GEARBOX(Transmission System)

Functions of transmission•The main purpose of the transmission is to provide a means to vary the leverage or torque ratio between the engine and the road wheels as required.
•The transmission also provides a neutral position so that the engine and the road wheels are disconnected even with the clutch in the engaged position.
•A means to back the vehicle by reversing the direction of rotation of the drive is also provided by the transmission.

Resistances to the vehicle motion•Resistance due to wind – proportional to the square of the vehicle speed
•Resistance due to gradient – remains constant at all speed.
•Miscellaneous – type of road, tyre friction, etc.

Types of gearbox•Sliding mesh gearbox

•Constant mesh gearbox

•Synchromesh gearbox

•Automatic transmission

Sliding mesh gearbox

        • Main components are clutch shaft, splined main shaft, lay shaft and gears having different sizes.
•  In order to mesh gears on the splined main shaft with appropriate gears on the lay shaft for obtaining different speeds they are moved to the right or to the left. It derives it name from the fact that the mashing of the gears takes place by sliding of gears on each other.

Constant mesh gearbox•All the gears on main shaft are in constant mesh with the corresponding gears on the counter shaft.
•Helical gears are employed for quite operation in this gearbox
•Gear shifting is done by shifting dog clutch to the left or right.

Synchromesh gearbox•In constant mesh gearbox there is a difficulty of double declutching.
•In this type of gear box synchromesh device is provided which avoids the necessity of double declutching.
•The parts which ultimately are to be engaged are first brought into the frictional contact which equalizes their speed, after which these may be engaged smoothly.

Gear selector mechanismTypes of mechanism (two types)
•Mechanism with gear selector lever on the top of the transmission case.
•It consists of gear lever, selector sleeve, selector fork, selector rods.
•Interlocking mechanism is provided to ensures that only one gear can be engaged at a time.

Automatic transmission•Three basic parts of an automatic transmission are
–A torque converter
–A gear train that usually has one or more planetary gear sets.
– a hydraulic system

Torque converter•Torque converter increases the torque in a ratio of 2:1 to 3:1
•It consists of three main parts,
–The impeller or the driving member
–The turbine or the driven member
–The stator

Planetary gear set

 •A simple gear set has a sun gear, about which planet pinions turn around.•These planet pinions are carried by a carrier and a shaft and are also in mesh with a ring gear, which is also called annulus or internal gear.
•The simple gear set is shown in figure can provide any one of the five conditions. It can,
•Increase speed an decrease torque (overdrive)•Decrease speed and increase torque (reduction)•Reverse the direction of rotation (reverse)•Acts as solid shaft  (direct drive)•Disconnect the driving shaft from the driven shaft (neutral)•If one member is held stationary and another is turned, there is a speed increase, a speed reduction, or reverse.
•If two members are locked together, the gear set acts like a solid shaft (direct drive or top gear).
•If no members are locked, no power is transmitted through the gear set (Neutral)Hydramatic transmission•Consists of three sets of planetary gears to obtain four forward speeds and one reverse speed
•It also consist of brake band and set of clutch to obtain different gear ratios