Drivetrain

Not to be confused with powertrain.

For other uses, see Drivetrain (disambiguation).

Engine and drivetrain of a transverse-engined front-wheel drive car

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.

Function

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.

Components

The precise components of the drivetrain vary, according to the type of vehicle.

Some typical examples:

Manual transmission car

Rear axle with hypoid bevel gear final drive

• Clutch
• Gearbox
  • Overdrive Only rarely fitted
• Propeller shaft
• Rear axle
  • Final drive
  • Differential

Automatic transmission car

• Torque converter
• Transmission
• Propeller shaft
• Rear axle
  • Final drive
  • Differential

Front-wheel drive car

Front wheel drive manual transaxle, showing the gearbox and final drive incorporated in the same housing

• Clutch
• Transaxle
  • Gearbox
  • Final drive
  • Differential
  • Drive shafts and constant-velocity joints to each wheel

Four-wheel drive off-road vehicle

Construction vehicle drivetrain, with permanent all-wheel drive

• Clutch
• Gearbox
• Transfer box
• Transmission brake
• Propeller shafts, to front and rear
• Front and rear axles
  • Final drive
  • Locking differential
  • Portal gear

See also

• Hybrid vehicle drivetrain, the drivetrain of hybrid vehicles
• Powertrain, the drivetrain plus engine