How hybrid cars work

After about 100 years on the road, the internal combustion engine in just about every car and small truck you see is showing its age. Its city-choking pollution and its insatiable thirst for fuel are causing problems from smog to global warming. Most cars are lucky to capture about one-third of the fuel’s energy; the rest is lost in the form of heat and noise.
Hybrid technology does it one better by combining a small gasoline engine with a high-torque electric motor and a battery, yielding top gas mileage and greener operations. Rigging up two under-the-hood power plants might sound wasteful, complicated, and prone to failure, but the practice can actually provide 50 percent more miles per gallon while cutting pollution by a third. Best of all, these cars drive as well, if not better, than their gasoline-only counterparts.
Acceleration
Braking
Cruising
Passing
Traditional car

Acceleration
From a dead stop, the car’s control computer taps the battery pack to power the electric motor and put the vehicle in motion. During this process, the gas engine doesn’t start up, so the car moves quietly and without burning any gas.

Braking
Hit the brakes, and regenerative braking takes over. In other words, a generator converts some of the car’s speed into electricity to charge the battery pack. That way, the hybrid is ready for the next battery-powered start.

Cruising
As the car hits about 15mph or 20mph, the electric motor reaches its limit, the gas engine quietly starts up and takes over, and all you should feel is a slight shudder. This gives a hybrid the power to reach and cruise at highway speeds and charge the battery simultaneously.

Passing
At the freeway on-ramp or while passing a slow-moving truck, both the hybrid’s electric and gasoline power plants combine to get to speed quickly and smoothly.

Traditional car
Whether it’s a three-cylinder econobox or a V-12 luxury cruiser, all internal combustion engines work by exploding gasoline to turn chemical energy into mechanical energy, then sending it through a transmission to drive the wheels.

Hybrid cars use different systems to capture wasted energy, from full hybrids, such as the Toyota Prius, to mild hybrids, which may only use the electric motor to add power during acceleration. In a full hybrid, both power plants shut off during traffic stops for an eerily quiet experience. Hit the accelerator, and the electric motor pushes the vehicle to about 15mph or 20mph for fuel-free driving that doesn’t burn an ounce of gas or cost a penny. After the car reaches a certain speed, the gas engine takes over to propel the vehicle to cruising speed, and if you need a little extra power to pass a truck, both power plants kick in.
Forget about having to plug a hybrid in to charge its batteries; the engine and brakes provide electricity. When the car cruises or slows down, regenerative brakes automatically charge the batteries by harnessing the car’s speed and converting it to electricity. If the batteries get low, for example, during extensive uphill driving, the engine revs up to generate more electricity. That way, the batteries stay fresh all the time.
Many hybrids also run on advanced continuously variable transmissions with an infinite variety of gear ratios to choose from rather than the traditional gearbox’s four or five. One very important piece of the puzzle is the power control module, a computer that makes decisions about where to send power in the car. This module monitors throttle, battery charge, and other running parameters, then channels energy to the wheels or battery, from the engine or the motor, as needed. It also shuts down and restarts the engine during traffic stops and starts.
Mild hybrids are less robust. The mildest replace the car’s generator with a strong motor/generator, so the engine can be turned off during traffic stops, and the motor can quickly and seamlessly start it up again when it’s time to accelerate. But in this case, the motor doesn’t actually move the car. There are other points on the scale from mild to full hybrid as well. For example, the full-hybrid system of the Toyota Prius uses a motor connected to the power train separately from the engine, allowing for more flexibility in power use. On the other hand, the Honda Civic Hybrid has a motor integrated between the engine and the transmission. As a result, the Honda system can’t drive the car under electric power for nearly as long as the Prius.