The Goal of a Transmission

Cars need transmissions because of the physics of the IC engine

First, any engine has a redline -- a maximum rpm value above which the engine cannot go without exploding

Second, engines have narrow rpm ranges where horsepower and torque are at their maximum

The transmission allows the gear ratio between the engine and the drive wheels to change as the car speeds up and slows down

You shift gears so the engine can stay below the redline and near the rpm band of its best performance

Manual Transmission Also known as stick shift or standard

transmission uses different sets of gears to change the gear ratio

The manual transmission locks and unlocks different sets of gears to the output shaft to achieve the various gear ratios

They allow a greater proportion of the engine's power to be used, and because they give drivers the greatest possible degree of control over the operation of the vehicle's power

Types of Gear Boxes Crash mesh or Sliding mesh

gear box

Constant mesh gear box

Synchromesh gear box

Sliding mesh gear box1. drive

shaft from engine

2. counter shaft

3. main shaft 4. I gear 5. II gear 6. III gear 7. top speed

engaging dogs

Sliding mesh gear box – I gear position

Sliding mesh gear box – II gear position

Sliding mesh gear box – III gear position

Sliding mesh gear box – reverse gear position

Sliding mesh gear box –Disadvantages Only Straight cut (Spur) can be

used. So more wear Straight-cut gears had to be

matched in speed before being brought into mesh together. The result was a horrible grinding noise - crashing the gears, as it was known

changing gear requires considerable skill

Double de-clutching This is to match the speed of the rotating parts

of the gearbox for the gear you wish to select to the speed of the input shaft driven by the engine. Once the speeds are matched, the gear will engage smoothly..

To perform it, the clutch is pressed and the gearbox shifted into neutral gear. The clutch is released, the throttle is "blipped" which applies power to the disengaged gearbox, thus speeding it up internally. The clutch is pressed for the second time and the gear lever moved (smoothly) to the desired gear. The clutch is released again, and the drive continues. This operation is suitable for a down change.

For an upchange, it is usually sufficient to allow the gear lever to rest momentarily in neutral and no "blip" is applied.

Constant mesh gear box

Constant mesh gear box Constant-mesh gearboxes are

quieter and slicker, also less wear because of Helical gears

More frictional losses due to meshing of all gears all time

But you still have to match the spinning speeds before you could engage the chosen gear, i.e. need for double-de-clutching

Synchromesh gear box In a synchromesh gearbox,

gears can freely rotate or be locked to the shaft

It consists of a sliding collar which bridges between two circular rings with teeth on them - one travels with the gear, one with the shaft. When the rings are bridged, the gear is locked to the shaft. To match the speed of the gear to that of the shaft as the gear is engaged, the collar initially applies a force to a cone shaped clutch which is attached to the gear. This spins the gear up or down in speed to match the shaft prior to engagement of the collar.