General Motors has revealed that the Chevrolet Volt/Vauxhall Ampera extended-range electric vehicle (E-REV) can be powered by no less than three motors in certain circumstances – and as a result, has struck controversy with its claim that the Volt is always electrically driven and not a hybrid.
It has previously concealed the inner detail of the Volt’s propulsion arrangements because, it says, it has been seeking a patent for its Voltec drive system.
According to GM’s director of hybrid powertrain engineering Barry Nitz, the system is “patent-protected now, so we can talk about it”.
The additional motor in the system is the Volt’s generator, which can also become a motor and operate in tandem with the petrol engine under the heavy demands of high-speed cruising, assisting the main traction motor that always drives the car.
The reason for bringing in a second electric motor is energy consumption – at high cruising speeds, the efficiency of an electric motor drops off, placing heavier demands on the battery. To overcome this, a planetary gearset blends the outputs of both the combined generator/motor and the petrol engine, and the tractive motor. GM describes this as ‘indirect electro-mechanical drive'.