Case Study: NVH: Vehicle full NVH development

NVH development of a small car was conducted as part of a full vehicle development project at MIRA. The project encompassed 2 prototype phases as well as Pilot build and pre-production vehicles.

Detailed competitor benchmarking measurements were made, using vehicles chosen both from local and European markets.  The purpose of the benchmarking was to establish ‘Best-in-class’ performance in the home market and to identify the additional steps necessary to allow the vehicle to be competitive in Europe. Using the benchmarking data, a comprehensive set of NVH targets was established.

When the Phase 1 prototype vehicles became available, Noise and Vibration measurements were carried out to establish their status against the targets.  Comparison of the Phase 1 prototypes to the NVH targets showed that the vehicle was uncompetitive in all areas, and was particularly poor for booming noise, powertrain harshness and wind noise as shown in Figure 1.

A root cause investigation was conducted to identify the optimum process to improve the vehicle. Noise path analysis was used to identify the structural paths by which noise was transmitted into the cabin.  Modal analysis techniques were applied to identify the causes of suspension and engine shake issues.  The poor wind noise and road noise performance was found to be due to poor sealing – ultrasonic leak detection and transmission loss measurements were used to identify the critical areas where the vehicle’s sealing needed to be improved.

The early analysis provided by MIRA enabled the customer to make significant improvements to the Phase 2 prototypes as can be seen in Figure 1.

Figure 1 shows the NVH performance of the Phase 1 and Phase 2 prototypes, and the simulator vehicle with respect to the target level.  The simulator vehicle meets or surpasses the target for most of the engine speed range.

A series of modified parts were designed and produced  by MIRA to address each of the NVH issues. Initially these were non-production feasible parts designed to validate the findings of the root cause investigation and to demonstrate potential improvements to the customer.  MIRA then worked with the customer’s designers to develop production feasible parts to address each of the NVH concerns.

A simulator vehicle was constructed using prototype parts in order to demonstrate the overall effect of the recommendations made by MIRA as seen in Figure 1.  The simulator vehicle met the target levels through most of the engine speed range and was a significant further improvement over the Phase 2 prototype vehicle.

MIRA was responsible for validation of the production solutions for each of the NVH issues – this enabled us to monitor the quality of the vehicle at each stage – Pilot Build, pre-production and finally into full series production.

Again, the customer was closely involved at all stages of the development programme to ensure maximum efficiency in developing production solutions and to ensure that design improvements could be incorporated into future products.

For the duration of this programme, customer engineers were present on site at MIRA to ensure transfer of relevant information and knowledge about the vehicle development programme.