new models: Alfa Romeo 156 ( 2003 Restyling )
|REAL SPORTSCAR HANDLING
The New Alfa 156 and Sportwagon confirm the geometry adopted on the previous model with its specific configuration of 'high' dual wishbone suspension at the front, MacPherson type rear suspension with transverse links of different lengths.
The choice of double wishbone geometry for the front suspension is Alfa Romeo's response to a specific requirement. What was wanted was a system that minimised yaw, responded with superlative precision to steering, threw in extra special traction and combined all these gifts with the ability to absorb and dampen road surface irregularities as effectively as the most comfortable cars in its class. With a double wishbone format, it becomes possible to allow the wheel considerable freedom of movement in the direction of motion without detriment to tyre grip on bends or to steering.
The car's road manners needed to be supported by a rear end that would provide super-stable handling at high speeds combined with the agility demanded of a true sports car on 'close mixed' routes, which is why Alfa Romeo opted for MacPherson type suspension with asymmetrical arms and refined elastokinetics. On the New Alfa 156 the rear suspension is connected to the chassis by a vacuum-cast aluminium cross-member. The MacPherson strut offers several advantages: low weight, comfort (guaranteed by ample wheel freedom and by its longitudinal flexibility) and ample scope for set-up modulation.
In addition, the special front and rear suspension geometry make it possible to endow the various joints, including the steering ball joints, with a carefully calibrated degree of 'give' without impairing steering precision. The combined effect of all these devices is superlative noise containment, combined with a capacity to absorb the tiny road surface irregularities that so often make for irritating bodyshell rattle.
The high double wishbone used on the front suspension is geometrically the most sophisticated way of reconciling ultra-flexible wheel travel with optimised control over tyre operating conditions. The development was a joint effort by the Fiat Research Centre and Alfa Romeo's Design Engineering and Experimental Unit.
The double wishbone structure consists of a cast iron lower link, a steel upright and a light alloy upper link, with the coaxial spring-damper assembly connected to the bodyshell via a flexible bushing and to the lower arm via a light alloy fork. To save space and enhance structural rigidity, the upper link is articulated onto an aluminium 'shell' anchored to the body to support the upper anchorage point of the spring-damper unit.
The suspension layout was designed to allow for camber recovery by the wheel in its roll and steer movements without altering kingpin offset (i.e. the distance between the centre of the tyre tread and the point of intersection between road surface and steering axle) in all load conditions.
The forward tilt of the upper link also makes it possible to control the kingpin angle (the transverse tilt of the steering axle) in even the most critical running conditions. This helps to maintain optimum front tyre grip even during rapid steering manoeuvres and also improves steering smoothness.
It all makes a significant contribution to the car's driveability and road manners:
- optimised tyre grip;
This layout is particularly advanced in both geometry and construction terms. It is based essentially on a telescopic vertical strut with a coaxial spring, two long transverse links and a longitudinal strut. The telescopic upright incorporates a pressurised dual-rate damper with a distinctly offset coil spring to minimise friction. The damper stop also comes into play in the final suspension travel phase and is made of 'Cellasto', a special closed-cell polyurethane that retains its smoothly flexible action over time. The two transverse links are pressed out of high tensile steel and are of different lengths in order to exploit the system's elastokinematic properties to produce a tiny steering effect. Toe-in is regulated by a cam system on the rear link that is lighter and simpler to repair than a traditional screw system. The two transverse arms and the anti-roll bar supports are anchored to a vacuum-cast light alloy sub-frame which weighs about 1.8 kg less than a conventional steel cross-member.
Alfa engineers have taken particular care over the way the suspension system is connected to the frame, aiming for maximum geometrical precision combined with minimum transmission of noise and vibration. All bodyshell anchorage points are very solid and equipped with special fitments like the 'shell' used on the front damper spring assembly and the way the damper attachment to the rear upright is separate from the spring support.
In order to optimise the system's absorption of tiny asperities in the road surface, friction has been minimised by using bushings with fluid-dynamic properties on the front upper wishbone and the anchorage points for the longitudinal struts at the rear, as well as Teflon seals for the damper rods.
Finally, the New Alfa Sportwagon can also be fitted with a Boge-Nivomat self-levelling hydropneumatic rear suspension to ensure constant ride height regardless of the weight transported.
Whenever the load alters, the system automatically adjusts the resistance offered by the rear suspension to restore the car to a preset level. In this way, the car maintains the same excellent performance (roadholding, stability and comfort) under all service conditions.
The 'Nivomat' is activated by kinetic energy generated by wheel movements in response to road surface roughness. When the New Alfa Sportwagon luggage compartment is unloaded, the car's rear goes down like that of any other car. After a few hundred metres, however, the system lifts the body and restores it to the original ride setting, which remains constant while the car is moving and even with the engine off (for 8-10 hours). In technical terms, the device operates as follows: the relative movement of rear axle and body pumps fluid form a high pressure reservoir inside the 'Nivomat' damper. The oil compresses gas bearings that stabilise pressure during loading and while the car is motion. When the car achieves an optimum ground clearance, a by-pass is automatically activated to maintain the clearance by allowing excess fluid to flow out into a low pressure reservoir from where it is recycled.
When a 'Nivomat' is fitted, a headlight alignment adjuster is naturally not required because the light beam is always at the correct angle.