Noise and vibration in brake Systems are a constant source of headaches for automotive manufacturers. Customers expect a new car should be free from defects and noises. At the same time they want to get a comfort and safety feeling. Apart from its environmental impact, noise (Fig. 1) is related to system malfunctioning or lack of quality of its components and, worse, it is perceived as a possible cause of accident.

(Fig. 1) Vibrating brake disc making noise

For this reason it is not surprising that when a driver detects unexpected noises or vibrations when braking its first reaction is of concern and insecurity. The same applies when, as a consequence of braking, the driver feels strange vibrations. Under these conditions the user does not hesitate to return the vehicle to the dealer until the problem is solved.

Similarly, in a sector such as wind, noise generated by heavy braking produced in the generators are to be subjected to restrictive legislation, especially when they are located to residential areas.

Noise emission in brakes depends on many factors and, depending on their nature, the study of how to eliminate it can be very diverse. For example, if it is classified by the frequency at which it occurs, it can be found “judder” vibrations involving the whole structure of the vehicle. Increasing in frequency “groan”, “moan” and “howl” can be found, ending up with “squeal” and “wire brush noise” (Fig. 2) at higher frequencies. Each of these has their own causes and, therefore, must be analyzed and corrected properly attending to them.

(Fig. 2) Classification of noises in brakes

The noise having more impact on vehicle claims is the “squeal” which is a pure tone (within the human audible range) ranging from 1,000Hz to 22,000Hz with sound levels near the brake between 60 and 120 decibels. The acceleration in the calliper and brake pads can exceed 20g. Noise can be continuous or may come and go in one revolution of braking. In addition, noise can affect the discomfort of the people inside a vehicle or passers who receive it from the outside.

The “squeal” phenomenon is usually due to instability in the friction interface between rotor and brake pads and to the coalescence of natural modes of two or more brake components at the appropriate environmental and functioning conditions.

In general, the “squeal” depends on a multitude of internal variables (design, material, operating pressure, quality of contact, …), external conditions (temperature, humidity, environment, …) and braking history (how the brake was used during its life).

There exists much literature on this problem but, so far, few tools have specifically been developed to help companies to design their products oriented at knowing how they impact the generation of noise in the system or how to amend it once detected.

CITEAN, based on the knowledge acquired over the years in projects and tests on brake systems, has launched the QUIET project, aimed at providing these tools to companies in the sector. The QUIET project is supported by a large number of computational (Fig. 3) and experimental (Fig. 4) resources available at CITEAN premises that will help in the proper characterization, prediction and validation of brake components.

In particular, the tools that will be developed throughout this project will assist companies in designing their products to reduce the likelihood of noise generation or, when the problem already occurred, in modifying them adequately to get rid of it.

For this project CITEAN will look to collaborate with various companies engaged in the manufacture of brake system components.

For more information contact CITEAN at info@citean.com.

(Fig. 4) Experimental resources