BMW 5 Series ‘clean sheet’ March 30, 2010
Posted by richard in : Minutiae of cars, Technology , trackback
BMW’s new F10 5 Series may be closely associated with the 7 Series and 5 Series GT, but this doesn’t mean it’s simply a modified version of those cars.
‘In terms of driving dynamics, we always start from a clean sheet,’ explained Jos van As. But how, given the interrelation of components? By starting from the start, not working backwards.
Van As talks through the methodology, showing the 5 is more than a scaled down 7 (or, indeed, a 1/6th-price Rolls-Royce Ghost…). His work begins before a CAD pixel is created, through a logical build-up process:
• DNA – ‘Here, we define proportions, weight distribution, drive concept, aero effects such as lift coefficient front and rear, and so on’
• Suspension – Spring and damper rates are decided upon (‘ride quality was the focus with F10’)
• Tyres – Design of car, weight of car under different load conditions (‘for example, we can decide what size wheels we can fit, and what pressures we need’)
• Steering – Ratio, speed of response (‘the 5 Series has EPAS, like the 7 Series, but the ratio is faster’)
Once you have all this, you can begin setting up the standard suspension. With the 5 Series, says van As, ‘a team of 4 engineers set up the standard car.
‘This standard car is the base; we add on dynamic features to this platform, all controlled by ICM.’
As yet, then, there are no specific ‘sport’ suspensions for the 5 Series, but more dynamic variations of the standard car, created through technological add-ons. That’s what you can achieve with electronic dampers and adaptive anti-roll, ‘all controlled by ICM’.
Sounds like a cop-out? Not at all, such is the advanced level of ICM. ‘It’s all interconnected, all systems are parameticised. The chassis alone has 45,000 parameters – so it is quite hard work to get it right!’
Here’s where a strong, stiff body-in-white becomes vital, says van As. ‘It is important we get a good structure so we can discover how one change interacts with another.’
While those high-end cars could indeed have a fair few suspension settings, ‘the customer does not need 45,000 (!), so they get 4. ‘
‘These characterise the car in 4 different ways – making 4 cars in 1 from a dynamic point of view.’
Shrunken 7 Series, then? No – it’s a fair bit more than that…
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In further 5 Series news… BMW says the only bespoke base setup for the F10 5 Series will be for the Chinese market.
This, says Jos van As, is because of a fundamental difference between Chinese and Western 5 Series buyers.
‘In Europe and the US, buyers, like to drive. In China, they prefer to be driven.’
This, BMW has developed a bespoke long-wheelbase 5 Series for the Chinese market, with more rear legroom and an even greater emphasis on riding comfort. This will call upon inter-team experience of both the 7 Series and Rolls-Royce Ghost.
Expect lower-frequency spring rates, which will work with the ride-benefiting characteristics of the longer wheelbase to make this the best-riding BMW 5 Series ever.
Building the car in China has allowed BMW more flexibility in sourcing bespoke components, such as a ‘high-comfort’ rear bench seat. It has also ensured the car can appeal to all markets without, for instance, ‘European’ sporting appeal being compromised by the need to cater for the fast-growing Chinese market.
I’d also wager it’s a trend BMW may use more and more in the future, as China’s world importance continues to rise… what do you reckon?
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