ADAPTIVE CRUISE CONTROL GENERAL INFORMATION
Requirements for Adaptive Cruise Control Regulation
The following information is necessary for the ACC
The distance of the vehicle in front.
Scheme 177
The time span between the transmission and the reception of the signal depends on the distance of the object. This means, the further away the object or vehicle is, the longer it takes for the signal to be transmitted and received.
The speed of the vehicle in front.
Scheme 178
If the distance to the vehicle in front decreases, the frequency of the signal sent increases. If the distance to the vehicle in front increases, the frequency of the signal decreases.
| Distance to the Vehicle in Front | The Time Span Between the Transmission and the Reception of the Signal | Frequency |
|---|---|---|
| Remains the same | The time span remains the same | Remains the same |
| Increases | The time span increases | Decreases |
| Decreases | The time span gets smaller | Increases |
The vehicle electronics monitor this frequency and send the speed value.
The position of the vehicle in front.
Scheme 179
The signal expands like a cone.
The signal strength decreases as the distance of the vehicle in the front increases.
In order to determine the position of the vehicle in front, it is also necessary to know the angle of the vehicle in front to your vehicle.
Scheme 180
A four-beam radar is used for this.
The angle information provides the relation of the amplitudes (signal strength) of the received (reflected) signals of the individual radar pulses
TECHNICAL DATA
| Range of the adaptive cruise control (ACC) system | Approximately 200 meters |
|---|---|
| Speed range of the ACC system | 20 to 200 km/h (12-120 mph) |
| Signal frequency of the ACC system | 76.5 gigahertz |
| Maximum braking effect of the ACC when compared to the maximum total braking effect | 25 % |
COMPONENTS
The adaptive cruise control (ACC) has many control modules which are interlinked with the individual vehicle systems.
These control modules communicate with each other via the different bus versions. The data bus on board diagnostic interface -J533-, which is connected to all the different bus versions, processes the data and sends it to the control module.
The control modules in the illustration are needed for the ACC to work. The control modules marked with a black dot are responsible for the core function. The other control modules are responsible for transmitting faults and for switching off the ACC. These control modules provide the visual and acoustic display for information and fault.
Scheme 181
- Distance Regulation Control Module -J428
- Engine Control Module -J623
- Transmission Control Module -J217- (optional)
- Airbag Control Module -J234
- Data Bus On Board Diagnostic Interface -J533
- Front Information Display Control Head -J685
- Front Information Display Control Head Control Module -J523
- Multimedia Control Head -E380
- Towing Recognition Control Module -J345- (optional)
- Comfort System Central Control Module -J393
- Vehicle Electrical System Control Module -J519
- Steering Column Electronic Systems Control Module -J527- /Steering Angle Sensor -G85
- Cruise Control Switch -E45
- Instrument Cluster Control Module -J285
- Steering Angle Sensor -G85
- Electromechanical Parking Brake Control Module -J540
- Active Steering Control Module -J792- (optional)
- ABS Control Module -J104
Note. Some control modules are optional, therefore only the control modules necessary for the ACC are installed.
Interlinking via the bus system. The wiring diagram shows the different bus versions and how the components are interlinked with each other.
| Pink | CAN chassis |
|---|---|
| Orange | CAN drive |
| Gray | CAN extended |
| Green | MOST Bus |
| Yellow | CAN comfort |
| Black | CAN diagnosis |
Sensor Information to the Individual Control Modules
The ACC also uses various sensors which provide information to the control modules.
| Component | Designation |
|---|---|
| G17 | Outside air temperature sensor |
| G44 | Right rear ABS wheel speed sensor (AWD vehicles only) |
| G45 | Right front ABS wheel speed sensor |
| G46 | Left rear ABS wheel speed sensor (AWD vehicles only) |
| G47 | Left front ABS wheel speed sensor |
| G85 | Steering angle sensor |
| G202 | Rotation rate sensor |
| G259 | Right adaptive cruise control sensor |
INFORMATION EXCHANGE
The exchange of data between the distance regulation control module -J428- and the other control modules is partially direct and partially indirect. If a direct exchange of the information does not take place, then the engine control module -J623- will send the status bit string to the distance regulation control module, which stores relevant information for the operating.
| Control Modules that Communicate Directly with the Distance Regulation Control Module | Control Modules that Communicate Indirectly with the Distance Regulation Control Module |
|---|---|
| Instrument Cluster Control Module -J285 | Front Information Display Control Head Control Module -J523 |
| Steering Column Electronic Systems Control Module -J527 | Comfort System Central Control Module -J393 |
| Access/Start Authorization Control Module -J518 | Transmission Control Module -J217- (only with automatic transmission) |
| Towing Recognition Control Module -J345- (only with trailer hitch) | Airbag Control Module -J234 |
| Steering Angle Sensor -G85 | Electromechanical Parking Brake Control Module -J540 |
| ABS Control Module -J104 | Active Steering Control Module -J792- (only with active steering) |
| Engine Control Module -J623 |
Overview of the different signals which are transmitted either directly or indirectly from the control modules to the distance regulation control module.
