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The Science Inside a Gasoline-electric Hybrid Vehicle

The Science Inside a Gasoline-electric Hybrid Vehicle

By Jeff Youngs, February 24, 2012
2009 Nissan Altima Hybrid EngineConsumers seeking the most fuel-efficient vehicles in the showroom today need look no further than a gasoline-electric hybrid vehicle. These tech-filled cars and trucks deliver unrivaled fuel economy in the city, and impressive highway mileage. As an added benefit, their physical appearance is nearly identical to a conventional vehicle, and hybrid gasoline-electric technology has been engineered to deliver a near-seamless consumer interface, meaning there is very little compromise to styling or to the driving experience.

A hybrid vehicle is defined as having more than one power source (e.g., a gasoline engine and an electric motor for propulsion; or fuel cells for energy storage and an electric motor for propulsion). In the case of a hybrid gasoline-electric vehicle, the primary source of power is a gasoline engine (commonly referred to as a "combustion engine," as fuel is exploded inside one or more cylinders) supplemented by a powerful electric motor.While their physical appearance and hardware often mirrors their traditional full-combustion counterparts (e.g., the Nissan Altima Hybrid, Toyota Camry Hybrid and Ford Fusion Hybrids are nearly identical to their conventional siblings), there is a great deal of technology-and many more mechanical components-hidden in the powertrain beneath the painted sheetmetal.

A gasoline-electric hybrid's powertrain is easiest to understand when it is broken into four major components: combustion engine, electric motor, transmission, and battery pack.

The Combustion Engine's Role in a Gas-electric Hybrid
The combustion engine in a gasoline-electric hybrid is tasked with accelerating the vehicle and charging the battery pack. As hybrid cars are designed to maximize fuel efficiency, most will have efficient, small-displacement, 4-cylinder engines under the hood. The combustion engine is designed with an automatic "start-stop" function, whereby the engine shuts down when the vehicle is stopped for more than a few seconds to conserve fuel.

The Role of the Electric Motor in a Gas-electric Hybrid
The electric motor serves dual roles in a gasoline-electric hybrid. First, it supplies supplemental power to assist the combustion engine (think of it as having a second hand to help push the vehicle forward). Second, it acts as a generator to recharge the battery pack during deceleration-called "regenerative braking." Just like the start-stop function, regenerative braking is completely automatic.

The Transmission's Role in a Gas-electric Hybrid
The transmission in a gasoline-electric hybrid is designed to be very efficient. For this reason, most are fitted with automatic transmissions (one exception is the Honda CR-Z, which offers a 6-speed manual transmission). These are either conventionally geared automatics (with torque converters) or continuously variable transmissions (CVTs) that are designed to operate with the engine at peak efficiency.

The Role of the Battery Pack in a Gas-electric Hybrid
The battery pack stores energy for the electric motor, just like a gasoline tank stores fuel for the combustion engine (interestingly enough, it takes 1,000 pounds of batteries to store as much energy as 7 pounds of gasoline). Unlike the familiar flashlight battery, the battery pack on a hybrid gasoline-electric vehicle is comprised of hundreds of small batteries working together to make a large amount of energy, as batteries are much more effective when they are arranged in this manner.

2009 BMW X6 DrivetrainPutting it all Together
The combustion engine, electric motor, transmission, and battery pack all work together to propel the hybrid gasoline-electric vehicle down the road. This is where the technology gets interesting. While a conventional automobile runs its internal combustion engine all the time, the hybrid will alternate between combustion engine and electric motor (or run both simultaneously) based on the vehicle's load and driver requirements. Sophisticated computers manage the engine and motor activity, making it appear nearly seamless to the driver.Hybrid gasoline-electric vehicle technology has proven to be very popular with consumers. With the exception of a few purpose-built models (Toyota Prius and Honda Insight) with unique styling that identifies them as hybrids, in many cases the styling of gasoline-electric hybrids is nearly spot-on with the conventional models-but efficiency is greatly improved. Making this technology even more attractive to buyers is the fact that all hybrid vehicles don't all have to be small compact cars. In fact, they can range from sporty (BMW X6 Hybrid) and luxurious (BMW Active 7 Hybrid) to utilitarian (Chevrolet Tahoe Hybrid) or workhorses (Dodge Ram Hybrid pickup).

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