Universal Joints

Cars are finely engineers devices, but some parts are surprisingly simple. One of them is the drive shaft. The job of the engine is to convert vertical energy into rotation that can power a wheel. This was first achieved using steam engines where the linear motion of steam was converted into power for wheels using complex joints. In combustion engines, power is transferred to the wheels via the drive shaft. 

Although they often contain universal joints that allow them a degree of flexibility, the shaft is little more than a spinning rod that transfers rotational energy from the engine to either the front wheels or the rear wheels. All-wheel drive requires a longer shaft and is a bit more complicated. While this solution might seem crude, it is in fact the most efficient option. The alternative would be to convert power into electricity and then back into rotational energy.

Extra information about universal joints

The efficiency of a combustion engine seldom exceeds 30 percent. The rest is lost as heat and some friction. Because the drive shaft delivers the working power to the wheels, it must be very efficient. This means that it is well lubricated and uses finely crafted joints that are resistant to effects from vibration. It is very precise and does not lose much power. If it did, then it would be torn apart by friction and heat.

Power from the engine goes from one of two places. Either power is transferred to the power converter in order to charge the battery or else it is use to drive the car. The engine also idles when it is stopped, at which point the drive chain might unlock from the idle engine so that no unnecessary forces are applied.

The drive shaft itself is simple, but it is controlled by a complex mechanism called the transmission. This is a complex system of gears that converts power from the engine into power for the drive shaft and also for the battery charger. This complexity is necessary because more force is needed to start a car than is needed to keep it in high speed. Also, traversing wet or icy terrain might require a higher gear ratio due to poor traction from the wheels.

The transmission determines how much power goes into the shaft and at what speed. It is possible for the shaft to rotate at a slow speed but with far more torque than at high speed. This is possible because of a high gear ratio that turns a faster spin into more power at a lower speed. Again, this is important when first starting a car. It is hard to break inertia, and a car is actually hardest to decelerate at low speeds because of all the power being applied by the engine.

The drive mechanism is remarkable for its resilience. The joins are precisely fashioned and well lubricated so they experience minimal friction and are able to spin at the incredibly high speed necessary to power a car on the highway. Future improvements might be possible, but it is hard to beat the capacity and longevity of the device already in your car.