International Journal of Mechanical Engineering and Technology (IJMET)
Volume 10, Issue 03, March 2019, pp. 178-187. Article ID: IJMET_10_03_018
Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=10&IType=3
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication
Scopus Indexed
COMFORT IMPROVEMENT AND KINETOSIS
REDUCTION BY THE USE OF A PENDULUM
TYPE CHILD TRAVEL SEAT
N. L. Pavlov
Department of Combustion Engines, Automobile Engineering and Transport,
Faculty of Transport,
Technical University of Sofia, 8 Kliment Ohridski Blvd., 1000 Sofia, Bulgaria
E. E. Sokolov
Department of Combustion Engines, Automobile Engineering and Transport,
Faculty of Transport,
Technical University of Sofia, 8 Kliment Ohridski Blvd., 1000 Sofia, Bulgaria
M. H. Peychev
Department of Combustion Engines, Automobile Engineering and Transport,
Faculty of Transport,
Technical University of Sofia, 8 Kliment Ohridski Blvd., 1000 Sofia, Bulgaria
D. I. Dacova
Department of Combustion Engines, Automobile Engineering and Transport,
Faculty of Transport,
Technical University of Sofia, 8 Kliment Ohridski Blvd., 1000 Sofia, Bulgaria
L. P. Kunchev
Department of Combustion Engines, Automobile Engineering and Transport,
Faculty of Transport,
Technical University of Sofia, 8 Kliment Ohridski Blvd., 1000 Sofia, Bulgaria
ABSTRACT
The current study analyses the effect of using a pendulum type tilting child seat on
the comfort improvement and the reduction of kinetosis (motion sickness) among
children traveling in an automobile. Road tests with registration of the accelerations
for a conventional child seat and a pendulum type tilting child seat are performed.
Results for the spectral densities of the linear accelerations along the orthogonal axes
are presented. The quadratic means of accelerations acting on both seats are
calculated and compared. Results for the motion sickness dose value are obtained. A
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N. L. Pavlov, E. E. Sokolov, M. H. Peychev, D. I. Dacova and L. P. Kunchev
calculation for the percent of people who can vomit is made and the results for both
seats – conventional and tilting, are compared.
Keywords: Child seat, kinetosis, comfort, acceleration and road testing.
Cite this Article: N. L. Pavlov, E. E. Sokolov, M. H. Peychev, D. I. Dacova and L. P.
Kunchev, Comfort Improvement and Kinetosis Reduction by the Use of a Pendulum
Type Child Travel Seat, International Journal of Mechanical Engineering and
Technology, 10(3), 2019, pp. 178-187.
http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=10&IType=3
1. INTRODUCTION
When travelling with different types of transport symptoms like nausea vomiting, headache
etc. can sometimes occur among passengers. These are typical symptoms of kinetosis, also
known as motion sickness. It is caused by a number of factors more or less convenient for
measurement and evaluation [1]. One of these factors is the value of acceleration acting on the
human organism, mainly in the lower frequencies of external impacts. While estimating the
impact of vibrations on kinetosis generation wide attention is paid to the ones with
frequencies from 0.1 to 4 Hz and especially to the ones with frequencies under 0.5 Hz [1, 2].
Car suspensions are designed to damp vibration in vertical direction. With frequent speed
changes and cornering horizontal vibrations which depend mainly on the traffic situation, the
road plan and the vehicle speed appear. In order to reduce the corners harmful impact on
human organism tilting car body is used in railway transport for curve motion. No such
practice is present in automobiles. It is easier to tilt only the seats or only the head of the
passenger [3, 4]. This however is related to certain problems concerning the seats positioning
and the passengers cosiness. It is well known that children are more susceptible to the
irritations causing kinetosis [5]. That is why the authors propose a special design of a
pendulum type tilting child seat. It is a passive one, i.e. it tilts under the impact of centrifugal
force, generated during cornering.
The aim of this article is to study the indicators of comfort for a child travelling on a
conventional seat and on a pendulum type tilting seat. Motion sickness dose value and the
percent of people who may vomit will be determined. The results obtained for both seats will
be compared.
