How Hybrids Work:
Hybrid-Electric Vehicles (HEV)

 

What is a Hybrid-Electric Vehicle? As gas prices climb, we hear more and more about the latest automotive alternative. A lot of prospective hybrid buyers desire improved fuel economy, others value cleaner emissions and others just have to have one. Development and production of hybrid vehicles by automakers is on the upswing. But how does this new technology work?

 

Hybrid Fundamentals:

 

A hybrid car, truck or SUV uses more than one means of propulsion -- in this case, an internal combustion engine combined with an electric motor.

As opposed to plugging your car into an electrical outlet (we'll get to that later), a hybrid-electric vehicle (HEV) uses a generator to charge a high-power battery. The generator is driven by two sources of rotational force. One is the conventional internal combustion engine, which keeps the vehicle electrically self-sufficient, and the other is a process referred to as "regenerative braking".

 

Cars and light-duty trucks use a hydraulic braking system which applies pressure at the brake pads or shoes, which contact the brake rotor or drum, respectively. This controlled friction slows the vehicle while wearing down the brake linings and disbursing heat. "Engine braking" is also used to aid in deceleration. This technique employs engine compression when downshifting. Both braking processes convert kinetic energy (motion) into heat (another form of energy), which is unused and discharged into the atmosphere.

Regenerative braking works in concert with standard brakes. When driving an HEV, upon initial depression of the brake pedal, the generator applies resistance to the drivetrain. This resistance slows the vehicle prior to the conventional brakes kicking in. A portion of the kinetic energy, which was previously wasted as heat, now rotates a generator and charges a battery, in turn powering an electric motor. The electric motor then assists the internal combustion engine, therefore transforming a newly harnessed source of power into additional miles per gallon and a reduced production of harmful emissions.

 

The HEV's onboard computer coordinates the system. Upon deceleration it activates regenerative braking to produce electricity. When that's not enough, engine power is directed to drive the generator and sufficiently charge the battery. The hybrid system also has the ability to shut off the engine while the vehicle is stopped, followed by an automatic restart, eliminating unnecessary fuel consumption at idle. Due to the high-torque characteristics of an electric motor, it's used more at low speeds, while the gas engine does most of the work on the highway, resulting in exceptionally high miles per gallon in city driving.

 

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