After much deliberation and the odd false start, what is now known as Fiat Group Automobiles (FGA) began work on its all-new Compact platform five years ago. The goal was to create a flexible new C-segment platform that would form the basis not only for Giulietta, the just-launched replacement for the 10-year-old Alfa Romeo 147, but also the successors to the Group’s other small family cars, including Fiat Bravo and Lancia Delta. Simplistically, that meant the platform had to excel in terms of steering feel and handling (Alfa); fuel efficiency and practicality (Fiat); and refinement (Lancia – VW Golf was the benchmark for road isolation and ride comfort). It also had to meet the latest safety and environmental standards.
From the start, Compact was destined not only for multiple brands, but also for the global market, which meant particular attention was paid to durability. The subsequent alliance between Fiat and Chrysler LLC has also added North America to the list of potential sales territories, so last winter the engineering team spent several months ensuring that the platform would also be suitable for use Stateside. To further increase its flexibility, this primarily two-wheel-drive architecture can easily be converted to an all-wheel-drive configuration. And while Giulietta took five years to finish, further cars off the platform could be engineered in as little as 18-20 months.
Current FGA C-segment cars use a mixture of steering and suspension configurations, but Compact brings a standard solution to the table that its creators say will be able to fulfill the requirements of all three brands.
The chosen steering is a fuel-saving, two-pinion electrically powered system. FGA’s chassis engineers, led by Philippe Krief, worked closely with the supplier, ZF Lenksysteme, to get the desired performance from the hardware: “Achieving steering feel is always the priority,” he says. “It’s driven first of all by good mechanical characteristics. The steering ratio of the Giulietta is 12.5:1 – very direct, with big loads on the tie rods. We worked hard to get maximum stiffness, low friction, and low inertia, working extensively on the electric motor in order to get steering angles quickly – we’ve achieved 1,000°/sec of input with no delay. Once he had good hardware, we could work on some algorithms in order to reproduce good feel. We’re happy with the results.”
The front suspension is a MacPherson strut whose geometry has been changed in order bring the camber control closer to that offered by the outgoing 147’s double-wishbone setup. The electric power steering was tuned to compensate for another of the double-wishbone’s lost advantages, good management of the steering axis, for example in the self-correction for road camber. Aluminum knuckles bring the unsprung mass down by 4kg.
The rear suspension is a compact, multilink setup that Krief says reconciles the conflicting demands of good handling performance (for which read Alfa) and low-cost, package-friendly solution (Fiat). The use of aluminum for suspension links and the rear crossmember is said to save 10kg compared with conventional multilink setups.
Giulietta has two classes of suspension tune, ‘heavy’ and ‘light’, which are primarily dependent on the engine mass. Within each class are two further options, Normal and Sport. Says Krief: “Normal should be close to the Golf in terms of ride, or even better in some areas, with the highest level of dynamic performance. Even in Sport, the comfort level is still very satisfactory.”
The application of Magneti Marelli’s SDC adaptive damping has transformed the ride quality of the MiTo Cloverleaf, but such a system is by no means certain to appear on Giulietta. “On MiTo the step between normal and adaptive damping is very high, but on Giulietta, where the global [ride/handling] trade-off is already OK, the step is not so big,” he explains. “So we’re looking at alternatives too, like frequency-dependent, two-valve passive dampers with a bypass system. It’s possible to get very close to the performance of an adaptive system with frequency-dependent dampers, but at a lower cost.”
Through the use of virtual analysis, FGA engineers on the Giulietta program were able to test ‘worst case’ ride and handling scenarios more comprehensively than even five years ago. With each chassis part or setting subject to a manufacturing tolerance around a nominal value, a ‘perfect storm’ is possible whereby several components or settings at the limit of their tolerances combine to create undesirable driving behavior.
For Giulietta, Krief’s chassis team carried out simulation work, primarily in Adams with a specific algorithm to generate the myriad cases to be tested, to virtually work through every conceivable combination and flag up anomalies that impacted on the car’s dynamic performance to such a degree that corrective action was required.
Alfa Romeo Giulietta
Dimensions: 4,351mm (L) x 1,798mm (W) 1,465mm (H). Wheelbase 2,634mm, track 1,554mm
Curb weight: 1,355-1,395kg depending on engine
Dampers: ZF Sachs
ARBs: 24 or 25mm hollow (F); 13 or 14mm (R)
Brake disc diameter (engine dependent): 281-330mm (F); 264-278mm (R)
ABS/ESC: Conti Teves; brake pre-fill in Dynamic mode
Steering: ZF Lenksysteme dual-pinion EPS; ratio 12.5:1; turning circle 10.9m
Wheels/tires: 7J x 16 or 7J x 17, 18in optional; 205/55 R16 or 225/45 R17, suppliers Pirelli, Continental, and Michelin