An Automatic Transmission is one where the gears are selected and changed automatically unlike in a Manual gearbox.
Internal components of an Automatic Transmission include:
- Torque Converter:
The way this works is, it hydraulically connects the engine to the transmission. The torque converter takes the place of a mechanical clutch, allowing the transmission to stay in gear while the vehicle is stationary without stalling. There are three main components in the torque converter, they are the Impeller, Turbine and Stator.
- Planetary Gearset:
The bands and clutches are actuated by hydraulic servos which provide 2 or more gear ratios.
- Clutches and Bands:
To change gear, one or two clutches are used to hold a member of the planetary gearset in place while allowing another to rotate.
The differential in a RWD vehicle is situated on the rear axle of the vehicle.
The internal components of a Final Drive Differential include:
- A Crown Wheel and a driving Pinion Gear
- Bevel Gears and smaller Pinion Gears (mounted on a driving pin)
How it works:
As the gearbox spins the drive shaft, the driving pinion gear on the end of it works in motion with the crown wheel which transfers the movement of the drive shaft through 90 degrees so that it can move the wheels. For the wheels to move, the two half shafts of the axle are splined into the holes of the bevel gears, this means that there is an allowance for different rotation speed through the two wheels.
This video gives a great explanation:
http://www.youtube.com/watch?v=wgGmHVV26lE
A Transaxle gearbox is one which has the differential built into it. These types of gearboxes are found in FWD vehicles.
The way it works:
The input shaft is connected to the flywheel, so as the flywheel spins so does the input shaft. On the input shaft there are driver gears. The lower the gear, the smaller the driver wheel is. Each driver gear links up with a driven gear on the output shaft and, conversely, the lower the gear, the bigger the driven gear.
These two shafts transfer the power into the differential which spins the axle.
Theory Background:
The purpose of the clutch is to assist with pull-offs and gear change. The way this works is, the clutch is attached to the pressure plate which is bolted onto the fly wheel. As the clutch pedal is depressed, the pressure plate gets pushed up against the clutch plate which stops the input shaft from spinning. This allows the selectors to engage a different gear.
