System functions

The system functions of the Active Cruise Control option are described below:

• Monitor object ahead
• Cruise control
• Lens heating
• Low-voltage cutout and high-voltage protection for ACC sensor
• Self-diagnosis and compensation for minor horizontal adjustments
• Influence on the dynamics in connection with a navigation system
• System limits

  Monitor object ahead 

  Objects are all vehicles in the same lane. The vehicles on other lanes are of no interest for the Active Cruise Control option.

  In the same lane, the vehicle immediately ahead is selected as the object.

  With the calculated expected same lane, the lateral deviation of each monitored object to the same lane can be determined.

  The radar waves received cannot distinguish between animals, vehicles and traffic signs. In order to prevent incorrect reactions, stationary objects and traffic in the other direction are ignored in the distance control.

  Cruise control 

  The Active Cruise Control option differentiates between 2 driving conditions:

  • Cruise control with specified set speed 

    A selected set speed (in the range 30 km/h - 180 km/h) is automatically maintained on open roads without vehicles driving ahead.

  • Cruise control with speed adapted to that of vehicle driving ahead 

    If a slower vehicle is detected on the vehicle's own track, the vehicle's own speed will be adapted to that of the vehicle driving ahead

    At the same time, a distance from this vehicle preset by the driver is established (4 fixed, timed separations can be selected).

    The timed separation from a vehicle driving ahead is no less than 1 second under stationary conditions. In certain conditions (e.g. when a vehicle cuts in a short distance ahead), this timed separation may briefly be less than 1 second.

Lens heating 

The lens of the ACC sensor is made of plastic. The built-in lens heating ensures better availability of the Active Cruise Control option in winter weather conditions.

The lens heating is activated by the ACC sensor. The heating is controlled via a pulse-width modulated signal (PWM signal). The heating coil is integrated into the lens of the ACC sensor

The lens heating is only activated within a certain ambient temperature range (approx. +5 °C to -5 °C).

Reason: Only at temperatures around zero is snow wet or moist. At temperatures well below this, snow will be dry. To prevent snow from thawing on the lens and creating an artificial coating, the heating is switched off below a certain ambient temperature. The current ambient temperature value is transmitted by the instrument cluster.

• Conditions for activation 
  • Engine ON
  • ACC ON
  • Ambient temperature between -5 °C and +5 °C
• Safety cutout 
  • Temperature in ACC sensor over 50 °C

    (measured by interior temperature sensor in ACC sensor control unit)

  • Voltage greater than 16 volts

  The safety cutout shuts down the lens heating. The Active Cruise Control option remains activated. (No fault memory entry)

• Monitoring 

  The lens heating is monitored for open and short circuits in the heating coil.

  If the monitoring reports a fault, the Active Cruise Control option will be shut down. (Fault memory entry)

Low-voltage cutout and high-voltage protection for ACC sensor 

The ACC sensor works with a supply voltage of 9 to 16 volts.

• Low-voltage cutout 

  If the on-board supply voltage drops below about 9 volts, the ACC sensor will perform a low-voltage cutout and a fault memory entry will be stored.

  The ACC sensor will be reactivated when the on-board supply voltage exceeds 9.8 volts again.

• Overvoltage protection 

  If the on-board supply voltage exceeds about 17.5 volts, the ACC sensor will perform a cutout with a fault memory entry.

  The ACC sensor will be reactivated when the on-board supply voltage drops below 17.0 volts again.

Self-diagnosis and compensation for minor horizontal adjustments 

External forces may change the alignment of the ACC sensor. A horizontal change leads to function limitations. (Function limitations encountered are, e.g.: reaction to vehicles in the next lane or late reaction to vehicles in the same lane).

Self-diagnosis allows the ACC sensor to compensate for minor horizontal adjustments of up to 1°.

If a horizontal adjustment of more than 1° is detected, the Active Cruise Control option will be deactivated and a fault will be stored in the fault memory. A check control message will be issued.

