Short answer: a car’s transmission connects the engine to the wheels.
But there’s a lot more to it than that! Whether it’s a manual or an automatic transmission, there is a ton of incredible engineering that goes into getting the power from the engine to the wheels. The group of parts that accomplish this is called the drivetrain, which includes the transmission, differential, and driveshaft or axles. Basically, everything between the engine and the wheels. We’ll focus on a car with the engine in the front and the driven wheels in the rear since there are slight differences between different layouts. However, it’s pretty much the same idea regardless of which wheels the engine drives.
So, let’s break it down a little. The transmission is the component directly connected to the engine and changes the output rotation speed through a series of gears that can be shifted depending on what the driver needs the car to do. The input shaft of the transmission is directly connected to the crankshaft of the engine, which is the part where the pistons rotate thousands of times per minute (think RPM! Revolutions Per Minute). The gear train is driven by this input shaft and alters the speed of the transmission’s output shaft through the beauty of gear ratios. I could totally geek out about gears, so maybe I’ll save that for another article. This is also where the distinction between manual and automatic cars comes from, based on whether the driver picks the gear or if the car’s computer does so.
Next, the output shaft connects to the driveshaft, which is basically a big cylinder of metal that transmits the rotation from the transmission at the front of the car to the differential at the back of the car. Front-wheel drive cars accomplish this through axles, which require much less strength due to the reduced distance between the transmission and the wheels and the fact that the power is split between two axles instead of one driveshaft. Both of these parts do have some pretty cool engineering built in as well since they need to account for angles between the output shaft and the differential (or the wheels of a front wheel drive car) and various loads throughout their operation.
After the driveshaft, there’s the differential. This part is located between the two rear wheels and essentially changes the direction of the rotation by 90 degrees, going from front to back to each side of the car — the wheels. Differentials utilize a complex gear system (I love my gears) in order to accomplish this with minimal mechanical power losses. The differential also splits the power between the wheels as needed. The outside wheel will need to rotate faster than the inside wheel during a turn, as each wheel follows a slightly different path throughout the turn. The differential has axles that connect to the wheels, completing the drivetrain!
There is still a LOT more depth to each of these parts, but this article gives a basic understanding of how your engine’s power gets to the wheels and moves your car. The drivetrain is one of my favorite parts of how a car works, so I hope you learned something and enjoyed reading!