2. METHODOLOGY AND EQUIPMENT
The experiments are conducted on a typical mountain road with a large number of turns. The
chosen route from Sofia to Mezdra is shown on fig. 1.
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Comfort Improvement and Kinetosis Reduction by The Use of a Pendulum Type Child Travel
Seat
Figure 1 Testing route
The designed pendulum type tilting seat, shown in fig. 2, is mounted on the rear seat of a
road vehicle (fig. 3). A conventional child seat is also mounted in the vehicle. Test dummies
with mass and geometric parameters equal to the mass and geometric parameters of children
are mounted on both seats. Three axial accelerometers are mounted on the seating surfaces
bellow the dummies. Data collection is done through a data acquisition device (DAQ). The
DAQ converts analog signals from accelerometers to digital and submits them to a mobile
computer. So, the data is recorded on the hard disc drive of the computer.
Figure 2 Pendulum type tilting child travel seat [6]
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N. L. Pavlov, E. E. Sokolov, M. H. Peychev, D. I. Dacova and L. P. Kunchev
Figure 3 Positioning of the conventional and the tilting seat in vehicle
3. RESULTS
The accelerations registered for the conventional and for the tilting seat along the x, y and z
axes are shown in fig.4-9.
Figure 4 Longitudinal acceleration measured on conventional child seat
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Figure 5 Longitudinal acceleration measured on tilting child seat
Figure 6 Lateral acceleration measured on conventional child seat
Figure 7 Lateral acceleration measured on tilting child seat
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N. L. Pavlov, E. E. Sokolov, M. H. Peychev, D. I. Dacova and L. P. Kunchev
Figure 8 Vertical acceleration measured on conventional child seat
Figure 9 Vertical acceleration measured on tilting child seat
The accelerations power spectral densities (PSD), determined from the recorded
acceleration values, are shown in fig. 10-12.
Figure 10 Power spectral densities of the longitudinal accelerations on conventional (red solid line)
and on tilting seat (black dashed line)
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Comfort Improvement and Kinetosis Reduction by The Use of a Pendulum Type Child Travel
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Figure 11 Power spectral densities of the lateral accelerations on conventional (red solid line) and on
tilting seat (black dashed line)
Figure 12 Power spectral densities of the vertical accelerations on conventional (red solid line) and on
tilting seat (black dashed line)
The results analysis for the accelerations power spectral densities shows that they are
almost equal for the x axis (Sax). That is easy to explain as the vibrations for both seats are
determined by the vehicle acceleration and deceleration. The minor differences noticeable in
the power spectral densities and the differences in the acceleration recordings (fig. 4 and 5)
are due to clearance in the tilting seat cylindrical joint and the different mount of both seats.
The accelerations power spectral densities along the y (Say) and the z (Saz) axes differ
significantly. This is a result from the tilt of the pendulum seat due to the centrifugal force
generated during cornering. As a result of the tilt the lateral accelerations drop but the ones
acting on the child vertical axis increase. The biggest change is noticed in the lower
frequencies which are the main reason for kinetosis (motion sickness).
Root mean square (r.m.s.) acceleration is the most common index for the evaluation of the
vibration intensity. Mathematically, r.m.s. acceleration can be expressed as [2]:
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N. L. Pavlov, E. E. Sokolov, M. H. Peychev, D. I. Dacova and L. P. Kunchev
1

a w    a w2 t dt 
T 0

T
1
2
(1)
where T is the duration of the measurement in seconds, a w t  is the weighted acceleration
as a function of time (time history), meters per second squared (m/s2) for translational
vibration [2].
The vibration total value of weighted r.m.s. acceleration, determined from vibration in
orthogonal coordinates is [2, 7]:

2
2
2
av  a wx
 a wy
 a wz

1
2
(2)
where a v is the root sum of squares;
a wx , a wy , a wz are the weighted r.m.s. accelerations in the x-axis, y-axis and z-axis,
respectively.
