Updated: Jul 31, 2022
By: Eric Denys
Photo courtesy of Link Engineering
NVH (Noise, Vibration & Harshness) is one of the most important characteristics to optimize during a vehicle development cycle. In order to meet the NVH targets, there are various noise reduction strategies that can be used:
ISOLATION: Reduce the transmitted vibration across structures.
The rubber mounts being used to isolate the vibration of the engine from the rest of the car is a perfect example.
BARRIERS & ENCLOSURES: Block the transmission of noise.
The dash panel is optimized to reduce the amount of the car engine noise entering the occupant’s cabin. The engine compartment also plays the role of a noise enclosure.
ABSORPTION: Absorb the sound energy and reduce the reflection of sound.
A soft absorbing foam could be used inside the car engine compartment to absorb some of the engine noise, which, in combination with the dash panel barrier will reduce the amount of noise transmitted to the cabin. Sound absorbing materials (Carpet, headliner…) are being used to tackle the noise that makes its way into the cabin.
DAMPING: Reduce the vibration, thus the radiated noise by converting vibration energy into heat. Damping materials are being used on a number of parts inside the car, including floors, wheel wells…
NOISE REDUCTION AT THE SOURCE: If the noise generated by the source (engine, tires, brakes…) is lower, then it will be much easier to meet the customer noise requirements.
This is one of the most effective approach to reduce noise.
So, which ones of these techniques can be used to reduce brake noise and pass the increasingly tougher, longer noise validation procedures designed by the OEMs?
While a “typical” NVH Engineer has a lot of arrows in his quiver, the job of a Brake NVH Engineer is a lot more challenging with fewer options at his disposal.
As mentioned above, one of the most effective techniques is to reduce the noise at the source. In the last 15 years, the brake industry formulators have made significant progress in designing quieter friction materials. When we used to measure 40-50% noise above 70dB during a typical SAE J2521 dyno test, we are now seeing levels around 20% or even lower, making it easier to meet the very stringent OEMs noise requirements.
Also, there has been an increasing focus on optimizing pad chamfers and pad shapes to improve the pads/rotor contact interface and pressure distribution, making the braking system more stable with fewer normal modes being excited.
So, what are the other options for the Brake NVH Engineer? I will discuss that in my next blog.