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

MODEL 212 as of model year 2014 

Fig 1: Cruise Control Function Diagram

Courtesy of MERCEDES-BENZ USA

Cruise control function requirements 

The units and values for the speed shown in the text should be assigned to the possible national versions. The details in "miles per hour (mph)" refer to vehicles with a miles indicator.

• Engine running or drivetrain operational
• Gear range "D" engaged (for transmission 722.9, 724.2, 725)
• Vehicle speeds:
  • Vehicle speed v≥30 to 250 km/h (v≥20 to 150 mph) or up to the respective maximum speed according to the motorization of the vehicle (without code 233 (DISTRONIC PLUS) or for vehicles with code 233 (DISTRONIC PLUS) and deactivated distance control)
  • Vehicle speed v≥30 up to 200 km/h (v≥20 up to 120 mph) (with code 233 (DISTRONIC PLUS) and activated distance control)

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.

The CC function is implemented dependent on the model and the equipment by the following control unit:

• Electronic Stability Program control unit (model 212 (except model 212.074/075/076/092/095/098/274/275/276/292/298) except CODE 233 (DISTRONIC PLUS))
• Regenerative braking system control unit (model 212.095/098/298)
• Premium Electronic Stability Program control unit (model 212 (except 212.095/098/298) with code 233 (DISTRONIC PLUS), model 212.074/075/076/092/274/275/276/292)

For vehicles with code 233 (DISTRONIC PLUS) transmits the radar sensors control unit function-relevant requests via the chassis FlexRay, chassis gateway control unit and chassis CAN 1 to the Electronic Stability Program control unit or the RBS control unit.

The Electronic Stability Program control unit or the regenerative braking system control unit processes these and prioritizes them according to the parameters evaluated for this purpose.

Operation of the CC function over the CC lever 

Fig 2: CC Lever Function Diagram

Courtesy 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.

Using the switches decelerate and fix in place and the switches accelerate and set, the set speed can be altered in Operation steps of v = 1 km/h (1 mph) or v = 10 km/h (5 mph).

Actuation up to the actuation point increases the set speed by v = 1 km/h (1 mph). If the switch is pressed beyond the actuation point then the set speed increases each time by v = 10 km/h (5 mph). If the switch is held at or beyond the actuation point the set speed is then altered every t = 0.6 s.

The following input factors are evaluated to implement the CC function:

• Signal "Engine running" or "Drivetrain operational" (function requirements)
• Engaged gear range (with transmission 722.9, 724.2, 725) (function requirements)
• Vehicle speed
• Driver request via the cruise control lever
• Accelerator pedal position

"Engine running" or "Drivetrain operational" signal:

The signal "Engine running" or "Drivetrain operational" is sent by the CDI control unit or ME-SFI [ME] control unit via chassis CAN 1 to the Electronic Stability Program control unit or the RBS control unit. For vehicles with code 233 (DISTRONIC PLUS) the CDI control unit or the ME-SFI [ME] control unit also transmits the signal via the chassis CAN 1, chassis gateway control unit and chassis FlexRay to the radar sensors control unit.

All acceleration, deceleration or switching requests are coordinated by the CDI control unit or the ME-SFI [ME] control unit. The CDI control unit or the ME-SFI [ME] control unit prioritizes the requests, in line with their relevance, taking additional variables into account such as the charge level of the high-voltage battery (A100g1), the operating condition of the ancillaries or requests from comfort systems such as the automatic air conditioning.

Engaged gear range:

The fully integrated transmission control unit sends the information about the gear range via drive train CAN, CDI control unit or ME-SFI [ME] control unit and chassis CAN 1 to the Electronic Stability Program control unit or the RBS control unit.

For vehicles with code 233 (DISTRONIC PLUS) the fully integrated transmission control unit also transmits the information via the drive train CAN, CDI control unit or ME-SFI [ME] control unit, chassis CAN 1, chassis gateway control unit and chassis FlexRay to the radar sensors control unit.

Vehicle speed:

The vehicle speed is calculated by the Electronic Stability Program control unit or the regenerative braking system control unit using the wheel speeds.

For vehicles with code 233 (DISTRONIC PLUS) the Electronic Stability Program control unit or the RBS control unit or the RBS control unit sends the wheel speed signals as well as via the chassis CAN 1, the chassis gateway control unit and the chassis FlexRay to the radar sensors control unit.

Driver request via the cruise control lever:

The driver request over the CC lever are directly read in by the steering column tube module control unit. The steering column tube module control unit transmits the control signals from the CC lever via chassis CAN 1 to the Electronic Stability Program control unit or the RBS control unit.

For vehicles with code 233 (DISTRONIC PLUS) the steering column tube module control unit also sends the request via the chassis CAN 1, chassis gateway control unit and chassis FlexRay to the radar sensors control unit.

Accelerator pedal position:

Operation of the accelerator pedal is registered by the accelerator pedal sensor.

The CDI control unit or the ME-SFI [ME] control unit directly reads in the signals from the accelerator pedal sensor and transmits these via chassis CAN 1 to the Electronic Stability Program control unit or the RBS control unit.

For vehicles with code 233 (DISTRONIC PLUS) the CDI control unit or the ME-SFI [ME] control unit also transmits the signals via the chassis CAN 1, chassis gateway control unit and chassis FlexRay to the radar sensors control unit.

