Transmission

Manual tranmission

In the case of a manual transmission, the flywheel, which is connected to the crankcase of the

engine, runs at a constant speed. Through the use of a manually operated clutch and a shifter,

engine power is reduced and increased significantly through the engagement or

disengagement of a series of larger and smaller gears. This shifting of gears will avoid a

correspondingly significant, inefficient, and potentially damaging increase of engine speed.

These gears are running at different speeds because they are of differing sizes. Larger gears

convert higher engine rpm into higher torque or energy at lower drive wheel speed by

spinning more slowly than the crankcase; smaller gears, conversely, convert lower engine rpm

into higher speed and efficiency by spinning faster than the crankcase.

Gear Selection

The input shaft has only one gear that engages with a gear on the secondary shaft. When it is

running and the clutch engaged, the transmission is said to be in “Neutral”. No gears on the

primary are engaged with gears on the secondary shaft. When shifting into first gear (for

example), the gear on the primary shaft is slowed down by a synchronisation mechanism, and

aligned with a gear on the secondary shaft. The current gear is always disengaged before the

next one is engaged.  When the clutch is re-engaged, rotational energy is transferred from the

transmission to the axle(s) by the drivetrain.

By using progressively smaller ratios, the speed of the vehicle can be maintained or increased

using less power from the engine.

Advantages of Manual transmission

1. Vehicles with manual transmission are usually cheaper than vehicles with automatic

transmission.

2. Manual transmission has better fuel economy as compared to automatic transmission. This

is because manual transmission has better mechanical and gear train efficiency compared

to automatic transmission. Manual transmission also has certain fuel-saving modes of

operation

3. It is cheaper to maintain a vehicle with manual transmission because a vehicle with

automatic transmission is more complicated device and requires more maintainence.

4. Manual transmission offers the driver more control of the vehicle. It also offers better

driving on steep and winding roads. Drivers of manual cars can also downshift to a lower

gear for more power.

5. Vehicles with manual transmission can be started using the push start way when the

battery goes flat.

6. Vehicles with manual transmission can be moved manually by pushing the vehicle at

neutral gear when the engine malfunctions.

7.

Automatic transmission

Automatic transmissions, called transaxles in front wheel drive vehicles, accomplish exactly

the same function through speed-torque conversion. A torque converter automatically engages

and disengages the correct gears in the proper ratio using a system of bands engaging and

disengaging the hydraulically operated clutch pack. This replaces the manually operated

clutch. While manual gearing is in line, the gears in an automatic car are in a "planetary"

arrangement, meaning they revolve around a stationary "sun" gear.

All of this is enabled through the use of gear reduction where larger gears that rotate more

slowly are exchanged via the clutch or the torque converter for smaller, more rapidly rotating

gears to increase the speed of the drive wheels. The reverse of the gearing exchange occurs

with a need to decrease speed. Therefore, the speed of the power source, the engine or motor,

is dampened or enhanced by the manual clutch or the torque converter and clutch pack to

increase the efficiency of, as well as decrease the wear and tear on, the engine while providing

the needed torque to thedrive shaft.

Gear Selection

Gear selection in automatic transmissions depends on many operational conditions, such as

vehicle speed, engine speed, performance mode (where fitted) selected as well as driver assist

systems such as traction control, stability control, automatic/autonomous braking and cruise

control.

Rotational energy is provided by a torque converter, a mechanism consisting of two freely

rotating parts. One half is attached to the engine and the other to the transmission input shaft.

The two halves of the converter are positioned very closely together. The fluid that circulates

between them is influenced by the rotational energy of the engine which in turn impacts the

transmission side of the converter. Torque is transferred from the engine to the transmission

thanks to the shearing strength of fluid.

In older automatic transmissions, the shifting action was accomplished by internal fluid

pressures overcoming spring tension – closing one circuit before opening another. This

control system produced harsh, jerky shifting. Modern systems moderate the action of the

controlling valve shuttles, providing almost seamless shifting.

Advantages of Automatic Transmission

1. Easy to drive

Driver of vehicles with automatic transmission do not have to shift the gear manually and step

on the clutch.

Continuously Variable Transmissions (CVT)

this transmission doesn’t use gears as its means of producing various vehicle speeds at

different engine speeds. Instead of gears, the system relies on a rubber or metal belt running

over pulleys that can vary their effective diameters. To keep the belt at its optimum tension,

one pulley will increase its effective diameter, while the other decreases its effective diameter

by exactly the same amount. This action is exactly analogous to the effect produced when

gears of different diameters are engaged.

Gear Selection

Since one pulley is driven by the engine and the other is connected to the drive shaft, an

infinite number of ratios can be produced. This enables it to always run at the most efficient

speed, regardless of the load placed on it. Microprocessor-controlled sensors quantify load

variations and by adjusting both pulleys, the optimum operating speed for the engine can be

maintained without any input from the driver.

Advantages

1. Constant, stepless acceleration throughout the engine’s optimum operating range

2. Provides a comfortable ride by eliminating “shift shock”

3. Better fuel efficiency

4. Faster response to changing driving conditions such as variations in throttle and engine

speed

5. Eliminates energy losses associated with torque converters. Bottom of Form