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Hybrid Powertrain Overview

Hybrid Powertrain Overview

One term we are increasingly going to come across in Car Guide Me is ‘Hybrid Powertrain’. As you can expect, hybrid is used because it uses the best of two or more systems, although the common usage is limited to a drive system that uses a conventional internal combustion engine of some sort, along with an electric powered motor. The electricity for this system is usually provided from batteries. Hybrid systems are further divided depending on how these batteries receive energy, whether from an external power source (plug-in hybrid) or from the regenerative brakes and on board generator feeding off the internal combustion engine.

Modern day hybrids, as seen on the Toyota Prius, use a fairly regular capacity four or six-cylinder engine that is tuned to maximise fuel efficiency. Any shortcoming of either torque or top-end power is made up for by the selective meshing of the electric motor to the transmission. A major plus point is that the battery bank has enough draw available to offer instant engine start up as well as allow the vehicle to move some distance at slow speeds.

If you view the cutaway of the Toyota Prius engine shown here, the Atkinson cycle four-cylinder engine is to our left, with the Electric motor on the right. The gears visible in between represent the gearbox sitting over the transaxle, delivering the torque through to the front wheels. This makes for a very compact assembly. The larger layout shows the location of the lithium-ion batteries at the rear of the car (just ahead of the fuel tank) in order to distribute weight evenly and the power line stretching between in yellow. The unit in between is the high voltage controller.

Some hybrid systems could split the drivetrain so that power to the front wheels is delivered through the engine and gearbox while the rear wheels could be driven by electric motors. Also, while it may look similar, the hybrid powertrain differs from an electric vehicle powered by a range extender internal combustion engine (used purely to power an on board generator for the batteries).

The range available purely in electric mode on a hybrid powertrain depends to a large extent on the capacity of the battery (usually Li-ion).

The Prius’ Li-ion battery

Some brands like Infiniti use their hybrid powertrain layouts to offer the powerful torque of the electric motor for quick getaways, as well as to stretch top-end power. That just goes to show how well developed the technology has become.

Another form of the hybrid layout, the Mild Hybrid is used as a bridge between regular stop/start systems and Hybrids. The Mild Hybrid electric motor is used along with the internal combustion unit to offer instant start up, and better fuel efficiency. However there is no point during which the electric motor alone drives the wheels.

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