Electric vehicles are generally quieter than internal combustion engine vehicles. This means that brake noise is more noticeable, which can worsen the overall driving experience and contribute to noise pollution in the surrounding environment. Since electric vehicles rely heavily on regenerative braking, the friction material of the brake pads tends to be thinner, and the brakes generally operate under colder and more humid conditions due to less frequent use when compared to brakes on vehicles with internal combustion engine. Additionally, the electric vehicles have an increased weight typically leading to the need for larger brake pads. These factors are often not favorable for preventing brake squeals, thus highlighting the need for more stringent noise damping requirements for the brake systems of electric vehicles. This study provides a brief review on anti-noise shims and their function as countermeasures for brake squeal noise with a specific focus on the critical requirements for electric vehicles. Four types of anti-noise shim adhesives are presented, and their advantages and disadvantages are discussed. These adhesives are used for bonding the anti-noise shim to the brake pad and include two acrylic adhesives optimized for damping at lower temperatures, one of which is suitable for use in electronic parking brakes. The other two adhesives are high-temperature damping adhesives, one of which is a high-performance silicone adhesive, and the other being a newly developed acrylic adhesive. The characterization of the adhesives includes standard T-pull and compressibility measurements. The damping behavior of the adhesives has been measured over a relevant temperature range in the audible range and can accurately be described using complex stiffness and Rayleigh damping. It is demonstrated how the damping effect of the different adhesives varies with steel thickness and whether the adhesive is bonded to a second viscoelastic layer such as rubber. The results are compared with finite element modeling of the suggested shim materials, which shows that an accurate modeling description has been formulated. Additionally, NVH (noise, vibration, and harshness) results from dynamometer tests are presented and discussed based on the damping behavior of the used anti-noise shims. The results obtained in this study show that four distinctly different anti-noise shim adhesives can be used to address specific NVH-related problems for electric vehicles. The study demonstrates that selection of adhesive combined with the additional components of the shim has a significant impact on damping properties and overall performance of the shim. Finally, by extracting fundamental material parameters of individual shim components, an accurate finite element description is found. This allows for a more accurate anti-noise shim representation in complex eigenvalue analyses on brake systems, which can ultimately reduce development costs and expensive dynamometer and vehicle testing time.
Dr. Martin Søgaard, Group R&D Manager, Meneta Advanced Shims Technology; Mr. Kasper Filtenborg, Research Engineer, Meneta Advanced Shims Technology; Mr. Jens Thuesen, R&D Brake Noise & Vibration Manager, Meneta Advanced Shims Technology; Mr. Halewijn Stikvoort, Senior Research Engineer, Meneta Advanced Shims Technology