Designing for comfort and reliability in an intelligent car seat

American Journal of Applied Sciences, Dec, 2008 by D.A. Wahab, N.F. Adull Manan, M.A. Hannan, S. Abdullah, A. Hussain

INTRODUCTION

Today, the automotive industry is advancing very rapidly. Each year new and better automotive components are introduced by the automotive manufacturers in view of improving passengers safety and comfort as well as aesthetics. Intelligent Safety System (ISS) for example, is aimed at optimising passenger safety and comfort (1). ISS is equipped with safety equipment to warn drivers on incoming road hazards. Developments related to automotive safety cost billions of dollars each year and that exclude casualties, death as well as its adverse effects to the environment (2), (3).

This research presents the development work on a car seat that incorporates a load cell sensory system. The load cells are used for detecting the weight and position of the passenger for the deployment of an air bag in an ISS. The car seat is part of the improved features of the ISS for detecting road hazards. It combines several subsystems such as a weight sensor, image detector, collision system and a tyre pressure monitoring system. The subsystems, which are mostly based on sensors, are combined to provide precise information for the deployment of the air bag. The air bag will be deployed under circumstances such as hazards occurring at a specific speed, the position of the driver to the air bag source and the presence of a driver in the vehicle.

The design of the car seat proposed in this study takes into consideration the use of the load cell type-sensory system that are based on the principles of the Wheatstone bridge i.e. the amplifier arrangement. A wave receiver equipment converts load to electrical current as the output. The load cell is capable of accurately detecting the passenger and position of the air bag (4), (5). Figure 1 shows the type of load cell used in the application.

[FIGURE 1 OMITTED]

While intelligent systems are embedded to ensure passenger safety, equally important are passenger comfort and aesthetics. The automotive industry encourages research and development in comfort analysis especially on the car seat and positioning of the human body(6), (7). According to Anderioni (8), understanding the biomechanics for the posture of driver is an important aspect of ergonomic design. A well designed-car seat design can avoid painful disorder such as low back pain that is due to improper sitting position (9), (10).

Anthropometrics, the study on human dimension such as measurement, shape, mass, centre of gravity, inertia of the human body and work capacity is necessary for ergonomic application (11). In determining the shape and dimension of a product, the features of the human body form the basis in determining size measurements. This is known as the human factors study that is concerned with the interaction of human and products. It is therefore the objective of this study to propose an ergonomic design for a car seat that is equipped with sensory systems for the deployment of an intelligent air bag system.

DESIGN AND METHODOLOGY

This research focuses on the design aspects for ensuring comfort and reliability in the intelligent car seat. For this purpose, the configuration and materials for the car seat were identified. The design of the car seat follows the standard methodology for engineering design starting from information gathering through to concept, embodiment and detail design. Design concepts were generated based on the identified design objectives. Possible design concepts were evaluated and selected based on identified design criteria and eventually the final concept was chosen. The final concept was then validated against structural and stress analysis using a computer aided engineering software focusing on the seat cushion, frame structure and load cell platform. Each of these components is subjected to different compressive loading to represent the weight of the driver and passenger.

RESULTS AND DISCUSSION

Design of the car seat: An ergonomic design of a car seat will require data on the compatibility of human size with the car seat. Turek's (12) guidelines on passenger comfort in a car seat as shown in Table 1 were referred to during the design of the seat cushion. The final design of the seat cushion is shown in Fig. 2.

Figure 2 shows the dimension of the car seat taking into consideration ergonomic requirements. The best position for driving comfort is lowering the knee at the same level as the thigh. In handling the foot pedal, the heels should be used instead of constantly twisting the ankle causing excessive torque to the vertebrae bones (13). Sitting on a hard seat cushion will adversely affect the pelvic bone. According to Mills and Gilchrist (14), sitting on a flat wooden bench will cause peak pressures on the buttocks as compared to sitting on a soft foam cushion. They noted that such high pressures are tolerable for short periods only. Figure 3 shows the pressure contours on a thin foam cushion and the 3-D pressure map. A high peak pressure causes discomfort to the passenger, hence poor quality of driving. Choosing the appropriate material for the seat cushion is also necessary to ensure passenger comfort. For the proposed design of the car seat, the dimension of the seat cushion is 475x226x488 mm in the respective width, thickness and length.