In series hybrids, all drive is via electricity, there is no rotating mechanical link between heat engine and wheels.
Just like a diesel-electric railway train, the intervening electric drive allows the fuel engine to run continuously at its most efficient operating point – in this case, the engine is a petrol two litre four-cylinder turbo from the company’s DTM racing car, running at 4,500 to 6,000rpm where specific consumption is <200g/kWh, according Audi.
This engine and its generator sit in the centre of the vehicle, feeding an electric motor on the front axle and an electric motor in the back axle – both derived from the MGU05 motor-generator unit, used in Audi’s FE07 Formula E car. “Only minor modifications had to be made to use the MGU in the Dakar Rally,” it said.
The electric axles are fixed ratio, each with a software-controlled limited-slip differential, and a virtual centre differential varies torque distribution between the front and rear axles.
The fourth component in the drive train is a ~52kWh lithium-ion battery weighing ~370kg and being charged at up to 220kW.
Total power output is ~300kW, limited by Dakar event rules. 0 to 100km/h is achieved in <4.5s on loose surfaces and top speed, also event-limited, is 170km/h.