Transmission
A transmission is a device for transmitting and adapting power
from its source to its point of application. Most transmissions
act by changing the angular velocity of the drive shaft, either
by step-variable means - gears, in automobiles - with fixed
ratios and no slip, or by stepless means with continuously
variable ratios but liable to slip. In an automobiles with
manual transmission, the flywheel on the engine crankshaft
is connected to the gearbox via the clutch, two plates that
are normally held tightly together by springs so that through
friction they rotate together. When the clutch pedal is depressed,
the plates are forced apart so that the engine is disengaged
from the rest of the transmission. This is necessary when
changing gear: sliding different sets of gears into engagement
by means of a manual lever. Modern gearboxes have synchromesh
in all forward gears: a coned clutch device that synchronizes
the rotation of the gears before meshing. The gearbox is coupled
to the final drive by a drive shaft with universal joints.
A crown wheel and pinion, connected to the half-shafts of
each drive wheel via a differential, complete the system.
In automatic transmission there is no clutch pedal or gear
lever; a fluid clutch (see fluid coupling), combined with sets of epicyclic
gears selected by a governor according to the program set
by the driver, provides a continuously variable torque ratio
for maximum efficiency at all speeds.
Hybrid electric vehicles can use a variety
of conventional and advanced transmissions based on the system
design of the vehicle, including continuously variable transmission,
automated shifted manual transmission, manual transmission,
and traditional automatic transmission with torque converter.
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