Influence on the dynamics in conjunction with a navigation system 

If the Active Cruise Control is coupled with a navigation system, this may have an influence on the dynamics. (Only possible in combination of CCC with the Professional navigation system option 609.)

Navigation systems provide additional information, such as the course of the road and the road category.

The road category is split up as follows:

• Motorways and well finished fast roads

  (faster acceleration)

• Main roads and highways

  (average acceleration)

• Urban driving

  (reduced acceleration)

On motorways and well finished fast roads, Active Cruise Control is expected to be highly dynamic. In other words, faster acceleration if the driving mode changes from following a car ahead to clear road ahead. The set speed is adjusted quickly.

On main roads and highways, Active Cruise Control is expected to be averagely dynamic. In other words, comfortable acceleration if the driving mode changes from following a car ahead to clear road ahead. The set speed is adjusted with an average acceleration behavior.

During urban driving, a reserved dynamic is expected of the Active Cruise Control. In other words, reduced acceleration behavior if the driving mode changes from following a car ahead to clear road ahead. The set speed is adjusted moderately.

The often difficult traffic situations during urban driving make reduced acceleration behavior necessary.

In addition, the number of bends on the road ahead is analyzed and the dynamic of the Active Cruise Control adjusted accordingly.

System limits 

If the limit of the functional range is reached, the driver is prompted to act (brake or swerve).

During operation, the following system functions requiring explanation (for the driver) can occur due to the limits of the functional range:

• Limited range and deceleration: 
  • The range of the ACC sensor is limited (approximately 120 meters).

    Rain, snow and fog absorb radar waves.

    This will significantly reduce the range of the ACC sensor.

  • The Active Cruise Control option is only able to effect limited deceleration via the DSC (dynamic stability control) (a maximum of 2.5 m/s 2; E65, E66: a maximum of 2.0 m/s2). This means that cruise control is only able to compensate for a limited relative speed.

  Operation of the Active Cruise Control is only possible in flowing traffic in a road speed range from 30 km/h to 180 km/h.

• Lateral monitoring range 

  The lateral monitoring range of the ACC sensor is limited, meaning that a monitored vehicle ahead could be lost due to a tight bend.

  In such cases, cruise control will not accelerate to the set speed for approximately 2 seconds. This will prevent the vehicle from accelerating too close to the vehicle ahead, which is possibly only briefly not being monitored.

  When driving straight ahead, this can cause a delayed reaction to another vehicle cutting in close in front.

  The vehicle cutting in will not be monitored by the cruise control until it is clearly in the same lane as the vehicle with the Active Cruise Control option.

• Display for monitored vehicle does not light up, the vehicle remains below the set speed and does not accelerate further. 

  Causes:

  • On sharp bends, the vehicle's speed will be controlled in such a way that lateral acceleration does not exceed a maximum of 4.0 m/s 2 to maintain driving comfort.
• Timed separation less than 1 second 

  The timed separation from a vehicle driving ahead is no less than 1 second in the adjusted status. In certain conditions (e.g. when a vehicle cuts in a short distance ahead), this timed separation may briefly be less than 1 second.

  If the deceleration induced by the cruise control is not sufficient, the driver will have to intervene directly.

• ACC sensor blind 

  If the ACC sensor is blinded, the Active Cruise Control option shuts down. (Blinding, e.g. due to extremely heavy snowfall, through a layer of ice on the sensor or through dirt)

  Cruise control can be reactivated after the ACC sensor has been cleaned.

• Bends cannot be detected in an anticipatory manner 

  The cruise control is unable to work in an anticipatory manner when the vehicle is cornering. It is only able to react to existing lateral acceleration when it is already on the bend. For this reason, the driver is responsible for ensuring that an appropriate speed is being driven as the vehicle enters the bend.

• Active Cruise Control deactivated after DSC intervention or brake application by the driver 

  Cruise control will be deactivated following DSC intervention or a brake application by the driver. (DSC intervention in the sense of enhanced operating stability.)

  Cruise control will then have to be reactivated at the cruise control steering-column stalk.