Cruise Control (CC), Function - GF30.30-P-0001KJE
ENGINE 780 in MODEL 453.091/391/491
with CODE 440 (Cruise control)
Function requirements, general
- Circuit 15 ON for display settings of the variable speed limiter
- Drivetrain operational for speed control
- Vehicle speed v ≥ 30 km/h (v ≥ 19 mph)
Cruise control/variable speed limiter, general points
The CC (TPM) function is subdivided into two main functions:
- Cruise control, function
- Variable speed limiter function (only vehicles without code 494 (USA version))
Cruise control, function
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 TEMPOMAT function is implemented in the electric drive control unit. The electric drive control unit evaluates the variables and implements the TEMPOMAT function.
The cruise control function is subdivided into the following subfunctions:
- Operation and display of the CC
- Evaluation of input factors
- Automatic speed control by the CC
Operation and display of the CC
Cruise control/variable speed limiter switch group on MFL
TEMPOMAT displays in instrument cluster with code K35 (Instrument cluster with monochrome display) shown on vehicle with engine 281
The CC is switched on by pressing the CC/variable speed limiter switch upwards. The CC symbol (1) is displayed in the multifunction display.
The desired speed is adjusted and stored over the accelerate and set switch. Using the "Resume from memory" switch the last stored or the current vehicle speed is set as the target speed. Using the accelerate and set switch and the decelerate and set switch the target speed can be altered. To do this press either the accelerate and set switch or the decelerate and set switch until the desired speed is reached; the speed is increased or decreased in steps of v = 1 km/h. Or hold down the accelerate and set switch or the decelerate and set switch until the desired speed is reached. The set target speed is displayed over the CC target speed display (2) in the multifunction display of the IC (except for code 494 (USA version)). For vehicles with code 494 (USA version) the note CC "SET" (2.1) for the activated CCs is displayed instead of the set speed. Using the switch off switch the CC can be temporarily deactivated. The cruise control is re-activated using the resume from memory switch. The CC is switched off again by switching the CC/variable speed limiter switch into the center position or by switching on the variable speed limiter function. The CC symbol (1) goes out.
Detailed information about information flow can be obtained from the Chapter "Evaluation of the input factors". Detailed information about operation can be taken from the operator's manual.
If the CC function is impaired, the CC error symbol (3) appears (CC symbol flashes) for t ≈ 10 s and then goes out again. For vehicles with code K36 (IC with a colored 8.9 cm (3.5") display) the fault message "CC nonfunctional" is also displayed in the multifunction display. The CC function is then deactivated automatically. To do this the ME-SFI [ME] control unit transmits the status of the CC with the respective request to activate the CC error symbol (3) via the interior CAN to the IC.
Evaluation of input factors
The following input factors are evaluated to implement the CC function:
- Operating status drivetrain operational (function requirement)
- Parking brake status
- Accelerator pedal position
- Gear range "D" engaged (function requirement)
- Reverse gear not engaged
- Vehicle speed (function requirements)
- Switch position and driver request over the CC/variable speed limiter switch group (function requirements)
- Brake pedal position
- Rotational speed and set motor torque of electric motor:
- Control intervention function of the Electronic Stability Program (ESP®)
- Autonomous brake intervention (vehicles with code 258 (Active brake assist))
- Deactivation in the case of crash
Operating status drivetrain operational (function requirement):
The electric drive control unit transmits the "Drivetrain operational" signal via the interior CAN to the instrument cluster.
Parking brake status:
The IC reads in the status of the parking brake over the parking brake indicator switch. For this purpose, the instrument cluster reads in the signal of the parking brake indicator switch via a direct line and transmits this status via the interior CAN to the electric drive control unit. If the parking brake is actuated, the CC cannot be activated. Also the speed control of the CC is interrupted if the parking brake is actuated.
Accelerator pedal position:
The electric drive control unit detects the accelerator pedal position and kickdown position via the direct signals of the accelerator pedal sensor and evaluates these. The vehicle can be accelerated beyond the specified speed in the case of kickdown in spite of the set limiter (except code 494 (USA version)). After the acceleration process the CC regulates the vehicle again to the set target speed.
Drive range "D" engaged (function requirement):
The information on the engaged drive range is read in via the drive program detection sensor via a direct line by the electric drive control unit. In addition, the drive range status is transmitted by the electronic selector lever module control unit via the electric drive CAN to the electric drive control unit. The TEMPOMAT can only be activated where gear range "D" is engaged.
