In the compression stroke, the piston squeezes the fuel-air mixture into a smaller space. Compressing the fuel-air mixture takes work, just as inflating a bicycle tire with a pump takes work. A spark plug lights the fuel in a gas engine, but if fuel ignites too early because of compression, a gas engine knocks, so spark timing must be precise. Higher-octane gasoline helps fuel ignite on time from the spark plug, not early from the piston's compression.
In a gas car with a transmission, a jolt is usually felt when the transmission shifts from one set of gears to another. A torque converter is a fluid-filled device that sends torque to the wheels in an automatic car, letting the engine idle while the car is stopped. A gearbox lets a gas engine run at efficient speeds no matter how fast the car is going. Most electric vehicles do not use a multi-speed transmission; the motors are usually single speed, and in an electric car, the motor delivers power to the drive wheels through a gearbox.
Electric motors work by electromagnetism: a force is applied when an electric current is in a magnetic field. A DC motor has field coils that create magnetic forces, a rotor (armature) that turns in that field, and a commutating device that reverses the forces. Two types of electric motors are used in electric vehicles: the direct current (DC) motor and the alternating current (AC) motor. An electric motor changes electrical energy into motion.
A differential lets the wheels spin at different speeds while both are still powered, as when a car turns a corner. One electric car layout uses a single large electric motor coupled to the rear wheels through a differential housing, while another layout uses two smaller motors that power each wheel separately through independent drive shafts. With wheel motors, the motors are attached directly to the wheel, which removes driveshafts and differentials.
A hybrid electric car has both an internal combustion engine and one or more electric motors. Parallel plug-in hybrids connect both the engine and the electric motor to the wheels. In a series plug-in hybrid, only the electric motor turns the wheels, and the gasoline engine only generates electricity. A plug-in hybrid can cost roughly $4 to $8 thousand more than a comparable non-plug-in hybrid, as of November 2026.
Only about 12%-30% of the energy in a conventional car's fuel moves it down the road, as of November 2026. EVs convert over 77% of the electrical energy from the grid to power at the wheels, as of November 2026. When an electric car's battery is charged, some energy is lost in changing AC power from the grid into DC power for the battery. An EV electric drive system loses 15% to 20% of the energy, compared with 64% to 75% for a gasoline engine, as of November 2026.
Words to know
- octane: fuel rating
- torque: twisting force
- armature: turning part
- gearbox: gear housing
- hybrid: engine-motor car
- differential: wheel speed gear
