In Detail: GM Voltec Range-Extended Electric Drivetrain
Designed to bridge the gap while hydrogen fuel cell and public charging infrastructure develops across Europe, both vehicles feature an efficient petrol engine to maintain battery charge once it drops below one third of its capacity. General Motors says this offers medium range electric motoring, without sacrificing long-range capability when needed.
- Range extender – The Euro 5 compliant 1.4-litre 16v petrol engine under the Ampera’s bonnet never directly turns its wheels. Instead, it’s used to turn a generator which maintains battery charge when it drops under 33% and boosts available power under heavy acceleration. This allows the Ampera to cover most of its mileage on electricity alone, with the backup of conventional refuelling times when needed.
- Battery pack – Installed in the transmission tunnel, the T-shaped battery pack is designed not to compromise interior or boot space, and gives the Ampera a low centre of gravity for sporty handling. The unit comprises 288 individually temperature controlled lithium ion pouch cells, each roughly the size of an A5 sheet of paper, and an advanced control module.
- Electric drive – As an electric motor reaches its maximum speed, its efficiency drops. The Ampera features two electric motors, one of which moves the car at lower speeds, and a second which works as a generator for the battery. At higher speeds, the generator becomes a second traction motor and provides extra power, allowing both to run as efficiently as possible.
- Transmission – The transmission system manages energy flow between the two electric motors and petrol range extender. There are three clutches to channel engine and motor power to where it’s needed most, and a planetary gearbox with geared final drive through which the electric motors turn the wheels.
- Charging port – Looking like a second fuel flap, the charging port is located on the front wing and is the main difference between the Volt and Ampera. Chevrolet’s system is designed for lower voltage American outlets, while the Vauxhall/Opel port has variable charging speeds which can be altered to suit different European countries.
- Charging – Plugged into a conventional home electricity socket, the Ampera and Volt can be topped up to full charge in as little as XXX hours, depending on the voltage of the outlet. In the United States, the Chevrolet Volt’s charging times can be controlled remotely using a smartphone application.
The battery’s thermal management system also uses mains-supplied electricity to preset the battery temperature before the car is driven. Not only does this adjust the temperature to the battery’s most efficient range, but it reduces the energy demand while the car is moving, maximising the available electric range.
- Low speed electric – At low speeds, the car is driven by one of its electric motors with power supplied by the battery. The second motor works as a generator, topping up battery charge while braking or driving down steep inclines. The range extender is inactive.
- High speed electric – Once the low speed motor reaches its maximum rotational speed, the Voltec drivetrain switches seamlessly to a two-motor operation to improve efficiency. In this mode it still consumes no fuel, but can recuperate braking energy to top up the battery charge.
- Range extended low speed – The range extender is activated once battery charge drops below 33%. At low speeds, the car uses a single electric motor to drive the wheels, while the engine powers the second electric motor as a generator to top up the battery. But the engine doesn’t run constantly, and can deactivate when not needed, such as on long downhill stretches where the battery can be charged using regenerative braking.
- Range extended high speed – At high speeds, both electric motors are used to move the car, while the range extender cuts in as needed to maintain battery charge and provide a power boost to the front wheels through the second electric motor.