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50th Anniversary of the 3-Point Seat Belt

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February 26, 2009

Volvo P544 under lights

Volvo P544 under lights

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February 24, 2009 It's now been 50 years since the first automobile with standard 3-point-safety belts left the assembly lines: the Volvo P544. Patented in 1958 by Volvo engineer Nils Bohlin, the 3-Point safety belt has become the most important automotive restraint system worldwide, saving an estimated one million lives so far - so it's definitely an anniversary worth celebrating. Not much has happened visually to the belt since 1958 and ongoing developments have focused on the systems that complement the belt to do its job better.

50 years of evolution with the Volvo’s 3-point seat belt

To the naked eye, the 3-point seat belt appears not to have changed over the past 50 years. However, the difference today is that the belt is part of a high-tech safety system under constant development. Volvo says that the three-point belt has played a central role for occupant protection in all Volvo's cars since its introduction in 1959 - the safety belt is critical in that it catches and restrains the occupant in the seat, but other systems complement the belt to do its job better.

Systems that compliment the seat belt in it safe operation

One example is the belt pre-tensioner which in the result of a collision, receives a signal from the crash sensor and tensions the belt against the body. This reduces the gap between the belt and the body making it easier for the belt to restrain the body as early as possible.

Force limiters that are integrated into the belts of modern Volvo cars also play a big part. Inbuilt sensors can pick up how quickly the belt is being reeled out and then the force limiters moderate the level of belt restriction. Volvo says that this ensures that the level of restraint is neither excessive, causing injury to the person from the belt; nor too low, in which case the person could be injured by being thrown into the airbag or instrument panel. This force limitation can be exploited in different ways, e.g. it may be higher in the belt at the start of the sequence, then switch to a lower level once the airbag takes over part of the task of energy absorption.

The main parameters that determine when and how the belt pre-tensioners, airbags and force limiters will be deployed are the size of the seat occupant and the type of collision. In order to make the right decision in each case, the car's on-board computer uses data obtained from thousands of pre-programmed collision scenarios and real-life accidents previously analyzed by Volvo. In the case of a collision, the information comes from sensors located all over the car. A main processor in the middle of the car collates the data and accordingly decides how the systems, including the safety belt, should interact. The level of sophistication is such that if the car is fitted with an integrated child booster cushion in the outside rear seat, the belt protection system will operate differently in this back seat to that in the front seats, in order to protect the smaller occupant.

What about the future?

The 4 Point Belt

Volvo is convinced that the seat belt will still be around in 2020 and way beyond that too. They say that the belt may look somewhat different; maybe even have a four-point attachment instead of three and it will probably be designed so it is easier to put on. They envisage that cars will be designed in the future to automatically avoid collision and only at this stage will we be able to do away with the belt.

The motorized Belt

Volvo says that the four-point belt has obvious advantages. For instance, it restrains the occupant more effectively if the car rolls over (one reason why rally cars are fitted with four-point safety harnesses or belts with even more attachment points). It also reduces the small risk of the seat occupant sliding out from under the three-point belt. However, the four-point belt also has disadvantages. They say that it should preferably be designed as a cross, forming an X pattern across the body. It is across the ribcage that the human body is strongest and has the best chance of absorbing incoming collision force. The challenge therefore is how best to effectively attach the upper point of the belt to the car where there is no natural attachment point in the bodywork.

The motorized belt is an exciting new technology that tightens the belt and places the driver in the right position in potentially hazardous situations, says Volvo. For instance, if the car is being driven more actively (e.g. wider steering wheel movement), there may be a benefit from having the support of the belt. The belt may also receive a signal from the car's collision warning system that an obstacle is approaching, or that the driver is beginning to be drowsy or inattentive. If so, the belt can provide a warning and alert the driver to the situation by pulling tight and positioning him or her in the seat. One benefit of this system is that it can be activated an unlimited number of times without being used up, unlike for instance pyrotechnical belt pre-tensioners.

Belts that are easier to use

Over a million lives saved so far - where to from here?

Far too many drivers still do not use their safety belts. Solutions that make usage more natural and convenient are therefore constantly being discussed. Volvo says that one alternative may be a belt buckle that rises from its place between the seats when someone sits down. This makes it easier, particularly in the rear seat, to find the buckle and use the belt. Other ideas involve showing the occupant how to use the belt with the help of strobe lights, or by sewing an illuminated strip into the belt to make it easier to find in the dark. Tests have also been conducted by Volvo on fully automatic systems where the belt is placed across the seat occupant and then fastened.

Volvo based on general and in-house statistics on accidents and belt use estimate that over 1 million lives have been saved through people wearing seat belts. The European Transport Safety Council (ETSC), "Increasing seat belt use", 2007 advise that if you are wearing a safety belt, your chances of surviving a collision improve by 50 percent We also know that a massive 75 percent of people thrown out of cars in accidents die in the process. (See the Prevention Institute).

Improvements in seat belt design are critical, but they are useless if you are not wearing them, so this needs to remain a key focus.

David Greig

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