Vehicle Drivetrain Lecture Notes

Factors to Consider When Choosing a Vehicle

• Type (sedan vs. SUV)
• Technology
• Safety features
• Drivetrain type

Definitions

• Drivetrain: Series of parts that make your wheels turn.
• Powertrain: Drivetrain plus the engine and other parts.

Types of Drivetrains

1. All-Wheel Drive (AWD) and Four-Wheel Drive (4WD) – power to all four wheels
2. Front-Wheel Drive (FWD) – power to front wheels
3. Rear-Wheel Drive (RWD) – power to rear wheels

Front-Wheel Drive (FWD)

• Mechanism: Transmission transfers power from the engine to the front wheels using a transaxle.
• History: Experimented in 1895; mainstream in 1930s with Citroën traction avant; popularized by original Mini.
• Pros:
  • Better fuel economy
  • More stable and better traction in hills and slippery roads
  • Cheaper design and manufacturing costs
  • More passenger and cargo space
  • Easier and less expensive maintenance
• Cons:
  • Handling suffers (tendency to understeer)
  • Worse acceleration compared to RWD

Rear-Wheel Drive (RWD)

• Mechanism: Power from the engine is delivered to the rear wheels via a propeller shaft and differential.
• History: Since 1885 with Benz's motor wagon; popular through the 1970s in America.
• Pros:
  • Better handling and acceleration
  • Better for towing
  • More flexible designs (engine placement)
  • Can handle larger engines
• Cons:
  • Less interior space
  • Difficult in wet and snowy conditions

Four-Wheel Drive (4WD)

• Mechanism: Power to all four wheels; features transfer case, differentials, locking hubs.
• History: First patented in 1893 by Brahma Joseph Diplock.
• Pros:
  • Ideal for off-roading and snowy conditions
  • Capability to shift between high and low ratios for torque control
• Cons:
  • Added cost, weight, and fuel inefficiency
  • Not ideal for everyday driving conditions

All-Wheel Drive (AWD)

• Mechanism: Similar to 4WD but typically FWD or RWD as primary mode; features center differential.
• History: Invented in 1903 by Dutch brothers Jacobus and Henrik Jan Spiker.
• Pros:
  • Better acceleration and grip in slippery conditions
• Cons:
  • Less fuel-efficient
  • More parts, weight, and expensive repairs

Summary

• No single drivetrain is best; it often depends on the vehicle's intended use.
• AWD and 4WD are better for low-traction and off-road conditions.
• FWD vehicles are cost-effective and offer better fuel economy.
• RWD vehicles offer better performance and flexibility.