Brake noise is one of the top customer complaint issues in the automotive industry. Though brake noise is predominantly a subjective annoyance issue which represents a high cost of warranty repair to the manufacturer, performance and durability may also be compromised through undesirable dynamic behavoir of the braking system. Manufacturer’s work with suppliers and sub-suppliers to develop new optimized brake systems or address issues with existing designs.
The dynamic behavior of the brake system is critical in the overall assessment of a vehicle’s braking functional and perceived performance. Because occupant comfort is of such high importance in automotive development, manufacturers aim to reduce warranty repair costs and offer better Noise Vibration and Harshness (NVH) to win market share by eliminating brake squeal. Especially in the premium vehicle segment, acoustic comfort is an important factor for potential buyers regarding their purchase decision. In addition, brake noise is increasingly perceived, the more other noise sources like engine noises are eliminated, for example by the use of modern electric drives.
The cause of the brake squeal is the friction between the brake disc and the brake pads and the resulting excitation of vibration modes at frequencies which are perceived as unpleasant by the human ear. In brake development, finite element models are used to determine such modes and to suppress their occurrence by suitably adapting the brake geometry or other design measures.
The Optomet scanning laser Doppler vibrometer allows the non-contact detection, analysis and 3D animated representation of vibrations occurring on the surfaces of the brake disc, pad and caliper.This enables the finite element model calculations to be precisely compared with and validated by the actual vibration behaviour.
To investigate the brake dynamics the brake can be excited to vibrate with a modal hammer, or the brake vibrations can be measured under operating conditions. The first method provides all modes of the braking system, but the influence of fastenings and couplings on the vibration behaviour is neglected, as well as typical modes experienced by the driver in the actual car. In the second method, scanning laser technology is used for operational vibration analysis of the system consisting of brake discs, pads and calipers on brake test dynos under conditions that are as close to real-world conditions as possible. However, the targeted stimulation of squeaking noises is usually not easily repeatable. The Optomet scanning laser vibrometers are designed to measure only when the brake squeal is occurring which saves time and improves testing efficiency.
The Optomet SWIR laser vibrometer technology is ideally suited for the measurement of brake systems and components in vehicle construction. The decisive advantage of the Optomet solution compared to conventional HeNe-based systems is particularly evident when measuring rotating brake discs on the dyno. Back-to-back tests of SWIR and HeNe vibrometers have shown that due to the excessive optical signal noise level, HeNe systems are unable to provide measurement data of sufficient quality or signal to noise ratio. The resonances to be examined are lost in the noise. The use of the Optomet SWIR laser vibrometer technology, on the other hand, brings about a dramatic improvement and in these applications delivers data with noise levels that are 40 dB to 50 dB below the resonance peaks.