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Cruise control (CC), function - GF30.30-P-0001RF

Model 205, 253 

Fig 1: Cruise Control (CC) Function Diagram
G10132883Courtesy of MERCEDES-BENZ USA

Function requirements, general 

Cruise control - general 

The cruise control regulates the vehicle speed constantly and automatically to the desired speed set by the driver. To do this, the cruise control evaluates the driver's commands and the current driving condition.

For vehicles with CODE 239 (DISTRONIC PLUS), function-related requests are transmitted via chassis FlexRay to the Electronic Stability Program control unit by the DISTRONIC electric controller unit or by the radar sensors control unit on vehicles with CODE 266 (DISTRONIC PLUS with Steer Assist and Stop & Go Pilot). The Electronic Stability Program control unit processes these and prioritizes them according to the respective own evaluated parameters.

CC operation 

Fig 2: Identifying Cruise Control Components
G10132884Courtesy of MERCEDES-BENZ USA

The cruise control is activated using the resume from memory switch. Here the last stored or momentary vehicle speed is set as the set speed.

The target speed can be altered in steps of v = 1 km/h or v = 10 km/h using the "decelerate and set" switch and the "accelerate and set" switch.

Actuation up to the actuation point increases the set speed by v = 1 km/h. When actuating beyond the over-center preload, the specified speed is altered in increments of v = 10 km/h. If the switch is held on or beyond the over-center preload then the specified speed is altered in increments of t = 0.6 s.

The following input factors are evaluated to implement the function: 

Operating condition for engine/drivetrain:

The CDI control unit or the ME-SFI [ME] control unit transmits the "Engine running" or "Drivetrain operational" signal via drive train CAN, powertrain control unit and chassis FlexRay to the Electronic Stability Program control unit and for vehicles with CODE 239 (DISTRONIC PLUS) also to the DISTRONIC electric controller unit or on vehicles with CODE 266 (DISTRONIC PLUS with Steer Assist and Stop & Go Pilot) to the radar sensors control unit.

IMPORTANT Model 205.047/147/247

The CDI control unit or the ME-SFI [ME] control unit, amongst other things, coordinates acceleration, deceleration or switching requirements. In doing so it prioritizes requests according to their relevance, while taking account of the additional variables such as the charge level of the high voltage on-board electrical system, the operating condition of the ancillaries or requests from the comfort systems such as the AAC.

Engaged gear range (transmission 722, 724, 725):

Information about the engaged gear range is transmitted by the fully integrated transmission control unit via drive train CAN, powertrain control unit and chassis FlexRay to the Electronic Stability Program control unit and for vehicles with CODE 239 (DISTRONIC PLUS) also to the DISTRONIC electric controller unit or on vehicles with CODE 266 (DISTRONIC PLUS with Steer Assist and Stop & Go Pilot) to the radar sensors control unit.

Vehicle speed:

The vehicle speed is calculated from the wheel speed signals. The Electronic Stability Program control unit directly reads in the wheel speed signals.

For vehicles with code 239 (DISTRONIC PLUS), the Electronic Stability Program control unit also transmits the wheel speed signals via chassis FlexRay to the DISTRONIC electric controller unit.

For vehicles with code 266 (DISTRONIC PLUS with Steer Assist and Stop & Go Pilot), the Electronic Stability Program control unit transmits wheel speed signals via the chassis FlexRay to the radar sensors control unit.

Driver request via the cruise control lever:

The steering column tube module control unit transmits the control signals of the CRUISE CONTROL lever via chassis FlexRay to the Electronic Stability Program control unit and for vehicles with CODE 239 (DISTRONIC PLUS) also to the DISTRONIC electric controller unit or for vehicles with CODE 266 (DISTRONIC PLUS with Steer Assist and Stop & Go Pilot) to the radar sensors control unit.

Accelerator pedal position:

The CDI control unit or the ME-SFI [ME] control unit transmits information about the accelerator pedal position via drive train CAN, powertrain control unit and chassis FlexRay to the Electronic Stability Program control unit and for vehicles with CODE 239 (DISTRONIC PLUS) also to the DISTRONIC electric controller unit or for vehicles with CODE 266 (DISTRONIC PLUS with Steer Assist and Stop & Go Pilot) to the radar sensors control unit.

The following initial parameters (requests) are issued to implement the function: 

Raise/reduce engine torque:

For vehicles without code 239 (DISTRONIC PLUS) and without code 266 (DISTRONIC PLUS with Steer Assist and Stop & Go Pilot), the Electronic Stability Program control unit evaluates the input factors and other driving dynamic requests and transmits the "Increase engine torque" or "Decrease engine torque" request via chassis FlexRay, powertrain control unit and engine CAN to the CDI control unit or the ME-SFI [ME] control unit.

The "Increase engine torque" or "Reduce engine torque" request is transmitted via chassis FlexRay to the Electronic Stability Program control unit by the DISTRONIC electric controller unit on vehicles with CODE 239 (DISTRONIC PLUS) or by the radar sensors control unit on vehicles with CODE 266 (DISTRONIC PLUS with Steer Assist and Stop & Go Pilot). The Electronic Stability Program control unit processes this and transmits it according to its priority via the chassis FlexRay, powertrain control unit and engine 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.

Engage targeted gear (downshift or upshift) (transmission 722, 724, 725):

On vehicles except CODE 239 (DISTRONIC PLUS) and except CODE 266 (DISTRONIC PLUS with Steer Assist and Stop & Go Pilot), the Electronic Stability Program control unit evaluates the input factors and other driving dynamic requests and transmits the "Engage targeted gear" request via chassis FlexRay, powertrain control unit and drive train CAN to the fully integrated transmission control unit.

