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Volvo S80. Passive Safety

Safety is far more than cut-away show cars, with highlighted details painted yellow with black stripes, and filled with stuffed airbags. Safety is very much parts of Volvo's soul and, as a result, it is always present, an integral part of the very first design work and a vital part at every stage of the development process.

If the active safety chapter can be summarised as active accident avoidance, passive safety can be summed up in three words: passenger protection priority.

One of Volvo's prerequisites is that every new Volvo has to be safer than the previous one. When it comes to the Volvo S80, this is very much the case.

One of the objectives when designing the Volvo S80 was to further to strengthen Volvo's position as the world leader in the field of passenger protection. This aim has been realised.

With two new and important technical features, the level of passenger protection has taken yet another step forward. It would perhaps be no exaggeration to say that the Volvo S80 is the safest passenger car on the market at present.

Although safety developments in the automotive industry have progressed by leaps and bounds in recent years, there is still some truth in the statement that a large car is safer than a small one. Size is related to safety. This is part of the laws of nature. A larger, heavier car suffers the least damage in a collision with a smaller, lighter car, thus providing better protection for its occupants. Crumple zones and energy absorption - two vital parameters - can be more effectively designed if there is more space.

A well-designed, rigid body structure is the perfect base on which to build. As mentioned in the chapter on active safety, the Volvo S80 has an extremely rigid body. Almost half of it is made of HSS steel with extremely strong sub-assemblies. Its "core" is the safety cage around which there is a structural network of members. This network is designed to absorb and dissipate crash energy and keep it away from the occupants by interacting and helping to conduct the energy around and away out into the members.

Belts and bags
Volvo has always claimed that the single most important protective feature in a car is the seat belt. The Volvo S80 has three-point belts on all five seating positions. What is more, they are all equipped with pyrotechnical pre-tensioners.

The pre-tensioners automatically tighten the belts in a crash, eliminating the slack which is normal in a belt. The front seat belts are also equipped with force limiters, which control and regulate the roll speed of the belt webbing and provide more gentle restraint. The front seat belts also have automatic belt height adjusters for optimum belt geometry.

Needless to say, the belt system in the Volvo S80 has been integrated with the airbag systems as these systems interact.

So the trigger levels and activation forces are determined in harmony with belt functions, such as the pre-tensioners and the force limiters.

Passenger airbag
The passenger airbag, an option, is invisibly stored under the upper part of the dashboard and is designed to activate in a "friendly" way in order to protect the passenger rather than being a risk. As a result, there are two trigger levels depending on how the passenger is sitting. In the USA, an airbag is mandatory but the use of seat belts is not and the airbag must therefore decide how much force it is going to use.

A belt sensor indicates whether or not the front seat passenger is wearing a seat belt and the airbag trigger level is adjusted accordingly.

If a seat belt is being used, the bag has a higher trigger level compared with a situation in which the passenger is not wearing a belt and is totally dependent on the bag for protection. This means that more crash energy is needed to trigger the bag when the passenger is wearing a seat belt than when he is not.

Back in the 1960s, Volvo pioneered the collapsible steering column, a feature which has been a self-evident part of every Volvo car since then.

In the Volvo S80, this function has been further improved and the steering wheel can be pushed further back, as a result of the collapsing function in both the lower and upper steering shaft which creates additional space for the steering wheel to be kept away from the driver. Belt and bag further protect the driver from contact with the steering wheel.

Two important new features, WHIPS and IC The Volvo S80 includes two important new safety features. Both of them protect what is perhaps the most vital parts the body, the neck and the sphere that sits on top of it.

WHIPS, Whiplash Protection System
In 1997, the Volvo Car Corporation presented the Whiplash Protection Study, WHIPS, which was an R&D project designed to produce a seat which would reduce the risk of whiplash injuries in rear-end collisions.

The WHIPS system has now been incorporated in the Volvo S80, making it perhaps the safest car on the market in rear-end collisions.

Although they are most frequently caused at low speeds in relatively minor accidents, whiplash injuries are extremely painful, both physically and mentally, for the people who incur them, as well as being difficult to detect and define. They are also perhaps the single most expensive injury in insurance terms.

Although they have still not been fully explained in medical terms, it is clear that whiplash injuries are caused by the sudden "whiplash" movement of the head - backwards and then forwards - when it is exposed to violence from behind, otherwise known as the catapult effect.

Since rear-end collisions often occur in city traffic, the Volvo WHIPS system is optimised to be most effective at speeds ranging from 15 km/h (10 mph) to 30 km/h (20 mph).

The WHIPS system is based on two mechanical parts and works in two stages. It is activated the moment the car is hit from behind.

The mechanical solutions are, firstly, a device between the seat cushion and the backrest that enables the backrest to move backwards throughout the operational sequence and, secondly, a wire frame suspended in a set of additional springs in the backrest which prevents the occupant being pressed too far back and thereby being subjected to the catapult effect.

During the first stage, after the impact, the body is thrown backwards and then cushioned in a controlled manner with the whole of the spine safely against the backrest. In order to reduce the g force, the backrest is allowed to move backwards with the occupant. This backward movement prevents the body being thrown forwards. The upper part of the backrest moves upwards and forwards, thereby providing extra support and protection for the neck and t head.

This is the first stage of the WHIPS function and is called the parallel phase.

