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Brake NVH Testing and Measurements 2011 Edition, March 29, 2011
Description / Abstract:
Introduction
Brake noise has been a problem since the earliest of vehicles. Whether the mechanisms were leather against a wooden wheel, brakes acting on the wheels of early trains, or modern passenger car disc brakes, braking a moving vehicle requires the dissipation of large amounts of energy. In such a rotating system, it is inevitable that a small fraction of this energy is turned into vibration and potentially noise. With a sufficient sound radiating surface, even this small amount of energy can produce significant sound levels. When one is dissipating hundreds of watts of power, a few tenths of watts in vibration and noise may not seem significant. However, even this amount of sound power can result in sound levels of 100 dB or more.
As has been often observed, every vehicle in the movies exhibits brake squeal. Brake noise can be seen from several perspectives: For some, the occurrence of squeal is seen as welcome confirmation that the brakes are working. For others, brake noise can be a minor irritation. Yet for others, brake noise may be seen as an indication that the brakes are not working properly. In the worst case, brake noise may lead to returns to the dealer and warranty claims.
Since the beginning of mass production of the automobile, brake noise has been an annoyance and consequently there have been attempts to quantify and understand the noise. While instrumentation has been available for brake noise measurement since the 1940s, it took more than five decades to develop useful and reliable measurement practices.
While brake noise is a common experience for those who ride in or operate vehicles, it has proven difficult to recreate in the laboratory. Developing a test apparatus that can reliably reproduce brake noise is a difficult undertaking. One must recreate all the vehicle operating conditions and provide a sufficient controlled acoustical environment to measure the resulting noise. The first internationally recognized brake noise test standard was not published until 2001. Therefore the standards of measurement and instrumentation to be discussed in this text will be those developed in the period from 2001 to the present. The discussion that follows will deal with current practices and procedures for quantifying and understanding brake noise.
Brake noise has been a problem since the earliest of vehicles. Whether the mechanisms were leather against a wooden wheel, brakes acting on the wheels of early trains, or modern passenger car disc brakes, braking a moving vehicle requires the dissipation of large amounts of energy. In such a rotating system, it is inevitable that a small fraction of this energy is turned into vibration and potentially noise. With a sufficient sound radiating surface, even this small amount of energy can produce significant sound levels. When one is dissipating hundreds of watts of power, a few tenths of watts in vibration and noise may not seem significant. However, even this amount of sound power can result in sound levels of 100 dB or more.
As has been often observed, every vehicle in the movies exhibits brake squeal. Brake noise can be seen from several perspectives: For some, the occurrence of squeal is seen as welcome confirmation that the brakes are working. For others, brake noise can be a minor irritation. Yet for others, brake noise may be seen as an indication that the brakes are not working properly. In the worst case, brake noise may lead to returns to the dealer and warranty claims.
Since the beginning of mass production of the automobile, brake noise has been an annoyance and consequently there have been attempts to quantify and understand the noise. While instrumentation has been available for brake noise measurement since the 1940s, it took more than five decades to develop useful and reliable measurement practices.
While brake noise is a common experience for those who ride in or operate vehicles, it has proven difficult to recreate in the laboratory. Developing a test apparatus that can reliably reproduce brake noise is a difficult undertaking. One must recreate all the vehicle operating conditions and provide a sufficient controlled acoustical environment to measure the resulting noise. The first internationally recognized brake noise test standard was not published until 2001. Therefore the standards of measurement and instrumentation to be discussed in this text will be those developed in the period from 2001 to the present. The discussion that follows will deal with current practices and procedures for quantifying and understanding brake noise.
Brake NVH Testing and Measurements 2011 Edition, March 29, 2011