GF32.50-P-0001SX Active Body Control (ABC), Function

GF32.50-P-0001SX Active body control (ABC), function
- with CODE (487) Active Body Control (ABC) [model 221.1]

Component Identification:

Description
On the Active Body Control (ABC) system a fully supporting suspension system is involved. Via four hydraulic suspension struts (plunger cylinder) each wheel can actively be subjected to variable forces. A hydraulic volume flow is produced by the radial piston pump and stored under high pressure in the central reservoir of the front and rear axle. As required, hydraulic fluid is supplied to the individual cylinders via the ABC valve units. The hydraulic fluid which is not currently needed is stored unpressurized in the oil reservoir. The oil is cooled down by the oil cooler.

The control intervention function is effective up to a frequency range of approx. 5 Hz. The ABC system requires for this a comprehensive system of sensors and actuators which are evaluated, actuated and monitored by the ABC control unit (N51/2).

The forces of the controllable plunger cylinders assist the forces of the coil springs and are able to adjust for deviations from tire uniformity.

The ABC control unit always adapts the suspension and damping characteristics to the driving situation.

Advantages of ABC system compared to conventional suspension:
^ As a result of the active body damping, it is possible to use very soft, passive shock absorbers which improve vibration and tire comfort considerably.
^ Despite the absence of stabilizer bars, the ABC system compensates the typical body roll when cornering and the pitch motion when accelerating or braking.
^ Vibrations and shocks which are caused by road bumps can be damped more effectively.
^ The required and usual handling characteristics are retained even when the vehicle is loaded.

The driver can influence the characteristics of the Active Body Control system can via the transmission modes button (A40/9s8) and the level adjustment switch (S6/2s10).

Component Identification:

Function of control
The ABC control unit records with the help of the following sensors:
^ Pressure sensors
^ Level sensors
^ Acceleration sensors
^ Lateral acceleration sensor

the current pressures in the ABC system, the forces acting on the vehicle and the relative travels between the wheels and the body level.

The ABC control unit continuously adapts the suspension and damping characteristic to the current driving condition.

The plunger cylinders are actuated via the ABC valve units. The actual values are constantly compared with the specified values and adapted accordingly.

Wake-up via CAN bus
The ABC control unit is woken up by opening a door or trunk lid. The opening of a door is detected via the rotary tumbler switch. The opening of the trunk lid is detected via the trunk lid rotary tumbler microswitch (M14/7s3). The information is transmitted by the corresponding door control unit or by the rear SAM control unit to the central gateway control unit via the interior CAN. This transmits the information to the ABC control unit via the chassis CAN. When the ignition is switched on the wake-up mode is terminated and the ABC control unit transfers to normal mode.

Initial check
In the initial check all the system tests summarized which are run through once after the system start. For this, for example, test actuations are carried out on the valve output stages. As the valve output stages have to be actuated immediately after the engine is started, they are already checked during the transition to the wake up mode.

The various tests of the initial check are staggered chronologically and are carried out according to need. All the components which are required for the function scope of wake-up mode, already have to be checked during the transition to wake-up mode. The initial check is processed completely at the latest after the engine is started. As during these tests the valve output stages are not actuated by the function algorithm, the initial check must be completed after a short time (approx. 3 s).

Change vehicle level
The driver can choose between normal level and an increased level by operating the level adjustment switch. The status of the level adjustment switch is read in by the upper control panel control unit via the upper control panel The upper control panel control unit transmits the status to the COMAND controller unit via telematics CAN. Via the central CAN the status is transmitted to the instrument cluster and via the interior CAN to the central gateway control unit. The central gateway control unit transmits the status to the ABC control unit via the chassis CAN.

If the vehicle is at normal level and the level adjustment switch is actuated and the level adjustment switch is operated, then the vehicle is raised to the increased level. The function LED lights up in the level adjustment switch. If the vehicle exceeds a defined speed threshold then the vehicle level is lowered. In the process though the driver's level choice is not erased. The vehicle level is raised again with reducing speed.

When the level adjustment switch is operated again the function LED is switched off again and the vehicle is lowered to normal level.

Change chassis alignment
The chassis adjustment depends on the selected transmission mode of the automatic transmission. If the transmission mode of the automatic transmission is changed, for example, from Comfort to Sport, the suspension performance map is also changed. The driver can change the suspension performance map by operating the transmission modes button.

The driver can choose between a comfort-oriented and sporty performance map. The selected setting is displayed in the instrument cluster. The performance map in position "M" (manual) corresponds to that of the position "S" (Sport).

On vehicles with code (494) USA version it is only possible to choose between transmission modes "S" and "C" (Comfort).

Block position (passive gearshift)
The block position of the ABC control unit cannot be selected manually. Blocking ensues software-controlled, as soon as the ABC system detects a reduction in wheel load, such as, for example, can occur when replacing a tire or during assembly operations in service. If blocking has been activated by the ABC control unit, the corresponding valve unit is deactivated. No driver information and no fault storage ensues. Blocking is erased automatically at a vehicle speed of more than 0 km/h.

Display of error messages
Errors or notes are shown in the multifunction display (A1p13) of the instrument cluster. The ABC control unit transmits the corresponding message to the central gateway control unit via the chassis CAN. The central gateway control unit transmits the message to the instrument cluster via the central CAN.