| Engine Control Module -J623 | Engine RPM Brake lamp switch position Engine control module operating condition Accelerator pedal signal |
|---|---|
| Transmission Control Module -J217 | Selector lever position Transmission emergency brake Transmission information |
| Steering Column Electronic Systems Control Module -J527 | Error messages Operating lever signals |
| Vehicle Electrical System Control Module -J519 | Windshield wiper function status Turn signal status Outside temperature |
| Towing Recognition Control Module -J345 | Brake lamp status |
| Steering Angle Sensor -G85 | Steering wheel angle |
| ABS Control Module -J104 | ASR/MSR/ESP ESP passive Wheel speed Gear speed/rotation direction Brakes are overheating Brake pressure Error messages Switch over, vehicle speed between FWD/AWD |
| Comfort System Central Control Module -J393 | Brake lamp status Key number for the remote key |
| Front Information Display Control Head Control Module -J523 | Show the status Change, standard setting (user request) |
| Instrument Cluster Control Module -J285 | Error messages Displayed speed Country |
Overview of the signal that are transmitter either directly or indirectly from the distance regulation control module to the control modules.
| Distance Regulation Control Module -J428 | Adaptive cruise control operating status Specified acceleration (in the deceleration case, negative) Permissible deviation Request instrument cluster displays, illumination and gong Forced activation ESP Standard setting (gong, time gap) |
EXPLANATION OF TERMS AND ABBREVIATIONS
| ABS | The Anti-Lock Braking System prevents the wheels from locking up when the brakes are applied. |
|---|---|
| ACC | The Adaptive Cruise Control is part of the cruise control system and maintains the appropriate distance to the vehicle in front within certain system limitations |
| ASR | Anti-Slip Regulation keeps the wheels from spinning when accelerating. When driving at full acceleration or poor ground conditions such as ice, snow, gravel or wet pavement (poor traction), one or more wheel could start to spin and the vehicle will pull to the side. |
| CAN | Controller Area Network is a serial data bus having a transmission rate of up to 1, 000, 000 bits. |
| ESP | Electronic Stabilization Program increases the control over the vehicle in a dynamic situations. |
| GRA (Cruise Control) | Cruise Control is an electronic system that controls the vehicle speed. |
| MSR | Engine Drag Control prevents the drive wheels from slipping when the driver either reduces the acceleration too quickly or downshifts when driving on a slippery surface. |
| MMI | The Audi MultiMedia Interface uses integrated controls to operate the vehicle systems and the Infotainment system. |
| RADAR | RADAR is the acronym for Radio Detection and Ranging and the designation for various detection and ranging methods and equipment based on electromagnetic wave within a radio frequency range. |
GENERAL INFORMATION, COMPONENTS
The following components are needed in order to have Open Road Cruise Control Function.
- Distance Regulation Control Module -J428
- Engine Control Module -J623
- Cruise Control Switch -E45
- Instrument Cluster Control Module -J285
- ABS Control Module -J104
- ABS Wheel Speed Sensors -G44, G45, G46, G47
FUNCTION DESCRIPTION
The driver activates the control and accelerates until the specified speed is reached, then pushed the SET button on the cruise control switch.
The ABS control module calculates the number of pulses from the speed sensors and sends this information to the instrument cluster/chassis CAN.
The instrument cluster control module needs to know the number of pulses in order to calculate the speed.
The distance regulation control module reads the speed signal, which the instrument cluster control module has sent to the chassis CAN. From that it calculates the acceleration necessary to maintain the previously set speed, and then sends this information to the engine control module.
Should the actual speed be different from the specified speed, the distance regulation control module will recognize this difference and will send a newly calculated specified acceleration to the engine control module.
The engine control module determines if it should increase or decrease the amount of fuel injected in order reach the specified acceleration or if it should activate the brakes (performed by the ABS control module).
SERVICE INFORMATION
If the engine control module was replaced, then the cruise control system must be coded.
The distance regulation control module -J428- works the same way as the radar principle.
Scheme 182
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.
Scheme 183
This is necessary to determine 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
Scheme 184
Scheme 185
Scheme 186
Scheme 187
- 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.
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. Refer to WHEELS, TIRES, WHEEL ALIGNMENT
- Applying the brakes will deactivate the distance control immediately.
- Pressing the clutch for more than 20 seconds also deactivates the distance control.
See also:
• WHEELS, TIRES, WHEEL ALIGNMENT