Active body control (ABC), function - GF32.50-P-0001LEA
MODEL 221.0 /1 with CODE (487) Active Body Control (ABC) as of Model Year 2010 /modification year 09 model refinement package
MODEL 216.3 except CODE (489) AIRmatic (air suspension with continuous damper adjustment) as of model year 2010 /YoM 09
Function requirements, general
- Circuit 15R ON
The circuit status is sent by the EZS control unit (N73) over the chassis CAN (CAN E).
General
The Active Body Control (ABC) system is a fully supporting suspension system with the aid of 4 hydraulic suspension struts is able to load each wheel actively with variable forces.
The control intervention functions of the ABC system extend to frequency range of approx. f = 5 Hz. The sensors and actuators involved in the ABC system are evaluated, actuated and monitored by the ABC control unit (N51/2).
2-pressure ABC concept (on model 221 as of model year 2011
/YoM 10 or model 216 as of model year 2011
/YoM 10 model refinement package with engine 157, 278)
The hydraulic pressure applied to the tandem pump, which used to be 180 bar constantly, can be reduced as required down to 10 bar depending on the driving condition via the ABC switchover valve (Y5).
Despite the reduced pressure feed, the system pressure is kept constant at a range of approx. 165 to 175 bar via a check valve. If the pressure requirements increase, the switchover valve is closed and the pump builds the system pressure back up to 180 bar.
The ABC switchover valve is located on the tandem pump. Actuation is by the ABC control unit.
By integrating the ABC switchover valve, the power output of the combustion engine to the ABC system can be reduced, saving fuel.
The ABC system contains the following electrical components:
- ABC control unit
- ABC pressure sensor (B4/5)
- Left front ABC pressure sensor (B4/8)
- Right front ABC pressure sensor (B4/9)
- Left rear ABC pressure sensor (B4/10)
- Right rear ABC pressure sensor (B4/11)
- Left rear level sensor (B22/7)
- Left front level sensor (B22/8)
- Right front level sensor (B22/9)
- Right rear level sensor (B22/10)
- Left front body acceleration sensor (B24/3)
- Right front body acceleration sensor (B24/4)
- Right rear body acceleration sensor (B24/6)
- ABC lateral acceleration sensor (B24/12)
- ABC switchover valve (on model 221 as of model year 2011
/YoM 10 or model 216 as of model year 2011
/YoM 10 model refinement package with engine 157, 278)
- ABC front axle valve unit (Y36/1)
- Rear axle ABC valve unit (Y36/2)
- ABC intake throttle valve (Y86/1)
A dynamically adjustable hydraulic cylinder is attached to each suspension strut. The hydraulic cylinders counteract the forces occurring while driving by movement parallel to the coil springs. The rolling motions of the body when cornering and the pitch motions when starting off or braking can thus be compensated. The ABC control unit continuously adapts the suspension and damping characteristic to the current driving condition.
The following values are recorded via the sensor system:
- Vertical body acceleration
- Travels between wheels and body
- Pressure in the suspension struts
Furthermore the lateral acceleration of the vehicle is used. The steering angle and vehicle speed are required for this.
The steering angle is recorded by the steering angle sensor (N49) and transmitted by the steering column tube module (N80) via the chassis CAN to the ABC control unit.
The vehicle speed is transmitted by the instrument cluster (A1) to the central gateway control unit via the central CAN (CAN F)N93 from here to the ABC control unit via the chassis CAN.
The recorded values are continuously compared with the specified values and adapted accordingly.
The suspension with the ABC system offers the following advantages compared with a conventional suspension:
- Active body damping means that very soft passive dampers can be used which provide better vibration comfort and ride.
- By active wheel load distribution (ARV) a reduction in yaw response of the vehicle is achieved in the event of a side wind suddenly occurring (model 221 only).
- In spite of a lack of stabilizer bars the typical rolling of the body when cornering and pitch motions when starting off or braking are adjusted.
- Vibrations and shocks due to road bumps can be damped effectively
- The handling characteristics are also retained in the loaded condition.
The ABC system consists of the following subfunctions:
- Wake up mode function sequence
- Initial test function sequence
- Level control function sequence
- Pressure supply function sequence
- Lock position function sequence
- Suspension adjustment function sequence
- System and warning messages function sequence
Wake up mode function sequence
The ABC control unit is woken up by opening a door or the trunk lid. An open door or open trunk lid are detected by the following components:
- Left rotary tumbler switch (A85s1) (model 216) or left front rotary tumbler switch (A85s1) (model 221)
- Right rotary tumbler switch (A85/1s1) (model 216) or right front rotary tumbler switch (A85/1s1) (model 221)
- Left rear rotary tumbler switch (A85/3s1) (model 221)
- Right rear rotary tumbler switch (A85/4s1) (model 221)
- Trunk lid rotary tumbler microswitch (M14/7s3)
The front/rear rotary tumbler switches are read in as follows:
- The left rotary tumbler switch (model 216) by the left door control unit (N69/1) or the left front rotary tumbler switch (model 221) by the left front door control unit (N69/1)
- The right rotary tumbler switch (model 216) by the right door control unit (N69/2) or the right front rotary tumbler switch (model 221) by the right front door control unit (N69/2)
- The left rear rotary tumbler switch (model 221) by the left rear door control unit (N69/3)
- The right rear rotary tumbler switch (model 221) by the right rear door control unit (N69/4)
The trunk lid rotary tumbler microswitch is read in by the rear SAM control unit with fuse and relay module (N10/2).
