With the emergence of hybrid, electric, and autonomous technology, vehicles have become quieter overall, which has caused more NVH complaints from consumers. Brake squeal noise is among those complaints. Since hybrid and electric vehicles employ regenerative braking, the conditions in which foundation brakes are used have changed. Brakes will now be used in low pressure and low temperature conditions more often. Therefore, NVH requirements for foundation brakes will be more focused on these conditions. Now, friction suppliers have the challenge of addressing brake squeal issues without compromising other aspects of the brake pad (hereafter “PAD”) performance. Although a relationship between some characteristics of the PAD and squeal noise performance has been confirmed with previous studies, the relationship of damping property of Under Layer (hereafter “UL”) material has not been confirmed. The UL is a material between the friction material and the back plate that is used to improve PAD durability and is widely used in today’s market. In this study, it is confirmed that the damping characteristics of UL in the PAD impacts brake squeal noise, specifically during low pressure and low temperature braking conditions. Two different types of UL materials were examined based on material structure and dynamic viscoelasticity. PAD damping ratio and squeal noise performance was also studied. The results show the raw material orientation in the UL material, which is created by manufacturing method, influences the anisotropic properties of the material. Therefore, dynamic viscoelasticity is dependent on the direction it is measured. Specifically, the damping element of the dynamic viscoelasticity, the loss modulus, is increased in the direction of the raw material orientation for high damping and high stiffness UL material. It also was determined that the loss modulus in the direction of the raw material orientation is effective for the bending vibration mode. Therefore, the study focuses on the PAD damping ratio and squeal noise performance in the 1st bending vibration mode of the PAD. It was determined that the PAD squeal noise performance improved due to the damping ratio increasing as loss modulus increases. In conclusion, this study proves that the high damping and high stiffness UL material is effective for squeal noise improvement in conditions that will be increasingly used during regenerative braking.

ADVICS North America: Ms. Leanne Johnson, Mr. Masato Nishioka