propelling it gears are connected to the These are quickly engaged or
gears are on the other. When a new gear is along the road. inner shaft. disengaged according to what
gears are needed.
selected, the supercar’s on-board computer
preselects the next gear needed on the other
shaft according to driving style and conditions,
so when it is time to change gear, the cog in
question takes mere milliseconds to engage
with the drivetrain, making sure that mighty
power from the engine is fed to the wheels as

efficiently and quickly as possible.

Odd gears
While these are engaged, the
car’s ECU preselects the next
gear on the alternative shaft.

Automatic vs manual gearboxes

The purists will always favour the better driver down, while a human can become lazy or forget
involvement offered from the physical ‘throw’ to change gear according to these parameters.
action when changing gears with a gear stick, Then there’s the safety and comfort factor: as
but the reality is that, as cars become ever cars produce more power, a bigger clutch is
faster and more powerful, automatic gearboxes needed to transfer the power to the gearbox,
are inevitably the future. The reason for this is which usually results in a very heavy clutch
threefold: they allow for quicker gear changes pedal on supercars. An automatic gearbox takes
as we’ve just discovered, plus they’re more away the clutch pedal, meaning you can drive
economical as the car’s on-board computer will the car in comfort without giving your left thigh
always select new gears to keep fuel usage an excessive workout!

128 How It Works