The respective signals are transmitted to central gateway control unit () via the interior CAN (CAN B) and from here to the ABC control unit via the chassis CAN.
As soon as the engine is running the ABC control unit changes over from wake up mode to normal mode.
Additional function requirements - initial check
- Circuit 61 ON
The status of circuit 61 is transmitted by the CDI control unit (N3/9) (model 221 with diesel engine) or by the ME-SFI [ME] control unit (N3/10) (with gasoline engine) via the chassis CAN.
Initial test function sequence
In the initial check all system tests are combined which are run through once after each system start. For this purpose test actuations are carried out at the output stages for example.
The various tests forming the initial check are time-graded and performed according to requirement. All components required for "wake-up mode" are already checked during the transition to wake-up mode.
Components such as output stages actuated immediately after the engine starts must likewise be checked during the transition to wake up mode.
The initial check is processed completely after the engine starts. As the output stages are not actuated by the function algorithm during these checks, the initial check must be concluded after t < 3 s.
Additional function requirements for level control
- Circuit 61 ON
Level control function sequence
The level control enables the adjustment of the ground clearance of the vehicle. Here the driver can select between the following levels using the level control switch (S6/2s10) in the cockpit switch group (S6/2):
- Normal level (normal ground clearance)
- Raised level (increased ground clearance)
The status of the level control switch is read in by the upper control panel control unit (N72/1) via the instrument panel LIN (LIN 1) and passed on to the central gateway control unit via the interior CAN. This passes on the signal to the ABC control unit via the chassis CAN.
The level control is realized with the aid of 4 hydraulic suspension struts.
If oil from the pressure circuit is delivered to a suspension strut via an activated control valve (linear motor valve), the vehicle level increases at the wheel in question.
The vehicle level reduces when oil from a suspension strut flows away into the return circuit.
If the vehicle is at the normal level when the level control switch is operated, the vehicle is raised to the raised level. The function indicator in the level control switch lights up.
If the vehicle exceeds a defined speed threshold, the vehicle level is lowered automatically. The adjusted level selection is not canceled in the process. The vehicle is raised again automatically when the speed drops.
The vehicle is lowered again to the normal level by renewed operation of the level control switch. The function indicator in the level control switch goes out.
The status of the level control switch is read in by the upper control panel control unit via the instrument panel LIN and transmitted to the central gateway control unit via the interior CAN. From there the signal is passed on to the ABC control unit via the chassis CAN and passed on to the instrument cluster via the central CAN. The instrument cluster stores the switch position so that after a restart the same level adjustment applies as before circuit 15R OFF.
The current driver requirement is shown by the function indicator as soon as the engine is running.
If the vehicle is in the normal level condition, the function indicator in the level control switch is switched off.
Vehicle levels
Model 221 without code (494) USA version:
- Comfort/Sport:
- Raised level +40 mm
- Normal level -0 mm
Model 221 with code (494) USA version:
- Comfort/Sport:
- Raised level +30 mm
- Normal level -0 mm
Model 216 without code (494) USA version:
- Comfort/Sport:
- Raised level +40 mm
- Normal level with circuit 61 OFF:
- Front axle (FA) -0 mm
- Rear axle (RA) +5 mm
- Normal level with circuit 61 ON:
- FA -5 mm
- RA -5 mm
Model 216 with code (494) USA version:
- Comfort/Sport:
- Raised level +30 mm
- Normal level with circuit 61 OFF:
- FA -0 mm
- RA -5 mm
- Normal level with circuit 61 ON:
- FA -5 mm
- RA +5 mm
If the vehicle exceeds or drops below a defined speed threshold, the vehicle level is lowered or raised automatically:
Model 221 without code (494) USA version:
| 0 km/h | Normal level | -0 mm |
| 65 km/h | Normal level | -0 mm |
| 140 km/h | Normal level | -15 mm |
| 0 km/h | Higher level | +40 mm |
| 30 km/h | Higher level | +40 mm |
| 60 km/h | Higher level | +30 mm |
| 210 km/h | Higher level | -15 mm |
Model 221 with code (494) USA version:
| 0 km/h | Normal level | -0 mm |
| 65 km/h | Normal level | -0 mm |
| 140 km/h | Normal level | -15 mm |
| 0 km/h | Higher level | +30 mm |
| 30 km/h | Higher level | +30 mm |
| 60 km/h | Higher level | +20 mm |
