Munich. The British premium automobile manufacturer
MINI highlights the sporty character of its current models in the
small segment with a new type of transmission. Extremely fast gear
changes, a high degree of shift comfort and optimised efficiency –
these are the benefits of the 7-speed Steptronic automatic
transmission with double clutch, available for the MINI 3 door, the
MINI 5 door and the MINI Convertible. It is offered in conjunction
with selected engine types and as an alternative to the standard
6-speed manual transmission. The new double clutch transmission
provides impressive shift dynamics for enhanced driving fun while at
the same including all the comfort features of an automatic transmission.
The double clutch transmission is operated by means of a newly
designed electronic selector lever which always returns to its
original position after changing between driving mode D, neutral
position N and reverse mode. The parking lock is activated by pressing
the P button. S mode can be activated from position D by shifting the
selector lever to the left: this supports a particularly sporty
driving style as well as allowing manual intervention in the choice of
position. The electronic control of the new double clutch transmission
for MINI also includes a shift strategy based on navigation data and
supports both the engine start/stop function and coasting so as to
reduce fuel consumption and emission levels.
Operating principle drawn from motor racing for enhanced
driving fun on the road.
The design principle of the double clutch transmission has been
adapted directly from motor racing. Just like on the race track, it
allows MINI drivers to undertake highly dynamic acceleration
manoeuvres by enabling upward gearshifts without torque interrupt. The
driver can keep the accelerator pressed down while the transmission
control sets the shift points so precisely within just a fraction of a
second that the ideal engine speed is always available after the
gearshift to ensure a continuous increase in speed.
This is possible due to the specific structure of the double clutch
transmission. It combines two partial transmissions in a single
housing. The core element of the system consists of two oil-cooled wet
clutches: one of these is responsible for the even transmission ratios
(2, 4, 6) while the other is for the uneven ratios (1, 3, 5, 7) and
reverse. During travel, one of the two clutches is open and the other
is closed. They interact when the driver shifts up or down: opening
one clutch activates closure of the second at the same time.
If the MINI is accelerated in third gear, for example, power
transmission occurs by means of the relevant clutch and the partial
gear for the uneven transmission ratios. At the same time, the
transmission control ensures that the next gear required – in this
case fourth gear – is already engaged in the partial transmission
responsible for the even transmission ratios. All that needs to be
done to shift up is to open the clutch of the third gear and close
that of the fourth gear. This happens simultaneously without any
interruption of pulling power – and if anything takes less time than
it would to activate the clutch pedal when driving with manual transmission.
The transmission control always knows which is the right gear.
In order to have the appropriate gear ready for the next shift, the
electronic control system of the new double clutch transmission
permanently analyses the driver’s intentions and the situation on the
road. This analysis incorporates the accelerator position, engine
speed, road speed and MINI driving mode. As a result, fast gearshifts
can be made to respond appropriately to sudden changes in the driving
situation. If acceleration has to be unexpectedly interrupted, for
instance, the double clutch transmission takes no more than a fraction
of second to make the next gear down available instead of the next
gear up.
The parallel opening and closing of the clutches makes acceleration
and deceleration manoeuvres not just faster but also smoother.
Acoustically, the gearshifts can only be perceived in the fast
succession of rev changes – also to be seen in the abrupt movements of
the tachometer needle. What is more, there are no load change
reactions as are common in conjunction with manual transmissions.
Seven gears for increased riding fun and enhanced comfort.
The increase in drive positions as compared to the 6-speed manual
transmission benefits both sporty flair and ride comfort. The seven
gears of the double clutch transmission enable a broader spread of
gears, thereby reducing the differences in engine speed between the
various drive positions. Together with the direct engine link that is
characteristic of the double clutch transmission, the small rev jumps
make for particularly intense driving fun when accelerating. This
applies to automated shifts in D and S modes as well as to manual
interventions in the selection of drive positions in M mode. In S mode
the gearshifts occur at increased engine speeds and with further
increased shift dynamics. In S mode, the driver can also spontaneously
switch to manual shifting. Here, manual gear selection is sequential.
The selector lever is briefly moved forward to shift down and raised
slightly in order to move up to the next higher gear.
In automated mode, driving fun can also be enhanced by linking the
transmission control to the optional MINI navigation system. The
double clutch transmission control unit is then able to draw on
navigation data to adapt its shift strategy to the given situation on
the road. When approaching a sharp bend or junction, for example, a
downshift is made early on so as to be able to make use of the engine
braking effect for deceleration purposes. When passing through two
bends in quick succession, the drive position engaged after
downshifting is maintained so as to avoid any unnecessary shifting and
ensure the ideal gear is available for powerful acceleration on
exiting the bend.
Like a conventional converter system, the double clutch transmission
also offers a crawl function that enables smooth set-off without
activating the accelerator, thereby increasing comfort when
manoeuvring or in stop-and-go traffic. The dual-mass flywheel with
integrated centrifugal pendulum develops its positive effect when
driving at low revs: it balances out rotational unevenness in the
event of sudden torque request, thereby promoting vibrational and
acoustic comfort when accelerating out of the low engine speed range.
Optimised efficiency with engine start/stop function and
coasting mode.
In addition, the electronic control system of the 7-speed double
clutch transmission offers a wide range of progressive functions to
increase the efficiency of the MINI. In order to avoid unnecessary
consumption of fuel when stopping at junctions, for example, the
double clutch transmission also allows use of the engine start/stop function.
What is more, the coasting function is available in both the MID and
GREEN driving modes. Here the drivetrain is decoupled as soon as the
driver removes their foot from the accelerator pedal. This allows the
MINI to roll along at idling speed – free of any engine braking effect
and at minimum fuel consumption. The coasting function can be adapted
more precisely to the driving situation if the vehicle is fitted with
a navigation system or driver assistance systems. If there is a need
to apply the brakes based on navigation data or camera images, for
example, because the MINI is approaching a junction or another road
user ahead, the coasting function is suppressed so as to be able to
make use of the engine braking effect.