The comfort criterion is assessed accordingly to the following guidelines acceleration [2,
8]:
Table 1 Comfort/discomfort ranges [2 and 8]
r.m.s. acceleration [m/s2]
Reaction
less than 0.315
between 0.315 and 0.63
between 0.5 and 1.0
between 0.8 and 1.6
between 1.25 and 2.5
greater than 2
not uncomfortable
a little uncomfortable
fairly uncomfortable
uncomfortable
very uncomfortable
extremely uncomfortable
It is noticeable that the ranges overlap. It comes from the subjective perception of
comfort. The assessment analysis should be from the down top on the table, for example a
value of r.m.s.=1.3 would be assessed as “very uncomfortable” and not as “uncomfortable”
[8]. Results for measured r.m.s. accelerations are shown in Table 2.
Table 2 Comparison of results of r.m.s.
r.m.s.
Child travel seat
Acceleration [m/s2]
Reaction
a wx
conventional
tilting
conventional
tilting
conventional
tilting
conventional
tilting
0.6027
0.6996
0.9093
0.7048
0.5884
0.6407
1.2395
1.1818
fairly uncomfortable
fairly uncomfortable
uncomfortable
fairly uncomfortable
fairly uncomfortable
fairly uncomfortable
uncomfortable
uncomfortable
awy
a wz
av
It is visible that the conventional seat accelerations measured along the x and z axes are
fairly uncomfortable. Along the y axis the r.m.s. acceleration value causes an uncomfortable
reaction. With the tilting seat values matching the fairly uncomfortable reaction of traveling
children are measured for the three directions.
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Comfort Improvement and Kinetosis Reduction by The Use of a Pendulum Type Child Travel
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According to [2] the motion sickness dose value (MSDV) may be calculated by:
MSDV  a wT
1
2
(3)
In the international standard ISO [2] recommends only the evaluation of the vertical
vibration effect on motion sickness, but some authors apply the method for the horizontal
(lateral and longitudinal) directions also [7, 9]. The percentage of people who may vomit in
meters per second on 1.5 degree (m/s1.5) is approximately [2]:
1
(4)
MSDV
3
The results of the MSDV and the percentage of persons who my vomit, are shown in
Table 3.
%vomiting 
Table 3 Comparison of results of MSDV and %vomiting
MSDV
Child travel seat
Dose value [m/s1.5]
People who may vomit
x
conventional
tilting
conventional
tilting
conventional
tilting
45.11
52.45
68.05
52.75
44.04
47.95
15.03 %
17.45 %
22.68 %
17.58 %
14.68 %
15.98 %
y
z
The highest percent of people who may vomit is calculated for the y axis of the
conventional seat. A reduction from 22.68% to 17.58% is observed with the use of a tilting
seat. At first sight this looks modest, however the reduction from 22.68 to 17.58 is a
significant drop of 22.7%. Along the other axis lower values of 17.58% are observed. This
means that the total percent of people who may vomit drops with the same motion sickness
value as the y axis percent.
4. CONCLUSION
The gathered results of the experiments show that the use of a pendulum type tilting child seat
aids for the decrease of the spectral densities of lateral accelerations acting on the travelling
child. As a result, the spectral density of the vertical accelerations increases, however it is
widely known that they are much easier for the human organism to withstand as it is used to
them in its everyday activities. The r.m.s. acceleration analysis marks a drop of the lateral
(along the y axis) acceleration so that from values causing uncomfortable reaction in the
conventional seat it drops to values causing a fairly uncomfortable reaction in the travelling
child. The percent of people who may vomit drops from 22.68% to 17.58%. During the
conduction of the experiment a forced vehicle speed reduction was necessary in some road
sectors with a lot of corners due to the presence of heavy trucks causing car columns. This
gives us a reason to think that during movement with higher speeds the efficiency of the
solution proposed will be higher. That’s why in our future work a research on the influence of
the vehicle speed on the potential of comfort improvement and kinetosis reduction with the
use of a pendulum type child travel seat will be done.
ACKNOWLEDGMENTS
This work was supported by the National Science Fund of the Ministry of Education and
Science of the Republic of Bulgaria [Grant No. ДМ 07/8 (December 17, 2016)].
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