Part 2
The DISTRONIC PLUS functions incl. BAS PLUS and PRE-SAFE brake include the following partial functions:- Function sequence for automatic speed control
- Function sequence for automatic distance control
- Function sequence for BAS PLUS and PRE-SAFE brake
Function sequence for automatic speed control
The automatic speed control (CC) function allows the driver to establish a speed within the vehicle speed range of v = 30 to v = 200 km/h (v = 20 mph to v = 120 mph) which the vehicle is then automatically regulated to keep at.
The automatic speed control (CC) function is activated over the CC lever. The specified speed can be set in v = 1 km/h or 10 km/h steps (1 mph or 5 mph steps).
Vehicles without code (494) USA version
The possibly active function Variable SPEEDTRONIC is deactivated and the SPEEDTRONIC LED goes out.
Actuation of the SPEEDTRONIC LED takes place using the switching logic integrated in the CC lever.
The steering column tube module control unit directly reads in the status of the SPEEDTRONIC LED and transmits this via the chassis CAN to the radar sensors control unit or the video and radar sensor system control unit.
1 km/h or 1 mph steps:
The accelerate and set switch must be actuated upwards to the actuation point or the decelerate and set switch must be actuated downwards to the actuation point.
10 km/h or 5 mph steps:
The accelerate and set switch must be actuated upwards beyond the actuation point or the decelerate and set switch must be actuated downwards beyond the actuation point.
If the respective switch is held at or beyond the actuation point then the set speed increases automatically by an interval of t = 0.6 s.
The selected vehicle speed range is displayed through lighting up of the segment ring around the speedometer (A1p8).
If the automatic speed control function is activated, the vehicle automatically accelerates up to the specified speed.
There is also active braking when driving down hills to maintain the specified speed.
Additional automatic distance control function requirements
- Cruise control lever in DISTRONIC PLUS position (SPEEDTRONIC LED Off)
- Target object (vehicle driving immediately ahead) detected by the radar sensor system
Function sequence for automatic distance control
The distance to the vehicle driving immediately ahead can be set over the DISTRONIC control in seven stages between about. t = 1.0 and 2.0 s.
The temporal data concerning the specified distance refers to the distance the vehicle has traveled at a particular speed. The distance to the vehicle driving immediately ahead should be at least 50% of the displayed speed value (example: v = 100 km/h requires a minimum distance of s = 50 m).
The radar sensors control unit or the video and radar sensor system control unit evaluates the input factors from the long distance and short distance radar sensors and records the vehicle driving immediately ahead as a target object.
The distance to the vehicle driving immediately ahead is displayed in the multifunction display for t = 5 s.
While taking account of the programmed setting on the CC lever, the radar sensors control unit or the video and radar sensor system control unit regulates the distance to the vehicle driving immediately ahead.
Vehicles without code (494) USA version
The active function automatic distance control is signaled to the driver through lighting up of the SPEEDTRONIC LED.
If the vehicle driving immediately ahead accelerates to above v = 200 km/h (v = 120 mph) or moves out of the detection range of the radar sensor system, the function automatic distance control switches over to the function automatic speed control.
The vehicle reacts by being regulated at the specified speed set by the driver.
Through selection of the operating level "DISTRONIC PLUS" in the menu "Assistant" in the IC, the distance graphic is shown permanently. Display of the distance graphic can be activated or deactivated independently of the activity of the automatic distance control function.
View of the multifunction display for an activated DISTRONIC PLUS function and a detected vehicle driving immediately ahead, shown on the multifunction display up to 31.5.11
D Speed of vehicle immediately ahead
E Own speed
F Target speed
G Vehicle moving immediately ahead (target object)
H Own vehicle
I Target distance (white line)
The partial function automatic distance control takes place within the system limits dependent on the input factors and consists of the following subfunctions:
- Function sequence for automatic acceleration and braking
- Automatic start-off function sequence (with Stop-and-Go traffic)
Function sequence for automatic acceleration and braking
The radar sensors control unit or the video and radar sensor system control unit reads in the following input factors from the respective components to regulate automatic acceleration:
- Intensity of acceleration of deceleration in longitudinal direction
- Motion/speed of target object
The DISTRONIC controller unit evaluates data about the detected target object, processes this and transmits appropriate information via the vehicle dynamics CAN to the radar sensors control unit or the video and radar sensor system control unit.
The radar sensors control unit or the video and radar sensor system control unit processes the input values and transmits the request to increase or reduce the engine torque via the chassis CAN to the Electronic Stability Program control unit.
The Electronic Stability Program control unit evaluates this information as well as further requests and passes them according to their relevance via the chassis CAN to the CDI control unit or the ME-SFI [ME] control unit. The CDI control unit or the ME-SFI [ME] control unit implements the request to increase or reduce the engine torque appropriately.
