Banishing the banshee

Few things are more irritating on a wet winter morning than the banshee-like screech of motorists’ brakes. Now, there’s a silent brake that puts an end to this misery.

Few things are more irritating on a wet winter morning than the banshee-like screech of motorists’ brakes.

This horrible noise occurs when the brake linings come into contact with the disks (rather like running a moist finger around the rim of a wineglass).

Like your singing wineglass, the pitch of the brake screech is determined by the structural shape of the disk. When a brake lining rubs against a brake disk, the disk begins to vibrate within the audible range, at 2 Kilohertz, hence the screech.

However, the development of the silent brake at Daimler Chrysler’s acoustics laboratory may soon put an end to this high-volume misery.

The research aims to eliminate screeching, even during emergency stops, through modifying the internal structure of brake disks.

Daimler Chrysler engineers began by removing a portion of the brake disk interior.

The disk consists of 2 plates, between them are 35 struts (the cooling ribs). These individual struts are aligned adjacently and run from the plate’s exterior to its centre. The researchers selected six cooling struts distributed evenly over the plate and milled out their exteriors. The disk was thus made softer at precisely these points. When excited by the brake linings, it vibrated at a reduced frequency of 1.9 Kilohertz at these locations, but at 2 kilohertz at the untreated points.

With the new design, the rotating disc required a certain amount of time to establish constant vibration at either of these two frequencies. And since these properties change within a split second, the brake disc is prevented from reaching a constant vibration, and screeching is eliminated.

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