Cylinder Deactivation

The Art of Driving Further with Less

Cylinder deactivation isn't new, but it's become a crucial tool for optimizing modern internal combustion engines. Known by various names such as ACT (Active Cylinder Technology), VCM (Variable Cylinder Management), or AFM (Active Fuel Management), this technology allows an engine to temporarily operate with fewer cylinders, thereby reducing fuel consumption and emissions.

How Does It Work?

The principle is simple: under light load (like during highway driving or going downhill), the engine cuts fuel injection and closes the intake and exhaust valves of certain cylinders. The pistons in these cylinders continue to move but without consuming fuel, acting like "air springs" that absorb and return energy without significant loss. The system is controlled by the engine control unit (ECU), which constantly monitors parameters like vehicle speed, engine load, and accelerator position to seamlessly activate or deactivate cylinders for the driver.

Advantages and Considerations

One of the main benefits of cylinder deactivation is the reduction of pumping losses, which improves engine efficiency under light load. This translates to better fuel economy, especially when driving at a constant speed. According to manufacturers, fuel savings can range from 5 to 25%, depending on the engine type and driving conditions.

However, this technology requires precise management to avoid vibrations and ensure an imperceptible transition between active and deactivated modes. Additional systems, such as active engine mounts or noise cancellation systems, are sometimes used to maintain acoustic and vibrational comfort.

Manufacturers and Associated Systems

Several manufacturers have adopted this technology, each with their own systems:

• Volkswagen: Active Cylinder Technology (ACT), used on 4-cylinder engines like the 1.4 TSI.

• General Motors: Active Fuel Management (AFM) and Dynamic Fuel Management (DFM), allowing certain cylinders to be deactivated based on power demand.

• Honda: Variable Cylinder Management (VCM), used on V6 engines to switch from 6 to 3 cylinders.

• Mercedes-Benz: Active Cylinder Control (ACC), used on some V12 engines.

• Audi: Cylinder on Demand (COD), deactivating cylinders on engines ranging from 4-cylinder to W12.

This technology is also present in vehicles from other manufacturers like Ford, Toyota, Porsche, Bentley, and Alfa Romeo, each adapting it to their own engines and management strategies.

Different Deactivation Systems

There are several technical approaches to deactivating cylinders:

• Hydraulic Systems: Use special hydraulic tappets to disengage the valves of the targeted cylinders.

• Electronic Systems: Employ actuators and solenoids controlled by the ECU to deactivate cylinders more flexibly and precisely.

• Mechanical Systems: Less common, these use physical mechanisms to disengage valve train components.

Some advanced systems, like GM's Dynamic Fuel Management, allow for variable cylinder deactivation, offering finer adaptation to power demand.

Conclusion

Cylinder deactivation illustrates how automotive engineering is evolving to meet the demands of energy efficiency and emission reduction. By dynamically adapting engine operation to real needs, this technology offers a clever solution to optimize performance without sacrificing comfort or responsiveness. At WOT, we applaud these innovations that push the boundaries of efficiency while preserving the essence of driving.