Human Subjective Response

Human Subjective Response to Steering Wheel Hand-Arm Vibration using Real Road Stimuli

Chapter 9: Human Subjective Response to Steering Wheel Hand-Arm Vibration using Real Road Stimuli

9.1 Introduction

Current evaluation methods used to estimate the human subjective response to steering wheel rotational vibration in the automotive industry are based on the use of either the original (unweighted) acceleration signal, the ISO Wh frequency weighted acceleration signal or the Ws frequency weighted acceleration signal. Automobile steering system designers and noise, vibration and harshness (NVH) experts apply one of these frequency weightings to the acceleration data which they measure at the steering wheel. However, the estimation using any one of the current evaluation methods applies to all the vibrational data in the measurement regardless of the magnitude of the vibration. Further, it has been continuously suggested by researchers (Morioka and Griffin, 2006; Ajovalasit and Giacomin, 2009) that only one weighting is not optimal to estimate the human perception at all vibrational magnitudes. Therefore the question has been raised regarding how many frequency weightings are necessary for quantifying the human perception of steering wheel hand-arm vibration.

From both previous research and from the findings described in this thesis it would appear that no single equal sensation curve, thus no single frequency weighting, would prove optimal at each point in time during a vibration measurement. In order to answer the question of how to best select frequency weightings, the research described in this chapter had set the following objectives.

To quantify the human subjective response to representative driving conditions, i.e. real road steering wheel vibrational stimuli.

To use a family of the equal sensation curves to obtain intensity estimates for the same set of representative driving conditions.

To establish the level of correlation between the subjective responses and the vibration metric obtained by means of the frequency weighting.

To use the test results to define recommendations regarding the choice of frequency weighting to use in automotive testing.

9.2 Laboratory Based Experimental Testing using Real Road Stimuli

A laboratory based experiment was carried out in order to obtain the subjective response to steering wheel hand-arm vibration using real road stimuli. The test facility was the same as described in this thesis in section 6.2.1. The test protocol was also the same as described in this thesis in section 6.3.3, except for the fact that the total elapsed time of the experiment was approximately 40 minutes rather than 60 minutes, due to use of only 21 road stimuli with three repetitions. The perceived intensity of subjective response was quantified by means of a Borg CR10 scale, as in the previous experiments which used sinusoidal or band-limited random vibration at the steering wheel.

9.2.1 Test Stimuli

The 21 road stimuli presented in chapter 5 can be considered to be typical of the automotive steering vibration problem, thus useful for the purpose of defining laboratory-based experiments which are representative of the automobile environment. The selected groups of stimuli respect the five criteria which were established in chapter 5 for the purpose of obtaining steering wheel vibrations ...