Active body control

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Active Body Control ( ABC ) is the brand name for a chassis technology ( active wheel suspension ) from Mercedes-Benz . It denotes a steel on a suspension -based electro-hydraulic active suspension system which in addition to the suspension and damping function of an equalization of the pitch and roll movements of the vehicle allows ( roll stabilization ). Because the vehicle is leveled by the hydraulic system, ABC vehicles do not need conventional stabilizers , which is unique in automotive engineering. In order to fulfill the functions, a vertically adjustable, one-way hydraulic cylinder (plunger) is attached to each spring strut. It continuously regulates the respective spring preload. Higher-frequency vibrations are dampened by conventional vibration dampers (shock absorbers). The system pressure is provided by a belt-driven radial piston pump . The system is only available for rear-wheel drive models . ABC hardness can be set in two levels: normal mode (softer) and sport mode (harder). There are also three vehicle level settings that can be preset: normal, higher, high. Despite the settings, the vehicle automatically adjusts the hardness and level to the road conditions, so that the driver can be completely relieved.

In 1994, however, the Citroën Xantia Activa with "Active Chassis Stabilization" (AFS) was the first vehicle that minimized body roll by means of an active hydropneumatic chassis.

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There is no evidence of the technical uniqueness of Active Body Control. See discussion: Active Body Control

However, only with the Active Body Control chassis is the spring of each individual wheel controlled directly and actively, which is why rolling movements are completely prevented. ABC is thus the first chassis in the world in which the suspension and body damping are actively controlled. To date, no other manufacturer has developed an equivalent chassis.

Further development

This technical system debuted in the then new CL-Class C215 series from 1999, as the first car from German production that was available with active control of the suspension and damping, which was then used in the related sedan series W220 (S600 and S65 AMG standard, except for the S320 CDI / S280 / S320 on request for the remaining models) was also installed.

In 2007, the ABC chassis in the Mercedes-Benz F 700 was expanded to include the pre-scan system. The ABC control can act in a predictive manner and thus significantly improve driving comfort thanks to the sensor-based scanning of the road ahead by lasers in the two headlights. See section Magic Body Control .

In the S-Class 221 series , the ABC chassis was supplemented by crosswind stabilization. The effects of crosswinds on the bodies are almost completely compensated. The sensors used are the yaw rate and lateral acceleration sensors of the Electronic Stability Control (ESP ).

Task and function of the sensors and actuators

In order to perform its tasks, the system obtains information from sensors and controls a number of actuators.

Sensors

Sensors convert information (physical quantities) such as B. temperature or the like in electrical signals and send them on.

Pressure sensor

The pressure sensor reports the respective hydraulic pressure to the control unit. This is regulated to approx. 180–210 bar via the suction throttle valve.

Oil temperature sensor

It measures the hydraulic oil temperature in the return.

Displacement sensors in the hydraulic cylinder (plunger)

It transmits the actual position of the actuating cylinder in the shock absorber to the control unit . These sensors have been replaced by pressure sensors on each plunger (spring leg) since the introduction of the W221 (predecessor model of the current S-Class).

Level sensors

They record the current level of the vehicle structure via the respective wishbone preparation. With adjustable threaded rods, the vehicles can be lowered by up to 80 mm without the chassis itself having to be laboriously converted.

Structure and acceleration sensors

They are used to measure the vertical acceleration in vehicle construction. They consist of electronic vibration modules that send their signals to the control unit. They are required to be able to record lifting movements of the body.

Lateral and longitudinal acceleration sensors

They determine the lateral and longitudinal dynamics of the vehicle and are required to compensate for rolling and pitching movements.

Signal acquisition and control module (SAM)

It activates the control unit via the remote control, the door contact switch or the trunk lighting. The control unit checks the vehicle level in order to lower it to the preselected level if necessary.

Actuators

Suction throttle valve

The suction throttle valve regulates the amount of oil sucked in by the oil pump so that an oil pressure of 180 bar to 210 bar can be built up and maintained in the ABC system. When de-energized, the valve is closed in order to maintain the pressure in the system.

Control valves

The actuating cylinders are moved by activating the control valves. This lowers or raises the structure on the corresponding wheel. This allows the contact pressure of the wheels to be increased for a short time. H. stronger traction.

