Cruise Control: Description and Operation
Adaptive Cruise Control (ACC)
General Information
- ACC optional, only available with Porsche Doppelkupplung (PDK)
- ACC is based on the standard cruise control functionality (cruise control = maintaining a constant speed)
- ACC controls speed and distance by activating brakes & engine
- The ACC control unit is connected to the gateway via CAN crash risks and communicates via: CAN drive, CAN chassis, CAN comfort and CAN MMI
Adaptive cruise control (ACC) control unit.
The ACC control unit is connected to the vehicle electrical system voltage via terminal 15 and is therefore only active when the ignition is switched on.
The radar sensor includes four antennas, which scan the area in front of the vehicle. The antennas are integrated into the housing of the ACC control unit and have a transmitter and receiver frequency of 76.5 GHz. Objects that are moving in the direction of travel reflect the emitted radar waves back to the sensor's antennas. Stationary objects are ignored. Vehicles that change lane are also detected.
ACC Topology
ACC Distance Regulation Function
The distance between the vehicle with ACC and the vehicle in front can be set in four intervals using the operating lever. These intervals are 1.0, 1.25, 1.75 and 2.25 seconds. If you multiply this time value by the current speed, the result is the distance between the ACC vehicle and the one in front.
If there is no vehicle in front, the ACC vehicle is in automatic acceleration (cruise control) mode. The regulator is located in the ACC control unit and not in the engine control unit as in vehicles with conventional cruise control.
If a vehicle in front enters the detection area of the ACC vehicle (changes lane), the ACC vehicle enters into tracking mode. The tracking regulator (in the ACC control unit) manages engine control unit requests via a coupling interface and PSM requests via an acceleration interface.
Operating Principle
In terms of functionality, adaptive cruise control (ACC) is based on the conventional cruise control principle. A distance regulator is superimposed on the cruise control, i.e. if the system does not detect a vehicle in front, the desired speed is set. If a vehicle is detected in front, the ACC attempts to keep the time gap with this vehicle as constant as possible. The distance is measured via a radar sensor. The brakes and engine are used as drive links. The driver can use an operating lever to change the desired speed and time gap with respect to the vehicle in front and also to accelerate and decelerate.
Designed as a comfort system, the ACC function supports the driver, particularly on multi-lane highways, in congested traffic and in the event of road construction or speed restrictions. Automatically adapting the vehicle speed to the speed of the vehicle in front increases versatility and comfort compared with a conventional cruise control system. The driver is incorporated into the ACC system's control loop by means of the appropriate controls and displays and if necessary is clearly requested to assume control of the vehicle speed.
Activating ACC
In automatic acceleration mode, the adaptive cruise control maintains any selected speed between approx. 19 and 130 mph (30 and 210 km/h) without the driver having to use the accelerator. If a vehicle travelling slower than the selected speed is detected in the same lane, the adaptive cruise control automatically maintains a specific distance. The adaptive cruise control applies the brakes if the distance between it and the vehicle in front is too small and accelerates if the distance increases.
The ACC function includes full cruise control functionality and is activated by pressing on the "ACC on/off" button on the bottom left operating lever of the combined steering column module (CSCM). The ACC system behaves like a cruise control system if no vehicle is detected in front. Once a vehicle has been detected in front, the ACC system enters into distance regulation mode.
The speed that can be set by the driver ranges from 19 to 130 mph (30 to 210 km/h). ACC is active in the speed range from 0 to 130 mph (210 km/h). If necessary, ACC applies the brakes until the vehicle comes to a stop.
Deactivating ACC
- On/Off switch
- PSM switched off
- Brake pedal pressed
- Accelerator pedal pressed (no control), accelerator pedal released, automatic ACC control
- No forward gear engaged
- Electric parking brake (EPB) pressed
- Door open
- Driver's seat belt not fastened
ACC is deactivated under the following individual conditions:
The off switch on the operating lever is set to "OFF", the brake pedal is pressed. A CAN signal from the PSM control unit is communicated to the ACC. The accelerator pedal is pressed, e.g. when passing. The automatic control system is disabled, automatic braking is discontinued. Once the accelerator pedal is released, ACC automatically takes control again. No forward gear is engaged, EPB is pressed, specific deactivation if a door is open or the driver's seat belt is not fastened. ACC applies the brakes until the vehicle comes to a stop. However, the vehicle is not held stationary and ACC is deactivated two seconds after the vehicle comes to a stop.
Adaptive cruise control is not available:
- When the ignition is switched off
- When PSM is switched off
- When the driver's door is opened and the seat belt on the driver's side has not been taught
- When large steering wheel movements are made, e.g. when parking or manoeuvring
- When the Porsche Doppelkupplung (PDK) selector lever position is N
- When uphill or downhill gradients are greater than 20%
If one of these situations arise while adaptive cruise control is switched on, it is switched off. A corresponding message will then appear on the multi-function display.
