The drivetrain of a motor vehicle is the group of components that deliver power to the driving wheels. This excludes the engine or motor that generates the power. In contrast, the powertrain is considered to include both the engine or motor and the drivetrain.
The market for drivetrain components is economically important and is estimated to reach US$314.4 billion by 2019. Market value by layout is approximately half for front-wheel drive, with a quarter each for rear-wheel drive (mostly in light commercial vehicles and trucks) and all-wheel drive.
The function of the drivetrain is to couple the engine that produces the power to the driving wheels that consume this mechanical power. This connection involves physically linking the two components, which may be at opposite ends of the vehicle and so requiring a long propeller shaft or drive shaft. The operating speed of the engine and wheels are also different and must be matched by the correct gear ratio. As the vehicle speed changes, the ideal engine speed must remain approximately constant for efficient operation and so this gearbox ratio must also be changed, either manually, automatically or by an automatic continuous variation.
The precise components of the drivetrain vary, according to the type of vehicle.
Some typical examples:
Manual transmission car
- Overdrive Only rarely fitted
- Propeller shaft
- Rear axle
Automatic transmission car
Front-wheel drive car
Four-wheel drive off-road vehicle
- Transfer box
- Transmission brake
- Propeller shafts, to front and rear
- Front and rear axles