automotive_squeakandrattle.jpg

Squeak & rattle testing

Squeak and rattle are all noises created by parts installed in a way that they interact to create annoying sounds. Squeak is caused by friction between parts, stick-slip and rattle by impact. Squeak and rattle noise is extremely irritating and a big reason for customer complaints. Even if the sound levels are low, squeak and rattle noise is audible because of the intermittent character and often a sound with a frequency content where sound masking is low. A vehicle without squeak and rattle is perceived to have a high build quality so it is more or less mandatory to achieve this. Masking levels are getting lower and lower, especially in electrical vehicles while the demand for less weight increases the design problems.

Squeak and rattle is caused by the relative motion between parts installed for example to close so they interact in a way to create the annoying squeak or rattle noise, sometimes only at certain environmental conditions. Squeak is caused by friction between parts, stick-slip and rattle by impact. Chassis and structural design, material selection, controlled tolerance chains are all important and shall be specified in the design targets and design guidelines.

Challenges:
Design guidelines and CAE methods to predict squeak and rattle in combination with production tolerances are continuously improving but squeak and rattle problems are very often detected at a very late stage, even after production start, and can be the reason for high warranty costs. Good tools are important for fast problem identification and verification of measures like adding felt tape. Improved correlation of measurements to subjective evaluation is also a continuous task for the engineers.

• Testing time has to be short since the access to prototypes is limited.
• Instrumentation must be fast and easy in a way to record repeatable results.
• The microphones must be installed to minimize structure borne sound.
• Microphone holders and cables shall not introduce any rattle noise.
• The installation shall be safe for the test engineer during vehicle test.
• Calibration verification must be easy to perform.

The transducers shall survive the tough daily usage in different environmental conditions and sometimes accidently being dropped.

Example:
The loudness for a component or a system is analysed in a NVH test rig with a silent shaker and a specified excitation for early approval of suppliers.
Subjective evaluation of a vehicle on a 4-poster with environmental control and at different types of test tracks and climate is performed as soon as vehicles are available. The subjective evaluation is supported by a microphone and headphone combination for root cause analysis, often with filtering possibilities to be able to isolate the problem area. Intensity testing and acoustic camera are other tools for noise source location.

The tests are repeated after durability testing to assure minimum degradation.