Comparison of Pad Stiffness under Static Pressure and Vibration with Small Amplitude

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. Then, the dynamic stiffness of the pad was measured by adding small-amplitude and high-frequency vibration. This dynamic stiffness was more than twice that of the static stiffness. Vibration with various amplitudes and frequencies was added to a pad and pad stiffness was measured to investigate why the dynamic stiffness of the pad differed from its static stiffness. The pressure-displacement characteristics of the pad exhibited hysteresis. Thus, pad stiffness increased immediately after decompression from pressurization had started. The hysteresis of the pad decreased when the excitation amplitude decreased and excitation frequency increased. When the amplitude was sufficiently small and frequency was sufficiently high, the stiffness of the pad increased and it approached the dynamic stiffness from static stiffness. Measurements of pad stiffness represent a fundamental technology that is required to develop squeal-less pads and it is necessary to take into consideration the change in stiffness that depends on measurement conditions.