Shut-off valves

They are closed when the engine is stopped, the vehicle is at a standstill and errors occur in order to avoid pressure loss. This also z. B. when changing a wheel or when working on a lifting platform prevents the actuating cylinders from being pulled apart.

Control processes

Start

When the vehicle door is opened, the ABC control unit is activated via the signal and control module. The actual level is compared with the target level via the level sensors. If the actual level does not correspond to the target level, the corresponding control valves are activated and the vehicle is brought to the target level.

Cornering

When cornering, the lateral acceleration sensor registers the centrifugal forces and transmits them to the control unit. From the front right and front left wheel speeds, which are forwarded to the control unit via the CAN bus , the control unit recognizes whether it is a left or right turn. In the case of a curve, the control unit activates the control valves in such a way that the plungers extend on the outside of the curve and thus the springs are preloaded. At the same time, the plungers on the inside of the curve are retracted and the springs are relaxed. A wobbling of the structure can be almost avoided. The actual level is compared with the target level via the level sensors. In the ABC sport mode, the vehicle is even tilted into a curve.

Acceleration / braking

When accelerating / braking, the longitudinal acceleration sensor registers acceleration forces in the longitudinal direction of the vehicle. The signal is transmitted to the control unit, which then controls the control valves in such a way that pitching movements of the vehicle body are prevented.

Straight ahead

When driving straight ahead, the control unit receives information on the vehicle speed via the CAN bus. The vehicle level is automatically lowered by activating the control valves by the control unit, depending on the pre-selected map . The vehicle can be raised by 25 mm or 50 mm at the driver's request (actuation of the level switch).

Vertical vibrations

If the vehicle swings in the direction of the vertical axis due to uneven road surfaces, these movements are transmitted from the bodywork acceleration sensors to the control unit. The level sensors also report the stop to the control unit, which then controls the control valves within the framework of the preselected map (e.g. sport, comfort) in such a way that the vibrations of the body are dampened and balanced.

Magic Body Control

In 2013, the Mercedes-Benz 222 series introduced the new predictive, active Magic Body Control suspension , which uses stereo cameras ( road surface scan ) to detect unevenness in the road ahead and adjust the dampers in good time. It is based on the Active Body Control chassis from the previous 221 series. The measurement accuracy of the stereo camera is between one and two millimeters and covers five to 15 meters of the area in front of the vehicle. In this way, body movements should also be compensated for. The system only works during the day if visibility is good and the road surface is uncovered (not when it is wet) and up to a speed of 130 km / h. The type of bump in the road is also important. While bumps and bumps can be reacted to, curbs and potholes do not. With the facelift in 2017, the system should work up to a speed of 180 km / h.

In 2014, the A 217 Magic Body Control was extended to include the curve inclination function. This curve tilting function reduces the lateral acceleration acting on the occupants .

Disadvantages of the ABC suspension

The hydraulic lines, which are made partly of rubber and partly of metal, last for about 10 years, after which you can expect loss of oil on the connections between the two materials. High oil loss leads to the destruction of the tandem pump. The tandem pump supplies the oil pressure to both the ABC suspension and the steering (two separate circuits).

In order to renew the hydraulic lines, one clearly has to intervene in the engine compartment. The (CL) 215 and (S) 220 models were not originally designed for ABC suspension and therefore there are numerous intersections and complications with other components of the engine compartment.

Another disadvantage of every active suspension built to date (also in the case of Citroen) is a feedback of the suspension with vibrations of the roadway (bridges) and auxiliary vehicles (with diesel engines) at low frequencies at low speeds (in traffic jams), which can be clearly felt in the passenger compartment.

vehicles

Web links

Individual evidence

  1. ↑ Mercedes-Benz Germany - News - MAGIC BODY CONTROL ( Memento of the original from December 27, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.mercedes-benz.de
  2. ↑ https://www.autozeitung.de/mercedes-s-klasse-2013-500-magic-body-control-v8-gn-401245-61945.html
  3. ↑ https://www.svz.de/ratgeber/auto/s-klasse-mit-fitness-studio-an-bord-id17418731.html