Hybrid Car

Exploring The Fundamentals Of HEVs

When the internal combustion engine was first invented in the late 19th century, it proved to be the driving force behind a century of transportation advancement. However, today’s automobile has changed little from that original concept, save minor performance enhancements and efficiency upgrades. In the 1990s, that picture changed with the wide-ranging success of the hybrid electric vehicle, or HEV.

An HEV is a car that combines a traditional engine with a large electric motor, enabling the vehicle to save fuel, pollute less, and reduce roadway noise. These types of vehicles are offered by nearly all major auto manufacturers, and provide the average consumer with a means to help the environment.

Hybrid Drivetrain

HEVs can be divided into two distinct categories: series and parallel. The first vehicle type, series, means that the engine powers a generator that either drives an electric motor or charges the battery bank. From the motor, the power transfers to the transmission and on to the wheels.

At low speeds, approximately 20 MPH or less, the engine will switch off and run in all-electric mode until the battery runs out, at which point the engine will restart in order to compensate. In addition to charging the battery via the engine, series cars also use regenerative breaking. Regenerative breaking is a technology that draws on the energy traditionally lost during braking and uses it to recharge the battery.

The second hybrid design is known as a parallel layout. In parallel vehicles, the engine and motor both interface with the transmission, which then transfers power to the wheels. The batteries in this type are recharged largely by regenerative breaking, but can also be fueled by the engine as well. Because the motor in this design is meant to supplement the engine, these cars are rarely able to enter into all-electric mode.

Hybrid Types

Besides drivetrain differences, hybrids are generally classified in two other categories: full and power assist.

Full HEVs are able to run on the engine or just the battery. For example, the Toyota Prius operates in five modes: electric vehicle mode, cruise mode, battery charge mode, power boost mode, and negative split mode. Depending on road load conditions, the power distribution will vary in order to maintain maximum efficiency.

Power assist cars use the engine as the main power source, with a motor installed to provide an extra burst of power when needed. A subset of power assist vehicles, known as mild hybrids, use oversized starter motors to shutdown the engine when coasting and braking.

That’s a brief overview of HEVs. They have become increasingly popular for their fuel efficiency and lower emissions. In a future column, we’ll explore the motor in more detail.

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Hybrid Cars