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

• Increase/reduce the drive torque
• Engage the targeted gear (downshift or upshift) (for transmission 722.9, 724.2, 725)
• Increase/reduce the braking torque

Increase/reduce the drive torque

The Electronic Stability Program control unit or the RBS control unit evaluates the input factors as well as further driving dynamics requests and sends the request "Increase/reduce drive torque" via chassis CAN 1 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. For vehicles with code 233 (DISTRONIC PLUS) the radar sensors control unit transmits the request "increase/reduce drive torque" via the chassis FlexRay, chassis gateway control unit and chassis CAN 1 to the Electronic Stability Program control unit or the RBS control unit. The Electronic Stability Program control unit or the RBS control unit processes this, prioritizes this and transmits it according to its priority via chassis CAN 1 to the CDI control unit or the ME-SFI [ME] control unit.

Engage targeted gear (for transmission 722.9, 724.2, 725): The Electronic Stability Program control unit or the RBS control unit evaluates the input factors as well as further driving dynamics requests and sends the request "Engage targeted gear" via chassis CAN 1, CDI control unit or ME-SFI [ME] control unit and drive train CAN to the fully integrated transmission control unit. This request is however to be understood as a switching recommendation.

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

For vehicles with code 233 (DISTRONIC PLUS) the radar sensors control unit transmits the request "Engage targeted gear" via the chassis FlexRay, chassis gateway control unit and chassis CAN 1 to the Electronic Stability Program control unit or the RBS control unit.

Raise/reduce braking torque:

The Electronic Stability Program control unit or the regenerative braking system control unit evaluates the input factors and actuates the traction system hydraulic unit accordingly. The traction system hydraulic unit reacts by increasing or reducing the braking torque. For vehicles with code 233 (DISTRONIC PLUS) the radar sensors control unit transmits the request "increase/reduce braking torque" via the chassis FlexRay, chassis gateway control unit and chassis CAN 1 to the Electronic Stability Program control unit or the RBS control unit.

The kinetic energy of the engine is converted into electrical energy over a generator (regenerative braking) within defined limits. If the required braking torque exceeds the deceleration through regenerative braking, then the regenerative braking system control unit also actuates the traction system hydraulic unit and therefore the service brake.

The cruise control function includes the following subfunctions:

• Function sequence for automatic speed control 
• Function sequence for SPEEDTRONIC 

Additional automatic speed control function requirements 

• Cruise control selected using SPEEDTRONIC switch (without code 494 (USA version) (SPEEDTRONIC LED off)
• Electronic Stability Program (ESP®) not passively switched (model 212 (except 212.074/075/076/092/274/275/276/292)
• ESP® not switched into "SPORT HANDLING MODE" (model 212.074/075/076/092/274/275/276/292.)

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 set speed is displayed in the speedometer. To do this, the Electronic Stability Program control unit or the RBS control unit sends corresponding information via chassis CAN 1, front SAM control unit and chassis CAN 2 to the instrument cluster.

For vehicles with code 233 (DISTRONIC PLUS), the radar sensors control unit transmits this information via the chassis FlexRay, chassis gateway control unit and chassis CAN 2 to the IC.

The following events deactivate the automatic speed control:

• Operation of the OFF switch
• Depressing the brake pedal
• Active regulation of the ESP®
• Speed v < 25 km/h (v < 17 mph)
• Gear range is not "D" (for transmission 722.9, 724.2, 725)

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

• Increase/reduce the drive torque
• Engage the targeted gear (downshift or upshift) (for transmission 722.9, 724.2, 725)
• Increase/reduce the braking torque

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).

Function sequence for SPEEDTRONIC 

The SPEEDTRONIC comprises the following subfunctions:

• Function sequence for variable SPEEDTRONIC (without code 494 (USA version)) 
• Function sequence for permanent limiter 

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

• Variable SPEEDTRONIC selected with SPEEDTRONIC switch (SPEEDTRONIC LED lights up)
• ESP® not passively engaged (model 212 (except 212.074/075/076/092/274/275/276/292))
• ESP® not switched into "SPORT HANDLING MODE" (model 212.074/075/076/092/274/275/276/292.)
• No "Kickdown" recognized

Function sequence for variable SPEEDTRONIC (without code 494 (USA version)) 

The maximum speed of the vehicle can be limited at any time to a freely selectable value (e.g. 50 km/h (31 mph) in urban traffic) via the variable SPEEDTRONIC. The driver can accelerate the vehicle up to the set limit.

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

• Reduce drive torque
• Engage targeted gear (shift down) (for transmission 722.9, 724.2, 725)
• Raise braking torque

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:

• Operation of the OFF switch
• Kickdown (accelerator pedal pressed by >90% and vehicle speed v <20 km/h (v < 12 mph) away from selected maximum speed)

Function sequence for permanent limiter 

The maximum speed of the vehicle can be limited in operation steps of v = 10 km/h or 5 mph from v = 160 to 240 km/h or v = 100 mph to 150 mph. Adjustment of the maximum speed takes place in the menu "Settings", "Vehicle" and "Limitation (winter tires)" in the instrument cluster. The instrument cluster sends the set maximum speed via chassis CAN 2, the front SAM control unit and chassis CAN 1 to the Electronic Stability Program control unit or the regenerative braking system control unit.

For vehicles with code 233 (DISTRONIC PLUS) the IC transmits the set maximum speed via chassis CAN 2, chassis gateway control unit and chassis FlexRay to the radar sensors control unit.

At about v = 10 km/h (v = 5 mph) before reaching the set maximum speed a message appears in the multifunction display which indicates limitation of the maximum speed. The driver can accelerate the vehicle up to the set maximum speed.

If the maximum speed was reached the following activities are started:

• Reduce drive torque
• Engage targeted gear (shift down) (for transmission 722.9, 724.2, 725)
• Reduce braking torque