Case Study: NVH: Power Train Noise Problem Solving Approach

The programme of work will commence following an initial technical meeting between MIRA and the customer’s engineers. During this meeting, the sound quality issue will be demonstrated to MIRA engineers. Following a drive appraisal a number of practical issues will be discussed, such as preferred interior noise measurement locations, standard test conditions and any existing data that could support and focus the efforts of the investigations.

The initial task of this project will be to define a noise target representing an improved acceptable condition. This will be done by performing a detailed sound quality analysis of the interior noise characteristics of the vehicle.

Binaural Head Accurate Reproduction of Measured Sound	NVH Sound Quality Suite

The following activities will be implemented to achieve an understanding of the root cause of the problem by investigating its potential sources and transmission paths:

Visual investigation – In order to identify any poor design features an initial visual assessment of the vehicle will be performed prior to commencing any test activities.

Source quantification – The body and engine side of the relevant powertrain and suspension mounts will be measured during this exercise under load and no load conditions. Intake and exhaust orifice noise may also be measured under load and no-load conditions during this exercise.

Driveline assessment – This activity will consist of basic disconnection exercises, including front and rear propshaft disconnections. In addition, propshaft torsional vibration measurements may be carried out on the vehicle whilst installed on the VSACD.

Cavity assessment – Booming noises are often directly related to the acoustic performance of the vehicle passenger compartment, as cavity resonances can amplify sources that otherwise would not be perceptible. This exercise will consist of measuring the acoustic field inside the vehicle cabin with an array of 6 to 8 microphones for a number of modified vehicle interiors. These modifications will be achieved by installing temporary baffle panels along and across the passenger compartment, opening windows, blocking empty cavies, etc.

Power Train Mount Measurement Transducers	In-car On-line Data Processing

The information from these five activities will highlight potential sources and weak paths of the issue under investigation. Additional more detailed test activities might be carried out at this stage to finalise the understanding of the problem, these might include:

In is anticipated that this investigation will provide enough information to develop a palliative measure to achieve the defined noise target and demonstrate the understanding of this NVH issue.

However, the issue under investigation might not be addressed fully during the described test activities, as the cause could be due to multiple complex interactions of sub-systems.   As a result it may not be feasible to offer a cost-effective solution.  If this is the case, MIRA will prepare a detailed summary of the findings and justified recommendations for further investigations.

The results from these activities will be presented to the customer’s engineers for discussion during an interim project review. It is anticipated that a number of possible countermeasures will be discussed during this review.

The programme of work will be concluded with the development and implementation of the necessary countermeasures, based on MIRA in-house made prototype parts, to demonstrate the understanding achieved during the investigation. The interior noise levels at the passenger compartment as well as the relevant vibration data will be acquired before and after any modification is implemented in the vehicle. This will provide the appropriate validation information. The modified vehicle will finally be demonstrated to the customer to support the presentation of the conclusions of this investigation.

All test activities will be performed on the MIRA Proving Ground and in MIRA’s NVH test facilities, such as the Vehicle Semi-Anechoic Chassis Dynamometer (VSACD).