Drivetrain

For other uses, seeDrivetrain (disambiguation).

Not to be confused withtransmission (mechanical device).

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

Adrivetrain(also frequently spelled asdrive trainor sometimesdrive-train) ortransmission system,is the group of components that deliver mechanical power from theprime moverto the driven components. Inautomotive engineering,the drivetrain is the components of a motor vehicle that deliver power to thedrive wheels.This excludes the engine or motor that generates the power. In marine applications, thedrive shaftwill drive apropeller,thruster, or waterjet rather than adrive axle,while the actual engine might be similar to an automotive engine. Other machinery, equipment and vehicles may also use a drivetrain to deliver power from the engine(s) to the driven components.

In contrast, thepowertrainis considered to include both theengineand/or motor(s) as well as the drivetrain.

Function

The function of the drivetrain is to couple the engine that produces the power to the driving wheels that use this mechanical power to rotate the axle. This connection involves physically linking the two components, which may be at opposite ends of the vehicle and so requiring a longpropeller shaftordrive shaft.The operating speed of the engine and wheels are also different and must be matched by the correctgear 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 automaticcontinuous variation.

Automotive 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

• Flywheel
  • Dual mass flywheelstill rare
• Clutch
• Gearbox
  • OverdriveSince the adoption of 5 speeds has become standard
• Propeller shaft
• Rear axle
  • Final drive
  • Differential

Automatic transmission car

• Torque converter
• Transmission
• Propeller shaft
• Rear axle
  • Spool
  • Differential

Front-wheel drive car

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

• Clutch
• Motor
  • Gearbox
  • Final drive
  • Differential
  • Drive shaftsandconstant-velocity jointsto 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 rearaxles
  • Final drive
  • Locking differential
  • Portal gear

Final drive

A cutaway view of an automotive final drive unit, which contains the differential

The final drive is the last in the set of components which delivers torque to thedrive wheels.In a road vehicle, it incorporates thedifferential.In a railway vehicle, it sometimes incorporates the reversing gear. Examples include theSelf-Changing GearsRF 28 (used in manyfirst-generation diesel multiple unitsofBritish Railways)and RF 11 used in theBritish Rail Class 03andBritish Rail Class 04diesel shunting locomotives. In amotor vehicle,thepowertrainconsists of the source of propulsion (e.g. the engine or electric motor) and the drivetrain system which transfers this energy into forward movement of the vehicle.

Powertrain

Definition

The powertrain consists of the prime mover (e.g. an internal combustion engine and/or one or more traction motors) and the drivetrain - all of the components that convert the prime mover's power into movement of the vehicle (e.g. thetransmission,driveshafts,differentialandaxles);whereas the drivetrain does not include the power source and consists of the transmission, driveshafts, differential and axles.

Power sources

Most passenger cars and commercial vehicles are powered by either aninternal combustion engine,electric motor(s) or a combination of the two.

The most common types of internal combustion engines are:

• petrol engines
• diesel engines
• ethanol blends(such asE85andE10)
• liquefied petroleum gas

Most purely electric vehicles use batteries for energy storage and are referred to asbattery electric vehicles.

Vehicles with both internal combustion engines and electric motors are calledhybrid vehicles.If a hybrid vehicle includes a charging socket, it is considered to be aplug-in hybrid,while vehicles that do not include a charging socket (therefore relying on the engine orregenerative brakingto charge the batteries) are considered to bemild hybrids.

See also

• Two-wheel drive– Type of drivetrain with two driven wheels
• Four-wheel drive– Type of drivetrain with four driven wheels
• 6×4 (drivetrain)– Type of drivetrain with 4 out of 6 driven wheelsPages displaying short descriptions of redirect targets
• Six-wheel drive– Type of drivetrain with all six wheels driven
• Eight-wheel drive– Vehicle system with 8 powered wheels
• H-drive– Drivetrain for off-road vehicles
• Continuous track– System of vehicle propulsion
• Hybrid vehicle drivetrain– Systems vehicles with multiple power sources use to transmit power to the wheels, the drivetrain ofhybrid vehicles
• Automotive safety– Study and practice to minimize the occurrence and consequences of motor vehicle accidents
• Driveline shunt
• Electric vehicle– Vehicle propelled by one or more electric motors
• Electric vehicle conversion– Process of converting a vehicle to use electric propulsion
• Giubo– Type of flexible coupling used to transmit rotational torque
• Gear train– Mechanical transmission using multiple gears
• Internal combustion engine– Engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber
• Propulsion transmission– Drivetrain transmitting propulsion powerPages displaying short descriptions of redirect targets