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

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MODEL 212.0/2 up to 28.2.13

Cruise control function requirements

The units and values given in the following text for the speed must 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
Drive position "D" engaged (for transmission 722 or 724)
Vehicle speed v≥30 km/h (v20 mph) up to the top speed of the vehicle
Vehicle speed for an active distance control v ≥ 30 to 200 km/h (for code (v ≥ 20 to 120 mph) (for code (233) DISTRONIC PLUS)

Cruise control - general

The CC function automatically regulates the vehicle speed as constant at the speed specified by the driver.

To do this the CC function evaluates the operator requests of the driver 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 (N30/4) (model 212 (except 212.074/077/095/098/274/277/298) without code (233) DISTRONIC PLUS)
RBS control unit (N30/6) (model 212.098/095/298 without code (233) DISTRONIC PLUS)
Electronic Stability Program Premium control unit (N30/7) (model 212 (except 212.095/098/298) without code (233) DISTRONIC PLUS, model 212.074/077/274/277)
Radar sensors control unit (N62/1) (model 212 up to 31.5.10 for code (233) DISTRONIC PLUS)
Video and radar sensor system control unit (N62/2) (model 212 as of 1.6.10 for code (233) DISTRONIC PLUS)

In the following text the Electronic Stability Program control unit, the RBS control unit and the Electronic Stability Program Premium control unit are designated the brake system control unit.

For vehicles with code (233) DISTRONIC PLUS the radar sensors control unit or the video and radar sensor system control unit transmits function-relevant requests via the chassis CAN (CAN E) to the brake system control unit. The brake system control unit receives and processes these and prioritizes them according to the respective own evaluated parameters.

Operation of the CC function over the CC lever

Fig 1: CC Lever Function Diagram

Courtesy of MERCEDES-BENZ USA

The CC function is activated over 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 respective switch is actuated beyond the actuation point then the set speed increases each time by v = 10 km/h (5 mph).

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

Operating condition of engine/drivetrain (function requirements)
Vehicle speed
Engaged gear range (for transmission 722 or 724) (function requirements)
Driver request via the cruise control lever
Accelerator pedal position

If the switch is held at or beyond the over-center preload the set speed is altered every t = 0.6 s.

Operating condition of engine/drivetrain:

The CDI control unit (N3/9) (for a diesel engine) or the ME-SFI [ME] control unit (N3/10) (for a gasoline engine) transmits the signal "Engine running" or "Drivetrain operational" via the chassis CAN to the brake system control unit and for vehicles with code (233) DISTRONIC PLUS also to the radar sensors control unit or to the video and radar sensor system control unit.

Vehicle speed:

The vehicle speed is calculated on the basis of the wheel speeds.

The wheel speeds are recorded by the following components:

Left front axle rpm sensor (L6/1)
Right front axle rpm sensor (L6/2)
Left rear axle rpm sensor (L6/3)
Right rear axle rpm sensor (L6/4)

The signals from the rpm sensors are read in and evaluated by the brake system control unit.

For vehicles with code (233) DISTRONIC PLUS the brake system control unit transmits the information about the wheel speeds via the chassis CAN to the radar sensors control unit or to the video and radar sensor system control unit.

Engaged drive position:

The electronic transmission control unit (N15/3) (transmission 722.6) or the fully integrated transmission control unit (Y3/8n4) (722.9 or 724.2) transmits information about the gear range via the chassis CAN to the brake system control unit and for vehicles with code (233) DISTRONIC PLUS also to the radar sensors control unit or to the video and radar sensor system control unit.

Driver request via the cruise control lever

The driver requests made over the CC lever are read in directly by the steering column tube module control unit (N80). The steering column tube module transmits the control signals from the CC lever via the chassis CAN to the brake system control unit and for vehicles with code (233) DISTRONIC PLUS additionally to the radar sensors control unit or to the video and radar sensor system control unit.

Accelerator pedal position:

Operation of the accelerator pedal is registered by the accelerator pedal sensor (B37).

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 the chassis CAN to the brake system control unit and for vehicles with code (233) DISTRONIC PLUS additionally to the radar sensors control unit or to the video and radar sensor system control unit.

