Car drivetrain – clutch, gearbox, drive axle and tractive force
Design & TechnologyMechanical EngineeringAges 16–17
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Mechanical Engineering
Power runs from the engine through the clutch, gearbox and drive shaft to the drive axle and wheels: each stage spins at a different speed set by its gear ratio. Click Shift up / Shift down and drag the throttle and road-slope sliders to watch the tractive force F_k = M_e·i_h·i_0·η/r_b, drag force and acceleration change; the tractive-force-vs-speed graph for all 5 gears shows why a low gear is strong but slow while a high gear is fast but weak.
Lesson: General structure of the car and its drivetrain: clutch, gearbox, drive shaft, final drive and differential
What it shows
A car's drivetrain carries engine torque through the clutch, gearbox, drive shaft and final drive to the wheels. Each gear multiplies the torque by its ratio, giving a tractive force F_k = M_e·i_h·i_0·η/r_b at the wheels, while the wheels turn slower by the same factor. The car speeds up only when F_k exceeds the total resistance: rolling resistance, the downhill component of the car's weight, and air drag, which grows with the square of speed. With gearbox ratios from 3.5 down to 0.8, low gears give strong pull at low speed and high gears give speed with little pull.
How to use
Set Initial gear to gear 1 and let the car pull away with the Throttle slider near 70 %. Click Shift up + as the speed rises and follow the green point on the tractive-force graph. Then raise the Slope slider to 15–20 %, increase Total vehicle mass and try shifting up again: note the gear at which the car starts slowing down. Click Disengage clutch while driving to see that no torque reaches the wheels.
Parameters you can change
- Initial gear Gear 1 (i = 3.5), Gear 2 (i = 2.0), Gear 3 (i = 1.4), Gear 4 (i = 1.0), Gear 5 (i = 0.8)
- Throttle opening 0–100 %
- Road slope 0–20 %
- Total vehicle mass 900–3000 kg
Questions to explore
- On a 15 % slope with a 2000 kg car, which gears still give a tractive force larger than the total resistance?
- What happens to the tractive force and the acceleration when you disengage the clutch while driving?
- On the tractive-force graph, why does each gear cover a different range of speeds?
