Drivetrain in Motorsport

In this article, I will be looking into the purpose of the drivetrain, drive modes, gearing, the gearbox and gear types, motorsport gearbox characteristics and roller chains vs belt drives. Please feel free to skip to the parts most relevant to you.


Drivetrain Purpose

The main role of the drivetrain is to transfer the power/energy from the engine or energy source to the ground. This allows the vehicle to start from rest and lets the vehicle stop by disconnecting the drive As well as this, it varies the speed ratio between the engine of the ratio making it possible to change this ratio.


Drive Modes

Predominantly, there are three type of drive modes:
  • Front wheel drive (FWD) - This involves a transverse engine where the transmission connects to the differential on the front axle shaft, 
  • Rear wheel drive (RWD) - This will involve a longitudinal engine where the transmission connects to a driveshaft that sends the torque to the rear axle and differential.
  • Four wheel drive (4WD) - The engine will have the transmission connected to the transfer case, where there will be two driveshafts coming off of the transmission for the front and rear axles respectively.

For a motorsport application:
  • FWD joints cannot handle the power transmission so is not used.
  • RWD is better as there is better traction at the back during acceleration,
  • It is difficult to balance a FWD car.
  • There must be space required for the front suspension of a FWD car.
  • The turning wheels should have the least amount of unsprung weight.

Gearing

In simple terms, the number of teeth going into a gear divided by the number of teeth coming out of the next gear is the gear ratio. The gearing makes it possible so that when the maximum RPM of the engine has been reached, by gearing the transmission and engine to  gear with a lower number of teeth and lever length, the engine can rev again and continue accelerating.

Power = torque x rotational speed


Gearbox

The input in the gearbox is a spline shaft with the output being the fixed cars. As well as this, there is oil to keep the gearbox and gears cool and to also help lubrication. The power from the engine is transferred by the input shaft into the gearbox. The countershaft and gear pairs are always engaged while the output gears are not fixed to the output shaft.


Gear Types

There are many different types of gears you can find such as:
  • Straight gear on spur - This has a high impact and noise, no thrust, simple and easy to manufacture and reverse whine.
  • Helical gear - This operates on a gradual engaging, has thrust and is the most common choice of gears for most gearboxes.
  • Strain bevel gear - For this type of gear, the shaft intersects but is not parallel. It has a high impact and noise.
  • Helical bevel gear - The shaft of this gear intersects but is also not parallel. With this type, there is thrust and low noise.

Motorsport Gearbox Characteristics

Here are some of the characteristics you will find in gearboxes that have a motorsport application:
  • Variable gear ratios
  • High number of gears (at least six).
  • High torque rating of 300-400 Nm+
  • Easy access to the gear pairs
  • Lubricating system integrated
  • Gears are small in size and inertia
  • Compact design
  • Lightweight and made from materials (usually aluminium or magnesium).

Roller Chain vs Belt Drives

For drive trains, they will either use roller chains or belt drives to transfer to torque between open gears. Here is a simple comparison between roller chains and belt drives:
  • Slip - Roller chain will have less slip than belt drives.
  • Tension - Roller chains are more in tension than belt drives too.
  • High torque application - Roller chains are much better for high torque applications.
  • Flexibility - Belt drives are far more flexible than roller chains.
  • Life (wear) - The roller chain will wear faster than belt drives.
  • System mass - Roller chains are heavier than belt drives.
  • Noise - Roller chains are nosier than belt drives.
  • Maintenance - Roller chains need to be maintained more than belt drives.