Following A Vehicle
Following A Vehicle
General Information, Components
The distance regulation control module (J428) works the same way as the radar principle.
Electromagnetic waves reflect off objects. The wave reflected back is actually an echo. The amount of time from when the signal was transmitted and when the signal was received back depends on the distance of the object. The distance in scenario B is twice as large as in scenario A in the illustration. The amount of time it take for the reflected signal to reach the receiver in scenario B is twice as long as in scenario A. In actual traffic situations (for example, driving on an expressway with several lanes or when driving around a curve), many vehicles can be within the view of the radar all at the same time.
This is necessary to determined which vehicle is driving in the same lane, or which vehicle has been selected for the selected distance. The distance regulation control module then determines the lane where additional input signals are necessary: especially from the rotation rate sensor, the speed sensors and the steering angle sensor. The signals then can be evaluated to determine the curve of the road. This "virtual" lane B is a result of the actual road curve around which the vehicle is driving "R" and a determined average lane width. The nearest object in the closest lane that the radar does not see will then be a virtual object for the distance control.
The following components are also involved:
• Instrument Cluster Control Module (J285)
• Steering Column Electronic Systems Control Module (J527)
• Cruise Control Switch (E45)
• Engine Control Module (J623)
• ABS Control Module (J104)
• ABS Wheel Speed Sensors (G44, G45, G46, G47)
Function Description
• The driver in the blue vehicle activates the control and then selects the speed "V" and the distance "a" using the cruise control switch. The steering column electronic systems control module reads the position of the switch and sends it to the distance regulation control module via the CAN Bus. The distance regulation control module reads the actual speed, that was sent from the instrument cluster control module to the chassis CAN and then sends the specified acceleration to the engine control module in order to reach the desired speed. The vehicle accelerates until the specified speed is reached.
• A vehicle in front in the same lane (red) is recognized by the distance regulation control module, which then sends the changed specified acceleration to the engine control module in order to hold the specified distance. The engine control module decides if it should either increase or decrease the amount of fuel being injected in order reach the specified acceleration or if it should activate the brakes (performed by the ABS control module). The speed "V" of the blue vehicle is reduced so that the distance "a" can be set.
• A second vehicle (motorcycle) starts to move into the safety zone of the vehicle in front. The specified acceleration calculated by the distance regulation control module cannot be made by the engine control module. This means the desired distance can no longer be maintained by applying the brake only and there could be a crash with the motorcycle. The driver will be alerted by an optical (inside the instrument cluster control module) and an acoustical warning (via the speaker) to actively apply the brakes in order to prevent a crash.
• The ACC deactivates when the driver applies the brakes. The driver can now go back to the set values before the using the brakes by using the Resume feature (by pulling on the cruise control switch) or by pushing the SET button. The motorcycle in front switches lanes. The radar sensor will recognize this. The blue vehicle accelerates again until the specified speed is reached.
Service Information
If the distance regulation control module (J428) was removed while working on the front of the vehicle, it must be aligned when it is installed again.
• Applying the brakes will deactivate the distance control immediately.
• Pressing the clutch for more than 20 seconds also deactivates the distance control.
A005A4009-030110