The way cars are propelled from point A to point B has evolved over the centuries, and continues to do so. From early steam and electric cars to modern combustion engines, hybrids, and EVs, automakers utilize many power sources to make cars go. Beyond the power plant, many other parts play a role in transmitting that power to the wheels.
Although the average vehicle owner doesn’t need to know all the nuances of their car’s power system, a basic understanding is useful. This information helps people make vehicle purchases, diagnose issues, reduce accidents, and better appreciate how everything works to maximize performance and efficiency. In this guide, we’ll introduce readers to the essentials of vehicle power. Let’s look at the fundamentals of an engine, the difference between a powertrain and a drivetrain, engines versus motors, and other things you should be more familiar with.
What Is an Engine?
For most of the 20th century, engines were the only accepted method of powering a vehicle, and they remain predominant today despite advances in EVs and other alternative technologies. At its core, an engine is a type of machine that burns fuel, converting the thermal energy (heat) it produces into mechanical power to move other parts, such as crankshafts and pistons.
There are two basic types of engines. For internal combustion engines (ICEs), the fuel combustion happens inside the engine’s cylinder, and the “working fluid” running through the engine is what provides the necessary heat. External combustion engines (ECEs) have a separate fuel-burning chamber and use an outside source to heat the fluid. Steam engines are an example of an ECE.
Because they are more compact and efficient, ICEs are the engines used in cars, motorcycles, boats, airplanes, and more. The engines can further be divided into reciprocating engines, with pistons moving up and down, or rotary engines, with triangular rotors. Reciprocating engines are more common because they are more fuel-efficient and produce lower emissions. Some cars, like the Mazda RX-7, use rotary engines for higher power output from a smaller package with fewer components.
Most ICEs burn gasoline or diesel as a fuel source. The air-fuel mixture in a gasoline engine is ignited with a spark, provided by spark plugs. Diesel engines simply use compression for ignition. Some engines run on alternative options, like biofuels.
Powertrain vs Drivetrain
These terms are often used interchangeably when discussing the chain of components that generate power, convert it to motion energy, and transfer it to the wheels. However, confusing them can lead to problems. Here’s how to tell the powertrain and drivetrain apart.
“Powertrain” is the more general term. It refers to the entire primary component system involved in the energy production and transfer process. This includes the engine, transmission, driveshaft, front and rear differentials, and axle shafts.
“Drivetrain,” on the other hand, only refers to the components that transmit the power to the wheels. As such, the engine is not included in this definition. The drivetrain also includes smaller components like the CV joints, flywheel, etc.
From there, you have four primary drivetrain types: front-wheel drive (FWD), rear-wheel drive (RWD), all-wheel drive (AWD), and four-wheel drive (4WD). Each can be paired with various transmissions (manual, automatic, CVT, etc.) The exact list of components depends on the drivetrain type. For example, 4WD vehicles have a transfer case, while AWD cars use a center differential. FWD and RWD have neither, since only one end of the car is powered. Automatic transmission cars use a torque converter to send power to the axles. A CVT, or continuously variable automatic transmission, uses pulleys and a belt or chain to transfer the engine’s power without using traditional gears. Manual transmission cars have a flywheel and a clutch that work together to send power to the wheels.
Motor vs Engine
I’ve heard and read many people refer to their EVs as having an engine. However, a true all-electric vehicle is powered by a motor. Again, like powertrain and drivetrain, people often think of engines and motors as one and the same. To be fair, they are similar in that both are machines for converting energy to mechanical power and motion.
The difference lies in the original energy source. While engines are designed to convert thermal energy from combustion into mechanical energy, motors are designed to convert electrical energy. They contain a stator and a rotor, each of which is magnetic. When electricity passes through the stator, an electromagnetic field is formed, which causes the rotor to spin and generate torque.
There are many motor types that set up the electromagnetic fields in different ways for certain applications. Most EVs use one of three motor types:
- Alternating current (AC) induction motors are the longest-lasting and most affordable design.
- Brushless direct current (BLDC) motors are known for being efficient and reliable.
- Permanent magnet synchronous motors (PMSMs) are the most efficient motors for high-performance vehicles.
Hybrids, both mild and partial, have an engine plus one or more motors, which combine to produce mechanical energy.
EV Battery vs Gas Car Battery
One way that electric and fuel-powered vehicles are alike is that they have a battery. Each converts chemical energy to electrical energy, but they are vastly different in their construction and how they are used.
The traditional car engine battery has two purposes: to supply electrical power to start the engine and to operate electrical components, such as lights and radios, while the car is off. To achieve this, manufacturers typically use a 12V lead-acid battery containing lead plates and an electrolyte solution. These interact chemically to produce the high current for the necessary jolt of electricity at start-up. The alternator then recharges the battery while the engine is running so it’s ready for the next start.
In EVs, though, the main battery must continuously provide energy to operate the drive motors, requiring a large reserve of electricity. A higher voltage is also required so they work more efficiently and charge faster. To achieve this, most EV manufacturers use lithium-ion batteries. They are energy-dense, perform well in high temperatures, last longer than lead-acid batteries, and don’t “bleed off” as much energy when not in use. Most batteries have a 400V or 800V architecture. The vehicle’s exact range and battery life depend on the battery size, measured in kilowatt-hours, and how powerful the vehicle is.
To fully recharge the battery, you must plug it into another power source, such as a wall outlet or DC fast charger. Some power can be replenished through regenerative braking, which creates electricity as you slow the vehicle and feeds it back to the battery, but this is nowhere near as much as the battery uses. Many EVs also have a separate 12V auxiliary battery to operate the on-board equipment and accessories.
Knowing What’s Under the Hood
With the increasing market share of EVs and hybrids, knowing how your vehicle is powered and how it works takes on higher importance. You don’t want to describe a gas-powered vehicle in electrical terminology or vice versa, as this can cause confusion on many fronts. Understanding the principles of engines, motors, powertrains, drivetrains, and batteries will give you a leg up. I hope this guide gives you the knowledge to discuss vehicle power plants, whether you’re analyzing the benefits of each or trying to describe a problem to a repair technician.