Bruits et vibrations des transmissions latérales Automotive driveshafts NVH

Reducing noise and vibration is one of the main research priorities for automakers, as it responds to strong customer demand. In this context, it goes without saying that equipment manufacturers are pursuing the same objectives, particularly in the powertrain sector, which covers everything from the flywheel to the wheels.

This article focuses on lateral transmissions (or wheel shafts), because in some cases they are associated with acoustic or vibratory phenomena (known as NVH, Noise Vibration and Harshness) experienced by the user.

These phenomena can be classified into three categories, depending on whether the role of transmission is direct, indirect or both:

• direct role: acoustic or vibratory excitation occurs at the level of the transmission itself. This is particularly true of hammering, which is directly linked to the forces generated by the sliding joint;

• indirect role: the excitation is no longer located in the transmission, but comes from another source. This is the case, for example, with the hum phenomenon, when a natural frequency of the wheel half-shaft amplifies a motor excitation;

• direct and indirect role: excitations come from the transmission on the one hand, and from another source, such as the engine, on the other. It is the combination of these various excitations that creates acoustic or vibratory discomfort. The typical case is that of the H ₂ /R ₆ beat, between two close frequencies, one coming from the engine and the other from a wheel seal. Another example is cooing, the modulation of an engine excitation by an unbalance or offset of the gearbox-side sliding joint.

This article describes all these phenomena in detail:

• subjective, reflecting users' sensations as closely as possible;

• measuring, defining and quantifying the physical parameters most closely related to subjective sensations;

• modeling, the aim being to explain phenomena in the most didactic physical and mathematical terms possible.

This approach enables us to learn about the acoustic and vibratory phenomena associated with transmission, both in terms of physical manifestations in the vehicle and in terms of understanding.

We also highlight the close relationship between measurement and modeling, which enables computing resources to be used for design, optimization and simulation.

At the end of the article, readers will find a glossary and...