Brake squeal is an uncomfortable noise that occurs while braking. It is an important issue in automobile quality to prevent brake products from squealing. Brake shims are widely used to reduce squeal occurrence rate.
The anti-squeal effect of shims is quantified as damping properties measured with a bending mode tester, instead of repeating many dynamometer tests. However, there are cases where measurement results have less correlation to actual squeal suppression rate. Therefore, the evaluation of the anti-squeal effect with a dynamometer or on an actual car is needed until the best shim can be selected.
To improve the predicted accuracy of the anti-squeal effect, the difference between measurement conditions and actual braking conditions of shims, was focused on. The bending mode tester measures loss factor under pressure-free conditions, even though shims are compressed by pistons or cylinders towards the backplate of the pad. From this view-point, new evaluation equipment was developed for brake shims’ damping property under pressure load.
For measurement with the developed method, two shims, which had the same structure except for the material difference of viscoelastic layer between two steel plates, were prepared. The measurement results of both two shims showed that the loss factor had low dependencies on the pressure load. It seems that the loss factor of the viscoelastic material has low pressure dependency. On the other hand, it was confirmed that the loss factor of them had the frequency dependency and the dependency differs by the materials of the viscoelastic layer.