Reverse gear not engaged
If the ESP® executes a control intervention, the Electronic Stability Program control unit transmits the information "ESP® control" via the interior CAN to the electric drive control unit, this then deactivates the TEMPOMAT function.
Autonomous brake application (vehicles with code 258 (Active brake assist)):
If the driver does not react to a collision-critical warning by the Brake Assist (proximity warning function with active brake application), the control unit proximity warning function with active brake application initiates autonomous braking and the reduction of engine torque via the control unit electronic stability program. The control unit proximity warning function with active brake application sends the status active brake assist (system status) of a stationary object or object in front, the relative speed in m/s as well as the distance to the stationary object or the object in front in diverse CAN messages via the front end CAN to the center SAM control unit. The center SAM control unit then sends these CAN messages via the interior CAN to the electronic stability program in order to initiate the braking torque. The Electronic Stability Program control unit evaluates the incoming requests, directly actuates the traction system hydraulic unit and transmits the engine torque reduction request and thus TEMPOMAT deactivation via the interior CAN to the electric drive control unit. The electric drive control unit transmits the engine torque reduction request via the electric drive CAN to the power electronics control unit.
Deactivation in the case of a crash:
In the case of a crash, the Supplemental Restraint System control unit transmits the crash signal via the interior CAN to the electric drive control unit, this then deactivates the TEMPOMAT.
Automatic speed control by the CC
Additional function requirements for automatic CC speed control:
- CC selected by the CC/variable speed limiter switch (the CC symbol (1) is displayed in the multifunction display)
- ESP® not switched passively
- Parking brake and brake not actuated
- Transmission in position "D"
Function sequence for automatic CC 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 target speed is displayed over the CC target speed display (2) in the multifunction display of the IC. The electric drive control unit transmits corresponding requests via the interior CAN to the instrument cluster for this purpose.
The following activities are started or initial parameters (requests) issued in order to reach or maintain the target speed:
- Increase/reduce engine torque
Raise/reduce engine torque:
The electric drive control unit evaluates the input factors as well as additional driving dynamic requirements and transmits the requests to increase or reduce the engine torque via the electric drive CAN to the power electronics control unit. The power electronics control unit then increases or reduces the engine torque to keep the vehicle at the driver's specified speed.
The following events lead to interruption of the automatic speed control:
- Operation of the OFF switch
- Depressing the brake pedal
- Active regulation of the ESP®
- Autonomous brake intervention (vehicles with code 258 (Active brake assist))
- Parking brake operated
- Gear range not "D"
Detailed information about the information flow of the events which lead to deactivation of the automatic speed control can be taken from the chapter "Evaluation of input factors".
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).
Variable speed limiter function (only vehicles without code 494 (USA version))
The status of the engaged reverse drive range is also detected via the drive program detection sensor and redundantly transmitted by the electronic selector lever module control unit via the electric drive CAN to the electric drive control unit. The CC cannot be activated for an engaged reverse gear.
Vehicle speed (function requirements)
The vehicle speed is calculated from the wheel speed from the front axle rpm sensors and the rear axle rpm sensors. The Electronic Stability Program control unit transmits relevant information on the vehicle speed via the interior CAN to the electric drive control unit.
Switch position and driver request over the CC/variable speed limiter switch group (function requirements)
The electric drive control unit reads in the driver's requests via the TEMPOMAT/limiter switch group via direct lines via the steering wheel clock spring contact. The electric drive control unit detects the corresponding driver's request via the respective different signal voltage that is applied for the different switch positions.
Brake pedal position:
The position of the brake pedal is read in over the signal from the brake lights switch. The electric drive control unit reads in the signal of the brake light switch via a direct line. Redundantly from this, the center SAM control unit also reads in the position of the brake light switch via a direct line and transmits the service brake status via the interior CAN to the electric drive control unit. The electric drive control unit deactivates the TEMPOMAT function in the case of an activated brake.
Rotational speed and set motor torque of electric motor:
The power electronics control unit transmits the rotational speed of the electric motor and the set motor torque for feedback to the electric drive control unit. The power electronics control unit evaluates these signals for feedback of the tempomat control. The TEMPOMAT can not be activated in the case of an implausible signal.
