This is how the electric compressor works in the V6 TDI engine of Audi

Audi switches to diesel in the sporty S versions of its Audi S4, S5, S6, S7 and SQ5. And it does so with a V6 TDI engine that features dual supercharging by electric compressor and turbo.

Many will wonder why Audi has switched to diesel in the V6 engine of its largest “S” models. The truth is that the switch to diesel is not for every market: outside Europe, the Audi S with V6 TFSI engine will continue to be offered.

But the upcoming emissions regulations are very restrictive, and the diesel engine is a very effective way to reduce the range’s average emissions for Audi. And if, in addition, you can offer a diesel that has nothing to envy from previous petrol models in terms of performance, and which also consumes very little, allowing the new Audi S TDI range to display the ECO environmental label from the DGT, then that says it all.

Audi “electrifies” its Audi S4, S5, S6, S7 and SQ5 models with a new version of the brand’s 3-litre V6 TDI engine, which benefits from two key technologies: Mild-Hybrid light hybridisation, and an electrically driven compressor.

Electric compressor = Instant response

The EPC electric compressor is the key to the system. It does not replace the conventional turbocharger driven by the exhaust gases; it complements it, creating a system we could consider as dual supercharging. Audi debuted this configuration in the first Audi SQ7, in that case with a V8 engine.

What the EPC electric compressor achieves is eliminating the characteristic response lag of turbocharged engines when there is not enough exhaust gas flow to drive the turbocharger that compresses the intake air. A more powerful and instant response to the accelerator is achieved.

To do this, Audi uses a compressor driven by an electric motor, which draws its energy from the 48-volt electrical system. The EPC compressor is placed after the intercooler, to be as close as possible to the throttle butterfly.

When the driver floors the accelerator but the energy of the exhaust gases on the turbine side of the conventional turbocharger is low, a valve closes the airflow and directs it to the EPC, which compresses it to a pressure that can reach 2.4 bar.

The advantage here is clear: the 7 kW electric motor is able to do what the exhaust gases cannot until there is sufficient flow, which is spinning the compressor turbine up to 70,000 rpm in less than 250 milliseconds.

For its part, the turbocharger, driven by the exhaust gases, features a variable-geometry turbine, and can handle an air flow of up to 1,100 kg per hour, generating a relative boost pressure of up to 2.4 bar.

You can see a schematic view of how the system works in the following video.

https://youtu.be/QBX30evwfFM

Furthermore, since the EPC works together with the Mild-Hybrid system and 48-volt technology, situations in which the battery runs out of energy are unlikely, which allows the EPC to apply its power as many times as necessary in succession.

The V6 TDI engine of the Audi “S” thus achieves a power of up to 257 kW (349 CV), with a maximum torque of 700 Nm, available from 2,500 rpm up to 3,100 rpm. It meets the Euro 6d-temp emissions standard, and in the case of the Audi S6, for example, it provides a range exceeding 1,100 km, with an acceleration from 0 to 100 km/h in just 5 seconds.