The NVH (Noise, Vibration, and Harshness) group at MAHLE Technology, Inc. uses state of the art technology to investigate engine related noise issues.

Instrumented engines and vehicles are put through a series of tests designed to provide both subjective and objective data that can be measured reliably to highlight and identify piston related noise. The NVH group supports the application engineers with testing expertise and a NVH knowledge base. However, we also work closely with our customers to help improve their testing and knowledge base as well.

Our tools include an LMS 32-channel data acquisition system and analysis software, sound quality software, DAT recorder, microphones, accelerometers and many other measurement transducers. We are equipped with a chilling system to cool engines to -20 degrees Celsius and a 300 HP dynamometer for engine testing.

As engines have become lighter and more powerful, piston NVH is becoming more critical. Less mass means that it takes less energy to transmit noise into the vehicle. We are able to diagnose not only piston noise, but also the type of noise, probable cause of the noise, and, most importantly, a course of action to improve the noise.

Acquired data is viewed as a "time domain trace" to ascertain whether there are vibrations due to piston excitation of the engine block. The data is then converted to an "angle domain trace" so that a particular vibration is related to crank angle.

Each piston noise has an angle characteristic. The two most common piston related noises are Croaking and Rattling.

Croaking has a diesel type sound and usually occurs from 8 to 20 degrees after Top Dead Center Combustion (TDCC). Rattling has a high pitched, metallic sound and usually occurs from 2 degrees before TDCC to 8 degrees after TDCC. These typically would be the first noises to investigate.
Microphone and accelerometer data are analyzed with Time-Variant Frequency Analysis, so that a clear indication of when the noise and vibration occur in time and whether a particular noise could be due to a piston motion.

Once the noise is narrowed down to a particular piston or pistons and the type of noise is characterized, audio recordings can be made so that both the customer and the engineer performing the tests can compare their perceptions of the noise. This is sometimes necessary because the position of the listener can make a substantial difference in the perceived level of the noise. It is also necessary to compare design improvements to the original noise concern.

New piston designs are evaluated by the Engineering Numerical Simulation (ENS) group and tested by NVH. Correlation, between actual and simulated data, results in the best product to the customer. This also results in a constantly improving model for future simulations.