ACC Detects the Following Obstacles
- Only moving objects (no stationary obstacles)
- Almost all standard road vehicles that can drive faster than the ACC minimum speed, e.g.:
- Passenger vehicles
- Light/heavy utility vehicles/semi truck/trailers
- Vehicles with trailers
- Buses/RVs
- Motorcycles
The radar sensor of the adaptive cruise control detects objects within a narrow, cone-shaped area in front of the vehicle. As a result, the detection of obstacles can be restricted. The system may brake too late or unexpectedly.
Staggered vehicles/vehicles cutting in.
If other vehicles are moving in and out of the ACC vehicle's lane, these vehicles will only be detected when they are fully in the relevant lane.
Vehicles with a small cross section/narrow vehicles.
Narrow or small vehicles are not detected or detected too late.
Entering or exiting a corner.
When entering or exiting a corner, vehicles are not detected or detected too early or the vehicle responds to vehicles in neighboring lanes.
Vehicles with large projections.
In the case of vehicles with oversized loads with large overhangs (e.g. lumber trucks), the end of the vehicle may not be detected correctly.
Setting the Distance
This is speed-sensitive and can be preselected in four stages. Adjustments are made using the rocker switch (Z) on the ACC operating lever. (Press downwards to decrease the distance/upwards to increase it.)
The distance (four bars in display) represent time intervals:
- Stage 1 = 1 second,
- Stage 2 = 1.25 seconds,
- Stage 3 = 1.75 seconds ~ half the speed reading,
- Stage 4 = 2.25 seconds.
In Stage 1 the vehicle tends to accelerate and brake more dynamically and more gently in the highest stage. When terminal 15 is off/on, the time gap corresponding to the statutory minimum distance (1.75 seconds) is preset by default or the driver preselects a personalized setting using the key.
NOTES:
- When adjusting the distance, the "ACC" main menu in the adaptive cruise control is displayed temporarily in the multi-function display.
- Increasing the distance - Move the rocker switch upwards. The distance is increased. The number of orange segments in the distance display increases.
- Decreasing the distance - Move the rocker switch downwards. The distance is decreased. The number of orange segments in the distance display decreases.
Feedback and Display
- Any braking intervention by the ACC is indicated to the vehicles behind by the brake lights.
- Vehicle passing (over take) requests are indicated visually to the driver (flashing) and acoustically via the instrument cluster (please brake, brake immediately).
- The passive or off status is indicated by the acronym displayed in ACC menu in the instrument cluster. The desired speed that is set (A) and a vehicle in front is displayed permanently to the driver in the instrument cluster (D).
- If a vehicle in front is detected and the distance with respect to this vehicle is adjusted, a vehicle symbol is displayed in the multi-function display. As described earlier, the distance is displayed in four stages.
The ACC system does not perform any safety functions and is therefore not a tool for preventing collisions, providing distance warnings, detecting the end of a tailback (no adjustment for stationary objects) for Stop & Go operation (no Full Speed Range (FSRA) ACC) and is not to be used where there is poor visibility (fog) or any kind of icy roads.
IMPORTANT: The driver maintains full responsibility for steering the vehicle at all times. Consequently, the driver can switch off the ACC distance regulator at any time (using the operating lever or by actuating the brake). If the situation is unclear, the driver must assume longitudinal control switch off ACC.
In cases where the system has detected that braking assistance is required from the driver, a red warning appears on the ACC screen with the instructions "over take" "Distance". An acoustic warning also sounds.
The corresponding warnings or instructions are displayed in the instrument cluster if the conditions for operating the ACC are not met, e.g. if there is an ABS or PSM intervention, or if the parking brake is pulled while driving. The system intervenes only to apply the brakes and completes the initiated braking manoeuvre before switching off. If required, the system can then be used again, provided the prerequisites for operating the ACC are met.
The corresponding warnings or instructions are displayed in the instrument cluster if the conditions for operating the ACC are not met, e.g. if there is an ABS or PSM intervention, or if the parking brake is pulled while driving. The system intervenes only to apply the brakes and completes the initiated braking manoeuvre before switching off. If required, the system can then be used again, provided the prerequisites for operating the ACC are met.
System and Multi-function Display Error Messages
ACC not available - Adaptive cruise control is not available, e.g. when manoeuvring.
ABS/PSM intervention - Adaptive cruise control was deactivated because of an ABS or PSM intervention.
Electric parking brake - Adaptive cruise control was deactivated because the electric parking brake was activated.
Selector lever position - Adaptive cruise control was deactivated because the Porsche Doppelkupplung (PDK) selector lever is not in position D or manual position M.
Not possible while stationary - Vehicle is stationary, e.g. while setting the desired speed.
Engine speed - Adaptive cruise control was deactivated because the engine speed limit was reached in manual position M of the Porsche Doppelkupplung (PDK) selector lever.
Gradient too steep - Uphill or downhill gradients greater than 20%: ACC cannot be enabled because the gradient of the road is too steep.
Stationary object - Operation is not possible because a stationary object was detected ahead.
PSM switched off - Adaptive cruise control is not available because PSM was switched off.
Diagnosis Setting
