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Marelli active suspensions: paradigm shift

LET’S SAY GOODBYE TO OIL – The Marelli presented its new one at the recent CES 2024 electromechanical active suspension (Fully Active Electromechanical Suspension System) which has as its active element a cylindrical actuator connected to a suspension arm which takes the place of the shock absorber (the elastic element remains), but manages to implement much more advanced functions of the simple damping of hydraulic shock absorbers, even active ones. In fact, it is a device that can deliver force and not just absorb it, thus being able to implement advanced functions such as the active reduction of roll and pitch (watch the video at the bottom of the article).

According to the company the product represents “a turning point for automotive technology, as it increases safety and improves vehicle performance and energy efficiency, guaranteeing an unparalleled driving experience.” Challenging declarations therefore, which however have a substantial background: Marelli in fact it speaks of a completely electromechanical system whose response time (a few milliseconds) makes it proactive, unlike hydraulic/mechanical suspensions.

SUSPENSION OR ROBOTS? – The assembly is defined as a “robotic system that actively controls the vertical dynamics of the suspension thanks to four actuators. Passive or semi-active analog suspensions are then transformed into fully digital suspensions.” Each actuator is composed of a electric motor brushless, a gear reducer, a stroke sensor and an electronic control unit. These components operate a lever that can rotate through a certain angle, measured by the sensor mentioned above, and is connected to the main suspension arm with a tie rod or lever system.

A similar solution was Audi’s eROT, which, however, did not reach production (Who to find out more).Each actuator in the system Marelli it therefore applies a force to the single suspension that can be modulated to perform any type of task. The first is it damping of the oscillations, which however promises to be explained in a particular way evolved: active operation in fact allows you to finely adjust the damping, leaving the suspension more “free” in short bumps and braking it more in slower stresses, for example limiting lateral lying when cornering. Same goes for the end of strokewhose management can simulate the Advanced Comfort hydraulic solutions seen for example on the new Citroën ë-C3.

ABSORB HOLES AND PRODUCE ENERGY – When the electric motor of the actuator is set in motion by the suspension arm, a energy recovery because it acts as a generator, in a perfectly similar way to what happens with the regenerative braking of the traction motors of electric cars. The higher the energy recovery, the more accentuated the damping: second Marelli regeneration allows on average recover 80% of the energy consumed by the system, which is excellent news for vehicles in general and electric vehicles in particular.

L’Central unity (ECU – Electronic Control Unit) check it out each actuator thanks to specific electronic hardware and integrated software, which evaluates the dynamics of the vehicle and calculate in real time the forces that each actuator must apply to the suspension. The results of these processing are signals that the ECU sends to the actuator inverter: the device converts the force request specified by the ECU into the current intensity (ampere) necessary to obtain it.

Management promises to be evolved because the system acts on the basis of many parameters: acceleration, suspension travel, steering angle, engine parameters, braking stresses, torque demand (accelerator pedal movement) and more. The whole thing is powered by 48 V because the powers brought into play in the actuators are quite high: for the same power, increasing the voltage allows you to reduce the intensity of the current, reducing losses in the cables which can also be thinner and lighter.

QUESTION OF FREQUENCIES – The technicians of Marelli they emphasize the fact that the system is effective for frequencies between 0 and 30 hertz (symbol Hz). The frequency of 1 Hz is equivalent to one oscillation per second and therefore falls within slow movements such as pitch during acceleration/braking and roll when cornering while the higher frequencies are generated with small irregularities in the road surface.

Marelli declares that its Fully Active Electromechanical Suspension System manages to reduce the acceleration transmitted from the vehicle to the passengers by 50-60%: the comfort should therefore improve a lot, remembering that vertical oscillations between 4 and 8 Hz cause fatigue, the head and neck are negatively affected by vibrations around 20 Hz, the abdomen is sensitive to frequencies between 5 and 7 Hz while “seasickness” born with oscillations around 0.7 Hz. The substantial neutralization of roll and pitch up to 0.5/0.6 g is also promised, promising values ​​considering that a good car in braking reaches approximately 1 g of deceleration.

Among the promised advantages is greater freedom for designers, given that the actuators can be placed under the bottom of the car and this too, together with the simplification allowed by being an “oil-free” solution and the weight contained in approximately 6 kg per actuator, has interested several manufacturers who are currently experimenting with Marelli. Another reason of interest is the possibility of varying the response of the suspensions by modifying the software and the scalability of the system towards various vehicle segments: interesting prospects, therefore, which we hope will be brought to series production.

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