Audi EREV patent: how the second-axle motor doubles as the generator

© A. Krivonosov

One electric motor instead of two separate units — that's the idea behind Audi's new patent. In a conventional series EREV, the internal combustion engine turns a dedicated generator, while electric motors at the wheels handle propulsion. Audi's patent hands the generator's job to the motor on the second axle, using controlled clutches to switch its role on the fly.

With a charged battery, the primary and secondary motors can drive different axles, forming all-wheel drive. When the charge runs low, the engine starts up and, through a clutch, turns the second motor into a generator. The strangest mode adds a third path: the gas engine can send torque straight to the wheels through that same motor and the transmission.

Technically, this setup is hard to call a pure EREV anymore. In a classic series-hybrid range extender, the engine is mechanically disconnected from the driven wheels. Here, Audi ends up with a multi-mode hybrid: the car can run as a pure EV, as a series hybrid, or use the engine directly for propulsion, depending on conditions.

The engineering upside is straightforward — a separate motor-generator becomes unnecessary, along with its dedicated power electronics, trimming cost and weight from the electric side. The trade-off is more clutches and more complex control logic. There's also a specific concern for Audi: if the second-axle motor is busy generating power at a given moment, keeping quattro all-wheel drive working as expected could get harder.

For the brand, mixing mechanical complexity with electrification is nothing new. In May, another Audi patent proposed overlapping the clutches in the S tronic gearbox for near-instant gear changes. It's a different technology, but the approach is similar: rather than simplifying the transmission, Audi keeps asking it to do more.

The brand's production hybrids are still built the conventional way for now. The Audi A5 Avant TFSI e-hybrid quattro, for instance, pairs a gas engine with an electric system in a classic PHEV layout and can cover up to 108 km on electric power alone in its Japanese specification. The new patented idea stands out specifically for trying to cut the number of electric machines without giving up the engine's mechanical link to the wheels.

For now, it's just a protected technical concept. The patent confirms neither a future production model nor a timeline, and the savings from one fewer electric motor only make sense if the clutches, control software, and maintenance of a multi-mode transmission don't eat up the advantage.