Car Drivetrains and Powertrain Explained

What is a car powertrain? We explain everything you want to know about drivetrains, powertrains, engine types, and electric motors all in one place.

Diving Into How Cars Move

All-wheel-drive vs four-wheel-drive, mid-engine vs front-engine, hybrids, EVs, and internal combustion are all buzz words or phrases that we hear in the automotive sphere often. Interestingly enough each one is important and provides vital information about the vehicle in question. Today we’re taking a look at all of those terms and more to get a better understanding of the cars, trucks, and SUVs that are all around us in daily life.

What is a Car Drivetrain vs a Powertrain?

These two words are used almost interchangeably but they do have different definitions. A drivetrain is made up of the components that deliver power from the source to the wheels. For example, think of a new Chevrolet Corvette. It’s powered by a V8 internal combustion engine. That engine sends its power to the rear wheels through an automatic transmission. In this example, the transmission and the rear axles that deliver the power to the rear wheels make up the drivetrain. When we want to refer to the entire system and include the engine we call that the powertrain.

Drive Layout and Transmission vs Transaxle

Powertrains can be devised in a number of different layouts. For example, the Corvette in our above example has the engine behind the passenger compartment. The transaxle sits behind the engine and delivers the engine’s power to the rear wheels. In the Chevy’s case it’s considered a mid-engine car because the engine is situated between the front and rear axle.

While it’s possible to have an engine in front of the driver and at the same time behind the front axle, it’s fairly rare to call such vehicles mid-engine. Most often they’re considered FR or front-engine with rear wheel drive. In fact, most sports cars and muscle cars utilize one of these two platforms placing the engine either behind the passenger compartment or just ahead of it while both tend to power the rear wheels.

The most common layout is front-wheel-drive or FF as you’ll sometimes see it. It’s popular because it’s cheap to produce and has no major drawbacks for everyday commuting. It’s also more fuel efficient than rear or all-wheel drive. FF-powered vehicles also use a transaxle so let’s talk about how that’s different from a transmission.

Porsche 911 Rear-Axle Steering - presskit.porsche.de

Transmissions simply allow an engine to change gear. They convert the power from the engine into different speeds through gear changes. A transaxle also incorporates the work of a differential into its main component core. A differential quite simply sends the power and torque that’s input into it to the driveshafts so that they in turn can power the wheels. As an example, most full-size pickup trucks use a transmission that is wholly dedicated simply to shifting gears and is completely different from the differentials on the vehicle.

Another notable powertrain layout is the RR or Rear engine with Rear wheel drive. Some of the most famous vehicles to use this layout are the Volkswagen Bug and the Porsche 911. All-wheel-drive or four-wheel-drive is another popular option. All-wheel-drive vehicles typically send a variable amount of power to all four wheels depending on the situation. Systems differ greatly among manufacturers. Many modern cars only send power to the rear wheels when the front wheels slip. Four-wheel-drive indicates that a vehicle is always sending some power, often equal or nearly equal amounts, to all four wheels.

Every vehicle uses some power source to drive at least one wheel if not at least one axle. Now let’s talk about how that power is created.

Internal Combustion Engines

For the last century or so the internal combustion engine has ruled the automotive world. If you’ve ridden in a car, truck, SUV, or bus there’s a good chance that you know a little about these kinds of engines. They most often use gasoline or diesel as their main fuel and ultimately combust those fuels once mixed with oxygen to create power. That power is delivered through the drivetrain to the wheels.

Hybrids

2016 - 2017 Toyota Prius Transaxle - pressroom.toyota.com

Hybrid engines combine an internal combustion engine with varying forms of electrification. For example, the Toyota Prius uses a large battery cell to power the car at low speeds. At speeds above 15 mph, the internal combustion engine provides a trickle charge to the battery at most times. Should a driver put the pedal to the metal, the battery supplements the power already provided by the gasoline engine. These sorts of systems inherently make internal combustion engines more fuel efficient by taking some of the workload off of them and putting it on the battery and electric motor.

Depending on the configuration, the electric motor is integrated into the engine, the transaxle, the transmission, or on a separate axle altogether. All of these systems are still considered to be a hybrid system since a battery is helping to propel the vehicle in addition to the internal combustion engine.

Plug-in hybrid vehicles work on the same identical principles with one noticeable difference. Typically, they have larger batteries and because they offer a literal plug-in they can be charged up independently of the internal combustion engine. Oftentimes these plug-in hybrid vehicles have a not insignificant amount of all-electric range (Apx. 20-50 miles) that they can travel at whatever speeds the driver needs. Because of that range they can be incredibly inexpensive to fuel when compared to a conventional internal combustion car or even some conventional hybrids.

All Electric Vehicles

Today, more and more companies are working hard to build all-electric vehicles for the masses. These cars, trucks, and SUVs use nothing but batteries and electric motors to go down the road. They don’t need conventional transmissions or transaxles either. Most brands tend to build their base electric vehicles with a single motor on the rear axle and a battery that extends the entire length and width of the floor of the vehicle. Adding another motor to the front makes the vehicle all-wheel-drive and those in search of more power and speed have gone beyond that to sell vehicles with three or even four motors all utilizing the energy from the main battery pack.