During the second stage, the WHIPS mechanism allows the backrest to tilt backwards, up to 15 degrees, thereby absorbing impact energy, reducing the movement of the body and heavily reducing the risk of the catapult effect which causes the whiplash injury.

Tests conducted by Volvo during the development of the system reveal that the WHIPS system can reduce the acceleration forces in the neck by some 50 per cent.

Rear seat passengers are not affected by the movements of the WHIPS front seats in an impact situation. They move in exactly the same way as the occupants of the front seats, making the entire movement parallel, without any negative interaction such as the legs being trapped and injured between the front and rear seats.

As the WHIPS system is activated as speeds as low as 15 km/h, this means that it must be easy to repair and it is. The mechanical parts that are affected are simple and inexpensive and, in most cases, they can be replaced without needing to replace the entire seat.

Side Impact Protection
Passenger protection in side impacts is perhaps the most difficult area in terms of safety development, because of the lack of space or the minimal crumple zone, only 25-30 cm. Passengers sit very close to the point of impact. This must therefore be compensated for in one way or another.

The SIPS structure has been extensively upgraded and its interacting components consist of the energy-absorbing elements in bottom rails, pillars, cross-members, roof and seats, plus energy-absorbing materials in the doors.

This has been supplemented with more, further improved padding in all the roof pillars and along the edges of the roof lining. This material has a hard feeling when it is touched, but it yields in a "friendly" manner and absorbs energy when it is hit in an impact.

The second step in the continued development of the sips system was the introduction of the sips bags in 1994 - now a standard item on all Volvo cars.

The Volvo side airbag is located in the outer part of the backrest and is therefore always in the optimum protective position in relation to the occupant.

sips further reduces the risk of severe chest and pelvic injuries as its function is to keep the occupant away from the side of the car.

In the Volvo S80, the side air bags are trigged by electronic sensors, one in the b pillar and one behind the rear door. Their position makes the reaction time from moment of impact to triggering the bag very short. A factor which is of vital importance in side impacts.

However, padding and side air bags cannot completely make up for what can happen to the head when the car is hit from the side.

So the time has now come to introduce the second major new safety feature in the Volvo S80. It is also the third stage in the development of side impact protection.

IC (Inflatable Curtain)
The Inflatable Curtain, is, was presented together with WHIPS as an R&D project. in 1997, the first technical system for this type of protection.

The purpose of the two systems is further to reduce the of injuries in a side impact by protecting the heads of the occupants. The curtains, one on each side, are woven in one piece and hidden inside the roof lining. They cover the upper part of the interior, from the A pillar to the rear side pillar, thereby protecting the occupants in the front and rear seats.

The IC is activated by the same sensors as the SIPS bags. They are "slave" sensors to a central sensor which determines where the impact is and which bag should be triggered in order to protect the occupants. The Inflatable Curtain is only activated on the side that is hit. If only the rear sensor is affected, the IC is activated but not the sips bag.

The ducts in the curtain are filled within 25 milliseconds by the same harmless gas as is used in the airbag and the curtain slowly starts to deflate after about three seconds in order to provide maximum protection in complicated collisions.

The ducts do not cover the entire surface of the curtain. Instead, they are concentrated in the areas which are most likely to be hit by the occupants' heads.

As a result, the need for gas is limited and the activation time is minimal.

The ducts act as controlled restraints on the head and prevent it hitting the inside of the car. The curtain also prevents the head from colliding with exterior objects which can sometimes be involved in an accidents, such as signposts and similar objects.

The size of the curtain also helps to keep the passengers inside the car instead of being partially thrown out of the side windows.

It does not matter whether a side window is open or closed when it comes to the protective capacity of the IC. When the curtain is activated, it hardly touches the side window but expands inwards, moving closer to the heads of the occupants.

Taking all these features into account, it is safe to call the Volvo S80 the best car in the world in terms of side impact protection. In fact, it may very well be the safest car on the road today.

Folding rear head restraints
The folding rear head restraints may appear to be a feature which is only designed for comfort, but this is only partially true. The rear head restraints fold forwards at the touch of a button in order to improve rear visibility.

However, if they are left folded forwards, it is impossible to travel in the rear seat without folding them back again. This ensures that they once again serve their original purpose as head restraints.

Young passenger protection
It goes without saying that the passenger protection in a Volvo does not simply apply to adult passengers who can sit safely strapped in one of the five seats. Volvo safety also includes the smallest and least protected passengers - children.

The Volvo S80 is naturally equipped for fitting the entire Volvo range of child safety seats.

In order to permit the installation of a rear-facing child seat in the front passenger position, the passenger airbag can be switched on and off using a switch. This switch, which only can be fitted by a Volvo dealer, works via the ignition key. When the ignition is turned on, an indicator lamp on the switch comes on and shows whether or not the passenger airbag is activated. If the switch suffers electronic failure, the SRS lamp comes on, just as it does if any other defect occurs in the SRS system.

Other child safety fittings include the integrated child booster cushion, which can be used with the centre rear seatbelt and adjustable head restraint for children aged four and up (the safest position in a car), and a safety seat fitted behind one of the front seats.

Although the WHIPS function is incorporated in the front seats, it does not interfere with the child seat or the function of the front seats in a rear-end collision.

Related page: Volvo S80 Original Press Release


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