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Breakthrough: The crumple zone – Part one
3 years ago
Twohig's thoughts on how the Porsche 911 has grown over the years are unprintable
But there is one driver of increased vehicle size (and, unfortunately, mass) that even I will mostly defend – and that’s the added millimetres and kilogrammes built into car’s crumple zones, those parts of the car’s structure designed to collapse in a high-speed crash and hence protect its occupants. These are, overwhelmingly, A Good Thing.
Now, building some extra metal bits into a car in order to let them crumple up in a crash seems so obvious that we might assume that they’ve always been there. But as is so often the way with the breakthroughs in this series, that’s not the case. Like Christopher Columbus and his egg, it took someone special to show the way.
Enter Béla Barényi. Born in Austria in 1897, Barényi may well deserve to be credited with saving more lives in automotive accidents than any other person – his only rival might be Nils Bohlin. After studying mechanical and electrical engineering in Vienna, he cut his teeth at some of the great marques of the inter-war period – Austro-Daimler, Steyr and Adler – before landing at the company he is most associated with, Daimler-Benz, in 1939. He would stay with them for many years, finally retiring in 1972.
"The energy released in a ‘standard’ EuroNCAP frontal impact is roughly the equivalent of putting a particularly healthy hand grenade under the bonnet of the car, gingerly attaching a string to its pin, sitting back into the driver’s seat, pulling the string hard, and counting to five…"
During most of this long career, Barényi concentrated on what we would now call passive safety – making cars safer in the event of a crash (as opposed to active safety – making them better able to avoid the crash in the first place). He was an amazingly prolific inventor – the exact number of his patents depends a little on how you count them, but it’s well over a thousand. Most of them were related to his beloved subject of passive safety, but not all – some would even argue that he came up with the original concept for the Volkswagen Beetle in 1925, five years before Professor Porsche’s design. But there is a lot of dispute about the genesis of the Beetle, so let’s leave that for another day…
But there is no dispute over the fact that Barényi filed the first patent describing what we would now call a crumple zone in 1937 – two years before he joined Mercedes-Benz. The first car to partially incorporate his ideas was the 1953 Benz Type 180 ‘Ponton’ (Pontoon), to be fully implemented on the 1959 W111 ‘Heckflosse’ (Tail-fin) range. But Barényi would continue to refine these ideas gradually over decades, and in so doing, laid the foundations of the basic structural principles that make all modern cars immensely safer than anything built before him.
Barényi honed his ideas on passive safety during decades at Mercedes-Benz
So, how does a crumple zone work? Well, it’s all about dissipating energy and managing deceleration.
It’s been a while since we had a little formula, hasn’t it? Here’s one for old times’ sake – the formula for kinetic energy, or the energy contained in a moving body:
Energy (in Joules) is one-half of the product of the mass of the body (in kg), times the square of the velocity (in metres-per-second).
So, the impact of a modest 1500kg car hitting a barrier at a sensibly legal speed of 64km/h (which happens to be the speed that EuroNCAP tests such things) will release 237kJ of energy.
A-ha, you say. 237. Great. It’s pretty meaningless, right? So let’s convert it into something a bit easier to grasp. It so happens that the lump of high explosive in a standard hand grenade is equivalent to 50g of TNT (grams of TNT is still used as the standard measure of explosive force) and 237kJ is the equivalent of 56g of TNT. Hence, the energy released in a ‘standard’ EuroNCAP frontal impact is roughly the equivalent of putting a particularly healthy hand grenade under the bonnet of the car, gingerly attaching a string to its pin, sitting back into the driver’s seat, pulling the string hard, and counting to five…
Put less scientifically, it’s an effing big bang.
“In a few hyper-violent tens of milliseconds, we see the work of two great engineers of the last century, Barényi and Bohlin, combine to make sure that the occupants emerge stunned and shocked, ears ringing and with a hefty insurance claim on their hands – but alive”
Barényi’s big idea was to use the energy required to collapse hollow metal structures to dissipate this energy safely – before it got to the human beings. His idea was to use the metal pressed box-sections that form the front side-members or ‘longitudinals’ of the car to absorb energy. Imagine crushing a fizzy drinks can – despite the flimsy sheet aluminium they are made of, it takes a surprisingly hefty shove, or a well-placed stamp of the heel, to crush them flat. This is the principle of the crumple zone – and safety engineers actually do refer to some of the sacrificial components in the front end of cars as ‘crush cans’.
Barényi’s invention also allowed engineers to handle the second problem – the deceleration of the crash. You see, human beings are – no disrespect meant – squishy bags of sloppy meat, loosely assembled about disappointingly flimsy bones. We don’t like high levels of acceleration. Anything above about 9g will cause even fit and healthy fighter pilots to black out. Anything above 30g will start to rupture internal organs. At 80g, bones break. So engineers pay a lot of attention to what’s called the ‘crash pulse’ – the graph of deceleration over time that can be recorded when a car hits an immobile barrier.
And what allows them to tune or adjust the crash pulse is Barényi’s invention. Next time you are filling up the washer bottle, peer into the depths of the front end of your car, and you will see his work in action – or rather, standing by for action. You’ll see that there is a cross-ways metal beam behind the front bumper – it may be steel or aluminium, and these days will hide coyly behind various cooling bobbins. That beam is bolted or welded to two crash cans, maybe 20 to 30cm long, almost certainly bolted to flat sandwich-like plates fixing them to the main body structure.
Barényi's big idea was to dissipate energy during a crash before it reached passengers inside the car
Those ‘cans’ are very carefully designed to collapse like a concertina in relatively slow crashes – up to 10km/h – hence protecting the more expensive structures behind them. In higher speed crashes, they will still help slow the initial impact a bit, but will quickly pass the real work onto their much stiffer, tougher chums lurking behind the crash plates – the front side members.
These will work together with the upper side members – the bits the top of the front wings or fenders hang from – to progressively collapse in a controlled manner, slowing the car down like a baseball coming to rest in a catcher’s mitt. As they do so, they will allow the restraint systems inside the car – the airbags and seatbelts – to do their vital work, priming and firing, further reducing those dangerous negative g-forces on those delicate bodies.
In a few hyper-violent tens of milliseconds, we see the work of two great engineers of the last century, Barényi and Bohlin, combine to make sure that the occupants emerge stunned and shocked, ears ringing and with a hefty insurance claim on their hands – but alive.
If there is a great Engineering Office in the sky, I hope these two men are up there, comparing notes.
In part two, published early next week, we will explore how the application of high-speed computing principles first designed for military applications allowed engineers to further refine the crumple zone