| 190 km/h | Higher level | -15 mm |
Model 216 without code (494) USA version:
FA(RA)
| 0 km/h | ||
| (Circuit 61 OFF) | Normal level | -0 mm (-5 mm) |
| 0 km/h | ||
| (Circuit 61 ON) | Normal level | -5 mm (+5 mm) |
| 65 km/h | Normal level | -5 mm (+5 mm) |
| 140 km/h | Normal level | -15 mm (-5 mm) |
| 0 km/h | Higher level | +40 mm (+40 mm) |
| 32 km/h | Higher level | +40 mm (+40 mm) |
| 60 km/h | Higher level | +6 mm (+16 mm) |
| 210 km/h | Higher level | -15 mm (-5 mm) |
Model 216 with code (494) USA version:
FA(RA)
| 0 km/h | ||
| (Circuit 61 OFF) | Normal level | -0 mm (- 5 mm) |
| 0 km/h | ||
| (Circuit 61 ON) | Normal level | -5 mm (+ 5 mm) |
| 65 km/h | Normal level | -5 mm (+ 5 mm) |
| 140 km/h | Normal level | -15 mm (-5 mm) |
| 0 km/h | Higher level | +30 mm (+ 40 mm) |
| 32 km/h | Higher level | +40 mm (+ 40 mm) |
| 60 km/h | Higher level | +20 mm (+ 30 mm) |
| 210 km/h | Higher level | -15 mm (-5 mm) |
Additional function requirements - pressure supply
- Circuit 61 ON
Pressure supply function sequence
A radial piston pump is used to supply the necessary pressure. Like the power steering pump, it is part of the tandem pump and is driven by the engine via a belt drive.
The hydraulic oil is drawn out of the oil reservoir.
The ABC intake throttle valve attached to the pump regulates the intake quantity and therefore the system pressure.
The oil quantity is determined dependent on the driving situation and cooled by means of an oil cooler.
The oil is delivered from the pump to the ABC front axle valve unit, to the ABC rear axle valve unit, to the rear axle central reservoir and to the front axle central reservoir.
The system pressure is monitored by the ABC pressure sensor.
Additional function requirements - blocking position
- Circuit 61 ON
Lock position function sequence
So that when the vehicle is raised intentionally, e.g. with a jack, oil is not continuously drained out of the hydraulic suspension struts back into the return circuit, in order to lower the vehicle, it is necessary to automatically detect this unloading of the wheels and from it to derive a blocking position.
The blocking position is a pure software product which prevents actuation of the hydraulic suspension struts.
If the blocking position has been set by the ABC control unit, the shutoff valves are closed and the control valves are no longer actuated.
There is no display in the instrument cluster and no fault is stored.
If the ABC control unit receives a vehicle speed signal of v > 0 km/h via the chassis CAN, the blocking position is canceled automatically. The normal function scope is then produced again.
The instrument cluster transmits the vehicle speed signal to the central gateway control unit via the central CAN. From there it is transmitted to the ABC control unit via the chassis CAN.
Additional function requirements - suspension adjustment
- Circuit 61 ON
Suspension adjustment function sequence
The suspension adjustment takes place via the suspension adjustment switch (S6/2s15) in the cockpit switch group. The performance map of the suspension is changed accordingly depending on the selection of one of the following modes:
- Comfort (switch not operated): Light-emitting diode (LED) OFF
- Sport (switch operated): LED ON
- Comfort (switch operated again): LED OFF
The signal for the selected suspension adjustment reaches the ABC control unit from the suspension adjustment switch via the following path:
- Instrument panel LIN
- Upper control panel control unit
- Interior CAN
- Central gateway control unit
- Chassis CAN
The signal for actuating the function LEDs in the suspension adjustment switch takes place through the ABC control unit in the opposite direction.
The ABC control unit stores the adjustment last selected so that after a restart the same performance map applies as before circuit 15R OFF.
System and warning messages function sequence
System and warning messages with handling instructions for the driver are shown in the multifunction display (A1p13) of the instrument cluster.
To output messages the ABC control unit transmits corresponding messages via the chassis CAN to the central gateway control unit and from there via the central CAN to the instrument cluster. There are various fault messages with different fault priority classes. The fault priority classes differ mainly with respect to the various acknowledgment options for the driver.
Fault messages:
- ABC fault (yellow)
- ABC fault STOP (red)
| Electrical function schematic for Active Body Control (ABC) | Model 216 | PE32.50-P-2050-97CAC | |
| Model 221 | PE32.50-P-2050-97SAC | ||
| Active Body Control (ABC), location of components | GF32.50-P-0001-01 LEA | ||
| Active body control (ABC), block diagram | GF32.50-P-0001-02LEA | ||
| Overview of system components, Active Body Control (ABC) | GF32.50-P-9997LE |