Active tilting function: Mercedes cars lean into bends
The tilting function is a world’s first in a series production car. It makes the vehicle lean into a curve much like motorcyclists. Thus, it offers a more comfortable feeling during a fast ride on a winding road. The lateral acceleration is reduced; the passenger sit tighter in their seats. According to Daimler, the goal of the function is not to achieve higher cornering speeds but more elegance and comfort.
The tilting function is activated by the Active Body Control (ABC) system: The base point of the steel springs integrated into the ABC suspension struts are raised actively by plunger cylinders on the outer side of the curve and lowered on the inner side. The deviation occurs as a function of speed and curve radius. A stereo camera behind the windscreen senses road bends up to 15 metres ahead and translates it by means of a suitable algorithm into control instructions to the ABC system. The camera findings are verified and cross-checked against the signals of a lateral acceleration sensor located in the ABC suspension.
In addition, the system takes into account signals from various acceleration sensors, level sensors at the suspension control arms and signals available on the FlexRay data bus such as speed. The system then uses the pressure sensors in the suspension struts to calculate the control signals for the servo-hydraulic valves at the front and rear axle to ensure precisely metred oil flows. In order to stabilise the body within very short time, the system builds up hydraulic pressures of up to 200 bar. The entire function is part of Daimler’s so-called Magic Body Control (MBC) suspension system for the rear-wheel drive models. The system also can be used to increase the ground clearance by up to 40mm upon operating a switch.
The stereo camera also identifies undulations of the road surface ahead and provides control signals to the MBC which in turn increases or reduces the load on each individual wheel within fractions of a second by means of hydraulic actuators, resulting in increased driving comfort. The downside is that the function works only in the daytime, since it is camera-based and hence depending on visual signals.
With the current implementation, the tilting function has arrived in series production. Daimler has conducted research on means to compensate for centrifugal cornering forces for more than 15 years. In 1997, the company presented the F 300 Life Jet research vehicle – a study aiming to combine the driving experience and cornering dynamics with the comfort of a car. The three-wheeler was equipped with Active Tilt Control (ATC): Sensors measured speed, acceleration, steering angle and yaw angle; an ECU computed in real-time the resulting angle of inclination.
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