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

Increase/reduce engine torque
Engage targeted gear (back or upshift) (transmission 722 and 724)
Increase/reduce braking torque

Increase/reduce engine torque

The brake system control unit evaluates the input factors as well as further driving dynamics requests and transmits the request "increase/reduce engine torque" via the chassis 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.

For vehicles with code (233) DISTRONIC PLUS the radar sensors control unit or the video and radar sensor system control unit the transmit request "increase/reduce engine torque" via the chassis CAN to the brake system control unit.

Engage targeted gear (transmissions 722 and 724):

The brake system control unit evaluates the input factors as well as further driving dynamic requests and transmits the request "Engage targeted gear" via the chassis CAN, CDI control unit or ME-SFI [ME] control unit and drive train CAN (CAN C) to the transmission control unit.

This request is, however, to be understood as a switching recommendation. The back or upshift of the A/T tales place autonomously by the transmission control unit itself, dependent on the current operating condition.

For vehicles with code (233) DISTRONIC PLUS the radar sensors control unit or the video and radar sensor system control unit the transmit request "engage target gear" via the chassis CAN to the brake system control unit.

Increase/reduce braking torque

The brake system control unit evaluates the input factors and actuates the traction system hydraulic unit (A7/3) appropriately. 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 or the video and radar sensor system control unit the transmit request "increase/reduce brake torque" via the chassis CAN to the brake system control unit.

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 with SPEEDTRONIC switch (without code (494) USA version) (SPEEDTRONIC light-emitting diode not illuminated)
Electronic Stability Program (ESP®) not switched to passive mode

Function sequence for automatic speed control

Through actuation of the "Resume from memory" switch the last specified speed stored is applied, provided a specified speed was stored since the last engine start. If no specified speed was stored, the current vehicle speed is set as the specified speed. The set speed is displayed in the speedometer (A1p8).

To this end the brake system control unit (A1) sends corresponding information over the chassis CAN to the instrument cluster.

For vehicles with code (233) DISTRONIC PLUS the radar sensors control unit or the video and radar sensor system control unit transmits this information via the chassis CAN to the IC.

The following events deactivate the automatic speed control:

Operation of the OFF switch
Depressing the brake pedal
Actuation of the clutch pedal (for transmission 711 and 716)
Operation of parking brake
Active regulation of the ESP®
Speed v < 25 km/h (v < 17 mph)
Gear range is not "D" (for transmission 722 or 724)

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

Increase/reduce engine torque
Engage targeted gear (back or upshift)
Increase/reduce braking torque

The driver also has the option to accelerate the vehicle 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:

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

D Function sequence for permanent limiter

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

Variable SPEEDTRONIC selected with SPEEDTRONIC switch (SPEEDTRONIC light-emitting diode illuminated)
ESP® not switched passively (without model 212.074/077/274/277)
ESP® up to 31.5.10 a shift is not made in the "ESP-Sport" mode; as of 1.6.10 a shift is not made in the "SPORT HANDLING MODE" (model 212.074/077/274/277)
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 in urban traffic) over 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 engine torque
Engage targeted gear (shift down)
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 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 IC.

The IC transmits the set maximum speed via the chassis CAN to the brake system control unit.

For vehicles with code (233) DISTRONIC PLUS the IC transmits the set maximum speed via the chassis CAN to the radar sensors control unit or to the video and radar sensor system control unit.

At about v = 10 km/h (v = 5 mph) before reaching the set maximum speed a message appears in the multifunction display (A1p13) 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 engine torque
Engage targeted gear (shift down)
Raise braking torque

Cruise control (CC), location of components		GF30.30-P-0001-01FL
Electrical function schematic for cruise control (CC)	Without code (233) DISTRONIC PLUS	PE30.30-P-2051-97DAA
Electrical function schematic for cruise control (CC)	With code (233) DISTRONIC PLUS	PE30.30-P-2051-97DAB
Cruise control (CC) block diagram		GF30.30-P-0001-08FL
Cruise control (CC), overview of system components		GF30.30-P-9994FL