Target setting and benchmarking for vehicle noise and vibration refinement

X. Wang,     RMIT University, Australia

Abstract:

In order to develop new vehicle products with well-refined noise and vibration performance, noise and vibration targets must be set up. Market research helps to select the best-in-class competitors' vehicles and determine benchmark vehicles to be studied. Benchmark analysis together with CAE modelling facilitates vehicle noise and vibration target setting and target cascading. This chapter summarizes objectives, significance and scope of vehicle noise and vibration target setting and benchmarking. Examples are given to illustrate how to conduct vehicle noise and vibration benchmarking, target setting and target cascading.

Key words

target setting

target cascading

benchmarking

interior noise target

exterior noise target

subjective evaluation

objective testing

whole-vehicle noise

vibration

components/subsystems noise

vibration

sound pressure level

sound quality

sound power

articulate index

statistical energy analysis

transfer path analysis

2.1 Introduction

As mentioned in Chapter 1, in the first phase of a vehicle development program, market analysis, benchmark study and target setting are important tasks. The object of benchmark study is to determine the best-in-class competitors. Requirement, design and performance constitute the three stages of the vehicle development process as shown in Fig. 2.1. The purpose of target setting is to establish design requirements. Vehicle targets are set based on the benchmark study, the voice of the customer and business/ industry/government regulation, as shown in Fig. 2.2.

2.1 Vehicle development process.

2.2 Basic inputs for vehicle development target setting [2].

Market analysis determines which group of customers the vehicle is targeting; customer wants from this group and competitors' vehicles for benchmark study are then determined. The competitors' vehicles are analysed to determine the competitor best-in-class systems and subsystems; overall vehicle specifications and targets are then determined as shown in Fig. 2.3.

2.3 Vehicle target setting process [2].

2.1.1 Objectives and significance of vehicle noise and vibration target setting and benchmarking

Benchmarking allows for greater understanding of vehicle systems, subsystems and components and their design targets. Apple-to-apple, back-to-back comparisons give information about what are good designs, and what are poor designs, and what are realistic design targets. The development focuses are then better calibrated. The purpose of the benchmark study is to identify the competitor best-in-class and facilitate noise and vibration target setting for the vehicle system, subsystems and components.

Setting vehicle noise and vibration targets is important for the successful operation of a vehicle development program, as it ensures that planned resources and efforts are directed towards better vehicle noise and vibration performance than that of competitors in order to satisfy customers at the beginning of the development process. Without it, individual system suppliers would determine their own interpretation of an appropriate level of noise and vibration. The final vehicle would most likely be truly refined only in some aspects and not in others. Excessive noise and vibration caused by one component or subsystem in the intended production vehicle would cause its design validation test to fail, lead to a large cost increase and time delay for the program, and jeopardize the program targets. The purpose of vehicle noise and vibration target setting is to ensure that the newly developed vehicle has no noise and vibration complaint issues and that it has superior noise and vibration performance when released to market.

2.1.2 Scope of vehicle noise and vibration target setting and benchmarking

Vehicle noise and vibration targets consist of interior and exterior targets, subjective and objective targets, noise level and sound quality targets. Exterior noise targets include whole-vehicle exterior targets and single-component exterior noise targets. The exterior pass-by noise targets must conform to the national design rules and standards. Interior targets include the whole-vehicle and single-component noise targets inside the vehicle cabin and ride quality (vibration) targets at idle, constant speeds and slow accelerations, wide open throttle run-up and overrun/coast-down driving conditions.

The noise and vibration targets for the whole vehicle system, individual components and subsystems are documented in the overall vehicle specification and system specifications by the brand holder, and adherence to them has become a condition of contract for any suppliers who implement an advanced product quality planning process.

Corresponding to vehicle noise and vibration targets, a benchmark study needs to be conducted on competitors' vehicles for noise and vibration performance of the interior and exterior, both subjectively and objectively, of the whole vehicle and of components/subsystems, and of the level and quality in all vehicle operating conditions.

2.2 Benchmarking of vehicle noise and vibration

Benchmark vehicles are selected according to similar style/platform capacity, cost, weight and targeted market segment agreed by the program team. They are tested for exterior noise including pass-by and idle; for interior disturbing noise including rattle/squeak, resonance noise, road noise, powertrain noise, auxiliaries, load reversal and gear noise; for communication and audio acoustics including hi/fi qualification and articulation index; for interior actuation noise including servo actuators and door closing; and for interior driving noise in conditions of acceleration and constant speed. The interior and exterior disturbing noise will need to be minimized, while interior driving noise, actuation noise and communication/audio acoustics can be designed as shown in Fig. 2.4. The vibration and ride quality are also tested in all vehicle operating conditions.

2.4 Benchmarked vehicle noise [4].

Subjective evaluation is an important part of vehicle development because its results are directly related to customers' feelings. Subjective evaluations are conducted in a group of people (more than three) and the results are produced from the statistical average of the group. Table 2.1 shows a vehicle subjective evaluation rating scale and rules. Table 2.2 shows a typical vehicle NVH subjective evaluation form.

Table 2.1

Vehicle subjective rating scale

(courtesy of General Motors Holden Ltd, 1999)

Table 2.2

Vehicle NVH subjective evaluation form