Electric drive unit housing ribbing for low noise radiation

Although propulsion noise often constitutes a minority of the overall noise in electric vehicles, it remains an important quality indicator due to its high-frequency tonal character, which is undesirable even at low levels. There are many factors that influence the interior car levels of propulsion noise, i.e. gear whine and electric motor whine. The primary ones to consider are the electric drive units (EDU) internal forces, but also secondary properties such as EDU housing design and encapsulation, vehicle sound pack and mount isolation play important roles. This work focuses on EDU housing design and more particularly on the housing ribbing that enables attachment point stiffness and housing strength, but which can also cause problems in terms of noise radiation. Numerical parameter studies on geometrical properties such as length dimensions, thickness and curvature were performed on single ribs of different types. For each design iteration, the key performance indicators radiated sound power, squared velocity and radiation efficiency were studied. The outcome of this work provides insights into which characteristics of ribbings that are central for radiated noise. For instance, it was proven that a rather small curvature of the outer edge of a rib can decrease the radiated noise but also that certain rib dimensions can result in extensive noise due to the interaction of the first bending mode with the peak in radiation efficiency.