The driver also has the possibility by using the accelerator pedal to manually intervene in acceleration of the vehicle (e.g. for an overtaking maneuver).
To do this the CDI control unit or the ME-SFI [ME] control unit reads in the accelerator pedal sensor signals (B37) directly and sends them via the chassis CAN to the radar sensors control unit or the video and radar sensor system control unit.
Automatic acceleration is put out of action for as long a the driver accelerates the vehicle using the accelerator pedal.
This process is optically displayed in the multifunction display with the message "DISTRONIC passive".
If the automatic distance control function requires a higher acceleration than the driver prescribes, the driver request is overlaid by the request for automatic distance control function.
If reduction of the engine torque is not sufficient to achieve the required distance, the radar sensors control unit or the video and radar sensor system control unit sends the request to brake via the chassis CAN to the Electronic Stability Program control unit.
The Electronic Stability Program control unit implements the request to brake through metered actuation of the traction system hydraulic unit (A7/3).
The driver also has the possibility by using the brake pedal to manually intervene in deceleration of the vehicle.
Function requirements for automatic start-off (with Stop-and-Go traffic)
- Brake pedal NOT OPERATED
The position of the brake pedal is detected by the brake light switch (S9/1). The Electronic Stability Program Premium control unit directly reads in the status of the brake light switch and transmits this via the chassis CAN to the radar sensors control unit or the video and radar sensor system control unit, which evaluates this appropriately.
Automatic start-off function sequence (with Stop-and-Go traffic)
Regulated driving off by the DISTRONIC PLUS function allows automatic driving off and stopping of the vehicle in Stop-and-Go traffic.
The driver must acknowledge the driving off process by actuating (pulling on) the "Resume from memory" switch.
The status of the "Resume from memory" switch is transmitted by the steering column tube module control unit via the chassis CAN to the radar sensors control unit or the video and radar sensor system control unit. The radar sensors control unit or the video and radar sensor system control unit receives these, evaluates them and then transmits the request to increase or reduce the engine torque to the Electronic Stability Program control unit. The Electronic Stability Program control unit evaluates this information as well as further requests and passes them according to their relevance via the chassis CAN to the CDI control unit or the ME-SFI [ME] control unit. the CDI control unit or the ME-SFI [ME] control unit implements this request appropriately and the vehicle starts off automatically.
Important function notes in special driving situations:
- The system does not operate for stationary objects (e.g. vehicles) unless a preceding vehicle is tracked to a standstill.
- If a vehicle cuts in between the host vehicle and the vehicle ahead (target vehicle), the system switches over to the new target vehicle.
- If the preceding vehicle turns off and there is another vehicle in front, the system only switches over to the new target vehicle if it is moving. In the event that a stationary obstruction is encountered, a signal tone and the DISTRONIC warning lamp (A1e59) warn the driver about the impending collision.
The special considerations arising from the following traffic situations should also be observed:
Obstacles and stationary vehicles
The DISTRONIC PLUS function does not brake for obstacles or stationary vehicles which were not previously detected as the target object.
If, for example, the detected vehicle turns off and there is an obstacle or stationary vehicles behind it, no automatic intervention by the brake system occurs.
Curves, curved entrances and exits:
The DISTRONIC PLUS function can only provides limited detection of vehicles in curves. The systems vehicle can then brake unexpectedly or late.
Vehicles moving across in front of one's own vehicle:
The DISTRONIC PLUS function may detect vehicles in cross traffic by mistake.
For an activated distance control the vehicle can start off unintended, (e g. at a traffic light with cross-traffic).
Function sequence for BAS PLUS and PRE-SAFE brake
The PRE-SAFE brake function assesses the situation of the traffic in front of the vehicle.
In a hazard situation within the following speed ranges, the vehicle is decelerated automatically by the PRE-SAFE brake function or an emergency braking maneuver by the driver is supported by the BAS PLUS system:
- Vehicle speed range for PRE-SAFE brake:
- v = 30 to 200 km/h (v = 20 to 120 mph) (up to 31.5.11)
- v = 7 to 200 km/h (v = 5 to 120 mph) (as of 1.6.11)
- Vehicle speed range for BAS PLUS:
- v = 30 to 250 km/h (v = 5 to 150 mph) (up to 31.5.11)
- v = 7 to 250 km/h (v = 5 to 150 mph) (as of 1.6.11)
In the case of stationary obstacles the PRE-SAFE brake function or the BAS PLUS function is only activated if the vehicle's own vehicle speed is a maximum of v = 72 km/h (v = 45 mph).
