Development of Shim Specifications

In the past, each noise shim supplier had its own specifications to describe the properties of their noise shims (often also called as shim or damping shim). Due to that, it was difficult to compare the physical properties of noise shims from different suppliers. The main task was to define common specifications for daily quality/development tests.

Traceability in prototype status and production was introduced establishing a clear declaration of noise shim deliveries with batch no. and “use by” date. Harmonization was created through standardized tests and procedures. In addition, a common noise shim database for all noise shim manufacturers was established. A more realistic compressibility test was developed to estimate the additional compressibility of noise shims based on bare pads under cold and hot conditions. These values are important to describe the axial decoupling at low pressure and the maximal displacement at high forces. Based on the noise shim corrosion test procedure noise shims with better endurance properties can be developed to ensure a stable NVH behaviour. Tests like Static / Torque endurance are important to describe the stability of the outer rubber layer of the noise shim under load. The T-pull test is the most common physical test to measure the bonding force between pad and noise shim. In the last update some improvements were introduced to guarantee more comparable and stable results. Another test used to describe the bonding behaviour of a damping noise shim is the Lap shear test. The recommended Noise Shim Visual Assessment for pad assembly is giving the possibility to characterize noise shims in the same manner after dynamometer or vehicle testing. Further standardizations regarding damping-/decoupling tests and CAE analysis is an issue to work on in the future.