The introduction of a Sound Quality Engineering Process to Jaguar Cars : executive summary

Abstract

The control of the noise and vibration generated by an automobile is referred to as Noise, Vibration and Harshness (NVH) engineering. It involves identifying the design detail required to reduce the noise and vibration inside the passenger compartment of the vehicle to levels that are acceptable to the customer. It also involves delivering an engine or a powertrain sound character that is both pleasing to the customer and that suits the character of the vehicle. Tuning the sound generated by a vehicle to deliver a particular character is referred to as Sound Quality Engineering. This document summarizes the work of the EngD research programme that was aimed at developing a structured process for engineering the Powertrain Sound Quality of an automobile. The need for developing a Sound Quality Engineering Process at Jaguar Cars was identified through a review of customer evaluations of the sound in Jaguar's vehicles and those of its competitors. This review established that Jaguar's existing vehicles were trailing the leading competition in terms of the delivery of Powertrain Sound Quality. The reason for this shortfall was that the NVH Department at Jaguar did not have a focus on delivering the customer requirements. Without this focus there was no means of using the customer level requirements, for Sound Quality to drive the vehicle design process. The EngD research programme resulted in the formulation and implementation of a Sound Quality Engineering Process at Jaguar Cars that addressed this need. The first part of the research programme involved developing a means of quantifying the differences in the subjective Sound Quality character perceived by the customer. It was established that the subjective nature of the Powertrain Sound Quality could be represented by two underlying dimensions; a measure of the degree of Refinement and a measure of degree of Powerfulness. An assessment technique was developed that enabled the subjective Sound Quality character for a given vehicle to be quantified through its location within a 2-Dimensional Sound Quality Space, the axes of which were defined by each of the two underlying dimensions of Sound Quality. This 2- Dimensional Sound Quality Space provided the means of quantifying the differences in the Sound Quality characters for all of the vehicles competing in the luxury vehicle sectors. It was applied to define subjective Sound Quality targets for all of the new vehicle programmes at Jaguar Cars. These targets identified the required improvements to each of the two underlying dimensions of Sound Quality needed to address the shortfalls in Jaguar Cars' existing vehicles. The second part of the research programme involved identifying the key acoustic features within the sound signatures of Jaguar's vehicles that were responsible for determining the differences in subjective perception between these vehicles and their competitors. The changes to these key acoustic features were related to the required improvements to each of the two dimensions of Sound Quality that were established from the subjective target setting process. The final part of the research programme involved developing techniques that linked these key acoustic features to the noise sources and paths that were responsible for generating them. Through this link it was possible to establish the changes to these noise sources and paths that were necessary to deliver the required changes to the key acoustic features. In this way the required improvements to each of the two underlying dimensions of Sound Quality were used to define the vehicle design specification at the concept stage of the vehicle development programme and consequently drive the vehicle design process. The ability to link the subjective customer level requirements for Sound Quality to the design detail specification has overcome the previously identified shortfall within the NVH development process at Jaguar Cars. The techniques developed during the EngD research programme were formulated into a Sound Quality Engineering Process. Although the process was developed for Jaguar Cars the findings from the research and the techniques developed have since been applied by the different brands within the Ford Motor Company. Within Jaguar Cars the process has been implemented across all of the new vehicle programmes. It has directly resulted in significantly improved Sound Quality characters in the new vehicles that have been recently introduced to the luxury vehicle market