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INTRODUCTION
TRANSMISSION
Transmission is the mechanism through which the driving torque of the
engine is transmitted to the driving wheel of the vehicle so that the motor
vehicle can move on the road. The reciprocating motion of the piston
turns a crankshaft rotating a flywheel through the connecting rod .The
circular motion of the crankshaft is to be now transmitted to the rear
wheels .It is transmitted through the clutch, gear box, universal joints,
propeller shaft or the drive shaft, differential and axles extending to the
wheels .The application of the engine power to the driving wheels
through all these parts is called POWER TRANSMISSION .The power
system is usually the same on all modern passenger cars and trucks, but
its arrangement may vary according to the method of drive and type of
transmission units.
PURPOSE OF TRANSMISSION:
● It enables the engine to be disconnected from the driving wheels.
● It enables the running engine to be connected to driving wheel
smoothly and without shock.
● It enables the leverage between the engine and the driving wheels
to be varied.
It enables the reduction of engine speed in the ratio of 4:1 in case
of passenger cars and in greater ratio in case of Lorries.
● It enables the driving wheels to be driven at different speeds.
● It enables turning the driving through 90 degrees.
● It enables the relative movement between the engine and the
driving wheel.
CLUTCH
In all vehicles using a transmission (virtually all modern vehicles), a
coupling device is used to separate the engine and transmission when
necessary. The clutch accomplishes this in manual transmissions. Without
it, the engine and tires would at all times be inextricably linked, and
anytime the vehicle stopped the engine would perforce stall. Without the
clutch, changing gears would be very difficult, even with the vehicle
moving already: deselecting a gear while the transmission is under load
requires considerable force, and selecting a gear requires the revolution
speed of the engine to be held at a very precise value which depends on
the vehicle speed and desired gear. In a car the clutch is usually operated
by a pedal; on a motorcycle, a lever on the left handlebar serves the
purpose.
1.When the clutch pedal is fully depressed, the clutch is fully disengaged, and no torque is transferred from the engine to the
transmission (and by extension to the drive wheels). In this uncoupled
state it is possible to select gears or to stop the car without stopping the
Engine.
2. When the clutch pedal is fully released, the clutch is fully engaged,
and practically all of the engine's torque is transferred. In this coupled
state, the clutch does not slip, but rather acts as rigid coupling, and power
is transmitted to the wheels with minimal practical waste heat.
3. Between these extremes of engagement and disengagement the clutch
slips to varying degrees. When the clutch slips it still transmits torque
despite the difference in speeds between the engine crankshaft and the
transmission input. Because this torque is transmitted by means of
friction rather than direct mechanical contact.
4. Considerable power is wasted as heat (which is dissipated by the
clutch). Properly applied, slip allows the vehicle to be started from a
standstill, and when it is already moving, allows the engine rotation to
gradually adjust to a newly selected gear ratio.
5. Learning to use the clutch efficiently requires the development of
muscle memory and a level of coordination analogous to that required to
learn a musical instrument or to play a sport.
6.A rider of a highlytuned motocross or offroad motorcycle may "hit"
or "fan" the clutch when exiting corners to assist the engine in revving to
the point where it delivers the most power.
DUAL CLUTCH TRANSMISSION
A semiautomatic transmission (also known as clutchless manual
transmission, dualclutch transmission, automated manual
transmission, egear, shifttronic, flappy paddle gearbox, or direct
shift gearbox) is a system which uses electronic sensors, processors and
actuators to do gear shifts on the command of the driver. This removes
the need for a clutch pedal which the driver otherwise needs to depress
before making a gear change, since the clutch itself is actuated by
electronic equipment which can synchronise the timing and torque
required to make gear shifts quick and smooth. The system was designed
by European automobile manufacturers to provide a better driving
experience, especially in cities where congestion frequently causes
stopandgo traffic patterns
Elaborated form of manual transmission in which two internal shafts,
each connected to the input via an electronically controlled clutch, are
coordinated such as to achieve an uniterrupted flow of torque to the
driven wheels during gear changes. As well as reducing acceleration
times, a dual clutch transmission also enchances refinement over a
convectional manual or manual gearbox.
