Technology: Crushable steering wheels save face in crashing cars

日期:2019-02-28 03:15:11 作者:徐焙 阅读:

By MICK HAMER A CRUSHABLE steering wheel now being installed in British cars will help to save drivers’ faces in an accident. The wheel is designed so that it deforms when a head hits it, instead of breaking delicate facial bones which are difficult to repair. The steering wheel was developed by the Transport and Road Research Laboratory, which is part of the Department of Transport. The new Rover 200, launched last week, has the crushable steering wheel developed by the TRRL. The new Vauxhall Cavalier has a similar design. Conventional steering wheels are made of plastic mounted around a metal frame. Since 1983, when drivers began having to wear seat belts, there has been an increase in facial injuries. In a sudden impact the driver’s head swivels forward, forcing the face into either the rim or the hub of the steering wheel. The impact can break bones in the face. In extreme cases the force of the impact can cause brain damage. The new steering wheel has energy-absorbing plastic foam on rim and hub; in an accident, it will produce a force of less than 1.7 newtons per square millimetre on the driver’s face. The TRRL has developed a test, which it hopes will become the basis of the new European legislation for safer steering wheels. Researchers drop a weight of 15 pounds (6.8 kilograms), wrapped in aluminium honeycomb, onto the steering wheel so that it has an impact velocity of 15 miles per hour (25 kilometres per hour). The honeycomb represents a driver’s face. If the honeycomb deforms by less than 1 millimetre, then the steering wheel passes the test. Slade Penoyre, one of the researchers at the TRRL who developed the safer steering wheel, said that of the new cars tested only the Rover 200 and the Vauxhall Cavalier passed. He said that the results from the Cavalier were impressive. The honeycomb face that is the basis of the test has to be precrushed. This is because the honeycomb has a high initial yield point under load, which then drops to around two-thirds the initial value. While developing the test, the TRRL found that the results based on the maximum load were less repeatable than the loading needed to continue crushing the honeycomb. Precrushing the honeycomb resolved this problem. The plastic padding on the hub of the new steering wheel has to be more than 28 millimetres thick, since this is the theoretical minimum which could reduce the force below the critical value. The padding over the hub of the steering wheel is in two layers, rather like a boxing glove. The hub is the part of the steering wheel most likely to cause brain damage. The rim of the wheel would probably crumple under a severe impact with a driver’s head. The top layer of the plastic foam is relatively spongy. Underneath, the foam is energy-absorbing. It can decelerate the head, and bring it to a stop, without exceeding 80 g, so that it does not strike the solid metal of the steering column. When the TRRL first developed the new wheel, it specified a force of 1.4 newtons per square millimetre (Technology, 29 August 1985). The laboratory raised the limit to 1.7 newtons because it corresponded to the aluminium honeycomb that was commercially available. Penoyre said the difference was not significant, because of uncertainty about the results of experiments to test damage to facial bones, which were carried out in the United States using corpses. Experiments on corpses are banned in Britain. Some 50 safety steering wheels have been in use since 1986, fitted on Austin Metros. In general, drivers have approved of the new wheel, with its thick soft rim. The only drawback so far reported is that drivers might find it harder to push their cars out of a snowdrift using the new steering wheel. The Department of Transport is pressing the EEC to order the crushable steering wheel to be installed in new cars. But given the time such legislation takes,