March 26, 2013

Our new car platform, EMP2

At Citroën, automotive engineering experts constantly strive to make our cars better in every way. With each new car generation, we want our cars to be safer, more comfortable, more efficient and, of course, to offer better value for money.

You might assume these various aims can’t all be realised at once – that vehicle design always requires tradeoffs. That if we update the C3 and make it stronger and even safer in a crash, for example, it must be heavier and less economical as a result.

Fortunately, that’s just not the case. Underscoring our company mantra, the solution is to apply plenty of ‘Créative Technologie’.

We’ve been doing exactly that with the new car platform we’ve developed to underpin our next generation of medium and large cars, called Efficient Modular Platform 2 or EMP2 for short.

In car industry jargon, a platform is a set of basic components shared among different models, encompassing the structural and mechanical parts you can’t see or touch unless you crawl under the car or start poking around under the bonnet. By creating common building blocks for car construction, rather than starting each car from scratch, we can adjust prices through economies of scale and also pool our engineering investments.

EMP2, developed by our parent company PSA, required €630 million of investment. But that huge cost in automotive design can be spread across a whole generation of new cars including family hatchbacks, saloons, coupés, Tourers, people carriers and even vans. The result is that all models share the benefits of the latest technology, while still remaining affordable to buy.

EMP2 allows our automotive designers to build new cars that are both lighter – up to 70kg (about the weight of a person)_and safer than before. It does this partly through employing the most appropriate materials – including steel, aluminium and plastic composites – and partly through putting strength where it’s needed and cutting weight where it’s not.

The most basic ingredient of a car body is still a flat sheet of steel. The sheets are fed into various giant presses in the factory, where they are stamped into complex shapes like the car’s roof, floor, door pillars and sills. The separate components are then joined together to create a stiff and strong body shell.

In the past, if a component like a door pillar needed to be stronger at the bottom than at the top, the whole thing was simply stamped from whatever thickness of steel was needed at the toughest end, leading to unnecessary weight. Now, with EMP2, we first roll out the steel as if it were pastry, creating a high-precision sheet of variable thickness. When pressed into shape, some parts of the resulting component are thicker and stronger than others – giving us the strength we need only where we want it, without excess weight.

Similarly, rather than starting with sheet metal that’s all the same basic type, with EMP2 we use a selection of very-high and even ultra-high-tensile steel alloys to create structures that are extremely stiff, light and strong. By adding strength and cutting weight, these alloys simultaneously bring benefits in crash safety, handling, acceleration and fuel economy.

The switch to stronger steel isn’t as simple as it sounds, because very tough materials are much more difficult to bend into shape. The strongest steels can only be stamped into shape once softened by fierce temperatures of around 1,000°C. That means we have to very carefully design each piece to be larger to begin with, because it will shrink as it cools. The resulting stamped and shrunk piece of strong steel then has to be joined to the rest of the body using high-temperature welding.

Despite the lasers we use to do this job, this isn’t science fiction. The first Citroën car built using EMP2 – the next C4 Picasso – will go on sale later this year.