73
3.3.3 Mechanical Modeling of Airbag
This section describes the mechanical characteristics of the airbag used for SnS
2
. This
section discusses the mechanical model and the physical principles of the right
and left airbag. Each airbag comprise of four air cells that are interconnected with
each other. The air cell size is affected by the head pressure from the passenger’s
head. A mechanical model is created to predict the mechanical behavior
of the airbag. The developed mechanical model is referring to the mathematical
model that was developed by Ofori‐Boateng 2003. The study defines
the physical characteristics of air inflated cushions for heavy truck seat. The
air inflated cushion has many air cells that are interconnected with each other.
Besides, the mathematical model considered driver’s weight as one of factors
that affect the air cell size. There were some similarities in mechanical characteristics
for the air inflated cushion and the airbag of SnS
2
such as air cell and
loading factor. The
Mechanical Characteristics of Airbag
The airbag in this study is a prototype that is used to support the neck as well as
to reduce SCM stress. The neck support includes interconnected airbags to allow
for the airflow between the bags. The interconnections also allow for the neck
support to support and rotate the passenger’s head near to the seat centre when
the passenger is in a contact position for some time. The mechanical model of the
airbag can be used to design an airbag that is reliable and able to withstand the
passenger head pressure.
The
Mechanical Modeling of Airbag
The behavior of the airbag can be modeled in a simplified schematic as shown in
Figure 3.17. The force that is caused by the weight of the supported head is equal
to the increased pressure in the airbag.
74
Figure 3.17 The schematic of the forces that act on the single airbag.
As illustrated in Figure 3.17, the total force that acts on the airbag is derived as:
1 1
1
A P
g m
A P
g m
F F
atm head
air airbag
× −
× −
× +
× =
∑ =
4.2 Where,
F
airbag
m
air
g P
1
A
1
m
head
P
atm
= =
= =
= =
= force
on airbag N mass
of air in airbag kg gravitational
force Nm
2
Kg
‐2
pressure of air in airbag Nm
‐2
area in airbag m
2
mass of passenger’s head kg
atmospheric air pressure Nm
‐2
75 The
airbag prototype is rectangular in shape; the volume of the airbag is described
as
V
supported
= l x w h ‐ x
4.3 Where,
V
supported
l w
h x
= =
= =
= Volume
of airbag when supporting head m
3
Length of airbag m
Width of airbag m
Height of airbag m
Height difference of airbag m
3.4 THE TOTAL DESIGN OF A SMART NECK SUPPORT SYSTEM
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