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The prevention of brake squeal is a significant task in brake development, because brake squeal is bothersome to users and consequently reduces a vehicle's commercial value. Due to the progress made by researchers in their efforts to gain insight into the mechanisms and causes of brake squeal, the number of brake squeal complaints has declined. However, brake squeal can appear long after the vehicle is produced, without any early sign. In order to maintain long-term high satisfaction among the vehicle owners, it is important to find the factors that create a gradual increase in the occurrence of brake squeal. In this study, we focus on the stiffness factor of brake pads. Also, brake-pad wear due to braking is virtually impossible to completely eliminate. Here, we examine the correlation between pad stiffness and squeal occurrence. This study presents experimental and analytical results of the influence of pad surface texture on disc brake squeal.

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 pads are composite materials made from dozens of ingredients intended to simultaneously satisfy various performances such as brake effectiveness, wear, noise and vibrations. For this reason, the friction phenomena that occur during braking are complicated. It is important to clarify the friction phenomena, but that is not easy because the associated complexities as mentioned above. We looked to acoustic emission (AE) as an online evaluation method of friction phenomena. AE is a non-destructive testing method that measures elastic stress waves caused by the deformation and fracturing of materials. In fact, it has been reported that the difference between abrasive wear and adhesive wear of a metal can be identified from the change in the frequency spectrum of AE signals. In this study, we verify whether differences in the friction phenomena of brake pads are detectable by the AE method. Three kinds of brake pads were used in the experiments.

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.

This study aims to incorporate the dynamic stiffness of pads into the finite element method (FEM) used for brake design in order to improve the accuracy of FEM analyses. In the first step, the vibration caused by a disk brake squeal is simulated in order to measure the dynamic stiffness of the brake pads. We then compare this result with the static stiffness result obtained from a past static compressive strain and show that these different modes of stiffness have different characteristics. The dynamic stiffness of the pad is higher than the static stiffness and is greatly dependent on pressure load. The next step is to show, from the squeal experiments using a simple squeal tester and FEM analysis, that it is dynamic stiffness and not static stiffness of the pads that correlates to squeal.

It is necessary to consider both pad stiffness in static and dynamic situations to develop brake pads that create effective braking and squeal less. Brake pads that have a high degree of static stiffness generally respond well when braking. A past study clarified that stiffness when vibration is added to a pad differs from static stiffness. This pad stiffness in dynamic situations depends on braking pressure and it is one of the causes of squeal generation. This research clarified that pad stiffness depends on the amplitude of excitation and its frequency, which was measured by using an experimental apparatus. This apparatus gave sufficient displacement to a pad for measuring static stiffness and gave vibration with sufficient frequency and amplitude to assess the stiffness of the pad when squeal was generated. First, the static stiffness of the pad was measured by adding static pressure.