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 being displayed and its relative G-force. The keypad is arranged to make the Electronic Vibration Analyzer (EVA) simple to program and use. Some of the functions include the ability to average readings as well as record, play back and freeze readings. The Electronic Vibration Analyzer (EVA) has a strobe balancing function that can be used to detect imbalance on rotating components such as a driveshaft or engine accessories.
| Item | Description |
|---|---|
| 1 | Electronic Vibration Analyzer (EVA) screen |
| 2 | Frequency mode displayed in Revolutions Per Minute (RPM) or Hertz (Hz) |
| 3 | Active sensor input (A or B) |
| 4 | Current active mode |
| 5 | G-force indicators or the strongest frequencies in descending strength of each vibration |
| 6 | Strength of each vibration |
| 7 | Frequency in Revolutions Per Minute (RPM)/ Hertz (Hz) of each vibration |
Record the readings taken with the diagnostic tool.
- Frequencies should be read in the "average" mode.
- Frequencies have a range of plus or minus 2 Hertz (Hz). A reading of 10 Hertz (Hz) can be displayed as an 8 Hertz (Hz) through 12 Hertz (Hz).
Vibrate Software
Vibrate Software is a diagnostic aid which will assist in pinpointing the source of unacceptable vibrations. The engine's crankshaft is the point of reference for vibration diagnosis. Every rotating component will have an angular velocity that is faster, slower or the same as the engine's crankshaft. Vibrate Software ® calculates the angular velocity of each component and graphically represents these velocities on a computer screen and on a printed vibration worksheet. The following steps outline how Vibrate Software ® helps diagnose a vibration symptom:
- Enter the vehicle information. Vibrate will do all the calculations and display a graph showing tire and driveline vibrations.
- Print a Vibration Worksheet graph. The printed graph is to be used during the road test.
- Road test the vehicle at the speed where the vibration is most noticeable. Record the vibration frequency Revolutions Per Minute (RPM) and the engine Revolutions Per Minute (RPM) on the worksheet graph. The point on the graph where the vibration frequency Revolutions Per Minute (RPM) reading and the engine Revolutions Per Minute (RPM) reading intersect indicates the specific component group causing the symptom.
- A frequency measurement tool capable of measuring vibration frequency and Revolutions Per Minute (RPM) will be needed.
- Provides graphics of diagnostic procedures to aid in testing components.
Reed Tachometer
The Reed tachometer is a hand-held vibration sensor which will assist in locating the source of unacceptable vibrations. The vibration sensor can be placed anywhere in the vehicle for testing purposes. The Reed tachometer contains several reeds that are tuned to vibrate or resonate at different frequencies ranging from 10 to 80 Hertz (Hz) or 600 to 4, 800 Revolutions Per Minute (RPM). Though the Reed tachometer is able to measure multiple frequencies, it does not measure amplitude.
Sirometer
The Sirometer measures frequency in Hertz (Hz) and Revolutions Per Minute (RPM). To use the Sirometer, place it on any vibrating component and slowly scroll the wire out by turning the knob. As the length of wire changes, so does its natural frequency. Find the length of wire that vibrates with the highest amplitude. This frequency will match that of the vibrating component. Read the frequency for that length of wire.
Combination EngineEAR/ChassisEAR
An electronic listening device used to quickly identify noise and the location under the chassis while the vehicle is being road tested. The ChassisEARs can identify the noise and location of damaged/worn wheel bearings, constant velocity joints, brakes, springs or axle bearings.
EngineEAR Basic Unit
An electronic listening device used to detect even the faintest noises. The EngineEARs can detect the noise of damaged/worn bearings in generators, coolant pumps, A/C compressors and power steering pumps. They are also used to identify noisy lifters, exhaust manifold leaks, chipped gear teeth and for detecting wind noise. The EngineEAR has a sensing tip, amplifier and headphones. The directional sensing tip is used to listen to the various components. Point the sensing tip at the suspect component and adjust the volume with the amplifier. Placing the tip in direct contact with a component will reveal structure-borne noise and vibrations, generated by or passing through, the component. Various volume levels can reveal different sounds.
Mechanic's Stethoscope
A mechanics stethoscope is an inexpensive tool for locating noises in motors and other moving parts. It can be used to help diagnose worn gears, faulty valves, coolant pump failure, damaged gaskets, defective bearings and body squeaks.
Squeak and Rattle Repair Kit
The Squeak and Rattle Repair Kit contains lubricants and self-adhesive materials that can be used to eliminate interior and exterior squeaks and rattles. The kit consists of the following materials:
- PVC (soft foam) tape
- Urethane (hard foam) tape
- Flocked (black fuzzy) tape
- Ultra High Molecular Weight (UHMW) (frosted) tape
- Squeak and rattle oil tube
- Squeak and rattle grease tube
Leak Detector
The Leak Detector is used to detect wind noises caused by leaks and gaps in areas where there is weatherstripping or other sealing material. It is also used to identify A/C leaks, vacuum leaks and evaporative emission noises. The Leak Detector includes a multi-directional transmitter (operating in the ultrasonic range) and a hand-held detector. The transmitter is placed inside the vehicle. On the outside of the vehicle, the hand-held detector is used to sweep the area of the suspected leak. As the source of the leak is approached, a beeping sound is produced which increases in both speed and frequency.