High-performance mechanical innovations introduced in the high-end automotive sector are increasingly to be considered as important legacies of the intense research and development activities sustained in the field of Formula 1.

One such technology that has recently been integrated into the design and production of commercial automobiles is active suspension. In addition to significantly improving the comfort of the driving experience, these mechanical devices also make an important contribution to the safety of those on board a car that is equipped with them.

Before going into detail, it is appropriate to specify precisely what is meant by active suspensions, indicating what are the mechanical components that make them different (in some ways opposite) from passive suspensions.

The most widespread and widely used suspension in the automotive sector is undoubtedly the passive one, thanks to which the transfer of relative motion between the road surface and the cockpit of the car can be modeled through a classic system Mass (M) - Spring (K) - Damper (r). The "passive" attribute is due to the absence of components that can actively perform work, but only absorb it in the case of the spring and dissipate it through the damper.

With active suspension we mean therefore a mechanical organ that manages the relative motion of the car with respect to the ground thanks to the presence of a motor able to regulate the distance between the passenger compartment and the axis of the wheel (and consequently, from the road floor). From this simple description it is possible to make some rather immediate considerations.

The innovation in question, of this level of advancement, is currently destined only for cars of a higher quality level, and one of the reasons is rather immediate: having to replace four passive components with as many components each with an independent motor involves a decidedly substantial cost. However, although this qualitative leap seems to be particularly costly, it is certainly not the one that has the greatest impact on the exclusivity of the technology, and to understand this it is enough to think of a term just used, namely "independence".

The four motors must be managed independently, which requires the installation of a dedicated on-board computer. A control unit processes and calculates the elongations of the actuators after analyzing the information collected by strategically placed sensors in order to scan the driving scenario in the smallest details, taking into account obstacles such as potholes or bumps, all at a frequency of 18Hz, or 18 "corrections" per second.

La complessità nel garantire il corretto funzionamento di un sistema così preciso dal punto di vista informatico, fa quasi passare in secondo piano la meccanica che si basa sul singolo attuatore. Esso è composto da un motore elettrico in grado di applicare una coppia pari a 1100 Nm su un puntone in titanio che tramite una filettatura è in grado di trasformare cinematicamente la rotazione in una traslazione verticale. È chiaro che, in questo nuovo sistema di approccio alla sospensione, i componenti caratteristici quali molla e smorzatore non sono stati eliminati del tutto, la loro presenza risulta comunque fondamentale al fine di garantire elasticità alla struttura.

In sintesi, il concetto di “sospensione attiva” racchiude al suo interno lo sfruttamento e l’ottimizzazione delle sinergie della nuova e della vecchia tecnologia, avente come obiettivo la massimizzazione delle prestazioni fornite da entrambe le protagoniste. Questa efficienza costruttiva ha visto una prima concretizzazione nel 2018 in occasione della presentazione e commercializzazione dell’Audi A8, fino a raggiungere livelli di perfezione nella solita Mercedes Classe S, soprannominata da sempre “L’ammiraglia”, nella sua ultima versione, presentata nell’appena concluso 2020.

If you have had the good fortune to try the experience personally, you have undoubtedly realized the feeling of lightness that you get when driving cars of this caliber, almost as if you were not moving on a road, inevitably provided with its imperfections, but on the floor of a shopping mall, perfectly smooth and level. This sensation is nothing but the result of the functioning of such suspensions and the ability they have in literally isolating the structure of the car from the surrounding environment. A more analytical confirmation of what has been described can be observed in the following graph, obtained from a numerical simulation in Simulink, in which the objective was precisely to compare the disturbances transmitted to the chassis by a passive suspension system (blue curve) compared to active suspensions (yellow curve).

A further guarantee for cars such as those under consideration is safety, which has been further improved thanks to the use of these suspensions, particularly in relation to accidents caused by side impacts. As soon as the lateral sensors detect the approach of material bodies at a speed of 25 km/h or more, the control unit commands an impulsive raising of the side panel by 8 cm. This amount is sufficient to ensure that a good part of the energy due to the impact is discharged on the lower part of the frame of the structure, which is the most rigid, limiting the stress suffered by the passengers of the car by about 50% in particularly critical areas such as chest or skull.

The incipient diffusion of such a complex technology still makes it an elite good, but in view of the great benefits it is able to bring, it also seems useless to say that it will be widely developed and improved in the future, so as to make it accessible to everyone and make moving on land safer and more pleasant.

Written by Lorenzo Campioni of the VGen Engineering Hub