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The NVH behavior of brake systems remains a core problem for the brake industry. Many efforts have been made to achieve a better system understanding, but the prediction of noise occurrence based on measurable parameters remains unsatisfactory. By considering the brake pad as one key component within the brake system, until today different measurement methods describing its material properties have been developed. This work analyses the correlation of all important “state of the art” friction material/pad parameter measurement methods to the NVH behavior of a specific brake system on a statistical basis. The answer to the question “does the NVH parameter for friction materials exist” ? will be derived from these correlation results.

Nowadays an important factor for the selection and development of friction materials is the compressibility value defined by the customer. This critical to quality aspect of a brake pad may be influenced both by the production process as well as the chemical pad formulation. Modifications to reach a target compressibility value during a development process of a brake pad come at a cost. While interfering with the production process and/or the pad formulation not only the compressibility value may change; most certainly the whole behavior of the brake pad will be subject to change. The compressibility value is a measure for pad deformation due to a standardized load collective. The total pad deformation after a compressibility test is a combination of elastic and plastic deformation as well as a creep portion depending on the viscosity of the material.

Creep groan of vehicles is the low frequency chassis vibration occurring at very low brake pressure and extremely slow speeds giving the driver a very uncomfortable feeling. It is the classic example of a self-excited brake vibration caused by the Stick-Slip Effect. The essay discusses the mechanisms leading to self-excitement of vibrations. In the first section of the essay the state of the art is presented by way of a literature investigation and the phenomenon of creep groan is described. Then, by measuring the vibration characteristics of a creep groaning brake it is demonstrated that apart from a tangential brake caliper movement, a twisting of the brake around the vertical axle takes place. This twisting modifies the pressure conditions of the contact areas of brake disk and brake liner. Based on the measured results of adhesion and sliding coefficients a finite element model is developed simulating the dynamic processes in the friction layer using contact algorithms.