1. INTRODUCTION
Vibration transmission to passengers has a large influence on
comfort, performance, and health.1 A comfortable ride is essential
for a vehicle to obtain passenger satisfaction. Because
of this, vehicle manufacturers are constantly seeking to improve
vibration comfort. Many factors influence the transmission
of vibration to and through the body. Transmission associated
with the dynamic system depends on the frequency and
direction of the input motion and the characteristics of the seat
from which the vibration exposure is received. Vibrations up to
12 Hz affect all of the human organs, while those above 12 Hz
have local effects.2 Low-frequency (4-6 Hz) cyclic motions,
like those caused by tires rolling over an uneven road, can resonate
the body. Just one hour of seated vibration exposure
may cause muscle fatigue and make the user more susceptible
to back injury.
This paper is a subdivision of a general research conducted to
evaluate vibro-acoustical comfort inside the vehicle compartment.
The first part was to define a vehicle acoustical comfort
index using objective and subjective evaluations.3 This paper
is an objective evaluation of vehicle vibration comfort, which
is the first step of the vibration comfort assessment. Analysis
of road conditions parameters, such as the International
Roughness Index (IRI), and their correlation with kurtosis and
the vibration dose value (VDV) can give useful information
about the effect of road roughness on passenger vibration comfort.
Further research may include a subjective vibration evaluation
(jury test), and the results of the subjective and objective assessments
may be used to define an index for vehicle vibration
comfort. This index eliminates the need for further subjective
estimations and can be a useful parameter in various correlation
analyses and vibration comfort predictions. It is believed
that specific results of a vibration comfort index are only valid
for the exact vehicle type. Still, different manufacturers can
use the same method to derive the vibration comfort index for
their products. Methods and general results of the current research
(like correlations conducted for VDV, IRI, kurtosis, and
velocity) are applicable for other researches as well.
Human responses to whole-body vibration can be evaluated
by two main standards—the British Standard 6841 (BS 6841)
(1987) and the International Standard 2631 (ISO 2631) (1997).
The BS 6841 considers a frequency range of 0.5-80 Hz.4 As
shown in Fig. 1, this standard recommends measuring four
axes of vibration on the seat (fore-aft, lateral, and vertical vibration
on the seat surface as well as fore-aft vibration at the
backrest) and combines them in an evaluation that assesses vibration
severity. The ISO 2631 suggests vibration measurements
in the three translational axes on the seat pan, but only
the axis with the greatest vibration is used to estimate vibration
severity.5
The current trend in vibration research is to use multi-axis values.
This may be seen in studies (such as those by Paddan and
Griffin6 and Hinz et al.7). Huston and Zhao examined how the
shape, frequency, and amplitude of mechanical shocks affect
the comfort response of the seated human.8 Recently, the effects
caused by different experimental design variables on subjective
response and vibration accelerations were investigated
by Jonsson and Johansson.9 In this study, ride comfort and vi-
1. INTRODUCTION
Vibration transmission to passengers has a large influence on
comfort, performance, and health.1 A comfortable ride is essential
for a vehicle to obtain passenger satisfaction. Because
of this, vehicle manufacturers are constantly seeking to improve
vibration comfort. Many factors influence the transmission
of vibration to and through the body. Transmission associated
with the dynamic system depends on the frequency and
direction of the input motion and the characteristics of the seat
from which the vibration exposure is received. Vibrations up to
12 Hz affect all of the human organs, while those above 12 Hz
have local effects.2 Low-frequency (4-6 Hz) cyclic motions,
like those caused by tires rolling over an uneven road, can resonate
the body. Just one hour of seated vibration exposure
may cause muscle fatigue and make the user more susceptible
to back injury.
This paper is a subdivision of a general research conducted to
evaluate vibro-acoustical comfort inside the vehicle compartment.
The first part was to define a vehicle acoustical comfort
index using objective and subjective evaluations.3 This paper
is an objective evaluation of vehicle vibration comfort, which
is the first step of the vibration comfort assessment. Analysis
of road conditions parameters, such as the International
Roughness Index (IRI), and their correlation with kurtosis and
the vibration dose value (VDV) can give useful information
about the effect of road roughness on passenger vibration comfort.
Further research may include a subjective vibration evaluation
(jury test), and the results of the subjective and objective assessments
may be used to define an index for vehicle vibration
comfort. This index eliminates the need for further subjective
estimations and can be a useful parameter in various correlation
analyses and vibration comfort predictions. It is believed
that specific results of a vibration comfort index are only valid
for the exact vehicle type. Still, different manufacturers can
use the same method to derive the vibration comfort index for
their products. Methods and general results of the current research
(like correlations conducted for VDV, IRI, kurtosis, and
velocity) are applicable for other researches as well.
Human responses to whole-body vibration can be evaluated
by two main standards—the British Standard 6841 (BS 6841)
(1987) and the International Standard 2631 (ISO 2631) (1997).
The BS 6841 considers a frequency range of 0.5-80 Hz.4 As
shown in Fig. 1, this standard recommends measuring four
axes of vibration on the seat (fore-aft, lateral, and vertical vibration
on the seat surface as well as fore-aft vibration at the
backrest) and combines them in an evaluation that assesses vibration
severity. The ISO 2631 suggests vibration measurements
in the three translational axes on the seat pan, but only
the axis with the greatest vibration is used to estimate vibration
severity.5
The current trend in vibration research is to use multi-axis values.
This may be seen in studies (such as those by Paddan and
Griffin6 and Hinz et al.7). Huston and Zhao examined how the
shape, frequency, and amplitude of mechanical shocks affect
the comfort response of the seated human.8 Recently, the effects
caused by different experimental design variables on subjective
response and vibration accelerations were investigated
by Jonsson and Johansson.9 In this study, ride comfort and vi-
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