Control intervention function of the Electronic Stability Program (ESP®)
Additional function requirements on the variable speed limiter:
- Variable speed limiter selected by the CC/variable speed limiter switch (the variable speed limiter symbol (4) is displayed in the multifunction display)
- ESP® not switched passively
- No kickdown detected
The permissible 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 speed limiter function. The driver can accelerate the vehicle up to the set limit. The permissible maximum speed set by the driver is displayed by the display in the multifunction display of the IC.
The variable speed limiter function is subdivided into the following subfunctions:
- Operation and display of the variable speed limiter
- Automatic speed limiter by the variable speed limiter
- Optical and acoustic warning
Limiter displays with code K35 (Instrument cluster with monochrome display) shown on vehicle with engine 281
Operation and display of the variable speed limiter
The variable speed limiter is switched on by pressing the CC/variable speed limiter switch downwards. The variable speed limiter symbol (4) is displayed in the multifunction display. The desired permissible maximum speed is adjusted and stored over the accelerate and set switch. The permissible maximum speed set by the driver is displayed by the permissible maximum speed variable speed limiter (5) display in the multifunction display of the IC. The last stored permissible maximum speed is set by the "Resume from memory" switch. The set permissible maximum speed can be altered over the decelerate and set switch and the accelerate and set switch. To do this press either the accelerate and set switch or the decelerate and set switch until the desired permissible maximum speed is reached; the permissible maximum speed is increased or decreased in steps of v = 1 km/h. Or hold down the accelerate and set switch or the decelerate and set switch until the desired permissible maximum speed is reached. The desired permissible maximum speed is then increased or decreased in steps of v = 10 km/h. The set permissible maximum speed is displayed by the permissible maximum speed variable speed limiter (5) display in the multifunction display of the IC.
Exceeding the permissible maximum speed set by the driver for kickdown:
If the driver fully depresses the accelerator pedal and the electric drive control unit detects the kickdown position, the limiter is temporarily deactivated and the vehicle can be accelerated beyond the maximum permissible speed set by the driver. In the multifunction display the warning variable speed limiter exceeding the maximum speed (6) (flashing display of the variable speed limiter permissible maximum speed) is displayed for the period in which the speed is exceeded. The variable speed limiter is activated again automatically as soon as the vehicle speed goes down below the permissible maximum speed set by the driver.
Detailed information about information flow can be obtained from the Chapter "CC function" in the subfunction "Evaluation of input factors".
Deactivation and switching off of the variable speed limiter:
Using the switch off switch the variable speed limiter can be temporarily deactivated. The variable speed limiter is re-activated with the last stored permissible maximum speed using the resume from memory switch.
The variable speed limiter is deactivated again (switched off) by switching the CC/variable speed limiter switch into the center position or by switching on the CC function. The variable speed limiter symbol (4) goes out.
If the variable speed limiter function is impaired, the variable speed limiter error symbol (7) appears (variable speed limiter symbol flashes) for t ≈ 10 s and then goes out again. For vehicles with code K36 (IC with a colored 8.9 cm (3.5") display) the fault message "Variable speed limiter nonfunctional" is also displayed in the multifunction display. This variable speed limiter function is deactivated automatically. For this purpose, the electric drive control unit transmits the limiter status with corresponding request to activate the limiter error symbol (7) and warning message via the interior CAN to the instrument cluster.
Detailed information about operation can be taken from the operator's manual.
Automatic speed limiter by the variable speed limiter
If the set limit was reached, the following activities are started:
- Reduce engine torque
Reduce engine torque:
The electric drive control unit evaluates the input factors as well as additional driving dynamic requirements and transmits the request to reduce the engine torque via the electric drive CAN to the power electronics control unit. The power electronics control unit reduces, as required, the engine torque to keep the vehicle at the maximum permissible speed set by the driver.
Optical and acoustic warning
If the vehicle exceeds the maximum permissible speed set by the driver and the activities "Reduce engine torque" and "Recuperative braking" are not sufficient to decelerate the vehicle to the maximum permissible speed set by the driver, the driver is warned via the speed exceedance limiter warning (6) (flashing display of limiter maximum permissible speed) that they must reduce the speed by braking. A warning tone is also output over the warning buzzer in the IC. The electric drive control unit transmits corresponding requests via the interior CAN to the instrument cluster for this purpose.
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