Automotive seat design

WHY WE NEED TO DESIGN SEATS
FACTOR FOR SEAT DESIGN
GEOMETRIC FEATURES OF SEAT DESIGN
ERGONOMICS,SIMULATION AND MODELING
VIBRATION APPROACH
PRESSURE APPROACH

1. A utomotive seat design BASIC ASPECTS OF

2. WHY WE NEED TO DESIGN SEATS The extended period of sitting include a higher risk of back problem, numbness and discomfort in the buttocks due to surface pressure and discomfort in the legs and feet from pressure under the thighs. Exposure to whole body vibration (WBV) associated with a prolonged seating is an important risk factor for low back pain (LBP) among drivers. Both vehicle suspension system and driver seat cushion designs have significant interest in reducing discomforts.

3. COMFORT SEATING Static and dynamic anthropometry data are considered for proper design of a comfortable and safe seat . The seat should position the driver with unobstructed vision and within reach of all vehicle controls. For this purpose appropriate seat adjustment features should be there. Proper back support, head rest, thigh support should be provided but there should not be and obstruction/ hindrance during arm or leg movement. Seat must accommodate the driver’s size and shape. Seat should be comfortable for extended period. Seat should provide a shape zone to the driver in a crash.

4. FACTOR FOR SEAT DESIGN The 95th percentile of male and 5th percentile female anthropometric data is generally considered for accommodation on seats. It fit at least for 90 percent of population. Position of the Body - Clear view and comfortable sitting posture are the factors considered for designing seat. The dimensioning is mostly depends on eye, hand and foot positioning. Posture of the Body - Seat should reduce postural stress and optimize muscular effort. Postural stress occurs due to adopting one posture for long period of time. Vibration and ride comfort - Vibration, shock and impacts are major factors for judgments. Thus, the seat design also must consider the vehicle suspension system and the vibration transmitted to the seated user.

5. GEOMETRIC FEATURES OF SEAT DESIGN Cushion’s length from seat back to the waterfall line is 440-550 mm is recommended. The breadth of the cushion is recommended 480 mm for clothing and leg splay. The measurement is based on 95th percentile of female hip breadth and additional space for comfort since female hips are greater than male hip breadth. Seat back height is recommended 509 mm by considering the small female, sitting shoulder height. Seat back breadth may be divided into lower and upper regions. The lower must accommodate a tapered shape from 432mm at the hip to 367 mm at the chest . 480mm is recommended for seat back breadth.

6. PRESSURE APPROACH Enhancement of comfort performance of automotive seats necessitates considerations of the human-seat interface pressure distribution under dynamic vibration environment. Seigler and Ahmadian formulated two techniques, namely, Seat Pressure Distribution (SPD) and Area Pressure Change ( aPcrms ) for the purpose to highlight the relative dynamics between different types of seat cushion, and their effect on driver comfort. The results show that the air-inflated seat cushion can provide significant improvements in pressure distribution between the seat cushion and the driver, therefore providing a more comfortable ride. The dynamics of air-inflated seat cushions is very different from that of foam cushions.

7. VIBRATION APPROACH A major portion of the vibrations enters the body through the seat. Whole-body vibrations, which are vertical vibrations, tend to affect the human body the most. These vibrations are transmitted to the buttocks and back of the occupant along the vertebral axis via the base and back of the seat. Van Niekerk et al conducted research to compare experimental data to the Seat Effective Amplitude Transmissibility (SEAT) values. The experiment used 16 different automobile seats ranging from sedans to SUVs and pickups. The SEAT value is the ratio of the vibration experienced on top of the seat and the vibration that one would be exposed to when sitting directly on the vibrating floor. SEAT values have been widely used to determine the vibration isolation efficiency of a seat .

8. ERGONOMICS,SIMULATION AND MODELING The automotive industry strongly encourages research in the field of objective comfort assessment, especially dedicated to the seat and the related postures. Driver posture is one of the most important issues to be considered in the vehicle design process. Cho and Yoon developed a biomechanical model of humans on a seat with a backrest for evaluating the vehicular ride quality. Wang et al studied the role of seat geometry and posture on the mechanical energy absorption characteristics of seated occupants under vertical vibration. The results reveal that the absorbed power is strongly dependent upon the individual anthropometry variables such as body mass, fat and mass index. A simulation is the execution of a model, represented by a computer program that gives information about the system being investigated. The simulation approach of analyzing a model is opposed to the analytical approach, where the method of analyzing the system is purely theoretical .

9. IMAGES OF SOFTWARE SIMULATION

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