In the 1950s and 1960s, as American automakers were busily
honing the art of the automatic transmission, European automakers tried to
stretch manual transmission technology as far as possible in an
attempt to offer the user-friendliness of automatic with a semblance of
the economy and performance of a stickshift. The semiautomatic
transmission was born.
First, let's consider the case for semiautomatic transmissions. I, along
with some American Everythingians, tend to forget that as a rule most
European and Japanese cars are of
smaller engine displacement than typical American fare.
These smaller engined cars are intended for the home market
and countries where fuel economy is important and taxation by
displacement is practiced. The cars are frequently fitted with
larger engines for export, and frequently only the US market gets the truly
large engine options as standard equipment.
The United States, with plentiful fountains of gasoline,
can allow for big engines with energy inefficient transaxles
as well as full-time, 60/40 split four wheel drive systems. In my opinion,
the low maintenance cost of driving in the US as well as
reasonable leasing have caused the sport utility
vehicle boomlet here. But that's a metanode in itself.
Semiautomatics are conceptually simple. Instead of depressing a clutch,
the driver either pulls in on a column shift or pushes down on a
floor mounted lever. Continuing to place pressure on the lever the driver
selects a gear, setting off without having to first find the moment
of resistance, the friction/bite point after which the car begins
forward momentum. Some cars (notably the Volkswagen Beetle) allow
the driver to continue accelerating through a shift; other systems still
require the driver to momentarily disengage the throttle while selecting
gears. The pressure placed on the gear lever trips a
switch, engaging a hydraulic clutch actuator (foot replacement) that
is released only after movement has been obtained. In this way the system
avoids use of a torque converter as found on an automatic transaxle.
The fully hydraulic nature of impellers and turbines in a
torque converter provide for
competent starts and shifts with little or no shudder, but with the price
of the added fuel consumption of keeping the flywheel rotating. Semiautomatic
transmissions combine mechanical and hydraulic aspects to preserve some
economy while attempting to provide fluid movement.
To stop the car, the driver avoids the need to depress a clutch or typically
touch the gear selector. He/she need only apply the brake, moving the selector
into neutral as the car winds to lower revolutions. In every
action the gear selection movements in manual and semiautomatic cars are
identical, save clutch actuation. Riding the clutch is possible only at
a stoplight, if one depresses the brake and holds 1st/low gear.
Many modern semiautomatics (Saab Sensonic) will emit a warning beep
if the car is left in low gear for more than 30 seconds, requiring tolerance
of incessant beeping in exchange for a quick getaway.
Towards the end of the 1950s certain European models began to sport
semiautomatics, though they were installed as afterthoughts and not well
integrated with platform design. Saab and Volkswagen were notable
early adopters, with Volvo and I believe Rover experimenting with
semiautomatic systems before offering fully automatic models with primitive
planetary gear setup, two or three forward gears lashed to power-spilling
torque converters. My experiences with Volvos tell me that the semiautomatic option
was not popular with their 1960s era models, possibly due to maintenance
issues or the performance/economy hit inherent with the clutchless design.
Nowadays semiautomatic setups have made a comeback,
but with a twist. Some models, such as cars produced by Renault,
Saab, and Mercedes-Benz, notably the Benz A-Class and Swatch models,
sport electronic semiauto versions that require gear shifting
at all times. Now popular in the United States are manumatic
transmissions, fully automatic transmissions with electronic
"shifting" of gears via a up/down shift gate. Manumatic drivers aren't
really choosing gears; rather they're ordering the automatic tranny's
"brain" to interrupt its preprogrammed cycle and do the master's bidding.
In my few test drives with manumatics the car does what it wants anyway,
obeying sometimes but frequently overriding driver input with what it thinks
might be a more cautious move (shifting above 4000 rpm seems to be real
risky for most car computers). Many manumatics refuse to go to redline;
many also drop the car to low gear at a full stop. All told, it's still
an attractive option for those who prefer auto but want to push the car
a bit sometimes, but not make stupid mistakes like testing the strength of
the tachometer needle.