Cruise Control: Description and Operation
Active Cruise Control With Stop and Go Function
NOTICE: Note restrictions in official approval.
Owing to restrictions regarding approval for highway use, in some markets ACC Active Cruise Control is offered without the Stop&Go function.No short-range sensors are installed on vehicles with ACC but without the Stop&Go function.
Notes for Service department
Observe the following information in Service:
- Diagnosis on the long-range sensor (LRR) is performed by the ICM control unit. The ICM control unit is thus the gateway for the LRR control unit. If the ICM control unit is defective or not connected it will be impossible to conduct any LRR diagnosis: The control unit does not respond.
- After replacement, the ICM control unit must be recoded.
- New code data must be programmed into the long-range sensor following replacement.
- The short-range sensors are automatically encoded based on the pin assignments in the connection plug (no special code-programming session required following replacement of a short-range sensor).
- Following replacement of a long-range sensor the new unit must be adjusted: Use the corresponding service function.
- On replacement of a short-range sensor, observe the exact installation position: in accordance with the repair instructions. Adjustment of the kind required for the long-range sensor is not required. Instead, the new sensor's installation angle must be stored in the ICM control unit: Use the corresponding service function.
Introduction
The following text describes the Active Cruise Control with Stop&Go function (optional equipment 5DF). Active Cruise Control with the Stop&Go function has been available in 5-Series and 6-Series vehicles since 2007. Stop&Go extends the functionality offered by the familiar Active Cruise Control by furnishing the following features:
- Intervention in engine and brake system is employed to control following distance and vehicle speed all the way to a complete vehicle stop
- Automatic driving off from a standstill after a short immobilization period (1 to 3 seconds)
- Adaptive dynamic brake control
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 in the instrument cluster. Furthermore, it is also possible to choose between 4 distances.
Brief component description
The following components are described for ACC:
Short-range sensors on left and right
The short-range sensors are radar sensors (Short Range Radar).
Two identical short-range sensors are installed in vehicles with ACC and the Stop&Go function. Each of the short range sensors is mounted on the front bumper bracket with a plastic bracket.
The sensor CAN (S-CAN) links the short-range sensors to the ICM Integrated Chassis Management control unit.
The short-range sensors discharge the following functions:
- Calculating position and movement data
- Short-range detection of objects up to a range of 30 meters from the front of the vehicle
The object data from the short-range sensors are used exclusively to support the ACC Stop&Go function (not for the adaptive Dynamic Brake Control).
LRR: long-range sensor
LRR stands for Long Range Radar.
The long-range sensor (former ACC sensor) is a radar sensor. At the same time, the long-range sensor is a control unit. This means the long-range sensor has a control unit address and can be diagnosed and programmed. A long-range sensor senses the distance, angle as well as speed of moving objects. The area covered is up to 150 meters ahead of the vehicle. These data are processed in the ICM control unit.
ICM: Integrated chassis management
The ICM control unit is installed in the centre console on the transmission tunnel.
For ACC with Stop&Go function, the ICM control unit performs the following tasks:
- Collating the data transferred by the radar sensor regarding 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 drive and brake actuators 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
- the long-range sensor (LRR)
- the short-range sensors
System functions
The following system functions are described:
- Functional networking
- Adaptive dynamic brake control
- Unexpected system behavior
Functional networking
For implementation of the Stop&Go function, a complex system network with distributed functions in other control units is necessary. Buses connect the ICM control unit with 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 braking intervention
SZL: Steering column switch Operating lever
cluster Steering angle
CIC: Navigation system Data from navigation system (influence on control variables)
Instrument panel: Instrument panel Diagram of the displays (ACC and Check Control messages)
CAS: Car Access System Terminal status and wake-up line
Door contact
EGS: Transmission control 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
The adaptive brake assist is a function of the ICM. 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. The long-range sensor recognizes heavy braking in the preceding vehicle. Dynamic Brake Control assists in braking in a manner that is most effective in preventing a collision.
The following functions are available:
- Precharging the brake system
- Adaptation of a number of parameters for the braking functions in the DSC according to the situation
- Visual alert for the driver in the instrument cluster when initial warning status is present
- 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 driver assistance control box. The point in time of the advance warning can be selected using the button (2 stages possible).
The adaptive dynamic brake control can also be switched on without activating the ACC Stop&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, 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.
- ACC responds to obstruction of the radar sensors from factors such as heavy snow deposits with self deactivation. A Check Control message is output to the driver. The ACC can be reactivated after cleaning the radar sensors.
NOTE: Multiple paint layers on the bumper in the vicinity of the short-range sensors can also obstruct these sensors' signal paths and render them "blind".
- 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.
We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.