Secondary or passive safety of Auto

If a crash does happen, secondary safety designshould protect the passengers by
1 Making sure that, in the event of an accident,the occupants stay inside the car
2 Minimizing the magnitude and duration of the deceleration to which they are subjected
3 Restraining the occupants so that they are not injured by secondary impacts within the car,and, if they do strike parts of the inside of the
vehicle, making sure that there is sufficient padding to prevent serious injury
4 Designing the outside of the vehicle so that the least possible injury is caused to pedestrians and others who may come into contact with the outside of the vehicle.
The primary concern is to develop efficient restraint systems which are comfortable to wear and easy to use. Manufacturers are now fitting automatic seatbelt tensioners. These automatic ‘body lock’ front seatbelt tensioners reduce the severity of head injuries by 20 per cent with similar gains in chest protection. In impacts over 12 mile/h (20 km/h) the extra tension in the seatbealt buckle triggers a sensor which tightens the lap and diagonal belts in 22 milliseconds, that is before the occupant even starts to move. In addition,because it operates at low speeds, it covers a broad spectrum of accident situations. Anti-submarining ramps built into the front seats further aid safety by reducing the possibility of occupants sliding under the belt .

There are also engineering features such as impact energy-absorbing steering columns, head restraints, bumpers, anti-burst door locks, and selfaligning steering wheels. Anti-burst door locks are to prevent unrestrained occupants from falling out of the vehicle, especially during roll-over. The chances of survival are much reduced if the occupant is thrown out. Broad padded steering wheels are used to prevent head or chest damage.
Collapsible steering columns also prevent damage to the chest and abdomen and are designed to prevent the steering column being pushed back into the passenger compartment whilst the front end is crumpling. The self-aligning steering wheel is designed to distribute force more evenly if the driver comes into contact with the steering wheel during a crash. This steering wheel has an energyabsorbing hub which incorporates six deformable metal legs. In a crash, the wheel deforms at the hub and the metal legs align the wheel parallel to the chest of the driver to help spread the impact and reduce chest, abdomen and facial injuries.
Body shells are now designed to withstand major collision and rollover impacts while absorbing shock by controlled deformation of structure in the front and rear of the vehicle. Vehicle design and accident prevention is based on the kinetic energy relationship of damage to a vehicle during a collision. Energy is absorbed by work done on the vehicle’s materials by elastic deformation. This indicates that, to be effective, bumpers and other collision-absorbing parts of a vehicle should be made of materials such as foam-filled plastics and heavy rubber sections. Data indicates that long energy-absorbing distances should be provided in vehicle design, and the panel assemblies used for this purpose should have a lower stiffness than the central section or passenger compartment of the vehicle. The  crumple zones are designed to help decelerate the car by absorbing the force of collision at a controlled rate, thereby cushioning the passengers and reducing the risk of injury (Figure 1.9). The safety cage (or safety cell) is the central section of the car body which acts as the passenger compartment. To ensure passenger safety, all body apertures around the passenger area should be reinforced by box-type profiles; seats should be secured rigidly to the floor; and heavy interior padding should be used around the dashboard areas. A strengthened roof construction, together with an anti-roll bar, afford additional
protection in case of overturning (Figure 1.10).
To counteract side impact manufacturers are now fitting, in both front and rear doors, lateral side supports in the form of twin highstrength steel tubular beams, which are set 90 mm apart to reduce the risk of the vehicle riding over the beams during side collision. These beams absorb the kinetic energy produced when the vehicle is struck from the side.
To further improve the body structure the BC-pillars are being reinforced at the points of attachment to the sill and roof, again giving more strength to the safety cage and making it stronger and safer when the vehicle is involved in collision (Figure 1.11a, b).
Visibility in design is the ability to see and be seen. In poor visibility and after dark, light sources must be relied upon. The lights on vehicles now are much more efficient than on earlier models.
The old tungsten filament lamp has given way to quartz-halogen lamps which provide much better illumination. The quartz-halogen lamp is able to produce a more powerful beam because the filament can be made hotter without shortening its lifespan. Hazard, reversing and fog lights are now fitted to most vehicles to improve safe driving.
In daylight, colour is probably the most import- ant factor in enabling cars to be seen. If a vehicle is coloured towards the red end of the spectrum, it can be less obvious to other road users than a yellow one, especially in sodium vapour street lights: a red car absorbs yellow light from the street light and reflects little, and so appears to be dark in colour, whereas a yellow car reflects the yellow light and appears more obvious. Silver vehicles will blend into mist and fog and become difficult to see.
Blind spots can be diminished firstly by good design of front pillars, making them slim and strong, and secondly by reducing the area of rear quarter sections. This elimination of blind spots is now being achieved by using bigger windscreens which wrap round the front A-post, and rear windows which wrap round the rear quarter section,giving a wider field of vision.
Many automotive manufacturers now believe that a seatbelt/airbag combination provides the best possible interior safety system. Airbags play an important safety role in the USA since the wearing of seatbelts is not compulsory in many of the states.
As competition to manufacture Europe’s safest car increases, more manufacturers including those inthe UK are starting to fit airbags. These Eurobags,or facebags as they are now called, since their mainfunction in Europe and the UK is to protect the facerather than the entire body in the event of collision,are less complex than their USA counterparts.The first automotive airbags were made morethan 20 years ago using nylon-based woven fab-rics, and these remain the preferred materialsamong manufacturers. Nylon fabrics for airbagsare supplied in two basic designs depending onwhether the airbag is to protect the driver or thefront passenger. The driver’s airbag is housed inthe steering wheel and requires special attentionbecause of the confined space (Figure 1.12). Thepassenger’s airbag system has a compartment door,located in front of the passenger in the dash area,which must open within 10 milliseconds anddeploy the airbag within 30 milliseconds. The vehi-cle has a crash sensor which signals the airbags todeploy on impact (Figure 1.13).