A car’s engine is the source of numerous noises and vibrations. These effects are not always desirable and are often even perceived as unpleasant. Specific measures can be taken to optimize engines in terms of noise and vibration. These improvements relate partly to the engine itself, but also partly to the area surrounding the engine in the engine compartment.

What does NVH stand for?

The abbreviation NVH stands for the English terms noise, vibration and harshness. Translated into German, this means noise, vibration and harshness. NVH describes audible and perceptible vibrations that can occur during the operation of machines such as engines. In automotive engineering, these effects are comprehensively investigated as early as the development stage.

• Noise: Noise is an auditory sensation that is typically caused by vibrations. These vibrations usually occur irregularly and with a variable structure. An internal combustion engine in a car can cause this effect.
• Vibrations: The term oscillations describes repetitive fluctuations of variables within a system. In mechanics and automobiles, these are usually recurring movements of bodies or masses. This applies to the car body, for example.
• Roughness: Roughness is the term used to describe a psychoacoustic sensation. In humans, this sensation does not depend exclusively on the volume, but also on the frequencies and duration. Certain modulation frequencies favor roughness.

NVH in relation to combustion engines

Noise and vibrations are often perceived as unpleasant by car drivers, and are sometimes perceived as annoying. This applies in particular to buzzing or humming noises or vibrations. These effects can occur with all types of combustion engines and can be transmitted from the engine to the bodywork. In addition to the acoustically perceptible engine noise, other effects occur when the combustion engine is in operation. For example, vibrations can be easily perceived via the driver’s seat, which is bolted to the bodywork. Engine vibrations can also be perceived by the driver as an annoying humming noise through the bodywork.

Differentiation between NVH and acoustic design

NVH describes vibrations and the resulting noise pattern. Measures in connection with NVH are generally aimed at counteracting these effects. Vibrations and noise development should be avoided or minimized as far as possible through appropriate interventions. In engine construction, acoustic design describes targeted measures to adapt noise. This involves, for example, the optimization of exhaust and intake noise.

Targeted NVH measures for combustion engines

NVH effects in combustion engines can be influenced by a range of measures. Manufacturers focus on optimizing components or installing additional components in the engine compartment of the car. In addition to improvements to the engine itself, the suspension of the unit and optimized noise insulation are also crucial.

1. Engine suspension: The suspension of an engine has a significant influence on the extent to which vibrations can be transmitted. Modern engine mounts or engine mounts connect the engine to the body and dampen vibrations at the same time.
2. Chain drive: The chain drives inside combustion engines can lead to undesirable effects in terms of NVH during operation. Calculations of the chain drive and a coordinated design of sprockets and chains lead to noise optimization.
3. Unit bearings: Auxiliary units and engine attachments are elastically mounted or connected to the engine via bearings. By optimizing installed bearing elements, it is often possible to effectively minimize the vibration transmission of engine units.
4. Engine cover: Modern combustion engines often have an engine cover. This cover on the top of the engine, which is usually made of plastic, is not just for visual reasons. The engine cover is often specially designed to dampen noise.
5. Hood insulation: The underside of a car’s hood is often fitted with insulation. The built-in insulating element reduces noise propagation and dampens any vibrations of the body part. The insulating mat is also heat-resistant.
6. Passenger compartment insulation: Insulating the passenger compartment from the engine compartment reduces noise transmission. Insulation elements installed in the interior behind trim parts prevent body parts such as doors and the vehicle roof from vibrating.

NVH optimization in automotive engineering

Automobile manufacturers are implementing NVH optimization measures in an increasingly targeted manner. This applies both to the development of individual engine parts and to the vehicle as a whole. In some cases, manufacturers are already using computer-aided simulation models during vehicle development. Finished prototypes are further optimized on the test bench. This can involve the engines on the one hand, but also the vehicle with the fully installed engine.

This is why manufacturers are increasingly relying on NVH optimization

Modern and consumption-optimized engines are more in demand in automotive engineering today than ever before. By reducing the number of cylinders, downsizing displacements and turbocharging, manufacturers are implementing new specifications with regard to fuel savings and pollutant emissions. However, the weight-optimized downsized engines are increasingly prone to undesirable vibrations and unfavourable acoustic behaviour. Manufacturers need to optimize these properties.

NVH with electric motors

Highly developed hybrid systems and electric motors are increasingly being used in automotive engineering. This presents manufacturers and developers with new challenges in terms of NVH. For example, the electric motors installed in electric cars tend to have completely different frequency patterns than those found in combustion engines. The materials and design of mounts and damping elements are often newly optimized and adapted in this context.