GF32.50-P-0001LE Active Body Control (ABC), Function
GF32.50-P-0001LE Active body control (ABC), function
- with CODE (487) Active Body Control (ABC) [model 221.1]
- except CODE (489) AIRMATIC (air suspension with continuous damper adjustment) [model 216.3]
General function requirements
^ Circuit 15R ON
The circuit status is transmitted by the EIS [EZS] control unit (N73) via 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).
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 front axle valve unit (Y36/1)
ABC rear axle 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 from the instrument cluster (A1) via the chassis CAN to the ABC control unit.
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.
- 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) (N69/1) by the left door control unit or the left front rotary tumbler switch (model 221) (N69/1) by the left front door control unit
- the right rotary tumbler switch (model 216) (N69/2) by the right door control unit or the right front rotary tumbler switch (model 221) (N69/2) by the right front door control unit
- the left rear rotary tumbler switch (model 221) (N69/3) by the left rear door control unit
- the right rear rotary tumbler switch (model 221) (N69/4) by the right rear door control unit (model 221)
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 (N93) 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) (with diesel engine) or by the ME-SFI 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 the function scope "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 less than 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. In this connection the driver can select between the following levels using the level control switch (S6/2s10):
- 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 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 (CAN A). 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 the 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 greater than 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 is dependent on the transmission mode. If, for example, the transmission mode is changed from Comfort to Sport, the performance map of the suspension is likewise changed. Via the transmission mode button (A40/9s8) in the central front operating unit (A40/9) the driver can select between the transmission programs "S" (Sport), "C" (Comfort) and "M" (Manual).
The status of the transmission mode button is transmitted by the central front operating unit to the COMAND controller unit via the telematics CAN A40/3/3. The COMAND controller unit passes on the status to the instrument cluster and central gateway control unit via the central CAN. The central gateway control unit transmits the status to the ABC control unit via the chassis CAN. The respective adjustment is displayed in the instrument cluster. The performance map in position "M" corresponds to that of position "S".
On vehicles with code (494) USA version it is only possible to select between the transmission programs "S" and "C".
The ABC control unit stores the adjustment last selected so that after a restart of the engine 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 the 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)
