Noise, Vibration and Harshness (NVH)

Tools and Techniques

The diagnostic tools allow for a systematic collection of information that is necessary to accurately diagnose and repair NVH problems. Remember that the vibrating source component (originator) may only generate a small vibration. This small vibration can in turn cause a larger vibration/noise to emanate from another receiving component (reactor), due to contact with other components (transfer path). For the best results, carry out the test as follows:

Test drive the vehicle with the vibration sensor inside the vehicle. Place the sensor in the vehicle according to feel.

If the condition is felt through the steering wheel, the source is most likely in the front of the vehicle. A vibration that is felt in the seat or floor only will most likely be found in the driveline, drive axle or rear wheels and tires.

Record the readings. Also note when the condition begins, when it reaches maximum intensity and if it tends to diminish above/below a certain speed.

If a vibration symptom is vehicle speed related, the tire and wheel Revolutions Per Minute (RPM)/frequency and driveshaft frequency should be calculated. Frequencies with an amplitude reading of 0.06 Gs or less are barely perceptible NVH levels. No corrective action is necessary.

Place the vibration sensor on or near the suspect area outside the vehicle. Continue the road test, driving the vehicle at the speed the symptom occurs, and take another reading. Compare the readings.

A match in frequency indicates the problem component or area.

The following diagnostic tools and techniques can be used separately or in conjunction with each other to aid in the diagnosis of NVH symptoms. They are listed in order of preference for ease in their use for locating these symptoms.

Noise, Vibration and Harshness (NVH) Analyzer (Vetronix)

The MTS 4000 and the MTS 4100 NVH analyzers are tools to aid in the identification and isolation of a noise, vibration or harshness symptom in a vehicle. They measure noise and vibration data and compare it with data obtained from the vehicle's PCM as well as vehicle variants that were entered by the user such as pulley size, axle ratio and tire size in order to provide possible sources. The MTS 4000 and the MTS 4100 have the following characteristics:

Interface with the vehicle's computer system Support and store vibration data input from 1 or 2 accelerometers Support and store noise data input from 2 microphones Provide a photo-tachometer for operation of the driveshaft balancing function Provide a strobe output capable of driving a standard timing light Contain a real-time clock circuit that provides time and date information which is used for tagging test data Have the capability to print to an external printer and interface with a personal computer Can be powered from a variety of power sources: cigarette lighter, AC power or the internal battery pack

The MTS 4000 and the MTS 4100 NVH analyzers have 4 main operating modes. The first is for vibration diagnosis. This mode measures data from 1 or 2 accelerometers simultaneously while obtaining data from the vehicle. Then it carries out a frequency analysis on the accelerometer information and compares the vibration frequencies with the frequencies associated with various rotating components within the vehicle. The data can be presented in 4 different display modes: principle component, bar chart, frequency spectrum or waterfall. All display mode formats contain the same common elements, such as amplitude.

The second is for noise diagnosis. This mode measures noise from 1 or 2 microphones simultaneously. All noise measurements are in decibels (dB). All frequency bands used for noise measurements are the same as for the vibration measurements, up to 1,000 Hertz (Hz).

The third is the strobe. A strobe or standard timing light can be connected to an analyzer, to provide a means for measuring rotation speed. The strobe function is used for isolating the source of a vibration.

Electronic Vibration Analyzer (EVA)

The Electronic Vibration Analyzer (EVA) is a hand-held electronic scan tool which will assist in locating the source of unacceptable vibrations. The vibration sensor can be remotely mounted anywhere in the vehicle for testing purposes. The unit displays the 3 most common vibration frequencies and their corresponding amplitudes simultaneously. A bar graph provides a visual reference of the relative signal strength (amplitude) of each vibration