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This paper deals with low-frequency squeal phenomena generated in floating type of car disc brake units. First, the vibration characteristics of low-frequency squeal (about 2 kHz) were investigated. Here, in order to reproduce the squeal, a bench-test apparatus consisting of an actual automotive disc brake unit was utilized, itself comprising a disc, pad, and caliper. With this, the associated frequency characteristics were experimentally determined. It was found that the squeal is caused by coupled out-of-plane vibration modes among the disc and caliper due to Coulomb friction. As an experimental countermeasure, a dynamic absorber was applied to the leading side or the trailing side of the inner caliper. It was found that squeal can be suppressed when the natural frequency of the dynamic absorber is tuned so as to be near the frequency of the squeal, and that squeal can be suppressed even without viscous damping of the dynamic absorber.

In recent years, automatic transmissions have become widely used in cars. Compared to manual transmissions, automatic transmissions suffer from poor fuel economy. In order to overcome this disadvantage, a lock-up clutch system in the torque converter has been applied. When the rotating speed of the turbine approaches that of the pump, the input shaft is directly connected to the gear train through friction by means of the lock-up clutch. In the process of slipping at the lock-up clutch, frictional vibration referred to as shudder sometimes occurs. When shudder occurs, the power train, as well as the tires and the car seats, vibrates. Therefore, the shudder adversely affects passenger comfort. In the present study, experiments are conducted to analyze the shudder mechanism using a bench test apparatus and an actual vehicle. The characteristics of friction in the lock-up clutch is found to have a negative slope with respect to the relative slip velocity.