The "Engage targeted gear" request is transmitted via chassis FlexRay to the Electronic Stability Program control unit by the DISTRONIC electric controller unit on vehicles with CODE 239 (DISTRONIC PLUS) or by the radar sensors control unit on vehicles with CODE 266 (DISTRONIC PLUS with Steer Assist and Stop & Go Pilot). The Electronic Stability Program control unit processes this and transmits it according to its priority via the chassis FlexRay, powertrain control unit and drive train CAN to the fully integrated transmission control unit.

This request is to be understood as a shift recommendation.

Downshifting or upshifting of the automatic transmission takes place autonomously by the fully integrated transmission control unit dependent on the current operating condition.

Raise/reduce braking torque:

On vehicles except CODE 239 (DISTRONIC PLUS) and except CODE 266 (DISTRONIC PLUS with Steer Assist and Stop & Go Pilot), the Electronic Stability Program control unit evaluates the input factors and actuates the traction system hydraulic unit correspondingly.

The "Increase braking torque" or "Reduce braking torque" request is transmitted via chassis FlexRay to the Electronic Stability Program control unit by the DISTRONIC electric controller unit on vehicles with CODE 239 (DISTRONIC PLUS) or by the radar sensors control unit on vehicles with CODE 266 (DISTRONIC PLUS with Steer Assist and Stop & Go Pilot). The Electronic Stability Program control unit evaluates these and actuates the traction system hydraulic unit appropriately.

The traction system hydraulic unit reacts by increasing or reducing the braking torque.

IMPORTANT For model the kinetic energy is converted within defined limits into electrical energy (regenerative braking). If the required braking torque exceeds the deceleration through regenerative braking, the regenerative braking system control unit also actuates Electronic Stability Program control unit and the traction system hydraulic unit and therefore the service brake.

Cruise control encompasses the following subfunctions:

Additional automatic speed control function requirements 

Function sequence for automatic speed control 

Through actuation of the "Resume from memory" switch the last set speed stored is applied, provided a set speed was stored since the last engine start. If no set speed was stored, the current vehicle speed is set as the set speed. The target speed is displayed in the multifunction display of the instrument cluster.

On vehicles except CODE 239 (DISTRONIC PLUS) and except CODE 266 (DISTRONIC PLUS with Steer Assist and Stop & Go Pilot), the Electronic Stability Program control unit transmits the set speed (target speed) via chassis FlexRay, electronic ignition lock control unit and user interface CAN to the instrument cluster.

The set speed (target speed) is transmitted to the instrument cluster via chassis FlexRay, electronic ignition lock control unit and user interface CAN by the DISTRONIC electric controller unit for vehicles with CODE 239 (DISTRONIC PLUS) or by the radar sensors control unit for vehicles with CODE 266 (DISTRONIC PLUS with Steer Assist and Stop & Go Pilot).

IMPORTANT The driver also has the option to accelerate beyond the set target speed through actuation of the accelerator pedal (for example when overtaking). The set speed is regulated again after removal of the acceleration request (releasing the accelerator pedal).

The following activities are started in order to reach or maintain the set speed:

The following events deactivate the automatic speed control:

Function sequence for SPEEDTRONIC 

The SPEEDTRONIC comprises the following subfunctions:

Additional function requirements for variable SPEEDTRONIC (without code 494 (USA version)) 

Function sequence for variable SPEEDTRONIC (except code 494 (USA version)) 

The variable SPEEDTRONIC can be used to limit the vehicle's maximum speed to a freely selectable value (e.g. v = 50 km/h in urban traffic). The driver can accelerate the vehicle up to the set limit.

If the set limit was reached, the following activities are started:

IMPORTANT If switching takes place on the variable SPEEDTRONIC on the CC lever, the automatic speed control is deactivated.

The following events deactivate the variable SPEEDTRONIC:

Function sequence for permanent limiter 

The maximum speed of the vehicle can be limited in steps of v = 10 km/h from v = 160 to 240 km/h. Adjustment of the maximum speed takes place in the menu "Settings", "Vehicle" and "Limitation (winter tires)" in the instrument cluster.

On vehicles except CODE 239 (DISTRONIC PLUS) and except CODE 266 (DISTRONIC PLUS with Steer Assist and Stop & Go Pilot), the instrument cluster transmits the selected maximum speed via user interface CAN, electronic ignition lock control unit and chassis FlexRay to the Electronic Stability Program control unit. For vehicles with code 239 (DISTRONIC PLUS), the instrument cluster transmits the set maximum speed via user interface CAN, electronic ignition lock control unit and chassis FlexRay to the DISTRONIC electric controller unit.

On vehicles with CODE 266 (DISTRONIC PLUS with Steer Assist and Stop & Go Pilot), the instrument cluster transmits the selected maximum speed via user interface CAN, electronic ignition lock control unit and chassis FlexRay to the radar sensors control unit.

Approximately v = 10 km/h before reaching the set maximum speed a message appears in the instrument cluster multifunction display that indicates a maximum speed limitation. The driver can accelerate the vehicle up to the set maximum speed.

If the set maximum speed is reached, the following activities are started:

Electrical function schematic for cruise control (CC) Model 205 except code 239 (DISTRONIC PLUS) except code 266 (DISTRONIC PLUS with Steer Assist and Stop & Go Pilot) PE30.30-P-2051-97FBA 
Electrical function schematic for cruise control (CC) Model 205 with code 239 (DISTRONIC PLUS) Model 205 with code 266 (DISTRONIC PLUS with Steer Assist and Stop & Go Pilot) PE30.30-P-2051-97FBB 
Overview of system components for driver assistance systems   GF54.00-P-9998RF
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