Most people know that cars come with two basic transmission types:
manuals, which require that the driver change gears by depressing a
clutch pedal and using a stick shift, and automatics, which do all of the
shifting work for drivers using clutches, a torque converter and sets of
planetary gears. But there's also something in between that offers the best
of both worlds the dualclutch transmission, also called the
semiautomatic transmission, the "clutchless" manual transmission and
the automated manual transmission.
In the world of racecars, semiautomatic transmissions, such as the
sequential manual gearbox (or SMG), have been a staple for years. But
in the world of production vehicles, it's a relatively new technology one
that is being defined by a very specific design known as the dualclutch,
or directshift, gearbox.
3. OPERATION OF DCT
In standard massproduction automobiles, the gear lever appears similar
to manual shifts, except that the gear stick only moves forward and
backward to shift into higher and lower gears, instead of the traditional
Hpattern. The Bugatti Veyron uses this approach for its 7speed
transmission. In Formula One, the system is adapted to fit onto the
steering wheel in the form of two paddles; depressing the right paddle
shifts into a higher gear, while depressing the left paddle shifts into a
lower one. Numerous road cars have inherited the same mechanism.
Hall Effect sensors sense the direction of requested shift, and this input,
together with a sensor in the gear box which senses the current speed and
gear selected, feeds into a central processing unit. This unit then
determines the optimal timing and torque required for a smooth clutch
engagement, based on input from these two sensors as well as other
factors, such as engine rotation, the Electronic Stability Program, air
conditioner and dashboard instruments.
The central processing unit powers a hydromechanical unit to either
engage or disengage the clutch, which is kept in close synchronization
with the gearshifting action the driver has started. The hydromechanical
unit contains a servomotor coupled to a gear arrangement for a linear
actuator, which uses brake fluid from the braking system to impel a
hydraulic cylinder to move the main clutch actuator.
The power of the system lies in the fact that electronic equipment can
react much faster and more precisely than a human, and takes advantage
of the precision of electronic signals to allow a complete clutch operation
without the intervention of the driver.
For the needs of parking, reversing and neutralizing the transmission, the
driver must engage both paddles at once, after this has been accomplished
the car will prompt for one of the three options.
The clutch is really only needed to start the car. For a quicker upshift, the
engine power can be cut, and the collar disengaged until the engine drops
to the correct speed for the next gear. For the teeth of the collar to slide
into the teeth of the rings not only the speed, but also the position must
match. This needs sensors to measure not only the speed, but the
positions of the teeth, and the throttle may need to opened softer or
harder. The even faster shifting techniques like powershifting require a
heavier gearbox or clutch or even a twinclutch gearbox.
4.BASIC DESIGN OF DUAL CLUTCH
TRNSMISSION
A dualclutch transmission offers the function of two manual gearboxes
in one. To understand what this means, it's helpful to review how a
conventional manual gearbox works. When a driver wants to change from
one gear to another in a standard stickshift car, he first presses down the
clutch pedal. This operates a single clutch, which disconnects the engine
from the gearbox and interrupts power flow to the transmission. Then the
driver uses the stick shift to select a new gear, a process that involves
moving a toothed collar from one gear wheel to another gear wheel of a
different size. Devices called synchronizers match the gears before they
are engaged to prevent grinding. Once the new gear is engaged, the driver
releases the clutch pedal, which reconnects the engine to the gearbox and
transmits power to the wheels.
So, in a conventional manual transmission, there is not a continuous flow
of power from the engine to the wheels. Instead, power delivery changes
from on to offto onduring gearshift, causing a phenomenon known as
"shift shock" or "torque interrupt." For an unskilled driver, this can result
in passengers being thrown forward and back again as gears are changed.