A driveshaft, also called a propeller shaft, connects a vehicle’s transmission to the differential. As far as propulsion systems go, the driveshaft has a pretty simple purpose: transmit torque between the engine/transmission system and the wheels. Drive shaft rotation energy is transferred to the wheels through a gear system housed in the differential. Barring a catastrophic mechanical failure or excessive vibration, drive shafts require little maintenance or repair.
A vehicle’s driving shaft has to be designed to meet high standards for the following performance metrics:
- Shear Stress and Vibration
- Warping when Exposed to Temperature Extremes
- Torque Transmission Efficiency
Usually, joints connect several propeller shaft components when the shaft has to be relatively long.
There are several prominent joint designs for propeller shafts. The most common are universal and constant-velocity joints. Universal joints have the advantage of allowing two components of a propeller shaft to pivot through a wide angle. This is advantageous in complicated machinery where the line between an engine/transmission and the differential is blocked by other components. Constant-velocity joints are specially designed to maintain constant rotation speed between two components of the driving shaft, even at significant angles. Universal joints generate vibration and angular momentum discrepancies if deviation angle becomes large enough. Joint design can be as important as the driveshaft itself.
As with everything, cost/performance tradeoffs are inevitable in drive shaft selection and repair. Constant-velocity joints are more expensive than universal joints but are usually worth the price in efficiency and durability. Drive shafts can be severely degraded by vibrations and improper joint alignment. Sudden braking/acceleration can also reduce driveshaft lifetime since doing so puts stress on the shaft, joint components and differential gears.