Cruise Control: Description and Operation

Active Cruise Control With Stop and Go Function

NOTE: More advanced Active Cruise Control.

With the launch of the new 5-Series, the new generation of ACC sensor replaces the previously used long-range sensor and the two short-range sensors.

Notes for Service department

The ACC sensor and the ACC control unit are one component. Short-range sensors are no longer installed. The function of the short-range sensors is now handled by the ACC sensor.
The ACC requires an ICM control unit (Integrated Chassis Management) or an LDM control unit (Longitudinal Dynamics Management) in addition to the ACC control unit. These control unit are then installed as follows:
- In the X6 an LDM control unit is installed as well as the ACC control unit. In addition, there is also another ICM control unit which is not however used for the ACC function.
- In the X5 an LDM control unit is installed as well as the ACC control unit.
- On all other vehicles, an ICM control unit is installed as well as the ACC control unit.

Observe the following information in Service:
- The diagnosis for the ACC control unit are performed by the ICM control unit or the LDM control unit.
The ICM control unit or LDM control unit is therefore a gateway for the ACC control unit. If the ICM control unit or LDM control unit is faulty or not connected, diagnosis cannot be carried out with the ACC control unit: The control unit does not respond.
- After any replacement, the ICM control unit or LDM control unit needs to be encoded again.
- After replacement, the ACC control unit must be recoded.
- In connection with frontal damage on the vehicle, make sure that the holder for the ACC control unit is not bent.
- After the ACC control unit is renewed, the unit must be put into operation again. Use the corresponding service function. The sensor does not require any mechanical setting.

Introduction
The following text describes the Active Cruise Control with Stop and Go function (optional equipment 5DF).
The Active Cruise Control with Stop and Go function has been available since 2007. The Stop and Go function expands the familiar Active Cruise Control feature by the following functions:
- Distance and cruise control up to a standstill through engine or brake intervention
- Automatic driving off from a standstill after a short immobilization period (1 to 3 seconds)
- adaptive Dynamic Brake Control (F0x, F1x)

The set speed can be selected from 30 km/h to 180 km/h: in convenient steps of 10 or fine steps of 1. The set speed is displayed on the instrument panel (or alternatively on the Head Up Display). Furthermore, it is also possible to choose between 4 distances.

Brief component description
The following components are described for the ACC:

ACC: Sensor and control unit
The ACC sensor is integrated in the ACC control unit. The ACC sensor is a radar sensor, which is capable of both long-range detection (up to 200 meters) and short-range detection (up to 60 meters) in front of the vehicle.
The ACC sensor detects the distance, angle and speed of moving objects. The relevant data is processed in the ICM control unit or the LDM control unit.







ICM and LDM: Integrated Chassis Management and Longitudinal Dynamics Management
The ICM control unit is installed on the transmission tunnel under the centre console.







LDM: Longitudinal Dynamics Management (only on X5 and X6 vehicles)
The LDM control unit is installed in the driver's side footwell (observe LHD and RHD vehicles).







The ICM or LDM control unit performs the following tasks for ACC with Stop and Go function:
- Summary of data transmitted by the ACC sensor on objects
- Evaluating the objects and selecting the object relevant to distance control
- Evaluating the control signals and generating display signals
- Regulating speed and distance
- Generating and sending the nominal values to the actuators drive and brake via the FlexRay
- Monitoring all input signals, the control unit (hardware) as well as the vehicle behavior for faults or implausible states

S-CAN: sensor CAN

The sensor CAN (S CAN) connects:
- The ICM control unit or LDM control unit
- The ACC sensor

System functions
The following system functions are described:
- Functional networking
- Adaptive dynamic brake control
- Unexpected system behavior

Functional networking











For implementation of the Stop and Go function, a complex system network with distributed functions in other control units is necessary. The ICM control unit or LDM control unit is connected across data buses to these other control units.

The following control units are networked for the overall function:

Control unit Function
DME or DDE: Engine control Implementation of the torque request "Engine on" signal
DSC: Dynamic stability control Driving condition Implementation of brake intervention
SZL: Steering column ACC operation
switch cluster E70, E71: Drop arm
F0x, F1x: Buttons on steering wheel Steering angle
CIC: Navigation system Data from navigation system (influence on control variables)
INSTRUMENT PANEL: Diagram of the
Instrument panel displays (ACC and Check Control messages)
control unit
HUD: Head-Up Display Diagram of the displays (ACC and Check Control messages)
CAS: Car access system Terminal status and wake-up line Door contact
EGS: Transmission control unit Driving position
AHM: Trailer module Identification of trailer towing
ACSM. Crash safety module Driver's seat occupancy (driver intends to exit)
Seat belt buckle contact (driver intends to exit)
RLS: Rain/rain/light sensor Road condition (wet)
FRM: Footwell module Activation, hazard warning flashers, door contact

adaptive Dynamic Brake Control (F0x, F1x)
The adaptive dynamic brake control is a function of the ICM control unit or LDM control unit. The adaptive dynamic brake control is only available on vehicles with Active Cruise Control with Stop&Go function.
The adaptive dynamic brake control provides its greatest benefit in emergency braking situations. When the driver of the vehicle ahead brakes sharply, the ACC sensor detects this situation. Dynamic Brake Control assists in braking in a manner that is most effective in preventing a collision.
The following functions are available:
- Pre-filling of the brake system
- Adaptation of a number of parameters for the braking functions in the DSC according to the situation
- visual warning for the driver on the instrument panel or Head Up Display in event of an advance warning
- visual and acoustic warning for the driver in the event of an acute warning

The adaptive Dynamic Brake Control can be switched on using the corresponding button in the assist system control box.
After the warning function as been switched on, the following can be set using the control centre:
- Switch prewarning on/off
- Adjust the time of the prewarning

This setting has no effect on the time of a warning where the ACC* requests driver intervention or braking.
The adaptive dynamic brake control can also be switched on without activating the ACC Stop and Go function.

Unexpected system behavior
A situation that requires explaining to the driver may occur if the function limits of the ACC system are reached.
Such situations are described in the following:
- Great differences in speed between the vehicle and the vehicle in front cannot be regulated by the system. In this case, a brake intervention on the part of the driver is necessary.
- The Active Cruise Control does not react to stationary traffic obstructions or oncoming traffic.
- The distance control is limited by the detection range of the radar sensors: in the event that vehicles cut in very closely and quickly in front of the vehicle, intervention on the part of the driver can be necessary.
- The leading vehicle may be lost when cornering due to the limited side field of view of the radar sensors. In this case, the acceleration to the set speed is briefly suppressed. Reason: this will prevent the vehicle from accelerating too close to the vehicle ahead, which is possibly only briefly not being monitored.
- If the ACC sensor is "blinded", for example if covered by snow, the ACC switches off. A Check Control message is output to the driver. The ACC can be reactivated after cleaning the radar sensors.

NOTE: Damage to the ACC sensor cover can cause the ACC sensor to malfunction.

- If ASC or DSC intervene for longer periods (with critical coefficients of friction), ACC switches off.
- Rain, fog and snow absorb the radar beams. This can significantly reduce the range of ACC. In extreme cases, ACC can no longer be used.
- Brows of hills and depressions may obstruct detection, causing objects to be lost.
- In very rare cases, objects can be sensed with incorrect measured values (usually the angle). For example, due to reflection of the radar beams from tunnel walls and guarding rails.
- At very low temperatures (below minus 20 deg C), the ACC sensor may only attain operating readiness after some delay. In this case, the ACC function cannot be activated. This is indicated in the instrument panel by "---".

No liability can be accepted for printing or other faults. Subject to changes of a technical nature