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Brake squeal is uncomfortable noise that occurs while braking. It is an important issue for automobile quality to prevent brake products from squealing. Brake shims are widely used to reduce squeal occurrence rate. In particular, laminated shims can effectively suppress squeal via the viscoelastic damping of an adhesive layer. However, there are cases where the damping performance at low temperature and the durability performance at high temperature deteriorate. In that regard, we thought of applying frictional damping to shims instead of relying on a temperature-sensitive adhesive layer. To study the application of frictional damping for shims, it is necessary to clarify the characteristics thereof. In order to quantify the damping performance of shims, loss factor has been generally measured with a bending mode tester. However, the influence of friction cannot be evaluated because it is measured under pressure-free condition.

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.

Brake squeal is uncomfortable noise that occurs while braking. So, it is an important issue of automobile quality to reduce the brake squeal occurrence. Although many researchers had reported about brake squeal, there are many examples that have not been understood well. For those squeals, some of occurrence mechanisms are assumed. The dµ/dv<0 theory is one of them, and the dµ/dv represents a slope of friction coefficient for sliding velocity. If the frictional force has a negative damping characteristic, that is dµ/dv<0, disc vibration may increase. It has been said for a long time that a negative dµ/dv characteristic affects brake squeal occurrence. Many researchers had measured the dµ/dv to clarify brake squeal factors. In those results, the slope of friction coefficient at steady sliding speed was used for the dµ/dv. However, the pad undergoes minute vibrations while the brake is squealing.