Bag to the future
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they be fitted in all trucks?
uch engineering effort VI has gone into providing .A. modern cars and light l ans with safety features which protect both driver and passenger in the event of an accident; but what are truck manufacturers doing to improve the lorry driver's lot?
Truck occupant safety has been largely ignored by manufacturers and legislators alike over the years, mainly because injuries and deaths have been than low Department of Transport statistics for 1991 show that 15,235 trucks, or 3.5% of all those registered, were involved in an accident causing injury—trucks over 3.5 tonnes GVW were involved in approximately one injury-causing accident for every two million km (1.25 million miles) travelled and one fatal accident every 35 million kilometres (21.5 million miles).
Of the 782 people killed in accidents involving trucks in 1991, just 65 were truck drivers or their passengers. Thanks to continually improving vehicle braking systems and vehicle handling, together with better roads and lighting, accidents involving trucks have fallen from 7,000 in 1979 to fewer than 4,500 in 1991. But nonetheless, 3,603 truck drivers and their passengers were either killed or injured in 1991.
When truck accidents do occur, they tend to happen most frequently on A-roads then B and C-roads and least of all on motorways. More than half of the accidents occur in built-up areas where the average speeds are 40mph or less and in these situations the energy of the moving truck is often absorbed by other vehicles involved in the accident, thus helping to reduce the chance of injury to the occupants.
SOLID OBJECT
On non-built-up roads and motorways where the speeds are likely to be higher, if the truck hits a solid object such as a bridge or a stationary truck, the higher amount of energy involved is dissipated much more quickly—with devastating consequences. There is little the designer can do to make a 38-tonner safe in the advent of a 60mph impact. But careful design can certainly make the crash less damaging to the occupants in lower speed accidents.
The most tried and tested method is the seatbelt which, suprisingly, is still not a legal requirement for vehicles of over 35 tonnes. All manufacturers provide fully tested seatbelt anchorage points as standard and most offer seat belts as an option. If belts are fitted the law says they must be worn. Most of today's truck seat belt systems are not user friendly, so they are not popular as CM's recent seatbelt survey highlighted (CM 4-10 March). A decisive 68% opposed the wearing of seatbelts. The problem is the attachment points are much further from the seat than in a car or van and even where inertia reel belts are fitted they do not work well with suspension seats. The simple answer is to attach the belt to the seat itself rather than the cab, but this means designing a seat that is strong enough to take the loads imposed in a crash which can be up to 25g (25 times the weight of the occupant). Even if the seat can be made strong enough, then the floor will probably need strengthening in order to withstand the loads transmitted by the seat Scania has developed and patented a seat with integral belts and at a recent seminar describing truck technology for the year 2000 (CM 1-7 July), Scania's vice president of product development, Kaj Holmelius, described how they could be used.
Holmelius says tests carried out in Sweden and the Netherlands show that the impact experienced by the occupant is halved by using integral seat belts simply because they fit closer to the body and are able to control the loads that much more effectively, Seatbelts on their own do a good job in restraining the driver and reducing potentially dangerous cuts and bruises but Holmelius can foresee other car and light van features, such as seat belt pre-tensioners and airbags, becoming commonplace on trucks in the future,
CRASH SIGNATURE
A conventional airbag, located in the steering wheel boss, would be relatively easy to install, says Holmelius, and beneficial in the case of a head-on collision. Usually in a car or light van, the airbag firing is controlled by a "crash signature" (see box). However although this technique is well proven in the case of a pressed steel monocoque structure collapsing under a frontal impact, it has yet to be applied to a structure as rigid as a truck chassis.
Holmelius says airbags on the interior side pillars on a cab could also give protection in a rollover but these will take time to develop into an effective system as rollovers happen over a relatively longer period of time and the structural damage is often minimal. Another area in heavy trucks where airbags could prevent injury is around the knees— the classic accident "target" for truck drivers and passengers. However Homelius admits: "A lot of development work is required." New sensors which provide the trigger signal will have to be developed.
The closer a seatbelt fits, the better it works and pre-tensioners are designed to take up any slack in the belt due to say, bulky clothing, in the instant before the occupant moves forward as a result of the impact.
Mounted horizontally below seat level, the pre-tensioner is built into the mounting point of the buckle and consists of a large compressed coil spring which is released when the trigger mechanism senses a deceleration of 27g or more. The spring extends by 50mm (2in) taking up that same amount of slack in both lap and diagonal lengths of belt.
Current systems as used in Ford light vans are purely mechanical but Scania is considering the possibility of a small explosive charge to power the system.
Another feature which could be fitted to trucks at very little cost is the scat belt "grabber". In a crash where a normal belt is used, even though the reel itself is locked, any spare belt left on the reel tightens up allowing a small extra amount of belt to spool out thus reducing its effectiveness. The grabber, which is triggered by the same signal as the airbag, overcomes this problem by clamping the belt webbing between powerful jaws before it can spool out.
Big breakthroughs in any field are rare, with progress coming from the steady applications of small improvements—there is still room for improvement in --\