The Audi 4.0t Engine represents a significant leap forward in automotive engineering, blending robust performance with enhanced fuel efficiency. This twin-turbo V8 engine, first introduced in Audi’s S models like the S6, S7, S8, and later in Bentley’s Continental GT, showcases Audi’s commitment to innovation. A key feature is its “cylinder on demand” technology, designed to reduce fuel consumption without sacrificing the exhilarating driving experience expected from a high-performance vehicle.
Cylinder on Demand Technology: Maximizing Efficiency
The core innovation of the audi 4.0t engine lies in its “cylinder on demand” (COD) system. This intelligent technology deactivates four of the eight cylinders during part-load operation. When the engine is cruising or under light load, specifically in third gear or higher and at low to moderate engine speeds, the system springs into action. It seamlessly shuts down cylinders 2, 3, 5, and 8, allowing the engine to run as a V4.
This cylinder deactivation is not just about reducing the number of active cylinders; it’s about optimizing efficiency. By operating on fewer cylinders when less power is needed, the engine’s active cylinders work at a higher load point, thus improving combustion efficiency. According to the New European Driving Cycle (NEDC) test, this technology reduces fuel consumption by approximately five percent and lowers CO2 emissions by 10 to 12 grams per kilometer. When combined with the start-stop system, which is standard in Audi S models and shuts off the engine when the car is stationary, the total emission reduction can reach up to 24 g/km of CO2.
The system is designed to be imperceptible to the driver and passengers. Sophisticated engineering ensures that there is no noticeable noise or vibration when the engine switches between eight and four-cylinder modes. This smooth transition is achieved through two key technologies: Active Noise Control (ANC) and active engine mounts.
How Cylinder Deactivation Works
The “cylinder on demand” system in the audi 4.0t engine is triggered under specific conditions: low engine load, engine speeds between 960 and 3,500 rpm, coolant temperature above 30°C (86°F), and in third gear or higher. When these criteria are met, the system closes the inlet and exhaust valves of cylinders 2, 3, 5, and 8.
This valve closure is managed by an enhanced Audi valvelift system (AVS). Sliding sleeves on the camshafts, electromagnetically controlled, engage “zero-lift” cams. These cams prevent the valve lifters from moving, thus keeping the valves closed. Simultaneously, the engine management system cuts off fuel injection and ignition to the deactivated cylinders. Prior to valve closure, fresh air is drawn into the combustion chambers, reducing pressure and minimizing energy loss from piston movement.
The transition between four and eight-cylinder modes is remarkably quick and smooth, taking place in just about 300 milliseconds. The instrument cluster display provides feedback, indicating when the four-cylinder mode is active, with the fuel consumption indicator bar turning green. If the driver demands more power by pressing the accelerator pedal firmly, the deactivated cylinders instantly reactivate, seamlessly restoring full V8 power.
Refinement and Comfort: Countering Noise and Vibration
A challenge with cylinder deactivation is managing potential noise and vibration. The audi 4.0t engine ingeniously addresses this through Active Noise Control (ANC) and active engine mounts, ensuring a refined and comfortable driving experience even in four-cylinder mode.
Active Noise Control (ANC)
ANC is a sophisticated system that actively cancels out unwanted engine noise. Microphones strategically placed in the car’s roof lining monitor the interior sound environment. The ANC control unit analyzes these sound signals, identifying and targeting potentially disruptive noise frequencies generated when the engine is running as a V4.
Once identified, the system generates “anti-noise” – sound waves that are precisely out of phase with the unwanted noise. These opposing sound waves are emitted through the car’s loudspeakers, effectively canceling out the undesirable engine noise through destructive interference. This ensures that occupants experience a quiet and undisturbed cabin, regardless of whether the engine is operating in four or eight-cylinder mode.
Active Engine Mounts
Complementing ANC, active engine mounts further enhance refinement by counteracting engine vibrations. Traditional engine mounts are often a compromise between comfort and handling. However, the audi 4.0t engine employs advanced electromagnetic active engine mounts that dynamically adapt to driving conditions.
Sensors detect vibrations originating from the engine, particularly when running as a V4. The active engine mounts then generate counter-oscillations, effectively neutralizing these vibrations before they can be transmitted to the car’s chassis and cabin. This technology uses an electromagnetic oscillating-coil actuator that rapidly adjusts to minimize vibrations, resulting in a smoother and more comfortable ride. These mounts are effective even at idle in eight-cylinder mode, further reducing typical V8 engine vibrations.
Performance and Specifications of the 4.0 TFSI
Beyond fuel efficiency, the audi 4.0t engine is engineered for high performance. It is a 4.0-liter (3,993 cc) twin-turbocharged V8, available in different power outputs depending on the Audi model. For the S6, S6 Avant, and S7 Sportback, it produces 309 kW (420 hp) and 550 Nm (405.66 lb-ft) of torque. In the S8, the engine is tuned to deliver a more potent 382 kW (520 hp) and 650 Nm (479.42 lb-ft) of torque.
Despite its high power output, the engine achieves impressive fuel economy. In the Audi S8, fuel consumption is around 10 liters per 100 km (23.52 US mpg), while the S6 and S7 Sportback achieve even better figures. This balance of power and efficiency is a testament to Audi’s engineering prowess.
Advanced Engine Technologies
The audi 4.0t engine incorporates a suite of cutting-edge technologies beyond “cylinder on demand.” These include:
- Twin-scroll turbocharging: Each cylinder bank is paired with a twin-scroll turbocharger, optimizing responsiveness and torque delivery by separating exhaust pulses to the turbine. This design enables rapid torque build-up even at low engine speeds.
- Innovative cylinder head design: The turbochargers and intercooler are positioned within the V of the engine, while the cylinder heads have exhaust ports on the inside and intake ports on the outside. This configuration results in a more compact engine, shorter gas flow paths, and enhanced thermal management.
- Thermal management system: A sophisticated thermal management system optimizes engine warm-up and operating temperatures, reducing friction and improving efficiency. It includes features like a switchable water pump and controlled oil jet cooling.
- Minimized internal friction: Advanced manufacturing techniques and materials, such as plate honing and diamond-like carbon (DLC) coating on gudgeon pins, minimize internal friction, further contributing to efficiency.
- Direct fuel injection (FSI): Fuel Stratified Injection (FSI) ensures precise fuel delivery directly into the combustion chamber, enhancing combustion efficiency and power.
Bentley’s Adoption of the 4.0 TFSI
The innovative audi 4.0t engine was not only destined for Audi’s high-performance S models but also found its way into Bentley vehicles, highlighting its versatility and advanced engineering. Bentley, involved in the engine’s development, adopted the 4.0 TFSI for its Continental GT. In Bentley applications, the “cylinder on demand” system is crucial for enhancing fuel efficiency in grand touring, where a blend of power and range is essential.
Bentley’s integration of this engine underscores its refined nature and harmonious power delivery, perfectly aligning with the grand tourer character of the Continental GT. The fuel savings achieved through cylinder deactivation are particularly significant in larger, luxury vehicles like Bentleys, contributing to both environmental responsibility and extended driving range.
Conclusion
The audi 4.0t engine stands as a remarkable achievement in modern engine design. Its “cylinder on demand” technology, coupled with ANC and active engine mounts, delivers a unique combination of exhilarating V8 performance and surprising fuel efficiency. Audi’s commitment to pushing technological boundaries is evident in every aspect of this engine, from its advanced turbocharging system to its innovative thermal management. The 4.0 TFSI not only enhances the driving experience of Audi S models and Bentley Continental GT but also sets a new benchmark for efficient performance in the automotive industry.
