ICSV 14 Cairns • Australia 9-12 July , 2007 1 DISC BRAKE SQUEAL : PROGRESS AND CHALLENGES
Brake squeal noise has been an ongoing concern with automotive brake systems since their inception. It is generated by the vibration of an unstable vibration mode of the brake system, usually with the brake rotor acting as a loudspeaker. The squeal noise that is of concern usually falls into a frequency range from 1 to 16 kHz. Although there is often not any degradation in the braking performance, most customers tend to interpret brake squeal noise as indicative of a defective brake. Furthermore, with improvements made in interior noise and comfort levels in vehicles, brake squeal noise has become an increasing source of customer dissatisfaction and is a major contributor to warranty cost. Research into predicting and controlling brake squeal has been conducted since the 1930s and despite significant research efforts in the past 2 decades, brake squeal still remains a challenging problem that is begging for a better understanding of its generation mechanisms and better methodologies for countermeasures other than empirical approaches. Brake squeal is a transient phenomenon and is highly dependent on geometries of brake components, complex interface conditions between components and material properties that are functions of both temperature and pressure. In this paper, recent developments in understanding and controlling brake squeal noise will be reviewed and challenges that remain to be met are discussed.
The method of feed-in energy on disc brake squeal
Brake squeal is studied in this paper by feed-in energy analysis. Based on the brake closed-loop coupling model, a calculation method of feed-in energy for squeal mode is derived. Result of the feed-in energy indicates squeal tendency of the brake system, while formula for calculating it discloses the relation among brake squeal phenomenon and structural parameters, such as frictional coefficient, geometric shape of brake pads, elastic modulus of frictional material, substructure modal shape, etc. The method also helps to analyze the effectiveness of various structural modification schemes attempted to eliminate the squeal noise. Finally, this method is illustrated by application to a typical squealing disc brake.
Properties of a monopivot centrifugal blood pump manufactured by 3D printing
An impeller the same geometry as the impeller of a commercial monopivot cardiopulmonary bypass pump was manufactured using 3D printing. The 3D-printed impeller was integrated into the pump casing of the commercially available pump to form a 3D-printed pump model. The surface roughness of the impeller, the hydraulic performance, the axial displacement of the rotating impeller, and the hemolytic properties of the 3D-printed model were measured and compared with those of the commercially available model. Although the surface roughness of the 3D-printed model was significantly larger than that of the commercially available model, the hydraulic performance of the two models almost coincided. The hemolysis level of the 3D-printed model roughly coincided with that of the commercially available model under low-pressure head conditions, but increased greatly under high-pressure head conditions, as a result of the narrow gap between the rotating impeller and the pump casing. The gap became narrow under high-pressure head conditions, because the axial thrust applied to the impeller increased with increasing impeller rotational speed. Moreover, the axial displacement of the rotating impeller was twice that of the commercially available model, confirming that the elastic deformation of the 3D-printed impeller was larger than that of the commercially available impeller. These results suggest that trial models manufactured by 3D printing can reproduce the hydraulic performance of the commercial product. However, both the surface roughness and the deformation of the trial models must be considered to precisely evaluate the hemolytic properties of the model.