The following example situation leads to activation of the function PRE-SAFE brake and also BAS PLUS function if necessary:
If a stationary object is detected in the lane by both the short and long range radar sensor systems (the lane is determined by the steering angle and vehicle speed, etc.), the PRE-SAFE brake function or the BAS PLUS function is activated.
The following illustration shows the example situation described as well as the chronological sequence of the BAS PLUS and PRE- SAFE brake functions.
Illustration of the principle of the BAS PLUS function and the PRE-SAFE brake function, illustrated on model 221
A1e59 DISTRONIC warning lamp
1 System vehicle equipped with DISTRONIC PLUS including BAS PLUS and PRE-SAFE brake
19 Stationary or significantly slower vehicle in own lane
t1 Approx. t = 2.6 s before possible accident; output of visual 1 and acoustic warning messages, activation of BAS PLUS
t2 About t = 1.6 s before a possible accident; automatic partial 2 braking by the PRE-SAFE brake; possibly also evasive maneuvers by the driver or hazard braking performed by the driver and supported by BAS PLUS
t3 Approx. t = 0.6 s until accident, automatic emergency braking 3 by PRE-SAFE brake
The PRE-SAFE brake function also includes a distance warning function which warns the driver visually and acoustically of moving or stationary obstacles in his lane. The distance warning in the speed ranges listed below:
- v = 30 to 250 km/h (v = 5 to 150 mph) (up to 31.5.11)
- v = 7 to 250 km/h (v = 5 to 150 mph) (as of 1.6.11)
In this case, differentiation is made between a static and a collision critical distance warning.
Static distance warning:
The static distance warning is triggered by the radar sensors control unit or the video and radar sensor system control unit when the time interval between the system vehicle and vehicle in front is less than t = 0.8 s (e.g. in moving traffic). To do this the radar sensors control unit or the video and radar sensor system control unit transmits a request for an optical warning via the chassis CAN to the instrument cluster which then actuates the DISTRONIC warning lamp.
Collision critical distance warning:
If a moving obstacle within the detection range of the radar sensor system is classified as accident-critical (a collision will occur within t less than 2.6 s), the radar sensors control unit or the video and radar sensor system control unit transmits the request for an optical and acoustic warning to the IC via the chassis CAN which reacts by actuating the DISTRONIC warning lamp and the warning buzzer (A1h1) (intermittent tone).
The request present for a warning output is switched off automatically when the situation is defused and cannot be deactivated during active regulation.
The AWS can be separately and independently activated by the automatic distance control function in the menu "PRE-SAFE brake" of the IC.
The distance warning function is basically active for an active DISTRONIC PLUS. If the function DISTRONIC PLUS is deactivated, actuation of the DISTRONIC warning lamp takes place by the function PRE-SAFE brake.
Visual warning message in instrument cluster when a safe distance is not maintained
A1e59 DISTRONIC warning lamp
J Distance warning readiness indicator
The radar sensors control unit or the video and radar sensor system control unit initiates a partial braking if the driver does not react to the acoustic and optical warning signals.
To do this the radar sensors control unit or the video and radar sensor system control unit calculates a braking torque while taking account of the driving dynamics input factors, which is transmitted via the chassis CAN to the ESP control unit.
The Electronic Stability Program control unit implements the request over the traction system hydraulic unit and brakes the vehicle according requirements.
If the driver then reacts with an emergency braking maneuver, the BAS PLUS function provides support for optimum utilization of the braking distance to the object.
The hazard braking is defined over the actuation speed and the actuation strength with which the brake pedal is actuated.
To do this the radar sensors control unit or the video and radar sensor system control unit uses data from the radar sensor system and calculates the necessary brake servo assistance while taking account of the distance and the closing speed to the obstacle.
To do this, the radar sensors control unit or the video and radar sensor system control unit transmits the appropriate requests via chassis CAN to the Electronic Stability Program control unit which actuates the hydraulic brake pressure over the traction system hydraulic unit.
If there is no actuation or the intensity of actuation of the brake pedal by the driver reduces, the brake servo assistance on the driver braking is reduces and the function BAS PLUS deactivated.
The function BAS PLUS will also be deactivated if the driver presses on the accelerator pedal. Operation of the accelerator pedal is detected by the accelerator pedal sensor.
The CDI control unit or the ME-SFI [ME] control unit reads in the accelerator pedal sensor signals directly and transmits them via the chassis CAN to the radar sensors control unit or the video and radar sensor system control unit.
If the driver does not react to the partial braking and if the radar sensors control unit or the video and radar sensor system control unit calculates that the collision with the obstacle is unavoidable, the radar sensors control unit or the video and radar sensor system control unit instigates emergency braking for t = 1 s and thereby reduces the possible consequences of the accident.
Emergency braking is not triggered if the front passenger seat is occupied and the front passenger is not wearing his seat belt.
