NO LAG Audi’s Prototype Electric Turbocharger

Audi is currently working on a new twin-turbo engine design. This prototype uses an electrically-driven turbocharger in conjunction with an exhaust driven turbo to completely eliminate turbo lag and massively increase standing-start performance. Tests showed a two car length increase in distance just three seconds from a standing start.

This new design is based off Audi’s new 3 litre V6 TDI twin turbo engine, and is described by the company as being in the ‘Development Phase’. This V6 diesel engine uses a conventional exhaust-driven main turbocharger with a small motor-driven turbocharger being used at low speeds.
This intelligent design is able to totally eliminate turbo lag by removing the gap between the driver pressing the accelerator and the time taken for the turbo’s boost to come on. Reduction of turbo lag has been the subject of engineer’s efforts for the past three decades. The problem is the need for a sufficient volume of exhaust gasses to be generated by the engine and then directed at the turbocharger, in order to get the turbo’s impellers spinning at high speed to generate the required boost.

This is not a problem when the engine is working at higher RPM, however, when the engine is at lower speeds, the volume of gas isn’t enough to spool the turbocharger up to its operating speed. Many performance shops and car manufacturers get around this problem by using two turbos which are set at different boost and RPM levels. The smaller turbo can be brought into action with smaller volumes of exhaust gas and bridges the gap until the bigger turbo can be brought into play.

Audi’s new system, however, totally eliminates lag, greatly boosts low-speed performance with massive gains in torque and is much simpler than the twin-turbo and triple turbo set-ups used by companies like BMW. Audi’s electric turbocharger is fitted in line with the induction system, sitting before the conventional turbo and the intercooler and is normally not operative. However, at very low speeds - particularly from standstill - the air charged by the main turbo is re-directed through the electric turbocharger which is already spinning at high speed and is then pushed with much greater force into the engine.

A brief drive of a prototype unit in an Audi A6 showed the electric twin turbo setup to be extremely effective. The torque boost from a standing start with the electric turbo working delivers what can probably be described as supercar like performance. Audi’s own real world track tests showed that back-to-back testing against a conventional V6 TDI powered car showed amazing results. The electric twin turbo car was two car lengths further down the road then the standard car, just three seconds after launch.

This early prototype showed there was virtually no drop in torque and power delivery as the electric turbo gave way to main the turbo. This is great news for the future of turbo powered vehicles in the performance car market. There’s no news on when the system will go into production, but the next-generation 2014 Audo A4 which is based on the new alloy, steel hybrid MLB platform, looks likely to receive this engine.

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