Engine NVH Optimisation

Engine NVH optimisation is a systematic engineering discipline that combines source control, transmission path optimisation, and active cancellation to minimise engine noise, vibration, and harshness without compromising powertrain performance. This directly impacts overall cabin refinement and ride quality.

At its core, NVH optimisation tackles the two primary excitation sources generated by combustion and mechanical movement. Combustion noise stems from in-cylinder gas pressure fluctuations, whereas mechanical noise arises from moving components such as piston slap, timing chain drive, and gear meshing. Among these, piston slap is one of the most prominent mechanical noise culprits; studies indicate that optimising piston-to-wall clearance and piston pin offset can slash slap kinetic energy by 31.1%.

🎯 Source Control: Suppressing Vibration and Noise at the Source

This represents the most fundamental approach, primarily executed during the engine design and calibration phases:

• Optimising the combustion process: Refining fuel injection strategies (such as 350-bar high-pressure common-rail injection) and adopting the Miller cycle enable a smoother combustion burn, thereby lowering combustion noise. Case studies demonstrate that such calibrations can cut combustion noise by up to 4dB.

• Balancing reciprocating inertia forces: Reciprocating inertia forces in multi-cylinder engines are a primary trigger of vibration. Implementing balancer shafts for precise dynamic balancing is crucial for vibration suppression. For instance, the twin balancer shaft design in Toyota TNGA engines cuts idling vibration amplitude by 35%.

• Minimising mechanical friction: Applying low-friction surface treatments such as Diamond-Like Carbon (DLC) coating to moving components like pistons effectively lowers frictional noise.

🔧 Path Optimisation: "Isolating" Vibration Along the Transmission Path

Vibration and noise travel into the cabin via structural routes such as the engine block and mounting system. Transmission path optimisation aims to isolate or attenuate these transfer paths.

• Structural stiffening and damping: Enhancing the structural rigidity of thin-walled components like the oil sump via topology optimisation mitigates resonance. For example, tackling oil sump resonance at 1,200Hz through structural redesign reduced its vibration velocity by 6.1dB.

• Upgrading the mounting system: The engine is secured to the chassis via mountings. Hydraulic engine mountings effectively isolate specific frequencies such as idling vibrations, boosting vibration isolation efficiency up to 90%.

🧠 Active Control Technology: Cancelling Noise with "Anti-Phase Sound Waves"

A rapidly evolving frontier, this active approach marks a significant leap beyond conventional passive isolation:

• Active engine mountings: By monitoring vibrations in real time via sensors and dynamically modulating mount stiffness and damping through electro-hydraulic actuators, this system adapts to varying operating conditions to further suppress cabin noise.

• Active Noise Cancellation (ANC) technology: By broadcasting sound waves of identical frequency but inverted phase to engine noise through the in-cabin speakers, active cancellation is achieved. Systems developed by specialists like Bose can effectively suppress low-frequency boom below 200Hz inside the cabin.

🌟 New Architectural Possibilities: The Boxer Engine Advantage

Beyond detail engineering, an engine’s core layout sets the ceiling for its NVH potential. Taking the 2.0T horizontally opposed (boxer) engine in the BYD Yangwang U7 as an example, its opposing pistons move horizontally to cancel out each other's inertia forces. This inherent physical balance makes it naturally smoother and quieter than inline or V-configured engines.

Engine NVH optimisation is an intricate, multidisciplinary engineering field. It demands meticulous fine-tuning across combustion dynamics, mechanical design, materials science, and acoustics—ultimately striking the perfect harmony between high performance and premium refinement.