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Trucks, buses, and trains
Semi-automatic transmissions have also made its way into the
truck and bus market in the early 2000s.
Volvo
offers its I-shift on its heavier trucks and buses, while ZF markets its ASTronic system for
trucks, buses and coaches. In North America, Eaton offers the "AutoShift" system
which is an add-on to traditional non-synchromesh manual
transmissions for heavy trucks[1].
These gearboxes
have a place in public
transport as they have been shown to reduce fuel
consumption in some specific cases.
In the UK though, semi-automatic transmission has been very
popular on buses for some time, from the 1950s right through to the
1980s, an example being the well known London Routemaster, although the latter could
also be driven as a fully automatic in the three highest gears.
Most heavy-duty bus manufacturers offered this option, using a
gearbox from Self-Changing Gears Ltd of Coventry,
and on urban single- and double-deck buses it was the norm by the
1970s. This coincided with the development of city buses with
engines and transmissions at the rear rather than the front, which
was beyond the capability of a manual gearchange/clutch linkage
from the driver's position. Leyland manufactured many buses with
semi-automatic transmission, including its Leopard and Tiger coaches. Fully automatic
transmission became popular with increasing numbers of continental
buses being bought in the UK, and more and more British
manufacturers began offering automatic options, mostly using
imported gearboxes, and semi-automatic transmission lost favour.
These days, very few buses with semi-automatic transmission remain
in service, although many are still on the roads with private
owners. Modern types of semi-automatic transmission though is
becoming more common, mostly replacing manual gearboxes in coaches
and small buses.
The Self-Changing Gears semi-automatic gearbox was also fitted
to the several thousand diesel railcars built for the British
railway system in the late 1950s-early 1960s, which lasted in
service until the 1990s-2000s. Their whole engine-transmission
system was based on that from the main bus manufacturers of the
period such as Leyland and AEC. Gear selection was by the train
driver with a hand-held lever as the train accelerated. Such trains
were formed of a number of such railcars coupled together and each
power car had two engine/semi-automatic gearbox units mounted under
the floor. Synchronising controls by control cables connected
through the train ensured all the gearboxes under all coaches of
the train changed gear together.
http://en.wikipedia.org/wiki/Semi-automatic_transmission#Trucks.2C_buses.2C_and_trains